A composite vacuum pump device suitable for a gas-steam combined cycle unit and a method for operating the same

Abstract

The present application relates to power generation equipment and heat cycle field, disclose a kind of composite vacuum pump device and its operating method suitable for gas-steam combined cycle unit, wherein, composite vacuum pump device, including unit condenser, further comprising suction line, Roots vacuum pump and vacuum water ring pump;Suction line one end is connected with the suction port of unit condenser, the other end is connected with the gas inlet of Roots vacuum pump, the exhaust port of Roots vacuum pump is connected with the gas inlet of vacuum water ring pump by interstage pipe line, the exhaust port of vacuum water ring pump is communicated with exhaust pipe line;Interstage pipe line is sequentially provided with outlet valve and check valve along gas flow direction;Two shafts are provided in the pump cavity of Roots vacuum pump, and rotor is mounted on each shaft, and two rotors are synchronously counter-rotated in the pump cavity when Roots vacuum pump operates;The present application has good adaptability, ensures production efficiency and new advantages of safety by taking Roots vacuum pump as main pump and vacuum water ring pump as pre-pump.

Description

Technical Field

[0001] This invention relates to a composite vacuum pump device and its operation method suitable for gas-steam combined cycle units, belonging to the technical field of power generation equipment and thermal cycles. Background Technology

[0002] In the thermal cycle of a thermal power plant, steam performs work in the turbine and then enters the condenser to cool into water, generating a large amount of non-condensable gases. If these gases are not discharged in time, the pressure inside the condenser will increase, thus reducing the efficiency of the turbine. The main task of the vacuum pump is to maintain a vacuum state by extracting gases from the condenser, thereby ensuring the normal operation of the power plant's thermal cycle. The vacuum pump is an indispensable key piece of equipment in the normal operation of a thermal power plant, and the condenser is a crucial component of the power plant's thermal cycle; its vacuum level directly affects the plant's efficiency. Therefore, the performance and reliability of the vacuum pump are of great significance for the safe and stable operation of the power plant.

[0003] With the widespread grid connection of new energy sources, gas-steam combined cycle units mostly undertake peak shaving tasks for the power grid, resulting in frequent start-ups and shutdowns. Their operation is mainly divided into two modes: single-cycle operation and combined-cycle operation. In single-cycle operation, the turbine does not participate in power generation, and the condenser vacuum only needs to be maintained at around 20 kPa. When entering combined-cycle operation, the turbine participates in power generation, requiring an extremely high condenser vacuum to increase turbine output.

[0004] Currently, gas-fired power plants typically install two high-power electric vacuum water ring pumps. For example, Chinese patent application CN201520123456.7 discloses a power plant in China with a total installed capacity of 2×300MW. The 300MW unit's circulating water system uses an open / closed circulation system, with each unit equipped with two vacuum water ring pumps, generally operating in a one-on-one standby mode. While electric vacuum water ring pumps are corrosion-resistant and suitable for pumping gases containing water vapor, their pumping efficiency in the high vacuum range is extremely low, resulting in huge power consumption and making them unsuitable for combined cycle operation. Replacing the electric vacuum water ring pumps with Roots vacuum pumps, however, is problematic because Roots vacuum pumps have poor pumping efficiency in the low vacuum range, making it difficult to maintain the condenser vacuum level during single-cycle operation. Summary of the Invention

[0005] To address the aforementioned problems in the existing technology, this invention provides a composite vacuum pump device and its operation method suitable for gas-steam combined cycle units.

[0006] The technical solution of the present invention is as follows: In a first aspect, the present invention provides a composite vacuum pump device suitable for a gas-steam combined cycle unit, including a unit condenser, and also including a pumping pipeline, a Roots vacuum pump and a vacuum water ring pump. One end of the extraction pipeline is connected to the extraction port of the unit condenser, and the other end of the extraction pipeline is connected to the inlet of the Roots vacuum pump. The exhaust port of the Roots vacuum pump is connected to the inlet of the vacuum water ring pump through the interstage pipeline. The exhaust port of the vacuum water ring pump is connected to the exhaust pipeline. An outlet valve and a check valve are sequentially installed along the gas flow direction on the interstage pipeline; The Roots vacuum pump has two parallel rotating shafts inside the pump chamber, and each shaft is equipped with a rotor with an 8-shaped structure. When the Roots vacuum pump is running, the two rotors rotate synchronously in opposite directions inside the pump chamber.

