NOx Reduction Rate Research Articles

Numerical and Experimental Analysis of SNCR Installation Performance in a Power Stoker Boiler

The correct design of effective SNCR (Selective Non-Catalytic Reduction) requires solving several technological challenges. For this purpose, CFD modeling and bench tests were used. This study investigated various parameters affecting the NOx reduction rate in a WR-25 stoker boiler. The first parameter analyzed was the NSR (normalized stoichiometric ratio), with a constant urea concentration of 12.5% in the solution injected into the boiler. CFD modeling indicated that increasing the NSR significantly enhances reduction efficiency, especially between NSR 1 and 2, where the efficiency more than doubles. Bench tests confirmed this trend across all boiler power levels, showing deeper reagent penetration in the chamber at higher NSR levels. However, further doubling of NSR did not yield significant efficiency improvements, likely due to limitations in chemical mixing under reagent excess conditions. Further, it was revealed that NOx reduction efficiency decreases as boiler power increases, probably due to reduced reagent residence time at the required thermodynamic conditions. Additionally, different nozzle tip designs were tested, with multi-hole nozzles (two-hole and three-hole), showing better NOx reduction than single-hole nozzles due to improved reagent distribution. Finally, a lower urea concentration in the reagent (12%) led to better NOx reduction compared to a 32.5% concentration, likely due to improved droplet penetration and mixing with flue gases.

Application of coalbed methane assisted iron ore sintering: Injection effect, pollutant abatement and economic evaluation

Hydrogen-rich gas injection, which has garnered widespread attention from academia and industry, is an effective method for reducing CO2 emissions during the sintering process and for improving sinter quality. Coalbed methane (CBM) is a cost-effective and reliable hydrogen-rich gas resource in China. In this study, we investigated the injection effect of CBM in assisting iron ore sintering. Additionally, we determined the appropriate injection parameters by systematic sintering pot tests and compared it with coke oven gas (COG). The impacts of CBM injection on pollutant abatement and combustion efficiency were analyzed based on the variations in the sintering flue gas composition, and a comprehensive economic evaluation was conducted. The results showed that injecting 0.51 vol% CBM between 5 and 13 min after ignition with 0.3 wt% coke breeze ratio reduction could significantly improve the sintering index and the uniformity of heat distribution within the sinter bed. Excessive injection would affect the bed permeability. CBM took advantage over COG at a gas–solid heat transfer ratio of 1:1.28. The four-stage cascade mode with a gradient of 0.18 vol% and the intermittent mode with an intermittent time of 0.5 min could optimize the injection effect. However, the cascade mode performed better. Besides, injecting CBM increased the emission reduction rates of CO and NOx and improved combustion efficiency by 5.72%, 4.47%, and 1.46%, respectively. Overall, the cost-savings were CNY 2.19 per ton sinter, and the annual production cost could be reduced by approximately CNY 6.71 million for a 265 m2 sintering machine. The profits achieved because of CBM injection can be further improved by increasing the bed permeability and mixed injecting with other gas media. This study provides an effective path for green transformation of sintering production.

Optimization of Integrated Energy Systems Based on Two-Step Decoupling Method

An integrated energy system (IES) plays a key role in transforming energy consumption patterns and solving serious environmental and economic problems. However, the abundant optional schemes and the complex coupling relationship among each piece of equipment make the optimization of an IES very complicated, and most of the current literature focuses on optimization of a specific system. In this work, a simulation-based two-step decoupling method is proposed to simplify the optimization of an IES. The generalized IES is split into four subsystems, and a two-layer optimization method is applied for optimization of the capacity of each piece of equipment. The proposed method enables fast comparison among abundant optional configurations of an IES, and it is applied to a hospital in Beijing, China. The optimized coupling system includes the gas-fired trigeneration system, the GSHP, and the electric chiller. Compared with the traditional distributed systems, the emission reduction rate of CO2 and NOX for the coupling system reaches 153.8% and 314.5%, respectively. Moreover, the primary energy consumption of the coupling system is 82.67% less than that of the traditional distributed energy system, while the annual cost is almost at the same level.

