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Study on the surface structure development of porous char particles in catalytic supercritical water gasification process

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FUEL PROCESSING TECHNOLOGY 2019年 193卷 73-81页

作者： Fan, Chao Jin, Hui Shang, Fei Feng, Huifang Sun, Jingli Xi An Jiao Tong Univ State Key Lab Multiphase Flow Power Engn SKLMF 28 Xianning West Rd Xian 710049 Shaanxi Peoples R China

Porous structure and its development have significant influence on the heat and mass transfer between char particle and surrounding fluid, and the unique properties of supercritical water might make this process different. In this work, the catalytic supercritical water gasification experiments of semi-coke were conducted with K2CO3 as the catalyst at 650 degrees C to 750 degrees C, and the porous structure was characterized by nitrogen adsorption and SEM. Both micropores of 1.8 nm and mesopores that were enlarged in the gasification process were detected. K2CO3 addition was found to obviously promote the development of mesopore structure, while temperature had no obvious influence on structure development. Specific surface area and pore volume increased after gasification by one to two orders of magnitude, most up to 600 m(2).g(-1) and 0.57 cm(3).g(-1), respectively. Fractal dimension D increased sharply firstly due to the formation of a large amount of pores in the initial stage and then began to decrease because of the plasticity of char. The obtained structure evolution rules would be used for the establishment and optimization of kinetic models and the study of heat and mass transfer characteristics between char particle and surrounding fluid.

关键词： Supercritical water gasification Porous structure Catalyst Nitrogen adsorption

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Taming NO oxidation efficiency by γ-MnO2morphology regulation

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CATALYSIS SCIENCE & TECHNOLOGY 2020年第17期10卷 5996-6005页

作者： Chen, Lei Zhang, Jinping Li, Yuxin Wu, Xiaomei Zhang, Zaoxiao Lu, Qiang He, Chi Xi An Jiao Tong Univ Sch Chem Engn & Technol Shaanxi Key Lab Energy Chem Proc Intensificat Xian Peoples R China Xi An Jiao Tong Univ State Key Lab Multiphase Flow Power Engn Xian Peoples R China Xi An Jiao Tong Univ Sch Energy & Power Engn Key Lab Thermofluid Sci & Engn MOE Xian 710049 Peoples R China North China Elect Power Univ Natl Engn Lab Biomass Power Generat Equipment Beijing 102206 Peoples R China Univ Chinese Acad Sci Natl Engn Lab VOCs Pollut Control Mat & Technol Beijing 101408 Peoples R China

Nitric oxide (NO) emitted from the combustion of fossil fuels has drawn global concern, and the oxidation of NO contributes greatly to the DeNO(x)process. Herein, single-crystal gamma-MnO(2)catalysts with well-defined hollow-sphere-, sea-urchin-, and flower-like morphologies (gamma-MnO2-HS, gamma-MnO2-SU, and gamma-MnO2-F) were rationally designed and synthesizedviaan environmental-friendly template-free hydrothermal strategy. The physicochemical properties of the prepared materials were characterized by XRD, FE-SEM, TEM, BET, XPS, H-2-TPR, O-2/NO-TPD andin situDRIFTS, and their catalytic activities in NO oxidation were evaluated. The results showed the gamma-MnO2-HS sample possessed the highest activity and could oxidize 91.1% of NO at 275 degrees C, which was obviously higher than those of the gamma-MnO2-SU and gamma-MnO2-F catalysts. It was found that the presence of abundant surface-adsorbed oxygen and the largest quantity of Mn(3+)over the gamma-MnO2-HS material respectively accelerated the processes of NO adsorption and O(2)activation, which greatly promoted the NO oxidation process. This work provides significant insights into NO oxidation over gamma-MnO(2)catalysts.

关键词： Nitric oxide

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Local degradation in proton exchange membrane fuel cells with dead-ended anode

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JOURNAL OF power SOURCES 2020年 477卷

作者： Yang, Yupeng Zhang, Xu Guo, Liejin Liu, Hongtan Xidian Univ Key Lab Elect Equipment Struct Design Minist Educ Xian 710071 Shaanxi Peoples R China Xi An Jiao Tong Univ Int Res Ctr Renewable Energy State Key Lab Multiphase Flow Power Engn Xian 710049 Shaanxi Peoples R China Univ Miami Clean Energy Res Inst Dept Mech & Aerosp Engn Coral Gables FL 33124 USA

