Diagnosis of bubble distribution in a three-phase bubble column reactor for dehydration of ortho-boric acid

Abstract

For the practical application of a three-phase bubble column as a reactor in the dehydration of ortho-boric acid, we investigated the bubble distribution and its effects on the reaction in a three-phase bubble column reactor (0.102 m ID x 2.0 m in height) operating at relatively low pressure (below the atmospheric pressure). Effects of reaction time, temperature, gas velocity, particle size and gas injection mode (even, wall-side, central and asymmetric distribution) on the fractional conversion of the reaction were determined. The complicated bubble distribution as well as bubbling phenomena in the reactor were diagnosed and interpreted by means of the attractor trajectories and correlation dimension which were obtained from the resultant pressure fluctuations. The fractional conversion was closely related to the attractor shape or correlation dimension of the pressure fluctuations in the reactor. The fractional conversion in the case of even distribution of gas injection exhibited the highest value in all cases studied, at which the attractor of pressure fluctuations was less scattered in the phase space, while their correlation dimension had the lowest value. When the gas was injected by means of wall-side distribution, the conversion level was higher than that in case of central or asymmetric distribution mode. Although a fluid-solid heterogeneous reaction model can be applicable to the reaction, deviations from the model become considerable when the gas injection mode changes from even to wall-side, central or asymmetric mode, orderly.