Turbo expander shaft seal structure and turbo expander shaft seal system

Abstract

The invention belongs to the technical field of power generation equipment, and discloses a turbo expander shaft seal structure and a turbo expander shaft seal system.The turbo expander shaft seal structure comprises a high-pressure cylinder, an intermediate-pressure cylinder and a low-pressure cylinder, and the high-pressure cylinder is provided with a rotor assembly and a shaft seal assembly; the position, corresponding to the shaft seal assembly, of the high-pressure cylinder is provided with a plurality of air outlet connectors, and leaked air at the shaft seal assembly can enter the exhaust end of the medium-pressure cylinder and the air inlet end of the low-pressure cylinder through the air outlet connectors. By arranging the air outlet connector, graded utilization of leaked air at the shaft seal assembly is achieved, the overall efficiency of a unit is improved, and the construction, operation and maintenance cost of the unit can be effectively reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of power generation equipment, and in particular to a turbine expander shaft seal structure and a turbine expander shaft seal system. Background Art

[0002] Compressed air energy storage technology, as a large-scale, long-term energy storage technology with large capacity, long cycle, safety, environmental protection and long life, has become one of the mainstream energy storage technologies in recent years. The air turbine generator set is a key equipment in the compressed air energy storage system. When the energy storage system is discharged, the turbine expander in the air turbine generator set can convert the stored high-pressure air into electrical energy by expanding the work. In order to prevent the working medium from leaking out of the cylinder into the turbine plant at the place where the turbine expander rotor passes through the cylinder, and to facilitate the recovery of valve stem leakage, a shaft sealing system needs to be set in the turbine. At present, there is no mature design method for the shaft sealing system of the turbine expander. For example, the use of a shaft sealing system similar to that of a steam turbine is costly and has low feasibility. Summary of the invention

[0003] The object of the present invention is to provide a turbine expander shaft seal structure which can utilize the shaft seal leakage in the high-pressure cylinder in a graded manner, thereby improving the operating efficiency of the unit and reducing the operating cost and layout cost.

[0004] To achieve this object, the present invention adopts the following technical scheme: a turbine expander shaft seal structure, including a high-pressure cylinder, a medium-pressure cylinder and a low-pressure cylinder, the high-pressure cylinder is equipped with a rotor assembly and a shaft seal assembly, the shaft seal assembly is installed in the high-pressure cylinder and arranged around the rotor assembly; the medium-pressure cylinder and the low-pressure cylinder are both connected to the rotor assembly; wherein the high-pressure cylinder is provided with a plurality of air outlet interfaces at the position corresponding to the shaft seal assembly, and the gas leakage at the shaft seal assembly can enter the exhaust end of the medium-pressure cylinder and the air inlet end of the low-pressure cylinder through the plurality of air outlet interfaces.

[0005] Preferably, the high-pressure cylinder has an intake side and an exhaust side in the axial direction of the rotor assembly, the shaft seal assembly includes a first shaft seal and a second shaft seal, the first shaft seal and the second shaft seal are respectively located at the exhaust side and the intake side, the outlet interface includes a first interface and a second interface, the first interface corresponds to the first shaft seal position, the second interface corresponds to the second shaft seal position, and the first interface and the second interface are both connected to the exhaust end of the medium-pressure cylinder.

[0006] Preferably, the second shaft seal is configured as a three-speed shaft seal, the first interface is located at the middle stage of the three-speed shaft seal, the air outlet interface also includes a third interface, the third interface is located at the inner stage of the three-speed shaft seal, and the third interface is connected to the air inlet end of the low-pressure cylinder.

[0007] Preferably, the first shaft seal and the second shaft seal are both configured as gear-type shaft seals.

[0008] Preferably, the high-pressure cylinder is provided with two exhaust pipes, and the first shaft seal and the second shaft seal are provided with air outlet holes at opposite ends thereof, respectively, and the air outlet holes are connected with the exhaust pipes accordingly.

[0009] Preferably, the exhaust pipe is located on the top surface of the high-pressure cylinder and is arranged vertically upward.

