Session: 07-02: Fluidized Bed Heat Exchangers

Paper Number: 164434

164434 - Development and Demonstration of a Novel High-Performance Particle-Supercritical Carbon Dioxide Heat Exchanger Employing Plate-Fin Bubbling Fluidized Beds 

Abstract: 

Inert oxide particle based thermal energy storage (TES) coupled to high-efficiency supercritical carbon dioxide (sCO₂) recompression closed Brayton cycles operating at over 700°C and 20 MPa have been identified for next-generation concentrated solar power (CSP) plants. The primary particle-sCO₂ heat exchanger (PHX), which facilitates the transfer of solar heat stored in the TES particles to the sCO₂ working fluid for dispatchable electric power generation, is projected to require overall heat transfer coefficients U_HX > 600 W m^-2 K^-1 and area specific costs < $2500 USD m^-2 to meet US Department of Energy 2030 SunShot cost targets of $150 USD kW_t^-1. The PHX is generally constructed from high-performance Ni-based alloys to meet the demanding temperature and pressure requirements, with manufacturing costs of current state-of-the-art printed-circuit or shell-and-tube architectures exceeding $4000 USD m^-2. Furthermore, PHXs to-date that employ moving packed-beds (MPB) and smooth-walled bubbling fluidized beds (BFB) on the particle-side have demonstrated U_HX < 400 W m^-2 K^-1, where performance limitations are attributed to low effective particle-wall heat transfer for MPBs and bubble-induced longitudinal dispersive mixing for BFBs. Therefore, development of a robust, scalable, and cost-effective PHX that provides highly effective heat transfer is crucial to enable commercial realization of Gen3 CSP with particle-based TES.

Brayton Energy has developed a novel, high-performance counterflow particle-sCO₂ PHX. The prototype test article comprises ten parallel heat exchanger cells with inter-cell narrow-channel bubbling fluidized beds (0.8 m long, 0.10 m wide, 9.5 mm deep). The heat exchanger cells feature Haynes® 230 construction and are qualified for 30-year service life at up to 25 MPa and 730°C. The internal vacuum brazed plate-fin architecture provides effective sCO₂ heat transfer coefficients ≥2000 W m^-2 K^-1 and total pressure drop ≤ 2% at design conditions with flow uniformity between the cells of ≤ 2%. A primary innovative feature of the PHX is the incorporation of brazed offset folded fins within the narrow-channel bubbling fluidized bed. The employed fin configuration increases the maximum effective particle-wall heat transfer coefficient compared to smooth-walls at 450°C from 600 W m^-2 K^-1 to 1200 W m^-2 K^-1 with Carbobead HTM HD350 (ρ_s = 3650 kg m^-3, d_p = 408 μm) and from 1200 W m^-2 K^-1 to over 2000 W m^-2 K^-1 with Carbobead HTM ID200 (ρ_s = 3340 kg m^-3, d_p = 210 μm). Additionally, particle-side fins have demonstrated an up to 65% reduction in longitudinal dispersion compared to smooth-walled bubbling fluidization, with dispersion suppression most pronounced with the HTM HD350 particles.

Experimental demonstration and characterization of the PHX test article is ongoing at Brayton’s Particle-sCO₂ Test Facility. The particle test stand comprises (i) a 120 kWe particle preheater with 150 discrete cartridge heaters to provide inlet particle temperatures up to 700°C; (ii) particle flow control and measurement with custom particle flow regulating and isolation valves and weigh hopper system; (iii) dilute pneumatic particle conveyance system to recirculate up to 500 g s^-1 of particles with >99% cyclone efficiency; and (iv) fluidizing gas handling system to provide filtered dry preheated air at up to 650°C and 10 g s^-1. The sCO₂ circulator comprises a triplex positive displacement pump, a sCO₂ recuperator, two series 60 kW_e radiant heaters, an air-cooled radiator to provide sCO2 flows at up to 750 g s^-1, 730°C, and 20 MPa. At commercially-relevant scales and operating conditions, the prototype PHX is projected to provide >90% effectiveness with overall U_HX > 800 W m^-2 K^-1 while keeping  manufacturing costs < $2000 USD m^-2. These results suggest that coupling Brayton Energy’s brazed plate-fin heat exchanger cell architecture with bubbling fluidized beds represents a promising pathway toward enabling high-performance and cost-effective Gen3 CSP.

Presenting Author: Jesse Fosheim Brayton Energy/ Colorado School of Mines

Presenting Author Biography: Jesse Fosheim is a senior mechanical engineer and principal investigator at Brayton Energy. He has over a decade of experience developing high-temperature energy conversion, storage, and management technologies for sustainable power, fuels, and industrial process heat applications. He holds a master’s degree from the University of Minnesota.