The objective of this paper is to describe the process technology and construction of the world's first seawater sulphate removal plant using membranes for the key treatment stages.
SUEZ and Techouse have jointly developed the water injection module for the Equinor FPSO Johan Castberg. The vessel will be stationed in the Barents Sea, north of the Arctic Circle in 360-390m of water. The water injection capacity is specified by the client as 180,000 barrels per day with a sulphate content of <40ppm and an oxygen content of <20ppb. The environmental challenges of this location meant that a fresh design perspective was required to operate the water injection plant to this specification. NORSOK engineering standards are also required.
The traditional treatment process for this type of installation is pre-filtration by multi-media, cartridge filtration, nanofiltration membranes for sulphate removal, followed by vacuum tower deoxygenation. This paper will describe the alternative process solutions proposed, using an all-membrane process train and describe the benefits in terms of weight, footprint and operability, plus progress with construction to date.
The water injection module is structurally complete as at September 2019 and is unique in that it is fully enclosed. Construction has been optimised by using the walls as a structural component rather than just cladding, thus keeping weight and structural complexity to a minimum.
Unique features of this plant are:
A fully enclosed water injection module
An all-membrane process train
The world's first full scale offshore membrane deoxygenation plant