WO2018142772A1 - Combustion burner and boiler provided with same - Google Patents

Abstract

Provided is a combustion burner (100A) provided with a fuel nozzle (110), a secondary air nozzle (120), a secondary air flow channel (121) formed between the secondary air nozzle (120) and the fuel nozzle (110), a secondary air introduction flow channel (130) that introduces at least some of secondary air flowing through the secondary air flow channel (121) into a fuel gas flow channel (111), and a flame stabilizer (140) disposed within the fuel nozzle (110), the relationship 2 ≤ L/W ≤ 5 being satisfied, where L is a gas-flow-direction distance along an axis (X1) from an introduction position (P1) where the at least some of the secondary air is introduced from the secondary air introduction flow channel (130) into the fuel gas flow channel (111) to an installation position (P4) where the flame stabilizer (140) is installed, and W is the minimum width of the fuel gas flow channel (111) extending from the introduction position (P1) to the installation position (P4).

Description

Combustion burner and boiler equipped with the same

The present invention relates to a combustion burner applied to a boiler for generating steam for power generation or factory use, and a boiler equipped with the combustion burner.

Conventionally, combustion provided with a fuel nozzle for supplying a fuel gas, which is a mixture of a pulverized carbon-containing solid fuel such as pulverized coal, and a carrier gas to the furnace, and an air nozzle for supplying air to the furnace from the outside of the fuel nozzle A burner is known (see, for example, Patent Document 1 and Patent Document 2).
The combustion burner of Patent Document 1 is provided with an additional air nozzle that ejects additional air having a velocity component in the circumferential direction of the fuel nozzle, and promotes mixing of the fuel and air conveyed by a low oxygen concentration carrier gas. is there. Further, the combustion burner of Patent Document 2 arranges a divergence cone near the center axis of the fuel nozzle to reduce the amount of fuel flowing along the center axis, and introduces heated gas into the fuel nozzle so that the central portion of the primary flow The fuel gasification is promoted by increasing the stoichiometric ratio of the fuel to the fuel.

Japanese Patent Laying-Open No. 2005-140480 (paragraphs 0081-0084) JP-T-2011-523013 (paragraph 0022)

A combustion burner is known in which a flame holder that forms a recirculation flow in the vicinity of the central axis of the fuel nozzle in the upstream portion of the fuel gas flow from the tip of the fuel nozzle is known. In the fuel nozzle where the flame holder is installed, the fuel is ignited by receiving radiation from the adjacent flame, and the high-temperature gas generated by the ignition is kept in the vicinity of the ignition part as a recirculation flow by the flame holder. Flame holding is performed. The case where this flame stabilizer is installed on the outer periphery of the mixed flow of pulverized coal and primary air is called outer periphery ignition or external flame holding, and the case where it is installed inside the cross section of the mixed flow is internal ignition or internal flame holding. That's it. Reduction of NOx can be realized by reducing nitrogen oxide (NOx) generated by combustion in a reducing atmosphere with insufficient air.
In order to improve the ignitability of the fuel at the tip of the fuel nozzle adjacent to the furnace, the ratio of the mass of air to the mass of, for example, coal (pulverized coal) as the carbon-containing solid fuel (hereinafter referred to as “A / C ratio”) It is desirable to promote ignition by surrounding flame radiation.

However, if the A / C ratio is too low, the oxidative combustion of the fuel near the tip of the fuel nozzle in the furnace increases with an increase in the unburned fuel, and the amount of NOx generated increases due to the high flame temperature. there's a possibility that.
On the other hand, if the A / C ratio in the fuel gas is too high, the release of combustible volatiles contained in the fuel is delayed due to the difficulty of receiving the radiation of the surrounding flame, and the delay in contact with the secondary air. There is a possibility that the amount of NOx generated increases due to the high flame temperature due to the oxidative combustion of the released volatile matter.

In the above-mentioned Patent Document 1, additional air is jetted in the vicinity of the fuel nozzle outlet in order to accelerate the ignition of the fuel conveyed by the carrier gas having a low oxygen concentration. However, in Patent Document 1, since many of the fuel particles flow along the outer partition wall of the fuel nozzle by the concentrator, external ignition or external flame holding is performed. In the external ignition method with a flame holder on the outer periphery of the nozzle, if the A / C ratio increases, the jet velocity of the pulverized coal flow only increases and the recirculation zone around the flame holder does not change. Will leave. Therefore, in Patent Document 1, the amount of NOx generated increases due to external ignition or external flame holding.

In Patent Document 2, a secondary flow is introduced into the upstream portion of the outlet end of the fuel injector in order to increase the stoichiometric ratio in the central portion of the primary flow. However, in Patent Document 2, the amount of fuel flowing to the outer peripheral side of the central shaft is increased by the diverging cone provided in the fuel injector, so external ignition or external flame holding is performed. Therefore, in Patent Document 2, the amount of NOx generated increases due to external ignition or external flame holding.

The present disclosure solves the above-described problem, and can reduce the amount of NOx generated by promoting the release of combustible volatiles contained in the fuel while suppressing the release of unburned fuel to the furnace. An object of the present invention is to provide a combustion burner and a boiler including the combustion burner.

In order to achieve the above object, a combustion burner according to the present disclosure includes a fuel gas flow that extends in a cylindrical shape along an axis and supplies a fuel gas obtained by mixing a fuel containing pulverized carbon-containing solid fuel and primary air to a furnace. A fuel nozzle that forms a path, a secondary air nozzle that extends in a cylindrical shape along the axis and through which secondary air having a higher temperature than the fuel gas flows, and is formed between the secondary air nozzle and the fuel nozzle A secondary air flow path for supplying the secondary air to the furnace, and a secondary air introduction flow path for introducing at least part of the secondary air flowing through the secondary air flow path into the fuel gas flow path And a flame holder disposed in the vicinity of a tip portion opened to the furnace in the fuel nozzle, wherein the secondary air introduction flow path is at least part of the secondary air to the fuel gas flow path. From the introduction position to introduce the flame holding 2 ≦ L / W ≦ 5, where L is the distance in the gas flow direction along the axis to the installation position, and W is the minimum width of the fuel gas flow path from the introduction position to the installation position. Fulfill.

According to the combustion burner of the present disclosure, at least a part of the secondary air having a temperature higher than that of the fuel gas flowing through the secondary air flow path is generated from the secondary air flow path by the secondary air introduction flow path. The fuel gas, which is a mixture of the pulverized fuel and the primary air, is guided to the fuel gas flow path. Since the flame holder is disposed in the vicinity of the tip of the fuel nozzle that opens to the furnace, the ignitability of the fuel at the outlet of the fuel gas passage is improved and the flammable volatile matter contained in the fuel is released. Since the combustion of fixed carbon is promoted and the reduction of NOx is promoted, the amount of NOx generated is reduced.

