Supercritical carbon dioxide compressor with gradient pressure drop

Abstract

The supercritical carbon dioxide compressor with the echelon pressure drop comprises an impeller main shaft, and a radial flow type impeller, a centrifugal compressor inlet volute chamber, a balance piston and a dry gas sealing body are sequentially arranged on the impeller main shaft from the working medium side to the atmosphere side. A dry gas seal vent hole position is arranged between the dry gas seal body and the balance piston; according to the dry gas sealing device, disturbance of working condition changes of a sealed machine to normal work of the dry gas sealing device can be effectively stabilized, the dry gas sealing device can keep the small thickness of a rigid gas film while reaching opening force, so that the better sealing effect is achieved, and the possibility that the dry gas sealing device is damaged due to the working condition changes is reduced; and the application value of the dry gas sealing technology in engineering practice is improved.

Description

Technical Field

[0001] The invention belongs to a high-pressure cascade pressure drop high-efficiency dry gas sealing device, and in particular relates to a supercritical carbon dioxide compressor with cascade pressure drop. Background Art

[0002] Dry gas seal is a micro-scale flow field non-contact gas film seal that relies on pressurization to form a rigid gas film between the dynamic and static ring seal end faces. After long-term research, it has gradually developed into a multi-end face sealing structure that can use a variety of sealing forms to cooperate with each other according to different application scenarios and purposes.

[0003] Compared with seals with simple structures such as labyrinth seals and floating ring seals, dry gas seals have the advantages of low leakage rate, low energy consumption, long life, and high efficiency, which can greatly reduce the wear and vibration problems that occur during equipment operation. When the dry gas sealing system is applied to supercritical fluid circulation, since the physical parameters and flow characteristics of the supercritical carbon dioxide circulating medium will show drastic nonlinear changes near the critical point, the high-density, low-viscosity supercritical carbon dioxide will highlight a strong real gas effect, which will strongly affect the stability of the dry gas sealing structure in the circulation system. In addition, since the size of the medium gas pressure outside the dry gas seal dynamic ring surface directly determines the working pressure of the dry gas seal and thus affects the thickness of the dry gas seal rigid gas film, combined with the high-pressure operating conditions of the compressor equipment, while ensuring that the pressure is sufficient to reach the opening force of the dynamic and static ring gap, minimizing the thickness of the rigid gas film can significantly improve the sealing of the dry gas seal. Therefore, adding a damping seal upstream of the dry gas seal dynamic ring to control the medium gas working pressure of the dry gas seal can make the mechanical equipment system have significant completeness and circulation benefits. At the same time, the low leakage ensures that very little medium gas escapes into the atmosphere, allowing the dry gas sealing system to work for a long time without having to consider replenishing the medium gas. This enables the dry gas sealing system to work for a long time in application scenarios with high requirements for sealing, such as underwater weapon platforms and manned space power systems.

[0004] In addition, thanks to the reasonable design of the cascade pressure drop structure, the volume of the control cabinet that integrates a large number of instruments, sensors, valve components, pipeline connections and gas boosting equipment in the traditional dry gas seal control system can be reduced to 1-2m, which reduces the space occupancy rate of the dry gas seal integrated system and can effectively meet the miniaturization of the supercritical carbon dioxide circulation system. Therefore, combined with advanced design concepts such as high sealing tightness and system miniaturization, a design method for a supercritical carbon dioxide compressor cascade pressure drop high-efficiency dry gas seal device with high cycle completeness and high space utilization is described.

[0005] The opening force of the gas film in the clearance between the stationary and rotating rings of a traditional dry gas seal is directly provided by the working medium at the inlet or outlet of the machine to be sealed (such as a compressor), without any other buffer device or pressure drop device in between. The disadvantage is that when the operating conditions of the machine to be sealed, such as the flow rate and rotational speed, change significantly, the thermophysical properties of the working medium, such as pressure and temperature, fluctuate greatly, which poses a great challenge to ensuring a uniform and stable gas film in the clearance between the stationary and rotating rings. This may lead to an excessive opening force of the gas film and an increase in working medium leakage when the flow rate is large, and a low opening force of the gas film and difficulty in meeting the normal operating conditions of the dry gas seal when the flow rate is small. Summary of the Invention

[0006] The object of the present invention is to provide a supercritical carbon dioxide compressor with a stepped pressure drop, which solves the above-mentioned deficiencies of the traditional dry gas seal device.

