A wastewater staged discharge control system and method

Abstract

The application provides a wastewater grading discharge control system and method, wherein a lower-stage wastewater container is connected with a first-stage wastewater discharge outlet of a COAP system through a first-stage wastewater discharge switch unit, the lower-stage wastewater container is connected with an alkali adding device, and the lower-stage wastewater container is connected with a lower-stage wastewater discharge unit; a middle-upper-stage wastewater container is connected with a second-stage wastewater first discharge outlet through a second-stage wastewater discharge switch unit, the middle-upper-stage wastewater container is connected with a middle-upper-stage wastewater discharge unit, and a second-stage wastewater second discharge outlet is connected with a first-stage water supplement inlet through a first-stage water supplement switch unit; a control unit is used for opening the first-stage wastewater discharge switch unit when a first-stage wastewater liquid level is higher than a corresponding upper limit; the lower-stage wastewater discharge unit is controlled to discharge water when a lower-stage wastewater liquid level is higher than a corresponding upper limit and a first PH value meets a requirement; the first-stage water supplement switch unit is controlled to be turned on at a fixed time to supplement water to the first-stage wastewater; and the middle-upper-stage wastewater discharge unit is controlled to discharge water when a middle-upper-stage wastewater liquid level is higher than a corresponding upper limit and a second PH value meets a requirement.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment technology, and in particular to a wastewater graded discharge control system and method. Background Technology

[0002] When applying the "Cryogenic Integrated Pollutant Removal Technology" (COAP), the first step is to cool the flue gas to sub-zero temperatures. This cooling process employs a four-stage spray cooling method to progressively reduce the flue gas temperature. Different stages of the cooling process generate different types of wastewater. Treating these different types of wastewater differently can better optimize resource allocation. However, currently, there is a lack of technology for treating the various types of wastewater generated during the deep cooling process of flue gas. Summary of the Invention

[0003] The present invention aims to at least partially solve one of the technical problems in the related art.

[0004] Therefore, the first objective of this invention is to propose a wastewater graded discharge control system to better optimize resource allocation.

[0005] The second objective of this invention is to propose a wastewater graded discharge control method.

[0006] To achieve the above objectives, the first aspect of the present invention proposes a wastewater graded discharge control system, comprising a first-stage wastewater discharge switch unit, a lower-stage wastewater container, a lower-stage wastewater discharge unit, a first-stage water replenishment switch unit, a second-stage wastewater discharge switch unit, an upper-middle-stage wastewater container, an upper-middle-stage wastewater discharge unit, and a control unit; the first inlet of the lower-stage wastewater container is connected to the first-stage wastewater outlet of the COAP system via the first-stage wastewater discharge switch unit, the second inlet of the lower-stage wastewater container is connected to an alkali addition device, and the outlet of the lower-stage wastewater container is connected to the lower-stage wastewater discharge unit; the inlet of the upper-middle-stage wastewater container is connected to the first outlet of the second-stage wastewater of the COAP system via the second-stage wastewater discharge switch unit, the outlet of the upper-middle-stage wastewater container is connected to the upper-middle-stage wastewater discharge unit, and the second outlet of the second-stage wastewater of the COAP system is connected to the first-stage wastewater replenishment inlet of the COAP system via the first-stage water replenishment switch unit;

[0007] For the lower stage wastewater, the control unit is used to open the lower stage wastewater discharge switch unit when the lower stage wastewater level is higher than the upper limit of the lower stage wastewater level; and to control the lower stage wastewater discharge unit to discharge water when the lower stage wastewater level is higher than the upper limit of the lower stage wastewater level and the first pH value meets the requirements.

[0008] For the wastewater in the middle and upper sections, the control unit is used to periodically control the first section water replenishment switch unit to turn on to replenish water to the first section of wastewater; when the wastewater level in the middle and upper sections is higher than the upper limit of the wastewater level in the middle and upper sections and the second pH value meets the requirements, the control unit controls the wastewater discharge unit in the middle and upper sections to drain water.

