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Junwu Wang - One of the best experts on this subject based on the ideXlab platform.
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An EMMS drag Model for coarse grid simulation of polydisperse gas–solid flow in circulating fluidized bed risers
Chemical Engineering Science, 2019Co-Authors: Zhiyuan Qin, Quan Zhou, Junwu WangAbstract:Abstract Polydisperse gas–solid systems are more common in both industry and the natural world than their monodisperse counterparts. This paper aims to investigate the hydrodynamics of polydisperse gas–solid flow systems by extending the energy minimization multiscale (EMMS) drag Model. The continuous particle size is discretized into several characteristic sizes, by which the polydisperse particles are classified into several discrete groups. A polydisperse EMMS drag Model is then developed by treating these particle groups as solid phases. Finally, the proposed drag Model is coupled with the Multifluid Model to simulate the hydrodynamics of polydisperse gas–solid flow in CFB risers. Extensive simulations are conducted to validate the effectiveness of the polydisperse EMMS drag Model and investigate the effects of gas–particle drag Models, kinetic theories, and particle–particle drag Models on the simulation results. It was found that (i) the polydisperse EMMS drag Model can predict the concentration and particle size distribution of polydisperse gas–solid flows better than the traditional drag Model; (ii) the particle–particle drag force has an important influence on the mixing and segregation of different particles whereas the particulate phase stress has only a very minor effect, especially when the superficial gas velocity is low. The second finding highlights the need for a suitable particle–particle drag Model that considers the effects of mesoscale structures, which will be the topic of our future study.
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Multifluid Modeling of Coal Pyrolysis in a Downer Reactor
Industrial & Engineering Chemistry Research, 2016Co-Authors: Zhan Shu, Chuigang Fan, Junwu WangAbstract:Downer is a promising reactor for coal pyrolysis, where the energy used for coal pyrolysis comes from the heat carrier particles. However, fundamental studies are limited regardless of its practical importance. To this end, a Multifluid Model is established to study the hydrodynamics, heat, mass transfer, and chemical reaction in a downer reactor: The conservation equations of mass, momentum, and energy are closed with proper Models for interphase mass, momentum, and heat transfer, including the particle radiation mechanism and with advanced kinetic theory for particulate phase stresses and particle–particle drag coefficients. Species transport equations, the reaction kinetic Model, and the water evaporation Model are also coupled. Computational fluid dynamics simulations highlight the importance of feeding temperature in coal pyrolysis and indicate that the gas–solid heat transfer and particle radiation are the major heat transfer mechanisms, whereas the direct particle–particle heat transfer is negligib...
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Multifluid Modeling of Coal Pyrolysis in a Downer Reactor
2016Co-Authors: Zhan Shu, Chuigang Fan, Junwu WangAbstract:Downer is a promising reactor for coal pyrolysis, where the energy used for coal pyrolysis comes from the heat carrier particles. However, fundamental studies are limited regardless of its practical importance. To this end, a Multifluid Model is established to study the hydrodynamics, heat, mass transfer, and chemical reaction in a downer reactor: The conservation equations of mass, momentum, and energy are closed with proper Models for interphase mass, momentum, and heat transfer, including the particle radiation mechanism and with advanced kinetic theory for particulate phase stresses and particle–particle drag coefficients. Species transport equations, the reaction kinetic Model, and the water evaporation Model are also coupled. Computational fluid dynamics simulations highlight the importance of feeding temperature in coal pyrolysis and indicate that the gas–solid heat transfer and particle radiation are the major heat transfer mechanisms, whereas the direct particle–particle heat transfer is negligible. The simulations prove qualitatively the rationality of the Model for coal pyrolysis
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evaluation of Multifluid Model for heat transfer behavior of binary gas solid flow in a downer reactor
Powder Technology, 2015Co-Authors: Zhan Shu, Quan Zhou, Junwu Wang, Chuigang FanAbstract:The heat transfer characteristics of different particles during coal pyrolysis process are of fundamental importance in a downer reactor, where hot sand particles often serve as the heat carrier for heating cold coal particles. Despite its urgent practical demands, fundamental studies on this topic were still very limited so far. To this end, this work carded out computational fluid dynamics (CFD) investigations of heat transfer behavior of binary gas-solid flow in a downer reactor using Multifluid Model. A modified gas-solid drag Model and a modified Gunn's gas-solid heat transfer coefficient Model were used to address the critical role of particle cluster structure. Furthermore, the effects of constant or temperature-dependent air properties, particle-particle drag force, and particle-particle heat transfer as well as the different choices of kinetic theories of granular flow were systematically evaluated, and then the optimized Models were identified. CFD simulations with the optimized Models show that CFD simulation has the ability to qualitatively capture the key heat transfer features in downers, based on the fact that a fairly good agreement with the available experimental data in the literature can be obtained and be further improved by taking the specific shape of inlet distributor into account. (C) 2015 Elsevier B.V. All rights reserved.
