JP2954659B2 - Pulverized coal burner - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pulverized coal combustion device, and more particularly to an operation range of load change in a combustion system operated by directly connecting a mill and a pulverized coal burner. And pulverized coal burners suitable for

[Conventional technology]

In recent years, Japan has been converting fuel from conventional heavy oil burning to coal burning in order to correct the dependence on petroleum due to the tight supply of heavy oil, and especially for commercial thermal power boilers, Large capacity thermal power plants are being constructed.

On the other hand, as a characteristic of recent power demand, the difference between the maximum and minimum loads has increased with the increase in nuclear power generation, and there has been a tendency to shift the boiler for thermal power generation from base load to load adjustment. Power generation in partial load operation is achieved by using a boiler in which the pressure is changed according to the load to perform a variable pressure operation. Efficiency can be improved by several percent.

For this reason, in the case of this coal-fired thermal power plant, few boiler loads are always operated at full load,
The so-called Daily Start Stop, such as increasing the load to 75% load, 50% load, 25% load, and 15% load, and then lowering or driving at night, or stopping operation at night.
The operation is shifting to a coal-fired thermal power plant that carries an intermediate load.

In addition, among coal-fired boilers that perform DSS operation, there are few that operate the full-load zone only with pulverized coal from start-up to full load.
At low load, light oil, heavy oil, gas, etc. other than pulverized coal are used as auxiliary fuel.

This is because, at the time of startup, exhaust gas and heated air for mill warming cannot be obtained from the coal-fired boiler, so that the mill cannot be operated (coal cannot be pulverized into pulverized coal).

In addition, light oil, heavy oil, gas, and the like are used because the turndown ratio of the mill cannot be obtained at a low load and the ignitability of the pulverized coal itself is poor.

For example, when using light oil or heavy oil as the auxiliary fuel at startup, boil the boiler using light oil as the auxiliary fuel up to 15% load from startup and change the auxiliary fuel from light oil to heavy oil from 15% load to 40% load When the load exceeds 40%, the auxiliary fuel heavy oil and the main fuel pulverized coal are co-fired to gradually reduce the amount of auxiliary fuel heavy oil, and the main fuel pulverized coal is increased to increase the pulverized coal co-firing. Increase the ratio and shift to substantial coal firing.

Hereinafter, the outline of the pulverized coal-fired boiler at the time of startup will be described with reference to FIGS. 10 and 11. Figures 10 and 11
The figure is a schematic system diagram of a pulverized coal-fired boiler and an enlarged sectional view of a conventional pulverized coal burner.

When the pulverized coal-fired boiler 1 shown in FIG. 10 is cold-started, first, the pulverized coal-fired boiler 7 shown in FIG. Thereafter, the heavy oil starting burner 3 is ignited. Then, only the heavy oil starting burner 3 is used to boil up to 25 to 35% of the boiler load. Thereafter, when the temperature in the furnace of the boiler furnace 4 is sufficiently increased, the pulverized coal fuel is supplied from the mill 5 shown in FIG. 10 to the pulverized coal supply pipe 6 and the pulverized coal burner 7 shown in FIG. It is sent from the nozzle 8 into the boiler furnace 4 and switched to pulverized coal only firing.

The pulverized coal transport medium is heat-exchanged with the boiler exhaust gas by the air heater 9 shown in FIG. 10 and then sent to the mill 5 to remove moisture adhering to the lump coal supplied from the coal bunker 10 and to the mill 5. The air is used as classification air of a built-in classifier (not shown), and further as conveying air for conveying the pulverized coal pulverized by the mill 5 to the pulverized coal burner 7.

