It seems simple enough: Take the salt out of water so it’s drinkable.
But it’s far more complex than it appears at first glance. It’s also increasingly crucial in a world where freshwater resources are progressively strained by population growth, development, droughts, climate change and more. That’s why researchers and companies from the United States to Australia are fine-tuning a centuries-old concept that might be the future of quenching the world’s thirst.
“When it comes to increasing water supplies, you have four options: Increase your amount of reuse, increase storage, conserve it or turn to a new source,” says Tom Pankratz, a desalination consultant and current editor of the weekly trade publication “Water Desalination Report.” “And for many places around the world, the only new source is desalination.”
Desalination technology has been around for centuries. In the Middle East, people have long evaporated brackish groundwater or seawater, then condensed the vapor to produce salt-free water for drinking or, in some cases, for agricultural irrigation.
Over time the process has become more sophisticated. Most modern desalination facilities use reverse osmosis, in which water is pumped at high pressure through semipermeable membranes that remove salt and other minerals.
Worldwide about 300 million people get some freshwater from more than 17,000 desalination plants in 150 countries. Middle East countries have dominated that market out of necessity and energy availability, but with threats of freshwater shortages spreading around the world, others are rapidly joining their ranks. Industry capacity is growing about 8 percent per year, according to Randy Truby, comptroller and past president of the International Desalination Association, an industry group, with “bursts of activity” in places such as Australia and Singapore.
In the United States, a $1 billion plant is being built in Carlsbad, California, to provide about seven percent of the drinking water needs for the San Diego region. When it goes online in late 2015 it will be the biggest in North America, with a 50-million-gallon-per-day capacity. And California currently has about 16 desalination plant proposals in the works.
But desalination is expensive. A thousand gallons of freshwater from a desalination plant costs the average US consumer $2.50 to $5, Pankratz says, compared to $2 for conventional freshwater.
It’s also an energy hog: Desalination plants around the world consume more than 200 million kilowatt-hours each day, with energy costs an estimated 55 percent of plants’ total operation and maintenance costs. It takes most reverse osmosis plants about three to 10 kilowatt-hours of energy to produce one cubic meter of freshwater from seawater. Traditional drinking water treatment plants typically use well under 1 kWh per cubic meter.
And it can cause environmental problems, from displacing ocean-dwelling creatures to adversely altering the salt concentrations around them.
Research into a suite of seawater desalination improvements is underway to make the process cheaper and more environmentally friendly — including reducing dependence on fossil fuel–derived energy, which perpetuates the vicious cycle by contributing to climate change that contributes to freshwater shortages in the first place.
Most experts say that reverse osmosis is as efficient as it’s going to get. But some researchers are trying to squeeze more by improving the membranes used to separate salt from water.
Membranes currently used for desalination are mainly thin polyamide films rolled into a hollow tube through which the water wicks. One way to save energy is to increase the diameter of the membranes, which is directly correlated with how much freshwater they can make. Companies are increasingly moving from eight-inch to 16-inch diameter membranes, which have four times the active area.
“You can produce more water while reducing the footprint for the equipment,” says Harold Fravel Jr., executive director of the American Membrane Technology Association, an organization that advances the use of water purification systems.
A lot of membrane research is focused on nanomaterials — materials about 100,000 times smaller than the diameter of a human hair. MIT researchers reported in 2012 that a membrane made of a one-atom-thick sheet of carbon atoms called graphene could work just as well and requires less pressure to pump water through than polyamide, which is about a thousand times thicker. Less pressure means less energy to operate the system, and, therefore, lower energy bills.
Graphene is not only durable and incredibly thin, but, unlike polyamide, it’s not sensitive to water treatment compounds such as chlorine. In 2013, Lockheed Martin patented the Perforene membrane, which is one atom thick with holes small enough to trap salt and other minerals but that allow water to pass.
Another popular nanomaterial solution is carbon nanotubes, says Philip Davies, an Aston University researcher who specializes in energy efficient systems for water treatment. Carbon nanotubes are attractive for the same reasons as graphene — strong, durable material packed in a tiny package — and can absorb more than 400 percent of their weight in salt.
Membranes have to be swapped out, so carbon nanotubes’ durability and high absorption rate could reduce replacement frequency, saving time and money.
Membrane technology all “sounds sexy, but it’s not easy,” Pankratz says. “There are engineering challenges when making something so thin that still maintains integrity.”
Graphene and carbon nanotubes are decades away from widespread use, says Wendell Ela, a University of Arizona chemical and environmental engineering professor. “I do see them having an impact, but it’s a ways out.”
Truby said barriers to commercialization include engineering such small materials and making new membranes compatible with current plants and infrastructure.
“It’ll be key to upgrade systems without tearing [them] down and building a whole new plant,” he says.
