Centrifugal compressor spindle, water injection cooling system and control method

Abstract

The invention discloses a centrifugal compressor main shaft, a water injection cooling system and a control method. The centrifugal compressor main shaft comprises an impeller side, a sealing side and a gear shaft. The impeller side comprises an impeller and a left shaft body; the left shaft body is connected with the impeller and the gear shaft; the sealing side comprises a first sealing assembly and a right side shaft body, and the right side shaft body is connected with the gear shaft and provided with the first sealing assembly. A first cooling water channel is arranged in the impeller side, a first drainage flow channel is arranged on the left shaft body, the first cooling water channel penetrates through the impeller and the left shaft body, and cooling water is drained through the first drainage flow channel after passing through the first cooling water channel; a second cooling water channel is arranged in the sealing side, the right shaft body is provided with a second drainage flow channel, the second cooling water channel penetrates through the first sealing assembly and the right shaft body, and cooling water is drained through the second drainage flow channel after passing through the second cooling water channel. In the running process of the compressor, efficient cooling of the thrust balance disc can be achieved, and the stability of a sealing gap is kept.

Description

Technical Field

[0001] The present invention belongs to the technical field of centrifugal compressors, and particularly relates to a main shaft of a centrifugal compressor, a water injection cooling system and a control method. Background Art

[0002] In the design of a supercritical carbon dioxide (SCO2) centrifugal compressor, as a fluid with special physical properties, supercritical carbon dioxide usually operates under relatively high pressure and temperature conditions. The sealing system plays a crucial role in this equipment, and its main purpose is to prevent gas from leaking from the inside of the compressor to the external environment to ensure the working safety and efficiency of the equipment.

[0003] However, in the actual application process, the operation of the thrust balance disk seal often faces the problem of too small a sealing gap, which may lead to equipment wear and even damage. The fundamental reason is that the thrust balance disk seal is affected by thermal expansion. In the high-temperature and high-pressure working environment of the centrifugal compressor, the sealing material will expand due to the increase in temperature, resulting in a gradual reduction in the sealing gap between it and the main shaft. This expansion effect exacerbates the friction between the thrust balance disk seal and the main shaft, which may in turn cause wear and leakage at the sealing part, and even lead to compressor failure. In addition, during the long-term operation of the compressor, the overheating problem of the impeller also needs to be solved urgently.

[0004] To solve the above problems, the existing technologies generally choose materials with a relatively small coefficient of thermal expansion to manufacture the thrust balance disk, and at the same time adopt a multi-stage sealing structure to reduce the expansion problem caused by temperature changes, share the axial force between the thrust balance disk and the main shaft, and delay wear. Also, for example, the patent application for invention CN112253491A discloses a multi-stage centrifugal supercritical carbon dioxide compressor, which includes a casing, a main shaft, an intermediate balance disk, a low-pressure stage impeller, a high-pressure stage impeller and an end balance disk. The main shaft is rotatably arranged in the casing, and the main shaft has a high-pressure end and a low-pressure end along the axial direction; the intermediate balance disk is sleeved on the main shaft, the low-pressure stage impeller is sleeved on the main shaft and is located on the side of the intermediate balance disk facing the low-pressure end. The low-pressure stage impeller includes a first-stage impeller and a second-stage impeller distributed along the axial direction of the main shaft. The high-pressure stage impeller is sleeved on the main shaft and is located on the side of the intermediate balance disk facing the high-pressure end. The second-stage impeller includes a third-stage impeller and a fourth-stage impeller distributed along the axial direction of the main shaft. The end balance disk is sleeved on the main shaft and is located at the air inlet of the fourth-stage impeller. However, it is not only limited by material limitations, but also the multi-stage sealing structure still cannot effectively avoid the sealing damage caused by temperature rise, and the complex structure also increases the manufacturing cost and maintenance difficulty. In addition, the cooling system of the existing supercritical carbon dioxide centrifugal compressor has poor dynamic response and often cannot respond immediately during the start-up and shutdown processes of the compressor, resulting in too large a temperature difference during the initial start-up and affecting the sealing performance.

[0005] Therefore, how to achieve efficient cooling during the operation of the compressor and reduce the influence of overheating and thermal expansion on the seal clearance is an urgent problem to be solved by those skilled in the art. Summary of the Invention

[0006] In view of the defects existing in the above-mentioned prior art, the present invention provides a main shaft of a centrifugal compressor, a water injection cooling system and a control method. It can achieve efficient cooling of the thrust balance disk during the operation of the compressor and maintain the stability of the seal clearance.

[0007] In a first aspect, the present invention provides a main shaft of a centrifugal compressor, which specifically includes: an impeller side, a seal side and a gear shaft; the impeller side includes an impeller and a left shaft body, the left end of the left shaft body is connected to the impeller, and the right end of the left shaft body is connected to the gear shaft; the seal side includes a first seal assembly and a right shaft body, the left end of the right shaft body is connected to the gear shaft, and a first seal assembly is arranged at the right end of the right shaft body; A first cooling water channel is arranged inside the impeller side, and a first drainage channel is arranged at the right edge of the left shaft body. The first cooling water channel penetrates through the impeller and the left shaft body, and the cooling water is discharged through the first drainage channel after passing through the first cooling water channel; A second cooling water channel is arranged inside the seal side, and a second drainage channel is arranged at the left edge of the right shaft body. The second cooling water channel penetrates through the first seal assembly and the right shaft body, and the cooling water is discharged through the second drainage channel after passing through the second cooling water channel.

[0008] Furthermore, the first cooling water channel includes a first water inlet channel and a first cooling channel. The first water inlet channel penetrates through the impeller and is communicated with the first cooling channel arranged inside the left shaft body, and the first cooling channel is communicated with the first drainage channel; The second cooling water channel includes a second water inlet channel and a second cooling channel. The second water inlet channel penetrates through the first seal assembly and is communicated with the second cooling channel arranged inside the right shaft body, and the second cooling channel is communicated with the second drainage channel; The inner diameter of the first cooling channel is not less than the inner diameter of the second cooling channel.

[0009] Furthermore, the ratio of the inner diameter of the first cooling channel to the inner diameter of the second cooling channel is 1.2 - 2.

[0010] Furthermore, the first water inlet channel includes a spiral water channel and a first water injection channel. The first water injection channel is in a cylindrical shape, the first water injection channel penetrates through the impeller, and the spiral water channel is wound around the outside of the first water injection channel and is arranged inside the left shaft body; The cooling water enters and passes through the first water injection channel and the spiral water channel respectively, and flows to the first cooling channel.

