D1C.1 Purging of natural gas pipelines with H2

A research study has been carried out as part of the HyDelta national research programme into purging the existing natural gas pipelines with hydrogen. The research described in this report is part of work package 1C "Pipes and indoor installations" and relates to research question 187. This question is as follows:

How can existing gas distribution pipelines be safely decommissioned as a natural gas pipeline and (simultaneously) commissioned as a hydrogen pipeline during the conversion to a hydrogen network? What are the associated costs?

During the conversion of the natural gas network to a hydrogen network, the natural gas in the distribution pipes needs to be replaced by hydrogen. On the assumption that no air enters the pipeline, this means that the natural gas can be directly displaced by hydrogen.

The purpose of this study is to determine whether purging of a natural gas pipeline with hydrogen can be carried out safely, and to establish the purging speed needed to obtain sufficient displacement of natural gas. An additional objective of this research is to determine the associated costs.

For the experiment, two pipes (DN 100 and DN 200) with a length of approximately 200 metres per diameter were placed on the Kiwa site in Apeldoorn. The test pipes (including a bridge pipe) were equipped with measuring points at three distances. The minimum purging speed was determined by filling the pipe with 100% natural gas. After that, hydrogen was introduced at different speeds.

The research study shows that hydrogen can be used to displace natural gas from existing natural gas pipelines. It proves that a natural gas distribution pipeline can immediately be recommissioned as a hydrogen distribution pipeline after the natural gas has been displaced. Furthermore, the study shows that purging natural gas with hydrogen including flaring is safe and technically feasible.

At a purging speed of 0.2 m/s in both the DN 100 and the DN 200, the natural gas is completely displaced by hydrogen. However, the conditions in practice when purging pipes may be less favourable compared to purging the test lines. For this reason, a safety factor of two is applied to be absolutely sure that the pipes have been completely purged. The minimum purging speed is therefore 0.4 m/s.

To reduce the duration of purging, a speed of 1.0 m/s is recommended. This also shortens the duration of an open flame (flaring). These minimum and recommended purging speed are in line with the report “Spoelen van waterstofleidingen” (Kiwa Technology GT-200289, reference [1]).

The estimated costs of purging main gas pipes with hydrogen are € 685 (excl. VAT) per kilometre. These costs are limited to the actual purging of the main pipelines. The preparation costs for the work (e.g. drawings, switching plans, KLIC reports) and the conversion to hydrogen in the homes, etc. have not been taken into account, as these are very specific for different sections of the network.