Bubble dynamics properties play a crucial and significant role in the design and optimization of gas-solid fluidized beds.In this study,the bubble dynamics properties of four B-particles were investigated in a quasi-t...Bubble dynamics properties play a crucial and significant role in the design and optimization of gas-solid fluidized beds.In this study,the bubble dynamics properties of four B-particles were investigated in a quasi-two-dimensional(quasi-2D)fluidized bed,including bubble equivalent diameter,bubble size distribution,average bubble density,bubble aspect ratio,bubble hold-up,bed expansion ratio,bubble radial position,and bubble velocity.The studies were performed by computational particle fluid dynamics(CPFD)numerical simulation and post-processed with digital image analysis(DIA)technique,at superficial gas velocities ranging from 2u_(mf) to 7u_(mf).The simulated results shown that the CPFD simulation combining with DIA technique post-processing could be used as a reliable method for simulating bubble dynamics properties in quasi-2D gas-solid fluidized beds.However,it seemed not desirable for the simulation of bubble motion near the air distributor at higher superficial gas velocity from the simulated average bubble density distribution.The superficial gas velocity significantly affected the bubble equivalent diameter and evolution,while it had little influence on bubble size distribution and bubble aspect ratio distribution for the same particles.Both time-averaged bubble hold-up and bed expansion ratio increased with the increase of superficial gas velocity.Two core-annular flow structures could be found in the fluidized bed for all cases.The average bubble rising velocity increased with the increasing bubble equivalent diameter.For bubble lateral movement,the smaller bubbles might be more susceptible,and superficial gas velocity had a little influence on the absolute lateral velocity of bubbles.The simulated results presented a valuable and novel approach for studying bubble dynamics properties.The comprehensive understanding of bubble dynamics behaviors in quasi-2D gas-solid fluidized beds would provide support in the design,operation,and optimization of gas-solid fluidized bed reactors.展开更多
The coal gasification fly ash(CGFA) is an industrial solid waste from coal gasification process and needs to be effectively disposed for environmental protection and resource utilization.To further clarify the feasibi...The coal gasification fly ash(CGFA) is an industrial solid waste from coal gasification process and needs to be effectively disposed for environmental protection and resource utilization.To further clarify the feasibility of CGFA to prepare porous carbon materials,the physicochemical properties of ten kinds of CGFA from circulating fluidized bed(CFB) gasifiers were analyzed in detail.The results of proximate and ultimate analysis show that the CGFA is characterized with the features of near zero moisture content,low volatile content as low as 0.90%-9.76%,high carbon content in the range of 37.89%-81.62%,and ultrafine particle size(d50=15.8-46.2 μm).The automatic specific surface area(SSA) and pore size analyzer were used to detect the pore structure,it is found that the pore structure of CGFA is relatively developed,and part of the CGFA has the basic conditions to be used directly as porous carbon materials.From SEM images,the microscopic morphology of the CGFA is significantly different,and they basically have the characteristics of loose and porous structure.XRD and Roman spectroscopy were used to characterize the carbon structure.The result shows that the CGFA contains abundant amorphous carbon structure,and thus the CGFA has a good reactivity and a potential to improve pore structure through further activation.Through thermal gravimetric analysis,it can be concluded that the order of reactivity of the CGFA under CO_(2) atmosphere has a good correlation with the degree of metamorphism of the raw coal.The gasification reactivity of the CGFA is generally consistent with the change trend of micropores combined with the pore structure.According to the physicochemical properties,the CGFA has a good application prospect in the preparation of porous carbon materials.展开更多
Zhtmdong coalfield is the largest intact coalfield worldwide and fluidized bed gasification has been considered as a promising way to achieve its clean and efficient utilization. The purpose of this study is to invest...Zhtmdong coalfield is the largest intact coalfield worldwide and fluidized bed gasification has been considered as a promising way to achieve its clean and efficient utilization. The purpose of this study is to investigate the phy- sicochemical properties and gasification reactivity of the ultrafme semi-char, derived from a bench-scale fluidized bed gasifier, using Zhundong coal as fuel. The results obtained are as follows. In comparison to the raw coal, the carbon and ash content of the semi-char increase after partial gasification, but the ash fusion temperatures of them show no significant difference. Particularly, 76.53% of the sodium in the feed coal has released to the gas phase after fluidized bed gasification. The chemical compositions of the semi-char are closely related to its particle size, attributable to the distinctly different natures of diverse elements. The semi-char exhibits a higher graphitization degree, higher BET surface area, and richer meso- and macropores, which results in superior gasification reactiv- ity than the coal char. The chemical reactivity of the semi-char is significantly improved by an increased gasifica- tion temperature, which suggests the necessity of regasification of the semi-char at a higher temperature. Conse- quently, it will be considered feasible that these carbons in the semi-char from fluidized bed gasitiers are rec- laimed and reused for the gasification process.展开更多
