SOLID FUEL BURNER

Abstract

A solid fuel burner is provided with a nozzle that is provided around the central axis of the burner, that includes a straight tube section having an opening opposed to a furnace, and a curved tube section continuous with the straight tube section, and that sprays out, from the opening to the furnace, a fluid mixture which is of a solid fuel and carrier gas of the solid fuel and which is flowing in the curved tube section; a first swirler that gives the fluid mixture a swirl at the burner central axis side of the straight tube section; and a second swirler that gives, at the burner central axis side downstream of the first swirler, the thud mixture a swirl opposite to that given by the first swirler.

Claims

1. A solid fuel burner provided in a throat of a wall surface of a furnace, comprising: a fuel nozzle which includes a straight tube section provided around a burner central axis and having an opening toward the furnace and a curved tube section continued to the straight tube section, wherein a mixed fluid of a solid fuel and a carrier gas thereof supplied to the curved tube section is sprayed from the opening of the straight tube section to the furnace; a first swirling means which is provided on the burner central axis side in the straight tube section, and is provided away from an inner wall of the fuel nozzle to apply a swirl to the mixed fluid; and a second swirling means which is provided on the burner central axis side downstream in a flow direction of the mixed fluid of the first swirling means, and is provided away from an inner wall of the fuel nozzle to apply a swirl to the mixed fluid in a direction reverse to that of the first swirling means, wherein the second swirling means is disposed on the upstream side in a direction in which the mixed fluid is carried from the opening of the straight tube section with a preset interval so that a swirl component by the second swirling means does not remain.

2. The solid fuel burner according to claim 1, wherein a flame stabilizer is provided on an outer periphery of the opening of the straight tube section.

3. A solid fuel burner provided in a throat of a wall surface of a furnace, comprising: a fuel nozzle which includes a straight tube section provided around a burner central axis and having an opening toward the furnace and a curved tube section continued to the straight tube section, wherein a mixed fluid of a solid fuel and a carrier gas thereof supplied to the curved tube section is sprayed from the opening of the straight tube section to the furnace; a first swirler which is provided in the straight tube section, includes a plurality of vanes installed in the circumferential direction, and is provided away from an inner wall of the fuel nozzle to apply a swirl to the mixed fluid; and a second swirler which is provided downstream in a flow direction of the mixed fluid of the first swirler in the straight tube section, includes a plurality of vanes disposed in the circumferential direction, is provided away from an inner wall of the fuel nozzle, and is installed in a direction reverse to a direction in which vanes of the first swirler are installed, wherein the second swirling means is disposed on the upstream side in a direction in which the mixed fluid is carried from the opening of the straight tube section with a preset interval so that a swirl component by the second swirling means does not remain.

4. The solid fuel burner according to claim 3, wherein a flame stabilizer is provided on the outer periphery of the opening of the straight tube section.

5. (canceled)

6. The solid fuel burner according to claim 3, wherein respective vanes of the second swirler are installed so that an installation angle of the respective vanes of the second swirler with respect to a burner central axis direction is equal to or smaller than the installation angle of the respective vanes of the first swirler with respect to the burner central axis direction.

7. The solid fuel burner according to claim 3, wherein a radial length of the respective vanes of the second swirler is equal to or shorter than the radial length of respective vanes of the first swirler.

8. The solid fuel burner according to claim 3, wherein a lateral width of respective vanes of the second swirler is the same as or smaller than the lateral width of respective vanes of the first swirler.

9. The solid fuel burner according to claim 1, wherein a disperser for solid fuel particles is provided in the curved tube section.

10. the solid fuel burner according to claim 9, wherein the disperser is installed on a lateral face of an oil burner provided on the burner central axis on a side facing a flow of the mixed fluid.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0049] FIG. 1 is a side view illustrating a partial cross-section of a solid fuel burner which is one example (Example 1) of the present disclosure.

[0050] FIG. 2(A) is a front view of a first swirler in FIG. 1 (view seen from a furnace side), FIG. 2(B) is a view seen from S1 in FIG. 2(A), FIG. 2(C) is a front view of a second swirler in FIG. 1, and FIG. 2(D) is a view seen from S2 in FIG. 2(C).

[0051] FIG. 3(A) is a diagram illustrating a particle concentration distribution in a radial direction of the burner of Example 1, and FIG. 3(B) is a diagram illustrating the particle concentration distribution in the radial direction of a burner used as a comparison.

[0052] FIG. 4 is a diagram illustrating swirl strength distributions in the vicinity of burner outlets of the burner of Example 1 and the burner of the comparative example.

[0053] FIG. 5 is diagrams comparing circumferential concentration distributions on outlet outer peripheral sides of the burner of Example 1 and the burner of the comparative example at the time of a high load.

[0054] FIG. 6 is diagrams comparing the circumferential concentration distributions on the outlet outer peripheral sides of the burner of Example 1 and the burner of the comparative example at the time of a low load.

[0055] FIG. 7 is a side view illustrating a partial cross-section of a solid fuel burner which is another example (Example 2) of the present disclosure.

[0056] FIG. 8(A) is a front view of a first swirler in FIG. 7, FIG. 8(B) is a view seen from S1 in FIG. 8(A), FIG. 8(C) is a front view of a second swirler in FIG. 7, and FIG. 8(D) is a view seen from S2 in FIG. 8(C).

