The hydrogen sector lacks a specification valid for the whole value chain, ranging from production to industrial end-users that partially use hydrogen as a feedstock for chemical processes, and which is also applicable for repurposed natural gas pipelines. This was the reason in 2019 for industry body the European Association for the Streamlining of Energy Exchange – Gas (EASEE-gas) to start drafting a Common Business Practice (CBP) for the harmonisation of a hydrogen quality specification.

The scope of this CBP covers hydrogen flowing through dedicated systems, meaning networks that were originally designed and used for natural gas transmission and rededicated after a safety and reliability assessment. It focusses on ‘industrial grade’ hydrogen, based on the expectation the large-scale production of hydrogen, necessary to operate a pipeline system, will take place partly by chemical conversion of hydrocarbons into hydrogen.

In contrast to electrolysis, these processes do not deliver inherent fuel-cell quality hydrogen. Another reason to focus on ‘industrial grade’ hydrogen is the observation from market forecasts that industry would take the lion’s share of the total hydrogen production. CBP 2022-001/01 ‘Hydrogen Quality Specification’ was published in 2022.

National activities

During the drafting period of the EASEE-gas CBP, the role of hydrogen in the energy transition started to gain traction, resulting in various studies looking into the different aspects of production, transmission, distribution and use of the fuel. In addition, national hydrogen specifications were drafted in various countries as they were needed to support initiatives for future hydrogen networks partly based on repurposed natural gas pipelines.

CEN standardisation

It was clear from the start that future hydrogen networks in European countries would be connected to form a large European network. To allow the free flow of hydrogen in such a network, one or more European hydrogen specifications were needed. Therefore, the European Committee for Standardisation (CEN) started drafting a Technical Specification (TS) specifying minimum requirements.

It was clear from the start that future hydrogen networks in European countries would be connected to form a large European network

Like the EASEE-gas CBP, the scope of the TS includes the whole value chain (producers, system operators, other related services and end-users) to produce, transport, store, deliver and/or use hydrogen with the possibility to employ rededicated (or adapted) natural gas infrastructure and/or connected applications in a safe way in the CEN member countries and, where applicable, without the risk to harm or damage the infrastructure or connected end-user applications.

However, it is recognised that, for some end-user applications that are particularly sensitive to some of the gas quality parameters and/or impurities, the minimum requirements given in the TS are not sufficient. In these cases, purification measures at the end-user site can be needed for upgrading the hydrogen quality before use. All available information gathered during the drafting of the EASEE-gas CBP and the various national specifications and all relevant international studies were incorporated in this new CEN Technical Specification, which was published as CEN TS 17977, ‘Gas infrastructure – Quality of gas – Hydrogen used in rededicated gas systems’, in 2023.

Minimum hydrogen concentration of 98 mol-%

During the development of the hydrogen quality specifications for repurposed pipelines, the general opinion was to base them on a minimum hydrogen concentration of 98 mol-%. Partly because no information—i.e. no experimental data—was available at that time on the behaviour of natural gas residuals left in the repurposed natural gas infrastructure. Another reason was the outcome of a Dutch study carried out by consulting firms DNV and KIWA under the auspices of the Dutch Ministry of Economic Affairs and Climate Policy that recommended a minimum hydrogen purity of 98 mol-% as an initial quality requirement for the Dutch hydrogen backbone.

However, the DNV KIWA report expressed the expectation that, as more hydrogen is produced through electrolysis and more knowledge is gained about transporting and storing it and the possibilities for its purification, the quality requirements can be adjusted to purities higher than 98 mol-% over time. Furthermore, it proposed reassessing the specifications three years after the hydrogen transport network is put into operation.

Requests from industrial end-users

Both the EASEE-gas CBP and the CEN TS 17977 suggest monitoring the developments in the hydrogen production and the experiences with repurposing natural gas infrastructure, foreseeing the possibility of an increasing hydrogen concentration, and propose therefore to review the specification after a few years.

Confronted with a proposed minimum hydrogen concentration of 98 mol-% in combination with a possible short-term review of the hydrogen specifications, large industrial end-users argued their chemical processes required an expensive on-site purification and asked for more clarity in the long term.

Behaviour of rededicated pipelines

Detailed investigations have taken place on converting natural gas pipeline to hydrogen. Measurements were carried out on a rededicated pipeline in the Netherlands and also on some pipelines preserved under nitrogen. These measurements showed that, after purging with nitrogen, the effects of natural gas residuals still present in the pipeline are almost neglectable and disappear completely in the long run. The results of the measurements were also underpinned in Germany by modelling the exchange of components between a small layer of liquids present at the pipeline wall and the hydrogen flowing alongside this pipeline wall.

Based on this work, and under the prerequisite that, during the conversion of the pipeline, the proper measures are taken to remove the natural gas residuals as much as possible, it has been concluded that the use of rededicated pipelines does not limit the minimum hydrogen concentration to a value of 98 mol-% and that alternatively, it was reasonable to consider a minimum hydrogen value of 99.5 mol-%.

It has been concluded that the use of rededicated pipelines does not limit the minimum hydrogen concentration to a value of 98 mol-%

Based on the comments of some end-users, the Dutch Ministry of Economic Affairs and Climate Policy ordered an additional study from DNV KIWA under the condition the proposed hydrogen specification should be valid for a longer period. In this follow-up study, the criterium to minimise the overall costs for purification in the whole value chain was unchanged compared with the initial DNV KIWA study. However, it was allowed to go up to a minimum hydrogen concentration of 99.5 mol-%, the current proposed upper value for operating rededicated natural gas pipelines. The study concluded that the specification based on a minimum hydrogen concentration of 99.5 mol-% is slightly favourable.

The next part of this three-part series will look in more detail at this proposal.

Click here to read part one and here to read part three.

This document has been drafted jointly by TSOs Hynetwork, Open Grid Europe, Thyssengas, Gasunie Deutschland, Fluxys Hydrogen based on a presentation made at a workshop on hydrogen quality organised on the 20 March 2024 in the framework of the Pentalateral Energy Forum. The presentation was discussed with TSO Transitgas and agreed upon by TSO Creos.

 

 

---

Authors: Mohammed Mohammed, Tobias van Almsick, Peter van Wesenbeeck, Yoran Vander Eeckt, Simon Vetter