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A bad valve that allowed hydrocarbons to slip into the wrong tank is the cause of a fire at a Tulsa, OK, refinery almost one year ago, officials confirmed this week.

The April 22 blaze atop Tank 13 at the HollyFrontier Corp. refinery caused no injuries nor significant damage to the refinery, officials said.

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The first thought was lightning on a stormy night was the cause, but officials ruled that out later on. HollyFrontier, then called Holly Corp. before its summer merger with Frontier Oil Corp., investigated the blaze but said it would not release findings to the public.

“Things that are material to us we are required publicly to note,” HollyFrontier spokesman Neale Hickerson said. “It was an incident which did occur, but there was little loss of property and no injuries.”

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State Department of Environmental Quality (DEQ) spokeswoman Skylar McElhaney confirmed that HollyFrontier officials revealed the fire’s cause. McElhaney sent the local newspaper, the Tulsa World, an email quoting from the company’s report about Tank 13’s ignition source.

The report indicated “a malfunctioning valve at the unifiner boot prevented the boot from holding a liquid level and allowed hydrocarbon to pass into the sour water system.”

Sour water has hydrogen sulfide present, and refineries remove sulfur from refined products to meet federal standards. A sour water degassing slop pump, as HollyFrontier called it, would normally remove hydrocarbon which gets past the protective boots.

“The combination of these two mechanical failures at the unifiner and the SWS (sour water stripper) allowed some hydrocarbon from the unifiner that is normally stored in a cooled tank to be routed to a heated tank (13),” the company told regulators.

HollyFrontier also reported details of unrelated, more recent flare gas recovery unit compressor shutdowns on April 5 and 10. The first shutdown was due to flare volume exceeding compressor capacity, while the April 10 event was likely due to malfunction of a pressure control valve, according to the DEQ.

The flareups lasted several hours and were both from HollyFrontier’s “Tulsa East” facility, formerly known as the Sinclair refinery. HollyFrontier bought the two Tulsa refineries from Sunoco and Sinclair in 2009 and connects the two units via a series of pipelines.

The Tulsa refinery can process 125,000 barrels per day. HollyFrontier produces gasoline, diesel, solvents, lubricants, asphalt and other products.

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