Dynamic behavior of fluidized bed reactors for gas phase LLDPE polymerization

Conference Dates

May 22-27, 2016


Gas phase processes are widely used for the polymerization of ethylene and propylene, where in contrast to most conventional fluidized bed reactor (FBR) systems, the solid phase (polymer) is of primary importance. Insightful knowledge of FB hydrodynamics is vital for proper gas-solid (G-S) reaction modeling, to ensure proper process development and control. Modeling flow patterns; size, distribution and velocity of bubbles is challenging. Large gas velocities are needed to ensure good mixing, uniform gas and condensate droplet distribution in the reaction zone is vital for heat removal and to further achieve higher production rates. Most of the numerical works and/or experimental data available are limited to 2D (or pseudo-2D) systems, smaller and pilot plant reactors, with very few actually modelling commercial scale units. Hence a continuous desire to increase the level of understanding by studying gas and particle flow structures in real commercial reactors is needed.

In this work we studied the dynamic behavior of a commercial fluidized bed LLDPE reactor through detailed mathematical modelling using a tanks-in-series approach for gas-liquid-solids. Numerical simulations are done with Barracuda CFD as an extension of the developed mathematical model especially for bubble dynamics. Plant data is used to validate and verify the mathematical model and CFD. Axial gradients, solids and gas, and temperature profiles are investigated. The effects of particle size, gas velocity, liquid holdup and powder recirculation on flow behaviors are also investigated. A good agreement has been observed between both numerical model and CFD predictions and the actual plant data.

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