Low-pressure exhaust device suitable for low-load operation of steam turbine and steam turbine

Abstract

The application relates to a low-pressure exhaust device suitable for low-load operation of a steam turbine and the steam turbine, wherein the low-pressure exhaust device is arranged around the periphery of a rotor at the root area of a low-pressure exhaust passage, the low-pressure exhaust device is sleeve-shaped as a whole and gradually expands from the low-pressure last-stage blade to an exhaust guide ring; the inside of the low-pressure exhaust device is divided into multiple chambers by a rib plate, the corresponding outer circular wall of each chamber is provided with a first axial gap, a second axial gap and a radial gap, the first axial gap and the second axial gap are staggered with each other and are inclined to a direction favorable to the flow of exhaust steam, and the radial gap connects the first axial gap and the second axial gap; the bottom of the low-pressure exhaust device is provided with a flow guide part, an internal flow guide passage and a flow guide pipeline. The low-pressure exhaust device can reduce the probability of water drop scouring the root area of the last-stage blade, and realizes long-term continuous operation of the steam turbine under low-load working conditions.

Description

Technical Field

[0001] This invention relates to the field of steam turbine technology, and more specifically to a low-pressure exhaust device suitable for low-load operation of steam turbines. This invention also relates to a steam turbine equipped with the aforementioned low-pressure exhaust device. Background Technology

[0002] Under high load conditions, the exhaust steam from the last stage moving blades of the steam turbine can evenly fill the exhaust passage, and all the steam flows from the last stage moving blades to the low-pressure exhaust passage.

[0003] However, when the turbine load decreases to a certain level, the mass of steam flowing out from the last stage moving blades decreases, the volumetric flow rate decreases, and the distribution of steam in the exhaust passage will become distorted. At this time, all the steam will converge towards the top of the exhaust passage, and a low-pressure zone will appear at the bottom of the exhaust passage. This low-pressure zone will draw back some of the steam discharged from the top of the exhaust passage, forming a vortex with reverse flow.

[0004] When a steam turbine is operating under low load conditions, a water spray desuperheating device needs to be activated to reduce the exhaust steam temperature in order to prevent the exhaust steam temperature from rising due to forced draft. At this time, some of the water droplets that are not fully atomized will be drawn into the vortex along with the exhaust steam, and together with the vortex, they will rush towards the root area of ​​the last-stage moving blade, causing water erosion at the root of the moving blade on the steam outlet side. Summary of the Invention

[0005] The purpose of this invention is to provide a low-pressure exhaust device suitable for low-load operation of steam turbines, so as to solve the above-mentioned technical problems.

[0006] Another object of the present invention is to provide a steam turbine equipped with the aforementioned low-pressure exhaust device.

[0007] To achieve the above objectives, the present invention provides a low-pressure exhaust device suitable for low-load operation of a steam turbine. This device surrounds the rotor periphery in the root region of the low-pressure exhaust channel and includes an outer circular wall and an inner circular wall. The outer and inner circular walls are connected by a front end plate and a rear end plate. The front end of the outer circular wall is close to the last-stage moving blade of the low-pressure turbine, and the rear end of the outer circular wall is connected to an exhaust guide ring. The low-pressure exhaust device is generally cylindrical and gradually expands from the last-stage moving blade of the low-pressure turbine towards the exhaust guide ring. The interior of the low-pressure exhaust device is divided into multiple chambers by stiffeners, and the outer circular wall corresponding to each chamber has a first... The device comprises an axial clearance, a second axial clearance, and a radial clearance. The first and second axial clearances are offset from each other and inclined in a direction favorable to exhaust flow. The radial clearance connects the first and second axial clearances. The outer circular wall at the bottom of the low-pressure exhaust device encloses the bottom region of the chamber to form a drainage section. The ribs at the bottom of the low-pressure exhaust device have openings at their lower edges that connect to each of the chambers to form an internal drainage path corresponding to the drainage section. The bottom of the last chamber is connected to a drainage pipe that extends to the lowest end of the cylinder.

