JPH09318014A - Pulverized coal combustion burner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To extend a reverse flow area of mixture gas, generated in a spot situated downstream from the periphery of the tip of a pulverized coal nozzle, to a downstream spot, to improve ignitability and flame stability of pulverized coal, and to reduce an amount of generating NOx. SOLUTION: A pulverized coal combustion burner comprises an expansion part 15 expanding in the axial direction and the orthogonal direction of a pulverized coal nozzle 2; and a parallel part 16 extended to the expansion part 15. The tip of a secondary air nozzle 12 is positioned in a spot situated downstream from the tip of the pulverized coal nozzle 2. Further, the pulverized coal combustion burner is extended to the parallel part 16 and provided with a contraction part contracted the axial direction and the orthogonal direction of the pulverized coal nozzle 2, and the expansion part 15 may be expanded from the tip of the pulverized coal nozzle 2. Further, an auxiliary nozzle is provided to inject air at an injection speed higher than the injection speed of secondary air 43 from the periphery of the tip of the secondary nozzle 12.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pulverized coal combustion burner which conveys and burns pulverized coal by air flow, and is particularly suitable for enhancing the ignitability and flame holding property of pulverized coal and reducing the nitrogen oxide concentration. Pulverized coal combustion burner.

[0002]

2. Description of the Related Art Conventionally, in the combustion of a pulverized coal combustion burner, nitrogen oxides (hereinafter referred to as "NO
x)) is a problem. In particular, since coal has a higher nitrogen content than gas fuel or liquid fuel, NOx generated during combustion of pulverized coal is larger than NOx generated during combustion of gas fuel or liquid fuel, and it is required to reduce this NOx. Has been.

Most of NOx generated during combustion of pulverized coal (about 80%) is so-called fuel NOx generated by oxidation of nitrogen contained in coal. In order to reduce this NOx, various pulverized coal combustion burners have been conventionally studied.

As one of the pulverized coal combustion burners for suppressing NOx, an oxidation region having a high oxygen concentration and an air ratio of 1 or more and a reducing region having a low oxygen concentration and an air ratio of 1 or less are formed in the flame. There is a so-called two-stage combustion pulverized coal combustion burner in flame.

[0005] Nitrogen content of the coal, hydrogen cyanide (hereinafter, referred to as "HCN") in initial combustion and the combustion region of insufficient oxygen or ammonia (hereinafter, referred to as "NH _3") are released into the gas phase as. While these nitrogen compounds are oxidized to NOx, they have the effect of reducing NOx under conditions of low oxygen concentration. The two-stage combustion pulverized coal combustion burner in the flame utilizes the NOx reduction reaction by this nitrogen compound.

[0006] As a means for forming such a reducing region of a low oxygen concentration atmosphere in a flame and completely burning coal, for example, JP-A-60-226609 and JP-A-6-26609 are disclosed.
There are those disclosed in JP-A 1-22105, JP-A 61-280302, JP-A 1-57004 and the like. These known combustion burners have a fuel nozzle that carries pulverized coal in an air stream as a center, and an air nozzle that coaxially ejects combustion air in a swirling flow outside the fuel nozzle.

FIG. 8 shows an example of the above-mentioned conventional combustion burner. The combustion burner 100 includes a pulverized coal nozzle 1 for ejecting a mixture 115 of pulverized coal and primary air.
01 and a secondary air nozzle 103 provided coaxially with the pulverized coal nozzle 101 on the outer side thereof and having a secondary air swirl vane 102 for ejecting the secondary air 116 as a swirl flow.
And the secondary air nozzle 10 coaxially with the pulverized coal nozzle 101.
3, a tertiary air nozzle 105 having a tertiary air swirl vane 104 for ejecting the tertiary air 117 as a swirling flow is provided. An oil gun 106 is provided at the position of the central axis of the pulverized coal nozzle 101. Further, a venturi 107 is provided on the upstream side of the pulverized coal nozzle 101, and a flame holding plate 108 is provided on the downstream end. Reference numeral 109 is a side plate, 110 is a water pipe, and 111
Is a damper, and 112 is a wind box.

The above-mentioned combustion burner 100 adjusts the oxygen concentration in the flame by supplying combustion air to the secondary air nozzle 103 and the tertiary air nozzle 105 in a divided manner. Further, by supplying the combustion air as a swirl flow, the mixing with the pulverized coal flowing in the central part of the swirl is delayed, and in the vicinity of the combustion burner 100, an insufficient amount of air causes a fuel excess state and a reducing flame is formed. Further, due to the swirling flow, negative pressure is generated near the center of the swirl, and combustion air flows toward the center of the swirl on the downstream side of the flame. Therefore, the combustion air and the pulverized coal are rapidly mixed on the downstream side of the flame, so that the flame becomes longer and the combustion efficiency is prevented from decreasing.

