Cycles of Concentration (COC) is a crucial metric in cooling tower operations that directly impacts water efficiency and operating costs.

COC indicates how often dissolved solids (minerals) have been concentrated in cooling tower water compared to makeup water (added water). The higher the COC, the less water is wasted through blowdown, thus saving water and chemical treatment.

Maximising COC in Cooling Towers

Maximising COC means operating the cooling tower with the highest possible water efficiency, without causing scaling or corrosion problems.

Key Factors to Maximise COC:

1. Good Makeup Water Quality:

   • Important Factor: This is the starting point. The lower the TDS and hardness of the makeup water, the higher the COC you can achieve before reaching mineral saturation.

   • Action: If your makeup water has high TDS or hardness, consider water pre-treatment such as:

     • Softener: Removes minerals that cause hardness (calcium, magnesium).

     • Reverse Osmosis (RO)/Nanofiltration: Significantly reduces TDS.

     • Demineralisation: Removes almost all mineral ions.

2. Program Chemical Treatment that is Effective:

   • Important Factor: Chemical inhibitors of scale and corrosion allow cooling tower water to tolerate higher mineral concentrations without forming scale or causing corrosion.

   • Action:

     • Use the appropriate scale chemical inhibitor for your water conditions (e.g., polymer dispersants, phosphonates, or azoles).

     • Use the appropriate corrosion inhibitor for your system materials.

     • Use biocide to control the growth of microorganisms that can form biofilms and trigger corrosion under deposits (under-deposit corrosion).

3. Control of Blowdown Precision:

   • Important Factors: Blowdown is the only way to remove excessive mineral concentrations. However, too much blowdown will lower the COC.

   • Action:

     • Use an online conductivity meter to monitor the TDS of the cooling tower water in real time.

     • Install an automatic blowdown valve connected to the conductivity meter, so that blowdown only occurs when the TDS reaches a specified limit. This is very important for maintaining COC at the maximum target.

4. Optimal Control of Drift Loss:

   • Important Factor: Drift loss is water lost that carries the same mineral concentration as the water in the basin. The higher the drift loss, the more water is ‘wasted’ and needs to be replaced, which can affect COC calculations.

   • Action: Ensure your drift eliminator is clean, undamaged, and functioning optimally. BHL cooling towers are designed with efficient drift eliminators.

5. Minimise Fouling:

   • Important Factor: Fouling (accumulation of sludge, dust, particles) can cover the filler and heat transfer surface, become a breeding ground for bacteria, and interfere with chemical treatment.

   • Action:

     • Install a Side Stream Filter to remove suspended particles from the circulating water.

     • Clean the basin and filler regularly.

COC (Cycles of Concentration) Formula Calculation

COC can be calculated in several ways, depending on the available data.

Most Common Formula (Based on TDS Concentration or Conductivity):

COC = TDS Concentration/Conductivity in Makeup Water TDS Concentration/Conductivity in Cooling Tower Water

• Example: If the TDS of the cooling tower water is 1500 ppm and the TDS of the makeup water is 300 ppm, then: COC = 300/1500 = 5

Formula Based on Water Loss:

COC = Drift Loss (D) + Blowdown (B) Evaporation Loss (E)

• This shows a direct relationship between evaporated water (without minerals) and water leaving the system carrying minerals (drift + blowdown).

Formula Based on Makeup Water:

COC = Drift Loss (D) + Blowdown (B) + Makeup Water (M)

• Given that M = E + D + B, then: COC = D + BE + D + B

Determining the Maximum COC Limit:

The achievable COC limit is determined by:

• The quality of the makeup water.

• The type of chemical treatment used.

• The system material's tolerance to scaling and corrosion.

• Critical water parameters such as hardness, alkalinity, chloride, and silica.

Important: Always consult with a water treatment expert (such as PT Jaya Sakti Internusa) to determine a safe and optimal COC target for your specific cooling tower system. Forcing the COC too high without adequate water treatment can cause severe scaling and damage.