In addition, since the flame holder holds the flame on the primary air side, even if the flow rate of the secondary air flowing through the secondary air flow path is reduced by guiding at least a part of the secondary air to the fuel gas flow path side, Good flame holding can be realized. In addition, when the flame holder is a structure, the recirculation zone formed around the flame holder is strengthened by mixing the secondary air and increasing the flow velocity around the internal flame holder. Can keep ignition strong. If ignition can be kept strong, the mixed flow of fuel and primary air will be supplied in a shortage of air, and the volatile matter and unburned matter of pulverized coal will have a NOx reduction effect. It can be fully reduced in the jet. On the other hand, since secondary air is supplied to the outside of the jet, the air is in an excessive state and the amount of NOx reducing substance is small, so that NOx produced on the outer periphery is difficult to be reduced, leading to an increase in the amount of NOx generated.

For this reason, if ignition can be maintained by increasing the A / C ratio with a combustion burner having a flame holder, the unburned portion of the fuel obtained by pulverizing the carbon-containing solid fuel is present at the outlet of the fuel gas passage. In addition to the reduction, the release of combustible volatiles contained in the pulverized fuel and the combustion of fixed carbon are promoted, and NOx is generated once and its reduction is promoted. Further, since the secondary air around the outer periphery of the fuel jet that is difficult to reduce NOx is reduced, the amount of NOx generated can be reduced.

In the combustion burner of the present invention, since at least a part of the secondary air is guided to the fuel gas flow path, it is not necessary to increase the flow rate of the primary air in order to increase the A / C ratio of the fuel gas. Therefore, it is possible to suppress problems such as an increase in the power of the ventilator due to an increase in the flow rate of the primary air, a decrease in the classification accuracy of the pulverizer, and an increase in the wear amount of the transport pipe that transports the fuel.

In the combustion burner of the present invention, the distance in the gas flow direction along the axis from the introduction position of the secondary air to the installation position of the flame stabilizer is L, and the fuel gas flow path from the introduction position to the installation position When the minimum width is W, 2 ≦ L / W ≦ 5 is satisfied. The reason why 2 ≦ L / W is set is to secure a sufficient distance for uniformly mixing the fuel gas passing through the flame holder with the secondary air. Moreover, L / W1 ≦ 5 is set to prevent an increase in the size of the combustion burner.
In this way, the combustion burner is prevented from being enlarged while ensuring a sufficient distance in the gas flow direction from when the secondary air is introduced into the fuel gas passage until it reaches the flame holder. In addition, ignition or flame holding by the flame holder can be performed in a state where the secondary air and the fuel gas have a more uniform concentration distribution.

According to the present disclosure, there is provided a combustion burner capable of reducing the amount of NOx generated by promoting the release of combustible volatile components contained in the fuel while suppressing the release of unburned fuel to the furnace. A boiler can be provided.

It is a schematic structure figure showing the pulverized coal burning boiler to which the combustion burner of a 1st embodiment was applied. It is a top view showing the combustion burner in the pulverized coal burning boiler of 1st Embodiment. It is a longitudinal cross-sectional view which shows the combustion burner of 1st Embodiment. It is an II arrow end view of the combustion burner shown in FIG. It is a perspective view which shows a part of combustion burner shown in FIG. It is a schematic block diagram showing the pulverized coal burning boiler of 2nd Embodiment. It is a longitudinal cross-sectional view which shows the combustion burner of 3rd Embodiment. It is an III-III arrow end view of the combustion burner shown in FIG. It is an III-III arrow end view of the combustion burner shown in FIG. It is a top view showing the combustion burner in the pulverized coal burning boiler of 4th Embodiment.

Hereinafter, preferred embodiments of the combustion burner of the present disclosure will be described in detail with reference to the accompanying drawings. It should be noted that the present disclosure is not limited by this embodiment, and when there are a plurality of embodiments, the embodiment includes a combination of the embodiments.

<First Embodiment>
The pulverized coal fired boiler to which the combustion burner of the first embodiment is applied uses pulverized coal obtained by pulverizing coal as a carbon-containing solid fuel, burns the pulverized coal with a combustion burner, and recovers heat generated by the combustion. It is a possible boiler.

As shown in FIG. 1, the pulverized coal fired boiler 10 of the present embodiment is a conventional boiler, and includes a furnace 11, a combustion device 12, and a flue 13. The furnace 11 has a rectangular hollow shape and is installed along the vertical direction. A combustion device 12 is provided at the lower part of the furnace wall constituting the furnace 11.

The combustion apparatus 12 has a plurality of combustion burners 100A, 100B, 100C, 100D, and 100E mounted on the furnace wall. In this embodiment, the combustion burners 100A, 100B, 100C, 100D, and 100E are arranged as a set having four equal intervals along the circumferential direction with the vertical direction in which the furnace 11 extends as the central axis. 5 sets (5 stages) are arranged along the vertical direction. In addition, although it was set as 5 sets here, it can be set to 6 sets or other arbitrary sets.

Each combustion burner 100A, 100B, 100C, 100D, 100E is supplied to a pulverized coal machine (mill; pulverizer) 31, 32, 33, 34, 35 via a pulverized coal supply pipe 26, 27, 28, 29, 30. It is connected to. Although not shown, the pulverized coal machines 31, 32, 33, 34, and 35 are supported in a housing so that the pulverization table can be driven to rotate with a rotation axis along the vertical direction, and face the upper side of the pulverization table. A plurality of crushing rollers are configured to be rotatably supported in conjunction with the rotation of the crushing table. Accordingly, when coal is introduced between a plurality of crushing rollers and a crushing table, pulverized coal that has been crushed to a predetermined size and classified by air for transportation (primary air) is supplied to the pulverized coal supply pipe 26, 27, 28, 29, 30 are supplied to the combustion burners 100A, 100B, 100C, 100D, 100E.

Further, the furnace 11 is provided with a wind box 36 at a mounting position of each combustion burner 100A, 100B, 100C, 100D, 100E, and one end portion of an air duct (secondary air supply pipe) 37 is provided in the wind box 36. The air duct 37 is connected to a blower 38 at the other end. Furthermore, the furnace 11 is provided with an additional air nozzle 39 vertically above the mounting position of each combustion burner 100A, 100B, 100C, 100D, 100E. The additional air nozzle 39 is connected to an end of a branched air duct 40 branched from the air duct 37. Therefore, the combustion air (secondary air) sent by the blower 38 is supplied from the air duct 37 to the wind box 36 and supplied from the wind box 36 to the combustion burners 100A, 100B, 100C, 100D, and 100E. In addition, combustion air (additional air) sent by the blower 38 can be supplied from the branch air duct 40 to the additional air nozzle 39.