[0007] In order to achieve the above object, the technical solution adopted by the present invention is as follows: A supercritical carbon dioxide compressor with a stepped pressure drop provided by the present invention includes an impeller main shaft. A radial impeller, a centrifugal compressor inlet volute, a balance piston, and a dry gas seal body are sequentially arranged on the impeller main shaft from the working medium side to the atmosphere side. Among them, a dry gas seal vent hole position is arranged between the dry gas seal body and the balance piston.

[0008] Preferably, a gap is arranged between the dry gas seal body and the balance piston, and the gap is the dry gas seal vent hole position.

[0009] Preferably, a positioning shoulder for limiting the dry gas seal body is arranged between the impeller main shaft at the balance piston and the impeller main shaft at the dry gas seal body.

[0010] Preferably, both the radial impeller and the balance piston are integrally arranged with the impeller main shaft.

[0011] Preferably, a centrifugal compressor upper end cover, a centrifugal compressor volute end cover, and a dry gas seal gland are sequentially arranged on the impeller main shaft from the working medium side to the atmosphere side. Among them, the centrifugal compressor upper end cover is installed on the radial impeller; the centrifugal compressor volute end cover is installed on the centrifugal compressor inlet volute and the balance piston; the dry gas seal gland is placed at the rear side of the dry gas seal body and is fixedly connected to the centrifugal compressor volute end cover.

[0012] Preferably, a second annular groove is opened on one side of the centrifugal compressor volute end cover close to the rotating upper end face of the balance piston. A second damping sealing ring is assembled in the second annular groove. The damping sealing inlet of the second damping sealing ring is communicated with the centrifugal compressor inlet volute, and the outlet is communicated with the dry gas seal vent hole position.

[0013] Preferably, a first annular groove is formed on the upper end cover of the centrifugal compressor, close to the side of the volute end cover of the centrifugal compressor, and a first damping seal is assembled in the first annular groove.

[0014] Preferably, a labyrinth seal is provided between the dry gas seal gland and the impeller main shaft.

[0015] Preferably, an angular contact bearing seat is further provided on the impeller main shaft, and an oil-lubricated angular contact ball bearing is provided between the angular contact bearing seat and the impeller main shaft; the angular contact bearing seat is placed at the rear side of the dry gas seal body.

[0016] Preferably, the balance piston includes a balance piston body, and a damping seal body is installed on one side of the balance piston body close to the volute end cover of the centrifugal compressor, and the balance piston body and the damping seal body are of an integral structure Compared with the prior art, the beneficial effects of the present invention are as follows: A supercritical carbon dioxide compressor with a stepped pressure drop provided by the present invention adds a balance piston between the dry gas seal and the machinery to be sealed, and a dry gas seal vent hole is provided between the dry gas seal body and the balance piston; at the same time, a second annular groove is formed on the volute end cover of the centrifugal compressor, close to the upper rotating end face of the balance piston, and a second damping seal ring is assembled in the second annular groove. The damping seal inlet of the second damping seal ring is communicated with the inlet volute of the centrifugal compressor, and the outlet is communicated with the dry gas seal vent hole. The balance piston, the dry gas seal vent hole and the second damping seal ring form a balance disk end face damping seal. The transition of this balance disk end face damping seal can effectively stabilize the disturbance of the normal operation of the dry gas seal caused by the change of the working conditions of the machinery to be sealed, so that the dry gas seal can maintain a smaller thickness of the rigid gas film while reaching the opening force, thereby achieving a better sealing effect, reducing the possibility of damage to the dry gas seal device due to changes in working conditions, and improving the value of the application of the dry gas seal technology in engineering practice. Specifically: The dry gas seal vent hole is connected to the dry gas seal body, reducing the pressure of the high-pressure medium gas in the inlet volute of the centrifugal compressor, increasing the pressure difference between the medium gas and the seal gas flowing into the dry gas seal body, and reducing the gap between the dynamic and static ring surfaces of the dry gas seal body, realizing better sealing performance of the dry gas seal body. The balance piston, as the primary sealing structure, is evenly machined on the balance piston end face of the impeller main shaft, which can significantly reduce the pressure of the medium gas flowing into the sealing cavity. Description of the Drawings

