The cooling water is closed and the water is not cooled in direct contact with the air. The water quality standard for closed system circulating cooling water should be determined according to the production process conditions (usually soft water or demineralized water). In a closed system, the heat is cooled by a heat exchange device with air or a water-to-water heat exchange device to recirculate the water supply system. The water in the closed circulating water system is not affected by the surrounding environment.
1. DC indirect cooling water system
The DC indirect cooling water system is discharged after the water is used once through the heat exchanger, and is used in a flooded area. For circulating cooling water systems with cooling pool cooling, if V/Q > 60 (V-cooling pool volume, m3; Q-circulating water volume, m3/h), it can be considered as DC cooling water system.
There are mainly the following methods for preventing scaling of the DC cooling water system.
(1) The temperature of the water is limited, and the hardness of the carbonate is less than 7 mmol/L, and the temperature of the water is controlled within an allowable range.
1) The allowable temperature tw for surface water that is stable at room temperature.
2) The allowable temperature tw for surface water unstable at normal temperature.
(2) Low-dose dosing method. Adding 0.3-0. 5mg/1-sodium tripolyphosphate or other scale inhibitor to the water prevents fouling of the DC cooling system. But not economic.
The natural water temperature varies with the season, weather and temperature. When the DC cooling water system has a large amount of water, it will cause the water body to warm up and damage the water ecosystem to cause thermal pollution. In order to protect the environment, the cooling water temperature emission standard is established or the temperature limit of the heat exhaust port and the mixing is used as a standard.
Second, open indirect circulating cooling water system
In the open indirect circulating cooling water system, after the heat exchanger is used, the water needs to be in direct contact with the air. According to the different contact modes of A- and air, it can be divided into water surface cooling, water spray cooling pool cooling and cooling tower. Cooling, etc. After the heat exchanged cooling water is cooled by the cooling tower, due to evaporation, concentration and direct contact with air, the water quality of the circulating cooling system will change as follows: 1 the turbidity increases; 2 the temperature rises to about 40 ° C in the cooling system Ca(03) is decomposed to produce CaC03 scale; 3 salt content is increased; pH value is increased; 5 dissolved oxygen is increased, which may cause oxygen corrosion of the circulating cooling equipment. Therefore, the open circulating cooling water treatment mainly prevents the heat exchanger from scaling, corrosion, the growth of the microbial microorganisms and the sludge deposit. In GB50050-2007 " Design Code for Industrial Circulating Cooling Water Treatment ", it is stipulated that the heat resistance of the water side of the heat transfer surface of the equipment should be less than 3.44X 10-4 m2·K/W; the water side adhesion rate of the heat transfer surface of the equipment is not 005mm/a。 The corrosion rate of the water side of the heat transfer surface of the copper alloy and stainless steel equipment should be less than 0. 005mm / a.
Third, closed circulating cooling water system
The cooling water is closed and the water is not cooled in direct contact with the air. The water quality standard for closed system circulating cooling water should be determined according to the production process conditions (usually soft water or demineralized water). In a closed system, the heat is cooled by a heat exchange device with air or a water-to-water heat exchange device to recirculate the water supply system. The water of the closed circulating water system is not affected by the surrounding environment, and there is no problem of various ions in the concentrated water. The mass concentration is constant, and the main problem of the closed circulating hot and cold water system is corrosion. The water-side corrosion rate of the heat transfer surface of the carbon steel equipment should be less than 0. 075mm / a; copper; the heat resistance of the water side of the closed-circuit cooling water system equipment should be less than 0. 86 X 10-4 m2 · K / W; 005mm/a。 The corrosion rate of the water side of the heat transfer surface of the alloy and the stainless steel equipment should be less than 0. 005mm / a.
4. Direct cold-opening circulating cooling water system
The direct cold-opening circulating cooling water system refers to a circulating cooling water system in which circulating cooling water is directly in contact with the cooled medium and the circulating cooling water is in direct contact with the atmosphere to dissipate heat.
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