JPH0289911A - Pulverized coal fuel feed device and operation method thereof - Google Patents

Abstract

PURPOSE:To enable production of high C/A pulverized coal fuel despite of increasing of device size and lowering of the separation a separator efficiency due to becoming more fine pulverized coal and to hold stabilization of flame by a method wherein a thin pulverized coal flow from a solid-gas concentrating device is continuously returned to a mill. CONSTITUTION:In a cyclone separator 9, through utilization of a difference in a specific gravity by means of a centrifugal force, a solid is separated, pulver ized coal and a part of air are separated being concentrated. Remaining thin fluid is recirculated to a mill 5 through a mill return duct 14 with the aid of a thin fluid outlet duct 12 and a mill recirculating fan 13. Pulverized coal fluid concentrated and separated by the cyclone 9 is joined with a pulverized coal flow, fed through a branch pipe 6a of a mill outlet fuel piping 6 to an ejector 10 through a flow rate regulating damper 15, for redispersion. The mixture, C/A of which is improved, is fed to a burner 8 for concentrated fluid through a high C/A fuel piping 11. High C/A pulverized coal fuel can be fed to a burner without substantially improving the efficiency of the mill 5 and despite low efficiency of the cyclone separator 9.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a pulverized coal fuel supply device for supplying pulverized coal obtained by crushing and separating coal to a burner of a combustion device such as a boiler, and the like. This article relates to a pulverized coal fuel supply operation method for handling equipment.

[Conventional technology]

Conventionally, a pulverized coal combustion system used for combustion in boilers, etc. uses a pulverized coal machine (hereinafter referred to as a mill) with a built-in classifier to directly supply pulverized coal to a pulverized coal burner. has been put into practical use.

The mill used in this combustion system includes a grinding table 51 as shown in FIG. 6, and this grinding table 51 rotates in conjunction with a gearbox 52. Simultaneously with this rotation, the ball 55 supported by the upper ring 53 and the lower ring 54 also rotates while sliding on the lower ring 54. Further, coal C of about 5 to 50 mm, which is supplied from a coal feeder (not shown) onto the crushing table 51 via the supply pipe 56, passes through the gap between the lower ring 54 and the ball 55 due to centrifugal force, and at the same time It is crushed and sent to the upper throat 57. On the other hand, primary air heated to around 300° C. is supplied to the upper throat 57 through the throat 58 and slit 59 by a forced draft fan (not shown). The thus pulverized coal is moved through the upper throat 57 by this secondary air.

Of the coal particles that have passed through the upper throat 57, only relatively fine particles are fed into the classifier 61 via the vane 60.
Coarse coal particles are separated from the air flow as the air flow rate decreases and are returned over the upper ring 53 onto the grinding table 51 again. (-order classification) Also, among the particles that entered the classifier 61, relatively coarse coal particles fall through the classifier 61,
It is returned to the grinding table 51 by the flapper 63 (
By adjusting the angle of the vane 60, the particle size of the coal sent to the coal conveyance pipe 62 without falling through the classifier 61 can be reduced to 200 mesh (74 μm or less) by 70%.
The granularity is adjusted to a certain degree.

The heated air thus introduced into the mill is used for drying raw coal fed to the mill, for classification within the mill, and as a transport fluid for pulverized coal to the burner. Therefore, the volume and temperature of the heated air are determined depending on the moisture content, crushability, combustibility, etc. of the raw coal, and have the characteristics as shown in FIG.

Figure 7 shows the relationship between mill load and C/A, where C/
A is pulverized coal supplied from the mill to the burner: C and air: A
As is clear from Figure 7, which shows the weight ratio between This phenomenon is unavoidable because it is necessary.

Figure 8 shows the ignition stability of coal by the relationship between the fuel ratio and C/A determined by the weight ratio of fixed carbon content and volatile content in coal. The fuel ratio is about 0.8 to 2°5, and as the fuel ratio increases, such as high fuel ratio coal of 2.5 or more and anthracite coal of 4 or more, the volatile content in the coal decreases.
It is not possible to ignite stably unless the C/A is high, therefore,
When using a mill having the characteristics shown in FIG. 7,
When coal has a high fuel ratio and C/A is low in the low load range as shown in the figure, ignition becomes unstable, which poses a serious problem in terms of safe operation of the boiler.

