JP4309771B2 - Multi-pipe once-through boiler - Google Patents

Description

  The present invention relates to a boiler having a combustion chamber, in particular, two annular water cooling walls made up of a plurality of water pipes and fins arranged concentrically, and an annular combustion chamber between an inner water cooling wall and an outer water cooling wall. In particular, the present invention relates to a multi-tube once-through boiler that can reduce NOx, reduce CO, and improve the heat absorption rate to a water-cooled wall.

In general, in a multi-pipe once-through boiler equipped with a premixed diffusion combustion burner, a method of supplying combustion air in multiple stages, a method of exhaust gas recirculation that recirculates part of the exhaust gas to the burner, etc. It has been practiced to reduce NOx emissions. In particular, in the gas-fired diffusion combustion using gas as fuel, the concentration combustion method by diversifying the fuel injection nozzle is adopted to reduce NOx, and in the oil-fired diffusion combustion using oil as fuel. NOx reduction is achieved by atomizing spray of oil fuel.
In these diffusion combustion systems, the combustion air is pumped around the fuel ejected from the nozzle of the burner, both are forcibly mixed, and the fuel mixed with the combustion air is burned in the combustion chamber. It is necessary to secure a convection distance until the fuel ejected from the burner nozzle burns out, and a large combustion chamber is required. In addition, the shape of the combustion chamber is restricted by the shape of the flame, and the combustion air rectification and the flame stabilization mechanism are required. As a result, in a multi-tube type once-through boiler equipped with a premixed diffusion combustion burner, there is a problem that the boiler itself inevitably increases in size.

By the way, in the field of once-through boilers, downsizing is increasingly advanced, and recently, in the case of a small once-through boiler with an evaporation amount of 2 t / h class, the furnace load has reached 5000 kW / m ³ h. In addition to this, in the convection heat transfer section where the combustion gas passes through the water tube group, the flow velocity of the combustion gas reaches 50 m / sec or more. In consideration of these pressure losses, a blower that can supply higher-pressure air is required to reduce the flame length further. However, problems such as power, cost, and larger size of the blower are necessary. The mixed diffusion combustion burner cannot be used.

On the other hand, in the case of a multi-tube type once-through boiler equipped with a premixed surface combustion burner, the premixed surface combustion burner is a porous material in which a premixed gas obtained by premixing gas fuel and combustion air is a ceramic or the like. Is supplied to the premixed gas dividing plate formed by, etc., is uniformly diffused to the premixed gas dividing plate and burns on its surface, so that the flame is dispersed on the surface of the premixed gas dividing plate, A large number of minute divided flames are formed. As a result, the premixed surface combustion burner has advantages such as being able to shorten the flame compared to the premixed diffusion combustion burner and greatly reducing NOx emissions, and so on. This burner is suitable for boiler miniaturization.
Therefore, in recent years, premixed surface combustion burners have been mounted in once-through boilers in order to reduce the size (for example, see Patent Document 1 and Patent Document 2).

However, in a multi-tube once-through boiler equipped with a premixed surface combustion burner, the fuel is limited to gas fuel only, and the premixed gas is burned at a relatively low air ratio (excess air ratio). There is a problem that the surface of the premixed gas dividing plate is heated, and the amount of NOx emission increases rapidly.
Even if the premixed gas is supplied to the premixed gas dividing plate in a non-uniform manner, the combustion temperature is not stable, and a local high temperature is generated in the surface combustion region. There is a problem that NOx is generated and NOx cannot be reduced.
Further, since the premixed gas dividing plate is generally formed of a porous material such as ceramic, the premixed gas dividing plate may be distorted or cracked due to a temperature difference generated on the premixed gas dividing plate, or There was also a problem of causing clogging.
Japanese Patent Laid-Open No. 7-12301 JP 11-294702 A

  The present invention has been made in view of such problems, and its purpose is to reduce NOx and CO, and to increase the amount of heat absorption per unit area of a water-cooled wall or the like to increase the boiler itself. An object of the present invention is to provide a multitubular once-through boiler that can be made compact.

In order to achieve the above object, according to the first aspect of the present invention, two annular water cooling walls comprising a plurality of water pipes and fins are arranged concentrically so that an inner water cooling wall and an outer water cooling wall are arranged. An annular combustion chamber is formed between the upper and lower ends of each water pipe of both water-cooling walls, and is connected to the upper header and the lower header in communication with each other. The upper end is formed with a throat that opens to the upper end of the combustion chamber, and the gas passage is formed at the lower end of the inner water cooling wall. Gas fuel and combustion air or gas are introduced from the throat into the combustion chamber. A premixed gas, which is a mixture of fuel and combustion air, is jetted in the tangential direction along the combustion chamber wall surface and burned to form a cyclone flame along the combustion chamber wall surface, and the combustion gas is injected into the combustion chamber. flow through the combustion chamber towards the top to the bottom in while turning It is characterized in the that way.

According to a second aspect of the present invention, a spiral swirl promoting guide body from the upper end side to the lower end side of the combustion chamber is disposed in the annular combustion chamber, and the combustion chamber is moved by the swirl promoting guide body. It is characterized in that the swirling of the flowing combustion gas is promoted.

  According to a third aspect of the present invention, there is provided a gas passage for reducing pressure loss that guides a part of the combustion gas flowing while swirling in the combustion chamber to a part of the inner water cooling wall to the gas passage on the downstream side of the combustion chamber. This is characterized in that a part of the combustion gas in the combustion chamber is short-passed from the pressure loss reducing gas passage port to the gas passage.

The invention of claim 4 of the present invention is a heat transfer water pipe group comprising a plurality of heat transfer water pipes whose upper and lower ends are connected to the upper header and the lower header in a continuous manner in a space surrounded by an inner water cooling wall. And a gas passage communicating with the flue in the gap between the heat transfer water tube group and the inner water cooling wall and the gap between the heat transfer water tube group, and a combustion chamber at the lower end of the inner water cooling wall. It is characterized in that a plurality of gas passages are formed through which the combustion gas flowing downward in the gas flows uniformly into the gas passage.

According to a fifth aspect of the present invention, a plurality of nozzles that open to the upper end of the combustion chamber are formed at the upper end of the outer water cooling wall, and gas fuel and combustion air or gas are introduced into the combustion chamber from each nozzle. It is characterized in that a premixed gas obtained by mixing fuel and combustion air is jetted in the tangential direction along the combustion chamber wall surface and burned.

