Steam Boiler Efficiency

Steam boiler efficiency is very important information to indicate among other factors the fuel usage, which in turn determines operating cost. There are several ways of defining steam boiler efficiency:

§         As-Found Efficiency: is the efficiency measured in the field for steam boilers existing in a state of repair or maintenance. It is used as the baseline for any subsequent efficiency improvements.
§         Tuned-Up Efficiency: is the efficiency after operating adjustments (low excess air) and minor repairs have been made.

§         Maximum Attainable Efficiency: is the result of adding currently available efficiency improvement equipment, regardless of the cost considerations.
§         Maximum Economically Achievable Efficiency: differs from that above in that it accounts for realistic cost considerations with efficiency improvement equipment added only if it is economically justifiable.

ASME Power Test Code PTC 4.1 has defined two methods for determination of efficiency:
§         The input & output method
The input-output method has defined the efficiency of steam boiler as the useful energy output divide by the energy input.

The energy input is measured in Btu/h. The following is an example of a simple way to calculate steam boiler efficiency

Question: A gas-steam boiler type fire tube has capacity of 12,300,000 Btu/h. The stack loss is 1,400,000 Btu/h. What is the efficiency of the steam boiler?

Stack Loss = 1,400,000 Btu/h
Input capacity = 13,500,000 Btu/h
Output of the steam boiler = 12,300,000 - 1,400,000 = 10,900,000 Btu/h

§         The heat loss method
     Calculation steam boiler efficiency based on the heat loss method is not simple; all parameter of heat loss should be considered. The total heat loss is the sum of heat losses due to steam leaks, radiation, blowdown, heating of combustion air, condensate, make up water, and stack.

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