Therefore, in the combustion apparatus 12, each combustion burner 100 </ b> A, 100 </ b> B, 100 </ b> C, 100 </ b> D, 100 </ b> E has a pulverized fuel mixture (fuel gas) obtained by mixing pulverized coal and carrier air (primary air) in the furnace 11. In addition to being able to blow, combustion air can be blown into the furnace 11. The combustion device 12 can form a flame by igniting the pulverized fuel mixture with an ignition torch (not shown).

In the furnace 11, a flue 13 is connected to an upper part in the vertical direction, and a superheater (super heater) 41, which is a heat exchanger for recovering heat of combustion gas as a convection heat transfer section, is connected to the flue 13. 42, reheaters 43 and 44, and economizers 45, 46, and 47 are provided, and heat exchange is performed between the combustion gas generated by the combustion in the furnace 11 and water or steam.

The flue 13 is connected to an exhaust gas pipe 48 through which the combustion gas subjected to heat exchange is discharged as exhaust gas on the downstream side of the gas flow. The exhaust gas pipe 48 is provided with an air heater 49 between the air duct 37 and performs heat exchange between the air flowing through the air duct 37 and the exhaust gas flowing through the exhaust gas pipe 48, and the combustion burners 100A, 100B, 100C, The temperature of combustion air supplied to 100D and 100E can be raised. The combustion air is heated to 280 ° C. to 320 ° C., for example.
Although not shown, the exhaust gas pipe 48 is provided with a denitration device, an electrostatic precipitator, an induction blower, and a desulfurization device, and a chimney is provided at the downstream end.

Therefore, when the pulverized coal machines 31, 32, 33, 34, and 35 are driven, the generated pulverized coal together with the air for conveyance (primary air), the pulverized coal supply pipes (fuel supply pipes) 26, 27, 28, 29, 30 is supplied to the combustion burners 100A, 100B, 100C, 100D, and 100E. Also, heated combustion air (secondary air) is supplied from the air duct 37 to the combustion burners 100A, 100B, 100C, 100D, and 100E through the wind box 36, and an additional air nozzle is supplied from the branch air duct 40. 39. The temperature of the carrier air (primary air) is low so that the pulverized coal does not ignite, and the combustion air (secondary air) is heated by the air heater 49, so the temperature is higher than the primary air and the pulverized fuel mixture. .

Then, the combustion burners 100A, 100B, 100C, 100D, and 100E blow the pulverized fuel mixture (fuel gas), which is a mixture of pulverized coal and carrier air, into the furnace 11 and the combustion air into the furnace 11. By igniting, a flame can be formed. Further, the additional air nozzle 39 can perform combustion control for blowing additional air into the furnace 11 and optimizing the amount of air with respect to the pulverized coal. In the furnace 11, the pulverized fuel mixture and the combustion air are burned to generate a flame. When a flame is generated in a region in the lower vertical direction in the furnace 11, the combustion gas (exhaust gas) rises in the furnace 11. And discharged to the flue 13.

That is, the combustion burners 100A, 100B, 100C, 100D, and 100E blow the pulverized coal mixture and the combustion air (secondary air) into the combustion region in the furnace 11, and ignite at this time, so that the flame swirls in the combustion region. Is formed. This flame swirl rises while swirling and reaches the reduction region. The additional air nozzle 39 blows additional air vertically above the reduction region in the furnace 11. In the furnace 11, the interior is maintained in a reducing atmosphere by setting the air supply amount to be less than the theoretical air amount with respect to the pulverized coal supply amount. The NOx generated by the combustion of the pulverized coal is reduced in the furnace 11, and then additional air (additional air) is supplied to complete the oxidation combustion of the pulverized coal, and the amount of NOx generated by the combustion of the pulverized coal is reduced. Reduced.

At this time, the water supplied from the water supply pump (not shown) is preheated by the economizers 45, 46 and 47, then supplied to the steam drum (not shown) and supplied to each water pipe (not shown) on the furnace wall. In the meantime, it is heated to become saturated steam and fed into a steam drum. Further, the saturated steam of the steam drum is introduced into the superheaters 41 and 42 and is heated by the combustion gas. The superheated steam generated by the superheaters 41 and 42 is supplied to a turbine (not shown) of the power plant. Further, the steam taken out in the middle of the expansion process of the steam supplied by the turbine is introduced into the reheaters 43 and 44, is again superheated, is returned to the turbine and expands, and the turbine is rotationally driven. In addition, although the furnace 11 was demonstrated as a drum type | mold (steam drum), it is not limited to this structure.

Thereafter, the exhaust gas that has passed through the economizers 45, 46, and 47 of the flue 13 is subjected to removal of harmful substances such as NOx by the supplied ammonia and catalyst in the denitration device (not shown) in the exhaust gas pipe 48, Particulate matter is removed with an electric dust collector, sulfur content is removed with a desulfurizer, and then discharged from the chimney into the atmosphere.

Here, although the combustion apparatus 12 is demonstrated in detail, since each combustion burner 100A, 100B, 100C, 100D, 100E which comprises this combustion apparatus 12 has comprised the substantially the same structure, it is located in the uppermost stage. Only the combustion burner 100A will be described.

As shown in FIG. 2, the combustion burner 100 </ b> A includes combustion burners 100 </ b> Aa, 100 </ b> Ab, 100 </ b> Ac, 100 </ b> Ad provided on four wall surfaces in the furnace 11. Each combustion burner 100Aa, 100Ab, 100Ac, 100Ad is connected to each branch pipe 26a, 26b, 26c, 26d branched from the pulverized coal supply pipe 26, and each branch pipe 37a, 37b, 37c branched from the air duct 37. , 37d are connected.

Therefore, each combustion burner 100Aa, 100Ab, 100Ac, 100Ad on each wall surface of the furnace 11 has a pulverized fuel mixture in which pulverized coal and transport air (primary air) are mixed with the furnace 11 in the center of the furnace 11. In contrast, the air is blown with a slight deviation angle, and combustion air (secondary air) is blown to the outside of the pulverized fuel mixture. Then, by igniting the pulverized fuel mixture from each combustion burner 100Aa, 100Ab, 100Ac, 100Ad, four flames F1, F2, F3, F4 can be formed, and this flame F1, F2, F3, F4 Is a flame swirl flow swirling counterclockwise as viewed from above the furnace 11 (in FIG. 2). In this example, the combustion burners 100Aa, 100Ab, 100Ac, and 100Ad may be arranged so as to form a flame swirl flow that rotates clockwise.

