chemical engineering research and design 86 ( 2 0 0 8 ) 329–343 available at www.sciencedirect.com journal homepage: www.elsevier.com/locate/cherd Population balance equations’ application in rotating fluidized bed polymerization reactor Azita Ahmadzadeh * , Hamid Arastoopour, Fouad Teymour, Matteo Strumendo Department of Chemical and Biological Engineering, Illinois Institute of Technology, Chicago, IL 60616, USA article info Article history: Received 14 May 2007 Accepted 6 February 2008 Keywords: Olefin polymerization Population balance Rotating fluidized bed Gas/solid flow Multiphase flow abstract Gas phase olefin polymerizations are now widely achieved in fluidized bed reactors. In flu- idized bed poly-olefin reactors, small catalyst particles (20–80 m) are introduced into the bed, and when exposed to the gas flow (monomer), polymerization occurs. At early stage of polymerization, the catalyst particles fragment into a large number of small particles then the polymer particles grow continuously, reaching a typical size of 1000–3000 m. A success- ful analysis of this process not only should account for the kinetics of the polymerization but also should include the particles mixing and particle size distribution in the reactor. Rotating fluidized bed reactors are the promising process to have a better control on the particle size distribution, particle separation and increasing the reactor efficiency. Due to the high rotational acceleration (e.g. 14 “g”) that can be imposed in these kinds of reactors, our preliminary results showed that the amount of throughput, i.e. monomer flow rate, can be increased without worrying of changing the fluidization regime from well mixed condition to slugging, so the production rate and in consequence the polymerization yield will increase. In this study the population balance approach is used to describe the evolution and growth of the particle size in gas–solid rotating fluidized bed olefin polymerization reactors along with CFD using Fluent program. The SMM (standard method of moments) method and QMOM (quadrature method of moments) method are used to solve the population balance equations; these are coupled with the conservation equations of mass and momentum for the gas and solid phases. Simulations have been performed with; a) constant particle growth rate and b) variable particle growth rate that is a function of polymerization reaction rate. © 2008 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved. 1. Introduction Low-pressure gas phase polymerization is widely used for polymerization of ethylene and propylene in fluidized bed reactors. In spite of the significant application of this kind of reactors, they have shown limited flexibility in achieving high gas throughput because of the possibility of slugging and the inability to provide suitable heat transfer rates. To over- come these disadvantages and enhance the efficiency of the fluidized reactors, the feasibility of using the rotating fluidized bed reactors for this purpose is studied in this paper by using computational fluid dynamic (CFD) approach. ∗ Corresponding author. E-mail address: ahmaazi@iit.edu (A. Ahmadzadeh). In brief summary, the gas-phase polymerization reaction in a fluidized bed begins when a catalyst particle, with a size of 15–100 m in diameter is injected into the reactor. The gas phase monomer diffuses through the boundary layer around the catalyst particle and through its pores to reach the active sites, where the polymerization takes place. In few seconds, the pores of the catalyst support will fill up with the polymer. Then the support ruptures into many fragments, often called micrograins, microparticles or primary particles. Once the par- ticles fragment, the volume of polymer inside the particle continues to grow as the monomer diffuses to the active sites. This process of expansion continues until the polymer parti- cles exit the reactor; at which point they would have reached 0263-8762/$ – see front matter © 2008 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved. doi:10.1016/j.cherd.2008.02.004