Engineers will suck CO2 from the ocean

CHEMICAL engineers at Brunel University London are developing a pilot plant to strip CO2 from seawater that will then suck emissions out of the atmosphere.

The SeaCURE plant will be built at the Sea Life centre in Weymouth where it will process 3,000 L of seawater per minute, removing an estimated 100 t/y of CO₂. The three-year project has received £3m (US$3.6m) of UK Government funding and the plant is scheduled to begin operating in 2024.

Salman Masoudi Soltani, Senior Lecturer in Chemical Engineering at Brunel University, and his research group will work to design, model and optimise the solvent-based CO2 capture process. The team aims to file a patent for the process so was unable to share the specific details of the process but Soltani said the key steps involve lowering the pH of the seawater to extract CO2. This CO2 stream will then be purified for use by industry, for example in building materials, or locked away in geological storage.

Asked what key processing engineering challenges the team must work to overcome, Soltani said: “Removal of CO₂ from seawater comes with an energy penalty and therefore, we will have to make sure our process is optimised from an energy point of view.”

Despite this, the team thinks there are efficiency benefits to be had by stripping CO2 from seawater rather than directly from the air where it is even less concentrated. The team calculates that stripping CO2 from 1 m³ of seawater is equivalent to stripping it from 150 m³ of air.

He also noted that because the process will involve returning the processed water back to the ocean, it’s essential that the team develops a process that makes it environmentally safe to do so. Once returned to the sea, the project partners say that the low dissolved carbon content of the processed water will then cause CO2 to be drawn from the atmosphere until the released seawater is chemically indistinguishable from the water that was sucked into the plant.

In April, the UN Intergovernmental Panel on Climate Change (IPCC) said large-scale deployment of CO2 removal technologies was unavoidable if net zero emissions are to be achieved. In a report published in 2019, it said CO2 removal technologies would need to remove 100bn–1,000bn t of CO2 over the course of the 21st Century to limit warming to 1.5°C. Technologies for direct air capture – or DAC – are already in commercial operation and interest is growing. Currently, the largest direct air capture and CO2 storage facility is operated by Climeworks in Iceland, which has a capacity to capture 4,000 t/y of CO2, showing the measure of the scaleup and scale-out challenge faced in achieving the IPCC projections. In May, the US Government pledged to invest US$3.5bn to develop four large-scale DAC hubs, each capable of capturing 1m t/y of CO2.

At scale, the SeaCURE process will use renewables to power its plants, and says that if proved successful, the technology could be deployed on the coast or offshore, where it would have the added benefit of avoiding competition with other land uses.

Soltani said: “Removal of carbon dioxide is a key technology to fight against climate change – one of the biggest threats to global ecosystems. In SeaCURE, we are developing a process which, unlike for post-combustion capture technologies, can be readily deployed anywhere in the world. This is an exciting opportunity to demonstrate the feasibility of our process at pilot scale in the UK where 100 t of CO₂ will be removed per annum by our process plant.”

Other partners in the project include the University of Exeter, Plymouth Marine Laboratory, and water engineering firm Eliquo Hydrok.