The composition of the coarse slag and fly ash in the furnace is not very different; why do they exist in two distinct forms?
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The composition of the coarse slag and fly ash in the furnace is not very different; why do they exist in two distinct forms?
Personally, I think ash and slag differ in terms of their morphology; the carbon content in fly ash is definitely higher than that in slag. In a gasification furnace, the temperature is set at the lowest level at which the ash and slag can still flow properly. Some of the materials melt to form a layer of slag that flows down along the walls of the furnace, and after being cooled by cold water, this results in coarse slag. Meanwhile, some coal particles, after burning, do not form slag but instead fall along with the airflow as fly ash.
In a fluidized bed, due to intense backmixing, fly ash is affected by the gasifying agent and the subsequent induced draft fan, and is entrained out owing to its low density. The large particles are discharged from below in the form of coarse slag! In a fluidized bed, when the coal powder vaporization agent enters from below and the raw gas exits from above, fly ash rises due mainly to gravity. When the coal powder vaporization agent enters from above and the gas exits from below, a quenching process is used; in my opinion, this is also mainly due to gravity, as the unslagged fly ash is carried away with the gas, while the slag goes into the quenching tank.
In gasification furnaces with a furnace temperature of 1600–1800, the slag is in a molten state; after being quenched by water in the slag pool, it takes on a granular form. The slag contains a high amount of minerals and low levels of residual carbon. The higher residual carbon content in the ash is mainly influenced by the furnace temperature; after a rapid reaction, the coal forms finer particles that are carried away by the syngas. . . . Of course, the mass of ash is less than that of slag. . . . Unique insights; please point out any mistakes. . . .
I would like to ask the original poster: since the composition of coarse slag and fly ash isn’t very different, which specific aspect are you referring to?