[0057] FIG. 9 is a side view illustrating a partial cross-section of a solid fuel burner which is another example (Example 3) of the present disclosure.

[0058] FIG. 10(A) is a front view of a first swirler in FIG. 9. FIG. 10(B) is a view seen from S1 in FIG. 10(A), FIG. 10(C) is a front view of a second swirler in FIG. 9, and FIG. 10(D) is a view seen from S2 in FIG. 10(C).

[0059] FIG. 11 is a side view illustrating a partial cross-section of a solid fuel burner which is another example (Example 4) of the present disclosure.

[0060] FIG. 12(A) is a front view of a first swirler in FIG. 11, FIG. 12(B) is a view seen from S1 in FIG. 12(A), FIG. 12(C) is a front view of a second swirler in FIG. 11, and FIG. 12D is a view seen from S2 in FIG. 12(C).

[0061] FIG. 13 is a diagram illustrating the swirl strength distribution in the vicinity of the burner outlet when the swirler is changed.

[0062] FIG. 14 is a side view illustrating a partial cross-section of a solid fuel burner which is another example (Example 4) of the present disclosure.

[0063] FIG. 15 is a side view illustrating a partial cross-section of a solid fuel burner which is another example (Example 5) of the present disclosure.

[0064] FIG. 16(A) is a perspective view of major parts in FIG. 15, FIG. 16(B) is an enlarged view of the major parts in FIG. 15, FIG. 16(C) is a cross-sectional view taken and seen on line A-A in FIG. 16(B), and FIG. 16(D) is a cross-sectional view taken and seen on line B-B in FIG. 16(B).

[0065] FIG. 17 is a view illustrating, a flow field of a mixed fluid when a particle disperser is not provided, wherein FIG. 17(A) is a side view, and FIG. 17(B) is a front view.

[0066] FIG. 18 is a view illustrating a flow field of a mixed fluid when a particle disperser is provided, wherein FIG. 18(A) is a side view, and FIG. 18(B) is a front view.

[0067] FIG. 19 is diagrams comparing the circumferential concentration distributions on outlet outer peripheral sides of the burner of Example 5 and the burner of the comparative example at the time of a low load.

[0068] FIG. 20 is a side view illustrating a partial cross-section of a solid fuel burner which is another example (Example 5) of the present disclosure.

[0069] FIG. 21 is a side view illustrating a partial cross-section of a conventional solid fuel burner.

DESCRIPTION OF EMBODIMENTS

[0070] Hereinafter, embodiments of the present disclosure will be described.

[0071] FIG. 1 is a side view (schematic view) illustrating a partial cross-section of a solid fuel burner according to one example of the present disclosure.

[0072] A solid fuel burner 1 provided in a throat 13a of a wall surface of a furnace 13 has a curved tube section 5 having a curved section of about 90 and a straight tube section 2 continued to the curved tube section 5, and includes a nozzle 9 having a circular cross-section for supplying a fuel, through which a mixed fluid of a finely powdered fuel and a carrier gas (solid-gas two-phase flow) flows. An oil burner 8 is provided on a central axis of the straight tube section 2.

[0073] Further, as the solid fuel, coal, biomass, or a mixture thereof may be used. In addition, as the carrier gas of the solid fuel, air is commonly used, but a mixed gas of a combustion exhaust gas and air may also be employed, and any type of the fuel and carrier gas may be used. In the present embodiment, an example, in which pulverized coal is used as the solid fuel and air is used as the carrier gas, is illustrated, and the nozzle 9 for supplying a fuel is also referred to as a primary air nozzle 9.

[0074] A tip of the straight tube section 2 is opened toward the furnace 13, and a mixed fluid of pulverized coal and the primary air supplied from a direction of an arrow A (lower side) to the primary air nozzle 9 passes through the curved tube section 5, and a direction thereof is changed by about 90, then flows from the straight tube section 2 toward the furnace 13 and is sprayed from the opening (an outlet of the primary air nozzle 9). The curved tube section 5 may have a vertical cross-sectional shape of an L shape or a U shape, and may have a plurality of corners as illustrated in the drawing. In addition, an, angle of the curved section of the curved tube section 5 is not limited to 90, and it may be larger or smaller than 90. As the curved tube section 5, an elbow pipe, a bend pipe or the like may be used.

[0075] Further, a secondary air nozzle 3 and a tertiary air nozzle 4 are disposed in a concentric pattern around the primary air nozzle 9, and secondary air and tertiary air are supplied toward the furnace 13. These air streams are sprayed so as to spread in an outer peripheral direction. Further, a flame stabilizer (flame stabilization ring) 10 having an end-widening shape (conical) toward the furnace 13 side is provided around the outlet of the primary air nozzle 9 and between the primary air nozzle 9 and the secondary air nozzle 3. Further, a burner with no flame stabilizer 10 installed therein is also included in the present embodiment

[0076] A circulation flow is formed on a downstream side (the furnace 13 side) of the flame stabilizer 10, and a mixture of the fuel and air sprayed from the primary air nozzle 9, the secondary air, a high-temperature combustion gas and the like flows into the circulation flow and remains therein. In addition, a temperature of the fuel particles rises due to radiant heat received from the furnace 13. With these effects, the solid fuel ignites on the downstream side of the flame stabilizer 10, and the flame is maintained. An oil fuel is supplied from the tip of the oil burner 8 installed on the central axis of the primary air nozzle 9. The oil fuel is used to start up the solid fuel burner 1.

