Cooling tower shutdowns and cleanings are an integral part of routine tower operation and are critical for maintaining cooling tower heat transfer, minimizing unwanted microbiological growth, reducing corrosion issues, and prolonging the life of your cooling tower system. The CTI (Cooling Technology Institute) and AWT (Association of Water Technologies) recommend semi-annual cleanings of tower basins and sumps to help keep your systems clean and free of debris. In addition to the tower being shut down for cleaning, this is also an excellent time for routine preventative maintenance to be performed such as greasing fan bearings, tightening belts and cleaning strainers.
Dirty towers play an active role in biological growth and Legionella positives!
Neglected tower prone to positive Legionella test results.
The picture above shows the condition of the distribution deck on a cross flow cooling tower system that had not been cleaned in many years. This tower system was prone to positive Legionella test results and high microbiological dip slide test results in part due to the excessive buildup of silt and particulates in both the distribution deck and tower sump. Following these findings Watertech was able to work closely with the customer and a trusted mechanical contractor to perform a tower cleaning during the next available building shut down. Additional testing performed after the cleaning has shown significant decreases in positive Legionella test results and microbiological dip slide readings. It’s safe to say a clean tower goes a long way towards controlling biological growth.
STEPS TO CLEAN YOUR COOLING TOWER
Below are the recommended procedures for shutting down your cooling tower system and performing a manual cleaning. You can also download this cleaning procedure from our
Knowledge Center.
Pre-Cleaning Disinfection
- Introduce heavy bleed off for several hours to drop pH and dissolved solids
a. Drop cycles of concentration to a lower pH (around 8 if possible)
- Oxidizing biocide with use of bio dispersant if applicable
- Bio dispersant should be added 30 minutes before the addition of the oxidizing biocide
a. Circulate throughout the cooling tower water system
- Chlorine addition
a. 5 ppm as free chlorine for a minimum of 5 hours
b. 25 ppm as free halogen for 2 hours
c. 50 ppm as free halogen for 1 hour
- Turn off the cooling tower fans until disinfectant is mixed
- Once disinfectant is mixed, return tower to normal operation.
- Once system is disinfected, dechlorinate (if necessary) and drain
Example of a clean system.
Mechanical Cleaning of Cooling Tower
- Cleaning methods that create spray and aerosolization should be avoided
- High pressure jetting should only be done if necessary
a. Make sure area is unoccupied, air inlets are blanked off, and tent off the area
- Follow manufacturers guidelines for maintenance
a. Fill may have limitations that you may need to consider
- “Cleaning staff that carry out water jetting, or other operations which could create aerosols, should wear suitable respiratory PPE”
a. Potential for bacteria exposure is always present
- Another chemical cleaning may be required post mechanical cleaning to remove deposits
Post-Cleaning Disinfection
1. System should be refilled and disinfected using the pre-cleaning procedure
2. If unable to achieve shock levels, the disinfectant level can be allowed to decay over the first few hours of operation and startup of normal water treatment chemicals.
3. If the system is going to be left idle, drain, and flush the system and leave empty
Example of a clean and healthy system.
Having your cooling tower cleaned is now easier than ever thanks to the relationships Watertech has built with reputable mechanical contractors. Many facilities don’t have available staffing or time to perform tower shutdowns and cleanings on their own. In these situations, Watertech can take the lead and work with our network of professionals to have your system cleaned as well as have any preventative maintenance performed at the same time.
Do you need help with your cooling water system?
If you have questions about your cooling water treatment or want more information on how to keep your system healthy and free of waterborne pathogens, click the link below to Request a Site Survey and one of our technical engineers will be in touch.
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Shawn Kenar | Watertech of America, Inc.
Shawn has worked with Watertech of America for 5 years as a Field Service Technician. He has a wide range of commercial and industrial water treatment experience. He also serves as a technical trainer at Watertech University our onsite training center. Prior to coming onboard at Watertech Shawn worked as a welder, this experience gives him additional insight when working with customers on specialized applications and processes.
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