Carbonization is the process of heating coal in the absence of air to produce coke. There are two types of carbonization: low temperature (500-700°C) which produces semi-coke and more liquid byproducts, and high temperature (>900°C) which produces denser coke and more gaseous byproducts. Coking coal undergoes carbonization to produce strong, porous coke for metallurgical purposes, while non-coking coal leaves a powdery residue and is not suitable for coke production.