A multitracer-gas method was proposed to study the secondary air(SA)mixing along the bed height in a circulating fluidized bed(CFB)using carbon monoxide(CO),oxygen(O_(2)),and carbon dioxide(CO_(2))as tracer gases.Expe...A multitracer-gas method was proposed to study the secondary air(SA)mixing along the bed height in a circulating fluidized bed(CFB)using carbon monoxide(CO),oxygen(O_(2)),and carbon dioxide(CO_(2))as tracer gases.Experiments were carried out on a cold CFB test rig with a cross-section of 0.42 m×0.73 m and a height of 5.50 m.The effects of superficial velocity,SA ratio,bed inventory,and particle diameter on the SA mixing were investigated.The results indicate that there are some differences in the measurement results obtained using different tracer gases,wherein the deviation between CO and CO_(2) ranges from 42%to 66%and that between O_(2) and CO_(2) ranges from 45%to 71%in the lower part of the fluidized bed.However,these differences became less pronounced as the bed height increased.Besides,the high solid concentration and fine particle diameter in the CFB may weaken the difference.The measurement results of different tracer gases show the same trends under the variation of operating parameters.Increasing superficial velocity and SA ratio and decreasing particle diameter result in better mixing of the SA.The effect of bed inventory on SA mixing is not monotonic.展开更多
The flow dynamics of binary particle mixtures in the fluidized bed needs to be monitored in order to optimize the related industrial processes.In this paper,electrostatic sensing and high-speed imaging are applied to ...The flow dynamics of binary particle mixtures in the fluidized bed needs to be monitored in order to optimize the related industrial processes.In this paper,electrostatic sensing and high-speed imaging are applied to measure the velocities of polyethylene and sand particles in the binary particle mixtures in fluidization.Experimental studies were conducted on a lab-scale cold circulating fluidized bed.Correlation function between electrostatic signals from upstream and downstream electrodes placed along the riser shows two peaks that represent transit times for the two types of particles.To verify the above results,high-speed imaging was adopted to capture the flow images of particle mixtures.Particle Image Velocimetry and Particle Tracking Velocimetry algorithms were utilized to process the resulted images in order to measure the velocities of polyethylene and sand particles.The reasons for two-peak correlation functions are illustrated based on the frequency spectrums of the mono-solid-phase electrostatic signals and the velocity difference between polyethylene and sand particles.Finally,comparisons on the velocities obtained from electrostatic sensing and high-speed imaging demonstrate the electrostatic sensor can roughly estimate the particle velocity of binary particle mixtures in the near wall region of the circulating fluidized bed.展开更多
In the service period,the instability of ballastless track bed are mostly related to the damage of interlayers which are mainly resulted from the incompatible thermal deformation of interlayers.The temperature field w...In the service period,the instability of ballastless track bed are mostly related to the damage of interlayers which are mainly resulted from the incompatible thermal deformation of interlayers.The temperature field within the ballastless track bed shows significant non-uniformity due to the large difference in the materials of various structure layers,leading to a considerable difference in the force bearing of different structure layers.Unit Ballastless Track Bed(UBTB)is most significantly affected by temperature gradient.The thermal deformation of interlayers within UBTB follows the trend of ellipsoid-shape buckling under the effect of the temperature gradient,resulting in a variation of the contact relationship between structure layers and a significant periodic irregularity on the rail.When the train travels on the periodically irregular rail,the structure layers are locally contacted,and the contact zone moves with the variation of the wheel position.This wheel-followed local contact greatly magnifies the interlayer stress,causes interlayer damage,and leads to a considerable increase in the bending moment of the track slab.Continuous Ballastless Track Bed(CBTB)is most significantly affected by the overall temperature variation,which may cause damage to the joint in CBTB.Under the combined action of the overall temperature rise and the temperature gradient,the interlayer damage continuously expands,resulting in bonding failure between structural layers.The thermal force in the continuous track slabs will cause the up-heave buckling and the sudden large deformation of the track slab,and the loss of constraint boundary of the horizontal stability.For the design of a ballastless track structure,the change of bearing status and structural damage related to the incompatible thermal deformation of interlayers should be considered.展开更多
