Showing papers on "NOx published in 1979"

The Role of NO and NO2 in the Chemistry of the Troposphere and Stratosphere

Abstract: Oxides of nitrogen play an important role in the radical chemistry of the atmosphere and in the production and destruction of tropospheric and stratospheric ozone. Ozone is a principal agent in forming the OH radical which attacks inert gases in the troposphere. The acidity of precipitation is in part the result of HNO3 and H2SO4 formed by reactions involving the OH radical. Fast removal processes for oxides of nitrogen in the lower troposphere are described. Long-distance transport of oxides of nitrogen in peroxy-acetyl nitrate also receives attention. In the stratosphere, the participation of NO and NO2 in reactions that influence the equilibrium of photochemical systems may render the total ozone abundance insensitive to additions of oxides of nitrogen.

Mechanism of ozone generation in air-fed ozonisers

Abstract: The mechanism of ozone generation in the silent discharge of air-fed ozonisers is studied theoretically and experimentally. The nitrogen oxides (NOx) formed in the silent discharge have been found to play an important role in the process of ozone generation due to the catalytic cycle for O3 destruction: NO+O3 to NO2+O2 and NO2+O to NO+O2. Taking this catalytic cycle into account, a mechanism is proposed to explain the characteristics of ozone generation in air-fed ozonisers. The electron impact dissociation coefficients of O2, N2 and O3 and the gas temperature in the silent discharge are estimated by the computer matching of the theoretical calculations to experimental results.

Three-way catalytic process for gaseous streams

Abstract: A process for the catalytic combustion of carbon monoxide and hydrocarbons and the catalytic reduction of the oxides of nitrogen contained in a gas stream. The process involves intimately contacting the gaseous stream with a catalyst bed comprising copper metal or copper ion and a high silica zeolite.

Computer modeling of smog chamber data: Progress in validation of a detailed mechanism for the photooxidation of propene and n‐butane in photochemical smog

Abstract: A detailed mechanism is presented for reactions occurring during irradiation of part-per-million concentrations of propene and/or n-butane and oxides of nitrogen in air. Data from an extensive series of well-characterized smog chamber experiments carried out in our 5800-liter evacuable chamber–solar simulator facility designed for providing data suitable for quantitative model validation were used to elucidate several unknown or uncertain kinetic parameters and details of the reaction mechanism. The mechanism was then tested against the data base from the smog chamber runs. In general, most calculated concentration–time profiles agreed with experiments to within the experimental uncertainties. Fits were usually attained to within ∼±20% or better for ozone, NO, propene, and n-butane, to within ∼±30% or better for NO2, PAN, methyl ethyl ketone, 2-butyl nitrate, butyraldehyde, and (in runs not containing propene) methyl nitrate, to within ⋐±50% or better for the minor products 1-butyl nitrate and propene oxide, and to within a factor of 2 for methyl nitrate in propene-containing runs. Propionaldehyde was consistently underpredicted in all runs; it is probably a chamber contaminant. For formaldehyde and acetaldehyde, the major products in both systems, fits to within ⋐±20% were often obtained, yet for a number of experiments, significantly greater discrepancies were observed, probably as a result of experimental and/or analytical problems. The good fits to experimental data were attained only after adjusting several rate constants or rate constant ratios related to uncertainties concerning chamber effects or the chemical mechanism. The largest uncertainty concerns the necessity to include in the mechanism a significant rate of radical input from unknown sources in the smog chamber. Other areas where fundamental kinetic and mechanistic data are most needed before a predictive, detailed propene + n-butane-NOx-air smog model can be completely validated concern other chamber effects, the O3 + propene mechanism, decomposition rates of substituted alkoxy radicals, primary quantum yields for radical production as a function of wavelength for aldehyde and ketone photolyses, and the mechanisms and rates of reactions of peroxy radicals with NO and NO2.

Fixation of Nitrogen in the Prebiotic Atmosphere

Abstract: Reactions between nitrogen and water in the air surrounding lightning discharges can provide an important source of nitric oxide even under conditions where oxygen is a minor atmospheric constituent. Estimates are given for the associated source of soluble nitrite and nitrate. It is shown that lightning and subsequent atmospheric chemistry can provide a source of nitrate for the primitive ocean as large as 106 tons of nitrogen per year, sufficient to fill the ocean to its present level of nitrate in less than 10^6 years.

Measurements of H2O2 and HNO3in rural air

Abstract: In a preliminary study of two new analytical techniques, we have measured hydrogen peroxide (H2O2) and nitric acid (HNO3) near ground level at a rural site near Boulder, Colorado during February, 1978. H2O2 was measured with a liquid-phase chemiluminescence technique. HNO3 in a sample air stream was converted to NO2 in a packed quartz tube at 350°C, and detected with a fast response NOx monitor. O3, CO, NO, and NO2 were also measured simultaneously. H2O2 was found between 0.3 and 3 ppb. HNO3 concentrations as high as 5 ppb were found with NOx always greater than HNO3 by at least a factor of 5.

