Showing papers on "NOx published in 1998"

Global simulation of tropospheric O3-NOx-hydrocarbon chemistry: 1. Model formulation

Abstract: We describe a global three-dimensional model for tropospheric O3-NOx-hydrocarbon chemistry with synoptic-scale resolution. A suite of 15 chemical tracers, including O3, NOx, PAN, HNO3, CO, H2O2, and various hydrocarbons, is simulated in the model. For computational expediency, chemical production and loss of tracers are parameterized as polynomial functions to fit the results of a detailed O3-NOx-hydrocarbon mechanism. The model includes state-of-the-art inventories of anthropogenic emissions and process-based formulations of natural emissions and deposition that are tied to the model meteorology. Improvements are made to existing schemes for computing biogenic emissions of isoprene and NO. Our best estimates of global emissions include among others 42 Tg N yr−1 for NOx (21 Tg N yr−1 from fossil fuel combustion, 12 Tg N yr−1 from biomass burning, 6 Tg N yr−1 from soils, and 3 Tg N yr−1 from lightning), and 37 Tg C yr−1 for acetone (1 Tg C yr−1 from industry, 9 Tg C yr−1 from biomass burning, 15 Tg C yr−1 from vegetation, and 12 Tg C yr−1 from oxidation of propane and higher alkanes).

Heterogeneous production of nitrous acid on soot in polluted air masses

Abstract: Polluted air masses are characterized by high concentrations of oxidized nitrogen compounds which are involved in photochemical smog and ozone formation. The OH radical is a key species in these oxidation processes. The photolysis of nitrous acid (HNO2), in the morning, leads to the direct formation of the OH radical and may therefore contribute significantly to the initiation of the daytime photochemistry in the polluted planetary boundary layer. But the formation of nitrous acid remains poorly understood: experimental studies imply that a suggested heterogeneous formation process involving NO2 is not efficient enough to explain the observed night-time build-up of HNO2 in polluted air masses1. Here we describe kinetic investigations which indicate that the heterogeneous production of HNO2 from NO2 on suspended soot particles proceeds 105 to 107 times faster than on previously studied surfaces. We therefore propose that the interaction between NO2 and soot particles may account for the high concentrations of HNO2 in air masses where combustion sources contribute to air pollution by soot and NOx emissions. We believe that the observed HNO2 formation results from the reduction of NO2 in the presence of water by C–O and C–H groups in the soot. Although prolonged exposure to oxidizing agents in the atmosphere is likely to affect the chemical activity of these groups, our observations nevertheless suggest that fresh soot may have a considerable effect on the chemical reactions occurring in polluted air.

The impact of nonmethane hydrocarbon compounds on tropospheric photochemistry

Abstract: Nonmethane hydrocarbons (NMHC) play an important role in global scale tropospheric photochemistry. The representation of NMHC chemistry in three-dimensional tropospheric chemistry transport models requires a highly parameterized description of only the most important processes, as the number of reactions and compounds involved is very large. In this paper a chemical scheme is presented, based on the Carbon Bond Mechanism 4 (CBM-4), modified for use in the global Tracer Model 3 (TM3). The original scheme has been extended with reactions important under background conditions, and reaction rates and product distributions have been updated. Box model tests show that the modified CBM-4 and a detailed reference mechanism agree well for a broad range of chemical conditions. Results of TM3 runs with and without NMHC chemistry are compared with observations, illustrating the effects of NMHC on key compounds of tropospheric photochemistry, such as ozone, the hydroxyl radical, carbon monoxide, and NOx. In particular, the simulation of ozone over polluted regions improves when NMHC chemistry is accounted for. Globally, the contribution of NMHC to net photochemical ozone production is estimated at about 40%, leading to a 17% increase of the tropospheric ozone column. OH is depleted over the continents owing to reactions with NMHC, which is most evident in regions with strong biogenic emissions. Although NMHC significantly influence the global OH distribution, their effect on its total tropospheric content appears to be marginal. Results of sensitivity runs with and without organic peroxy nitrates show that this N reservoir may significantly change the global NOx distribution, leading to a NOx increase over the oceans of the order of 50%. This increase improves the agreement between simulated and observed nitrate levels at remote stations, although large discrepancies remain. In general, the present treatment of NMHC reproduces the main features of tropospheric chemistry.

