A method for purifying combustion exhaust gas

摘要

The method for purifying combustion exhaust gas according to the present invention utilizes a NH3 decomposing catalyst. The NH3 decomposing catalyst in the present invention is capable of converting substantially all of the NH3 in the combustion exhaust gas to N2 when the air-fuel ratio of the exhaust gas is lean and the temperature of the catalyst is within a predetermined optimum temperature range. Further, when the exhaust gas contains NOx in addition to NH3, the NH3 decomposing catalyst is capable of reducing the NOx in the optimum temperature range even though the air-fuel ratio of the exhaust gas is lean. In the present invention, the conditions of the exhaust gas containing NOx are adjusted before it is fed to the NH3 decomposing catalyst in such a manner that the temperature of the exhaust gas is within the optimum temperature range and the air-fuel ratio of the exhaust gas is lean. Further, NH3 is added to the exhaust gas before it is fed to the NH3 decomposing catalyst. Therefore, a lean air-fuel ratio exhaust gas, at a temperature within the optimum temperature range, which contains both the NOx and NH3 is fed to the NH3 decomposing catalyst, and the NOx, as well as the NH3, in the exhaust gas is completely resolved by the NH3 decomposing catalyst.