JP5556870B2 - boiler - Google Patents

Description

  The present invention relates to a boiler. In detail, it is related with the boiler provided with the downcomer which connects a lower header and an upper header.

2. Description of the Related Art Conventionally, there is known a boiler having a relatively small amount of water that includes a can body that heats a plurality of water pipes connected between a lower header and an upper header with a burner (see, for example, Patent Document 1).
A boiler having a relatively small amount of retained water as in Patent Document 1 has a short steaming time until steam is generated and has good followability to load fluctuations, so that the operation efficiency of the boiler is increased.

  In the boiler as in Patent Document 1, since the can water is pushed up from the water pipe to the upper header by the steam generated by boiling the can water in the water pipe, the can water staying in the upper header is efficiently transferred to the lower header. In order to recirculate, a downpipe that communicates the lower header and the upper header is provided.

JP 2010-78204 A

However, when canned water staying inside the upper header is returned to the lower header through the downpipe, a vapor phase pool is generated in the upper region of the downpipe, and the canned water stays inside the upper header. In some cases, a sufficient amount of canned water reflux cannot be obtained.
On the other hand, if measures such as an increase in the size of the upper header and an increase in the number of downcomers are taken in order to obtain the desired amount of recirculation of the can water, an increase in the size and cost of the boiler will be caused.

  This invention is for solving the said subject, The objective is to provide the boiler which acquires the desired recirculation | reflux amount of can water through a downpipe, without causing the enlargement and cost increase of a boiler. is there.

  The present invention includes a plurality of water pipes extending in the vertical direction, a lower header arranged below the plurality of water pipes and connected to lower ends of the plurality of water pipes, and arranged above the plurality of water pipes. A can body having an upper header connected to upper ends of the plurality of water pipes and a burner for heating the plurality of water pipes, the steam generated in the water pipe and pushed up from the water pipe by the upper header. A boiler in which a gas-liquid separation space for separating the can water is formed, the boiler further comprising: a downcomer pipe communicating the lower header and the upper header; and a water supply pipe connected to the downcomer pipe About.

  The downcomer has a horizontal portion extending in a horizontal direction from the upper header, a bent portion bent downward from the horizontal portion, and a vertical portion descending vertically from the bent portion. The water supply pipe is preferably connected to the bent portion from directly above the bent portion of the downcomer.

  Moreover, it is preferable that the opening diameter of the connection part with the said downcomer of the said water supply pipe is smaller than the pipe diameter of the said downcomer.

  Moreover, it is preferable that the opening center of the connection part with the said downcomer of the said water supply pipe | tube corresponds with the pipe center axis | shaft of the said vertical direction part of the said downcomer.

  ADVANTAGE OF THE INVENTION According to this invention, the boiler which acquires the desired recirculation amount of can water can be provided through a downpipe, without causing the enlargement of a boiler and cost increase.

It is a schematic structure figure showing the boiler concerning a 1st embodiment of the present invention. It is a schematic block diagram which shows the boiler body which concerns on the said embodiment. It is operation | movement explanatory drawing at the time of the water supply which concerns on the said embodiment. It is the elements on larger scale which expand and show the connection part with the downcomer of the water supply pipe which concerns on 2nd Embodiment of this invention.

  Embodiments of the present invention will be described below with reference to the drawings.

<First Embodiment>
First, the configuration of the boiler 1 according to the first embodiment will be described.

FIG. 1 is a schematic configuration diagram illustrating a boiler 1 according to the present embodiment. FIG. 2 is a schematic configuration diagram illustrating the can 10 of the boiler 1 according to the present embodiment.
The boiler 1 shown in FIGS. 1 and 2 includes a can 10, a downcomer 20, an external water level detection unit 30, and a control unit 40.

  As shown in FIGS. 1 and 2, the can 10 includes a boiler housing 11, a plurality of water pipes 12, a lower header 13, an upper header 14, and a burner 16. The can 10 burns fuel and heats the can water (boiler water) in the water pipe 12.

  The boiler casing 11 has a cylindrical shape and constitutes a main part of the outer shape of the can body 10. The boiler casing 11 is disposed with a cylindrical axis line along the vertical direction.

