Effect of sorbent hydration on the average activity of CaO in a Ca-looping system

It is well known that the solid sorbents used in calcium looping CO2 capture systems experience a reduction in carrying capacity with the number of cycles. Several sorbent reactivation schemes have been proposed as means of overcoming this deactivation process. This work analyzes the integration of a reactivation process in a Ca-looping cycle by means of a hydration reactor. The mass balances involved in this three-reactor systems must then be solved in order to evaluate the effect of the different variables on the average activity of the sorbent. The positive impact of reactivation by hydration (i.e. average increase in activity of the sorbent arriving at the carbonator) is discussed in conjunction with the negative impacts on the overall operation of the system (e.g. steam consumption, etc.) and on the large reactivation reactors. Two different scenarios employing different degrees of hydration have been evaluated. The results obtained show that steam is used more efficiently when only a small fraction of the circulating solids is hydrated to a high degree. Moreover, the performance of the sorbent reactivation step is better when low make up flows of limestone are used.