[0017] Figure 1 is the dry gas seal device body; Figure 2 is the installation of the stepped pressure drop high-efficiency dry gas seal device for the supercritical carbon dioxide compressor; Figure 3It is a high-pressure and high-speed self-circulating dry gas seal control system for a supercritical carbon dioxide compressor. Specific Embodiment

[0018] In the following description, for the purpose of illustration rather than limitation, specific details such as specific system structures and technologies are presented to thoroughly understand the embodiments of the present application. However, those skilled in the art should clearly understand that the present application can also be implemented in other embodiments without these specific details. In other cases, detailed descriptions of well-known systems, devices, circuits, and methods are omitted to avoid unnecessary details from hindering the description of the present application.

[0019] Embodiment 1 As Figure 1 shown, a supercritical carbon dioxide compressor with a stepped pressure drop provided in this embodiment includes a casing, an impeller main shaft, a radial-flow impeller 1, an upper end cover 2 of the centrifugal compressor, a balance piston 3, a dry gas seal body 4, a labyrinth seal, a dry gas seal gland 5, an oil-lubricated angular contact ball bearing 6, an angular contact bearing housing 7, a dry gas seal vent hole position 8, an inlet volute 9 of the centrifugal compressor, and a volute end cover 10 of the centrifugal compressor, where: The radial-flow impeller 1 and the balance piston 3 are integrally provided on the impeller main shaft. The inlet volute 9 of the centrifugal compressor is arranged on the impeller main shaft. The radial-flow impeller 1 is arranged on the inlet side of the inlet volute 9 of the centrifugal compressor, and the balance piston 3 is arranged on the back side of the inlet volute 9 of the centrifugal compressor.

[0020] The inlet volute 9 of the centrifugal compressor forms a complete volute structure through the seal of the balance piston 3.

[0021] The dry gas seal body 4 is also sleeved on the impeller main shaft. The dry gas seal body 4 is placed on the rear side of the balance piston 3, and a dry gas seal vent hole position 8 with an annular cavity is provided between the dry gas seal body 4 and the balance piston 3.

[0022] The upper end cover 2 of the centrifugal compressor, the volute end cover 10 of the centrifugal compressor, and the dry gas seal gland 5 are sequentially arranged on the impeller main shaft from the working fluid side to the atmosphere side. Among them, the upper end cover 2 of the centrifugal compressor is sleeved on the radial-flow impeller 1; the volute end cover 10 of the centrifugal compressor is sleeved on the inlet volute 9 of the centrifugal compressor and the balance piston 3; the dry gas seal gland 5 is placed on the rear side of the dry gas seal body 4 and is fixedly connected to the volute end cover 10 of the centrifugal compressor by bolts to position the dry gas seal body 4.

[0023] There is a rotational gap between the radial-flow impeller 1 and the upper end cover 2 of the centrifugal compressor to ensure that no interference or collision occurs between the radial-flow blades and the upper end cover 2 of the centrifugal compressor during rotation.

[0024] A first annular groove is formed on the upper end cover 2 of the centrifugal compressor, near the side of the volute end cover of the centrifugal compressor. A first damping sealing ring is assembled in the first annular groove, so that the upper end cover 2 of the centrifugal compressor is tightly fitted with the volute end cover 10 of the centrifugal compressor.

[0025] A second annular groove is provided between the volute end cover 10 of the centrifugal compressor and the side of the upper rotating end face of the balance piston 3. A second damping sealing ring is assembled in the second annular groove. The damping sealing inlet of the second damping sealing ring communicates with the inlet volute 9 of the centrifugal compressor, and the outlet communicates with the dry gas seal vent hole position 8, so as to form a stepped pressure drop between the inlet volute 9 of the centrifugal compressor and the dry gas seal vent hole position 8. A labyrinth seal is provided between the dry gas seal gland 5 and the impeller main shaft. The labyrinth seal serves as a relay node for the pressure balance between the outlet end of the dry gas seal and the atmosphere side to control the stepped reduction of the outlet gas pressure of the dry gas seal to the atmosphere side pressure.