[0007] Furthermore, the impeller of the vacuum water ring pump is eccentrically mounted inside the pump chamber of the vacuum water ring pump.

[0008] Furthermore, each rotor is coated with a polytetrafluoroethylene anti-corrosion and wear-resistant coating on its outer surface, and each rotor has a cooling cavity inside, which is filled with a phase change heat-absorbing material.

[0009] Furthermore, the Roots vacuum pump is also equipped with bearing seats that are matched one-to-one with the two rotating shafts. Both rotating shafts are connected to the corresponding side bearing seats. Thermal expansion displacement sensors are installed on both sides of the bearing seats. Piezoelectric ceramic fine-tuning push rods are connected to the bottom of both sides of the bearing seats. The thermal expansion displacement sensors and the piezoelectric ceramic fine-tuning push rods are electrically connected by a PLC control circuit.

[0010] Furthermore, the composite vacuum pump device also includes a bypass extraction pipeline, one end of which is connected to the extraction pipeline, and the other end of which is connected to the interstage pipeline between the outlet valve and the check valve. A pneumatic bypass valve is provided on the bypass extraction pipeline.

[0011] Furthermore, an inlet pressure sensor is installed at the inlet of the Roots vacuum pump, and an interstage pressure sensor is installed at the inlet of the vacuum water ring pump. The composite vacuum pump device also includes a PLC control module, which is electrically connected to the Roots vacuum pump, the vacuum water ring pump, the outlet valve, the pneumatic bypass valve, the inlet pressure sensor, and the interstage pressure sensor.

[0012] Secondly, the present invention provides an operating method for the aforementioned composite vacuum pump device applicable to gas-steam combined cycle units, comprising the following steps: Single-cycle operation steps: During the unit startup preparation stage, when the unit condenser needs to establish a vacuum, start the vacuum water ring pump to perform preliminary vacuuming of the unit condenser. Combined cycle operation procedure: When the unit needs to increase the condenser vacuum to improve unit efficiency, shut down the vacuum water ring pump and start the Roots vacuum pump to continuously evacuate the unit condenser.

[0013] Furthermore, in the single-cycle operation step: the PLC control module opens the pneumatic bypass valve, closes the outlet valve, and starts the vacuum water ring pump.

[0014] Furthermore, in the combined cycle operation step: the PLC control module monitors the value of the bypass pressure sensor in real time. When the monitored value reaches the set threshold, the PLC control module opens the outlet valve, closes the pneumatic bypass valve and the vacuum water ring pump, and starts the Roots vacuum pump.

[0015] Furthermore, the aforementioned operating method also includes a variable operating condition adjustment step: When the unit condenser needs to switch from combined cycle operation to single cycle operation, the PLC control module monitors the intake pressure sensor value in real time. When the monitored value reaches the set threshold, the PLC control module opens the pneumatic bypass valve, closes the outlet valve and the Roots vacuum pump, and starts the vacuum water ring pump.

[0016] The present invention has the following beneficial effects: This invention uses a Roots vacuum pump as the main pump and a vacuum water ring pump as a pre-pump. Before unit startup, when the condenser is established, the vacuum water ring pump is started to initially evacuate the condenser. At this stage, the Roots vacuum pump only acts as a conduit. Once the required vacuum level is reached inside the condenser, the water ring pump is stopped, and the Roots vacuum pump is started. The Roots vacuum pump uses two figure-eight rotors rotating synchronously in opposite directions within the pump chamber to create a volume difference, thus continuously extracting non-condensable gases from the condenser. In this case, the vacuum water ring pump only acts as a conduit. Through this setup, this invention retains the high pumping speed characteristic of the Roots vacuum pump in the high vacuum range while compensating for its insufficient pumping efficiency in the low vacuum range by incorporating a vacuum water ring pump. This allows it to adapt to the variable operating conditions of frequent switching between single-cycle and combined-cycle operation. Compared to existing technologies, it offers advantages such as better adaptability, ensured production efficiency, and enhanced safety. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the structure of Embodiment 1 of the present invention; Figure 2 This is a schematic diagram of the first internal structure of the Roots vacuum pump in Embodiment 2 of the present invention; Figure 3 This is a schematic diagram of the second internal structure of the Roots vacuum pump in Embodiment 2 of the present invention; Figure 4 This is a schematic diagram of the structure of Embodiment 3 of the present invention; Figure 5 This is a schematic diagram of module connections according to Embodiment 3 of the present invention.

