A CO2 centrifugal compressor adapted to exhaust at 450℃ and its shaft sealing system

Abstract

The application discloses a CO2 centrifugal compressor suitable for 450 DEG C exhaust and a shaft sealing system thereof, and belongs to the field of compressor design. In order to solve the problems that the shaft sealing leakage of the existing CO2 centrifugal compressor is too large in time accumulation, and it is difficult to simultaneously realize high efficiency and safe operation under the condition of 450 DEG C exhaust temperature, the application adds adjustable sealing gaskets between a volute and a casing and improves the structure of the back of a centrifugal impeller, so that when the exhaust temperature reaches 450 DEG C, a smaller gap is formed between the centrifugal impeller and the volute, and the unit can be safely and efficiently operated. Meanwhile, the shaft sealing system adopts a combined structure of single-end face dry gas sealing and carbon ring sealing, and is matched with a leakage recovery device, so that the shaft end sealing leakage of the CO2 centrifugal compressor is reduced by more than 90%, and the system operation cost caused by the leakage of the working medium is greatly reduced. The application is mainly used for the CO2 centrifugal compressor suitable for 450 DEG C exhaust and the adaptive shaft sealing system thereof.

Description

Technical Field

[0001] This invention relates to the field of compressor design, and more specifically to a CO2 centrifugal compressor adapted to exhaust at 450°C and its shaft sealing system. Background Technology

[0002] Supercritical CO2 power generation and compressed CO2 energy storage, as high-efficiency technologies in the current energy field, have become core research directions for the upgrading of the new energy industry and the development of energy storage technology due to their advantages such as high energy conversion efficiency, compact system structure, and environmental friendliness. As the core power equipment in such systems, the CO2 centrifugal compressor's operating performance directly determines the efficiency, stability, and operating costs of the entire system. With the industry's increasing demands for system energy density and efficiency, the operating conditions of CO2 centrifugal compressors are continuously developing towards higher temperatures and pressures, with exhaust temperatures gradually exceeding 400℃ and even reaching 450℃. This places stringent requirements on the compressor's structural strength, thermal stability, sealing performance, and other core indicators.

[0003] Under high-temperature exhaust conditions, the core components of a CO2 centrifugal compressor are susceptible to deformation due to temperature stress and high-pressure media. The dynamic and static clearance between the centrifugal impeller and the volute is a key factor affecting compressor efficiency. Axial and radial deformation of components at high temperatures can cause the dynamic and static clearance to deviate from their optimal values. If the clearance is too large, it can cause media backflow, significantly reducing compression efficiency; if the clearance is too small, there are safety risks associated with component friction and collision. How to balance efficient compressor operation and structural safety under 450℃ high-temperature exhaust conditions has become a pressing technical challenge in the industry. Meanwhile, the shaft seal structure between the compressor's high-speed shaft and the casing, as a key component preventing CO2 refrigerant leakage, directly affects the system's operating costs and refrigerant utilization rate.

[0004] Currently, most CO2 centrifugal compressors in the industry use a single-end dry gas seal as the core shaft seal structure. While this structure offers advantages such as high sealing reliability and low friction loss, unavoidable working fluid leakage still exists at the sealing end face. Typical leakage can reach 25-40 Nm³ / h, and after 24 hours of continuous operation, the cumulative leakage can reach 600-960 Nm³. To maintain normal operation, supercritical CO2 power generation and compressed CO2 energy storage systems require a continuous supply of large amounts of CO2 working fluid, significantly increasing daily operating costs and causing media waste and environmental problems due to leakage. Furthermore, existing shaft seal systems lack a targeted leakage gas recovery and utilization mechanism; most leaked CO2 working fluid is directly vented, reducing working fluid utilization and failing to meet the sealing gas supply and regulation requirements under high-temperature and high-pressure conditions, making it difficult to meet the long-term stable operation requirements of CO2 centrifugal compressors under 450℃ exhaust conditions.

[0005] Meanwhile, the existing CO2 centrifugal compressor's structural design does not fully consider the strengthening of component rigidity and the design of adjustable clearance under high-temperature conditions. The centrifugal impeller is prone to axial deformation under high temperature and high pressure, which further aggravates the deviation of dynamic and static clearance. The connection structure between the volute and the casing lacks flexible clearance adjustment means, and cannot adjust the dynamic and static clearance in real time according to the deformation of components under high-temperature conditions, making it difficult to balance the efficiency and safety performance of the compressor under high-temperature conditions.

[0006] In summary, existing CO2 centrifugal compressors face multiple technical challenges under high-temperature exhaust conditions of 450℃, including large shaft seal leakage, low working fluid utilization, high operating costs, non-adjustable dynamic and static clearances, and insufficient high-temperature structural stability. These challenges severely restrict their large-scale application in high-end energy fields such as supercritical CO2 power generation and compressed CO2 energy storage. There is an urgent need to develop a CO2 centrifugal compressor and its matching shaft seal system that is suitable for high-temperature exhaust conditions, has excellent sealing performance, adjustable structure, and balances efficiency and safety. Summary of the Invention

[0007] To address the problem that the leakage of shaft seals in existing CO2 centrifugal compressors is too large over time, and that it is difficult to balance high efficiency and safe operation under exhaust temperature of 450°C, this invention proposes a CO2 centrifugal compressor and its shaft seal system adapted to exhaust temperature of 450°C.

