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Cooling Tower Systems Management

The safe management of Cooling towers.

Hydrochem (UK) Ltd provides a total solution to cooling tower system management, from service visits and monitoring, cleaning, refurb and cleaning works to risk assessment and water treatment systems and chemical supply.

Hydrochem (UK) Ltd ensure that Clients are running their systems in an economical and safe manner. 

Cooling towers are subject to many factors which can affect the efficiency and performance of the systems. Careful consideration should be given to ensure that the most efficient and effective treatment system is in place.

Without adequate control the systems can be prone to damage from corrosion, scaling and microbiological factors.

For our full cooling systems treatment chemical range click here.

What are the Effects of These Problems?

If not properly controlled, these problems can have a direct, negative impact on the value of the entire process or operation.

Examples of problems that corrosion, deposition, and biological fouling can create are as follows:

• Increased maintenance cost

• Equipment repair or replacement cost

• More frequent shutdowns for cleaning and replacement of system components

• Reduced heat transfer efficiency and therefore reduced energy efficiency 

• Increased fuel costs for power generation plants 

• Increased energy consumption by refrigeration chillers

• Possible product yield reduction or even plant shutdown 

• Product quality problems and increased product rework 

• Environmental compliance problems 

• Increased greenhouse gas emissions due to higher energy use

  • Corrosion

    Manufacturing of common metals used in cooling systems, such as mild steel, involves removing oxygen from the natural ore. Cooling water systems are an ideal environment for the reversion of the metal to the original oxide state. This reversion process is called corrosion.

    What is Corrosion? 

    Corrosion is an electrochemical process by which a metal returns to its natural oxide state. For example, mild steel is a commonly used metal in cooling water systems that is very susceptible to corrosion. Corrosion causes loss of metal thickness or even penetration of tube walls which can cause leakage of process fluids into the cooling water or vice versa. Corrosion is generally a greater concern with the more common, lower cost materials like mild steel.

    How does Corrosion take Place? 

    For corrosion to occur, a corrosion cell, consisting of an anode, a cathode, and an electrolyte must exist. Metal ions dissolve into the electrolyte (water) at the anode. Electrically charged particles (electrons) are left behind. These electrons flow through the metal to other points (cathodes) where electron-consuming reactions occur. The result of this activity is the loss of metal and often the formation of a deposit.

    What Water Characteristics Affect Corrosion? 

    The most important factors are: 

    • Oxygen and other dissolved gases 

    • Dissolved and suspended solids 

    • Alkalinity or acidity (pH) 

    • Velocity • Temperature 

    • Microbial activity

    What Methods are used to Prevent Corrosion? 

    Corrosion can be prevented or minimized by one or more of the following methods: 

    • When designing a new system, choose corrosion-resistant materials to minimize the effect of an aggressive environment. 

    • Apply protective coatings such as paints, metal plating, tar, or plastics. 

    • Protect cathodically, using sacrificial anodes or other methods such as impressed current. • Add protective film-forming chemical corrosion inhibitors that the water can distribute to all wetted parts of the system.

    What is the Cost of Corrosion? 

    Corrosion can increase costs of any process. It causes fouling that reduces heat exchange efficiency and reduces the process efficiency. If severe enough, corrosion can cause failure of an exchanger, requiring either retuning or replacement. This has direct cost for the equipment being replaced and costs to shut down the process while repairs are completed (see Material Costs Chart above).

  • Micro biological activity

    Cooling water systems provide an ideal environment for microbial organisms to grow, multiply, and cause deposit problems in heat exchange equipment. Microbial growth can strongly influence corrosion, fouling, and scale formation, if not controlled properly. Macrofouling can occur in once-through cooling systems or water intakes in lakes and rivers. Various species of clams, mussels, and other marine organisms can attach to the piping, reducing water flow and increasing corrosion.

    What is Microbial Contamination? 

    The uncontrolled growth of microorganisms can lead to deposit formation that contributes to fouling, corrosion, and scale. 

    What are Microbial Slimes? 

    Microbial slimes are masses of microscopic organisms and their waste products. These slime layers are usually sticky and effective in trapping foulants present in the bulk water. 

    How do Slime Layers Impact Cost of Operation?

     Microbial slime, like other fouling materials, reduces the efficiency of heat transfer. In fact, microbial slime is more insulating than other common deposits. The slime can trap other deposits, making the problem worse. 19 Biofilms are more insulating than other types of heat exchanger deposits. 

    How do Microorganisms Enter a Cooling Water System? 

    There are two primary modes of entry of microorganisms into cooling water systems. One is the makeup water in which microorganisms are already present. Another is via airborne microorganisms that are blown into the cooling tower. 

    What Factors Contribute to Microbial Growth? 

