Discuss the impact of moisture content in coal quality on gasification?

This post was last edited by lflsedin on 2015-9-6 21:29. Regarding the impact of moisture in coal on gasification, first of all, coal moisture can be divided into external water, which is the water that adheres to the surface of the coal during extraction, transportation, and washing processes, and internal water, which includes liquid water and crystalline water. Liquid water is the water that enters the pores of the coal during its formation process, while crystalline water is associated with water-containing minerals formed alongside minerals. The factor that has the greatest impact on coal is internal water, namely liquid water. In the coal slurry preparation process, the grinding is not sufficient to allow water to flow out of the pores; the higher the water content in these pores, the greater the surface tension of the coal particles. This results in a high concentration of water, leading to a low actual concentration of coal and a high water content. As a consequence, less carbon content reaches the gasification furnace, which increases the oxygen consumption required for gasification.

As for how the moisture in coal affects gasification, the effects of internal and external moisture are different; internal moisture primarily influences the slurry-forming properties of coal, with higher levels of internal moisture resulting in poorer slurry-forming capabilities. The external water directly affects the concentration of the coal slurry. In other words, water affects the coal slurry, and the coal slurry in turn affects the gasification reaction.

The impact of moisture content in coal quality on gasification during the drying stage

Drying stage? Are you referring to the pre-drying of coal before gasification for powder production?

Primarily the impact on coal slurry, and thus the impact on the furnace

The moisture in coal exists in three forms: external moisture, internal moisture, and crystalline water. External moisture and internal moisture belong to free water, which is the water bound to coal through physical adsorption or sorption. External moisture is present on the surface of coal particles, in the gaps between them, as well as in the non-capillary voids, while internal moisture is found within the capillaries of the coal. Crystal water is water that is bonded to the minerals in coal through chemical bonds, and it is part of the mineral crystal lattice. The moisture content in coal is related to its degree of metamorphism, showing a regular pattern as the degree of metamorphism increases. Coal with a high moisture content has certain impacts on its transportation, storage, drying, and subsequent use in gasification processes. High moisture content will inevitably increase your transportation costs, which account for the largest portion of the expenses ； There are also certain difficulties in storage; coal with high moisture content has a younger coal quality. It has a high volatile content, and is prone to volatilization during storage; poor ventilation can pose a danger ； The moisture content at the outlet of the coal grinding and drying process is kept under control. If coal with high moisture content enters the coal grinder, drying will require a large amount of circulating air, which results in significant waste of thermal energy ； In terms of vaporization at later stages, it generally affects coal consumption; and affecting coal consumption means affecting costs, that is, money.

High coal moisture content means that it is difficult to control the concentration of the coal slurry prepared, and this concentration tends to be on the low side in gasification furnaces using coal slurry. The impact is greater on pulverized coal gasification, with the main effect occurring in the transportation of pulverized coal. Generally, to be used in pulverized coal gasification, the pulverized coal must be dried to a moisture content of less than 2%

It also varies depending on the gasification method; in the case of pressurized gasification of pulverized coal, the moisture content of the coal only affects the temperature of the gas at the outlet.