Maximum NO Reduction Research Articles

Research on the effect of CO2 and H2O on NO reduction of biomass char by the equivalent characteristic spectrum method via an on-line mass spectrometer

Despite extensive experimental studies on NO reduction by biomass char, the impact of high concentrations of CO2 and H2O on the NO-char reaction remains insufficiently understood. This study investigates the effects of CO2, H2O, and CO2+H2O atmospheres on NO reduction by biomass char in a micro-fluidized bed (MFB). Experiments were conducted at 900 °C, with CO2 concentrations ranging from 20 % to 80 % and H2O concentrations from 10 % to 40 %. The results show that increasing concentrations of CO2 and H2O accelerate the NO reduction rate. However, under high CO2 and H2O concentrations, both the maximum NO reduction efficiency and the mass consumption of nitrogen decrease. In a CO2 atmosphere, nearly all nitrogen from NO converts to N2, but this conversion efficiency declines in the presence of H2O. When both CO2 and H2O are present, H2O predominantly governs the NO consumption rate. Additionally, the apparent activation energy for NO reduction is higher in an H2O atmosphere compared to a CO2 atmosphere at similar concentrations.

Study on the Catalytic Activity Modification of Pr and Nd Doped Ce0.7Zr0.3O2 Catalysts for Simultaneous Removal of PM and NOX

Cerium-zirconium composite oxides (Ce0.7Zr0.3O2) have a remarkable effect on catalytic removal of carbon particles (PM) and nitrogen oxides (NOX) emitted from diesel engine, in order to further improve the thermal stability, oxygen storage capacity and low temperature catalytic REDOX performance of cerium zirconium composite oxides (Ce0.7Zr0.3O2), a small amount of Pr and Nd rare earth elements are doped to improve the catalytic activity of cerium zirconium composite oxides. In this paper, the composite oxide of Pr6O11–Nd2O3–CeO2–ZrO2 is prepared by unsteady co-precipitation method, and the physicochemical properties of the composite oxide catalyst are analyzed by BET, SEM, XRD and ICP. The gas adsorption capacity and catalytic activity of composite oxide catalysts are measured by temperature programmed reaction technology (TPR). The results show that the composite oxide of Pr0.05Nd0.05Ce0.6Zr0.3O2 prepared by using rare earth elements Pr and Nd inhibits the growth process of grain, refining the grain, and improving the sintering phenomenon at high temperature. The addition of Pr and Nd causes lattice defects, increases the number of oxygen vacancies, and improves the mobility of lattice oxygen, namely promotes oxide oxygen storage property, gas adsorption and catalytic oxidation reduction ability. After modification, Pr0.05Nd0.05Ce0.6Zr0.3O2 has good resistance to high temperature aging performance, prolongs the service life, reduces the PM lowest ignition temperature and minimum catalytic activity temperature of nitrogen oxide, and promotes the NOX reduction rate. For Pr0.05Nd0.05Ce0.6Zr0.3O2, the lowest ignition temperature of PM is about 150 °C, and the lowest catalytic activity temperature of NO is about 130 °C. The maximum CO2 production rate is 68.3%, and the maximum NO reduction rate is 45%.

A new quantitative method via on-line mass spectrometer: Application in biomass char/NO reaction

A novel quantitative analysis method via on-line mass spectrometer (OMS) was developed to calculate the mass flows of the reactants and products for the reaction between NO and biomass char in micro-fluidized bed. The experimental results showed that the quantitative method could accurately calculate the mass flow rate of each gas even though there were ion currents overlapping at mass-to-charge ratio (m/z) = 12,16, and 28 when CO, CO2 and N2 were simultaneously present in OMS. Furthermore, the method facilitated the quantitative analysis of gaseous reactants and products, thereby enabling the assessment of mass conversions of carbon (C) and nitrogen (N) in the NO reduction reaction. It was observed that CO was the predominant carbon-containing product in the reaction involving biomass char and NO at 900 °C, with over 96 % of nitrogen in NO participating in the reduction reaction being converted to N2. This study also revealed that increasing the fluidization number, NO concentration, and temperature in the micro-fluidized bed could significantly accelerate the conversion processes of C and N in the reduction of NO by biomass char. The peak mass flow rates of CO, CO2, and N2 were found to increase correspondingly with higher NO concentrations and temperature levels. The NO reduction process over sawdust char was compared to that of corncob char, showing a higher maximum NO reduction efficiency. The reaction order with respect to NO concentration was determined to be 0.82 for corncob char and 0.68 for sawdust char. Additionally, the apparent activation energies were determined to be 92.35 kJ/mol for corncob char and 125.60 kJ/mol for sawdust char, respectively.

