JPH0451724B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a pulverized coal burner such as a boiler, and in particular to a pulverized coal suitable for reducing nitrogen oxides (NOx) and unburned matter in pulverized coal combustion exhaust gas. It concerns burners.

[Background of the invention]

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 greater than NOx generated during combustion of gaseous and liquid fuels, and therefore it is desired to reduce NOx as much as possible.

NOx generated during the combustion of various fuels is broadly classified into thermal NOx and fuel NOx. Thermal NOx is generated when nitrogen in the combustion air is oxidized by oxygen, while fuel NOx is produced by the oxidation of N in the fuel.

Combustion methods to suppress the generation of NOx include the two-stage combustion method, which divides and supplies combustion air into multiple stages, and the gas recirculation method, which mixes combustion exhaust gas with a low oxygen concentration into the combustion area. be.

All of these low NOx combustion methods suppress the reaction between nitrogen and oxygen by lowering the temperature of the combustion flame through low oxygen combustion.

However, between thermal NOx and fuel NOx, the amount of thermal NOx can be suppressed by lowering the combustion temperature;
NOx generation is less dependent on combustion temperature.

Therefore, although conventional combustion methods aimed at lowering the flame temperature are effective for the combustion of gaseous and liquid fuels with low N content, they do not reduce the NOx generated.
It has little effect on the combustion of pulverized coal fuel, which contains nearly 80% fuel NOx.

FIGS. 1 and 2 are schematic diagrams of a conventional pulverized coal burner.

Pulverized coal is supplied from a pulverized coal supply pipe 1 to a pulverized coal supply nozzle 2 together with air for pulverized coal conveyance (primary air).In order to avoid accumulation of pulverized coal within this pulverized coal supply nozzle 2, a constriction section 3 is provided. is arranged to increase the flow velocity of the pulverized coal, but this means that when the heat from the flame 10 flows back into the pulverized coal supply nozzle 2, the flame propagation velocity is faster than the flow velocity of the pulverized coal. This may cause the flame 10 to flow back into the pulverized coal supply nozzle 2 and cause an explosion.
In order to prevent these explosion accidents, the flow velocity is locally increased and the fuel is injected into the furnace 4.

On the other hand, the combustion air flows from the wind box 5 into the secondary air passage 7 partitioned by the partition plate 6, and flows into the air register 8.
It is supplied into the furnace 4 from the flame stabilizer 9.

The pulverized coal injected into the furnace 4 and the secondary air swirled by the air register 8 are transferred to a flame stabilizer 9.
The flow is obstructed by this, and a recirculation back area A is formed at the tip of the flame stabilizer 9.

A mixed flow of pulverized coal and primary and secondary air is supplied to this recirculation back area A, and heat from the flame 10 in the wake is supplied by the recirculation back area A to cause ignition.

The small flame generated in this recirculation back area A is given a swirl by the pulverized coal conveying air (primary air) from the pulverized coal supply nozzle 2 and the secondary air from the secondary air passage 7, and is turned into a flame stabilizer. 9 and forms a so-called flame 10.

However, since the combustion air in the pulverized coal burner shown in Figure 1 is supplied with more than the theoretical amount of air, combustion occurs actively and unburned matter decreases, but on the contrary, the concentration of nitrogen oxides decreases. becomes high, making it impossible to reduce NOx.

Therefore, in the pulverized coal burner shown in Fig. 1, combustion is performed with a combustion air amount that is less than the theoretical air amount, and the insufficient combustion air is supplied to the downstream side of the furnace 4 from an after-air port (not shown). So-called two-stage combustion is used to reduce the concentration of nitrogen oxides.

FIG. 2 is a schematic diagram of a pulverized coal burner that employs conventional exhaust gas mixing.

In FIG. 2, numerals 1 to 10 are the same as those in FIG. 1, 11 is a secondary air damper, 12
is a secondary air swirling vane, 13 is a tertiary air passage, 1
4 is an air register, 15 is an exhaust gas supply pipe, 16 is an exhaust gas passage, and 17 is an exhaust gas swirl vane.

