NO Oxidation Efficiency Research Articles

High-Efficiency Removal of NOx From Flue Gas by Multitooth Wheel-Cylinder Corona Discharge Plasma Facilitated Selective Catalytic Reduction Process

In this paper, a plasma-assisted selective catalytic reduction (SCR) process was employed for the conversion of nitrogen oxides (NO x ) from flue gas to nitrogen (N2) and water (H2O) using V2O5-WO3/TiO2 catalyst over a broad reaction temperature (125 °C–550 °C) range. Ammonia (NH3) was used as a reducing agent, and nonthermal plasma was generated in a multitooth wheel-cylinder corona discharge reactor driven by a dc power supply. In order to optimize the geometry of the corona discharge reactor, the discharge power and the NO oxidation efficiency were compared for different discharge gaps and sawtooth slice numbers of the multitooth wheel electrode, respectively. The effects of reaction temperature, water vapor, and SO2 concentration on the plasma facilitated SCR of NO x were also investigated. The experimental results showed that shorter discharge gap (11 mm) appeared to be more advantageous with respect to NO oxidation. NO oxidation efficiency was less affected by sawtooth slice number. The plasma-assisted SCR process enhanced the catalytic activity of SCR catalyst and exhibited a remarkable improvement in NO x removal efficiency at a temperature range of 125 °C–300 °C. The presence of water vapor in plasma-assisted SCR process significantly improved the NO x removal, especially at low temperature. The addition of SO2 suppressed the NO x removal in plasma-assisted SCR process; however, the NO x removal was greatly promoted by the presence of SO2 and H2O, indicating that water vapor can significantly ameliorate the SO2 inhibiting effect in the plasma-assisted SCR process.

Removal of NO in Mist by the Combination of Plasma Oxidation and Chemical Absorption

A coaxial nonthermal plasma (NTP) reactor was used for oxidizing and removing NO in mist. The effects of gas/mist components on O3 formation, NO oxidation, and NOx removal by NTP in simulated flue gas after wet desulfurization were investigated. The presence of mist results in the significant decrease of O3 concentration. Formation of active species, such as OH and HO2, would promote the reactions between NO and OH/HO2. Thus, the NO oxidation, NOx removal, and energy efficiency are significantly improved in the presence of mist. The promotion effects of mist component on the NO oxidation and NOx removal follow the order: Na2SO3 mist > FeSO4 mist > Na2SO4 mist. Increase of the mist pH can enhance the absorption of nitrogen oxides with the mist. Adding SO2 to the gas mixtures or raising the NO2/NOx ratio of simulated gas increases the NOx removal efficiency. This process demonstrates that NO oxidation by NTP and subsequently absorption by mist are feasible and have great value to practical application.

Correlation of morphology with catalytic performance of CrOx/Ce0.2Zr0.8O2 catalysts for NO oxidation via in-situ STEM

The influence of drying condition on the formation of Ce0.2Zr0.8O2 was investigated and the NO oxidation efficiency over them was evaluated. These catalysts were investigated in detail by means of X-ray diffraction (XRD), High resolution transmission electron microscope (HR-TEM), Brunauer–Emmett–Teller (BET) surface area analysis, X-ray photoelectron spectroscopy (XPS) and NO(O2) Temperature-programmed desorption (NO(O2)-TPD). The results demonstrated that the slow drying rate caused by the decrease of the temperature and the use of the vacuum benefited for more Zr doped into CeO2 lattice and hence generated more Ce3+ on the surface, thus benefitting for the adsorption amount of O2. TEM results display the special morphology of the catalysts, which prepared under the conditions of slow drying rate. Gas-cell in-situ STEM confirms that the slow drying rate and the nature of the solvent made the particles growing along the (111) facet and finally displayed the coralloid particles. The coralloid catalysts prepared at the low drying temperature in the vacuum oven exhibited the highest NO oxidation efficiency, which reached 50.54% at 350°C.

