JPS63243695A - Automatic blow down system for cooling tower - Google Patents

Abstract

PURPOSE:To hold the quality of cooled water stably in a given level for a long period of time, by making the data base of control by temperature and flow rate. CONSTITUTION:The evaporating rate of spray water is operated by a valve control device 19 from a temperature difference between temperatures of cooled water at the inlet port side and the outlet port side of a sealed cooling tower 1, the flow rate of cooled water and the latent heat of evaporation. Further, the amount of blow down is operated from the rate of evaporation and the discharging of water is controlled by controlling the opening degree of a water discharge control valve 17 so that the water discharging flow rate of a water discharging pipeline 15, branched from a spray water pipeline 10, is equalized to the amount of blow down. Fresh water, corresponding to the amount of spray water which is a decrement in the main body 1 of a cooling tower due to evaporation and discharging of water, is supplemented by a water feeding means, so that the level of the spray water in a lower water tank 8 is kept in constant at all times. According to this method, the quality of the spray water in the sealed cooling tower 1 may be kept at a given level stably for a long period of time.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention relates to an automatic blowdown device for a cooling tower, and particularly to spray water in a closed cooling tower or cooled water in an open cooling tower. This invention relates to an automatic blowdown device for a cooling tower that can stably maintain water quality at a certain standard over a long period of time.

(Prior Art) Conventionally, cooling towers used to cool objects to be cooled can be broadly classified into closed cooling towers and open cooling towers. The difference between a closed cooling tower and an open type cooling tower is that the former cools the water to be cooled by sprinkling water and blowing air through a heat exchanger, whereas the latter cools the water to be cooled by direct contact with the cooling outside air. It is to cool down. Although there is a difference between the spray water and the cooled water, there is no difference in the basic principle of cooling using latent heat of vaporization, and the common problem is deterioration of the water quality of the spray water and the cooled water. be. In the following description, a closed cooling tower will be described as an example.

In a closed cooling tower, water to be cooled is circulated in a heat exchanger that forms part of the cooling tower body, and the water is stored in a lower water tank provided below the heat exchanger. The water to be cooled is cooled by using the latent heat generated by the evaporation of the sprayed water by spraying the sprayed water through the spraying water piping with a water spraying means and by blowing cooled outside air.

In addition, this type of closed cooling tower is equipped with a water supply means that automatically replenishes the shortage of spray water in the lower water tank and maintains the level of spray water in the lower water tank at a constant level. , the amount lost due to evaporation of water sprinkled in the heat exchanger may have been replenished.
Condensation of sprinkled water progresses and water quality deteriorates. As a result of this deterioration of water quality, tendencies such as scale formation and increase in corrosion factors become noticeable, which both lead to fatal troubles such as decreased performance of the closed cooling tower and shortened operating life. Therefore, a blowdown device is required to forcibly drain a portion of the spray water through a drainage pipe branched from the spray water pipe and replace the spray water. Blowdown devices equipped with controllers have been developed in order to stabilize the

Now, as this type of blowdown device, one having the following control configuration is employed. That is, the water quality of a portion of the sprayed water flowing through a drainage pipe branched from the sprayed water pipe is detected by detecting the conductivity of the sprayed water using, for example, a conductivity meter as a water quality detector. The detected conductivity value is within the preset tolerance 1! If the water becomes higher than the water rate, the drain control valve installed on the drain pipe that branches off from the spray water pipe is fully opened to drain the water.
Conversely, when the conductivity value becomes lower than the allowable conductivity value, the drainage control valve is fully opened to stop drainage. Through this series of operations, the conductivity of the sprayed water is stabilized within the range of allowable conductivity values of the controller.
Excessive deterioration of the water quality of sprayed water can be prevented.

However, such a blowdown device has the following problems. In other words, as a detection item for the water quality of the sprayed water, we use conductivity, which can easily serve as a guideline to indicate the tendency of corrosion or scale formation, and we use a conductivity meter as the water quality detector, which has a lifespan of 9 calibrations. It is the easiest water quality detector to handle among the existing water quality detectors in terms of ease of use and two calibration levels. However, since this conductivity meter is a detector that measures electrical resistance, it uses an N pole as its detection part, but if water scale, scale, etc. from sprayed water adhere to this electrode, detection errors will occur. ,
It is necessary to keep the electrode surface clean at all times. In particular, when detecting the conductivity of sprayed water with very poor water quality, it is necessary to clean the sprayed water at short intervals, making it impossible to stably maintain the quality of the sprayed water at a constant level over a long period of time.

