Gas Quality/gas composition Data - evidence of value required
Karen Thompson
Operational Liaison and Business Delivery Manager at National Grid
Good morning.
We are still struggling to gain insight from the industry on what value would be attained of having this data and what the blockers are of not currently receiving this and keen to utilise this forum and/or ops forum and 121's to understand and prioritise industry views on this if required. To date feedback has only been received on why this data should not be provided at the level to which NG currently has this available.
If you could please vote as soon as possible with a clear indication of how value could be attained from this raw data (operational or commercial) or what analysis/insight it could enable. Do ensure this feedback details how this can create value for the end consumer and/or enable the journey towards decarbonisation.
We had intended to reflect some test data on this site but we have received strong feedback from industry players that any data sourced downstream from a supply point (even where there a a number of supply points at the entry level) could lead to identification of a single supply point where (as is often the case) only one supply point flowing. This is not to say it couldn't and wouldn't be possible to still provide but would need due industry regulatory consultation.
For added context the type of data around gas composition that could be made available is:
- Wobbe
- H2O dewpoint
- CO2
- CV
- H2S
- Hydrocarbon dewpoint
- ICF
- Nitrogen
- Sulphur
- Specific gravity
Please let me know your thoughts on this discussion board, via the voting functionality or by contacting me direct on karen.thompson@nationalgrid.com
1. Anonymous on
Issue
Wobbe Index (WI) Rate of Change and absolute levels are more of an operational/commercial issue for CCGTs than directly personnel safety. However, plant failures and NOx emission deviations have apparently occurred on combustion systems elsewhere following gas composition deviations.
WI or Calorific Value allowable ranges are currently set at ±5% from design point. This is generally the range for a selected set of fuel nozzle hardware. Re-tuning of fuel splits has often been required to cope with smaller quality variations; to maintain acceptable combustion dynamics and emissions.
A possible 52.85 and 47.2 (10.7)% Wobbe range for premixed GT combustion systems would lead to a high likelihood of increased combustion dynamics, increases in NOx emissions and reduced flame stability.
We have experience of operating GTs from the three main OEMs. Each machine has its own ‘design point’ fuel specification and an allowable range above and below this point for the main parameters.
It is very difficult to predict the magnitude of such changes and the potential cost impact this might have. However, commercial loss and potential trips or brown outs may result from possible asset failures resulting from damaging combustion dynamics.
Solution – information provision & notification
At each large CCGT site , gas composition information is available in real-time and is regularly analysed by engineers. Calculations of fuel gas properties are frequently undertaken using the software GasVLe.
In addition, we employ data modelling software (SmartSignal) which track properties such as molar composition and Wobbe Index.
A solution is for NG control room to contact a specific site if they were to see a step change in gas quality/ rate of change of WI that may cause a problem. A threshold that would set our warning, rather than responding to every small change presents a pragmatic solution.
A 3% Wobbe Index step change deviation would be an appropriate trigger for NG flagging to the CCGT control room with 2 hours notice. Is it possible for NG to facilitate this at specific exit sites close to entry points?
Hydrogen
The potential introduction of up to 20% hydrogen would likely have a significant impact on current GT premixed combustion systems.
Until recently, GT fuel specifications from the main OEMs do not permit anything other than either trace quantities of this constituent, or in one case up to 5%. The introduction of this level of H2 would likely also reduce methane content below OEM guidelines.
Flame speed and auto ignition properties would change significantly. These changes may be suitable for domestic appliances with diffusion flames, but premixed combustion is far more complicated. Engagement with OEMs is therefore recommended.
Premixed combustion is a complicated trade-off of temperature, dynamics, NOx and flame stability; increasing temperature whilst at the same time widening gas quality may affect the ability of the new generation of CCGTs to operate reliably in the >60% efficiency region. However, we note that OEMs have recently stated that new plant may have increased ability to manage higher H2 %.