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(187c) CFD Modeling of Electrostatic Effects On Catalyst and Fine Particles in Fluidized-Bed Reactors

Authors: 
Rokkam, R. G., Iowa State University
Fox, R. O., Iowa State University
Muhle, M. E., Univation Technologies


Electrostatic charges are known to influence the hydrodynamics of gas solid fluidized bed reactors. Excessive charges on particles cause agglomeration and wall sheeting (Hendrickson, 2006). Charges on particles are formed due to particle-particle and particle-wall collisions. When particles collide and separate there is charge formed on the particles and this phenomena is known as Triboelectrification. The development and verification of the electrostatic model with a simple test case is presented in AICHE fall meeting, 2008 (Rokkam et al, 2008). In this work the application of the electrostatic model on pilot plant reactor will be presented and two cases are considered here:

(1) Continuous Catalyst Injection: The objective is to study the electrostatic effects on catalyst particles. The multi-fluid model solves for one gas and four solid phases and the catalyst is injected after the bed is fully fluidized. Three cases are run with different charge on catalyst (positive, zero, negative). The charge magnitude is approximated to realistic conditions.

(2) Effect of Electrostatics on Entrainment: The objective is to study the electrostatic effects on fine polymer particles. Multi-fluid model solves for one gas phase and four solid phases. The bed is initialized with a uniform distribution of fine particles and other solid phases.

An Eulerian-Eulerian based multi-fluid model is used to solve the hydrodynamics of gas-solid fluidized-bed reactor. The multi-fluid model is solved in commercial CFD code Fluent 6.3 and uses the kinetic theory granular flow to calculate the solids pressure and viscosities. The volume fraction and diameter of the solid phases are obtained from Chemical reaction engineering model and quadrature method of moments (Fan et al, 2007). Time dependent two-dimensional simulations are done on a pilot-plant scale fluidized bed reactor.

REFERENCES

Fan R, Fox R O, Muhle M E. Role of intrinsic Kinetic and Catalyst Particle Size Distribution in CFD Simulations of Polymerization Reactors. 12th International Conference in Fluidization in Vancouver, Canada. 2007

Hendrickson G. Electrostatics and gas-phase fluidized bed polymerization reactor wall sheeting. Chemical Engineering Science. 2006; 61(4), 1041-1064.

Rokkam R G, Fox R O, Muhle M E. Cfd Modeling of Polymerization Fluidization Reactor. Presented at Annual AICHE Meeting,Philadelphia. 2008