Degree Type

Dissertation

Date of Award

2012

Degree Name

Doctor of Philosophy

Department

Chemical and Biological Engineering

First Advisor

Rodney Fox

Abstract

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, particle elutriation, bubble size, bubble shape etc. Accumulation of electrostatic charges in the fluidized-bed can lead to operational issues. In this work a first-principles electrostatic model is developed and coupled with a multifluid computational fluid dynamic (CFD) model to understand the effect of electrostatics on the dynamics of a fluidized-bed. The multifluid CFD model for gas-particle flow is based on the kinetic theory of granular flow closures. The electrostatic model is developed based on a fixed, size-dependent charge for each type of particle (catalyst, polymer, polymer fines) phase. The combined CFD model is first verified using simple test cases, validated with experiments and applied to a pilot-scale polymerization fluidized bed reactor. The

CFD model reproduced qualitative trends in particle segregation and entrainment due to electrostatic charges observed in experiments. For the scale up of fluidized bed reactor, filtered models are developed and implemented on pilot scale reactor.

DOI

https://doi.org/10.31274/etd-180810-447

Copyright Owner

Ram Ganesh Rokkam

Language

en

File Format

application/pdf

File Size

131 pages

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