Effect of oxygen on nonthermal plasma reactions of nitrogen oxides in nitrogen

Real diesel engine exhaust emission control: indirect non-thermal plasma and comparison to direct plasma for NOX, THC, CO, and CO2

Recently, diesel engine exhaust emission control by non-thermal plasma (NTP) technology has been shown to be promising. However, carbon and soot deposition on the inner surface of the NTP reactor for direct plasma processing decreased the efficiency of the plasma process throughout the experiments. In the present work, the feasibility of indirect plasma processing was investigated as an innovative and novel method compared to direct plasma processing. Air was directed through an NTP at an applied voltage of VP-P  = 7 kV and a flow rate of 1-4 L/min, and then, it was combined with engine exhaust gas at a flow rate of 5 L/min. In this case, the maximum conversion of NOX was 64.9% at 4 L/min. However, for direct plasma processing at 5 L/min, NO conversion was 58%, which proves that the indirect NTP process can decrease NOX concentration effectively. The maximum conversion for unburned hydrocarbon (UHC), carbon monoxide (CO) and carbon dioxide (CO2) was obtained as 2%, 4% and 0.7% at 4, 2 and 3 L/min in indirect plasma processing; While their remove rate for direct plasma processing was 16.3%, -0.5% and 13.2%, respectively.

Selective Catalytic Reduction of NO by NH3 Using a Combination of Non-Thermal Plasma and Mn-Cu/ZSM5 Catalyst

Dielectric barrier discharge (DBD) could generate non-thermal plasma (NTP) with the advantage of fast reactivity and high energy under atmosphere pressure and low-temperature. The presented work investigated the selective catalytic reduction (SCR) of nitric oxide (NO) using a combination of NTP and an Mn-Cu/ZSM5 catalyst with ammonia (NH3) as a reductant. The experimental results illustrate that the plasma-assisted SCR process enhances the low-temperature catalytic performance of the Mn-Cu/ZSM5 catalyst significantly, and it exhibits an obvious improvement in the NO removal efficiency. The reaction temperature is maintained at 200 °C in order to simulate the exhaust temperature of diesel engine, and the 10% Mn-8% Cu/ZSM5 catalyst shows the highest NO removal performance with about 93.89% at an energy density of 500 J L−1 and the selectivity to N2 is almost 99%. The voltage, frequency and energy density have a positive correlation to NO removal efficiency, which is positively correlated with the power of NTP system. In contrast, the O2 concentration has a negative correlation to the NO removal, and the NO removal efficiency cannot be improved when the NO removal process reaches reaction equilibrium in the NTP system.

Reaction kinetic study of nonthermal plasma continuous degradation of acetone in a closed-loop reactor

Nonthermal plasma (NTP) degradation has been shown to be a promising method for volatile organic compounds (VOCs) removal from air. However, there have been few studies on the degradation of indoor VOCs using NTP, and even less on their reaction kinetics. In this study, NTP degradation of acetone, a representative of oxygenated VOCs, in a closed-loop reactor operating in recirculation mode was investigated. Acetone and organic by-products were characterized in real-time by proton transfer reaction time-of-flight mass spectrometry. The results showed that approximately 85.7% of the acetone degraded within 7.5 h with dielectric barrier discharge treatment at 4.3 W. Methanol, acetaldehyde, formic acid, and acetic acid were observed to be the main organic byproducts with concentrations time-dependent on the order of ppb/ppm. The concentrations of the inorganic by-products O₃ and NO₂ are also time-dependent and can decrease to nearly 0 after a sufficient degradation time. Based on the concentration measurement in real-time, several rate laws were used to fit the concentration variations of acetone and the organic by-products, and it was observed that they strictly followed the simple kinetic reaction rate laws: acetone followed the first-order rate law, and formic acid formation followed the one-half-order rate law, etc. This study provides a good example of characterizing NTP removal of VOCs in airtight spaces and has important theoretical and practical significance in designing a better NTP device, predicting NTP degradation reaction rate, and accelerating the practical application of NTP technology for indoor air treatment.

Application of Non-Thermal Plasma for NOx Reduction in the Flue Gases

Over the years, ever more stringent requirements on the pollutant emissions, especially NOX, from combustion systems burning natural gas are introduced by the European Union (EU). Among all NOX reduction methods, the flue gas treatment by plasma is widely applied and could be used for both small scale and domestic combustion systems. However, the removal efficiency depends on concentrations of oxygen, water vapor, traces of hydrocarbons, and nitrogen oxides in flue gas. In order to analyze the application of the NOX reduction for small-scale or domestic combustion systems, experiments of NOX reduction by non-thermal plasma from real flue gases originating from premixed methane combustion at different equivalence ratio (ER) values were performed. It was determined that the residual oxygen in flue gas plays an important role for improvement of NO to NO2 oxidation efficiency when O2 concentrations are equal to or higher than 6%. The power consumption for the plasma oxidation constituted approximately 1% of the burner power. In the case of ozone treatment, the addition of O3 to flue gas showed even more promising results as NO formed during combustion was fully oxidized to NO2 at all ER values.

