Non-stoichiometric methanation as strategy to overcome the limitations of green hydrogen injection into the natural gas grid

The utilization of power to gas technologies to store renewable electricity surpluses in the form of hydrogen enables the integration of the gas and electricity sectors allowing the decarbonization of the natural gas network through green hydrogen injection. Nevertheless, the injection of significant amounts of hydrogen may lead to high local concentrations that may degrade materials (e.g. hydrogen embrittlement of pipelines) and in general be not acceptable for the correct and safe operation of appliances. Most countries have specific regulations to limit hydrogen concentration in the gas network. The methanation of hydrogen represents a potential option to facilitate its injection into the grid. However, stoichiometric methanation will lead to a significant presence of carbon dioxide, limited in gas networks, and requires an accurate design of several reactors in series to achieve relevant concentrations of methane. These requirements are smoothed when the methanation is undertaken under non-stoichiometric conditions (high H/C ratio). This study aims to assess to influence of non-stoichiometric methanation under different H/C ratios on the limitations presented by the pure hydrogen injection. The impact of this injection on the operation of the gas network at local level has been investigated and the fluid-dynamics and the quality of gas blends have been evaluated. Results show that non-stoichiometric methanation could be an alternative to increase the hydrogen injection in the gas network and facilitates the gas and electricity sector coupling.