JP7646296B2 - Boiler furnace wall structure and boiler chemical cleaning method - Google Patents

Description

The present invention relates to a boiler furnace wall structure and a boiler chemical cleaning method.

A known structure is to provide a nose pipe (nose wall tube) on the rear wall of the furnace that bulges into the interior of the furnace in order to promote mixing of the combustion gas in the boiler furnace and to prevent the high-temperature combustion gas from passing through heat exchangers such as superheaters located at the top (downstream side) of the furnace without coming into contact with them. Because nose pipes have a complex structure and the flow rate of the internal fluid is low, they are the area where scale buildup is most noticeable on the inner surface of the tube.

Patent Document 1 describes a method of chemically cleaning a boiler in which a part of the furnace wall tube is a nose wall tube, by providing a temporary piping for circulating cleaning water and a temporary circulation pump, and circulating cleaning water throughout the entire furnace wall tube. In this cleaning method, in addition to the temporary piping, a first additional temporary piping that connects to the nose wall inlet header and a second additional temporary piping that connects the temporary piping upstream of the circulation pump to the nose wall outlet header are provided, and when chemically cleaning the entire furnace wall tube, a part of the cleaning liquid from the temporary circulation pump is circulated from the first additional temporary piping to the nose wall tube via the nose wall inlet header. In other words, when circulating the cleaning liquid throughout the entire furnace wall tube, additional cleaning water is circulated through the nose wall tube.

JP 2019-82314 A

If the entire furnace wall tube, including the nose wall tube group, is chemically cleaned as in the method of Patent Document 1, it takes a long time to clean. Also, if an area with little scale adhesion is chemically cleaned, the inner surface of the water tube may be eroded and damaged by the cleaning liquid. For this reason, instead of or in addition to full-area cleaning in which the entire furnace wall tube is chemically cleaned, it is possible to exclude areas of the entire furnace wall tube other than the nose wall tube group as non-cleaned areas from the cleaning target, and chemically clean only the nose wall tube group as the cleaning area.

However, when only the nose wall tube group is chemically cleaned in the structure of Patent Document 1 (chemically cleaning the nose wall tube group alone), the cleaning liquid flows through the cleaning area while the water tubes in the non-cleaning area are filled with water, and the liquid concentration gradient that occurs at the boundary between the cleaning area and the non-cleaning area causes the cleaning liquid to diffuse into the non-cleaning area, causing the scale to partially dissolve in the non-cleaning area, and the scale pieces remain in place while they are about to detach, or accumulate in areas with a low flow rate, which may cause overheating damage due to heat transfer inhibition during subsequent boiler operation.

The present invention aims to provide a boiler furnace wall structure and chemical cleaning method that allows the nose wall tube group to be chemically cleaned separately without the non-cleaning area that does not include the nose wall tube group being affected by the cleaning liquid.

In order to achieve the above object, the first aspect of the present invention is a furnace wall structure for a boiler in which the furnace wall comprises a first wall tube group, a second wall tube group, and a nose wall tube group, and comprises a first wall tube outlet header, a nose wall inlet header, a nose wall outlet header, a second wall tube inlet header, a nose wall inlet connecting pipe, a nose wall outlet connecting pipe, an inlet connecting pipe opening/closing valve, an outlet connecting pipe opening/closing valve, a first connecting pipe, and a second connecting pipe. The first wall tube group, the second wall tube group, and the nose wall tube group are each composed of a plurality of water tubes, and the first wall tube group and the second wall tube group are connected via the nose wall tube group.

The first wall tube outlet header is connected to the downstream end of each water tube in the first wall tube group. The nose wall inlet header is connected to the upstream end of each water tube in the nose wall tube group. The nose wall outlet header is connected to the downstream end of each water tube in the nose wall tube group. The second wall tube inlet header is connected to the upstream end of each water tube in the second wall tube group.

The nose wall inlet connecting pipe connects the first wall pipe outlet header and the nose wall inlet header. The nose wall outlet connecting pipe connects the nose wall outlet header and the second wall pipe inlet header. The inlet connecting pipe opening/closing valve can open and close the nose wall inlet connecting pipe. The outlet connecting pipe opening/closing valve can open and close the nose wall outlet connecting pipe.

