JP4952373B2 - boiler - Google Patents

Description

  The present invention relates to various boilers including steam boilers, hot water boilers, heat medium boilers, waste heat boilers and exhaust gas boilers. In particular, the upper header and the lower header are connected by a plurality of vertical heat transfer tubes arranged in a cylindrical shape, and the exhaust gas discharged radially from the upper outer peripheral portion of the heat transfer tube row is a cylindrical can body. The present invention relates to a multi-tube boiler having a can that leads to a flue through a cover.

  As disclosed in the following patent documents, a plurality of inner water tubes are arranged in a cylindrical shape between an annular upper header and a lower header to form an inner water tube row. A large number of outer water pipes are arranged in a cylindrical shape so as to surround the outer water pipe, and an inner vertical fin extending downward from the upper header is provided between the inner water pipes, and a lower pipe is provided between the outer water pipes. There is known a can body provided with outer vertical fins extending upward from the base.

  In a boiler having such a can, the inside of the inner water tube row is a combustion chamber, and the space between the inner water tube row and the outer water tube row is a combustion gas flow path. And a combustion chamber and a combustion gas flow path are connected by the clearance gap between the inner side water pipes formed by having not provided the inner side vertical fin in the lower part of the inner side water pipe row | line | column. Further, the combustion gas flow path and the flue are communicated by a gap between the outer water pipes formed by not providing the outer vertical fins in the upper part of the outer water pipe row.

Therefore, when fuel is burned from the burner installed at the top of the can into the combustion chamber, the combustion gas is reversed at the lower portion of the combustion chamber, and the combustion gas flow path between the inner water tube row and the outer water tube row is formed. It flows upward and is discharged as exhaust gas from the upper part of the can to the flue. During this time, the combustion gas exchanges heat with the water in each water pipe, and the water in each water pipe is heated.
JP-A-62-155401 (FIG. 1) Japanese Patent No. 3373127 (FIG. 1)

  In the boilers disclosed in each of the above patent documents, the flue is connected to the upper part of the can body because the exhaust gas is discharged from the upper outer peripheral portion of the outer water tube row. However, there are cases where it is desired to connect the flue to the lower portion of the can body, not the upper portion of the can body. For example, when installing an economizer for heating the feed water to the boiler using the heat of the exhaust gas, it is convenient to derive the exhaust gas from the lower part of the can body.

  Specifically, the economizer may want to let the exhaust gas flow from the bottom to the top. However, in the configuration in which the exhaust gas is led out from the upper part of the can body, the economizer installation position is upward, and the overall size is compact. Cannot be configured. It is possible to install an economizer in the lower part and connect the upper part of the can body and the lower part of the economizer with a flue, or let exhaust gas flow from the upper part to the lower part of the economizer, but the piping is only complicated. Also, it is impossible to make a compact configuration for the piping. Moreover, since the surface area of the exhaust gas passage is increased, the heat dissipation loss is increased.

  On the other hand, it is not preferable that the connection position of the flue to the cylindrical can cover for receiving the exhaust gas discharged radially from the upper outer peripheral portion of the outer water tube row is simply set downward because pressure loss occurs.

  The problem to be solved by the present invention is to prevent the pressure loss from the can body cover to the flue and reduce the heat dissipation loss, and to enable exhaust gas to be derived from the lower part of the can body with a compact configuration. is there.

  This invention was made in order to solve the said subject, and invention of Claim 1 is arranged in the cylindrical form between the upper header and the lower header, and comprises the some heat exchanger tube row | line | column. A heat transfer tube, a cylindrical can body cover for receiving exhaust gas discharged radially from the upper outer peripheral portion of the heat transfer tube row, and provided in a part of the circumferential direction of the can body cover, from the cylindrical surface of the can body cover The boiler is characterized by having a bulge duct that bulges outward and is provided to extend downward from the upper portion of the can body cover, and to which a flue is connected.

