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Show PROBLEM DESCRIPTION At the outset of demonstration testing, Radian's patented Hybrid Low NOx Cogeneration Process consisted of the following steps: 1. Thermal and/or catalytic reduction with excess fuel to remove all oxygen from the incoming flue gas . In theory, the excess fuel will then react with the NO according to the following reactions: CO + NO .... CO2 + 1/2 N2 H2 + NO .... H20 + 1/2 N2 2. Cooling of the products from step 1. 3. Mixing of products with excess combustion air. (1) (2) 4. Catalytic oxidation of excess combustibles to less than 100 ppmv CO (dry basis). The first demonstration test, which used only thermal reduction in step 1, failed to achieve the target level of 25 ppmv NOx • Instead, at reasonable amounts of excess fuel (2 to 4% CO), the NOx level was reduced about 80% in the thermal reduction step. No further reduction of NOx occurred downstream of the reduction furnace, since steps 3 and 4 represent oxidizing conditions. To achieve greater than 90% NOx destruction, the excess combustibles were increased to a level of 6 to 8 percent. In this range, the NOx was reduced by 90 to 95% across the thermal burnout step, but appreciable by-product bound nitrogen compounds (primarily NH3 and HCN) were formed in the reduction step. Although the mechanisms for NH3 and HCN formation are quite complicated and involve up to 75 reaction mechanisms, for simplicity, the following two reversible reactions may be considered: NO + CO + 1/2 H2 = HCN + 02 NO + 3/2 Hz ~ NH3 + 1/2 02 (3) (4) Note that under reducing conditions (CO and H2 with no oxygen present) and with increased concentrations of NO, the formation of HCN and NH3 increases. These compounds were subsequently oxidized across the oxidation catalyst and produced up to 250 ppmv NOx • However, by using slightly less than stoichiometric air in step 3, so that the remaining NOx could react with excess combustibles (resulting in about 2000 ppmv CO) across the catalyst in step 4, NOx levels were reduced to less than 10 ppmv. This emission level was well below the 25 ppmv NOx target -2- |