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Show AFRC90 Paper #36 1990 AFRC Int'l Symposium Remoyal of nitric oxide from gas streams via direct chlorine injection Abstract Eric M. Hixson Environmental Technology Laboratory Applied Engineering Research & Process Development The Dow Chemical Company Midland, Michigan 48667 A method for the removal of nitric oxide from gas streams is described. This patented Dow process consists of injection of gaseous chlorine into a NO-laden gas stream followed by rigorous scrubbing using an acidic aqueous solution. Comparable trials using water and different concentration brines are also reviewed. Removal efficiencies of +90% were observed in laboratory situations. Removal was found to be highly dependent upon gas stream Cl2:NO partial pressure ratio, scrubber temperature and pH. The process was determined to be highly mass transferred controlled and a reaction mechanism is proposed for the corresponding liquid phase chemistry. Introduction The oxides of nitrogen (NOx) are considered to be major constituents of air pollution. The monoxide form, nitric oxide (NO), is the combustion chemistry precursor for the many other oxides (i.e. N02, N204, N20S) held responsible, in part, for photochemical smog, acid rain, etc. Because of their participation in these environmentally sensitive areas, the emission of NOx from combustion systems is coming under some severe regulatory pressure. Hence, industry and government are investigating several reduction methods for these emissions. In 1981, the Dow Chemical Company was issued a patent for a process involving the direct, intimate contact of combustion off-gases with chlorine gas, followed by a thorough scrubbing of the mixture with an aqueous mixture of hydrochloride and hypochlorite. This work examines the performance of this system on a laboratory scale and seeks to propose reaction and physical paths by which the process is carried out. Studying the effects of changes in gas stream partial pressures, system temperature, and scrubbing medium pH, the end result is design criteria for a commercial combustion and/or incineration unit scrubbing system capable of meeting the current NOx regulatory requirements. The paper will proceed as follows: - brief discussion of experimental apparatus and analytical techniques used - compilation of results from experimentation - detailed theoretical discussion of those results - the study's conclusions Experimental The investigation was divided into two different parts; the first looking at possible gas-phase reactions and the other concentrating upon the reaction/processes occurring at the liquid-gas interface of the scrubbing system. A schematic of the equipment layout may be found in Figure #1. In both systems, the main component was a plug flow reactor. In the gas-phase work, this reactor consisted of a helically coiled quartz tube in a high temperature tube furnace. Gases would be metered into the system using thermal mass flow meters and allowed to mix thoroughly. The reaction mass -1- |