Next, the combustion burner 100A will be described in detail.
As shown in the longitudinal sectional view of FIG. 3, the combustion burner 100 </ b> A of the present embodiment includes a fuel nozzle 110, a secondary air nozzle 120, a secondary air introduction flow path 130, and a flame holder 140. 3 is a cross-sectional view taken along the line II-II of a combustion burner 100A shown in FIG. 4 to be described later.

The fuel nozzle 110 is a member formed to extend in a cylindrical shape along the axis X1. The fuel nozzle 110 forms therein a fuel gas passage 111 for supplying the pulverized fuel mixture supplied from the pulverized coal supply pipe 26 to the furnace 11.
The fuel nozzle 110 includes a distal end side nozzle 110a disposed adjacent to the furnace 11, and a proximal end side nozzle 110b disposed upstream of the distal end side nozzle 110a. The distal end side nozzle 110a and the proximal end side nozzle 110b are connected in a state where the secondary air introduction flow path 130 is disposed therebetween.

The shape of the portion of the tip side nozzle 110a facing the furnace 11 is a shape extending straight in the same direction as the gas flow direction of the pulverized fuel mixture. This is to prevent the pulverized coal contained in the pulverized fuel mixture from being guided to the outer peripheral side with respect to the central axis (axis line X1) of the fuel gas passage 111. When the pulverized coal contained in the pulverized fuel mixture is led to the outer peripheral side, the pulverized coal burns in the region in the high-temperature and high-oxygen concentration furnace 11, and the amount of NOx generated increases in the region where NOx is not reduced. End up. Therefore, the shape of the part where the tip side nozzle 110a faces the furnace 11 performs internal flame holding or internal ignition as a shape that suppresses external flame holding or external ignition.

As shown in FIGS. 3 and 4, the minimum width W1 of the front end side nozzle 110a of the fuel gas flow path 111 is larger than the minimum width W2 of the base end side nozzle 110b of the fuel gas flow path 111. This is because the flow rate of secondary air introduced from the secondary air introduction passage 130 to the fuel gas passage 111 increases, so that the flow rate of the pulverized fuel mixture flowing through the front end side nozzle 110a becomes the base end side nozzle 110b. This is so as not to increase more than the flow rate of the pulverized fuel mixture flowing through the fuel cell.
Therefore, the relationship between the minimum width W1 and the minimum width W2 is that the cross-sectional area of the tip nozzle 110a at the second position P2 on the downstream side of the gas flow with respect to the first position P1 is It is set to be larger than the cross-sectional area of the base end side nozzle 110b at the third position P3. Introducing a part of the secondary air from the secondary air introduction flow path 130 to the fuel gas flow path 111 suppresses problems due to an increase in the flow rate of the finely divided fuel mixture flowing through the fuel gas flow path 111, The internal flame holding can be stabilized.

The secondary air nozzle 120 is a member that is formed so as to extend in a cylindrical shape along the axis X1 and is disposed so as to surround the outside with respect to the axis X1 of the fuel nozzle 110. The secondary air nozzle 120 forms an annular secondary air flow path 121 that supplies secondary air to the furnace 11 between its inner peripheral surface and the outer peripheral surface of the fuel nozzle 110. A part of the combustion air (secondary air) flowing into the secondary air nozzle 120 is introduced from the secondary air introduction flow path 130 to the fuel gas flow path 111, and the other is in the secondary air flow path 121. It is supplied to the furnace 11 from the tip.

The secondary air introduction flow path 130 is a flow path for introducing a part of the secondary air flowing through the secondary air flow path 121 to the fuel gas flow path 111. 4 (end view of the combustion burner shown in FIG. 3 as viewed in the direction of arrow II) and FIG. 5, the secondary air introduction flow path 130 includes an upper introduction portion 131 disposed vertically above the fuel gas flow path 111. 132, 133, 134 and lower introduction portions 135, 136, 137, 138 disposed vertically below the fuel gas passage 111.

FIG. 5 is a perspective view showing a part of the combustion burner 100A shown in FIG. 3 with the secondary air nozzle 120 removed. In FIG. 5, the part arrange | positioned inside the fuel nozzle 110 among the secondary air introduction flow paths 130 is shown with the broken line.
In FIG. 5, arrows indicated by solid lines indicate the secondary air introduced from the secondary air passage 121 to the fuel gas passage 111 and the secondary air flowing through the secondary air passage 121 without being guided to the fuel gas passage 111. Indicates air. On the other hand, an arrow indicated by a broken line indicates a pulverized fuel mixture flowing through the fuel gas passage 111.

The upper introduction portions 131, 132, 133, and 134 are arranged in a dispersed manner at a certain interval along a horizontal direction perpendicular to the gas flow direction of the pulverized fuel mixture along the axis X1. Similarly, the lower introduction parts 135, 136, 137, and 138 are dispersed and arranged at a constant interval along a horizontal direction perpendicular to the gas flow direction of the pulverized fuel mixture along the axis X 1. Here, the intervals at which the upper introduction portions 131, 132, 133, and 134 and the lower introduction portions 135, 136, 137, and 138 are arranged are constant along the horizontal direction, but they may be arranged at arbitrary intervals. .

As shown in FIG. 4, a space in which the pulverized fuel mixture flows is provided between the upper introduction portion 131 and the upper introduction portion 132 at the vertical position where the upper introduction portions 131, 132, 133, and 134 are disposed. A space through which the pulverized fuel mixture flows is provided between the upper introduction portion 132 and the upper introduction portion 133, and a space through which the pulverized fuel mixture flows is provided between the upper introduction portion 133 and the upper introduction portion 134. It has been.

In addition, at the position in the vertical direction where the lower introduction portions 135, 136, 137, and 138 are arranged, a space is provided between the lower introduction portion 135 and the lower introduction portion 136 to allow the pulverized fuel mixture to flow therethrough. A space in which the pulverized fuel mixture flows is provided between 136 and the lower introduction portion 137, and a space in which the pulverized fuel mixture flows is provided between the lower introduction portion 137 and the lower introduction portion 138.
Thus, since the pulverized fuel mixture and the introduced secondary air circulate at the same position in the vertical direction, the pulverized fuel mixture and the introduced secondary air can be mixed well.

