JP4947319B2 - Once-through boiler - Google Patents

Description

  The present invention relates to a once-through boiler that generates steam by burning solid biomass fuel such as wood chips and pellets.

As a measure to reduce carbon dioxide (CO ₂ ) in order to prevent global warming, instead of using fossil fuels such as coal and oil, combustion using solid biomass fuel that is processed into chips or pellets of wood The use of heat is drawing attention.
According to such a combustion apparatus using biomass fuel, there is an advantage that not only the amount of generated CO ₂ can be suppressed, but also the fuel itself is inexpensive, so that it is excellent in economic efficiency.

Therefore, in recent years, an attempt to use the biomass fuel as a fuel for a small once-through boiler, which is a kind of the combustion apparatus, has begun. This small once-through boiler is equipped with a number of vertical water pipes and upper and lower headers with an inner diameter of 150 mm or less, and has a small and simple structure with a heat transfer area limited to 10 m ² or less. It is inherently safe, and is characterized by loose legal regulations and easy handling.

  For example, in Patent Document 1 below, an annular inner water cooling wall that forms a circular combustion chamber inward, an annular outer water cooling wall disposed at an outer position of the inner water cooling wall, and an inner water cooling An annular combustion gas passage formed between the wall and the outer water cooling wall and communicating with the combustion chamber and the flue, respectively, and an upper portion connected in communication with the upper and lower ends of each water pipe of both water cooling walls Composed of a header and lower header, and a combustion device that is disposed in the lower part of the combustion chamber and burns wood pellets as fuel, and injects the wood pellets into the combustion chamber from the wood pellet supply port provided in the upper part of the combustion chamber for combustion A wood pellet fired steam boiler has been proposed in which the combustion gas and the incinerated ash generated by the apparatus are discharged from the combustion chamber to the flue through the combustion gas passage.

JP 2008-64370 A

  By the way, this type of once-through boiler generally has a structure in which an inner row water pipe and an outer row pipe formed by a large number of straight pipes of about 50 to 60 mmφ are connected to upper and lower headers having an inner diameter of 150 m or less. The combustion gas flow path between the row water pipe and the outer row pipe becomes extremely narrow. For this reason, especially when a fuel with a large amount of ash, such as biomass fuel, is used, the combustion ash in the combustion gas adheres to the outer peripheral surface of the water pipe that performs heat exchange or accumulates in the combustion gas flow path. Thus, there is a problem that the boiler efficiency is lowered and, in a severe case, the combustion gas passage is blocked to obstruct the combustion itself.

  In particular, in the conventional wood pellet fired steam boiler, the wood pellets were crushed during the transportation of the wood pellets because the wood pellets were introduced from the supply port provided in the upper part of the combustion chamber and burned by the combustion device. There is a problem in that fine particles having a small particle diameter are not burned down to the hearth but are accompanied by fuel gas and are discharged unburned.

  In addition, since combustion ash is also transported to the exhaust gas outlet along with the combustion gas, there are many unburned components mixed in the exhaust gas. As a result, sootfire is caused by the unburned components in the flue. There is also a problem that sparks are scattered from the chimney.

  The present invention has been made in view of the above circumstances, and even when biomass fuel is used as a fuel source, it suppresses the occurrence of harmful effects such as a decrease in boiler efficiency and blockage of a combustion gas flow path caused by combustion ash. It is an object of the present invention to provide a once-through boiler that makes it possible.