[0011] Further, the spiral water channel includes at least two variable pitch spiral water channels. Each variable pitch spiral water channel is a multi-spiral ring structure, including an inlet ring, a support ring, and an outlet ring that are connected in sequence. Cooling water enters the variable pitch spiral water channel from the water inlet of the inlet ring, flows through the support ring, and then flows to the first cooling flow channel from the water outlet of the outlet ring; The water inlets of the variable pitch spiral water channels are equally angularly distributed in the cross-section of the first water inlet flow channel, and the support rings of the variable pitch spiral water channels are arranged in a cross and equally spaced manner; Along the flow direction of the cooling water, the pitch of the spiral rings in each variable pitch spiral water channel increases in equal proportion; In adjacent spiral rings, the pitch ratio of the rear spiral ring to the front spiral ring is 1.1 - 1.5.

[0012] Further, the second water inlet flow channel includes a toothed water channel and a second water injection channel. The second water injection channel penetrates the first sealing component from the central position of the first sealing component, and the toothed water channel penetrates the first sealing component through the edge part of the first sealing component; The toothed water channel and the second water injection channel form an annular second water inlet flow channel. Cooling water enters and passes through the second water injection channel and the toothed water channel respectively, and then flows to the second cooling flow channel.

[0013] Further, the toothed water channel includes a water inlet section, a toothed cooling section, and a water outlet section that are connected in sequence. The toothed cooling section is arranged inside the edge part of the first sealing component; The inner wall of the toothed cooling section is provided with a number of racks, and the distance between adjacent racks is consistent.

[0014] In a second aspect, the present invention provides a water injection cooling system for the main shaft of a centrifugal compressor, including: the above-mentioned main shaft of the centrifugal compressor, a first electric valve, a second electric valve, a first circulating water pump, a second circulating water pump, a circulating cooling water tank, and a monitoring unit; The circulating cooling water tank, the first circulating water pump, the first electric valve, and the impeller side form a first cooling loop. Cooling water returns to the circulating cooling water tank after passing through the first circulating water pump, the first electric valve, and the first cooling water channel from the circulating cooling water tank; The circulating cooling water tank, the second circulating water pump, the second electric valve, and the sealing side form a second cooling loop. Cooling water returns to the circulating cooling water tank after passing through the second circulating water pump, the second electric valve, and the second cooling water channel from the circulating cooling water tank; The monitoring unit is signal-connected to the first electric valve and the second electric valve, and is used to monitor and adjust the volume flow rate of the cooling water in the first cooling loop and the second cooling loop.

[0015] Further, the monitoring unit is also used to monitor the inlet water temperature of the first cooling water channel, the outlet water temperature of the first drainage flow channel, the inlet gas temperature of the compressor, and the outlet gas temperature of the compressor; Adjusting the volume flow rate of the cooling water in the first cooling loop includes: Determine the optimal heat generation power on the impeller side and the heat absorption power of the cooling water according to the inlet temperature of the first cooling water channel, the outlet temperature of the first drainage channel, the inlet gas temperature of the compressor, and the optimal outlet gas temperature of the compressor. Determine the optimal cooling water volume flow rate of the first cooling loop according to the optimal heat generation power on the impeller side and the heat absorption power of the cooling water. According to the real-time temperature of the outlet gas of the compressor and the optimal outlet gas temperature of the compressor, and in combination with the optimal cooling water volume flow rate of the first cooling loop and the mass flow rate of the cooling water on the impeller side when the opening of the first electric valve is maximum, determine the current opening of the first electric valve and control the first electric valve.

[0016] Further, the optimal cooling water volume flow rate of the first cooling loop satisfies the following relationship:

[0017] Wherein, is the mass flow rate of the compressor gas, is the specific heat capacity at constant pressure of the gas, is the optimal outlet gas temperature of the compressor, is the inlet gas temperature of the compressor, is the specific heat capacity at constant pressure of the cooling water, is the outlet temperature of the first drainage channel, is the inlet temperature of the first cooling water channel, is the optimal cooling water volume flow rate of the first cooling loop, is the density of the cooling water.

[0018] Further, according to the real-time temperature of the outlet gas of the compressor and the optimal outlet gas temperature of the compressor, and in combination with the optimal cooling water volume flow rate of the first cooling loop and the mass flow rate of the cooling water on the impeller side when the opening of the first electric valve is maximum, determining the current opening of the first electric valve includes: Determine the optimal opening of the first electric valve according to the optimal cooling water volume flow rate of the first cooling loop; Determine the temperature change of the outlet gas of the compressor according to the current temperature of the outlet gas of the compressor and the optimal outlet gas temperature of the compressor; Determine the current opening of the first electric valve according to the temperature change of the outlet gas of the compressor and the optimal opening of the first electric valve.

[0019] Wherein, the optimal opening of the first electric valve satisfies the following relationship:

[0020] Wherein, is the opening of the first electric valve, is the mass flow rate of the cooling water on the impeller side when the opening of the first electric valve is the largest, the mass flow rate of the compressor gas, is the specific heat capacity of the gas at constant pressure, is the specific heat capacity of the gas at constant pressure, is the optimal temperature of the gas at the compressor outlet, is the temperature of the gas at the compressor inlet, is the specific heat capacity of the cooling water at constant pressure, is the outlet temperature of the water in the first drainage channel, is the inlet temperature of the water in the first cooling water channel.

[0021] The current opening of the first electric valve satisfies the following relationship:

[0022] wherein, is the current opening of the first electric valve, is the current temperature of the gas at the compressor outlet, is the upper limit of the temperature of the gas at the compressor outlet.

[0023] Furthermore, the monitoring unit is also used to monitor the outlet temperature of the second drainage channel and the inlet temperature of the second cooling water channel, and adjust the volume flow rate of the cooling water in the second cooling loop, specifically including: Conduct a force analysis on the impeller side to determine the frictional heat power on the seal side; Based on the outlet temperature of the first drainage channel and the inlet temperature of the second cooling water channel, and combined with the frictional heat power on the seal side, determine the heat power to be absorbed; Based on the optimal expansion gap of the thrust balance disk, and combined with the heat power to be absorbed, determine the mass flow rate of the cooling water in the second cooling loop; Based on the mass flow rate of the cooling water in the second cooling loop and the mass flow rate of the cooling water when the second electric valve is at the maximum opening, give the opening of the second electric valve and control the second electric valve.

