We developed an evaluation module to calculate the carbon capture efficiency of a fluidized bed carbonator via the semi-empirical modeling of the solvent activity of lime particles. Since the solvent activity is affected by regeneration cycle number, reactor temperature, and particle size, two design parameters for the particle activity model, i.e., the characteristic time (t*) and the maximum conversion of particles (XN), were determined as functions of the carbonator operating conditions by applying the partial least square (PLS) method to experimental data reported in the literature. The validity of the proposed approach was shown, and the effects of reactor design factors on the carbonator performance are discussed by means of appropriate simulation studies.