  According to the first aspect of the present invention, the cylindrical can cover receives exhaust gas discharged radially from the upper outer peripheral portion of the heat transfer tube array. A bulge duct is formed at a part of the can body cover in the circumferential direction and bulges outward in the radial direction and extends downward from the upper part. And since a flue is connected to a can cover through this bulge duct, exhaust gas can be led out from the lower part of a can, preventing pressure loss and heat dissipation loss. Moreover, the overall configuration can be made compact.

  The invention according to claim 2 is arranged so as to surround a plurality of inner heat transfer tubes arranged in a cylindrical shape between the upper header and the lower header and constituting the inner heat transfer tube row, and the inner heat transfer tube row, A plurality of outer heat transfer tubes arranged in a cylindrical shape between the upper header and the lower header and constituting an outer heat transfer tube row, and the adjacent inner heat transfer tubes leaving a lower end portion of the inner heat transfer tube row. A plurality of inner vertical fins provided to close the gap between the heat tubes, and a plurality of outer vertical fins provided to close the gap between the adjacent outer heat transfer tubes, leaving the upper end of the outer heat transfer tube row. And provided between the upper header and the lower header, or between the upper header and the outer heat transfer tube row at the portion having the outer vertical fin so as to surround the outer heat transfer tube row. Cylindrical can body cover and the can cover Provided in a part of the direction, bulges outward from the cylindrical surface of the can body cover, and extends downward from the upper portion of the can body cover. A boiler comprising an outlet duct.

  According to invention of Claim 2, a cylindrical can cover receives the waste gas discharged | emitted radially from the upper outer peripheral part of an outer side heat exchanger tube row | line | column. A bulge duct is formed at a part of the can body cover in the circumferential direction and bulges outward in the radial direction and extends downward from the upper part. And since a flue is connected to a can cover through this bulge duct, exhaust gas can be led out from the lower part of a can, preventing pressure loss and heat dissipation loss. Moreover, the overall configuration can be made compact.

  According to a third aspect of the present invention, a casing is further provided so as to surround the can body cover, and combustion air is supplied from the inner heat transfer tube array via a space between the can body cover and the casing. The boiler according to claim 2, wherein the boiler is also fed into an inner combustion chamber.

  According to the third aspect of the present invention, since the boiler supply air is preheated, the heat dissipation loss can be further reduced. Moreover, the thermal stress generated in the can cover can be relaxed.

  Furthermore, in the invention according to claim 4, the clearance cross-sectional area between the outer heat transfer tube array arranged on the outermost side and the can cover provided with the bulging duct is equal to or larger than the cross-sectional area of the flue. It is carried out, It is a boiler of any one of Claims 1-3 characterized by the above-mentioned.

  According to the fourth aspect of the present invention, the exhaust gas cross-sectional area on the can body side at the location where the bulging duct is provided is equal to or larger than the cross-sectional area of the flue, so the pressure from the can body cover to the flue Loss can be reliably prevented.

  According to the boiler of this invention, while preventing the pressure loss from a can body cover to a flue and reducing heat dissipation loss, exhaust gas can be derived from the lower part of the can body with a compact configuration.

Next, an embodiment of the present invention will be described.
The type of the boiler of the present invention is not particularly limited, and is, for example, a steam boiler, a hot water boiler, a heat medium boiler, a waste heat boiler, or an exhaust gas boiler. In either case, the boiler is a multi-tube boiler, typically a multi-tube small once-through boiler.

  Specifically, the boiler includes a can body configured by connecting an upper header and a lower header with a plurality of heat transfer tubes. The upper header and the lower header are arranged vertically in parallel with each other, and each has a hollow annular shape. Each heat transfer tube is arranged vertically and connects between the upper header and the lower header. That is, each heat transfer tube has an upper end connected to the upper header, and a lower end connected to the lower header. Each heat transfer tube is arranged along the circumferential direction between the upper header and the lower header, thereby forming a cylindrical heat transfer tube array.