[0008] A CO2 centrifugal compressor adapted to exhaust at 450℃ includes a volute, a casing, a gas seal, a speed increaser housing, a centrifugal impeller, a high-speed shaft, and a shaft seal structure. The volute is located on one end of the casing and is detachably connected to the casing by fastening bolts. The casing is located outside one end of the speed increaser housing and is detachably connected to the speed increaser housing by a flange. One end of the high-speed shaft is inserted into the speed increaser housing and connected to a power source located inside the speed increaser housing. The other end of the high-speed shaft extends outside the speed increaser housing and is rotatably connected to the casing by the shaft seal structure. The gas seal is embedded in the casing near the volute and is detachably connected to the casing by fastening bolts. The centrifugal impeller is located between the volute and the casing and is fixed to the end of the high-speed shaft by mounting bolts. A dynamic and static clearance is provided between the centrifugal impeller and the volute.

[0009] Furthermore, a sealing gasket is provided between the volute and the casing. By replacing the sealing gaskets of different thicknesses, the size of the dynamic and static clearance between the volute and the centrifugal impeller can be adjusted.

[0010] Furthermore, a locking nut for axially limiting the shaft seal structure is provided between the centrifugal impeller and the shaft seal structure. The locking nut is sleeved on the high-speed shaft and threadedly connected to the high-speed shaft.

[0011] Furthermore, a bearing is provided between the high-speed shaft and the gearbox housing, and the bearing is rotatably connected to the gearbox housing;

[0012] Furthermore, the centrifugal impeller includes a disc, which is fixed to the end of the high-speed shaft by mounting bolts. Multiple blades are machined equidistantly along the circumferential direction on the side of the disc facing the volute. A first reinforcing ring and a second reinforcing ring are coaxially mounted from the inside to the outside on the side of the disc facing the high-speed shaft.

[0013] Furthermore, the shaft seal structure includes a dry gas seal structure and a single-stage carbon ring seal structure. The casing is machined with a main sealing gas inlet channel, a leakage gas recovery channel and an isolation gas inlet channel. The main sealing gas inlet channel, the leakage gas recovery channel and the isolation gas inlet channel are all connected to the shaft seal structure.

[0014] A shaft sealing system adapted to a CO2 centrifugal compressor with exhaust gas at 450℃;

[0015] The shaft sealing system includes a centrifugal compressor inlet pipe, a centrifugal compressor outlet pipe, a main sealing gas inlet pipe, a leak gas recovery pipe, and an isolation gas inlet pipe. The inlet end of the centrifugal compressor inlet pipe is connected to the CO2 inlet, the outlet end of the centrifugal compressor inlet pipe is connected to the compressor inlet, the inlet end of the centrifugal compressor outlet pipe is connected to the compressor exhaust end, and the outlet end of the centrifugal compressor outlet pipe is connected to the CO2 outlet.

[0016] The main sealing gas inlet pipeline includes a main sealing gas inlet main line and a return branch line. The inlet end of the main sealing gas inlet main line is connected to the inlet pipeline of the centrifugal compressor, and the outlet end of the main sealing gas inlet main line is connected to the main sealing gas inlet channel. The inlet end of the return branch line is connected to the outlet pipeline of the centrifugal compressor, and the outlet end of the return branch line is connected to the main sealing gas inlet main line.

[0017] The inlet end of the leak gas recovery pipeline is connected to the leak gas recovery channel, and the outlet end of the leak gas recovery pipeline is connected to the inlet pipeline of the centrifugal compressor.

[0018] The inlet end of the isolation gas inlet pipe is connected to the main sealing gas inlet main line, and the outlet end of the isolation gas inlet pipe is connected to the isolation gas inlet channel.

[0019] Furthermore, on the main sealing gas inlet line, a valve, a purification device, a booster pump unit, and an electric heater are connected in series from the inlet end to the outlet end, and on the return branch line, a valve and a cooler are connected in series from the inlet end to the outlet end.

[0020] The booster pump unit includes valve No. 3, valve No. 4 and booster pump. Valve No. 3 and booster pump are connected in series in the main sealing gas inlet main line, and valve No. 4 is connected in parallel to valve No. 3 and booster pump.

[0021] Furthermore, a leak gas recovery unit is connected in series on the leak gas recovery pipeline. The leak gas recovery unit includes a pressure stabilizing tank, a bypass vent valve, a booster main gas valve, a booster inlet cooler, a booster inlet pressure stabilizing tank, a recovery compressor, a booster outlet cooler, a booster outlet pressure stabilizing tank, and a booster bypass regulating valve. The pressure stabilizing tank, booster main gas valve, booster inlet cooler, booster inlet pressure stabilizing tank, recovery compressor, booster outlet cooler, and booster outlet pressure stabilizing tank are connected in series in the leak gas recovery pipeline along the airflow direction.

[0022] The pressure tank is equipped with a venting bypass, a bypass venting valve is connected in series on the venting bypass, a safety branch is connected in parallel on the bypass venting valve, and a safety valve is connected in series on the safety branch.

[0023] A regulating bypass is connected in parallel to the recovery compressor and the booster outlet cooler. The inlet end of the regulating bypass is connected to the booster inlet pressure stabilizing tank, and the outlet end of the regulating bypass is connected to the booster outlet pressure stabilizing tank. The booster bypass regulating valve is connected in series on the regulating bypass.

[0024] Furthermore, valve number five is connected in series on the isolation gas inlet pipe.