The particle flow pattern, mixing and granule segregation in a tapered fluidized bed have been studied along with the hydrodynamics. At first the bed of varying total mass and granule fractions is fluidized then the b...The particle flow pattern, mixing and granule segregation in a tapered fluidized bed have been studied along with the hydrodynamics. At first the bed of varying total mass and granule fractions is fluidized then the bed is defluidized to freeze the composition, the bed is sectioned to layers and the composition in each layer is determined by sieving. Materials used in the present study are dolomite and glass beads with different B.S.S Sizes. A series of unsteady, three fluid CFD simulations were performed using FLUENTTM 6.2. Simulation parameters viz. solution technique, grid, maximum packing fraction and operating conditions like gas velocity were investigated for relative effects on particle mixing and segregation. Good arrangement of solid volume fraction profile was obtained between the experimental results and simulation results for regular particles.展开更多
Researches on solids mixing and segregation are of great significance for the operation and design of fluidized bed reactors.In this paper,the local and global mixing and segregation characteristics of binary mixtures...Researches on solids mixing and segregation are of great significance for the operation and design of fluidized bed reactors.In this paper,the local and global mixing and segregation characteristics of binary mixtures were investigated in a gas–solid fluidized bed by computational fluid dynamics-discrete element method(CFD-DEM)coupled approach.A methodology based on solids mixing entropy was developed to quantitatively calculate the mixing degree and time of the bed.The mixing curves of global mixing entropy were acquired,and the distribution maps of local mixing entropy and mixing time were also obtained.By comparing different operating conditions,the effects of superficial gas velocity,particle density ratio and size ratio on mixing/segregation behavior were discussed.Results showed that for the partial mixing state,the fluidized bed can be divided into three parts along the bed height:complete segregation area,transition area and stable mixing area.These areas showed different mixing/segregation processes.Increasing gas velocity promoted the local and global mixing of binary mixtures.The increase in particle density ratio and size ratio enlarged the complete segregation area,reduced the mixing degree and increased the mixing time in the stable mixing area.展开更多
The current separator with air dense medium fluidized bed can only turn out two products at the same time with a single separating density. The double density fluidized bed means that two separating areas with differe...The current separator with air dense medium fluidized bed can only turn out two products at the same time with a single separating density. The double density fluidized bed means that two separating areas with different densities are formed in a fluidized cascade. In each separating area, the bed density is uniform and meets the technical requirement of coal preparation respectively. Therefore, the processed materials can be separated into three products according to density. In this paper, the fluidized behaviors of binary dense media were experimentally studied and the distribution characteristics of particle concentration and bed density in different bed structure were discussed. The segregation and mixing mechanisms of binary dense media were analyzed. It was testified that the pyramidal part designed in the bed structure played a key role in the formation of double density fluidized bed. The pyramidal part intensified the segregation of binary particles between two separating areas and strengthened the mixing in the low density area, which made for the density uniform of the area.展开更多
