Fluidization of potato starch in a stirred vibrating fluidized bed

Abstract

A novel gas-solid reactor for cohesive C-powders such as potato starch is introduced, designed and characterized, the so-called stirred vibrating fluidized bed. The effects of a sinusoidal vibration of the gas distributor and/or stirring of the bed are investigated. The fluidization index, bed expansion, torque and visual behaviour of the bed are determined as a function of air velocity, bed height and moisture content of the starch, stirrer type and speed and vibration frequency and amplitude. For a potato starch bed of 0.76 m initial height and 0.288 m diameter with a moisture content W = 13.1 weight% dry basis, channel formation can be suppressed only if the aerated bed is effectively stirred. With flat stirrer blades this can be realized for stirring speeds above 1.67 rps provided the interblade distance is below 124 mm. Even then, the bed consists of agglomerates (flocks) of starch. Alternatively, vibration of the gas distributor of the aerated bed at best results in channel elimination in the lower part of the bed only. Sufficient vibration, however, can destroy starch agglomerates even at the surface of a bed of 0.76 m. By simultaneously applying both vibration and stirring of the aerated bed, it is possible to eliminate both channelling and starch agglomeration. Even homogeneous fluidization is possible. Optimal combinations of stirring and vibration parameters are reported for various bed heights and moisture contents.