Background

Rapid and cost-effective development of the hydrogen distribution infrastructure is needed to enable a transition towards renewable energy supply systems. In addition to hydrogen production – from natural gas, water, and biomass – the transport, storage, and distribution of hydrogen need to be modelled and adapted to specific net zero pathways.

Pipeline transportation is an economical and sustainable way to deliver hydrogen [1]. At present, Germany and Europe benefit from highly interconnected natural gas pipeline networks which have a high level of acceptance in society. The demand for hydrogen in Germany in 2032 is projected to reach 279 TWh – significant compared to the 847.5 TWh of current natural gas consumption [2]. This will necessitate a hydrogen pipeline network, which is indeed currently being drafted, its total size estimated at 11,700 km [3].

In this context, the extent to which the current natural gas network can be repurposed for hydrogen transportation is amongst the open questions and constitutes the focus of this study. What are the technical requirements for a retrofit? How much of the hydrogen demand could be accommodated by the existing pipelines? Under which circumstances would a new-built network be economically advantageous? Further, the comparison will depend on the defossilization trajectory, i.e., the hydrogen quantities demanded by the sectors, and possibly their seasonal and daily intermittency.

Methodology

The mathematical representation of hydrogen transport in pipelines is often overlooked or simplified in the existing literature, with assumptions such as constant friction factors and constant hydrogen property parameters over long distances. Such simplifications can lead to inaccuracies in energy and economic evaluations, and even compromise the feasibility of network design. To address these aspects, the present study adopts an approach that integrates comprehensive thermodynamic analysis with economic evaluation of hydrogen transport. Moreover, the current state of research lacks an up-to-date methodology for determining potential hydrogen network configurations based on scenarios with varying demand from economic sectors (power, heat, transport, industry) as well as supply sources. Hence, we represent multiple supply and demand scenarios in the model. This research develops a mixed integer nonlinear programming (MINLP) model for the purpose of topology or network design optimization. The case study focuses on the Irish gas network, selected for its reliable data availability, which aids in estimating hydrogen demand scenarios and pinpointing location coordinates. This research provides novel insights into retrofitting infrastructure for hydrogen transport. It evaluates the economic viability of both new-built and retrofit scenarios, offering a better understanding of the infrastructure requirements and economic implications associated with each scenario.

Preliminary results

This contribution quantitatively examines design and operation of hydrogen pipeline systems in both new-built (i.e., greenfield) scenarios and retrofit (i.e., brownfield) scenarios. The study focuses on understanding the differences in infrastructure requirements and economics between these scenarios. In addition, we explore the resolution of specific technical challenges associated with retrofitting pipelines. The capacity and limitations of utilizing existing natural gas pipelines are evaluated. Further, the research addresses the optimization of retrofitted networks by evaluating the addition or removal of network elements.

The first preliminary results of the sensitivity analysis show the effect of flow rate, pipe diameter and length on pressure drop in hydrogen networks, which differ from natural gas pipelines. The simulation results suggest variations in pressure distribution that lead to higher CAPEX, OPEX, and increased need for compressor units at stations for hydrogen networks compared to natural gas networks. In the context of line-packing, i.e., storing energy in the pipelines by compressing the fluid, the results express a delicate balance between sizing optimization and energy storage capacity. In addition, it is observed that the hydrogen network can withstand the erosion velocity limit while ensuring energy security for the demand side.

The operating costs of high-pressure natural gas networks are primarily related to compressor operating costs, which represent a significant proportion of the companies' total budget, typically exceeding 60% of the total pipeline cost, with approximately 3 to 5% of the gas transported being consumed by compressors [4], [5]. Global optimization strategies can reduce fuel consumption at compressor stations by up to 20% [5]. According to the results of the operation optimization, the pipeline network's discharge pressure can be found to be adequate for maintaining the desired flow rate without requiring compression during the considered time trajectory.

Furthermore, the research suggests that repurposing the entire existing natural gas network may not be the most cost-effective solution. This conclusion is drawn from the retrofit with decommissioning (RET/DEC) network design option, indicating that a more sophisticated approach may be necessary for optimal economic efficiency. The network design optimization shows substantial overlap between the existing network and the new-built design, but significant differences in which specific pipe segments are built. Importantly, evaluating multiple demand scenarios reveals the limits to the hydrogen demand that can be accommodated by the current pipeline infrastructure. This is primarily due to the erosional velocity constraints inherent in the network for safety purposes.

However, even at higher total lengths, retrofit networks have significantly lower total annual cost (TAC). This indicates that retrofitting existing infrastructure could be a cost-effective strategy for expanding the hydrogen transport network. Nevertheless, it’s important to consider the lower lifetime of the retrofit networks and the operational pressure considerations of the pipelines. These factors could impact the long-term viability and cost-effectiveness of retrofitting strategies. Therefore, a comprehensive evaluation that takes into account both economic and operational factors is crucial for informed decision-making in the development of hydrogen transport networks.

References:

[1] O. Faye, J. Szpunar, and U. Eduok, “A critical review on the current technologies for the generation, storage, and transportation of hydrogen,” Int. J. Hydrogen Energy, vol. 47, no. 29, pp. 13771–13802, Apr. 2022, doi: 10.1016/j.ijhydene.2022.02.112.

[2] “Hydrogen Core Network - FNB Gas.” https://fnb-gas.de/en/hydrogen-core-network/ (accessed July 24, 2023).

[3] S. Cerniauskas, A. Jose Chavez Junco, T. Grube, M. Robinius, and D. Stolten, “Options of natural gas pipeline reassignment for hydrogen: Cost assessment for a Germany case study,” Int. J. Hydrogen Energy, vol. 45, no. 21, pp. 12095–12107, Apr. 2020, doi: 10.1016/j.ijhydene.2020.02.121.

[4] X. Wu, C. Li, Y. He, and W. Jia, “Operation Optimization of Natural Gas Transmission Pipelines Based on Stochastic Optimization Algorithms: A Review,” Math. Probl. Eng., vol. 2018, 2018, doi: 10.1155/2018/1267045.

[5] M. Hamedi, R. Z. Farahani, and G. Esmaeilian, “Optimization in Natural Gas Network Planning,” Logist. Oper. Manag. Concepts Model., pp. 393–420, Jan. 2011, doi: 10.1016/B978-0-12-385202-1.00019-0.