Hydrodynamics of a gas-solid fluidized bed with thermally induced interparticle forces

In this study, a polymer coating approach was applied to increase and adjust the level of cohesive interparticle forces (IPFs) in a gas-solid fluidized bed. This novel approach is based on coating spherical inert particles with a polymer material having a low glass transition temperature followed by using the coated particles in a gas-solid fluidized bed. Since the level of artificial IPFs inside the bed depends on the temperature of the coated particles, it was simply controlled by the temperature of the inlet air. Accordingly, the system temperature was gradually varied near and slightly above the glass transition temperature of the polymer, between 20 and 40 °C, to investigate the influence of IPFs on the fluidization behavior of the bed at different superficial gas velocities, covering fixed bed state, bubbling, and turbulent fluidization regimes. The study of hydrodynamics was carried out through the visual observation of bed height, the measurement of bed pressure drop, and the recording pressure signals in the windbox and dense bed. Experimental results indicated that enhancing the level of IPFs in the bed can alter the fluidization behavior of the bed from Geldart (Geldart, 1973) group B behavior to Geldart group A and even Geldart group C behaviors, result in a fixed bed with a looser structure that can hold more gas inside, increase the characteristic fluidization velocities, such as minimum fluidization velocity and transition velocity from a bubbling to turbulent fluidization regime, increase the tendency of the fluidizing gas passing through the emulsion phase in the bubbling regime, and result in a noticeably larger bubble size at gas velocities slightly higher than the bubbling to turbulent transition velocity of the bed without IPFs.