The performance of pearlescent pigment significantly affected by the grain size and the roughness of deposited film. The effect of TiCl_(4) concentration on the initial deposition of TiO_(2) on mica by atmospheric pre...The performance of pearlescent pigment significantly affected by the grain size and the roughness of deposited film. The effect of TiCl_(4) concentration on the initial deposition of TiO_(2) on mica by atmospheric pressure chemical vapor deposition(APCVD) was investigated. The precursor concentration significantly affected the deposition and morphology of TiO_(2) grains assembling the film. The deposition time for fully covering the surface of mica decreased from 120 to 10 s as the TiCl_(4) concentration increased from 0.38%to 2.44%. The grain size increased with the TiCl_(4) concentration. The AFM and TEM analysis demonstrated that the aggregation of TiO_(2) clusters at the initial stage finally result to the agglomeration of fine TiO_(2) grains at high TiCl_(4) concentrations. Following the results, it was suggested that the nucleation density and size was easy to be adjusted when the TiCl_(4) concentration is below 0.90%.展开更多
To break through the thermodynamic limitation that sodium fluosilicate only can be completely decomposed at high temperature,the technology of pre-decomposition under SiF_(4) atmosphere and deep decomposition under ai...To break through the thermodynamic limitation that sodium fluosilicate only can be completely decomposed at high temperature,the technology of pre-decomposition under SiF_(4) atmosphere and deep decomposition under air condition at lower temperature was developed.The hydrolysis reaction of sodium fluosilicate can be effectively restrained when drying under vacuum or low temperature.Thermal decomposition results of sodium fluosilicate indicate that temperature has a very significant effect on its decomposition.The decomposition ratio can reach 79.4%at 600℃ for 1 h,and 99.6% at 700℃ for 1 h under air condition,respectively.Gas velocity and the type of inert gas have no significant effect on its decomposition.Fine particles affect its decomposition performance due to agglomeration,while coarse particles have good thermal decomposition performance without significant differences.The decomposition reaction process in fluidized bed satisfies the classical Avrami Erofe'EV model,with the reaction order of 1.5 and the activation energy of 61.35 kJ·mol^(-1).展开更多
Ultrafine or nano-sized of tungsten carbide(WC)is the key material to prepare ultrafine grained cemented carbides.In this paper,nano-sized WC powders were directly prepared by using industrial nano-needle violet tungs...Ultrafine or nano-sized of tungsten carbide(WC)is the key material to prepare ultrafine grained cemented carbides.In this paper,nano-sized WC powders were directly prepared by using industrial nano-needle violet tungsten oxide(WO2.72)as the raw material,a fluidized bed as the reactor,and CO as the carbonization gas.The relationship between particle sizes and reaction temperatures,residence times,atmospheres has been investigated systematically.In addition,the physical–chemical indexes(such as residual oxygen,total carbon and free carbon)of the products were measured.The results indicated that the particle size of WC increased with the increase of temperature from 800 to 950°C.As the residence time increased,the particle size decreased gradually,and then increased due to slight sintering.The introduction of hydrogen reduced the carbonization rate,and is not beneficial to obtaining nano-sized WC.Products that satisfy the standard were obtained when WO2.72 reacted with CO at 850°C,900°C and 950°C for 3.0 h,2.5 h and 2.0 h,respectively.The particle sizes of the three samples calculated from the specific surface area were 46.4 nm,53.2 nm and 52.1 nm,respectively.展开更多
The deactivation mechanism of Co/MgO catalyst for the reforming of methane with carbon dioxide was investigated. The conversion of CH4 displayed a significant decrease in the initial stage caused by carbon deposition....The deactivation mechanism of Co/MgO catalyst for the reforming of methane with carbon dioxide was investigated. The conversion of CH4 displayed a significant decrease in the initial stage caused by carbon deposition.There were two types of cokes, carbon nanotubes(CNTs) and carbon nano-onions(CNOs). The number of the CNO layers that coated on the surface of Co nanoparticles(NPs) increased rapidly in the initial reforming time,which was responsible for the deactivation of the Co/MgO catalyst. The deposition of CNOs was attributed to the oxidation of Co NPs. Therefore, the deactivation of the Co/MgO catalyst was originated from the first oxidization of the Co NPs into Co3 O4 by O species(OH intermediate, CO_2, H2 O) during the reforming reaction,which accelerates the formation of coke that blocked the active metal, thus led to catalyst deactivation.展开更多
In the present paper, multi-walled carbon nanotubes(MWCNTs) are successfully assembled on graphite felt(GF) using sucrose pyrolysis method for the first time. The in situ formed pyrolytic carbon is chosen as the binde...In the present paper, multi-walled carbon nanotubes(MWCNTs) are successfully assembled on graphite felt(GF) using sucrose pyrolysis method for the first time. The in situ formed pyrolytic carbon is chosen as the binder because it is essentially carbon materials as well as CNTs and GF which has a natural tendency to achieve high bonding strength and low contact resistance. The MWCNTs/GF electrode is demonstrated to increase surface area, reduce polarization, lower charge transfer resistance and improve energy conversion efficiency comparing with GF. This excellent electrochemical performance is mainly ascribed to the high electro-catalytic activity of MWCNTs and increasing surface area.展开更多
