is about thermal gasifier plant

timer Asked: Nov 11th, 2016

Question description

I need your help to complete my report, i have to do a summary (0.5 page), abstract (0.5 page), Introduction(0.75 page), theory (0.75 page), and conclusion (0.5 page). refrence

please make sure that do not do plagiarism, but cite your work. in MLA format

the subject is about********** (thermal gasifier plant) we have to do a report and i will do the process and result later. just write general topics that makes me get in the work

i have upload similar work to just get an idea but you can search in google.

is about thermal gasifier plant
Baltic Forum for Innovative Technologies for Sustainable Manure Management KNOWLEDGE REPORT Thermal Gasification of Manure By Ksawery Kuligowski & Sari Luostarinen WP6 Energy potentials December 2011                             Baltic MANURE WP6 Energy potentials      THERMAL GASIFICATION OF MANURE      Ksawery Kuligowski & Sari Luostarinen                                                    The project is partly financed by the European Union European Regional Development Fund 1    PREFACE    This  report  offers  an  overview  of  thermal  gasification  of  manure.  Thermal  gasification  is  an  emerging  technology,  not  developed  on  full‐scale  at  the  time  of  writing.  However,  it  holds  a  promise for a new way to utilise the energy content of manure. Bearing this in mind, the following  report  is  mostly  based  on  the  technology  developed  by  Peder  Stoholm  from  DONG  Energy,  Denmark, in a Low Temperature‐Circulated Fluidised Bed (LT‐CFB) 500 kW gasifier.     This report was mostly written by Ksawery Kuligowski (University of Gdánsk – POMCERT, Poland)  with scientific support and editing into the published form by Sari Luostarinen (WP6 leader, MTT  Agrifood  Research  Finland).  The  authors  would  like  to  express  their  gratitude  to  Peder  Stoholm  and  Anders  Boisen  from  DONG  Energy  for  hospitality  during  the  visit  at  'Pyroneer'  thermal  gasification  demonstration  plant  in  Kalundborg,  Denmark  (26th  of  May,  2011)  –  the  up‐scaled  version of the LT‐CFB gasifier. The authors are also grateful for SP Technical Research Institute of  Sweden for providing constructive comments to this report. They would also like to acknowledge  Assoc.  Prof.  Tjalfe  G.  Poulsen  from  Aalborg  University,  where  the  research  on  potential  use  of  thermally gasified manure took place.    This  report  was  produced  as  part  of  work  package  6  “Manure  Energy  Potentials”  in  the  project  “Baltic  Forum  for  Innovative  Technologies  for  Sustainable  Manure  Management  (Baltic  MANURE)”.  The  project  aims  at  turning  manure  problems  into  business  opportunities,  one  of  which is using biogas technology as part of manure management. The project is partly funded by  the European Union European Regional Development Fund (Baltic Sea Region Programme 2007‐ 2013).     The  authors  would  like  to  thank  all  the  partners  involved  in  Baltic  MANURE  WP6  for  their  co‐ operation during writing.     December 2011    the authors          The project is partly financed European Regional Development Fund by the European Union - 2    CONTENT  1  Introduction .......................................................................................................................... 4  2  Basic theory of thermal gasification...................................................................................... 4  2.1  Pre‐treatment ........................................................................................................................... 4  2.2  Pyrolysis ................................................................................................................................... 6  2.3  Thermal gasification ................................................................................................................. 6  3  Energy use and advantages over combustion ....................................................................... 6  4  Syn gas purification and use ................................................................................................. 7  4.1  Syn gas purification ................................................................................................................... 8  4.2  Biofuels from syn gas ................................................................................................................ 8  4.3  Emissions during thermal gasification ....................................................................................... 8  5  Possibilities and barriers for implementing the technology ................................................... 9  6  Description of the pilot experiments in Denmark ................................................................ 10  6.1  Description of manure pellets ................................................................................................. 10  6.2  Thermal gasification in LT‐CFB ................................................................................................ 11  6.3  Characteristics and use of the residue from LT‐CFB ................................................................. 11  Ash chemistry ........................................................................................................................................... 12  Element mobility and P extraction potential ............................................................................................ 12  Application of ash in agriculture ............................................................................................................... 13  Ash spreading techniques on land ............................................................................................................ 14  Summary of ash reuse .............................................................................................................................. 14  Changes in the residue as compared to original manure ......................................................................... 14  Changes during storage ............................................................................................................................ 15  6.3.1  6.3.2  6.3.3  6.3.4  6.3.5  6.3.6  6.3.7  6.4  7    Future possibilities .................................................................................................................. 15  REFERENCES ........................................................................................................................ 15          The project is partly financed European Regional Development Fund by the European Union - 3    1. Introduction  Thermal gasification is a process which converts carbonaceous materials into combustible gases.  The resulting gas is called syn gas which can be more efficiently converted to high quality energy,  such as electricity, than achieved by direct combustion of the fuel. Thermal gasification has been  already  widely  applied  to  coal  and  wood,  while  its  application  to  mechanically  separated  solid  fraction of animal manure has so far been rather limited on a commercial scale. There have been  some experiments, either on co‐gasification with other biomass fuels or solely for manure carried  out in pilot/demonstration plants in Denmark [1‐4] and in the USA [31].     In  order  to  solve  the  challenge  of  high  quantities  of  agricultural  manure  and  of  phosphorus  balance in the environment without a necessity to restrict animal production, animal manure must  be utilized on site or transported to places with a deficit of phosphorus. Since the transportation  of  raw  slurry  with  its  high  water  content  is  expensive  and  inefficient,  farm‐scale  mechanical  separation of the manure (raw or anaerobically digested) into solid and liquid fractions may offer a  solution [5, 6]. The liquid fraction can be used as nitrogen fertilizer, whereas the phosphorus‐rich  solid fraction could be further dried and thermally gasified to recover heat and electricity.     Previous  studies  have  shown  that  a  technological  chain  consisting  of  anaerobic  digestion  in  a  biogas plant and subsequent thermal gasification of the dried pellets from the manure digestate,  recovers up to 60% of the energy contained in the original raw materials. This is only slightly more  than  anaerobic  digestion  alone  (50‐55%),  as  the  calculations  take  into  account  the  energy  loss  during the dewatering, drying and pelletizing of the digestate and the loss of nitrogen during the  thermal processes [7]. In spite of considerable reduction of the input dry manure mass (2‐3 times)  during  thermal  gasification,  the  energy  gain  is  currently  rather  insignificantly  higher  than  for  biological  processes  alone  (anaerobic  digestion).  Therefore,  this  technology  is  still  under  development and requires further research and feasibility evaluations.   2. Basic theory of thermal gasification  Thermal gasification relies on chemical processes at elevated temperatures (>700oC), contrary to  biological  processes  such  as  biogas  technologies.  Depending  on  the  raw  materials  used,  it  may  require  pre‐treatment  (drying).  Then  the  process  proceeds  in  two  phases,  i.e.  pyrolysis  and  thermal gasification [1].  2.1 Pre‐treatment  The  fuel,  suitable  for  thermal  gasification,  must  have  a  certain  heating  value.  Usual  fuels  used  and/or tested for thermal gasification have a wide range of heating values from 7.5 to 37.6 GJ/t  (Tables 1‐3). Different fuels can also be mixed and co‐gasified, e.g. coal with feedlot and chicken  litter  biomass  (Table  2).  The  necessity  for  pre‐treatment,  mostly  involving  drying,  is  mainly  dependent  on  the  moisture  content  of  the  fuel  (dry  matter,  DM).  Additionally,  grinding  may  be  needed for fuels with large particles, such as coal, in order to ensure a greater contact area for the          The project is partly financed European Regional Development Fund by the European Union - 4    better heat transfer through the fuel. The lower heating value (LHV) is determined by subtracting  the heat of vaporizing water vapor from the higher heating value (HHV).     Table 1. Comparative approximate analysis of different fuels. Fuel [Reference]  Dry matter (%)  Higher heating value HHV (GJ/t)  Coal [17]  85–97  16–32  Biomass, generally [17]  65–90  13–18  Waste, generally [17]  40–60  8‐10  Manure, pellets [4]  90  15.3  Digested manure, pellets [4]  90  11.3  Poultry litter [31]  80–65  15.3*  Turkey litter [31]  70  11.8*  Swine solids [31]  42  19.3*  *dry basis  Table 2. Comparative approximate analysis of coal, biomass and their mixtures [30]. Fuel  Dry matter (%)  Higher heating value HHV (GJ/t), dry basis  Coal  79  27.7  Feedlot biomass  89  16.8  Chicken litter  92.5  10  Coal and feedlot biomass (50:50 w/w)  84  21.9  Coal and chicken litter (50:50 w/w)  86  18.1  Table 3. Lower heating value for different fuels [32]. Fuel  Dry matter (%)  Lower heating value LHV (GJ/t)  Coal  88.5  24.8  Vegetable oils  0.0  37.6  Straw  87.3  14.6  Treated wood  85.4  15.3  Untreated wood  80.2  14.8  Grass/plants  75.8  13.1  Sludge  67.5  8.2  Manure  56.4  7.5            The project is partly financed European Regional Development Fund by the European Union - 5    When  gasifying  manure,  the  pre‐treatment  involves  solid‐liquid  separation  (mechanical  separation,  dewatering),  drying  and  pelletizing.  The  national  legislation  should  be  considered  when organizing the pre‐treatment. For example in Denmark, drying and pelletizing of manure is  not  allowed  at  farm‐scale  due  to  the  vicinity  of  pig  feed.  Slurry  separation  using  screw  presses,  vibration  filters  or  decanters  is  already  practiced  e.g.  in  Denmark  and  in  the  Netherlands  using  mobile,  containerized  units,  easy  to  relocate  from  farm  to  farm  (examples  of  Danish  producers:  Samson  Bimatech,  ManuPower,  SB  Engineering,  Vredo;  in  the  Netherlands  more  high‐tech  including reverse osmosis and ultra filtration). In Denmark, the separation results in around one  (1)  million  tons  of  slurry  separated  each  year  (3%  of  total  slurry  production)  [33].  Pelletizing  of  manure/digestate is still a novel technology, therefore not common on a commercial scale yet.    The  drying  of  the  digestate  may  consume  more  than  5.3  MJ/kg  manure  DM,  which  constitutes  almost 50% of the HHV of the resulting pellets from digested manure [25]. Another option is  to  use  solar  energy  to  dry  the  manure,  preferably  in  a  glasshouse  and  controlled  conditions.  Such  approach is already used for drying sewage sludge. Drying of manure could also be done using the  excess of heat from the biogas plant, offering also a valid use for the biogas‐based heat. Summing  up the overall energy efficiency of the manure handling chain leading to thermal gasification could  be strongly improved by appropriate heat management during drying.  2.2 Pyrolysis   After drying, the first process that the fuel undergoes is pyrolysis, which initiates at around 230 oC.  During pyrolysis, thermally unstable components, such as lignine in biomass are broken down and  evaporated  with  other  volatile  components.  The  resulting  pyrolysis  gas  consists  mainly  of  tar  (condensible  hydrocarbons  or  hydrocarbons  with  C6  and  higher,  including  polycyclic  aromatic  hydrocarbons, PAH), methane (CH4), steam or nitrogen (when using air as gasification agent, see  below) and carbon dioxide (CO2). The solid residual contains carbon structures (coke) and ashes.  The tar formed during pyrolysis can be sticky like asphalt. It is also known to be highly carcinogenic  and  represents  a  great  challenge  to  the  machinery  —  e.g.  internal  combustion  engines  and  turbines — when the gas produced is transported, stored, and used [1].  2.3 Thermal gasification   The  actual  gasification  happens  at  temperatures  above  700  oC  when  the  glowing  coke  and  pyrolysis  gas  are  allowed  to  react  with  a  gasification  agent,  such  as  oxygen,  air  or  steam.  The  gasification agent is normally injected in small amounts. The coke is gradually broken down into  gases,  such as carbon monoxide (CO), carbon dioxide and hydrogen (H2 from the steam reaction)  or nitrogen (N2 if air is used as gasification agent). The gasification can take place in a pile of coke  — a fixed bed — or e.g. in a fluid bed [1].  3. Energy use and advantages over combustion  Thermal gasification has already been widely applied to coal and wood; however its application to  the solid fraction of animal manure is still limited on a commercial scale. There have been some  research  experiments,  either  on  co‐gasification  with  other  biomass  fuels  or  solely  for  manure  carried out in pilot/demonstration plants in Denmark [1‐4] and in the USA [31].          The project is partly financed European Regional Development Fund by the European Union - 6      When  comparing  thermal  gasification  and  direct  combustion  of  combustible  fuels,  thermal  gasification allows for a broader range of very low grade and difficult biomass and waste fuels to  be  used.  Additionally,  no  problems  regarding  agglomeration  have  been  encountered,  in  spite  of  using  only  ordinary  silica  sand  as  bed  material  for  many  hours  of  operation  (some  combustion  technologies may also control bed temperature and influence ash behavior).     Thermal  gasification  uses  only  a  hot  cyclone,  without  prior  raw  gas  cooling,  which  allows  for  retaining ash at around 95% efficiency. Partly evaporative ash components, such as potassium and  phosphorus  can  be  retained  roughly  as  efficiently  as  the  ash  in  general.  Hence  the  boiler  is  protected and ash mixing avoided when using the syn gas for co‐firing with coal or waste. Thermal  gasification  also  allows  for  easy  and  clean  handling  of  large  ash  streams,  while  the  lower  temperature  (<750oC)  than  that  of  combustion  (>1000oC)  makes  the  corrosive  compounds  (i.e.  potassium  chloride  KCl)  retained  in  the  ash,  enriching  the  fertilizer  value  of  the  residues  and  causing no corrosion in the boiler [1‐4].    Before  transport,  the  syn  gas  of  thermal  gasification  would  require  an  extra  cleaning  stage  to  remove tar, as the syn gas cannot be transported hot and the cooled tar would condensate and  cause problems, such as clogging.  However, when upgraded (purified), the syn gas as an energy  carrier,  can  be  transported  over  long  distances.  Hence  the  heat  can  be  recovered  even  at  long  distances from the location of the gasifier. This makes the installation of the plant independent of  the location (rural, urban) in opposition of the combustion plant, in which some heat is lost while  transporting steam or hot water over long distances (urban location more appropriate).     Additionally, more electricity can be produced during thermal gasification than during combustion,  which  relates  to  better  electricity  production  rate  of  a  gas  engine  (40%)  than  a  steam  turbine  (25%)  [7].  These  values,  however,  are  given  for  large‐scale  power  plants,  and  for  small‐scale  gasifiers the efficiency is likely to be lower.     Thermal gasification results in less gaseous (nitrogen oxides NOx) and dioxin emissions, and as all  nitrogen  is  converted  to  gaseous  nitrogen,  none  is  leached  to  waterways.  Also,  ash  from  combustion  of  manure  is  more  contaminated  with  zinc,  copper  and  chromium,  and  has  less  potassium (the key macro‐element after phosphorus) than ash from thermal gasification [9]. Ash  from  gasification  is  also  characterized  with  more  readily‐usable  phosphorus  than  ash  from  combustion [16].  4. Syn gas purification and use  When  it  comes  to  syn  gas  itself,  its  further  application  (i.e.  injection  into  natural  gas  grid)  significantly depends on its content of impurities. The pollutants involved in these processes may  include sub‐micron particulate matter, tars, ammonia, metals, dioxins, furans and acid gases. The  syn gas purification can be achieved with proven, reliable scrubbing (absorption) and adsorption  technologies, similar to the processes used in conventional scrubbing of gases from combustion.  However, a pre‐treatment with tar removal may be necessary.           The project is partly financed European Regional Development Fund by the European Union - 7    4.1 Syn gas purification  The  syn  gas  may  simply  be  directed  through  the  thermal  process  destroying  the  tar  at  high  temperature without the need for a separate purification step. The trade‐off, however, is a lower  energy content of the syn gas. Alternatively, the tar may be removed in a separate scrubber. This  approach has a lower outlet temperature and results in higher energy content in the purified syn  gas, but results in tars that are more difficult to remove. The main challenge of tar removal relates  to  the  fouling  that  can  occur  in  the  initial  stages  of  condensing  and  collecting  the  tars.  The  "tar  balls", which are long‐chained hydrocarbons, have a tendency to agglomerate and stick together,  and  subsequently  foul  the  equipment.  Tar  removal  processes  also  produce  liquid  wastes  with  higher organic concentrations, which increase the complexity of subsequent water treatment.  4.2 Biofuels from syn gas  Conversion of syn gas into alkenes is a well‐known industrial process using both low temperature  Fischer–Tropsch  (LTFT)  and  high  temperature  Fischer–Tropsch  (HTFT)  routes.  There  are  several  possibilities  for  modifying  the  classical  Fischer–Tropsch  process  to  yield  predominantly  alkenes.  These  are  production  of  alkanes  and  subsequent  steam  cracking  to  lower  alkenes,  upgrading  of  Fischer–Tropsch liquids into lower alkenes and modification of Fischer–Tropsch catalyst to achieve  higher  selectivity  for  alkene  formation.  Solid  acid  catalysts,  such  as  zeolite,  can  catalyze  the  conversion  of  syn  gas  into  methanol,  which  is  subsequently  converted  into  alkenes.  Through  appropriate choice of process conditions, catalyst formulation and morphology of the catalyst, a  product mixture with higher content of lower alkenes can be obtained [19].    The  catalytic  reforming  of  methane  and  naphtha  are  well‐established  petrochemical  processes,  and  in  recent  years  gasification  technology  is  becoming  increasingly  focused  on  catalytic  processing. The specific objective is then to transform the light and heavy hydrocarbons in the syn  gas.  There  are  numerous  publications  in  the  literature  on  experimental  investigations  into  the  catalytic conditioning of the raw gas obtained in biomass gasification processes. Much of the work  in  this  field  has  involved  commercial  reforming  catalysts,  which  for  reasons  both  technical  and  economic contain nickel as the active element.    The  industrial  feasibility  of  such  processes  depends  mainly  on  the  cleaning  technologies  for  the  product gas. The aim is to separate dust and convert the condensable tar into permanent gases so  that they can be rendered into an acceptable fuel for internal combustion engines, gas turbines,  fuel cells or other local utilities, as well as for a chemical feedstock for such processes as methanol  synthesis [20].  4.3 Emissions during thermal gasification  Thermal  gasification  technology  practically  provides  no  emissions,  apart  from  the  gases  (mainly  methane and carbon dioxide) emitted with the syn gas. However proper management of the gases  with  no  leakages  within  the  plant  (production,  storage,  upgrading,  transport)  ensures  no  emissions.  When  comparing  several  technology  chains  for  manure:  (i)  anaerobic  digestion  with  pre‐treatment,  (ii)  combustion  of  either  raw  manure  or  manure  digestate  and  (iii)  thermal  gasification  of  manure  digestate,  followed  by  land  application  of  residues  from  each,  they  reportedly  yield  the  same  savings  for  carbon  dioxide  (120–130  kg  CO2  per  ton  of  raw  manure          The project is partly financed European Regional Development Fund by the European Union - 8    treated).  The  only  scenario  with  slightly  lower  savings  (about  110  kg  CO2  per  ton  raw  manure  treated) was observed for thermal gasification of pellets from raw manure, omitting the anaerobic  digestion  step.  Still,  the  differences  between  the  scenarios  reported  are  relatively  small  and  changes  in  the  input  data  therefore  may  change  the  relative  succession  of  the  scenarios  with  respect to carbon dioxide balances [7].  5. Possibilities and barriers for implementing the technology  Technically thermal gasification is unproblematic and can be fully automated, but manure fibres  should,  according  to  the  EU  Waste  Combustion  Directive  (2000/76/EF),  be  treated  as  waste,  resulting  in  regulations  for  the  quality  of  combustion  gases  to  be  released.  This  results  in  requirements for detailed measurements and possibly also purification (including commissioning,  registering, monitoring), which are not economically applicable for farm‐scale gasification. As the  result manure fibres should in practice be treated in large gasification units or CHP plants only, and  most likely in combination with other biomasses, such as straw, wood chips or household wastes.     Regulations  for  heating  should  also  be  considered.  Changes  in  excise  taxation  of  the  heat  produced  at  such  plants  could  be  implemented.  Alternatively,  it  could  be  forbidden  via  spatial  planning to establish own heating plants or heating plants that do not use a prescribed fuel.    Any technologies that result in products that are intended for sale/export out of the farm/region  have the drawbacks that the markets do not currently exist or are not yet fully developed for the  products.    The technologies are to some extent proven, but their environmental and economic performances  are especially researched in case of fibre fractions from pig slurry. Such research would also clarify  whether some policy measures could make it more feasible to implement thermal gasification for  manure [16].     The gasifier may also be used in the following:   Co‐firing with coal, oil or gas in existing power plant boilers,   Indirect firing in gas turbines,   In large Stirling engines,   Direct firing in gas turbines,   In combustion engines or fuel cells (with gas cleaning)   In production of liquid fuels.    The  technology  for  thermal  gasification  of  manure  is  not  presently  available  as  standalone  technology  at  farm‐scale.  Therefore,  economic  feasibility  studies  should  be  made  in  all  target  countries.  According  to  Polish  data,  the  investment  cost  of  an  installation  running  for  other  biomass fuels than manure is within a range of 1‐5 million EUR/MW installed [17]. In general, the  technology  is  still  difficult  to  implement  technically,  with  legislative  challenges  in  relation  to  the  interpretation of the EU Waste Combustion Directive [16].          The project is partly financed European Regional Development Fund by the European Union - 9    6. Description of the pilot experiments in Denmark   Several  experiments  in  Denmark  have  been  undertaken  using  the  Low  Temperature  Circulating  Fluidized Bed (LT‐CFB) pilot gasifier of 500 kW, designed especially for difficult, low grade biomass  and waste fuels, such as the agricultural biomass of cereal straw, energy crops and animal manure.  The  necessary  high  fuel  flexibility  is  achieved  through  a  novel  but  simple  combination  of  a  preceding  fast  pyrolysis  in  a  fast  fluidized  bed  chamber  and  subsequent  char  gasification  in  a  slowly fluidized bubbling bed chamber. The LT‐CFB gasifier allows for an efficient gasification at a  very well‐controlled maximum process temperature, which is usually below 750oC [3, 4].  6.1 Description of manure pellets   The manure used in the experiments made with the 500 kW LT‐CFB gasifier was first digested in  the Fangel biogas plant, Denmark (Table 4), then dried and pelletized. The pre‐treatment steps of  the manure digestate involved mechanical separation (from 4 to 30% DM) and drying with steam  or flue gases (from 30 to 90% DM). The owner of the biogas plant is Fangel Miljø‐ & Energiselskab  A.m.b.a.  The  plant  processes  mesophilically  (37  °C)  pig  and  cattle  slurry  and  small  amounts  of  poultry  and  mink  slurry  from  26  animal  farms  from  the  area.  In  addition  to  slurry,  intestinal  content and flotation sludge from an abattoir, dairy waste, as well as waste from food processing  industry, tannery industry and medicinal industry is supplied. The biomass is heated using a heat  exchanger system and sanitised at 60 °C for 3½ hours, before digestion. After digestion, part of the  digested  biomass  is  mechanically  separated  into  solid  and  liquid  fractions.  