Study On Transport Characteristics Of Liquid-Solid In Loop Reactor

Multiphase flow was a fundamental physical phenomenon in the natural world and was widely applied in the fields of industry, agriculture, national defense and environmental protection. In a long time, multiphase flow reaction engineering was considered a discipline area which was very difficult to be described and disposed by mathematic simulation and accurate test. It involves fluid dynamics, thermodynamics, heat transfer, mass transfer, chemical reaction and rheology. There are many problems to be solved in the multiphase flow reaction engineering, which was full of challenge. The thesis established a mathematic model of loop reactor based on the kinetic theory of granular, two-fluid model, mass transfer model and liquid-solid heat transfer model, and investigated the multiphase flow transport characteristics of momentum, heat and mass and polymerization behaviors of propylene.The creative works of the thesis could be summarized as following:1. An Euler-Euler two-fluid model based on the kinetics of granular was built to study the flow patterns of liquid-solid two-phase flow in pipeline. The mean pressure gradients were simulated at different slurry inlet velocity which is greater than the sedimentation velocity of particles. The comparison of simulated results and experimental results showed that the presented model is available to describe tubular pressure gradients and slurry flow patterns. The transition and development of liquid-solid flow with the distance of flow were investigated. Liquid-solid flow reached the full developed pattern when the ratio of the distance of flow to tubular diameter was larger than fifty. The slurry flow pattern and volume fraction distribution were presented at different slurry velocity. The slip velocity magnitude was usually small, and the effect of the slip velocity on the slurry flow was negligible in the heterogeneous and sliding bed flow.2. An Euler-Euler two fluid model based on the kinetics of granular was established to simulate the flow patterns of liquid-solid two-phase in tubular loop reactor. The mean pressure gradients were simulated at different slurry inlet velocity when the slurry inlet velocity was higher than the sedimentation velocity of particles. The comparison of numerical results with the calculated value of empirical equation for liquid-solid two-phase flow showed that the presented model is available todescribe pressure gradients and slurry flow patterns in tubular loop reactor. The simulation results showed that the volume fraction and velocity distributions of liquid-solid two-phase flow were different at up-section, curve- section and down-section of tubular loop reactor and that the hypothesis of plug flow of liquid-solid two phase in loop reactor has some deviation. The slip velocity of liquid-solid existed at slurry velocity of v=3m·s^-1. The slip velocity magnitude decreased with slurry velocity increasing and could be neglected at slurry velocity v=7m·s^-1 Turbulence kinetic energy distributions were non-uniform at curve- section in tubular loop reactor. Turbulence kinetic energy was very large at the surrounding wall. At the same cross section, the turbulence kinetic energy increased with slurry velocity increasing at curve- section in tubular loop reactor.3. Based on the two-fluid momentum transfer model, the liquid-solid mass transfer model was built by considering the characteristics of propylene polymerization reaction kinetics and heat transfer in tubular loop reactor. The transport characteristics of mass in an industrial loop reactor of propylene polymerization were studied. The comparison of numerical solid volume fraction with the measured value in the industrial reactor showed that the presented mass transfer model was available to describe mass transfer in tubular loop reactor. Volume fraction of solid was found to be different at up-section, curve- section and down- section of tubular loop reactor. Volume fraction of solid was uniform at up-section, but non-uniform at curve- section and down- section of tubular loop reactor. Liquid-solid flow tended to uniform flow along the flow direction at down- section of tubular loop reactor. At curve- section of loop reactor, the solid particle concentration at lateral wall increased with the increase of particle diameter and slurry velocity because of the secondary flow action enhancement. Therefore the solid particle concentration at curve- section was much more non-uniform.4. The liquid-solid heat transport characteristics in an industrial tubular loop reactor of propylene polymerization was discussed based on the mathematic model considering the two-fluid momentum transfer, mass transfer, heat transfer and polymerization reaction kinetics of propylene. The simulated results of reaction temperature have good agreement with the measured value in the industrial equipment, which showed that the presented mathematic model of the loop reactor was available to describe heat transfer in tubular loop reactor. Temperature distributions were different at up-section, curve- section and down- section of tubular loop reactor.Temperature distribution was centrosymmetrical at up-section, but temperature distributions were not centrosymmetrical at curve-section and down-section of tubular loop reactor. With increase of inlet slurry velocity and solid volume fraction the temperature distributions at up-section, curve-section and down-section of tubular loop reactor reduced. The cooling capacity of jacket increased with the decrease of cool water temperature or cooling wall temperature.