In this study, the flow stability of the flat-bottomed hopper was investigated via GPU-based discrete element method(DEM) simulation. With the material height inside the hopper reducing, the fluctuation of the flow ra...In this study, the flow stability of the flat-bottomed hopper was investigated via GPU-based discrete element method(DEM) simulation. With the material height inside the hopper reducing, the fluctuation of the flow rate indicates an unstable discharge. The flow regions of the unstable discharge were compared with that of the stable discharge, a key transformation zone, where the voidage showed the largest difference between unstable and stable discharge, was revealed. To identify the relevance of the key transformation zone and the hopper flow stability, the voidage variation of the key transformation zone with material height reducing was studied.A sharp increase in the voidage in the key transformation zone was considered to be the standard for judging the unstable hopper flow, and the ‘Top–Bottom effect' of the hopper was defined, which indicated the hopper flow was unstable when the hopper only had the top area and the bottom area, because the voidage of particles in the top area and the bottom area were both variables.展开更多
For the magnetized fluidized bed(MFB)with the binary mixture of Geldart-B magnetizable and nonmagnetizable particles,the magnetically induced segregation between these two kinds of particles occurs at high magnetic fi...For the magnetized fluidized bed(MFB)with the binary mixture of Geldart-B magnetizable and nonmagnetizable particles,the magnetically induced segregation between these two kinds of particles occurs at high magnetic field intensities(H),leading to the deterioration of the fluidization quality.The critical intensity(H_(ms))above which such segregation commences varies with the gas velocity(U_g).This work focuses on establishing a segregation model to theoretically derive the H_(ms)–U_g relationship.In a magnetic field,the magnetizable particles form agglomerates.The magnetically induced segregation in essence refers to the size segregation of the binary mixture of agglomerates and nonmagnetizable particles.Consequently,the segregation model was established in two steps:first,the size of agglomerates(d_A)was calculated by the force balance model;then,the H_(ms)–U_g relationship was obtained by substituting the expression of d_Ainto the basic size segregation model for binary mixtures.As per the force balance model,the cohesive and collision forces were 1_2 orders of magnitude greater than the other forces exerted on the agglomerates.Therefore,the balance between these two forces largely determined d_A.The calculated d_A increased with increasing H and decreasing U_g,agreeing qualitatively with the experimental observation.The calculated H_(ms)–U_ g relationship agreed reasonably with the experimental data,indicating that the present segregation model could predict well the segregation behavior in the MFB with the binary mixture.展开更多
The present work focuses on a numerical investigation of the solids residence time distribution(RTD) and the fluidized structure of a multi-compartment fluidized bed, in which the flow pattern is proved to be close to...The present work focuses on a numerical investigation of the solids residence time distribution(RTD) and the fluidized structure of a multi-compartment fluidized bed, in which the flow pattern is proved to be close to plug flow by using computational fluid dynamics(CFD) simulations. With the fluidizing gas velocity or the bed outlet height rising, the solids flow out of bed more quickly with a wider spread of residence time and a larger RTD variance(σ2). It is just the heterogeneous fluidized structure that being more prominent with the bed height increasing induces the widely non-uniform RTD. The division of the individual internal circulation into double ones improves the flow pattern to be close to plug flow.展开更多
The present study investigated the vaporization kinetics of MgCl_2,CaCl_2 and their binary melts in a fluidized bed at1073-1273 K,and developed a vaporization model for the binary melts to explore the possibility of a...The present study investigated the vaporization kinetics of MgCl_2,CaCl_2 and their binary melts in a fluidized bed at1073-1273 K,and developed a vaporization model for the binary melts to explore the possibility of achieving enhanced vaporization rate for the feedstock containing CaO greater than 0.2 wt%.The vaporization rate constant of MgCl_2 is more than seven times than that of CaCl_2 at 1273 K.The vaporization rate of the binary melt was significantly affected by the composition,a small quantity of CaCl_2 can remarkably deteriorate the overall vaporization rate.Experimental results coincide well with the numerical simulation by the vaporization model which regards the evolution of vaporization rate with melts composition.A correlation between the necessary operation temperature and the CaO/(CaO + MgO) of the feedstock was proposed.Predictions reveal that a similar vaporization rate for 0.2 wt%-0.4 wt%CaO content feedstock with 0.2 wt%could be achieved at lower than 1365 K.展开更多