Sensitivity of the predicted CO‐OH‐CH4 perturbation to tropospheric NO x concentrations

Abstract: Measurements indicate that ambient NOx(NO + NO2) concentrations vary over at least an order of magnitude in the troposphere. Thus it is of interest to study atmospheric chemistry with NOx concentrations covering this range. In this paper we present steady state calculations which show that as NOx concentrations are increased from very low values, the hydroxyl radical concentration increases at first and then decreases. This change of behavior occurs at a concentration of NO2 of about 0.23 ppb in the model. Also, the response of the atmosphere to increased CO fluxes undergoes a qualitative change as a function of the concentration of NOx. At low levels of NOx concentration, an increase in CO fluxes into the atmosphere depletes the OH concentration and increases the concentrations of CH4 and H2, as reported in the literature. However, at high values of NOx concentration, increased CO fluxes give rise to an increase in the OH concentration and, consequently, a decrease in the concentrations of CH4 and H2.

The August 1972 solar proton event and the atmospheric ozone layer

Abstract: OXIDES of nitrogen are generally accepted to be important for regulating the atmospheric ozone content through catalytic reactions first described by Crutzen1 and Johnston2. In the stratosphere, nitric oxide is produced naturally by the reaction of nitrous oxide, emanating from the biosphere, with excited oxygen atoms generated by ozone photolysis at wavelengths shorter than about 310 nm. As Crutzen et al.3 have pointed out, large amounts of nitric oxide may also be produced by high-energy solar protons, mainly at geomagnetic latitudes greater than 60°, and altitudes above about 35 km. The ozone measurements reported here made during an intense solar proton event in August 1972 suggest that NO production rates due to ionising particles are higher than those calculated by Crutzen et al.

Combustion method for reducing NOx and smoke emission

Abstract: A combustion method which can reduce the emission of NOx and smoke. In sharp contrast to the conventional combustion method, the method of the invention can remarkably reduce the emission of both of NOx and the smoke simultaneously, by adopting a specific flow pattern of fuel and combustion air in the combustion chamber, the pattern has been obtained as a result of studies and experiments concerning the influence of the intensity of mixing of the fuel and the combustion air on the emission of NOx.

Treatment of exhaust gas streams

Abstract: The treatment of gas streams such as exhaust gases from internal combustion engines to remove carbon monoxide and hydrocarbons by oxidative combustion and NOx constituents by reduction to nitrogen and water is accomplished by contacting the gas streams with a catalyst composition comprising a Group VIII metal supported on the surfaces of the pores of a hydrothermally stable hydrophobic form of zeolite Y.

Selective adsorption of NO{HD x {b from gas streams

Abstract: In the process for selectively adsorbing NOx from nitric acid plant acid absorber tower tail gas streams wherein the tailgas stream, comprising water vapor, oxygen, nitrogen and unreacted NOx is first dried by passage through a silica adsorbent mass and thereafter the NOx is selectively adsorbed in a zeolitic molecular sieve bed, the improvement which comprises utilizing as the molecular sieve adsorbent a zeolite Y composition having a high degree of ionic character coupled with a high degree of acid stability.

An estimate of the nitrogen oxides (NOx) removal rate in an urban atmosphere

Abstract: A mathematical model developed to estimate nitrogen oxide diffusion in urban atmosphere is presented. The model was devised with NO/sub x/ atmospheric data taken from the St. Louis and Los Angeles areas. Daytime and nighttime atmospheric variations that affect chemical diffusion of atmospheric NO/sub x/ are accomodated by the model. 9 references, 1 table.

Pollution-free coal combustion process

Abstract: A continuous process for the combustion of solid fuels in the presence of strong sulfuric acid under conditions such that oxides of nitrogen are not formed and oxides of sulfur and particles of ash are effectively prevented from contaminating the gaseous products released to the atmosphere.

Method of reducing oxides of nitrogen concentration in regeneration zone flue gas

Abstract: A method for controlling the oxides of nitrogen concentration in the exit flue gas from the regeneration zone of a catalytic cracking unit employing carbon monoxide combustion promoters which comprises monitoring the oxides of nitrogen concentration in the exit flue gas and adjusting the concentration of combustion promoter present in the regeneration zone to maintain the oxides of nitrogen concentration below a predetermined limit.

