Classification of Brown Coal
Brown coal, also known as lignite, is a fossil fuel that has characteristics between those of coal and peat. It is amongst the lowest rank of coal due to its relatively low heat content. It is extracted from open-cut mines located close to surface. Brown coal is composed of plant debris that has undergone alteration due to diagenesis over millions of years.
Brown coal can be classified according to several different criteria. For example, the level of carbon content can be used to divide it into three major categories: high, medium and low. High-carbon brown coal consists of more than 50 per cent carbon, medium-carbon is comprised of between 35 and 50 per cent carbon, and low-carbon coal has less than 35 per cent carbon.
The level of moisture content in brown coal is another way to distinguish it. Brown coal can have low moisture content, where the mass of water molecules is below 10 per cent of its dry mass, medium-water content, where the mass of water molecules is between 10 and 20 per cent of its dry mass, or high-water content, where the mass of water molecules is 20 per cent or higher.
Brown coal can also be divided based on its degree of maturity. This can be determined by examining samples and determining the amount of liptinite, or organic plant occurrances, as well as the degree of maturation of the organic matter found in the coal. If the sample contains more than 70 per cent of liptinite, it is considered to be immature coal. However, if the liptinite content is lower than 70 per cent, then the coal is considered to be mature.
The degree of oxidation in brown coal can also be used to classify it. Oxidation occurs when the coal is exposed to air, converting the combustible hydrocarbon materials in the coal into air pollutants. If the coal has undergone limited oxidation, it can be classed as “brown coal in situ”. If there has been extensive oxidation, the coal is referred to as “oxidized brown coal”.
The final criterion for classifying brown coal is by its particle size. Brown coal can be divided into three major categories: lump, peat and “ultrafine” coal. Lump coal is the largest in size and has a particle size greater than 53mm. Peat is of medium size, with a particle size between 0.3 and 53mm. Ultrafine coal is the smallest size, measuring below 0.3mm.
In conclusion, brown coal can be divided into different categories based on several criteria, such as carbon content, water content, degree of maturity and oxidation, and particle size. Classifying brown coal according to these parameters can help to aid its extraction and utilization.