  The heat transfer tube rows are not limited to one row, but may be two rows, three rows, or more. For example, the can body includes an inner heat transfer tube row and an outer heat transfer tube row. In this case, the inner heat transfer tube row is composed of a plurality of inner heat transfer tubes arranged in a cylindrical shape between the upper header and the lower header. The outer heat transfer tube row is composed of a plurality of outer heat transfer tubes arranged in a cylindrical shape between the upper header and the lower header so as to surround the inner heat transfer tube row. When a plurality of heat transfer tube rows are provided in this way, each heat transfer tube row is arranged in a concentric cylindrical shape.

  The can body is normally closed on one side in the vertical direction and provided with a burner on the other side in the vertical direction. In this way, the inside of the heat transfer tube array arranged on the innermost side is the combustion chamber, and fuel can be burned from the burner into the combustion chamber. However, when a waste heat boiler or an exhaust gas boiler is used, the can body is closed on one side in the vertical direction, and the exhaust gas is introduced from the other opening in the vertical direction. That is, in the case of a waste heat boiler or an exhaust gas boiler, exhaust gas is introduced into the space inside the heat transfer tube array arranged on the innermost side.

  Combustion gas from the combustion chamber (exhaust gas in the case of a waste heat boiler or an exhaust gas boiler) circulates in a can through a set path so that heat exchange with the heat transfer tube is effectively performed. For example, when the can body includes an inner heat transfer tube row and an outer heat transfer tube row, the inner heat transfer tube row leaves the lower end portion of the inner heat transfer tube row so as to close the gap between the adjacent inner heat transfer tubes. Is provided. The outer heat transfer tube row is provided with an outer vertical fin so as to close the gap between the adjacent outer heat transfer tubes, leaving the upper end portion thereof. However, in each heat transfer tube row, the heat transfer tubes adjacent in the circumferential direction may be in close contact with each other, and the lower end portion or the upper end portion may be reduced in diameter to provide a gap between the adjacent heat transfer tubes. The combustion gas flows in the can through the gaps between the inner heat transfer tubes and the gaps between the outer heat transfer tubes formed in this way.

  In any case, the combustion gas is discharged from the outer periphery of the upper end portion of the outer heat transfer tube array arranged on the outermost side. That is, the exhaust gas after heat exchange with each heat transfer tube is discharged radially from the gap between the outer heat transfer tubes at the upper end of the outer heat transfer tube row.

  The exhaust gas discharged radially from the upper end portion of the outer heat transfer tube row is received by a can body cover provided on the outer periphery of the can body. The can cover is typically cylindrical. And the can cover is between the upper header and the lower header, or between the upper header and the place where the outer vertical fin of the outer heat transfer tube row is provided so as to surround each heat transfer tube row. Provided. At this time, the can cover has a gap between the lower header and the middle of the outer heat transfer tube row sealed while a gap with the upper header is sealed. The can cover provided between the upper header and the lower header preferably has a large diameter portion. The large diameter portion is preferably provided above the peripheral side wall of the can body cover.

  The can body cover is provided with a bulging duct that bulges outward in the radial direction and extends downward from the upper part in a part of the circumferential direction. When providing a large diameter part in a can body cover, it is good to provide a bulging duct in this large diameter part. The bulging duct may be formed by bulging the peripheral side wall of the can body cover itself, or by welding a member separate from the can body cover to the opening formed in the peripheral side wall of the can body cover. May be provided. Moreover, you may provide a heat insulating material in the inner surface facing the outer side heat exchanger tube row | line in a bulging duct. A flue is connected to the can body cover through the downward extension part of the bulging duct. Thereby, a flue is connected to a can lower part. Combustion gas from the combustion chamber is discharged to the flue as exhaust gas after heat exchange with each heat transfer tube.

