By James Chater

In the last few years, unexpectedly heavy rainfall triggered a downturn in the desalination in industry. This period is now in the rear mirror, drought is back (not that it ever went away), and the desalination industry is recovering. Building work is especially intensive in the Middle East, with Africa and Asia not far behind. These projects will provide a steady market for stainless steel (especially duplex grades), valves and pumps.

The seawater desalination plant at Carlsbad, California, built by IDE Technologies, Poseidon Water and NRG Energy. It will start supplying water to San Diego County in 2016.

The scramble for desalination is bullish for duplex

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“When the well runs dry…Those of us of a certain age who grew up in North America or Europe will remember a time when our tap water was unmetered. Those days are gone for ever. Our water bills are a continual reminder of the fact that we can no longer take our water supply for granted. And many populations have experienced a ruder awakening still, in the form of severe shortages over a prolonged period. Droughts have occurred in many areas of the United States, especially California. More recently, it has been Brazil’s turn. This is all the more surprising for a country that produces an estimated 12% of the world’s fresh water. Clearly, town planners did not see how Sao Paulo’s rapid population growth would impact demand, and a crisis is unfolding that will affect not only the water supply but also threatens to create an energy shortage, given the importance of hydroelectricity.

…we know the worth of water”Building desalination plants offer a viable solution to water shortages, provided the carbon emissions are kept low. The downside is that if the rains come back, the operators of desalination plants lose out. This has happened in Australia, Spain and South Africa, where there is now an overcapacity of plants. If desalination plants are a form of insurance, it is a costly one!

Outlook With that caveat said, the long-term prospects for desalination look good. The market is growing by about 9% a year. Doosan Heavy Industries and Construction has declared its optimism for the desalination sector after winning an order for a MED plant at Yanbu, Saudi Arabia.

Evaporator at the Yanbu desalination plant, Saudi Arabia.

The SWRO desalination plant at Sorek, Israel, was commissioned in 2013. It was built by IDE and Hutchison Water.

The Qingdao desalination plant. Photo: Abengoa.

ProjectsThe Middle East is in fact the main engine of growth in the desalination business; Asia and Africa are not far behind. Apart from the MED project at Yanbu, Saudi Arabia is also at work on a giant RO plant at Rabigh. Dow Chemical, GdF Suez, Hyflux, Hitachi, Veolia and Degrémont are pouring into the region to supply their expertise to governments in Saudi Arabia, Oman, Qatar, UAE and Iraq. Both MED and RO are being used, and solar power is playing a significant role. In Africa, governments are taking unprecedented steps to acquire desalination capacity. The continent’s largest plant, built by Hyflux, was completed in 2014 at Magtaa, Algeria. Almost at the same time, Ghana completed a plant near Accra. Other plants are planned in Ghana, Cape Verde, Tanzania and Tunisia. Morocco has asked Spain’s Abengoa to build a plant at Agadir and is seeking USD 27 billion in private investments to continue its building programme. China’s intractable climate (extremes of drought and flooding), combined with rapid urbanization and industrialization, has created a huge demand for water treatment, including desalination along its eastern seaboard. The country aims to produce 2.2 million m³/d of desalinated seawater by 2015, compared with 660,000 m³/d in 2011. In 2014 alone it increased capacity by 16%. India’s desalination market is growing even faster: 19% per year between 2014 and 2019. Current projects include a third plant at Chennai and two plants in the Ramanathapuram and Tuticorin districts.

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Energy inputIn view of the need to reduce emissions and ecological considerations, energy input is an important issue for desalination. The lower and cleaner this input is, the better. Another advantage of the greener technologies is that sun, wind and wave can be used to power small desalination units in remote areas more cost-effectively than grid-based energy. The persistence of “grey” technologies is epitomized by the recently completed Shuqaiq Steam Power Plant in Saudi Arabia, which is powered by oil-fired steam! Many of China’s proposed plants will be powered by coal, raising concerns about carbon emissions. At the greener end of the spectrum, solar energy is making significant progress. The Middle East abounds in solar desalination projects, most of which are

Industries served by desalinationSeveral industries make use of desalinated water. One important group is shale gas, oil sands and mining. This is why BP has recently bought shares in a Canadian water treatment company, Saltworks Technologies. BP is following in the footsteps of other companies, including Cenovus Energy, ConocoPhillips and Teck Resources. In 2014 it was reported that the water treatment market for hard-rock mining will grow 85% by 2019. Conventional oil and gas and steel are also steady customers of water treatment companies. Desalination will likely play a more important role in a number of industries. An Australian study issued by the Commonwealth Scientific and Industrial Research Organisation (CSIRO) has considered whether desalination is an attractive option for crop irrigation. Adding nutrients to the desalinated water could make it cost-effective. On ships, desalination is used to turn seawater into drinking water. Finally, and rather unexpectedly, desalination is used on golf courses. RO developer Desalitech Inc was asked to supply a water purification system using its Closed Circuit Desalination (CCD) system to the Kittansett Club golf course in Marion, Massachusetts, USA. The contract was awarded after it was found that seawater had entered into a freshwater well used for irrigation.

Using a MED seawater desalination solution, IDE has been delivering boiler feed water and potable water to India’s Gujarat oil refinery for the last 15 years.

