Reduction of gaseous pollutants in combustion flue gas

A method of reducing nitrogen oxides in the exhaust gases of combustion apparatus, comprising:

• a. burning fuel in a primary combustion zone with substantially less than the stoichiometric amount of air,
• b. controlling the temperature of the burning reaction below that at which significant amounts of nitrogen oxides are produced whereby substantial amounts of carbon monoxide and unburned hydrocarbons are produced in the combustion products,
• c. dispersing into the combustion products, before substantial heat is extracted therefrom, sufficient combustion supporting gas to oxidize substantially all of the carbon monoxide and hydrocarbons in a secondary combustion zone,
• d. controlling the temperature of the reaction in the secondary combustion zone below that at which significant amounts of nitrogen oxides are produced,
• e. controlling the total amount of combustion supporting gas supplied to said primary and secondary combustion zones so that said total amount is substantially equal to the stoichiometric amount,
• f. proportioning the total amount of said combustion supporting gas between said combustion zones in such manner that an increase or decrease in the air supplied to the secondary combustion zone is accompanied by an inverse decrease or increase, respectively, of combustion supporting gas supplied to said primary combustion zone, and
• g. regulating the amount of combustion supporting gas supplied to said combustion zones in accordance with the carbon monoxide content of the exhaust gases from the secondary combustion zone.

A method of reducing nitrogen oxides in the exhaust gases of combustion apparatus, comprising:

• a. burning fuel in a primary combustion zone with substantially less than the stoichiometric amount of air,
• b. controlling the temperature of the burning reaction below that at which significant amounts of nitrogen oxides are produced whereby substantial amounts of carbon monoxide and unburned hydrocarbons are produced in the combustion products,
• c. dispersing into the combustion products, before substantial heat is extracted therefrom, sufficient combustion supporting gas to oxidize substantially all of the carbon monoxide and hydrocarbons in a secondary combustion zone,
• d. controlling the temperature of the reaction in the secondary combustion zone below that at which significant amounts of nitrogen oxides are produced,
• e. controlling the total amount of combustion supporting gas supplied to said primary and secondary combustion zones so that the total amount is substantially equal to the stoichiometric amount,
• f. proportioning the total amount of air between said primary and secondary combustion zones, and
• g. sensing the carbon monoxide content of the exhaust gases from said secondary combustion zone and increasing the combustion supporting gas supplied to the secondary zone and reducing the combustion supporting gas supplied to the primary zone in accordance with increased carbon monoxide being sensed, and further, decreasing the supporting gas supplied to the secondary zone and increasing the supporting gas supplied to the primary zone in accordance with decreased carbon monoxide being sensed.

A method of reducing nitrogen oxides in the exhaust gases of combustion apparatus, comprising:

• a. burning fuel in a primary combustion zone with substantially less than the stoichiometric amount of air,
• b. controlling the temperature of the burning reaction below that at which significant amounts of nitrogen oxides are produced whereby substantial amounts of carbon monoxide and unburned hydrocarbons are produced in the combustion products,
• c. dispersing into the combustion products, before substantial heat is extracted therefrom, sufficient combustion supporting gas to oxidize substantially all of the carbon monoxide and hydrocarbons in a secondary combustion zone,
• d. controlling the temperature of the reaction in the secondary combustion zone below that at which significant amounts of nitrogen oxides are produced,
• e. sensing the level of a constituent in the gases from said secondary combustion zone, and
• f. controlling the amount of combustion supporting gas in accordance with the level of said constituent.