Pilot-scale Fluidization Study On A Novel Cr-v Bimetallic Catalyst For Ethylene Polymerization

Chromium catalysts have been dominating the industrial production of commercial polyolefins. As the envelope continued to be pushed by a new proprietary Chromium-Vanadium bimodal HDPE catalyst which was developed in our laboratory, theoretical and experimental methods are to be adopted in this research to investigate into the pilot-scale process for the novel catalyst by designing cold flow model equipment of one kilogram silica capacity in a bid to understand the operation pattern of fluidized bed-including fluidizing phenomena, bed expansion, optimum range of air inlet velocities and radial and axial distribution of bed pressure drop through trials at different superficial gas velocities and solid loads. Fluent is also adopted to simulate fluidized bed of the same size as the cold model to perceive insightfully such flow pattern as solid holdup and velocity distribution, and to cross-check conclusions drawn from the cold model experiments in the viewpoint of numerical simulation.Thus in this work, a cold flow model installation of fluidized bed is designed with inner diameter of120mm, fluidizing section height of910mm, a distributor plate with the nozzle ratio of2.83%and pressure taps on the bed sides every other10cm.1kg silica is filled at an aspect ratio of2.52. Results show that the silica specimen is a Geldart B type particle, which expands at a ratio lower than1.7under well fluidizing velocities. Additionally, the operation velocity should be greater than1.18cm/s so that a stable stage of the bed pressure drop over velocity can be reached. And the velocity ranging from2.21to2.95cm/s promises a uniform axial pressure drop distribution at all bed regions except the bottom one, uniform movement of scattered small bubbles can be observed and overall bed pressure drop maintains stable. When the velocity goes above3.68cm/s, non-bottom bed regions no longer show its uniformity in axial pressure drop distribution, because higher gas inlet separates dense and dilute phase only to make fluidizing pattern worse with collateral damage of particle collision and more unnecessary gas intake. Verifications by CFD simulation present the existence of a higher pressure drop at bed bottom and a uniform distribution at higher regions. The central bed has upward velocities with lower solid holdup owing to the influence from fluid drag force, and near the bed side particles go downward with slightly higher solid holdup after being squeezed by bubble movement in the bed center. This thesis can ultimately provide reference to the further development of the hot flow fluidized bed for catalyst support calcination.