We offer two ways to clean a cooling tower/chiller. The first being a mechanical cleaning and the second being a chemical cleaning. At times, you may have to encompass both methods in order to accomplish the task at hand. Consult your water treatment representative and have him assist you in determining the best procedure.
Chemical cleanings involve three distinct separate procedures. One being the use of a dispersant to loosen biomasses and get into difficult areas. The second being the use of acid for severe scaling. The third is disinfecting for bacteria, Legionella prevention and elimination. You have to determine which method is best suited for your situation. You may have to use a combination of the three in some cases. Consult your water treatment specialist if you have any questions.
Cooling Tower Pre-Cleaning Preparation
Whether you are mechanically or chemically cleaning a cooling tower, these steps must first take place. It is important that each step be adhered to. The order of the steps can be fluctuated but each step must be done to insure your safety.
- The tower must be isolated from the system. Turn off and secure the electrical service to the tower. Be sure the tower fan is off, the main circulating pumps are off, and the temperature sensors are off or put in a none operational mode. Lock out and tag out the main power switch.
- Close the valves that supply and return water to and from the tower.
- Close the make up water valve to the tower.
- Open bottom drain of the tower. Remove overflow pipe.
- Remove the grate covering the suction intake for cleaning if possible.
- Have a separate garden hose ready, charged, and place in tower once the tower has been drained out. Have your squeegee, broom, and shovel ready and place in tower.
- Suit up with water proof boots, coveralls, gloves, hat, and face protection.
- Begin your cleaning. Once cleaned, reverse the procedure for startup.
This type of cleaning will involve the use of a power washer, a garden hose with power spray nozzle, shovel, broom, and squeegee. This type of cleaning in designed to remove all algae, slight scale, dirt, mud, and collected debris. The purpose is annual cleanings and removal of dirt to regain cooling performance. At times it is strictly cosmetic.
Starting at the hot deck, using the pressure washer, wash cooling tower blades, screen, inside of exhaust collar, and hot deck. Remove the covers of the hot deck and be sure all drain holes are free of scale and debris. Wash entire area where water flows to the fill. Make note if any spray nozzles are missing or broken. Inform chief engineer if they are.
Be careful when cleaning the fill with a pressure washer. The pressure and stream will cause the fill to break easily and snap off. Use a spray stream and not a straight stream. Clean the fill from top to bottom, outside and inside. Wash the sump area, also outside and under the fill.
Clean the inside of the tower fill, top to bottom, the walls, and under the fan blades. Remove all signs of algae, dirt and debris from float valve. Using the shovel or squeegee, be sure the floor of the sump is clean and free of all mud and deposition. Use your hose to clean under fill and inside of fill. After wash out is over, check to be sure no loose scale has broken off and isn’t lodged somewhere in the bottom of fill.
When finished, shut the drain, reset overflow pipe, and open the make up valve to refill tower. Add sufficient chemical for startup. Consult with your water treatment rep. for the correct amount of chemical to add to the tower. Once the tower is filled, slowly open supply and return valves. Tower may add more water once the supply and return valves are open as to displace trapped air. Remove lockout and tagout materials. Have chief engineer inspect tower and have him start electrical service to start tower. Watch the water level to be sure it remains at sufficient levels for operation. Once tower is in service, have chief engineer sign off on your report that tower cleaning is completed.
This is much more involved than a mechanical cleaning. You need to first establish the purpose of the chemical cleaning. This is very important. Consult with your water treatment rep. There are several steps/tests that need to be performed prior to the actual cleaning. This is very important.
Types of Chemical Cleaning
The use of a biodispersant alone will help remove dirt and loosen bio masses for easy removal. This is the most favorable safest, and easiest type of chemical cleaning. The use of a biodispersant along with either an algaecide (chlorine) or biocide will insure that all biomasses, silt, and deposition are reduced and can more easily be mechanically removed.
If a tower has not been used, is in a stagnant state or is highly fouled and needs cleaning, a bacteria test must be performed first to determine bacteria levels. If bacteria levels exceed the Center of Disease Control’s regulation of ten to the fifth levels, the tower must be disinfected. High levels of chlorine and sodium bromide are to used along with a biocide, either gluteraldehyde or isothiazalin, and a biodispersant to insure that all traces of biological growth are killed. These chemicals must be recirculated for 2-6 hrs. before the actual mechanical cleaning process begins. Tower must be retested for bacteria conditions prior to discharge of chemicals and the mechanical process can begin.
Scaled Cooling Towers and Chillers
If a tower is heavily scaled, and an acid cleaning is determined to be the most effective way of reducing or removing the scale, your water treatment specialist must be contacted. He will determine the type and amount of acid that is needed to descale the tower. Once the correct acid is determined, the acid will be added via a special chemical tank and recirculating pump. The solution will be recirculated for several hours. Once the acid has exhausted itself (determined by a pH test and physical inspection), it is neutralized and then dumped. If a second application is needed, the water treatment rep. will re-apply the solution with new acid and recirculate it for several more hours. Once the water treatment rep. determines that the scale has been dissolved, or loosened off where it can be mechanically removed, he will neutralize the solution, retest, and drain the tower. This will insure that the internal portion of the tower is safe to begin the mechanical cleaning. Safety is primary at all times. Be sure the service rep. is completely dressed and covered before entering the tower.
Your water treatment rep. will analyze the scale and determine the most effective acid to use to dissolved the scale. The neutralization process involves a blend of caustic chemicals to insure that the tower solution has a pH of 7.0 to 7.4. before discharge. This is a time consuming process and requires a great deal of work to insure the safety of the service reps. Time and materials plus labor are charged for this process.
The mechanical cleaning is the least costly of the three processes. The disinfection is next followed by the descaling. The water treatment division will work hand in hand with the service reps. who are assigned to clean a tower.
Consult with your water treatment rep. if you have a tower cleaning scheduled. This will give him sufficient time to order the necessary chemicals and materials based upon his review. We want to make your job easier and insure your safety.