The CaO hydration behavior of four Ca-based sorbents (Deyang, Yangguan, Dawa, and Kuzuu) with different CaO contents was examined. A high-pressure thermogravimetric apparatus was used to measure the hydration rates at high temperatures (773-923 K) and high steam pressures (1.3-2.3 MPa). CaO hydration occurred at high temperatures up to 923 K at high steam pressure. The hydration rates and the final CaO conversion values varied substantially among the different sorbents. Hydration rate and CaO conversion decreased with increasing CaO content. The order of CaO hydration rate with respect to the difference between the reactant steam pressure and the equilibrium steam pressure (P-H2O-P*(H2O)) varied with CaO content. The apparent activation energy for rate constant k also varied with CaO content. (c) 2007 Elsevier B.V. All rights reserved.