Economic impacts of feeding microalgae/wood blends to hydrothermal liquefaction and upgrading systems

Abstract

Experimental work observed a synergetic effect of using microalgae/wood blended feedstocks for hydrothermal liquefaction (HTL) conversion with a yield advantage over using microalgae only or wood only as the feedstock. Experimental results for HTL and hydrotreating were used to develop the techno-economic analysis (TEA) for a blended feedstock HTL and biocrude upgrading system. For the blended feedstock system, wood is blended with algae feedstock during the lower algal productivity seasons (winter, fall, and spring) to match the maximum algal seasonal production rate. Adding woody biomass led to a 34% larger plant scale than the algae-only system with the same assumptions for algae seasonal productivity. In addition, low-cost woody biomass led to lower blended feedstock cost than the algae-only case. Blended feedstock also eliminated the need for drying a portion of the algae during summer and spring for winter and fall use, a requirement of the algae-only case, and thus reduced the related capital and operating costs. Economic analysis results indicated that, with feeding of microalgae/wood blended feedstock, the minimum fuel selling price (MFSP) to produce naphtha and diesel blendstock was reduced by 21% and the conversion-only cost (excluding cost for feedstock) was reduced by 13% compared to the algae-only case. Sensitivity analysis identified algae feedstock cost, algae blend ratios, and biocrude yields as key factors affecting the MFSP of the blended feedstock system.