Inhibitory Effect of Na and Al on the Sintering Phenomenon of Calcium-Based Sorbents during Calcium Looping
Cheng Shen, Laihong Shen, Jingchun Yan, Peng Wang, Xianglei Yin
Abstract
The sintering of calcium-based sorbents is the main factor restricting the development of calcium looping technology to capture CO2. In this work, in order to improve the cyclic CO2 capture performance of calcium-based sorbents in long-term cycles, the simultaneous addition of Al2O3 and trace NaBr was used to slow down the sintering of sorbents. The results showed that the effective CaO conversion rate of the sorbent doped with NaBr and Al2O3 was nearly double that of the sorbent doped with Al2O3 alone. The effective CaO conversion rate of the 90Ca–10Al–Na sorbent after 20 cycles was 53.2%, which was mainly attributed to the synergistic effect of Na and Al. Ca12Al14O33 formed by the reaction of Al2O3 and CaO plays a very good role in supporting the framework of the sorbent and can slow down the sintering of the sorbent. While NaBr was not involved in the reaction, it increased the number of pores in the sorbent. Therefore, the CaO conversion rate of the sorbent modified with Na and Al synergistically has been greatly improved. As the content of Al2O3 increased, the effective CaO conversion rate of the modified sorbent decreased due to the formation of other calcium–aluminum compounds [Ca3Al2(OH)12 and Ca3(Al(OH)6)2]. The microstructures of the calcined sorbents were analyzed by X-ray diffraction, Brunauer–Emmett–Teller, and scanning electron microscopy tests. In addition, the 70Ca–30Al–Na sorbent was subjected to the cyclic CO2 capture performance experiment for up to 64 h on a fixed-bed thermogravimetric analyzer, and the final morphology state of the sorbent was observed.