This desktop study looks at the theoretical impact of hydrogen blends in conventional gas mixtures on hydrocarbon dewpoint and water dewpoint (HCDP/WDP).
HCDP/WDP tell us when liquid drop out will occur. There is a requirement to monitor this under Gas Safety (Management) Regulations (GSMR) as the liquids can cause damage to National Transmission System (NTS) assets and downstream customers equipment e.g. Power Station turbines or Distribution Networks.
HCDP/WDP is currently calculated by using a calculation which is not designed to include hydrogen mixes.
The Distribution Networks do not check for HCDP/WDP as National Grid Gas Transmission (NGGT) check at the entry point to the NTS only. The Distribution Networks therefore assume the gas is safe to transport and use as NGGT have checked it.
Benefits
The benefit of this project will be to gain an understanding of how the hydro carbon dewpoint calculations could need to be changed in a hydrogen blend scenario. The GDNs do not check for this and so it is the responsibility of NGGT to complete this.
Learnings
Outcomes
In conclusion from the Technical Report supplied by DNV:
As both hydrocarbon and water dew point are legally compliant factors to consider for natural gas transmitted and distributed throughout the UK, it is important to understand the potential impact that addition of hydrogen may have as use of hydrogen blends is considered as part of the approach to reduce the carbon emission impact from pipeline natural gases.
A programme of study was undertaken to evaluate the impact of hydrogen on both the hydrocarbon and water dew points. A literature review was performed, and this highlighted that there have been limited studies on the impact of hydrogen on dew points for natural gas (and hydrocarbon) mixtures.
Data that was obtained has been used to support a thermophysical properties study, using the GasVLe software suite as this is currently used by National Grid to calculate hydrocarbon dew point at the entry points. The results obtained from this study show that the addition of up to 20 mol% hydrogen to natural gas does not significantly affect the hydrocarbon dew point or the water dew point. That is, the change in temperature is less than the generally accepted uncertainty of the temperature calculation of around 2 to 3 °C.
It is recommended that if hydrogen is injected that for all calculations the same equation of state should be used when hydrogen is present and when hydrogen is absent. This avoids any possible discontinuity in the results as a consequence of changing methods.
We do not propose further research on this subject at this time as the semi-empirical models demonstrate acceptable alignment with the current equations of state.
Lessons Learnt
There were no significant issues or lessons learnt during this project as it consisted of a short, desktop research-based program that completed its objectives. One point to note was that the project highlighted the specialist knowledge of hydrocarbon dewpoint calculations and the requirement to pass this knowledge on to others in the industry before it is lost.