According to a sixth aspect of the present invention, at least one air supply port for the secondary combustion air that opens to the upper end portion side of the combustion chamber is formed at the downstream side of the firing port and at the upper end portion of the outer water cooling wall. Gas fuel and combustion air or premixed gas ejected from the spark outlet into the combustion chamber are burned under an air ratio of 1 or less to form a primary combustion zone in the downstream region of the spark outlet, The secondary combustion air is jetted in the tangential direction along the wall of the combustion chamber from the air supply port into the combustion chamber, and is agitated and mixed with the primary combustion gas generated in the primary combustion zone. It is characterized in that a secondary combustion zone is formed in the downstream region of the air supply port by burning under the conditions of 1 to 1.5.

  According to the seventh aspect of the present invention, at least the outer peripheral surface of each heat transfer water tube forming the heat transfer water tube group has a plurality of fins alternately with respect to the opposite heat transfer water tubes and perpendicular to the longitudinal direction of the heat transfer water tubes. And the combustion gas flowing into the gas passage from the gas passage port flows in a zigzag shape from one end of the gas passage to the other end.

  In the invention according to claim 8 of the present invention, a plurality of fins are formed stepwise with respect to the adjacent heat transfer water pipe and in the longitudinal direction of the heat transfer water pipe at least on the outer peripheral surface of each heat transfer water pipe forming the heat transfer water pipe group. It is characterized in that it is mounted vertically and the combustion gas flowing into the gas passage from the gas passage port flows while turning from one end side to the other end side of the gas passage.

  According to the ninth aspect of the present invention, a plurality of fins are attached radially and parallel to the longitudinal direction of the heat transfer water pipe at least on the outer peripheral surface of each heat transfer water pipe forming the heat transfer water pipe group, and gas is supplied from the gas passage port. The combustion gas that has flowed into the passage is characterized by flowing from one end of the gas passage to the other end while contacting the fins.

According to the first aspect of the present invention, an annular water cooling wall is disposed concentrically to form an annular combustion chamber between an inner water cooling wall and an outer water cooling wall. A water-cooling wall is formed with a spark opening that opens into the combustion chamber, and a premixed gas that is a mixture of gas fuel and combustion air or gas fuel and combustion air is mixed along the combustion chamber wall surface into the combustion chamber. It is jetted in the tangential direction and burned to form a cyclone flame along the wall of the combustion chamber in the combustion chamber, and the combustion gas is allowed to flow while swirling in the combustion chamber. The cyclone flame has a large surface area, and the cyclone flame extends so as to give up the inner surface of the outer water-cooled wall by centrifugal force. Therefore, the radiation characteristics are improved and the cyclone flame is cooled, and the flame temperature is lowered to a relatively low temperature. Kept. As a result, in the multitubular once-through boiler according to claim 1 of the present invention, generation of NOx in the combustion chamber is suppressed. However, since a part of the combustion gas circulates in the annular combustion chamber and returns to the outlet, the exhaust gas recirculation action by the combustion gas is obtained, and the generation of NOx is further suppressed.
The multi-tube once-through boiler according to claim 1 of the present invention applies heat to both the inner water cooling wall and the outer water cooling wall by radiant heat transfer by the cyclone flame, and the cyclone flame is subjected to centrifugal force by the outer water cooling wall. Heat is also given to the outer water-cooled wall by contact heat transfer by giving up the inner surface, so the heat absorption rate to the water-cooled wall is greatly improved. As a result, the boiler itself can be reduced in size.
Furthermore, the multi-tube once-through boiler according to claim 1 of the present invention is a long flame in which the cyclone flame swirls in the combustion chamber, so that the convection distance until the gas fuel ejected from the firing port burns out in the combustion chamber can be increased. , Generation of CO can be suppressed.
In addition, in the multitubular once-through boiler according to the first aspect of the present invention, since the combustion gas generated in the combustion chamber flows while swirling in the combustion chamber, the contact time between the combustion gas and the water cooling wall becomes longer, and the Heat can be reliably and satisfactorily recovered.

The multitubular once-through boiler according to claims 2 to 9 of the present invention can further exhibit the following effects in addition to the above effects.
That is, in the multi-tube type once-through boiler according to the second aspect of the present invention, a spiral turning promotion guide body is arranged in the combustion chamber, and the turning promotion guide body promotes the turning of the combustion gas flowing in the combustion chamber. Since the combustion gas is swirled in the combustion chamber by a predetermined number of turns, heat transfer to the inner water cooling wall and the outer water cooling wall is promoted.
According to a third aspect of the present invention, there is provided a multi-tube once-through boiler having a gas passage for reducing pressure loss that leads a part of the combustion gas in the combustion chamber to a gas passage on the downstream side of the combustion chamber in a part of the inner water cooling wall. Since a part of the combustion gas in the combustion chamber is short-passed from the pressure loss mitigation gas passage to the gas passage, the pressure loss that increases in proportion to the number of revolutions of the combustion gas in the combustion chamber is increased. It can be mitigated, and an increase in the size of the blower can be prevented.
According to a fourth aspect of the present invention, a multitubular once-through boiler is provided with a heat transfer water tube group including a plurality of heat transfer water tubes in a space surrounded by an inner water cooling wall, and the heat transfer water tube group and the inner water cooling Since the gas passage through which the combustion gas that has passed through the combustion chamber flows is formed in the gap between the wall and the heat transfer water tube group, the heat can be more reliably and satisfactorily recovered from the combustion gas.
The multi-tube once-through boiler according to claim 5 of the present invention forms a plurality of nozzles in the outer water cooling wall, and mixes gas fuel and combustion air or gas fuel and combustion air from each nozzle into the combustion chamber. The premixed gas is jetted in the tangential direction along the combustion chamber wall surface and burned, so that the swirl flow strength of the combustion gas can be promoted and switching during turndown combustion is good Can be done.
According to the sixth aspect of the present invention, the multi-tube once-through boiler has a water outlet and an air supply port formed on the outer water cooling wall, respectively, and gas fuel and combustion air or premixed gas ejected from the fire outlet into the combustion chamber. A primary combustion zone that forms a reduction combustion region with a flame temperature of 1500 ° C. or less is formed in the downstream region of the firing port under the condition of an air ratio of 1 or less, and for secondary combustion from the air supply port to the combustion chamber While agitating and mixing with the primary combustion gas generated in the primary combustion zone by jetting air, the primary combustion gas is burned under the conditions of a total air ratio of 1.1 to 1.5 to the downstream region of the air outlet Since the secondary combustion zone is formed, the generation of thermal NOx can be suppressed, and the primary combustion gas is completely burned in the secondary combustion zone, thereby suppressing the generation of CO.
In the multi-tube once-through boiler according to claims 7 to 9 of the present invention, a large number of fins are attached to a plurality of heat transfer water tubes forming the heat transfer water tube group, so that the heat transfer area is increased and the combustion gas is increased. Heat can be recovered well. In particular, when fins are attached to multiple heat transfer water pipes so that the combustion gas flows in a zigzag or swirling manner in the gas passage, the contact time between the heat transfer water pipe and the combustion gas becomes longer, and combustion occurs. Heat can be recovered from gas more reliably and satisfactorily.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
1 and 2 show a multitubular once-through boiler according to a first embodiment of the present invention. The multitubular once-through boiler has an inner water-cooling shape having a circular cross-sectional shape composed of a plurality of water tubes 1a and fins 1b. An outer water cooling wall 2 which is concentrically arranged at the outer peripheral position of the wall 1 and the inner water cooling wall 1 and has a circular cross-sectional shape composed of a plurality of water pipes 2a and fins 2b, the inner water cooling wall 1 and the outer water cooling wall 1 An annular combustion chamber 3 formed between the water cooling wall 2, a gas fuel supply pipe 5 and a combustion air supply pipe 6 connected to a nozzle 4 formed in the outer water cooling wall 2, and both water cooling walls 1 , 2 are arranged in a space surrounded by the upper and lower headers 8 and 8 connected to the upper and lower ends of the water pipes 1a and 2a, respectively, and the water cooling wall 1 on the inner side. Are a plurality of heat transfer water pipes 9a connected to the upper header 7 and the lower header 8 in a continuous manner. A heat transfer water tube group 9, a gap between the heat transfer water tube group 9 and the inner water cooling wall 1, a gas passage 10 for the combustion gas G formed in the gap between the heat transfer water tube group 9, and the like. F and combustion air A are jetted in the tangential direction along the wall surface of the combustion chamber 3 into the combustion chamber 3 from the spout 4 and diffusely burned to form a cyclone flame C along the wall surface of the combustion chamber 3 in the combustion chamber 3. At the same time, the combustion gas G is swirled in the combustion chamber 3 from one end side to the other end side, and then flows into the gas passage 10.

