Significant NOx Reduction Research Articles

Development of a highly efficient low-emission diesel engine-powered co-generation system and its optimization using Taguchi method

A highly efficient low-emission co-generation system using a 2000-cc common-rail direct-injection (CRDI) diesel engine with an after-treatment device (re-combustor) is developed. The co-generation concept is utilized to produce electric power by a generator as well as to recover waste heat from the exhaust gases. A re-combustor is installed at the exhaust gas outlet to perform secondary burning of the exhaust gases, resulting in an improvement of the system's thermal efficiency as well as a reduction of exhaust gas emissions. The main components of the re-combustor are coiled Pyromax wires installed in a ceramic housing, diesel oxidation catalyst (DOC), and diesel particulate filter (DPF). The tests are conducted at four water flow rates (10, 15, 20, and 25 LPM) and four electric power outputs (5, 15, 25, and 35 kW). In general, a great deal of time and expense are required to determine the optimum experimental conditions for the maximum efficiency of a co-generation system. However, in the present study, the optimum experimental conditions for the present system are found using the Taguchi method and analysis of variance (ANOVA), resulting in significant savings of time and expense. The results show that the present co-generation system achieves a maximum total efficiency of 85.7%, and a significant reduction of CO, NOx, and PM by 73.3%, 34.3%, and 94%, respectively.

NOx reduction using amine reclaimer wastes (ARW) generated in post combustion CO2 capture

Amine reclaimer wastes (ARW) generated in CO2 capture processes demand suitable disposal means. Such wastes contain remaining amine, NH3 and other degradation compounds. This study investigated the potential of using ARW as a NOx reducing agent, under laboratory conditions in a flow reactor. A simulated flue gas containing about 500ppm of NO and 5% O2 was injected with liquid ARW under different stoichiometric ratios (TN/NO – total N to nitric oxide ratio) and temperatures. The ARW was obtained from a distillation monoethanolamine reclaimer in an industrial CO2 capture facility with a coal fired boiler. The results indicate that ARW has a significant NOx reduction potential when injected with TN/NO ratios in excess of 1. The optimum temperature is close to 950°C, where 40% reduction in NOx is recorded with a TN/NO ratio of 1.6. Increasing TN/NO to 8.5 resulted in a 96% reduction. At low TN/NO ratios (<1.6), the NOx reduction potential of ARW is comparable to that of monoethanolamine, but lower than that of NH3. Nevertheless, the fact that ARW is a waste product, together with its demonstrated NOx reduction capability and its calorific value contribution, makes it attractive as an additive to combustion processes, including cement industry kilns.

Utilization of Waste Hydraulic Oil as Fuel in Diesel Engine

Production of alternative diesel fuel has been increasing drastically in many Asian countries. Since the reduction of petroleum production by Organization of Petroleum Exporting Countries (OPEC), the research on alternative fuel for diesel engine has gain interest. The target of this project is to substitute some percentage usage of conventional diesel fuel with waste substance without compromising on engine performance and exhaust emissions. This study has produced two type of alternative fuels. A test fuel consisting 30% of water into diesel fuel with the existence of additive or emulsifier (span 80) is called as DW Emul. Another test fuel which is named as DHW Emul produced by blending 30% of water into a mixture consisting of 20% of waste hydraulic oil and 80% of diesel fuel with the existence of span 80. The engine performance and exhaust emissions of DW Emul and DHW Emul are measured and has been compared with the conventional diesel fuel. A 600cc single cylinder direct injection diesel engine was used. The experiment was conducted at 1500 rpm with variable engine loads. Results show that DHW Emul and DW Emul has higher brake specific fuel consumption (BSFC). However, by considering the total use of diesel fuel contained in DW Emul, the quantity was lower at all loads. The same goes for DHW Emul at low load but deteriorate at high load which show slightly higher compared with of using 100% conventional diesel fuel. DHW Emul has suppressed CO emission that is usually high of using emulsion fuel to the level similar to conventional diesel fuel. NOx and Smoke emissions for DHW Emul are lower than conventional diesel. The use of DHW Emul can give significant reduction of NOx and Smoke emissions without deterioration of CO emission.

