JPH0424404A - Pulverized-coal burner - Google Patents

Abstract

PURPOSE:To reduce the consumption of auxiliary fuel and improve the igniting stability of a pulverized-coal burner to allow performing high frequent start-and-stop operation (DSS) at a low load by a method wherein during start-up of a mill and low load operation, a flow path is changed so as to close a pulverized coal nozzle, so that a high concentration pulverized coal flow is formed inside inlet and outlet ducts, and the igniting stability is maintained by a low load operation flame stabilizer, and also. CONSTITUTION:During high load operation, a high-concentration pulverized-coal flow path 23 is located outside an inlet duct 18 and an outlet duct 19, and a low-concentration pulverized coal flow path 24 is located inside the inlet and outlet ducts 18 and 19. Therefore, the pulverized coal in a pulverized-coal flow path 25 flows along the high-concentration pulverized-coal flow path 23 at a high concentration, and along the low-concentration pulverized coal flow path 24 at a low concentration, so that a stable combustion is maintained by a high-load operation flame stabilizer 15. On the other hand, during very low load operation, a nozzle 21 is moved toward a boiler furnace 4 side until the nozzle 21 comes in contact with the inlet duct 18, so that the high-concentration pulverized-coal flow path 23 is located inside the inlet and outlet ducts 18 and 19 and the low-concentration pulverized coal flow flow path 24 is located outside the inlet and outlet ducts 18 and 19. As a result, the pulverized coal in the pulverized-coal flow path 25 flows along the high-concentration pulverized-coal flow path 23 at a high concentration, and along the low-concentration pulverized coal flow flow path 24 at a low concentration, so that a stable combustion is maintained by a low load operation flame stabilizer 20, allowing DSS operation.

Description

[Detailed Description of the Invention] [Industrial Field of Application] The present invention relates to a pulverized coal combustion device, and particularly to a combustion system in which a mill and a pulverized coal burner are directly connected and operated to expand the operating range of load changes. The present invention relates to a pulverized coal burner suitable for.

[Conventional technology] In recent years, in Japan, due to the tight supply of heavy oil, in order to correct the dependence on oil, there has been a shift from traditional heavy oil-burning to coal-burning, especially in commercial thermal power generation boilers. A large-capacity coal-fired thermal power plant is being constructed.

On the other hand, as a feature of recent electricity demand, with the growth of nuclear power generation, the difference between the maximum and minimum loads has also increased, and there is a tendency to shift boilers for thermal power generation from base load use to load adjustment use. The boiler is operated under variable pressure by changing the pressure according to the load.

By using a variable pressure boiler that operates in a supercritical pressure region during so-called full load operation and in a subcritical pressure region during partial load operation, the power generation efficiency during partial load operation can be improved by several percent.

For this reason, in these coal-fired thermal power plants, there are few cases in which the boiler load is always operated at full load, and the load is reduced to 75% during the day.
Frequent startup and shutdown operations include increasing and decreasing the load to 5% load, 50% load, 25% load, 15% load, or stopping operation at night.
There is a transition to coal-fired thermal power that handles intermediate loads through 5 tart and 5 top (simply referred to as DDS) operations.

Furthermore, among coal-fired boilers that perform DDS operation, there are few that operate the entire load range from startup to full load using only pulverized coal;
At low loads, light oil, double fuel oil, gas, etc. other than pulverized coal are used as auxiliary fuel.

This is because, at startup, exhaust gas and heated air for mill warming cannot be obtained from the coal-fired boiler, and therefore the mill cannot be operated and the coal cannot be pulverized into pulverized coal.

Furthermore, light oil, single heavy fuel oil, gas, etc. are used because the turndown ratio of the mill cannot be maintained at low loads, and the ignitability of pulverized coal itself is poor.

For example, when using light oil and double fuel oil as auxiliary fuel at start-up, the boiler is heated up using light oil as auxiliary fuel from the time of startup until 15% load, and from 15% load to 40% load the auxiliary fuel is changed from light oil to heavy oil. When the load reaches 40% or more, the auxiliary fuel heavy oil and the main fuel pulverized coal are co-fired, and the amount of auxiliary fuel heavy oil is gradually reduced, while the main fuel pulverized coal amount is increased to increase the pulverized coal co-firing ratio. As a result, there will be a transition to virtually exclusive coal combustion.

