Double-layer cylinder interlayer multi-rotor arm spiral heat insulation ring for steam turbine

Abstract

The application provides a steam turbine double-layer cylinder interlayer multi-rotation-arm spiral heat insulation ring, and aims at fundamentally solving the temperature difference between upper and lower layers of a steam turbine double-layer cylinder interlayer. The application relates to the field of steam turbine double-layer cylinder heat insulation, and at least one group of multi-rotation-arm arc segment heat insulation rings are arranged in a spiral manner in the double-layer cylinder interlayer. The spiral arrangement direction of the multi-rotation-arm arc segment heat insulation rings is consistent with the spiral arrangement direction of the front shaft seal leakage flow in the interlayer, the spiral inclination angle θ is consistent with the spiral inclination angle of the front shaft seal leakage flow in the interlayer, each group of heat insulation rings comprises at least two rotation arms, each rotation arm is a rotationally symmetrical structure, and is uniformly distributed in the circumferential direction on the cross section perpendicular to the axial direction. The arrangement can maintain the rotation intensity of the front shaft seal leakage flow during the forward flow, so that the high-temperature leakage flow can be evenly filled around the entire interlayer along the circumference, and the generation of the temperature difference between the upper and lower layers and the temperature fluctuation caused by the collision of the cold and hot steam flows can be avoided to the maximum extent.

Description

Technical Field

[0001] This invention belongs to the field of heat insulation for double-layer cylinders of steam turbines, and specifically relates to a multi-rotor spiral heat insulation ring for double-layer cylinders of steam turbines. Background Technology

[0002] High-power power plant steam turbines typically employ a double-cylinder structure in their high and intermediate pressure cylinders due to the high inlet steam pressure and temperature. This includes both traditional double-cylinder and cylindrical cylinder structures. For safe unit operation, temperature monitoring points are installed in both the upper and lower cylinders during the cylinder design phase. Figure 7 In the schematic diagram of the existing double-layer cylinder sandwich structure shown, the upper cylinder temperature measuring point is 5.1 and the lower cylinder temperature measuring point is 5.2.

[0003] According to the structural design of the double-layer cylinder, one end of the double-layer cylinder interlayer is connected to the leakage gap of the front shaft seal, and the other end is connected to the cylinder exhaust chamber. The interlayer space often contains a cat's claw structure to support the inner cylinder and an inlet pipe, and may also contain an extraction pipe and a make-up valve pipeline. Therefore, in reality, the steam flow within the double-layer cylinder interlayer may include not only the steam flow from the front shaft seal leakage, but also steam leakage from the inlet pipe, air leakage from the extraction pipe, and air leakage from the make-up valve pipe. For example, after long-term operation, leakage may occur in the pipe seal, as well as multiple steam flows such as exhaust backflow. Due to the significant temperature differences between these steam flows, and the complexity of the installation and operation of large units, the double-layer cylinder structure in actual engineering units often suffers from a large temperature difference between the upper and lower cylinder halves.

