Chemical Looping Combustion
Chemical looping combustion (CLC) is a combustion concept where air and fuel are never mixed. Thus, CO2 is not diluted by N2 and gas‐gas separation is inherently avoided. CLC has unique potential for reducing energy and cost penalty for CO2 capture, as it avoids the costly gas separation of other CO2 capture technologies. The principle of CLC is shown in Figure 1. Metal oxides are used to selectively transport oxygen from the air reactor (AR) to the fuel reactor (FR). Ideally, the FR exhaust stream contains only CO2 and H2O while the AR exhaust stream is oxygen‐depleted air. This means that 100% of the fuel carbon is captured as CO2 available in concentrated form after simple condensation of the steam from the FR exhaust stream. The total heat release from CLC is equal to that of direct combustion and, thus, the energy penalty is reduced to the CO2 compression and purification efforts all capture processes will have in common. This gives CLC a unique position among the options to capture CO2 from combustion processes.
The three approaches discussed for carbon capture, i.e. post-combustion, oxy-firing and MEA scrubbing, all have in common large costs and energy penalties for gas separation and/or gasification. 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 separation. This is in large contrast to CLC where the CO2 separation is inherent in the technology, and thus no gas separation is needed. CLC is probably the only technology we know today where a significant breakthrough could be envisaged for avoiding the large energy penalty of gas separation normally CO2 capture studies for power plants and associated performances assume very large installations. 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.