For non-catalytic gas-solid reaction, it is desirable to match the mean residence time(MRT) of particles and complete conversion time(t_c) in a fluidized bed. In this study, the MRT differences(MRT ratios) between the...For non-catalytic gas-solid reaction, it is desirable to match the mean residence time(MRT) of particles and complete conversion time(t_c) in a fluidized bed. In this study, the MRT differences(MRT ratios) between the coarse particles and the fine particles were investigated in a continuous fluidized bed with a side exit by varying the superficial gas velocity, feed composition and particle size ratio. The results show that the MRT ratio increases firstly and then decreases with increasing the gas velocity. By controlling the gas velocity and the feed composition of coarse particles, the MRT ratio can be modulated from 1.8 to 10.5 at the gas velocity of 1.0 m·s^(-1) for the binary mixture with the size ratio of 2.2. The MRT ratio can reach to ~ 12 at the gas velocity of 1.2 m·s^(-1)for the particle size ratio of 3.3. The present study has endeavored to obtain fundamental data for an effective plant operation to meet the need of synchronously complete conversion of particles with different sizes during the film diffusion controlling reaction.展开更多
MXenes have aroused intensive enthusiasm because of their exotic properties and promising applications.However,to date,they are usually synthesized by etching technologies.Developing synthetic technologies provides mo...MXenes have aroused intensive enthusiasm because of their exotic properties and promising applications.However,to date,they are usually synthesized by etching technologies.Developing synthetic technologies provides more opportunities for innovation and may extend unexplored applications.Here,we report a bottom-up gas-phase synthesis of Cl-terminated MXene(Ti_(2)CCl_(2)).The gas-phase synthesis endows Ti_(2)CCl_(2) with unique surface chemistry,high phase purity,and excellent metallic conductivity,which can be used to accelerate polysulfide conversion kinetics and dramatically prolong the cyclability of Li-S batteries.In-depth mechanistic analysis deciphers the origin of the formation of Ti_(2)CCl_(2) and offers a paradigm for tuning MXene chemical vapor deposition.In brief,the gas-phase synthesis transforms the synthesis of MXenes and unlocks the hardly achieved potentials of MXenes.展开更多
In this study,a CFD model coupled with heterogeneous flow structure,mass transfer equations,and chemical reaction kinetics is established to forecast the pyrolusite reduction reaction behavior.Compared with the previo...In this study,a CFD model coupled with heterogeneous flow structure,mass transfer equations,and chemical reaction kinetics is established to forecast the pyrolusite reduction reaction behavior.Compared with the previous studies which ignore the volume change of solids phase,the influence of volume shrinkage on reaction and flow behavior is explored in this research.Volume shrinkage of pyrolusite is proved to be non-negligible in predicting the conversion rate.The negligence of volume shrinkage leads to the overestimation of conversion rate for its inaccurate estimation of surface area for reaction.Besides,the influence of volume shrinkage on the reaction is found smaller in the scaled-up reactor.展开更多
Developing sustainable and powerful heterogeneous catalytic systems to convert sulfides into high-value sulfoxide products has become a particularly appealing field and an arduous challenge.In this work,two porous pol...Developing sustainable and powerful heterogeneous catalytic systems to convert sulfides into high-value sulfoxide products has become a particularly appealing field and an arduous challenge.In this work,two porous polyoxometalate-pillared metal-organic frameworks,formulated as H_(3n)[Cu_(3)(pidc)_(2)(H_(2)O)_(2.5)]_(2)[PW_(12)O_(40)]_n·x H_(2)O (n=1.5,x=6 for 1,n=1,x=12 for 2;and H_(3)pidc=2-(3-pyridinyl)-1H-imidazole-4,5-dicarboxylic acid),were consciously manufacture and employed for heterogeneously catalyzed sulfide-sulfoxide transformation.Structural analysis shows that 1 and 2 exhibit similar porous frameworks with nearly identical two-dimensional metal-organic layers further pillared by tetradentate POM ligands with different coordination modes,which also result in the porosity of 1 being almost twice that of 2.In catalyzing the conversion of methyl phenyl sulfide (MPS) to methyl phenyl sulfoxide (MPSO),1 can convert nearly 100%of MPS into MPSO within 30 min,while 2 achieved the similar results requires 50 min.The higher activity of 1 may be attributed to its larger channel that can provide more active sites and more efficient mass transfer process.Systematic structure-activity analyses and mechanistic studies revealed dual-reaction pathways driven by POM sites and metal sites assisted by the structural microenvironment.展开更多
The effects of superficial gas velocity and mechanical stirring speed on the precise regulation of flow regimes for cohesive SiO2 powders(mean diameter is 16μm)were experimentally investigated in a stirring-assisted ...The effects of superficial gas velocity and mechanical stirring speed on the precise regulation of flow regimes for cohesive SiO2 powders(mean diameter is 16μm)were experimentally investigated in a stirring-assisted fluidized bed.The results showed that compared with the agglomerates formed in the non-assisted fluidization of cohesive SiO2 powders,the introduction of mechanical stirring could effectively reduce the size of agglomerates and well disperse the agglomerates during fluidization.The best regulation range of agglomerate particulate fluidization can be achieved at 600 rpm when agglomerate sizes were reduced to below 200μm.Further investigation based on the operational phase diagram revealed that transformations of flow regimes were dominated by both stirring speed and gas velocity.The stirring applied enlarges the operational range of agglomerate particulate fluidization(APF)with a delayed onset of bubbling for cohesive particles.However,the exorbitant speed increases the collision velocity and contact area between small agglomerates,which results in the formation of unstable agglomerates and the whirlpool of powder.展开更多
