Coal is one of fuel type for energy generating, beside natural gas and petroleum. By virtue of way of its use as energy producer is classified :
a. Primary energy producer where coal that is directly utilized for industry, for example usage of coal as component of bunker burning (in cement industry and power station of steam power), combustion of chalk, brick, pass, locomotive fuel, process reducer metallurgy, conventional coke, fuel doesn't smoke.
b. Secondary energy producer where coal that is indirectly utilized for industry for example usage of coal as component of solid burning (briquette), liquid fuel (conversion becomes liquid fuel) and gas (conversion becomes gas fuel), fuel in metal infusion industry (in the form of coke). Besides coal is utilized not as component of burning for example as reduction at tin forge, factory ferro nickel, iron industry and steel, purification at chemistry industry (in the form of activated carbon), calcium carbide making (in the form of coke or semi-carbonized coke).
Fuel Type
Common fuel type utilized in industry is :
a. Gas fuel : natural gas
b. Liquid fuel : petroleum
c. Solid fuel : coal
Third the fuel basically is consisted of :
1. Combustible Material
That is material which can be burned or oxidized by oxygen from the air. The material in general is consisted of : Fixed Carbon, Hydrocarbon Compounds, Sulfur, Nitrogen, phosphor, etc.
2. Non Combustible Material
That is material which cannot be burned or oxidized by oxygen. This material remains in solid existence so-called ash (ash) is containing SiO2, Al2O3, Fe2O3, CaO and Alkali and gas existence which is in the form of H2O or CO2.
Coal fuel many containing non combustible materials in the form of ash and water, while practical oil fuel do not contain non combustible materials except sometime a few carbon dioxide. Content non combustible materials in fuel generally do not be filed a desire for by will reduce combustion value or reduces flatness temperature.
The Happening Of Impurities
Like known coal taken away from result of mining containing pollutant material (impurities). Recognized 2 type impurities that is inherent impurities and external impurities.
a. Inherent Impurities is wafting pollutant which there is in coal. Coal which have been washed out (form of block), when burned out simply still giving rest of ash. This wafting pollutant concomitant when happened coal forming process (when still in the form of gelly). This pollutant cans be in the form of mineral like gypsum, an hydrate, pyrite, silica, marcasite and earns also is in the form of animal bones (known there are compound phosphor from result of ash analysis).
b. External of Impurities, be pollutant outside coming from mining process for example brought it closing layer, this very common case and difficult to be obviated especially at strip mine activity
Sources : Batubara and Gambut, Ir. Sukandarrumidi, MSc, Ph.D. Gajah Mada University Press