Method and apparatus for emission control

A converter for substantially reducing the amount of NOx in exhaust gases from a fossil-fueled engine, using lean-burn combustion, said exhaust gases containing noxious materials including NOx, hydrocarbons, carbon monoxide, carbonaceous particulate matter and mixtures thereof, said converter comprising a container with an inlet and an outlet for the exhaust gases and a catalyst bed, a switching valve for periodically reversing the flow of the exhaust gases through the catalyst bed by reversing the flow between the inlet and the outlet of the container, said catalyst bed having a catalyst which is effective for NOx reduction to N2 through the reaction of NOx with a chemical reductant, said catalyst being effective with regards to said NOx reduction within a certain temperature window and at a molar ratio between the amounts of chemical reductant and NOx above a certain minimum ratio at which said catalyst is effective with respect to NOx reduction, means for heating up or cooling down the catalyst bed thereby maintaining the temperature inside the catalyst bed within the temperature window at which the catalyst is effective with respect to NOx reduction, a reductant delivery system for adding chemical reductant to the exhaust gases thereby maintaining the ratio between the molar amounts of chemical reductant and NOx above the certain minimum ratio at which said catalyst is effective with respect to NOx reduction, the catalyst bed being divided into two parts and a soot trap is provided between said two parts of catalyst bed, a first catalyst bed on the inlet side of the converter and a second catalyst bed on the outlet side of the converter, said trap being capable of collecting carbonaceous particulate matter and withstanding heating above a certain temperature limit, at which the collected carbonaceous particulate is burned thereby regenerating said trap.

A converter for substantially reducing the amount of NOx in exhaust gases from a fossil-fueled engine, using lean-burn combustion, said exhaust gases containing noxious materials including NOx, hydrocarbons, carbon monoxide, carbonaceous particulate matter and mixtures thereof, said converter comprising a container with an inlet and an outlet for the exhaust gases and a catalyst bed, a switching valve for periodically reversing the flow of the exhaust gases through the catalyst bed by reversing the flow between the inlet and the outlet of the container, said catalyst bed having a catalyst which is effective for NOx reduction to N2 through the reaction of NOx with a chemical reductant, said catalyst being effective with regards to said NOx reduction within a certain temperature window and at a molar ratio between the amounts of chemical reductant and NOx above a certain minimum ratio at which said catalyst is effective with respect to NOx reduction, means for heating up or cooling down the catalyst bed thereby maintaining the temperature inside the catalyst bed within the temperature window at which the catalyst is effective with respect to NOx reduction, a reductant delivery system for adding chemical reductant to the exhaust gases thereby maintaining the ratio between the molar amounts of chemical reductant and NOx above the certain minimum ratio at which said catalyst is effective with respect to NOx reduction, the catalyst bed having a high temperature lean-NOx catalyst bed flanked by soot traps, said traps further flanked by low temperature lean-NOx catalyst beds on the inlet and outlet sides of the converter.