Research On Gas Dispersion In Viscous Liquid Stirred Reactor

Gas-liquid reactors are widely applied in many process industries, for instance, petrochemical, biochemical and sewage treatment process. With the intensification of gas-liquid reaction process and the scale-up of equipment, new requirements for optimizing the existing reactors or designing novel reactors with high performance are appearing. And the viscosity of most fluid is moderate or high in these process industries, which is different from the water-air system. The gas-dispersion in viscous fluid is the important and difficult points, which proposes more new requirements for designing of reactors.Firstly, proposing and designing a set of experiment equipment are conducted, including the designing of ring gas distributor and the theory of relative experiment, in this paper. Then did research on the gas-dispersion in water and mixture between water and malt syrup, whose viscosity ranges from18～59.5mPa·S and contains the viscosity interval. So this project is practical. The results show that the proportion of larger bubbles and extent of nonuniformity of bubble size are both grow larger as the viscosity of fluid boosts, while the mass transfer rate is opposite. For the ability of detaining bubble boosts, the whole average gas volume fraction turns more. Meanwhile, by means of CFD numerical simulation, the result reveals that the dead zone decreases and the distribution of local gas volume fraction turns more homogenization. Since the centre of vortex and the location of impeller discharge zone change, the local gas volume fraction does not always turn larger as the viscosity of fluid boosts.Through the comparison of gas-liquid dispersion with different lower impeller, the result reveals that the radial-flow impeller with turbine disc has a good performance in hindering from the escaping of bubbles and decreasing bubble size. For the larger impeller tip velocity has a significant influence in decreasing the bubble size and boost the transfer rate, the PCBDT impeller has the best performance among the three impellers in experiment. In the viscous fluid, the rate of bubble coalescence and break-up both decrease, but the bubble coalescence rate is still prevailing. Compared to the gas inflation rate, the speed of agitator has a better performance. Because strengthening it is beneficial for boosting the local gas volume fraction and decreasing the nonuniformity of bubble size. The DO experiment reveals that the pressure above the liquid level has the best performance in promoting the rising of DO; while DO is also slightly boost as the liquid temperature becomes higher.The result of CFD show that the change of operating conditions or the properties of fluid can easily lead to the centre of vortex and the location of impeller discharge zone change, which is a main reason for the change of local gas volume fraction. In the combination of axial-radial impeller, the whole flow field is dependent on the lower impeller. Meanwhile the rising velocity of bubbles has a significant influence on the liquid flow field. The matching between the experimental and simulative result is good in the upper zone while bad in the lower zone, which is induced by the reason of injection effect from tiny hole and bubble models.