Multi-stage pressure matching steam turbine shaft seal leakage steam cascade recovery system and method

Abstract

The invention discloses a multi-stage pressure matching steam turbine shaft seal leakage steam cascade recovery system and method, and belongs to the technical field of energy conservation and consumption reduction of coal-fired units. Shaft seal steam leakage is treated in a mode of using energy according to quality and matching in a cascade mode, the system is provided with the high-pressure steam collecting pipe, the medium-pressure steam collecting pipe and the low-pressure steam collecting pipe in a grading mode to be connected with cylinder shaft seal steam leakage openings of different pressure grades, the steam collecting pipes are matched according to the sequence of the high pressure, the medium pressure and the low pressure for steam of different grades, and recycling devices of different qualities are distributed. The steam is directionally led to recovery equipment with corresponding parameters, steam pressure matching and heat energy gradient utilization are achieved, and meanwhile, a pressure regulating valve is arranged at an outlet of each steam collecting pipe, so that the opening degree of the valve is automatically regulated according to downstream user pressure; the system has the advantages that the heat energy utilization efficiency is improved, heat energy quality depreciation caused by steam mixing is avoided, the pipeline water attack risk is reduced, and the operation safety of the system is improved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of energy saving and consumption reduction of coal-fired units, and relates to a multi-stage pressure matching steam turbine shaft seal steam leakage stage recovery system and method. BACKGROUND

[0002] At present, steam turbine shaft seal steam leakage problems exist in current thermal power units, and the steam leakage parameters of different pressure grade cylinders are significantly different: the high-pressure cylinder steam leakage pressure can reach 1.2 MPa or above, the medium-pressure cylinder steam leakage pressure ranges from 0.3 to 0.8 MPa, and the low-pressure cylinder steam leakage pressure is lower than 0.2 MPa. The traditional treatment method is to mix steam of different grades and then uniformly lead to low-pressure recovery equipment (such as a condenser or a deaerator), and this extensive recovery mode has serious defects: on the one hand, mixing high-grade steam with low-grade steam will cause serious devaluation of thermal energy quality, resulting in energy waste; on the other hand, direct mixing of steam of different pressure grades can easily cause water hammer phenomenon in the pipeline system, threatening the safe operation of equipment. In addition, when the mixed steam parameters do not match the requirements of downstream steam equipment, the thermal system efficiency will also be reduced. The existing technology lacks effective means for grading pressure matching and directional recovery of shaft seal steam leakage, which cannot guarantee the safety of system operation and is difficult to achieve efficient gradient utilization of thermal energy. SUMMARY

[0003] The present application aims to overcome the shortcomings of the prior art and provide a multi-stage pressure matching steam turbine shaft seal steam leakage stage recovery system and method to solve the problem that mixing steam of different grades and then uniformly leading to low-pressure recovery equipment in the prior art will cause many defects.

[0004] To achieve the above-mentioned purpose, the present application adopts the following technical solutions: A multi-stage pressure matching steam turbine shaft seal steam leakage stage recovery system, comprising a high-pressure cylinder, a steam outlet of the high-pressure cylinder being connected with an inlet of a reheat steam pipeline, an outlet of the reheat steam pipeline being connected with a medium-pressure cylinder, a steam outlet of the medium-pressure cylinder being connected with a low-pressure cylinder, a steam outlet of the low-pressure cylinder being connected to a condenser, an outlet of the condenser being connected with a low-pressure heater, and the low-pressure heater being connected with a deaerator; Further comprising a high-pressure steam collecting pipe, a medium-pressure steam collecting pipe and a low-pressure steam collecting pipe; an inlet of the high-pressure steam collecting pipe and a shaft seal steam leakage port of the high-pressure cylinder are connected, and an outlet of the high-pressure steam collecting pipe is connected with the deaerator; an inlet of the medium-pressure steam collecting pipe and a shaft seal steam leakage port of the medium-pressure cylinder are connected, and an outlet of the medium-pressure steam collecting pipe is connected with the low-pressure heater; an inlet of the low-pressure steam collecting pipe and a shaft seal steam leakage port of the low-pressure cylinder are connected, and an outlet of the low-pressure steam collecting pipe is connected with a heat network heater; A pressure regulating valve is arranged on each of the high-pressure steam collecting pipe, the medium-pressure steam collecting pipe and the low-pressure steam collecting pipe.

