Flow rate control in a plug-flow reactor for liquid organic hydrogen carriers dehydrogenation

Abstract

Liquid organic hydrogen carriers can store hydrogen for later release through dehydrogenation reactions. The kinetic rate depends on the temperature, pressure, and hydrogen concentration itself, so it varies throughout the discharge. As such, control systems are needed to meet the end-user power demand. An innovative plug flow reactor coupled with two vessels is introduced and accurately sized. Multiple strategies are implemented in a Matlab/Simulink model to test the efficacy of control methods based on pressure, temperature, and mass flow rate. The results obtained with the simulations highlight a dramatic drop in performance (utilisation factor lower than 80%) associated with relatively high power demands (higher than 70% in the case of temperature control), whereas low demands are met with satisfactory degrees of utilisation under both pressure and temperature control. Control over the mass flow rate of external fluid leads to lackluster results and should only be chosen as an auxiliary controlled variable. Lastly, Ragone diagrams for pressure and temperature control are presented and used to identify the optimal system sizing range: effective discharge duration should be in the range 10–40h with pressure control or 5–40h with temperature control to achieve a utilisation factor of at least 80%.