Patent attributes
To provide an exhaust gas purifying method and an exhaust gas purifying system capable of efficiently purging the sulfur accumulated in a NOx occluding reduction type catalyst, while preventing fuel consumption from deteriorating and preventing NOx, HC, and CO from being discharged into the atmosphere, in an exhaust gas purifying system constituted by combining a NOx purifying function by the NOx occluding reduction type catalyst with a PM purifying function by a DPF. In an exhaust gas purifying system (1) for performing NOx purification by a NOx occluding reduction type catalyst (42) and PM purification by an DPF (41), it is judged whether sulfur purge of the NOx occluding reduction type catalyst is required and when it is judged that the sulfur purge is required, it is further judged whether the PM quantity (PMst) accumulated in the DPF (41b) exceeds a predetermined judgment value (PMst0), and when the PM quantity (PMst) exceeds the judgment value (PMst0), sulfur purge control is performed after performing the DPF regeneration control.