(Problems to be Solved by the Invention) As described above, in the conventional blowdown equipment, the control database is water quality and a water quality detector (conductivity meter) is used. Accurate detection characteristics cannot be obtained under severe conditions such as the quality of water or cooled water in an open cooling tower, and the water quality of sprayed water or cooled water cannot be maintained at a stable level for a long period of time. The problem was that I couldn't do it.

The present invention was made to solve the above-mentioned problems, and its purpose is to improve the stability, reliability, and maintainability of the detector by using the temperature and flow port as the control database, and to improve the stability, reliability, and maintainability of the detector. An object of the present invention is to provide an automatic blowdown device for a cold W tower that can stably maintain the quality of sprayed water in a cooling tower or liquid-cooled N water in an open type cooling tower at a constant level over a long period of time.

[Structure of the Invention] (Means for Solving the Problems) In order to achieve the above object, in the first invention, an inlet-side cooled water pipe,
The water to be cooled is circulated through the outlet-side cooled water piping, and the spray water stored in the lower water tank provided at the lower part of the heat exchanger is sprayed by the water spraying means through the spray water piping. In a hermetically sealed cooling tower that cools the water by blowing cooled outside air, the first step detects the temperature of the water flowing through the inlet-side cooled water pipe and the outlet-side cooled water pipe, respectively. A second temperature detector, a first flow rate detector that detects the flow rate of the cooled water flowing through the inlet-side cooled water pipe or the outlet-side cooled water pipe, and a first flow rate detector installed on the drainage pipe branched from the spray water pipe. a drain control valve;
The temperature difference between the humidity of the cooled water detected by the second flow rate detector that detects the flow rate of the waste water flowing through the drain pipe and each temperature detector.

The flow rate of the cooled water detected by the first flow rate detector.

The amount of evaporation of the sprayed water is calculated based on the latent heat of vaporization, and the amount of blowdown is calculated from the amount of evaporation of this sprayed water.
In addition, a valve control device is provided to control the opening degree of the drainage control valve so that this blowdown is equal to the drainage flow rate detected by the second flow rate detector, and a valve control device that controls the opening degree of the drainage control valve so that the blowdown flow rate detected by the second flow rate detector is equal to the drainage flow rate detected by the second flow rate detector. The automatic blowdown device is characterized in that it comprises a water supply means for supplying fresh water equivalent to the spraying hydraulics and keeping the water level of the sprayed water in the lower water tank constant. The water to be cooled stored in the lower water tank provided in the lower part of the tower body is sprinkled onto the main body of the cooling tower by a water spraying means through the outlet side cooled water pipe and the inlet side cooled water pipe. In a 6N open-air cooling tower that cools water by blowing cooled outside air into the tower, the temperature of the water flowing through the inlet-side cooled water pipe and the outlet-side cooled water pipe is detected, respectively. 1st. Second
a temperature detector, a first flow rate detector that detects the outflow of the cooled water that circulates to the cooling tower body through the outlet-side cooled water piping and the inlet-side cooled water piping, and a The temperature difference between the temperature of the cooled water detected by the drain control valve installed on the drain pipe, the second flow rate detector that detects the flow m of the waste water flowing through the drain pipe, and each temperature sensor, 1
The amount of evaporation of the sprayed water is calculated based on the outflow of the cooled water detected by the flow rate detector and the latent heat of vaporization, and the amount of blowdown is calculated from the amount of evaporation of this sprayed water. A valve control device that controls the opening degree of the drainage control valve so that the drainage flow rate detected by the second flow rate detector is equal to the drainage flow rate, and a valve control device that controls the opening degree of the drainage control valve so that the drainage flow rate detected by the second flow rate detector is equivalent to the amount of water to be cooled that has decreased due to evaporation and drainage in the cooling tower main body. By replenishing fresh water, the bottom water (a
and a water supply means for keeping the level of the water to be cooled in the cooling water at a constant level.

(Function) In the automatic blowdown system described above, the valve control device controls the temperature difference between the cooled water on the inlet side and the cooled water on the outlet side of the cooling tower main body, and the flow rate of the cooled water.