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cfd study of mixing and segregation in cfb risers extension of emms drag Model to binary gas solid flow
Chemical Engineering Science, 2015Co-Authors: Quan Zhou, Junwu WangAbstract:The Energy Minimization Multi-Scale (EMMS) drag Model, using Sauter mean particle diameter to represent real particle size distribution, has proven to be effective in improving the accuracy of continuum Modeling of gas-solid flow. Nevertheless, mixing and segregation characteristics in circulating fluidized bed (CFB) risers are very important in many situations, which necessitates the explicit consideration of the effects of particle size distribution on the bed hydrodynamics. To this end, an attempt is made to extend the EMMS drag Model to binary gas-solid system, where four input parameters that can be obtained from computational fluid dynamics (CFD) simulation, including two slip velocities between gas and each particle phase and two particle concentrations of each phase, are used to solve the proposed EMMS drag Model. Heterogeneous indexes, which are used to modify the drag correlation obtained from homogeneous fluidization, are then predicted and fed into Multifluid Model (MFM) to predict the dynamical behavior of mixing and segregation of binary gas-solid flow in a CEO riser. The effects of different drag force Models, kinetic theories and particle-particle drag force Models are also systematically evaluated. It was shown that (i) MFM with the proposed EMMS drag Model and the kinetic theory developed by Chao et al. (Chemical Engineering Science 2011,66: 3605-3616) is able to correctly predict the mixing and segregation pattern in the studied riser, while MFM with homogenous drag forces and the simplified kinetic theory available in commercial software FLUENT completely fails; and (ii) with or without particle-particle drag force has a substantial influence upon the particle behavior. (C) 2014 Elsevier Ltd. All rights reserved.
Quan Zhou - One of the best experts on this subject based on the ideXlab platform.
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An EMMS drag Model for coarse grid simulation of polydisperse gas–solid flow in circulating fluidized bed risers
Chemical Engineering Science, 2019Co-Authors: Zhiyuan Qin, Quan Zhou, Junwu WangAbstract:Abstract Polydisperse gas–solid systems are more common in both industry and the natural world than their monodisperse counterparts. This paper aims to investigate the hydrodynamics of polydisperse gas–solid flow systems by extending the energy minimization multiscale (EMMS) drag Model. The continuous particle size is discretized into several characteristic sizes, by which the polydisperse particles are classified into several discrete groups. A polydisperse EMMS drag Model is then developed by treating these particle groups as solid phases. Finally, the proposed drag Model is coupled with the Multifluid Model to simulate the hydrodynamics of polydisperse gas–solid flow in CFB risers. Extensive simulations are conducted to validate the effectiveness of the polydisperse EMMS drag Model and investigate the effects of gas–particle drag Models, kinetic theories, and particle–particle drag Models on the simulation results. It was found that (i) the polydisperse EMMS drag Model can predict the concentration and particle size distribution of polydisperse gas–solid flows better than the traditional drag Model; (ii) the particle–particle drag force has an important influence on the mixing and segregation of different particles whereas the particulate phase stress has only a very minor effect, especially when the superficial gas velocity is low. The second finding highlights the need for a suitable particle–particle drag Model that considers the effects of mesoscale structures, which will be the topic of our future study.