Others are looking beyond reverse osmosis to another process known as forward osmosis. In forward osmosis, seawater is drawn into the system by a solution that has salts and gases, which creates a high osmotic pressure difference between the solutions. The solutions pass through a membrane together, leaving the salts behind.
Ela says forward osmosis will “probably be most efficient as a pretreatment and not as a stand-alone treatment at commercial seawater plants” because reverse osmosis performs better at large scale. As a pretreatment, forward osmosis can lengthen reverse osmosis membranes’ lifespan and promote overall system health by reducing the needed disinfectants and other pretreatment options.
The process should use less energy than reverse osmosis, Ela says, since it’s driven by thermodynamics. But last summer MIT scientists reported that forward osmosis for desalination might prove more energy intensive than reverse osmosis due to the high salt concentration in the solution resulting from the first step.
British company Modern Water operates the first commercial forward osmosis plant in Oman, in the Arabian Peninsula’s southeastern coast. At 26,000 gallons per day, the system has a much smaller capacity than most large-scale reverse osmosis systems. Company officials did not return requests for comments on the plant. However a company report noted that the plant had a 42 percent reduction in energy compared to reverse osmosis.
Heather Cooley, water program director with the Pacific Institute, a California-based sustainability research organization, says most forward osmosis technology is still in the research and development phase, and that commercial use is five to 10 years out.
Another approach to reducing the energy cost of desalination is RO-PRO, or reverse osmosis pressure retarded osmosis. RO-PRO works by passing an impaired freshwater source, such as wastewater, through a membrane into the highly saline solution leftover from reverse osmosis, which would normally be discharged to the ocean. The mixing of the two produces pressure and energy that is used to power a reverse osmosis pump.
Inspired by a system used by Statkraft, a Norway-based hydropower and renewable energy company, University of Southern California environmental engineering professor Amy Childress and colleagues are now piloting RO-PRO in California. Childress says “optimistic” estimates show RO-PRO can reduce the energy needed for reverse osmosis 30 percent. She notes that some unspecified companies have shown interest in their pilot.
Recapturing and Renewable Energy
Fravel says many plants are trying to recapture energy from within the process. Turbochargers, for example, take kinetic energy from the outgoing stream of concentrated saltwater and reapply it to the side of incoming seawater. “You might have 900 [pounds per square inch] on the feed side and the concentrate might be coming out at 700 psi. That’s a lot of energy in the concentrate stream,” he says.
Incorporating renewables into the energy input side of things is a particularly promising approach to enhancing desalination’s sustainability.Pretreating water before it goes to membranes can also save energy. “The better you can clean water before it goes into reverse osmosis, the better it runs,” Fravel says. Plants in Bahrain, Japan, Saudi Arabia and China are using pretreatment for a smoother reverse osmosis process.
Incorporating renewables into the energy input side of things is a particularly promising approach to enhancing desalination’s sustainability. Currently an estimated 1 percent of desalinated water comes from energy from renewable sources, mainly in small-scale facilities. But larger plants are starting to add renewables to their energy portfolio.
After years of struggling with drought, Australia brought six desalination plants online from 2006 to 2012, investing more than $10 billion. The plants all use some renewables for power, mostly through nearby wind farms that put energy into the grid, Pankratz says. And the Sydney Water desalination plant, which supplies about 15 percent of water to Australia’s most populous city, is powered by offsets from the 67-turbine Capital Wind Farm about 170 miles to the south.
Solar energy is attractive for many heavy desalination countries — particularly those in the Middle East and the Caribbean where sun is plentiful. In one of the more ambitious projects, the United Arab Emirates energy company Masdar announced in 2013 it’s working on the world’s largest solar powered desalination plant, capable of producing more than 22 million gallons per day, with a planned launch in 2020.
Plans to use seawater, of course, must consider the implications for sea life. A lot of desalination facilities use open ocean intakes; these are often screened, but the desalination process can still kill organisms during intake or inside the plant’s treatment phases, Cooley says. New subsurface intakes, which go beneath the sand to use it as a natural filter, could help alleviate this concern.
Also, there’s the problem of how to get rid of a lot of very briny water after desalination. Every two gallons a facility takes in means one gallon of drinkable water and one gallon of water that is about twice as salty as when it came in. Most plants discharge this back into the same body of water that serves as the intake source.
Ela says smaller plants, such as the forward osmosis plant in Oman, could be the future of desalination technology.The RO-PRO technology offers one way to reduce the salt concentration in the discharge, which can harm bottom-dwelling creatures. Another method gaining popularity is the use of diffusers, a series of nozzles that increase the volume of seawater mixing with the concentrate discharge preventing spots of high salt.