Nox gas sensing characteristics of wo3 thin films activated by noble metals (pd, pt, au) layers

Abstract: WO3-based gas sensor devices have been fabricated by reactive rf sputtering on glass substrates. Palladium (Pd), platinum (Pt), gold (Au) noble metals (100–600 A) were evaporated as activator layers onto WO3 thin films and Al layers (1500 A) were sputtered on top of them as upper electrodes for sensor output. The described sensing element was found to possess excellent sensitivity towards NO and NO2 gases, at low temperatures (100–300°C). The optimum operating temperature was 150 and 200°C for Pt, Pd and Au, respectively. The resistance of the thin-film gas sensor increases reversibly in the presence of low concentrations of NO (0–440 ppm) and NO2 (0–10 ppm) gases in air. The activator layers have an promotional effect on the speed of response to NOx at low temperatures and on selectivity enhanced with respect to other reducing gases (CO, CH4, H2, SO2, H2S, NH3). The temperature dependence of response and recovery times has been examined. The influence of the thickness of the noble metals on NOx gases sensitivity has been investigated. The NO and NO2 gases calibration curves have been recorded for the optimum performances of each fabricated sensor-device.

Global simulation of tropospheric O3-NOx-hydrocarbon chemistry: 2. Model evaluation and global ozone budget

Abstract: Results from a global three-dimensional model for tropospheric O3-NOx-hydrocarbon chemistry are presented and evaluated with surface, ozonesonde, and aircraft measurements. Seasonal variations and regional distributions of ozone, NO, peroxyacetylnitrate (PAN), CO, ethane, acetone, and H2O2 are examined. The model reproduces observed NO and PAN concentrations to within a factor of 2 for a wide range of tropospheric regions including the upper troposphere but tends to overestimate HNO3 concentrations in the remote troposphere (sometimes several fold). This discrepancy implies a missing sink for HNO3 that does not lead to rapid recycling of NOx; only in the upper troposphere over the tropical South Atlantic would a fast conversion of HNO3 to NOx improve the model simulation for NOx. Observed concentrations of acetone are reproduced in the model by including a large biogenic source (15 Tg C yr−1), which accounts for 40% of the estimated global source of acetone (37 Tg C yr−1). Concentrations of H2O2 in various regions of the troposphere are simulated usually to within a factor of 2, providing a test for HOx chemistry in the model. The model reproduces well the observed concentrations and seasonal variations of ozone in the troposphere, with some exceptions including an underestimate of the vertical gradient across the tropical trade wind inversion. A global budget analysis in the model indicates that the supply and loss of tropospheric ozone are dominated by photochemistry within the troposphere and that NOx. emitted in the southern hemisphere is twice as efficient at producing ozone as NOx emitted in the northern hemisphere.

Influence of increased isoprene emissions on regional ozone modeling

Abstract: The role of biogenic hydrocarbons on ozone modeling has been a controversial is- sue since the 1970s. In recent years, changes in biogenic emission algorithms have resulted in large increases in estimated isoprene emissions. This paper describes a recent algorithm, the second generation of the Biogenic Emissions Inventory System (BEIS2). A sensitivity analysis is performed with the Regional Acid Deposition Model (RADM) to examine how increased isoprene emissions generated with BEIS2 can influence the modeling of elevated ozone concentrations and the response of ozone to changes to volatile organic compound (VOC) and nitrogen oxide (NOx) emissions across much of eastern North America. In- creased isoprene emissions are found to produce a predicted shift in elevated ozone concen- trations from VOC sensitivity to NOx sensitivity over many areas of eastern North America. Isoprene concentrations measured near Scotia, Pennsylvania, during the summer of 1988 are compared with RADM estimates of isoprene and provide support for the veracity of the higher isoprene emissions in BEIS2, which are about a factor of 5 higher than BEIS 1 during warm, sunny conditions.