[0010] Preferably, a first check valve is provided between the first interface and the exhaust end of the medium-pressure cylinder.

[0011] The object of the present invention is to provide a turbine expander shaft seal system which can reduce system energy loss and reduce construction and operation and maintenance costs.

[0012] To achieve this object, the present invention adopts the following technical scheme: a turbine expander shaft sealing system, including a control valve group, a return air main pipe and the above-mentioned turbine expander shaft sealing structure, the control valve group is respectively connected to the return air main pipe and the turbine expander shaft sealing structure, and the gate rod leakage of the control valve group can flow into the intake end of the low-pressure cylinder through the return air main pipe.

[0013] Preferably, a check valve group is provided between the control valve group and the gas return main pipe.

[0014] Preferably, the control valve group comprises a high-pressure main air valve, which is connected to the high-pressure cylinder pipeline, and air leakage from the valve stem of the high-pressure main air valve can flow into the exhaust end of the low-pressure cylinder.

[0015] The beneficial effects of the present invention are as follows: by setting the air outlet interface, on the one hand, under the premise that the original shaft seal assembly ensures the sealing, the air leakage at the shaft seal assembly is connected to the exhaust end of the downstream medium-pressure cylinder and the air inlet end of the low-pressure cylinder, so as to realize the graded utilization of the air leakage at the shaft seal assembly and improve the overall efficiency of the unit; on the other hand, the air leakage at the shaft seal assembly is graded and enters the exhaust end of the medium-pressure cylinder and the air inlet end of the low-pressure cylinder, without the need to set up a traditional shaft seal fan to discharge the air leakage, and the existing shaft seal air supply device can be reduced, thereby reducing the electricity consumption of the unit and effectively reducing the construction and operation and maintenance costs of the unit.

[0016] The present invention also provides a turbine expander shaft seal system, which can recycle the gas leakage at the high-pressure cylinder and the control valve group, reduce system energy loss, and reduce construction and operation and maintenance costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 is a cross-sectional view of a high-pressure cylinder of the present invention;

[0018] Figure 2 is a cross-sectional view of the exhaust end of the medium pressure cylinder of the present invention;

[0019] Figure 3 It is a schematic structural diagram of the turbine expander shaft seal system of the present invention.

[0020] In the figure:

[0021] 100, high-pressure cylinder; 110, inner cavity; 111, second interface; 112, first check valve; 120, blade; 130, shaft seal assembly; 131, first shaft seal; 132, second shaft seal; 133, air outlet; 140, air inlet side; 141, air inlet; 142, air supply port; 150, exhaust side; 151, exhaust port; 160, exhaust pipe;

[0022] 200, medium pressure cylinder;

[0023] 300, low pressure cylinder;

[0024] 400, control valve group; 410, high-pressure main air valve; 420, high-pressure air regulating valve; 430, high-pressure air supply valve; 440, medium-pressure air supply valve;

[0025] 500, air return main pipe;

[0026] 600. Second check valve. DETAILED DESCRIPTION

[0027] The present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. It is to be understood that the specific embodiments described herein are only used to explain the present invention, rather than to limit the present invention. It should also be noted that, for ease of description, only parts related to the present invention, rather than all structures, are shown in the accompanying drawings.

[0028] In the description of the present invention, unless otherwise clearly specified and limited, the terms "connected", "connected", and "fixed" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0029] In the present invention, unless otherwise clearly specified and limited, a first feature being "above" or "below" a second feature may include that the first and second features are in direct contact, or may include that the first and second features are not in direct contact but are in contact through another feature between them. Moreover, a first feature being "above", "above" and "above" a second feature includes that the first feature is directly above and obliquely above the second feature, or simply indicates that the first feature is higher in level than the second feature. A first feature being "below", "below" and "below" a second feature includes that the first feature is directly below and obliquely below the second feature, or simply indicates that the first feature is lower in level than the second feature.