[0077] In addition, a supplied to the secondary air nozzle 3 and the tertiary air nozzle 4 may be adjusted and controlled with a flow rate and a flow velocity of air by a flow rate adjustment member (such as a damper, air register, or the like) (not illustrated).

[0078] In order to improve ignitability of the pulverized coal, it is necessary to increase a fuel concentration in the vicinity of the flame stabilizer 10 at the burner outlet. Since the pulverized coal concentration is required to be set to a certain value or more when igniting the pulverized coal, it is particularly important to increase the fuel concentration in the vicinity of the flame stabilizer 10 at the time of a low load in which an average concentration of the pulverized coal is low.

[0079] Therefore, by applying a swirl to the mixed fluid, it becomes possible to increase the fuel concentration in the vicinity of the flame stabilizer 10 due to its centrifugal effect. For that purpose, it is important to move the pulverized coal flowing around the oil burner 8 at the central part of the primary air nozzle 9 (on the central axis side of the cylindrical nozzle cross-section) to an outer peripheral side (radially outside, in the vicinity of the inner wall 9a). Meanwhile, there is no need to move the pulverized coal flowing in the vicinity of the inner wall 9a of the primary air nozzle 9.

[0080] Therefore, a first swirler 6 is provided at an entrance portion of the straight tube section 2 immediately after the curved tube section and the central part of the primary air nozzle 9, and the pulverized coal flowing through the central part of the primary an nozzle 9 is moved to the outer peripheral side. The first swirler 6 includes a plurality of plate-shaped vanes 6a attached to an outer periphery of the oil burner 8. Further, in the region immediately after passing through the curved tube section 5, there is no need to apply a swirl to the mixed fluid flowing in the vicinity of the inner wall 9a of the primary air nozzle 9, such that an end part of the vane 6a is installed away from the inner wall 9a.

[0081] If the swirl is strongly applied to the mixed fluid at the outlet of the primary air nozzle 9, the pulverized coal particles splatter to the outer peripheral side of the solid fuel burner 1 within the furnace 13, such that stability of the flame is decreased, and a NOx emission amount is increased as described above. Accordingly, it is necessary to weaken the swirl strength before the mixed fluid is sprayed into the furnace 13. In the present embodiment, as a second swirler 7 on the downstream side of the first swirler 6, similar to the first swirler 6, a plurality of plate-shaped vanes 7a are attached to the outer periphery of the oil burner 8. These swirlers 6 and 7 are a fixed type swirl in which each vane does not move.

[0082] FIG. 2 illustrates diagrams of the first swirler and the second swirler in FIG. 1. FIGS. 2(A) and 2(C) illustrate front views, respectively, FIG. 2(B) illustrates a view seen from S1 in FIG. 2(A), and FIG. 2(D) illustrates a view seen from S2 in FIG. 2(C). Further, in order to reduce the number of particles that can pass through the swirlers 6 and 7 without colliding with the swirlers 6 and 7, when viewing from the furnace 13, the respective swirlers 6 and 7 are installed so that the respective vanes 6a and 7a are not overlapped with each other as illustrated in FIGS. 2(A) and 2(C), but it is not particularly limited to this arrangement.

[0083] As illustrated in FIG. 2, the direction of the vanes 7a of the second swirler 7 is reversed to the direction of the vanes 6a of the first swirler 6, such that the swirl strength of the mixed fluid at the outlet of the primary air nozzle 9 is weakened.

[0084] In the example of FIG. 1, the directions of the vanes 6a and the vanes 7a (the direction of the swirl around the central axis) are reverse to each other, but the shapes and sizes of the respective vanes 6a and 7a are set to be all the same, and installation angles thereof with respect to the burner central axis direction of the respective vanes 6a and 7a are set to be the same as each other. Further, in the illustrated example, the number of the respective vanes 6a and 7a is set to be four by four, but it may be larger or smaller than four, and it may be appropriately changed according to the size of the burner 1. In addition, although it is not always necessary to equally provide the respective vanes 6a and 7a in the circumferential direction, by making them be equal, it is possible to prevent a strong swirl from being applied to only a part of them.

[0085] Further, if the directions of the vanes 6a and the vanes 7a are reverse to each other, the shapes, sizes, installation angles, and the like of the vanes 6a and vanes 7a may be different from each other. In addition, both the vanes 6a and the vanes 7a are not necessarily provided on the burner central axis, and may contact the inner wall 9a, but for the following reasons, it is preferable to provide these vanes on the burner central axis or install them away from the inner wall 9a.

[0086] As the mixed fluid passes through the curved tube section 5, concentration distributions occur in the circumferential direction and the radial direction of the cylindrical nozzle cross-section. Then, the flow passing through a void between the vanes 6a of the first swirler 6 and the inner wall 9a among the mixed fluids, in which the concentration distribution has occurred, becomes a flow in such a manner that the concentration distribution produced in the circumferential direction is maintained toward the nozzle outlet.

[0087] Meanwhile, the mixed fluid flowing on the central axis side becomes a flow which is expanded toward the radial outside of the cylindrical nozzle cross-section on the downstream side thereof by the vanes 6a of the first swirler 6, so that the pulverized coal is condensed to the inner wall 9a side.

