Double-unit double-stage centrifugal compressor and operation control method

Abstract

The invention discloses a double-unit double-stage centrifugal compressor and an operation control method, and belongs to the technical field of centrifugal compressors. Comprising an evaporator, a low-pressure-stage compressor, a high-pressure-stage compressor, a power saver and a condenser. S2, collecting the cold water outlet temperature and the cooling water outlet temperature after the water pump operates; s3, estimating the running pressure ratio 1t of the unit; according to the design pressure ratio of the low-pressure-stage compressor, the low-pressure-stage compressor is started, the high-pressure-stage compressor is not started, and on the contrary, the high-pressure-stage compressor is started to operate after operation starting feedback of the low-pressure-stage compressor is completed; and S4, in the operation process, if the operation pressure ratio is larger than or equal to the design pressure ratio of the low-pressure-stage compressor, the high-pressure-stage compressor is switched into operation. The mode that the low-pressure-stage compressor and the high-pressure-stage compressor are connected in series is adopted, and by controlling the low-pressure-stage compressor and the high-pressure-stage compressor, stable and efficient working condition operation of the centrifugal compressor is achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of centrifugal compressors, and in particular to a dual-machine dual-stage centrifugal compressor and an operation control method thereof. Background Art

[0002] At present, the country pays more and more attention to energy conservation and emission reduction. Centrifugal compressors have been vigorously promoted and used due to their high cooling / heating capacity, low noise and high energy efficiency.

[0003] With regard to the above-mentioned related technologies, the applicant found that for medium- and high-temperature heat pumps above 65°C and low-temperature ice storage units below -10°C, due to the limitation of compression ratio, conventional single / two-stage centrifugal compressors cannot meet the working conditions. Therefore, how to achieve stable and efficient operation of centrifugal compressors to meet the working conditions has become a difficult problem that needs to be solved urgently. Summary of the invention

[0004] In view of the deficiencies in the prior art, the present invention provides a dual-machine two-stage centrifugal compressor and an operation control method, which adopts a method of connecting a low-pressure stage compressor in series with a high-pressure stage compressor, and realizes stable and efficient operation of the centrifugal compressor to meet working conditions through the control of the compressor.

[0005] The technical solution of the present invention to solve the above technical problems is as follows: A dual-machine two-stage centrifugal compressor comprises an evaporator, a low-pressure stage compressor, a high-pressure stage compressor, a power economizer and a condenser. The low-pressure stage compressor is provided with a low-pressure stage guide vane and a low-pressure stage guide vane actuator, the high-pressure stage compressor is provided with a high-pressure stage guide vane and a high-pressure stage guide vane actuator, and the low-pressure stage compressor is connected in series with the high-pressure stage compressor.

[0006] Furthermore, the high-pressure compressor is connected to a high-pressure air intake electric butterfly valve, a high-pressure motor cooling solenoid valve and a high-pressure oil cooling solenoid valve.

[0007] Furthermore, it includes a control box and a control module, the evaporator is provided with a cold water outlet temperature sensor and an evaporation pressure sensor, the condenser is provided with a cooling water outlet temperature sensor and a condensation pressure sensor, the low-pressure stage compressor is provided with a low-pressure stage exhaust pressure sensor, the high-pressure stage compressor is provided with a high-pressure stage exhaust pressure sensor, and the power economizer is provided with a power saving pressure sensor.

[0008] Furthermore, the power economizer is connected to an air supply electric valve.

[0009] Furthermore, the evaporator is connected to a hot gas bypass valve.

[0010] A dual-machine two-stage centrifugal compressor operation control method comprises the following steps: S1: Startup decision completed; S2: After the water pump is running, the cold water outlet temperature and the cooling water outlet temperature are collected. The control module sets the outlet water target temperature according to the current operation mode and estimates the operating pressure ratio of the unit according to the written calculation logic; S3: When the estimated operating pressure ratio of the unit is less than the design pressure ratio of the low-pressure compressor, the low-pressure compressor starts and the high-pressure compressor does not start. Conversely, after the low-pressure compressor operation start feedback is completed, the high-pressure compressor starts running; S4: During operation, if the operating pressure ratio is ≥ the design pressure ratio of the low-pressure compressor, the high-pressure compressor will be put into operation.