Calculate the amount of evaporation of the spray water or cooled water from the latent heat of evaporation, then calculate the blowdown ω from this amount of evaporation, and calculate the amount of blowdown and the drainage flow rate of the drainage pipe branched from the spray water pipe or the cooled water on the outlet side. Drainage control is performed by controlling the opening degree of the drainage control valve so that the drainage flow rate of the drainage pipe branched from the water pipe becomes equal. In addition, fresh water equivalent to the amount of sprayed water or cooled water reduced due to evaporation and drainage in the cooling tower body is replenished by the water supply means, and the level of sprayed water or cooled water in the lower water tank is always kept constant. dripping As a result of the above, the quality of the water sprayed in the closed cooling tower or the water to be cooled in the open cooling tower is stably maintained at a constant level over a long period of time.

(Example) First, the concept of the present invention will be described.

As mentioned above, deterioration in the water quality of sprayed water in closed cooling towers or cooled water in open cooling towers is caused by condensation due to evaporation, so it is necessary to quantitatively detect the amount of evaporation of sprayed water or cooled water. If water of stable quality such as tap water can be supplied, the amount of blowdown (drainage type) can be calculated by calculation.

Therefore, by controlling the drainage so that the blowdown amount calculated by this calculation is always equal to the flow rate actually discharged, the quality of the spray water or the water to be cooled can be maintained at a constant level.

In this regard, an example is given of a closed cooling tower.

A closed cooling tower cools the sprayed water by evaporating it when it hits the heat exchanger.In other words, the amount of heat cooled by the sealed cooling tower is the energy required for the sprayed water to turn into steam, so it is calculated as follows. The formula holds true.

E-Q/R... (1) Here, E is evaporation loss < J2/H), Q is cooling heat amount (K
cal), R is the latent heat of vaporization (Kcal/ff1) T:
be.

Further, the cooling heat IQ is calculated from the following equation depending on the conditions of the water to be cooled.

Q= G Difference (dec+
> is.

From the above, the evaporation amount E of the sprayed water is determined, and once this evaporation ME and the target water quality are determined, the blowdown amount can be calculated. In other words, how to determine the target water quality is
For example, how many times can the concentration of spray water be allowed?
If this allowable value is determined by the concentration factor (referred to as the concentration factor), the following equation holds true.

B=E・1/(N-1) ・・・・・・(3) Here, B is blowdown ffi (g/H), N is thick fl
It is a multiple.

Once the blowdown ff1B is determined from the above, if the drainage is controlled so that the discharge flow rate of the sprayed water is equal to this blowdown, water corresponding to (evaporation amount + drainage flow rate) is replenished from the water supply means, and the sprayed water is The water quality is N of the makeup water being replenished.
It becomes possible to maintain a state of twice the concentration. In addition, the same thing as above can be said about an open type cooling tower.

Hereinafter, an embodiment of the present invention based on the above-mentioned idea will be described with reference to the drawings.

FIG. 1 shows an example of the configuration of an automatic blowdown device for a closed cooling tower according to the present invention. In FIG. 1, a closed cooling tower 1 is constructed as follows. That is,
The cooling water that has exchanged heat with the object to be cooled 2 is sent as cooling water by the cooling water pump 3 through the inlet-side cooling water pipe 4 into the heat exchanger 5 that constitutes a part of the hermetic cooling tower 1. The cooled water is cooled and returned to the cooled body 2 through the outlet-side cooled water piping 6 and circulated there. In addition, cooling outside air is taken in by a blower 7, and spray water stored in a lower water tank 8 provided below the heat exchanger 5 is sent through a spray water pipe 10 by a sprinkler pump 9, and is sent to a sprinkler device 11. A part of the sprayed water is evaporated and discharged to the outside of the closed cooling tower 1 together with the cooled outside air.

