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Novel combustion principle with inherent capture of CO2
using combined manganese oxides that release oxygen

Final Report Summary - NOCO2 (Novel combustion principle with inherent capture of CO2 using combined manganese oxides that release oxygen)

Conventional CO2 capture processes have large costs associated with gas separation. Chemical-looping combustion (CLC), a new combustion principle, avoids this entirely by using metal oxides to carry oxygen from air to the fuel. In this project, novel manganese based oxygen carriers with the ability not only to react with combustible gases, but also to release gaseous oxygen for direct oxidation of solid fuel, have been developed. The programme includes detailed studies of manganese-based combined oxide oxygen carriers, in combination with studies of fluidized-bed reactor design, actual operation in pilot plants and modelling to provide a basis for commercialization and scale up of this new principle of combustion.
Four families of manganese based combined oxide materials suitable for the application were identified and investigated: I) Mn-Fe-oxides, II) doped and undoped Mn-Si-oxides, III) Mn-Fe-Si-oxides, and IV) doped and undoped Mn-Ca-oxides. Oxygen carriers of these types have been manufactured using industrially relevant methods, comprehensively characterized with a range of techniques, and examined with respect to their ability to release gaseous O2, react with gaseous and solid fuel, and resistance to attrition and fuel impurities. Naturally occurring manganese ores have also been examined as an option for low-cost oxygen carriers, as they naturally contain significant amounts of Fe and Si. The main conclusions are that all proposed materials are capable of releasing gas phase O2, can have sufficient reactivity with fuel and have adequate oxygen transfer capacity. High resistance to attrition in combination with inertness towards sulphur is more difficult to achieve, but Mn-Si-oxides doped with small amounts of Ti are promising in all aspects. Also some of the natural ores have sufficient stability.
Another part of the project involves experimental and CFD examination of fluidized bed reactor systems suitable for the process. The main achievements here include the development of a validated 1-dimensional model of a chemical looping fuel reactor. Also the fate of volatile fuel gases released during chemical looping combustion of solid fuels was studied by means of cold flow experiments and CFD modelling. These efforts are of great value for the understanding of the design of CLC reactors, and also facilitate interpretation of data measured in existing pilot units.
The third part of the project involves verification and investigation of the concept by operation in pilot units. Nine campaigns have been conducted in a small 300 W chemical-looping combustor. Oxygen carriers examined include manufactured materials, i.e. three of category III (Mn-Fe-Si-oxides) and two of category II (doped and undoped Mn-Si-oxides), as well as natural Mn ores (category III). Fuel conversion is satisfactory, but most materials showed unacceptable behaviour with respect to attrition. A selected manufactured material showed the best performance ever in 10 kW operation with solid fuels. Moreover, some of the much cheaper Mn ores showed excellent results in 10-kW and 100-kW operation. Most important, the operation of the 100-kW pilot has clearly demonstrated the possibility to reach high performance for all the three essential performance criteria. Thus, approximately 90% fuel conversion, 90% gas conversion and close to 100% CO2 capture was achieved. Further, material oxygen-carrier integrity was confirmed. These results are unique, so far only small pilots have shown comparable results.
Finally, a study examining the design of a full-scale 1000 MWth CLC power plant has been performed. It is concluded that a full-scale CLC plant can be designed to have large similarities to conventional circulating fluidized bed (CFB) boilers. The expected additional cost of CLC is likely to give a cost of around 20 €/tonne CO2 avoided, i.e. likely less than half of the cost of competing technologies.
In summary, the project provides proof-of-concept. The high performance clearly demonstrates the technical viability of this process and the full scale design and cost analysis clearly demonstrates the uniquely low CO2 capture costs. This is a consequence of the obvious advantage of this process, the large costs of gas separation necessary in other CO2 capture technologies can be avoided.