As part of the transition of energy supply to renewable energies, chemical energy carriers are of particular importance since they allow seasonal storage of large amounts of renewable electricity. Furthermore, renewable generated methane as substitute natural gas has the advantage that the infrastructure for distribution and storage already exists. Moreover, technologies for reconversion and utilization as fuel are state of the art.
The methane synthesis is an essential step in the power-to-gas process and during thermochemical conversion of biomass. Especially the high heat of the catalytic conversion from carbon oxides and hydrogen to methane poses a major challenge. At the same time strict regulations are imposed on the product gas quality which is to be achieved.
First of all the aim of the present work was the experimental study and evaluation of various methods to control the temperature rise in the catalyst bed and to maximize the methane yield. For this purpose, several wall-cooled tubular reactors were used. It could be shown that the heat development can be controlled by an activity profile in the catalyst bed as well as by a staged feed or recirculation of product gas. Besides a precise stoichiometry adjustment and an adequate water content, sufficient synthesis pressures and suitable reactor temperatures are to be provided in order to obtain a high methane content in the product gas.
In addition to the experimental work, simulations of entire process chains for production of renewable methane were carried out with the process simulation software IPSEpro. The focus was on the power-to-gas process with two different carbon dioxide containing feed gases as well as on the conversion of synthesis gas from an AER biomass gasifier. Energetically favorable procedural interconnections were initially developed and then visualized and evaluated using Sankey diagrams. Moreover, a sensitivity analysis was carried out to examine the influence of relevant process parameters with regard to their influence on the overall process.
These studies allow a detailed comparison of process variants and thereby contribute to the design of methanation processes for generation of substitute natural gas.