[0004] like Figure 7The schematic diagram of the double-layer cylinder jacket structure shows that the two ends of the jacket are connected to the front shaft seal leakage point 5.4 and the cylinder exhaust chamber 5.5, respectively. The leakage flow from the front shaft seal comes from the high-temperature and high-pressure inlet steam. Although the shaft seal reduces temperature and pressure, the temperature and pressure are still higher than the exhaust steam in the exhaust chamber. Furthermore, given the complexity of actual unit operating conditions, a pressure difference inevitably exists between the two ends of the jacket in the actual unit. Assuming there are no pipe leaks in the jacket, the flow within the jacket will primarily be the flow of the front shaft seal leakage flow into the jacket and towards the end closer to the exhaust pipe 5.6. Furthermore, because the front shaft seal leakage flow rotates strongly with the rotor before entering the interlayer, this rotation continues as it enters the interlayer. Therefore, the front shaft seal leakage flow initially flows in a spiral shape towards the exhaust side within the interlayer, with the steam flow rotation direction consistent with the rotor's rotation direction. However, as the various structures within the interlayer obstruct and interfere with the airflow, and due to the flow's own dissipation, the rotational force of this spiral flow weakens. Since the exhaust pipe is located in the lower cylinder, the front shaft seal leakage flow initially fills the interlayer space between the upper and lower cylinders with a strong rotational force during its spiral flow towards the exhaust side. However, as the rotational force weakens and it gradually approaches the exhaust side, more shaft seal leakage flow will enter the exhaust pipe connected to the lower cylinder through the interlayer space. In the interlayer space near the exhaust pipe side, because more shaft seal leakage flow tends to accumulate in the lower half of the interlayer, this can lead to a certain "void area" forming in the upper half of the interlayer space. Consequently, some of the exhaust steam from the upper half of the exhaust chamber will flow backward into the upper half of the interlayer towards the intake chamber 5.3. Because the exhaust steam temperature is much lower than the shaft seal leakage flow, this results in a lower local temperature in the upper half of the jacket and a higher temperature in the lower half, causing a temperature difference between the upper and lower cylinder jackets. Furthermore, the high-temperature shaft seal leakage steam entering the jacket from the inlet side meets the exhaust steam entering from the upper half of the jacket from the exhaust pipe side. The interface between these two steam flows may oscillate back and forth due to pressure disturbances on both sides during operation. If the temperature probe is located in this area, the temperature fluctuations in the upper jacket will be clearly visible. Additionally, if local leaks occur in various pipe seals after prolonged unit operation, the resulting sudden temperature changes in the jacket will further exacerbate the temperature differences within the jacket.

[0005] To address the temperature difference between the upper and lower halves of a double-walled cylinder, a common method is to add one or even two annular heat-insulating rings perpendicular to the axial direction to the inner wall of the outer cylinder. The hope is that these rings will block the flow within the interlayer, creating two flow-free "dead chambers." Ideally, when a significant temperature difference exists between different areas of these "dead chambers," the temperature will eventually become uniform through natural heat transfer. However, considering installation and the radial expansion characteristics of the inner and outer cylinders, a gap must be maintained between the annular heat-insulating ring and the outer wall of the inner cylinder. This gap is often ten to several tens of times larger than the gap between the diaphragm and the steam seal, meaning the flow within the interlayer cannot be completely blocked. To address this issue, some scholars and engineers have even proposed designing steam seal teeth or brushes at the ends of the heat-insulating rings, or using various elastic sealing devices to enhance their sealing effect. Currently, following the approach of blocking interlayer flow, one or even multiple annular heat-insulating rings are frequently installed within the interlayer. While this approach alleviates the temperature difference between the upper and lower cylinders to some extent during normal operation of the unit, it cannot fundamentally solve the temperature difference problem, and the temperature difference between the upper and lower cylinders in the double-layered cylinder jacket remains a significant issue. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a multi-arm spiral heat insulation ring for the sandwiched space of a steam turbine double-cylinder unit. On one hand, it addresses the low-temperature exhaust steam backflow caused by the high-temperature leakage flow from the front shaft seal within the sandwiched space. On the other hand, since the sandwiched flow in actual double-cylinder units can only be weakened, not eliminated, and since the sandwiched flow in actual units cannot be completely blocked, the multi-arm spiral heat insulation ring is designed based on the principle of "prevention is worse than cure," aiming to fundamentally solve the problem of temperature difference between the upper and lower layers of the double-cylinder sandwiched space.

[0007] To achieve the objective of this invention, the technical solution adopted is as follows: A multi-arm spiral heat insulation ring for a double-layer cylinder jacket of a steam turbine includes at least one set of multi-arm arc segment heat insulation rings. The multi-arm arc segment heat insulation rings are spirally arranged in the double-layer cylinder jacket. The spiral direction of the multi-arm arc segment heat insulation rings is consistent with the rotation direction of the leakage flow of the front shaft seal in the jacket. The spiral angle θ of the multi-arm arc segment heat insulation rings is consistent with the spiral angle of the leakage flow of the front shaft seal in the jacket. Each set of multi-arm arc segment heat insulation rings includes m spiral arms, where m ≥ 2. Each spiral arm of each set of multi-arm arc segment heat insulation rings is rotationally symmetric. Each spiral arm of each set of multi-arm arc segment heat insulation rings is evenly distributed circumferentially on a cross section perpendicular to the axial direction, and the projected arc segment of each spiral arm on the cross section perpendicular to the axial direction occupies 1 / m of the entire circumference.

