MethFuel: Producing renewable methane efficiently and flexibly.

The MethFuel group has the task of taking a close look at the generation of methane from renewable sources (RE-methane). The future general introduction of RE-methane across the market will depend largely on how efficiently and cheaply it can be produced. Because the production chain for RE-methane still involves high costs, optimization of the power-to-gas (PtG) process remains the primary focus of the MethFuel group’s work. With this aim foremost, the nine group members are concentrating on component development for the key PtG technologies: water electrolysis, CO₂ harvesting and methanation. New and advanced developments planned for these three key technologies chiefly relate to production equipment, energy and ecological efficiency and to improved plant operation concepts capable of coping better with the fluctuating nature of renewable energies.

The technological advances achieved by MethFuel, as compared with the current state-of-the art, will be assessed toward the end of the project. Separate evaluation of progress in the individual key technologies would be inadequate because only evaluation of an entire PtG process chain can reflect interactions between the individual technologies. This is why the work of the MethFuel group also covers conceptual approaches and the techno-economical evaluation of different PtG process chains.

Project partner ElfER is lab-testing SOEC cells from various manufacturers in order to optimize the operation of large SOEC plants and experimental results are being used for cell modeling at the Karlsruhe Institute for Technology (ITCP). Numerical simulation is then used to optimize cell operating conditions. The results will provide a basis for developing a stack model for integration in the PtG model developed by ElfER for RE-methane production and this will facilitate propositions on optimum operating conditions.

At 2.5% of global reserves, stocks of fresh water vital for electrolysis are extremely limited. The ability to use seawater as a resource in the long term would therefore represent a huge advantage and would enable the production of regenerative hydrogen directly on-site at offshore wind farms using seawater electrolyzers. The salt-content of seawater, the foreign ions released and the concomitant competing reactions mean that seawater electrolysis is extremely difficult and so far it has remained largely unexplored. For this reason, in the context of MethFuel, a feasibility study is to be carried out at the Technical University of Berlin (ECEMS). This will involve investigation of the influence of various membranes, commercial catalyzers and porous carrier layers as well as pH-value and salt concentration, in particular with regard to the degradation behavior of components. These investigations will ultimately facilitate the development of a durable and thus economically feasible electrolysis cell.

Within the framework of MethFuel, KIT EBI ceb in Karlsruhe and the Research Center of the German Technical and Scientific Association for Gas and Water (DVGW) are also investigating the harvesting of CO₂ from CHP plant exhausts and from air by means of a gas scrubbing process that employs ionic liquids. Ionic liquids exhibit negligible vapor pressures and can thus be brought into contact with larger gas flows without problems. Whilst conventional processes require the scrubbing medium to be heated to high temperatures to re-release the dissolved gases for continued processing, with ionic liquids the gas phase can simply be pumped off via the scrubbing medium so that the CO₂ contained can be released for further use. This uses far less energy than heating and can achieve more than 50% energy savings as compared with conventional methods.

In the case of CO₂ production from CHP plant exhausts, the process can be implemented as described using ionic liquids by means of pressure swing adsorption. Harvesting CO₂ from ambient air poses a further challenge because of the extremely low concentration of CO₂. Whilst the CO₂ will dissolve in the scrubbing medium, pressure reduction is not enough to achieve degassing again and moderate heating of the scrubbing medium is needed. Nevertheless, compared with the latest status of conventional technology, this process still reduces energy consumption as only the scrubbing medium (not the entire equipment set-up) needs to be heated.

Using pressure swing adsorption for both cases also means that the same plant can be used to harvest CO₂ alternately from both sources. This creates synergies where the approach is employed in PtG process chains. Partners in the project are also conducting fundamental experimental investigations based on a process-modeling approach where the model is validated in mini-plant trials and subsequent up-scaling to appropriate plant dimensions is possible.

To evaluate the combined benefits of optimized individual technologies, project partners use an iterative process to input key characteristic values for core technologies into the overall view of PtG process chains. All significant factors, including, for example, fuel quality dependent on investment and operating costs, are continuously shared with the other MethQuest groups to ensure that support for their work is application-oriented.