FIG. 11 shows a pulverized coal burner 7 of the prior art. The pulverized coal burner 7 is provided with a light oil ignition burner 2 and a heavy oil starter burner 3 to constitute the pulverized coal burner 7. . The combustion air in the wind box 11 is turned into the boiler furnace 4 after being swirled by the secondary air register 12 and the tertiary air register 13. On the other hand, the pulverized coal is sent to the pulverized coal nozzle 8 of the pulverized coal burner 7 through the pulverized coal supply pipe 6, while only passing through the venturi 14,
It is blown into the boiler furnace 4 almost in a state close to a free jet. The pulverized coal burner 7 was provided with a high-load flame stabilizer 15, and the swirling of the combustion air produced a reverse flow region, which only maintained the flame in a flow velocity region lower than the flame propagation speed.
Therefore, the diffusion of the pulverized coal particles is good, but on the other hand, the flame becomes unstable, and the pulverized coal burner 7 is very easily influenced by the operating conditions on the air side. Reference numeral 16 in FIG. 10 is a heavy oil tank, and 17 is a light oil tank. On the other hand, in a region where the load on the mill 5 (pulverized coal burner 7) is low, the pulverized coal supplied from the mill 5—the pulverized coal concentration (C / A) in the air flow is low, and ignition stability is deteriorated.

FIG. 12 shows the weight ratio of pulverized coal (C) and air (A) supplied to the pulverized coal burner 7 from the mill 5 with respect to the burner (mill) load on the horizontal axis and the burner (mill) load on the vertical axis (C / C). FIG. 4 is a characteristic curve diagram showing the characteristic curve (referred to as A).

From Fig. 12, it can be seen that as the burner (mill) load decreases,
It can be seen that the C / A is low,
This is a phenomenon peculiar to mills that cannot be stopped due to classification.

As shown in Fig. 12, C / A at 15% burner load
0.08, the pulverized coal becomes extremely lean, and the air ratio at which the primary air flow affects combustion varies depending on the type of coal, but in any case exceeds 1. Therefore, in this load, since only primary air becomes excess air,
No secondary or tertiary air is required, but in fact, due to the characteristics of Juan,
Also, as a measure to prevent burning of the pulverized coal burner 7, the air ratio in the vicinity of the pulverized coal burner is considerably high because the secondary and tertiary air is supplied considerably, and the flame is unstable because the pulverized coal particles are further diluted. become.

[Problems to be solved by the invention]

As described above, in the pulverized coal burner using the auxiliary fuel, the usage amount of the auxiliary fuel increases every frequent start-stop operation, and in the combustion system in which the pulverized coal-air flow is directly supplied from the mill to the pulverized coal burner, the mill (burner) is used. When the load is low, there is a disadvantage that the ignitability of the pulverized coal burner is deteriorated and the unburned matter increases.

The present invention is intended to solve such conventional disadvantages, and aims at reducing auxiliary fuel and improving the ignition stability of pulverized coal burners.
An object of the present invention is to provide a pulverized coal burner that can perform low-load operation in DSS operation.

[Means for solving the problem]

In order to achieve the above-mentioned object, the present invention provides a pulverized coal nozzle provided with a high-load flame stabilizer at the furnace end and a pulverized coal fixed in the pulverized coal nozzle and flowing through the pulverized coal nozzle by inertia force. Particle pilot biased outward, in the pulverized coal nozzle, and fixed to the pulverized coal flow direction downstream of the particle pilot, partitioning the outer flow path and the inner flow path,
A duct member having, for example, an inlet duct and an outlet duct provided with a low-load flame stabilizer at the furnace side end, and a pulverized coal that is disposed in the pulverized coal nozzle and flows through the pulverized coal nozzle is biased inward by inertial force. And a nozzle that can move in the axial direction of the pulverized coal nozzle, wherein the nozzle is disposed on the upstream side in the pulverized coal flow direction from the particle pilot when the burner is under a high load, and the nozzle is configured such that when the burner is under a low load, the nozzle It is characterized by being arranged between a pilot and the duct member.

[Action]

When the burner load of the pulverized coal burner is low (when the mill is started and the load is low), move the nozzle that changes the pulverized coal flow path inside the pulverized coal nozzle and place the dense pulverized coal inside the inlet duct and outlet duct. A flow is formed, and ignition stability is ensured with a low-load flame stabilizer.

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,
A dense pulverized coal stream is formed outside the inlet duct and outlet duct to ensure ignition stability with a high-load flame stabilizer.

〔Example〕

 Hereinafter, embodiments of the present invention will be described with reference to the drawings.

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 an upper half of a pulverized coal nozzle. The figure shows a high load, FIG. 4 shows a low load, and FIG. 5 shows an extremely low load.

