21 August 2008 00:00 [Source: ICB]
Desalination is a growth market for chemical companies supplying water additives and membranes
HOW MANY desalination plants would you guess there are around the world? 100? 1,000? 10,000? In fact, there are more than 13,000, and the number is rising.
The figures reflect growing water scarcity worldwide. Driven by higher living standards, irrigated agriculture and industrialization, global water consumption has increased sixfold over the past century, even though the population has only doubled.
With the situation tending toward crisis, desalination has become a growth industry, one in which chemical manufacturers play a key role.
Saudi Arabia, which received its first desalination plant in 1907, today accounts for 24% of global capacity, and more than half the global total is in the Middle East or North Africa, according to the International Desalination Association (IDA).
In the US, which holds 16%, the second-largest share of global capacity, large desalination plants have been installed in California, Texas and Florida. Spain has become a major destination for new capacity, and the Caribbean is also a growth region. A giant plant in Perth, Australia, is powered in part by wind.
The greatest growth, however, is in China, where per capita water availability is only one-fourth of the global average. Here, desalination capacity is increasing at 17-18% per year, according to Paul Turgeon, president and chief operating officer of US-based BWA Water Additives. He puts growth, globally, at 15%.
Two classes of desalination dominate: thermal and membrane. Thermal desalination is an energy-intensive process in which sea or brackish water is distilled to separate it from the soluble salts. Because of their energy requirements, thermal plants are located where energy is relatively inexpensive - mainly in the Middle East or where they can use the waste heat generated by processes such as manufacturing.
According to a 2008 study from the National Research Council (NRC), based in Washington D.C, US, thermal processes such as multistage flash, multiple-effect distillation and mechanical vapor compression account for 43% of global desalination.
Membrane processes operate by selectively restricting or permitting the passage of ions. The most widely employed membrane process is reverse osmosis (RO), which employs pressure to force water through a membrane that relies on surface charge to restrict the passage of dissolved salts.
Other membrane processes are electrodialysis, electrodialysis reversal and nanofiltration (NF). The energy requirements are lower than thermal processes, but the advantage must be balanced with the cost of the membranes and their maintenance. Altogether, membrane processes are responsible for 56% of global desalination, says the NRC.
Less than 1% of capacity operates by alternative technologies such as ion exchange.
ADDING TO SUBTRACT
Chemical products are used at all stages of desalination in both thermal and membrane applications, says Turgeon.
"In pretreatment, chemicals can be used to remove suspended solids, and to eliminate or prevent biological growth," he explains. "For posttreatment, chemicals are used to protect the distribution systems for the desalinated water."
The company's products for the desalination market, Belgard and Flocon, include antiscalants, microbiological control agents and membrane cleaners, as well as a software tool called Flodose and technical support.
Demand for water additives used in desalination is growing at the same rate as desalination capacity, says Turgeon. He estimates the market is worth $350m (€238m)/year. The contribution of antiscalants is $250m, with $150m going to membrane plants and $100m to thermal plants.
He puts BWA's share of the thermal market at 60%. "We have a strong position, and we see that continuing because we have a very strong product range, and we have some new product developments that we'll be introducing. We see ourselves improving our share."
BWA's new products are antiscalants that can be used at higher operating temperatures with undiminished performance.
"On the thermal side, the focus is on building plants that operate much more efficiently, and they can do that if they run at higher temperatures," Turgeon explains. "One of the limiting factors, however, is controlling scale." Some salts, such as calcium sulfate, are actually less soluble at higher temperatures, he points out. "You need a very robust antiscalant to deal with those more difficult conditions. This reduces the need to add new capacity, in the case of retrofits, and also reduces the environmental footprint of a plant by producing more water per unit of energy used."
BWA's portion of the membrane side, where service companies play an important role, is about 10%, says Turgeon. "If you adjust for back-integrated service companies, we are the market leader."
COSTS ARE DROPPING
Chemical companies play a fundamental role in developing and manufacturing the membranes that make processes such as RO possible. Leaders in this market are US-based Dow Water Solutions and Hydranautics, a subsidiary of Japanese diversified materials manufacturer Nitto Denko.