In order to solve the above problems, the once-through boiler according to claim 1 is disposed in a combustion furnace in which a combustion chamber is formed, an exhaust gas passage connected to the combustion furnace, and upper and lower portions of the combustion furnace. Upper and lower headers, and upper and lower ends connected to the upper header and the lower header, respectively, and are provided at intervals along the inner wall of the combustion furnace and connected to each other by flat fins. A plurality of ring-shaped outer water pipe groups composed of outer water pipes, upper and lower ends connected to the upper header and the lower header, respectively, spaced apart from each other inside the outer water pipe group and connected to each other by flat fins. An annular inner water tube group consisting of inner water tubes, and forming the first opening between the inner water tubes of the inner water tube group, A combustion gas flow path communicating with the combustion chamber is formed between the pipe group and the outer water pipe group, and the combustion gas flow path and the exhaust gas passage are communicated between the outer water pipes of the outer water pipe group. And at the lower end of the outer water pipe, an R portion is formed gradually toward the inner wall from the connecting portion with the lower header, and further on the downstream side of the exhaust gas passage. An economizer for preheating water supply to the lower header is provided, and the economizer has a cylindrical shape with the upper and lower ends closed, and a main body to which the exhaust gas passage is connected to the upper part, and an inner side of the main body. A cylindrical inner pipe that is disposed with a gap and that has a lower end that opens to a lower portion in the main body and an upper end that extends outward from the main body and serves as an exhaust gas pipe. Between the inner pipe It is characterized in that the water feed preheating pipe spiraling in the vertical direction is arranged.

  According to a second aspect of the present invention, in the first aspect of the present invention, a third opening is formed between the outer water pipes of the R portion, and an ash is formed below the third opening. -It is characterized by the formation of a bowl receiving space.

The invention according to claim 3 is the invention according to claim 1 or 2 , characterized in that the exhaust gas passage is an upper part of the main body and is connected in a tangential direction of the main body. Further, the invention according to claim 4 is the invention according to any one of claims 1 to 3 , wherein at least the lower part of the main body has a taper whose inner diameter gradually decreases from the upper side to the lower side. And an ash receiving box is connected to the lower end portion.

  According to the invention described in any one of claims 1 to 4, at least at the lower end portion of the outer water pipe, the R portion that gradually goes from the connecting portion with the lower header upward toward the inner wall side is formed. The flow path width of the combustion gas flow path formed between the inner water tube group and the outer water tube group can be made wider than before. As a result, the combustion gas flow rate in the combustion gas flow path can be reduced, and the accompanying combustion ash can be dropped from the combustion gas flowing into the combustion gas flow path. It is possible to prevent the inner water tube group or the outer water tube group from adhering to the surface or blocking the combustion gas flow path.

  In this case, in particular, according to the invention described in claim 2, the third opening is formed between the R portions formed in the lower end portion of the outer water pipe, and the ash / ash is formed below the third opening. Since the soot receiving space is formed, the falling combustion ash can be dropped and collected from the third opening to the ashes and soot receiving space. For this reason, it becomes possible to prevent combustion ash from being accompanied by combustion gas, causing a sootfire in the flue, and scattering of sparks from the chimney.

  By the way, when providing an economizer that preheats the water supply using the heat of the exhaust gas on the downstream side of the exhaust gas passage of this type of once-through boiler, the water supply preheating pipe is formed in a spiral shape (coiled) to form a cylinder. If the exhaust gas passing through the central space of the preheating pipe passes through without contributing to the heat exchange, the heat of the exhaust gas is effectively used. Is difficult. Even if the coil diameter of the preheating tube is reduced, there is a limit because the preheating tube is flattened.

In this regard, in the first aspect of the invention, when an economizer for preheating water supply is provided on the downstream side of the exhaust gas passage, the economizer has a double-pipe structure of a cylindrical main body and a cylindrical inner pipe. The preheating pipe is piped between the main body and the inner pipe so as to draw a spiral in the vertical direction, and the exhaust gas passage is connected to the upper portion of the main body, and the lower end portion of the inner pipe is opened to the lower portion of the main body. The upper end is an exhaust gas pipe extending outward from the main body.

  For this reason, the combustion gas sent from the exhaust gas passage is introduced between the upper part of the main body and the inner pipe, and in the process of flowing downward as a swirling flow, heat is exchanged with the preheating pipe to supply the internal water supply. In order to preheat, compared with the case where exhaust gas is a linear flow, the heat transfer efficiency can be further increased, and thus the water supply can be efficiently preheated. In addition, by bending the preheating tube into a diameter that does not flatten and forming a spiral shape in the vertical direction, a desired heat transfer area can be secured, and space is not wasted and the main body and the inside Can be installed between the pipes.

