Chico Proano, Andrés Gabriel; (2024) Combined multi-scale modelling and experimentation for lignin-rich biomass pyrolysis. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Biomass pyrolysis is a key alternative for supporting a shift towards more environmentalfriendly energy generation and chemicals production. However, biomass pyrolysis’ complexity and the lack of information for non-woody biomass, specially for high-lignin feedstocks, have hindered pyrolysis applications. Such limitations make it necessary to develop robust and easy-to-implement modelling approaches, but they also demand information regarding lignin-rich biomass properties for supporting future process design and large-scale operations. This work initially presents a particle model, based on energy, mass and momentum conservation, which includes a boundary immobilisation formulation to describe thermally-thick biomass pyrolysis for different combinations of moisture and pyrolysis temperatures. Temperature gradients and pyrolysis product distribution are determined by solving the resulting model with gPROMS ModelBuilder®. The easy-to-solve model allows to include preliminary economic and energy efficiency indicators. The variety of kinetic models, and the lack of lignin-rich biomass pyrolysis kinetics, made it necessary to select one type of lignin-rich biomass, palm kernel shells (PKS), to study its properties and pyrolysis kinetic model. Finally, this work explores an approach to couple a particle and a pilot-scale reactor model with experimental PKS kinetics, as an alternative to have some insights of the implementation of a combined multi-scale pyrolysis modelling strategy. The results from the particle model suggest that it can predict temperature and composition within a thermally-thick particle. Furthermore, the PKS experimental analysis show that lignin-rich biomass behaves differently than conventional cellulose-rich biomass during pyrolysis and it highlights the need of having experimental data for this type of biomass. Finally, the developed pyrolysis multi-scale modelling strategy proved to be helpful for overcoming the difficulties for describing biomass pyrolysis inherent complexity. Such strategy required the description of granular flow at a reactor level and its coupling with a particle model and experimental kinetics to describe an auger reactor. In conclusion, multi-scale biomass pyrolysis is a complex and information demanding process. However, when kinetics information are determined experimentally and further included within a particle and a reactor model, it is possible to describe pyrolysis effectively so as to support future process design and optimization.

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