Experimental Study And Numerical Simulation On The Hydrodynamics In Gas-Liquid (slurry) Reactors

Gas-liquid (slurry) reactors have been widely used in petrochemical, biochemical, energy and environmental processes. Study on the hydrodynamic behavior in such reactors can provide guidance in optimizing the existing reactors or developing and designing a novel reactor with high performance, which is very important to the more and more intense energy and environmental problems. In this work, with developing the reactor for direct synthesis of dimethyl ether from syngas as application background, the hydrodynamic behaviors in gas-liquid (slurry) reactors were systematically studied by both experimental measurement and numerical simulation.Measuring techniques for multiphase flows were studied and developed. A fiber optic probe was developed for measuring the bubble behavior, in which the signal analysis and data processing algorism were proposed and the corresponding software was developed. The application of the Doppler ultrasound velocimetry DOP2000 in liquid-solid and gas-liquid two-phase flows was studied, and the methods of measuring solid concentration in a liquid-solid system and measuring bubble rise velocity and liquid velocity simultaneously in a gas-liquid system with low gas holdup were proposed. Laser Doppler velocimetry with a modified probe structure was used to measure the liquid velocity in a gas-liquid system with a relatively high gas holdup, and good results were obtained.The hydrodynamic behaviors in an external loop airlift slurry reactor (ALSR) were systematically studied. The influences of the superficial gas velocity,solid holdup and flowing resistance on gas holdup, bubble size, bubble rise velocity and liquid velocity were systematically studied. A hydrodynamic model for predicting the gas holdup and suspension circulation velocity was developed for ALSR based on momentum balance, and was successfully used to design a pilot scale ALSR for direct synthesis dimethyl ether from syngas. Numerical simulations were carried out on the hydrodynamics in a gas-liquid (slurry) system in the framework of two-fluid formulation coupled with a k-( turbulence model. Based on analysis of the two-fluid model reported in literature, improvement was made in the description of interphase forces and turbulence modification. The improved model was implemented in CFX4.4 and numerical simulations were carried out. Comparison with the experimental data shows that the interphase forces and turbulence modification have notable influence on the hydrodynamics in a gas-liquid (slurry) system and the improved model in this work has a good prediction ability.Population balance model (PBM) was used to describe the bubble size distribution in a gas-liquid system, and bubble coalescence and breakup models with different mechanism were proposed. The proposed model was numerically solved to calculate the bubble size distribution, and was successful in predicting the regime translation theoretically and in obtaining good results of the bubble size distribution both in homogeneous and heterogeneous bubble regimes.A CFD-PBM coupling model was proposed to combine the advantages of CFD to predict the entire flow field and of PBM to predict the local bubble size distribution. In the CFD-PBM coupling model, the bubble breakup and coalescence were taken into account and the bubble size distribution was predicted, which in turn, was used to calculate the interphase forces and turbulence modification, showing good ability to predict the hydrodynamic behaviors both in homogenous and heterogeneous bubble regimes.