Combustion and emission of rapeseed oil blends in diesel engine

Combustion and emission characteristics of rapeseed plant oil (RSO) and its blends with diesel fuel have been investigated in a multi-cylinder direct injection diesel engine. Plant oils have high viscosities compared to diesel and this affects the performance and durability of automotive diesel engines when used for longer time periods. Despite these adverse effects the exhaust emissions analysis show a significant reduction in NOx and relatively higher amount of soot for RSO compared to diesel fuel. An attempt has been made to reduce soot emissions from the combustion of RSO to exploit the advantage of its low NOx emissions. The strategy of varying injection parameters such as injection pressures and injection timings have been used in this work to reduce the soot emissions for blends of 50% and 30% RSO in diesel fuel. Using this strategy it was possible to achieve diesel equivalent levels of soot emission for 30% RSO blend. Under diesel equivalent soot emission levels, it was also possible to achieve a further reduction in NOx emissions by up to 22% for 30% RSO blend, this was achieved at the expense of THC, CO and BSFC. The exhaust soot particle number concentrations for 30% RSO blend reduces with an increase in injection pressure and retarded injection timing. However, when compared to diesel, the exhaust soot particle number concentration for 30% RSO blend was still higher, even after diesel equivalent level of soot emission was achieved.

Advanced Fluid Research On Drag reduction In Turbulence Experiments –AFRODITE–

A hot topic in today's debate on global warming is drag reduction in aeronautics. The most beneficial concept for drag reduction is to maintain the major portion of the airfoil laminar. Estimations show that the potential drag reduction can be as much as 15%, which would give a significant reduction of NOx and CO emissions in the atmosphere considering that the number of aircraft take offs, only in the EU, is over 19 million per year. An important element for successful flow control, which can lead to a reduced aerodynamic drag, is enhanced physical understanding of the transition to turbulence process.

Impact of the Overfire Air Location on Combustion Improvement and NOx Abatement of a Down-Fired 350 MWe Utility Boiler with Multiple Injection and Multiple Staging

A new technology based on multiple injection and multiple staging has been developed specifically for severe asymmetric combustion and particularly high NOx emissions within a down-fired 350 MWe utility boiler. The aim of the present work is to evaluate the performance of the furnace with the new technology with respect to different overfire air (OFA) locations and then to obtain an optimal setup to recommend as a retrofit for the furnace in the future. Numerical simulations of combustion characteristics and NOx emissions were conducted within the furnace at three different OFA location settings, i.e., OFA on arches but close to the furnace center, OFA on the furnace throat, and OFA on the upper furnace. Good agreement was found between simulations and in situ measurements with the original technology. Asymmetric combustion removals and significant NOx reductions were validated for all three OFA location settings. NOx emissions, carbon in fly ash, and gas temperatures at the furnace exit varied largely over different OFA settings. Both carbon in fly ash and gas temperatures in the furnace outlet for OFA on the furnace throat and OFA on the upper furnace are higher than for OFA on arches. The setting with OFA on the upper furnace achieved the highest NOx emissions, whereas that with OFA on arches enabled the lowest. To establish efficient furnace-operating conditions with the new technology, OFA on arches but close to the furnace center was recommended as the optimal OFA location according to simulation results.

The Used of Aqueous Urea Solution in Reduction of Noxious Emissions in Bio Fuel Combustion System Using Selective Non-Catalytic Reduction

Selective Non-Catalytic Reduction (SNCR) of nitric oxide was studied experimentally by injecting different concentrations of aqueous urea solution; urea and ammonia in a pilot-scale Bio-fuel fired tunnel furnace at 3-4 % excess oxygen level and with low ppm of baseline NOx ranged from 65 to 75 ppm within the investigated temperature range. The furnace simulated small-scale combustion systems where the operating temperatures are usually in the range of about 973 to 1323 K and NOx emission level remains below 100 ppm. NOx reductions were studied with the variation of different parameters such as injection temperature, residence time, Normalized Stoichiometric Ratio (NSR) of the reagent, carrier gas pressure, etc. A significant result shows that for NSR, at higher NSR, ammonia could give significant reduction of NOx at the investigated injection temperature. Meanwhile, for the effect of residence time, both aqueous solution shows that the NOx reduction increased with increase in residence time. Finally for the effect on injection temperature, both aqueous solution, up to a certain temperature NOx reduction continued to increase with increasing injection temperature and afterward the reduction decayed with further increase in temperature.