[0009] In the wastewater graded discharge control system provided in the first aspect of the present invention, the control unit is further configured to close the wastewater discharge switch unit when the wastewater level of the first stage is lower than the lower limit of the wastewater level of the first stage.

[0010] In the wastewater graded discharge control system provided in the first aspect of the present invention, the control unit is further configured to control the shutdown of the wastewater discharge unit when the wastewater level in the lower stage is lower than the lower limit of the wastewater level in the lower stage.

[0011] In the wastewater graded discharge control system provided in the first aspect of the present invention, for the lower stage wastewater, the control unit is further configured to control the start of the alkali addition device when the first pH value is less than the set lower limit of pH value, and control the stop of the alkali addition device when the first pH value is greater than the set upper limit of pH value.

[0012] In the wastewater graded discharge control system provided in the first aspect of the present invention, the first stage wastewater discharge switch unit adopts a first stage wastewater discharge valve.

[0013] In the wastewater graded discharge control system provided in the first aspect of the present invention, the lower wastewater discharge unit adopts a lower wastewater pump.

[0014] In the wastewater graded discharge control system provided in the first aspect of the present invention, the third inlet of the lower wastewater container is connected to the fourth wastewater outlet of the COAP system via the MVR system.

[0015] In the wastewater graded discharge control system provided in the first aspect of the present invention, the fourth inlet of the lower wastewater container is connected to the salt production system of the COAP system.

[0016] The wastewater graded discharge control system provided in the first aspect of the present invention further includes three overflow pipes, which are used to connect the three wastewater discharge outlets of the COAP system and the two-stage spray equipment of the COAP system.

[0017] To achieve the above objectives, a second aspect of the present invention provides a wastewater graded discharge control method, applied to the wastewater graded discharge control system provided in the first aspect of the present invention, the method comprising:

[0018] When the wastewater level of a section is higher than the upper limit of the wastewater level of a section, the wastewater discharge switch unit of that section is opened; when the wastewater level of a section is lower than the lower limit of the wastewater level of a section, the wastewater discharge switch unit of that section is closed.

[0019] When the wastewater level in the lower section is higher than the upper limit of the wastewater level in the lower section and the first pH value meets the requirements, the wastewater discharge unit in the lower section is controlled to discharge water.

[0020] When the first pH value is less than the set lower limit of pH value, the alkali addition device is started; when the first pH value is greater than the set upper limit of pH value, the alkali addition device is stopped.

[0021] A timed control unit is activated to replenish water into a wastewater section.

[0022] When the wastewater level in the upper and middle sections is higher than the upper limit of the wastewater level in the upper and middle sections and the second pH value meets the requirements, the wastewater discharge unit in the upper and middle sections is controlled to discharge water.

[0023] The present invention provides a wastewater graded discharge control system and method. The control system includes a first-stage wastewater discharge switch unit, a lower-stage wastewater container, a lower-stage wastewater discharge unit, a first-stage water replenishment switch unit, a second-stage wastewater discharge switch unit, an upper-middle-stage wastewater container, an upper-middle-stage wastewater discharge unit, and a control unit. The first inlet of the lower-stage wastewater container is connected to the first-stage wastewater outlet of the COAP system via the first-stage wastewater discharge switch unit; the second inlet of the lower-stage wastewater container is connected to an alkali addition device; and the outlet of the lower-stage wastewater container is connected to the lower-stage wastewater discharge unit. The inlet of the upper-middle-stage wastewater container is connected to the first outlet of the second-stage wastewater of the COAP system via the second-stage wastewater discharge switch unit; and the outlet of the upper-middle-stage wastewater container... Connected to the upper and middle stage wastewater discharge unit, the second outlet of the second stage wastewater of the COAP system is connected to the first stage wastewater inlet of the COAP system via the first stage water replenishment switch unit. For the lower stage wastewater, the control unit is used to open the first stage wastewater discharge switch unit when the first stage wastewater level is higher than the upper limit of the first stage wastewater level; and to control the lower stage wastewater discharge unit to drain water when the lower stage wastewater level is higher than the upper limit of the lower stage wastewater level and the first pH value meets the requirements. For the upper and middle stage wastewater, the control unit is used to periodically control the first stage water replenishment switch unit to conduct water to replenish the first stage wastewater; and to control the upper and middle stage wastewater discharge unit to drain water when the upper and middle stage wastewater level is higher than the upper limit of the upper and middle stage wastewater level and the second pH value meets the requirements. In this case, considering that a large amount of condensate will be generated during the second and third stage spraying of flue gas during the cooling process, the wastewater in the lower section corresponding to the first stage spraying and the wastewater in the middle and upper sections corresponding to the second and third stage spraying are treated separately for emission control. The condensate generated by the second stage spraying is also recycled and used to replenish the wastewater in the first stage at regular intervals to control the pollutant concentration in the first stage wastewater. This reduces the wastewater treatment cost and realizes the recycling of condensate water resources, thereby optimizing resource allocation.