  With such a configuration, in the boiler of the present invention, exhaust gas can be derived from the lower portion of the can body. Thereby, when installing the economizer which preheats the water supply to a boiler by heat exchange with exhaust gas, it can be set as a compact structure as the whole boiler. That is, when installing an economizer, the lower part of the can and the lower part of the economizer can be connected by a flue, so the upper part of the can and the lower part of the economizer are connected by a flue and the flue is routed up and down. There is no need, and the economizer can be easily installed below, and the can body and the economizer can be installed close to each other. Furthermore, in the present invention, the bulging duct is provided so as to bulge from the can cover. Thereby, since the surface area becomes small compared with the flue at the time of piping up and down, an expansion | swelling duct can reduce heat dissipation loss. Furthermore, the bulge duct can prevent pressure loss when exhaust gas is guided from the can cover to the flue. By the way, the vertical cross-sectional area of the flue should be larger than the area obtained by adding the bulging cross-sectional area of the bulging duct to the cross-sectional area of the cylindrical gap between the outer heat transfer tube array arranged on the outermost side and the can cover. preferable. Thereby, the pressure loss of the exhaust gas from the can cover to the flue can be surely prevented.

  By the way, in this invention, it is good also as a structure which provides a casing so that a can body cover may be surrounded and sends combustion air to a combustion chamber via the space between a can body cover and a casing. Since the combustion air is preheated by the intake air to the blower or the discharge air from the blower, it is possible to reduce the heat dissipation loss. Further, the can cover can be cooled.

Hereinafter, specific embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a schematic longitudinal sectional view showing an embodiment of the boiler of the present invention, and FIG. 2 is a sectional view taken along line II-II. The boiler 1 of this embodiment is a multi-tube small once-through boiler provided with a cylindrical can body 2. The can body 2 is configured by connecting the upper header 3 and the lower header 4 with a plurality of water tubes (heat transfer tubes) 5, 5,..., 6, 6,. .

  The upper header 3 and the lower header 4 are vertically spaced apart from each other in parallel, and each has a hollow annular shape. Further, the upper header 3 and the lower header 4 are respectively arranged horizontally and on the same axis.

  Each of the water pipes 5 and 6 is arranged vertically, and the lower end is connected to the lower header 4 while the upper end is connected to the upper header 3. The water pipes 5 and 6 are sequentially arranged in the circumferential direction of the upper header 3 and the lower header 4 to constitute a cylindrical water pipe row. In the present embodiment, the inner water tube row 7 and the outer water tube row 8 are arranged in a concentric cylindrical shape. The inner water tube row 7 is composed of inner water tubes 5, 5,... Arranged in a cylindrical shape. On the other hand, the outer water tube row 8 is configured by outer water tubes 6, 6,... Arranged in a cylindrical shape so as to surround the inner water tube row 7.

  Inner vertical fins 9 are provided in the inner water tube row 7 so as to close the gap between the adjacent inner water tubes 5 and 5, leaving a setting region at the lower end. That is, the gap between the inner water pipes 5 and 5 is closed by the inner vertical fin 9 leaving the setting region at the lower end. The inner water tube row 7 is provided with a gap between the adjacent inner water tubes 5 and 5 at the lower end where the inner vertical fin 9 is not provided. The gap is a communication portion (referred to as an inner row communication portion) 10 for communicating the inner side and the outer side of the inner water tube row 7.

  The outer vertical fin 11 is provided in the outer water pipe row 8 so as to close a gap between the adjacent outer water pipes 6 and 6 while leaving a setting region at the upper end. That is, the gap between the outer water pipes 6 and 6 is closed by the outer vertical fin 11 while leaving the set area at the upper end. The outer water pipe row 8 has a gap between the adjacent outer water pipes 6 and 6 at the upper end where the outer vertical fin 11 is not provided. The gap is a communication portion (referred to as an outer row communication portion) 12 for communicating the inner side and the outer side of the outer water tube row 8.

