Dye production thermal wastewater treatment MVR (mechanical vapor recompression) system and control method thereof

Abstract

The invention discloses an MVR (mechanical vapor recompression) system for dye production hot wastewater treatment. The MVR system comprises a crystal separator, an inverter compressor, a forced circulation heat exchanger, a forced circulation pump, a compressor air inlet pipe, a compressor air outlet pipe and the like, an air inlet thermometer, an air inlet pressure gauge and an air inlet flow meter are arranged on the compressor air inlet pipe, and an air outlet thermometer and an air outlet pressure gauge are arranged on the compressor air outlet pipe. The control method of the system comprises the steps that S1, the compressor test board tests data; step S2, calculating dimensionless parameters; s3, calculating dimensionless parameters of the operation condition; s4, actual working condition parameters are calculated, and an actual working condition flow efficiency characteristic curve is fitted; and S5, the position of the actual working condition point flow in the characteristic curve is judged. Through intelligent frequency conversion of the compressor, different working conditions are adapted, the compressor operates in a high-efficiency working range, and waste of electric energy is reduced; automatic deviation correction can be achieved, the frequency of shutdown maintenance of the system is reduced, and the continuous working period of the system is prolonged.

Description

Technical Field

[0001] The invention relates to the technical field of MVR, and in particular to an MVR system for treating thermal wastewater from dye production and a control method thereof. Background Art

[0002] In the MVR system, in order to increase the heat exchange efficiency of the subsequent heat exchanger, atomized water is generally sprayed at the outlet of the steam compressor to reduce the superheat of the outlet steam. The amount of water and the atomization effect of the sprayed water will affect the temperature measurement near the temperature measuring point of the compressor outlet. It is difficult to accurately detect the operating efficiency of the MVR system steam compressor during use. During the operation of the MVR system, the compressor work, the deposition and heat exchange efficiency of the heat exchange tubes in the heat exchanger, and the blockage of the defoamer packing in the separator are all changing dynamically, which leads to the flow and pressure characteristics of the entire MVR pipe network system changing all the time, and the wastewater composition of the dye industry is complex and there are component changes. When the working characteristics of the compressor and the system pipe network characteristics are poorly matched, it is difficult to adjust in time by manual adjustment alone, and the professional quality of the equipment operator is very high; when the system pipe network parameters deviate from the design value, directly opening the anti-surge valve will make the compressor run very inefficient and waste electricity. Summary of the invention

[0003] The purpose of the present invention is to provide an MVR system for treating thermal wastewater from dye production and a control method thereof, which can adapt to different working conditions through intelligent frequency conversion of the compressor, so that the compressor can operate in a high-efficiency working range and reduce the waste of electric energy; it can automatically correct deviations, reduce the number of system shutdowns for maintenance, extend the continuous working cycle of the system, and make the owner's daily use and maintenance simpler and easier to operate.

[0004] The above technical objectives of the present invention are achieved through the following technical solutions: A dye production thermal wastewater treatment MVR system comprises a crystal separator, a variable frequency compressor, a forced circulation heat exchanger, a forced circulation pump, a non-condensable gas condenser, and a gas-liquid separator, wherein the upper portion of the crystal separator is connected to the variable frequency compressor through a compressor air inlet pipe, and the variable frequency compressor is connected to the air inlet end of the forced circulation heat exchanger through a compressor air outlet pipe; the bottom of the crystal separator is connected to the inlet end of the forced circulation pump through a first liquid pipe, and the outlet end of the forced circulation pump is connected to the liquid inlet end of the forced circulation heat exchanger through a second liquid pipe; the liquid outlet end of the forced circulation heat exchanger is connected to the crystal separator through a third liquid pipe; the forced circulation heat exchanger is connected to a non-condensable gas outlet pipe and a first condensed water outlet pipe, the non-condensable gas outlet pipe is connected to the gas-liquid separator through the non-condensed gas condenser, and the gas-liquid separator is connected to a second condensed water outlet pipe; The gas-liquid separator is connected to a vacuum pump; the raw materials of the crystallization separator come from the raw water of the pretreatment industrial section and the separated liquid from the centrifugal mother liquid tank; the first liquid pipe is connected to a discharge salt slurry pump through a third bypass pipe, and the discharge salt slurry pump is connected to the thickening kettle.