[0011] Further, the following steps are included: S5: Set target temperature: The condition is that the actual outlet water temperature Ta of the fixed frequency unit = the set target temperature; S6: The control system collects the evaporation pressure, the first-stage compression exhaust pressure, and the second-stage exhaust pressure, and the control module calculates the operating pressure ratio of the high-pressure and low-pressure stage compressors; S7: When (high-pressure stage operating pressure ratio - low-pressure stage operating pressure ratio) / low-pressure stage operating pressure ratio < -5%, the guide vane opening of the low-pressure stage compressor is maintained, and the guide vane of the high-pressure stage compressor is opened according to the set control cycle and control pulse; S8: When (high-pressure stage operating pressure ratio - low-pressure stage operating pressure ratio) / low-pressure stage operating pressure ratio>5%, the guide vane opening of the low-pressure stage compressor is maintained, and the guide vane of the high-pressure stage compressor is closed according to the set control cycle and control pulse; S9: When -5%≤(high-pressure stage operating pressure ratio - low-pressure stage operating pressure ratio) / low-pressure stage operating pressure ratio≤5%, the guide vane opening of the high-pressure stage compressor is maintained.

[0012] Further, the following steps are included: S10: Set target temperature: The condition is that the actual outlet water temperature Ta of the inverter unit = the set target temperature; S11: The control system collects evaporation pressure, first-stage compression exhaust pressure, and second-stage exhaust pressure, and the control module calculates the operating pressure ratio of the high-pressure and low-pressure compressors; S12: When (high-pressure stage operating pressure ratio - low-pressure stage operating pressure ratio) / low-pressure stage operating pressure ratio < -5%, the frequency and guide vane opening of the low-pressure stage compressor are maintained, and the guide vanes of the high-pressure stage compressor are opened according to the set control cycle and control pulse; after the guide vanes of the high-pressure stage compressor are opened to 100%, the frequency of the high-pressure stage compressor is increased according to the set control cycle and control pulse; S13: When (high-pressure stage operating pressure ratio - low-pressure stage operating pressure ratio) / low-pressure stage operating pressure ratio>5%, the frequency and guide vane opening of the low-pressure stage compressor are maintained, and the frequency of the high-pressure stage compressor is reduced according to the set control cycle and control pulse; when the frequency of the high-pressure stage compressor reaches the lower limit of the surge point frequency, the guide vane of the high-pressure stage compressor is reduced according to the set control cycle and control pulse; S14: When -5%≤(high-pressure stage operating pressure ratio - low-pressure stage operating pressure ratio) / low-pressure stage operating pressure ratio≤5%, the operating frequency and guide vane opening of the high-pressure stage compressor are maintained.

[0013] Further, the following steps are included: S15: Set target temperature: The condition is satisfied that the actual water outlet temperature Ta = set target temperature; S16: The control system collects the first-stage compression exhaust pressure and the economizer pressure, and the control module calculates the difference between the economizer pressure and the first-stage compression exhaust pressure; S17: When the economizer pressure minus the first-stage compression exhaust pressure < the set lower limit, the air supply electric valve is closed according to the set control cycle and control pulse; S18: When the economizer pressure - the first-stage compression exhaust pressure > the set upper limit, the air supply electric valve opens according to the set control cycle and control pulse; S19: When the set lower limit ≤ economizer pressure - first-stage compression exhaust pressure ≤ the set upper limit, the opening of the air supply electric valve is maintained.

[0014] Further, the following steps are included: S20: Low-pressure and high-pressure compressors operate simultaneously; S21: The following conditions are met at the same time: The actual operating pressure ratio is ≤ the lower limit of the set pressure ratio of the low-pressure compressor; Actual water outlet temperature Ta = set target temperature; The operating load of the low-pressure compressor is ≤80%; S22: The high-pressure compressor is cut off and the low-pressure compressor operates alone; S23: Any one of the following conditions is met: The actual operating pressure ratio is ≥ the upper limit of the set pressure ratio of the low-pressure compressor; The actual outlet water temperature does not reach the set target temperature and the operating load of the low-pressure compressor is ≥90% and lasts for 900s; S24: The high-pressure stage compressor is put into operation.

[0015] In summary, compared with the prior art, the above technical solution has the following beneficial effects: (1) The present invention adopts a method of connecting a low-pressure compressor and a high-pressure compressor in series, and realizes the stable and efficient operation of the centrifugal compressor to meet the working conditions by controlling the low-pressure compressor and the high-pressure compressor; (2) According to theoretical calculations, when the pressure ratio meets the low-pressure operating conditions, the energy efficiency value of only running the low-pressure compressor is 20% to 30% higher than that of running the low-pressure compressors at the same time, and the energy saving effect is obvious; (3) Combining theoretical calculations with actual test results, when the air supply pressure is controlled within a reasonable range, the unit's operating energy efficiency can be improved by 8% compared to the absence of air supply, with significant energy-saving effects. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 A system structure connection diagram in an embodiment of the present invention; Figure 2 is a startup flow chart in an embodiment of the present invention; Figure 3 It is a constant frequency unit operating pressure ratio control diagram in an embodiment of the present invention; Figure 4 It is a control diagram of the operating pressure ratio of the variable frequency unit in the embodiment of the present invention; Figure 5 is a pressure control diagram of a power economizer in an embodiment of the present invention; Figure 6 This is a control diagram for cutting out / adding in the high pressure stage compressor in an embodiment of the present invention.