The  liquid  fraction  is  used in the biological gas purification filter. The main part of the digested biomass is transported  to the 23 decentralised storage tanks with a total capacity of 25,000 m3, close to the fields. The  surplus of digested biomass is sold each year to the crop farmers in the neighbourhood [34].    Table 4. Main data of the Fangel biogas plant [34]. Main data  Value  Unit  Animal manure  124  tons/day  Alternative biomass  19  tons/day  Biogas production  2.2  mill. Nm3/year  Digester capacity1  3750  m3 Process temperature   37  °C  Pasteurisation MGRT  3,5  hours at 60 °C  Gas storage capacity  50  m3 Utilisation of biogas  CHP‐plant/gas boiler    Biomass transport vehicle   20  m3 vacuum tanker  Average transport distance   6.5  km  25.3  mill. DKK  2  Investment cost 3 3 1) 2 × 1600 m + 550 m , 2) including storage capacity           The project is partly financed European Regional Development Fund by the European Union - 10    The  resulting  pellets  (Fig.  1)  from  dried  digestate  of  Fangel  biogas  plant  (f  (  4mm)  have  been  shown to have a rather good HHV, 11.3 GJ/t (15.3 GJ/t s for pellets from raw manure) [4, 8].                   Figure 1. Pellets from digested pig manure (90% DM).Photo: Ksawery Kuligowski, POMCERT. 6.2 Thermal gasification in LT‐CFB  In the gasification experiments, small fuel particles were entered into the pyrolysis chamber and  rapidly pyrolysed at ~650°C due to good thermal contact with the mainly re‐circulated sand and  ash particles. Due to the low temperature and retention time in the pyrolysis chamber essentially  only light tars and no PAH were formed.     The residual char, pyrolysis gases and inert particles were then blown upwards into the primary  cyclone, which separated char and inert particles into a bubbling bed char reactor. There the char  was gasified at typically ~730°C using air and steam. The char gas and fine ash particles left the top  of the char reactor and entered the pyrolysis chamber. Heavier inert particles were re‐circulated  into the pyrolysis chamber from the bottom of the char reaction chamber while acting as a heat  carrier.  The  heat  liberated  due  to  the  mainly  exothermic  reactions  in  the  char  reactor  was  consumed  by  the  mainly  endothermic  processes  in  the  pyrolysis  chamber.  Therefore,  the  exit  stream  out  of  the  pyrolysis  chamber  had  an  even  lower  temperature  compared  to  the  temperature  in  the  char  reactor.  No  extra  pressure  was  applied  in  the  gasifier  chamber.  Pressurized gasification  has  so  far  only  been applied  to  coal,  wood,  peat,  straw  and  sawdust,  as  well as in processes of co‐gasification of coal with biomass [26‐29].    Ash  particles  formed  may  have  recirculated  several  times  but  eventually  the  main  part  typically  escaped through the primary cyclone and was separated by the more efficient secondary cyclone.  A  further  coarser  ash  stream  may  be  drained  from  the  bottom  of  the  gasifier,  and  in  these  two  ways, typically around 95% of the ash was retained.  6.3 Characteristics and use of the residue from LT‐CFB  Residues from coal combustion are already widely used in the markets of construction materials  as  an  additive  to  concrete  in  cement  plants  or  as  a  soil  filler,  e.g.  in  bridge  embankments.  The  fertilizer  value  of  coal  ash  is  lower  than  the  potential  ashes  from  gasifying  biomass  due  to  the  lower  phosphorus  content  and  contamination  with  radioactive  elements.  Wood  ashes  can  normally  be  used  as  soil  filler  in  forests  and  parks,  avoiding  its  application  for  plants  directly  consumed by humans and/or animals.            The project is partly financed European Regional Development Fund by the European Union - 11    No data on the characteristics of residual ashes from full‐scale thermal gasification of manure is,  to our knowledge, available, but the results from Danish pilot experiments are described below.  Figure 2 shows the ash from thermal gasification of pelletized digested pig manure.               Figure 2. Ash from thermal gasification of pellets from digested pig manure. Photo: Ksawery Kuligowski, POMCERT. 6.3.1 Ash chemistry  The  main  component  of  the  ash  from  the  thermal  gasification  experiments  using  digested  pig  manure  was  calcium  (Ca,  Table  5).  The  relatively  high  content  of  phopshorus  (54.4  g/kg)  and  potassium (34.7 g/kg) made the ash a good candidate for fertilizer. Other elements were iron (Fe),  sulfur  (S),  magnesium  (Mg)  and  sodium  (Na).  Among  heavy  metals,  the  greatest  concentrations  were recorded for zinc (Zn), strontium (Sr) and copper (Cu). Main minerals found in the ash were  calcite and quartz. Ash phosphorus occurred in the form of a mixture of carbonate‐ and hydroxy‐ apatite, which form various, irregular crystals with dimensions of up to 100 mm. Table 5 shows the  basic chemical composition of the ash from the pilot‐gasification experiments.    Table 5. Concentration of chosen elements in the ash (ICP-OES). SD denotes standard deviation. Analysis  Total Ca  Total P1  P soluble in water2  P soluble in  ammonium citrate2  Total K3  Total Fe  Total S  Total Mg  Unit  g/kg  311  54.4  0.1*10‐3    (SD)  12.2  4.3  0.043*10‐3  45*10‐3  34.7  29.2  21.1  20.7  2.4*10‐3  0.36  1.75  0.14  1.2  Analysis  Total Na  Total Mn  Total Zn  Unit  g/kg  9.1  0.7  1.04    (SD)  0.64  0.04  0.02  Total Sr  Total Cu  Total Ni  Total Pb  pH (1:25 H2O)  0.4  0.26  0.02  0.93*10‐3  12  0.02  0.26*10‐3  0.09*10‐3 0.21*10‐3   1  Measured by UV‐VIS spectrometry in H2SO4 extracts [9]  Shown as %  of Total P  3  Measured by Energy Dispersive X‐Ray Fluorescence (EDXRF) [9]  2  6.3.2 Element mobility and P extraction potential  The ashes were leached in order to test the mobility of the elements and especially phosphorus.  Leaching with water removed up to 65% of potassium, 48% of sodium, 41% of molybdenum, 21%  of  sulphur,  14%  of  aluminum,  10%  of  selenium  and  9%  of  calcium  from  the  ash  using  a  1:200  (w/w) ash:water load. However, the water soluble phosphorus in ash was very low (< 0.1% of total          The project is partly financed European Regional Development Fund by the European Union - 12    P).  The  optimal  sulphuric  acid  requirement  (measured  as  mass  of  acid  applied  per  mass  of  phosphorus  extracted)  was  0.98  kg  H2SO4/kg  ash  at  an  acid  concentration  of  0.6  M,  yielding  phosphorus extraction of 94%. This is approximately three times more acid than used in industrial  production of phosphorus fertilizer from phosphate rock (acid requirement about 6‐7 kg H2SO4/kg  P recovered). The use of higher acid concentrations (2 M) did not improve phosphorus dissolution,  but increased zinc release. Removal of calcite equivalent to 70% of initial ash mass reduced ash pH  from 12 to 6 and concentrated total phosphorus (two times higher), water soluble phosphorus (10  times higher) and citric acid soluble phosphorus (1.5 times higher) [10], [11].  6.3.3 Application of ash in agriculture  Ashes from thermally gasified, pre‐digested pig manure were also used as fertilizers on fields. In  general,  leaching  of  phosphorus  from  ash‐amended  soils  was  very  low  (<0.5%  of  phosphorus  applied in ash) compared with the inorganic fertilizer used, disodium phosphate (DSP) (97% and  12% of phosphorus applied in soils with low and high phosphorus sorption capacity, respectively).  Phosphorus  leaching  depended  on  irrigation  rate  and  soil  sorption  capacity  (clay  content  and  organic  matter),  but  did  not  depend  on  whether  long‐term  ash‐soil  incubation  had  taken  place  prior to onset of irrigation [10].     On acidic soil, ash was an effective liming agent (2% addition by mass raised soil pH from 4.5 to  7.9).  It  also  increased  soil  electrical  conductivity  (20%  higher),  water  holding  capacity  and  soil  bicarbonate‐extractable  phosphorus  (available  phosphorus;  3‐6  times  more).  Removal  of  lime  prior to ryegrass fertilization on acidic, sandy soil did not have any significant effect on plant yield  compared  to  using  ash  containing  lime,  as  soil  acidity  gradually  dissolved  the  lime  in  ash  treatments  and  enhanced  phosphorus  availability.  However,  plant  phosphorus  uptake  from  ash  with lime removed was three times higher than that of lime‐containing ash. For high phosphorus  application rate (1066 mg P/kg soil), the yields in ash treatments were almost as good as for using  the inorganic fertilizer of monocalcium phosphate (MCP). Heavy metal uptake by plants was minor  [14].    The  field  tests  for  the  growth  of  barley  and  ryegrass  on  two  Danish  (one  sandy  and  one  loamy)  agricultural soils  over  two  growing  seasons  indicated  that  application  of  ash  for  20  kg  P/ha  only  slightly increased barley  DM yield compared to no addition. However, total phosphorus uptake in  barley was the same as for addition of 20 kg P/ha DSP during the first year (1.2 g P/m2) and 15%  higher in a new experiment in the second year. Tripling ash application rate to 60 kg P/ha in both  sandy  and  loamy  soil  had  no  significant  effect  on  barley  DM  yield  and  phosphorus  uptake  was  comparable  to  the  application  of  20  kg  P/ha  in  ash.  Performance  of  neutralized  phosphorus  containing acid extract from the ash was as good as DSP in sandy soil both in terms of barley DM  yield and phosphorus uptake. Despite the low background phosphorus level in both soils, the rye  grass crop grew very well and application of extra phosphorus in the form of ash therefore did not  produce any significant increase in grass DM yield and phosphorus uptake. Soil pH was noticed to  increase from 6.3 to 6.8 in both soils 18 months after ash application [12].          The project is partly financed European Regional Development Fund by the European Union - 13    6.3.4 Ash spreading techniques on land  Because the ash from thermally gasified manure was a very fine material with almost 80% w/w of  particles ranging in diameter between 75‐250 μm [9], it is sensitive for wind erosion. In order to  prevent its loss after fertilization, several techniques can be recommended:  1. Mixing with topsoil – this was the case during the field experiments shown in [12] and [14],  however on a large scale, rather time consuming and unpractical,  2. Injection with water – the drawback of ash having a highly hydrophobic nature (big wetting  angle) resulting in inhomogeneous distribution in water,   3. Granulation  (techniques  already  developed  for  other  kinds  of  ashes,  e.g.  wood  [21,  22,  23]),  4. Mixing with sewage sludge to provide mineral‐organic fertilizer.  6.3.5 Summary of ash reuse  In general, ash from thermally gasified manure releases phosphorus in a slower rate than mineral  fertilizers,  providing  lower  plant  yields  but  in  parallel  lower  leachability.  Therefore  it  is  not  recommended as a starter fertilizer; however, its supplementation in later stages of growth may  be an option. In spite of lower yields, phosphorus uptake from ash is similar to the uptake from  mineral  fertilizers.  The  mismatch  between  relatively  good  phosphorus  uptake  and  poorer  plant  yields  is  probably  due  to  other  factors,  such  lime  content  and  toxicity  from  heavy  metals.  Long‐ term field studies with ash application and testing of residual effects are needed also to verify the  accumulation of phosphorus and heavy metals in the soil.  6.3.6 Changes in the residue as compared to original manure  Thermal  gasification  of  manure  concentrates  acid‐extractable  metals  in  the  ash  as  compared  to  the original pellets. The other factor which may affect these measurable concentrations is the half‐ organic nature of the pellets (38‐44% ash content) and totally mineral nature of ash. Therefore, in  order  to  compare  the  chemical  characteristics  of  these  two  materials,  the  concentrations  were  referred  to  incombustible  matter  (IM),  which  in  case  of  pellets  denotes  the  ash  content.  Even  then, most of the measured elements were detected at higher concentrations in the ash than in  the  pellets.  Only  phosphorus  range  was  quite  similar.  Table  6  shows  the  comparison  between  basic  chemical  composition  of  pellets  from  digested  pig  manure  and  ash  from  its  thermal  gasification.    Table 6. Comparison of chemical composition between pellets and ash as measured by UV-VIS spectrometry in H2SO4 extracts (P) and FAAS (remaining metals). IM – incombustible matter [9]. Pellets  g/kg IM  38–57  11  0.81  0.07  0.18  0.03  Analysis  Total P  Total K  Total Zn  Total Cu  Total Cr  Total Ni  Ash  g/kg IM  54.4  15  1.25  0.20  0.09  0.12          The project is partly financed European Regional Development Fund by the European Union - 14    6.3.7 Changes during storage  During storage of ash, the transformation of lime from calcium oxide (CaO) into calcium carbonate  (calcite) may occur. The lime in the ash is abundant in two forms; calcium oxide (burnt lime) and  calcium carbonate (limestone, calcite) depending on its age. In the beginning of storage, calcium  oxide  present  in  the  ash  can  react  with  water  from  the  atmosphere  forming  calcium  hydroxide  (Ca(OH)2)  and  further  reacting  with  carbon  dioxide  forming  calcium  carbonate  (CaCO3,  carbonization).    This  may  have  a  negative  effect  on  ash  pre‐treatment  prior  to  phosphorus  extraction  due  to  limited  dissolution  of  calcium  at  later  ash  ages.  The  reason  for  low  calcium  removal from the ash is in fact that calcium oxide rapidly forms calcium hydroxide with a very low  water solubility (0.18 g Ca(OH)2 in 100 ml H2O at 0oC), thus only minor amounts of calcium oxide  present in fresh ash can be dissolved in water [11, 13, 15].  6.4 Future possibilities  The  use  of  low  value  fuels  for  production  of  electricity  at  efficiencies  around  45%  is  within  the  scope of the LT‐CFB gasifier, which is expected to be feasible in sizes from around 5 to around 100  MW  of  fuel  input.  Based  on  more  intensive  purification,  the  gas  can  also  be  used  for  more  demanding  applications,  and  the  possibility  of  producing  liquid  fuels/products  may  also  be  considered [3, 4]. However, production of fuels would require extensive and expensive purification  stages as well as most likely a change into steam gasification.     The  technology  (LT‐CFB)  presented  in  this  report  is  now  being  upgraded  in  the  6  MW  demonstration plant owned by DONG Energy in Kalundborg, Denmark. The demonstration plant is  described  in  more  detail  in  the  separate  Baltic  MANURE  report  “Examples  of  existing  good  practices in manure energy use” (available at   7. REFERENCES  [1] Babu, B.S. (2006): Perspectives on biomass gasification. IEA Bioenergy Agreement. Proceedings  of the workshop; Task 33: Thermal Gasification of Biomass, Vienna, 3 May 2004, pp. 5‐7,    [2]  Henriksen  U.  (2011)  From  Biomass  Gasification  Group,  About  BGG,  What  is  gasification?: , accessed on April 05, 2011,    [3] Stoholm, P., 2007. Gasification of problematic biofuels. Bioenergy Research 20, 8‐10,    [4] Stoholm, P., Ahrenfeldt, J., Henriksen, U., Gómez, A., Krogh, J., Nielsen, G. R., Sander, B., Danish  Fluid Bed Technology ApS (DFBT), c/o CAT, Technical University of Denmark (DTU‐Risø), University  of Castilla – La Mancha, Anhydro A/S, DONG Energy A/S., 2008. The Low Temperature CFB Gasifier  – 500 kW test on biogas fiber residue. Proceedings of the 16th European Biomass Conference, 2‐6  June, Valencia, Spain,    [5] Møller, H.B, Lund I., Sommer, S.G., 2000. Solid‐liquid separation of livestock slurry: efficiency  and cost. Bioresource Technology, 74, 223‐229,            The project is partly financed European Regional Development Fund by the European Union - 15    [6]  Zhang,  R.H.,  Lei,  F.,  1998.  Chemical  treatment  of  animal  manure  for  solid‐liquid  separation.  Transactions of the Asae, 41, 1103‐1108,    [7] Poulsen, T. G., T. Prapaspongsa, Hansen, J. Aa., 2008. Energy and greenhouse gas balances for  pig  manure  using  alternative  treatment  options.  Proceedings  of  the  ISWA/WMRAS  World  Congress, Singapore, November, 2008,    [8] Personal conversation with Peder Stoholm – one of the developers of LT‐CFB technology,    [9]  Kuligowski,  K.,  Poulsen,  T.  G.,  Stoholm,  P.,  Pind,  N.,  Laursen  J.,  2008.  Nutrients  and  heavy  metals distribution in thermally treated pig manure. Waste Management and Research, 26, 347‐ 354,    [10] Kuligowski, K., Poulsen, T. G., 2009. Phosphorus leaching from soils amended with thermally  gasified piggery waste ash. Waste Management, 29, 2500‐2508,    [11] Kuligowski, K., Poulsen, T. G., 2010. Phosphorus and zinc dissolution from thermally gasified  piggery waste ash using sulphuric acid. Bioresource Technology, 101, 5123‐5130,    [12] Kuligowski, K., Poulsen, T. G., Rubæk, G. H., Sørensen, P., 2010. Plant‐availability to barley of  phosphorus in ash from thermally treated animal manure in comparison to other manure based  materials and commercial fertilizers. European Journal of Agronomy, 33, 293‐303,    [13]  Kuligowski,  K.,  Gilkes,  R.  J.,  Poulsen,  T.  G.,  Yusiharni,  B.  E.,  2010.  The  composition  and  dissolution  in  citric  extractants  of  ash  from  the  thermal  gasification  of  pig  manure.  Chemical  Engineering Journal, 163, 1‐9,    [14]  Kuligowski,  K.,  Gilkes,  R.  J.,  Poulsen,  T.  G.,  Yusiharni,  B.  E.,  2010.  Ash  from  the  thermal  gasification  of  pig  manure  –  effects  on  ryegrass  yield,  element  uptake  and  soil  properties  (submitted to Australian Journal of Soil Research on 24.10.2010),    [15]  Cohen,  Y.  and  Kirchmann,  H., 2007.  Phosphorus  dissolution  from  ash  of  incinerated  sewage  sludge and animal carcasses using sulphuric acid. PhD thesis. Department of Soil Sciences, Swedish  University of Agricultural Sciences, Uppsala, Sweden,    [16]  Foged,  Henning  Lyngsø.  2010.  Best  Available  Technologies  for  Manure  Treatment  –  for  Intensive  Rearing  of  Pigs  in  Baltic  Sea  Region  EU  Member  States.  Published  by  Baltic  Sea  2020,  Stockholm. 102 pp.    [17]  Conference  „Biomass  –  Waste  –  Energy  2011”,  Institute  of  Fluid  Flow  Machinery  Polish  Academy  of  Sciences  and  the  Foundation  of  Energy  Saving  in  Gdansk,  within  projects:  REGNA  (Nature‐Friendly Development of Gminas) under the Norwegian and EEA Financial Mechanism and  Bioenergy Promotion under the Baltic Sea Region Programme 2007‐2013, March 10th, 2011,            The project is partly financed European Regional Development Fund by the European Union - 16    [18]  Bartocci  A,  2009.  Air  pollution  control  innovations,  gasification  syngas  cleaning.  Envitec  Industrial  Gas  Cleaning  Systems,  available  at:‐pollution‐control‐ innovations/bid/20053/Gasification‐syngas‐cleaning,    [19]  S.  Ch.  Roy,  H.  L.  Prasad,  P.  Dutta,  A.  Bhattacharya,  B.  Singh,  S.  Kumar,  S.  Maharaj,  V.  K.  Kaushik, S. Muthukumaru Pillai, M. Ravindranathan, 2001. Conversion of syn‐gas to lower alkenes  over Fe‐TiO2‐ZnO‐K2O catalyst system. Applied Catalysis A: General, 220, 153‐164,    [20]  S.  Rapagná,  H.  Provendier,  C.  Petit,  A.  Kiennemann,  P.  U.  Foscolo,  2002.  Development  of  catalysts  suitable  for  hydrogen  or  syn‐gas  production  from  biomass  gasification.  Biomass  and  Bioenergy, 22, 377‐388,    [21] K. Väätäinen, E. Sirparanta, M. Räisänen, T. Tahvanainen, 2010. The costs and profitability of  using  granulated  wood  ash  as  a  forest  fertilizer  in  drained  peatland  forests.  Biomass  and  Bioenergy,  In  Press,  Corrected  Proof,  Available  online  6  October  2010,  1‐7,    [22]  F.  Medici,  L.  Piga,  G.  Rinaldi,  2000.  Behaviour  of  polyaminophenolic  additives  in  the  granulation  of  lime  and  fly‐ash.  Waste  Management,  20,  491‐498,    [23] K. Prabhakaran, K. G. K. Warrier, Pradeep. K. Rohatki, 2001. Preparation of free flowing fly ash  granules containing multifunctional molecules, 27, 749‐754,    [24]  R.  G.  Nielsen,  P.  Stoholm,  M.  B.  Nielsen,  J.  Krogh,  N.  Norholm,  S.  Antonsen,  B.  Sander,  U.  Henriksen,  B.  Qvale,  2005.  THE  LT‐CFB  GASIFIER  –  FIRST  TEST  RESULTS  FROM  THE  500  KW  TEST  PLANT.  Presented  at:  European  Biomass  Conference  &  Exhibition,  Biomass  for  Energy,  industry  and climate protection. Paris, 2005,    [25] Comments from SP Technical Research Institute of Sweden    [26] H. Kitzler, C. Pfeifer, H. Hofbauer, 2011. Pressurized gasification of woody biomass ‐ Variation  of parameter. Fuel Processing Technology, 92, 908‐914,    [27]  K.  Svoboda,  M.  Pohořelý,  M.  Hartman,  J.  Martinem,  2009.  Pretreatment  and  feeding  of  biomass for pressurized entrained flow gasification. Fuel Processing Technology, 90, 629‐635,    [28]  Cai  Liang,  Xiaoping  Chen,  Pan  Xu,  Bo  Liu,  Changsui  Zhao,  Chuanlong  Xu,  2011.  Effect  of  moisture  content  on  conveying  characteristics  of  pulverized  coal  for  pressurized  entrained  flow  gasification. Experimental Thermal and Fluid Science, In Press, Corrected Proof, Available online 29  March  2011,    [29] J. Fermoso, B. Arias, M.G. Plaza, C. Pevida, F. Rubiera, J.J. Pis, F. García‐Peña, P. Casero, 2009.  High‐pressure  co‐gasification  of  coal  with  biomass  and  petroleum  coke.  Fuel  Processing  Technology, 90, 926‐932.            The project is partly financed European Regional Development Fund by the European Union - 17    [30]  S.  Priyadarsana,  K.  Annamalaia,  J.  M.  Sweetenb,  M.  T.  Holtzapplec,  S.  Mukhtard,  2005.  Co‐ gasification  of  blended  coal  with  feedlot  and  chicken  litter  biomass.  Proceedings  of  the  Combustion Institute, 30, 2973–2980.    [31] T. R. Miles, A. R. Miles, B. R. Bock, 2004. Demonstration of energy and nutrient recovery from  animal  manure.  Proceedings  of  the  to  the  2nd  World  Congress  and  Technology  Exhibition  on  Biomass for Energy Industry and Climate Protection, Rome, 10‐14 May, 2004.    [32]  Ptasinski,  K.J.,  Prins,  M.J.  and  Pierik,  A.,  2007.  Exergetic  evaluation  of  biomass  gasification.  Energy, 32, 568–574.    [33] T. Q. Frandsen, 2010. Introduction to bioenergy in Denmark. Status and trends. Polish‐Danish  Bioenergy Meeting, Gdansk, 7 October, 2010.     [34] T. A. Seadi, 2000. Danish centralised biogas plants – plant description. University of Southern  Denmark, 2000.          The project is partly financed European Regional Development Fund by the European Union - 18    This report in brief About the project Thermal gasification is an emerging technology for the utilization of manure energy content with proven advantages over conventional combustion. The Baltic Sea Region is an area of intensive agricultural production. Animal manure is often considered to be a waste product and an environmental problem. While the technology is ready for many other fuels (e.g. coal, wood, waste) its development for low calorific problematic (i.e. corrosive) fuels, such as manure, is still work in progress. The economic feasibility is not proven yet, and the environmental legislation still needs to be adjusted for farm-scale installations. The long-term strategic objective of the project Baltic Manure is to change the general perception of manure from a waste product to a resource. This is done through research and by identifying inherent business opportunities with the proper manure handling technologies and policy framework. However, thermal gasification holds promise for energy production from manure while also offering reduction of manure-based emissions, providing the energy storage in the resulting syn-gas and reuse options for phosphorous and micronutrients from the ash. To achieve this objective, three interconnected manure forums has been established with the focus areas of Knowledge, Policy and Business. Read more at This report on thermal gasification of manure was prepared as part of Workpackage 6 on Manure Energy Potentials in the project Baltic Manure. Part-financed by the European Union (European Regional Development Fund)
