Showing papers on "NOx published in 1990"

Permutation reactions of organic peroxy radicals in the troposphere

Abstract: Organic peroxy radicals are important intermediates in the atmospheric photooxidation of hydrocarbons. Laboratory studies indicate that these radicals react among themselves (permutation reactions) at rates which should compete with those for reaction with HO2 and NOx under some atmospheric conditions. Using the available laboratory data, we have developed a simplified method of representing the large number of atmospheric peroxy radical permutation reactions, and have included this in a detailed mechanism of hydrocarbon photooxidation. The potential importance of these reactions was studied for relatively low NOx conditions such as may be observed in the marine planetary boundary layer (PBL) and the Amazon PBL. The effects of the permutation reactions include suppression of organic peroxy radical concentrations, higher HO2 and H2O2 concentrations, shorter lifetimes for PAN and other peroxyacyl nitrates (with concomitant faster release of NOx), and production of substantial concentrations of alcohols and organic acids (including acetic acid). If the kinetic and mechanistic data used in the present study are at least roughly realistic, the peroxy radical reactions probably play an important role in the photochemistry of the clean troposphere.

Changes in the global concentration of tropospheric ozone due to human activities

Abstract: THERE is evidence from records of ground-level measurements1–6 that the average tropospheric concentration of ozone in the Northern Hemisphere has increased. In particular, the comparison of recent observations with those made at the Montsouris laboratory in Paris between 1876 and 19105,6, suggests that the surface concentration of ozone at mid to high latitudes has more than doubled in the past 100 years. This has potential implications for a wide range of environmental issues both because of the direct effects of elevated concentrations of ozone on man and ecosystems7,8 and because ozone is a radiatively active gas which could contribute significantly to global warming if its concentration were to increase9–12. We have used a global tropospheric model to simulate the chemistry of the pre-industrial atmosphere and that of the present day. The model results for surface ozone concentrations in the pre-industrial atmosphere agree well with the Montsouris data, and the calculated concentrations for the present day agree with recent observations of a wide range of chemical species. Estimates of the future growth in emissions of nitrogen oxides (NOx) (ref. 13) have been used to make similar calculations for the year 2020. On the basis of these estimates, the global tropospheric concentration of ozone will continue to increase at a rate faster than during the past 100 years. The potential for further increases in tropospheric ozone needs to be taken into account when assessing the impact of air pollution emissions and the adequacy of measures to control them.

15N/14N ratios of NOx from vehicle engines and coal‐fired power stations

Abstract: Preliminary data are presented for the 15 N/ 14 N ratios of the two main sources of anthropogenic NOx. Contrary to expectation, the δ 15 N values of NO x emitted from vehicle exhausts (−13 to −2‰) and coal-fired boilers (+ 6 to + 13‰) are different from isotopic composition of the nitrogen in their fuel + air mixtures (∼ 0‰). These differences may reflect variable effects of kinetic isotopic fractionation in the formation (vehicles) and destruction (boilers) of NO, and have important consequences for the use of nitrogen isotopes in atmospheric studies. DOI: 10.1034/j.1600-0889.1990.00007.x-i1

A product study of the gas-phase reaction of methacrolein with the OH radical in the presence of NOx

Abstract: The gas-phase reaction of methacrolein with the OH radical, in the presence of NOx, was investigated at 298 ± 2 K and atmospheric pressure of air. Hydroxyacetone, methylglyoxal, a peroxyacyl nitrate identified as CH2 C(CH3)C(O)OONO2 (peroxymethacryloyl nitrate), formaldehyde, CO, and CO2 were observed to be the major products. The product yield data for these compounds show that OH radical addition to the >C C< bond accounts for ca. 50% of the overall reaction, with the remaining ca. 50% proceeding via H—atom abstraction from the CHO group. The data suggest that the alkoxy radical formed following the addition of OH to the terminal carbon atom, decomposes primarily to give the formyl radical plus hydroxyacetone. A lower limit ratio of 5: 1 has been estimated for OH radical addition to the terminal carbon atom of the double bond relative to addition on the inner carbon atom.

