(376e) Comparative Thermodynamic Evaluation of Oxygen Carriers for Chemical Looping Combustion
Chemical looping combustion (CLC) is an emerging technology for clean energy-production from fossil and renewable fuels. In CLC, an oxygen carrier (typically a metal) is first oxidized with air. The hot metal oxide is then reduced in contact with a fuel in a second reactor, thus combusting the fuel. Finally, the reduced metal is transferred back to the oxidizer, closing the materials “loop”. CLC is essentially an ‘oxy-fuel combustion’ which allows for flame-less, NOx-free combustion without requiring expensive air separation, and thus produces sequestration-ready CO2-streams without significant energy penalty. However, a major hurdle towards technical implementation of CLC is the development of stable and efficient oxygen carrier materials.
We present a detailed thermodynamic study of a wide range of metals as potential oxygen carriers for the combustion of a typical coal-derived syngas (Eastman gasifier coal gas). The materials were evaluated with regard to attainable syngas conversion as well as coke formation at equilibrium conditions for a stoichiometric feed of the respective oxygen carrier and syngas. A wide range of operating temperatures (700-1200oC) and pressures (1 – 30 bar) was investigated. A special focus was put on the formation of metal sulfides due to sulphur contaminants in the feed gas stream.
We found that no single carrier material shows a 'perfect' combination of desired properties (high syngas conversion and high resistance to coking and sulfide formation). However, appropriate combination of different metals could allow for the desired carrier properties. The results will be discussed in detail in the presentation.