JP2002168403A - Exhaust heat recovery steam generator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a exhaust heat recovery steam generator which can be simplified in structure and reduced in cost. SOLUTION: This exhaust heat recovery steam generator is provided with a casing 21 lined with a thermal insulating material and a plurality of vertical side-face back stays 25 which are directly fixed to the periphery of the casing 21 in a state where the stays 25 are protruded downward from the bottom face of the casing 21. The self-weight of the steam generator is supported by the back stays 25.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust heat recovery boiler for recovering exhaust heat from exhaust gas sent from a gas turbine.

[0002]

2. Description of the Related Art FIG. 10 shows a conventional waste heat recovery boiler. In the figure, reference numeral 1 denotes a boiler casing.
A heat transfer tube group 2 shown in FIG. 11A is disposed inside the casing 1. The tube group 2 is supported by a hot beam 3 penetrating the casing 1. The casing 1 has a substantially cubic shape, and an H-shaped reinforcing member, that is, a backstay 5 is provided on the peripheral wall surface in a vertical and horizontal direction at a predetermined pitch. Reference numeral 7 denotes a supporting steel frame, which supports the weight of the exhaust heat recovery boiler and the horizontal force due to an earthquake or the like. The hot beam 3 is
Is supported by a supporting steel frame 7 on the outside. The state is shown in FIG. The casing 1 has an outer heat insulating structure in which a heat insulating material 1a is provided on the outer peripheral surface. The hot beam 3 is welded to the casing 1 while penetrating the casing 1. And outside the casing 1, it is supported by the beam of the support steel frame 7 in a non-adhered state.

In an exhaust heat recovery boiler having such a structure, exhaust gas from a gas turbine or the like is guided into a casing 1 from a duct inlet 10 and performs heat exchange in a process of passing through a heat transfer tube group 2 therein. The low temperature exhaust gas flows out of the chimney 11 at the upper part of the casing. here,
During operation, the inside of the casing 1 becomes high temperature and an internal pressure is applied, but a back stay 5 provided around the casing 1 suppresses the swelling of the casing.

[0004]

However, in the above-mentioned conventional exhaust heat recovery boiler, the back stay 5 against internal pressure and the supporting steel frame 7 supporting its own weight are separate members, so that the structure is complicated and the cost is low. There was a problem of inviting up.

The present invention has been made in view of the above circumstances, and has as its object to provide an exhaust heat recovery boiler capable of simplifying the structure and reducing the cost.

[0006]

According to a first aspect of the present invention, there is provided a casing provided with a heat insulating material on an inner surface thereof, wherein the casing is oriented vertically and a lower end protrudes below a bottom surface of the casing. And a plurality of side vertical backstays directly fixed to the periphery of the casing, and its own weight is supported by the side vertical backstays.

[0007] In this heat recovery steam generator, the side vertical backstay opposes the internal pressure of the casing,
Supports the weight of the exhaust heat recovery boiler. That is, it has both a conventional backstay and a supporting steel frame.

According to a second aspect of the present invention, in the exhaust heat recovery boiler according to the first aspect, the casing and the side vertical backstay are located at a predetermined distance or more from a base surface on which the exhaust heat recovery boiler is installed. It is characterized by being welded.

If the side vertical backstay has a short portion (hereinafter, referred to as a leg) projecting downward from the bottom surface of the casing, the thermal stress at the base of the leg increases, possibly exceeding the allowable stress. In the exhaust heat recovery boiler, the welding is not performed at a predetermined distance from the base surface, so that the leg is elongated, and the stress generated at the base of the leg of the side vertical backstay is reduced.

According to a third aspect of the present invention, in the exhaust heat recovery boiler according to the first or second aspect, a horizontal truss to which the horizontal swing of the casing is transmitted is provided so as to surround the casing. It is characterized by.

In this exhaust heat recovery boiler, the swing of the casing is transmitted to the horizontal truss, and further transmitted from the horizontal truss to the ground through the side vertical backstay. Thereby, the load acting on the casing flows to the ground.