Note that, as shown in FIG. 3, a part of the member forming the secondary air introduction flow path 130 (the back side as the back side) forms a part of the fuel gas flow path 111. In particular, in the fuel gas flow path 111 from the third position P3 to the first position P1, a portion where the lower surface 133a of the upper introduction portion 133 and the upper surface 137a of the lower introduction portion 137 are arranged is a cross-sectional area of the fuel gas flow passage 111. The shape is gradually reduced. Therefore, the lower surface 133a and the upper surface 137a are easily worn by direct contact with the flow of pulverized coal in the pulverized fuel mixture. Therefore, it is preferable to install a wear-preventing member (for example, a ceramic plate-like member) in the portions of the lower surface 133a and the upper surface 137a facing the fuel gas flow path 111 in order to suppress wear.

The flame holder 140 is arranged on the upstream side of the gas flow in the ejection direction of the pulverized fuel mixture with respect to the tip side nozzle 110a of the fuel nozzle 110 adjacent to the furnace 11, and is used for ignition and flame holding of the pulverized fuel mixture. It functions as. The flame holder 140 has long widened portions 141, 142, and 143 that are formed to extend along the horizontal direction. As shown in FIG. 3, the widened portions 141, 142, and 143 are disposed in the vicinity of the tip portion 110 c where the fuel nozzle 110 faces the furnace 11, with an interval along the vertical direction.

In the present embodiment, as shown in FIG. 3, the widened portions 141, 142, and 143 have an isosceles triangular cross section, and in the gas flow direction toward the gas flow downstream side of the gas flow direction of the pulverized fuel mixture. The width of the orthogonal cross section is widened, and the front end is disposed on a plane orthogonal to the flow direction of the pulverized fuel mixture. The widened portions 141, 142, and 143 are not limited to the isosceles triangular cross section, and may have a split shape that separates the flow of the pulverized fuel mixture and forms a recirculation region downstream of the gas flow. For example, the cross section may be Y-shaped.

Here, the pulverized fuel mixture flowing through the fuel gas passage 111 and the secondary air introduced from the secondary air passage 121 are gently diffused and mixed to be supplied to the furnace 11 with a uniform concentration distribution. This will be explained. In addition, in the following description, although the upper introduction part 133 which the secondary air introduction flow path 130 has is demonstrated, since it is the same also about the upper introduction parts 131,132,134, description is abbreviate | omitted. Similarly, although the lower introduction part 137 which the secondary air introduction flow path 130 has is demonstrated, since it is the same also about the lower introduction parts 135,136,138, description is abbreviate | omitted.

The pulverized fuel mixture supplied from the pulverized coal supply pipe 26 to the fuel gas passage 111 flows from the proximal nozzle 110b to the distal nozzle 110a along the direction indicated by the arrow 201 in FIG. The gas flows from the third position P3 in the gas flow direction toward the first position P1.
On the other hand, combustion air (secondary air) supplied from the air duct 37 to the secondary air nozzle 120 flows into the secondary air flow path 121 along the directions indicated by arrows 301 and 302 in FIG.

A portion of the secondary air that has flowed into the secondary air flow path 121 flows into the upper introduction portion 133 along the direction indicated by the arrow 303 and is introduced vertically downward toward the axis X1 that is the central axis of the fuel nozzle 110. Then, it flows into the fuel gas flow path 111 along the direction indicated by the arrow 305. Further, part of the secondary air that has flowed into the secondary air flow path 121 flows into the lower introduction portion 137 along the direction indicated by the arrow 304, and vertically upwards toward the axis X 1 that is the central axis of the fuel nozzle 110. And flows into the fuel gas flow path 111 along the direction indicated by the arrow 306.

Here, the direction along the axis X2 indicated by the arrow 305 is the same direction as the axis X1, and the direction along the axis X3 indicated by the arrow 306 is the same direction as the axis X1. Therefore, the upper introduction part 133 and the lower introduction part 137 introduce a part of the secondary air into the fuel gas flow path 111 at a flow rate having a main component in the gas flow direction of the pulverized fuel mixture along the axis X1. The introduced secondary air is introduced from the secondary air introduction channel 130 to the fuel gas channel 111 at a flow velocity having a main component in the gas flow direction of the pulverized fuel mixture. Mix while gently diffusing without causing large disturbances.

Moreover, since the upper introduction parts 131, 132, 133, and 134 are arranged at intervals along the horizontal direction orthogonal to the gas flow direction of the pulverized fuel mixture, the introduced secondary air and the fine powder are arranged. The fuel mixture is mixed in a state adjacent to the fuel gas passage 111. Similarly, since the lower introduction portions 135, 136, 137, and 138 are discretely arranged along the horizontal direction orthogonal to the gas flow direction of the pulverized fuel mixture, the introduced secondary air and The pulverized fuel mixture is mixed in a state adjacent to the fuel gas flow path 111. The introduced secondary air and the pulverized fuel mixture are mixed in a state adjacent to each other in the fuel gas passage 111, and further, the secondary air introduction passage 130 is dispersed to a plurality of introduction portions, thereby increasing the chance of gas diffusion. Can improve diffusibility and make it uniform. Thereby, compared with the case where secondary air is introduced into the fuel gas flow path 111 from a single introduction part, the secondary air and the pulverized fuel mixture are better without being ignited in the region in contact with the secondary air. Mixed.

In order to mix and homogenize the gas mixture between the pulverized fuel mixture and each introduced secondary air, the upper introduction portions 131, 132, 133, and 134 of the secondary air introduction flow path 130, and the lower introduction It is preferable that the portions 135, 136, 137, and 138 introduce secondary air at the same flow rate and the same flow rate so as to be symmetrical with respect to at least the axis X1. For this reason, it is preferable that the flow path cross-sectional areas of the upper introduction parts 131, 132, 133, and 134 and the lower introduction parts 135, 136, 137, and 138 are at least symmetrical with respect to the axis X1.
Also, in the operation of the combustion burner 100A, when it is assumed from the flame holding condition in the flame holder 140 that it is not mixed and homogenized by gas diffusion of the pulverized fuel mixture and each introduced secondary air Can be made symmetric with respect to the axis X1 by adjusting the cross-sectional areas of the upper introduction portions 131, 132, 133, and 134 and the lower introduction portions 135, 136, 137, and 138 with a damper (not shown). Is possible.

