Methods to improve the thermal efficiency of heating furnaces

Thread Content

Reducing the flue gas temperature: Theoretically, the flue gas temperature can be reduced to near the ambient temperature, but there are limitations to the actual reduction in flue gas temperature. Economically, this is restricted by the initial investment required, while technically it is limited by the dew point of the flue gases. Taking both factors into account, the flue gas temperature is generally designed to be no less than 150°C. 2. Reduce the excess air coefficient to minimize smoke loss. Heating furnaces generate heat through the combustion of fuel; in industrial furnaces, it is not possible for the fuel to burn completely with the theoretical amount of air – complete combustion can only occur when there is a certain amount of excess air present. The ratio of the actual amount of air used for combustion to the theoretical amount of air is called the excess air coefficient. The excess air coefficient for heating furnaces in typical refineries ranges from 1.05 to 1.25; if fuel gas is used, it can be kept lower, at a range of 1.05 to 1.15. If the excess air coefficient is too high, a large amount of excess air will carry away heat during exhaust, increasing exhaust losses and reducing thermal efficiency. It can be seen that, to improve furnace efficiency, the excess air coefficient should be reduced within the allowable range. 3 Reducing incomplete combustion losses: Among the exhaust loss, in addition to the physical heat losses mentioned earlier, there are also chemical heat losses caused by incomplete combustion. Incomplete combustion not only reduces thermal efficiency but also causes air pollution; therefore, incomplete combustion should be minimized to reduce carbon monoxide emissions. As can be seen from the above analysis, to improve the efficiency of the furnace under normal operation, it is essential to control the levels of oxygen and carbon monoxide; as long as these two parameters remain within the appropriate ranges, the efficiency of the heating furnace can be increased.