Industrial Circulating Water Treatment Technology

1. Why does a circulating water system need treatment?

Relevant industry reports indicate that in untreated circulating water systems, the average equipment lifespan can be reduced by 40%–60%, maintenance costs can increase 2–3 times, and energy consumption can rise by 15%–30%. More seriously, the probability of sudden failures can increase more than tenfold. Circulating water treatment affects equipment lifespan, production efficiency, and even enterprise safety.

2. What are the 'culprits' affecting the circulating water system?

The three main problems faced by industrial circulating cooling water systems are scale, corrosion, and microbial growth. These three factors are interconnected and do not occur independently. Once scale forms, it can block water flow and create favorable conditions for bacterial growth. Bacterial slime deposits can trap scale particles, thereby accelerating scale formation. Microorganisms find suitable breeding grounds in the rust layers produced by corrosion, creating a vicious cycle.

Circulating water usually produces calcium carbonate (CaCO3) and magnesium carbonate (MgCO3) scale. Makeup water, air, corrosion products, and biofilm produced by microorganisms contribute to scale formation. The hardness of scale is about 1/50 to 1/100 that of steel and tends to accumulate on the surfaces of heat exchangers and condensers. For every 1 mm increase in scale thickness, heat transfer efficiency decreases by 10-15%, and energy consumption increases by 5-8%.

(2) Corrosion
Corrosion products and biofilm produced by microorganisms accumulate in the system. The hardness of scale is about 1/50 to 1/100 that of steel and accumulates on the surfaces of heat exchangers and condensers. For every 1 mm increase in scale thickness, heat transfer efficiency decreases by 10-15%, and energy consumption increases by 5-8%. Corrosion occurs in two main forms in heat exchange equipment: microbial corrosion, where bacteria, algae, and other microorganisms produce acidic biofilm; and electrochemical corrosion, where sulfate, chloride, and other ions accumulate. Corrosion is pervasive, but the internal structure of cooling systems makes it difficult to prevent its development. These byproducts can cause material and equipment damage, environmental pollution, and even potential leaks. According to relevant regulations, the annual corrosion rate of carbon steel should not exceed 0.075 mm/year, and that of copper should not exceed 0.005 mm/year. Poor system operation and management can result in corrosion rates exceeding permissible limits by ten times.

(3) Microbial Growth
Air and domestic water contain high concentrations of bacteria, algae, fungi, and other microorganisms, which can circulate within the cooling water system. Algae can rapidly proliferate, forming dense layers on the cooling tower walls, fill media, and cooling water tank walls. The main effect is a reduction in the cooling tower's efficiency in cooling hot water, thereby decreasing the heat transfer efficiency of circulating water. Portions of detached algae can be carried with the cooling water to heat exchanger surfaces, forming scale. Theoretically, bacteria account for about 70% of all microorganisms in circulating water. Their metabolic activity produces large amounts of biofilm, which deposits as scale; some bacteria also produce acidic substances that corrode equipment. Under nutrient-rich conditions, microorganisms can proliferate extensively, causing water pollution and odor. The presence of odor and deterioration of water quality increases the frequency of system cleaning, thereby raising maintenance costs.

3. Circulating Water Treatment Technology

(1) Chemical treatment technology
The chemical method mainly adds chemicals containing the functions of scale inhibition, sterilization and algae inhibition, and corrosion inhibition to the water body to control the quality of circulating water.

Common corrosion inhibitors mainly include chromates, phosphates, molybdates, mercaptobenzothiazoles, etc. The most commonly used and effective way to control microbial growth is to use fungicides. Effective fungicides should have a broad spectrum, are easy to decompose or degrade after killing, are compatible with corrosion inhibitors, and can peel off biological slime. In general, fungicides can be divided into oxidizing fungicides (such as hypochlorous acid) and non-oxidizing fungicides. Oxidizing fungicides have strong bactericidal and algaecological effects, but increase the corrosion tendency of metal materials. Non-oxidizing fungicides also kill microorganisms efficiently and extensively, and have strong biofilm penetration and dispersion capabilities, but most of them are difficult to degrade and need to be used together.

(2) Physical treatment technology
Instead of adding chemicals to the circulating water system, the physical method uses an energy field. It mainly includes high-voltage electrostatic method, magnetization method, and ultrasonic method.

The high-voltage electrostatic method is to generate a "high-voltage electrostatic field" in water through an electrostatic generator, which charges impurities, thereby generating mutual repulsion and preventing impurities from precipitating. The water flow is able to easily carry these impurities away.

Magnetization is the application of a magnetic field to a body of water. Charged particles (dirt particles) in the water form structurally stable aggregates that in turn continuously produce suspended dirt particles, thereby preventing dirt deposition. At the same time, the water pressure increases after magnetization, and the microbial cells lose water and lose their activity.

The ultrasonic method uses an ultrasonic field to disperse and crush the scale in the water, making it difficult to adhere to the heat exchange equipment to form scale. The high temperature and high pressure generated by the rupture of cavitation bubbles in the water can effectively kill microorganisms.

(3) Electrochemical treatment technology
Electrochemical treatment technology can effectively reduce corrosion and deposition in circulating water with high ion concentrations. This technology is just as effective as chemical treatment techniques in preventing corrosion and scaling. The electrochemical treatment process produces oxidants that work in synergy with high currents to inactivate and eventually remove microorganisms.

(4) Biological treatment technology
The main technologies include microbial flora optimization, biodispersant dosing, etc.

Microbial flora optimization is to add specific microbial liquid to the industrial circulating cooling water, with the help of microbial metabolism, to decompose the organic pollutants in the circulating cooling water and inhibit the proliferation of harmful microorganisms.

Biodispersants are preparations that effectively disperse suspended solids such as silt, grease, and sediment.