[0026] An angular contact bearing housing 7 is also sleeved on the impeller main shaft. The angular contact bearing housing 7 is placed at the rear side of the dry gas seal gland 5 for positioning the dry gas seal gland 5.

[0027] An oil-lubricated angular contact ball bearing 6 is provided between the angular contact bearing housing 7 and the impeller main shaft.

[0028] In this embodiment, the inner ring surface of the dry gas seal body 4 is separated from the relay node of the dry gas seal vent hole position 8 through the front end of the dry gas seal. The fluid leaks from the inlet volute 9 of the centrifugal compressor, flows through the second damping seal on the upper rotating end face of the balance piston 3 and enters the dry gas seal vent hole position 8, then passes through the dynamic and static ring gas film gap in the dry gas seal body 4, and finally reaches the atmosphere side through the labyrinth seal. The dry gas seal vent hole position 8 can establish a pressure transition region between the inlet volute 9 of the centrifugal compressor and the dry gas seal body 4 with the help of the second damping seal on the upper rotating end face of the balance piston. Such a transition region is of positive significance for reducing and buffering the high pressure on the inlet side of the dry gas seal, reducing the dynamic and static ring gas film gap in the dry gas seal body 4, and thus reducing the leakage amount of the working medium.

[0029] The fluid in the inlet volute 9 of the centrifugal compressor is decompressed and leaks to the moving ring side of the dry gas seal body 4 through the balance piston 3 of the centrifugal compressor. Under the rated operating conditions, the pressure of the medium gas is lower than the pressure of the inlet volute 9 of the centrifugal compressor, the temperature does not exceed 100°C, and the rated speed of the supercritical carbon dioxide compressor unit is 30,000 rpm. The allowable range of variable operating conditions is: the pressure of the medium gas is 4.0 - 7.0 MPa, the pressure of the sealing gas is 4.2 - 7.5 MPa, the temperature of the sealing gas is 75 - 120°C, the filtration accuracy is <1 μm, the rotational speed of the moving ring is 10,000 - 33,000 rpm, and other parameters: the outer diameter of the sealing ring is 46 mm, the thickness of the sealing ring is 45 mm, the material of the shaft section is Ti55, the heat treatment process of the shaft section is double annealing, and the temperature requirement on the atmosphere side is -10 - 50°C.

[0030] The dry gas seal body 4 is formed by two pairs of dry gas seal friction pairs facing each other to form a sealed chamber. The externally introduced dry and clean carbon dioxide is used as the main sealing gas and injected into the sealed chamber. It is required that the pressure of the injected inert gas is 0.2 - 0.3 MPa higher than the pressure of the gas medium to be sealed inside the machine.

[0031] The pre-charged gas source of the dry gas seal body 4 directly draws gas from the high-pressure tank of the circulation system with a maximum pressure of 15.0 MPa, a maximum temperature of 200°C, and a maximum flow rate of 150 Nm 3 / h. The high-pressure tank and the gas supply pipeline need to be insulated according to the maximum temperature. After the pre-charged gas temperature of 75 - 120°C and pressure of 4.2 - 7.5 MPa is de-liquefied, filtered, and decompressed, the pressure and temperature are reduced to the range of 4.2 - 7.5 MPa and 75 - 120°C through the automatic control of the pneumatic diaphragm regulating valve before it can be used as the seal of the dry gas seal device. In addition, it is required that the charging volume of the sealing gas does not exceed 50 Nm 3 / h. The corresponding structural parameters are: the diameter of the balance piston is 85 mm, the thickness is 10 mm, and the damping seal gap is 0.2 mm.

[0032] Example 2 Based on Example 1, a supercritical carbon dioxide compressor with a stepped pressure drop provided in this example, the dry gas seal body 4 includes a shaft sleeve 41, an O-ring 42, a moving ring 43, a corrugated belt 44, a stationary ring 45, a push ring 46, a spring seat 47, and a compression sleeve 48, where: The moving ring 43 and the stationary ring 45 are sleeved on the shaft sleeve 41, and the moving ring 43 and the stationary ring 45 are in contact with each other; the spring seat 47 is sleeved on the stationary ring 43, and a push ring 46 is arranged between the spring seat 47 and one end of the stationary ring 43.