Emissions lifetimes and ozone formation in power plant plumes

Abstract: The concept of ozone production efficiency (OPE) per unit NOx is based on photochemical models and provides a tool with which to assess potential regional tropospheric ozone control strategies involving NOx emissions reductions. An aircraft study provided data from which power plant emissions removal rates and measurement-based estimates of OPE are estimated. This study was performed as part of the Southern Oxidants Study-1995 Nashville intensive and focuses on the evolution of NOx, SO2, and ozone concentrations in power plant plumes during transport. Two approaches are examined. A mass balance approach accounts for mixing effects within the boundary layer and is used to calculate effective boundary layer removal rates for NOx and SO2 and to estimate net OPE. Net OPE is more directly comparable to photochemical model results than previous measurement-based estimates. Derived net production efficiencies from mass balance range from 1 to 3 molecules of ozone produced per molecule of NOx emitted. A concentration ratio approach provides an estimate of removal rates of primary emissions relative to a tracer species. This approach can be combined with emissions ratio information to provide upper limit estimates of OPE that range from 2 to 7. Both approaches illustrate the dependence of ozone production on NOx source strength in these large point source plumes. The dependence of total ozone production, ozone production efficiency, and the rate of ozone production on NOx source strength is examined. These results are interpreted in light of potential ozone control strategies for the region.

Promotion effect of potassium on the catalytic property of CuFe2O4 for the simultaneous removal of NOx and diesel soot particulate

Abstract: Modification of CuFe2O4 catalyst for the simultaneous NOx-soot removal has been studied by doping alkali metals (Li, Na, K, Cs), vanadium and platinum. In pre-doped catalysts, designated as Cu1−xAxFe2O4 (A : dopant), potassium was superior to the other alkali metals and vanadium with respect to enhancing the activity and selectivity to NOx reduction into N2, and the optimum doping level of potassium was x=0.05. Such a promotion effect of potassium was also observed with the impregnated 5 mol% K/CuFe2O4 catalyst. The impregnation of platinum to CuFe2O4 and Cu0.95K0.05Fe2O4 resulted in a decrease in the selectivity to N2 formation with the activity being almost unchanged. The high catalytic performance, especially high selectivity, was realized only when the proper amount of potassium is doped in the Cu–Fe spinel catalyst. XPS analysis showed the segregation (enrichment) of potassium on the surface, and too much doping of potassium might cause the covering of active sites of the Cu–Fe spinel oxide.

Atmospheric ammonia and ammonium transport in Europe and critical loads: a review

Abstract: The atmosphere in Europe is polluted by easily available nitrogen (ammonium and nitrate) mainly from livestock (NH3), traffic (NOx) and stationary combustion sources (NOx). The nitrogen emission from various European sources decreases in the order: agriculture, road traffic, stationary sources and other mobile sources (including vehicular emissions from agriculture), with annual emissions of approximately 4.9, 2.7, 2.7 and 0.8 Mt N respectively. The emissions have increased dramatically during the latest decades. In the atmosphere the pollutants are oxidised to more water soluble compounds that are washed out by clouds and eventually brought back to the earth's surface again. Since ammonia is emitted in a highly water soluble form it will also to a substantial degree be dry deposited near the source. Ammonia is, however, the dominant basic compound in the atmosphere and will form salts with acidic gases. These salt particles can be transported long distances especially in the absence of clouds. The deposition close to the source is substantial, but hard to estimate due to interaction with other pollutants. Far from the source the deposition of ammonium is on an annual average halved approximately every 400 km. This short transport distance and the substantial deposition near the source makes it possible for countries to control their ammonium deposition by decreasing their emissions, provided that there is no country with much higher emission in the direction of the prevailing wind trajectory. When the easily available nitrogen is deposited on natural ecosystems (lakes, forests), negative effect can occur. The effect is determined by the magnitude of the deposition and the type of ecosystems (its critical load for nitrogen). In order to reduce the negative effects by controlling the emissions in a cost-efficient way it is necessary to use atmospheric transport models and critical loads.

Tungsten trioxide (WO3) sputtered thin films for a NOx gas sensor

Abstract: WO3 thin films have been deposited by reactive rf sputtering onto low-cost glass substrates as gas sensitive coatings. The properties of the grown films have been investigated by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), secondary ion mass spectrometry (SIMS) in order to characterize their structure, composition, surface chemistry. The d.c. electrical response to different gases of the WO3 thin films has been measured in the temperature range from 100 to 400°C showing an increase of electrical resistance with a good sensitivity towards NOx gas at 250°C. WO3 thin films oppositely detect also NH3, H2, H2S, SO2 gases by decreasing the electrical resistance and are practically insensitive to interfering gases like CO, CH4 in the same temperature range. The sensing characteristics of the NOx gas detector based on tungsten trioxide (WO3) thin films are reported.

