Carbon Capture Method Shows Promise

July 27, 2011
A packed-bed combustion process may be the answer to cost-effective CO2 capture.

A variation of the chemical looping combustion (CLC) process is at the heart of a new European Union (EU) project that aims to demonstrate a cost-effective capture technology for carbon dioxide (CO2). The hope is that the new process, which has already been lab tested with promising results, could herald new types of power generation plants with integrated CO2 capture.


The €8.2 million ($11.7 million) project, called DemoCLOCK, is being led by independent research organization SINTEF, Trondheim, Norway.

"CLC itself is believed to be on the verge of becoming one of the most cost-effective ways of capturing CO2 from power plants. DemoCLOCK aims to demonstrate the technical, economical and environmental feasibility of implementing a packed-bed-based CLC concept in large-scale power plants. This version of CLC is even less complex and more compact than the original CLC concept," says Shahriar Amini, SINTEF, project coordinator of DemoCLOCK.

Traditional CLC technology prevents dilution of CO2 in the large amounts of nitrogen left over from air used in the combustion process. It does this by never allowing direct contact between the air and the fuel. It uses two reactors -- an air reactor and a fuel reactor; an oxygen carrier in the form of metal oxide granules circulates between them. In the air reactor, oxygen is transferred to the oxygen carrier by oxidation, producing lots of heat and a harmless stream of oxygen-poor air. The resulting oxygen-rich oxygen carrier is then transferred to the fuel reactor, where it provides the fuel with oxygen in the total absence of nitrogen.

Fuel reacts with the oxygen carrier in a reduction reaction and produces an exit stream of CO2 and steam. Capturing the CO2 from this stream is very easy because it only needs to be cooled down for the water to condense out, leaving a stream of pure CO2. The oxygen-poor oxygen carrier can then be transported back to the air reactor to repeat the process.

However, in the new version -- a packed-bed CLC, the oxygen carrier material is fixed in a reactor and alternatively exposed to fuel gas and air streams. This arrangement essentially combines the fuel and air reactor into a single reactor that has all the CO2 capture advantages of the standard CLC process.

Another major advantage to this setup is the oxygen carrier material no longer has to be transferred between the two reactors. This greatly simplifies the process and is expected to speed up its commercialization.

The packed-bed CLC will be used to convert gasified solid hydrocarbons (syngas) into hot streams of CO2 and oxygen-poor air that can potentially be used for electricity generation. Packed-bed reactor technology thus opens up the prospect of using various types of fuel such as coal, petroleum coke and biomass.

"In comparison with currently available CO2 capture techniques, our concept will reduce power-generation energy losses and do so in a cost-effective way," notes Amini.

All the partners in the DemoCLOCK project are working towards proof of feasibility: the medium-scale demonstration of a 500kW packed- bed CLC reactor at Elcogas's integrated gasification combined cycle (IGCC) power plant in Puertollano, Spain, the largest IGCC plant in Europe.

Other partners in the project include Céramiques Techniques et Industrielles (CTI), Salindres, France; Energy Research Centre of the Netherlands (ECN), Petten, the Netherlands; and Foster Wheeler Italiana, Corsico, Italy.

The packed-bed CLC concept originally was developed by a research group at Eindhoven University of Technology in the Netherlands, also one of the project partners.

In a separate development, SINTEF and two other European research institutes --
TNO, The Hague, the Netherlands; and IFP Energies nouvelles (IFPEN), Rueil-Malmaison, France -- are joining forces in the newly-established Tri4CCS Alliance aimed at making the capture, transport and storage of CO2 (CCS) safer and more cost-effective.

"As a group, we are large enough to tackle the scientific challenges that will emerge when, in the course of a few years, Europe commissions its planned demonstration and full-scale CCS plants," says alliance spokesman Nils A Røkke, vice president climate technologies, SINTEF.

According to Røkke, the expertise of the alliance will help ensure that carbon capture plants are environmentally friendly and as cost-effective as possible.

"Research results will play a decisive role in gaining the public's acceptance for underground storage of CO2, and there, too, the work of the alliance will be important," he adds.

Seán Ottewell is Chemical Processing's Editor at Large. You can e-mail him at [email protected].

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