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Chemical Kinetics Simulation on Nitrogen Migration Characteristics During Co-Combustion of Ammonia and Coal Under Deeply Fuel-Air Multistage Conditions

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SSRN 2024年

作者： Dai, Liangxu Wang, Chang'an Hou, Yujie Ma, Guowei Chen, Yongxu Hurera, Abu Zhou, Lei Che, Defu State Key Laboratory of Multiphase Flow in Power Engineering School of Energy and Power Engineering Xi’an Jiaotong University Xi’an710049 China China Energy Science and Technology Research Institute Co. Ltd. Nanjing210046 China

mmonia, a carbon-free fuel, is attracting an ever-increasing attention. Coal/ammonia co-combustion in coal-fired power plants is considered an effective and fast approach to achieving the global decarbonization goal. However, one bottleneck of the utilization of ammonia fuel is the possible increased NOx emissions. The supply strategy of ammonia can affect the reduction of NOx by NH3. Few studies have explored the influence of ratios of ammonia as a secondary fuel and the secondary air volume on NOx emissions, which could be effective methods to reduce pollution. In this work, a chemical kinetics model was established to study the NOx behaviors during coal/NH3 co-firing in deeply fuel-air multistage conditions. The effects of the ammonia distribution strategies such as the ratio of NH3 as a secondary fuel, the injection position of secondary fuel, and corresponding air distribution with different NH3 co-firing ratios (CR-NH3) on the ammonia reactivity for NOx-reduction were studied. The results show that ammonia should be used as a primary fuel entering the main combustion zone under small CR-NH3 conditions to mitigate the NOx emissions;otherwise, ammonia is inclined to be used as a secondary fuel entering the reduction zone under large CR-NH3 conditions. NOx generation is also found to primarily occur in the burnout zone in fuel-air multistage combustion. Thus, the burnout zone should be given priority to decrease the NOx emissions. With the delay of secondary fuel injection in the reduction zone, the escaping ammonia keeps increasing in the outlet of the reduction zone. Then it is completely burned in the burnout zone, which leads to an increase in NOx emissions. The volume flow rate of NOx shows a downward trend on the whole with the ratio of secondary air increased. The air distribution can alter the function of the reduction zone in both generating and eliminating NO. The findings can provide some guidance to effectively decrease NOx emissions in coal/NH3 co-fi

关键词： Coal

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An Operation Optimization of Cooling System for Reactor Shutdown in Pebble Bed Gas-Cooled Reactor

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SSRN 2024年

作者： Liu, Junfeng Wang, Chenglong Qiu, Suizheng Wang, Boyuan Shaanxi Key Laboratory of Advanced Nuclear Energy and Technology Shaanxi Engineering Research Center of Advanced Nuclear Energy Xi’an Jiaotong University Xi’an710049 China Xi’an Thermal Power Research Institute Co. Ltd Xi’an710049 China State Key Laboratory of Multiphase Flow in Power Engineering China

For the emergency shutdown of a high temperature gas-cooled reactor pebble-bed module (HTR-PM) in its operation conditions, in the current design method with a low-flow auxiliary steam cooling technical solution, there are some security and economic issues, i.e. high thermal shock, long cooling time, and temperature drop rate exceeding the limit. To solve these problems, an optimized design method for the shutdown cooling system is presented. Through a simulation model of the shutdown cooling system based on Matlab/Simulink, the dynamic characteristics of the shutdown cooling system in its operation conditions are obtained, involving shutdown, low flow cooling, and water supply start-up stages. The results showed that with the optimized design method, the safety of the core and steam generator can both be ensured during the cooling process, and the cooling rate is significantly improved. Therefore, the optimized design method is feasible and advanced. © 2024, The Authors. All rights reserved.

关键词： Cooling

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Synthesis of Co3o4@C/Ti3c2tx Mxene-Type Composites for Enhanced Electromagnetic Wave Absorption

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SSRN 2024年

作者： Hou, Yunxi Jia, Zhen Zheng, Hanli Hu, Zewei Shen, Lu Liu, Dongyu Li, Lu Liu, Shiwei Liu, Yue Yu, Shitao Key Laboratory of Multiphase Flow Reaction and Separation Engineering of Shandong Province State Key Laboratory Base of Eco-chemical Engineering College of Chemical Engineering Qingdao University of Science and Technology Qingdao266042 China A VIC Research Institute for Special Structures of Aeronautical Composites 19 Jiqi Road Jinan250000 China

