Patent Application
20150083365
1. Field
The disclosed concept pertains generally to a steam generator, and in particular to a steam generator including anti-vibration bars. The disclosed concept also pertains to a method of securing tubes in a steam generator against vibration with a number of anti-vibration bars.
2. Background Information
Heat exchangers having tube bundles are commonly employed in pressurized water nuclear reactor systems. A steam generator generally comprises a vertically oriented shell, a tube bundle formed of tubes which each comprise two vertical components that meet at a bend portion, a tube sheet for supporting the tubes at the ends opposite the bend portion, a dividing plate that cooperates with the tube sheet and a hemispheric channel head to form a primary fluid inlet header at one end of the tube bundle and a primary fluid outlet header at the other end of the tube bundle. A primary fluid inlet nozzle is in fluid communication with the primary fluid inlet header and a primary fluid outlet nozzle is in fluid communication with the primary fluid outlet header. The steam generator secondary side comprises a wrapper disposed between the tube bundle and the shell to form an annular chamber made up of the shell on the outside and the wrapper on the inside, and a feedwater ring disposed above the bend portion of the tube bundle.
The primary fluid having been heated by circulation through the reactor core enters the steam generator through the primary fluid inlet nozzle. From the primary fluid inlet nozzle, the primary fluid is conducted through the primary fluid inlet header, through the inside of the tube bundle, out the primary fluid outlet header, through the primary fluid outlet nozzle to the reactor coolant pump for recirculation. At the same time, feedwater is introduced to the steam generator secondary side through a feedwater nozzle which is connected to the feedwater ring inside the steam generator. Upon entering the steam generator, the feedwater mixes with water returning from moisture separators positioned above the tube bundle referred to as the recirculation stream. This mixture, called the downcomer flow, is conducted down the annular chamber between the shell and the wrapper until the tube sheet near the bottom of the annular chamber causes the water to change direction, passing in heat exchange relationship with the outside of the tubes and up through the inside of the wrapper. While the water is circulating in heat exchange relationship with the tube bundle, heat is transferred from the primary fluid in the tubes to the water surrounding the tubes, causing a portion of the water outside the tubes to be converted to steam. The steam-water mixture then rises and is conducted through a number of moisture separators that separate any entrained water from the steam, and the steam vapor then exits the steam generator and is circulated typically through a turbine generator to generate electricity in a manner well known in the art.
The portion of the steam generator primarily including the bend portion of the tubes and below to the channel head is typically referred to as the evaporator section. The portion of the steam generator above the tubes that includes the moisture separators is typically referred to as the steam drum. Feedwater enters the steam generator through an inlet nozzle which is disposed in the upper portion of the cylindrical shell. The feedwater is distributed and mixed with water removed by the moisture separators and then flows down the annular channel surrounding the tube bundle.
The tubes are supported at their open ends by conventional means whereby the ends of the tubes are welded to the tube sheet which is disposed generally transverse to the longitudinal axis of the steam generator. A series of tube support plates or grids arranged in an axial spaced relationship to each other are provided along the straight portion of the tubes in order to support the straight section of the tubing. Regarding the tube bundle, various steam generators utilize different tube configurations, for example wherein the bend portion is curved or U-shaped, or wherein the vertical components of the tubes each bend at sharp angles, forming a relatively horizontal shaped bend portion.
Located within the bend portion of the tubes are a plurality of anti-vibration bars which are typically disposed between each column of tubes. The anti-vibration bars provide support and do not substantially interfere with the flow of the moisture laden steam. The anti-vibration bars are intended to prevent excessive vibrations of the individual tubes of the entire tube bundle; vibrations which can potentially damage the tubes. It is well known that the bend portion of the tube bundle is more severely affected by the vibrations, and, because of the bend configuration, more difficult to adequately support in order to eliminate the vibrations.
Typical motion of the tubes experiencing normal vibration is transverse to the plane of the U-bend and therefore such vibration is referred to as out-of-plane vibration. Under unusual conditions, tubes can also experience in-plane vibration. In such situations, adjacent tubes in a given column can contact one another, resulting in severe damage to the tubes. The manufacturing and assembly of the tube bundle are major obstacles to a mechanical solution to this problem. Hence, current anti-vibration bar assembly designs do not significantly restrict in-plane motion of the tubes.
These needs and others are met by the disclosed concept in which a solid anti-vibration bar having an increased thickness is structured to be located within a tube bundle.
In accordance with one aspect of the disclosed concept, a steam generator is provided. The steam generator has a primary side for circulating a heated fluid and a secondary side for circulating a fluid to be heated by the heated fluid circulating in the primary side. The steam generator includes: a channel head for receiving the heated fluid; a tube sheet that separates the channel head from the secondary side; a tube bundle having a plurality of tubes, arranged in rows and columns, the tube bundle extending from the channel head, through the tube sheet and through at least a portion of the secondary side; and a first number of solid anti-vibration bars. The plurality of tubes includes a first column of tubes, the first column of tubes comprising a first tube having a curved center line disposed in a first plane. The plurality of tubes further includes a second column of tubes, each of the first number of anti-vibration bars being disposed between the first column of tubes and the second column of tubes. The second column of tubes comprises a second tube having a curved center line disposed in a second plane, the second plane being parallel to and spaced a distance from the first plane. Each of the tubes has a tube outer diameter. Each of the first number of anti-vibration bars has a thickness generally transverse to the first and second planes. The thickness of each of the first number of anti-vibration bars is greater than the distance between the first and second planes minus the tube outer diameter.