[0005] The compressor inlet pipe is provided with an inlet thermometer, an inlet pressure gauge and an inlet flow meter, and the compressor outlet pipe is provided with an outlet thermometer and an outlet pressure gauge. The inlet thermometer, the inlet pressure gauge, the inlet flow meter, the outlet thermometer and the outlet pressure gauge are all electrically connected to the controller, and the controller controls the variable frequency compressor and the forced circulation pump.

[0006] The disperse dye wastewater enters the crystallizer separator. Since the disperse dye wastewater has a certain temperature, its evaporated steam rises through the compressor inlet pipe and enters the variable frequency compressor for compression. The compressed high-temperature and high-pressure gas enters the disperse dye wastewater in the forced circulation heater through the compressor outlet pipe for heating. The heated disperse dye wastewater flows back to the crystallizer through the third liquid pipe for re-evaporation, and the disperse dye wastewater in the crystallizer is forced to be pumped into the forced circulation heater through the forced circulation pump and the first liquid pipe and the second liquid pipe. By reusing the heat energy in the disperse dye wastewater, the energy utilization rate is improved and the energy consumption is reduced.

[0007] The system is further configured as follows: a first bypass pipe is provided between the compressor inlet pipe and the compressor outlet pipe, an anti-surge valve is provided on the first bypass pipe, the anti-surge valve is electrically connected to the controller, and the surge problem can be reduced after the anti-surge valve is opened.

[0008] The system is further configured as follows: the crystallizer separator is connected to a suction pump through a fourth liquid pipe, the suction pump is connected to a scale inhibitor, the suction pump is controlled by a controller, the scale inhibitor can be pumped into the crystallizer through the suction pump, and then enters the forced circulation heat exchanger through the forced circulation pump, and the scale inhibitor can reduce scaling of disperse dye wastewater in the forced circulation heat exchanger.

[0009] The system is further configured as follows: an automatic spray head is provided on the upper part of the crystal separator, and water is sprayed by the automatic spray head to flush the demister in the crystal separator, and the amount of evaporated water vapor is increased to a certain extent, and the amount of steam entering the compressor is increased. Whether the automatic spray head discharges water is controlled by a controller through an electromagnetic valve, etc.

[0010] The system is further configured as follows: the compressor outlet pipe is connected to raw steam via a second bypass pipe, a solenoid valve is provided on the second bypass pipe, the solenoid valve is electrically connected to the controller, and the forced circulation heater can be heated by the raw steam to realize an auxiliary regulation function.

[0011] The system is further configured as follows: a fifth pressure gauge is provided on the crystal separator, and the fifth pressure gauge is located on the upstream side of the demister in the crystal separator; the pressure on the upstream side of the demister can be detected by the fifth pressure gauge, and the pressure on the downstream side of the demister can be detected by the air intake pressure gauge, so that the pressure difference on both sides of the demister can be obtained; The forced circulation heat exchanger is provided with a sixth pressure gauge and a third thermometer for monitoring relevant working conditions inside the forced circulation heat exchanger. The fifth pressure gauge, the sixth pressure gauge and the third thermometer are all electrically connected to the controller.

[0012] A control method for a dye production thermal wastewater treatment MVR system comprises the following steps: Step S1: test data of the compressor test bench; the test data includes the variable frequency compressor inlet temperature T1, the variable frequency compressor inlet pressure P1, the flow rate Q, the variable frequency compressor outlet temperature T2 and the outlet pressure P2; during the test, the variable frequency compressor speed N remains unchanged, the initial test speed is mostly the rated speed of the variable frequency compressor, the impeller outlet outer diameter is D, and 5 operating points are tested, including the near-surge point I and the highest efficiency point III at this speed where the compressor is close to the surge condition. The compressor inlet temperature T1 is measured by the inlet temperature meter, the variable frequency compressor inlet pressure P1 is measured by the inlet pressure meter, the flow rate Q is measured by the inlet flow meter, and the variable frequency compressor outlet temperature T2 and outlet pressure P2 are measured by the outlet temperature meter and outlet pressure meter respectively.

