JP2509564B2 - Reheater for steam turbine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial field of application) The present invention relates to, for example, a nuclear power plant.
The present invention relates to a steam turbine reheating device that reheats saturated steam after removing moisture from steam having high wetness to superheated steam.

(Prior Art) Generally, in a nuclear power plant using a boiling water type or pressurized water type light water reactor or a new converter, the steam delivered to the steam turbine is compared with steam in a thermal power plant using fossil fuel, It is so-called moist steam, which has much more moisture. Moisture in the wet steam must be removed because it not only erodes the blades of the steam turbine but also reduces the efficiency of the steam turbine.

Therefore, in a nuclear power plant, a corrugated plate-type moisture separator with a drain pocket, such as a chevron type, is installed between the high-pressure turbine and the low-pressure turbine to reduce the amount of steam contained in the high-pressure turbine exhaust steam to about 10%. Moisture is reduced to 1% or less. Furthermore, if the steam with reduced humidity is heated by a reheater that uses extracted steam from the high-pressure turbine or steam generated in the reactor as a heating source, and a reheat cycle that supplies superheated steam to the low-pressure turbine is adopted, , Not only contributes to the efficiency improvement of the low-pressure turbine,
It is possible to saturate the erosion of the low pressure turbine by the moist steam.

The moisture separator and the reheater are generally contained in one housing and are called a moisture separator reheater. Among them, the conventional ones used as this type of reheating device can be roughly classified into a one-stage reheating type and a two-stage reheating type. The former is a type of reheating with steam generated in the reactor, whereas the latter is the second stage with steam generated from the high pressure turbine to reheat the first stage and steam generated in the reactor. Is a form of reheating. Each of these reheating devices is a cross-flow multitubular heat exchanger of a type in which steam on the reheat side is caused to flow inside the pipe and steam on the reheated side is caused to flow outside the pipe.

That is, in FIG. 7 showing a conventional reheater, the inside of the reheat steam head 16 is divided by a partition wall 19 into a high temperature chamber 20 and a low temperature chamber.
It is divided into 21, and the high temperature chamber 20 has a reheated steam introduction pipe.
A drain discharge pipe 23 and a bend vapor discharge pipe 24 are connected to the low temperature chamber 21. Further, the low temperature chamber 21 is provided with a manhole 25 for the entry and exit of people. Further, the tube plate 26 of the reheat steam header 16 is connected with a plurality of U-shaped heat transfer tubes 17 whose both ends communicate with the high temperature chamber 20 and the low temperature chamber 21, and the plurality of heat transfer tubes 17 are provided. It is supported by a support plate 27 of. The support plate 27 is axially positioned by stay bolts 28.
As shown in FIG. 8 (AA cross section of FIG. 7), the stay bolt 28 is generally attached to the support plate 27 at three positions of 28a, 28b, 28c in the vertical direction. The support plate 27 is a shroud
15 The horizontal position of the shroud 15
Slide on the rail 14 below.

Next, the flow of steam on the reheat side and steam on the reheated side of the reheater will be described. First, the reheater shown in FIG. 7 is housed in the housing of the moisture separator / reheater together with the moisture separator as described above. Therefore, the steam to be reheated, which flows around the U-shaped heat transfer tube 17 of the reheater as shown by the arrow, has its moisture sufficiently reduced by the moisture separator in the housing. The steam to be reheated exchanges heat with the reheated steam flowing in the heat transfer tube 17, becomes superheated steam, and finally flows out from the superheated steam discharge tube and is sent to the low-pressure turbine.

On the other hand, the reheat side steam, which is the extracted steam from the high-pressure turbine or the steam generated by the reactor, flows into the high temperature chamber 20 of the reheat steam header 16 through the reheat steam introduction pipe 22 in FIG. It is distributed to the heat transfer tubes 17 and flows in the tubes. During this time, the reheated steam exchanges heat with the reheated steam flowing outside the heat transfer pipe 17, so that the reheated steam is gradually condensed and flows out from the drain discharge pipe 23. The reheated steam that has not been completely condensed flows out from the vent steam discharge pipe 24.

(Problems to be Solved by the Invention) Meanwhile, the temperature of the reheated steam rises as the turbine load increases, and at the same time, the temperature rises by passing through the reheater. The stay bolt 28, which defines the axial position of the support plate 27, thermally expands more toward the outlet side due to the temperature rise of the steam to be reheated. Therefore, as the turbine load increases, the support plate 27 slides on the tube plate 26 while inclining as shown in FIG. In order to prevent the inclination of the support plate 27 due to the difference in vertical expansion of the stay bolts, in JP-A-60-86394, the material of the stay bolts 28 is changed in the vertical direction so that the thermal expansion amounts of the stay bolts are equal. ing.

