Bed Of Inert Particles Research Articles

High efficiency disperse dryer - an innovative process for drying of solutions, suspensions and pastes in a fluidized bed of inert particles

In this paper, an innovative fluidized bed dryer with inert particles is presented. The system can be used for drying of solutions, suspensions and pastes in order to obtain a powdered product. The experiments were performed in a pilot-scale dryer with a cylindrical column 0.215 m in diameter and 1.2 mm height, with glass spheres as inert particles. The material used for drying was CuSO4 solution. The effects of operating conditions on the dryer throughput and product quality were investigated. Main performance criteria, i.e. specific water evaporation rate, specific heat consumption and specific air consumption, were quantified. Nearly isothermal conditions were found due to thorough mixing of the particles. The energy efficiency of the dryer was also assessed. Simple heat and mass balances predicted the dryer performance quite well.

Combustion in vortex chambers with a fluidized particle bed

This paper is devoted to methods of estimating the combustion regimes of gaseous fuel in vortex chambers of various designs in the presence of a bed of inert particles in the chamber, which rotate with the gas flow. A simple geometric criterion for determining the possibility of fuel combustion in the particle bed without the formation of a flame above the bed is proposed.

Характер кипящего слоя инерта вблизи газораспределительной решетки

Характер кипящего слоя инерта вблизи газораспределительной решетки

Liquid-Solid Coupling Characteristics in the Fluidized Bed Evaporator for Tobacco Refined Liquid

Consider a two-phase liquid-solid coupling effect, using Euler - Euler two-fluid model is solved using standard viscous term with k-ε model and the velocity pressure coupling a simple algorithm to simulate liquid-solid two-phase flow characteristics of the fluid flow method bed, the applicability of the model to assess the drag. Different effects of a two-stage flow characteristics of fluidized bed flow characteristics, fluid and operating conditions affect the physical properties of the paper. We found from the simulation is the use of different drag coefficient models will greatly affect the results, which drag force model Syamlal - O'Brien is more suited to study the coupling characteristics of liquid flow in a fluidized bed of solid than Gidaspow. And velocity of the inert particles increase with the viscosity of the liquid increase. Further, the maximum speed of the inert particles in a fluidized bed by a central, which means the settling velocity in the fluidized bed of inert particles is the slowest; increasing liquid density and lead to increased speed of the inert particles; volume of the inert particles Score changes can also affect the speed of the particle velocity distribution, and there is no linear relationship.

Mass Transfer around a Sphere Buried in a Packed Bed

The transport phenomenon of mass transfers between a moving fluid and a reacting sphere buried in a packed bed, with “uniform velocity”, was analysed numerically, for solute transport by both advection and diffusion to obtain the concentration field and, from it, the dimensionless concentration boundary layer thickness, , for , and . The bed of inert particles is taken to have uniform voidage. For this purpose, numerical solutions of the partial differential equations describing mass concentration of the solute were undertaken to obtain the concentration boundary layer thickness as a function of the relevant parameters. Finally, mathematical expressions that relate the dependence with the Peclet number and inert particle diameter are proposed to describe the approximate size of the concentration boundary layer thickness.

Particle-fluid mass transfer in multiparticle systems at low Reynolds numbers

The problem of mass transfer between active solid particles and a fluid in multiparticle systems is examined with a focus on the stagnant and the low Reynolds number cases. This problem has attracted significant attention with regard to operation of fixed and fluidized beds. It is recognized that different Sherwood numbers can be defined depending on the choice of the reference concentration difference (driving force). An effective Sh has often been used to analyze experimental data based on an overall concentration difference across the bed. A local Sh can also be introduced based on a concentration difference close to the active particle. However, the use of these two different Sherwood numbers implies a different implementation of the mass balance equations.The mass balance equations are here analytically solved both under stagnant and non-stagnant conditions in a multiparticle system under suitable simplifying assumptions. Equations for the effective and local Sherwood numbers are derived for the general case and for the asymptotic limits. Allowance is given for the variation of bed voidage and volume fraction of active particles in the bed. It is shown that the local Sh only depends on geometrical and fluid-dynamics considerations and accordingly has a general validity. On the contrary, the effective Sh also depends on the assumptions made in deriving the mass balance equations across the bed (e.g., fluid plug flow). The use of the local Sh is therefore suggested.Results show that for Re→0 the limiting value of the local Sh is always a finite number, while the effective Sh tends to zero linearly with Re. It is shown that this result is simply a consequence of the plug flow assumption made in the bed mass balance. The general expressions derived here compare very well to experimental trends for the cases of large Reynolds numbers and of few isolated active spheres immersed in a bed of inert particles, where most of the reported experimental data gather. Unfortunately, for the most controversial case of very low Re in beds made entirely of active particles no reliable data appears to be available to check the accuracy of the expressions.