[0013] Step S2: Calculate dimensionless parameters; dimensionless parameters include dimensionless flow , dimensionless pressure head ψ, variable efficiency ηp.

[0014] Step S3: Calculate dimensionless parameters of operating conditions; Step S4: Calculate actual working condition parameters and fit the actual working condition flow efficiency characteristic curve; Step S5: Determine whether the actual operating point flow rate is at the characteristic curve position.

[0015] Since the outlet temperature of the variable frequency compressor cannot be monitored after spraying, the compressor efficiency cannot be directly measured. Based on the inlet flow rate monitored under this working condition and the flow efficiency curve fitted at this speed, the point on the efficiency curve corresponding to the inlet flow rate is the efficiency point of this working condition. The fitted efficiency curve is a general polynomial, and it is easy to determine the efficiency at the highest point of the fitted curve. And the corresponding flow rate Qt. This paper takes the efficiency curve fitted by a quadratic polynomial as an example, according to the set operating efficiency range ( ), calculate the flow operating range of this operating condition (Qt-C1, Qt+C2), compare the operating flow Q and the flow interval (Qt-C1, Qt+C2), where b is the set efficiency interval width, and C1 and C2 are calculated values.

[0016] The method is further configured as follows: step S5 comprises: S5.1: The actual operating point flow is within the set flow range, that is, Qt-C1≤Q≤Qt+C2, the variable frequency compressor operates within the set efficiency range, the variable frequency compressor does not make adjustments, and the output signal is that the variable frequency compressor operates in the high efficiency range; S5.2: When the actual operating point flow rate is outside the set flow rate range, it is judged to be biased to the left or right.

[0017] The method is further configured as follows: S5.2 includes: S5.2.1: When the actual operating point flow is on the right side of the set flow range, that is, Q>Qt+C2, it means that the operating condition is on the right side of the compressor characteristic line. This usually occurs when the system has just been fed and the mother liquor concentration is low. At this time, the steam generator produces more steam, reducing the compressor frequency; the amount of steam supplied to the evaporator generator by the variable frequency compressor becomes smaller, and the amount of steam generated will gradually decrease.

[0018] S5.2.2: When the actual operating point flow is on the left side of the set flow range, that is, Q<Qt-C1, it means that the operating condition is on the left side of the compressor characteristic line. Generally, it occurs during the evaporation process as the mother liquor concentration becomes higher and higher. At this time, the steam generator produces less steam, and the frequency of the variable frequency compressor is increased; the amount of steam supplied by the compressor to the evaporation generator increases, and the amount of steam generated will gradually increase.

[0019] The method is further configured as follows: S5.2.2 includes: S5.2.2.1: If the highest frequency is not reached, increase the frequency of the variable frequency compressor; S5.2.2.2: The highest frequency has been reached, and the distance from the surge warning position is determined to determine whether the warning is triggered; including S5.2.2.2.1: Trigger the early warning, the anti-surge valve opens to a certain degree, and prompts manual maintenance; S5.2.2.2.2: If no warning is triggered, determine whether other status parameters deviate and adjust them automatically.

[0020] When the operating point is on the left side of the curve and has reached the maximum frequency, it is no longer possible to adjust the matching of the compressor and the evaporation system by increasing the frequency.

[0021] When the compressor is on the left side of the characteristic line and reaches the maximum frequency, determine the relationship between the near-surge flow Qc corresponding to the near-surge point of the characteristic curve and the operating flow. Generally, a 10% surge margin is reserved. When Q>1.1Qc, determine the operating parameters of the evaporation system.

[0022] When the scaling of the forced circulation heat exchanger after the compressor or the blockage of the demister before the compressor becomes more and more serious, the system operating condition will cause the surge alarm to be triggered on the left side of the compressor, the anti-surge valve will open to a certain degree, and a prompt will be given to perform manual maintenance.

