A method for measuring circulating water flow in a cooling tower

Abstract

The present invention provides a method for measuring the circulating water flow of a cooling tower, including: arranging measuring points of the cooling tower, measuring measuring points of the cooling tower and collating the measuring results. The present invention utilizes the energy conservation principle of heat transfer between the air and the circulating water of the cooling tower, measures the inlet water temperature, outlet water temperature, inlet air dry bulb temperature, relative humidity and outlet air temperature of the cooling tower, calculates the circulating water process, can accurately obtain the circulating water flow of the cooling tower, and realizes the effective measurement and monitoring of the circulating water flow of the power plant.

Description

Technical Field

[0001] The invention relates to the technical field of cooling tower circulating water flow measurement, in particular to a cooling tower circulating water flow measurement method. Background Art

[0002] The circulating water flow rate of the cooling tower is a key parameter for the operation of a thermal power plant. The circulating water flow rate is directly related to the water temperature in and out of the cooling tower, the condenser end difference, the unit back pressure, and the power consumption rate of the power plant. The measurement and monitoring of the circulating water flow rate of the power plant is of great significance to the operation of the power plant.

[0003] At present, most domestic power plants lack the measurement and real-time monitoring of circulating water flow in power plants. They mainly test the outlet pressure of the circulating water pump, and then infer the circulating water flow based on the characteristic curve of the relationship between the outlet pressure and flow of the pump. The inferred flow rate deviates greatly from the actual water volume. A few power plants measure by adding ultrasonic flowmeters to the circulating water jelly pipes. Due to the large diameter of the circulating water pipeline, a long straight pipe section is required. Few power plants have a straight pipe section length in the circulating water pipeline system that meets the installation requirements of ultrasonic flowmeters. Therefore, accurate measurement and monitoring of circulating water flow has always been a difficult problem for power plants. Summary of the invention

[0004] In view of the above-mentioned prior art, the present invention proposes a method for measuring the circulating water flow rate of a cooling tower to accurately obtain the circulating water flow rate of the cooling tower.

[0005] The present invention provides a method for measuring the circulating water flow rate of a cooling tower, comprising the following steps:

[0006] S1. Arrangement of measuring points of cooling tower: Several outlet air temperature and air velocity measuring points are arranged at the throat of cooling tower. The air velocity at this position is uniform and not easily disturbed by the wind from the external environment. The outlet air temperature and air velocity of cooling tower can be accurately measured. Several inlet air temperature measuring points are arranged around the cooling tower, and they are 1.5-2.0m away from the ground. Atmospheric pressure measuring points are arranged in an open area 50m away from the cooling tower. A vertical shaft is arranged in the cooling tower, and the inlet water temperature measuring points are arranged in the vertical shaft. A water collecting tank and several water collecting tanks are arranged in the cooling tower. The water collecting tank connects the vertical shaft and the water collecting tank. The outlet water temperature measuring point is arranged at the end of the water collecting tank.

[0007] S2. Measurement of each measuring point of the cooling tower: Arrange each measuring instrument according to the arrangement requirements of each measuring point in step 1. When the cooling tower is running, measure the above parameters in real time to obtain the measurement results of each measuring point;

[0008] S3, measurement result collation: collate the measurement results of each measuring point obtained in step 2, and the specific collation steps are as follows:

[0009] 1) Calculate the enthalpy of the air entering the tower: calculate the average dry-bulb temperature and wet-bulb temperature of the air entering the tower;

[0010]

[0011] Among them, θ j —Average dry bulb temperature of air entering the tower, °C; θ j,k —Dry bulb temperature of air entering the tower at the kth measuring point, °C;

[0012]

[0013] Among them, τ j —Average wet bulb temperature of air entering the tower, °C; τ j,k —Wet-bulb temperature of air entering the tower at the kth measuring point, °C;

[0014]

[0015] in, is the relative humidity of the air entering the tower; —Saturated steam pressure corresponding to the wet bulb temperature of the air entering the tower, Pa; p a — atmospheric pressure, Pa; —Saturated steam pressure corresponding to the dry bulb temperature of the air entering the tower, Pa;

[0016] Where, the saturated steam pressure p" v According to the Guillet formula published by Guillet in 1939:

