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(292a) Cfd Modeling of Polymerization Fluidization Reactor

Rokkam, R. G., Iowa State University
Fox, R. O., Iowa State University
Muhle, M. E., Univation Technologies

Polyethylene is one of the most widely used plastics, and over 60 million tons are produced worldwide every year. Polyethylene is obtained by the catalytic polymerization of ethylene in gas and liquid phase reactors. The gas phase processes are more advantageous, and use fluidized bed reactors for production of polyethylene. Since they operate so close to the melting point of the polymer, agglomeration is an operational concern in all slurry and gas polymerization processes. Electrostatics and hot spot formation are the main factors that contribute to agglomeration in gas-phase processes. Electrostatic charges in gas phase polymerization fluidized bed reactors are known to influence the bed hydrodynamics, elutriation, bubble size etc. Accumulation of electrostatic charges in the fluidized bed can lead to operational issues. The objective of this work is to develop a multi-fluid model which can explain the electrostatic behavior in gas-solid fluidized beds. The particles are assumed to carry a prescribed charge. A Poisson equation is solved for the electric field which develops due to presence of charged particles. A multi-fluid model solves mass and momentum equation for one gas and three solid phases. The diameter and volume fraction of the solid phases is obtained from the reaction engineering model and quadrature method of moments. Kinetic theory of granular flow is used for calculating particle pressure and viscosities. Time dependent three dimensional simulations have been performed on a pilot plant reactor using Fluent 6.3.