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A provision of assemblies and methods for treating exhaust gases from combustion devices to reduce air contaminants in the exhaust gas. The exhaust from a combustion device is cooled, followed by passing the exhaust through first and second catalytic chambers with an oxygen enrichment means in betwe

A provision of assemblies and methods for treating exhaust gases from combustion devices to reduce air contaminants in the exhaust gas. The exhaust from a combustion device is cooled, followed by passing the exhaust through first and second catalytic chambers with an oxygen enrichment means in between the catalytic chambers. The catalytic chambers comprise at least one catalyst that substantially reduces nitrogen oxides or carbon monoxide or both.

대표청구항 ▼

1. A method for treating air contaminants in an exhaust gas from a rich burn, spark ignition internal combustion engine, the method comprising the steps of: (i) controlling combustion of air-fuel mixture of the rich burn, spark ignition internal combustion engine to produce an exhaust gas that is su

1. A method for treating air contaminants in an exhaust gas from a rich burn, spark ignition internal combustion engine, the method comprising the steps of: (i) controlling combustion of air-fuel mixture of the rich burn, spark ignition internal combustion engine to produce an exhaust gas that is substantially free of oxygen;(ii) passing the exhaust gas to an exhaust cooling stage wherein the exhaust gas is cooled to a predetermined temperature prior to catalytic conversion;(ii) passing the exhaust gas from the exhaust cooling stage to a first stage catalyst for substantially reducing NOx and carbon monoxide content in the exhaust gas;(iv) enriching the exhaust gas at a location only downstream from the first stage catalyst with oxygen; and(v) passing the exhaust gas from the first stage catalyst after enriching with oxygen to a second stage catalyst for substantially reducing carbon monoxide content, before exiting via an outlet. 2. The method of claim 1, further comprises placing an oxygen sensor for the control of air to fuel ratio between the exhaust cooling stage and the first stage catalyst. 3. The method of claim 1, wherein the fuel comprises natural gas. 4. The method of claim 1, wherein the exhaust gas is cooled to a predetermined temperature range of 575 to 659 degrees Fahrenheit. 5. The method of claim 1, wherein the air to fuel ratio is controlled by a system utilizing a venturi mixer and an electronically controlled valve. 6. The method of claim 1, wherein the exhaust gas is cooled to a predetermined temperature range of 392 to 795 degrees Fahrenheit. 7. The method of claim 1, wherein the concentration of NOx that is emitted to the atmosphere is less than 3.7 ppm corrected to 15% oxygen based on time-average data taken over an extended period. 8. The method of claim 1, wherein the concentration of carbon monoxide that is emitted to the atmosphere is less than 8.5 ppm corrected to 15% oxygen based on time-average data taken over an extended period. 9. The method of claim 1, wherein the cooling stage protects the first stage catalyst from damage due to sintering. 10. The method of claim 1, wherein the substantial catalytic removal of carbon monoxide in the second stage catalyst allows the engine to achieve 3.7 ppm NOx and 8.5 ppm CO, both corrected to 15% oxygen, over a substantially broad range of air to fuel ratios. 11. The method of claim 1, wherein the concentration of ammonia that is emitted to the atmosphere is less than 1.85 ppm corrected to 15% oxygen based on time-average data taken over an extended period. 12. The method of claim 1, wherein the air to fuel ratio of the combustion device is dithered. 13. The method of claim 2, wherein cooling fins are placed between the first stage catalyst and second stage catalyst. 14. The method of claim 1, wherein all exhaust gas passes through the exhaust cooling stage before passing to the first stage catalyst. 15. A method of limiting the generation of NOx on a second stage catalyst receiving an exhaust from a rich burn, spark ignition internal combustion engine, the method comprising: controlling combustion of air-fuel mixture of the rich burn, spark ignition internal combustion engine to produce an exhaust gas that is substantially free of oxygen;providing at least one exhaust cooling stage where the exhaust is cooled to a predetermined temperature before being passed to a first stage catalyst for substantially reducing NOx and carbon monoxide content in the exhaust gas,enriching the exhaust gas at a location only downstream from the first stage catalyst with oxygen; andpassing the exhaust gas from the first stage catalyst after enriching with oxygen to the second stage catalyst of at least two catalyst stages, whereby the formation of NOx in the exhaust that passes over the second stage catalyst is substantially limited based on an average of measurements taken over an extended time period. 16. The method of claim 15, wherein the exhaust cooling stage cools the exhaust to 390 to 480 degrees Fahrenheit. 17. An apparatus for treating an exhaust gas discharged from a rich-burn, spark ignited internal combustion engine, comprising: an exhaust cooling stage configured to cool the exhaust gas discharged from the rich burn, spark ignition internal combustion engine to a predetermined temperature prior to a catalytic conversion;an oxygen sensor, located between the exhaust cooling stage and a first stage catalyst, for generating a signal for use by a system to control the air to fuel ratio of the mixture supplied to the engine;passing exhaust gas from the exhaust cooling stage to the first stage catalyst to substantially reduce NOx and carbon monoxide content in the exhaust gas;an oxygen enrichment stage configured to enrich the exhaust gas at a location only downstream from the first stage catalyst with oxygen;a second stage catalyst adapted to receive the exhaust gas from the oxygen enrichment stage to substantially reduce carbon monoxide content in the exhaust gas; andan outlet for allowing the treated exhaust from the rich burn, spark ignition internal combustion engine to exit the apparatus. 18. The apparatus of claim 17, wherein the exhaust cooling stage cools the exhaust gas to a predetermined temperature range of 575 to 659 degrees Fahrenheit.