The ash fusion point of coal gasified from water-coal slurry!

It should be just right and appropriate! Around 1250–1300℃ I guess! Too high a temperature affects the operating temperature of the gasification furnace and can cause wear on the refractory bricks; too low a temperature makes it difficult to control the temperature of the gasification furnace, which is detrimental to the reaction process!

This mainly depends on the slag discharge method of the gasification furnace. If liquid slag discharge is used, the operating temperature must be higher than the ash fusion point of the coal; consequently, the higher the ash fusion point of the coal, the higher the operating temperature required for gasification, which is considered unfavorable. When the ash fusion point of the coal exceeds 1500°C, a solvent needs to be added. In the case of dry slag discharge, the melting point of the ash has little impact.

To ensure an appropriate slag discharge temperature and a sufficiently low furnace temperature, it is desirable for the ash to have a low melting point. However, during gasification or combustion, coal with low ash fusibility tends to form slag easily, which can disrupt the normal progress of the gasification process or make it difficult to clean the boiler. The ash fusion point alone is not a sufficient parameter to determine the quality of coal; it is usually considered in conjunction with coal ash viscosity or other factors. Correspondingly, there is the [Slagging Rate (Clin) GB/T 1572—2001]. It is best to select the operating temperature based on the flat section of the ash’s viscosity-temperature characteristic curve, as this provides sufficient operational flexibility and ensures stable operation. In my opinion, the coking in the radiation section of the gasifier at Ningmei Methanol is also related to this factor

There is no such thing as high or low; only what is suitable matters. For the 6.50 MPa Texaco technology, around 1250 is the best value, as reported in official sources; in actual production, however, the value is around 1300.

The poster is absolutely right; the ash fusion point is just one parameter that cannot be used to determine the quality of coal. Moreover, in the case of coal slurry gasification, which involves liquid slag discharge, the ash fusion point should not be too high – it is generally required to be below 1300. For coals with a high ash fusion point, fluxes need to be added. If the ash fusion point is too low, it can also cause problems. The responses from the other members above were excellent. To ensure smooth operation and reduce wear on the refractory bricks, the operating temperature should not be too high, as this can also affect the efficiency of gasification.

For liquid slag discharge, it’s better if the ash has a low melting point; generally speaking

The poster is referring to coal water slurry gasification furnaces. The most common types of such furnaces in China are GE’s Texaco gasification furnace and East China University of Science and Technology’s OBM coal water slurry gasification furnace. The operating temperature of these furnaces is limited by the refractory bricks; it generally does not exceed 1400 degrees. Therefore, to ensure liquid slag discharge, the melting point of the ash must be below 1350 degrees, leaving a margin of 50 degrees. It’s different in the case of pulverized coal gasification; Shell can use operating temperatures of up to 1500, or even higher. The water wall structure used requires a lower operating temperature and is suitable for coal types with a high ash fusion point. The future development will definitely be water-cooled wall-type pulverized coal gasification – that’s the trend!

For gasifiers that use liquid slag discharge, two factors are particularly important: one is the ash melting point of the coal, and the other is the viscosity-temperature behavior of the coal ash.

Our company uses Shell gasification technology, with a requirement that the ash fusion point be less than 1380

If the ash melting point is used as a criterion to define the application of gasification technology, Texaco ensures that the ash melting point is below 1350 degrees, while SHELL requires it to be no higher than 1600 degrees. However, these two temperatures are approximate values provided by the patent holders; the actual values depend on the operating conditions of each company, as well as the wear and tear of the refractory bricks or materials used, the ease with which slag can be removed, and whether the slag particles might have an impact on downstream processes. Furthermore, although SHELL claims to be capable of operating at high ash melting points, when the temperature exceeds 1500, it is recommended to use coal as a fuel to ensure the proper operation of the gasifier.

First, the slag discharge method for the gasification furnace must be determined, followed by the viscosity range of the ash, and then the corresponding temperature range.