In one of the more novel recent studies addressing ocean discharge, Davies of Aston University heated up briny discharge with solar energy to convert magnesium chloride into magnesium oxide, which he calls “a good agent to absorb carbon dioxide.” The research is still is the nascent stages, but could have the dual environmental benefit of reducing discharge and removing CO2 from the ocean using solar power to zap the concentrate.
Ela says smaller plants, such as the forward osmosis plant in Oman, could be the future of desalination technology. A lot of the newer innovations could make economic sense on a smaller scale, and companies wouldn’t have to invest so much in infrastructure, he says.
“Instead of large plants, we might get down to 10,000 gallons per day desalination plants,” Ela says. “I see decentralization and small desalination plants serving small communities.”
This also would provide environmental benefits such as allowing renewable energy to play a larger role, since it’s much easier to power small plants with solar and wind than large ones, he says.
Pankratz says desalination will always be more expensive than treating freshwater. Still, innovations will help desalination become an increasingly workable option as the demand for freshwater grows in an increasingly thirsty world.
Those who believe that man-made greenhouse gases are responsible for global warming are also firm in the conviction that it was caused dominantly by CO2 emissions from the developed countries (inset). However, a little-known analysis from the United Nations Framework Convention on Climate Change (UNFCCC), concludes that greenhouse gas emissions from the developed countries in fact caused significantly less than half of the global warming through 2000. In this post I briefly review this analysis and its implications.
The analysis in question was performed in 2007 by the MATCH (Modelling and Assessment of Contributions to Climate Change) Group at the behest of the UNFCCC, the 1992 ageement that underpins the Kyoto and Paris Agreements. MATCH performed the analysis by compiling a data base of greenhouse gas emissions (CO2, methane and nitrous oxide) from various countries and regions, including emissions from wood-burning, deforestation and agriculture, and by running the emissions through climate models to see how much warming each country/region had generated. The results were summarized on this pie chart:
And a very interesting pie chart it is too. Assuming that the sum of the contributions from the USA, OECD Europe, Oceania (Australia and New Zealand), Japan and Canada represents the warming contribution of the developed countries we find that these countries were responsible for only 41% of the global temperature increase between 1890 and 2000. The remaining 59% was caused by emissions from Latin America, Africa, the Middle East and Asia less Japan, which with the exception of Singapore and arguably South Korea include all the world’s developing countries, along with the Former Soviet Union and East European countries, which at the time had nowhere near reached developed country income levels and mostly still haven’t.
The MATCH report broadly confirms this percentage split (note that the findings are “robust” and that “long-lived greenhouse gases” presumably do not include methane):
This paper finds that the relative contributions of different nations to global climate change— attributing only emissions of long-lived greenhouse gases—are robust, despite the varying model complexity and differences in calculated absolute changes. For the default calculations, the average calculated contributions to the global mean surface temperature increase in 2000 are about 40% from OECD90, 14% from Eastern Europe and Former Soviet Union, 24% from Asia and 22% from Africa, Latin America and the Middle East.
The OECD90 is a mix of 36 countries, dependences and islands that includes the USA, Canada and the Western European democracies plus one country that shouldn’t be there (Turkey). It does not include Australia, New Zealand and Japan. Adding the 5% contribution from these countries shown on the pie chart gives an approximate 45/55 developed/developing country split when methane emissions, most of which come from the developing countries, are excluded.
But that was the position in 2000. What has happened since then? Data on total greenhouse gas emissions by country and region are not readily available so we have to look at CO2 emissions. Figure 1 shows BP’s estimates of annual CO2 emissions between 1965 and 2015, taken from the 2016 Statistical Review, for the developed countries, China and the other developing countries. The estimates do not include CO2 emissions from wood burning and deforestation and also do not include methane and nitrous oxide, so they will underestimate the contribution of developing countries to total greenhouse gas emissions:
Figure 1: CO2 emissions from the developed countries, China and the other developing countries, 1965-2015. According to BP they “reflect only those through consumption of oil, gas and coal for combustion related activities” and “do not allow for any carbon that is sequestered, for other sources of carbon emissions, or for emissions of other greenhouse gases”.
Developed country CO2 emissions decreased marginally between 2000 and 2015 while developing country CO2 emissions, driven largely by China, increased by 80%. The developed countries accounted for slightly over half of the world’s CO2 emissions in 2000 but less than a third in 2015. It’s impossible to make a firm estimate but it’s reasonable to suppose on the basis of these results that if the MATCH group were to update its results to 2015 it would find that the developed countries have caused less than 40% of the global warming to date and the developing countries more than 60%.