Process for the removal of SOx and NOx from gaseous mixture containing the same

Abstract: A combination process is provided in which a gaseous mixture comprising SOx and NOx is reacted with cerium oxide at a temperature ranging from about 500° C. to about 700° C. to form cerium oxysulfate and a gas which is at least partially desulfurized. The latter is contacted with cerium oxysulfate at a temperature ranging from about 500° C. to about 700° C. in the presence of ammonia at net oxidizing conditions to reduce the NOx content of the gaseous mixture. The process may be conducted in one reaction zone or in a plurality of reaction zones. The cerium oxide reactant may be regenerated by reacting cerium oxysulfate with a reducing gas such as hydrogen.

Method of purifying exhaust gas of internal combustion engine

Abstract: PURPOSE:To completely remove NOX, by controlling the supplied quantity of ammonia depending on the measured quantity, NOX concentration and temperature of exhaust gas, and supplying the ammonia to the downstream of a position when the measurement of NOX is achieved. place. CONSTITUTION:Signals obtained by an NOX concentration measuring unit 2 and an exhaust gas quantity measuring unit 3 are integrated to calculate the total quantity of NoX contained in exhaust gas to produce the first ammonia control signal 4. The ratio of the quantity of ammonia to that of NOX is determined by a ratio setting unit 5 from the first ammonia control signal 4 and a signal corresponding to the temperature in a denitration reactor 1 to supply a signal to a flow controller 6. A signal is applied from the controller 6 to a flow meter 9 and a control valve 10 to regulate the degree of opening of the control valve to supply a prescribed quantity of ammonia from an ammonia feeder 8 to injection nozzles 13 provided in the exhaust outlet duct 12 of an internal combustion engine 7.

Disposal of oxides of nitrogen and heat recovery in a single self-contained structure

Abstract: A self-contained single structure for NOX disposal and heat recovery, comprising a burner means (12), including means to supply NOX (oxides of nitrogen) gases (146) to be reduced, primary air (130) in less-than-stoichiometric flow rate, and gaseous fuel (128) at selected flow rate. The gases flow into a first reducing section (114), in which the fuel is burned in a reducing atmosphere, and the NOX gases are reduced. Fire tubes (124) carrying water or steam are positioned to receive heat from the burning gases. At the outlet of the reducing section precooled stack gases (135) are injected (137) into the flame so as to cool the hot products of combustion. The direction of flow of hot gases is turned to 90° (164) in a second section. At the end of the second section the direction of flow is turned 90° so as to be counter to the first direction in a third or oxidizing section (182) to which secondary air is added (172) and a fourth or boiler section (124) accepts the hot gases from the oxidizing section to recover the waste heat.

Pollutant formation and control in spark-ignition engines

Abstract: Publisher Summary Spark-ignition engines are a major source of urban air pollution. The engine exhaust is the source of nitrogen oxides and carbon monoxide emissions. This chapter discusses the dimensions of the problem and indicates the relative importance of mobile and stationary sources. It reviews the fundamental aspects of pollutant formation and control in the spark-ignition (SI) engine concepts. The exhaust reactors and catalytic converters provide substantial additional reductions in emissions before the exhaust gases enter the atmosphere. While nitric oxide (NO) and nitrogen dioxide (NO2) are grouped together as NOx emissions, NO is the only oxide of nitrogen produced in significant quantities inside the engine. It is formed in the burning and burned gases. The chemistry of NO formation in gas phase mixtures of O, N, C, and H has been extensively studied in shock tubes, stirred reactors, flames, and rate constants for the important reactions have been determined. NO forms in both the flame front and the post-flame gases. However, the formation in the post-flame gases is generally much more important under typical SI engine conditions because compression to higher temperatures occurs post-combustion.

Oxides of nitrogen and the clouds of Venus

Abstract: Nitric oxide may be produced in the atmosphere of Venus by lightning storms in the clouds. The paper suggests that the odd nitrogen thus formed may play an important part in the chemistry of the clouds. Specifically, production rates for NO2 in the limiting case of high NO concentrations are estimated. If the NO density is high, it is suggested that NO2 may catalyse the production of sulfuric acid aerosol from sulfur dioxide and water vapor, and may also form nitrogen-sulfur compounds such as nitrosyl sulfuric acid, NOHSO4. The large partricles seen by the Pioneer Venus sounder probe may contain considerable quantities of NOHSO4. If this is the case, odd nitrogen must be present in the atmosphere in at least a parts-per-million mixing ratio.

Redn. of nitrogen- and sulphur-oxide emissions from combustion - by preheating the fuel e.g. by combustion gases to 150-450 deg. C

Abstract: Pollutant emissions of SO2 and/or NOX during the burning of conventional fuels are reduced by preheating the fuel to at least 150 deg C before it comes into contact with high concns of O2. The temp of preheating depends on the fuel (being lower for lighter fuels) and on the effect required. Partic. pref are temps above 200 deg C, to a max of approx 450 deg C. Where a gas-atomising nozzle is used, both the fuel and the atomising medium (eg air) should be preheated. Preheating may be done in a heat exchanger, pref against combustion gases. Process is simple, and can be added to existing installations without great expenditure. The CO concn is also reduced.

