Exergy-based control strategy design and dynamic performance enhancement for parabolic trough solar receiver-reactor of methanol decomposition reaction

Abstract

The parabolic trough solar receiver-reactors of methanol decomposition reaction (PTSRR-MDR) enable efficient hydrogen production with solar energy at users’ end. Solar fluctuations affect the solar-to-chemical efficiency, hydrogen yield and system stability, indicating the necessity for an appropriate control strategy. In this study, dynamic and thermodynamic models of PTSRR-MDR with Cu/ZnO/Al2O3 as catalyst were developed. Results of thermodynamic analysis show that an optimal flow rate exists for methanol to achieve the maximum solar-to-chemical exergy efficiency of the PTSRR-MDR. The temperature increases sharply and exceeds the catalyst sintering temperature when the methanol flow rate decreases under its optimal value. Then, control objectives to achieve the maximum efficiency are obtained with a temperature margin of 3 °C to guarantee the PTSRR-MDR safety. Control strategies based on Dynamic Matrix Control (DMC), Forward-Feedback Control (FFC) and Ramp Control (RC) were evaluated under dynamic simulations. Results show that strategies based on DMC, FFC, and RC increase the solar-to-chemical exergy efficiency from 14.76% to 16.31%, 16.28%, and 15.65%, respectively. The Integral Squared Error (ISE) of methanol conversion rate under three methods are 1.46, 0.32 and 5.28, respectively, indicating that strategy based on FFC is considered most suitable for PTSRR-MDR operation control.