  In this multitubular once-through boiler, heat absorption to the boiler water flowing in the water pipe 1 a of the inner water cooling wall 1 flows through the radiant heat transfer by the cyclone flame C in the combustion chamber 3 and the combustion chamber 3. The heat absorption by the boiler water flowing in the water pipe 2a of the outer water cooling wall 2 is performed by the contact heat transfer (convection heat transfer) by the combustion gas G, and the radiation heat transfer by the cyclone flame C in the combustion chamber 3 And the contact heat transfer caused by the cyclone flame C giving up the inner surface of the outer water cooling wall 2 by centrifugal force and the contact heat transfer caused by the combustion gas G flowing in the combustion chamber 3. Heat absorption into the boiler water flowing in the heat transfer water pipe 9 a is performed only by contact heat transfer by the combustion gas G flowing in the gas passage 10.

Specifically, the inner water cooling wall 1 is formed by connecting a plurality of water pipes 1a in a ring and connecting adjacent water pipes 1a with strip-like fins 1b extending in the vertical direction. The cross-sectional shape is an airtight structure with a circular shape. A gas passage 10 through which the combustion gas G passes is formed in the space surrounded by the inner water cooling wall 1 by disposing the heat transfer water tube group 9 in the space.
Further, a plurality of gas passage ports 11 through which the combustion gas G in the combustion chamber 3 flows uniformly into the gas passage 10 are formed at the lower end portion of the inner water cooling wall 1 by cutting out the lower end portion of the fin 1b. In addition, a combustion gas outlet 13 that guides the combustion gas G that has passed through the gas passage 10 to the flue 12 is formed at the upper end of the inner water cooling wall 1.

The outer water cooling wall 2 is formed by connecting a plurality of water pipes 2a in a ring shape in parallel with the inner water cooling wall 1 and connecting adjacent water pipes 2a with strip-like fins 2b extending in the vertical direction. The cross-sectional shape is an airtight structure with a circular shape. The outer water cooling wall 2 is arranged concentrically with the inner water cooling wall 1 at the outer peripheral position of the inner water cooling wall 1 so as to form an annular combustion chamber 3 with the inner water cooling wall 1. It has become.
A gas outlet 4 is formed at the upper end of the outer water cooling wall 2 so as to open to one end (upper end) of the annular combustion chamber 3. Gas fuel F and combustion air A are supplied from the pipe 5 and the combustion air supply pipe 6, and these can be ejected into the combustion chamber 3 from the nozzle 4. At this time, the direction of the burning port 4, the gas fuel supply pipe 5 and the combustion air supply pipe 6 is such that the gas fuel F and the combustion air A are tangent along the combustion chamber 3 wall surface from the burning port 4 into the combustion chamber 3. It is set so that it can be ejected in the direction.
Further, a combustion gas outlet 14 communicating with the flue 12 and a combustion gas outlet 13 formed in the inner water cooling wall 1 is formed at the upper end of the outer water cooling wall 2, and the combustion gas in the gas passage 10 is formed. G flows from the combustion gas outlets 13 and 14 formed in the water cooling walls 1 and 2 to the flue 12.
In addition, both combustion gas outlets are provided between the combustion gas outlet 13 formed in the inner water cooling wall 1 and the combustion gas outlet 14 formed in the outer water cooling wall 2 so that the combustion gas G does not flow into the combustion chamber 3. A refractory 15 is provided to partition the combustion chambers 13 and 14 and the combustion chamber 3.

  The upper header 7 and the lower header 8 are both formed in a hollow structure, and are connected to upper and lower ends of the water pipes 1a and 2a of the inner water cooling wall 1 and the outer water cooling wall 2, respectively. The upper header 7 is connected to a steam pipe provided with a steam separator, etc., and the lower header 8 is connected to a water supply pipe provided with a water supply pump or the like (both not shown). A refractory 15 is lined on the lower surface side of the upper header 7 and the upper surface side of the lower header 8, and is protected from the high-temperature combustion gas G.

  The heat transfer water tube group 9 is disposed in a space surrounded by the inner water cooling wall 1, and a plurality of heat transfer pipes whose upper and lower ends are connected to the upper header 7 and the lower header 8 in communication with each other. It consists of a water tube 9a. The plurality of heat transfer water tubes 9 a forming the heat transfer water tube group 9 are arranged at a constant pitch in a space surrounded by the inner water cooling wall 1. Accordingly, a gas passage 10 communicating with the combustion chamber 3 and the flue 12 is formed in the gap between the heat transfer water tube group 9 and the inner water cooling wall 1 and the gap between the heat transfer water tube group 9.