  In addition, the combustion ash and soot accompanying the combustion gas are lowered from the inner wall of the main body by the centrifugal force due to the swirl flow and the velocity component downward when the flow direction changes upward from the lower end of the inner tube. Can be dropped and separated.

  As a result, it is possible to more reliably prevent combustion ash from being accompanied by the combustion gas and causing sootfire in the flue downstream from the exhaust gas pipe, or scattering of sparks from the chimney. .

At this time, particularly when the exhaust gas passage is connected in the tangential direction of the upper portion of the main body as in the invention described in claim 3 , the swirling flow can be smoothly generated, and further, claim 4 is further provided. If at least the lower part of the main body is formed in a tapered shape whose inner diameter gradually decreases from the upper side to the lower side as in the invention described in the above, the so-called cyclone effect further improves the separation effect of combustion ash and soot. Can do.

It is the whole longitudinal section showing one embodiment of a once-through boiler concerning the present invention. It is the cross-sectional view seen in the AA line of FIG. It is a longitudinal cross-sectional view which expands and shows the principal part of the economizer of FIG. It is a cross-sectional view of FIG. It is a front view of the X section of FIG. It is a front view of the Y section of FIG. It is a longitudinal cross-sectional view which shows the shape of the upper-and-lower part header in the other embodiment of this invention, an outer side water pipe, and an inner side water pipe. It is a perspective view which shows typically arrangement | positioning with the upper-and-lower part header, an outer side water pipe, and an inner side water pipe in other embodiment of this invention. It is a longitudinal cross-sectional view which shows the economizer in other embodiment of this invention. It is a longitudinal cross-sectional view which shows the economizer in other embodiment of this invention.

  1 to 6 show an embodiment of a once-through boiler according to the present invention. This once-through boiler is provided at a cylindrical combustion furnace 1 whose ceiling is closed and at the bottom of the combustion furnace 1. A combustion apparatus 2, a fuel supply apparatus 3 for supplying biomass fuel obtained by processing wood into chips to the combustion apparatus 2, an exhaust gas passage 4 for discharging combustion gas from the combustion furnace 1, and a downstream of the exhaust gas path 4 And an economizer 5 provided on the side.

  Here, a cylindrical fuel introduction pipe 6 is disposed at the center of the combustion device 2, and primary combustion air is introduced into the combustion furnace 1 from the lower side opened to the atmosphere on the outer periphery of the fuel introduction pipe 6. A flow path 7 for inflow is formed. In addition, an refractory brick 8 is arranged in an annular shape above the outer periphery of the fuel introduction pipe 6, and an air ejection pipe 9 for ejecting combustion secondary air is provided on the outer periphery of the refractory brick 8. It is installed. The lower end portion of the fuel introduction pipe 6 is connected to the fuel supply device 3.

  The fuel supply device 3 has a fuel pit 10 into which the biomass fuel is introduced, a lower end portion of the fuel pit 10 connected to one end portion, and a lower end portion of the fuel introduction pipe 6 connected to the other end portion. A stalker box 11, a stalker screw 12 that is rotatably provided in the stalker box 11 and has a spiral blade that feeds solid fuel supplied from the fuel pit 10 to the fuel introduction pipe 6, and rotation of the stalker screw 12 The gear motor 13 is configured to rotate the shaft 12a. As described above, this once-through boiler is a so-called subduction type in which biomass fuel is supplied from the bottom.

  On the other hand, the combustion furnace 1 has a combustion chamber 14 formed therein, an outer peripheral portion thereof is covered with a heat insulating material 15, and the exhaust gas passage 4 is connected to a side surface thereof. An annular lower header 16 is disposed at the lower portion of the combustion furnace 1, and an annular upper header 17 having the same diameter is provided at an upper portion facing the lower header 16.

Further, the lower header 16 and the upper header 17 are connected to upper and lower ends of a plurality of outer water pipes 18 and inner water pipes 19 arranged in the vertical direction.
Here, the plurality of outer water pipes 18 are piped at equal intervals in the circumferential direction along the inner wall of the heat insulating material 15 of the combustion furnace 1, and the adjacent outer water pipes 18 are made of strip-like fins. 20 is connected. As a result, a substantially cylindrical outer water tube group 21 composed of a plurality of outer water tubes 18 and fins 20 is formed.