The present study investigated the influence of high temperature oxidation and reduction pretreatments on the leaching rate of Panzhihua ilmenite.The as-pretreated ilmenite was leached with 20%HCl at 105℃.The leachin...The present study investigated the influence of high temperature oxidation and reduction pretreatments on the leaching rate of Panzhihua ilmenite.The as-pretreated ilmenite was leached with 20%HCl at 105℃.The leaching process was controlled by the phases and microstructures that evolved during the pretreatment processes.The leaching kinetics of pure hematite,ilmenite and pseudobrookite were characterized to clarify the phase effect on the iron-leaching rate;the rate of iron leaching occurs in the following order in the HCl solution:hematite(ferric iron) > ilmenite(ferrous iron)>>pseudobrookite(ferric iron).Therefore,the often-cited notion that ferrous iron dissolves faster in HCl solutions than ferric iron when explaining the pretreatment effects is inaccurate.Moreover,the oxidation pretreatment(at 600-1000℃ for 4 h)cannot destroy the dense structure of the Panzhihua ilmenite.Therefore,the influence exerted by the oxidation on the leaching process is primarily determined by the phase change;oxidation at 600 and 700℃slightly increased the rate of iron leaching because the ilmenite was transformed into hematite,while the oxidation at 900-1000℃ significantly reduced the rate of iron leaching because a pseudobrookite phase formed.The reduction effect was subsequently investigated;the as-oxidized ilmenite was reduced under H_2 at 750℃ for 30 min.The reduction significantly accelerated the rate of subsequent iron leaching such that nearly all of the iron had dissolved after leaching for 2h in 20%HCl at 105℃.This enhanced iron-leaching rate is mainly attributed to the cracks and holes that formed during the reduction process.展开更多
Ultrafine hematite powder was reduced to produce ultrafine iron powder in a 50%Ar-50%H_2 atmosphere at 450-550℃ in a fluidized bed reactor.The ultrafine hematite powder shows the typical agglomerating fluidization be...Ultrafine hematite powder was reduced to produce ultrafine iron powder in a 50%Ar-50%H_2 atmosphere at 450-550℃ in a fluidized bed reactor.The ultrafine hematite powder shows the typical agglomerating fluidization behavior with large agglomerates fluidized at the bottom of the bed and small agglomerates fluidized at the upper part of the bed.It was found that defluidization occurred even at the low temperature of 450℃ with low metallization rate.Defluidization was attributed mainly to the sintering of the newly formed iron particles.Granuation was employed to improve the fluidization quality and to tackle the defluidization problem,where granules fluidized like a Geldart's group A powder.Granulation was found to effectively reduce defluidization during reduction,without however sacrificing reduction speed.The asreduced iron powders from both the ultrafine and the granulated hematite exhibited excellent sintering activity,that is,fast sintering at temperature of as low as^580σ_(RR)~2),which is much superior as compared to that of nano/ultrafine iron powders made by other processes.展开更多
In this work,a new drag model for TFM simulation in gas-solid bubbling fluidized beds was proposed,and a set of equations was derived to determine the meso-scale structural parameters to calculate the drag characteris...In this work,a new drag model for TFM simulation in gas-solid bubbling fluidized beds was proposed,and a set of equations was derived to determine the meso-scale structural parameters to calculate the drag characteristics of Geldart-B particles under low gas velocities.In the new model,the meso-scale structure was characterized while accounting for the bubble and meso-scale structure effects on the drag coefficient.The Fluent software,incorporating the new drag model,was used to simulate the fluidization behavior.Experiments were performed in a Plexiglas cylindrical fluidized bed consisting of quartz sand as the solid phase and ambient air as the gas phase.Comparisons based on the solids hold-up inside the fluidized bed at different superficial gas velocities,were made between the 2D Cartesian simulations,and the experimental data,showing that the results of the new drag model reached much better agreement with experimental data than those of the Gidaspow drag model did.展开更多
A novel two-stage reduction process for synthesis of ultrafine nickel powder with a high purity and low density in a fluidized bed reactor has been developed in this work.The raw ultrafine NiO particles are first pre-...A novel two-stage reduction process for synthesis of ultrafine nickel powder with a high purity and low density in a fluidized bed reactor has been developed in this work.The raw ultrafine NiO particles are first pre-reduced using hydrogen at lower temperatures(340-400 ℃),followed by further reduction at higher temperatures(500-600 ℃).The self-agglomeration of Ni particles formed during low-temperature reduction decreases the sintering activity of the newly formed ultrafine Ni particles,leading to good fluidization quality,even for the subsequent high-temperature reduction process.The agglomerated Ni particles have a high Ni content(above 99wt%),a low density(0.78 g/cm^3) and a uniform particle size(approximately 100μm).A concept design for a novel two-stage fluidized bed reactor process used to produce high-purity Ni powder was also proposed.This approach may be extended to the synthesis of other ultrafine/nanosized metals or metal oxides through a fluidization method.展开更多
基金the support from National Natural Science Foundation of China (22208355, 22178363 and 21978300)the financial support and mica samples from Changzi Wu and RIKA technology CO., LTD.