On the other hand, the automatic blowdown device is configured as follows. In other words, W! A first degree detector 12 for detecting the temperature of the cooled water flowing through the pipe 4 is provided on the cooled water pipe 4 on the inlet side of the heat exchanger 5 in the closed cooling tower 1. A second humidity detector 13 for detecting the temperature of the water to be cooled flowing through the pipe 6 is provided on the outlet side of the water pipe 6 to be cooled, and a first humidity detector 13 for detecting the flow rate of the water to be cooled flowing through the pipe 6 is provided. A flow m detector 14 is provided. In addition, closed cooling tower 1
A drain pipe 15 is provided branching from the spray water pipe 10 on the discharge side of the water sprinkler pump 9, and a second flow detector 16 is further provided on the drain pipe 15 to detect the flow rate of the waste water flowing through the pipe 15. In addition, a drainage control valve 17 for controlling the flow rate of drainage flowing through the pipe 15 is provided and connected to the drain bit 18. Furthermore, 19 is a valve control device, which is configured as follows. That is, the above 1. Second
The output signals from the temperature detectors 12 and 13 of
This first . second converter 20.21
The output signals from the subtracters 22 are respectively inputted to the subtracter 22, where six temperature differences between the cooled water temperatures on the inlet side and the outlet side are calculated and output. Further, the output signal from the subtracter 22 and the output signal from the first flow rate detector 14 are respectively input to a multiplier 2.
3, and here the evaporation aQ of the sprayed water is calculated and output. Furthermore, the output signals from the multipliers 23 are respectively input to the divider 24, and the latent heat of evaporation value R of the spray water set in advance in the divider 24 and the output signal Q from the multiplier 23 are input.
From this, the evaporation loss ff1E of the sprayed water is calculated and output. Furthermore, the output signal from the divider 24 is input to a multiple multiplier 25, and by inputting the concentration multiple N to the multiple multiplier 25, the blowdown amount B is calculated and output.

and the output signal from this multiple multiplier 25.

The output signals from the second flow rate detector 16 are respectively input to the valve opening degree controller 26, and the opening degree of the drainage control valve 17 is controlled so that the values of the respective output signals are always equal. On the other hand, fresh water equivalent to the amount of sprayed water reduced due to evaporation and drainage in the heat exchanger 5 is replenished from a water supply tank (not shown) via a pole tap 27 serving as a water level adjustment valve, and the sprayed water in the lower water tank 8 is replenished. Trying to keep the water level constant.

Next, the operation of the automatic blowdown device configured as described above will be described.

In FIG. 1, the temperature of the cooled water on the inlet side of the closed cooling tower 1 is determined by the first temperature detector 12 and the first converter 20.
In addition, the second temperature detector 13 and the second converter 21 send out the temperature of the cooled water on the outlet side of the closed cooling tower 1 as a common signal, and the output signal from the first and second converters 20 and 21 is 11°t2 are each input to the subtracter 22, and the output of Δt is sent from the subtracter 22 according to the subtraction formula (tx-t2). This Δt corresponds to the temperature difference ΔT (deG) of the water to be cooled between the inlet side and the outlet side of the closed cooling tower 1. Further, the flow rate of the water to be cooled on the outlet side of the hermetic cooling tower 1 is detected by the first flow m detector 14, and the output q is sent out as a common signal as in the case of temperature detection. Then, the output signal Δt from the subtracter 22 and the output signal q from the first flow rate detector 14 are both input to the multiplier 23, and within the multiplier 23, (Δ
The output q is sent out by the multiplication formula of tXg).

This output q is an output signal corresponding to the amount of cooling heat Q of the hermetic cooling tower 1, and the amount of cooling heat that changes every moment due to changes in the load of the heat source and fluctuations in the outside air temperature dry bulb temperature is sent out as a signal without a time lag, and is divided by 24 as an input. The divider 24 calculates (q
/r) output e is sent out. This output e is output information corresponding to the evaporation loss ff1E of the sprayed water.

Furthermore, the output e sent from the divider 24 is input as an input signal to the multiple multiplier 25. Multiple multiplier 2
In step 5, the blowdown rate, which is the discharge flow rate of the sprayed water, is calculated by inputting as a numerical value the concentration ratio that is allowable as sprayed water with respect to the quality of the water supplied to the lower water tank 8 at the pole tap 27. Ru. That is, when the allowable concentration factor n (-allowable water quality of water supply/water quality of water supply) is input to the multiple multiplier 25, the multiple multiplier 25 calculates ex1/
By sending out an output equivalent to 1 bt of drainage flow using the calculation formula (n-1') and constantly draining the spray water equivalent to this, it is possible to maintain the water quality of the spray water at all times n times higher than the water quality of the supplied water. Become. On the other hand, the actual drainage flow rate is constantly detected by the second flow rate detector 16, and an output b2 corresponding to this drainage flow rate is sent out. The output b1 from the multiple multiplier 25 and the output b2 from the second flow rate detector 16 are both input to the valve opening controller 26, which outputs the values of The opening degree of the drainage control valve 17 is controlled so that the values are always equal. In other words, the valve opening controller 2
6 sends a signal to open the drainage control valve 17 when the output b1 > b2, and a signal to close the drainage control valve 17 when the output bl < t)2, so that the output bt=output Control will be performed to keep it at b2. On the other hand, the decrease in the amount of sprayed water due to evaporation in the heat exchanger 5 and the above-mentioned drainage appears as a drop in the water level of the sprayed water in the lower water tank 8, but the water level of the sprayed water in the lower water tank 8 is kept constant by the pole tap 27. It is replenished to maintain the water level. That is, fresh water corresponding to the decrease in the sprayed water is constantly replenished from a water supply tank (not shown).