[0017] Explanation of the reference numerals: 1. Evaporator; 2. Low-pressure compressor; 21. Low-pressure guide vane actuator; 22. Low-pressure guide vane; 3. Condenser; 4. High-pressure compressor; 41. High-pressure guide vane actuator; 42. High-pressure guide vane; 43. High-pressure suction port electric butterfly valve; 44. High-pressure motor cooling solenoid valve; 45. High-pressure oil cooling solenoid valve; 5. Power saver; 51. Air supply electric valve; 6. Hot gas bypass valve; 7. Control box. DETAILED DESCRIPTION

[0018] The principles and features of the present invention are described below in conjunction with all the accompanying drawings. The examples given are only used to explain the present invention and are not used to limit the scope of the present invention.

[0019] The embodiment of the invention discloses a dual-machine two-stage centrifugal compressor.

[0020] Reference Figure 1A dual-machine two-stage centrifugal compressor comprises an evaporator 1, a low-pressure stage compressor 2, a high-pressure stage compressor 4, a power economizer 5 and a condenser 3. The low-pressure stage compressor 2 is provided with a low-pressure stage guide vane 22 and a low-pressure stage guide vane actuator 21, the high-pressure stage compressor 4 is provided with a high-pressure stage guide vane 42 and a high-pressure stage guide vane actuator 41, and the low-pressure stage compressor 2 is connected in series with the high-pressure stage compressor 4.

[0021] The high-pressure compressor 4 is connected to a high-pressure air intake electric butterfly valve 43 , a high-pressure motor cooling solenoid valve 44 and a high-pressure oil cooling solenoid valve 45 .

[0022] It also includes a control box 7 and a control module. The evaporator 1 is provided with a cold water outlet temperature sensor and an evaporation pressure sensor. The condenser 3 is provided with a cooling water outlet temperature sensor and a condensation pressure sensor. The low-pressure stage compressor 2 is provided with a low-pressure stage exhaust pressure sensor. The high-pressure stage compressor 4 is provided with a high-pressure stage exhaust pressure sensor. The power economizer 5 is provided with a power-saving pressure sensor.

[0023] As shown below, T01 represents the cold water outlet temperature, T02 represents the cooling water outlet temperature, P01 represents the evaporation pressure, P02 represents the first-stage compression exhaust pressure, P03 represents the second-stage exhaust pressure, P04 represents the condensation pressure, and P05 represents the economizer 5 pressure.

[0024] Among them, the cold water outlet temperature sensor outputs the value of the cold water outlet temperature T01, the cooling water outlet temperature sensor outputs the value of the cooling water outlet temperature T02, the evaporation pressure sensor outputs the value of the evaporation pressure P01, the low-pressure stage exhaust pressure sensor outputs the value of the first-stage compression exhaust pressure P02, the high-pressure stage exhaust pressure sensor outputs the value of the second-stage exhaust pressure P03, the condensing pressure sensor outputs the value of the condensing pressure P04, and the economizer 5 pressure sensor outputs the value of the economizer 5 pressure P05.

[0025] The energy saver 5 is connected to an air supply electric valve 51. The evaporator 1 is connected to a hot gas bypass valve 6.

[0026] The present invention adopts a method of connecting a low-pressure compressor 2 and a high-pressure compressor 4 in series, and realizes stable and efficient operation of the centrifugal compressor to meet working conditions by controlling the low-pressure compressor 2 and the high-pressure compressor 4.

[0027] Reference Figure 2 , a dual-machine two-stage centrifugal compressor operation control method, comprising the following steps: S1: Startup decision completed; S2: After the water pump is running, the cold water outlet temperature T01 and the cooling water outlet temperature T02 are collected. The control module sets the outlet water target temperature according to the current operation mode and estimates the operating pressure ratio of the unit according to the written calculation logic; S3: the estimated operating pressure ratio of the unit is less than the design pressure ratio of the low-pressure compressor 2, the low-pressure compressor 2 is started, and the high-pressure compressor 4 is not started. On the contrary, after the low-pressure compressor 2 operation start feedback is completed, the high-pressure compressor 4 is started; S4: During operation, if the operating pressure ratio value is ≥ the design pressure ratio of the low-pressure stage compressor 2, the high-pressure stage compressor 4 is switched into operation.

