Studies on pyrolysis of vegetable market wastes in presence of heat transfer resistance and deactivation.

In the present investigation, the pyrolysis of predried vegetable market waste (dp=5.03 mm) has been studied using a cylindrical pyrolyser having diameter of 250 mm under both isothermal and non-isothermal conditions within the temperature range of 523923 K with an intention to investigate the effective contribution of different heat transfer controlling regime namely intra-particle, external along with kinetically control regime on the overall global rate of pyrolysis. Thermogravimetric method of analysis was utilized to obtain experimental data for both isothermal and non-isothermal cases by coupling a digital balance with the pyrolyser. The pyrolysis of vegetable market waste has been observed to exhibit deactivated concentration independent pyrolysis kinetics, analogous to catalytic poisoning, throughout the entire range of study. The deactivation is of 1st order up to 723 K and follows the 3rd order in the temperature range of 723<T?923 K. Starting from the mechanistic approach, a set of differential heat and mass balance equations has been developed and a general equation containing a specific parameter (dimensionless temperature, θ) is presented which can conveniently be used to simulate concentration time histories of the participating components by assigning different expressions for θ developed in the present investigation. A detailed procedure of simulation work under different controlling regime has also been outlined. A comparison of experimental data with the simulated values under isothermal conditions shows that the system is kinetically controlled at lower temperature region (T?723 K). However, at higher temperature region (723<T<923 K), the pyrolysis process is controlled by intra-particle heat transfer resistance. While studying the pyrolysis process under non-isothermal conditions, a segregated ramp function of furnace temperature rise has been used. The transient profiles of the reactant and products have been simulated following the similar procedure followed under isothermal conditions. When experimental data and simulated values are compared, it is observed that unlike the case of isothermal condition, the global pyrolysis rate is controlled by intra-particle heat transfer resistance. Copyright 2005 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]