Control Of Nitrogen Oxide Emissions Research Articles

Impacts of interstate transport of pollutants on high ozone events over the Mid-Atlantic United States

The impacts of interstate transport of anthropogenic nitrogen oxides (NOx) and volatile organic compound (VOC) emissions on peak ozone formation in four nonattainment areas (i.e., Baltimore, Philadelphia-Wilmington-Atlantic City, Pittsburgh-Beaver Valley and Washington, DC) in the Mid-Atlantic U.S. were quantified in this study. Regional air quality and sensitivities of ground-level ozone to emissions from four regions in the eastern U.S. were simulated for three summer months (June, July and August) in 2007 using the U.S. EPA's Community Multiscale Air Quality model with the decoupled direct method 3D. The emissions inventory used in this study was the 2007 Mid-Atlantic Regional Air Management Association Level 2 inventory, developed for State Implementation Plan screening modeling for the Ozone Transport Commission region. The modeling results show that responses of peak ozone levels at specific locations to emissions from EGU (i.e., electric generating unit) and non-EGU sources could be different. Therefore, emissions from EGU and non-EGU sources should be considered as two different control categories when developing regional air pollution mitigation strategies. Based on the emission inventories used in this study, reductions in anthropogenic NOx emissions (including those from EGU and non-EGU sources) from the Great Lake region as well as northeastern and southeastern U.S. would be effective for decreasing area-mean peak ozone concentrations during the summer of 2007 in the Mid-Atlantic ozone air quality nonattainment areas. The results also show that reductions in anthropogenic VOC emissions from the northeastern U.S. would also be effective for decreasing area-mean peak ozone concentrations over the Mid-Atlantic U.S. In some cases, reductions in anthropogenic NOx emissions from the Great Lake and northeastern U.S. could slightly increase area-mean peak ozone concentrations at some ozone monitors in the Pittsburgh-Beaver Valley and Washington, DC areas. However, the disbenefit of the slight increase in ozone concentrations attributed to the NOx emission controls was far outweighed by the overall ozone air quality benefits over the Mid-Atlantic region.

Optimization of FOME (fish oil methyl esters) blend and EGR (exhaust gas recirculation) for simultaneous control of NOx and particulate matter emissions in diesel engines

There is world-wide interest in the search for alternatives to petroleum derived fuels for diesel engines. Key driving factors are depleting fossil-fuel reserves all over the globe as well as the environmental impact of burning fossil fuels that cause pollution and global warming. Bio-diesel derived from edible oils, non-edible oils and animal fats can be used in diesel engines with little or no modification. Non-land-based renewable sources are becoming important for the production of biodiesel due to limited availability of land. Under these circumstances, fish oil extracted from wastes of processed marine fish and refined through transesterification becomes an attractive alternative for the production of biodiesel. In this work, performance and emission characteristics of FOME (fish oil methyl ester) and its blends are evaluated in a direct-injection single-cylinder constant-speed diesel engine primarily used in the agricultural sector. It is seen that 20% FOME blend gives almost the same brake thermal efficiency with lower unburned hydrocarbons, carbon monoxide and soot emissions but higher NOx (nitrogen oxides) emissions compared to diesel fuel. EGR (Exhaust Gas Recirculation) is used to control NOx emissions. Percentage of EGR is varied to determine optimum EGR for 20% FOME blend.

The observed response of Ozone Monitoring Instrument (OMI) NO2 columns to NOx emission controls on power plants in the United States: 2005–2011

We show that Aura Ozone Monitoring Instrument (OMI) nitrogen dioxide (NO2) tropospheric column data may be used to assess changes of the emissions of nitrogen oxides (NOx) from power plants in the United States, though careful interpretation of the data is necessary. There is a clear response for OMI NO2 data to NOx emission reductions from power plants associated with the implementation of mandated emission control devices (ECDs) over the OMI record (2005–2011). This response is scalar for all intents and purposes, whether the reduction is rapid or incremental over several years. However, it is variable among the power plants, even for those with the greatest absolute decrease in emissions. We document the primary causes of this variability, presenting case examples for specific power plants.