文摘The performance of pearlescent pigment significantly affected by the grain size and the roughness of deposited film. The effect of TiCl_(4) concentration on the initial deposition of TiO_(2) on mica by atmospheric pressure chemical vapor deposition(APCVD) was investigated. The precursor concentration significantly affected the deposition and morphology of TiO_(2) grains assembling the film. The deposition time for fully covering the surface of mica decreased from 120 to 10 s as the TiCl_(4) concentration increased from 0.38%to 2.44%. The grain size increased with the TiCl_(4) concentration. The AFM and TEM analysis demonstrated that the aggregation of TiO_(2) clusters at the initial stage finally result to the agglomeration of fine TiO_(2) grains at high TiCl_(4) concentrations. Following the results, it was suggested that the nucleation density and size was easy to be adjusted when the TiCl_(4) concentration is below 0.90%.
基金financial support from the National Natural Science Foundation of China (22078326,21878305,22078342)the financial supports of the National Key Research and Development Project of China (2020YFC1909701)。
文摘To break through the thermodynamic limitation that sodium fluosilicate only can be completely decomposed at high temperature,the technology of pre-decomposition under SiF_(4) atmosphere and deep decomposition under air condition at lower temperature was developed.The hydrolysis reaction of sodium fluosilicate can be effectively restrained when drying under vacuum or low temperature.Thermal decomposition results of sodium fluosilicate indicate that temperature has a very significant effect on its decomposition.The decomposition ratio can reach 79.4%at 600℃ for 1 h,and 99.6% at 700℃ for 1 h under air condition,respectively.Gas velocity and the type of inert gas have no significant effect on its decomposition.Fine particles affect its decomposition performance due to agglomeration,while coarse particles have good thermal decomposition performance without significant differences.The decomposition reaction process in fluidized bed satisfies the classical Avrami Erofe'EV model,with the reaction order of 1.5 and the activation energy of 61.35 kJ·mol^(-1).
基金the financial support from the National Natural Science Foundation of China(Grant No.21878305)。
文摘Ultrafine or nano-sized of tungsten carbide(WC)is the key material to prepare ultrafine grained cemented carbides.In this paper,nano-sized WC powders were directly prepared by using industrial nano-needle violet tungsten oxide(WO2.72)as the raw material,a fluidized bed as the reactor,and CO as the carbonization gas.The relationship between particle sizes and reaction temperatures,residence times,atmospheres has been investigated systematically.In addition,the physical–chemical indexes(such as residual oxygen,total carbon and free carbon)of the products were measured.The results indicated that the particle size of WC increased with the increase of temperature from 800 to 950°C.As the residence time increased,the particle size decreased gradually,and then increased due to slight sintering.The introduction of hydrogen reduced the carbonization rate,and is not beneficial to obtaining nano-sized WC.Products that satisfy the standard were obtained when WO2.72 reacted with CO at 850°C,900°C and 950°C for 3.0 h,2.5 h and 2.0 h,respectively.The particle sizes of the three samples calculated from the specific surface area were 46.4 nm,53.2 nm and 52.1 nm,respectively.
基金Supported by the National Natural Science Foundation of China(21736010,U1462128,91334108)the State Key Development Program for Basic Research of China(2015CB251402)
文摘The deactivation mechanism of Co/MgO catalyst for the reforming of methane with carbon dioxide was investigated. The conversion of CH4 displayed a significant decrease in the initial stage caused by carbon deposition.There were two types of cokes, carbon nanotubes(CNTs) and carbon nano-onions(CNOs). The number of the CNO layers that coated on the surface of Co nanoparticles(NPs) increased rapidly in the initial reforming time,which was responsible for the deactivation of the Co/MgO catalyst. The deposition of CNOs was attributed to the oxidation of Co NPs. Therefore, the deactivation of the Co/MgO catalyst was originated from the first oxidization of the Co NPs into Co3 O4 by O species(OH intermediate, CO_2, H2 O) during the reforming reaction,which accelerates the formation of coke that blocked the active metal, thus led to catalyst deactivation.
基金financial support of the National Natural Science Foundation of China (project no. 51504231, 51504232, 51774262 and 21325628)Open Project of State Key Laboratory of Complex Nonferrous Metal Resources Clean Utilization (project no. CNMRCUKF1704)
文摘In the present paper, multi-walled carbon nanotubes(MWCNTs) are successfully assembled on graphite felt(GF) using sucrose pyrolysis method for the first time. The in situ formed pyrolytic carbon is chosen as the binder because it is essentially carbon materials as well as CNTs and GF which has a natural tendency to achieve high bonding strength and low contact resistance. The MWCNTs/GF electrode is demonstrated to increase surface area, reduce polarization, lower charge transfer resistance and improve energy conversion efficiency comparing with GF. This excellent electrochemical performance is mainly ascribed to the high electro-catalytic activity of MWCNTs and increasing surface area.
