Chemical-looping technologies for solid fuels

摘要

In chemical-looping combustion (CLC), an oxygen carrier provides lattice oxygen forrncomplete combustion of a fuel for heat and power production. The reduced metal oxide is thenrnoxidized in a separate reactor. The combustion products CO_2 and H_2O are obtained in purernform, without any nitrogen in the gas. As no gas separation work is needed, this could be arnbreakthrough technology for carbon capture (CCS). Normally, the fuel reactor and air reactorrnare designed utilizing inter-connected fluidized beds. The same underlying reversible redoxrnreactions of CLC can be used for other fuel conversion technologies. These include fluidizedrnbed processes for gas, solid and liquid fuels for heat, power, syngas or hydrogen production.rnSome of these concepts were suggested as far back as the 1950’s, while others have justrnrecently been proposed. Chalmers University of Technology has been involved in CLCrnresearch for over 18 years, and this paper will provide a review of some recent developmentsrnwith respect to CLC with solid fuels, including coal and biomass. Further, the paper willrnprovide an overview some related technologies where Chalmers is conducting researchrnincluding Chemical-looping gasification (CLG) and Oxygen Carrier Aided Combustionrn(OCAC). Both of these processes utilize oxygen carriers in the form of metal oxide particlesrnfor converting solid fuels. In CLG, the fuel is not oxidized completely but rather a purernsyngas/hydrogen stream is produced effectively in the fuel reactor, which could be utilized forrnchemical or fuel production. Oxygen carrier aided combustion (OCAC) uses oxygen carrierrnparticles instead of sand directly in the furnace of a normal fluidized bed boiler. This enablesrninternal oxygen transfer, with positive effects obtained with respect to emissions of nitrogenrnoxides and carbon monoxide, in addition to reduced corrosion problems when utilizingrndifferent wastes and biomass as fuel. This technology was developed around 2012, and is todayrncommercial and employed in several CFB units in Sweden.