New gauge reduces error in flare-drum level

Feb. 14, 2000
Replacing an old mechanical gauge with a radar gauge on a blowdown drum improved reliability and reduced maintenance costs for Preem Raffinaderi AB's refinery in Gothenburg, Sweden.

Replacing an old mechanical gauge with a radar gauge on a blowdown drum improved reliability and reduced maintenance costs for Preem Raffinaderi AB's refinery in Gothenburg, Sweden.

The new radar gauge sits atop the flare-blowdown drum at the Preem refinery.
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In April 1999, Preem purchased a Saab TankRadar Pro to replace its level instrument on an existing blowdown drum. The blowdown drum connects the refinery process area and the flare.

The gauge helps maintain a hydrocarbon liquid level in the drum, which is part of the refinery's safety-alarm system. If a failure occurs in the refinery process, the safety system evacuates gases and liquids via safety valves and piping to the blowdown drum.

The new gauge measures the level and controls the pumps automatically by sending a 4-20 ma signal to the distributed control system (DCS).

The radar gauge also decides when to analyze the liquids. The refinery set limit values in the DCS system for low-level alarm, pump cut-off, analysis of the product, pump cut-in, and high-level alarm.

Preem's old mechanical level gauge stood in a standpipe outside the tank. The standpipe could wrongly influence the level readings because it collected deposits of rust and salt. The new gauge reduces maintenance in this way and also eliminates the need to open and close the pump.

Thus, the new gauge improved reliability and accuracy and reduced maintenance costs. Preem says that its old mechanical gauge could create an error span of more than 500 mm because of density differences between the product in the standpipe and in the tank. The new gauge has an error span of plus or minus 5 mm.