Growing concern about water usage by U.S. electric power generation is being prompted by a number of factors, including projected increases in power demand due to population growth, competing uses for water, and recent drought conditions in various parts of the country. Our overview presents diverse perspectives from industry experts about current and future challenges of balancing power generation needs with declining water availability.
In our modern world, water and energy production are inextricably connected. The treatment and delivery of water for human consumption and industrial purposes require large amounts of electricity. Conversely, many of the power generation facilities that produce electricity—such as coal-fired, solar thermal, and nuclear power plants—use large amounts of water.
In most power plants, water is taken from nearby water bodies—including oceans, rivers, and lakes—and then returned to the water source via a once-through (open loop) cooling water system. The use of water intake cooling systems promotes maximum capacity and efficiency for a given thermal or nuclear power plant technology. The cooler intake water enables power plants to operate with lower vacuum pressures in the steam turbine condensers, which, in turn, maximizes the power extracted by the low-pressure section of the steam turbines and provides the highest possible fuel efficiency.
POWER has written extensively on the need to develop more efficient cooling water technologies. Examples (all available at http://www.powermag.com) include “Appraising Our Future Cooling Water Options” (June 2010), “Determining Carbon Capture and Sequestration’s Water Demands” (March 2010), “Conserve Water by Improving Cooling Tower Efficiency” (January 2009), “New Coal Plant Technologies Will Demand More Water” (April 2008), and “Costlier, Scarcer Supplies Dictate Making Thermal Plants Less Thirsty” (January 2008).
In order to tackle this complicated topic from a variety of viewpoints, in February, POWER interviewed industry leaders from an energy research institute, a leading national energy laboratory, a U.S. water and energy technology manufacturer, and a large consulting firm. From regulations to technical innovations, our experts offer insights into trends concerning the interdependence of water and power.
Water Availability Issues in Power Production
“Water availability already is an issue across the U.S., affecting nearly every region,” said Kent Zammit, senior program manager of the Environment–Water and Ecosystems Division at the Electric Power Research Institute (EPRI). “In addition to over-allocation, climate variability (including droughts) is causing regional shortages, as we have seen in Texas, across the Southeast, and other areas.”
As existing power plants using a once-through cooling process are retired, they will likely be replaced by plants using closed cycle cooling because of new fish protection regulations, he explained. For wet cooling systems (cooling towers), it is preferable to use freshwater, but some installations are now using degraded water sources. Others are adopting dry cooling or hybrid cooling systems, but each of these has drawbacks, such as higher capital costs, lower unit efficiency, higher parasitic load (due to fan horsepower), and additional maintenance.
Barbara Carney is the chemical engineer/project manager of the Existing Plants Division, Strategic Center for Coal at the U.S. Department of Energy’s National Energy Technology Center, also known as the National Energy Technology Laboratory (NETL). She pointed out that increased concern for water usage comes from, among other things, the addition of carbon capture technology on power plants that requires increased water usage and additional power generation capacity due to the power loss associated with carbon capture. She also noted that requirements of the Clean Water Act 316(b) tend to result in decreased water withdrawals (from, for example, once-through cooling) but increased consumption (for example, for evaporation from cooling towers). Her center has initiated research in three main areas: advanced cooling technologies, water reuse and recovery, and use of nontraditional sources of process and cooling water.
According to Heiner Markhoff, president and CEO of water and process technologies for GE Power & Water, the current and near-term challenges related to cooling requirements of thermal power generation are the amount of freshwater that is taken into a cooling system and the volume and salinity of water that is eventually discharged back into the original waterway.
The problem related to salinity was also mentioned by William Heins, general manager of thermal evaporative technology in the water and process technologies division of GE Power & Water. “In a power plant, as you cycle up the cooling water, it gets increasingly concentrated with salt. If the cooling tower blowdown is discharged back into the river, then you are increasing the salinity, or the salt content, of the river. Therefore, if you can reduce or eliminate the water that you are discharging back to the river, you have succeeded in lowering the amount of salt that reenters the river, thereby improving the water quality,” he said.
Bill Kemp, vice president of Black & Veatch’s management consulting division, focused on the impact of water scarcity on the power generation sector. Increasing shortfalls in water supplies could result in numerous new restrictions or limitations on both thermal and hydroelectric capacity. “We could see new or additional restrictions on the siting of thermal plants, reduced hydroelectric generation, and limited withdrawals from rivers during the summer,” Kemp said. “In periods of more serious drought, the physical ability of major coal or nuclear power plants to obtain sufficient cooling water could be threatened. Generation operators are realizing this situation is not so far-fetched.”