The first connecting pipe branches off from the nose wall inlet connecting pipe downstream of the inlet connecting pipe on-off valve. The first connecting pipe is closed when the boiler is operating, and a first cleaning liquid flow pipe can be connected to it during chemical cleaning. The second connecting pipe branches off from the nose wall outlet connecting pipe upstream of the outlet connecting pipe on-off valve. The second connecting pipe is closed when the boiler is operating, and a second cleaning liquid flow pipe can be connected to it during chemical cleaning. The first cleaning liquid flow pipe is connected to the first connecting pipe, and the second cleaning liquid flow pipe is connected to the second connecting pipe, and cleaning liquid flows in from one of the first cleaning liquid flow pipe and the second cleaning liquid flow pipe, and cleaning liquid flows out from the other, so that cleaning liquid flows through each water pipe of the nose wall tube group.

The second aspect of the present invention is a method for chemically cleaning a boiler in which the furnace wall includes a first wall tube group, a second wall tube group, and a nose wall tube group. The first wall tube group, the second wall tube group, and the nose wall tube group are each composed of a plurality of water tubes. A first wall tube outlet header is connected to the downstream end of each water tube of the first wall tube group, and a nose wall inlet header is connected to the upstream end of each water tube of the nose wall tube group. A nose wall outlet header is connected to the downstream end of each water tube of the nose wall tube group, and a second wall tube inlet header is connected to the upstream end of each water tube of the second wall tube group. The first wall tube outlet header and the nose wall inlet header are connected by a nose wall inlet connecting pipe, and the nose wall outlet header and the second wall tube inlet header are connected by a nose wall outlet connecting pipe. The first wall tube group and the second wall tube group are communicated via the nose wall tube group.

In the method of this aspect, an inlet connection pipe on-off valve capable of opening and closing the nose wall inlet connection pipe and an outlet connection pipe on-off valve capable of opening and closing the nose wall outlet connection pipe are provided. A first connection pipe is provided that branches off from the nose wall inlet connection pipe downstream of the inlet connection pipe on-off valve, is closed when the boiler is operating, and can be connected to a first cleaning liquid flow pipe during chemical cleaning. In addition, a second connection pipe is provided that branches off from the nose wall outlet connection pipe upstream of the outlet connection pipe on-off valve, is closed when the boiler is operating, and can be connected to a second cleaning liquid flow pipe during chemical cleaning.

During chemical cleaning, the inlet connection pipe on-off valve and the outlet connection pipe on-off valve are closed. The first connection pipe is connected to the first cleaning liquid circulation pipe, and the second connection pipe is connected to the second cleaning liquid circulation pipe. Cleaning liquid flows into one of the first and second cleaning liquid circulation pipes and flows out of the other, thereby circulating the cleaning liquid through each water pipe in the nose wall tube group.

According to the structure of the first aspect and the method of the second aspect, by closing the inlet connecting pipe on-off valve and the outlet connecting pipe on-off valve, the flow range (cleaning area) of the cleaning liquid from one side of the first cleaning liquid flow pipe to the other side of the second cleaning liquid flow pipe can be reliably blocked from the non-cleaning area (e.g., the first wall pipe group and the first wall pipe outlet header, etc.) upstream of the inlet connecting pipe on-off valve and the non-cleaning area (e.g., the second wall pipe inlet header and the second wall pipe group, etc.) downstream of the outlet connecting pipe on-off valve. Therefore, the non-cleaning area that does not include the nose wall pipe group is not affected by the cleaning liquid, and the nose wall pipe group can be chemically cleaned independently.

In addition, if the flow rate of the cleaning liquid is set so that all the water tubes that make up the furnace wall are targeted for cleaning, the flow rate will be slow in the nose wall tube group, making it difficult for the cleaning liquid to flow, and the temperature of the cleaning liquid will also be likely to drop, so that scale cannot be sufficiently removed and the desired cleaning effect may not be obtained. In contrast, in the first and second aspects described above, the nose wall tube group can be chemically cleaned independently, so that chemical cleaning can be performed under optimal flow rate and liquid temperature conditions in the nose wall tube group, and the desired cleaning effect can be obtained.

