GB 50050-2007Code for design of industrial recirculating cooling water treatment (English PDF)

2.1 Terminology

2.1.1 Recirculating cooling water system

A water supply system that uses water as the cooling medium and runs in circulation, consisting of heat exchange equipment, cooling equipment, treatment facilities, water pumps, pipelines and other related facilities.

2.1.2 Surface water surface water

Refers to the water existing on the land surface exposed to the atmosphere, such as rivers, lakes, glaciers and swamps, excluding sea water.

2.1.3 Open system open system

A general term for indirect cooling open and direct cooling systems.

2.1.4 indirect open recirculating cooling water system indirect open recirculating cooling water system the circulating cooling water system with indirect heat transfer between the circulating cooling water and the cooled medium and the direct contact between the circulating cooling water and the atmosphere for heat dissipation is referred to as the indirect cooling open system.

2.1.5 Direct open recirculating cooling water system

The circulating cooling water system in which the circulating cooling water is in direct contact with the cooled medium to exchange heat and the circulating cooling water is in direct contact with the atmosphere to dissipate heat is referred to as the direct cooling system.

2.1.6 Indirect closed recirculating cooling water system indirect closed recirculating cooling water system the circulating cooling water system in which the circulating cooling water and the cooled medium indirectly transfer heat and the circulating cooling water does not come into contact with the atmosphere is referred to as a closed system.

2.1.7 Pharmacy chemicals

Various chemicals used in circulating cooling water treatment.

2.1.8 Total count of aerobic heterotrophic bacteria

The number of heterotrophic colonies per milliliter of water was counted by the bacterial plate count method, and the unit was CFU/mL.

2.1.9 Biological slime slime

A viscous substance in which microorganisms and their secreted mucus are mixed with other organic and inorganic impurities.

2.1.10 Biological slime amount slime content

The volume of biological slime contained in the circulating cooling water measured by the biological filter method, the unit is mL/m3.

2.1.11 Fouling resistance

The numerical value of the decrease in heat transfer efficiency due to deposits on the heat transfer surface of the heat exchange equipment, in m2·K/W.

2.1.12 Corrosion rate corrosion rate

The annual average corrosion depth calculated from metal corrosion weight loss, in mm/a.

2.1.13 Adhesion rate

The amount of dirt growth per month on the unit heat transfer surface of the heat exchanger, in mg/(cm2·month).

2.1.14 System water volume system capacity volume

The sum of all water volumes in the circulating cooling water system, in m3.

2.1.15 Cycle of concentration

Ratio of circulating cooling water to make-up water salinity.

2.1.16 Monitoring test coupon

Standard metal test strips placed in monitoring heat exchange equipment, test tubes or tower pools for monitoring corrosion.

2.1.17 Prefilming

The process of circulating the pre-film liquid through the heat exchange equipment to form a uniform and dense protective film on the metal surface.

2.1.18 Side stream

The part of water that is diverted from the circulating cooling water system and treated before returning to the system.

2.1.19 Permitted retention time of chemicals

The effective time of the agent in the circulating cooling water system.

2.1.20 Amount of makeup water

It refers to the amount of water lost during the operation of the supplementary circulating cooling water system, and the unit is m3/h.

2.1.21 Amount of blowdown

Under the condition of determined concentration multiple, the amount of water that needs to be discharged from the circulating cooling water system, the unit is m3/h.

2.1.22 Reclaimed water reclaimed water

After the sewage is treated, the water quality meets the water utilization requirements.

2.1.23 Stability index stability index

Refers to the difference between twice the saturated pH of the water and the actual pH of the water. This is used to determine the corrosion or scaling tendency of the water.

2.1.24 Scaling inhibition

Inhibit or delay the formation and growth of scale in the circulating cooling water system.

2.1.25 Corrosion inhibition

Inhibit or delay the process of metal corrosion in the circulating cooling water system.

