METHOD FOR THE CLEANING OF EXHAUST GAS FROM A COMPRESSION IGNITION ENGINE

摘要

A method for the cleaning of exhaust gas from a compression ignition engine, comprising the steps of injecting a first amount of an aqueous urea solution into the gas; in a first mode of operation and at an exhaust gas temperature of between 150 and 220° C. hydrolysing the first amount of urea to ammonia reducing agent in presence of a first catalyst comprising vanadium oxide supported on titania and subsequently removing part of nitrogen oxides contained in the exhaust gas by contacting the gas mixed with the ammonia reducing agent through a second catalyst comprising platinum on titania and/or alumina; and in a second mode of operation and at an exhaust gas temperature above 220° C. removing a part of the nitrogen oxides in presence of the first catalyst and the ammonia reducing agent and subsequently oxidising hydrocarbons, carbon monoxide and remaining amount of the ammonia reducing agent further contained in the exhaust gas by passing the gas through the second catalyst.

主权项

1. A method for the cleaning of an exhaust gas from a compression ignition engine, comprising the steps of
injecting an aqueous urea solution into the exhaust gas; in a first mode of operation and at an exhaust gas temperature of between 150 and 220° C. catalytically hydrolysing the aqueous urea solution to an ammonia reducing agent by contact with a first catalyst comprising vanadium oxide supported on titania and subsequently removing part of nitrogen oxides contained in the exhaust gas by contacting the exhaust gas mixed with the ammonia reducing agent with a second catalyst arranged downstream of the first catalyst and comprising platinum on titania and/or alumina; and in a second mode of operation and at an exhaust gas temperature above 220° C. decomposing the aqueous urea solution to the ammonia reducing agent and removing a part of the nitrogen oxides contained in the exhaust gas by reaction with the ammonia reducing agent in presence of the first catalyst and subsequently oxidising hydrocarbons, carbon monoxide and ammonia further contained in the exhaust gas leaving the first catalyst by contacting the exhaust gas with the second catalyst.