Using a finite element method (FEM) program, a Portland cement concrete slab trackbed (So), and a sub- track asphalt roadbed (RAC-S) were modeled under high- speed train loads to analyze their responses to groun...Using a finite element method (FEM) program, a Portland cement concrete slab trackbed (So), and a sub- track asphalt roadbed (RAC-S) were modeled under high- speed train loads to analyze their responses to ground vibration attenuation, by considering 10, 15, 20, 25, and 30 thick sub-track asphalt layer replaced on the top of the upper subgrade. FEM results show that the vibration amplitude of RAC-S is at least three times lower than the vibration for So. The maximum vibration amplitude of RAC-S is linearly increased with train speed. The vertical acceleration is found to be reduced by more than 10 % when the asphalt layer thickness is increased from 10 to 20 cm. However, the reduction in vertical acceleration is only about 1% when the thickness of the asphalt layer changes from 20 to 30 cm. The vibration level is slightly lower if the asphalt layer has higher resilient modulus in the seasons of autumn or winter. This theoretical analysis indicates that a railway substructure that consists of a 10-20 cm thick high modulus asphalt layer located at the top of trackbed shows a good performance in ground vibration control for high-speed rails.展开更多
The effect of flow direction on hydrodynamics and mixing in the upflow and downflowcirculating fluidized beds is discussed in details.Similar profiles of gas and solids velocities andsolids concentration are found in ...The effect of flow direction on hydrodynamics and mixing in the upflow and downflowcirculating fluidized beds is discussed in details.Similar profiles of gas and solids velocities andsolids concentration are found in both risers and downers.When the flow is in the direction ofgravity(downer),the radial profiles of gas and particle velocity are more uniform than that inthe riser,the solids mixing is very small and the flow pattern approaches plug flow,while theflow is against gravity(riser),the solids backmixing significantly increase and the flow pattern isfar from plug flow.Among many of factors the flow direction has the largest influence onhydrodynamics and axial mixing of gas and solids.展开更多
Conical spouted beds operating with high-density particles(ρp>2500 kg/m^(3))have recently gained attention because of their potential use as nuclear fuel coaters for next-generation nuclear reactors.In the literat...Conical spouted beds operating with high-density particles(ρp>2500 kg/m^(3))have recently gained attention because of their potential use as nuclear fuel coaters for next-generation nuclear reactors.In the literature,the number of axial gas mixing studies in conical and conical-cylindrical spouted beds is very limited and all axial mixing studies were carried out with relatively light particles(ρp≤2500 kg/m^(3)).Therefore,the objective of this study was to generate experimental data that can be used to explain the gas axial mixing behavior in conical spouted beds operating with both low-and high-density particles.Experiments were conducted in two(γ=30°,60°)conical spouted beds with three different types of particles:zirconia(ρp=6050 kg/m^(3)),zirconia toughened alumina(ρp=3700 kg/m^(3))and glass beads(ρp=2460 kg/m^(3)).In order to be able to compare experimental data obtained at different conditions,a 1-D convection-diffusion gas mixing model originally developed by San Joséet al.(1995)was implemented to determine the axial dispersion coefficients.The results show that the axial dispersion coefficients range between m^(2)/s and m^(2)/s,increase with superficial gas velocity and are higher than the corresponding dispersion coefficients of fixed beds,lower than the dispersion coefficients of fluidized beds and in the same range with the cylindrical spouted beds reported in the literature.The corresponding Peclet numbers were in the range of 0.6–7.8 for all operating conditions and slightly higher Peclet numbers were obtained with glass beads indicating the relative importance of gas convective transport over gas dispersion for light particles compared to heavy particles.展开更多
