Comprehensive feasibility assessment of a poly-generation process integrating fast pyrolysis of S. japonica and the Rankine cycle

Abstract

Marine macroalgae or seaweeds are increasingly becoming strong candidates for sustainable biofuel feedstocks of the future. This study features a large-scale process design and comprehensive analysis of an industrial-scale (400,000 tons dry feedstock per year) poly-generation pyrolysis process that utilizes 3rd generation biofuel feedstock, Saccharina japonica brown seaweed, and produces diesel-range hydrocarbon fuel, heat, and power. Process design relied predominately on published experimental data regarding fast pyrolysis of S. japonica in a fixed-bed reactor system, followed by dewatering and catalytic upgrading of the produced biocrude. The design featured acid wash pretreatment for the reduction of mineral content, and subsequently a Rankine power cycle utilizing biochar. The design also considered two distinct cases of on-site hydrogen production and hydrogen purchase. Based on the experimental data, a rigorous steady-state flowsheet model was constructed using Aspen Plus for each design case. The results of comprehensive techno-economic assessment, sensitivity, and Monte Carlo analyses provided insight into capital cost for the process, minimum product selling price, and selling price ranges. Finally, the process is compared with traditional crude oil extraction and processing in terms of significant reductions in CO2 emissions, hence providing strong evidence of its environmental sustainability.