Feasibility study on application of low-grade fuels (naphtha and ethanol) in blended-fuel- and convergence-combustion modes

Since electrification is difficult in the sector where heavy-duty diesel engines are used, research is still needed to improve air pollutants. In addition, it is necessary to search for fuel to solve the depletion of fossil fuels and to study appropriate combustion methods according to fuel characteristics. In this study, naphtha or ethanol was selected as a fuel that could replace a certain fraction of diesel fuel. This study aims to compare both methods of supplying and burning naphtha or ethanol with diesel. The method of supplying naphtha or ethanol blended directly with diesel and burning it is suitable for naphtha. Since ethanol has a lower heating value, blended-fuel combustion mode with ethanol reduces IMEPnet. However, this method of separate injection and burning is only suitable for ethanol. When naphtha is utilized in convergence combustion, a wetting phenomenon arises due to its limited evaporation characteristics, leading to a reduction in fuel delivery. The NOx reduction rate was higher in the convergence combustion mode than that in the blended-fuel combustion mode. However, both the combustion methods led to an increase in the THC and CO emissions.

Multifaceted benefits of magnesium hydroxide dosing in sewer systems: Impacts on downstream wastewater treatment processes

Magnesium hydroxide [Mg(OH)2] is a non-hazardous chemical widely applied in sewer systems for managing odour and corrosion. Despite its proven effectiveness in mitigating these issues, the impacts of dosing Mg(OH)2 in sewers on downstream wastewater treatment plants have not been comprehensively investigated. Through a one-year operation of laboratory-scale urban wastewater systems, including sewer reactors, sequencing batch reactors, and anaerobic sludge digesters, the findings indicated that Mg(OH)2 dosing in sewer systems had multifaceted benefits on downstream treatment processes. Compared to the control, the Mg(OH)2-dosed experimental system displayed elevated sewage pH (8.8±0.1vs 7.1±0.1), reduced sulfide concentration by 35.1%±4.9% (6.7±0.9mgSL−1), and lower methane concentration by 58.0%±4.9% (19.1±3.6mgCODL−1). Additionally, it increased alkalinity by 16.3%±2.2% (51.9±5.4mgCaCO3L−1), and volatile fatty acids concentration by 207.4%±22.2% (56.6±9.0mgCODL−1) in sewer effluent. While these changes offered limited advantages for downstream nitrogen removal in systems with sufficient alkalinity and carbon sources, significant improvements in ammonium oxidation rate and NOx reduction rate were observed in cases with limited alkalinity and carbon sources availability. Moreover, Mg(OH)2 dosing in upstream did not have any detrimental effects on anaerobic sludge digesters. Magnesium-phosphate precipitation led to a 31.7%±4.1% reduction in phosphate concertation in anaerobic digester sludge supernatant (56.1±10.4mgPL−1). The retention of magnesium in sludge increased settleability by 13.9%±1.6% and improved digested sludge dewaterability by 10.7%±5.3%. Consequently, the use of Mg(OH)2 dosing in sewers could potentially reduce downstream chemical demand and costs for carbon sources (e.g., acetate), pH adjustment and sludge dewatering.

Emissions and energy/exergy efficiency in an industrial boiler with biodiesel and other fuels

Industrial boilers are significant equipment in industrial operations used to provide steam or heat for production. More than 80% of fire-tube boilers use heavy oil in small and middle industries in Taiwan. Due to biodiesel as a sustainable fuel, the objective of this study is to measure experimentally and evaluated energy and exergy analysis of the fire-tube boiler using biodiesel (BD), undistilled biodiesel (UB), low sulfur oil (LSO), and ultra-low sulfur diesel (ULSD), and the various mixing ratios of undistilled biodiesel and low sulfur oil (UB90, UB70, and UB50) to reduce emissions from fire-tube boilers. Results from BD and UB are comparable, and UB exhibited a high NOx reduction rate of 68.9% and a high SO2 reduction rate of 99.5% compared to LSO. The boiler that employed UB decreased CO2 emissions, NOx, and SO2 emissions. NOx emission increases with increasing LSO content. The boiler’s maximum energy efficiency when using BD is 86.6%, and the overall exergy efficiency is 44.8%. The boiler with UB70 had the lowest energy efficiency of 73.5% and the lowest exergy efficiency of 38.7% because of the increased heat loss. The Benefits of this study are not only for boiler applications but also for government policy references.