Export of reactive nitrogen from North America during summertime: Sensitivity to hydrocarbon chemistry

Abstract: The global influence on tropospheric chemistry of nitrogen oxides (NOx = NO + NO2) emitted by fossil fuel combustion may be strongly modulated by nonmethane hydrocarbon (NMHC) chemistry taking place in the continental boundary layer. This effect is investigated using a three-dimensional, continental-scale model of tropospheric O3-NOx-NMHC chemistry over North America in summer. The model includes detailed representation of NMHC chemistry including in particular isoprene. Model results are evaluated with observations for ozone, reactive nitrogen species, and photochemical tracers at a number of sites in North America. Sensitivity analyses are conducted to explore the effects of assumptions regarding the aerosol chemistry of peroxy radicals and the fate of hydroxy organic nitrates produced from the oxidation of isoprene. A budget analysis for the United States in the model indicates that 9% Of NOx. emitted from fossil fuel combustion is exported out of the continental boundary layer as NOx, 3.5% is exported as peroxyacetyl nitrate (PAN), and 3.7% is exported as other organic nitrates. Isoprene is the principal NMHC responsible for the formation and export of organic nitrates, which eventually decompose to provide a source of NOx in the remote troposphere. Export of NOx. and organic nitrates from the U.S. boundary layer is found to be a major source of NOx. on the scale of the northern hemisphere troposphere and on the scale of the upper troposphere at northern midlatitudes. Proper representation of isoprene chemistry in the continental boundary layer is important for simulation Of NOx in global tropospheric chemistry models.

Seasonal budgets of reactive nitrogen species and ozone over the United States, and export fluxes to the global atmosphere

Abstract: A three-dimensional, continental-scale photochemical model is used to investigate seasonal budgets of 03 and NO3. species (including NOx and its oxidation products) in the boundary layer over the United States and to estimate the export of these species from the U.S. boundary layer to the global atmosphere. Model results are evaluated with year-round observations for 03, CO, and NO, species at nonurban sites. A seasonal transition from NO, to hydrocarbon-limited conditions for 03 production over the eastern United States is found to take place in the fall, with the reverse transition taking place in the spring. The mean NOx/NOy molar ratio in the U.S. boundary layer in the model ranges from 0.2 in summer to 0.6 in winter, in accord with observations, and reflecting largely the seasonal variation in the chemical lifetime of NOx. Formation of hydroxy organic nitrates during oxidation of isoprene, followed by decomposition of these nitrates to HNO 3, is estimated to account for 30% of the chemical sink of NOx in the U.S. boundary layer in summer. Model results indicate that peroxyacylnitrates (PANs) are most abundant in the U.S. boundary layer in spring (25% of total NO3.), reflecting a combination of active photochemistry and low temperatures. About 20% of the NOx emitted from fossil fuel combustion in the United States in the model is exported out of the U.S. boundary layer as NOx or PANs (15% in summer, 25% in winter). This export responds less than proportionally to changes in NOx emissions in summer, but more than proportionally in winter. The annual mean export of NOx and PANs from the U.S. boundary layer is estimated to be 1.4 Tg N yr - , representing an important source of NOx on the scale of the northern hemisphere troposphere. The eventual 03 production in the global troposphere due to the exported NOx and PANs is estimated to be twice as large, on an annual basis, as the direct export of 03 pollution from the U.S. boundary layer. Fossil fuel combustion in the United States is estimated to account for about 10% of the total source of 03 in the northern hemisphere troposphere on an annual basis.

Staged reductant injection for improved NOx reduction

Abstract: An external reductant (2) for an SCR vehicular NOx emission control system is selectively injected to SCR catalysts (5A, 5B) which are only at catalytically active temperatures thereby avoiding reductant absorption in catalytically unactive catalysts and improving conversion response time

An experimental and kinetic calculation of the promotion effect of hydrocarbons on the NO-NO2 conversion in a flow reactor

