Desalination Expands, but Energy Challenges Remain

Fearing widespread water scarcity, companies and governments around the world are scoping out desalination technologies to convert seawater to potable water. That's a rocky path that involves lots of energy and high costs-and potentially high rewards.

At the ballyhooed Paris climate conference last December, a little-noticed event occurred that could lead to important developments for electric generators. At the Paris meeting, some 80 signatories-including national governments, energy and water industries, research groups, universities, and nongovernmental organizations-launched the Global Clean Water Desalination Alliance. The group's focus, which it calls "H₂O minus CO₂," is on how to reduce carbon dioxide emissions from the energy-intensive process of turning seawater into a potable product.

A press release from Paris announcing the organization's founding noted that access to clean water is "already a major challenge for as much as one-quarter of the world's population," and that some forecasts are "predicting that by 2030, 47% of the global population will face water scarcity." It's not that the world is short of water-which covers some 70% of the planet's surface and is entirely renewable-but that most of it is seawater.

Turning to the Sea

Just a couple of weeks after the Paris meeting, a $1 billion reverse-osmosis (RO) desalination plant in Carlsbad, Calif., went into service next door to NRG Energy's 950-MW gas-fired Encina power plant, nearly 25 years after its conception during an early 1990s California drought (Figure 1). Construction began in late 2012, amid the most recent of many Golden State droughts.

1. California streaming. The Claude "Bud" Lewis Carlsbad Desalination Plant, which went into operation north of San Diego in December 2015, can supply up to 10% of the San Diego area's water. It operates on the same site as NRG's soon-to-retire Encina power plant. While it's the largest desalination plant in the Western Hemisphere, Carlsbad is dwarfed by plants in the Middle East. Courtesy: Poseidon Water

The Carlsbad project is the largest desalination plant in the Western Hemisphere and is designed to produce up to 50 million gallons (190,000 m³) of water per day, supplying the San Diego County Water Authority with up to 10% of its water needs. Poseidon Water of Boston, which develops large-scale seawater RO plants co-located with coastal power plants, owns the facility. Poseidon's CEO is Carlos Riva, a veteran of the U.S. independent power industry. IDE Americas, a subsidiary of Israel's IDE Technologies, provided the Carlsbad design, and J.F. Shea Co. and Kiewit Corp. built it. The water authority has a contract to buy up to 56,000 acre-feet of water per year from Poseidon under a 30-year water-purchase agreement.

Until Encina shuts down in 2017, the Carlsbad plant will take up to 100 million gallons per day of once-through cooling water from the power plant, filtering it to reduce particulates before sending it through RO (shown in the header photo). After half of the intake is converted into pure water, the briny residue will go into the power plant's discharge channel and back to the sea. After Encina shuts down, the desalination plant will continue using the plant intake to draw directly from the ocean.

Some local environmental groups opposed the project. They are also campaigning against another Poseidon plant under development up the coast in Huntington Beach, near the planned 450-MW repowered gas-fired AES Huntington Beach Power Plant, scheduled to operate in 2019. According to Orange County Coastkeeper, "If the Poseidon desalination plant is built on the Huntington Beach floodplains, the project will require structural protection barriers such as seawalls, groins, breakwaters and other coastal armoring structures, triggering an additional suite of costs and impacts to our state and coast."

Mixed Record

California's desalination interest comes naturally. The state is suffering through a severe four-year drought, while its entire western boundary is the briny Pacific Ocean. Given that ample evidence of far worse droughts exists in the geologic history of the region, California has long seen desalination as a way to provide drinkable water, if only as a backstop to normal supplies. Santa Barbara last summer-in the midst of the current drought-approved spending $55 million to bring a mothballed desalination plant back into service. That plant was built in the early 1990s, about the same time planning began on the Carlsbad plant.

But Santa Barbara closed its plant in 1992, when that drought abated. According to the Los Angeles Times, the facility was never used beyond testing. Mayor Helene Schneider told the newspaper last year, "Desalination has been a last resort. The way the drought has continued these last four years, we are really getting at that last resort."