According to a fourth aspect of the present invention, in the heat recovery steam generator of the third aspect, the horizontal truss has a truss aggregate passed between the adjacent side vertical backstays on the casing side. The truss aggregate is characterized in that the distance between the backstays is provided to be variable within a predetermined range.

Since the temperature of the casing is higher than that of the horizontal truss, there is a difference in thermal expansion between the two. Therefore, instead of providing the horizontal truss with the distance between the side vertical backstays being fixed, the horizontal truss is provided variably as in the present invention to absorb this difference in thermal expansion.

According to a fifth aspect of the present invention, in the exhaust heat recovery boiler according to the fourth aspect, one of the side vertical backstay and the truss aggregate is provided with a casing formed by being vertically drilled. A long slot is provided in the outer peripheral direction,
The other is provided with a pin to be inserted into the elongated hole.

If the horizontal truss and the casing are made movable in and out of the casing, a horizontal load acting on the casing will not flow through the horizontal truss.
For this reason, by using a long hole extending in the direction of the outer peripheral surface of the casing as in the present invention, the distance between the side vertical backstays can be varied, and the distance between the casing and the horizontal truss is restricted in the inward and outward directions of the casing. The load is transmitted to the horizontal truss.

[0016] The invention according to claim 6 is the invention according to claims 1 to 5.
The exhaust heat recovery boiler according to any of the preceding claims, further comprising a brace that connects the adjacent side vertical backstays obliquely below the bottom surface of the casing, and the brace is located behind a substantially central portion of the casing in the front-rear direction. It is characterized by being provided in.

In the present invention, the brace is arranged so as to avoid the duct entrance side on the front surface where the strength due to thermal elongation is the strictest, so that the rigidity of the casing on the duct entrance side is suppressed low, and the generation of thermal stress is suppressed. Can be suppressed.

[0018] The invention according to claim 7 is the invention according to claims 1 to 6.
The exhaust heat recovery boiler according to any one of the preceding claims, wherein the side wall of the casing is formed by connecting a plurality of casing components having flange portions on both sides at the flange portions.

Since the casing and the side vertical backstay are welded, a compressive stress is generated in the casing in a vertical direction due to a temperature difference between the casing and the vertical side stay. However, in the present invention, the flange portion is reinforced. Thereby, buckling of the casing is prevented.

[0020] The invention according to claim 8 is the invention according to claims 1 to 7.
In any one of the exhaust heat recovery boilers described above, the bottom surface of the casing is supported by a hearth backstay that faces the front-rear direction of the casing.

The dimensions of the casing change due to thermal expansion. However, since the side vertical backstay is fixed to the side surface, a compressive stress is generated in the left-right direction of the bottom surface of the casing, which may cause buckling. In this example, since the bottom surface of the casing is supported by the hearth backstay, buckling is prevented.

According to a ninth aspect of the present invention, in the exhaust heat recovery boiler according to the eighth aspect, a bottom surface of the casing is provided.
The furnace bottom backstay is slidably provided in the front-rear direction of the casing, and a backstay reinforcing material is passed between the side vertical backstays located on both sides of the casing and opposed to each other, and the reinforcing material allows the The furnace bottom backstay is supported.

In the present invention, since the hearth backstay and the casing slide, the difference in thermal expansion due to the temperature difference between the casing and the hearth backstay is absorbed.

According to a tenth aspect of the present invention, in the exhaust heat recovery boiler according to any one of the first to ninth aspects, a heat transfer tube group is accommodated in the casing, and the heat transfer tube group is connected to the casing. A sealing means having a U-shaped cross section is provided therebetween, and one end of the sealing means is fixed to the heat transfer tube group side, and the other end is urged by the casing.

