JPH02298703A - Pulverized coal burner - Google Patents

Abstract

PURPOSE:To allow the burner to contrive low NOx by providing a contracted part in a pulverized coal feed pipe of a denitrification burner to arrange a resistor so as to allow the flow of pulverized coal to go toward the center of a furnace in a pulverized coal burner in which the denitrification burner and an after-air port are provided to set the air ratio at a specified value. CONSTITUTION:In pulverized coal firing equipment in which a denitrification burners 8, 9 and an after air port shown in no figure are provided upward of a main burner and an excess air ratio in a burner part is set equal to or less than 0.9, a contracted part 37 is formed in a pulverized coal feed pipe 36 of the denitrification burners 8, 9 to arrange a resistor 38. In this constitution, a momentume having combustion air is increased by the part 37 and a resistor 38 even if air for the denitrification burners 8, 9 is lowered and combustion gas of the denitrification burners 8, 9 is allowed to reach the center part of a boiler furnace 1 to perform denitrification combustion so as to actualize low NOx.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a combustion device for reducing nitrogen oxides (NOx), and particularly to a pulverized coal burner that achieves a significant reduction in NOx during combustion of pulverized coal. It is.

[Prior Art] Due to recent changes in the fuel situation, coal-fired boilers that use coal as the main fuel are increasing among commercial boilers that are starting to be used in large-scale power plants.

In this coal-fired boiler, the coal is pulverized by a pulverizer into pulverized coal with an amount of about 70% passing through 200 meshes, for example, in order to improve the combustion efficiency of one coal combustion.

However, fossil fuels contain N in addition to fuel components such as C and H, and pulverized coal in particular has a higher N content than gaseous fuels or liquid fuels.

Therefore, NOx generated during combustion of pulverized coal is larger than NOx generated during combustion of gaseous fuel and liquid fuel, and therefore, it is desired to reduce NOx as much as possible.

NOx generated during the combustion of various fuels is thermal (Th
eraml) N Ox and Fuel NO
Thermal NOx is broadly classified into 2 types, but thermal NOx is generated by the oxidation of nitrogen in the combustion air, and is highly dependent on flame temperature, and the higher the flame temperature, the more thermal NOx is generated. do. On the other hand, Funiel NOx is N in fuel.
It is generated by the oxidation of N in the fuel, and is highly dependent on the oxygen concentration in the flame.
Minutes tend to become fuel NOx.

Combustion methods to suppress the generation of NOx include a multistage combustion method in which combustion air is divided into multiple stages and injected, and an exhaust gas recirculation method in which combustion exhaust gas with a low oxygen temperature is mixed into the combustion area. All of these low NOx combustion methods reduce the temperature of the combustion flame through low oxygen combustion.
The purpose is to suppress the generation of thermal NOx.

However, between thermal NOx and fuel NOx,
It is thermal NOx that can suppress the amount of NOx generated by lowering the combustion temperature, and the amount of fuel NOx generated has little dependence on combustion temperature.

Therefore, conventional combustion methods aimed at lowering the flame temperature are effective for combustion of gaseous fuels and liquid fuels with low nitrogen content, but they usually contain a large amount of nitrogen (1 to 2 wt%). The effect on pulverized coal combustion is small.

On the other hand, the combustion mechanism of pulverized coal consists of the pyrolysis process of pulverized coal in which volatile components are released, the combustion process of the released volatile components, and the combustion process of combustible solid components (hereinafter referred to as char) after pyrolysis. Become.

The combustion rate of this volatile component is much faster than that of the solid component, and the regulated component burns at the early stage of combustion. In addition, during the thermal decomposition process, the N contained in the pulverized coal is divided into two types: one that is volatilized and released like other combustible solid components, and the other that remains in the char.

Therefore, fuel NOx generated during pulverized coal combustion is
NOx from volatile N minutes and NO from N minutes in char
Among fuel NOx, fuel NOx from char is generated for the first time when char burns, so NOx continues to be generated until after combustion.
This measure is an important point.

