Renewable natural gas, sometimes referred to as biomethane, is a combustible gas primarily utilized for energy generation. It typically shares similar qualities with fossil-derived natural gas, in particular, a methane concentration of at least 90%. The critical distinction concerning the energy transition lies in the origin of its carbon content. The carbon in renewable natural gas derives from plant sources rather than fossil reserves.
Technical and commercial characteristics #
Processed renewable natural gas can be used in the existing natural gas instrastructure without limitation. It also does not come with a need to replace equipment and modify the infrastructure. Furthermore, it is greenhouse gas neutral. As of today, it has not been possible to produce renewable natural gas at prices competitive with natural gas. This has resulted in the in the shutdown of certain technically operational plants, such as the GoBiGas plant in Sweden. Clearly, the competitiveness of biomethane ultimately also depends on the taxes imposed on fossil natural gas and the availability of it. Price parity will eventually be reached, once natural gas reserves decline and carbon taxes become higher.
Different means to produce the gas exist. An often-used approach is to utilize the underground anaerobic digestion in landfills by collecting the produced biogas below the surface. Renewable natural gas can also be produced from biomass (biowaste, crop for energy production, wood, etc.) in anaerobic digestors or gasification plants. Finally, the gas can be produced synthetically using green hydrogen.
In a defossilized future industry, these methane sources will have to be renewable. In other words, the fossil methane will have to be replaced with non-fossil carbon-neutral methane such as biogas. However, the quantity of methane that can be produced with biomass is limited. As an example, corn-cob-mix, a particularly valuable fuel for biomethane production, is considered. One ton of corn-cob-mix generates about 105 Nm3 of methane, i.e., 69 kg. Other fuels yield typically less or much less. Since biomass production for fuel competes with biomass production for human consumption and implies increased land use, it is evident that supply will become an issue.
Doubling the production #
The gas coming out of a anaerobig digestor plant is typically composed of up to half of carbon dioxide, while the rest is methane. If green hydrogen generated with renewable electricity is available, it can be used within a Sabatier process to transform the excess carbon dioxide into additional methane. This doubles the methane output of the plant. In simple words, the amount of biomass input remains the same, and the output of carbon-neutral methane is doubled.
Together with its partners EPFL and Gaznat, GRZ has upscaled a novel catalytic methanation reactor that implements this process. It works at an average temperature of around 250°C and a pressure of about 10 bar. After a first system had been commissioned in an industrial environment in Sion in the year 2021. Subsequently, the technology was upscaled and coupled with a 0.5 MWe electrolyzer. This industrial-scale plant was inaugurated in summer 2023 at Gaznat’s facility in Aigle and is shown below:
More information about the UPSOM reactor currently being rolled out can be found on the product page.
