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Several exhaust gas regulations are being implemented to prevent the hazardous emissions of volatile organic compounds (VOCs) and particulate matter (PM) from paint and print factories. The VOCs generate photochemical oxidants and suspended PM, such as PM2.5, which has become a global environmental problem. We evaluate the catalytic nonthermal plasma (NTP) technique for controlling the emission of VOCs. The article proposes a wet-type catalysis plasma reactor to extend the treatment of water-soluble VOCs. Initial evaluation of the proposed technique involves simultaneous removal of nanoparticles along with individual VOCs, toluene, acetaldehyde, acetic acid, and ammonia, at a relatively high gas flow rate of 10 L/min. Further, pellets of α-alumina and TiO2 spheres are employed in the NTP reactors for assessing their catalytic performance. We install an MnO2 catalytic reactor downstream of the plasma reactor for ozone removal. Simultaneous treatment of typical VOCs and nanoparticles using dry and wet-type catalytic NTP reactors shows that the wet-type reactor has superior average particle collection efficiency of 100%. However, the dry-type NTP with α-alumina shows a higher toluene removal efficiency of 91% compared to 73% in the wet type. Further, the respective removal efficiencies for acetaldehyde, acetic acid, and ammonia are 100%, 100%, and 95%. Notably, the toluene removal efficiency drops to 65% with the TiO2 catalyst. [ABSTRACT FROM AUTHOR]

This study developed a highly efficient electrostatic precipitator (ESP) type air conditioner to reduce the particulate matter (PM) concentration in a subway station. A polyethylene terephthalate film coated carbon sheet nonmetallic electrode was used as a collection plate to reduce the weight instead of the metallic collection plate, and the carbon fiber ionizer was used to minimize the ozone generation. When the flow velocity in a duct was 1 m/s with −5.0 kV applied to the ionizer and −5.0 kV to the collection plates, the 0.3-μm PM0.3 removal efficiency increased up to 97.47%. Holes in the collection plates were used to attach connecting tubes to maintain a constant distance. The strength and shape of the electric field were analyzed using COMSOL. The electric field quickly dissipated in the hole areas, and the field strength converged to 0. The collection plates were extended to compensate for the reduced collection area due to the holes. As a result, when the flow rate in the duct was 1 m/s, −5.0 kV was applied to the ionizer, and the electric field strength was up to −1.5 kV/mm, the PM0.3 removal efficiency was increased to 99.08%. This behavior resembled that of conventional collection plates. The ESP developed in this study corresponds to a higher MERV13 grade than the MERV10 grade filter currently installed in the air conditioner of the subway station and has almost no pressure drop, so it is expected to contribute to the improvement of air quality and energy efficiency of subway stations. [ABSTRACT FROM AUTHOR]

A two-stage electrostatic precipitator (ESP) with a reduced footprint, external ion-injection discharge, and water film on the collection plate was developed for long-term operation. For optimal particulate matter (PM) removal efficiency, the ionizer of the external ion injection system was fixed at a distance of 5 mm from the bias plate. Under these operating conditions, the 0.3-μm PM (PM0.3) removal efficiency was reduced to approximately 70% due to low migration velocity. The application of an additional collection plate extended the residence time of the charged particles in the electric field, which resulted in a removal efficiency exceeding 95%. However, long-term operation (675 min) of the two-stage ESP with external ion-injected discharge resulted in spark generation due to contamination of the ionizer, and the PM2.5 and PM10 removal efficiencies decreased linearly from 80.4% to 62.2% and 87.7% to 68.2%, respectively. Changing the ionizer to a pin shape with electrical specifications similar to those of carbon fibers resulted in water film formation on the collection plate. The PM2.5 and PM10 removal efficiencies remained at their initial levels for 120 min. The two-stage ESP with external ion-injected discharge operating with a water film is likely suitable for long-term operation in an industrial setting. [ABSTRACT FROM AUTHOR]

An integrated electrostatic precipitator (ESP) and wet scrubber system were developed to control nitrogen oxides (NOx) and particulate matter (PM) emissions from a semiconductor manufacturing process. The integrated system consisted of a NO oxidizer, wet scrubber, and ESP. In the NO oxidizer, NO gas was fully oxidized to NO2 by O3 before the flow gas entered the wet scrubber. To control NO2, Na2S was used as a reducing agent, and NaOH was added to suppress H2S in the wet scrubber. The NO2 removal efficiency could be controlled by maintaining an oxidation-reduction potential higher than −330 mV, and H2S was suppressed by keeping the pH higher than 11. To ensure there was no PM peak during the cleaning cycle, dual-type cylindrical collection plates containing a water film were designed. A negative voltage of 15 kV was applied to the collection plate, and the PM removal efficiency was higher than 95%. The experimental particle-removal efficiency was higher than the theoretical value because the ion loading by plasma in the point of use scrubber was greater than the theoretically calculated value. In addition, the PM removal efficiency was maintained at 95% for 60 min through the water film. The integrated ESP and scrubber system were able to control NOx and PM for long periods at a removal efficiency of over 95%. [ABSTRACT FROM AUTHOR]

