The World Health Organization (WHO, Geneva, Switzerland) estimates that there are more than 1 billion people who lack fresh water. By midcentury, that number is expected to swell to 4 billion. That bad news is good news for composites: Almost 60% of the world’s population lives less than 60 km from a seacoast. Seawater desalination, therefore, is poised to become one of the main alternative freshwater resources in those regions. In fact, the market for products and services used to convert seawater into potable water was estimated to be about US$2 billion back in 2000. Market research firm The Freedonia Group (Cleveland, OH, US) predicts that the desalination market will expand to more than US$18 billion by 2020.
Filament wound glass/polyester composites have quietly found application in several stages of the most-used seawater reverse osmosis (SWRO) desalination technique. (To read more about composites in SWRO applications, click on “Composites slake the world's thirst,” under Editor’s picks,” at top right.)
SWRO plants around the world use many miles of corrosion-resistant fiberglass-reinforced polymer (FRP) low-pressure piping as a distribution network, primarily over land, to carry seawater from the ocean to the plant, to distribute the potable water that is produced, to carry the brine (salt and impurities) back to the ocean, and for internal plant treatment piping and energy-recovery devices. Fiber-reinforced plastic also forms storage tanks and piping used in desalination plants to contain sodium hypochlorite (NaOCl) used in chlorination of desalination process water, and for sulfuric acid — very difficult to store in metal but readily handled in fiberglass/epoxy vinyl ester tanks and piping at ambient temperatures and concentrations below 50%, says Thomas Johnson, corrosion industry manager for resin producer Ashland Performance Materials (Dublin, OH, US). The vessels that encase the key reverse osmosis (RO) membranes are predominately filament wound FRP.
Meanwhile, electric utilities, particularly those in weather-beaten and/or hard-to-access locations, are still overcoming their cautious approach to take advantage of fiberglass for power transmission towers, distribution poles and cross-arms, as well as the aluminum conductor cables they support. Composite-reinforced aluminum conductor (CRAC) cables, conductors in which the traditional steel strength members are replaced with a pultruded continuous-fiber core, are designed by developers to increase power-transmission efficiency by 200%, reduce cable weight, and mitigate the phenomenon of thermal sag (heat-related elongation of steel conductor cores) that is often the culprit in power outages. Because CRAC cabling weighs less than steel-cored cable, it was, for more than a decade, expected to be an attractive alternative for upgrading power lines. An increased number of cables can be hung from each existing tower, increasing power transmission capability without the huge expense of erecting new towers or obtaining additional rights of way. Progress, however, had been slow. But in the 2012-2014 time frame, these high-temperature, low-sag (HTLS) composite-cored conductors finally took some leaps.
A new market entry in 2014 was Celanese Corp. (Dallas, TX, US) and Southwire Co. LLC (Carrollton, GA, US), North America’s largest wire and cable producer, have introduced a new option for utility transmission lines: the C7 Overhead Conductor, which features a lightweight and high strength-to-weight, multi-element composite core of Celstran continuous fiber-reinforced thermoplastic rods (CFR-TPR), made by Celanese. The conductor cable reportedly nearly doubles the transmission capacity, yet exhibits less sag than a conventional aluminum conductor steel-reinforced (ACSR) cable of the same diameter.