CG4007 Sustainable Energy Processes Steam Design Project The line diagram illustrates the essential elements of a steam system in a production unit. The items of equipment are listed on page 2. The company uses a steam turbine to generate electricity for power and lighting. The forced circulation evaporator is used to produce three different products from three different feed solutions. As a member of the Energy Management Department you are asked to prepare a report, which includes: A concise description of the system; A complete heat and mass balance of the system for one product, quoting answers to four significant figures; The thermal efficiency of the boiler and of the super heater; The overall thermal efficiency of the system and suggestions for how it could be improved. During steady state test runs on the system for each of the three products the data listed on pages 3 and 4 were obtained. 1 SCHEDULE OF EQUIPMENT ITEMS 1 Deionizer unit 2 Boiler water feed tank 3 Boiler 4 Superheater 5 Live steam distillation unit 6 Steam turbine 7 Steam turbine condenser 8 Evaporator heat exchanger 9 Evaporator flash vessel 10 Evaporator surface condenser 11 Evaporator jet condenser 12 De-superheater 13 Evaporator condenser seal tank 14 Product seal tank 15 Boiler water feed pump 16 Boiler oil feed pump 17 Boiler forced draught (F.D.) fan 18 Boiler induced draught (I.D.) fan 19 Super heater oil feed pump 20 Super heater forced draught (F.D.) fan 21 Boiler induced draught (I.D.) fan 22 Turbine condenser condensate pump 23 Evaporator circulation pump 24 Product transfer pump 25 Pressure reducing valve 26 Temperature control valve 27 Flow control valve 2 STREAM PRODUCT Temperature ºC A B C Feed water to deionizer unit 15 15 15 Air to boiler 20 20 20 Air to super heater 20 20 20 300 300 300 Cooling water to turbine condenser (when required) 10 10 10 Cooling water from turbine condenser (when required) 25 25 25 Condensate from turbine condenser (when required) 120 120 120 Condensate from evaporator heat exchanger 120 120 120 Flash vessel temperature 69 69 69 Deionised water to evaporator condenser 15 15 15 Deionised water from evaporator condenser 60 60 60 Cooling water to evaporator jet condenser 10 10 10 Contaminated effluent from jet condenser 25 25 25 Feed to evaporator 20 20 20 Product from evaporator 69 69 69 Oil to boiler 0.228 0.228 0.290 Oil to super heater 0.030 0.030 0.038 Live steam to distillation unit 0.500 0.500 0.500 Feed to evaporator 2.20 2.64 4.00 Feed to evaporator, solids content 5.0 10.0 8.0 Feed to evaporator, water content 95.0 90.0 92.0 Product from evaporator, solids content 30.0 53.0 32.0 Product from evaporator, water content 70.0 47.0 68.0 Superheated steam Flow rate (kg s-1) Composition (% w/w) 3 STREAM Temperature ºC PRODUCT A B C Boiler 20.0 20.0 20.0 Super heater 20.0 20.0 20.0 Turbine inlet 20.0 20.0 20.0 Turbine exhaust 2.50 2.50 2.50 Turbine condenser (when required) 2.50 2.50 2.50 Evaporator heat exchanger 2.50 2.50 2.50 Flash vessel 0.30 0.30 0.30 Evaporator surface condenser 0.30 0.30 0.30 Evaporator jet condenser 0.30 0.30 0.30 Boiler exhaust 0.97 0.97 0.97 Flash vessel exhaust 0.97 0.97 0.97 Power produced from turbine (103 W) 750 750 750 Pressure (bar absolute) Dryness fraction 4 NOTES ON PRESENTATION 1. Present your neatly written report in a folder or binder. 2. Start a new page for each new item of equipment in the heat and mass balance. Prepare complete heat and mass balances over items 1 to 12 inclusive. 3. When commencing the heat and mass balance over an item, draw a box and draw lines to indicate streams; the inlet streams on the left hand side, the outlet streams on the right hand side. Heat losses are generally shown as leaving the bottom of the box. Attach to each stream the information which is known and which has to be calculated. See examples 1 and 2 on the pages which follow. 4. When you have completed the calculations for each item of equipment end that item with a table for the mass balance and a table for the heat balance. See examples 1 and 2 on the pages which follow. 5. Entering the results of your calculations into the master heat and mass balance sheet should assist you in preparing suggestions for improving the overall thermal efficiency. 5 EXAMPLE ITEM 9 EVAPORATOR FLASH VESSEL ?W ?W 2.00 kgs-1 15% w/w solids 85% w/w water 20ºC Heat from heat exchanger Vapour Product Feed 0.30 bar abs. 0.97 dryness fraction ? kg s40% w/w solids 60% w/w water 69ºC Feed Total flow rate = 2.00 kg s-1 Solids flow rate = 2.00 x 0.15 = 0.300 kg s-1 Water flow rate = 2.00 x 0.85 = 1.700 kg s-1 Check total flow rate = 2.000 kg s-1 Product Total flow rate of solution containing 40% solids = 0.300 0.4 = 0.750 kg s-1 Water flow rate = 0.750 x 0.60 = 0.450 kg s-1 Solids flow rate = 0.300 kg s-1 Check total flow rate = 0.750 kg s-1 Water to be evaporated Water in – water out = 1.700 – 0.450 = 1.250 kg s-1 Heat balance Heat in 2.00 kg s-1 of feed at 20ºC = 2.00 x 83.9 x 103 = 167.8 x 103W Heat in 0.750 kg s-1 of product at 69ºC = 0.750 x 289 x 103=216.8 x 103 = 216.8 x 103W Heat in 1.250 kg s-1 of dry vapour at 0.30 bar absolute = 1.250[289 + (0.97 x 2336)]103 = 3194 x 103W Heat to be added in heat exchanger = (3194 + 216.8 – 167.8)103 = 3243 x 103 6 7