Fig. 6 is a characteristic curve diagram showing the distribution ratio of primary air on the horizontal axis, the pulverized coal concentration ratio on the vertical axis, and Fig. 7 is a characteristic curve diagram showing the burner load on the horizontal axis and C / A on the vertical axis. 8 and 9 are sectional views of a pulverized coal burner showing another embodiment.

In FIGS. 1 to 9, reference numerals 3 to 15 denote the same components as those of the prior art.

18 and 19 are inlet ducts and outlet ducts arranged in the pulverized coal nozzle 8 to change the concentration of pulverized coal, 20 is a low-load flame stabilizer provided at the end of the outlet duct 19, and 21 is moved along the pulverized coal nozzle 8 Nozzle, 22 is a particle pilot, and 23, 24, 25 are pulverized coal passages.

FIG. 1 shows the position of the nozzle 21 when the load is high, and FIG. 2 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) by a pulverized coal supply pipe 6 to an arrow A in FIG.
Is supplied to the pulverized coal nozzle 8 of the pulverized coal burner 7, enters the boiler furnace 4 through the nozzle 21, the particle pilot 22, the inlet duct 18, and the outlet duct 19, and receives a high-load flame stabilizer 15.
Combustion is stable.

In this pulverized coal burner 7, the combustion air is further supplied to a wind box 11.
Inside, it is divided into a secondary air register 12 and a tertiary air register 13 and is preferably supplied with a turning force. Nozzle 21
Although not shown, the actuator is slid in the pulverized coal nozzle 8 by an actuator, a roller with a bearing, or the like, and is controlled so as 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 channel 25 flows into the pulverized coal channel 23 located outside the inlet duct 18 and the outlet duct 19, and the pulverized coal flows through the inlet duct 18 and the outlet. Since the dilute pulverized coal flow flows through the pulverized coal flow path 24 located inside the duct 19, the flame is stably burned by the high-load flame stabilizer 15.

On the other hand, when the load is extremely low as shown in FIG. 2, the pulverized coal in the pulverized coal passage 25 is located inside the inlet duct 18 and the outlet duct 19 because the nozzle 21 moves toward the boiler furnace 4 and comes into contact with the inlet duct 18. The rich pulverized coal flow flows through the pulverized coal flow path 24,
Since the dilute pulverized coal flow flows in the pulverized coal flow path 23 located outside the inlet duct 18 and the outlet duct 19, the flame is stably burned by the low-load flame stabilizer 20.

Hereinafter, a description will be given separately with reference to FIGS. 3 to 5 when the load is high, when the load is low, and when the load is extremely low.

3, the pulverized coal stream A is supplied to the pulverized coal flow path 25 in the pulverized coal nozzle 8, and firstly, when passing through the nozzle 21 on the upstream side and the particle pilot 22 on the downstream side. As shown in the figure, the pulverized coal is biased to one side due to inertial force (specific gravity is about 1000 times or more of air), and the dense pulverized coal flow is concentrated in the outer pulverized coal passage 23 partitioned by the downstream inlet duct 18. A _B flows. Next, the dilute pulverized coal flow flowing into the inner pulverized coal flow path 24 partitioned by the inlet duct 18 is
It flows as lean pulverized coal flow A _R to the pulverized coal flow path 24. Also,
Air A _A from the resistance distribution as shown by the arrow
Into a gap-shaped flow path formed between the pulverized coal flow and the dilute pulverized coal flow A _R in the inner pulverized coal flow path 24, and finally into the boiler furnace 4. flow a _C, is supplied is divided as lean pulverized coal flow a _R.

Here, in the arrangement of the nozzle 21 at the time of high load, when the pulverized coal flow is supplied to the inlet duct 18 and the outlet duct 19 by the operation of the particle pilot 22 as described above, a large amount because of that the pulverized coal is separated supply, C / a of the thick pulverized coal flow a _C is higher than the C / a of the lean pulverized coal flow a _R. Therefore, the high-load pulverized coal stream is stably burned by the high-load flame stabilizer 15. In this case, the nozzle 21 has an inlet duct 18 has a function of adjusting the flow rate of the concentrated pulverized coal flow A _B of the outlet duct 19, by a good normal load zone of flame stability for the fully open state, the flow path resistance At the same time, the pressure difference of the pulverized coal burner 7 is reduced, and at the same time, the flow rate of the pulverized coal is kept as low as possible to suppress damage due to abrasion.

