NOx Yield Research Articles

Applying composite fuels based on coal and finely dispersed wood in heat power engineering

Results of experimental research of thermal decomposition of composite fuels based on 2B brown coal (Borodinskoe deposit) and wastes of timber industry (finely dispersed wood) are presented. Elemental composition of researched fuels has been defined and technically analyzed. Kinetic constants have been calculated within Arrhenius model of the first order. It has been determined that with an increase of wood concentration up to 50% in composite fuel, its energy characteristics decrease by less than 2%, the maximum temperature of fuel thermal decomposition reduces by 9%, while SOx and NOx yield reduces by 50%, and fly ash – by 75%. An effective composite fuel composition of 50%/50% has been established. Results of performed experimental studies illustrate possible applications of composite fuels based on brown coal and wood at thermal power plants.

Ammonia Oxidation Process Catalyzed by Pt@XO2 (X = Ti, Zr, Ce, and Ce/Zr) Prepared by Photoreduction Process

In the nitric acid industry, platinum loss is the second largest cost due to vaporization of the Pt gauze catalyst at high temperature. In this research, Pt is loaded on TiO2, ZrO2, CeO2, and ceria–zirconia solid solution by photoreduction and used as catalysts for ammonia oxidation. Results show that Pt content of the obtained catalysts is effectively reduced to 0.08 wt %, but their catalytic performance is better than that of the traditional Pt gauze between 300 and 800 °C. The best catalyst, 3Pt@CeO2 with 0.0797 wt % Pt content, enabled complete ammonia transformation at 300 °C and 80% NOx yield at 800 °C with the space velocity of 235 000 h–1 and the oxygen-to-ammonia ratio of 15 in ambient pressure. After 50 h of continuous operation, no observable decay in performance was detected. Such excellent performance is ascribed to the lattice oxygen provided by CeO2 and the formation of Pt–Ce–O. These results provide a promising method of improving the current industrial Pt catalysts.

Nitrogen Fixation and NO Conversion using Dielectric Barrier Discharge Reactor: Identification and Evolution of Products

The recombination (synthesis and conversion) of nitric oxide was investigated using dielectric barrier discharge reactor at atmospheric pressure. In this work, products identification and its evolution of different gas components have been studied. In the NO/O2/N2 systems, nitric oxide (NO) can be removed via chemical oxidation and chemical reduction, and corresponding products are NO2 and N2, respectively. In the O2/N2 systems, N2O5 producing from the interaction of NO3 with NO2 was also observed. There is an optimum SED at which the highest NOx yield and best NO conversion efficiency will be achieved. In the H2O/O2/N2 systems, the formation of NO2, HNO2 and HNO3 were observed in both NF and NO conversion. The N2O molecule, as a byproduct of plasma chemical reaction, was observed in all the experiments when the H2O or O2 is presence in the simulated gas. The lowest energy cost of NO conversion is achieved at the SED of 1250 J/L.

Performance and emissions of long-chain alcohols as drop-in fuels for heavy duty compression ignition engines

The experimental research reported in this paper evaluates the potential of blends consisting of different biomass derived alcohols and vegetable oils as possible drop-in components in fossil Diesel fuel to overcome the need for modifications in engine hardware or calibration settings. Two C8-alcohols (n-octanol and its isomer 2-ethylhexanol) and two C10-alcohols (n-decanol and its isomer 2-propylheptanol) were blended with hydrotreated vegetable oil (HVO), rapeseed methyl ester (RME) and fossil Diesel. The blends were prepared to mimic the properties of standard Diesel fuel, in particular the cetane number was held constant. The percentage of fossil Diesel in the blends was 0%, 10% or 20%. The impact of the fuel composition on performance and emissions in a Volvo D13 single cylinder heavy duty research engine operated with standard engine settings was analyzed.Experiments revealed that the engine performance with the different blend compositions resembled that with standard Diesel with regard to the indicated thermal efficiency. Owing to the lower heating value of the fuel blends, the specific fuel consumption of the blends was about 6% higher than that of Diesel. Emissions were found to be similar among all alcohol-HVO blends. Compared to Diesel emissions, a reduction of carbon monoxide was measured for the blends. The yields of HC and NOx did not vary significantly for the different fuel blends. Soot emissions were substantially lower compared to those obtained with neat Diesel fuel. The lowest soot emissions were achieved with the fully renewable fuel composition, which did not contain any aromatic structures. Evaluation of the particle size distribution showed that the number of particles in agglomeration mode was substantially higher for standard Diesel fuel than for the blends. Alcohol-HVO-blends particle sizes were mainly in the nucleation mode range. Overall, the obtained results indicate that blends mainly containing long-chain alcohols could be a potential replacement for fossil Diesel fuel.

