JPH086901B2 - Pulverized coal low nitrogen oxide burner - Google Patents

Description

TECHNICAL FIELD The present invention relates to a pulverized coal low nitrogen oxide burner used for a pulverized coal burning boiler or the like.

[Prior Art] In addition to fuel components such as carbon and hydrogen in fossil fuels,
Contains nitrogen. In particular, coal has a higher nitrogen content than gas fuel or liquid fuel. Therefore, the amount of nitrogen oxides generated during combustion of coal is larger than that generated during combustion of gaseous fuel, and there is a demand for reducing the amount of nitrogen oxides as much as possible.

Nitrogen oxides generated during combustion of various fuels are classified into thermal nitrogen oxides and fuel nitrogen oxides depending on the generation mode. The thermal nitrogen oxides are produced by oxidizing nitrogen in combustion air with oxygen, and the fuel nitrogen oxides are produced by oxidizing a nitrogen component during combustion. In order to suppress the generation of these nitrogen oxides, conventionally, there are a multistage combustion method in which combustion air is divided and supplied in multiple stages, and an exhaust gas recirculation method in which combustion exhaust gas having a low oxygen concentration is mixed into a combustion region. The common principle of these low nitrogen oxide combustion methods is to suppress the reaction between nitrogen and oxygen by lowering the temperature of the combustion flame. However, it is the thermal nitrogen oxides whose generation can be suppressed by the decrease of the combustion temperature, and the generation of fuel nitrogen oxides has little dependence on the combustion temperature. Therefore, the combustion method of lowering the flame temperature is effective in reducing nitrogen oxides from combustion with a low nitrogen content. DWPers
Fuel nitrogen oxides play a role in the combustion of coal, as evidenced by the experiments by hing and JOL Wendt.
Since it occupies 80%, the conventional low nitrogen oxide combustion method is less effective. Regarding this, the influence of frame temperament and call composition on thermal and fuel nu-ex; the sixty symposium on conversion p389-399 the conversion institute 1976, the influence of fl
ame temperature and coal composition onthermal and
fuel NO _X ; The Sixteenth Symposium (International)
on Combustion, P389−399, The Combustion Institute, 19
76.

The combustible components in coal can be roughly classified into volatile components and solid components. According to the characteristics peculiar to this coal, the combustion composition of pulverized coal is the pyrolysis process of pulverized coal from which volatile components are released, and the combustible solid component after pyrolysis (hereinafter referred to as char).
Combustion process. The burning rate of the volatile component is faster than that of the solid component, and the volatile component burns in the initial stage of combustion. Further, in the thermal decomposition process, the nitrogen component contained in the coal is divided into those that are volatilized and released and those that remain in the char, like many combustible components. Therefore, the fuel nitrogen oxides generated during combustion of pulverized coal are divided into nitrogen oxides from volatile nitrogen components and nitrogen oxides from nitrogen components in char.

However, as pointed out by DW Pershing and JOL Wendt, in the case of coal combustion, most of the nitrogen oxidation is generated from volatile nitrogen components, and as a low-nitrogen oxide combustion method, a technology targeting this is required. To be done.

It is known that volatile nitrogen components become compounds such as NH ₃ and HCN in the initial process of combustion and in the combustion region where oxygen is insufficient. These nitrogen compounds react with oxygen to form nitrogen oxides, and also serve as reducing agents that react with generated nitrogen oxides to decompose the nitrogen oxides into nitrogen. The nitrogen oxide reduction reaction by this nitrogen compound proceeds in the coexisting system with the nitrogen oxide, and in the reaction system in which the nitrogen oxide does not coexist, most of the nitrogen compound is oxidized to the nitrogen oxide. This reduction reaction tends to proceed under a high temperature condition such as combustion as the atmosphere becomes lower in oxygen concentration. Therefore, in order to reduce the nitrogen oxides generated from the coal combustion flame, the technical key is how to create this low oxygen concentration atmosphere.

A burner for forming a low oxygen concentration atmosphere known in the flame has been used as a burner for combustion as shown in JP-A-61-295402 and JP-A-61-235604. There is a burner that delays the mixing of excess air and low air ratio combustion flames by moving secondary or tertiary air away from the combustion jets.