[0009]

However, the above conventional combustion burner 100 can suppress NOx and improve combustion efficiency by supplying combustion air as a swirling flow, but swirling to secondary air. When a flow velocity is applied, the secondary air flows radially outward at the tip of the nozzle due to the centrifugal force, so that the secondary air easily joins with the tertiary air. This further delays the mixing of pulverized coal and secondary air. If the pulverized coal and the secondary air do not mix near the tip of the secondary air nozzle, the air required for ignition of the pulverized coal is insufficient, so combustion does not proceed,
A high temperature region may not be formed near the tip of the nozzle.
For this reason, the combustion efficiency of the pulverized coal is reduced, the consumption of oxygen does not proceed, and the reduction region is not formed quickly. If the reduction region is not sufficiently formed, NO in the two-stage combustion in the flame
Since x cannot be suppressed, the amount of NOx generated may increase.

Further, when the combustion burner is operated under a low load, there is a restriction that the flow velocity of the pulverized coal flowing in the pulverized coal conveying pipe cannot be reduced to a certain speed or less. This is because if the flow rate of the pulverized coal is too slow, the pulverized coal may settle inside the carrier pipe and block the pipe, or the flame may flow back into the carrier pipe. Therefore, when operating the combustion burner at a low load, it is necessary to keep the flow rate of the air supplied to the pulverized coal transport pipe constant below a certain load and reduce the flow rate of the air supplied to the air nozzle. Don't

When the amount of air supplied to the air nozzle decreases, the swirling force of the air weakens and the air mixes with the pulverized coal in the vicinity of the combustion burner, not in the latter stage of the flame. Furthermore, if the turning force weakens,
The negative pressure induced at the tip of the pulverized coal nozzle weakens, and the reverse flow region (circulation flow) is formed on the downstream side around the tip of the pulverized coal nozzle.
Becomes smaller, and the ignition and flame holding properties of pulverized coal are weakened. As a result, the reduction region is less likely to be formed and NOx is likely to be generated.

Under high temperature conditions such as high temperature combustion, the NOx reduction reaction by this nitrogen compound is more likely to proceed as the atmosphere becomes lower in oxygen concentration. Therefore, in order to reduce NOx generated in the combustion of pulverized coal, the formation of an atmosphere with a low oxygen concentration becomes a problem. Also, in order to completely burn the coal, it is necessary to mix it with air downstream of the flame.

An object of the present invention is to solve the above problems and to provide a pulverized coal combustion burner which enhances the ignitability and flame holding property of pulverized coal and produces a small amount of NOx.

[0014]

In order to achieve the above object, the present invention provides a pulverized coal nozzle for ejecting a mixture of pulverized coal and primary air, and a pulverized coal nozzle provided coaxially outside the pulverized coal nozzle. In a pulverized coal combustion burner provided with a secondary air nozzle having a secondary air swirl flow generator that ejects secondary air as a swirl flow, the secondary air nozzle is located downstream of the tip of the pulverized coal nozzle. It has a backflow region expansion means for expanding the backflow region of the generated mixed gas to the downstream side.

The secondary air nozzle is provided on the downstream side around the tip of the pulverized coal nozzle by having a backflow region expanding means for extending the reverse flow region of the mixed gas generated on the downstream side around the tip of the pulverized coal nozzle to the downstream side. High-temperature burned gas circulates in the reverse flow region, and ignites pulverized coal flowing by the reverse flow region. Further, by giving a swirl flow to the secondary air, a negative pressure region is formed inside the swirl flow. In the negative pressure region inside the swirl flow, a reverse flow region that flows from downstream to upstream is formed.
And, because part of the pulverized coal ejected together with the primary air passes through this reverse flow region, the time during which the pulverized coal stays in the flame increases, the unburned content of the pulverized coal decreases, and the ignitability and flame holding property of the pulverized coal are reduced. And the combustion efficiency is increased, the range of the reduction region of the low oxygen concentration atmosphere existing in the flame is increased toward the downstream side, and the amount of NOx generated is reduced.

Further, in the above pulverized coal combustion burner, the backflow region expanding means maintains the jetting direction of the secondary air of the secondary air nozzle in the axial direction of the pulverized coal nozzle, and the axial direction of the pulverized coal nozzle. It expands in the direction perpendicular to. The reverse flow region expansion means keeps the secondary air jetting direction of the secondary air nozzle in the axial direction of the pulverized coal nozzle, and expands in the direction perpendicular to the axial direction of the pulverized coal nozzle because of the action of the pulverized coal combustion burner. In addition, the axial velocity of the secondary air is slowed down, and the swirling flow of the secondary air more reliably enlarges the reduction region toward the downstream side to reduce the amount of NOx generated.

