Dual-stage series control method for a dual-stage series control Roots steam compressor

Abstract

The present invention provides a two-stage series control method for a two-stage series control Roots steam compressor, which includes a first-stage compressor and a second-stage compressor. A double-shaft extended variable-frequency motor is provided between the first-stage compressor and the second-stage compressor. The two ends of the shaft of the double-shaft extended variable-frequency motor are respectively connected to the first-stage compressor and the second-stage compressor. The reference state flow rate Q of the first-stage compressor N1 is equal to the reference state flow rate Q of the second-stage compressor N2 , and the compression ratio ε1 of the first-stage compressor is approximately equal to ε2 of the second-stage compressor, achieving a more energy-saving purpose; the use of a double-shaft extended variable-frequency motor has a higher direct connection transmission efficiency and is convenient for frequency conversion starting; it meets the requirements of a two-stage series compression ratio ε ≤ 3.5 and a two-stage temperature rise △℃ ≤ 34℃, with high transmission efficiency and high intelligent control level.

Description

Technical Field

[0001] The present invention relates to the technical field of Roots steam compressors, and particularly to a two-stage series control method for a two-stage series control Roots steam compressor. Background Art

[0002] There are also many types of steam compressors on the market. For example, MVR steam compressors can be divided into Roots steam compressors and single-stage high-speed centrifugal steam compressors, etc. The compression ratio ε of traditional MVR Roots steam compressors is ≤2.1, the single-stage temperature rise △℃ is ≤25℃, and the Roots steam compressor lacks intelligent control during operation and maintenance. Aiming at the deficiencies of the small compression ratio, low temperature rise and low intelligent control level of the Roots steam compressor, the present invention proposes a new solution. After the new solution is implemented, it meets the requirements of a two-stage series compression ratio ε≤3.5, a two-stage temperature rise △℃≤34℃, high transmission efficiency and high intelligent control level. Summary of the Invention

[0003] In view of the technical problems of the small compression ratio, low temperature rise and low intelligent control level of the traditional Roots steam compressor, the present invention provides a two-stage series control Roots steam compressor, and designs the reference state flow rate Q of the first-stage compressor N1 to be equal to the reference state flow rate Q of the second-stage compressor N2 and designs the compression ratio ε1 of the first-stage compressor to be approximately equal to ε2 of the second-stage compressor, achieving a more energy-saving purpose; adopting a double-shaft extended variable-frequency motor, the double-shaft direct connection has higher transmission efficiency and is convenient for variable-frequency starting; it meets the requirements of a two-stage series compression ratio ε≤3.5 and a two-stage temperature rise △℃≤34℃, with high transmission efficiency and high intelligent control level.

[0004] To this end, the technical solution of the present invention is a two-stage series control method for a two-stage series control Roots steam compressor, including the following steps:

[0005] (1) The trial operation startup control method of the Roots steam compressor: First, perform the detection before starting the Roots steam compressor, and then check whether the Roots steam compressor meets the startup logic. It can only be started when all requirements are met, otherwise the alarm light indicator will light up;

[0006] (2) The startup control method of the Roots steam compressor: The starting frequency of the double-shaft extended variable-frequency motor is 10Hz, and it is increased by 10Hz each time. Note that the interval time is at least 15 seconds. After the current and pressure are stable, the frequency is increased; after the frequency of the double-shaft extended variable-frequency motor reaches the full frequency, slowly close the electric butterfly valve;

[0007] (3) The normal operation control method of the Roots steam compressor: The Roots steam compressor runs without abnormality for about 20 minutes under no-load, and then is connected to the system for operation. During the operation process, it can only operate normally when all operating condition requirements are met, otherwise the alarm light indicator will light up;

[0008] Among them, the operating conditions of the Roots steam compressor include:

[0009] C1. Solenoid valves I, II, III, and IV are all fully open;

[0010] C2. The flow rates of rotameters I, II, III, and IV are 80 - 120% of the required flow rate;

[0011] C3. The electric butterfly valve is closed;

[0012] C4. The pressure of pressure transmitter III is 50 - 100 kPa higher than the rated requirement of the outlet pressure of the first - stage compressor;

[0013] C5. The pressure of pressure transmitter VII is 50 - 100 kPa higher than the rated requirement of the outlet pressure of the second - stage compressor;

[0014] C6. The pressures of pressure transmitters I, IV, and VI are 95 - 105% of the required pressure;

[0015] C7. The temperatures of temperature transmitters I, II, and III are the required temperature ±1.5°C;

[0016] C8. The main motor current ≤ 105% of the rated current and the time higher than the rated current does not exceed 1 minute;