The dead-ended anode (DEA) configuration can simplify proton exchange membrane fuel cell (PEMFC) systems and reduce system cost. However, the DEA configuration can also accelerate fuel cell degradation during long-term operations. Understanding the degradation mechanisms is crucial to improve fuel cell durability. In this study, experiments are performed to investigate the local degradation phenomena in PEMFCs during DEA operations. The detailed degradation mechanisms are revealed through various electrochemical analysis. The local polarization curves show that the local fuel cell performance decreases are very non-uniform and the inlet area suffers the most severe performance decrease. Electrochemical measurements indicate that the most serious carbon corrosion in catalyst layer occurs near the anode outlet. However, the most severe local membrane degradation is observed near the anode inlet. Furthermore, we observe that the pressure swing anode supply mode can significantly mitigate fuel cell degradation during DEA operation. The water and gas distributions in the anode are much more uniform with the periodical oscillatory flow under pressure swing mode, reducing local membrane dehydration and avoiding local hydrogen starvation. Thus, both the local membrane degradation and local carbon corrosion are significantly mitigated under the pressure swing mode.

关键词： Proton exchange membrane fuel cell Dead-ended anode Local degradation Pressure swing

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Microscale drag model considering the effect of interface between dense and dilute phases for gas-solid suspensions at moderate Reynolds numbers

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INTERNATIONAL JOURNAL OF multiphase flow 2022年 157卷

作者： Ma, Teng Li, Yu Zhou, Qiang Chen, Xiao Xi An Jiao Tong Univ Sch Chem Engn & Technol Xian 710049 Shaanxi Peoples R China Univ Shaanxi Prov Engn Res Ctr New Energy Syst Engn & Equipment Xian 710049 Shaanxi Peoples R China Xi An Jiao Tong Univ State Key Lab Multiphase Flow Power Engn Xian 710049 Shaanxi Peoples R China

Particle-resolved direct numerical simulations of flows past various fixed structures of spheres are performed to study the drag force at local Reynolds numbers up to 250. At the gas-solid interface, the drag force is found to be 5% similar to 800% of that estimated by BVK law (Beetstra et al. AIChE Journal, 2007, 53(2):489-501) at different particle Reynolds numbers and solid volume fraction gradients. Thus a microscale drag model at the cluster interface is developed as a function of the particle Reynolds number and the solid concentrations of dense and dilute phases. Assessments of the proposed drag model are performed with direct numerical simulations of flows past plug-like, spherical, ellipsoidal clusters as well as bubble-containing structures. The results show that the new model well captures the drag variations at microscales of several sphere diameters and correlates well with the solid concentrations and velocities of dense and dilute phases.

关键词： Gas-solid flows The drag force Particle-resolved direct numerical simulations Clusters of particles

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Load cycling rate of power-to-heat molten salt thermal storage and power generation system: Dynamic modeling and performance evaluation

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JOURNAL OF ENERGY STORAGE 2025年 125卷

作者： Hu, Wenting Liu, Ming Zhang, Jihong Zhang, Shunqi Yan, Junjie Xi An Jiao Tong Univ State Key Lab Multiphase Flow Power Engn Xian 710049 Peoples R China Xian Thermal Power Res Inst Co Ltd Xian 710054 Peoples R China

To develop a low-carbon power system with high renewable energy penetration, this study proposes a novel power-to-heat energy storage and power generation (P2HES-PG) system, which utilizes molten salt thermal storage technology to achieve flexible heat-power decoupling and rapid load regulation. By establishing dynamic models, the rapid load cycling dynamic characteristics and exergy destruction evolution of the P2HES-PG system under different load ranges were investigated. The results demonstrate that, within a 25% THA amplitude, the maximum load down rates in the high, medium, and low load ranges are 15%, 12%, and 11% Pe min- 1, respectively, while the maximum load up rates reach 17%, 14%, and 11% Pe min- 1, exceeding the ramping rate of conventional power units. During load cycling processes, significant fluctuations in molten salt circulation flowrate were observed, directly affecting the thermal storage/release dynamics of the steam generator (SG) and the system's thermal performance. Dynamic exergy analysis indicates the condenser maintains a stable 20% exergy destruction share, while turbine and mechanical contributions increase with higher loads, and the regenerative system peaks at 13.97% during the low-load range loading down process. The SG exhibits lower exergy destruction than ideal conditions during the loading down process and higher destruction during the loading up process, providing a theoretical basis for optimizing system control strategies and improving system variable load energy efficiency.