Further, in the above pulverized coal combustion burner, the backflow region expanding means includes an enlarged portion which expands in a direction perpendicular to the axial direction of the pulverized coal nozzle, and the pulverized coal nozzle which is extended to the enlarged portion. It has a parallel portion parallel to the axial direction. The above-mentioned fine powder is one in which the backflow region expanding means has an enlarged portion that expands in a direction perpendicular to the axial direction of the pulverized coal nozzle and a parallel portion that extends in this enlarged portion and is parallel to the axial direction of the pulverized coal nozzle. In addition to the action of the charcoal-burning burner, the expanded portion can reduce the axial velocity of the secondary air. Since the swirling force of the secondary air does not change, the negative pressure acting on the central part of the swirling flow becomes strong, and the jetting direction of the secondary air can be directed to the central direction of swirling. Therefore, the barrier between the pulverized coal nozzle and the secondary air nozzle, that is, the backflow region formed on the downstream side of the flame holding plate, is enlarged, and the pulverized coal flowing near the center of the swirl and the secondary air are quickly mixed. Let Since the high temperature combustion gas, which is a mixed gas, flows in the backflow region, it has a function of promoting ignition of pulverized coal. Therefore, the ignition position of the pulverized coal approaches the pulverized coal combustion burner, and the combustion efficiency of the pulverized coal is improved. Then, since the temperature rises near the pulverized coal combustion burner and the consumption of oxygen progresses, the reduction region becomes large and the generation of NOx is suppressed.

Further, in any of the above pulverized coal combustion burners, the tip of the secondary air nozzle is located downstream of the tip of the pulverized coal nozzle. In the case where the tip of the secondary air nozzle is located on the downstream side of the tip of the pulverized coal nozzle, in addition to the action of any of the above pulverized coal combustion burners, the reduction region is further enlarged.

Further, in the above pulverized coal combustion burner, the backflow region expanding means has a contracting part extending in the parallel part for contracting in a direction perpendicular to the axial direction of the pulverized coal nozzle, and the expanding part is It expands from the tip position of the pulverized coal nozzle. What has a reduction part extending in a parallel part and an expansion part expanding from the tip position of the pulverized coal nozzle is
In addition to the action of the above pulverized coal combustion burner, the jetting direction of the secondary air can be easily and surely directed toward the center of swirling.

Further, in any one of the above pulverized coal combustion burners, the backflow region expanding means has an ejection speed higher than the ejection speed of the secondary air ejected from the secondary air nozzle from around the tip of the secondary air nozzle. It has an auxiliary nozzle for ejecting gas. In addition to the action of any one of the above pulverized coal pulverized coal combustion burners, the reverse flow region expansion means has an auxiliary nozzle that ejects gas at a ejection velocity higher than the ejection velocity of secondary air The jet flow at a higher speed axially flows outside the secondary air that tends to flow outward, so that the radial flow of the secondary air can be suppressed. Therefore, the secondary air is rapidly mixed with the pulverized coal flowing near the center of the swirl, the ignition position of the pulverized coal approaches the pulverized coal combustion burner, and the combustion efficiency of the pulverized coal is improved. Then, since the temperature rises near the pulverized coal combustion burner and oxygen consumption progresses, the reduction region becomes large and the generation of NOx is suppressed.

Further, in any one of the above pulverized coal combustion burners, there is provided a tertiary air swirl flow generator which is provided outside the secondary air nozzle coaxially with the pulverized coal nozzle and ejects tertiary air as a swirl flow. A tertiary air nozzle is provided, and the flow path of the secondary air and the flow path of the tertiary air are separated by a predetermined distance. Provided with a tertiary air nozzle having a tertiary air swirl generator outside the secondary air nozzle,
By separating the flow path of the secondary air and the flow path of the tertiary air by a predetermined distance, in addition to the action of any of the above pulverized coal combustion burners, it is possible to widen the interval between the secondary air nozzle and the tertiary air nozzle. The tertiary air is separated from the secondary air and mixed with the pulverized coal on the downstream side of the flame. Therefore, the reduction region formed on the upstream side of the flame is widened to suppress the generation of NOx.