Rotating packing bed(RPB) has a better mixing performance than traditional mixers and shows potential application in the petroleum industry. However, acquisition of information about the mixing process directly throug...Rotating packing bed(RPB) has a better mixing performance than traditional mixers and shows potential application in the petroleum industry. However, acquisition of information about the mixing process directly through experiments is difficult because of the compact structure and complex multiphase flow pattern in RPB. To study the mixing characteristic, Fluent, the computational fluid dynamics(CFD) software, was used to explore the effect of airflow field on droplet diameter. For conducting calculations, the gas-liquid two-phase flow inside the packing was simulated with the RNG k-ε turbulence model and the Lagrange Discrete Phase Model(DPM), respectively. The numerical calculation results showed that coalescence and breakup of droplets can take place in the gas phase flow inside the packing and can be strengthened with increased rotating speed, thereby leading to the enlargement of the average diameter.展开更多
Developing catalysts with not only hydrogenation activity but also cracking activity is very important for the advancement of suspended-bed hydrocracking technology.Within this respect,MoS_(2)/SiO_(2)-Al_(2)O_(3)bifun...Developing catalysts with not only hydrogenation activity but also cracking activity is very important for the advancement of suspended-bed hydrocracking technology.Within this respect,MoS_(2)/SiO_(2)-Al_(2)O_(3)bifunctional catalyst is a kind of typical catalysts with both hydrogenation and cracking activity.Herein,a series of Zr-doped SiO_(2)-Al_(2)O_(3)mixed oxides were synthesized by a sol-gel coupled with hydrothermal method.The synthesized mixed oxides were characterized for chemical structures and acidic properties.It is found that doping SiO_(2)-Al_(2)O_(3)with Zr atoms significantly increases the numbers of acidic sites.The Zr-doped SiO_(2)-Al_(2)O_(3)mixed oxides were then combined with dispersed MoS_(2),which was in-situ produced from oil-soluble Mo precursors,to fabricate a novel kind of bifunctional catalysts for suspended-bed hydrocracking of heavy oils.Owing to the significantly increased numbers of acidic sites in Zr-doped SiO_(2)-Al_(2)O_(3)mixed oxides,corresponding bifunctional catalysts demonstrate much enhanced activity for suspended-bed hydrocracking of heavy oils in relative to MoS_(2)/SiO_(2)-Al_(2)O_(3)bifunctional catalysts.展开更多
A mixing-precipitation model based on the modified coalescence-redispersion model was presented to describe the flow,mixing,nucleation and growth in a rotating packed bed(RPB) .The model was coupled with population ba...A mixing-precipitation model based on the modified coalescence-redispersion model was presented to describe the flow,mixing,nucleation and growth in a rotating packed bed(RPB) .The model was coupled with population balance,mass balance and crystallization kinetics.It predicted well the influence of coalescence prob-ability,which represents the mixing intensity among droplets,on the particle number density,supersaturation and mean particle size of the produced precipitates.The effects of the radial thickness of packing,liquid flow rate and rotating speed on the product particle size were also investigated.The results indicate that the needed radial length of packing is short for sparingly soluble substance precipitation(about 40-50 mm in this work) ,and the mean parti-cle size of precipitates decreases with the increase of rotating speed and liquid flow rate,respectively.The validity of this model was verified by experiment on BaSO4 precipitation in RPB.展开更多
基金the Key Project of the National Research Program of China(2020YFB0606201)。
文摘A multitracer-gas method was proposed to study the secondary air(SA)mixing along the bed height in a circulating fluidized bed(CFB)using carbon monoxide(CO),oxygen(O_(2)),and carbon dioxide(CO_(2))as tracer gases.Experiments were carried out on a cold CFB test rig with a cross-section of 0.42 m×0.73 m and a height of 5.50 m.The effects of superficial velocity,SA ratio,bed inventory,and particle diameter on the SA mixing were investigated.The results indicate that there are some differences in the measurement results obtained using different tracer gases,wherein the deviation between CO and CO_(2) ranges from 42%to 66%and that between O_(2) and CO_(2) ranges from 45%to 71%in the lower part of the fluidized bed.However,these differences became less pronounced as the bed height increased.Besides,the high solid concentration and fine particle diameter in the CFB may weaken the difference.The measurement results of different tracer gases show the same trends under the variation of operating parameters.Increasing superficial velocity and SA ratio and decreasing particle diameter result in better mixing of the SA.The effect of bed inventory on SA mixing is not monotonic.