[0024] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0025] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the following description of the embodiments taken in conjunction with the accompanying drawings, wherein:

[0026] Figure 1 This is a block diagram of a wastewater graded discharge control system provided in an embodiment of the present invention;

[0027] Figure 2 This is a flowchart of a wastewater graded discharge control method provided in an embodiment of the present invention. Detailed Implementation

[0028] Exemplary embodiments will now be described in detail, examples of which are illustrated in the accompanying drawings. When the following description relates to the drawings, unless otherwise indicated, the same numerals in different drawings denote the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with those of the present invention. Rather, they are merely examples of apparatuses and methods consistent with some aspects of the embodiments of the present invention as detailed in the appended claims.

[0029] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0030] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified. It should also be understood that the term "and / or" as used in this invention refers to and includes any or all possible combinations of one or more associated listed items.

[0031] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0032] Considering that the COAP flue gas cooling system employs a four-stage spray circulation cooling method, with industrial water used for the first, second, and third stages and calcium chloride solution for the fourth stage, and additional wastewater discharge from the salt production system, the condensate from different cooling stages of the spray tower exhibits varying water quality, resulting in differences in wastewater quality. Therefore, classifying and treating the wastewater generated during the flue gas condensation process would optimize resource allocation and utilization.

[0033] Based on this, the present invention proposes a wastewater graded discharge control system and method to better optimize resource allocation. In this invention, the wastewater graded discharge control system can be simply referred to as the system.

[0034] In this embodiment, the wastewater graded discharge control system includes a first-stage wastewater discharge switch unit, a lower-stage wastewater container, a lower-stage wastewater discharge unit, and a control unit. The first inlet of the lower-stage wastewater container is connected to the first-stage wastewater outlet of the COAP system via the first-stage wastewater discharge switch unit, the second inlet of the lower-stage wastewater container is connected to an alkali addition device, and the outlet of the lower-stage wastewater container is connected to the lower-stage wastewater discharge unit.

[0035] In this embodiment, a wastewater discharge switch unit can be a wastewater discharge valve.

[0036] In this embodiment, the lower wastewater discharge unit can be a lower wastewater pump.

[0037] In this embodiment, the third inlet of the lower wastewater container is connected to the four wastewater outlets of the COAP system via an MVR (mechanical vapor recompression) system. Four spray pumps are installed between the four wastewater outlets of the MVR system and the COAP system.

[0038] In this embodiment, the fourth inlet of the lower wastewater container is connected to the salt production system of the COAP system.

[0039] In this embodiment, the wastewater graded discharge control system further includes a first-stage water replenishment switch unit, a second-stage wastewater discharge switch unit, an upper-middle-stage wastewater container, and an upper-middle-stage wastewater discharge unit. The inlet of the upper-middle-stage wastewater container is connected to the first outlet of the second-stage wastewater of the COAP system via the second-stage wastewater discharge switch unit. The outlet of the upper-middle-stage wastewater container is connected to the upper-middle-stage wastewater discharge unit, and the second outlet of the second-stage wastewater of the COAP system is connected to the first-stage wastewater replenishment inlet of the COAP system via the first-stage water replenishment switch unit.

