If there's one big environmental concern surrounding power plants that burn material such as coal in order to produce power, it's the amount of carbon dioxide that they release into the atmosphere. Various experimental technologies have been developed for removing most or all of the CO2 from smokestack effluents, although no one system appears to have been universally accepted as of yet. One technology that shows some promise, and that could perhaps be used in conjunction with other systems, is called Chemical Looping Combustion (CLC). Norwegian research group SINTEF is now building a special new type of CLC system, for use in the DemoCLOCK pilot project, to be installed at Spain's Elcogas Puertollano power plant.
When fuel is burnt in a regular power plant, the fire is fed by oxygen in the air. The CO2 that results is diluted in nitrogen in the air, which makes it difficult to economically separate, capture and store. In a CLC system, this problem is avoided by never allowing the fuel and the air to come into contact with one another. Instead, they are housed in two separate units, a fuel reactor and an air reactor. In the air reactor, through the heat-producing process of oxidation, oxygen is drawn from the air and transferred to metal oxide granules. Those granules are then transferred to the fuel reactor, where they react with the fuel, creating more heat.
The exit stream from the fuel reactor consists of only CO2 and H2O - no nitrogen. The H2O can easily be condensed out of the mixture, leaving nothing but easily-captured pure carbon dioxide. The depleted metal oxide carrier granules are cycled back to the air reactor for reuse, while the heat created in both reactors can be used to spin turbines, which in turn generates electricity.
The medium-scale 500kW DemoCLOCK will be a little different, in that it will be a packed bed system. It will only have a single reactor, in which the carrier granules will alternately be exposed to the air, in order to get "charged up," and then to the fuel gas, in the absence of air. It should offer the same performance as a traditional CLC system but will be more compact, and simpler, as the carrier won't need to be moved back and forth.
The packed bed system was originally developed by a team at The Netherlands' Eindhoven University of Technology. DemoCLOCK has a budget of EUR 8.2 million (US$11.8 million), and is being funded by the European Union. It includes ten other industry partners, besides SINTEF.