关键词： Molten salt thermal storage Model development Dynamic characteristics Load cycling rate Exergy analysis

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Mxene-Derived Ni/Tio2-X/Ti3c2 Catalyst for Enhanced Photothermal Co2 Methanation: Unraveling the Roles of Photoexcited Carriers

SSRN

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SSRN 2025年

作者： Sun, Fan Xin, Yu Xing, Xueli Lou, Jiahui Wang, Qiliang Hong, Hui International Research Center for Renewable Energy State Key Laboratory of Multiphase Flow in Power Engineering Xi’an Jiaotong University Xi’an710049 China Institute of Engineering Thermophysics Chinese Academy of Sciences Beijing100190 China School of Aeronautics and Astronautics University of Chinese Academy of Sciences Beijing100049 China Huaneng Clean Energy Research Institute Beijing102209 China Shandong Institute of Advanced Technology Jinan250100 China Department of Architecture and Built Environment University of Nottingham NottinghamNG7 2RD United Kingdom Institute of Engineering Thermophysics China

Photothermal catalysis has emerged as a promising approach for CO2 conversion, which combines photo and thermal energy to drive catalytic reactions efficiently. While light can lower activation barriers and enhance reaction rates, the interplay between light and heat within the catalytic framework remains largely unexplored. In this study, we investigate the critical role of photoexcited carriers in enhancing catalytic performance under solar irradiation, unraveling their contribution to the CO2-to-CH4 conversion process. A multilayer accordion-like Ni/TiO2-x/Ti3C2 catalyst, which exhibits excellent photothermal and photoelectric response characteristics was fabricated for efficient photothermal CO2 methanation. Experimental results demonstrated that introduction of light during thermal catalysis markedly enhanced the CO2 conversion rate, with a 55% increase achieved at 275 ºC. Furthermore, the required temperature for maximum CO2 conversion rate was reduced by 50 ºC compared to the thermal-driven process. Meanwhile, the effects of concentrated ratio and incident wavelength on CO2 conversion were also examined, revealing a synergistic effect between photogenerated carriers and thermal energy. Further characterizations, including steady-state and transient photoluminescence spectroscopy, in-situ XPS, in-situ EPR, in-situ DRITFs, were employed to elucidate the enhancement mechanisms of photogenerated carriers in the catalytic reaction. At the same time, an outdoor experimental prototype was developed to verify the feasibility of photogenerated carrier-thermal synergistically driven CO2 methanation. The findings provide valuable insights into the role of photo-generated carriers in photothermal CO2 methanation, offering new perspectives for the design of efficient photothermal catalysts and advancing solar catalytic CO2 conversion technologies. © 2025, The Authors. All rights reserved.

关键词： Methanation

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Periodical oscillation of particle-laden laminar flow within a tubular photocatalytic hydrogen production reactor predicted by discrete element method

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INTERNATIONAL JOURNAL OF HYDROGEN ENERGY 2021年第15期46卷 9653-9665页

作者： Geng, Jiafeng Tang, Junwang Cai, Wenfang Wang, Yechun Jing, Dengwei Guo, Liejin Xi An Jiao Tong Univ State Key Lab Multiphase Flow Power Engn Xian 710049 Peoples R China Xi An Jiao Tong Univ Int Res Ctr Renewable Energy Xian 710049 Peoples R China UCL Dept Chem Engn London WC1E 7JE England Xi An Jiao Tong Univ Sch Chem Engn & Technol Xian 710049 Shaanxi Peoples R China Xi An Jiao Tong Univ Dept Environm Sci & Technol Xian 710049 Shaanxi Peoples R China

Besides their wide existence in various industrial processes, nanoscale particle suspensions are also the important media for some emerging technologies such as photocatalytic hydrogen production. The circulating flow properties of the nanoparticles in the fluid are of great concern for their practical use. In our study, a modified experimental system was set up based on Malvern laser particle analyzer that can estimate the nanoparticle concentration and size distribution in a laminar nanoparticle circulating flow. We found that the particle concentration and size distribution were periodical oscillation with time in such flow. Understanding the oscillation mechanism is capable of promote the energy efficiency of photocatalytic hydrogen production. A simulation based on Discrete Element Method (DEM) was conducted to understand this particular oscillation mechanism by studying the single particle movement and trajectory properties in the solid-liquid suspension. The simulation results agree well with the tendency obtained by the experimental results and are capable of better understanding the oscillation characteristics. The simulation results also reveal that the nanoparticles tend to gather in the middle region (the higher velocity region) of the tube after several cycles. Moreover the gravity is of great significance in the circulating flow of solid-liquid suspension because the particle swarms tend to distribute a little below the axial center line of the straight tube. These obtained results are credible for understanding the nanoscale particle transport phenomenon in many natural or industrial processes. In particular, our results are helpful for the understanding and effective control of the movement and distribution of photocatalyst particles in the tubular photocatalytic reactor, which is believed to significantly affect the incident radiation distribution and finally the energy conversion efficiency of the photocatalytic process. (C) 2020 Hydrogen Energy Pu

