Chemical-Looping Combustion (CLC) of Solid Fuels (SF-CLC) A Discussion of Operational Experiences, Costs, Upscaling Strategies and Negative Emissions (Bio-CLC)

Paper in proceeding, 2018

Chemical-Looping Combustion (CLC) is a technology which ideally is able to avoid all the costs associated with gas separation, well known to be the major cost, as well as the major reason for large loss in energy efficiency, of CO2 Capture and Storage (CCS). The reason is that the oxygen is transferred from air to fuel using an oxygen-carrier, thus avoiding the mixing of air and fuel, meaning that the combustion products, CO2 and H2O, end up in a separate stream. The H2O is easily removed by condensation resulting, ideally, in a pure CO2 stream. Furthermore, when applied to solid fuels a CLC boiler may be constructed very similar to a circulating fluidized bed (CFB) boiler, and analyses of the cost differences indicate a low added investment cost for a CLC boiler as compared to a CFB boiler. The CLC process has been operated in more than 39 smaller pilots, for a total of more than 10,000 h. The experience with solid fuels show a large variation in performance depending on pilot design, operational conditions, solids inventory, oxygen carrier and fuel. However, there is at present no experience of the process at commercial or semi-commercial scale, although oxygen-carrier materials have been successfully used in commercial boilers for a related process, Oxygen-Carrier Aided Combustion (OCAC) during more than 20,000 h of operation. The paper discusses the lessons learned from pilot operation, the costs, strategies for scale-up, as well as the use of CLC for biomass combustion, i.e. Bio-CLC, in order to attain negative CO2 emissions.