Hydrogen blending into the gas distribution grid: the case study of a small municipality

Hydrogen blending into the gas network may offer an alternative concept for the storage of the exceeding energy from renewable power sources, improving the flexibility of the energy system through the integration of the electricity and gas networks. This scenario foresees the use of electrolyzers to convert power into hydrogen gas. The gas grid could both provide storage and act as the transport facility of the produced gas, taking advantage of the robustness and extensiveness of an already existing energy infrastructure. In this work, a steady state and multi-species thermal-fluid-dynamic model of the gas network is applied to a portion of the Italian distribution network, located in EmiliaRomagna, covering a surface of 2,900 ha and having a throughput of 8.25 MSm3 /year of natural gas. The receiving potential capacity of the existing infrastructure is assessed with respect to hydrogen injection. Fluid-dynamic effects of the hydrogen blending are considered and commented. The maximum allowable percentage of injectable hydrogen is calculated on a nodal basis, referring to the actual gas network configuration. The current Italian regulation on distributed injection (DM 19/02/2007) of gases into the natural gas network only allows injecting gases having nearly the same quality of natural gas (UNI-EN 437), thus excluding any blending practice. However, in the simulated scenario here proposed, it is assumed that gas quality requirements are on the network as a whole (i.e., after blending of hydrogen in the grid) rather than at the single injection point. By exploiting the qualitytracking feature of the model, the constraint of quality assessment at the injection point is thus relaxed. Once the blending limit is known for each node, the amount of injectable hydrogen is calculated accordingly, taking into account the amount of natural gas already flowing through the node itself. The node with the major injection capability is the designated one for the injection and used for the simulation of the case study. Finally, a comparison between the ‘base case’ and the ‘maximum hydrogen injection case’ is presented and discussed showing how hydrogen blending into the gas grid may lead to a reduction on the fossil natural gas supply of up to 2,1%.