final audit :utilization of flue gas energy p m v subbarao professor mechanical engineering...
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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….
s
1
2
3
4
5
6
2f
2s
4523 hhmhhm mreheatsteafmainsteam
DPNL SH
Platen SHT
R
RHTR
LTSH
Economiser
APH ESP ID Fan
drum
Furnace
BCWpump
Bottom ash
stack
screentubes
Thermal Structure of A Boiler Furnace
Furnace ater wall absorption
Platen SH
Pendent SHCSH
Reheater
Combustion Losses C & R losses
Hot Exhaust Gaslosses
Sequence of Energy Exchange from Flue Gas to Steam
PLATEN SH
FLUE GAS
EVAPORATORWater Wall
COVECTIVE LTSH
RH PENDENT SH
Fuel Power
Furnace absorption
Platen SH
Final SHLTSH
Reheater
Combustion Losses C & R losses Hot Exhaust Gaslosses
~4000C
Details of 500 MW(e) Capacity Indian Power Unit
• Main steam Flow rate: 425 kg/s.
• Main Steam Temperature: 5400C
• Reheat Steam Flow rate: 38.7 kg/s.
• Air Flow Rate: 577.06 kg/s.
• Coal Flow Rate: 73.8 Kg/s.
500 MW
Gas Temperatures
• Platen Super Heater:• Inlet Temperature: 1236.4 0C• Outlet Temperature: 1077 0C• Final Super Heater:• Inlet Temperature: 1077 0C• Outlet Temperature: 962.4 0C• Reheater:• Inlet Temperature: 962.4 0C• Outlet Temperature: 724.3 0C• Low Temperature Super
Heater:• Inlet Temperature: 724.30C• Outlet Temperature: 481.3 0C
Steam Temperatures
• Platen Super Heater:• Inlet Temperature: 404 0C• Outlet Temperature: 475 0C• Final Super Heater:• Inlet Temperature: 475 0C• Outlet Temperature: 540 0C• Reheater:• Inlet Temperature: 345 0C• Outlet Temperature: 5400C• Low Temperature Super
Heater:• Inlet Temperature: 3590C• Outlet Temperature: 404 0C
Design Calculated
1 Adiabatic Flame Temp (K) 1957 1966
2 FEGT (0C) 1102 1117
3 Platen SH-I Outlet (0C) 932 951
4Platen SH-II Outlet-I outlet (0C) 859 878
5 RH 3rd & 2nd outlet (0C) 595 604
6 RH 1st Stage outlet (0C) 510 531
7 Economiser outlet (0C) 385 398
8 APH Outlet (0C) 138 151
Flue Gas Temperature At different regions of Furnace:210 MWe)
Steam and Gas Paths
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.
500 MW
LMTD for various Devices
Surface Area of Heat Exchangers: 500 MW
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
Tube Bank Arrangement
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/m2 s
• The waterside resistance should not exceed 5 – 8 %. Of drum pressure.
• Flue gas velocity : 7 – 13 m/s.
Thermal Balance in Economizer.
• The energy absorbed by steam
• The convective heat lost by flue gas
• Overall Coefficient of Heat Transfer, U
)( ,,, inecooutecosteamconabs hhmQ
TUAQ ecolosscon
,
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 tmax /tmin > 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.
min
max
minmax
log3.2t
t
ttt
2minmax tt
t
Complex Flow
• Parallel flow and counter flow may simultaneously exist in one section of an economizer.
• This is called complex flow.
• 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 Ktd is determined by flow type and the thermal parameters.
copa ttt 5.0
copa tt 92.0
cotd tKt
Gas Temperatures
• Platen Super Heater:• Inlet Temperature: 1236.4 0C• Outlet Temperature: 1077 0C• Final Super Heater:• Inlet Temperature: 1077 0C• Outlet Temperature: 962.4 0C• Reheater:• Inlet Temperature: 962.4 0C• Outlet Temperature: 724.3 0C• Low Temperature Super Heater:• Inlet Temperature: 724.30C• Outlet Temperature: 481.3 0C• Economizer:• Inlet Temperature: 481.3 0C• Outlet Temperature: 328.5 0C
Steam Temperatures
• Platen Super Heater:• Inlet Temperature: 404 0C• Outlet Temperature: 475 0C• Final Super Heater:• Inlet Temperature: 475 0C• Outlet Temperature: 540 0C• Reheater:• Inlet Temperature: 345 0C• Outlet Temperature: 5400C• Low Temperature Super Heater:• Inlet Temperature: 3590C• Outlet Temperature: 404 0C• Economizer:• Inlet Temperature: 254 0C• Outlet Temperature: 302 0C
Furnace absorption
Platen SH
Pendent SHCSH
Reheater
Economizer APH
Combustion Losses C & R losses Hot Exhaust Gaslosses