JPH11230503A - Thermal radiation shielding device for duct burner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thermal radiation shielding device for a duct burner for protecting an inlet duct from the radiation heat from the duct burner, so that an exhaust gas is a specified temperature at low load of a gas turbine, related to an exhaust gas boiler wherein a heat is recovered from the exhaust gas of gas turbine. SOLUTION: A thermal radiation shielding device of a duct burner is formed of a duct plate 02 of heat-resistant steel plate, etc.,and provided with a thermal radiation shielding plate 11 for protecting an inlet duct 03 from thermal radiation of a duct burner 04 when an exhaust gas G id heated by the duct burner 04 which provided between the inlet duct 03 for guiding the exhaust gas G discharged from a gas turbine into an exhaust gas boiler 01 and the duct burner 04 which is set in the inlet duct 03 and ignited when a load of the gas turbine 01 is small for heating the exhaust gas G of low temperature flowing from the gas turbine into the exhaust gas boiler 01 so that the exhaust gas G is kept at an inlet temperature specified for the exhaust gas boiler.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a duct burner installed in an inlet duct for introducing exhaust gas from an exhaust port of a gas turbine through an exhaust port of a gas turbine for recovering heat, and the temperature of the gas turbine decreases when the gas turbine is under a low load. The radiant heat generated by the duct burner, which heats the exhaust gas, prevents the lining, which is installed to prevent heat from entering the entrance duct surface, from scattering or falling off. The present invention relates to a radiant heat shielding device for a duct burner, which can prevent the outflow of high-temperature gas from a burnout or a burnt place, and can stably operate an exhaust gas boiler and assure safety.

[0002]

2. Description of the Related Art In order to improve the efficiency of a gas turbine plant, exhaust gas having a temperature of about 600 ° C. discharged from a gas turbine is introduced into an exhaust gas boiler to recover heat of the exhaust gas. However,
Since the load of a gas turbine plant used for power generation or the like fluctuates depending on the season, time, or the like, the temperature of the exhaust gas discharged from the gas turbine fluctuates, and the operation rate of the exhaust gas boiler may become unstable.

For this reason, a duct burner is installed in an inlet duct for introducing exhaust gas discharged from an exhaust port of a gas turbine into an exhaust gas boiler, and when the temperature of the exhaust gas fluctuates, in particular, the load on the gas turbine is reduced and the exhaust gas is reduced. When the temperature of the exhaust gas boiler is reduced, the exhaust gas boiler is set to a designed inlet temperature by a duct burner to supply the exhaust gas to the exhaust gas boiler, and the exhaust gas boiler is operated stably and efficiently. .

[0004] FIG. 3 is a graph showing the relationship between the amount of heat retained in the exhaust gas discharged from the gas turbine and its effective use to improve the efficiency of the gas turbine plant. An exhaust gas boiler is installed on the outlet side, so that even when the gas turbine is under low load, the gas temperature at the inlet of the exhaust gas boiler is maintained at a specified temperature, and the exhaust gas boiler is operated stably to efficiently recover heat from exhaust gas. FIG. 4 is a perspective view of a conventional heat recovery device.

As shown in FIG. 1, a duct plate 02 made of a heat-resistant steel plate having a thickness of about 6 mm is provided between the exhaust port of the gas turbine and the exhaust gas boiler 01 so as to have a top, bottom, left, and right sides. Exhaust gas G
Is introduced into the exhaust gas boiler 01. When the load of a gas turbine (not shown) is low, a duct burner 04 is provided in the inlet duct 03 to keep the inlet gas temperature of the exhaust gas boiler 01 at a specified temperature.
Is installed, and the exhaust gas G introduced into the inlet duct 03 is heated by the radiant heat generated by the flame of the duct burner 04 to maintain the inlet gas temperature of the exhaust gas boiler 01 at a specified temperature.

The exhaust gas G discharged from the exhaust port of the gas turbine is oxygen-rich, with a considerable amount of unburned oxygen in the combustion air remaining. In performing this, it is not necessary to supply combustion air specifically to the duct burner 04, and by supplying only fuel, combustion can be performed with oxygen in the exhaust gas G and the low-temperature exhaust gas G can be heated.