When there is a short path having a smaller flow path resistance than the heat transfer tube group in the gas flow direction in the furnace,
The gas flow rate passing through the heat transfer tube group is reduced, and the heat exchange performance is reduced. In the present invention, the interval between the casing and the heat transfer tube group inside the casing varies due to a temperature difference. Since one end of the sealing means is urged by the casing, the width of the sealing means also fluctuates in accordance with the change in the interval, so that there is no gap that creates a short path between the heat transfer tube group and the casing.

According to an eleventh aspect of the present invention, in the exhaust heat recovery boiler according to any one of the first to tenth aspects, the heat transfer tube group and the heat transfer tube group fixed to the heat transfer tube group are provided in the casing. A horizontally oriented hot beam is accommodated therein, and the hot beam is not fixed to the casing, and is supported by the side vertical backstay with the casing interposed therebetween.

In the present invention, the difference in thermal expansion between the hot beam and the casing is absorbed by sliding the hot beam on the side vertical backstay.

[0028]

Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows an exhaust heat recovery boiler of this example. In the figure, reference numeral 21 denotes a boiler casing, which has a substantially cubic shape. FIG. 2 shows a partial cross-sectional view of the casing 21. As shown in the drawing, the casing 21 has an inner surface heat retaining structure in which a heat insulating material 21a is provided on the inner surface. A duct inlet 21b is provided on a front surface of the casing 21. Further, a chimney 21c is provided at the center of the upper surface. The bottom of the casing 21
It is an inclined surface that rises from the front to the rear.

A plurality of side vertical backstays 25 are welded to the peripheral wall surface of the casing 21 at a predetermined horizontal pitch. The side vertical backstay 25 is a casing 2
1 protrudes below the bottom surface, and supports the weight of the casing 21 on the base surface G. Reference numerals 28a and 28b are horizontal trusses that absorb the horizontal load of the casing 21 and suppress the out-of-plane deformation of the side vertical backstay 25. Reference numerals 29a and 29b denote braces provided at the furnace bottom to support horizontal force due to an earthquake. The brace 29a, 29b
Are provided side by side in the front-rear direction. Forward brace 2
9 a is located at a substantially central portion of the casing 21 in the front-rear direction.

FIG. 3 shows the detailed structure of the casing 21. The wall of the casing 21 is configured by combining casing constituent members 22 provided with flange portions 22a on the left and right. Each casing component 22 adjacent to each other,
The flange portion 22a is fixed by a bolt 23 in a state where the flange portions 22a abut against each other. If necessary, a sealing means 24 such as packing is interposed between the flanges to prevent gas leakage in the furnace.
Between the flange portions 22a of each casing component 22,
The side vertical backstay 25 is welded. Further, rib members 22b as reinforcing members are provided at predetermined intervals in the vertical direction.

FIGS. 4A to 4C show the bottom of the casing 21. FIG. In the figure, reference numeral 21d denotes the casing 2
1 is a reinforcing member that is fixed to the bottom of the casing 1 and forms a part of the casing 21 and faces the width direction of the casing 21.
A plurality is provided at predetermined intervals in the front-rear direction.
Reference numeral 26 denotes an H-shaped furnace bottom backstay. Reinforcing material 21d
A plurality of rows of rails 21e are fixed in the width direction to guide the furnace bottom backstay 26 movably in the longitudinal direction of the casing 21. The hearth backstay 26 has a state in which the flange portion 26a is accommodated in the rail 21e. Reference numeral 27 denotes a backstay reinforcing member which extends between the side vertical backstays 25 facing the casing 21 in the width direction and reinforces the side vertical backstays 25. The furnace bottom backstay 26 is supported by the backstay reinforcing member 27.

FIG. 5A is a side sectional view showing the internal structure of the casing 21. As shown in FIG. In the drawing, reference numeral 30 denotes a heat transfer tube group housed in the casing 21. The heat transfer tube group 30 is suspended and supported by a hot beam 31 located above the heat transfer tube group 30. The hot beam 31 faces the width direction of the casing 21. Details of this part
(B). The casing 21 has a bulging portion 21 e bulging outward along the shape of the hot beam 31. That is, the hot beam 31 is on the side vertical backstay 25 with the casing 21 interposed therebetween. The hot beam 31 and the casing 21 (the bulging portion 21e) are not fixed to each other, are slidable with each other, and the casing 21 and the side backstay 25 are seal-welded.

