Importance

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Abstract

The present invention relates to methods for selectively reducing NO.sub.x so that nitrogen can be removed from emission effluent streams and NO.sub.x emissions can be reduced to very low levels. In addition, the present invention teaches a method whereby NO.sub.x and SO.sub.x may be simultaneously removed from the effluent stream. The present invention teaches the reduction of NO.sub.x with --NH and --CN containing selective reducing agents such as ammonium sulfate, urea, and NH.sub.3. Initially, the selective reducing agent is decomposed in a fuel-rich environment to form highly reactive decomposition products. The reaction of the selective reducing agent to produce its decomposition products, such as NH, NH.sub.2, and related reaction intermediates, takes place in an oxygen-free, fuel-rich decomposition zone with the reaction temperature in the range of from about 300.degree. F. to about 2400.degree. F. After the selective reducing agent is decomposed in the absence of oxygen, the decomposition products are contacted with the effluent stream containing NO.sub.x. At this point the oxygen level of the stream must be carefully controlled to provide an excess of oxygen so that the selective reduction of the NO.sub.x species will occur. It may be necessary at this point to inject air into the effluent stream in order to maintain the proper oxygen-rich (fuel-lean) conditions for NO.sub.x reduction. In this second 'reaction zone', NO.sub.x reduction takes place at temperatures of from approximately 500.degree. F. to approximately 2600.degree. F. The present invention can also be used in conjunction with SO.sub.x control technology. Specifically, species used to control SO.sub.x, such as limestone, dolomite, quicklime, and hydrated lime, can be added in conjunction with the selective reducing agent for simultaneous NO.sub.x and SO.sub.x control.

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First Claim