Development of variable timing fuel injection cam for effective abatement of diesel engine emissions

Fossil fuel run diesel engines are being favored in light, medium and heavy duty applications as they exhibit higher fuel conversion efficiencies. Direct injection diesels are still facing challenges to obtain trade-off between oxides of nitrogen and particulate emissions. There are sophisticated strategies such as common rail direct injection, particulate filters with associated sensors and actuators but limited to expensive comfort vehicles. In the present experimental study, a mechanically operated simple component, variable timing fuel injection cam, is designed for a 510cc automotive type naturally aspirated, water-cooled, direct injection diesel engine. Modifications in the fuel injection cam and gear train are carried out to suit the existing engine configuration. Variable speed tests are carried out for testing the efficacy of component on both engine and chassis dynamometers for performance and emissions. It is observed that the engine which is already retarded could further be retarded with variable timing fuel injection cam. Significant reductions in NOx and smoke emission levels are achieved. Combined effect of VIC with 7% EGR could reduce CO by about 88%, HC+NOx by 37% and PM emissions by 90%. The Engine incorporated with the designed component and EGR, successfully satisfied the existing emission norms with improved power and specific fuel consumption.

Experimental investigation of performance and emissions on low speed diesel engine with dual injection of solar generated steam and pongamia methyl ester

An experimental investigation has been carried out to examine the effects of steam injection into the intake manifold of a single cylinder, low speed, direct injection diesel engine fuelled with biodiesel palm methyl ester. Steam injection is generally carried out by non–conventional energy source. The addition of steam in to the intake manifold of the engine was carried out by vaporizing the water inside a boiler and heat is supplied by the solar concentrated parabolic dish. Biodiesels are known to produce higher NOx when compared to the neat diesel. Addition of steam to the combustion chamber of diesel engine has known effects of reducing the dangerous emissions of NOx but it is not clearly known about the engine performance and emissions. To examine this, an experimental investigation has been carried out on a single cylinder low speed diesel engine with steam injection in to the intake manifold during the suction stroke on the performance and engine emissions. Experiment results shows that there is a significant reduction in smoke levels and NOx during the steam injection both for the diesel fuel and pongamia methyl ester. Also there is a significant improvement of engine performance in terms of specific fuel consumption and brake thermal efficiency with steam injection.

Cocombustion of Pulverized Coal with Waste Plastic and Tire Rubber Powders

The generation of scrap tires in the world is approximately 1 billion per year and is set to increase in the foreseeable future as the number of cars on the roads increases. In this paper we present results from a pilot scale study on the cofiring of fine tire rubber (FTR) powder and plastic (high-density polyethylene, HDPE) with pulverized coal (PC) with a view to an application in power generation as an alternative to biomass, particularly their role in the combustion behavior of PC. We have performed experiments with a South African (SAf) coal and a South American (SAm) coal of different composition for a range of cofiring levels, up to 25%, and several configurations of combustion air distribution (air-staging). The fuels were fired through the burner and particular regard was paid to the effect on CO2, NOx, SO2, and carbon burnout. The results show that coal quality has a significant role during cofiring. In present investigations when HDPE was cofired with the SAm coal, a significant reduction in NOx was observed. Lower NOx emissions are achieved due to the different combustion behavior of the fuels. That is, modifying the primary combustion zone environment makes it more difficult for the intermediate HCN and NH3 species to oxidize to NOx due to the reduced O2 concentration at the point of fuel-N release in the flame. The influence of the tire-N content is thought to be small in the flames studied. We have seen around 20% NOx reductions when cofiring tire with the SAf coal for a 20% tire/coal cofiring ratio but insignificant NOx reductions when cofiring tire with SAm coal under the same conditions, indicating similar combustion characteristics and flame dynamics. In all cases, good burnout was achieved with less than 8% carbon in ash. The reduction of NO by the cofiring of tire-coal and plastic-coal fuel blends was further compared to historical literature involving the cofiring of biomass. It is noted that the ignition behavior of fuels of tire and plastic may differ to that of biomass; however, the overall reduction in NO is still observed in both cases. Historical air-staged experiments involving the cofiring of biomass were not able to provide similarly high reductions of NO to the staged cofiring of tire-coal and plastic-coal fuel blends. It is thought that the particle size of the biomass fired is a significant factor that is influencing the NO reduction efficiencies within a staged flame.