Interaction between Fe-based oxygen carriers and n-heptane during chemical looping combustion

Chemical looping combustion (CLC) uses a metal oxide (the oxygen carrier) to provide oxygen for the combustion of a fuel and gives an inherent separation of pure CO2 with minimal energy penalty. In solid-fuel CLC, volatile matter will interact with oxygen carriers. Here, the interaction between iron-based oxygen carriers and a volatile hydrocarbon (n-heptane) was investigated in both a laboratory-scale fluidised bed and a thermogravimetric analyser (TGA). Experiments were undertaken to characterise the thermal decomposition of the n-heptane occurring in the presence and in the absence of the oxygen carrier. In a bed of inert particles, carbon deposition increased with temperature and acetylene appeared as a possible precursor. For a bed of carrier consisting of pure Fe2O3, carbon deposition occurred once the Fe2O3 was fully reduced to Fe. When the Fe2O3 was doped with 10mol% Al2O3 (Fe90Al), deposition started when the carrier was reduced to a mixture of Fe and FeAl2O4, the latter being very unreactive. Furthermore, when pure Fe2O3 was fully reduced to Fe, agglomeration of the fluidised bed occurred. However, Fe90Al did not give agglomeration even after extended reduction. The results suggest that Fe90Al is promising for the CLC of solid fuels.

Behavior of Pieces of Plastic Sheet in Solid‐Liquid Fluidized Bed with Stirring

AbstractA solid‐liquid fluidized bed of inert particles can be used to separate pure objects from a mixture. Pieces of plastic sheet were selected as the objects to be separated. To estimate the separation characteristics, the behavior of pieces of plastic sheet in the bed was examined experimentally. Slow stirring was used to improve the fluidization state of the bed. The object size and the volume ratio of objects to inert particles were varied. The use of stirring of the bed was effective in improving the fluidization state of the bed, and the objects, which sank in the bed without stirring, moved from the bottom to the upper portion of the bed at a certain liquid velocity. This liquid velocity increases with decreasing object size, and it also increases as the volume ratio of objects to inert particles in the bed increases. When the volume ratio of objects to inert particles is too high, the objects are distributed throughout the entire bed, regardless of the liquid velocity.

Numerical Analysis of Drying Characteristics of Wet Material Immersed in Fluidized Bed of Inert Particles

The drying characteristics of a relatively large wet material immersed in a fluidized bed of inert particles were examined theoretically. Calculations of heat transfer and evaporation of water on the material surface were included in a discrete element method–computational fluid dynamics (DEM-CFD) simulation. Only the preheating and constant drying rate periods were considered in the simulation. Our simulation made it possible to calculate the relation between the behavior of the fluidizing particles and the drying characteristics. The drying rate increased with an increase in the number of fluidizing particles in contact with the material and the number of fluidizing particles changed with time; that is, the drying rate fluctuated. When the drying rate increased, the fluid temperature decreased and the vapor content of the fluid increased around the material; that is, the temperature and vapor content of the fluid were associated with the behavior of the fluidizing particles.

Prediction of the Behavior of a Liquid‐Fluidized Bed of Inert Particles Used for Separation by Density

AbstractA liquid‐fluidized bed of inert particles was used to separate a pure object from a mixture. One (binary solid‐liquid‐fluidized bed) or two (tertiary solid‐liquid‐fluidized bed) types of objects with relatively large‐sized particles were immersed in an inert‐particle bed, and the bed behavior was observed for different liquid velocities. The void fraction and apparent density of the inert‐particle suspension were predicted by considering the effect of the change in object position for different liquid velocities. The prediction method, which considers the change in the minimum fluidization velocity, accurately expressed the changes in the void fraction and the apparent density of the bed with the position of the objects in the bed. Using this method, the liquid velocity required to separate a certain kind of object from a mixture can be predicted.