This structure differs from the pulverized coal burner shown in Fig. 1 in that there is no flame stabilizer 9 at the tip of the pulverized coal supply nozzle 2, and the combustion air system is divided into two, with a secondary air passage. 7, secondary air is supplied via a secondary air damper 11 and secondary air swirling vane 12, and tertiary air is supplied from a tertiary air passage 13 to a swirling force by an air register 8.

Further, exhaust gas is supplied between the pulverized coal supply nozzle 2 and the secondary air from an exhaust gas supply pipe 15 via an exhaust gas passage 16 and an exhaust gas swirling vane 17.

In this way, there is no flame stabilizer 9, but the secondary air is supplied by the secondary air swirling vane 12, and the tertiary air is supplied by the air register 14.
Since the turning force is given by
Since the tertiary air forms a recirculation back area A similar to that in FIG. 1, there is no problem with the supply of heat from the flame 10.

Since the outer periphery of the flame 10 is covered with the exhaust gas flow, the generation of nitrogen oxides can be controlled due to the lack of combustion air, but the amount of unburned matter tends to increase.

However, the pulverized coal that has flown into the recirculation back area A formed by the swirling force of the secondary and tertiary air bursts into flame 10 due to the centrifugal force caused by the swirling force.
The larger the grain size of the pulverized coal, the stronger the tendency for it to be blown to the outside of the pulverized coal, and the more unburned coal is generated.

As described above, in the pulverized coal burner of FIG. 2, nitrogen oxides can be reduced due to the lack of combustion air, but unburned matter cannot be reduced.

[Purpose of the invention]

The present invention attempts to eliminate such conventional drawbacks, and its purpose is to increase combustion efficiency by reducing unburned content in ash during pulverized coal combustion, and to reduce the amount of NOx generated in exhaust gas. To provide a pulverized coal burner that can reduce

[Summary of the invention]

In order to achieve the above-mentioned object, the present invention provides an air passage for supplying combustion air on the outer periphery of a pulverized coal supply nozzle that injects a mixed fluid of pulverized coal and a carrier medium into a furnace, and combusts pulverized coal. In the downstream part of the flow path of the pulverized coal supply nozzle, a flow path constriction part that narrows the flow path inward in the radial direction, and a flow passage enlarged part that reaches the nozzle tip from the flow constriction part are continuous. The pulverized coal having a relatively large particle size and the pulverized coal having a relatively small particle size are supplied to the pulverized coal supply nozzle together with a conveying medium, and the pulverized coal having a relatively large particle size is supplied to the flow path constriction section. The flow rate of the pulverized coal is accelerated by passing through the pulverized coal, and the inertial force causes the pulverized coal to travel almost straight into the furnace.As the pulverized coal with the relatively small particle size passes through the enlarged channel, the flow rate of the pulverized coal decreases. The present invention is characterized in that it is configured to be separated from the pulverized coal having a relatively large particle size and dispersed around the outer periphery of the pulverized coal flow having a relatively large particle size.

[Embodiments of the invention]

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

FIG. 3 is a schematic diagram of the configuration of a pulverized coal burner according to the present invention, and FIG. 4 is a schematic diagram showing the locus of motion of the pulverized coal flow and gas flow in the pulverized coal burner of FIG. 3.

In FIGS. 3 and 4, numerals 1 to 14 are the same as the conventional ones, and 18 is a flow passage enlarged portion provided at the tip of the pulverized coal supply nozzle 2.

In such a structure, pulverized coal is supplied together with primary air from the pulverized coal supply pipe 1, and after the pulverized coal flow rate is accelerated at the throttle part 3 of the pulverized coal supply nozzle 2,
It is supplied into the furnace 4.

On the other hand, combustion air is supplied into the furnace 4 from the outer periphery of the pulverized coal supply nozzle 2, with swirling force applied to the secondary air by the secondary air swirling vanes 12 and tertiary air by the air register 14.

The operating locus of the pulverized coal flow and gas flow in the furnace 4 at this time will be explained using FIG. 4.

In Figure 4, the solid line arrow in the figure indicates the operating trajectory of coarse pulverized coal with a large particle size in the pulverized coal, and the dotted line arrow in the figure indicates the operating trajectory of the gas flow and fine pulverized coal. The fine pulverized coal with small particle size (20 μm or less) in the pulverized coal takes substantially the same motion trajectory as the gas flow.