Study of the interaction between NH3 and NO in the reduction zone of air-staged ammonia combustion under high moisture atmosphere

NH3 is used as a hydrogen-rich fuel, and the water vapor content produced by combustion can reach 30%. However, high NOx emission is one of the main problems restricting its application. The air-staged combustion is an effective low-NOx combustion strategy, subdividing the combustion process into three typical sections: the main combustion zone, the reduction zone, and the burnout zone. Fully utilizing the reaction between NH3 and NO in the reduction zone is expected to achieve an effective control of NOx emission. This research aims to explore the reduction ability of the residual NH3 on NO reduction in the reduction zone under high moisture atmosphere formed by ammonia combustion. An isothermal flow reactor was used to study the kinetic characteristics of the NH3/NO reaction under no-oxygen or residual low-oxygen condition in a wide temperature range (1073–1773K) and a high water vapor content range (0–50%). Additionally, three chemical kinetic models were used in simulations. The results showed that oxygen significantly changes the effect of water vapor on the NH3/NO reaction. In the absence of oxygen, water vapor has less effect on NH3/NO reaction at lower temperatures (<1500K). In the presence of oxygen, the increase of water vapor content leads to a significant shift of the reaction temperature window to higher temperatures and a decrease of the maximum NO reduction efficiency. Finally, the remarks about using residual NH3 to complete NOx removal in ammonia combustion were discussed.

Investigation on NO reduction behavior within complex atmosphere during pilot ignition of low calorific gas

Low calorific gas (LCG) is largely produced in industries and agricultures, but its utilization is difficult due to the poor combustibility and high NO x emission. The pilot ignition combustion has the potential to improve LCG’s combustibility and also reduce NO production with combining air stage approach. However, the complex atmosphere created under pilot ignition condition could complicate the NO reduction (by CH4) behavior and should be clarified. This paper is aimed at gain a deep insight on this issue by exploring the interaction between temperature and atmosphere, the individual role of α and CH4 concentration (or its ratio to NO), and the influence of CO and CO2 presence. The results show that with dropping α, the maximum NO reduction ratio increases, but a higher temperature is needed to achieve this value. Under fuel rich condition, NO reduction was accompanied with HCN formation, which must be considered to analyze the effective reduction. The CO2 generated from pilot flame or originally contained in LCG could inhibit the NO reduction, with this effect being more pronounced at a fuel rich atmosphere. For a CO/CH4 duel reactive LCGs, CO reduces the NO reduction ratio at lower temperature, but improves at higher temperature.

NO emission and burnout characteristics in co-combustion of coal and sewage sludge following high-temperature preheating

Due to the high content of volatile nitrogen in sewage sludge, co-combustion of coal and sewage sludge easily leads to high emission of nitric oxides (NOx). To solve this problem, we applied the high-temperature preheating technology to promote the advance conversion of fuel-nitrogen into N2 so as to reduce NOx emission. In this study, a two-stage drop-tube furnace system was employed. The effects of sludge proportion, excess air ratio in the preheating zone (λ1), preheating temperature, and combustion temperature on NO emission and burnout were investigated. Our results showed that with the preheating treatment, increasing the sludge proportion reduced NOx emission and promoted char burnout. NO emission was the lowest when λ1 increased to 0.5. Under this condition, 62% of the fuel nitrogen could be converted to the gaseous species, in which the portion of N2 was 89.7%. By controlling λ1 to 0.5 and sludge proportion to 15%, the maximum NO reduction of 62% was achieved. The emitted NO and unburnt carbon in fly ash were reduced by 48.3% and 43.2%, respectively, when the preheating temperature increased to 1200 °C. The effect of combustion temperature strongly depended on the stoichiometry ratio. In oxygen-deficient regions, NO emission decreased with the increase of temperature, while an opposite trend appeared in oxygen-rich regions. The critical excess air ratio in our experiments was around 0.8.

