(33a) Importance of Cohesion Strength Measurements As Flowability Indicator of Powders in a Fluidized Bed

It is well known that the difference in bulk material properties such as particle size, shape and density as well as surface moisture influences the flowability of fine powders [1]. Fluidized beds are commonly treated as i) at "incipient fluidization" mode whilst the packed-bed of particles are about to "break" solid-solid surface contact and ii) in "suspension mode" whilst the particles are fully-suspended in the carrier fluid which supports their weight and is subject to fluid-solid surface interactions [2]. This study links cohesion strength with the flowability of commonly used industrial fine powders (i.e. Cement, Barite, Bentonite, Alumina and Silicon carbide). The solid like structures observed in cohesive powders can be broken by pre-consolidating and initiating shearing using an Anton Paar MCR Rheometer with Powder Cell and a fluidization set with controlled gas flow [3].

Cohesion strength is determined via shearing the sample following a protocol where the sample is compressed at low consolidations with an air-permeable piston and then a spoke-shaped geometry penetrates the sample and shears it. Warren Spring cohesion is calculated as the maximum value.

Furthermore comparisons on shear rate dependent viscosity and Brookfield Powder Flow Tester (using annular shear cell) contribute to the calculations which determine the flowability of the powders and allow the characterization of harsh cohesive powders.

[1] Valverde J.M., Castellanos A. Effect of particle size and interparticle force on the fluidization behaviour of gas fluidized beds. Phys. Rev. E 67, 051305 (2003)

[2] Rietema, K The dynamics of fine powders, Elsevier, London (1991)

[3] Salehi H, Schutz D, Romirer R, Barletta D, Poletto M. On the use of a powder rheometer to characterize the powder flowability at low consolidation with torque resistances. AIChE Journal http://dx.doi.org/10.1002/aic.15934