  By the way, each inner water pipe 5 may further be provided with an inner horizontal fin (not shown) protruding from the outer peripheral surface, if desired. Similarly, each outer water pipe 6 may further be provided with an outer lateral fin (not shown) protruding from the outer peripheral surface, if desired. A plurality of horizontal fins can be provided in each of the water pipes 5 and 6 apart from each other in the vertical direction. Moreover, each horizontal fin is normally provided extending in the shape of a flange outward in the radial direction of each water pipe 5, 6. At this time, a swirling flow can be generated in the combustion gas by inclining by a desired angle with respect to the horizontal direction.

  Moreover, in the example of illustration, the lower end part of each inner side water pipe 5 is formed in the reduced diameter part 13 rather than the upper part from it. This is to ensure the desired flow rate of the combustion gas passing through the inner row communication portion 10. Therefore, if the flow rate of the combustion gas passing through the inner row communication portion 10 can be ensured as desired, the reduced diameter portion 13 is not essential. The size of the inner row communication portion 10 depends on the gap between the adjacent inner water pipes 5 and 5 and the height position of the lower end portion of the inner vertical fin 9. The dimensions may be adjusted. On the other hand, in the illustrated example, the reduced diameter portion 13 is not formed at the upper end portion of each outer water pipe 6, but the reduced diameter portion 13 may be formed in the same manner as each inner water pipe 5.

  A refractory material 14 is provided on the lower surface of the upper header 3 and the upper surface of the lower header 4 so as to cover the connecting portions between the headers 3 and 4 and the water tubes 5 and 6. At this time, the refractory material 14 on the lower header 4 side is provided so as to block the central portion of the lower header 4. A columnar or truncated conical recess 15 is formed at the center of the refractory material 14 on the lower header 4 side.

  A cylindrical can cover 16 is provided between the upper header 3 and the lower header 4 so as to surround the outer water tube row 8. In the illustrated example, the can cover 16 is formed in a stepped cylindrical shape with the large-diameter portion 17 disposed above and the small-diameter portion 18 disposed below. The can body cover 16 has a gap between the upper end header 3 and the upper header 3 sealed at the upper end, and a gap with the lower header 4 sealed at the lower end. Here, the cylindrical gap between the small diameter portion 18 and the outer water tube row 8 may be filled with a heat insulating material (not shown).

  The large-diameter portion 17 of the can body cover 16 is provided with a bulging duct 19 that bulges outward in the radial direction and extends in the vertical direction at a part in the circumferential direction. The bulging duct 19 in the illustrated example has a substantially rectangular shape in side view. In the bulging duct 19, the wall surface in the bulging direction is a cylindrical surface concentric with the can cover 16 in FIG. 2, but this may be linear in a plan view. Further, the vertical dimension of the bulging duct 19 can be changed as appropriate. A flue 20 is connected to the lower end of the bulging duct 19.

  The flue 20 has a short cylindrical shape with the axis line extending in the left-right direction, and an economizer 22 is connected to the tip of the flue 20 via a hollow box-shaped connection portion 21. The hollow box-like connection portion 21 has an inclined lower end surface for directing the exhaust gas from the flue 20 to the upper economizer 22. In this way, the exhaust gas from the lower part of the peripheral side surface of the can body 2 is guided upward from the lower part of the economizer 22 through the flue 20. In FIG. 2, the longitudinal sectional area of the flue 20 is made larger than the area obtained by adding the bulging cross-sectional area of the bulging duct 19 to the cross-sectional area of the cylindrical gap between the outer water pipe row 8 and the large-diameter portion 17. This is preferable in that pressure loss of exhaust gas from the can cover 16 to the flue 20 is prevented.

  As is well known, the economizer 22 is for heating the feed water introduced from the lower header 4 of the boiler 1 into the water pipes 5 and 6. For this purpose, the economizer 22 is provided with a water supply path 23 to the lower header 4. Thereby, in the economizer 22, the exhaust gas introduced from below heats the feed water to the boiler 1. The exhaust gas is led out from the upper exhaust cylinder 24.