[0040] In this embodiment, the first-stage water replenishment switch unit can be a two-stage spray pump.

[0041] In this embodiment, the upper and middle section wastewater discharge unit can be a middle and middle section condensate pump.

[0042] In this embodiment, the system also includes three overflow pipes. These three overflow pipes connect the three wastewater outlets of the COAP system to the two-stage spray system of the COAP system. Specifically, one end of the three overflow pipe connects to the two-stage spray system of the COAP system, and the other end extends through the three wastewater outlets of the COAP system into the three wastewater receiving chamber. The wastewater from the three stages in the wastewater receiving chamber enters the three overflow pipes through the three overflow ports on the three overflow pipes and then reaches the two-stage spray system for two-stage spraying.

[0043] In this embodiment, for the lower wastewater section, the control unit is used to open the wastewater discharge switch unit when the wastewater level is higher than the upper limit (e.g., 1.4 meters); to close the wastewater discharge switch unit when the wastewater level is lower than the lower limit (e.g., 1 meter); to control the lower wastewater discharge unit to drain water when the wastewater level is higher than the upper limit (e.g., 3.5 meters) and the first pH value meets the requirement (e.g., the first pH value is greater than 7); and to control the lower wastewater discharge unit to close when the wastewater level is lower than the lower limit (e.g., 1 meter). The control unit is also used to control the alkali addition device to start when the first pH value is less than the set lower limit (e.g., 6), and to control the alkali addition device to stop when the first pH value is greater than the set upper limit (e.g., 8).

[0044] For the upper and middle sections of wastewater, the control unit is used to periodically activate the first-stage water replenishment switch unit to replenish water to the first-stage wastewater; it is also used to continuously activate the second-stage wastewater discharge switch unit, ensuring a continuous flow of wastewater from the second stage to the upper and middle sections of wastewater. Furthermore, it is used to control the upper and middle section wastewater discharge unit to discharge water when the upper and middle section wastewater level is above the upper limit and the second pH value meets the requirements. Finally, it is used to control the upper and middle section wastewater discharge unit to shut down when the upper and middle section wastewater level is below the lower limit.

[0045] If the concentrated wastewater from the MVR system and the wastewater generated by the salt production system are also included in the wastewater graded discharge control, taking as an example a first-stage wastewater discharge switch unit using a first-stage wastewater discharge valve, a lower-stage wastewater discharge unit using a lower-stage wastewater pump, a first-stage makeup water switch unit using a second-stage spray pump, a second-stage wastewater discharge switch unit using a second-stage wastewater discharge valve, and an upper-middle-stage wastewater discharge unit using an upper-middle-stage condensate pump. Figure 1 This is a block diagram of a wastewater graded discharge control system provided in an embodiment of the present invention.

[0046] Specifically, in combination Figure 1 The specific discharge control process of the wastewater graded discharge control system is as follows:

[0047] Regarding the downstream wastewater, considering that it collects wastewater from the first-stage spraying, concentrated wastewater from the MVR system, and wastewater from the salt production system, these three parts of the wastewater contain a large amount of SO4. 2- SO3 2- and NO3 - The wastewater is highly acidic and must first be neutralized through alkali treatment in the wastewater classification and discharge control system before being sent to the wastewater treatment system for further disposal. Specific control methods are as follows:

[0048] 11) Monitor the wastewater level of a section. When the wastewater level of a section is higher than 1.4 meters, open the wastewater discharge valve of the section to discharge the wastewater to the next section wastewater pool (i.e., the next section wastewater container). When the wastewater level of a section drops to 1 meter, close the wastewater discharge valve of the section.