[0025] The beneficial effects of this invention are as follows:

[0026] 1. This application provides a CO2 centrifugal compressor and its shaft sealing system adapted to 450℃ exhaust temperature. By setting an adjustable-thickness sealing gasket between the volute and the casing, different thickness gaskets can be flexibly replaced according to the thermal deformation characteristics of components under high-temperature conditions. This allows for precise adjustment of the dynamic and static clearance between the volute and the centrifugal impeller, structurally avoiding the loss of media backflow efficiency caused by excessive clearance at high temperatures, and eliminating the safety hazards of component friction and collision caused by insufficient clearance. Simultaneously, a composite reinforcement structure of a reinforcing ring and circumferentially distributed back ribs is designed on the back of the centrifugal impeller, significantly improving the structural rigidity of the impeller and effectively suppressing axial deformation of the impeller towards the blades under high temperature and pressure, ensuring the long-term stability of the dynamic and static clearance. The compressor structure of this application can stably adapt to the extreme exhaust temperature of 450℃, significantly improving compression efficiency while ensuring the safe and trouble-free operation of the unit, thus solving the core industry problem of balancing efficiency and safety under high-temperature conditions.

[0027] 2. This application provides a CO2 centrifugal compressor and its shaft sealing system adapted to 450℃ exhaust. It abandons the traditional single-end dry gas seal structure and adopts a combined shaft sealing design with a dry gas seal structure and a single-stage carbon ring seal structure. Combined with the synergistic effect of the dedicated main sealing gas inlet channel, leakage gas recovery channel, and isolation gas inlet channel on the casing, a multi-layered sealing protection system is formed. Simultaneously, the shaft sealing system is designed with a dual-inlet main sealing gas supply scheme according to different compressor operating conditions, achieving precise control of sealing gas pressure and temperature. The isolation gas specifically blocks the interference of lubricating oil mist on the sealing structure, improving sealing performance from both the sealing structure and gas path control dimensions. In practical applications, the CO2 working fluid leakage of the shaft end seal is significantly reduced from the traditional 25~40 NM³ / h to below 2 NM³ / h, with an absolute working fluid leakage reduction of over 90%. This completely solves the problem of excessive accumulation of working fluid leakage over time in traditional structures and significantly reduces the amount of CO2 working fluid replenishment during system operation.

[0028] 3. This application provides a CO2 centrifugal compressor and its shaft sealing system adapted to exhaust gas at 450℃. By significantly reducing leakage and recovering and reusing leaked gas, it fundamentally reduces the procurement and replenishment costs of CO2 working fluid, which is one of the core operating costs in the long-term operation of supercritical CO2 power generation and compressed CO2 energy storage systems. Simultaneously, the compressor's efficient and stable operation at 450℃ improves the energy conversion efficiency of the entire energy system and reduces energy loss. The modular structural design reduces equipment maintenance and downtime costs, achieving a dual reduction in equipment operating costs and system operating costs. The technical solution of this application does not require significant modifications to existing energy systems to replace and adapt the compressor, possessing good compatibility and scalability. It provides core equipment technology support for the large-scale development of high-end energy fields such as supercritical CO2 power generation and compressed CO2 energy storage, possessing significant economic value and industry-driving significance. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the CO2 centrifugal compressor in this application;

[0030] Figure 2 This is a schematic diagram of the sealing structure in the CO2 centrifugal compressor of this application;

[0031] Figure 3 This is a schematic diagram of the composition of the leak gas recovery unit in the CO2 centrifugal compressor of this application;

[0032] Figure 4 This is a connection diagram of the shaft sealing system adapted to a CO2 centrifugal compressor in this application;

[0033] Figure 5This is a schematic diagram of the centrifugal impeller in the CO2 centrifugal compressor of this application;

[0034] In the diagram: 1-Voltage, 2-Casing, 3-Sealing gasket, 4-Gas seal, 5-Gearbox housing, 6-Mounting bolt, 7-Centrifugal impeller, 8-High-speed shaft, 9-Locking nut, 10-Shaft seal structure, 11-Dry gas seal structure, 12-Single-stage carbon ring seal structure, 13-Leakage gas recovery unit, 14-Pressure stabilizing tank, 15-Bypass vent valve, 16-Boosting main gas valve, 17-Boosting inlet cooler, 18-Boosting inlet pressure stabilizing tank, 19- 20-Recovery compressor, 21-Boost outlet cooler, 22-Boost outlet pressure stabilizing tank, 24-Boost bypass regulating valve, 25-Back ribs, 26-Reinforcing ring, 27-Centrifugal compressor inlet pipe, 28-Cooler, 29-Purification device, 30-Boost pump, 31-Electric heater, 32-Disc, 33-Blade, A-Main sealing gas inlet channel, B-Leakage gas recovery channel and C-Isolation gas inlet channel. Detailed Implementation

[0035] Specific implementation method one: Combining Figures 1 to 5 This embodiment describes a CO2 centrifugal compressor adapted to exhaust at 450°C. It includes a volute 1, a casing 2, a gas seal 4, a speed increaser housing 5, a centrifugal impeller 7, a high-speed shaft 8, and a shaft seal structure 10. The volute 1 is mounted on one end of the casing 2 and is detachably connected to it via fastening bolts. The casing 2 is located outside one end of the speed increaser housing 5 and is detachably connected to it via a flange. One end of the high-speed shaft 8 is inserted into the speed increaser housing 5 and connected to a power source located within it. The other end of the high-speed shaft 8 extends outside the speed increaser housing 5 and is rotatably connected to the casing 2 via the shaft seal structure 10. The gas seal 4 is embedded in the casing 2 near the volute 1 and is detachably connected to it via fastening bolts. The centrifugal impeller 7 is located between the volute 1 and the casing 2 and is fixed to the end of the high-speed shaft 8 via mounting bolts 6. A dynamic-static clearance is provided between the centrifugal impeller 7 and the volute 1.