Atmospheric emissions of European SECA shipping: long-term projections

We modeled the projections of the major atmospheric emissions from shipping of the European sulphur emission control area that includes the Baltic Sea, the North Sea, and the English Channel until 2040. Emission projections were calculated separately for every ship on annual basis, and the model took into account traffic growth, fleet renewal, and the forthcoming regulations. The regulation on sulfur content of ship fuels will drastically decrease the emissions of sulfur oxides and particulate matter (PM2.5). As the regulation on nitrogen oxides (NOx) only affects the new diesel engines, the decrease in emissions will be seen parallel with the fleet renewal. Globally internalized limits will turn NOx emissions to decrease with moderate traffic growth. However, by designating the Baltic Sea and the North Sea as NOx emission control areas, more drastic decrease would occur. CO2 emissions will stay almost constant through the studied timeline. Results show that European Commission's CO2 target for 2050 will not be reached without implementation of market based measures among the North Sea and the Baltic Sea fleets. Results present new information for decision makers to further develop international regulations of shipping especially in the Baltic Sea and the North Sea.

Major Factors Influencing the Health Impacts from Controlling Air Pollutants with Nonlinear Chemistry: An Application to China

Predicting the human-health effects of reducing atmospheric emissions of nitrogen oxide (NOx) emissions from power plants, motor vehicles, and other sources is complex because of nonlinearity in the relevant atmospheric processes. We estimate the health impacts of changes in fine particulate matter (PM2.5) and ozone concentrations that result from control of NOx emissions alone and in conjunction with other pollutants in and outside the mega-city of Shanghai, China. The Community Multiscale Air Quality (CMAQ) Modeling System is applied to model the effects on atmospheric concentrations of emissions from different economic sectors and geographic locations. Health impacts are quantified by combining concentration-response functions from the epidemiological literature with pollutant concentration and population distributions. We find that the health benefits per ton of emission reduction are more sensitive to the location (i.e., inside vs. outside of Shanghai) than to the sectors that are controlled. For eastern China, we predict between 1 and 20 fewer premature deaths per year per 1,000 tons of NOx emission reductions, valued at $300-$6,000 per ton. Health benefits are sensitive to seasonal variation in emission controls. Policies to control NOx emissions need to consider emission location, season, and simultaneous control of other pollutants to avoid unintended consequences.

Air-pollution emission control in China: Impacts on soil acidification recovery and constraints due to drought

The Chinese government has established compulsory targets to reduce sulfur dioxide (SO2) and nitrogen oxide (NOx) emissions by 8% and 10%, respectively, during 2010–2015. In this study, the effect of the policy was evaluated by predicting the recovery of acidified forest soil in Chongqing, an area severely impacted by acid rain in southwest China. Since precipitation has decreased significantly in this area in recent years, the impact of drought on soil acidification was also considered. A dynamic acidification model, MAGIC, was used to predict future trends in soil chemistry under different scenarios for deposition reduction as well as drought. We found that the current regulation of SO2 emission abatement did not significantly increase soil water pH values, the Ca2+ to Al3+ molar ratio (Ca/Al), or soil base saturation to the level of 2000 before 2050. NOx emission control would have less of an effect on acidification recovery, while emission reduction of particulate matter could offset the benefits of SO2 reduction by greatly decreasing the deposition of base cations, particularly Ca2+. Continuous droughts in the future might also delay acidification recovery. Therefore, more stringent SO2 emission control should be implemented to facilitate the recovery of seriously acidified areas in China.

Simultaneous removal of NO and SO2 from combustion fuel gases using supported copper oxide catalysts

