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Boiler Flue Gas Economizer Calculations
- Thread starter EnerEn
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Most people use the simple method of Q=UA*LMTD, where
Q= heat transferred from gas to water,
U= overall heat transfer coefficient, inclcuding resistance to heat transfer caused by fouling and tube metal conductivity( extended surfaces need to include a fin efficiency)
A= total surface area of the heat exchanger
A simple starting point is to assume a gas velocity thru the bank of 50-60 fps , and the UA = 1.5 *WgCp,g ( this is equivalent to an NTU = UA/WCp = 1.5 ). The number of tubes operating in parallel to yield a tubeside water velocity of 10-15 fps.
A more accurate method is the e-NTU method, but I think you might not be ready for that yet.
Q= heat transferred from gas to water,
U= overall heat transfer coefficient, inclcuding resistance to heat transfer caused by fouling and tube metal conductivity( extended surfaces need to include a fin efficiency)
A= total surface area of the heat exchanger
A simple starting point is to assume a gas velocity thru the bank of 50-60 fps , and the UA = 1.5 *WgCp,g ( this is equivalent to an NTU = UA/WCp = 1.5 ). The number of tubes operating in parallel to yield a tubeside water velocity of 10-15 fps.
A more accurate method is the e-NTU method, but I think you might not be ready for that yet.
Hi there:
On the gas side, it would be good to know the flue gas composition.
There is a possibility that you can deal with the enthalpy values directly for the amount of heat that gets exchanged.
Q = (h gas in - h gas out) * gas mass flow rate [kW]
Q = (h water out - h water in) * water mass flow rate [kW]
Then you figure out the required surface for such amount of heat transfer, as indicated above.
Thanks,
Gordan Feric, PE
Engineering Software
On the gas side, it would be good to know the flue gas composition.
There is a possibility that you can deal with the enthalpy values directly for the amount of heat that gets exchanged.
Q = (h gas in - h gas out) * gas mass flow rate [kW]
Q = (h water out - h water in) * water mass flow rate [kW]
Then you figure out the required surface for such amount of heat transfer, as indicated above.
Thanks,
Gordan Feric, PE
Engineering Software
The ESCOA manual has a calculator included for sizing economizers.
It can be downloaded from this page:
It can be downloaded from this page:
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