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 determining 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.

Calcium looping (CaL) has been identified to be a valuable candidate for CO2 capture and has entered a stage of large‐scale experiment and application. However, the serious loss‐in‐capacity problem will result in the production of a large amount of waste CaO, which not only increases the economic cost of the capture process, also generates a huge risk of secondary pollution. In this work, the waste CaO from CaL was first proposed to be used for SO2 removal by wet desulfurization and the SO2 sorption characteristics were comprehensively studied. Through experimental test and analysis, it is found that CaL‐spent CaO derived from dolomite can achieve higher efficiency than that from the limestone in SO2 removal. The effect of CaL cycle on the SO2 removal performance is observed to be small when the cycle number is under 40. Beyond that, the SO2 removal capacity decreases quickly, which is thought to be due to the variation in slaking rate determined by the compromise between the surface area and pore size distribution of the material. Furthermore, sulfation performance of waste CaO is found to be superior with a particle size smaller than 0.4 mm. This work proves the feasibility of the utilization of CaL‐spent CaO in wet SO2 removal, and could be beneficial for understanding the SO2 sorption characteristics of CaL‐spent materials. © 2017 Society of Chemical Industry and John Wiley & Sons, Ltd.

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