Antifoaming agent injection system and antifoaming agent injection method

Abstract

This invention provides an antifoaming agent injection system that suppresses the generation of excessive foam, optimizes the injection process of the antifoaming agent, and reduces the risk of malfunctions. [Solution] The defoaming agent injection system 10 includes a defoaming agent injection device 2 that injects a defoaming agent into a storage tank 5 in which liquid is stored, a radar-type level sensor 3 that detects the foam height h, which is the height from a reference plane to the surface of the foam layer formed on the liquid surface, at multiple different height levels, and a control device 1 that controls the defoaming agent injection device 2 according to the level of foam height h detected by the radar-type level sensor 3. When the foam height h rises to a first level, the control device 1 causes the defoaming agent injection device 2 to inject the defoaming agent, and after the injection of the defoaming agent has started, when the foam height h falls to a second level lower than the first level, the control device 1 stops the injection of the defoaming agent by the defoaming agent injection device 2.

Description

Technical Field

[0001] The present invention relates to a defoaming agent injection system and a defoaming agent injection method. Background Art

[0002] In the wastewater treatment process of water treatment, excessive generation of foam may be a problem. For example, in an aeration tank used for biological treatment utilizing the action of microorganisms or a regulation tank for wastewater (raw water) arranged upstream of the aeration tank, foam may be generated in the liquid by aeration or the like. In addition, foam may be generated when a large impact is applied to wastewater as the wastewater overflows from a high position such as a weir. In such a storage tank, if foam is excessively generated, the foam may overflow from the storage tank.

[0003] Even in manufacturing processes such as papermaking and food production, excessive foam generation may adversely affect product quality and productivity. For example, when washing food materials (e.g., potatoes etc.) using water stored in a storage tank, foam may be generated on the water surface. In this case, if excessive foam is generated, sufficient washing may not be performed, or the foam may overflow from the storage tank.

[0004] In order to suppress excessive foam generation, it is generally performed that a worker visually observes the liquid level in the storage tank, and when foam is generated more than necessary, the worker injects a defoaming agent into the storage tank to suppress foam generation. However, such manual work is time-consuming and places a heavy burden on workers.

[0005] As a method for automatically injecting a defoaming agent, a method of continuously injecting the defoaming agent into a storage tank at a constant injection rate has been proposed. However, in this method, the injection rate is set in consideration of the maximum foam generation amount so that a sufficient defoaming effect can be obtained even when foam is generated rapidly. For this reason, depending on the foam generation amount, the defoaming agent is injected excessively, resulting in an increase in chemical cost.

[0006] Therefore, a method for automatically adjusting the defoaming agent has been proposed (Patent Document 1). This method involves quantitatively measuring the degree of foaming at the liquid surface using non-contact detection means such as an ultrasonic level meter or a laser rangefinder, and adjusting the amount of defoaming agent added according to the measured degree of foaming. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Patent No. 5685878 [Overview of the project] [Problems that the invention aims to solve]

[0008] However, in the method described in Patent Document 1, non-contact detection means such as ultrasonic level meters and laser distance meters are at risk of malfunction due to environmental influences such as water droplets and steam.

[0009] The object of the present invention is to provide an antifoaming agent injection system and an antifoaming agent injection method that can suppress the generation of excessive foam, optimize the injection process of the antifoaming agent, and reduce the risk of malfunction. [Means for solving the problem]

[0010] To achieve the above objective, according to one aspect of the present invention, an antifoaming agent injection system is provided, comprising: an antifoaming agent injection device for injecting an antifoaming agent into a storage tank in which a liquid is stored; a radar-type level sensor for detecting the foam height, which is the height from a reference plane to the surface of a layer of foam formed on the surface of the liquid, at a plurality of different height levels; and a control device for controlling the antifoaming agent injection device according to the foam height level detected by the radar-type level sensor, wherein the control device causes the antifoaming agent injection device to inject the antifoaming agent when the foam height rises to a first level, and stops the injection of the antifoaming agent by the antifoaming agent injection device when the foam height falls to a second level lower than the first level after the injection of the antifoaming agent has started.