[Problems to be Solved by the Invention] In the above-described conventional combustion method, secondary or tertiary air is jetted as a straight flow from an air nozzle radially separated from the combustion jet port. Therefore, the mixing of the low air ratio flame and the excess air is delayed, and it is easy to form a region with a low oxygen concentration in the low air ratio flame, but the combustion time becomes longer and the combustion rate is increased due to the delay of mixing. descend. Alternatively, there is a problem that the combustion device becomes large. Further, in the conventional technology, the fuel nozzle and the secondary air ejection nozzle have an annular shape, and when ash adheres to the tip of the fuel nozzle during operation, or when the load ejection speed or air ejection speed changes, However, there is a problem in that the ignition position is changed and the combustion flame cannot be stably formed due to the flame. As a result, there are problems that the emission amount of nitrogen oxides increases and the combustion rate decreases.

The present invention is intended to solve such a problem. That is, it is an object of the present invention to provide a low nitrogen oxide burner which improves the mixing method of excess air and low air flame. More specifically, the ignition and flame holding properties are improved, a low oxygen concentration region is efficiently formed in the flame center, and after the nitrogen oxides are reduced and reduced in this region, the unburned fuel remaining in this region is reduced. By rapidly advancing the mixing of the air with the complete fuel air in the low oxygen concentration wake, it is possible to prevent a decrease in the combustion rate and an increase in the size of the combustion device, and at the same time, to provide a means for reducing nitrogen oxides. Especially.

[Means for Solving the Problems] The above object of the present invention is achieved by further improving the mixing method of combustion air and combustion. That is, a pulverized coal nozzle for ejecting a mixed flow of pulverized coal and primary air,
A secondary air nozzle arranged concentrically with the nozzle on the outer periphery thereof, and a tertiary air nozzle arranged on the outer periphery of the secondary air nozzle concentrically with the pulverized coal nozzle, similarly to the secondary air nozzle. The pulverized coal burner provided has a swirl flow generator for ejecting secondary air and tertiary air as a swirl flow, and the ejection passage of the secondary air is formed in a polygonal shape, the tip of which is a polygonal reducer. Arrange the block body of the structure, further, between the secondary air nozzle and the tertiary air nozzle,
A spacer was installed to delay mixing of the secondary air and the tertiary air, and the outer tube of the tertiary air nozzle was made longer than the pulverized coal nozzle and the secondary air nozzle.

[Operation] In the burner of the present invention, the burner is constituted by the tubular fuel nozzle, the polygonal secondary air nozzle, and the tubular tertiary air nozzle, so that the vortex flow of the secondary air jet is formed at the vertex of the polygonal shape. Since it is possible to form a mixed layer region that is formed to promote the deceleration effect of the injected fuel and promotes the mixing of the fuel and the pulverized coal, the acceleration of ignition and the flame holding property are improved. Further, the spacer installed between the secondary air nozzle and the tertiary air nozzle delays the mixing of the secondary air and the tertiary air by keeping a distance in the radial direction, thereby reducing the nitrogen oxides. Form a region. The swirl generator installed in the tertiary air nozzle further delays the mixing with the fuel jetted as a straight flow by making the tertiary air a swirl flow, and utilizes a region of low static pressure generated inside the swirl flow, Mixing of unburned fuel remaining in the reducing atmosphere with the tertiary air can be promoted in the downstream stream of the flame to prevent the flame from becoming longer and the combustibility to be reduced. In addition, the tertiary air nozzle prevents the phenomenon that the tertiary air, which appears when the swirling strength of the tertiary air is increased, from spreading too much in the radial direction, and also improves the efficiency of generating the tertiary air swirl flow. It is longer than the other nozzles, and a swirl flow promotion section is provided. Further, in the present invention, since the combustion air is decomposed into secondary air and tertiary air and can be injected, the air amount of secondary air for ignition and low air flame and the tertiary air for complete combustion, and the ejection speed are It can be controlled independently and can cope with the change in the type of pulverized coal used. Further, the spacer and the swirl generator installed between the secondary air nozzle and the tertiary air nozzle function to clearly distinguish the role of each air.