  The multi-tube once-through boiler is provided with a pilot burner (not shown). The pilot burner is provided so that the pilot flame faces the firing port 4, and ignites the combustion gas G and the combustion air A ejected from the firing port 4 into the combustion chamber 3.

  According to the multi-tube type once-through boiler configured as described above, the gas fuel F and the combustion air A supplied to the firing port 4 through the gas fuel supply tube 5 and the combustion air supply tube 6 are supplied to the firing port 4. From the inside of the combustion chamber 3, it is jetted in the tangential direction along the wall surface of the combustion chamber 3 to be forcibly mixed, and ignited by a pilot burner to perform diffusion combustion. That is, the gas fuel F and the combustion air A are jetted into the combustion chamber 3 in the tangential direction along the combustion chamber 3 wall surface from the firing port 4, so that the cyclone along the combustion chamber 3 wall surface is formed in the combustion chamber 3. Flame C is formed. At this time, the combustion gas G and the combustion air A ejected from the firing port 4 have the combustion chamber 3 wall surface (the inner water cooling wall 1 outer surface and the outer water cooling wall 2 inner surface) as water pipes 1a, 2a and fins 1b, 2b. Therefore, mixing is promoted by the vortex generated on the downstream side of the water pipes 1 and 2.

The cyclone flame C has a large surface area, and the cyclone flame C extends so as to give up the inner surface of the outer water-cooled wall 2 due to centrifugal force. Therefore, the cyclone flame C is cooled with improved radiation characteristics, and the flame temperature is relatively low. To be kept. As a result, the generation of NOx in the combustion chamber 3 is suppressed. However, since a part of the combustion gas G circulates in the annular combustion chamber 3 and returns to the firing port 4, the generation of NOx is further suppressed by the exhaust gas recirculation action by the combustion gas G.
The cyclone flame C releases heat to the outer water cooling wall 2 by contact heat transfer caused by the flame giving up the inner surface of the outer water cooling wall 2 by centrifugal force in addition to the radiant heat transfer. That is, heat absorption to the boiler water flowing in the water pipe 2a of the outer water cooling wall 2 is performed by contact heat transfer due to contact with the cyclone flame C in addition to radiation heat transfer by the cyclone flame C. Heat absorption to the wall 2 is promoted. However, the cyclone flame C releases heat to the inner water cooling wall 1 by radiant heat transfer, and also gives heat to the boiler water flowing in the water pipe 1a of the inner water cooling wall 1.
Furthermore, the cyclone flame C is a long flame descending while turning in the combustion chamber 3, and the convection distance until the gas fuel F ejected from the firing port 4 burns out in the combustion chamber 3 is earned. Occurrence can be suppressed.

Then, the combustion gas G generated by diffusion combustion flows from the upper side to the lower side while turning in the combustion chamber 3, and while descending in the combustion chamber 3, the inner water cooling wall 1 and the outer water cooling are caused by contact heat transfer. While heating the wall 2, the gas uniformly flows into the gas passage 10 from the gas passage port 11 formed in the inner water-cooled wall 1.
The combustion gas G that has flowed into the gas passage 10 flows in the gas passage 10 from the lower side to the upper side while contacting the heat transfer water tube group 9 and the inner water cooling wall 1, and contacts the gas passage 10 while rising in the gas passage 10. Heat is applied to the plurality of heat transfer water tubes 9a forming the heat transfer water tube group 9 and the inner water cooling wall 1 by heat transfer, and then discharged from the flue 12 through the combustion gas outlets 13 and 14 to the outside of the boiler.

  3 and 4 show a multi-pipe once-through boiler according to a second embodiment of the present invention. The multi-pipe once-through boiler is a multi-pipe once-through boiler having the above-described structure (shown in FIGS. 1 and 2). And a premixed gas supply for supplying a premixed gas F ′ obtained by mixing the gas fuel F and the combustion air A to the spout 4 formed at the upper end of the outer water cooling wall 2. The pipe 16 is connected, and the premixed gas F ′ is ejected from the nozzle 4 into the combustion chamber 3 along the wall surface of the combustion chamber 3 in the tangential direction for premix combustion, and into the combustion chamber 3 wall surface. A cyclone flame C is formed along the same, and the combustion gas G is swung from the upper side to the lower side while swirling the combustion gas G, and then flows into the gas passage 10.

The multitubular once-through boiler has the same structure as the multitubular once-through boiler shown in FIGS. 1 and 2 except that the premixed gas supply pipe 16 is connected to the nozzle 4. And the same reference number is attached | subjected to the same site | part and member as the multitubular once-through boiler of FIG. 2, and the detailed description is abbreviate | omitted.
In addition, the premixed gas F ′ supplied to the firing port 4 is a premixed gas F ′ with high mixing accuracy without mixing unevenness, in which the gas fuel F and the combustion air A are sufficiently mixed. Of course.
This multitubular once-through boiler can achieve the same effects as the multitubular once-through boiler shown in FIGS.

FIG. 5 shows a multi-pipe once-through boiler according to a third embodiment of the present invention. The multi-pipe once-through boiler is opened at one end (upper end) of the combustion chamber 3 in a part of the outer water-cooled wall 2. A plurality of firing ports 4 are formed, and gas fuel F and combustion air A are ejected from each firing port 4 into the combustion chamber 3 along the wall surface of the combustion chamber 3 in the tangential direction for combustion. is there.
That is, this multi-tube once-through boiler is formed with two nozzles 4 at the upper end of the outer water cooling wall 2 in a state of being opposed to each other by 180 ° in the circumferential direction of the combustion chamber 3, and 4 are connected to the gas fuel supply pipe 5 and the combustion air supply pipe 6 respectively, and the gas fuel F and the combustion air A are connected to the combustion chamber 3 from the two nozzles 4 in the same circumferential direction and on the wall surface of the combustion chamber 3. After tangentially jetting and diffusing and burning, a cyclone flame C is formed in the combustion chamber 3 along the wall surface of the combustion chamber 3, and the combustion gas G is swirled while flowing in the combustion chamber 3 from above to below. The gas is allowed to flow into the gas passage 10.