In late 2015 and early 2016-thanks in large part to the current El Nino climate event-California and the West Coast have been deluged with rain at lower elevations and heavy snows in the mountains, a key to water availability in the dry summer months. Whether the interest in desalination will continue in the face of the El Nino effects is an open question, but experts note that much more rain and snow would be necessary to get the state back to normal conditions.

Elsewhere in the U.S., desalination plans have also encountered opposition. Last December, the New York Public Service Commission (PSC) rejected a plan by France's Suez Environment water giant, which acquired local water company United Water New York, for a desalination plant in Rockland County that would draw from the Hudson River. United Water provides most of the water for Rockland.

In 2006, the PSC ordered United Water to come up with a way to produce more drinkable water without disrupting the river. The company offered a $150 million plan for a desalination plant using brackish water not far from the Indian Point nuclear power plant.

Local environmental groups formed the Rockland Water Coalition to fight the project. They argued that the need was not as dire as regulators said in 2006, was too expensive, used too much energy, and could impact endangered river species.

In nixing the Suez project late last year, PSC Chairman Audrey Zibelman said, "The record demonstrates that circumstances have changed since the commission first asked the company to develop a new long-term water supply in 2006." Hudson Riverkeeper's Paul Gallay, opposing the project, said, "The Public Service Commission's ruling confirms what Rockland residents and Riverkeeper supporters have known for years: Desalination is flat-out unnecessary and wasteful, given options for increased water conservation and better management of existing supplies."

Power-Intense Process

The major challenge for desalination is that all current technologies require a lot of energy (see sidebar). According to Raphael Semiat of Technion, the Israel Institute of Technology, it takes 3.5 kWh to purify a cubic meter of seawater using the most energy-efficient technology: 1.3 kWh to pump seawater to the plant and 2.2 kWh for the RO process. That's why big desalination plants almost always have their own dedicated power plants-and most of those plants are powered by fossil fuels.

Desalination Technologies Separating salts and other impurities from H2O is a well-understood process with a long history. Desalination of seawater, brackish water, and recycled water is widely practiced around the world in a variety of ways. Generally, two types of separation technologies-thermal and membrane-dominate, each with about half of the global market (for a more detailed discussion, see "Adding Desalination to Solar Hybrid and Fossil Plants" in the May 2010 issue online at powermag.com). Thermal Desalination Thermal technologies use heat to vaporize seawater, condensing the steam as pure water. The three approaches used with thermal desalination are multi-stage flash distillation (MFD), multi-effect distillation (MED), and vapor compression distillation (VCD). In MFD, feedwater is heated under high pressure and then flows as a liquid into a successive series of chambers with progressively lower pressures. Because each stage is lower in pressure than the one before, the liquid water continues to flash to steam, which is collected by heat exchange tubing running through each stage. MFD technology dates to the 1950s. MFD plants dominate the thermal sector, and many have been built in the Middle East, where water is scarce but energy resources are cheap and plentiful. MED was first used in the late 1950s and early 1960s. In MED plants, a series of evaporator vessels are held at progressively lower temperatures and pressures. Because the boiling point of water decreases as pressure decreases, the vapor boiled off in one vessel can be used to heat the next, and only the first vessel requires an external source of heat. Three MED plants with combined capacity of 3.5 million gallons (13,250 m3) per day operate in the U.S. Virgin Islands, serving as the principal water supply. VCD uses heat from compression of vapor, rather than an external heat source. Typically, a mechanical compressor is used, often powered by a diesel engine. These desalination units are generally small and can be used at hotels, resorts, and in industrial applications. Membrane Desalination Membrane technologies separate salts from water using exceptionally fine screens or membranes. The two categories are electrodialysis (ED) and reverse osmosis (RO). ED, introduced in the 1960s, is voltage-driven and generally used for treating brackish water. Most salts dissolved in water are negatively or positively charged ions. The technology uses electrodes of opposite charge to attract the ions, with membranes to permit selective passage of either positively charged cations or negatively charged anions. An ED stack consists of several hundred such cells that the feedwater is pumped through. RO is the latest technology, commercialized in the 1970s and based on Israeli research and development. It is the most widely used desalination technology in the U.S. This process reverses normal osmosis-in which a solvent moves from zones of low solute concentration to zones of high concentration-by applying pressure to the zone of high concentration. This causes the pure solvent-in this case, purified water-to flow continuously to the low-concentration side of the membrane. RO works for both seawater and brackish water, and removes all impurities, not just salt. ED and RO can be used together, with the ED stack treating both the RO feedwater and its brine stream.

