THE PYROLYSIS KINETICS OF BAGASSE AT LOW HEATING RATES

Thermogravimetric Analysis (TGA) was used to study the thermal degradation of wet and dry bagasse at low heating rates (5 to 50-degrees-C min-1) under a nitrogen atmosphere. For engineering purposes, it was found that a single first-order reaction gave the simplest and best fit to the rapid pyrolysis zone between 195 and 395-degrees-C, with an activation energy of 93.2 kJ mol-1 and pre-exponential factor of 4.33 x 10(4) s-1. These values have no chemical significance, but have been derived for use in modelling studies of the ignition and combustion of bagasse. Sample moisture content up to 18% by weight had no effect on the degradation, because moisture evaporation was complete before pyrolysis commenced at these low heating rates. The choice of the final mass from the TGA curve significantly affected the deduced kinetic parameters. The final sample mass at the end of the rapid pyrolysis zone was 26.2% of the dry sample mass. Some earlier workers neglected the subsequent slow pyrolysis zone and took the final sample mass to be the ash content. If this were done for the experiments reported here, then lower activation energies in the range 58.6 to 71.2 kJ mol-1 would be obtained, illustrating the importance of using the correct final sample mass.