The plurality of water pipes 12 are arranged in the boiler casing 11 so as to extend in the vertical direction in accordance with the axis of the boiler casing 11. The water pipe 12 holds can water heated by the combustion of the burner 16.
The plurality of water tubes 12 constitute an inner water tube group 12A arranged in an annular shape, and an outer water tube group 12B arranged in an annular shape coaxial with the inner water tube group 12A outside the inner water tube group 12A. The central axes of the inner water tube group 12 </ b> A and the outer water tube group 12 </ b> B coincide with the central axis of the boiler casing 11.

The inner water tube group 12A is arranged such that adjacent water tubes 12 are in contact with each other, except for a part.
The outer water tube group 12B is spaced from the inner water tube group 12A so as to form a predetermined space with the inner water tube group 12A, and is disposed in the vicinity of the inner wall of the boiler casing 11.

The lower header 13 is configured by an annular container, and is disposed below the plurality of water pipes 12 inside the boiler casing 11. The lower header 13 is connected to the lower ends of the plurality of water pipes 12.
The lower header 13 is connected to a main drain pipe 50 that discharges the canned water inside the lower header 13. In the middle of the main drain pipe 50, a main drain valve 51 for adjusting the amount of drainage in the main drain pipe 50 is provided.

The upper header 14 is configured by an annular container, and is disposed above the plurality of water pipes 12 in the boiler casing 11. The upper header 14 is connected to the upper ends of the plurality of water pipes 12.
Connected to the upper portion of the upper header 14 is a steam outflow pipe 15 through which the steam inside the upper header 14 flows out.

  As shown in FIGS. 1 and 2, the upper header 14 is configured to be higher than the lower header 13. A gas-liquid separation space 14 </ b> A is formed inside the upper header 14. Further, a baffle plate 17 and a swing suppression plate 18 are disposed inside the upper header 14.

  The gas-liquid separation space 14 </ b> A is a space that separates the steam generated in the water pipe 12 and the can water pushed up from the water pipe 12. Inside the upper header 14 in which the gas-liquid separation space 14A is formed, a gas-liquid interface AEF that is an interface between steam and can water pushed up from the water pipe 12 is present during boiler operation.

  The baffle plate 17 is disposed above the gas-liquid interface AEF inside the upper header 14, that is, in the vicinity of the steam outlet pipe 15. The baffle plate 17 separates fine water droplets contained in the water vapor rising from the gas-liquid interface AEF from the water vapor.

  The swing suppression plate 18 is disposed below the gas-liquid interface AEF inside the upper header 14. The swing suppression plate 18 is preferably arranged so as to sink as much as possible in the canned water staying inside the upper header 14. In this embodiment, the connection portion between the downcomer pipe 20 and the upper header 14 described later is provided. It arrange | positions below the center, ie, the centerline C1 extended in the horizontal direction shown in FIG. The swing suppression plate 18 suppresses swing of the can water pushed up from the water pipe 12.

  The burner 16 is disposed at the center in the upper header 14. The burner 16 has a fuel injection nozzle and an air supply nozzle (not shown), and directs the fuel supplied from the fuel pipe 53 and the fuel amount of which is adjusted by the fuel supply valve 54 from the fuel injection nozzle to the inside of the boiler casing 11. While spraying, air is supplied from the air supply nozzle to the inside of the boiler casing 11, the flame is released downward to burn the fuel, and the plurality of water tubes 12 are heated.

A space below the burner 16 from which the flame is released, that is, a space surrounded by the inner water tube group 12 </ b> A arranged in an annular shape inside the boiler casing 11 constitutes the combustion chamber 60. In the combustion chamber 60, fuel is combusted and exhaust is generated.
Below the combustion chamber 60, that is, the upper surface and the center of the lower header 13 are covered with a refractory material 70.

  A space between the outer side of the upper part of the outer water pipe group 12 </ b> B and the inner wall protruding to the outside of the boiler casing 11 constitutes an exhaust passage 80. The exhaust passage 80 discharges the exhaust generated in the combustion chamber 60 from the boiler casing 11 through an exhaust pipe (not shown).

The downcomer 20 connects the lower header 13 and the upper header 14 on the outside of the can 10, and communicates the lower header 13 and the upper header 14. The downcomer 20 lowers the can water pushed up by the upper header 14 to the lower header 13.
The connecting portion of the downcomer 20 with the lower header 13 is only required to allow the canned water inside the downcomer 20 to flow into the lower header 13, and is provided in the middle of the lower header 13. On the other hand, the connection portion of the downcomer 20 with the upper header 14 is provided at the lower portion of the upper header 14 so that canned water staying inside the upper header 14 can be lowered as much as possible.