However, in addition to the difference in thermal expansion of the bolts of the stay holt, the cause of the inclination of the support plate 27 is a moment that acts because the point of action of the stay bolt's expanding force and the point of action of the frictional force of the sliding portion do not match. That is, as shown in FIG. 9, the resultant force of the expansion forces Fa, Fb, Fc due to thermal expansion and the reaction point of the frictional force Ff of the support plate 27 and the rail 14, which are the reaction forces, are different. Therefore, a moment M is generated in the support plate fixed to the rail in order to satisfy the balance of the force in the rotation direction. This moment M not only bends the stay bolt 28 but also tilts the support plate 27. As a result, the support plate
Since the rail 27 and the rail 14 are in line contact with each other, a high surface pressure is locally generated, which makes smooth sliding difficult. In the worst case, the support plate 27 and the rail 14 are locked, so that the elongation of the heat transfer tube is restricted and the heat transfer tube may be damaged.

An object of the present invention is to provide a steam turbine reheater which improves a support structure of a support plate that supports a group of tube bundles and prevents the support plate from sliding smoothly and damaging a heat transfer tube.

[Structure of Invention]

(Means for Solving Problems) A steam turbine reheater according to the present invention supports a large number of U-shaped heat transfer tubes and a weight of a tube bundle composed of support plate stay bolts supporting the U-shaped heat transfer tubes. In a steam turbine reheating device supported by a plate and a supporting member such as a surrounding plate that supports the supporting plate, the supporting plate and the supporting member are in surface contact with each other and slide at approximately the center in the height direction of the supporting plate. Movably attached, and when the difference in thermal expansion between the tube bundle and the support member is allowed by sliding of the surface contact between the support plate and the support member, the sum of the moments generated by the thermal expansion difference between the upper and lower positions of the stay bolt. Is set to 0 at the surface contact portion.

(Operation) The moment due to the displacement of the action point of the reaction force due to the thermal expansion of the stay bolt and the friction of the sliding portion of the support plate is eliminated, and the inclination of the support plate due to this moment can be eliminated.

(Embodiment) An embodiment of the present invention is shown in FIGS. FIG. 1 is a bird's-eye view of a tube bundle portion of a steam turbine reheater according to the present invention. FIG. 2 shows a view of this from the axial direction.

1 and 2, a large number of heat transfer tubes 17 are support plates.
The support plate 27 is supported by the Sutebolt 28a,
The axial position is determined by 28b and 28c. In addition, there is a protrusion 1 at approximately the center of the support plate 27, and this portion is fitted into a groove 2 provided in the surrounding plate 15 to support the weight of the support plate 27. Normally, the lower surface of the projection 1 is in contact with the groove 2 of the enclosing plate 15 as shown in FIG. Supported by 2. That is, since the projection 1 also serves to prevent the tube bundle from rising, the conventional stopper 18 shown in FIG. 8 is unnecessary.

Further, in the reheater of the present invention, the supporting plate 27 farthest from the tubular member 26 is viewed from the lateral direction as shown in FIG. 6, and the operation and effect of the present invention will be described. Assuming that the force due to the thermal expansion of the stay bolt due to the temperature rise of the heated steam is Fa, Fb, Fc from above as shown in the figure, the frictional force Ff acts on these as the reaction force on the lower surface of the protrusion and the sliding surface 7 of the groove. To work.