[0024] Furthermore, the mass flow rate of the cooling water in the second cooling loop satisfies the following relationship:

[0025] In the formula, m2 is the mass flow rate of the cooling water in the second cooling loop, α is the thermal expansion coefficient of the sealing material of the thrust balance disk, F n is the radial positive pressure that generates friction force on the thrust balance disk, D is the diameter of the thrust balance disk, n is the rotational speed of the thrust balance disk, T3 is the inlet temperature of the second cooling water channel, δ maxis the maximum allowable expansion gap of the sealing material of the thrust balance disk, δ0 is the initial design gap of the sealing material of the thrust balance disk, T4 is the maximum outlet water temperature corresponding to the maximum allowable expansion gap of the second drainage channel, B is the multiple of the best expansion gap of the sealing material of the thrust balance disk, and B < 1.

[0026] Further, the opening degree of the second electric valve satisfies the following relationship:

[0027] In the formula, K2 is the opening degree of the second electric valve, A is the effective pressure-bearing area of the impeller, p1 and p2 are the outlet pressure of the compressor and the inlet pressure of the compressor respectively, and m 2,max is the cooling water mass flow rate of the second cooling loop when the opening degree of the second electric valve is the largest, that is, the maximum cooling water mass flow rate of the second cooling loop.

[0028] Thirdly, the present invention also provides a control method for water injection cooling of the main shaft of a centrifugal compressor. Using the above water injection cooling system, it specifically includes the following steps: Set the valve opening degree of the first electric valve, turn on the first circulating water pump, and the cooling water circulates from the circulating cooling water tank through the first circulating water pump, the first electric valve and the first cooling water channel to cool the impeller side of the main shaft of the centrifugal compressor, and then return to the circulating cooling water tank. The monitoring unit monitors and controls the opening degree of the second electric valve to adjust the volume flow rate of the cooling water; Set the valve opening degree of the second electric valve, turn on the second circulating water pump, and the cooling water circulates from the circulating cooling water tank through the second circulating water pump, the second electric valve and the second cooling water channel to cool the sealing side of the main shaft of the centrifugal compressor, and then return to the circulating cooling water tank. The monitoring unit monitors and controls the opening degree of the second electric valve to adjust the volume flow rate of the cooling water.

[0029] The centrifugal compressor main shaft, water injection cooling system and control method provided by the present invention have at least the following beneficial effects: (1) Independent cooling water channels are respectively arranged inside the impeller side and the sealing side of the main shaft for impeller side cooling and sealing side cooling respectively, realizing the integrated design of partition precise temperature control water injection cooling and sealing structure. Combining water injection cooling with the sealing structure enables the thrust balance disk to be continuously and stably cooled during operation, avoiding the problem of unstable sealing gap caused by thermal expansion.

[0030] (2) The impeller side adopts a variable pitch spiral water channel to enhance the heat transfer efficiency through turbulence; the carbon ring sealing side adopts an equidistant toothed channel water channel to effectively increase the heat transfer area.

[0031] (3) Automatically adjust the flow rate of the cooling water according to the temperature change and load condition inside the compressor, control the temperature of the impeller and the thrust balance disk, maintain the stability of the clearance between the seal of the thrust balance disk and the main shaft, and avoid frictional damage caused by too small a seal clearance. Compared with the traditional external cooling system and fixed flow rate system, the main shaft water injection cooling and control strategy of the present invention is more targeted and efficient, can achieve rapid and precise temperature adjustment under different working conditions, and prevent seal failures. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 It is a schematic structural diagram of a main shaft of a centrifugal compressor provided by the present invention; Figure 2 It is a schematic structural diagram of a spiral water channel of a certain embodiment provided by the present invention; Figure 3 It is a schematic cross-sectional view at the first drainage channel of a certain embodiment provided by the present invention; Figure 4 It is a schematic cross-sectional view at the second drainage channel of a certain embodiment provided by the present invention; Figure 5 It is a schematic diagram of a main shaft water injection cooling system of a centrifugal compressor provided by the present invention; Figure 6 It is a flow chart of a main shaft water injection cooling control method of a centrifugal compressor provided by the present invention.

[0033] DESCRIPTION OF THE REFERENCE NUMERALS: 1 - impeller side, 11 - impeller, 12 - left shaft body, 13 - first drainage channel, 14 - first water inlet channel, 15 - first cooling channel, 16 - spiral water channel, 161 - inlet ring, 162 - support ring, 163 - outlet ring, 17 - first water injection channel, 2 - seal side, 201 - first outlet, 202 - second outlet, 21 - first seal, 22 - right shaft body, 23 - second drainage channel, 24 - second water inlet channel, 25 - second cooling channel, 26 - toothed water channel, 27 - second water injection channel, 2 - seal side, 3 - gear shaft, 411 - first annular housing, 412 - second annular housing, 421 - first pipe body, 422 - second pipe body, 100 - main shaft of centrifugal compressor, 200 - first electric valve, 300 - second electric valve, 400 - first circulating water pump, 500 - second circulating water pump, 600 - circulating cooling water tank, 700 - control unit. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0034] To better understand the above technical solutions, the following will describe the above technical solutions in detail in conjunction with the accompanying drawings of the specification and specific embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0035] The terms used in the embodiments of the present invention are only for the purpose of describing specific embodiments, and are not intended to limit the present invention. The singular forms "a", "the" and "said" used in the embodiments of the present invention and the appended claims are also intended to include the plural forms, unless the context clearly indicates otherwise. "Plural" generally includes at least two.

[0036] It should also be noted that the term "comprising", "including" or any other variant thereof is intended to cover a non-exclusive inclusion, so that a commodity or device including a series of elements not only includes those elements, but also includes other elements not explicitly listed, or also includes elements inherent to such commodity or device. Without further limitation, the element defined by the statement "including one..." does not exclude the existence of another identical element in the commodity or device including the said element.