Effect of various admixtures on the properties of Mn-substituted cordierite

The effect of various admixtures (graphite, sawdust, mullite–silica fiber, vermiculite, boric acid, different size fractions of cordierite, corundum microspheres) in the cordierite stock (mixture of talc, clay, manganese oxide, and aluminum hydroxide) on the formation of Mn-substituted cordierite has been investigated. The admixtures exert an effect on the degree of cordierite formation, on the impurity phase content of the product (including its Mn2O3 content), on the surface concentration of manganese cations, on their oxidation state, on the texture of the catalysts, and on their ammonia oxidation activity. The highest NOx yield is observed with the catalysts containing a coarse fraction of cordierite and corundum microspheres, which are characterized by a high surface concentration of oxidized manganese cations and have large transport pores.

The catalytic performance of Ti-PILC supported CrOx–CeO2 catalysts for n-butylamine oxidation

A series of titanium pillared clays (Ti-PILC) materials are synthesized by different preparation conditions and the influence of the texture/structure nature of Ti-PILC on the catalytic performance of Ti-PILC supported CrOx–CeO2 mixed oxide (CrCe/Ti-PILC) catalysts for n-butylamine oxidation is investigated. The titanium pillared clays materials possess larger specific surface area and abundant porous structure with some irregular pore channel and nonuniform pore size distribution, due to the collapse of layered structure during pillaring process. The preparation conditions have significant impact on texture/structure properties of Ti-PILC. The synergistic effect between CrOx–CeO2 and Ti-PILC supports is promoted due to outstanding texture/structure properties of Ti-PILC, which enhances the catalytic activity for n-butylamine oxidation over Ti-PILC supported CrOx–CeO2 catalysts, especially for the 8CrCe(6:1)/Ti-PILC(12,20) catalyst. All the catalysts show a good control quality of NOx, and the yield of NOx is limited within 1 % at T98.

Tropospheric nitric acid columns from the IASI satellite instrument interpreted with a chemical transport model: Implications for parameterizations of nitric oxide production by lightning

AbstractThis paper interprets tropical tropospheric nitric acid columns from the Infrared Atmospheric Sounding Interferometer (IASI) satellite instrument with a global chemical transport model (GEOS‐Chem). GEOS‐Chem and IASI columns generally agree over the tropical ocean to within 10%. However, the GEOS‐Chem simulation underestimates IASI nitric acid over Southeast Asia by a factor of 2. The regional nitric acid bias is confirmed by comparing the GEOS‐Chem simulation with additional satellite (High Resolution Dynamics Limb Sounder, Atmospheric Chemistry Experiment Fourier Transform Spectrometer) and aircraft (Pacific Exploratory Mission (PEM)‐Tropics A and PEM‐West B) observations of the middle and upper troposphere. This bias appears to be driven by the lightning NOx parameterization, both in terms of the magnitude of the NOx source and the ozone production efficiency of concentrated lightning NOx plumes. We tested a subgrid lightning plume parameterization and found that an ozone production efficiency of 15 mol/mol in lightning plumes over Southeast Asia in conjunction with an additional 0.5 Tg N would reduce the regional nitric acid bias from 92% to 6% without perturbing the rest of the tropics. Other sensitivity studies such as modified NOx yield per flash, increased altitude of lightning NOx emissions, decreased convective mass flux, or increased scavenging of nitric acid required unrealistic changes to reduce the bias.