[0088] For this reason, as a result of overlapping the above two flows with each other, the mixed fluid flowing in the vicinity of the inner wall 9a is subjected to some stirring effect by swirling, but it exhibits a tendency in which the concentration distribution produced in the circumferential direction is maintained toward the nozzle outlet, and further the pulverized coal concentration is increased.

[0089] Herein, on the downstream side of the second swirler 7, due to the action of the vanes 7a, the swirling flow is weakened (or disappears) when viewing the cylindrical nozzle cross-section as a whole, but the pulverized coal concentration of the mixed fluid flowing in the vicinity of the nozzle inner wall 9a exhibits a tendency of being maintained to the nozzle outlet part (end edge part) due to an inertial force acting in the flowing direction of the pulverized coal particles.

[0090] As illustrated in FIG. 2, by installing the vanes 6a and the vanes 7a away from the inner wall 9a, the mixed fluid flowing between the end parts of the respective vanes 6a and 7a and the inner wall 9a becomes a flow so as to be maintained toward the nozzle outlet, such that a high fuel concentration in the vicinity of the inner wall 9a may be maintained.

[0091] Although the radial lengths of the respective vanes 6a and 7a are not particularly limited, it is desirable that the diameters of the vanes are set to be 50 to 75% of the inner diameter of the primary air nozzle 9. If the diameters of the respective vanes 6a and 7a are larger than 75%, the swirling component may easily remain in the fluid flowing on the outer peripheral side of the primary air nozzle 9. Further, if the diameters of the respective vanes 6a and 7a are too large, it is difficult to install and remove these vanes, and maintainability is deteriorated. Meanwhile, if the diameters of the respective vanes 6a and 7a are smaller than 50%, a concentration of particles to the outer peripheral side of the primary air nozzle 9 is insufficient.

[0092] FIG. 3(A) illustrates the particle concentration distribution in the radial direction of the burner 1 in FIG. 1, and FIG. 3(B) illustrates the particle concentration distribution in the radial direction of the burner used as a comparison. A fluid analysis by a k- model was performed under a condition that the air and the pulverized coal flow at a rated load condition amount of the burner from the direction of an arrow A in FIG. 1, and the concentration distribution of the pulverized coal particles at the outlet of the primary air nozzle 9 was calculated.

[0093] Further, the burner used as the comparison has a structure in which the swirler is not installed at all and the swirlers 6 and 7 are removed from the burner having the structure of FIG. 1. An origin of the horizontal axis in each drawing is the central axis of the primary air nozzle 9, that is, an installation part of the oil burner 8, and it illustrates approaching the nozzle inner wall 9a with increasing the radial distance. That is, it illustrates that the distance in the radial direction from the central axis becomes larger according to the direction of the arrow (right direction) on the horizontal axis. The scales of the respective axes in FIGS. 3(A) and 3(B) are the same as each other. The pulverized coal concentration is an average in the circumferential direction of the concentration measured at a position where the radial distances are, the same as each other. It illustrates that the concentration becomes higher according to the direction of the arrow (upper direction) on the vertical axis. It can also be seen from FIG. 3(A) that the pulverized coal concentration in the vicinity of the inner wall 9a is increased due to a swirling action by the first swirler 6 and the second swirler 7.

[0094] In order to compare with the burner 21 of FIG. 21, the effect of the present example was further verified.

[0095] The burner 21 of FIG. 21 is identical to the burner 1 of FIG. 1 in that the swirl vane 26 is provided in the pulverized coal supply pipe 29. In addition, a straightening plate 27 is installed at the burner outlet in order to weaken the swirling force. However, in the burner 21 of FIG. 21, the swirl vane 26 is attached in contact with the inner wall 29a of the pulverized coal supply pipe 29, and there is no void between the swirl vane 26 and the inner wall 29a. Similarly, the straightening plate 27 is attached to the inner wall 29a, and is installed away from the central axis.

[0096] FIG. 4 illustrates swirl strength distributions in the vicinity of the burner outlets of the burner 1 in FIG. 1 and the burner of the comparative example. The fluid analysis by the k- model was executed under a condition that the air and the pulverized coal flow at a rated load condition amount of the burner 1 and with a burner having the same structure as the burner of FIG. 1, but with varied swirler shape and installation method, from the direction of the arrow A in FIG. 1, similar to the case of FIG. 3. Then, the swirl strength distribution of the air at the burner outlet crass-section in the primary air nozzle 9 was calculated. In this fluid analysis, numerical values of both the concentration distribution of the pulverized coal and the swirl strength distribution are calculated.

[0097] The origin of FIG. 4 is the central axis of the primary air nozzle 9 (the installation part of the oil burner 8). The horizontal axis illustrates a radial distance from the central axis, and it illustrates approaching the inner wall 9a with increasing the radial distance. In the present specification, the swirl strength refers to a circumferential average value of the swirl strengths (a flow velocity component in a swirl direction (circumferential direction) to a flow velocity component in a main current direction (axial direction)), which are measured at the same radial distance as each other.

[0098] Since there are clockwise and counterclockwise in the swirl direction as viewed from the furnace 13, two axes (vertical axis) are illustrated in FIG. 4 so that the direction of swirl may be determined.