[0023] The outstanding effects of the present invention are: Compared with the existing technology, the dimensionless parameter automatic measurement method is used to automatically adjust the frequency of the MVR compressor according to this method to ensure that the compressor operates in the high-efficiency range, realize intelligent power saving, and solve the problem that it is difficult to accurately detect the operating efficiency of the MVR system steam compressor during use; and make the daily use and maintenance of the owner simpler and easier to operate; Due to the complex composition of wastewater in the dye industry and the changes in components, the operating conditions of the MVR system fluctuate frequently. When the system operating conditions deviate, the control system takes corresponding measures according to the state parameters and automatically corrects the deviation; When long-term operation causes parameters to deviate significantly and continuously, a shutdown alarm is triggered and manual intervention is performed according to the automatic prompts. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 is a schematic diagram of this system; Figure 2 This is the control flow chart of this system; Figure 3 These are the flow-pressure ratio characteristic curve and flow efficiency characteristic curve of the compressor.

[0025] Figure numerals: 1, crystal separator; 2, variable frequency compressor; 3, forced circulation heat exchanger; 4, forced circulation pump; 5, non-condensable gas condenser; 6, gas-liquid separator; 7, compressor inlet pipe; 8, compressor outlet pipe; 9, first liquid pipe; 10, second liquid pipe; 11, third liquid pipe; 12, non-condensable gas outlet pipe; 13, first condensate outlet pipe; 15, second condensate outlet pipe; 16, intake thermometer; 17, intake Pressure gauge; 18. Air inlet flow meter; 19. Air outlet thermometer; 20. Air outlet pressure gauge; 21. First bypass pipe; 22. Anti-surge valve; 23. Fourth liquid pipe; 24. Suction pump; 25. Antiscaling agent; 26. Automatic sprinkler head; 27. Second bypass pipe; 28. Solenoid valve; 29. ​​Vacuum pump; 30. Third bypass pipe; 31. Discharge salt slurry pump; 32. Fifth pressure gauge; 33. Sixth pressure gauge; 34. Third thermometer. DETAILED DESCRIPTION

[0026] The specific implementation of the present invention is further described in detail below in conjunction with the accompanying drawings and examples. The following examples are used to illustrate the present invention, but are not intended to limit the scope of the present invention.

[0027] The following references Figures 1 to 3 The embodiments of the present invention are described as follows: A dye production thermal wastewater treatment MVR system comprises a crystal separator 1, a variable frequency compressor 2, a forced circulation heat exchanger 3, a forced circulation pump 4, a non-condensable gas condenser 5, and a gas-liquid separator 6, wherein the upper part of the crystal separator 1 is connected to the variable frequency compressor 2 through a compressor air inlet pipe 7, and the variable frequency compressor 2 is connected to the air inlet end of the forced circulation heat exchanger 3 through a compressor air outlet pipe 8; the bottom of the crystal separator 1 is connected to the inlet end of the forced circulation pump 4 through a first liquid pipe 9, and the outlet end of the forced circulation pump 4 is connected to the liquid inlet end of the forced circulation heat exchanger 3 through a second liquid pipe 10; the liquid outlet end of the forced circulation heat exchanger 3 is connected to the crystal separator 1 through a third liquid pipe 11; the forced circulation heat exchanger 3 is connected to a non-condensable gas outlet pipe 12 and a first condensed water outlet pipe 13, the non-condensable gas outlet pipe 12 is connected to the gas-liquid separator 6 through the non-condensed gas condenser 5, and the gas-liquid separator 6 is connected to a second condensed water outlet pipe 15; The gas-liquid separator 6 is connected to a vacuum pump 29; the raw materials of the crystallization separator come from the raw water of the pretreatment industrial section and the separated liquid from the centrifugal mother liquid tank; the first liquid pipe 9 is connected to a discharge salt slurry pump 31 through a third bypass pipe 30, and the discharge salt slurry pump is connected to the thickening kettle.

[0028] The compressor inlet pipe 7 is provided with an inlet thermometer 16, an inlet pressure gauge 17 and an inlet flow meter 18, and the compressor outlet pipe 8 is provided with an outlet thermometer 19 and an outlet pressure gauge 20. The inlet thermometer 16, the inlet pressure gauge 17, the inlet flow meter 18, the outlet thermometer 19 and the outlet pressure gauge 20 are all electrically connected to the controller, and the controller controls the variable frequency compressor 2 and the forced circulation pump 4.