  A water supply pipe 90 for supplying water into the downcomer 20 is connected to the upper part of the downcomer 20. A water supply pump 91 that adjusts the amount of water supply in the water supply pipe 90 is provided in the middle of the water supply pipe 90.

As shown in FIG. 1, a sub-drain pipe 55 that discharges can water flowing through the downpipe 20 is connected to the lower part of the downpipe 20. The sub-drain pipe 55 can discharge heated and concentrated can water. In the middle of the sub drain pipe 55, a sub drain valve 56 for adjusting the amount of drainage in the sub drain pipe 55 is provided.
When the electrical conductivity of the can water flowing through the downpipe 20 exceeds the predetermined threshold when the concentration blow is performed, the sub drain valve 56 is opened by the control unit 40, and the concentrated can water is passed through the sub drain pipe 55. To the outside. In carrying out the concentration blow, the control unit 40 stores the combustion time before the concentration blow is performed, and the execution timing is determined based on the combustion time.
Details of the downpipe 20 and the water supply pipe 90 will be described later.

  The external water level detection unit 30 includes a water level control cylinder 31 outside the can body 10, and communication pipes 32 a and 32 b respectively connected to the top and bottom of the water level control cylinder 31, between the water level control cylinder 31 and the upper header 14. The water level control cylinder 31 and the lower header 13 are connected. The external water level detection unit 30 is held inside the can body 10 by circulating the can water inside the can body 10 through the communication pipes 32 a and 32 b and detecting the water level in the water level control cylinder 31. Estimate the water level of the can water.

  The water level control cylinder 31 has a plurality of rod-shaped electrodes 33a, 33b, and 33c disposed therein. The plurality of rod-shaped electrodes 33 a, 33 b, and 33 c have different downward lengths, and detect different water levels in the water level control cylinder 31.

  The control unit 40 is installed outside the can 10 and receives detection signals from the plurality of rod-shaped electrodes 33a, 33b, 33c of the external water level detection unit 30. Further, in accordance with these detection signals, a drive signal is transmitted to drive parts such as the fuel supply valve 54, the feed pump 91, the main drain valve 51, and the sub drain valve 56 of the burner 16 to control the drive part.

  For example, when the water level in the can 10 decreases, the dryness of the steam increases, but the boiler 1 may be overheated. On the other hand, when the water level in the can 10 rises, overheating of the boiler 1 can be prevented, but the dryness of steam may be reduced. For this reason, the control part 40 balances obtaining desired dryness of a vapor | steam, and preventing overheating of the boiler 1, and also does not raise the concentration of the can water in the can 10 excessively. As described above, the in-can water level control for controlling the drive parts such as the fuel supply valve 54, the water supply pump 91, the main drain valve 51, and the sub drain valve 56 of the burner 16 according to the water level detected by the external water level detection unit 30 is performed.

Next, details of the downpipe 20 and the water supply pipe 90 will be described.
As shown in FIG. 2, the downcomer 20 includes an upper horizontal portion 21, an upper bent portion 22, a vertical direction portion 23, a lower bent portion 24, and a lower horizontal portion 25.

  The upper horizontal portion 21 is connected to the lower portion of the upper header 14 and extends in the horizontal direction from the upper header 14 to the upper bent portion 22.

The upper bent portion 22 is bent at a right angle downward from the upper horizontal portion 21. The upper bent portion 22 has a horizontal end portion 22a having a predetermined length in the extending direction from the upper horizontal portion 21 at a position bent downward at a right angle.
The connection from the upper horizontal direction portion 21 to the upper bent portion 22 is performed by joining flanges 21f and 22f1 that both end portions have.
Further, at the end of the horizontal end portion 22a, the closing plate 26 is joined to the flange 22f2 at the end portion.

The vertical portion 23 descends in the vertical direction from the upper bent portion 22 to the lower bent portion 24.
The vertical portion 23 is formed integrally with the upper bent portion 22 and the lower bent portion 24.

The lower bent portion 24 is bent at a right angle from the vertical direction portion 23 in the horizontal direction. The lower bent portion 24 has a horizontal end 24a having a predetermined length in a direction opposite to the lower horizontal portion 25 at a position bent at a right angle in the horizontal direction.
At the end of the horizontal end 24a, the closing plate 27 is joined to the flange 24f1 at the end.