Oxidation of ammonia to NOx in a two bed reactor (Pt gauzes + oxide monolytic layer): Experimental studies and mathematical modelling

The behavior of one- and two-bed systems consisting of Pt–Rh gauze pack (the first bed) and monolith honeycomb catalyst (the second bed) in the conditions corresponding to those in the industrial medium pressure plant for NH3 oxidation to NOx was experimentally studied. At complete NH3 conversion in the gauze pack installation of the monolith results in the increase of the temperature in the gauzes and NOx yield. One dimensional mathematical model with heat and mass exchange between gas and solid phases and considering the effect of monolith as a heat shield was developed. The effect of monolith was supposed to consist preferentially in increasing the coefficients of heat and mass exchange between gas and solid phases in the gauze pack and determined by “hydrodynamic factor” γ depending on monolith geometry. It results in the shift of temperature front towards the frontal gauze and the reasonable increase of NOx yield.

The effectiveness of N2O in depleting stratospheric ozone

Recently, it was shown that of the ozone‐depleting substances currently emitted, N2O emissions (the primary source of stratospheric NOx) dominate, and are likely to do so throughout the 21st century. To investigate the links between N2O and NOx concentrations, and the effects of NOxon ozone in a changing climate, the evolution of stratospheric ozone from 1960 to 2100 was simulated using the NIWA‐SOCOL chemistry‐climate model. The yield of NOx from N2O is reduced due to stratospheric cooling and a strengthening of the Brewer‐Dobson circulation. After accounting for the reduced NOx yield, additional weakening of the primary NOxcycle is attributed to reduced availability of atomic oxygen, due to a) stratospheric cooling decreasing the atomic oxygen/ozone ratio, and b) enhanced rates of chlorine‐catalyzed ozone loss cycles around 2000 and enhanced rates of HOx‐induced ozone depletion. Our results suggest that the effects of N2O on ozone depend on both the radiative and chemical environment of the upper stratosphere, specifically CO2‐induced cooling of the stratosphere and elevated CH4 emissions which enhance HOx‐induced ozone loss and remove the availability of atomic oxygen to participate in NOx ozone loss cycles.

Various compositions of burner gas fuel and air streams for lower CO and NOx yield

The maximum temperature can be reduced and fuel combustion with the smallest possible amount of air can be achieved by optimizing the configuration of the fuel and the air streams and by adapting these streams to the firebox geometry. In this work, powerful secondary gas stream systems were modified in three ways in a rectangular prolonged firebox. The measurements established that the flow rate and geometrical distribution of these streams can determine the CO production rate, the excess air ratio must be finely tuned for complete combustion, and all these factors determine the production of NOx. If CO burn out is not achieved, it is reasonable to separate the gas into finer streams. The calculations demonstrate that long gas streams with higher flow rates along the firebox produce more CO, and a longer firebox is needed for the complete burn off of CO. In a second case, a very fine gas injection with streams grouped in packages near the burner was utilized in a firebox containing curved flame torches. Low CO yields were achieved, and the fuel combustion at nearly stoichiometric conditions resulted in lower NOx emissions.

NOX production by impulse sparks in air

An experimental study on the production of NOX by impulse sparks in air is presented. The emphasis is placed on the dependence of the NOX yield on the signature of the discharge current waveforms. A voltage and two current impulses were used in the experiments to create a spark and the NOX production was measured by the method of chemiluminescence. The results show that, for a given current waveform, the NOX production varies linearly with the peak current and the gap length. In addition, it was found that the NOX yield increases with the duration of the current for a given peak current.

