Biogas blending into the gas grid of a small municipality for the decarbonization of the heating sector

Abstract

The practice of blending biogas into the gas network, especially at the distribution level, offers the opportunity to use biogas as a substitute of fossil gas. The ‘greening’ of the gas network through biogas blending would indeed take advantage of the robustness and extensiveness of an already existing energy infrastructure. A steady state and multi-component thermal-fluid-dynamic model of the gas network is applied to a portion of the Italian distribution network. The receiving potential capacity of the existing infrastructure is assessed with respect to biogas injection. Fluid-dynamic aspects of this practice are considered and commented. The maximum allowable percentage of injectable biogas (purified from sulphur compounds, O2 and siloxanes but not upgraded to bio-methane by removing CO2) is calculated on a nodal basis, referring to the actual gas network configuration, and in agreement with the quality constraints set by the current regulation (UNI/TR 11537:2016). A major hypothesis has been assumed in this work: gas quality requirements are enforced on the network as a whole (i.e., after blending the injected gas into grid) rather than at the injection point, which is instead the current prescription of most of the EU countries. By exploiting the quality-tracking feature of the model, the constraint on the quality assessment at the injection point is thus relaxed and its effect on the grid gas quality has been quantified. Results from the case study shows how biogas blending into the gas grid may lead to a reduction on the fossil natural gas dependence of up to 4.7%.