Clean Heat and Power Using Biomass Gasification for Industrial and Agricultural Projects February 2010 Prepared by: Carolyn J. Roos, Ph.D. WSU Extension Energy Program P.O. Box 43165 • Olympia, WA 98504-3165 (360) 956-2004 • Fax (360) 236-2004 • TDD (360) 956-2218 WSUEEP08-033 Rev. 5, 2010 Cooperating agencies: Washington State University Extension Energy Program, U.S. Department of Energy, Alaska Energy Authority, Idaho Office of Energy Resources, Montana Department of Environmental Quality Energy Program, and Oregon Department of Energy blank About the Author Carolyn Roos, Ph.D., is a mechanical engineer with the Washington State University Extension Energy Program. She provides technical support to the Northwest Clean Energy Application Center with a focus on clean heat and power (CHP), waste heat recovery, district heating, and biopower/gasification CHP applications. She has experience in building systems‘ energy efficiency, mechanical design in hydroelectric facilities, and solar thermal applications. Carolyn provides technical assistance to commercial and industrial clients on energy system efficiency topics. She can be contacted by email at Acknowledgements This study was funded by the Northwest Clean Energy Application Center with support funding from the U.S. Department of Energy‘s Industrial Technologies Program and from the State of Washington. Disclaimer While the information included in this guide may be used to begin a preliminary analysis, a professional engineer and other professionals with experience in biomass drying should be consulted for the design of a particular project. Neither the Northwest Clean Energy Application Center nor its cooperating agencies, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the Northwest Clean Energy Application Center or its cooperating agencies. i Executive Summary The use of biomass to generate heat power, fuels and chemicals is crucial in achieving energy independence and increasing our use of renewable energy sources. In our transition to renewable energy, gasification promises to play a major role in large part because its products can make use of existing infrastructure and equipment associated with fossil fuel use. This guidebook is intended for use by the forest products and food processing industries. It can also be used by farmers, ranchers and others who have access to biomass materials. Gasification is a thermal conversion process in which both heat and a combustible product gas are produced. Combustion, in contrast, produces only heat, most commonly in a boiler to generate steam for production of electricity using a steam turbine. With gasification, generation of a combustible gas is key to its importance. A gaseous fuel makes the use of reciprocating engines, gas turbines and fuels cells possible in the generation of electricity, thereby increasing electrical efficiency. Gasification also makes possible a highly efficient configuration for generating electricity, referred to as an integrated gasification combined cycle (IGCC). Further, gasification can facilitate the use of biomass for heat and power because gaseous fuels can be distributed by pipeline from a gasification plant for use in other locations, either on site or off. Gasification of biomass and the use of the product gas in boilers and furnaces have a long and proven history. However, using the product gas for efficient electricity generation with engines, turbines and fuel cells has been hampered until recently by technical difficulties in removing tars from the product gas. Tar removal technologies have advanced in recent years and have now been successfully demonstrated and proven reliable. With these advances, biomass gasification for generation of heat and power has now emerged into commercialization. In the U.S., construction will begin in 2009 on a 42 MWe commercial-scale project in Tallahassee, Florida, and another 28 MWe gasifier is planned for Forsythe, Georgia. Around the world, more than 100 biomass gasifier projects are operating or ordered. In addition to heat and power, there is a wide array of co-products possible with gasification. This can improve the cost effectiveness of a gasification project. The product gas can be used as a feedstock to produce hydrogen and liquid hydrocarbons, such as ethanol, diesel and chemical feedstocks. Biochar has several potential markets and also gives gasification the potential of a carbon neutral or carbon negative energy solution. Both combustion and gasification produce ash, which also can be marketed. This guide is a practical overview of gasification on the small (<1 MW) and medium scales appropriate for food processors, farmers, forest products industries and others with access to biomass materials. The selection and application of gasifiers, engines and turbines, feedstock preparation and handling equipment, gas clean up technologies, and other ancillary equipment are discussed. Practical strategies for avoiding slagging, fouling and corrosion in the gasifier and downstream equipment are discussed. ii Contents About the Author .................................................................................................... i Acknowledgements ................................................................................................ i Disclaimer .............................................................................................................. i Executive Summary .............................................................................................. ii Introduction ........................................................................................................... 1 What is Gasification? ............................................................................................ 3 Why Gasification? ................................................................................................. 4 Comparison with Other Thermal Conversion Processes ...................................... 6 System Equipment ................................................................................................ 9 Product Gas Composition ................................................................................... 23 Feedstock Characteristics and Requirements .................................................... 24 Reducing Slagging, Fouling and Corrosion ......................................................... 29 Gas Clean-Up ..................................................................................................... 32 Marketable Co-Products ..................................................................................... 35 Environmental Benefits ....................................................................................... 39 Industry Applications ........................................................................................... 41 Demonstration Projects ....................................................................................... 42 Other Information Resources .............................................................................. 52 References ......................................................................................................... 55 iii List of Tables Table 1. Summary of Bioenergy Conversion Technologies ................................. 2 Table 2. Comparison of Combustion, Gasification and Pyrolysis ......................... 8 Table 3. Predominant Components of Products from Fast Pyrolysis and Gasification .......................................................................................... 8 Table 4. Summary of Selected Biomass Gasifier Types .................................... 15 Table 5. Typical Energy Contents of Producer Gas, Syngas and Natural Gas .. 23 Table 6. Typical Heating Value, Moisture Content and Ash Content of Selected Biomass Feedstocks .......................................................................... 26 Table 7. Characteristics of Common Biomass Feedstocks ................................ 27 Table 8. Chemical Contents of Product Gas from Selected Biomass Fuels ...... 27 Table 9. Biomass Characteristics As Compared to Coal ................................... 28 Table 10. Typical Tar and Particulate Contents of Gasifier Types ..................... 34 Table 11. Tolerance of End-Use Devices for Tar*.............................................. 34 Table 12. Examples of European Biomass Gasification Projects....................... 47 Table 13. Examples of North American Biomass Gasification Projects ............. 49 List of Figures Figure 1. Updraft and Downdraft Fixed-Bed Gasifiers* ...................................... 11 iv Introduction Biomass feedstocks are becoming increasingly valuable as the demand for renewable fuels has increased and the supply of wood fuels has diminished with the decline in the housing market. Bark, wood chips, and shavings, once considered waste and disposal problems, are now commodities with demand coming from domestic forest products companies, as well as European markets. Other biomass residuals, such as food processing and agricultural wastes, are increasingly being looked upon as fuel sources. As cellulosic ethanol production emerges into commercialization, demand for wood and agricultural residuals will only increase. These trends will likely continue as a whole range of new technologies and uses, summarized in Table 1, are added to traditional technologies and uses. Volatile prices for conventional energy sources have significantly changed the economics of efficiently using our biomass resources. With rising electricity prices and increasing demand for renewable energy, base load biomass-fired clean heat and power1 (CHP) systems become more attractive. It is now more important than ever that we use our biomass resources efficiently. Biomass gasification can achieve higher efficiencies in generating electricity and lower emissions compared to combustion technologies. Further, gasification increases the possible uses of biomass since the product gas has value not just as a fuel in itself, but also as a feedstock to produce other fuels, such as ethanol and hydrogen, and as a chemical feedstock. Biomass gasification has trailed coal gasification due to technical differences deriving from the characteristics of the feedstocks, as well as the typical scale of operation. Technological advances particular to biomass gasification have been successfully demonstrated and commercial-scale projects are proceeding. Around the world, more than 100 biomass gasifier projects are operating or ordered. In the U.S., construction will begin in 2009 on a 42 MWe commercial-scale project in Tallahassee, Florida, and another 28 MWe gasifier is planned for Forsythe, Georgia. Small-scale gasification is moving ahead as well in the U.S. A 300 kW farm-scale demonstration using straw as a feedstock and a 320 kW project at a sawmill have been constructed and are now beginning operation. This publication focuses on gasification of biomass on the small and medium scales appropriate for food processors, farmers, forest products industries and others with access to biomass materials. This guide focuses primarily on woody biomass and food and agricultural residues. 1 ―Clean heat and power‖ or CHP refers to clean, efficient local energy generation, including but not limited to combined heat and power, recycled energy, bioenergy, and other generation sources that lead to a demonstrable reduction in global greenhouse gas emissions. 1 Table 1. Summary of Bioenergy Conversion Technologies Technology Technology Status Possible Products Facility Type Biogas, power, heat, soil amendments and fertilizers, and other coproducts including animal bedding. Dairies, food processors, confined animal feedlots, wastewater treatment facilities Ethanol and distiller‘s dried grains and coproducts including fiber, bran, germ and oil. Cellulosic ethanol, chemical feedstocks, hydrogen, and other coproducts Biofuels, agricultural and food and beverage processing industries Wide range of facility types, including forest products, agricultural and food industries Wide range of facility types, including forest products, agricultural and food processing industries Forest products industries Biochemical Conversion Anaerobic Digestion Ethanol Fermentation Lignocellulosic Conversion Mature with continuing research and development on co-products and high solids/strength digesters Mature with efforts to reduce the carbon footprint Research & Development with pilot and commercial-scale demonstration projects in development Biofuels and biorefineries, especially in the forest products industry Thermochemical Conversion Combustion Mature Power, heat, soil amendments, and other co-products Biomass Gasification Demonstration emerging into commercialization Power, heat, combustible gas, chemical feedstocks, hydrogen, biochar, soil amendments Biomass Pyrolysis Demonstration Power, heat, liquid fuel (―bio-oil‖), combustible gas, chemical feedstocks, soil amendments, biochar 2 What is Gasification? Gasification is a thermal conversion process – as is combustion – in which both heat and a combustible product gas are produced. One method of gasification, referred to as ―partial oxidation,‖ is very similar to combustion except that it occurs with insufficient oxygen supply for complete combustion to occur. In a second method, the biomass is indirectly heated in the absence of oxygen or air, with steam as the oxidizing agent. The product gas is either a medium-energy content gas referred to as ―synthetic gas‖ or ―syngas‖ or a low-energy content gas often referred to as ―producer gas.‖2 Syngas consists primarily of carbon monoxide and hydrogen. Higher quality syngas can be produced by indirect heating or by using pure oxygen as the oxidizing agent (―oxygenblowing‖). Producer gas results if air is used as the oxidizing agent (―air-blowing‖), which dilutes the combustible components of the gas with nitrogen. Generally, producer gas is adequate for power generation and avoids the energy use associated with oxygen production. Syngas is required for chemical production. The product gas can be burned in conventional boilers, furnaces, engines and turbines, or co-fired with natural gas, with minor modifications to conventional equipment. Since both producer gas and syngas have lower heating values than propane or natural gas, enlarging orifices and adjusting control settings may be required. The product gas can also be used in solid-fuel boilers as a reburn fuel that is injected into the boiler. As a note on terminology, the term ―gasifier‖ has been applied to staged-air combustion appliances in which product gas generated in a first stage is burned in a second stage of an integrated unit or closely coupled unit with no provision for collecting the product gas. However, in this guide, the terms ―gasifier‖ and ―gasification‖ are used to refer only to equipment that is designed to obtain both a combustible product gas and heat as separate products. 2 It is quite common and accepted to use the term ―syngas‖ to refer to the product gas in general, whether syngas or producer gas as defined here. However, other references make a clear distinction in terminology, as does this guide. Some references also use the term ―biogas‖ to refer to the product gas of biomass gasification. However, this is easily confused with the methane rich-gas produced by anaerobic digestion, which is more commonly referred to as biogas. 3 Why Gasification? Gasification has several advantages that make it an appropriate choice in certain types of projects. Gasification occurs at lower temperatures than combustion. Because gasification is a lower temperature process than combustion, gasifiers can have longer lifetimes and lower maintenance costs than combustion appliances, such as woodfired boilers. Likewise, air emissions are generally lower with gasification since nitrogen and sulfur oxides are created at higher temperatures. A variety of products are possible with gasification. The gasification process results in co-products that can result in other revenue streams for a project. Syngas can be used as a feedstock to produce other fuels (such as ethanol, methanol, naptha, hydrogen, gasoline and diesel) and as a feedstock for chemicals (such as acetic acid, dimethyl ether, and ammonia). The oils, char and ash that are often generated in gasification may be marketable precursors for products such as soil amendments, filtration media and cement additive. The char in particular can have a high value as a co-product. Gasification has synergies with existing fossil fuel infrastructure. Gasification has synergies with fossil fuel use that can facilitate our transition to renewable energy. As an example of a synergistic opportunity, liquid transportation fuels produced from syngas can be distributed through our current fueling infrastructure. Also, syngas and producer gas can be co-fired with natural gas in conventional turbines and fuel cells or co-fired in coal-fired boilers to generate electricity. Bio-hydrogen produced from syngas can be used in conjunction with hydrogen produced from natural gas. Facilities that currently use coal syngas in the production of chemicals can supplement it with syngas from biomass using existing infrastructure. Gaseous fuels are easier to transport than solid biomass. Gaseous fuels can be distributed by pipeline from a gasification plant for direct use in other locations. There are various scenarios where this would be an advantage. As one example, a gasifier could be located at the most convenient point of biomass collection with the product gas piped to users located off site. As another example, available space within a manufacturing facility may prohibit locating a biomass-fired boiler or furnace and its ancillary equipment within the facility. In this case, a gasifier could be located elsewhere with the product gas piped to the point of use. As a note of caution, the gasifier should still be located where there is a use for its heat to achieve the high efficiencies possible with CHP systems. Landfill gas use in this country serves as an illustration of this potential. Of the approximately 500 landfill gas projects existing in the U.S., about a third pipe the gas in dedicated pipelines to nearby industrial customers to offset fossil fuel use. Biogas pipelines range from 200 yards to more than 20 miles. 4 Use of turbines, engines and fuel cells increases efficiency of electricity generation. An important advantage of gasification compared to combustion is its potential to achieve higher efficiencies and lower emissions. Generating a gaseous fuel makes the use of reciprocating engines, gas turbines and fuel cells possible in the generation of electricity. Gas turbines, fuel cells and engines are more efficient electrical generation technologies than the steam cycle to which solid biomass is limited. The efficiency of a biomass-fired steam turbine system is between 20% and 25%. In comparison, syngas-fueled engines and turbines can achieve system efficiencies in the range of 30% to 40%, with higher efficiencies possible in integrated combined cycles. In considering overall efficiency, it is important to examine losses in the gasification process itself in converting biomass to the product gas in addition to improved electrical efficiency. If the chars and tars that result in gasification are reburned and the heat of gasification is recovered, high conversion efficiencies can be achieved. Gasification makes biomass-fired integrated combined cycles possible. Gasification makes possible a highly efficient configuration for generating electricity (that is not possible with combustion of biomass), referred to as an integrated gasification combined cycle (IGCC). In an IGCC system, the product gas is first burned in a gas turbine to generate electricity (topping cycle). Second, waste heat from both the turbine and the gasifier is recovered in a heat recovery boiler and used to generate electricity by a steam turbine (bottoming cycle). Such a system can achieve high electrical efficiencies of 42% to 48%. If low-pressure steam is also recovered from the steam turbine and other heat recovery opportunities in the system are taken advantage of, overall efficiencies of 60% to more than 90% can be achieved. Note that IGCC systems are cost effective only on larger scales due to the high capital cost of the gasifier, gas turbine, boiler and steam turbine, plus ancillary equipment. The first project to demonstrate the IGCC technology operated from 1993 to 2000 in Varnamo, Sweden, producing 6 MWe of power and 9 MWth of heat in short stints for research and development purposes. The IGCC plant soon to begin construction in Tallahassee, Florida, will deliver both methanated syngas and high efficiency, renewable power to the City of Tallahassee. Gasification can facilitate combined heat and power. If heat from both the gasification process and electrical generation are recovered, overall efficiencies of 60% to more than 90% can be achieved. Such combined heat and power (CHP) is possible with both combustion and gasification. But because gaseous fuels can be piped over a distance, gasification can facilitate combined heat and power projects in cases where the best use of heat from the gasifier and the best or most convenient use of the product gas are not in close proximity. In the most cost effective CHP projects, heat recovery is cascaded through a series of applications with each step using a lower temperature. Heat can be recovered from the gasification process and from electrical generation equipment. Waste heat can be used in a variety of ways, such as generating steam and hot water, space heating, generating 5 power using an organic Rankine cycle turbine, or meeting cooling and refrigerating needs with absorption chillers. Comparison with Other Thermal Conversion Processes Combustion, gasification and pyrolysis are three thermal conversion processes by which energy is obtained from biomass. Distinctions between these three processes are summarized in Tables 2 and 3. In short, combustion occurs with sufficient oxygen to completely oxidize the fuel, i.e. convert all carbon to carbon dioxide, all hydrogen to water, and all the sulfur to sulfur dioxide. Gasification occurs with insufficient oxygen or with steam such that complete oxidation does not occur. Pyrolysis occurs in the absence of an oxidizing agent (air, oxygen, or steam). As an intermediate process between combustion and pyrolysis, gasification is sometimes referred to as ―partial oxidization‖ and sometimes as ―partial pyrolysis.‖ Gasification, combustion and pyrolysis each have advantages and disadvantages. In any particular project, it is important to evaluate the goal of the project, the biomass resources available, and particular needs of the facility in choosing a thermal conversion process. Gasification versus Combustion In choosing between gasification and combustion, consider if generating a product gas is an advantage. Also, consider the possibility of achieving higher electrical efficiency by burning the product gas in an engine or turbine, as opposed to generating electricity by the conventional steam cycle. Another factor to consider is that gasification projects may be eligible for more grants and incentives than the more tried and true combustion projects—at least for a time. Greater carbon emission reductions may also bring in revenue in carbon offset markets. In a financial analysis comparing gasification and combustion options, the lower operating and maintenance costs and longer equipment lives possible with gasification should be considered. The lower air emissions of gasifiers (and possibly reduced cost of air emissions equipment) should be considered in estimating capital costs. Gasifiers may be designed and operated to favor thermal efficiency over production of a char, or vice versa. In comparison, combustion appliances are operated to maximize efficiency by minimizing char. In a financial analysis of a gasification project, the value of producing char as a marketable byproduct versus achieving high efficiency may be a consideration. Note some gasifiers are designed to produce no char and their thermal efficiency can be very similar to that of a well-tuned combustion appliance. Combustion technologies are well-established and widespread. While gasification has been successfully demonstrated in projects of several megawatts in size over a number of years, it is still an emerging commercial technology. As capital costs drop, operating 6 experience increases, and the economic value of carbon emission reductions increases, cost effectiveness of gasification compared to combustion will improve. At this point in time, if the primary end use is electricity generation on relatively small scales, combustion of biomass in a biomass-fired boiler with electricity generated using a steam turbine will likely be more cost effective than a gasification system generating electricity with an internal combustion engine or turbine. Similarly, if the desired product is only heat, whether for industrial process heat, space heating, or water heating, a biomass-fired boiler or furnace will likely be most cost effective at this time, although other factors discussed above may in some cases tip the balance toward gasification. Gasification versus Pyrolysis Another promising thermal conversion technology, sometimes confused with gasification, is pyrolysis. While gasification occurs with restricted oxygen, pyrolysis occurs in the absence of oxygen or steam. In pyrolysis, biomass is heated to the point where volatile gases and liquids are driven off and then condensed into a combustible, water soluble liquid fuel called bio-oil (not to be confused with bio-diesel.) Bio-oil from fast pyrolysis3 is a low viscosity, dark-brown fluid with a high tar content and a water content of 15% to 20%. Bio-oil can be burned in a boiler, upgraded for use in engines and turbines, or used as a chemical feedstock. Being a liquid fuel, bio-oil is easier to transport than syngas but its corrosiveness makes long-term storage difficult. Both gasification and pyrolysis produce char, which can be used as a soil amendment, precursor to activated carbon, or burned. Slow pyrolysis results in a higher percentage of char (up to 35%), if that is a more desired co-product. Such uses of the biochar can make gasification and pyrolysis carbon neutral or even carbon negative (refer to the section ―Environmental Advantages‖ below). Pyrolysis is a less mature technology compared to gasification. There are fewer manufacturers of pyrolysis reactors and a small number of demonstration projects, which have shorter histories. Manufacturers of pyrolysis reactors are Dynamotive, BEST, Lurgi and Ensyn Technologies. BEST has had one pilot project and one small demonstration project. Dynamotive has two demonstration projects. For more information on pyrolysis, refer to IEA Bioenergy‘s PyNe website at and the Bioenergy Technology Group‘s website at In choosing between gasification and pyrolysis, consider whether the higher production of biochar in pyrolysis is desirable in your case. Also, consider whether a liquid fuel is more advantageous in your particular application than a gaseous fuel. In particular, a liquid fuel, such as bio-oil, has a higher energy density than syngas, which reduces 3 Fast pyrolysis occurs at a relatively low temperature of around 500°C (900°F) and the biomass has short residence times of 2 seconds or less. Intermediate and slow pyrolysis occur at higher temperatures and have longer residence times. As residence time increases, char content increases (up to about 35%), tar content decreases and water content of the bio-oil increases (up to about 75%). 7 transportation costs. On the other hand, bio-oil is corrosive, which increases transportation and storage costs. Table 2. Comparison of Combustion, Gasification and Pyrolysis Oxidizing Agent Typical Temperature Range with Biomass Fuels Principle Products Principle Components of Gas Combustion Gasification Pyrolysis Greater than stoichiometric supply of oxygen* Less than stoichiometric oxygen* or steam as the oxidizing agent Absence of oxygen or steam 800oC to 1200oC (1450oF to 2200oF) 800oC to 1200oC (1450oF to 2200oF 350oC to 600oC (660oF to 1100oF) Heat Heat and Combustible gas Heat, Combustible liquid and Combustible gas CO2 and H2O CO and H2 CO and H2 * In stoichiometric combustion, air supply is the theoretical quantity necessary to completely oxidize the fuel. For cellulosic biomass, which has an average composition of C6H10O5, the stoichiometric air supply is 6 to 6.5 lb of air per lb of biomass. Table 3. Predominant Components of Products from Fast Pyrolysis and Gasification Oil and Char Tars, Water Product Gas (Solid) (Liquid) Fast pyrolysis Medium temperature, T=~500oC Short residence time (<2 s) Gasification Higher temperature, T>800oC 1. 2. 