Hybrid process for nitrogen oxides reduction

Claim 1

A process for reducing the nitrogen oxide concentration in the effluent from the combustion of a carbonaceous fuel, the process comprising: a) introducing into the effluent a first treatment agent comprising a nitrogenous composition selected from the group consisting of urea, ammonia, hexamethylenetetramine, ammonium salts of organic acids, 5- or 6-membered heterocyclic hydrocarbons having at least one cyclic nitrogen, hydroxy amino hydrocarbons, NH 4 -lignosulfonate, furfurylamine, tetrahydrofurylamine, hexamethylenediamine, barbituric acid, guanidine, guanidine carbonate, biguanidine, guanylurea sulfate, melamine, dicyandiamide, biuret, 1,1'-azobisformamide, methylol urea, methylol urea-urea condensation product, dimethylol urea, methyl urea, dimethyl urea, calcium cyanamide, and mixtures thereof under conditions effective to reduce the nitrogen oxides concentration and ensure the presence of ammonia in the effluent; b) introducing into the effluent a second treatment agent comprising an oxygenated hydrocarbon at an effluent temperature of about 500° F. to about 1600° F. under conditions effective to oxidize nitric oxide in the effluent to nitrogen dioxide and ensure the presence of ammonia at a weight ratio of ammonia to nitrogen dioxide of about 1:5 to about 5:1, and c) contacting the effluent with an aqueous scrubbing solution having a pH of 12 or lower under conditions effective to cause nitrogen dioxide to be absorbed therein.