A generator cooling water corrosion control device

Abstract

The present invention discloses a generator cooling water corrosion control device, wherein the generator outlet is connected to a spray device in a cooling water tank, an exhaust collecting pipe is provided on the top of the cooling water tank, the outlet of the exhaust collecting pipe is connected to a variable frequency vacuum pump via a vacuum pump inlet valve, a vacuum pressure sensor is provided on the inner side of the top of the cooling water tank; the cooling water tank outlet is divided into two paths, one of which is connected to the generator inlet, and the other is connected to a circulation spray pipe on the top of a mixing device via a cooling water pump outlet water inlet valve, the mixing device is filled with polytetrafluoroethylene filler balls, the outlet of the alkali liquid tank is connected to the dosing spray pipe in the mixing device via a variable frequency metering pump and a metering pump outlet valve in turn, the bottom of the mixing device is connected to a conductivity meter; the bottom outlet of the mixing device is connected to the inlet of the cooling water tank via an electric flow regulating valve and a circulation flow meter in turn, the device and method can reduce the corrosion of copper wire rods by cooling water to a minimum.

Description

Technical Field

[0001] The invention belongs to the field of cooling water treatment in power plants and relates to a cooling water corrosion control device for generators. Background Art

[0002] The chemical water treatment method of the generator stator cooling water system directly affects the safe operation of the generator. Many accidents that occur during the operation of the generator are directly related to or closely related to the stator cooling water. With the changes in the structure, parameters and capacity of the generator, the copper corrosion and deposition in the part where the generator stator cooling water circulates are becoming more and more serious.

[0003] The generator stator cooling water uses desalted water as make-up water. The desalted water contains saturated dissolved oxygen and carbon dioxide. Carbon dioxide causes the stator cooling water to be weakly acidic. The weakly acidic water and dissolved oxygen work together to cause corrosion of the generator stator copper wire rods. The deposition of copper corrosion products will cause the generator stator wire rods to become blocked, causing the wire rods to heat up and the unit to be forced to trip, affecting the safe operation of the generator. Summary of the Invention

[0004] The purpose of the present invention is to overcome the shortcomings of the above-mentioned prior art and provide a generator cooling water corrosion control device and method, which can minimize the corrosion of cooling water on copper wire rods.

[0005] To achieve the above object, the present invention discloses a generator cooling water corrosion control device, comprising a generator, a cooling water tank, a vacuum pump inlet valve, a variable frequency vacuum pump, a mixing device and an alkali solution tank;

[0006] The outlet of the generator is connected to the spray device in the cooling water tank. An exhaust collection pipe is provided on the top of the cooling water tank. The outlet of the exhaust collection pipe is connected to the variable frequency vacuum pump through the vacuum pump inlet valve. A vacuum pressure sensor is provided on the inner side of the top of the cooling water tank.

[0007] The outlet of the cooling water tank is divided into two routes, one of which is connected to the inlet of the generator, and the other is connected to the circulating spray pipe on the top of the mixing device through the outlet water valve of the cooling water pump. The mixing device is filled with polytetrafluoroethylene filler balls. The outlet of the alkali liquid tank is connected to the dosing spray pipe in the mixing device through the frequency conversion metering pump and the metering pump outlet valve in turn. The bottom of the mixing device is connected to the conductivity meter; the bottom outlet of the mixing device is connected to the inlet of the cooling water tank through the electric flow control valve and the circulating flow meter in turn.

[0008] The generator cooling water corrosion control device of the present invention is further improved in that:

[0009] Furthermore, an exhaust valve is provided at the exhaust port on the top of the mixing device.

[0010] Furthermore, the outlet of the cooling water tank is divided into two paths after passing through the cooling water pump.

[0011] Furthermore, the dosing spray pipe and the circulation spray pipe are both located above the polytetrafluoroethylene filler balls.

[0012] Furthermore, a dissolved oxygen analyzer is provided at the inlet of the generator.

[0013] Furthermore, a supporting orifice plate is provided at the bottom of the mixing device, and polytetrafluoroethylene filler balls are located above the supporting orifice plate.

