Steam hydration of CFBC bottom ashes in a rotary kiln

• CFBC bottom ashes are hydrated in a rotary kiln using 200 °C steam.
• The hydration reaction conversion reaches 90% in 5 min.
• Reactivated sorbent shows desulfation reactivity comparable to fresh limestone.

Circulating fluidized bed combustion boiler bottom ashes (BA) are hydrated in a 15 rpm rotary kiln using 200 °C steam. After different hydration time, BA particles are characterized by the particle size distribution, the BET specific surface area, the pore size distribution and the thermogravimetry analysis. Calcium oxide in the BA core reacts with steam and produces calcium hydroxide. The molar volume expansion of this reaction breaks the calcium sulfate shell, causing the reduction of the particle size, the increasing of the specific surface area and the total pore volume. The reaction conversion increases with the increasing of the steam hydration time and reaches ca. 90% after 5 min hydration time. The pore size distribution of BA after the hydration reaction affects its desulfation reactivity. After 5 min steam treatment, the hydrated BA shows the greatest desulfation reactivity, which is comparable to that of the fresh limestone particles.