[0018] The reference numerals in the figure are as follows: 1. Unit condenser; 2. Extraction line; 3. Roots vacuum pump; 4. Vacuum water ring pump; 5. Interstage line; 6. Exhaust line; 7. Outlet valve; 8. Check valve; 9. Shaft; 10. Rotor; 11. Impeller; 12. Cooling cavity; 13. Phase change heat absorption material; 14. Bearing housing; 15. Thermal expansion displacement sensor; 16. Piezoelectric ceramic fine-tuning push rod; 17. Bypass extraction line; 18. Pneumatic bypass valve; 19. Inlet pressure sensor; 20. Interstage pressure sensor; 21. PLC control module. Detailed Implementation

[0019] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0020] Example 1: Please refer to Figure 1 In a first aspect, this embodiment provides a composite vacuum pump device suitable for a gas-steam combined cycle unit, including a unit condenser 1, and further including an extraction pipeline 2, a Roots vacuum pump 3, and a vacuum water ring pump 4; wherein, the Roots vacuum pump 3 serves as the main pump, and the vacuum water ring pump 4 serves as the pre-pump; one end of the extraction pipeline 2 is connected to the extraction port of the unit condenser 1, and the other end of the extraction pipeline 2 is connected to the inlet of the Roots vacuum pump 3, so that non-condensable gas in the unit condenser 1 can enter the Roots vacuum pump 3 through the extraction pipeline 2; the exhaust port of the Roots vacuum pump 3 is connected to the inlet of the vacuum water ring pump 4 through an interstage pipeline 5, and the exhaust port of the vacuum water ring pump 4 is connected to an exhaust pipeline 6, so that non-condensable gas entering the Roots vacuum pump 3 can enter the vacuum water ring pump 4 through the interstage pipeline 5 and be discharged to the outside through the exhaust pipeline 6; An outlet valve 7 and a check valve 8 are sequentially installed along the gas flow direction on the interstage pipeline 5. The outlet valve 7 is used to control the opening and closing state of the interstage pipeline 5, and the check valve 8 is used to prevent the backflow of working fluid in the vacuum water ring pump 4 after the unit is shut down. Two parallel rotating shafts 9 are installed in the pump chamber of the Roots vacuum pump 3. Each rotating shaft 9 is equipped with a rotor 10 with an 8-shaped structure. When the Roots vacuum pump 3 is running, the two rotors 10 rotate synchronously in opposite directions in the pump chamber to form a volume difference, thereby enabling the extraction of non-condensable gas in the unit condenser 1. The impeller 11 of the vacuum water ring pump 4 is eccentrically installed in the pump chamber of the vacuum water ring pump 4. When the vacuum water ring pump 4 is running, the rotation of the impeller 11 drives the internal working fluid to form a water ring that adheres to the inner wall of the pump chamber under the action of centrifugal force, so as to realize the intake, compression and discharge of non-condensable gas.

[0021] With the aforementioned setup, this embodiment uses the Roots vacuum pump 3 as the main pump and the vacuum water ring pump 4 as the pre-pump. Before unit startup, when the condenser 1 is established under vacuum, the vacuum water ring pump 4 is started to initially evacuate the condenser. At this time, the Roots vacuum pump 3 only serves as a conduit. Once the required vacuum level is reached inside the condenser, the water ring pump is stopped, and the Roots vacuum pump 3 is started. The Roots vacuum pump 3 uses two rotors 10 that rotate synchronously in opposite directions within the pump chamber to create a volume difference, thereby continuously extracting non-condensable gases from the condenser 1. In this case, the vacuum water ring pump 4 only serves as a conduit. This approach retains the high pumping speed characteristic of the Roots vacuum pump 3 in the high vacuum range while compensating for its insufficient pumping efficiency in the low vacuum range by using the vacuum water ring pump 4. This allows the system to adapt to the variable operating conditions of frequent switching between single-cycle and combined-cycle operation.