  Each of the outer water pipes 18 is formed with an R portion 18a that gradually goes from the connection portion with the lower header 16 toward the heat insulating material 15 at the lower end portion, and with the upper header 17 at the upper end portion. An R portion 18b is formed from the portion toward the heat insulating material 15 gradually downward.

On the other hand, each inner water pipe 19 is formed of a straight pipe, and is arranged inside the outer water pipe group 21 at equal intervals in the circumferential direction. These inner water pipes 19 are also connected to each other by strip plate-like fins 22. As a result, a substantially cylindrical inner water tube group 23 having a plurality of inner water tubes 19 and fins 22 is formed.
As a result, a combustion gas flow path 24 is formed between the outer water tube group 21 and the inner water tube group 23.

  As shown in FIGS. 2 and 5, between the upper portions of the three inner water pipes 19 located in the vicinity of the connection part of the exhaust gas passage 4, an opening for communicating the combustion chamber 14 and the combustion gas flow path 24. A (first opening) 25 is formed. In addition, an opening (second opening) 26 that connects the combustion gas flow channel 24 and the exhaust gas flow channel 4 is formed between the central portions of the three outer water pipes 18 facing the connection portion of the exhaust gas flow channel 4. ing.

  Further, between the outer water pipe 18 and the inner water pipe 19 positioned between the openings 25 and 26, a band plate-like wall portion 27 for preventing the openings 25 and 26 from directly communicating is provided. It has been. Thereby, a flow path of the combustion gas is formed from the combustion chamber 14 to the exhaust gas passage 4 around almost the entire circumference of the combustion gas passage 24.

  Further, an ash / soot receiving space 28 is formed on the outer periphery of the lowermost portion of the combustion furnace 1 over the entire circumference. Then, as shown in FIG. 6, no fins are provided between the lower portion of the outer water pipe 18 exposed in the ash / soot receiving space 28 and the R portion 18 a, thereby opening (third opening) 29. Is formed.

  On the other hand, as shown in FIG. 3 and FIG. 4, the economizer 5 connected to the downstream side of the exhaust gas flow path 4 includes a cylindrical main body 30 whose upper and lower ends are closed, and a cylinder provided in the main body 30. A double pipe structure is formed by the inner pipe 31 having a shape. A preheating pipe 32 is piped between the main body 30 and the inner pipe 31 so as to draw a double spiral in the vertical direction. In the figure, reference numeral 32 a is an inlet pipe for preheated water supply, 32 b is an outlet pipe, and the outlet pipe 32 b is connected to the lower header 16 in the combustion furnace 1.

  Further, the exhaust gas passage 4 is connected to the tangential direction of the main body 30 at the upper end portion of the main body 30. Further, the lower end of the inner pipe 31 opens at the lower part of the main body 30, and the upper part penetrates the top plate of the main body 30 and is drawn out to the outside as an exhaust gas pipe 33. An exhaust gas fan 34 is provided downstream of the exhaust gas pipe 33.

  In the once-through boiler for biomass fuel cooking having the above-described configuration, the combustion primary air is introduced from the bottom of the combustion device 2 by the suction force of the exhaust gas fan 34, and is introduced into the fuel pit 10 and fuel is introduced by the fuel supply device 3. Biomass fuel sent to the pipe 6 is burned. At the same time, the combustion gas is swirled in the combustion chamber 14 by ejecting the combustion secondary air from the air ejection pipe 9 toward the center direction and the circumferential direction of the combustion chamber 14. Raise. As a result, the residence time of the combustion gas in the combustion chamber 14 is significantly increased, so that unburned gas, flame and combustion air can be mixed efficiently. Note that the ash of the biomass fuel burned in the combustion device 2 is discharged to the lower ash receiving box 35.

