Environment-friendly and cost-effective CO2 capture
Capturing CO2 without chemicals
With a new membrane that allows only CO2 to pass, the flue gas from coal-fired and gas-fired power plants can be treated without the use of amines or other chemicals. Project manager May-Britt Hägg asserts that the costs involved will be the same or less
The Norwegian University of Science and Technology (NTNU) in Trondheim is on the cutting edge of research on membranes, and its success is thrusting Norway into the international spotlight in this field.
Patented method
The petroleum industry already employs membranes for separating gases, but usually under high pressure. NTNU has long worked on membranes for gas sweetening. Now a research group headed by Professor May-Britt Hägg of the Department of Chemical Engineering has developed membranes that are highly effective even at low pressures.
Professor May-Britt H�gg is the project manager. Photo: SINTEF
“We have optimised the membrane characteristics for CO2 in terms of both permeability and selectivity. So far the tests have gone extremely well. But we need to demonstrate the method on a larger scale,” reports Professor Hägg, who heads the project “Clean Energy by Using High Performance Membranes” (CEPEME), which receives funding under the CLIMIT programme.
There are many research groups around the world involved in developing membranes for CO2 capture, but so far NTNU has documented the best results. Now its membrane has been patented, the result of years of materials research on membranes made of polymer-carbon composites.
The membrane
The membrane is constructed of a porous support layer and a thin membrane. The CO2 molecules dissolve in the membrane and diffuse through it by binding to a transporter molecule, passing through to the other side (Se the graphic at the end of this article). This process involving the CO2 molecules occurs extremely quickly compared to the other molecules in the gas mixture, very few of which manage to pass through.
The membrane technology for CO2 capture is comparable to how our lungs expel CO2. Imagine how small the pressure differential is across the lungs when we breathe. CO2 reacts with an enzyme in the lungs and is transported at high speed through the lung wall. Much work remains before NTNU’s CO2 membrane can match that speed.
Membrane sheets are rolled up to create space-saving modules. Ill: NTNU
The experiments were conducted using large, flat “sheets” of the membrane. In a fully operational capture facility, the sheets could either be rolled up to save space, or the filter could be made of packed hollow fibres whose inner or outer side is covered by the membrane. Professor Hägg explains that hollow fibres are preferable because they would make it possible to build the most compact facilities.
CO2 capture facilities would be built of modules, which would simplify tailoring capacity to specific needs.
“This modular design will be an essential part of the challenge. Our goal is to transport the CO2 rapidly through the membrane and remove it on the other side without having to alter the pressure too much,” says Professor Hägg, “since such alteration can get expensive quickly.”
The NTNU researchers have encountered a great deal of interest from power producers in the EU hoping to test the membrane on actual flue gas streams in coal-fired power plants.
“Current calculations show that membrane capture of CO2 is economically competitive with amine capture. But the main advantage of using membranes is the environment-friendly process – no solvents are needed. And being module-based allows for easy upscaling of capacity.”
Next step: increasing the scale
As a follow-up to their research project, the group is readying the construction of a pilot facility implementing their methods. The first phase will employ flat membranes with a surface area of about one square meter – substantially larger than the laboratory’s 25-cm2 membrane. Meanwhile, the researchers will continue developing a membrane consisting of hollow fibres.
“Phase 1 will tell us how durable the membrane is over time in actual gas streams,” explains Professor Hägg. “If all goes well, we will plan a second phase after about three years for upscaling the membrane module to approximately 10 m2. Where to locate that pilot will be discussed during the project’s first phase.”
The membrane is constructed of a porous support layer covered with a thin (700-nanometre) polymer layer. CO2 capture occurs in two stages: diffusion through the thin polymer membrane and then transport through the support layer. Illustration: Kolbjørn Skarpnes/NTNU Info
PROJECT FACTS
Project title: Clean Energy by Using High Performance Membranes (CEPEME)
Project owner: NTNU
Partners: Statoil, Alstom
Project period: 2005-2008
Overall budget: NOK 8.5 million
Funding allocated under the CLIMIT programme: NOK 5 million
- Published:
- 28.05.2009
- Last updated:
- 04.06.2009
