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Cooling tower water will contain a variety of contaminants which are bad for the system and bad for people around the tower. Due to the open operation of most cooling towers, these systems are plagued with the scaling of tower fill, pipe, and condenser tubes. The tower water, left untreated, will contain biofilm, sediment, and debris. Internal water treatment is one method of changing the water quality by adding chemicals to the water. This basic introduction to internal water treatment will explore the types of chemical treatment used in cooling towers.
What is Internal Water Treatment?
Internal water treatment is the addition of chemicals into the cooling tower water to change the water quality. Cooling tower water chemical treatment accomplishes two things. The first is to disinfect the fluid from bacteria such as Legionella, which will help protect people and reduce system damage. The second is to reduce corrosion and scale in the piping system. Let’s look at both options.
Disinfection of the Tower Water
Chemicals are added to the tower system to control the level of biologicals in the system fluid. The traditional chemicals used are chlorine and bromine.
CHLORINE: Chlorine dosing kills bacteria and other microorganisms. Just like swimming pools, chlorine is a readily available oxidizing biocide. Its main draw for owners is the first cost. Chlorine will be less dollars per pound compared with bromine. Chlorine gas is very harmful to people. The handling of chlorine must come with a stringent safety program. This may be a reason to look at another option.
BROMINE: Bromine is overtaking chlorine as the biocide of choice for cooling towers due to its effectiveness at higher pH. Owners may find they use less chemicals than when using chlorine. Bromine is less dependent on pH than chlorine. It can manage the higher pH we often see in towers.
Both chlorine and bromine have EPA restrictions for discharge of the fluid. The chlorine discharge restrictions become tighter each decade. For this reason, and others, there are systems that use a combination of the two chemicals.
DOSING: These chemicals are dosed into the system automatically about three times per week through a chemical feeder system. There are solid pucks of chemicals that may be used but they require more labor and attention and are not normally used in commercial applications.
Corrosion and Scale Inhibitors
Open systems with constant makeup water continually introduce oxygen into the metal tower components. The tower water is constantly evaporating as it cools. This evaporation removes the water but leaves behind any solids. Over time more solids build up and problems show up in the system. Corrosion and scale inhibitors reduce this issue.
SCALE INHIBITORS: Polyphosphates or other chemical compounds are added to cooling towers to prevent scale buildup. They also can help control the pH of the fluid. The scale inhibitors prevent calcium and magnesium crystals from forming and attaching to the pipe and equipment.
CORROSION CONTROL: Polyphosphates, molybdates, and others prevent corrosion. (Don’t get hung up on the chemical names, this is a basics blog.) Corrosion is the destruction of the metals in the tower and condenser system. The chemicals act to keep oxygen under control and to give it a tantalizing alternative to the metal. There are compounds to coat the pipe and equipment to protect it.
DISPERSANTS: Many of the compounds mentioned as well as others are also dispersants. They keep the solids in suspension and help them coagulate for easy removal. There are also foaming agents to reduce the amount of foam in the water. Foam will reduce the heat transfer required in the tower and the condenser.
PH CONTROL: We have a fight going on in the tower system. These chemicals affect the pH of the water. In fact, your chemical specifications may call for higher pH in tower systems. The fight is with your specified pump materials. The pump seal normally used has an acceptable pH range of 7 -9. pH adjustment agents keep the pH in a range required by the chemicals. If the expected pH is over 9.0, specify different seals in the pumps. Click here for more on that topic.
THE ENVIRONMENT AND THE AQUIFER: All these internal water treatment products change the water chemistry. Open cooling towers send water to drain by their nature. The engineer should be aware of Federal, State, or Local codes which limit the type and amount of product added to the water to drain.
There are other ways to:
- Save the Cooling Tower System
- Save the Cost of Operating a Cooling Tower
- Save the World for Future Generations
We will address these great savings when we discuss External Water Treatment in the next R. L. Deppmann Monday Morning Minutes.
Water Solutions Group offers innovative water quality solutions for cooling tower systems.
Water Solutions Group is a separate division of the R.L. Deppmann Company created to provide end users and engineers with a valuable resource in efforts to improve water quality. Proper water quality management protects the equipment, operations, occupants, and environment. Water quality should be considered at the time of design to ensure safe and efficient operating systems. Our intimate knowledge of water systems positions Water Solutions Group to be the ideal partner when evaluating operational issues that may arise because of poor water quality.