NO 산화를 위한 Mn계 촉매상 과산화수소 분해를 이용한 건식산화제 생성

The NO oxidation process has been applied to improve a removal efficiency of NO included in exhaust gas. In this study, to produce a dry oxidant for the NO oxidation process, the catalytic H2O2 decomposition method was proposed. A variety of the heterogeneous solid-acidic Mn-based catalysts were prepared for the catalytic H2O2 decomposition and the effect of their physico-chemical properties on the catalytic H2O2 decomposition were investigated. The results of this study showed that the acidic sites of the Mn-based catalysts has an influence on the catalytic H2O2 decomposition. The Mn-based catalyst having the abundant acidic sites within the wide temperature range in NH3-TPD shows the best performance for the catalytic H2O2 decom- position. Therefore, the NO oxidation efficiency, using the dry oxidant produced by the H2O2 decomposition over the Mn-based catalyst having the abundant acidic properties under the wide temperature range, was higher than the others. As a remarkable result, the best performances in the catalytic H2O2 decomposition and NO oxidation was shown when the Mn-based Fe2O3 support catalyst containing K component was used for the catalytic H2O2 decomposition.

Simultaneous removal of SO2 and NOx with ammonia combined with gas-phase oxidation of NO using ozone

A process for simultaneous desulfurization and denitrification was proposed, which was made up of ozone as the oxidizing agent for NO and ammonia solution as absorbent. The results showed that the presence of SO2 and the concentration changes of NO and SO2 have little impact on the oxidation of NO, the oxidation efficiency of NO can achieve over 90% when the molar ratio of O3/NO is 1.0. The presence of NOx had little effects on the absorption of SO2, an appropriate increase of SO2 concentration was favorable to the NOx absorption. The removal efficiency of SO2 and NOx reached 99.34% and 90.01% at pH 10, flow rate 0.95 Nm3/h, n[O3]/n[NO] 1.0, initial SO2 concentration 2000 mg/Nm3, initial NO concentration 200 mg/Nm3, ammonia concentration 0.3%, oxygen content of the simulated flue gas 12%, oxidation reaction temperature 423K and absorption reaction temperature 298K in the experimental system.

Behavior of Oxidizing Substances on NO Gas Oxidation in Fenton System

There are variety of active substances in Fenton system, such as H2O2, HO2-, O2-·, ·OH and HO2·. In this paper, the oxidation of H2O2, HO2-, O2-·, ·OH and HO2· on NO gas was determined respectively with experimental methods. The results showed that direct oxidation of gaseous NO by H2O2, HO2- and O2-·was weak. ·OH and HO2· had strong oxidizing capacity on gaseous NO, especially ·OH. With the acceleration of ·OH and HO2· generation rate, the oxidizability of Fenton system on NO gas was stronger, but O2 generation rate also accelerated. Rapid decomposition of H2O2 is the premise to realize high NO oxidation efficiency using H2O2, but how to avoid the invalid decomposition of H2O2 is the key to increase use ratio of H2O2.

Experimental Study on Simultaneous Desulfurization and Denitrification by Ozone Oxidation Combined with Alkaline Wastewater Washing

It is important to develop low cost and efficient technique for simultaneous removal of SO2and NOXfrom flue gas. In this paper, ozone oxidation and alkaline wastewater washing process was employed for flue gas desulfurization and denitrification in a 75t/h coal-fired boiler. In order to optimize the operation parameters for SO2and NOXremoval, the influence of several parameters, such as molar ratio of [O3]/[NO] and flue gas temperature on the oxidation rate of NO, oxidation rate of NO, alkaline water level in aeration tank, alkaline water rate and mole ratio of [NaOH/ (SO2+NOx)] on the removal efficiency of SO2and NOXhave been studied. The experimental results showed that molar ratio of [O3]/[NO] had limited effect on the oxidation of SO2, while NO oxidation efficiency improved with the increase of [O3/NO] molar ratio and it reached to ~ 90% at molar ratio of [O3]/[NO] = 1.4. Flue gas temperature performed slight influence on the oxidation of NO in the range of 60 to 120 °C, and had adverse impact on the removal of SO2and NOX. NOXremoval rate was enhanced with increasing NO oxidation rate and achieved to a high level at NO oxidization rate of ~50%. Mole ratio of [NaOH/ (SO2+NOx)] had significant impact on the removal rate of NOX, while it showed limited effects on that of SO2. The increase of alkaline aeration water level and alkaline water rate would definitely lead to a higher removal rate for both SO2and NOX. An optimized removal rate of 93.6% for SO2, 77.6% for NOXand 99.1% for dust were obtained under the water level of 20cm and volume of 74.5t/h.

