(398e) Agglomeration in Wet Gas Fluidized Systems

Unit operations involving liquid-wetted particles, which are partially or fully fluidized by a gas, are common in chemical process industries. Agglomeration of particles in these devices, desirable in applications such as granulation and unwanted in others, affects flow patterns and other transport characteristics. When two wet particles collide, a liquid bridge forms whose filling rate is dictated by particle size, as well as surface tension and viscosity of the liquid. The liquid bridge gives rise to capillary and viscous inter-particle interaction forces (Lian 1993, Mikami 1998, Pitois 2000, Willett 2000, Shi 2008, Mohan 2014, Ennis 1990).

In the present study, we consider a dilute assembly of uniformly wetted particles fluidized by a gas, and examine the initial formation and growth of agglomerates. Specifically, we follow the dynamics of agglomeration through CFD-DEM simulations of a collection of particles in a periodically repeating domain (Zhou 2010, Kloss 2012). Snapshots obtained from these simulations are then analyzed to extract agglomerate size distribution, agglomerate slip velocities, and liquid bridge coordination number distribution. Simulations have been done for different liquid loading levels, surface tension and viscosity values.

Our simulations reveal two stages of agglomeration: an initial growth phase where the agglomerate size and liquid-bridge coordination number increase rapidly with time, followed by a much more gradual evolution of the agglomerate size distribution and liquid bridge coordination number towards statistically steady values.

The roles of viscous and capillary forces on these two-stage agglomerate growth events will be discussed in this presentation.   

References :

Ennis, B. J., Li, J., Tardos, G. I. & Pfeffer, R., 1990. The influence of viscosity on the strength of an axially strained pendular liquid bridge. Chem. Engng Sci. , Volume 45, pp. 3071-3088.

Kloss C. , Goniva C., Hager A., Amberger S., Pirker S., 2012. Models, algorithms and validation for opensource DEM and CFD-DEM, Progress in Computational Fluid, v. 12, No. 2-3. pp. 140-152.

Lian, G., Thornton, C., Adams,M.J., 1993. “A theoretical study of the liquid bridge forces between two rigid spherical bodies. Journal of Colloid and Interface Science 161,138–147.

Mikami, T., Kamiya, H. & Horio, M., 1998. Numerical simulation of cohesive powder behavior in a fluidized bed.. Chem. Eng. Sci., 53(10), pp. 1927–1940.

Mohan, B., Christoph Kloss C., Johannes Khinast J., and Radl S., 2014. “Regimes of Liquid Transport through Sheared Beds of Inertial Smooth Particles.” Powder Technology 264, pp. 377–95.

Pitois, O., Moucheront, P., Chateau, X., 2000. Liquid bridge between two moving spheres: an experimental study of viscosity effects. Journal of Colloid and Interface Science 231,26–31.

Shi D., McCarthy J.J. , Numerical simulation of liquid transfer between particles, Powder Technology. 184 (2008) 64–75.

Willett, C. D., Adams, M. J., Johnson, S. A. & Seville, J. P. K., 2000. Capillary Bridges between Two Spherical Bodies. Langmuir, v. 16, pp. 9396-9405.

Zhou Z. Y., Kuang S. B., Chu K. W., Yu A. B., 2010. Discrete particle simulation of particle–fluid flow: model formulations and their applicability. J. Fluid Mech., v. 661, pp. 482-510.