JP2740201B2 - Pulverized coal burner - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a pulverized coal combustion device used for a pulverized coal-fired boiler, and particularly to a pulverized coal combustion device using a flame-retardant fuel or performing load change operation. The present invention relates to a pulverized coal burner suitable for stable combustion of a boiler.

[Conventional technology]

In recent years, demand for pulverized coal-fired boilers has been rapidly increasing due to instability of oil fuel prices. In a pulverized coal-fired boiler, three types of fuels are generally used, such as heavy oil as an auxiliary fuel for starting and light oil for ignition, in addition to pulverized coal as a main fuel. Auxiliary fuels used at low loads of pulverized coal-fired boilers are mainly light oil and heavy oil with good ignitability, and their usage ratio is low. The frequency is also higher than before, and the ratio of supplementary fuel costs to main fuel is also increasing.

 FIG. 3 shows a schematic system diagram of a conventional pulverized coal-fired boiler.

Coal from the coal bunker 1 is supplied to a mill 5 via a coal supply pipe 2, a coal feeder 3, and a coal supply pipe 4, and is pulverized by the mill 5 into pulverized coal. This pulverized coal is supplied to the pulverized coal supply pipe 6,
Pulverized coal is supplied to a boiler 11 from a pulverized coal concentrator 7, a pulverized coal lean side pipe 8, and a pulverized coal concentrated side pipe 9 via a pulverized coal burner 10.

On the other hand, the exhaust gas from the boiler 11 exchanges heat with air in the heat exchanger 12, and is discharged outside the system. On the other hand, the fuel air is supplied from the fuel air pipe 14 to the boiler 11 via the flow control valve 15 by the fuel air fan 13.

A part of the fuel air is supplied from the fuel air fan 13 to 1.
Flow control valve from primary air piping 18 by primary air fan 16
The mixture is supplied to the mill 5 via the pipe 17 and supplied to the boiler 11 as pulverized coal transport air.

Although the above description is about the general flow of coal, exhaust gas, and fuel air, the pulverized coal combustion system conventionally used in the boiler 11 has a pulverizer 5 ( Mill) pulverized coal into pulverized coal burner 10
A combustion system that feeds directly to In this combustion system, heated primary air is introduced for drying raw coal supplied to the mill 5, classifying inside the mill 5, and transporting the pulverized coal to the pulverized coal burner 10. Therefore, the primary air amount and the air temperature are determined according to the moisture, crushability, and combustibility of the raw coal.

Fig. 4 shows the weight ratio of pulverized coal (C) and air (A) supplied from the mill to the pulverized coal burner with respect to the mill load (hereinafter C / A).
). From this figure, as the mill load decreases
It turns out that C / A becomes low. This is a phenomenon peculiar to a mill for conveying and classifying pulverized coal.

FIG. 5 shows data on the ignition stability of coal. The horizontal axis of the figure shows the fuel ratio (hereinafter referred to as FR), which is the weight ratio between fixed carbon and volatile matter in coal. The FR of coal generally used in pulverized coal-fired boilers is about 0.8 to 2.5, and coal with high FR such as high fuel ratio coal with FR of 2.5 or more and anthracite with FR of 4 or more is: Unless C / A is high, stable ignition cannot be achieved. Therefore, when a mill having the characteristics shown in Fig. 4 is used, ignition becomes unstable when pulverized coal with a high FR is used or in a lean state with a low C / A in a low load range.
There is a problem in safe driving of the boiler.

As a countermeasure, the low C / A fluid from the mill is branched into a high C / A fluid (high fine powder concentration) and a low C / A fluid (low fine powder concentration) by using inertia force, etc. It is effective to adopt a configuration in which C / A fluid is used for stable combustion in a pulverized coal burner.

FIG. 6 shows a conventional example based on this concept. The coal supply pipe 4 and the primary air pipe 18 are connected to the mill 5, and the cyclone separator 7 is further connected to the pulverized coal supply pipe 6 from the mill 5. It is connected. In the cyclone separator 7, the fluid on the side with high C / A due to inertia force is transferred to the high concentration side pipe 9.
Supply to a thicker burner not shown, while low C / A
Is supplied to the lean burner (not shown) from the low concentration pipe 8.