[0011] According to another aspect of the present invention, there is a method for injecting an antifoaming agent into a storage tank containing a liquid, characterized in that a radar-type level sensor that detects the foam height, which is the height from a reference plane to the surface of a layer of foam formed on the surface of the liquid, at a plurality of different height levels is used to detect the foam height level at predetermined time intervals, and when the foam height rises to a first level, the antifoaming agent is injected into the storage tank, and after the injection of the antifoaming agent has started, when the foam height falls to a second level lower than the first level, the injection of the antifoaming agent is stopped. [Effects of the Invention]

[0012] According to the present invention, it is possible to suppress the generation of excessive foam, optimize the injection process of the defoaming agent, and reduce the risk of malfunctions. [Brief explanation of the drawing]

[0013] [Figure 1] This is a schematic diagram showing the configuration of an antifoaming agent injection system according to the first embodiment of the present invention. [Figure 2] This is a block diagram showing the configuration of a radar-type level sensor. [Figure 3] Figure 1 shows a flowchart illustrating one procedure for the automatic defoaming agent injection process performed by the defoaming agent injection system. [Figure 4] This is a schematic diagram showing the configuration of an antifoaming agent injection system according to a second embodiment of the present invention. [Figure 5] Figure 4 is a flowchart showing one procedure of the automatic defoaming agent injection process performed by the defoaming agent injection system. [Figure 6] This is a schematic diagram showing the configuration of an antifoaming agent injection system according to a third embodiment of the present invention. [Figure 7] This is a schematic diagram illustrating the mounting configuration of a radar-type level sensor. [Figure 8] This is a schematic diagram showing an example of a wastewater treatment system. Mode for Carrying Out the Invention

[0014] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. However, the constituent elements described in the embodiments are merely illustrative, and are not intended to limit the scope of the present invention thereto.

[0015] (First Embodiment) FIG. 1 is a schematic diagram showing the configuration of a defoamer injection system according to a first embodiment of the present invention. In FIG. 1, solid-line arrows indicate pipes or flow paths, and broken-line arrows indicate signal lines or signals.

[0016] Referring to FIG. 1, the defoamer injection system 10 automatically injects a defoamer into a storage tank 5 that stores raw water (liquid) and has a foam layer 8 formed on the liquid surface. The storage tank 5 is, for example, a storage tank (tank) used in wastewater treatment processes, food manufacturing processes, and the like, but is not limited thereto. Any storage tank may be used as long as a foam layer is formed on the liquid surface. Although not shown in FIG. 1, the storage tank 5 has a function of stirring the injected defoamer.

[0017] The defoamer injection system 10 includes a control device 1, a defoamer injection device 2, and a radar level sensor 3. The defoamer injection device 2 includes a defoamer storage tank 2a that stores a defoamer, and an injection pump 2b for injecting the defoamer stored in the defoamer storage tank 2a into the storage tank 5.

[0018] The radar level sensor 3 is attached to the opening 5a of the storage tank 5. The radar level sensor 3 detects the foam height h, which is the height from the reference surface 5b (e.g., the bottom surface) to the surface of the foam layer 8, at a plurality of different height levels. The radar level sensor 3 can arbitrarily set a plurality of levels (detection positions) for detecting the foam height h. In the present embodiment, at least two levels H1 and L are set. Here, level H1 can be referred to as a first level, and level L can be referred to as a second level lower than the first level. The radar level sensor 3 outputs a signal indicating the foam height h. Note that the radar level sensor 3 may be configured to output a signal indicating level H1 when the foam height h reaches level H1, and output a signal indicating level L when the foam height h reaches level L.

