Metallurgic coke is used as a fuel and as a reducing agent in smelting iron ore in a blast furnace. Coke from coal is grey, hard and porous, and has a heating value of 29.6 MJ/kg.
Byproducts of this conversion of coal to coke include coal tar, ammonia, light oils, and “coal gas”.
Petroleum coke is the solid residue obtained in oil refining, which resembles coke but contains too many impurities to be useful in metallurgical applications.
Coal gasification breaks down the coal into its components, usually by subjecting it to high temperature and pressure, using steam and measured amounts of oxygen.
This leads to the production of syngas, a mixture mainly consisting of carbon monoxide (CO) and hydrogen (H2).
In the past, coal was converted to make coal gas, which was piped to customers to burn for illumination, heating, and cooking.
At present, the safer natural gas is used instead. South Africa still uses gasification of coal for much of its petrochemical needs.
Gasification is also a possibility for future energy use, as the produced syngas can be cleaned-up relatively easily leading to cleaner burning than burning coal directly.
The cleanliness of the cleaned-up syngas is comparable to natural gas, enabling to burn it in a more efficient gas turbine rather than in a boiler used to drive a steam turbine.