[0028] Reference Figure 3 , S5: Set target temperature: The condition satisfies that the actual outlet water temperature Ta of the fixed frequency unit = the set target temperature; S6: The control system collects the evaporation pressure, the first-stage compression exhaust pressure, and the second-stage exhaust pressure, and the control module calculates the operating pressure ratios of the high-pressure and low-pressure stage compressors respectively; S7: When (high-pressure stage operating pressure ratio - low-pressure stage operating pressure ratio) / low-pressure stage operating pressure ratio < -5%, the guide vane opening of the low-pressure stage compressor 2 is maintained, and the guide vane of the high-pressure stage compressor 4 is opened according to the set control cycle and control pulse; S8: When (high-pressure stage operating pressure ratio - low-pressure stage operating pressure ratio) / low-pressure stage operating pressure ratio>5%, the guide vane opening of the low-pressure stage compressor 2 is maintained, and the guide vane of the high-pressure stage compressor 4 is closed according to the set control cycle and control pulse; S9: When -5%≤(high-pressure stage operating pressure ratio-low-pressure stage operating pressure ratio) / low-pressure stage operating pressure ratio≤5%, the guide vane opening of the high-pressure stage compressor 4 is maintained.

[0029] Reference Figure 4 , S10: Set target temperature: The condition satisfies that the actual outlet water temperature Ta of the inverter unit = the set target temperature; S11: The control system collects evaporation pressure, first-stage compression exhaust pressure, and second-stage exhaust pressure, and the control module calculates the operating pressure ratio of the high-pressure and low-pressure compressors; S12: When (high-pressure stage operating pressure ratio - low-pressure stage operating pressure ratio) / low-pressure stage operating pressure ratio < -5%, the frequency and guide vane opening of the low-pressure stage compressor 2 are maintained, and the guide vanes of the high-pressure stage compressor 4 are opened according to the set control cycle and control pulse; after the guide vanes of the high-pressure stage compressor 4 are opened to 100%, the frequency of the high-pressure stage compressor 4 is increased according to the set control cycle and control pulse; S13: When (high-pressure stage operating pressure ratio - low-pressure stage operating pressure ratio) / low-pressure stage operating pressure ratio>5%, the frequency and guide vane opening of the low-pressure stage compressor 2 are maintained, and the frequency of the high-pressure stage compressor 4 is reduced according to the set control cycle and control pulse; when the frequency of the high-pressure stage compressor 4 reaches the lower limit of the surge point frequency, the guide vane of the high-pressure stage compressor 4 is reduced according to the set control cycle and control pulse; S14: When -5%≤(high-pressure stage operating pressure ratio-low-pressure stage operating pressure ratio) / low-pressure stage operating pressure ratio≤5%, the operating frequency and guide vane opening of the high-pressure stage compressor 4 are maintained.

[0030] Reference Figure 5 , S15: Set target temperature: the condition is satisfied that the actual water outlet temperature Ta = set target temperature; S16: The control system collects the first-stage compression exhaust pressure and the pressure of the power economizer 5, and the control module calculates the difference between the pressure of the power economizer 5 and the first-stage compression exhaust pressure; S17: When the pressure of the economizer 5 minus the first-stage compression exhaust pressure < the set lower limit, the air supply electric valve 51 is closed according to the set control cycle and control pulse; S18: When the pressure of the economizer 5 minus the first-stage compression exhaust pressure>the set upper limit, the air supply electric valve 51 is opened according to the set control cycle and control pulse; S19: When the set lower limit (for example, 10 KPa) ≤ the pressure of the economizer 5 - the first-stage compression exhaust pressure ≤ the set upper limit (for example, 30 KPa), the opening of the air supply electric valve 51 is maintained.

[0031] Reference Figure 6 , S20: the low-pressure stage and high-pressure stage compressors 4 operate simultaneously; S21: The following conditions are met at the same time: The actual operating pressure ratio is ≤ the lower limit of the set pressure ratio of the low-pressure compressor 2; Actual water outlet temperature Ta = set target temperature; The operating load of low-pressure compressor 2 is ≤80%; S22: The high-pressure compressor 4 is cut off, and the low-pressure compressor 2 operates alone; S23: Any one of the following conditions is met: The actual operating pressure ratio is ≥ the set pressure ratio upper limit of low-pressure compressor 2; The actual outlet water temperature does not reach the set target temperature and the operating load of the low-pressure compressor 2 is ≥90% and lasts for 900s; S24: The high-pressure stage compressor 4 is put into operation.