基金Supported by the State Key Development Program for Basic Research of China(2015CB251402)the National Natural Science Foundation of China(21325628,91334108)the Mole-8.5 Supercomputing System developed by Institute of Process Engineering,Chinese Academy of Sciences
文摘In this study, the flow stability of the flat-bottomed hopper was investigated via GPU-based discrete element method(DEM) simulation. With the material height inside the hopper reducing, the fluctuation of the flow rate indicates an unstable discharge. The flow regions of the unstable discharge were compared with that of the stable discharge, a key transformation zone, where the voidage showed the largest difference between unstable and stable discharge, was revealed. To identify the relevance of the key transformation zone and the hopper flow stability, the voidage variation of the key transformation zone with material height reducing was studied.A sharp increase in the voidage in the key transformation zone was considered to be the standard for judging the unstable hopper flow, and the ‘Top–Bottom effect' of the hopper was defined, which indicated the hopper flow was unstable when the hopper only had the top area and the bottom area, because the voidage of particles in the top area and the bottom area were both variables.
基金Supported by the National Natural Science Foundation of China(21325628)the Major Research Plan of the National Natural Science Foundation of China(91334108)the Scientific Instrument Developing Project of the Chinese Academy of Sciences(YZ201641)
文摘For the magnetized fluidized bed(MFB)with the binary mixture of Geldart-B magnetizable and nonmagnetizable particles,the magnetically induced segregation between these two kinds of particles occurs at high magnetic field intensities(H),leading to the deterioration of the fluidization quality.The critical intensity(H_(ms))above which such segregation commences varies with the gas velocity(U_g).This work focuses on establishing a segregation model to theoretically derive the H_(ms)–U_g relationship.In a magnetic field,the magnetizable particles form agglomerates.The magnetically induced segregation in essence refers to the size segregation of the binary mixture of agglomerates and nonmagnetizable particles.Consequently,the segregation model was established in two steps:first,the size of agglomerates(d_A)was calculated by the force balance model;then,the H_(ms)–U_g relationship was obtained by substituting the expression of d_Ainto the basic size segregation model for binary mixtures.As per the force balance model,the cohesive and collision forces were 1_2 orders of magnitude greater than the other forces exerted on the agglomerates.Therefore,the balance between these two forces largely determined d_A.The calculated d_A increased with increasing H and decreasing U_g,agreeing qualitatively with the experimental observation.The calculated H_(ms)–U_ g relationship agreed reasonably with the experimental data,indicating that the present segregation model could predict well the segregation behavior in the MFB with the binary mixture.
基金Supported by the National Natural Science Foundation of China(21406237 and 21325628)the State Key Development Program for Basic Research of China(2015CB251402)
文摘The present work focuses on a numerical investigation of the solids residence time distribution(RTD) and the fluidized structure of a multi-compartment fluidized bed, in which the flow pattern is proved to be close to plug flow by using computational fluid dynamics(CFD) simulations. With the fluidizing gas velocity or the bed outlet height rising, the solids flow out of bed more quickly with a wider spread of residence time and a larger RTD variance(σ2). It is just the heterogeneous fluidized structure that being more prominent with the bed height increasing induces the widely non-uniform RTD. The division of the individual internal circulation into double ones improves the flow pattern to be close to plug flow.
基金Supported by the National Natural Science Foundation of China(NSFC)Distinguished Young Scholar project(No.21325628)
文摘The present study investigated the vaporization kinetics of MgCl_2,CaCl_2 and their binary melts in a fluidized bed at1073-1273 K,and developed a vaporization model for the binary melts to explore the possibility of achieving enhanced vaporization rate for the feedstock containing CaO greater than 0.2 wt%.The vaporization rate constant of MgCl_2 is more than seven times than that of CaCl_2 at 1273 K.The vaporization rate of the binary melt was significantly affected by the composition,a small quantity of CaCl_2 can remarkably deteriorate the overall vaporization rate.Experimental results coincide well with the numerical simulation by the vaporization model which regards the evolution of vaporization rate with melts composition.A correlation between the necessary operation temperature and the CaO/(CaO + MgO) of the feedstock was proposed.Predictions reveal that a similar vaporization rate for 0.2 wt%-0.4 wt%CaO content feedstock with 0.2 wt%could be achieved at lower than 1365 K.
基金Supported by the China National Funds for Distinguished Young Scientists(21325628)National Natural Science Foundation of China(91334108)the State Key Laboratory of Multiphase Complex Systems,Institute of Process Engineering,Chinese Academy of Sciences(MPCS-2012-A-02 and MPCS-2014-A-03)
文摘For non-catalytic gas-solid reaction, it is desirable to match the mean residence time(MRT) of particles and complete conversion time(t_c) in a fluidized bed. In this study, the MRT differences(MRT ratios) between the coarse particles and the fine particles were investigated in a continuous fluidized bed with a side exit by varying the superficial gas velocity, feed composition and particle size ratio. The results show that the MRT ratio increases firstly and then decreases with increasing the gas velocity. By controlling the gas velocity and the feed composition of coarse particles, the MRT ratio can be modulated from 1.8 to 10.5 at the gas velocity of 1.0 m·s^(-1) for the binary mixture with the size ratio of 2.2. The MRT ratio can reach to ~ 12 at the gas velocity of 1.2 m·s^(-1)for the particle size ratio of 3.3. The present study has endeavored to obtain fundamental data for an effective plant operation to meet the need of synchronously complete conversion of particles with different sizes during the film diffusion controlling reaction.
