The unqualified gas of Huizhou water heater will not be delivered. Inquiring about relevant information shows that due to a poisoning incident, Huizhou market supervision department cracked down on unqualified gas. Coal gas is a combustible gas processed from coal. According to the processing method, gas properties and uses, it can be divided into water gas, semi-water gas and air gas (or producer gas) obtained from coal gasification. These gases are also collectively called low calorific value gases because of their low calorific value. The gas obtained by dry distillation and coking of coal is called coke oven gas.