[0005] The further improvement of the present application is that: Preferably, a three-way pipe is arranged on the high-pressure steam collecting pipe, the medium-pressure steam collecting pipe and the low-pressure steam collecting pipe, and an outlet of each three-way pipe is connected to a drain tank.

[0006] Preferably, a drain valve is arranged on the pipeline connecting each three-way pipe and the drain tank.

[0007] Preferably, the pressure of the high-pressure steam collecting pipe is greater than or equal to 1.2 MPa.

[0008] Preferably, the pressure of the medium-pressure steam collecting pipe is 0.3-0.8 MPa.

[0009] Preferably, the pressure of the low-pressure steam collecting pipe is less than or equal to 0.2 MPa.

[0010] Preferably, a double-layer thermal insulation sleeve is arranged on the pipe wall of the high-pressure steam collecting pipe.

[0011] Preferably, the medium-pressure steam collecting pipe and the low-pressure steam collecting pipe are inclined relative to the vertical direction.

[0012] Preferably, each pressure regulating valve is controlled by a PID controller.

[0013] A recovery method of a steam turbine shaft seal steam leakage gradient recovery system based on the above multi-stage pressure matching, when the actual pressure of any one pressure regulating valve is greater than the set pressure, the opening of the pressure regulating valve is adjusted, and if the actual pressure of the pressure regulating valve is still greater than the set pressure after adjustment, the three-way valve on the corresponding steam collecting pipe is opened to connect the steam collecting pipe and the drain tank.

[0014] Compared with the prior art, the present application has the following beneficial effects: The present application discloses a multi-stage pressure matching steam turbine shaft seal steam leakage gradient recovery system, which connects different pressure grade cylinder shaft seal steam outlets to corresponding parameter recovery equipment through hierarchical arrangement of high-pressure steam collecting pipes, medium-pressure steam collecting pipes and low-pressure steam collecting pipes, realizes steam pressure matching and heat energy gradient utilization, has the advantages of improving heat energy utilization efficiency, avoiding heat energy quality depreciation caused by steam mixing, reducing pipeline water hammer risk and improving system operation safety.

[0015] Further, in order to prevent steam mutual channeling, pressure-temperature double signal feedback is provided to avoid water hammer caused by insufficient steam superheat degree.

[0016] To ensure the safety of the unit, each branch is provided with an overpressure relief valve and a drain tank, and the condenser is provided with a standby shaft seal, which is automatically switched when the user is unavailable. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 The system structure diagram of the present application is shown in the figure. Wherein: 1, high-pressure steam collecting pipe; 2, medium-pressure steam collecting pipe; 3, low-pressure steam collecting pipe; 4, pressure regulating valve; 5, drain valve; 6, drain tank; 7, high-pressure cylinder; 8, medium-pressure cylinder; 9, low-pressure cylinder; 10, heat supply network heater; 11, condenser; 12, low-pressure heater; 13, deaerator. DETAILED DESCRIPTION

[0018] The present application will be further described in detail below with reference to the accompanying drawings: The embodiments of the present application are described in detail below, and examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference signs represent the same or similar elements or elements having the same or similar functions throughout. The embodiments described below by reference to the accompanying drawings are exemplary and are only used to explain the present application, and cannot be understood as a limitation of the present application.