A lining is provided on the inner peripheral surface of the inlet duct 03 to protect the inlet duct 03 from the temperature of the exhaust gas G. In particular, a duct plate 02 around which the duct burner 04 is installed is provided with a lining. , Duct burner 04
Is activated, the radiant heat of the duct burner 04 causes
Because the surface is directly exposed to the heated exhaust gas G that reaches ℃, a special lining 05, which is different from the lining when applied to other parts of the duct plate 02, is applied as shown in FIG. Like that. This lining 05
The inlet duct 03 surrounds the upper, lower, left and right sides of the duct burner 04 within a range of about 1 m upstream and about 2 m downstream in the flow direction of the exhaust gas G at the mounting position of the duct burner 04.
It is constructed on the inside.

That is, during operation of a normal gas turbine, the duct plate 02 surrounding the duct burner 04 exposed to the exhaust gas G having a temperature of about 600 ° C. Since it is directly exposed to a high temperature of about 1000 ° C., as shown in FIG.
An anchor 06 erected on the inner surface is provided with a lining 05 that holds the refractory material 07 and is structurally different from the lining applied to other parts.

However, such a lining 05
However, since the duct plate 02 on which the anchor 06 holding the refractory material 07 is erected is formed of a heat-resistant steel plate having a thickness of about 6 mm, the pulsation of the exhaust gas G passing through the inside of the inlet duct 03 And the refractory material 07 held by the anchor 06 scatters or falls off. Therefore, the lining 05 must be repaired every year. In the worst case, the operation of the gas turbine plant is stopped. There is a problem that a situation that needs to be repaired may occur.

As shown in FIG. 4B, such a lining 05 is a liner support stud 08 erected on the inner surface of the duct plate 02 and encloses a heat insulating material 09, and has a thickness of about 2 mm. A stainless steel plate 010 made of SUS410 or the like is also used. However, such a lining 0
5, the thermal expansion coefficient of the stainless steel plate 010 is large, and the stainless steel plate 010 is not held by the liner support studs 08 due to the thermal expansion due to radiant heat during operation of the duct burner 04, the stainless steel plate 010 scatters, and the exhaust gas boiler 01 There has been a problem that a damage accident may occur and the operation of the gas turbine plant must be stopped.

The lining of the inner surface of the duct plate 02, which is located away from the position where the above-described duct burner 04 is installed and is relatively less affected by the radiant heat of the duct burner 04, is expensive as shown in FIG. Therefore, there is no need to make a lining that requires long manufacturing and installation man-hours.
Furthermore, the duct plate 02 can be made of a high-temperature heat-resistant steel plate, and the lining work can be omitted.

[0012]

SUMMARY OF THE INVENTION The present invention is directed to a duct plate, which is directly exposed to high-temperature radiant heat, which is heated to about 1000 ° C. when the duct burner is operated, and is attached to an inner surface of a duct plate surrounding the duct burner. The lining was scattered and dropped, and it was necessary to repair the lining every year, or there were many accidents caused by the stainless steel plate being scattered due to thermal expansion, causing the gas turbine plant to shut down. In order to solve the problems of the conventional inlet duct, the upper, lower, left and right sides of the duct burner installed inside the inlet duct are surrounded by radiant heat shielding plates, and the inner surface of the inlet duct near the installed duct burner is exposed to high temperature radiant heat. The duct plate is stretched so as not to be directly exposed and surrounds the top, bottom, left and right of the duct burner. Even lining is stretched on the surface,
The lining can be of the same design as a normal lining that can withstand the exhaust gas temperature of about 600 ° C other than the duct burner installation part, and since the thermal expansion of the lining becomes uniform, the lining can be prevented from scattering, falling off and burning. Can prevent the scattering of stainless steel plates, or ensure stable operation of exhaust gas boilers, that is, operation of gas turbine plants, even with inlet ducts made of high-temperature heat-resistant steel plates without lining. It is an object to provide a radiation heat shielding device for a duct burner.

[0013]

Therefore, the radiant heat shielding device for a duct burner according to the present invention has the following means.

(1) An inlet duct formed of a duct plate such as a heat-resistant steel plate and for introducing exhaust gas discharged from a gas turbine into an exhaust gas boiler for recovering heat from the exhaust gas;
Installed in the inlet duct, it is ignited when the gas turbine load is small, heats the low temperature exhaust gas flowing from the gas turbine to the exhaust gas boiler, and keeps the exhaust gas at the inlet temperature specified in the exhaust gas boiler A radiant heat shielding plate is provided between the duct burner and protects the inlet duct from radiant heat of the duct burner when the exhaust gas is heated by the duct burner.

