A surface-reactive soot population balance model is developed to decouple the gas-phase and surface-reaction effects of ammonia on soot formation in ethylene counterflow diffusion flames. The model extends the conventional HACA-based framework by incorporating reactions of NH3, NH2, and HCN at soot active sites, and is solved using a moment projection method coupled with the OPPDIF-CHEMKIN flame solver. The model is applied to a series of ethylene/NH3 counterflow diffusion flames with different ammonia substitution ratios. The predicted soot profiles show reasonable agreement with experimental measurements. The strong monotonic decrease in soot formation with increasing ammonia addition is correctly captured. A decoupled analysis reveals that ammonia suppresses soot predominantly through gas-phase inhibition of aromatic precursor formation and PAH growth. Ammonia activation consumes H radicals and redirects part of the reactive hydrocarbon pool into nitrogen-containing intermediates, thereby reducing the formation of PAHs which strongly weaken soot inception. From the perspective of soot particle dynamics, the reduction in soot number density is governed mainly by decreased inception, while the reduction in soot volume is controlled primarily by weakened C2H2-based surface growth. Surface nitridation provides an additional but secondary suppression route by occupying soot active sites and indirectly inhibiting the dominant hydrocarbon-driven growth pathway. These results clarify the dominant gas-phase and secondary surface-reaction effects of ammonia on soot suppression and provide a mechanistic framework for soot modeling in ammonia-assisted combustion systems.

Hydrogen/polyoxymethylene dimethyl ether (PODEn) dual-fuel reactivity-controlled compression ignition (RCCI) represents a promising pathway toward high-efficiency and low-emission combustion; however, its practical implementation is challenged by hydrogen’s strong reactivity and the complex thermochemical interactions introduced by high-reactivity fuel injection. In this study, a combined experimental and numerical investigation is conducted to optimize and elucidate H2/PODEn RCCI combustion employing a split PODEn injection strategy. A validated computational fluid dynamics model is used to generate a high-fidelity dataset, which is integrated with a machine-learning surrogate and multi-objective optimization to efficiently explore the high-dimensional operating space. The premixed hydrogen ratio and pilot-injection quantity ratio are identified as the dominant parameters governing in-cylinder reactivity stratification, heat-release characteristics, and energy-loss mechanisms. The optimal strategy featuring a high hydrogen premixed ratio and a moderate pilot-injection ratio establishes a favorable reactivity gradient characterized by a highly reactive core and a lean peripheral region dominated by the premixed hydrogen background. Engine experiments under optimized conditions confirm the predicted performance gains, achieving simultaneous reductions of 8.3% in equivalent indicated specific fuel consumption and 30.4% in NOx emissions relative to the baseline case. Detailed analyses of combustion phasing, emission formation pathways, and energy distribution reveal that split-injection-enabled reactivity control effectively moderates hydrogen-driven heat release while enhancing oxidation completeness. These findings demonstrate the effectiveness of split injection for harnessing hydrogen’s reactivity in RCCI engines and provide transferable calibration guidance for future hydrogen-assisted high-efficiency combustion systems.

Nitrogen (N) doping in porous carbon adsorbents has been proven to be one of the effective strategies to enhance formaldehyde (HCHO) adsorption performance. However, the intrinsic promoting mechanism of specific nitrogen species (pyridinic-N, pyrrolic-N, and graphitic-N) remains unclear, hindering the rational design of porous carbon adsorbents. Herein, we prepared a series of nitrogen-doped porous biochars with alterable N species via one-step pyrolysis of urea and waste jujube pits in different proportions (BCU-x, x = 0-3), and the correlation between specific N species and HCHO adsorption performance was established for the first time. Experimental results show that the amount of surface pyrrolic-N (N-5) groups was the dominant factor in determining HCHO adsorption performance. Combined with DFT calculation results, it was revealed that the introduction of pyrrolic-N species significantly increased the inhomogeneity of electrostatic potential (ESP) distribution and the maximum absolute ESP value of carbonaceous models (increased from 15.94 kcal mol-1 to 50.15 kcal mol-1) and consequently enhanced the affinity between polar HCHO and carbonaceous models (varied from -4.98 kcal mol-1 to -7.85 kcal mol-1). Specifically, the O atom of HCHO tended to interact with the H atom attached to the pyrrolic-N moiety, and a hydrogen bond interaction (N-H⋯O[double bond, length as m-dash]CH2) existed. Therefore, the BCU-2 sample with the richest pyrrolic-N species exhibited the optimal HCHO adsorption capacity, of up to 21.25 mg g-1, which was nearly 3.5 times higher than that of pristine biochar. This study clarifies the intrinsic promotion mechanism of specific nitrogen species in HCHO adsorption and provides general guidelines for the further design of high-performance carbonaceous adsorbents for HCHO removal.