基金This work was supported by Basic Frontier Scientific Research of the Chinese Academy of Sciences(ZDBS-LY-JSC041)the National Natural Science Foundation of China(22178348)+1 种基金the open research fund of the State Key Laboratory of Mesoscience and Engineering(MESO-23-D06)the Youth Innovation Promotion Association CAS(292021000085).We also thank Wenchang Wang at Shimadzu(China)for help with the XPS analysis.
文摘MXenes have aroused intensive enthusiasm because of their exotic properties and promising applications.However,to date,they are usually synthesized by etching technologies.Developing synthetic technologies provides more opportunities for innovation and may extend unexplored applications.Here,we report a bottom-up gas-phase synthesis of Cl-terminated MXene(Ti_(2)CCl_(2)).The gas-phase synthesis endows Ti_(2)CCl_(2) with unique surface chemistry,high phase purity,and excellent metallic conductivity,which can be used to accelerate polysulfide conversion kinetics and dramatically prolong the cyclability of Li-S batteries.In-depth mechanistic analysis deciphers the origin of the formation of Ti_(2)CCl_(2) and offers a paradigm for tuning MXene chemical vapor deposition.In brief,the gas-phase synthesis transforms the synthesis of MXenes and unlocks the hardly achieved potentials of MXenes.
基金grateful to the National Natural Science Foundation of China(grant No.21878304 and 21736010)the Strategic Priority Research Program of the Chinese Academy of Sciences(grant No.XDA29040200)the Science Fund for Creative Research Groups of the National Natural Science Foundation of China(grant No.21921005).
文摘In this study,a CFD model coupled with heterogeneous flow structure,mass transfer equations,and chemical reaction kinetics is established to forecast the pyrolusite reduction reaction behavior.Compared with the previous studies which ignore the volume change of solids phase,the influence of volume shrinkage on reaction and flow behavior is explored in this research.Volume shrinkage of pyrolusite is proved to be non-negligible in predicting the conversion rate.The negligence of volume shrinkage leads to the overestimation of conversion rate for its inaccurate estimation of surface area for reaction.Besides,the influence of volume shrinkage on the reaction is found smaller in the scaled-up reactor.
基金financially supported by the National Natural Science Foundation of China (Nos. 21371027, 20901013)Natural Science Foundation of Liaoning Province (No. 2015020232)Fundamental Research Funds for the Central Universities (Nos. DUT19LK01, DUT15LN18)。
文摘Developing sustainable and powerful heterogeneous catalytic systems to convert sulfides into high-value sulfoxide products has become a particularly appealing field and an arduous challenge.In this work,two porous polyoxometalate-pillared metal-organic frameworks,formulated as H_(3n)[Cu_(3)(pidc)_(2)(H_(2)O)_(2.5)]_(2)[PW_(12)O_(40)]_n·x H_(2)O (n=1.5,x=6 for 1,n=1,x=12 for 2;and H_(3)pidc=2-(3-pyridinyl)-1H-imidazole-4,5-dicarboxylic acid),were consciously manufacture and employed for heterogeneously catalyzed sulfide-sulfoxide transformation.Structural analysis shows that 1 and 2 exhibit similar porous frameworks with nearly identical two-dimensional metal-organic layers further pillared by tetradentate POM ligands with different coordination modes,which also result in the porosity of 1 being almost twice that of 2.In catalyzing the conversion of methyl phenyl sulfide (MPS) to methyl phenyl sulfoxide (MPSO),1 can convert nearly 100%of MPS into MPSO within 30 min,while 2 achieved the similar results requires 50 min.The higher activity of 1 may be attributed to its larger channel that can provide more active sites and more efficient mass transfer process.Systematic structure-activity analyses and mechanistic studies revealed dual-reaction pathways driven by POM sites and metal sites assisted by the structural microenvironment.
基金The authors are grateful to the support by the National Natural Science Foundation of China(Grant Nos.21908227,21736010 and 22178363).
文摘The effects of superficial gas velocity and mechanical stirring speed on the precise regulation of flow regimes for cohesive SiO2 powders(mean diameter is 16μm)were experimentally investigated in a stirring-assisted fluidized bed.The results showed that compared with the agglomerates formed in the non-assisted fluidization of cohesive SiO2 powders,the introduction of mechanical stirring could effectively reduce the size of agglomerates and well disperse the agglomerates during fluidization.The best regulation range of agglomerate particulate fluidization can be achieved at 600 rpm when agglomerate sizes were reduced to below 200μm.Further investigation based on the operational phase diagram revealed that transformations of flow regimes were dominated by both stirring speed and gas velocity.The stirring applied enlarges the operational range of agglomerate particulate fluidization(APF)with a delayed onset of bubbling for cohesive particles.However,the exorbitant speed increases the collision velocity and contact area between small agglomerates,which results in the formation of unstable agglomerates and the whirlpool of powder.