[0017] (4) Alarm protection interlock control method for the normal operation of the Roots steam compressor: When one of the alarm protection conditions is met, the alarm indicator light is on and a sound alarm is issued;

[0018] Among them, the alarm protection conditions for the normal operation of the Roots steam compressor include:

[0019] D1. Alarm when the pressure of pressure transmitter III is lower than the rated requirement of the outlet pressure of the first - stage compressor + 35 kPa or higher than the outlet pressure rated requirement + 135 kPa;

[0020] D2. Alarm when the pressure of pressure transmitter VII is lower than the rated requirement of the outlet pressure of the second - stage compressor + 35 kPa or higher than the outlet pressure rated requirement + 135 kPa;

[0021] D3. Alarm when the flow rate of any one of rotameters I, II, III, and IV < 85% of the required flow rate;

[0022] D4. Alarm when the temperature of any one of temperature transmitters I, II, and III exceeds the required temperature ±1.5°C

[0023] D5. Alarm when the main motor current is greater than 95% of the rated current;

[0024] D6. Alarm when the pressure deviation of any one of pressure transmitters I, IV, and VI is greater than 3%;

[0025] D7. Alarm when the pressure difference between the inlet and outlet of the steam compressor is equal to 98% of the predetermined set value;

[0026] D8. Alarm when the normal operating frequency of the steam compressor is close to the set minimum frequency + 3 Hz;

[0027] D9. Alarm when the pressure of either Pressure Transmitter III or V is close to 125% of the low point set value or 75% of the high point set value;

[0028] (5) The shutdown alarm protection interlock control method for the Roots steam compressor. When one of the shutdown alarm protection conditions is met, the alarm indicator light turns on and a sound alarm is issued. When the shutdown signal is sent to the DCS, the electric butterfly valve is opened. After complete pressure relief, the variable frequency motor and the variable frequency motor cooling fan are turned off, all solenoid valves are closed, and the cooling water is closed;

[0029] The two-stage series control Roots steam compressor includes a first-stage compressor and a second-stage compressor. There is a double-shaft extension variable frequency motor between the first-stage compressor and the second-stage compressor. The two ends of the double-shaft extension variable frequency motor are respectively connected to the first-stage compressor and the second-stage compressor. The reference state flow rate Q N1 of the first-stage compressor is N2 equal to the reference state flow rate Q of the second-stage compressor, and the compression ratio ε1 of the first-stage compressor is approximately equal to ε2 of the second-stage compressor;

[0030] The Roots steam compressor is also provided with a first-stage compressor inlet end N1, a first-stage compressor seal water inlet end N2, a first-stage compressor mechanical seal coolant pipeline inlet end N3, a first-stage compressor mechanical seal coolant pipeline outlet end N4, a second-stage compressor seal water inlet end N5, a second-stage compressor outlet end N6, a second-stage compressor mechanical seal coolant pipeline inlet end N7, a first-stage compressor mechanical seal coolant pipeline outlet end N8, and a reflux pipeline N9;

[0031] A temperature transmitter I and a pressure transmitter I are installed on the first-stage compressor inlet end N1. A seal liquid connecting pipe and a bellows compensator I are installed between the first-stage compressor inlet end N1 and the first-stage compressor;

[0032] A solenoid valve I, a pressure transmitter II, and a rotameter I are installed on the first-stage compressor seal water inlet end N2;

[0033] A solenoid valve II, a pressure transmitter III, and a rotameter II are installed on the first-stage compressor mechanical seal coolant pipeline inlet end N3;

[0034] A pressure transmitter VI and a temperature transmitter III are installed on the second-stage compressor outlet end N6;

[0035] At the inlet end N7 of the coolant pipeline of the second-stage compressor mechanical seal, a rotameter IV, a pressure transmitter VII, and a solenoid valve IV are installed.

[0036] The reflux pipeline N9 connects the inlet end N2 of the sealing water of the first-stage compressor and the outlet end N6 of the second-stage compressor. An electric butterfly valve is installed on the reflux pipeline N9. The outlet of the first-stage compressor and the inlet of the second-stage compressor are connected through an intermediate pipe. A temperature transmitter II and a pressure transmitter IV are installed on the intermediate pipe.

[0037] The intermediate pipe is connected to the inlet end N5 of the sealing water of the second-stage compressor. A rotameter III, a pressure transmitter V, and a solenoid valve III are installed at the inlet end N5 of the sealing water of the second-stage compressor.

[0038] Preferably, a bellows compensator II is provided between the second-stage compressor and the outlet end N6 of the second-stage compressor.

[0039] Preferably, the inspection contents before starting the Roots steam compressor are as follows:

[0040] A1. Manual barring is normal.

