Characteristic of a system for the production of synthetic natural gas (SNG) for energy generation using electrolysis, biomass gasification and methanation processes

Power to Gas (PtG) technology is a promising method for energy storage in medium and large scale, allowing also counteracting the destabilization of power systems in which intermittent sources play an important role. It typically involves the use of electricity from renewable sources (such as wind and solar) for hydrogen production in the electrolysis process (in which oxygen is also produced). Hydrogen can be used directly (e.g. as fuel for transport), stored, injected to the grid (however, with some restrictions) or further processed into fuels or chemicals. From the energy systems point of view an interesting option is to produce synthetic natural gas (SNG) as it has a very similar composition to natural gas and can be used within well-known power generation technologies (such as gas engines and gas turbines), easily stored or injected directly to the natural gas grid. In order to produce SNG from renewable hydrogen several components have to be added to the system, in particular a methanation unit, in which carbon dioxide or carbon monoxide is converted into methane with the use of hydrogen. These many solutions of PtG systems should be assessed from the thermodynamic and economic points of view. In this paper various concepts of PtG structures are presented and characterized. The possible sources of electricity, use of hydrogen and oxygen, carbon sources for the methanation process and potential uses of SNG are briefly discussed. A simplified case study of a system composed of a renewable energy source, electrolyzer, biomass gasification, methanation installation and gas engine was made. Finally, a simplified SWOT analysis was made to assess the main advantages and disadvantages of the proposed solution.