The radiant heat shield plate is made of a heat-resistant steel plate such as Incoloy 800 or other heat-resistant material that is less likely to burn or deform even when the exhaust gas is heated by the duct burner. In this case, the arrangement is such that the resistance of the exhaust gas discharged from the gas turbine including the mounting device is reduced, and this is combined with the arrangement of the duct burner that generates a flame in the flow direction of the exhaust gas. Thus, it is preferable that the back pressure of the gas turbine does not rise as much as possible. However, it is preferable that the radiant heat shield plate is always provided as a consumable that can be replaced by a certain degree of burnout or deformation, and is inexpensive so that the replacement can be used systematically when the gas turbine is stopped.

Preferably, the radiant heat shield plate has a cylindrical shape in which the upstream and downstream sides of the duct burner are open when arranged around the duct burner. It is preferable to provide a gap between the outer periphery of the radiant heat shield plate and the inner peripheral surface of the inlet duct so that exhaust gas can flow. Further, the inner peripheral surface of the inlet duct including the vicinity of the duct burner mounting position is approximately 60
It is desirable to provide a lining that can withstand a temperature of 0 ° C., or to form the inlet duct with a heat-resistant steel plate or the like that withstands such a temperature and has a uniform thermal expansion even without lining.

The radiant heat shielding device for a duct burner according to the present invention employs the following means in addition to the above-mentioned means (1).

(2) The radiant heat shield plate is formed in a cylindrical shape surrounding the upper, lower, left and right excluding the upstream side and the downstream side of the duct burner and protecting the inlet duct from the radiant heat of the duct burner. An axis was provided in the direction of flow.

The cross-sectional shape of the radiant heat shield plate formed in a cylindrical shape does not necessarily have to be a perfect circle, but may have an arc portion such as an elliptical shape.

The radiant heat shielding device for a duct burner according to the present invention includes the following means in addition to the above-mentioned means (1).

(3) The radiation heat shield plate is detachably fixed to the inner surface of the duct plate forming the inlet duct, and can be easily replaced in a short time at any time when the gas turbine is stopped.

For this purpose, it is desirable that the radiant heat shield plate is mounted at intervals on the inner surface of the duct plate forming the bottom plate of the inlet duct, and the fixed mounting is performed by a detachable screw or the like. It is preferable that these mounting devices be made of a material that does not burn out even at high temperatures, and that they are robust so that they do not generate vibration even due to pulsation of exhaust gas passing around.

The radiant heat shielding device for a duct burner according to the present invention employs the following means in addition to the above-mentioned means (1).

(4) The length of the radiant heat shield plate in the flow direction of the exhaust gas is prevented from being thermally deformed in the inlet duct due to the radiant heat of the duct burner at both the upstream and downstream sides starting from the position of attachment and detachment to the inner surface of the duct plate. It was made as long as possible.

The radiant heat shield plate varies depending on the magnitude of the radiant heat of the duct burner.
The length is preferably about 1 m on the upstream side and about 2 m on the downstream side.

[0026]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view showing a radiant heat shielding device for a duct burner according to an embodiment of the present invention. FIG. 1 is an overall perspective view showing a first embodiment of a radiant heat shielding device for a duct burner according to the present invention, and FIG. 2 is a side view showing details of an attached state of the radiant heat shielding device shown in FIG. In the drawing, the same or similar members as those shown in FIG. 3 are denoted by the same reference numerals, and description thereof will be omitted as much as possible.

As shown in the figure, depending on the output of the exhaust gas boiler 01, the gas turbine exhaust port not shown is connected to the exhaust gas boiler inlet duct of the exhaust gas boiler 01, and the exhaust gas G discharged from the gas turbine exhaust port is connected. Usually, two duct burners 04 are installed on a duct plate 02 which forms the bottom surface of an inlet duct 03 having a rectangular cross-sectional shape.

