APPARATUS FOR CONTROLLING INJECTION AMOUNT OF AMMONIA

PURPOSE:To eliminate the response delay at the time of rising in load, by providing comparators for comparing a necessary NH3 flow amount signal with an actually measured NH3 flow amount signal and injecting a constant amount of NH3 when the former is smaller than the latter or the deviation of both signals is small. CONSTITUTION:The signals from an inlet NOX concn. detector 12 and an air flow amount detector 14 are sent to an operator 18 through a function converter 16 to calculate a total NOX amount signal 19 while a necessary mol ratio setting signal 23 is calculated and this signal 23, the correction signal 27 obtained from an outlet NOX concn. detector 24 through an adder 26 and the total NOX amount signal 19 are operated by an operator 28 to calculate a necessary NH3 flow amount signal 29 which is, in turn, compared with an actually measured NH3 flow amount signal 31 by a comparator 32 and a deviation signal 33 is sent to a proportional integrator 34. A low signal selector 40 is provided to the downstream side of said integrator 34 and when a valve opening degree signal 35 comes to zero or the actually measured NH3 flow amount signal 31 is smaller than the necessary NH3 flow amount signal 29, an NH3 flow amount control valve 39 is opened to inject a constant flow amount of NH3.