Hybrid low NOx process for destruction of bound nitrogen compounds

Claim 1

A process for treating an exhaust stream which includes one or more noxious compounds containing chemically bound nitrogen, to produce an effluent stream that is reduced in oxides of nitrogen for discharge into the atmosphere; said process comprising: adding to said exhaust stream a source of oxygen and sufficient fuel to create a fuel-rich mixture, the quantity of fuel being sufficient to react with the available oxygen; providing said fuel-enriched stream to a thermal reactor and reacting therein said fuel, noxious compounds, and available oxygen, to provide a heated oxygen-depleted stream which includes by-product chemically bound nitrogen compounds; cooling said oxygen-depleted stream to 800° to 1000° F. by passing same through a first heat exchanger; adding conversion oxygen to said cooled stream from said first heat exchanger, and passing the cooled oxygen-augmented stream over a first catalyst bed under overall reducing conditions, the quantity of conversion oxygen added being in stoichiometric excess of the amount of chemically bound nitrogen in said stream, but less than the amount of combustibles; whereby the bound nitrogen is first dissociated and oxidized to NO 2 , and then the NO 2 is reduced by the excess combustibles; cooling said stream from said first catalyst bed to a temperature of about 450° to 550° F. by passing said stream through a second heat exchanger; adding air to the resulting cooled stream to produce a further cooled stream at a temperature of about 400° to 500° F., and having a stoichiometric excess of oxygen; and passing said stream having said stoichiometric excess of oxygen over an oxidizing catalyst bed at said temperature of 400° to 500° F. to oxidize any unreacted chemically bound nitrogen compounds, to thereby provide an effluent stream for discharge.