Self-reactivation of spent limestone to enhance its CO2 capture capacity in multiple cycles
Calcium looping process is a kind of cost-effective and high-efficiency CO2 capture technology.A certain amount of fresh calci-um based sorbent should be supplemented to the process and corresponding amount of spent sorbent is discharged.It is of significant to re-alize in situ reutilization of such a quantity of spent calcium based sorbent.A dual-fixed bed reactor was employed to prepare the spent limestone and investigate the cyclic carbonation conversions of spent limestone after self-reactivation.XRD,SEM and N2 adsorption analy-sis were employed to discuss the mechanism that self-reactivation improves the CO2 capture capacity of spent limestone.The results show that when placed in a constant humidity environment,spent limestone can absorb the H2O in the air to form Ca(OH)2 and go on to form calcium hydroxide hydrate when the value of water absorption φ is 100％.The limit value for φ is 130％.CO2 capture capacity of the spent limestone is dramatically enhanced after self-reactivation,which is proportional to φ.Compared with CaCO3,the CO2 capture ca-pacity of spent limestone is much more sensitive to φ.When φ is 130％,the CO2 capture capacity of the spent limestone after self-reacti-vation is even higher than that of the fresh limestone.The microstructure analysis results show that due to the sintering occurred under high temperature calcination,the CaO grain size in calcined limestone increases from 41.9 nm to 72.2 nm.The micro-pores are blocked.The pore volume and BET surface area decrease dramatically.After self-reactivation,the CaO grain size in the calcined limestone obviously decreases,and plenty of pores are regenerated on the surface.When φ is 130％,the CaO grain size decreases to 35.1 nm,the pore vol-ume and BET surface area are recovered to 70.5％and 107.6％those of the calcined fresh limestone,especially the pore volume that dis-tributed in 10-100 nm is regenerated dramatically.Therefore,the CO2 capture capacity of spent limestone can be enhanced by self-reacti-vation.The self-reactivation process can accelerate the attrition rate of spent limestone.However,even when φ is 100％,the diameter of the sorbent particle only decreases by 0.55％per hour.To sum up,the spent limestone after self-reactivation can sufficiently be used as supplementary sorbent instead of fresh limestone in calcium looping process for CO2 capture.
CO2 capturecalcium loopingcalcium based sorbentsinteringself-reactivationattrition characteristics
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