Activated carbon fibers loaded with MnO2 for removing NO at room temperature

Abstract MnO 2 loaded on activated carbon fibers (MnO 2 @ACF) were successfully prepared using co-precipitation methods, the as-prepared MnO 2 @ACF were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), temperature-programmed desorption (TPD), X-ray photoelectron spectroscopy (XPS) and N 2 adsorption/desorption analysis. The results showed that MnO 2 particles were highly dispersed with a strong interaction between MnO 2 particles and ACFs. MnO 2 loaded on ACF can promote the catalytic oxidation efficiency of NO into NO 2 remarkably, the loaded amount of MnO 2 has an obvious effect on the NO oxidation efficiency over MnO 2 @ACF. The optimal amount of MnO 2 for MnO 2 @ACF is 3.64 wt.%, and the oxidation efficiency of NO was increased from 20.1% over A15 to 30.6% over MnO 2 @ACF.

Simultaneous Removal of NO and SO2 from Flue Gas by Ozone Oxidation and NaOH Absorption

Exhaust flue gas from fossil fuel combustion usually contains a large quantity of SO2 and NO. In this paper, a process of simultaneous removal of NO and SO2 by ozone oxidation combined with NaOH absorption was chosen. The main investigations involved O3 decomposition, factors affecting NO oxidation (O3 dosage, reaction temperature, NO initial concentration, and presence of SO2), and NaOH absorption. The results indicated O3 decomposition rate increased as temperature rose and was less affected by initial concentration of O3. The optimal temperature for NO oxidation was 150 °C. NO oxidation efficiency increased with the increase of O3 dosage at a fixed temperature. NO initial concentration and the presence of SO2 had a slight effect on NO oxidation. The NO oxidation efficiency remained above 90% when nO3/nNO was 1. Absorption by NaOH solution resulted in the final removal of above 99% NO, 90% NO2, and nearly 100% SO2 at pH above 11.

Experimental Study on NO Pre-Oxidation in C<sub>3</sub>H<sub>6</sub>/NO/N<sub>2</sub>/O<sub>2</sub> Mixture by Non-Thermal Plasma

By using self-designed non-thermal plasma reactor, the influences of discharge power, initial concentration of C3H6 and O2 concentration on NO pro-oxidation in C3H6/NO/N2/O2 mixture were studied. The obtained results indicate that with the increasing of discharge power, NO2/NOx ratio grows firstly and then decreases after reaching a peak value, while NOx conversion efficiency and N2O concentration gradually rise. Increasing initial concentration of C3H6 or O2 concentration would help to enhance NO oxidation efficiency. With the same discharge power, NOx conversion efficiency grows with the increasing of C3H6 initial concentration while reduces with the increasing of O2 concentration. Controlling the concentration of C3H6 and O2 in exhaust gas can lead the NO2/NOx ratio to reach 50%, which is benefit to NOx conversion with SCR system.

Hydrocarbon Assisted NO Oxidation with Non-thermal Plasma in Simulated Marine Diesel Exhaust Gases

The NO oxidation performance in a non-thermal plasma (NTP) reactor under realistic synthetic exhaust gas compositions is investigated. The gas compositions differ mainly in the NO–NO2 ratio and represent different modes of operation of a marine diesel engine. It is found that the maximum NO oxidation efficiency is independent on the NO–NO2 ratio. Up to 55 % of the NO is mainly oxidised to NO2 in all gas mixtures being analysed. However, the specific energy density needed to reach the highest NO oxidation varies with the gas composition between 15 and 60 J/L. The performance of the NTP-reactor was significantly improved by the addition of propene (C3H6) acting as an additional oxidising agent. The energy consumption for NO–NO2 conversion was found to be between 20 and 45 eV/NO, depending on the ratio of the added propene as well as the initial concentrations of nitrogen oxides.

