2. Final Audit :Utilization of Flue Gas Energy P M V Subbarao Professor Mechanical Engineering Department Minimize Final Exhaust Gas Temperature…. Properly Utilize Enthalpy of Flue Gas….

3. s 1 2 3 4 5 6 2f 2s

4. DPNLSH Platen SHTR RHTRRHTR LTSH Economiser APH ESP ID Fan drum Furnace BCW pump Bottom ash stack screen tubes Thermal Structure of A Boiler Furnace

5. Furnace ater wall absorption Platen SH Pendent SH CSH Reheater Combustion LossesC & R losses Hot Exhaust Gas losses

6. Sequence of Energy Exchange from Flue Gas to Steam PLATEN SH FLUE GAS EVAPORATOR Water Wall COVECTIVE LTSH RH PENDENT SH

7. Fuel Power Furnace absorption Platen SH Final SH LTSH Reheater Combustion LossesC & R losses Hot Exhaust Gas losses ~400 0 C

8. Details of 500 MW(e) Capacity Indian Power Unit Main steam Flow rate: 425 kg/s. Main Steam Temperature: 540 0 C Reheat Steam Flow rate: 38.7 kg/s. Air Flow Rate: 577.06 kg/s. Coal Flow Rate: 73.8 Kg/s.

9. 500 MW

10. 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 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

11. DesignCalculated 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)

12. Steam and Gas Paths

13. Suggested Fluid Velocities Flue gas velocities: 10 – 18 m/s. Steam in super heaters & reheaters: 10 – 25 m/s. Water Wall circulation : 0.35 – 3.5 m/s.

14. 500 MW

15. LMTD for various Devices

16. Surface Area of Heat Exchangers: 500 MW

17. Economizer The economizer preheats the feed water by utilizing the residual heat of the flue gas. It reduces the exhaust gas temperature and saves the fuel. Modern power plants use steel-tube-type economizers. Design Configuration: divided into several sections : 0.6 – 0.8 m gap

18. Tube Bank Arrangement

20. Thermal Structure of Economizer Out side diameter : 25 – 38 mm. Tube thinckness: 3 – 5 mm Transverse spacing : 2.5 – 3.0 Longitudinal spacing : 1.5 – 2.0 The water flow velocity : 600 – 800 kg/m 2 s The waterside resistance should not exceed 5 – 8 %. Of drum pressure. Flue gas velocity : 7 – 13 m/s.

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

22. Mean Temperature Difference The average temperature difference for parallel flow and counter flow is expressed as It is also called log mean temperature difference When t max / t min > 1.7, the average temperature may be expressed as: Generally, the flow direction of the flue gas is perpendicular to the axes of tubes. If number of bends are more than four, the flow can be treated as counter or parallel flow.

23. Complex Flow Parallel flow and counter flow may simultaneously exist in one section of an economizer. This is called complex flow.

24. For a given set of inlet and outlet temperatures of the fluids, The temperature difference of parallel flow is the greatest, The temperature difference of counter flow is the lowest And that of complex flow is in between. The average temperature difference in a complex flow can be calculated as: When Otherwise, the temperature difference is determined by The value of K td is determined by flow type and the thermal parameters.

27. 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 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

28. Furnace absorption Platen SH Pendent SH CSH Reheater Economizer APH Combustion LossesC & R losses Hot Exhaust Gas losses