Inlet NO Concentration Research Articles

Global Kinetic Modelling of a Supplier Barium- and Potassium-Containing Lean NOx Trap

Kinetic modeling, in combination with flow reactor experiments, was used in this study to simulate a supplier lean NOx trap (LNT). The LNT catalyst used is a commercial catalyst that contains barium and potassium as storage components. The results presented in this paper are a continuation of a previous study, where a global kinetic model for NOx storage was developed for a model Pt/Rh/BaO/Al2O3 catalyst. In this work, a simplified model is used, where NO oxidation, nitrite, and nitrate formation are lumped together into one reaction, and the model predicts the total NOx. In this model, only one reaction step must be tuned for each storage component: that is, in our case, one reaction for the formation of barium nitrate and one reaction for potassium nitrate. A broad range of experimental conditions was used when developing this model; five temperatures (200, 300, 400, 500, and 600 degrees C) and three different inlet NO concentrations (100, 200, and 300 ppm) were used. Water and CO2 were present in all experiments, because these can affect the storage behavior. The reductant used in the regeneration period was CO. Long lean and rich cycles were used to capture the kinetics of the reactions accurately. The model was able to describe all 15 experiments well and could adequately capture the amount of stored NOx during the lean period and the NOx conversion during the rich period, including the NOx breakthrough peak that occurred at the beginning of the rich period. The model was validated with short lean-rich cycling experiments, where the lean period was 30 s and the rich period was 2 s. The model could predict the outlet NOx concentration well, and the error for the average conversion was only 1%-2% in the validation simulations.

Design of a DBD wire-cylinder reactor for NO x emission control: experimental and modelling approach

The objective of this work was to develop a wire-cylinder dielectric barrier discharge reactor for NO x removal from a gas mixture simulating exhaust gases. NO conversion was investigated as a function of parameters such as high voltage (HV) electrode material, dielectric material, NO concentration and reactor gap. A complete decomposition path is proposed from 18O 2 isotope experiments. Finally, a model consisting of ‘Continuous Stirred Tank Reactors’ (CSTR) cascade with multiple injections of atomic oxygen is proposed in order to explain the relationships between the reactor parameters (inlet flow, inlet NO concentration, electrical energy density and electrical gap) and the experimental results (outlet NO x concentration). Optimization of the model parameters permitted the authors to fit experimental and calculated results with a maximum absolute error of about 5% on NO conversion.

Reducing nitric oxide into nitrogen via a radio-frequency discharge

NO/N 2/O 2/H 2O mixtures are usually converted into HNO 3 and/or NO 2 using different discharge approaches. In this study, a radio-frequency discharge was successfully used to reduce NO mainly into N 2 at a low pressure (4 kPa). The influences of experimental parameters, including carrier gas, inlet concentration of NO, O 2, steam, and applied power, are discussed. At least 95.7% of the total N atoms converted from NO into N 2. Other traces of byproducts were N 2O and HNO 2, but neither HNO 3 nor NO 2 were detected. In addition, conversion of NO apparently increased with elevated applied power or decreased inlet concentration of O 2, reaching 92.8% and 74.2% for the NO/N 2/O 2 (2%) and NO/N 2/O 2 (6%)/H 2O (10%) mixtures, respectively, at 120 W. In addition, from the optical emission spectra, a large amount of N 2 (first positive band and second positive band) and NO (γ system) were observed, and the important reactions for NO removal and N 2 formation are proposed.

Catalytic activation of ceramic filter elements for combined particle separation, NOx removal and VOC total oxidation

The development of a catalytically active filter element for combined particle separation and NOx removal or VOC total oxidation, respectively, is presented. For NOx removal by selective catalytic reduction (SCR) a catalytic coating based on a TiO2–V2O5–WO3 catalyst system was developed on a ceramic filter element. Different TiO2 sols of tailor-made mean particle size between 40 and 190nm were prepared by the sol–gel process and used for the impregnation of filter element cylinders by the incipient wetness technique. The obtained TiO2-impregnated sintered filter element cylinders exhibit BET surface areas in the range between 0.5 and 1.3m2/g. Selected TiO2-impregnated filter element cylinders of high BET surface area were catalytically activated by impregnation with a V2O5 and WO3 precursor solution. The obtained catalytic filter element cylinders show high SCR activity leading to 96% NO conversion at 300°C, a filtration velocity of 2cm/s and an NO inlet concentration of 500vol.-ppm. The corresponding differential pressures fulfill the requirements for typical hot gas filtration applications. For VOC total oxidation, a TiO2-impregnated filter element support was catalytically activated with a Pt/V2O5 system. Complete oxidation of propene with 100% selectivity to CO2 was achieved at 300°C, a filtration velocity of 2cm/s and a propene inlet concentration of 300vol.-ppm.

