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

A dynamic model of a moving packed-bed particle-to-sCO(2) 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-sCO(2) heat exchanger is to raise the sCO(2) temperature to 700 degrees C at a pressure of 20 MPa. The control system adjusts both the particle and sCO(2) mass flow rates as well as an sCO(2) bypass to obtain the desired sCO(2) turbine inlet and particle outlet temperatures for a prescribed thermal duty. The control system is demonstrated for disturbances in particle and sCO(2) inlet temperatures as well as changes in thermal duty for part-load operation. A feed-forward control strategy that adjusts the sCO(2) 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 sCO(2) turbine inlet and particle outlet temperature (> 40 degrees C) during the transient. To reduce both sCO(2) and particle temperature deviations, a feedback control strategy was investigated, where sCO(2) 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 sCO(2) 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 sCO(2) power cycles.