[0049] 12) Ensure that the pipeline between the third inlet of the lower wastewater container and the MVR system is in a conductive state so that the wastewater discharge from the MVR system is continuous;

[0050] 13) Ensure that the pipeline between the fourth inlet of the lower wastewater container and the salt production system of the COAP system is in a conductive state so that the wastewater discharge from the salt production system is continuous.

[0051] 14) Monitor the wastewater level in the lower wastewater tank. If the wastewater level is greater than 3.5 meters and the pH of the wastewater is greater than 7, start the wastewater pump to send the wastewater to the wastewater treatment system to achieve drainage. If the wastewater level is less than 1 meter, stop the wastewater pump.

[0052] 15) Monitor the pH of the wastewater in the lower wastewater tank. If the pH is less than 6, start the alkali addition device. If the pH is greater than 8, stop the alkali addition device.

[0053] For the wastewater from the middle and upper stages, considering that the wastewater generated by the second and third stage spraying is mainly condensate, the condensate from the second and third stage spraying was collected and disposed of according to the actual situation, such as water resource recovery or being sent to the water treatment system or circulating water makeup. Specific control methods are as follows:

[0054] 21) The operation of the second-stage spray pump is controlled at regular intervals so that the condensate (i.e. the wastewater of the second stage) generated in the second stage is replenished to the first stage at regular intervals, thereby controlling the concentration of pollutants in the first stage spray pump, and then discharged with the wastewater at the lower end.

[0055] 22) The condensate (i.e., the wastewater from the third stage) generated in the third stage continuously flows to the second stage spray through the overflow pipe of the third stage;

[0056] 23) Control the second-stage wastewater discharge valve to keep it open so that the condensate generated in the second stage can flow continuously to the middle and upper stage condensate pool (i.e., the middle and upper stage wastewater container) through the corresponding overflow pipe.

[0057] 24) Considering the relatively good water quality, large volume, and acidic nature of the upper and middle section condensate, it can be used as makeup water for the circulating water while neutralizing the pH of the circulating water, or it can be directly treated in the water treatment system for reuse. Therefore, the liquid level of the upper and middle section condensate in the upper and middle section condensate tank is monitored. If the liquid level of the upper and middle section condensate is higher than the corresponding upper limit and the pH is higher than the corresponding set value, the upper and middle section condensate pump is started to send the upper and middle section condensate to the water treatment system or to make up for the circulating water, thus achieving drainage; if the liquid level of the upper and middle section condensate is lower than the corresponding lower limit, the upper and middle section condensate pump is stopped.

[0058] The following are embodiments of the method of the present invention. For details not disclosed in the embodiments of the method of the present invention, please refer to the system embodiments of the present invention. The embodiments of the method of the present invention propose a wastewater graded discharge control method. This wastewater graded discharge control method is applied to the wastewater graded discharge control system of the above system embodiments for graded discharge control of wastewater.

[0059] Figure 2 This is a flowchart of a wastewater graded discharge control method provided in an embodiment of the present invention.

[0060] like Figure 2 As shown, the wastewater graded discharge control method includes:

[0061] Step S101: When the wastewater level of a section is higher than the upper limit of the wastewater level of a section, the wastewater discharge switch unit of a section is opened; when the wastewater level of a section is lower than the lower limit of the wastewater level of a section, the wastewater discharge switch unit of a section is closed.

[0062] Step S102: When the wastewater level in the lower section is higher than the upper limit of the wastewater level in the lower section and the first pH value meets the requirements, control the wastewater discharge unit in the lower section to discharge water.

[0063] Step S103: When the first pH value is less than the set lower limit of pH value, control the start of the alkali addition device; when the first pH value is greater than the set upper limit of pH value, control the stop of the alkali addition device.

[0064] Step S104: Timely control the first water replenishment switch unit to turn on to replenish water to the first wastewater;

[0065] Step S105: When the wastewater level in the upper and middle sections is higher than the upper limit of the wastewater level in the upper and middle sections and the second pH value meets the requirements, the wastewater discharge unit in the upper and middle sections is controlled to discharge water.