[0037] As Figure 1 shown, the present invention provides a main shaft of a centrifugal compressor, which specifically may include: an impeller side 1, a seal side 2 and a gear shaft 3; the impeller side 1 includes an impeller 11 and a left shaft body 12, the left end of the left shaft body 12 is connected to the impeller 11, and the right end of the left shaft body 12 is connected to the gear shaft 3; the seal side 2 includes a first seal assembly 21 and a right shaft body 22, the left end of the right shaft body 22 is connected to the gear shaft 3, and a first seal assembly 21 is arranged at the right end of the right shaft body 22; A first cooling water channel is arranged inside the impeller side 1, and a first drainage channel 13 is arranged at the right edge of the left shaft body 12. The first cooling water channel penetrates through the impeller 11 and the left shaft body 12, and the cooling water is discharged through the first drainage channel 13 after passing through the first cooling water channel; A second cooling water channel is arranged inside the seal side 2, and a second drainage channel 23 is arranged at the left edge of the right shaft body 22. The second cooling water channel penetrates through the first seal assembly 21 and the right shaft body 22, and the cooling water is discharged through the second drainage channel 23 after passing through the second cooling water channel. Preferably, the first cooling water channel and the second cooling water channel are coaxially arranged, which can ensure high structural stability during the operation of the main shaft and reduce energy loss. The first seal assembly includes a thrust balance disk.

[0038] The cooling water channel is arranged inside the main shaft, which features a compact design, saves space, reduces the overall weight of the compressor, and lowers the complexity and cost of the cooling system. By injecting water from the inside for cooling, the water flow directly acts on the thrust balance disk sealing area and the impeller, effectively reducing the temperature at the sealing area and the impeller, and avoiding problems such as thermal expansion caused by temperature rise. By separately arranging independent first and second cooling water channels inside the impeller side and the sealing side respectively, impeller side cooling and sealing side cooling can be carried out respectively to achieve zonal temperature control and improve the utilization rate of energy and water resources. The second cooling water channel is arranged inside the sealing side, combining water injection cooling with the sealing structure, enabling the thrust balance disk to be continuously and stably cooled during operation, and avoiding the problem of unstable sealing clearance caused by thermal expansion.

[0039] As Figure 1 shown, the first cooling water channel includes a first water inlet flow channel 14 and a first cooling flow channel 15. The first water inlet flow channel 14 penetrates through the impeller 11 and is connected to the first cooling flow channel 15 arranged inside the left shaft body. The first cooling flow channel 15 is connected to the first drainage flow channel 13. Through the connection of the first water inlet flow channel and the first cooling flow channel, the circulation cooling of the cooling water from the inside of the impeller side can be realized, improving the cooling effect on the impeller side. The second cooling water channel includes a second water inlet flow channel 24 and a second cooling flow channel 25. The second water inlet flow channel 24 penetrates through the first sealing assembly 21 and is connected to the second cooling flow channel arranged inside the right shaft body 25. The second cooling flow channel 25 is connected to the second drainage flow channel 23. Through the connection of the second water inlet flow channel and the second cooling flow channel, the circulation cooling of the cooling water from the inside of the sealing side can be realized, improving the cooling effect on the sealing side.

[0040] In a supercritical carbon dioxide centrifugal compressor, the main shaft size on the impeller side is relatively large, mainly to meet the mechanical strength and stability requirements under high-pressure and high-density working conditions. The high-density characteristic of supercritical carbon dioxide causes the impeller to bear large centrifugal and axial forces during operation. A larger main shaft size can provide higher bending and torsional strength, reduce deformation and fatigue damage, thereby improving the reliability of the equipment. Based on this, in the embodiment of the present invention, by setting the inner diameter of the first cooling flow channel to be not less than that of the second cooling flow channel, the heat transfer area can be relatively increased, the heat transfer efficiency on the impeller side can be improved, the temperature on the impeller side can be effectively reduced, the influence of thermal expansion on the impeller side can be reduced, and deformation and stress concentration caused by high temperature can be avoided, thereby improving the mechanical strength and stability of the impeller side and extending the service life.

[0041] Preferably, the inner diameter ratio of the first cooling flow channel 15 to the second cooling flow channel 25 is 1.2 - 2.

[0042] As Figures 1 - 2As shown, the first water inlet channel 14 is provided in the part where the left shaft penetrates the impeller, that is, the first water inlet channel 14 is arranged inside the end where the left shaft is fixed to the impeller. The first water inlet channel 14 includes a spiral water channel 16 and a first water injection channel 17. The first water injection channel is cylindrical and penetrates the impeller. The spiral water channel 16 is wound around the outside of the first water injection channel 17 and is arranged inside the left shaft. Cooling water enters and passes through the first water injection channel 17 and the spiral water channel 16 respectively, and flows to the first cooling channel 15. By setting the spiral water channel, the path of the cooling water can be increased, the heat exchange area can be increased, and thus the cooling effect on the impeller can be improved. The first water injection channel can exchange heat with the cooling water in the spiral water channel to improve the heat exchange effect of the spiral water channel, and can also directly cool the impeller, thereby realizing the multi-stage cooperative cooling of the impeller (the first-stage cooling of the impeller by the spiral water channel, the second-stage cooling of the impeller by the first water injection channel, and the third-stage cooling of the impeller indirectly on the basis of the cooling of the impeller by the first water injection channel), ensuring that the temperature on the impeller side is within the safe operating range.

[0043] In the actual application scenario, the spiral water channel can include at least two variable pitch spiral water channels. Each variable pitch spiral water channel is a multi-spiral ring structure, including an inlet ring 161, a support ring 162, and an outlet ring 163 that are connected in sequence. Cooling water enters the variable pitch spiral water channel from the water inlet of the inlet ring, and after passing through the support ring, flows to the first cooling channel from the water outlet of the outlet ring. The water inlets of each variable pitch spiral water channel are equally angularly distributed in the cross-section of the first water inlet channel, and the support rings of each variable pitch spiral water channel are arranged crosswise and equidistantly.

[0044] By setting multiple variable pitch spiral water channels, the heat exchange efficiency can be improved and the cooling effect of the variable pitch spiral water channels on the impeller can be improved without increasing the size of the variable pitch spiral water channels. And the equally angular distribution design can ensure the best spacing between each variable pitch spiral water channel, so that each variable pitch spiral water channel can achieve a better cooling effect. Among them, along the flow direction of the cooling water, the pitch of the spiral rings in each variable pitch spiral water channel increases in equal proportion, so as to achieve the effect of variable pitch. And increasing the pitch along the flow direction of the cooling water can meet the structural characteristics of the impeller being narrow in the front and wide in the back, match the gradient change of its heat generation area, and thus better realize the cooling of the impeller.

[0045] In adjacent spiral rings, the pitch ratio of the rear spiral ring to the front spiral ring is 1.1 - 1.5. The spiral rings with a smaller pitch near the left end of the impeller are arranged more closely and have a larger heat exchange area, which can quickly exchange heat with the impeller at the initial stage of cooling water injection. As the cooling water flows, the pitch between the spiral rings increases and the arrangement becomes gradually sparse, which is conducive to the rapid outflow of the cooled cooling water and entering the first cooling channel, improving the heat exchange efficiency and achieving the purpose of quickly cooling the impeller.