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evaluation of Multifluid Model for heat transfer behavior of binary gas solid flow in a downer reactor
Powder Technology, 2015Co-Authors: Zhan Shu, Quan Zhou, Junwu Wang, Chuigang FanAbstract:The heat transfer characteristics of different particles during coal pyrolysis process are of fundamental importance in a downer reactor, where hot sand particles often serve as the heat carrier for heating cold coal particles. Despite its urgent practical demands, fundamental studies on this topic were still very limited so far. To this end, this work carded out computational fluid dynamics (CFD) investigations of heat transfer behavior of binary gas-solid flow in a downer reactor using Multifluid Model. A modified gas-solid drag Model and a modified Gunn's gas-solid heat transfer coefficient Model were used to address the critical role of particle cluster structure. Furthermore, the effects of constant or temperature-dependent air properties, particle-particle drag force, and particle-particle heat transfer as well as the different choices of kinetic theories of granular flow were systematically evaluated, and then the optimized Models were identified. CFD simulations with the optimized Models show that CFD simulation has the ability to qualitatively capture the key heat transfer features in downers, based on the fact that a fairly good agreement with the available experimental data in the literature can be obtained and be further improved by taking the specific shape of inlet distributor into account. (C) 2015 Elsevier B.V. All rights reserved.
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cfd study of mixing and segregation in cfb risers extension of emms drag Model to binary gas solid flow
Chemical Engineering Science, 2015Co-Authors: Quan Zhou, Junwu WangAbstract:The Energy Minimization Multi-Scale (EMMS) drag Model, using Sauter mean particle diameter to represent real particle size distribution, has proven to be effective in improving the accuracy of continuum Modeling of gas-solid flow. Nevertheless, mixing and segregation characteristics in circulating fluidized bed (CFB) risers are very important in many situations, which necessitates the explicit consideration of the effects of particle size distribution on the bed hydrodynamics. To this end, an attempt is made to extend the EMMS drag Model to binary gas-solid system, where four input parameters that can be obtained from computational fluid dynamics (CFD) simulation, including two slip velocities between gas and each particle phase and two particle concentrations of each phase, are used to solve the proposed EMMS drag Model. Heterogeneous indexes, which are used to modify the drag correlation obtained from homogeneous fluidization, are then predicted and fed into Multifluid Model (MFM) to predict the dynamical behavior of mixing and segregation of binary gas-solid flow in a CEO riser. The effects of different drag force Models, kinetic theories and particle-particle drag force Models are also systematically evaluated. It was shown that (i) MFM with the proposed EMMS drag Model and the kinetic theory developed by Chao et al. (Chemical Engineering Science 2011,66: 3605-3616) is able to correctly predict the mixing and segregation pattern in the studied riser, while MFM with homogenous drag forces and the simplified kinetic theory available in commercial software FLUENT completely fails; and (ii) with or without particle-particle drag force has a substantial influence upon the particle behavior. (C) 2014 Elsevier Ltd. All rights reserved.
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Evaluation of Multifluid Model for heat transfer behavior of binary gas–solid flow in a downer reactor
Powder Technology, 2015Co-Authors: Zhan Shu, Quan Zhou, Junwu Wang, Chuigang FanAbstract:The heat transfer characteristics of different particles during coal pyrolysis process are of fundamental importance in a downer reactor, where hot sand particles often serve as the heat carrier for heating cold coal particles. Despite its urgent practical demands, fundamental studies on this topic were still very limited so far. To this end, this work carded out computational fluid dynamics (CFD) investigations of heat transfer behavior of binary gas-solid flow in a downer reactor using Multifluid Model. A modified gas-solid drag Model and a modified Gunn's gas-solid heat transfer coefficient Model were used to address the critical role of particle cluster structure. Furthermore, the effects of constant or temperature-dependent air properties, particle-particle drag force, and particle-particle heat transfer as well as the different choices of kinetic theories of granular flow were systematically evaluated, and then the optimized Models were identified. CFD simulations with the optimized Models show that CFD simulation has the ability to qualitatively capture the key heat transfer features in downers, based on the fact that a fairly good agreement with the available experimental data in the literature can be obtained and be further improved by taking the specific shape of inlet distributor into account. (C) 2015 Elsevier B.V. All rights reserved.
