JPH0244111A - Pulverized coal combustion method - Google Patents

Abstract

PURPOSE:To reduce the generation amount of NOX and to improve combustibility of pulverized coal by a method wherein combustion in a low air ratio in which NH3 is produced from a nitrogen compound in pulverized coal is effected at the former stage, and combustion in an air ratio of at least 1 is effected at the latter stage. CONSTITUTION:An auxiliary fuel injection nozzle 9 is arranged, and a flame stabilizer 4 is positioned along the tip of a pulverized coal injection nozzle 1. Pulverized coal is injected in a state, in which pulverized coal is spread in a furnace by means of primary air G1, through a flame stabilizer 4. In this case, the inner side of the flame stabilizer 4 is brought into a negative pressure state, and a part of secondary air G2 injected through a nozzle 2 is drawn in a position inside the pulverized coal and primary air G1 injection nozzle 1. By means of warp plates 5 and 6 positioned at the tips of the nozzles 2 and 3 and inclined at a given angle with the injection directions of the secondary air G2 and tertiary air G3, mixture of most of airs G2 and G3 with a mixture flow of pulverized coal and the primary air G1 at a central part is delayed. Combustion in a low air ratio is effected at the former stage by means of a mixture flow of the primary air and pulverized coal. At the latter stage, the secondary air and tertiary air are mixed together to perform combustion in an air ratio of at least 1.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a pulverized coal combustion method, and particularly to a pulverized coal combustion method suitable for achieving low NOx combustion.

[Background of the invention]

In pulverized coal combustion, a large amount of fuel Nox is generated because the N content in the coal is high. For this reason,
Environmental measures are necessary. For example, at fixed emission sources of pollutants such as thermal power plants, unburned carbon and NOx generated due to incomplete combustion of pulverized coal are subject to total volume regulations, and in the event of an emergency, it is necessary to control the amount of NOx generated. . Currently, the development of low NOx combustion technology is being promoted to improve combustion methods and suppress the generation of NOx.

Specifically, studies are underway to put this into practical use through the development of low NOx burners and the combination of multistage combustion methods.

[Purpose of the invention]

An object of the present invention is to provide a pulverized coal combustion method that can reduce the amount of NOx generated and improve the combustibility of pulverized coal.

[Summary of the Invention] An object of the present invention is to provide a method of combustion in which a mixed flow of pulverized coal and air is ejected from a burner, in which combustion is performed at a low air ratio to generate NH from nitrogen compounds in pulverized coal in the first stage. This is achieved by causing combustion to occur at an air ratio of 1 or more in the subsequent stage.

It is preferable that the burner used in the present invention includes a nozzle for ejecting a mixed flow of primary air and pulverized coal, a nozzle for ejecting secondary air, and a nozzle for ejecting tertiary air.

In particular, it is desirable to provide a secondary air jet nozzle around the outer periphery of the mixed flow jet nozzle of primary air and pulverized coal, and a tertiary air jet nozzle around the outer periphery of the secondary air jet nozzle. It is desirable that the secondary air be generated as a swirling flow.

Using a burner with this structure, combustion is performed at a low air ratio in the first stage using a mixed flow of primary air and pulverized coal, and combustion is performed at a low air ratio in the latter stage by mixing secondary air and tertiary air. It is desirable to have this done.

By changing the distribution ratio of secondary air and tertiary air and adjusting the position where the two are mixed, it is possible to further improve the combustibility of pulverized coal and at the same time suppress the amount of NOx generated.

[Embodiments of the invention]

FIG. 1 shows an embodiment of a burner used in the method of the invention. In this embodiment, the pulverized coal combustion burner is of a concentric cylindrical type, but it is not limited to the concentric cylindrical type, and other cylindrical types may be used.

