Dynamic modeling of a particle/supercritical CO₂ heat exchanger for transient analysis and control

Abstract

A dynamic model of a moving packed-bed particle-to-sCO₂ heat exchanger and control system for concentrating solar power (CSP) applications is presented. The shell-and-plate heat-exchanger model allows for numerically investigating the transient operation and control of the heat addition to the power cycle in a particle-based CSP plant. The aim of the particle-to-sCO₂ heat exchanger is to raise the sCO₂ temperature to 700 degrees C at a pressure of 20 MPa. The control system adjusts both the particle and sCO₂ mass flow rates as well as an sCO₂ bypass to obtain the desired sCO₂ turbine inlet and particle outlet temperatures for a prescribed thermal duty. The control system is demonstrated for disturbances in particle and sCO₂ inlet temperatures as well as changes in thermal duty for part-load operation. A feed-forward control strategy that adjusts the sCO₂ and particle mass-flow rates as functions of measured inlet temperatures and a steady-state model solution was able to return the heat exchanger to the desired operating condition, but not without experiencing significant deviations in the sCO₂ turbine inlet and particle outlet temperature (> 40 degrees C) during the transient. To reduce both sCO₂ and particle temperature deviations, a feedback control strategy was investigated, where sCO₂ and particle mass-flow rates based on the steady-state model solution were corrected based on measured outlet temperature deviations. The feedback control strategy maintains sCO₂ turbine inlet and particle outlet temperature to within 16 degrees C of the set points with a three-minute settling time for step changes in inlet conditions and thermal duty. This finding demonstrates the possibility of dynamically dispatching next-generation particle-based CSP plants driving sCO₂ power cycles.