Validation of flow simulation and gas combustion sub-models for the CFD-based prediction of NOx formation in biomass grate furnaces

While reasonably accurate in simulating gas phase combustion in biomass grate furnaces, CFD tools based on simple turbulence–chemistry interaction models and global reaction mechanisms have been shown to lack in reliability regarding the prediction of NOx formation. Coupling detailed NOx reaction kinetics with advanced turbulence–chemistry interaction models is a promising alternative, yet computationally inefficient for engineering purposes. In the present work, a model is proposed to overcome these difficulties. The model is based on the Realizable k–ϵ model for turbulence, Eddy Dissipation Concept for turbulence–chemistry interaction and the HK97 reaction mechanism. The assessment of the sub-models in terms of accuracy and computational effort was carried out on three laboratory-scale turbulent jet flames in comparison with the experimental data. Without taking NOx formation into account, the accuracy of turbulence modelling and turbulence–chemistry interaction modelling was systematically examined on Sandia Flame D and Sandia CO/H2/N2 Flame B to support the choice of the associated models. As revealed by the Large Eddy Simulations of the former flame, the shortcomings of turbulence modelling by the Reynolds averaged Navier–Stokes (RANS) approach considerably influence the prediction of the mixing-dominated combustion process. This reduced the sensitivity of the RANS results to the variations of turbulence–chemistry interaction models and combustion kinetics. Issues related to the NOx formation with a focus on fuel bound nitrogen sources were investigated on a NH3-doped syngas flame. The experimentally observed trend in NOx yield from NH3 was correctly reproduced by HK97, whereas the replacement of its combustion subset by that of a detailed reaction scheme led to a more accurate agreement, but at increased computational costs. Moreover, based on results of simulations with HK97, the main features of the local course of the NOx formation processes were identified by a detailed analysis of the interactions between the nitrogen chemistry and the underlying flow field.

Catalytic performance of pillared interlayered clays (PILCs) supported CrCe catalysts for deep oxidation of nitrogen-containing VOCs

Na-montmorillonite (Na-mmt) and different pillared interlayered clays (Al-PILC, Zr-PILC, Ti-PILC and Al2O3/Ti-PILC) supported CrCe catalysts for the deep oxidation of nitrogen-containing VOCs (NVOCs) are synthesized and characterized by a combination of X-ray diffraction, N2 adsorption/desorption, high resolution transmission electron microscopy, temperature-programmed reduction, temperature-programmed desorption and adsorption capacity tests techniques. The results indicate that a porous structure named “house of cards” forms during the pillaring and calcination processes. Both porous structure and acidity play important roles in deep oxidation of NVOCs. The mesoporous structure and the proper acid sites improve the catalytic activity of supported CrCe catalysts. Among all these catalysts, CrCe/Ti-PILC and CrCe/Al2O3/Ti-PILC exhibit higher catalytic activity than other catalysts. N-butylamine and ethylenediamine with –NH2 groups are easier to be destructed may be involved in the stronger adsorption on the acid sites of the catalysts. Much too strong adsorption of ethylenediamine on the acid sites leads to a lower activity compared with n-butylamine. Acetonitrile with C≡N bond and little interaction with acid sites is the most difficult to be decomposed. All the catalysts show a good control quality of NOx, and the yield of NOx is limited within 2% during the whole experimental temperature range.

Global chemical transport model study of ozone response to changes in chemical kinetics and biogenic volatile organic compounds emissions due to increasing temperatures: Sensitivities to isoprene nitrate chemistry and grid resolution

Global modeling studies show a wide variability in the response of the O3 budget to climate change as projected by applying Intergovernmental Panel on Climate Change scenarios in climate models. We employ sensitivity studies to elucidate the major uncertainties in the response of tropospheric O3 to perturbations in biogenic volatile organic compounds (BVOC) emissions and reaction rate coefficients due to changes in temperature. The change in global O3 burden due to an increase in BVOC emissions associated with a +5 K depends critically on the assumed treatment for the fraction of NOx recycled (0–100%) from isoprene nitrate (+9 to +34 Tg), in contrast to the chemical reaction rate coefficients response (−8 to −9 Tg). The model O3 burden shows sensitivity (40 Tg) to the NOx recycling efficiencies (0–100%) similar to the burden's sensitivity to the grid resolution (4° × 5°–1° × 1°). The correlation of O3 with total alkyl nitrates (ΣANs) in the surface air at a California forest site shows sensitivity to the NOx recycling (40–100%) similar to the correlation's sensitivity to the horizontal resolution (4° × 5°–1° × 1°). The results of the sensitivity simulations imply that the slope of O3 to ΣANs might be used to constrain the yield of isoprene nitrate and NOx recycling fraction, but better agreement could be achieved by using a higher‐resolution model with even higher NOx recycling from isoprene nitrate. Our results suggest that the reduction of NOx recycling from isoprene nitrate be set apart from that due to the effect of the grid resolution in the chemical transport model.