[Embodiment] FIGS. 1 and 2 show a first embodiment of the present invention. This burner is a cylindrical pulverized coal flow path 11 from which a mixture of pulverized coal and primary air for conveying the same is ejected, and a polygonal secondary for ejecting secondary air installed on the outer periphery thereof. The air flow path 12, a polygonal reducer 15 at the tip of the secondary air flow path 12, and a cylindrical tertiary air flow path 13 installed on the outer circumference of the secondary air flow path 12. Further, in the pulverized coal flow path 11, a liquid fuel nozzle 14 used as an auxiliary when preheating the combustion furnace is arranged, and liquid fuel such as heavy oil is jetted at the time of preheating.

Swirling flow generators 16 and 17 are installed in the secondary air flow path 12 and the tertiary air flow path 13, respectively, and are used to adjust the swirling strength of the secondary and tertiary air jets.
Reference numerals 6 and 17 denote radial flow generators, which adjust the magnitude of the tangential velocity component (swirl component) of the secondary and tertiary air flowing in from the radial direction by changing the blade angle.

Between the secondary air passage 12 and the tertiary air passage 13, a spacer 18 having a polygonal shape on the inner side and an annular shape on the outer side is provided in order to slow the mixing of the secondary air and the tertiary air.

In FIG. 1, 19 is a block, 20 is an arrow indicating the inflow of secondary air, 21 is an arrow indicating the inflow of tertiary air, 22 is a wind box, 23 is an air inlet, and 24 is the introduction of combustion air. It is an arrow shown.

In the pulverized coal low-nitrogen oxide burner configured as shown in FIG. 1 and FIG. 2, the pulverized coal ejected from the pulverized coal flow passage 11 has primary air for transporting it and secondary air. It is ignited by air, and a flame with a low air ratio is formed in the flame center. This low air ratio flame is stabilized by the polygonal reducer 15 and the secondary air flow rate shown in FIG.

FIG. 3 shows an aspect of the primary jet flow and the secondary air jet flow of the burner shown in FIGS. 1 and 2. That is, the square reducer 15 shown in FIG. 2 causes the secondary air (see the arrow 20 in FIG. 3) to generate vortexes at four locations corresponding to the apex of the reducer 15, and the boundary with the pulverized coal flow to be ejected. The mixed layer 25 is easily formed on the surface, the jet flow of the pulverized coal and the primary air for transportation that is jetted is decelerated, the ignition is promoted, and the flame holding property can be improved by the formation of the vortex.

FIG. 4 shows a second embodiment of the present invention. This second
In the embodiment, the polygonal reducer 15 has a regular hexagonal cross section. In the second embodiment as well, like the reducer 15 having the square cross section shown in FIG. 2, swirling flows of secondary air are generated at the six apexes, and the similar effect is obtained for promoting ignition of pulverized coal.

Further, in the burner of the present invention, the spacer 18 arranged between the tertiary air and the secondary air jet delays the mixing of the tertiary air and the low air specific flame, so in the low air specific flame, in the vicinity of the burner, After the oxygen in the combustion air is consumed by the ignition, a reducing atmosphere having a low oxygen concentration is formed. The tertiary air is used to completely burn the remaining unburned fuel after the nitrogen oxides have been reduced in the reducing atmosphere. Therefore, after the nitrogen oxides have been reduced, the tertiary air must rapidly mix with the central stream to oxidize the remaining unburned fuel.

For this, like the burner shown in the above-mentioned known example,
A burner that ejects tertiary air as a straight flow from a position separated in the radial direction is effective in forming a reducing atmosphere because the mixing of the central jet and the tertiary air jet proceeds slowly, but it is effective in the reducing atmosphere. It does not mix rapidly with the remaining unburned fuel, resulting in a longer flame. Or, it has a drawback that the amount of unburned fuel emitted increases.

On the other hand, in the burner shown in FIG. 1, the tertiary air is ejected as a swirling flow. Since the tertiary air ejected as a swirling flow has a flow direction different from that of the fuel ejected as a rectilinear flow, it is less likely to be mixed in the vicinity of the burner outlet than that ejected as a rectilinear flow. Also, as the swirl strength increases, the static pressure in the central part decreases, so that in the wake of the flame, a circulation flow with a flow from the wake toward the burner surface is formed, which is the opposite of the fuel flow direction. The circulating flow promotes the mixing of the tertiary air with the central stream in the wake.