Here, FIGS. 7 (a) and 7 (b) show the relationship between the outlet pipe diameter, the critical particle diameter, and the collection efficiency in the cyclone separator 7 of FIG. 6, based on the dimensions and operating conditions of the standard cyclone. It was done. For example, as an actual pulverized coal burner
Considering the pulverized coal amount of 5 t / h, the outlet pipe diameter of the cyclone separator 7 is about 670 mm, and the limit particle diameter is about 25 μm from FIG. 7 (a). When the particle size distribution of the pulverized coal is 200 wt% and the distribution index is n = 2, the trapping efficiency is reduced to 55% from the partial classification efficiency curve in FIG. 7 (b).

Therefore, this cyclone separator merely divides the gas stream into two and cannot concentrate the gas stream.

[Problems to be solved by the invention]

When using the cyclone method as a conventional technology,
This is effective when the collection efficiency of the cyclone separator 7 is high. However, when using high-fuel-grade coal with flame retardancy, measures at low load where C / A is reduced, and efficiency due to upsizing of the equipment, etc. Is not considered, and in practical use C / A
In the case where the temperature decreases, there is a problem that the flame cannot be stabilized and the unburned portion increases due to the blow-off of the flame.

In addition, it is often difficult to convert an existing pulverized coal-fired boiler to a pulverized coal-fired boiler that uses high-fuel-ratio coal as its main fuel.

An object of the present invention is to provide a pulverized coal burner capable of stably burning from a low load to a high load.

[Means for solving the problem]

In order to achieve the above-mentioned object, the present invention provides a pulverized coal supply pipe through which a mixed flow of pulverized coal and a carrier gas flows, and is disposed in the pulverized coal supply pipe and interlinks with the flow direction of the mixed flow. And a plurality of flow dividing members, such as louvers, provided at predetermined intervals along the flow direction of the mixed flow, and the pulverized coal is supplied into the pulverized coal supply pipe by the flow dividing members and the intervals. In a pulverized coal burner forming a high-concentration flow region and a low-concentration flow region, an opening area adjusting means, such as a movable cylinder described later, for adjusting an opening area of a space formed between the flow dividing members. Is provided.

[Action]

By adjusting the opening area of the space formed between the flow dividing member and the flow dividing member by the opening area adjusting means, the amount of the carrier gas diverted through the space can be changed. Since the pulverized coal concentration in the concentration flow region can be reliably controlled, stable combustion can be performed from a low load to a high load.

〔Example〕

Hereinafter, embodiments of the present invention will be described with reference to the drawings, but before that, experimental data of the inventors will be described.

Although it was predicted that the collection efficiency would decrease as the size of the equipment increased even with the use of cyclones, it was experimentally confirmed that these predictions were adapted to low pulverized coal concentrations. . In the transport of pulverized coal, the concentration of pulverized coal is generally high, particles are likely to aggregate, and the apparent particle size is considerably larger than the primary particle size at the time of pulverization.

FIG. 8 shows the relationship between the C / A at the cyclone inlet and the collection efficiency (η) when a cyclone was used. C / A
It can be seen from this figure that the trapping efficiency also increases as the value of (pulverized coal concentration increases). In pulverized coal burners
C / A is preferably 0.8 or more for stable combustion. 50 primary air
If the concentration is branched to the high concentration side and the low concentration side by%, the collection efficiency in the cyclone may be 90% or more. Therefore, if the C / A at the cyclone inlet is 0.15 or more, this condition can be satisfied. However, the C / A from the actual mill will not be less than 0.3, and it will be overspecified to select a cyclone as a concentrator.

The concentration of pulverized coal when a branch pipe is used will be described with reference to FIG. When a T-shaped pipe having an angle θ with respect to the pulverized coal supply pipe 6 is arranged, the pulverized coal proceeds straight due to inertial force, so that the pulverized coal concentration in the high-concentration side pipe 9 becomes rich and the low-concentration side having an angle is formed. The pulverized coal concentration in the pipe 8 becomes lean.