Nitrogen oxide (NOx) and sulphur dioxide (SO2) emissions produced by the combustion of fuel in stationary sources, such as power stations, industrial heaters or cogeneration plants, cause significant environmental problems. Selective catalytic reduction (SCR) is a well established process for the control of NOx emissions mainly due to its efficiency, selectivity and economics. High removal efficiencies for both NOx and SO2 can be achieved with the use of copper oxide catalysts, as they act as sorbents for the latter - forming copper sulfate - and catalyze the reduction of the former - to N2, in the presence of NH3. An added advantage is that these catalysts are relatively easy to be regenerated under reducing conditions. This study examines the deactivation and regeneration procedures of copper oxide catalysts/sorbents that are supported on Al2O3, SiO2, CeO2-Al2O3, in the presence of SO2 and identifies the appropriate conditions for the simultaneous removal of NO and SO2. The results obtained indicate that copper oxide supported on alumina, ceria-alumina and silica carriers, can be used as effective catalysts for the simultaneous removal of NO and SO2. Furthermore, they can be easily regenerated with a gas mixture of 1 % NH3/Ar at an optimum temperature of 673 K and they retain their initial activity. Thus, the use of regenerative fixed bed catalytic reactor appears as one of the most promising technologies however, further research focusing in new catalytic materials performance is necessary.

Non-volatile particle characteristics of a light-duty diesel engine with pilot injections and exhaust gas recirculation

A pilot injection has been used widely in diesel engines for the control of nitrogen oxide emissions and noise. However, very little information on the characteristics of particulate matter emissions with a pilot injection is available. In this paper, the non-volatile particle emissions of a light-duty common-rail production diesel engine under the impact of a pilot injection are studied in terms of the particle number concentration and the particle size distribution with the measurements taken with a scanning mobility particle sizer. For various key parameters such as the fuel quantity and the injection timing, the results illustrate how a pilot injection alongside a main injection could affect particulate matter emissions, which are also shown to be closely related to the engine mode and the exhaust gas recirculation level. It is revealed that advancing the pilot injection generally reduces the number and size of particles in both the accumulation mode and the nucleation mode. It is also found that an increase in the pilot fuel quantity increases the total number and size of particles, with a significant impact on the number of accumulation-mode particles, which overwhelms the decrease in the number of nucleation-mode particles.

Most effective combustion technologies for reducing Nox emissions in aero gas turbines

The growth in air transportation volume has important global environmental impacts associated with the potential for climate change. Jet aircraft emissions are deposited directly into the upper atmosphere and some of them have a greater warming effect than gases emitted closer to the surface. One of the key issues that is addressed in virtually every aero gas turbine application is emissions, particularly Nox emissions. There are different technologies for nitrogen oxide emission control in aircraft gas turbines. In this paper, we have briefly reviewed the technologies with the greatest potential to reduce Nox emissions in aero engines.

Effects of Emulsified Fuel on the Performance and Emission of Direct Injection Diesel Engine

AbstractVarious control methods for reducing nitrogen oxides (NOx) emissions of diesel engines have been developed to conform to strict emission regulations. One of the methods for controlling NOx emissions is to use emulsified fuel. This study investigates the effects of emulsified fuels on the diesel engine performance and main pollutant emission characteristics. Four different emulsified water–diesel fuel mixtures (0, 5, 10, 15, and 20% by mass) were used in the engine tests. The tests were conducted in a single-cylinder naturally aspirated direct injection (DI) four-stroke diesel engine under full load conditions. It has been observed that while brake power and torque slightly decrease, the brake efficiency considerably increases. NOx emissions have decreased with the increase in the mass rate of water in the mixtures. Optimum water rate in the mixture was found to be 20%. The maximum increase in brake efficiency was 17.5% at 1,200 rotations per minute (rpm) with E20 (emulsified fuel with 20% water co...

The importance of the location of sodium chlorite application in a multipollutant flue gas cleaning system

