Patent ID: 7972581

Claim:
A method of treating nitrogen oxide-containing gas by bringing gas generated on combustion of fuel in a burner into contact with an oxidation catalyst, to thereby decrease nitrogen oxides contained in the gas, comprising: a combustion step of burning hydrocarbon-containing fuel in the burner, thereby generating gas free of hydrocarbons but containing oxygen, nitrogen oxides, and carbon monoxide; a hazardous-substance decreasing step of bringing the gas into contact with an oxidation catalyst, thereby oxidizing carbon monoxide contained in the gas by oxygen and reducing nitrogen oxides by carbon monoxide; and a concentration ratio adjusting step of adjusting a concentration ratio of oxygen, nitrogen oxides, and carbon monoxide in gas on a primary side of the oxidation catalyst to a predetermined concentration ratio in which a concentration of nitrogen oxides on a secondary side of the oxidation catalyst is decreased to substantially zero or a value equal to or lower than a predetermined value and a concentration of carbon monoxide on the a secondary side of the oxidation catalyst is also decreased to substantially zero or a value equal to or lower than a predetermined value.