In this multi-pipe once-through boiler, the two water outlets 4 are formed in the outer water cooling wall 2 so as to face each other, and the gas combustion supply pipe 5 and the combustion air supply pipe 6 are connected to each of the fire outlets 4 respectively. Other than that, it is configured in the same structure as the multi-tube once-through boiler shown in FIGS. 1 and 2, and the same reference numerals are assigned to the same parts and members as the multi-tube once-through boiler of FIGS. Detailed description thereof is omitted.
This multitubular once-through boiler can achieve the same effects as the multitubular once-through boiler shown in FIGS. However, since this multi-pipe once-through boiler is provided with the two spouts 4, the strength of the swirling flow of the combustion gas G can be promoted and the switching at the time of the turn-down combustion can be performed satisfactorily.

  FIG. 6 shows a multi-pipe once-through boiler according to a fourth embodiment of the present invention. The multi-pipe once-through boiler has two holes 4 at the upper end of the outer water cooling wall 2 in the circumferential direction of the combustion chamber 3. They are formed in a state of being opposed to each other at an interval of 180 °, and the premixed gas supply pipes 16 are respectively connected to the respective spouts 4 so that the premixed gas F ′ is the same in the combustion chamber 3 from the two spouts 4. And in the tangential direction of the wall surface of the combustion chamber 3 and premixed combustion is performed to form a cyclone flame C along the wall surface of the combustion chamber 3 in the combustion chamber 3 and the combustion chamber 3 while swirling the combustion gas G The room flows from the upper side to the lower side and then flows into the gas passage 10.

The multitubular once-through boiler is the same as that shown in FIGS. 1 and 2 except that the two water inlets 4 are formed on the outer water cooling wall 2 so as to face each other, and the premixed gas supply pipes 16 are connected to the water outlets 4 respectively. The multi-tube once-through boiler shown in FIG. 2 has the same structure, and the same parts and members as those of the multi-tube once-through boiler shown in FIGS. 1 and 2 are denoted by the same reference numerals, and detailed description thereof is omitted. To do.
The multitubular once-through boiler can achieve the same effects as the multitubular once-through boiler shown in FIG.

FIG. 7 shows a multi-pipe once-through boiler according to a fifth embodiment of the present invention. The multi-pipe once-through boiler is located on the downstream side of the firing port 4 through which the combustion gas G and the combustion air A are jetted and outside. An air supply port 17 for the secondary combustion air A ′ that opens to one end (upper end) of the combustion chamber 3 is formed in a part of the water cooling wall 2 of the combustion chamber 3. And combustion air A are jetted to cause primary combustion in the downstream region of the firing port 4, and secondary combustion air A ′ is jetted from the air supply port 17 into the combustion chamber 3 to downstream of the firing port 4. The primary combustion gas generated in the side region is stirred and mixed, and the primary combustion gas is completely burned in the downstream region of the air supply port 17.
In other words, this multi-tube once-through boiler is formed by forming the firing port 4 and the air supply port 17 at the upper end of the outer water cooling wall 2 in a state of being opposed to each other by 180 ° in the circumferential direction of the combustion chamber 3. The gas fuel supply pipe 5 and the combustion air supply pipe 6 are connected to the port 4, and the secondary combustion air supply pipe 6 ′ is connected to the air supply port 17. Is blown into the combustion chamber 3 along the wall of the combustion chamber 3 in the tangential direction and diffused and burned under the condition of an air ratio (excess air ratio) of 1 or less, Combustion zone Z1 (reduction combustion region) is formed, and secondary combustion air A ′ is ejected from the air supply port 17 into the combustion chamber 3 along the wall surface of the combustion chamber 3 in the tangential direction thereof. Is mixed with the primary combustion gas generated in step 1, and the primary combustion gas is mixed with the total air ratio (excess air). ) Is burned downstream region of the air injection port 17 under the conditions of 1.1 to 1.5 is obtained so as to form a secondary combustion zone Z2 (complete combustion region).

In this multitubular once-through boiler, an air supply port 17 is formed on the outer water cooling wall 2 so as to face the firing port 4, and a secondary combustion air supply tube 6 'is connected to the air supply port 17, respectively. Other than that, it is configured in the same structure as the multi-tube once-through boiler shown in FIGS. 1 and 2, and the same reference numerals are assigned to the same parts and members as the multi-tube once-through boiler of FIGS. Detailed description thereof is omitted.
This multitubular once-through boiler can achieve the same effects as the multitubular once-through boiler shown in FIGS. However, this multi-tube once-through boiler combusts the gas fuel F and the combustion air A ejected from the firing port 4 under the condition that the air ratio is 1 or less, and the flame temperature is 1500 ° C. in the downstream region of the firing port 4. Since the following primary combustion zone Z1 (reduction combustion region) is formed, generation of thermal NOx can be suppressed, and the primary combustion gas generated in the primary combustion zone Z1 is ejected from the air supply port 17. This is agitated and mixed with the secondary combustion air A ′, and this is subjected to secondary combustion under the conditions of a total air ratio of 1.1 to 1.5, and a secondary combustion zone Z2 (complete combustion region) in the downstream region of the air supply port 17 Therefore, the primary combustion gas is completely burned in the secondary combustion zone Z2, and the generation of CO is suppressed.

  8 and 9 show a multi-pipe once-through boiler according to a sixth embodiment of the present invention, and the multi-pipe once-through boiler faces the gas passage 10 of the water pipe 1a that forms the inner water-cooled wall 1. And a plurality of substantially arc-shaped fins 18 and a plurality of triangular fins 18 on the outer peripheral surface of each heat transfer water tube 9a forming the heat transfer water tube group 9 alternately with respect to the heat transfer water tubes 9a facing each other, and The heat transfer water pipe 9a is attached vertically to the longitudinal direction of the heat transfer water pipe 9a so that the combustion gas G flowing into the gas passage 10 from the gas passage port 11 flows in a zigzag manner in the gas passage 10 from below to above.

This multitubular once-through boiler is a multitubular type shown in FIGS. 1 and 2 except that fins 18 are attached to the water pipe 1a of the inner water cooling wall 1 and the heat transfer water pipes 9a of the heat transfer water pipe group 9. The structure is the same as that of the once-through boiler, and the same parts and members as those of the multi-tube once-through boiler of FIGS. 1 and 2 are denoted by the same reference numerals, and detailed description thereof is omitted.
This multitubular once-through boiler can achieve the same effects as the multitubular once-through boiler shown in FIGS. However, in this multi-tube once-through boiler, the heat transfer area is widened by the fins 18, and the combustion gas G flows in a zigzag manner in the gas passage 10 so that the contact time of the heat transfer water pipe 9a and the like becomes long. The heat can be reliably and satisfactorily recovered from the combustion gas G.

