Idle pump station revived as oil heater

A pump station once relegated to standby status is now playing an important role in keeping the trans-Alaska oil pipeline running safely in winter, says operator Alyeska Pipeline Service Co.

Pump Station 7, located about 50 miles north of Fairbanks, is not needed to pump oil under normal operating conditions. But during cold stretches, the station is being used to heat crude oil.

Oil enters the pipeline on the North Slope at about 110 degrees. In years gone by, the oil stayed plenty warm on its 800-mile journey down the line. But with the Slope’s steep decline in production, the crude is traveling slower, allowing the oil to chill. This invites serious problems, such as potentially damaging ice formation in the line.

Teams have installed additional piping and new values at Pump Station 7, as well as Pump Station 4, to conduct recirculation of oil, Alyeska reports in the January edition of its newsletter, The Line. With recirculation, oil is looped back through the pumps several times, which adds energy to the flow of oil and thus heat.

The newsletter explains: “During recirculation, a portion of the crude stream passes through drag valves that produce a pressure drop to develop heat. That same crude oil then flows through a full head pump that adds more heat with friction and increases the pressure. The crude oil goes through yet another drag valve, dropping the pressure again and producing additional heat before the oil re-enters the pipeline.”

Alyeska says it’s been doing oil recirculation at several pump stations for two years.

Creating friction actually means the pipeline system “is running less efficiently, but what the pipeline loses in efficiency, it gains in heat.”

Some pump stations have been overhauled in recent years. Pump Station 7 is using an existing “legacy” pump to heat oil, Alyeska says.

—Wesley Loy