JPH01256708A - Low NOx combustion method for pulverized coal and burner for pulverized coal combustion - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a combustion method and a combustion device for a pulverized coal boiler, and particularly to a combustion method and a combustion device suitable for reducing the amount of NOx generated within a pulverized coal combustion flame. This invention relates to a low NOx combustion method for pulverized coal and a burner for pulverized coal combustion.

[Conventional technology]

In addition to fuel components such as carbon and hydrogen, fossil fuels also contain nitrogen (
N) minutes are included. In particular, coal has a higher N content than gaseous fuel or liquid fuel.

Therefore, during the combustion of coal, NOx, i.e. NO.

N oxides such as NO
There is a strong desire to reduce Ox.

NOx generated during combustion of various fuels is classified into thermal NOx and fuel NOx depending on the form of generation. Thermal NOx is generated by oxidizing nitrogen in combustion air with oxygen, and fuel NOx is generated by oxidizing N in fuel. In order to suppress the generation of NOx, conventional methods include a multistage combustion method in which combustion air is divided into multiple stages and supplied, and an exhaust gas circulation method in which combustion exhaust gas with low elemental content is mixed into the combustion region.

The common principle of these low NOx combustion methods is to suppress the reaction between nitrogen and oxygen by lowering the temperature of the combustion flame. However, thermal NOx can be suppressed by lowering the combustion temperature, and fuel NOx
The generation of x has little dependence on combustion temperature. Therefore,
Combustion methods that reduce flame temperature are effective in reducing NOx from fuels with low N content. However, D.
, W., Pershing and J.O.L., W.
As is clear from the experimental results in the following paper by Endt, in the case of coal combustion, fuel NOx accounts for about 80%, so conventional combustion methods have little effect.

The Influence of Flame Temperature and Call Composition on Thermal and Fuel, NOO
ce of flaoge temperature
and coal coo+position on
thermal and fuelNox; Th
e 5ixteenth Symposium (Int
ernational) on Combustion
, P389-399゜The Combustion
In5titut, 1976) The combustible components in coal can be roughly divided into volatile components and solid components. According to the unique properties of coal, the combustion of pulverized coal consists of a thermal decomposition process of the pulverized coal in which volatile matter is released, and a combustion process of combustible solid components (hereinafter referred to as char) after the thermal decomposition. The burning rate of volatile matter is faster than that of char, and volatile matter is burned in the initial combustion process. In addition, during the thermal decomposition process, the N content in the coal is also divided into those that are volatilized and released like other combustible components and those that remain in the char.

Therefore, fuel N generated during pulverized coal combustion.

The gas is NOx from volatile N and N from N in char.
It can be divided into Ox.

However, D. W. Pershing and J.
As pointed out by O. L. and Wendt, in the case of coal combustion, most of the NOx is generated from volatile N, and a technology that targets this is required as a low NOx combustion method.

It is known that volatile N becomes compounds such as NH, HCN, etc. in the initial stage of combustion and in the oxygen-deficient combustion region. These nitrogen compounds not only react with oxygen to become NOx, but also react with generated NOx and serve as reducing agents that decompose NOx into N2.

This NOx reduction reaction by nitrogen compounds proceeds in a system in which NOx coexists, and in a reaction system in which NOx does not coexist, most of the nitrogen compounds are oxidized to NOx.

This reduction reaction progresses more easily under high-temperature conditions such as combustion, and in a lower oxygen atmosphere.

Therefore, in order to reduce NOx generated from coal combustion flames, the technical key is how to create this low oxygen concentration atmosphere.

The burner for burning pulverized coal for forming a low oxygen concentration atmosphere in the flame, which has been known so far, was disclosed in Japanese Patent Laid-Open No. 61-12.
As shown in Japanese Patent Application Laid-open No. 2408 and Japanese Patent Application Laid-Open No. 61-235604, there is a burner that delays the mixing of excess air with a low air ratio combustion flame by separating the secondary or tertiary air for combustion from the fuel injection hole. There is.

[Problem to be solved by the invention]

In the conventional combustion method described above, secondary air or tertiary air is ejected as a straight flow from an air nozzle that is radially distant from the fuel injection port. Therefore.

Mixing of the low air ratio flame and excess air is delayed, and a region with low oxygen concentration can easily be formed within the low air ratio flame, but the combustion time is lengthened due to the delayed mixing, and the combustion rate is reduced. Another problem is that the combustion device becomes larger.

