When you read the words pure water, you think of things like “healthy,” “clean,” and “clear.” You don’t think of terms like “corrosivity” or “pure water attack.” In the truest sense of the term, however, pure water can have a significantly negative impact on the performance of your evaporative media and your operations as a whole.
In data centers, manufacturing, and other industrial environments where cooling is important, scale prevention and efficiency are more critical than ever. With this heightened focus on scale prevention, the purity of the water passing through your evaporative media is a critical consideration. As we look at the purity levels of a water source, however, the answer to how pure the source should be to be scale-dissolving and not scale-forming becomes a bit murky.
In this article, we will explore the potentially negative impact of overly pure water on your equipment and evaporative media and look at how to determine where you stand on the scale, as this can dramatically impact system integrity and performance.
Suggested Reading: The Ultimate Kuul Product Guide
When assessing the purity of water within the scope of evaporative media, water quality is measured in megohms of resistivity, with ultra-pure water reaching a theoretical maximum of 18.2 megohms. Reaching a level of purity this extreme could only be achieved through processes like Electric Deionization (EDI) or ion exchange.
The level of purity described above is typically seen in specialized industries like semiconductor manufacturing or nuclear power. This lack of dissolved salts can cause what we referred to earlier, a pure water attack, when ultra-pure water becomes corrosive if left unmonitored. As such, it is important to take steps to measure the purity of the water in your evaporative cooling systems to avoid a negative impact on your media and equipment.
On the opposite end of the spectrum is brackish water, which contains high concentrations of dissolved salts, metals, and organic matter. This type of water generally requires significant treatment to become suitable for industrial applications.
High concentrations of dissolved minerals in brackish water can lead to scale deposition on filtration membranes, ion exchange resins, and other equipment and needs to be addressed to limit the negative impact.
To effectively evaluate water quality for evaporative media, conductivity serves as a primary indicator. Kuul™ Evaporative media can handle conductivity levels up to 3,000 µS/cm, accommodating a range of water qualities.
Our team assesses each water sample using empirical data and scaling indices, with a focus on the Langelier Saturation Index (LSI). This index, which incorporates alkalinity, calcium content, conductivity, pH, and water temperature, provides a snapshot of whether water will be scale-forming or scale-dissolving:
To minimize scaling risk, it’s common to adjust the water’s pH, reduce salt concentrations, or decrease alkalinity to maintain an LSI closer to the balanced 0.0.
For inlet water with an LSI well below -0.5, the risk of pure water attack increases. Our modeling programs use concentration cycles with a target LSI of at least -0.5 to prevent corrosivity in process water.
Corrosivity in ultra-pure water is primarily due to factors that pre-treatment systems, like softeners, don’t address—namely, dissolved oxygen, carbon dioxide, and pH levels. A softener is one of the most common treatment vessels for polishing water but it will not impact the aforementioned issues. While some corrosion is likely to occur whenever a metal is exposed to water these aforementioned variables are known catalysts for corrosion.
Dissolved oxygen can accelerate corrosion by disrupting the protective hydrogen film on metal surfaces, allowing further corrosion to take hold. This effect is exacerbated by factors like pH, pressure, and temperature. In evaporative cooling systems, ambient air provides a significant source of dissolved oxygen, heightening corrosion risks.
Carbon dioxide dissolves in water to form carbonic acid, which corrodes steel and low-alloy metals, potentially leading to pitting and leaks. While a greater concern in high-pressure systems, the formation of carbonic acid can also impact low-pressure environments, especially in ultra-pure water where pH buffering capacity is low.
The pH of water in an evaporative system must be carefully controlled to prevent both scaling and corrosion. Pure water has low alkalinity, meaning it lacks the natural buffering capacity to resist pH fluctuations. Alkalinity is a measurement of the carbonate and bicarbonate levels in the water. As we purify our makeup water and lower its alkalinity, we reduce its natural ability to buffer pH changes. This sensitivity can lead to weak acids, like carbonic acid, or additional treatments to prevent legionella and other micro bio in a system to have a heightened impact pushing the water into a more scale forming or scale dissolving LSI value.
When using pure or ultra-pure water on Condair’s Kuul™ evaporative media, understanding both the water quality and the operating conditions is critical. We recommend setting both upper and lower limits for cycles of concentration in these systems.
The lower limit helps avoid corrosion, while the upper limit prevents scale formation and other hygiene concerns that can arise at higher concentrations.
Our reports provide an LSI value for both the inlet water quality and projected full-operation water quality, including alkalinity, pH, and LSI, allowing us to optimize each system’s efficiency and mitigate risks associated with scaling and pure water attack.
With these tools and our extensive data, we can align each evaporative system for optimal efficiency, minimizing the risks of both scaling and pure water attack while safeguarding the longevity of the system.
Schedule a consultation today to assess the potential for Pure Water Attack within your systems and learn how the team at Condair can help.
Thomas joins us as a Water Chemical Engineer, bringing 3 years of experience in Industrial Water Treatment, where he worked with Reverse Osmosis, Boiler, and Cooling Systems. Additionally, he spent two years supporting the production of Ion Exchange Resin, with a focus on quality and process improvements in specialized applications, including Nuclear, Ultra Pure, and Potable Water Systems.
© 2024 Condair Evaporative Technologies. All Rights Reserved.
