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脱除实验，并对实验结果进行了分析。本工作的主要结论如下：(1)阻挡放电通常具有丝状微放电模式。由于高能电子自由基的形成只发生在较薄的微放电通道中，我们认为尽可能地减小这种微放电，增加微放电的次数，才能获得更好的NO去除性能。我们发现，随着阻挡材料温度的升高或使用丙烯酸酯阻挡层，阻挡放电模式由灯丝模式转变为类辉光模式。利用非常简单的针面放电装置，研究了阻挡层材料温度改变放电模式的原因。我们发现表面放电随温度而变化，并且在表面d…的顶部。电荷量越大，就会出现一些类似放电的发光模式。这一现象被认为是导致放电方式改变的原因。(3)作为一种新的方法，我们制作了一个实验系统，用来测试放电、催化和氨气的组合效果。氨是由溶解在水中的尿素加热超过160℃而产生的。进行了各种实验，结果表明，氨气、放电和催化三者联合使用，可以在相对较低的温度下(如200℃)直接还原尾气中的NOx，而不排放的催化剂在400℃以上的温度下工作。即使在废气中添加氨并进行等离子体处理，脱除NOx的性能也没有得到改善。(4)废气再循环(EGR)显著降低了发动机的NOx排放。因此，如果在等离子体处理之前采用EGR，将会减轻等离子体工艺的负荷。结果表明，10%的EGR可以将等离子体过程的能量降低到不使用EGR时的1/4。研究了利用废气再循环技术实现脱氮器的自动控制。通过控制放电装置的放电功率和EGR率，可以将出口NO浓度控制在一个较低的恒定水平。(5)对于等离子体工艺的综合评价，我们认为EGR和臭氧注入相结合是最好的。它可以将等离子体能量降到最低，满足了工业对能耗的需求。它可以实现比传统方法低得多的NOx水平控制。尿素、排放和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。然而，排放装置的高温运行并不稳定，尿素作为氨源还需要额外的成本。较少

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