Patent ID: 9206722
Filing Date: 2015-12-08
Classification: B01D,F01N,Y02A,Y02T

Abstract:
1. A method for reducing nitrogen oxide levels in diesel engine exhaust gases with the aid of an exhaust gas treatment system including, in the direction of flow of the exhaust gas, in this order: a feeder for feeding at least one of ammonia and a compound decomposing to form ammonia as the reducing agent into the exhaust gas to be cleaned; one or more SCR catalytic converters which form a first SCR unit; an ammonia sensor for determining the ammonia concentration in the exhaust gas downstream from the first SCR unit; one or more SCR catalytic converters and/or an ammonia oxidation catalytic converter which form a second SCR unit; and a nitrogen oxide sensor (NO setting the quantity of the at least one of ammonia and a compound decomposing to form ammonia to be fed into the exhaust gas using the ammonia concentration in the exhaust gas downstream from the first SCR unit determined with the aid of an ammonia sensor and the nitrogen oxide concentration in the exhaust pipe determined with the aid of an NO feeding the set quantity of the at least one of ammonia and the compound decomposing to form ammonia into the exhaust gas; wherein the predefined setpoint value is a function of the spatial velocity of the exhaust gas with respect to at least the first SCR unit and of the mean temperature of at least the first SCR unit.