[0019] The control device 1 controls the defoamer injection device 2 according to the level of the foam height h detected by the radar level sensor 3. Specifically, the control device 1 detects the level of the foam height h at predetermined time intervals using the radar level sensor 3. Then, when the foam height h rises to level H1 (the first level), the control device 1 causes the defoamer injection device 2 to start injecting a defoamer, and after the start of defoamer injection, when the foam height h drops to level L (the second level), the control device 1 stops the injection of the defoamer by the defoamer injection device 2.

[0020] The storage tank 5 is provided with a pump 6 for discharging the stored liquid. An opening 5c is provided in the upper part of the storage tank 5, and a level switch 4 for detecting the liquid level height (water level) is attached to this opening 5c. The level switch 4 is, for example, of a float type, and two float portions for detecting the upper limit and the lower limit of the liquid level height are arranged vertically. The level switch 4 outputs a signal indicating that the liquid level height has reached the upper limit when the liquid surface reaches the upper float portion, and outputs a signal indicating that the liquid level height has reached the lower limit when the liquid surface reaches the lower float portion. Note that the level switch 4 is not limited to the float type. As the level switch 4, other types such as capacitance type, electrode type, and high-frequency type may be used.

[0021] The control device 1 controls the liquid discharge operation of the pump 6 based on the output of the level switch 4. Specifically, when the liquid level rises and reaches the upper limit, the control device 1 operates the pump 6 to discharge the liquid, and then stops the pump 6 when the liquid level falls and reaches the lower limit. This allows the liquid level to be positioned between the upper and lower limits. In this case, it is preferable to set the level L of the radar-type level sensor 3 to a position higher than the upper limit of the liquid level. For example, if the level L is set to a position lower than the upper limit of the liquid level, the liquid level may exceed the level L, and in such a state, it becomes difficult to detect that the foam height h has fallen to the level L. By setting the level L higher than the upper limit of the liquid level, it becomes possible to reliably detect that the foam height h has fallen to the level L. Note that the liquid level height control using the level switch 4 and the pump 6 is not directly related to the operation of automatic defoaming agent injection, so the level switch 4 and the pump 6 may be omitted if liquid level height control is not required.

[0022] Next, the configuration and initial setup of the radar-type level sensor 3 will be described. Figure 2 is a block diagram showing the configuration of the radar-type level sensor 3. As shown in Figure 2, the radar-type level sensor 3 has a sensor unit 3a and a setting / processing unit 3b. The sensor unit 3a emits millimeter-wave radio waves toward the surface to be measured and receives the reflected waves from the surface to be measured. The setting / processing unit 3b can analyze the state of the reflected waves (for example, the time from when the radio waves are emitted until the reflected waves are received) and calculate the distance from the sensor unit 3a to the surface to be measured.

[0023] Although not shown in Figure 2, the setting / processing unit 3b includes an input operation unit and a display unit that shows the detection level and setting level. The operator can arbitrarily set multiple levels (detection positions) using the input operation unit while checking the display unit. The setting / processing unit 3b may be configured integrally with the sensor unit 3a, or it may be a separate unit that can communicate with the sensor unit 3a. In the latter case, the setting / processing unit 3b and the sensor unit 3a may be connected via a communication line, or they may be configured to communicate wirelessly. In this case, the setting / processing unit 3b can be installed in any location.

[0024] To perform the initial setup, the sensor unit 3a first emits millimeter-wave radio waves toward the reference surface 5b and receives the reflected waves from the reference surface 5b. The setting / processing unit 3b then calculates the distance from the sensor unit 3a to the reference surface 5b. The operator sets the levels L and H1 on the input operation unit while checking the display on the display unit. As a result, the setting / processing unit 3b can detect the bubble height h at levels L and H1 based on the distance to the reference surface 5b.

[0025] Next, the automatic defoaming agent injection process of the defoaming agent injection system 10 of this embodiment will be described. Figure 3 is a flowchart showing one procedure for the automatic defoaming agent injection process. First, the control device 1 starts the automatic defoaming agent injection process and checks the output of the radar-type level sensor 3 (step S1). Next, the control device 1 determines, based on the output of the radar-type level sensor 3, whether or not the foam height h has risen to level H1 (step S2).