60% to 70% 10% to 15% 10% to 25% Up to 20%1 Up to +20%2 ~85% Updraft gasifiers produce 10% to 20% tar, while tar content from downdraft gasifiers is low. Downdraft gasifiers produce 20% or more char, while char content from updraft gasifiers is low. 8 System Equipment A gasification project will consist of various components. In addition to the gasifier, a gasification project may have a turbine or reciprocating engine, generator set, pellet mill, grinder, biomass dryer, material feeders, gas clean-up equipment, and gas storage and handling equipment. Types of Gasifiers Types of gasifiers currently used in biomass gasification include fixed-bed, fluidized-bed and indirectly heated steam gasifiers. Characteristics of these types of gasifiers are summarized in Table 4. Other types of gasifiers, discussed only briefly here, include entrained bed, plasma arc, and super-critical water gasifiers. Within these general classifications, there are many different designs that have been developed. For examples of a number of fluidized bed gasifiers refer to ―Combustion and Gasification in Fluidized Beds‖ (Basu 2006). Fixed-Bed Downdraft and Updraft Gasifiers The most common types of fixed-bed gasifiers are downdraft (or co-current type) and updraft (or counter-current type). More recently, designs that combine characteristics from updraft and downdraft gasifiers have been developed. Fixed-bed gasifiers operate on a smaller scale than other types and so are often the most suitable choice for many types of biomass projects, such as at food processing facilities. Updraft gasifiers can have capacities of about 10 MW or less. Downdraft gasifiers can have capacities of about 2 MW or less. The defining difference between updraft and downdraft gasifiers is the direction of gas flow through the unit, as shown in Figure 1. In downdraft gasifiers, the oxidizing agent (air or pure oxygen with or without steam) enters at the top of the gasifier with product gas exiting at the bottom. Gas flow is the reverse in updraft gasifiers. Downdraft gasifiers produce syngas that typically has low tar and particulate content. They can produce as much as 20% char, but more typically char content is 2% to 10%. While production of char reduces the quantity of energy contained in the syngas, it can be used as a fuel (charcoal) and reburned in the gasifier, or marketed as a soil amendment or as a precursor for activated charcoal filtration medium. Because char often has a high value, gasifiers are sometimes operated to produce high quantities of char at the expense of gas production. Downdraft gasifiers are easy to control. They have outlet temperatures of 800°C (1450°F) and operating temperatures of 800°C to 1200°C (1450°F to 2200°F). Efficiency can be on par with updraft gasifiers, if heat from hot product gas is transferred to inlet air. A drawback of downdraft gasifiers is that the feedstock must have a moisture content of about 20% or lower. As discussed in the Section 9 ―Feedstock Characteristics and Requirements‖ below, materials meeting this limit include dry woods, nut shells, and rice husks. Other materials can be dried, but drying moist feedstocks impacts the cost effectiveness of a project because of the cost of the dryer and the energy required for drying. The updraft gasifier has been the principal gasifier used for coal for 150 years. Updraft gasifiers have high thermal efficiency, are easy to control, and are more tolerant of fuel switching than downdraft gasifiers. Updraft gasifiers have outlet temperatures of 250°C (480°F) and operating temperatures of 800°C to 1200°C (1450oF to 2200oF). An advantage is that they can handle moisture contents as high as 55%. A disadvantage is that they have high tar production and so require more extensive cleaning of the syngas. Tar removal from the product gas has been a major problem in updraft gasifiers. Manufacturers of updraft gasifiers include PRM (Primenergy, USA), Nexterra (Canada), Emery (USA), Lurgi (Germany), Purox (USA), and Babcock Wilcox Volund (Denmark). Manufacturers and suppliers of downdraft gasifiers include Biomass Engineering, Ltd. (UK), Community Power Corporation (USA), Dasag Energy (Switzerland), Fluidyne (New Zealand), Martezo (France), Biomass Engineering LTD/Shawton Engineering (UK), Ankur Scientific Energy Technologies (India), Thermogenics (USA), and Associated Engineering Works (India). VTT Energy in cooperation with Condens Oy and Entimos Oy (all from Finland) offer a combination updraft-downdraft fixed-bed gasifier. These are designed to achieve the higher efficiencies of updraft gasifiers with the low tar production of downdraft gasifiers. 10 Figure 1. Updraft and Downdraft Fixed-Bed Gasifiers* Updraft (Counter-Current) Gasifier Downdraft (Co-Current) Gasifier * There are many variations in specific designs. For example, solid fuel is not fed from the top in some designs. Fluidized Bed Gasifiers In fluidized bed gasifiers, the oxidizing agent and fuel are mixed in a hot bed of granular solids. Solid fuel and bed particles are fluidized by gas flow. The bed is usually composed of sand, limestone, dolomite or alumina. Gases and remaining solids are separated afterwards by cyclone. There are two types of fluidized bed gasifiers: bubbling and circulating. Bubbling fluidized bed gasifiers are appropriate for medium size projects of 25 MWth or less, while circulating fluidized bed gasifiers can range from a few MWth up to very large units. Fluidized bed gasifiers are especially good for biomass gasification. They have very good fuel flexibility and so can be considered true multifuel units. Wood waste, straw, and refuse-derived fuel, as examples, can be gasified in the same unit, although the heat output varies with the heat value of the fuel. Fluidized bed gasifiers reduce gas contaminant problems often associated with agricultural biomass. Due to their lower operating temperatures, ash does not melt, which makes its removal relatively easy and reduces problems with slagging. Sulfur and chloride are absorbed in the bed material, reducing fouling and corrosion. Fluidized bed gasifiers are more compact and have higher throughput than fixed bed gasifiers. Their efficiency is lower, but can be improved by recirculating gas. The product gas has low tar content, but has a high level of particulates. Manufacturers and suppliers of fluidized bed gasifiers for biomass include Energy Products of Idaho (USA), Foster Wheeler (Finland), METSO Power (formerly Kvaerner, Finland), Carbona (formerly Tampella, Enviropower, Vattenfall, USA), Lurgi (Germany), TPS Termiska (Sweden), Cratech (USA), Stein (UK), Gas Technology Institute (USA), Southern Electric International (USA), Sur-Lite Corp. (USA), Enerkem/Biosyn (Canada), Sydkraft (Sweden), Elsam/Elkraft (Denmark), 11 Biomass Technology Group (USA), and ABB (Switzerland). Manufacturers often specialize in gasification of particular types of feedstocks. While some of these have focused on woody biomass and/or agricultural wastes, others specialize in black liquor and paper mill sludges, and others on municipal solid waste. Indirectly Heated Steam Fluidized Bed Gasifiers Indirectly heated steam gasification was specifically designed to take advantage of the particular properties of biomass, such as high reactivity, low ash, low sulfur, and high volatile matter. The development of other types of biomass gasifiers was heavily influenced by coal gasification technology and so they are not optimum for biomass. For example, the high reactivity of biomass means that greater throughputs (i.e. higher rate of gasification) are possible with indirectly heated steam gasifiers, but the throughputs of other types of gasifiers are very limited. Throughputs of indirectly heated gasifiers can be several times that of other types of gasifiers. The SilvaGas or Taylor-type indirectly heated gasifier consists primarily of two chambers: the gasifier and the combustor. In the gasifier, the biomass mixes with steam and a heated solid medium, such as sand, in a circulating fluidized bed. No air or oxygen is added. The biomass is rapidly converted into syngas, char and tars at a temperature of approximately 850°C (1550°F). The solid particles – char and sand – are separated from the gas stream and directed to the combustor where the char is burned, reheating the circulating sand to 1000°C (1800°F). The reheated sand is then conveyed back to the gasifier to supply energy for gasification of the incoming biomass. The bubbling fluidized bed indirect gasifier developed by Manufacturing and Technology Conversion International, Inc (MTCI), primarily used for black liquor and paper mill sludges, is similar in that it consists of two stages, a lower combustor and an upper steam reforming stage. Indirectly heated gasifiers are inherently more complicated than directly-heated systems due to the need for a separate combustion chamber, and so have a higher capital cost. This is offset to a certain degree compared to oxygen-blown gasifiers because an oxygen separation plant (with its efficiency penalty) is not required. Indirectly heated gasifiers produce high quality syngas without the need for separation of oxygen from air for use as the oxidizing agent. The syngas has a higher percentage of methane and higher hydrocarbons, which poses a greater challenge in producing liquid fuels, chemicals and hydrogen. Significantly fewer emissions are produced in this process. In particular, not having oxygen in the gasifier makes it impossible to form dioxins if a chlorine-containing feedstock (such as processed municipal solid waste or recycled paper pulp sludges) is used. In the U.S. a 12 MW SilvaGas gasifier was demonstrated in 2000 to 2002 at the existing wood combustion facility at the McNeil Generating Station in Burlington, 12 Vermont. A 42 MWe SilvaGas-type gasifier will be installed in Tallahassee, Florida, with construction to begin in early 2009. Developers and manufacturers of this type of gasifier include FERCO/SilvaGas (USA), Manufacturing and Technology Conversion International, Inc. (USA), TRI, Inc. (USA), Taylor Biomass Energy (USA), the Technical University of Denmark, and Repotec (Austria). Other Types of Gasifiers Entrained Bed Gasifiers: In entrained bed gasifiers, fine fuel particles are suspended by the movement of gas to move it through the gasifier. An example of an entrained bed gasifier is the Chemrec black liquor gasifier. A Chemrec gasifier was installed in 1996 at the Weyerhaeuser mill in New Bern, North Carolina. Entrained bed gasifiers require large scale to be cost effective and so are not practical for many biomass projects. Supercritical Water Gasifiers: Materials with moisture contents up to 95% can be gasified with the use of supercritical water. This process is still in development, but promises to widen the range of possible feedstocks. For more information on supercritical water gasification, refer to Biomass Technology Group‘s website at Plasma Arc Gasifiers: In plasma arc gasification, electricity is fed to a torch, which has two electrodes, creating an arc. Inert gas is passed through the arc, heating the process gas to internal temperatures as high as 14,000°C (25,000°F). The temperature a few feet from the torch can be as high as 3,000°C to 4,000°C (5,000° to 8000ºF.) Because of these high temperatures the waste is completely destroyed and broken down into its basic elemental components. Plasma arc gasification has been used in the gasification of municipal solid waste, especially in Asia. Close-coupled Gasifiers: ―Close-coupled‖ or ―multi-stage‖ gasifiers4 are essentially staged-air combustion appliances (i.e. boilers or furnaces). Staged-air combustion is a conventional technology that is widely applied in both large and small combustion appliances. In any combustion of a solid – whether in a woodstove, furnace or boiler – volatile materials are first pyrolyzed and gasified followed by full combustion of gases. Most commonly, these processes occur in a single stage. In staged-air boilers and furnaces, thermal conversion occurs in two stages of an integrated unit. In the first stage, the biomass is gasified by restricting air flow. In the second stage, sufficient air is supplied for full combustion of the gases. A product gas is not extracted from staged-air combustion appliances as a separate product. In this guide, 4 Integrated staged-air combustion appliances units are sometimes called ―two-stage‖ or ―multi-stage‖ gasifiers, not to be confused with indirectly heated steam gasifiers, which are also often referred to as ―twostage‖ or ―dual-stage‖ gasifiers. 13 the term ―gasifier‖ refers only to appliances that produce a combustible gas as a separate product. The primary advantage of staged-air combustion compared to conventional singlestage boilers and furnaces is reduced air emissions. There can be an efficiency penalty compared to single stage combustion appliances due to greater production of char. A small-scale example of a ―close-coupled gasifier‖ is ChipTec‘s Wood Energy Biomass Gasification System (see On a larger scale, Primenergy‘s projects in Stuttgart, Arkansas, and Little Falls, Minnesota, combust the syngas in a closely coupled combustor to generate electricity in a steam cycle. Other Types: Many other gasifier concepts have been developed and manufactured. The reference ―Initial Review and Evaluation of Process Technologies and Systems Suitable for Cost-Efficient Medium-Scale Gasification for Biomass to Liquid Fuels‖ (Olafsson, et al. 2005) provides a comprehensive summary with advantages and disadvantages of each. In addition to those discussed here, other types discussed are crossdraft fixed bed gasifiers, the Lurgi dry ash gasifier, slagging gasifiers, cyclone gasifiers, vertical vortex gasifiers, horizontal vortex pyrolyser, ablative pyrolysers, vacuum pyrolysers, screwing gasifiers, twin screw pyrolysers, rotary kiln gasifiers, heat pipe gasifiers, the thermal ballasted latent heat gasifier, the ―Carbo-V‖ gasifier and the NREL thermochemical process development unit. 14 Table 4. Summary of Selected Biomass Gasifier Types Typical Temperatures Gasifier Type Downdraft Fixed Bed Updraft Fixed Bed Bubbling Fluidized Bed Scale 5 kWth to 2 MWth <10 MWth <25 MWth Reaction Operating 1000°C 800°C (1800°F) (1450°F) 1000°C 250°C (1800°F) (480°F) 850°C 800°C (1550°F) (1450°F) Circulating Fluidized Bed A few MWth up to 100 MWth 850°C 850°C (1550°F) (1550°F) Indirectly Heated Steam Gasification Large scale 850°C 800°C (1550°F) (1450°F) Fuel Requirements Moisture Content Flexibility (%) Less tolerant of <20% fuel switching Requires uniform particle size Large particles Efficiency Gas Characteristics Very good Very low tar Moderate particulates up to 50%-55% More tolerant of fuel switching than downdraft Excellent Very high tar (10% to 20%) Low particulates High methane <5 to 10% Very fuel flexible Can tolerate high ash feedstocks Requires small particle size Good Moderate tar Very high in particulates <5 to 10% Very fuel flexible Can tolerates high ash feedstocks Requires small particle size Very Good Flexible Very flexible, does not require sizing, pelletizing or drying Excellent 15 Other Notes Small Scale Easy to control Produces biochar at low temperatures. Low throughput. Higher maintenance costs Small- and Medium-Scale Easy to control Can handle high moisture content Low throughput Medium Scale Higher throughput Reduced char Ash does not melt Simpler than circulating bed Low tar Very high in particulates Medium to Large Scale Higher throughput Reduced char Ash does not melt Excellent fuel flexibility Smaller size than bubbling fluidized bed High methane yield Very high throughput Low emissions, even with high chlorine feedstocks such as MSW High capital cost Engines and Turbines In addition to the steam cycle, three electricity generation technologies used in gasification power projects are: gas turbines, internal combustion engines, and fuel cells. These three technologies require gas cleaning to remove tars and particulates prior to use. Fuel cells in particular have very high gas cleaning requirements that are not discussed here. For more information, refer to Fuel Cells 2000 ( Producer gas and syngas have lower heating values than propane or natural gas and so some modifications to combustion equipment, such as enlarging orifices in burners, may be required. If they are used to supplement natural gas or propane, rather than replacing it, orifices may not need to be enlarged, depending on the fraction of syngas or producer gas. For a discussion of various engines, turbines, and fuel cells used with syngas or producer gas refer to the International Energy Agency‘s ―Review of Energy Conversion Devices‖ Reciprocating Engines Converting a natural gas powered, internal combustion engine to run on syngas or producer gas is relatively simple. Reciprocating engines have advantages of low capital cost, small size, easy start-up, reliability, good load-following characteristics and good heat recovery potential. They have much lower requirements for gas cleaning than microturbines. Commercially available reciprocating engines for power generation range from 0.5 kW up to several megawatts. Manufacturers of reciprocating engines that have been used in biopower projects include General Motors, General Electric Jenbacher, Caterpillar, Wartsila, Guascor, Tessari Energia, and DEUTZ. As one example, a General Electric Jenbacher website states that their engines are ―designed from the outset to run on gas (not diesel engine conversions) – either natural gas, biogas or special gases. All engines are able to operate with various natural gas, biogas and syngas fuel specifications.‖ Refer to External combustion Stirling engines can also be used in biopower applications. Manufacturers of Stirling engines include Sigma Elektroteknisk (Norway), Whisper Tech of Christchurch (New Zealand), Kockums Air Independent Propulsion System (Sweden), Sunpower (USA), STM Power (USA), and Free Breeze (Canada). Microturbines Microturbines offer several potential advantages compared to engines, including compact size and lighter weight, greater efficiency, lower emissions, and low 16 operations and maintenance costs. On the downside, their tolerance for tars and particulates is lower and so require more extensive gas clean-up. Manufacturers of microturbines include Capstone, Turbec, Bowman Power Systems, Ingersoll Rand, Elliot Energy Systems, and UTC Power. In the 1993 to 2000 IGCC demonstration project at Varnamo, Sweden, power was generated with a standard gas turbine that was only slightly modified. ―The modifications made, i.e. air extraction, modified burners and combustion chambers, proved to perform extremely well and no pilot flame was ever needed for maintaining a stable combustion.‖ Tar removal was largely accomplished by using magnesite as the fluidized bed material (Ducente 2006). Operation of a 30 kW Capstone microturbine using syngas is described in the study ―Micro Gas Turbine Operation with Biomass Producer Gas,‖ available at The Capstone micro gas turbine is a standard 30 kWe version without modifications except for software settings altered to manage the lower calorific value of the gas. The required power output is entered manually. The software selects the corresponding operating conditions… A separate compressor is needed to compress gas to the required entrance pressure of about 4 bar. In our tests, the micro gas turbine starts up on natural gas. When operating conditions are stable, we gradually replace natural gas by producer gas until the gas valve is fully opened or until operation becomes unstable. For measurements requiring prolonged operation, slightly more natural gas is added than the minimum needed. That way, the operating system retains a margin to counteract fluctuations in the heating value of producer gas. Gas clean-up in that study is summarized as follows: The gas is cooled to 400°C before dust is removed by a cyclone. Tar is removed by the OLGA system developed by ECN and marketed by Dahlman. A water scrubber removes NH3 and reduces the water content to the water vapour pressure near the temperature of the surroundings. 17 Size Reduction Size reduction is often required before biomass can be used either for direct feed into the gasifier or prior to drying or densification into pellets or briquettes. Smaller particles take up less storage space, are easier to feed and require less energy to dry. The size of the particles fed into the gasifier must meet the requirements of the particular gasifier used. In general, fluidized-bed gasifiers require smaller size than fixed-bed gasifiers. Generally size reduction is accomplished by chopping, shredding, or impact with either portable diesel-powered or stationary electric-powered equipment. Agricultural crops and woody biomass typically have different equipment requirements. Many manufacturers and suppliers who can help with selecting the appropriate equipment can be found on the internet. Hammermills, which reduce size by impact, may be used with woody fuels and also are used as agricultural choppers to prepare hay, grasses, stalks and stovers. Rotating cutters can handle similar feedstocks, but have smaller capacities than hammermills. Chipping and hammer hogging are two preferred methods of reducing woody fuels. Hammermills, or hammer hogs, are necessary for dirty wood or bark with soil or stones. For grinding stumps or dirty small branches, use a hammermill mounted on a forwarder or on a tub grinder. Disc chippers or drum chippers are often used on clean wood, such as off-cuts, edging, and slabs. Disc chippers are also used for forest residues like large branches and tops. In small secondary processing industries like pallet manufacturers or joineries, tooth shredders are often used. Size of woody material may also need to be reduced at the point of collection. Loading into trucks and size reduction can accomplished together using balers and bundlers. Bundlers and grapplers may be equipped with chain saw blades or rotary blades, such that as material is picked up it is also cut into manageable lengths. Densification Densification of the feedstock by pelletizing or briquetting facilitates automatic handling, increases feedstock flexibility by mixing different feedstocks, and ensures the correct particle size and uniformity. Densification also reduces transportation costs and storage requirements. Pellet Mills A pellet mill compresses and molds the biomass into the shape of a pellet. Pellet mills are available from small to large sizes. Pellet mills require feedstocks with low moisture contents. As one manufacturer put it, ―if the moisture content is too high, instead of pellets, you‘ll have material squirting out of it.‖ According to manufacturer‘s representatives, CPM pellet mills require about 25% moisture content (MC) or less. Bliss pellet mills require 10% to 15% MC. The material 18 type should be consistent. Most materials will need grinding and drying prior to pelletizing. Wood chips are easier to pelletize than low density biomass such as straw. Straw pellets tend to break easily if not handled with care and are more sensitive to moisture, which can cause problems when handling. Manufacturers of pellet mills include: Andritz Sprout Bauer Bliss Industries, Inc. Buhler (Canada) Inc. CPM and Roskamp Champion GEMCO Energy Machinery Janicki Industries Pellet Pros Pelleting Concepts International, Inc. Pellet Systems International Pellet Systems International and Bliss Industries have mills suitable for low capacity systems. Balers and Bundlers Mobile balers and bundlers can be used to densify raw biomass at the collection site, so it can be transferred more cost effectively to a preprocessing or gasification facility. There are many manufacturers of balers for agricultural products. U.S. manufacturers of balers and bundlers for forest residues include: Forest Concepts, UPM Tilhill, John Deere, o Refer to /1490d_general.html SuperTrak, Inc, European manufacturers include: Rogbico (Sweden), Fixteri Oy (Finland), Pinox Oy (Finland) Torrefaction Torrefaction is a biomass pre-treatment method in the research and development phase that in future projects may reduce overall costs in some cases. Biomass torrefaction is 19 carried out at approximately 200°C to 300°C (400°F to 600°F) in the absence of oxygen. The biomass is completely dried and partially decomposes, losing its tenacious and fibrous structure. Some of its volatile matter is driven off as a gas. More mass than energy is lost to the gas phase, resulting in energy densification. The gas can be recovered and used in the process, so does not represent a loss. When combined with pelletization, very energy-dense fuel pellets are produced, which reduces transportation costs if the biomass is pre-treated remotely. The grindability of the biomass is improved significantly. Biological degradation of torrefied biomass does not occur, facilitating long-term storage. Biomass Dryers and Dewatering Equipment Overall efficiency can often be improved by dewatering and drying biomass prior to gasification. Drying also improves air emissions and can reduce problems with plugging of feeders. Corrosion problems due to hydrochloric acid formation are improved by burning a drier fuel. Commonly hot exhaust gases from the boiler, engine or turbine are recovered for biomass drying. Dewatering equipment includes drying beds, filters and screens, presses, and centrifuges. Passive dewatering methods, such as using filter bags that are impervious to rain but allow moisture to seep out, can achieve moisture contents as low as 30% at low cost, but long periods of time – on the order of two to three months – may be required. There are many types of dryers used in drying biomass, including direct- and indirectfired rotary dryers, conveyor dryers, cascade dryers, flash or pneumatic dryers, and superheated steam dryers. Selecting the appropriate dryer depends on many factors including the size and characteristics of the feedstock, capital cost, operation and maintenance requirements, environmental emissions, energy efficiency, waste heat sources available, available space, and potential fire hazard. Small biomass projects may choose a simple dryer such as a perforated floor bin dryer to dry the feedstock in batches. Some materials, such as park trimmings or husks and stalks, can be allowed to dry naturally by storing in a covered, open area or by taking advantage of open-air solar drying. The final moisture content of air-dried materials usually varies from about 15% to 35%, depending on the size and characteristics of the material and ambient conditions. Open-air drying is slow and depends on weather conditions. The pile may need stirring or turning to facilitate drying. Open-air drying is generally not suitable for high water content feedstocks since they tend to decompose quickly. For more information, refer to ―Biomass Drying and Dewatering for Clean Heat & Power‖ (Roos, 2008) available from the Northwest Clean Heat and Power Regional Application Center at . 