Adetoyese Olajire Oyedun

Development of life cycle water footprints for the production of fuels and chemicals from algae biomass

This study develops life cycle water footprints for the production of fuels and chemicals via thermochemical conversion of algae biomass. This study is based on two methods of feedstock production - ponds and photobioreactors (PBRs) - and four conversion pathways - fast pyrolysis, hydrothermal liquefaction (HTL), conventional gasification, and hydrothermal gasification (HTG). The results show the high fresh water requirement for algae production and the necessity to recycle harvested water or use alternative water sources. To produce 1 kg of algae through ponds, 1564 L of water are required. When PBRs are used, only 372 L water are required; however, the energy requirements for PBRs are about 30 times higher than for ponds. From a final product perspective, the pathway based on the gasification of algae biomass was the thermochemical conversion method that required the highest amount of water per MJ produced (mainly due to its low hydrogen yield), followed by fast pyrolysis and HTL. On the other hand, HTG has the lowest water footprint, mainly because the large amount of electricity generated as part of the process compensates for the electricity used by the system. Performance in all pathways can be improved through recycling channels.

An Assessment of the Effects of Biomass Processing Methods on Power Generation

Biomass can be cofired with coal in different forms. It could be in “as-received” forms (e.g., forest residues, straw in form of bales) or processed forms (e.g., chopped straw, pellets). Pelletization, one of the processed forms, improves the bulk and energy density of the biomass used as a fuel in cofiring and biomass combustion plants. However, pellets increase feedstock cost compared to “as-received” biomass cost, which could negatively affect the cost of producing power from cofiring and combustion plants. In this study, we developed technoeconomic models to evaluate cofiring of different biomass forms with coal and 100% biomass combustion plant.