f 261 HyPurge - Direct Purging of Networks to Hydrogen for H100 Fife, Final Report

The HyPurge project aimed to explore the comparative challenges in purging gas network pipes to hydrogen compared to purging to Natural Gas. A comparative study has been carried out investigating the purging performance of hydrogen and methane on pipe diameters across the range of sizes to be used by SGN in the H100 Fife project.
The most significant discovery of the project is that the very low density of hydrogen does not make direct purging between air and hydrogen impossible or even difficult. In many cases direct purging a system in like for like conditions is more efficient for hydrogen than for methane. At the time of writing, it is believed that this is due to the higher coefficient of diffusion for hydrogen.
These findings should provide SGN with confidence that direct purging is a viable option for commissioning and decommissioning the networks for H100 Fife.
Over 750 direct purges, or purge related tests have been carried out during this project. The results provide evidence to fill the knowledge gap regarding direct purging performance between air and hydrogen.
Key messages from this work are: 1) Hydrogen purges are generally more efficient than Natural Gas purges. The total volume of air-fuel mixture created in a purge involving hydrogen is likely to be less than one involving Natural Gas.
In tests, purges from air to hydrogen have been consistently more efficient than purges from air to methane. Purges from both fuel gases back to air have a relatively similar performance to each other. The low density of hydrogen did not present any challenges for direct purging operations. This means that less fuel-air mix, and less fuel in total, is released for a hydrogen purge compared to a Natural Gas purge. 2) Hydrogen purges are generally more flammable than Natural Gas purges. The flammable volume of air-fuel mixtures created inside the pipe during a purge involving hydrogen is likely to be greater than one involving Natural Gas.
Although less air-fuel mixture is created during a hydrogen purge, the wider flammable range of hydrogen means that the volume of mixture that is flammable inside the pipe is greater for a hydrogen purge than for a Natural Gas purge. 3) The total volume of flammable air-fuel mixtures generated outside of the pipe during a purge involving hydrogen is likely to be less than one involving Natural Gas. The upper flammable limit does not prevent vented fuel becoming flammable once it mixes with air outside of the pipe.
This report was submitted to HSE for their assessment of the safety evidence for 100% hydrogen heating, which can be found at Hydrogen heating: HSE assessment of the safety evidence - GOV.UK.
Queries should be directed to DESNZ: https://www.gov.uk/guidance/contact-desnz.