Hydrodynamics Of Multi-stage Airlift Loop Reactor And Its Application In Separation Process

Because of the advantages of simple construction, high mixing performance, low power consumption and good mass/heat transfer efficiency, Airlift loop reactors(ALR) are widely used in aerobic fermentation, wastewater treatment. Due to the complexion of the multiphase flow, there are still many remaining problems. In this work, flow patterns and hydrodynamic parameters in ALR were investigated by experiments and simulations. A multi-stage loop packing flotation column(MSLPFC) and a multi-stage loop packing extraction column(MSLPEX) was proposed based on ALR, and the performance of the MSLPFC and MSLPEX were investigated by experimental measurements.A 2-D airlift loop reactor(2-D ALR) was developed. PIV experiment was carried out to investigate the hydrodynamics of the 2-D ALR with different draft tubes. Three different regimes are observed under different conditions, the horizontal liquid velocity profiles are different in the three regimes. It is found that the draft tube structure is of great importance in determining the hydrodynamics of ALRs, especially the effect of the spacing of draft baffles is obvious. The results of the experiment may serve as a step to further optimize and design of ALR.Then 2-D and 3-D simulations were carried out by CFD method to investigate the hydrodynamics behavior with the same conditions as those in the experiment. The results showed a satisfactory agreement between the 2-D simulation and the experiment. Furthermore, the results of 3-D simulation indicated that the key factor of deciding liquid circulation flow rate was area ratio of riser/downcomer rather than diameter ratio.A novel flotation column was developed based on the multistage separation technologies, structured packing and airlift loop device. Then experiments were carried out to test the aerating performance and coal slime flotation performance of the MSLPFC. The experimental results show that the gas holdup and the bubble size increases with increasing the aeration quantity. The addition of foaming agent(surfactant) leads to the bubbles become smaller and more stable, and the gas holdup also increased. In flotation process, the flow pattern in the colunmn is regular due to the liquid recirculation; the multistage structure weakens the axial back-mixing; the packings extend the residence time. The results of continuous feeding indicate that the concentrate coal can’t satisfy the industry standard. But it could reach excellent separation performance when extend the residence time of coal slime.A novel liquid-liquid packing extraction column was developed based on the airlift loop device and droplet-film alternate flow packing. Mass transfer efficiency and hydrodynamic parameters were obtained by experimental methods. It is found that the dispersed phase droplet break up in the inner tube and coalesce in the annular space, it Increases the frequency of the droplet surface renewal and enhances the mass transfer efficiency. Meanwhile, the continuous phase circulates in each stage, this increases the extractant effective and provides larger processing capacity. Compared with Super Mini Ring packing and hybrid packing extraction column, the results show that the mass transfer efficiency of MSLPEC is almost same as HPEC, and 24% higher than SMRPEC; the processing capacity of MSLPEC is 68% higher than HPEC, and 52% higher than SMRPEC.A novel multi-scale optimization strategy of ALRs based on constructal theory was proposed. It is actually an optimization process mainly aimed at optimizing the smallest unit and the order of the construct. In this strategy, combining small-scale module in a particular order formed the macro-scale structured ALR, the column is just the compact package with many small units.