[0014] Furthermore, it also includes a PLC controller, which is connected to a touch screen, a variable frequency metering pump, a conductivity meter, a dissolved oxygen analyzer, an electric flow control valve, a circulation flow meter, a vacuum pressure sensor and a variable frequency vacuum pump.

[0015] The present invention discloses a method for controlling corrosion of generator cooling water, comprising the following steps:

[0016] The cooling water output from the cooling water tank is divided into two routes. One route enters the generator after the dissolved oxygen content is tested by a dissolved oxygen analyzer, and the other route is sprayed into the mixing device through a circulating spray pipe. The alkali solution output from the alkali solution tank enters the dosing spray pipe through a variable frequency metering pump and the metering pump outlet valve, and then is sprayed into the mixing device through the dosing spray pipe. The conductivity of the water at the bottom of the mixing device is tested by a conductivity meter. The water output from the bottom of the mixing device enters the cooling water tank through an electric flow control valve and a circulating flow meter. The vacuum degree in the cooling water tank is tested by a vacuum pressure sensor.

[0017] The frequency of the vacuum pump is calculated based on the dissolved oxygen content detected by the dissolved oxygen analyzer, the set dosing conductivity, and the vacuum pressure value detected by the vacuum pressure sensor. The variable frequency vacuum pump is controlled based on the calculated frequency of the vacuum pump to minimize the corrosion rate of the constant cooling water.

[0018] The further improvement of the generator cooling water corrosion control method of the present invention is:

[0019] Furthermore, it also includes:

[0020] The opening of the electric flow regulating valve is controlled according to the flow signal measured by the circulation flow meter and the preset circulation flow value, so that the flow measured by the circulation flow meter is stabilized in the range of 950L / h to 1050L / h.

[0021] Furthermore, it also includes:

[0022] The frequency of the variable frequency metering pump is controlled according to the conductivity signal measured by the conductivity meter and the preset circulating conductivity value, so that the conductivity measured by the conductivity meter is stabilized in the range of 0.8 to 1.2 μS / cm.

[0023] The present invention has the following beneficial effects:

[0024] During specific operation, the generator stator cooling water corrosion control device and method described in the present invention calculates the frequency of the vacuum pump based on the dissolved oxygen content detected by the dissolved oxygen analyzer, the set dosing conductivity, and the vacuum pressure value detected by the vacuum pressure sensor. The variable frequency vacuum pump is controlled based on the calculated frequency of the vacuum pump to minimize the corrosion rate of the stator cooling water, reduce the corrosion rate of the stator cooling water, prevent the deposition of copper corrosion products, prevent the generator stator wire rods from being blocked, prevent the wire rods from heating up and the unit from being forced to trip, and ensure the safe operation of the generator. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The accompanying drawings, which constitute part of the present invention, are intended to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are intended to explain the present invention and do not constitute an undue limitation of the present invention. In the accompanying drawings:

[0026] Figure 1 It is a structural diagram of the present invention.

[0027] Among them, 1 is a PLC controller, 2 is a touch screen, 3 is an alkali liquid tank, 4 is a mixing device, 5 is a polytetrafluoroethylene filler ball, 6 is a dosing spray pipe, 7 is a circulating spray pipe, 8 is a conductivity meter, 9 is an exhaust valve, 10 is a constant cooling water pump outlet water inlet valve, 11 is an electric flow regulating valve, 12 is a circulating flow meter, 13 is a variable frequency metering pump, 14 is a metering pump outlet valve, 15 is a dissolved oxygen analyzer, 16 is a spray device, 17 is an exhaust collection pipe, 18 is a vacuum pressure sensor, 19 is a vacuum pump inlet valve, 20 is a variable frequency vacuum pump, and 21 is a supporting orifice plate. DETAILED DESCRIPTION

[0028] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0029] In the description of the present invention, it is to be understood that the terms “include” and “comprise” indicate the presence of the described features, wholes, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, wholes, steps, operations, elements, components and / or collections thereof.