Experimental research on effects of multi-layer injection of the high-temperature preheated pulverized coal on combustion characteristics and NOx emission

Under the background of carbon peak and carbon neutrality, cleanandefficientutilization ofcoal is imperative in China. As a novel combustion technology, the coal self-preheating combustion technology has broadprospectsforapplication, nevertheless, previous studies have mainly focused on limiting NOx generation by simply applying air staging method in the combustor, which made further NOx reduction difficult to achieve. Combining the advantages of reburning technology, this study firstly realized the multi-layer injection of the high-temperature preheated fuel (PF), and investigated the effects of the reburning fuel fraction (RFF), the location of the reburning fuel injection port (RFL) and the coal type on combustion characteristics and NOx emissions. The results revealed that the generated high-temperature PF could continuously and stably enter the down-fired combustor (DFC) for subsequent combustion. In the intensely reducing atmosphere inside the self-preheating device, the released fuel-N was mainly converted to N2, and the combustion performance of the preheated coal char which could be used as an excellent fuel close to gas reburning effect was greatly modified compared with raw coal. To simultaneously achieve efficient and clean combustion of pulverized coal, the favorable RFF and RFL were 10.62%∼15.48% and 600 mm ∼ 800 mm, respectively, corresponding to the residence time in the primary combustion zone and the reburning zone in the range of 0.91 ∼ 0.99 s and 0.87 ∼ 1.11 s, respectively. What’s more, under the same reburning parameters, Alxa lignite coal had the largest NOx reduction rate (32.15%), with NOx emission of 51.36 mg/m3 (@6%O2), while Jincheng anthracite coal had the lowest NOx reduction rate (5.34%) and the highest NOx emission (149.91 mg/m3, @6%O2), and Shenmu bituminous coal achieved ultra-low NOx emission (45.75 mg/m3, @6%O2) with the NOx reduction rate of 28.05%, suggesting that on the basis of air staging, multi-layer injection of PF had more advantages for clean and efficient combustion of high volatile coal.

Railway Emission Trends in China Based on Fuel Life Cycle Analysis

Railway transportation is one of the main modes of modern transportation. Under the dual constraints of air quality improvement and carbon neutrality achievement, clarifying the emission trend of CO2 and pollutants in railway transportation is of great significance for pollution and carbon reduction in the transport sector. In this study, the CO2 and pollutant emission characteristics of Chinese railways from 2001 to 2018 were analyzed based on the fuel life cycle method. Then, railway emission trends from 2019-2030 were assessed combined with scenario analysis. The results showed that with the advancement of railway electrification, the use of new diesel locomotives, and the continuous upgrading of fuel standards, the total CO2 and pollutant emissions in the fuel life cycle of railway transportation showed an upward and downward trend, respectively. In 2018, the total emissions of CO2, NOx, CO, BC, and SOx from railway transportation were 3780.29×104t, 11.98×104t, 3.94×104t, 0.20×104t, and 3.08×104t, respectively. Accelerating the improvement of power structure and reducing unit energy consumption were the best single control strategies to reduce railway emissions of CO2, SOx, NOx, BC, and CO, respectively. Under the comprehensive scenario of actively responding to railway pollution and carbon reduction, the emission reduction rates of CO2, NOx, CO, BC, and SOx could reach 35%, 37%, 39%, 32%, and 45%, respectively. The stagnation of power structure reform or the railway electrification process will lead to a significant increase in total emissions of railway transportation. Therefore, the pollution and carbon reduction of railway transportation requires continuous attention.

Elimination of NH3 by Interfacial Charge Transfer over the Ag/CeSnOx Tandem Catalyst

Selective catalytic oxidation of NH3 is the most promising method for removing low-concentration NH3. However, achieving high activity and N2 selectivity remains a great challenge. A Ag/CeSnOx tandem catalyst with dual active centers was designed and synthesized, which couples the NH3 over-oxidation on the noble metal active sites with NOx reduction on the support. The tandem catalyst exhibited excellent NH3 selective catalytic oxidation (NH3–SCO) performance at 200–400 °C. Based on various characterization techniques and DFT calculations, it was identified that the silver species on the Ag/CeSnOx catalysts existed as AgO nanoparticles (AgO NPs), and the electrons on the support were more easily transferred to AgO NPs, which promoted the oxidation activity of AgO and the reduction performance of the CeSnOx support. The coupling between the AgO NPs and CeSnOx helped balance the NH3 oxidation rate and the NOx reduction rate. In addition, the uniform adsorption of gaseous NH3 on the oxidation and reduction sites was also demonstrated by theoretical calculations, which is a prerequisite for tandem catalysis. By in situ DRIFTS, we revealed that the NH3–SCO reaction over Ag/CeSnOx catalysts mainly follows the internal selective catalytic reduction mechanism. It was characterized by excessive oxidation of NH3 to NOx on AgO NPs. At a temperature lower than 200 °C, NOx was reduced to N2 by the adsorbed NH3 on the AgO. When the temperature was higher than 200 °C, NOx was reduced to N2 by NH3 or NH4+ adsorbed on the CeSnOx support. Therefore, the charge transfer at the Ag/CeSnOx catalyst interface and the coordination of atomic scale catalytic sites have realized the conversion of NH3 to N2 through NOx in a tandem catalytic mode.