  10 and 11 show a multi-pipe once-through boiler according to a seventh embodiment of the present invention, and the multi-pipe once-through boiler faces the gas passage 10 of the water pipe 1a forming the inner water-cooled wall 1. On the outer peripheral surface of each heat transfer water tube 9a forming the heat transfer water tube group 9, a plurality of substantially arc-shaped fins 18 and a plurality of triangular fins 18 are stepped with respect to the adjacent heat transfer water tubes 9a. And it attaches perpendicularly | vertically to the longitudinal direction of the heat-transfer water pipe | tube 9a, and the combustion gas G which flowed in in the gas passage 10 from the gas passage port 11 flows through the gas passage 10 turning from upper to lower.

This multitubular once-through boiler is the same as that shown in FIGS. 1 and 2 except that fins 18 are attached to the water pipe 1a of the inner water cooling wall 1 and the heat transfer water pipe 9a of the heat transfer water pipe group 9. The same structure as a boiler is comprised, the same site | part and member as the multitubular once-through boiler of FIG.1 and FIG.2 are attached | subjected, and the detailed description is abbreviate | omitted.
This multitubular once-through boiler can achieve the same effects as the multitubular once-through boiler shown in FIGS.

  12 and 13 show a multitubular once-through boiler according to an eighth embodiment of the present invention, and the multitubular once-through boiler faces the gas passage 10 of the water pipe 1a that forms the inner water-cooled wall 1. And strip-shaped fins 18 are attached radially and parallel to the longitudinal direction of the heat transfer water pipe 9a to the outer peripheral surface of each heat transfer water pipe 9a forming the heat transfer water pipe group 9, and from the gas passage port 11 to the gas passage The combustion gas G that has flowed into the gas passage 10 flows in the gas passage 10 from below to above while contacting the fins 18.

This multitubular once-through boiler is the same as that shown in FIGS. 1 and 2 except that fins 18 are attached to the water pipe 1a of the inner water cooling wall 1 and the heat transfer water pipe 9a of the heat transfer water pipe group 9. The same structure as a boiler is comprised, the same site | part and member as the multitubular once-through boiler of FIG.1 and FIG.2 are attached | subjected, and the detailed description is abbreviate | omitted.
This multitubular once-through boiler can achieve the same effects as the multitubular once-through boiler shown in FIGS.

  FIGS. 14 to 17 show multitubular once-through boilers according to the ninth and tenth embodiments of the present invention. The multitubular once-through boiler swirls the combustion gas G in the combustion chamber 3 by a predetermined number of turns. In order to promote the swirling of the combustion gas G and reduce the pressure loss that increases in proportion to the swirling number of the combustion gas G in the combustion chamber 3, the combustion chamber 3 is provided in the annular combustion chamber 3. 3 is provided with a spiral turning promotion guide body 19 from one end side to the other end side, and the turning promotion guide body 19 promotes the turning of the combustion gas G flowing in the combustion chamber 3. A gas passage 20 for reducing pressure loss is formed in a part of the inner water cooling wall 1 to guide part of the combustion gas G flowing while swirling in the combustion chamber 3 to the gas passage 10 on the downstream side of the combustion chamber 3. , An appropriate amount of the combustion gas G in the combustion chamber 3 is transferred to the pressure loss reducing gas passage 2. From the gas passage 10 is short-pass, is obtained so as to relieve the increasing pressure loss in proportion to the number of turns of the combustion gas G in the combustion chamber 3.

That is, as shown in FIGS. 14 and 15, the multitubular once-through boiler according to the ninth embodiment of the present invention has a heat-resistant metal material or ceramic material on the outer surface of the inner water-cooling wall 1 and the inner surface of the outer water-cooling wall 2. A spiral promoting guide body 19 made of a strip-like fin formed by, for example, is attached spirally from the upper end side to the lower end side of the combustion chamber 3, and on the fin 1 b of the inner water cooling wall 1, A plurality of pressure loss mitigating gas passages 20 through which a part of the combustion gas G in the combustion chamber 3 flows into the gas passage 10 in a short circuit is formed at predetermined intervals.
The turning promotion guide body 19 is provided with each water cooling wall 1, 2 due to the thermal stress due to heat absorption from the high-temperature combustion gas G and the concentration of the thermal load of the mounting portion of the turning promotion guide body 19 on the water cooling wall 1, 2. The water pipes 1a and 2a are formed in a shape that does not cause breakage.
Further, the position where the pressure loss mitigating gas passage port 20 is provided is such that when the combustion gas G passing through the pressure loss mitigating gas passage port 20 passes through the combustion chamber 3, the water cooling walls 1 and 2 are deprived of heat. It is desirable to provide the combustion gas G at a position where the temperature of the combustion gas G becomes equal to the temperature of the combustion gas G flowing into the gas passage 10 from the gas passage port 11 provided at the lower end of the combustion chamber 3.

This multitubular once-through boiler is the same as that shown in FIG. 1 except that the water cooling walls 1 and 2 are provided with the turning promotion guide body 19 and the inner water cooling wall 1 is formed with a pressure loss reducing gas passage 20. 2 and the same structure as the multi-tube once-through boiler shown in FIG. 2, and the same reference numerals are attached to the same parts and members as those of the multi-tube once-through boiler shown in FIGS. Omitted.
This multitubular once-through boiler can achieve the same effects as the multitubular once-through boiler shown in FIGS. However, this multitubular once-through boiler is provided with a spiral turning promoting guide body 19 in the combustion chamber 3 to promote the turning of the combustion gas G flowing in the combustion chamber 3 so that the combustion gas G is burned. Since the inside of the chamber 3 is swirled by a predetermined number of turns, heat transfer to the inner water cooling wall 1 and the outer water cooling wall 2 is further promoted. Further, this multitubular once-through boiler is formed with a pressure loss reducing gas passage 20 for short-passing an appropriate amount of combustion gas G in the combustion chamber 3 to the gas passage 10 in a part of the inner water cooling wall 1. Therefore, the pressure loss that increases in proportion to the number of revolutions of the combustion gas G in the combustion chamber 3 can be relaxed, and an increase in the size of the blower can be prevented.