[0017]

[0018] Where, T is temperature in degrees Kelvin, K;

[0019] P" v ——Saturated steam pressure corresponding to temperature T, 10 5 Pa;

[0020]

[0021] Among them, i j —Enthalpy of air entering the tower, J / kg; other symbols are the same as before;

[0022] 2) Calculate the tower air enthalpy:

[0023]

[0024] Among them, θ o —Average dry bulb temperature of air leaving the tower, ℃; θ o,k —Dry bulb temperature of air leaving the tower at the kth measuring point, ℃; the air leaving the tower is saturated air, so τ o =θ o , τ o,k =θ o,k , where τo —Average wet bulb temperature of air leaving the tower, ℃; τ o,k —Wet-bulb temperature of air leaving the tower at the kth measuring point, °C;

[0025]

[0026] Among them, i o —Enthalpy of air out of the tower, J / kg;

[0027] ——The saturated steam pressure corresponding to the wet bulb temperature of the air leaving the tower, Pa;

[0028] 3) Calculate the tower air mass flow rate:

[0029]

[0030] Among them, ρ d —Dry air density, i.e. 1m 3 The mass of dry air in wet air, kg / m 3 ; R d —The gas constant of dry air is 287.14 J / (kg·K); the air out of the tower is saturated air, T=273.15+θ o

[0031]

[0032] Among them, V o —Average air velocity out of the tower, m / s; V o,k —Average air velocity out of the tower at the kth measuring point, m / s;

[0033]

[0034] Among them, m a —Dry air mass flow, kg / s; R o —Tower throat radius, m; S h — Cross-sectional area of ​​the tower throat;

[0035] 4) Calculate the temperature difference between the circulating water inlet and outlet:

[0036]

[0037] Where, t2—water temperature out of the tower, ℃; t 2,k —Water temperature out of the tower at the kth measuring point, °C; Δt=t1-t2, where Δt is the circulating water temperature difference, °C; t1 is the water temperature in the tower, °C;

[0038] 5) Calculate circulating water flow:

[0039] Q w =ma *(i o -i j ) / C w *Δt,

[0040] Among them, Q w —Circulating water flow, Kg / s; C w —Specific heat of water, J / (kg·℃).

[0041] Preferably, in S1, the outlet air temperature and air flow rate measuring points are arranged on two mutually perpendicular diameters in an equal-area ring manner, and the outlet air temperature and air flow rate measuring points are not less than 10; the distance between the outlet air temperature and air flow rate measuring points and the tower center is: Among them, R n —The distance from the tower center to each outlet temperature and air velocity measurement point, m; R—Tower throat radius, m; n—

[0042] The numbers of the air temperature and air velocity measurement points at the tower center; m—the number of equal area rings.

[0043] Preferably, in S2, a first platinum resistance thermometer and an impeller anemometer are arranged at the outlet air temperature and air flow rate measuring points, and the impeller anemometer is installed perpendicular to the air flow direction.

[0044] Preferably, the resolution of the first platinum resistance thermometer is not less than 0.2°C, and the accuracy is not less than level 0.5.

[0045] Preferably, the accuracy of the impeller anemometer is ±0.1°C.

[0046] Preferably, in S2, a second platinum resistance thermometer is arranged at the tower inlet air temperature measuring point.

[0047] Preferably, in S2, a barometer is arranged at the atmospheric pressure measuring point, and the accuracy of the barometer is not less than level 0.25.

[0048] Preferably, in S2, a third platinum resistance thermometer is arranged at the tower inlet water temperature measuring point, the resolution of the third platinum resistance thermometer is not less than 0.1°C, and the accuracy is not less than 0.5 level, ensuring that the third platinum resistance thermometer is submerged by the water level in the shaft.

[0049] Preferably, in S2, a fourth platinum resistance thermometer is arranged at the outlet water temperature measuring point.

[0050] Compared with the prior art, the beneficial effects of the present invention are as follows: the present invention utilizes the energy conservation principle of heat transfer between the cooling tower air and the circulating water, and calculates the circulating water process by measuring the cooling tower inlet water temperature, tower outlet water temperature, inlet air dry bulb temperature, relative humidity and tower outlet air temperature, so as to accurately obtain the cooling tower circulating water flow rate and realize effective measurement and monitoring of the circulating water flow rate of the power plant. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Figure 1 It is a schematic structural diagram of an embodiment of the present invention.