20 Material Handling Equipment Feeding is required to move material into and out of storage and into the gasifier. Handling biomass fuels has proven to be difficult in general. Material handling equipment should be designed considering that the particle size and composition of the feedstock may vary. It should also be designed so maintenance and cleaning can be performed without a stoppage. This can be achieved by introducing buffer stocks of ready-treated fuel in the vicinity of the feed equipment. Types of feeders include belt feeders, gravity chutes, screw conveyors, pneumatic injection, moving hole feeders, chain conveyors, augers, and ram feeders. Material can also be moved using heavy equipment such as wheel loaders, front-end loaders and clamshell cranes. In selecting material handling equipment, the following factors should be considered: Feedstock Characteristics: Both belt conveyors and chain conveyors can transfer granular or aggregate product over a distance. Scraper chain conveyors, which move the material over a stationary surface with a chain that has scrapers attached, are often used with sawdust, bark and wood chips. For conveying fine materials such as dust or coarse grain over a short distance, a screw conveyor is generally used. If the material is very fine, such as fine dust or fine grain (0 to 5 mm), pneumatic injection devices can be used. Augers, which use a screw to feed fuel on a belt, are often used for hog fuel. Coarse materials can be transported with a scraper chain conveyor. Ram feeders, which are essentially hydraulic pushers, are used on materials that are fibrous or sticky or have long lengths. Moving hole feeders are especially used if particles such as flakes are mixed with denser solids, to avoid compaction. Proximity and Level Changes: Screw feeders are only practical for transporting material over short distances. For longer distances, consider belt conveyors or scraper chain conveyors. Scraper chain conveyers can be used for level changes while belt conveyors cannot. Fuel Metering: Scraper chain conveyors can both mix the material and meter the feed, which belt conveyors also do not. Screw feeders can meter fuel into the gasifier at a particular rate. A feeding system that cannot meter fuel, such as a belt conveyor or gravity chute, are often fed into a separate metering device, such as a screw. Gasifier pressure: Screw feeders can be used for feeding into high pressure gasifiers up to several atmospheres. In contrast, gravity chutes require slightly less than atmospheric. Fuel Dispersal: Some types of feeders, such as pneumatic feeding systems, by nature disperse fuel well as it is being fed into the gasifier. Others, such as screw feeders and gravity chutes, do not disperse the fuel well. In these cases, fuel spreaders may be required. Minimizing Feeder Plugging: Screw feeders are prone to plugging, which can be reduced by drying the feedstock and using variable-pitch screws, variable diameter 21 screws, and multiple screws. Multiple screws are especially effective in handling biomass fuels to avoid plugging. Mixing Fuel Additives: Limestone or other fuel additives to reduce slagging and fouling may also need to be fed into the gasifier or mixed with the fuel. Fuel additives may be pneumatically injected into the gasifier or may be mixed as it is fed into a hopper by a screw or scraper chain conveyor or other feeder that will mix the fuel. For more information, refer to ―The Handbook of Biomass Combustion and Co-Firing‖ (Van Loo & Koppejan 2008) and ―Combustion and Gasificaton in Fluidized Beds‖ (Basu 2006). Feedstock Storage Storage options include covered or uncovered open areas, designated rooms in an existing building, hoppers and silos. Silos may have sloping floors or moving floors. Moving floor silos, in which fuel is moved into a feeder such as an auger at one end of the silo, are generally used only in large installations because of their expense. Sloping floor silos are often constructed of plywood and have a rotating arm that pushes fuel into a feeder inlet along the center of the floor. Gravity hoppers, to which material enters the top and is removed from the bottom, are suitable for dense materials such as wood pellets. Lighter materials do not flow well out of a hopper. Gas Storage The product gas may be diverted and compressed to provide buffer storage capacity. Storage compensates for fluctuations in demand from its end use. Other Ancillary Equipment The gasifier also will usually require ash or biochar removal equipment. Gas cleanup equipment will generally be required downstream of the gasifier, as discussed in the Section ―Gas Cleaning‖ below. In oxygen-blown gasifiers, an oxygen plant is required. If wet scrubbers are used for tar removal, water treatment will be required. The project may also include equipment such as boilers, absorption chillers and heat exchangers for heat recovery, depending on the application. 22 Product Gas Composition The product gas is primarily composed of carbon monoxide and hydrogen, and if air is used as the oxidizing agent, nitrogen. The product gas will also have smaller quantities of carbon dioxide, methane, water and other contaminants, such as tars, char, and ash. The percentages of each of these components depends on a number of parameters, including the temperature and pressure of gasification, feedstock characteristics and moisture content, and whether air or oxygen with or without steam is used for the process. Significant methane is only produced at high temperatures. More char is produced at lower temperatures, below about 700°C (1300°F), with a corresponding decrease in energy content of the product gas. Product gas heating values typically vary from 15% to 40% of natural gas, as shown in Table 5. Table 5. Typical Energy Contents of Producer Gas, Syngas and Natural Gas Energy Content 3 Producer Gas Syngas Natural Gas (MJ/m ) 2.5 to 8 10 to 20 38 23 Btu/ft3 65 to 220 270 to 540 1,028 Feedstock Characteristics and Requirements Almost any carbon containing material can be gasified, provided the material meets requirements of the particular equipment. Moisture content and chemical content of feedstocks should be carefully considered. Also, different kinds of gasifiers have different requirements for particle size and uniformity. Moisture Content Moisture content is critical in combustion, gasification and pelletization. Maximum moisture contents required for gasification depend on the gasifier type. Downdraft fixed bed gasifiers cannot tolerate moisture contents above about 20%. Updraft fixed bed gasifiers and fluidized bed gasifiers can tolerate higher moisture contents of 50% and 65%, respectively. Moisture contents can be as high as 95% in gasifiers using the supercritical water process, but this type of gasifier is still in the research and development phase. Pellet mills also generally require moisture contents of less than 15% to produce stable and durable pellets. Wastes with very high moisture contents often cannot be dried cost effectively except perhaps by passive dewatering methods, such as using filter bags. For these wastes, conversion technologies such as anaerobic digestion and fermentation will likely be more cost effective than combustion or gasification. The moisture contents of some common biomass feedstocks are summarized in Table 6. Chemical Content The chemical content of biofuels influences slagging, fouling and corrosion of gasifier and heat exchanger components.5 For most biomass fuels, silicon, potassium, calcium, chlorine, sulfur and to some extent phosphorous, are the principal elements involved in the fouling of surfaces. In general feedstocks for gasification should preferably have a high carbon-to-nitrogen ratio, low sulfur content, low chlorine content, and low silica content. The molar ratio of sulfur to chlorine (S/Cl) should also be low since strong corrosion tends to occur when S/Cl is below 2 and moderate corrosion when S/Cl is 2 to 4. The ash content of common biomass materials is summarized in Table 6. Tables 7 and 8 give more detail on selected biomass fuels. Alkali salts, potassium in particular, are responsible for much of the fouling, sulfation, corrosion and silicate formation found in biomass boilers. Straws, other grasses and herbaceous materials, younger tissues of woody species, nut hulls and shells, and other annual biomass contain about 1% potassium dry weight. The leaves and branches of 5 Slagging occurs when a material is melted and then condenses on surfaces or accumulates as hard, dense particles or ―clinkers‖. Fouling refers to deposits on surfaces that have not melted. 24 wood have higher levels of potassium than the mature stem wood. Sodium and potassium salts in ash vaporize at temperatures of about 700 oC (1300oF). As a vapor, they are not easily separated by physical methods such as filtration. Condensation begins at about 650oC (1200oF), first on particulates in the gas forming clinkers and then on cooler surfaces in the system as slag. High silica content is associated with slagging. However, high silica alone does not present much of a problem. It is the combination of high silica with alkali and alkaline metals, especially potassium, that can lead to the formation of slag. Thus, rice hulls, which may contain 20% silica by weight but have low potassium content, do not easily slag. But many types of straw, grasses and stover – which have both high silica and potassium – are very prone to slagging. Fouling and slagging seem to be worsened by the presence of chlorine which increases the mobility of inorganic compounds. Also, chlorine is absorbed by metals at high temperatures, rather than just building up on surfaces, and so results in corrosion. The ash that remains after a material is burned is indicative of the mineral content, i.e. Na, K, etc. Ash is easily measured by burning the material completely and weighing the sample before and after. Hence, much more data is available on ash content than on specific chemical contents. Low ash content also reduces disposal costs, assuming the ash isn‘t put to a useful purpose such as a soil amendment or cement additive. Gasifiers especially for straw and other biofuels with high alkali and chlorine contents have been developed. Fluidized bed gasifiers are in general better suited for these materials due to their lower operating temperatures. Foster Wheeler and Energi E2 performed successful pilot projects gasifying straw in a fluidized bed gasifier 1999 to 2001. The Purox gasifier, designed for gasification of municipal solid waste, operates in ―slagging mode‖ in which all the ash is melted on a hearth. The gasifier developed by Taylor Biomass Energy being demonstrated at the Gady Farm in Spokane, Washington, is also designed especially for straws and grasses. 25 Table 6. Typical Heating Value, Moisture Content and Ash Content of Selected Biomass Feedstocks Higher Heating Value (Btu/lb) Corn Stover Grape Pomace Pellets Coal Wood: Logging Residue Land Clearing Debris Clean Wood, temperate zones Bark Straw Switchgrass 7,700 to 8,000 8,300 10,000 to 14,000 Moisture Content (%) Dry: 7 to 30 Moist: 50 to 65 14 12 7,000 to 10,000 Dry: 10 to 12 Moist: 40 to 60 8,000 to 10,000 7,500 8,000 to 8,200 30 to 60 15 15 to 20 Ash %, dry basis 6 to 13 6 8 to 14 4 8 0.1 to 1 3 to 8 6 to 10 3 to 8 Sources: 1. Energy Research Centre of the Netherlands, ―Phyllis Database‖, 2. Krzysztof J., Ptasinski, Mark J., Prins and Anke Pierik , ―Exergetic evaluation of biomass gasification,‖ Energy, Volume 32, Issue 4, April 2007, Pages 568-574 3. Savoie, P. and S. Descôteaux, ―Artificial drying of corn stover in mid-size bales‖, Canadian Biosystems Engineering, Volume 46 2004, 4. Ragland, Kenneth W. and Andrew J. Baker, ―Mineral Matter in Coal and Wood-Replications for Solid Fueled Gas Turbines‖ University of Wisconsin, Madison, WI and U.S. Forest Products Laboratory, Madison, WI, 5. RGW Enterprises, ―Clean Energy and Environment Project Feasibility Study‖, Richland, Washington, July 2007 6. U.S. Department of Energy, Energy Efficiency and Renewable Energy Office, ―Biomass Feedstock Composition and Property Database‖, 7. U.S. Department of Energy, Energy Efficiency and Renewable Energy Office, ―Biomass Energy Data Book, Appendix B‖, 8. Van Loo, Sjaak, and Jaap Koppejan, ―The Handbook of Biomass Combustion and Co-Firing,‖ Earthscan Publishing, London, 2008. 26 Table 7. Characteristics of Common Biomass Feedstocks Crop Residues Poultry Litter Herbaceous Biomass (Switchgrass, Miscanthus, Reed canary grass, Johnson grass) Forest Residues Woody Biomass (Hybrid poplar, Black locust, Maple, Willow, Short rotation woody crops) Ash content: 5% to15 by weight High in silica and potassium (K) Slagging problems at high gasification temperatures (>900°C) Clinker formation Reduce slagging and clinker formation by K removal and feedstock washing Ash content: 15% to 20% by weight High in Silica and K Very high slagging properties Secondary reactions creating cyanide gas High ash High in silica and K High lignin content, and therefore high tar production High in ash due to soil contamination Low K and therefore less slagging potential High in particulate matter Low ash content Low in silica and K Minimal slagging problems High cost of production as an energy crop From: 2007.pdf Table 8. Chemical Contents of Product Gas from Selected Biomass Fuels C % 51 54 49 49 50 H2 % 6.3 6.1 6.3 6.3 6.3 S % 0.02 0.1 0.03 0.1 0.3 O2 % 42 40 44 43 43 N2 % 0.1 0.5 0.4 0.5 0.8 Ash % 0.3 4 2 5 5 Cl % 0.01 0.02 0.01 0.4 0.5 Na (mg/kg) 20 300 Wood, coniferous Bark, coniferous Poplar Straw, Wheat, Rye, Barley 500 Straw, Rape 500 Reed canary grass, 49 6.1 0.2 43 6.4 200 1.4 0.6 summer harvest Reed canary grass, 49 5.8 0.1 44 0.9 5.6 0.1 200 delayed harvest From: * Values in red indicate problematic feedstocks. 27 K (mg/kg) 400 2,000 3,000 10,000 10,000 12,000 2,700 Comparison of Coal and Biomass Coal and biomass have very different properties and each presents different challenges and advantages. There is much more experience gasifying coal than gasifying biomass and conventional designs for coal have often been troublesome when used with 100% biomass. Compared to coal, biomass fuels have varying chemical content, so each type of biomass must be considered separately. But several generalizations can be made. Sulfur and ash is typically lower in biomass, but alkali metal content and silica content, which lead to slagging, is often greater in biomass. Volatile matter is generally much greater in biomass. At the low end, volatile matter comprises only about 5% of anthracite coal, while wood contains more than 75%. Therefore, wood is more easily converted to gas and produces less char but more tar. Efficient use of char within the gasifier is more important in coal gasification. Biomass can be co-fired with coal in conventional gasifiers. The Tampa Electric Polk Power Station, for example, co-fires 5% biomass in its slurry-fed Texaco gasifier to generate 260 MWe without any major problems. The Dernkolec Power Plant in Buggenum, Netherlands, co-fires 34% biomass with coal in a Shell gasifier to produce 250 MWe of electricity. Their biomass has included sewage sludge, chicken litter, and wood waste. Table 9 compares typical characteristics of biomass to those of coal. Table 9. Biomass Characteristics As Compared to Coal Volatile matter content Oxygen content Sulfur content Ash content Alkali metal content Hydrogen to Carbon Ratio Heating value Tar reactivity Greater Greater Lower Lower Greater, especially for agricultural wastes Greater Lower Greater for woody biomass 28 Reducing Slagging, Fouling and Corrosion Combustion and gasification of biomass feedstocks have been more challenging than with coal in part due to problems with slagging, fouling and corrosion. Slagging occurs when ash and other components of the reaction gases melt and condense on surfaces. Fouling refers to deposits that build up on surfaces, but have not melted. Strategies for reducing slagging, fouling and corrosion problems in biomass boilers include use of fuel pretreatment, automatic surface cleaning, temperature control, and feedstock selection. Slagging and fouling problems will be similar in nature in both biomass boilers and gasifiers. Therefore, references on problems in biomass combustion can be useful in considering potential problems and their solutions in gasification. Fuel Management Fuel management strategies for reducing slagging, fouling and corrosion include using fuel additives, washing the feedstock, and screening dirty fuels. Some feedstocks may need to be avoided altogether or mixed with less problematic fuels. Fuel Additives Fuel additives including limestone, clays, and minerals based on calcium, magnesium and/or iron have been used to reduce slagging in biopower combustion appliances. Examples are magnesium oxide, dolomite, kaolin, kaolinite, clinochlore, and ankerite. Such additives have been shown to be effective particularly in fluidized-bed boilers, which have good mixing. These materials may also be used effectively as bed materials. One commercial additive that reduces ash fouling in biomass power plants is ―CoMate‖ produced by Atlantic Combustion Technologies ( ). CoMate is not mixed with the fuel, but added directly to the unit on its own in a dedicated feeder. Site ports can be taken advantage of for inlets. Washing Washing straw has been shown to reduce its amount of chlorine and potassium significantly and so reduces problems with slagging and fouling. Washing can be accomplished by controlled washing or by simply leaving the straw on the field for a time after harvest, exposing it to rain (―gray straw‖). Some organic material will also be leached out. In a Danish study, the energy losses associated with controlled washing, drying and leaching of organic matter amounted to approximately 8% of the calorific content of the straw. This cost was offset by the prolonged life of the boilers. 29 Screening Trommel screening dirty fuels can dramatically decrease ash and slagging problems in plants that burn field and urban wood residues. In wood fuels, screening out fines reduces problems because ash-forming elements tend to be concentrated in the smaller particles. Reducing Problematic Fuels Dirty or problematic fuels can be mixed with cleaner burning fuels to reduce fouling. For example, nuts, shells and straws might be limited to less than 5% to 10% of the fuel mix. It is important to avoid using feedstocks, especially grasses and straws, in a gasifier for which it was not designed. Temperature Control Temperature can be used to control deposits to a certain extent, especially as a short term or intermittent solution. Slagging can be avoided by operating the gasifier in one of two temperature regimes:   Low temperature operation that keeps the temperature well below the flow temperature of the ash. High temperature operation that keeps the temperature above the melting point of ash. In addition, gas streams throughout the system should be maintained above the dew points of its corrosive contents. In particular, sulfur and chlorine result in low temperature corrosion if they are allowed to condense out on surfaces. Reducing temperature to control deposits also reduces the capacity and can have undesirable economic consequences. System Design Certain system design options reduce the potential for fouling and corrosion. These include: Corrosion-Resistant Materials When selecting materials for components that will come in contact with reaction gases in or downstream of the gasifier, to avoid corrosion choose high chromium stainless steels, such as AC66. Automatic Surface Cleaning The system should include some method of automatic surface cleaning, such as using sootblowers, acoustic horns or pulse detonation systems. Acoustic or sonic horns use relatively intense sound pressure to dislodge particulates. They have been used over the last 15 years to clean dry particulate deposits from a 30 variety of equipment, including boilers, economizers, ducts, fans, hoppers, cargo holds, dryers, electrostatic precipitators, and bag filters. Sonic horns are not effective in removing non-particulate accumulation, such as sintered ash. Acoustic horns are omni-directional, and so can clean hard to reach areas, in contrast to conventional sootblowers. The advantages of acoustic horns over sootblowers are illustrated in the article ―SCR Catalyst Cleaning: Sootblowers vs. Acoustic Horns‖ in Power Engineering magazine, available at: …acoustic horns are relatively inexpensive (one-fourth the cost of a steam sootblower), don't require structural steel for support, and have only one moving part, a titanium diaphragm that might need to be replaced after three to five years. The acoustic horns operate on standard plant compressed air, and 70-90 psi air plumbing is all that is required to make them operational. (Solenoids are used to fire the horns; from the solenoid to the horn, flex hose is usually used.) Another option is pulse detonation, which employs a detonation-initiated blast wave to break up and remove deposits from surfaces. An advantage of pulse detonation over both acoustic horns and sootblowers is the ability to remove harder deposits. Each pulse detonation combustor can clean a relatively large area and reach areas that are inaccessible to conventional sootblowers. For more information, refer to ―A Comparison of Online Backpass Cleaning Technologies: Detonation, Acoustic and Conventional Steam or Air Sootblowing‖ 31 Gas Clean-Up The major contaminants produced during gasification are particulates, alkali compounds, tars and char, nitrogen containing compounds, and sulfur. Gas cleaning is required before use in engines and turbines, but little or no gas cleaning is required for burner applications. Tars can clog engine valves, cause deposition on turbine blades or fouling of a turbine system leading to decreased performance and increased maintenance. In addition, tars interfere with synthesis of fuels and chemicals from syngas. For more information on gas cleaning technologies, refer to: ―Initial Review and Evaluation of Process Technologies and Systems Suitable for Cost-Efficient Medium-Scale Gasification for Biomass to Liquid Fuels‖ (Olafsson et al. 2005) ―The Handbook of Biomass Combustion & Co-Firing‖ (Van Loo et al. 2008) ―Biomass Gasifier Tars: Their Nature, Formation and Conversion‖ (Milne et al 1998) ―Gasification Technologies: A Primer for Engineers and Scientists‖ (Rezaiyan and Cheremisinoff 2005) Particulate Removal Gas emerging from gasifiers may contain particulates consisting of ash, char, and (for fluidized bed gasifiers) bed materials. Particulate control technologies include cyclones, electrostatic filters, bag filters, spray changers, and impingement scrubbers. For nonsticky particles larger than about 5 mm, a cyclone separator is the best choice. For particles smaller than 5 mm, normally electrostatic filters, bag filters and scrubbers are used. Tar Content and Removal The type of system used for tar removal depends on the quality of the gas produced by the gasifier. Syngas from most downdraft gasifiers typically does not have high tar content. In fact, downdraft gasifiers were developed specifically to minimize tar. In contrast, the syngas of updraft gasifiers can contain about 100 times more tar than that of downdraft gasifiers. Fluidized bed gasifiers can produce low tar content product gas, largely depending on the bed material, as discussed below. Typical tar contents of gas produced by gasifier type are shown in Table 10. In addition to gasifier type, feedstock strongly influences tar content of the product gas. Woody biomass in particular results in high tar content syngas. Agricultural and food wastes tend to have lower tar contents. The requirement for tar removal also depends on the end use of the syngas. Burners have higher tolerance for tar than engines, which in turn have higher tolerance than turbines, as 32 shown in Table 11. Syngas from downdraft gasifiers has been used successfully with internal combustion engines to generate power without significant tar removal. For example, Community Power Corporation‘s Biomax syngas only requires separation and filtration of particulates before use in a reciprocating engine, which removes much of the tars as well ( In general, tar is removed from the product gas by chemical or physical methods or by condensation. Chemical methods are catalytic cracking, thermal cracking, plasma reactors and use of catalytic beds. Physical methods are cyclones, filters, electrostatic precipitators and scrubbers. Condensation is accomplished by cooling the gas. Using physical methods, sticky particles such as tars are usually collected in a liquid, as in a scrubber or in a cyclone, bag filter or electrostatic filter whose collecting surfaces are continually coated with a film of flowing liquid. The gasification project in Harboore, Denmark, discussed in the section ―Demonstration Projects,‖ uses gas cooling and a wet electrostatic precipitator. The Moissannes project in France (also discussed in ―Demonstration Projects‖) uses the ―OLGA‖ tar removal method, which uses an oil solvent to collect and absorb tars instead of water. For information on the OLGA tar removal method, refer to ―Tar Removal from Biomass Product Gas: Development and Optimisation of the OLGA tar removal technology‖ (Boerrigter et al. 2005) available at In fluidized bed gasifiers, the bed materials can serve as a catalyst for tar reduction. Clay-derived materials, including activated clay, acidified bentonite, and clay housebrick, have worked well for this purpose. Ordinary clay housebrick captures more than twice that by sand. On the other hand, some bed materials – notably dolomite and limestone, but not magnesite – will recarbonate during cool down, which results in fouling and deposits will occur in different locations in the gasifier system and in downstream systems. In the fluidized bed gasifier in the demonstration project at Varnamo, Sweden, magnesite was chosen as the bed material to obtain a low tar content gas. Low tar gases produced by most downdraft gasifiers can be treated with a ceramic fiber filter followed by condensation and perhaps by a scrubber. Biomass Engineering, Ltd. in the UK has used this approach in 250 kWe modules. Filters manufactured by Glosfume (UK, have been used for downdraft gasifiers at the 100 kWe scale. (Refer to Fluidyne‘s "Californian Mk5 Andes Class Gasifier,‖ August 2009 High tar gases produced by updraft gasifiers or many fluidized bed gasifiers may use particulate filtration followed by condensation. Condensation systems used in many Indian gasifiers consist of direct contact with water followed by packed bed filters. GTI/Carbona‘s fluidized bed gasifiers (3 MWe and greater) use a ceramic filter as a reactive surface and filter. Tars pass through the filter and are reformed downstream. The proprietary OLGA system developed by ECN and marketed by Dahlman uses organic solvents to remove tars. The OLGA system has been demonstrated at PRM Energy‘s 1.0 MWe system at Moissannes, France where cleaned syngas is burned in a 33 Caterpillar engine. The OLGA system is generally not cost effective for projects less than about 1 MWe in size. Envitech ( designed scrubbers for a 1 MWe fixed bed updraft gasifier for a demonstration project in Limoge, France. They also designed the 320 kWe Tallon Lumber project ( Several manufacturers are in the process of developing or have developed proprietary tar removal systems. For example, Nexterra has developed a thermal cracking method to achieve engine grade syngas that is approved for use in GE Jenbacher reciprocating engines. Nexterra has signed a strategic alliance agreement with GE Energy to commercialize this application and will be starting a commercial demonstration at a university in British Columbia, Canada. Table 10. Typical Tar and Particulate Contents of Gasifier Types Gasifier Type Downdraft fixed bed Updraft fixed bed Bubbling fluidized bed Circulating fluidized bed Tar Content (g/Nm3) ~1 Typically 0.5, ranging from 0.02 to 4 ~100, Typically ranging from 20 to 100 ~10, Typically ranging from 1 to 15 ~10, Typically ranging from 1 to 15 Particulate Content (g/Nm3) 0.1 to 0.2 0.1 to 1.0 2 to 20 10 to 35 Table 11. Tolerance of End-Use Devices for Tar* End-Use Limits (g/Nm3)** Combustion Large Internal Combustion Engines 0.010 to 0.100 Gas Turbines 0.0005 to 0.005 Compressors 0.050 to 0.500 Fuel Cells Very low * From ** mg/Nm3 is ―mg per normal cubic meters‖. Normal conditions are 0°C and a pressure of 1.013 bar. 34 Marketable Co-Products The wide array of co-products possible with gasification can improve the cost effectiveness of a gasification project. While combustion produces only heat, gasification can be used to produce heat, as well as syngas and solid carbon char or ―biochar.