[0030] In the description of this embodiment, the terms "upper", "lower", "right", etc., directions or positional relationships are based on the directions or positional relationships shown in the drawings, and are only for the convenience of description and simplification of operation, rather than indicating or implying that the device or element referred to must have a specific direction, be constructed and operated in a specific direction, and therefore cannot be understood as limiting the present invention. In addition, the terms "first" and "second" are only used to distinguish in the description and have no special meaning.

[0031] Reference Figures 1 to 3 As shown, a turbine expander shaft seal structure provided according to an embodiment of the present application includes a high-pressure cylinder 100, an intermediate-pressure cylinder 200 and a low-pressure cylinder 300, the high-pressure cylinder 100 is equipped with a rotor assembly and a shaft seal assembly 130, the high-pressure cylinder 100 is provided with an inner cavity 110, the rotor assembly is rotatably connected to the high-pressure cylinder 100 and is arranged in the inner cavity 110, and the shaft seal assembly 130 is installed in the inner cavity 110 of the high-pressure cylinder 100 and is arranged around the two ends of the rotor assembly passing through the inner cavity 110. The intermediate-pressure cylinder 200 and the low-pressure cylinder 300 are both connected to the rotor assembly.

[0032] Among them, the high-pressure cylinder 100 is provided with a plurality of gas outlet interfaces at the position corresponding to the shaft seal assembly 130, that is, the gas outlet interfaces are opened on the side wall of the high-pressure cylinder 100 around the shaft seal assembly 130, and the gas leakage at the shaft seal assembly 130 can enter the exhaust end of the medium-pressure cylinder 200 and the intake end of the low-pressure cylinder 300 through the plurality of gas outlet interfaces. In other words, the plurality of gas outlet interfaces are respectively connected to the exhaust end of the medium-pressure cylinder 200 and the intake end of the low-pressure cylinder 300, and the gas leakage pressure at the gas outlet interface is greater than the pressure at the exhaust end of the corresponding medium-pressure cylinder 200 or the pressure at the intake end of the low-pressure cylinder.

[0033] It can be understood that by setting the air outlet interface, on the one hand, under the premise that the original shaft seal assembly 130 ensures sealing, the air leakage at the shaft seal assembly 130 is connected to the exhaust end of the downstream medium-pressure cylinder 200 and the air inlet end of the low-pressure cylinder 300, so as to realize the graded utilization of the air leakage at the shaft seal assembly 130 and improve the overall efficiency of the unit; on the other hand, the air leakage at the shaft seal assembly 130 is graded and enters the exhaust end of the medium-pressure cylinder 200 and the air inlet end of the low-pressure cylinder 300, without the need to set up a traditional shaft seal fan to discharge the air leakage, and the existing shaft seal air supply device can be reduced, which greatly reduces the actual manufacturing cost, improves the compactness of the structure of the high-pressure cylinder 100, reduces the electricity consumption of the unit, and effectively reduces the construction and operation and maintenance costs of the unit.

[0034] Reference Figure 1 As shown, it can be understood that the high-pressure cylinder 100 has an intake side 140 and an exhaust side 150 in the axial direction of the rotor assembly, the rotor assembly is provided with blades 120, the blades 120 are located between the intake side 140 and the exhaust side 150, the intake side 140 is provided with an intake port 141 and an air supply port 142 for introducing high-pressure gas, and the exhaust side 150 is provided with an exhaust port 151 for discharging high-pressure gas.

[0035] The shaft seal assembly 130 includes a first shaft seal 131 and a second shaft seal 132. The first shaft seal 131 is located at the exhaust side 150, and the second shaft seal 132 is located at the intake side 140. The outlet interface includes a first interface and a second interface 111. The first interface corresponds to the position of the first shaft seal 131, and the second interface 111 corresponds to the position of the second shaft seal 132. The first interface and the second interface 111 are both connected to the exhaust end of the medium pressure cylinder 200. Specifically, the part of the side wall of the inner cavity 110 surrounding the first shaft seal 131 forms an annular leakage cavity b1 at the leakage position of the first shaft seal 131 (when there are multiple leakage positions of the first shaft seal 131, the leakage cavity b1 corresponds to the leakage position where the leakage pressure of the first shaft seal 131 is greater than the exhaust end pressure of the medium pressure cylinder 200), and the first interface is opened on the side wall of the leakage cavity b1. The position of the second interface 111 can refer to the description of the first interface above, and will not be repeated here.

