Conjugate heat transfer model for feedback control and state estimation in a volumetric solar receiver

Abstract

Open volumetric solar receivers (VSRs) are a promising technology for concentrated solar power plants due to their capability to provide heat using ambient air as the working fluid operating at temperatures over 700°C. Nevertheless, VSRs are challenged by the unsteadiness and high intensity of the radiation flux, which may cause unreliable or unsafe outflow temperatures, and may compromise the lifetime of the porous ceramic absorbers due to extreme thermal loads, thermal shock or thermal fatigue. We propose a data assimilation framework to address these matters using blower actuation, measurements from sensors located in the outflow stream of air, and a model for the conjugate heat transfer in an open VSR. We formulate said model and compare it against full three-dimensional CFD simulations to show that it captures the relevant dynamics while reducing the computational cost enough to allow for online calculations. A linear quadratic Gaussian (LQG) controller is used with the model to perform simultaneous state estimation and feedback control in three simulated scenarios. Our framework proves capable of stabilizing outflow air temperatures during the passing of a cloud, estimating the radiation flux hitting the absorber during daily operation, monitoring temperature cycling in the solid matrix, and avoiding extreme temperature gradients during start-up procedures. Artificial noise and disturbances are added to the system for all scenarios and the LQG controller proves to be robust, rejecting disturbances and attenuating noise, as well as compensating for model uncertainty.