STRATIFICATION AND ROLLOVER IN LIQUEFIED NATURAL-GAS STORAGE TANKS

During October 1993 a rollover occurred in a British Gas liquefied nat ural gas storage tank. The pressure in the tank rose rapidly and the t wo process relief valves on the tank lifted. The emergency relief valv es subsequently lifted and natural gas vented from the tank for two ho urs. Approximately 150 tonnes of gas were vented to the atmosphere. Th e tank had been filled during July as part of the commissioning run of a modified liquefaction plant. The modified plant produced a product which was up to 13 kg cm(-1) (3%) lighter than the heel of the tank. T his was sufficient to cause a stratification in the tank. The tank sto od for 68 days after which the rollover occurred.