Gas composition is currently monitored at entry points to the Gas Transmission System with “All-in-One” gas quality monitoring devices. These devices provide, and are primarily suitable for, monitoring energy content and combustion stability. In their current form, limitations exist in the detection of contaminants. For example, the devices were not historically designed to detect some of the expected potential contaminants.
The Gas Safety (Management) Regulations (GS(M)R) (1996) state that gas “…shall not contain solid or liquid material that may interfere with the integrity or operation of pipes or any gas appliance within the meaning of regulation 2(1) of the Gas Safety (Installation and Use) Regulations 1998 that a consumer could reasonably be expected to operate.”
National Grid network entry conditions go slightly further and state that gas “…shall not contain solid, liquid or gaseous material that may interfere…”. One of the reasons for this is that materials may be in vapour phase at the entry point, but if found in sufficient quantities may subsequently condense out to the liquid phase at within the downstream gas network due to changing pressure and temperature regimes.
Detection & quantification of contamination levels would enable National Grid to comply with the legal requirement of not transporting solids or liquids by either:
- Encouraging gas suppliers to improve their gas conditioning processes based on the evidence of detection
- Providing reliable and accurate information to facilitate the operational decision to shut down an offending incomer pipeline.
The development of a multi technique liquid or liquid bearing gas detection system would enhance National Grid’s enforcement of it’s GS(M)R obligations. The progamme aims to provide a series of operational options for the reliable detection of liquids within National Transmission System (NTS). The programme will develop and trail a prototype detection system based on commercially available technologies.
Benefits
The approach being taken is to consider using more than one detection method to give a greater chance of detecting liquid contamination.
For example, vertical ultrasonics will be assessed for detecting a level of liquid, horizontal ultrasonics will be assessed for detecting aerosol liquids, multi-FID will be used to detect liquid slugs, laser technology will be assessed for detecting particular molecules, irrespective of their phase, nitrogen purging of standard analysers will be assessed to see whether this improves their performance with liquid contamination.
This approach enables a range of composite detection systems to be configured for specific sites. This offers a wide range of installation options ensuring a wide range of gas quality detection capability.
