Hydrodynamics of compartmented fluidized beds under uneven fluidization conditions

Fluidized beds may be conveniently applied to demanding thermal and thermochemical processes thanks to their inherently good thermal performances: bed-to-surface heat transfer coefficients, effective thermal diffusivities. Collection and thermal storage of solar radiation in Concentrated Solar Power (CSP) systems is one challenging example of this application. Thermal properties may be further enhanced by non-conventional design and operation of fluidized beds based on uneven or unsteady (pulsed) fluidization. A novel concept of solar receiver for CHP (combined heat and power) generation consisting of a compartmented dense gas fluidized bed has been proposed to effectively accomplish collection of incident solar radiation, heat transfer to the working fluid of the thermodynamic cycle and thermal energy storage. This application, like others of the same kind, poses the objective of achieving controlled compartmentation of a large scale fluidized bed by selectively promoting fluidization in some regions while keeping others in a fixed state. This task may be accomplished by means of a compartmented windbox, without physical partitioning or internals immersed in the bed. This study addresses this problem by investigating the hydrodynamics of a near-2D dense gas-fluidized bed operated at ambient conditions and equipped with a compartmented fluidizing gas distributor. The hydrodynamics was characterized by pressure measurement at different locations in the bed to mark the onset of local fluidization and to map the extension and location of fluidized and de-fluidized regions in the bed for different choices of operating conditions. An important follow-up of the study is the analysis of the dynamics of the bubble and emulsion phase in an unevenly fluidized bed. Dynamical patterns of bubble and emulsion phases have been scrutinized by analysis of space- and time-resolved void fraction profiles obtained by electrical capacitance measurements.Altogether results indicate that a perfectly compartmented fluidized bed cannot be obtained simply using a compartmented windbox. However a proper choice of fluidizing gas partitioning between the compartments enables good control of the local fluidization conditions, of gas cross-flow between the compartments, of large-scale solids circulation.