Nitrogen oxide removal by non-thermal plasma for marine diesel engines

The transportation industry plays an important role in the world economy. Diesel engines are still widely used as the main power generator for trucks, heavy machinery and ships. Removal technology for nitrogen oxides in diesel exhaust are of great concern. In this paper, a gas supply system for simulating the marine diesel engine exhaust is set up. An experimental study on exhaust denitration is carried out by using a dielectric barrier discharge (DBD) reactor to generate non-thermal plasma (NTP). The power efficiency and the denitration efficiency of different gas components by NTP are discussed. The exhaust gas reaction mechanism is analyzed. The application prospects of NTP are explored in the field of diesel exhaust treatment. The experimental results show that the power efficiency and energy density (ED) increase with the input voltage for this system, and the power efficiency is above 80% when the input voltage is higher than 60 V. The removal efficiency of NO is close to 100% by NTP in the NO/N₂ system. For the NO/O₂/N₂ system, the critical oxygen concentration (COC) increases with NO concentration. The O₂ concentration plays a decisive role in the denitration performance of the NTP. H₂O contributes to the oxidative removal of NO, and NH₃ improves the removal efficiency at low ED while slightly reducing the denitration performance at high ED. CO₂ has little effect on NTP denitration performance, but as the ED increases, the generated CO gradually increases. When simulating typical diesel engine exhaust conditions, the removal efficiency increases first and then decreases with the increase of ED in the NO/O₂/CO₂/H₂O/N₂ system. After adding NH₃, the removal efficiency of NO_x reaches up to 40.6%. It is necessary to add reducing gas, or to combine the NTP technology with other post treatment technologies such as SCR catalysts or wet scrubbing, to further increase the NTP denitration efficiency.

The experimental study on exhaust denitration is carried out by using dielectric barrier discharge (DBD) reactor to generate non-thermal plasma (NTP).

Conversion of dilute nitrous oxide (N2O) in N2 and N2–O2 mixtures by plasma and plasma-catalytic processes

Production and conversion of N₂O occur simultaneously, with production and conversion being dominant at room and high temperature, respectively.

Novel electrostatic precipitator using unipolar soft X-ray charger for removing fine particles: Application to a dry de-NOX process

The novel electrostatic precipitator (ESP), consisting of a soft X-ray charger and a collection part, was demonstrated and applied to a dry de-NOX process to evaluate its performance in by-product particle removal. NOX gas was oxidized by ozone (O3) and neutralized by ammonia (NH3) sequentially, and finally converted to an ammonium nitrate (NH4NO3) aerosol with ∼ 100-nm peak particle diameter. The unipolar soft X-ray charger was introduced for charging the by-product particles in this dry de-NOX process. For the highest particle collection efficiency, the optimal operating conditions of the soft X-ray charger and collection part were investigated by adjusting the applied voltage of each device. The results showed that ∼ 99% of NOX was removed when the O3/NOX ratio was increased to 2 (i.e., the maximum production conditions of the NH4NO3 by-product particles by the gas-to-particle conversion process). The highest removal efficiency of particle (∼ 90%) was observed with operating conditions of positive polarity and an applied voltage of ∼ 2-3 kV in the charger chamber. The unipolar soft X-ray charger has potential for particle removal systems in industrial settings because of its compact size, ease of operation, and non-interruptive charging mechanism.

The byproduct generation analysis of the NOx conversion process in dielectric barrier discharge plasma

Abatement of NO_x through non-thermal plasma (NTP) processes has been developed over the past several years.

High-efficiency removal of NOx using a combined adsorption-discharge plasma catalytic process

A combined adsorption-discharge plasma catalytic process was used for the removal of NO(x) using zeolites as catalysts without external heating. It was found that the types of plasma carrier gases exert great effect on the conversion of adsorbed NO(x). The conversion of adsorbed NO(x) is much lower in N(2) plasma than in Ar plasma, which is attributed to the reverse reaction, NO(x) formation reaction. The momentary increase of oxygen species derived from the decomposition of adsorbed NO(x) is considered to be the main cause as their collisions with nitrogen species can generate NO(x) again. Thus, solid carbon was added to the catalyst to act as a scavenger for active oxygen species to improve the conversion of adsorbed NO(x) in N(2) plasma. A NO(x) removal rate of 97.8% was obtained on 8.5wt.% carbon mixed H-ZSM-5 at an energy efficiency of 0.758 mmol NO(x)/W·h.