Circulating cooling water treatment

Circulating cooling water treatment

1Scope of application

Injection molding machine, mold water cooling system;

Industrial circulating cooling water system (smelting, petrochemical, brewing, power plant);

Central air conditioning (hotels, schools, subways, office buildings, public facilities);

With the development and improvement of China's industry, municipal facilities, and living conditions, the amount of water used for cooling circulation has rapidly increased. The use of circulating water is mostly through regular water replacement or chemical treatment. After long-term operation, the circulating water appears yellow brown, and algae and bacteria grow in the water, resulting in a decrease in the cooling effect of the process and an increase in energy consumption. Especially for ultra large circulating water systems, the regular replacement and replenishment time of water is long, and the water consumption is high, leading to high costs. The shortage of water sources in northern regions is particularly high consumption. Therefore, it is necessary to treat large cooling circulating water systems to keep the circulating water clear, algae free, and bacteria free for a long time.

2、 The main problems of circulating cooling water system

1.1.corrosion

The main cause of corrosion is the presence of dissolved oxygen in water. Oxygen can easily undergo oxidation reactions with carbon steel or other metals in the presence of water as a medium, generating metal oxides that gradually erode the metal and lose its original strength. Acidic substances, scaling, and bacterial adhesion can promote corrosion under the scale. Metal erosion can easily cause perforation and leakage, and its corrosion products can also deposit to form rust, reducing heat transfer efficiency. The circulating water also appears yellow brown.

1.2.scaling

There are two main reasons for scaling: one is hard scale, which is caused by the evaporation of circulating cooling water to remove heat and also concentrate minerals. When the concentration reaches a certain level, minerals such as CaCO3 (calcium carbonate) in the water will become supersaturated and crystallize. This type of scale is as hard as stone and difficult to remove mechanically; Another method is to continuously wash the air with circulating cooling water, so as to remove dust from the air and accumulate it in the system. This not only breeds bacteria but also gradually deposits to form sludge and scale. The sludge and scale formed by mineral crystallization can have a significant impact on heat transfer efficiency, not only wasting a lot of energy but also easily causing strong pore corrosion under the scale, accelerating the damage of metal equipment.

1.3.Microbial algae slime

Circulating cooling water has good conditions for the growth of bacteria and algae, rich in nutrients, suitable temperature, moderate acidity and alkalinity, and bacteria in water and air can easily enter the system. Once the seeds of these bacteria and algae have a good growth environment, they will multiply rapidly. The mucus secreted by the bacteria is prone to adhere to dust and form bacterial scale, seriously affecting heat exchange and even blocking the heat exchanger. In summer, about 60% of air conditioning circulating water systems without sterilization central treatment automatically trip due to high snow pressure caused by bacterial scale. Its impact on heat conduction exceeds that of typical hard water scale and sludge scale. The growth of algae will produce some residues and increase sludge and scale.

3、 Main solutions

2.1.Cleaning pre film:The system performs cleaning, pre coating, and removal of scale, corrosion products, oil stains, dust, and other impurities on the metal surface, and passivates the metal surface to form a protective film.

2.2.Medication corrosion inhibition:Through an online automatic dosing control system, corrosion and scale inhibitors are added in small quantities at regular or continuous intervals to prevent metal corrosion and scale deposition. Corrosion and scale inhibitors contain corrosion inhibiting components that can continuously repair the protective film generated during pre coating; The anti scaling component can keep minerals stable in water even when they exceed their saturation solubility and will not crystallize; Dispersible components can disperse dust, corrosion products, and phosphates generated after the decomposition of corrosion and scale inhibitors.

2.3.Sterilization and algae killing:Intermittent addition of bactericidal and algicidal agents to control the number of bacteria and algae within a limited range. Regularly test the water quality and adjust it appropriately to ensure that the water quality and chemical concentration are within the normal range..

2.4.Side flow filtration:A primary water intake is installed on the main inlet and outlet pipes of the air conditioning circulating water system. Through secondary pressurization, a portion of the circulating water is filtered through a filter (non valve gravity or mechanical) to remove mud, algae, pipeline debris, and rust attachments from the water. Maintain the turbidity of the circulating water in a clear state, improve the energy efficiency of the cooler, and alleviate scaling in the circulating pipeline.

4、 Process improvement

Considering the large pipeline network of the already built cooling circulating water system, it is necessary for precision molds, furnace bodies, andCentral air conditioning and other circulating cooling water use secondary sealed cooling, which exchanges heat with the cooling water of the cooled object through plate heat exchangers and outdoor cooling towers. Purified or softened water is used for sealed water, while tap water or reclaimed water is used for external circulating water. This process only requires regular cleaning of the plate heat exchanger. As the plate heat exchanger can be disassembled and cleaned, the heat exchange effect after cleaning is the same as that of newly installed systems, and it has been adopted by more and more enterprises. The main principle is as follows: