Conductivity in cooling tower water refers to the water’s ability to conduct electricity, which is determined by the concentration of dissolved salts and minerals in the water. High conductivity indicates high concentrations of dissolved solids and minerals, while low conductivity indicates low concentrations. Cooling towers rely on the basic water evaporation process to remove waste heat, but if not properly managed, these systems can be damaged and become less efficient. Conductivity is a key measurement for maintaining concentration cycles and water quality in cooling towers, as it can help identify issues before they cause significant damage.
Understanding Conductivity Measurements
Conductivity is typically measured in units of Siemens per centimeter (S/cm) or microsiemens per centimeter (µS/cm). The conductivity of pure water is around 0.055 µS/cm at 25°C, while the conductivity of seawater is around 50,000 µS/cm.
To calculate the cycles of concentration in a cooling tower, the conductivity of the blowdown water is divided by the conductivity of the makeup water. This ratio is approximately equal to the ratio of the volume of makeup water to blowdown water. For example, if the conductivity of the blowdown water is 2,000 µS/cm and the conductivity of the makeup water is 500 µS/cm, the cycles of concentration would be 4 (2,000 µS/cm / 500 µS/cm = 4).
Controlling Conductivity in Cooling Tower Water
To control conductivity in cooling tower water, a conductivity controller can be installed to automatically control blowdown. The controller continuously measures the conductivity of the cooling tower water and discharges water only when the conductivity set point is exceeded. Typical conductivity set points for cooling towers range from 1,000 to 3,000 µS/cm, depending on the specific application and water quality requirements.
Flow meters can also be installed on the make-up and blowdown lines to check the ratio of make-up flow to blowdown flow and ensure it matches the target cycles of concentration. This helps to maintain the proper balance of water in the system and prevent issues related to high or low conductivity.
Troubleshooting Conductivity Issues
When conductivity is always too low, it could indicate water leakage from the cooling system or clean water entering the system. In this case, it’s important to identify and address the source of the issue to prevent wasting treatment chemicals and water.
When conductivity is always too high, it’s often due to issues with the blowdown valve, such as it being too small or clogged, or contamination from the process or contaminated water entering the system. In this case, the blowdown valve may need to be cleaned or replaced, and the source of contamination identified and addressed.
Monitoring and Maintaining Cooling Tower Water Quality
Regular monitoring of conductivity levels and other key parameters, such as pH and temperature, can help ensure the proper management of cooling tower water and prevent costly damage. It’s recommended to keep a log of make-up and blowdown quantities, conductivity, and cycles of concentration to monitor trends and quickly identify any issues.
Some key considerations for maintaining cooling tower water quality include:
- Monitoring and adjusting the blowdown rate to maintain the target cycles of concentration
- Regularly cleaning and maintaining the cooling tower and associated equipment
- Treating the water with appropriate chemicals to control scale, corrosion, and biological growth
- Monitoring and addressing any changes in the cooling system or process that could affect water quality
By properly managing conductivity and other water quality parameters, you can help ensure your cooling tower system operates at high efficiency and prevent costly damage and downtime.