[0008] Furthermore, three sets of multi-rotor arc-shaped heat insulation rings are preferred.

[0009] Furthermore, the helical tilt angle θ is an acute angle, preferably 60° to 80°, and even more preferably 75°.

[0010] Furthermore, the rotating arms of each group of multi-rotor arc segment heat insulation rings are preferably one of two-rotor arms, three-rotor arms, or four-rotor arms.

[0011] Furthermore, the rotation direction of each rotating arm is the same as that of the rotor, and the helical inclination angle θ is the same as the helical inclination angle of the front shaft seal leakage flow in the interlayer.

[0012] The helical angle of the front axle seal leakage flow gradually decreases from the intake side to the exhaust side. That is, the value decreases slightly closer to the exhaust side, but this decrease can be ignored overall. The helical angle of the front axle seal leakage flow in the cylinder can be predicted by CFD flow simulation. This angle is related to the size and shape of the interlayer space, the design of the front axle seal, etc.

[0013] Preferably, the multi-arm arc segment heat insulation ring is a double-arm type, with 2-5 sets of double-arm arc segment heat insulation rings arranged axially. In each set, the first arm of the heat insulation ring cooperates to form a single arm penetrating the entire cylinder jacket, and the second arm of the heat insulation ring in each set also cooperates to form another single arm penetrating the entire cylinder jacket. Figure 2 As shown.

[0014] Furthermore, three sets of double-arm arc-segment heat insulation rings are arranged along the cylinder interlayer, with each arm in each set fully located in either the upper or lower cylinder. Each arm's projection on the circumferential cross-section occupies a 180° arc segment, thus avoiding cutting the arms during installation. The acute helical angle between each arm and the axial direction is θ. Figure 3 As shown.

[0015] Preferably, the multi-arm arc segment heat insulation ring is a four-arm structure. The heat insulation ring 1 arm in each group cooperates with each other to form a single arm that penetrates the entire cylinder jacket. The heat insulation ring 2 arms in each group cooperate with each other to form a second single arm that penetrates the entire cylinder jacket. The heat insulation ring 3 arms in each group cooperate with each other to form a third single arm that penetrates the entire cylinder jacket. The heat insulation ring 4 arms in each group cooperate with each other to form a fourth single arm that penetrates the entire cylinder jacket.

[0016] Furthermore, the multi-arm arc-segment heat insulation ring is a four-arm design, with 2-5 sets of four-arm arc-segment heat insulation rings arranged axially. Each of the four arms in each set occupies 1 / 4 of the circumference in a cross-section perpendicular to the axial direction, and they are rotationally symmetrical. The acute helical angle θ between each arm and the axial direction is also θ. The spiral advance direction of the heat insulation ring is from the cylinder inlet side to the exhaust side. Looking along the spiral advance direction of the heat insulation ring, the rotation direction of the heat insulation ring is the same as the rotor's rotation direction. Figure 4 As shown.

[0017] Furthermore, three sets of four-arm arc-shaped heat insulation rings are arranged along the cylinder interlayer. The first set is located between the steam inlet pipe and the steam replenishment pipe to avoid the two steam inlet pipes of the lower cylinder. The second set is located behind the steam replenishment pipes of the upper and lower cylinders to avoid the steam replenishment pipes. The third set has two arms in the upper cylinder to avoid the steam extraction pipe of the lower cylinder.

[0018] In addition, in some special cases, if a certain spiral arm interferes with other structures in the interlayer, the axial position of the spiral arm group can be slightly adjusted, and the angle of the spiral arm group can be adjusted within the above-mentioned spiral tilt angle range to avoid interference; however, if the above measures are ineffective, the spiral arm can be flexibly omitted while the other spiral arms in the group are retained.

