The two-stage gasifier is composed of a retort section and a gasification section from top to bottom. Coal first enters the furnace body from the top coal bunker through two sets of lower coal valves. The coal is fully dried and retorted at low temperature for a long time in the retort section, gradually forming semi-coke and entering the gasification section. The hot semi-coke fully reacts with the gasification agent blown from the bottom of the furnace in the gasification section. It passes through the reduction layer and oxidation layer in the furnace to form ash, which is automatically discharged from the ash basin driven by the grate.

During the low-temperature carbonization of coal, the gas generated mainly by the precipitation of volatile components is called carbonization gas. The top gas that makes up the two-stage furnace accounts for about 40% of the total gas. It has a high calorific value, a low temperature, and contains a large amount of tar. This kind of tar is a product of low-temperature carbonization and has good fluidity. It can be collected by electrostatic precipitator and used as chemical raw materials and fuel. In the gasification section, the hot semi-coke and vaporizing agent undergo a series of chemical reactions such as reduction and oxidation to generate gas, which is called gasification gas.

compositionTwo-stage gas generatorThe bottom gas, accounting for about 60% of the total gas volume, has a relatively low calorific value and a high temperature. Because the coal has sufficient time for low-temperature carbonization in the carbonization section, the coal entering the gasification section has become semi-coke, so the gasified gas generated has no tar, and because it is close to the grate ash layer, it contains a small amount of fly ash. The bottom gas can be processed by equipment such as cyclone dust collector and air cooler. In this way, users who use cold purified gas can use upper cold purified gas without using water washing method, thereby avoiding the disadvantage of being unable to process a large amount of phenolic water.

The two-stage gasifier has two outlets, upper and lower, which can output gas with different calorific values. Its gasification efficiency and comprehensive thermal efficiency are both higher than that of a single-stage furnace. The coal is completely retorted in the upper section of the furnace, and the lower section gas is basically free of tar. The upper section gas contains a small amount of light tar, which is not easy to block the pipeline. The calorific value is high and stable, the operation is flexible, the degree of automation is high, and the labor intensity is low. It does not pollute the environment, saves water significantly, occupies a small area, and has low long-term operating costs.