HG 20522-1992 Design regulations for cooling towers in chemical enterprises
Some standard content:
Industry Standard of the People's Republic of China
Design Regulations for Cooling Towers in Chemical Enterprises
HG 20522-92
Editor: Eighth Design Institute of the Ministry of Chemical Industry
Approval Department: Ministry of Chemical Industry
Editorial Center for Engineering Construction Standards of the Ministry of Chemical Industry
1992 Beijing
1 General Principles
1.0.1 The design of cooling towers in chemical enterprises shall meet the requirements of safe production, economic rationality, environmental protection, energy conservation, water conservation and land conservation, as well as convenience for construction, operation and maintenance.
1.0.2 The design of cooling towers in chemical enterprises shall actively develop and conscientiously adopt advanced technologies on the basis of constantly summarizing production practice experience and scientific experiments. 1.0.3 These regulations apply to the design of newly built and expanded mechanical ventilation wet cooling towers in chemical enterprises. When designing projects in other industries, relevant industry regulations may be followed. If there are no regulations in the relevant industry, these regulations may be followed. 1.0.4 The boundaries of large, medium and small cooling towers are divided as follows: Large: single-cell cooling water load is greater than 1500m2/h. Medium: single-cell cooling water load is greater than 500m2/h and less than or equal to 1500m*/h.
Small: single-cell cooling water load is less than or equal to 500m3/h. 1.0.5 The amount of cooling water required by the heat exchanger and condenser is related to the cooling water temperature t, t,. The design of the cooling tower should be closely coordinated with the chemical process, and multiple schemes should be compared to achieve advanced technology and economic rationality.
1.0.6 An independent circulating cooling water system should be set up in the following situations: 1.0.6.1 When the cooling water contains special chemicals, such as the cooling water system of acetylene, biogas, carbon black, caustic soda, sulfuric acid, phosphate fertilizer and other devices. 1.0.6.2 When the heat exchanger material has special requirements for the cooling water quality. 1.0.7
The design of circulating cooling return water pipe system should consider the return water residual pressure on the tower to save energy.
1.0.8When the technical economy, meteorological parameters and process parameters are suitable (temperature difference is less than 1
8℃, high cooling amplitude is 5~~7℃), natural ventilation wind tube type cooling tower can be used. 1.0.9The heat exchange characteristics of cooling tower should adopt the actual measured data of prototype tower. When the actual measured data of prototype tower is lacking, the test data of simulation tower can be used, and the test data of simulation tower can be corrected by 0.85~1.00.
1.0.10In addition to implementing these regulations, the design of cooling tower of chemical enterprises should also comply with the provisions of relevant current national standards and specifications. 2. Value selection and collation of meteorological parameters
2.0.1The meteorological parameters of meteorological stations that can represent the meteorological characteristics of the cooling tower location should be selected. If necessary, a meteorological observation station should be set up at the location of the cooling tower. 2.0.2 Meteorological parameters should be based on the daily average values of the three hottest months of the recent five consecutive years.
2.0.3 Meteorological parameters should be taken as the arithmetic average of the values measured four times or three times during the day and night as the daily average values.
2.0.4 The design of cooling towers in chemical enterprises should be based on the wet bulb temperature frequency statistics method. The cooling tower water temperature after cooling should be calculated using the average wet bulb temperature of no more than five days in the hottest period of each year and other corresponding meteorological parameters. -
General Provisions
3.0.1 The thermal calculation of cooling tower design should adopt the method of exact difference or empirical method, and should also follow the following basic equations:
Counterflow Cooling Tower
Where: N-
AtCp_B
-Cooling number;
Water temperature difference, ℃;
Average humidity difference/kg, thousand air (kcal/kg, dry air);-Specific heat of water, J/kg·C (kcal/kg·C);Mass coefficient of moisture content difference, kg/m2. h (kg/kg); V-Packing volume, m°;
-Cooling water flow, kg/h;
-Correction coefficient (see Table 3.0.1.1). K
Cross-flow cooling tower
AtC,_ BH
In the formula: N-
Ain—-Kiq
-Cooling number:
Water temperature difference, C;
Aim———Average flame difference, J/kg, kcal/kg, dry air (kcal/kg, dry air); Cp
-Specific heat of water, J/kg·C (kcal/kg); Mass coefficient of mixed mass difference, kg/mh (kg/kg); q--Water density, kg/m2·h;
H-Packing height, m;
Correction coefficient (see Table 3.0.1.1).