[0022] Secondly, this embodiment provides an operating method for a composite vacuum pump device applicable to a gas-steam combined cycle unit, comprising the following steps: Single-cycle operation steps: During the unit start-up preparation stage, when the unit condenser 1 needs to establish a vacuum, the vacuum water ring pump 4 is started. The vacuum water ring pump 4 performs preliminary vacuuming of the unit condenser 1. The non-condensable gas in the unit condenser 1 is discharged to the outside through the extraction pipeline 2, the Roots vacuum pump 3, the interstage pipeline 5, the vacuum water ring pump 4, and the exhaust pipeline 6 in sequence. Combined cycle operation steps: When the unit needs to increase the vacuum of the condenser 1 to improve the unit efficiency, after the required vacuum level is reached inside the condenser, the vacuum water ring pump 4 is turned off and the Roots vacuum pump 3 is started to continuously evacuate the condenser 1. The non-condensable gas in the condenser 1 is discharged to the outside through the extraction pipeline 2, the Roots vacuum pump 3, the interstage pipeline 5, the vacuum water ring pump 4 and the exhaust pipeline 6 in sequence.

[0023] As the core executing component of this invention, the Roots vacuum pump 3 needs to withstand frequent start-stop cycles and the suction of humid gases. Traditional rotors 10 are mostly made of cast iron, which is prone to rusting and easily jams due to frictional heat generated at high speeds. Therefore, based on Embodiment 1, Embodiment 2 is proposed.

[0024] Example 2: Please refer to Figure 2 and Figure 3This embodiment provides a composite vacuum pump device suitable for gas-steam combined cycle units, including all the structures in Embodiment 1. Furthermore, the outer surface of each rotor 10 is coated with a polytetrafluoroethylene (PTFE) anti-corrosion and wear-resistant coating. This PTFE coating not only isolates the rotor 10 from water vapor corrosion, but its extremely low coefficient of friction also prevents the rotor 10 from seizing up during slight friction. Simultaneously, each rotor 10 has a cooling cavity 12 inside. In this embodiment, the cooling cavities 12 are located at both ends of the rotor 10, arranged in a circular array around the centerline of the rotor 10 ends. The number of cooling cavities 12 at each rotor 10 end should not exceed five, preferably three. Each cooling cavity 12 is filled with a phase change heat-absorbing material 13. As described above, the cooling cavity 12 provides the necessary sealed installation space for the phase change heat-absorbing material 13 while ensuring the structural strength and operational stability of the rotor 10. When the Roots vacuum pump 3 frequently starts and stops, causing an excessively high instantaneous temperature rise within the pump chamber, the phase change heat-absorbing material 13 can melt and absorb a large amount of latent heat, thereby maintaining a constant temperature for the rotor 10 and preventing the rotor 10 from expanding due to heat and causing the gaps between its components to disappear. The phase change heat-absorbing material 13 can be made of materials such as paraffin wax.

[0025] Since thermal expansion is still unavoidable under high-frequency peak-shaving conditions, to further prevent the two rotors 10 from jamming, in this embodiment, the Roots vacuum pump 3 is also equipped with bearing seats 14 that are matched one-to-one with the two rotating shafts 9. Both rotating shafts 9 are connected to the corresponding side bearing seats 14, and thermal expansion displacement sensors 15 are installed on both sides of the bearing seats 14. When the rotor 10 expands due to heat, the heat generated is conducted to the rotating shafts 9 and the bearing seats 14, causing the rotating shafts 9 and the bearing seats 14 to expand thermally. The thermal expansion displacement sensors 15 detect the deformation of the two side bearing seats 14 to indirectly detect the thermal expansion state of the rotor 10. Piezoelectric ceramic fine-tuning push rods 16 are connected to the bottom of both side bearing seats 14, and the thermal expansion displacement sensors 15 and the piezoelectric ceramic fine-tuning push rods 16 are electrically connected by a PLC control circuit. When the thermal expansion displacement sensor 15 detects that the expansion change value of the bearing housing 14 reaches the set threshold, it can send an electrical signal to the PLC control circuit. After receiving this signal, the PLC control circuit can convert it into an action signal to drive the piezoelectric ceramic fine-tuning push rod 16 to work. By pushing the bearing housing 14, the center distance between the two bearing housings 14 is displaced by micrometers, so as to dynamically compensate for the gap that disappears between the two rotors 10, thereby further preventing the two rotors 10 from jamming.