[0008] Optionally, the outer circular wall is integrally formed with the exhaust guide ring at the root of the moving blade, and the low-pressure exhaust device replaces the front half of the exhaust guide ring.

[0009] Optionally, the front end of the outer circular wall extends beyond the inner circular wall by a certain distance.

[0010] Optionally, the first axial clearance and the second axial clearance are greater than the radial clearance.

[0011] Optionally, the low-pressure exhaust device is divided into an upper part and a lower part, which are combined to form a whole.

[0012] Optionally, the chord length of the drainage part is 400mm-600mm, and the opening depth of the rib plate is 10mm-30mm.

[0013] Optionally, the first axial clearance is 8mm-12mm, the second axial clearance is 8mm-12mm, and the radial clearance is 3mm-6mm.

[0014] Optionally, the outer circular wall is divided into multiple roof tile-shaped guide sections. The head of each guide section is partially thinned on the outer circular side, and the end face is machined into a bevel. The tail of each guide section is partially thinned on the inner circular side, and the end face is also machined into a bevel. The thinned tail of the previous guide section overlaps with the thinned head of the next guide section, leaving a guide section joint formed by the first axial gap, the second axial gap, and the radial gap.

[0015] Optionally, each of the flow guide sections is supported on the inner circular wall by stiffeners, and each of the chambers communicates with a flow guide section joint. Each chamber and the corresponding flow guide section joint constitute an independent working unit.

[0016] Optionally, the outer side of the chamber is provided with radially distributed reinforcing ribs.

[0017] Optionally, the reinforcing rib is C-shaped and connects the low-pressure exhaust device to the front of the exhaust guide ring.

[0018] Optionally, the pressure in the space at the lower end of the diversion pipe is close to the pressure in the condenser and lower than the exhaust pressure of the last stage moving blades.

[0019] Optionally, two circular holes are opened side by side laterally at the bottom of the last chamber, and each circular hole is connected to a drainage tube.

[0020] To achieve the other objective mentioned above, the present invention provides a steam turbine, wherein a low-pressure exhaust device is provided at the bottom of the low-pressure cylinder exhaust passage of the steam turbine, and the low-pressure exhaust device is a low-pressure exhaust device suitable for low-load operation of the steam turbine as described in any of the above claims.

[0021] Compared with existing technologies, this invention adds a low-pressure exhaust device to the low-pressure exhaust passage of the steam turbine. This device has three functions: guiding flow, suppressing vortex size growth, and collecting moisture. By changing the surface structure of the low-pressure exhaust passage and adding an absorption device, it can limit the reverse flow and size growth of the vortex. When the vortex size decreases, the number of water droplets it carries also decreases. Some water droplets are also sucked into the device along with the steam, reducing the probability of water droplets scouring the root region of the last-stage moving blades, thus enabling the steam turbine to operate continuously for a long time under low-load conditions.

[0022] The steam turbine provided by the present invention is equipped with the aforementioned low-pressure exhaust device. Since the low-pressure exhaust device has the above-mentioned technical effects, the steam turbine equipped with the low-pressure exhaust device should also have the corresponding technical effects. Attached Figure Description

[0023] Figure 1 A longitudinal cross-sectional view of the low-pressure exhaust device provided in an embodiment of the present invention;

[0024] Figure 2 for Figure 1 A magnified view of part I in the middle;

[0025] Figure 3 for Figure 1 A magnified view of a portion of part II;

[0026] Figure 4 for Figure 1AA sectional view.

