2011-02-08 - Temperature and pressure sensors from ABB’s UK Measurement Products business are helping to maintain safety at the world’s largest above ground liquid natural gas (LNG) tanks at National Grid’s Isle of Grain terminal.
The four tanks, each holding 200,000 m3 of LNG, are 50 metres high, larger than the Albert Hall. They form Phase 2 and 3 of an expansion plan that will eventually see the site capable of supplying 20% of the UK’s gas demand.
Phase 2 involved the building of three large LNG storage tanks, as well as six vaporisers, six ex tank pumps, four boil-off gas compressors, a control room and other ancillary facilities. Phase 3 added another LNG tank, a further four vaporiser units, another four ex tank pumps and two boil-off gas compressors, as well as a new jetty and loading point. These expansions have raised the site’s import capacity to 14.8 million tonnes of LNG per annum.
For Phase 2, ABB supplied 93 temperature units and 99 pressure units, while for Phase 3, it supplied 74 temperature units and 140 pressure units. These are used throughout the site on every process line and utility. A typical application is in the management of boil-off vapour, which is produced in the tanks and liquid fill lines during normal operations by heat transfer from the surroundings. This vapour is collected in the boil-off header. LNG is injected into the gas stream if the temperature rises above minus 80°C. The boil-off vapours are compressed and liquefied in the recondenser.
The recondenser pressure is normally maintained within an operating band by varying the flow of LNG to the top of the vessel. If the pressure goes outside the normal operating range, then gas can be vented from the top of the vessel back to the BOG header or cover gas can be added from the export system.
Some of the ABB temperature sensors were of a clamp-on design, allowing them to be installed around the pipe work rather than needing to intrude through the pipe wall. This minimised the number of flanged/screwed connections in LNG lines to reduce potential leak points.
“Safety and accuracy are key concerns in projects such as this,” says Les Slocombe, Business Development Manager for ABB’s UK Measurement Products business. “Designed and tested to the leading international standards, our temperature and pressure sensors and transmitters are widely used around the world in similar projects to this and have been proven to provide our customers with safe, reliable operation, even in the toughest operating conditions.”