A new Power-to-Gas technology was validated in collaboration between PSI and Energie360°. By way of "direct methanation of biogas", the CH4 yield of biogas is considerably increased. For this purpose, H2 was added in a test facility to the biogas from the sewage treatment plant as well as a bio-waste digestion plant on the Zurich-Werdhölzli site. Several subprojects supported the experimental investigations and helped to focus the experiments.
One of the subprojects dealt with the question of the potential of suitable biogas plants in Switzerland which are suitable for direct methanation of biogas (Power-to-Gas). The focus was, on one hand, on existing waste water treatment plants (WWTP) and on the other hand on industrial biogas plants, which are digesting green waste. Agricultural biogas plants were not the subject of this analysis. The most important results from this subproject are that the largest potential of units are plant with an average size of 200 m3 of biogas per hour (11 GWh/a). There is a potential of 39 plants of this size in Switzerland.
A further subproject was the techno-economic assessment of several concepts for "direct methanation of biogas" for the plant size of 200 m3 of biogas per hour. Various catalytic methanation processes were analysed with two different ways of hydrogen removal (membrane versus two-stage methanation). On the basis of this study, the concept of fluidised-bed methanation with a downstream hydrogen membrane was further investigated, as this concept is more flexible in the operation of a commercial plant.
The pilot plant COSYMA was built at PSI in 2016 for the long duration experiments. On the ESI platform the plant was commissioned and a first series of scientific methanation test were performed. In January 2017 the plant was installed on the Zurich-Werdhölzli site close to an existing biogas upgrading plant and connected to the gas grid.
In a further subproject, sorbent based gas cleaning was reviewed. Promising sorbent materials were selected and tested in the laboratory and integrated into the pilot plant COSYMA. For the continuous documentation and monitoring of the long-duration test with the pilot plant, improved gas diagnostic systems were successfully implemented (mGC, liquid quench system). This way, it could be detected at an early stage if impurities such as H2S, dimethylsulphide (DMS) or siloxanes were no longer sufficiently removed by the gas purification.
In the first half of 2017, the 1’000 hour long-time experiment was successfully carried out in Werdhölzli with a single catalyst charge. The predicted gas quality of the methanation was reached. The experimental results of fluidised bed methanation and gas cleaning can be scaled up from the COSYMA scale to that of an industrial plant of 200 m3 biogas per hour.
Outcomes of the project have been regularly reported in journals and on events. Within the scope of this long-duration experiment, the project was also presented to an interested public.