[0033] A spring is arranged between the push ring 46 and the spring seat 47.

[0034] A corrugated belt 44 is arranged between the moving ring 43 and the shaft sleeve 41.

[0035] A compression sleeve 48 is provided between the stationary ring 45 and the shaft sleeve 41, and the compression sleeve 48 is fixedly connected to the shaft sleeve 41 by bolts.

[0036] An O-ring is provided between the stationary ring 45 and the spring seat 47, and the spring makes the stationary ring 45 fit with the rotating ring 43 fixed on the impeller main shaft under the seal no-load state.

[0037] A row of micron-level arc grooves are provided on one surface of the rotating ring 43 that fits with the stationary ring 45. As the rotating ring 3 rotates, the gas is pumped inward to the root of the arc groove, and the groove-free area outside the root is called the sealing dam. The sealing dam blocks and inhibits the gas flow, increasing the gas film pressure. The pressure between the mating surfaces causes the surface of the stationary ring 45 to separate from the rotating ring 43, maintaining a very small gap, generally about 3 microns. When the closing pressure generated by the gas pressure and the spring force is equal to the opening pressure of the gas film, a stable equilibrium gap is established.

[0038] The balance gap establishment mechanism will generate a gas film with quite high stability between the stationary ring 45 and the rotating ring 43 assembly, so that the end faces can remain separated, non-contact, and not easily worn under general power operation conditions, extending the service life.

[0039] The compression sleeve 48, the shaft sleeve 41 and the rotating ring 43 are installed together to form a rotating assembly with the impeller main shaft; the stationary ring 45, the push ring 46, the spring and the spring seat 47 together form a stationary assembly.

[0040] The shaft diameter of the compression sleeve 48 is Φ30mm. Its main functions are to fix the shaft sleeve and the rotating ring of the dry gas seal and seal the device, preventing foreign matters from entering the interface between the static and dynamic rings of the dry gas seal to contaminate the dry gas seal. The shaft sleeve is installed on the transmission shaft outside the inlet volute 9 of the centrifugal compressor, and its medium gas side is adjacent to the balance piston of the high-speed rotor of the supercritical carbon dioxide compressor unit.

[0041] The dry gas seal body 4 must use an external seal gas during operation to ensure the normal operation of the dry gas seal. The source of the seal gas is an external high-pressure storage tank. The high-pressure carbon dioxide in the storage tank is filtered and decompressed through different pipeline valves in the pipeline network and is used as the seal gas of the dry gas seal device and the fluid medium for the operation of the centrifugal compressor respectively. To ensure the normal operation of the dry gas seal system, the seal gas pressure in the dry gas seal body 4 is always 0.2 - 0.5MPa higher than the pressure in the seal cavity (medium gas) in the dry gas seal body 4.

[0042] The inlet volute 9 of the centrifugal compressor is connected to the gas source.

[0043] Before the front gas enters, the dry gas seal body 4 must pass the gas-liquid separation device of the dry gas seal control system to remove liquid and filter the front gas, and the filtration accuracy is not greater than 1mm.

[0044] The sealing gas pre-stage gas must be heated by a pipeline tracing heater before entering the dry gas seal body to prevent condensation phase change from occurring on the dynamic and static ring end faces after the sealing gas pre-stage gas enters the dry gas seal body.

[0045] The Figure 3 One path is led out from the carbon dioxide source as the working gas of the dry gas seal. After being regulated to 0.2 MPa by the ball valve and the filter pressure reducing valve PCV1, it then passes through the flowmeter FG, the orifice plate SO1, and the check valve, and enters the dry gas seal cavity from the seal GBI port (NPT1 / 4).

[0046] When the dry gas seal on the medium side fails or the pressure of the carbon dioxide source is short-term lower than the pressure of the medium to be sealed, which may directly cause the failure of the dry gas seal on the medium side. At this time, the dry gas seal on the atmosphere side acts as a safety seal, and the process medium will not leak to the atmosphere, realizing a safe shutdown.

