The environmental performance of a fossil-free ship propulsion system with onboard carbon capture – a life cycle assessment of the HyMethShip concept

Abstract

The climate impact caused by the shipping industry has increased over the past decades despite attempts to improve the energy efficiency of vessels and lower induced emissions. A tool in reducing climate and other environmental impacts is new low emissions propulsion technologies. These new technologies need to reduce harmful emissions not only in the tailpipe but also over the entire life cycle. This study uses life cycle assessment to investigate the life cycle environmental impact of a propulsion concept currently under development: the HyMethShip concept. The HyMethShip concept combines electro-methanol energy storage, an onboard pre-combustion carbon capture system, and a dual fuel internal combustion engine. The concept aims for an almost closed CO₂ loop by installing CO₂ capture onboard. The CO₂ is unloaded in port and converted into electro-methanol which is used to fuel the ship again. This is made possible by a pre-combustion process converting electro-methanol to hydrogen and CO₂. The assessment is conducted from well-to-propeller and focuses on ship operation in the North Sea in 2030. The results indicate that this technology could be an alternative to reduce the climate impact from shipping. The results show a lower impact on acidification, climate change, marine eutrophication, particulate matter, photochemical ozone formation, and terrestrial eutrophication compared to internal combustion engines run on either marine gas oil (0.1% sulphur content), biogenic methanol, fossil methanol, or electro-methanol. Electricity with low climate and environmental impact is likely required to achieve this, and low NO_x emissions from combustion processes need to be maintained. A potential trade-off is higher toxicity impacts from the HyMethShip concept compared to most other options, due to metal needs in wind power plants.