[0041] A2. The oil level in the oil tank is normal.

[0042] A3. The rotation direction of the fan is correct when the main motor is jogged.

[0043] A4. The main and auxiliary normal cooling water is turned on.

[0044] After the above points are all satisfied, proceed to the next step.

[0045] Preferably, the shutdown alarm protection conditions during the normal operation of the Roots steam compressor include:

[0046] E1. When the pressure of the pressure transmitter III is lower than the rated requirement of the outlet pressure of the first-stage compressor +20 kPa or higher than the rated requirement of the outlet pressure +150 kPa, an alarm is given and the machine is shut down when the upper and lower limits are exceeded.

[0047] E2. When the pressure of the pressure transmitter VI is lower than the rated requirement of the outlet pressure of the second-stage compressor +20 kPa or higher than the rated requirement of the outlet pressure +150 kPa, an alarm is given and the machine is shut down when the upper and lower limits are exceeded.

[0048] E3. When one of the solenoid valves I, II, III, and IV is closed, an alarm is given and the machine is shut down.

[0049] E4. When the flow rate of one of the rotameters I, II, III, and IV is <80% of the required flow rate, an alarm is given and the machine is shut down.

[0050] E5. When the temperature of one of the temperature transmitters I, II, and III exceeds the required temperature ±2 °C, an alarm is given and the machine is shut down.

[0051] E6. Alarm when the main motor current is close to the rated current. Alarm and stop when the main motor current > 105% of the rated current or the time higher than the rated current exceeds 1 minute.

[0052] E7. Alarm and stop when the pressure deviation of any one of the pressure transmitters I, IV, and VI is greater than 5%.

[0053] E8. Alarm and stop when the forced cooling fan of the double-shaft extended variable-frequency motor fails.

[0054] E9. Alarm and stop when the pressure difference between the inlet and outlet of the steam compressor exceeds the predetermined set value.

[0055] E10. Alarm and stop when the normal operating frequency of the steam compressor is lower than the set minimum frequency.

[0056] E11. Alarm and stop when the pressure of any one of the pressure transmitters III and V is lower than or higher than the set value.

[0057] The beneficial effects of the present invention are as follows: The present invention includes a first-stage compressor and a second-stage compressor. A double-shaft extended variable-frequency motor is provided between the first-stage compressor and the second-stage compressor. The two ends of the shaft of the double-shaft extended variable-frequency motor are respectively connected to the first-stage compressor and the second-stage compressor. The reference state flow rate Q N1 of the first-stage compressor is designed to be equal to the reference state flow rate Q N2 of the second-stage compressor, that is, Q N1 =Q N2 ; The pressure ratio ε1 of the first-stage compressor is designed to be approximately equal to the pressure ratio ε2 of the second-stage compressor, that is, ε1≈ε 21 ≈, achieving a more energy-saving purpose; The double-shaft extended variable-frequency motor is adopted, and the double-shaft direct connection has higher transmission efficiency and is convenient for frequency conversion start-up; It meets the requirements of the double-stage series pressure ratio ε≤3.5 and the double-stage temperature rise △℃≤34℃, with high transmission efficiency and high intelligent control level. Description of the Drawings

[0058] Figure 1 is the overall structural schematic diagram of the double-stage series control Roots steam compressor;

[0059] Figure 2 is the start-up test run and operation logic diagram of the double-stage series control of the Roots steam compressor;

[0060] Figure 3 is the alarm protection logic diagram of the double-stage series control of the Roots steam compressor;

[0061] Figure 4 is the shutdown alarm protection logic diagram of the double-stage series control of the Roots steam compressor.

[0062] Symbol Explanation in the Figures:

[0063] 1. Temperature transmitter Ⅰ; 2. Pressure transmitter Ⅰ; 3. Solenoid valve Ⅰ; 4. Pressure transmitter Ⅱ; 5. Rotameter Ⅰ; 6. Sealing liquid connection pipe; 7. Bellows compensator Ⅰ; 8. First-stage compressor; 9. Solenoid valve Ⅱ; 10. Pressure transmitter Ⅲ; 11. Rotameter Ⅱ; 12. Double-shaft extended frequency conversion motor; 13. Second-stage compressor; 14. Intermediate connection pipe; 15. Temperature transmitter Ⅱ; 16. Pressure transmitter Ⅳ; 17. Rotameter Ⅲ; 18. Pressure transmitter Ⅴ; 19. Solenoid valve Ⅲ; 20. Bellows compensator Ⅱ; 21. Pressure transmitter Ⅵ; 22. Temperature transmitter Ⅲ; 23. Rotameter Ⅳ; 24. Pressure transmitter Ⅶ; 25. Solenoid valve Ⅳ; 26. Electric butterfly valve. Detailed implementation mode

[0064] The present invention will be further described below in conjunction with embodiments.

