Problems related to the slagging properties of raw coal

Adhesiveness has a significant impact on gasifiers with solid slag discharge, especially fixed-bed gasifiers. Coal with high cohesion tends to cause a range of problems in fixed-bed gasifiers, such as slag accumulation and poor slag discharge. However, for gasifiers with liquid slag discharge, adhesiveness is not a problem and has minimal impact.

Slagging tendency refers to whether the ash and slag generated during the gasification and combustion of coal will form lumps, and the degree of such lumping. The slagging tendency of coal ash is measured by its slagging rate. Under certain blowing conditions, when coal is burned to completion, the mass percentage of slag with a size greater than 6 mm in its ash represents the slagging rate of that coal under those blowing conditions. Using coal that tends to form slag can easily affect the proper operation of the gasification furnace. Slagging tendency is related to the ash melting point (ash composition) and viscosity of the coal. If the composition is similar, higher ash content leads to slag formation more easily than lower ash content. The caking tendency of coal also partially determines the slag discharge method in the gasifier.

For the four-nozzle fluidized bed, the slagging property is good; the coal slag particles are large, making it easier for them to settle under the influence of gravity in the quenching chamber. Driven by the circulating water in the lock hopper, these particles enter the lock hopper, resulting in effective slag removal； At the same time, the amount of slag is large, and less fly ash is carried in the syngas, which reduces the load on the slag treatment system. It also prevents blockages in the black water pipes and valves, as well as reducing wear on those pipes and valves. Isn’t that better for the system? From what perspective are you thinking about this? Please explain I have considered one aspect on my own; are you considering the utilization rate of coal and the gasification efficiency? The combustion inside the furnace must have completely consumed the oxygen. The large amount of slag wraps around the coal used in the reaction, resulting in a reduction in the specific surface area of the coal involved in the gasification reaction; does this lead to low effective utilization rates of the coal and low gasification efficiency?

The moderator of pyp222 explained the definition of slagging; generally, this is not done in the coal quality analysis for fluidized bed gasification, but it is used in fixed-bed systems and boilers.