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Such non-conformities in cooling water systems negatively affect the heat transfer efficiency of heat exchangers and other materials within the system. At the same time, substances like clay and scale that accumulate in the fills of the cooling tower affect its evaporation efficiency. These sediments formed within the cooling system must be removed from the system after a certain point.
Previously, hydrofluoric acid and ammonium bifluoride were used to remove such unwanted substances from cooling water systems. However, the use of these chemicals for cleaning purposes in cooling water systems is extremely dangerous and toxic. It has also been determined that these chemicals have a corrosive effect on metals. Additionally, from ammonium bifluoride, ammonia is released, which causes negative effects on the system through its corrosive action on copper metals. The heat exchangers in cooling systems are made of copper. Cleaning cooling water with these chemicals results in the formation of calcium fluoride. The calcium fluoride compound has an effect that reduces heat transfer.
The structural components of cooling towers are made of cement. Cement dissolves when exposed to fluoride.
Recently, new methods have been emerging. This method is used to remove unwanted deposits from metal surfaces and non-metal surfaces, such as plastic cooling tower components, in cooling towers. It has been found to be more effective compared to cleaning processes performed with ammonium bifluoride.
Removing Water Hardness in the Cooling Tower Cleaning Method
If the water used in the cooling water system has a hardness above 200 ppm, it should be softened using chelating agents. The water softening process is carried out with EDTA (Ethylenediaminetetraacetic acid) and citric acid .
Under the effect of chelating agents, calcium-containing sediments swell due to the water's hardness level. In the process of removing deposits from cooling towers, the swollen sediments detach more easily from the surfaces they have penetrated.
During cleaning of cooling towers, the pH of the water in the system is maintained in a range between 7.0 and 11.0. This keeps the effect of corrosion, which occurs at low pH levels, to a minimum. To maintain the desired pH level, Na2CO3, NaHCO3, and NaCl are used. The amount used can be added as needed. (Approximately 10000 ppm)
Removing Sediments in Cooling Water Systems
After adding the chelating agents, compounds containing phosphonate or phosphate are added at a concentration between 300-20000 ppm. The phosphate or phosphonate-containing compounds are as follows.
These are;
- 1-Hydroxyethylidene-1,1-Diphosphonic Acid (HEDP)
- Tetrapotassium Pyrophosphate (TKPP)
- Sodium Tripolyphosphate (STPP)
- Sodium Hexametaphosphate (SHMP)
This process is carried out for a period of 1 to 5 days until the unwanted sediments are cleaned from the surfaces they have penetrated. During the cleaning process in cooling towers, the pH value must be between 7.0 and 11.0.
What Chemicals Are Used to Remove Deposits in Cooling Water Systems?
Hydrochloric acid, Sulfuric acid, Citric acid, Sodium hydroxide, Potassium hydroxide, Polyacrylamide, Sodium polyphosphate, Sodium nitrite, Benzotriazole