  A burner 25 is provided at the center of the upper header 3 downward. The burner 25 is supplied with fuel and combustion air. By operating the burner 25, fuel is burned in the can 2. At this time, the inside of the inner water tube row 7 functions as the combustion chamber 26.

  Combustion gas resulting from the combustion of fuel in the combustion chamber 26 is led to the combustion gas flow path 27 between the inner water tube row 7 and the outer water tube row 8 via the inner row communication portion 10. Then, the combustion gas is led out to the cylindrical gap between the outer water pipe row 8 and the can cover 16 via the outer row communication portion 12. After that, the exhaust gas is led to the flue 20 through the bulging duct 19 formed in the can cover 16 and discharged from the flue 20 to the outside through the economizer 22 and the exhaust pipe 24. At this time, the combustion gas exchanges heat with the water in the water pipes 5 and 6, and the water in the water pipes 5 and 6 is heated. Thereby, steam can be taken out from the upper header 3, and the steam is sent to a steam use facility (not shown) via a steam separator (not shown).

  In the present embodiment, a cylindrical casing 28 is provided so as to surround the can body cover 16. In the cylindrical space between the can cover 16 and the casing 28, the upper end is opened and the lower end is closed. In addition, a suction port of the blower 30 is connected to the lower portion of the peripheral side wall of the casing 28 through a communication path 29. The blower 30 is for sending combustion air into the burner 25.

  Accordingly, the outside air is sent to the combustion chamber 26 as combustion air from the position surrounding the burner 25 above the upper header 3 through the space between the can body cover 16 and the casing 28. Thereby, the preheating of the combustion air can be achieved by the intake air to the blower 30. In addition, the can cover 16 can be cooled. However, the combustion air may be preheated not by suction into the blower 30 but by discharge from the blower 30. Specifically, the discharge air from the blower 30 may be sent to the combustion chamber 26 as combustion air through the space between the can body cover 16 and the casing 28.

  According to the boiler 1 of the present embodiment, the bulging duct 19 is configured to also serve as a part of the can body cover 16. Therefore, compared with the case where the upper part of the can body cover 16 and the economizer 22 are simply connected directly by the flue 20, heat dissipation loss can be reduced. Furthermore, the bulging duct 19 can prevent the pressure loss of the exhaust gas from the can cover 16 to the flue 20. Moreover, in this embodiment, the flue 20 is connected to the lower part of the can body 2. Thereby, when installing the economizer 22, since the economizer 22 lower part and the can body 2 lower part can be easily connected by the flue 20, the economizer 22 can be installed comparatively downward, and the economizer 22 and the can body 2 The separation distance can be shortened. Therefore, it can be set as the compact structure as the boiler 1 whole. Moreover, in the boiler 1 of a present Example, the casing 28 is provided so that the can cover 16 may be surrounded. Thereby, since the combustion air is preheated, a heat dissipation loss can be reduced.

  Further, in this embodiment, each water tube row 7 (8) has a configuration in which a gap is provided between adjacent water tubes 5, 5 (6, 6), and vertical fins 9 (11) are provided in the gap. With such a configuration, it is possible to allow combustion gas to flow into the gaps between the water pipes 5, 5 (6, 6), to prevent the gaps from becoming dead spaces, and the vertical fins 9 (11) Heat transfer efficiency from the combustion gas to each water pipe 5 (6) can be increased. Further, since the exhaust gas is discharged radially from the entire circumference of the upper end portion of the outer water tube row 8, the exhaust gas is guided to the flue 20 through the bulging duct 19 formed in the can body cover 16. An even exhaust gas flow can be ensured in the entire circumferential direction of the eight.

