Countercurrent moving bed carbonator for CO2 capture in decoupled calcium looping systems

Abstract

Calcium Looping can be a suitable technology to address the CO2 capture from disperse flue gas sources, including shipping, by decoupling carbonation and calcination steps and by using the CaCO3 as CO2 transport media. In this work we present the design of a moving bed carbonator especially suited for these applications. The Ca-sorbent material (porous CaO or Ca(OH)2 in the form of pebbles or pellets) is fed to the top of the reactor at ambient conditions and is preheated by the gases leaving the reactor. Then the carbonated solids leave the reactor at the bottom at a temperature close to that of the inlet gases. A basic countercurrent reactor model has been developed to identify operational windows and other suitable conditions to achieve optimum carbonation temperatures of 600–700 °C in the central carbonation zone of the reactor. Gas velocities of 1–3 m/s and solid residence times in the carbonation zone of between 2 and 13 h are needed to carbonate spheres of Ca-based materials of 1 to 2 cm up to its maximum conversion of 0.6 for CaO and 0.8 for Ca(OH)2. The thermal and mechanical similarities of the proposed reactor with those of shaft kilns should accelerate the scaling up of this new reactor concept.