Hydrodynamics of compartmented fluidized beds under uneven fluidization conditions

Abstract

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.

Scaling-up the Calcium-Looping Process for CO₂ Capture and Energy Storage

“…Salatino et al (Salatino et al, 2016) analyzed the thermal performance of a bubbling fluidized bed of sand particles to store energy from CSP in a sensible form. To evaluate the hydrodynamics of the process, a near-2D f luidized bed prototype was constructed ( Migliozzi et al, 2017). The use of compartmented dense gas f luidized beds was proposed by Chirone et al (Fig.…”

Fluidized Beds for Concentrated Solar Thermal Technologies—A Review

“…Uneven and unsteady fluidization are the keys for enhancing bed thermal diffusivity and bed-to-surface heat transfer (Salatino et al, 2016;Tregambi et al, 2016;Migliozzi et al, 2017) underlying the use of compartmented FB solar receiver with inherent TES. The concept outlined in Figure 3 (Solimene et al, 2017) and Table 1 (Type D) is implemented in a beam-down solar collection/reflection scheme.…”

“…This goal has been pursued proposing a compartmented windbox with independent feeding of the fluidizing gas. In a dedicated experimental campaign (Migliozzi et al, 2017) the effectiveness of uneven bed fluidization by a compartmented gas distributor was tested. Further experiments (Tregambi et al, 2016) were directed to assess the potential of uneven fluidization to improve heat transfer from the highly irradiated beam footprint on the bed, e.g.…”

110th Anniversary: Calcium Looping Coupled with Concentrated Solar Power for Carbon Capture and Thermochemical Energy Storage

“…Indirect heating of the FB may be accomplished by concentrating the solar radiation onto a cavity or an exposed surface, whence heat is eventually transferred to the solid suspension by convection/conduction. , Direct heating of the FB may be accomplished by concentrating solar radiation directly onto the fluidized suspension, via openings or optically accessible windows and transparent walls. − Direct heating enables higher process temperature, as bed solid is directly heated by the concentrated radiation (i.e., no heat flux limitations due to cavity/walls are foreseen). However, axial/radial gradients inside the bed can be established owing to the highly concentrated and uneven incident solar radiation with a potential impact on the performance of reactive materials. − The use of an uneven and unsteady fluidization strategy to enhance the bed thermal diffusivity and limit the time/spatial temperature nonhomogeneity is currently being pursued. ,, …”