[0019] In the prior art, the shaft seal steam leakage phenomenon is common in the steam turbine side of thermal power generating units, and the steam leakage parameters of different regions differ greatly. The high-pressure side has a higher steam leakage pressure, and the low-pressure side has a lower steam leakage pressure, but the prior art usually mixes the steam of different parameters and then leads it to a single low-pressure recovery point. This processing method causes the thermal energy value of high-grade steam to be reduced, and the mismatch between the mixed steam parameters and the user demand may cause pipeline water hammer or heat efficiency loss. For example, when the high-pressure steam leakage is mixed with the low-pressure steam leakage, the overall temperature of the steam decreases and cannot be directly used for equipment requiring high-temperature steam, resulting in energy waste.

[0020] Referring to Figure 1 The present application provides a multi-stage pressure matching steam turbine shaft seal steam leakage gradient recovery system, which comprises a high-pressure cylinder, a medium-pressure cylinder and a low-pressure cylinder in a conventional thermal power generating unit; a steam inlet of the high-pressure cylinder is communicated with a superheated steam outlet of a boiler, a steam outlet of the high-pressure cylinder is communicated with a reheated steam inlet of the boiler, a reheated steam outlet of the boiler is communicated with a steam inlet of the medium-pressure cylinder, a steam outlet of the medium-pressure cylinder is communicated with a steam inlet of the low-pressure cylinder, a steam outlet of the low-pressure cylinder is communicated with a condenser, an outlet of the condenser is communicated with a low-pressure heater, and the low-pressure heater is communicated with a deaerator; an inlet of a high-pressure steam collecting pipe is communicated with a shaft seal steam leakage port of the high-pressure cylinder, and an outlet of the high-pressure steam collecting pipe is communicated with the deaerator; an inlet of a medium-pressure steam collecting pipe is communicated with a shaft seal steam leakage port of the medium-pressure cylinder, and an outlet of the medium-pressure steam collecting pipe is communicated with the low-pressure heater; an inlet of a low-pressure steam collecting pipe is communicated with a shaft seal steam leakage port of the low-pressure cylinder, and an outlet of the low-pressure steam collecting pipe is communicated with a heat supply network heater; and a pressure regulating valve is arranged on each of the high-pressure steam collecting pipe, the medium-pressure steam collecting pipe and the low-pressure steam collecting pipe.

[0021] Specifically, the outlet of the medium-pressure steam collecting pipe is connected with the hot side inlet of the low-pressure heater, the outlet of the low-pressure steam collecting pipe is communicated with the hot side inlet of the heat network heater, and the hot side outlets of the low-pressure heater and the heat network heater are recovered to the condenser.

[0022] The shaft seal steam generated by the high-pressure cylinder is transported to the deaerator through the high-pressure steam collecting pipe, and a pressure regulating valve on the high-pressure steam collecting pipe adjusts the opening degree according to the working pressure requirement of the deaerator, so as to maintain the stable pressure in the high-pressure steam collecting pipe. The shaft seal steam of the medium-pressure cylinder is transported to the low-pressure heater through the medium-pressure steam collecting pipe, and the pressure regulating valve adjusts the pipeline pressure according to the steam parameter requirement of the low-pressure heater. The shaft seal steam of the low-pressure cylinder is transported to the heat network heater through the low-pressure steam collecting pipe, and the pressure regulating valve ensures that the low-pressure steam pressure matches the working condition of the heat network heater. Through the staged recovery, the steam of different pressure grades is respectively introduced into the corresponding thermal equipment, so as to avoid the steam grade reduction after mixing.

[0023] Compared with the prior art, the present application realizes the staged pressure matching by arranging the multi-stage steam collecting pipes and the pressure regulating valves. The present application eliminates the mutual interference of different pressure steam through the independent conveying path and the pressure control. The thermal energy value of the steam of each pressure grade is reserved by directly matching the user requirement. The present application can avoid the thermal energy loss caused by the mixing of the shaft seal steam of different pressures, protect the steam quality from being devalued under the premise of ensuring the system safety, maximize the use of the steam leakage energy, reduce the risk of water hammer, and improve the thermal efficiency of the steam recovery system. The high-pressure steam is directly used for the deaerator which needs high temperature and high pressure, the medium-pressure steam is used for the low-pressure heater, and the low-pressure steam is used for the heat network heater, so as to realize the accurate matching of the steam parameters. The dynamic control of the pressure regulating valve ensures the pressure stability of each recovery path, and further optimizes the system operation reliability.

