Determination of Optimal Expansion Strategies for Biogas-to-Liquid and Biogas-CHP Units for Flexible Biogas Plants

Abstract

This thesis investigates the technical and economic feasibility of a flexible biogas plant system that combines a Biogas-to-Liquid (BGtL) plant—using a novel low-temperature microwave plasmacracking plant for syngas production and Fischer-Tropsch synthesis (FTS) for FT-syncrude production—with a Combined Heat-and-Power Unit (CHPU), considering different expansion strategies. Using a Mixed-Integer Linear Programming (MILP) model and real German electricity price data from 2023, various operating scenarios were simulated based on the arbitrage and unit commitment problem. Results show that, under current market conditions, separate operation of BGtL and CHPU is more profitable than combined operation, mainly due to higher specific investment costs and limited spot market volatility. While flexible CHPU benefits from overbuilding and flexibility bonuses, BGtL achieves better returns when run steadily. However, simulated large BGtL plants can already produce FT-syncrude at competitive costs, and combined flexible operation may become attractive as electricity markets evolve and investment costs decrease. The presented model and results provide a basis for future optimization and techno-economic assessment of hybrid biogas systems.