That's where the alliance announced in Paris-led by Masdar, the United Arab Emirates' (UAE's) renewable energy company, and the International Desalination Association-comes in. The alliance said its "goal is to seek solutions that will substantially reduce the projected increase in CO₂ emissions from the desalination process, as global demand for drinking water continues to grow." The group said it is seeking "a decrease in emissions from 50 [million tons of CO₂] up to as much as 270 [million tons] per year by 2040."

Government-owned Masdar last November began development on a pilot seawater desalination plant using solar energy, which the company says it will run at small scale for 15 months. "These technologies have never been used on a utility scale anywhere in the world," said Masdar. Just days after the announcement at the Paris COP21 meeting, the UAE and China signed a deal to work together to combine Masdar's desalination technology with low-cost solar photovoltaic technology developed in China.

There are currently about 15,000 desalination plants operating around the world, with the largest in Saudi Arabia, the UAE, and Israel. The Saudi Shoaiba complex produces over 232 million gallons (880,000 m³) daily, while the Al Jubail complex produces over 211 million gallons (800,000 m³) per day. The big Saudi plants use a variety of desalination technologies.

Israel's Sorek plant (Figure 2) is the largest RO plant in the world, with a daily output of 165 million gallons (624,000 m³). The developer, IDE Technologies, is a key player in the Carlsbad, Calif., project and also has projects under way or under development in Israel, China, India, Australia, Chile, Italy, and Germany, using a variety of desalination technologies.

2. Standing tall. Israel's Sorek facility is the largest reverse osmosis (RO)-based desalination plant in the world. Unlike at most other plants, the RO membranes at Sorek are mounted vertically to reduce footprint and support requirements. Courtesy: IDE Technologies

Desalination's Long History

Turning seawater into drinking water is nothing new. Greek sailors boiled seawater to get potable water. Romans used clay to filter brackish water to drink and boiled seawater in ceramic urns, although they may have been as interested in retrieving the salt as the water.

In 1791, then-U.S. Secretary of State Thomas Jefferson offered a technical paper describing a simple way to distill seawater for sailors to drink. It was printed on the back of shipboard papers to ensure a source of freshwater in an emergency.

Australia's Victoria state government recounts "wood-fired stills at the Coolgardie goldfields 100 years ago, solar ponds at Coober Pedy and electrodialysis for the first plant at Yulara."

When steam ships began to ply the high seas in the 19th and 20th centuries, seawater conversion technologies allowed sailors to create freshwater as needed, freeing holds to store more lucrative cargos. According to a paper by Rensselaer Polytechnic Institute, "By the Second World War, hundreds of mobile desalination units were in use and all major vessels had them." The technology was known in those days as "desalting."

A feared "water crisis" after World War II pushed the U.S. Congress in 1952 to pass the "Saline Water Act," establishing an Office of Saline Water in the Interior Department. A 1958 article in the New York Times proclaimed hyperbolically, "In the future-not so long as time is measured-Americans will be taking the 'water cure' on a mass scale. That does not, however, presage a large drop in the intake of hard liquor. Rather, it means that many communities, industrial plants and other organizations probably will be using fresh water distilled from the sea."

The Interior Department's desalination office went through several reorganizations over the years. It funded research and development (R&D) of desalination technologies and left behind an archive of articles and papers. It no longer exists as a separate government bureaucracy.

One of the first demonstration plants built with federal funds was in Freeport, Texas, in 1961. Dow Chemical erected a million-gallon-per-day plant using thermal technology at a cost of $1.2 million. It produced water for Dow operations and the city of Freeport. President John Kennedy officially started the plant by pressing a button from his office in the White House, an event that mirrored President Dwight Eisenhower kicking off the Shippingport nuclear plant in Pennsylvania in 1957 from the Oval Office. Then-Vice President Lyndon Johnson attended the Freeport event in Texas, his home state.