[0030] It should also be understood that the terms used in the present specification are only for the purpose of describing particular embodiments and are not intended to limit the present invention. As used in the present specification and the appended claims, the singular forms "a", "an", and "the" are intended to include the plural forms unless the context clearly indicates otherwise.

[0031] It should be further understood that the term "and / or" as used in the present specification and the appended claims refers to and includes any and all possible combinations of one or more of the associated listed items. For example, A and / or B may represent: A exists alone, A and B exist simultaneously, and B exists alone. In addition, the character " / " in the present invention generally indicates that the associated objects are in an "or" relationship.

[0032] It should be understood that although the terms "first," "second," and "third" may be used to describe preset ranges in embodiments of the present invention, these preset ranges should not be limited to these terms. These terms are merely used to distinguish one preset range from another. For example, without departing from the scope of embodiments of the present invention, the first preset range may also be referred to as the second preset range, and similarly, the second preset range may also be referred to as the first preset range.

[0033] The word "if," as used herein, may be interpreted as "at the time of" or "when" or "in response to determining" or "in response to detecting," depending on the context. Similarly, the phrases "if it is determined" or "if (stated condition or event) is detected" may be interpreted as "when it is determined" or "in response to the determination" or "when detecting (stated condition or event)" or "in response to detecting (stated condition or event)," depending on the context.

[0034] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings herein can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the drawings is not intended to limit the scope of the claimed invention, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0035] The accompanying drawings illustrate various schematic diagrams of structures according to embodiments disclosed herein. These figures are not drawn to scale; for clarity, some details are exaggerated and some details may be omitted. The shapes of the various regions and layers shown in the figures, as well as their relative sizes and positional relationships, are merely exemplary and may deviate in practice due to manufacturing tolerances or technical limitations. Those skilled in the art may design regions / layers with different shapes, sizes, and relative positions as needed.

[0036] Example 1

[0037] refer to Figure 1 The generator cooling water corrosion control device of the present invention includes a PLC controller 1, a touch screen 2, an alkali liquid tank 3, a mixing device 4, a polytetrafluoroethylene filler ball 5, a dosing spray pipe 6, a circulating spray pipe 7, a conductivity meter 8, an exhaust valve 9, a cooling water pump outlet water inlet valve 10, an electric flow regulating valve 11, a circulating flow meter 12, a variable frequency metering pump 13, a metering pump outlet valve 14, a dissolved oxygen analyzer 15, a spray device 16, an exhaust collection pipe 17, a vacuum pressure sensor 18, a vacuum pump inlet valve 19, a variable frequency vacuum pump 20 and a supporting orifice plate 21.

[0038] The outlet of the generator is connected to the spray device 16 in the cooling water tank. An exhaust collecting pipe 17 is provided on the top of the cooling water tank. The outlet of the exhaust collecting pipe 17 is connected to the variable frequency vacuum pump 20 through the vacuum pump inlet valve 19. A vacuum pressure sensor 18 is provided on the inner side of the top of the cooling water tank.

[0039] The outlet of the cooling water tank is divided into two paths after passing through the cooling water pump, one of which is connected to the inlet of the generator, and the other is connected to the circulating spray pipe 7 at the top of the mixing device 4 through the cooling water pump outlet water valve 10. The mixing device 4 is filled with polytetrafluoroethylene filler balls 5. The outlet of the alkali liquid tank 3 is connected to the dosing spray pipe 6 in the mixing device 4 through the variable frequency metering pump 13 and the metering pump outlet valve 14 in turn, wherein the dosing spray pipe 6 and the circulating spray pipe 7 are both located above the polytetrafluoroethylene filler balls 5, and the bottom of the mixing device 4 is connected to a conductivity meter 8; the bottom outlet of the mixing device 4 is connected to the inlet of the cooling water tank through the electric flow regulating valve 11 and the circulating flow meter 12 in turn, and an exhaust valve 9 is provided at the exhaust port on the top of the mixing device 4.