Experimental and density functional theory investigation of the NO reduction mechanism by semichars preheated in Ar and CO2/Ar atmospheres

The extensive utilization of coal-based solid fuels in thermal power plants has led to massive emissions of greenhouse gases (GHG) and gaseous pollutants, resulting in serious environmental issues. In this study, the NO reduction reactivity of semichars preheated in Ar and Ar/CO2 atmospheres was investigated via temperature-programmed reduction (TPR) experiments. Based on the TPR-DTPR method, the NO initial temperature, the maximum NO reduction rate, and the NO reduction indices of different semichars were determined. Compared with CO2/Ar pretreatment, the inert pretreatment enhanced the NO reduction index of the semichar. The CO2/Ar pretreatment was beneficial for decreasing the total Raman area and the ratio of I(Gr+VL+Vr)/ID due to the preferential consumption of high-reactivity structures and the condensation of aromatic ring structures. Furthermore, the detrimental effect of CO2/Ar treatment on semichar reactivity was relevant to the volumetric fraction, exerting an extraordinary correspondence with Rr. Density functional theory (DFT) was employed further to analyse the NO reduction mechanisms by semichars derived from Ar and CO2/Ar atmospheres. For the inert pretreatment, the NO reduction pathways consisted of two pathways (path 1 and path 2). Path 1 was supported by thermodynamics and dynamics. The energy barrier of the rate-determining step was 280.53 kJ/mol. Owing to the difference in the evolutionary pathways of C(O) on the semichar surface, the reaction between NO and the semichars derived from the CO2/Ar atmospheres could be summarized as two pathways (path 3 and path 4). Path 3 was identified as the better method, and the energy barrier of the rate-determining step was 285.39 kJ/mol. The slightly adverse effects of CO2/Ar pretreatment on NO heterogeneous reduction were determined by coupling the experimental and theoretical methods, providing new insights into nitrogen migration and transformation mechanisms.

Coupling selective catalytic reduction process inside a coke oven regenerator: The influence of mixing parameters on NO reduction

Many coking plants have adopted the process of preheating flue gas to apply medium and low temperature selective catalytic reduction (SCR) denitrification technology, which increases the NOx treatment cost, fuel consumption, and generates secondary pollutants. Based on the unique temperature distribution characteristics of the coke oven regenerator, this work proposes a method for synergizing SCR inside the regenerator to remove NOx. A 3-D numerical model of the synergy between heat storage and SCR reaction was constructed to study the influence of mixing parameters (atomization angle, injection velocity, nozzles number) on the NO reduction and NH3 distribution. The validity of the model was verified. The results showed that the uneven distribution of NH3 near the catalytic layer and the small SCR coating area limited the NO reduction efficiency. Increasing the number of nozzles was more beneficial than the injection velocity and atomization angle for improving the NH3 distribution uniformity and NO reduction efficiency, achieving a maximum NO reduction efficiency of 37.1% (reduced to 251.6 mg/m3). Further research found that the NO reduction capacity of the co-operative SCR model cannot exceed 36% without changing the thermal storage brick structure. When the inlet NO concentration is less than 235 mg/m3, the reaction model ensures that the outlet NO concentration meets the national emission standards.

Dual role of O2 concentration on the reducing gases produced and NO reduction during sewage sludge combustion in pilot scale cement precalciner.

The reducing gases produced and NO reduction by sewage sludge combustion were investigated in a self-made cement precalciner. The dual role of O2 concentration (0-5vol%) in the production characteristics of reducing gases and the reduction efficiency of NO were evaluated experimentally. TG-FTIR analysis demonstrated that the key reducing gaseous species produced by sewage sludge combustion were HCN, NH3, CO, and CH4. And experiments demonstrated that O2 concentration had pronounced effects on NH3 distribution, the maximum production rate was obtained at an O2 concentration of 3vol%. Meanwhile, the reducing gases NH3 and CO were the key species for NO reduction in the cement precalciner, and the reduction efficiency of NO, when reduced by NH3, increased with an increase in O2 concentration, while the reduction performance of NO by CO was limited by O2 concentration. Therefore, O2 concentration greatly influences NO reduction efficiency by sewage sludge combustion; the maximum NO reduction efficiency was 61.67% at an O2 concentration of 3vol%. The difference in NO reduction by sewage sludge combustion under different O2 concentrations was primarily attributed to NH3 production rate and NO reduction by NH3 and CO, which is greatly affected by O2 concentration. Sewage sludge combustion can result in NO reduction in the cement kiln flue gas and resource utilisation of sewage sludge.