  Next, the combustion gas that has risen in the combustion chamber 14 flows into the combustion gas flow path 24 from the opening 25 formed between the inner water pipes 19 of the inner water pipe group 23, and between the inner water pipe group 23 and the outer water pipe group 21. In the meantime, the water supply preheated by the economizer 5 is further heated to generate steam. At this time, in the combustion gas flow path 24, the combustion ash and soot accompanying the combustion gas fall along the outer water tube group 21 and receive ash / soot from an opening 29 formed in the lower portion of the outer water tube group 21. Collected in space 28. The combustion ash and soot that have fallen into the ash / soot receiving space 28 in this way are cleaned and removed from the cleaning port 28a.

  The combustion gas flowing in the combustion gas passage 24 is discharged from the opening 26 formed in the outer water tube group 21 to the exhaust gas passage 4, and between the main body 30 and the inner tube 31 in the downstream economizer 5. Are introduced from the tangential direction. Thereby, combustion gas preheats the feed water in the preheating pipe 32 by flowing downward between the main body 30 and the inner pipe 31 while drawing a spiral. Finally, the inside of the inner pipe 31 rises from the lower end of the inner pipe 31 and is sucked into the exhaust gas pipe 33.

  At this time, the combustion gas efficiently exchanges heat with the preheating pipe 32 and preheats the internal water supply in the process of flowing downward as a swirling flow between the main body 30 and the inner pipe 31. The water supply can be preheated. Thereby, the size (heat transfer area) of the preheating tube 32 can be reduced by about 30%. In addition, the combustion ash and soot accompanied by the combustion gas are caused to flow by the centrifugal force due to the swirling flow and the downward velocity component when the flow direction changes upward from the lower end portion of the inner tube 31. It can be separated from the inner wall by dropping downward.

  As described above, according to the once-through boiler having the above-described configuration, the biomass fuel can be burned by the down-loading type combustion device 2 and the combustion of the unburned fuel can be promoted by the combustion secondary air. By forming the R portion at the lower end portion of the outer water pipe 18, the passage width of the combustion gas passage 24 formed between the inner water pipe group 23 and the outer water pipe group 21 can be made wider than before. Therefore, the flow rate of the combustion gas in the combustion gas flow path 24 can be slowed to drop the accompanying combustion ash, so that the surface of the inner water tube group 23 and the outer water tube group 21 in which the combustion ash is a heat exchange part It is possible to prevent the fuel gas from adhering to the gas or blocking the combustion gas flow path.

  Moreover, an opening 29 is formed between the R portions 18 a formed at the lower end of the outer water pipe 18, and an ash / soot receiving space 28 is formed below the opening 29. The falling combustion ash can be smoothly dropped from the opening 29 into the ash / soot receiving space 28 and collected.

  Furthermore, since the combustion gas discharged from the combustion furnace 1 is sent to the economizer 5 having a double-pipe structure, and a swirling flow is generated downward, heat exchange with the preheating pipe 32 is performed. The remaining combustion ash and soot can also be separated and collected by the economizer 5, so that it is possible to generate sootfire in the flue downstream from the exhaust gas pipe and to prevent sparks from scattering from the chimney. Can be prevented.

  In the above embodiment, the R portion 18a that gradually goes from the connecting portion with the lower header 16 toward the heat insulating material 15 is formed at the lower end portion of the outer water pipe 18, and the upper header 17 is formed at the upper end portion. Only the case where the combustion gas passage 24 having a wide passage width is formed between the inner water tube group 23 and the inner water tube group 23 by forming the R portion 18b gradually going downward from the connecting portion to the heat insulating material 15 has been described. However, the present invention is not limited to this.

  That is, as shown in FIG. 7 (a), the R portion 18a is formed only at the lower end portion of the outer water pipe 18, and the upper end portion is connected to the upper header 17 as a straight pipe, and at the upper end portion of the inner water pipe 19, The same effect can be obtained by forming the R portion 19b that gradually goes downward from the connecting portion with the upper header 17 toward the center of the combustion chamber 14.

  Further, as shown in FIG. 7B, if similar R portions 18a, 18b, 19a, and 19b are formed at the upper and lower ends of the outer pipe 18 and the inner pipe 19, respectively, combustion with a wider channel width is achieved. The gas flow path 24 can be formed.