An object of the present invention is to provide a low NOx combustion method for pulverized coal that improves the method of mixing excess air and a low air ratio flame, and a burner for combustion of the pulverized coal.

[Means to solve the problem]

In order to achieve the above object, the pulverized coal of the present invention has low NOx
In the combustion method, the pulverized coal is combusted by supplying primary air, which transports the pulverized coal, and secondary and tertiary air, which divides and supplies the remaining combustion air, through separate nozzles. Low NO of pulverized coal
x In the combustion method, the combustion process of pulverized coal.

(a) A mixture of primary air and pulverized coal is ejected from a pulverized coal nozzle, and the ejected air is mixed with secondary and tertiary air over a distance equal to or longer than the inner diameter of the ejection port of the pulverized coal nozzle. (2) A first mixing process in which the mixture with the secondary air is slowly promoted to promote ignition after the storage is suppressed and preserved; There is a method characterized by two mixing processes and completing combustion through the following steps.

The pulverized coal combustion burner that implements the above-mentioned pulverized coal low NOx combustion method includes a pulverized coal nozzle that airflows pulverized coal using primary air and blows out the pulverized coal, and a pulverized coal nozzle that blows out the pulverized coal, and the remaining combustion air. In a pulverized coal combustion burner comprising a secondary air nozzle and a tertiary air nozzle which are decomposed and supplied from the outside of the pulverized coal nozzle, the pulverized coal nozzle has an enlarged cross-section portion at the tip thereof, and a flame stabilizing portion at the tip thereof. There is a burner characterized in that it includes a cross-section reduced part that also serves as a ring, and a spacer provided between the secondary air nozzle and the tertiary air nozzle.

Furthermore, it is more effective even if the enlarged section of the pulverized coal nozzle is concentric, or if the flame-holding ring is annular.

[Effect]

In the pulverized coal low NOx combustion method configured as above,
The combustion process consists of a first mixing process and a second mixing process, and in the first mixing process, the air-fuel mixture is ejected from the pulverized coal nozzle using primary air for transporting pulverized coal, ignites the pulverized coal, and the ejected Since the pulverized coal is stored by suppressing its mixing with secondary air and tertiary air at a distance equal to or longer than the inner diameter of the ejection port of the pulverized coal nozzle, a low oxygen concentration region is formed in the center of the flame, and the pulverized coal The high concentration of NOx generated at the center of the flame where
2 and NOx is reduced. In the second mixing process, tertiary air is rapidly mixed.

The combustion rate is improved by promoting the combustion of unburned fuel. In the first mixing process, if the distance over which the air-fuel mixture is ejected and stored from the pulverized coal nozzle is less than the inner diameter dimension of the pulverized coal nozzle ejection port, the suppression of mixing with secondary air and tertiary air will be insufficient and This will not result in a low oxygen concentration area.

In the pulverized coal combustion burner for carrying out the above-mentioned pulverized coal low NOx combustion method, the pulverized coal nozzle has an enlarged section at the tip, so the cross-sectional area of the mixed air flow of pulverized coal and primary air is The streamlines of the mixed air flow widen, reducing the flow velocity of the mixed air flow and increasing the outer secondary air flow velocity. The expanded streamlines of the mixed gas flow become contracted at the cross-sectional reduction part that also serves as a flame-holding ring at the tip of the pulverized coal nozzle, and are ejected. Since pulverized coal in the air mixture has inertia,
Pulverized coal tends to concentrate at the center of the nozzle at the enlarged cross-sectional area, and the larger the particles, the greater the inertial force, so the pulverized coal concentrates at the center. Therefore, a high-concentration pulverized coal flow is formed on the downstream side of the flame-holding ring at the nozzle tip, so a low 0□ concentration region is formed in the center of the flame, reducing NOx and NOx.
x Reduce concentration. A mixed layer with secondary air is formed on the outer periphery of this pulverized coal flow, and this mixed layer becomes a vortex, which effectively ignites and holds the flame of the pulverized coal on the trailing side of the flame-holding ring. . In addition, by providing a spacer between the secondary air nozzle and the tertiary air nozzle, the tertiary air nozzle is separated from the pulverized coal nozzle, and after the formation of the low 02 concentration region in the center of the flame, the unburned In order to sufficiently mix the fuel with the air for complete combustion, the mixing speed with the tertiary air on the downstream side is increased, and the primary jet is mixed with the secondary and tertiary jets, resulting in complete combustion. and reduce NOx
Reduce.