According to the present invention, the nose wall tube group can be chemically cleaned separately without the non-cleaning area not including the nose wall tube group being affected by the cleaning liquid.

1 is a schematic diagram showing the overall configuration of a boiler according to an embodiment of the present invention. FIG. 2 is a perspective view showing a schematic external appearance of the boiler shown in FIG. 1 . FIG. 2 is a perspective view showing the configuration of a furnace tube wall of the boiler of FIG. 1. FIG. 1 is a piping diagram for chemically cleaning the nose wall tube group alone. FIG. 5 is a piping system diagram as viewed from the direction of arrow V in FIG. 4.

The furnace wall structure of a boiler according to one embodiment of the present invention will be described with reference to the drawings. Figure 1 shows an example of the configuration of a boiler with an opposed combustion system in which burners 3 are installed facing each other on the furnace front wall 11 and the furnace rear wall 12 of the boiler, and fuel is supplied from the burners 3 and burned in the furnace 1. As fuel, solid fuels such as pulverized coal made from crushed coal, heavy oil, natural gas, etc. are used.

As shown in Figures 1 and 2, the boiler includes furnace walls, which are a furnace front wall 11 constituting the front side of the furnace 1, a furnace rear wall 12 opposing the furnace front wall 11 and constituting the rear side of the furnace 1, a pair of furnace side walls 13 opposing each other between the furnace front wall 11 and the furnace rear wall 12 and constituting the side of the furnace 1, a furnace ceiling wall 14 constituting the ceiling of the furnace 1, and a rectangular cylindrical furnace auxiliary side wall portion 2 arranged on the upper downstream side (furnace rear wall 12 side) of the furnace 1. Burners 3 that supply pulverized coal fuel and air into the furnace 1 and burn them are installed in multiple stages in the vertical direction on the furnace front wall 11 and furnace rear wall 12 at the bottom of the furnace 1. A heat transfer tube group (not shown) is suspended from the upper part of the furnace 1.

The furnace auxiliary side wall 2 forms a gas flow path 4 that continues from the top of the furnace 1 in a substantially horizontal direction, and the combustion gas G generated in the furnace 1 flows through the gas flow path 4 of the furnace auxiliary side wall 2 to the rear heat transfer section (not shown). The furnace auxiliary side wall 2 includes a furnace auxiliary side wall 15 that forms the side of the gas flow path 4, a ceiling wall 16 that forms the ceiling of the gas flow path 4, and a bottom wall 17 that forms the bottom surface of the gas flow path 4.

The furnace front wall 11, furnace rear wall 12, furnace side wall 13, furnace auxiliary side wall 15, and bottom wall 17 of the furnace auxiliary side wall section 2 are composed of a membrane wall in which water tubes (steel pipes, heat transfer tubes) 5 and fins (steel plates, membrane bars) 6 are arranged alternately and formed into a panel shape by welding (see Figure 3). The fluid flowing through the water tubes 5 is water, steam, or a mixture of water and steam. The furnace spiral rear wall tube 21 constituting the lower part of the furnace rear wall 12, the furnace auxiliary side wall tube 22 constituting the furnace auxiliary side wall 15, and the bottom wall 17 of the furnace auxiliary side wall section 2 and the nose wall tube 23 constituting the nose section 7 described later are all water tubes 5 that form a membrane fall. The nose wall tube 23 is bent more complexly than the other water tubes 5.

The lower peripheral walls of the furnace 1 (furnace front wall 11, furnace rear wall 12, and furnace side wall 13) are formed by water pipes 5 (spiral pipes 8) that spirally wind diagonally upward around the furnace 1. Of the upper peripheral walls of the furnace 1, the furnace front wall 11 and furnace side wall 13 are formed by water pipes 5 (vertical pipes 9) that extend in a substantially vertical direction.

A nose section 7 that juts out (bulges out) in a "<" shape toward the inside of the furnace 1 is installed at the top of the furnace rear wall 12. The flow path at the top of the furnace 1 is narrowed by the nose section 7, so the combustion gas G flowing down inside the furnace 1 is mixed rapidly. In addition, the nose section 7 bends the flow of the combustion gas G inside the furnace 1 toward the furnace front wall 11, preventing the combustion gas G near the furnace rear wall 12 from flowing downstream without directly contacting the heat transfer tube group at the top of the furnace 1.

