System for and method of removing NOx from exhaust gases

摘要

An NOx removal system has a combustion apparatus (64) for applying energy to a load based on a predetermined combustion control process, an NOx remover (68) for reacting NOx emitted from the combustion apparatus (64) with NH3 to produce N2 and H2O, an NH3 and/or urea introducing apparatus (72) connected upstream of the NOx remover (68), for introducing NH3 and/or urea into a gas passage (66) extending from the combustion apparatus (64) to the NOx remover (68), and an NOx sensor (70) connected downstream of the NOx remover (68), for generating a detected signal based on NH3 and NOx contained in a gas discharged from the NOx remover (68). A controller (72) controls a rate at which NH3 and/or urea is introduced into the gas passage (66) by the NH3 and/or urea introducing apparatus (72) while repeatedly increasing and reducing the rate, in response to the detected signal generated by the NOx sensor (70). The NOx removal system, which employs NH3 and/or urea as a reducing agent, is capable of accurately controlling the rate at which NH3 and/or urea is introduced into the gas passage (66) through a simple arrangement, and minimizing the discharge of NH3 and NOx.