Parkhurst & Wendel, L.L.P.
Method of removing NO.sub.x from exhaust gases
 A method for removing nitrogen oxides out of the exhaust gas from a combustion apparatus is provided by reducing the nitrogen oxides with injected ammonia or urea to produce nitrogen and water. The method further includes the provision of at least one, sensor placed downstream from the nitrogen oxides removal step for measuring the concentration of the residual ammonia and nitrogen oxides in the exhaust gas after the nitrogen oxides removal step. The method also further includes the provision of a controller for controlling the rate that the ammonia and/or urea is injected into the exhaust gas so that the rate of ammonia and/or urea injection is repeatedly increased and decreased in response to the signal generated by the sensor about a reference value plus the average of the increased and reduced rates of ammonia and urea injection. 
NGK Insulators, Ltd.
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Nobuhide Hiroshi
Kato Kurachi