Safety on a Refrigerated Ethylene Tank

During a several-day outage of the refrigeration unit outage, the ethylene tank absorbed ambient heat and the internal pressure increased. The backup plan to cool by auto refrigeration as vapor escaped via the open relief valve was underway. As planned, a flow of steam was routed to the stack in hopes of safely dispersing the cold gases. 

However, about 12 hours later, a small tank seam leak developed. Steam hoses were directed near the leak to heat and disperse the vapor as the tank was emptied as sales conditions allowed. The large atmospheric liquid ethylene tank could not be emptied quickly, for there were no other tanks available to store to liquid ethylene. 

The 8-inch (20.3 cm) safely relief valve discharge line had frozen solid. It is easy to understand that hot steam does not stay warm very long when it contacts — 155°F(—101° C) ethylene. The steam quickly condensed and then the water froze. No one seemed to anticipate the shortcomings of the original faulty suggestion. 

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