So many businesses rely on cooling towers to perform vital services such as air conditioning, manufacturing and electric power generation. But cooling towers also pose several problems in their upkeep that closed systems lack. Chemical control of the water in the cooling tower is critical to your cooling system and the tower’s integrity.
Poor pH balance or lackadaisical cooling tower pH control could result in expensive damage or contamination to your system. Understanding why cooling towers are a prime source of contamination for the system and how to correct problems will help you preserve your system and protect it from harm.
Why Does Unbalanced pH Happen?
The pH measures the balance of acid and base in a substance. The more alkaline — baser — a material is, the higher its pH. The neutral pH of cooling tower water is 7.0. For every 1.0 increase in pH, the alkalinity increases by ten times, according to the Environmental Defense Fund (EDF). Measurements below 7.0 correspond to acidic substances. Stronger acids have lower pH values.
Imbalances in cooling tower pH occur because fresh water is composed of more than just oxygen and hydrogen. Minerals dissolved in the water play a significant role in changing the pH of the cooling tower’s water. These minerals can collect and create scale.
In cooling towers, the main mineral accumulation is calcium carbonate. This product comes from the reaction with calcium, heat and bicarbonate. Unfortunately, this scale source increases the pH of the water, making it more alkaline, according to the Office of Efficiency & Renewable Energy. Acids like ascorbic, hydrochloric and sulfuric can be used to combat the rise in pH, but a combination of the material of the cooling tower and the acid used can have negative consequences.
The allowable pH range for your cooling tower will not necessarily be the same as for others. The material the tower is made from determines the allowable pH of the water as well as possible treatments against scale and corrosion. Galvanized steel’s optimum pH ranges from 6.5 to 9.0, but type 316 stainless steel has a broader pH range, from 6.5 to 9.5. Other measurements such as conductivity, hardness and alkalinity also have different target values depending on the tower’s material due to a reaction between the metal and minerals in the water.
Which Water Treatments Work and Which Cause Complications?
Water treatment options are not universal for all cooling towers. For example, while the Office of Energy Efficiency & Renewable Energy suggests using acids to neutralize alkaline water in cooling towers, this may not always be the best course of action.
In one example cited by Power Engineering, when the standard method of reducing alkalinity involved adding sulfuric acid, the carbonate in the water turned into carbon dioxide. To complement the treatment, experts also treated the water with sodium dichromate, which created toxic hexavalent chromium. Since then, acid treatments have not been as popular, replaced by alkaline phosphates with anodic and cathodic scale inhibitors. All polymer treatments currently are increasing in popularity. Always get a customized plan for treating your cooling tower’s water for the best results.
Why Is It Important to Optimize the pH Balance of Cooling Tower Water?
Maintaining correct pH levels for your tower is critical to preventing scale and corrosion. The exact values depend on the metal the cooling tower is made from. If you have doubts about the proper pH levels, ask your water treatment company for recommendations for the appropriate water chemistry.
A pH between 6.5 and 7.5 is considered the ideal range for reducing scale formation, says the EDF, though some non-acid treatments for scale prevention can increase the cooling tower PH range up to 8.5. The pH also depends on the cycles of concentration — COC. Operating at higher COC allows the tower water to have a higher pH, even up to 10.0.
When maintaining the proper pH levels for preventing scale, other problems may arise. For instance, Power Engineering notes that chlorine does not kill microbes as effectively in water more alkaline than a pH of 7.5. If you have bacteria or other microbial life growing in the water, chlorine may not be the best treatment option, especially if the water has a high pH. Other choices exist besides chlorine that are more effective at high pH values, such as chlorine dioxide, which works well regardless of the pH of the water.
One means of protecting against corrosion in towers made of stainless steel, copper or steel is increasing the pH to 8.5 or above, according to the EDF. Raising the COC allows the carbonate in the water to grow, boosting the alkalinity. Higher alkaline levels, though prone to scale formation, prevent corrosion in certain types of metal and also inhibit bacterial growth.
When the pH deviates outside the prescribed range, the tower and its water can both experience problems, such as:
- White Rust: As the pH rises above 8.3 and the water has an excessive number of carbonate ions, cooling towers made of galvanized steel can develop white rust.
- Aluminum Corrosion: With pH values above 8.0, the chance of aluminum corroding in a cooling tower increases. The likelihood of corrosion is even higher at pH values above 8.4.
- Iron Corrosion: With neutral pH values between 7.5 and 8.0, iron-containing metals in the cooling tower can experience corrosion.
- Corrosion From Pollutants: Open towers in urban areas have a particular problem with corrosion. The water in the tower gets exposed to acid rain-causing gases. These same gases make the water in the tower corrosive by reducing the pH of the water. Monitoring for corrosion with weighted coupons and balancing the pH of the water can mitigate the effects of having an open cooling tower in a pollution-prone area.
While these problems exist, they can be controlled and corrected. With careful monitoring and control of the water chemistry, you can optimize the pH balance while reducing the chances of corrosion and scale.
What You Can Do to Optimize the pH Balance
Optimizing your cooling tower’s quality requires a multi-step approach to the process. Following all these steps will ensure you have the proper chemistry in the water of the cooling tower. Also, do not stop the process after using it once. Maintaining the water chemistry in a cooling tower is a continual process that requires constant vigilance and control.
