Development of removal Apparatuses of Exhausted Gases by Using Microwave Discharge and Photochemical Processes

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The NO removal by a microwave-absorbent assisted discharge of an NO/N_2 mixture has been studied at NO and N_2 flow rates of 10 and 1000 sccm, respectively. Although discharge could be not be maintained at high N_2 pressure above 50 Torr without using microwave absorbents, stable microwave discharge could be maintained at an atmospheric pressure by using such a microwave absorbent as graphite, Zr, or W rod. One long rod or two short rods of absorbents were inserted into the center of the microwave cavity. Conversion of NO obtained by using two rods was higher than that by using one rod, though the branching ratios of such oxides as CO, CO_2, ZrO_2, and WO_3 were higher in the former case. A high NO conversion of 97% was achieved by using two short rods of graphite.Photochemical removal of N_2O and NO_2 by 193 am ArF excimer laser has been investigated in N_2 or air at atmospheric pressure. N2_O was nearly completely converted to N_2 and O_2 without NOx emission in N_2 and air at a low N_2O concentration of 100 ppm after laser irradiation for 15 mm at a laser power of 100 mJ/pulse. A reasonable agreement was found between experimental results and calculated values, indicating that our model calculation was valid. NO_2 was efficiently converted into N_2, O_2, and NO in N_2 or air in the NO_2 concentration range of 240-3000 ppm at a laser power of 80 mJ/pulse, and the relative formation ratios of N_2:NO in N_2 and air were 1:0.38〜0.79 and 1:0.41〜0.63, respectively. NO_2 was completely oxidized into N_2O_5 in air at low NO_2 pressure of 100 ppm. The major conversion process in air in this low NO_2 pressure range was oxidation of NO_2 into N_2O_5 via NO_3 due to effects of O_3.