An effective NOx-reduction aftertreatment system for a marine diesel engine that employs combined nonthermal plasma (NTP) and adsorption is investigated. The system can also treat particulate matter (PM) that employs a diesel particulate filter (DPF) and its regeneration by NTP-induced ozone. The effect of the combined reduction of accumulated PM and NOx is studied. The marine diesel engine of interest provides an output power of 1 MW at 100% of the engine load. The NOx reduction is composed of repeated adsorption and desorption flow processes using NTP combined with NOx adsorbents. With a view toward practical use, experiments on a higher number of cycles are carried out. The amount of adsorbents is 105 kg, which is greater than that in the authors’ previous study. As a result, NOx reduction efficiency by NTP is higher than in the previous study and is greater at higher amounts of adsorbents owing to higher NOx desorption. Furthermore, DPF regeneration with plasma-induced O3 injection is achieved simultaneously. This aftertreatment system demonstrates an excellent energy efficiency of 114 g(NO2)/kWh. The present aftertreatment can generate a synergistic effect of PM and NOx reduction. [ABSTRACT FROM AUTHOR]

Indoor air quality was improved by controlling particulate matter (PM) consisting of components such as house dust and bacteria, using an atmospheric pressure plasma. Two types of electrode, which generate corona discharges, were placed inside a reactor and energized to generate a nonthermal plasma, i.e., a disc-type reactor and a needle-type reactor. A plasma can decompose harmful substances by various active species such as reactive radicals (e.g., N^\ast,\;O^\ast,\;\and\;OH^\ast) and ions, and a strong electric field. The particle collection rate depended on the discharge voltage, number of mesh filters, flow rate, and reactor characteristics. The dust-collecting rate in the case of the disc-type reactor was 95% and in the case of the needle-type reactor was 98%. Formaldehyde removal was also performed to confirm the improved performance of the nonthermal plasma and reduction of formaldehyde to below the permitted value of 0.08 ppm. [ABSTRACT FROM AUTHOR]

A simultaneous reduction of particulate matter (PM) and \NOx emitted from diesel engines has been realized by means of a barrier-type packed-bed nonthermal plasma (NTP) application driven by a pulse high-voltage power supply under oxygen-lean conditions. \BaTiO3 particles having a large dielectric constant ( \sim10 000) are used as packed pellets, and carbon PM is loaded among the pellets. \NOx is reduced by N radicals, and PM is incinerated by oxygen radicals induced either by \NO \rm x or by ozone (\O3) reduction under elevated local temperatures among the pellets. From the photographs of the pellets, it can be confirmed that the carbon PM or soot is removed under the condition of lean oxygen, resulting in the simultaneous removal of the PM and \NOx. An optimal value for the mass of the loaded PM exists, and when the loaded PM mass is greater than a threshold value, the effect of the NTP induced by the partial discharge is too weak to simultaneously reduce the PM and \NOx. Under the optimized plasma condition, the experiment yields energy efficiencies of 2.2 g/kWh for the PM incineration and 4.3 \g(\NO2)/\kWh for the \NOx reduction in the experiment. [ABSTRACT FROM AUTHOR]

Over the years, we have investigated particulate matter (PM) and NOx. reduction using nonthermal plasma-chemical hybrid processes without using catalysts. Among nonthermal plasma hybrid processes, the ozonizer combined with the chemical hybrid reactor was investigated using a 479 cc (5.5 kW) power generation diesel engine. The PM deposited on the diesel particulate filter can be incinerated by ozone and NO2 in a wide range of flue gas temperature. The NO was oxidized to form NO2 by ozone, and NO2 was reduced by the 3% Na2SO3 chemical reactor. As the results, PM deposited on both metal and ceramic filters were successfully removed even at ambient temperature. The rate of PM incineration depends on the amount of ozone injected and was significantly higher than the rate of PM generation. Using 2.4% ozone concentration with a flow rate of 10 L/min, 82% of NO having 720 L/min was oxidized to NO2, and 78% of NO,. was removed as a chemical scrubber. However, NOx removal was deteriorated about 10% after 1-h operation. This was attributed to Na2SO3 oxidation by air, which was evidenced by the reduction of pH in the chemical reactor. [ABSTRACT FROM AUTHOR]