[0024] In some embodiments of the present application, a three-way valve is arranged on each of the high-pressure steam collecting pipe 1, the medium-pressure steam collecting pipe 2 and the low-pressure steam collecting pipe 3, and one outlet of each three-way valve is commonly connected to a drain tank 6. The arrangement of the drain tank can ensure the safety of the system pressure. A pressure regulating valve 4 is arranged on each steam collecting pipe for adjusting the pressure, and a drain tank is arranged to drain the drain water.

[0025] Further, a drain valve is arranged on the pipeline connected between each three-way valve and the drain tank. When the shaft seal steam flows in the steam collecting pipe, the steam will produce condensate water due to the temperature drop. The condensate water can be drained to the drain tank in a directional manner, and the steam continues to flow to the target recovery equipment through the arrangement of the drain valve between the three-way valve and the drain tank. Through the arrangement of the drain valve and the drain tank, the water hammer risk caused by the accumulation of condensate water in the shaft seal steam recovery pipeline can be effectively prevented, the pressure stability of the steam collecting pipe is maintained, and the safety and thermal cycle efficiency of the system operation are improved.

[0026] In some embodiments of the present application, the design pressure of the high-pressure steam collecting pipe 1 is greater than or equal to 1.2 MPa; the pressure regulating valve is provided to maintain the stable steam pressure in the pipe, avoiding the energy degradation caused by the mixing of high-pressure steam and low-pressure steam. The pressure greater than or equal to 1.2 MPa means that the pressure inside the steam collecting pipe is monitored in real time by a pressure sensor, and when the pressure is lower than the threshold value, the valve opening is automatically adjusted to ensure that the steam parameters match the steam demand of the deaerator, preventing the steam from being directly utilized due to insufficient pressure. When the pressure in the high-pressure steam collecting pipe decreases due to steam flow fluctuation, the valve opening is reduced to increase the pressure in the pipe; when the pressure exceeds the threshold value, the valve opening is increased to release the excess pressure. In this way, the steam is always maintained at a sufficient pressure to directly enter the deaerator for thermal circulation, without causing energy loss by throttling and depressurizing, and avoiding the risk of water hammer caused by the mixing of high-pressure steam and low-pressure system.

[0027] In some embodiments of the present application, the design pressure of the medium-pressure steam collecting pipe 2 is in the range of 0.3-0.8 MPa; this pressure range matches the medium-pressure cylinder seal steam leakage parameters, which can avoid pipe vibration caused by excessive pressure or steam condensation caused by low pressure, and by limiting this pressure range, the medium-pressure cylinder steam leakage can be independently transported to the matching low-pressure heater, avoiding the energy degradation caused by the mixing of high-grade steam and low-grade steam.

[0028] The inlet of the low-pressure steam collecting pipe 3 is connected with the shaft seal steam leakage port of the low-pressure cylinder 9, and the outlet is communicated with the heat network heater 10, and the design pressure of the low-pressure steam collecting pipe 3 is less than or equal to 0.2 MPa. The steam is transported to the low-pressure heater at a stable pressure, and is directly used for heating the condensed water, avoiding the loss of thermal efficiency or the risk of pipe water hammer caused by pressure fluctuation. The pressure threshold matches the working pressure range of the heat network heater, which can avoid the steam parameters exceeding the bearing capacity of the downstream equipment. When the pressure is lower than the set value, the regulating valve reduces the opening to maintain the stable system pressure. Through the hierarchical pressure control, the low-pressure steam is directly transported to the heat network heater for heat energy utilization, avoiding the parameter mismatch caused by the mixing with high-pressure steam.

