[ Duplex / Desalination ]
[ Duplex / Desalination ]
Valve selection for desalination plants: a technical perspective focused on Africa
This paper presents valve selection as a cost-effective lever to boost reliability and lower lifecycle cost in seawater reverse osmosis plants. Recognizing the impact of varying seawater chemistry and temperatures on valve materials, recommendations are provided that emphasize region-specific material selection and align with a total cost of ownership analysis.
By Abdellah El Khobzi and Ömer Yildiz, Starvalve – Kocaeli / Türkiye
Introduction Globally, desalination provides over 100 million cubic meters of potable water daily, and the International Desalination Association( IDA) estimates that Africa’ s installed capacity will grow by 10 – 15 % annually by 2030. However, high energy consumption, brine disposal, and corrosion under tropical marine environments remain significant obstacles. Therefore, optimizing valve selection is both an economic and environmental necessity for the sustainable expansion of desalination infrastructure. Africa is among the regions facing the most severe water scarcity. The United Nations projects that by 2030, more than 40 % of the continent’ s population will live in water-stressed areas. To address this challenge, coastal nations such as Egypt, Morocco, South Africa, and Namibia are increasingly investing in seawater desalination. Desalination plants are complex systems requiring reliable components for optimal operation. Among these, valves play a crucial role in flow control, pressure management, and isolation. Improper valve selection can lead to premature failure, costly maintenance, and reduced plant efficiency. A typical seawater reverse osmosis( SWRO) system is designed to handle a feed salinity of about 35,000 parts per million( ppm) of total dissolved solids( TDS). The process separates this stream into two outputs: high-quality freshwater with a TDS of less than 500 ppm and a concentrated brine stream( reject) with a salinity between 55,000 and 70,000 ppm. The overall efficiency, known as the system recovery rate, generally ranges from 35 % to 45 %, while the process can accommodate feedwater temperatures from 15 ° C to 35 ° C.
Valve requirements in a SWRO A standard SWRO process involves four main stages: seawater intake, pre-treatment, high-pressure reverse osmosis, and post-treatment with brine discharge. Typical pressures range from 1 – 3 bar at the intake, 3 – 6 bar during pretreatment, up to 80 bar in the reverse osmosis( RO) stage, and less than 10 bar during post-treatment. Each stage has distinct valve and materials requirements: Intake & pre-treatment: In this initial stage, valves must handle raw seawater, which is often abrasive due to sand and silt. Materials like aluminum-bronze( AB) or valves with erosion-resistant linings are highly suitable here. High-pressure reverse osmosis: This is the core of the plant, where operating pressures can reach up to 80 bar
Super duplex valves can deliver a significantly lower TCO over the lifetime of a desalination plant. Image shows a Starvalve super duplex butterfly valve
( 1,160 psi) to overcome osmotic pressure. These operating pressures require leak-free, high-pressure valves. Super duplex stainless steel is the preferred material for this critical application due to the material’ s strength and corrosion resistance. Post-treatment & brine discharge: This final stage involves processing two quite different flows: firstly, the treated water( with low corrosivity) and secondly a