Understanding the Sulfation Pattern of CaO-Based Sorbents in a Novel Process for Sequential CO2 and SO2 Capture

The CaO-based sorbent is considered to be a potential candidate for high-temperature CO2 capture. However, its application is limited by the loss in CO2 sorption activity with increasing number of calcium looping (CaL) cycles, which leads to vast spent sorbents with a potential for pollution. To solve the problem, the optimized utilization of CaO-based sorbents through a novel process to achieve sequential CO2 capture and SO2 retention is studied in the work, and the sulfation pattern of spent CaO coming from CaL process under different variables is investigated. It is observed that spent CaO-based sorbents experiencing dozens of carbonation/calcination cycles under severe CaL conditions have even a better capacity for SO2 capture than the fresh CaO. By use of a combination of testing approaches, the phenomenon is revealed to be related to the variation of the sulfation pattern of CaL-spent CaO, and pores with a diameter of approximately 60-100 nm in the material are thought to be the key factor determibing the capacity of spent sorbents for SO2 retention. On the basis of the results, a novel sulfation model is proposed to understand the reaction behavior of the highly cycled CaO in SO2 capturing. Moreover, it is found that sulfation mode of CaL-spent CaO is sensitive to the variation of calcination in CaL process and particle size of the CaO-based sorbents.