Showing papers on "NOx published in 1989"

Nanogram nitrite and nitrate determination in environmental and biological materials by vanadium (III) reduction with chemiluminescence detection.

Abstract: Nitrite in environmental water samples is reduced at room temperature to nitric oxide in acidic medium containing vanadium (III). Nitrate is also rapidly reduced after heating to 80-90 degrees C. Nitric oxide is removed from the reaction solution by scrubbing with helium carrier gas and is detected by means of a chemiluminescence NOx analyzer. Nanogram detection limits are obtained. The method has the advantage of not requiring highly acidic solutions for nitrate reduction and has been applied to the analysis of a variety of environmental waters, sediment, plant materials, and human urine and blood serum.

On the disproportionate role of tropospheric ozone as a filter against solar UV‐B radiation

Abstract: Increases in tropospheric ozone due to photochemical production, mostly due to growing industrial and technological NOx- emissions, in the industrialized northern hemisphere can overcompensate for increased UV-B radiation resulting from ozone depletions due to chlorine-catalyzed reactions in the stratosphere. This is especially the case in the summer months, because during this period a large fraction of the UV, which reaches the surface as diffuse radiation, is scattered by air molecules, droplets and aerosol particles in the troposphere. This causes a relatively longer path through tropospheric than through stratospheric ozone. Analyses using calculated, as well as observed ozone profiles at the station Hohenpeisenberg in Bavaria, FRG, show, that decreases of UV-B radiation at the earth's surface are possible even when total ozone declines.

Natural Gas Vehicles - A Review of the State of the Art

Abstract: This paper reviews the present state of the art in natural gas vehicles, focusing on engine technology and emissions. Natural gas engines generally show very low emissions of reactive hydrocarbons, carbon monoxide, and particulate matter, but NOx emissions can be fairly high. Approaches to NOx control include stoichiometric operation using a three-way catalyst and air-fuel ratio feedback, and «lean-burn/fast-burn» engines with NOx controlled through reduced flame temperature

Nitrogen oxides produced from lightning

Abstract: Independent measurements of nitrogen oxides (NOx = NO + NO2) were made in proximity to lightning using both a chemiluminescent NOx analyzer and an absorption spectrometer (COSPEC) tuned to the NO2 absorption at Langmuir Laboratory (elevation 3300 m), near Socorro, New Mexico. COSPEC data obtained from three separate lightning events, two from distant storms and one from direct observation of the plume from a single flash a few hundred meters away, yielded 4 to 10 × 1026 molecules NO2/flash after normalizing to flashes at sea level. Measurements from the NOx analyzer during two different thunderstorms indicated that the ratio of NO to NOx can remain high (0.7–0.8±0.1) for several minutes after a flash. Combining the data from the COSPEC with the NOx analyzer yields a production rate of approximately 3×1027 molecules N0x/flash. If 100 flashes/second is an assumed global lightning flash frequency, this production rate becomes 100 TgN/yr (TgN/yr = 1012 g nitrogen/yr) as an order of magnitude estimate.

A comparison of three photochemical oxidant mechanisms

Abstract: Three chemical mechanisms recently developed for use in urban- and regional-scale oxidant models have been compared. Approximately 400 simulations were conducted using an atmospheric model to determine the degree to which the mechanisms yield comparable predictions of ozone and other oxidants. The simulations were carried out over a range of initial conditions for a number of scenarios representative of urban and rural environments. Sensitivity studies were conducted to assess the effect of varying parameters, such as the initial ratio of volatile organic compounds (VOC) to oxides of nitrogen (NOx), the composition of the VOC mixture, and the temperature. The mechanisms were found to yield nearly identical predictions for ozone, peroxyacetylnitrate, and nitric acid under most conditions. Differences, however, were noted in simulations with (1) high NOx levels, (2) high levels of aromatic hydrocarbons, and (3) low afternoon temperatures. Predictions of hydrogen peroxide were in good agreement except at high VOC/NOx ratios where differences of as much as a factor of 3 were found.