Water Supply Competitors
Agriculture is by far the largest consumer of water, if one takes into account that a large portion of the water used by power plants is for once-through cooling that is returned to its source water body, although at a slightly elevated temperature, according to Zammit. Other water-intensive sectors include municipalities and industrial manufacturing. U.S. Geological Survey data shows national averages (Figures 1 and 2), but sector use can vary dramatically from watershed to watershed.
|1. Domestic and industrial water withdrawals. A large portion of the water used by power plants is for once-through cooling, where cooling water is returned to the source water body at a slightly elevated temperature. Courtesy: EPRI|
|2. Conspicuous consumption. Agricultural irrigation is by far the largest consumer of freshwater in the U.S. In recent years, however, the agricultural sector has improved irrigation practices in order to cut down on water use. Courtesy: EPRI|
There are many ways to address water shortages as they occur, Zammit pointed out. Each sector has options, and some sectors have already begun to address water use. For instance, agricultural irrigation practices have improved dramatically. Municipalities are now using treated sewage effluent for irrigation and groundwater recharge. Power companies are adopting water conservation technologies and using degraded water sources such as effluent and mine water.
“In addition to the electric power generation sector in North America, two of the fastest growing sectors that GE focuses on for wastewater reuse and recovery are the unconventional gas industry and the heavy oil recovery industry,” Markhoff said.
The unconventional natural gas industry and the heavy oil recovery industry are rapidly growing and are also related to the power industry in that either natural gas or oil is being recovered. Both industries are fairly big water users and are focusing on recovering and reusing those waters to minimize the amount of freshwater used and amount of water that is discharged back into the waterways (Figure 3).
|3. Recycling produced water. Grizzly Oil Sands selected GE’s water evaporation technology for its Algar Lake project near Fort McMurray, Alberta, Canada. By using GE’s water evaporation process, the company expects to recycle up to 97% of the produced water from the bitumen production project. Courtesy: General Electric|
“The unconventional gas industry recovers different forms of gas,” Heins said. “For instance, in the Marcellus Shale in Pennsylvania, there are fracking operations where rock is fractured underground to allow gas to come up and be recovered. This unconventional gas recovery uses a fair amount of water.”
When the natural gas is captured from these wells, the water used to fracture the rock flows back with the gas. Heins explained. GE has developed technologies—both mobile technologies and fixed plants that treat and reuse the wastewater—that have a number of impacts (Figure 4). One benefit is using a lot less freshwater; another is the need to dispose of a lot less wastewater. In the past, wastewater would be taken by truck over long distances to be disposed of. “For example, in some instances, water would have to be trucked from Pennsylvania to Ohio to be disposed of via deep well injection,” Heins said. “Therefore, by recovering and reusing a lot more of that water, we minimize not only the amount of water that is discharged, but also the trucking of the water.”
|4. Have evaporator, will travel. The GE mobile evaporator is a 50-gallons-per-minute, truck-mounted, mechanical vapor recompression system. It is designed to enable on-site frack water recycling, reducing the volume of wastewater and freshwater that needs to be hauled to and from natural gas production sites. The mobile evaporator will enable natural gas producers to significantly decrease their transportation and water disposal costs. Courtesy: General Electric|
Almost every sector that produces a product or uses energy also requires water in one form or another, said Ralph Eberts, executive vice president of Black & Veatch’s global water business. “Today, we see a growing number of manufacturers and global brands investigating how their respective operations can become water-neutral. The recent winner of the Stockholm Water Prize for Industry was Nestle. This is a company that has realized that water represents a significant cost and a significant limitation to its operations and as a company has become more conscientious in its use of water,” Eberts said.
Discharge Constraints Due to New Regulations
The U.S. Environmental Protection Agency (EPA) is in the process of revising effluent guidelines for steam electric plants under the Clean Water Act, Zammit explained. The focus to date has been on flue gas desulfurization system wastewater.
“In addition, stricter water quality criteria and new Total Maximum Daily Load standards are providing new challenges for the removal of trace metals and other constituents from wastewater,” Zammit said.
