Master the method of calculating coal fired boiler efficiency is very important to a factory. Because you can know the current situation of your boiler, and you can decide whether or not you need to take action to run coal fired boiler at the best efficiency. A practical and simple method for calculating the efficiency of coal fired boilers is given in this article. Practical assumptions are used to simplify the otherwise elaborate calculations of the Boiler test codes. The Losses method is used to calculate boiler efficiency. Each of the different Losses is calculated to determine the efficiency.
For a coal fired boiler to calculate these losses we require the following data.
Higher Heating Value of coal on as Fired Basis HHV- kJ / kg
Proximate Analysis of Coal on as Fired basis which include:
Fixed Carbon FC %
Volatile Matter VM %
Hydrogen % in coal. This normally available only from an Ultimate analysis. This can be used from a past historic data for similar type of coal. The value normally is in the range of 2 - 4 %.
Gas temperature at boiler exit - Tg °C
Ambient Temperature - Dry bulb - Ta °C
Oxygen in Flue gas on a dry basis - O2 %
The oxygen measurement should be from a location near to the Temperature point.
On line Oxygen, measurements are normally on wet basis.
Sampled Oxygen measurements are on dry basis. In coal fired units O2 % ( dry basis)= (O2 % ( wet basis)) / 0.9
Unburnt Carbon in ash U %
In large coal fired plants, ash collection is in different locations. This is mainly at the Furnace bottom and the Precipitator Hoppers. The U % should be on a weighted average basis. A ratio of 85: 15 is practical between furnace bottom and precipitator ash collection.
U %=[U-fly ash x 85 + U-bot ash x 15] / 100
If you have collected all of the date, you can calculate the efficiency of coal fired boiler right now.