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flow and residence time distribution characteristics in continuous hydrothermal reactor under different heating schemes

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Chemical engineering Science 2025年

作者： Yi Li Junying Wang Xiaoyu Li Hui Jin State Key Laboratory of Multiphase Flow in Power Engineering Xi’an Jiaotong University Shaanxi 710049 PR China

Residence time distribution (RTD) is of significance for reflecting materials or intermediate products dispersion and actual reaction time inside continuous hydrothermal reactors of supercritical water gasification technology. Generally, RTD is strictly related to flow field, which can be affected by wall heating schemes. In order to propose methods to regulating RTD, effects of different heating schemes on flow and RTD characteristics are investigated and compared by numerical simulation. The results indicate that increasing heat flux, interrupting boundary flow by interlace heating, and setting cooling walls can significantly regulate RTD. By analyzing the correspondence of flow and RTD, the mechanisms of increasing materials and intermediate products dispersion can be attribute to the increase of flow instability and the generation of additional vortices. For example, in the cases of present work, the narrow-strip double-vortex generated by mixing between thermal boundary flow and branch flow may significantly increase average residence time and materials distribution range from 10.93 s and 1.00 to 22.83 s and 1.51. In the region above branch inlet without time-averaged vortex structure, the increasing of flow instability caused by wall heating is observed to widen materials distribution range from 0.75 to 0.99. Heating scheme customized according to these mechanisms can regulating RTD as expected, proving the feasibility and significance of regulating RTD by heating schemes.

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Editorial of special issue (SI) "Multi-scale physics on fluid flow and heat transfer (Multi-scale PFFHT)"

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International Journal of Heat and Fluid flow 2025年

作者： Cheng, Lixin Bai, Bofeng Zhang, Haibin Wissink, Jan Gerard School of Engineering and Built Environment Sheffield Hallam University City Campus Howard Street SheffieldS11WB United Kingdom State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong University Xi'an710049 China School of Chemical Engineering and Technology Xi'an Jiaotong University Xi'an710049 China Department of Mechanical and Aerospace Engineering Brunel University of London Kingston Lane UxbridgeUB8 3PH United Kingdom

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Simulation study on mineral transformation behaviors and ash fusion characteristics during high-alkali coal combustion under deep peaking conditions

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Fuel 2025年 399卷

作者： Liu, Jiamiao Ma, Guowei Du, Yongbo Wang, Chang'an Zhao, Yonggang Wu, Wanzhu Shi, Longping Zhao, Lin Che, Defu State Key Laboratory of Multiphase Flow in Power Engineering School of Energy and Power Engineering Xi'an Jiaotong University Xi'an710049 China National Energy Group Science and Technology Research Institute Co. Ltd. Nanjing210046 China Company Xi'an710076 China Huayuan Power Plant National Energy Group Hami Coal Power Co. Ltd. Hami839000 China

The safe and efficient combustion of high-alkali coal under deep peaking conditions remains a critical research focus. Boiler operating parameters under such conditions frequently fluctuate, markedly though incompletely understood in their influence on fouling and slagging, necessitating further investigation. Here, mineral transformation and ash fusion characteristics during high-alkali coal combustion in the main combustion zone were simulated through thermodynamic equilibrium calculations, addressing its fouling issues under deep peaking conditions. Variable loads were decomposed into distinct factors for analysis due to challenges of direct simulation. Additionally, the plasma ashing method was employed to prepare ash samples. High-alkali coals with distinct properties exhibit significant variations in mineral distribution, elemental evolution, ash fusion temperature, and viscosity. Abundant fayalite (Fe2SiO4) was observed in Hongshaquan (HSQ) coal, forming stable mineral phases with other components. In Shaerhu (SEH) coal, sodium primarily exists in the gaseous phase at high temperatures, significantly contributing to fouling. Meanwhile, Jiangjunmiao (JJM) and Wucaiwan (WCW) coals demonstrate limited mineral phases but higher ash fusion temperatures, with over 30 % of iron in the gaseous phase. The mineral transformation and ash fusion behaviors in various local combustion atmospheres follow consistent trends. The formations of gaseous sodium hydroxide (NaOH(g)) and sodium oxide in the slag phase (Na2O(slag)) are promoted with weakening reducing atmospheres, while total gaseous sodium content decreases. The slag phases of calcium, magnesium, and iron increase, accompanied by a decline in ash viscosity. However, unburned carbon inversely influences mineral transformation and ash fusion characteristics compared to excess air coefficients. This research provides theoretical support for overcoming the key technical challenges associated with high-alkali coal combus

关键词： Iron analysis

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Laminar Flame Structure-Dependent Exergy Destruction Behavior at Auto-Ignition Time Scale:A Case Study of Dimethyl Ether(DME)

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Journal of Thermal Science 2024年第4期33卷 1257-1271页