Some regulators are also writing in stricter limits for National Pollution Discharge Elimination System permits around thermal discharge for once-through cooling. Zammit emphasized that “all of these rules are creating more constraints on the operation of existing and new power plants and also creating difficulties with the retrofit of required air quality control equipment in cases where it impacts wastewater quality.”
“Many power plants, especially in the southwestern United States, have turned to zero–liquid discharge technology, which means you are recovering and reusing 100% of the wastewater and discharging nothing,” Heins said. “With the zero–liquid discharge process, the wastewater is recovered and reused, usually with an evaporation or a distillation process.”
Regulations that limit or eliminate the use of water intake cooling systems are likely to require power plant owners to install less-effective cooling systems or shut down their plants, Heins said. Assuming the power plant’s remaining usable life and other economic and physical space factors support the investment in a new cooling system, the total power plant capacity and efficiency will be reduced. Heins asserted that “this reduced capacity and efficiency would require more fuel to be consumed to generate an equivalent amount of electricity, resulting in increased generation costs, and in the case of fossil generation, increased emissions of greenhouse gases and other pollutants.”
Markhoff added that with a broad program of eliminating water intake cooling systems, the resulting reduction of total plant capacities would require a corresponding investment in new plant capacity.
“Making predictions regarding the type and magnitude of this ‘replacement’ plant capacity would not be prudent,” Markhoff said. “However, most plants that use water intake cooling systems operate at high capacity factors, implying that intermittent sources such as renewables may not meet grid operation requirements, and higher–capacity factor generation may be more suitable.”
Andy Byers, associate vice president of Black & Veatch’s global energy business, pointed out that individual states are setting more and more stringent water quality standards for streams and lakes, which often create challenges for thermal power plants that discharge effluents to these water bodies. Because many plant processes may result in not only adding, but also concentrating, pollutants already present in the water supply before returning them to the regulated water body, power plant effluents often cannot meet the new water quality limits without further treatment.
“In some cases, the additional treatment to meet these in-stream standards may be so challenging or costly that plants may chose to install a zero–liquid discharge system where most all of the wastewater is reused, consumed, and/or evaporated on-site,” Byers said. “While this serves to maintain the stream’s water quality, it also reduces its flow, and therefore may be counterproductive to addressing other water scarcity issues.”
The EPA is expected to finalize its proposed new cooling water intake rulemaking for existing facilities by July 2012, Byers explained. Because the cooling water intake flow applicability threshold was dropped to 2 million gallons per day, this rule as proposed will regulate not only power plants with once-through cooling but also some with closed cycle cooling tower systems. Depending upon the final requirements, many power plants may be able to achieve compliance by upgrading their intake design and operations to minimize impacts to fish and aquatic species.
“The final regulations, however, may force some plants to convert from once-through cooling to closed cycle cooling towers, which, in addition to being costly, will also result in a reduction of plant efficiency and power output,” Byers said.
Before the EPA released its proposed rule in March 2011, many analysts who had assumed the rule would require all power plants with once-through cooling systems to convert to closed loop cooling towers forecasted that the associated costs would force a significant number of plants to shut down entirely. Byers pointed out that “while the rule as currently proposed may still (alone or in conjunction with other EPA regulatory drivers) induce some plants to retire, the proposed rule’s requirements provide more options for continued operation, and in any event, the five-year phase-in period for compliance, would not force those decisions until closer to the end of the current decade.”
Trends in the Power Sector’s Water Usage
Zammit explained that water resources vary “dramatically from watershed to watershed, depending on current uses, allocation (over-allocation), changes in land use and runoff, overdraw of groundwater aquifers, and the aforementioned climate changes.”
Although EPRI has water management risk analysis tools that can be used to examine sector water requirements, sustainability goals, and conservation options for a given watershed, it is difficult to predict what impacts will be related to each sector. For instance, much of the new power generation in the arid Southwest has been natural gas combined cycle units with air cooling, which reduces utility water use per net megawatt-hour. Zammit added that “this trend is expected to continue with lower natural gas prices. Also, wind and solar photovoltaic are playing roles in reducing power sector water use. Municipal demands are growing, but so is effluent reuse” (Figures 5 and 6).
|5. Cutting water use in power generation. New technological developments in power generation are helping to reduce water use. For example, much of the new power generation in the arid Southwest has been from natural gas combined cycle units with air cooling, which reduces utility water use per net MWh. Courtesy: EPRI|
|6. A range of water footprints. Water use varies widely among the different power plant types. For example, nuclear power generation is the most water-intensive, while solar photovoltaic and wind energy use no water to generate electricity. Analysis assumes closed cycle wet cooling towers are used. Courtesy: EPRI|
Developing Generation Technologies That Conserve Water
NETL’s advanced cooling technology projects are attempting to increase the efficiency of cooling processes, including using less water and making dry cooling less power intensive. Carney pointed out that “water recovery from power plants has been most successful in condensing the water from the flue gas and not only capturing this water but also capturing some of the energy lost with the water and putting it back into the power cycle.”
