Cooling Tower CleaningCooling Tower Cleaning and Pretreatment chemicals. New cooling systems require care at startup to assure proper cleaning and passivation is implemented. Additionally, systems that have been laid up or drained also require care during startup. Systems not properly cleaned and passivated at start-up may develop:
- Rapid corrosion of the new galvanized cooling towers referred to as white rust
- Deposition of dirt and debris found in the piping systems.
- Microbiological control issues.
- Fouling by oils and greases from uncleaned piping systems.
The problems associated with the rapid corrosion of galvanized cooling towers have become an increasing issue in recent years with the advancement of alkaline and/or low phosphate based treatment programs.
To assure all of these problems are minimized at startup and beyond, certain precleaning and passivation measures should be utilized prior to introducing a load to the cooling system. The table below summarizes several major tower manufactures guidelines for initial treatment of galvanized cooling towers and associated cooling systems:
Cooling Tower Manufacturers –Start-up Water Chemistry
BAC Towers: Passivation Treatment Passicvation requires the use of inorganic PO4 treatment which helps passivate zinc coating, pH Balance 6.5 to 8.0, Hardness > 30 ppm must be maintained.
Evapco Towers: 400-450 ppm PO4 w/ 100 ppm Ca (as CaCO3) for 45 – 60 days. pH Balance 6.5 to 8.0, 100 to 300 PPM of hardness must be maintained.
Marley Towers: Use inorganic PO4 for at least 8 weeks to help passivate zinc coating. pH Balance 6.5 to 8.0, 100 to 300 PPM of hardness must be maintained.
While the cooling tower manufacturers’ recommendations are generally considered to be conservative, properly precleaning and passivation of cooling systems is a critical art of the overall treatment program. The following is a step-by-step procedure to the cleaning of a new system after initial mechanical cleaning to remove all trash and debris:
- Where possible, heat the water in the system to 130-180oF. Heating speeds the reaction and reduces the time and/or the concentration of the cleaning solution required to clean the system.
- Add PC-ALK at the rate of 0.5-1.0% (i.e. 0.5-1.0 gals. /100 gals. water contained in the system).
- If the system water is heated to the recommended temperature, cleaning should be completed in 12-24 hours. Where heating is not possible, the solution can be safely circulated in the system for several days.
- After the circulating time has been reached, the system should be drained and flushed with clean, clear water until the flushing remains clear.
Immediately after completion of the cleaning of the new system, a pasivation program should be implemented. To achieve this passivation, we recommend the use of PT1133.
PT1133 is normally shot fed to the system adding 15 lbs per 1000 gallons of system volume into the sump of the tower and then recirculating the water for 12 to 24 hours with no bleed-off and no load. This should develop a phosphate level of approximately 400 ppm in the system. After the designated time period, the blowdown is opened while continuing to circulate without load. When the phosphate residual in the system is reduced to <15 ppm, the regular treatment can be initiated and the system started up for normal operation. Cycles should be limited to assure pH less than 8.5 for 30 days. If the system is drained or subjected to acidic conditions, pretreatment should be repeated. Order your Cooling Tower Cleaning chemicals today.
If initial sanitization of the tower is required, a 10.0 ppm free halogen (as Cl2) residual can be maintained in the system for up to 24 hours. However, passivation or re-passivation with PT1133 should be performed after the sanitization phase is completed.
The system should not be put under load until the cleaning, sanitization (if required), and passivation are complete.
For smaller systems, PT1133 is available in diluted forms.
For systems with very low calcium hardness (<50 ppm), please contact ChemWorld.com for additional treatment recommendations.
For more information, please contact us at 800-658-7716 or email our sales consultant at JZajac@ChemWorld.com.