Since its introduction around 4,000 years ago, coal – a naturally occurring combustible solid – has been utilized as a fuel source for heating and cooking and, in more recent times, for the generation of electricity. Additionally, coal is an essential raw material in a range of manufacturing applications.
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Destructive distillation or carbonization of coal results in the production of hydrocarbon gases and coal tar. These are then used in a range of applications from dyes, plastics, and solvents to synthesized drugs and organic chemicals.
Recoverable coal reserves contain over twice the potential for energy production as the Middle East’s proven oil reserves. The USA holds the biggest coal reserves in the world, making up over a quarter of the world’s total proven coal reserves.
Around 100 countries have recoverable coal reserves including China, Russia, Canada, Australia, Poland, the United Kingdom, India, Germany, Colombia, and Brazil.
Coalification
Coal began to form over 200 million years ago during the Carboniferous Period. Decaying plant material sank into the ground before being transformed by high pressure and temperature into peat and later into coal. This change is known as coalification.
The World Coal Association states that coalification influences coal’s physical and chemical properties combined with the rate of this influence which are referred to as the coal’s rank. Four ranks of coal exist, dictating coal with the smallest to largest amount of carbon content. These are: lignite, subbituminous, bituminous and anthracite.
The quality of a coal deposit is further determined by:
- The types of vegetation from which the coal originated
- How long the coal has been forming in the deposit
- The depths the coal is buried at
- Pressures and temperatures at those depths
Trace Elements
Like any other geological material, coal often contains trace elements like cadmium, chromium, nickel, beryllium, molybdenum, zinc, copper, antimony, lead, cobalt, manganese, vanadium, and arsenic.
Some of these trace elements are air pollutants or otherwise considered to be hazardous. Coal ash also retains these trace elements and following the combustion of coal, some elements become concentrated within specific streams like fly ash, bottom ash and flue gas particulate matter.
Ash Properties
As coal is burned, waste products are produced. These are known as Coal Combustion Products (CCPs) or Coal Combustion Residuals (CCR). These CCPs/CCRs can include bottom ash, fly ash, synthetic gypsum, boiler slag and other by-products common in power plants.
This ash can form fused deposits (slag) on surfaces that are exposed to high temperatures, as well as binding to lower temperature surfaces (foul).
When designing a boiler, it is essential that coal ash is analyzed to ascertain its fouling and slagging potential. The composition of ash and the quality of coal very much depends on the location and rank of the coal in question.
Application of Portable XRF in Coal Mining
Portable X-Ray Fluorescence (PXRF) instruments can analyze coal in the same way they would analyze any other geological sample. PFRX allows for low limits of detection (LOD) of certain elements, making it especially suitable for coal applications.
For example, As, Pb and possibly S in coal seams could be quantified using PXRF. Hg and Se in coal are lower than their LOD by PXRF.
PXRF applications within the coal mining industry include quantifying major elements and then using this data to calculate coal’s ash content.
PXRF is however, just one of many technologies that allow for increased efficiency within all forms of mining operations.
This information has been sourced, reviewed and adapted from materials provided by Thermo Fisher Scientific.
For more information on this source, please visit Thermo Scientific Portable Analyzers for Material ID.