Process for operating an exhaust gas treatment unit

Details Process for operating an exhaust gas treatment unit Process for operating an exhaust gas treatment unit

B - Operations, Transporting

01

D

B01D 53/92 (2006.01) B01D 53/94 (2006.01) F01N 3/08 (2006.01) F01N 3/20 (2006.01) F01N 13/02 (2010.01)

Patent

CA 2267010

The invention relates to a process for operating an exhaust gas treatment unit for an internal combustion engine which is operated with lean normalised air/fuel ratios over most of the operating period. The exhaust gas treatment unit contains a nitrogen oxides storage catalyst with an activity window .DELTA.T NOX for the storage of nitrogen oxides at normalised air/fuel ratios of greater than 1 and release of the nitrogen oxides at normalised air/fuel ratios of less than or equal to 1 and a sulfur trap, located upstream of the nitrogen oxides storage catalyst, with a sulfur desorption temperature T S,DeSOx above which the sulfates stored on the sulfur trap are decomposed at normalised air/fuel ratios of less than or equal to 1. The nitrogen oxides contained in the exhaust gas are stored on the nitrogen oxides storage catalyst and the sulfur oxides are stored on the sulfur trap at normalised air/fuel ratios greater than 1 and exhaust gas temperatures T K within the activity window T NOX, wherein at the same time the exhaust gas temperature just upstream of the sulfur trap is lower than its sulfur desorption temperature T S,DeSOx. By cyclic lowering of the normalised air/fuel ratio in the exhaust gas to less than 1 the stored nitrogen oxides are released again from the storage catalyst. (Conclusion of a storage cycle). After each predetermined number N1 of nitrogen oxides storage cycles, sulfur is removed from the sulfur trap. This takes place by raising the exhaust gas temperature just upstream of the sulfur trap to above its sulfur desorption temperature T S,DeSOx and also lowering the normalised air/fuel ratio in the exhaust gas to less than 1.

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