Fly Ash-CaO sorbents modified with chlorides and hydroxides for CO2 capture in high-temperature flue gas

CaO-based sorbents are among the most promising materials for capturing CO from high-temperature flue gas in coal-fired power plants. Fly ash, a solid waste product generated by coal-fired power plants, can be utilized as a calcium source for the in-situ preparation of CaO-based sorbents to capture CO from high-temperature flue gas. Nevertheless, the inherent characteristics of fly ash, such as its low adsorption capacity and poor activity, present challenges in its utilization. Doping is an effective method for enhancing the adsorption capacity and activity of sorbents. In this study, fly ash-CaO sorbents were doped and hydrated with six common chlorides and hydroxides in order to investigate the potential effects of the dopants on the sorbents. The carbonation performance of these sorbents was evaluated in a calcination/carbonation reaction system, and the modified sorbents were characterized using multiple methods to elucidate the underlying mechanisms. The results indicate that the carbonation conversion of the six modified sorbents is in the order of Fe(OH)Fe(Cl) > KCl > NaCl > KOH>NaOH. The element enhancement of the modified sorbents at the same doping ratio is in the order of Fe > K> Na, and Cl exhibit better synergistic effects with K and Na compared to OH. Some dopants improve the carbonation reaction kinetics of the sorbents, promoting the overall reaction shift towards the rapid reaction stage. This study provides a promising pathway for the reuse of solid waste fly ash and the development of CaO-based sorbents suitable for rapid reaction scenarios.