[0019] The above technical solution has the following beneficial effects: like Figure 1 The single-arm heat insulation ring shown is arranged in a spiral shape within the interlayer, representing an ideal configuration. However, due to the space occupied by structures such as inlet and outlet pipes, claw-like structures, and bosses within the interlayer, and considering the installation characteristics of the upper and lower cylinders during the processing and installation of the heat insulation ring, a single spiral arm cannot axially penetrate the entire interlayer. Therefore, this invention uses several sets of multi-arm arc-segment heat insulation rings axially to achieve the spiral arm heat insulation ring configuration throughout the entire interlayer. Based on the single-arm heat insulation ring, the number of spiral arms is appropriately increased in a circumferentially rotationally symmetrical manner, thus forming a multi-arm heat insulation ring. The multiple spiral arms work together to effectively guide the leakage flow in the interlayer along a predetermined path. This configuration maintains the rotational force of the front shaft seal leakage flow during its forward flow, allowing the high-temperature leakage flow to evenly fill the entire interlayer circumference. Furthermore, when a local insertion tube seal failure causes local leakage, the spirally advancing leakage flow carries the local leakage flow along with it, which can more quickly eliminate the local temperature fluctuations caused by the insertion tube leakage. This design allows the leakage flow to fill the entire interlayer relatively evenly along the circumference, resulting in essentially uniform pressure across the circumferential cross-section of the interlayer. This reduces the likelihood of localized "void zones" in the circumferential direction, thus preventing backflow of exhaust steam near the exhaust chamber. Therefore, this design minimizes both the temperature difference between the upper and lower cylinders and the temperature fluctuations caused by the clash of hot and cold steam flows. Furthermore, the grouped arrangement of the rotating arm segments avoids interference with inlet pipes, exhaust pipes, claw-like structures, bosses, extraction pipes, and make-up pipes, ensuring the practical operability of the invention. The specific number of groups can be flexibly adjusted based on the axial length of the cylinder interlayer. The geometric design of each group of rotating arms is identical, differing only in their axial direction. Attached Figure Description

[0020] Figure 1 A schematic diagram of an ideal spiral single-arm heat insulation ring structure; Figure 2This is a schematic diagram of a double-arm spiral heat insulation ring structure; Figure 3 This is a schematic diagram of the structure of a double-arm spiral heat insulation ring with a split surface in the top and bottom directions; Figure 4 This is a schematic diagram of a four-arm spiral heat insulation ring structure; Figure 5 This is a schematic diagram of the double-arm spiral heat insulation ring structure in the double-layer cylinder of the 600MW steam turbine in Example 1; Figure 6 This is a schematic diagram of the four-arm spiral heat insulation ring structure in the double-layer cylinder of the 600MW steam turbine in Example 2; Figure 7 This is a schematic diagram of a double-layer cylinder sandwich structure in the prior art; In the diagram: 1.1 - Outer cylinder, 1.2 - Inner cylinder, 1.3 - Arm 1 of the first heat insulation ring, 1.4 - Arm 2 of the first heat insulation ring, 1.5 - Arm 1 of the second heat insulation ring, 1.6 - Arm 2 of the second heat insulation ring, 1.7 - Arm 1 of the third heat insulation ring, 1.8 - Arm 2 of the third heat insulation ring, 1.9 - Interlayer space, 1.10 - Double-layer cylinder exhaust chamber; 2.1 - Outer cylinder, 2.2 - Inner cylinder, 2.3 - Arm 1 of the first heat insulation ring, 2.4 - Arm 2 of the first heat insulation ring, 2.5 - Arm 3 of the first heat insulation ring, 2.6 - Arm 4 of the first heat insulation ring, 2.7 - Arm 1 of the second heat insulation ring, 2.8 - Arm 2 of the second heat insulation ring, 2.9 - Arm 3 of the second heat insulation ring, 2.10 - Arm 4 of the second heat insulation ring, 2.11 - Third heat insulation ring 1. Ring 1 arm; 2.12 - Third group of heat insulation ring 2 arm; 2.13 - Third group of heat insulation ring 3 arm; 2.14 - Third group of heat insulation ring 4 arm; 2.15 - Interlayer space; 2.16 - Double-layer cylinder exhaust chamber; 3.1 - Steam inlet pipe; 3.2 - Steam exhaust pipe; 3.3 - Outer cylinder; 3.4 - Inner cylinder; 3.5 - Double-rotating-arm spiral heat insulation ring; 4.1 - Steam inlet pipe; 4.2 - Steam exhaust pipe; 4.3 - Steam replenishment pipe; 4.4 - Steam extraction pipe; 4.5 - Outer cylinder; 4.6 - Inner cylinder; 4.7 - Four-rotating-arm spiral heat insulation ring; 5.1 - Upper cylinder temperature measuring point; 5.2 - Lower cylinder temperature measuring point; 5.3 - Steam inlet chamber; 5.4 - Front shaft seal; 5.5 - Steam exhaust chamber; 5.6 - Steam exhaust pipe; 5.7 - Traditional heat insulation ring; 5.8 - Steam extraction insertion pipe. Detailed Implementation

[0021] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be further described in detail below with reference to the accompanying drawings.

