EXHAUST-GAS-CLEANING SYSTEM AND METHOD FOR CONTROLLING THE SAME

It effectively controls an exhaust gas to a target excess-air-ratio of an NOx purge or an SOx purge without using a lambda value of the exhaust gas. The exhaust purification system includes: an NOx reduction type catalyst (32) which is provided in an exhaust system of an internal combustion engine (10), and reduces and purifies NOx in an exhaust gas; and regeneration treatment units (60 and 70) which recover an NOx purification capacity of the NOx reduction type catalyst (32) by lowering an excess-air-ratio of the exhaust gas to a predetermined target excess-air-ratio, in which the regeneration treatment units (60 and 70) include target setting units (66 and 76) which set a target injection amount of at least one of a post injection and an exhaust pipe injection required for setting an excess-air-ratio of the exhaust gas to the target excess-air-ratio based on a suction air amount of the internal combustion engine, the target excess-air-ratio, and a fuel injection amount of the internal combustion engine, and an injection controller (50) which controls an injection amount of at least one of the post injection and the exhaust pipe injection based on the target injection amount input from the target setting units (66 and 76).