[0046] As Figure 1As shown in the figure, the second inlet water flow channel includes a toothed water channel 26 and a second water injection channel 27. The second water injection channel 27 penetrates through the first sealing assembly from the central position of the first sealing assembly, and the toothed water channel 27 penetrates through the first sealing assembly through the edge part of the first sealing assembly; the toothed water channel 26 and the second water injection channel 27 form an annular second inlet water flow channel, and the cooling water enters and passes through the second water injection channel 27 and the toothed water channel 26 respectively, and flows to the second cooling flow channel 25. By setting the toothed water channel, the cooling of the outer edge of the thrust balance disc can be realized, and the structure of the toothed water channel can also further increase the heat exchange area of the cooling water, thereby improving the cooling effect on the sealing structure; while the second water injection channel can realize the cooling of the toothed water channel, it can also complete the cooling of the thrust balance disc, thereby improving the cooling effect on the first sealing assembly and avoiding the problem of thermal expansion of the sealing structure.

[0047] Among them, the toothed water channel can include a water inlet section, a toothed cooling section and a water outlet section that are connected in sequence. The toothed cooling section is arranged inside the edge part of the first sealing assembly; a number of racks are provided on the inner wall of the toothed cooling section, and the distance between adjacent racks is the same.

[0048] Thus, it can be ensured that the flow velocity of the cooling water passing through the racks is the same, avoiding the situation where part of the cooling surface fails to achieve heat exchange due to stall. The design of the rack cooling section can effectively increase the heat exchange area and ensure a good cooling effect at the thrust balance disc; among them, the racks on the same inner wall in the toothed cooling section can be separated or continuous. The separated type means that the racks are arranged in a ring on the inner wall, and the continuous type means that the racks are arranged in a spiral ring on the inner wall. In the actual application scenario, the rack includes a back side and an inclined side. The back side is perpendicular to the inner wall, and the inclined side inclines from the inner wall towards the flowing direction of the cooling water, so as to obtain the effects of guiding the flow and increasing the cooling path. In addition, a plurality of water inlet cooling channels and water outlet cooling channels can be respectively provided in the water inlet section and the water outlet section, and the toothed cooling section is an annular cavity and is connected to the water inlet cooling channels and the water outlet cooling channels.

[0049] As Figure 3 shown, in this embodiment, the first drainage flow channel 13 of the left shaft body discharges the cooling water through the first drainage flow pipe. Specifically, the first drainage flow pipe includes a first annular housing 411 and a first pipe body 421 communicating with the first annular housing 411. The first annular housing 411 is sleeved on the left shaft body, and the first outlet 201 of the first cooling flow channel 15 is located inside the first annular housing 411. The structure of the first drainage flow pipe cooperating with the left shaft body can enable the cooling water in the first cooling flow channel 15 to enter the first annular housing 411 through the first outlet 201 when the main shaft of the centrifugal compressor rotates, and finally realize the function of discharging the cooling water through the first drainage flow channel 13 communicating with the inside of the first annular housing 411. As Figure 4As shown in the figure, the second drainage channel 23 of the right shaft body discharges the cooling water through the second drainage pipe. Specifically, the second drainage pipe includes a second annular housing 412 and a second pipe body 422 communicating with the second annular housing 412. The second annular housing 412 is sleeved on the right shaft body, and the second outlet 202 of the second cooling channel 25 is located inside the second annular housing 412. The structure of the second drainage pipe cooperating with the right shaft body enables the cooling water in the second cooling channel 25 to enter the second annular housing 412 through the second outlet 202 when the main shaft of the centrifugal compressor rotates, and finally discharges the cooling water through the second drainage channel 23 communicating with the inside of the second annular housing 412, realizing the function of discharging the cooling water.

[0050] Furthermore, multiple first drainage channels and multiple second drainage channels can be provided. The multiple first drainage channels and multiple second drainage channels are respectively arranged perpendicular to the axes of the left shaft body and the right shaft body, and the multiple first drainage channels and multiple second drainage channels are respectively arranged at equal intervals along the circumferences of the left shaft body and the right shaft body, which can ensure better drainage effects of the first drainage channel and the second drainage channel, and at the same time avoid the influence of the centrifugal force of the drainage channel on the overall rotation of the main shaft when discharging the cooling water.

[0051] The traditional cooling method of centrifugal compressors often requires complex external cooling channels and equipment. The main shaft water injection cooling in this embodiment realizes cooling through the cooling channels inside the main shaft. Compared with the traditional cooling system, the main shaft water injection cooling in this embodiment can adjust the temperature of the sealing area more quickly. The sealing area refers to the area where the housing of the compressor forms a seal for the main shaft. Further, on the basis of cooling the main shaft, this embodiment can better cool and exchange heat in the areas where the impeller and the thrust balance disk with more concentrated temperature are located, ensuring that the seal always maintains an ideal working state when the compressor starts, stops or the load changes, and avoiding the seal failure problem caused by too large temperature difference or instantaneous load change.

[0052] In high-temperature and high-pressure environments, the stability of sealing performance is crucial. The main shaft water injection cooling solution can effectively avoid the negative impact of too high temperature on the sealing performance through real-time cooling. Especially during long-term high-load operation, it can maintain higher sealing reliability.

[0053] In addition, the main shaft of the centrifugal compressor of the present invention is not only applicable to SCO2 centrifugal compressors, but can also be extended to other rotating mechanical equipment in high-temperature and high-pressure environments, such as gas turbines, steam compressors, etc., and has strong adaptability and broad application prospects.

[0054] The operating principle of the main shaft of the centrifugal compressor of the present invention is as follows: During the long-term operation of the centrifugal compressor, due to factors such as gas compression, component friction, and motor heating, heat is generated, and problems such as overheating of the impeller and expansion of the seal will occur.

[0055] After the main shaft of the centrifugal compressor of the present invention operates, cooling water can be injected into the cooling water channel on the impeller side. Specifically, cooling water is respectively injected into the first water injection flow channel and the spiral water channel inside the left shaft body; the spiral water channel has a large heat exchange area, and the cooling water therein exchanges heat fully with the impeller, taking away the heat generated by the rotation of the impeller; at the same time, the cooling water in the first water injection flow channel exchanges heat with the heated cooling water in the spiral water channel, further improving the cooling effect of the impeller. The cooling water in the first water injection flow channel and the spiral water channel converges in the first cooling flow channel, exchanges heat with the left shaft body, and then is discharged through the first drainage flow channel, realizing the cooling of the impeller side and avoiding overheating of the impeller.