[0029] A first bypass pipe 21 is provided between the compressor air inlet pipe 7 and the compressor air outlet pipe 8 , and an anti-surge valve 22 is provided on the first bypass pipe 21 .

[0030] The crystal separator 1 is connected to a suction pump 24 via a fourth liquid pipe 23 , and the suction pump 24 is connected to an antiscalant 25 .

[0031] An automatic spray head 26 is provided on the upper portion of the crystal separator 1 .

[0032] The compressor outlet pipe 8 is connected to the raw steam through a second bypass pipe 27 , and a solenoid valve 28 is provided on the second bypass pipe 27 , and the solenoid valve 28 is electrically connected to the controller.

[0033] The crystal separator 1 is provided with a fifth pressure gauge 32, and the fifth pressure gauge 32 is located at the upstream side of the demister in the crystal separator 1; The forced circulation heat exchanger 3 is provided with a sixth pressure gauge 33 and a third thermometer 34 , and the fifth pressure gauge, the sixth pressure gauge and the third thermometer are all electrically connected to the controller.

[0034] A control method for a dye production thermal wastewater treatment MVR system comprises the following steps: Step S1: test data of the compressor test bench; the test data include the variable frequency compressor inlet temperature T1, the variable frequency compressor inlet pressure P1, the flow rate Q, the variable frequency compressor outlet temperature T2 and the outlet pressure P2; during the test, the variable frequency compressor speed N remains unchanged, the initial test speed is mostly the rated speed of the variable frequency compressor, the impeller outlet outer diameter is D, and 5 operating points are tested, including the near-surge point I and the highest efficiency point III where the compressor is close to the surge condition.

[0035] Step S2: Calculate dimensionless parameters; dimensionless parameters include dimensionless flow , dimensionless pressure head ψ, variable efficiency ηp.

[0036]

[0037] The inlet and outlet pressure ratio of the variable frequency compressor is recorded as Pr=P2 / P1; The inlet and outlet temperature ratio of the variable frequency compressor is recorded as Tr=T2 / T1; The specific heat ratio k of steam at this temperature is automatically obtained based on the entered steam property data table. In the following formula, n is the polynomial index.

[0038] Ideal gas polytropic process formula:

[0039]

[0040] Variable compression work per unit mass of gas

[0041] Where R is the gas constant.

[0042]

[0043] The dimensionless parameters of the five operating points are calculated by the above formula: ,ψ,ηp.

[0044] Step S3: Calculate dimensionless parameters of operating conditions; For example, the compressor speed is increased to operating condition N2;

[0045]

[0046] In the above formula, the impeller outlet outer diameter D is a constant, and the compressor speed N, flow rate Q, and variable compression work is a variable; Empirical formula , where a is an empirical constant.

[0047] Step S4: Calculate actual working condition parameters and fit the actual working condition flow efficiency characteristic curve; Substitute the inlet parameters of 5 operating points and calculate the outlet parameters corresponding to the 5 operating points at the operating frequency N2. Use these operating points to fit and plot the compressor flow-pressure ratio characteristic and flow-efficiency characteristic curve at this frequency.

[0048] Step S5: Determine whether the actual operating point flow rate is at the characteristic curve position.

[0049] Since the outlet temperature of the variable frequency compressor cannot be monitored after spraying, the compressor efficiency cannot be directly measured. Based on the inlet flow rate monitored under this working condition and the flow efficiency curve fitted at this speed, the point on the efficiency curve corresponding to the inlet flow rate is the efficiency point of this working condition. The fitted efficiency curve is a general polynomial, and it is easy to determine the efficiency at the highest point of the fitted curve. And the corresponding flow rate Qt. This paper takes the efficiency curve fitted by a quadratic polynomial as an example, according to the set operating efficiency range ( ), calculate the flow operating range of this condition (Qt-C1, Qt+C2), compare the operating flow Q and flow interval (Qt-C1, Qt+C2), where b is the set efficiency interval width, C1, C2 are calculated values, such as Figure 3 shown.