On the other hand, as shown in FIGS. 16 and 17, the multi-tube once-through boiler according to the tenth embodiment of the present invention is provided in the combustion chamber 3 with a water pipe 19a (or water supply pipe) and an outer peripheral surface of the water pipe 19a in the longitudinal direction. A swirl promoting guide body 19 composed of a strip-like fin 19b attached along the spiral is arranged spirally from the upper end side to the lower end side of the combustion chamber 3, and the water tube of the swirl promoting guide body 19 is arranged. The upper and lower end portions of 19a are connected to the upper header 7 and the lower header 8 in communication with each other, and a part of the combustion gas G in the combustion chamber 3 is introduced into the gas passage 10 to the fin 1b of the inner water cooling wall 1. A plurality of pressure loss mitigating gas passages 20 to be introduced in a short circuit are formed at predetermined intervals.
Of course, the fin 19b of the turning promoting guide body 19 is formed of a heat-resistant metal material, a ceramic material, or the like.

This multitubular once-through boiler has a swirl promoting guide body 19 including a water pipe 19a and a fin 19b disposed in the combustion chamber 3, and a gas passage 20 for reducing pressure loss is formed in the inner water cooling wall 1. Except for this, it has the same structure as the multi-tube once-through boiler shown in FIGS. 1 and 2, and the same parts and members as those of the multi-tube once-through boiler shown in FIGS. Detailed description thereof will be omitted.
This multitubular once-through boiler can achieve the same effects as the multitubular once-through boiler shown in FIGS. 14 and 15.

  The multi-tube once-through boiler according to each of the above embodiments has the structure of a multi-tube once-through boiler, but other structures can be used as long as the combustion chamber 3 is a water-cooled wall. It may be a boiler to be presented. For example, the present invention may have a structure such as a natural circulation boiler or a forced circulation boiler.

  In the multitubular once-through boiler (shown in FIG. 7) according to the fifth embodiment, the gas fuel supply pipe 5 and the combustion air supply pipe 6 are connected to the firing port 4, and the gas is fed from the firing port 4. After fuel F and combustion air A are jetted into the combustion chamber 3 for primary combustion, secondary combustion air A ′ is jetted from the air supply port 17 into the combustion chamber 3 to secondary combustion the primary combustion gas. However, in the multi-tube recirculation boiler according to another embodiment, the premixed gas supply pipe 16 for supplying the premixed gas F ′ to the nozzle 4 is connected and premixed from the nozzle 4. After the gas F ′ is jetted into the combustion chamber 3 for primary combustion, the secondary combustion air A ′ is jetted from the air supply port 17 into the combustion chamber 3 so that the primary combustion gas is secondary burned. Also good.

  The multitubular once-through boiler according to the fifth embodiment (shown in FIG. 7) has a two-stage combustion structure in which only one air supply port 17 is formed in the downstream region of the firing port 4. In the multi-tube recirculation boiler according to another embodiment, a plurality of air supply ports 17 are formed in the downstream region of the firing port 4, and the combustion air A is blown into multiple stages to burn. Also good.

  In the multi-pipe once-through boilers according to the sixth, seventh, eighth, ninth and tenth embodiments (shown in FIGS. 8, 10, 12, 14 and 16) Only one port 4 is formed, and the gas fuel supply pipe 5 and the combustion air supply pipe 6 are connected to the firing port 4. However, in the multitubular reflux boiler according to another embodiment, Instead of the gas fuel supply pipe 5 and the combustion air supply pipe 6, the premixed gas supply pipe 16 may be connected to the gas outlet 4, or a plurality of gas outlets 4 may be formed. Both air supply ports 17 may be formed.

  In the multi-pipe once-through boiler according to the sixth, seventh and eighth embodiments (shown in FIGS. 8, 10 and 12), the heat transfer water pipe 9a and the like have a substantially arc-shaped fin 18, The triangular fins 18 and the strip-shaped fins 18 are attached in an appropriate arrangement, but the shape, attachment position, attachment method, etc. of the fins 18 are not limited as long as the heat exchange rate can be improved. May be.

  In the multi-pipe once-through boiler according to the ninth embodiment (shown in FIGS. 14 and 15), both the inner water-cooling wall 1 and the outer water-cooling wall 2 have fin-like turning promoting guide bodies. However, in the multi-pipe once-through boiler according to another embodiment, a fin-shaped swirl promoting guide body 19 is provided on either the inner water-cooling wall 1 or the outer water-cooling wall 2. You may make it attach.

  In the multitubular once-through boiler according to the tenth embodiment (shown in FIGS. 16 and 17), a swirl promoting guide body 19 comprising a water pipe 19a with a fin 19b is disposed in the combustion chamber 3. However, in the multi-tube once-through boiler according to another embodiment, the diameter of the water pipe 19a is large, and when the water pipe 19a is disposed in the combustion chamber 3, the inner water cooling wall 1 and the outer water cooling are provided. If the gap between the wall 2 and the wall 2 is small, the fins 19 may be omitted. That is, the turning promoting guide body 19 may be formed only from the water pipe 19 a (or the water supply pipe), and this may be spirally arranged in the combustion chamber 3.

  In the multi-pipe once-through boiler according to the ninth embodiment (shown in FIGS. 14 and 15), fin-shaped swirl promoting guide bodies 19 are attached to both water cooling walls 1 and 2, and In the multi-pipe once-through boiler according to the tenth embodiment (shown in FIGS. 16 and 17), a turning promoting guide body 19 including a water pipe 19a with a fin 19b is arranged in the combustion chamber 3. However, in the multitubular once-through boiler according to another embodiment, both the fin-like swirl promoting guide body 19 and the swirl promoting guide body 19 including the water pipe 19a are disposed in the combustion chamber 3. You may make it do.

  In the multi-pipe once-through boiler according to the ninth and tenth embodiments (shown in FIGS. 14 to 17), the fins 18 are not provided in the heat transfer water tubes 9 a of the heat transfer water tube group 9. In the multi-tube once-through boiler according to another embodiment, the outer circumferential surface of each heat transfer water tube 9a and the surface facing the gas passage 10 of the water tube 1a forming the inner water cooling wall 1 are substantially arc-shaped. The fins 18, the triangular fins 18, and the strip-shaped fins 18 may be attached in an appropriate arrangement.