[0029] It should be noted that the high-pressure cylinder 7 usually has 2-4 shaft seals, each shaft seal may include multiple steam leakage ports, and each shaft seal steam leakage port is connected with the high-pressure steam collecting pipe 1; the medium-pressure cylinder usually has 2-3 shaft seals, each shaft seal has 1-2 steam leakage ports, and each shaft seal steam leakage port is connected with the medium-pressure steam collecting pipe 2; the low-pressure cylinder has two shaft seals, and each shaft seal steam leakage port is connected with the low-pressure steam collecting pipe 3.

[0030] In some embodiments of the present application, the high-pressure steam collecting pipe 1 adopts a double-layer heat preservation sleeve structure to reduce heat loss. Specifically, stainless steel or ceramic material can be used as the inner sleeve, the outer sleeve is wrapped with polyurethane foam material, and the middle is filled with aluminum silicate fiber to achieve heat insulation. The high-pressure steam collected by the high-pressure steam collecting pipe has a high temperature. If a single-layer pipe wall structure is used, the steam heat is easily lost to the external environment through the pipe wall, resulting in a decrease in steam temperature and pressure fluctuations. The double-layer heat preservation sleeve structure blocks the direct contact of steam with the external environment through the inner sleeve, and the outer sleeve further reduces heat conduction. At the same time, the middle heat insulation layer inhibits heat radiation and convection. Thus, the high-pressure steam can maintain stable temperature and pressure during transportation to the deaerator. This structure maintains the temperature and pressure parameters of the steam by reducing heat exchange between the high-pressure steam and the environment, avoids the decrease in parameters of high-grade steam due to heat loss during transportation, and avoids the decrease in recovery efficiency or the risk of water hammer caused by condensation of steam in the pipeline due to parameter mismatch.

[0031] In some embodiments of the present application, the pipelines of the medium-pressure steam collecting pipe 2 and the low-pressure steam collecting pipe 3 are arranged obliquely to avoid water accumulation caused by condensation of low-temperature steam.

[0032] Specifically, the oblique arrangement of the pipelines of the medium-pressure steam collecting pipe and the low-pressure steam collecting pipe allows the condensate water generated during steam flow to flow downward along the pipe wall under the action of gravity and finally collect in the drain tank. The inclination angle of the pipeline can be dynamically adjusted according to the steam flow rate, temperature, and condensate water generation amount, for example, by adjusting the height difference of the support frame or using a connection flange with adjustable angle. Thus, the separation efficiency of steam and condensate water is improved, and the two-phase flow state in the pipeline is optimized.

[0033] Specifically, the oblique arrangement of the pipelines of the medium-pressure steam collecting pipe and the low-pressure steam collecting pipe allows the condensate water generated during steam flow to flow downward along the pipe wall under the action of gravity and finally collect in the drain tank. The inclination angle of the pipeline can be dynamically adjusted according to the steam flow rate, temperature, and condensate water generation amount, for example, by adjusting the height difference of the support frame or using a connection flange with adjustable angle. Thus, the separation efficiency of steam and condensate water is improved, and the two-phase flow state in the pipeline is optimized.

[0034] In some embodiments of the present application, all pressure regulating valves are self-operated pressure regulating valves that can automatically adjust the valve opening according to the pressure of the downstream user to prevent steam cross-contamination. The valve group is equipped with pressure-temperature double signal feedback, PID regulation and temperature compensation to avoid water hammer and ensure the safety of the pipeline valve.

[0035] Control logic: when P 实际 > P 目标 and T > 30℃, it means that the pressure in the pipeline is too large, then adjust the opening of the corresponding pressure regulating valve 4, if the opening is opened to the maximum and still cannot adjust to the target pressure value, then open the three-way valve and the drain valve 5 of the corresponding steam collecting pipe, and discharge the drain and part of the steam to the drain tank 6 to prevent water hammer.