Furthermore, by making the enlarged section of the pulverized coal nozzle concentric, and by making the flame stabilizing ring circular, the mixing of the primary, secondary, and tertiary jets is stabilized.

〔Example〕

An embodiment of the present invention will be described below with reference to FIGS. 1 to 6. An example of the configuration of a pulverized coal combustion burner for achieving the combustion method of the present invention is shown in FIG. This burner has a concentric ring shape, and has a pulverized coal nozzle 2 in its center that spouts pulverized coal together with primary air for transporting pulverized coal.* Inside the pulverized coal nozzle 2 is a liquid combustion nozzle used to preheat the combustion furnace. 1 is placed. A secondary air nozzle 3 is arranged on the outer periphery of the pulverized coal nozzle 2. A tertiary air nozzle 4 is arranged on the outer periphery of the secondary air nozzle 3.

A pulverized coal nozzle tip 8 with an expanded nozzle cross section is attached to the tip of the pulverized coal nozzle 2, and an annular flame-holding ring 9 is attached to the tip, so the flow path shape at the tip of the pulverized coal nozzle 2 is , which becomes an enlarged section and a reduced section of the cross section. The tertiary air nozzle 4 is spaced apart from the secondary air nozzle 3 so that a tertiary air jet can be ejected in a straight direction.

The secondary and tertiary air nozzles 3 and 4 are swirl generators 6 and 7, respectively.
is installed and used to adjust the swirl strength of the secondary and tertiary air jets. Further, each flow rate of primary air, secondary air, and tertiary air can be arbitrarily controlled by a device (not shown).

The functions of the pulverized coal combustion burner of the present invention having the above-mentioned configuration will be explained using FIG. 2. FIG. 2 is a characteristic diagram showing the mixing ratio of the primary jet of the mixture of pulverized coal and conveying air shown in FIG. Also listed.

During pulverized coal combustion, argon (Ar) is injected into the primary jet stream, and helium (Ha) is injected into the secondary air to become a tracer gas, and the concentration of each tracer gas at the center of the flame is analyzed 1.
Next, add argon (Ar) to the primary jet.

Helium (He) is injected into the tertiary air, the concentration of each tracer gas in the flame center is analyzed, and from the results of these two analyses, the standard mixing parameter Φg1 is used to evaluate the mixing using the following formula based on the concentration of each tracer gas. I asked for

Φg1=1−(Unφg x / Q 11φm,
) In the formula, φg indicates the mixing index of the primary jet obtained from the tracer concentration at each measurement point in the flame and the tracer inlet concentration, and φg1 indicates that the tracer in the primary jet is completely mixed with the secondary and tertiary air. When the standard mixing parameter Φg□ in the formula 0, which indicates the complete mixing index when mixed with , is 1, φg1
1, indicating that the inlet concentration of the tracer and the measurement point concentration are equal, and that the primary jet is not mixed with the secondary and tertiary air and is preserved. When Φg□ is 0, φg; φ
g.

This shows that the primary jet has completely mixed with the secondary air and tertiary air. Inner diameter d
, (outlet diameter) is expressed as a logarithm and is made dimensionless. In addition, under condition A of the pulverized coal combustion burner of the present invention in the figure, the ejection velocity v1 of the primary jet is 12.6 m/
s, primary air ratio (ratio of input air amount to theoretical air amount) λ1 = 0.16, condition B is V, =: 15.2
m/s, λ, = 0.21, and the effective range of the primary air ratio λ is 0.15 to 0.25.

Also.

In the conventional technology, V, = 15 m/s, λ, = 0.21
The results are shown under the following conditions. When the pulverized coal combustion burner of the present invention shown in FIG. 1 is used, the mixing parameters Φg1 and ff
The relationship 1n (L/do) is expressed as a linear relationship with a bending point, and the slope of the straight line is gentle on the upstream side near the burner, and the slope of the straight line becomes large on the downstream side of the bending point. In contrast, in burners of the prior art, the mixing process is represented by a single straight line, and the mixing progresses with the same slope. The slope of these straight lines represents the mixing speed of air, and the larger the slope, the higher the mixing speed. In the conventional technology, the mixing parameter Φg0 is Q n (L/d o) = O1, so L
At the distance of =do, it is already less than 1, and mixing is fast,
The primary jet is not preserved. From this result, when using the burner of the present invention, Qn(L/d,)f'
ql, i.e. L: (2-3) X d.