At a steady load, the load of the gas turbine which is operated by discharging the exhaust gas G at a temperature of about 600 ° C. is reduced, and the exhaust gas G temperature is determined by changing the exhaust gas G temperature at the time of the steady load of the gas turbine to the inlet. When the temperature of the exhaust gas boiler 01, which is designed as the specified temperature of the gas temperature, does not reach the specified temperature, the duct burner 04 is ignited and reheated, and the exhaust gas G is cooled to the inlet temperature specified in the exhaust gas boiler 01. To hold.

The exhaust gas G of the gas turbine contains sufficient oxygen necessary for the combustion of the duct burner 04. Therefore, it is not necessary to supply new combustion air for the combustion of the duct burner 04, Exhaust gas G can be heated only by the supply. Further, the radiant heat generated by the combustion of the duct burner 04 is
The lining 05 installed on the surface of the surrounding duct plate 04 is heated to 1000 ° C. or more, causing thermal deformation and scattering due to the extreme heating of the lining 05, and accidents such as burning of the duct plate 02 occur frequently. It will be.

Further, in order to prevent the occurrence of an accident due to the extreme heating of the lining 05, it is conceivable to construct the lining 05 with a refractory material, ceramics or the like having a high heat resistance. Cracking and falling off due to rapid heating, and the accompanying burning of the duct plate 02, occur repeatedly, and an accident occurs.

In order to solve this problem, in the present embodiment, the radiant heat shield plate 11 is installed around the inner surface of the inlet duct 03, particularly around the portion where the duct barber 04 is attached, so that the radiant heat shield plate 11 is used when the duct burner 04 is used. Is prevented from directly hitting the lining 5 installed on the surface of the duct plate 02. The radiant heat shield plate 11 is made of a heat-resistant steel plate such as a cylindrical incoro 800 and is installed inside the inlet duct 03. However, even when the duct burner 04 is not used, the flow of the exhaust gas G from the gas turbine is not hindered. That is, the exhaust gas G flowing in the inlet duct 03 is arranged so as to generate as little resistance as possible.

The radiation heat shield plate 11 may be made of a material other than the above-mentioned heat-resistant steel plate as long as the material can prevent burning or thermal deformation even when the exhaust gas G is heated by the duct burner 04. However, it is desirable that the radiation heat shielding plate 11 be considered as a consumable item and be made of a material that is not so expensive, has a simple structure, and is made of a cheap material.

Further, when installing in the inlet duct 03, the exhaust gas discharged from the gas turbine including the mounting device described later is arranged so as to reduce the resistance of the exhaust gas G as described above. The flow is not hindered, and the duct burner 04 is also designed to generate a flame in the flow direction of the exhaust gas G, and is arranged so as to reduce the resistance so that the back pressure of the gas turbine does not rise as much as possible. Thus, a decrease in the efficiency of the gas turbine due to an increase in the back pressure is prevented.

Further, the inner peripheral surface of the inlet duct 03, including the vicinity of the mounting portion of the duct burner 04, is provided with a lining 5 that can withstand a temperature of about 600 ° C. during the normal operation of the gas turbine, or without lining. However, it is made of a heat-resistant steel sheet that withstands such a temperature and has a uniform thermal expansion.

The radiant heat shield plate 11 is resistant to thermal deformation and is easy to form. Therefore, the radiant heat shield plate 11 has a cylindrical shape as described above. The size of the duct burner should be large enough to avoid deformation by touching the inner surface directly.
In order to prevent the lining 5 from being deformed or dropped off due to the radiant heat of 4, the outer diameter can be provided at an appropriate distance from the surface of the lining 5 so as to be provided for each duct burner 04. This means that a gap is provided between the outer peripheral surface of the radiant heat shield plate 11 and the inner peripheral surface of the inlet duct 03, and the exhaust gas G passes through this gap, so that the resistance can be reduced and the temperature can be reduced. The exhaust plate G cools the duct plate 02 heated by the radiant heat of the duct burner 04.

The radiation heat shielding plate 1 formed in a cylindrical shape
The cross-sectional shape of 1 may not necessarily be a perfect circle, but may be a cylindrical shape having an arc portion such as an elliptical shape.

The length of the radiant heat shield plate 11 is slightly longer than the end of the flame so that the flame of the duct burner 04 does not directly touch the lining 5 with the mounting point of the duct burner 04 as a base point. In this manner, the length of the lining 5 is also set such that thermal deformation due to the radiant heat of the flame is not applied to the lining 5 on the upstream side of the duct burner 04. More specifically, the length of the radiant heat shield plate 11 is preferably about 1 m on the upstream side and about 2 m on the downstream side, with the mounting portion of the duct burner 04 at the center.