[0065] Figures 1-4 This is an embodiment of a two-stage series control Roots steam compressor of the present invention, which includes a first-stage compressor 8 and a second-stage compressor 13. A double-shaft extended frequency conversion motor 12 is provided between the first-stage compressor 8 and the second-stage compressor 13. The two ends of the shaft of the double-shaft extended frequency conversion motor 12 are respectively connected to the first-stage compressor 8 and the second-stage compressor 13. The Roots steam compressor is driven by the double-shaft extended frequency conversion motor 12, and the double-shaft direct connection has higher transmission efficiency and is convenient for frequency conversion starting.

[0066] The reference state flow rate Q of the first-stage compressor 8 N1 is equal to the reference state flow rate Q of the second-stage compressor 13 N2 , that is, Q N1 =Q N2 ; The pressure ratio ε1 of the first-stage compressor is approximately equal to the pressure ratio ε2 of the second-stage compressor, that is, ε1≈ε 21 ≈, achieving a more energy-saving purpose.

[0067] This Roots steam compressor is also provided with a first-stage compressor inlet end N1, a first-stage compressor sealing water inlet end N2, a first-stage compressor mechanical seal coolant pipeline inlet end N3, a first-stage compressor mechanical seal coolant pipeline outlet end N4, a second-stage compressor sealing water inlet end N5, a second-stage compressor outlet end N6, a second-stage compressor mechanical seal coolant pipeline inlet end N7, a first-stage compressor mechanical seal coolant pipeline outlet end N8 and a return pipeline N9.

[0068] A temperature transmitter Ⅰ1 and a pressure transmitter Ⅰ2 are installed on the first-stage compressor inlet end N1. The temperature transmitter Ⅰ1 and the pressure transmitter Ⅰ2 are instruments for the first-stage compressor inlet end N1, and have on-site display and remote transmission functions.

[0069] There is a filling liquid connecting pipe 6 and a bellows compensator Ⅰ7 installed between the inlet end N1 of the first-stage compressor and the first-stage compressor 8. The filling liquid connecting pipe 6 is a cooling pipe fitting for eliminating the overheating of the first-stage compressor 8, and the bellows compensator Ⅰ7 is for eliminating the vibration between the pipeline and the first-stage compressor 8.

[0070] An electromagnetic valve Ⅰ3, a pressure transmitter Ⅱ4, and a rotameter Ⅰ5 are installed on the inlet end N2 of the filling water for the first-stage compressor. The pressure transmitter Ⅱ4 and the rotameter Ⅰ5 are instruments for the inlet end N2 of the filling water for the first-stage compressor, with on-site display and remote transmission functions; the electromagnetic valve Ⅰ3 controls the opening of the filling liquid, the pressure transmitter Ⅱ4 controls the pressure of the filling liquid, and the rotameter Ⅰ5 is used to monitor the inlet flow rate of the filling liquid connecting pipe.

[0071] An electromagnetic valve Ⅱ9, a pressure transmitter Ⅲ10, and a rotameter Ⅱ11 are installed on the inlet end N3 of the coolant pipeline for the mechanical seal of the first-stage compressor. The electromagnetic valve Ⅱ9 controls the opening of the coolant for the mechanical seal of the first-stage compressor, the pressure transmitter Ⅲ10 controls the pressure of the coolant for the mechanical seal of the first-stage compressor, and the rotameter Ⅱ is used to monitor the flow rate of the coolant for the mechanical seal of the first-stage compressor.

[0072] The outlet of the first-stage compressor 8 is connected to the inlet of the second-stage compressor 13 through an intermediate connecting pipe 14. A temperature transmitter Ⅱ15 and a pressure transmitter Ⅳ16 are installed on the intermediate connecting pipe 14. The temperature transmitter Ⅱ15 and the pressure transmitter Ⅳ16 are inlet instruments for the second-stage compressor 13, with on-site display and remote transmission functions.

[0073] The intermediate connecting pipe 14 is connected to the inlet end N5 of the filling water for the second-stage compressor. The filling liquid of the second-stage compressor eliminates the overheating of the second-stage compressor. A rotameter Ⅲ17, a pressure transmitter Ⅴ18, and an electromagnetic valve Ⅲ19 are installed on the inlet end N5 of the filling water for the second-stage compressor. The rotameter Ⅲ17 is used to monitor the inlet flow rate of the filling liquid connecting pipe, the pressure transmitter Ⅴ18 controls the pressure of the filling liquid, and the electromagnetic valve Ⅲ19 controls the opening of the filling liquid.

