Showing papers on "NOx published in 1992"

Control of combustion-generated nitrogen oxide emissions: Technology driven by regulation

Abstract: Nitrogen oxides in the atmosphere contribute to photochemical smog, to the formation of acid rain precursors, to the destruction of ozone in the stratosphere and to global warming. Over the past 150 years, global emissions of nitrogen oxides into the atmosphere have been increasing steadily. A significant amount of the nitrogen oxide emissions is attributed to combustion of biomass and fossil fuels. Increasingly stringent NOx emissions regulations are being implemented in a number of industrialized countries. These regulations have driven and continue to drive the development of NOx emissions control techniques. This paper reviews existing and some emerging technologies for reduction of NOx emissions from combustion sources and examines the prospects of these technologies for meeting stricter emissions regulations. Both combustion modification and post-combustion methods for NOx reduction are considered. The important role of research on the chemistry of nitrogen oxides in combustion gases in development and optimization of emissions control techniques is described.

Catalytic reduction of nitrogen oxides with methane in the presence of excess oxygen

Abstract: We discovered a family of catalysts that can effectively reduce NOx with methane in the presence of excess oxygen This new catalytic chemistry offers an alternative means for controlling NOx emissions Complete reduction of nitric oxide was obtained at 400°C over a Co-ZSM-5 catalyst The presence of oxygen in the feed greatly enhances the nitric oxide reduction activity on Co-ZSM-5, and the nitric oxide conversion is strongly related to the inlet methane level On the other hand, Cu-ZSM-5, which is a unique catalyst for the direct nitric oxide decomposition, is a poor catalyst for nitric oxide reduction by methane in the presence of excess of oxygen

NOx decreasing apparatus for an internal combustion engine

Abstract: A lean NOx reduction catalyst capable of reducing NOx through reaction of H 2 with NOx at low temperatures below 350° C. is installed in a downstream portion of an exhaust pipe of an internal combustion engine in or near a muffler. Such an NOx reduction catalyst comprises, for example, Pt/zeolite catalyst. An H 2 generator is installed so as to supply the H 2 to an inlet side of the NOx reduction catalyst. The H 2 generator may include a reforming catalyst for reforming methanol, LPG, or natural gas to generate H 2 . The generated H 2 flows to the NOx reduction catalyst where it reacts with NOx to purify the exhaust gas.

The role of nitric oxide in endotoxic shock: effects of NG-monomethyl-L-arginine.

Abstract: The role of nitric oxide (NO) in the changes in blood pressure and plasma levels of nitrate and nitrite (NOx) and alanine aminotransferase (ALT) were determined over a 5-h period in anesthesized rats after intravenous administration of S. typhosa endotoxin (LPS, 4 mg/kg). Rats treated with LPS showed a sustained fall in blood pressure accompanied by an increase in plasma NOx and ALT. Forty percent of these rats died during the experiment. There was no change in blood pressure in rats treated with dexamethasone (1 mg/kg) 1 h before and 2 h after LPS and the increase in NOx and ALT was significantly inhibited. None of the rats in this group died. Administration of 10 mg/kg of NG-monomethyl-L-arginine (L-NMMA) prevented the fall in blood pressure and partially prevented the increase in NOx and ALT. None of the animals in this group died. In contrast, 300 mg/kg of L-NMMA caused an initial increase in blood pressure followed by a rapid fall and enhanced the increase in ALT while abolishing the elevation of NOx. All of these animals died before the end of the experiment. However, when rats treated with high doses of L-NMMA were given a continuous infusion of S-nitroso-N-acetylpenicillamine (SNAP, 300 micrograms/kg/h), the blood pressure was maintained at control levels and no mortality was observed.(ABSTRACT TRUNCATED AT 250 WORDS)

