The most commonly used construction material for desalination plants is steel, including carbon steel as well as stainless steel. However, the growing need for fresh water is putting new and greater pressure on desalination performance. Key industry requirements include a need for larger, easier-to-install water plants, with longer life-times and lower maintenance requirements. With a more complex process and an increased use of processing chemicals comes the need for greater chemical resistance, as well as corrosion resistance.
Composite materials
Composite materials are able to replace the existing material in desalination applications. A good and best known example is the use of glassfibre reinforced plastic (GRP) pipes and fittings. GRP offers a number of key benefits when compared to traditional materials. For instance, in a large diameter filtration tank, the use of GRP offers the following advantages:
• cost savings on installation and maintenance
• lower cost of ownership
• smooth inner liner: lower friction for lower operational (energy)
• 4 x lighter than steel
• pipe lengths of up to 12 m (all diameters)
• less complexity: fewer joints present fewer opportunities for leakage
• long, trouble-free lifetime of 50 years
• totally corrosion free
A recent study, which compared a GRP pipe system with a concrete pipe system in a specific application, demonstrated that the concrete solution required more than four times the number of joints, increasing both complexity and the risk of leakage.
GRP has been proven to be particularly suitable for the production of large diameter filtration tanks and high pressure applications such as after pump section pipelines. As chemicals used to clean the installations are very corrosive for metals, GRP’s corrosion resistance is a key benefit. Plant owners will also recognize that this will lead to a significant reduction in maintenance costs as well as increase the life of the installation.
Barcelona desalination plant
The ATLL (Aigües Ter Llobregat) reverse osmosis (RO) desalination plant in Barcelona, Spain, produces water for urban consumption and is one of the largest seawater desalination plants in Europe with a capacity of 200,000 m³ (200 million litres) per day.
Spainish company, Protecciones Plásticas (Protesa) was responsible for the manufacturing, supply and erection of the pipes and fittings in GRP, corresponding to the intermediate and low pressure circuits of the Llobregat desalination plant. Protesa selected DSM Composite Resin’s Atlac resins for the piping and fitting parts of the intake and pre-treatment lines, designed and engineered by UTE (Degrémont- Suez-Drace), for high pressure salt removal of the RO process.
The scope of Protesa for this project included the pipelines and fittings of the seawater pumping section, sand filters, brine line, raw water pumping, water product line, micro filtration system lines and the suction to high pressure pumps in the pre-treatment process of the plant. Practically all the overhead pipes provided in the plant were fabricated and installed by Protesa by means of chemically welded joints. The total project covers about 15 kms of different pipes: collecting pipes, impulsion pipes and process pipes with diameters ranging from 0.1 m to 2.0 m.
Atlac resins
Atlac resins were selected specifically to provide greater resistance against corrosion by both the existing marine environment and the water treatment process, which involves adding chemical treatment products such as sodium hypochlorite, ferric chloride, sodium bisulphate and/or sulphuric acid during the normal operation of the desalination plant. Atlac was able to meet all the technical requirements, combined with easy process-ability and a low peak exotherm. Moreover, the resin offers drinking water contact approval, which was a key Protesa requirement for this particular application.
The GRP pipes and fittings, fabricated using a crossed filament winding process, provide support and coverage to the process lines in the seawater desalination plant. The mechanical specific properties of the Atlac 580, chosen by Protesa for this project, are competitive with other classic materials such as steel, yet they offer corrosion proof qualities, unique and inherent to high performance vinyl ester materials. In addition, they significantly lower the direct and indirect costs of the installation.
Conclusion
In a changing world, where fresh water is rapidly becoming a vital commodity, it is imperative that we do everything we can to minimize loss, whilst maximizing output and efficiency.
Engineers looking for effective solutions will increasingly find that thanks to its material properties, GRP is the material of choice. Innovative technologies such as RO and dedicated materials such as DSM’s Atlac grades, designed specifically for the desalination industry, are making a vital contribution, ensuring that we prepare for tomorrow’s challenges today.