Sulphate Removal System

Using nanofiltration, SRS technology removes sulphate as a small volume, high concentration stream and can reduce direct purge volumes by as much as 95%, or can eliminate the handling of toxic barium compounds and disposal of sulphate-containing solid waste.

The economics are usually attractive, typically offering 1-3 year recovery of capital investment, depending on plant conditions.

The SRS Nanofiltration Concept. Simple and Efficient

Patented by Aker Solutions, SRS technology is based on a selective filtration of brine through a nanofiltration membrane under high pressure. The nanofiltration membrane has charged groups that selectively reject multivalent anions such as SO4=, while allowing monovalent ionic species such as Cl- from the feed solution to pass through.

The nanofiltration membranes are supplied as compact cylindrical spiral wound membrane elements, which are installed in special high-pressure housings.

To optimize the lifetime and performance of the SRS membranes, depleted brine from the electrolyzers is cooled to 45º C, passed through activated carbon to remove residual chlorine, and filtered to remove fine particles before entering the SRS unit.

SRS Flow Pattern. Sulphate Lean Brine is Recycled to the Chloralkali Plant

The SRS feed brine is then pumped under high pressure through the SRS membranes, where sulphate is rejected, creating a sulphate-lean permeate stream for recycle back to the chloralkali plant.

The retained stream increases in sulphate concentration and decreases in volume as it is progressively filtered in a number of membrane stages, creating a sulphate-rich reject stream, which is disposed at a typical concentration of 100 g/L Na2SO4.

Aker Solutions delivers SRS technology as pre-assembled, skid-mounted process systems, including equipment, piping, instrumentation, and valves, all constructed in suitable materials for chloralkali brine conditions.

SRS Process.  SRS is Delivered as a Fully Assembled Process System.

The skid-mounted SRS modules are pre-assembled and ready for installation at site, requiring only the following simple steps:

• Mount the skid on concrete. 
• Connect the piping tie-ins.
• Expand the motor control centre to power the SRS high pressure pump motor
• Install motor and instrument cables.
• Program simple SRS interlocks in the plant control system.

FEATURES AND BENEFITS

• Aker Solutions, with over 40 years of chloralkali plant design and construction experience, offers commercially proven sulphate removal technology with lower operating costs and environmental benefits.
• Commercially Proven Technology. The first SRS was commissioned in September 1997, and about 50 other units have since been installed at chloralkali plants around the world.
• Fast Payback of Capital Investment. The capital cost of the SRS can be recovered within a short time through the elimination of barium, or through the recovery of salt, where a brine purge is employed to control sulphate.
• Low SRS Operating Costs. The main input to the SRS is electrical power for operation of the SRS feed pump.
• Easy to Install and Connect. A skid-mounted unit is provided complete with equipment, piping and instrumentation and requires a small number of piping, electrical, and instrument connections. This allows for fast and easy installation at site.
• Simple Operation and Maintenance. The system has simple operating and maintenance procedures and requires minimum attention. It runs on a continuous basis, handling only clean, non-hazardous, liquid streams.
• Low Effluent Volumes. The SRS generates a highly concentrated, low volume effluent stream with a concentration typically at 100 g/L of sodium sulphate, providing an environmental improvement to direct purge or barium treatment for sulphate control.
• High Salt Recovery. For plants that use a purge stream to control sulphate, the SRS can recover over 90% of the NaCl salt that would otherwise be wasted and reduce plant salt consumption by up to 20% if high sulphate salt is used.
• Potentially Lower Salt and Chemical Costs. After installing an SRS, the chloralkali plant may be able to switch to a less expensive salt supply (with a higher sulphate content), to use waste sulphuric acid instead of the hydrochloric acid for brine dechlorination.  These options can offer lower operating costs for the chloralkali plant.

References: About 50 SRS units have been sold worldwide. Please contact Aker Solutions for reference lists.