[0022] Example 1 A double-arm spiral heat insulation ring for a steam turbine double-cylinder jacket includes at least three sets of double-arm arc-segment heat insulation rings. The double-arm arc-segment heat insulation rings are spirally arranged within the double-cylinder jacket, with their forward rotation direction consistent with the rotation direction of the leakage flow from the front shaft seal within the jacket. The spiral angle of the double-arm arc-segment heat insulation ring is 60°–80°, consistent with the spiral angle of the leakage flow from the front shaft seal within the jacket. Each set of double-arm arc-segment heat insulation rings includes two arms. These two arms in each set are rotationally symmetrical and are evenly distributed circumferentially on a cross-section perpendicular to the axial direction. The projected arc segments of these two arms on the cross-section perpendicular to the axial direction each occupy 1 / 2 of the entire circumference. Figure 2 , Figure 3 As shown, the first set of heat insulation ring 1 arm 1.3, the second set of heat insulation ring 1 arm 1.5 and the third set of heat insulation ring 1 arm 1.7 cooperate with each other to form a single rotating arm that penetrates the entire cylinder jacket. The first set of heat insulation ring 2 arm 1.4, the second set of heat insulation ring 2 arm 1.6 and the third set of heat insulation ring 2 arm 1.8 also cooperate with each other to form another single rotating arm that penetrates the entire cylinder jacket.

[0023] Example 2 A four-arm spiral heat insulation ring with a double-layer cylinder jacket for steam turbines is provided. Three sets of four-arm arc-shaped heat insulation rings are arranged axially. Each set of four arms occupies one-quarter of the circumference in a cross-section perpendicular to the axial direction and are rotationally symmetrical. The acute helical angle of each arm with respect to the axial direction is 60°–80°. The spiral advance direction of the heat insulation ring is from the steam inlet side to the steam outlet side of the cylinder. Viewed along the spiral advance direction of the heat insulation ring, the rotation direction of the heat insulation ring is the same as the rotor rotation direction. Figure 4 As shown, the first set of heat insulation rings, arm 2.3, arm 2.7, and arm 2.11 cooperate to form the first single-rotary arm that penetrates the entire cylinder jacket. The first set of heat insulation rings, arm 2.4, arm 2.8, and arm 2.12 cooperate to form the second single-rotary arm that penetrates the entire cylinder jacket. The first set of heat insulation rings, arm 2.5, arm 2.9, and arm 2.13 cooperate to form the third single-rotary arm that penetrates the entire cylinder jacket. The first set of heat insulation rings, arm 2.6, arm 2.10, and arm 2.14 cooperate to form the fourth single-rotary arm that penetrates the entire cylinder jacket.

[0024] Example 3 like Figure 5 As shown, in the double-layer cylinder of the actual 600MW turbine, three sets of double-spinning spiral heat insulation rings 3.5 are set along the turbine axis in the interlayer between the double lower steam inlet pipe 3.1 and the double lower steam outlet pipe 3.2, and between the outer cylinder 3.3 and the inner cylinder 3.4. When viewed from the steam inlet side to the steam outlet side, the unit rotor rotates counterclockwise.

[0025] Example 4 like Figure 6 As shown, the four-arm spiral heat insulation ring in the double-layer cylinder of the 600MW actual unit turbine is affected by the structure of the steam inlet pipe 4.1, the exhaust pipe 4.2, the extraction pipe 4.4, and the make-up pipe 4.3 in the interlayer space. Therefore, the spiral heat insulation ring in this embodiment is set in three groups. The first group is set between the steam inlet pipe and the make-up pipe, mainly to avoid the two steam inlet pipes of the lower half cylinder. The second group is set after the make-up pipes of the upper and lower cylinders to avoid the make-up pipes. The third group only sets two spiral arms in the upper half cylinder and omits the two spiral arms in the lower half to avoid the extraction pipe of the lower half cylinder.

