An extraordinary pilot project installed on a 240-meter (787-foot) container ship has demonstrated that it is possible to capture at least 78% of emissions from cargo ship stacks and convert the carbon dioxide into limestone pellets that can be offloaded and sold upon arrival in port. London-based startup Seabound, funded by $1.5 million from the UK government, is working with global shipping company Lomar to install carbon capture equipment on one of its older and dirtier-burning ships, a mid-sized vessel capable of carrying more than 3,200 shipping containers.
Seabound's small prototype system itself can fit in several shipping containers, taking up only a small amount of space on board a ship. It is designed as a retrofit device that can be installed on a ship's exhaust pipe to capture the carbon dioxide and sulfur emitted when dirty marine diesel is burned.
The exhaust gases are pushed into a pile of calcium oxide, also known as quicklime, a relatively cheap and abundant material widely used in construction, agriculture and other fields around the world. Carbon dioxide reacts readily with quicklime at room temperature to form calcium carbonate, or limestone, so the particles bind tightly and capture the carbon dioxide.
If you buy and sell quicklime in North America, the price at the end of last year was about US$200 per ton, while food-grade calcium carbonate is selling for up to US$727 per ton, and the price of buying industrial-grade lime in Europe is US$340 per ton, although we suspect that the lime extracted directly from the exhaust of marine diesel engines may not be of sufficient quality. Here’s the crux of the matter: By capturing smokestack emissions and storing them in pellets, the system takes advantage of a cheap commodity and converts it into a more valuable commodity, thereby providing a revenue stream that helps offset the capital and operating costs of running the system.
Over the months on board the container ship, the young Seabound team conducted a series of tests, gradually increasing the emissions capture rate until it reached 78% carbon capture efficiency and over 90% sulfur capture, but the team says the system was ultimately able to capture up to 95% of emissions in its most efficient form.
The film crew filmed this trial voyage into a short film, introducing more information:
During testing, the prototype captured about 1 ton of CO2 emissions per day, so it certainly won't be able to capture the entire exhaust plume. A medium-sized container ship may carry about 150,000 tons of cargo and may emit about 600 tons of carbon dioxide at sea every day. Capturing 95% of that would increase emissions.
Taking a step back, let’s take a quick 15-day trip from China to the West Coast of the United States. Calculated based on a 95% capture rate, 8,550 tons of carbon dioxide will eventually be captured. The theoretical maximum capture rate of quicklime is 78.6%, so nearly 11,000 tons of quicklime are required. Add the weight of the storage container, and the weight of the system itself... This can easily reach about one-fifth of the rated tonnage of the ship, and some voyages are three times this number.
This is by no means a disparagement of Seabound's approach, but simply serves to illustrate the difficulty of solving the problem. The carbon emissions from freighters account for approximately 3% of total global carbon emissions, making them an extremely difficult emission source to decarbonize. Progress is being made with ammonia, methanol and other cleaner solutions, but there are no easy solutions. Shipboard carbon capture solutions like this could play an important role in the transitional period of the coming decades, and we wish the Seabound team all the best as they make this idea a reality.
Alisha Fredriksson, CEO and co-founder of Seabound, said in a press release: "Our pilot project shows that we can capture carbon emissions directly on board ships in a simple and cost-effective way. This breakthrough shows that the shipping industry does not have to wait for new fuels or solutions to reduce future emissions, we can start capturing carbon emissions from existing fleets today."