A water cooling tower is a heat exchanger system that cools hot water coming from a facility by evaporating a portion of it and releasing the vapor into the atmosphere, while returning the remaining portion—which has reached the required temperature—to the facility for use.
Power plants, large HVAC systems, and the chemical industry generate large amounts of waste heat, which is typically discharged into a nearby lake or river. However, sometimes the water flow is limited, or thermal pollution must be considered a significant factor. In such cases, the waste heat is released into the atmosphere, and the cooling water acts as a medium for heat transfer between the heat source and the atmosphere.
Reusing this water—which has undergone various processes—without depleting existing water sources, removing unwanted heat from the water, and discharging it into the environment in a harmless and cost-effective manner is only possible by constructing a cooling tower.
In a cooling tower, a portion of the water that comes into contact with the ambient air evaporates, causing the water temperature to drop. The evaporated water enters the air as moisture, causing an increase in the air’s specific humidity and relative humidity. In a cooling tower, water can theoretically be cooled to no lower than the wet-bulb temperature of the inlet air. The more efficient the cooling tower, the closer the water temperature can be brought to the wet-bulb temperature in practice. In practice, the water temperature can be cooled to a temperature 4°C or 5°C above the wet-bulb temperature of the inlet air. An amount of makeup water equal to the amount of water evaporated must be added to the cooling tower’s water basin. An energy balance is performed based on the amount of water added (the amount of water evaporated).
Basic Terms in Cooling Towers:
Dry-Bulb Temperature: This refers to the temperature obtained when measuring with any temperature-measuring instrument—such as a thermocouple, thermometer, or similar device—without the influence of moisture or radiation in the air.
Wet-Bulb Temperature: If we wrap a thin, damp cloth around the dry-bulb of a thermometer and hold it in front of a fan, the moisture in the cloth, driven by the wind, absorbs latent heat and begins to evaporate, and we observe that the temperature on the thermometer gradually decreases. When the drop comes to an end, we call the temperature we read the WET-BULB TEMPERATURE. The wet-bulb temperature varies depending on the dry-bulb temperature and the humidity level of the environment. If the air is not saturated with moisture, the wet-bulb temperature will be lower than the dry-bulb temperature. We can explain this phenomenon similarly to how our hand cools down when we pour a small amount of cologne on it due to evaporation.
Dew Point Temperature: When moist air is cooled at constant pressure, the temperature at which the water vapor it contains begins to condense is called the dew point temperature.
Relative Humidity: Relative humidity is the ratio of the amount of water vapor present in a given volume of air at a specific pressure and temperature to the maximum amount of water vapor that air of the same volume could hold under the same temperature and pressure conditions; it is expressed as a percentage (%).
Specific Humidity (Humidity Ratio): The ratio of the mass of water vapor in a given volume of moist air to the mass of dry air is called absolute or specific humidity.
Cooling: During cooling, the specific humidity of the air remains constant, but its relative humidity increases. If the relative humidity rises to an undesirable level, it may be necessary to reduce the amount of water vapor in the air—in other words, to remove moisture. To achieve this, the air must be cooled to a temperature lower than its dew point.
Approach: The approach is defined as the difference between the temperature of the water leaving the cooling tower and the wet-bulb temperature of the incoming air.
Sensible Heat: The amount of heat transferred to the external environment to raise the dry-bulb temperature of the air (provided that the specific humidity remains constant).
Latent Heat: The heat required to convert a certain amount of water into steam without changing its temperature or pressure is called latent heat. If this water vapor mixes with the air, the latent heat of the water that turned into steam is also transferred to the air. Similarly, if a certain amount of vapor in the air is condensed, latent heat is removed from the air. For example, let’s consider a closed room. Let’s assume the temperature of this room is 25°C. Let’s suppose we introduce a certain amount of water vapor at 25°C into this room. Let’s also assume there is a thermometer hanging on the wall of the room. There will be no increase in temperature on this thermometer. However, we did supply heat energy to this closed system—the room. What happened to this energy? The enthalpy (heat capacity) of the air in the room increased. In other words, its latent heat increased. When latent heat is added to the air, the dry-bulb temperature of the air remains constant. However, the wet-bulb temperature rises. Its enthalpy and specific humidity increase.
Some of the water treatment products we have developed at Cemkimsan Kimya and manufacture at our plants include:
CK 229: A phosphonate-based water treatment chemical used for scale and corrosion control in open and semi-open cooling towers. It disrupts the crystal structure of minerals that cause scaling, transforming them into an amorphous state, and facilitates their removal through blowdown. It prevents corrosion on copper surfaces.
CK 429: A fully organic conditioning chemical used for scale and corrosion control in open and semi-open cooling towers. It is effective at high pH levels without the need for acid. Its fully organic formulation makes it environmentally friendly. It prevents corrosion on copper surfaces.
C BIOCIDE 886: A biocide designed for controlling microorganisms in industrial process water in open cooling towers. It prevents the growth of algae, bacteria, and fungi. It prevents blockages, contamination, and corrosion caused by this biological growth. It can be safely used on metal surfaces containing copper.
CK 699: An additive used to regulate pH and alkalinity in cooling systems. It prevents scaling caused by high pH levels.
CK 180: A fully organic dispersant used for scale control in open cooling towers. It prevents suspended solids in water from aggregating, settling, and adhering to metal surfaces, thereby preventing scale buildup in cooling towers. It provides clean surfaces that allow corrosion inhibitors to easily reach metal surfaces. When applied at high doses, it also gradually removes existing scale deposits.
Hakan ÇOBAN
Chemical Engineer
Water Treatment Consultant
Source:
https://www.ttmd.org.tr/PdfDosyalari/Dergi-Eki-41-1-1.pdf
https://muhendislik.sdu.edu.tr/assets/uploads/sites/148/files/sogutma-kulesi-12022015.pdf
http://eng.harran.edu.tr/~hbulut/Elemanlar.pdf
TMMOB Chamber of Chemical Engineers Water Handbook
Cemkimsan Chemistry Lecture Notes