How to increase the ash melting point of coal

This post was last edited by hjh7169 on 2016-4-19 09:49. Why is it necessary to increase the ash fusion temperature? Isn’t a low ash fusion temperature better? It’s possible to use coal with a higher ash fusion temperature in combination with it. Moreover, why must the ash fusion temperature be increased? Can’t we just lower the furnace temperature instead?

The coal we use on site has a low ash fusion point; several chain boilers that use this coal suffer from slagging problems. Purchasing coal from external sources increases costs and adds complexity, so I was wondering if there are any viable methods to increase the ash fusion point of this coal.

Try to mix in some coal with a high ash fusion point.

The problem of slag adhesion can be resolved by lowering the furnace temperature; then why raise the ash melting point?

If the coal layer is thin, increase the grate speed; if that doesn’t work, reduce the calorific value of the coal and mix in some coal ash or soil, stones, or something similar

Check if there is bauxite in the vicinity. Bauxite is used to produce alumina. Its tailings (which are extremely cheap) are rich in alumina with a high melting point; when mixed into bauxite tailings in appropriate proportions, it can significantly increase the melting point of the coal fed into the furnace. Of course, experimental research is needed to determine the mixing ratio.

Ash melting point of coal: It refers to the ash remaining after coal combustion; it is the temperature at which this ash begins to soften and deform under high temperatures, and it is expressed as a temperature range. It has a lot to do with the atmosphere; with different atmospheres, the temperature differences are significant. Especially when the iron oxide content in the ash is high. Ash fusion point, also known as coal ash fusibility, is an important indicator for coal used in power generation and gasification. Coal ash is a mixture of various minerals; it does not have a fixed melting point, but rather a range of melting temperatures. Due to the different mineral components of coal, its ash fusion point is lower than that of any single component within it. At certain temperatures, these components also form an eutectic. In its molten state, this eutectic has the ability to dissolve other high-melting-point substances present in the coal ash, thereby altering the composition of the melt as well as its melting temperature. The method commonly used for determining the melting point of ashes is the pyramidal method; refer to GB219-74 for details. Coal ash is mixed with dextrin and molded into pyramidal shapes, which are then heated in a high-temperature furnace. Four characteristic temperatures are determined based on the changes in the shape of these ash pyramids: ① Deformation temperature, denoted as DT, formerly known as T1 ； ②Softening temperature, symbol: ST, formerly known as T2 ； ③Hemispheric temperature, symbol HT ； ④Flow temperature, symbol: FT, formerly known as T3. Among the four indicators of ash fusion behavior, the most commonly used is the softening temperature, namely ST(T2). ST is generally used to evaluate the fusibility of coal ash. Real-world example: A coal-based methanol plant where the coal has a high fixed carbon content and a low ash melting point, leading to easy slag formation. Solution: Since the factory is located in a desert, sand and coal from the area around the factory were mixed together and used in combustion to increase the ash fusion point of the coal, thereby resolving the problem of slag formation in the factory. This method has been in practical use for 5 years; for coal used in the gasifiers for coal-to-methanol production, please refer to the specifications for boiler coal.

The two heat transfer oil furnaces in this unit use coal ash, which has a low melting point of just over ST 900°C