The multiple furnace spiral rear wall tubes 21 in the lower part of the furnace rear wall 12 constitute a first wall tube group 24, the multiple furnace secondary side wall tubes 22 in the furnace secondary side wall 15 constitute a second wall tube group 25, and the multiple nose wall tubes 23 in the nose section 7 constitute a nose wall tube group 26. The upper part of the nose wall tube 23 (nose wall tube group 26) constitutes the bottom wall 17 of the furnace secondary side wall section 2, and the first wall tube group 24 and the second wall tube group 25 are connected via the nose wall tube group 26.

As shown in Figures 4 and 5, a furnace spiral rear wall outlet header (first wall tube outlet header) 31 is connected to the downstream end of each furnace spiral rear wall tube 21 of the first wall tube group 24, and a nose wall inlet header 32 is connected to the upstream end of each nose wall tube 23 of the nose wall tube group 26. A nose wall outlet header 33 is connected to the downstream end of each nose wall tube 23 of the nose wall tube group 26, and a furnace secondary side wall inlet header (second wall tube inlet header) 34 is connected to the upstream end of each furnace secondary side wall tube 22 of the second wall tube group 25.

The furnace spiral rear wall outlet header 31 and the nose wall inlet header 32 are connected by a nose wall inlet connection pipe 35, and the nose wall outlet header 33 and the furnace secondary side wall inlet header 34 are connected by a nose wall outlet connection pipe 36. The nose wall inlet connection pipe 35 is provided with an inlet connection pipe opening/closing valve 37 that can open and close the pipe line, and the nose wall outlet connection pipe 36 is provided with an outlet connection pipe opening/closing valve 38 that can open and close the pipe line. The inlet connection pipe opening/closing valve 37 and the outlet connection pipe opening/closing valve 38 are opened when the boiler is operating, and closed when the nose section 7 is chemically cleaned.

When the boiler is in operation, a portion of the fluid flowing upward through the spiral tube 8 (see Figure 1) reaches the downstream end of the furnace spiral rear wall tube 21 (first wall tube group 24), then flows through the furnace spiral rear wall outlet header 31, the nose wall inlet connecting pipe 35, the nose wall inlet header 32, the nose wall tube group 26, the nose wall outlet header 33, the nose wall outlet connecting pipe 36, the furnace secondary side wall inlet header 34, and the furnace secondary side wall tube 22 (second wall tube group 25), before flowing into the furnace secondary side wall outlet header 41.

A first connecting pipe 39 branching from the nose wall inlet connecting pipe 35 is provided on the nose wall inlet connecting pipe 35 downstream of the inlet connecting pipe opening/closing valve 37. The first connecting pipe 39 is closed when the boiler is in operation, and is connected to a first cleaning liquid flow pipe 54 described later during chemical cleaning of the nose section 7, connecting the nose wall inlet connecting pipe 35 and the first cleaning liquid flow pipe 54. The first connecting pipe 39 is made of, for example, a metal pipe. In this case, one end of the first connecting pipe 39 is hermetically welded to the outer circumferential surface of the nose wall inlet connecting pipe 35, and the other end opening of the first connecting pipe 39 is closed by hermetically welding a lid body. The inside of the first connecting pipe 39 communicates with the inside of the nose wall inlet connecting pipe 35 through a hole formed in the nose wall inlet connecting pipe 35. During chemical cleaning, the other end opening of the first connecting pipe 39 is opened by cutting off the lid, and then the first cleaning liquid flow pipe 54 is connected to the first connecting pipe 39 by welding. After chemical cleaning is completed, the weld is cut off to remove the first cleaning liquid flow pipe 54 from the first connecting pipe 39, and the lid is welded to the other end opening of the first connecting pipe in a hermetic manner to close the other end opening.

