Circulating water treatment --water recycling systems of this knowledge, do you know?

Circulating water treatment/Recycling water systems of this knowledge, do you know?

Industrial circulating cooling water system in the operation process, due to water evaporation, wind loss and other circumstances so that the circulating water is constantly concentrated, which contains salts over the standard, anion and cation increase, pH value changes significantly, resulting in deterioration of water quality. The temperature, pH and nutrients of circulating water are favorable for microbial reproduction, and sufficient sunlight on the cooling tower is an ideal place for algae growth. The scale control and corrosion control, microbial control, etc., the inevitable need for circulating water treatment.

Circulating water operation in the process of the main problems:

(1) scale: due to the circulating water in the cooling process of evaporation, so that the salt concentration in the water continues to increase, more than the solubility of certain salts and precipitation. Common calcium carbonate, calcium phosphate, magnesium silicate scale. The texture of the scale is relatively dense, greatly reducing the efficiency of heat transfer, 0.6 millimeters of scale thickness will make the heat transfer coefficient reduced by 20%.

(2) dirt: dirt is mainly composed of organic matter in the water, microbial colonies and secretions, silt, dust, etc., the texture of the scale is fluffy, not only reduces the heat transfer efficiency and also cause corrosion under the scale, shorten the service life of the equipment.

(3) corrosion: circulating water corrosion of heat transfer equipment, mainly galvanic corrosion, resulting from equipment manufacturing defects, sufficient oxygen in the water, corrosive ions in the water (Cl-, Fe2 +, Cu2 +) as well as microbial secretion of mucus generated by the dirt and other factors, corrosion of the consequences of a very serious, uncontrolled very short period of time, even if the heat exchanger, water piping equipment scrapped.

(4) microbial slime: because the circulating water is dissolved in sufficient oxygen, the right temperature and eutrophic conditions, very suitable for microbial growth and reproduction, if not controlled in time will quickly lead to water quality deterioration, odor, black, cooling tower a large number of slime scale deposition and even blockage, cooling effect of cooling has decreased dramatically, and equipment corrosion has increased. Therefore, circulating water treatment must control the propagation of microorganisms.

Microbial hazards

microorganisms in the circulating cooling water from two aspects.

First, the cooling tower in the water evaporation process needs to introduce a large amount of air, microorganisms are also brought into the cooling water with the air;

Second, the cooling water system of the supplemental water more or less microorganisms, these microorganisms are also with the supplemental water into the cooling water system. Algae in the sunlight, will be in the water with carbon dioxide, bicarbonate and other carbon sources such as photosynthesis, absorption of carbon as nutrients and release of oxygen, therefore, when the algae bloom, it will increase the content of dissolved oxygen in the water, is conducive to the depolarizing effect of oxygen, corrosion process is accelerated as a result.

Microbial reproduction in the circulating water system, will make the circulating water color black, malodor, pollution of the environment. At the same time, a large number of slime will be formed to reduce the cooling efficiency of the cooling tower, wood deterioration and decay. Slime deposited in the heat exchanger, so that the heat transfer efficiency and head loss increase, deposited on the metal surface of the slime will cause serious corrosion under the scale, while it also isolates the corrosion and scale inhibitor on the metal role, so that the agent can not play a due corrosion and scale inhibition performance.

Microbial slime in addition to accelerate corrosion under the scale, some bacteria in the metabolic process, biological secretions will also be directly on the metal constitutes corrosion. All these problems lead to circulating water system can not be long-term safe operation, affecting the production, resulting in serious economic losses, therefore, the harm of microorganisms and scale, corrosion on the cooling water system is as serious as the harm, or even say, the three comparisons up to the control of microbial hazards is the first.

The movement of microorganisms in circulating water can be measured by the following chemical analysis program:

(1) residual chlorine (free chlorine) chlorination sterilization should pay attention to the residual chlorine time and residual chlorine, because the microbial reproduction of serious will make the circulating water chlorine consumption greatly increased.

(2) ammonia circulating water generally does not contain ammonia, but due to leakage of process media or inhalation of ammonia in the air will make the water appear to contain ammonia, this time can not be taken lightly, in addition to actively looking for ammonia leakage points, but also pay attention to the water whether it contains nitrite, the ammonia content in the water is best to be controlled in the 10mg / l or less.

(3) NO2- when the water appears to contain ammonia and nitrite, said the water has been nitrite bacteria will be converted to ammonia nitrite, then the circulating water system will become very difficult to add chlorine, chlorine consumption increases, the residual chlorine is difficult to meet the target, the water is best to control the NO2-content of less than 1mg/l.

(4) Chemical Oxygen Demand (COD) microbial reproduction in the water will increase COD, because the mucus secreted by the bacteria increase the organic content of the water, so through the analysis of chemical oxygen demand, you can observe the microbial changes in the water trends, COD in the water under normal circumstances is best less than 5mg / l (KMnO4 method).

The harm caused by microorganisms in circulating water is very serious, if you want to take measures after the microorganisms cause harm is often twice the effort but also cost a lot of biocides and money. Therefore, it is very necessary to comprehensively monitor the microbial situation of circulating cooling water beforehand.

Concentration times

circulating water concentration times refers to the circulating water system in the operation process, due to water evaporation, wind loss and other circumstances so that the circulating water is constantly concentrated times (to supplement the water as a benchmark for comparison), which is an important measure of water quality control is an important comprehensive indicators. Concentration times low, water consumption, sewage are large and the effectiveness of water treatment chemicals can not give full play to; concentration times high can reduce the amount of water, saving water treatment costs; but concentration times too high, the tendency of water scaling will increase, scaling control and corrosion control will increase the difficulty of water treatment chemicals will fail, not conducive to the control of microorganisms, so the concentration of the circulating water times to have a reasonable control index.

Scale formation

In the circulating water system, scale is formed by supersaturated water-soluble components, there are various salts dissolved in the water, such as bicarbonate, carbonate, chloride, silicate, etc., in which the dissolved bicarbonate, such as Ca (HCO3)2, Mg (HCO3)2 is the most unstable, and is very easy to decompose to generate carbonate. Therefore, when the cooling water in the dissolved bicarbonate more, the water flow through the heat exchanger surface, especially the surface of the higher temperature, it will be thermally decomposed; water dissolved phosphate and calcium ions, but also will produce calcium phosphate precipitation; calcium carbonate and Ca3 (PO4) 2, etc. are difficult to dissolve with the general salts are also different, and its solubility is not with the increase in temperature, but with the increase in temperature and decrease. Therefore, in the heat exchanger heat transfer surface, these insoluble salts are easy to reach the state of supersaturation and water crystallization, especially when the water flow rate is small or rough heat transfer surface, these crystalline precipitates will be deposited on the heat transfer surface, the formation of what is usually called scale, due to the crystallization of these scales are dense, relatively hard, also known as hard scale, the common components of the scale: calcium carbonate, calcium sulfate, calcium phosphate, magnesium salts, silicates, and so on. The common scale components are: calcium carbonate, calcium sulfate, calcium phosphate, magnesium salt, silicate.

Circulating water treatment technology according to the characteristics of the enterprise circulating water system and process conditions, combined with the local water quality characteristics, choose the water treatment program suitable for the operating conditions of the enterprise, through the dosing and other measures to control the circulating water indicators within a certain range of operation, not only to ensure that the production equipment of the long cycle of operation, but also to improve the utilization rate of circulating water.

The utilization of recycled water treatment technology can bring significant economic benefits to enterprises, but also bring good social benefits to society. So the application of recycled water treatment technology is very necessary.