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 ...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.展开更多
During the solid fluidization exploitation of marine natural gas hydrates,the hydrate particles and cuttings produced via excavation and crushing are transported by the drilling mud.The potential flow safety issues ar...During the solid fluidization exploitation of marine natural gas hydrates,the hydrate particles and cuttings produced via excavation and crushing are transported by the drilling mud.The potential flow safety issues arising during the transport process,such as the blockage of pipelines and equipment,have attracted considerable attention.This study aims to investigate the impact of hydrate adhesion features,including agglomeration,cohesion,and deposition,on the flow transport processes in solid fluidization exploitation and to provide a reference for the design and application of multiphase hydrate slurry transport in solid fluidization exploitation.We established a numerical simulation model that considers the hydrate adhesion properties using the coupled computational fluid dynamics and discrete element method(CFD-DEM)for the multiphase mixed transport in solid fluidization exploitation.An appropriate model to simulate the adhesion force of the hydrate particles and the corresponding parameter values were obtained.The conclusions obtained are as follows.Under the same operating conditions,a stationary bed is more likely to form in the transport process due to the hydrate adhesion forces;adhesion forces can increase the critical deposition velocity of the mixture of hydrate particles and cuttings.Hydrate adhesion lowers the height of the solid-phase moving bed,while the agglomeration and cohesion of particles can intensify the aggregation and deposition of hydrate debris and cuttings at the bottom of the pipe.These particles tend to form a deposit bed rather than a moving bed,which reduces the effective flow area of the pipeline and increases the risk of blockage.展开更多
基金the financial support provided by National Key R&D Project of China(grant No.2020YFB0606303)the technical supports received from Sam Clark in CPFD Software,LLC of USA,and from Hi-Key Technology Incorporated of China.
文摘Bubble dynamics properties play a crucial and significant role in the design and optimization of gas-solid fluidized beds.In this study,the bubble dynamics properties of four B-particles were investigated in a quasi-two-dimensional(quasi-2D)fluidized bed,including bubble equivalent diameter,bubble size distribution,average bubble density,bubble aspect ratio,bubble hold-up,bed expansion ratio,bubble radial position,and bubble velocity.The studies were performed by computational particle fluid dynamics(CPFD)numerical simulation and post-processed with digital image analysis(DIA)technique,at superficial gas velocities ranging from 2u_(mf) to 7u_(mf).The simulated results shown that the CPFD simulation combining with DIA technique post-processing could be used as a reliable method for simulating bubble dynamics properties in quasi-2D gas-solid fluidized beds.However,it seemed not desirable for the simulation of bubble motion near the air distributor at higher superficial gas velocity from the simulated average bubble density distribution.The superficial gas velocity significantly affected the bubble equivalent diameter and evolution,while it had little influence on bubble size distribution and bubble aspect ratio distribution for the same particles.Both time-averaged bubble hold-up and bed expansion ratio increased with the increase of superficial gas velocity.Two core-annular flow structures could be found in the fluidized bed for all cases.The average bubble rising velocity increased with the increasing bubble equivalent diameter.For bubble lateral movement,the smaller bubbles might be more susceptible,and superficial gas velocity had a little influence on the absolute lateral velocity of bubbles.The simulated results presented a valuable and novel approach for studying bubble dynamics properties.The comprehensive understanding of bubble dynamics behaviors in quasi-2D gas-solid fluidized beds would provide support in the design,operation,and optimization of gas-solid fluidized bed reactors.
基金This work was financially supported by the Special Research Assistant Fund Project of Chinese Academy of Sciences.
