Effect of pore size distribution of calcium oxide high-temperature desulfurization sorbent on its sulfurization and consecutive oxidative decomposition

CaS formed from the CaO sorbent during desulfurization in coal gasifiers must be converted to CaSO₄ before disposal. CaS is mainly decomposed to CaO and SO₂, and then the CaO is converted to CaSO₄ by SO₂ in the presence of H₂O and O₂. However, the inner portion of the CaS particles cannot be converted to CaO and CaSO₄, because the pores are plugged and oxidative gases (H₂O and O₂) cannot come into contact with the interior of the CaS particles. In this study, the effect of the pore-size distribution of the CaO sorbent on the sulfurization and consecutive oxidative decomposition of the formed CaS in the presence of H₂O at high temperature have been investigated, using three samples with different pore structures but similar surface areas. The following results have been obtained: (i) the macroporous CaS can be easily converted, because the oxidative decomposition of the macroporous CaS occurs without pore plugging; (ii) pores with a size of > 100 nm in the sorbent can have an important role during the sulfurization and consecutive decomposition of the formed CaS; and (iii) the molar CaO/CaSO₄ ratio in the decomposed CaS sample is affected by the pore structure.