Determination of Carbonation/Calcination Reaction Kinetics of a Limestone Sorbent in low CO2 Partial Pressures Using TGA Experiments

The carbonation/calcination reaction cycle of a limestone sorbent was used in a novel greenhouse calcium looping process to provide the heat and CO2 requirement of greenhouses. The unique conditions of this process (low temperature and low CO2 partial pressure) led to the determination of the carbonation/calcination reaction kinetic parameters in a temperature range of 400 to 800 oC and CO2 partial pressures of 0.04 to 0.16% (400 to 1600 ppm) which were carried out experimentally via a thermo-gravimetric analyzer (TGA). Various gas-solid reaction mechanisms were considered to determine the best reaction mechanism for the carbonation reaction. The diffusion function or G(x) = x2 had the best least-square linear fit, which resulted in a first order reaction for the carbonation reaction in the greenhouse calcium looping process. Moreover, the activation energy and pre-exponential factor of the carbonation reaction were established to be 19.7 kJ mol-1 and 295.8 min-1 kPa-1. The same methodology for reaction mechanism determination was carried out for the calcination reaction and G(x)=1-(1-x)1/3 was found to have the best linear fit. The activation energy and pre-exponential factor determined for the calcination reaction were 103.6 kJ mol-1 and 6.9 × 106 min-1, respectively.