基金financial supports from the National Natural Science Foundation of China (No.61403138)Beijing Natural Science Foundation (No.3202028)+1 种基金funded by the National Research Foundation (NRF), Prime Minister’s Offce, Singapore under its Campus for Research Excellence and Technological Enterprise (CREATE) programmeGrant Number R-706-001-102–281, National University of Singapore。
文摘The flow dynamics of binary particle mixtures in the fluidized bed needs to be monitored in order to optimize the related industrial processes.In this paper,electrostatic sensing and high-speed imaging are applied to measure the velocities of polyethylene and sand particles in the binary particle mixtures in fluidization.Experimental studies were conducted on a lab-scale cold circulating fluidized bed.Correlation function between electrostatic signals from upstream and downstream electrodes placed along the riser shows two peaks that represent transit times for the two types of particles.To verify the above results,high-speed imaging was adopted to capture the flow images of particle mixtures.Particle Image Velocimetry and Particle Tracking Velocimetry algorithms were utilized to process the resulted images in order to measure the velocities of polyethylene and sand particles.The reasons for two-peak correlation functions are illustrated based on the frequency spectrums of the mono-solid-phase electrostatic signals and the velocity difference between polyethylene and sand particles.Finally,comparisons on the velocities obtained from electrostatic sensing and high-speed imaging demonstrate the electrostatic sensor can roughly estimate the particle velocity of binary particle mixtures in the near wall region of the circulating fluidized bed.
基金supported by the National Natural Science Foundation of China(grant numbers 52278466).
文摘In the service period,the instability of ballastless track bed are mostly related to the damage of interlayers which are mainly resulted from the incompatible thermal deformation of interlayers.The temperature field within the ballastless track bed shows significant non-uniformity due to the large difference in the materials of various structure layers,leading to a considerable difference in the force bearing of different structure layers.Unit Ballastless Track Bed(UBTB)is most significantly affected by temperature gradient.The thermal deformation of interlayers within UBTB follows the trend of ellipsoid-shape buckling under the effect of the temperature gradient,resulting in a variation of the contact relationship between structure layers and a significant periodic irregularity on the rail.When the train travels on the periodically irregular rail,the structure layers are locally contacted,and the contact zone moves with the variation of the wheel position.This wheel-followed local contact greatly magnifies the interlayer stress,causes interlayer damage,and leads to a considerable increase in the bending moment of the track slab.Continuous Ballastless Track Bed(CBTB)is most significantly affected by the overall temperature variation,which may cause damage to the joint in CBTB.Under the combined action of the overall temperature rise and the temperature gradient,the interlayer damage continuously expands,resulting in bonding failure between structural layers.The thermal force in the continuous track slabs will cause the up-heave buckling and the sudden large deformation of the track slab,and the loss of constraint boundary of the horizontal stability.For the design of a ballastless track structure,the change of bearing status and structural damage related to the incompatible thermal deformation of interlayers should be considered.
文摘The particle flow pattern, mixing and granule segregation in a tapered fluidized bed have been studied along with the hydrodynamics. At first the bed of varying total mass and granule fractions is fluidized then the bed is defluidized to freeze the composition, the bed is sectioned to layers and the composition in each layer is determined by sieving. Materials used in the present study are dolomite and glass beads with different B.S.S Sizes. A series of unsteady, three fluid CFD simulations were performed using FLUENTTM 6.2. Simulation parameters viz. solution technique, grid, maximum packing fraction and operating conditions like gas velocity were investigated for relative effects on particle mixing and segregation. Good arrangement of solid volume fraction profile was obtained between the experimental results and simulation results for regular particles.
基金supported by the National Key Research and Development Program of China(2020YFA0714400)the National Nature Science Foundation of China(51925602,51888103)。
文摘Researches on solids mixing and segregation are of great significance for the operation and design of fluidized bed reactors.In this paper,the local and global mixing and segregation characteristics of binary mixtures were investigated in a gas–solid fluidized bed by computational fluid dynamics-discrete element method(CFD-DEM)coupled approach.A methodology based on solids mixing entropy was developed to quantitatively calculate the mixing degree and time of the bed.The mixing curves of global mixing entropy were acquired,and the distribution maps of local mixing entropy and mixing time were also obtained.By comparing different operating conditions,the effects of superficial gas velocity,particle density ratio and size ratio on mixing/segregation behavior were discussed.Results showed that for the partial mixing state,the fluidized bed can be divided into three parts along the bed height:complete segregation area,transition area and stable mixing area.These areas showed different mixing/segregation processes.Increasing gas velocity promoted the local and global mixing of binary mixtures.The increase in particle density ratio and size ratio enlarged the complete segregation area,reduced the mixing degree and increased the mixing time in the stable mixing area.