1. Determine Water Quality
Start by taking measurements of the water’s pH, alkalinity, hardness and conductivity. These values will establish a baseline for where the water started before treatment. These measurements each play parts in the formation of scale or corrosion. You should measure:
- pH: The acidity or alkalinity of the water can determine whether scale grows or not. With lower COC, a scale can form at higher pH values, but having higher COC could allow you to increase the pH to the range between 9.0 and 10.0. The advantage of such an alkaline pH is its ability to inhibit biological growth and reduce the need for algae and bacteria treatments.
- Hardness: The amount of magnesium and calcium in the water determines the hardness. Harder water has more of these minerals in it, which solidify and deposit in areas of higher temperature. In a cooling tower, this creates an uneven buildup of scale in warm spots.
- Alkalinity: The number of alkaline substances in the water will neutralize any acids added and raise the pH of the water. Carbonate, hydroxide and bicarbonate are the most frequently encountered alkaline minerals in cooling tower water.
- Conductivity: Conductivity is directly related to how many minerals are in the water. More minerals can create problems with scale and corrosion. Raising the blowdown rates can drop the conductivity, says the EDF. One way of calculating the cycles of concentration is dividingthe conductivity of the cooling water by the conductivity of the makeup water.
Also, you will need the makeup water quality value. This number will make it easier to find the target cycles of concentration for your system.
2. Establish Target Cycles of Concentration
To establish the target cycles of concentration, use the makeup water quality. The value of the makeup water quality comes from either the company treating your cooling tower water or from your municipality. There are several means of calculating COC, one of which is the following provided by the EDF:
- Cycles of Concentration = Makeup Volume ÷ Blowdown Volume
Use this formula to identify the COC your tower currently uses. You can also employ this formula to periodically monitor water use to ensure you’re not wasting water. Remember, COC and water efficiency are directly linked, so keeping track of COC will help you see if your facility is losing water.
The number of cycles of concentration must carefully balance the need for efficiency and the requirement to keep out scale formation. A higher number of cycles will allow more dissolved minerals to accumulate in the water, leading to scale and corrosion. Evaporation will do the same. But more COC will increase the water efficiency. There are ways to improve water efficiency without increasing COC. Depending on the water makeup, you could reuse wastewater from other facility processes in the cooling tower, as long as the water chemistry in the tower remains unchanged.
For better water efficiency, maximize the COC without sacrificing solids accumulation. According to the Office of Efficiency & Renewable Energy, raising the COC from three to six cuts blowdown by 50 percent and makeup water by 20 percent. Most towers use between two and four COC. If you can increase the COC while keeping the water chemistry balanced, it will help your facility to become more water efficient.
3. Monitor COC and Water Performance
Keep an eye on the chemical balance in your water. Use real-time monitors to get the most accurate, up-to-date information that reflects changes in evaporation and water use. Couple these monitors with automating devices to get the most out of the data you collect. Regular monitoring of the COC and water quality will ensure your water is at the optimum balance to prevent the formation of scale, corrosion and bacterial formation.
4. Automate Your Processes
Cut down on the use of chemicals added needlessly to your cooling tower water by installing an automated chemical dispenser that regulates the water chemistry automatically. These devices only put chemicals to treat the water in response to chemical levels outside preset values. Real-time monitoring of the water chemistry maximizes the efficiency of these devices while adhering to the requirement to frequently monitor the water.
Other means you can use to automate maintaining the upkeep of your cooling tower water include:
- Flow Meters: These meters can measure the flow of blowdown and makeup lines to ensure you’re not wasting water.
- Conductivity Controllers: Conductivity controllers regulate the blowdown. If the conductivity setpoint is exceeded in the tower’s water, the controller will release water from the tower.
- pH Monitors: Monitoring the pH on a continual basis will give you the information you need to determine whether the water treatment methods you’re using are working as they should.
5. Protect Your Equipment
Though you may have adequate monitoring of water chemistry and automatic chemical controls, you still need to take measures to protect your equipment. Even in well-controlled environments, your tower could again experience corrosion. Use coupons to measure wear rates. Doing so will verify how well the water treatment works.
Secondly, don’t neglect regular inspections and repairs of your tower and all monitoring and chemical control equipment. If your monitoring equipment fails, you will not have the vital data you need to make correct changes to the water chemistry. Also, if the automated systems for controlling flow or conductivity fail, your system will not operate as efficiently as it should.
6. Work With Your Vendor
Once you’ve established the parameter to optimize your cooling tower’s water quality, work with your water treatment company. The vendor will have the supplies and methods necessary to get your cooling tower water within your established chemical ranges, such as pH. Communicate all your expectations thoroughly, and don’t be afraid to ask questions.
If the water treatment vendor is reputable, it will design a customized plan to help you reach the best chemistry for the water in your tower to prevent corrosion and scale. Since every situation is different, you will need to be ready to answer any questions about your facility and cooling tower. Accurate answers to these will ensure you get the best water treatment and the ideal water quality to prevent damage to your equipment.
Preserving the water in the tower from contamination will also protect the rest of the system the water circulates through. Because cooling towers have outside exposure, they are the most significant source of water contamination for their water systems. Treating the water in your cooling tower for pH can prevent problems like rust and corrosion in the entire system.
Contact Chardon Labs for Water Treatment
Water treatment is just one of the many things we do at Chardon Labs. We provide the means to keep your cooling tower water chemically balanced. We do not only sell chemicals. Our job is to create clean systems for our customers. We will make a system customized to your water and cooling tower design.
If you want your facility to have a cleaner cooling tower, contact us at Chardon Labs. We will discuss your facility’s needs. This information will help us construct the best solutions for keeping your cooling tower water perfectly balanced. Using chemically stable water will prevent problems and extend the life of your cooling tower and all the parts the water circulates through. We look forward to assisting you.