Date of Award
Doctor of Philosophy
Chemical and Biological Engineering
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.
Ram Ganesh Rokkam
Rokkam, Ram Ganesh, "Computational fluid dynamic modeling of fluidized bed polymerization reactors" (2012). Graduate Theses and Dissertations. 12558.