As mentioned above, in the automatic blowdown device for a closed cooling tower according to this embodiment, the control database is water quality and the control database is different from the conventional automatic blowdown device that uses a water quality detector (conductivity meter). The use of temperature and flow rate detectors as temperature and flow rate databases significantly improves the stability, reliability and maintainability of the detectors, and with this the stability of the entire automatic blowdown equipment. .

Reliability will also be improved. This allows stable operation over a long period of time, making it possible to maintain the quality of the sprayed water in the closed cooling tower 1 at a constant level. In addition, unlike conventional water quality detectors, which control water quality using only one factor, the blowdown control is performed by quantitatively determining the absolute factor of water quality deterioration called evaporation loss. There is no deterioration of water quality due to
It becomes possible to ensure balanced water quality.

Furthermore, since the cooling capacity of the hermetic cooling tower 1 is used as the basic condition for all control, the load on the heat source is low.

It is possible to perform stable drainage control without time lag, regardless of fluctuations in the cooling outside air conditions.

It should be noted that the present invention is not limited to the above embodiments, but can also be implemented as follows.

FIG. 2 shows an example of the configuration of an automatic blowdown device for an open cooling tower according to the present invention, and parts corresponding to those in FIG. 1 are designated by the same reference numerals.

Open cooling towers differ from closed cooling towers in that the water to be cooled is cooled by directly contacting the outside air without going through a heat exchanger, and the cooling principle is exactly the same. In other words, the spray water in a closed cooling tower and the cooled water in an open cooling tower are under exactly the same conditions and conditions, but the deterioration in water quality affects all the equipment in the cooled water system, making the problem even more serious. It can be said that it is serious.

Therefore, in the embodiment shown in FIG. 2, a first pipe is installed in the inlet-side cooled water pipe 4 from the cooling water pump 3 to the water sprinkler 11 of the open cooling tower 28 to detect the temperature of the cooled water flowing through the pipe 4. A temperature detector 12 is provided, and a first flow rate detector 14 for detecting the flow rate of the water to be cooled flowing through the pipe 4 is also provided on the outlet side water pipe 6 to be cooled leading to the outlet of the lower water tank 8.

A second temperature detector 13 is provided to detect the temperature of the water to be cooled flowing through the pipe 4, and the flow rate of the waste water flowing through the pipe 15 is detected in the drain pipe 15 branched from the cooled water pipe 6 on the outlet side. A second flow rate detector 16 is provided, and
A drainage control valve 17 is provided to control the flow rate of drainage flowing through the pipe 15, and a portion of the water to be cooled is discharged to the drain bit 18. The configuration of the valve control all device 19 is exactly the same as that of the embodiment shown in FIG.

Further, 29 is a filler made of a porous material provided to enhance the cooling effect.

Also in this embodiment, the first temperature detector 12, the second
Based on the respective output signals from the humidity detector 13 and the first flow m detector 14, the blowdown is calculated by performing the same calculation as described above, and this blowdown rank and the second flow mound detection are calculated. By controlling the opening degree of the drainage control valve 17 so that the drainage flow rate detected by the device 16 is always equal, the quality of the water to be cooled can be stabilized to a certain standard, similar to the quality of the sprayed water in Fig. 1. It is possible to keep it.

In addition, the present invention can be modified and implemented in various ways without changing the gist thereof.