Combustion and Emissions Characterization of Soy Methyl Ester Biodiesel Blends in an Automotive Turbocharged Diesel Engine

Recent increases in petroleum fuel costs, corporate average fuel economy (CAFE) regulations, and environmental concerns about CO2 emissions from petroleum based fuels have created an increased opportunity for diesel engines and non-petroleum renewable fuels such as biodiesel. Additionally, the Environmental Protection Agencies Tier II heavy duty and light duty emissions regulations require significant reductions in NOx and diesel particulate matter emissions for diesel engines. As a result, the diesel engine and aftertreatment system is a highly calibrated system that is sensitive to fuel characteristics. This study focuses on the impact of soy methyl ester biodiesel blends on combustion performance, NOx, and carbonaceous soot matter emissions. Tests were completed using a 1.9 L, turbocharged direct injection diesel engine using commercially available 15 ppm ultra low sulfur (ULS) diesel, a soy methyl ester B20 biodiesel blend (20 vol % B100 and 80 vol % ULS diesel), and a pure soy methyl ester biodiesel. Results show a reduction in NOx and carbonaceous soot matter emissions, and an increase in brake specific fuel consumption with the use of biodiesel. Further, traditional methodology assumes that diesel fuels with a high cetane number have a reduced ignition delay. However, results from this study show the cetane number is not the only parameter effecting ignition delay due to increased diffusion burn.

Experimental Study on Effects of Nozzle Hole Geometry on Achieving Low Diesel Engine Emissions

Three injectors with different nozzle geometries were tested in a multicylinder diesel engine with a high-pressure common-rail injection system. Various injection pressures were tested along with exhaust gas recirculation to achieve low NOx and soot emissions. The injectors used in the study included a six-hole nozzle, a ten-hole nozzle, and a six-hole convergent nozzle with a K-factor of 3. All three injectors had the same flow numbers. All three injectors tested were effective in reducing NOx and soot emissions at appropriate conditions. It was found that low temperature combustion can be achieved by using high levels of exhaust gas recirculation with late injection timings. High injection pressures significantly reduced soot emissions at conventional injection timings. The effect of injection pressure was not significant at retarded injection timings, i.e., 5 ATDC. The convergent nozzle was found to produce higher soot emissions compared with the straight-hole nozzle under the same injection conditions. Effects of the convergent nozzle on NOx emissions and fuel consumption were not significant. The small nozzle size in the ten-hole injector can generate smaller fuel drops and lead to better atomization. The ten-hole injector appeared to have better air utilization and resulted in significant reductions in NOx and soot emissions over a wide range of operating conditions.

모형연소기에서 연료-공기의 혼합정도 및 당량비가 NOx 배출과 열 방출량에 미치는 영향에 대한 연구

Lean premixed combustors are used for significant NOx reduction which one of issues in current gas turbine combustor. This study was investigated to estimate the effects of the unmixedness of fuel-air, equivalence ratio on the instability mechanism, NOx emission and combustion oscillation in a lean premixed combustor. The experiments were conducted in a dump combustor at atmospheric pressure conditions using methane as fuel. The swirler angle was 45°, the degrees of fuel-air mixing were 0, 50 and 100 and inlet temperature was 650K. The equivalence ratio was ranging from 0.5 to 0.8. This paper shows that NOx emission was increased when the degree of fuel-air mixing is increased in same equivalence ratio and when equivalence ratio is increased. And the range of the combustion instability was enlarged as a function of increasing of the degree of fuel-air mixing.

Sulfur Recovery from Acid Gas Using the Claus Process and High Temperature Air Combustion (HiTAC) Technology