In any one of the above pulverized coal combustion burners, the backflow region expanding means expands the outside of the secondary air nozzle in a direction perpendicular to the axial direction of the pulverized coal nozzle so that the tertiary air nozzle It has a flow path reducing portion for reducing the flow path. When the reverse flow region expanding means has a flow path reducing portion for reducing the flow path of the tertiary air nozzle by expanding the outside of the secondary air nozzle in the direction perpendicular to the axial direction of the pulverized coal nozzle, the tertiary air is a nozzle flow path. While flowing through, the flow is biased toward the outer circumference of the flow path by the swirling force. For this reason, most of the air flows through the outer circumference of the nozzle at the outlet of the tertiary air nozzle, and even if the inner peripheral side flow passage is narrowed at the nozzle outlet, the pressure loss hardly increases, and the tertiary air flows at the nozzle outlet. Ejects as a radially outward flow. Therefore, the mixing of the tertiary air and the pulverized coal near the pulverized coal combustion burner can be delayed, the reduction region near the pulverized coal combustion burner is enlarged, and the generation of NOx is suppressed. Also, the diameter of the pulverized coal combustion burner can be reduced.

Further, a pulverized coal nozzle for ejecting a mixture of pulverized coal and primary air, and a secondary air swirling flow provided coaxially with the pulverized coal nozzle on the outer side thereof for ejecting secondary air as a swirling flow. In a pulverized coal combustion burner provided with a secondary air nozzle having a generator, the secondary air nozzle slows down the ejection speed of the secondary air of the secondary air nozzle at the tip of the secondary air nozzle, and The ejection direction of the secondary air is kept in the axial direction of the pulverized coal nozzle. When the secondary air nozzle slows down the secondary air ejection speed at the tip of the secondary air nozzle and keeps the secondary air ejection direction in the axial direction of the pulverized coal nozzle, the swirling force of the secondary air does not change. Therefore, the negative pressure acting on the central part of the swirling flow becomes strong. Therefore, the backflow region formed on the downstream side of the barrier between the pulverized coal nozzle and the secondary air nozzle becomes large. Since high-temperature combustion gas flows in the backflow region, it has a function of promoting ignition of pulverized coal. For this reason,
The ignition position of the pulverized coal approaches the pulverized coal combustion burner, and the combustion efficiency of the pulverized coal is improved. Then, the temperature rises near the pulverized coal combustion burner and the consumption of oxygen progresses, so that the reduction region becomes large and the generation of NOx is suppressed.

In the above pulverized coal combustion burner,
The tip of the secondary air nozzle is located downstream of the tip of the pulverized coal nozzle. When the tip of the secondary air nozzle is located on the downstream side of the tip of the pulverized coal nozzle, the reduction region is further increased in addition to the function of the pulverized coal combustion burner.

Further, according to the present invention, at the tip of the pulverized coal nozzle,
By providing the flame holding plate which obstructs the flow, the backflow region formed on the downstream side of the barrier (flame holding plate) between the pulverized coal nozzle and the secondary air nozzle is enlarged. Therefore, the ignition position of the pulverized coal approaches the pulverized coal combustion burner, and the combustion efficiency of the pulverized coal is improved. Then, since the temperature rises near the pulverized coal combustion burner and the oxygen consumption progresses, the reduction region becomes large and the generation of NOx is suppressed.

Further, in the present invention, by expanding the flow path of the secondary air nozzle from the position of the flame holding plate provided at the tip of the pulverized coal nozzle, the flow velocity in the axial direction of the secondary air from the position of the flame holding plate. Can be decelerated and the swirling flow velocity can be maintained. At this time, the size of the backflow region formed downstream of the flame holding plate is determined by the swirling strength of the secondary air. Therefore, even if the amount of combustion air is small, the swirling strength of the secondary air may be maintained,
The pressure loss can be reduced and the operation becomes easier than in the case where the swirling strength of the tertiary air having a large flow rate is maintained.

As described above, the combustion air is divided and supplied to the pulverized coal nozzle, the secondary air nozzle, and the tertiary air nozzle which eject the air-fuel mixture of pulverized coal and primary air. A reducing region is formed on the upstream side and an oxidizing region is formed on the downstream side of the flame, so that NOx can be suppressed.

[0028]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of a pulverized coal combustion burner according to the present invention will be described in detail below with reference to the drawings.
Note that, in FIGS. 1 to 7, the same structures and working portions are denoted by the same reference numerals.

FIG. 1 is a sectional view showing a first embodiment of a pulverized coal combustion burner according to the present invention. The pulverized coal combustion burner 1 of the first embodiment is a mixture of pulverized coal and primary air 4
Pulverized coal nozzle 2 for ejecting 1 and this pulverized coal nozzle 2
Is provided outside of the central axis 3 of the
Secondary air nozzle 12 having a secondary air swirl vane 13 which is a secondary air swirl flow generator for ejecting 3 as a swirl flow
And a secondary air swirl vane 27 that is a secondary air swirl flow generator that is provided outside the secondary air nozzle 12 coaxially with the central axis 3 of the pulverized coal nozzle 2 and ejects the tertiary air 44 as a swirl flow. And a secondary air nozzle 26.