[0032] A dual-machine two-stage centrifugal compressor operation control method. After the startup decision is completed, the control box 7 collects the cold water outlet temperature T01 and the cooling water outlet temperature T02, and combines the target outlet temperature setting value of the current unit and the design operating conditions when running at full load. The control module estimates the operating pressure ratio of the unit according to the written calculation logic according to the current operating mode. If the estimated operating pressure ratio is less than the design pressure ratio of the low-pressure stage compressor 2, the low-pressure stage compressor 2 starts to run, and the high-pressure stage compressor 4 does not run. The control process is detailed in Figure 2 .

[0033] If the estimated pressure ratio is ≥ the designed pressure ratio of the low-pressure stage compressor 2, after the low-pressure stage compressor 2 operation start-up feedback is completed, the high-pressure stage compressor 4 starts to operate.

[0034] Before startup, the system's operating pressure ratio estimation process is as follows: For an ice storage unit with a target chilled water outlet temperature of -10°C, assume that the design pressure ratio of the low-pressure compressor 2 is 3.0, the design cooling water temperature difference of the unit is 5°C, the design approach temperature difference of the evaporator 1 and the condenser 3 is 1.5°C, and the cooling water temperature before startup is 10°C; Estimated evaporation temperature Te = -10℃-1.5℃ = -11.5℃, check the R134a refrigerant physical parameter table P01 = 76KPa; Estimated condensing temperature Tc = 10℃ + 5℃ + 1.5℃ = 16.5℃, check the R134a refrigerant physical parameter table P03 = 412KPa; It is estimated that the pressure ratio during full load operation = (P03+101) / (P01+101) = 2.9 ≤ the set pressure ratio upper limit 3.0, the low-pressure stage compressor 2 starts running, and the high-pressure stage compressor 4 does not run.

[0035] During the soft loading stage, the control box 7 will collect the evaporation pressure P01, the first-stage compression exhaust pressure P02, and the second-stage exhaust pressure P03, and calculate the operating pressure ratio of the low-pressure stage compressor 2 = (P02+101) / (P01+101) and the operating pressure ratio of the high-pressure stage compressor 4 = (P03+101) / (P02+101) through the internal algorithm. The above calculated values ​​are compared and fitted with the anti-surge curve designed for the compressor, and the opening of the low-pressure stage guide vane 22 and the motor operating frequency, and the opening of the high-pressure stage guide vane 42 and the motor operating frequency are controlled above the surge point to ensure stable operation of the compressor.

[0036] On this basis, the control box 7 compares the target outlet water temperature with the actual outlet water temperature fed back, and controls the opening rate of the guide vanes and the motor frequency according to the PID settings to load.

[0037] After the soft loading is completed (actual water outlet temperature = target temperature), the unit enters the stable operation stage. Taking into account the unit's operating energy efficiency and energy regulation range, when selecting the compressor, the design pressure ratio of the high-pressure stage / low-pressure stage compressor 2 is basically the same; the flow rate of the compressor is selected according to the exhaust volume of the low-pressure stage compressor 2 + the air supply volume of the energy saver 5 = the suction volume of the high-pressure stage compressor 4.

[0038] Therefore, during the actual operation of the unit, ensuring the balance of the operating pressure ratio of the high / low pressure compressors is the key to ensuring the efficient operation of the unit. In order to solve the problem of uneven distribution of operating pressure ratios that may occur under partial load and non-design conditions, at this stage, the data acquisition module collects the evaporation pressure P01, the first-stage compression exhaust pressure P02, and the second-stage exhaust pressure P03. The control module calculates and writes the operating pressure ratio of the high-pressure compressor 4 and the operating pressure ratio of the low-pressure compressor 2, and then calculates the imbalance rate of the operating pressure ratio of the high / low pressure compressors. When the imbalance rate is greater than the set upper limit, the high-pressure compressor 4 is unloaded; when the imbalance rate is less than the set lower limit, the high-pressure compressor 4 is loaded, and when the set lower limit ≤ imbalance rate ≤ set upper limit, the operating load of the high-pressure compressor 4 is maintained.

[0039] in: Low-pressure compressor 2 operating pressure ratio = (P02+101) / (P01+101) High pressure compressor 4 operating pressure ratio = (P03 + 101) / (P02 + 101) High / low pressure stage compressor operating pressure ratio imbalance rate = (high pressure stage compressor 4 operating pressure ratio - low pressure stage compressor 2 operating pressure ratio) / high pressure stage compressor 4 operating pressure ratio * 100%.

