Common aspects of cooling water

Common to both designs:

Interaction of air and water flow allows partial temperature equalization and water evaporation.The air, now saturated with water vapor, exits the top of the cooling tower. A "collection basin" or "cold water basin" is used to collect and contain cooling water after interaction with the airflow.Both crossflow and counterflow designs are available for both natural draft and mechanical draft cooling towers.

Wet Cooling Tower Material Balance 

Quantitatively speaking, the material balance around a wet evaporative cooling tower system is controlled by operational variables such as make-up volume flow, evaporative and windage losses, discharge rate, and enrichment period.In the adjacent figure, the water drawn from the tower basin is cooling water passing through process coolers and condensers in industrial facilities.The cold water absorbs heat from the hot process stream that needs to be cooled or condensed, and the absorbed heat heats the circulating water (C).The warm water returns to the top of the cooling tower and drips down onto the fill material inside the tower.As it drips down, it comes into contact with ambient air rising through the tower, either through natural draft or forced draft using large fans in the tower. This contact causes a small amount of water to be lost in the form of windage or drift (W), and some water (E) to evaporate.The heat needed to evaporate the water comes from the water itself, which cools the water down to its original basin water temperature before it can be recirculated.The evaporated water leaves its dissolved salts in the bulk of the unevaporated water, increasing the salt concentration in the circulating cooling water.To prevent the salt concentration in the water from becoming too high, a portion of the water is pumped or drained (D) for disposal. Makeup fresh water (M) is supplied to the tower basin to compensate for evaporative water, windage loss water and pumped water losses.

Maintenance

Clean cold water basins and surfaces of visible dirt and debris with any visible biofilm (i.e. slime).Sanitizer and other chemical levels in cooling towers and hot tubs should be maintained and regularly monitored.Water quality (especially aerobic bacteria levels) should be checked regularly, as the presence of other organisms can support Legionella by producing the organic nutrients needed for growth.

Water treatment

In addition to treating circulating cooling water in large industrial cooling tower systems to minimize scale and fouling, the water is filtered to remove particulates, and biocides and algaecides are added to prevent growth that could interfere with the continuous flow of water. Under certain conditions, microbial biofilms such as bacteria, fungi, and algae will grow rapidly in cooling water, reducing the heat transfer efficiency of cooling towers.Using chlorine or other chemicals can reduce or prevent biofilm.Common industry practice is to use both oxidizing and non-oxidizing biocides to complement each other and ensure a wider range of attack. In most cases, use continuous low-level oxidizing biocides followed by alternating periodic bursts of non-oxidizing biocides.

Algicides and biocides

As the name suggests, algaecides are designed to kill algae and other associated plant-like microorganisms in water.Bactericides can reduce remaining biological matter, improving the system and maintaining clean and efficient water in cooling towers.When it comes to water sanitizers, one of the most common choices is bromine.

Antiscalants

One of the problems that cause the most damage and stress to water tower systems is fouling.When unwanted substances or pollutants in the water build up in an area, it creates deposits that grow over time.This can cause a range of problems from narrowing of the pipe to complete blockage and equipment failure.The water consumption of the cooling tower comes from drift, water release, and evaporation loss.The water that is immediately replenished into the cooling tower due to the loss is called make-up water.The function of make-up water is to make the machinery and equipment run safely and stably.