Greening the gas network – The need for modelling the distributed injection of alternative fuels

The recent unfolding of natural gas sources, especially unconventional gas shales and substituted natural gas from renewables, can boost the transition toward a low carbon energy system. However, it is necessary to study how the gas network, traditionally supplied with fossil fuel gas, could be operated in a more complex scenario that includes multiple and distributed energy sources. This work deals with the development of a mathematical model able to simulate transmission pipeline networks under steady-state condition while adopting a non-isothermal approach. A review of modelling approaches of fluid flow in gas pipelines and gas pipeline networks is provided. An algebraic formulation to describe compressible fluid networks is also described in detail and implemented for the first time in this work with the aim to simulate the distributed injection of green fuel gasses into the natural gas network. Hydrogen blending (e.g., from power-to-gas systems) and substituted natural gas (e.g., from biogas upgrading or power-to-gas systems) injection are considered. A numerical simulation of a regional-scale natural gas transmission system is performed where green gasses are injected into the grid. In the case of hydrogen blending, the maximum quantity of injectable hydrogen in each node is calculated to achieve a 10% blend as an upper constraint. In conclusion, the impact of green fuels injection in the gas network on the resulting natural gas quality (i.e., Wobbe index, gas gravity, higher heating value) is investigated thoroughly.