Systematic variations in the concentration of NO x (NO Plus NO2) at Niwot Ridge, Colorado

Abstract: Measurements of the concentrations of NO and NO2 were made in the rural troposphere during a year's period in 1980–1981, during the summers of 1983, 1984, and 1987, and during the fall of 1984. The field site was located near Niwot Ridge, Colorado, at an elevation of 3 km. NO was measured with a chemiluminescence instrument, and NO2 was photolyzed to NO and measured by the same instrument. The performance of this instrument is discussed in detail. Aspects of the NOx (sum of NO and NO2) concentrations discussed include the overall distribution, the seasonal and diurnal cycles, the interannual variations, and the correlation with meteorological parameters. The meteorological dependence of [NOx] elucidates the mechanisms that transport NOx to the site. Even though the Denver urban area lies downwind from the site with respect to the prevailing winds, it is NOx from that area that predominates and is responsible for the enhanced acidic deposition and elevated ozone levels at the site. The valley-mountain flow that is primarily responsible for this transport also may be an important mechanism for transporting anthropogenic pollution from the planetary boundary layer to the free troposphere. The major photochemical loss processes of NOx are reaction of NO2 with hydroxyl radicals to form HNO3 and the formation of PAN (peroxyacetyl nitrate) and perhaps other organic nitrates in the summer and reaction of NO2 with O3 to form NO3, N2O5, and further oxidized species in the winter.

Catalyst for purification of exhaust gases

Abstract: A catalyst for purification of exhaust gases, comprising a support substrate, a catalyst carrier layer formed on the support substrate and catalyst ingredients loaded on the catalyst carrier layer, wherein the catalyst carrier layer comprises alumina, cerium oxide, zirconium oxide and at least one oxide of rare earth element except cerium and lanthanum, and at least a part of cerium oxide, zirconium oxide and oxide of rare earth element except cerium and lanthanum is present in the form of composite oxide and/or solid solution. The catalyst for purification of exhaust gases is capable of purifying exhaust gases containing carbon monoxide (CO), hydrocarbons (HC) and nitrogen oxides (NOx).

Environmental effects of N fertilizer use - An overview.

Abstract: In recent years concern has grown over the contribution of nitrogen (N) fertilizers to the environmental problems of nitrate pollution of waters and the pollution of the atmosphere with nitrous oxide, other oxides of nitrogen, and ammonia. These gases potentially contribute to the ‘greenhouse effect’ or global heating because of their increasing concentrations in the atmosphere and to the destruction of the stratospheric ozone layer, which protects the earth from ultraviolet radiation. In light of these concerns, proposals to mitigate these problems have been considered, and others will be forthcoming. When they have been used in high amounts, fertilizers and animal manures have created problems of nitrate pollution. Nitrous oxide (N2O) is a greenhouse gas and may also contribute to the destruction of the stratospheric ozone when it is converted to nitric oxide. N2O is primarily produced in the biological processes of nitrification and denitrification. Nitric oxide and nitrogen dioxide are also produced in biological processes and are important in atmospheric reactions in the troposphere and stratosphere. There is little indication that N fertilizers contribute very much to the production of nitrous oxide. More research is needed to characterize and measure the emissions of the oxides of nitrogen and ammonia and to make better estimates of global emissions based on process-related models. More efforts to increase the efficiency of nitrogen fertilizer use through modifications or use of inhibitors of biological processes as well as better management of rates, timing, and incorporation are needed to ensure increased food production while conserving natural resources.

Comparison between NOx Evolution Mechanisms of Wild-Type and nr1 Mutant Soybean Leaves

Abstract: The nr1 soybean (Glycine max [L.] Merr.) mutant does not contain the two constitutive nitrate reductases, one of which is responsible for enzymic conversion of nitrite to NOx (NO + NO2). It was tested for possible nonenzymic NOx formation and evolution because of known chemical reactions between NO2− and plant metabolites and the instability of nitrous acid. It did not evolve NOx during the in vivo NR assay, but intact leaves did evolve small amounts of NOx under dark, anaerobic conditions. Experiments were conducted to compare NO3− reduction, NO2− accumulation, and the NOx evolution processes of the wild type (cv Williams) and the nr1 mutant. In vivo NR assays showed that wild-type leaves had three times more NO3− reducing capacity than the nr1 mutant. NOx evolution from intact, anerobic nr1 leaves was approximately 10 to 20% that from wild-type leaves. Nitrite content of the nr1 mutant leaves was usually higher than wild type due to low NOx evolution. Lag times and threshold NO2− concentrations for NOx evolution were similar for the two genotypes. While only 1 to 2% of NOx from wild type is NO2, the nr1 mutant evolved 15 to 30% NO2. The kinetic patterns of NOx evolution with time were completely different for the mutant and wild type. Comparisons of light and heat treatments also gave very different results. It is generally accepted that the NOx evolution by wild type is primarily an enzymic conversion of NO2− to NO. However, this report concludes that NOx evolution by the nr1 mutant was due to nonenzymic, chemical reactions between plant metabolites and accumulated NO2− and/or decomposition of nitrous acid. Nonenzymic NOx evolution probably also occurs in wild type to a degree but could be easily masked by high rates of the enzymic process.