The secondary air nozzle 12 is a reverse flow region 4 of the mixed gas 45 generated on the downstream side around the tip 6 of the pulverized coal nozzle 2.
It has a reverse basin expansion means 14 for expanding 6 to the downstream side. The backflow region expanding means 14 keeps the ejection direction of the secondary air 43 in the axial direction 4 of the pulverized coal nozzle and expands it in the direction 5 perpendicular to the axial direction 4 of the pulverized coal nozzle.

Further, the backflow region expanding means 14 is an enlarged portion 15 which is a part of a conical surface which is enlarged in the axial direction 4 and the orthogonal direction 5 of the pulverized coal nozzle, and the pulverized coal nozzle which is extended to the enlarged portion 15 and extends. And a cylindrical parallel portion 16 parallel to the axial direction 4 of. The tip 18 of the secondary air nozzle of the first embodiment is located downstream of the tip 6 of the pulverized coal nozzle. Further, the reverse flow region expanding means 14 reduces the ejection speed of the secondary air 43 at the tip 18 of the secondary air nozzle and keeps the ejection direction of the secondary air in the axial direction 4 of the pulverized coal nozzle.

Further, the pulverized coal combustion burner 1 of the first embodiment is provided with an oil gun 8 which passes through the pulverized coal nozzle 2 and extends along the central axis 3 thereof, so that the pulverized coal combustion burner 1 is started up or It is designed to be able to support combustion during low-load combustion.
The pulverized coal nozzle 2 is connected to a pulverized coal transfer pipe (not shown) on the upstream side. Inside the pulverized coal nozzle 2 is provided a venturi 9 which is a narrowed portion that narrows the inner diameter of the nozzle.

The secondary air 43 and the tertiary air 44 are introduced into the wind box 36 by a blower (not shown),
The air swirl vanes 13 and 27 constituted by swirl vanes form a swirl flow, which is ejected from the secondary air nozzle 12 and the tertiary air nozzle 26, respectively. Flow path 29 for tertiary air
Is an annular flow path constituted by the partition wall 33, the furnace wall 40 and the outside of the secondary air nozzle 12. The flow path 19 for the secondary air is an annular flow path constituted by the outside of the pulverized coal nozzle 2, the partition wall 34, and the inside of the secondary air nozzle 12.
The blade angle of the air swirl blade can be adjusted by an opening adjusting rod (not shown), and the swirling strength of the secondary air and the tertiary air can be changed.

The pulverized coal combustion burner of the first embodiment having the above structure operates as follows. That is, the backflow region expanding means 14 expands in the axial direction 4 of the pulverized coal nozzle in a direction 5 orthogonal to the expanded portion 15, and the parallel portion 16 extending in the expanded portion 15 and parallel to the axial direction 4 of the pulverized coal nozzle. Since the secondary air 43 flows along the inner wall of the flow path 19 due to the swirling force and the nozzle area is expanded in the vicinity of the outlet of the secondary air nozzle, the secondary air 43 has a jet velocity in the direction shown by the arrow 20 in FIG. Becomes slower and the momentum in the axial direction 4 becomes weaker.

Further, by supplying the secondary air 43 and the tertiary air 44 as a swirling flow, a negative pressure region is formed inside the swirling flow. Since the momentum of the swirling flow is preserved, the swirl number indicating the strength of swirling becomes high. Therefore, the negative pressure caused by the swirling of the secondary air 43 is increased. In the negative pressure region inside the swirl flow, a reverse flow region 46 that flows from the downstream side toward the upstream side is formed. In this way, since the swirling force of the secondary air 43 does not change, the negative pressure acting on the central part of the swirling flow becomes strong, and the jetting direction of the secondary air 43 can be directed to the central direction of swirling. Since the pulverized coal flowing nearby and the secondary air are rapidly mixed, the barrier between the pulverized coal nozzle 2 and the secondary air nozzle 12, that is, the backflow region 46 formed on the downstream side of the flame holding plate 11 becomes large. .

Since the high temperature combustion gas flows in the backflow region 46, it has a function of promoting ignition of pulverized coal. Since a part of the pulverized coal ejected together with the primary air passes through the backflow region 46, providing the backflow region in the flame increases the time during which the pulverized coal stays in the flame. For this reason, the temperature rises near the pulverized coal combustion burner 1 and oxygen consumption progresses, the unburned content of the pulverized coal decreases, and together with the flame holding plate 11 and the swirling flow, the ignitability and flame holding of the pulverized coal are reduced. In addition to improving the combustion efficiency and the combustion efficiency, the reduction region is enlarged toward the downstream side to reduce the amount of NOx generated.