[0066] It should be noted that the foregoing explanation of the wastewater graded discharge control system embodiment also applies to the wastewater graded discharge control method of this embodiment, and will not be repeated here.

[0067] The sequence numbers of the above embodiments of the present invention are for descriptive purposes only and do not represent the superiority or inferiority of the embodiments.

[0068] The wastewater graded discharge control system and method of this invention includes a first-stage wastewater discharge switch unit, a lower-stage wastewater container, a lower-stage wastewater discharge unit, a first-stage water replenishment switch unit, a second-stage wastewater discharge switch unit, an upper-middle-stage wastewater container, an upper-middle-stage wastewater discharge unit, and a control unit. The first inlet of the lower-stage wastewater container is connected to the first-stage wastewater outlet of the COAP system via the first-stage wastewater discharge switch unit; the second inlet of the lower-stage wastewater container is connected to an alkali addition device; and the outlet of the lower-stage wastewater container is connected to the lower-stage wastewater discharge unit. The inlet of the upper-middle-stage wastewater container is connected to the first outlet of the second-stage wastewater of the COAP system via the second-stage wastewater discharge switch unit; and the outlet of the upper-middle-stage wastewater container... The outlet is connected to the upper and middle stage wastewater discharge unit. The second outlet of the second stage wastewater of the COAP system is connected to the first stage wastewater inlet of the COAP system via the first stage water replenishment switch unit. For the lower stage wastewater, the control unit is used to open the first stage wastewater discharge switch unit when the first stage wastewater level is higher than the upper limit of the first stage wastewater level. When the lower stage wastewater level is higher than the upper limit of the lower stage wastewater level and the first pH value meets the requirements, the control unit controls the lower stage wastewater discharge unit to drain water. For the upper and middle stage wastewater, the control unit is used to periodically control the first stage water replenishment switch unit to conduct water to replenish the first stage wastewater. When the upper and middle stage wastewater level is higher than the upper limit of the upper and middle stage wastewater level and the second pH value meets the requirements, the control unit controls the upper and middle stage wastewater discharge unit to drain water. In this scenario, considering the large amount of condensate generated during the second and third stage spraying of flue gas during the cooling process, the wastewater from the lower stage corresponding to the first stage spraying and the wastewater from the middle and upper stages corresponding to the second and third stage spraying are treated separately for emission control. The condensate generated from the second stage spraying is also recycled and used to replenish the first stage wastewater at regular intervals to control the pollutant concentration in the first stage wastewater. As a result, the wastewater from the COAP system is discharged in stages, reducing wastewater treatment costs and simultaneously achieving the recycling of condensate water resources, thus optimizing resource allocation.

[0069] The accompanying drawings show structural schematic diagrams according to embodiments disclosed in this invention. These drawings are not drawn to scale, and some details have been enlarged for clarity, and some details may have been omitted. The shapes of the various regions and layers shown in the drawings, as well as their relative sizes and positional relationships, are merely exemplary and may deviate from reality due to manufacturing tolerances or technical limitations. Furthermore, those skilled in the art can design regions / layers with different shapes, sizes, and relative positions as needed.

[0070] It should be understood that the various forms of processes shown above can be used to reorder, add, or delete steps. For example, the steps described in this invention can be executed in parallel, sequentially, or in different orders, as long as the desired result of the technical solution disclosed in this invention can be achieved, and this invention does not impose any limitations on them.

[0071] The specific embodiments described above do not constitute a limitation on the scope of protection of this invention. Those skilled in the art should understand that various modifications, combinations, sub-combinations, and substitutions can be made according to design requirements and other factors. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this invention should be included within the scope of protection of this invention.