Many natural gas combustion devices work under non-atmospheric pressure, and the pressure has a significant impact on the combustion process. In order to promote the practical application and theoretical research of combustion under different pressures, after summarizing the experimental devices and challenges they faced to achieve elevated pressure and low-pressure combustion, this paper focuses on the influence of pressure on the laminar flame velocity, flame stability and soot formation of C1-C3 alkanes. The results of experiments and kinetic models show that the laminar flame velocity decreases with the increase of pressure, and the prediction accuracy of the kinetic model also decreases at elevated pressure. In the functional relationship of laminar flame velocity and pressure, the law of exponential change with equivalence ratio is different in reports. Elevated pressure accelerates the flickering intensity of diffusion flame and the thermal-diffusion instability as well as hydrodynamic instability of premixed flame. Elevated pressure promotes the soot formation in the diffusion flame, but the maximum yield of soot does not increase after exceeding the critical pressure. The pressure exponent of soot is related to the type of alkane and the pressure range. Finally, based on the summary of existing research, future research needs are presented

To further reduce the combustion instability behavior in high-altitude areas, a synergistic suppression of buoyancy-driven methane laminar diffusion flame flicker was achieved by sub-atmospheric pressure combined with co-flow air, and the suppression mechanism was revealed through the schlieren technique. As the pressure decreases, the fluid density gradient within the shear layer decreases, slowing down the formation of vortices. When the co-flow air increases, the vortex is accelerated to rise until the vortex forms downstream of the flame and the flame flicker is completely suppressed. The suppression of flame flicker by sub-atmospheric pressure and co-flow air was nonlinear. The flicker frequency, oscillation amplitude, and flame mean height of flames were assessed for a pressure of 0.5-1.0 atm and co-flow air of 4-16 L/min. The sub-atmospheric pressure reduces the flicker frequency, which increases with increasing co-flow air. The reduction rate of oscillation amplitude at sub- atmospheric pressure varied among different co-flow air flow rates. The initial and that almost realize flame stabilization co-flow air flow rates are more effective than the intermediate flow rate in reducing the oscillation amplitude. The flame mean height decreases monotonically with decreasing pressure, but there is a small peak in the downward trend with increasing co-flow air

The electrochemical reduction of NH4HCO3 to syngas can bypass the high energy consumption of high-purity CO2 release and compression after the ammonia-based CO2 capture process. This technology has broad prospects in industrial applications and carbon neutrality. A zeolitic imidazolate framework-8 precursor was introduced with different Ag contents via colloid chemical synthesis. This material was carbonized at 1000 °C to obtain AgZn zeolitic imidazolate framework derived nitrogen carbon catalysts, which were used for the first time for boosting the direct conversion of NH4HCO3 electrolyte to syngas. The AgZn zeolitic imidazolate framework derived nitrogen carbon catalyst with a Ag/Zn ratio of 0.5:1 achieved the highest CO Faradaic efficiency of 52.0% with a current density of 1.15 mA·cm–2 at –0.5 V, a H2/CO ratio of 1–2 (–0.5 to –0.7 V), and a stable catalytic activity of more than 6 h. Its activity is comparable to that of the CO2-saturated NH4HCO3 electrolyte. The highly discrete Ag-Nx and Zn-Nx nodes may have combined catalytic effects in the catalysts synthesized by appropriate Ag doping and sufficient carbonization. These nodes could increase active sites of catalysts, which is conducive to the transport and adsorption of reactant CO2 and the stability of *COOH intermediate, thus can improve the selectivity and catalytic activity of CO.

To reduce nitric oxide (NO) emissions from coal-fired industrial boilers, char waste could be collected from the tail flue and fed into the furnace to reduce NO, which would also decrease the incomplete combustion loss. Nitriding treatment could be used to enhance the NO reducibility of char waste. In this paper, char with nitriding treatment (nitriding char) was prepared from Shenhua char and urea. The effect of nitriding treatment on char reducing NO at high temperatures (700 ?-900 ?) was studied using a fixed-bed experimental system and various urea masses and pretreatment times. Increasing the urea mass and decreasing the pretreatment time resulted in more urea residue being present in the char, which increased the nitrogen complex which existed in the form of C(N) and caused the surface enrichment of nitrogen element, but blocked the pore structure. In an inert atmosphere, the NO reduction rates of all the nitriding chars were higher than that of the raw char, but there was an optimal limit parameter for the urea mass and pretreatment time. The presence of 2 vol% O-2 was not conducive to the NO reduction by nitriding char because of the higher char-nitrogen (char-N) content resulting from the nitriding treatment, which generated more NO and offset the benefit of the nitriding treatment. This paper provides a useful NO control strategy in coal-fired industrial boilers, and the relevant process route has achieved a 20%-35% decrease in NO emissions in engineering applications.

