JPH0249443Y2 - - Google Patents

Description

[Detailed description of the invention] [Field of industrial application] The present invention is a boiler that injects primary air and secondary air into a common combustion chamber and burns the fuel injected from a burner in multiple stages in a common combustion chamber. This relates to low NOx combustion equipment for boilers.

[Conventional technology]

A conventional combustion process in such a boiler will be explained with reference to the drawings. Figures 1 and 2
The figure shows a conventional combustion device installed in front of a two-body water tube boiler and a combustion chamber provided along the longitudinal direction of the drum of the same boiler, and a combustion device 1 is installed in the front of the combustion chamber 2. 3 is a burner gun, and 4 is a combustion flame of fuel injected from the burner gun 3. 5 is primary air and 6 is secondary air. 7 is a steam drum, 8 is a water drum, 9 is an air inlet,
10 is a combustion gas outlet. 11 is a primary throat for introducing primary air 5, 12 is a secondary air 6
The boiler shown in the figure generally has the structure of a conventional two-stage combustion boiler for reducing NOx, and the throat section is divided into a primary throat 11 and a secondary throat 12. As a dual structure, primary air 5 and secondary air 6 are supplied into the combustion chamber 2 in parallel.

Conventionally, Japanese Patent Publication No. 55-21922 describes a three-stage combustion type combustion furnace having a primary combustion zone 7, a secondary combustion zone 8, and a tertiary combustion zone 11 (column 4, lines 33 to 33). (See column 5, line 18, Figure 1).

However, the combustion furnace described in Japanese Patent Publication No. 55-21922 merely describes the prerequisites for the present invention.

Further, JP-A No. 53-141931 describes a multiple swirl burner that uniformly supplies secondary air as a swirl flow.
The publication describes a boiler that is supplied with exhaust gas.

However, these three publications state that the feature of the present invention is that ``the secondary air and the exhaust gas are introduced approximately tangentially, the O ₂ concentration in the secondary air and the subsequent air is reduced, and NOx more effectively suppress generation.”
There is no mention of this technical idea.

[The problem that the idea attempts to solve]

In the conventional configuration shown in FIG.
is configured to flow along the outer periphery of the primary combustion zone 4a of the combustion flame 4, and then to be supplied to the secondary combustion zone 4b behind the flame 4 to perform two-stage combustion,
Therefore, overall, near the tip of the burner gun 3, primary combustion occurs in a reducing atmosphere due to lack of air, and behind that, secondary combustion occurs to complete combustion. However, when viewed partially, even in the primary combustion zone 4a, the outer periphery of the flame is in contact with the secondary air 6, and a portion of the secondary air is supplied as shown in the area P surrounded by the broken line in the figure. There is a region in which the combustion occurs, and this region becomes an oxidizing atmosphere, thus generating NOx, which inhibits low-NOx combustion.

In order to prevent this drawback, a method has been proposed in which only the primary air is supplied from the burner section, and the secondary air is introduced from the side of the combustion chamber 2 in the direction of the arrow R, as shown in Figure 2. However, as is clear from Fig. 2, the secondary air can only be introduced in three directions, resulting in deterioration of combustion or unevenness of the supplied air, creating a partial oxidation/reduction region, making it difficult to effectively supply the air. cannot be realized. Therefore, in the double-barrel water tube boiler having the structure shown in FIGS. 1 and 2, secondary air is not supplied from the side, or even if it is supplied, the NOx reduction effect is poor.

FIG. 3 shows a conventional combustion system in a large boiler. In large boilers, as shown in Figure 3,
A reversal section S of combustion gas is generated within the combustion chamber, and therefore, in the same way as the side secondary air supply in FIG. As a result, it is possible to mix well and to uniformly supply secondary air to the inside of the flame.

Based on the example of the large boiler mentioned above or the results of experiments conducted using a combustion test furnace, supplying primary air and secondary air separately is more effective in reducing NOx than supplying both at once. Based on the current situation where the results of A device that achieves this reduction can be provided.

The present inventor has developed a two-body water tube boiler equipped with a combustion device as shown in FIGS. 4 and 5. In FIGS. 4 and 5, the blower 13
The air supplied from the primary air 5 and secondary air 6
and then feed each of them toward the combustion chamber 2. FIG. 4 shows an example in which the secondary air 6 is arranged in two rows in the vertical direction.
As shown in Figure 5, both are in the secondary combustion zone 4.
They are introduced from around b along the arrow T in the direction of entering the combustion flame, and their flow is introduced in a direction that produces a swirling flow within the cross section of the combustion flame. As a result, the supply of secondary air is made uniform, and the secondary air, which tends to be supplied only to the outer surface of the combustion flame in the methods shown in Figures 1 and 2, is replaced by incomplete combustion inside the flame. Since it can sufficiently penetrate into the area, it improves the burnout of fuel and exhibits the effect of reducing NOx. Although not shown in the figure, in Figure 4,
As shown in the combustion device 1 in FIG. 1, the introduction mode of the combustion air supplied from the air inlet 9 is a double structure with a primary throat and a secondary throat, so that both the primary air and the secondary air are It is also possible to adopt an introduction mode in which the air is supplied in parallel from the lower part of the combustion chamber 2, and in this case, the air introduced from the side of the combustion chamber in the direction of arrow T becomes tertiary air.

Normally, the amount of air after the secondary is equal to the total amount of air supplied.
Although it is said to be around 20%, it is known that when mixing secondary air and combustion gas, mixing efficiency is better if the volume on the air side is larger than the combustion gas volume.

