Stability Of Fluidized Bed Research Articles

DDPM simulation of the erosion of immersed tubes in a pulsating fluidized bed

In this study, the effects of the type of pulsating inlet waveform, pulsation frequency, and pulsation amplitude on the stability of fluidized beds and the erosion of immersed tubes were investigated by numerical simulation. Compared with rectangular and triangular inlet flows, sinusoidal flow induced the lowest immersed-tube erosion rate and pressure-drop fluctuation in the fluidized bed. Furthermore, under sinusoidal flow with a pulsation frequency of 1 Hz and pulsation amplitude of 0.25um, the immersed-tube erosion rate was lower by 1.8 %, standard deviation of pressure drop by 14.16 %, and energy generated from bubble rupture by 47.83 % than those under uniform flow. A dimensionless parameter χp that can represent immersed-tube erosion during pulsating flow was proposed, which reflects the effect of particle flow characteristics, particle fluidization degree, and pulsation frequency on immersed-tube erosion.

Printed monolith adsorption as an alternative to expanded bed adsorption for purifying M13 bacteriophage

An ordered 3D printed chromatography stationary phase was used to purify M13 bacteriophage (M13) directly from crude cell culture. This new approach, which offers the same advantages as expanded bed adsorption (EBA) with regard to tolerating solids-laden feed streams but without the corresponding issues associated with fluidized bed stability that affect the latter, can be described as “printed monolith adsorption (PMA)”. PMA columns (5, 10 and 15 cm length by 1 cm diameter) were made via a wax templating method from cross-linked cellulose hydrogel and functionalized with a quaternary amine ligand. The recovery of M13 was found to be strongly linked to load flow rate, with the highest recovery 89.7% ± 6% for 1.4 × 1011 pfu/mL of resin occurring at 76 cm/h with a 10 cm column length. A recovery of 87.7% ± 5% for 1.49 × 1011 pfu/mL of media was achieved with a 15 cm column length under conditions comparable to a reported EBA process. The PMA process was completed three times faster than EBA because PMA flow rates can readily be adjusted during operation, with high flow rates and low back pressure, which is unique to the ordered monolithic media geometry used. Equilibration, wash, and cleaning steps were carried out at high flow rates (611 cm/h), minimizing process time and were limited only by the volumetric flow rate capacity of the pumps used, rather than column back pressure (<0.1 MPa at 611 cm/hr). Initial capture of M13 appears to occur on the surface of the monolith solid phase (i.e. the mobile phase channel walls) and subsequently, at a slower rate, within the internal pores of the solid phase media. The difference in binding rate between these two sites is likely caused by slow pore diffusion of the large M13 particles into the pores, with similar slow diffusion out of the pores resulting in tailing of the elution peak. The results indicate that PMA is a promising technology for the efficient purification of viruses directly from crude cell culture.

The process optimization for separation performance and fluidization stability based on air dense-medium fluidized bed

Dry mineral separation methods are based on the pseudo-fluid properties of two-phase gas-solid fluidization during the air dense medium fluidized bed separation. In this paper, the air dense medium fluidized bed separation method was introduced for coal deashing. In order to better understand the impact of separation performance of air dense medium fluidized bed, the uniform stability of fluidized bed on separation performance the factors (fluidization number (N), height-to-diameter ratio (λ) and feeding volume fraction (γ)) were varied. The process optimization of these three factors was investigated. The results showed that the fluidization number was the main factor reflect on fluidized characteristics. The separation efficiency achieved the optimal value when the feeding volume fraction reached 13%. The segregation stabilized at 0.90–0.95, with the possible deviation ranged from 0.10 to 0.15. Further, the yield of cleaned coal is 78.5–80%, and ash content reduced by 75–78%. The dense medium fluidized bed can achieve efficient deashing of coal. Highlights Factors to influence the uniform stability of fluidization within ADMFB. The Process optimization for separation performance was conducted. Synthesizing the separation test results get formulas about feeding volume fraction y and feed rate q. The yield of the cleaned coal is around 80% while its ash decreased to 10%.

