Kinetic Modeling of Solid, Liquid and Gas Biofuel Formation from Biomass Pyrolysis

Modeling of biomass pyrolysis can be understood as several critical multicomponent, multiphase and multiscale processes. The characterization of the biomass and selection of the reference species of cellulose, hemicellulose, lignins and extractives have a major effect on the results. Intrinsic differences exist between hardwood, softwood and grass/cereals and must be taken into account. Thermochemical processes such as pyrolysis, gasification and combustion involve several kinetic mechanisms, first in the solid phase for the devolatilization of the biomass, then in the gas phase for the secondary reactions of released products, and finally for the heterogeneous reactions of the char residue. These mechanisms involve a large number of chemical species and reactions and make modeling computationally intensive. For reactor-scale simulations, mechanistic equations need to be simplified, while maintaining their descriptive capability. For example, lumping procedures can allow detailed compositions of oil, gas and char residue to be obtained. In this chapter, the catalytic effect of ash on pyrolysis products is discussed. Secondary or successive gas phase reactions of pyrolysis products complete the kinetic model and allow optimal conditions for bio-oil production to be determined. On the scale of both the particle and the reactor, mathematical modeling of the thermochemical process requires descriptions of coupled transport and kinetic processes. Examples and comparisons with experimental data are used to show the validation and the reliability of a general model. Additional examples for the application of models are taken from the large-scale German project Oxyflame, which works on combustion of solid fuels in oxy-fuel atmospheres.