[0026] If the result of step S2 is "No", the control device 1 executes the process of step S1 again after a predetermined time has elapsed. If the result of step S2 is "Yes", the control device 1 operates the injection pump 2b for a certain period of time to inject the defoaming agent into the storage tank 5 (step S3).

[0027] After the injection pump 2b stops, and after a certain period of time has elapsed, the control device 1 checks the output of the radar-type level sensor 3 (step S4). Next, the control device 1 determines, based on the output of the radar-type level sensor 3, whether or not the foam height h has dropped to level L (step S5).

[0028] If the result of step S5 is "No", the control device 1 executes the process of step S3 again. If the result of step S5 is "Yes", the control device 1 terminates the automatic defoaming agent injection process.

[0029] According to the defoaming agent injection system 10 of this embodiment described above, the defoaming agent can be automatically injected in response to changes in foam height h, thereby suppressing the generation of excessive foam and eliminating the need for monitoring and defoaming agent injection by operators, thus reducing the burden on operators. Furthermore, compared to methods of continuous injection of defoaming agents, this method allows for the injection of the appropriate amount of defoaming agent at the optimal timing in response to the rapid generation of foam. This optimizes the defoaming agent injection process and reduces chemical costs.

[0030] Furthermore, compared to non-contact detection methods such as ultrasonic level meters and laser rangefinders, the radar-type level sensor 3 uses millimeter-wave radio waves with strong directivity, making it less susceptible to environmental influences such as water droplets and steam. Therefore, the risk of malfunction can be reduced. Furthermore, while ultrasonic level meters and laser distance meters require periodic maintenance due to contamination of the detection unit, using the radar-type level sensor 3 eliminates the need for such periodic maintenance. Furthermore, since the detection range of ultrasonic level meters and laser distance meters widens as the distance to the reference plane increases, they can be affected by structures and side walls within the storage tank depending on their mounting location. Therefore, there are limitations on the mounting location of ultrasonic level meters and laser distance meters. In contrast, the radar-type level sensor 3, which uses millimeter-wave radio waves with strong directivity, is less affected by structures and side walls, thus mitigating the limitations on mounting location.

[0031] (Second embodiment) Figure 4 is a schematic diagram showing the configuration of an antifoaming agent injection system according to a second embodiment of the present invention. In Figure 4, solid arrows indicate piping or flow paths, and dashed arrows indicate signal lines or signals. The antifoaming agent injection system 11 of this embodiment differs from the antifoaming agent injection system 10 shown in Figure 1 in some aspects of the antifoaming agent injection process using the radar-type level sensor 3. Components identical to those in the antifoaming agent injection system 10 are denoted by the same reference numerals, and their detailed descriptions are omitted.

[0032] In the initial setup of the radar-type level sensor 3, levels H1, H2, and L are set. Levels H1 and L are as described in the first embodiment. Level H2 can be called a third level, which is higher than the first level (level H1). The radar-type level sensor 3 outputs a signal indicating the bubble height h. In this embodiment, the radar-type level sensor 3 is configured to output a signal indicating level H1 when the bubble height h reaches level H1, a signal indicating level H2 when the bubble height h reaches level H2, and a signal indicating level L when the bubble height h reaches level L.

[0033] The control device 1 controls the injection operation by the defoaming agent injection device 2 according to the foam height h detected by the radar-type level sensor 3. Specifically, similar to the first embodiment, when the foam height h rises to level H1 (first level), the control device 1 causes the defoaming agent injection device 2 to inject defoaming agent, and when the foam height h falls to level L (second level), it stops the injection of defoaming agent by the defoaming agent injection device 2. Furthermore, when the foam height h rises to level H2 (third level), the control device 1 increases the amount of defoaming agent injected by the defoaming agent injection device 2 to the amount injected when the foam height h rose to level H1.

