Daily management of circulating water treatment equipment operation

The management of circulating water is often said to be "one-third chemical treatment and seven-tenths management," highlighting the importance of management. After the circulating water treatment equipment enters normal operation, during the processes of heating, evaporation, and cooling, the cooling water is gradually concentrated, and its water quality indicators will change. Daily operation management mainly involves timely adjustments based on changes in water quality, with regular analysis of the circulating water every shift.

1. Calcium hardness, total alkalinity:

Total alkalinity is an indicator in circulating water treatment control. When the concentration factor is stable and there is no other external interference, the change in total alkalinity can indicate the scaling trend of the system. Hardness refers to the sum of the Ca2+ and Mg2+ concentrations in the water, and is also an important indicator in circulating water operation control. The calcium hardness and total alkalinity of the circulating water must be controlled within the required range of the formula. According to the calculation, this system controls calcium hardness (as CaCO3) + total alkalinity at around 1100 mg/L; if the water quality conditions change, the water stabilization formula must be adjusted accordingly.

2. pH value:

Because circulating cooling water releases CO2 in the cooling tower, its pH value continuously increases with the increase in the concentration factor. When the concentration factor is constant, the pH value of the circulating water also tends to be stable. The pH value is generally controlled between 8.0 and 9.2.

3. Total phosphorus and chloride ions:

The purpose of determining total phosphorus in circulating water is to calculate the content of organic phosphorus in the circulating water. The corrosion inhibitor contains organic phosphonates. Based on the total phosphorus analysis data of the system, the dosage is appropriately increased or decreased to control the total phosphorus in the circulating water between 6.0 and 8.0 mg/L; if the total phosphorus is lower than 6.0 mg/L, increase the dosage of the corrosion inhibitor to reach the target range; if it exceeds 8.0 mg/L, appropriately reduce the dosage.

Excessive Cl- concentration in circulating water will accelerate equipment corrosion, especially stainless steel equipment, which is very sensitive to Cl-. Therefore, monitoring and control are necessary during operation; the Cl- concentration in circulating water generally does not change. In the absence of external introduction of chloride ions, it can represent the change in salinity in the circulating water, so the Cl- concentration is often used to calculate the concentration factor. Based on the system water quality, Cl- should be controlled at around 100 mg/L.

4. Slime:

Due to suitable temperature, good ventilation, and sufficient sunlight, the circulating water system becomes an ideal environment for the growth of various microorganisms. In this environment, the rapid proliferation of microorganisms is natural. Even when the microbial control work is well done, the total number of bacteria may reach 104～105/mL. If not controlled properly, the total number of bacteria can easily reach 106～108/mL. The harm of microorganisms is multifaceted, mainly the harm of biological slime. The slime in the circulating water system is mainly the general term for the attachments, sediments, and suspended matter caused by the activities of microorganisms. Once biological slime is formed, it must be sterilized, cleaned, and removed. If conditions permit, a thorough cleaning should be carried out during maintenance. During operation, strict sterilization and removal control should be implemented. If shutdown is impossible, non-stop chemical cleaning can be performed.

5. Concentration factor:

The salinity of fresh supplementary water and the salinity of circulating water after the concentration process are different. The ratio of the two is called the concentration factor, which is an important indicator of circulating water. Since salinity analysis is relatively troublesome, in production, the concentration of a certain ion that is not easily consumed and can be quickly measured in the circulating water, or the conductivity, is often used to replace salinity for calculating the concentration factor. For example, the solubility of chloride is very high, and it will not precipitate in the circulating water, and the Cl- concentration will not change. In the absence of external introduction of chloride ions, it can represent the change in salinity in the circulating water, so the Cl- concentration is often used to calculate the concentration factor. Generally, a low concentration factor means high water consumption and high wastewater discharge; a high concentration factor can reduce water consumption and save water treatment costs. However, an excessively high concentration factor will cause the hardness, alkalinity, and turbidity of the circulating cooling water to increase too much, greatly increasing the tendency of water scaling, thus increasing the difficulty of scaling and corrosion control, and increasing the residence time of water treatment chemicals in the cooling water system, leading to hydrolysis. Therefore, the K value of circulating cooling water is not the higher the better. Considering both water saving and the water quality of the concentrated circulating water, the concentration factor of this system is selected as 3.0 times.

6. Bacteria:

Persistently use oxidizing and non-oxidizing bactericides alternately to jointly control the growth of bacteria and algae in the cooling water treatment equipment. Oxidizing bactericides include: chlorine dioxide, TH-404, and sodium hypochlorite; non-oxidizing bactericides include: isothiazolinones, TH-406, and 1227. Each addition concentration is 100-200 mg/L (based on the retained water volume).