Recovery of CaO by Reductive Decomposition of Spent Gypsum in a CO−CO<INF>2</INF>−N<INF>2</INF> Atmosphere

Reductive decomposition of spent CaSO<INF>4</INF> was studied using a packed-bed reactor to regenerate an alternative CaO sorbent. The reactor was operated at various process conditions including an increasing CO concentration, CO/CO<INF>2</INF> concentration ratio (0.067−1), and temperature (1123−1273 K). In all cases, N<INF>2</INF> was used as a balancing gas. The regeneration of CaO from CaSO<INF>4</INF> was found to be most effective in the CO−CO<INF>2</INF>−N<INF>2</INF> atmosphere and strongly depended on the CO/CO<INF>2</INF> concentration ratio. At 1273 K, an apparent conversion value of 0.91 for the decomposition of CaSO<INF>4</INF> to CaO was obtained in a 2 vol % CO and 30 vol % CO<INF>2</INF> atmosphere. On the other hand, in a CO−N<INF>2</INF> atmosphere, CaS was predominantly produced. The SO<INF>2</INF> absorption capacity of CaO regenerated from CaSO<INF>4</INF> was higher than that of limestone-calcined CaO. A larger pore diameter of the regenerated CaO was considered to be responsible for the higher SO<INF>2</INF> absorptivity.