(480f) Experimental Study of a Riser-Based Carbon Stripper in a Solid Fuel-Chemical Looping Combustion System

Chemical looping combustion (CLC) has emerged as a promising combustion process with low-cost CO₂ separation. In fuel reactors of solid-fuel chemical looping combustion, the solid fuel gasification takes much longer time than the reduction of oxygen carriers. The slip of char particles into the air reactor will result in a decreased carbon capture efficiency. Therefore, carbon stripping is a critical process step which separates fuel particles from oxygen carrier particles. Carbon strippers were adopted in different reactor systems, including a 100 kW_th system in Chalmers, a 1 MW_th system in Darmstadt, and a 50 kW_th system in CSIC. Hongming et al. demonstrated that a riser-based carbon stripper can effectively separate fuel particles from oxygen carrier particles. Therefore, it is necessary to investigate the separation characteristics and technology cost of the riser-based carbon stripper in a three-fluidized-bed CLC system.

A three-fluidized-bed system was constructed based on Glickman’s simplified scaling ratios. The system is comprised of a fuel reactor, an air reactor and a carbon stripper in between. The fuel reactor is a bubbling fluidized bed; the air reactor is a riser which transports solid particles back into the fuel reactor, and the carbon stripper is riser-based. Plastic beads and ilmenite particles were used to simulate the fluidization behavior of char particles and oxygen carrier particles. Pressure profile, solid circulation rate, separation ratio and separation efficiency were measured and calculated to study the separation characteristics of the carbon stripper.

Long-term stable operations were achieved and results have proven the feasibility of the proposed three-reactor system. Solid circulation rate can be easily controlled by adjusting the fluidization gas velocity of loopseals. With an increase of gas velocity in the carbon stripper, more particles were elutriated back to the fuel reactor and the separation ratio and separation efficiency increased. With mixture feeding rates below 17 kg/m²s, the separation efficiency increased from 71% to 97% as the gas velocity increased from 0.8 m/s to 1.6 m/s. Energy-cost ratios were calculated, and gas velocity higher than 0.8 m/s and mixture feeding rates lower than 17 kg/m²s were preferred.

The separation characteristics of a carbon stripper is of vital importance to the operation of a three-fluidized-bed CLC system. The results of this paper reveals that carbon strippers can be used to increase the carbon capture efficiency and that riser is an economically feasible way to realize carbon stripping in a CLC system.