Enhanced fluidization of nanosized TiO2 by a microjet and vibration assisted (MVA) method

A microjet and vibration assisted (MVA) fluidized bed was developed to enhance the fluidization quality of nanosized TiO2 particles. Two commercially available TiO2 nanopowders, P25 and P90, were tested. Fluidization quality was assessed by determining the non-dimensional bed height as well as the non-dimensional pressure drop. Smooth fluidization of the TiO2 nanopowders was observed in the MVA system. The non-dimensional bed height for the nanosized TiO2 in the MVA system optimized at about 5 and 7 for P25 and P90 TiO2, respectively, at a resonance frequency of 50 Hz. The non-dimensional pressure drop was also determined and showed that the MVA system exhibited a lower minimum fluidization velocity for both of the TiO2 types as compared to fluidization that employed only vibration assistance. Additional experiments were conducted with the MVA to characterize the synergistic effects of vibrational intensity and gas velocity on the P25 and P90 fluidized bed heights. Mathematical relationships were developed to correlate vibrational intensity, gas velocity, and fluidized bed height in the MVA. To test the mathematical model, 18 additional experimental points were gathered for both P25 and P90 under varying conditions. The actual and model-predicted non-dimensional bed heights were found to correlate well, with less than 14% error between values. The non-dimensional bed height in the MVA system is comparable to previously published P25 TiO2 microjet assisted (MA) fluidization employed with the addition of an alcohol that was used to minimize electrostatic attraction within the system. However, the MVA system achieved similar results without the addition of a chemical, thereby expanding the potential chemical reaction engineering and environmental remediation opportunities for fluidized nanoparticle systems. Fluidized bed stability was greatly improved when the dual effects of vibration and microjet assistance were used.

COMPARATIVE ANALYSIS OF COAL BENEFICIATION PERFORMANCE IN GAS-SOLID FLUIDIZED SEPARATION BEDS WITH DIFFERENT BED STRUCTURES

Fluidization characteristics and separation properties of fluidized beds with different bed structures were studied. The stability of fluidized beds with different structures decreases with the increase of bed height. The uniformity and stability of density of rectangular fluidized bed is better than that of square and circular fluidized bed at the same bed height. The influence of fine coal content on the density distribution of fluidized bed has little relation with the bed structure. Separation results showed that ash segregation degrees of the three fluidized beds were generally high and the separation effects were good when the static bed height was 130 mm, the fluidization number was 1.5, and the fine coal content was 10%. The rectangular gas-solid fluidized bed has the best separation effect: the lowest ash content of cleaned coal is 20.11% and the probable error Ep is 0.11g/cm3. Its Ep value is significantly better than that of square fluidized bed (Ep=0.155 g/cm3) or circular fluidized bed (Ep=0.16 g/cm3).

Effect of the secondary air distribution layer on separation density in a dense-phase gas–solid fluidized bed

Dry coal separation has been the most significant process in the field of coal beneficiation to date, because of its special advantage of operation with no water consumption. Mineral dry separation research has received wide attention, particularly in countries and regions experiencing drought and water shortages. During the process of dense coal gas–solid fluidized bed beneficiation, the material is stratified according to its density; the high density material layer remains at the bed bottom, and thus the high density coarse particle bed becomes an important influencing factor in fluidized bed stability. In the steady fluidization stage, a small number of large radius bubbles are the direct cause of unsteady fluidization in the traditional fluidized bed. The dispersion effect of the secondary air distribution bed for air flow is mainly apparent in the gas region; when the particle size exceeds 13mm, the secondary air distribution bed has a synergistic effect on the density stability of the upper fluidized layer. When the particle size is small, especially when less than 6mm, particles will constantly move, accounting for instability of the secondary air distribution bed and distorting the stability of the upper fluidized bed. Under optimum operation conditions, the probable deviation E of gas–solid separation fluidized with a high density coarse particle layer can be as low as 0.085g/cm3.

Study on particle dynamics in different cross sectional shapes of air dense medium fluidized bed separator

Dry coal washing is gaining popularity on account of its ability to produce clean coal without the use of water which is becoming to be a costly resource for beneficiation. Air dense medium fluidized bed separation (ADMFBS) is one of the dry beneficiation techniques which is used for cleaning of coal. Fine magnetite particles are used as medium to make pseudo-fluid by fluidization method. The effectiveness of ADMFBS depends on stability of the fluidized bed. In the present work, an attempt has been made to study the stability characteristics of different cross-sectional shapes of fluidized bed having same cross-sectional area. Different indicators like fluidization index, particulate expansion function, pressure drop of bed and distributor, minimum fluidization and bubbling velocities were used to characterize the stability of fluidized bed. The effect of different operating and design parameters on the homogeneity and stability of the fluidized bed was studied. It was observed that cross sectional shape of the fluidized bed column has a significant effect on the stability of the bed. Moreover, rectangular cross-sectional shape provides better stability properties compared to square or circular shape.

