Chemical-looping combustion - status of development
Paper i proceeding, 2008
Chemical-looping combustion (CLC) is a combustion technology with inherent
separation of the greenhouse gas CO2. The technique involves the use of a metal oxide as an
oxygen carrier which transfers oxygen from combustion air to the fuel, and hence a direct
contact between air and fuel is avoided. Two inter-connected fluidized beds, a fuel reactor and
an air reactor, are used in the process. In the fuel reactor, the metal oxide is reduced by the
reaction with the fuel and in the air reactor; the reduced metal oxide is oxidized with air. The
outlet gas from the fuel reactor consists of CO2 and H2O, and almost pure stream of CO2 is
obtained when water is condensed. Considerable research has been conducted on CLC in the
last years with respect to oxygen carrier development, reactor design, system efficiencies and
prototype testing. In 2002 the process was a paper concept, albeit with some important but
limited laboratory work on oxygen carrier particles. Today more than 600 materials have been
tested and the technique has been successfully demonstrated in chemical-looping combustors in
the size range 0.3 – 50 kW, using different types of oxygen carriers based on the metals Ni, Co,
Fe, Cu and Mn. The total time of operational experience is more than a thousand hours. From
these tests it can be established that almost complete conversion of the fuel can be obtained and
100% CO2 capture is possible. Most work so far has been focused on gaseous fuels, but the
direct application to solid fuels is also being studied. Moreover, the same principle of oxygen
transfer is used in chemical-looping reforming (CLR), which involves technologies to produce
hydrogen with inherent CO2 capture. This paper presents an overview of the research performed
on CLC and CLR highlights the current status of the technology.