Scaling and Deposit Control for Industrial Cooling Towers
Industrial cooling towers play a critical role in manufacturing, building comfort systems, chemical processing, and power generation. They remove excess heat from industrial processes and transfer it to the atmosphere primarily through evaporation. Cooling towers are prone to scale formation, and if not properly controlled, can severely impact their efficiency and operating costs and eventually lead to equipment failure.
Importance of Scale Control
Scale formation occurs when dissolved minerals, such as calcium, magnesium, and silica, in the cooling water precipitate and are deposited in the cooling tower and other heat transfer surfaces. Effective scale control offers numerous benefits, including:
- Improved Efficiency: By preventing scale buildup, water treatment systems can operate at optimal efficiency, ensuring the smooth flow of water and heat transfer. This leads to enhanced process performance and reduced energy consumption.
- Extended Equipment Life: Scale deposits can cause corrosion and damage to equipment surfaces. Implementing scale control measures helps minimize equipment degradation, extending their lifespan and reducing the need for frequent replacements.
- Reduced Maintenance and Downtime: Scale-related issues, such as reduced flow rates and heat transfer, can lead to system failures, increased maintenance requirements, and costly downtime. Proper scale control minimizes the need for unscheduled maintenance, resulting in increased operational productivity.
- Cost Savings: By preventing scale formation and maintaining equipment efficiency, industrial water treatment systems experience reduced energy costs, lower chemical consumption, and decreased maintenance expenses, resulting in significant long-term cost savings.
Understanding the Causes of Scale Formation
There are many factors that influence scale formation in industrial cooling systems. Understanding these factors and how they interact is crucial for developing an effective scale control program:
- Water Quality
- Water Temperature
- pH and Alkalinity
- Cycles of Concentration (COC)
- System Design and Operation
The quality of the makeup water used in the cooling system plays a major role in scale formation. The chemical composition of makeup water is highly dependent upon the source and varies in mineral content, alkalinity, and total dissolved solids.
The first step in developing or optimizing a scale prevention program is to have the water tested for chemical composition. Knowing the chemical composition of the makeup water helps us understand how it will affect the bulk water chemistry as it is cycled up during operation. Water sources containing high levels of dissolved minerals, such as calcium, magnesium, and silica, increase the likelihood of scale formation.
As the temperature increases, the solubility of minerals decreases, which leads to the precipitation of scale-forming compounds. Understanding the temperature at the heat transfer surfaces (not just the bulk water) is important when selecting the proper chemical treatment program.
In an ideal situation, we would measure the temperature at the heat transfer zone. When that isn’t possible, the rule of thumb is to add 20 – 30 degrees Fahrenheit to the bulk water temperature to estimate the temperature at the heat transfer surfaces.
pH and Alkalinity
The pH and alkalinity levels of the cooling water have a direct impact on scale formation. Higher pH and alkalinity levels increase the potential for scale formation.
Cycles of Concentration (COC)
During normal operation, makeup water is added to the cooling tower to replace the water lost due to evaporative cooling, blowdown, and drift. Since the solids stay in the bulk water, the dissolved solids “cycle up” in concentration.
Systems running higher cycles of concentration are more difficult to treat when it comes to potential scale formation. The elevated levels of dissolved solids require more complex chemical treatment strategies and chemical combinations to prevent scale deposition.
Cooling towers create an ideal environment for the growth of microorganisms and algae. The unchecked growth of microorganisms and biofilms creates nucleation sites where scale formation can begin to develop.
System Design and Operation
Inadequate design features, such as insufficient heat exchange surface area or improper flow distribution, can lead to localized high-temperature zones, which promote scale formation. Improper system operation, such as inadequate blowdown or insufficient water treatment, will also increase scaling in the system.
Chemical Treatment Programs for Scale Prevention
Once we have gathered the data for the system and makeup water, we can put together a scale control and prevention program. A successful scale prevention program will involve a combination of the four major categories:
- Scale Inhibitors: Scale inhibitors are chemical compounds that can be added to the cooling water to control scale formation. These inhibitors work by interfering with the crystal growth process, preventing the formation of hard deposits. Polyphosphates, phosphonates, and certain organic polymers are commonly used as scale inhibitors in cooling tower systems.
- Dispersants: Dispersants help prevent scale formation by keeping the precipitated minerals in suspension, inhibiting their deposition on heat transfer surfaces. These chemicals disperse the small particles of scale-forming minerals throughout the water, preventing their agglomeration and subsequent deposition on the surfaces. Polymeric dispersants and phosphonate-based dispersants are widely used in industrial cooling systems.
- Antiscalants: Antiscalants are specialized chemicals designed to prevent the formation of scale by inhibiting the crystallization of dissolved minerals. They work by binding to the mineral surfaces, disrupting the crystal lattice, and preventing the adherence of scale-forming compounds. Antiscalants are effective in controlling various types of scale, including calcium carbonate, calcium sulfate, and silica.
- Biocides: As mentioned earlier, biofilm formation in cooling towers can contribute to scaling problems. The use of biocides helps control microbial growth and the development of biofilms. Regular biocide treatment, coupled with proper water management practices, can significantly reduce the potential for scale formation.
An effective water treatment program not only needs to control scale formation, it also needs to be cost-effective. This is where the expertise of a water treatment professional and quality chemical blender comes into play.
The selection of treatment chemicals and the formulation used will be tailored to the system’s operating conditions and the makeup water chemistry. There is a wide variety of specific chemicals to choose from in each of the four main categories, each one with its own targeted function.
A cooling tower with high scaling potential for calcium phosphate requires a different blend of scale inhibitors than one where calcium carbonate is the main concern. The type and concentration of the biocide used can also impact the selection of the scale inhibitor(s).
Combining the right chemicals from each category in the right proportions creates a synergistic effect that improves performance and reduces the overall cost of the treatment program.
Best-In-Class Water Treatment Support
The formation of scale deposits can significantly impact the efficiency of cooling systems, increase energy consumption, and lead to equipment failure.
Designing an effective program requires a detailed understanding of cooling tower design, operation, makeup water quality, and the system’s history. A skilled water treatment professional will utilize this information to develop a treatment program that will specifically apply to your system and water chemistry. Download our one-sheet to better understand the causes of scale formation and the chemical treatment programs available to prevent scale formation.
Implementing a chemical treatment program, along with regular monitoring and maintenance, will help to ensure long-term reliability, efficiency, and economical operation of your cooling tower system.
Contact QualiChem to speak with our team to assist with choosing the proper technology for your cooling tower system.