It is known that volatile N becomes compounds such as NH, HCN, etc. in the initial process of combustion and in the oxygen-deficient combustion region. In addition to reacting with oxygen to form NOx, these nitrogen compounds can also serve as reducing agents that decompose the generated NOx into nitrogen.

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.

In addition, the production of reducing substances progresses more rapidly as the atmosphere becomes lower in oxygen concentration.

As described above, an effective method for reducing NOx during combustion of pulverized coal is a combustion method in which a volatile nitrogen compound having reducing properties and NOx coexist, and the nitrogen compound reduces NOx to nitrogen.

In other words, a combustion method that eliminates generated NOx and NOx precursors by using reducing nitrogen compounds such as NH, which is a precursor of NOx, is effective for reducing NOx. be.

FIG. 13 is a schematic system diagram of a pulverized coal-fired boiler, FIG. 14 is an enlarged sectional view of the denitrification burner shown in FIG. 13, and FIG. 15 is a sectional view showing a state of mixing of flames from the main burner and the denitrification burner.

In FIG. 13, a front side wall 2 and a rear side wall 3 of a boiler furnace 1 are shown.
Main burners 4, 5, 6, 7 and denitrification burners 8, 9 are arranged in order from the bottom to the top of the boiler furnace 1.

An after air port 10.11 for reducing NOx is provided above the denitrification burners 8 and 9, and an after air port 10.
Air is supplied from the one can after air box 13 to the after air ports 10 and 11 from the morning after air air box 14 and the afternoon after air air box 15, respectively.

On the other hand, main burner 4. ．． 5, 6, 7. Coal is fed to the denitrification burner 8°9 by sending the coal from the coal bunker 16 to the mill 18 from the coal feeder 17 and pulverizing it within the mill 18.

Coarse particles in the pulverized coal are separated in the mill 18 by a classifier (not shown), returned to the crushing section in the mill 18, and re-pulverized to become pulverized coal.

This pulverized pulverized coal is supplied from the mill 18 through a pulverized coal pipe 19 to main burners 4, 5, 6, 7 and denitrification burners 8, 9.

On the other hand, the combustion air to the morning wind box 12, afternoon wind box 13, morning after air wind box 14, and afternoon after air wind box 15 is pressurized by the forced draft fan 20, and then passed through the air preheater 2.
1, air duct 22° air volume adjustment damper 23, air duct 2
4 to each wind box 12°13.14.15.

In this way, from the mill 18, the pulverized coal pipe 19 to the main burner 4.5,
6, 7, the pulverized coal supplied to the denitrification burners 8, 9 is combusted in the boiler furnace 1 by the combustion air supplied to each wind box 12, 13, 14.
, 7. A main combustion region 25 and a denitrification combustion region 26 are formed in the boiler furnace 1 where the denitrification burner 8.9 is located, and an after combustion region 27 is formed in the boiler furnace 1 where the after air ports 10 and 11 are located.

Also, in the boiler, exhaust gas is supplied to the hopper 28 for steam temperature control during partial load from an exhaust gas recirculation fan 29 and an exhaust gas recirculation passage 30, and from the outlet of the exhaust gas recirculation fan 29 to the air passage 24 for low NOx measures. An exhaust gas duct 31 is provided for mixing exhaust gas into the combustion air.

Denitrification combustion in the boiler furnace 1 is carried out at each main burner 4°5.6
, 7, the amount of air in the wind box 12 is smaller than the theoretical amount of air required to burn the pulverized coal supplied to the denitrification burners 8 and 9.
After the air is supplied from 13 and burned, the insufficient amount of air is supplied to the after air port 10 of the morning and after air wind boxes 14° and 15.
．． 11 to achieve complete combustion.

Therefore, the main combustion area 25. In the denitrification combustion region 26, a reduction flame is formed, so that the nitrogen content in the pulverized coal is prevented from oxidizing and becomes chemically stable N2.