Device for purifying exhaust of internal combustion engine

Abstract: NOx absorbent (18) is disposed in the exhaust gas path in the internal combustion engine and exhaust gas is adapted to flow constantly through said absorbent (18) during the operation of said engine. NOx absorbent (18) absorbs NOx when an air-fuel ratio of exhaust gas flowing into said absorbent (18) is lean and, when an air-fuel ratio of exhaust gas becomes equal to the theoretical air-fuel ratio or rich, it discharges NOx having been absorbed therein. Over almost the entire range of operation of the engine, lean mixed gas is burnt in the combustion chamber (3) and NOx generated at this time is absorbed by said absorbent (18). An air-fuel ratio of exhaust gas flowing into the NOx absorbent (18) is periodically made equal to the theoretical one or rich and NOx having been absorbed by the absorbent (18) is discharged and reduced at the same time.

Method for apparatus for combusting fuel in a combustion chamber

Abstract: To avoid high NOx emissions, the fuel is oxidized with an extremely high exhaust gas recirculation ration substantially without flames and without pulsations.

Nitrogen oxides decreasing apparatus for an internal combustion engine

Abstract: In an exhaust purification apparatus of an internal combustion engine having an NOx adsorption and release material (2) in an exhaust conduit (6), a heater (24) is provided close to the NOx adsorption and release material (2). When an NOx adsorption operation continues for a predetermined period, the heater (24) is switched on to raise the temperature of the NOx adsorption and release material (2) above a predetermined temperature, for example, 500°C. When the temperature of the NOx adsorption and release material (2) is high, the NOx adsorption and release material (2) releases absorbed NOx and is regenerated. Released NOx is contacted with a reduction catalyst (4).

The fate of nitrogen in supercritical-water oxidation☆

Abstract: Supercritical water oxidation is carried out at temperatures ca. 600 °C and pressures ca. 23 MPa, with a partial pressure of oxygen ca. 2 MPa. Both thermodynamic and kinetic calculations are consistent with the experimental observation that under these conditions, regardless of the oxidation state of nitrogen in the starting material, the predominant effluent species of nitrogen is N2. Fuel-bound nitrogen can result in nitrous oxide, a species which can persist in the process effluent gas due to kinetic limitations. The absence of NOx in the process effluent gas agrees with the low rates of reaction between N2 and O2 at supercritical water oxidation temperatures.

A novel ozone sensor for direct eddy flux measurements

Abstract: A small, lightweight (1.5 kg) and fast-response ozone sensor for direct eddy flux measurements has been built. The basis for detection is the chemiluminescence of an organic dye adsorbed on dry silica gel in the reaction with ozone. The chemiluminescence is monitored with a cheap and small blue-sensitive photomultiplier. At a flow rate of 100 l min-1 the ozone sensor has a 90% response time of significantly better than 0.1 s with a detection limit lower than 50 ppt at S/N=3. There are no interferences from other atmospheric trace gases like NOx, H2O2 and PAN. Water vapour and SO2 enhance the chemiluminescence efficiency of the ozone sensor. Since their response times are 22 seconds and 30 minutes, respectively, no correlation between rapid ozone fluctuations and those of these two trace gases is noticed by the ozone sensor when operating at a frequency of 10 Hz.

Global Emissions of Nitrogen and Sulfur Oxides in Fossil Fuel Combustion 1970–1986

Abstract: Statistical models previously introduced by the authors for estimating emission rates from rates of fuel combustion have been utilized to obtain emissions of nitrogen and sulfur gases in fossil fuel combustion for every country in the world for every year from 1970 to 1986. Changes in the global emission rates of these gases are presented together with the trends over individual continents. Global emissions of NOx increased by nearly a third in this period, i.e., from 18 Mt N/year in 1970 to 24 Mt N/year in 1986. Emissions of SOx increased by approximately 18 percent, from 57 Mt S/year in 1970 to 67 Mt S/year in 1986. The geographical distribution of NOx and SOx emissions for 1986 are presented on a latitude-longitude grid suitable for use in three-dimensional simulations of atmospheric chemistry in general circulation models.

