Importance

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Abstract

First, an emission amount of nitrogen oxide can be decreased to zero as much as possible and, an emission amount of carbon monoxide is decreased to a permissible range. Second, energy saving by combustion at a low air ratio close to 1.0 is realized. Third, air ratio control is performed stably in a combustion region at a low air ratio. Provided is a boiler, including: a premixed burner; a water pipe group for, by heat exchanging with a gas produced by the premixed burner, suppressing a temperature of the gas to thereby suppress a concentration of nitrogen oxide to a predetermined value or less; an oxidation catalyst for oxidizing carbon monoxide contained in the gas after the passage through the water pipe group by oxygen and for reducing nitrogen oxide contained therein by carbon monoxide; and an air-ratio adjusting device for adjusting an air ratio of the premixed burner, in which: the premixed burner and the water pipe group have such characteristics that when the air ratio is a set air ratio, a concentration ratio of oxygen, nitrogen oxides, and carbon monoxide in the gas on a primary side of the oxidation catalyst becomes a predetermined concentration ratio; the oxidation catalyst has such characteristics that when the concentration ratio is a predetermined concentration ratio, a concentration of nitrogen oxides on a secondary side of the oxidation catalyst is substantially zero while a concentration of carbon monoxide is decreased to substantially zero or a predetermined value or less; and the predetermined concentration ratio is kept to be constant by being controlled to the set air ratio by the air-ratio adjusting device.

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First Claim