[0040] As an embodiment of the present invention, the number of exhaust collection pipes 17 is four, which is conducive to the uniform discharge of oxygen and carbon dioxide. A variable frequency vacuum pump 20 is used to form a negative pressure at the top of the constant cooling water tank, and the oxygen and carbon dioxide in the constant cooling water are removed through the spray device 16 and the exhaust collection pipe 17.

[0041] As an embodiment of the present invention, a dissolved oxygen analyzer 15 is provided at the inlet of the generator.

[0042] As an embodiment of the present invention, a supporting orifice plate 21 is provided at the bottom of the mixing device 4 , and the polytetrafluoroethylene filler balls 5 are located above the supporting orifice plate 21 .

[0043] As an embodiment of the present invention, it also includes a PLC controller 1, which is connected to a touch screen 2, a variable frequency metering pump 13, a conductivity meter 8, a dissolved oxygen analyzer 15, an electric flow control valve 11, a circulation flow meter 12, a vacuum pressure sensor 18 and a variable frequency vacuum pump 20.

[0044] The circulation spray pipe 7 is located above the dosing spray pipe 6; a plurality of through holes are provided on the downward surfaces of the circulation spray pipe 7 and the dosing spray pipe 6, with a hole diameter of φ2.

[0045] The generator cooling water corrosion control method of the present invention comprises the following steps:

[0046] The cooling water output from the cooling water tank is divided into two paths, one of which enters the generator after the dissolved oxygen content is detected by the dissolved oxygen analyzer 15, and the other is sprayed into the mixing device 4 through the circulating spray pipe 7. The alkali liquid output from the alkali liquid tank 3 enters the dosing spray pipe 6 through the frequency conversion metering pump 13 and the metering pump outlet valve 14, and then is sprayed into the mixing device 4 through the dosing spray pipe 6 to increase the pH value of the cooling water. The conductivity of the water at the bottom of the mixing device 4 is detected by the conductivity meter 8. The water output from the bottom of the mixing device 4 enters the cooling water tank through the electric flow regulating valve 11 and the circulating flow meter 12, and the vacuum degree in the cooling water tank is detected by the vacuum pressure sensor 18.

[0047] The PLC controller 1 calculates the frequency of the vacuum pump based on the dissolved oxygen content detected by the dissolved oxygen analyzer 15, the set dosing conductivity, and the vacuum pressure value detected by the vacuum pressure sensor 18, and controls the variable frequency vacuum pump 20 based on the calculated frequency of the vacuum pump to minimize the corrosion rate of the stator cooling water, thereby preventing the deposition of copper corrosion products, preventing the stator wire rods in the generator from being blocked, preventing the wire rods from heating up, and preventing the unit from being forced to trip, thereby ensuring the safe operation of the generator.

[0048] The PLC controller 1 controls the opening of the electric flow regulating valve 11 according to the flow signal measured by the circulation flow meter 12 and the preset circulation flow value, so that the flow measured by the circulation flow meter 12 is stable in the range of 950L / h to 1050L / h.

[0049] The return water of the cooling water is sprayed into the cooling water tank through the spray device 16, the vacuum pump inlet valve 19 is opened, and the variable frequency vacuum pump 20 is started to form a negative pressure area in the cooling water tank, and the dissolved oxygen and carbon dioxide are discharged to the outside through the exhaust collection pipe 17.

[0050] The PLC controller 1 controls the frequency of the variable frequency metering pump 13 according to the conductivity signal measured by the conductivity meter 8 and the preset circulation conductivity value, so that the conductivity measured by the conductivity meter 8 is stabilized in the range of 0.8 to 1.2 μS / cm.

[0051] The PLC controller 1 detects the dissolved oxygen content in the cooling water through the dissolved oxygen analyzer 15 and finds that it is less than 100 ppb. The PLC controller 1 measures the vacuum pressure in the cooling water tank through the vacuum pressure sensor 18 and finds that it is less than 10 kPa. The frequency of the variable frequency vacuum pump 20 is calculated and controlled based on the dissolved oxygen setting value of 100 ppb, the vacuum pressure of 10 kPa, and the circulating conductivity value of 1.0 μS / cm.

