Theenergy value ofcoal, orfuel content, is the amount ofpotential energy coal contains that can be converted intoheat.[1] This value can be calculated and compared with differentgrades of coal and other combustible materials, which produce different amounts of heat according to their grade.
Whilechemistry provides ways of calculating theheating value of a certain amount of a substance, there is a difference between thistheoretical value and its application to real coal. The grade of a sample of coal does not precisely define itschemical composition, so calculating the coal's actual usefulness as a fuel requires determining its proximate and ultimate analysis (see "Chemical Composition" below).
Chemical composition of the coal is defined in terms of its proximate and ultimate (elemental) analyses. The parameters of proximate analysis aremoisture,volatile matter, ash, and fixed carbon. Elemental or ultimate analysis encompasses the quantitative determination ofcarbon,hydrogen,nitrogen,sulfur andoxygen within the coal. Additionally, specific physical and mechanical properties of coal and particularcarbonization properties
Thecalorific valueQ of coal [kJ/kg] is the heat liberated by its completecombustion with oxygen.Q is a complex function of the elemental composition of the coal[citation needed].Q can be determinedexperimentally using calorimeters.Dulong suggests the following approximate formula forQ when the oxygen content is less than 10%:
whereC is the mass percent of carbon,H is the mass percent of hydrogen,O is the mass percent of oxygen, andS is the mass percent of sulfur in the coal. With these constants,Q is given in kilojoules per kilogram.
| Coal types by grade (lowest to highest) |  | |
|---|---|---|
| Coal combustion | ||
| Coal mining |
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Notes: [1] Peat is considered a precursor to coal. [2] Graphite is only technically considered a coal type. | ||