A second connecting pipe 40 branching from the nose wall outlet connecting pipe 36 is provided on the nose wall outlet connecting pipe 36 upstream of the outlet connecting pipe opening/closing valve 38. The second connecting pipe 40 is closed when the boiler is in operation, and is connected to a second cleaning liquid flow pipe 55 described later during chemical cleaning of the nose section 7, and communicates the nose wall outlet connecting pipe 36 and the second cleaning liquid flow pipe 55. The second connecting pipe 40 is made of, for example, a metal pipe, like the first connecting pipe 39. In this case, one end of the second connecting pipe 40 is hermetically welded to the outer circumferential surface of the nose wall outlet connecting pipe 36, and the other end opening of the second connecting pipe 40 is closed by hermetically welding a lid body. The inside of the second connecting pipe 40 communicates with the inside of the nose wall outlet connecting pipe 36 through a hole formed in the nose wall outlet connecting pipe 36. During chemical cleaning, the other end opening of the second connecting pipe 40 is opened by cutting off the lid, and then the second cleaning liquid flow pipe 55 is connected to the second connecting pipe 40 by welding. After chemical cleaning is completed, the weld is cut off to remove the second cleaning liquid flow pipe 55 from the second connecting pipe 40, and the lid is welded to the other end opening of the second connecting pipe 40 in a hermetic manner to close the other end opening.

In addition, FIG. 4 shows an example in which one furnace spiral rear wall outlet header 31 and one nose wall inlet header 32 are connected by multiple (six in the illustrated example) nose wall inlet connection pipes 35, each nose wall inlet connection pipe 35 is provided with an inlet connection pipe opening/closing valve 37 and a first connection pipe 39, one nose wall outlet header 33 and two furnace auxiliary side wall inlet headers 34 are each connected by multiple (three each in the illustrated example) nose wall outlet connection pipes 36, each nose wall outlet connection pipe 36 is provided with an outlet connection pipe opening/closing valve 38 and a second connection pipe 40, but the number of furnace spiral rear wall outlet headers 31, nose wall inlet headers 32, nose wall inlet connection pipes 35, nose wall outlet headers 33, furnace auxiliary side wall inlet headers 34, and nose wall outlet connection pipes 36 is not limited to this and can be set arbitrarily.

When chemically cleaning the nose section 7, a cleaning liquid circulation pipe 51 is temporarily installed in the boiler. A cleaning chemical injection section 52 is connected to the cleaning liquid circulation pipe 51, and a cleaning liquid circulation pump 53 is provided in the middle of the cleaning liquid circulation pipe 51. The cleaning liquid containing the cleaning chemical injected from the cleaning chemical injection section 52 is sent by the cleaning liquid circulation pump 53. One end and the other end of the cleaning liquid circulation pipe 51 form a first cleaning liquid circulation pipe 54 connected to the first connection pipe 39 and a second cleaning liquid circulation pipe 55 connected to the second connection pipe 40. The flow direction of the cleaning liquid by the cleaning liquid circulation pump 53 may be set to either a first direction in which the cleaning liquid flows out from the first cleaning liquid circulation pipe 54 or a second direction in which the cleaning liquid flows out from the second cleaning liquid circulation pipe 55. In this embodiment, a case where the flow direction of the cleaning liquid is set to the first direction will be described. Note that a valve for opening and closing the pipe may be provided in the cleaning liquid circulation pipe 51, and a cleaning liquid tank for storing the cleaning liquid may be provided.

When chemically cleaning the nose section 7, the inlet connecting pipe on-off valve 37 and the outlet connecting pipe on-off valve 38 are closed, and then the first connecting pipe 39 is opened and the first cleaning liquid flow pipe 54 is connected to the first connecting pipe 39. The second connecting pipe 40 is also opened and the second cleaning liquid flow pipe 55 is connected to the second connecting pipe 40.

The cleaning liquid circulation pump is then driven to allow cleaning liquid to flow from the first cleaning liquid flow pipe 54 into the first connecting pipe 39. The cleaning liquid that has flowed into the first connecting pipe 39 flows through the nose wall inlet connecting pipe 35, the nose wall inlet header 32, the nose wall pipe group 26 (nose wall pipes 23), the nose wall outlet header 33, and the nose wall outlet connecting pipe 36, and flows out of the second connecting pipe 40 and returns to the second cleaning liquid flow pipe 55. The circulating supply of cleaning liquid causes the cleaning liquid to flow through each nose wall pipe 23 of the nose wall pipe group 26, and the nose wall pipes 23 are chemically cleaned.

