Client: Daewoo Shipbuilding & Marine Engineering Co. (DSME)

Process: Seawater Ultrafiltration and Sulphate Removal

Country: Angola

Contract Description: Supply of Seawater Ultra-filtration (UF) and Sulphate Removal (SRP) Packages

Contract Start Date: October 2010

Contract Completion Date: January 2012

SRP Capacity: 374,230 BPD (59,491 m3/day) 

UF Capacity: 391,288 BPD (62,203 m3/day)

SRP Seawater Recovery: 75% 

Seawater Characteristics: 35,990 (TDS) 

SRP Permeate Output: < 40mg/l sulphate

Project Description:

The Clov FPSO will be moored within the Cravo-Lirio-Orquidea-Violeta (CLOV) fields located offshore Angola within the northern part of Block 17 about 40km from Girassol at a water depth of approx. 1,290m. The Ultrafiltration (391,288 BPD) and Sulphate Removal (374,230 BPD) Packages will be installed on the FPSO topsides to provide the necessary seawater treatment for subsea well injection.

Project Scope:

The Ultrafiltration Package comprises of a single-lift UF membrane module with integral backwash system (2 x 100% high efficiency backwash pumps) and a separate UF backwash tank designed for installation on the FPSO. Six UF membrane racks are provided to allow for 1 rack on backwash and 1 spare which can be taken off-line for maintenance. The fine filtered seawater (0.01µm) from the UF system provides the feed for the Sulphate Removal Package. Ultrafiltration provides a significant weight/footprint reduction and improved water quality compared with conventional seawater filtration technology.

The Sulphate Removal Package comprises of an SRP membrane module, SRP/UF Clean-in-Place (CIP) skid, SRP HP Feed Pumps and piping manifold assemblies.

Process Description:

Pressurised seawater is supplied to the UF systemfrom upstream coarse filters. UF hollow fibre membranes, installed in housings, are arranged in multiple racks with back-flushing performed using treated water from the downstream UF Backwash Tank. In addition, provision for hypochlorite dosing is provided to facilitate clean in-place of the membrane arrays.

Filtered water from the UF Package flows to the SRP HP Pumps which provide the required feed pressure for the sulphate removal system. The SRP module consists of racks of nano-filtration membranes which remove sulphate ions from the feed water. The membranes are arranged in a single pass configuration comprising of two stages in order to achieve the required low sulphate product water. The concentrate from the 1ststage is sent to the 2ndstage for further treatment. The permeate water from the 1stand 2ndstages is routed to the downstream 'MINOX' Deaeration Package. The SRP system operates at 75% recovery i.e. 25% of the feed stream is rejected as concentrate by way of the Water Disposal Caisson.