When it comes to boiler efficiency, it is an important term which should be considered. Boiler efficiency is a combined result of efficiency of different components of a boiler. A boiler has many sub systems whose efficiency affects the overall boiler efficiency. Couple of efficiency which finally decide the boiler efficiency are-
1. Combustion efficiency
2. Thermal efficiency
Apart from these efficiency, there are some other losses which also play a role while deciding the boiler efficiency and hence need to be considered while calculating the boiler efficiency. However, the most important factors need to be considered are boiler combustion efficiency and boiler thermal efficiency.
Combustion boiler efficiency generally describes the ability of a burner to burn the entire fuel into the boiler combustion chamber (furnace). The efficiency of this type is calculated from the amount of fuel that does not burn along with the amount of air combustion air (air excess). Burning boiler can be said to be efficient if there is no remaining fuel in the end outlet of boiler combustion chamber, so does the number of residual air.
To obtain high combustion efficiency, burner and boiler combustion chamber must be designed as optimal as possible. On the other hand differences in the use of fuels also affect the efficiency of combustion. It is known that liquid fuel and gas (LNG and HSD) produce higher combustion efficiency than solid fuels such as coal.
Calculating the combustion efficiency of the boiler is not difficult, we just need to reduce the total amount of heat energy released by thermal energy burning that passes out through the stack (chimney) divided by the total heat energy.
ηcombustion : boiler combustion efficiency (%)
Qin : The total heat of combustion energy (calories; Joule)
Qlosses : Heat energy passing out through the chimney (calories; Joule)
The only difficult thing in calculating the combustion efficiency is how to pursuit the optimal number. Combustion efficiency is characterized by the overall fuel burning in the combustion chamber. While the control parameters are used to ensure the overall fuel burning, is the amount of air combustion (air excess) coming out through the stack. The more the amount of air excess coming out through the chimney, then the more likely the amount of unburned fuel can pass through the chimney. But you should remember that the more the amount of excess water passing through the chimney, the amount of heat energy escaping the rest of airborne is also growing. Therefore there is an optimum number of excess amounts of air, so that the boiler combustion efficiency can obtain the most optimal number.
Boiler thermal efficiency shows how the performance in terms of its function as a heat exchanger. The efficiency calculation will show how effective the transfer of heat energy from the combustion process of fuel into the air. However, the efficiency calculation is not very accurate, because it does not account for the loss of heat radiation and convection that are not absorbed by water. In addition, the calculation of the thermal efficiency of the boiler cannot be used for economic analysis, because these calculation doesn’t take notice carefully the amount of fuel consumed. On this basis we will not discuss more about the calculation of the thermal efficiency of the boiler.