Highly efficient microwave absorbing materials have attracted widespread attention due to the harmful effects of electromagnetic pollution on the human body and electronic equipment. In this paper, Co3O4@C composites with core-shell structure were prepared by hydrothermal method using a simple strategy, and then Ti3C2Tx was assembled with core-shell Co3O4@C by electrostatic self-assembly method, which resulted in the successful attachment of Co3O4@C to the lamellar structure of Ti3C2Tx and the formation of MXene-based composite wave-absorbing Co3O4@C/Ti3C2Tx material. The composites exhibit strong electromagnetic wave absorption when the mass ratio of Co3O4@C to Ti3C2Tx was 1:2, with a minimum reflection loss of -35.2 dB at a matched thickness of only 4.5 mm. Excellent electromagnetic wave absorption performance Co3O4@C/Ti3C2Tx composite material was mainly attributed to the synergistic effect of the multiple reflection absorption of the core-shell structure and the high conductivity and large specific surface area of MXene material. These results indicate that Co3O4@C/Ti3C2Tx composites were promising candidates for electromagnetic absorption and provide new ideas for the design of MXene-based magnetic absorption materials. © 2024, The Authors. All rights reserved.

关键词： Composite materials

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Influence of Bi3+ Doping on the Electrochemical Properties of Ti/Sb-Sno2/Pbo2 Electrode for Zinc Electrowinning

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SSRN 2024年

作者： Wu, Jia Kang, Xuanqi Xu, Shuangwen Wei, Zhen Xu, Shangyuan Liu, Kang Feng, Qing Jia, Bo Wang, Yunhai Xían Taijin New Energy & Materials Sci-Tech CO. Ltd Xi’an710016 China Department of Environmental Science and Engineering State Key Laboratory of Multiphase Flow in Power Engineering Xi’an Jiao tong University Xi’an710049 China

Bi3+ doped Ti/Sb-SnO2/PbO2 electrode materials were fabricated by electrodeposition to improve its electrochemical performance in zinc electrowinning. The surface morphology, chemical composition and hydrophilicity of the as-prepared electrodes are characterized by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and contact angle. The electrochemical measurement and the accelerate lifetime experiment are also conduct to investigate the electrocatalytic performance and stability of the electrodes. The results showed that Bi3+ modification electrode has an important effect on the coating morphology, crystal structure, surface hydrophilicity, electrocatalytic activity and stability. The electrode prepared from the solution containing 2 mmol·L-1 Bi(NO3)3 (marked as the Ti/Sb-SnO2/2Bi-PbO2 electrode) exhibits the best hydrophilicity performance (θ=21.6°) and the longest service life (1196 h). During the electrochemical characterization analysis, the Ti/Sb-SnO2/2Bi-PbO2 electrode showed the highest oxygen evolution activity, which can be attributed to the highest electroactive surface (qT*=21.20 C·cm-2) and the best charge transfer efficiency. DFT calculation demonstrate that the doping of Bi lead to the decrease in the OER reaction barrier and increase the DOS of the electrode, which further enhanced the catalytic activity and conductivity of the electrode. Moreover, the simulated zinc electrowinning experiment demonstrate that the Ti/Sb-SnO2/2Bi-PbO2 electrode consume less energy than other electrodes. Therefore, it is expected that the Bi modified electrodes may become a very promising electrode material for zinc electrowinning in the future. © 2024, The Authors. All rights reserved.

关键词： Hydrophilicity

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Numerical Investigation on Combustion Characteristics and NOx Emission of Double-Reheat Tower Boiler at Different Loads 9th

Numerical Investigation on Combustion Characteristics and NO...

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9th International Symposium on Coal Combustion, ISCC 2019

作者： Zhang, Yan Ma, Shihao Guo, Jin Li, Yuesheng Zhu, Zhengrong He, Jiaqi Deng, Lei Che, Defu State Key Laboratory of Multiphase Flow in Power Engineering School of Energy and Power Engineering Xi’an Jiaotong University Xi’an 710049 China Guangdong Institue of Special Equpiment and Research Foshan528251 China Guangdong Institue of Special Equipment Inspection and Research Shunde Institue of Inspection Foshan528300 China

ISBN: (纸本)9789811616563

In this study, a three-dimensional numerical investigation using a finite volume method is presented to obtain the velocity, temperature, and species distributions in a 660 MW double-reheat tower boiler fed with bituminous coal. The refined oxidation model of HCN and NO-char reaction model were used to substitute the default model by the user-defined functions (UDFs). The effects of different loads and excess air ratios on combustion characteristics and NOx emission were studied numerically. The results show that temperature distribution is more uneven at the upper part of the furnace and the NOx emission increases as the load decreases. The temperature distributions in the furnace have little differences under three different excess air ratios. That the oxygen concentration increases significantly as the increase of excess air ratios leads to an increase of NOx emission at the furnace outlet. The minimum NOx concentration at the furnace outlet, 308 ppm, appears under 100% THA with excess air ratio of 1.15. The simulation results in this study can provide reference for optimization of combustion characteristics in double-reheat tower boiler and illustrate a method to reduce NOx emission. © 2022, Tsinghua University Press.