[0027] In the picture:

[0028] 100. Low-pressure exhaust device; 101. Exhaust guide ring; 102. Cylinder; 103. Condenser; 104. Water spray desuperheating device;

[0029] 1. Low-pressure exhaust passage; 2. Rotor; 3. Last stage moving blade; 4. Chamber; 5. Guide section; 6. Head; 7. Tail; 8-1 Outer circular wall; 8-2 Inner circular wall; 9. Front end plate; 10. Rear end plate; 11. Support rib; 12. Reinforcing rib; 13. Second guide section; 14. Tongue-shaped structure; 15. Last guide section; 16. Circular hole; 17. Drainage pipe. Detailed Implementation

[0030] To enable those skilled in the art to better understand the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0031] In this document, terms such as "upper," "lower," "inner," and "outer" are established based on the positional relationships shown in the accompanying drawings. Depending on the drawings, the corresponding positional relationships may also change. Therefore, they should not be interpreted as an absolute limitation on the scope of protection. Moreover, relational terms such as "first" and "second" are only used to distinguish one component from another that has the same name, and do not necessarily require or imply any such actual relationship or order between these components.

[0032] To control water erosion in the root region of the last-stage moving blades during low-load operation of the steam turbine, the first consideration is to effectively suppress the generation of counter-flowing vortices in the root region of the last-stage moving blades on the steam outlet side. Even if the vortices cannot be completely eliminated, reducing the size of the vortices and the number of water droplets they carry can reduce the scouring of the moving blades by the water droplets, which is also an effective way to prevent water erosion of the blades.

[0033] To suppress the generation and growth of vortices in the reverse flow region at the root of the last-stage moving blades, it is necessary to modify the structure of the exhaust channel or add control equipment within it. Therefore, this invention achieves the above-mentioned function by modifying the surface structure of the exhaust channel and adding control equipment. The approach is as follows: first, to limit the reverse flow of steam by designing a unidirectional flow surface; second, to reduce the size of the vortex by utilizing the principle of pressure difference absorption; and third, to reduce the number of water droplets carried by the vortex.

[0034] As the size of the vortex decreases, the number of water droplets it carries also decreases. Some of the water droplets will be drawn into the device along with the backflowing steam, thus reducing the chance of water droplets scouring the moving blades.

[0035] Please refer to Figures 1 to 4 , Figure 1 A longitudinal cross-sectional view of the low-pressure exhaust device provided in an embodiment of the present invention; Figure 2 for Figure 1 A magnified view of part I in the middle; Figure 3 for Figure 1 A magnified view of a portion of part II; Figure 4 for Figure 1 AA sectional view.

[0036] As shown in the figure, in one specific embodiment, the low-pressure exhaust device 100 provided by the present invention, which is suitable for low-load operation of steam turbine, is generally sleeve-shaped. Its radial dimension gradually increases from the low-pressure last-stage moving blade 3 to the exhaust guide ring 101, and surrounds the rotor periphery in the root region of the low-pressure exhaust channel.

[0037] The low-pressure exhaust device 100 has an outer circular wall 8-1 and an inner circular wall 8-2. The front end of the outer circular wall 8-1 extends beyond the inner circular wall 8-2 by a certain distance. The outer circular wall 8-1 and the inner circular wall 8-2 are connected by a front end plate 9 and a rear end plate 10. The front end of the outer circular wall 8-1 is close to the low-pressure final stage moving blade 3 to receive the exhaust of the moving blade. The tail end of the outer circular wall 8-1 is connected to the exhaust guide ring 101. Its interior is divided into multiple chambers 4 by a supporting rib plate 11. Each chamber 4 has a first axial gap B, a second axial gap D, and a radial gap C on the corresponding outer circular wall 8-1. The first axial gap B and the second axial gap D are staggered and inclined in a direction that is conducive to the exhaust flow. The radial gap C connects the first axial gap B and the second axial gap D.

[0038] The outer circular wall 8-1 is integrally formed with the exhaust guide ring 101 at the root of the moving blade, which is equivalent to replacing the front half of the exhaust guide ring 101 with a low-pressure exhaust device 100. Therefore, the low-pressure exhaust device has at least three functions: forward flow guidance, suppression of vortex size growth, and moisture collection.