The primary jet is preserved up to a distance of It is characterized by Furthermore, when operating conditions A and B of the present invention shown in FIG. 2 are compared, in both conditions A and B, Φg1=1 near the burner, and the primary jet flow is preserved. When mixing is started, the gradient of the straight line is greater under condition B than under condition A, so the mixing speed is faster. Also, the complete mixing position where Φg0 is 0 is also A.

Mixing was completed in the order of A and B, depending on the conditions of B.

However, the burner of the present invention is characterized in that even if such operating conditions are changed, the combustion process of pulverized coal consists of a two-stage mixing process after the primary jet storage.

The above describes the mixing process of the primary jet, secondary air, and tertiary air jet of the pulverized coal combustion burner of the present invention.

Next, changes in the NOx and 0□ concentrations in the flame under the same conditions as in FIG. 2 above, where the air mixing process is different, will be explained using FIGS. 3A, 3B, and 4A to 4C. Figures 3A and 3B show the comparison results between the conventional technology and the present invention regarding NOx and 0□ concentration changes in the gas flow direction from the burner surface at the center of the flame. A and B show changes in gas composition during combustion under the same operating conditions as A and B of the prior art and the present invention in FIG. 2 above. 0. In the burners of the prior art and the present invention, the concentration is consumed and decreased by ignition of pulverized coal at the burner surface, and the 02 concentration is already low approximately 0.5 m downstream from the burner surface, forming a low oxygen concentration region. . Further, in both the conventional technology and the present invention, a portion of the N content in the coal is released as NOx when combustion starts, so NOx increases.

It has the effect of being reduced and reduced in low oxygen concentration areas.

However, the difference between the present invention and the prior art is that N in Figure 1 is
The Ox concentration increases in the order of conditions A and B using the burner of the present invention, and then the conventional technology. This is largely influenced by the pulverized coal concentration at the center of the flame immediately after it is ejected.

As one of the data showing this, Figs.
In the conventional technology shown in FIG. 4A, which shows the results of comparison under the three conditions, compared to each condition of the present invention, a low oxygen concentration region of 02=1% or less is formed in a wide range in the furnace radial direction near the burner surface. There is. This indicates that the pulverized coal is dispersed in the radial direction of the furnace from the center of the flame immediately after being ejected, and combustion is proceeding in the radial direction of the furnace. =1% or less is formed downstream of the burner surface, and although this region is narrow, it exists in the center of the flame. On the other hand, condition B in Figure 4C
In this case, as in A, a region of 02=1% or less is formed in the center of the flame, but this region is formed larger than in A. Conditions A and B of the present invention are characterized by the presence of a low 03 concentration region near the center of the flame, and unlike the prior art, the flame does not spread over a wide area immediately after being ejected.

It can be seen that pulverized coal is concentrated in the center of the flame and combustion is progressing. As described above, a low O2 concentration region is essential for promoting the reduction reaction of NOx generated. Low 0□
It is preferable that the concentration region be formed closest to the burner surface, but in the conventional technology in which the concentration region is formed widely in the radial direction of the furnace, the NOx concentration discharged on the downstream side is This is higher than the operating conditions A and B of the present invention, and the method in which pulverized coal is dispersed and burned has a small NOx reduction effect. On the other hand, under the conditions of the present invention, in which pulverized coal is collected at the center of the flame and a low O2 concentration region is formed at the center of the flame, the emitted NOx concentration is also low, and the low NOx effect is greatly improved, resulting in NOx reduction. The effect is great.

Above are the results of NOx, O, concentration changes shown in Figures 3A and 3B and the 0□ concentration distribution shown in Figures 4A to 40, and the primary jet flow, secondary and 3rd order jet flow shown in Figure 2 above. In comparison with the mixing process of secondary air, in the conventional technology, the primary jet is not stored on the burner surface, and the effect of making the pulverized coal concentrate in the flame center immediately after ejection is small, so the primary jet is This indicates that it spreads and becomes easier to mix with secondary and tertiary air. On the other hand, in A and B of the present invention, since the pulverized coal exists in the center, the primary jet flow has less spread, and as a result, the mixing with the secondary and tertiary air is controlled, and the Saved. After that, after the mixing started, there was a low 0□ in the center of the flame, even though the mixing was progressing quickly.
A region of concentration is formed and extends into the wake. it is,
This indicates that the oxygen in the air that is mixing from the outer periphery is rapidly consumed because combustion is progressing rapidly. Also, because the amount of N remaining in the char is reduced.

