Seawater flows to parallel operated Sulphate Removal Units, to achieve the specified sulphate level.
SRP trains each consist of two stages of pressure vessels, each vessel contains nano filtration membrane elements in series. The brine reject from the 1st stage pressure vessels is used as feed to the 2nd stage pressure vessels. This staging configuration is required to obtain 75% product water recovery.
The nanofiltration membranes are specifically designed to remove sulphate ions from seawater used for water injection. Whilst removing approximately 99% of the divalent sulphate ions a large percentage of the monovalent ions pass through the membrane thus maintaining salinity in the injected water.
When the desired feed water quality is achieved (mainly in terms of Redox potential) and seawater is available from the pre-treatment system, the SRP Feed pumps will start up. The control system will then ensure that conversion and plant output is achieved and maintained.
The flow downstream of the feed pump system is controlled to maintain a constant pre-set nanofiltration permeate flow from each SR Unit. A control valve maintains the reject brine flow. These valves modulate automatically to maintain product water output at the selected conversion of 75%.