Therefore, according to the burner shown in FIG. 1, the mixing of the fuel and the tertiary air in the vicinity of the burner is suppressed, and the mixing in the downstream is promoted, so that the reducing atmosphere necessary for reducing the nitrogen oxides is formed. And the remaining unburned fuel is easily oxidized after the reducing atmosphere is formed.

In order to achieve such an optimal mixed state of the tertiary air and the flow of the flame central portion, it is necessary to set the swirling strength of the tertiary air to an optimum value and increase the swirling flow generation rate. It has been clarified through experiments that it is effective to make the outer tube of the tertiary air nozzle longer than many nozzles.
Such an improvement improves the flame holding property because the circulating flow is stably formed not only around the flame holding plate but also around the spacer 18 installed between the secondary and tertiary air nozzles.

In the embodiment of FIG. 1, the outer tube of the tertiary air passage 13 is formed by the block 19. There are various conceivable shapes of the outer tube of the tertiary air passage 13 other than that shown in FIG. It is effective to make the diameter of this outer tube as large as possible, but if the combustion chamber around the burner is formed by a water tube, as in a boiler, it is not easy to modify the existing combustion chamber, so the outer tube It is often impossible to increase the diameter.

As can be easily imagined, the spacer 18 installed between the secondary and tertiary flow passages should be as large as possible, and the space between the secondary air flow passage 12 and the tertiary air flow passage 13 should be increased so that the fuel of the tertiary air is It is effective for low nitrogen oxides to slow the mixing with the
The width of the circular pipe that constitutes 13 becomes smaller, making it difficult to work. When the structure of the block 19 according to the present invention is used, by increasing the swirling strength of the tertiary air, the tertiary air can be jetted along the inner wall of the block. Therefore, the spacer 18 is enlarged, and the secondary air and the tertiary air flow path are formed. The same effect can be obtained by increasing the interval between them.

Next, the effect of the present invention will be described in detail with reference to FIGS. 5 to 7 based on the experimental results using the burner shown in FIGS. 1 and 2.

FIG. 5 shows the results of a combustion test conducted by crushing Pacific coal, supplying pulverized coal of 74 μm or less and 80% of 20% at 25 to 25 kg / h, and under an air excess ratio of 1.1. A conventional burner has a secondary air flow path formed in a circular tube shape, and the burner of the present invention has a square shape and a tip thereof forms a reducer. Comparing the nitrogen oxide (NO _x ) emissions at the combustion furnace outlet (gas residence time of 3 seconds) with a constant coal supply rate of 25 kg / h, the burner of the present invention showed about 70 pp compared to the conventional burner.
m Low and little change over time. On the other hand, in the conventional burner, as described above, when ash adheres to the pulverized coal jet, the pulverized coal jet and the secondary air jet are distorted, resulting in a flame. In addition, it becomes difficult to form a low oxygen region in the central portion, and the amount of nitrogen oxides discharged increases. That is, there is a drawback that the low oxygen region for promoting the reduction reaction of nitrogen oxide cannot be stably formed. In addition, the pulverized coal supply rate was changed from 25 kg / h to 20 kg / h, and at that time, even when the excess air ratio was adjusted to 1.1, the change in the exhausted nitrogen oxide concentration was large in the conventional burner. On the other hand, since the burner of the present invention has a very small change, it is clear that the ignition promotion and flame holding effect are good.

6 and 7 show examples of other experimental results showing the effect of the present invention. First, Fig. 6 shows the pulverized coal supply amount of 25
Outlet O ₂ obtained by changing the tertiary air amount with constant kg / h
It shows the relationship between the (oxygen) concentration and the NO _x (nitrogen oxide) emission concentration. It is clear that low nitrogen oxides can be achieved with the burner configuration of the present invention. Next, FIG. 7 shows the results of sampling the char at the outlet of the combustion furnace and analyzing the unburned components in this char under the experimental conditions shown in FIG. It has been shown that the burner of the present invention has an extremely small amount of unburned matter in the char as compared with the conventional burner and can obtain a high burning rate.

Therefore, according to the experimental results shown in FIGS. 5, 6 and 7 described above, the burner of the present invention has excellent ignition and flame holding properties, and has a remarkable effect of achieving high efficiency combustion and low nitrogen oxides. .