As a combustion system to deal with such problems, Japanese Patent Application Laid-Open No. 61-192113 and Japanese Utility Model Application No. 62-24
The method described in Publication No. 209 and the like has been proposed. These combustion systems are, in principle, capable of producing low C
The pulverized coal flow of /A is branched into a fluid with a high C/A (il! thick fluid) and a fluid with a low C/A (lean fluid) using inertia, and the flame is stabilized with a burner that burns the thick fluid. It is a system that allows you to

FIG. 5 shows an example of the above-described combustion system, in which coal 82 and air 83 are introduced into a mill 81, and a cyclone separator, for example, is installed as a separator using inertial force in the middle of a fuel pipe 84 from the mill 81. 85 has been installed. The concentrated fluid with high C/A due to the inertial force in the cyclone separation f%85 is introduced into the concentrated fluid burner 86, and the low C/A fluid from which most of the pulverized coal has been removed is introduced into the flow rate adjustment damper 87.
The FR fluid is introduced into the dilute FR fluid burner 90 via the dilute fluid piping 88 having a dilute fluid piping 88 .

FIGS. 9(A) and 9(CB) show the relationship between the outlet pipe diameter, the critical particle diameter, and the collection efficiency in the cyclone separator, calculated based on standard cyclone dimensions and operating conditions.

From FIG. 9, when considering a fuel amount of 5 t/h as a large capacity burner, the cyclone diameter is about 1500 mm and the outlet pipe diameter is about 670 mm. In this case, the particle size that can be separated by centrifugal force is 25 μm, the particle size distribution of pulverized coal is 200 mesh baths 90%, and the distribution index n = 2.
In this case, the collection efficiency decreases to as much as 55%. Therefore, since the collection efficiency is about 55%, in this cyclone separator, the airflow is simply divided into two, and it is actually difficult to obtain a concentrated fluid with a high C/A.

[Problem to be solved by the invention]

As mentioned above, the conventional combustion system is only effective when the efficiency of the cyclone for separating pulverized coal is high, and it is a countermeasure for high fuel ratio coal with a flammability and low load when C/A decreases. As a result, the reduction in efficiency due to finer particle size of pulverized coal and larger size of the equipment was not considered, and in practical use, the actual C/A decreased, the flame lifted and stability could not be maintained, and the flame detector There have been problems such as malfunctions and increased unburned losses.

The purpose of the present invention is to solve the above-mentioned problems of the prior art, to be able to generate Wl pulverized coal fuel with high C/A, despite the decrease in separation efficiency of the separator due to the increase in the size of the equipment and the miniaturization of pulverized coal.
An object of the present invention is to provide a pulverized coal fuel supply device that can maintain flame stability.

[Means to solve the problem]

The above purpose is to introduce the pulverized coal flow conveyed from the mill into a solid gas concentrator such as a cyclone separator, and supply it to a compressor pulverized coal flow burner, etc. on the pulverized fluid outlet side of this solid gas concentrator. ,
and a device configured to return the lean pulverized coal stream from the solid gas concentrator to the mill, and a device configured to continuously supply concentrated fluid from the solid gas concentrator to a burner etc. during operation of the combustion device, and to This is achieved by a method of operation in which a lean pulverized coal stream from the vessel is continuously returned to the mill.

[Effect]

? If the amount of gas in the pulverized coal fuel supply system is constant, the amount of fluid supplied to the mill (mainly air) is reduced and the temperature is increased, depending on the amount of recirculation to the mill, and the amount of pulverized coal fluid C/ A increases by the amount of recycled pulverized coal.

When the C/A of the pulverized coal fuel at the mill outlet increases, the solid air
As a result, the C/A of the pulverized coal fuel at the outlet of the compressor increases.
Even when the solids collection rate in the solid gas 1 condenser is low, the C/A of the rich side outlet can be improved by controlling the amount of air extracted.
can be maintained at a predetermined value, and ignition stability in the burner can be maintained.