Further, as shown in FIGS. 3 and 4, the first position P <b> 1 (secondary air is introduced) where the secondary air introduction passage 130 introduces a part of the secondary air into the fuel gas passage 111 along the axis X <b> 1. The distance in the gas flow direction from the introduction position) to the fourth position P4 (installation position where the flame stabilizer 140 is installed) at the upstream end of the flame holder 140 is L, and the distance in the tip side nozzle 110a of the fuel gas passage 111 is When the minimum width is W1 (W), the following expression (1) is satisfied.
2 ≦ L / W1 ≦ 5 (1)

As shown in Expression (1), the distance L from the first position P1 to the fourth position P4 is made sufficiently larger than the minimum width W1 of the tip side nozzle 110a, so that the fuel gas flow path 111 is formed at the first position P1. The introduced secondary air and the pulverized fuel mixture are sufficiently mixed so as to obtain a uniform concentration distribution.
Further, the mixing of the introduced secondary air and the pulverized fuel mixture is selected by adjusting and optimizing the shape and size of the secondary air introduction flow path 130. The reason why 2 ≦ L / W1 is set is that the pulverized fuel mixture passing through the flame holder 140 is a pulverized fuel mixture uniformly mixed with the introduced secondary air. In addition, by selecting to increase the shape and size of the secondary air introduction flow path 130, the mixing with the introduced secondary air is promoted. Since there is a case where ignition occurs between secondary air having a temperature higher than that of air, there is an upper limit of the shape and size of the secondary air introduction flow path 130. In order to prevent the upper limit of the shape and size of the secondary air introduction flow path 130 and the enlargement of the combustion burner 100A, L / W1 ≦ 5.
The pulverized fuel mixture mixed with the secondary air at the first position P1 circulates in the direction indicated by the arrows 202, 203, 204 from the first position P1 toward the fourth position P4 in the direction indicated by the arrows 202, 203, 204, and holds the flame. The upstream end of the vessel 140 is reached.

The pulverized fuel mixture is separated by the widened portions 141, 142, and 143 of the flame stabilizer 140 into the upper and lower parts in the vertical direction and recirculated immediately after the widened portions 141, 142, and 143 are downstream in the gas flow direction. It flows into the furnace 11 while forming a region. The pulverized fuel mixture which is separated and then recirculated by the flame holder 140 is burned and flame-held. At this time, by introducing a part of the secondary air to the fuel gas passage 111, the combustion of the pulverized coal in the pulverized fuel mixture is promoted by increasing the A / C ratio, and the unburned portion decreases. . Although NOx is generated at this time, since the release of combustible volatiles contained in the pulverized coal is promoted and the downstream side of the flame holder 140 is in a reducing atmosphere with insufficient air, the generated NOx is reduced early. Therefore, the amount of NOx generated is reduced.

The operation and effect of the combustion burner 100A of the present embodiment described above will be described.

According to the combustion burner 100 </ b> A of the present embodiment, at least a part of the secondary air having a temperature higher than that of the fuel gas flowing through the secondary air flow path 121 is separated from the secondary air flow path 121 by the secondary air introduction flow path 130. The fuel gas passage 111 through which the fine fuel mixture is circulated is introduced. Since the flame holder 140 is disposed in the vicinity of the tip 110c that opens to the furnace 11 in the fuel nozzle 110, the ignitability of the fuel at the outlet of the fuel gas passage 111 is improved and the combustibility contained in the fuel is increased. Since the release of volatile matter is promoted and the reduction of NOx is promoted, the amount of NOx generated is reduced.

Further, in the combustion burner 100A of this embodiment, since at least a part of the secondary air is guided to the fuel gas passage 111, it is necessary to increase the flow rate of the primary air in order to increase the A / C ratio of the fuel gas. There is no. For this reason, there are problems such as an increase in the power of the ventilator due to an increase in the flow rate of the primary air, a decrease in the classification accuracy of the pulverized coal machines 31, 32, 33, 34, and 35, and an increase in the amount of wear on the transport pipe that carries the fuel Can be suppressed.

In the combustion burner 100A of the present embodiment, the distance in the gas flow direction along the axis X1 from the secondary air introduction position (first position P1) to the flame holder 140 installation position (fourth position P4). Is L, and 2 ≦ L / W ≦ 5 is satisfied, where W is the minimum width of the fuel gas passage 111 from the introduction position to the installation position. The reason why 2 ≦ L / W is set is to ensure a sufficient distance for uniformly mixing the fuel gas passing through the flame holder 140 with the secondary air. Moreover, L / W1 ≦ 5 is set to prevent the combustion burner 100Ac from becoming large.
By doing so, the combustion burner 100Ac is prevented from being enlarged while a sufficient distance in the gas flow direction from when the secondary air is introduced into the fuel gas passage 111 to the flame holder 140 is secured. The flame holder 140 can perform ignition or flame holding in a state where the introduced secondary air and fuel gas have a more uniform concentration distribution.

In the combustion burner 100A of the present embodiment, the secondary air introduction channel 130 introduces at least part of the secondary air into the fuel gas channel 111 at a flow rate having a main component in the gas flow direction.
According to the combustion burner 100A of the present embodiment, the secondary air is introduced from the secondary air introduction channel 130 to the fuel gas channel 111 with a flow velocity of the main component in the gas flow direction of the fuel gas. Mixing while gently diffusing without causing large turbulence when joining with gas.

In the combustion burner 100A of the present embodiment, the flame holder 140 is formed so as to extend along a direction intersecting with the gas flow direction and has a cross-sectional width orthogonal to the gas flow direction toward the downstream side in the gas flow direction. There may be widened portions 141, 142, 143 that become wider. By providing the flame stabilizer 140 with the widened portions 141, 142, and 143, it is possible to suitably perform internal flame holding.

Second Embodiment
Next, the pulverized coal burning boiler according to the second embodiment of the present disclosure will be described.
The pulverized coal burning boiler 10A of the second embodiment is a modification of the pulverized coal burning boiler 10 of the first embodiment, and is the same as the pulverized coal burning boiler 10 of the first embodiment, except as specifically described below. It is assumed that there is a description, and the description below is omitted.

The pulverized coal-fired boiler 10 according to the first embodiment allows the entire amount of air (outside air) blown by the blower 38 to pass through the air heater (heat exchanger) 49 and the combustion air supplied from the air duct 37 to the wind box 36. The temperature was raised to 280 ° C to 320 ° C. On the other hand, the pulverized coal fired boiler 10A of the present embodiment passes a part of the air blown by the blower 38 through the air heater (heat exchanger) 49, while the other of the air blown by the blower 38 is an air heater (heat exchange). Instrument) 49 is not allowed to pass.

The pulverized coal burning boiler 10A of the present embodiment is adjusted so that the combustion air supplied to the wind box 36 in this way is lower in temperature than the pulverized coal burning boiler 10 of the first embodiment. Hereinafter, the pulverized coal burning boiler 10A of the present embodiment will be described in detail.

As shown in FIG. 6, the pulverized coal burning boiler 10A of the present embodiment includes an air duct 37A, an air duct 37B, and an air duct 39C as air ducts that guide the air blown by the blower 38 to the wind box 36. Have.
A part of the air blown by the blower 38 is supplied to the air duct 37A, and the other is supplied to the air duct 37B.

