Height Of Fluidized Bed Research Articles

Volume contraction behaviour of binary solid–liquid fluidized beds

Contrary to the widely held notion that the total bed height of a binary solid fluidized bed will be the sum of heights of the two individual mono-component beds fluidized at the same velocity, significant negative deviations have been observed in our experimental investigation. The negative deviations, signifying a contraction of the total volume of the binary solid fluidized bed, could sometimes be as high as 25% of the actual volume. The volume contraction has been found to depend mainly upon the degree of solids mixing prevailing in the bed irrespective of whether it is fully fluidized or not. The composition of the binary solid fluidized was another important factor that influenced the contraction behaviour of the bed besides the size ratio of the two constituent solid species of the binary present in the bed.

External loop inversed fluidized bed airlift bioreactor (EIFBAB) for treating high strength phenolic wastewater

A 4 l external loop inversed fluidized bed airlift bioreactor (EIFBAB) was constructed, characterized and tested for treating high strength phenolic wastewater. Expanded polystyrene beads (S.G. 0.713, 1.0– 1.18 mm diameter) were used as supporting materials, for immobilizing Pseudomonas putida ATCC11172, in the downcomer of the EIFBAB. A unique feature of this bioreactor is the installation of a globe valve between the riser and the downcomer sections. By adjusting the valve opening, gas holdup in the riser and liquid circulation velocity were decoupled from the gas velocity. The effect of the extent of valve opening, under cell-free condition, on gas holdup and liquid circulation velocity was investigated for gas velocities, which ranged from 0.01 to 0.12 ms −1 . It was found that gas holdup in the riser could be increased by a minimum of 55% (at 0.1 ms −1 gas velocity) to as much as 85% (at 0.01 ms −1 ) by closing the valve. The data for gas holdup were modelled using a power law correlation while a Langmuir–Hinshelwood kinetics model was used for the liquid circulation velocity. The latter was rationalized based on an energy balance approach. The advantage of the EIFBAB was demonstrated for batch biodegradation of phenol at concentrations of up to 3000 mg l −1 . It was found that at high phenol concentrations, biodegradation was oxygen limited, and the EIFBAB was ideal for increasing the gas holdup by closing the valve at higher gas flow rates while maintaining the same fluidization bed height.

Water Vapor Sorption Characteristics of Powder Type Organic Sorbent in a Moist Air Fluidized Bed.

This paper has dealt with water vapor sorption characteristics of powder type organic sorbent bed by flowing a moist air. The powder type sorbent was fluidized in a rectangular vessel by the moist air flow. The sorption rate of vapor and the variation in temperature in the sorbent bed were measured under various air temperature and humidity conditions. It was found that the volume of the sorbent particles increased with in an increase in the amount of water vapor sorption. Finally, Sherwood number for water vapor mass transfer was expressed in terms of Reynolds number, the modified Stefan number, the ratio of sorbent particle diameter to fluidized bed height and Schmidt number.

Flow and Heat Transfer Characteristics in Liquid-Solid Swirl Fluidized Bed Using Centrifugal Force.

A liquid-solid swirl fluidized bed (SFB) using centrifugal force is proposed for the application of a seeding method and the enhancement of heat transfer in processes utilizing geothermal energy, and the corresponding flow and heat transfer characteristics are experimentally examined. In the lower part of the SFB, many particles are carried by swirl flow. When liquid velocity is constant, fluidized bed height is lower in SFB than in the conventional fluidized bed (FB). The fluidized bed height in SFB depends on the initial bed height. The heat transfer coefficient is higher in SFB than in FB, and increases with increasing initial bed height.

Modeling of direct recovery of lactic acid from whole broths by ion exchange adsorption.