[0099] A solid line B illustrates the swirl strength distribution of the burner 1 (in which the first swirler (and the second swirler 7 are installed away from the inner wall 9a) of FIG. 1, a one-dot, chain line C illustrates the swirl strength distribution of a case in which there is no second swirler 7 of the burner 1 of FIG. 1 (wherein the first swirler 6 is provided with being installed away from the inner wall 9a (Comparative Example 1), and a broken D illustrates the swirl strength distribution of a case in which the second swirler 7 of the burner 1 of FIG. 1 is not provided and the first swirler 6 is installed in contact with the inner wall 9a (Comparative Example 2).

[0100] In Comparative Example 1 (one-dot chain line C), the swirl strength of the primary air nozzle 9 at the central part (origin side) was strong, but the swirl strength on the outer peripheral side of the primary air nozzle 9 was weakened. The reason is that the vanes 6a of the first swirler 6 are installed only in the central part of the primary air nozzle 9. However, it can be said that the swirl strength thereof on the outer peripheral side is comparatively strong.

[0101] Meanwhile, in a case in which two swirlers 6 and 7 of the example (solid line B) are attached so that the directions of the vanes 6a and 7a are reversed to each other, a swirl was applied to the central part, but the swirl was not applied to the outer peripheral side. Since the swirl is applied to the central part, the mixed fluid flowing through the central part of the primary air nozzle 9 moves to the outer peripheral side.

[0102] Thereby, the particle concentration in the vicinity of the flame stabilizer 10 of the primary air nozzle 9 is increased. In addition, since swirl is not applied to the outer peripheral side of the primary air nozzle 9, the pulverized coal particles moved to the outer peripheral side do not scatter to the outer periphery of the burner in the furnace 13.

[0103] On the other hand, in Comparative Example 2 (broken line D), a strong swirl is applied to the outer peripheral side of the primary air nozzle 9. Since the swirl is also applied to the central part of the primary air nozzle 9, there is an effect of increasing the particle concentration in the vicinity of the flame stabilizer 10 of the primary air nozzle 9. However, since the swirl strength on the outer peripheral side of the primary air nozzle 9 is strong, it becomes difficult to adjust the swirl strength at the burner outlet. Accordingly, also in the burner 21 illustrated in FIG. 21, since the swirl vane 26 and the straightening plate 27 are in contact with the inner wall 29a of the pulverized coal supply pipe 29, it can be said that the same problem occurs.

[0104] Next, the concentration distribution of the pulverized coal is calculated, then the effect of the present example is further verified, and the results thereof are illustrated in FIGS. 5 and 6. FIG. 5 illustrates the concentration distribution at the time of a high load in which the average concentration of pulverized coal is high, and FIG. 6 illustrates the concentration distribution at the time of a low load in which the average concentration of pulverized coal is low. As illustrated in FIGS. 5(A) and 6(A), the concentration distribution of the pulverized coal on the outermost peripheral side of the primary air nozzle 9 is illustrated along the circumferential direction. By setting the position on the left side to be 0, the concentration was measured clockwise as viewed from the furnace 13, and the position was represented by an angle. FIGS. 5B and 6B illustrate the concentration distribution of the pulverized coal in the burner 1 of FIG. 1, and FIGS. 5C and 6C illustrate the concentration distribution of the pulverized coal in the burner of the comparative example 2. It illustrates that the concentration of the pulverized coal on the vertical axis becomes higher according to the direction of the arrow (upper direction).

[0105] The concentration distributions of the pulverized coal under the rated load condition amount of the burner of FIG. 1 and the burner of the comparative example 2 were calculated using the fluid analysis by the k- model similar to the case of FIG. 3.

[0106] In these burners, since the pulverized coal is concentrated due to a centrifugal effect at the curved tube section 5, there is tendency of easily increasing the pulverized coal concentration on the upper side (outside the curved section).

[0107] In the case of Comparative Example 2, the particle concentration is substantially equal over the entire circumference. That is, since the vanes 6a of the first swirler 6 are in contact with the inner wall 9a, the swirling strength on the outer peripheral side of the primary air nozzle 9 is strong, and the pulverized coal on the outer peripheral side is agitated to be a uniform concentration. Accordingly, as illustrated in FIGS. 5(C) and 6(C), there is no concentration change in the circumferential direction. Meanwhile, in the burner 1 of FIG. 1, since the swirling force at the central part of the primary air nozzle 9 is strong, but swirl is not adequately applied to the outer peripheral part, the pulverized coal on the outer peripheral side is not agitated much. Therefore, in terms of the concentration distribution in the circumferential direction, there occurs portions with high and low pulverized coal concentrations, respectively.

[0108] FIGS. 5 and 6 also illustrate an ignition lower limit concentration E. In order to achieve stable combustion in the burner, it is necessary for at least a part of the pulverized coal concentration to exceed the ignition lower limit concentration E. When there is a place where the pulverized coal concentration exceeds the ignition lower limit concentration E, a flame is formed at the place, and the flame propagates around the place. Under conditions in which the load is high and the average pulverized coal concentration is also high, as illustrated in FIGS. 5(B) and 5(C), both of the pulverized coal concentrations exceed the ignition lower limit concentration E, and there is no difference therebetween.

[0109] When the load is low and the average pulverized coal concentration is also low, in Comparative Example 2, as illustrated in FIG. 6(C), there is no place where the pulverized coal concentration is locally high, and the pulverized coal concentration in all regions becomes below the lower limit concentration E, such that stable combustion is not achieved. Further, it is not necessary for the pulverized coal concentration to exceed the ignition lower limit concentration E in all positions, and as illustrated in FIG. 6(B), there is a region in which the pulverized coal concentration is locally high. If the concentration exceeds the ignition lower limit concentration E, it is possible to achieve the stable combustion even under a low load condition.

