Annular Carbon Stripper for Chemical-Looping Combustion of Coal

Abstract

The carbon stripper (CS), which is a fluidization bed aimed at separating char particles from oxygen carriers during coal-fired chemical looping combustion (CLC), is vital for achieving high carbon capture efficiency of a CLC system. An effectively designed CS could transport most char particles back to the fuel reactor and simultaneously allow most oxygen carriers to reach the air reactor. An annular carbon stripper was designed, and a cold model apparatus was built for operation and optimization. The CS consists of an annular fluidized bed and a center riser. The riser was inserted into the annular fluidized bed, and the fluidized bed was divided into the annular zone and the cylindrical zone. Plastic beads were used to simulate char particles, and ilmenite was used as the oxygen carrier. The effect of operational parameters (solid feeding rate and gas velocities) and particle properties (average size of plastic beads and mass concentration of plastic beads) on the separation efficiencies of plastic beads and ilmenites was investigated in detail. The main parameters of the CS structure (the length of the annular zone and the diameters of the riser and annular fluidized bed) were studied and optimized. The axial distribution of the solid volume fraction and the mass concentration of light particles along the annular fluidized bed were measured, and the fluidization behavior in the CS was analyzed. The separation process in the annular CS and the important factors influencing the separation of binary particles were discussed. Under the optimized structure and operational conditions, the annular CS could be an effective apparatus to completely separate char particles from oxygen carriers, which could greatly improve carbon capture efficiency during the operation of a coal-fired CLC.