Evaluation of CO₂ Carrying Capacity of Reactivated CaO by Hydration

Abstract

Steam hydration has been proposed as a suitable technique for improving the performance of CaO as a regenerable sorbent in CO2-capture systems. New hydration experiments conducted in this study confirm the reported improvements in the capacity of sorbents to carry CO2. An examination of the textural properties of the sorbent after hydration and mild calcination revealed a large increase in the area of the reaction surface and the formation of a fraction of pores ≈20 nm diameter that enhance the CO2 carrying capacity and increase the carbonation reaction rate. However, these changes in textural properties also lead to lower values of crushing strength as measured in the reactivated particles. Experiments conducted with a high hydration level of the sorbent [Ca molar conversion to Ca(OH)2 of 0.6] in every cycle produced a 6-fold increase in the sorbent residual CO2 carrying capacity. This improvement has been estimated to be achieved at the expense of a very large consumption of steam in the system (about 1.2 mol of steam/mol of captured CO2). The trade off between the improvements in CO2 capture capacity and steam consumption is experimentally investigated in this work, with it being concluded that there is need to design a comprehensive sorbent reactivation test that takes into account all of the hydration reactivation processes.