Lactic acid fermentation process with L. casei CRL 686 was performed. The static adsorption isotherm over a strong anionic exchange resin, Amberlite IRA-400 was measured, and the static binding capacity parameters were quantified. Early recovery of lactic acid from this lactate producer from unclarified culture broth was performed in a liquid solid fluidized bed, with the resin as the solid adsorbent, and the dynamic adsorption capacity was calculated. Good agreement was found between static and dynamic binding capacity values. The fluidized bed height was twice the settled bed height and the overall process was controlled by the liquid solid mass transfer. This operation was also simulated by continuously well stirred tanks arranged in series and superficial solid deactivation as in a gas solid catalytic reactor. The deactivation process takes into account liquid channeling and agglomerations of solid induced by the viscosity of the broth and also by the cells during the adsorption. These patterns were also verified by experimental observations, and are in agreement with the results found in the literature. The breakthrough data together with others from previous works were satisfactorily fitted until the 90% dimensionless concentration was reached for both culture broths. The model could be used in future studies on predictions about the liquid solid fluidized bed behavior and other different operating conditions.

A new concept of bioartificial liver based on a fluidized bed bioreactor.

Many bioartificial livers have been developed, but most of them suffer from difficulty when being scaled up and from poor efficiency of mass transfer between the plasma and the immobilized hepatocytes. We present a new concept of bioartificial liver based on the fluidized bed motion of hepatocytes entrapped in alginate beads. The bioreactor is designed to offer stable behavior. The maximum fluid perfusion velocity is determined to avoid any bead release from the bioreactor. The fluidized bed height depends on the amount of beads and the velocity employed. Under the optimized operating conditions, the mass transfer between perfusion fluid and beads is very efficient; only 10 min are necessary to reach concentration equilibrium. Hence, this fluidized bed bioartificial liver appears to be a promising tool for a liver support system in the treatment of acute liver failure.

Influence of aerodynamics of a circulation fluidized bed on intensity of external heat transfer

The authors present results of an experimental investigation of external heat transfer over the height of a circulation fluidized bed.

Entrainment and Overflow of Particles from Continuous Pressurized Fluidized-Bed Gasifier

Gasification of four different kinds of coal chars were carried out in a 1.0 ton/day fluidizedbed gasifier within a range of the following operating conditions; the gasification temperature from 1150 to 1320K, the total pressure from 0.6 to 1.9MPa, the superficial gas velocity from 0.5 to 0.8m/s, the steam to air and/or oxygen ratio from 0.8 to 2.5, and the fluidized bed height of 0.2, 0.4 and 0.6m. The experiments were focussed to examine the effects of the above operating variables, particularly the properties of fed char particles, on the rates of entrainment of fine particles from the freeboard and overflow of bed particles through the overflow pipe as well as on their microphotographic properties and carbon content.Microphotographs of the entrained and overflow particles showed that distribution of fine ash particles and extent of dilatation of the residual char particles depended on the properties of fed char particles. The rate of entrainment exhibited a variation corresponding to the size distribution of fed char particles and the attrition characteristics of gasifying char particles. The weight fractions of entrained particles were about 0.2 to 0.5 of the fed char particles under the present operating conditions. Among the chars used so far, the maximum entrainment rate was observed for Blair Athol coal char due to its highest content of fine particles and possibly to its most fragile structure for rapid heating.The fraction of entrained particles increased with the superficial gas velocity while that of overflow particles decreased. Also, increase of the fraction with the pressure became appreciable when the pressure exceeded 1MPa. The content of fine particles in the entrained particles increased with the carbon conversion and the fluidized bed height, which might be attributed to fine ash formation by attrition of ash layer on the surface of gasifying char particles.

Dynamic Model of Nitrification in Fluidized Bed

Fixed‐film nitrification was studied in a pilot‐scale fluidized bed treating municipal secondary effluent. A mechanistic mathematical model incorporating reaction stoichiometry, diffusion, multisubstrate kinetics with product inhibition, fluidization, and a reactor model developed from the observed residence‐time distribution, was developed to predict the steady‐state and short‐term dynamic performance of the reactor. The model equations were solved using orthogonal collocation with trial functions tailored to the spherical‐shell biofilm geometry, and a semi‐implicit third‐order Runge‐Kutta integration technique. The steady‐state model closely fit measured concentration profiles using the maximum specific growth rates for Nitrosomonas and Nitrobacter as adjustable parameters. The dynamic model predicted observed responses to step and impulse changes in ammonium and nitrite concentrations to within 3 mg/L without further parameter adjustment. The fluidization model predicted the observed fluidized bed height within 1 cm. External mass transfer resistance was small for the conditions employed and was not included in the model.