That is, pulverized coal can be separated even with a simple T-shaped branch structure, but is not preferred.

FIG. 10 shows the relationship between the angle θ formed by the branch pipe and the collection efficiency. Under these experimental conditions, the flow rate in the branch pipe 9 was set to 50% when the branch entrance was 100%. A collection efficiency of 50% indicates that no particles have been separated. From FIG. 10, it can be seen that the trapping efficiency increases from an angle θ of around 45 degrees.

FIG. 11 shows a basic flow of a particle concentration experiment apparatus using a louver. In the figure, a mixed flow 19 of pulverized coal and primary air flows in the axial direction of the pulverized coal burner 10 and collides with a louver 20. The primary air flow collides with the louver 20 and then
And flows along the side wall of the pulverized coal burner 10 as indicated by the solid arrow. However, since the flow is obstructed by the resistance plate 22, a flow indicated by a broken line also occurs between the louvers 20, 21. Particles flowing along the side wall of the pulverized coal burner 10 have inertia, so the high concentration side flow 23, louver
The group of particles flowing to the center along 21 becomes the low concentration side flow 24.

FIG. 12 shows the relationship between the angle θ of the louvers 20 and 21 and the collection efficiency. In this experimental condition, as in the case of the T-tube, the amount of air flowing inside the louver was set to 50% of the inlet. From this figure, it can be seen that the trapping efficiency increases as the angle θ increases, and that the trapping efficiency increases rapidly when the angle θ exceeds 90 degrees. This characteristic corresponds to the T value shown in FIG.
Similar to the characteristics of a pipe, but the collection efficiency is
20 and 21 show higher values, and in this example, louvers 20 and 21 were used.

FIG. 1 is a side sectional view of a pulverized coal burner according to an embodiment of the present invention, and FIG. 2 is a side view taken along line AA of FIG. The pulverized coal burner of the present invention is characterized in that the pulverized coal concentrator is incorporated in the pulverized coal burner.

In FIGS. 1 and 2, a mixed flow 19 with pulverized coal conveyed by primary air extends in a direction intersecting with the flow direction of the mixed flow 19 and at a predetermined rate along the flow direction of the mixed flow. Is divided into a high concentration particle side flow 23 and a low concentration side flow 24 by a plurality of louvers 20 provided at intervals G. In order to stabilize flame holding in pulverized coal combustion, it is necessary to increase the concentration of pulverized coal particles and reduce the speed of the particles. Usually mill 5
In the pulverized coal combustion burner 10 using the pulverized coal, when the load decreases, the pulverized coal concentration at the inlet of the pulverized coal burner 10 decreases. For this reason, it is necessary to adjust the concentration and the flow rate according to the load of the pulverized coal burner 10. Here, a movable cylinder 25 is installed as a control means at the center of the pulverized coal burner 10, and the opening area of the gap G formed between the louvers 20 can be adjusted by taking in and out of the movable cylinder 25, thereby reducing the opening area. The amount of the concentration side stream 24 could be adjusted.

By providing the louver 20 inside the pulverized coal burner 10, the high concentration side flow 23 flows along the inner side wall of the pulverized coal burner 10, and the flame is held by the outer flame stabilizer 26. On the other hand, the low concentration side stream 24
Flows through the center of the pulverized coal burner 10 through the space between the louvers 20 and is held by the inner peripheral flame stabilizer 27. Here, the inner flame holder 27 is
It does not merely stabilize the flame, but also acts as a separator to delay mixing and diffusion of the high concentration stream 23 and the low concentration stream 24.

