Design Considerations for Fluidized-Bed Particle Heat Exchangers for Next-Generation CSP

Using Finned-Wall, Narrow-Channel Fluidized Beds to Boost Overall Heat Transfer Coefficients

Abstract

Concentrating solar power plants can store heat in large beds of hot particles, then release that heat on demand to run a supercritical CO2 power cycle. The hard part is the heat exchanger that transfers heat from the particles to the CO2: it has to deliver CO2 to the turbine above 700 °C at 20 MPa, and do it cheaply. Recent moving packed-bed and fluidized-bed designs have reached overall heat transfer coefficients below 400 W/m²K. At that performance, you need a lot of surface area made from expensive nickel-based alloys, which pushes cost above the targets set for next-generation CSP. Fluidized beds transfer heat from particles to walls better, but the particles mix back and forth along the flow direction (axial dispersion), which flattens the temperature profile, shrinks the log-mean temperature difference, and cuts the heat actually delivered to the CO2. This study shows that adding fins to the walls of a narrow fluidized-bed channel raises the effective bed-to-wall heat transfer coefficient and suppresses that axial mixing at the same time. A reduced-order model built on experimentally derived correlations explores what those gains mean for full heat exchanger designs. The result: overall heat transfer coefficients above 1000 W/m²K, suggesting a route to affordable particle-to-CO2 heat exchangers.