Abstract: The main route to nitrogen dioxide (NOz) formation in combustion systems is through the oxidation of nitric oxide (NO). This process was originally invcstigafed in order to explain the high proportion of NOz found in NOx emissions from the exhaust of gas turbine engines [l]. Moreover, the understanding of the NO-NO2 conversion mechanism is relevant to a number of issues including NOz emission from unflued space heaters, development of NOx control technologies, behavior of NO/N02 in the atmosphere, formation and reduction chemistry of NOx, and the probe sampling techniques for NOx concentration measurements. Originally, the NO-NO2 conversion was thought to proceed through the rapid oxidation of NO by oxidative radicals without much attention to the effect of fuels on the conversion [2-41. Although, in later studies, it was revealed that the conversion was greatly promoted by small quantities of fuels such as hydrocarbons, Hz, CO, and methanol [S-9]. In our former experiment and model calculation of the NO-NO2 conversion in the mixing of hot combustion gas with cold air and nine different fuels [6], the results indicated that NO-NO2 conversion appeared only in the low temperature range, and showed a strong dependence on fuel type. Thus, the interaction between the NO-NO2 reactions and the oxidation reactions of the fuel in the low temperature range must be .understood in order to explain the effect of fuel type on the NO-NO2 conversion and consequently to predict the NO/NO2 emission levels from combustion systems.

High-temperature potentiometric/amperometric nox sensors combining stabilized zirconia with mixed-metal oxide electrode

Abstract: Electrochemical sensors using stabilized zirconia and oxide electrodes were tested for detecting NO or NO2 potentiometrically and amperometrically at high temperature. For a mixed-potential-type NOx sensor of two-electrode structure, CdCr2O4 was found to give fairly excellent NOx sensing characteristics among the perovskite-type and spinel-type oxides tested. The CdCr2O4-attached device gave a linear correlation between EMF and the logarithm of NO or NO2 concentration at 500–600°C. The mixed potential sensing mechanism was also verified. In order to improve the sensitivity and selectivity to NO, the above device was modified to three-electrode structure. With a fixed bias voltage being applied between the sensing (oxide) and counter (Pt) electrodes, the voltage between the sensing and reference (Pt) electrodes was measured as a sensing signal. The responses to NO and NO2 were found to be enhanced and suppressed with a positive bias, respectively. The tubular device with two-electrode structure was tested for amperometric detection of NOx. A CdCr2O4-attached tubular device was found to show quick and selective response to NO over NO2 at 500 and 550°C, if the oxide sensing electrode was polarized at +100 mV versus the reference Pt electrode. The NOx sensing mechanisms of the three-electrode device were proposed and discussed on the basis of the sensing characteristics obtained.

Sources and chemistry of NOx in the upper troposphere over the United States

Abstract: The origin of NOx in the upper troposphere over the central United States is examined using aircraft observations obtained during the SUCCESS campaign in April–May of 1996 Correlations between NOy (sum of NOx and its oxidation products) and CO at 8–12 km altitude indicate that NOx originates primarily from convective transport of polluted boundary layer air Lightning and aircraft emissions appear to be only minor sources of NOx Chemical steady state model calculations constrained by local observations of NO underestimate the measured NOx/NOy concentration ratio at 8–12 km altitude by a factor of two on average The magnitude of the underestimate is correlated with concentrations of condensation nuclei, which we take as a proxy for the age of air in the upper troposphere We conclude that the NOx/NOy ratio is maintained above chemical steady state by frequent convective injections of fresh NOx from the polluted boundary layer and by the long lifetime of NOx in the upper troposphere (5–10 days) In contrast to previous studies, we find no evidence for fast heterogeneous recycling from HNO3 to NOx in the upper troposphere

Promoted Fe/ZSM-5 catalysts prepared by sublimation : de-NOx activity and durability in H2O-rich streams

Abstract: Fe/ZSM-5 catalysts with an Fe/Al ratio 1:0, were prepared by sublimation of FeCl3 into H/ZSM-5 They display high activity and durability for the selective catalytic reduction of NOx to N2, both in dry and wet gas flows These catalysts have now been modified by exchanging a second cation into the zeolite Mere neutralization of zeolite protons by Na+ lowers the selectivity for NOx reduction to N2, but the cations Ce3 + and La3 + act as true catalyst promoters With isobutane as the reductant in a simulated vehicular emission gas, almost 90% of NOx is reduced to N2 at 350°C over the La-promoted catalyst The presence of 10% H2O in the feed does not impair the catalyst performance at high temperature; in the temperature region below 350°C it even increases the N2 yield The beneficial effect of La is due to its lowering of the catalyst activity for the undesired combustion of the hydrocarbon No signs of zeolite destruction are evident after 100 h TOS in a wet gas flow at 350°C Carbonaceous deposits causing a slight deactivation are easily removed in an O2/He flow at 500°C; this in situ regeneration fully restores the original activity

