Simulation and optimization of a liquid organic hydrogen carrier based hydrogen train system

The transition of the transport sector from fossil fuels to carbon dioxide free technologies is an enormous challenge. Liquid organic hydrogen carrier (LOHC) fueled trains are an attractive option for all non-electrified railway lines currently operated by diesel trains. The driving unit of a LOHC fueled train consists of LOHC storage tanks, a hydrogen release unit, a heating unit, a fuel cell and a battery. In our study, the LOHC system dibenzyl toluene/perhydro-dibenzyl toluene is selected. The dimensioning of the individual units is not straightforward as a smaller battery would require a larger fuel cell and the choice of a fuel cell influences the size of the heating unit, as the waste heat from a solid oxide fuel cell (SOFC) can be used for the dehydrogenation process. However, a SOFC of the same power class is larger and heavier than a proton exchange membrane fuel cell (PEMFC) and reduction of the size of the heating unit can result in an increase of the fuel cell size. By using a genetic optimization algorithm, we can minimize volume, mass and total driving costs of the model-based driving unit. The optimized driving unit contains a 722 kW fuel cell, a 820 kW hydrogen release unit and a 523 kWh battery. This configuration results in a volume around 45 m3, a total mass around 27 t and driving costs around 3 EUR/km for the SOFC scenario and 60 m3, 26 t and 2.4 EUR/km for the PEMFC scenario.