Effect of heating rate on the non-isothermal burning mechanism of sunflower seed shell

Woody shells of sunflower seed were burned in a Thermogravimetric analyzer to investigate the non-isothermal burning mechanisms and the kinetic parameters up to 900°C at the heating rates of 5, 10, and 40°C/min. Temperature intervals of 105-400°C, 400-500°C, 500-600°C, and 600°C-final temperature were considered. The integral method of "Coats-Redfern" was used to calculate the kinetic parameters, and various model equations for rate controlling mechanisms were tried to find the best fitted mechanisms for both the whole temperature range as well as the individual temperature intervals. As a result of the increase in heating rate, decomposition of sunflower seed shell increased due to enhance of both driving force of mass and heat transfers inside the particle. Chemical kinetics was found to be suitable controlling mechanism between 105-400°C for all the heating rates. However, the dominant mechanisms changed from chemical kinetics to diffusion control or branching core model at higher temperature regions. In case of the lowest heating rate (5°C/min), diffusional effects were in effect between 400-500°C. On the other hand, higher heating rates might overcome the diffusional effects and changed the governing mechanism in the favor of the branching core model at this temperature interval.