Hereinafter, an overview of the startup of the pulverized coal-fired boiler will be explained using FIG. 10 and FIG. 11.

FIGS. 10 and 11 are a schematic system diagram of a pulverized coal-fired boiler and an enlarged sectional view of a conventional pulverized coal burner.

When cold-starting the pulverized coal-fired boiler 1 shown in FIG. 10, first, the light oil ignition burner 2 of the pulverized coal burner 7 shown in FIG. 11 is used to heat up to 15% of the boiler load.

After that, the heavy oil starting burner 3 is ignited. Then, only the heavy oil starting burner 3 is used to heat up to 25 to 35% of the boiler load. Thereafter, when the temperature inside the boiler furnace 4 has risen sufficiently, the pulverized coal supply pipe 6 shown in FIG. 11 is connected to the mill 5 shown in FIG. Pulverized coal fuel is supplied to the pulverized coal burner 7, sent through the pulverized coal nozzle 8 into the boiler furnace 4, and switched to pulverized coal exclusive combustion.

The medium for transporting the pulverized coal undergoes heat exchange with the boiler exhaust gas by the air heater 9 shown in FIG. It is used as classification air for a built-in classifier (not shown), and also as transport air for transporting the pulverized coal pulverized in the mill 5 to the pulverized coal burner 7.

FIG. 11 shows a conventional pulverized coal burner 7, which is equipped with a light oil ignition burner 2 and a heavy oil starting burner 3, which constitute the pulverized coal burner 7. . Combustion air in the wind box 11 is swirled by a secondary air register 12 and a tertiary air register 13, and then is introduced into the boiler furnace 4. On the other hand, the pulverized coal passes through the pulverized coal supply pipe 6 to the pulverized coal nozzle 8 of the pulverized coal burner 7.
However, during that time, it only passes through the venturi 14 and is blown into the boiler furnace 4 in a state close to a free jet. This pulverized coal burner 7 has a flame stabilizer 15 for high load.
was provided, and the swirling of the combustion air created a backflow region, and the flame was only maintained in the flow velocity region below the flame propagation velocity. Therefore, the diffusion of the pulverized coal particles is good, but on the other hand, the flame becomes unstable and is highly dependent on the operating conditions on the air side of the pulverized coal burner 7. In addition, the reference numeral 16 in FIG. 10 is a heavy oil tank, and the reference numeral 17 is a light oil tank.

On the other hand, the pulverized coal concentration (C
/A) becomes low, resulting in poor ignition stability.

Figure 12 shows the weight ratio (hereinafter referred to as C/A) of pulverized coal (C) and air (A) supplied from the mill 5 to the pulverized coal burner 7 (hereinafter referred to as C/A) with respect to the burner load on the horizontal axis and the burner (mill) load on the vertical axis. ) is a characteristic curve diagram showing.

From FIG. 12, it can be seen that C/A decreases as the burner (mill) load decreases, but this is a phenomenon unique to mills that is unavoidable due to the transportation and classification of pulverized coal.

The C/A at 15% burner load is 0.08 as shown in Figure 12, and the pulverized coal is extremely lean, and the air ratio that the primary air amount affects combustion at that time is:
It varies depending on the type of coal, but exceeds 1 in all cases. Therefore, under this load, only the primary air will cause excess air, and 2° tertiary air will not be necessary. However, due to the characteristics of the fan, and as a measure to prevent burnout of the pulverized coal burner 7, secondary air is required. In order to supply a considerable amount of tertiary air, the air ratio in the vicinity of the pulverized coal burner becomes quite high, and the pulverized coal particles are further diluted, making the flame unstable.

[Problems to be Solved by the Invention] As described above, in a pulverized coal burner that uses auxiliary fuel, the amount of auxiliary fuel used increases each time the operation is started and stopped frequently, and the pulverized coal-air flow is directly transferred from the mill to the pulverized coal burner. In the combustion system that supplies pulverized coal, when the mill (burner) load is low, the ignitability of the pulverized coal burner deteriorates, resulting in an increase in unburned content.

The present invention aims to eliminate such conventional drawbacks,
The purpose is to reduce auxiliary fuel and improve the ignition stability of the pulverized coal burner.
To provide a pulverized coal burner capable of performing low-load operation in S operation.