On the other hand, in the after-combustion region 27, due to air shortage, after-air is supplied from the after-air port 10.11 to the combustibles (mainly char) remaining in the main combustion region 25 and the denitrification combustion region 26 to achieve complete combustion. The flame becomes an oxidizing flame.

In addition, FIG. 14 shows denitrification burners 8 and 9 of the prior art, in which 2 and 3 are the front side wall and the rear side wall, 32 is a flame stabilizer, and 3 is a denitrification burner.
3 is a heavy oil burner.

FIG. 15 shows the gas flow within the boiler furnace 1 using the conventional denitration burner 8.9 for denitration in the furnace.

Normally, the amount of combustion gas from the in-furnace denitrification burners 8, 9 is smaller than that from the main burners 4, 5, 6.7, and therefore lacks the ability to penetrate into the center of the boiler furnace 1. That is, as shown in FIG. 15, the front side wall 2 of the boiler furnace 1 is
, the denitrification burner flame 35 runs along the rear side wall 3, and mixing of the main burner flame 34 and the denitrification burner flame 35 is not preferable in denitrification combustion.

[Problems to be Solved by the Invention] When the pulverized coal flow in the conventional denitrification burners 8 and 9 shown in FIG. Spread radially. Normally, this spread angle is always positive unless the pulverized coal flow is a supersonic flow.

Therefore, even if the momentum of the pulverized coal is increased, the penetration force of the pulverized coal cannot be effectively utilized because it spreads at the nozzle outlet.

On the other hand, in order to increase the denitrification effect of the denitrification burners 8 and 9, it is necessary to increase the penetration power of the denitrification burners 8 and 9. However, if the flow velocity of the pulverized coal and the primary air for transporting the pulverized coal is simply increased in order to increase the momentum of the denitrification burners 8 and 9, the flow velocity exceeds the flame propagation velocity, resulting in poor ignition and flame holding. This causes problems such as an increase in unburned content and difficulty in controlling the load.

The present invention attempts to eliminate such drawbacks of the prior art, and its purpose is to provide a pulverized coal burner that can perform denitrification combustion by increasing the penetration force from the denitrification burner.

[Means for Solving the Problems] In order to achieve the above-mentioned objects, the present invention provides a reduced portion in the pulverized coal supply pipe of a denitrification burner, and provides resistance for directing the pulverized coal flow toward the center in the pulverized coal supply pipe. This is the arrangement of the body.

[Operation] By providing the pulverized coal supply pipe with a reduced portion and arranging the resistor, the pulverized coal flow at the outlet of the denitrification burner can be directed toward the central axis of the denitrification burner even at subsonic speeds.

Therefore, the penetration force of pulverized coal into the furnace can be increased, and a large backflow space is created in the flame stabilizer installed around the outer periphery of the denitrification burner nozzle, allowing high-pitched combustion gas in the boiler furnace to efficiently return to the flame stabilizer. As a result, the combustion gas from the denitrification burner can be efficiently mixed with the combustion gas from the main burner, and the flame can be stabilized.

[Example] Embodiments of the present invention will be described below with reference to the drawings.

Fig. 1 is an enlarged cross-sectional view of a denitrification burner according to an embodiment of the present invention, Fig. 2 is a cross-sectional view showing the relationship between the denitrification burner of Fig. 1 and the main burner, and Figs. 3 (A) and (B) are conventional 3(C) and (D) are explanatory diagrams showing the combustion characteristics of the denitrification burner according to the embodiment of the present invention, and FIGS. 4 and 5 are characteristic curves of the denitrification burner. Figure 6 is a cross-sectional view showing the mixing state of flames from the main burner and the denitrification burner,
FIG. 7 is a sectional view of the flame of the denitrification burner according to the embodiment of the present invention, FIG. 8 is a sectional view taken along the line ■-■ in FIG. 7, FIG. 9 is a comparison of combustion characteristics, and FIGS. 11 and 12 are cross-sectional views of a denitrification burner showing other embodiments.