About 450,000 membranes are dedicated to desalination, according to Paige Gourley, manager, proposals and service contracts, at Hydranautics. Indeed, sales total $175m200m per year, or roughly one-third of the entire membrane market, says Gourley.
RO membranes are complex. The most widespread design is the thin-film composite, in which a non-woven support web is coated with a microporous support layer that is itself coated with a barrier layer, explains Ian Lomax, manager, large projects at Dow Water Solutions.
"In our membranes, we generally use a polyester for the nonwoven web, onto which we coat a microporous polysulfone layer. Two monomers are then reacted directly on the surface of the polysulfone layer to form a polyamide layer. The characteristics of the polyamide layer can be tailored to have the flux and salt rejection required for various applications," Lomax says.
Other polymers used by manufacturers are polyether sulfones, polyacrylonitrile, cellulose acetate and cellulose triacetate. Some RO membranes are also produced as hollow fine fibers using fiber-spinning technology.
The most important performance characteristics of RO membranes are flux (rate of water flow) and salt rejection. Tolerance to pH and the ability to withstand high pressures are other important features.
"In recent years, membrane chemists have made great strides in reducing the pressure required to force water through the membrane and in improving the amount of salt rejected by the membrane," observes Rich Franks, manager, RO/NF applications and technical support Americas, at Hydranautics.
Manufacturers have been able to increase the active area - and hence the flow rate and salt rejection - by using thinner membrane sheets and fitting more of them into the RO element.
"In the early 1990s, the technology produced an element with a flow rate of 4,000 gallons per day [gpd] and a salt rejection of 99.4%," says Lomax.
"Dow's current technology allows a flow rate of 9,000 gpd or more with a salt rejection of 99.75%. These improvements have helped lower capital and operating costs as well, since a second RO pass is seldom needed. Energy requirements have also lessened due to the reduction in pressure requirements achieved by the more efficient membranes," Lomax adds
Dow has developed 16inch (40cm) membranes with a surface area more than four times that of the standard 8inch variety. The new 16inch RO modules lower the capital cost of desalination by 10-20%, says Lomax.
Membranes typically last for three to five years. Biofouling, scaling, plugging and degradation reduce their useful life, while pretreatment of the water and proper maintenance and operation extend it. The design and structural integrity of the membrane itself also plays a role.
"Desalination continues to make stridesin affordability," maintains Gourley. She points to work that Hydranautics has completed through the Affordable Desalination Collaboration (ADC).
"Current ADC testing, conducted at the US Navy's Seawater Desalination Test Facility in Port Hueneme [California], achieved two milestones: the development of a data set benchmarking seawater RO (SWRO) performance for localized applications, and demonstration of SWRO's affordability in comparison with traditional sources of potable water," says Gourley.
"During the nine-week test phase, Hydranautics SWC5 [RO membrane element] provided superior salt rejection, while requiring lower than average net driving pressure," she adds.
At optimized operating conditions and using an energy recovery device, the SWC5 membrane can produce potable-quality permeate at an energy consumption as low as 1.7 kW/h/m3, Gourley says.
Recent Dow innovations for efficiency include the ILEC system of interlocking end caps. "ILEC eliminates the need for interconnectors, which have been a weak spot in the performance of RO systems," says Lomax. "ILEC allows interlocking the adjacent elements in the system with no possibility of leakage and deterioration of the permeate or fresh water in the central core."
Both Dow Water Solutions and Nitto Denko-Hydranautics have been investing to keep up with demand for membranes. In June, Dow announced an $88m expansion at its Edina, Minnesota, site that will increase the company's membrane output by 25%.
Earlier this year, Nitto Denko began construction of a $60m unit for manufacturing RO membranes in Shiga, Japan. When it is completed in March 2009, it will increase the site's membrane capacity by 60%. In total, expansions planned for the next five years will triple the company's production capacity, says Gourley.
"Desalination is a thriving global concern," she adds.
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