Electricity + Control 2019

PRESSURE + LEVEL MEASUREMENT + INSTRUMENTATION

Measuring the liquid-liquid interface

In this case study, Magnetrol outlines how magnetostrictive technology was used to assist an oil refinery in meeting the challenge of accurately measuring the liquid- liquid interface in its process equipment.

I nterface applications are among the toughest challenges in process industries. In the oil & gas and petrochemical industries specifical- ly, the need for interface measurement arises whenever immiscible liquids, those incapable of mixing, are held within the same vessel. The lighter medium rises to the top and the heavier settles at the bottom. Immiscible liquids meet along an interface layer where they undergo some amount of emulsification. This emulsion layer (also referred to as a ‘rag’ layer) may form a narrow, distinct boundary, but more frequently it is a broader gradient of the mixed liquids. Gen- erally, the thicker the emulsion layer, the great- er the measurement challenge. Measuring this liquid-liquid interface requires instrumentation that is precise and reliable. While monitoring the top, or total level, is critical for safety and over- fill prevention, knowing the level of an interface is necessary for maintaining product quality and operations efficiency. Improving accuracy and reliability Recently, Magnetrol ® assisted a refinery in Germany to improve the interface level measure- ment in a separator.This refinery, one of the largest in the Bavarian region, produces around eight mil- lion tons of crude oil every year.The process equip- ment includes a petrol-soapy water interface and, after a certain period of time, salt from the soapy water enters the petrol. This was causing a longer runtime of the petrol through the upper media. It also changed the dielectric value of the petrol. This changing value was causing malfunctions in the interface level measurement system the refinery was using at the time – sometimes presenting up to a 20% mismatch of the interface level. The instrumentation failed six times over a period of two years.

Magnetrol suggested the use of magnetostric- tive technology to monitor the liquid-liquid inter- face. Magnetostrictive level measurement uses a low-energy pulse that travels the length of a wire. A return signal is generated from the precise loca- tion where the magnetic field of a float intersects the wire. A timer precisely measures the elapsed time between the generation of the pulse and the return of the acoustic signal. Each cycle occurs ten times per second, providing real-time and highly accurate level data. Magnetrol installed the Jupiter ® JM4 magneto- strictive transmitter in the application. It was able to measure the interface more precisely than the previous level transmitter, as the density of the petrol was not affected by the salt in the same way as the dielectric was. No interface measurement is identical, so having a breadth of level technolo- gies to choose from is critical. In this case, relying on a technology with floats that uses buoyancy principles provided improved interface level meas- urement. Since installation of the Jupiter JM4 just over eight months ago, there have been no level instrumentation failures and the magnetostrictive technology has assisted in preventing water from entering equipment downstream of the separator.

The Jupiter JM4 magnetostrictive transmitter.

Acknowledgements to Magnetrol International for permission to publish this article.

Take Note! In the oil & gas and petro- chemical industries spe- cifically, the need for interface measurement arises whenever immisc- ible liquids are held in the same vessel. Magnetostrictive level measurement provides real-time and highly ac- curate level data.

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For more information: email: marketing@magnetrol.be or visit: www.magnetrol.com

Electricity + Control

JUNE 2019

31