Liza Unity

Client: SBM Offshore

Process: Sulphate Removal and Reverse Osmosis

Country: Liza Field - Offshore Guyana

Contact Description: Seawater Treatment Modules

Contract Date: October 2018

Contract Completion Date: Ongoing

SRP / RO Capacity: 263,244 BPD (41,856 m3/day) / 1,700 BPD (5,040 m3/day)

Sea Water Conversion: 75% and 40%

Sea Water Feed Quality: 36,390 mg/l (TDS)

Product Water Output Quality:  <40 mg/l sulphate / < 800 mg/l TDS






Project Description:

The project is for the design, procurement and supply of equipment and construction technical assistance for a sea water treatment plant sized for 263,244 BPD (41,856 m3/day) of low sulphate water and 31,700 BPD (5,040 m3/day) of low salinity water for the Liza Unity FPSO, which will operate in the Liza Field, offshore Guyana. 

Project Scope:

The project scope consists of two modules; one module for sea water treatment plant comprising Sea Water Lift Valve Sets, Coarse Strainers, Multi Media Fine Filtration, Guard Cartridge Filters, Chemical Dosing Systems, Piping, Valves and Instrumentation and a second module comprising SR & RO HP Feed Pumps, Sulphate Removal & Reverse Osmosis Membrane Systems, Common Clean In Place System, downstream Vacuum Deaerator Package, Water Injection Booster Pumps, Piping, Valves and Instrumentation.


Process Description:

Basket type coarse filters remove particulate matter from the feed stream to the SRP plant nominally down to 500 microns.

The feed stream is directed to a UF Membrane pre-treatment. The UF Membrane System treats the SRP feed water to remove the majority of particles greater than 0.02 µm. The process uses Dow hollow fibre membrane technology in ‘dead-end’ filtration mode without the need for continuous cross flow velocity. The filtrate quality is typically expected to have an SDI < 2.5 and will minimise the requirement for downstream cleaning of the SR membranes provided the water injection system is operated in accordance with the operating instructions. To facilitate the process, air scour blowers will be provided in order to produce scour air for flushing the UF units.

The fine filtered seawater is routed to the suction of the Sulphate Removal Unit Feed Pumps to boost the conditioned water to the required feed pressure for the SR trains.   The feed pressure to each SRU is controlled based on the permeate flow set point. The SRU produces 75% of the feed flow as low sulphate permeate Seawater.  The low sulphate SW from each SRU is merged and then directed to the deaerator. The remaining 25% of the feed flow ends up as high sulphate content reject seawater and is directed overboard.

The water then enters the Vacuum Deaerator to remove dissolved oxygen from the water. The deaerator tower mechanically removes oxygen down to 50ppb. Oxygen scavenger is dosed to the sump of the deaerator to chemically reduce the remaining oxygen to levels of 20ppb or less.

The deaerated, low sulphate injection water from the deaerator is routed to the water injection booster pumps. These pumps are provided to boost pressure to the desired pressure at the TP.

A small amount of the water from the discharge of the SRP Feed Pumps is directed to the SWRO system which comprises of SWRO pumps and SWRO trains. The SWRO pumps deliver the pressure and flow required for the Reverse osmosis membranes to convert 40% of the flow to low salinity wash water. The permeate from the SWRO package is routed to the TP at 5 barg.

Two membrane clean in Place (CIP) systems are supplied for offline cleaning of membranes. SRP and SWRO membranes have a common CIP package, whereas the UF system has a dedicated CIP system.

Chemical dosing packages are supplied as required for the water treatment technologies offered as part of the scope of supply.