‖ Syngas can be used as a feedstock to produce hydrogen and liquid hydrocarbons, such as ethanol and chemical feedstocks. Biochar has several potential uses and gives gasification the potential of a carbon neutral or carbon negative energy solution. Both combustion and gasification produce ash, which also can be marketed. Markets for Biochar Biochar is a fine-grained charcoal composed primarily of organic carbon (75% to 85%). Production of biochar is significant in downdraft gasifiers in particular. It is also produced in even larger quantities in pyrolysis, 10% to 15% in fast pyrolysis and as much as 35% in slow pyrolysis. Biomass-based carbon, especially from wood, has a long history of uses for its adsorption, thermal and electrical properties. Activated carbon is used in filtration media. In the metallurgical industry it is used to reduce the iron ore in pig iron, in stainless steel, and in the production of some metal alloys. Carbon black is used as an electrically conductive additive in batteries. Coke, which is essentially coal charcoal, is now used for most applications formerly served by wood products. The only significant markets for wood carbonization products in the U.S. at present are activated carbons and charcoal briquettes. However, an economic incentive to switch back from coke to wood char can be expected in the near future driven by the implementation of carbon taxes and/or carbon cap-and-trade systems, as well as by the existing, growing markets in carbon offsets. Already switching from charcoal to coke in Brazil‘s steel industry is being discouraged in projects implemented under the Clean Development Mechanism of the Kyoto Protocol. The char produced in gasification and pyrolysis generally contains a significant quantity of impurities. Biochar can be considered a low grade carbon black. For many applications, the char would need to be upgraded to remove impurities, diminishing its economic value. Biochar Soil Amendment As a soil amendment, biochar improves soil texture, holds moisture and releases fertilizer slowly. Biochar resists decomposition, so it persists in the soil. It also sequesters carbon in the soil and so helps to mitigate global warming. 35 Activated Carbon Precursor Biochar has high value as a precursor for activated carbon. Activated carbon is produced from charcoal by exposing it to high temperatures in an airless environment. It is then treated with oxygen, which opens up tiny pores between the carbon atoms, resulting in very high surface area per volume of material. Solid Fuel Biochar can be reburned as a solid fuel in the gasifier itself. In fluidized bed systems, char in the gas may be captured in a cyclone and returned to the bottom of the bed. Alternatively, char may also be removed from the bottom of the gasifier and used elsewhere. Steel Manufacturing Reductant Until the 20th century charcoal was widely used in the steel industry. Now Brazil is the only country where charcoal is still predominant over coke in steel manufacturing. Use of charcoal as a reductant in steel manufacturing significantly reduces greenhouse gas emissions, decreases emissions of sulfur dioxide, oxides of nitrogen and results in improved steel quality. On the small scale, some blacksmiths are promoting the use of wood charcoal over coal in their forging operations, despite certain advantages of coke (easy ignition, hotter flame, energy efficiency). Reasons for the switch are that wood charcoal burns more cleanly, results in fewer health hazards to the blacksmith, presents less of a disposal problem, and is a renewable resource. Markets for Ash Ash has markets as a soil amendment, cement additive, steel industry tundish powder, and sand replacement. Soil Amendment Biomass ash may be added to fertilizers as a soil amendment, unlike coal ash which may contain toxic metals and other contaminants. Biomass ash can be a significant source of potassium, calcium, magnesium, sodium and sulfur. Ash contains phosphorous, also, but it is present in a form that has very poor soil solubility. The slow release of phosphorous may not be a problem if used as a fertilizer for perennials such as trees. Care must be taken to ensure that the biomass is not contaminated by, for example, paints and wood preservatives. Biomass from household, industrial and municipal solid wastes may contain organic pollutants and heavy metals. Heavy metals that may be in contaminated biomass include cadmium, zinc and arsenic. In addition, biomass ashes are less attractive in commercial fertilizers than mineral sources because their mineral content per volume is lower. 36 Steel Industry Tundish Powder Rice hull ash has been used widely in steel mills as a tundish power, which serves as an insulating cover on tundishes and ladles containing molten steel. Rice hull ash flows over and covers the steel surface well and does not crust or cause metal sculls during use. Cement Additive Biomass ash can be used in certain cement blends, mortars and aggregates. If it does not contain aggregates such as slag and clinkers, it often can be recycled to cement kilns without prior treatment. Biomass fly ash often contains alkali metals, chlorine and phosphates that can make it unsuitable for concrete. The fly ash of each type of biomass must be analyzed to evaluate its suitability. Rice hull ash (RHA) in particular has been used in the cement industry in the manufacture of low cost building blocks and in the production of high quality cement. At 35% replacement, RHA cement has improved compressive strength due to its higher percentage of silica. It also has improved resistance to acid attack compared to Portland cement. Replacing 10% Portland cement with RHA can improve resistance to chloride penetration, which has application in the marine environment. Several studies have combined fly ash and RHA in various proportions. In general, concrete made with Portland cement containing both RHA and fly ash has a higher compressive strength than concrete made with Portland cement containing either RHA or fly ash on their own. Sand Replacement If sand is used as a bed material in fluidized bed gasifiers, bottom ashes will consist largely of sand and can be used to replace the sand used in road construction and landscaping. Solid Fuel Fly ashes may also contain significant quantities of carbon (>35% by weight) and so can be reburned as fuel. Fly ash can be pelletized for this purpose by adding water and/or a binder. Chemical Feedstocks A very large number of chemicals can be produced from syngas. Those with the largest markets include ethanol, methanol, naptha, gasoline, diesel, hydrogen, acetic acid, dimethyl ether, and ammonia. As an illustration of the potential, syngas from coal and natural gas is currently used to manufacture 30% of the gasoline and diesel used in South Africa. 37 For the production of chemicals, syngas that is undiluted with nitrogen must be used. This means it must be oxygen-blown or heated indirectly. Also, the methane content of the gas should be low. Bio-Hydrogen Bio-hydrogen can be produced from biomass by several processes. Of these, gasification coupled with water gas shift is a mature commercial process with only small adaptations required for application to biomass. This process is currently near cost competitive with production of hydrogen by steam reforming of methane, depending on relative costs of natural gas and biomass. Hydrogen can be used in either internal combustion engines or fuel cells. Since fuel cell vehicles are not commercially available yet and a distribution infrastructure for hydrogen will not be realized in the short term, bio-hydrogen is considered a longer-term option for the transport sector. 38 Environmental Benefits Environmental benefits of biomass gasification compared to combustion of solid biomass may include: Reduced carbon emissions by improvements in energy efficiency Reduced carbon emissions by closing the carbon cycle and carbon sequestration Reduced NOx emissions Reduced use of fertilizers and runoff of nutrients from soils amended with Biochar Reduced Carbon Emissions by Efficiency Improvements As discussed previously, gasification has potential to increase energy efficiency compared to combustion of biomass in a steam cycle. These carbon emission reductions may be tradable in carbon offset markets. Significant production of biochar reduces energy efficiency, if the char is not reburned. But biochar offers other environmental advantages that can more than make up for its energy efficiency penalty, as discussed below. Reduced Carbon Emissions by Closing the Carbon Cycle and Carbon Sequestration Both fossil fuels and biomass release carbon dioxide when they burn. The carbon released when burning fossil fuels originates from oil reserves, not from the atmosphere. Hence, fossil fuels are carbon positive in that they add new carbon dioxide to the atmosphere. In contrast, combustion of biomass, taken by itself, is carbon neutral because the carbon released was first absorbed from the atmosphere by the biomass as it grew. In other words, the carbon cycle is closed. Combustion of biomass may still be carbon positive overall if fossil fuels are used in their production and transportation. Use of biomass has the potential of being carbon negative if, in using or producing it, carbon is stored in a form that is not released to the atmosphere. As one example, constructing a building of wood stores carbon in the structure for as long as the building is maintained. As another example, grasses tend to build up carbonaceous material in the soil as they grow. Using biochar produced in the gasification process as a soil amendment is a third example. Biochar is largely resistant to decomposition and, once put in the soil, most of it remains there orders of magnitude longer than other organic amendments. This effectively absorbs carbon from the atmosphere and stores it in the soil. For more information on the environmental benefits of biochar, refer to the website of the International Biochar Initiative at 39 Reduced Fertilizer Use and Runoff in Biochar-Amended Soils Biochar as a soil amendment significantly increases the efficiency of and reduces the need for traditional chemical fertilizers, while greatly enhancing crop yields. Production and transportation of chemical fertilizers is fossil fuel intensive and so reducing their use reduces associated carbon emissions. Moreover, char-amended soils have shown 50% to 80% reductions in nitrous oxide emissions, reduced runoff of phosphorus into surface waters, and reduced leaching of nitrogen into groundwater. Reduced NOx Emissions The product gas will generally have low NOx concentrations because gasification temperatures are not high enough to produce NOx in significant quantities. However, when the product gas is burned in a boiler, turbine or engine, NOx will be produced as it is in most combustion systems and with all fuels. Nevertheless, it is easier to control the combustion of a gaseous fuel than the combustion of a solid fuel. Better control of combustion provides the opportunity to reduce NOx formation. 40 Industry Applications Pulp and Paper Industry The pulp and paper industry is a prime candidate for implementation of gasification for a number of reasons. The industry is seeking alternative products to help improve the economics of the paper-making. The industry already has a supply of woody feedstocks with the infrastructure necessary to handle them and has wide experience with wood-fired combined heat and power. The scale of pulp and paper plants is conducive to implementation of forest biorefineries. Aging wood-fired boilers in need of replacement might be considered for replacement with gasifiers. Besides production of chemical feedstocks, syngas can be used to offset natural gas use in, for example, lime kilns as in the Domtar draft pulp mill in Kamloops, BC, which uses a Nexterra updraft gasifier with hog fuel. Start up of the full-scale commercial operation of this project is expected in June 2009. Wood Products Industry The waste wood available in lumber mills, cabinet shops, plywood plants and other wood products facilities can be gasified to generate electricity for onsite use and sale to the grid with heat recovered for process heat. Examples of process heating needs are lumber drying, veneer drying, and hot water for log conditioning. Projects are operating or in development at Tallon Lumber in North Canaan, Connecticut, Tolko Industries in Heffley Creek, British Columbia, and the Grand Forks Truss Plant in Grand Forks, North Dakota. Petroleum and Petrochemical Industries Petroleum refineries and many petrochemical facilities have existing infrastructure that can be used in the production and/or upgrade of biofuels. The petroleum industry has become interested in biofuels largely because of recent mandatory requirements for blending of biofuels with gasoline and diesel being implemented in a number of countries and U.S. states. Food Processing Industries and Agriculture Facilities processing dry foods or having relatively dry wastes are candidates for gasification. Examples of feedstocks that have been used include grape pomace, olive waste, rice hulls, grass and straw, distillery grain, and corn stover. The Port of Benton gasification project at the FruitSmart facility in Prosser, Washington, demonstrated the feasibility of using grape pomace to offset propane use in fruit dryers. 41 Demonstration Projects There are many biomass gasifiers currently operating or planned in industrial applications in North America, Europe and Asia. Examples in North America and Europe are summarized in Tables 12 and 13, although this list is not all inclusive. Small-Scale U.S. Demonstration Projects There are many small-scale biomass gasification projects of less than 1 MWe in various phases located around the world. In the U.S. small-scale projects include the following: Mount Wachusett Community College – Gardner, Massachusetts Mount Wachusett Community College has been gasifying wood chips to generate electricity and meet campus space heating and cooling needs since October 2006. The gasifier is a 50 kW Biomax with an 8.1 liter GM turbocharged engine and genset. The feedstock is 1.5 tons per day of green wood chips. The system is operated 24 hours per day, 6 days per week. Tallon Lumber – North Canaan, Connecticut The Tallon Lumber sawmill biomass gasification project will use a downdraft gasifier and engine to generate 320 kW of electricity and 1800 MMBtu/h of heat at a midsize sawmill in North Canaan, Connecticut. Sawmill waste residue consisting of wood chips and sawdust will fuel the gasifier. The system is designed to satisfy the plant‘s peak electrical demand, the peak thermal demand of the kiln, and space heat for the planer building. The startup testing and system shakedown is planned for the first quarter of 2009. The gasifier and generator were originally commissioned in 2005. However, after running the plant for only 53 hours, it was decided clean up of tars in the gas needed improvement. The original electrostatic precipitator was replaced with a wet scrubber. The Connecticut Clean Energy Fund Project Status Quarterly Update summarized the status of the project as of the end of 2008: In Q4 of 2007, Kraftpower performed an inspection of the Schmitt Engine, performed service, and ran the engine in order to ensure proper function and readiness for the next stage in facility start-up. The Envitech venturi scrubber was installed in May 2008. The rotary airlock, which will automatically remove ash and char material produced by the gasifier, was also installed. Once the system was assembled, it was tested for two hours. 42 A new radiator was installed when higher heat output was generated from the new configuration. The plant was tested and determined to adequately remove particulates from the gas stream. However, the engine generator developed software problems that need to be resolved before a complete system shakedown occurs. Schmitt Enertec and Kraftwork have been contacted to resolve the issues by February 2009. The plant will then undergo a full test run. Port of Benton / FruitSmart – Prosser, Washington A short-term pilot project was conducted in 2006 by the Port of Benton at the FruitSmart food processing facility near Prosser, Washington. Different combinations of wood pellets, sawdust and chips, mint residue, grape pomace, spent hops, cow manure, wheat straw, and waste glycerin from a nearby biodiesel plant – 60 tons total – were pelletized and gasified in a downdraft gasifier. The producer gas supplemented propane use in an industrial drying operation, offsetting 40% of FruitSmart‘s propane costs. As could be expected, gasification of the wheat straw was problematic. Slagging occurred and the heat exchanger was punctured in an attempt to chip off the slag. Steps toward a permanent demonstration project with pellet mill are underway. The port‘s long term goals are to use gasification to offset fossil fuels for industries within the port district and encourage a manufacturing facility for the production of gasifiers. Funding for this project has been included in a federal appropriation bill that is awaiting passage. The design is complete, but the project is on hold until the funding is released. Gady Farm – Spokane, Washington A one-year pilot project at the Gady Farm has begun operation to demonstrate the gasification of grass straw, a notoriously troublesome feedstock. The dual-stage gasifier developed by Taylor Biomass Energy ( and the Western Research Institute (WRI) is designed specifically to minimize problems associated with gasifying straw. The pilot gasifier will process 500 to 2000 pounds per hour of grass straw. The syngas, after cleaning, is being used to generate electricity using a 300 kW reciprocating engine/generator. Existing farm equipment will be utilized to collect, chop and pelletize, and store the straw, and convey it to the gasification reactor. Farm Power, the project‘s developer, also plans to contract with WRI to develop ancillary technology to convert syngas into liquid fuel and to test this technology on the farm. It is estimated that 60 gallons of fuel could be synthesized from a ton of straw. Pacific Northwest farmers generate 10 million tons of waste straw annually, which is sufficient to provide 420 million gallons of liquid fuel or approximately 8% of the region‘s transportation fuel usage. 43 This project illustrates the benefits of choosing a scale that is appropriate for use at the source of the feedstock, which reduces collection costs, as described in ―Grass straw gasifier ready to fire up‖ by Scott Yates in Capital Press ( D=38915&TM=66134.16): Costs of straw collection and transportation make long distance shipment to large, centralized conversion facilities uneconomical. Development of on-farmscale technologies for conversion of this biomass to energy provides the potential to develop a distributed network for power and liquid fuel production in rural communities. This pilot project is supported by a $750,000 U.S. Department of Energy grant in cooperation with the U.S. Department of Agriculture‘s Agricultural Research Service, the Pacific Northwest National Laboratory and the Bonneville Power Administration. The project developer is Farm Power. Inland Power & Light will purchase electricity that is not used on site through a net metering agreement. The project is composed of three tasks: development of feedstock, processing, handling and storage cost estimates; gasifier system development; and on-farm testing of the resulting gasification and power generation system. The Taylor gasifier used in this project is similar to the FERCO SilvaGas gasifier described above in that it has two chambers, one for gasification and the other for combustion, with a fluidized bed medium that circulates between the two chambers. In the Taylor gasifier, gasification of the straw takes place in the annulus between an outer tube and an inner (draft) tube. Char remaining after the gasification – plus supplemental fuel – are oxidized with air within the inner draft tube to generate the energy needed for gasification in the outer tube. Heat is transferred from the inner tube to the annular gasification section with the aid of steel balls that are pneumatically conveyed by the combustion products. For more information on the gasifier refer to ―Gasification of Kentucky bluegrass (Poa pratensis l.) straw in a farm-scale reactor‖ (Boeteng et al. 2006). Medium-Scale Demonstration Projects (1 MW and Greater) There are many medium-scale biomass gasification projects in various phases located around the world, as summarized in Tables 12 and 13. Numerous gasification projects that do not burn the gas in engines or turbines have been in operation for decades. But projects generating electricity in turbines and engines have much shorter histories. Four projects are summarized here. The first two demonstrate successful gas clean-up technology with generation of electricity by burning the product gas in an internal combustion engine: the Babcock Wilcox gasifier in Harboore, Denmark, and the PRM updraft gasifier in Moissanes, France. The 40 MWe Foster Wheeler fluidized bed gasifier in Lahti, Finland, illustrates the potential to co-fire the product gas with other fuels. The 40 MWe commercial-scale project in Tallahassee, Florida, will use an 44 indirectly heated steam gasifier. Construction on the Florida project will begin in early 2009. Harboore, Denmark – Babcock & Wilcox Volund Gasifier with Wet ESP Gas Clean-Up At this 1.5 MWe project wood chips are gasified in an updraft gasifier. The gasifier has been operating since 1994, providing district heating. Since 2005, it has also been generating electricity by burning syngas in two gas engines. Gas clean up is accomplished by cooling the gas and then passing it through a wet electrostatic precipitator (ESP). Treating the tar-contaminated water from the wet precipitator was problematic, but a successful solution has been developed. The meeting notes of the International Energy Agency‘s Second Semiannual Task Meeting held in October 2007 are available at reported: The 1.3 MWe capacity Harboore plant is in operation, producing 0.85 MWe, and 3.3 MWth district heat. During 2005, the gasifier has logged in 8200 hours and the gas engine for 7619 hours, and in 2006, the gasifier has logged in 8146 hours and the gas engine for 7947 hours. The Volund BMG technology is licensed to JFE, a Japanese company which has built and successfully commissioned a 7.5 MWth plant in Japan, producing 2 MWe, employing the same gas cleaning as at the Harboore plant. A second plant of 10 MWth is currently being planned to produce 3 MWe. The wood tars may be used locally for sanitary applications. Note that the capacity of this project has been increased to 1.5 MWe since this IEA summary was written. Moissannes, France – PRM Energy Gasifier with OLGA Gas CleanUp At the commercial demonstration project located in Moissannes, France (near Limoges), wood waste and distillery residue are gasified in a ―pseudo updraft‖ gasifier. Cleaned gas is burned in a Caterpillar engine to generate 1 MWe of power (4 MWth). This project was commissioned in 2006 as a demonstration for 6 future commercial 12.5 MWe (40 MWth) plants. Despite good operation in 2006 and the first part of 2007, the plant was not operated during most of 2007 and 2008 for administrative reasons. The project‘s final permit included more stringent demands than its initial temporary permit and required additional investments and downtime. Optimization and duration tests are scheduled. In this demonstration project (and in a 0.5 MWth pilot project that preceded the demonstration) the syngas was successfully cleaned using the OLGA tar removal process, previously described. Tar removal from the syngas has been a major problem in updraft gasifiers. 45 Lahden Lämpövoima Oy -- Lahti, Finland Producer gas is co-fired with coal at the Lahden Lämpövoima Oy‘s Kymijärvi power plant at Lahti, Finland. Paper and textiles, wood and peat, as well as shredded tires, plastics and municipal solid waste are gasified in a Foster Wheeler air-blown circulating fluidized bed gasifier that was installed in 1997. The plant has a total maximum capacity of 167 MWe. On an annual basis, approximately 15% of fuel needs are met by gasification. Capital cost of the gasification plant was $15 million. The hot product gas is led through an air preheater to two burners, which are located below the coal burners in the boiler. The bottom ash extraction system was designed to remove the non-combustibles from the municipal solid waste, as well as nails and other metals from urban wood waste. The gasifier has been in operation since 2002. Availability increased consistently in the first few years and in 2005, 2006 and 2007, the gasifier was available more than 7000 hours of the year and the engine, more than 6000 hours. Tallahassee Renewable Energy Center – Tallahassee, Florida (Construction to Begin January 2009) Biomass Gas & Electric (BGE) of Tallahassee will install an indirectly heated steam gasifier using the SilvaGas process in this 42 MWe commercial-scale project. BGE will sell both electricity and 60 million Btu‘s of methanated gas to the City of Tallahassee‘s pipeline. Construction is proposed to commence by January 2009, with a proposed in-service date by January 2011. The feedstock will be wood chips, which will be screened and sized at a different location. 46 Table 12. Examples of European Biomass Gasification Projects Location End Use Gasifier Manufacturer Gasifier Type Electrical Generation Feedstock Notes Wood Chips Operation of GE Jenbacher gas engines on syngas began in 2005. Plant availability up to 8000 hrs/year operation by 2006. District heating has been provided for more than 70,000 hours of operation between 1994 and 2005. 3 MWe Wood chips Planned Fluidized bed 40 MWe Peat, wood, tires and trash PRM Energy Updraft. 