The high content of the AAEMs in Zhundong (ZD) coal causes easily slagging on the heating surface of boilers, and the addition of rice husk hydrochar (RHC) is expected to alleviate slagging by introducing SiO2 content. ZD coal is co-fired with RHC according to different blend ratios, co-combustion ashes are prepared subsequently at different temperatures. The co-combustion characteristics of blends are studied firstly by using TGA, considering the combustion process can bring impacts on ash characteristics. Then the effects of the blend ratio and ashing temperature on the ash characteristics are discussed. The ash samples are characterized by XRF, ICP-AES, XRD and SEM. The results show that an increase in the blend ratio of the RHC reduces the ignition temperature and lengthens the burnout time, which transforms the ash characteristics. The contents of quartz, gehlenite and andalusite greatly increase. The number of fine particles in the ash decreases, while the particle size increases. The ash fusion temperatures (AFTs) are at the lowest value at 8:2 and exceed totally that of ZD coal at 7:3. Considering to increase the AFTs of ZD coal, at least the blend ratio of 7:3 of ZD coal and RHC is recommended for co-combustion.

Chemiluminescence is a major spontaneous emission inflame and can be used in combustion diagnostics to evaluate various flame characteristics. OH* chemiluminescence is a good indicator for heat release rate analysis in alkane flames. In this paper, a high-resolution ultra-violet imaging system was used to capture the OH* chemiluminescence images. The experiments were conducted in a pilot-scale system with a 300 kW combustion chamber. The variety of temperature distribution is evaluated using the outlet temperature distribution factor. The heat release rate dynamic characteristics were discussed by criteria of distribution uniformity on the spatial and temporal dimensions and the characteristic frequency results obtained by three different methods. The result shows that operating conditions with a uniform outlet temperature distribution always have more uniform spatial distribution and smaller temporal fluctuation amplitude of heat release rate. Frequency results obtained by different methods match very well when the heat load ratio is over 70%. The flame frequency characteristics correlate well with the turbulence property compared with the unmixedness of fuel and air. But the oscillation amplitude of heat release is mainly affected by the unmixedness.

Exhaust gas recirculation (EGR) is an option proposed to augment the CO2 content in the exhaust gas for the efficient removal of CO2. In the field of micro-gas turbine (MGT), EGR is also a feasible solution to improve the part-load performance and fuel flexibility. This research combined EGR with an adjustable fuel feeding combustor to assess the part-load performance of a 300 kW MGT and the flame spatio-temporal characteristics. The radical chemiluminescence intensity of hydroxyl is selected to represent the heat release rate (HRR) in natural gas flames. The influence of EGR on HRR was investigated experimentally under various load ratios (50%-100%) and EGR ratios (0-20%). In addition, the temperature at the combustion chamber outlet is also measured. The results show that EGR can effectively reduce OTDF when the load ratio is high. Both the spatial distribution non-uniformity and fluctuation amplitude of HRR are suppressed after applying EGR. And EGR can also reduce the influence of mixing on HRR spatiotemporal characteristics. At last, the frequency characteristics of HRR are analyzed. The result shows that the flame frequency has a strong correlation with the characteristic frequency of turbulence.(C) 2022 Published by Elsevier Ltd.

Utilization of the excess capacity from power plants by electrocatalytic methods to reduce the products from ammonia-based carbon capture technology to chemicals such as syngas is valuable and meaningful. Direct electrocatalytic reduction of NH4HCO3 electrolyte to syngas without CO2 bubbling is rarely reported. A porous Br-modified Ag catalyst with trace amounts of Br on the surface was investigated in 1.0, 2.0 M, and saturated NH4HCO3 electrolyte without CO2 bubbling. This catalyst can generate CO and H-2 at ratios with ranges from 2:1 to 3:1. The highest CO Faradaic efficiency of 77.8% was observed with the CO current density of 13.8 mA cm(-2) at -0.6 V vs RHE in saturated NH4HCO3 electrolyte. By contrast, the Ag catalyst with high selectivity for electrochemical reduction of CO2 to CO cannot catalyze CO production under this condition. On the Br-modified Ag catalyst, the trace amounts of Br formed a chemical bond with Ag in the Helmholtz surface, leading to changes in the electronic state and structure of Ag. The results are beneficial to the adsorption of intermediates. Thus, the remaining Br may serve as active contributors to promote the selectivity and catalytic activity of the electrochemical reduction both on the Br-modified Ag catalyst and in the NH4HCO3 electrolyte. (C) 2020 Published by Elsevier Ltd.