[Means for Solving the Problems] In order to achieve the above-mentioned object, the present invention includes an inlet duct and an outlet duct for changing the pulverized coal concentration in a pulverized coal nozzle, and a low-load flame stabilizer at the tip of the outlet duct. In addition, a nozzle was installed upstream of the inlet duct to change the pulverized coal flow path.

[Operation] When the burner load of the pulverized coal burner is low (when the mill starts up and when the load is low), the nozzle that changes the pulverized coal flow path in the pulverized coal nozzle is moved in the direction of closing, and the inlet duct and outlet duct are A dense pulverized coal flow is formed inside the cylinder, and a low-load flame stabilizer ensures ignition stability.

On the other hand, when the burner load of the pulverized coal burner is high, the nozzle that changes the pulverized coal flow path in the pulverized coal nozzle is moved in the direction of opening to form a dense pulverized coal flow outside the inlet and outlet ducts, resulting in a high load. Ensure ignition stability with a flame holder.

[Example code] Embodiments of the present invention will be described below with reference to the drawings.

1 and 2 are cross-sectional views of a pulverized coal burner according to an embodiment of the present invention, and FIGS. 3, 4, and 5 are enlarged sectional views showing the upper half of a pulverized coal nozzle. The figure shows at high load.
Fig. 4 shows the case at low load, and Fig. 5 shows the case at extremely low load.

Figure 5 is a characteristic curve diagram in which the horizontal axis shows primary air distribution ratio and the vertical axis shows pulverized coal concentration ratio. Figure 6 is a characteristic curve diagram in which the horizontal axis shows burner load and the vertical axis shows C/A. , FIG. 7, and FIG. 8 are sectional views of a pulverized coal burner showing other embodiments.

In FIGS. 1 to 8, numerals 3 to 15 indicate the same parts as the conventional ones.

18.19 is an inlet duct and an outlet duct arranged in the pulverized coal nozzle 8 to change the pulverized coal concentration; 20 is an outlet duct 19;
21 is the pulverized coal nozzle 8.
22 is a particle pilot, 23
．． 24 is a rich pulverized coal flow path, a lean pulverized coal flow path, and 25 is a pulverized coal flow path.

FIG. 1 shows the position of the nozzle 21 when the load is high, and FIG. 3 shows the position of the nozzle 21 when the load is extremely low.

In FIG. 1, pulverized coal and primary air for conveyance are supplied from a mill (not shown) through a pulverized coal supply pipe 6 to a pulverized coal nozzle 8 of a pulverized coal burner 7 as shown by arrow A in FIG. 21, particle pilot 22, inlet duct 18,
It enters the boiler furnace 4 through the outlet duct 19 and is stably combusted by the high-load flame stabilizer 15. In this pulverized coal burner 7, the combustion air is further divided into a secondary air register 12 and a tertiary air register 13 in a wind box 11, and six nozzles 21, which are preferably supplied with swirling force, are not shown in the figure. However, the pulverized coal nozzle 8 is slid within the pulverized coal nozzle 8 by an actuator, a roller with a bearing, etc., and is controlled to satisfy the required performance of the burner.

At the time of high load shown in FIG. 1, the pulverized coal in the pulverized coal flow path 25 flows into the rich pulverized coal flow path 23 located outside the inlet duct 18 and the outlet duct 19, and Since the lean pulverized coal flow flows through the lean pulverized coal flow path 24 located inside the outlet duct 19, stable combustion is achieved in the high-load flame stabilizer 15.

On the other hand, at extremely low load as shown in FIG. A rich pulverized coal flow flows through the rich pulverized coal flow path 23, and a lean pulverized coal flow flows through the lean pulverized coal flow path 24 located outside the inlet duct 18 and the outlet duct 19. Stable combustion occurs at 20.

Hereinafter, with reference to FIGS. 3 to 5, the explanation will be made separately for high load, low load, and extremely low load.

