Hydrodynamics of a Multisized Particle Mixture in Shallow Fluidized Bed With Immersed Tubes

Inert solid particles have made the integration of more efficient power cycles with super high operating temperatures into the concentrated solar power (CSP) station feasible. Fluidized bed heat exchangers with feature of high heat transfer coefficient have great application potential in the particle-based CSP. However, the parasitic loads of the additional fluidizing gas loop and the finely sieved monosized particles may deteriorate the economic efficiency of the integrated system. In order to cope with this problem, a conceptual design of a shallow fluidized bed (SFB) heat exchanger is proposed for the new generation CSP technology. Fluidization characteristics of bauxite particles with a nonuniform particle size distribution in SFB with immersed tubes are investigated with a combination of experimental measurements and computational fluid dynamics simulations. Results show that the static bed height and opening area ratio of the distributor has insignificant influence on the range of semifluidized region and the minimum fluidization velocity U_mf. The standard deviation of bed pressure drop σ in the grid region can be used as an alternative criterion for identifying the fluidization state. A range of superficial velocity that distinguishes two different solid circulation patterns exists, with its boundary values being four times and eight times the U_mf, respectively. The immersed tubes can inhibit the asymmetric particle circulation patterns from developing in the SFB, but cause a substantial increase in the σ within the grid region.