Producing Renewable Methane – Demonstration of CCU from Biomass
13 Pages Posted: 4 Apr 2019 Last revised: 2 May 2019
Producing renewable methane can contribute in several ways to the mitigation of greenhouse gas emissions. When produced from biomass – either by anaerobic digestion of green waste, sewage sludge etc. or by gasification of lignocellulosic biomass and subsequent gas cleaning and methanation – a significant amount of CO2 is produced in addition to the methane, due to the oxygen content in the biomass. This biogenic CO2 is then available almost without additional cost or efficiency losses for further synthesis of chemicals (CCU), replacing in this way equivalent amounts of fossil CO2. Renewable methane is one of the potential synthesis products derived from this CO2. It can be used as a green energy carrier, as long as the additional hydrogen needed for the synthesis is produced by electrolysis in Power-to-Gas applications from renewable energy resources like wind, hydropower or photovoltaics.
A techno-economic assessment of several concepts for CCU within Power-to-Gas applications was conducted, considering direct methanation of biogas, i.e. “in situ” (without CO2 separation) synthesis of methane from biogenic CO2. Various catalytic methanation processes were analyzed with respect to how the residual hydrogen (after the synthesis step) can be minimized (either separated or converted further). On the basis of this study, the concept for fluidized-bed methanation with a downstream hydrogen membrane was chosen for the presented work, as this concept is most flexible in the operation of a commercial plant.
A 20 kWCH4 pilot plant (COSYMA) was built and commissioned at the Energy System Integration (ESI) Platform of the Paul Scherrer Institut (PSI) in Switzerland to prove the validity of the proposed concept. In a subproject, promising sorbent materials were tested in the laboratory and integrated into the COSYMA pilot plant to protect the nickel-based methanation catalyst from being poisoned by sulfur compounds present in biogas. Then, the COSYMA was installed close to an existing biogas production plant and connected to the gas grid. A 1ˈ100 hour long-duration experiment was successfully conducted with a single catalyst charge. The predicted gas quality of the methanation was reached and the gas was injected into the natural gas grid. These experimental results of fluidized bed methanation and gas cleaning can now be scaled up from the COSYMA scale to that of an industrial plant.
Keywords: CO2 for energy (storage), GHGT-14
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