Improving combustion and lowering NO emissions of an industrial coal swirl burner by optimizing its nozzle structure

• Simulation and comparison are conducted for the burner before and after optimization. • Entrained effect of secondary air on primary air is enhanced with retrofitting ISACS. • Retrofitting ISACS has significant effects on the combustion characteristics. • Optimized burner performs better in NOx reduction, flame stability and burnout rate. To accommodate rapidly growing but highly variable renewable power in the grid and large variations in power demand, coal-fired power plants need to be flexibly operated through fast and wide load changes, still with high efficiency and reliability and low emissions. Towards reliable implementation in a power plant under flexible operation, this paper comprehensively investigates the improvement of an industrial low-NO x swirl burner via numerical simulation and various field tests. Burner aerodynamics, which play a vital role in its performance, are largely affected by the burner nozzle structure. For the low-NO x swirl burner under study, the inner secondary air cone structure is found to have the most significant impact on the burner aerodynamics and the combustion performance. For the coal fired in the power plant, the newly designed inner secondary air cone structure, which is a kind of an extended smooth diverging duct, greatly facilitates the entrainment of the primary air into the surrounding swirl secondary air stream and largely enhances lateral mixing. A large recirculation zone is formed between the primary air and the inner secondary air stream, stabilizing ignition and combustion under flexible operation conditions. This is particularly important for low-load operation. Comparatively, reducing the secondary air duct area for a higher axial momentum of the secondary air stream and adding a new particle separation ring for more dispersed particle distribution are found to have a minor impact on the burner aerodynamics. The optimized burner nozzle structure via numerical simulation has been finally adopted by the power plant for the burner retrofit, on which various field tests have been performed on the retrofitted burner. The tests show that the nozzle structure optimization remarkably improves the burner performance, which is also consistent with the numerical prediction. This study also provides useful guidance for optimizing the swirl burners of the similar type.

Emissions Characteristics and Engine Performance from the Interaction Effect of EGR and Diesel-Ethanol Blends in Diesel Engine

Recently, most of the researchers focused on provide lower greenhouse gas emissions that emitted from diesel engines by using renewable fuels to be good alternative to the conventional diesel fuel. Ethanol can be derived from renewable sources such as sugar cane, corn, timber and dates. In the current study, the ethanol fuel used in the tests was derived from the dates. The effects of using exhaust gas recirculation (EGR) diesel-ethanol blend (E10) with on engine performance and emissions characteristics have been studied in diesel engine under various engine loads. This study focused the use of oxygen in the bio-ethanol composition to compensate for the decrease occurred by the addition of EGR, which improves the engine performance and reduces its emissions. In this experiment, the ratios of EGR were 10%, 20% and 30% as well as 10% ratio of ethanol was blended into the diesel fuel blend under fixed engine speed. A traditional (without additional systems to reduce emissions) four cylinders direct injection (DI) diesel engine was used for all tests. The brake specific fuel consumption (BSFC) increased with increasing the EGR ratio by 10%, 20% and 30% by 18.7%, 22.4% and 37.4%, respectively. The thermal efficiency decreased under variable conditions of engine load for different ethanol blends. Furthermore, the emissions of NOX decreased when fuelled B10 into the engine in comparison with diesel under low engine load. Significant reduction in the NOx emissions were found when applied EGR in the tests than to the absence EGR for E10 blend and diesel. The NOx reduction rate was 12.3%, 30.6% and 43.4% when EGR rate was 10%, 20% and 30%, respectively. In addition, the concentrations of HC and CO emissions decreased more by 8.23% and 6.4%, respectively, when using E10 in comparison with the diesel for various engine loads. It is indicated that the oxygen reduction by EGR effect was compensated from ethanol blend combustion. The results showed that the combination use of E10 and EGR leads to significant reduction in engine emissions accompanied with partial reduction in the engine performance.

