Date of Award
Doctor of Philosophy in Mechanical Engineering-Engineering Mechanics (PhD)
College, School or Department Name
Department of Mechanical Engineering-Engineering Mechanics
Utilizing biomass provides a possible near-term alternative solution for fossil energy dependence in both electricity generation and transportation. Though thermochemical conversion can produce solid/liquid fuels that are compatible in existing infrastructure, detailed scientific chemical and mechanistic understanding are still being developed. In contribution to these efforts, this work is focused on development of a semiempirical, lumped parameter, chemical kinetic model to describe the degradation of woody biomass.
The initial kinetic model was developed in the torrefaction region to describe the gas-phase evolution of products (water, organic acids, permanent gases, and furfural) through a three consecutive reaction model. In this model, the initial biomass degrades through several solid intermediates that represent of partially degraded polymers to produce the observed gas-phase species through product detachment. The model was able to well describe the measured species transients, and revealed important considerations between processing severity (time, temperature) and enhancement of solid fuel properties. After the model was calibrated to predict the weight distribution between products, it was able to describe the elemental composition of the solid material up to removal of approximately thirty percent of the initial dry sample mass. Engineering considerations such as process efficiency based on the intrinsic reaction (mass and energy yield) were explored.
The model was then extended into a more traditional pyrolysis range (up to 425°C), while avoiding any significant secondary thermal reactions. Here the model was extended in similar fashion to six consecutive reactions to describe to observed product evolution. It was found that the model not only describes the gas-phase species from cellulose, hemicellulose, and lignin, but also the entirety of torrefaction and pyrolysis within a single unified mechanism, implying that they are similar processes that occur at kinetically different rates due to process temperature. The presented kinetic parameters, process chemistry, and dynamic product removal traces offer unique insight into the thermal degradation mechanism. The unified model predictions were then explored to present product distribution/composition over the complete processing range, and obtain model validation. Also of great importance, the presented model is able to account for differences in solid degradation due to variation in woody feedstock.
Klinger, Jordan L., "MODELING OF BIOMASS TORREFACTION AND PYROLYSIS AND ITS APPLICATIONS", Dissertation, Michigan Technological University, 2015.