In addition, in order to increase the C/A of pulverized coal fuel, the -a reduced pulverized coal from the solid gas concentrator is temporarily stored in a bottle or the like, and then transported by conveying air to achieve the desired C/A. There is a risk that the stored pulverized coal fuel may cause a fire due to spontaneous combustion.

In the pulverized coal fuel supply method of the present invention, when operating the combustion device,
Since pulverized coal fuel has no storage area and is constantly transported, risks such as fire can be avoided.

〔Example〕

Embodiments of the present invention will be described below based on the drawings.

FIG. 1 is a system diagram showing one embodiment of the pulverized coal fuel supply device of the present invention, and shows an example in which the present invention is applied to an anthracite coal boiler that burns pulverized coal.

In this device, the raw coal in the coal bunker 1 is transferred to the chute 2.
A predetermined amount of raw coal is supplied to a metering feeder 3 through a chute 4 and introduced into a mill 5.

The mill outlet fuel pipe 6 is connected to a coal feed pipe 62 in FIG. It's communicating. The mill outlet fuel pipe 6 is connected to an air inlet of a cyclone separator 9 serving as a solid air condenser, and an ejector 10 is installed on the particulate material recovery part side of the cyclone separator 9. And ejector 10
A branch pipe 6a of the mill outlet fuel pipe 6 is connected to the
/A It is connected to the burner 8 for concentrated fluid via the fuel pipe 11. A diluted fluid outlet duct 12 is arranged at the air outlet of the cyclone separator 9.
is connected to a mill return duct 14 via a mill recirculation fan 13.

The mill return duct 14 communicates with the interior of the classifier 61 in FIG. Further, a flow rate adjustment damper 15 is installed in the branch pipe 6a of the mill outlet fuel distribution v6, so as to adjust the flow rate of the working fluid introduced into the ejector 10 side.

The combustion air duct 16 is a forced blower (FDP) 17.
The air is branched into three flow paths via an air preheater 18a, and a flow rate adjustment duct 19 is interposed in each branch duct. The combustion air duct 16 also includes a primary air fan 20.
, as the primary air duct 21 via the air preheater 18b,
It communicates with the heated air inlet section (indicated by A in the figure) in FIG. Note that the branch pipe 1 is connected to the air preheater 18b.
6a is arranged, and a flow rate adjustment damper 2 is installed in this branch pipe 16a.
2 is interposed.

In addition, the exhaust gas duct 23 of the boiler furnace 7 is connected to the air preheater 1
It is connected to the outside of the system via 8a and 18b.

Next, the operation of the device configured as described above will be explained.

The raw coal in the coal bunker 1 is supplied to a metering feeder 3 via a chute 2, and a predetermined amount of raw coal required for the boiler load is introduced into a mill 5 via a chute 4. On the other hand, a part of the air from the combustion air duct 16 passes through the secondary air fan 20 and is introduced into the air preheater 18b by the flow rate adjustment damper 22. The flow rate is adjusted, and the air is preheated by the air preheater 18b. Heated air at a predetermined temperature is introduced into the mill 5 through the primary air duct 21. This heated air is introduced into the mill 5 through the flow path (indicated by A in the figure) in FIG. 6, and is used for drying, classifying, and transporting the raw coal.

The pulverized coal sent from the coal feed pipe 62 in the mill 5 to the mill outlet fuel pipe 6 together with primary air is introduced into the air inlet of the cyclone separator 9. At this time, part of the fluid containing pulverized coal from the mill outlet pipe 6 flows through the branch pipe 6a.
The flow rate of the powder is adjusted by a regulating damper 15, and the powder is introduced into the ejector 10 on the powder outlet side of the cyclone separator 9.

In the cyclone separator 9, solids are separated using the difference in specific gravity due to centrifugal force, and part of the pulverized coal and air is concentrated and separated, and the remaining diluted fluid is sent to the diluted fluid outlet duct 12 and the mill recycler. Mill return duct 1 by circulation fan 13
4 and circulates to mill 5.

The pulverized coal fluid concentrated and separated in the cyclone separator 9 is passed from the branch pipe 6a of the mill outlet fuel pipe 6 to the flow rate adjustment damper 15.
It joins with the pulverized coal flow supplied to the ejector 11 via the pulverized coal flow, is redispersed, has a high C/A, and is supplied to the concentrated fluid burner 8 through the high C/A fuel pipe 11.