As shown in FIGS. 3A and 3B, the amount of NOx re-increased on the downstream side is reduced, and as a result, the concentration of NOx discharged can be controlled.

Next, the combustion rate of pulverized coal particles was compared between the combustion burner of the present invention shown in FIG. 1 and the prior art. In the conventional technology, as shown in Fig. 2, the standard mixing parameter Φg > = O
The position where , that is, the position where the mixing of the primary jet and the secondary and tertiary jets is completed, is on the downstream side compared to any of the conditions of the present invention. Therefore, the combustion rate decreases by the amount of delay in the supply of air to complete combustion. Comparing the combustion rate at the combustion furnace outlet (residence time of about 3 seconds) between the conventional technology and the present invention, the conventional technology is 97%, and the present invention is 97% under operating condition A.
It was 98% under operating condition B, and 99% under operating condition B, making it clear that in addition to the NOx reduction effect, it also had the effect of improving the combustion rate (not shown). The shape of the pulverized coal nozzle and its function will be explained using FIGS. 5 and 6. The pulverized coal nozzle 2 in the combustion burner of the present invention is characterized by having the enlarged section of the pulverized coal nozzle tip 8 and the reduced section that also serves as the flame-holding ring 9 provided at the tip, as described above. A mixture 13 of pulverized coal and primary air is introduced from a tubular flow path with an inner diameter d1, and then guided to an enlarged cross-section flow path with an inner diameter d2, so that the streamlines of the air mixture 13 widen. Next, by the reduced cross-section part which also serves as the flame-holding ring 9 with the inner diameter d0 at the tip,
The expanded streamlines of the air-fuel mixture 13 turn into contractions and are ejected. The pulverized coal in this air-fuel mixture 13 has an inertial force unlike gas, so it concentrates at the center of the nozzle. The larger the particle size, the greater the inertial force of the pulverized coal, and the larger the particle size, the more effective it can be in the center of each nozzle. Figure 6 shows
FIG. 6 is a schematic diagram showing the characteristics of the pulverized coal nozzle of the present invention shown in FIG. Ru. On the downstream side of the flame-holding ring 9, a low-pressure area is formed around the outer periphery of the pulverized coal flow 15 in the highly concentrated storage, and a mixture M16 of primary air and secondary air is formed, and this mixed layer 16 is formed by a vortex flow. So,
It effectively acts on the ignition of pulverized coal and flame holding on the downstream side of the flame holding ring 9. The flame-holding ring 9 promotes ignition and forms a flame, thereby improving combustibility. The shape of the pulverized coal nozzle that brings about this effect is based on the results of various studies: d, = (1,1-1.5)Xd.

Q=(2~3)Xd,,d,=(0,7~0.9)Xd
.

It has been found that shapes and dimensions that satisfy the following relationship are preferable.

Further, the inner diameter d0 of the flame stabilizing ring 9 is determined by the jetting speed of the mixture 13 of pulverized coal and primary air, and the jetting speed V
, = 12@/s or more and 25 m8 or less has been experimentally confirmed to be effective for promoting the ignition of pulverized coal (not shown). The shape of the flame-holding ring 9 to be formed is preferably annular, and if slits or holes are provided on the ring as in the prior art, when a part of the air-fuel mixture 13 passes through these slit channels or annular channel, the flow rate will be reduced. This creates an unbalance in the flame, which tends to cause the flame to tilt, making it impossible to maintain a stable flame. Therefore, it is most effective in forming a flame to form a ring shape whose cross section is evenly reduced, as in the present invention shown in FIG.

Next, as shown in FIG. 2, in order to preserve the air-fuel mixture immediately after ejection, the flow velocity of the air-fuel mixture 13 and the flow velocity of the secondary air ejected from the secondary air nozzle 3 adjacent to the pulverized coal nozzle 2 must be adjusted. has an important role. The larger the difference in flow velocity between the two, the easier it is to form a mixed layer 16 at the interface between the two, which speeds up the mixing and makes it difficult for the air-fuel mixture 13 to be preserved. Regarding the flow velocity ratio between the two, the relationship between the jetting speed V of the air-fuel mixture 13 and the jetting speed v2 of the secondary air is Vy/V, = 1.0 to 1.
．． Combustion conditions that result in a range of 5 are preferred.