[0034] Next, the automatic defoaming agent injection process of the defoaming agent injection system 11 of this embodiment will be described. Figure 5 is a flowchart showing one procedure for the automatic defoaming agent injection process. First, the control device 1 starts the automatic defoaming agent injection process and checks the output of the radar-type level sensor 3 (step S11). Next, the control device 1 determines, based on the output of the radar-type level sensor 3, whether or not the foam height h has risen to level H1 (step S12).

[0035] If the result of step S12 is "No", the control device 1 executes the process of step S11 again after a predetermined time has elapsed. If the result of step S12 is "Yes", the control device 1 operates the injection pump 2b for a certain period of time to inject the defoaming agent into the storage tank 5 (step S13). Let X1 be the amount of defoaming agent injected at this time. The injection amount X1 can be set appropriately considering the foam generation state. The injection amount X1 may be the total injection amount when the injection pump 2b is operated for a certain period of time, or the injection amount per unit time.

[0036] After the injection pump 2b stops, and after a certain period of time has elapsed, the control device 1 checks the output of the radar-type level sensor 3 (step S14). Then, based on the output of the radar-type level sensor 3, the control device 1 determines whether the foam height h has risen further to level H2 (step S15).

[0037] If the result of step S15 is "No", the control device 1 performs the determination in step S18, which will be described later. If the result of step S15 is "Yes", the control device 1 operates the injection pump 2b for a certain period of time to inject the defoaming agent into the storage tank 5 (step S16). Let the amount of defoaming agent injected at this time be X2 (>X1). In step S16, the injection amount increases compared to the injection amount in step S13. For example, the total injection amount when the injection pump 2b is operated for a certain period of time may be increased, or the injection amount per unit time may be increased.

[0038] After the injection pump 2b stops, and after a certain period of time has elapsed, the control device 1 checks the output of the radar-type level sensor 3 (step S17). Then, based on the output of the radar-type level sensor 3, the control device 1 determines whether or not the foam height h has dropped to level L (step S18).

[0039] If the result of step S18 is "No", the control device 1 executes the process in step S16 again. If the result of step S18 is "Yes", the control device 1 terminates the automatic defoaming agent injection process.

[0040] The defoaming agent injection system 11 of this embodiment described above also provides the same effects as in the first embodiment. In addition, when the foam height h rises to level H2, the amount of defoaming agent injected is increased. This reliably prevents foam from rapidly generating and overflowing from the storage tank 5.

[0041] (Third embodiment) Figure 6 is a schematic diagram showing the configuration of an antifoaming agent injection system according to a third embodiment of the present invention. In Figure 6, solid arrows indicate piping or flow paths, and dashed arrows indicate signal lines or signals. The antifoaming agent injection system 12 of this embodiment differs from the antifoaming agent injection system 11 shown in Figure 4 in that it has an alarm device 7. The same reference numerals are used for components that are the same as those in the antifoaming agent injection system 11, and their detailed descriptions are omitted.

[0042] The alarm device 7 outputs an alarm. The alarm device 7 may be one or more of the following: a transmitter that sends an alarm signal to an external device, a speaker that outputs an alarm sound, and a display device capable of displaying an alarm. Communication between the transmitter and the external device may be wireless communication or communication via a communication line. The display device may be a warning light or a liquid crystal display that displays a warning message.

[0043] In this embodiment, the control device 1 performs the automatic defoaming agent injection process shown in Figure 5, and when the radar-type level sensor 3 detects that the foam height h exceeds level H2 for a predetermined number of consecutive times, the alarm device 7 outputs an alarm.

[0044] According to the defoaming agent injection system 12 of this embodiment described above, in addition to the effects described in the first and second embodiments, the alarm device 7 outputs an alarm, which can inform the manager or operator of the defoaming agent injection system 12 that, for example, there is a possibility that foam may overflow from the storage tank 5. Here, the manager or operator may be located not only at the location where the storage tank 5 is installed, but also in a remote location.

