Patent ID: 6935102

Claim:
A method of controlling the concentration of nitrogen oxides (NO x ), hydrocarbons (HC) and carbon monoxide (CO) in waste gases, such as burner fumes and the exhaust gases of internal combustion engines, wherein the waste gases are passed through a catalyst for catalytic cleansing of said gases, said method comprising the steps of: establishing a first lambda value (λ1) of a supplied fuel-air mixture to be less than a value λ=1; passing the products of combustion of the supplied fuel-air mixture as waste gases through a first catalyst and then through a final catalyst, wherein the gases escape directly to the atmosphere after the final catalyst, and wherein the CO-concentration of the gases passing through the first catalyst is sufficiently high to reduce NO x to N 2 so that the NO x concentration is reduced to a predetermined value; introducing oxygen (O 2 ) into the gases between the first catalyst and the final catalyst in a quantity sufficient to oxidize both CO and HC to CO 2 and H 2 O so that the CO-concentration is reduced to a predetermined value; measuring a final lambda value (λ2) in the waste gases at a point downstream of said final catalyst; transmitting a signal representative of the final lambda value to a control device that has an associated memory; and controlling a an airflow control valve positioned in an air inlet conduit upstream of a combustion zone for regulating inlet oxygen supply in relation to inlet fuel supply of the supplied fuel-air mixture at a fuel-air inlet upstream of the combustion zone based upon an output provided by the control device, so that said final lambda value (λ2) is within a predetermined range whose lower limit is higher than a value λ=1.