[0110] From the above description, according to the present example, the mixed fluid having the concentration distribution produced by the curved tube section 5 is moved outward in the radial direction from the central part by the first swirler 6 to increase the fuel concentration in the vicinity of the inner wall 9a, and a reverse swirl is applied thereto by the second swirler 7, such that the swirl strength may be reduced at once. Accordingly, even in the burner 1 without the flame stabilizer 10, if it is in the state that the fuel concentration in the vicinity of the inner wall 9a is high and the swirl strength is reduced, ignitability of the outlet of the primary air nozzle 9 is improved. In addition, it is not necessary to secure the flow path length of the mixed fluid, and the sizes of the primary air nozzle 9 and the burner 1 are not increased.

[0111] Further, by providing the flame stabilizer 10 in the outlet of the primary air nozzle 9, the ignitability and the stability of the flame are further improved, and effects of improving the stability of the flame and reducing the NOx emission amount are further enhanced. In addition, the first swirler 6 and the second swirler 7 may be easily formed with a simple configuration that the respective vanes 6a and 7a are attached to the outer periphery of the oil burner 8. Further, by attaching the vanes 6a and 7a away from the inner wall 9a, the effect of improving the stability of the flame is also enhanced and stable combustion mast be achieved. Furthermore, it is easy to install and remove the vanes 6a and 7a, and the maintainability is enhanced.

EXAMPLE 2

[0112] FIG. 7 is a side view (schematic view) illustrating a partial cross-section of a solid fuel burner 1 according to another example of the present disclosure. FIG. 8 illustrates a first swirler and a second swirler in FIG. 7, wherein FIGS. 8(A) and 8(C) are front views, respectively, FIG. 8(B) is a view seen from S1 in FIG. 8(A), and FIG. 8(D) is a view seen from 82 in FIG. 8(C).

[0113] In the present example, the installation angle of the vanes 7a of the second swirler 7 with respect to the burner central axis direction is smaller than the installation angle of the vanes 6a of the first swirler 6, and the other configurations are the same as those of the solid fuel burner 1 according to Example 1. As such, even if the installation angle of the vanes 7a of the second swirler 7 and the installation angle of the vanes 6a of the first swirler 6 are changed, the same effects as those of Example 1 are obtained.

[0114] Further, since there is no particular limitation on the positions of the axial direction of the first swirler 6 and the second swirler 7, various examples are illustrated. In particular, there is no difference in action and effect. These are the same as the other examples.

EXAMPLE 3

[0115] FIG. 9 is a side view (schematic view) illustrating a partial cross-section of a solid fuel burner 1 according to another example of the present disclosure. FIG. 10 illustrates a first swirler and a second swirler in FIG. 9, wherein FIGS. 10(A) and 10(C) are front views, respectively, FIG. 10(B) is a view seen from S1 in FIG. 10(A), and FIG. 10(D) is a view seen from S2 in FIG. 10(C).

[0116] In the present example, the radial length of the vanes 7a of the second swirler 7 is set to be shorter than the radial length of the vanes 6a of the first swirler 6, thus to decrease the size as a whole. The other configurations are the same as those of the solid fuel burner 1 according to Example 1. Therefore, the installation angle and the shape of the vanes 6a and the vanes 7a are the same as those of Example 1. As such, even if the radial length of the vanes 7a of the second swirler 7 and the radial length of the vanes 6a of the first swirler 6 are changed, the same effects as those of Example 1 may be obtained.

EXAMPLE 4

[0117] FIG. 11 is a side view (schematic view) illustrating a partial cross-section of a solid fuel burner 1 according to another example of the present disclosure. FIG. 12 illustrates a first swirler and a second swirler in FIG. 11, wherein FIGS. 12(A) and 12(C) are front views, respectively, FIG. 12(B) is a view seen from S1 in FIG. 12(A), and FIG. 12(D) is a view seen from S2 in FIG. 12(C).

[0118] In the present example, the lateral width of the vanes 7a of the second swirler 7 is set to be smaller than the lateral width of the vanes 6a of the first swirler 6, thus to have a narrow shape. The other configurations are the same as those of the solid fuel burner 1 according to Example 1. Therefore, the installation angle and the radial length of the vanes 6a and the vanes 7a are the same as those of Example 1. As such, even if the lateral width of the vanes 7a of the second swirler 7 and the lateral width of the vanes 6a of the first swirler 6 are changed, the same effects as those of Example 1 are obtained.

[0119] Hereinafter, the results of further intensive verification performed by changing three conditions of the installation angle, the radial length, and the lateral width of the respective vanes 6a and 7a of the first swirler 6 and the second swirler 7 are illustrated. FIG. 13 illustrates the swirl strength distributions in the vicinity of the burner outlet when the swirler is changed. The fluid analysis by the k- model was executed under a condition that the air and the pulverized coal flow at a rated load condition amount of the burner from the direction of an arrow A in FIG. 1 similar to the case of FIG. 4.