In this study, removing sulfur dioxide (SO2), nitrogen oxides (NOx), and mercury (Hg) from simulated flue gas was investigated in two laboratory-sized bubbling reactors that simulated an oxidizing reactor (where the NO and Hg0 oxidation reactions are expected to occur) and a wet limestone scrubber, respectively. A sodium chlorite solution was used as the oxidizing agent. The sodium chlorite solution was an effective additive that enhanced the NOx, Hg, and SO2 capture from the flue gas. Furthermore, it was discovered that the location of the sodium chlorite application (before, in, or after the wet scrubber) greatly influences which pollutants are removed and the amount removed. This effect is related to the chemical conditions (pH, absence/presence of particular gases) that are present at different positions throughout the flue gas cleaning system profile. The research results indicated that there is a potential to achieve nearly zero SO2, NOx, and Hg emissions (complete SO2, NO, and Hg removals and ∼90% of NOx absorption from initial values of 1500 ppmv of SO2, 200 ppmv of NOx, and 206 μg/m3 of Hg0) from the flue gas when sodium chlorite was applied before the wet limestone scrubber. However, applying the oxidizer after the wet limestone scrubber was the most effective configuration for Hg and NOx control for extremely low chlorite concentrations (below 0.002 M) and therefore appears to be the best configuration for Hg control or as an additional step in NOx recleaning (after other NOx control facilities). The multipollutant scrubber, into which the chlorite was injected simultaneously with the calcium carbonate slurry, appeared to be the least expensive solution (when consider only capital cost), but exhibited the lowest NOx absorption at ∼50%. The bench-scale test results presented can be used to develop performance predictions for a full- or pilot-scale multipollutant flue gas cleaning system equipped with wet flue gas desulfurization scrubber. Implications The control of NOx, Hg, and SO2 emissions from coal-fired combustors is an important, worldwide concern affecting environmental pollution. In both the European Union and the United States, NOx and SO2 emissions are subject to newly tightened emission limits. This paper investigated the NOx, Hg, and SO2 removals in a flue gas cleaning system equipped with a classical wet limestone scrubber, enhanced by a solution of sodium chlorite. This paper demonstrated that the location at which the sodium chlorite is applied in a flue gas cleaning system affects the control of these pollutants and discusses how possible solutions could be practically implemented.

Design and operational considerations for selective catalytic reduction technologies at coal-fired boilers

By the end of 2010, China had approximately 650GW of coal-fired electric generating capacity producing almost 75% of the country’s total electricity generation. As a result of the heavy reliance on coal for electricity generation, emissions of air pollutants, such as nitrogen oxides (NOx), are increasing. To address these growing emissions, the Ministry of Environmental Protection (MEP) has introduced new NOx emission control policies to encourage the installation of selective catalytic reduction (SCR) technologies on a large number of coalfired electric power plants. There is, however, limited experience with SCR in China. It is therefore useful to explore the lessons from the use of SCR technologies in other countries. This paper provides an overview of SCR technology performance at coal-fired electric power plants demonstrating emission removal rates between 65% and 92%. It also reviews the design and operational challenges that, if not addressed, can reduce the reliability, performance, and cost-effectiveness of SCR technologies. These challenges include heterogeneous flue gas conditions, catalyst degradation, ammonia slip, sulfur trioxide (SO3) formation, and fouling and corrosion of plant equipment. As China and the rest of the world work to reduce greenhouse gas emissions, carbon dioxide (CO2) emissions from parasitic load and urea-to-ammonia conversion may also become more important. If these challenges are properly addressed, SCR can reliably and effectively remove up to 90% of NOx emissions at coal-fired power plants.

Spray characteristics of four-hole injectors used for a hydrocarbon lean nitrogen oxide catalyst system in a diesel engine

Among emission reduction technologies, a hydrocarbon lean nitrogen oxide trap is a cost-effective solution for nitrogen oxide emission control in light-duty vehicles. However, the hydrocarbon lean nitrogen oxide trap leads to high fuel consumption because diesel fuel is normally used as a reducing agent (i.e. a reductant). It is necessary to establish injection conditions corresponding to the maximum nitrogen oxide conversion in the hydrocarbon lean nitrogen oxide trap system. A uniform distribution of the reducing agent is desirable, and the spray characteristics of the reductant, such as atomization and penetration, must be well understood in order to establish a good performance of the hydrocarbon lean nitrogen oxide trap. With this goal in mind, the spray characteristics and behaviour of a port fuel injector with four holes were analysed using visualization and r.m.s. image-processing techniques. The Sauter mean diameter distribution of the injector was measured using a Malvern system. The liquid agents employed in this study were ISO 4113 and n-heptane, which have properties similar to those of diesel and gasoline fuels respectively. These results elucidated the feasibility of a secondary injection system for the hydrocarbon lean nitrogen oxide trap.

