Coal is a fossil fuel derived from organic matter that has been converted by geological processes over millions of years into solid form. It is a black or dark brown combustible substance consisting of carbon and other compounds. Coal has been used for fuel since antiquity and is still the worlds most important energy source.
Coal quality is an important factor in determining its usability. Coal is classified based on its thermal stability, which is then further divided into grade classes. Thermal stability is a measure of how well the coal stands up to heat without producing gases or ash. It is used to gauge the potential for coal to be successfully used for a variety of purposes.
The most important coal quality indicator is its ranking according to the American Society for Testing and Materials (ASTM) standard, where coal is divided into grades A through G. Grades A and B are the highest quality, while grades C through G are progressively lower in quality. To meet the ASTM standard, coal must have a specific rank depending on its heating value and volatile matter content. The rank indicates the temperature at which certain volatiles, like water, are released.
The highest grade of coal, Grade A, is categorized as having high levels of fixed carbon, low moisture and ash content, and no volatile matter. It has a high heating value and is the most sought-after grade of coal as it is the cleanest burning. Grade A coal also has a high thermal stability due to the extremely low-sulfur content, making it ideal for metallurgical and steam applications.
Grade B coal is still a high quality coal, though it may contain more moisture, ash, and volatile matter than Grade A coal. It has good thermal stability and is suitable for a variety of applications, such as power plants and residential heating.
Grades C through F are considered medium grades of coal, with varying levels of moisture, ash, volatile matter, and heating value. These grades are suitable for electricity production, industrial applications and residential heating, as they have decent thermal stability.
The lowest grade of coal, Grade G, has the lowest fixed carbon content, highest levels of moisture andash, and highest levels of volatile matter. This low-grade coal typically has a low thermal stability, but it is still useful for some industrial applications.
In order to determine the thermal stability of coal, a variety of tests are performed. These tests measure the amount of volatile matter, moisture, ash and fixed carbon, as well as the heating value of the coal. These tests allow for an accurate assessment of the thermal stability of the coal and its suitability for different applications.
The thermal stability of coal is an important mineralogical property to consider when purchasing or mining for this fossil fuel. By understanding the coal grades and their thermal stability, coal producers and purchasers can make informed decisions about which type of coal will best suit their needs.
