A Japanese concept study has identified the technical and political challenges of using onboard carbon capture and storage to drive down emissions from big ships.
The use of wind-generated electricity and onboard carbon capture could cut emissions dramatically on board a very large crude carrier (VLCC), according to a concept study by Mitsubishi Heavy Industries (MHI). But don’t expect owners to rush to shipyards any time soon.
The Japanese shipyard and engineering group’s CC-Meth (Carbon Capture-Methanation Cycle) project investigated the onboard production of clean methane or methanol fuel by combining hydrogen (generated through electrolysis using electricity from wind turbines) and carbon dioxide removed from the air by carbon capture.
Onboard plant would include a carbon capture and storage unit – comprising four towers for cooling the exhaust, absorbing CO2, treating the exhaust and regenerating the CO2 – as well as liquefaction and storage facilities. For methane fuel, cryogenic tanks would be needed. For methanol, simple hull structure tanks coated with zinc would suffice. Even without cooling, the system configured for methanol would still consume more power because of the greater amount of CO2 that would need to be captured from the exhaust.
There is a catch. According to MHI’s calculations, the system would add more than US$45M to the cost of a conventional VLCC, with the methane fuel system costing around US$15M and the carbon capture and storage plant around US$30M. Even with a carbon tax of around US$200 a tonne (around US$45,000 a day for a VLCC) and with a price of electricity nearly 10 times lower than Japan’s cheapest wind-generated power today, payback would take 20 years.
Return on investment is just one obstacle in a project designed to highlight the challenges – both political and technical – that shipping’s decarbonisation poses for larger vessels. One problem is the size and weight of the carbon capture units. The system envisioned for MHI’s project uses the amine treatment method that has been deployed on land. Each of the four towers is around the size of a scrubber unit, and the weight of the whole system would be over 4,500 tonnes, or nearly 2% of the vessel’s deadweight.
Another stumbling block is the fact that the carbon capture is not totally effective, with a capture rate of around 86%. The technology is expected to improve over time, but initially this configuration will not provide a vessel that offers no carbon emissions. The ship would therefore be partially subject to any carbon tax or other market-based measure imposed.
Despite these considerable hurdles, the production of either methane or methanol fuel by combining hydrogen and onboard carbon capture may be the most feasible route for large vessels such as VLCCs to decarbonise, explains Kazuki Saiki of MHI. Electricity is not feasible for propulsion except on small ships, nuclear power has too many political challenges and direct renewable energy (such as wind or solar energy) is too unreliable.
“We don’t believe this is the only solution, but it is one direction we can take,” says Mr Saiki. “The costs can be reduced dramatically with competition, and I am confident that shipbuilders can overcome the technical challenges of scaling down the carbon capture unit.”
The study also highlights that taking carbon out of big ships requires not only technical answers, and not only shipping. “I think we would also need to ask industries beyond ours to help bear the costs, because shipping may not be able to do this alone,” Mr Saeki concludes. “We need both a political and a technical approach to reducing greenhouse gas emissions.”