What Is TDS In Cooling Towers

Emily Green

Emily is a senior R & D engineer at Oasis Bingfeng Fluid Equipment Co., Ltd. With over 10 years of experience in the cooling equipment industry, she has played a key role in the development of the company's core products, including closed cooling towers and air coolers.

TDS value is the core water quality control index of cooling tower operation, directly determining scaling, corrosion and microbial reproduction risks of open and semi-closed cooling systems, and improper TDS management will cause huge hidden dangers to cooling efficiency and equipment service life.

The formation mechanism of high TDS in cooling tower water lies in the continuous concentration cycle of water.

Cooling towers rely on water evaporation to remove heat, while pure water vaporizes into air, and all dissolved mineral substances cannot evaporate and remain in the circulating water continuously.

With the continuous loss of water, the concentration of soluble solids keeps rising, and the TDS value increases linearly with the operation time.

Even if the factory replenishes fresh tap water or well water every day, the new water will bring new mineral components, further accelerating TDS accumulation.

For open cooling towers exposed to the atmosphere, outdoor dust, industrial acid mist, salt fog and organic impurities will continuously dissolve into the circulating water, which will further push up the TDS level.

In coastal factories, chloride ions in salt fog significantly increase TDS; in mining and chemical parks, sulfates and heavy metal dissolved solids make TDS exceed the standard faster.

Closed cooling systems have lower TDS rising speed because the internal medium is isolated from air, yet long-term operation and regular water replenishment will still lead to slow TDS concentration.

Excessively high TDS brings three major fatal hazards to cooling tower and supporting equipment. The first hazard is severe scaling. Calcium and magnesium salts are the main components of TDS. When TDS exceeds the set threshold, the solubility limit of calcium carbonate, magnesium silicate and other precipitates is broken, and crystalline scale adheres to the surface of heat exchangers, coil pipes and condenser tubes.

Scale has extremely low thermal conductivity, which greatly reduces heat exchange efficiency. When the scale thickness reaches 0.3mm, the heat dissipation capacity of cooling equipment drops by more than 20%, leading to equipment overheating, production shutdown and increased power consumption of fans and water pumps.

Manual pickling and mechanical descaling require long downtime and high maintenance costs, and frequent pickling will erode metal pipe walls and cause hidden leakage risks.

The second hazard is accelerated metal corrosion. Chloride and sulfate ions in TDS are strong corrosive media. High TDS circulating water forms an electrochemical corrosion environment on carbon steel pipes, stainless steel coils and pump casings.

Chloride ions will penetrate the passive film on the metal surface, causing pitting corrosion and perforation of heat exchange coils, especially duplex stainless steel and copper pipes in closed cooling towers.

In severe cases, cooling medium leakage will pollute production equipment such as battery production lines and pharmaceutical reactors. High TDS also intensifies galvanic corrosion between different metal materials in the pipeline system, shortening the service life of valves, circulating pumps and connecting fittings by half or more.

The third hazard is massive breeding of microorganisms and biological slime. High-concentration dissolved solids contain rich nutrients such as nitrogen and phosphorus, which provide a suitable growth environment for bacteria, algae and fungi.

A large amount of biological slime adheres to the inner wall of pipelines and fillers, blocking water flow channels and reducing cooling water circulation volume.

Biological slime also forms a covering layer on the metal surface, where the difference in oxygen concentration will induce localized corrosion under the mud. At the same time, microorganisms will decompose organic matter to produce acidic substances, further aggravating pipeline corrosion and forming a vicious cycle of scaling, slime and corrosion.

Cooling tower operation relies on blowdown to control TDS within the safe range. Each type of cooling equipment has a fixed TDS control standard according to pipe material and working condition.

Ordinary carbon steel open cooling towers generally control TDS below 1000ppm; stainless steel closed cooling coils require TDS lower than 600ppm; coastal anti-corrosion equipment limits TDS under 400ppm to reduce chloride content.

When the online TDS detector finds that the numerical value exceeds the standard, the automatic blowdown valve opens to discharge high-concentration wastewater, and fresh low-TDS make-up water is supplemented to dilute the circulating water and reduce the overall TDS concentration. Operators will also add scale inhibitors, corrosion inhibitors and biocides to slow down the hazards caused by TDS accumulation, but chemical agents can only delay concentration risks and cannot fundamentally reduce TDS, so regular blowdown is still the core control method.

Improper TDS control will also increase production operating costs. Excessive blowdown to reduce TDS leads to huge waste of water resources, rising water and sewage treatment fees; insufficient blowdown causes frequent scaling and corrosion failures, increasing maintenance, replacement and shutdown losses. Therefore, real-time TDS monitoring and automatic proportional blowdown have become standard configurations of modern industrial cooling towers, balancing water consumption and equipment safety.

To sum up, TDS represents all dissolved mineral and organic impurities in cooling tower circulating water. Its continuous concentration caused by water evaporation is the root of scaling, corrosion and biological slime problems.

Strictly controlling TDS within the design safety range through blowdown and water quality chemical treatment is the key to stable, efficient and long-life operation of all open and closed cooling tower systems. Ignoring TDS monitoring will lead to reduced cooling efficiency, frequent equipment damage and substantial economic losses for industrial production lines.