关键词： Particle-laden flow DEM simulation Periodical oscillation Particles trajectory

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Toward a fundamental understanding of factors affecting the function of cocatalysts in photocatalytic water splitting

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CURRENT OPINION IN GREEN AND SUSTAINABLE CHEMISTRY 2019年 17卷 21-28页

作者： Chen, Yubin Feng, Xiaoyang Guo, Xu Zheng, Wenyu Xi An Jiao Tong Univ Int Res Ctr Renewable Energy State Key Lab Multiphase Flow Power Engn Xian 710049 Shaanxi Peoples R China

Although numerous cocatalysts in photocatalytic water splitting have been studied, the fundamental understanding of factors affecting the function of cocatalysts is limited. This brief review summarizes the progress of cocatalysts in the last 3 years. The effects of intrinsic characters of cocatalysts including morphology, crystallization, and composition are first examined. The influence of interfacial coupling of cocatalysts with host photocatalysts, such as cocatalyst location, built-in electric field, and contact manner, is subsequently discussed. To confirm the active species of cocatalysts, some in situ/operando characterization techniques are finally introduced. It is expected that this brief review would provide useful information to design efficient cocatalysts for photocatalytic water splitting.

关键词： Electric fields

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PORE STRUCTURE AND ITS EVOLUTION IN CHAR DURING SUPERCRITICAL WATER GASIFICATION PROCESS

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JOURNAL OF POROUS MEDIA 2019年第2期22卷 195-207页

作者： Jin, Hui Fan, Chao Guo, Liejin Zhao, Xiao Cao, Changqing Wei, Wenwen Xi An Jiao Tong Univ State Key Lab Multiphase Flow Power Engn SKLMF 28 Xianning West Rd Xian 710049 Shaanxi Peoples R China

Pore structure and its evolution provide key information for the heat and mass transfer in char particles and are important for supercritical water gasification reactor design. Supercritical water gasification was conducted in an autoclave, and nitrogen adsorption and scanning electron microscopy were applied for pore characterization in char. Specific surface area and pore volume showed an increasing tendency, but the growth of the specific surface area obviously slowed down as the reaction proceeded. Micropores with pore size of about 1.8 nm in original char increased obviously in quantity but remained nearly constant in size in the gasification process, whereas mesopores showed an increasing trend in both quantity and size from 3 to 5.5 nm. The surface fractal dimension calculated through the Frenkel-Halsey-Hill equation increased first and then decreased. These evolution characteristics may provide useful information for the establishment and optimization of kinetic models for supercritical water gasification.

关键词： supercritical water gasification nitrogen adsorption pore structure fractal dimension

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Experimental investigation on liquefaction of plastic waste to oil in supercritical water

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WASTE MANAGEMENT 2019年 89卷 247-253页

作者： Bai, Bin Jin, Hui Fan, Chao Cao, Changqing Wei, Wenwen Cao, Wen Xi An Jiao Tong Univ State Key Lab Multiphase Flow Power Engn SKLMF 28 Xianning West Rd Xian 710049 Shaanxi Peoples R China

In order to solve the problem of low thermal conductivity and high viscous molten liquid reaction product in the process of plastic liquefaction, the experiments of high impact polystyrene (HIPS) plastic liquefaction were carried out in supercritical water. In this paper, the effects of different operating conditions (temperature, time, feedstock concentration and pressure) on liquid products were studied. It is found that the novel phenomenon that the liquid products of HIPS plastic were mainly toluene and ethylbenzene rather than styrene, which was a product of polystyrene. The experimental results showed that plastic first depolymerized to form styrene and 1,3-diphenylpropane, which were then converted to toluene and ethylbenzene. The increase in temperature promoted this transformation process and some traces of polycyclic aromatic hydrocarbons also produced. At 490 degrees C, the maximum carbon liquefaction rate of 77.0 wt% was obtained, which was 6 times higher than the conventional pyrolysis, and the content of toluene and ethylbenzene were 14 wt% and 51.3 wt%, respectively. Increasing the reaction pressure and prolonging the reaction time all promoted the progress of the plastic liquefaction reaction, while increasing the feedstock concentration caused the carbon liquefaction rate to increase first and then slightly decrease. (C) 2019 Elsevier Ltd. All rights reserved.

关键词： Supercritical water HIPS plastic Liquefaction Operating conditions

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