Surface and lightning sources of nitrogen oxides over the United States: Magnitudes, chemical evolution, and outflow

We use observations from two aircraft during the ICARTT campaign over the eastern United States and North Atlantic during summer 2004, interpreted with a global 3‐D model of tropospheric chemistry (GEOS‐Chem) to test current understanding of regional sources, chemical evolution, and export of NOx. The boundary layer NOx data provide top‐down verification of a 50% decrease in power plant and industry NOx emissions over the eastern United States between 1999 and 2004. Observed NOx concentrations at 8–12 km altitude were 0.55 ± 0.36 ppbv, much larger than in previous U.S. aircraft campaigns (ELCHEM, SUCCESS, SONEX) though consistent with data from the NOXAR program aboard commercial aircraft. We show that regional lightning is the dominant source of this upper tropospheric NOx and increases upper tropospheric ozone by 10 ppbv. Simulating ICARTT upper tropospheric NOx observations with GEOS‐Chem requires a factor of 4 increase in modeled NOx yield per flash (to 500 mol/flash). Observed OH concentrations were a factor of 2 lower than can be explained from current photochemical models, for reasons that are unclear. A NOy‐CO correlation analysis of the fraction f of North American NOx emissions vented to the free troposphere as NOy (sum of NOx and its oxidation products) shows observed f = 16 ± 10% and modeled f = 14 ± 9%, consistent with previous studies. Export to the lower free troposphere is mostly HNO3 but at higher altitudes is mostly PAN. The model successfully simulates NOy export efficiency and speciation, supporting previous model estimates of a large U.S. anthropogenic contribution to global tropospheric ozone through PAN export.

Nitric oxide yield from combustion of a low calorific gasification product gas: numerical and experimental study

The nitrogen oxide yield in a combustor burning an ammonia rich product gas from a bubbling bed gasifier has been investigated. The measurements showed a surprisingly small effect of the excess air in the combustor on the NOx emissions. To understand the reason for this behaviour the nitrogen chemistry in the combustor has been studied using CFD combined with a detailed description of the fuel-N chemistry. With higher oxygen excess a NOx yield of 22% is calculated compared to a measured NOx yield of 21%. In the case with lower oxygen excess the corresponding numbers are 20% and 18%, respectively.

Emissions Performance of the Parker Macrolaminate Premixer Tested Under Simulated Engine Conditions

Single-injector high-pressure rig evaluation of the prototype Parker macrolaminate dual fuel premixer (previously tested at NETL, Mansour et al., 2001) with pressure swirl macrolaminate atomizers was conducted under simulated engine operating conditions running on No. 2 diesel fuel (DF2). Emissions, oscillations and lean blowout (LBO) performance on liquid fuel at high, part and no load operating points (pressures of 160, 100, 120 psig, and inlet temperatures of 690, 570, 590°F, respectively) and various pressure drops (ΔP/P) and air fuel ratio conditions were investigated. The results indicate that the Parker premixer design has the potential to reduce the DF2 NOX emission to below 15 ppmv, 15% O2. At simulated high load conditions with a nominal flame temperature TPZ of 2700°F, the NOX and CO emissions are approximately 10 and 2.5 ppmv at 15% O2, respectively. These NOX results have not been corrected for fuel bound nitrogen (FBN). From the studies of Lee (2000), small amounts of FBN in the liquid fuel generally are completely converted over to fuel NOX under lean premixed conditions. The fuel tested has a nominal 60 ppmw of FBN which converts to an estimated fuel NOX of 4 ppmv at 15% O2. These results compare extremely favorable to existing commercially available premixer technologies tested under similar rig operating conditions. More importantly, the NOX yield for the Parker Macrolaminate premixer appears to be independent of operating conditions (from high to no load and various pressure drop conditions). Variations in combustor pressure, inlet temperature T2 and residence time (τ) or pressure drop (ΔP/P) does not seem to have an effect on the formation of NOX. According to Leonard and Stegmaier (1993), insensitivity of NOX formation to operating conditions is a good indication of high degree of premixing. Additionally, the premixer NOX data is only 1 to 2 ppmv higher than the jet stirred reactor (JSR) results (ran at T2=661°F,PCD=1 atm and TPZ=2762°F with similar DF2) of Lee et al. (2001) further confirming the quality of premixing achieved. Combustion driven oscillations was not investigated by tuning the rig so that oscillations would not be a factor.