Combustion air passes through a forced blower (FDP) 17, an air preheater 18a, and a flow rate adjustment damper 19, and then is delivered to a burner 8 for concentrated fluid.
and is supplied to the boiler furnace 7.

The boiler exhaust gas is cooled by heat exchange in a steam superheater, reheater, feed water heating economizer, etc. (not shown), and then passes through the exhaust gas duct 23 to air preheaters 18a and 18b where it is used as primary air and for combustion. After being used to heat the air, it is discharged from the chimney through a dust collector, induced draft fan, etc. (not shown).

Figures 2 and 2 are system diagrams of the main parts of the equipment shown in Figure 1, and this diagram shows the specific C/A value in each part of the coal 100
A case where the weight ratio of 0% and 100% air is 0.5 will be explained.

Mill 5 has 100% raw coal from chute 4 and 100% air from chute 4.
70% is supplied from the secondary duct 21. Here, C/A of the fluid supplied to the mill 5 is.

Furthermore, pulverized coal 2 is supplied from the mill return duct 14 as a recirculating bone.
0% and 30% air is supplied. Here, by calculation similar to the above, C/A-0,33 of the pulverized coal fluid returned from the mill return duct 14 to the mill 5 is obtained.

Therefore, in the mill outlet fuel pipe 6, pulverized coal is 120%
The air is 100%, and C/A=0.6. This fluid is divided into parts, and one part is supplied to the cyclone separator 9, where the separation efficiency is 67%, and the concentrated outlet side is supplied with 40% pulverized coal, and 20% air is supplied to the ejector 11 with C/A-1,0. Furthermore, as described above, a fluid with C/A=0.33 circulates on the dilute fluid outlet duct 12 side.

On the other hand, the branch fluid in the branch pipe 6a of the mill outlet fuel pipe 6 is
The flow rate adjustment damper 15 serves as the working fluid for the ejector lO, which is merged and redistributed with the fluid on the rich outlet side.
= 0.71, high C/A combustion is performed.

Such a method makes it possible to supply fine fuel with high C/A to the burner without substantial improvement in the efficiency of the mill 5 and despite the low efficiency in the cyclone separator 9. . Furthermore, if necessary, by adjusting the C/A and bypass flow rate of the pulverized coal fluid introduced into the mill 5, and the amount of recirculation of the pulverized coal flow to the mill 5, it is possible to cope with changes in coal type, boiler load fluctuations, etc. It also becomes easier.

In the present invention, the branch pipe 6a in FIG. 1 can be omitted, and combustion air or the like can be introduced as the working fluid into the ejector 10 on the concentration outlet side of the cyclone separator 9. In this case as well, by recirculating the pulverized coal fuel to the mill 5, the C/A of the pulverized coal fuel at the outlet of the mill 5 increases, and even if the collection efficiency of the cyclone separator 9 is low, the burner can be heated by adjusting the flow rate of the working fluid. The CIA of pulverized coal fuel supplied to the pulverized coal fuel can be adjusted.

FIG. 3 is a schematic configuration diagram showing another embodiment of the pulverized coal fuel supply device of the present invention.

3, the difference from the embodiment shown in FIG. 1 is that a row reseal 31 is installed on the concentration outlet side of the cyclone separator 9, and the thin fluid outlet duct 12 of the cyclone separator 9 is branched into a The branch pipe 12a is connected to the boiler furnace 7, and a flow rate adjustment damper 32 is interposed in the middle of the branch pipe 12a. Therefore, the third
In the figure, the same or equivalent components as those in the embodiment shown in FIG. 1 are denoted by the same reference numerals, and the explanation of the structure will be omitted.

