Lime shells obtained from the lagoons of Kerala Coast have been decomposed with a view to study the effect of particle size. A modified TGA has been used to study the decomposition kinetics at various temperatures. Conversion time data obtained showed typical sigmoidal behaviour and the decomposition kinetics could be fitted to the Prout-Tompkins model at all temperatures and for all particle sizes studied. Arrhenius kinetic parameters showed normal type of compensation behaviour indicating an isokinetic temperature of 730degreesC. A theoretical explanation for these observed compensation behaviour and isokinetic temperature has been given. Further, the calcined lime shell has been tested for the capture of CO2 and SO2 using TGA. Effects of temperature of decomposition and particle size have been studied in this case. A theoretical, explanation based on pore size distribution of the calcined lime for this special behaviour has been given.