What is a Bleedoff/Blowdown Cooling Tower? Why is it crucial for your system?
In cooling tower operations, there is one vital process that is often misunderstood but has a significant impact on system efficiency and durability: blowdown.
What is blowdown/ Bleedoff?
Blowdown is the process of deliberately removing some of the water from the cooling tower basin to control the concentration of minerals and impurities dissolved in the water.
Why is Blowdown Necessary?
The water used in cooling towers is never 100% pure. It contains minerals such as calcium, magnesium, chloride, and silica. During the cooling process, water continuously evaporates. However, these minerals do not evaporate and remain in the system.
If the evaporated water is continuously replaced with makeup water (new water) without performing blowdown, the concentration of minerals will continue to accumulate. This condition is called High Total Dissolved Solids (TDS).
Negative Impacts if Blowdown is Not Performed:
Scaling: Highly concentrated minerals will settle and form hard crusts on the fill, pipes, and heat exchangers. This scale acts as an insulator, drastically reducing heat transfer efficiency.
Corrosion: High concentrations of chloride and other impurities accelerate the corrosion process in metal components of cooling towers and cooling systems.
Microbiological Growth: Environments with high mineral content are ideal places for algae, bacteria, and biofilm to multiply, clogging the system and increasing the risk of Legionella.
Reduced Efficiency: The system will work harder to reach the desired temperature, resulting in increased energy consumption and electricity costs.
By performing blowdown, we remove water with high mineral concentrations and replace it with new, cleaner water, thereby maintaining the chemical balance of the water.
How Often Should Blowdown Be Performed? What are the signs that blowdown is necessary?
There are two types of cooling tower blowdown: timer-based, which can be performed several times a day with the desired amount, and sensor-based, which is not performed based on a schedule (daily/weekly), but based on the condition of the water itself. This is what distinguishes sensor-based blowdown from timer-based blowdown.
Key Guidelines for When to Perform Blowdown:
Cycles of Concentration (COC):
This is the MOST IMPORTANT parameter. COC is the ratio between the TDS concentration in the circulating water and the TDS concentration in the makeup water.
Simple Formula: COC = Circulating TDS / Makeup TDS
For example, if the TDS of the makeup water is 200 ppm and the TDS of the water in the cooling tower is 600 ppm, then the COC is 3.
The ideal COC target is usually between 3 and 5. Above that number, the risk of scaling and corrosion becomes very high. Below that, you are considered to be wasting water (inefficient).
Electrical Conductivity:
Since TDS is directly proportional to the conductivity of water, we can use an automatic conductivity controller to measure and control blowdown.
The controller will automatically open the blowdown valve when the conductivity reaches the set point (predetermined point) that has been adjusted to the desired COC.
Visual and Chemical:
Although not as accurate as measurements, changes in the water such as it starting to look cloudy or water chemistry test results showing an imbalance can be an indication of the need for blowdown.
Conclusion: Controlled Blowdown = Efficiency + Longevity
Blowdown is not a waste of water, but rather a smart water management strategy. Doing it correctly based on COC data will provide significant benefits:
Prevents scaling and corrosion
Saves water and operating costs
Maintains heat transfer efficiency
Extending the service life of cooling towers
Tips:
For best results, install an Automatic Blowdown Controller that works based on conductivity readings. This tool will ensure that blowdown is only performed when absolutely necessary, so that no water is wasted and system efficiency is always maintained.
Need Help Optimising Your Blowdown System?
Our team of water treatment experts is ready to assist in analysing your water and recommending the most ideal blowdown and COC strategies for your factory operations.