Further, the radiation heat shielding plate 11 is connected to the entrance duct 0.
3 so as to be detachably fixed to the inner surface of the duct plate 02 forming the base plate 3 and can be easily replaced at any time when the gas turbine is stopped, so as to be installed on the inner surface of the duct plate 02 forming the bottom plate of the inlet duct 03. ing. Also, the fixed mounting on the duct plate 02,
In order to make it detachable, it is made with a screw or the like made of a material that does not burn out even at high temperatures, and that it can be firmly fixed without vibration even due to pulsation of exhaust gas passing around.

Next, referring to FIG.
The attachment of the radiation heat shield plate 11 to the upper surface 2 will be described.

On the lower surface of the outer periphery of the radiation heat shielding plate 11, a rib 1 is provided.
2 and a plate 13 are provided at both ends, and bolts 14 protruding from the upper surface of the lining 5 are attached to the plate 13.
Through the hole provided in
The radiation heat shield plate 11 can be replaced at any time when certain deformation or burnout is remarkable at the time of regular inspection or the like. That is, as described above, the radiant heat shield plate 11 is manufactured as a consumable item and is always stocked, and when the deformation and burning are remarkable, as well as at regular inspections, the radiant heat shield plate 11 is replaced systematically. Thus, it is possible to reliably prevent the operation stop of the gas turbine plant due to the burning of the lining 5 or the like.

The fuel burned by the duct burner 04 is supplied by a heat-resistant fuel pipe 16 provided through the duct plate 02, the lining 5, and the through hole 15 of the radiation heat shield plate 11.

[0042]

As described above, the radiant heat shielding device for a duct burner according to the present invention is formed of a duct plate such as a heat-resistant steel plate, and is configured to remove exhaust gas discharged from a gas turbine.
An inlet duct that is introduced into an exhaust gas boiler that recovers heat from exhaust gas, and is installed in the inlet duct, ignited when the gas turbine load is low, and heats the low-temperature exhaust gas that flows from the gas turbine into the exhaust gas boiler, Is interposed between the exhaust gas boiler and a duct burner that maintains the inlet temperature specified by the exhaust gas boiler.
The radiant heat of the duct burner does not directly hit the duct plate, and a radiant heat shield plate for protecting the inlet duct is provided.

As described above, by enclosing the periphery of the duct burner with the radiant heat shield plate, the inlet duct provided on the upstream side of the exhaust gas boiler has the same design as the duct plate provided separately from the normal duct burner mounting portion. In addition, the thermal expansion is made uniform, the causes of troubles such as falling off of the refractory material are eliminated, and the emergency stop of the gas turbine or the exhaust gas boiler due to these troubles is also eliminated, so that stable operation can be guaranteed. In addition, even if the lining of the inlet duct is designed and manufactured under the same conditions for the installation part of the duct burner, the thermal expansion of the lining is also uniform, so there is no dropping, scattering, burning, Spouting is prevented, and stable and safe operation is guaranteed.

The inlet duct of the gas turbine exhaust gas boiler is exposed to high-temperature exhaust gas at 600 ° C. during normal operation.
Not only can it be lined on the inner surface of the duct or made of high-temperature heat-resistant material, but also the duct plate near the duct burner mounting part that heats the exhaust gas can be made in the same way, so there is no need to make a special specification lining, so inexpensive lining or Inlet ducts can be manufactured with inexpensive high-temperature heat-resistant materials, and manufacturing costs can be reduced.

The radiant heat shielding plate of the radiant heat shielding device for a duct burner of the present invention surrounds the upper, lower, left and right sides except for the upstream and downstream sides of the duct burner, and protects the inlet duct from the radiant heat of the duct burner. Formed in the inlet duct in the direction of the flow of the exhaust gas.

As a result, the radiant heat shield plate is resistant to thermal deformation, furthermore easy to manufacture, can be made inexpensive and can be used as a consumable, and reliably prevent operation stop due to burnout of the inlet duct. it can. Furthermore, the resistance of the flow of exhaust gas can be reduced, and despite the installation of the radiant heat shield plate, the rise in the back pressure of the gas turbine is reduced so that the efficiency of the gas turbine does not decrease. be able to.