Photochemical Ozone Creation Potentials: A study of Different Concepts

Abstract: Photochemical ozone creation potentials (POCP) have been calculated for 75 organic compounds and carbon monoxide. The creation potentials are calculated using different concepts; peak ozone concentrations and the average formation of ozone, including the amount deposited, during two or four days. The calculations were made by a single-box trajectory model with meteorological and chemical conditions chosen to correspond to a summer high-pressure situation in southern Sweden. Under these conditions, over a 96-hour average, POCPs show that ethene and acrolein are the most efficient ozone producers, followed by higher alkenes, aromatics, alkanes and ethers which can be considered as mediate ozone producers. Chlorinated species, alcohols and ketones are very weak producers of ozone. The relative POCPs differ depending on the method of calculation and the chemical (NOX) environment.

Catalyst for purifying exhaust gas

Abstract: A catalyst for purifying an exhaust gas, which comprises a first component having the activity for reducing nitrogen oxides with ammonia and a second component having at least one of the activity for forming nitrogen oxide from ammonia and the activity for forming carbon dioxide from carbon monoxide. The first component is formed of a composition containing oxide of at least one member selected from titanium, vanadium, tungsten and molybdenum and the second component is formed of a composition containing a salt of a noble metal selected from platinum, palladium and rhodium or any one of these noble metals preliminarily supported on a porous material selected from zeolite, alumina and silica. A method of purifying an exhaust gas containing NOx, CO and leak NH₃ by the catalyst.

Measurements of nitric oxide and nitrogen dioxide during the Mauna Loa Observatory Photochemistry Experiment

Abstract: NO and NO2 were simultaneously measured by photolytic conversion / chemiluminescence techniques during the Mauna Loa Observatory Photochemistry Experiment (MLOPEX). The field site, located at an elevation of 3.4 km on the north side of the Mauna Loa Volcano, was subject to two airflow regimes which typically corresponded to upslope (marine boundary layer plus island sources) conditions during the day and downslope (middle free tropospheric) conditions at night to mid-morning. Median values of NOx (NOx = NO + NO2) were 37 and 31 pptv during upslope and downslope conditions, respectively, with the downslope measurements consistent with previous measurements made from aircraft in the middle free troposphere over the North Pacific. Although the difference in median NOx mixing ratios in the upslope and downslope regimes is small, the influence of island sources of NOx is apparent. Indeed, the median upslope values were approximately 2.5 times greater than measurements made previously in the remote marine boundary layer. The data have been examined according to downslope / free tropospheric and upslope air flow regimes for relationships between NOx and the various species that were measured simultaneously (e.g., peroxyacetyl nitrate (PAN), HNO3, NO3, NOy, O3, CO, and hydrocarbons). While positive correlations between NOx and O3 and PAN were typically observed in free tropospheric air, these correlations were considerably weaker than those observed during previous campaigns. This is likely primarily due to the lower sampling altitude during the MLOPEX study. NOx and dew point temperature were weakly anticorrelated in free tropospheric air masses. Linear correlations between NOx and the peroxides, formaldehyde, alkyl nitrates, and hydrocarbons were also weak in the free tropospheric air masses at the MLO. NOx/NOy was typically on the order of 0.1–0.2 in free tropospheric flow. Considerably higher values of NOx/NOy, were occasionally observed under upslope conditions. The NOx/NOy and HNO3/NOx values obtained under downslope conditions were similar to those previously obtained during aircraft measurements in the middle free troposphere over the northeast Pacific. On the whole, the downslope air masses sampled appear to be characteristic of well-aged, marine free tropospheric air, and this conclusion is supported by 10-day trajectory analyses.