Thereby, as shown in FIG. 2, the combustion method with the mixing process of the present invention is achieved in which the primary jet is stored near the burner. Furthermore, after the formation of the low 02 concentration region, in order to increase the mixing speed of the tertiary air on the downstream side and complete the mixing of the primary jet with the secondary and tertiary jets, as shown in Figure 1, A spacer 10 is provided between the secondary air nozzle 3 and the tertiary air nozzle 4 to separate the tertiary air nozzle 4 from the pulverized coal nozzle 2, and to make the outer periphery of the tertiary air nozzle 4 protrude by a refractory material 11. This can be achieved by blowing out tertiary air as a swirling flow.

This effect can be achieved by using the secondary air nozzle 3 without providing the spacer 10.
This greatly reduces NOx and improves the combustion rate, which cannot be achieved with conventional burners that have a tertiary air nozzle immediately on the outer periphery of the burner. Furthermore, by improving the combustion rate of the combustion burner, it is possible to prevent the burner from becoming larger.

〔Effect of the invention〕

Since the present invention has been achieved as described above, it produces the effects described below.

By the low NOx combustion method of pulverized coal of the present invention, pulverized coal is ignited while the primary jet is stored near the combustion burner surface, and after ignition, combustion proceeds while slowly promoting mixing.
After that, mixing can be rapidly promoted and an air mixing process can be obtained, so the combustion rate can be easily increased.Furthermore, a low air ratio flame is formed in the center of the flame, and the NOx generated by low 02 concentration area
The reduction reaction of N can proceed easily.

X can be reduced.

Also, in the pulverized coal combustion burner of the present invention, if one condition is selected by changing the air mixing process, even lower N
Oxification and combustion rate can be improved.

Further, by making the enlarged section of the pulverized coal nozzle concentric, and by making the flame stabilizing ring circular, it is possible to further reduce NOx and improve the combustion rate.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal sectional view showing the configuration of a pulverized coal combustion burner according to the present invention, and FIG. 2 is a graph showing the relationship between the distance from the burner tip of the pulverized coal combustion burner and the standard mixing parameter.
3A and 3B are graphs showing the relationship between the distance from the burner tip and the NOx concentration and O2 concentration, respectively.
Figures 40 to 40 are diagrams showing the 02 concentration distribution in the vertical and horizontal distances from the center of the burner tip, Figure 5 is a perspective view showing the structure of the pulverized coal nozzle of the pulverized coal combustion burner according to the present invention, and Figure 6 is 6 is a schematic diagram showing the operation of the pulverized coal nozzle of FIG. 5. FIG. 2...Pulverized coal nozzle, 3...Secondary air nozzle, 4...
...Tertiary air nozzle, 9...Flame holding ring. 10...Spacer, 13...Mixture mixture, 14...2
Next air, 15...Pulverized coal flow, 16...Mixed layer.

Claims (1)

[Claims] 1. The pulverized coal is produced by supplying the primary air that airflows the pulverized coal, and the secondary and tertiary air that divides and supplies the remaining combustion air through separate nozzles. In the low NO_x combustion method for pulverized coal, the combustion process of the pulverized coal includes: (a) ejecting a mixture of primary air and pulverized coal from a pulverized coal nozzle; A first mixing process in which mixing with secondary and tertiary air is suppressed and stored for a distance equal to or longer than the inner diameter of the jet nozzle, and then mixing with secondary air is slowly promoted to promote ignition; (b) Next, a second mixing process in which mixing with tertiary air is rapidly progressed to complete combustion;
＿x combustion method. 2. A pulverized coal nozzle that transports pulverized coal using primary air and jets it out; a secondary air nozzle that divides the remaining combustion air and supplies it from the outside of the pulverized coal nozzle; and tertiary air. A pulverized coal combustion burner comprising: a pulverized coal nozzle having an enlarged cross-section portion at the tip thereof, a reduced cross-section portion serving as a flame-holding ring at the tip thereof, the secondary air nozzle and the tertiary air nozzle; A pulverized coal combustion burner characterized by comprising a spacer provided in the middle of the pulverized coal combustion burner. 3. The pulverized coal combustion burner according to claim 2, wherein the pulverized coal nozzle has a concentric enlarged section. 4. The pulverized coal combustion burner according to claim 2, wherein the flame stabilizing ring is annular.