CFD Modeling of Electrostatic Forces in Gas-Solid Fluidized Beds

Abstract

Electrostatic charges in gas-solid fluidized beds are known to influence the bed dynamics, bubble shape and size, particle agglomeration, segregation and entrainment. In practice, accumulation of electrostatic charges in fluidized beds can lead to operational issues. The present work focuses on the modeling of electrostatics in gas-solid fluidized beds. The particles are assumed to carry a prescribed size-dependent charge, and charge generation and dissipation are not modeled. To consider the effects of bi-polar charging the polarity of the charge carried by fine particles is taken opposite to that of coarse particles. The magnitude of particle charges is approximated to realistic charges reported in the literature. The principal objective is to develop a multi-fluid Euler-Euler model that can describe electrostatic forces on charged particles in gas-solid fluidized beds. The multi-fluid model is solved in a commercial CFD code (ANSYS Fluent 6.3) and uses the kinetic theory of granular flow for calculating solids pressure and viscosity. The electric field, generated by the presence of charged particles, is solved for at every time step in the time-dependent simulation. The electrostatic forces, proportional to the gradient of the electric field and the particle charge, lead to charge-dependent forces on the particles. The electrostatic model has been developed and applied to a two-dimensional fluidized bed. Charge-dependent segregation is found to vary with the polarity and magnitude of the charge on the solid phase as a function of the particle size.