The heat transfer tube group 30 is placed in the furnace as described above.
However, if there is a gap (short path) having a smaller flow path resistance than the heat transfer tube group 30 in the gas flow direction in the furnace, the gas flow bypasses the short path. The gas flow rate passing through the group 30 is reduced, and the heat exchange performance is reduced. For this reason, as shown in FIG. 6, a U-shaped plate 32 is provided between the heat transfer tube group 30 and the casing 21 as sealing means in order to prevent a short path. The U-shaped plate 32 has one end side 32a fixed to the heat transfer tube group 30 side and the other end 32b side biased to the casing 21 in a non-fixed state. In the other side surface shown in FIG. 7, one end of the U-shaped plate 33 is fixed to a partition plate for partitioning the heat transfer tube group 30 provided in the vertical direction, thereby preventing a short path.

Next, the mounting state of the horizontal trusses 28a, 28b will be described with reference to FIG. Horizontal truss 28
b (28a) is the outer frame 35 and the outer frame 35
1, the lattice-shaped steel members 36a, 36b, 36c,
36d, and a reinforcing steel member 37 for interconnecting the outer frame 35 and the steel frame 36. Regarding the side vertical backstays 25 provided on both sides of the casing 21,
One steel frame (truss aggregate) 36a is located between the adjacent side vertical backstays 25, and this steel frame 3
A long hole 3 long in the longitudinal direction of the casing 21 is provided at one end of 6a.
8a, the other end is provided with a round hole 38b in the vertical direction. The side surface vertical backstay 25 whose both ends of the steel frame material 36a face each other has a horizontal surface 39 in the middle of the height direction.
The horizontal surface 39 is provided with pins 39a extending upward. This pin 39
a is a long hole 38a and a round hole 38b at both ends of the steel frame material 36a.
Respectively. Similarly, a horizontal surface 40 is formed in the height direction on the side vertical backstays 25 provided on the front and rear side walls of the casing 21, and a pin 40a extending upward is provided on the horizontal surface 40. I have. On the other hand, the steel frame member 36b facing the front and rear sides of the casing 21 has long holes 4 long in the width direction of the casing 21.
An assembling member 41 provided with 1a is provided. The pin 40a of the side vertical backstay 25 is inserted into the elongated hole 41a.

In the exhaust heat recovery boiler constructed as described above, the back stay 5 which has conventionally countered the internal pressure and the supporting steel frame 7 which supports its own weight are separate members. In addition, the side vertical backstay 25 supporting the own weight of the exhaust heat recovery boiler
And the structure is simplified. While the casing 21 undergoes thermal expansion, a side surface vertical backstay 25 is welded to the periphery, so that a compressive stress is generated in the left-right direction of the bottom surface of the casing 21 and buckling may occur. In this example, since the bottom surface of the casing 21 is supported by the hearth backstay 26, buckling is prevented. Although a compressive stress due to a temperature difference also acts in the front-rear direction of the casing 21, buckling does not occur because the casing 21 is reinforced by the reinforcing member 21d, the backstay reinforcing member 27, and the hearth backstay 26.

Since the conventional casing 1 has an outer heat retaining structure as shown in FIG. 11B, the temperature difference between the hot beam 3 and the casing 1 is small. For this reason, they were welded to each other. In this example, since the inner heat retaining structure is used, the temperature difference between the casing 21 and the hot beam 31 is large. For this reason, when these are welded, there is a possibility that the seal portion is cracked due to a difference in thermal expansion. In this example, as shown in FIG. 5, the casing 21 and the hot beam 31 are not welded to each other, and the hot beam 31 is slid with the side vertical backstay 25 inside the bulging portion 21e of the casing 21. , The difference in thermal expansion can be absorbed.

