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Show It was reported that Thermal DENOx on a utility boiler reduced NOx emissions by 30% to 50% and that addition of catalyst into the existing duct upstream of the preheater increased overall reductions to 50% to 60%. No data were presented on catalyst volume, space velocity, or other parameters necessary to calculate cost impact. It seems reasonable to assume that both NOx reduction and cost would be between Thermal and SCR. It could be speculated that the initial quantities of catalyst would improve NOx reduction relatively more than costs would increase which would result in a minimum value of cost per ton of NOx removed for some small amount of catalyst. 2.5 NOx SCRUBBING 2.5.1 Process Description Wet scrubbing of NOx requires separation of NO from a flue gas stream since substantially all of the nitrogen oxides in flue gas are present as NO. NO has very low solubility in water. Therefore, NO scrubbing involves complex processes including: Special solutions (e.g., iron chelate, sodium sulfide, or potassium permanganate) to react with NO, or Gas-phase oxidation of NO to NO (e.g., using CIO or 0.) 2 2 3 and then scrubbing the NO which is highly soluble in water and reactive with bases. Much of the work on NOx wet scrubbing has been done in Japan. The advantages of wet NOx scrubbing compared to dry NOx removal are (1) simultaneous^O and NOx removal, and (2) high efficiency in the presence of particulates. The major disadvantages are (1) high capital and operating costs, and (2) the contamination of waste water with nitrates and chlorides. Additional disadvantages of land requirements, water usage, and disposal of solid wastes affect the utility of wet NOx scrubbers. Wet NOx scrubbing technologies fall into four categories: 4-25 P-233 |