Bituminous coal: Encyclopedia II - Bituminous coal - Uses

Bituminous coal - Uses

Bituminous coals are graded according to vitrinite reflectance, moisture content, volatile content, plasticity and ash content. Generally, the highest value bituminous coals are those which have a specific grade of plasticity, volatility and low ash content, especially with low carbonate, phosphorus and sulphur.

Plasticity is vital for coking and steel making, where the coal has to behave in a manner which allows it to mix with the iron oxides during smelting. Low phosphorus content is vital for these coals, as phosphorus is a highly deleterious element in steelmaking.

Coking coal is best if it has a very narrow range of volatility and plasticity. This is measured by the Free Swelling Index test. Tar content, volatile content and sweiiling index are used to select coals for coke blending.

Volatility is also critical for steel making and power generation, as this determines the burn rate of the coal. High volatile content coals, while easy to ignite often are not as prized as moderately volatile coals; low volatile coal may be difficult to ignite although it will contain more energy per unit volume. The smelter must balance the volatile content of the coals to optimise the ease of ignition, burn rate and energy output of the coal.

Low ash, sulphur and carbonate coals are prized for power generation because they do not produce much boiler slag and they do not require as much effort to scrub the flue gases to remove particulate matter. Carbonates are deleterious as they readily stick to the boiler apparatus. Sulphide contents are also deleterious in some fashion as this sulphur is emitted and can form smog, acid rainand haze pollution. Again, scrubbers on the flue gases aim to eliminate particulate and sulphur emissions.

In order to meet the increasing sophistication of smelters, refiners and power producers it is usual for coals to be blended to optimise their plasticity, ash and volatile content as well as their energy ouput.

Adapted from the Wikipedia article "Uses", under the G.N U Free Docmentation License. Please also see http://en.wikipedia.org/wiki