Synthetic Gas Production via Power-to-Gas Process

Production and Distribution of Electricity and Heat

The Power-to-Gas (PtG, P2G) process consists in the renewable or excess electricity conversion towards synthetic gaseous products, usually hydrogen (H2) or synthetic natural gas/methane (SNG). SNG is produced through a two-step process via two alternative pathways: i) water electrolysis; low-temperature electrolysis delivers H2; CO2 methanation follows to produce synthetic methane (CH4) starting from the produced H2 and CO/CO2 coming from an external source (e.g., CO2 captured from the flue gas of an an industrial process, a fossil power plant or biogas plant); ii) a co-electrolysis; high-temperature co-electrolysis delivers syngas (H2+CO mixture) that becomes then the feed of the methanation section that converts syngas into SNG. Methanation can be performed following two main routes, namely biological methanation and catalytic methanation. Catalytic methanation refers generally to a catalyzed relatively-high-temperature methane synthesis process. Four main reactor categories can be identified: i) fixed-bed reactors, ii) fluidized-bed reactors, ii) three-phase reactors and iv) structured reactors. Biological methanation consist of the biochemical conversion of biomass into a CH4/CO2 mixture by microorganisms already present in the starting organic material. Fixed-bed reactors have a TRL 7 for adiabatic design and TRL 6 for isothermal design; fluidized-bed reactors are at the prototype level (TRL 6); three-phase reactors are being investigated at the lab scale (TRL 4), whereas structured reactors are even less developed (TRL 3). Biological methanation have reached a pilot to demonstration scale level, with a TRL between 6 and 7. There are worldwide more than 150 already completed, recent or planned projects for several applications, mainly at the research level up to the pilot-scale level. More than half of the projects focus on PtH route, being the rest including also an either biological or chemical methanation step. Most of the projects are in Europe, mainly in Germany, Denmark, or Netherlands. Two important methanation plants are the Audi e-gas project, that represents the largest and the most industrially exploited project at present and the Limeco project in Dietlikon (Switzerland), that integrates a municipal waste incineration plant with a wastewater treatment plant delivering sewage gas in the same location, with an installed electrolyser capacity of 2.5 MWel. The average size for hydrogen-related projects is around 430 kWel, that reduces to an average value around 380 kWel for methanation projects, resulting in an overall average plant size around 407 kWel in early 2019. As benchmark values, the projected average plant size in 2050 for chemical methanation plants is 1.56 MWel, followed by biological methanation plants with 0.61 MWel and by hydrogen projects with 0.45 MWel, for an overall averaged value of 0.7 MWel

27-07-2022

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