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3.0.2 The exhaust air temperature of the designed cooling tower shall be calculated according to the following formula: KAt
Where: ij -——air inlet temperature, J/kg, dry Air (kcal/kg, dry air); At
—water temperature difference, ℃;
In—mass flow rate ratio of air and water; K—correction coefficient (see Table 3.0.1.1). 3.0.3 To improve the overall efficiency of cooling tower fans, the following measures should be taken: The design of the fan duct diffusion section should adopt a truncated cone or parabola shape. 3.0.3.11
3.0.3.2 The distance from the fan blade tip to the fan duct should be controlled. The clearance of the inner wall is equal to or less than 30mm.
3.0.3.3 For cross-flow cooling towers, the height from the top of the filler to the lower edge of the fan suction section should be controlled to be equal to or greater than 0.2 times the fan diameter. 3.0.3.4 For counter-flow cooling towers, the height of the contraction section from the top of the fill to the lower edge of the fan suction section should be controlled to be equal to or greater than 0.5 times the fan diameter. When designing a counter-flow cooling tower, the water density and wind speed in the tower should be based on the following formula: 3.0:4
Data:
3.0.4.1 Large and medium cooling towers: water density: 7~12m/m2h; wind speed in the tower: 1.5~~2.3m/s. ||tt| |3.0.4.2 Small cooling tower: water density: 8~16m2/m2h wind speed in the tower: 2.0~2.5m/s.
When designing a cross-flow cooling tower, the water density should be controlled at 7.5~~ 58m2/3. 0. 51
m\h; The wind speed inside the tower is controlled at 1.8~3.3m/s. For multi-row cooling towers, the factors affecting floor space, humid and hot air return and interference 3.0.6=
should be considered. The ratio of length and width of each row should be selected according to the following data: large and medium cooling towers are 3:1～4:1; small cooling tower is 41～5:1.
The spacing between rows of counter-current towers arranged in multiple rows should be in accordance with the provisions of Table 3.0.7. 3.0.7
Watering area of a single tower in a tower row, m
Clear distance between tower rows, m
3.0.8 For counter-current towers arranged in multiple rows, when the tower row When the length is less than 70m, considering the influence of hot and humid air backflow and interference, it is advisable to add 0.1~0.3℃ to the wet bulb temperature value selected in the design.
3.0.9 For multi-row cross-flow tower groups, when When the tower length is less than 70m, considering the influence of hot and humid air backflow and interference, it is advisable to add 0.1 to 0.5℃.
For multi-compartment tower groups, appropriate separation measures should be taken in the water collection pool under the tower according to the chemical process commissioning procedures and the cooling tower fan maintenance conditions. 9
. Design calculation
Thermal calculation
Thermal calculation of countercurrent cooling towers should follow the following regulations: 4.1.1
4.1.1.1 For the thermal calculation of medium and small cooling towers with a cooling water temperature difference of 6~15℃, the average flame difference method (logarithmic mean method) should be adopted. 4.1.1.2 For the thermal calculation of large cooling towers with a cooling water temperature difference of 6~15℃, the Simpson approximate integration method should be adopted.
4.1.1.3 For the thermal calculation of large, medium and small cooling towers with a cooling water temperature difference greater than 15℃ and newly developed cooling towers, the Simpson approximate integration method should be adopted. 4.1.2 The thermal calculation of cross-flow cooling towers should follow the following regulations: 4.1.2.1 The thermal calculation of medium and small cooling towers with a cooling water temperature difference of 6~15℃ should adopt the Berman approximate solution method (B. Nusselt formula). 4.1.2.2 The thermal calculation of large cooling towers with a cooling water temperature difference of 6~~15C should adopt an authenticated computer program. When the conditions are not available, the segmented integration method should be adopted. 4.1.2.3 The thermal calculation of large, medium and small cooling towers and newly developed cooling towers with a cooling water temperature difference greater than 15℃ should adopt an authenticated computer program. 10
4.2 Ventilation resistance calculation
4.2.1 The ventilation resistance coefficient of the cooling tower should adopt the measured data of the prototype tower. When there is a lack of measured data, it can be calculated according to the empirical method. 4.2.2 The total resistance coefficient calculated step by step according to the empirical method is often too small, and an appropriate margin should be left when selecting the fan.
Calculation of water loss
The water loss of the cooling tower should be determined based on the amount of water lost due to evaporation, wind and sewage. The evaporation loss of the cooling tower is preliminarily determined to be 4.3. 1
percent of the circulating water entering the cooling tower, which can be calculated according to the following empirical formula: Pe-KAt
Where: P. Evaporation loss rate, %;
At-the temperature difference between the inlet and outlet water of the cooling tower, CK--coefficient, 1/℃ (adopted according to Table 4.3.1). Ambient air temperature, ℃
K, 1/℃
The wind loss of the mechanical ventilation cooling tower accounts for 0.2%~0.3% of the circulating water entering the cooling tower.
4.3.3 The sewage loss should be calculated and determined based on the requirements for the circulating water quality11
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