At the time of high load as shown in FIG. 3, the pulverized coal flow A is supplied to the pulverized coal flow path 25 in the pulverized coal nozzle 8, and first, when it passes through the nozzle 21 located upstream and the particle pilot 22 located downstream. , the pulverized coal is biased to one side due to inertia as shown in the figure (
(specific gravity is approximately 1000 times or more that of air), wake inlet duct 1
A dense pulverized coal flow AB with high concentration flows through the outer rich pulverized coal flow path 23 partitioned by 8. Next, the pulverized coal flow that has flowed into the lower lean pulverized coal flow path 24 partitioned by the inlet duct 18 transfers most of the pulverized coal to the lower lean pulverized coal flow path 24 through the outlet duct 19 due to inertial force. Lean pulverized coal flow A
c, most of the air AA is separated from the resistance distribution so as to flow into the gap-like flow path formed by the inlet duct 18 and the outlet duct 19, and furthermore, the air AA is separated from the dense pulverized coal flow path 23 in the bypass dense pulverized coal flow path 23. It merges with the pulverized coal flow Al11 to become a dense pulverized coal flow Ac, and finally the rich pulverized coal flow Ac flows into the boiler furnace 4.

It is divided and supplied as a lean pulverized coal stream AR.

Here, in this arrangement of the nozzle 21 at the time of high load, the inlet duct 18. When the pulverized coal flow is supplied to the outlet duct 19, the inlet duct 18. already separates and supplies more pulverized coal to the lean pulverized coal channel 24. Despite the function of the outlet duct 19, the C/A of the rich pulverized coal flow Ac is the same as the C/A of the lean pulverized coal flow A.
/A will be higher. Therefore, the high C/A pulverized coal flow is stably combusted by the high load flame stabilizer 15. At this time, the nozzle 21 is connected to the inlet duct 18. It has a function of adjusting the flow rate of the dense pulverized coal flow A8 in the outlet duct 19, and is fully opened in a normal load cloth with good flame stability to reduce flow path resistance and lower the differential pressure of the pulverized coal burner 7. At the same time, the flow rate of pulverized coal is kept as low as possible to suppress damage caused by wear.

The particle pilot 22 causes the flow of pulverized coal to flow into the rich pulverized coal flow path 23 at high load, so that the pulverized coal concentration becomes high in the rich pulverized coal flow path 23, and is combusted by the high load flame stabilizer IS. do. Inlet duct 18. Outlet duct 19
In the high load region, it is not necessary to increase the C/A of the lean pulverized coal flow path 24, so it is preferable to increase the pulverized coal concentration of the rich pulverized coal flow path 23 in terms of burner operation.

When the load is low in FIG. 4, the pulverized coal flow A supplied to the pulverized coal nozzle 8 is 1
Particle Pilot 22. Nozzle 21° Inlet duct 18. By the outlet duct 19, arrow All.

Pulverized coal flows are formed as shown by AR and AC. here,
The nozzle 21 and particle pilot 22 are different from when under high load.
With the relative position, the nozzle 21 is set closer to the boiler furnace 4 than the particle pilot 23.

For this reason, as shown in FIG.
c is supplied, and furthermore, an inlet duct 18, an outlet duct 1
The pulverized coal flows A to the lean pulverized coal flow path 24 and the rich pulverized coal flow path 23 formed at 9.

Even in Ac, the concentration in the rich pulverized coal channel 23 increases due to inertial force, and the coal is combusted by the low-load flame stabilizer 20.

That is, the feature of this embodiment is that the combination of the nozzle 2] and the particle pilot 22 allows the downstream inlet duct 18. The particle concentrations feeding the two flow paths to the outlet duct 19 have been reversed.

When the load is extremely low as shown in Fig. 5, by fully opening the nozzle 21, the outlet duct 19
Eliminate pulverized coal flow bypassing the inlet duct 18. The pulverized coal is supplied to the rich side pulverized coal flow path 23 of the outlet duct 19. With this operation, the inlet duct 18. Outlet duct 19
functions at maximum efficiency and can maintain the pulverized coal flow Ac at the required value to the low load flame stabilizer 20 which requires a high C/A.

As a result of considering the above functions, we decided to create an inlet duct 18. to increase the concentration of pulverized coal. As the structure of the outlet duct 19, the narrowest flow passage cross-sectional area S of the outlet duct 19, (the third
The narrowest cross-sectional area S in the other flow path of the outlet duct 19 (flow path where AC flows in the figure). (A in Figure 3
When R is a flow path) and the flow path cross-sectional area of the pulverized coal nozzle 8 is S, (SO+S,)/S is 0.5 to 0.9, S,
/ (S, +SO) shall be 0.4 or less, and the minimum area SR of the portion that can be considered as one flow path constructed between the flow path partition structural members (the flow path indicated by AA in Figure 3) shall be S. It was discovered that the structure of the concentrating separator should be designed to be larger than the above.

