Modeling of thermochemical conversion of biomass

Biomass is promising as renewable resource, comprising a broad range of different types of biomaterials, such as wood, forest and agricultural residues, waste from wood and food industry, algae, energy grasses, straw, bagasse and sewage sludge. These materials are widely available and many of them are residues from different economic activities, generating costs for disposal and sometimes even environmental issues. Harvesting these materials is a possible solution for substitution of fossil fuels and treatment of residues.
The thermochemical route of biomass conversion is promising. By providing heat to the feedstock, it releases its volatile matter giving multiple products, depending on the feedstock and the operating conditions. The yield of these products can be enhanced by selecting the proper technologies. This conversion path is a very complex multicomponent, multiphase, and multiscale problem. Because of its complexity, modeling this process is still a challenge, but consists an essential step to better understand the aspects involved and provide tools to the design of optimized reactors and processes.
A predictive and comprehensive model for both characterization and chemical kinetics of biomass thermochemical conversion was developed. The workflow consists on: Collection of literature experimental data, characterization of feedstocks, kinetic mechanisms that describe each step of the process, validation of the simulations with the collected experimental data.
The model proposes some innovative and interesting features:
• Comprehensiveness – Can be applied for a wide range of feedstock composition,
covering both lignocellulosic and algae biomass;
• Flexibility – Can be further improved in order to account for new experimental
evidences;
• Predictivity – The models were developed and validated for many feedstocks in
several different conditions. In this way, no experimental data is needed to
perform the simulations. All the information needed are the characteristics of
your feedstock and the operating conditions. When experimental data is
available, the user can choose whether to use it or rely on the model predictions;
• Compatibility of Kinetic Mechanisms– A combination of semi-detailed and
detailed kinetic mechanisms are present for the different facets of the problem.
They are proposed in a CHEMKIN-like format, which make them compatible with
each other;
• Species – The reference components and the products released are defined with
a combination of real and lumped species;
• Computational cost – As a result of the simplification degree adopted in this
model, it is efficient for more complex simulations, involving particle and reactor
scales. Despite these simplifications, the model generates a great level of details.

The validation of large amounts of experimental data shows the robustness of the model. It remains flexible to include new experimental evidences and to be extrapolated when required. It was not found in literature another model that covers all these steps of biomass thermochemical conversion in a single formulation, being able to simulate the majority of processes currently available. The model is a useful tool to the development of optimized reactor designs for improving industrial processes efficiency. Besides providing reliable predictions in many cases, uncertainties still exist due to the level of simplification adopted in the selection of reference species and the definition of the reactions. The model could be further improved in the future by considering the catalytic effect of each metal present in
the ashes, the intra-component interactions, the effect of the polymerization and branching degrees, among others.