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CFD study of mixing and segregation in CFB risers: Extension of EMMS drag Model to binary gas–solid flow
Chemical Engineering Science, 2015Co-Authors: Quan Zhou, Junwu WangAbstract:The Energy Minimization Multi-Scale (EMMS) drag Model, using Sauter mean particle diameter to represent real particle size distribution, has proven to be effective in improving the accuracy of continuum Modeling of gas-solid flow. Nevertheless, mixing and segregation characteristics in circulating fluidized bed (CFB) risers are very important in many situations, which necessitates the explicit consideration of the effects of particle size distribution on the bed hydrodynamics. To this end, an attempt is made to extend the EMMS drag Model to binary gas-solid system, where four input parameters that can be obtained from computational fluid dynamics (CFD) simulation, including two slip velocities between gas and each particle phase and two particle concentrations of each phase, are used to solve the proposed EMMS drag Model. Heterogeneous indexes, which are used to modify the drag correlation obtained from homogeneous fluidization, are then predicted and fed into Multifluid Model (MFM) to predict the dynamical behavior of mixing and segregation of binary gas-solid flow in a CEO riser. The effects of different drag force Models, kinetic theories and particle-particle drag force Models are also systematically evaluated. It was shown that (i) MFM with the proposed EMMS drag Model and the kinetic theory developed by Chao et al. (Chemical Engineering Science 2011,66: 3605-3616) is able to correctly predict the mixing and segregation pattern in the studied riser, while MFM with homogenous drag forces and the simplified kinetic theory available in commercial software FLUENT completely fails; and (ii) with or without particle-particle drag force has a substantial influence upon the particle behavior. (C) 2014 Elsevier Ltd. All rights reserved.
Chuigang Fan - One of the best experts on this subject based on the ideXlab platform.
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Multifluid Modeling of Coal Pyrolysis in a Downer Reactor
Industrial & Engineering Chemistry Research, 2016Co-Authors: Zhan Shu, Chuigang Fan, Junwu WangAbstract:Downer is a promising reactor for coal pyrolysis, where the energy used for coal pyrolysis comes from the heat carrier particles. However, fundamental studies are limited regardless of its practical importance. To this end, a Multifluid Model is established to study the hydrodynamics, heat, mass transfer, and chemical reaction in a downer reactor: The conservation equations of mass, momentum, and energy are closed with proper Models for interphase mass, momentum, and heat transfer, including the particle radiation mechanism and with advanced kinetic theory for particulate phase stresses and particle–particle drag coefficients. Species transport equations, the reaction kinetic Model, and the water evaporation Model are also coupled. Computational fluid dynamics simulations highlight the importance of feeding temperature in coal pyrolysis and indicate that the gas–solid heat transfer and particle radiation are the major heat transfer mechanisms, whereas the direct particle–particle heat transfer is negligib...
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Multifluid Modeling of Coal Pyrolysis in a Downer Reactor
2016Co-Authors: Zhan Shu, Chuigang Fan, Junwu WangAbstract:Downer is a promising reactor for coal pyrolysis, where the energy used for coal pyrolysis comes from the heat carrier particles. However, fundamental studies are limited regardless of its practical importance. To this end, a Multifluid Model is established to study the hydrodynamics, heat, mass transfer, and chemical reaction in a downer reactor: The conservation equations of mass, momentum, and energy are closed with proper Models for interphase mass, momentum, and heat transfer, including the particle radiation mechanism and with advanced kinetic theory for particulate phase stresses and particle–particle drag coefficients. Species transport equations, the reaction kinetic Model, and the water evaporation Model are also coupled. Computational fluid dynamics simulations highlight the importance of feeding temperature in coal pyrolysis and indicate that the gas–solid heat transfer and particle radiation are the major heat transfer mechanisms, whereas the direct particle–particle heat transfer is negligible. The simulations prove qualitatively the rationality of the Model for coal pyrolysis
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evaluation of Multifluid Model for heat transfer behavior of binary gas solid flow in a downer reactor
Powder Technology, 2015Co-Authors: Zhan Shu, Quan Zhou, Junwu Wang, Chuigang FanAbstract:The heat transfer characteristics of different particles during coal pyrolysis process are of fundamental importance in a downer reactor, where hot sand particles often serve as the heat carrier for heating cold coal particles. Despite its urgent practical demands, fundamental studies on this topic were still very limited so far. To this end, this work carded out computational fluid dynamics (CFD) investigations of heat transfer behavior of binary gas-solid flow in a downer reactor using Multifluid Model. A modified gas-solid drag Model and a modified Gunn's gas-solid heat transfer coefficient Model were used to address the critical role of particle cluster structure. Furthermore, the effects of constant or temperature-dependent air properties, particle-particle drag force, and particle-particle heat transfer as well as the different choices of kinetic theories of granular flow were systematically evaluated, and then the optimized Models were identified. CFD simulations with the optimized Models show that CFD simulation has the ability to qualitatively capture the key heat transfer features in downers, based on the fact that a fairly good agreement with the available experimental data in the literature can be obtained and be further improved by taking the specific shape of inlet distributor into account. (C) 2015 Elsevier B.V. All rights reserved.