关键词： Furnaces

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A kinetics and dynamics study on the auto-ignition of dimethyl ether at low temperatures and low pressures 38th

A kinetics and dynamics study on the auto-ignition of dimeth...

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38th International Symposium on Combustion, 2021

作者： Huang, Wenlin Zhao, Qian Huang, Zuohua Curran, Henry J. Zhang, Yingjia State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong University Xi'an 710049 China Combustion Chemistry Centre School of Chemistry Ryan Institute MaREI Nui Galway Ireland

Dimethyl ether (DME)/air mixtures at various equivalence ratios from lean (0.5) to extremely rich (5.0) were ignited behind reflected shock waves at a fixed pressure (3.0 atm) over the temperature range 625 K– 1200 K. The ignition behavior was different from that at high-pressures, with a repeatable ignition delay time fall-off feature observed experimentally in the temperature transition zone from the negative temperature coefficient (NTC) regime to the high-temperature regime. The fall-off behavior showed strong equivalence ratio dependence and disappeared completely at an equivalence ratio of 5.0. A local ignition kernel postulate was implemented numerically to quantifiably examine the inhomogeneous premature ignition. At low temperature, no pre-ignition occurs in the mixture. A conspicuous discrepancy was observed between the measurements and constrained UV simulations at temperatures beyond the NTC regime. A third O₂ addition reaction sub-set was incorporated into AramcoMech 3.0, together with related species thermochemistry calculated using the G3/G4/CBS-APNO compound method, to explore the low-temperature deviation. The new reaction class did not influence the model predictions in IDT, but the updated thermochemistry does. Sensitivity analyses indicated that the decomposition of hydroperoxy-methylformate plays a critical role in improving the low-temperature oxidation mechanism of DME.

关键词： Ethers

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Rate-limiting factors in thin-film evaporative heat transfer processes

arXiv

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arXiv 2024年

作者： Zhao, H. Poole, R. Zhou, Z. Wolfson School of Mechanical Electrical and Manufacturing Engineering Loughborough University Loughborough LeicestershireLE11 3TU United Kingdom State Key Laboratory of Multiphase Flow in Power Engineering Xi’an Jiaotong University Xi’an710049 China

In this paper, we present a theoretical study aimed at investigating the rate-limiting factors in thin-film evaporative heat transfer processes, considering the finite-rate evaporation kinetics. The problems of evaporation of a flat thin-film in either pure vapours or vapour-inert-gas mixtures are analysed based on the non-dimensionalised macroscopic transport equations for continuum fluids, coupled with out-of-equilibrium kinetic boundary conditions. Both the full numerical solutions and asymptotic analytical solutions at slow evaporation limit are provided and applied to analyse thin water film evaporation. Existing solutions, assuming negligible heat transfer in the gas domain, or negligible temperature jump across the non-equilibrium kinetic layer, or more boldly a thermodynamically equilibrial interface (i.e. its temperature is at the saturation temperature), can be fully recovered from the more general solutions presented here. Our results show that while these assumptions hold in special cases, they can lead to significant errors in many conditions, especially when the film thickness δ is reduced to a few micrometers or thinner. We show that the conventional views that the rate-limiting factors in thin-film evaporative heat transfer is either the heat diffusion through the liquid film or the mass transfer in the gas domain only apply to thick film (i.e. δ λ where λ is the mean free path in the vapour phase). As δ decreases to a few micrometer or smaller (more precisely when the Knudsen number Kn increases beyond O(1) in an pure vapour environment or when the kinetic Peclet number Pe is reduced below O(1) in inert gases), the interfacial thermal resistance due to the evaporation kinetics can be on the same orders of magnitude as the thermal resistance in the liquid film. The analysis also allow us to compare the heat transfer processes during the evaporation of a thin-film in pure vapours to those in inert gases, providing deeper insight into the effectiveness

关键词： Thin films

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Multi-Objective Optimization and Configurations Comparison of Closed-Air Brayton Cycle

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SSRN 2023年

作者： Qian, Yiran Gu, Zhenzhen Song, Meihui Yang, Yi Zhao, Quanbin Chen, Weixiong Yan, Junjie State Key Laboratory of Multiphase Flow in Power Engineering Xi’an Jiaotong University Xi’an710049 China China Institute of Atomic Energy P.O. Box 275-32 Beijing102413 China