Magneto-Stabilization of Fluidized Beds as due to Short Ranged Interparticle Forces

We present an experimental study on the stabilization of bubbling gas-fluidized beds of magnetic powders by interparticle forces induced by an externally applied magnetic field in the cross-flow configuration. The samples tested consist of magnetite and steel powders in a range of particle size dp between 35 and 110 microns, allowing us to investigate the effect of particle size and material properties on magnetic stabilization. According to our observations, the stabilization physical mechanism is ruled by the jamming of particle chains created due to attractive forces induced between the magnetized particles. Even in the case of the horizontally applied field, these chains are mechanically stable at orientations close to the gas flow direction in agreement with the prediction of a chain model based on the balance between gas flow shear and interparticle magnetic force fm. Since fm is increased as dp is increased, the critical gas velocity at marginal stability vc for a fixed field strength B is seen to increase with dp. The yield stress of the stabilized bed s increases steadily as the gas velocity v0 is decreased below vc. Thus, s is increased with dp for fixed v0 and B. It is inferred also from our results that natural aggregation of fine particles due to the universal van der Waals interaction enhances the yield stress of the magnetically stabilized bed. A main conclusion is that interparticle short ranged attractive forces play an essential role on magnetic stabilization of fluidized beds.

Stability Study of an Air Dense Medium Fluidized Bed Separator for Beneficiation of High-Ash Indian Coal

Indian high ash noncoking coal contains a substantial quantity of near-gravity materials (NGM). The presence of NGM needs beneficiation in dense medium separation process. Air dense medium fluidized bed separator (ADMFBS) uses the magnetite medium to improve the separation efficiency of beneficiation of high NGM coal. Stability of the particulate fluidized bed in this system is the essential prerequisite for the separation of heavy and light particles. In this study, the characterization of medium and particulate fluidized bed was assessed to maintain the nonbubbling condition. Stability of the fluidized bed was characterized by different expressions like fluidization index, particulate expansion function, Froude number of particle, Reynolds number of particle, and pressure drop ratio using the minimum fluidization velocity, minimum bubbling velocity, pressure drop of distributor and bed, bed porosity, air viscosity, aspect ratio, density of air, and density of medium. It was found that the fluidization indexes of this system for different experimental runs are around 1 to 2. The system was scaled up from laboratory to pilot scale, having a feed throughput capacity of 600 kg/hr. Indian high ash noncoking coal at particular size (−25 + 6 mm) was used in continuous operation. The partition number was calculated based on washability data of product and reject. The Ep and imperfection value for the pilot-scale ADMFBS was found to be 0.12 and 0.071, respectively.

Hydrodynamic and Thermal Modelling of Gas-Particle Flow in Fluidized Beds

In this study a mathematical model has been developed to simulate two dimensional fluidized beds with uniform fluidization. The model consists of two sub models for hydrodynamic and thermal behavior of fluidized beds on which a FORTRAN program entitled (NEWFLUIDIZED) is devolved .The program is used to predict the volume fraction of gas and particle phases, the velocity of the two phases, the gas pressure and the temperature distribution for two phases. Also the program calculates the heat transfer coefficient. Besides that, the program predicts the fluidized bed stability and determines the optimum input gas velocity for fluidized beds to achieve the best thermal behavior. The hydrodynamic model is verified by comparing its results with the computational fluid dynamic code MFIX [1]. The thermal model was tested and compared to the available previous experimental correlations. The model results show good agreement with MFIX results and the thermal model of the present work confirms Zenz [2] and Gunn [3] equations.

The effect of interparticle forces on the stability of fluidized beds

Mecanisme par lequel les forces entre les particules peuvent influence le comportement dynamique du lit tout en demeurant neutres a l'etat d'equilibre. Exemple d'application: stabilisation magnetique d'un lit fluidise

Stability of Catalytic Reactors: A Critical Review

A critical review of stability studies of heterogenous catalytic systems, including biochemical systems, which can be effectively used to design and operate commercial reactors covers definitions and theoretical concepts of instability; the stability of catalyst pellets, including multiple steady states in a catalyst pellet, intraparticle stability, and parameter ranges and conditions of industrial practice; the stability of fixed-bed reactors, including the phenomena of multiplicity due to macroscale thermal feedback, creeping, parametric sensitivity, stability of a group of multistable particles, and hot spots; the stability of fluidized beds; and the stability of biochemical reactors.