[0045] In the defoaming agent injection systems 10-12 described above, there are several ways in which the radar-type level sensor 3 can be attached to the storage tank 5. Figure 7 is a schematic diagram illustrating the mounting configuration of the radar-type level sensor 3. The mounting configuration of the radar-type level sensor 3 will be briefly explained below with reference to Figure 7.

[0046] In the example shown in Figure 7(a), the opening 5a of the storage tank 5 is covered with a resin lid member 9a. The radar-type level sensor 3 is positioned outside the lid member 9a. In the radar-type level sensor 3, millimeter-wave radio waves emitted by the sensor unit 3a pass through the lid member 9a and reach the surface of the foam layer 8, and the reflected waves from the surface of the foam layer 8 pass through the lid member 9a and are received by the sensor unit 3a. The setting / processing unit 3b can analyze the state of the reflected waves received by the sensor unit 3a and calculate the distance from the sensor unit 3a to the surface of the foam layer 8.

[0047] In the example shown in Figure 7(b), the opening 5a of the storage tank 5 is covered with a metal lid member 9b. Millimeter-wave radio waves emitted by the sensor unit 3a cannot pass through the lid member 9b. For this reason, the sensor unit 3a is located inside the lid member 9b, and the setting / processing unit 3b is located outside the lid member 9b. The lid member 9b is provided with a through hole for passing a communication line connecting the sensor unit 3a and the setting / processing unit 3b. In the radar-type level sensor 3, the millimeter-wave radio waves emitted by the sensor unit 3a reach the surface of the bubble layer 8, and the reflected waves from the surface of the bubble layer 8 are received by the sensor unit 3a. The setting / processing unit 3b can analyze the state of the reflected waves received by the sensor unit 3a and calculate the distance from the sensor unit 3a to the surface of the bubble layer 8.

[0048] In the example shown in Figure 7(c), at least the upper part 51 of the storage tank 5 is made of a resin member 5d. The radar-type level sensor 3 is positioned outside the resin member 5d. In the radar-type level sensor 3, millimeter-wave radio waves emitted by the sensor unit 3a pass through the resin member 5d and reach the surface of the foam layer 8, and the reflected waves from the surface of the foam layer 8 pass through the resin member 5d and are received by the sensor unit 3a. The setting / processing unit 3b can analyze the state of the reflected waves received by the sensor unit 3a and calculate the distance from the sensor unit 3a to the surface of the foam layer 8. The resin member 5d constitutes the entire upper part 51 of the storage tank 5, but is not limited to this. A part of the upper part 51 may be formed by the resin member 5d. Alternatively, the entire storage tank 5 may be formed by the resin member 5d. According to the configuration shown in Figure 7(c), in existing storage tanks that were not intended for sensor installation, such as existing storage tanks without lids (however, at least the upper part is made of a resin material), the surface of the foam layer 8 can be detected by the radar-type level sensor 3 without performing any processing such as drilling holes for the sensor.

[0049] Depending on the type of liquid stored in the storage tank 5, corrosive gases may be generated. As shown in Figure 7, the mounting configuration of the radar-type level sensor 3 allows corrosive gases to leak out of the opening 5a by covering it with the lid members 9a and 9b.

[0050] (Examples of application) The defoaming agent injection systems 10-12 described above can be applied to all processing processes that use storage tanks that store liquids and form a layer of foam on the liquid surface, such as wastewater treatment processes and food manufacturing processes. Figure 8 is a schematic diagram showing an example of a wastewater treatment system. The wastewater treatment system includes a raw water tank 21, a regulating tank 22, an aeration tank 23, a sedimentation tank 24, and a discharge tank 25. The raw water tank 21 stores wastewater. Here, the wastewater is, for example, organic wastewater such as industrial wastewater or domestic wastewater, but is not limited to this.

[0051] The wastewater stored in the raw water tank 21 undergoes pH and flow rate adjustments in the adjustment tank 22 before flowing into the aeration tank 23. The aeration tank 23 supplies oxygen to the wastewater by exposing it to air. Biological treatment using the action of microorganisms takes place in the aeration tank 23, and the biologically treated water flows into the sedimentation tank 24. In the sedimentation tank 24, the sludge is separated by sedimentation, and the supernatant flows into the discharge tank 25 as treated water.