[0052] Among them, 1. Cooling tower; 2. Outlet air temperature and air velocity measuring points; 3. Inlet air temperature measuring point; 4. Collection tank; 5. Atmospheric pressure measuring point; 6. Vertical shaft; 7. Inlet water temperature measuring point; 8. Water collecting tank; 9. Outlet water temperature measuring point. DETAILED DESCRIPTION

[0053] In order to make the technical means, creative features, objectives and effects achieved by the present invention easy to understand, the present invention is further explained below with reference to specific diagrams.

[0054] Example

[0055] like Figure 1 As shown, a method for measuring the circulating water flow rate of a cooling tower comprises the following steps:

[0056] S1. Arrangement of measuring points of cooling tower: Several outlet air temperature and air velocity measuring points 2 are arranged at the throat of cooling tower 1; inlet air temperature measuring points 3 are arranged around cooling tower 1, and 4 inlet air temperature measuring points 3 are evenly arranged along cooling tower 1; atmospheric pressure measuring points 5 are arranged in an open area 50m away from cooling tower; a vertical shaft 6 is arranged at the center of cooling tower 1, and inlet water temperature measuring points 7 are arranged in the vertical shaft 6; a water collecting pool 4 and four water collecting tanks 8 are arranged in cooling tower 1, and outlet water temperature measuring points 9 are arranged at the end of water collecting tank 8 near the edge of water collecting pool 4. Water collecting tank 8 is triangular, one end of which is connected to the vertical shaft 6 at the center of the tower, and the other end is connected to the edge of water collecting pool 4. Water collecting tank 8 extends from the center of the tower to the edge of water collecting pool 4 with a certain slope (the center of the tower is high, and the edge of the water collecting pool is low), so that the circulating water flows out along water collecting tank 8, which is convenient for real-time and accurate measurement of the outlet water temperature of cooling tower.

[0057] Among them, the outlet air temperature and air velocity measuring point 2 are arranged on two mutually perpendicular diameters in the form of equal area rings. The distance between the outlet air temperature and air velocity measuring point 2 and the tower center is: Among them, R n —The distance from the tower center to each outlet air temperature and air velocity measuring point, m; R—Tower throat radius, m; n—The number of each outlet air temperature and air velocity measuring point starting from the tower center; m—The number of equal area rings.

[0058] S2, measurement of each measuring point of the cooling tower: arrange each measuring instrument according to the arrangement requirements of each measuring point in step 1, and measure the above parameters in real time when the cooling tower is in operation to obtain the measurement results of each measuring point; wherein, arrange a first platinum resistance thermometer and an impeller anemometer at the outlet air temperature and air flow rate measuring point 2, the impeller anemometer is installed perpendicular to the air flow direction, the resolution of the first platinum resistance thermometer is not less than 0.2°C, the accuracy is not less than 0.5 level, and the accuracy of the impeller anemometer is ±0.1°C; arrange a second platinum resistance thermometer at the inlet air temperature measuring point 3; arrange a barometer at the atmospheric pressure measuring point 5, the accuracy of the barometer is not less than 0.25 level, and the resolution is 0.1hPa; arrange a third platinum resistance thermometer at the inlet water temperature measuring point 7, the resolution of the third platinum resistance thermometer is not less than 0.1°C, the accuracy is not less than 0.5 level, and at the same time ensure that the third platinum resistance thermometer is submerged by the water level in the shaft 6; arrange a fourth platinum resistance thermometer at the outlet water temperature measuring point 9.