[0050] S5.1: The actual operating point flow is within the set flow range, that is, Qt-C1≤Q≤Qt+C2, the variable frequency compressor operates within the set efficiency range, the variable frequency compressor does not make adjustments, and the output signal is that the variable frequency compressor operates in the high efficiency range; S5.2: When the actual operating point flow rate is outside the set flow rate range, it is judged to be biased to the left or right.

[0051] The S5.2 includes: S5.2.1: When the actual operating point flow is on the right side of the set flow range, that is, Q>Qt+C2, it means that the operating condition is on the right side of the compressor characteristic line. This usually occurs when the system has just been fed and the mother liquor concentration is low. At this time, the steam generator produces more steam, reducing the compressor frequency; the amount of steam supplied to the evaporator generator by the variable frequency compressor becomes smaller, and the amount of steam generated will gradually decrease.

[0052] S5.2.2: When the actual operating point flow is on the left side of the set flow range, that is, Q<Qt-C1, it means that the operating condition is on the left side of the compressor characteristic line. Generally, it occurs during the evaporation process as the mother liquor concentration becomes higher and higher. At this time, the steam generator produces less steam, and the frequency of the variable frequency compressor is increased; the amount of steam supplied by the compressor to the evaporation generator increases, and the amount of steam generated will gradually increase.

[0053] The S5.2.2 includes: S5.2.2.1: If the highest frequency is not reached, increase the frequency of the variable frequency compressor; S5.2.2.2: The highest frequency has been reached, and the distance from the surge warning position is determined to determine whether the warning is triggered; S5.2.2.2.1: Trigger the early warning, the anti-surge valve opens to a certain degree, and prompts manual maintenance; S5.2.2.2.2: If no warning is triggered, determine whether other status parameters deviate and adjust them automatically.

[0054] When the operating point is on the left side of the curve and has reached the maximum frequency, it is no longer possible to adjust the matching of the compressor and the evaporation system by increasing the frequency.

[0055] When the compressor is on the left side of the characteristic line and reaches the maximum frequency, determine the relationship between the near-surge flow Qc corresponding to the near-surge point of the characteristic curve and the operating flow. Generally, a 10% surge margin is reserved. When Q>1.1Qc, determine the operating parameters of the evaporation system.

[0056] The monitoring points of the evaporation system are the compressor inlet pressure, the pressure difference before and after the demister, the material temperature in the mother liquid tank and the current of the forced circulation pump.

[0057] When the forced circulation heat exchanger is heated unevenly, the local temperature is too high, or the components in the wastewater are affected, the scale gradually settles on the inner wall of the heat exchange tube, affecting the heat exchange efficiency of the heat exchanger. As the amount of heat absorbed in the mother liquid tank decreases, less steam is generated, the compressor inlet pressure decreases, the outlet pressure increases, and the pressure difference before and after the demister is normal. Due to the gradual blockage in the heat exchanger, the current of the forced circulation pump increases. When the current exceeds the set value, the suction pump is started to automatically add the scale inhibitor into the mother liquid tank to reduce the thickness of the scale, slow down the scaling, and increase the compressor inlet pressure.

[0058] Since dye wastewater contains highly viscous organic matter, it is easy to clog the separator's demister filler during evaporation, resulting in an increase in the pressure difference before and after the demister, a decrease in the compressor inlet pressure, and a decrease in the compressor inlet density due to the pressure reduction, a decrease in the compressor's steam production, and a decrease in the steam production of the steam generator. The operating point moves to the left side of the compressor's operating characteristic curve. At this time, turn on the automatic spray nozzles before and after the demister, and rinse the demister with a small amount of water every 30 seconds or 1 minute to relieve the demister blockage. At the same time, increase the steam supply to the heat exchanger, appropriately increase the material temperature, and increase the steam production of the steam generator. The compressor inlet pressure rises.

[0059] When the scaling of the forced circulation heat exchanger after the compressor or the blockage of the demister before the compressor becomes more and more serious, the system operating condition will cause the surge alarm to be triggered on the left side of the compressor, the anti-surge valve will open to a certain degree, and a prompt will be given to perform manual maintenance.