为探索高效、廉价的燃煤工业锅炉脱硝技术,以适宜工业应用的苹果木热解焦炭和热解兰炭作为NO还原剂,在微波反应系统中研究微波辐射对两种样品还原NO能力的影响,并结合红外测温实验,以及两种样品的孔隙结构、热重反应性等理化性质,对还原实验结果进行分析.研究结果表明:和热解兰炭相比,苹果木热解焦炭的孔隙结构更加发达,BET比表面积和孔容积更大,易于着火,燃烧反应速度较早达到最大值,并最先燃尽;但其燃烧剧烈强度、前期反应能力、可燃性以及燃烧性能偏弱.未施加微波时,苹果木热解焦炭对NO的还原能力强于热解兰炭;施加微波后,两种样品还原NO的能力较未施加微波时均有所增强;微波辐射有效促进了焦炭对NO的还原,且这种促进效果和微波功率成正比关系;微波辐射对热解兰炭的NO还原的促进效果较苹果木热解焦炭明显.红外测温实验结果表明,经过不同功率的微波辐射后,两种样品表面温度均有不同程度的提高,说明微波具有明显的热效应,促进了焦炭对NO的还原.

烟气余热回收技术是提高燃气锅炉供暖效率的关键技术之一.针对供暖回水温度高于烟气露点温度,传统烟气余热回收技术烟气余热回收能力受限的问题,提出烟气源/水源CO2热泵回收燃气锅炉烟气余热方案,分析了各方案的系统效率和天然气消耗量,以及CO2热泵制热系数对系统效率和燃料节约率的影响规律.研究结果表明:烟气源CO2热泵余热回收供暖系统方案可提升系统效率12.54百分点以上,比水源CO2热泵余热回收方案高约0.50百分点,年可节约天然气用量13.87％～17.88％;CO2热泵制热系数较小时有利于提高燃气节约量.

Local flue gas recirculation (LFGR) is an effective technology for reducing nitrogen oxide (NOx) emissions from coal-fired industrial boilers. The temperature and reaction atmosphere changes when flue gas is recycled, thereby affecting both the grate-fired process and NOx emission. In this paper, the boundary of LFGR was simulated by changing the experimental parameters. On a small-scale one-dimensional fixed-bed system, the effects of temperature, O-2 flux, and CO, CO2, and recycled NO concentrations on oxidation-reduction layering and char nitrogen conversion during the char grate-fired process were studied. The effect of temperature and recycled flue gas components on nitric oxide (NO) emissions during the char grate-fired process was then analyzed based on the mass proportion of oxygen-absent and oxygen-present parts. The results show that, with the introduction of recycled flue gas, increasing the temperature will also increase the reduction layer mass and proportion, and, subsequently, inhibit NO emissions; increasing the O-2 flux will reduce the reduction layer proportion and subsequently promote NO emissions; increasing the CO and CO2 concentrations will reduce the NO emitted from the oxidation layer, yet has limited effects on the entire char bed; and recycled NO will significantly reduce the NO emissions. The effect of LFGR-induced changes in temperature and reaction atmosphere on NO emissions can be ascribed to the negative effect of the increase in O-2 flux and the positive effect of the increase in temperature and CO, CO2, and recycled NO concentrations.

AbstractThe advantages of the direct combustion of agricultural biomass for power generation are restricted due to the drawbacks of this biomass and the deep peak shaving trend. Hydrothermal carbonization can improve the physical and thermochemical properties of raw materials. Corn stalk samples were selected as the research object in this study. Corn stalk hydrochars were prepared with reaction pressures of 0–3 MPa, reaction temperatures of 160–240 °C, and residence times of 1–10 h. The effects of the process parameters on the physicochemical properties of hydrochar and on the removal of alkali and alkaline earth metals (AAEMs) were studied by measuring the hydrochar mass, energy yield, product composition, morphology, as well as the removal efficiency of AAEMs. The results indicated that the corn stalk hydrochar had higher mass and energy yields than the raw corn stalk. X‐ray diffraction showed that the carbon content in the hydrochar was greater than that in raw corn stalk. Scanning electron microscopy showed that the reaction temperature played a more significant role in the hydrothermal carbonization process than the reaction pressure and residence time.