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Evaluation of Multifluid Model for heat transfer behavior of binary gas–solid flow in a downer reactor
Powder Technology, 2015Co-Authors: Zhan Shu, Quan Zhou, Junwu Wang, Chuigang FanAbstract:The heat transfer characteristics of different particles during coal pyrolysis process are of fundamental importance in a downer reactor, where hot sand particles often serve as the heat carrier for heating cold coal particles. Despite its urgent practical demands, fundamental studies on this topic were still very limited so far. To this end, this work carded out computational fluid dynamics (CFD) investigations of heat transfer behavior of binary gas-solid flow in a downer reactor using Multifluid Model. A modified gas-solid drag Model and a modified Gunn's gas-solid heat transfer coefficient Model were used to address the critical role of particle cluster structure. Furthermore, the effects of constant or temperature-dependent air properties, particle-particle drag force, and particle-particle heat transfer as well as the different choices of kinetic theories of granular flow were systematically evaluated, and then the optimized Models were identified. CFD simulations with the optimized Models show that CFD simulation has the ability to qualitatively capture the key heat transfer features in downers, based on the fact that a fairly good agreement with the available experimental data in the literature can be obtained and be further improved by taking the specific shape of inlet distributor into account. (C) 2015 Elsevier B.V. All rights reserved.
Qingang Xiong - One of the best experts on this subject based on the ideXlab platform.
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Overview of Computational Fluid Dynamics Simulation of Reactor-Scale Biomass Pyrolysis
ACS Sustainable Chemistry & Engineering, 2017Co-Authors: Qingang Xiong, Yang Yang, Yaoyu Pan, Jingchao Zhang, Kun Hong, Giulio Lorenzini, Shurong WangAbstract:Computational fluid dynamics (CFD) has been widely used in both scientific studies and industrial applications of reactor-scale biomass pyrolysis. In this Perspective, the state-of-the-art progress in CFD Modeling of reactor-scale biomass pyrolysis was summarized and discussed. First, because of the importance of biomass pyrolysis reaction kinetics to the predictability of CFD, the commonly used pyrolysis reaction kinetics in CFD Modeling of reactor-scale biomass pyrolysis were reviewed. The characteristics of each reaction kinetics were described. Then, the theoretical basis and practical applications of three main CFD Modeling approaches, i.e., porous media Model, Multifluid Model, and discrete particle Model for simulating reactor-scale biomass pyrolysis were presented. The activities and progresses with respect to each CFD Modeling approach for reactor-scale biomass pyrolysis were reviewed. Aspects such as experimental validation, Modeling speed, and capability were discussed. Finally, the paper was c...
