Client: MODEC Offshore Production Systems

Process: Sulphate Removal

Country: Offshore Angola - Block 31

Contract Description: Seawater Treatment System - Modules 15A & 15B

Contract Date: January 2009

Contract Completion Date: February 2010

Capacity: 200,000 BPD (31,800 m3/day)

Sea Water Conversion: 75%

Sea Water Feed Quality: 35,938 mg/l (TDS)

Product Water Output Quality: 40 mg/l sulphate



Project Description:

The Project is for the design, supply of a water injection plant sized for 200,000 BPD (31,800 m3/day) of low sulphate water for the PSVM FPSO, which will operate in the Block 31 Field, ultra deepwater offshore Angola.A Wash Water RO System is also provided, sized for 20,000 BPD (3,180 m3/day).

Project Scope

The Project scope consists of a Seawater Treatment Plant in two off single lift modules arrangement comprising: Electro-Chlorination Unit, Seawater Coarse Strainers, Dual Media Fine Filtration, Upstream Vacuum Deaerator Package, HP Feed Pumps, Guard Cartridge Filters, Sulphate Removal Membrane System, Wash Water Membrane System, Common Chemical Cleaning System, Piping, Valves and Instrumentation, Foam Fire Fighting System and water injection plant Controls co-ordination with main SCADA system.

Process Description:

Coarse filtration is provided by a set of automatic backwashable coarse strainers rated at 80µm.An electro-chlorination unit provides hypochlorite for disinfection of the water injection system. Fine filtration is then achieved by a set of dual media fine filters, complete with air scour, followed by a set of guard cartridge filters to provide fine filtration down to 5µm prior to the membrane trains. The set of fine filters supplies feed water for three (3) SRP trains and one (1) SWRO train (in two banks).

The conditioned water is routed to a vacuum deaerator package, boosted to the required feed pressure and then forwarded to the Sulphate removal trains. Each membrane train is fitted with pressure vessels containing SR90-440i nanofiltration elements.A recovery of 75% is achieved by a 2:1 brine staged configuration. Brine reject from the process is discharged overboard, while the low Sulphate permeate is forwarded onwards to the water injection pumps (provided by others) for injection to the wells at the required pressure. A dedicated clean in place (CIP) package, consisting of cleaning tank, heater, pump and cartridge filter vessel is provided for membrane cleaning purposes. A SWRO package plant is also provided to supply process wash water for the vessel.