Air staged premixed dry low NOx combustor

Abstract: This invention relates to fuel staged premixed dry low NOx gas turbine combustors of the type that are constructed with multiple concentric cylinders (3a-f) to which fuel manifolds (8a-e) are mounted. The cylinders (3a-f) are spaced in a staggered arrangement. Such structures of this type achieve stable combustion over a wide range of fuel-to-air ratios and low flame temperatures in the combustor resulting in low emissions of nitrogen oxides (NOx).

Relationship of peroxyacetyl nitrate to active and total odd nitrogen at northern high latitudes: influence of reservoir species on NOx and O3.

Abstract: Measurements of peroxyacetyl nitrate (PAN), NO, NO2, HNO3, NOy (total odd nitrogen), and O3 were made in the high-latitude troposphere over North America and Greenland (35 degrees to 82 degrees N) during the Arctic Boundary Layer Expedition (ABLE 3A) (July-August 1988) throughout 0-to 6-km altitudes. These data are analyzed to quantitatively describe the relationships between various odd nitrogen species and assess their significance to global tropospheric chemistry. In the free troposphere, PAN was as much as 25 times more abundant than NOx. PAN to NOx ratio increased with increasing altitude and latitude. PAN was found to be the single most abundant reactive nitrogen species in the free troposphere and constituted a major fraction of NOy, PAN to NOy ratios were about 0.1 in the boundary layer and increased to 0.4 in the free troposphere. A 2-D global photochemical model with C1-C3 hydrocarbon chemistry is used to compare model predictions with measured results. A sizable portion (approximately 50%) of the gaseous reactive nitrogen budget is unaccounted for, and unknown organic nitrates and pernitrates are expected to be present. Model calculations (August 1, 70 degrees N) show that a major fraction of the observed NOx (50 to 70% of median) may find its source in the available PAN reservoir. PAN and the unknown reservoir species may have the potential to control virtually the entire NOx availability of the high latitude troposphere. It is predicted that the summer NOx and O3 mixing ratios in the Arctic/sub-Arctic troposphere would be considerably lower in the absence of the ubiquitous PAN reservoir. Conversely, this PAN reservoir may be responsible for the observed temporal increase in tropospheric O3 at high latitudes.

Functional forms of nitrogen in coals and the release of coal nitrogen as NOx precursors (HCN and NH3)

Abstract: The influence of coal nitrogen on the pyrolytic release of NOx precursors, (HCN and NH3), has been investigated for a range of Australian coals. Functional forms of nitrogen in the coals were determined by X-ray photoelectron spectroscopy. Pyrrolic-type nitrogen predominated (50–60% coal nitrogen), but pyridinic and quaternary forms were also detected. The proportion of pyridinic increased and that of quaternary decreased with increasing carbon contents of the coals. Four coals, ranging in rank from brown to bituminous and in nitrogen content from 0.6–2.0%, dry ash free basis, were pyrolyzed in a fluidized bed reactor at temperatures ranging from 500 to 1100°C, gas residence times of 0.3–0.5 s and particle heating rates of 104 K s−1. Formation of HCN and NH3 occurred at higher temperatures than that required for maximum tar yields; cracking reactions of the tars are a probable source of HCN and NH3. However, the results show that release of nitrogen from structures which are not volatilised as tar also occurs. The major nitrogen-containing components of the tars were identified and quantified by gas chromatography. Nitrogen contained in pyridinic groups was more stable than that in pyrrolic groups; thus, a higher pyrolysis temperature was necessary to release nitrogen as HCN and NH3 from the pyridinic groups. For the range of coals and pyrolysis conditions studied here, however, nitrogen release (as a proportion of total coal nitrogen), in the form of NOx precursors, did not depend on coal type or coal nitrogen content.

Exhaust treatment system and method

Abstract: A moving fluid containing pollutants including NOx compounds is subjected to a relatively low-power alternating-current dielectric discharge for a relatively long time duration. In this manner, pollutants are oxidized and dissociated while the temperature of the fluid is kept low enough to prevent the formation of new NOx pollutants.