Diversity of chemical composition and combustion reactivity of various biomass fuels

• Chemical composition and combustion kinetics were measured simultaneously in a TGA.
• Straw char pellets had the largest variability for combustion properties.
• Wood char pellets had the smallest variability for combustion properties.
• The differences in predictions between the two applied reaction models were small.
• The accuracy of kinetics for different pellets strongly affected model prediction.

A simple and fast method for measuring simultaneously the chemical compositions and combustion reactivities of biomasses and evaluating their heterogeneity was developed using a commercial thermogravimetric analyzer. Wood, straw, and bark pellets were selected as the biomass fuels. Compared to the variations observed for volatiles and char contents, the variations of moisture and ash contents for the three types of biomass were large in an individual pellet. The straw char was more reactive than the bark char and wood char, probably due to the high ash content of the straw, which is especially rich in potassium. Furthermore, the variations of the characteristic temperatures and kinetics in an individual pellet increased from the wood char to bark char to straw char. The experimental results for char combustion can be described by the two simple reaction models: the volumetric model and the shrinking particle model. For each type of biomass, the differences in predictions between the two reaction models were much smaller than the differences in the accuracy of the measured kinetics for the different particles. For the kinetic parameters, the activation energy E and the natural logarithm of apparent pre-exponential factor A∗ (lnA∗) showed a linear correlation in the two applied models (A∗=e(0.2140E-8.713)A∗=e(0.2140E-8.713)), while the measured activation energies of the two applied reaction models were also linear (Eshrinkingparticle=0.8136EvolumetricEshrinkingparticle=0.8136Evolumetric). The performed analyses revealed that 10 biomass samples could ably characterize the conversion of a batch of biomass char particles and the average kinetics of the reactions. In addition, the distribution of conversion rates of the different chars in a batch at a specific time or temperature could be estimated from the standard deviation of the average value for the kinetics.