1. Introduction
Coal is one of the world’s most important energy sources, as it is both plentiful and relatively inexpensive to mine. As such, it is essential to understand the chemical makeup of coal in order to use it more efficiently and effectively. One of the most important coal quality parameters is the yield of volatile matter, which in turn yields information about the coal’s heat value and other properties. The yield of volatile matter is usually measured in terms of the percentage of the total mass that vaporizes when the coal sample is heated in an oven for a specified time.
On the other hand, another important measure of coal’s quality is its ability to produce coke and one indicator of this is the yield of volatile material as well as its characteristic composition, including the quality number (CN). This is particularly important for coal used in the steel industry, as the coke serves as an essential fuel and reducing agent. The type and quality of coke are important structural components of the blast furnace and affects the productivity of the furnace as well as the quality of the steel produced.
The most important coal quality factor for the coking process is the amount of volatile matter and the quality number (CN). The volatile matter yield is used to indicate the coal’s heat value, and the quality number indicates how easy it is to reduce the coal to coke. In this article, we will discuss the classification of coal’s yield of volatile matter and its impacts on coke making, as well as the grades of coke produced.
2. Classification of Coal’s Volatile Matter Yield
The most common measure used to assess the quality of coal is the yield of volatile matter. This is determined by heating coal samples in an oven at a specified temperature and then measuring the mass of hydrocarbons (or volatile matter) vaporized. The results are usually reported as the percentage of the total weight of the sample that was vaporized.
Classification of coal based on this measure can be divided into three categories. The first category is the low volatile matter yield, which is usually specified to be less than 22%. This type of coal tends to have a lower heat value, which may lead to problems in coking production.
The second category is the medium volatile matter yield, is usually specified to be between 22-30%. This type of coal usually provides a more consistent heat value, as well as better coke making properties.
The third category is the high volatile matter yield, which is typically specified to be greater than 30%. This type of coal tends to provide a higher heat value, but also can be difficult to reduce to coke due to high reactivity.
3. Coke Making and the Quality of Coke Produced
Coking coal is a type of coal specifically used in the process of making coke. This process is generally carried out by heating coal in the absence of air, which produces a fuel called coke. The quality of the coal used in such processes is very important, as it affects the quality of coke produced. The yield of volatile matter and the quality number are used to measure the coking properties of coal.
Coal with a high volatile matter yield usually has poor coking properties because the high volatile content leads to formation of excess carbon dioxide, which reduces the coke’s quality. On the other hand, coal with a low volatile matter yield usually has excellent coking properties, leading to better coke production.
The coke produced from coking coal also has different grades depending on the amount of volatile matter and quality number. In general, coke with a low volatile matter yield is called ‘Foundry grade’, while coke with a medium or high volatile matter yield is called ‘Forge grade’.
4. Conclusion
In conclusion, coal’s volatile matter yield is an important measure of its quality. Coal with a low volatile matter yield tends to have a low heat value, while coal with a high volatile matter yield tends to have a higher heat value. The yield of volatile matter can also be used to classify the coal into categories, as well as assess its coking properties. Finally, the quality of the coke produced from coking coal is also affected by its volatile matter yield, with a low yield producing a higher grade of coke than a high yield.