1.0 MW Wood and distillery grain residue Electricity PRM Energy Updraft 12.5 MWe Wood and distillery grain residue Värnamo, Sweden Electricity and Liquid Fuels Foster Wheeler IGCC 6 MWe Wood chips Gussing, Austria Electricity, mixed alcohols, heat Repotech Circulating Fluidized Bed 2 MWe Local wood Harboore, Denmark - Demonstration Electricity and District Heat Babcock & Wilcox Voland Updraft Harboore, Denmark - Commercial Electricity and District Heat Babcock & Wilcox Voland Updraft Lahti, Finland Electricity and District Heat Foster Wheeler Moissannes, France - Demonstration Electricity Moissannes, France - Commercial Plant 1.5 MWe 47 A 200-megawatt coal-fired plant that added a 40 MWe fluidized bed gasifier. Successful operation. Successful operation in 2006 and part of 2007, but not running now due to permit problems. Uses the OLGA organic solvent gas clean up. Commercial scale 12.5 MWe project in development. Plant availability up to 6500 hours by 2005. Restarted in 2006 for condition assessment with liquid fuel production starting in 2007. Plant availability up to 6500 hours of operation by 2005. GE Jenbacher gas engines. Beginning pilot of FischerTropsch synthesis to produce biodiesel and syngas. Plans for a fuel cell. Location End Use Gasifier Manufacturer Gasifier Type Electrical Generation Feedstock Notes Operational in 2008. Design Based on demonstration at Gussing. Electric efficiency of 32%. GE Jenbacher gas engine. Organic Rankine Cycle will recover heat from gasifier to generate electricity. Possibility of biomethane production. Operational since 2002. As of June 2008, plant has 15,000 hours of run time on GE Jenbacher gas engines. Commissioned in late 2006. Start up of one JMS 316 engine in 2004/2005 and two more in 2005/2006. District heat output of 4.3 MWth. Fuel is dried to less than 30% by waste heat from the existing Kokemäki district heating plant. Commissioning February 2008. Official opening delayed until April 2009. GE Jenbacher gas engines. Unique design of tar cracker. Total investment cost is 30 million Euros. Expected pay-back time is ~10 years. Oberwart, Austria Electricity. Biomethane Repotech Circulating Fluidized Bed 2 .7 MWe Wood Spiez, Switzerland Electricity Pyroforce Dual-zone /Fixed bed downdraft 200 kWe Commercially shredded wood Kokemäki, Finland Electricity and District heat Condens Oy / Novel Fluidized Bed 1.8MWe Wood Skive, Denmark Electricity Carbona Fluidized bed 5.4 MWe 110 tpd Wood Pellets Vario, Sweden Co-firing syngas in lime kiln Metso CFB Thermal Only 75 tpd bark Operating since 1986. 35 MWth. 144 tpd olive waste Operating since 2002 but in 2005 experimental tests were still on-going due to gas clean-up problems. Six Guascor gensets, model 560 FBLD. Rossanno, Italy Electricity PRM Updraft 4 MWe 48 Table 13. Examples of North American Biomass Gasification Projects Location Joseph C. McNeil Generating Station Burlington VT End Use Electricity Gasifier Manufacturer Future Energy Resources Company (Silvagas) Gasifier Type Indirect steam Electrical Generation Feedstock Status 7 MW 76 tons per hr forest thinnings and waste wood Silvagas technology successfully demonstrated in Phase 1 (1996 to 2001) in which product gas was supplied to the existing 50MWe biomass boiler, adding 6 to 7 MWe capacity. Phase 2 involving gas clean-up and use of gas turbines was stopped in 2001due to pending bankruptcy of FERCO. FERCO Enterprises became Silvagas in 2006. 28 MWe Wood waste, sawmill residue, and herbaceous agricultural waste from adjacent land fill Planned as of August 2007. Will generate electricity by steam cycle. Biomass Gas and Electric Forsythe, GA Electricity Future Energy Resources Corporation Biomass Gas and Electric Tallahassee, FL Electricity. Methanated biogas Future Energy Resources Corporation (Silvagas) Indirect steam 42 MWe Wood chips Construction to begin January 2009. Will use Silvagas technology demonstrated at McNeil Generating Station. BG&E estimates it can deliver electricity at 7 cents/kwh. FruitSmart: short term demo Prosser WA Syngas offset propane use in dryers. CPC Biomax Downdraft Thermal Only Various Ended due to slagging of gasifier with straw feedstock Grape pomace Planned demonstration of biomass pelletization and gasification at Prosser Wine and Food Park. Design complete but put on hold waiting for funding. Project has received a federal appropriation that has not yet passed. FruitSmart: long term demo Prosser WA Electricity. CPC Biomax Updraft Downdraft 500 kWe 49 Location Gady Farm Spokane, WA End Use Electricity. Liquid fuels. Gasifier Manufacturer Taylor Biomass Energy and WRI Gasifier Type Dual-bed indirect air Electrical Generation Feedstock Status Grass and straw Cleaned product gas will be burned in engine. 320 kW Wood Commissioning 2005 but operation stopped due to gas clean-up problems. Original electrostatic precipitator was replaced with a venturi wet scrubber in May 2008. The startup testing and system shakedown is planned for the 1st quarter of 2009. 50 kW 1.5 tpd of green wood chips Operating Reports that project was terminated due to ―feedstock problems‖. In 2007 the Biomax 25 unit was returned to CPC ―after not living up to expectations. 300 kW Tallon Lumber Electricity for on-site use and sale. Heat for lumber kiln. Pudhas Energy Mount Wachusett Community College Gardner, MA Electricity, Campus heating & cooling CPC Biomax Siskiyou Opportunity Center Mt Shasta, CA Electricity Community Power Corp. (CPC) Downdraft 25 kW Woodchips and nutshells Tolko plywood plant Heffley Creek BC Syngas for drying kilns Nexterra Updraft Thermal only 28 MMBtu/h 13,000 bone dry tonnes per year of wood residue Successful operation producing 38 MMBtu/hr net useable heat Updraft Thermal Only 60 MMBtu/h Hog fuel Commercial scale project. Due to economic conditions Domtar decided to postpone project until pulp and paper industry recovers. Updraft Thermal Only 8 MMBtu/h Hog fuel Successful 8 MMBtu/h pilot scale project to demonstrate technology for commercial scale project at the same site. Domtar Paper Mill Kamloops, BC (Commercial Project) Domtar Paper Mill Kamloops, BC (Pilot Project) Syngas for lime kiln (60 MMBtu/h) Syngas for lime kiln (8 MMBtu/h) Developers: Nexterra, Weyerhaeuser and Paprican (Now FP Innovations) Developers: Nexterra, Weyerhaeuser and Paprican (Now FP Innovations) Downdraft 50 Location End Use Gasifier Manufacturer Gasifier Type Electrical Generation Feedstock Status Completed performance and emissions tests in 2009. The 72 MMBtu/hr system provides 60,000 lbs/hr of steam and 1.4 MWe of electricity. University of South Carolina, Columbia, SC Electricity and Steam Nexterra / Johnson Controls Updraft Grand Forks Truss Plant, Grand Forks ND Electricity and Heat EERC Center for Renewable Energy Downdraft 50 kW Wood waste, sawdust. 4 to 6 cubic yards daily Planned as of July 2007 Dockside Green, Victoria BC District heating and hot water Nexterra Updraft Thermal only Urban wood waste The 8 MMBtu/hr system has been completed and is undergoing commissioning in 2009. Steam for mill Nexterra Updraft Thermal only Wood residue from mill and local construction debris Scheduled for completion Q4 2009. District heating Nexterra / Johnson Controls Updraft Thermal only Municipal wastewater biosolids Scheduled to be operational in 2011. 60,000 lb/hr District Heating Nexterra Updraft Thermal only Wood residue Planned Syngas for ethanol production Frontline Bioenergy Ethanol feedstock only Wood chips and corn cobs Phase 1: 100 tons/day Phase 3: 300 tons/day Currently operating in first of three phases of implementation. When 3rd phase is implemented syngas will displace 90% of plant‘s natural gas. Kruger Products Tissue Mill, New Westminster BC Oak Ridge National Labs in Oak Ridge Tennessee. University of Northern British Columbia Prince George, BC Chippewa Valley Ethanol Company Benson, MN 1.4 MWe 51 Other Information Resources The following resources are available for more information on biomass-fired combined heat and power systems. International Energy Agency, Task 33 The International Energy Agency (IEA) is an excellent online source for current updates on the status of thermal gasification technology and projects worldwide, including North America. The main webpage for their ―Task 33: Thermal Gasification‖ program can be found at . National Renewable Energy Laboratory NREL‘s Biomass Research website is U.S. Department of Energy You can find background on biomass gasification on the Department of Energy‘s website at The Department of Energy‘s ―Biomass Feedstock Composition and Property Database‖ contains characteristics of a variety of biomass feedstocks at Oak Ridge National Laboratory Oak Ridge National Laboratory has a database of biomass characteristics available at Bioenergy Lists Bioenergy Lists is a website ―for people involved in the development of gasification systems.‖ It offers information on current topics, pictures and reports. Their database of manufacturers & suppliers of gasifiers is available at: Biomass Energy Foundation The website of the Biomass Energy Foundation was developed by Dr. Tom Reed, who co-authored ―Survey of Biomass Gasification-2001‖ for the National Renewable Energy Laboratory. Their database of manufacturers, 52 equipment suppliers and research facilities involved in gasification is available at Energy Research Center of the Netherlands (ECN) The ECN has compiled a number of resources on renewable energy. Among them is ―Phyllis,‖ an extensive database of information on the composition of biomass and waste at Clean Energy Application Centers The U.S. Department of Energy‘s Industrial Technologies Program and its eight regional Clean Energy Application Centers provide assistance to facilities considering CHP, district energy and waste energy recovery. These centers can offer technology, application and project development information, case studies and other publications, workshops and other educational opportunities, and contacts for local resources. U.S. Clean Heat and Power Association Gulf Coast Clean Energy Application Center Texas, Louisiana and Oklahoma Intermountain Clean Energy Application Center Arizona, Colorado, New Mexico, Utah, and Wyoming Mid-Atlantic Clean Energy Application Center Delaware, Maryland, New Jersey, Pennsylvania, Virginia, West Virginia and Washington D.C. Midwest Clean Energy Application Center Illinois, Indiana, Iowa, Michigan, Minnesota, Missouri, Ohio, Wisconsin Northeast Clean Energy Application Center Connecticut, Maine, Massachusetts, New Hampshire, New York, Rhode Island, and Vermont Northwest Clean Energy Application Center Alaska, Idaho, Montana, Oregon and Washington 53 Pacific Region Clean Energy Application Center California, Hawaii and Nevada Southeast Clean Energy Application Center Alabama, Arkansas, Florida, Georgia, Kentucky, Mississippi, South Carolina, North Carolina, Tennessee U.S. Environmental Protection Agency The U.S. Environmental Protection Agency‘s CHP Partnership ( works to support the development of new CHP projects and promote their energy, environmental, and economic benefits. 54 References Basu, Prabir, ―Combustion and Gasificaton in Fluidized Beds,‖ CRC Press, Boca Raton, FL, 2006. Boateng, A.A., G.M.Banowetz, J.J. Steiner, T.F. Barton, D.G. Taylor, K.B. Hicks, H. ElNashaar, and V.K. Sethi, ―Gasification of Kentucky Bluegrass (Poa Pratensis I.) Straw in a Farm-Scale Reactor‖ Biomass and Bioenergy, 31:153-161, 2007. Boerrigter, Harold, Sander van Paasen, Patrick Bergman, Jan-Willem Konemann, and Rob Emmen, ―Tar Removal from Biomass Product Gas: Development and Optimisation of the OLGA tar removal technology.‖ 14th European Biomass Conference & Exhibition, Paris, France, October 2005, Brown, Robert C., Jerod Smeenk, and Clenn Norton, ―Development of analytical techniques and scrubbing options for contaminants in gasifier streams intended for use in fuel cells.‖ Submitted to the Chariton Valley Resource Conservation and Development and the U.S. Department of Energy Biomass Power Program, 2001. Ciferno, Jared P. and John J. Marano, ―Benchmarking Biomass Gasification Technologies for Fuels, Chemicals and Hydrogen Production,‖ prepared for U.S. Department of Energy, National Energy Technology Laboratory,‖ June 2002. Cummer, Keith R. and Robert C. Brown, ―Ancillary equipment for biomass gasification,‖ Biomass and Bioenergy, Volume 23, pp. 113-128, 2002. Ducente, AB, ―Large scale gasification of Biomass for Biofuels and Power,‖ prepared for the European Commission Directorate-General Energy and Transport, Sweden, 2006. This report discusses the IGCC demonstration project at Varnamo, Sweden. International Energy Agency, ―Review of Energy Conversion Devices‖ Klass, Donald L., Biomass for Renewable Energy, Fuels, and Chemicals, Academic Press, San Diego, California, 1998. Lettner, Friedrich, Helmut Timmerer, Peter Haselbacher, ―Biomass gasification – State of the art description,‖ Graz University of Technology - Institute of Thermal Engineering Inffeldgasse 25B, 8010 Graz, Austria, prepared for the European Union, December 2007. This document provides overviews of gas cleaning and water treatment technologies, in addition to gasifier technologies. on_V09e.pdf 55 Mater Engineering, LTD and T.R. Miles Consulting, Inc., ―Energy Conversion Systems Analysis for a Biomass Utilization Project in Central Oregon using CROP Modeling,‖ prepared for the Bonneville Environmental Foundation, October 2005. This reference provides a discussion of market potential and demand for other value-added wood products, including biochar and bio-oil. Matsumura, Yukihiko, Tomoaki Minowa, Biljana Potic, Sascha R.A. Kersten, Wolter Prins, Willibrordus P.M. van Swaaij, Bert van de Beld, Douglas C. Elliott, Gary G. Neuenschwander, Andrea Kruse and Michael Jerry Antal Jr., ―Biomass gasification in near- and super-critical water: Status and prospects,‖ Biomass and Bioenergy, Volume 29, pp. 269–292, 2005. McCormick, A. Tofa, ―A Comparison of Online Backpass Cleaning Technologies: Detonation, Acoustic and Conventional Steam or Air Sootblowing,‖ Energy Central, July 13, 2007 Miles, Thomas R., Thomas R. Miles Jr., Larry L. Baxter, Richard W. Bryers, Bryan M. Jenkins, and Lawrence L. Owens, ―Alkali Deposits Found in Biomass Power Plants,‖ Summary Report prepared for the National Renewable Energy Laboratory, Golden, CO, April 15, 1995 This reference includes strategies for minimizing alkali deposits. Milne, T.A., R.J. Evans and N. Abatzoglou, ―Biomass Gasifier ‗Tars‘: Their Nature, Formation, and Conversion,‖ National Renewable Energy Laboratory, Golden, CO November 1998, Olofsson, Ingemar, Anders Nordin, and Ulf Soderlind, ―Initial Review and Evaluation of Process Technologies and Systems Suitable for Cost-Efficient Medium-Scale Gasification for Biomass to Liquid Fuels,‖ University of Ulmea, Sweden, 2005, This reference provides a survey of all types of gasifiers: fixed bed, fluidized bed, entrained flow, indirect, plasma arc, and several other concepts. It also covers gas cleaning and processing techniques and processes for synthetic fuels and chemicals. Pels, Jan R., Danielle S. de Nie, and Jacob H.A. Kiel, ―Utilization of ashes from biomass combustion and gasification,‖ published at the 14th European Biomass Conference & Exhibition, Paris, France, October 2005 Ptasinski, Krzysztof J., Mark J. Prins, and Anke Pierik, ―Exergetic evaluation of biomass gasification,‖ Energy, Volume 32, Issue 4, April 2007, Pages 568-574. Ragland, Kenneth W., and Andrew J. Baker, ―Mineral Matter in Coal and WoodReplications for Solid Fueled Gas Turbines,‖ University of Wisconsin, Madison, WI and 56 U.S. Forest Products Laboratory, Madison, WI, Reed, T. and A. Das, ―Biomass Downdraft Gasifier Engine Systems Handbook,‖ Solar Energy Research Institute, 1988, available from This reference provides information on small-scale and low-tech gasifiers. Reed, T. and S. Gaur, ―A Survey of Biomass Gasification: 2001,‖ prepared for the National Renewable Energy Laboratory, 2001. Rezaiyan, John, Gasification Technologies: A Primer for Engineers and Scientists, CRC Press, Boca Raton, FL, 2005. RGW Enterprises, ―Clean Energy and Environment Project Feasibility Study,‖ Prepared for the Port of Benton, Richland, Washington, July 2007. Roos, Carolyn J., Biomass Drying and Dewatering for Clean Heat & Power, Northwest Clean Heat and Power Regional Application Center, 2008, wer.pdf. Savoie, P. and S. Descôteaux, ―Artificial drying of corn stover in mid-size bales,‖ Canadian Biosystems Engineering, Volume 46 2004, Wright, Lynn, Bob Boundy, Bob Perlack, Stacy Davis and Bo Saulsbury, Biomass Energy Data Book: Edition 1, Prepared for the U.S. Department of Energy, Energy Efficiency and Renewable Energy Office, Prepared by the Oak Ridge National Laboratory, Oak Ridge, Tennessee, September 2006, Vamvuka, D., D. Zografos, and G. Alevizos, ―Control methods for mitigating biomass ash-related problems in fluidized beds,‖ Bioresource Technology, September 2007. Van Loo, Sjaak, and Jaap Koppejan, ―The Handbook of Biomass Combustion and CoFiring,‖ Earthscan Publishing, London, 2008. Williams, Rob, Nathan Parker, Christopher Yang, Joan Ogden and Bryan Jenkins (UC Davis, Institute of Transportation Studies), H2 production Via Biomass Gasification, prepared for Public Interest Energy Research (PIER) Program, California Energy Commission, July 2007. Yoshida, Yoshikuni, Kiyoshi Dowaki, Yukihiko Matsumura, Ryuji Matsuhashi, Dayin Li, Hisashi Ishitani, and Hiroshi Komiyama, ―Comprehensive comparison of efficiency and CO2 emissions between biomass energy conversion technologies – position of 57 supercritical water gasification in biomass technologies,‖ Biomass & Energy, Volume 25, pages 257-272, 2003. 58
          IEA Bioenergy, Task 33 – Thermal Gasification of Biomass    Workshop  Thermal biomass gasification in small scale  13‐15 May 2014, Ischia, Italy    Summary by Dr. Jitka Hrbek, Vienna University of Technology  Checked by Prof. Kevin Whitty, University of Utah    IEA Bioenergy Task 33 Workshop: Thermal biomass gasification in small scale   Page1     Table of contents      List of tables    List of figures    Introduction    Presentations overview    MARCO FANTACCI, BIO&WATT GASIFICATION S.r.l., Italy  Energy conversion of biomass through pyrogasification process: presentation of an  industrial solution     ANDREA DUVIA, Gammel Duvia Engineering Srl, Italy  Biomass cogeneration: Activities and experience with plants based on biomass  gasification    MARCEL HUBER, Syncraft, Austria  The floating‐fixed‐bed ‐ status of a unique staged gasification concept on its way to  commercialization    GIOVANNA RUOPPOLO, CNR – National Research Council, Italy  Fluidized bed gasification and co‐gasification of biomass and wastes    PAOLA AMMENDOLA , CNR – National Research Council, Italy  Development of catalytic systems for tar removal in gasification processes    PAOLA AMMENDOLA , CNR – National Research Council, Italy  Relevance of biomass comminution phenomena in gasification processes    OSVALDA SENNECA, CNR – National Research Council, Italy  Gasification kinetics of biogenic materials and wastes    SIMEONE CHIANESE, University of Naples and TUV of Vienna, Italy  H2 4 Industries    SIMEONE CHIANESE, NADIA CERONE , ENEA, Italy   Gasification of fermentation residues from second generation ethanol for production  of hydrogen rich syngas in a pilot plant     Summary    IEA Bioenergy Task 33 Workshop: Thermal biomass gasification in small scale   ……………3 ……………3 ……………4 …………….5 …………….6 .…………..7 ………….13 ………….14 ………….16 ………….18 ………….21 ………….22 ………….24 ………….28 Page2     List of tables  Table 1: Presentations overview  Table 2: Gasification of lignin: parameters  Table 3: Gasification of lignin – results      List of figures  Figure 1: Plant layout an main subsystems  Figure 2: The gasification reactor  Figure 3: The producer gas conditioning section   Figure 4: Further Bio&Watt projects under development  Figure 5: Standard Spanner gasification module   Figure 6: Pelazzo turnkey plant: system concept  Figure 7: Updraft gasifier – actual design  Figure 8: Process scheme of a CraftWERK  Figure 9: The fluidized bed gasifier  Figure 10: Comparison with conventional catalysts at 700°C (pyrolysis conditions)    Figure 11: Effect of operating temperature (pyrolysis conditions)    Figure 12: Effect of pelletization ‐ Char attrition tests results – carbon conversion    Figure 13: The framework  Figure 14: Güssing biomass gasification plant  Figure 15: Experimental unit for hydrogen production  Figure 16: Gasification of lignin in updraft reactor; PRAGA plant – process scheme     Figure 17: PRAGA plant      IEA Bioenergy Task 33 Workshop: Thermal biomass gasification in small scale   Page3     Introduction  Combined heat and power generation (CHP) or cogeneration has been considered worldwide as the  major  alternative  to  traditional  systems  in  terms  of  significant  energy  saving  and  environmental  conservation.  The  most  promising  target  in  the  application  of  CHP  lies  in  energy  production  for  buildings, where small‐scale CHP is usually installed.   Generally  speaking,  the  concept  “small‐scale  CHP”  means  combined  heat  and  power  generation  systems with electrical power less than 100 kW.   Small‐scale  CHP  systems  are  particularly  suitable  for  applications  in  commercial  buildings,  such  as  hospitals,  schools,  industrial  premises,  office  building  blocks,  and  domestic  buildings  of  single  or  multifamily  dwelling  houses.  Small‐scale  CHP  systems  can  help  to  meet  a  number  of  energy  and  social  policy  aims,  including  the  reduction  in  greenhouse  gas  emissions,  improved  energy  security,  investment  saving  resulted  from  the  omission  of  the  electricity  transmission  and  distribution  network, and the potentially reduced energy cost to consumers.   Small‐scale  and  micro‐scale  biomass  CHP  systems  can  reduce  transportation  cost  of  biomass  and  provide heat and power where they are needed.   Of  all  the  renewable  energy  resources,  biomass  is  plentiful  and  prominent.  Wind  energy  and  solar  energy  have  the  limitation  of  intermittent  nature  and  therefore,  they  can  only  be  used  in  the  diversified systems to contribute where fossil fuel‐based power generation provides base‐load power  when the sun is not shining or the wind is not blowing.   Biomass  is  the  world’s  fourth  largest  energy  source,  contributing  to  nearly  14%  of  the  world’s  primary  energy  demand.  For  many  developing  countries,  the  contributions  of  biomass  to  their  national  primary  energy  demands  are  much  higher,  from  ca.  20%  to  over  90%.  Biomass  energy  systems  contribute  to  both  energy  and  non‐energy  policies.  The  life  cycle  of  a  sustainable  biomass  energy system has a nearly neutral effect on the atmospheric carbon dioxide concentration.  The  workshop  “Thermal  biomass  gasification  in  small  scale”  offered  interesting  information  in  this  field,  from  research  organisations  as  well  as  industry.  Furthermore,  new  contacts  and  areas  of  cooperation were outlined.              IEA Bioenergy Task 33 Workshop: Thermal biomass gasification in small scale   Page4     Table 1: Presentations overview  MARCO FANTACCI, BIO&WATT GASIFICATION S.r.l., Italy  Energy conversion of biomass through pyrogasification process: presentation of an industrial  solution   ANDREA DUVIA, Gammel Duvia Engineering Srl, Italy  Biomass cogeneration: Activities and experience with plants based on biomass gasification  MARCEL HUBER, Syncraft, Austria  The floating‐fixed‐bed ‐ status of a unique staged gasification concept on its way to  commercialization  GIOVANNA RUOPPOLO, CNR – National Research Council, Italy  Fluidized bed gasification and co‐gasification of biomass and wastes  PAOLA AMMENDOLA ,CNR – National Research Council, Italy  Development of catalytic systems for tar removal in gasification processes  PAOLA AMMENDOLA , CNR – National Research Council, Italy  Relevance of biomass comminution phenomena in gasification processes  OSVALDA SENNECA,CNR – National Research Council, Italy  Gasification kinetics of biogenic materials and wastes  SIMEONE CHIANESE, University of Naples and TUV of Vienna  H2 4 Industries  SIMEONE CHIANESE, NADIA CERONE , ENEA, Italy  Gasification of fermentation residues from second generation ethanol for production of hydrogen  rich syngas in a pilot plant             IEA Bioenergy Task 33 Workshop: Thermal biomass gasification in small scale   Page5         IEA Bioenergy Task 33 Workshop: Thermal biomass gasification in small scale   Page6   MARCO FANTACCI, BIO&WATT GASIFICATION S.r.l., Italy  Energy conversion of biomass through pyrogasification process: presentation of an  industrial solution  The Bio&Watt gasification plant was presented. Its key characteristics can be seen below:       Capacity: 200‐300 kWel per single module  Compact design: soil occupancy of the gasification module ca 14 m2, of the whole plant ca  400 m2  Easy maintenance to achieve higher reliability  Closed cycle: no waste products (the ash from biomass gasification fed into the plant), all the  energy potential of the biomass is exploited  Broad range of applicable fuels (biomass pre‐treatment needed)      Figure 1: Plant layout and main subsystems        IEA Bioenergy Task 33 Workshop: Thermal biomass gasification in small scale   Page7     Figure 2: The gasification reactor  A. downdraft  B. fixed bed/stratified  C. double fire  D. no refractory  The gasification reactor design focuses on simplicity, easy maintenance, energy conversion as well as  low tar production.  The aim of the syngas conditioning is fouling prevention, syngas de‐dusting, syngas cooling (from  700°C to < 40°C), and tar separation. No mechanical filtration is provided.   IEA Bioenergy Task 33 Workshop: Thermal biomass gasification in small scale   Page8     Figure 3: The producer gas conditioning section (cyclone, wet scrubber, electrostatic  precipitator)    For  tar  separation  the  process  water  from  the  wet  scrubber  and  wet  ESP  is  sent  to  a  specifically  designed  settling  tank    in  order  to  separate  tar.  The  focus  is  put  on  complete  tar  separation  from  process water and reuse of water in a closed‐loop cycle.    Figure 4: Further Bio&Watt projects under development  ANDREA DUVIA, Gammel Duvia Engineering Srl , Italy  IEA Bioenergy Task 33 Workshop: Thermal biomass gasification in small scale   Page9   Biomass cogeneration: Activities and experience with plants based on biomass gasification  The company Gammel Duvia Engineering Srl with more than 10 years of industrial experience with  leading  European  partners  and  customers  offers  complete  engineering  service  for  the  tendering,  integrated  design  and  realisation  of  biomass  power  plants.  It  has  strong  technical  and  commercial  background in the biomass cogeneration, geothermal and industrial heat recovery sectors.   Projects  Standard turnkey plant  „Pezzolato Energia” based on fixed bed downdraft gasifier  Pezzolato with headquarters in Envie (CN) is a company active since 1976 in the production design  and sale of biomass treatment devices (chipping machines, splitting machines, sawmill machines).   In 2013 Pezzolato decided to evaluate the opportunity to enter the energy cogeneration market with  main focus on small gasification  plants (< 200 kWel).    Gammel Duvia Engineering was selected as consultant for:   • Technology and market analysis of European market for small biomass gasifiers  • Evaluation of potential business models and partners  • Technology and market analysis of European market for small biomass  dryers  • Business development strategy  and negotiation with specific customers    After  evaluation  of  over  50  potential  suppliers,  Spanner  Re2  (Germany)  has  been  selected  as  technology provider.  