Oxidation of unsymmetrical dimethylhydrazine over heterogeneous catalysts: Solution of environmental problems of production, storage and disposal of highly toxic rocket fuels

The catalytic oxidation of unsymmetrical dimethylhydrazine (UDMH) by air has been studied in a vibro-fluidized catalyst bed laboratory kinetic setup over catalysts CuxMg1−xCr2O4/γ-Al2O3, 32.9%Ir/γ-Al2O3 and β-Si3N4 in a temperature range 150–400°C. The catalyst CuxMg1−xCr2O4/γ-Al2O3 was found to be optimal regarding high yields of CO2 and low yields of NOx. A probable mechanism of UDMH heterogeneous catalytic oxidation is proposed. Catalyst CuxMg1−xCr2O4/γ-Al2O3 has been further used in the pilot plant specially designed for the destruction of UDMH. Results of testing the main fluidized bed catalytic reactor for UDMH oxidation and the reactor for selective catalytic reduction of NOx with NH3 are presented. These results prove that the developed UDMH destruction technology is highly efficient and environmentally safe.

Transfer of mass‐independent fractionation in ozone to other oxygen‐containing radicals in the atmosphere

Mass‐independent fractionation (MIF) of ozone has been observed in both the troposphere and stratosphere. Because ozone is a photochemically active species, its MIF signature can be imparted to other atmospheric molecules. Using a photochemical equilibrium model for short‐lived radical species, I have computed the expected MIF for typical mid‐latitude conditions. The model accounts for about ∼70% of recent measurements of Δ177O for H2O2 in rainwater, and predicts large MIF for NOx and ClO species (∼40–70‰), and their products (ClONO2 and HNO3). Furthermore, in the stratosphere oxygen exchange reactions between OH and NOx yield OH with Δ17O from 2 to 45‰. Stratospheric water produced during H abstraction by OH would be similarly mass‐independently fractionated. In the troposphere rapid exchange between OH and H2O erases any MIF signature in OH. These model results depend on several O exchange reactions with unknown activation energies or with rate coefficients known only as upper limits.

NOx production in spark and corona discharges

This paper presents an experimental study on the production of NO and NO2 as a function of electrical energy in laboratory sparks and corona. The results show that both the NO and NOx yield increase almost linearly with the energy per unit length of the discharge. From the data, it is estimated that the spark discharges with energy in the range of 0.5–2.5J generate (2.76±0.2)×1016 NO molecules/J and (2.97±0.2)×1016 NOx molecules/J. In order to test the effect of humidity on the NOx production, experiments were conducted both at 37% and 87% relative humidity. However, any significant difference in the NO or NOx yield with humidity was not detected. Experiments were also conducted to evaluate NOx production in corona discharges. In the experiment, a DC corona discharge is maintained by applying a high voltage to the central wire of a coaxial metal cylinder. The applied voltage and the current were measured as a function of time and from this the energy dissipation in the corona is estimated. The results show that the efficiency of corona (with an average current of about 300μA) in producing NOx is 5.7×1014 and 3.6×1014molecules/J, respectively, for positive and negative polarity. The NOx yield was slightly higher for positive corona while the NOx production in corona is in general two orders of magnitude smaller than that of spark discharges.