[0036] The CO2 centrifugal compressor adapted to 450℃ exhaust temperature provided in this embodiment adopts a modular design. The volute 1 and the casing 2, and the casing 2 and the speed increaser housing 5 are detachably connected by fastening bolts and flanges. Core components such as the gas seal 4 and the centrifugal impeller 7 are also detachable structures fixed by bolts, which facilitates on-site assembly, later maintenance and component replacement. A sealing gasket 3 is provided between the volute 1 and the casing 2. By replacing the sealing gasket 3 with different thicknesses, the size of the dynamic and static clearance between the volute 1 and the centrifugal impeller 7 can be adjusted. The inner diameter of the sealing gasket 3 is 278mm, the outer diameter is 303mm, and the thickness is between 5.0-5.5mm. In order to save costs, a set of sealing gaskets can be processed at intervals of 0.1mm within the range. Each set of sealing gaskets consists of 6 pieces, including a base gasket with a basic thickness of 5.0mm and a thickened gasket with a thickness of 0.1mm. During operation, the number of thickened gaskets can be increased or decreased according to the size requirements of the dynamic and static clearance.

[0037] To ensure the reliability of the shaft seal structure 10 during operation, a locking nut 9 for axially limiting the shaft seal structure 10 is provided between the centrifugal impeller 7 and the shaft seal structure 10. The locking nut 9 is sleeved on the high-speed shaft 8 and threadedly connected to the high-speed shaft 8. A bearing is provided between the high-speed shaft 8 and the speed increaser housing 5 and is rotatably connected to the speed increaser housing 5 through the bearing, and the high-speed shaft 8 is supported by the bearing.

[0038] The centrifugal impeller 7 includes a disc 32, which is fixed to the end of the high-speed shaft 8 by mounting bolts 6. Multiple blades 33 are machined circumferentially at equal intervals on the side of the disc 32 facing the volute 1. A first reinforcing ring 25 and a second reinforcing ring 24 are coaxially mounted from the inside to the outside on the side of the disc 32 facing the high-speed shaft 8. The first reinforcing ring 25 has an inner diameter of 55 mm, an outer diameter of 71 mm, and an axial thickness of 6 mm. The second reinforcing ring 24 has an inner diameter of 96 mm, an outer diameter of 99 mm, and an axial thickness of 2 mm. The first reinforcing ring 25 and the second reinforcing ring 24 are used to increase the rigidity of the disc 32 and reduce the axial deformation of the centrifugal impeller 7 from the disc 32 to the blades 33 under high temperature and high pressure. At the same time, the first reinforcing ring 25 and the second reinforcing ring 24 are also used for weight distribution of the high-speed shaft 8, the centrifugal impeller 7, and the mounting bolts 6 during the high-speed dynamic balance test.

[0039] The shaft seal structure 10 includes a dry gas seal structure 11 and a single-stage carbon ring seal structure 12. The casing 2 is machined with a main sealing gas inlet channel A, a leakage gas recovery channel B, and an isolation gas inlet channel C. These channels are all connected to the shaft seal structure 10. The main sealing gas, leakage gas, and isolation gas are all CO2. The main sealing gas inlet channel A supplies gas to the dry gas seal structure 11 and the single-stage carbon ring seal structure 12. The leakage gas recovery channel B supplies gas to the dry gas seal structure 11 and the single-stage carbon ring seal structure 12. The gas leaked from the sealing structure 12 is recovered. The isolation gas inlet channel C is used to fill the dry gas sealing structure 11 and the single-stage carbon ring sealing structure 12 with isolation gas to prevent lubricating oil mist from entering the shaft end sealing structure. In this embodiment, a combined shaft seal design of dry gas sealing structure and single-stage carbon ring sealing structure is adopted. With the synergistic effect of the main sealing gas inlet channel, leakage gas recovery channel and isolation gas inlet channel specially arranged on the casing, a multi-layer sealing protection system is formed, which greatly improves the sealing performance of the shaft seal structure and helps to reduce the leakage of sealing working fluid.

[0040] Specific Implementation Method Two: Combining Figures 1 to 5 This embodiment describes a shaft sealing system adapted to a CO2 centrifugal compressor with exhaust at 450°C. It includes a centrifugal compressor inlet pipe 26, a centrifugal compressor outlet pipe 27, a main sealing gas inlet pipe, a leakage gas recovery pipe, and an isolation gas inlet pipe. The inlet end of the centrifugal compressor inlet pipe 26 is connected to the CO2 inlet, the outlet end of the centrifugal compressor inlet pipe 26 is connected to the compressor inlet, the inlet end of the centrifugal compressor outlet pipe 27 is connected to the compressor exhaust end, and the outlet end of the centrifugal compressor outlet pipe 27 is connected to the CO2 outlet.

[0041] The main sealing gas inlet pipeline includes a main sealing gas inlet main line and a return branch line. The inlet end of the main sealing gas inlet main line is connected to the centrifugal compressor inlet pipeline 26, and the outlet end of the main sealing gas inlet main line is connected to the main sealing gas inlet channel A. The inlet end of the return branch line is connected to the centrifugal compressor outlet pipeline 27, and the outlet end of the return branch line is connected to the main sealing gas inlet main line.

[0042] The inlet end of the leak gas recovery pipeline is connected to the leak gas recovery channel B, and the outlet end of the leak gas recovery pipeline is connected to the centrifugal compressor inlet pipeline 26.

[0043] The inlet end of the isolation gas inlet pipe is connected to the main sealing gas inlet, and the outlet end of the isolation gas inlet pipe is connected to the isolation gas inlet channel C. Other components and connections are the same as in Specific Implementation Method 1.