[0059] S3, measurement result collation: collate the measurement results of each measuring point obtained in step 2, and the specific collation steps are as follows:

[0060] 1) Calculate the enthalpy of the air entering the tower: Calculate the average dry-bulb temperature and wet-bulb temperature of the air entering the tower:

[0061]

[0062] Among them, θ j —Average dry bulb temperature of air entering the tower, °C; θ j,k —Dry bulb temperature of air entering the tower at the kth measuring point, °C;

[0063]

[0064] Among them, τ j —Average wet bulb temperature of air entering the tower, °C; τ j,k —Wet-bulb temperature of air entering the tower at the kth measuring point, °C;

[0065]

[0066] in, is the relative humidity of the air entering the tower; —Saturated steam pressure corresponding to the wet bulb temperature of the air entering the tower, Pa; p a — atmospheric pressure, Pa; —Saturated steam pressure corresponding to the dry bulb temperature of the air entering the tower, Pa;

[0067]

[0068] Among them, i j —Enthalpy of air entering the tower, J / kg; other symbols are the same as before;

[0069] 2) Calculate the tower air enthalpy:

[0070]

[0071] Among them, θ o —Average dry bulb temperature of air leaving the tower, ℃; θ o,k —Dry bulb temperature of air leaving the tower at the kth measuring point, ℃; the air leaving the tower is saturated air, so τ o =θ o , τ o,k =θ o,k， Among them, τ o —Average wet bulb temperature of air leaving the tower, ℃; τ o,k —Wet-bulb temperature of air leaving the tower at the kth measuring point, °C;

[0072]

[0073] Among them, i o —Enthalpy of air out of the tower, J / kg;

[0074] p"τ O ——The saturated steam pressure corresponding to the wet bulb temperature of the air leaving the tower, Pa;

[0075] 3) Calculate the tower air mass flow rate:

[0076]

[0077] Among them, ρ d —Dry air density, i.e. 1m 3 The mass of dry air in wet air, kg / m 3 ; R d —The gas constant of dry air is 287.14 J / (kg·K); the air out of the tower is saturated air, T=273.15+θ o

[0078]

[0079] Among them, V o —Average air velocity out of the tower, m / s; V o,k —Average air velocity out of the tower at the kth measuring point, m / s;

[0080]

[0081] Among them, m a —Dry air mass flow, kg / s; R o —Tower throat radius, m; S h — Cross-sectional area of ​​the tower throat;

[0082] 4) Calculate the temperature difference between the circulating water inlet and outlet:

[0083]

[0084] Where, t2—water temperature out of the tower, ℃; t 2,k —Water temperature out of the tower at the kth measuring point, °C; Δt=t1-t2, where Δt is the circulating water temperature difference, °C; t1 is the water temperature in the tower, °C;

[0085] 5) Calculate circulating water flow:

[0086] Q w =m a *(i o -i j ) / C w *Δt,

[0087] Among them, Q w —Circulating water flow, Kg / s; C w —Specific heat of water, J / (kg·℃).

[0088] The above are only implementation modes of the present invention, and are not intended to limit the patent scope of the present invention. Any equivalent structure made using the contents of the specification and drawings of the present invention, directly or indirectly used in other related technical fields, is also within the patent protection scope of the present invention.

