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Integrating fluidized bed heat exchangers and particle thermal energy storage with sCO₂ recompression Brayton cycles for concentrating solar power
Hernandez, Xavier
Hernandez, Xavier
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2023
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Oxide particles provide a cost-effective solution for thermal energy storage (TES) in future concentrating solar power (CSP) plants that implement supercritical carbon dioxide (sCO2) cycles at firing temperatures above 700°C. However, the design of effective particle-sCO2 HXs (HX) remains a challenge. Recent studies have explored how mild fluidization of gravity-fed particle flows can increase overall particle-sCO2 heat transfer coefficient, U_{\mathrm{HX}} to \approx 600 W m2 K-1 by decreasing thermal resistance between the particles and the walls. A test apparatus was set up to study heat transfer in a single-channel fluidized bed at temperatures up to 500°C. Particle-to-wall heat transfer coefficient, h_{\mathrm{T,\ w}} increases to a maximum at each temperature at intermediate gas velocities. Correlations for h_{\mathrm{T,\ w}} fitted to the experimental data are implemented into a quasi 1-D model of a particle-sCO2 HX core with narrow-channel fluidized particle beds and micro-channel sCO2 counter-flows in the HX walls bounding the fluidized bed.
A process model of an sCO2 recompression Brayton cycle (RCBC) with turbine firing temperatures > 700°C was integrated with the 1-D particle-sCO2 HX model and a particle TES sub-system model to assess optimal operating conditions for CSP. Am optimization routine was used to identify HX designs and operating conditions which reduced HX costs ($ kWth-1) and full-system costs based on the levelized cost of electricity, LCOE ($ kW-1 h-1). Test results from a baseline 40-kWth demonstration HX provided a basis to scale HX performance to a multi-unit 100-MW CSP plant with TES. Full plant process model suggests HX costs below 150 $ kWth-1 and LCOE < 0.06 $ kW-1 h-1 cost targets can be achieved with particle-{\rm sCO}_2 HXs operating at mild fluidization conditions with predicted U_{\mathrm{HX}} = 464 W m-2 K-1 and with low parasitic losses due to small fluidizing gas mass flow rates below 2% of the net losses. An effective fluidized-bed particle-sCO2 HX design was identified for a 100-MWe CSP plant with TES at a HX cost of 130 $ kWth-1 and LCOE = 0.055 $ kW-1 h-1.
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