National Grid operates LNG bulk storage facilities that perform re-gasification of LNG stored in thermally-insulated tanks at -260°F. These operations provide peak demand distribution to residential and commercial customers. When exposed to atmospheric temperatures, LNG absorbs warm air, beginning the regasification process and returns to a natural gas. NFPA 59A and 49 CFR part 193 provide regulations for storing and safeguarding these LNG operations. LNG can escape as a fluid from the tank or during loading, unloading and regasification processes, creating a hazardous condition. Impounding dikes that surround the tank and transport vehicles provide spill containment, and sump pump systems that are permanently installed to remove rainwater. To mitigate the danger of leaking LNG in these containment areas, it is essential to detect the presence of LNG before it enters the sump pit and is pumped outside of the dike containment system, exacerbating the hazardous condition. A previous method of LNG leak detection involved very long (200’) bimetallic thermocouple sensors that often failed due to wear and the buildup of snow and ice.
UE’s One Series certified Safety System consisting of a temperature transmitter, logic solver and safety relay in a single explosion proof enclosure represented a significant cost-effective upgrade of the fire & gas system. This Class I, Div. 1 device uses a cryogenic temperature RTD to monitor for the presence of LNG in wells and spillways in the dike containment area. When LNG is detected, the One Series Safety System initiates a direct emergency shutdown of the sump pump while simultaneously signaling the DCS to fill the dike containment area with foam to prevent the ignition of fugitive natural gas. Often a voting mechanism of these safety systems will be employed to maximize availability. By combining sensor, logic solver and relay into a self-contained, SIL certified field mounted safety system, operators have reduced complexity, lowered installed cost and gained the confidence to standardize on the One Series Safety System. By acting directly to shut down pumps, National Grid gains more achieved risk reduction and faster system response times.
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