Thermogravimetric Study of Biomass Pyrolysis Kinetics. A Distributed Activation Energy Model with Prediction Tests

Abstract

ABSTRACT. The pyrolysis of four biomasses (corn stalk, rice husk, sorghum straw and wheat straw) was studied at different temperature -time functions in inert gas flow by thermogravimetric analysis (TGA). Linear and stepwise heating programs were employed. A distributed activation energy model (DAEM) with three pools of reactant (three pseudocomponents) was used due to the complexity of the biomass samples of agricultural origin. Compensation effects were observed between the kinetic parameters similarly to the works of other investigators. The compensation effects result in ambiguous parameter values hence they were eliminated by decreasing the number of the unknown parameters. For this purpose part of the kinetic parameters was assumed to be the same for the four biomasses. This approach also helps to express the similarities of the samples in the model. The sixteen experiments were evaluated simultaneously by the method of least squares to obtain dependable kinetic parameters. 2The resulting models described well the experimental data and were suitable for predicting experiments at higher heating rates. The checks on the prediction capabilities were considered to be an essential part of the model verification.

Thermal Decomposition Kinetics of Woods with an Emphasis on Torrefaction

“…Two stepwise temperature programs were employed which also served to increase the amount of experimental information for the kinetic evaluation. 22,[26][27][28][29] Figure 2 shows a test on the employed sample masses. The comparison of experiments with 3 and 10 mg initial sample masses (solid and dashed curves) indicates that the enthalpy change of the decomposition does not result in a considerable thermal lag at the higher sample mass.…”

“…[22][23][24][25][26][27][28][29] According to this model the sample is regarded as a sum of M pseudocomponents, where M is usually between 2 and 4. Here a pseudocomponent is the totality of those decomposing species which can be described by the same reaction kinetic parameters in the given model.…”

“…The situation was similar in two recent works describing biomass pyrolysis by DAEMs. 28,29 The existence of various ill-definition problems (compensation effects) is well known in non-isothermal reactions. A similar problem was reported by de Jong et al in 2007 for DAEMs.…”

“…[22][23][24][25] The increased number of unknown model parameters required the least squares evaluation of larger series of experiments with linear and non-linear temperature programs. 22,[26][27][28][29] The model parameters obtained in this way allowed accurate prediction outside the domain of the experimental conditions of the given kinetic evaluations. 22,26,28,29 The prediction tests helped to confirm the reliability of the model.…”

“…22,[26][27][28][29] The model parameters obtained in this way allowed accurate prediction outside the domain of the experimental conditions of the given kinetic evaluations. 22,26,28,29 The prediction tests helped to confirm the reliability of the model. The complex decomposition of the biomass pseudocomponents can be approximated formally by n-order (power-law) kinetics, too.…”