Session: 06-03: CSP Receivers and Reactors II

Paper Number: 156002

156002 - Impacts of Pulsed Fluidization on Heat Transfer and Bubble Hydrodynamics in Bubbling Fluidized Beds 

Abstract: 

Oxide particles have been identified as a pathway for high-temperature thermal energy storage for next generation central-tower CSP plants to drive efficient sCO₂ power cycles for lower-cost dispatchable renewable electricity.  Several different approaches have been tested to address the challenge of capturing heat into the oxide particles at high temperatures in central-tower particle receivers.  These include directly radiated designs such as the centrifugal receiver and falling curtain designs[1], and indirect receivers which include an up-flow fluidized-bed receiver[2], quartz tube receivers[3], and counterflow fluidized tubular planar cavity receivers[4].   Indirect particle receivers, which use small, low-cost particles (e.g., silica sand), must achieve high heat transfer rates (>1000 W/m²K) to reach particle temperatures above 700°C, while maintaining wall temperatures below 900°C under solar fluxes >200 kW/m². Mild bubbling fluidization has been shown to achieve the necessary heat transfer rates in these indirect particle receivers[5].

Pulsed fluidization has been considered to further improve bed-wall heat transfer performance and control particle flow structures in fluidized bed particle receivers. Research in fluidized bed dryers has indicated that pulsed gas flows during fluidization can provide more homogeneous fluidization while decreasing gas flow demands[6,7], and associated parasitic losses due to fluidization.  In this study, a series of narrow-channel fluidized bed heat transfer tests explored how pulsed fluidization impacts bed-wall heat transfer, axial dispersion, and flow stability in a lab-scale fluidized bed.  These results show that pulsing the fluidizing gas at frequencies from 0-2 Hz with a 50% duty cycle has no significant impact on bed-wall heat transfer. While pulsed fluidization did not significantly increase heat transfer, its potential to reduce bubble coalescence could improve operational stability in taller fluidized beds where uniform heat distribution is critical.  Recent lab scale flow visualization work with continuous gas flows has shown bulk flow instabilities with higher fluidizing gas velocities, which can be mitigated through pulsed gas flow. This improved stability is especially relevant to the taller fluidized beds considered for particle receivers which may be susceptible to the development of slug flow as bubbles coalesce. In addition to impacts upon flow stability, pulsed fluidization offers a pathway to control the degree of axial dispersion within the bed. High degrees of axial dispersion in fluidized beds have previously been shown to decrease the log mean temperature difference in particle heat exchangers, thus reducing the overall performance significantly[8]. The oscillations in the gas flow limit the length scales of mixing within the fluidized beds, enabling a pathway to control the degree of mixing within the bed while still achieving high local bed-wall heat transfer. This paper details and quantifies the results and impacts of pulsed fluidization on heat transfer, flow stability, and axial mixing in a lab-scale narrow channel fluidized bed, supporting improved particle-HX and particle receiver design for next-generation CSP-TES systems.

[1] Ho, C. A review of high-temperature particle receivers for concentrating solar power. Applied thermal engineering. 109. 958-969, (2016)

[2] Le Gal, A. et al., “Experimental results for a MW-scale fluidized particle-in-tube solar receiver in its first test campaign” Solar Energy 262. 111907. 2023.

[3] Yu, Y. et al. “Performance modeling of quartz tube for gravity-driven solid particle solar receiver” INJHMT 207, 123937. 2023.

[4] Jiang, K. “Experimental performance of gas-solid countercurrent fluidized bed particle solar receiver with high-density suspension” Applied Thermal Engineering 213. 118661. 2022.

[5] Martinek, Janna, and Zhiwen Ma. 2024. A Planar-Cavity Receiver Configuration for High-Temperature Solar Thermal Processes: Preprint. Golden, CO: National Renewable Energy Laboratory. NREL/CP-5700-87566

[6] Jia, D. “Heat and mass transfer in pulsed fluidized bed of biomass” PhD Dissertation. University of British Columbia. 2017.

[7] Zhang, D. “Heat transfer in a pulsed bubbling fluidized bed” Power Technology 168, 21-31. 2006.

[8] Arhur-Arhin, W. et al. "Demonstration of a multi-channel fluidized bed particle–supercritical carbon dioxide heat exchanger for concentrating solar applications" Applied Thermal Engineering Volume 248, Part B. 123242. 2024.

Presenting Author: Keaton Brewster Colorado School of Mines

Presenting Author Biography: Keaton is a PhD candidate in mechanical engineering at the Colorado School of Mines. He works in gas-solid fluidized bed heat and mass transfer for applications in indirect particle receivers and particle-sCO2 heat exchangers. This has led to collaboration on related projects with Brayton energy and the National Renewable Energy Laboratory.