The particle pilot 22 causes the flow of pulverized coal to flow to the outer pulverized coal flow path 23 when the load is high, so that the pulverized coal concentration becomes higher in the outer pulverized coal flow path 23, and is burned by the high-load flame stabilizer 15. To do. The inlet duct 18 and the outlet duct 19 do not need to increase the C / A of the inner pulverized coal flow path 24 particularly in a high load area, so that the pulverized coal concentration in the outer pulverized coal flow path 23 is better for the burner. Operationally favorable.

At the time of low load in FIG. 4, the pulverized coal flow A supplied to the pulverized coal nozzle 8 is similar to the case of high load in FIG.
But particle pilot 22, the nozzle 21, the inlet duct 18, the outlet duct 19, the arrows A _B, A _R, to form a pulverized coal flow as shown by A _C. Here, the difference from the high load state is the relative position between the nozzle 21 and the particle pilot 22, and the nozzle 21 is set closer to the boiler furnace 4 than the particle pilot 23. Therefore, the inlet duct 18 as shown in FIG. 4, a high concentration of the pulverized coal flow A _C inside the pulverized coal flow path 24 of the outlet duct 19 is supplied, further, the inlet duct 18, inside each at the outlet duct 19 the pulverized coal flow a _R to pulverized coal passage 24 and pulverized coal passage 23 formed outside, even in a _C, the inside of the pulverized coal passage due to the inertial force 2
The pulverized coal concentration of 4 becomes high and it is burned by the low load flame stabilizer 20.

That is, the feature of the present embodiment is that the combination of the nozzle 21 and the
18, where the particle concentration supplied to the two flow paths to the outlet duct 19 is reversed.

When the load is extremely low as shown in FIG. 5, the pulverized coal flow bypassing between the inlet duct 18 and the outlet duct 19 is eliminated by fully closing the nozzle 21, and the entire flow rate is reduced to the inlet duct 1.
8, supply to the pulverized coal flow path 24 inside the outlet duct 19. By this operation, the inlet duct 18 and the outlet duct 19 function with maximum efficiency, and the pulverized coal stream A is supplied to the low-load flame stabilizer 20 that requires a high C / A.
_C can be held at the required value.

As a result of examining the functions as described above, as a structure of the inlet duct 18 and the outlet duct 19 for increasing the pulverized coal concentration, the narrowest passage cross-sectional area S _i of the outlet duct 19 (see FIG. 3)
Flow path A _C flows), the narrowest flow path sectional area S ₀ (A _R flows flow path in FIG. 3 in the other flow path of the outlet duct 19), the flow path cross-sectional area S of the pulverized coal nozzle 8 Then (S ₀ +
S _i ) / S is set to 0.5 to 0.9, S _i / (S _i + S ₀ ) is set to 0.4 or less, and 1 is formed between the flow path partitioning structural members.
Minimum area S _R of the portion which can be regarded as the flow path (flow path through which the 3 A _A in the figure) is found that may be set larger such concentrates separator structure than S _0.

The six figures, the primary air distribution ratio to the second view structure with a high C / A side (= 100 × air flow in the air flow rate / A in A _C) and pulverized coal concentration factor (= 100 × the relationship between the pulverized coal flow) in pulverized coal flow rate / a in a _C shown in the diagram. The figure shows that S _i / (S _i + S ₀ ) is 0.4 and C / in the pulverized coal stream A supplied to the pulverized coal nozzle 8 is
A (entrance C / A) of 0.2 is shown. Curve B in the figure
Shows the results when (S ₀ + S _i ) / S is 0.5 and the curve C is 0.9.