[0120] A broken line F illustrates a case in which the diameters of the respective vanes 6a and 7a are set to be 75% of the inner diameter of the primary air nozzle 9, and the installation angle is set to be 30 on both the upstream side and the downstream side in the exhaust gas flow direction. A one-dotted chain line G illustrates a case in which the diameter of the vanes 6a on the upstream side is set to be 75% of the inner diameter of the primary air nozzle 9, the installation angle is set to be 45, the diameter of the vanes 7a on the downstream side is set to be 75% of the inner diameter of the primary air nozzle 9, and the installation angle is set to be 25. A solid line H illustrates a case in which the diameter of the vanes 6a on the upstream side is set to be 75% of the inner diameter of the primary air nozzle 9, the installation angle is set to be 30, the diameter of the vanes 7a on the downstream side is set to be 50% of the inner diameter of the primary air nozzle 9, and the installation angle is set to be 45. A broken line J illustrates a case in which the diameter of the vanes 6a on the upstream side is set to be 75% of the inner diameter of the primary air nozzle 9, the installation angle is set to be 30, the diameter of the vanes 7a on the downstream side is set to be 75% of the inner diameter of the primary air nozzle 9, and the installation angle is set to be 45. The lateral widths of the respective vanes 6a and 7a were the same as each other.

[0121] Similar to the case of FIG. 4, the swirl strength distribution of the air at the burner outlet cross-section in the primary air nozzle 9 was calculated.

[0122] The condition necessary for improving the stability of the flame and suppressing the NOx emission amount is that the swirl strength on the outermost peripheral side of the primary air nozzle 9 is minimized as much as possible. Since the pulverized coal concentration on the outermost peripheral side of the primary air nozzle 9 is high, if the swirling strength in this region is strong, the pulverized coal on the outermost peripheral side scatters around the burner 1, such that the stability of the flame is deteriorated, and the NOx concentration is increased. Meanwhile, since there is not much pulverized coal near the central part of the primary air nozzle 9, an influence applied to the combustion performance is small, even if the swirl strength at the central part is strong.

[0123] In the broken line F (Example 1), the swirl strength at the central part of the primary air nozzle 9 is relatively large, but on the outer peripheral side of the primary air nozzle 9, the swirl strength becomes about zero. In addition, in the one-dotted chain line G (Example 2), the swirl strength at the central part of the primary air nozzle 9 becomes small. The swirl strength on the outer peripheral side is slightly larger than the broken line F, but it is a small value. Meanwhile, a case, in which the installation angle of the vanes 7a of the second swirler 7 is large, is indicated by a broken line J. In this case, the swirl strength is slightly increased also on the outer peripheral side of the primary air nozzle 9.

[0124] However, as illustrated by the solid line H, even if the installation angle of the vanes 7a of the second swirler 7 is large, when the diameter of the vanes 7a is small, it becomes to the swirl strength distribution similar to the one-dot chain line G. Further, when the average value of the swirl strength is taken over the entire region from the central part to the outer peripheral part, it becomes substantially zero.

[0125] Further, although not illustrated, the swirl strength distribution in a case (Example 4), in which the lateral width of the vanes 7a of the second swirler 7 is decreased, and the other conditions are the same as those of the vanes 6a of the first swirler 6, it also becomes the swirl strength distribution similar to Example 2 (one-dot chain line G). Accordingly, from this fact, it can be seen that, as a difference between the cases in which the lateral width of the vane 7a of the second swirler 7 is small and large, there is the same difference of action as the magnitude of the installation angle and the diameter of the vanes 7a of the second swirler 7.

[0126] From the above description, it is preferable that the vanes 7a of the second swirler 7 on the downstream side of the first swirler 6 satisfy the following conditions.

[0127] (1) The radial length of the vanes 7a is equal to or smaller than the radial length of the vanes 6a of the first swirler 6.

[0128] (2) The installation angle of the vanes 7a is equal to or smaller than the installation angle of the vanes 6a.

[0129] (3) The lateral width of the vanes 7a is equal to or smaller than the lateral width of the vanes 6a.

[0130] In addition, there is no particular limitation on the installation position and interval of the first swirler 6 and the second swirler 7. This is common to all examples. For example, as illustrated in FIG. 14, the first swirler 6 and the second swirler 7 may be installed away from each other as compared with other illustrated examples. Further, if the second swirler 7 is provided in the vicinity of the burner outlet, it is conceivable that a strong swirl component remains at the burner outlet, and the coal particles widely scatter in the furnace 13, and the NOx concentration is increased, such that it is preferable to slightly separate the second swirler from the outlet.

EXAMPLE 5

[0131] FIG. 15 illustrates a side view illustrating a partial cross-section of a solid fuel burner according to another example of the present disclosure. FIG. 16(A) illustrates a perspective view of major parts (inside of the nozzle 9) in FIG. 15, FIG. 16(B) illustrates a view of the major parts in FIG. 15, FIG. 16(C) illustrates a cross-sectional view taken and seen on line A-A in FIG. 16(B), and FIG. 16(D) illustrates a cross-sectional view taken and seen on line B-B in FIG. 16(B).

[0132] A solid fuel burner 1 of the present example is different from the solid fuel burner of the above-described respective examples in an aspect that a disperser 14 of pulverized coal particles is disposed on the upstream side of the first swirler 6 and in a space of the curved tube section 5 located on a root side of the oil burner 8, and the flame stabilizer 10 is not installed. Specifically as illustrated in FIG. 16, the disperser 14 is a plate-shaped member having a plane part, and is attached to, the lateral face of the oil burner 8 so that the plane part faces the upstream side of the curved section of the curved tube section 5.