After chemical cleaning is completed, the first cleaning liquid flow pipe 54 is removed from the first connecting pipe 39 and the first connecting pipe 39 is closed, the second cleaning liquid flow pipe 55 is removed from the second connecting pipe 40 and the second connecting pipe 40 is closed, and then the inlet connecting pipe opening/closing valve 37 and the outlet connecting pipe opening/closing valve 38 are opened.

According to this embodiment, during chemical cleaning of the nose section 7, the inlet connecting pipe opening/closing valve 37 and the outlet connecting pipe opening/closing valve 38 are closed, so that the flow range (cleaning area) of the cleaning liquid from the first cleaning liquid flow pipe 54 to the second cleaning liquid flow pipe 55 can be reliably blocked from the non-cleaning area upstream of the inlet connecting pipe opening/closing valve 37 (e.g., the first wall tube group 24 and the furnace spiral rear wall outlet header 31, etc.) and the non-cleaning area downstream of the outlet connecting pipe opening/closing valve 38 (e.g., the furnace auxiliary side wall inlet header 34 and the second wall tube group 25, etc.). Therefore, the non-cleaning area not including the nose wall tube group 26 is not affected by the cleaning liquid, and the nose wall tube group 26 can be chemically cleaned independently.

In addition, if the flow rate of the cleaning liquid were set to cover the entire water tubes 5 that make up the furnace wall, the flow rate would be slow and difficult to flow in the nose wall tube group 26, and the temperature of the cleaning liquid would also be likely to drop, making it difficult to fully remove scale and potentially resulting in the desired cleaning effect not being achieved. In contrast, in this embodiment, the nose wall tube group 26 can be chemically cleaned independently, so that chemical cleaning can be performed under optimal flow rate and liquid temperature conditions in the nose wall tube group 26, and the desired cleaning effect can be achieved.

The present invention is not limited to the above-described embodiments and modifications, which are merely examples, and various modifications can be made according to the design, etc., without departing from the technical concept of the present invention, even if they are not the above-described embodiments.

For example, in the above embodiment, an example was described in which the furnace spiral rear wall tube 21 constitutes the first wall tube group 24 and the furnace auxiliary side wall tube 22 constitutes the second wall tube group 25, but water tubes 5 other than these may also constitute the first wall tube group 24 and/or the second wall tube group 25.

In addition to the cleaning in the above embodiment (single cleaning of the nose wall tube group 26), chemical cleaning may be performed to clean the entire water tubes 5 that make up the furnace wall.

1: Furnace 2: Furnace auxiliary side wall 3: Burner 4: Gas flow path of furnace auxiliary side wall 5: Water tube 6: Fin 7: Nose 8: Spiral tube 9: Vertical tube 11: Furnace front wall 12: Furnace rear wall 13: Furnace side wall 14: Furnace ceiling wall 15: Furnace auxiliary side wall 16: Ceiling wall of furnace auxiliary side wall 17: Bottom wall of furnace auxiliary side wall 21: Furnace spiral rear wall tube 22: Furnace auxiliary side wall tube 23: Nose wall tube 24: First wall tube group 25: Second wall tube group 26: Nose wall tube group 31: Furnace spiral rear wall outlet header (first wall tube outlet header)
32: Nose wall inlet header 33: Nose wall outlet header 34: Furnace secondary side wall inlet header (second wall tube inlet header)
35: Nose wall inlet connection pipe 36: Nose wall outlet connection pipe 37: Inlet connection pipe on-off valve 38: Outlet connection pipe on-off valve 39: First connection pipe 40: Second connection pipe 41: Furnace auxiliary side wall outlet header 51: Cleaning liquid circulation pipe 52: Cleaning chemical injection section 53: Cleaning liquid circulation pump 54: First cleaning liquid circulation pipe 55: Second cleaning liquid circulation pipe

Claims (2)

