Verification of the hydrodynamics of a polyethylene fluidized bed reactor using CFD and imaging experiments

Abstract

X-ray fluoroscopy was used to produce images that showed the behavior of bubbles in a laboratory scale gas-solid fluidized bed reactor, used for the production of polyethylene. Software was developed and validated to identify and track the bubbles from image frame to image frame. Properties such as the bubble diameter, and axial velocity were obtained and compared with correlations by Werther (1978), and Kunii and Levenspiel (1991). Several parameters were varied to determine the sensitivity of the software, and determine if trends, resulting from the variation of the parameters, such as superficial gas velocity, settled bed height and mean particle size, matched those obtained by other researchers in literature. The second part of the research was to determine if a commercial computational fluid dynamic package Fluent 6.0.20 could simulate the behavior of bubbles. Using a Eulerian­Eulerian model, a parametric study was conducted to determine the effect of input variables, closing equations and solution techniques on the bubble properties. It was determined that the effective solid viscosity, calculated using the kinetic theory of granular flow played an important role in determining the bubble properties. While the bubble diameters of the experiments and simulations were comparable, the bubble axial velocities for the simulation were considerably higher. In general, it was found that the behavior of polyethylene particles in a gas-solid fluidized bed reactor did not conform exactly to theory, and as a result, is worthy of extended studies to determine the properties that govern its behavior