[0036] During the operation of the steam turbine, the high-pressure collecting pipe, the medium-pressure collecting pipe and the low-pressure collecting pipe are respectively monitored in real time by pressure sensors. When the actual pressure of a certain stage of the collecting pipe exceeds the corresponding set pressure, the drive device of the pressure regulating valve of the stage receives a control signal, and the valve core position is changed by a linear displacement mechanism to increase the flow passage area. For example, when the pressure of the high-pressure collecting pipe exceeds 1.2 MPa, the opening of the pressure regulating valve is automatically increased to guide the excess steam to the deaerator; when the pressure of the medium-pressure collecting pipe exceeds 0.8 MPa, the valve opening is increased to make the steam flow into the low-pressure heater at a higher speed. Thus, the dynamic balance of the steam pressure of each stage is achieved, and the deviation of the mixed steam parameters from the requirements of the downstream equipment is avoided.

[0037] Compared with the prior art, the conventional method uniformly transports the shaft seal steam leakage of different pressure levels to a single recovery point, resulting in direct mixing of high-pressure steam and low-pressure steam, causing loss of energy grade. The method matches the pressure by stages, so that the high-pressure, medium-pressure and low-pressure steam leakage enters the deaerator, the low-pressure heater and the heat network heater respectively, while maintaining the independent operation of each circuit, and through pressure closed-loop control, the steam parameters are always adapted to the working condition requirements of the corresponding recovery equipment.

[0038] Through the above technical scheme, the application can effectively eliminate the phenomenon of water hammer caused by mismatch of steam parameters, avoid thermodynamic loss caused by mixing of high-grade steam and low-grade steam, prevent the risk of seal failure caused by overpressure of the collecting pipe through dynamic pressure regulation, and improve the safety and energy utilization efficiency of the system.

[0039] The safety drain design of the application mainly includes two aspects: considering that the user may need to switch the recovery mode when the user is unavailable, and to increase the flexibility of the unit operation, a shaft seal heater is arranged at the condenser to facilitate the switching of the operation to the conventional mode.

[0040] Based on the above scheme, the application can significantly increase the shaft seal steam leakage recovery rate and reduce the coal consumption for power supply by arranging multiple-stage collecting pipes and corresponding pressure regulating valves. At the same time, due to the diversion of low-pressure steam to the heat network heater, the condenser heat load is reduced, which helps to improve the vacuum degree of the unit. On the other hand, in order to ensure the smooth operation of the scheme, two types of safety measures are arranged, one is to arrange a three-way connection drain tank on each collecting pipe, and a drain valve is arranged on the connecting pipeline to release pressure when the pressure is too high; further, when the system fails and cannot be used, the shaft seal leakage is output to the shaft seal heater.

[0041] In terms of operation and maintenance, intelligent feedback control avoids manual operation and reduces the workload.

[0042] In the description of the application, it needs to be understood that the orientation or positional relationship indicated by the terms "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential" and the like is based on the orientation or positional relationship shown in the drawings, and is only for the purpose of facilitating the description of the application and simplifying the description, and does not indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the application. In addition, the features defined as "first", "second" can be explicitly or implicitly included one or more of the features. In the description of the application, the meaning of "a plurality of" is two or more, unless otherwise specified. In the description of the application, the first feature "above" or "below" the second feature can include that the first and second features are in direct contact, or that the first and second features are not in direct contact but are in contact through another feature between them.

[0043] In the description of the application, the first feature "above", "above" and "above" the second feature includes that the first feature is directly above and obliquely above the second feature, or only indicates that the first feature is higher than the second feature in horizontal height.

[0044] In the description of the application, it should be noted that, unless otherwise specified and limited, the terms "mounting", "connection", "connection" should be understood broadly, for example, it can be fixedly connected, or it can be detachably connected, or integrally connected; it can be mechanically connected, or it can be electrically connected; it can be directly connected, or it can be indirectly connected through an intermediate medium; it can be the communication between two elements. For those skilled in the art, the specific meaning of the above terms in the application can be understood according to the specific circumstances.

