Development of Water Requirement Factors for Biomass Conversion Pathways

Abstract

This study develops the water requirement factors for different thermo-chemical and biochemical biomass conversion pathways for production of biofuels and biopower. Twelve biomass conversion pathways based on six biomass feedstocks are assessed. For all these pathways integrated water and energy requirement factors are developed. The biomass feedstocks considered for bioethanol production are corn, wheat, corn stover, wheat straw, and switchgrass. The biomass feedstock considered for biodiesel production is canola seed. Three biomass feedstocks are considered for biopower generation using direct combustion of biomass and bio-oil produced from the feedstocks through fast pyrolysis. These three feedstocks are corn stover, wheat straw and switchgrass. The water requirement is also evaluated for biofuels production based on wheat, wheat straw and canola seed in Alberta. Agriculture residues based ethanol production pathways are water and energy efficient, consuming only 0.3 liters of water per MJ of net energy value (NEV), whereas biopower pathways consume about 1.2 – 1.5 liters of water per MJ of NEV due to their lower energy efficiency. The pathway for producing ethanol from switchgrass is the most energy efficient, but consumes 117 liters of water per MJ of NEV. Producing biopower through the direct combustion of switchgrass and from combustion of switchgrass based bio-oil consumes 278 and 344 liters of water per MJ of NEV, respectively. Wheat and corn based ethanol production pathways consume 653 and 409 liters of water per MJ of NEV, respectively. Canola seed based biodiesel production pathway consumes 176 liters of water per MJ of NEV. Water demand in Alberta due to biofuels production will be 12.7% higher than the projected demand in 2025, but it can be met using existing resources.