Blowdown is a method for controlling scale buildup in a cooling tower—but how can you be sure you’re using it effectively? In this article, we’ll explain the science behind blowdown, the risks of under- and over-use, and the important role conductivity plays in finding the right balance.
In addition to removing heat from water through evaporation, cooling towers also act as air scrubbers, collecting dirt, debris, mineral salts, and other microbiological material that gets sucked inside. As water moves through the circuit and evaporates, the dissolved solids that are left behind can form a gritty sludge. If not treated, that sludge can build up on condenser tubes and heat exchanger surfaces, eventually hardening into a scale that can affect the overall efficiency of your system.
How can scaling be treated?
Proper cooling tower treatment starts by reviewing the makeup water and operating parameters of your system to find the right chemical balance for controlling scaling, deposition, fouling, and corrosion.
Once the right chemical program is designed, a fundamental method known as blowdown can be used to help maintain the proper water and chemistry balance inside the cooling tower.
What is cooling tower blowdown?
Blowdown is a method for controlling the amount of total dissolved solids (TDS) in a cooling tower. By removing a portion of recirculated water from the tower, the blowdown method helps keep impurities at acceptable levels and supports the proper functioning of the cooling tower system.
Striking the right balance
Finding the right blowdown balance for your system is key. Over-reliance on blowdown can result in excessive makeup water consumption and corrosive water conditions, while too little blowdown can promote the development of scale as dissolved solids harden inside the circuit.
Overusing blowdown
The frequent use of blowdown will decrease the potential for scaling in your cooling tower system, but it can actually open the door to other problems that reduce efficiency and increase operating costs, including:
- Wasted Water: Too much blowdown forces the tower makeup water valve to open and add water to maintain the sump level. This unnecessary use of water is caused by high blowdown
- Increased Sewage Costs: All that wasted water increases hydraulic loading and sewage costs due to the increased water volume to the sewer
- Wasted Chemicals: All the chemistry fed to help prevent deposition is unnecessarily bled out of the system with the blowdown
- Potential for Increased Corrosion: Without the proper chemical treatment, blowdown can actually accelerate corrosion in your system
Underusing blowdown
On the other hand, trying too hard to conserve water beyond the boundaries of your chemical treatment program will present its own set of potential issues:
- Increased Scaling and Deposition: All the chemistry fed to help prevent deposition is overwhelmed and can’t maintain the solubility limits, so the water becomes over saturated. Scaling of tower fill and condenser will increase energy costs, and fouled blowdown lines from scale and debris can exacerbate the situation.
- Corrosion: The higher concentration of TDS will drive up the corrosion potential and exceed the limits that can be controlled with your existing chemical treatment program.
- Microbiological Growth: The high cycles and retention time means that biological activity can increase and put a greater demand on the biocides to control bio-growth in your system.
So, how can you control your application of blowdown while also maintaining acceptable levels of TDS?
The conductivity factor
Conductivity, or the measure of water’s ability to conduct electricity, is an easily measured parameter that is directly proportional to TDS. The more TDS you have accumulating in your cooling tower, the higher the conductivity levels will be, and vice versa. Your water treatment chemical program is designed to function within a certain control range of conductivity that allows you to “cycle up”, or concentrate, the water in your tower.
Conductivity controllers can be extremely helpful for monitoring and adjusting conductivity levels. When employed, the set points on the conductivity controller will activate a blowdown valve, thereby regulating the amount of blowdown that occurs.
Properly employed conductivity control—based on your equipment, water temperature, and chemistry—will minimize water consumption and optimize scale and corrosion control in your system.
How QualiChem can help
An efficient, effective water treatment program balances the right use of treatment chemicals and blowdown to maintain your system’s water quality. QualiChem designs cooling tower water treatment chemical programs that eliminate excessive blowdown while also solving scale, corrosion, and microbiological issues.
Contact us today and learn how we can blend the proper chemistry for your cooling system operation.