[0056] Independent of the cooling water channel on the impeller side, cooling water can also be injected into the cooling water channel on the seal side. Specifically, water is respectively injected into the second water injection flow channel and the toothed water channel inside the right shaft body; the toothed water channel is an annular cavity arranged according to the thrust balance disk and has a large heat exchange area, and the cooling water therein exchanges heat fully with the first seal assembly to cool the thrust balance disk; the cooling water in the second water injection flow channel cools the right shaft body. The cooling water in the second water injection flow channel and the toothed water channel converges in the second cooling flow channel, further exchanges heat with the right shaft body, and is discharged through the second drainage flow channel, realizing the cooling of the seal side and ensuring the stability of the seal clearance.

[0057] As Figure 5 shown, the present invention provides a water injection cooling system for the main shaft of a centrifugal compressor, which may include: the above-mentioned main shaft 100 of the centrifugal compressor, a first electric valve 200, a second electric valve 300, a first circulating water pump 400, a second circulating water pump 500, a circulating cooling water tank 600 and a monitoring unit 700; The circulating cooling water tank, the first circulating water pump, the first electric valve and the impeller side form a first cooling loop, and the cooling water returns to the circulating cooling water tank after passing through the first circulating water pump, the first electric valve and the first cooling water channel from the circulating cooling water tank; The circulating cooling water tank, the second circulating water pump, the second electric valve and the seal side form a second cooling loop, and the cooling water returns to the circulating cooling water tank after passing through the second circulating water pump, the second electric valve and the second cooling water channel from the circulating cooling water tank; The monitoring unit is signal-connected to the first electric valve and the second electric valve, and is used to monitor and adjust the volume flow rate of the cooling water in the first cooling loop and the second cooling loop.

[0058] The monitoring unit is also used to monitor the inlet temperature of the first cooling water channel, the outlet temperature of the first drainage flow channel, the inlet gas temperature of the compressor, and the outlet gas temperature of the compressor; Adjusting the volume flow rate of the cooling water in the first cooling loop includes: S1: Determine the optimal heat generation power on the impeller side and the heat absorption power of the cooling water based on the inlet temperature of the first cooling water channel, the outlet temperature of the first drainage channel, the inlet gas temperature of the compressor, and the optimal outlet gas temperature of the compressor; S2: Determine the optimal cooling water volume flow rate of the first cooling loop based on the optimal heat generation power on the impeller side and the heat absorption power of the cooling water; S3: Based on the real-time temperature of the outlet gas of the compressor and the optimal outlet gas temperature of the compressor, and in combination with the optimal cooling water volume flow rate of the first cooling loop and the cooling water mass flow rate on the impeller side when the opening of the first electric valve is maximum, determine the current opening of the first electric valve and control the first electric valve.

[0059] In one embodiment, adjusting the cooling water volume flow rate of the first cooling loop is achieved by controlling the valve opening of the first electric valve based on the analysis of the inlet temperature of the first cooling water channel, the outlet temperature of the first drainage channel, the inlet gas temperature of the compressor, and the outlet gas temperature of the compressor.

[0060] In S1, to determine the optimal heat generation power of the impeller, the following relationship is satisfied:

[0061] Wherein, is the heat generation power of the impeller, is the mass flow rate of the compressor gas, is the specific heat capacity at constant pressure of the gas, is the optimal outlet gas temperature of the compressor, is the inlet gas temperature of the compressor; To determine the heat absorption power of the cooling water on the impeller side, the following relationship is satisfied:

[0062] Wherein, is the heat absorption power of the cooling water, m1 is the mass flow rate of the cooling water on the impeller side of the compressor, is the specific heat capacity at constant pressure of the cooling water, is the outlet temperature of the first drainage channel, is the inlet temperature of the first cooling water channel; In S2, when determining the optimal cooling water volume flow rate of the first cooling loop, when the cooling water dissipates heat to the impeller side, it is necessary to satisfy , determine the optimal lower limit of the mass flow rate of the cooling water on the impeller side, and obtain the optimal cooling water volume flow rate corresponding to the impeller side, that is, the optimal cooling water volume flow rate of the first cooling loop, which satisfies the following relationship:

[0063] Wherein, m1 is the mass flow rate of the cooling water on the impeller side of the compressor, is the mass flow rate of the compressor gas, is the specific heat capacity at constant pressure of the gas, is the temperature of the gas at the compressor outlet, is the temperature of the gas at the compressor inlet, is the specific heat capacity at constant pressure of the cooling water, is the outlet temperature of the first drainage channel, is the inlet temperature of the first cooling water channel, is the optimal cooling water volume flow rate of the first cooling loop, is the density of the cooling water; In S3, according to the real-time temperature of the gas at the compressor outlet and the optimal temperature of the gas at the compressor outlet, and in combination with the optimal cooling water volume flow rate of the first cooling loop and the mass flow rate of the cooling water on the impeller side when the opening of the first electric valve is the largest, determine the current opening of the first electric valve, including: Determine the optimal opening of the first electric valve according to the optimal cooling water volume flow rate of the first cooling loop; Determine the temperature change of the gas at the compressor outlet according to the current temperature of the gas at the compressor outlet and the optimal temperature of the gas at the compressor outlet; Determine the current opening of the first electric valve according to the temperature change of the gas at the compressor outlet and the optimal opening of the first electric valve.

[0064] Among them, the optimal opening of the first electric valve satisfies the following relationship:

[0065] In the formula, is the opening of the first electric valve, is the mass flow rate of the cooling water on the impeller side when the opening of the first electric valve is the largest, is the mass flow rate of the compressor gas, is the specific heat capacity at constant pressure of the gas, is the optimal temperature of the gas at the compressor outlet, is the temperature of the gas at the compressor inlet, is the specific heat capacity at constant pressure of the cooling water, is the outlet temperature of the first drainage channel, is the inlet temperature of the first cooling water channel.

[0066] The current opening of the first electric valve satisfies the following relationship:

[0067] Among them, is the current opening of the first electric valve, is the current temperature of the gas at the compressor outlet, is the upper limit of the temperature of the gas at the compressor outlet.