Elsewhere in Asia, South Korea has completed its first desalination plant at a POSCO steel mill, and Pakistan has just inaugurated Asia’s largest RO plant.Of the various projects in the United States, one of the most ambitious is the RO plant at Carlsbad in San Diego County, California. The plant operator, Israel’s IDE Technologies, has selected Protec Arisawa and Dow Water & Process Solutions to provide the pressure vessels and membranes. Further south, Mexico has just announced plans to build six RO plants along its coast, and projects are planned in Chile, Peru and Argentina. In Europe, Cyprus has just inaugurated its sixth desalination plant, Jersey is proposing to extend its RO plant at La Rosière, Corbiere, while the UK’s Southern Water is considering a plant at Southampton.

at the demo or pilot phase. Abengoa, however, has broken new ground: it is building the world’s first large-scale solar-powered desalination plant in north-east Saudi Arabia.Desalination from wave and tidal energy is still in the development phase. Australia’s Carnegie Wave Energy is running a demonstration project using submerged buoys tethered to seabed pump units. In Europe, 4NRg is developing a prototype that will harness wave or tidal energy to create drinking water. Somewhere between “green” and “grey” is nuclear-powered desalination, being pursued by Russia’s Rosatom, which has assembled a group of experts to win customers for its desalination technologies.

TechnologyDesalination techniques range from membrane systems, of which reverse osmosis (RO) is the most important, to thermal systems such as Multistage Flash Distillation (MSF) and Multi-Effect Distillation (MED). Membrane systems are less energy-intensive than thermal systems, so RO is the technology of choice for most new Phase 3 of the Yanbu desalination plant in Saudi Arabia.

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plants. Nevertheless, the huge amounts of energy are required to push seawater through the membranes.Operators are forever seeking ways of reducing energy input still further, but the efficacy of some of these technologies is still unproven. Forward osmosis (FO) has been touted as a means to achieve zero-liquid discharge with low energy consumption, and a laboratory in Beijing is engaged on research. However, a group of researchers in the US has claimed that FO desalination of seawater is significantly less energy-efficient than RO. Similarly, pressure retarded osmosis (PRO), which exploits a salinity gradient between two water sources – typically using seawater as the draw solution and river water as feed solution – has been tried in Norway, but another US team has challenged its efficacy. LTTD (low-temperature distillation desalination) looks more promising. Building on thermal desalination technology, LTTD condenses water at low temperature and pressure, using “waste” heat recycled from various sources. The technique is being developed by Switzerland’s Watersolutions AG and is being researched at the University of Western Australia. Another promising piste is electrochemical desalination. First reported in 2013, this alternative to membrane systems consumes very little energy and requires no elaborate equipment, just a battery. Based on a system of microchannels and a bipolar electrode, the system exploits the voltage differential between two channels to separate ions to produce partially desalinated water.

MaterialsThe high-chloride, high-temperature conditions in desalination plants

pumps that are on standby, ready to take over in the event of failure. Therefore the materials must be adapted not only to operating conditions but also to standby conditions, which can include under-deposit corrosion, crevice corrosion and microbiologically influenced corrosion (MIC). As with other components of desalination plants, use of duplex stainless steel is increasing. Duplex can be found in the toughest applications, such as the source pump, the filter feed and booster pump, the high-pressure feed pump (duplex or super duplex) and the high-pressure booster pump. Material selection for valves follows similar criteria as for pumps, except that with valves the use of linings is possible. The materials need to be resistant to corrosion (especially pitting), fast flow and cavitation. In the severe environment of the membrane feed process, 300-series materials are inadequate, and even materials such as duplex 2205 and austenitic 904L are at risk of failure. Better is a 6%Mo alloy such as 254 SMO, but in recent years it has been found that super duplex (such as SAF 2507) is more cost-effective.

Sources and referenceswww.desalination.biz; “Materials for saline water, desalination and oilfield brine pumps”, 2nd edn, 1995, www.nickelinstitute.org; www.pennstainless.com/blog/2012/08/duplex-usage-in-desalination-plants; Ben Lee, “The unique requirements for valves in SRO applications”, Valve Magazine, 24/2 (spring 2012), 36-40 (www.valvemagazine-digital.com). Quotation in opening two headings is from Benjamin Franklin.

Did you know?The desalination plant at Magtaa, Algeria, is Africa’s largest, with a capacity for half a million cu metres per day. It was opened by Hyflux in November 2014.

Ghana opened its first desalination plant in February 2015. It is located in Accra suburb, Nungua, and will provide 66 million litres per day.

South Korea has completed construction of its first desalination plant, for Posco’s steel mill at the port of Gwangyang.

Asia’s largest RO plant began operation in Pakistan’s drought-ridden Sindh province.

necessitate the use of corrosion-resistant materials capable of withstanding the most severe conditions. This requirement is especially true of the intake side of the operation, where the saltwater is handled. After the desalination phase, milder austenitic grades such as 316 can be used. For the more saline conditions, 300-series grades have long proved inadequate, and it became customary to replace them with 6%Mo grades. After that, duplex stainless steels gained in popularity as they provided similar corrosion resistance at lower cost due to the lower percentage of alloying materials. In addition, duplex steels offered twice the strength of austenitics, allowing weight savings. Duplex grades have proved their worth in a number of applications, including evaporators, high-pressure piping and water processing components. Duplex 2205 was used for the first time at the Melittah plant in Libya in 2003, then at Skikda, Algeria, in 2004-5. After that, Outokumpu offered its DualDuplex™ Evaporator concept, which uses 2205 or the milder lean grades LDX 2101® and 2304, depending on the severity of the application. Other plants built according to this concept include the Taweelah B extension in Abu Dhabi, the Jebel Ali L plant in Dubai and the Ras Abu Fontas plant in Qatar. For high-pressure piping, super duplex SAF 2507 offers the same resistance to pitting and crevice corrosion as 254 SMO, but with twice the strength and at a far lower cost. This grade was used at the Singspring plant in Singapore, commissioned in 2005. Material selection for pumps is a complex issue. Most plants are equipped with pumps that are operational and

On 22 January 2013 the first intake of seawater took place at Perth’s second desalination plant at Binningup (Australia).