CHEMICAL-LOOPING COMBUSTION - STATUS OF DEVELOPMENT

Abstract

Chemical-looping combustion (CLC) is a combustion technology with inherent\nseparation of the greenhouse gas CO2. The technique involves the use of a metal oxide as an\noxygen carrier which transfers oxygen from combustion air to the fuel, and hence a direct\ncontact between air and fuel is avoided. Two inter-connected fluidized beds, a fuel reactor and\nan air reactor, are used in the process. In the fuel reactor, the metal oxide is reduced by the\nreaction with the fuel and in the air reactor; the reduced metal oxide is oxidized with air. The\noutlet gas from the fuel reactor consists of CO2 and H2O, and almost pure stream of CO2 is\nobtained when water is condensed. Considerable research has been conducted on CLC in the\nlast years with respect to oxygen carrier development, reactor design, system efficiencies and\nprototype testing. In 2002 the process was a paper concept, albeit with some important but\nlimited laboratory work on oxygen carrier particles. Today more than 600 materials have been\ntested and the technique has been successfully demonstrated in chemical-looping combustors in\nthe size range 0.3 – 50 kW, using different types of oxygen carriers based on the metals Ni, Co,\nFe, Cu and Mn. The total time of operational experience is more than a thousand hours. From\nthese tests it can be established that almost complete conversion of the fuel can be obtained and\n100% CO2 capture is possible. Most work so far has been focused on gaseous fuels, but the\ndirect application to solid fuels is also being studied. Moreover, the same principle of oxygen\ntransfer is used in chemical-looping reforming (CLR), which involves technologies to produce\nhydrogen with inherent CO2 capture. This paper presents an overview of the research performed\non CLC and CLR highlights the current status of the technology.