▁it ▁with ▁fresh ▁sor b ent ▁( o ften ▁in ▁the ▁carbon ate ▁form ). ▁The ▁size ▁of ▁the ▁pur ge ▁stream ▁compared ▁with ▁the ▁amount ▁of ▁sor b ent ▁going ▁round ▁the ▁cycle ▁affect s ▁the ▁process ▁consider ably . ▁ ▁Background ▁ ▁In ▁the ▁Ca - loop ing ▁process , ▁a ▁Ca O - based ▁sor b ent , ▁typically ▁derived ▁from ▁lim estone , ▁react s ▁via ▁the ▁revers ible ▁reaction ▁described ▁in ▁Equ ation ▁() ▁and ▁is ▁repeatedly ▁cy c led ▁between ▁two ▁vessels . ▁ ▁The ▁forward , ▁end oth erm ic ▁step ▁is ▁called ▁calc ination ▁while ▁the ▁back ward , ▁ex oth erm ic ▁step ▁is ▁carbon ation . ▁ ▁A ▁typical ▁Ca - loop ing ▁process ▁for ▁post - comb ust ion ▁CO 2 ▁ ▁capture ▁is ▁shown ▁in ▁Figure ▁ 1 , ▁followed ▁by ▁a ▁more ▁detailed ▁description . ▁ ▁Fl ue ▁gas ▁containing ▁CO 2 ▁is ▁fed ▁to ▁the ▁first ▁vessel ▁( the ▁carbon ator ), ▁where ▁carbon ation ▁occurs . ▁The ▁Ca CO 3 ▁formed ▁is ▁passed ▁to ▁another ▁vessel ▁( the ▁calc iner ). ▁Cal c ination ▁occurs ▁at ▁this ▁stage , ▁and ▁the ▁reg ener ated ▁Ca O ▁is ▁quickly ▁passed ▁back ▁to ▁the ▁carbon ator , ▁leaving ▁a ▁pure ▁CO 2 ▁ ▁stream ▁behind . ▁As ▁this ▁cycle ▁continues , ▁Ca O ▁sor b ent ▁is ▁constantly ▁replaced ▁by ▁fresh ▁( re active ) ▁sor b ent . ▁The ▁highly ▁concentr ated ▁CO 2 ▁from ▁the ▁calc iner ▁is