In FIG. 1, an auxiliary fuel (for example, heavy oil for preheating or propane) injection nozzle 9 is arranged in the center of the burner, and a concentric pulverized coal injection nozzle 1 is provided adjacent to this. A flame stabilizer 4 is provided along the tip of the pulverized coal injection nozzle 1. This flame stabilizer 4 has a structure that expands in a curved shape with respect to the diameter of the nozzle 1, and when the pulverized coal is ejected into the furnace through the flame stabilizer 4 by the primary air G1, the flame stabilizer 4
It erupts in a state that spreads along the . At this time, the inside of the flame stabilizer 4 (the side in contact with the mixed flow of pulverized coal and primary air G1) becomes negative pressure, and the secondary air jetted from the nozzle 2 flows into the pulverized coal and the inside of the jetting nozzle 1. A part of the air G2 is drawn in. As a result, the pulverized coal forms a stable flame from the flame stabilizer 4 and is combusted. Further, at the tip of the secondary air jetting nozzle 2, a deflecting plate 5 is arranged which is inclined at a predetermined angle with respect to the jetting direction of the secondary air G2 (the axial direction of the nozzle). The baffle plate 5 delays the mixing of most of the secondary air G2 with the mixed flow of the pulverized coal and the primary air G1 in the center. Further, at the tip of the nozzle 3 for ejecting the tertiary air G, a deflector plate 6 is arranged which is inclined at a predetermined angle with respect to the ejecting direction of the tertiary air G3 (the axial direction of the nozzle).

Here, FIG. 2 shows the secondary air jet nozzle 2 under a constant condition that the angle θ3 of the deflector plate 6 of the tertiary air jet nozzle 3 is 10 degrees.
This is data obtained by examining the influence of the angle θ2 of the deflecting plate 5. The experimental conditions are as follows.

ΔPulverized coal combustion furnace dimensions: φ600m, length 5000mmΔ
Coal to be tested: Taiheiyo coal, a fine powder pulverized to 80% through a 200 mesh sieve was used.

ΔCoal supply amount; 20 kg/h ΔJ′eX empty% ml (J 1 ; 30 N m
/hΔThird air nozzle diameter I); φ300 side A mixed flow of primary air and pulverized coal performs combustion at a low air ratio called air Jtl-U-1J2 mixed flow with secondary air and pulverized coal. Next, air is mixed in L4-, so combustion with an air ratio of 1 or more is performed A
')

In Figure 2, X in the vertical axis X/D3 is the burner surface f) y
There is a distance C in the ejection direction of r, D, l: i: 3 method air ejection nozzle 3σ month-1 diameter, therefore X, / D
, 133rd air center part (combustion flame) 1,1-diffuses and shows the value when -C comes, Zunawaji, (+2" 1
Under the condition of 0-=65 degrees, diffusion IJ to the central part of rt, a-dimensional space: X/D, occurs at the position of ξ3.2 1. It shows that there is.

FIG. 3 shows the angle of the baffle plate 5 of the secondary air jet nozzle 2 being 0.
2 is constant at 10 degrees, and the ('l) of the tertiary air jet nozzle 3 is
The angle of raze・耘j6 is 0. It is a day that is influenced by cypress. Figure 3: From Figure 3, the diffusion position of tertiary air to the center of the large combustion flame, X/D'i, is -1.03
1t=y] must be 0 degrees or more.

Consisting of a mixed flow jetting nozzle 1 of one blow of air G and pulverized coal, a secondary air jetting nozzle 2 having a diagonal plate at its tip, and a tertiary air jetting nozzle 3 having a deflecting plate 3 at its tip,
J′ one, and F bubble generator 7 for the secondary air jet nozzle 2 and the tertiary air jet nozzle 3. The results of the combustion test of pulverized coal in a pulverized coal combustion burner equipped with L3 are shown in Figures 4jE and 5 (not shown), and the experimental conditions were 0. = 20 degrees, and θ is 30 degrees.
Figures 2 and 3 are the same as the experimental conditions.
2 Figure 4 shows 9' combustion in a pulverized coal combustion burner! Changes in oxygen concentration in the direction of the flame center axis are also shown, as in Figure 5 Lj, 1.1
” shows the change in Noxi degree in the flow direction above the flame center.

In both FIGS. 4 and 5, the horizontal axes represent the flow direction (direction) and the tertiary air nozzle (organized using the ratio of 1 radius and L5)-o.