In FIG. 1, reference numeral 1 denotes a boiler furnace, 2 and 3 front and rear walls, 8 and 9 denitrification burners, and 32 a flame stabilizer, which is the same as the conventional one.

36 is a pulverized coal supply pipe for the denitrification burners 8 and 9, 37 is a reduction portion, and 38 is a resistor disposed within the pulverized coal supply pipe 36.

In such a structure, the difference between the conventional denitrification burner shown in FIG. 14 and the denitrification burner according to the embodiment of the present invention shown in FIG. As shown in Fig. 1, the flame stabilizer 32 was attached to the pulverized coal supply pipe 36, but the denitrification burners 8 and 9 in Fig.
The difference is that a reduced part 37 having a nozzle structure with a constricted tip is provided between the pulverized coal supply pipe 36 and the flame stabilizer 32, and a resistor 38 is disposed within the pulverized coal supply pipe 36.

In other words, in a coal-fired boiler, in order to efficiently reduce NOx, the selection of pulverized coal fuel and the denitrification burner 8, 9
It is important to efficiently contact and mix the combustion gas from the main burner 4゜5.6.7 with the combustion gas from the main burner.
In the conventional denitrification burners 8 and 9, the denitrification burners 8,
When the air ratio to 9 decreases, the momentum of the combustion air also decreases, making it difficult for the combustion gas to reach the center of the boiler furnace 1, resulting in poor mixing with the combustion gas containing a large amount of NOx, resulting in denitrification combustion. can't do it.

However, in the denitrification burners 8 and 9 shown in FIG. 1, even if the air ratio to the denitrification burners 8 and 9 decreases,
7 and the resistor 38 increase the momentum of the combustion air, the denitrification burner 8,
9 combustion gas arrives and denitrification combustion can be performed.

FIG. 2 shows an example in which the denitrification burners 8, 9 of the present invention are combined with conventional pulverized coal main burners 4, 5, 6, 7. Second
The figure shows a system in which the pulverized coal sent to the denitrification burners 8 and 9 is switched to the denitrification burners 8 and 9 by a pulverized coal flow path switcher 39 shown in the figure. This is because the structure of the denitrification burners 8 and 9 of the present invention makes it difficult to incorporate a heavy oil burner 33, etc., as shown in FIG.

Therefore, the single heavy oil burner 33 is started, and even with only oil, 100%
A switching burner 40 is provided to allow load relief. Since the switching burner 11 allows the air ratio to be made the same between the burners, it becomes possible to use normal combustion and denitrification combustion. Of course, it is used exclusively for denitrification combustion in the furnace, and the heavy oil burner 40
If there is no need to take a 100% load, the switching burner 40 shown in the figure is not necessary.

FIG. 3 shows the combustion characteristics of the conventional denitrification burner and the denitrification burner of the present invention.

Figure 3 (A) shows the particle flow in the vicinity of a conventional denitrification burner. a m 1 v 1 is the momentum of the primary air and pulverized coal shown by the solid line, and m2v2 is the combustion momentum shown by the broken line. Indicates the momentum of secondary air. (
m: mass flow rate, ■=flow velocity) When the air ratio in the barring section is high, the momentum n,2v2 of the combustion air exceeds that of the pulverized coal jet, so the flight trajectory 41 of the pulverized coal particles becomes large. It curves and returns to the flame holder 32, creating a flame surface 42 behind the flame holder 32, and stable flame holding is performed.

FIG. 3(B) shows a case where denitrification combustion is performed using a conventional denitrification burner, but the pulverized coal particles do not return to the flame stabilizer 32 because the air ratio is lowered to 0.9 or less. This is because the momentum m2v2 of the combustion air decreases due to the decrease in the amount of secondary air shown by the broken line, making it difficult to form a backflow region.

FIG. 3(C) shows an example in which a resistor (cone) 38 is arranged at the center of the denitrification burner. Due to the effect of the resistor (cone) 38, a space is created between the secondary air shown by the broken line and the pulverized coal flow shown by the solid line, making it easier for the particles to return, but the flame surface 42 is slightly blown away.

