Mechanism And Prediction Model Of Gas Absorption Enhancement By Dispersed Particles

Mass transfer enhancement by introducing a third dispersed phase into gas absorption systems is an important intensification method. The effect of three kinds of dispersed particles with different properties, including reactive solid particles, adsorptive solid particles and dispersed liquid drops, on the enhancement of gas absorption was studied respectively. Two models (macroscopic and microcosmic models) were developed to interpret the mechanism of mass transfer in this paper.Based on the whole gas absorption system, various influence factors were taken into account in the macroscopic model in which the enhancement of gas absorption obtained by the dispersed particles is an overall effect of all particles. The macroscopic model considers the comprehensive effects of whole system and accordingly could be applied conveniently. Differently, the microcosmic model investigates the influence of each single particle on concentration field and velocity field, particle interactions and shielding effect of the first particles, and hence the micro mechanism of mass transfer enhancement by particles can be understanded clearly. The two models are mutually complementary and confirmed, and closely relative each other. Due to the strong interaction among particles, only a simple superposition of the effects of single particles will lead to large errors, however this disadvantage is overcome in macroscopic model considering the effect of dispersed particles entirely and systematically, the enhancement of gas absorption at a certain time should be a macroscopic result from the combined action of many particles.For reactive particles, a model was presented to describe the influence of the size distribution of particles and dissolving effect on enhancement factor. It was shown that the dissolution and the initial size distribution of particles are of key importance to the gas absorption when the particles could be dissolved easily or a fast reaction occurs. The enhancement factor would be considerably overpredicted if the particle dissolution effects are ignored.According to the experimental results of the modification of zeolite and the absorption enhancement by solid particles with different hydrophobicities, it could be found that the particles with an enhancement effect on the gas absorption rate should have two properties, i.e. hydrophobicity and a high adsorption capacity for the solute. A novel mass transfer model was developed and various effect factors were discussed, the phenomena that the enhancement factors increased quickly with solid concentration initially and then gradually reached a constant value were explained reasonably by the present model.In terms of the characteristics of liquid-liquid dispersed system, the initial decrease of gas absorption rate was considered as a result of interfacial contamination, and the concept of "effective diffusion coefficient"was proposed. According to the formation mechanism of emulsion, an adsorptive film by emulsifiers exists around each particle, and obstructs the diffusion of the solute between the two liquids, consequently leading to added resistance of mass transfer.The absorption of CO2 into different dispersed systems was investigated experimentally in a thermostatic reactor, and the models presented in this paper were validated. The calculated results agreed well with the experimental data, indicating the rationality of the models.