Here, the protrusion 1 of the present invention includes stay bolts 28a, 28b, 28c.
It is installed at a position where the point of action of the resultant force of forces Fa, Fb, and Fc due to the thermal expansion of is coincident with the sliding surface. That is, as shown in FIG. 6, the distance between the sliding surface and the stay bolts 28a to 28c is a, b,
The protrusions are installed at positions such that a * Fa = b * Fb + c * Fc, where c. Looking at the tube bundle immediately before sliding when the rail (sliding surface 7 of the groove 2 of the enclosing plate 15) is provided approximately at the center of the supporting plate 27, the upper and lower stay bolts 28a and 28c are If it is considered that the sliding force is small because it is not constrained by the rails and thermal expansion occurs at the same temperature, the sliding force is equal, and the distance from the contact surface is also equal, so that the forces in the rotational direction are balanced. This relationship applies to any support plate. Therefore, just before the tube bundle slides, only the frictional force is generated on the support plate 27 fixed to the rail, no moment is generated, the contact surface is kept substantially horizontal, and the surface pressure is reduced, so that the sliding force is reduced. The mobility is also good. As described above, the support plate 27 tries to slide on the rail as the stay bolt 28 thermally expands, but can slide only when the sliding force exceeds the frictional force between the support plate 27 and the rail. Here, since it is considered that the stay bolt 28 thermally expands at the same temperature,
The frictional force corresponds to the weight of the tube bundle supported by each supporting plate multiplied by the friction coefficient, and the sliding force corresponds to the force (compressive force) that restrains the thermal expansion of the stay bolt 28. That is, when the sliding force exceeds the frictional force and the tube bundle slides, only the compressive force generated in the stay bolt 28 is released. Thereafter, as the temperature rises, the compressive force is accumulated inside the stay bolt 28. Then, when the sliding force again exceeds the frictional force, the tube bundle slides in a stepwise manner such that the tube bundle slides. As a result, the bending force acting on the stay bolts 28a to 28c is much smaller than that of the conventional type shown in FIG.
The protrusion 1 of 27 and the groove 2 of the shroud 15 can slide with a relatively small surface pressure while maintaining a substantially uniform surface contact.

Further, in order to make the supporting plate 27 smooth by sliding, as shown in the embodiment of FIG. 3, a sled 3 may be attached to the lower portion of the protrusion 1 with a material having a good slidability to make a large contact area.

Further, as shown in the embodiment of FIG.
The mounting support plate 27 may be moved in the axial direction with a small force.

In addition, as shown in the embodiment of FIG.
It may be supported by the projection 6 provided from the surrounding plate 15.

The same effect can be obtained by applying the supporting plate 27 sliding method of the present invention to a heat exchanger such as a feed water heater as well as the steam turbine reheater.

〔The invention's effect〕

As described above, in the present invention, the supporting plate slides smoothly by making the sliding position of the supporting plate and the surrounding plate coincide with the point of action of the resultant force of expansion and contraction of each stay bolt. As a result, the heat transfer tube and the support plate slide smoothly, and the reliability of the turbine reheater is improved.

[Brief description of drawings]

FIG. 1 is a perspective view showing a tube bundle portion of a steam turbine reheater according to the present invention, FIG. 2 is a front view seen from an axial direction of FIG. 1, and FIGS. 3, 4, and 5 are books. FIG. 7 is a front view showing a tube bundle portion according to another embodiment of the invention, and FIG. 6 is a schematic view showing the action points and directions of the thermal expansion force and friction force of the stay bolt for explaining the action of the present invention. FIG. 8 is a cross-sectional front view showing a steam turbine reheating device, FIG. 8 is a side view of a conventional tube bundle portion viewed from an axial direction, and FIG. 9 is a sliding force between a support plate and a support structure in the conventional tube bundle portion. It is a schematic diagram for doing. 1 ... Protrusion, 2 ... Groove 3 ... Sledge, 4 ... Roller 5 ... Notch, 6 ... Protrusion from enclosure plate 7 ... Sliding surface, 14 ... Rail 15 ... Enclosure plate, 16 …… Reheated steam header 17 …… Heat transfer pipe, 18 …… Stopper 19 …… Partition plate, 20 …… High temperature chamber 21 …… Low temperature chamber, 22 …… Reheated steam introduction pipe 23 …… Drain discharge pipe, 24 ...... Vent steam discharge pipe 25 …… Manhole, 26 …… Tube plate 27 …… Support plate, 28 …… Stay bolt

Claims (1)

(57) [Claims] 1. The weight of a tube bundle comprising a large number of U-shaped heat transfer tubes, a supporting plate for supporting the U-shaped heat transfer tubes, and stay bolts,
In a steam turbine reheater supported by the supporting plate and a supporting member such as a surrounding plate that supports the supporting plate, the supporting plate and the supporting member have a surface substantially at the center in the height direction of the supporting plate. It is attached so as to be in contact with and slidable, and when the difference in thermal expansion between the tube bundle and the support member is allowed by the sliding of the surface contact portion of the support plate and the support member, the stay bolt is moved up and down. The sum total of the moments generated by the difference in thermal expansion is 0 at the face-to-face contact portion.