No formation and its reduction through co-flow methane reburn in a pulverised coal combustion process under various overall equivalence ratio

Computational simulation has been carried out to investigate the NO formation/depletion in pulverized coal combustion process. Newlands Bituminous coal is injected along with career air through a central hole of an axi-symmetric burner. A certain amount of co-flow methane is injected coaxially as reburn fuel. The effect of overall equivalence ratio on NO formation and NO reburn are mainly focused in this study. Species concentration for various species are also investigated, because both NO formation and depletion are related closely to various species concentration. From the study it is observed that, at overall equivalence ratio φ=0.8 and 1.0, although the rate of Thermal-NO, Prompt-NO and Fuel-NO formation is high but due to narrow reaction zone and higher air velocity, a weak NO concentration field is observed. On the other hand, a higher NO concentration has been observed with higher equivalence ratio (ratio φ=3.0, 6.0 and 9.0). It also has been observed, the maximum NO reduction efficiency at φ=0.8, 1.0 and 3.0 is in between 1% to 7%, whereas for φ=6.0 and 9.0, the maximum NO reduction efficiency is 27% and 34% respectively. Therefore, co-flow methane injection NO reduction method is more suitable for highly rich mixture conditions. Moreover, the percentage of coal burnout is also relatively higher for higher equivalence ratio condition.

Experimental investigation on NO emission and burnout characteristics of high-temperature char under the improved preheating combustion technology

In order to avoid the formation of NO from the nitrogen-containing pyrolysis components in the main combustion zone under preheating combustion technology, an improved preheating combustion technology was proposed. A two-stage drop-tube furnace was built to study the NO emission and combustion characteristics of high-temperature char (HTC) under the improved preheating combustion technology. The char was first heated to the initial pyrolysis temperature(600℃,800℃ and 1000℃) in the upper furnace under the atmosphere of nitrogen, before being burned in the second furnace. The influence of important operating parameters such as HTC temperature(600℃,800℃ and 1000℃), combustion temperature (1200℃,1300℃ and 1400℃)and excess air ratio (0.6 ∼ 1.4)were analyzed. The results show that raising the HTC temperature helps to reduce NO emissions. The maximum NO reduction efficiency is 21.1 % when the excess air ratio(α) = 1.0, which differs from the reported literature results of room-temperature char (RTC). In HTC, there is no absolute correlation observed between the BET area and NO reduction. The release of C and N is altered by pre-ignition of char at HTC; additionally, the evolution of nitrogen functional groups during the pyrolysis process is more key influencing factors. The stoichiometric ratio has a considerable influence on the effects of combustion temperature on NO emission. When there is a lack of oxygen, NOx emissions decrease as the temperature rises, whereas under oxygen-rich situations the converse is true. With the increase in HTC temperature from 600 °C to 1000 °C, the critical excess air ratio steadily increases from 0.75 to 0.85. The carbon concentration of fly ash can be reduced by increasing both the HTC and the combustion temperature. The largest reduction in carbon content in fly ash is 28.6 % at α = 1.0.

Experimental and kinetic study of NO-reburning by syngas under high CO2 concentration in a jet stirred reactor

The NO-reburning by syngas is investigated by the jet-stirred reactor (JSR) experiments and kinetic modeling. The effects of CO2 and methane are studied systematically under different reaction temperatures (T), equivalence ratios (Φ) and initial ratios of hydrogen to carbon monoxide (α). The kinetic modeling is carried out by the present modified detailed mechanism consisting of 151 species and 1408 reactions. The modeling results obtained using the present modified mechanism demonstrate the good consistency with experiments under most of the conditions. The CO2 has significant inhibitory effect on the NO-reburning by syngas independent of variations in T, Φ and α. The maximum NO reduction efficiency is remarkably reduced than that under N2 condition by at least 76%. The addition of 1000 ppm methane has been found to increase the NO-reburning by the syngas for CO2 conditions by at least 243%. The effects of CO2 and CH4 must be considered for NO-reburning by syngas as the actual syngas contains CO2 and methane. Considering the presence of CO2 and CH4, the optimal condition to maximize the NO reduction efficiency is T ≈ 1150 K, Φ ≈ 1.67 and α ≈ 1. The mechanism under this optimal condition is determinate by pathway and sensitivity analyses. The critical reactions for NO-reburning by syngas in the presence of CO2 and CH4 are identified, which are important for future mechanism development and application of NO-reburning by syngas.