[0039] The chord length of the drainage section A is 400mm-600mm, and the opening depth of the supporting rib plate 11 is 10mm-30mm. The first axial clearance B and the second axial clearance D are greater than the radial clearance C. The first axial clearance B is 8mm-12mm, the second axial clearance D is 8mm-12mm, and the radial clearance C is 3mm-6mm.

[0040] Specifically, the outer circular wall 8-1 is divided into multiple roof-shaped guide sections 5. These guide sections 5 are connected end to end to form a continuous guide wall surface. The head of the guide section 5 is locally thinned on the outer circular side, and the end face is machined into a bevel. The tail of the guide section 5 is locally thinned on the inner circular side, and the end face is also machined into a bevel. The thinned tail of the previous guide section 5 overlaps with the thinned head of the next guide section 5, but a gap is left between them. Between every two guide sections 5, there is a first axial gap B and a second axial gap D of about 10 mm in the direction of steam flow (axial direction), and a radial gap C of 3 mm to 4 mm in the direction almost perpendicular to the guide wall surface (radial direction).

[0041] The first axial gap B, the second axial gap D, and the radial gap C together form the guide section joint. This overlapping method of forming the guide section joint, like the overlapping structure of roof tiles, only facilitates fluid flow in one direction, that is, it is conducive to the smooth flow of exhaust gas through the last stage moving blades, but not conducive to the flow of the counter-vortex at the blade root.

[0042] The joints between the head and tail sections of each guide section are characterized by a large axial clearance and a small radial clearance. The axial clearance is inclined in the direction favorable to exhaust steam flow, while the smaller radial clearance facilitates the formation of a low-pressure zone within the chamber. This structure is unfavorable for the growth of vortices and countercurrent flow, while simultaneously promoting the generation of pressure differentials and the collection of water droplets.

[0043] This exhaust device can effectively reduce the size of the vortex and collect the water droplets carried by the vortex, preventing the water droplets from washing away the root area of ​​the last stage moving blade.

[0044] Each guide section 5 is supported on the inner circular wall 8-2 by a support rib plate 11. Each chamber 4 is connected to a guide section joint. Each chamber 4 and the corresponding guide section joint form an independent working unit.

[0045] The tilt angle 'a' of each joint can be obtained through analysis and calculation to achieve maximum working efficiency, ensuring that each unit does not affect the others during operation.

[0046] To enhance the rigidity of the exhaust device, several radially distributed reinforcing ribs 12 are welded to the outside of the chamber 4. The C-shaped reinforcing ribs 12 connect the low-pressure exhaust device 100 to the front of the exhaust guide ring 101.

[0047] The low-pressure exhaust device 100 and the exhaust guide ring 101 are divided into an upper body and a lower body. The upper body and the lower body are combined to form a whole. The structures of the upper body and the lower body are not exactly the same.

[0048] The outer circular wall 8-1 at the bottom of the low-pressure exhaust device 100 encloses the bottom area of ​​the chamber 4 to form the drainage section A. The support rib 11 at the bottom of the low-pressure exhaust device 100 has an opening at the lower edge that connects each chamber 4 to form an internal drainage path corresponding to the drainage section A. The bottom of the last chamber 4 is connected to a drainage pipe 17, which extends downward to the lowest end of the cylinder.

[0049] Specifically, each guide section 5 of the lower half of the exhaust device is broken at the bottom with a chord length of approximately 500 mm, starting from the second section. The tail of the first guide section 5 extends out over a width of approximately 500 mm at the bottom to form a tongue-shaped structure, the end of which is welded to the head of the last guide section 5. The supporting ribs 11 of each guide section 5 shorten their height by approximately 20 mm over a width of approximately 500 mm at the bottom, creating a distance of approximately 20 mm between them and the inner circular wall of the chamber 4.