电厂实际运行中发现,水蒸气能够降低选择性非催化还原反应(SNCR)烟气脱硝过程中脱硝剂的用量,对脱硝和燃烧产生一定的促进作用.围绕水蒸气在不同脱硝技术中的作用效果和反应机理,对相关文献进行总结.研究发现,水蒸气对SNCR脱硝、再燃脱硝以及先进再燃脱硝技术均有促进强化作用.水蒸气的加入能促进SNCR脱硝反应中OH自由基的产生,可与NH3还原剂反应生成NH2基团,从而提高脱硝效率.水蒸气对再燃脱硝的促进作用,主要通过提高挥发分中HCN、NH3等析出促进NO还原.添加水蒸气可以使先进再燃技术的脱硝效率提高到80％以上,水蒸气对生物质先进再燃脱硝与对再燃脱硝的作用机理类似,而对煤粉先进再燃作用机理不详.综上,水蒸气对先进再燃脱硝的作用机理应包括对SNCR脱硝与再燃脱硝2部分的共同促进作用及2者之间的相互作用,但目前研究较少关注水蒸气对再燃燃料的影响.应进一步研究水蒸气对先进再燃脱硝的作用机理和操作条件,为水蒸气在脱硝技术中的应用提供有力理论支撑.

The crucial technology of combining the excess capacity from power plants and the electrocatalytic reduction method to realize the direct conversion of products from ammonia-based CO2 capture to syngas of CO and H-2 is to research and develop catalysts for direct electrochemical NH4HCO3 reduction. The electrochemical performance of halogen (Cl, Br, and I)-modified Ag electrodes by cyclic voltammetry (CV) oxidation and reduction treatment carried out in supersaturated NH4HCO3 electrolyte without CO2 bubbling. All of the halogen-modified catalysts realized the direct reduction of NH4HCO3 to syngas of CO and H-2. Among them, the Br-modified Ag catalysts have CO Faradaic efficiency of 74.0% at - 0.5 V versus reversible hydrogen electrode much higher than that of Cl- (38%) and I- (39.8%) modified Ag catalysts. The H-2/CO ratio on the Br-modified Ag catalyst is approximately 0-3, which is conducive to the reserve of multi-carbon raw materials and the process of Fischer Tropsch synthesis. Furthermore, the Cl-modified Ag catalyst could control the H-2/CO ratio of syngas in a wide range of 0.6-6.0 under low potential (from -0.3 to -0.7 V), which is beneficial to apply to different industrial production.

Flue gas recirculation (FGR) technology and oxy-fuel combustion strategy are combined to recycle CO2 in a CFB combustor and to limit the emission of NOx and CO2. The combustion process in O-2/N-2 and O-2/CO2 atmospheres is numerically investigated in the CFB combustor. The NOx emission can be effectively reduced using FGR technology both in O-2/N-2 atmosphere or O-2/CO2 atmosphere, which is inversely proportional to the FGR ratio. With O-2/CO2 mixtures as the oxidant, the average combustion temperature is lower than that with O-2/N-2 mixtures when the mole fraction of O-2 is 21%. However, increasing FGR ratio has little effect on NOx emission and CO2 enrichment, even if CO2 gas is enriched in the flue gas. While using O-2/CO2 mixtures as the oxidant, CO2 could account for more than 90 vol.% in the dried flue gas, thus the CO2 can be easily captured from the flue gas.

为揭示褐煤的碳黑生成特性与Na在煤衍生碳黑形成过程中的作用,采用电感耦合等离子体发射光谱仪、X射线光电子能谱仪和傅里叶变换红外吸收光谱仪研究分别担载了空白、物理吸附态Na(ANa)与离子可交换态Na(INa)的酸洗伊敏褐煤在沉降炉中不同停留时间下热解所产生碳黑的产率、表面与整体化学特性.结果表明:在表面增长阶段,褐煤的碳黑产率增幅远超焦油产率降幅;当停留时间足够长时,碳黑产率有所降低,含氧官能团含量升高;担载Na可以降低碳黑产率,但INa对碳黑的抑制作用比ANa强得多,且INa可以使热解气溶胶中醚与砜的含量升高.这些现象说明:在褐煤二次热解过程中,小分子芳香化合物、脂肪族物质与轻质气体也会通过表面增长提高碳黑产率.褐煤热解气中含氧物质可以在停留时间足够长时表现出对碳黑的氧化作用.INa可以保持与焦炭或挥发分之间有机结合状态,在一次热解过程减少初级焦油释放,在二次热解过程中促进挥发分与含氧物质结合;而ANa在一次热解过程中作用不明显.在二次热解过程中,气化的ANa与INa抑制碳黑形成的作用机制相同.