Polygeneration-Annex: Integrating hydrogen into syngas-based gasoline production

As a result of the rising share of renewable energy in Germany, suitable energy storage solutions are needed. At the same time, existing base-load lignite-fired power plants suffer from low capacity utilization and frequent load changes. In combination with a Coal-to-Liquids (CTL) facility, the power generation utilization might increase. By using the existing power plant infrastructure, investment costs for the CTL facility can be reduced. Such combined polygeneration concepts, called 'Annex', have been developed at TU Bergakademie Freiberg. Previously, polygeneration concepts based on Methanol - to - Gasoline (MTG), Methanol - to - Olefins and Fischer - Tropsch synthesis have been analyzed. In addition, the Annex CTL plant can be used to store energy by incorporating renewable hydrogen from electrolysis into the synthesis step. Such a concept offers the advantage to lower CO2 emissions and could be used to store renewable excess power. In the current study, concepts based on entrained-flow gasification and MTG synthesis are analyzed. This concept is compared to a stand-alone synthesis route. Linking a 52 MWel alkaline water electrolysis to the synthesis plant, hydrogen can be integrated in the CTL plant. Four different concepts for hydrogen integration are investigated. Fluctuations in hydrogen supply could be counter-balanced through storage tanks or Demand Side Management in the CTL Annex plant. A techno-economic study is conducted using the commercial software package Aspen Plus. An analysis of efficiencies, carbon emissions and production costs is provided. An overall system efficiency of 36.5-37.6% is determined.