Medium-scale Hydrogen Pipeline Network Design: An optimization-based planning method considering the existing natural gas network and allowing for pipeline conversion

In 2021 the German gas TSOs published the Wasserstoffnetz 2030, a map representing a hydrogen network for the year 2030 along with key figures. For the purpose of designing a hydrogen pipeline network, an optimization-based method
has been developed and implemented. The method considers the existing natural gas network as an underlying topology above which the hydrogen network is to be designed. Furthermore, the approach allows for the conversion of natural gas
pipelines to hydrogen operation. The design method determines initially the set of convertible pipelines within the existing natural gas network based on its connectivity, independently from a potential natural gas supply-demand scenario. This
conservative approach results in a kernel of convertible pipelines and hence lower shares of converted pipelines (approx. 23% lengthwise) in the candidate hydrogen networks compared to the Wasserstoffnetz 2030 (72.6%). Subsequently, the
optimization model determines an optimal network providing a hydrogen supplydemand scenario inline with that of the Wasserstoffnetz 2030. The gas pipeline transportation hydraulic, topological and economic aspects constitute the optimization model building blocks. The model is formulated as a disaggregated problem consisting in a: a local search sub-module based on topological considerations responsible for generating a neighborhood of candidate networks (tree
topologies) to be evaluated, a NLP sub-module responsible for sizing and evaluating the minimal cost of each candidate network. The second sub-module is nested in the former, resulting in a path dependent local search. The chosen network
instance, a modified version of GasLib-135 (135 node, 170 edge) and the hydrogen supply-demand scenario associated to it enable a coherence in terms of scale with the Wasserstoffnetz 2030. The method creates a neighborhood of 190
candidate networks and yields a solution network having a cost of 6232.85 Me, corresponding to a 5.87% (388.69 Me) decrease of cost relatively to the initial candidate network, i.e. the minimum (lengthwise) tree spanning the initial gas
network. The yielded minimal cost is coherent with the 6000 Me announced for the Wasserstoffnetz 2030. The solution network presents pipeline diameters ranging from 0.08 to 1.16 m and its results are validated using the simulation
software pandapipes. Additionally, the cost of the candidate networks appears to be bounded below which suggest some robustness to the quality of the solution. A further results analysis supports that the cost decrease is the effect of a better
suitability of the candidate networks topology to the flow situation (induced by the supply-demand scenario) rather than the effect of an increased reliance of the networks on the converted pipelines.