Microreactor power system has characteristics of efficient, compact and high environmental adaptability. In this study, closed-air Brayton cycle (CABC) is proposed as the microreactor thermoelectric conversion system, and thermodynamic model of CABC with different configurations are established. The cycle parameters and component’s structure are designed using system-component combined design method. To obtained the optimal system design scheme, the Genetic Algorithm (GA) and the Non-dominated Sorting Genetic Algorithm II (NSGA-II) are separately applied for single-objective optimization and multi-objective optimization. According to multi-objective optimization results, the IRRC has the highest cycle efficiency of 35.4% and the ratio of power to mass of 59.1 kW·t-1 , respectively, and the RRC has the highest power density of 179.6 kW·m-3 . Similar performance with IRRC and simpler structure make the RRC the optimal configuration of CABC. Compared with single-objective optimization, the design results of multi-objective optimization are more balanced in terms of three performance indicators, meaning that the optimized design scheme has a better comprehensive performance. © 2023, The Authors. All rights reserved.

关键词： Multiobjective optimization

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Transferring the available fused cyclic scaffolds for high—throughput combinatorial design of highly energetic materials via database mining

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Fuel 2022年第PartA期324卷

作者： Wen, Linyuan Yu, Tao Lai, Weipeng Liu, Maochang Wang, Bozhou Shi, Jinwen Liu, Yingzhe State Key Laboratory of Fluorine & Nitrogen Chemicals Xi'an Modern Chemistry Research Institute Xi'an710065 China International Research Center for Renewable Energy State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong University Xi'an710049 China

Recently, the fused cyclic compounds have been the object of an increased interest in the field of energetic materials (EMs) due to the trade-off between energy and safety. Compared with the fused cyclic EMs consisting of the azoles or azines, the oxazole-based fused EMs which possibly possess higher energy–density are very lacking. Here, we proposed an efficient approach to design the highly energetic oxazole-based fused materials. The domain-related knowledge promoted an advanced database search for the aromatic oxazole-based scaffolds from the buyable subset of the ZINC20 database, ensuring scaffolds are available for purchase. Then, 171 target scaffolds were transferred into the EM field and cooperated with combinatorial design to construct a chemical space containing over 107 potential energetic molecules. The high-throughput screening was performed in four aspects, namely, density, difficulty of synthesis, detonation performance, and sensitivity, to accelerate the search for candidates. Meanwhile, the statistical analysis through the hierarchical filtrations clarified the potential of 2r-3s and 2r-4s scaffold types for creating highly energetic molecules. Finally, several candidates stood out owing to nearly 10000 m/s detonation velocity and acceptable predicted sensitivity, elucidating the effectiveness of our approach. We anticipate this investigation could not only be a vital point for subsequent fused cyclic EM research, but also offered a new avenue for material design in other fields. © 2022 Elsevier Ltd

关键词： Scaffolds

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Characteristics of Bubble Dynamic Behavior on the Surface of Photoelectrode Under the Influence of a Vertical Magnetic Field

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SSRN 2023年

作者： Feng, Yuyang Wang, Yechun Zhang, Bo Cao, Zhenshan Liu, Miaomiao Zhen, Canghao Guo, Liejin State Key Laboratory of Multiphase Flow in Power Engineering Xi’an Jiaotong University Xi’an710049 China Xinjin Weihua Institute of Clean Energy Research Nanhai District Guangdong Province Foshan City China

The magnetohydrodynamic (MHD) flow around the bubble induced by the Lorentz force owing to the applied magnetic field significantly affects the behavioral characteristics of the bubble on the electrode surface. However, the mechanism of the impact of a magnetic field perpendicular to the electrode on the dynamic behavior of bubbles remains unclear. In this study, the evolution law of a single oxygen bubble on the surface of a TiO2 photoelectrode under the influence of a vertical magnetic field with different magnetic induction intensities was investigated. The vertical magnetic field effectively promoted the rapid detachment of bubbles from the electrode surface, and greatly improved the gas evolution efficiency. The mass transfer was dominated by single-phase free convection during bubble evolution. Under the influence of the vertical magnetic field, the mass transfer coefficient near the electrode was enhanced, and the adverse effects of bubbles on mass transfer were counteracted when they entered the reaction-controlled growth phase. The further multiphysics simulation found that the MHD convection decreased the local supersaturation of reaction product oxygen molecules near the electrode, thereby reducing concentration overpotential and increasing the reaction rate. This study provides an experimental and theoretical basis for promoting the bubble detachment and the reaction rate on the gas evolving electrode surface during photoelectrochemical water splitting. © 2023, The Authors. All rights reserved.

关键词： Efficiency

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