[0074] A bellows compensator Ⅱ20 is provided between the second-stage compressor 13 and the outlet end N6 of the second-stage compressor. The bellows compensator Ⅱ20 is for eliminating the vibration between the pipeline and the second-stage compressor 12.

[0075] A pressure transmitter Ⅵ21 and a temperature transmitter Ⅲ22 are installed on the outlet end N6 of the second-stage compressor. The pressure transmitter Ⅵ21 and the temperature transmitter Ⅲ22 are instruments for the outlet end N6 of the second-stage compressor, with on-site display and remote transmission functions.

[0076] At the inlet end N7 of the coolant pipeline of the second-stage compressor mechanical seal, a rotameter Ⅳ23, a pressure transmitter Ⅶ24, and a solenoid valve Ⅳ25 are installed. The rotameter Ⅳ23 is used to monitor the coolant flow rate of the second-stage compressor mechanical seal. The pressure transmitter Ⅶ24 controls the pressure of the coolant of the second-stage compressor mechanical seal. The solenoid valve Ⅳ25 controls the opening of the coolant of the second-stage compressor mechanical seal.

[0077] The reflux pipeline N9 connects the inlet end N2 of the sealing water of the first-stage compressor to the outlet end N6 of the second-stage compressor. An electric butterfly valve 26 is installed on the reflux pipeline N9. The function of the electric butterfly valve 26 is for the no-load start-up and no-load shutdown of the first-stage and second-stage compressors. When starting up and shutting down, the electric butterfly valve is opened to cooperate with the frequency conversion motor speed regulation to achieve the function of no-load start-up and no-load shutdown.

[0078] Embodiment 2

[0079] After checking that the manual turning of the shaft is normal, the oil level in the oil tank is normal, the main motor is jogged and the rotation direction of the fan is correct, the cooling water of the main and auxiliary oil tanks is opened, and the electric butterfly valve is opened, etc., a two-stage series control Roots steam compressor meets the start-up logic and starts up. Starting up must meet all requirements, that is, the "AND" logic, to start up. Otherwise, the alarm light indicator will light up.

[0080] There is no abnormality after about 20 minutes of no-load operation, and it is connected to the system for operation. During the operation process, all requirements must be met, that is, the "AND" logic, to operate normally. Otherwise, the alarm light indicator will light up. See the start-up test run and operation logic diagram in Figure 2 .

[0081] A two-stage series intelligent control Roots steam compressor has a separate operation safety protection (alarm) logic, which is used as a pre-warning before shutdown. See the appendix Figure 3 .

[0082] When one shutdown condition is met, the alarm indicator light will light up and a sound alarm will be issued. When the shutdown signal is transmitted to the DCS, the electric butterfly valve is opened for shutdown, that is, the "OR" logic. See the shutdown logic diagram in Figure 4 .

[0083] A two-stage series control method for a Roots steam compressor is as follows:

[0084] (1) The start-up control method for the trial operation of the Roots steam compressor. First, perform the detection before the start-up of the Roots steam compressor, and then check whether the Roots steam compressor meets the start-up logic. Starting up must meet all requirements to start up. Otherwise, the alarm light indicator will light up.

[0085] The detection content before the start-up of the Roots steam compressor is as follows:

[0086] A1. The manual turning of the shaft is normal;

[0087] A2. The fuel tank oil level is normal;

[0088] A3. The main motor is jogged to run, and the rotation direction of the fan is correct;

[0089] A4. The main and auxiliary normal cooling water is turned on;

[0090] After the above points are all satisfied, proceed to the next step.

[0091] The startup logic of the Roots steam compressor includes:

[0092] B1. The forced cooling fan of the double-shaft extended variable-frequency motor starts;

[0093] B2. The electric butterfly valve opens;

[0094] B3. Solenoid valves I, II, III, and IV are opened;

[0095] B4. The flow rates of the rotameters I, II, III, and IV are 80 - 120% of the required flow rate;

[0096] B5. The wiring and display of all pressure transmitters are normal;

[0097] If any of the above points cannot be satisfied, the machine cannot be started.

[0098] (2) The startup control method of the Roots steam compressor is as follows:

[0099] (2.1) The starting frequency of the double-shaft extended variable-frequency motor is 10 Hz, and it is increased by 10 Hz each time. Pay attention to an interval of at least 15 seconds, and increase the frequency after the current and pressure are stable;

[0100] (2.2) After the frequency of the double-shaft extended variable-frequency motor reaches the full frequency, slowly close the electric butterfly valve.