Figure 6 shows the distribution ratio of primary air to the high C/A side in the structure shown in Figure 2 (=100X air flow rate in Ac/air flow rate in A).
The relationship between and the pulverized coal concentration rate (=100x pulverized coal flow rate in Ac/pulverized coal flow rate in A) is shown in a diagram. The figure is S, / (
The case where S, +So) is 0.4 and C/A (inlet C/A) in the pulverized coal flow A supplied to the pulverized coal nozzle 8 is 0.2 is shown.

Curve B in the figure shows the results when (So+S, )/S is 0.5 and curve C is 0.9. FIG. 7 also shows the C/A of the pulverized coal flow Ac on the enrichment side, which is uniquely calculated from the relationship between the inlet C/A, the vertical axis, and the horizontal axis. Ac
In the case of C/A='0.2, it is the same value as the inlet C/A, so naturally the distribution of pulverized coal and the distribution of air to the Ac flow have the same value. Therefore, the practical range of C/A is C/A≧0.25, taking ignition stability into consideration, and preferably the opening position of the nozzle 21 may be adjusted so as to maintain the value of 0.3 or more.

When (S, +S,)/S is set to a value smaller than 0.5,
This is not preferable because the amount of wear caused by the pulverized coal flow becomes significantly greater than the improvement in distribution efficiency. Moreover, it is not preferable to set it at 0.9 or more because it will ensure the thickness of the structural member and reduce the distribution efficiency.

8 and 9 show other embodiments, in which the particle pilot 22 is replaced by a bend 26.
As shown in Fig. 8, by moving the nozzle 21, a rich pulverized coal flow Ac and a lean pulverized coal flow A
The other explanations are the same as those in FIGS. 1 to 5.

The one in FIG. 9 is provided with a particle pilot 22 in place of the vent 26 in FIG. 8, and a rich pulverized coal flow Ac and a lean pulverized coal flow A2 are created by opening and closing the nozzle 21.

[Effects of the Invention] According to the present invention, it is possible to reduce the amount of auxiliary fuel even under extremely low loads, improve the ignition stability of the pulverized coal burner, and perform DSS operation.

[Brief explanation of the drawing]

1 and 2 are sectional views of a pulverized coal burner according to an embodiment of the present invention, and FIGS. 3, 4, and 5 are enlarged sectional views showing the upper half of a pulverized coal nozzle. Fig. 3 shows the case at high load, Fig. 4 shows the case at low load, and Fig. 5 shows the case at extremely low load. Figure 6 is a characteristic curve diagram in which the horizontal axis shows primary air distribution ratio and the vertical axis shows pulverized coal concentration ratio. Figure 7 is a characteristic curve diagram in which the horizontal axis shows burner load and the vertical axis shows C/A. , FIG. 8 and FIG. 9 are cross-sectional views of a pulverized coal burner showing other embodiments, FIG. 10 is a schematic system diagram of a pulverized coal-fired boiler, FIG. 11 is an enlarged cross-sectional view of a conventional pulverized coal burner, In Figure 12, the horizontal axis is the mill load, and the vertical axis is C.
It is a characteristic curve diagram showing /A. 3... Start-up burner, 8... Pulverized coal nozzle, 15... Flame stabilizer for high load, 18... Inlet duct, 19 Outlet duct, 20... Low load flame holder,
21...Nozzle. Fig. 1 Fig. 2 Fig. 3 Fig. 5 Fig. 6 Fig. 7 Fig.

Claims (1)

[Claims] A device for burning pulverized coal by arranging a high-load flame stabilizer at the tip of a pulverized coal nozzle and a starting burner at approximately the center of the pulverized coal nozzle, wherein pulverized coal is placed in the pulverized coal nozzle. A pulverized coal burner comprising an inlet duct and an outlet duct for changing the concentration, a low-load flame stabilizer provided at the tip of the outlet duct, and a nozzle for changing the pulverized coal flow path upstream of the inlet duct.