JPH0440601B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a tube bank structure for a boiler, and more particularly to a tube bank structure that reduces generation of thermal stress and increases rigidity.

FIG. 1 shows a schematic external structure of the combustion chamber of the boiler and the entire furnace.

This type of boiler forms a flat tube group by joining tubes with fins (membrane bars) to keep them airtight, and the combination of these tube groups creates a box-shaped combustion. It consists of a chamber and a furnace. In FIG. 1, the combustion chamber is mainly constituted by a water wall tube group 1, a cage side wall tube group 2, a cage floor wall tube group 3, a ceiling wall tube group 4, and the like.

FIG. 2 shows the details of part A in FIG. 1, and shows the conventional structure of the connection part of each tube group (commonly called the water wall/cage connection part) as seen from the outside of the boiler furnace. FIG. 3 shows a BB' view of FIG. 2.

First, as shown in FIGS. 2 and 3, a membrane bar 8a is attached to the water wall tube 5, a membrane bar 8b is attached to the cage side tube 6, and a membrane bar 8c is attached to the cage floor tube 7, which are continuous in the tube axis direction. and weld 9
Planar tube groups 1, 2, and 3 connected with airtightness
is formed.

Here, in FIG. 1, FIG. 2, and FIG. 3, a water wall tube group 1 formed from a water wall tube 5 and a membrane bar 8a as a first membrane bar forming the tube group, and a cage side A membrane bar 8 as a first membrane bar forming a tube group with the tube 6
The cage side wall tube group 2 formed from the tube group b is engaged with the cage side wall tube group 2 by a membrane bar 8d serving as a second membrane bar that joins the tube group.

Similarly, the cage floor wall tube group 3 formed by the cage floor tube 7 and the membrane bar 6c is connected to the water wall tube group 1 by the membrane bar 8e.

Therefore, in the vicinity of section C in Figure 2, three types of tube groups come together in a complex way, and this is a discontinuous part in shape that requires the most attention in terms of strength for structures, especially structures where thermal stress occurs. will be formed.

Furthermore, in section C in Fig. 2, the membrane bar 8d, which serves as the second membrane bar, is structurally cut in the middle, so that it has no choice but to form a so-called membrane bar end, which further promotes shape discontinuity. .

On the other hand, the flow of fluid (hot water or steam) in each tube group due to the boiler operation system first increases in temperature as it flows from the bottom to the top of the water wall tube group, and then
After passing through various other equipment systems, the air enters the cage side wall pipe group 3 and the cage side wall header 10 located below, and flows upward again inside the cage side pipe 6, further increasing the temperature. Therefore, the temperature of the fluid in each tube group in section A naturally differs, and stress is generated due to expansion and contraction of each tube group.

In addition, there is a toe of the membrane bar 8d connecting the water wall pipe 5 and the cage side pipe 6 in this part, and most of these stresses are concentrated on this membrane bar toe.

Figures 4A and 4B represent C in Figure 2.
This figure shows the details of the weld toe of the membrane bar. Generally speaking, this toe is a place where strain (stress) is concentrated due to its shape, so a smooth rounded finish (indicated by numeral 30 in the figure) after turning welding is not possible. However, it does not concentrate stress more than other parts and does not lick.

In particular, during boiler startup, shutdown, and various load fluctuations, repeated pressure due to the factors mentioned above concentrates on this weld toe, causing fatigue damage to accumulate in this area and sometimes causing fatigue cracks. There is also a great possibility that

For example, in Fig. 4A, fatigue cracks 11 occur in the direction of X' due to in-plane bending of the tube group, that is, repeated stress in the X direction, and in the Y' direction due to stress in the axial direction of the tube group, that is, the Y direction. there's a possibility that.

Furthermore, out-of-plane stress in the tube group, ie, repetitive stress in the Z direction, may also occur.

Such complex repeated stress loads not only cause fatigue cracks to occur at the weld toe of the membrane bar, but also often propagate through the thickness of each pipe, which is the pressure area, and lead to internal fluid leakage. This is considered a serious problem because the function of the entire system is impaired as a result.

In other words, in the joining part shown in part A, three types of tubes with different temperature conditions and deformation behaviors are combined in one place, and the toe of the membrane bar, which is weak in strength, is located in that part. Moreover, the toe of the membrane bar not only becomes a stress concentration source due to its shape, but also serves as a fulcrum for stress or strain loading, and is therefore subject to adverse strength conditions.

This invention was constructed in view of the above-mentioned problems, and prevents stress concentration at the joints of each tube group (pipe wall), prevents fatigue damage to the tube wall, and at the same time improves safety. The purpose is to provide a tube wall structure.

In short, this invention consists of a plurality of planar tube groups formed by a tube and a first membrane bar,
The plurality of planar tube groups are joined by a second membrane bar, and the second membrane bar connects the plurality of planar tube groups in a tube group structure having a toe cut in the middle of the tube. Attach a patch plate so as to span the surface of the toe and cover the toe,
The plate is provided with an opening so that the toe can be viewed from the outside.

Examples of the present invention will be described below.

FIG. 9 shows an embodiment of this invention.
The water wall structure will be explained with reference to FIG. It is.

The present invention is characterized in that a reinforcing member (pattern) having an opening is provided in the connecting portion.