The characteristics A to C shown in FIG. 5 correspond to the results of a combustion test under the same conditions. A in the figure is: tertiary air volume G, and secondary airscape (the distribution ratio of j2 is C; □/G, ?2,
B shows the results under Ga/G, :3, IJ, (Ha/G, = 4) under 15.-setting and 7-conditions.This combustion test The supply amount was kept constant and did not vary; only G was changed.

Masochist! -11-a Total amount of Kouki foxes GT (-20 x 4
- G Z 10 G] ) lj; fine powder t; 11 to burn 2, - necessary theory constriction G (for 11, (]-
17() The conditions for o = 1.2 and 111, C- are assumed to be constant. As a result, A(a s / a 27:2
), combustion progresses from the bar = - side, and from the burner side 11.). 0. is consumed and a low 08 region is formed, -'5.4'L. This tendency 1', i n ,
The same applies to the condition e of (:).

FIG. 4 shows the change in density between (-), dark I\r4' and the corresponding No. As a result of A in Figure 4), when combustion occurs on the burner surface, N in the coal is released as NOx.
C, NOx singing degree (3, shows a tendency to increase -5 t, 0
．． Concentration decreases /'': In the low 02 region, N H from N compounds in coal decreases.
This is because the denitrification reaction that reduces NOx to N occurs due to the coexistence of J'i, l, NOx, etc. 1. However, the characteristics of A in Figure 4 (Then low 0
．． The area is short. ,'-:,1j1.This is because the secondary air G and the 3-blown air G are mixed together, and G s /
G 2-2 under the present conditions ℃; = 4-t, the mixing of air becomes faster. It is expressed with - and mouth. As shown in FIG. 5, the NOx concentration tends to increase by ξ, J2 as O7 increases. This is low 0. N of 8NH3 exists in the area
This is because the oxidation reaction of OX/\ progresses (1) and the N compounds contained in the char are converted to NOx (11, a). Therefore, under the condition that G,!G,=2 of J″′,
Furnace D NOx ”” 200 ppm and Ic,
The effect of reducing NOx 'fr is small. , 29, the characteristics of B in Figures 4 and 5 are G i / G Z
``Tertiary air''
As shown in FIG. 4, by increasing It is possible to maintain the area for a long time. If this is shown in Figure 5, the gaseous reaction (due to NH of NOx) will also be stimulated, and NOx? ! IA degree is 80G 17
In contrast, the condition number of G 2 '' 2 is significantly reduced.

Even at locations where O2 concentration increases due to tertiary air mixing,
7"' means less increase in NOx.

This means that l'tT I(, is N0
xO') Since it is consumed in the first stage, the air is mixed with 1-
Since the amount of NH3 in p is small, the amount that is oxidized to NOx is also reduced, and the longer low o8 region lengthens the combustion time of the char, and the N content in the char is also released into the gas. The ratio becomes higher, and NO from 98 minutes of char
This is due to the fact that the amount of x generation also decreases.

Under this condition of G, /G, = 3, the furnace outlet NOx value is 11
00 pp, making it possible to reduce NOx to 1/2 compared to the condition of G3/G=2. Furthermore, the results of measurement under the condition of G, /G, = 4 are shown in curves C in Figures 4 and 5 showing changes in 0□ concentration and NOx concentration, and as G3 increases, the ejection speed of G. As G becomes higher and the momentum of G increases, the agitation and mixing becomes slower for the fuel in the center.
Since the low O2 area on the central axis can be maintained for a longer period of time, the NOx reduction reaction can be promoted, and the NOx at the furnace outlet can be reduced to 70p.
It became pm.

In other words, low NOx can be achieved by controlling G and G2 within the range of G 3 / G * > 2, and these operations change the angles of the secondary air and tertiary air registers. It can be easily achieved by just

Next, from the results under each of these conditions A-C, the position where secondary and tertiary air mixes (
When the position Jl-WQ in FIG. 4 is rearranged in relation to the slow draw diameter D3 of the tertiary air nozzle 3, it can be expressed as follows. First, under condition A, X/D.

