Recovery of CaO by Reductive Decomposition of Spent Gypsum in a CO-CO ₂-N₂ Atmosphere

Reductive decomposition of spent CaSO₄ 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/CO₂ concentration ratio (0.067-1), and temperature (1123-1273 K). In all cases, N₂ was used as a balancing gas. The regeneration of CaO from CASO₄ was found to be most effective in the CO-CO ₂-N₂ atmosphere and strongly depended on the CO/ CO ₂ concentration ratio. At 1273 K, an apparent conversion value of 0.91 for the decomposition of CASO₄ to CaO was obtained in a 2 vol % CO and 30 vol % CO₂ atmosphere. On the other hand, in a CO-N ₂ atmosphere, CaS was predominantly produced. The SO₂ absorption capacity of CaO regenerated from CASO₄ was higher than that of limestone-calcined CaO. A larger pore diameter of the regenerated CaO was considered to be responsible for the higher SO₂ absorptivity.