Correctly understanding boiler efficiency

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Correctly understanding boiler efficiency and combustion efficiency: Combustion efficiency reflects the burner’s ability to burn fuel. Combustion efficiency is usually measured by the amount of unburned fuel and excess air in the flue gases. The lower the amount of unburned fuel and excess air in the flue gas, the higher the combustion efficiency of the boiler. Well-designed gas and fuel burners enable complete combustion of the fuel, with the excess air ratio also being able to be kept within 15%. By reducing the excess air ratio, less heat is used by the burner to heat the air, thereby increasing the thermal energy available to heat the load. The combustion efficiency of a boiler is closely related to the fuel used; generally, when the fuel is gas or oil, the boiler’s combustion efficiency is higher than when the fuel is solid. Thermal efficiency: Thermal efficiency is an indicator used to measure the heat exchange efficiency of a boiler. It reflects the heat exchange capacity of the boiler to transfer thermal energy from the combustion system to the water or steam inside the boiler. It does not take into account the heat loss from the boiler shell, flue, etc.; therefore, the boiler’s thermal efficiency cannot truly reflect its fuel utilization efficiency, nor is it suitable for conducting economic evaluations of the boiler. Boiler efficiency: This parameter is often used as a substitute for boiler thermal efficiency and fuel-steam efficiency. When using the term “boiler efficiency,” it is necessary to clarify what exactly it refers to Because if it refers to thermal efficiency, it does not take into account the heat loss from the boiler, and thus it does not represent the actual efficiency of the boiler. If it refers to fuel-steam efficiency, then it takes into account the heat loss from the boiler, thereby reflecting the boiler’s true overall efficiency. Fuel-steam efficiency: This indicator is used to represent the overall efficiency of a boiler, taking into account its heat transfer efficiency as well as various heat losses. “\"Fuel-steam efficiency\" is an indicator for measuring the actual efficiency of a boiler, and it is very suitable for economic evaluations. We can determine the fuel-steam efficiency using two methods: the input-output method and the heat loss method. Input-output method: It is based on the ratio of the boiler’s output to its input, that is, the boiler’s output (in kilojoules) divided by the boiler’s input (in kilojoules), followed by multiplication by 100%. Heat loss method: Based on the total heat loss of the boiler. The heat losses of a boiler include the heat carried away by dry flue gas and water vapor, heat loss due to radiation, and convective heat loss (heat carried away by air), among others. 100% minus the total heat loss rate of the boiler is the fuel-to-steam efficiency. (This article was first published on the WeChat official account “Fured Steam Energy Saving”. ）