文摘The current separator with air dense medium fluidized bed can only turn out two products at the same time with a single separating density. The double density fluidized bed means that two separating areas with different densities are formed in a fluidized cascade. In each separating area, the bed density is uniform and meets the technical requirement of coal preparation respectively. Therefore, the processed materials can be separated into three products according to density. In this paper, the fluidized behaviors of binary dense media were experimentally studied and the distribution characteristics of particle concentration and bed density in different bed structure were discussed. The segregation and mixing mechanisms of binary dense media were analyzed. It was testified that the pyramidal part designed in the bed structure played a key role in the formation of double density fluidized bed. The pyramidal part intensified the segregation of binary particles between two separating areas and strengthened the mixing in the low density area, which made for the density uniform of the area.
基金supported by National Natural Science Foundation of China(No.51308429)the Fundamental Research Funds for the Central University(WUT:2013-IV-067)Opening Funds for Highway Engineering Key Laboratory of Sichuan Province(No.LHTE004201304)
文摘Using a finite element method (FEM) program, a Portland cement concrete slab trackbed (So), and a sub- track asphalt roadbed (RAC-S) were modeled under high- speed train loads to analyze their responses to ground vibration attenuation, by considering 10, 15, 20, 25, and 30 thick sub-track asphalt layer replaced on the top of the upper subgrade. FEM results show that the vibration amplitude of RAC-S is at least three times lower than the vibration for So. The maximum vibration amplitude of RAC-S is linearly increased with train speed. The vertical acceleration is found to be reduced by more than 10 % when the asphalt layer thickness is increased from 10 to 20 cm. However, the reduction in vertical acceleration is only about 1% when the thickness of the asphalt layer changes from 20 to 30 cm. The vibration level is slightly lower if the asphalt layer has higher resilient modulus in the seasons of autumn or winter. This theoretical analysis indicates that a railway substructure that consists of a 10-20 cm thick high modulus asphalt layer located at the top of trackbed shows a good performance in ground vibration control for high-speed rails.
基金Supported by the National Natural Science Foundation of China and Tsinghua University Foundation.
文摘The effect of flow direction on hydrodynamics and mixing in the upflow and downflowcirculating fluidized beds is discussed in details.Similar profiles of gas and solids velocities andsolids concentration are found in both risers and downers.When the flow is in the direction ofgravity(downer),the radial profiles of gas and particle velocity are more uniform than that inthe riser,the solids mixing is very small and the flow pattern approaches plug flow,while theflow is against gravity(riser),the solids backmixing significantly increase and the flow pattern isfar from plug flow.Among many of factors the flow direction has the largest influence onhydrodynamics and axial mixing of gas and solids.
基金This work was carried out with the financial support of the Scientific and Technological Research Council of Turkey(Project No:MAG 115M392)。
文摘Conical spouted beds operating with high-density particles(ρp>2500 kg/m^(3))have recently gained attention because of their potential use as nuclear fuel coaters for next-generation nuclear reactors.In the literature,the number of axial gas mixing studies in conical and conical-cylindrical spouted beds is very limited and all axial mixing studies were carried out with relatively light particles(ρp≤2500 kg/m^(3)).Therefore,the objective of this study was to generate experimental data that can be used to explain the gas axial mixing behavior in conical spouted beds operating with both low-and high-density particles.Experiments were conducted in two(γ=30°,60°)conical spouted beds with three different types of particles:zirconia(ρp=6050 kg/m^(3)),zirconia toughened alumina(ρp=3700 kg/m^(3))and glass beads(ρp=2460 kg/m^(3)).In order to be able to compare experimental data obtained at different conditions,a 1-D convection-diffusion gas mixing model originally developed by San Joséet al.(1995)was implemented to determine the axial dispersion coefficients.The results show that the axial dispersion coefficients range between m^(2)/s and m^(2)/s,increase with superficial gas velocity and are higher than the corresponding dispersion coefficients of fixed beds,lower than the dispersion coefficients of fluidized beds and in the same range with the cylindrical spouted beds reported in the literature.The corresponding Peclet numbers were in the range of 0.6–7.8 for all operating conditions and slightly higher Peclet numbers were obtained with glass beads indicating the relative importance of gas convective transport over gas dispersion for light particles compared to heavy particles.