[0044] The shaft sealing system provided in this embodiment is used in conjunction with the shaft sealing structure of a CO2 centrifugal compressor that is adapted to exhaust at 450°C. The main sealing gas inlet line consists of a valve, a purification device 29, a booster pump unit, and an electric heater 31 connected in series from the inlet to the outlet. The return branch line consists of a valve and a cooler 28 connected in series from the inlet to the outlet. The booster pump unit includes a valve, a valve, and a booster pump 30. The valve and the booster pump 30 are connected in series in the main sealing gas inlet line, and the valve is connected in parallel with the valve and the booster pump 30. The selection of the main sealing gas intake location depends on the operating conditions. Before the CO2 centrifugal compressor starts, during CO2 refrigerant charging, during compressor start-up, and during shutdown, the main sealing gas intake location is selected at the compressor inlet pipe 26. During normal operation of the CO2 centrifugal compressor, the main sealing gas intake location is selected at the compressor inlet pipe 27, at which point the booster pump 30 stops working.

[0045] Leakage gas recovery channel B operates only under normal operating conditions of the CO2 centrifugal compressor. The leakage gas recovery pressure is set to 1.5-3.0 bar. A leakage gas recovery unit 13 is connected in series on the leakage gas recovery pipeline. The leakage gas recovery unit 13 includes a pressure stabilizing tank 14, a bypass vent valve 15, a booster main gas valve 16, a booster inlet cooler 17, a booster inlet pressure stabilizing tank 18, a recovery compressor 19, a booster outlet cooler 20, a booster outlet pressure stabilizing tank 21, and a booster bypass regulating valve 22. The pressure stabilizing tank 14, the booster main gas valve 16, and the booster inlet... The inlet cooler 17, the booster inlet pressure stabilizing tank 18, the recovery compressor 19, the booster outlet cooler 20, and the booster outlet pressure stabilizing tank 21 are connected in series along the airflow direction of the leak gas recovery pipeline. The opening condition of the booster main gas valve 16 is that the working fluid pressure in the pressure stabilizing tank 14 is ≥0.15MPa. The booster inlet cooler 17 and the booster outlet cooler 20 are water-cooled, with an inlet water temperature ≤32℃ and an inlet water pressure of 0.45-0.6MPa. The recovery compressor 19 adopts a two-stage compression, diaphragm compressor structure.

[0046] To ensure the safety of the pressure stabilizing tank 14, a venting bypass is provided on the pressure stabilizing tank 14. The bypass venting valve 15 is connected in series on the venting bypass. The opening condition of the bypass venting valve 15 is that the working fluid pressure in the pressure stabilizing tank 14 is >0.4MPa. A safety branch is connected in parallel on the bypass venting valve 15, and a safety valve is connected in series on the safety branch.

[0047] To ensure the safe operation of the recovery compressor 19 and the booster outlet cooler 20, a regulating bypass is connected in parallel to the recovery compressor 19 and the booster outlet cooler 20. The inlet end of the regulating bypass is connected to the booster inlet pressure stabilizing tank 18, and the outlet end of the regulating bypass is connected to the booster outlet pressure stabilizing tank 21. The booster bypass regulating valve 22 is connected in series in the regulating bypass. When the pressure difference between the booster outlet pressure stabilizing tank 21 and the booster inlet pressure stabilizing tank 18 exceeds 9.3 MPa, the booster bypass regulating valve 22 opens, and the recovery compressor 19 and the booster bypass regulating valve 22 form a return flow path.

[0048] The isolation gas inlet channel C only operates when the CO2 centrifugal compressor is started and the system is charged with CO2 working fluid, during the start-up and shutdown of the CO2 centrifugal compressor. The isolation gas is drawn from the main sealing gas. The working pressure of the isolation gas is set to 1.2-1.5 bar. A valve No. 5 is connected in series on the isolation gas inlet pipeline. The working status of the isolation gas inlet pipeline is determined by the opening and closing of the valve No. 5.

[0049] Taking a compressed CO2 energy storage centrifugal compressor as an example, the inlet pressure is 6.8MPa, the temperature is 245℃, the outlet pressure is 21MPa, the temperature is 402℃, the flow rate is 24700NM3 / h, the speed is 27000r / min, and the impeller diameter is 156mm.

[0050] After applying the CO2 centrifugal compressor and its matching shaft sealing system provided in this application, the leakage of the shaft end sealing structure is reduced from 25 NM3 / h to below 2 NM3 / h, and the absolute leakage of the working fluid at the shaft end is reduced by more than 90%, significantly reducing the system operating costs caused by working fluid leakage. By adding adjustable sealing gaskets and annular ribs on the back of the centrifugal impeller, the cold gap between the centrifugal impeller and the volute is reduced by 0.2 mm when the exhaust temperature reaches 450℃, ensuring safe operation of the unit while significantly improving efficiency.

[0051] This invention may have other embodiments. Without departing from the spirit and essence of this invention, those skilled in the art can make various corresponding changes and modifications according to this invention, but these corresponding changes and modifications should all fall within the protection scope of the appended claims.

[0052] Working principle:

[0053] The compressor body is based on centrifugal compression as its core principle. It achieves pressure and temperature increase of CO2 medium through power transmission. At the same time, it relies on structural designs such as adjustable sealing gaskets and double-reinforced centrifugal impellers to offset component deformation under high temperature and high pressure, adapting to extreme exhaust conditions of 450℃, and balancing compression efficiency and operational safety. The specific working process is as follows:

[0054] 1. Power transmission and centrifugal compression: The power source inside the speed increaser housing 5 outputs power to drive the high-speed shaft 8 to rotate at high speed around its own axis; the centrifugal impeller 7, which is fixed at the end of the high-speed shaft 8 by the mounting bolts 6, rotates synchronously with the high-speed shaft 8. The CO2 medium that enters the compression chamber between the volute 1 and the casing 2 is accelerated and pressurized under the centrifugal force of the blades 33 of the centrifugal impeller 7, completing the centrifugal compression process. The compressed high-temperature and high-pressure CO2 medium is discharged from the exhaust port of the volute 1 and enters the subsequent process system to realize the pressurized transportation of the CO2 medium.