The lower horizontal portion 25 is connected to the middle portion of the lower header 13 and extends in the horizontal direction from the lower bent portion 24 to the lower header 13.
The connection from the lower bent portion 24 to the lower horizontal portion 25 is performed by joining flanges 24f2 and 25f that both have at the ends.

  The upper horizontal portion 21, the upper bent portion 22, the vertical portion 23, the lower bent portion 24, and the lower horizontal portion 25 have the same tube diameter.

As shown in FIG. 2, the water supply pipe 90 is connected to the upper bent portion 22 from directly above the upper bent portion 22 of the downcomer pipe 20. Specifically, the connection is made in a state where the opening center Co of the connection portion of the water supply pipe 90 with the downcomer 20 coincides with the pipe center axis C2 of the vertical portion 23 of the downcomer 20. For this reason, the water supplied from the water supply pipe 90 falls linearly into the downcomer pipe 20 in the vertical direction.
The diameter of the water supply pipe 90 is smaller than the diameter of the downcomer pipe 20, and the opening diameter of the connection portion with the downcomer pipe 20 is smaller than the diameter of the downcomer pipe 20.

Next, the operation of the boiler 1 according to this embodiment will be described.
The boiler 1 according to the present embodiment has a relatively small amount of can water, and the water level of the water pipe 12 is lower than the upper end of the water pipe 12 when the burner 16 stops combustion.

When the burner 16 starts combustion, the can water held in the plurality of water pipes 12 is heated and boiled. When the can water in the water pipe 12 boils, a part of the can water is pushed up from the water pipe 12 to the upper header 14 by the steam generated by boiling. Thereby, inside the upper header 14, steam is present at the top and canned water pushed up from the water pipe 12 is present at the bottom, and the gas-liquid interface AEF is separated from both.
Since the boiler 1 according to the present embodiment achieves gas-liquid separation by the upper header 14 as described above, a separator (gas-liquid separator or brackish water separator) is not provided, and the gas-liquid separation space is provided in the upper header 14. 14A is formed.

In such a state of the boiler 1, a downcomer pipe 20 that communicates the lower header 13 and the upper header 14 is provided in order to efficiently return the canned water staying in the upper header 14 to the lower header 13.
However, when canned water staying inside the upper header 14 is returned to the lower header 13 through the downcomer 20, a vapor phase pool is generated in the upper region of the downcomer 20, and the vapor phase pool stays inside the upper header 14. In some cases, it may be impossible to obtain a sufficient amount of recirculation of can water.

  Therefore, in the boiler 1 which concerns on this embodiment, the water supply pipe 90 is connected to the upper side bending part 22 from right above the upper side bending part 22 of the downcomer pipe 20, and the drawing-in effect of the can water by water supply is exhibited.

FIG. 3 is an operation explanatory diagram at the time of water supply according to the present embodiment.
Specifically, as shown in FIG. 3 (1), water is supplied from a water supply pipe 90 connected to the upper bent portion 22 from directly above the upper bent portion 22 of the downcomer pipe 20, and the steam in the downcomer pipe 20 is An endothermic reaction that condenses is generated, and a negative pressure due to the ejector effect is generated in the upper region of the downcomer 20 by the dynamic pressure of the jet of feed water. Due to the condensation and negative pressure of these vapors, the canned water staying in the upper header 14 is drawn into the downcomer 20 and the precipitation is induced (the effect of drawing in the canned water by the water supply). Increase reflux.

  In particular, the water supply pipe 90 is connected to the upper bent part 22 from directly above the upper bent part 22, and the water supplied from the water supply pipe 90 is supplied directly to the vertical direction part 23 of the downpipe 20. This increases the probability that the feed water contacts the steam in the downpipe 20 to easily cause an endothermic reaction due to the feed water, and also facilitates the ejector effect due to the dynamic pressure of the jet of the feed water caused by the fall of the feed water in the air, Improve the effect of drawing canned water by water supply.

  Moreover, since the opening diameter of the connection part of the water supply pipe 90 with the downcomer 20 is made smaller than the diameter of the downcomer 20, the water supply from the water supply pipe 90 is separated from the inner wall of the downcomer 20. It is supplied without passing through the inner wall of the tube 20. As a result, the water supply falling in the air without passing through the inner wall of the downcomer 20 is likely to come into contact with the steam in the downcomer 20, and the dynamic pressure of the jet of the water supply is increased to easily produce the ejector effect.

