The main functions and types of hot air furnace.

At present, there are a lot of cement production lines need to use high moisture raw materials, in this case, need to use a large number of external heat sources to dry the material, at this time, hot air furnace has become a most conventional choice. The hot flue gas from hot air furnace is generally used to dry ore, limestone, phosphate, gypsum, slag clay, raw coal and other materials.How to configure hot air furnace and design hot air furnace system to achieve the purpose of drying materials should be combined with China's national conditions and fuel resources, and fully understand the mechanical characteristics and process requirements of vertical mill at home and abroad.

According to the different fuels used, hot air furnaces can be divided into coal, oil (heavy oil, diesel), gas (natural gas, blast furnace gas) hot air furnaces.The hot air furnace used oil or gas is easy to completely burn and has high thermal efficiency. The equipment can be developed to miniaturization or large-scale. However, its application is limited because the fuel price is almost three to four times that of coal. Therefore, coal is the main fuel of hot blast stove in our country, but there are also a few enterprises use blast furnace gas as fuel for hot air furnace.

Coal-fired hot air furnace is mainly divided into boiling type, horizontal type and vertical type according to its structure. The early horizontal hot air furnace used raw coal as fuel, the furnace was equipped with a grate, and the coal and slag were added manually or mechanically.Because it is difficult to burn out lump coal and clean up coal slag, the thermal efficiency of hot air furnace is low and it is difficult to scale up. On this basis, some production enterprises have changed the horizontal hot air furnace to burn pulverized coal, although it saves manpower, but the combustion efficiency still needs to be improved, in addition, it is difficult to use industrial waste as an alternative fuel. At the same time, the coal-burning hot air furnace with horizontal structure is prone to coking in production, and the pulverized coal combustion is incomplete, which affects the stable operation of the drying system.

Boiling hot air furnace is the most widely used in China at present, the technology is relatively mature and reliable, low energy consumption, low investment cost, a wide range of coal varieties, simple operation, high thermal efficiency. However, boiling hot air furnace will inevitably emit sulfur-containing waste gas that is harmful to the environment, which is extremely incompatible with the requirements of China's industrial policy on environmental protection in recent years, especially in the surrounding areas near big cities and scenic spots, there are very strict limits on sulfur-containing waste gas emissions, and individual regions even adopt a "zero tolerance" policy for the "sulfur emission" index of new projects.

In order to improve the efficiency of coal burning and meet the demand of large-scale production, vertical hot air furnace with 100% coal burning has appeared. Its advantages are:

（1）（1）Can burn a variety of different calorific value and volatile (10% ~ 60%) of coal, can also burn a variety of alternative solid fuel (volatile 30% ~ 80%), such as waste wood chips, coke breeze, etc.

（2）Wide range of heating capacity (3MW ~ 60MW);

（3）（3）High degree of automation, generally equipped with burner monitoring system, fuel fineness control, fault safety system, etc.