Effect of Re-burn Fuel Stream Location on NO Reduction in a Model Pulverized Coal Combustor

I is missing this work, a computational simulation has been performed to investigate the positional effect of reburn fuel injection on NO-reburn. Reburn fuel methane is injected across the coal injection plane at different axial positions of the combustor. Various major NO source mechanisms are considered for NO formation and NO reburn mechanism is used for NO depletion. Temperature profile, species concentration are also investigated, as both NO formation and depletion rate depends on these parameters. It has been observed that, a high temperature flame exists near coal inlet, when the reburn fuel injection plane is closer to coal inlet. On the other hand, the temperature of the flame near the coal inlet decreases when the reburn fuel injection position is far away from coal inlet region. Moreover, NO sources are observed near coal inlet region, when the reburn fuel is injected closer to coal inlet. On the other hand, only Fuel-NO is observed near coal inlet, when the reburn fuel is injected away from the coal inlet. Maximum NO reduction efficiency is observed at outlet plane when reburn fuel is injected closer to inlet, whereas a relatively lower NO reduction efficiency has been observed at outlet plane when reburn fuel is injected far away from coal inlet region.

A kinetic evaluation and optimization study on NOx reduction by reburning under pressurized oxy-combustion

Pressurized oxy-combustion is an emerging and more efficient technology for carbon capture, utilization, and storage than the first generation (atmospheric) oxy-combustion. NOx is a major conventional pollutant produced in pressurized oxy-combustion. In pressurized oxy-combustion, the utilization of latent heat from moisture and removal of acid gases (NOx and SOx) are mainly conducted in an integrated direct-contact wash column. Recent studies have shown that NOx particular inlet concentration should be maintained before direct contact wash column to remove NOx and SOx efficiently. As a result, minimizing NOx for environmental reasons, avoiding corrosion in carbon capture, utilization, and storage, and achieving effective NOx and SOx removal in direct contact wash columns are crucial. Reburning is a capable and affordable technology for NOx reduction; however, this process is still less studied at elevated pressure, particularly in pressurized oxy-combustion. In this paper, the kinetic evaluation and optimization study on NOx reduction by reburning under pressurized oxy-combustion was conducted. First, the most suitable mechanism was selected by comparing the results of different kinetic models with the experimental data in literature at atmospheric and elevated pressures. Based on the validated mechanism, a variety of parameters were studied at high pressure, i.e., comparing the effects of oxy and the air environment, different reburning fuels, residence time, H2O concentration, CH4/NO ratio, and equivalence ratio on the NO reduction. The results show that de-NOx efficiency in an oxy environment is significantly enhanced compared to the air environment. Improvement in the de-NOx efficiency is considerably higher with a pressure increase of up to 10 atm, but the effect is less prominent above 10 atm. The formation of HCN is significantly reduced while the N2 formation is enhanced as the pressure increases from 1 to 10 atm. The residence time required for the maximum NO reduction decreases as the pressure increases from 1 atm to 15 atm. At the higher pressure, the NO reduction rises prominently when the ratio of CH4/NO increases from 1 to 2; however, the effect fades after that. At higher pressure, the NO reduction by CH4 reburning decreases as the H2O concentration increases from 0 to 35%. The optimum equivalence ratio and high pressure for maximum NO reduction are 1.5 and 10 atm, respectively. This study could provide guidance for designing and optimizing a pressurized reburning process for NOx reduction in POC systems.