The radiant heat shield plate of the radiant heat shield device for a duct burner according to the present invention is detachably fixed to an inner surface of a duct plate forming an inlet duct, and can be easily replaced at any time when the gas turbine is stopped. And
The radiant heat shield plate is susceptible to thermal deformation, burnout, etc. like the burner duffizer cone used in ordinary boilers, so treat it as a consumable, keep spare parts as a permanent spare, and investigate when the boiler stops. If parts replacement is performed systematically by judging the durability, operation is not hindered and stable operation is guaranteed.

That is, the radiation heat from the duct burner is 1
Heat-resistant steel (incoloy 80
0), etc., so that it can be replaced if necessary. If a permanent spare is kept, and it is replaced at any time when the gas turbine is stopped, it depends on the scattering and falling off of the lining. The risk of burning of the duct plate and high-temperature gas ejection can be prevented beforehand, and stable operation can always be guaranteed, and the risk of duct deformation, burning, and high-temperature gas ejection can be avoided.

The radiant heat shield plate of the radiant heat shield device for a duct burner according to the present invention may be arranged such that the length of the radiant heat shield plate in the flow direction of the exhaust gas is upstream and downstream with respect to the position of attachment and detachment to the inner surface of the duct plate. Both sides have a length that prevents thermal deformation of the inlet duct due to radiant heat from the duct burner.

Thus, in the radiant heat shielding device for a burner of the present invention, the portion heated by the radiant heat of the duct burner is effectively shielded, and the radiant heat shielding plate can be made smaller, so that the manufacturing and mounting costs can be reduced. At the same time, the increase in the resistance of the exhaust gas due to the installation of the radiation heat shield plate can be suppressed, and the reduction in plant efficiency can be minimized.

[Brief description of the drawings]

FIG. 1 is an overall perspective view showing a first embodiment of a radiation heat shielding device for a duct burner according to the present invention,

FIG. 2 is a side view showing details of a mounting state of the radiant heat shielding device shown in FIG. 1;

FIG. 3 is an overall perspective view showing a state where a conventional duct burner is installed in an inlet duct;

FIG. 4 is a view showing a lining provided to protect an inlet duct from heating of a conventional duct burner;
FIG. 4B is a cross-sectional view of a lining that holds a refractory material with an anchor, and FIG. 4B is a cross-sectional view of a lining that holds a heat insulating material with a stainless steel plate.

[Explanation of symbols]

 01 Exhaust gas boiler 02 Duct plate 03 Inlet duct 04 Duct burner 5,05 Lining 06 Anchor 07 Fireproof material 08 Liner support stud 09 Insulation material 010 Stainless steel plate 11 Radiant heat shield plate 12 Rib 13 Plate 14 Bolt 15 Through hole 16 Fuel pipe

Claims (4)

[Claims] An inlet duct for introducing the exhaust gas into an exhaust gas boiler for recovering heat of an exhaust gas from a gas turbine; and an inlet duct installed in the inlet duct, ignited when the gas turbine load is small, and flowing into the exhaust gas boiler. A radiant heat shield plate interposed between the exhaust gas boiler and a duct burner for maintaining the exhaust gas boiler at a specified temperature, and protecting the inlet duct from radiant heat generated by the duct burner during heating. A radiant heat shielding device for a duct burner, characterized in that: 2. The radiant heat shielding plate includes a cylindrical member that surrounds the upper, lower, left and right sides of the duct burner and protects the inlet duct from radiant heat of the duct burner, and the flow of the exhaust gas in the inlet duct. The radiant heat shielding device for a duct burner according to claim 1, wherein the radiant heat shielding device is disposed so as to be axially oriented in the direction of. 3. The radiant heat shielding device for a duct burner according to claim 1, wherein the radiant heat shielding plate is detachably fixed to an inner surface of the duct plate forming the entrance duct. 4. The radiant heat shield plate can prevent thermal deformation of the inlet duct due to radiant heat of the duct burner on both the upstream side and the downstream side with respect to a mounting position of the duct burner on the inner surface of the duct plate. 2. The radiant heat shielding device for a duct burner according to claim 1, wherein the length is set to be a length in a flow direction of the exhaust gas.