2.2 Symbols

A——cooling tower air flow rate (m3/h);

Ac——dosing amount of sulfuric acid (kg/h);

C——air dust content (g/m3);

Cmi——the content of a certain component in supplementary water (mg/L);

Cms——supplemented water suspended solids content (mg/L);

Crs - suspended solids content in circulating cooling water (mg/L);

Cri——the content of a certain component in circulating cooling water (mg/L);

Csi——the content of a certain component in the water after side stream treatment (mg/L);

Css——Suspended solids content in filtered water (mg/L);

Gf——dosing amount for the first time (kg);

Go—dosage of oxidizing biocide (kg/h);

Gr—dosage dosage during system operation (kg/h);

g—dosage per liter of circulating cooling water (mg/L);

go—dosage of oxidized biocide per liter of circulating cooling water (mg/L);

Ks—sedimentation coefficient of suspended solids;

k——evaporation loss coefficient (1/°C);

Mm—Alkalinity of supplemented water (mg/L, calculated as CaCO3);

Mr - circulating cooling water to control alkalinity (mg/L, calculated as CaCO3);

N—concentration multiple;

Qb——the amount of sewage (m3/h);

Qb1——forced sewage discharge volume (m3/h);

Qb2——the amount of water lost during the treatment of circulating cooling water, that is, the amount of natural sewage (m3/h);

Qe——the amount of evaporated water (m3/h);

Qm——Supplementary water volume (m3/h);

Qr——circulating cooling water volume (m3/h);

Qsf - side filter water volume (m3/h);

Qsi——side flow treatment water volume (m3/h);

Qw——Water loss by wind (m3/h);

RSI - Stability Index;

Td——design residence time (h);

deltat——The temperature difference between the circulating cooling water entering and exiting the cooling tower (°C);

V——system water volume (m3);

Ve - water volume in circulating cooling water pumps, heat exchangers, other water treatment facilities and other equipment (m3);

Vp——the volume of water in the process production equipment (m3);

Vk——water volume of expansion tank or water tank (m3);

Vr——the volume of the circulating cooling water pipe (m3);

Vt - pool water volume (m3).

3.1 General provisions

3.1.1 The circulating cooling water treatment plan should be determined according to the water balance plan and salt balance plan of the whole plant, combined with the comprehensive technical and economic comparison of the water treatment process of the whole plant. The design plan should include the following.

1 Supplementary water source, water quantity, water quality and treatment plan;

2 Design concentration ratio, scale and corrosion inhibition, cleaning and pre-membrane treatment scheme and control conditions;

3 System drainage treatment plan;

4 side stream water treatment scheme;

5 Microbiological control program.

3.1.2 The amount of circulating cooling water shall be determined according to the maximum hourly water consumption of the production process.

3.1.3 The collection of supplementary water quality data should meet the following requirements.

1 Supplementary water is surface water, and monthly water quality analysis data should not be less than one year;

2 The supplementary water is groundwater, and the full analysis data of water quality from season to season should not be less than one year;

3 Supplementary water is reclaimed water, and monthly full analysis data of water quality should not be less than one year, including reclaimed water source composition and treatment process, etc.;

4 The water quality analysis items should meet the requirements of Appendix A of this specification, and the water quality analysis error should meet the requirements of Appendix B of this specification.

3.1.4 The water quality design basis for supplementary water shall adopt the average value of water quality analysis data, and check the equipment capacity with the most unfavorable water quality.

3.1.5 The control conditions and indicators of the circulating cooling water heat exchange equipment of the intercooling open system shall meet the following regulations.