作者： WU Honghuan HUANG Wenlin ZHAO Hao SUN Wuchuan HUANG Zuohua ZHANG Yingjia State Key Laboratory of Multiphase Flow in Power Engineering Xi’an Jiaotong UniversityXi’an710049China

Hybrid deflagration/auto-ignition flame structures coexist in the combustion of advanced *** exergy destruction caused by different irreversible processes under varied flame regimes is thus important for understanding engine *** this study,the flame propagation modes for the premixed DME/air mixtures are numerically investigated under engine-relevant *** entropy generation and exergy destruction characteristics are compared under different flame *** reveal that as the typical premixed flame transition towards auto-ignition front,the exergy destruction from heat conduction and species mass diffusion gradually vanish and are dominated by chemical *** distributions of temperature and species mole fraction in the flame domain are analyzed to clarify the exergy destruction behaviors caused by heat conduction and mass ***,by dividing the DME oxidation process into four stages,the main reaction channels that contribute to the increase in exergy destruction from chemical reaction have been *** is found that the production and consumption of CH_(2)O and HO_(2) radical dominate the exergy destruction behavior during DME *** this basis,the kinetic mechanism of low-temperature chemistry causing greater exergy destruction is ***,low-temperature chemistry leads to significant exergy destruction due to(a)the large irreversibility of itself and(b)(mainly)the enhancement of H_(2)O_(2)loop reactions by low-temperature reaction *** the reduction of combustion irreversibility is promising to be achieved by reasonably regulating the fuel oxidation path.

关键词： exergy destruction flame structures entropy generation low-temperature chemistry DME

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Simulation Study on Hydrogen-Heating-power Poly-Generation System based on Solar Driven Supercritical Water Biomass Gasification with Compressed Gas Products as an Energy Storage System

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Journal of Thermal Science 2020年第2期29卷 365-377页

作者： JIN Hui WANG Cui FAN Chao State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong UniversityXi'an 710049China

Supercritical water gasification driven by solar energy is a promising way for clean utilization of biomass with high moisture content, but direct discharge of liquid residual causes energy waste and decreases energy efficiency. To reduce energy waste, a poly-generation system for hydrogen-rich gas production coupling heat supply and power generation based on supercritical water gasification of biomass driven by concentrated solar energy was established in this paper, which also provided a novel energy storage method to overcome the shortcomings of solar discontinuity. Thermodynamic model of the system was proposed and life cycle assessment(LCA) of the system was conducted. Influence of different parameters(temperature of 600℃ to 800℃, outlet temperature of heat exchanger of 42℃ to 56℃, biomass slurry concentration of 5% to 6.5%) on the gasification performance, energy and exergy efficiency, energy distribution and global warming potential(GWP) was discussed. The results indicated that hydrogen yield increased as gasification temperature increased since free radical reaction was enhanced which gas production reaction was classified into. Molar fraction of hydrogen increased as gasification temperature increased and reached 65.6% at 750℃. Energy and exergy efficiency of the system reached 74.84% and 34.87% at 700℃ and 600℃ respectively and that of gas production was 18.15% at 650℃, which was the highest. Increasing reaction temperature and decreasing biomass slurry concentration were effective ways to decrease GWP. Optimal operating parameter was reaction temperature of 650℃, outlet temperature of heat exchanger of 50℃ and biomass concentration of 5%.

关键词： biomass supercritical water gasification poly-generation system thermodynamics analysis energy storage life cycle assessment

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Effects of physical properties of supercritical water on coarse graining of particle cluster

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Particuology 2023年第11期82卷 166-178页

作者： Xiaoyu Li Huibo Wang Yi Li Hui Jin State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong UniversityXi'an710049China

The coarse graining of particle cluster is of great significance to the study of a fluidized bed. The effects of variations in the physical properties of supercritical water on the coarse graining of particle cluster are investigated in this work. The drag coefficient distributions of the particle cluster are not influenced by the physical properties. However, the physical properties have effects on the values of drag coefficient. The effects of physical properties are weaker in the case of large particle concentrations. Furthermore, the physical properties lead to that the effect of particle cluster wake on the drag of downstream particles being significantly different from that of constant property flow. The variation trend of drag of coarse graining particle is consistent with that of isolated particle. The physical properties lead to significant differences in the values of drag. In this paper, the dominance of the effects of physical properties in a variety of cases is confirmed. Finally, a physical properties effect model is developed accordingly.