[0060] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present invention. These improvements and modifications of the above assumptions should also be regarded as the scope of protection of the present invention.

Claims

1. A dye production thermal wastewater treatment MVR system, comprising a crystallization separator (1), a variable frequency compressor (2), a forced circulation heat exchanger (3) and a forced circulation pump (4); characterized in that: The upper part of the crystal separator (1) is connected to the variable frequency compressor (2) via a compressor air inlet pipe (7), and the variable frequency compressor (2) is connected to the air inlet end of the forced circulation heat exchanger (3) via a compressor air outlet pipe (8); the bottom of the crystal separator (1) is connected to the inlet end of the forced circulation pump (4) via a first liquid pipe (9), and the outlet end of the forced circulation pump (4) is connected to the liquid inlet end of the forced circulation heat exchanger (3) via a second liquid pipe (10); the liquid outlet end of the forced circulation heat exchanger (3) is connected to the crystal separator (1) via a third liquid pipe (11); The compressor air inlet pipe (7) is provided with an air inlet thermometer (16), an air inlet pressure gauge (17) and an air inlet flow meter (18), and the compressor air outlet pipe (8) is provided with an air outlet thermometer (19) and an air outlet pressure gauge (20).

2. The MVR system for treating thermal wastewater from dye production according to claim 1, characterized in that: A first bypass pipe (21) is provided between the compressor air inlet pipe (7) and the compressor air outlet pipe (8), and an anti-surge valve (22) is provided on the first bypass pipe (21).

3. The MVR system for treating thermal wastewater from dye production according to claim 1, characterized in that: The crystal separator (1) is connected to a suction pump (24) via a fourth liquid pipe (23), and the suction pump (24) is connected to an antiscalant (25).

4. The MVR system for treating thermal wastewater from dye production according to claim 1, characterized in that: An automatic spray head (26) is provided on the upper portion of the crystallization separator (1).

5. The MVR system for treating thermal wastewater from dye production according to claim 1, characterized in that: The compressor outlet pipe (8) is connected to raw steam via a second bypass pipe (27), and a solenoid valve (28) is provided on the second bypass pipe (27).

6. The MVR system for treating thermal wastewater from dye production according to claim 1, characterized in that: The crystal separator (1) is provided with a fifth pressure gauge (32), and the fifth pressure gauge (32) is located on the upstream side of the demister in the crystal separator (1); The forced circulation heat exchanger (3) is provided with a sixth pressure gauge (33) and a third thermometer (34).

7. A control method for the MVR system for treating thermal wastewater in dye production, characterized in that: The following steps are involved: Step S1: compressor test bench test data; Step S2: Calculate dimensionless parameters; Step S3: Calculate dimensionless parameters of operating conditions; Step S4: Calculate actual working condition parameters and fit the actual working condition flow efficiency characteristic curve; Step S5: Determine whether the actual operating point flow rate is at the characteristic curve position.

8. The control method of a dye production thermal wastewater treatment MVR system according to claim 7, characterized in that: The step S5 comprises: S5.1: The actual operating point flow is within the set flow range, the variable frequency compressor does not make adjustments, and outputs a signal; S5.2: When the actual operating point flow rate is outside the set flow rate range, it is judged to be biased to the left or right.

9. The control method of a dye production thermal wastewater treatment MVR system according to claim 8, characterized in that: The S5.2 includes: S5.2.1: The actual operating point flow is on the right side of the set flow range, reducing the compressor frequency; S5.2.2: When the actual operating point flow is on the left side of the set flow range, increase the frequency of the variable frequency compressor.

10. The control method of a dye production thermal wastewater treatment MVR system according to claim 9, characterized in that: The S5.2.2 includes: S5.2.2.1: If the highest frequency is not reached, increase the frequency of the variable frequency compressor; S5.2.2.2: The highest frequency has been reached, and the distance from the surge warning position is determined to determine whether the warning is triggered; including: S5.2.2.2.1: Trigger the early warning, the anti-surge valve opens to a certain degree, and prompts manual maintenance; S5.2.2.2.2: If no warning is triggered, determine whether other status parameters deviate and adjust them automatically.

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