The air duct 37C mixes air that has passed through the air heater 49 and has become high temperature (280 ° C. or higher and 320 ° C. or lower) and air that has not passed through the air heater 49 (0 ° C. or higher and 40 ° C. or lower). A duct leading to the wind box 36. The air guided from the air duct 37 </ b> C to the wind box 36 is supplied to the secondary air nozzle 120.

The temperature of the air led from the air duct 37C to the wind box 36 is adjusted to be a predetermined temperature. Here, the predetermined temperature is a temperature in a temperature range of 100 ° C. or more and 300 ° C. or less. By setting it as 100 degreeC or more, it is suppressed that dew condensation arises inside the air duct 37C. Further, by setting the temperature to 300 ° C. or lower, the problem that the pulverized fuel mixture is ignited by the secondary air guided from the secondary air nozzle 120 to the fuel gas passage 111 is suppressed. The predetermined temperature may be a temperature in the temperature range of 150 ° C. or more and 250 ° C. or less. The predetermined temperature may be a temperature in the temperature range of 175 ° C. or more and 225 ° C. or less.

The temperature of the air guided from the air duct 37C to the wind box 36 is adjusted by the ratio between the flow rate of air guided from the blower 38 to the air duct 37A and the flow rate of air guided from the blower 38 to the air duct 37B. The ratio between the flow rate of air guided from the blower 38 to the air duct 37A and the flow rate of air guided from the blower 38 to the air duct 37B may be a fixed ratio. In addition, a damper (not shown) is provided in one of the air duct 37A and the air duct 37B, and by adjusting the opening of the damper, the flow rate of air guided from the blower 38 to the air duct 37A and the air duct from the blower 38 are adjusted. You may adjust a ratio with the flow volume of the air guide | induced to 37B.

According to the pulverized coal burning boiler 10A of the present embodiment described above, high-temperature air (280 ° C. or higher and 320 ° C. or lower) that has passed through the air heater 49 and normal temperature (0 ° C. or higher and 40 ° C. or lower) that does not pass through the air heater 49. ) In an appropriate amount, the temperature of the secondary air introduced into the fuel gas channel 111 can be lowered to an appropriate temperature (for example, 100 ° C. or more and 300 ° C. or less). Thereby, the malfunction which the fuel which grind | pulverized coal with the high temperature secondary air introduce | transduced into the fuel gas flow path 111 ignites can be suppressed.

<Third Embodiment>
Next, a pulverized coal fired boiler according to a third embodiment of the present disclosure will be described.
The pulverized coal burning boiler according to the third embodiment is a modification of the pulverized coal burning boiler 10 according to the first embodiment, and is the same as the pulverized coal burning boiler 10 according to the first embodiment, unless otherwise described below. The description below will be omitted. The combustion burner 100F provided in the pulverized coal burning boiler of the present embodiment is different from the combustion burner 100A provided in the pulverized coal burning boiler 10 of the first embodiment in that a rectifying unit 150 is provided inside the fuel gas flow path 111. .

Hereinafter, the combustion burner 100F of the present embodiment will be described with reference to the drawings. The combustion burner 100F of the present embodiment is a modification of the combustion burner 100A of the first embodiment, and is the same as the combustion burner 100A of the first embodiment except for the case described below. Is omitted.

As shown in FIG. 7, in the combustion burner 100 </ b> F of the present embodiment, the secondary air introduction flow path 130 introduces a part of the secondary air into the fuel gas flow path 111 and the upstream of the flame holder 140. A rectifying unit 150 is provided between the end and the fourth position P4.
The rectifying unit 150 agitates the pulverized fuel mixture in the fuel gas flow path 111, and drifts of the pulverized coal generated when the pulverized fuel mixture flows through the pulverized coal supply pipe 26 (the concentration of the pulverized coal in the flow path cross section). This is a member for eliminating (bias). The rectification unit 150 is disposed upstream of the flame holder 140 in the fuel nozzle 110 in the gas flow direction.

As shown in FIG. 8 (an end view taken along the line III-III of the combustion burner 100F shown in FIG. 7), the combustion burner 100F of this embodiment is arranged in an annular shape so as to surround the inner peripheral surface of the fuel nozzle 110. A rectifying unit 150 that locally reduces the cross-sectional area of the gas flow path 111 is provided. The rectifying unit 150 of the present embodiment agitates the passing pulverized fuel mixture, and eliminates the uneven concentration of pulverized coal in the cross section of the fuel gas channel 111.

In addition, although the rectification | straightening part 150 shown in FIG. 8 was cyclically | annularly arranged so that the internal peripheral surface of the fuel nozzle 110 might be surrounded, another aspect may be sufficient.
For example, as shown in FIG. 9 (an end view taken along the line III-III of the combustion burner 100F shown in FIG. 7), a plurality of rectangular rectifying portions 150A are spaced so as to surround the inner peripheral surface of the fuel nozzle 110. You may arrange.

According to the combustion burner 100F provided in the pulverized coal burning boiler of the present embodiment described above, the pulverized coal is prevented from drifting in the fuel gas passage 111, and the secondary air and the pulverized fuel mixture have a more uniform concentration distribution. In this state, the flame holder 140 can ignite or hold the flame.
In the above description, the secondary air introduction channel 130 passes through the rectifying unit 150 and the rectifying unit 150A downstream of the first position P1 where the secondary air is introduced into the fuel gas channel 111 in the gas flow direction. Although provided on the side, other modes may be used.

For example, the rectifying unit 150 and the rectifying unit 150 </ b> A are arranged on the upstream side in the gas flow direction from the first position P <b> 1 where the secondary air introduction channel 130 introduces a part of the secondary air into the fuel gas channel 111. You may make it provide in the nozzle 110b.
Further, for example, the rectification unit may be provided inside the pulverized coal supply pipes 26, 27, 28, 29, 30. In this case, the rectifying unit may have an annular shape so as to be along the inner peripheral surface of the pulverized coal supply pipe having a circular sectional view.
In this way, a sufficient distance in the gas flow direction from the rectifying unit to the flame holder 140 is ensured, and the pulverized fuel mixture stirred in the rectifying unit is supplied to the flame holder 140 without any disturbance. can do.

<Fourth embodiment>
Next, a pulverized coal fired boiler according to a fourth embodiment of the present disclosure will be described.
The pulverized coal burning boiler according to the fourth embodiment is a modification of the pulverized coal burning boiler 10 according to the first embodiment, and is the same as the pulverized coal burning boiler 10 according to the first embodiment, unless otherwise described below. The description below will be omitted. The combustion burner 100G provided in the pulverized coal burning boiler of the present embodiment is different from the combustion burner 100A provided in the pulverized coal burning boiler 10 of the first embodiment in that a secondary air introduction pipe 26A is provided.

