The heat is lost through the furnace wall, depending on the composition of the refractory wall material and its thickness. However, there needs to be an economic consideration between the optimum thickness of insulation and heat loss. The heat loss is greater in small furnaces, the ratio between the shell wall to the volume of the radiation portion decreases with an increase. On the other hand, if you’re looking for info about a gas furnace that can be used at home instead of at a factory, we recommend you to visit furnacebuzz.com and find out more about residential gas furnaces.
The size of the heat loss depends on the hot air released through the stack. The flue gas flow rate increases with increasing excess air, therefore, furnaces should be operated with adequate excess air. Excess air that is too small will cause fuel losses due to a number of unburnt fuel. Losses of this fuel might be greater than the efficiency obtained because it reduces excess air. Because it needs to be pursued to produce perfect combustion without any unburnt fuel.
Flue gas temperature is a major factor causing heat loss. For this reason, efforts should be made to cool the temperature of the flue gas, by recovering the residual heat through a heat transfer process. To cool the flue gas, the cold fluid must be contacted (heated). With this process, flue gas temperatures that are too high can be lowered, which is often referred to as heat efficiency.
Some ways to do heat efficiency:
1. Steam production: steam production does not reduce fuel consumption, it will actually be profitable, if steam can be utilized
2. Recycle flue gas heat for preheating combustion air: when flue gas exits the convection section it can be cooled through a heat transfer device, where the air used for combustion is passed inside. This process requires an air blower. One of the problems with cooling flue gases is corrosion caused by sulfuric acid condensation. This depends on how much sulfur is contained in the fuel.