Corrosion and fouling potential in diesel exhausts

Abstract: The exhaust gases from five large diesel engines--1500 to 6400 kW (2000 to 8900 hp)--were sampled at three sites over a range of engine operating conditions using fuels with 0.05 to 0.8 percent sulfur. Measurements of SO2, SO3, CO, CO2, H2O, NO, NOX, chlorides, acid dew point, peak rate temperature of acid deposition, particulate loading, particle sizing, particulate composition and smoke number were made to characterize the diesel exhaust. Total particulate emissions varied directly with fuel sulfur content. Fifty percent or greater of the total particulate emissions were less than or equal to 0.3 micrometers in size. The fouling and corrosion potential of diesel exhaust gas can be approximated given the fuel analysis and engine operating conditions.

Oxides of nitrogen formed in high-intensity methanol combustion

Abstract: The oxidation of methanol in a jet-stirred reactor has been studied to characterize the mechanisms of methanol combustion and nitric oxide formation in a high-intensity, turbulent environment. Fuel/air equivalence ratios of 0.7 to 1.4 were investigated at a constant temperature of 1870 K and mean reactor residence times of ca. 2.5 msec. Total NO x was measured along with major cornbustion products, CO, CO 2 , H 2 O, O 2 , CH 4 , and C 2 H 2 . Emission spectroscopy was used to determine oxygen atom concentration as well as relative levels of electronically excited radical species, OH • , CH • , and C 2 • . Comparative measurements were repeated with methane as the fuel under similar reactor conditions. Measured NO x for methanol was 8.5 ppm maximum at equivalence ratio 1.10. The ratio of methanol-NO x to methane-NO x varied between one-half for fuel-lean combustion to one-third for equivalence ratios at or above stoichiometric. Molecular O 2 , atomic-O and calculated OH were essentially the same for both fuels. At fuel-rich conditions, methanol demonstrated higher carbon monoxide. Concentrations of CH 4 and C 2 H 2 were markedly higher with methane fuel, as were CH • and C 2 • while OH • was slightly higher. Evidence indicated the persistence of the C−O bond in the methanol molecule during oxidation. The NO x , O-atom, and O 2 concentrations indicated that the extended Zeldovich mechanism was insufficient to explain the difference in observed NO x for methanol and methane. It was hypothesized that hydrocarbon fragments played an important role in NO x formation in the stoichiometric and rich mixtures; it was concluded that low methanol-NO x was due to low hydrocarbon levels.

Analytical apparatus and method employing purified ozone

Abstract: Ozone generated for chemiluminescent reaction in an analyzer for the measurement of oxides of nitrogen, for example, is purified by passing the ozone through a bed of silica gel, thereby removing substances that interfere with the analysis.

Flame modifier to reduce NOx emissions

Abstract: A method and apparatus for modifying the flow pattern of post ignition combustion products of a flame, preferably an oil fueled and air sustained flame, are disclosed which substantially reduces the concentration of NO x emissions

Reactions of NH3 with NO in coal-derived combustion products

Abstract: The selective homogeneous gas-phase reduction of nitric oxide with ammonia is a promising approach for the control of nitric oxide emissions from combustion sources. A laboratory study at a scale of 3,000,000 Btu/hr was conducted to evaluate the process in coal-fired power plants. Four coals (Utah bituminous, New Mexico subbituminous, Illinois bituminous, and Pittsburgh bituminous) were tested to determine levels of NOx reduction achievable as well as byproduct emissions. In addition to coal type, the primary variables investigated were (1) the amount of ammonia injected, (2) the temperature of the combustion products at the point of injection, and (3) the effect of the simultaneous addition of hydrogen with ammonia in the NOx removal process. The results of these experiments showed that NOx reductions of 65% were obtained with ammonia injection into coal-derived combustion products at an ammonia injection ratio of one mole of ammonia per mole of NOx. These results were similar to those obtained with natural gas firing in the same system and were comparable to those previously obtained with other natural gas- and oil-fired systems. However, the temperature dependence was found to vary from coal to coal. The Navaho exhibited peak reductions at the lowest temperature, 1720°F, while the Illinois coal showed peak reduction occurring at 1830°F. Typically, natural gas exhibited peak reductions at 1750°F. The unexplained variation in optimum process temperature with coal type indicates that evaluation testing would be prudent in situations where maximum NOx control is desired and where no previous experience is available for the coal in question. The simultaneous addition of small quantities of hydrogen can be used to increase the NO reductions and decrease ammonia emissions at temperatures lower than the optimum.