Performance assessment of integrated energy systems for the production of renewable hydrogen energy carriers

Department of Mechanical, Chemical and Materials Engineering, University of Cagliari, Via Marengo 2, 09123 Cagliari, Italy

^* Corresponding author: francesco.lonis@unica.it

Abstract

To guarantee a smooth transition to a clean and low-carbon society without abandoning all of a sudden liquid fuels and products derived from fossil resources, power-to-liquids processes can be used to exploit an excess of renewable energy, producing methanol and dimethyl ether (DME) from the conversion of hydrogen and recycled CO₂. Such a system could behave as an energy storage system, and/or a source of fuels and chemicals for a variety of applications in several industrial sectors.

This paper concerns the conceptual design, performance analysis and comparison of small-scale decentralised integrated energy systems to produce methanol and DME from renewable hydrogen and captured CO₂. Renewable hydrogen is produced exploiting excess RES. Water electrolysis is carried out considering two different technologies alternatively: commercially mature low temperature alkaline electrolysers (AEL) and innovative high temperature solid oxide electrolysers (SOEC). A first conversion of hydrogen and CO₂ takes place in a catalytic reactor where methanol is synthesised through the hydrogenation process. Methanol is then purified in a distillation column. Depending on the final application, methanol can be further converted into DME through catalytic dehydration in another catalytic reactor. The chemical (either methanol or DME) is stored at ambient conditions and used as necessary.

To predict the performance of the main components and of the overall system, numerical simulation models were developed using the software Aspen Plus. The performance and efficiencies of each section and of the overall systems were evaluated through extensive mass and energy balances. Globally, the overall power-to-liquids efficiency was found to be above 0.55 for all the different configurations, both considering a powerto-methanol or a power-to-DME process.