Residence time distribution in spouted bed drying of maltodextrin solutions on a bed of inert particles

AbstractResidence time distributions (RTD) for aqueous maltodextrin solutions were determined in two kinds of spouted bed dryers: (1) conventional spouted bed (CSB) 0.305 m diameter with a bed of polypropylene beads and (2) spout‐fluid bed 0.143 m diameter with draft tube submerged in a bed of FEP® pellets (S‐FBDT). RTD, mean residence time tm, and spread of the distribution σ2, were determined at different drying temperatures, spouting velocities, bed depths, spraying pressures, and feed concentrations. Average values of tm and σ2 were 6.5 min and 26.6 min2 for the CSB and 6.9 min and 36 min2 for the S‐FBDT, respectively, for all operating conditions except spraying pressure. RTD curves were well represented by the response of an ideal stirred tank with a superimposed bypass of 15% on average for the CSB and 7% on average for the S‐FBDT dryer for all operating conditions. Increase in spraying pressure produced a reduction of tm and an increase in the bypass fraction of the product in both dryers. © 2011 Canadian Society for Chemical Engineering

Effect of Volume Fraction of Material on Separation by Density Difference in a Liquid‐Fluidized Bed of Inert Particles

AbstractA liquid‐fluidized bed was used to separate a pure material from a mixture. A quantity of relatively large sized material was immersed in an inert‐particle fluidized bed and the behavior of materials was examined for different liquid velocities. In particular, the volume fraction of the material was varied and its effect on the separation characteristics was examined.The material floats on the inert‐particle fluidized bed when the density of the material is lower than the apparent density of the bed, regardless of the volume fraction of the material. The apparent density of the bed can be adjusted by changing the liquid velocity. The materials in the upper portion of the bed affect the properties of the bed below them, i.e., the void fraction decreases and the apparent density increases in the inert‐particle suspension when materials are present in the upper portion of the bed. Therefore, the materials float on the bed although the apparent density of the inert‐particle suspension obtained from the case without material is less than the density of the material at a relatively high volume fraction of material. This phenomenon occurs more easily for lighter and smaller materials. This means that small inert particles and low liquid velocities are the optimum operating conditions for the separation.

Analysis of the Influence of Dimensionless Vibration Number on the Drying of Pastes in Vibrofluidized Beds

The purpose of this work is to evaluate the operation of a vibrofluidized bed of inert particles in the transient and steady-state regimes for water evaporation and for drying of domestic sewage sludge. The feeding rate was initially set on 10 mL/min and this value has been gradually raised at 4 mL/min increments until saturated moist conditions were obtained at the bed exit. The bed was operated at 80 and 100°C, with inlet air velocities 20 and 40% above the minimum fluidization velocity. The dimensionless vibration numbers (Γ) were 0.00 and 4.00, the latter one with amplitudes of 0.003 and 0.015 m. For the conditions investigated, the effect of Γ on the drying dynamics was observed to depend on the amplitude and frequency of vibration. The use of vibration with lower amplitude and higher frequency provided the highest powder production. For paste feeding rates from 14 to 38 mL/min, the moisture content of the dried sewage sludge powder varied from around 5 to 10% on a wet basis, tending to increase with the increase of paste feeding rates.

Boundary layer thickness of cylinders and plane surfaces immersed in packed beds in alignment with the flow

In this work, boundary layer development was investigated for a mass transfer process between a moving fluid and a slightly soluble cylinder or plane surface buried in a packed bed, in alignment with the direction of flow. The bed of inert particles is taken to have uniform voidage. For this purpose, numerical solutions of the partial differential equations describing mass concentration of the solute were undertaken to obtain the concentration boundary layer thickness as a function of the relevant parameters. Mathematical expressions that relate the dependence with the Peclet number and aspect ratio of the immersed active surfaces are proposed to describe the approximate size of the concentration boundary layer thickness.

Correlation of mass transfer in the fluidized bed of inert particles

It has been shown that within a broad interval of the rates of the electrolyte flow in a fluidized bed of inert particles the mass transfer rate of electroreduction of ions of nonferrous metals varies insignificantly. Based on the constancy of the flow rate of the electrolyte in the bulk of the fluidized bed of inert particles we have proposed a simple correlation of mass transfer for conditions of uniform liquefaction. Correctness of the mass transfer equations with the account of accepted assumptions has been confirmed by the calculations of diffusion coefficients from the experimental data on the proposed correlation.