Flux of NOx between Soil and Atmosphere: Importance and Soil Microbial Metabolism

Abstract: Nitric oxide and nitrogen dioxide (NO + NO2 = NOx) are trace gases which occur only in amounts of less than 1 ppbv in the clean atmosphere. A comparison of the standard redox potentials of NO and NO2 among other biologically relevant nitrogen species is given in Table 5. A comparison of the atmospheric abundance, life time, and major sources and sinks is given in Table 1. The latter data are compiled from SCOPE reports (Soderlund and Svensson, 1976; Crutzen, 1983). Compared to other atmospheric nitrogen compounds the reactivity of NOx is quite large and thus, relatively large fluxes are required to maintain even small atmospheric mixing ratios. On the other hand, even small variations in fluxes result in large variations in the atmospheric mixing ratios. Since atmospheric NOx plays a key role in the chemistry of the atmosphere, the knowledge of the temporal and spatial distribution of sources and sinks of NOx are extremely important for atmospheric models. The role of soils and of microbial denitrification for NOx exchange between terrestrial ecosystems and the atmosphere is presently very uncertain and thus of special interest.

Two stage process for combusting fuel mixtures

Abstract: This invention is a comparatively high pressure combustion process having a two stages in which a fuel is stepwise combusted using specific catalysts and catalytic structures and, optionally, having a final homogeneous combustion zone. The choice of catalysts and the use of specific structures, including those employing integral heat exchange, results in an overall catalyst structure which is stable due to its comparatively low temperature. The product combustion gas is at a temperature suitable for use in a gas turbine, furnace, boiler, or the like, but has low NOx content.

Low NOx emission in gas turbine system

Abstract: An improved gas turbine combustor is provided which reduces nitric oxide emissions through premixing of the fuel gas and air and feeding the mixture through a venturi, providing an air cooled passage around the venturi, and extending the passage downstream toward the combustion zone to optimize the stability of the combustion and reduce NOx and CO emissions.

Background reactivity in smog chambers

Abstract: Data from several smog chamber reaction vessels have been analyzed in an attempt to elucidate the chemical species which are responsible for chamber specific background phenomena, and the nature of the processes which determine the heterogeneous interactions of those species. There is good evidence for the emission of a compound which yields both NOx, and free radicals (probably HONO) and emissions of reactive organics (e.g. HCHO) may also be deduced. Total integrated chamber emission of these compounds may be as high as 20 to 60 ppb during a typical smog chamber experiment. In addition to the direct emission of these contaminants, the surface reaction of NO2 and H2O to HONO is examined. In some cases this reaction may have as great an effect on a smog chamber experiment as the emission of trace contaminants. Overall chamber perturbations to gas phase chemistry have been estimated for several experiments and were found to be less than 20 percent in the majority of cases, although higher perturbations were found in experiments involving compounds of low reactivity such as butane.

Removal of nitrogen and sulphur oxides from waste gas using a phosphorus/alkali emulsion

Abstract: SULPHUR and nitrogen oxides emitted by the combustion of fossil fuels in power plants have an important role in acid-rain production1. Most of the flue-gas desulphurization scrubbers installed to date involve wet limestone processes, which are efficient in SO2 control but are incapable of removing nitric oxide. Here we report a new and efficient method for the combined removal of SO2and NOX from flue gas, using aqueous emulsions containing yellow phosphorus and an alkali. The products comprise sulphate, nitrate and phosphate salts which can be used as fertilizer materials. The process described here may also be applied to stationary sources other than power plants, such as smelters, nitric acid plants and municipal incinerators for NOX control.

Chemiluminescent method for continuous monitoring of nitrous acid in ambient air.

Abstract: A continuous-flow method for measuring atmospheric HNO2 concentration in real time has been developed that uses a chemiluminescent NOx monitor. A Na2CO3 solution strips gaseous HNO2 from the atmosphere by means of pulling an air sample and the solution through a glass coil and mixing continuously with ascorbic acid solution which reduces nitrite to NO. The mixture is led into a gas-liquid separating coil consisting of microporous PTFE tubing. The NO evolved from the separating coil is swept out by a stream of clean air and detected with a chemiluminescent NOx monitor. The technique utilizes a dual flow system and dual channel NOx monitor to correct positive interferences from NO2 and peroxyacetyinitrate (PAN). The concentration of HNO2 is determined by difference between the two measurements. Sensitivity of the method is a function of the ratio of sampling flow rate to carrier gas flow rate, which permits readily a highly sensitive measurement.

Method and device for combustion of fuel in a combustion chamber

Abstract: To avoid high NOx emissions, the fuel is oxidised essentially without a flame and free of pulsations with extremely high recycling of the combustion waste gases.