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assessment of devolatilization schemes in predicting product yields of biomass fast pyrolysis
Environmental Progress, 2014Co-Authors: Qingang Xiong, Soroush Aramideh, Songcharng KongAbstract:Three devolatilization schemes to simulate biomass fast pyrolysis were tested and validated in this study. Fast pyrolysis is an attractive process in converting lignocellulosic biomass to valued products. Accurate numerical Models can help understand the conversion process and be used for reactor design and optimization. This study used a numerical Model that considered the multiphase hydrodynamics and chemical reactions of biomass fast pyrolysis. The gas and solid phases were simulated by using a Multifluid Model that considered multiple species in each phase. Three devolatilization schemes for biomass fast pyrolysis were incorporated into the Model to simulate the tempo-spatial evolutions of all phases and species. The predicted product yields were compared and validated using experimental data. It was found that the best predictions were given by a scheme that used three components to represent biomass and also considered organic liquid cracking into gas. Under the reactor conditions studied, all three devolatilization schemes predicted relatively fast decomposition of biomass and the reactor hydrodynamics was not significantly affected by the specifics of the devolatilization schemes. Overall, an accurate devolatilization scheme to simulate the chemical changes of biomass particles is essential to predicting the product yield of biomass fast pyrolysis at the reactor scale. © 2014 American Institute of Chemical Engineers Environ Prog,, 33: 756–761, 2014
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assessment of devolatilization schemes in predicting product yields of biomass fast pyrolysis
Environmental Progress, 2014Co-Authors: Qingang Xiong, Soroush Aramideh, Songcharng KongAbstract:Three devolatilization schemes to simulate biomass fast pyrolysis were tested and validated in this study. Fast pyrolysis is an attractive process in converting lignocellulosic biomass to valued products. Accurate numerical Models can help understand the conversion process and be used for reactor design and optimization. This study used a numerical Model that considered the multiphase hydrodynamics and chemical reactions of biomass fast pyrolysis. The gas and solid phases were simulated by using a Multifluid Model that considered multiple species in each phase. Three devolatilization schemes for biomass fast pyrolysis were incorporated into the Model to simulate the tempo-spatial evolutions of all phases and species. The predicted product yields were compared and validated using experimental data. It was found that the best predictions were given by a scheme that used three components to represent biomass and also considered organic liquid cracking into gas. Under the reactor conditions studied, all three devolatilization schemes predicted relatively fast decomposition of biomass and the reactor hydrodynamics was not significantly affected by the specifics of the devolatilization schemes. Overall, an accurate devolatilization scheme to simulate the chemical changes of biomass particles is essential to predicting the product yield of biomass fast pyrolysis at the reactor scale. © 2014 American Institute of Chemical Engineers Environ Prog,, 33: 756–761, 2014
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Modeling effects of operating conditions on biomass fast pyrolysis in bubbling fluidized bed reactors
Energy & Fuels, 2013Co-Authors: Qingang Xiong, Soroush Aramideh, Songcharng KongAbstract:This numerical study investigates the effects of operating conditions on the product yields of a biomass fast pyrolysis reactor. A numerical approach that combines a Multifluid Model and pyrolysis reaction kinetics was applied to simulate the biomass fast pyrolysis process in a bubbling fluidized-bed reactor. The Model was first validated using experimental data, and a parametric study was conducted. Operating parameters were varied to characterize their effects on the final product yields. For the reactor studied, it was found that the maximum tar yield could be obtained by maintaining both the wall temperature and the inlet temperature of nitorgen at approximately 800 K. The inlet velocity of nitrogen at about 0.6 m/s also produced favorable results. Simulations indicated that the optimal biomass particle diameter and the feeding rate were 900 μm and 1.92 kg/h, respectively, for tar production. Larger sand particle diameter and deeper initial sand bed also favored the tar yield.
Zhan Shu - One of the best experts on this subject based on the ideXlab platform.
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Multifluid Modeling of Coal Pyrolysis in a Downer Reactor
Industrial & Engineering Chemistry Research, 2016Co-Authors: Zhan Shu, Chuigang Fan, Junwu WangAbstract:Downer is a promising reactor for coal pyrolysis, where the energy used for coal pyrolysis comes from the heat carrier particles. However, fundamental studies are limited regardless of its practical importance. To this end, a Multifluid Model is established to study the hydrodynamics, heat, mass transfer, and chemical reaction in a downer reactor: The conservation equations of mass, momentum, and energy are closed with proper Models for interphase mass, momentum, and heat transfer, including the particle radiation mechanism and with advanced kinetic theory for particulate phase stresses and particle–particle drag coefficients. Species transport equations, the reaction kinetic Model, and the water evaporation Model are also coupled. Computational fluid dynamics simulations highlight the importance of feeding temperature in coal pyrolysis and indicate that the gas–solid heat transfer and particle radiation are the major heat transfer mechanisms, whereas the direct particle–particle heat transfer is negligib...
