2. Effect of Furnace Heat Transfer on Maximum Cycle Pressure Understanding of Fuel to Cycle Connections….. P M V Subbarao Professor Mechanical Engineering Department I I T Delhi

3. Heat available for Radiation Incomplete combustion loss Unburned Carbon loss Loss due to slag Energy brought in by preheated air & fuel.

4. Simplified Approach Emitted Radiation heat flux of flames: Emitted Radiation = Available Heat Heat flux absorbed by walls : Thermal efficiency factor, . The rate of heat absorption

5. Thermal Efficiency Factor,  If clean water wall is a perfect black body all radiation falling on it will be absorbed. Fouling (  leads to drop in emissivity of the wall. Water walls consists of tubes which generate an angular coefficient, x. Angular coefficient varies with the location of water wall. Thermal efficiency factor is defined as the fraction of incident radiation absorbed by the tubes: The average thermal efficiency factor is calculated as

6. 1: c > 1.4 d 2: c = 0.8 d 3: c = 0.5 d 4: C = 0 5: Fully cooled

7. Performance of Analysis of Furnace Get Fuel Ultimate Analysis. Compute Equivalent Chemical Formula. Select recommended Exhaust Gas composition. Carry out first law analysis to calculate Adiabatic Combustion Temperature. Total number of moles of wet exhaust gas for 100 kg of fuel : n ex.gas = P+Q+R+T+U+V 100 X CV of fuel =  n ex. Gas h f,gas Calculate Adiabatic Flame Temperature. Calculate total heat transfer area of furnace, A fur

8. Furnace Characterization Criteria M Temperature Field Coefficient T fl combustion temperature T fe Furnace Exit Gas Temperature A fur Total surface area of furnace m c Flow rate of fuel

9. Details of Furnace Heat Transfer: 500 MW(e) Load : 500 MW Coal Flow Rate: 73.76 kg/s Ambient air flow rate: 577.06 kg/s Actual air-fuel ratio: 7.82 Main Steam Flow rate: 425 kg/s Reheat Steam Flow rate: 381.7 kg/s Heat absorbed by water wall: 509.19MW Furnace Exit Temperature: 1219.5 0 C Overall Heat transfer coefficient for furnace: 109 W/m 2 0 C

13. Excess airT ad (K)FEGT (K)O 2 % 0222011661.91 10208513263.5 20196613904.84 30186414716.0 40177615617.0

14. Super heaters Super heater heats the high-pressure steam from its saturation temperature to a higher specified temperature. Super heaters are often divided into more than one stage. The enthalpy rise of steam in a given section should not exceed –250 – 420 kJ/kg for High pressure. > 17 MPa –< 280 kJ/kg for medium pressure. 7 Mpa – 17 MPa –< 170 kJ/kg for low pressure. < 7 MPa

16. Thermal Balance Equation for Platen SH Energy given out by flue gas: Energy absorption for a Platen SH:

17. Mechanism of Heat Transfer : Generalized Newton’s Law of Cooling Rate of heat transfer from hot gas to cold steam is proportional to: Surface area of heat transfer Mean Temperature difference between Hot Gas and Cold Steam. T hot gas,in T cold steam,in T hot gas,out T cold steam,out

18. T hot gas,in T cold steam,in T hot gas,out T cold steam,out T hot gas,in T cold steam,in T hot gas,out T cold steam,out

19. Log Mean Temperature Difference Rate of Heat Transfer U Overall Heat Transfer Coefficient, kW/m 2.K

20. Thermal Balance in Super Heater. The energy absorbed by steam The convective heat lost by flue gas Overall Coefficient of Heat Transfer, U Platen SH, U (W/m 2 K)120 – 140 Pendent SH, U (W/m 2 K)120 – 140 Convective SH, U (W/m 2 K) 60 – 80

21. Thermal Balance in Economizer. The energy absorbed by steam The convective heat lost by flue gas Overall Coefficient of Heat Transfer, U

22. Thermal Balance in Air Pre-Heater. The energy absorbed by air The convective heat lost by flue gas Overall Coefficient of Heat Transfer, U

23. Model: 500 MW

24. Gas Temperatures Platen Super Heater: Inlet Temperature: 1236.4 0 C Outlet Temperature: 1077 0 C Final Super Heater: Inlet Temperature: 1077 0 C Outlet Temperature: 962.4 0 C Reheater: Inlet Temperature: 962.4 0 C Outlet Temperature: 724.3 0 C Low Temperature Super Heater: Inlet Temperature: 724.3 0 C Outlet Temperature: 481.3 0 C Economizer: Inlet Temperature: 481.3 0 C Outlet Temperature: 328.5 0 C Air Pre Heater: Inlet Temperature: 328.5 0 C Outlet Temperature: 133 0 C Steam Temperatures Platen Super Heater: Inlet Temperature: 404 0 C Outlet Temperature: 475 0 C Final Super Heater: Inlet Temperature: 475 0 C Outlet Temperature: 540 0 C Reheater: Inlet Temperature: 345 0 C Outlet Temperature: 540 0 C Low Temperature Super Heater: Inlet Temperature: 359 0 C Outlet Temperature: 404 0 C Economizer: Inlet Temperature: 254 0 C Outlet Temperature: 302 0 C Air Pre Heater: Inlet Temperature: 38 0 C Outlet Temperature: 276.5 0 C

25. LMTD for various Devices: Model

26. Model: 500 MW

28. Heat Transfer coefficients (W /m 2 K) 210 MW(e) 123456 Platen-IPlaten-2 RH 3rd & 2nd RH 1st EcoAPH Final hco323443516315.4 hr102967154.9110 hg1341301141067915.4 U129126103977315.4 hs /100 41.8240.810.3111.159.850

29. Design Calculate d 1Adiabatic Flame Temp (K)19571966 2FEGT ( 0 C)11021117 3Platen SH-I Outlet ( 0 C)932951 4 Platen SH-II Outlet-I outlet ( 0 C)859878 5RH 3rd & 2nd outlet ( 0 C)595604 6RH 1st Stage outlet ( 0 C)510531 7Economiser outlet ( 0 C)385398 8APH Outlet ( 0 C)138151 Flue Gas Temperature At different regions of Furnace:210 MWe)

31. FG O 2 ExcessCO CO loss FG tempDFLBAFAU/C U/C lossTotal loss %Air (%)ppmKJ/Kg( 0 C)KJ/KgU/C % %KJ/Kg 0.31.453000224.4121970.75.11.20.56534.11729.2 0.52.441412112.2123992.08.51.150.74703.51807.8 0.73.45109782.01251013.48.21.10.71676.01771.4 0.83.9645534.01271034.77.310.64607.11675.9 0.94.4731523.61301066.76.20.90.55526.31616.6 151299.61321088.05.00.90.49462.71560.4 1.15.531098.151331104.03.90.780.393751487.2 1.26.0697.57.291371120.02.80.770.33316.71444.1 1.36.6493.61411184.01.90.620.25237.01424.7 1.57.6934.52.51431205.30.70.550.17157.61365.5 1.89.389.50.711491269.40.210.480.12114.91384.9 210.53001531312.00.360.370.199.31411.4 2.513.51001571354.70.370.250.0873.91428.6 316.67001611397.40.270.230.0764.31461.7 3.520001681472.00.270.220.0661.81533.9 423.53001771568.00.270.220.0661.81629.9