Ash Content

Coal is different from other commodities in how varied its uses are and how non-homogenous coal seams can be. For example, gold analyses are done to determine the grade (g/t) - how many grams of gold per tonne of rock you can extract. For coal, the analyses done are so much more and goes back to the seam's original depositional environment.

Coal is classified according to rank. An increase in rank means that the coal was subjected to greater amounts of metamorphism and burial which caused an increase in the organic carbon content of the coal. In other words, the longer and the deeper the plant material was buried under sediments, the more water and gas was pressured out so that mostly carbon remained. Coal rank increases from peat, lignite, subbituminous, bituminous to anthracite. Coal in the different classes or ranks differ in their chemical and physical properties. Also, the different coal types are used in different industries such as coal gasification to create fuels, combustion for energy generation or in the metallurgical industry as coking coal.

One company's plan to promote clean coal - singing coal! :-)

The typical and basic analyses done on coal is proximate analyses. The coal is crushed in a laboratory to get a representative sample and then the various tests are done. The proximate analysis consists of ash content, volatile matter content, inherent moisture and fixed carbon content. These are all given as percentages and add up to 100%.

Ash content is what remains after all the carbon matter has combusted - the inorganic leftovers. The volatile matter are the gasses released during combustion. Inherent moisture is the water within the coal particles and the fixed carbon is the actual carbon content within the coal.

The ash and volatile matter content give a very good indication of the coal quality. For specific purposes, the ash and volatile matter will be required to fall within a specific range. Consistency in the coal is important for efficient plant operations. Ash content and volatile matter will also show you if anything has affected the coal after deposition. For example, if any igneous intrusions have gone through or nearby the coal seam, the heat from the molten rock would have burnt the coal and so removed most of it's volatile matter. This will be evident in a lower volatile matter content and higher ash content.

Coal analyses form an integral part in understanding a coal seam and ensuring it's used for the most efficient purpose. People say working in gold and platinum is difficult due to the many faults and very deep shafts - I say try building a good forecasting model for a coal deposit based on endless tables of analyses! :-)