Atmospheric Pollutants and Plant Metabolism

Abstract: Large amounts of sulfur dioxide (SO2) and nitrogen oxides (NOx) are continuously released into the atmosphere. When they react with water, these gases can form sulfurous acid (H2SO3), nitrous acid (HNO2) and nitric acid (HNO3). The weak acids are easily oxidized to the strong acids sulfuric acid and nitric acid. Photodissociation of nitrogen dioxide (NO2) in the atmosphere produces oxygen radicals which give rise to the formation of ozone (O3).

NOx sensor having catalyst for decomposing NOx

Abstract: An NOx sensor having an electrochemical cell having a solid electrolyte body and a first and a second electrode, a portion that permits restricted communication of the first electrode with an external measurement gas space, a catalyst disposed adjacent the first electrode for decomposing NOx, a device for applying a current between the first and second electrodes, a current measuring device for detecting a current flowing between the first and second electrodes, an oxygen partial pressure measuring device for detecting an oxygen partial pressure of the atmosphere surrounding the first electrode, and a control device for calculating the concentration of NOx contained in the measurement gas in the external space, based on a first and a second current value. The current value is detected by the current measuring device when the oxygen partial pressure detected by the oxygen partial pressure measuring device is higher than a predetermined level above which the decomposition of NOx by the catalyst will not occur and below which the decomposition of NOx will occur. The second current value is detected when the oxygen partial pressure is lower than the predetermined level.

Improvements in pollution control

Abstract: Pollutants from the exhaust of a lean running internal combustion engine are reduced by the engine having an exhaust catalyst capable of oxidising hydrocarbons and carbon monoxide and reducing NOx to nitrogen and being fitted with engine management means arranged to provide transient additional enrichment during periods of acceleration. A novel exhaust catalyst for this purpose is carried by a washcoat and is capable of oxidising hydrocarbons and carbon monoxide and reducing NOx to nitrogen and contains in addition 0.1 - 20% by weight of iron based on the total weight of catalyst and washcoat.

Glassmelting method with reduced NOx generation

Abstract: A glassmelting method wherein glassforming materials are preheated prior to entering the melting vessel by direct contact with combustion products from the melting vessel produced by combustion carried out with pure oxygen or oxygen-enriched air.

Vanadium Oxides (V2Ox) Catalysts for Dry-Type and Simultaneous Removal of Sulfur Oxides and Nitrogen Oxides with Ammonia at Low Temperature

Abstract: In order to develop highly functional catalysts for a dry-type, simultaneous removal of sulfur oxides (SOx) and nitrogen oxides (NOx) the catalytic activities of V2Ox/TiO2, V2Ox/TiO2/AC(activated carbon) and V2Ox/AC (4

Reduced Nox combustion method

Abstract: A combustion method enabling reduced NO x formation wherein fuel and oxidant are separately injected into a combustion zone in a defined velocity relation, combustion gases are aspirated into the oxidant stream prior to intermixture with the fuel, and the fuel is maintained free from contact with oxygen until the intermixture.

The Effects of CO2 Enrichment and Nitrogen Oxides on some Calvin Cycle Enzymes and Nitrite Reductase in Glasshouse Lettuce