When the load on the pulverized coal burner 10 is low, the pulverized coal concentration decreases, so it is necessary to increase the pulverized coal particle concentration.
For this reason, when the load is low, the movable cylinder 25 is pulled out to the position shown by the broken line in FIG. By retracting the movable cylinder 25 to the position indicated by the broken line in this manner,
The center side of the pulverized coal burner 10 of the louver 20 opens, and the mixed flow 19
Among them, the C / A of the high-concentration stream 23 becomes rich because the amount of primary air separated into the low-concentration stream 24 increases. On the other hand, when the load of the pulverized coal burner 10 is the highest, the pulverized coal concentration at the inlet of the pulverized coal burner 10 is the highest, so that the movable cylinder 25 is inserted to the position shown by the solid line in FIG. All of 19 flows as the high concentration side stream 23. By operating such a movable cylinder 25, a high-concentration pulverized coal stream can always be sent to the outer peripheral flame stabilizer 26, so that a stable fuel can always be obtained not only in a high fuel ratio coal but also in a wide load band. Incidentally, reference numeral 28 in FIGS. 1 and 2 denotes a starting burner.

FIG. 13 shows another embodiment. The difference from the one shown in FIG. 1 is that the inclination angle of the louver 2 is not parallel but widened toward the center of the pulverized coal burner 10. With this structure, the cross-sectional area of the flow path of the low concentration side flow 24 can be made uniform, and the louver 20
The particle velocity in the inside can be made uniform, the flow velocity can be improved particularly in the branch portion, and the separation efficiency is improved because the particle flow is rapidly reversed.

FIG. 14 shows the movable cylinder 25 installed on the outer periphery of the louver 20. With this method, exactly the same concentration effect can be obtained.

〔The invention's effect〕

ADVANTAGE OF THE INVENTION According to the pulverized coal burner which concerns on this invention, the burning of high fuel ratio coal whose fuel ratio exceeds 4 becomes possible. Furthermore, in the combustion of bituminous coal, even in partial load operation where the C / A at the mill outlet is reduced, stable combustion is possible, and the frequency of using auxiliary fuels such as oil and gas is reduced, resulting in significant costs. You can save money.

Furthermore, space is saved because auxiliary equipment such as a cyclone is not used, and it is particularly suitable for remodeling a pulverized coal burner.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional view of a pulverized coal burner according to an embodiment of the present invention,
FIG. 2 is a side view taken along the line AA of FIG. 1, FIG. 3 is a schematic configuration diagram of a conventional boiler and a combustion system for high combustion ratio coal fuel, and FIG.
Fig. 5 is a characteristic curve showing the relationship between mill load and pulverized coal concentration (C / A) at the burner inlet when a pulverized coal concentrator is not used. Fig. 5 shows the stability of the relationship between C / A and fuel ratio (FR). Fig. 6 is a characteristic curve diagram showing the ignition region and the ignition unstable region, Fig. 6 is a flow path diagram in the mill and the pulverized coal concentrator (cyclone), and Figs. 7 (a) and (b) show the trapping characteristics of the conventional cyclone. FIG. 8 is a characteristic curve diagram showing the relationship between the C / A at the cyclone inlet and the total collection efficiency, FIG. 9 is a diagram illustrating the concentration of pulverized coal in the branch pipe, and FIG. Is a characteristic curve diagram showing the relationship between the branching angle and the collection efficiency in FIG. 9, FIG. 11 is a cross-sectional view of an experimental device using a louver, and FIG. 12 is a louver angle when the louver in FIG. 11 is used. 13 and FIG. 14 are cross-sectional views showing another embodiment. 6 ... pulverized coal supply pipe, 20,21 ... louver, 25 ... movable cylinder, 26 ... outer flame holder, 28 ... start-up burner.

Claims (1)

(57) [Claims] 1. A pulverized coal supply pipe through which a mixed flow of pulverized coal and a carrier gas flows, and a pulverized coal supply pipe disposed in the pulverized coal supply pipe, extending in a direction intersecting with the flow direction of the mixed flow, and And a plurality of flow dividing members provided at predetermined intervals along the flow direction of the pulverized coal. In the pulverized coal burner to be formed, an opening area adjusting means for adjusting an opening area of an interval formed between the flow dividing member and the flow dividing member is provided.