Removal Of VOCs Using Non-thermal Plasmas Assisted By Adsorption Or Catalysis

With the industry developing, the emission of hazardous gasous pollutants grows fast, especially the emission of volatile organic compounds (VOCs), which causes detrimental influences on both human health and global environment. Non-thermal plasma (NTP) techniques have great industrial potential for VOCs removal with relatively low power consumption and high removal efficiency. At present, many researches have been focused on NTP techniques applying in VOCs control. In this study, a wire-cylinder dielectric barrier discharge (DBD) reactor was adopted to investigate the decomposition of dimethyl sulfide (DMS), the influence of balance gas on decomposition of DMS and decomposition of DMS by NTP+activated carbon (AC). A laboratory scale experiment on removal of leather industrial waste gas was carried out. A demonstration project on spray painting VOCs control by NTP techniques was established. The main conclusions of this paper are as follows:(1) Under the experimental condition, the conversion of DMS increases with a increasemnt of peak voltage, pulse frequency and resident time. High initiate concentration causes a reduction of DMS conversion. However, energy cost decreases with increasing of the initial DMS concentration. In the cases of DMS removal, the main byproducts are NOx, SO2 and O3. The concentration of O3 and NOX in outlet gas decreases and SO2 concentration increases with an increasement of the initial DMS concentration. The selection of SO2 is enhanced at a higher peak voltage. High energy electrions and free radicals play important roles in decomposition of DMS in NTP.(2) The breakthrough voltage of DMS in Ar is lower than that of DMS in N2, both of which are proportional to the gas pressures. The breakthrough voltage in this DBD reactor with DMS in air is 2.4 kV at a 1 atm. At a fixed peak voltage, DMS in smaller dielectric strength balance gas is easier to decomposition by NTP. The humidity in balance gas strongly affects DMS decomposition by NTP. Proper humidity improves conversion and energy efficiency. The highest DMS removal efficiency is achieved with the gas stream containing 0.3 vol% H2O in air. Oxygen plays an important role in decomposition of DMS in NTP. Oxygen reacts with high energy electrons to form O3 and O radical, resulting in boosting DMS decomposition. The presence of O2 in balance gas determines the amount of NOx, SO2 and O3 produced.5% oxygen is the optimum concentration in decomposition of DMS, due to relatively higher conversion of DMS and fewer yields of O3, NOx and SO2.(3) Peak voltage and initial dimethylamine (DML) concentration are important factors that influence the DML removal efficiency and energy yield. The conversion of DML of 761 mg/m3 reaches 100% at a peak-voltage of 41.25 kV. Higher oxygen content (0-21%) promotes production of active species such as ozone, leading to higher DML conversion. Humidity enhances the amount of OH radicals and inhibits ozone production in reactor, which codetermines the optimum humidity of 0.3% under the experiment conditions (0-0.8%). When DML and DMS were decomposed together, synergistic actions exist in the processes, leading to higher conversion, higher energy yield and less byproducts formation. The energy yield is promoted from 2.13 to 5.20 mg/kJ.(4) The DMS exhausted AC is regenerated efficiently in the discharge zone by DBD. The regeneration efficiency keeps above 90% after 4 regeneration cycles. The regeneration efficiency increases with the energy density increasing. Under the experimental conditions, an appropriate humidity level in balance gas promotes AC regeneration. A promoting effect of low O2 concentration (<5%) and a adverse effect of high O2 concentration (>5%) on AC regeneration are obtained in the study. DBD process can make surface area, pore volume of AC increase. And successive AC regeneration processes cause wall destruction and pores blockage, resulting in reduction of adsorption capacity. Surface chemistry of AC also plays an important role in adsorption capacity. Increasing carboxylic groups produced by DBD weakens the affinity of DMS toward the surface of AC.(5) NTP assistanted by AC can improve DMS conversion dramasticly. The humidity in balance gas strongly influences DMS decomposition by NTP+AC system.25% of relative humidity is optimum for DMS decomposition in NTP+AC system. NTP+AC system can effectively control the byproducts. NTP at a propriate energy density can modify AC surface and keep AC adsorbable for long term. (6) NTP combined UV can efficiently remove spray painting VOCs. In demonstration project, the emission of waste gas from plant reaches the standard after treatment.