【作者】 冯发达；

【导师】 闫克平；

【作者基本信息】 浙江大学 ， 环境科学， 2014， 博士

【摘要】 挥发性有机物(VOCs)是一种重要的空气污染物。我国人为源VOCs排放总量很大,典型行业的VOCs污染非常严重。针对大风量、低浓度的VOCs,传统治理技术的应用受到投资、运行费用及效率等因素的制约。低温等离子体催化技术被认为是VOCs处理中很有发展前途的技术之一。低温等离子体的产生方法很多,如电晕放电、脉冲放电、介质阻挡放电、电子束、微波等。目前的等离子体发生方法,仍难于同时满足高能量效率和经济可靠的供电电源这两个条件。采用等离子体处理VOCs会产生如CO、O3、NOx和气溶胶等副产物,结合催化剂能够控制气相副产物,但前段产生的气溶胶会引起催化剂的失活。针对等离子体发生技术和处理VOCs中存在的问题,本文主要研究一种采用直流电源供电的等离子体发生方法,通过反电晕放电在蜂窝催化剂上产生等离子体；基于反电晕等离子体发生方法,提出由催化剂反电晕结合前置介质阻挡放电模块及后置催化剂模块组成的VOCs处理工艺系统。主要研究内容和结论如下：(1)研究了蜂窝催化剂反电晕放电的特性和放电机制。催化剂反电晕放电,不仅在催化剂沿面产生等离子体,同时还在蜂窝孔道内产生等离子体；中间辅助网电极能够限制电流的发展,使反电晕放电更均匀,其电压值在放电过程不断变化和调整,有利于反电晕等离子体的发生。负电晕放电可实现稳定的反电晕放电；不同的蜂窝孔径、催化剂种类、蜂窝厚度以及湿度等因素都对反电晕等离子体产生影响。在施加电压为30kV、放电电流为12.7μA/cm2的条件下,反电晕放电的离子风流速可达1.99m/s,气流通过蜂窝催化剂后,流速仍达0.5m/s。催化剂反电晕放电的臭氧产量与电流密度正相关；采用AgMnOx/Al2O3催化剂反电晕去除甲苯,在能量密度为285.6J/L时,去除效率为94.8%。催化剂反电晕能够捕集和降解气溶胶；在电压为30kV,电流358μA条件下,颗粒物的收集效率为94.0%。(2)研究了两段式反应器去除正已烷时,催化剂种类、能量密度、湿度、温度等因素的影响。AgMnOx催化剂对正已烷的去除效率、等离子体催化协同作用、相同臭氧消耗量时的正已烷去除量、臭氧需求因子均具有明显的优势。(3)采用列管DBD、BCD和催化剂组成等离子体催化复合体系去除VOCs.该工艺能够克服等离子体催化处理VOCs产生的气溶胶引起的不利影响；催化剂反电晕放电能够有效利用放电离子风,有利于克服催化剂床层阻力引起的压降。列管DBD的臭氧产率和甲苯去除效率分别为4.08和0.40molecules/heV.等离子体处理VOCs产生的气溶胶主要成分为C-C和C-H。结合催化剂反电晕放电后,臭氧和甲苯去除效率均提高。(4)等离子体中,VOCs的去除主要是自由基反应过程,其去除效率和等离子体能量密度成线性关系。更多还原

【Abstract】 Volatile organic compounds (VOCs) is an important air pollutant. The total anthropogenic source VOCs emission in China is very large, and the VOCs pollution in typical industry is very serious. For the large flow and low concentration of VOCs, the application of traditional control technology is restricted by the factors such as investment, operation cost and removal efficiency. The non-plasma catalysis technology is considered to be one of the promising technologies for VOCs treatment. There are several techniques to generate non-thermal plasmas, such as corona discharge, pulsed corona, dielectric barrier discharge (DBD), electron beam and microwave, etc.. Nowadays, the plasma generation techniques are still difficult to satisfy both the conditions of high energy efficiency and the economic and reliable power supply. By-products such as CO, ozone, NOx and aerosol can be produced in the plasma VOCs treatment process. By combined with the catalyst, plasma catalysis can control the gas phase by-products, but the aerosol produced in the plasma process can induce the deactivation of catalyst.On the problems of plasma generation technology and VOCs treatment, plasma generation method powered by DC power source is studied in this work. For this method, the plasma is generated on honeycomb catalyst in the process of back corona discharge. Based on the back corona plasma generation method, a hybrid VOCs treatment system consists of back corona discharge reactor combined with a tubular DBD reactor up-stream and catalyst bed down-stream is proposed.The main research contents and results are as follows:(1) The characteristics of the back corona discharge on honeycomb catalyst and the discharge mechanism are investigated in this section. Based on back corona discharge on honeycomb catalyst, the plasmas are generated both of along the surface and in the channel of honeycomb catalyst. Middle auxiliary electrode can limit the development of current and produce uniform back corona plasma. The changing and adjusting of voltage value in middle auxiliary electrode is benefit the generation of back corona plasma.By using the negative corona discharge, stable back corona discharge can be realized. The factors of honeycomb pore size, catalyst type, thickness of honeycomb, and humidity can affect the back corona plasma generation. A flow velocity of1.99m/s of ionic wind can be realized in BCD at an applied voltage of30kV and a discharge current density of12.7μA/cm2. And at the downstream of honeycomb catalyst, flow velocity of0.5m/s still can be achieved.The ozone generation of back corona discharge on catalyst is directly proportional to the discharge current. For AgMnOx/Al203catalyst,94.8%toluene removal efficiency is observed at the specific input energy of286J/L. The total particle weight removal efficiency is about94%at the applied voltage of30kV and discharge current of358μA.(2) For removal of n-hexane in two-stage plasma catalysis reactor, the influences of catalyst type, energy density, humidity, and temperature are investigated in this section. The AgMnOx catalyst has a higher performance of n-hexane removal efficiency, plasma catalysis synergy effect, the removed amount of the n-hexane at the same ozone consumption, the ozone demand factor.(3) The hybrid plasma catalysis reactor mainly consists of3stages that are the tubular DBD reactor, back corona discharge reactor and catalyst bed. This hybrid process can overcome the adverse effect of aerosols produced in the process of plasma catalysis for VOCs removal. The ionic wind due to the back corona discharge can be actively used to reduce the pressure drop of the reactor.The G-value of ozone generation and toluene removal in tubular DBD reactor is about4.08molecules/heV and0.40molecules/heV, respectively. The C-C and C-H are the main components of aerosols produced in plasma process for VOCs removal. Both of ozone decomposition and toluene removal efficiency are improved by combined with back corona discharge on catalyst.(4) The main reaction of VOCs removal is radical reaction process in plasma. The amount of the pollutant removed is directly proportional to the plasma energy density.更多还原