(22b) Computation of Sheeting Phenomena IN Fluidized Bed Polymerization Reactors

Fluidized bed polymerization reactors are known to form solid sheets next to the reactor walls (Hendrickson, Chemical Engineering Science 61 (2006) 1041 ? 1064: Xie, et al, Ind. Eng. Chem. Res. 33 (1994) 449-479) Hendrickson suggests that this phenomenon may be due to electrostatics We have measured the charge to mass ratio of 841 µm polypropylene particles in a small fluidized bed and used these data to solve the Poisson's equation for the voltage distribution in a 3 m diameter commercial fluidized bed polymerization reactor. The multiphase CFD kinetic theory based model and the computer code without the electric field is described in the book, Computational Techniques, D. Gidaspow and V. Jiradirok, Nova Science Publishers 2009. With the electric field generated by the particles, the volume fraction of the particles at the wall becomes as high as 0.5 versus 0.25 in the bulk of the bed. With no electric field the time-average volume fractions are all approximately 0.23. Hence the sheeting phenomena in the polymerization reactor have been explained to occur due to migration of particles caused by the electric field generated by the surface charge of particles.