Kinetic modeling of the pyrolysis of coal, biomass and waste fuels is presented using a power-law model in terms of multiple parallel reactions. The behaviour of the overall conversion rate of the pyrolysis products is derived from the summation of each reaction's conversion rate, while the exponential integral for the computation of individual conversion is evaluated by Hastings rational approximation. Global optimization techniques and the Global Optimization Toolbox for Maple were used in order to minimize globally the sum of squares of errors. Comparison with literature results derived using local scope search methods supports the assumption that the problem is non-convex, thus necessitating the use of global optimization, which leads to a very good agreement between the computational and experimental values of the overall conversion rate vs. temperature derived from a non-isothermal thermogravimetric analyzer.

**Keywords:** Pyrolysis, Kinetic modeling, Global Optimization Toolbox for
Maple, Exponential integral