Coal is a naturally-occurring combustible solid. Since its introduction about 4,000 years ago, coal has been used as a fuel for heating, cooking, and, in the modern age, for generating electricity. Coal is also an important source of raw materials for manufacturing. The destructive distillation (carbonization) of coal produces hydrocarbon gases and coal tar, from which chemists have synthesized drugs, dyes, plastics, solvents, and numerous other organic chemicals..
Recoverable coal reserves contain more than twice the energy-producing potential of the Middle East’s proven oil reserves. The United States holds the world’s largest coal reserves. The US coal reserves are comprising more than one quarter of the total proven coal reserves in the world. About 100 countries have recoverable reserves of coal; Canada, China, Russia, Poland, Australia, Great Britain, South Africa, Germany, India, Brazil, and Colombia have the largest reserves.
Coal began forming more than 200 million years ago during the Carboniferous Period, when decaying plant material sank into the ground and was transformed by high temperature and pressure into peat and then coal. The degree of such change is called coalification. According to the World Coal Association, coalification influences coal’s physical and chemical properties and is referred to as the ‘rank’ of the coal. The four ranks of coal, from the least to the most carbon content, are lignite, sub-bituminous, bituminous and anthracite. The quality of each coal deposit is determined by:
- Varying types of vegetation from which the coal originated
- Depths of burial
- Temperatures and pressures at those depths
- Length of time the coal has been forming in the deposit
Coal, similar to any other geological material, can contain trace elements such as antimony, arsenic, beryllium, cadmium, chromium, cobalt, copper, lead, manganese, molybdenum, nickel, vanadium, and zinc. Some of these trace elements are considered hazardous air pollutants. Coal ash retains these trace elements; following coal combustion, some trace elements become concentrated in certain particle streams, for example, bottom ash, fly ash, and flue gas particulate matter.
During the coal burning process, waste products are produced which are known as Coal Combustion Products (CCPs) or Coal Combustion Residuals (CCR). CCPs include fly ash, bottom ash, boiler slag, synthetic gypsum, and other power plant by-products. Ash can form fused deposits (slag) on surfaces exposed to high temperature. It can also bind to lower temperature surfaces (foul). Before starting boiler design, it is very important to analyze coal ash to evaluate its slagging and fouling potential. Ash composition and coal quality varies depending on the location and rank of coal.
Application of Portable XRF in Coal Mining
Portable X-ray Fluorescence (PXRF) instruments can analyze coal in a manner similar to any other geological sample. PFRX offers low limits of detection (LOD) of some elements, which makes it suitable for coal applications. For example, As, Pb, and possibly S in some coal seams can be quantified by PXRF. Hg and Se in coal are lower than their LOD by PXRF. PXRF applications in coal mining include the quantification of major elements and using this data to calculate ash content of coal.
PXRF is just one of many technologies enabling greater efficiencies in all types of mining operations. Check out these resources to learn about the latest mining industry solutions.