Fluidization Of Powders Research Articles

Fluidization of powders showing degrees of cohesiveness—II. Experiments on rates of de-aeration

Experiments have been done on the de-aeration characteristics of 18 powders with mean sizes of 3–125 μm and densities 364–5000 kg m −3. Powders in Geldart's Group A de-aerate at a constant rate analogous to sedimentation in a liquid, and a standardised de-aeration time has been correlated with the powder and gas properties. Cohesive Group C powders de-aerate exponentially with time similar to the final solids consolidation stage observed in solid/liquid systems.

Fluidization of cohesive powders

Relatively small changes in particle size and other parameters which affect interparticle forces can transform a fine free-flowing powder into one which is cohesive. The influence of these parameters on the fluidization behaviour of fine powders has been investigated and can be readily assessed by measuring the ratio of tap to aerated bulk density.

Fluidization of powders showing degrees of cohesiveness—I. Bed expansion

The expansion characteristics of non-bubbling fluidized beds of powders having mean sizes from 125 to 3 μm have been measured. The ratio of the tapped bulk density to most loosely packed bulk density gives a good indication of the cohesivity of the powder and has been used in conjunction with the Richardson-Zaki equation to correlate the data.

Electrodynamic fluidization and degassing of powders

Electrodynamic fluidization and degassing of powders

Interpretation of Geldart's type A, B, C and D powders by taking into account interparticle cohesion forces

By taking into account interparticle cohesion forces, one can derive limiting conditions which result in a classification of powders which is equivalent to the definition given by Geldart [1]. Separation of powder type A from powder type C follows from the condition that free particle motion is suppressed by the dominance of cohesion forces in the case of powder type C. Separation of powder group B from powder group A is defined by the unimportance of cohesion forces on fluidization behavior in the case of powders of type B. Separation of powder group D from powder group B is defined by the fact that for minimum fluidization of powders of type D the dynamic pressure of the fluidizing agent exceeds a distinct value depending on particle size and density difference.

Fluidization of fine powders with air in the particulate and the bubbling regions

Several fractions of a silica—alumina catalyst and an impregnated catalyst were fluidized with air to check published bubble point correlations and to determine the expansion of the dense phase in the bubbling region. The minimum bubbling velocities were fairly close to those reported by Geldart and others, but U mb varied with only the 0.6 power of the particle size. The dense phase expansion was significant even at velocities much above U mb and corresponded to relative velocities up to 2 – 3 times U mf .

The possibilities of fluidization of cohesive powders in cones

The possibilities of fluidization of cohesive powders in cones

Homogeneous fluidization of fine powders using various gases and pressures

Homogeneous fluidization of fine powders using various gases and pressures

Fluidization of a bed of solid particles

As is known, fluidization of a bed of solid particles by liquid or gas filtration takes place for certain critical values of the parameters of the filtration regime. The determination of these critical values and the nature of the transition is of interest in connection with the development of fluidization technology in many branches of industry, and also in connection with certain other questions, among which we note the problem of the suspension of a sand plug in an oil well. The two-dimensional fluidization problem has been examined previously [1] as the problem of the limiting equilibrium of a medium which cannot withstand arbitrarily small tensile stresses. This model describes well the behavior of many types of bulk media encountered in practice. However, many cases lie beyond the limits of this model because of the presence of bonding forces between the particles. Bonding may be due to the adhesive forces which arise during the fluidization of fine powders [2, 3], and/or to magnetic and electrostatic forces [3, 4]. Another example is the agglomeration of particles during gas fluidization when small amounts of liquid are injected [5]; still another is the case in which sand particles are surrounded by thin films of oil when a sand plug is suspended in an oil well. In the present paper an extension of the results obtained in [1] is used to examine fluidization of a bed with account taken of the bonding forces between the particles. The two- and three-dimensional problems are studied.

Batch Production of Pharmaceutical Granulations in a Fluidized Bed I: Effects of Process Variables on Physical Properties of Final Granulation

The investigation concerns the effects of process variables associated with the fluidized bed granulation technique on the physical properties of the final granulation. The process variables investigated include binder solution addition rate, air pressure to the binary nozzle, inlet air temperature during the granulation cycle, and binary nozzle position with respect to the fluidized solids. When the rate at which the aqueous binder solution added to the fluidized bed of powders was increased, the ability of the solution to wet and penetrate the solids was enhanced, resulting in: (a) a larger average granule size, (b) a less friable granulation, (c) a more fluid granulation, and (d) a decreased granulation bulkiness. Similar results, also traceable to enhanced binder solution efficiency, occurred with a decrease either in the binary nozzle air pressure or in the inlet air temperature during the granulation cycle. The position of the binary nozzle with respect to the fluidized powders had significant effects upon the average granule size and granule friability. The effects upon the granulation flow properties and bulkiness, however, were slight.

The effect of temperature on the fluidization of silver powders

AbstractFluidization tests on pure silver and silver catalyst powder show that agglomeration occurs when the bed is heated, which finally results in bed collapse at a comparatively low temperature. If the bed temperature is held constant in the agglomerating temperature range, an induction period is observed before fluidization ceases. A study of the induction period as a function of temperature (10–60°C.) leads to an activation energy of 18 kcal. for the overall agglomeration process for pure silver. Agglomeration is believed to be due to sintering.

Gasification of Carbon by Carbon Dioxide in Fluidized Powder Bed

Gasification of Carbon by Carbon Dioxide in Fluidized Powder Bed