  Further, since the opening center Co of the connection portion of the water supply pipe 90 with the downcomer pipe 20 is made to coincide with the pipe center axis C2 of the vertical direction portion 23 of the downcomer pipe 20, the water supply from the water supply pipe 90 is supplied to the downcomer pipe 20. It is supplied without being transmitted along the inner wall of the downcomer 20 while being separated from the inner wall. Also by this, the water supply falling in the air without passing through the inner wall of the downcomer 20 is likely to come into contact with the steam in the downcomer 20, and the dynamic pressure of the jet of the water supply is increased to easily produce the ejector effect.

  As described above, the amount of recirculated can water through the downcomer 20 is increased, and the amount of recirculated can water inside the can body 10 is increased.

  Further, the water supply from the water supply pipe 90 connected to the upper bent portion 22 from directly above the upper bent portion 22 shown in (1) of FIG. 3 is caused in the downpipe 20 by an endothermic reaction as shown in (2) of FIG. To condense the steam. This condensed vapor falls and is contained in the can water of the downcomer 20 and raises the inlet temperature of the water pipe 12 of the lower header 13 as shown in (3) of FIG. As a result, the superheat limit water level of the water pipe 12 decreases as shown in (4) of FIG. 3, and the heating amount of the water pipe 12 increases as shown in (5) of FIG. (Vapor velocity) increases. For this reason, the inner wall of the water pipe 12 becomes easy to get wet, and overheating of the boiler 1 is suppressed.

  Moreover, in order to supply new boiler water to the canned water in the concentrated downcomer 20, the new boiler water and the concentrated can water that have electrical conductivity set to a predetermined range are stirred, Local concentration becomes difficult to occur, and the concentration of the can water is made uniform. For this reason, the concentration of the can water in the inside of the lower header 13 is also reduced, and the anticorrosion effect of the lower header 13 is also improved.

  According to the boiler 1 which concerns on the above this embodiment, there exist the following effects.

(1) The boiler 1 is configured to include a downcomer 20 that communicates the lower header 13 and the upper header 14 and a water supply pipe 90 that is connected to the downcomer 20. Thereby, the water supply supplied from the water supply pipe 90 to the downpipe 20 causes an endothermic reaction in which the vapor in the downpipe 20 is condensed, and the ejector effect is generated in the upper region of the downpipe 20 by the dynamic pressure of the jet of the water supply. The negative pressure caused by Therefore, since the canned water staying in the upper header 14 can be drawn into the downpipe 20 and the precipitation can be induced (the effect of drawing canned water by the water supply), the amount of recirculated canned water through the downpipe 20 can be increased, There is no need to implement measures such as increasing the size of the header 14 or increasing the number of downcomers 20. Therefore, the desired amount of recirculation of can water can be acquired through the downcomer 20 without increasing the size and cost of the boiler 1.
Further, the water supply from the water supply pipe 90 connected to the downcomer pipe 20 condenses the vapor in the downcomer pipe 20 by an endothermic reaction, and the condensed vapor is contained in the can water of the downcomer pipe 20, and the water pipe 12 of the lower header 13. Increase the inlet temperature. As a result, the superheat limit water level of the water pipe 12 decreases, the amount of heating of the water pipe 12 increases, and the amount of evaporation (steam velocity) generated in the water pipe 12 increases, so that the inner wall of the water pipe 12 is easily wetted, and the boiler 1 Can be prevented from overheating.

  (2) The downpipe 20 includes the upper horizontal portion 21, the upper bent portion 22, and the vertical portion 23, and the water supply pipe 90 extends from directly above the upper bent portion 22 to the upper bent portion 22. Connected. Thereby, the water supply from the water supply pipe 90 can be directly supplied to the vertical direction portion 23 of the downcomer pipe 20. Therefore, the endothermic reaction due to the water supply can be easily generated, the ejector effect can be easily generated, and the effect of drawing the can water by the water supply can be further improved.

  (3) The opening diameter of the connection portion of the water supply pipe 90 with the downcomer 20 is made smaller than the diameter of the downcomer 20. Thereby, the water supply from the water supply pipe 90 can be supplied without being transmitted through the inner wall of the downcomer pipe 20 while being separated from the inner wall of the downcomer pipe 20. Therefore, it is possible to further improve the effect of drawing water from the water supply.

