Abstract
To facilitate the development of value-chains for hydrogen to supply hard-to-abate sectors with clean hydrogen, reusing existing infrastructure for natural gas has been proposed. To analyze the viability of admixing, i.e., blending hydrogen into natural gas, we present an optimization tool designed to evaluate strategies for transporting hydrogen in natural gas using admixing or repurposing natural gas pipeline for hydrogen transport. The model is formulated as a mixed-integer non-linear optimization problem that brings together pooling and flow-pressure formulations, which are central components in gas-network optimization. A key methodological contribution is the introduction of a new piecewise-linear representation of the flow-pressure relationship in multi-gas networks, enabling computationally efficient modeling and non-linear gas dynamics. The model is implemented as an extension of the open-source energy system modeling framework EnergyModelsX (EMX). We demonstrate its application with a case study based on existing transmission networks to evaluate operational strategies to achieve increased hydrogen penetration.