Process design analysis of a hybrid power-and-biomass-to-liquid process – An approach combining life cycle and techno-economic assessment

Abstract

Techno-economically and ecologically optimized processes require understanding of trade-offs between efficiencies, costs and environmental impacts. For this purpose, DLR’s in-house tool TEPET for techno-economic analysis was enhanced to enable simultaneous life cycle assessment (LCA). Within this study a hybrid Power-and-Biomass-to-Liquid concept is analysed that can switch between a biomass alone and hydrogen enhanced operation. In order to integrate the techno-economic and ecological results, a dimensionless cost-impact factor is introduced, which gets minimised when both costs and environmental impacts are low. The methodology is applied to investigate process parameter variations within this process concept. The varied process parameters are H2/CO ratio, H2 conversion in the Fischer-Tropsch synthesis and CO2 recycle rate to the gasification. Furthermore, the influence of LCA allocation methods on the preferable set of process parameters was examined. Results show a correlation of lowest environmental impact with high fuel efficiency (energetic fuel output per overall energetic input) for economic allocation. For energetic allocation, high process efficiency (ratio of overall energetic output to overall energetic input) leads to the lowest environmental impact. High carbon efficiency is especially important when biomass has a big impact on a certain category. Sensitivity studies for the global warming potential demonstrate a low sensitivity to the investigated process parameter variations compared with changes in input parameters like biomass and electricity source or transport distance. As the net production cost (NPC) are more sensitive towards the process parameter variations, the cost-impact factor is lowest for the set of process parameters with the lowest NPC.