[0055] 2. Adaptation of dynamic and static clearance under high temperature conditions: An adjustable sealing gasket 3 is installed between the volute 1 and the casing 2. According to the thermal deformation characteristics of components such as the volute and centrifugal impeller at 450℃, the dynamic and static clearance between the volute 1 and the centrifugal impeller 7 can be adjusted by replacing or adding or removing the sealing gasket 3. This allows the cold clearance to be precisely reduced by 0.2mm, which avoids CO2 medium backflow and reduced compression efficiency caused by excessive clearance at high temperatures, and also eliminates safety hazards such as component friction and collision caused by excessive clearance. This ensures that the dynamic and static clearance is within the optimal working range under high temperature conditions.

[0056] 3. High-temperature deformation protection of the centrifugal impeller: The impeller 7 has a first reinforcing ring 25 and a second reinforcing ring 24 coaxially arranged from the inside to the outside on the side of the impeller 32 facing the high-speed shaft 8. The double reinforcing ring structure greatly improves the structural rigidity of the impeller 32 and effectively suppresses the axial deformation of the impeller 32 towards the blade 33 under high temperature and high pressure, further ensuring the long-term stability of the dynamic and static clearance between the centrifugal impeller and the volute. At the same time, the double reinforcing ring can be used to adjust the weight of the high-speed shaft 8, the centrifugal impeller 7 and the mounting bolts 6 during the high-speed dynamic balancing test, improving the stability of the equipment during high-speed rotation.

[0057] 4. Stable support and limiting of auxiliary structures: The bearing between the high-speed shaft 8 and the gearbox housing 5 provides rotational support for the high-speed shaft, ensuring smooth power transmission; the locking nut 9 between the centrifugal impeller 7 and the shaft seal structure 10 is threaded to the high-speed shaft 8, axially limiting the shaft seal structure 10, preventing displacement of the shaft seal structure during high-speed operation, and ensuring the sealing effectiveness of the shaft seal structure; in addition, the compressor body adopts a modular and detachable design, with the volute and the casing, and the casing and the gearbox housing connected by fastening bolts and flanges, providing structural convenience for equipment assembly and maintenance;

[0058] The shaft seal system is a sealing and recovery system supporting the compressor body, which uses CO2 as the only sealing / isolating / recovery working medium. Through the coordinated cooperation of the main seal gas inlet pipeline, the isolation gas inlet pipeline, and the leakage gas recovery pipeline, it adapts to all operating conditions of the compressor, realizes low-leakage sealing at the shaft end, and performs full-process recovery and treatment on a small amount of leaked CO2 working medium before returning it to the compressor inlet to complete the recycling of the working medium. It is corely divided into three modules: main seal gas supply, isolation gas supply, and leakage gas recovery and reuse, and each module realizes automatic switching according to the compressor operating conditions. The specific working process is as follows:

[0059] (1) Main seal gas supply module

[0060] The core function of the main seal gas is to deliver CO2 with adapted pressure and temperature to the shaft seal structure 10, so as to form a stable seal gas film on the sealing surfaces of the dry gas seal structure 11 and the single-stage carbon ring seal structure 12, and block the outward leakage of high-temperature and high-pressure CO2 working medium in the compression chamber of the compressor. This module adopts a dual gas intake mode of the inlet pipeline 26 and the outlet pipeline 27 of the centrifugal compressor, and completes the switching of gas intake positions according to the compressor operating conditions through the regulation of the valve group and pipeline equipment. The specific operating condition logic is as follows:

[0061] Working conditions of pre-start charging, start-up and shutdown: close the No.2 valve of the return branch, open the No.1 valve of the main seal gas inlet main path. The CO2 working medium enters the main path from the inlet pipeline 26 of the centrifugal compressor, sequentially passes through the purification device 29 to remove impurities, is pressurized by the booster pump unit (the No.3 valve is opened, the No.4 valve is closed, and the booster pump 30 works), is regulated to an adapted temperature by the electric heater 31, and then is sent into the main seal gas inlet duct A on the casing 2 to the shaft seal structure 10 to form a seal gas film;

[0062] Normal operating condition: the compressor outlet is at the 21MPa level of high-temperature and high-pressure CO2, which has the self-pressure supply capability. At this time, the booster pump 30 is closed (the No.3 valve is closed, the No.4 valve is opened to realize the bypass of the booster pump unit), and the No.2 valve of the return branch is opened. The CO2 working medium enters the return branch from the outlet pipeline 27 of the centrifugal compressor, is cooled by the cooler 28 and then merges into the main seal gas inlet main path, then is sent into the duct A after purification and temperature regulation, and the seal gas supply is realized by using the self-pressure of the outlet medium, which greatly reduces the system energy consumption.

[0063] (2) Isolation gas supply module

[0064] The core function of the isolation gas is to block the lubricating oil mist from the side of the gearbox housing 5 from entering the shaft seal structure 10, thus preventing lubricating oil from contaminating the sealing surface, damaging the sealing gas film, and affecting the sealing performance. This module draws air from the main sealing gas inlet and controls its on / off state through valve No. 5. It only operates during the charging, start-up, and shutdown conditions before the compressor starts. Under normal operating conditions, valve No. 5 is closed, and the isolation gas path stops working. During operation, the isolation gas is regulated by valve No. 5 and then sent into the shaft seal structure 10 through the isolation gas inlet channel C, forming an isolation gas curtain between the dry gas sealing structure 11 and the single-stage carbon ring sealing structure 12. This completely isolates the lubricating oil mist from the sealing structure. The working pressure of the isolation gas is precisely controlled at 1.2-1.5 bar, ensuring the isolation effect while avoiding interference with the sealing gas film.