[0133] That is, the plane part is directed to face the flow of the mixed fluid of the solid fuel and the carrier gas thereof introduced into the curved tube section 5. In addition, the first swirler 6 and the second swirler 7 are installed so that the respective vanes 6a and 7a are overlapped with each other as viewed from the furnace 13, but these swirlers may be disposed so as not to be overlapped with each other, as illustrated in Example 1 and the like.

[0134] FIG. 17 is a schematic view illustrating a flow field of the mixed fluid of the burner 1 pursuant to FIG. 1 without the disperser 14, wherein FIG. 17(A) is a side view, and FIG. 17(B) is a front view FIG. 18 is a schematic view illustrating a flow field of the mixed fluid of the burner 1 in FIG. 15 provided with the disperser 14, wherein FIG. 18(A) is a side view, and FIG. 18(B) is a front view.

[0135] FIGS. 17 and 18 illustrate a difference in the flow field of the mixed fluid depending on the presence or absence of the disperser 14. First, the flow field in a case in which the disperser 14 of FIG. 17 is not provided will be described. The mixed fluid supplied from the lower side of the curved tube section 5 moves via the curved tube section 5, such that the direction of the flow in the outlet direction of the straight tube section 2 (in the central axis direction of the primary air nozzle 9) is bent by about 90. At this time since the centrifugal force acts on the mixed fluid, when viewing the primary air nozzle 9 after passing through the curved tube section 5 as a cross-section, it becomes a state in which the pulverized coal is biased in the direction on which the centrifugal force acts. In the illustrated example, it shows the part in which the pulverized coal concentration in the vicinity of the inner wall 9a in an upper half of the primary air nozzle 9 is high. Even in this case, by applying the above-described first swirler 6 and the second swirler 7, it is possible to form a state in which the pulverized coal concentration exceeds the ignition lower limit concentration E (FIG. 6(B) even when the average pulverized coal concentration is low such as at the time of a low load or the like, but from the viewpoint of stable combustion of the burner, it is desirable to further enlarge the region in which the pulverized coal concentration exceeds the ignition lower limit concentration E.

[0136] Next, the flow field in a case in which the disperser 14 of FIG. 18 is provided will be described. In the present example, since the disperser 14 is disposed in the curved tube section 5, the disperser 14 becomes an obstacle when viewed from the mixed fluid supplied to the curved tube section 5. Thereby, the flow direction of the mixed fluid is changed in a direction (circumferential direction) bypassing the disperser 14. In addition, a part of the pulverized coal collides with the plane part of the disperser 14, and the concentration of the pulverized coal on the upper side (outside of the curved section) of the primary air nozzle 9 due to the centrifugal effect at the curved tube section 5 is mitigated. As a result, like a flow line L2, there is an effect of enlarging a high concentration region of the pulverized coal in the circumferential direction on the nozzle outer peripheral side by the first swirler 6 and the second swirler 7.

[0137] FIG. 19 illustrates the concentration distribution when the average pulverized coal concentration is low at the time of a low load. Similar to the case of FIG. 3, the fluid analysis by the k- model was executed. FIG. 19(B) is a diagram in which the concentration distribution (indicated by a one-dot chain line M) by the burner 1 of the present example is added to FIG. 6(B), and FIG. 19(C) is the same as FIG. 6(C).

[0138] According to the present example, the state in which the pulverized coal concentration concentrates on the upper side of the primary air nozzle 9 by the disperser 14 is mitigated, and the high concentration region of the pulverized coal acts so as to be enlarged in the circumferential direction. Accordingly, even when the average pulverized coal concentration is low, the mixed fluid is dispersed to the outer peripheral side of the primary air nozzle 9, whereby the region in which the pulverized coal concentration exceeds the ignition lower limit concentration E becomes wide, and stable combustion of the burner may be achieved.

[0139] In addition, FIG. 15 and the like illustrate the case in which the radial length of the vanes 7a of the second swirler 7 is set to be shorter than the radial length of the vanes 6a of the first swirler 6, but the respective vanes 6a and 7a of the first swirler 6 and the second swirler 7 may be the same as or different from each other in terms of the installation angle, the radial length, and the lateral width, and of course, these configurations belong within the scope of the present example. In addition, as illustrated in FIG. 20, the flame stabilizer 10 may be installed in the burner 1 of FIG. 15, and in this case, the effects of improving the stability of the flame and reducing the NOx emission amount are further enhanced.

INDUSTRIAL APPLICABILITY

[0140] The present disclosure has industrial availability as a burner apparatus using a solid fuel.

DESCRIPTION OF REFERENCE NUMERALS

[0141] 1, 21 solid fuel burner

[0142] 2, 22 straight tube section

[0143] 3 secondary air nozzle

[0144] 4 tertiary air nozzle

[0145] 5, 25 curved tube section

[0146] 6 first swirler

[0147] 7 second swirler

[0148] 8 oil burner

[0149] 9 primary air nozzle

[0150] 10 flame stabilizer

[0151] 13 furnace

[0152] 14 particle disperser

[0153] 23 secondary air supply pipe

[0154] 24 tertiary air supply pipe

[0155] 26 swirl vane

[0156] 27 adjustment vane (straightening plate)

[0157] 28 liquid fuel injection pipe

[0158] 29 pulverized coal supply pipe