Enhancement in cyclic stability of the CO2 adsorption capacity of CaO-based sorbents by hydration for the calcium looping cycle

• The rate of the decay of the carbonation conversion is reduced by steam hydration.
• The regeneration and recovery of limestone can be effectively improved by hydration.
• A particle size sorbent of lower than 1.5 μm exhibited higher regeneration and recovery.
• Liquid water hydration is suitable to regeneration of particle size larger than 250 μm.

In this paper, the reactivation of limestone was effectively enhanced and recovered by steam and/or liquid water hydration processes. The decay rate of the activity in carbonation conversion was improved by the steam hydration of the sorbents during decarbonation/carbonation reactions. The carbonation conversion activity of limestone with a particle size of 1.5 μm remains at 65% with hydration under 2.9 mol% steam after 20 decarbonation/carbonation cycles, while the un-hydrated sorbent shows a lower carbonation conversion of 34%. The activity preservation in the carbonation conversions of three representative particle size ranges of 1.5, 37–74, and 250–500 μm are 30, 14, and 6% after 20 cycles, respectively, with a hydration treatment of 2.9 mol% steam. Pore formation and roughness on the sorbents induced by steam hydration contributed significantly to the enhanced carbonation conversion during the decarbonation/carbonation cycles. The sorbent, with a particle size of approximately 1.5 μm, exhibited higher regeneration and recovery of carbonation conversion. Combined with the liquid water hydration, the carbonation conversion activity of the limestone can recover 80–90% of the original.