This paper is an educational article of coal gasification. Basic reac-tions of coal gasification are classified into thermal cracking, hydrogasification, hydro-methanation, water gas reaction, producer gas reaction and combustion. Concerning each reaction, theoretical treatments on the effects of pressure, temperature and volume of chemical spesies are elucidated. These treatments are applied to illustrate the chemical changes in three types of simplified furnaces of perfect coal gasification, hydrogasification and gasification with desulfurization.
