Method could revolutionise subsea CO2 removal

Engineers in England and the US are developing a chemical-free way of removing carbon dioxide from the air inside submarines.

Prof Stan Kolaczkowski and his team from Chemical Engineering at Bath University are collaborating with mechanical engineers from Duke University in the US in developing a CO2 removal system that uses sea water and Dixon rings in deep-sea submersible vehicles and other submersible human habitats.

The project is funded by a three-year grant worth £380,000 from the US Office of Naval Research (ONR).

At present, chemicals such as calcium hydroxide are used to chemically react with the CO2. Although it is known that sea water has potential to absorb CO2, the aim of this project is to develop a system that will be compact and work in a submersible environment where space is very limited.

Based on technology developed in 1948, Dixon rings consist of a fine wire mesh folded into a ring of approximately 3mm in size. The space in the wire mesh provides an extended surface area for the absorption of the CO2.

Many rings are packed into a column, through which gas and liquid flow in a counter-current direction. The combination of salt water and Dixon rings form a compact gas scrubbing unit, which removes CO2 from a closed-circuit breathing environment before safely discharging it into the sea.

Using this system, chemicals to absorb CO2 will no longer be needed in the submersible environment and time spent on the sea bed could be extended.

Prof Kolaczkowski said: ‘Chemical engineers are excited about using Dixon rings in applications where gaseous or volatile species are transferred between gas and liquid phases, and where the device needs to be compact.

‘With the Computational Fluid Dynamic modelling skills at S and C Thermofluids, we will make rapid progress with developing novel and compact gas scrubbers. The removal of carbon dioxide from exhaled air is a great application. There will be many more possibilities to consider.’

Dr Lew Nuckols of Duke University said: ‘An estimated 90 per cent of human-produced carbon dioxide is absorbed by oceans. The research at Bath, in partnership with us, could revolutionise techniques to remove metabolically produced carbon dioxide from subsea operations.’

‘Any research aimed at carbon-dioxide absorption is very beneficial,’ said Dr Tony Smith of S and C Thermofluids in Bath. ’We’re pleased to be working on this project, particularly because there will be experimental validation of the predictions.

‘Being a diver, I am aware of the difficulties with supplying sufficient quantities of breathable air underwater. This research is looking at a very practical and elegant solution to a difficult problem.’