The gas produced in the gasification process will carry fine particles with different ash ratios out of the furnace after combustion, and the inclusions are called fly ash. Fly ash contains unreacted carbon, which will bring losses to the energy conversion of raw coal. The greater the content of small particles in raw materials, the greater the air velocity and the more things brought out. Therefore, the lower the mechanical strength of raw materials, the worse the thermal stability, and the more small particles and powders produced in the process of fixed bed gasification, the greater the loss. However, fluidized bed and entrained flow bed also limit the minimum fineness of coal entering the furnace. The carbon content of fly ash is expressed as the percentage of carbon in fly ash. The less fly ash, the lower carbon content and the higher gasification efficiency. [2]

Carbon content of ash

Unreacted raw materials are wrapped by molten ash and cannot contact with gasification agent, so they are discharged out of the furnace together with ash and carbon. The carbon content of ash is related to the ash content of raw coal, the properties of ash, operating conditions and gasifier structure. The carbon content of ash is expressed by the percentage of carbon in ash. Generally, the carbon content of ash discharged from fixed bed and fluidized bed gasifier is required to be lower than 10%. The carbon content of ash in dry feed entrained flow bed is generally below 10%, and that of coal water slurry feed is generally between 5%- 10%. Generally, the carbon content in ash discharged from pressurized gasifier is about 5%; Atmospheric gasifier is about15%; The carbon content of slag in liquid slag gasifier is below 2%. [2]