Method of combustion and combustion apparatus to minimize Nox and CO emissions from a gas turbine

Abstract: A staged combustion apparatus for a gas turbine to lower the concentration of NO x and CO in the exhaust gases. Combustion occurs in a first and second stage, the first stage being sub-stoichiometric combustion and the second stage being above-stoichiometric combustion. Cyclonic combustion occurs in one of the first and second combustion stages and a swirling pattern of combustion occurs in the other of the combustion stages. Steam injection is provided to further lower the concentration of NO x in the exhaust emissions from the gas turbine.

Steam generating system with NOx reduction

Abstract: A method and system for flue gas recirculation is disclosed which will minimize NOx production from hydrocarbon combustion. In the present invention a furnace having an oxygen-bearing primary source of combustion air, a mixing chamber, a combustion chamber in downstream communication with the mixing chamber and an exhaust section downstream of the combustion chamber is provided with a flue gas recirculation line. The recirculation line establishes communication between the exhaust section and the mixing chamber for the return of combustion products as a secondary source of combustion air which is relatively lean in oxygen and is combined with the primary source of combustion air in the mixing chamber. The ratio of flow rates for the primary and secondary sources of combustion air is controlled by a signal generated by a sensor which senses the oxygen concentration in the mixing chamber.

Measurements of the nitric acid to NOx ratio in the troposphere

Abstract: Nitric acid concentrations, measured by both teflon/nylon filter packs (FP) and the tungstic oxide denuder (DEN), are compared with the average NO(x) concentrations from LIF and chemiluminescent methods. The HNO3/NO(x) ratio based on FPs ranged from 0.8 to 10.4, with a mean of 3.4. The DEN nitric acid concentrations produced ratios ranging from less than 0.3 to 9.8, with a mean of 2.6. Average marine ratios were larger than those from continental regions, in part due to continental anthropogenic sources of NO(x).

Second-Generation Low-Emission Combustors for ABB Gas Turbines: Tests Under Full-Engine Conditions

Abstract: An experimental rig was constructed which made it possible to research the influence of air mass flow, pressure, preheating temperature, and fuel/air ratio on the behavior of a full-scale burner. Because the investigations were carried out in the high pressure test facility at the DLR in Cologne, and not in a real gas turbine, the parameters could be varied independently of one another. Based on these systematic measurements, it is possible to predict flame stability limits and emissions for any gas turbine under any operating condition. For example, it can be shown that NOx emissions from the GT8 with ABB’s new second-generation premixing burners will not exceed 25 ppm (for 15% O2) and COwet will be less than 8 ppm at full load (16 bar, 420°C). In addition, the data measured were compared to results obtained from correlations frequently used, such as that NOx is proportional to p0.5. It was shown that this equation is too optimistic even if the flame type remains unchanged.Copyright © 1990 by ASME

Apparatus and method of lowering nox emissions using diffusion processes

Abstract: An apparatus and method for reducing nitrogen oxide emissions from furnace flue gas is provided in which natural gas or other fluid fuel which has little or no fixed nitrogen is introduced into the upper portion of the furnace. The fuel diffuses by laminar or turbulent diffusion into oxygen-rich flue gas where it reacts with oxygen and nitric oxide to form CO2, H2O and N2, thus reducing the nitrogen oxide emissions from the furnace. In this manner, the amount of nitrogen oxide in the flue gas is reduced. The apparatus and method can be easily applied to new furnaces or retrofitted on existing furnaces.

Process for the selective, non-catalytic reduction of the emissions from oil-fired boiler plants

Abstract: In this process for selective non-catalytic reduction of the pollutant emission from oil-fired boiler plants, chemical compounds affecting the combustion process are added to the liquid fuel or to the combustion air, including salts of organic acids, such as naphthenates, octoates and tallates, sulphonic acid salts, salts of saturated or unsaturated fatty acids, oleic acids, tall oil with metals from the group comprising K, Ba, Mg, Ca, Ce, Mn, Fe and rare earth metals, organometal compounds such as carbonyl compounds, mixed cyclopentadienyl-carbonyl compounds or aromatics complexes of the transition metals Fe or Mn in solutions miscible with the liquid fuel. To minimise the NOx values in the waste gas and the dust loading, coupled with economical chemicals consumption, a reducing agent is added to the firing chamber (burner chamber) via a boiler-dosing system, using a liquid or also gaseous carrier stream, as an aqueous solution of urea or also urea precursors such as ammonia or ammonium carbonate, which can also contain further constituents such as alkanols, alkanecarboxylic acids, alkanals or alkanones.