Development of an Innovative Circulating Fluidized-Bed with Microwave System for Controlling NOx

ABSTRACTSelective catalytic reduction (SCR) and selective non-catalytic reduction (SNCR) technique are widely used to control nitrogen oxides emissions. However, both techniques have a general shortcoming known as NH3 slip. This research introduced the design of activated carbon in a circulating fluidized-bed with microwave system and developed an innovative de-NOx technique. The whole system demonstrated the capability and advantage of reducing reductant cost and continuous process. The experiments investigated microwave to regenerate activated carbon (AC) in order to increase adsorption and destruction efficiency while reducing energy consumption. In the NOx abatement process, activated carbon adsorbed NO and NO2 and then utilized microwave heating technology to regenerate itself because of microwave’s high energy utilization and strong penetration ability. The specific surface areas of AC increased from 673.03 to 834.52 (m2/g) when microwave power was increased from 0 to 550 W, respectively, in this study. Through increasing the specific surface area, the microwave treatment further improved the NOx adsorption capacity and rate. In consequence, the results indicated that destruction efficiency of NO and NO2 at 200 ppm could reach about 80% with microwave power of 350 W and above 85% of 550 W. The destruction efficiency at 550 W for NOx was about 77%.

Thermal modelling of modern diesel engines: proposal of a new heat transfer coefficient correlation

Existing methods for predicting heat fluxes and temperatures in internal combustion engines, which take the form of correlations to estimate the heat transfer coefficient on the gas-side of the combustion chamber, are based on methodology developed over the past 50 years, often updated in view of more recent experimental data. The application of these methods to modern diesels engines is questionable because key technologies found in current engines did not exist or were not widely used when those methods were developed. Examples of such technologies include: high-pressure common rail and variable fuel injection strategies including retarded injection for nitrogen oxides emission control; exhaust gas re-circulation; high levels of intake boost pressure provided by a single- or double-stage turbocharger and inter-cooling; multiple valves per cylinder and lower swirl; and advanced engine management systems. This suggests a need for improved predicting tools of thermal conditions, specifically temperature and heat flux profiles in the engine block and cylinder head. In this paper a modified correlation to predict the gas-side heat transfer coefficient in diesel engines is presented. The equation proposed is a simple relationship between Nu and Re calibrated to predict the instantaneous spatially averaged heat transfer coefficient at several operating conditions using air as gas in the model. It was derived from the analysis of experimental data obtained in a modern diesel engine and is supported by a research methodology comprising the application of thermodynamic principles and fundamental equations of heat transfer. The results showed that the new correlation adequately predicted the instantaneous coefficient throughout the operating cycle of a high-speed diesel engine. It also estimated the corresponding cycle-averaged heat transfer coefficient within 10 per cent of the experimental value for the operating conditions considered in the analysis.

Measurement and Control of NOx Emissions at Two AC Electric Arc Furnaces

Nitrogen oxides (NOx) are important air polluting gas species. The emission of nitrogen oxides from industrial plants is strictly regulated in most industrial countries around the world and the emissions limits have been and will be lowered further in the future. Therefore it is important to know typical emissions values of processes like electrical steelmaking. In a second step it is also vital to investigate measures to control and reduce the NOx emissions of the electric steelmaking process. This will ensure the ability to compete with other steel production technologies and also with alternative production sites. In this paper the results of measurements and trials regarding the formation of NOx in the electric arc furnace (EAF) are reported. The measurements and trials have been conducted at two European industrial EAFs and their goal was to investigate the influence of current and modified operational practices on the emission of NOx at these EAFs. The results of the work performed have lead to control strategies to minimize NOx formation within the electric steelmaking process.

A review of NOx storage/reduction catalysts: mechanism, materials and degradation studies

The catalytic removal of nitrogen oxides (NOx) from lean-burn exhaust emissions is one of the major challenges in environmental catalysis. Among the NOx emission control technologies, NOx storage/reduction (NSR) is currently regarded as one of the most practical technologies for lean-burn gasoline and diesel vehicles. This review gives a comprehensive overview of NSR technology, including the NSR reaction mechanisms, degradation mechanisms and NSR catalyst developments. The NSR reaction and degradation mechanisms will be addressed based on a typical NSR catalyst such as Pt/BaO/Al2O3, along with the concurrent new NSR catalyst developments for enhancing the NSR performance and alleviating their sulfur poisoning and thermal degradation.