[0068] In addition, the monitoring unit is also used to monitor the outlet temperature of the second drainage channel and the inlet temperature of the second cooling water channel, and to control the valve opening of the second electric valve based on the analysis of the outlet temperature of the second drainage channel and the inlet temperature of the second cooling water channel. Specifically, it includes: Perform a force analysis on the impeller side to determine the frictional heat power on the seal side; Determine the heat power to be absorbed based on the outlet temperature of the first drainage channel and the inlet temperature of the second cooling water channel, and in combination with the frictional heat power on the seal side; Determine the cooling water mass flow rate of the second cooling loop based on the optimal expansion gap of the thrust balance disk and in combination with the heat power to be absorbed; Give the opening of the second electric valve and control the second electric valve based on the cooling water mass flow rate of the second cooling loop and the cooling water mass flow rate when the second electric valve is at its maximum opening.

[0069] Among them, the frictional heat power P on the seal side fri can be determined by the radial positive pressure corresponding to the pressure difference before and after the impeller and the rotational speed of the thrust balance disk, and satisfies the following relationship:

[0070] In the formula, μ is the friction coefficient of the seal material corresponding to the thrust balance disk, F n is the radial positive pressure that generates frictional force on the thrust balance disk, D is the diameter of the thrust balance disk, and n is the rotational speed of the thrust balance disk.

[0071] The heat power transferred from the impeller side to the seal side can be determined based on the outlet temperature of the first drainage channel and the inlet temperature of the second cooling water channel. Combining with the frictional heat power on the seal side, the heat power to be absorbed can be obtained, and it satisfies the following relationship:

[0072] In the formula, Q total is the heat power to be absorbed, and T3 is the inlet temperature of the second cooling water channel; After determining the heat power to be absorbed, the cooling water mass flow rate of the second cooling loop can be obtained in combination with the optimal expansion gap of the thrust balance disk, and it satisfies the following relationship:

[0073] In the formula, m2 is the cooling water mass flow rate of the second cooling loop, α is the thermal expansion coefficient of the seal material of the thrust balance disk, δ max is the maximum allowable expansion gap of the seal material of the thrust balance disk, δ0 is the initial design gap of the seal material of the thrust balance disk, T4 is the maximum outlet temperature corresponding to the maximum allowable expansion gap of the second drainage channel, and B is the multiple of the optimal expansion gap of the seal material of the thrust balance disk, B < 1, is the volume flow rate of the cooling water in the second cooling loop, is the density of the cooling water.

[0074] Determining the opening degree of the second electric valve includes: obtaining the cooling water mass flow rate of the second cooling loop when the opening degree of the second electric valve is the largest (the maximum opening degree K 2,max = 100%), and the determined volume flow rate of the cooling water in the second cooling loop, and giving the opening degree of the second electric valve to satisfy the following relationship:

[0075] In the formula, K2 is the opening degree of the second electric valve, m 2,max is the cooling water mass flow rate of the second cooling loop when the opening degree of the second electric valve is the largest, that is, the maximum cooling water mass flow rate of the second cooling loop. Among them, the adjustment of the cooling water mass flow rate or the volume flow rate of the cooling water can be completed by adjusting the valve opening degree. In addition, in this embodiment, the thrust balance disk is a symmetric structure, the gas pressure distribution of the compressor is uniform, and the thrust balance disk is in a dynamic balance state. When calculating the frictional heat power on the sealing side, the radial normal pressure corresponding to the frictional force is equal to the axial thrust generated by the gas acting on the impeller, that is , at this time, the opening degree of the second electric valve can satisfy the following relationship:

[0076] In the formula, A is the effective pressure-bearing area of the impeller, that is, the projected area of the impeller in the axial direction, and p1 and p2 are the outlet pressure of the compressor and the inlet pressure of the compressor respectively.

[0077] Of course, the following method can also be used to control the opening degree of the second electric valve: Monitor the outlet water temperature of the cooling water in the second drainage channel ; Establish through experiments or simulation the relationship between and the sealing expansion gap; When increases, the opening degree of the second electric valve can be increased according to the PID control algorithm, and the volume flow rate of the cooling water in the second cooling loop can be increased to avoid overheating; When decreases, the opening degree of the second electric valve can be decreased according to the PID control algorithm, and the volume flow rate of the cooling water in the second cooling loop can be lowered.

[0078] The water injection cooling system for the main shaft of a centrifugal compressor can automatically adjust the volume flow rate of the cooling water injected into the first cooling water channel and the second cooling water channel according to the temperature change and load condition inside the compressor, so as to precisely control the temperature of the impeller and the first sealing assembly, avoid overheating of the impeller and ensure the stability of the sealing clearance. Compared with the traditional fixed-flow cooling system, this intelligent control system can more efficiently handle different working conditions and improve the adaptability and accuracy of the system.

[0079] As Figure 6 shown, the present invention also provides a control method for water injection cooling of the main shaft of a centrifugal compressor. Using the above water injection cooling system, it specifically includes the following steps: Set the valve opening of the first electric valve, and turn on the first circulating water pump. The cooling water circulates from the circulating cooling water tank through the first circulating water pump, the first electric valve and the first cooling water channel to cool the impeller side of the main shaft of the centrifugal compressor, and then returns to the circulating cooling water tank. The monitoring unit monitors and controls the valve opening of the first electric valve to adjust the volume flow rate of the cooling water; Set the valve opening of the second electric valve, and turn on the second circulating water pump. The cooling water circulates from the circulating cooling water tank through the second circulating water pump, the second electric valve and the second cooling water channel to cool the sealing side of the main shaft of the centrifugal compressor, and then returns to the circulating cooling water tank. The monitoring unit monitors and controls the valve opening of the second electric valve to adjust the volume flow rate of the cooling water.

[0080] Although the preferred embodiments of the present invention have been described, those skilled in the art can make additional changes and modifications once they learn the basic creative concepts. Therefore, the appended claims are intended to be construed as including the preferred embodiments and all changes and modifications falling within the scope of the present invention. Obviously, those skilled in the art can make various changes and variations to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalent technologies, the present invention also intends to include these modifications and variations.