[0101] (3) The normal operation control method of the Roots steam compressor: The Roots steam compressor runs without abnormality for about 20 minutes under no load, then is connected to the system for operation. During the operation process, it must meet all the requirements of the operating conditions to operate normally, otherwise the alarm light indicator will light up.

[0102] The operating conditions of the Roots steam compressor include:

[0103] C1. Solenoid valves I, II, III, and IV are all open;

[0104] C2. The flow rates of the rotameters I, II, III, and IV are 80 - 120% of the required flow rate;

[0105] C3. The electric butterfly valve is closed;

[0106] C4. The pressure of pressure transmitter III is 50 - 100 kPa higher than the rated requirement of the outlet pressure of the first-stage compressor;

[0107] C5. The pressure of the pressure transmitter VII is 50 - 100 kPa higher than the rated requirement of the outlet pressure of the second-stage compressor.

[0108] C6. The pressures of the pressure transmitters I, IV, and VI are 95 - 105% of the required pressure.

[0109] C7. The temperatures of the temperature transmitters I, II, and III are the required temperature ±1.5°C.

[0110] C8. The current of the main motor ≤ 105% of the rated current and the time higher than the rated current does not exceed 1 minute.

[0111] (4) Alarm protection interlock control method for the normal operation of the Roots steam compressor. When one of the alarm protection conditions is met, the alarm indicator light turns on and a sound alarm is issued.

[0112] The alarm protection conditions for the normal operation of the Roots steam compressor include:

[0113] D1. Alarm when the pressure of the pressure transmitter III is lower than the rated requirement of the outlet pressure of the first-stage compressor + 35 kPa or higher than the outlet pressure rated requirement + 135 kPa.

[0114] D2. Alarm when the pressure of the pressure transmitter VII is lower than the rated requirement of the outlet pressure of the second-stage compressor + 35 kPa or higher than the outlet pressure rated requirement + 135 kPa.

[0115] D3. Alarm when the flow rate of one of the rotameters I, II, III, and IV < 85% of the required flow rate.

[0116] D4. Alarm when the temperature of one of the temperature transmitters I, II, and III exceeds the required temperature ±1.5°C.

[0117] D5. Alarm when the current of the main motor is greater than 95% of the rated current.

[0118] D6. Alarm when the pressure deviation of one of the pressure transmitters I, IV, and VI is greater than 3%.

[0119] D7. Alarm when the pressure difference between the inlet and outlet of the steam compressor is equal to 98% of the predetermined set value.

[0120] D8. Alarm when the normal operating frequency of the steam compressor is close to the set minimum frequency + 3 Hz.

[0121] D9. Alarm when the pressure of one of the pressure transmitters III and V is close to 125% of the low point set value or 75% of the high point set value.

[0122] (5)When the Roots steam compressor is operating normally, the shutdown alarm protection interlock control method is as follows: when one of the shutdown alarm protection conditions is met, the alarm indicator light will turn on and a sound alarm will be issued. When the shutdown signal is sent to the DCS, the electric butterfly valve will be opened. After complete pressure relief, the variable-frequency motor and the variable-frequency motor cooling fan will be turned off, all solenoid valves will be closed, and the cooling water will be shut off.

[0123] The shutdown alarm protection conditions when the Roots steam compressor is operating normally include:

[0124] E1. When the pressure of pressure transmitter III is lower than the rated requirement of the first-stage compressor outlet pressure + 20 kPa or higher than the rated requirement of the outlet pressure + 150 kPa, an alarm will be issued and the machine will stop when the upper and lower limits are exceeded;

[0125] E2. When the pressure of pressure transmitter VI is lower than the rated requirement of the second-stage compressor outlet pressure + 20 kPa or higher than the rated requirement of the outlet pressure + 150 kPa, an alarm will be issued and the machine will stop when the upper and lower limits are exceeded;

[0126] E3. When one of the solenoid valves I, II, III, and IV is closed, an alarm will be issued and the machine will stop;

[0127] E4. When the flow rate of one of the rotameters I, II, III, and IV is < 80% of the required flow rate, an alarm will be issued and the machine will stop;

[0128] E5. When the temperature of one of the temperature transmitters I, II, and III exceeds the required temperature by ±2°C, an alarm will be issued and the machine will stop;

[0129] E6. When the main motor current is close to the rated current, an alarm will be issued. When the main motor current > 105% of the rated current or the time higher than the rated current exceeds 1 minute, an alarm will be issued and the machine will stop;

[0130] E7. When the pressure deviation of one of the pressure transmitters I, IV, and VI is greater than 5%, an alarm will be issued and the machine will stop;

[0131] E8. When the forced cooling fan of the double-shaft extension variable-frequency motor fails, an alarm will be issued and the machine will stop;

[0132] E9. When the pressure difference between the inlet and outlet of the steam compressor exceeds the predetermined set value, an alarm will be issued and the machine will stop;

[0133] E10. When the normal operating frequency of the steam compressor is lower than the set minimum frequency, an alarm will be issued and the machine will stop;

[0134] E11. When the pressure of one of the pressure transmitters III and V is lower than or higher than the set value, an alarm will be issued and the machine will stop.