[0050] Thus, each chamber 4 is connected to the others by an opening approximately 500 mm long and 20 mm wide. Two round holes are opened horizontally side by side at the bottom of the last chamber 4, and each round hole is connected to a drain pipe 17 extending to the bottom of the cylinder. The drain pipe 17 creates a low-pressure zone in the exhaust device chamber.

[0051] The pressure in the space at the lower end of the drainage pipe 17 is close to the pressure in the condenser 103. This pressure is lower than the exhaust pressure of the last stage moving blade 3. Therefore, a low-pressure zone is formed in the chamber of the low-pressure exhaust device 100. This causes some vortex clusters and the water droplets they carry to be sucked into the chamber 4 of the low-pressure exhaust device 100 under the action of pressure difference. The water droplets are discharged from the drainage pipe 17 under the action of gravity and pressure difference.

[0052] Because the structure of the lower half of cylinder 102 is more conducive to the flow of steam, when the turbine is running under low load conditions, the size of the vortex formed by the exhaust of the last stage moving blade 3 in the lower half of the cylinder is smaller than that in the upper half of the cylinder. Therefore, setting a sealing plate of about 500mm in width in the lower half of the cylinder will not affect the device's ability to suppress the size of the vortex.

[0053] As shown by the solid lines with arrows in the figure, the entire flow field and the spray direction of the water spray desuperheating device 104 indicated by the dashed lines with arrows are shown. Under the action of pressure difference, part of the vortex and the water droplets it carries are sucked into the chamber 4 of the low-pressure exhaust device 100 and discharged through the diversion pipe 17, thereby reducing the probability of water droplets scouring the root of the last stage moving blade 3 and enabling the turbine to operate continuously under ultra-low load conditions.

[0054] The above embodiments are merely preferred embodiments of the present invention and are not limited thereto. Targeted adjustments can be made according to actual needs to obtain different implementation methods. For example, the longitudinal section of chamber 4 may have other shapes, etc. Since there are many possible implementation methods, they will not be listed here.

[0055] In addition to the aforementioned low-pressure exhaust device, the present invention also provides a steam turbine equipped with the aforementioned low-pressure exhaust device. The steam turbine has a low-pressure exhaust device at the bottom of its low-pressure cylinder exhaust passage, and the low-pressure exhaust device is the same as described above. For the remaining structure of the steam turbine, please refer to the prior art, which will not be repeated here.

[0056] The low-pressure exhaust device and steam turbine suitable for low-load operation of steam turbines provided by the present invention have been described in detail above. Specific examples have been used to illustrate the principles and implementation methods of the present invention, and the descriptions of the above embodiments are only for the purpose of helping to understand the core ideas of the present invention. It should be noted that those skilled in the art can make several improvements and modifications to the present invention without departing from the principles of the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

Claims

1. A low-pressure exhaust device suitable for low-load operation of steam turbines, characterized in that, The low-pressure exhaust device (100) surrounds the rotor periphery in the root region of the low-pressure exhaust channel. The low-pressure exhaust device (100) includes an outer circular wall (8-1) and an inner circular wall (8-2), which are connected by a front end plate (9) and a rear end plate (10). The front end of the outer circular wall (8-1) is close to the low-pressure final stage moving blade (3), and the rear end of the outer circular wall (8-1) is connected to the exhaust guide ring (101). The low-pressure exhaust device (100) is located in the entire... The body is cylindrical and gradually expands from the low-pressure final stage moving blade (3) towards the exhaust guide ring (101); the interior of the low-pressure exhaust device (100) is divided into multiple chambers (4) by supporting ribs (11), and the outer circular wall (8-1) of each chamber (4) has a first axial clearance (B), a second axial clearance (D) and a radial clearance (C). The first axial clearance (B) and the second axial clearance (D) are offset from each other and inclined in a direction that is conducive to the exhaust flow. The radial clearance (C) connects to the... The first axial clearance (B) and the second axial clearance (D) are described; the outer circular wall (8-1) at the bottom of the low-pressure exhaust device (100) closes the bottom area of ​​the chamber (4) to form a drainage section (A); the supporting rib (11) at the bottom of the low-pressure exhaust device (100) has an opening at its lower edge connecting each of the chambers (4) to form an internal drainage path corresponding to the drainage section (A); the bottom of the last chamber (4) is connected to a drainage pipe (17), the drainage pipe (17) extends... Extending to the lowest end of the cylinder; the outer circular wall (8-1) is divided into multiple roof tile-shaped guide sections (5). The head of the guide section (5) is partially thinned on the outer circular side and the end face is processed into a bevel. The tail of the guide section (5) is partially thinned on the inner circular side and the end face is also processed into a bevel. The thinned tail of the previous guide section (5) overlaps with the thinned head of the next guide section (5) and leaves a guide section joint formed by the first axial gap (B), the second axial gap (D) and the radial gap (C).