A furnace wall structure for a boiler, the furnace wall comprising a first wall tube group, a second wall tube group, and a nose wall tube group, the first wall tube group, the second wall tube group, and the nose wall tube group each being composed of a plurality of water tubes, and the first wall tube group and the second wall tube group being in communication with each other via the nose wall tube group,
a first wall tube outlet header connected to a downstream end of each water tube of the first wall tube group;
a nose wall inlet header connected to an upstream end of each water tube of the nose wall tube group;
a nose wall outlet header connected to a downstream end of each water tube of the nose wall tube group;
a second wall tube inlet header connected to an upstream end of each water tube of the second wall tube group;
a nose wall inlet connecting pipe connecting the first wall pipe outlet header and the nose wall inlet header;
a nose wall outlet connecting pipe connecting the nose wall outlet header and the second wall pipe inlet header;
an inlet connection pipe opening/closing valve capable of opening and closing the nose wall inlet connection pipe;
an outlet connection pipe opening/closing valve capable of opening and closing the nose wall outlet connection pipe;
a first connecting pipe that branches off from the nose wall inlet connecting pipe downstream of the inlet connecting pipe on-off valve, that is closed during operation of the boiler, and that can be connected to a first cleaning liquid flow pipe during chemical cleaning;
a second connecting pipe which branches off from the nose wall outlet connecting pipe on the upstream side of the outlet connecting pipe on-off valve, which is closed during operation of the boiler, and to which a second cleaning liquid flow pipe can be connected during chemical cleaning,
a furnace wall structure for a boiler, characterized in that , during chemical cleaning, the first cleaning liquid circulation pipe is connected to the first connecting pipe, the second cleaning liquid circulation pipe is connected to the second connecting pipe, and with the inlet connecting pipe on-off valve and the outlet connecting pipe on-off valve closed, the cleaning liquid flows in from one of the first cleaning liquid circulation pipe and the second cleaning liquid circulation pipe and flows out from the other, thereby causing the cleaning liquid to flow through each water tube of the nose wall tube group. A method for chemical cleaning of a boiler, the method comprising the steps of: a furnace wall comprising a first wall tube group, a second wall tube group, and a nose wall tube group, the first wall tube group, the second wall tube group, and the nose wall tube group each being constituted by a plurality of water tubes, a first wall tube outlet header being connected to a downstream end of each water tube of the first wall tube group, a nose wall inlet header being connected to an upstream end of each water tube of the nose wall tube group, a nose wall outlet header being connected to a downstream end of each water tube of the nose wall tube group, and a second wall tube inlet header being connected to an upstream end of each water tube of the second wall tube group, the first wall tube outlet header and the nose wall inlet header being connected by a nose wall inlet connecting pipe, the nose wall outlet header and the second wall tube inlet header being connected by a nose wall outlet connecting pipe, and the first wall tube group and the second wall tube group being communicated with each other via the nose wall tube group,
an inlet connecting pipe opening/closing valve capable of opening and closing the nose wall inlet connecting pipe, and an outlet connecting pipe opening/closing valve capable of opening and closing the nose wall outlet connecting pipe,
a first connecting pipe which branches off from the nose wall inlet connecting pipe downstream of the inlet connecting pipe on-off valve, which is closed during operation of the boiler, and to which a first cleaning liquid flow pipe can be connected during chemical cleaning;
a second connecting pipe is provided which branches off from the nose wall outlet connecting pipe on the upstream side of the outlet connecting pipe on-off valve, which is closed during operation of the boiler, and to which a second cleaning liquid flow pipe can be connected during chemical cleaning;
The inlet connecting pipe on-off valve and the outlet connecting pipe on-off valve are closed,
The first cleaning liquid flow pipe is connected to the first connecting pipe;
The second cleaning liquid flow pipe is connected to the second connection pipe;
and causing the cleaning liquid to flow through each water tube of the nose wall tube group by causing the cleaning liquid to flow in from one of the first cleaning liquid circulation pipe and the second cleaning liquid circulation pipe and to flow out from the other of the first cleaning liquid circulation pipe and the second cleaning liquid circulation pipe while keeping the inlet communication pipe on-off valve and the outlet communication pipe on-off valve closed.

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