Pulsed corona discharge driven by Marx generator: Diagnostics and optimization for NOx treatment

A compact, repetitive Marx generator with an external trigger is constructed and coupled with a wire-to-plate corona reactor for a positive pulsed corona discharge studies. The reactor resistance and capacitance behavior during the pulse was observed. It was found that the reactor's capacitance increases three times during the pulse due to the streamer propagation from anode to grounded electrode. Using the time development of the capacitance and resistance during the pulse and the reactor inter-electrode distance, the streamer velocity has been calculated to be 1 × 106 m/s, for system arrangement presented in this work. As an indicator of chemical activity of pulsed corona, ozone production was measured. Emission spectroscopy measurements in the UV region were performed to detect species that appear in the discharge and to determine vibrational and rotational temperatures, which are found to be 3200 K and 340 K respectively. As a measure of pollution control potential of the constructed pulsed corona system, NO oxidation efficiency was investigated and compared with results presented in literature. It was shown that pulsed corona systems with significantly longer pulse durations are competitive with several times shorter pulse duration systems, which implies that chemical efficiency of secondary streamers is comparable with efficiency of primary streamers.

Study of Geometry Structure on a Wire–Plate Pulsed Corona Discharge Reactor

The wire-plate pulsed corona discharge reactor has been regarded as the plasma reactor with highest efficiency for controlling pollutants such as NO and SO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> in flue gas with high-voltage and short-duration positive pulsed corona discharge. A laboratory-scale pulsed corona discharge reactor with wire-plate electrode configuration is established for optimizing the geometry structure of the wire-plate plasma reactor. In this paper, three different methods are used to optimize the wire-to-wire distance and wire-to-plate distance of the plasma reactor. There are experiments with different conditions including various electrical parameters, streamer parameters, and NO oxidation efficiency. The same results are obtained from all the three experiments. The results indicate that short wire-to-plate distance should be adopted to increase the input energy of the plasma reactor but not too short to cause spark discharge in the reactor. Moreover, the wire-to-wire distance should be at least twice as large as wire-to-plate distance, to reduce the interferences between adjacent wire electrodes.

Diesel Lean NOx-Trap Thermal Aging and Performance Evolution Characterization

The work described in this paper focuses on the impact of thermal aging on NOx trap structure and functions. They were evaluated on a Synthetic Gas Bench (SGB) and correlated with the analysis of the structural and chemical evolution of the catalyst. A FTIR Operando study allowed to further analyse the mechanisms occurring on the catalyst surface and highlight the most critical points. NOx trap samples were hydrothermally aged in a furnace up to 900°C under an oxidising flow. The main following impacts on the material were highlighted: reduction of the surface area, sintering of Pt yielding a decrease of the NO oxidation efficiency and hence of the NOx storage capacity, and a loss of CO and HC conversion, barium structural evolution into BaAl2 O4 also being partly responsible for the loss of NOx storage capacity. Other possibilities for loss of NSC are: the transition of -Al2 O3 to -Al2 O3 and the evolution of Ba crystalline structure which needs further analysis. Both XRD and surface IR Operando studies show that hydrothermal aging has a rather homogeneous impact on all materials: alumina phase transition and BaAl2 O4 production, which all lead to a partial decrease of all storage sites.

Oxidation and Removal of NO From Flue Gas by DC Corona Discharge Combined With Alkaline Absorption

The effects of discharge polarity, discharge electrode configuration, and O2/CO2 ratio on NO oxidation by nonthermal plasma (NTP) and NOx removal by the combination of NTP and alkaline absorption in simulated flue gas were investigated in a combined system of a wire-cylinder plasma reactor and a bubble absorber. The preoxidation of NO by dc corona discharge is effective in promoting the NOx absorption. Both the NO oxidation efficiency and the NOx removal efficiency increase with the increase of applied voltage. The positive dc discharge exhibits much higher O3 formation and NO oxidation performances than the negative one. The increase of the discharge zone length and tooth slice number significantly influences the energy density in the plasma reactor and improves the NO oxidation efficiency for a fixed applied voltage. Increasing the O2/ CO2 ratio in the simulated flue gas obviously enhances the NO oxidation and NOx removal.

NO Catalytic Oxidation Behaviors over CoOx/TiO2 Catalysts Synthesized by Sol–Gel Method

CoOx/TiO2 catalysts synthesized by sol–gel method were investigated for the oxidation of NO to NO2 in excess oxygen. NO oxidation efficiency increased sharply as oxygen concentration increased, while NO concentration showed a negative effect. Under the conditions of 30,000 h−1 GHSV, 600 ppm NO, 4% O2, 9% CoOx/TiO2 (450) had the highest NO oxidation efficiency and reached the equilibrium at 300 °C with a conversion of 79.8%. The XPS results determined that Co3O4 was the main active phase in 9% CoOx/TiO2 (450) prepared by sol–gel method.