Evaluation of real-world emissions of China V heavy-duty vehicles fueled by diesel, CNG and LNG on various road types.

Natural gas has been widely considered as an alternative fuel to diesel on heavy-duty vehicles (HDVs). To evaluate the real-world emissions, 19 diesel HDVs, 3 CNG HDVs and 9 LNG HDVs were tested using portable emission measurement system on urban, suburban and freeway roads . The results show that average emission rates of CO, HC and NOx from diesel, CNG and LNG HDVs tend to rise with the increasing of VSP. Due to different emission control strategies and complicated driving cycle, NOx reduction rates of real-world emission factors are lower than those of the corresponding limits from China II to China V diesel HDVs. CO and NOx emission factors from all tested HDVs on urban road are generally higher than those on suburban road in the same velocity intervals, which means driving behaviors on different road types have great influence on emission factors in the same velocity intervals. NOx emission factors from LNG HDVs are higher than those from diesel HDVs, indicating that using China V LNG HDVs instead of China V diesel HDVs could not be an ideal alternative for freeway transportation. As CO and NOx comprehensive emission factors from China V CNG HDVs are higher than those from China V diesel, even higher than China IV diesel HDVs, China V CNG HDVs are unable to be considered as cleaner vehicles when compared to China V diesel HDVs in the study. It is noticeable that HC emission factors from CNG and LNG HDVs are extremely higher compare with diesel HDVS. NO2 emission factors from LNG HDVs are 2.14-9.19 and 4.74-8.53 times than those from diesel and CNG HDVs with various road types. Our study can provide development road map for different fuel types of HDVs and the reference for new emission legislation of HDVs.

Multi-objective optimization of the Atkinson cycle gasoline engine using NSGA Ⅲ coupled with support vector machine and back-propagation algorithm

This paper presents an optimization method using Non-dominated Sorting Genetic Algorithm (NSGA) Ⅲ to drive support vector machine (SVM). In the NSGA Ⅲ algorithm, brake specific fuel consumption (BSFC), NOx and CO2 are optimized by changing the engine control parameters including spark angle, VVT-I (intake), VVT-E (exhaust) and exhaust gas recirculation (EGR). The engine GT-Power physical model is used to generate training data for the SVM, and verify the accuracy of the results of NSGA Ⅲ algorithm during the optimization process. The SVM with fast calculation speed is used in the calculation of NSGA Ⅲ fitness evaluation. In addition, enhancing training is utilized to improve the accuracy of the SVM model in this research. When the optimization method is applied to the Atkinson cycle gasoline engine, its high efficiency has been presented. In the three plans obtained by GT-Power physical model with all four parameters optimized, the maximum reduction rates of BSFC, NOx, CO2 and CO (g/kW·h) reached 7.07%, 35.90%, 6.62% and 5.50% respectively. The SVM model is compared with back-propagation algorithm, and the result proves that SVM is more suitable for such problems. Finally, based on the Pareto optimal solution obtained by the optimization method, it significantly promotes the solution of multi-objective optimization problems. Theoretically, the time cost of the optimization method in this paper can reach 1/23 of that for the optimization algorithm directly driving physical model.

Forecasting of Emission Co-reduction of Greenhouse Gases and Pollutants for the Road Transport Sector in Lanzhou Based on the LEAP Model