Further, when the hot beam 31 slides, the casing 21 and the heat transfer tube group 30
However, since the ends of the U-shaped plates 32 and 33 are urged by the casing 21, the width of the U-shaped plates 32 and 33 is also changed according to the change in the distance, and the heat transfer tube group is changed. There is no gap between the casing 30 and the casing 21 to create a short path.

Further, the casing 21 and the horizontal truss 28
Compared with a and 28b, the casing 21 has a high temperature, so that a difference in thermal expansion occurs between the two. In this example, the pins 39a and 40a of the side vertical backstay 25 move within the elongated holes 38a and 41a of the steel members 36a and 36b, so that the difference in thermal expansion of the casing 21 can be absorbed. In addition, the long holes 38 of the steel members 36a, 36b
Since the pins 39a and 40a inserted into the casings 21a and 41a are in a restraining state in the inside and outside directions of the casing 21, the horizontal load applied to the casing 21 due to an earthquake or the like can be released to the horizontal trusses 28a and 28b. The load transmitted to the horizontal trusses 28a and 28b escapes to the base surface G via the side vertical backstay 25.

Also, as shown in FIG.
Since the a and 29b are arranged avoiding the duct entrance side where the stress generated at the joint between the side vertical backstay 25 and the casing 21 due to the thermal expansion of the casing 21 is the strictest, the side vertical back on the duct entrance side is provided. Stay 25
The rigidity of the casing 21 is kept low, and excessive thermal stress is prevented from being generated at the joint between the side vertical backstay 25 and the casing 21. The casing 21 is a casing component 2
2 is fixed with its flange portions 22a abutting each other. Casing 21 and side vertical backstay 25
Is welded, compressive stress is generated in the casing 21 in the vertical direction. However, the flange portion 22a is reinforced, thereby preventing the casing 21 from buckling.
In addition, by combining the side surface vertical backstay 25 and the rib portion 22b with the casing constituent member 22 in advance, manufacturing becomes easy.

Note that the distance from the base surface G to the bottom surface of the casing 21 may be reduced depending on the position of the duct on the turbine side, as shown in FIG. In this case, the distance that the side vertical backstay 25 projects downward from the bottom surface of the casing 21 is reduced. This part (leg)
Is shorter, the thermal stress at the joint between the leg base and the side vertical backstay 25 and the casing 21 increases,
The allowable stress may be exceeded. To prevent this,
As shown in FIGS. 9A to 9C, the casing 21 and the side vertical backstay 25 are not welded at the lower part of the casing 21. That is, the welding portion between the casing 21 and the side vertical backstay 25 is set to a predetermined distance L or more from the base surface G. With such a configuration, it is possible to reduce the stress generated at the base of the leg of the side vertical backstay 25 and the joint end between the side vertical backstay 25 and the casing 21.

The long holes 3 formed in the steel frame material 36a and the like
The hole 8a and the round hole 38b may be holes longer than pins, instead of slots or the like, and the pins may be loosely fitted into the holes.

[0042]

As described above, the following effects can be obtained in the present invention. According to the first aspect of the present invention, since the side vertical backstay is directly fixed to the casing, the side vertical backstay opposes the internal pressure of the casing and supports the own weight of the exhaust heat recovery boiler. That is, since both the conventional backstay and the supporting steel frame are provided, the structure is simplified, and the arrangement base can be reduced, so that the cost can be reduced.

According to the second aspect of the present invention, the welding is performed at a predetermined distance or more from the base surface on which the exhaust heat recovery boiler is installed, and the leg is elongated by not welding the predetermined distance from the base surface. Therefore, it is possible to reduce the stress generated at the base of the leg of the side vertical backstay and at the end where the side vertical backstay and the casing are joined.

