The lungs of birds and the swim bladders of fish are the inspiration behind a new microvascular filtering system for removing carbon dioxide from the exhaust fumes of electric power stations.
Existing carbon dioxide scrubbing solutions rely on considerable amounts of expensive packing, often running down towers of up to 30m in height to ensure a large-surface area for carbon dioxide exchange. The new solution – a gas exchange system made up of small tubes that work in a similar way to blood vessels – draws upon the biological attributes of avian lungs, which have an extremely efficient gas exchange system to support the oxygen requirements of energy-intensive flights. Fish, on the other hand, require precise control over the pressure in their swim bladders to adjust their buoyancy and move up or down in the water column, a technique which the solution also employs.
“Biological systems [have] spent an incredible amount of time and effort moving towards optimisation”, says lead researcher Aaron Esser-Kahn, from the University of California Irvine. “We’re trying to learn from nature.”
The research team’s model involves the use of alternating, micro-sized tubes made of porous materials for efficient gas exchange. One tube would carry waste fumes, the other a carbon dioxide absorbing liquid. The greenhouse gas would pass between the tubes and be transported away for appropriate disposal. For optimum effectiveness, the tubes must have the largest amount of surface area possible for exchanging gas.
Using computer simulations, the team was able to calculate the effectiveness of the nine possible packing solutions for the gas exchange tubes. Both the hexagonal pattern used by birds and the square pattern from fish swim bladders were very efficient. However, the most effective pattern – two small tubes alternating with each large tube – is not found in nature. Pilot tests show that it is 50% more efficient than the bird lung and swim bladder alternatives.
Roger Aines, a researcher from the Lawrence Livermore National Laboratory, calls the work by the Esser-Kahn group “an exciting development” for carbon dioxide capture systems. “Creating surface area is the biggest problem in capturing carbon dioxide”, he says. “There is an enormous amount of gas to be transferred, and it is just too slow if you can’t use a lot of transfer surface – just like a bird’s lung.”
The researchers are now looking for ways to improve the efficiency of their carbon capture units by modifying the sizes and wall thickness of the membrane tubes. It may also be possible to modify the filter design to work with other applications, such as car exhaust pipes. – Ian Randall
Photo credit: Erika Mitchell/iStockphoto/Thinkstock