Capturing Carbon Dioxide in Submersible Human Habitats
Chemical Engineers at the University of Bath have been awarded US$
554,858 over 3 years to collaborate with Mechanical Engineers at Duke University in the US to
tackle the removal of carbon dioxide from gaseous streams. Professor
Stan Kolaczkowski and Dr
Serpil Awdry will be collaborating with Dr
Lew Nuckols of Mechanical
Engineering at Duke University, Dr Tony Smith of
S&C Thermofluids, and
Croft Engineering.
In order to explore the sea bed, submersible vehicles and other enclosed underwater living habitats are positioned onto the sea bed, and personnel may live there for extended periods while they perform exploratory studies. During the extended period of working and living on the sea bed, it is essential that personnel have air which they can breathe, and that the carbon dioxide which they exhale is removed from their habitat. Otherwise, if the CO 2 builds-up in the circulated air they will suffer from CO 2 poisoning. At present, chemicals such as calcium hydroxide, Ca(OH) 2 , are used to chemically react with the CO 2. If possible, it would be preferable to remove the use of these chemicals from the submersible habitat.
Although it is already known that sea water has the potential to absorb CO 2, the trick in this application is to develop a system that will be compact, and work in a submersible environment where space is very limited. The use of Dixon rings offers a potential solution. Dixon rings are based on technology that was developed in 1948, and although at that time they were superior to many forms of packing, they were expensive, and so they were only used in very specialist applications. With advances in manufacturing techniques, and financial sponsorship for a specialist application, they have recently had a revival and costs have become more attractive. In simple terms, the Dixon ring consists of a fine wire mesh that is folded into a ring (e.g. 3 mm in size). The space in the wire mesh (just visible) provides an extended surface area for mass transfer. Many of these rings are then packed into a column, through which gas and liquid flow in a counter-current manner. The combination of salt water and Dixon rings will facilitate the design of a compact gas scrubbing unit, which will enable the CO 2 to be removed from the closed-circuit breathing environment, and then safely discharged to the surrounding sea. There will be no need to keep chemicals to absorb the CO 2 in the submersible environment, and the duration of operation on the sea bed could be extended.
Prof Stan Kolaczkowski: “ Chemical Engineers are excited about the possibility of 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. The removal of carbon dioxide from exhaled air is a great application, and there will be many more opportunities to consider. Croft Engineering Ltd, have managed to reduce the manufacturing cost of Dixon rings, and with the CFD (computational fluid dynamic) modelling skills at S&C Thermofluids Ltd, we will make rapid progress with the development of novel and compact gas scrubbers”.
Dr Lew Nuckols: “ It has been estimated that 90% of the carbon dioxide produced by humans is absorbed by the oceans. The research underway at the University of Bath, in partnership with Duke University, could revolutionize the techniques to remove metabolically-produced carbon dioxide from sub-sea operation.”
Dr Tony Smith: “ Any research aimed at carbon dioxide absorption is very beneficial. We look forward to applying and extending our packed bed filter CFD modelling capabilities to this technology, and we’re very pleased to have the opportunity to work on this project, particularly because there will be experimental validation of the predictions. Having done some diving myself, I am very 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.”
