Level Solution For Difficult North Sea Application

When a leading oil and gas exploration and production company asked Able Instruments (UK) to assist with an urgent and difficult measurement requirement on two of their platforms in the North Sea, Able Instruments stepped up to meet the challenge.

Two manned production and drilling facilities required replacement of the existing pneumatic level transmitters on the NGL knockout drums. The original level shutdown system was made up of float switches, which had been historically problematic and unable to cope with varying Specific Gravities of the liquids. The float switches can be subject to unknown failures which only become apparent when a shutdown demand is placed on the instruments.

Due to Able’s competitiveness and ability to meet challenging target delivery dates on previous projects, Able was commissioned to find a reliable solution to the problem with strict target dates in mind.

The plant operators are required to monitor and control the level in the NGL condensate knock out drums to avoid overspill of water to the system, which has caused plant upset in the past. The operators must be able to gain confidence with the instruments, allowing them to concentrate on more critical systems during plant start up. It is essential that the instruments used are reliable and can cope with the demanding process conditions and accurately measure the level in the vessels.

Notwithstanding this, the solution must stand up to the normal rigors of offshore life in the North Sea, to include extreme cold weather, saline atmosphere, strong winds etc.

Nucleonic measurement was discounted as it was considered too expensive and required support steel works to install. Magnetic level gauges alone, on liquids with varying SG’s, had previously failed in reliability and displacement methods were discounted due to process requirements.

ABLE deduced that the ABLE Fusion system would be the most reliable and accurate solution to this measurement problem. ABLE Fusion is a level measurement system which combines the operation of a float operated magnetic level indicator with guided wave radar to offer two independent proven level technologies in one system.

The magnetic level indicator offers a clear visual level display and can be supplied with a reed chain transmitter, magnetostrictive transmitter or switches for high and low level alarm requirements, operating in conjunction with the level indicator float.

The guided wave radar offers an independent level measurement based on high frequency microwave pulses that are transmitted along a guide rod. The pulses are reflected back by the liquid surface to a receiver, providing a level measurement accuracy of +/-3mm.

The visual indication or transmitter output from the magnetic level indicator can be compared to the guided wave radar to provide the confidence of accurate liquid level measurement, either locally or in a control room.

The combination of technologies provide the operator with a fault tolerant, reliable level system suitable for applications where critical level measurement and redundancy is required, particularly in the offshore, petrochemical, power and pharmaceutical industries.