In accordance with another aspect of the disclosed concept, a method is provided for securing tubes within a steam generator against vibration, the tubes being disposed in a tube bundle and arranged in rows and columns, with lanes between the columns. The method comprises: providing a first column of tubes, the first column of tubes comprising a first tube having a curved center line disposed in a first plane; providing a first number of solid anti-vibration bars; and providing a second column of tubes, each of the first number of anti-vibration bars being disposed between the first column of tubes and the second column of tubes, the second column of tubes comprising a second tube having a curved center line disposed in a second plane, the second plane being parallel to and spaced a distance from the first plane. Each of the tubes has a tube outer diameter. Each of the first number of anti-vibration bars has a thickness generally transverse to the first and second planes. The thickness of each of the first number of anti-vibration bars is greater than the distance between the first and second planes minus the tube outer diameter.
A full understanding of the disclosed concept can be gained from the following description of the preferred embodiments when read in conjunction with the accompanying drawings in which:
Referring now to the drawings,
The tube bundle 4 is encircled by a wrapper 30 which forms an annular passage 32 between the wrapper 30 and the shell and transition portions 6,14, respectively. The top of the wrapper 30 is covered by a lower deck plate 34 which includes a plurality of openings 36 in fluid communication with a plurality of riser tubes 38. Swirl vanes 40 are disposed within the riser tubes 38 to cause steam flowing therethrough to spin and centrifugally remove some of the moisture contained within the steam as it flows through this primary centrifugal separator. The water separated from the steam in this primary separator is returned to the top surface of the lower deck plate 34. After flowing through the primary centrifugal separator, the steam passes through a secondary separator 42 before reaching a steam outlet nozzle 44 centrally disposed in the dished head 8. The water separated from the steam in the secondary separator 42 is returned to mix with the water returned from the primary separator above the lower deck plate 34.
The feedwater inlet structure of this steam generator 2 includes a feedwater inlet nozzle 46 having a generally horizontal portion called a feedring 48 and discharge nozzles 50 elevated above the feedring 48. Feedwater, which is supplied through the feedwater inlet nozzle 46, passes through the feedwater ring 48, exits through the discharge nozzles 50 and mixes with water which was separated from the steam and is recirculated. The mixture then flows down above the lower deck plate 34 into the annular downcomer passage 32. The water then enters the tube bundle 4 at the lower portion of the wrapper 30 and flows among the tubes 3 and up the tube bundle 4 where it is heated to generate steam.
As previously mentioned, the tube bundle 4 has a plurality of anti-vibration bars (not shown in
As will be discussed in connection with
The first column of tubes 210 may be either in the middle of the tube bundle 200 or may be at an end. Located between the first column of tubes 210 and the second column of tubes 230 is an anti-vibration bar 220. The anti-vibration bar 220 is solid and has a thickness 222. Referring to
As seen in
Similar to the thickness 222 of the anti-vibration bar 220, the thickness 242 of the anti-vibration bar 240 is generally transverse to planes 236,256 and is greater than the distance 201 between the columns of tubes 230,250. In operation, this increased thickness prevents significant in-plane (see, for example, planes 216,236,256) motion in the columns of tubes 210,230,250, advantageously corresponding to a significant decrease in in-plane vibration within the tube bundle 200. As seen in
Similarly, the anti-vibration bar 240 includes a number of bends 244 that are curved and are structured to wind between the second column of tubes 230 and the third column of tubes 250. The bends 224,244 enable the thicknesses 222,242 of the anti-vibration bars 220,240 to be greater than the thicknesses 122,142 of the anti-vibration bars 120,140. Furthermore, while the thicknesses 122,142 of the anti-vibration bars 120,140 are no greater than the distance 101, the thicknesses 222,242 of the anti-vibration bars 220,240 are only limited by the distance 203 between adjacent centers minus two times the radius 202 (e.g., the tube outer diameter 204).
As seen, the distance 301 corresponds to the distance 306 minus two times a radius 302 (e.g., a tube outer diameter 304). In a similar manner as the anti-vibration bars 220,240, the anti-vibration bar 320 is structured to wind between the first column of tubes 310 and the second column of tubes 330. However, while the anti-vibration bars 220,240 include a number of bends 224,244 that are curved, the anti-vibration bar 320 includes a number of bends 324 that are substantially jagged. The bends 324 of the anti-vibration bar 320, like the bends 224,244 of the anti-vibration bars 220,240, allow the anti-vibration bar 320 to have the increased thickness 322. Furthermore, similar to the anti-vibration bars 220,240, in operation, the increased thickness 322 of the anti-vibration bar 320 prevents significant in-plane (see, for example, planes 316,336) motion with the columns of tubes 310,330 advantageously corresponding to a significant decrease in in-plane vibration within the tube bundle 300.
As seen in
As seen, the anti-vibration bar 460 is substantially located along a longitudinal axis 465 and the anti-vibration bar 480 is substantially located along a longitudinal axis 485.
As seen in
Located between the second column of tubes 530 and the third column of tubes 550 is an anti-vibration bar 540 that is substantially similar to the anti-vibration bars 120,140 seen in
In this manner, in-plane vibration within the tube bundle 500 can be significantly reduced by including the anti-vibration bar 520, while costs can advantageously be saved by including the anti-vibration bar 540 in accordance with existing designs.
The foregoing description of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed, and other modifications and variations may be possible in light of the above teachings. The embodiments were chosen and described in order to best explain the principles of the invention and its practical application to thereby enable others skilled in the art to best utilize the invention in various embodiments and various modifications as are suited to the particular use contemplated. It is intended that the appended claims be construed to include other alternative embodiments of the invention except insofar as limited by the prior art.
As employed herein, the term “solid” shall mean being without an internal cavity or opening. As employed herein, the term “number” shall mean one or an integer greater than one (i.e., a plurality).