Experimental and numerical investigation of the combustion characteristics and NO emission behaviour during the co-combustion of biomass and coal

As a promising technology for pollutant reduction, biomass-coal co-combustion has attracted worldwide attention. In this study, experiments combined with simulations were conducted to explore the combustion characteristics and NO emission behaviour, as well as their interrelations during the co-combustion process of biomass and coal. The experimental results reveal an obvious decrease in the NO concentration with an increased biomass blending ratio by weight. A maximum NO reduction of 24% was found when 50% biomass was blended with coal, which mainly occurred in the stage of stable char combustion and was attributed to non-catalytic effect related to free radicals. Moreover, the higher biomass blending ratio led to a more violent combustion reaction during the devolatilization stage, while the reaction remained constant during the char combustion stage. As the temperature increased from 800 °C to 1000 °C, the fuel-N/NO conversion ratio increased for the blend with 30% biomass and 70% coal, which resulted from the combined contributions of devolatilization and char combustion. Although the rise in temperature also led to an increase in the combustion rates of the fuel samples, the effect of the temperature on NO emission turned out to be more sensitive than that on the combustion rate. Additionally, when the oxygen concentration increased from 6 vol% to 21 vol%, the NO conversion ratio decreased, which is attributed to the promotion effect of the higher O2 concentration on homogeneous NO reduction. The simulation data were in good agreement with the experimental results, and demonstrated that there were six elementary reactions dominating the NO transformation. Moreover, homogeneous NO reduction plays a vital role in decreasing NOx emissions.

Experiments and kinetic modeling of NO reburning by CH4 under high CO2 concentration in a jet-stirred reactor

This paper presents new experimental results on NO reduction by CH4 under both N2 and CO2 atmospheres in a jet-stirred rector (JSR). The experiments are simulated using an updated reaction mechanism, and simulations are consistent with experiments. Both experiments and simulations suggest that there is a critical equivalence ratio (Φ) to achieve the maximum NO reduction at a fixed reaction temperature (T), and the critical Φ is increased with the increase of T. The maximum NO reduction in the CO2 atmosphere is achieved at T ≈ 1300 K, Φ ≈ 1.4, and CH4/NO ratio = 20 with a maximum reduction efficiency of 63%. When the CH4/NO ratio ≤5, relative to the N2 atmosphere, the NO reburning in the CO2 atmosphere is reduced by around 40%–60% at temperatures above 1100 K. Interestingly, at 1100 K the maximum NO reduction does not occur at fuel-rich environments but at Φ ≈ 0.7 due to the low reactivity to produce hydrocarbon radicals at low temperatures. Moreover, at 1300 K, as CO2 concentration increases from 30% to 60%, the critical Φ is reduced from 1.4 to 1.2 and the NO reduction efficiency is reduced by around 7% owing to the enhanced inhibition of CH4 oxidation. To improve reburning in oxy-fuel combustion, it is recommended to operate reburn zone at moderate temperatures (i.e., 1300–1400 K), the critical Φ (e.g., Φ ≈ 1.4 if T = 1300 K), long residence times (τ ≥ 2 s), and large reburning fuel/NO ratio (≥15).

Effects of water vapor and Na/K additives on NO reduction through advanced biomass reburning

NO reduction through advanced reburning (AR) was carried out in an entrained flow reactor. Four types of biomass fuels, rice husk (RH), camphor leaves (CL), saw dust (SD) and wood charcoal (WC), were selected as reburning fuels. Effects of reaction temperature in the reburning zone (T2), biomass species, water vapor and alkali metal additives (Na2CO3, NaOH, NaCl and KCl) on NO reduction were investigated. The roles of these factors in the reaction pathways and possible mechanism were discussed. Results indicate that NO removal efficiency increases first and then decreases as temperature increases within 850–1150°C. The maximum NO reduction efficiency is around 60.1–73.8% at optimal reaction temperature in the AR process. NO reduction also appears to increase and then decrease as the water vapor content increase from 0% to 15%, with a peak NO reduction at water vapor of 2–6%. Na/K additives have certain promoting effect on NO reduction in the AR process, following the sequence of NaCl>NaOH∼Na2CO3>KCl. Concentration of Na-additives (NaCl, Na2CO3) has little effect on NO reduction when its concentration is higher than 50ppm. The improvement of Na-additives in NO reduction can be promoted by water vapor significantly. More than 11.4% increment in NO reduction is achieved by AR with rice husk in presence of 4% water vapor and 100ppm Na-additives (NaCl, Na2CO3) in comparison to that without water and additives, and the maximum NO removal efficiency gets up to 85.5%.