Also shows C / A of the inlet C / A and the vertical axis, the uniquely calculated by concentration-side from the relation of the horizontal axis pulverized coal flow A _C in Figure 7. For C / A = 0.2 in A _C, for the same value as the inlet C / A, the same value and of course distribution and allocation of air pulverized coal into the A _C flow. Therefore, the practical C / A range is
Considering ignition stability, C / A ≧ 0.25, preferably
The opening position of the nozzle 21 may be adjusted so as to maintain 0.3 or more.

Setting (S ₀ + S _i ) / S to a value smaller than 0.5 is not preferable because the amount of abrasion caused by the pulverized coal stream becomes significantly larger than the distribution efficiency. Further, a value of 0.9 or more is not preferable because the thickness of the structural member is secured and the distribution efficiency is reduced.

8 and 9 show another embodiment. In FIG. 8, a bend 26 is provided instead of the particle pilot 22, and the nozzle 21 is movable as shown in FIG. but produces a rich pulverized coal flow a _C and dilute pulverized coal flow a _R by, the other description is the same as the first drawing of Figure 5.

Those of Fig. 9 which was a particle pilot 22 is provided in place of the bend 26 of Figure 8, open the nozzle 21, it is intended to make a thick pulverized coal flow A _C and dilute pulverized coal flow A _R by closing.

〔The invention's effect〕

ADVANTAGE OF THE INVENTION According to this invention, auxiliary fuel can be reduced, the load stability of a pulverized coal burner can be improved, and DSS operation can be performed even at the time of an extremely low load.

[Brief description of the drawings]

1 and 2 are cross-sectional views of a pulverized coal burner according to an embodiment of the present invention, FIG. 3 is an enlarged cross-sectional view showing the upper half of a pulverized coal nozzle under a high load, and FIG. 5 is an enlarged sectional view showing the upper half of the pulverized coal nozzle of FIG. 5, FIG. 5 is an enlarged sectional view showing the upper half of the pulverized coal nozzle under extremely high load, and FIG.
FIG. 7 is a characteristic curve showing the distribution ratio of the secondary air, the pulverized coal concentration rate on the vertical axis, and FIG. 7 is a characteristic curve showing the burner load on the horizontal axis and C / A on the vertical axis. Is a sectional view of a pulverized coal burner showing another embodiment, FIG. 10 is a schematic system diagram of a pulverized coal fired boiler,
FIG. 11 is an enlarged sectional view of a conventional pulverized coal burner, and FIG. 12 is a characteristic curve diagram in which a horizontal axis indicates a mill load and a vertical axis indicates C / A. 3 ... Start-up burner, 8 ... Pulverized coal nozzle, 15 ... High-load flame stabilizer, 18 ... Inlet duct, 19 ... Outlet duct, 20
…… Low load flame stabilizer, 21 …… Nozzle.

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Hiroyuki Kaku 3-36 Takara-cho, Kure City, Hiroshima Prefecture Inside the Kure Research Institute, Inc. (72) Inventor Shigeki Morita 6-9 Takara-cho Kure City, Hiroshima Prefecture Babkotsuk Day (72) Inventor Hironobu Kobayashi 4026 Kuji-cho, Hitachi City, Ibaraki Prefecture Inside Hitachi Research Laboratory, Hitachi Ltd. (56) References JP-A-3-50408 (JP, A) Shokai Sho 62- 142610 (JP, U) (58) Field surveyed (Int. Cl. ⁶ , DB name) F23D 1/00

Claims (1)

(57) [Claims] 1. A pulverized coal nozzle provided with a high-load flame stabilizer at the furnace end, and a particle pilot fixed in the pulverized coal nozzle and biasing the pulverized coal flowing through the pulverized coal nozzle outward by inertia force. And a duct fixed in the pulverized coal nozzle and on the downstream side in the pulverized coal flow direction of the particle pilot to partition an outer flow path and an inner flow path and to provide a low-load flame stabilizer at a furnace side end. And a nozzle arranged inside the pulverized coal nozzle and biasing the pulverized coal flowing through the pulverized coal nozzle inward due to inertial force, and having a nozzle movable in the axial direction of the pulverized coal nozzle. The nozzle is disposed upstream of the particle pilot in the pulverized coal flow direction, and the nozzle is configured to be disposed between the particle pilot and the duct member when a burner has a low load. And pulverized coal burner.