[0047] The method for judging whether the dry gas seal works normally mainly observes the reading of the flowmeter FG meter: under normal circumstances, the sealing gas flow is stable. If any one end of the double-ended dry gas seal operates abnormally, it will cause a significant increase in the flow rate to exclude pipeline and interface leakage. When the indication value of the flowmeter is greater than 100 NL / h, it proves that the seal has failed. At this time, the standby pump should be started immediately, and after the pump is stopped, check and analyze the cause of the failure.

[0048] When the dry gas seal on the medium side fails, the dry gas seal on the atmosphere side will also play a safety sealing role, and the process medium will not leak to the atmosphere. If the dry gas seal on the atmosphere side fails, a large amount of carbon dioxide will directly leak to the atmosphere.

[0049] Before the dry gas seal control system is started, the supply of the PLAN74 isolation gas must be opened first. Open the supply valve, adjust the pressure reducing valve, and observe the pressure gauge reading until it is 0.2 MPaG higher than the medium pressure. After the sealing gas pressure value reaches the aforementioned value and is stable, the equipment can be started; after the equipment stops, the supply of the PLAN74 isolation gas can be stopped, otherwise the seal will be damaged.

[0050] The above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them; although the present application has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application, and should all be included within the protection scope of the present application.

Claims

1. A supercritical carbon dioxide compressor with a stepped pressure drop, characterized in that, It includes an impeller main shaft, on which a radial impeller, a centrifugal compressor inlet volute, a balance piston and a dry gas seal body are sequentially arranged from the working fluid side to the atmosphere side. Among them, a dry gas seal vent hole position is arranged between the dry gas seal body and the balance piston.

2. The supercritical carbon dioxide compressor with stepped pressure drop according to claim 1, wherein A gap is arranged between the dry gas seal body and the balance piston, and the gap is the dry gas seal vent hole position.

3. The supercritical carbon dioxide compressor with stepped pressure drop according to claim 1, characterized in that, A positioning shoulder for limiting the dry gas seal body is arranged between the impeller main shaft at the balance piston and the impeller main shaft at the dry gas seal body.

4. A supercritical carbon dioxide compressor with a stepped pressure drop according to claim 1, characterized in that, Both the radial impeller and the balance piston are integrally arranged with the impeller main shaft.

5. A supercritical carbon dioxide compressor with a stepped pressure drop according to claim 1, characterized in that, On the impeller main shaft, a centrifugal compressor upper end cover, a centrifugal compressor volute end cover and a dry gas seal gland are sequentially arranged from the working fluid side to the atmosphere side. Among them, the centrifugal compressor upper end cover is installed on the radial impeller; the centrifugal compressor volute end cover is installed on the centrifugal compressor inlet volute and the balance piston; the dry gas seal gland is placed at the rear side of the dry gas seal body and is fixedly connected with the centrifugal compressor volute end cover.

6. The supercritical carbon dioxide compressor with a stepped pressure drop according to claim 5, characterized in that, A second annular groove is formed on one side of the centrifugal compressor volute end cover close to the rotating upper end face of the balance piston. A second damping sealing ring is assembled in the second annular groove. The damping seal inlet of the second damping sealing ring is communicated with the centrifugal compressor inlet volute, and the outlet is communicated with the dry gas seal vent hole position.

7. A supercritical carbon dioxide compressor with a stepped pressure drop according to claim 5, characterized in that, A first annular groove is formed on one side of the centrifugal compressor upper end cover close to the centrifugal compressor volute end cover. A first damping seal is assembled in the first annular groove.

8. The supercritical carbon dioxide compressor with stepped pressure drop according to claim 5, characterized in that, A labyrinth seal is arranged between the dry gas seal gland and the impeller main shaft.

9. The supercritical carbon dioxide compressor with stepped pressure drop according to claim 1, characterized in that, An angular contact bearing seat is further arranged on the impeller main shaft. An oil-lubricated angular contact ball bearing is arranged between the angular contact bearing seat and the impeller main shaft; the angular contact bearing seat is placed at the rear side of the dry gas seal body.

10. The supercritical carbon dioxide compressor with stepped pressure drop according to claim 1, characterized in that, The balance piston includes a balance piston body. A damping seal body is installed on one side of the balance piston body close to the centrifugal compressor volute end cover, and the balance piston body and the damping seal body are of an integral structure.

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