Before explaining the embodiment of the present invention with reference to FIG. 9, the mounting structure of the backing plate will be explained with reference to FIGS. 5 to 8. That is, the water wall pipe 5 and the membrane bar 8
A water wall tube group 1 consisting of a, and a cage side wall tube group 2 consisting of a cage side tube 6 and a membrane bar 8b.
The outside of the boiler combustion chamber (indicated by reference numeral 31 in Figure 6)
A plurality of rectangular pieces 12 are attached to. Furthermore, a backing plate (reinforcing plate) 13 having a size that spans a plurality of pieces 12 and having a rectangular shape, for example, is attached to the outside thereof. This attachment is performed by welding the bridge 12 and the pipes 5 and 6 over almost the entire circumference, excluding a part of the periphery, of the backing plate 13, as indicated by the reference numeral 32.

Regarding the shape and connection method of each of these parts, details are shown in Fig. 7 representing the vicinity of section E in Fig. 5, and details of the cross-sectional structure of F-F' in Fig. 7 are shown in Fig. 8. show. That is, the plurality of pieces 12 provided on the outside of each tube group (outside the furnace) are joined by welding 14 over the entire length on both sides in the longitudinal direction, and the surfaces of the pieces are at the same position as the apex of the outer circumference of each tube. .
(See FIG. 8) By implementing such a joining method, heat conduction and various loads from each tube can be reliably transmitted via this piece 12 to the backing plate 13 attached to the outside thereof. In other words, it is taken into consideration that the tube, bridge, and backing plate are integrated in terms of thermal and mechanical loads.

Although the thickness of the piece 12 is not particularly specified, it is preferably approximately the same as that of the membrane bar in consideration of the space at the mounting position. Ideally, the length of this piece 12 should be approximately 30 to 50 mm longer at each end than the length of the backing plate 13 in the width direction, as shown in FIG.

The upper side (outside) of each piece joined in this way
Attach the backing plate 13 to. This patch plate 13 has a length of 5 to 6 times the diameter of the tubes on both sides of the joint between tube groups 1 and 2, and a length of 300 to 500 mm in the width direction.
The wall thickness is preferably 2 to 3 times that of the membrane bar. This patch plate is shown in Figures 5 and 7.
As shown in the figure, the tube at the end of the water wall tube 5 and the cage side tube 6 (the tube that becomes the connecting part, the reference numeral 5' in the figure,
With the exception of only the lower part (indicated by 6'), the other parts are connected and fixed by welding 15 to the tube and piece over the entire circumference. Since both ends of the fillet weld 15 become sources of stress concentration, it is also significant to locate them on the surface of the piece (indicated by numerals 15' and 15'') rather than on the surface of the tube, which is the pressure part.

The mounting structure of the backing plate 13 has been described above, and an embodiment of the present invention will be further described with reference to FIG.

In FIG. 9, the same parts as in FIGS. 5 to 8 are designated by the same reference numerals.

In FIG. 9, an opening 33 is provided near the center of the backing plate 13, so that the membrane bar weld toe, the water wall pipes 5' and 6' on both sides thereof, and a part of the cage floor pipe 7 can be visually seen from the outside. It has characteristics in that. In this way, it is easy to inspect the parts where stress is most concentrated, and the safety of the device can be further improved.

By implementing this invention, the following effects can be achieved.

(a) Since the rigidity of the joints of various flat tube groups is greatly increased, these joints can be made strong enough to withstand thermal stress.

(b) The generated stress can be dispersed and the stress will not be concentrated at the toe of the membrane bar as in the past, so together with the above-mentioned increase in rigidity, the physical strength of the attachment part will be dramatically improved. .

(c) Since the toe of the membrane bar, where the greatest thermal stress occurs during boiler operation, can be inspected without removing the cover plate, it is possible to easily improve the safety of the entire flat tube group of the boiler.

[Brief explanation of drawings]

Figure 1 is a perspective view showing a schematic structure of the entire combustion chamber of the boiler, Figure 2 is a detailed view of section A in Figure 1, Figure 3 is a view taken along line B-B' in Figure 2, and Figure 4. A is second
A detailed structural view of section C in the figure, B is a sectional view taken along line C-C' of A in the figure, and FIG. , FIG. 6 is a perspective view taken along line D-D' in FIG. 5, FIG. 7 is a detailed structural view of section E in FIG. The figure is an external structural diagram showing an embodiment of the present invention. 1...Water wall tube group, 2...Cage side wall tube group, 5...
...Water wall tube, 8a, 8b, 8c, 8d, 8e... Membrane bar, 12... Piece, 13... Backing plate, 1
5... Fillet weld, 33... Opening.

Claims (1)

[Scope of Claims] 1 Consists of a plurality of planar tube groups formed of a tube and a first membrane bar, the plurality of planar tube groups are joined by a second membrane bar, and the second The membrane bar has a tube group structure having a toe section cut in the middle of the tube, and a patch plate is attached so as to span the surface of the plurality of planar tube groups and cover the toe section, and the membrane bar has a toe section cut in the middle of the tube. A tube group structure for a boiler, characterized in that the plate has an opening so that the toe can be visually seen from the outside. 2. The attachment of the patch plate to the surface of the planar tube group is performed by fillet welding via a piece, and the end of the fillet weld is located on the surface of the piece. Boiler tube group structure described in section.