1 The flow velocity of the circulating cooling water pipe should be greater than 1.0m/s;

2 The shell-side velocity of circulating cooling water should be greater than 0.3m/s;

3.The side wall temperature of the cooling water on the heat transfer surface of the equipment should not be higher than 70°C. When the temperature of the heat exchange medium is higher than 115°C, heat recovery measures should be taken before cooling with circulating cooling water;

4 The thermal resistance value of dirt on the water side of the heat transfer surface of the equipment should not be greater than 3.44×10-4m2·K/W;

5 The adhesion rate on the water side of the heat transfer surface of the equipment should not exceed 15mg/(cm2·month), and the oil refining industry should not exceed 20mg/(cm2·month);

6 The corrosion rate of the water side of the heat transfer surface of carbon steel equipment should be less than 0.075mm/a, and the corrosion rate of the water side of the heat transfer surface of copper alloy and stainless steel equipment should be less than 0.005mm/a.

3.1.6 The thermal resistance value of the dirt on the water side of the heat transfer surface of the closed system equipment should be less than 0.86×10-4m2·K/W, and the corrosion rate should meet the provisions of Item 6 of Article 3.1.5 of this code.

3.1.7 The water quality index of the circulating cooling water of the intercooling open system should be based on the water quality of the make-up water and the structural form, material, working conditions, thermal resistance of dirt, corrosion rate, properties of the heat-exchanging medium combined with water treatment chemicals Formula and other factors are determined comprehensively, and should meet the requirements in Table 3.1.7.

Table 3.1.7 Water Quality Index of Circulating Cooling Water in Intercooled Open System

3.1.8 The water quality index of the circulating cooling water in the closed system shall be determined according to the characteristics of the system and the requirements of the water-using equipment, and shall comply with the provisions in Table 3.1.8.

Table 3.1.8 Closed system cooling water quality indicators

Note. (1) The electrical conductivity of the shared circulation system of the dual-water internal cooling unit in thermal power plants and the independent cooling water system of the rotor should not exceed 5.0µS/cm (25°C).

(2)The copper content in the cooling water of the double-water internal cooling unit should not exceed 40.0µg/L.

(3) Control only when pH4 side stream water treatment

4.0.1 When one of the following situations occurs in the design of circulating cooling water treatment, side flow water treatment facilities shall be installed.

1.The circulating cooling water is polluted during the circulation process and cannot meet the requirements of the circulating cooling water quality standard;

2 After technical and economic comparison, it is necessary to use side flow water treatment to increase the design concentration factor.

4.0.2 The design scheme of side flow water treatment shall be determined based on the water quality standard of circulating cooling water, combined with factors such as the type and quantity of impurities to be removed.

4.0.3 When side flow water treatment is used to remove alkalinity, hardness, oil, certain ions or other impurities, the amount of side flow water shall be based on the concentrated or polluted water quality components, the water quality standard of circulating cooling water and the water quality after side flow treatment. Requirements, etc., shall be calculated and determined according to the following formula.

In the formula. Qsi——side flow treatment water volume (m3/h);

Cmi——the content of a certain component in supplementary water (mg/L);

Cri——the content of a certain component in circulating cooling water (mg/L);

Csi——The content of a certain component in the water after side stream treatment (mg/L).

4.0.4 The side filter treatment of the indirect cooling open system shall comply with the following regulations.

1 The cold open system should be equipped with side filter treatment facilities, and the small or intermittently running circulating cooling water system should be determined according to the specific situation.

The side filtration water volume of the two cold open systems can be calculated by the following formula.

In the formula. Qsf - side filter water volume (m3/h);

Cms——supplemented water suspended solids content (mg/L);

Crs - suspended solids content in circulating cooling water (mg/L);

Css——Suspended solids content in filtered water (mg/L);

A——cooling tower air flow rate (m3/h);

C——air dust content (g/m3);

Ks——sedimentation coefficient of suspended solids, which can be determined through experiments. When there is no data, 0.2 can be used.

3 When data such as air dust content is lacking, the side filtration water volume of the intercooled open system should be 1% to 5% of the circulating water volume, and it can be appropriately increased for dusty areas or areas with high air dust index.

Media filters such as sand and multi-media should be used for the side-flow water filtration treatment facilities of the 4-room cold-open system.

5 The turbidity of the outlet water of the bypass filter should be less than 3.0...