[Effects of the Invention] As explained above, according to the present invention, the stability, reliability, and maintainability of the detector are improved by using temperature and flow rate as the control database, and the control database improves the stability, reliability, and maintainability of the detector. It is possible to provide an automatic blowdown device for a cooling tower that can stably maintain the quality of water to be cooled in a type cooling tower at a constant level over a long period of time.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an automatic blowdown device for a closed cooling tower according to one embodiment of the present invention, and FIG. 2 is a block diagram showing an automatic blowdown device for an open type cooling tower according to another embodiment of the present invention. be. DESCRIPTION OF SYMBOLS 1... Sealed cooling tower, 2... Cooled object, 3... Cooling water pump, 4... Inlet side cooled water piping, 5... Heat exchanger, 6... Outlet side cover Cooling water piping, 7...Blower,
8... Lower water tank, 9... Watering pump, 1o... Sprinkling water piping, 11... Watering device, 12... First temperature detector, 13... Second temperature detector , 14...first
Flow rate detector, 15...Drainage piping, 16...Second flow ω detector, 17...Drainage control valve, 18...Drain pit, one...Valve control device, 20. ...First converter, 21...Second converter, 22...Subtractor, 23
... Multiplier, 24 ... Divider, 25 ... Multiple multiplier, 26 ... Valve opening controller, 27 ... Pole tap, 28 ... Open cooling tower, 29 ...・Filling material. Applicant's agent Patent attorney Takehiko Suzue No. 10 Figure 2

Claims (2)

[Claims] (1) The water to be cooled is circulated through the inlet-side cooled water pipe and the outlet-side cooled water pipe in the heat exchanger that constitutes a part of the cooling tower body, and the heat exchanger In a closed cooling tower, the water to be cooled is cooled by spraying water stored in a lower water tank provided in a lower part of the tower by a water spraying means through water spray piping and by blowing cooled outside air, a first temperature detector that detects the temperature of the cooled water flowing through the inlet-side cooled water pipe; a second temperature detector that detects the temperature of the cooled water flowing through the outlet-side cooled water pipe; a first flow rate detector that detects the flow rate of the cooled water flowing through the inlet-side cooled water pipe or the outlet-side cooled water pipe; and a drainage control valve provided on a drainage pipe branched from the spray water pipe. , a temperature difference between the temperature of the cooled water detected by the second flow rate detector that detects the flow rate of the waste water flowing through the drain pipe and each of the temperature detectors, and the temperature difference of the cooled water detected by the first flow rate detector. The amount of evaporation of the sprayed water is calculated based on the cooling water flow rate and the latent heat of evaporation, the amount of blowdown is calculated from the amount of evaporation of this sprayed water, and the amount of blowdown and the amount of blowdown are detected by the second flow rate detector. a valve control device that controls the opening degree of the drainage control valve so that the discharged water flow rate is equal to the discharged water flow rate; 1. An automatic blowdown device for a cooling tower, comprising a water supply means for maintaining a constant level of sprayed water in a water tank. (2) The water to be cooled stored in the lower water tank provided at the lower part of the cooling tower body is sprinkled and circulated through the outlet side cooled water pipe and the inlet side cooled water pipe by a water spraying means. , in an open type cooling tower configured to cool the water to be cooled by blowing cooled outside air against the water spray, a first cooling tower for detecting the temperature of the water to be cooled flowing through the water to be cooled pipe on the inlet side; a temperature detector; a second temperature detector that detects the temperature of the cooled water flowing through the outlet-side cooled water pipe; and a second temperature detector that detects the temperature of the cooled water flowing through the outlet-side cooled water pipe and the inlet-side cooled water pipe to circulate to the cooling tower main body. a first flow rate detector that detects the flow rate of the water to be cooled; a drainage control valve provided on a drainage pipe branched from the outlet-side cooling water pipe; and a drainage control valve that detects the flow rate of the drainage water flowing through the drainage pipe. The spray water is calculated based on the temperature difference between the temperature of the cooled water detected by the second flow rate detector and each of the temperature detectors, the flow rate of the cooled water detected by the first flow rate detector, and the latent heat of vaporization. The amount of evaporation of the sprayed water is calculated, and the amount of blowdown is calculated from the amount of evaporation of this sprayed water, and the amount of blowdown is calculated from the amount of evaporation of the sprayed water. A valve control device that controls the opening degree of the control valve, and a water level of the cooled water in the lower water tank that is kept constant by replenishing fresh water equivalent to the amount of cooled water that has decreased due to evaporation and drainage in the cooling tower main body. An automatic blowdown device for a cooling tower, comprising: a water supply means for maintaining water supply;