FIG. 3(D) shows a case where the momentum of the secondary air is increased in addition to FIG. 3(C). By bringing the ratio of the momentum of the pulverized coal flow to the momentum of the secondary air close to that of conventional combustion conditions using a conventional denitrification burner, stable flame holding can be achieved.

FIG. 4 shows the velocity component of the pulverized coal particles in the axial direction of the burner versus the axial distance in the conventional denitrification burner and the denitrification burner according to the present invention. u/u.

indicates the speed ratio to the initial speed. FIG. 4 shows experimental data, and the particle size of the pulverized coal used in the experiment was 75% passing through a 20O mesh (74 μm), and the mass flow rate ratio of the pulverized coal to the air conveying it was 0.6.

In Figure 4, the speed ratio relative to the axial distance is 1.0 for a while.
, which indicates the length of the potential core.

Compared to conventional denitrification burners, the potential core of the denitrification burner of the present invention is longer, and the distance at which the axial speed is reduced to 1/2 is also approximately 50% longer, increasing the penetrating force. This is thought to be because the effect of No. 38 causes pulverized coal particles with a large specific gravity to be collected on the central axis of the denitrification burner, increasing inertial force and making it difficult for the particles to diffuse in the radial direction.

FIG. 5 shows the momentum m2v2 of secondary air and the momentum m2v2 of primary air and the momentum of pulverized coal in a denitrification burner with a parallel throat and a resistor 38 of the present invention inserted into pulverized coal piping 36. The relationship between the ratio of m 1 v 1 and the unburned content at the furnace outlet was obtained using an experimental device. This fifth
As can be seen from the figure, when the momentum m2v2 of the secondary air is small, a sufficient backflow area cannot be obtained, so the amount of unburned matter becomes high, and in the case of the denitrification burner of the present invention, the ratio of m'2v2 to m1vl is 3.
It was found that the unburned matter was the smallest at 0.

As described above, the denitrification burner 8 of the present invention shown in FIG.
, 9, the penetrating force from the denitrification burners 8 and 9 increases even during denitrification combustion, so that the main burner flame 34 and the denitrification burner 35 are better mixed, and denitrification combustion can be performed.

FIG. 7 is a cross-sectional view of the flame near the denitrification burner according to the present invention, and FIG. 8 is a fixed view taken along the line ■--■ in FIG. 7th
According to the denitrification burner shown in FIGS. and 8, a denitrification burner flame 35 exists in the flame stabilizer 32, and an ignition source for the pulverized coal flow 44 exists. However, the momentum of the pulverized coal flow 44 in the axial direction is maintained by the effect of the resistor 38, and the denitrification burner flame 35 has an elongated shape as shown in the figure.

Further, since diffusion with the secondary air 43 is also suppressed, the denitrification burner flame 35 tends to exist only outside the pulverized coal flow 44. Further, inside the pulverized coal flow 44, as shown in FIG. 8, particles 45 receive radiant heat 46 from the denitrification burner flame 35 and release volatile matter 47. However, in the center of the pulverized coal flow 44, it is difficult for the radiant heat 46 to reach the center, and since there is a lack of oxygen, the pulverized coal particles remain or the N content in the fuel is released into the gas phase, resulting in a state of HCN or NH3. It is transported to the center of the furnace, where it efficiently contacts the mainstream combustion gas and reduces NOx in the mainstream combustion gas.

FIG. 9 shows a comparison of combustion characteristics between a conventional denitrification burner and a denitrification burner according to the present invention.

Curve A in the figure shows the relationship between NOx and unburned content in the ash produced by a conventional denitrification burner. Curve B shows the combustion characteristics when a resistor is attached to the pulverized coal feed pipe in addition to a conventional air throat widened by 25 degrees. Curve C shows the case where a resistor is attached to the parallel throat.

In addition, when a resistor is attached, the influence of its position is also shown in a straight line. At the O position, the tip of the resistor is
It shows the case where it coincides with the tip of the pulverized coal supply pipe, + indicates when it is inserted into the furnace, and - indicates when it is pulled out.