Transport and production of NO X in electrified thunderstorms: Survey of previous studies and new observations at midlatitudes

Abstract: First airborne NOx (NO+NO2) measurements in anvils of active thunderstorms in Europe were performed in summer 1996 over southern Germany and Switzerland (47°-49°N). This field experiment LINOX (lightning-produced NOx) was designed to study the production of NOx by lightning discharges and the transport in convective storms. With the research aircraft Falcon of the Deutsches Zentrum fur Luft- und Raumfahrt, about 20 anvil penetrations were performed including measurements of NO, NO2, CO2, O3, and meteorological parameters. In thunderstorm anvils, mean NOx mixing ratios between 0.8 and 2.2 ppbv were measured with peak values reaching up to 4 ppbv. A considerable part of these enhancements could be attributed to the transport of polluted air from the planetary boundary layer (PBL) using CO2 as tracer for PBL air. NOx produced by lightning can be obtained by subtracting the fraction of NOx transported from the PBL from total NOx measured in the anvil. The NOx/CO2 correlation in larger cumulus clouds without lightning was used as reference for the transport of PBL air in the anvils. In smaller LINOX thunderstorms the contribution from lightning, respectively, PBL transport to anvil NOx, was about equal. However, in medium and large LINOX thunderstorms the contribution from lightning dominated (60–75%). For these kind of thunderstorms it was estimated that ∼1.0±0.5 ppbv NOx resulted from lightning production. The observations were used to quantify the NOx production per thunderstorm and to give a rough estimate of the annual production of NOx. For the global lightning nitrogen budget the uncertainties were considerable (0.3–22 Tg(N) yr−1). The mean value for the global NOx production rate by lightning in the upper troposphere was estimated to 4 Tg(N) yr−1.

Kinetics and mechanism of the reduction of nitric oxides by H2 under lean-burn conditions on a Pt–Mo–Co/α-Al2O3 catalyst

Abstract: The kinetics and the mechanism of the selective reduction of nitric oxides (NOx) by hydrogen is studied on a trimetallic Pt–Mo–Co/a-Al2O3 catalyst under oxidising conditions. This system is interesting in view of an exhaust gas control of power plants or lean-burn cars. It can be shown that the NO dissociation is the crucial step, dominating the overall reaction behaviour and that it depends on temperature and on the partial pressure of H2. With increasing temperatures the reaction reveals an autocatalytic behaviour resulting in bistability and hysteresis. At higher temperatures, where no bistability is found, the NO/H2 as well as the competing O2/H2 reaction occur only above a certain critical partial pressure of H2. The kinetics of the NO/H2/O2 reaction are established using a modified Langmuir–Hinshelwood model (T=142°C–160°C, yO2>4%) which takes into account the critical H2 partial pressure. The model describes the experimental data within ±15%. The determined activation energies are: 63 kJ/mol for the NOx consumption, 77 and 45 kJ/mol for the N2 and N2O formation, respectively, and 130 kJ/mol for the O2/H2 reaction. Adsorption enthalpies are determined to -59 kJ/mol for the adsorption of H2, -77 kJ/mol for the adsorption of NO and -97 kJ/mol for the adsorption of O2. An interesting feature of the reaction is the enhancement of the NO/H2 reaction by oxygen for low partial pressures of O2. This appears to be the first study where a promoting effect of oxygen for the NO/H2 reaction is found on a platinum supported catalyst.

Method for reducing NOx and fuel emissions in a furnace

Abstract: In a method of this invention, a first oxidant flow including oxygen and/or air, is injected into an exhaust gas flow from a primary burn zone in a furnace combustion chamber. The first oxidant flow is injected into the exhaust gas flow in a secondary burn zone downstream from the primary burn zone, but inside of the furnace chamber so that heat released from combustion of the first oxidant flow can be used for the purpose to which the furnace is applied. Also, the injection of the first oxidant flow into the secondary burn zone combusts fuel pollutants that might otherwise be released from the furnace into the atmosphere. The method can also include mixing a gaseous hydrocarbon fuel flow with the exhaust gas flow from the secondary burn zone to reduce the NOx, level in the exhaust gas. Also, the method can include mixing a second oxidant flow including air and/or oxygen, with the exhaust gas, preferably after reducing the NOx. If the furnace is a regenerative type, the air flow can be mixed with the exhaust gas flow in proximity to the entrance of a regenerator to heat the regenerator. The invention also includes a related system.

