Institute of Chemical Engineering
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INNOCUOUS - Development of Chemical Looping Combustion

Fig. 1: Chemical Looping Combustion

Chemical looping combustion is a typical dual fluidized bed technology where chemically active bed material, i.e. metal oxide, is circulated between two fluidized bed reactors separated with respect to the gas phase (Fig. 1). In the so-called fuel reactor, a hydrocarbon fuel is oxidized by oxygen released from the bed material. In case of full oxidation, CO2 and H2O are the products in the fuel reactor. In the so-called air reactor, the bed material is re-oxidized with air. The air reactor releases oxygen-depleted hot air.  

The CLC system typically operates at temperatures of 800-1000°C. At common global excess air ratios around 1.2, additional heat must be withdrawn directly from the reactors. In practice, the extent in which fuel oxidation happens in the fuel reactor depends on the availability of oxygen and on the kinetics of the elementary gas-solid reactions A key-issue for the industrial feasibility of CLC is the availability of oxygen carriers suitable from both the technical and the economical point of view.

Fig.2: DCFB System der CLC

The three approaches discussed for carbon capture, i.e. pre-combustion, oxy-firing and post combustion, have large costs and energy penalties for gas/gas separation and/or gasification in common. The fundamental features of the process steps causing these penalties are well known since long and, to the best of our knowledge, no very significant technological break-through is foreseen with respect to gas/gas separation. This is in large contrast to CLC where the CO2 separation is inherent in the technology, and thus no gas/gas separation is needed. CLC is discussed as a potential break-through technology with respect to CO2 avoidance costs. With respect to power generation, there are basically two routes possible for CLC in large scale application in the future: (i) pressurized CLC combined with gas turbine combined cycles for gaseous or liquid fuels or (ii) CLC for solid fuels. It is, however, likely that technology development will require intermediate steps and operating experience at relevant size. A development of CLC for large scale application naturally leads through small to intermediate scale application. Therefore, the present project addresses the key challenge of optimizing the oxygen carrier particles to achieve high technical, economical and environmental performance for operation with ash-free fuels. The results are summarized by providing a comprehensive next scale CLC design review.




Projectass. Dipl.-Ing. Karl Mayer

Projectass. Dipl.-Ing. Dr.techn. Stefan Penthor