[0040] Combined with actual test experience, when the operating pressure ratio imbalance of the high / low pressure stage compressor 2 is within the range of ±5%, the operating energy efficiency of the unit is not much different. For fixed frequency units, when (high pressure stage operating pressure ratio - low pressure stage operating pressure ratio) / high pressure stage operating pressure ratio < -5%, the opening of the low pressure stage guide vane 22 is maintained, and the high pressure stage guide vane 42 is opened according to the set control cycle and control pulse; when (high pressure stage operating pressure ratio - low pressure stage operating pressure ratio) / high pressure stage operating pressure ratio > 5%, the opening of the low pressure stage guide vane 22 is maintained, and the high pressure stage guide vane 42 is closed according to the set control cycle and control pulse; when -5% ≤ (high pressure stage operating pressure ratio - low pressure stage operating pressure ratio) / high pressure stage operating pressure ratio ≤ 5%, the opening of the high pressure stage guide vane 42 is maintained. For details of the control process, see Figure 3 .

[0041] For the variable frequency unit, when (high pressure stage operating pressure ratio - low pressure stage operating pressure ratio) / high pressure stage operating pressure ratio < -5%, the opening of the low pressure stage guide vane 22 and the compressor frequency are maintained, and the high pressure stage guide vane 42 is opened according to the set control cycle and control pulse. After the high pressure stage guide vane 42 is opened to 100%, the frequency of the high pressure stage compressor 4 is increased according to the set control cycle and control pulse; when (high pressure stage operating pressure ratio - low pressure stage operating pressure ratio) / high pressure stage operating pressure ratio > 5%, the opening of the low pressure stage guide vane 22 and the compressor frequency are maintained, and the frequency of the high pressure stage compressor 4 is reduced according to the set control cycle and control pulse. When the frequency of the high pressure stage compressor 4 reaches the lower limit of the surge point frequency, the high pressure stage guide vane 42 is closed according to the set control cycle and control pulse; when -5% ≤ (high pressure stage operating pressure ratio - low pressure stage operating pressure ratio) / high pressure stage operating pressure ratio ≤ 5%, the high pressure stage guide vane 42 and the frequency of the compressor are maintained. For details of the control process, please refer to the attached Figure 4 .

[0042] After the soft loading is completed (actual water outlet temperature = target temperature), the unit enters the stable operation stage. To ensure the improvement effect of the intermediate air supply process on the energy efficiency of the dual-machine two-stage unit, the air supply pressure needs to be controlled. The control process is as follows: the data acquisition module collects the economizer 5 pressure P05 and the first-stage compression exhaust pressure P02. The program calculates the difference between the economizer 5 pressure P05 and the first-stage compression exhaust pressure P02.

[0043] When P05-P02<set lower limit, the air supply electric valve 51 is closed according to the set control cycle and control pulse; when P05-P02>set upper limit, the air supply electric valve 51 is opened according to the set control cycle and control pulse; when the set lower limit ≤ P05-P02 ≤ the set upper limit, the opening of the air supply electric valve 51 is maintained. Combined with theoretical calculations and actual test results, when the air supply pressure is controlled within a reasonable range, the unit's operating energy efficiency can be improved by 8% compared to the process without air supply, and the energy saving effect is obvious. Combined with theoretical calculations and actual test experience, when 10KPa≤P05-P02≤30KPa, the unit's operating energy efficiency is the highest. For details of the control process, see Figure 5 .

[0044] When the temperature of cooling water is relatively low or the temperature of heat source water is relatively high, the system operating pressure ratio will be relatively low during the stable operation stage of the unit. When (P04+101) / (P01+101)≤the lower limit of the set pressure ratio of the low-pressure compressor 2, and the following conditions 1 and 2 are met at the same time, the high-pressure compressor 4 will be cut off from operation after a delay of 300s, thereby improving the operating energy efficiency of the unit and achieving energy-saving effects.

[0045] Condition 1: The outlet temperature of ice water / hot water must reach the preset target value; Condition 2: The operating load of low-pressure compressor 2 must be lower than 80%. This condition is mainly to avoid the problem that after the high-pressure compressor 4 is cut off, the working capacity of low-pressure compressor 2 cannot meet the customer's load requirements, resulting in frequent cutting and adding of high-pressure compressor 4. Figure 6 .

[0046] The high-pressure compressor 4 is removed from operation as follows: the hot gas bypass valve 6 is opened, the evaporator 1 and the condenser 3 are connected, and the actual operating pressure ratio of the unit is further reduced. After the hot gas bypass valve 6 is fully opened, the low-pressure compressor 2 and the high-pressure compressor 4 are simultaneously unloaded. After the high-pressure guide vane 42 is unloaded to the dynamic surge limit, the high-pressure compressor 4 is removed from operation. Thereafter, the high-pressure suction port electric butterfly valve 43, the high-pressure oil cooling solenoid valve 45, and the high-pressure motor cooling solenoid valve 44 are all closed to isolate the high-pressure compressor 4 from the system.

