Hydrogen network topology optimization by MINLP: Comparing retrofit with new-built design scenarios

Rapid and cost-effective development of a hydrogen distribution infrastructure is an indispensable element of the transition from the current fossil-based to a completely renewables-based energy supply system. In addition to sustainable hydrogen production, e.g. by water electrolysis, biogas reforming or biomass gasification, a comprehensive system for the transport, storage, and distribution of green hydrogen must be established and adapted to specific net-zero pathways. The mathematical modeling and optimization of hydrogen transport in pipeline networks have often been overlooked or simplified in the existing literature. Such simplifications can lead to inaccuracies in energetic and/or economic evaluations, and even jeopardize the feasibility of a model-based network design. In the present work, we develop a mixed-integer nonlinear programming (MINLP) approach for the topology optimization of a hydrogen pipeline network. It minimizes the total installed cost (TIC) while ensuring gas pipeline hydraulics, logical, and safety constraints. The Irish gas network (re-)design is considered as a case study for this extensible MINLP model. For covering both short- and long-term objectives in topology optimization, three different hydrogen demand scenarios are investigated. In addition, different network design scenarios are considered to assess the feasibility and benefits of different topologies. The results of this case study show that repurposing the entire existing Irish natural gas network is not the most cost-effective solution. Importantly, the evaluation of multiple demand scenarios reveals the limits of hydrogen demand that can be accommodated by the current pipeline infrastructure. This raises questions regarding the design of a hydrogen network facing an increasing demand over time.