Chenghang Zheng

Plasma-catalytic removal of a low concentration of acetone in humid conditions

A coaxial dielectric barrier discharge (DBD) plasma reactor has been developed for plasma-catalytic removal of low concentration acetone over MOx/γ-Al2O3 (M=Mn, Co, or Cu) catalysts. The effect of relative humidity of air (RH) on the discharge characteristics, acetone removal efficiency, CO2 selectivity, and byproduct formation with and without catalyst has been investigated. The results show that increasing the RH leads to a decrease of the specific energy density (SED) of the DBD, while packing γ-Al2O3 supported metal oxide catalysts into the discharge gap enhances the SED of the discharge. The maximum acetone removal of 75.3% is achieved at an optimum RH of 10% using CoOx/γ-Al2O3 beyond which the removal efficiency of acetone decreases with the increase of the RH. Higher RH inhibits the formation of energetic electrons while water can be adsorbed onto the catalyst surface and block active sites on the catalyst surface. It is found that increasing the air humidity enhances both CO2 selectivity and carbon balance, but decreases the formation of ozone. However, the formation of NOx slightly increases with increasing the gas humidity. In addition, the presence of these catalysts in the discharge significantly decreases the formation of unwanted byproducts (O3 and NOx) and promotes the deep oxidation of acetone towards CO2 with an increased carbon balance.

Investigation of the promotion effect of WO3 on the decomposition and reactivity of NH4HSO4 with NO on V2O5–WO3/TiO2 SCR catalysts

In this study, we systematically investigated the interaction between NH4HSO4 and WO3-promoted V2O5/TiO2 catalysts in the selective catalytic reduction of NO with NH3, along with the promotion effect of WO3 on the decomposition and reactivity of NH4HSO4 with NO. In the NH4HSO4-deposited samples, WO3 addition increased the electron cloud density around the S atoms in SO42−, which was beneficial for the reduction of S atoms with +6 formal oxidation number, as in NH4HSO4, to those in the +4 oxidation state, as in SO2. Consequently, WO3-doping led to an increase in the amount of SO2 released at low-temperature regions during the heating process as well as an obvious enhancement in the decomposition behavior of NH4HSO4, as illustrated by decreases in temperatures attributed to the weight loss peaks. Meanwhile, the introduced WO3 had a slight promotion effect on the reactivity of NH4HSO4 with NO, together with an inhibitory effect on the production of N2O during the reaction process. Finally, WO3-promoted catalysts exhibited enhanced SO2-resistance.

Fine particle migration and collection in a wet electrostatic precipitator

ABSTRACT Electrostatic precipitation is considered as an effective technology for fine particle removal. A lab-scale wet electrostatic precipitator (ESP) with wire-to-plate configuration was developed to study particle migration and collection. The performance of the wet ESP was evaluated in terms of the corona discharge characteristics, total removal efficiency and fractional removal efficiency. The corona discharge characteristics and particle removal abilities of the wet ESP were investigated and compared with dry ESP. Particle removal efficiency was influenced by discharge electrode type, SO2 concentration, specific collection area (SCA) and particle/droplet interaction. Results showed that the particle removal efficiency of wet ESP was elevated to 97.86% from 93.75% of dry ESP. Three types of discharge electrodes were investigated. Higher particle removal efficiency and larger migration velocity could be obtained with fishbone electrode. Particle removal efficiency decreased by 2.87% when SO2 concentration increased from 0 ppm to 43 ppm as a result of the suppression of corona discharge and particle charging. The removal efficiency increased with higher SCA, but it changed by only 0.71% with the SCA increasing from 25.0 m2/(m3/s) to 32.5 m2/(m3/s). Meanwhile, the increasing of particle and droplet concentration was favorable to the particle aggregation and improved particle removal efficiency. Implications: This work tends to study the particle migration and collection under spraying condition. The performance of a wet electrostatic precipitator (ESP) is evaluated in terms of the corona discharge characteristics, total particle removal efficiency, and fractional particle removal efficiency. The effects of water droplets on particle removal, especially on removal of particles with different sizes, is investigated. The optimization work was done to determine appropriate water consumption, discharge electrode type, and specific collection area, which can provide a basis for wet ESP design and application.

Controllable synthesis of hierarchical MnOx/TiO2 composite nanofibers for complete oxidation of low-concentration acetone

A novel hierarchical MnOx/TiO2 composite nanofiber was fabricated by combining the electrospinning technique and hydrothermal growth method. The synthesized nanomaterial, which comprised primary TiO2 nanofibers and secondary MnOx nanoneedles, was further investigated for complete catalytic oxidation of volatile organic compounds for the first time, and this presented high-oxidation performance on low-concentration acetone. The morphological, structural, physicochemical characterization, and catalytic performance analyses demonstrated that the highest catalytic activity was achieved from the obtained MnOx/TiO2 nanofiber catalyst with 30wt.% manganese loading. This finding can be ascribed to the synergistic effect of the specific hierarchical nanofibrous morphology, the abundant surface-adsorbed oxygen, the superior redox property, and the sufficient specific surface.

