Bio-FLASHCHAIN® theory for rapid devolatilization of biomass 3. Predicting total yields for torrefied grasses and agricultural residues

Abstract

This paper extends the interpretation of volatiles yields from torrefied woods in Part 2 to torrefied grasses and agricultural residues (AgRes). The analysis retains the original reaction mechanism and depolymerization kinetics, and implements the fuel constitution submodel from Part 2 that uses the carbon aromaticity added during torrefaction to determine the impacts on primary devolatilization behavior. Torrefaction replaces bridges with char links within macromolecules of both cellulose and lignin and these added char links are entirely responsible for the reductions in volatiles yields, since the primary devolatilization of torrefied biomass abides by the same reaction kinetics as the parent raw biomass. The added char links are estimated without any adjustable parameters, given only an ultimate analysis for the torrefied biomass, plus an ash content for AgRes. Consequently, depolymerization statistics, rather than chemical kinetics, govern the reductions in volatiles yields from torrefied samples. The predictions are validated with volatiles yields from 10 grasses and 20 torrefied grasses, and from 6 AgRes and 16 torrefied AgRes for heating rates from 10 °C/min to almost 104 °C/s; temperatures from 470 to 1200 °C; pressures from 0.1 to 3 MPa; with contact times from tens of milliseconds through tens of minutes.