  The boiler of the present invention is not limited to the configuration of the above embodiment, and can be changed as appropriate. For example, in the above embodiment, the can cover 16 is provided between the upper header 3 and the lower header 4, but the upper header 3 and the location where the outer vertical fins 11 of the outer water tube row 8 are provided. A can cover may be provided between the two. In this case, the outer water pipe row 8 and the outer vertical fin 11 are sealed at the lower end thereof with respect to the lower header 4. Thereby, combustion gas or exhaust gas does not contact the outer peripheral part of the outer water pipe row 8. Therefore, the refractory material 14 on the upper surface of the lower header 4 need not be provided on the outer peripheral side of the outer water tube row 8.

  In the above embodiment, the inner water tube row 7 and the outer water tube row 8 are provided, but the number of water tube rows can be appropriately increased or decreased. Moreover, in the said Example, although the lower part of the can body 2 was obstruct | occluded and the burner 25 was provided in the upper part of the can body 2, on the contrary, the upper part of the can body 2 was obstruct | occluded and the lower part of the can body 2 was made. A burner 25 may be provided. Moreover, in the said Example, although the water supply to the boiler 1 was performed through the economizer 22 upper end part from the economizer 22 lower end part, conversely, it goes through the economizer 22 lower end part from the economizer 22 upper end part. It may be broken. By the way, the bulging duct 19 may be provided with a heat insulating material 31 on the inner surface of the wall surface in the bulging direction as shown by a two-dot chain line. Thereby, the heat radiation to the outside can be suppressed.

  Moreover, although the said Example demonstrated the example applied to the steam boiler, it is applicable similarly to a hot water boiler and a heat-medium boiler. Furthermore, in the said Example, if waste gas is introduce | transduced inside the inner side water pipe line 7 instead of providing the burner 25, it can be set as a waste-heat boiler or waste gas boiler.

It is a schematic longitudinal cross-sectional view which shows one Example of the boiler of this invention. It is II-II sectional drawing of FIG.

Explanation of symbols

1 Boiler 3 Upper header 4 Lower header 5 Inner water tube (inner heat transfer tube)
6 Outside water pipe (outside heat transfer pipe)
7 Inner water tube row (inner heat transfer tube row)
8 Outside water tube row (outside heat transfer tube row)
9 inner vertical fin 11 outer vertical fin 16 can body cover 19 bulge duct 20 flue 26 combustion chamber 28 casing

Claims (4)

A plurality of heat transfer tubes arranged in a cylindrical shape between the upper header and the lower header to form a heat transfer tube array;
A cylindrical can cover for receiving exhaust gas discharged radially from the upper outer periphery of the heat transfer tube row;
The can body cover is provided at a part of the circumferential direction of the can body cover, bulges outward from the cylindrical surface of the can body cover, and extends downward from the upper portion of the can body cover. And a bulging duct to which a road is connected. A plurality of inner heat transfer tubes arranged in a cylindrical shape between the upper header and the lower header to form an inner heat transfer tube row;
A plurality of outer heat transfer tubes that are arranged in a cylindrical shape between the upper header and the lower header so as to surround the inner heat transfer tube row and constitute an outer heat transfer tube row,
A plurality of inner longitudinal fins provided to close the gap between the adjacent inner heat transfer tubes, leaving the lower end of the inner heat transfer tube row;
A plurality of outer vertical fins provided to close the gap between the adjacent outer heat transfer tubes, leaving the upper end of the outer heat transfer tube row;
Provided between the upper header and the lower header, or between the upper header and the outer heat transfer tube row at the location having the outer vertical fin so as to surround the outer heat transfer tube row. A cylindrical can cover,
The can body cover is provided at a part of the circumferential direction of the can body cover, bulges outward from the cylindrical surface of the can body cover, and extends downward from the upper portion of the can body cover. And a bulging duct to which a road is connected. A casing is further provided so as to surround the can body cover,
The boiler according to claim 2, wherein combustion air is sent into a combustion chamber inside the inner heat transfer tube row through a space between the can cover and the casing. The gap cross-sectional area between the outer heat transfer tube array arranged on the outermost side and the can cover provided with the bulging duct is equal to or larger than the cross-sectional area of the flue. The boiler according to any one of 3.

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