[0026] To improve the automation level of the composite vacuum pump device provided in Embodiment 1 for practical application, Embodiment 3 is proposed based on Embodiment 1.

[0027] Example 3: Please refer to Figure 4 and Figure 5 Firstly, this embodiment provides a composite vacuum pump device suitable for gas-steam combined cycle units, including all the structures in Embodiment 1. Further, the composite vacuum pump device also includes a bypass extraction pipeline 172. One end of the bypass extraction pipeline 172 is connected to the extraction pipeline 2, and the other end is connected to the interstage pipeline 5 between the outlet valve 7 and the check valve 8. A pneumatic bypass valve 18 is installed on the bypass extraction pipeline 172. The bypass extraction pipeline 172 is used to replace the Roots vacuum pump 3 and the vacuum water ring pump 4 in single-cycle or combined-cycle operation of the unit, serving as the required channel. The Roots vacuum pump 3 is equipped with an inlet pressure sensor 19, and the vacuum water ring pump 4 is equipped with an interstage pressure sensor 20. The compound vacuum pump device also includes a PLC control module 21. The PLC control module 21 is electrically connected to the Roots vacuum pump 3, the vacuum water ring pump 4, the outlet valve 7, the pneumatic bypass valve 18, the inlet pressure sensor 19, and the interstage pressure sensor 20, respectively, for the required data acquisition and operation control.

[0028] Secondly, this embodiment provides an operation method for the aforementioned combined vacuum pump device applicable to gas-steam combined cycle units, including the following steps: Single-cycle operation steps: During the unit start-up preparation stage, when the unit condenser 1 needs to establish a vacuum, the PLC control module 21 opens the pneumatic bypass valve 18, closes the outlet valve 7, and starts the vacuum water ring pump 4. The vacuum water ring pump 4 performs preliminary vacuuming on the unit condenser 1, and the non-condensable gas in the unit condenser 1 is discharged to the outside through the extraction pipeline 2, the bypass extraction pipeline 172, the interstage pipeline 5, the vacuum water ring pump 4, and the exhaust pipeline 6 in sequence.

[0029] Combined cycle operation steps: When the unit needs to increase the vacuum of the condenser 1 to improve unit efficiency, the PLC control module 21 monitors the bypass pressure sensor value in real time. At this time, the value detected by the bypass pressure sensor is the gas pressure value inside the condenser. When the monitored value reaches the set threshold, it indicates that the condenser has reached the required vacuum level. After this, the PLC control module 21 opens the outlet valve 7, closes the pneumatic bypass valve 18 and the vacuum water ring pump 4, and starts the Roots vacuum pump 3. The Roots vacuum pump 3 continuously evacuates the condenser 1. The non-condensable gas in the condenser 1 is discharged to the outside through the extraction pipeline 2, the Roots vacuum pump 3, the interstage pipeline 5, the vacuum water ring pump 4, and the exhaust pipeline 6 in sequence.

[0030] Variable operating condition adjustment steps: When the unit condenser 1 needs to switch from combined cycle operation to single cycle operation, the PLC control module 21 monitors the value of the inlet pressure sensor 19 in real time. At this time, the value detected by the bypass pressure sensor is the gas pressure value inside the unit condenser. When the monitored value reaches the set threshold, it indicates that the vacuum level inside the unit condenser has dropped to the required value. After this, the PLC control module 21 opens the pneumatic bypass valve 18, closes the outlet valve 7 and the Roots vacuum pump 3, and starts the vacuum water ring pump 4. The vacuum water ring pump 4 performs the required vacuuming operation on the unit condenser 1.

[0031] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made based on the content of the present invention's specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A composite vacuum pump device suitable for gas-steam combined cycle units, comprising a unit condenser (1), characterized in that: It also includes a vacuum pumping line (2), a Roots vacuum pump (3), and a vacuum water ring pump (4). One end of the extraction pipe (2) is connected to the extraction port of the condenser (1) of the unit, and the other end of the extraction pipe (2) is connected to the inlet of the Roots vacuum pump (3). The exhaust port of the Roots vacuum pump (3) is connected to the inlet of the vacuum water ring pump (4) through the interstage pipe (5). The exhaust port of the vacuum water ring pump (4) is connected to the exhaust pipe (6). An outlet valve (7) and a check valve (8) are sequentially installed on the interstage pipeline (5) along the gas flow direction. The Roots vacuum pump (3) has two parallel rotating shafts (9) installed in the pump chamber. Each rotating shaft (9) is equipped with a rotor (10) arranged in a figure-eight shape. When the Roots vacuum pump (3) is running, the two rotors (10) rotate synchronously in opposite directions in the pump chamber.