  (4) The opening center Co of the connection portion of the water supply pipe 90 with the downcomer 20 is made to coincide with the pipe center axis C2 of the vertical direction portion 23 of the downcomer 20. Thereby, the water supply from the water supply pipe 90 can be supplied without being transmitted through the inner wall of the downcomer pipe 20 while being separated from the inner wall of the downcomer pipe 20. Therefore, it is possible to further improve the effect of drawing water from the water supply.

  Note that the present invention is not limited to the first embodiment described above, and modifications, improvements, and the like within the scope that can achieve the object of the present invention are included in the scope of the present invention.

  Although the water supply pipe 90 which concerns on 1st Embodiment was connected to the upper side bending part 22 from right above the upper side bending part 22 of the downcomer pipe 20, it is not restricted to this. For example, the water supply pipe 90 may be connected in the middle of the vertical direction portion 23 of the downcomer pipe 20.

<Second Embodiment>
In 2nd Embodiment, since the structure of the connection part with the downcomer pipe 20 of the water supply pipe 90 differs from 1st Embodiment, since other parts are the same, the characteristic part is demonstrated and description is similar about the structure. Omitted.

The structure of the connection part with the downcomer 20 of the water supply pipe 90 which concerns on 2nd Embodiment is demonstrated.
FIG. 4 is a partially enlarged view showing an enlarged connection portion of the water supply pipe 90 according to the present embodiment with the downcomer pipe 20.
In the present embodiment, the water supply pipe 90 has a water supply inner pipe 90a.
The water supply inner pipe 90 a extends in the vertical direction from the connecting portion with the upper bent portion 22 of the downcomer pipe 20 to the inside of the vertical direction portion 23.
The water supply inner pipe 90a is connected to the water supply pipe 90 in a state in which the central axis C3 coincides with the pipe central axis C2 of the vertical portion 23 of the precipitation pipe 20, and has the same pipe diameter as that of the water supply pipe 90. The tip is extended to a height position similar to the water level of the can water in the water pipe 12.

  In the boiler 1 according to the present embodiment, the tip of the water supply inner pipe 90a is extended to a height level similar to the water level of the can water in the water pipe 12, so that the water can be circulated in the downpipe 20 When supplied at a speed higher than the speed, the pressure is reduced near the tip of the feed water inner pipe 90a, and a flow is generated that draws much can water in the vertical direction. As a result, the canned water staying inside the upper header 14 is drawn into the downpipe 20 to induce precipitation (the effect of drawing in canned water by the water supply), and the amount of recirculated canned water through the downpipe 20 is increased.

  In addition, since the tip of the water supply inner pipe 90a extends to a height similar to the level of the can water in the water pipe 12, the generation of sound due to hammering that occurs when the tip of the water supply inner pipe is too high is prevented. To do.

DESCRIPTION OF SYMBOLS 1 ... Boiler 10 ... Can body 12 ... Water pipe 12A ... Inner water pipe group 12B ... Outer water pipe group 13 ... Lower header 14 ... Upper header 14A ... Gas-liquid separation space 15 ... Burner 20 ... Precipitation pipe 21 ... Upper horizontal direction part 22 ... Upper side Bending part 23 ... Vertical direction part 24 ... Precipitation pipe AEF ... Gas-liquid interface Co ... Center of opening C2 ... Pipe center axis

Claims (4)

A plurality of water pipes extending in the vertical direction;
A lower header disposed below the plurality of water pipes and connected to lower ends of the plurality of water pipes;
An upper header disposed above the plurality of water pipes and connected to upper ends of the plurality of water pipes;
A can body having a plurality of burners for heating the water pipes, and a gas-liquid separation space for separating the steam generated in the water pipes and the can water pushed up from the water pipes is formed in the upper header. A boiler,
A downcomer pipe communicating the lower header and the upper header;
A boiler further comprising a water supply pipe connected to the downcomer. The downcomer has a horizontal portion extending horizontally from the upper header, a bent portion bent downward from the horizontal portion, and a vertical portion descending vertically from the bent portion,
The boiler according to claim 1, wherein the water supply pipe is connected to the bent portion from directly above the bent portion of the downcomer.   The boiler according to claim 2, wherein an opening diameter of a connection portion of the water supply pipe with the downcomer pipe is smaller than a pipe diameter of the downcomer pipe.   The boiler according to claim 3, wherein an opening center of a connection portion of the water supply pipe with the downcomer coincides with a pipe center axis of the vertical portion of the downcomer.

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