NOx REMOVAL SYSTEM AND METHOD

摘要

PROBLEM TO BE SOLVED: To provide a NOx removal device and its method capable of efficiently making nitrogen oxides in exhaust gas exhausted from an internal combustion engine harmless. SOLUTION: Ammonia and/or urea is added to exhaust gas exhausted from the internal combustion engine 12 by an injector 14 in a catalyst front pipe 13a and exhaust gas is subsequently reduced and denitrified in denitration catalyst 15. Ammonia in exhaust gas passing through denitration catalyst 15 is detected by an ammonia sensor 16. As an ammonia sensor element installed in the ammonia sensor 16, the ammonia sensor element in which an sensor output for ammonia of 300 deg.C and 800 ppm in concentration is more than twice a sensor output for nitrogen monoxide of 300 deg.C and 800 ppm in concentration is preterably used when the temperature of a detecting part is held at 580 deg.C.