Further, by positioning the tip 18 of the secondary air nozzle on the downstream side of the tip 6 of the pulverized coal nozzle, the backflow region 46 formed on the downstream side of the flame holding plate 11 becomes large, so that a further reduction region is formed. Enlarge.

Further, as described above, the pulverized coal nozzle 2
Although a venturi 9 which is a narrowing portion for narrowing the inner diameter of the nozzle is provided inside, the venturi 9 is provided to temporarily increase the flow rate and prevent flashback of pulverized coal.

Further, since the secondary air passage has a constant area at its nozzle outlet, the secondary air is ejected in the axial direction. Therefore, the secondary air is separated from the tertiary air, and the vortex formed between the secondary air and the tertiary air becomes large. The vortex formed between the secondary air and the tertiary air has an effect of delaying the mixing of the tertiary air and the pulverized coal, and mixing the tertiary air on the downstream side of the flame to widen the reduction region. Furthermore, since the burnt gas circulates in this vortex, the temperature rises, which has the effect of promoting the ignitability of the pulverized coal. Therefore, the combustion efficiency is improved and the NOx emission amount is reduced.

Further, the primary air has a role of conveying pulverized coal and a role of combustion air, and the secondary air has a role of supplementing air necessary for igniting pulverized coal. . The tertiary air plays a role of replenishing the air necessary for completely burning the pulverized coal. In order not to discharge unburned matter, the total amount of primary air, secondary air, and tertiary air should be slightly larger than the amount of air required to completely burn pulverized coal (hereinafter referred to as theoretical air amount). There is a need. Normally, supply up to 1.2 times the theoretical air amount,
Burn with excess air. Further, the ratio of primary air is 20 to 25% of the total amount of air in order to avoid ignition in the pulverized coal pipe.
It is desirable that the ratio of the secondary air is 15 to 30% of the total amount of air, and the rest is supplied as tertiary air.

FIG. 2 is a sectional view showing a second embodiment according to the present invention. Pulverized coal combustion burner 1 of the second embodiment
Is a tertiary air nozzle 26 that is provided outside the secondary air nozzle 12 coaxially with the pulverized coal nozzle 2 and has a tertiary air swirl vane 27 that is a tertiary air swirl flow generator that ejects the tertiary air 44 as a swirl flow. Provided, the flow path 1 of the secondary air 43
9 and the flow path 29 of the tertiary air 44 are separated by a predetermined distance 38. The predetermined distance 38 is equal to the secondary air flow path 19
It is formed by inserting a spacer 39 between the secondary air flow path 29 and the secondary air flow path 29. In this way, the secondary air nozzle 12
By forming a predetermined distance 38 between the secondary air 43 and the secondary air nozzle 26, the tertiary air 44 is separated from the secondary air 43 and mixed with the pulverized coal on the downstream side of the flame. Therefore, the reduction region formed on the upstream side of the flame is widened, and the generation of NOx is suppressed.

FIG. 3 is a sectional view showing a third embodiment according to the present invention. Pulverized coal combustion burner 1 of the third embodiment
Has a reducing portion 17 extending in the parallel portion 16 and reducing in the direction 5 perpendicular to the axial direction 4 of the pulverized coal nozzle,
The expansion part 15 is provided with a reverse flow area expansion means 14 that expands from the position 6 of the tip of the pulverized coal nozzle 2. The one having the contracting section 17 extending in the parallel section 16 and the expanding section 15 expanding from the tip of the pulverized coal nozzle can easily and surely direct the ejection direction of the secondary air 43 to the center direction of the swirl. At this time, the secondary air 43 enlarges the backflow region 46 formed on the downstream side of the barrier between the pulverized coal nozzle 2 and the secondary air nozzle 12 by the swirling flow, and at the same time, the secondary air 43 and the pulverized coal flowing near the center of the swirling flow quickly. As a result, the ignition position of the pulverized coal approaches the pulverized coal combustion burner 1, and the combustion efficiency of the pulverized coal is improved.
Then, the temperature rises near the pulverized coal combustion burner 1, and oxygen consumption progresses. Therefore, the reduction region becomes large and N
Suppress the generation of Ox.

FIG. 4 is a sectional view showing a fourth embodiment according to the present invention. Pulverized coal combustion burner 1 of the fourth embodiment
Is provided with the reverse flow region expanding means 14 having an auxiliary nozzle 25 for ejecting gas at a jet velocity higher than the jet velocity of the secondary air 43 from around the tip 18 of the secondary air nozzle. The auxiliary nozzle 25 is provided in the spacer 39 that separates the secondary air flow path 19 and the tertiary air flow path 29, and gas is ejected from the auxiliary nozzle 25 in the axial direction 4 at a flow velocity faster than the ejection speed of the secondary air 43 and the tertiary air 44. Then, the ejection direction of the secondary air 43 is limited by the jet flow from the auxiliary nozzle 25.

