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(22e) CFD Modeling of Aggregation and Breakage In Gas-Solid Fluidized Beds

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


Fluidized-bed reactors are widely used in chemical, petroleum, food, pharmaceutical, polymer and biochemical industries. It is important to understand the dynamics of the fluidized beds for the scale-up to commercial reactors. Agglomeration in gas-solid fluidized beds is known to influence the bed dynamics, bubble shape, size and bed circulation patterns (Hendrickson, 2006). Agglomeration in fluidized beds can be caused due to electrostatics or thermal effects. Direct quadrature method of moments (DQMOM) is implemented in a multi-fluid model for simulating polydisperse gas-solid fluidized-bed reactors (Fan et al, 2004). DQMOM is based on the direct solution of the transport equation for weights and abscissas of the quadrature approximation. The moments of the distribution can be obtained from the weights and abscissas. The calculation of the quadrature approximation through this direct formulation presents the advantage of being directly applicable to multi-variate PBE. The aggregation and breakage kernels obtained from kinetic theory (based on collisions). Two-dimensional time dependent simulations are run using MFIX (Multiphase Flow with Interphase Exchanges). Kinetic theory of granular flow (KTGF) and frictional theory are used to compute the solids pressure and viscosities. No slip boundary condition for gas phase and free slip boundary condition for the solid phase are used. Two and Three nodes are used to represent the PSD and describe the phenomena like elutriation and segregation. CFD prediction of evolution of the PSD in a fluidized bed reactor with aggregation and breakage will be presented.

References

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

Fan R., Marchisio D.L. and Fox R. O., Application of the direct quadrature method of moments to polydisperse gas-solid fluidized beds, Powder Technology, 139, 7-20, 2004.