The effects of steam injection on the performance and emission parameters of a Miller cycle diesel engine

The application of the Miller cycle into the internal combustion engines is proposed to decrease NOx emissions, in the recent years. Another NOx control technique is the steam injection method (SIM). In this study, the application of these methods together into a single cylinder, direct injection diesel engine is experimentally and theoretically performed. Two different Miller cycles, which provide 5 and 10 crank angle (CA) retarding compared to standard condition, are applied with two different camshafts. SIM is applied at three different injection rates which are 10%, 20% and 30% of the fuel mass. The results obtained are compared with standard conditions in terms of the performance and emissions. The simulation results are verified with experimental data with non-notable errors. In the experimental results, NO and CO2 emissions decreased up to 48% and 2.2%; HC and CO emissions increased by 46% and 34% with the penalty by 6.4% and 9.2% for the effective power and efficiency. The optimum condition has been defined as 10 CA retarding and 30% steam injection rate (C62-S30) in terms of the maximum NO reduction. The results demonstrate that the combination can be applied into the diesel engines to minimize NO and CO2 emissions.

An experimental study of NO reduction by biomass reburning and the characterization of its pyrolysis gases

The reduction of NO by reburning using three biomass samples (rice husk, sawdust and corncob) was investigated in a horizontal fixed-bed quartz reactor. The temperatures were ranging from 800 to 1200°C. The influence of the oxygen concentration entering the reburning zone, the particle size of the biomass and the initial NO concentration on the NO reduction efficiency were studied experimentally. In order to improve the understanding of the relative contribution of each of the pyrolysis gases on the NO reduction, the CO, H2, hydrocarbons (mainly CH4), HCN, and NH3 concentrations in the outlet gas from the reburning zone were measured at combustion temperatures of 800–1200°C. The experimental results indicated that the biomass type had a significant influence on the NO reduction efficiency. The maximum NO reduction efficiency of sawdust reburning (55±2.4%) was much higher than those of rice husk reburning (43±1.8%) and corncob reburning (44±2.1%). For reburning with sawdust, a highly efficient NO reduction was achieved at oxygen inlet concentrations of 0–1 vol%, particle sizes of 160–370μm and initial NO concentration of 800ppmv. For the present operating conditions, the difference in NO reduction for the three biomass samples could be ascribed to differences in the yield of pyrolysis gases through the homogeneous reactions. Hydrocarbons (mainly CH4) were the key species for reducing the emissions of NO, whereas CO and H2 had little effect on NO reduction. The sum of the HCN and NH3 concentrations could reflect the tendency for the conversion of the NO entering the reburning zone into N2.

Experimental study on reburning/advanced reburning performance of limestone modified by wood vinegar for NO reduction under O2/CO2 atmosphere

NO reduction characteristics of reburning/advanced reburning using limestone modified by wood vinegar and calcium acetate, as well as selective non-catalytic reduction using ammonia, are investigated in a drop-tube system under O2/CO2 atmosphere. Results show that NO reduction efficiency of limestone modified by wood vinegar and calcium acetate through basic reburning increases first and then decreases with increasing temperature. The maximum NO reduction efficiency of 82.70% and 78.52% can be obtained at 1323 K, respectively. High oxygen concentration is not conducive to NO reduction. The optimum reburning fuel fraction and residence time for basic reburning is 14%–17% and 0.8 s, respectively. The maximum NO reduction efficiency of selective non-catalytic reduction is 95.41% at 1173 K in temperature window of 1142–1335 K. With increasing oxygen concentration, NO reduction efficiency declines continuously. The optimum [NH3]/[NO] molar ratio and residence time for selective non-catalytic reduction is 1.5 and 1.2 s, respectively. NO reduction efficiency of reburning is significantly increased, while the reaction temperature window is obviously broaden when ammonia is injected into reburning zone at [NH3]/[NO] molar ratio of 0.75. The maximum NO reduction efficiency of limestone modified by wood vinegar and calcium acetate advanced reburning is 93.49% and 92.79% at 1323 K, respectively.