Atmospheric Oxidation of Toluene in a Large-Volume Outdoor Photoreactor: In Situ Determination of Ring-Retaining Product Yields

Abstract: Experiments on the photooxidation of toluene/NOx/air mixtures were performed in the European Photoreactor (EUPHORE), a large-scale outdoor reaction chamber located in Valencia/Spain. The objective of the study was the in situ determination of the yields of ring-retaining products by differential optical absorption spectroscopy (DOAS) and the elucidation of their formation pathways. The experiments were performed with toluene concentrations between 0.68 and 3.85 ppm and initial NOx concentrations ranging from 3 to 300 ppb, i.e., down to the range actually observed in the lower atmosphere. The ring-retaining product yields were found to be 5.8 ± 0.8%, 12.0 ± 1.4%, 2.7 ± 0.7%, and 3.2 ± 0.6% for benzaldehyde, o-cresol, m-cresol, and p-cresol, respectively. Under the experimental conditions, no dependency of the yields on the NOx concentration or the toluene/NOx ratio could be found. The formation kinetics of the cresols are in line with a “prompt” formation mechanism, i.e., abstraction of a hydrogen atom fro...

Method and device for selective catalytic nox reduction

Abstract: The invention relates to a method and a device for selective catalytic NOx reduction in waste gases containing oxygen, using ammonia and a reduction catalyst (9). According to the said method, gaseous ammonia is provided by heating a solid storage medium, said storage medium being introduced into a container (1). The inventive method and device are particularly suitable for use in automobiles.

The effects of carbon dioxide in exhaust gas recirculation on diesel engine emissions

Abstract: The investigation was conducted on a high-speed direct injection diesel engine and was concerned with the effects of exhaust gas recirculation (EGR) on diesel engine combustion and emissions. In particular, the effects of carbon dioxide(CO₂), a principal constituent of EGR, on combustion and emissions were analysed and quantified experimentally. The use of CO₂ to displace oxygen(O₂) in the inlet air resulted in reduction in the O₂ supplied to the engine(dilution effect), increased inlet charge thermal capacity(thermal effect), and, potentially, participation of the CO₂ in the combustion process (chemical effect). In a separate series of tests the temperature of the engine inlet charge was raised gradually in order to simulate the effect of mixing hot EGR with engine inlet air. Finally, tests were carried out during which the CO₂ added to the engine air flow increased the charge mass flowrate to the engine, rather than displacing some of the O₂ in the inlet air. It was found that when CO₂ displaced O₂ in the inlet charge, both the chemical and thermal effects on exhaust emissions were small. However, the dilution effect was substantial, and resulted in very large reductions in exhaust oxides of nitrogen (NO_x) at the expense of higher particulate and unburned hydrocarbon (uHC) emissions. Higher inlet charge temperature increased exhaust NO_x and particulate emissions, but reduced uHC emissions. Finally, when CO₂ was additional to the inlet air charge(rather than displacing O₂), large reductions in NO_x were recorded with little increase in particulate emissions.

Low-temperature selective catalytic reduction of NOx by metal oxides supported on active carbon fibers

Abstract: Selective catalytic reduction (SCR) of NO x at 323–423 K, which is at a relatively lower temperature than that in conventional SCR method using V 2 O 5 /TiO 2 -anatase catalyst, was studied. Catalytic components investigated were transition-metal oxides supported on pitch-based active carbon fibers (ACF). Three transition-metal oxides, Fe 2 O 3 , Co 2 O 3 and Mn 2 O 3 were tested as catalytic components, and as a result, Mn 2 O 3 showed the best activity among these metal oxides. As a support material, ACF showed the highest effect among three support materials, including granular active carbons (GAC), and γ-Al 2 O 3 . The activity of Mn 2 O 3 /ACF catalyst increased in proportion to the reaction temperature, and NO conversion reached 92% at 423 K. ACF contribute to make highly dispersed metal-oxides particles and large gas-contact surface area.