1 is a schematic longitudinal sectional view of a multitubular once-through boiler according to a first embodiment of the present invention. It is a schematic cross-sectional view of the multitubular once-through boiler shown in FIG. It is a schematic longitudinal cross-sectional view of the multi-tube type once-through boiler which concerns on the 2nd Embodiment of this invention. FIG. 4 is a schematic cross-sectional view of the multitubular once-through boiler shown in FIG. 3. It is a schematic cross-sectional view of the multitubular once-through boiler according to the third embodiment of the present invention. It is a schematic cross-sectional view of the multitubular once-through boiler according to the fourth embodiment of the present invention. FIG. 9 is a schematic cross-sectional view of a multitubular once-through boiler according to a fifth embodiment of the present invention. It is a schematic longitudinal cross-sectional view of the multi-tube type once-through boiler which concerns on the 6th Embodiment of this invention. It is a schematic cross-sectional view of the multitubular once-through boiler shown in FIG. It is a schematic longitudinal cross-sectional view of the multi-tube type once-through boiler which concerns on the 7th Embodiment of this invention. It is a schematic cross-sectional view of the multi-tube once-through boiler shown in FIG. It is a schematic longitudinal cross-sectional view of the multi-tube type once-through boiler which concerns on the 8th Embodiment of this invention. It is a schematic cross-sectional view of the multi-tube once-through boiler shown in FIG. It is a schematic longitudinal cross-sectional view of the multitubular once-through boiler which concerns on the 9th Embodiment of this invention. It is a schematic cross-sectional view of the multi-tube once-through boiler shown in FIG. It is a schematic longitudinal cross-sectional view of the multitubular once-through boiler which concerns on the 10th Embodiment of this invention. It is a schematic cross-sectional view of the multi-tube once-through boiler shown in FIG.

Explanation of symbols

  1 is an inner water cooling wall, 1a is a water pipe, 1b is a fin, 2 is an outer water cooling wall, 2a is a water pipe, 2b is a fin, 3 is a combustion chamber, 4 is a spout, 7 is an upper header, 8 is a lower header, 9 is a heat transfer water tube group, 9a is a heat transfer water tube, 10 is a gas passage, 11 is a gas passage port, 17 is an air supply port, 18 is a fin, 19 is a swirl promoting guide body, and 20 is a gas passage for reducing pressure loss. Mouth, A for combustion air, A 'for secondary combustion air, C for cyclone flame, F for gas fuel, F' for premixed gas, G for combustion gas, Z1 for primary combustion zone, Z2 for secondary combustion zone.

Claims (9)

Two annular water cooling walls composed of a plurality of water pipes and fins are concentrically arranged to form an annular combustion chamber between the inner water cooling wall and the outer water cooling wall, and the upper and lower sides of the water pipes of both water cooling walls. A multi-tube type once-through boiler having end portions connected to an upper header and a lower header in communication with each other, and forming an opening at the upper end portion of the outer water cooling wall on the upper end side of the combustion chamber, In addition, a gas passage port is formed at the lower end of the inner water cooling wall, and a premixed gas obtained by mixing gas fuel and combustion air or gas fuel and combustion air from the opening into the combustion chamber is applied to the combustion chamber wall surface. along by burning and ejected to the tangential direction, to form a cyclone flame along the combustion chamber wall surface in the combustion chamber and the combustion chamber while swirling the combustion gas in the combustion chamber to flow toward the top to the bottom This is a multi-tube type once-through boiler. A spiral turning promotion guide body from the upper end side to the lower end side of the combustion chamber is disposed in the annular combustion chamber so that the turning of the combustion gas flowing in the combustion chamber is promoted by the turning promotion guide body. The multi-pipe once-through boiler according to claim 1, wherein   A gas passage for reducing pressure loss is formed in a part of the inner water cooling wall to guide a part of the combustion gas flowing while swirling in the combustion chamber to a gas passage on the downstream side of the combustion chamber. The multi-tube type once-through boiler according to claim 1 or 2, wherein a short path is made from the pressure loss reducing gas passage to the gas passage. A heat transfer water tube group comprising a plurality of heat transfer water tubes whose upper and lower ends are connected to the upper header and the lower header in communication with each other is disposed in a space surrounded by an inner water cooling wall, and the heat transfer water tube the gas passage communicating with the flue formed in the gaps of the gap and the heat transfer water tube group of the group and the inner water wall, also the combustion gas flowing downward in the combustion chamber to the lower end of the inner water wall The multi-pipe once-through boiler according to claim 1, 2 or 3, wherein a plurality of gas passage ports for uniformly flowing into the gas passage are formed. A plurality of nozzles that open to the upper end of the combustion chamber are formed at the upper end of the outer water cooling wall, and gas fuel and combustion air or gas fuel and combustion air are mixed from each nozzle into the combustion chamber. 5. A multi-tube once-through boiler according to claim 1, wherein the premixed gas is jetted in the tangential direction along the combustion chamber wall surface and burned. . At least one air supply port for secondary combustion air that opens to the upper end of the combustion chamber is formed at the upper end of the water cooling wall on the downstream side of the soot and is blown into the combustion chamber from the soot. Gas fuel and combustion air or premixed gas are burned under conditions of an air ratio of 1 or less to form a primary combustion zone in the downstream region of the firing port, and secondary combustion from the air supply port into the combustion chamber The working air is jetted in the tangential direction along the wall surface of the combustion chamber and mixed with the primary combustion gas generated in the primary combustion zone, and the primary combustion gas is mixed under the condition of the total air ratio of 1.1 to 1.5. 6. The multipipe according to claim 1, wherein a secondary combustion zone is formed in a downstream region of the air supply port by combustion. Type once-through boiler.   At least on the outer peripheral surface of each heat transfer water tube forming the heat transfer water tube group, a plurality of fins are attached to the opposite heat transfer water tube and perpendicular to the longitudinal direction of the heat transfer water tube, and from the gas passage port to the gas passage The multi-pipe once-through boiler according to claim 4, 5, or 6, wherein the combustion gas flowing into the gas passage flows in a zigzag shape from one end side to the other end side of the gas passage.   At least on the outer peripheral surface of each heat transfer water tube forming the heat transfer water tube group, a plurality of fins are attached to the adjacent heat transfer water tube in a stepwise manner and perpendicular to the longitudinal direction of the heat transfer water tube. The multi-pipe once-through boiler according to claim 4, 5 or 6, wherein the combustion gas flowing into the gas passage is swirled from one end side to the other end side of the gas passage. .   A plurality of fins are attached radially and parallel to the longitudinal direction of the heat transfer water pipe on the outer peripheral surface of each heat transfer water pipe forming at least the heat transfer water pipe group, and the combustion gas flowing into the gas passage from the gas passage port is the gas passage. The multi-pipe once-through boiler according to claim 4, wherein the multi-tube type once-through boiler is configured to flow while coming into contact with the fin from one end side to the other end side.

Images