Coal with low ash melting point is likely to cause coking or dust accumulation in waste pots?

The lower melting point of ash means it can be lower than the furnace temperature. However, since the slag is discharged in liquid form, it should not easily cause coking or ash accumulation. However, it may be possible if the ash content is high.

The low melting point of ash is not the direct cause of coking. As long as the temperature is properly controlled, there will be no problem.

Let's see if it's appropriate for me to understand it this way.: The coal ash with a low melting point is in a molten state when the temperature is relatively high and has not yet reached the waste pot. When it reaches the waste pot, the temperature is lower than the temperature in the previous air duct. At this time, the solidification conditions are reached, so it solidifies on the wall of the heat exchange tube of the waste pot... The above explanation is a bit far-fetched, please criticize and correct me!

The melting point of coal-based ash used in the shell waste pot process is preferably around 1350°C. If the ash melting point is too low, it will be difficult to hang slag and the effect of "slag-resistant slag" will not be achieved, thereby damaging the membrane water wall. If the ash melting point is too high, it will be difficult for the ash to form molten liquid slag, so flux is added to improve it to ensure process indicators. The problem of ash formation in waste pots should be determined by the working conditions of the quenching section and the quality of the coal.: 1) It is appropriate for the K+Na content in general coal quality to be less than 5%, otherwise the low melting point K+Na will solidify under the decreasing temperature conditions of the waste pot to form gray scale. ； 2) Excessively high chilling temperature will also cause a large amount of fly ash to enter the waste pot without returning to the gasifier and cause scaling.

The "ash melting point is too low" and the "coal gasification" you are talking about are not specific. How low is it? What gasifier? For shell coal-fired gasifiers, there is a limited range for the ash melting point of coal. The ash melting point of the pulverized coal entering the furnace is generally required to be controlled at about 1350 degrees. The gasifier temperature should be operated at 150-200 degrees higher than the ash melting point to ensure a certain thickness of slag on the membrane wall of the gasifier and good fluidity of the slag toward the fire surface to protect the equipment. If the melting point of coal ash entering the furnace is too low (below 1250 degrees? ), if the gasifier still maintains the original operating temperature, the membrane wall slag layer will become thinner and the amount of by-product steam will increase. It is necessary to lower the gasifier temperature and deviate from the optimal control range of the shell gasifier, which will cause the carbon conversion rate to drop significantly and the CO2 content in the syngas to drop significantly. If the CO2 control method is used, it will require increasing O/C and raising the temperature of the gasification furnace, causing large fluctuations in furnace temperature and making it difficult to stabilize. For ash with a steep viscosity-temperature characteristic curve, when the temperature changes too fast, the fluidity of the slag changes, which ultimately makes it difficult to stabilize the membrane wall slag layer of the gasification furnace, causing the equipment to lose protection. Secondly, when the amount of quenching gas remains unchanged, due to the decrease in ash melting point, at the same temperature, the amount of solidified slag returned to the gasifier decreases, and the amount of fly ash brought into the waste pot system increases, and the relative degree of ash accumulation will increase. Third, when the temperature of the gasifier is too low and the density of the slag water increases, the slag water system will be overloaded and suffer serious consequences. Therefore, when there is a positive correlation between ash content and ash melting point, shell requires that fly ash circulation should be used when the coal ash content is too low. No matter which type of gasifier, from the perspective of stable and economic operation, there are selective requirements for coal type and coal quality. Not all coals are easy to use! Sinopec is already trying to standardize coal usage guidelines for shell gasifiers. In fact, there are currently many types of gasifiers, all of which have their own coal-use ranges. If some scientific research units can calm down and develop coal-use guidance standards for different gasifiers, wouldn't it be a great contribution to the coal chemical industry?