[0036] The end pressures of the intake side 140 and the exhaust side 150 of the high-pressure cylinder 100 are higher than the atmospheric pressure, and the leakage temperature of the first shaft seal 131 and the second shaft seal 132 is slightly higher than the ambient temperature. By setting the first interface and the second interface 111, the leakage of the first shaft seal 131 and the second shaft seal 132 is introduced into the exhaust end of the turbine intermediate pressure cylinder 200, so that this part of the leakage can be mixed with the exhaust gas of the intermediate pressure cylinder 200 and enter the low-pressure cylinder 300 after reheating to perform work. The leakage of the first shaft seal 131 and the second shaft seal 132 is fully recycled to improve the utilization rate of the turbine medium and the efficiency of the unit.

[0037] Among them, the first shaft seal 131 and the second shaft seal 132 are both configured as gear-type shaft seals. Specifically, the first shaft seal 131 includes a shaft seal body, a shaft seal ring and a pressure block for fixing the shaft seal body. The shaft seal body is an upper and lower split structure. The upper and lower split shaft seal bodies are fixedly connected by bolts, and the pre-tightening force of the bolts can provide sufficient stress to ensure the airtightness of the center dividing surface. The shaft seal body is installed in the inner cavity 110 through the pressure block, and the shaft seal ring is installed in the shaft seal body and arranged around the rotor assembly. The inner circumferential wall of the shaft seal ring and the outer circumferential wall of the rotor assembly are provided with mutually matching comb tooth structures, and the comb tooth structure forms a labyrinth channel that can pressurize and cool the gas. The structure of the second shaft seal 132 can refer to the previous description of the first shaft seal 131, and will not be repeated here.

[0038] Configuring the first shaft seal 131 and the second shaft seal 132 as gear-type shaft seals can simplify the structure of the shaft seal assembly 130 , improve the sealing performance of the first shaft seal 131 and the second shaft seal 132 , reduce air leakage, and improve the stability of the shaft seal assembly 130 .

[0039] It should be added that the rotor assembly is usually equipped with a balancing disk at the intake side 140, and the shaft seal assembly 130 also includes a third shaft seal arranged around the balancing disk. The structure of the third shaft seal can refer to the above description of the first shaft seal 131 and will not be repeated here.

[0040] Furthermore, the second shaft seal 132 is configured as a three-stage shaft seal. In the axial direction of the rotor assembly, the three-stage shaft seal is divided into an inner stage, a middle stage and an outer stage in the direction from the fan blade to the first shaft seal 131. There is air leakage in the inner stage, the middle stage and the outer stage. The first interface is located at the middle stage of the three-stage shaft seal. The air outlet interface also includes a third interface. The third interface is located at the inner stage of the three-stage shaft seal. The third interface is connected to the air inlet end of the low-pressure cylinder 300.

[0041] Specifically, the part of the side wall of the inner cavity 110 surrounding the second shaft seal 132 forms annular leakage chambers b2 and b3 at the leakage point of the second shaft seal 132 (the leakage chamber b2 corresponds to the leakage position where the leakage pressure of the second shaft seal 132 is greater than the intake end pressure of the low-pressure cylinder 300, and the leakage chamber b3 corresponds to the leakage position where the leakage pressure of the second shaft seal 132 is less than the intake end pressure of the low-pressure cylinder 300 and greater than the exhaust end pressure of the medium-pressure cylinder 200), the third interface is opened on the side wall of the leakage chamber b2, and the second interface 111 is opened on the side wall of the leakage chamber b3.