8 to 10 show a third embodiment of the present invention. That is, FIG. 8 is basically the same burner configuration as the case of FIG. 1 shown above, but is different from FIG. 1 in that the outside of the tip of the pulverized coal flow passage 11 (secondary air flow passage) The flame holding plate 26 is installed on the (12 side). Further, in the case of the square secondary air flow path 12, four flame holding plates 26 are arranged so as to be located at the apexes of the square. By arranging the flame holding plate 26 in this way, the downstream side is formed because the downstream side of the flame holding plate 26 has a negative pressure, and as shown in FIG.
A region of the mixed layer 25 spreads around 27, and mixing and promotion of ignition of the secondary air for ignition of pulverized coal are further promoted, which is effective for stable flame formation.

[Advantages of the Invention] The present invention provides a pulverized coal burner having a pulverized coal flow channel, a secondary air flow channel, and a tertiary air flow channel, in which the pulverized coal ejection port has a circular tubular shape, and the secondary air ejection port is It is composed of a polygonal reducer arranged so as to surround the pulverized coal jet, and is made of a circular tube arranged so as to surround the tertiary air jet or the secondary air flow path. As described above, according to the present invention, high efficiency and low nitrogen oxide can be achieved at the same time, and further, the flame-holding property is improved, so that the load fluctuation followability is good.

[Brief description of drawings]

FIG. 1 is a sectional side view showing a first embodiment of the present invention, and FIG.
1 is a rear view of the burner shown in FIG. 1 taken along the line AA, FIG. 3 is an explanatory view of the operation of the burner of FIG. 1, and FIG. 4 is a rear view showing a second embodiment of the present invention. FIG. 7 is an explanatory diagram of an experimental result showing the effect of the present invention, FIG. 6 is another explanatory diagram of the same,
The figure is also another explanatory view, FIG. 8 is a sectional side view showing a third embodiment of the present invention, FIG. 9 is a rear view seen from the arrow BB of FIG. 8, and FIG. It is explanatory drawing of the effect | action of the burner of FIG. 11 …… Pulverized coal flow path, 12 …… Secondary air flow path, 13 …… Third air flow path, 15 …… Reducer, 16,17 …… Swirl flow generator, 18 …… Spacer, 19 …… Block, 22 …… Wind box, 26 …… Flame holding plate.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Keishin Kobayashi 4026 Kuji Town, Hitachi City, Hitachi, Ibaraki Prefecture Hitachi Research Laboratory, Ltd. (72) Kenichi Soma 4026 Kuji Town, Hitachi City, Ibaraki Prefecture Hitachi, Ltd. Hitachi, Ltd. (72) Inventor Toru Inada 4026 Kujimachi, Hitachi City, Hitachi, Ibaraki Prefecture Hitachi Research Institute, Ltd. (72) Norio Arashi 4026, Kujicho, Hitachi City, Ibaraki Hitachi, Ltd. Hitachi Institute, Ltd. (72) Inventor Yasuo Iwai 4026 Kuji Town, Hitachi City, Ibaraki Prefecture Hitachi Research Laboratory, Hitachi, Ltd. (72) Inventor Tadahisa Masai 6-9 Muromachi, Kure City, Hiroshima Prefecture

Claims (3)

[Claims] 1. A pulverized coal burner having a flow passage for ejecting pulverized coal by air and a secondary air flow passage and a tertiary air flow passage for dividing combustion air and each having a swirling flow generator. A cylindrical pulverized coal jet, a secondary air jet composed of a polygonal reducer arranged to surround the pulverized coal jet, and a secondary air flow passage arranged to surround the secondary air passage. A pulverized coal low-nitrogen oxide burner, which is provided with a circular tube-shaped tertiary air outlet. 2. A plurality of protrusions are arranged on the outer pipe portion of the pulverized coal jet outlet so as to correspond to the polygonal vertices of the secondary air reducer arranged so as to surround the pulverized coal flow passage. The burner according to claim 1. 3. The partition wall of the secondary air jet port and the tertiary air jet port is made of a refractory material, and the outer wall of the tertiary air flow passage is located at a position projecting from the secondary air jet port. Burner described in paragraph.