How to control scaling in closed cooling towers

During the operation of closed cooling towers, due to the existence of evaporation ratio, the concentration multiple of spray water directly affects the degree of scaling, and the concentration multiple is particularly important.

The concentration multiple refers to the ratio of the content of substances concentrated due to evaporation in circulating cooling water to the content of the same substance in make-up water, or the ratio of make-up water to sewage volume. The calculation method is as follows: The ratio of the salt content of circulating cooling water to make-up water is called the concentration ratio. This indicator is generally calculated based on the ratio of the chloride ion (or potassium ion) content in circulating water and make-up water. The salt content of fresh water is different from that of circulating water after the concentration process. The ratio N between the two is called the concentration multiple and is expressed as follows:

N =SCirc / SMake

Where SCirc --- the salt content of circulating water, mg/L;

SMake --- the salt content of fresh water, mg/L;

It is troublesome to calculate the concentration multiple based on the salt content. In practice, it is often necessary to select a certain ion concentration or conductivity in the circulating water that is not easy to consume but can be quickly measured to replace the salt content for the calculation of the concentration multiple. Generally, the concentration multiple is calculated based on the CL- concentration. However, if liquid chlorine is used as a biocide in the circulating water and CL- is introduced, it is not appropriate to calculate the concentration multiple based on CL-. Therefore, SiO2, K+, etc. are usually used to calculate the concentration multiple. The ratio of the example concentration in the circulating water to the corresponding ion in the make-up water. Intuitively speaking, it is the ratio of the circulating water to the make-up water. It is a standard for measuring water quality. It is widely used in circulating water such as industrial cooling water.

Increasing the concentration multiple of circulating cooling water can reduce the amount of make-up water, thereby saving water resources; it can also reduce the amount of sewage discharged, thereby reducing environmental pollution and the amount of wastewater treatment. In addition, increasing the concentration multiple can also save the consumption of water treatment agents, thereby reducing the cost of cooling water treatment. However, increasing the concentration multiple too much will increase the hardness, alkalinity and turbidity in the circulating cooling water too much, and the scaling tendency of the water will increase a lot, making scaling control too difficult. It will also increase the content of corrosive ions (such as Cl and SO4) and corrosive substances (such as H2S, SO2 and NH3) in the circulating cooling water, and the corrosiveness of the water will increase, making corrosion control more difficult; increasing the concentration multiple too much will also increase the residence time of the reagent (such as polyphosphate) in the cooling water system and hydrolyze. Therefore, the higher the concentration multiple of cooling water, the better. Generally, the thermal power system can be controlled at 5 to 8 times, and the chemical industry and oil refining can be controlled at 2 to 4 times.

Generally, we increase the concentration multiple of cooling water by controlling the evaporation amount. The benefits are: increasing the concentration multiple of cooling water can reduce the amount of supplementary water and save water resources; increasing the concentration multiple of cooling water can reduce the amount of sewage discharged, thereby reducing environmental pollution and wastewater treatment; increasing the concentration multiple of cooling water can save the consumption of water treatment agents, thereby reducing the cost of cooling water treatment;

Excessively increasing the concentration multiple of cooling water also has the following disadvantages: excessively increasing the concentration multiple of cooling water will make the hardness and alkalinity of cooling water too high, and the scaling tendency of water will increase;

Therefore, if we want to ensure the treatment effect of cooling water, we must control the concentration multiple of cooling water. Usually, the concentration multiple of closed cooling tower spray circulation cooling water is generally controlled at 4 to 5.