NCS Flare Gas Recovery Case Study

Transvac Utilises Waste Energy To Recover Flare Gas On Major Norwegian Platform


Background

Reduction in flaring volumes is a major target for all offshore facilities operating in the Norwegian Continental Shelf (NCS) area. The main aims are to avoid wasting valuable energy and reduce the environmental impact of harmful emissions and greenhouses gases such as carbon dioxide. For many new facilities, a zero-flare approach is being taken. For existing facilities, retrofitting of flare gas recovery systems is being implemented to minimise the amount of normal flaring.

Solution

An opportunity was identified on an existing Norwegian platform where production rates have declined over time, leading to spare capacity in a gas compression chain which was being operated on a high recycle rate.

Transvac was asked to design and manufacture an Ejector set that could utilise this waste energy to recover a mixture of low pressure flare gases from the flare system knock-out pot with the aim to reduce CO2 emissions by up to 75% and recycle gas back into the process.

Platform Diagram

The two-stage Ejector set used HP gas from upstream of the 2nd stage after-cooler as the motive fluid to entrain the low-pressure flare gas and discharged the combined stream to the suction of the 2nd stage compressor.

A recycle from the discharge of the Ejector set was used to regulate the suction pressure of the Ejector as the flare rate varied, to prevent the knock-out pot entering a sub-atmospheric condition.

Equipment

Transvac designed and manufactured a 2 stage Ejector set, including patented Size 8 and Size 10 Universal Design Gas Ejectors with LP and Discharge Silencers. All manufactured in Duplex with acoustic lagging on the Ejectors.

Size 8 Ejector
Size 8 Ejector With Acoustic Insulation
Size 10 Silencer
Size 10 Silencer

Complete Technical Support

Transvac were involved in all stages of the project from initial feasibility to FEED, HAZOP, detailed design and supply of the two-stage Gas Ejector set designed to boost atmospheric flare gas to 5.5 Barg.

To provide maximum operating flexibility, Transvac supplied patented Universal Design Ejectors which have removable internals (nozzles & diffusers). The Universal Design feature proved to be invaluable as it allowed for the operating point of the system to be altered very easily part way through the contract. A last-minute change to the operating point was required, allowing the client to install a different set of internals to those originally planned. The final set of internals installed were designed for the current flare rate of 900 Sm3/h, but the Universal Design Ejector bodies have been designed to be able to handle the maximum expected future flare rate of 2500 Sm3/h.

Due to the equipment being installed in an area which already had a high background noise level, the noise emitted by the new equipment needed to be minimised as much as possible. To achieve this, Transvac also supplied inline suction and discharge Silencers, acoustic insulation on the Ejectors and Anti-Vibration mounts for all the equipment. All other connecting pipework was acoustically insulated on site by the Contractor.

Client Comment

“The system works and we recycle flare gas as planned. To all who have participated in the project to make it a success, thank you very much for the great effort!”

Flare Gas Recovery Ejectors Installed

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