What Are The Water Quality Control Indicators for Cooling Towers?

What are the water quality control indicators for cooling towers? The water quality control of cooling towers is crucial for ensuring the efficient operation of the cooling system and extending the service life of the equipment. The main indicators of water quality control mainly include the following seven aspects. This article introduces them for reference:

1. pH value range: 

Usually controlled between 6.5 and 9.0. Importance: Both excessively high and low pH values can have adverse effects on the cooling tower system. If the pH value is too low (too acidic), it will accelerate the corrosion of metal parts such as pipes and heat exchangers. However, if the pH value is too high (overly alkaline), it may lead to an aggravation of scaling. For instance, when the pH value is lower than 6.0, the corrosion rate of carbon steel will significantly accelerate. When the pH value is higher than 9.0, calcium, magnesium and other ions in water are prone to form scale such as calcium carbonate and magnesium hydroxide.

2. Hardness range: 

The total hardness (calculated as calcium carbonate) is generally expected to be controlled below 200-500 mg/L. Importance: The hardness of water is mainly caused by calcium, magnesium ions, etc. During the circulation of water with high hardness, due to temperature changes and water evaporation, these ions are prone to form scale. Scale can reduce heat exchange efficiency, increase energy consumption and may also clog pipes. For instance, in some areas with relatively hard water quality, if water softening treatment is not carried out, the surface of the heat exchanger in the cooling tower may form scale in a short period of time, greatly reducing the cooling effect.

3. Conductivity range: 

Generally controlled below 1500-3000μS/cm. Importance: Conductivity is an indicator for measuring the content of electrolytes in water, reflecting the amount of dissolved salts in water. Excessively high electrical conductivity indicates that there are more dissolved salts in the water, which will increase the water's corrosiveness and tendency to scale. Meanwhile, during the evaporation and concentration process of water with high electrical conductivity, salts are more likely to precipitate, causing damage to the system.

4. Turbidity range:

 Generally, it is required not to exceed 10NTU(scattering turbidity unit). Importance: Turbidity mainly reflects the amount of suspended particles in water. Water with high turbidity may contain impurities such as sediment, microorganisms and organic matter. These impurities will deposit inside the cooling tower, forming dirt that affects the heat exchange efficiency and provides a breeding ground for microorganisms. For instance, when there are many sediment particles in the water, they may deposit along with the water flow at the bends or narrow parts of the cooling pipes, causing local blockages.

5. Alkalinity range:

 Generally controlled within 100-300mg/L(calculated as calcium carbonate). Importance: Alkalinity measures the total amount of substances in water that can accept protons (H⁺), mainly including carbonate ions, bicarbonate ions, etc. Excessive alkalinity can lead to scaling, especially under alkaline conditions, where calcium, magnesium and other ions in water are more likely to precipitate and form scale. At the same time, alkalinity also affects the stability of water's pH value.

6. Chloride ion concentration range: 

Generally, it is required to be lower than 200mg/L. Importance: Chloride ions are highly corrosive ions. In the water of cooling towers, high concentrations of chloride ions can cause severe corrosion to metal materials such as stainless steel and carbon steel, leading to equipment damage. Even materials with good corrosion resistance may experience problems such as pitting and crevice corrosion after long-term use in a high-chloride ion environment.

7. Microbial indicators:

 Total bacterial count: Generally, it is required not to exceed 1000CFU(colony-forming units) per milliliter. Fungi and algae: Their growth should be controlled as much as possible to avoid the formation of biofilms and blockages. Importance: The breeding of microorganisms in cooling tower water can cause many problems. Microorganisms such as bacteria, fungi and algae can form biofilms. Biofilms not only reduce the efficiency of heat exchange but also act as isolation, making it difficult for fungicides and other agents to take effect. Moreover, the metabolic products of microorganisms may cause water quality deterioration, produce unpleasant odors and corrode equipment. For instance, when algae multiply in large quantities on the surface of a cooling tower exposed to light, they form a layer of green, sticky and slippery substance, which affects the appearance and normal operation of the cooling tower.