The secondary air 43 tends to flow outward in the radial direction by the centrifugal force due to the swirling flow, but the jet flow from the auxiliary nozzle 25 flows outside the secondary air 43 in the axial direction 4 at a higher speed, so The secondary air 43 is jetted in the direction shown by the arrow 23 in the figure, and can suppress the radial flow in the right-angled direction 5. Therefore, the secondary air 43 rapidly mixes with the pulverized coal flowing near the center of swirling, and the ignition position of the pulverized coal approaches the pulverized coal combustion burner 1.

Since the auxiliary nozzle 25 has a small cross-sectional area, the flow rate is small and the jet flow is attenuated when the auxiliary nozzle 25 moves away from the nozzle. Further, due to the swirling of the secondary air 43, the negative pressure intensifies in the vicinity of the pulverized coal combustion burner 1, and the backflow region 46 increases and becomes stable. For this reason, the ignition and flame holding properties of the pulverized coal are enhanced, the ignition is promoted, the temperature rises near the pulverized coal combustion burner 1, oxygen consumption proceeds, the combustion efficiency of the pulverized coal improves, and the reduction region also increases. It spreads and the effect of suppressing NOx is enhanced.

FIG. 5 is a view taken in the direction of arrow I in FIG. 4, and FIG. 6 is a view taken in the direction of arrow I similar to FIG. As the shape of the auxiliary nozzle 25, as shown in FIG.
As shown in FIG. 6 and FIG. 6, it is formed in a plurality of jet ports 25b and the like divided in the circumferential direction.

FIG. 7 is a sectional view showing a fifth embodiment according to the present invention. Pulverized coal combustion burner 1 of the fifth embodiment
Is a reverse flow region expansion having a flow passage reducing portion 28 for reducing the flow passage 29 of the tertiary air nozzle 26 by enlarging the outside of the secondary air nozzle 12 in the direction 5 perpendicular to the axial direction 4 of the pulverized coal nozzle 2. Means 14 are provided.

In the case where the reverse flow region expanding means 14 has the flow passage contracting portion 28, the tertiary air 44 flows toward the outer periphery of the flow passage while being displaced by the swirling force while the tertiary air 44 flows in the flow passage 29. Most of the air flows around the outer circumference of the nozzle, and even if the flow passage 29 is narrowed by expanding the outside of the secondary air nozzle 12 at the nozzle outlet, the pressure loss hardly increases. By narrowing the flow path of the tertiary air 44 from the inside, the tertiary air 44 is ejected as a radially outward flow at the nozzle outlet. Therefore, the mixing of the tertiary air 44 and the pulverized coal near the pulverized coal combustion burner 1 can be delayed, the reduction region near the pulverized coal combustion burner 1 is enlarged, and NOx generation is suppressed. Further, the secondary air nozzle 1
As a result of expanding the diameter of the outside of 2, it is possible to reduce the diameter of the pulverized coal combustion burner 1.

In the pulverized coal combustion burner 1 according to the first to fifth embodiments described above, the flame holding plate 11 is provided at the tip of the pulverized coal nozzle 2. Since the flame holding plate 11 protrudes inside the pulverized coal nozzle 2 and exists as an obstacle to the flow of the primary air and the secondary air, the downstream side of the flame holding plate 11 becomes a negative pressure, and the pulverized coal and the combustion air are The backflow region 46 is easily formed. The high temperature combustion gas stays in the backflow region 46 and has a function of igniting the pulverized coal flowing there. Further, when the secondary air or the tertiary air is ejected as a swirling flow, the negative pressure on the downstream side of the flame stabilizing plate 11 is further increased by the centrifugal force, and the reverse flow region 4
6 is large and stable.

[0050]

EFFECTS OF THE INVENTION According to the pulverized coal combustion burner of the present invention, the ignitability and flame holding property of the pulverized coal are enhanced and the combustion efficiency is enhanced.
The reduction region is enlarged toward the downstream side to reduce the amount of NOx generated.

[Brief description of drawings]

FIG. 1 is a sectional view showing a first embodiment of a pulverized coal combustion burner according to the present invention.

FIG. 2 is a sectional view showing a second embodiment similar to FIG.

FIG. 3 is a sectional view showing a third embodiment similar to FIG. 1;

FIG. 4 is a sectional view showing a fourth embodiment similar to FIG. 1;

5 is a view on arrow I of FIG. 4. FIG.

6 is a view similar to that of FIG. 5, taken in the direction of the arrow I. FIG.

FIG. 7 is a sectional view showing a fifth embodiment similar to FIG.