Abstract: Glasshouse lettuce (cvs Pascal and Talent) was grown during late autumn and early winter in an atmosphere polluted with nitrogen oxides (NOx) generated from direct-fired natural gas burners used for C02 enrichment and warm air heating (high C02 + NOx treatment). Concentrations of 0-3-0-4 vpm NOx were detected during the daytime when near 3-fold C02 enrichment (1 000 vpm) was practised without heating. In cold weather, the C02 and NOx levels were dependent on the amount of heating required to maintain minimum temperatures of 5 °C (night) and 7 °C (day). Concentrations of between 2 000-5 000 vpm C02 and 1-2-5 vpm NOx were recorded at night during an intensely cold period in early January just prior to sampling for leaf enzymes. The plants were compared with those grown in unpolluted atmospheres with either a natural (340 vpm) or an enriched level (1 000 vpm) of C02. Pascal grown in elevated C02 had less activity per g fresh weight of RuBPc (E.C. 4.1.1.39), 3PGA phosphokinase (E.C. 2.7.2.3) and NADP-G3P dehydrogenase (E.C. 1.2.1.13) than plants grown in a normal ambient C02 atmosphere. The cytoplasmic enzyme PEPc (E.C. 4.1.1.31) was not significantly affected by the pure C02 enrichment. With high C02 + NOx the activities of the Calvin cycle enzymes were restored to values close to those present in non-enriched plants, while the activity of PEPc was increased. The activity of nitrite reductase (NiR) (E.C. 1.7.7.1) was increased in Pascal and Talent by high C02+NOx. Immunoblotting techniques were used to show that the increase in activity of this enzyme was accompanied by an increase in the steady-state concentration of the protein. Only one molecular form of NiR was detected by immunoblotting, and it would appear that the 'induction' of NiR activity resulted from increased net enzyme synthesis rather than activation of pre-existing enzyme. At the time of sampling no visible damage by high C02 +NOx was evident and the lack of symptoms may have been associated with the enhanced levels of nitrite reductase in these cultivars.

The effects of oxides of nitrogen and carbon dioxide enrichment on photosynthesis and growth of lettuce (Lactuca sativa L.)

Abstract: summary The response of glasshouse crops to the nitrogen oxide pollutants which may be generated during enrichment with O2 has been studied in controlled environments. Lettuce (Lactuca sativa L. cv. Ambassador) was grown in air containing either low CO2, (380μmol mol−1), high CO2, (1200 μmol mol −1), or high CO2 plus oxides of nitrogen? (NOx)- Carbondioxide enrichment increased the rate of emergence and expansion of leaves and the growth of Young plants. Addition of NOx (2μmol mol−1 NO and c. 0.5 μmol mol−1 NO2) to CO2-enriched air significantly reduced the yield, compared with the ‘clean, high CO2 treatment, without producing visible symptoms of toxicity. Fumigation of single plants in high CO2, with NOx rapidly inhibited photosynthesis per unit leaf area. This did not appear to be due to a reduction in stomatal conductance. Removal of NOx from the atmosphere caused a rapid and complete recovery in the rate of photosynthesis. Studies were made of the effects of growing Plants for long periods in atmospheres containing high CO2 and NOx on the photosynthetic capacity of single leaves when measured in NOx-free air. The decrease in photosynthetic rate as the fourth leaf aged occurred earlier in plants grown in CO2-enriched air than in those from the low CO2 treatment. Leaves which developed in the CO2-enriched air containing NOx did not suffer any long-term damage to photosynthetic activity in comparison with those of the ‘clean’ high CO2. In mature leaves the principal long-term effect of enrichment (with or without NOx was to reduce the rate of photosynthesis in saturating CO2. In contrast, there was less effect on the rate of Photosynthesis in low CO2. The absence of a long-term effect of NOx, on the photosynthetic capacity suggested that photosynthesis by the lettuce crop will be inhibited only during the transient periods of NOx accumulation in the glasshouse.

Process and apparatus using two-stage boiler injection for reduction of oxides of nitrogen

Abstract: This invention relates to methods and apparatus for reducing NOx in combustion effluent gases which comprise a two-stage injection process. NHi precursors (such as liquid-phase urea or ammonium hydroxide, or the like) are injected into the flue gas at temperatures greater than 1400°F in a first injection zone to reduce NO to nitrogen. This step is followed by injecting a peroxyl initiator, such as a hydrocarbon material (for example, methanol) into the flue gas at temperatures less than 1400°F to oxidize residual NO to NO2 in a second injection zone. NHi precursors and the peroxyl initiator are injected into the flue gas stream in first injection zone (12) and second injection zone (14), respectively, of boiler (10). An injection manifold (16) is supplied by a compressor (18) which provides air to injection nozzle (20).

