Model Predictive Control of the Hydration Process in a Lime-Based Thermochemical Energy Storage System

Abstract

Thermochemical energy storage systems offer a sustainable solution for storing excess renewable energy. This work focuses on a particular application based on CaO/Ca(OH)2 for heat storage. To ensure safe and efficient hydration of CaO (storage discharging), a control strategy is required. A nonlinear controller design model is developed and refined, incorporating input delays and pump dynamics in the cooling water circuit. With experimental data, the parameters and input delays in the system model are identified. A model predictive control (MPC) strategy is then designed, with four objectives targeting reactor temperature, cooling water temperature and thermal output power. A proportional-integral-derivative (PID) controller is implemented for comparison. The control strategies are evaluated in terms of tracking performance, energy transfer and real-time feasibility. Simulation results show that MPC effectively tracks system temperatures and power while fulfilling input, output and state constraints. The results also confirm the real-time feasibility of the MPC approaches.