2. The low-pressure exhaust device suitable for low-load operation of steam turbines according to claim 1, characterized in that, The outer circular wall (8-1) is integrally formed with the exhaust guide ring (101) at the root of the moving blade, and the low-pressure exhaust device (100) replaces the front half of the exhaust guide ring (101).

3. The low-pressure exhaust device suitable for low-load operation of steam turbines according to claim 1, characterized in that, The front end of the outer circular wall (8-1) extends beyond the inner circular wall (8-2) by a certain distance.

4. The low-pressure exhaust device suitable for low-load operation of steam turbines according to claim 1, characterized in that, The first axial clearance (B) and the second axial clearance (D) are greater than the radial clearance (C).

5. The low-pressure exhaust device suitable for low-load operation of steam turbines according to claim 1, characterized in that, The low-pressure exhaust device (100) is divided into an upper part and a lower part, which are combined to form a whole.

6. The low-pressure exhaust device suitable for low-load operation of steam turbines according to claim 1, characterized in that, The chord length of the drainage part (A) is 400mm-600mm, and the opening depth of the supporting rib plate (11) is 10mm-30mm.

7. The low-pressure exhaust device suitable for low-load operation of steam turbines according to claim 1, characterized in that, The first axial clearance (B) is 8mm-12mm, the second axial clearance (D) is 8mm-12mm, and the radial clearance (C) is 3mm-6mm.

8. The low-pressure exhaust device suitable for low-load operation of steam turbines according to claim 1, characterized in that, Each of the flow guide sections (5) is supported on the inner circular wall (8-2) by a support rib plate (11). Each of the chambers (4) is connected to a flow guide section joint. Each of the chambers (4) and the corresponding flow guide section joint constitute an independent working unit.

9. The low-pressure exhaust device suitable for low-load operation of steam turbines according to claim 1, characterized in that, The outer side of the chamber (4) is provided with radially distributed reinforcing ribs (12).

10. The low-pressure exhaust device suitable for low-load operation of a steam turbine according to claim 9, characterized in that, The reinforcing rib (12) is C-shaped and connects the low-pressure exhaust device (100) to the front of the exhaust guide ring (101).

11. The low-pressure exhaust device suitable for low-load operation of a steam turbine according to claim 1, characterized in that, The pressure in the space at the lower end of the diversion pipe (17) is close to the pressure in the condenser (103), and the exhaust pressure of the low-pressure final stage moving blade (3).

12. The low-pressure exhaust device suitable for low-load operation of a steam turbine according to claim 11, characterized in that, The bottom of the last chamber (4) has two round holes arranged horizontally side by side, and each round hole is connected to a drainage pipe (17).

13. A steam turbine, wherein a low-pressure exhaust device is provided at the bottom of the low-pressure cylinder exhaust passage, characterized in that, The low-pressure exhaust device is any one of the low-pressure exhaust devices suitable for low-load operation of steam turbines as described in any one of claims 1 to 12.

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