Removal of SO2 and NOX from Stack Gas by Reaction with Calcium Hydroxide Solids

Abstract: Previous workers have shown that simultaneous SO2/NOX removal can be obtained in a dry scrubbing system with Ca(OH)2 promoted by an additive such as NaOH, and that fly ash and product recycle improve the reactivity of the solids toward SO2. To test SO2/NOX removal with fly ash and product recycle, bench-scale experiments with a packed bed reactor were performed at bag filter conditions. The most reactive solid for NOX removal was prepared by slurrying Ca(OH)2 with fly ash, CaSO3, and NaOH. The best conditions for NOX removal were the greatest temperature (125°C) and greatest concentrations of SO2 (1500 ppm) and O2 (20 percent). At the best conditions, NOX removed in 1 hour was 3-4 moles per 100 moles Ca(OH)2, compared to 5-10 moles SO2 removed per 100 moles Ca(OH)2. The best SO2 removal was obtained at the highest relative humidities/lowest temperatures (55% RH/ 65°C) with solids prepared by slurrying Ca(OH)2 with fly ash and NaOH. At these conditions, SO2 removed In 1 hour was 60-80 moles per 100 moles C...

Advanced NOx reduction processes using-NH and -CN compounds in conjunction with staged air addition

Abstract: The effectiveness of combustion modifications for the control of nitrogen oxide emissions from coal fired combustors is most often limited by problems due to carbon burnout or flame impingement. This paper presents new data on the use of selective reducing agents suggesting that a hybrid control scheme is possible which uses combustion modification to provide those conditions which optimize, the selective reduction process. Very low emission levels appear possible that can presently only be achieved by catalytic reduction. The experimental studies were conducted in a tunnel furnace which simulated the thermal environment within a pulverized coal boiler. Application of each of the agents (ammonia, urea, cyanuric acid, and ammonium sulfate) to an overall fuel lean environment, produced NO reduction behavior very similar to that of thermal deNO x . However, if the agent was added to the fuel rich zone of a rich/lean staged combustor, very high NO reductions were obtained after the leanout point. The result of the staging was to extend the effectiveness of the agent to lower temperatures relative to overall lean injection. Parametric variations indicated that, in addition to temperature, the most important variable was the rich zone stoichiometry. Kinetic modeling suggests that the rich zone acts primarily as a source of CO. At the rich/lean transition the CO is oxidized and excess OH is produced by the, usual chain branching reactions. For low initial CO concentrations the excess radicals, are consumed by: NH 3 +OH=NH 2 +H 2 O HNCO+H=NH 2 +CO The NH 2 is then available for reaction with NO to eventually yield N 2 . The strong rich zone stoichiometry dependence is exerted mainly through the amount of CO, supplied to the lean zone. Insufficient CO will limit the extent of the initial NH 3 or HNCO reaction.

Reducing NOx emissions with zinc catalyst

Abstract: A process for regeneration of cracking catalyst while minimizing NO x emissions is disclosed. A zinc-based DeNO x catalyst is present in an amount and in a form which reduces NO x emissions. Relatively small amounts of zinc oxides impregnated on a separate support having little or no cracking activity are preferred. The zinc NO x reduction catalyst can be a separate particle additive, or can be made in situ by adding a solution or dispersion of zinc or a compound thereof to the cracking unit, or to the hydrocarbon feed to the cracking unit.

Process for the improvement of the corrosion resistance of metallic materials

Abstract: A subject of the invention is a process for improving the corrosion resistance of a metallic material, characterized in that the metallic material is subjected cold to a surface treatment by a low-temperature plasma, at a pressure of 1 to 10 3 Pa in an atmosphere comprising at least one gas chosen from the following; oxygen, ozone, nitrogen, hydrogen, air, carbon dioxide, carbon monoxide, the oxides of nitrogen, water, combustion gases and mixtures of these with a neutral gas.

