Water-Chemical Regime of Open Recirculating Cooling Systems | ITS Water Group
The growing shortage of water resources is prompting industrial enterprises to implement resource-saving technologies. Open recirculating cooling systems, which include cooling towers, are critical elements of industrial infrastructure. They play a key role in heat removal in industries such as metallurgy, energy, and petrochemicals.
The efficiency of open recirculating cooling systems directly depends on the quality of the cooling water. Without effective management of the water-chemical regime, these systems may lose performance, increase water consumption, and raise environmental risks. Therefore, optimizing the water-chemical regime is a strategic priority that combines technological efficiency with environmental responsibility.
Principle of Operation of Cooling Systems
The basic principle of operation of open recirculating cooling systems is evaporative cooling, which takes place in cooling towers. During operation, hot process water is supplied to the top of the cooling tower, where it is sprayed through nozzles and evenly distributed across the sprinkler system. As the water flows down in a thin film, it intensively contacts the air stream moving upwards (either by natural draft or fans). During partial evaporation, some of the water absorbs latent heat of vaporization, causing a reduction in the temperature of the main volume of circulating water. The resulting cooling ensures effective heat dissipation from the process equipment.
Managing the water-chemical regime in open recirculating cooling systems involves controlling the main processes that determine the system's stability and the quality of the circulating water. These processes include:
- The circulation of water between heat exchangers and the cooling tower, which ensures heat removal from the process equipment and its dispersion into the surrounding environment;
- Evaporation, where part of the water turns into vapor, causing the concentration of dissolved salts in the remaining water to increase;
- Blowdown (discharge of some concentrated water) to maintain a stable salt balance, prevent scale formation, and avoid corrosion.
A key indicator of the cooling system’s efficiency is the concentration factor, which reflects the degree of increase in the concentration of dissolved salts in the circulating water compared to the makeup water. The value of this factor determines the balance between evaporative losses, blowdown, and system makeup. Optimal indicators are achieved by adjusting blowdown intensity and applying chemical (reagent) treatment of the water, which ensures stable salt conditions, prevents scale formation, corrosion, and biofouling.
Operational Issues of Open Recirculating Cooling Systems
The main problems that arise during the operation of open cooling systems are scale formation, corrosion, and biological fouling. These processes directly affect the heat exchange efficiency, equipment reliability, and the sanitary safety of the system.
- Scale formation occurs due to oversaturation of water with calcium, magnesium salts, and carbonates that crystallize on heat exchange surfaces. Even a thin layer of deposits (approximately 1 mm) can reduce the heat transfer coefficient by 15–20% and significantly increase the system’s energy consumption.
- Corrosion develops under the action of dissolved oxygen, chloride ions, and microbial by-products. In environments with unstable pH and high electrical conductivity, the corrosion rate of carbon steels can reach 0.5 mm/year, leading to pipeline damage, leaks, and emergency downtime.
- Biological fouling is caused by the growth of bacteria, algae, and fungi that form stable biofilms. These biofilms reduce heat exchange efficiency, increase hydraulic resistance, and accelerate corrosion. Particularly dangerous are Legionella bacteria and sulfate-reducing bacteria, which pose both technical and sanitary risks.
Monitoring the water-chemical regime includes regular measurement of pH, electrical conductivity, corrosion rates, and microbiological parameters. The use of automatic analyzers in combination with periodic laboratory tests allows for timely adjustments to the system’s chemical regime and prevents the development of undesirable processes.
Reagent-Free Operation of Recirculating Cooling Systems
Reagent-free operation of open recirculating cooling systems is only possible if the incoming water has low mineralization and a stable salt composition. In such cases, the concentration factor is maintained at 2.0–2.5, which prevents excessive accumulation of dissolved salts in the circulating water.
However, this mode comes with several significant drawbacks:
- A substantial increase in blowdown volume — when 100 m³/h evaporates, blowdown water may reach around 100 m³/h;
- Excessive consumption of fresh water, which is 3–5 times higher than in reagent-treated systems;
- Increased operational costs for water supply and wastewater disposal.
- Despite the apparent environmental attractiveness of reagent-free operation, this scheme creates additional pressure on water resources and increases the risk of uncontrolled scale formation and localized corrosion damage to heat exchange surfaces.
Economic Feasibility of Reagent Use
The use of reagent treatment in recirculating cooling systems involves the implementation of stabilization programs (scale inhibitors, corrosion inhibitors, dispersants) and biocidal programs (oxidizing and non-oxidizing biocides). This approach allows for effective control of scaling, corrosion, and biological fouling, ensuring the stability of the heat technical characteristics of the equipment.
The main benefits of reagent treatment include:
- Reducing fresh water consumption by 60–80% due to an increased concentration factor;
- Extending the service life of equipment by 2–3 times by reducing corrosion rates and deposit formation;
- Cutting energy consumption by 15–25% due to improved heat transfer in heat exchangers.
Thus, rational management of the water-chemical regime is a key condition for energy-efficient and reliable operation of cooling systems. Reagent treatment helps optimize costs, reduce the anthropogenic load on the environment, and increase the economic efficiency of production.
ITS Water Group provides comprehensive solutions for reagent water treatment, including audits, reagent selection, and automation system implementation.
Visit our website for consultation and to calculate the economic effect of our services.
Our experienced specialists will help optimize the operation of your cooling systems and reduce maintenance costs.