FIG. 8 is a sectional view of a pulverized coal combustion burner according to a conventional technique.

[Explanation of symbols]

 1 Pulverized coal combustion burner 2 Pulverized coal nozzle 4 Axial direction 5 Right angle direction 6 Tip 12 Secondary air nozzle 13 Secondary air swirl vane (secondary air swirl generator) 14 Reverse flow region expansion means 15 Expanded part 16 Parallel part 17 Reduced Part 18 Tip 19 Flow path 25 Auxiliary nozzle 26 Tertiary air nozzle 27 Tertiary air swirl vane (tertiary air swirl generator) 28 Flow path reducing part 29 Flow path 38 Predetermined distance 41 Mixture 43 Secondary air 44 Tertiary air 45 Mixing Gas 46 Backflow region

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Masayuki Taniguchi 7-1, 1-1 Omika-cho, Hitachi-shi, Ibaraki Hitachi Ltd. Hitachi Research Laboratory (72) Inventor Choshiro Kitazawa 7-chome, Omika-cho, Hitachi-shi, Ibaraki No. 1 Incorporated company Hitachi Ltd. Hitachi Research Laboratory (72) Inventor Minoru Tamura 7-1-1 Omika-cho, Hitachi City, Ibaraki Prefecture Incorporated Hitachi Ltd. Hitachi Research Laboratory (72) Inventor Kenji Kiyama Kure City, Hiroshima Prefecture 6-9 Takaracho Babcock Hitachi Kure Factory

Claims (10)

[Claims] 1. A pulverized coal nozzle for ejecting an air-fuel mixture of pulverized coal and primary air, and a secondary air swirl flow provided coaxially with the pulverized coal nozzle on the outer side thereof and ejecting secondary air as a swirl flow. In a pulverized coal combustion burner provided with a secondary air nozzle having a generator, the secondary air nozzle is configured to extend a reverse flow region of a mixed gas generated on a downstream side around a tip end of the pulverized coal nozzle to a downstream side. A pulverized coal combustion burner having a basin expansion means. 2. The backflow region expanding means according to claim 1, wherein the jet direction of the secondary air of the secondary air nozzle is kept in the axial direction of the pulverized coal nozzle and is perpendicular to the axial direction of the pulverized coal nozzle. Pulverized coal combustion burner characterized by being expanded in the direction. 3. The backflow region expanding means according to claim 1, wherein the expanding portion expands in a direction orthogonal to the axial direction of the pulverized coal nozzle, and the axial direction of the pulverized coal nozzle extends in the expanding portion. A pulverized coal combustion burner characterized by having parallel parallel portions. 4. The pulverized coal combustion burner according to claim 1, wherein a tip of the secondary air nozzle is located downstream of a tip position of the pulverized coal nozzle. . 5. The backflow region expanding means according to claim 3, wherein the backflow region expanding means has a reducing part extending in the parallel part and contracting in a direction perpendicular to the axial direction of the pulverized coal nozzle, and the expanding part includes the fine powder. A pulverized coal combustion burner characterized by expanding from the tip of a charcoal nozzle. 6. The backflow region expanding means according to claim 1, wherein the backflow region expanding means has a jet velocity higher than a jet velocity of the secondary air jetted from the secondary air nozzle from around the tip of the secondary air nozzle. A pulverized coal combustion burner having an auxiliary nozzle for ejecting gas. 7. The tertiary air swirling flow generator according to claim 1, which is provided outside the secondary air nozzle coaxially with the pulverized coal nozzle and ejects tertiary air as a swirling flow. A pulverized coal combustion burner comprising a tertiary air nozzle, wherein the flow path of the secondary air and the flow path of the tertiary air are separated by a predetermined distance. 8. The backflow region expanding means according to claim 1, wherein the backflow region expanding means expands the outside of the secondary air nozzle in a direction perpendicular to the axial direction of the pulverized coal nozzle. A pulverized coal combustion burner having a flow passage reducing portion for reducing the flow passage. 9. A pulverized coal nozzle for ejecting an air-fuel mixture of pulverized coal and primary air, and a secondary air swirl flow provided coaxially with the pulverized coal nozzle on the outer side thereof and ejecting secondary air as a swirl flow. In a pulverized coal combustion burner provided with a secondary air nozzle having a generator, the secondary air nozzle slows down the ejection speed of the secondary air of the secondary air nozzle at the tip of the secondary air nozzle, and A pulverized coal combustion burner, characterized in that the ejection direction of the secondary air is kept in the axial direction of the pulverized coal nozzle. 10. The pulverized coal combustion burner according to claim 9, wherein the tip of the secondary air nozzle is located downstream of the tip of the pulverized coal nozzle.