How is the combustion efficiency of a boiler calculated?

There are many ways to calculate boiler efficiency, and it seems that ASME’s method is used more frequently these days. For the online efficiency of boilers, it is necessary to have online monitoring of the carbon content in fly ash; however, based on what I’ve learned from power plants, this monitoring seems to not be very accurate.

For fuel-gas boilers, a simple way to estimate it, in my opinion, is to measure the exhaust gas temperature, which allows for an approximate calculation.

Using positive balance is simpler; it just involves dividing the heat output by the heat input.

The counterbalance method can also be used: q2, q3, q4, q5, q6 (for layer-fired boilers, these represent the heat losses due to ash and slag). To determine q2, it is necessary to know the flue gas temperature; this value can be calculated using the formula for flue gas losses. Such formulas are available in most books on industrial boilers. The formula for calculating q6 can also be found. For q3, q4, and q5, linear charts can be used for calculation; these charts are also included in most boiler-related books. Finally, efficiency is calculated as 1 – (q2 + q3 + q4 + q5 + q6). For boilers that use fuel or gas, the heat losses due to ash and slag can be ignored

If the coal fed into the furnace can be monitored, a positive balance can be calculated

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The best approach is to calculate the heat absorption based on the temperature of the superheated steam leaving the steam drum, the temperature of the steam entering the drum, and the flow rate, and then divide this value by the heat content of the coal fed into the furnace. Then efficiency is obtained