Sulfur-bearing compounds are very detrimental to the environment and to industrial process equipment. They are often obtained or formed as a by-product of separation and thermal processing of fuels containing sulfur, such as coal, crude oil and natural gas. The two sulfur compounds, which need special attention, are: hydrogen sulfide (H2S) and sulfur dioxide (SO2). H2S is a highly corrosive gas with a foul smell. SO2 is a toxic gas responsible for acid rain formation and equipment corrosion. Various methods of reducing pollutants containing sulfur are described in this paper, with a focus on the modified Claus process, enhanced by the use of High Temperature Air Combustion (HiTAC) technology in the Claus furnace. The Claus process has been known and used in the industry for over 100 years. It involves thermal oxidation of hydrogen sulfide and its reaction with sulfur dioxide to form sulfur and water vapor. This process is equilibrium-limited and usually achieves efficiencies in the range of 94-97%, which have been regarded as acceptable in the past years. Nowadays strict air pollution regulations regarding hydrogen sulfide and sulfur dioxide emissions call for nearly 100% efficiency, which can only be achieved with process modifications. High temperature air combustion technology or otherwise called flameless (or colorless) combustion is proposed here for application in Claus furnaces, especially those employing lean acid gas streams, which cannot be burned without the use of auxiliary fuel or oxygen enrichment under standard conditions. With the use of HiTAC it has been shown, however, that fuel-lean, Low Calorific Value (LCV) fuels can be burned with very uniform thermal fields without the need for fuel enrichment or oxygen addition. The uniform temperature distribution favors clean and efficient burning with an additional advantage of significant reduction of NOx, CO and hydrocarbon emission.

Laboratory deactivation testing for the stability of FCC CO combustion promoters

Realistic lab deactivation facilitates the development of low NOx, CO combustion promoters for fluid catalytic cracking (FCC) applications. Cyclic deactivation, which provides a close simulation of the FCC operation, can address many possibilities for the deactivation of CO combustion promoters. Here we present our results using a combination of cyclic deactivation and a coke combustion test to predict additive performance after deactivation. By using this newly developed method, CO combustion promoters with exceptional performance were identified. These novel materials feature CO reduction performance similar to that of Pt-based promoters while still offering significant NOx reduction relative to Pt. Examples are also given using a more traditional hydrothermal deactivation approach.

Phenomenology of NOx Adsorber Catalysts

Lean phase operation of lean NOx adsorbers or lean NOx traps (LNTs) is analyzed using data from highly controlled isothermal bench-flow experiments on Pt/K/Al2O3 catalysts. Simulated diesel exhaust was used for inflow in the experiments. Pt promotes the oxidation of NO, the primary component of engine-out NOx, to NO2 which is more easily adsorbed and stored as KNO3. While the presence of Pt was found to be essential for capturing the NOx from the exhaust, it was seen that the NOx storage efficiency did not increase indefinitely with increasing Pt loading. Pt loading at a given temperature of operation is optimal when the rate of NO oxidation to NO2 is nearly equal to the NO2 adsorption rate at the sorbent sites. The NOx storage efficiency seems to be kinetically limited at lower temperatures and equilibrium limited at higher temperatures. When the lean/NOx capture operation was started from a fully regenerated condition, the NOx storage efficiency under most conditions was found to be independent of the reductant mixture used for regenerating the catalyst. The experiments also indicate the possibility of a significant NOx reduction reaction even under the highly oxidizing conditions. This reduction reaction seems to be of fractional order and is more significant at lower temperatures. More detailed analysis of the outflow from the reactor using Fourier-Transform-Infrared (FTIR) spectroscopy is being planned to identify the final product of this reduction reaction.

Flue gas Hg measurements from coal-fired boilers equipped with wet scrubbers

The U.S. EPA has indicated they are considering additional SO2 and NOx emission reductions, and EPA is under a consent agreement to propose mercury reduction regulations by 2004 for the utility industry. The boiler manufacturers and the utility industry have developed improved combustion modification techniques to reduce NOx emissions. These advanced combustion modification techniques, plus selective catalytic reduction (SCR), offer the potential to reduce NOx emissions at reduced cost. Wet and dry FGD systems have been shown to reduce SO2 emissions by up to 95%. CONSOL has shown that conventional wet FGD and ESP systems can remove an average of 67±6% of the inlet mercury. These data show that utility boilers equipped with ESP-scrubber combinations are removing two-thirds of the mercury in the as-fired coal at no added cost. The mercury speciation data show that 80 to 95% of the oxidised mercury, as determined by the Ontario Hydro method, is removed by the scrubber. The average mercury material balance closure at the six plants was 103±8%. The mercury removed from the scrubber reported to the scrubber by-product. Standard leachate testing conducted on fixated and unfixated scrubber by-product from one test showed no mercury leaching. Mercury volatility was evaluated by heating the scrubber by-product 140°F for eleven weeks. After eleven weeks, no loss of mercury was reported. Based on these findings, there may be combinations of environmental control systems that can achieve significant SO2, NOx, and mercury reductions at lower cost than the conventional approach of three add-on processes FGD for SO2 control, selective catalytic reduction for NOx control, and carbon injection for mercury control.

