Producer gas is manufactured by passing air and steam through a bed of hot coal or coke at a temperature of 980 to 1540 °C, depending on the fusion points of the fuel ash. The primary purpose of the steam (25 to 30% of the weight of the coke) is to employ the exothermic energy from thereaction between carbon and oxygen to supply energy (heat) to the endothermic carbon-steam reaction.
C + O2 → CO2
CO2 + C → 2CO
C + H2O → CO + H2
CO + H2O → CO2 + H2
The initial reaction is the formation of carbon dioxide, and, as the gases progress up the bed, the carbon dioxide is reduced to carbon monoxide and the water vapor is partly decomposed to yield hydrogen, carbon monoxide, and carbon dioxide. Producer gas has about 15 percent of the heating value of natural gas.
Producer gas was once used for industrial heating, but its use is now diminished and it finds only occasional use in industrial operations.