Dedicating the plant, Kennedy said, "No water resources program is of greater long-range importance than our efforts to convert water from the world's greatest and cheapest natural resources-our oceans-into water fit for our homes and industry. Such a breakthrough would end bitter struggles between neighbors, states and nations."

Today, Interior's Bureau of Reclamation runs a modest desalination and water purification research program, funding basic research and pilot desalination projects on a cost-shared basis. Last July, the bureau selected nine projects for $1.49 million in federal support. According to the agency, the grants will support $13.5 million in overall research spending on desalination. The Department of Energy (DOE) also funds desalination R&D.

What's Ahead for Desalination?

Massachusetts Institute of Technology (MIT) researchers are testing a new approach to desalination that relies neither on energy-intense thermal distillation nor RO membrane technology, which can clog and decrease the efficiency of the process. According to a university press release, "Instead, the system uses an electrically-driven shockwave within a stream of flowing water, which pushes salty water to one side of the flow and fresh water to the other, allowing easy separation of the two streams."

MIT professor Martin Bazant says the approach is "a fundamentally new and different separation system." It is a continuous process that Bazant claims may be relatively easy to scale up. According to MIT, one of the uses for the technology could be to clean up the large amounts of wastewater generated by hydraulic fracking for gas and oil.

More conventionally, researchers at Egypt's Alexandria University are looking at a combination of low-tech filtration and evaporation, which could lower desalination power requirements. In a paper in the September edition of the journal Water Science & Technology, the researchers describe a filtration technique known as "pervaporation," which passes saline water through a fairly simple membrane to remove large molecules and then vaporizes the filtered water. The technology is now used in wastewater treatment to separate organic solvents from the water stream.

According to Ahmed El-Shafei, one of the paper's authors, "Using pervaporation eliminates the need for electricity that is used in classic desalination processes, thus cutting costs significantly." The Alexandria University team is working on a pilot unit to test the concept at a larger scale.

General Electric, meanwhile, is examining an old approach to desalination-freezing water to separate salts from pure ice. Conventional freezing technology has proved uncompetitive because of its high energy requirements. With a grant from the DOE, GE engineers are using small, 3-D-printed turbines to compress air, salt, and water (Figure 3). According to a GE press release, the mixture flows "through a hyper-cooling loop that freezes seawater." GE's Vitali Lissianski said, "Freezing seawater to treat it is nothing new, but the way we are doing it is very different. We're tapping into our wealth of technical knowledge in turbo-machinery to devise a cost-effective solution."

3. Turbine desalination? General Electric (GE) is researching a new approach to desalination that involves compressing air and saltwater using small 3-D-printed turbines and freezing the compressed mixture. Once frozen, the salt can be separated from the ice. Courtesy: GE

Renewable energy may also play a role in advanced desalination technologies. In addition to the collaboration between the UAE's Masdar and Chinese photovoltaic firms, San Francisco's WaterFX firm is developing a solar-thermal desalination technology in California's Panoche Water and Drainage District in the Central Valley. The aim is to produce agricultural irrigation water from wastewater, drainage water, runoff, saline groundwater, and industrial process water. The project uses parabolic solar collectors to heat mineral oil that then flows to a heat pump, and the heat pump distills the feedwater.

Nuclear, meanwhile, remains an oft-discussed but little-used energy source for desalination. According to the World Nuclear Association, most of the few nuclear plants worldwide with operational desalination facilities use their output for plant make-up rather than supplying potable water. Though some attention is being devoted toward small nuclear as an energy source (see "Small Modular Reactors Speaking in Foreign Tongues" in the January 2015 issue), high costs are likely to continue to deter meaningful deployment of nuclear-powered desalination plants.

Forecasting whether any of these new technologies will survive the test of the market is impossible. Nor is it certain that the current surge in interest in desalination will continue. But many-from around the world-are betting substantial sums that it will. a-

-Kennedy Maize is a frequent POWER contributor.

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