[0052] In the wastewater treatment system shown in Figure 8, foam is generated in the adjustment tank 22 and aeration tank 23 by aeration, etc. Any of the defoaming agent injection systems 10 to 12 can be applied to the adjustment tank 22 or aeration tank 23. For example, the storage tank 5 shown in any of Figures 1, 4, or 7 can be applied to the adjustment tank 22 or aeration tank 23 to control the injection of the defoaming agent. Note that the storage tank 5 does not necessarily have a pump 6 and a level switch 4. For example, the storage tank 5 may be an aeration tank or treated water tank that is used while constantly overflowing. Alternatively, the storage tank 5 may be a water tank used to wash food ingredients (e.g., potatoes) using the stored water. [Explanation of Symbols]

[0053] 1 Control device 2. Antifoaming agent injection device 3. Radar-type level sensor 4-level switch 5 Storage tank 6 pumps 8. Layer of foam 10. Antifoaming agent injection system

Claims

1. An antifoaming agent injection device that injects an antifoaming agent into a storage tank containing liquid, A radar-type level sensor that detects the bubble height, which is the height from a reference plane to the surface of the bubble layer formed on the liquid surface, at multiple different height levels, The device includes a control device that controls the defoaming agent injection device according to the level of foam height detected by the radar-type level sensor, The defoaming agent injection system is characterized in that the control device causes the defoaming agent injection device to inject the defoaming agent when the foam height rises to a first level, and stops the injection of the defoaming agent by the defoaming agent injection device when the foam height falls to a second level lower than the first level after the injection of the defoaming agent has started.

2. The defoaming agent injection system according to claim 1, wherein when the foam height rises to a third level higher than the first level, the control device increases the amount of defoaming agent injected by the defoaming agent injection device to an amount greater than the amount injected when the foam height rose to the first level.

3. It has an alarm device that outputs an alarm, The defoaming agent injection system according to claim 2, wherein the control device causes the alarm device to output the alarm when the radar-type level sensor detects that the foam height exceeds the second level a predetermined number of times consecutively.

4. The aforementioned storage tank has an opening at the top, and the opening is covered with a resin lid member. The defoaming agent injection system according to claim 1, wherein the radar-type level sensor detects the foam height via the lid member.

5. At least a portion of the aforementioned storage tank is made of a resin component, The defoaming agent injection system according to claim 1, wherein the radar-type level sensor detects the foam height via the resin member.

6. The radar-type level sensor comprises a sensor unit that emits millimeter-wave radio waves toward the surface of the foam layer and receives reflected waves from the surface, and a processing unit that analyzes the state of the reflected waves received by the sensor unit and calculates the distance from the sensor unit to the surface, wherein the sensor unit is located inside the storage tank and the processing unit is located outside the storage tank, the defoaming agent injection system according to claim 1.

7. The defoaming agent injection system according to claim 1, wherein an upper and lower limit is set for the height of the liquid level in the storage tank, and the second level of the radar-type level sensor is higher than the upper limit of the liquid level.

8. The aforementioned liquid is wastewater. The defoaming agent injection system according to any one of claims 1 to 7, wherein the storage tank is an aeration tank that exposes the wastewater to air and supplies oxygen to the wastewater, or a wastewater adjustment tank located upstream of the aeration tank.

9. A method for injecting an antifoaming agent into a storage tank containing a liquid, A radar-type level sensor is used to detect the bubble height, which is the height from a reference plane to the surface of the bubble layer formed on the liquid surface, at multiple different height levels, and the bubble height level is detected at predetermined time intervals. When the foam height rises to the first level, the defoaming agent is injected into the storage tank. A method for injecting an antifoaming agent, characterized in that, after the injection of the antifoaming agent is started, when the foam height drops to a second level lower than the first level, the injection of the antifoaming agent is stopped.

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