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Boiler Efficiency

Boiler Efficiency

Boiler Efficiency

(OP)
Hi there,

Can anyone help to clarify the boiler efficiency calculation particularly on the output part?

Control Volume is only on the boiler
Example: Assuming that there is no blowdown,

Mass balance:
Mass of feedwater = mass of steam
Energy Balance:
Mass of feedwater X Feedwater enthalpy = Mass of steam X Steam enthalpy

So the output on boiler efficiency equation would be:
Mass of steam X Steam enthalpy - Mass of FW X FW enthalpy
Replacing mass of FW to mass of steam would give us
Mass of steam (Steam enthalpy - FW enthalpy)

Now usually have blowdown to remove impurities
Looking at the same control volume with blowdown would give the following equations:

Mass balance:
Mass of FW = mass of steam + mass of blowdown
Energy Balance:
Mass of FW X FW enthalpy = mass of steam X steam enthalpy + mass of blowdown X blowdown enthalpy

Then the output on the boiler efficiency would be:
Mass of blowdown X blowdown enthalpy + mass of steam X Steam enthalpy - Mass of FW X FW enthalpy
Replacing of Mass of FW would give
Mass of BD X BD enthalpy + mass of steam X Steam enthalpy - mass of steam X FW enthalpy - mass of BD X FW enthalpy
or
Mass of Steam ( Steam enthalpy - FW enthlapy) + Mass of Blowdown (Steam enthalpy - FW enthalpy)

Am I doing it right?
Sorry for the long equations. Hope you guys can understand what I'm trying to ask.

RE: Boiler Efficiency

I would suggest you read the power test code ASME PTC 4.1 to get a better idea of how boiler efficiency is calculated, or read the book "Steam" by B&W , in particulate the chapter on combustion and boiler efficiency.

"Whom the gods would destroy, they first make mad "

RE: Boiler Efficiency

Your energy balance equations should include heat input eg

Mass of feedwater X Feedwater enthalpy + Heat Input = Mass of steam X Steam enthalpy

je suis charlie

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