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近年来,发展高效低耗的挥发性有机化合物(volatile organic compounds,VOCs)脱除技术迫在眉睫。目前,已形成系列VOCs排放控制技术,包括物理吸附法[1-2]、等离子体法[3-6]、生物处理法[7-8]、氧化法[9-11]等。其中,等离子体法因其脱除效率高、反应迅速、且无二次污染等优点被认为有一定应用前景。等离子法是利用如滑动电弧、脉冲电晕、介电屏障等对空气放电产生·OH和臭氧等强氧化性物质,将VOCs氧化为清洁小分子碎片(CO2、H2O、H2等),以实现VOCs的脱除。而该方法中,强氧化自由基O3和·OH的含量对VOCs脱除效率有重要影响[12-15]。ZHU等[16]采用介质阻挡放电脱除苯时发现,生成的O3浓度与苯脱除率呈正相关。亦有研究表明,O3和·OH能有效脱除烷烃、苯、甲苯等VOCs[17-19],甚至多环芳烃和二恶英[20-21]。
目前,VOCs脱除领域的研究多较为宏观,对微观层面的温度、浓度、速度场的模拟计算等内容较少。随着计算流体力学(CFD)的发展[22],如Fluent等仿真软件可用于实际工程应用中,以降低设计成本、缩短开发时间等[23]。MOUSAVI等[24]对实验室规模的生物质锅炉进行CFD模拟,研究并确定了氮氧化物形成的不同途径及其贡献。TEODOSIU等[25]将办公设备产生的VOCs排放进行CFD模拟,并分析其健康风险。
O3和·OH对甲苯脱除的反应机理类似[26-27]。由于甲基的活化,O3和·OH均优先攻击甲苯的1,2c—c键位和2碳位,之后在O3和·OH的破坏下,苯环开始断裂。本研究以甲苯作为典型VOCs,利用化学反应耦合CFD方法对VOCs脱除效率的提升进行研究,探索O3/·OH对甲苯的脱除规律,分析影响脱除效率的关键因素,以期确定含甲苯焚烧废气脱除净化的较优反应条件,为实际工业应用提供参考。
O3/·OH簇射烟气脱除甲苯的数值模拟
Numerical simulation study on toluene removal by O3/·OH radical shower in flue gas
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摘要: 利用Fluent软件耦合化学反应机理对O3与·OH簇射烟气脱除甲苯进行了数值模拟。针对圆形面为入射面的圆柱形管道,通过模拟计算不同位置截面上的甲苯平均浓度,得到管道各个位置的甲苯脱除效率。在不同温度、射流速度、气体组分、自由基配比等工况条件下,模拟研究O3/·OH对甲苯的脱除规律,分析影响O3/·OH对甲苯脱除效率的关键因素。结果发现,提升温度对脱除效率有较大提升,而自由基浓度、射流速度、水分浓度与氧气浓度等参数均对脱除甲苯效率均有一定影响。由于在复杂的烟道系统中O3具有更长的活性周期,因此,比·OH有更高的甲苯脱除效率,约4%的优势。当O3和·OH混合配比为20%时,脱除效率较其他配比情况要高出约5%,这表明·OH和O3可协同进行甲苯脱除。本研究可为优化含甲苯的焚烧废气脱除净化技术提供参考。Abstract: The removal of toluene by O3/·OH radical shower in flue gas was simulated numerically using Fluent software coupled with chemical reaction mechanism. The removal efficiency of toluene in the different cylindrical pipe was obtained by simulating the average toluene concentration on different sections of the cylindrical pipe with the circular surface as the incident surface. The removal of toluene by O3/·OH was simulated under different operating conditions such as temperature, jet velocity, gas composition and free radical ratio, and the key factors affecting the removal efficiency of toluene by O3/·OH were analyzed. The results showed that the removal efficiency was greatly improved by increasing the temperature, and the free radical, water and oxygen proportion, jet velocity had certain effects on the removal efficiency of toluene. Due to the longer activity cycle of O3 radical in complex flue system, O3 has a higher toluene removal efficiency than ·OH, with an advantage of about 4%. When the ratio of O3 and OH was 20%, the removal efficiency was about 5% higher than that of other ratios, indicating that there was a certain synergistic effect between ·OH and O3 radicals. This study can provide reference for optimizing the removal and purification technology of toluene containing incineration waste gas.
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Key words:
- ·OH radical /
- ozone O3 /
- reaction mechansim /
- methylbenzene /
- Fluent simulation
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