According to the third aspect of the present invention, since the horizontal truss is provided so as to surround the casing, the swing of the casing is transmitted from the horizontal truss to the ground via the side vertical backstay. This allows the load acting on the casing to flow to the ground.

According to the fourth aspect of the present invention, the horizontal truss has, on the casing side, truss aggregates passed between the adjacent side vertical backstays. Is variably provided within a predetermined range, so that the difference in thermal expansion between the casing and the horizontal truss is absorbed.

According to the fifth aspect of the present invention, one of the side vertical backstay and the truss aggregate is provided with a long hole formed in the vertical direction and elongated in the outer peripheral surface direction of the casing. On the other hand, a pin inserted into the long hole is provided, so that the distance between the side vertical backstays can be changed, and the distance between the casing and the horizontal truss in the inward and outward directions of the casing. Being restrained, the load can be transmitted to the horizontal truss.

According to the sixth aspect of the present invention, the brace is disposed so as to avoid the duct entrance side on the front surface where the stress generated at the joint between the side vertical backstay and the casing due to the thermal expansion of the casing is most severe. By doing so, the rigidity of the side vertical backstay on the duct entrance side can be kept low, and the generation of thermal stress in the front side vertical backstay can be suppressed.

According to the seventh aspect of the present invention, since the side wall of the casing is constituted by a plurality of casing components, the casing and the side vertical backstay are welded to each other, so that the temperature of the casing and the vertical backstay are maintained. Even if a compressive stress is generated due to the difference, the buckling of the casing is prevented by the flange portion of the casing component.

According to the eighth aspect of the present invention, since the bottom surface of the casing is supported by the hearth backstay, it is possible to prevent buckling due to compressive stress generated in the lateral direction of the bottom surface of the casing.

According to the ninth aspect of the present invention, since the hearth backstay and the casing slide, the difference in thermal elongation due to the temperature difference between the casing and the hearth backstay can be absorbed.

According to the tenth aspect of the present invention, since the sealing means is provided between the heat transfer tube group and the casing, the sealing means is provided in accordance with a change in the distance between the heat transfer tube group and the casing. The width of the sealing means fluctuates, and a gap that creates a short path between the heat transfer tube group and the casing is not formed, so that a decrease in heat exchange efficiency can be prevented.

According to the eleventh aspect of the present invention, the hot beam is not fixed to the casing, and is supported by the side vertical backstay with the casing interposed therebetween. By sliding on the backstay, the difference in thermal expansion between the hot beam and the casing can be absorbed.

[Brief description of the drawings]

FIG. 1 is a perspective view showing an appearance of an exhaust heat recovery boiler shown as one embodiment of the present invention.

FIG. 2 is a partial sectional view showing a heat retaining structure of a casing used in the exhaust heat recovery boiler.

FIG. 3 is a partial sectional view of the casing.

4A and 4B are diagrams showing a bottom portion of the casing, wherein FIG. 4A is a side view, FIG. 4B is a sectional view taken along line AA of FIG. 4A, and FIG. 4C is a sectional view taken along line BB of FIG. .

FIG. 5 is a view showing a state in which the exhaust heat recovery boiler supports a hot beam, and FIG. 5B is a partially enlarged view of FIG.

FIG. 6 is a cross-sectional view of a U-shaped plate, which is an internal structure of the exhaust heat recovery boiler and seals a gap between a heat transfer tube group and a casing.

FIG. 7 is a cross-sectional view of a U-shaped plate for sealing a gap between a heat transfer tube group and a casing, showing a side view different from FIG. 6;

FIG. 8 is a view showing the connection between the casing and the horizontal truss.

FIG. 9 is a view showing exhaust heat recovery boilers having different heights.

FIG. 10 is a perspective view showing the appearance of a conventional heat recovery steam generator.