From this Fig. 9, in addition to the resistor, the parallel throat is N
It can be seen that it is effective in reducing Ox and unburned matter.

10 to 12 show other embodiments.

In the one shown in FIG. 10, a pulverized coal disperser 48 is installed upstream of the resistor 38 in order to disperse the pulverized coal and eliminate uneven flow at the burner outlet. Pulverized coal disperser 48
．． The material to be used is one with excellent wear resistance, such as ceramics.

Furthermore, in order to increase the momentum of the secondary air (combustion air) 43 in the axial direction, the parallel part of the burner throat 49 is made longer, and the opening distance in the radial direction is set as X.
Let Z be the length of the parallel portion, so that Z/L is at least 2 or more.

Now, the denitrification burners 8 and 9 of the present invention can be applied not only to denitrification burners having an air swirler but also to various combustion devices as long as flame holding is possible at the nozzle outlet.

, FIG. 11, and FIG. 12 show examples in which a resistor 38 is attached to a denitrification burner that does not use a combustion air swirler. By restricting the pulverized coal flow 44 and attaching the resistor 38, the pulverized coal flow 44 at the nozzle outlet is directed toward the burner center axis, forming a flow path for the secondary air (combustion air) 43.

A gap is created between the pulverized coal flows 44, and this gap can be used as a flame stabilizer 32.

In such a structure, the burner nozzle and the resistor 3
8, even if it is not an axis-symmetric shape.

You can get the same effect.

[Effects of the Invention] According to the present invention, the performance of the denitrification burner in a pulverized coal-fired boiler is improved, and the mixing and diffusion of combustion gas is promoted in the furnace, which not only reduces NOx but also makes the furnace more compact. can be realized.

On the other hand, the instability of the flame that was observed in conventional denitrification burners with low air ratio combustion is eliminated, and stable combustion can be performed even when the load changes. effect can be obtained.

[Brief explanation of the drawing]

Fig. 1 is an enlarged sectional view of a denitrification burner according to an embodiment of the present invention, Fig. 2 is a sectional view showing the relationship between the denitrification burner of Fig. 1 and the main burner, and Figs. 3(A) and (8) are conventional FIG. 3 (C) is an explanatory diagram showing the combustion characteristics of the denitrification burner. (D) is an explanatory diagram showing the combustion characteristics of the denitrification burner according to the embodiment of the present invention, Figures 4 and 5 are characteristic curve diagrams of the denitrification burner, and Figure 6 is the mixture of flames from the main burner and the denitrification burner. A cross-sectional view showing the state, Figure 7 is a cross-sectional view of the denitrification burner flame,
FIG. 8 is a sectional view taken along the line ■-■ in FIG. 7, FIG. 9 is a comparison of combustion characteristics, and FIGS. 10, 11, and 12 are sectional views of denitrification burners showing other embodiments. FIG. 13 is a schematic system diagram of a pulverized coal-fired boiler, FIG. 14 is a sectional view of a conventional denitrification burner, and FIG. 15 is a sectional view showing a mixed state of the flames of the main burner and denitrification burner No. 9. 4.5, 6, 7... Main burner, 8, 9...
... Denitrification burner, 10, 11 ... After air port, 36 ... Pulverized coal supply pipe, 37 ...
-Reduced part, 38...Resistor. m1 Figure 6 Figure 2 Figure 3 Figure 4 ↑ x/Xo = /, 3 Figure 5 Figure 14 Figure 15

Claims (1)

[Scope of Claims] A denitrification burner for burning pulverized coal and an after air port are provided above a main burner for burning pulverized coal, and the air ratio (combustion air amount/theoretical air amount) in the burner portion is 0.9 or less. The pulverized coal is burned in a pulverized coal, characterized in that the pulverized coal supply pipe of the denitrification burner is provided with a reduced portion, and a resistor is arranged in the pulverized coal supply pipe to direct the flow of the pulverized coal toward the center. Burna.