Electrical generation plants are among the heaviest water users industrially, second only to agriculture. As public concern for water scarcity continues to grow, power plants can expect to see new regulations targeting their use of water, as well as increasing costs for sourcing and discharging water. To stay viable in the long term, electrical generation facilities will need to stay on top of new processes and technologies for conserving water use in the coming years.
So “how can you reduce water used in electrical generation?” In this article, we’ll discuss how water is used by electrical generation facilities and explore some common strategies for cutting water use.
Water use varies by cooling system
Whether fueled by natural gas, coal, nuclear, or other means, thermal power plants use steam turbines to produce electricity. This water-intensive process involves heating water to form steam, which is then passed through a steam turbine and converted to electricity by a generator. Once the steam passes through the turbine, it is cooled, and the collected water is heated again to continue the electrical generation cycle. Cooling accounts for the greatest use of water in electrical generation operations, but the amount of water used depends upon the type of cooling system used, as outlined below.
Once-through cooling systems
Once-through cooling systems are often cheapest method of cooling, but they can be the heaviest in water use since water is drawn, fed through a condenser unit, and discharged instead of cycling through and being reused. Because large water volumes are needed for this process, once-through cooling is not usually viable unless a plant is located close to its water source. Even then, once-through cooling has significant environmental impact since the used cooling water is returned at a higher temperature and may contain contaminants such as biocides or other materials. Water scarcity and environmental concerns are therefore driving stricter regulation of once-through cooling, forcing many plants to look for ways to conserve water use without impacting profitability.
Evaporative cooling systems
Evaporative cooling systems work by bringing hot water into contact with cool air, causing heat energy to dissipate through evaporation. Also known as “semi-open” cooling systems, these units come in a few design variations, but all typically occupy a smaller footprint comparative to once-through cooling systems and are able to cool to a lower temperature.
Dry cooling systems
Dry cooling systems, also known as air condensers, differ from traditional water-cooling systems that work by exposing hot turbine exhaust steam to cold source water in a condenser unit. Instead, dry cooling technologies use air circulation. Dry cooling systems accomplish this by using fans and heat exchangers, and therefore consume little to no water.
Strategies for reducing water use
Integrating water-saving processes and technologies into existing electrical generation facilities is often costly and challenging, though there are ways that both old and new power plants can conserve water use. The practicality of any approach varies greatly from one plant to the next based on the availability of water resources, location, climate, and other factors. A few of the most common water-saving approaches are outlined below.
Use alternative water sources
Traditional surface and groundwater can be costly to source in the large volumes needed by electrical generation plants. The availability and cost of alternative sources of water can vary by location but are often comparatively cheaper and are readily available. These include: treated sewage, high salinity water (seawater, brackish water, some groundwater), water from mining operations, produced water from oil and gas wells, agricultural runoff, and storm water. When deciding whether alternative or degraded water sources are a viable choice for your plant, you’ll also need to consider the costs of transporting the water to your facility and treating it to meet the specifications of your cooling equipment or other equipment, as well as the costs of treating and discharging the resulting wastewater. In some locations, however, the comparatively lower cost of sourcing degraded water can more than make up for the additional costs of pretreatment and wastewater treatment.
A promising way to reduce net water consumption at power plants is to recycle water that has been used for other processes. Reclaimed water is more and more being used by power plants looking to increase production, as well as by facilities in arid or drought-prone locations. Recycling water for cooling purposes typically calls for some form of treatment to make the stream safe for high-heat applications, to prevent scaling, or to otherwise meet the specifications of cooling equipment. The exact treatment plan will vary significantly depending upon the source of the recycled water, and what contaminants are present.
Switch to a dry or hybrid cooling process
As detailed above, dry cooling processes use little to no water, making them an attractive choice for power plants in drought-prone areas, or in locations where water sourcing costs are high or expected to rise in coming years. Dry cooling processes are not without their drawbacks, however. Comparative to traditional wet cooling, dry cooling systems have higher upfront and higher operating costs, are less efficient and reliable at warmer temperatures, and demand a larger footprint. Hybrid systems combine wet cooling with dry cooling systems to solve some of these drawbacks, allowing them to function reliably in higher temperatures and a smaller footprint.
Switching from once-through to closed-cycle cooling
Closed-cycle cooling systems use significantly less water than once-through systems, making them an appealing option where water sourcing costs are high. All the same, closed-cycle cooling systems can demand significant capital investment, not only for the cooling equipment itself, but also for any needed pretreatment equipment. Additionally, closed-cycle cooling towers are often less efficient in terms of energy consumption and emissions, so facilities must also be careful to weigh these factors in selecting an appropriate water conservation strategy.
How can SAMCO help?
SAMCO has over 40 years’ experience custom-designing and manufacturing water treatment systems for a range of applications in power generation, so please feel free to reach out to us with your questions. With water minimization strategies, considering water quality and associated treatment go hand in hand. SAMCO can review your goals and help your facility plan a treatment solution.
For more information or to get in touch, contact us here to set up a consultation with an engineer or request a quote. We can walk you through the steps for developing the proper solution and realistic cost for optimizing water use at your electrical generation facility.
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