Development of an Eulerian multiphase CFD model for simulating a liquid organic hydrogen carrier dehydrogenation reactor

Abstract

Hydrogen has emerged as a promising candidate for energy storage, offering an alternative to fossil fuels as a primary fuel source. It can be safely stored in a liquid organic hydrogen carrier (LOHC) and recovered upon demand through the reversible hydrogenation/dehydrogenation of the LOHC. Voyex, a technology-driven startup, is developing a novel LOHC that can be loaded onto ships and dehydrogenated onboard, providing hydrogen for ship propulsion as an alternative to fossil fuels. The successful implementation of this new technology requires a dehydrogenation reactor that may provide the conditions necessary for LOHC dehydrogenation to meet the ship's power demand.

This work develops a computational fluid dynamics (CFD) model to simulate the LOHC dehydrogenation reaction within a cocurrent upward-flow fixed-bed reactor. While lab-scale studies have examined the effect of operating conditions on the dehydrogenation of specific LOHCs, only a few works have studied LOHC dehydrogenation reactors and the inner flow details have yet to be understood. A CFD model will allow for a better understating of the flow, temperature, and species distribution within the reactor, and help gain more insight into the design and operating parameters on the reactor performance as measured by conversion and hydrogen yield.

This thesis delves into the distinct phenomena at play within an LOHC dehydrogenation reactor including hydrodynamics, heat transfer, species transport, and reaction kinetics, discussing ways to incorporate them into a numerical model. These effects are brought together in an Eulerian multiphase CFD model, as this approach is found to provide a good balance between modelling accuracy and computational demand.

The result of this research is a computationally inexpensive Eulerian multiphase CFD model capable of adapting to various LOHC systems and reactor configurations. Through multiple sensitivity analyses, the impact of design variables including reactor dimensions, temperature, flow rate, and catalyst pellet diameter on reactor performance is explored. These analyses yield valuable insights and design parameters to enhance reactor efficiency. Additionally, these analyses lead to several design improvement proposals such as raising the reactor inlet temperature, using a low inlet LOHC mass flux, incorporating gas-liquid separation methods, adding internal heating mechanisms, and employing internal baffles to disrupt flow and enhance heat transfer. The findings underscore potential for reactor design improvements, thereby proving the CFD model as a research and design tool for packed-bed multiphase reactors.