基金financially supported by the Natural Science Foundations of China(No.21206153,21376229)the Excellent Youth Science and Technology Foundation of Province Shanxi of China(No.2014021007)+1 种基金the Natural Science Foundation of Shanxi Province(Grant No.2011021012,2012011008-2)the Program for the Outstanding Innovative Teams of Higher Learning Institutions of Shanxi(201316)
文摘Rotating packing bed(RPB) has a better mixing performance than traditional mixers and shows potential application in the petroleum industry. However, acquisition of information about the mixing process directly through experiments is difficult because of the compact structure and complex multiphase flow pattern in RPB. To study the mixing characteristic, Fluent, the computational fluid dynamics(CFD) software, was used to explore the effect of airflow field on droplet diameter. For conducting calculations, the gas-liquid two-phase flow inside the packing was simulated with the RNG k-ε turbulence model and the Lagrange Discrete Phase Model(DPM), respectively. The numerical calculation results showed that coalescence and breakup of droplets can take place in the gas phase flow inside the packing and can be strengthened with increased rotating speed, thereby leading to the enlargement of the average diameter.
基金the National Key Research&Development Program of China(2018YFA0209403)the National Natural Science Foundation of China(U1662108)the Science and Technology Project of Fujian Province(FG-2016002).
文摘Developing catalysts with not only hydrogenation activity but also cracking activity is very important for the advancement of suspended-bed hydrocracking technology.Within this respect,MoS_(2)/SiO_(2)-Al_(2)O_(3)bifunctional catalyst is a kind of typical catalysts with both hydrogenation and cracking activity.Herein,a series of Zr-doped SiO_(2)-Al_(2)O_(3)mixed oxides were synthesized by a sol-gel coupled with hydrothermal method.The synthesized mixed oxides were characterized for chemical structures and acidic properties.It is found that doping SiO_(2)-Al_(2)O_(3)with Zr atoms significantly increases the numbers of acidic sites.The Zr-doped SiO_(2)-Al_(2)O_(3)mixed oxides were then combined with dispersed MoS_(2),which was in-situ produced from oil-soluble Mo precursors,to fabricate a novel kind of bifunctional catalysts for suspended-bed hydrocracking of heavy oils.Owing to the significantly increased numbers of acidic sites in Zr-doped SiO_(2)-Al_(2)O_(3)mixed oxides,corresponding bifunctional catalysts demonstrate much enhanced activity for suspended-bed hydrocracking of heavy oils in relative to MoS_(2)/SiO_(2)-Al_(2)O_(3)bifunctional catalysts.
基金Supported by the National Natural Science Foundation of China(20821004 20325621) Beijing Municipal Commission of Education(JD100100403)
文摘A mixing-precipitation model based on the modified coalescence-redispersion model was presented to describe the flow,mixing,nucleation and growth in a rotating packed bed(RPB) .The model was coupled with population balance,mass balance and crystallization kinetics.It predicted well the influence of coalescence prob-ability,which represents the mixing intensity among droplets,on the particle number density,supersaturation and mean particle size of the produced precipitates.The effects of the radial thickness of packing,liquid flow rate and rotating speed on the product particle size were also investigated.The results indicate that the needed radial length of packing is short for sparingly soluble substance precipitation(about 40-50 mm in this work) ,and the mean parti-cle size of precipitates decreases with the increase of rotating speed and liquid flow rate,respectively.The validity of this model was verified by experiment on BaSO4 precipitation in RPB.