文摘The coal gasification fly ash(CGFA) is an industrial solid waste from coal gasification process and needs to be effectively disposed for environmental protection and resource utilization.To further clarify the feasibility of CGFA to prepare porous carbon materials,the physicochemical properties of ten kinds of CGFA from circulating fluidized bed(CFB) gasifiers were analyzed in detail.The results of proximate and ultimate analysis show that the CGFA is characterized with the features of near zero moisture content,low volatile content as low as 0.90%-9.76%,high carbon content in the range of 37.89%-81.62%,and ultrafine particle size(d50=15.8-46.2 μm).The automatic specific surface area(SSA) and pore size analyzer were used to detect the pore structure,it is found that the pore structure of CGFA is relatively developed,and part of the CGFA has the basic conditions to be used directly as porous carbon materials.From SEM images,the microscopic morphology of the CGFA is significantly different,and they basically have the characteristics of loose and porous structure.XRD and Roman spectroscopy were used to characterize the carbon structure.The result shows that the CGFA contains abundant amorphous carbon structure,and thus the CGFA has a good reactivity and a potential to improve pore structure through further activation.Through thermal gravimetric analysis,it can be concluded that the order of reactivity of the CGFA under CO_(2) atmosphere has a good correlation with the degree of metamorphism of the raw coal.The gasification reactivity of the CGFA is generally consistent with the change trend of micropores combined with the pore structure.According to the physicochemical properties,the CGFA has a good application prospect in the preparation of porous carbon materials.
基金the support of the National Natural Science Foundation of China(No.21306193)the International Science&Technology Cooperation Program of China(No.2014DFG61680)
文摘Zhtmdong coalfield is the largest intact coalfield worldwide and fluidized bed gasification has been considered as a promising way to achieve its clean and efficient utilization. The purpose of this study is to investigate the phy- sicochemical properties and gasification reactivity of the ultrafme semi-char, derived from a bench-scale fluidized bed gasifier, using Zhundong coal as fuel. The results obtained are as follows. In comparison to the raw coal, the carbon and ash content of the semi-char increase after partial gasification, but the ash fusion temperatures of them show no significant difference. Particularly, 76.53% of the sodium in the feed coal has released to the gas phase after fluidized bed gasification. The chemical compositions of the semi-char are closely related to its particle size, attributable to the distinctly different natures of diverse elements. The semi-char exhibits a higher graphitization degree, higher BET surface area, and richer meso- and macropores, which results in superior gasification reactiv- ity than the coal char. The chemical reactivity of the semi-char is significantly improved by an increased gasifica- tion temperature, which suggests the necessity of regasification of the semi-char at a higher temperature. Conse- quently, it will be considered feasible that these carbons in the semi-char from fluidized bed gasitiers are rec- laimed and reused for the gasification process.
基金supported by the National Key R&D Program of China(2020YFA0714400).
文摘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.
基金supported by the National Natural Science Foundation of China under the projects“Characteristics of argillaceous-silt natural gas hydrate reservoirs in the South China Sea and the gas-liquid-solid multiphase heat and mass transfer mechanisms”(U19B2005)“Study on the decomposition mechanism and transportation rules of natural has hydrate slurry in the solid fluidization exploitation of combustible ice”(51874323).
文摘During the solid fluidization exploitation of marine natural gas hydrates,the hydrate particles and cuttings produced via excavation and crushing are transported by the drilling mud.The potential flow safety issues arising during the transport process,such as the blockage of pipelines and equipment,have attracted considerable attention.This study aims to investigate the impact of hydrate adhesion features,including agglomeration,cohesion,and deposition,on the flow transport processes in solid fluidization exploitation and to provide a reference for the design and application of multiphase hydrate slurry transport in solid fluidization exploitation.We established a numerical simulation model that considers the hydrate adhesion properties using the coupled computational fluid dynamics and discrete element method(CFD-DEM)for the multiphase mixed transport in solid fluidization exploitation.An appropriate model to simulate the adhesion force of the hydrate particles and the corresponding parameter values were obtained.The conclusions obtained are as follows.Under the same operating conditions,a stationary bed is more likely to form in the transport process due to the hydrate adhesion forces;adhesion forces can increase the critical deposition velocity of the mixture of hydrate particles and cuttings.Hydrate adhesion lowers the height of the solid-phase moving bed,while the agglomeration and cohesion of particles can intensify the aggregation and deposition of hydrate debris and cuttings at the bottom of the pipe.These particles tend to form a deposit bed rather than a moving bed,which reduces the effective flow area of the pipeline and increases the risk of blockage.
