Energy and Environmental Research

Shih L Chen

William Randall Seeker

Loc Ho

David W Pershing

Michael P Heap

James M McCarthy

Peter M Maly

John C Kramlich

Method for controlling N.sub.2 O emissions from stationary combustion systems having variable flue gas temperatures are disclosed. The N.sub.2 O emissions are controlled by the introduction of a N.sub.2 O control agent, such as an alkaline compound, into the effluent stream. In addition, the present invention discloses methods for controlling N.sub.2 O emissions from stationary combustion systems having variable flue gas temperatures while reducing NO.sub.x emissions. Use of an NO.sub.x reducing agent and an N.sub.2 O control agent, such as urea and monosodium glutamate, enlarges the temperature window for effective selective noncatalytic NO.sub.x reduction while significantly eliminating N.sub.2 O emissions commonly experienced with urea injection. Further, the present invention discloses methods for controlling N.sub.2 O emissions from stationary combustion systems having variable flue gas temperatures while reducing SO.sub.x emissions. Use of an NO.sub.x reducing agent, an SO.sub.x reducing agent, and an N.sub.2 O control agent, such as urea, an alkaline-earth metal compound, and an alkali-metal compound, respectively, enlarges the temperature window for effective NO.sub.x and SO.sub.x reductions while significantly eliminating N.sub.2 O emissions.

Methods for controlling N.sub.2 O emissions and for the reduction of NO.sub

Techniques for enhancing the burnout zone chemistry for NO.sub.x reduction are disclosed. The key parameters for the enhancement of burnout zone chemistry are: (a) a reaction temperature in the range from about 1300.degree. F. to about 1900.degree. F., and optimally in the range from 1400.degree.-1700.degree. F.; (b) a carbon monoxide concentration below about 0.5 percent; and (c) the presence of nitrogenous reducing species. By controlling the stoichiometry associated with reburning to produce a slightly fuel-rich region for selective reducing agent injection, reductions can be achieved at relatively low temperatures which approach those obtained by conventional catalytic reduction.

Advanced reburning for reduction of NO.sub.x emissions in combustion

Methods for reducing NO.sub.x emissions from stationary combustion systems having variable flue gas temperatures are disclosed. Use of an annonium salt of an organic acid enlarges the temperature window for effective selective noncatalytic NO.sub.x reduction thereby accounting for variable flue gas temperatures. Currently preferred ammonium salts of organic acids include ammonium formate, ammonium acetate, and ammonium oxalate. Mixtures of urea and either an ammonium salt of an organic acid or a metallic salt of an organic acid provide an even greater temperature window for NO.sub.x reduction. Currently preferred metallic salts of organic acids include Ca(COOH).sub.2, Ca(CH.sub.3 COO).sub.2, Ca(C.sub.2 H.sub.5 COO).sub.2, Mg(COOH).sub.2, Mg(CH.sub.3 COO).sub.2, and Mg(C.sub.2 H.sub.5 COO).sub.2.

Methods for enlarging the useful temperature window for NO.sub.x

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 cyanuric acid. Initially, cyanuric acid is decomposed to form decomposition products. The reaction of cyanuric acid to produce its decomposition products, such as isocyanic acid or related reaction intermediates, takes place in an oxygen-free, fuel rich, decomposition zone with the reaction temperature in the range of from about 1000.degree. F. to about 3000.degree. F. After the cyanuric acid is decomposed in the absence of oxygen, the decomposition stream is mixed 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. 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 the second 'reaction zone,' reduction takes place at temperatures of from approximately 1200.degree. F. to approximately 2600.degree. F. The present invention can also be combined 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 to the cyanuric acid for injection into the effluent stream. Thus, simultaneous NO.sub.x and SO.sub.x control can be achieved.

Methods of reducing NO.sub.x and SO.sub.x emissions from combustion

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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Irvine, CA, United States of America

Shih L Chen