Valve 2, X/D343 under conditions B and X/D under conditions C.
D. It was illusion 4. Therefore, increasing G, /G, means increasing X/D, and the inventors' study results set G, /G, > 3 and the condition that X/D, > 3. This is effective in achieving low NOx combustion.

Also, from Figures 2 and 3, the conditions for setting X/Dff are:
The angle of the deflector plate 5 of the secondary air jet nozzle 2 is 10 to 65.
The angle of the baffle plate 6 of the tertiary air jet nozzle 3 is 10 degrees or more. Therefore, when the baffle plate has these angles, low NOx combustion can be efficiently achieved.

Furthermore, the reason why the swirlers 7 and 8 are provided in the secondary air nozzle 2 and the tertiary air nozzle 3 is that the primary air burns the pulverized coal under low air ratio conditions, and the flame and the secondary and tertiary air nozzles are
This is effective for promoting proper mixing of the next air, and when there are no swirlers 7 and 8 and the swirling flow is not ejected, the second
Mixing of secondary air and tertiary air becomes faster. Therefore, the swivel
The space between the deflecting plates has the effect of slowing down the mixing of secondary and tertiary air with the flame of pulverized coal combustion.6 [Effects of the Invention] According to the present invention, the ignitability of pulverized coal is improved and the flame holding effect is achieved. It has a low NOx effect, which increases the amount of NOx generated and the amount of NOx generated is less than 1 oopp m. The amount of NOx generated can be controlled simply by controlling the secondary air and tertiary air, which can greatly contribute to improved reliability.

[Brief explanation of the drawing]

Figure 1 is a schematic diagram of a pulverized coal burner for explaining the combustion method of the present invention, and Figures 2 and 3 are characteristics showing the relationship between the angle of the baffle plate and the diffusion position of tertiary air to the center of the combustion flame. 4 and 5 are characteristic diagrams showing combustion characteristics depending on the distribution of the tertiary air amount and the secondary air amount. 1... A nozzle that ejects a mixed fluid of primary air and pulverized coal. 2... Secondary air jet nozzle, 3... Tertiary air jet nozzle, 4... Flame stabilizer, 5.6
... deflection plate, 7, 8 ... swirler, 9 ... auxiliary fuel nozzle.

Claims (1)

[Scope of Claims] 1. In a method in which a mixed flow of pulverized coal and air is ejected from a burner and combusted, combustion is performed at a low air ratio to generate NH_3 from nitrogen compounds in pulverized coal in the first stage, and in the second stage, A pulverized coal combustion method characterized by performing combustion at an air ratio of 1 or more. 2. In claim 1, the burner includes a mixed flow jetting nozzle that jets out a mixed flow of primary air and pulverized coal, and mixing secondary air into the mixed flow jetted from the mixed flow jetting nozzle. A secondary air jetting nozzle and a tertiary air jetting nozzle for mixing tertiary air into the mixed flow are provided, and the mixed flow jetted from the mixed flow jetting nozzle performs the combustion at the low air ratio, and the mixed flow is A pulverized coal combustion method characterized in that combustion is performed at a later stage with an air ratio of 1 or more by mixing the secondary air and the tertiary air. 3. Claim 2, wherein the burner includes a mixed flow jet nozzle that spouts a mixed flow of primary air and pulverized coal, and a swirling flow of secondary air provided around the outer periphery of the mixed flow jet nozzle. A pulverized coal combustion method comprising: a secondary air jetting nozzle that jets out a secondary air jetting nozzle; and a tertiary air jetting nozzle that is provided around the outer periphery of the secondary air jetting nozzle and jetting out a swirling flow of tertiary air. . 4. In claim 2, the tertiary air amount G
_3 and the distribution of secondary air amount G_2 (G_3/G_2) to 3
A method of combustion of fine powder characterized by controlling the above conditions. 5. In claim 2, the diameter D_3 of the tertiary air jet nozzle and the distance in the jet direction from the burner surface X
3 in the area where X/D_3 shown by the relationship with is 3 or more
A pulverized coal combustion method characterized by mixing air with combustion flame ejected from another nozzle.