[0042] The high-pressure cylinder 100 is fed with high-pressure gas through the air inlet 141 of the air inlet side 140. Since the second shaft seal 132 is installed at the air inlet side 140, the gas leakage quality of the second shaft seal 132 is relatively high (i.e., the gas leakage pressure, temperature and other parameters are relatively large, and the gas leakage energy density is relatively high). The second shaft seal 132 is configured as a three-speed shaft seal, which can separate high-quality gas leakage from ordinary gas leakage, so that the high-quality gas leakage first enters the air inlet end of the low-pressure cylinder 300 through the third interface to start working directly, and then the subsequent leakage of ordinary gas leakage is introduced into the exhaust end of the turbine medium-pressure cylinder 200 through the second interface 111. The graded utilization of the gas leakage at the second shaft seal 132 is realized, and the overall efficiency of the unit is improved.

[0043] It should be noted that when the first shaft seal 131 and the second shaft seal 132 are arranged to utilize the leakage in a cascade, a suitable intermediate number of stages (i.e., the number of shaft seal gears) can be selected according to the pressure parameters at various locations of the inner cavity 110. For example, the second seal on the intake side 140 has a higher leakage quality, and the second shaft seal 132 is configured as a three-gear shaft seal. The first shaft seal 131 on the exhaust side 150 has a general leakage quality, and the second shaft seal 132 is configured as a two-gear shaft seal. The pressure of the air extraction point between the first shaft seal 131 and the second shaft seal 132 is greater than the intake pressure, the pressure of the third interface on the leakage chamber b3 is greater than the intake end pressure of the low-pressure cylinder 300, and the pressure of the first interface on the leakage chamber b1 and the second interface 111 on the leakage chamber b2 is greater than the exhaust end pressure of the medium-pressure cylinder 200, thereby avoiding air backflow and ensuring the smoothness and stability of the unit. Optionally, when the first interface, the second interface 111 and the third interface are connected, they can be connected through an external pipeline, or they can be diverted through a unique internal interlayer design, which will not be repeated here. Optionally, the first shaft seal 131 and the second shaft seal 132 are also provided with leakage holes, and part of the air is collected into the chamber at the waist of the high-pressure cylinder 100 through the leakage holes, and finally discharged into the atmosphere through the exhaust port 151 of the high-pressure cylinder 100, thereby further reducing the leakage of the shaft seal assembly 130.

[0044] Reference Figure 1 and Figure 2 As shown, it can be understood that the high-pressure cylinder 100 is provided with two exhaust pipes 160, and air ports are respectively provided at the opposite ends of the first shaft seal 131 and the second shaft seal 132, that is, air outlet holes 133 are respectively provided at the outer ends of the first shaft seal 131 and the outer ends of the second shaft seal 132, and the air outlet holes 133 are correspondingly connected to the exhaust pipes 160.

[0045] By providing the exhaust pipe 160, low-quality leakage gas at the ends of the first shaft seal 131 and the second shaft seal 132 can be discharged into the atmosphere, thereby preventing the axial leakage of relatively high-temperature leakage gas from affecting the bearing seat outside the high-pressure cylinder 100, thereby effectively improving the structural rationality of the turbine expander shaft seal structure.

[0046] Furthermore, the exhaust pipe 160 is located on the top surface of the high-pressure cylinder 100 and is vertically arranged upward.

[0047] The exhaust pipe 160 is arranged vertically, and the temperature difference between the inner cavity 110 and the external air is used to guide the relatively high-temperature leakage gas at the ends of the first shaft seal 131 and the second shaft seal 132 to rise vertically and flow out of the high-pressure cylinder 100, so that low-quality leakage gas is quickly discharged without increasing the peripheral size of the high-pressure cylinder 100, thereby further improving the structural rationality of the pressure cylinder 100.

[0048] Reference Figure 1 and Figure 3 As shown, it can be understood that a first check valve 112 is provided between the first interface and the exhaust end of the medium-pressure cylinder 200 .

[0049] The first interface is located at the exhaust side 150 of the high-pressure cylinder 100, and the air leakage is relatively large. By setting the first check valve 112, the air leakage backflow from the second interface 111 into the exhaust end of the medium-pressure cylinder 200 can be avoided, thereby improving the working smoothness and stability of the high-pressure cylinder 100.

