1. The part of the lower cross-section of the gasifier hopper with smaller dimensions is called“throat”，“throat”The size determines the gas production capacity and quality of the gasifier.

2To ensure sufficient mixing of materials and air“throat”Arrange multiple air nozzles. Usually there is an external spray(Air is sprayed from the outer wall of the throat towards the center)Internal spraying(Air is sprayed outward from the central supply pipe at the throat)There are two forms of arrangement, with the first form being more commonly used.

3. The outer wall of the gasifier hopper is welded with fins to increase the heat exchange area between the produced gas and the hopper, reduce the temperature of the produced gas, and improve the thermal efficiency of the gasifier.

4The gasifier has a flame temperature stabilization effect, which means that when the reaction temperature is too high, the reduction reaction, which absorbs heat, is relatively intensified, thereby reducing the gas temperature; When the reaction temperature is low, the reduction reaction slows down relatively, and the exothermic oxidation reaction dominates, which in turn increases the gas temperature. The flame temperature remains stable at800~1200℃In this way, the gas components produced are relatively stable.

5. Due to“throat”The existence of this makes the gasification capacity of a down draft gasifier lower than that of other structural forms of gasifiers with the same external dimensions, especially an up draft gasifier.

Air is blown into the side wall air nozzle of the gasifier, and the flow direction of the produced gas is consistent with the direction of material falling. Therefore, a down draft gasifier is also known as a co current gasifier. The air blown in mixes with the material and burns, and this area is called the oxidation zone, with a temperature of about900~1200℃The heat generated is used to support the cracking reaction in the pyrolysis zone and the reduction reaction in the reduction zone; The upper part of the oxidation zone is the pyrolysis zone, with a temperature of about 300-700 ℃In this region, the volatile matter in biomass（Cracking gas, tar, and moistureSeparated; The upper part of the pyrolysis zone is the drying zone, where the material is preheated; The lower part of the oxidation zone is the reduction zone, and the CO produced in the oxidation zone₂Charcoal and water vapor undergo reduction reactions in this area, while residual tar undergoes cracking reactions in this area, producingCOAnd H₂The temperature in this area is approximately700~900℃The gas rich in tar from the pyrolysis zone must pass through a high-temperature oxidation zone and a reduction zone dominated by hot coke, where the tar is cracked at high temperatures, resulting in a significant reduction of tar in the produced gas.