Overall Evaluation of Plasma Exhaust Gas Cleaning Method for Diesel Engine Generator

在原有研究方案的基础上，进行了各种NOx去除实验，并对实验结果进行了分析。以下是本研究的主要结论。(1)阻挡放电通常采用丝状微放电方式。由于高能电子形成自由基只发生在较薄的微放电通道中，我们认为微放电越小越好，微放电次数越多越好，对NO的去除效果越好。我们发现，通过提高阻挡材料的温度或使用丙烯酸阻挡层，阻挡层的放电模式由丝状模式转变为发光模式。结果表明，辉光放电方式对NO的去除率提高了170%。(2)采用非常简单的针平放电装置，研究了阻挡材料温度改变放电方式的原因。我们发现，表面放电随温度的变化而变化，在表面d的顶部，放电更多，出现一些类似辉光的放电模式。这种现象被认为是放电方式改变的原因之一。(3)作为一种新方法，我们制作了一个实验系统，可以测试放电、催化和氨结合的效果。氨是由溶解在水中的尿素加热到160℃以上而产生的。我们进行了各种实验，得出结论：氨、排放和催化的直接组合可以在相对较低的温度下（如200℃）减少废气中的NOx，尽管使用的催化在400℃以上的温度下工作而不排放。即使在废气中加入氨并进行等离子体处理，NOx的去除性能也没有提高。(4)废气再循环（EGR）大大减少了发动机的氮氧化物排放。因此，如果在等离子体处理前应用EGR，将减轻等离子体处理过程的负荷。结果表明，10%的EGR可使等离子体过程的能量降低到未应用EGR的1/4。研制了EGR脱硝装置的自动控制装置。通过控制排放装置的排放功率和EGR速率，可以使排放口NO浓度保持在较低的恒定水平。(5)对等离子体工艺进行综合评价，认为EGR和臭氧喷射相结合的工艺效果最好。可将等离子体能量降至最低，满足工业对能耗的要求。它可以实现比传统方法更低的氮氧化物水平控制。由尿素，排放物和SCR产生的氨的组合具有不需要水洗涤器的优点。等离子体可以显著降低可控硅的工作温度。但是，排放装置的高温运行不太稳定，而且氨源尿素需要额外的成本。少

Based on the original scheme of research, various NOx removal experiments were carried out, and analyzed the results. The followings are the principal conclusion of this work.(1)Barrier discharge usually has a filamentary micro-discharge mode. As the radical formation by high energy electrons occur only in the thin micro-discharge channels, we considered that to make such micro-discharge as small as possible and to increase the number of micro-discharges would be better for NO removal performance. We found that by increasing the temperature of barrier materials or by using acrylic barrier, the barrier discharge mode changed from filamentary mode to glow like mode. The glow like discharge mode was confirmed to increase the NO removal efficiency by 170%.(2)The reason why the temperature of barrier material changes the discharge mode was investigated using very simple needle to plane discharge device. We found that the surface discharge changes with temperature and at the top of surface d … More ischarge, some glow like discharge mode appears. This phenomenon is considered to be a cause of the change of discharge mode.(3)As a new method, we made an experimental system, with which we can test the effect of a combination of discharge, catalysis and ammonia. Ammonia is generated from urea resolved in water by heating it over 160℃. Various experiments were carried out, and we had a conclusion that a combination of ammonia, discharge and catalysis directly can reduce NOx from exhaust gas at relatively lower temperature such as 200℃, although the catalysis used work at the temperature more than 400℃ without discharge. Even if we added ammonia in exhaust gas and plasma treatment was done, the NOx removal performance is not improved.(4)The exhaust gas recirculation (EGR) reduces the emission of NOx from engine considerably. Therefore, if we apply EGR before the plasma treatment, the load of the plasma process will be lightened. It was demonstrated that EGR of 10% could decrease the energy for plasma process to 1/4 of the case without EGR application. The automatic control of NOx removal apparatus using EGR was developed. By controlling the discharge power of discharge device and EGR rate, we can keep the outlet NO concentration to a low constant level.(5)As for over all evaluation of the plasma process, we concluded that a combination of EGR and ozone injection would be the best. It can reduce the plasma energy to minimum, and meets the industrial demand of energy consumption. It can achieve much lower NOx level control than conventional ways. A combination of ammonia generated from urea, discharge and SCR has a merit that the water scrubber is not necessary. Plasma can lower the operating temperature of SCR considerably. However, the higher temperature operation of discharge device is not so stable, and there need another cost for urea for ammonia source. Less