Concentration distribution in the wake of a sphere buried in a granular bed through which fluid flows

The concentration distribution in the wake of a soluble sphere immersed in a granular bed of inert particles, through which fluid flows with “uniform velocity”, has been obtained numerically, for solute transport by both advection and diffusion/dispersion. Fluid flow in the granular bed around the sphere was assumed to follow Darcy’s law and, at each point, dispersion of solute was considered in both the cross-stream and streamwise directions. The elliptic PDE equation, resulting from a differential material balance on the solute, was solved numerically over a wide range of values of the relevant parameters (Peclet number and Schmidt number). The solution gives the concentration contour plots and, for each concentration level, the width and downstream length of the corresponding contour surface were determined. General expressions are presented to predict contaminant “plume” size downstream of the polluting source.

Spouted Beds of Inert Particles for Drying Suspension

ABSTRACT A brief review of Brazilian research on drying process in spouted beds shows its relevance and evolution trends. Needs for applying this technique to dry pasty materials are discussed, focusing on a new model approach in order to overcome operational problems with particle agglomeration and with thermal efficiency. Based on this approach, two cases, drying of black liquor in a conical spouted bed of inert polypropylene particles under intermittent operation and drying of egg emulsion in a conical spouted bed of inert glass beads under continuous operation, are presented and analyzed.

Mathematical modeling of biowall reactors for in-situ groundwater treatment

In this paper we develop a comprehensive model for the remediation of contaminated groundwater in a passive, in-ground reactor, generally known as a biowall. The model is based on our understanding of the component transport and biokinetic processes that occur as water passes through a bed of inert particles on which a biofilm containing active microbial degraders, typically aerobic bacteria, is developing. We give a detailed derivation of the model based on accepted engineering formulations that account for the mass transport of the contaminant (substrate) to the surface of the biofilm, its diffusion into the biofilm to the proximity of a microbe, and its subsequent destruction within that degrader. The model has been solved numerically and incorporated in a robust computer code. Based on representative input values, the results of varying key parameters in the model are presented. The relation between biofilm growth and biowall performance is explored, revealing that the amount of biomass and its distribution within the biowall are key parameters affecting contaminant removal.

Mass transfer from cylinders and plane surfaces buried in packed beds in alignment with the flow direction

The present work describes the mass transfer process between a moving fluid and a slightly soluble cylinder buried in a packed bed, in alignment with the direction of flow. The bed of inert particles is taken to have uniform voidage. Numerical solution of the partial differential equation (PDE) describing mass conservation of the solute gave the concentration field near the soluble surface and the mass transfer flux was integrated to give values of the Sherwood number as a function of the relevant parameters. A mathematical expression is proposed (given as Eq. (32) in the paper) that describes accurately the dependence found numerically between the value of the Sherwood number and the values of Peclet number and aspect ratio, L / d 1 , of the cylinder. For large enough diameter of the cylinder, the problem degenerates into mass transfer from a plane surface and the same equation applies, with L / d 1 = 0 . The equation was tested through the measurement of diffusivity for different solutes released by slightly soluble solids, and the experimental values obtained were in excellent agreement with the values found in literature. An important feature of the paper is the detailed discussion of the finite difference method adopted, with emphasis on the high-resolution schemes used in the discretisation of the convection term of the PDE.

Drying of Black Liquor in Spouted Bed of Inert Particles

This work is aimed at developing a low-cost technique to produce powdery fuel from wood and nonwood black liquors. This consists in injecting the liquor into a bed of inert polypropylene particles spouted by hot gas. The liquor coats these particles with a thin film, which is then dried and reduced to powder during particle circulation inside the bed. The powder is carried away by an exhaust gas and separated in a cyclone. Attrition between particles, resulted from particle circulation, induces high shear rates in the thin liquor film reducing its viscosity and making possible to process it. If particle circulation is optimized, the drying temperature can be well controlled to avoid agglomeration and adhesion to the dryer wall. A methodology developed for operating and controlling such variables in a semi-pilot unit is discussed to make feasible the continuous production of the powdery fuel. Using Eucalyptus and Bamboo liquors and the experimental factorial design, the effects of the drying operational variables on powder quality and efficiency are analyzed to optimize this process. Results demonstrate that the powder produced is a particulate fuel with the net calorific value varying from 13,579 (Eucalyptus) to 14,673 (Bamboo) kJ/kg, at the residual moisture content from 9.5% (Eucalyptus) to 6.3% (Bamboo). Although the powder production efficiency can reach high values (>60%), the thermal performance of the dryer given in terms of the energy factor is unsatisfactory so possible modifications to the dryer are pointed out.