Chemical-looping combustion in combination with integrated coal gasification-a way to avoid CO2 emission from coal fired power plants without a significant decrease in net power efficiency

To avoid CO₂ emission, different gas separation techniques like membrane separation and absorption have been suggested to separate CO₂ from the other exhaust gases before the exhaust is released into the atmosphere. This separation is, however, estimated to be rather costly due to the large volume of dilute gas that needs to be treated and the energy consumed in the separation process. In chemical-looping combustion (CLC), CO₂ and the other combustion products are already separated in the combustion process. This is because fuel and air never enter the same reactor. Instead of oxidizing the fuel with oxygen from the combustion air, the fuel is oxidized by an oxygen carrier, that is, an oxygen containing compound, for instance a metal oxide. In this way the CO₂ and H₂ O formed at oxidation of the fuel are not diluted by excess air as in conventional combustion. Chemical-looping combustion is also thought to result in a higher fuel energy conversion efficiency. This increase in efficiency is achieved due to the more ordered fuel combustion reaction that reduces the irreversible entropy production. It is also possible to recover some of the heat from the exhaust within the CLC system. In this paper, estimations of the performance of a chemical-looping combustion combined cycle system with integrated coal gasification and NiO, Fe₂O₃ or Mn₃O₄ as an oxygen carrier is compared to the performance of a similarly simulated conventional IGCC-system. Calculations show that the systems reach about the same net power efficiencies but then the chemical-looping systems have an added advantage of CO₂ separation