[0135] However, as described above, these are only specific embodiments of the present invention, and the scope of implementation of the present invention cannot be limited thereby. Therefore, the replacement of equivalent components or the equivalent changes and modifications made according to the scope of protection of the present invention patent should still fall within the scope covered by the claims of the present invention.

Claims

1. A two-stage series control method for a two-stage series control Roots steam compressor, comprising the following steps: (1) Commissioning startup control method for the Roots steam compressor: First, conduct inspections before starting the Roots steam compressor, and then check whether the Roots steam compressor meets the startup logic. It can only be started when all requirements are met; otherwise, the alarm light indicator will be on. (2) Startup control method for the Roots steam compressor: The starting frequency of the double-shaft extended variable-frequency motor is 10 Hz, increasing by 10 Hz each time, with an interval of at least 15 seconds. Wait until the current and pressure are stable before increasing the frequency. After the frequency of the double-shaft extended variable-frequency motor reaches the full frequency, slowly close the electric butterfly valve. (3) Normal operation control method for the Roots steam compressor: After about 20 minutes of no abnormality during no-load operation of the Roots steam compressor, connect it to the system for operation. During the operation process, it can only operate normally when all operating condition requirements are met; otherwise, the alarm light indicator will be on. Among them, The operating conditions of the Roots steam compressor include: C1. Solenoid valves I, II, III, and IV are all fully open; C2. The flow rates of rotameters I, II, III, and IV are 80 - 120% of the required flow rate; C3. The electric butterfly valve is closed; C4. The pressure of pressure transmitter III is 50 - 100 kPa higher than the rated requirement of the first-stage compressor outlet pressure; C5. The pressure of pressure transmitter VII is 50 - 100 kPa higher than the rated requirement of the second-stage compressor outlet pressure; C6. The pressures of pressure transmitters I, IV, and VI are 95 - 105% of the required pressure; C7. The temperatures of temperature transmitters I, II, and III are within ±1.5°C of the required temperature; C8. The main motor current ≤ 105% of the rated current and the time exceeding the rated current does not exceed 1 minute; (4) Alarm protection interlock control method during normal operation of the Roots steam compressor: When one alarm protection condition is met, the alarm indicator light will be on and a sound alarm will be issued. Among them, the alarm protection conditions during normal operation of the Roots steam compressor include: D1. Alarm when the pressure of pressure transmitter III is lower than the rated requirement of the first-stage compressor outlet pressure + 35 kPa or higher than the outlet pressure rated requirement + 135 kPa; D2. Alarm when the pressure of pressure transmitter VII is lower than the rated requirement of the second-stage compressor outlet pressure + 35 kPa or higher than the outlet pressure rated requirement + 135 kPa; D3. Alarm when the flow rate of any one of rotameters I, II, III, and IV < 85% of the required flow rate; D4. Alarm when the temperature of any one of temperature transmitters I, II, and III exceeds ±1.5°C of the required temperature; D5. Alarm when the main motor current is greater than 95% of the rated current; D6. Alarm when the pressure deviation of any one of pressure transmitters I, IV, and VI is greater than 3%; D7. Alarm when the pressure difference between the inlet and outlet of the steam compressor is equal to 98% of the predetermined set value; D8. Alarm when the normal operation frequency of the steam compressor is close to the set minimum frequency + 3 Hz; D9. Alarm when the pressure of any one of pressure transmitters III and V is close to 125% of the low point set value or 75% of the high point set value; (5)Roots steam compressor normal operation shutdown alarm protection interlock control method. When one shutdown alarm protection condition is met, the alarm indicator light will turn on and a sound alarm will be issued. When the shutdown signal is transmitted to the DCS, the electric butterfly valve will be opened. After complete pressure relief, the frequency conversion motor and the frequency conversion motor cooling fan will be shut down, all solenoid valves will be closed, and the cooling water will be shut down. The two-stage series control Roots steam compressor used in the two-stage series control method includes a first-stage compressor and a second-stage compressor. A double-shaft extended variable-frequency motor is provided between the first-stage compressor and the second-stage compressor. The two ends of the double-shaft extended variable-frequency motor are respectively connected to the first-stage compressor and the second-stage compressor. The reference state flow rate Q of the first-stage compressor N1 is equal to the reference state flow rate Q of the second-stage compressor N2 and the compression ratio ε1 of the first-stage compressor is approximately equal to ε2 of the second-stage compressor; The Roots steam compressor is also provided with a first-stage compressor inlet end N1, a first-stage compressor seal water inlet end N2, a first-stage compressor mechanical seal coolant pipeline inlet end N3, a first-stage compressor mechanical seal coolant pipeline outlet end N4, a second-stage compressor seal water inlet end N5, a second-stage compressor outlet end N6, a second-stage compressor mechanical seal coolant pipeline inlet end N7, a first-stage compressor mechanical seal coolant pipeline outlet end N8, and a return pipeline N9. A temperature transmitter I and a pressure transmitter I are installed on the first-stage compressor inlet end N1. A seal liquid connection pipe and a bellows compensator I are installed between the first-stage compressor inlet end N1 and the first-stage compressor. A solenoid valve I, a pressure transmitter II, and a rotameter I are installed on the first-stage compressor seal water inlet end N2. A solenoid valve II, a pressure transmitter III, and a rotameter II are installed on the first-stage compressor mechanical seal coolant pipeline inlet end N3. A pressure transmitter VI and a temperature transmitter III are installed on the second-stage compressor outlet end N6. A rotameter IV, a pressure transmitter VII, and a solenoid valve IV are installed on the second-stage compressor mechanical seal coolant pipeline inlet end N7. The return pipeline N9 connects the first-stage compressor seal water inlet end N2 and the second-stage compressor outlet end N6. An electric butterfly valve is installed on the return pipeline N9. The outlet of the first-stage compressor is connected to the inlet of the second-stage compressor through an intermediate connection pipe. A temperature transmitter II and a pressure transmitter IV are installed on the intermediate connection pipe. The intermediate connection pipe is connected to the second-stage compressor seal water inlet end N5. A rotameter III, a pressure transmitter V, and a solenoid valve III are installed on the second-stage compressor seal water inlet end N5.