[0045] In the description of the application, the description of the terms "one embodiment", "some embodiments", "illustrative embodiment", "example", "specific example", or "some examples" means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the application. In this specification, the illustrative description of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0046] Although embodiments of the application have been shown and described, those skilled in the art can understand that various changes, modifications, replacements and variations can be made to these embodiments without departing from the principles and spirit of the application, and the scope of the application is defined by the claims and their equivalents.

[0047] The above description is only the preferred embodiment of the present application, and is not intended to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A multi-stage pressure-matched turbine shaft seal leakage steam recovery system, characterized in that, Includes a high-pressure cylinder (7), the steam outlet of which is connected to the inlet of a reheat steam pipeline, the outlet of which is connected to an intermediate-pressure cylinder (8), the steam outlet of which is connected to a low-pressure cylinder (9), the steam outlet of which is connected to a condenser (11), the outlet of which is connected to a low-pressure heater (12), and the low-pressure heater (12) is connected to a deaerator (13). It also includes a high-pressure steam collection pipe (1), a medium-pressure steam collection pipe (2), and a low-pressure steam collection pipe (3); the inlet of the high-pressure steam collection pipe (1) is connected to the shaft seal leakage port of the high-pressure cylinder (7), and the outlet of the high-pressure steam collection pipe (1) is connected to the deaerator (13); the inlet of the medium-pressure steam collection pipe (2) is connected to the shaft seal leakage port of the medium-pressure cylinder (8), and the outlet of the medium-pressure steam collection pipe (2) is connected to the low-pressure heater (12); the inlet of the low-pressure steam collection pipe (3) is connected to the shaft seal leakage port of the low-pressure cylinder (9), and the outlet of the low-pressure steam collection pipe (3) is connected to a heat network heater (10). Pressure regulating valves (4) are provided on the high-pressure steam collecting pipe (1), the medium-pressure steam collecting pipe (2) and the low-pressure steam collecting pipe (3).

2. The multi-stage pressure-matched turbine shaft seal leakage recovery system according to claim 1, characterized in that, Each of the high-pressure steam collecting pipe (1), medium-pressure steam collecting pipe (2) and low-pressure steam collecting pipe (3) is equipped with a tee, and one outlet of each tee is connected to a condensate tank (6).

3. The multi-stage pressure-matched turbine shaft seal leakage recovery system according to claim 2, characterized in that, Each of the three-way valves and the drain tank (6) is equipped with a drain valve (5) on the pipe.

4. The multi-stage pressure-matched turbine shaft seal leakage recovery system according to claim 1, characterized in that, The pressure of the high-pressure steam collecting pipe (1) is ≥1.2MPa.

5. A multi-stage pressure-matched turbine shaft seal leakage recovery system according to claim 1, characterized in that, The pressure of the medium-pressure steam collecting pipe (2) is 0.3-0.8 MPa.

6. The multi-stage pressure-matched turbine shaft seal leakage recovery system according to claim 1, characterized in that, The pressure of the low-pressure steam collection pipe (3) is ≤0.2MPa.

7. A multi-stage pressure-matched turbine shaft seal leakage recovery system according to claim 1, characterized in that, The high-pressure steam collecting pipe (1) is provided with a double-layer heat-insulating sleeve on its pipe wall.

8. A multi-stage pressure-matched turbine shaft seal leakage recovery system according to claim 1, characterized in that, The medium-pressure steam collecting pipe (2) and the low-pressure steam collecting pipe (3) are inclined relative to the vertical direction.

9. A multi-stage pressure-matched turbine shaft seal leakage recovery system according to claim 1, characterized in that, Each of the pressure regulating valves (4) is controlled by a PID controller.

10. A method for recovering steam leakage from a turbine shaft seal in a multi-stage pressure-matched cascade recovery system as described in claim 1, characterized in that, When the actual pressure of any pressure regulating valve (4) is greater than the set pressure, adjust the opening of the pressure regulating valve (4). If the actual pressure of the pressure regulating valve (4) is still greater than the set pressure after adjustment, open the three-way valve on the corresponding steam collecting pipe to connect the steam collecting pipe and the steam trap (6).

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