With the continuous increase in transportation activities, the transportation sector has become an important source of global greenhouse gases. In 2019, road vehicles accounted for nearly three-quarters of the CO2 emissions of the entire transportation sector and will be the key to achieving carbon peaks in the transportation sector. At the same time, air pollutants emitted by road vehicles are also one of the threats to the environment and human health. Based on the long-range energy alternatives planning system (LEAP) model, we constructed the baseline (BAU) scenario, low-carbon (LC) scenario, and enhanced low-carbon (ELC) scenario for the development of the road transport sector in Lanzhou from 2015 to 2040 and simulated energy consumption and emission co-reduction of greenhouse gases and pollutants under policies and measures. The results showed that the energy consumption and CO2 emissions of the LC scenario will peak in 2026, whereas those in the ELC scenario will peak in 2020. In these two scenarios, pollutant emissions such as NOx, CO, HC, PM2.5, and PM10 began to decline sharply between 2015 and 2017, and the downward trend will slow down gradually around 2023. Based on the feasibility of measures and the cost of abatement, the LC scenario can be used as a road vehicle carbon peak scenario in Lanzhou. In this scenario, the reduction rates of energy consumption, CO2, NOx, CO, HC, PM2.5, and PM10 emissions will reach -24.17%, -26.57%, -55.38%, -65.91%, -72.87%, -76.66%, and -77.18% compared with those under the BAU scenario by 2040. At present, the road vehicles in Lanzhou City should focus on structural optimization measures such as clean-energy use of public transportation, electrification of small passenger cars, and phasing out old cars, as well as vigorously promoting low-carbon travel and improving energy efficiency accompanying the development of automotive technology. These efforts will effectively control CO2 and pollutant emissions by road vehicles, and carbon peaks will be achieved as soon as possible. In addition, it is necessary to pay attention to the changes in vehicle types during the implementation of these measures, which most contribute CO2 and various pollutants, in order to make the measures more targeted by changing the number or the market share of new energy of focused vehicle types.

Decoupled combustion of alcohol extracted herb residues with blending wasted activated coke: Insight into in-situ NOx emission control by pyrolysis products

By a self-established dual fluidized bed combustion apparatus, alcohol extracted herb residues (AEHRs), as well as their derived char and on-line volatiles, were firstly directly combusted to investigate and compare the characteristics of the resulting NOx emissions; and then, the AEHRs were subjected to decoupled combustion (DC) with addition of wasted activated coke (WAC), to realize their safe disposal/clean energy recovery. The result showed that, the DC exhibited a desirable NOx reduction effect, and the on-line volatiles, especially those from pyrolysis at 600 ℃, played a crucial role in the in-situ NOx control. The WAC inhibited NOx formation, due to its lower ash content and containing significantly fewer light metals (mainly K and Mg) than the AEHR char. When subjected to DC at the optimized conditions (600 °C pyrolysis, 850 °C combustion, excessive air ratio (ER) = 1.3 and secondary air proportion = 0.5), blending 20% WAC into the AEHR further reduced the NOx emission concentration from 217.03 to 163.82 mg m−3, corresponding to a 70.40% NOx reduction rate when compared to 553.41 mg m−3 for conventional combustion of the AEHR. Splitting the primary air revealed that the char + WAC contributed 18.81–26.51% of the total NOx reduction amount during the AEHR + WAC DC, justifying the necessity for DC to simultaneously make good use of the hot char and the on-line volatiles for reducing NOx.

LoTOx 시스템 적용 폐기물 소각로의 경제성 분석 및 효율적 운전 방안

The purpose of this study was to investigate how to improve the combustion gas treatment method of domestic waste incinerator comprising SNCR and SCR by adopting the LoTOx (ozone low-temperature oxidation) system. NOx reduction performance, efficient operation plan, and economic feasibility of the LoTOx system not yet commercialized in domestic field were studied. First, by applying the LoTOx system to actual waste incineration facilities, it was possible to compare and evaluate the NOx reduction performance with conventional SCR facilities currently widely used. The NOx reduction rate was close to 90% based on combustion gas of 110℃. If the temperature of the combustion gas was lowered further, the NOx reduction rate was much closer to the theoretical expected value, and the reduction rate of 90% or more can be shown. Second, economic benefits in terms of initial investment and operating cost were analyzed for an existing combined SNCR and SCR system, by replacing SCR with the LoTOx ozone oxidation system. The initial investment cost was 73.6% compared to the SCR facility, and the longer the operating period, the greater the cumulative operating cost is reduced. The LoTOx system could be predicted to fall to 61.2% of the SCR facility in the fifth year and 55.3% in the tenth year. Third, based on the experiment and existing papers, several factors impacting the efficiency of the operation of the LoTOx system were identified. It was possible to present the most efficient operation plan such as the temperature of the processing gas, the installation method of the cooling water pipe of the ozone generator, input voltage, and gas flow rate.

Effect of Exhaust Gas Recirculation Combined with Selective Catalytic Reduction on NO x Emission Characteristics and Their Matching Optimization of a Heavy-Duty Diesel Engine.