[0050] Reference Figure 3 As shown, a turbine expander shaft sealing system provided according to an embodiment of the present application includes a control valve group 400, a return air main pipe 500 and the above-mentioned turbine expander shaft sealing structure, the control valve group 400 is respectively connected to the return air main pipe 500 and the turbine expander shaft sealing structure, and the gate rod leakage of the control valve group 400 can flow into the intake end of the low-pressure cylinder 300 through the return air main pipe 500.

[0051] Specifically, the control valve group 400 includes a high-pressure main air valve 410, a high-pressure air regulating valve 420, a high-pressure air supply valve 430, a medium-pressure main air valve, a medium-pressure air regulating valve and a medium-pressure air supply valve 440. The high-pressure main air valve 410 is provided with two air outlet branches, the high-pressure air regulating valve 420 is respectively connected to one of the air outlet branches and the air inlet 141 on the high-pressure cylinder 100, and the high-pressure air supply valve 430 is respectively connected to the other air outlet branch and the air supply port 142 on the high-pressure cylinder 100. The connection between the medium-pressure main air valve, the medium-pressure air regulating valve, the medium-pressure air supply valve 440 and the medium-pressure cylinder 200 can refer to the above description of the high-pressure cylinder 100, and will not be repeated here. Among them, the gate stem leakage of the high-pressure air regulating valve 420, the gate stem leakage of the high-pressure air supply valve 430 and the gate stem leakage of the medium-pressure air supply valve 440 are all connected to the return air main pipe 500, and the gate stem leakage of the high-pressure air regulating valve 420, the gate stem leakage of the high-pressure air supply valve 430 and the gate stem leakage of the medium-pressure air supply valve 440 are all greater than the intake end pressure of the low-pressure cylinder 300, so that the gate stem leakage of the control valve group 400 can flow into the intake end of the low-pressure cylinder 300 through the return air main pipe 500 to directly perform work.

[0052] The turbine expander shaft seal system provided by the embodiment of the present invention includes the above-mentioned turbine expander shaft seal structure. Therefore, the turbine expander shaft seal system provided by the embodiment of the present invention can reuse the leakage of the shaft seal assembly 130 and the gate rod leakage of the control valve group 400, effectively improve the unit operation efficiency, and reduce the unit gas consumption. In addition, since most of the leakage is recycled, there is no need to set up a shaft seal fan for the small amount of leakage discharged into the atmosphere, which effectively reduces the unit construction and operation and maintenance costs, saves costs and reduces factory electricity consumption.

[0053] It should be added that in the turbine expander shaft seal system, the pipelines between the components should be connected and fixed by butt welding. Under the premise that butt welding cannot be used, the insertion welding structure can be used. The weld penetration should be ensured, and the height of the fillet weld should not be less than the smaller value of 0.7 times the minimum wall thickness of the parent material and 6mm. This ensures the structural strength of the pipeline and improves the high temperature and high pressure resistance of the pipeline.

[0054] Reference Figure 3 As shown, it can be understood that a check valve group is provided between the control valve group 400 and the return gas main pipe 500. Specifically, the check valve group includes a plurality of second check valves 600, and the second check valves 600 are provided in a one-to-one correspondence with the high-pressure gas regulating valve 420, the high-pressure gas replenishing valve 430 and the medium-pressure gas replenishing valve 440.

[0055] By providing the check valve group, the backflow of leaked gas from the control valve group 400 into the gas return main pipe 500 can be avoided, thereby improving the working smoothness and stability of the turbine expander shaft seal system.

[0056] Furthermore, the gas leakage from the valve stem of the high-pressure main air valve 410 can flow into the exhaust end of the low-pressure cylinder 300 .