Due to the swirling force of secondary air and tertiary air,
This is because the enlarged flow path portion 18 of the pulverized coal supply nozzle 2 creates a recirculation back area A, thereby exerting the effect of classifying fine pulverized coal and coarse pulverized coal.

In other words, the pulverized coal supplied from the pulverized coal supply nozzle 2 shown in FIG. However, when it reaches the tip C from the front B, the coarse pulverized coal goes straight into the furnace 4 due to the recirculation back area A generated by the swirling force of the secondary and tertiary air. The fine pulverized coal is pushed back in the direction of the front B by riding on the gas flow indicated by the dotted line arrow that forms this recirculation back area A, and the fine pulverized coal is thermally decomposed near this front B, and the generated gas is transferred to the outside D. The fine pulverized coal is transported to the tip C and burned.

In this manner, the center of the flame 10 is located at the tip C, and since the combustion temperature is highest at the tip C, both the coarse pulverized coal and the fine pulverized coal are completely combusted.

FIG. 5 is a schematic configuration diagram of a pulverized coal burner showing another embodiment of FIG. 3.

The difference between the pulverized coal burner in Fig. 5 and the pulverized coal burner in Fig. 3 is that in the pulverized coal burner in Fig. 3, secondary and tertiary air was supplied, but in the pulverized coal burner in Fig. 5, secondary and tertiary air was supplied. , exhaust gas is supplied from the exhaust gas supply pipe 15 to the outer periphery of the flow passage enlarged portion 18 of the pulverized coal supply nozzle 2 via the exhaust gas passage 16 and the exhaust gas swirling vane 17, and from the outer periphery of the exhaust gas from the secondary air passage 7 via the air register 8. The next point is to supply air.

Note that the flow passage enlarged portion 18 of the pulverized coal supply nozzle 2 was widened toward the end to reduce collision wear caused by the pulverized coal.

By supplying exhaust gas from the outer periphery of the pulverized coal supply nozzle 2 in this way, the division of the combustion area between the tip C and the outer side D explained in FIG. 4 is strengthened by the exhaust gas. It is effective in reducing NOx in specific coal.

FIGS. 6 and 7 are a schematic diagram of a pulverized coal burner according to another embodiment, and a schematic diagram showing movement trajectories of a pulverized coal flow and a gas flow.

6 and 7, numerals 1 to 18 are the same as those in FIGS. 3 and 5, and 19 is a reduced portion provided within the pulverized coal supply nozzle 2. In FIG.

In other words, the one in Fig. 6 has a reduced part 19 in the pulverized coal supply nozzle 2 and a flow passage enlarged part 18 at the tip, which further improves the separation effect between coarse pulverized coal and fine pulverized coal. As the pulverized coal in the pulverized coal supply nozzle 2 passes through this reduced portion 19, its flow velocity increases more and more, increasing the inertial force that causes it to move straight into the furnace 4.

As a result, the inertia of the coarse pulverized coal to move straight into the furnace 4 becomes stronger, and a large amount of coarse pulverized coal is distributed on the burner center axis, and the fine pulverized coal moves straight into the enlarged portion 18 due to the force of inertia to move straight into the furnace 4. As it loses and spreads outward,
The centrifugal force caused by the swirling of secondary and tertiary air causes it to be blown further and further outward.

In this way, a flame is formed by the coarse pulverized coal on the central axis of the burner, and a flame is formed by the fine pulverized coal around the outer periphery.

These are schematically represented as shown in FIG.