  Moreover, in this embodiment, although the case where it applied to what provided the cyclic | annular upper header 17 and the lower header 16 in the cylindrical combustion furnace 1 was demonstrated, as shown in FIG. The present invention can be similarly applied to a once-through boiler in which a straight tubular upper header 17a and a lower header 16a are provided on both upper and lower sides of a combustion furnace (not shown).

Further, the structure of the economizer 5 is not limited to that shown in the above embodiment.
For example, instead of the economizer 5, as shown in FIG. 9, a tapered portion 30 a having an inner diameter that gradually decreases from the top to the bottom is formed in the lower portion of the main body 30, and an ash receiver is formed at the lower end of the tapered portion 30 a. An economizer 37 in which the boxes 36 are connected can also be used.

According to such a once-through boiler using the economizer 37, the desired preheating effect in the preheating pipe 32 and the tapered portion 30a formed in the main body 30 are further improved by the so-called cyclone effect to further improve the separation effect of combustion ash and soot. In addition, the separated combustion ash and the like can be directly collected in the ash receiving box 36.
Furthermore, as shown in FIG. 10, according to the economizer 38 in which the length of the tapered portion 30a in the main body 30 is increased, the collection efficiency of combustion ash and soot can be further increased.

  It can be used as a once-through boiler that generates steam by burning solid biomass fuel such as wood chips and pellets.

DESCRIPTION OF SYMBOLS 1 Combustion furnace 2 Combustion apparatus 3 Fuel supply apparatus 4 Exhaust gas passage 5, 37, 38 Economizer 14 Combustion chamber 16 Lower header 17 Upper header 18 Outer water pipe 18a, 18b, 19a, 19b R part 19 Inner water pipe 20, 22 Fin 21 Outer water pipe Group 23 inner water tube group 24 combustion gas flow path 25 opening (first opening)
26 opening (second opening)
28 Ash / Gray receiving space 29 Opening (third opening)
30 Main body 30a Taper part 31 Inner pipe 33 Exhaust gas pipe 36 Ash receiving box

Claims (4)

A combustion furnace in which a combustion chamber is formed, an exhaust gas passage connected to the combustion furnace, an upper header and a lower header respectively disposed above and below the combustion furnace, and upper and lower headers respectively above and below An annular outer water tube group consisting of a plurality of outer water tubes connected to each other by flat plate fins and connected at intervals along the inner wall of the combustion furnace, and an upper header and a lower header. Each of the upper and lower ends is connected, and is provided with an annular inner water tube group composed of a plurality of inner water tubes connected to each other by flat fins while being provided at intervals inside the outer water tube group,
By forming a first opening between the inner water pipes of the inner water pipe group, a combustion gas flow path communicating with the combustion chamber is formed between the inner water pipe group and the outer water pipe group, and the outer side is formed. A second opening for communicating the combustion gas passage and the exhaust gas passage is formed between the outer water pipes of the water pipe group, and the lower end of the outer water pipe is directed upward from a connection portion with the lower header. gradually forming a R portion toward the inner wall Te, further, on the downstream side of the exhaust gas passage, it is provided an economizer for preheating the feed water to the lower header, and the economizer, the upper and lower end is closed The main body has a cylindrical shape, and the exhaust gas passage is connected to the upper part of the main body. The main body is disposed with an interval inside the main body, and the lower end opens to the lower part of the main body. Extending towards Once-through boiler comprising an inner tube of a tubular comprising an exhaust gas tube, between the body and the inner tube, characterized in that the water feed preheating pipe spiraling in the vertical direction is arranged Te.   The once-through boiler according to claim 1, wherein a third opening is formed between the outer water pipes of the R portion, and an ash / soot receiving space is formed below the third opening. . The once-through boiler according to claim 1 or 2, wherein the exhaust gas passage is connected to a tangential direction of the main body at an upper portion of the main body . The body, at least its lower portion, one from above is formed in a tapered shape whose inner diameter becomes gradually smaller toward downward, and claims 1, characterized in that ash receiving box in the lower end portion connected to 3 once-through boiler according to any.

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