Claims

1. A method for measuring the circulating water flow rate of a cooling tower, characterized in that: The steps include: S1. Arrangement of measuring points of cooling tower: several outlet air temperature and air velocity measuring points are arranged at the throat of cooling tower; several inlet air temperature measuring points are arranged around cooling tower; atmospheric pressure measuring points are arranged at least 50m away from cooling tower; a vertical shaft is arranged in cooling tower, and inlet water temperature measuring points are arranged in the vertical shaft; a water collecting tank and several water collecting tanks are arranged in cooling tower, and the water collecting tanks connect the vertical shaft and the water collecting tank, and the outlet water temperature measuring points are arranged at the end of the water collecting tanks; S2. Measurement of each measuring point of the cooling tower: Arrange each measuring instrument according to the arrangement requirements of each measuring point in step 1. When the cooling tower is running, measure the above parameters in real time to obtain the measurement results of each measuring point; S3, measurement result collation: collate the measurement results of each measuring point obtained in step 2, and the specific collation steps are as follows: 1) Calculate the enthalpy of the air entering the tower: calculate the average dry-bulb temperature and wet-bulb temperature of the air entering the tower; Among them, θ j —Average dry bulb temperature of air entering the tower, °C; θ j,k —Dry bulb temperature of air entering the tower at the kth measuring point, °C; Among them, τ j —Average wet bulb temperature of air entering the tower, °C; τ j,k —Wet-bulb temperature of air entering the tower at the kth measuring point, °C; in, is the relative humidity of the air entering the tower; —Saturated steam pressure corresponding to the wet bulb temperature of the air entering the tower, Pa; p a — atmospheric pressure, Pa; —Saturated vapor pressure corresponding to dry bulb temperature, Pa; Among them, i j —Enthalpy of air entering the tower, J / kg; other symbols are the same as before; 2) Calculate the tower air enthalpy: Among them, θ o —Average dry bulb temperature of air leaving the tower, ℃; θ o,k —Dry bulb temperature of air leaving the tower at the kth measuring point, ℃; the air leaving the tower is saturated air, so τ o =θ o , τ o,k =θ o,k , where τ o —Average wet bulb temperature of air leaving the tower, ℃; τ o,k —Wet-bulb temperature of air leaving the tower at the kth measuring point, °C; Among them, i o —Enthalpy of air out of the tower, J / kg; ——The saturated vapor pressure corresponding to the average wet bulb temperature of the air leaving the tower, Pa; 3) Calculate the tower air mass flow rate: Among them, ρ d —Dry air density, i.e. 1m 3 The mass of dry air in wet air, kg / m 3 ; R d —The gas constant of dry air is 287.14 J / (kg·K); the air out of the tower is saturated air, T=273.15+θ o Among them, V o —Average air velocity out of the tower, m / s; V o,k —Average air velocity out of the tower at the kth measuring point, m / s; Among them, m a —Dry air mass flow rate, kg / s; R o —Tower throat radius, m; S h — Cross-sectional area of ​​the tower throat; 4) Calculate the temperature difference between the circulating water inlet and outlet: Where, t2—water temperature out of the tower, ℃; t 2,k —Water temperature out of the tower at the kth measuring point, °C; Δt=t1-t2, where Δt is the circulating water temperature difference, °C; t1 is the water temperature in the tower, °C; 5) Calculate circulating water flow: Q w =m a *(i o -i j ) / C w *Δt, Among them, Q w —Circulating water flow, Kg / s; C w —Specific heat of water, J / (kg·℃).

2. The cooling tower circulating water flow measurement method according to claim 1, characterized in that: In S1, the outlet air temperature and air velocity measuring points are arranged on two mutually perpendicular diameters in an equal-area ring manner, and the outlet air temperature and air velocity measuring points are not less than 10; the distance between the outlet air temperature and air velocity measuring points and the tower center is: Among them, R n —The distance from the tower center to each outlet air temperature and air velocity measuring point, m; R—Tower throat radius, m; n—The number of each outlet air temperature and air velocity measuring point starting from the tower center; m—The number of equal area rings.

3. The cooling tower circulating water flow measurement method according to claim 1, characterized in that: In S2, a first platinum resistance thermometer and an impeller anemometer are arranged at the outlet tower air temperature and air velocity measurement points.

4. The cooling tower circulating water flow measurement method according to claim 3, characterized in that: The resolution of the first platinum resistance thermometer is not less than 0.2°C, and the accuracy is not less than level 0.

5.

5. The cooling tower circulating water flow measurement method according to claim 3, characterized in that: The accuracy of the impeller anemometer is ±0.1°C.

6. The cooling tower circulating water flow measurement method according to claim 1, characterized in that: In S2, a second platinum resistance thermometer is arranged at the tower inlet air temperature measuring point.

7. The cooling tower circulating water flow measurement method according to claim 1, characterized in that: In S2, a barometer is arranged at the atmospheric pressure measuring point, and the accuracy of the barometer is not less than level 0.

25.

8. The cooling tower circulating water flow measurement method according to claim 1, characterized in that: In S2, a third platinum resistance thermometer is arranged at the tower inlet water temperature measuring point.

9. The cooling tower circulating water flow measurement method according to claim 8, characterized in that: The resolution of the third platinum resistance thermometer is not less than 0.1°C, and the accuracy is not less than level 0.

5.

10. The cooling tower circulating water flow measurement method according to claim 1, characterized in that: In S2, a fourth platinum resistance thermometer is arranged at the outlet water temperature measuring point.

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