As noted, processes and compositions for the reduction of nitrogen oxides in effluents from the combustion of carbonaceous fuels have been developed extensively over recent years. With the increased attention to the health risks and environmental damage caused by agents such as smog and acid rain, it is expected that NO.sub.x reduction research will continue to be pursued.
In the past, most processes for reducing nitrogen oxides levels have concentrated on achieving maximum NO.sub.x reductions without addressing the problems raised by the production of other pollutants, such as ammonia and carbon monoxide. More recently, in a unique application of nitrogen oxides reducing principles, Epperly, Peter-Hoblyn, Shulof, Jr., and Sullivan, in U.S. Pat. No. 4,777,024, disclose a method of achieving substantial nitrogen oxides reductions without the production of a major amount of other pollutants through a multiple stage treatment agent injection process. Although minimizing the production of other pollutants, this process, like any process which involves the high temperature introduction of nitrogenated compounds such as urea or ammonia, will still generate some other pollutants.
This is also the case with the method of U.S. Pat. No. 4,780,289, issued to Epperly, O'Leary and Sullivan, which discloses another method for maximizing NO.sub.x reductions while minimizing other pollutants. Although minimized, such other pollutants are still present.
In Izumi et al., U.S. Pat. No. 4,350,669, the patentees disclose a process for reducing nitrogen oxides in combustion exhaust gases which comprises adding an oxygen-containing hydrocarbon and/or its precursor to the exhaust gas to oxidize nitric oxide to nitrogen dioxide, which can then be scrubbed out of the effluent using an absorbing solution. The process of Izumi et al., though, still has the disadvantage of allowing nitrites and nitrates to be discharged from the boiler with the discharge water.
What is needed, therefore, is a process for effectively reducing the nitrogen oxides concentration in an effluent which does not cause the release into the atmosphere of substantial amounts of ammonia nor the discharge in the discharge water of substantial amounts of nitrites.