D2a.2 The impact of 16 bar hydrogen grids compared to 8 bar

Hydrogen distribution grids with a max design pressure of 16 bar are being considered for industrial DSO grids, particularly to serve customers that demand minimum 8 bar (e.g., for feedstock), to avoid unnecessary depressurization and recompression of high-pressure hydrogen in-feed, to enlarge capacity of the pipelines, and to decrease the total system cost. However, beyond these expected benefits of applying 16 bar hydrogen distribution in specific regions, an overview of the operational consequences of max 16 bar grids compared to max 8 bar grids is at this moment not yet been made. This research provides a high-level overview of the current knowledge on max 16 bar versus max 8 bar grid operation and identifies the knowledge gaps that must be addressed to arrive at a finalised max 16 bar hydrogen grid concept.

The decision to design hydrogen distribution grids at either 8 or 16 bar will likely be made on a regional or project-specific basis. It will mainly depend on the availability of customers in an area that demand or prefer to receive hydrogen at higher pressure (e.g. min 8 bars). For 8 bar hydrogen grids it is typically envisioned that, as much as possible and available, the existing natural gas grid will be repurposed for hydrogen. For 16 bar hydrogen grids new pipelines and materials suitable for 16 bar hydrogen are required, resulting in more limited reuse of existing infrastructure.

Before the implications of max 16 bar hydrogen grids can be meaningfully assessed, it is important to establish the current view on max 8 bar hydrogen distribution and how it differs from max 8 bar natural gas distribution. While the difference between natural gas and hydrogen distribution is not the primary focus of this report, this essential background information is discussed in detail in Appendix B. To this end, desk study and expert interviews were conducted to provide an overview of the 8 bar natural gas grid concept and the perspective for 8 bar hydrogen grids. Subsequently, additional research and interviews offered insights into the potential implications of 16 bar hydrogen grid operation compared to 8 bar operation.

The most important differences in grid concept between 8 bar natural gas or hydrogen distribution grids are:

·        Safety: Hydrogen distribution grids will be operated on at least similar safety levels as natural gas. However, due to different gas characteristics the emphasis will be placed on different aspects. For example, a hydrogen/air mixture has a larger flammability range and at higher concentrations also lower ignition energy than a natural gas/air mixture, making it more prone to ignition and explosion. As a result, for hydrogen grids, pipelines will be purged with nitrogen during (de)commissioning and maintenance to prevent explosive mixtures.

·        Work environment: Because hydrogen is a different medium than natural gas, personnel must be specifically trained to work with it safely and understand the differences. Working safely in a hydrogen environment requires, among other things, different work procedures, suitable detection sensors (e.g., in personal protective equipment), and the use of ATEX-IIC-certified tools.

·        Standards, norms and guidelines: Almost all standards, norms and guidelines for gas distribution are written for natural gas. The NEN 7244 has recently been updated and is made hydrogen-ready but is not formally applicable yet for hydrogen. Several other important norms and guidelines, such as the NEN 1059 and VIAG, hydrogen-specific adaptations are also in development. However, as these have not yet been formally adopted, DSOs will initially need to rely on self-developed guidelines.

·        Balancing: Hydrogen grids are (initially) expected to have lower volumes in the grid and lower storage capacities compared to natural gas. Additionally, they are expected to receive significant feed-in from decentralized hydrogen production. These aspects require other methods for grid balancing via flow control at the entry and exit points. It should be noted, however, that this is not exclusive to hydrogen, as flow control is also considered in certain sections of the natural gas grid with high levels of local biomethane feed-in.

The most important grid concept implications between 8 and 16 bar hydrogen distribution grids are:

·        Safety: At higher grid pressures, pipeline leaks (either due to external or integrity-related damage) can have a larger impact because the higher pressure drives gas out at a faster rate. Therefore, it is important that additional mitigation measures are applied in order to maintain the same risk level (see Chapters 4.2.1 and 4.2.3.2). Personnel also requires extra training to understand and manage the increased risks associated with 16 bar operation.

·        Materials: PE is suitable for hydrogen distribution at max 8 bar but cannot be used at 16 bar. Therefore, steel is currently the preferred material for max 16 bar grids. Other materials could be of interest for future applications. For example, polyamide A-U12 is currently limited in use because only a small range of pipeline diameters and compatible components are available.

Overall, from the expert interviews and existing literature no significant technical or safety concerns were identified or anticipated for 16 bar hydrogen distribution. A key difference between hydrogen distribution at both 8 and 16 bar compared to natural gas distribution is that hydrogen practices are not yet standardized, requiring a detailed evaluation of specific design criteria for every project. Additionally, a few knowledge gaps remain, with a complete list provided in the conclusion section of this report. The most important ones are summarized below:

·        What decision framework and criteria should the DSO apply to justify the decision for a max 16 bar grid in a certain area? And based on what considerations (e.g. number of customers preferring minimum 8 bar, volumes, locations, availability of natural gas grid that can be repurposed, etc.) should this be evaluated?

·        Assessment on purchasing specifications of grid components: which components are already suitable for max 16 bar and which are not? For example, are existing steel pipelines suitable for max 16 bar hydrogen grids?

·        Which tools and equipment should be adapted or added to construct and maintain 16 bar hydrogen grids?

·        What are the cost differences in pipelines, components and grid management for 16 bar distribution grids compared to 8 bar grids?

·        What are the soft implications of max 16 bar distribution? What stakeholders need to be involved, informed and embedded in the discussions? For example, to require permits and inform stakeholders.