Simultaneous oxidation of NO, SO2 and Hg0 from flue gas by pulsed corona discharge

A process capable of simultaneously oxidizing NO, SO2, and Hg0 was proposed, using a high-voltage and short-duration positive pulsed corona discharge. By focusing on NO, SO2, and Hg0 oxidation efficiencies, the influences of pulse peak voltage, pulse frequency, initial concentration, electrode number, residence time and water vapor addition were investigated. The results indicate that NO, SO2 and Hg0 oxidation efficiencies depend primarily on the radicals (OH, HO2, O) and the active species (O3, H2O2, etc.) produced by the pulsed corona discharge. The NO, SO2 and Hg0 oxidation efficiencies could be improved as pulse peak voltage, pulse frequency, electrode number and residence time increased, but they were reduced with increasing initial concentrations. By adding water vapor, the SO2 oxidation efficiency was improved remarkably, while the NO oxidation efficiency decreased slightly. In our experiments, the simultaneous NO, SO2, and Hg0 oxidation efficiencies reached to 40%, 98%, and 55% with the initial concentrations 479 mg/m3, 1040 mg/m3, and 15.0 microg/m3, respectively.

Non-catalytic Oxidation of NO to NO2 by Addition of Alcohol

An experimental study on the non-catalytic NO oxidation using methanol, ethanol, or acetaldehyde as an additive was performed, and the results were investigated by numerical analysis and sensitivity analysis using a chemical reaction model. It is found that the maximum NO oxidation efficiency when employing methanol is greater than 0.85, whereas the maximum using ethanol is approximately 0.6. Although it is known that methanol and ethanol have different oxidation reaction routes, non-catalytic NO oxidation may even be realized using the latter. Moreover, relative to utilizing alcohol, lower oxidation efficiency are observed using acetaldehyde. Thus, employing alcohols with ignition points above 600 K may be suitable for the non-catalytic NO oxidation.

Simultaneous removal of NO x, SO 2 and Hg in nitrogen flow in a narrow reactor by ozone injection: Experimental results

A process capable of removing NO x , SO 2 and mercury simultaneously was proposed, which utilizes the injection of ozone and assist with a glass made alkaline washing tower. Experiments were conducted in a quartz flow reactor within an electrical heated furnace. Oxidation properties of NO and Hg, removal efficiency of NO and SO 2 behind the washing tower were investigated. Results show that the oxidation efficiency of NO and Hg greatly depends on the amounts of ozone injected. With the increasing amounts of ozone added to the main flow, NO and Hg oxidation efficiency all improved individually. About 85% of NO can be oxidized with 200 ppm of ozone added and 89% of elemental Hg can be oxidized with 250 ppm of ozone added. The optimal temperature for NO oxidation should be lower than 473 K, and the optimal temperature range for mercury was 473 K to 523 K. The appearance of SO 2 has little effect on the NO oxidation process. NO has priority compared to mercury when react with ozone. With the assistance of washing tower, about 97% of NO and nearly 100% of SO 2 can be removed simultaneously with 360 ppm of ozone added.

Two-stage catalyst system for selective catalytic reduction of NOx by NH3 at low temperatures

Three catalysts, 1wt.% Pt/Al2O3, 20wt.% Cu/Al2O3, and 1wt.% Pt–20wt.% Cu/Al2O3 were evaluated for the oxidation of NO by O2 and the selective catalytic reduction (SCR) of NOx by NH3 in the absence and presence of H2O. The Pt/Al2O3 catalyst exhibited the largest values in NO oxidation efficiency and NOx removal efficiency among the three catalysts. The presence of H2O caused a drop in the NO oxidation and the SCR activities. The SCR performance was significantly improved when Pt/Al2O3 and Cu/Al2O3 catalysts were employed sequentially in a reactor. The highest SCR performance was achieved using two separate stages: oxidation of NO by O2 over the Pt/Al2O3 catalyst followed by reduction of NO2 by NH3 over the Cu/Al2O3 catalyst. Under the condition with H2O, the two-stage catalyst system showed NOx removal efficiency over 80% at low temperatures below 200°C, which was the highest value among the catalyst systems used in this study. The physical and chemical properties of the catalysts were determined using nitrogen adsorption, XRD, TPR, and pulse CO chemisorption experiments.