Another notable feature of Figure 1 is that it shows no sign of any appreciable carbon leakage from the developed countries to China or the other developing countries. China’s explosive emissions growth began in 2002 but developed country emissions continued to grow through 2005 and did not begin to decrease until the global recession of 2008-9 (which cut annual global CO2 emissions by about 2 billion tonnes below what they would otherwise have been, a number roughly equal to the combined annual emissions of Germany, France, Italy, Spain and the UK. This is more proof, if any were needed after the breakup of the Soviet Union in the early 1990s, that economic collapse is the best way to cut emissions.) And China can hardly claim that it was unaware of the potential impacts of its actions on global temperatures. Its emissions began to skyrocket in the year it ratified the Kyoto Protocol:
Figure 2: China’s CO2 emissions, 1965-2015
And now China is regarded as a world leader in the fight against climate change. Amazing how short human memories are.
So where does this leave us? I venture to suggest that much of what has so far been agreed at climate conferences has been a result of the guilt complex suffered by the developed country delegates, who believing that they caused global warming felt compelled to take the lead in fixing it. (Kyoto, where only the developed countries committed to anything resembling meaningful emissions cuts while everyone else got a free ride, is an example.) Yet here we have data from the UNFCCC – which started the blame game – disputing this conclusion. One wonders what might have changed if the results of the MATCH study had been widely publicized, which for obvious reasons they weren’t.
And there is of course another potential contributor to global warming that lets both the developed and the developing nations off the hook – the forces of nature, about which we can do little except react.
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Current market conditions seem to be adding to its popularity, perhaps because wet compression allows operators to instantly respond to demands for more power. Mee Industries recently built seven wet compression systems for GE 7FA turbines in Florida and we are currently building four systems MHI 501F machines for a plant in Mexico. OEMs are also starting to embrace the technology.
Our friend Jose Pontes, a bi-monthly CleanTechnica contributor, recently posted an article detailing electric bus sales in China during 2016 over at the EV Sales blog. The figures allow those of us living elsewhere in the world to get more than a bit envious about China’s progress (those of us who don’t like breathing the…
FEBRUARY 3, 2017
By Donn Dears
The only potential solution for the problems caused by wind and solar generated electricity is storage.
But are there limits to storage? Is it possible to provide sufficient storage to allow the closing of a large number of fossil fuel power plants?
The CAISO Duck Curve defines the potential problems if wind and solar are to provide 80% of the grid’s electricity. See, Wind and Solar Inflict Pain.
It’s not possible to know the exact amount of storage that would be required to allow enough fossil fuel power plants to be shut down to cut CO2 emissions from power generation by 80%.
Without the ability to shut down these fossil fuel power plants, it would require consumers to pay a capacity charge to reimburse the utilities for keeping these plants operational, or, alternatively, allow the utilities to go bankrupt and then be nationalized by the government.
While it’s not possible to know precisely how much storage is needed to replace the fossil fuel power generation capacity that must be shut down, a reasonable estimate is that approximately 400,000 MW of storage, with sufficient operational use in hours, is required to replace the electricity that’s lost with the closure of fossil fuel power plants.
This estimate is derived by calculating the amount of coal-fired and natural gas power plants that must be closed to achieve an 80% reduction in CO2 emissions. An 80% reduction in CO2 emissions from fossil fuel power plants requires shutting down 441,000 MW of coal-fired and natural gas power plants.
Unless there is adequate storage of electricity, the fossil fuel power plants must be kept operational, and be ready to go online when the sun stops shining and the wind stops blowing.
Is it possible to have 400,000 MW of storage? Or anything close to that amount of storage?
Pumped storage and Compressed Air Storage (CAES) can store large amounts of electricity, but there are insufficient locations around the United States to accommodate the approximately 400,000 MW of storage needed.
Only two CAES facilities have been built thus far. One, at Huntorf Germany, in 1978, the second at McIntosh, Alabama, in 1991. Huntorf is rated 321 MW, McIntosh is rated 110 MW. A third CAES facility is proposed for the Intermountain Power Generation site in Utah, which is to be rated around 300 MW.
Note that these amounts of storage using CAES are minuscule when compared with the amount of storage needed.
There currently is 20,000 MW of pumped storage in the United States, with the potential for an additional 31,000 MW. While substantial, it still falls far short of the storage capacity needed to eliminate a large portion of fossil fuel generating capacity.
Other Storage Alternatives
Batteries and other possible storage mediums lack the necessary size, and have other additional limitations.
Batteries, for example, have relatively short lives and would have to be replaced periodically, which adds to their cost as a storage option.
Storage, using batteries, costs at least $2,000,000 per MW. A recent trial by Pacific Gas & Electric of battery storage cost more than twice this amount.
It’s virtually impossible to build sufficient storage capacity in the United States to allow for the closure of large amounts of fossil fuel power plants.
By using wind and solar, we are not only faced with the higher cost of electricity from these sources, but also having to pay for retaining nearly all of our existing fossil fuel power plants.
Reposted from Power For USA by Donn Dears.