Traditionally, power plants are located next to large rivers, and water is withdrawn as needed for cooling, Carney said. Newer sources of water are reclaimed wastewater, underground mine pool water, produced water from oil and natural gas production, and other sources that may need treatment prior to usage. Many projects have inventoried these sources, tested the waters, investigated impediments to use, and explored treatment methods to increase usage.
“Alternative water sources continue to replace freshwater usage for cooling for power plants, and this is probably the biggest trend in water management in the power sector,” Carney said. “Although no specific projects can be cited, it is likely that many of the NETL projects on alternative sources have assisted in this implementation.”
For example, Nalco Co., working with NETL, recently completed testing of a prototype electrodeionization (EDI)/scale inhibitor that would allow more alternative water sources to be used. Carney pointed out that “although the EDI process is not commercialized yet, they did have improvements to scale inhibitors for calcite, gypsum, and silica that will be used at power plants.”
Another successful technology, not yet used commercially, is a flue gas drying process that was demonstrated at the pilot scale by Lehigh University, Carney said. The condensing heat exchangers dealt with the acid environment in the flue gas, and calculations show that they are cost-effective when the recovered heat is used to preheat boiler feedwater. The recovered water could be used to replace 10% to 33% of required cooling water. The process may also be used to dry flue gas for carbon capture applications.
Another recent NETL project Carney mentioned is the prototype Air2Air Water Conservation Cooling Tower that was constructed by SPX Cooling Technologies at the San Juan Generating Station in New Mexico (Figure 7). It was tested from 2008 through 2009 and provided cooling for 35 MW of power production.
|7. A cool way to conserve water. The prototype Air2Air Water Conservation Cooling Tower that was constructed by SPX Cooling Technologies at the San Juan Generating Station in New Mexico in collaboration with the National Energy Technology Laboratory is on the left. It is larger and has no plume, as compared with the existing cooling towers on the right. It was tested from 2008 to 2009 and provided cooling for 35 MW of power production. The ambient temperature was 27F with a relative humidity of 65% when this photograph was taken. Source: National Energy Technology Laboratory|
The tower saved 18.5% of the water lost in cooling at this location with no degradation of thermal performance on the condenser and no freezing problems. Carney said, “depending on climate, this technology could save 10% to 25% of the water lost to evaporation from cooling towers.”
The commercial product arising from this work is called the ClearSky Plume Abatement Tower; it can be viewed at http://www.spxclearsky.com. Carney pointed out that, although the technology is currently marketed as plume abatement, some customers are interested in it due to the water savings.
Although not a part of this prototype tower, it is possible to collect the water that is condensed, which is very clean and nearly pure, resulting in an inexpensive, low-energy water treatment method, Carney explained. With the technology’s current configuration, the water just flows back into the tower and replaces withdrawals and decreases the amount of salty blowdown water that needs to be discharged. Additional improvements to Air2Air Technology will be finished in 2012.
“Currently, NETL is receiving no funding for power plant water issues,” Carney said. “Funding for thermoelectric power plant cooling/water management was discontinued in 2009, and the remaining projects will wrap up shortly. The research focus for the Existing Plants Program has shifted to carbon capture. There is some research now in the carbon sequestration program for water usage.”
New Initiatives to Promote Sustainable Water Usage
Recently, the U.S. government made some moves nationally to deal with water scarcity, and state governments also have taken action, especially in arid areas and those that are most heavily affected by freshwater shortages, Markhoff said. Areas such as the Southwest, including California, currently have very serious demands on their water supplies and have already taken measures to require zero liquid discharge at power plants. He emphasized: “As the dynamics change throughout the rest of the country in the coming years, however, we expect eventual changes in policy and more stringent requirements to appear in other states as well.”