Ozone in Central England: the impact of 20 years of precursor emission controls in Europe

Episodic peak ozone levels over the 1990–2007 period appear to have declined strongly whilst annual mean daily maximum levels have risen over the same period at monitoring sites within the midlands regions of the UK. Sensitivity studies carried out with a photochemical trajectory model have shown that European policies to control Volatile Organic Compound (VOC) and Nitrogen Oxides (NOx) emissions are the likely cause of the decline in episodic peak levels. There appeared to have been little influence on the episodic peak from changes in intercontinental trans-Atlantic transport but an overwhelming influence on the annual mean daily maximum levels. Non-linear relationships between VOC and NOx emission controls and ozone, together with the ambition level set by policy-makers, appear to explain why ozone levels in Central England still do not meet internationally accepted air quality guidelines despite two decades of policy actions within Europe.

A Case Study of the Relative Effects of Power Plant Nitrogen Oxides and Sulfur Dioxide Emission Reductions on Atmospheric Nitrogen Deposition

The contrasting effects of point source nitrogen oxides (NOx) and sulfur dioxide (SO2) air emission reductions on regional atmospheric nitrogen deposition are analyzed for the case study of a coal-fired power plant in the southeastern United States. The effect of potential emission reductions at the plant on nitrogen deposition to Escambia Bay and its watershed on the Florida–Alabama border is simulated using the three-dimensional Eulerian Community Multiscale Air Quality (CMAQ) model. A method to quantify the relative and individual effects of NOx versus SO2 controls on nitrogen deposition using air quality modeling results obtained from the simultaneous application of NOx and SO2 emission controls is presented and discussed using the results from CMAQ simulations conducted with NOx-only and SO2-only emission reductions; the method applies only to cases in which ambient inorganic nitrate is present mostly in the gas phase; that is, in the form of gaseous nitric acid (HNO3). In such instances, the individual effects of NOx and SO2 controls on nitrogen deposition can be approximated by the effects of combined NOx + SO2 controls on the deposition of NOy (the sum of oxidized nitrogen species) and reduced nitrogen species (NHx), respectively. The benefit of controls at the plant in terms of the decrease in nitrogen deposition to Escambia Bay and watershed is less than 6% of the overall benefit due to regional Clean Air Interstate Rule (CAIR) controls.

Experimental Study on the Effect of Urea and Additive Injection for Controlling Nitrogen Oxides Emissions

Selective noncatalytic reduction (SNCR) for nitrogen oxides (NOx) abatement, using urea (the NOxOUT process) as an N-agent was conducted experimentally on a multifunctional combustion facility. Results showed that the NOxOUT process resulted in 90.1% NO reduction at 1,273 K if the N-agent-to-NO mole ratio (NSR) varied between 1.5 and 2. Also, oxygen concentration of the inlet gas clearly impacted the process. NOx reduction was reduced by 17.1% when oxygen concentration was increased from 2.7 to 3.6%. If the concentration was increased further, decline of NOx reduction would become smooth. At the same time, ample residence time must be guaranteed, and a minimum value of 1.2 s was required for a thorough NOx reduction. The temperatures where 90% of the maximum reductions are achieved in low and high temperature zones are seen as the lower and upper limit temperature, respectively. The range between the lower and upper limit temperature is defined as a “temperature window.” Different reagents lead to different maximum reductions and the “temperature window” changes accordingly. Based on these findings, synergistic effect of additives was studied to broaden the narrow “temperature window” of SNCR. Sodium carbonate, ethanol, glycerol, and acetic acid, with a concentration of 200 ppm, respectively, were selected as additives, and the “temperature window” was broadened by 40–80 K. Different additives presented different characteristics. Sodium carbonate simultaneously broadened the “temperature window” toward low and high temperature zones and slightly compromised the maximum NOx reduction. The organic compounds mainly showed effect in low temperature zone and reduced the maximum NOx reduction by 11–14%. This investigation is performed from operating parameters to additive injection, which makes the effect of additive obvious. It is hoped that the conclusions of this work could further ascertain the NOxOUT process and make a contribution to the industrialization of the SNCR technology.