토양 Bio-Filter를 이용한 질소산화물 제거특성

Soil biofiltration is an environmentally-sound technology for elimination of VOCs, odorous and NOx compounds from a low concentration, high volume waste gas streams because of its simplicity and cost-effectiveness. This study was performed to evaluate effect of removal of gaseous NOx using a soil and a yellow soil. Over of NOx from a soil and a yellow soil was removed at the inlet NO concentrations of ppb, respectively. The bio-filter using a soil media was capable of purifying NOx with a different natural processes. Although some of the processes are quite complex, they can broadly be summarized as adsorption into soil pore water, and biochemical transformations by soil bacteria. When the filteration bio-reactor was applied to a soil and a yellow soil, effective NOx removal was obtained for several times and months. These results show that a soil biofilter can be of use as an alternative advanced NOx treatment system.

Characteristics of reducing NO using urea and alkaline additives

The reduction of nitric oxide using urea solution combined with alkali salt additives has been studied in a flow tube. The inlet concentration of NO was 500 ppm, with airflow rates of 3 and 5 L/min. Reduction of NO was studied from 650 to 1050 °C with urea solutions of 0.3 to 1 mol/L. The efficiency of reduction of NO increased by 44% in the presence of urea alone. A further increase in efficiency was observed in the presence of NaOH as additive; in fact, efficiency increased by more than 25 and 75% when 0.5 and 1 mol/L NaOH, respectively, were added with the urea solution. The efficiency of reduction of NO increased with all additives, but descended in the order NaOH, Na 2CO 3, NaNO 3, HCOONa, and CHCOONa. The maximum efficiencies of NaOH and NaNO 3 are 74 and 73%, respectively.

NOxAbatement by Catalytic Traps: On the Mechanism of NOxTrapping Under Automotive Conditions

NO x adsorption was measured with a barium based NO x storage catalyst at an engine bench equipped with a lean burn gasoline direct injection engine (GDI). In order to study the influence of gas phase NO2 on the NO x storage efficiency two different precatalysts were used: One with excellent NO oxidation activity to produce a high NO2 concentration and another pre-catalyst without NO oxidation activity and therefore high NO concentration at the NO x storage catalyst inlet. Both pre-catalyst had excellent HC and CO conversion efficiency and therefore the CO and HC concentration at the NO x storage catalyst inlet was practically zero. No lean NO x reduction was observed. Under that conditions, experiments with NO x storage catalysts of different length show that a high NO2 inlet concentration did not enhance the NO x storage efficiency. Moreover, we observed reduction of NO2 to NO over the NO x storage catalyst. However, in presence of a high NO inlet concentration NO2 formation was observed which may proceed parallel to NO x storage.

627 DME燃焼排気ガスのNOx触媒による浄化におけるN_2Oの生成(OS5-6 環境負荷とエンジン・燃焼システム-2)(OS5 環境とエネルギー問題)

The formation of N_2O in the catalytic purification of simulated DME engine exhaust gas is investigated. Main parameters are catalytic reactor temperature and NO inlet concentration. The results show that there is a possibility of the considerable N_2O formation in the process of catalytic NO reduction. The amount of N_2O formation changes with NO concentration in the simulated exhaust gas, and then shows the maximum value as a function of catalyst temperature. Therefore, N_2O formation characteristic during NOx reduction is very important factor in the performance evaluation of the NOx catalyst for DME engine exhaust gas.

The Role of Ammonium‐Sulfur Aerosols on Nitrogen Oxides Removal by Pulsed Corona Enhanced Wet Electrostatics Precipitation with Ammonia and Ozone Injection