[0047] After the high-pressure stage compressor 4 is isolated, the hot gas bypass valve 6 is closed, and the low-pressure stage compressor 2 is loaded according to the control logic of the soft loading stage until it runs stably.

[0048] When the low-pressure stage compressor 2 operates alone, if one of the following conditions is met, the high-pressure stage compressor 4 needs to be put into operation to ensure safe operation of the system.

[0049] Condition 1: The actual operating pressure of the unit is ≥ the set pressure ratio upper limit of the low-pressure compressor 2, which lasts for 5s; Condition 2: The outlet water temperature of ice water / hot water does not reach the preset target value, and the operating load of low-pressure stage compressor 2 is higher than 90% for 900 seconds.

[0050] When the control box 7 determines that the above conditions are met, the high pressure compressor 4 enters the control program for operation. The control process is detailed in Figure 6 .

[0051] The high pressure compressor 4 is put into operation as follows: Control the operation of the oil pump of the high-pressure stage compressor 4 and the high-pressure stage guide vane 42; the high-pressure stage suction port electric butterfly valve 43 and the hot gas bypass valve 6 are all opened. After the hot gas bypass valve 6 is opened, the actual operating pressure of the unit is further reduced. After the low-pressure stage compressor 2 is unloaded to near the dynamic surge limit, the high-pressure stage compressor 4 is put into operation, and the high-pressure stage oil cooling solenoid valve 45 and the high-pressure stage motor cooling solenoid valve 44 are opened to cool the refrigeration oil and the motor of the high-pressure stage compressor 4.

[0052] After the high-pressure compressor 4 is added, the hot gas bypass valve 6 is closed, and the low-pressure compressor 2 and the high-pressure compressor 4 are loaded and operated according to the control program of the second stage.

[0053] The above control logic is based on the premise that safety and alarm control are not triggered. If safety and alarm control are triggered, the compressor will execute according to the corresponding protective control logic; if the guide vane opening calculated by the above control logic conflicts with the dynamic surge limit of the compressor, the dynamic surge limit control will take precedence.

[0054] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A dual-machine, dual-stage centrifugal compressor, characterized in that: The invention comprises an evaporator (1), a low-pressure compressor (2), a high-pressure compressor (4), a power economizer (5) and a condenser (3); the low-pressure compressor (2) is provided with a low-pressure guide vane (22) and a low-pressure guide vane actuator (21); the high-pressure compressor (4) is provided with a high-pressure guide vane (42) and a high-pressure guide vane actuator (41); the low-pressure compressor (2) and the high-pressure compressor (4) are connected in series.

2. A dual-machine, dual-stage centrifugal compressor according to claim 1, characterized in that: The high-pressure compressor (4) is connected to a high-pressure air intake electric butterfly valve (43), a high-pressure motor cooling solenoid valve (44) and a high-pressure oil cooling solenoid valve (45).

3. A dual-machine, dual-stage centrifugal compressor according to claim 1, characterized in that: It comprises a control box (7) and a control module, wherein the evaporator (1) is provided with a cold water outlet temperature sensor and an evaporation pressure sensor, the condenser (3) is provided with a cooling water outlet temperature sensor and a condensation pressure sensor, the low-pressure compressor (2) is provided with a low-pressure exhaust pressure sensor, the high-pressure compressor (4) is provided with a high-pressure exhaust pressure sensor, and the power saver (5) is provided with a power saving pressure sensor.

4. A dual-machine, dual-stage centrifugal compressor according to claim 1, characterized in that: The energy saver (5) is connected to an air supply electric valve (51).

5. The dual-machine, dual-stage centrifugal compressor according to claim 1, characterized in that: The evaporator (1) is connected to a hot gas bypass valve (6).

6. A dual-machine two-stage centrifugal compressor operation control method according to any one of claims 1 to 5, characterized in that: The steps include: S1: Startup decision completed; S2: After the water pump is running, the cold water outlet temperature and the cooling water outlet temperature are collected. The control module sets the outlet water target temperature according to the current operation mode and estimates the operating pressure ratio of the unit according to the written calculation logic; S3: If the estimated operating pressure ratio of the unit is less than the design pressure ratio of the low-pressure compressor (2), the low-pressure compressor (2) is started and the high-pressure compressor (4) is not started. On the contrary, after the low-pressure compressor (2) operation start feedback is completed, the high-pressure compressor (4) is started; S4: During operation, if the operating pressure ratio value is ≥ the design pressure ratio of the low-pressure stage compressor (2), the high-pressure stage compressor (4) is switched into operation.