关键词： Supercritical water Variations in physical properties Fluidized bed Coarse grain method Particle drag

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Molecular sieving through a graphene nanopore： non-equilibrium molecular dynamics simulation

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Science Bulletin 2017年第8期62卷 554-562页

作者： Chengzhen Sun Bofeng Bai State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong University Xi'an 710049 China

Two-dimensional graphene nanopores have shown great promise as ultra-permeable molecular sieves based on their size-sieving effects. We design a nitrogen/hydrogen modified graphene nanopore and conduct a transient non-equilibrium molecular dynamics simulation on its molecular sieving effects. The distinct time-varying molecular crossing numbers show that this special nanopore can efficiently sieve CO_2 and H_2S molecules from CH_4 molecules with high selectivity. By analyzing the molecular structure and pore functionalization-related molecular orientation and permeable zone in the nanopore, density distribution in the molecular adsorption layer on the graphene surface, as well as other features, the molecular sieving mechanisms of graphene nanopores are revealed. Finally, several implications on the design of highly-efficient graphene nanopores, especially for determining the porosity and chemical functionalization, as gas separation membranes are summarized based on the identified phenomena and mechanisms.

关键词： Graphene nanopore Molecular sieve Molecular dynamics Gas separation membrane

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Drag coefficient and volume fraction of bubbles in a supercritical water fluidized bed

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Particuology 2021年第4期19卷 127-138页

作者： Hao Wang Youjun Lu State Key Laboratory of Multiphase Flow in Power Engineering Xi’an Jiaotong UniversityXi’an 710049China

The supercritical water fluidized bed(SCWFB)is a recently introduced reactor for biomass gasification that does not release *** groups of Geldart B-type quartz sands with different particle sizes were fluidized at a system pressure of 20-27 MPa and system temperature of 410-570℃.A series of experiments were performed for determining the drag coefficient and volume fraction of *** effects of the particles’size,superficial velocity,system pressure,and temperature on the drag coefficient and volume fraction are *** addition,a correlation between experimental and computed values is demonstrated for both the drag coefficient and volume fraction in *** relative error of the correlation is within±30%.The results of this study provide significant guidance for the scaling-up design of SCWFBs and for the development of supercritical water gasification technology.

关键词： Supercritical water fluidized bed Bubbles Drag coefficient Volume fraction

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Discrete particle simulation of mixed sand transport

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Particuology 2012年第2期10卷 221-228页

作者： Fengjiun Xiao Lieiin Guo Debiao Li Yueshe Wang State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong UniversityXi'an 710049China

An Eulerian/Lagrangian numerical simulation is performed on mixed sand transport. Volume averaged Navier-Stokes equations are solved to calculate gas motion, and particle motion is calculated using Newton＇s equation, involving a hard sphere model to describe particle-to-particle and particle-to-wall collisions. The influence of wall characteristics, size distribution of sand particles and boundary layer depth on vertical distribution of sand mass flux and particle mean horizontal velocity is analyzed, suggesting that all these three factors affect sand transport at different levels. In all cases, for small size groups, sand mass flux first increases with height and then decreases while for large size groups, it decreases exponen- tially with height and for middle size groups the behavior is in-between. The mean horizontal velocity for all size groups well fits experimental data, that is, increasing logarithmically with height in the middle height region. Wall characteristics greatly affects particle to wall collision and makes the fiat bed similar to a Gobi surface and the rough bed similar to a sandy surface. Particle size distribution largely affects the sand mass flux and the highest heights they can reach especially for larger particles.

关键词： Mixed sand transportHard sphere modelSand mass fluxParticle horizontal mean velocity

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Numerical simulation of the drag and heat-transfer characteristics around and through a porous particle based on the lattice Boltzmann method

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Particuology 2021年第5期19卷 99-107页

作者： Mingyue Zhang Qiuyang Zhao Zujie Huang Lei Chen Hui Jin State Key Laboratory of Multiphase Flow in Power Engineering Xi’an Jiaotong UniversityXi’an 710049China

Porous particle flow is universal in nature and ***,in previous numerical simulations,porous particles have usually been assumed to be *** is necessary to study the flow and heat-transfer characteristics around porous particles because they are greatly different from those of impermeable *** this study,two-dimensional steady flow and heat transfer around and through a porous particle with a constant temperature placed in a cold fluid were numerically *** effects of the Reynolds number(Re)and Darcy number(Da)on the flow and heat-transfer characteristics were investigated in *** investigated ranges of the parameters were 10≤Re≤40 and 10^(−6)≤Da≤10^(−2).It is sophisticated to simulate porous particles with traditional simulation methods because of their complicated ***,the lattice Boltzmann method was used to solve the generalized macroscopic governing equations because of its *** drag coefficient decreased with increasing Re or Da,but the decrease was not prominent in the range 10^(−6)≤Da≤10^(−4).The heat-transfer efficiency of the front surface was much stronger than that of the rear *** heat-transfer efficiency between the particle and the fluid increased with increasing Re or ***,for 10^(−6)≤Da≤10^(−4),the increase was not prominent and the heat-transfer enhancement ratio was slightly larger than ***,the effect of Da became more prominent at larger *** addition,new correlations for the drag coefficient and surface-averaged Nusselt number were obtained based on the simulated results.

关键词： Porous particle Darcy-Brinkman-Forchheimer model flow and heat-transfer characteristics Lattice Boltzmann method Correlation

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