Hydrogen release from LOHC systems: Dehydrogenation using burner based direct heating and characterization by liquid phase thermometry
Year: 2024
Type: dissertation
Abstract: When using hydrogen as an energy carrier, liquid organic hydrogen carrier (LOHC) systems represent a particularly promising technology for its transport and safe long-term storage. The liquid organic compounds can be reversibly charged and discharged with hydrogen. Chemical bonding of hydrogen to a liquid offers the advantages of storage under ambient conditions in low-cost containers and easy handling while making extensive use of the existing infrastructure for liquid fuels in e.g. automotive applications. LOHC systems could be used to supply hydrogen at refueling stations in order to enable the accelerated development of a hydrogen infrastructure. However, the release of the hydrogen stored in the LOHC is accompanied with a high energy requirement (at least 27 % of the hydrogen stored in the LOHC is needed for this reaction with additional losses, e.g. for heating to reaction temperature). Thus, for an economic application of the LOHC technology, it is necessary to optimize the dehydrogenation reactor with respect to power density and system dynamics in order to achieve an energy efficient operation of the storage technology. In the framework of the present work this goal is addressed in two different ways. On the one hand, the heat exchanger unit for the hydrogen release reaction will be heated directly with a porous media burner for the first time. At the moment, research has mostly focused on indirect heating of the dehydrogenation reactor. The approach of a direct heat input via a burner promises significant potentials for increasing the efficiency and the dynamics of the reaction compared to existing systems due to the reduced system inertia and the lower heat losses. Both direct heating of a dehydrogenation unit with a porous media burner and the associated optimization of the reactor geometry are in focus. On the other hand, an optical measurement technique will be used for the first time to detect temperature fields in the reaction volume during hydrogen release. So far, no comparable work exists in the literature. In particular, the spatial resolution of temperature fields is of great interest with regard to the strong endothermic reaction in order to localize and characterize existing cool spots and overheating areas and thus to optimize the heat supply in future dehydrogenation reactors. The measurement technique of laser-induced phosphorescence for temperature field measurements during the release of hydrogen from the LOHC material perhydro-dibenzyltoluene (H18-DBT) is therefore applied in a model system. The work consequently considers optimization potentials in the dehydrogenation of a LOHC system and identifies ways to increase the dynamics and efficiency of the hydrogen release reaction.
Author: Bollmann, Jonas
Language: English
Subfield: Materials Chemistry
Field: Materials Science
Domain: Physical Sciences
Open Access status: gold
OpenAlex ID: W6945767762
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