Cryogenic technology project keeps its cool over carbon targets

The Naval Architect: March 2020

Denmark-based decarbonICE, a carbon capture and storage solution, was initiated by the Maritime Development Center (MDC) in Copenhagen, Denmark. The project is already backed by shipping companies including DSME, BV and scrubber manufacturers, CleanWater.

The proposed technology would transform carbon emissions from ship exhaust fumes into dry ice powder using a cryogenic process, which is then cast into capsules and deposited in the soft sediment of the seabed. DecarbonICE envisions the technology could be seamlessly integrated into normal shipboard operations on both newbuilds and existing vessels.

The only change would be that ships fitted with the technology would be required to periodically drop torpedo-shaped capsules of dry ice from the back of the vessel down into the seabed. Based on a now-expired patent filed by French cryogenicist Denis Clodic, the process would run constantly while the ship is travelling through waters of 500m depth or above. As each ‘Carbon Descent Vehicle’ (CDV) is discharged then formation of the next CDV would begin.

Because the CO₂ dry ice has a density of 1.6t/m³, 60% heavier than that of water, the CDV will drop towards the bottom of the ocean at a rate of 20-25m/s. As the -80°C CDV becomes embedded in the soft sediment of the seafloor it undergoes a series of reactions with the warmer 2-3°C water.

“Instead of discharging CO₂ to the atmosphere and creating climate change and damage to the upper ocean water, we discharge the CO₂ to the seabed sediments, where it becomes permanently stored, primarily as CO₂ hydrate,” says Henrik O Madsen, the former CEO of DNV GL who chairs decarbonICE’s steering committee.

Madsen compares decarbonICE technology to scrubbers, as CDVs are a post combustion solution to carbon emissions, which can be used on existing propulsion systems that run on current fuels such as HFO, MGO and LNG. He believes that the technology could ultimately be combined with future carbon neutral fuels to make shipping ‘carbon negative’.

Carbon reacts with water depending upon its state and decarbonICE plans to prevent CDVs from sublimation as they descend and once stored. The project has determined that according to carbon’s phase diagram, CDVs will not return to a gaseous state once they reach a depth over 500m where the pressure surpasses 50Par.

He stresses that decarbonICE is working closely with geologists and marine experts to identify areas of the seabed that are suitable for carbon storage and to advise on the ecological impact. “We are in the process of categorising the seabed along major shipping lanes and identifying where the seabed is soft enough, we are guaranteed the CDV to fully penetrate,” says Madsen.

The project also plans to cover its CDVs with a ‘spray paint like’ coating, of around 5mm thickness, to avoid carbon escaping as gas while it travels through the water, though it has yet to determine what material the coating will be made from. “We wish to avoid any material that is not natural to the environment. Water or CO₂ hydrate seem like the two most promising cladding materials at the moment,” explains Madsen.

United Nations Convention for the Law of the Sea (UNCLOS) requirements specify that CO₂ cannot be discharged on the seabed, but decarbonICE is currently unable to evaluate each specific landing site for its CDVs.

DecarbonICE’s technology is still in its embryonic phase. Madsen confirms that during 2020 the project aims to complete a visibility study, which may include laboratory experiments on descent vehicles. Meanwhile, plans to start an approval process for its technology are already in motion, “we will apply for approval under the London Convention and Protocol, which is managed by IMO, and do not expect any international body to challenge such an approval.”