Zeolites as specific adsorbents for NOX and CO

Abstract: The use of zeolites rich in silicic acids having an Si:Al ratio of 1:1 to 100:1 as specific adsorbents for NOX or CO is proposed. Because of their property of specifically adsorbing NOX or CO, these zeolites, in particular those zeolites doped with such metals as Ca, Co, Ni, Fe, Cu, Ag, Pt or Ru, and having the above mentioned ratio of Si to Al, are especially suitable for the production of specific NOX or CO sensors based on semiconductors. Such sensors can be used as sensors for exhaust gases of automotive vehicles, for example.

Radial swirlers for low emissions gas turbine combustion

Abstract: Radial swirler were investigated for gas turbine combustor applications. with low NOx emissions as the main aim of the project. The flow regime of the combustor which was imposed by the radial swirler flow was shown by flow visualisation to feature a conical shaped swirling shear layer boundary and a comer recirculation zone. The flow patterns was independent of the swirl-vane angle but was a function of the swirler passage depth. A minimum swirler expansion ratio of 1.8 was required to achieve an adequate combustion efficiency. A high efficiency was not achieved in the weak region until there was a significant outer expansion and associated recirculation zone. However, there was a little influence of the expansion ratio on the weak extinction limit. Various non-conventional fuel injection methods such as swirler vane passage. radial central and wall injection were used with gaseous propane and natural gas and liquid kerosene and gasoil. Passage injection was undertaken to exploit the twin benefits of peripheral fuel injection and partial fuel and air mixing upstream of the swirlers outlet. Generally, most of the mixing between fuel/air took place in the shear layer. However, there was a major influence of the method of fuel injection on the NOx emissions. Low NOx emissions were achieved with the radial central injection, but ultra-low NOx emissions, comparable with the premixed situation, were achieved for passage and wall injection. This was due to the dependency of the local shear layer mixing near the swirler exit on the fuel placement as shown by the radial gas analysis traverse results in the plane just downstream of the radial swirler. Staged air and fuel combustion was investigated using lean-lean combustion concept. Low NOx emissions compatible with a high combustion efficiency was demonstrated with stable switching from pilot to main stage combustion. Finally, a double radial swirler with a high air flow was investigated using co and counter swirl and demonstrated ultra low NOx with a good stability with central injection into counter rotating swirler. These systems were shown to have the potential for dry solution to the industrial gas turbine NOx emissions regulations with a very high combustion efficiency.

Exhaust gas cleaning device for lean burn engine

Abstract: PURPOSE: To realize a high NOx cleaning efficiency in a lean burn engine by leading HC contained in the fuel into a catalytic converter as a deoxidating agent at the time of decomposing NOx. CONSTITUTION: HC and CO contained in the exhaust gas discharged from an engine 1 is cleaned with a ternary catalytic converter 4 while NOx is mainly cleansed with an NOx decomposing type catalytic converter 2. When the engine 1 is operating in the lean burn range, an ECU 9 determines from the detection signal of an HC measuring instrument 7 whether HC is contained by more than a reference value in the exhaust gas passed through the catalytic converter 2. If HC is not contained by more than the reference value, a solenoid valve 6 is controlled to open, and HC is pruged from a canister 3 and led to the catalytic converter 2. As a result, the catalytic converter 2 is able to securely decompose NOx in the exhaust gas with the HC serving as a deoxidating agent. COPYRIGHT: (C)1991,JPO&Japio

Dual-catalyst system to broaden the window of operability in the reduction of nitrogen oxides (NOx) with ammonia

Abstract: The objective of this research was to determine if a dual-catalyst system for NO reduction with NH 3 can achieve a given percent NO reduction over a wider range of temperatures and space velocities than either catalyst used alone in the same total reactor volume. The superiority of the dual-catalyst system was demonstrated experimentally, and a model was developed which predicted its performance very well from data on the individual catalysts

Thermally stabilized combustion

Abstract: Thermally stabilized combustion has a number of unique characteristics which permit the generation of steam or other forms of process energy from the heat of combustion of a gaseous or clean liquid fuel in remarkably compact, integrated apparatus while truly minimizing the concentrations of NOx, CO and unburnt fuel in the effluent. These characteristics, which have been identified by a long-range program of research, are described and the advantages and limitations of this process are discussed.