基金financial support from the National Basic Research Program of China(grant No. 2013CB632603)the Chinese Academy of Sciences(project No.KGCX2-EW215)
文摘The present study investigated the influence of high temperature oxidation and reduction pretreatments on the leaching rate of Panzhihua ilmenite.The as-pretreated ilmenite was leached with 20%HCl at 105℃.The leaching process was controlled by the phases and microstructures that evolved during the pretreatment processes.The leaching kinetics of pure hematite,ilmenite and pseudobrookite were characterized to clarify the phase effect on the iron-leaching rate;the rate of iron leaching occurs in the following order in the HCl solution:hematite(ferric iron) > ilmenite(ferrous iron)>>pseudobrookite(ferric iron).Therefore,the often-cited notion that ferrous iron dissolves faster in HCl solutions than ferric iron when explaining the pretreatment effects is inaccurate.Moreover,the oxidation pretreatment(at 600-1000℃ for 4 h)cannot destroy the dense structure of the Panzhihua ilmenite.Therefore,the influence exerted by the oxidation on the leaching process is primarily determined by the phase change;oxidation at 600 and 700℃slightly increased the rate of iron leaching because the ilmenite was transformed into hematite,while the oxidation at 900-1000℃ significantly reduced the rate of iron leaching because a pseudobrookite phase formed.The reduction effect was subsequently investigated;the as-oxidized ilmenite was reduced under H_2 at 750℃ for 30 min.The reduction significantly accelerated the rate of subsequent iron leaching such that nearly all of the iron had dissolved after leaching for 2h in 20%HCl at 105℃.This enhanced iron-leaching rate is mainly attributed to the cracks and holes that formed during the reduction process.
基金the financial supports from National Science and Technology Support Program of the Ministry of Science and Technology(MOST),China(Grant No.2012BAB14B03)National Scientific Instrument Development Program of MOST,China(Grant No.2011YQ12003908)
文摘Ultrafine hematite powder was reduced to produce ultrafine iron powder in a 50%Ar-50%H_2 atmosphere at 450-550℃ in a fluidized bed reactor.The ultrafine hematite powder shows the typical agglomerating fluidization behavior with large agglomerates fluidized at the bottom of the bed and small agglomerates fluidized at the upper part of the bed.It was found that defluidization occurred even at the low temperature of 450℃ with low metallization rate.Defluidization was attributed mainly to the sintering of the newly formed iron particles.Granuation was employed to improve the fluidization quality and to tackle the defluidization problem,where granules fluidized like a Geldart's group A powder.Granulation was found to effectively reduce defluidization during reduction,without however sacrificing reduction speed.The asreduced iron powders from both the ultrafine and the granulated hematite exhibited excellent sintering activity,that is,fast sintering at temperature of as low as^580σ_(RR)~2),which is much superior as compared to that of nano/ultrafine iron powders made by other processes.
基金supports from the State Key Development Program for Basic Research of China(973 Program)under Grant Nos.2009CB219904,2013CB632603the National Science and Technology Support Program of Ministry of Science and Technology of the People's Republic of China(Grant No. 2012BAB14B03)
文摘In this work,a new drag model for TFM simulation in gas-solid bubbling fluidized beds was proposed,and a set of equations was derived to determine the meso-scale structural parameters to calculate the drag characteristics of Geldart-B particles under low gas velocities.In the new model,the meso-scale structure was characterized while accounting for the bubble and meso-scale structure effects on the drag coefficient.The Fluent software,incorporating the new drag model,was used to simulate the fluidization behavior.Experiments were performed in a Plexiglas cylindrical fluidized bed consisting of quartz sand as the solid phase and ambient air as the gas phase.Comparisons based on the solids hold-up inside the fluidized bed at different superficial gas velocities,were made between the 2D Cartesian simulations,and the experimental data,showing that the results of the new drag model reached much better agreement with experimental data than those of the Gidaspow drag model did.
基金the National Special Project for Development of Major Scientific Equipment(2011YQ12003908)the China National Funds for Distinguished Young Scientists(21325628) for their financial support
文摘A novel two-stage reduction process for synthesis of ultrafine nickel powder with a high purity and low density in a fluidized bed reactor has been developed in this work.The raw ultrafine NiO particles are first pre-reduced using hydrogen at lower temperatures(340-400 ℃),followed by further reduction at higher temperatures(500-600 ℃).The self-agglomeration of Ni particles formed during low-temperature reduction decreases the sintering activity of the newly formed ultrafine Ni particles,leading to good fluidization quality,even for the subsequent high-temperature reduction process.The agglomerated Ni particles have a high Ni content(above 99wt%),a low density(0.78 g/cm^3) and a uniform particle size(approximately 100μm).A concept design for a novel two-stage fluidized bed reactor process used to produce high-purity Ni powder was also proposed.This approach may be extended to the synthesis of other ultrafine/nanosized metals or metal oxides through a fluidization method.