This invention was made in view of the above points,
Mixing the exhaust gas with the secondary air or supplying the exhaust gas with the secondary air promotes miscibility, and the mixing reduces the O ₂ concentration in the secondary air, significantly reducing NOx formation. The purpose is to provide a low NOx combustion device for a boiler that can reduce NOx emissions.

[Means to solve the problem]

In order to achieve the above object, the boiler low NOx combustion device of the present invention, as shown in Fig. 6, introduces primary air and secondary and subsequent air, respectively, and combines the fuel injected from the burner into a common combustion system. In a boiler that performs multistage combustion within a chamber 2, an air introduction pipe 6 for secondary and subsequent air is connected to the peripheral wall of the combustion chamber 2 in a substantially tangential direction of the combustion flame in a cross section of the combustion flame, and the air introduction pipe 6 is connected to the peripheral wall of the combustion chamber 2. An exhaust gas feed pipe 15 for introducing the exhaust gas of the boiler is installed in the middle of the
It is characterized by the connection of

In the above configuration, instead of connecting the exhaust gas feed pipe 15 midway through the air introduction pipe 6, the exhaust gas feed pipe 15 is connected to the combustion chamber 2 in the same direction as the air introduction pipe 6, as shown in FIG. In some cases, it is connected to the surrounding wall.

[Effect]

By supplying the secondary and subsequent air and exhaust gas approximately tangentially into the combustion chamber 2 while mixing, this mixed gas protrudes into the combustion flame, improving mixing properties, and the secondary and subsequent air It effectively suppresses NOx production by reducing the O ₂ concentration inside.

〔Example〕

Examples of the present invention will be described below.

Example 1 FIG. 6 shows an example of a low NOx combustion device for a boiler according to the present invention. In Figure 6, 14
is a blower for sucking exhaust gas and sending it to the combustion chamber, and the exhaust gas from the blower 14 is mixed with the secondary air 6 from the blower 13 at a confluence point 16 through a gas feed pipe 15. After this, the mixed gas is introduced into the combustion chamber 2 along the direction of arrow T. By introducing the gas mixture in the direction of arrow T, the gas mixture is introduced into the combustion flame,
The procedure for generating swirling flow is the same as in the case of FIG. 4. In this way, by mixing the exhaust gas with the secondary air, promotion of miscibility is achieved, and since the O ₂ concentration in the secondary air is reduced by mixing, it is possible to It is effective in preventing the production of NOx due to high O ₂ concentration.

Embodiment 2 FIG. 7 shows another embodiment of the low NOx combustion device for a boiler according to the present invention.

In this example, the mixing of the secondary air and exhaust gas in Example 1 is performed within the combustion chamber after introduction into the combustion chamber, and the principle is the same as that in FIG. 6. That is, in FIG. 7, secondary air 6 is introduced into the combustion chamber 2 along the direction of arrow T in the same manner as the introduction in the direction of arrow T in FIG. 6, and the flow of these introductions is The exhaust gas from the blower 14 is introduced into the combustion chamber 2 in the direction of the arrow T' which is close to and parallel to these. Therefore, the effect obtained is also the same as that in Fig. 6. Almost equivalent.

[Effect of idea]

Since the low NOx combustion device for the boiler of the present invention is configured as described above, the supply of primary air and the supply of secondary air are separated and supplied separately, and as a result, the generation of NOx is reduced. In addition, the manner in which the secondary air is introduced into the combustion zone is such that it causes uniformity, so the formation of partial oxidation zones or reduction zones due to non-uniformity of the supplied air is avoided, which contributes to NOx reduction. It has an excellent effect in enhancing the effect. Furthermore, since the exhaust gas from the boiler is mixed with the air from the secondary stage onwards, or is introduced at the same time, the O ₂ in the air from the secondary stage onwards is reduced.
The concentration decreases, resulting in the effect that NOx production can be further suppressed.

[Brief explanation of drawings]

Figure 1 is an enlarged sectional view to explain the combustion process of a conventional double-barrel water tube boiler, Figure 2 is a sectional view taken along the - line in Figure 1, and Figure 3 is an illustration of the combustion process in a conventional large boiler. Figure 4 is a cross-sectional view for explaining the combustion process in the boiler developed by the present inventor, Figure 5 is a cross-sectional view taken along the - line in Figure 4, and Figures 6 and 7 are from this book. FIG. 3 is a cross-sectional view for explaining the combustion process in different embodiments of the low NOx combustion device for the boiler of the invention. DESCRIPTION OF SYMBOLS 1... Combustion device, 2... Combustion chamber, 3... Burner gun, 4... Combustion flame, 4a... Primary combustion area, 4
b...Secondary combustion zone, 5...Primary air, 6...Secondary air, 7...Steam drum, 8...Water drum, 9...
... Air inlet, 10 ... Combustion gas outlet, 11 ... Primary throat, 12 ... Secondary throat, 13, 14
...Blower, 15...Gas feed pipe, 16...Confluence point.

Claims (1)

[Scope of Claim for Utility Model Registration] 1. In a boiler in which primary air and secondary air are respectively introduced and fuel injected from a burner is combusted in multiple stages in a common combustion chamber 2, combustion flame within a cross section of the combustion flame. An air introduction pipe 6 for secondary and subsequent air is connected to the peripheral wall of the combustion chamber 2 in a substantially tangential direction, and an exhaust gas feed pipe 15 for introducing boiler exhaust gas is connected in the middle of the air introduction pipe 6. A low NOx combustion device for a boiler that is characterized by: 2. Request for registration of a utility model characterized in that instead of connecting the exhaust gas feed pipe 15 midway through the air introduction pipe 6, the exhaust gas feed pipe 15 is connected to the peripheral wall of the combustion chamber 2 in the same direction as the air introduction pipe 6. A low NOx combustion device for a boiler according to item 1.