Fluidized Bed Pressure Drop Research Articles

Introducing an efficient capped fluidized bed and quantifying its flow and heat transfer performance

Fluid-solid particle beds have a very wide range of industrial applications but there are few publications relating to a general method to quantify solid particle bed performance for a comparative efficiency study. The conventional approach of characterizing bed efficiency involves bubble sizes, bubble frequency, byproduct quantity for bed reactors, and pressure drop for minimum fluidization. However, different solid particle beds have different states with varying flow rates, which makes the comparative study more difficult to achieve. In this work, a common approach to measure solid particle bed efficiency in terms of heat transfer is presented. The two cases considered here are 1) When work is done by the particles such as in a catalytic reactor, and 2) When work is done on the particles such as in cooling/drying of particles. In addition to the packed bed and fluidized bed, a solid particle bed called a capped fluidized bed is introduced. The Eulerian–Lagrangian method, also known as CFD-DEM simulation, is adopted for this analysis. Numerical simulations show potentially significant advantages of capped beds over packed and fluidized beds under certain fluidization states. Capped fluidized bed pressure drop is comparatively lower than that for a packed bed and similar to a fluidized bed, which allows it to operate at a wider range of flow states. Current fluidized bed performance is limited by the entrainment and possible loss of particles at high flow rates. However, the capped fluidized bed restricts the particles from leaving the bed and thus permits higher flow rate operation. Further experimental research is required to more completely characterize this type of solid particle bed.

Particle fluidization characteristics and transition in a hot gas-solid fluidized bed with liquid injection

The particle fluidization characteristics and transition in a hot gas-solid fluidized bed with liquid injection were investigated on the basis of pressure drop of fluidized bed, the side wall temperature distribution and the weight fraction of agglomerates. It was found that the particle fluidization behavior was controlled by liquid bridge force under low induction heating power, whereas both solid bridge force and liquid bridge force take control of fluidization under higher induction heating power. With increasing liquid injection flowrate, the particle fluidization behavior experienced four types, named fast defluidization, gradual defluidization, agglomerating fluidization and stable fluidization, respectively. Further the transition behaviors between different fluidization types of particles were investigated, and four fluidization regions were distinguished. A dimensionless number ζ was proposed based on the theoretical analysis of interparticle forces and bubble expansion force, thereby establishing the connection between lab-scale experiments and industrial fluidized beds, and providing guidelines for their safe operation. • The combined effect of both solid bridge force and liquid bridge force were investigated on fluidization behaviors. • Four types of particle fluidization behaviors from stable fluidization to defluidization were distinguished. • The transition boundary of different particle fluidization types was determined. • The stable operating domain of the reactor was determined. • A dimensionless number was proposed to classify particle fluidization behaviors.

Minimum fluidization velocity growth due to bed inventory increase in an Air Dense Medium Fluidized Bed

Minimum fluidization velocity is one of the most important fluidization characteristics when applying an Air Dense Medium Fluidized Bed to dry coal beneficiation. Measurements were carried out for magnetite particles (150–300 μm) and the binary mixtures of magnetite mixed with sand/gangue/coal particles (300–425 μm) to determine the influence of bed inventory on the characteristics at incipient fluidization state. The experimental results demonstrate that the minimum fluidization velocities of both single and binary mixtures of solid particles increase with increasing bed mass, which has not properly accomplished by the existing equations. The correlation proposed by Wen and Yu has been modified to predict the minimum fluidization velocity as a function of bed inventory. It only requires the knowledge of Archimedes number and the pressure drop of fluidized bed. This correlation is in reasonable agreement with almost all available data in the literature and the present work.

CHARACTERIZATION OF AN EXPERIMENTAL FACILITY FOR BUBBLING FLUIDIZED BED COMBUSTOR

Fluidized bed technology offers an attractive way for energy production with clean environment by the combustion of even low-grade waste derived fuels (WDF). This paper reports experimental results concerning the characterization of a small-scale bubbling atmospheric fluidized bed combustor with WDF batch feeding. The combustor having 0.215 m inner diameter and 1.88 m height is equipped with a packed-bed sandwich-type fluidizing air distributor. The experimental fluidized bed combustor (EFBC) is provided with facility items necessary for the operation, control, and measurements. Results of the measured fluidized bed pressure drop and temperature were investigated for cold flow, hot flow, and combustion tests during the characterization procedure. The results of these tests clearly indicated the good fluidization characteristics inherent to well-controlled operation of the EFBC facility. The characterization tests also indicated the reproducible and safe operation characteristics of the EFBC facility without appreciable leakage of fluidizing air and exhaust gases. Moreover, the obtained uniformity of the fluidized bed temperature together with the high estimated values of bed-to-immersed cooling coil heat transfer coefficient, added more evidence on the good combustion characteristics of the investigated EFBC facility.

Large‐scale oxidation of multi‐walled carbon nanotubes in fluidized bed from ozone‐containing gas mixtures

Abstract100 g of multi‐walled carbon nanotubes (MWCNTs) tangled in balls of 388 μm in Sauter diameter were treated per run in a pre‐industrial scale fluidized bed reactor, using ozone‐based gaseous mixtures at ambient temperature. The influence of ozone concentration and of the addition of water vapour was studied, for treatment durations between 1 h and 20 h. The process behaviour was analyzed in terms of fluidized bed pressure drop and temperature profile. The nature and amount of the grafted oxygen based functions were analyzed, as the structural modifications created. An oxidation mechanism in two steps was evidenced, showing the grafting of hydroxyl, phenol, and ether functions in a first step and then of lactone, quinone, carbonyl, and carboxylic groups. A moderate etching of the MWCNT outer walls was observed. The amount of grafted functions and of structural defects increased with treatment duration and was highly exalted by the presence of water vapour. All the results obtained showed that the oxidation was uniform on the whole powder of the bed and from the outer part to the centre of the balls, probably thanks to the high fluidization quality maintained all along the ozone treatment.

