Removal of NOx from Combustion Exhaust gas by Using Radicals in Arc Plasma

利用混合电弧等离子体中产生的自由基，发展了一种脱除燃烧废气中NOx的技术。通过将混合气体(Ar+NH_3)、(Ar+H_2)和(Ar+柴油)送入弧等离子体炬中，产生氨、氢和柴油中的NH_2、NH、HC、N、H等自由基，这些自由基分别与模拟废气(N_2+NO)和(Air+N_2+NO)在反应器中混合。当气体中不含O2时，NO的减少是由于生成了无害的产物N_2、H_2O和CO_2。在目前的实验条件下，热脱除NOx过程以及氨、氢和柴油的氧化是不可取的。在气体(空气+N_2+NO)的情况下，NOx随着等离子体输入功率的增加而增加。实验考察了等离子体输入功率、NH_3/NO、H_2/NO和柴油/NO摩尔比、阴极长度和气体流量对NOx脱除效率的影响。实验结果表明：(1)NOx脱除效率随等离子体输入电压的增大和喷嘴出口与排气管的距离比L/d的减小而增大。当氢、氨和柴油的摩尔比大于化学计量比时，在模拟废气(N_2+NO)的情况下，NOx的脱除率随NH_2、NH、H、N、HC等自由基的增加而增加。(2)对于氧气浓度为3.2%的模拟废气(空气+N_2+NO)，在氧气浓度为4.2%时，氮氧化物浓度随氢或柴油的喷射而降低，而当氧气浓度为4.2%时，NO_x被氨基减少，而在柴油喷射的情况下，阳极喷嘴上有沉积。

A technique for removing the NOx contained in combustion exhaust gas has been developed by using radicals produced in the mixing arc plasma. By feeding the gas mixture (Ar+NH_3), (Ar+H_2) and (Ar+diesel oil) into arc plasma torch, ammonia, hydrogen and diesel oil radicals such as NH_2, NH, HC, N, H are produced, and these radicals are mixed in a reactor with the simulated exhaust gases (N_2+NO) and (Air+N_2+NO) respectively. The NO decreases as a result of the formation of the innocuous products N_2, H_2O and CO_2 when the O_2 is not contained in the gas. Under present experimental conditions, the thermal De-NOx process and the oxidation of ammonia, hydrogen and Diesel oil are not expected. In the case of the gas (Air+N_2+NO), NOx increase with increasing input power to plasma. The effects of input power to plasma, molar ratio NH_3/NO, H_2/NO and diesel oil/NO, cathode length and gas flow rate on the NOx removal rate are investigated experimentally.Experimental results are summarized as follows ;(1) The NOx removal rate increases with increasing input voltage of plasma and with decreasing the distance ratio L/d between nozzle exit and exhaust pipe. When the hydrogen, ammonia and diesel oil injections at a molar ratio greater than stoicheiometric value, the NOx removal rate increases with increasing of these radicals such as NH_2, NH, H, N, HC in the case of simulated exhaust gas (N_2+NO).(2) As for the simulated exhaust gas (Air+N_2+NO) under a oxygen concentration of 3.2 %, the NOx concentration decreases by hydrogen or diesel oil injections, and the NOx decreases by ammonia radicals at a oxygen of 4.2 %, while the deposits on the anode nozzle are observed in the case of diesel oil injection.