Exhaust gas recirculation (EGR) and selective catalytic reduction (SCR) have become important technologies to reduce the NOx emission of heavy-duty diesel engines and meet the increasingly stringent emission regulations. This paper studied the effect of EGR combined with SCR on the NOx emission characteristics of a heavy-duty diesel engine based on the engine bench test. The results showed that the NO reduction rate of EGR-coupled SCR increased with the increase of engine load, and the effect was no longer significant when the NO reduction rate exceeded a certain limit under the same working conditions. EGR combined with SCR has little effect on NO2 emission reduction, and the increase of engine speed can significantly improve the efficiency of the NO2 reduction rate at 75 and 100% load. 25% opening of the EGR valve (OEV) and 50% OEV have very similar effects on the NOx reduction rate when the engine speed is at a low level. Compared with low engine speeds, increased OEV or ammonia NOx molar ratio (ANR) had a more obvious effect on the NOx reduction rate at high engine speeds. SCR combined with low valve-opening EGR had a more significant effect on the NOx reduction rate. The increase of OEV led to the increase of fuel consumption rate, but the effect on the fuel consumption rate decreased gradually with the increase of diesel engine speed. Meanwhile, this study optimized the matching relationship between OEV and ANR based on the data of the genetic algorithm, which provides a theoretical research method and application basis for diesel engine-matching of EGR and SCR.

Dynamic Change of Active Sites of Supported Vanadia Catalysts for Selective Catalytic Reduction of Nitrogen Oxides.

Selective catalytic reduction of NOx by ammonia (NH3-SCR) on V2O5/TiO2 catalysts is a widely used commercial technology in power plants and diesel vehicles due to its high elimination efficiency for NOx removal. However, the mechanistic aspects of the NH3-SCR reaction, especially the active sites on the V2O5/TiO2 catalysts, are still a puzzle. Herein, using combined operando spectroscopy and density functional theory calculations, we found that the reactivity of the Lewis acid site was significantly overestimated due to its conversion to the Brønsted acid site. Such interconversion makes it challenging to measure the intrinsic reactivity of different acid sites accurately. In contrast, the abundant V-OH Brønsted acid sites govern the overall NOx reduction rate in realistic exhaust containing water vapor. Moreover, the vanadia species cycle between V5+═O and V4+-OH during NOx reduction, and the re-oxidation of V4+ species to form V5+ is the rate-determining step.

Evaluating the emission reduction efficiency of automatic mooring system and cold ironing: the case of a port in Izmit Bay

ABSTRACT Maritime transportation contributes to air pollution, which adversely affects life on Earth. Ship-borne emissions, especially in port areas, threaten public health. This study evaluated the emission reduction rates when Automatic Mooring System (AMS) and Cold Ironing (CI) methods were applied separately, and together at a port in Izmit Bay. We used Entec and EPA methodologies to estimate ship-borne emissions. As a result, when only the AMS was used as a reduction method instead of the current situation, in which no reduction method is used, the emission reduction rates of CO2, NOx, PM, and SO2 were 3.58%, 3.55%, 11.19% and 3.45%, whereas these rates were 21.21%, 88.85%, 47.17% and 2.33% respectively when only the CI was used. Additionally, when both systems were applied together, emission reduction rates increased to 24.79% for CO2, 92.40% for NOx, 58.37% for PM, and 5.78% for SO2.

Fundamental Study on Hydrogen Low-NOx Combustion Using Exhaust Gas Self-Recirculation

Hydrogen is expected to be a next-generation energy source that does not emit carbon dioxide, but when used as a fuel, the issue is the increase in the amount of NOx that is caused by the increase in flame temperature. In this study, we experimentally investigated NOx emissions rate when hydrogen was burned in a hydrocarbon gas burner, which is used in a wide temperature range. As a result of the experiments, the amount of NOx when burning hydrogen in a nozzle mixed burner was twice as high as when burning city gas. However, by increasing the flow velocity of the combustion air, the amount of NOx could be reduced. In addition, by reducing the number of combustion air nozzles rather than decreasing the diameter of the air nozzles, a larger recirculation flow could be formed into the furnace, and the amount of NOx could be reduced by up to 51%. Furthermore, the amount of exhaust gas recirculation was estimated from the reduction rate of NOx, and the validity was confirmed by the relationship between adiabatic flame temperature and NOx calculated from the equilibrium calculation by chemical kinetics simulator software.