    The most important factor is the degree of microbial contamination being introduced into a system. Next in importance are: 

    1. Nutrients – For instance, hydrocarbons or other carbon sources can serve as food for slime-forming organisms. 

    2. Atmosphere – Organism growth depends upon the availability of oxygen or carbon dioxide. 

    3. Location – Such factors as the amount of light and moisture may significantly affect growth rates. 

    4. Temperature – Organisms that make up slime tend to flourish between 40 and 150°F (4.4 and 65.6°C).

  • Legionella

    Is Legionella a Concern in Cooling Water? 

    Yes, if a system isn’t managed correctly then conditions suitable for the proliferation of Legionella bacteria may be created. Every cooling system is subject to strict legislation, with severe penalties being dealt for non-compliance. Risk assessment is the first stage to ensuring safe operation.

    How do Legionella Grow in Cooling Systems? 

    Legionella can live and multiply as a parasite in protozoa. As they multiply, Legionella will burst the protozoa and be released into the water. Legionella can survive in biofilms that provide a source of complex nutrients. Some believe that Legionella may be able to multiply within biofilms even outside of host protozoa. 

    How can Legionella be controlled? 

    No biocide is specific for Legionella. However, traditional oxidizing biocides such as chlorine and bromine have proven effective in controlling Legionella in cooling systems. A program that includes non-oxidizing biocides together with oxidizers is also effective. Key elements of any program are proper control of biocide dosages, monitoring microbial levels in the system, and maintaining a clean system. These are part of a complete Legionella risk reduction management plan

    What Types of Chemicals are used for Microbial Control? 

    Three general classes of chemicals are used in microbial control: 

    1. Oxidizing biocides 

    2. Non-oxidizing biocides 

    3. Bio dispersants

  • Scaling

    Minerals such as calcium carbonate, calcium phosphate, and magnesium silicate are relatively insoluble in water and can precipitate out of the water to form scale deposits when exposed to conditions commonly found in cooling water systems.

    Types of scaling commonly found in cooling tower systems-

    • Calcium carbonate 

    • Calcium phosphate

    • Magnesium silicate 

    • Silica

    Why Does Scale Form? 

    Scale results when dissolved ions in the water exceed the solubility of a given mineral. Four principal factors determine whether or not a water is scale forming: 

    1. Temperature 

    2. Alkalinity or acidity (pH) 

    3. Amount of scale-forming material present 

    4. Influence of other dissolved materials, which may or may not be scale-forming

    How Can Scale Formation Be Controlled?

    There are four basic means to control scale: 

    1. Limit the concentration of scale forming minerals by controlling concentration ratio or by removing the minerals before they enter the system. “Concentration ratio” is the ratio of dissolved solids in the blowdown to dissolved solids in the makeup.  An ion exchange softener is one way to reduce hardness in supply water.

    2. Feed acid to keep the common scale-forming minerals (such as calcium carbonate) dissolved. Most, but not all, minerals are more soluble at lower pH. 

    3. Make mechanical changes in the system to reduce the chances for scale formation. Increased water flow and exchangers with larger surface areas are examples. 4. Treat with chemicals designed to prevent scale

  • Fouling

    The deposition of suspended material in heat exchange equipment is called fouling. Foulants can come from external sources such as dust around a cooling tower or internal sources such as by-products of corrosion

    What is Fouling? 

    Fouling is the accumulation of solid material, other than scale, in a way that hampers the operation of plant equipment or contributes to its deterioration. Examples of common Foulants are: 

    • Dirt and silt 

    • Sand • Corrosion products 

    • Natural organics • Microbial masses 

    • Aluminium phosphates 

    • Iron phosphate

    What Influences Fouling in a Cooling System? 

    The most important factors influencing fouling are: 

    • Water characteristics 

    • Temperature

    • Flow velocity

    • Microbial growth 

    • Corrosion 

    • Contamination

    How can Fouling be controlled? 

    Fouling can be controlled mechanically or by the use of chemical treatments. The best method of control depends upon the type of fouling. Control of fouling in the cooling system involves three major tactics: 

    1. Prevention – The best approach is to prevent foulants from entering the cooling system. This may include mechanical changes or addition of chemicals to clarify makeup water. 

    2. Reduction – Take steps to remove or reduce the volume of foulants that unavoidably enter the system. This may involve side stream filtering or periodic tower basin cleaning. 

    3. Ongoing Control – Take regular action to minimize deposition of the foulants in the system. This can include adding chemical dispersants and air rumbling or back flushing exchangers. 

    For our full cooling systems treatment chemical range click here.

    Formed in 1987Hydrochem (UK) Ltd are the longest serving independent water treatment company in the North East., we provide a total solution to the management and control of water systems.

    Hydrochem…providing solutions for a safer environment.


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