Technology solutions exist to overcome challenges related to water scarcity, according to Kemp. The key challenge is economics and understanding what solution will best balance water, economics, and environmental factors for a specific plant in a specific location. Options include air cooling technology, similar to what was deployed by Pacific Gas & Electric for its Gateway Generating Station in Antioch, Calif. The Gateway plant’s dry cooling technology uses 97% less water and produces 96% less discharge than a conventional water cooling system and avoids the use of river water. Kemp added that hybrid systems that use a combination of dry and wet cooling are another technology option.
“There is no free lunch, however,” Kemp said. “The cooling technologies that use less water are more expensive to install, reduce the performance efficiency of the generating technology, and end up increasing fuel consumption and greenhouse gas emissions per MWh generated.”
An area of potential growth in the U.S. is the use of recycled or reclaimed water. Kemp pointed out that “this is used in other parts of the world, particularly Singapore, with tremendous success. The Calpine power generation station in Mankato, Minn. is also a good example of the benefits of using recycled water for cooling thermal power stations.”
Eberts also has some strong opinions about what future steps need to be taken in the U.S. to deal with increasing challenges related to water availability. “First and foremost, we must increase education and awareness about the true value of water,” he said. “We need to start making positive steps toward cost recovery for water treatment and water transmission infrastructure and not be reliant on subsidies that are reliant on public will. We need to continue to invest in our water infrastructure. History shows us that it is better to plan, maintain, and invest, rather than wait until a crisis to act. Delaying and deferring could result in paying two to three times more for infrastructure than what it would have cost under a reasonable and planned schedule.”
Eberts said that state and federal governments need to recognize the value of water and the need for investment in our country’s buried infrastructure. He added that “state-to-state regulations for water varies widely—we need more consistency for water use when siting power plants.”
Likewise, Byers pointed out that from an environmental regulatory standpoint, the nation as a whole would benefit from a more coordinated and comprehensive national policy that balances the goals of improving water quality and stemming water scarcity. Where technology may advance one goal, economics may drive us in another direction. The demand for energy and water will only continue to grow with increasing population, and the interdependency of energy and water must be recognized in managing the future of the U.S.
“The extent to which we can ensure sufficient water remains available for appropriate use in efficient energy production will be essential to securing reliable delivery of electricity, which in turn is critical to our continued global economic prospects and individual well-being,” Byers said.
Long-Term Water Management Challenges
Given the complexity of the water/energy interdependence issue, it’s not surprising that our experts had a variety of views about how water scarcity problems will be addressed over the next 25 years.
For example, Kemp pointed out that utility leaders from across the country rated water supply as the top environmental concern in Black & Veatch’s “2011 Electric Utility Industry Survey” (http://www.bv.com/ electricutilitytrends). Water effluent was also among the top five environmental concerns. Kemp emphasized that survey respondents viewed water management as having the greatest potential to significantly impact the electric power industry in the near term. The industry’s concerns about water supplies have risen considerably over the past five years during which the annual survey has been administered.
“Water supply, water effluent, and water management will all be primary areas of concern and risk mitigation for the foreseeable future for power and natural gas producers,” Kemp said.
In contrast, other experts we spoke with were optimistic that over the next 25 years, through innovative technologies and sensible governmental policies, the power industry will be more successful in protecting our nation’s water resources.
For example, Markhoff commented that in the long term, the importance of minimizing freshwater make-up and the importance of eliminating salty water or saline water discharge back to those waterways will become significantly more important, even in areas that do not have significant regulation today.
“In the next 25 years, you will see an increase in those trends and regulations to minimize the amount of discharge and minimize the amount of freshwater make-up,” Markhoff said. “In the short term, it will be a slow progression. However, the areas that are the most affected, like the southwest United States, already have a lot of those regulations in place, and in the near term you will see those trends continue.”
In a similar vein, Zammit emphasized that “we are seeing this as a serious short-term problem in some watersheds and isolated regions of the country. But, as mentioned before, as power generation is retired and replaced with less-water-intensive generation technologies, we should see the electric power industry decrease its water intensity over the long term.”
In order to meet our future electricity and water needs here in the U.S., we have to begin planning now and determine what investments we need to make in upgrading our nation’s generation technologies and water treatment infrastructure. Our public and private entities must work together to successfully create reliable, cost-effective, and sustainable sources of energy and water that help promote growth in the U.S economy.
— Angela Neville, JD, is POWER’s senior editor.