[0065] (iii) Leakage gas recovery and reuse module

[0066] This module is the core recovery unit of the shaft seal system. It operates only under normal compressor operation conditions, with the recovery pressure controlled between 1.5-3.0 bar. It collects, processes, and pressurizes any small amount of CO2 leaking from the shaft seal structure, then returns it to the compressor inlet pipe 26 to achieve recirculation of the working fluid. This completely avoids the waste of working fluid caused by directly venting leaked gas. The specific processing flow is as follows:

[0067] Leakage gas collection: A small amount of CO2 working fluid leaking from the sealing surface of the shaft seal structure is collected through the leakage gas recovery channel B on the casing 2 and enters the leakage gas recovery pipeline;

[0068] Pressure stabilization, buffering, and on / off control: Leaking gas first enters the pressure stabilizing tank 14 to complete pressure buffering and stabilization. When the working fluid pressure in the pressure stabilizing tank 14 is ≥0.15MPa, the main pressurizing valve 16 automatically opens, and the leaking gas enters the subsequent processing stage. If the pressure in the pressure stabilizing tank 14 is >0.4MPa, the bypass vent valve 15 opens to release pressure, and the safety valve in its parallel safety branch provides emergency safety protection to prevent the pressure stabilizing tank from being damaged by overpressure.

[0069] Cooling and pressurization: After opening, the leaking gas first enters the pressurization inlet cooler 17 (water-cooled type, inlet water temperature ≤32℃, inlet water pressure 0.45-0.6MPa) to complete the cooling, and then enters the two-stage compression diaphragm recovery compressor 19 for pressurization after being stabilized by the pressurization inlet pressure tank 18, to adapt to the pressure conditions of the compressor inlet.

[0070] Secondary cooling and reflux: The leaked gas after being pressurized by the recovery compressor enters the pressurization outlet cooler 20 for further cooling, then flows through the pressurization outlet pressure stabilizing tank 21 for stabilization, and finally flows back to the centrifugal compressor inlet pipe 26, re-enters the compression chamber to participate in centrifugal compression, completing the closed-loop recovery of leaked gas.

[0071] Overpressure protection: When the pressure difference between the booster outlet pressure stabilizing tank 21 and the booster inlet pressure stabilizing tank 18 exceeds 9.3MPa, the booster bypass regulating valve 22 will automatically open to form a return flow path for the recovery compressor, thereby preventing equipment damage to the recovery compressor due to overpressure difference and ensuring the stable operation of the recovery unit.

[0072] III. Overall Collaborative Working Principle

[0073] The CO2 centrifugal compressor and shaft sealing system of this application are integrated into one design. The compressor body completes the high-temperature and high-pressure compression of CO2 medium through the centrifugal compression principle. Relying on the structural design of adjustable sealing gaskets and double-reinforced centrifugal impeller, the deformation of components under high temperature of 450℃ is offset, ensuring the optimal dynamic and static clearance and achieving efficient and safe compression under high-temperature conditions. The matching shaft sealing system is based on a combination structure of dry gas seal + single-stage carbon ring seal. Through the gas path design of dual gas intake and working condition control, low leakage sealing at the shaft end is achieved. At the same time, the small amount of leaked CO2 working medium is recovered, treated and refluxed throughout the entire process to complete the recycling of working medium.

[0074] With the two working together, the compressor can stably adapt to the extreme exhaust conditions of 450℃. The CO2 working fluid leakage of the shaft end seal is reduced from the traditional 25~40 NM³ / h to below 2 NM³ / h, and the absolute leakage of the working fluid is reduced by more than 90%. This not only solves the industry problem of balancing compressor efficiency and safety under high temperature conditions, but also fundamentally reduces the amount of CO2 working fluid to be replenished, significantly reducing the operating costs of supercritical CO2 power generation and compressed CO2 energy storage systems, and achieving the integrated goal of high temperature compression, low leakage sealing and working fluid recovery.

Claims

1. A CO2 centrifugal compressor adapted to exhaust gas at 450℃, characterized in that: It includes a volute (1), a casing (2), an air seal (4), a gearbox housing (5), a centrifugal impeller (7), a high-speed shaft (8), and a shaft seal structure (10). The volute (1) is located on one end of the casing (2) and is detachably connected to the casing (2) by fastening bolts. The casing (2) is located outside one end of the gearbox housing (5) and is detachably connected to the gearbox housing (5) by a flange. One end of the high-speed shaft (8) is inserted into the gearbox housing (5) and is located in the gearbox housing (5). The power source inside is connected, and the other end of the high-speed shaft (8) extends to the outside of the gearbox housing (5) and is rotatably connected to the casing (2) through the shaft seal structure (10). The gas seal (4) is embedded in the end of the casing (2) near the volute (1) and is detachably connected to the casing (2) through fastening bolts. The centrifugal impeller (7) is set between the volute (1) and the casing (2) and is fixed to the end of the high-speed shaft (8) through mounting bolts (6). There is a dynamic and static clearance between the centrifugal impeller (7) and the volute (1).