7. The operation control method of a dual-machine two-stage centrifugal compressor according to claim 6, characterized in that: The steps include: S5: Set target temperature: The condition is that the actual outlet water temperature Ta of the fixed frequency unit = the set target temperature; S6: The control system collects the evaporation pressure, the first-stage compression exhaust pressure, and the second-stage exhaust pressure, and the control module calculates the operating pressure ratios of the high-pressure and low-pressure compressors respectively; S7: When (high-pressure stage operating pressure ratio - low-pressure stage operating pressure ratio) / low-pressure stage operating pressure ratio < -5%, the guide vane opening of the low-pressure stage compressor (2) is maintained, and the guide vane of the high-pressure stage compressor (4) is opened according to the set control cycle and control pulse; S8: When (high-pressure stage operating pressure ratio - low-pressure stage operating pressure ratio) / low-pressure stage operating pressure ratio>5%, the guide vane opening of the low-pressure stage compressor (2) is maintained, and the guide vane of the high-pressure stage compressor (4) is closed according to the set control cycle and control pulse; S9: When -5% ≤ (high pressure stage operating pressure ratio - low pressure stage operating pressure ratio) / low pressure stage operating pressure ratio ≤ 5%, the guide vane opening of the high pressure stage compressor (4) is maintained.

8. The operation control method of a dual-machine two-stage centrifugal compressor according to claim 7, characterized in that: The steps include: S10: Set target temperature: The condition is that the actual outlet water temperature Ta of the inverter unit = the set target temperature; S11: The control system collects evaporation pressure, first-stage compression exhaust pressure, and second-stage exhaust pressure, and the control module calculates the operating pressure ratio of the high-pressure and low-pressure compressors; S12: When (high-pressure stage operating pressure ratio - low-pressure stage operating pressure ratio) / low-pressure stage operating pressure ratio < -5%, the frequency and guide vane opening of the low-pressure stage compressor (2) are maintained, and the guide vanes of the high-pressure stage compressor (4) are opened according to the set control cycle and control pulse; after the guide vanes of the high-pressure stage compressor (4) are opened to 100%, the frequency of the high-pressure stage compressor (4) is increased according to the set control cycle and control pulse; S13: When (high-pressure stage operating pressure ratio - low-pressure stage operating pressure ratio) / low-pressure stage operating pressure ratio>5%, the frequency and guide vane opening of the low-pressure stage compressor (2) are maintained, and the frequency of the high-pressure stage compressor (4) is reduced according to the set control cycle and control pulse; when the frequency of the high-pressure stage compressor (4) reaches the lower limit of the surge point frequency, the guide vane of the high-pressure stage compressor (4) is reduced according to the set control cycle and control pulse; S14: When -5%≤(high pressure stage operating pressure ratio - low pressure stage operating pressure ratio) / low pressure stage operating pressure ratio≤5%, the operating frequency and guide vane opening of the high pressure stage compressor (4) are maintained.

9. The operation control method of a dual-machine two-stage centrifugal compressor according to claim 8, characterized in that: The steps include: S15: Set target temperature: The condition is satisfied that the actual water outlet temperature Ta = set target temperature; S16: The control system collects the first-stage compression exhaust pressure and the pressure of the power economizer (5), and the control module calculates the difference between the pressure of the power economizer (5) and the first-stage compression exhaust pressure; S17: When the pressure of the energy saver (5) minus the first stage compression exhaust pressure is less than the set lower limit, the air supply electric valve (51) is closed according to the set control cycle and control pulse; S18: When the pressure of the power economizer (5) minus the first stage compression exhaust pressure>the set upper limit, the air supply electric valve (51) is opened according to the set control cycle and control pulse; S19: When the set lower limit ≤ the pressure of the economizer (5) - the first stage compression exhaust pressure ≤ the set upper limit, the opening of the air supply electric valve (51) is maintained.

10. The operation control method of a dual-machine two-stage centrifugal compressor according to claim 9, characterized in that: The steps include: S20: the low-pressure compressor (2) and the high-pressure compressor (4) operate simultaneously; S21: The following conditions are met at the same time: The actual operating pressure ratio is ≤ the lower limit of the set pressure ratio of the low-pressure compressor (2); Actual water outlet temperature Ta = set target temperature; The operating load of the low-pressure compressor (2) is ≤80%; S22: The high-pressure compressor (4) is cut off, and the low-pressure compressor (2) operates alone; S23: Any one of the following conditions is met: The actual operating pressure ratio is ≥ the set pressure ratio upper limit of the low-pressure compressor (2); The actual outlet water temperature does not reach the set target temperature and the operating load of the low-pressure compressor (2) is ≥90% and lasts for 900 seconds; S24: The high-pressure compressor (4) is put into operation.

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