Particle fluidization

A phosphate-sludge conditioner blend may be employed because the deposit control agent or sludge conditioner limits and controls crystal formation (threshold and crystal distortion effects) and ensures particle fluidization (dispersion effect). 

CATALYTIC DEGRADATION OF IGH DENSITY POLYETHYLENE AND POLYPROPYLENE INTO LIQUID FUEL IN A POWDER-PARTICLE FLUIDIZED BED... 

Fig.4. Visualization of nano-particle fluidization (Top of the vessel, observation from front side)...

Numerical simulation of particle fluidization behaviors in a rotating fluidized bed... 

So far, some researchers have analyzed particle fluidization behaviors in a RFB, however, they have not well studied yet, since particle fluidization behaviors are very complicated. In this study, fundamental particle fluidization behaviors of Geldart s group B particle in a RFB were numerically analyzed by using a Discrete Element Method (DEM)- Computational Fluid Dynamics (CFD) coupling model [3]. First of all, visualization of particle fluidization behaviors in a RFB was conducted. Relationship between bed pressure drop and gas velocity was also investigated by the numerical simulation. In addition, fluctuations of bed pressure drop and particle mixing behaviors of radial direction were numerically analyzed. 

In this study, particle fluidization behaviors in a RFB were numerically analyzed by using a DEM-CFD coupling model [3]. The particle motion was calculated by DEM, which calculates the motion of each particle by integrating the Newton s equations for individual particle step by step, allowing for the external forces acting on a particle. Equations of transitional and rotational motions for individual particles are as follows ... 

Fig. 3 shows the calculated and experimental results of particle fluidization behaviors in a RFB. A high-speed video camera (FASTCAM MAX, Photoron CO., Ltd.) was used for visualization of actual particle fluidization behavior. The bubbling fluidization behaviors, such as the bubble formation, eruption and particle circulation with rotational motion, could be well simulated, and these behaviors were also observed in the experimental results. 

Fig. 6 shows the FFT spectrum for calculated bed pressure drop fluctuations at various centrifugal accelerations. The excess gas velocity, defined by (Uo-U ,, was set at 0.5 m/s. Here, 1 G means numerical result of particle fluidization behavior in a conventional fluidized bed. In Fig. 6, the power spectrum density function has typical peak in each centrifugal acceleration. However, as centrifugal acceleration increased, typical peak shifted to high frequency region. Therefore, it is considered that periods of bubble generation and eruption are shorter, and bubble velocity is faster at hi er centrifugal acceleration. 

Archimedes number /VAr a, PtfifApd3 A/Ar - Pf = fluid density Ap = solid density — fluid density (Buoyant x inertial)/ (viscous) forces Settling particles, fluidization... 

Glicksman, L. R., and McAndrews, G., The Effect of Bed Width on the Hydrodynamics of Large Particle Fluidized Beds, Powder Technol., 42 159... 

Kato, K., Takaradu, T., Matsuo, N., and Suto, T., Residence-Time Distribution of Fine Particles in a Powder-Particle Fluidized Bed, Int. Chem. Eng., 34 605(1994)... 

Nakagawa, N., Li, Z., Bai, D., and Kato, K., Fundamental Study of Fine Particle Residence in a Powder-Particle Fluidized Bed / Effect of Fine Powder Concentration, Preprint Fluidization VIII, 1 287 (1995)... 

External mass transfer resistance was neglected, as reported by [63] in biofilm reactors with granular particles (fluidized bed, airlift) the Biot number was generally larger than 100. 

For the case of equal density but differently sized particles fluidized in a bed with a nozzle-type distributor, Geldart (1992) recommends operating the bed at a gas velocity of 1.5 Ucf, where m / is the minimum velocity for complete fluidization, which may be well above the minimum fluidizing velocity found by the usual experimental method. 

Data Since this is a large-particle fluidized bed containing cloudless bubbles, assume plug flow of gas through the unit. Also assume that the volume of gases released by the solids is small compared to the volume of carrier gas passing through the bed. 

For Group B particles, there is no particulate fluidization regime. In this case, Umf equals Umb. The bubble size increases with the bed height and bed expansion is moderate. For Group B particle fluidization, there exists no maximum stable bubble size. 

In the Davidson and Harrison s (1963) maximum stable bubble size model, the bubble disintegration takes place when the relative velocity between the bubble and the particles exceeds the particle terminal velocity. Considering that, for a vertical gas-solid flow system, choking occurs when the maximum stable bubble size is equal to the column size, Yang (1976) obtained the following choking criterion for fine particles fluidization ... 

For a given system, hmm varies mainly with particle and gas properties. For coarse particle fluidization at U > Umf, the heat transfer is dominated by gas convection. Thus, /tmax can be evaluated from Eq. (12.50). On the other hand, hmax in a fine particle bed can be reasonably evaluated from the equations for hpc. In general, hmM is a complicated function... 

Fluidized-bed electrode — A - three-dimensional electrode consisting of a bed of individual electronically conducting particles fluidized by an appropriate upward flow of electrolyte. The solid particles/solution system behaves like a single fluid. A perforated distributor through which the electrolyte is admitted to operate the fluidization supports the bed. Current enters (or leaves) the bed via metallic feeders (or collectors) in contact with the particulate suspension. 

G. Lno, T. Snto, S. Yasu, and K. Kato, Catalytic Degradation of High Density Polyethylene and Polypropylene into Liqnid Fuel in a Powder-Particle Fluidized Bed, Polym. Deg. Stabil, 70, 97-102 (2000). 

G. Luo, T. Suto, S. Yasu and K. Kato. Catalytic degradation of high density polyethylene and polypropylene into liquid fuel in a powder-particle fluidized bed. Polymer Degradation and Stability, 70, 97-102 (2002). 

Increasing the gas flow just passing the point of minimum fluidization conditions the onset of particle fluidization will occur when the drag forces acting on the particles due to the upward moving gas are balanced by the weight of the solid particles [30]. 

Moving-bed reactor (Fig. 1.3b)—vessel where solid particles (either reactant or catalyst) are continuously fed and withdrawn. The gas flow is maintained to allow the downward movement of the particles. Fluidized-bed reactor (Fig. 1.3c)—vessel filled with fine particles (e.g., smaller than 500 p.m) that are suspended by the upward flowing fluid. The fluidized bed provides good mixing of the particles and, consequently, a uniform temperature. 

---