The effect of sawdust on the rate of limestone carbonation/calcination reactions was studied in a thermogravimetric analyzer applying a grain model for the calcium-based sorbent, namely Havelock limestone (0.50-1.41 mm). Two samples were employed for calcination under N-2 at 850 degrees C: one containing limestone, and the other a mixture containing limestone and sawdust. The resulting limestone samples were observed under a scanning electron microscope (SEM), while the quantitative influence of calcination conditions was examined by BET surface areas. The presence of sawdust during calcination caused a significant increase in the initial rate of carbonation, which has been attributed to the enhancement of CaO surface area. The presence of H-2 which is emitted from sawdust pyrolysis was assumed to be responsible for reduction of limestone sintering. (C) 2012 Elsevier B.V. All rights reserved.