The energy value of

coal Coal is a combustible black or brownish-black sedimentary rock, formed as rock strata called coal seams. Coal is mostly carbon with variable amounts of other elements, chiefly hydrogen, sulfur, oxygen, and nitrogen. Coal is formed when ...

, or fuel content, is the amount of

potential energy In physics, potential energy is the energy held by an object because of its position relative to other objects, stresses within itself, its electric charge, or other factors. Common types of potential energy include the gravitational potenti ...

coal contains that can be converted into

heat In thermodynamics, heat is defined as the form of energy crossing the boundary of a thermodynamic system by virtue of a temperature difference across the boundary. A thermodynamic system does not ''contain'' heat. Nevertheless, the term is ...

. This value can be calculated and compared with different

grade Grade most commonly refers to: * Grade (education), a measurement of a student's performance * Grade, the number of the year a student has reached in a given educational stage * Grade (slope), the steepness of a slope Grade or grading may also ref ...

s of coal and other combustible materials, which produce different amounts of heat according to their grade. While

chemistry Chemistry is the scientific study of the properties and behavior of matter. It is a natural science that covers the elements that make up matter to the compounds made of atoms, molecules and ions: their composition, structure, proper ...

provides ways of calculating the

heating value The heating value (or energy value or calorific value) of a substance, usually a fuel or food (see food energy), is the amount of heat released during the combustion of a specified amount of it. The ''calorific value'' is the total energy relea ...

of a certain amount of a substance, there is a difference between this

theoretical A theory is a rational type of abstract thinking about a phenomenon, or the results of such thinking. The process of contemplative and rational thinking is often associated with such processes as observational study or research. Theories may be ...

value and its application to real coal. The grade of a sample of coal does not precisely define its

chemical composition A chemical composition specifies the identity, arrangement, and ratio of the elements making up a compound. Chemical formulas can be used to describe the relative amounts of elements present in a compound. For example, the chemical formula for ...

, so calculating the coal's actual usefulness as a fuel requires determining its proximate and ultimate analysis (see "Chemical Composition" below).

Chemical composition

Chemical composition of the coal is defined in terms of its proximate and ultimate (elemental) analyses. The parameters of proximate analysis are

moisture Moisture is the presence of a liquid, especially water, often in trace amounts. Small amounts of water may be found, for example, in the air (humidity), in foods, and in some commercial products. Moisture also refers to the amount of water vapo ...

, volatile matter, ash, and fixed carbon. Elemental or ultimate analysis encompasses the quantitative determination of

carbon Carbon () is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent—its atom making four electrons available to form covalent chemical bonds. It belongs to group 14 of the periodic table. Carbon ma ...

hydrogen Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-to ...

nitrogen Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at se ...

sulfur Sulfur (or sulphur in British English) is a chemical element with the symbol S and atomic number 16. It is abundant, multivalent and nonmetallic. Under normal conditions, sulfur atoms form cyclic octatomic molecules with a chemical formul ...

and

oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements ...

within the coal. Additionally, specific physical and mechanical properties of coal and particular

carbonization Carbonization is the conversion of organic matters like plants and dead animal remains into carbon through destructive distillation. Complexity in carbonization Carbonization is a pyrolytic reaction, therefore, is considered a complex proces ...

properties The calorific value '' ''Q'''' of coal J/kgis the heat liberated by its complete

combustion Combustion, or burning, is a high-temperature exothermic redox chemical reaction between a fuel (the reductant) and an oxidant, usually atmospheric oxygen, that produces oxidized, often gaseous products, in a mixture termed as smoke. Combus ...

with oxygen. ''Q'' is a complex function of the elemental composition of the coal. ''Q'' can be determined

experiment An experiment is a procedure carried out to support or refute a hypothesis, or determine the efficacy or likelihood of something previously untried. Experiments provide insight into cause-and-effect by demonstrating what outcome occurs whe ...

ally using calorimeters. Dulong suggests the following approximate formula for ''Q'' when the oxygen content is less than 10%: :''Q'' = 337''C'' + 1442(''H'' - ''O''/8) + 93''S'', where ''C'' is the mass percent of carbon, ''H'' is the mass percent of hydrogen, ''O'' is the mass percent of oxygen, and ''S'' is the mass percent of sulfur in the coal. With these constants, ''Q'' is given in kilojoules per kilogram.

References

*"Using Charcoal Efficiently." Food and Agriculture Organization of the United Nations. Retrieved 10 Nov 2011

*"Combustion Training." (c)2011 E Instruments International, LL

{{DEFAULTSORT:Energy Value Of Coal Coal technology Thermodynamic properties

Chemical composition

See also

References