Claims

1. A wastewater graded discharge control system, characterized in that, The system includes a first-stage wastewater discharge switch unit, a lower-stage wastewater container, a lower-stage wastewater discharge unit, a first-stage water replenishment switch unit, a second-stage wastewater discharge switch unit, an upper-middle-stage wastewater container, an upper-middle-stage wastewater discharge unit, and a control unit. The COAP system is a low-temperature integrated pollutant removal system using a four-stage spray circulation cooling method, comprising a first-stage spray section, a second-stage spray section, a third-stage spray section, and a fourth-stage spray section connected in sequence. The first inlet of the lower-stage wastewater container is connected to the first-stage wastewater outlet of the COAP system via the first-stage wastewater discharge switch unit, the second inlet of the lower-stage wastewater container is connected to an alkali addition device, and the outlet of the lower-stage wastewater container is connected to the lower-stage wastewater discharge unit. The inlet of the upper and middle section wastewater container is connected to the first outlet of the second section wastewater of the COAP system via the second section wastewater discharge switch unit. The outlet of the upper and middle section wastewater container is connected to the upper and middle section wastewater discharge unit. The second outlet of the second section wastewater of the COAP system is connected to the first section wastewater inlet of the COAP system via the first section water replenishment switch unit. For the lower stage wastewater, the control unit is used to open the lower stage wastewater discharge switch unit when the lower stage wastewater level is higher than the upper limit of the lower stage wastewater level; and to control the lower stage wastewater discharge unit to discharge water when the lower stage wastewater level is higher than the upper limit of the lower stage wastewater level and the first pH value meets the requirements. For the wastewater in the middle and upper sections, the control unit is used to periodically control the first section water replenishment switch unit to turn on to replenish water to the first section wastewater; when the wastewater level in the middle and upper sections is higher than the upper limit of the wastewater level in the middle and upper sections and the second pH value meets the requirements, the control unit is used to control the wastewater discharge unit in the middle and upper sections to drain water. The third inlet of the lower wastewater container is connected to the fourth wastewater outlet of the COAP system via the MVR system. It also includes three overflow pipes, which are used to connect the three wastewater outlets of the COAP system and the two-stage spray equipment of the COAP system.

2. The wastewater graded discharge control system according to claim 1, characterized in that, The control unit is also used to close the wastewater discharge switch unit when the wastewater level of a section is lower than the lower limit of the wastewater level of a section.

3. The wastewater graded discharge control system according to claim 1, characterized in that, For the lower stage wastewater, the control unit is also used to control the shutdown of the lower stage wastewater discharge unit when the lower stage wastewater level is lower than the lower limit of the lower stage wastewater level.

4. The wastewater graded discharge control system according to claim 1, characterized in that, For downstream wastewater, the control unit is also used to start the alkali addition device when the first pH value is less than the set lower limit of pH value, and to stop the alkali addition device when the first pH value is greater than the set upper limit of pH value.

5. The wastewater graded discharge control system according to claim 1, characterized in that, The wastewater discharge switch unit uses a wastewater discharge valve.

6. The wastewater graded discharge control system according to claim 1, characterized in that, The lower wastewater discharge unit uses a lower wastewater pump.

7. The wastewater graded discharge control system according to claim 1, characterized in that, The fourth inlet of the lower wastewater container is connected to the salt production system of the COAP system.

8. A method for graded discharge control of wastewater, characterized in that, The wastewater graded discharge control system according to any one of claims 1-7, the method comprising: When the wastewater level of a section is higher than the upper limit of the wastewater level of a section, the wastewater discharge switch unit of that section is opened; when the wastewater level of a section is lower than the lower limit of the wastewater level of a section, the wastewater discharge switch unit of that section is closed. When the wastewater level in the lower section is higher than the upper limit of the wastewater level in the lower section and the first pH value meets the requirements, the wastewater discharge unit in the lower section is controlled to discharge water. When the first pH value is less than the set lower limit of pH value, the alkali addition device is started; when the first pH value is greater than the set upper limit of pH value, the alkali addition device is stopped. A timed control unit is activated to replenish water into a wastewater section. When the wastewater level in the upper and middle sections is higher than the upper limit of the wastewater level in the upper and middle sections and the second pH value meets the requirements, the wastewater discharge unit in the upper and middle sections is controlled to discharge water.

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