The analysis of coal is an important aspect that is necessary for its various uses in power plants, energy production, and its utilization for industrial purposes. The qualities of a particular coal sample are determined by measuring physical, chemical and combustion properties. A few of these properties are intrinsic, while some depend upon the composition of the coal sample. An important part of the analysis of coal is the physical properties of the coal, including its size, density, hardness, and its color. The color of the coal is an indication of its grade and can be used to determine its use in different applications.
One of the commonly used methods of determining the grade of coal is the use of the benzene extractable (benzene extractable wax or brown coal wax) value. This method determines the amount of waxes that can be extracted from the coal using benzene. The benzene extractable wax is used to grade the coal quality by giving a measure of the softening and heat-evolution properties of the coal.
The determination of the grade of coal can be done in two ways, either by measuring the amount of benzene extractable wax that can be extracted from a sample or by measuring the softening and heat-evolution properties of the sample. In order to determine the benzene extractable wax, the coal is heated to 60°C in a beaker that has been filled with 500mL of benzene. The temperature is maintained for 3 hours. After that, the extracted wax is weighed and expressed in milligrams per sample.
The softening and heat-evolution properties of the coal are also measured in order to determine the grade. For this, a shaker jar apparatus is used. In this, the sample is heated to 40°C in a boiling tube, filled with a known amount of boiling water and the temperature is maintained for 30 minutes. After that, the sample is quickly substituted, taken out and the remaining water in the jar is measured. On the basis of this, the softening property of the coal is expressed in celsius degree.
The results of the analysis of the benzene extractable wax, as well as the softening and heat-evolution properties, are combined to obtain an overall rating for the coal sample. This rating is expressed as a benzene extractable wax grade. This grade is used to determine the grade of the coal, which degrees from low (poor quality) to high (good quality).
The benzene extractable wax grade of coal is an important property that helps in determining the type of coal that is suitable for different applications. For example, low grades of coal have lower calorific value and are not suitable for burning in power plants, while higher grades of coal are better for burning and are a better source of heating and electricity generation.
Overall, the importance of the analysis of the grade of coal through the determination of the benzene extractable wax value cannot be overemphasized. It is an important tool that helps in determining the suitability of coal for various applications.