Highly efficient removal of sulfuric acid aerosol by a combined wet electrostatic precipitator

Eliminating sulfuric acid aerosol from flue gas is of vital importance to improve air quality. In this paper, a wet electrostatic precipitator (WESP) assisted with novel pre-charger was proposed to efficiently remove sulfuric acid aerosol. Parameters including residence time, gas temperature and SO3 concentration were studied to find the key factors influencing sulfuric acid aerosol removal. Results showed that the removal efficiency of sulfuric acid aerosol increased with the increasing residence time and the decreasing gas temperature. The maximum corona current was reduced from 0.79 to 0.28 mA when the SO3 concentration increased from 0 to 25 ppm, and the removal efficiency also decreased with the increasing SO3 concentration. A novel perforated pre-charger was designed to improve the WESP performance for sulfuric acid aerosol removal. With assistance of the pre-charger, the removal efficiency was improved from 90.3 to 95.8%, and the corresponding emission concentration was lower than 2 mg m−3. Moreover, the removal efficiency could be further improved to 97.8% with a heat exchanger, and the corresponding emission concentration could be lower than 1 mg m−3.

Exploring the role of V2O5 in the reactivity of NH4HSO4 with NO on V2O5/TiO2 SCR catalysts

In this study, attention was focused on the interactions between NH4HSO4 and vanadium species in the selective catalytic reduction (SCR) of NO with NH3, along with the role of vanadium species in the reactivity of NH4HSO4 with NO on V2O5/TiO2 catalysts. Both vanadium and sulfate species occupied the TiO2 surface basic hydroxyl groups; the decreased TiO2 surface basic sites resulting from the introduction of NH4HSO4 in turn promoted the formation of polymeric vanadium species. Given increases in vanadium content, formation of polymeric vanadium species and reactive electrophilic oxygen species on the catalysts occurred, which was an important reason for the enhanced reactivity of NH4HSO4 with NO on the high V content catalysts. Besides, a higher electron cloud density around the S atoms in SO42− could be detected for the high V content catalysts, on which SO42− would be easily reduced to SO2 during the TPSR process. In situ diffuse reflectance infrared Fourier transform spectroscopy confirmed that NH4+ in NH4HSO4 functioned as a reductant during reaction with gaseous NO, while S-containing functional groups were stabilized as tridentate sulfate anions on the catalyst surface.

Experimental investigation of sulfite oxidation enhancement in a micro-pore aeration system

Seawater wet flue gas desulfurization is a promising process for coal-fired power plants. The relationship between sulfite oxidation and different parameters in the process of desulfurization seawater recovery was investigated in a laboratory-scale experimental system. The results suggest that the effect of pH on the KS(IV) shows a trough shape, and the best KS(IV) was achieved in the pH of 5.8. High temperature, salinity and alkalinity show a positive effect on the oxidation of S(IV), whereas the effect of flow rate is more complicated. It is found that micro-pore aeration has a better performance than coarse aeration with low flow rate, which is good for energy savings. In addition, a multi-layer perceptron model has been designed for prediction of the influence of different factors on sulfite oxidation by micro-pore aeration. The results demonstrated that the top five factors were pH, alkalinity, temperature, aeration depth and flow rate.

Experimental study of NO2 reduction in N2/Ar and O2/Ar mixtures by pulsed corona discharge

Non-thermal plasma technology has been regarded as a promising alternative technology for NOx removal. The understanding of NO2 reduction characteristics is extremely important since NO2 reduction could lower the total NO oxidation rate in the plasma atmosphere. In this study, NO2 reduction was experimentally investigated using a non-thermal plasma reactor driven by a pulsed power supply for different simulated gas compositions and operating parameters. The NO2 reduction was promoted by increasing the specific energy density (SED), and the highest conversion rates were 33.7%, 42.1% and 25.7% for Ar, N2/Ar and O2/Ar, respectively. For a given SED, the NO2 conversion rate had the order N2/Ar>Ar>O2/Ar. The highest energy yield of 3.31g/kWh was obtained in N2/Ar plasma and decreased with increasing SED; the same trends were also found in the other two gas compositions. The conversion rate decreased with increasing initial NO2 concentration. Furthermore, the presence of N2 or O2 led to different reaction pathways for NO2 conversion due to the formation of different dominating reactive radicals.

Planar Laser-Induced Fluorescence Diagnostics for Spatiotemporal OH Evolution in Pulsed Corona Discharge

OH radicals play an important role in pollutant removal in nonthermal plasmas. It is crucial to clarify the behavior of OH radicals in this process. A time-resolved 2-D OH radial distribution was investigated in a pulsed corona discharge by planar laser-induced fluorescence at atmospheric pressure and room temperature. The OH evolutions under different gas components were studied, and the evolution process was simulated. The OH decay processes were found to be divided into two periods: a fast decay period and a slow decay period. The O, N, and HO2 are dominant radicals for OH generation and decay. The OH radicals are mainly generated near a nozzle electrode. The concentration variations of O2, NO, and H2O in the background gas led to different OH density evolutions. The OH distribution zones were different as gas components varied. The maximum area of OH radical distribution after discharge decreased by 20% as O2 increased from 5% to 8 %, and it decreased by 69% as NO (150 ppm) was added into the background gas.

Catalytic Oxidation of Dimethyl Sulfide Over Commercial V-W/Ti Catalysts: Plasma Activation at Low Temperatures

This paper investigated the enhancement of plasma on dimethyl sulfide (DMS) removal over commercial V-W/Ti catalysts. The effects of catalyst composition, discharge power, and gas temperature on DMS removal in the plasma-based system were analyzed. The results showed that the V0.9-W/Ti catalyst exhibited the best performance toward DMS removal due to its highest reducibility among the employed samples. The introduction of plasma exhibited a synergistic effect on catalysts and significantly enhanced the removal of DMS over the studied temperature range, especially in high discharge power cases. The activation energy Ea of DMS removal in the presence of plasma was dramatically reduced to less than 10% of the catalysis only case, indicating different DMS removal pathways in plasmaactivated catalysis system. The reaction mechanisms of DMS were also discussed based on the reaction products.