Properties:   • Cogeneration  system    based  on  fixed  bed  downdraft  gasifier  coupled  with  dry  syngas  cleaning and 5,7 l gas motor.   • Standard  product with  45 kWel gross power.  • Standard module size suitable  for placing into containers.   •  > 250 reference plants and > 2.000.000 operation hours runtime.  • High biomass quality requirements  for optimal operation (humidity content < 10%, low fines  content).  • Preferred  scope  of  supply  limited  to  standard  core  system  (without  dryer,  installation,  building, grid connection, etc).         IEA Bioenergy Task 33 Workshop: Thermal biomass gasification in small scale   Page10     Figure 5: Standard Spanner gasification module     Pezzolato  is  proposing  a  turnkey  supply  based  on  Spanner  gasification  technology  and  proprietary  solutions for drying and conditioning of the Biomass. Plant size 50 – 300 kWel.    Figure 6: Pelazzo turnkey plant: system concept    Pezzolato has installed a first reference unit (45 kWel) at his headquarters in Envie (CN) in Q3/2013.  Initially  the  reference  plant  has  been  used  for  operational  tests  with  different  biomass  types/qualities  and  development  of  proprietary  solutions  for  dryer/  biomass  pretreatment.   Commercial operation from Q2/2014.   Supply  of  first  customer  unit  (45  kWel)  to  Prato  (turnkey  system  including  gasifier,  dryer,  biomass  pretreatment and special small size chipper Model  PTH 250) in June 2014.   IEA Bioenergy Task 33 Workshop: Thermal biomass gasification in small scale   Page11   Fixed bed updraft gasifier developed by partner Gammel Engineering   Gammel Engineering has more than 20 years of experience in the engineering of bioenergy systems.  Among  the  references  there  are  more  than  20  biomass  cogeneration  plants  with  different  technological solutions and heat uses, e.g. :         Plössberg (heat for pellet production; 2000 kW; ORC)   Ruderatshofen (drying of animal food and district heating; 2000 kW; ORC)  Weissenhorn (heating and high temperature process heat; 600 kW, ORC)   Cham (district heating and process steam  1500 kWel; steam turbine)   Taufkirchen (district heating ; 4500 kW; steam turbine )   Sauerlach (district heating ; 500 kWel; ORC)  Wolnzach (from heat only to cogeneration; 450 kW;ORC)     Figure 7: Updraft gasifier – actual design            MARCEL HUBER, Syncraft, Austria  IEA Bioenergy Task 33 Workshop: Thermal biomass gasification in small scale   Page12   The  floating‐fixed‐bed  ‐  status  of  a  unique  staged  gasification  concept  on  its  way  to  commercialization  The  Syncraft  Engineering  is  a  high‐tech  development  company  for  biomass  cogeneration  plants,  as  well as planning and implementation of CraftWERK plants.  CraftWERK plants are based on a floating bed technology. The core of the technology is a lifted and  propelled against gravity, floating fixed bed. This unique process setup enables to process standard  raw material, produces a clean producer gas and simultaneously allows a maximum of efficiency.      Highest efficiency  CraftWERK as a thermal base load units in existing district heating networks allow maximum  utilization of raw materials and overall efficiencies > 70%  Low value fuel   Wood  chips  G30  ‐  G50  used  without  any  special  requirements,  and  therefore  raw  material  costs of 90 €/t instead of 200 €/t for pellets or 150 €/t for G100 chips of heartwood.  Low operating costs   Simple and low‐maintenance gas cleaning   No expensive excipients or process materials needed  Low emissions  10  times  lower  emission  than  actual  limits  according  to  TA  Luft  without  expensive  gas  treatment;  1000  times  lower  tar‐concentration  in  the  product  gas  as  the  other  reference  systems (Güssing)    Figure 8: Process scheme of a CraftWERK        IEA Bioenergy Task 33 Workshop: Thermal biomass gasification in small scale   Page13   Product range:   CraftWERK 700 – commercially available  Power: 180 kWe and 275 kWth @ 0,8 m³/h  Efficiency: 28% electric  Space requirement: < 200m² / H=8m  Specialty: highly efficient 6‐cyl. gas engine from 2G     CraftWERK 1200 – prototype in final development stage  Power : 350 kWe and 500 kWth @ 1,4 m³/h  Efficiency : 29% electric  Space requirement : 200m² / H=10m  Specialty : adaptable to limit tariff 300kW Italy     CraftWERK 1600 – prototype will be built 2015    Power : 475 kWe and 670 kWth @ 1,9 m³/h  Efficiency : 30% electric  Space requirement : 250m² / H=10m  Specialty : adjusted to limit tariff 500kW Austria          GIOVANNA RUOPPOLO, CNR – National Research Council, Italy  Fluidized bed gasification and co‐gasification of biomass and wastes  The  production  of  chemicals,  hydrogen,  biofuels  and  energy  by  syngas  conversion  produced  from  biomass  gasification  may  be  considered  a  very  promising  route,  more  efficient  compared  to  combustion  and  pyrolysis,  but  for  its  complete  exploitation  some  technological  barriers  have  to  be  overcome.   The two main challenges of biomass gasification process are a relevant production of syngas and a  relatively low production of TAR. TAR species produced during gasification can be efficiently removed  via catalytic methods.  Gasification  process  carried  out  in  fluidized  bed  reactors  meets  these  requirements  thanks  to  the  uniform temperature and to the high heating rate of the reacting particles (more than 100°C∙s‐1). In  addition  this  reactor  configuration  is  characterized  by  good  fuel  flexibility  and  by  the  possibility  of  using a catalytic bed promoting in turn TAR conversion directly inside the gasifier. It is also reported  that  fuel  pretreatments,  such  as  pelletization,  torrefaction  and  compaction  or  their  co‐processing  with coal or wastes are suitable options to overcome the limitation of the low energetic density of  biomasses. In addition co‐gasification can also induce beneficial synergistic effects in tar conversion  and in preventing bed agglomeration phenomena.  IEA Bioenergy Task 33 Workshop: Thermal biomass gasification in small scale   Page14   The  presentation  offered  an  overview  on  the  research  activity  carried  out  at  IRC  on  gasification  of  wood and wood/coal/waste pellet in a fluidized bed reactor.   In particular the attention was paid on       relevance of the use of a suitable catalyst system to reduce tar formation   the  adopting  of  a  conical  shape  gas  distributor  and  of  a  central  spout  as  a  strategy  to  decrease the segregation phenomena  the use of pelletization strategy  the possibility to use the co‐gasification of biomass and plastic to produce a syngas prone  for its direct use in the methanol synthesis process.      Figure 9: The fluidized bed gasifier    The  fluidized  bed  gasifier  consisted  of  two  vertical  stainless  steel  tubes  connected  by  a  conical  adapter, the lower tube had an Internal Diameter (ID) of 140 mm and was 1010 mm in height, and  the upper tube had an ID of 200 mm and was 1800 mm high.    IEA Bioenergy Task 33 Workshop: Thermal biomass gasification in small scale   Page15   The main results obtained during different experimental campaign and carried out using a fluidized  bed gasifier:    The presence of a catalytic bed, especially in the case when an “ad hoc” reactor configuration  is  used:  adoption  of  a  central  jet  in  addition  to  the  conical  distributor,  increases  hydrogen  rich syngas yield and decreases tar production. However some expected negative effects of  such configuration on attrition phenomena has been highlighted    The effect of equivalent ratio and the presence of steam affect the performance of gasifier  less than the presence of catalyst provided that the segregation phenomena are negligible     The use of pellets results into beneficial effects on solid particles emissions but when mixed  pellets are used there is an important role played by properties of the parent fuels   Among  the  mixed  pellet  tested,  the  biomass/plastic  pellets  exhibited  promising  results  in  terms of the hydrogen yield even if they suffered from a higher production of  tar          PAOLA AMMENDOLA , CNR – National Research Council, Italy  Development of catalytic systems for tar removal in gasification processes    This  research  activity  focused  on  a  development  of  a  new  catalytic  system  for  conversion  of  tar  produced during biomass gasification in order to overcome the typical drawbacks (low activity, coke  deactivation) of conventional catalysts.     The  innovative  catalytic  system  is  a  ‐alumina‐supported  lanthanum‐cobalt  perovskite  (20  wt  %)  promoted with small amounts of rhodium (0.1 to 1wt%) which was proposed for the high reforming  activity of the noble metal and the good oxygen availability of perovskite, respectively. In addition,  the  large  dispersion  of  rhodium  into  the  LaCoO3  matrix  inhibits  its  possible  sintering  at  high  temperatures, typical of biomass gasification (800‐900°C).    In  order  to  investigate  the  catalytic  properties  by  modifying  both  the  catalyst  formulation  and  the  operative parameters, an experimental plant at a laboratory scale, which allows the contact between  catalyst and a real mixture of biomass devolatilization products, has been set up. It consisted of two  connected  fixed  bed  micro‐reactors,  heated  independently  in  two  different  electric  furnaces  and  it  was  equipped  with  an  analysis  system  for  detection  and  characterization  of  all  gaseous  and  liquid  products.  This  set  up  allowed  an  easy  and  economic  catalytic  screening,  allowing  the  use  of  small  amounts of catalytic material.     The  activity  in  biomass  tar  conversion  of  the  novel  catalytic  formulation  has  been  compared,  in  pyrolysis conditions, to that of conventional catalysts (olivine, dolomite, Ni/Al2O3). It was found that  the  novel  catalyst  was  able  to  completely  convert  tar  and  light  hydrocarbons  contained  in  the  biomass devolatilization products, but also to significantly increase the syngas yield due to prevailing  of  reforming  properties,  being  by  far  more  active  than  the  Ni/Al2O3  catalyst,  which  was  the  most  effective among the conventional materials.     IEA Bioenergy Task 33 Workshop: Thermal biomass gasification in small scale   Page16     Figure 10: Comparison with conventional catalysts at 700°C (pyrolysis conditions)    Moreover, the catalyst had a limited sensitivity to coke deactivation. These findings were supported  by  the  study  of  redox  properties  of  the  active  phases  deposited  on  the  alumina  support  by  TPR  analysis.     The study of catalytic activity and redox properties also led to define the best catalytic formulation.  The best performances were obtained with catalysts containing both rhodium and perovskite due to  the  synergic  effect  of  the  two  phases  coupling  the  highest  reforming  activity  with  the  lowest  coke  deposition.    In  addition,  the  deposition  of  the  perovskite  layer  prevents  the  encapsulation  of  rhodium  into  the  alumina  matrix  which  led  to  the  formation  of  a  less  active  rhodium  aluminate.  The  very  good  performances of the proposed catalyst have been correlated to its easy reducibility  under  reaction  conditions.    A very efficient tar conversion activity was maintained also for rhodium content as low as 0.1 wt%  thus  strongly  limiting  the  amount  of  the  expensive  precious  metal.  Likewise,  the  operation  temperature  can  be  lowered  to  600°C  keeping  the  same  performances  observed  at  high  temperatures.       Figure 11: Effect of operating temperature (pyrolysis conditions)  IEA Bioenergy Task 33 Workshop: Thermal biomass gasification in small scale   Page17     The  performance  of  the  alumina  supported  Rh–LaCoO3  has  been  also  studied  for  catalytic  tar  conversion  in  the  presence  of  H2S  and  has  been  compared  with  that  in  the  absence  of  these  poisoning agents.    Results  showed  that  the  perovskite  layer  preserves  to  large  extent  Rh  from  poisoning.  When  saturation  limits  are  overcome  highly  dispersed  rhodium,  associated  to  the  reforming  centres,  is  mainly affected and, as a consequence, the formation of reforming products decreases balanced by  the production of total oxidation and cracking species.     This  catalyst  keeps  its  original  reforming  properties  showed  for  S‐free  feed  also  in  the  presence  of  high  sulphur  concentration.  The  preservation  from  sulphur  poisoning  of  dispersed  rhodium  oxide,  active in tar reforming, was confirmed by DRIFT and TPR experiments.    To investigate the thermal and chemical stability of the alumina‐supported rhodium‐based catalysts  repeated cycles of tar conversion at 700°C followed by regeneration of the temporarily deactivated  catalyst by oxidation of coke deposited on the surface up to 800°C were carried out in order to test  the catalysts lifetime.     The  catalysts  containing  rhodium  show  a  satisfactory  physical  and  chemical  stability,  dispersion  of  rhodium  on  Al2O3  surface  being  preserved  even  at  800°C.  They  maintain  the  original  performance  and chemical properties of the fresh sample also after several cycles. On the contrary, the significant  modification  of  the  redox  properties  of  cobalt  in  the  LaCoO3/Al2O3  catalyst  after  the  first  conversion/regeneration cycle is related to a partial deactivation due to the irreversible migration of  cobalt into the alumina lattice.    The  catalytic  performance  of  the  rhodium‐based  catalyst  was  also  evaluated  in  the  presence  of  different levels of O2 at 700°C to explore its effect on both the quality of the syngas produced and the  extent of coke deposition.     A slight reduction of H2 yield and a negligible reduction of CO yield, compensated by water and CO2  formation,  respectively,  were  observed  coupled  to  the  total  disappearance  of  coke  deposition  at  3000 ppm O2. This represents a good result, since under these conditions catalyst regeneration can  be avoided.     A  very  recent  development  of  this  research  activity  was  also  the  possibility  to  use  this  catalytic  systems  in  secondary  reactors  in  the  form  of  honeycombs,  reducing  the  pressure  drops  across  the  reactor and its blocking due to solid particulate.    PAOLA AMMENDOLA, CNR – National Research Council, Italy  Relevance of biomass comminution phenomena in gasification processes  This  research  activity  was  carried  out  in  a  lab‐scale  fluidized  bed  apparatus,  on  fragmentation  and  attrition  by  abrasion  of  two  biomass  fuels,  namely  wood  chips  and  wood  pellets,  under  both  combustion and gasification conditions.     The aim was to highlight the effect of pelletization, i.e. of their different mechanical strength, on the  biomass behaviour during combustion and gasification in a fluidized bed, in terms of fuel particle size  distribution and overall carbon conversion.   IEA Bioenergy Task 33 Workshop: Thermal biomass gasification in small scale   Page18   Indeed,  biomass  fuels  are  characterized  by  a  low  energy  specific  content  if  compared  with  fossil  fuels. Fuel pre‐treatments like pelletization or torrefaction/compaction are appealing techniques to  increase  the  bulk  density  and  energy  specific  content,  to  improve  the  fuel  properties  (e.g.  homogenizing, stabilizing and strengthening the fuel particles), and to simplify the design of handling  and storage devices.    Fluidized  bed  (FB)  technology  is  considered  as  one  of  the  most  suitable  choices  for  biomass  conversion (combustion, gasification), because of its fuel flexibility.       Figure 12: Effect of pelletization ‐ Char attrition tests results – carbon conversion    Upon devolatilization and possible primary fragmentation, a fragile char particle is generated which  undergoes attrition by abrasion and fragmentation; with attrition we mean all those phenomena that  determine the breakage of the parent particle with generation of a number of fragments.     These  phenomena  are  well  known  to  affect  the  reliability  and  efficiency  of  FB  combustion  and  gasification processes. They may significantly change the particle size distribution of the fuel in the  bed which influences the rate and the mechanism of fuel particle conversion, as well as the particle  heat and mass transfer coefficients.     On  the  other  hand,  attrition  may  cause  the  elutriation  of  fine  material  from  the  bed  (i.e.  the  entrainment  with  the  gas  flow  to  the  reactor  exit)  those  results  in  the  reduction  of  fuel  residence  time and the loss of unconverted carbon, which, in turn, affect the conversion efficiency.    With  this  respect,  it  has  been  underlined  that  the  relevance  of  attrition  and  fragmentation  phenomena  is  emphasized  when  using  high‐volatile  fuels  instead  of  coals,  since  highly  porous  and  friable or even incoherent chars are formed upon devolatilization.  IEA Bioenergy Task 33 Workshop: Thermal biomass gasification in small scale   Page19   Primary  fragmentation  tests  showed  that  for  wood  pellets  limited  fragmentation  occurred  during  devolatilization,  with  a  fragmentation  probability  around  30%  and  particle  multiplication  factor  of  1.4, indicating that the pelletization procedure was able to give sufficient mechanical strength to the  particles.     On the contrary, wood chips were subject to extensive fragmentation as witnessed by large values of  the particle multiplication factor and of the fragmentation probability, significantly influencing both  the average particle size and the particle size distribution of the fuel in the bed.    Results of char attrition experiments carried out under inert, combustion and gasification conditions  showed that the carbon loss by elutriation is critical only during gasification, especially for the wood  chips char.     A gasification‐assisted attrition mechanism was proposed to explain the experimental results, similar  to  the  well‐known  combustion‐assisted  attrition  patterns  already  documented  for  coal  under  oxidizing  conditions.  The  low  reactivity  of  the  generated  fines  under  gasification  conditions  makes  the  loss  of  carbon  by  fines  elutriation  much  more  significant  than  that  typically  found  under  combustion conditions. Approximately half of the fixed carbon of the wood chips char was elutriated  away during the gasification experiments, determining a significant loss of conversion efficiency. On  the  contrary,  the  higher  mechanical  strength  of  the  wood  pellets  appears  to  be  beneficial  for  reducing carbon elutriation and for obtaining a higher carbon conversion.     Another  option  to  overcome  the  limitation  of  the  low  energetic  density  of  biomasses  is  offered  by  their  co‐processing  with  coal,  because  the  latter  has  an  almost  double  energetic  density.  This  measure also turns out to be useful when the primary fuel (i.e., the biomass) is temporarily lacking  because  of  seasonal  availability.  Of  course,  the  process  must  be  flexible  toward  the  change  of  the  fuel properties. This is the case of fluidized‐bed (FB) gasification that is acknowledged to have great  flexibility and high efficiency in conversion of several solid fuels.    To this aim a study on the devolatilization, fragmentation, and attrition of three pelletized fuels, one  based on wood and the other two based on a mixture of wood and coal, has been also carried out in  the  lab‐scale  FB  apparatus  and  under  gasification  conditions  and  for  comparison  under  inert  or  combustion conditions.     Similar and relatively long devolatilization times were observed for the three types of pellets in the  range  of  90‐100  s.  Pellet  breakage  by  primary  fragmentation  upon  devolatilization  appeared  to  be  rather limited for all fuels, indicating that fuel pelletization gives sufficient mechanical strength to the  particles. On the contrary, secondary fragmentation and attrition by abrasion of char particles during  gasification were extensive, especially at large carbon conversions, suggesting a gasification‐assisted  attrition  enhancement  effect.  This  mechanism,  associated  with  the  low  reactivity  of  the  generated  fines, made also in this case the loss of carbon by fine elutriation during char gasification much more  significant than that found under combustion conditions. Larger carbon losses were associated with  fuel pellets with a lower reactivity.            IEA Bioenergy Task 33 Workshop: Thermal biomass gasification in small scale   Page20   OSVALDA SENNECA, CNR – National Research Council, Italy  Gasification kinetics of biogenic materials and wastes  Biogenic fuels include a rather wide category of materials, ranging from raw vegetal materials to solid  refuses of industrial and civil origin. Inorganics and/or metals are often present in biogenic fuels at  levels distinctively higher than in traditional fuels. This may produce unusual effects.     The presence of metals and inorganics makes biogenic fuels more or less reactive than conventional  solid fuels, moreover it affects the yields in gaseous, liquid and solid products in a way that cannot be  predicted a‐priori and requires appropriate consideration. Kinetic models of different complexity are  required  to  describe  the  complex  patterns  of  reaction  that  can  be  encountered  in  some  biogenic  fuels.     The  classical  framework  of  pyrolysis  followed  by  combustion  of  char  and  lastly  its  gasification  is  in  fact oversimplified for many biogenic fuels. A modified framework is proposed to take into account  the possibility of overlapping between different processes according to the temperature levels and  the alternation of inert/oxidizing gaseous atmospheres..     This  presentation  offered  an  overview  of  experimental  results  obtained  for  different  biogenic  fuels  based  on  thermal  analysis  and  lab‐scale  reactors.  Kinetic  models  for  pyrolysis,  oxidative  pyrolysis,  char combustion and gasification and well as for secondary reactions of tars and volatiles assessed  for different fuels are also presented.       Figure 13: The framework  IEA Bioenergy Task 33 Workshop: Thermal biomass gasification in small scale   Page21   SIMEONE CHIANESE, University of Naples, Italy and TUV of Vienna, Austria  H2 4 Industries  Hydrogen production plays a very important role in the development of hydrogen economy. One of  the promising hydrogen production approaches is conversion from biomass, which is abundant, clean  and renewable. Thermochemical (pyrolysis and gasification) and biological (biophotolysis, water–gas  shift reaction and fermentation) processes can be practically applied to produce hydrogen.  This experimental work was provided using FICFB plant in Güssing and an experimental unit for  hydrogen production.  The product gas for water gas shift unit was taken after the product gas filter (see the following  figure).    Figure 14: Güssing biomass gasification plant    IEA Bioenergy Task 33 Workshop: Thermal biomass gasification in small scale   Page22     Figure 15: Experimental unit for hydrogen production  Parameters for Catalyst Evaluation  • CO Conversion (XCO)  • | | % | / /   Water Gas Shift Reaction Selectivity (WGSR Selectivity)  % | | | | | ⁄ | ⁄     Conclusions:   An  increase  in  CO  conversion  was  observed  as  the  temperature  increased  and  the  space  velocity decreased   The hydrogen sulphide loading effect was investigated, where a decreased catalytic activity  was  observed  as  the    H2S  concentration  increased,  although  the  catalyst  showed  a  good  resistance to hydrogen sulphide poisoning deactivation   The selectivity of the water gas shift reaction was evaluated and a methanation reaction was  detected    IEA Bioenergy Task 33 Workshop: Thermal biomass gasification in small scale   Page23     SIMEONE CHIANESE, NADIA CERONE, ENEA, Italy  Gasification of fermentation residues from second generation ethanol for production of hydrogen  rich syngas in a pilot plant  The gasification of lignin takes place in updraft reactor – PRAGA plant. The process scheme can be  seen in the following figure.    Figure 16: Gasification of lignin in updraft reactor; PRAGA plant – process scheme     The tests were carried out using lignin as a feedstock and operating the gasification at the following  conditions and atmospheric pressure.    IEA Bioenergy Task 33 Workshop: Thermal biomass gasification in small scale   Page24       Figure 17: PRAGA plant    Table 2: Gasification of lignin: parameters  IEA Bioenergy Task 33 Workshop: Thermal biomass gasification in small scale   Page25       Table 3: Gasification of lignin – results    The future work in this field      To optimise of gasification parameters (ER, steam/biomass, feeding rate)  To improve the analytics of tar determination  To maximize the hydrogen content  To model in ChemCad the process by using the kinetic parameters (TGA) and comparison  with experimental output          IEA Bioenergy Task 33 Workshop: Thermal biomass gasification in small scale   Page26   Summary  Small  scale  biomass  gasification  has  been  a  technological  option  that  has  raised  a  lot  of  interest  during the last years.    The  security  of  supply  and  climate  change  issues  and  the  linked  recent  growth  of  the  local  power  generation  by  means  of  renewable  energy  technologies  are  providing  real  opportunities  for  the  development of small scale biomass gasification systems.  The  workshop  offered  a  good  overview  and  important  information  on  small  scale  biomass  gasification in Italy and Austria. The research organisations as well as the representatives of industrial  companies active in this field participated on the workshop.  All the presentations can be found at the Task 33 website. (www.ieatask            IEA Bioenergy Task 33 Workshop: Thermal biomass gasification in small scale   Page27

Tutor Answer

(Top Tutor) Studypool Tutor
School: UC Berkeley
Studypool has helped 1,244,100 students
flag Report DMCA
Similar Questions
Hot Questions
Related Tags
Study Guides

Brown University

1271 Tutors

California Institute of Technology

2131 Tutors

Carnegie Mellon University

982 Tutors

Columbia University

1256 Tutors

Dartmouth University

2113 Tutors

Emory University

2279 Tutors

Harvard University

599 Tutors

Massachusetts Institute of Technology

2319 Tutors

New York University

1645 Tutors

Notre Dam University

1911 Tutors

Oklahoma University

2122 Tutors

Pennsylvania State University

932 Tutors

Princeton University

1211 Tutors

Stanford University

983 Tutors

University of California

1282 Tutors

Oxford University

123 Tutors

Yale University

2325 Tutors