AbstractThe removal of nitrogen oxides (NO and NO2) has been investigated in a bench‐scale pulsed‐corona enhanced wet electrostatic precipitator (wESP). The 70 Hz pulsed voltage is applied up to 60 kV. Simulated flue gases with NOx concentration up to 1200 pp m have been used to determine the feasibility of NOx removal in the wESP. NO must be oxidized to NO2 before any removal takes place. NOx removal efficiency increased with gas residence time, inlet NO concentration and applied corona power. In the air stream with 10 seconds gas residence time, up to 20% of 1000 pp m NO (22% of NOx) was removed at a 20 watt pulsed corona. The amount of in‐situ ozone was not enough to be considered as a major NOx removal mechanism in this wESP. Ozone injection improved the NOx removal for both the corona and non‐corona cases by oxidizing NO. With 300 pp m of ozone, the removal of 750 pp m NO was increased from 18% to 50% by oxidation, but total NOx removal was improved only to 25%.However, very high NOx removals were measured in simulated flue gas that contained ammonia, sulfur dioxide and ozone. For instance, in a 3% oxygen, 11% CO2 simulated flue gas with 800 pp m NO and 70% relative humidity at 8.6 sec of gas residence time, 30 kV corona discharge, the removal efficiency of NO was only 5%. Injecting NH3 only (NH3/NOx ratio 1) at 32 watts corona power, NO removal was increased to 10%. With the co‐presence of 2400 pp m SO2, 200 pp m ozone injection (no ammonia) increased NO removal to 36% by oxidation, but total NOxremoval only to 17%. After co‐injecting 312 pp m ozone and 2900 pp m NH3 (stoichiometry ratio 0.53), total N0X removal was increased to 79%. It was determined that the ammonium salt aerosols produced from the reaction of ammonia and sulfur dioxide enhanced the NOx removal substantially. The significance of this catalyzing effect by the in‐situ ammonium salt aerosols is addressed in this paper.

Low temperature interactions between hydrocarbons and nitric oxide: An experimental study

Gas reburning is a NO x control technique that can be applied in different combustion systems. In it, gas is injected into the furnace downstream of the primary burners to form a substoichiometric zone followed by the injection of burnout air. The variables that influence the chemistry in the reducing zone (temperature between 900 and 1450 K, reburn fuel type, stoichiometry, NO concentration and residence time), which is mainly controlled by the interactions between hydrocarbon radicals and NO, have been studied in a laboratory scale flow reactor. A significant NO reduction efficiency can be obtained with proper operating conditions. The NO destruction is closely coupled to the hydrocarbon oxidation regime, which differs depending on the hydrocarbon fuel considered, and NO is to a significant extent converted to HCN. The concentration of hydrocarbons and oxygen, and the temperature are important parameters affecting the results obtained, whereas the inlet NO concentration and the residence time only have a minor effect. The practical implications of the present results for gas reburning are discussed.

96/05241 Experimental study and modeling of the influence of the inlet NO concentration in the natural gas reburning process

96/05241 Experimental study and modeling of the influence of the inlet NO concentration in the natural gas reburning process

Trade-Off Between NOx and N2O in Fluidized-Bed Combustion of Coals

NO and N 2 O formation and destruction was studied in a laboratory-scale fluidized-bed combustor for a set of coals ranging from lignite to anthracite. For a given coal, the sum of fuel-N conversions to N 2 O and NO was found to be remarkably constant over a range of temperatures, although emission levels of individual species were strongly temperature-dependent (NO increases and N 2 O decreases with increasing temperature). A similar behavior was observed for the formation of NO and N 2 O during combustion of chars. This trade-off between N 2 O and NO emissions can be regarded as a constant conversion of fuel-bound nitrogen to N 2 . The influence of NO addition on the formation of N 2 O and N 2 was investigated in packed-bed gasification experiments using char prepared from a bituminous coal. The inlet concentration of NO was at a level typical for fluidized-bed combustion. It was found that NO reduction on char surface was strongly enhanced in the presence of oxygen. The majority of the added NO was converted to N 2 , but some N 2 O was also formed. The temperature-governed trade-off between emissions of NO and N 2 O, and the formation of N 2 O and N 2 from NO reduction, are qualitatively explained on the basis of known heterogeneous and homogeneous NO/N 2 O chemistry.

The catalytic reduction of nitric oxide over supported ruthenium catalysts

The activity of supported ruthenium catalysts for reducing NO to N 2 in an exhaust-like feedstream has been examined in laboratory experiments. The rate and temperature of NO removal is largely dependent on the NO inlet concentration and independent of the concentration of reducing agents in the system. The selectivity for nitrogen formation, however, is dependent on the concentration of the reducing agents CO and H 2 as well as the concentration of NO. No evidence was found for an ammonia intermediate in the conversion of nitric oxide to elemental nitrogen over ruthenium. The high selectivity of ruthenium for the NO to N 2 conversion is explained and compared with the behavior of platinum and palladium catalysts.