Demonstration of a Biogas Methanation Combined with Membrane Based Gas Upgrading in a Promising Power-to-Gas Concept

The further development of photovoltaic and wind power as renewable energies with their production rate fluctuations both on short- and medium-time-scale result in the necessity of smarter grids and higher energy storage capacities. One very prominent and promising technology for meeting this future electric energy storage demand is the concept of power-to-gas. Here, the excess electric energy is converted to hydrogen using alkaline or PEM electrolysis. Most concepts incorporate an immediate subsequent conversion to methane using a local carbon dioxide source and a process of thermo-catalytic or biological methanation. After a final gas upgrading mainly comprising the separation of H2, CO2 and H2O the thereby produced SNG can be fed to the natural gas grid owning a huge potential for energy storage and distribution. The current work presents the joint research efforts undertaken by the authors in the field of power-to-gas processes. A process chain consisting of a coupled hydrogen dark fermentation and a biogas fermentation, a thermo-catalytic methanation step and product gas upgrading applying membrane-based gas-permeation is developed and demonstrated on laboratory scale. The described process chain has been demonstrated on a scale of roughly 0.5 m³(STP)/h and experimental results will be presented. Special emphasize is laid on the analysis of the methanation performance considering the changing content of the mixed raw biogas. It is shown that the combination of methanation with membrane-base gas separation technology provides significant advantages for process integration.