Claims

1. A main shaft of a centrifugal compressor, characterized in that, Specifically include: impeller side, seal side and gear shaft; the impeller side includes an impeller and a left shaft body, the left end of the left shaft body is connected to the impeller, and the right end of the left shaft body is connected to the gear shaft; the seal side includes a first sealing assembly and a right shaft body, the left end of the right shaft body is connected to the gear shaft, and the right end of the right shaft body is provided with a first sealing assembly; A first cooling water channel is arranged inside the impeller side, and a first drainage channel is arranged at the right edge of the left shaft body. The first cooling water channel penetrates through the impeller and the left shaft body, and the cooling water is discharged through the first drainage channel after passing through the first cooling water channel; A second cooling water channel is arranged inside the seal side, and a second drainage channel is arranged at the left edge of the right shaft body. The second cooling water channel penetrates through the first sealing assembly and the right shaft body, and the cooling water is discharged through the second drainage channel after passing through the second cooling water channel. The first cooling water channel includes a first water inlet channel and a first cooling channel. The first water inlet channel penetrates through the impeller and is communicated with the first cooling channel arranged inside the left shaft body. The first cooling channel is communicated with the first drainage channel; 2. The main shaft of the centrifugal compressor according to claim 1, characterized in that The second cooling water channel includes a second water inlet channel and a second cooling channel. The second water inlet channel penetrates through the first sealing assembly and is communicated with the second cooling channel arranged inside the right shaft body. The second cooling channel is communicated with the second drainage channel; The inner diameter of the first cooling channel is not less than the inner diameter of the second cooling channel. The ratio of the inner diameter of the first cooling channel to the inner diameter of the second cooling channel is 1.2 - 2.

3. The centrifugal compressor main shaft according to claim 2, characterized in that, The first water inlet channel includes a spiral water channel and a first water injection channel. The first water injection channel is in a cylindrical shape, the first water injection channel penetrates through the impeller, and the spiral water channel is wound around the outside of the first water injection channel and is arranged inside the left shaft body; 4. The centrifugal compressor main shaft according to claim 2, characterized in that, The cooling water enters and passes through the first water injection channel and the spiral water channel respectively and flows to the first cooling channel. The spiral water channel includes at least two variable pitch spiral water channels. Each variable pitch spiral water channel is a multi - spiral ring structure, including an inlet ring, a support ring and an outlet ring which are connected in sequence. The cooling water enters the variable pitch spiral water channel from the water inlet of the inlet ring, passes through the support ring, and then flows to the first cooling channel from the water outlet of the outlet ring; 5. The centrifugal compressor main shaft according to claim 4, wherein, The water inlets of each variable pitch spiral water channel are equally - angled distributed in the cross - section of the first water inlet channel, and the support rings of each variable pitch spiral water channel are arranged in a cross - equal - spacing manner; Along the flowing direction of the cooling water, the pitch of the spiral rings in each variable pitch spiral water channel increases in equal proportion; In adjacent spiral rings, the pitch ratio of the rear spiral ring to the front spiral ring is 1.1 - 1.

5. The second water inlet channel includes a toothed water channel and a second water injection channel. The second water injection channel penetrates through the first sealing assembly from the central position of the first sealing assembly, and the toothed water channel penetrates through the first sealing assembly through the edge part of the first sealing assembly; 6. The main shaft of the centrifugal compressor according to claim 2, characterized in that The toothed water channel is arranged around the second water injection channel. The cooling water enters and passes through the second water injection channel and the toothed water channel respectively and flows to the second cooling channel. The toothed water channel includes a water inlet section, a toothed cooling section and a water outlet section which are connected in sequence. The toothed cooling section is arranged inside the edge part of the first sealing assembly; 7. The main shaft of the centrifugal compressor according to claim 6, wherein A number of rack teeth are arranged on the inner wall of the toothed cooling section, and the distance between adjacent rack teeth is consistent. Include:

8. A water injection cooling system for the main shaft of a centrifugal compressor, characterized in that, The centrifugal compressor main shaft, the first electric valve, the second electric valve, the first circulating water pump, the second circulating water pump, the circulating cooling water tank and the monitoring unit as described in any one of claims 1 - 7; ​ The circulating cooling water tank, the first circulating water pump, the first electric valve and the impeller side form a first cooling loop. Cooling water returns to the circulating cooling water tank after passing through the first circulating water pump, the first electric valve and the first cooling water channel from the circulating cooling water tank. The circulating cooling water tank, the second circulating water pump, the second electric valve and the seal side form a second cooling loop. Cooling water returns to the circulating cooling water tank after passing through the second circulating water pump, the second electric valve and the second cooling water channel from the circulating cooling water tank. The monitoring unit is signal-connected to the first electric valve and the second electric valve, and is used to monitor and adjust the volume flow rate of the cooling water in the first cooling loop and the second cooling loop.

9. The centrifugal compressor main shaft water injection cooling system according to claim 8, wherein, The monitoring unit is also used to monitor the inlet water temperature of the first cooling water channel, the outlet water temperature of the first drainage channel, the inlet gas temperature of the compressor, and the outlet gas temperature of the compressor. Adjusting the volume flow rate of the cooling water in the first cooling loop includes: Determining the optimal heat generation power on the impeller side and the cooling water heat absorption power according to the inlet water temperature of the first cooling water channel, the outlet water temperature of the first drainage channel, the inlet gas temperature of the compressor and the optimal outlet gas temperature of the compressor. Determining the optimal volume flow rate of the cooling water in the first cooling loop according to the optimal heat generation power on the impeller side and the cooling water heat absorption power. Determining the current opening degree of the first electric valve and controlling the first electric valve according to the real-time outlet gas temperature of the compressor and the optimal outlet gas temperature of the compressor, and in combination with the optimal volume flow rate of the cooling water in the first cooling loop and the mass flow rate of the cooling water on the impeller side when the opening degree of the first electric valve is the largest.

10. A control method for water injection cooling of the main shaft of a centrifugal compressor, characterized in that, Adopting the water injection cooling system as described in claim 8 or 9, specifically including the following steps: Set the valve opening degree of the first electric valve, turn on the first circulating water pump. Cooling water passes through the first circulating water pump, the first electric valve and the first cooling water channel from the circulating cooling water tank to cool the impeller side of the main shaft of the centrifugal compressor, and then returns to the circulating cooling water tank. The monitoring unit monitors and controls the valve opening degree of the first electric valve and adjusts the volume flow rate of the cooling water. Set the valve opening degree of the second electric valve, turn on the second circulating water pump. Cooling water passes through the second circulating water pump, the second electric valve and the second cooling water channel from the circulating cooling water tank to cool the seal side of the main shaft of the centrifugal compressor, and then returns to the circulating cooling water tank. The monitoring unit monitors and controls the valve opening degree of the second electric valve and adjusts the volume flow rate of the cooling water.

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