FIG. 11 is a view showing a conventional exhaust heat recovery boiler, in which a hot beam is supported.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 21 Casing 22 Casing constituent member 22a Flange part 25 Side vertical backstay 26 Hearth backstay 26a Hearth backstay flange 27 Backstay reinforcing material 28a, 28b Horizontal truss 29a, 29b Brace 30 Heat transfer tube group 31 Hot beam 32, 33 U-shaped plate (seal means) 36a, 36b Steel frame (truss aggregate) 38a Slot 39a Pin 40a Pin 41a Slot

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Hiroshi Aramaki, Inventor, 2-5-1, Marunouchi, Chiyoda-ku, Tokyo, Japan Mitsui Heavy Industries, Ltd. (72) Inventor, Toshiyuki Kawaguchi 1-1, Akunouramachi, Nagasaki-shi (72) Inventor Masaaki Fujita 1-1, Akunoura-cho, Nagasaki City, Nagasaki Prefecture Mitsubishi Heavy Industries, Ltd.Nagasaki Shipyard (72) Inventor Chimitsu Yokoyama 2-5-1 Marunouchi, Chiyoda-ku, Tokyo Sanishi Heavy Industries Co., Ltd.

Claims (11)

[Claims] 1. A casing having an inner surface provided with a heat insulating material, and a plurality of side faces which are directed vertically and are directly fixed to the periphery of the casing with a lower end protruding below a bottom surface of the casing. An exhaust heat recovery boiler, comprising: a vertical backstay, wherein its own weight is supported by the side vertical backstay. 2. The exhaust heat recovery boiler according to claim 1, wherein the casing and the side vertical backstay are welded at a predetermined distance or more from a base surface on which the exhaust heat recovery boiler is installed. Waste heat recovery boiler. 3. The exhaust heat recovery boiler according to claim 1, wherein a horizontal truss to which the horizontal vibration of the casing is transmitted is provided so as to surround the casing. boiler. 4. The exhaust heat recovery boiler according to claim 3, wherein the horizontal truss has a truss aggregate passed between adjacent side vertical backstays on a casing side, and the truss aggregate is An exhaust heat recovery boiler, wherein a distance between the back stays is variably provided within a predetermined range. 5. The exhaust heat recovery boiler according to claim 4, wherein one of the side vertical backstay and the truss aggregate is vertically elongated and long in the outer peripheral surface direction of the casing. And a pin inserted into the long hole is provided on one of the other sides. 6. The exhaust heat recovery boiler according to any one of claims 1 to 5, further comprising a brace for connecting the adjacent side vertical backstays obliquely below a bottom surface of the casing, wherein the brace includes: An exhaust heat recovery boiler provided behind a substantially central portion in a front-rear direction of a casing. 7. The exhaust heat recovery boiler according to claim 1, wherein a side wall of the casing is formed by connecting a plurality of casing components having flange portions on both sides to each other at the flange portions. An exhaust heat recovery boiler characterized by: 8. The exhaust heat recovery boiler according to claim 1, wherein a bottom surface of the casing is supported by a hearth backstay that faces in a front-rear direction of the casing. Recovery boiler. 9. The exhaust heat recovery boiler according to claim 8, wherein the furnace bottom backstay is provided on the bottom surface of the casing so as to be slidable in the longitudinal direction of the casing, and is located on both side surfaces of the casing and faces each other. An exhaust heat recovery boiler, wherein a backstay reinforcing member is passed between the side vertical backstays, and the furnace bottom backstay is supported by the reinforcing member. 10. The exhaust heat recovery boiler according to claim 1, wherein a heat transfer tube group is accommodated in the casing, and a cross section U is provided between the heat transfer tube group and the casing. An exhaust heat recovery boiler is provided with a letter-shaped sealing means, one end of which is fixed to the heat transfer tube group side and the other end of which is urged by the casing. 11. The heat recovery steam generator according to claim 1, wherein a heat transfer tube group and a hot beam fixed to the heat transfer tube group and oriented in a substantially horizontal direction are provided in the casing. Wherein the hot beam is not fixed to the casing, and is supported by the side vertical backstay with the casing interposed therebetween.