Classification of hot air furnaces: direct and indirect hot air furnaces

Classification of hot air furnaces: direct and indirect hot air furnaces
Hot blast stove is one of the very important technologies developed during the Industrial Revolution, as the hot air in the stove refers to the preheating of air blown into the blast furnace or other metallurgical processes, greatly reducing fuel consumption. Hot air also allows for higher furnace temperatures, thereby increasing furnace capacity.
Hot air furnaces can be mainly divided into direct and indirect hot air furnaces.
The direct hot air furnace utilizes fuel for direct combustion, and forms hot air through high purification treatment. It directly contacts the material for heating, drying, or baking. The fuel consumption of this method is about half that of using steam or other indirect heaters. Therefore, a direct hot air stove can be used without affecting the quality of the dried product. Fuel can be divided into: (1) solid fuels, such as coal and coke. (2) Liquid fuels, such as diesel, heavy oil (3) gaseous fuels, such as gas, natural gas, liquefied gas, etc. The high-temperature combustion gas obtained from the fuel combustion reaction further comes into contact with the external air, mixes to a certain temperature, directly enters the drying room or baking room, and comes into contact with the material to be dried. It is heated and evaporated to obtain dry products. In order to utilize the combustion reaction heat of these fuels, it is necessary to add a set of fuel combustion equipment. For example, coal-fired engines, fuel burners, gas burners, etc,
Indirect hot air furnaces are mainly suitable for drying materials that are not allowed to be contaminated, or for drying heat-sensitive materials with lower temperatures. For example: milk powder, pharmaceuticals, synthetic resins, fine chemicals, etc. This heating device uses steam, heat transfer oil, smoke, etc. as carriers to heat the air through various forms of heat exchangers. The most fundamental problem of indirect hot blast furnaces is heat exchange. The larger the heat exchange area, the higher the heat conversion rate, the better the energy-saving effect of the hot air stove, and the longer the lifespan of the furnace body and heat exchanger. On the contrary, the size of the heat exchange area can also be identified from the flue gas temperature. The lower the flue gas temperature of the hot air stove, the higher the heat conversion rate, and the larger the heat exchange area.