Hereinafter, the combustion burner 100G of the present embodiment will be described with reference to the drawings. The combustion burner 100G of the present embodiment is a modification of the combustion burner 100A of the first embodiment, and is the same as the combustion burner 100A of the first embodiment except for the case described below. Is omitted.
As shown in FIG. 10, the combustion burner 100 </ b> A of the present embodiment is composed of combustion burners 100 </ b> Ga, 100 </ b> Gb, 100 </ b> Gc, and 100 </ b> Gd provided on four wall surfaces in the furnace 11.

As shown in FIG. 10, the combustion burner 100 </ b> G of the present embodiment includes a secondary air introduction pipe 26 </ b> A that supplies a part of the secondary air flowing through the air duct 37 to the pulverized coal supply pipe (fuel supply pipe) 26. . Part of the secondary air flowing through the air duct 37 is supplied to the pulverized coal supply pipe 26 from the secondary air introduction pipe 26A. Therefore, the amount of air supplied to the fuel gas passage 111 of the combustion burner 100G of the present embodiment is larger than the amount of air supplied to the fuel gas passage 111 of the combustion burner 100A of the first embodiment. On the other hand, the amount of air supplied to the secondary air flow path 121 of the combustion burner 100G of the present embodiment is smaller than the amount of air supplied to the secondary air flow path 121 of the combustion burner 100A of the first embodiment.

According to the pulverized coal burning boiler of the present embodiment, the fuel gas can be produced without increasing the flow rate of the pulverized fuel mixture in the flow path from the pulverized coal machine (pulverizer) 31 for pulverizing the pulverized coal to the pulverized coal supply pipe 26. The amount of primary air supplied to the flow path 111 can be increased. Therefore, it is possible to suppress problems such as an increase in the power of the ventilator that ventilates the primary air to the pulverized coal machine 31, a decrease in classification accuracy of the pulverized coal machine 31, and an increase in the wear amount of the transfer pipe that conveys fuel.

Further, according to the pulverized coal fired boiler of the present embodiment, the amount of air supplied to the fuel gas passage 111 is larger than that of the pulverized coal fired boiler of the first embodiment and supplied to the secondary air passage 121. There is little air quantity. Therefore, the speed difference between the flow rate of the pulverized fuel mixture jetted from the fuel gas channel 111 to the furnace 11 and the flow rate of the secondary air jetted from the secondary air channel 121 to the furnace 11 is reduced. It is possible to suppress a problem that the outer periphery flame holding and the outer periphery ignition are performed due to the turbulence of the air flow.

<Other embodiments>
In each of the above-described embodiments, the combustion device 12 is configured by arranging the four combustion burners 100A, 100B, 100C, 100D, and 100E provided on the wall surface of the furnace 11 along the vertical direction in five stages. It is not limited to. That is, the combustion burner may be arranged at the corner without being arranged on the wall surface. The combustion apparatus is not limited to the swirl combustion method, and may be a front combustion method in which the combustion burner is disposed on one wall surface, or an opposed combustion method in which the combustion burner is disposed opposite to the two wall surfaces. Further, the combustion burners 100A, 100B, 100C, 100D, and 100E of the combustion device 12 are not limited to the rectangular tube shape, and may be, for example, a cylindrical shape.

10, 10A Pulverized coal fired boiler 11 Furnace 12 Combustion device 26, 27, 28, 29, 30 Pulverized coal supply pipe (fuel supply pipe)
31, 32, 33, 34, 35 Pulverized coal machine (pulverizer)
36 Wind box 37 Air duct (secondary air supply pipe)
38 Blower 49 Air heater (heat exchanger)
100A, 100B, 100C, 100D, 100E, 100F, 100G Combustion burner 110 Fuel nozzle 110a Tip side nozzle 110b Base end side nozzle 110c Tip portion 111 Fuel gas passage 120 Secondary air nozzle 121 Secondary air passage 130 Secondary air Introduction channel 131,132,133,134 Upper introduction part 135,136,137,138 Lower introduction part 140 Flame stabilizer 141,142,143 Widening part 150 Rectification part

Claims (7)

1. A fuel nozzle that forms a fuel gas passage that extends in a cylindrical shape along an axis and supplies a fuel gas obtained by mixing a fuel obtained by pulverizing a carbon-containing solid fuel and primary air to a furnace;
   A secondary air nozzle that extends in a cylindrical shape along the axis and through which secondary air having a temperature higher than that of the fuel gas flows;
   A secondary air flow path formed between the secondary air nozzle and the fuel nozzle for supplying the secondary air to the furnace;
   A secondary air introduction flow path for introducing at least a part of the secondary air flowing through the secondary air flow path into the fuel gas flow path;
   A flame holder disposed in the vicinity of a tip opening to the furnace in the fuel nozzle,
   The distance in the gas flow direction along the axis from the introduction position where the secondary air introduction flow path introduces at least part of the secondary air into the fuel gas flow path to the installation position of the flame stabilizer is defined as L. A combustion burner satisfying 2 ≦ L / W ≦ 5, where W is the minimum width of the fuel gas flow path from the introduction position to the installation position.
2. The combustion burner according to claim 1, wherein the secondary air introduction channel introduces at least a part of the secondary air into the fuel gas channel at a flow rate having a main component in the gas flow direction.
3. The flame stabilizer is formed so as to extend along a direction intersecting with the gas flow direction, and has a widened portion in which a width of a cross section perpendicular to the gas flow direction is widened toward a downstream side in the gas flow direction. The combustion burner according to claim 1 or claim 2 having.
4. The combustion burner according to claim 1 or 2, further comprising a rectifier disposed upstream of the flame holder in the fuel nozzle in the gas flow direction.
5. A furnace,
   A boiler provided with the combustion burner of Claim 1 or Claim 2 installed with respect to this furnace.
6. A fuel supply pipe for supplying a fuel gas obtained by mixing a fuel containing pulverized carbon-containing solid fuel and primary air to the fuel gas flow path;
   An air duct for supplying secondary air blown by a blower to the secondary air flow path;
   The boiler according to claim 5, further comprising: a secondary air introduction pipe that supplies a part of the secondary air flowing through the air duct to the fuel supply pipe.
7. A heat exchanger that performs heat exchange between the combustion gas and air on the downstream side of the gas flow of the combustion gas ejected from the combustion burner in the furnace;
   The boiler according to claim 5, further comprising: an air duct that mixes air that has passed through the heat exchanger and air that has not passed through the heat exchanger and supplies the mixed air to the secondary air nozzle.

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