[0057] The high-pressure main gas valve 410 generally has strong sealing performance and less leakage, so the leakage of the gate stem of the high-pressure main gas valve 410 is usually not worth recycling. The leakage of the gate stem of the high-pressure main gas valve 410 is directly connected to the exhaust end (exhaust tower) of the low-pressure cylinder 300, and then directly discharged into the atmosphere, eliminating the meaningless recovery pipeline structure and further reducing the layout cost of the turbine expander shaft seal system.

[0058] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention. For those skilled in the art, various obvious changes, readjustments and substitutions can be made without departing from the protection scope of the present invention. It is not necessary and impossible to list all the embodiments here. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the claims of the present invention.

Claims

1. A turbine expander shaft seal structure, characterized in that: include: A high-pressure cylinder (100) is provided with a rotor assembly and a shaft seal assembly (130), wherein the shaft seal assembly (130) is installed in the high-pressure cylinder (100) and is arranged around the rotor assembly; The medium-pressure cylinder (200) and the low-pressure cylinder (300) are both connected to the rotor assembly; The high-pressure cylinder (100) is provided with a plurality of air outlet interfaces at positions corresponding to the shaft seal assembly (130), and air leakage at the shaft seal assembly (130) can enter the exhaust end of the medium-pressure cylinder (200) and the air inlet end of the low-pressure cylinder (300) through the plurality of air outlet interfaces.

2. The turbo expander shaft seal structure according to claim 1, characterized in that: The high-pressure cylinder (100) has an intake side (140) and an exhaust side (150) in the axial direction of the rotor assembly. The shaft seal assembly (130) comprises a first shaft seal (131) and a second shaft seal (132). The first shaft seal (131) and the second shaft seal (132) are respectively located at the exhaust side (150) and the intake side (140). The outlet port comprises a first port and a second port (111). The first port corresponds to the position of the first shaft seal (131), and the second port (111) corresponds to the position of the second shaft seal (132). Both the first port and the second port (111) are connected to the exhaust end of the medium-pressure cylinder (200).

3. The turbo expander shaft seal structure according to claim 2, characterized in that: The second shaft seal (132) is configured as a three-speed shaft seal, the first interface is located at the middle stage of the three-speed shaft seal, the air outlet interface also includes a third interface, the third interface is located at the inner stage of the three-speed shaft seal, and the third interface is connected to the air inlet end of the low-pressure cylinder (300).

4. The turbo expander shaft seal structure according to claim 2, characterized in that: The first shaft seal (131) and the second shaft seal (132) are both configured as gear-type shaft seals.

5. The turbo expander shaft seal structure according to any one of claims 2 to 4, characterized in that: The high-pressure cylinder (100) is provided with two exhaust pipes (160), and opposite ends of the first shaft seal (131) and the second shaft seal (132) are respectively provided with exhaust holes (133), and the exhaust holes (133) are correspondingly connected to the exhaust pipes (160).

6. The turbo expander shaft seal structure according to claim 5, characterized in that: The exhaust pipe (160) is located on the top surface of the high-pressure cylinder (100) and is arranged vertically upward.

7. The turbo expander shaft seal structure according to any one of claims 2 to 4, characterized in that: A first check valve (112) is provided between the first interface and the exhaust end of the medium-pressure cylinder (200).

8. Turbine expander shaft seal system, characterized in that: It comprises a control valve group (400), a return air main pipe (500) and a turbine expander shaft seal structure as described in any one of claims 1 to 7, wherein the control valve group (400) is respectively connected to the return air main pipe (500) and the turbine expander shaft seal structure, and gas leakage from a gate rod of the control valve group (400) can flow into the air inlet end of the low-pressure cylinder (300) through the return air main pipe (500).

9. The turboexpander shaft seal system according to claim 8, characterized in that: A check valve group is provided between the control valve group (400) and the gas return main pipe (500).

10. The turboexpander shaft seal system according to claim 8, characterized in that: The control valve group (400) comprises a high-pressure main air valve (410), the high-pressure main air valve (410) being connected to the pipeline of the high-pressure cylinder (100), and air leakage from the valve stem of the high-pressure main air valve (410) can flow into the exhaust end of the low-pressure cylinder (300).

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