Modeling adsorption in liquid—solid fluidized beds

Under certain conditions, the breakthrough time in a fluidized-bed adsorber is considerably shorter than that in a comparable fixed-bed adsorber. This phenomenon is probably due to the appreciable macroscale or axial mixing occurring in the solid and liquid phases of the fluidized bed. An axial dispersion model has been adapted to characterize the fluidized-bed adsorber. The model takes into account the effects of axial mixing in the solid and liquid phases, mass transfer resistance in the laminar fluid boundary surrounding an individual adsorbent particle, and diffusional resistance within the particle. The model has been solved numerically to simulate the performance of a laboratory-scale adsorber. The results of the simulation closely represent experimental observations over wide ranges of the influent flow rate, fluidized-bed height and adsorbent particle size.

Particles segregation in fluidized bed binary systems

Binary systems have been divided into six groups according to their minimum fluidization velocities, densities, and size of particles. A concentration profile of fluidized bed has been studied. Experimental results have indicated that interval (45 - 90 sec.) is necessary for concentration profile generation. The profile appears to be uninfluenced by original arrangement of system components, the composition of bulk and grid region being in mutual equilibrium. Superficial velocity strongly affects system equilibrium, especially at higher jetsam concentrations. The best segregation of the system was achieved at velocities close to the minimum fluidization velocity of the binary system. The binary systems of the 3rd and 6th types change from segregated to mixed fluidized bed if gas velocity increases. The binary system of the 1st type was difficult to mix up since flotsam entrained partially if velocity of air was increased. The equilibrium concentration profile was uninfluenced by the size of the equipment - provided fluidized bed height was above a critical limit.

Expansion of three-phase fluidized bed

This article reports on experimental studies of the expansion of a three-phase fluidized bed, used in hydroprocessing heavy petroleum residual stocks, in relation to the catalyst bed height and the linear velocities of liquid and gas. The height of the settled bed of catalyst was varied from 200 to 1000 mm. The rising gas-liquid flow fluidizes and expands the catalyst bed. The height of the three-phase fluidized bed in the column with transparent walls was determined visually by passing a light beam through the column. It is determined that the dependence of the height of the spray zone on the gas velocity is due to the fact that the gas flow emerges from the upper level of the fluidized bed in the form of a jet, capturing solid-phase particles and ejecting them from the bed with an energy that is proportional to the linear velocity of the gas.

Charge transfer rate in liquid-solid and gas-liquid-solid fluidized bed electrodes.

Copper deposition from acidic aqueous solutions containing copper ion was studied in rectangular fluidized bed electrodes for liquid-solid and gas-liquid-solid systems. The effective specific resistance of particle phase, ρm, was determined by comparison of the experimental potential profile with the theoretical one. The value of ρm decreased with increase in gas velocity, and the gas flow increased the total cell current by 10-30% at a given cell voltage in the range of 15 to 30% bed expansion. No explicit effects of fluidized bed height and particle diameter on ρm were observed. The overall effective specific resistance of bed, ρb, was measured with an alternating current bridge circuit, and the relationship between ρm and ρb is discussed. The charge transfer in the particle phase was analysed by the parallel effective resistance model based on the charge conductive mechanism and the collision mechanism.

A method for the calculation of biological film volume in a fluidized bed biological reactor

In a fluidized biological reactor, knowledge of the volume of the biological film surrounding each growth support particle is critical to the proper engineering of such reactors. A system of equations has been developed to correlate fluidized bed height with biological film volume. The predictions of the developed correlation have been compared to experimentally measured values. The comparison indicates good agreement when growth is fully developed in the reactor.

Gas‐solid fluidized systems: Average mass transfer potentials of shallow beds

AbstractAn experimental investigation has been conducted on the direct establishment of mass transfer driving forces for the vaporization of n‐decane from Celite particles fluidized by air. Ranges of particle sizes and reactor diameters were employed.Concentration profiles of n‐decane were determined and were integrated to obtain the actual average concentration difference for the entire bed. The ratio of the actual driving force to the corresponding log‐mean value has been correlated with the average particle size, the fluidized bed height, and the modified Reynolds number to produce two relationships capable of predicting these ratios to within 2.5% (83 runs). The results for these mass transfer studies should also be applicable to comparable studies on heat transfer in fluidized beds.