[0052] The present invention can achieve a dissolved oxygen content in the cooling water of less than 100 ppb, a vacuum pressure in the cooling water tank of less than 10 kPa, a circulating conductivity value stable in the range of 0.8 to 1.2 μS / cm, and a cooling water pH of more than 8.0, thereby controlling the copper corrosion rate of the generator cooling water to the lowest level and ensuring stable and safe operation of the generator.

[0053] Example 2

[0054] A computer device includes a memory, a processor, and a computer program stored in the memory and executable on the processor. When the processor executes the computer program, the steps of the generator cooling water corrosion control method are implemented. The memory may include internal memory, such as a high-speed random access memory, and may also include non-volatile memory, such as at least one disk storage device. The processor, network interface, and memory are interconnected via an internal bus. The internal bus may be an industrial standard architecture bus, a peripheral component interconnect standard bus, an extended industrial standard architecture bus, etc. The bus may be divided into an address bus, a data bus, a control bus, etc. The memory is used to store programs. Specifically, the program may include program code, and the program code includes computer operating instructions. The memory may include internal memory and non-volatile memory, and provides instructions and data to the processor.

[0055] Example 3

[0056] A computer-readable storage medium stores a computer program, which, when executed by a processor, implements the steps of the generator cooling water corrosion control method. Specifically, the computer-readable storage medium includes, but is not limited to, volatile memory and / or non-volatile memory. The volatile memory may include random access memory (RAM) and / or cache memory, etc. The non-volatile memory may include read-only memory (ROM), hard disk, flash memory, optical disk, magnetic disk, etc.

[0057] Those skilled in the art will appreciate that the embodiments of the present application can be provided as methods, systems, or computer program products. Therefore, the present application can adopt the form of a complete hardware embodiment, a complete software embodiment, or an embodiment in combination with software and hardware. Moreover, the present application can adopt the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to magnetic disk storage, CD-ROM, optical storage, etc.) that contain computer-usable program code.

[0058] The present application is described with reference to the flowcharts and / or block diagrams of the methods, devices (systems), and computer program products according to the embodiments of the present application. It should be understood that each process and / or box in the flowchart and / or block diagram, as well as the combination of the processes and / or boxes in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the steps in the process. Figure 1 a process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0059] These computer program instructions may also be stored in a computer readable memory that can direct a computer or other programmable data processing device to work in a specific manner, so that the instructions stored in the computer readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 a process or multiple processes and / or boxes Figure 1 The function specified in one or more boxes.

[0060] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operational steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing the instructions executed on the computer or other programmable device for implementing the process. Figure 1 a process or multiple processes and / or boxes Figure 1 A step that specifies a function in one or more boxes.

[0061] Those skilled in the art will readily identify other embodiments of the present invention after considering the specification and disclosure of the invention. This application is intended to cover any variations, uses, or adaptations of the present invention that follow the general principles of the invention and include common knowledge or customary techniques in the art not disclosed herein. The description and examples are to be considered as exemplary only, with the true scope and spirit of the invention being indicated by the following claims.

[0062] It should be understood that the present invention is not limited to the exact construction described above and shown in the drawings, and that various modifications and changes may be made without departing from the scope thereof. The scope of the present invention is limited only by the appended claims.

[0063] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any way. Any simple modification, change and equivalent structural change made to the above embodiment based on the technical essence of the present invention shall still fall within the scope of protection of the technical solution of the present invention.