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Multifluid Modeling of Coal Pyrolysis in a Downer Reactor
2016Co-Authors: Zhan Shu, Chuigang Fan, Junwu WangAbstract:Downer is a promising reactor for coal pyrolysis, where the energy used for coal pyrolysis comes from the heat carrier particles. However, fundamental studies are limited regardless of its practical importance. To this end, a Multifluid Model is established to study the hydrodynamics, heat, mass transfer, and chemical reaction in a downer reactor: The conservation equations of mass, momentum, and energy are closed with proper Models for interphase mass, momentum, and heat transfer, including the particle radiation mechanism and with advanced kinetic theory for particulate phase stresses and particle–particle drag coefficients. Species transport equations, the reaction kinetic Model, and the water evaporation Model are also coupled. Computational fluid dynamics simulations highlight the importance of feeding temperature in coal pyrolysis and indicate that the gas–solid heat transfer and particle radiation are the major heat transfer mechanisms, whereas the direct particle–particle heat transfer is negligible. The simulations prove qualitatively the rationality of the Model for coal pyrolysis
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evaluation of Multifluid Model for heat transfer behavior of binary gas solid flow in a downer reactor
Powder Technology, 2015Co-Authors: Zhan Shu, Quan Zhou, Junwu Wang, Chuigang FanAbstract:The heat transfer characteristics of different particles during coal pyrolysis process are of fundamental importance in a downer reactor, where hot sand particles often serve as the heat carrier for heating cold coal particles. Despite its urgent practical demands, fundamental studies on this topic were still very limited so far. To this end, this work carded out computational fluid dynamics (CFD) investigations of heat transfer behavior of binary gas-solid flow in a downer reactor using Multifluid Model. A modified gas-solid drag Model and a modified Gunn's gas-solid heat transfer coefficient Model were used to address the critical role of particle cluster structure. Furthermore, the effects of constant or temperature-dependent air properties, particle-particle drag force, and particle-particle heat transfer as well as the different choices of kinetic theories of granular flow were systematically evaluated, and then the optimized Models were identified. CFD simulations with the optimized Models show that CFD simulation has the ability to qualitatively capture the key heat transfer features in downers, based on the fact that a fairly good agreement with the available experimental data in the literature can be obtained and be further improved by taking the specific shape of inlet distributor into account. (C) 2015 Elsevier B.V. All rights reserved.
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Evaluation of Multifluid Model for heat transfer behavior of binary gas–solid flow in a downer reactor
Powder Technology, 2015Co-Authors: Zhan Shu, Quan Zhou, Junwu Wang, Chuigang FanAbstract:The heat transfer characteristics of different particles during coal pyrolysis process are of fundamental importance in a downer reactor, where hot sand particles often serve as the heat carrier for heating cold coal particles. Despite its urgent practical demands, fundamental studies on this topic were still very limited so far. To this end, this work carded out computational fluid dynamics (CFD) investigations of heat transfer behavior of binary gas-solid flow in a downer reactor using Multifluid Model. A modified gas-solid drag Model and a modified Gunn's gas-solid heat transfer coefficient Model were used to address the critical role of particle cluster structure. Furthermore, the effects of constant or temperature-dependent air properties, particle-particle drag force, and particle-particle heat transfer as well as the different choices of kinetic theories of granular flow were systematically evaluated, and then the optimized Models were identified. CFD simulations with the optimized Models show that CFD simulation has the ability to qualitatively capture the key heat transfer features in downers, based on the fact that a fairly good agreement with the available experimental data in the literature can be obtained and be further improved by taking the specific shape of inlet distributor into account. (C) 2015 Elsevier B.V. All rights reserved.