Reactivation Experiments Of Spent Dolomite-based Sorbernt For CO₂ Capture

The capture and storage of carbon dioxide?CO₂?has emerged as a potentially technology pathway to control the global warming caused by anthropogenic emission of CO₂ into the atmosphere.The calcium looping process?CLP?is a promising capture process,which is based on the reversible gas –solid reaction between CaO and CO₂ to form Ca CO3.Dolomite as a kind of naturally occurring Ca-based sorbents shows superior recycling stability in carbonation/calcination cycles for CO₂ capture.However,the separation between Ca and Mg during recycling weaken s the resistance of sorbents for sintering resulting in the reduction of CO₂ carrying activity.As for this problem,the following three aspects of the study were carried out:?1?the effects of calcination conditions on the separation characteristics of Ca and Mg in dolomite-based absorbent;?2?the effects of Composite ball-milling on the activity of spent dolomite-based sorbent;?3?study on the mechanism of reactivation of spent dolomite-based absorbent by composite ball-milling.The separation of Ca and Mg in dolomite begins from the first calcination.In this paper,the separation characteristics of Ca and Mg during the first calcination process of dolomite was investigated by using the change of Ca and Mg ratios on the sample surface before and after calcination.The separation trend of Mg migrat ing to surface of absorbent and the Ca migrating inside was verified.The results show that the particle size of the absorbent particles and the temperature had little effect on the separation of Ca and Mg.While the increase of the carrier gas flow and the prolong residence time during the calcination process will promoted the separation.This paper presents a novel method for reactivation of spent dolomite-based sorbents.Experiments to obtain spent sorbent were performed in a tube furnace by carrying out calcium looping process tests?calcination at 950 ? in a 100% CO₂ atmosphere and carbonation at 700 ? in a 100% CO₂ atmosphere?.Then reactivation was achieved by ball milling with H2 O and dry ice.The characterization of reactivated material by X-Ray Powder Diffraction?XRD?confirmed the transformation from oxide?CaO/MgO?to carbonate?Ca CO3/Ca Mg?CO3?2?.At the same time,wet ball milling of spent sorbent allowed efficient particle size reduction and the effective dispersion of Mg and Ca in the particles.This improved CO 2 carrying capacity was tested in calcination/carbonation tests performed in a thermogravimetric analyzer?TGA?.Spent sorbent after reactivation had even better characteristics for CO₂ capture than that of the fresh dolomite sorbent after 5th cycle.Moreover,after 10 cycles the carbonation degree for the reactivated sorbent were still above 70%,significantly higher than the spent sorbent.Furtherly,we explore the mechanism of regeneration of dolomite phase in the activation by ball-milling with dry ice by means of XRD and TG.Phase evolution process from spent sorbents?Ca O & Mg O?into dolomite?Ca Mg?CO3?2?had been obtained: firstly,carbonation of spent sorbents was completed to produce CaCO3 and Mg CO3·3H2O,followed by Ca CO3 and Mg CO3·3H2O synthesizing Ca Mg?CO3?2.This paper also discussed the key role of water in the formation of dolomite phase,and confirms the liquid-phase environment provided by it promoted the carbonation process of the CaO & Mg O and the formation of the dolomite.