That is, first, in the front region B where the diameter rapidly expands from the reduced portion 19, the first stage of separation occurs between the coarse pulverized coal that maintained its inertial force to move straight and the fine pulverized coal that lost its straight moving force, and then Then, in the area of the tip C, the fine pulverized coal is blown outward in the direction D by the collision between the primary air flow and the recirculation back area A caused by the secondary and tertiary air which is the swirling flow, and the fine pulverized coal is blown away to the outside direction D and becomes coarse pulverized powder. The charcoal continues to move straight ahead and a second stage of separation occurs. As a result, due to the separation of coarse pulverized coal and fine pulverized coal in the front B and tip C regions, coarse pulverized coal is present in the vicinity of the center axis of the front burner in the pulverized coal injection direction, that is, in the region on the back side E of the furnace 4. A flame is formed near the outer periphery, that is, in the area outside D, due to the fine particles of pulverized coal, and in the vicinity of the central axis of the burner in the forward direction of the pulverized coal jetting direction, where the ambient temperature is high (1500℃ or higher), coarse particles with poor combustibility are formed. By burning pulverized coal, it is possible to burn fine pulverized coal with good combustibility near the outer periphery where the ambient temperature is relatively low (below 1500°C), so it is possible to effectively reduce the unburned content in the ash. Furthermore, since split flames can be formed, the NOx concentration in the exhaust gas can be reduced.

Figure 8 is a characteristic curve diagram with NOx on the vertical axis and unburned content on the horizontal axis. Curve F in the figure is experimental data for the conventional pulverized coal burner shown in Figures 1 and 2, and curve G is the experimental data for the conventional pulverized coal burner shown in Figures 1 and 2. 3 shows experimental data for the pulverized coal burner of the present invention shown in FIGS. 3, 5, and 6. FIG.

The experimental conditions are as follows. The inner diameter of the test furnace is 600 mm, the length is 5 m, the fireproof insulated caster wall (200 mm), the pulverized coal is 200 mesh pass 80% bituminous coal at 50 kg/H, the air is at room temperature, and the primary, secondary, and tertiary air is 2:3. :5 (weight ratio) from separate systems.

Also, the angle of the secondary air swirling vane 12 is +45
The angle of the air register 14 was kept constant at 50%.

As a result, in the conventional pulverized coal burner, as shown by curve F, the amount of NOx and unburned matter are large, but in the pulverized coal burner of the present invention, as shown by curve G, the amount of NOx is large.
Both unburned content was reduced.

〔Effect of the invention〕

In the present invention, since the enlarged portion is provided at the tip of the pulverized coal supply nozzle, it is possible to separate the pulverized coal into coarse pulverized coal and fine pulverized coal, thereby reducing unburned content and reducing NOx.

[Brief explanation of the drawing]

1 and 2 are schematic diagrams of a conventional pulverized coal burner, and FIGS. 3, 5, and 6 are schematic diagrams of a pulverized coal burner according to an embodiment of the present invention. Figure 7 is a schematic diagram showing the movement trajectory of the pulverized coal flow and gas flow in the pulverized coal burners of Figures 3 and 6, and Figure 8 is a characteristic curve diagram with NOx on the vertical axis and unburned content on the horizontal axis. It is. 2...Pulverized coal supply nozzle, 7, 13...Air passage, 18...Flow passage expansion part.

Claims (1)

[Scope of Claims] 1. An air passage for supplying combustion air is provided around the outer periphery of a pulverized coal supply nozzle that injects a mixed fluid of pulverized coal and a carrier medium into a furnace, and pulverized coal is combusted, comprising: In the downstream part of the flow path of the pulverized coal supply nozzle, a flow path constriction part that constricts the flow path inward in the radial direction and a flow passage enlarged part that reaches from the flow constriction part to the nozzle tip are continuously provided, By supplying pulverized coal with a relatively large diameter and pulverized coal with a relatively small particle size to the pulverized coal supply nozzle together with a conveying medium, and the pulverized coal with a relatively large particle size passing through the flow channel constriction part. , the pulverized coal flow rate is accelerated, and the pulverized coal is made to travel almost straight into the furnace due to inertial force, and the pulverized coal with the relatively small particle size passes through the enlarged channel, so the pulverized coal flow rate decreases and the particle size is compared. A pulverized coal burner characterized in that it is configured to separate pulverized coal having a relatively large particle size and disperse it around the outer periphery of a pulverized coal flow having a relatively large particle size. 2. A pulverized coal burner according to claim 1, characterized in that a swirling force applying means is provided in an air passage provided on the outer periphery of the pulverized coal supply nozzle.