Energy and Environmental Research

Other

The United States of America As Represented by the Administrator of the

The United States of America As Represented by the Environmental

David W Pershing

Michael P Heap

Shih L Chen

James M McCarthy

George B Martin

James M Munro

George P Carver

Dennis M Zallen

G Blair Martin

Dee P Rees

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.

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

Methods and apparatus for reducing pollutant emissions, and in particular, for reducing NO.sub.x and particulate emissions, from spreader-stoker-fired furnaces. A combustible material is introduced into the spreader-stoker-fired furnace and combusted while the stoichiometric ratio of oxygen to combustible material in different regions of the furnace is carefully controlled. Control of the stoichiometric ratio is accomplished by controlling the amount of air injected into different regions of the furnace and by controlling the amount of smaller particles of combustible material or fines introduced into the furnace.

Reducing pollutant emissions from a spreader-stoker-fired furnace by

A method and apparatus for reducing pollutant emissions, and in particular, for reducing NO.sub.x and particulate emissions, from a spreader-stoker-fired furnace and from a fluidized bed combustor. A combustible material of various sized particles is obtained and those smaller particles which would normally combust during the suspension phase of the spreader-stoker-fired furnace or fluidized bed combustor are separated from the larger particles. The larger particles of combustible material are then introduced into the spreader-stoker-fired furnace or fluidized bed combustor and combusted to produce heat.

Reducing pollutant emissions by fines removal

The following specification discloses a process and burner for combusting fossil fuels such as coal to provide low SO.sub.x and NO.sub.x emissions. The process includes pulverizing the coal together with an alkaline material, such as limestone in an amount calculated to provide an alkaline metal stoichiometric equivalent of one to seven times the stoichiometric equivalent of the sulphur contained in the coal. The resulting pulverized coal-limestone mix is then combusted under fuel rich conditions. For example, 25% of the theoretical air required to combust the coal is preheated and injected into the combustion zone together with the pulverized coal-limestone mixture. The primary or transport air is swirled to increase mixing and to stabilize the flame. Preheated secondary air is introduced to the combustion zone. The amount of the preheated secondary air amounts to approximately 40% to about 100% of the theoretically required air. Finally, the balance of the stoichiometric air required to combust the coal along with a 25% to 40% excess is added to the combustion zone.

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Salt Lake City, UT, United States of America

David W Pershing