The Effect of Mixing Model and Mixing Characteristics on Nox Reduction during Reburning

The current study is part of a broader investigation, which deals with the application of a novel concept of integrated design to combustor modeling using computational fluid dynamic (CFD) methods. The main objective is the reduction of NOx emissions. The current work addresses the effects of mixing optimization and mixing model on NOx reduction during reburning. Numerical simulations of the reburning process are conducted on a pilot-scale 0.5 MM Btu/h down-fired combustor (DFC) and compared with experimental data. Optimized mixing conditions resulted in a significant reduction in NOx levels. A “reburn calculator” including the two-stage Lagrangian mixing model is used for predicting the NOx emissions in the DFC, and the results are compared with CFD-based simulations. Modeling results showed that for this case mixing is dominant over the chemistry, and hence the use of an advanced fluid dynamics model and a simplified chemistry scheme is adequate. Validation tests were conducted on optimized configurations using natural gas and coal water slurry as reburn fuels. The NOx reduction obtained with the optimized configurations was as high as 75%, an almost 30% increase over the previous experiments on nonoptimized configurations. This study showed that an integrated approach, which includes mixing optimization, can be used effectively for a reburn case application, achieving significant NOx reduction. The effect of integration was demonstrated both theoretically and experimentally as applied to a pilot-scale DFC.

Performance of a Diesel Engine Using Transesterified Fuel from Vegetable Oil. Effects of Water Emulsification.

This paper investigates engine performance with an emulsified fuel including used frying oil composed of vegetable oils discarded from restaurants and households. A single cylinder DI diesel engine was operated with transesterified fuel from used frying oil, the so called biodiesel. Compared with gas oil, the BSEC of neat biodiesel improved at high loads and retarded injection timings, while the smoke density was reduced at all operating conditions. The engine performance with fairly stable emulsions of biodiesel and water was also examined, and emulsified biodiesel with 30% (vol.) water showed a significant reduction in NOx (1 100 to 400 ppm) while maintaining the minimum BSEC value achieved with gas oil. It was also found that using biodiesel emulsion at a rated output, the trade-off relation NOx vs. BSEC and NOx vs. smoke improved slightly over the gas oil emulsion.

99/03846 Dry bottom ash removal. Ash cooling vs. boiler efficiency effects: Carrea, E. et al. FACT (Am. Soc. Mech. Eng.), 1998, 22, (1), 501–505

This paper describes a combined experimental and theoretical study which was undertaken to quantify the impact of fuel and process parameters on reburning effectiveness and provide the scaling information required for commerical application of reburning under highly varied industrial conditions. Initially parametric screening studies were conducted in a 25 KW refractory-lined tunnel furnace. These studies were supported by large scale testing in a 3.0 MW pilot scale facility. The work at both scales focused on the importance and the fate of the reactive nitrogen species within the reburning zone.The results of this study confirm the potential of the reburning process for significant NOx reductions, but they also demonstrate that a constant reburning effectiveness cannot be assumed under all conditions. The NOx reduction possible through reburning depends primarily on the NO concentration at the end of the primary zone; the stoichiometry, temperature, and residence time in the fuel-rich reburning zone; the mixing and stoichiometry of the reburning fuel jet; and the temperature in the final burnout zone. At the optimum reburning stoichiometry (SR2=0.9) the exhaust emissions correlate linearly with the sum of the primary NOx and the equivalent reburning fuel nitrogen. Optimum effectiveness requires adequate primary zone residence time to insure complete combustion of the primary fuel. Reburning zone residence times of at least 400 ms are desirable and high temperatures favor molecular nitrogen formation. Rapid mixing of the reburning fuel enhances the effectiveness of the NOx destruction process but it can potentially detract from the overall process efficiency with coal reburning due to increased conversion of reburning fuel nitrogen unless the fuel is transported with an essentially inert gas stream. Extremely low exhaust emission levels can be achieved with coal reburning if the final burnout zone can be operated at a temperature low enough to promote in-situ thermal de-NOx.