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挥发性有机污染物(volatile organic compounds, VOCs)是生成光化学烟雾、PM2.5的重要前驱体,其种类繁多,部分属于有毒有害物质,会对自然环境和人身健康造成严重危害[1–4]。低温等离子体技术具有常温常压下能产生高能电子和活性物质、处理浓度范围广、对污染物无选择性及操作简单等优点,被广泛应用于对VOCs的处理[5–8]。
低温等离子体降解VOCs是利用放电产生的高能电子、自由基、臭氧等活性粒子,与VOCs分子碰撞后诱导激发其电离及解离,从而实现对VOCs的高效降解。常见低温等离子体反应器主要有电晕放电和介质阻挡放电(dielectric barrier discharge, DBD)两种。传统电晕放电装置常采用产生非均匀电场 (线-筒[9] 、线-板[10]或针-板[11]) 的电极结构。DBD反应器除采用非均匀电场电极的结构外,还可使用产生均匀电场 (板-板[12]、同轴圆筒[13]) 的电极结构。使用传统线-筒反应器处理VOCs的过程中,气体降解产生副产物气溶胶会粘附在线电极表面使放电间距减小,导致火花放电、甚至弧光放电,引起放电等离子体状态的改变,影响降解效果的稳定性,甚至可能导致反应器燃爆。在实际应用中,气溶胶沉积在电极表面会降低设备使用寿命,需要定时清洗或更换电极,造成运行和维护成本的增加。YAO等[14]利用线-板电极降解甲苯时发现,在线电极及板电极周围都会产生黄褐色气溶胶,并且随着时间的增加,气溶胶沉积量增加,颜色变深。ZHANG等[15]利用线-筒式反应器降解苯乙烯时发现随着处理时间和污染物浓度的增加,气溶胶等油类副产物容易沉积在反应器壁和线电极表面,这些沉积物影响了DBD运行状态及其对VOCs的降解性能。KARATUM等[16]观察到使用线-筒式反应器处理VOCs时,线电极表面及出口管呈现黄褐色,同时反应器的出口处积累了大量的深褐色小颗粒,且随着处理时间的增加,沉积物会造成反应器的堵塞。李杰等[17]采用V型收尘极板将电除尘器的粉尘收集区与放电区分开,解决了电除尘器收集高比电阻粉尘反电晕放电问题;有研究者改进了低温等离子体翘片-杆DBD电极结构,将翘片的凹槽用于沉积气溶胶副产物,翘片的刃沿用于产生放电,使DBD在实验时间内对VOCs的处理性能基本稳定[18–21]。但是由于DBD电极结构气隙间距小,会造成处理大流量VOCs污染气体时阻力大的问题。
本课题组将翘片-筒式电晕流光放电等离子体电极结构的放电区域(翘片尖端-筒)与副产物粘附区域(连接翘片的轴线)分开,研究翘片-筒式脉冲放电特性,优化翘片的布置方法,探究反应器对二氯甲烷降解效果及能量效率,以期获得工艺参数最优值,进而考察反应器运行的稳定性及气溶胶沉积情况,从而为低温等离子体处理VOCs废气的性能提升提供参考。
翘片-筒式脉冲电晕流光放电装置对二氯甲烷的降解效果及其稳定性
Degradation effect and system stability of dichloromethane by fins-cylinder pulse corona streamer discharge
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摘要: 传统结构线-筒式电晕放电装置在降解VOCs时生成的副产物会粘附在放电区域(线电极)上,使得放电间距减小,导致降解效果不稳定。翘片-筒式脉冲电晕流光放电等离子装置的电极结构可将放电区域(翘片尖端-筒)与副产物粘附区域(连接翘片的轴线)分开,从而维持装置的放电强度和稳定性。当翘片-筒式脉冲电晕流光放电反应器相邻翘片间距/放电间距为1,在37 kV下,反应器功率为0.95 W,能量体积密度为和23.6 mJ·L−1,为最优电极配置;处理二氯甲烷2 h后的降解效率呈现小幅度下降后稳定在35%。因此,放电形成的气溶胶部分沉积在凹槽处,可维持反应器稳定的放电强度及对二氯甲烷的降解效率。本研究结果可为低温等离子体处理VOCs废气的性能提升提供参考。Abstract: The conventional structure of corona discharge is mainly wire-cylinder, and the by-products generated during the degradation of VOCs will adhere to the discharge area (wire electrode) to reduce the discharge spacing, resulting in unstable degradation effect. Therefore, this study proposed a fins-cylinder pulsed corona streamer discharge plasma electrode structure, which separated the discharge area (tip of fins-cylinder) from the by-product adhesion area (axis connecting the fins)to enhance the system discharge intensity and stability. The results showed that the fins electrode structure with adjacent fin spacing/discharge spacing (A/B=1) was the best electrode design, with highest values of reactor power and energy volume density at 31 kV being 0.98 W and 37.9 mJ·L−1, respectively. The degradation efficiency of dichloromethane decreased slightly after 2 h treatment and then stabilized at 35%. Aerosols produced by the discharge were partially deposited in the grooves without substantially altering the electrode discharge, which guaranteed the stability of the intensity of the discharge and the degradation efficiency of dichloromethane.. This study can serve as a foundation for future research on low temperature plasma treatment of VOC exhaust gas.
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Key words:
- fins-cylinder /
- corona streamer discharge /
- plasma /
- degradation /
- volatile organic compounds(VOCs)
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表 1 气相有机产物组成信息表
Table 1. Information on the composition of gaseous organic products
名称 时间/min 分子式 匹配度 氯甲烷 5.34 CH3Cl 98.5% 乙醇 6.63 C2H6O 99.6% 二氯甲烷 8.20 CH2Cl2 99.1% 2-甲基戊烷 9.98 C6H14 95.4% 三氯甲烷 11.28 CHCl3 93.9% 四氢呋喃 11.82 C4H8O 97.4% 1,2-二氯乙烷 12.27 C2H4Cl2 91.0% 四氯化碳 13.54 CCl4 99.3% 正辛烷 19.64 C8H18 97.4% 庚醛 22.84 C7H14O 95.0% 癸烷 27.32 C10H22 96.3% 壬醛 30.49 C9H18O 90.1% 3-甲基十一烷 34.49 C12H26 97.3% 3-甲基十一烷 34.49 C12H26 97.3% -
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