Degree Type

Thesis

Date of Award

2015

Degree Name

Master of Science

Department

Chemical and Biological Engineering

First Advisor

Rodney O. Fox

Abstract

A one-dimensional multiphase Computational Fluid Dynamics (CFD) model was successfully developed in MATLAB and applied toward modeling the behavior of a generalized liquid-solid tubular loop polypropylene polymerization reactor. The model equations were based on a two-fluid Eulerian model with the key assumption that a constant value for overall circulation is maintained throughout the reactor profile. Features implemented into the model include the kinetic theory of granular flow, a one-dimensional turbulence model, growth of the solid phase due to polymerization, harvesting of the solid phase through an overall pressure drop PI control system, and overall circulation rate controlled through a specifiable pump performance curve. The purpose of this model was to identify potential causes of axial maldistribution and pressure oscillations in tubular loop reactors and examine the response of the reactor control system to any maldistribution developed. Without considering any growth or harvesting of the solid phase, hydrostatic force drove only a small variation in solid phase concentration between the upward and downward legs. There were no significant changes to this observation when the fluid viscosity or the particle average size, maximum packing, or restitution coefficient were varied. When growth and harvesting of the solid phase were applied to a uniform reactor profile, sustained maldistribution of the solid phase was developed in the form of periodic regions of more concentrated solid phase. These in turn caused significant pressure oscillations. Upon the introduction of preexisting highly concentrated plugs, the growth of the longer plugs was sustained until the plug concentration approached maximum packing. Application of a pump performance curve resulted only in the dampening of the developed pressure oscillations. While changes to the control system such as lengthening the control response interval and building in a delay to the response were successful in mitigating the formation of plugs and sustained pressure oscillation starting from a uniform reactor profile, those modifications were not so successful when handling an initially-applied plug. It is recommended that a more robust control system than the overall pressure drop be used to more effectively control the solid phase profile of tubular loop polymerization reactors.

DOI

https://doi.org/10.31274/etd-180810-4338

Copyright Owner

Michael Christopher Baker

Language

en

File Format

application/pdf

File Size

193 pages

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