Claims

1. A method for controlling corrosion of generator cooling water, characterized in that: Based on a generator cooling water corrosion control device, the generator cooling water corrosion control device comprises a generator, a cooling water tank, a vacuum pump inlet valve (19), a variable frequency vacuum pump (20), a mixing device (4) and an alkali liquid tank (3); The outlet of the generator is connected to the spray device (16) in the cooling water tank. An exhaust collecting pipe (17) is provided on the top of the cooling water tank. The outlet of the exhaust collecting pipe (17) is connected to the variable frequency vacuum pump (20) via a vacuum pump inlet valve (19). A vacuum pressure sensor (18) is provided on the inner side of the top of the cooling water tank. The outlet of the fixed cooling water tank is divided into two paths, one of which is connected to the inlet of the generator, and the other is connected to the circulation spray pipe (7) at the top of the mixing device (4) through the fixed cooling water pump outlet water valve (10). The mixing device (4) is filled with polytetrafluoroethylene filler balls (5). The outlet of the alkali liquid tank (3) is connected to the dosing spray pipe (6) in the mixing device (4) through the variable frequency metering pump (13) and the metering pump outlet valve (14). The bottom of the mixing device (4) is connected to the conductivity meter (8); the bottom outlet of the mixing device (4) is connected to the inlet of the fixed cooling water tank through the electric flow regulating valve (11) and the circulation flow meter (12). A dissolved oxygen analyzer (15) is provided at the inlet of the generator; The following steps are involved: The cooling water output from the cooling water tank is divided into two paths, one of which enters the generator after the dissolved oxygen content is detected by the dissolved oxygen analyzer (15), and the other path is sprayed into the mixing device (4) through the circulation spray pipe (7). The alkali solution output from the alkali solution tank (3) enters the dosing spray pipe (6) through the frequency conversion metering pump (13) and the metering pump outlet valve (14), and is then sprayed into the mixing device (4) through the dosing spray pipe (6). The conductivity of the water at the bottom of the mixing device (4) is detected by the conductivity meter (8). The water output from the bottom of the mixing device (4) enters the cooling water tank through the electric flow regulating valve (11) and the circulation flow meter (12), and the vacuum degree in the cooling water tank is detected by the vacuum pressure sensor (18); The frequency of the vacuum pump is calculated based on the dissolved oxygen content detected by the dissolved oxygen analyzer (15), the set dosing conductivity, and the vacuum pressure value detected by the vacuum pressure sensor (18). The variable frequency vacuum pump (20) is controlled based on the calculated frequency of the vacuum pump to minimize the corrosion rate of the cooling water.

2. The method for controlling corrosion of generator cooling water according to claim 1, characterized in that: Also includes: The opening of the electric flow regulating valve (11) is controlled according to the flow signal measured by the circulation flow meter (12) and the preset circulation flow value, so that the flow measured by the circulation flow meter (12) is stabilized within the range of 950L / h to 1050L / h.

3. The method for controlling corrosion of generator cooling water according to claim 1, characterized in that: Also includes: The frequency of the variable frequency metering pump (13) is controlled according to the conductivity signal measured by the conductivity meter (8) and the preset circulation conductivity value, so that the conductivity measured by the conductivity meter (8) is stabilized in the range of 0.8~1.2μS / cm.

4. The method for controlling corrosion of generator cooling water according to claim 1, characterized in that: An exhaust valve (9) is provided at the exhaust port on the top of the mixing device (4).

5. The method for controlling corrosion of generator cooling water according to claim 1, characterized in that: The outlet of the cooling water tank is divided into two paths after passing through the cooling water pump.

6. The method for controlling corrosion of generator cooling water according to claim 1, characterized in that: The dosing spray pipe (6) and the circulation spray pipe (7) are both located above the polytetrafluoroethylene filler balls (5).

7. The method for controlling corrosion of generator cooling water according to claim 1, characterized in that: A supporting orifice plate (21) is provided at the bottom of the mixing device (4), and polytetrafluoroethylene filler balls (5) are located above the supporting orifice plate (21).

8. The method for controlling corrosion of generator cooling water according to claim 1, characterized in that: The device further comprises a PLC controller (1) and a touch screen (2), wherein the PLC controller (1) is connected to the touch screen (2), a variable frequency metering pump (13), a conductivity meter (8), a dissolved oxygen analyzer (15), an electric flow regulating valve (11), a circulation flow meter (12), a vacuum pressure sensor (18) and a variable frequency vacuum pump (20).

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