2. The double-stage series control method of a double-stage series control Roots steam compressor according to claim 1, characterized in that A bellows compensator II is provided between the second-stage compressor and the second-stage compressor outlet end N6.

3. The double-stage series control method of a double-stage series control Roots steam compressor according to claim 1, characterized in that, The inspection content before starting the Roots steam compressor is as follows: A1. Manual turning of the shaft is normal. A2. The oil level in the oil tank is normal. A3. The main motor is jogged and the rotation direction of the fan is correct. A4. The main and auxiliary normal cooling water is turned on. After the above points are all met, proceed to the next step.

4. The double-stage series control method of a double-stage series control Roots steam compressor according to claim 1, characterized in that, The shutdown alarm protection conditions during the normal operation of the Roots steam compressor include: E1. The pressure of the pressure transmitter III is lower than the rated requirement of the first-stage compressor outlet pressure +20 kPa or higher than the rated requirement of the outlet pressure +150 kPa. When exceeding the upper and lower limits, an alarm will be issued and the machine will be shut down. E2. The pressure of the pressure transmitter VI is lower than the rated requirement of the second-stage compressor outlet pressure +20 kPa or higher than the rated requirement of the outlet pressure +150 kPa. When exceeding the upper and lower limits, an alarm will be issued and the machine will be shut down. E3. When any one of the solenoid valves I, II, III, and IV is closed, an alarm will be issued and the machine will be shut down. E4. When the flow rate of any one of the rotameters I, II, III, and IV < 80% of the required flow rate, an alarm will be issued and the machine will be shut down. E5. When the temperature of any one of the temperature transmitters I, II, and III exceeds the required temperature by ±2°C, an alarm is given and the machine stops. E6. When the main motor current is close to the rated current, an alarm is given. When the main motor current > 105% of the rated current or the time above the rated current exceeds 1 minute, an alarm is given and the machine stops. E7. When the pressure deviation of any one of the pressure transmitters I, IV, and VI is greater than 5%, an alarm is given and the machine stops. E8. When the forced cooling fan of the double-shaft extended variable-frequency motor fails, an alarm is given and the machine stops. E9. When the pressure difference between the inlet and outlet of the steam compressor exceeds the preset value, an alarm is given and the machine stops. E10. When the normal operating frequency of the steam compressor is lower than the set minimum frequency, an alarm is given and the machine stops. E11. When the pressure of any one of the pressure transmitters III and V is lower than or higher than the set value, an alarm is given and the machine stops.

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