recently completed a test of an onboard carbon capture system as it cruised around the Persian Gulf. It is one of a small but growing number of ships trying to reduce their climate footprint by capturing and storing their carbon dioxide emissions onboard – but finding space for tonnes of CO2 is a challenge.at University College London says some existing systems increase fuel use by a third just to catch half of CO2 emissions.
The systems, and the carbon they capture, also take up room on board that would normally be used for valuable cargo. “Space is an issue,” saysat TNO, a research organisation in the Netherlands. “Especially when you’re talking about long voyages.” Each tonne of combusted fuel forms around 3 tonnes of CO2, saysat the Cyprus Marine & Maritime Institute. When it is captured and stored, the added mass can affect a ship’s stability and reduce its fuel efficiency.
To save energy, Seabound moves part of its process onshore. On the ship, exhaust is looped through a calcium oxide sorbent, which reacts with CO2 to form solid calcium carbonate pebbles. The company then waits to recharge the sorbents until the pebbles are offloaded at port for permanent storage. The trade-off is space. Seabound’s approach means a ship must carry tanks of sorbent along with every tonne of captured CO2.
Such systems could appear attractive to cut emissions now, says Smith. But the rapid scale-up of cleaner shipping fuels may soon make them obsolete – unless they can achieve very high rates of capture at a low enough cost. “Shipping faces a very short time to decarbonise, because it has started so late,” he says.