Minimum fluidization velocities for supercritical water fluidized bed within the range of 633–693 K and 23–27 MPa

Supercritical water fluidized bed is a new reactor concept for biomass gasification. In this paper, an experimental study on the hydrodynamics of a supercritical water fluidized bed was conducted. The frictional pressure drops of a fixed bed and a fluidized bed were measured for a temperature ranging from 633 to 693K and pressure ranging from 23 to 27MPa. The results show that the Ergun formula for calculating the frictional pressure drop of a fixed bed can still be applied in supercritical water conditions. The average deviation between Ergun formula and experiment results is 13.3%. A predicting correlation for the minimum fluidization velocity in a supercritical water fluidized bed was obtained based on the experimental results of a fixed bed and the fluidized bed pressure drop. The average error between the correlation and experiment results was about 3.1%. The results in this paper are useful for the design of SCW fluidized bed.

Fluidization of nanoagglomerates in a rotating fluidized bed

AbstractAgglomerates of nanoparticles were fluidized in a rotating fluidized bed (RFB) system at different rotating speeds corresponding to 10, 20, 30 and 40 times the gravity force (9.8 m/s2). The powders, fumed silica Aerosil® R974, Aerosil® R972 and Aeroxide® TiO2 P25, with a primary particle size of 12, 16 and 21 nm, respectively, form micron sized nanoagglomerates having a very low bulk density of around 30 kg/m3 for the fumed silicas, and a somewhat higher bulk density of about 90 kg/m3 for Aeroxide® TiO2 P25. Their fluidization behaviors are described by the fluidized bed expansion, pressure drop and minimum fluidization velocity (Umf). It was found that the fumed silica agglomerates expanded considerably while the TiO2 agglomerates showed very little bed expansion. The minimum fluidization velocities for Aerosil® R974 and R972 ranged from 0.02 to 0.07 m/s and from 0.13 to 0.20 m/s for Aeroxide® TiO2 P25; Umf increased at higher rotating speeds for all powders. At gas velocities above Umf, the fluidized bed pressure drop of fumed silica agglomerates was higher than theoretically estimated by mathematical models found in the literature. Thus, it is believed that for these light particles additional tangential momentum effects may increase the bed pressure drop and a revised model is proposed. In addition, the agglomerate size and external void fraction of the bed are predicted by using a fractal analysis coupled with a modified Richardson‐Zaki equation for data obtained with Aerosil® R972. © 2006 American Institute of Chemical Engineers AIChE J, 2006

Aerodynamics of a vibrated fluid bed

AbstractResults of an experimental study on the aerodynamics of a vertically vibrated fluidized bed of cross‐section 0.2 × 0.2 m are presented and discussed. Variables studied included frequency (0‐105 s−1), amplitude (0‐5xl0−3 m), bed height (12.5‐100×10−3 m), particle size (900‐3900 μm), particle density (570‐890 kgm−3), particle shape factor (0.55‐1.00) and the particle surface characteristics, i.e. presence of surface moisture.The effect of vibrational parameters on the fluidized bed pressure drop, the newly defined minimum mixing velocity, Umm and overall aerodynamic behaviour of the bed is discussed on the basis of quantitative as well as visual observations. Empirical correlations are proposed for δPmf and Umm, which were both found to decrease significantly with increase in the vibrational acceleration.

CENTRIFUGAL FLUIDIZATION: EFFECTS OF PARTICLE DENSITY AND SIZE DISTRIBUTION

Based on the model of the centrifugal fluidized bed as a homogeneous viscous rotating fluid, the equation for conservation of momentum in the tangential direction is solved to obtain expressions for bed pressure drop and the radial variations of tangential velocity within the bed region. Comparisons with available data on bed pressure drop indicate that the fluidized bed rotates as a rigid body. Experimental data are also presented on minimum fluidization velocity and bed pressure drop with different particle densities and size distributions, verifying the validity of the available models for packed bed and fluidized bed pressure drop and minimum fluidization velocity in a centrifugal fluidized system.

Pressure drop and power requirements in a stirred fluidized bed

AbstractThe paper reports fundamental observations on the effect which stirring of fluidized solids has on the pressure drop. Typical power requirements are also given.The experimental pilot unit was of 6‐in. diameter and 12 in. high. A special blade or paddle type of stirrer had been built which permitted the evaluation of the effects of blade positioning, blade spacing relative to sense of rotation, as well as the effect of stirrer immersion and rotational speed.The observations disclosed that blade positioning relative to sense of rotation had a very profound effect on pressure drop as well as on power requirements. When the solids circulation pattern as normally induced by the stirrer was of the same general character as that ordinarily encountered in a dense phase fluidized charge, the resulting pressure drop was always considerably lower than the conventional unstirred fluidized bed pressure drop. Furthermore for this type of stirrer the power requirements were also lowest. For other stirrer designs and other induced solids convection patterns the pressure drop was less influenced and the power requirements were much greater.The solids used for the study were a relatively coarse silica sand for which both pressure drop as well as power requirement data were reported. Power requirement data were also obtained for a much finer alumina powder. When one emphasized the effect which particle properties, especially surface characteristics may have the level of the power data was much lower, although the data were of the same character as the characteristic values pertaining to the sand.