[0026] In the currently common 600MW and 1000MW thermal power units, 3-4 sets of multi-rotor arm arcs and double-rotor or quadruple-rotor arms are usually set according to the actual situation.

[0027] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A multi-arm spiral heat insulation ring with a double-layer cylinder jacket for a steam turbine, characterized in that: It includes at least one set of multi-arm arc segment heat insulation rings; the multi-arm arc segment heat insulation rings are spirally arranged in the double-layer cylinder jacket, and the spiral direction of the multi-arm arc segment heat insulation rings is consistent with the rotation direction of the front shaft seal leakage flow in the jacket; the spiral angle θ of the multi-arm arc segment heat insulation rings is consistent with the spiral angle of the front shaft seal leakage flow in the jacket; Each group of multi-arm arc segment heat insulation rings includes m arms, where m ≥ 2; each arm of each group of multi-arm arc segment heat insulation rings is rotationally symmetric to each other, and each arm of each group of multi-arm arc segment heat insulation rings is evenly distributed circumferentially on a cross section perpendicular to the axial direction, and the projected arc segment of each arm on the cross section perpendicular to the axial direction occupies 1 / m of the entire circumference; The rotation direction of each arm of the multi-arm arc segment heat insulation ring is the same as that of the rotor, and the helical inclination angle θ is the same as the helical inclination angle of the front shaft seal leakage flow in the interlayer. The angle of the helical tilt θ is 60° to 80°.

2. The multi-arm spiral heat insulation ring with double-layer cylinder jacket for steam turbines according to claim 1, characterized in that: The multi-arm arc segment heat insulation ring consists of 2-5 sets.

3. The multi-arm spiral heat insulation ring with double-layer cylinder jacket for steam turbines according to claim 1, characterized in that: When the multi-arm arc segment heat insulation ring is a double-arm type, 2-5 sets of double-arm arc segment heat insulation rings are set in the axial direction. The first arm of the heat insulation ring in each set cooperates with each other to form a single arm that penetrates the entire cylinder jacket. The second arm of the heat insulation ring in each set also cooperates with each other to form another single arm that penetrates the entire cylinder jacket.

4. The multi-arm spiral heat insulation ring with double-layer cylinder jacket for steam turbines according to claim 1, characterized in that: When the multi-arm arc segment heat insulation ring is a double-arm type, the double-arm arc segment heat insulation ring is arranged in 3 groups along the cylinder interlayer, and each arm in each group is completely located in the upper or lower half of the cylinder, and the projection of each arm on the circumferential cross section occupies a 180° arc segment.

5. The multi-arm spiral heat insulation ring with double-layer cylinder jacket for steam turbines according to claim 1, characterized in that: When the multi-arm arc segment heat insulation ring is a four-arm type, the first arm of the heat insulation ring in each group cooperates to form a single arm that penetrates the entire cylinder jacket, the second arm of the heat insulation ring in each group cooperates to form a second single arm that penetrates the entire cylinder jacket, the third arm of the heat insulation ring in each group cooperates to form a third single arm that penetrates the entire cylinder jacket, and the fourth arm of the heat insulation ring in each group cooperates to form a fourth single arm that penetrates the entire cylinder jacket.

6. The multi-arm spiral heat insulation ring with double-layer cylinder jacket for steam turbines according to claim 1, characterized in that: When the multi-arm arc segment heat insulation ring is a four-arm type, 2-5 sets of four-arm arc segment heat insulation rings are set in the axial direction. The four arms in each set occupy 1 / 4 of the circumference in the cross section perpendicular to the axial direction and are rotationally symmetrical to each other.

7. The multi-arm spiral heat insulation ring with double-layer cylinder jacket for steam turbines according to claim 1, characterized in that: When the multi-arm arc segment heat insulation ring is a four-arm ring, three sets of the four-arm arc segment heat insulation ring are arranged along the cylinder interlayer. The first set is arranged between the steam inlet pipe and the steam replenishment pipe, the second set is arranged behind the steam replenishment pipes of the upper and lower cylinders, and the third set has two arms arranged in the upper half cylinder.

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