2. The composite vacuum pump device for a gas-steam combined cycle unit according to claim 1, characterized in that: The impeller (11) of the vacuum water ring pump (4) is eccentrically installed inside the pump chamber of the vacuum water ring pump (4).

3. A composite vacuum pump device suitable for gas-steam combined cycle units according to claim 1, characterized in that: Each rotor (10) is coated with a polytetrafluoroethylene anti-corrosion and wear-resistant coating on its outer surface. Each rotor (10) has a cooling cavity (12) inside, and each cooling cavity (12) is filled with a phase change heat-absorbing material (13).

4. A composite vacuum pump device suitable for gas-steam combined cycle units according to claim 3, characterized in that: The Roots vacuum pump (3) is also equipped with bearing seats (14) that are matched one-to-one with the two rotating shafts (9). Both rotating shafts (9) are connected to the corresponding side bearing seats (14). Both side bearing seats (14) are equipped with thermal expansion displacement sensors (15). Both side bearing seats (14) are connected to piezoelectric ceramic fine adjustment push rods (16) at the bottom. The thermal expansion displacement sensors (15) and piezoelectric ceramic fine adjustment push rods (16) are electrically connected by a PLC control circuit.

5. A composite vacuum pump device suitable for gas-steam combined cycle units according to claim 1, characterized in that: The composite vacuum pump device also includes a bypass extraction pipeline (17)(2), one end of which is connected to the extraction pipeline (2), and the other end of which is connected to the interstage pipeline (5) between the outlet valve (7) and the check valve (8). A pneumatic bypass valve (18) is provided on the bypass extraction pipeline (17)(2).

6. A composite vacuum pump device suitable for a gas-steam combined cycle unit according to claim 5, characterized in that: The Roots vacuum pump (3) is equipped with an inlet pressure sensor (19), and the vacuum water ring pump (4) is equipped with an interstage pressure sensor (20). The composite vacuum pump device also includes a PLC control module (21), which is electrically connected to the Roots vacuum pump (3), the vacuum water ring pump (4), the outlet valve (7), the pneumatic bypass valve (18), the inlet pressure sensor (19), and the interstage pressure sensor (20).

7. A method for operating a combined vacuum pump device for a gas-steam combined cycle unit as described in any one of claims 1 to 6, comprising the following steps: Single-cycle operation steps: During the unit start-up preparation stage, when the unit condenser (1) needs to establish a vacuum, start the vacuum water ring pump (4) to perform preliminary vacuuming on the unit condenser (1); Combined cycle operation steps: When the unit needs to increase the vacuum of the condenser (1) to improve the unit efficiency, shut down the vacuum water ring pump (4) and start the Roots vacuum pump (3) to continuously evacuate the condenser (1).

8. The operating method of a combined vacuum pump device suitable for a gas-steam combined cycle unit according to claim 7, characterized in that: In the single-cycle operation step: the PLC control module (21) opens the pneumatic bypass valve (18), closes the outlet valve (7), and starts the vacuum water ring pump (4).

9. The operating method of a combined vacuum pump device suitable for a gas-steam combined cycle unit according to claim 7, characterized in that: In the combined cycle operation step: the PLC control module (21) monitors the value of the bypass pressure sensor in real time. When the monitored value reaches the set threshold, the PLC control module (21) opens the outlet valve (7), closes the pneumatic bypass valve (18) and the vacuum water ring pump (4), and starts the Roots vacuum pump (3).

10. The operating method of a combined vacuum pump device suitable for a gas-steam combined cycle unit according to claim 7, characterized in that: It also includes variable operating condition adjustment steps: When the condenser (1) of the unit needs to switch from combined cycle operation to single cycle operation, the PLC control module (21) monitors the value of the inlet pressure sensor (19) in real time. When the monitored value reaches the set threshold, the PLC control module (21) opens the pneumatic bypass valve (18), closes the outlet valve (7) and the Roots vacuum pump (3), and starts the vacuum water ring pump (4).

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