2. A CO2 centrifugal compressor adapted to exhaust at 450℃ according to claim 1, characterized in that: A sealing gasket (3) is provided between the volute (1) and the casing (2). By replacing the sealing gasket (3) of different thicknesses, the size of the dynamic and static clearance between the volute (1) and the centrifugal impeller (7) can be adjusted.

3. A CO2 centrifugal compressor adapted to exhaust at 450℃ according to claim 1, characterized in that: A locking nut (9) for axially limiting the shaft seal structure (10) is provided between the centrifugal impeller (7) and the shaft seal structure (10). The locking nut (9) is sleeved on the high-speed shaft (8) and threadedly connected to the high-speed shaft (8).

4. A CO2 centrifugal compressor adapted to exhaust at 450℃ according to claim 1, characterized in that: A bearing is provided between the high-speed shaft (8) and the gearbox housing (5) and is rotatably connected to the gearbox housing (5) through the bearing.

5. A CO2 centrifugal compressor adapted to exhaust at 450℃ according to claim 1, characterized in that: The centrifugal impeller (7) includes a disc (32), which is fixed to the end of the high-speed shaft (8) by mounting bolts (6). Multiple blades (33) are machined circumferentially at equal intervals on the side of the disc (32) facing the volute (1). A first reinforcing ring (25) and a second reinforcing ring (24) are coaxially mounted from the inside to the outside on the side of the disc (32) facing the high-speed shaft (8).

6. A CO2 centrifugal compressor adapted to exhaust at 450°C according to claim 1, characterized in that: The shaft seal structure (10) includes a dry gas seal structure (11) and a single-stage carbon ring seal structure (12). The casing (2) is machined with a main sealing gas inlet channel (A), a leakage gas recovery channel (B) and an isolation gas inlet channel (C). The main sealing gas inlet channel (A), the leakage gas recovery channel (B) and the isolation gas inlet channel (C) are all connected to the shaft seal structure (10).

7. A shaft sealing system adapted to a CO2 centrifugal compressor with exhaust gas at 450°C as described in claim 6, characterized in that: The shaft sealing system includes a centrifugal compressor inlet pipe (26), a centrifugal compressor outlet pipe (27), a main sealing gas inlet pipe, a leak gas recovery pipe, and an isolation gas inlet pipe. The inlet end of the centrifugal compressor inlet pipe (26) is connected to the CO2 inlet port, the outlet end of the centrifugal compressor inlet pipe (26) is connected to the compressor inlet end, the inlet end of the centrifugal compressor outlet pipe (27) is connected to the compressor exhaust end, and the outlet end of the centrifugal compressor outlet pipe (27) is connected to the CO2 outlet port. The main sealing gas inlet pipeline includes a main sealing gas inlet main line and a return branch line. The inlet end of the main sealing gas inlet main line is connected to the centrifugal compressor inlet pipeline (26). The outlet end of the main sealing gas inlet main line is connected to the main sealing gas inlet channel (A). The inlet end of the return branch line is connected to the centrifugal compressor outlet pipeline (27). The outlet end of the return branch line is connected to the main sealing gas inlet main line. The inlet end of the leak gas recovery pipeline is connected to the leak gas recovery channel (B), and the outlet end of the leak gas recovery pipeline is connected to the centrifugal compressor inlet pipeline (26). The inlet end of the isolation gas inlet pipe is connected to the main sealing gas inlet main line, and the outlet end of the isolation gas inlet pipe is connected to the isolation gas inlet channel (C).

8. A shaft sealing system adapted to a CO2 centrifugal compressor with exhaust gas at 450°C, as described in claim 7, is characterized in that: On the main sealing gas inlet line, a No. 1 valve, a purification device (29), a booster pump unit and an electric heater (31) are connected in series from the inlet end to the outlet end. On the return branch line, a No. 2 valve and a cooler (28) are connected in series from the inlet end to the outlet end. The booster pump unit includes valve No. 3, valve No. 4 and booster pump (30). Valve No. 3 and booster pump (30) are connected in series in the main sealing gas inlet main line, and valve No. 4 is connected in parallel to valve No. 3 and booster pump (30).

9. A shaft sealing system adapted to a CO2 centrifugal compressor with exhaust gas at 450°C, as described in claim 7, is characterized in that: A leak gas recovery unit (13) is connected in series on the leak gas recovery pipeline. The leak gas recovery unit (13) includes a pressure stabilizing tank (14), a bypass vent valve (15), a booster main gas valve (16), a booster inlet cooler (17), a booster inlet pressure stabilizing tank (18), a recovery compressor (19), a booster outlet cooler (20), a booster outlet pressure stabilizing tank (21), and a booster bypass regulating valve (22). The pressure stabilizing tank (14), the booster main gas valve (16), the booster inlet cooler (17), the booster inlet pressure stabilizing tank (18), the recovery compressor (19), the booster outlet cooler (20), and the booster outlet pressure stabilizing tank (21) are connected in series on the leak gas recovery pipeline in the direction of airflow. The pressure stabilizing tank (14) is equipped with a venting bypass, and the bypass venting valve (15) is connected in series on the venting bypass. A safety branch is connected in parallel on the bypass venting valve (15), and a safety valve is connected in series on the safety branch. A regulating bypass is connected in parallel to the recovery compressor (19) and the booster outlet cooler (20). The inlet end of the regulating bypass is connected to the booster inlet pressure stabilizing tank (18), and the outlet end of the regulating bypass is connected to the booster outlet pressure stabilizing tank (21). The booster bypass regulating valve (22) is connected in series on the regulating bypass.

10. A shaft sealing system adapted to a CO2 centrifugal compressor with exhaust gas at 450°C, as described in claim 7, is characterized in that: A valve No. 5 is connected in series on the isolation gas inlet pipe.

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