Kinetic Analysis of Dried Biosolid Pyrolysis

Biosolid pyrolysis can be a feasible route to biochar production and energy recovery for water resource recovery facilities that generate dried biosolids. In this study, nonisothermal thermogravimetric analysis with nonlinear model-fitting has been used to obtain the pyrolysis kinetics of a commercially available dried biosolid. Five pseudo-component decomposition reactions were observed during pyrolysis and were modeled as parallel nth-order reactions. To obtain the kinetic parameters associated with the decomposition process, nonlinear regression was first used to fit the model to thermogravimetric data, and the results were then used as initial guesses to fit the more sensitive derivative thermogravimetric data. To ensure that the kinetic parameters did not correspond to a local minimum of the objective function representing the difference between experimental and calculated data, initial guesses for activation energies were varied over a range of 10-200% of the base case, with corresponding variations in the pre-exponential factors. Confidence that the regression yielded unique kinetic parameters representing a global minimum in the objective function was achieved through the fact that the procedure converged to the same set of kinetic parameters for 95% of the wide range of initial guesses.