In the cyclone separator 9, solids are separated using the difference in specific gravity caused by centrifugal force, and pulverized coal and a part of air are subjected to f4 condensation separation. The remaining lean fluid reaches the lean fluid outlet (12). A part of this lean fluid is circulated to the mill 5 via the mill return duct 14 by the mill recirculation fan 13, and the flow rate of the remaining lean fluid is adjusted by the flow rate adjustment damper 32, and the flow rate of the remaining lean fluid is regulated by the branch pipe 12a to the boiler furnace 7.
supplied to

From the pulverized coal fluid separated and concentrated by the cyclone Mli1, only the pulverized coal in the fluid is extracted by the rotary seal 31, and is supplied to the ejector lO from the branch pipe 6a of the mill outlet fuel pipe 6 via the flow rate adjustment damper 15. The pulverized coal is redispersed by the pulverized coal flow, has a high C/A, and is introduced into the concentrated fluid burner 8 through the high C/A fuel pipe 11.

FIG. 4 is a system diagram of essential parts of the apparatus shown in FIG. 3.

With reference to this figure, specific C/A values at each part will be explained in the case where the weight ratio of coal OO% to 100% air is 0°5.

The mill 5 is supplied with 100% raw coal from the chute 4 and 80% heated air (C/A-0,63) from the primary air duct 21. In the mill outlet fuel pipe 6, a pulverized coal flow (pulverized coal 1O%, air 20%, C/A-0,25) is combined with a pulverized coal flow (pulverized coal 10%, air 20%, C/A-0,25) that is recirculated by the mill return duct 14.
11% pulverized coal, 100% air, C/A-0.55).

Therefore, the amount of primary air required for the coal supplied to the mill is the same as the conventional amount based on the mill outlet fuel piping. Therefore, although the amount of pulverized coal particles in the mill outlet fuel pipe 6 increases by 10%, the pressure loss of the pulverized coal flow through the cyclone separator 9 is rather reduced, so there is almost no power loss. Flow 11 for mill outlet fuel pipe 6! When the flow rate of the pulverized coal flow supplied to the branch pipe 6a is reduced to 1/2 by controlling the damper 15, the cyclone separator 9 receives C/A-0.55 (55% pulverized coal, 50% air). Supplied.

Here, the collection efficiency in the cyclone separator 9 is set to 55%.
Then, cyclone-collected pulverized coal (coal 30%, air O
%) is redispersed by the working fluid C/A-0,55 (55% pulverized coal, 50% air) supplied from the branch pipe 6a to the ejector 10 via the flow rate adjustment damper 15, resulting in high C/A
C/A=0 to the burner 8 for concentrated fluid via the fuel pipe 11
85° (85% pulverized coal, 50% air).

On the other hand, from the cyclone separator 9 to the lean fluid outlet duct 12
C/A=0.25 (pulverized coal 25%, air 50%)
is exhausted. This pulverized coal flow is returned to the mill return duct 14 and the branch pipe 12a at a ratio of 2:3, respectively. In this case, the mill return duct 14 has C/A=0.
25 (pulverized coal 1O%, air 20%), branch pipe 1
The pulverized coal flow introduced by the lean fluid burner 33 via 2a is C/A=0.25 (13115%, air 20%
), therefore, the burner 8 for concentrated fluid has C/A
= 0.85 pulverized coal flow is introduced into the lean fluid burner 3.
In step 3, a pulverized coal flow with C/A=0.25 is introduced to perform concentrated combustion.

In this way, the absolute amount of primary air amount is also 2 due to the amount of recirculation to the mill 5 and the branch pipe 12a in the cyclone separator 9.
Since it can be reduced by 0%, there are advantages such as being able to cover the draft loss caused by the ejector 10.

FIG. 5 is a system diagram of main parts of a conventional apparatus shown in comparison with the embodiments shown in FIGS. 2 and 4.

In Figure 5, the coal 82 from the chute is 100%, 1
100% of the heated air 83 is supplied from the next air duct,
The weight ratio is set to 0.5.

Also in the mill outlet fuel pipe, the entire amount is introduced into the cyclone separator 85 with exactly the same distribution as above. Here, the burner 86 for concentrated fluid is C/A-0,85 (pulverized coal 8
5%, air 50%), C/A=
Adjusted to 0.15 (pulverized coal 15%, air 50%). However, in this case, in order to ensure a collection efficiency of 85% for pulverized coal particles by the flow f adjustment damper 87, it actually becomes more difficult as the capacity of the cyclone separator 85 is increased.

Comparing the embodiment of the present invention with the conventional example described above, it is found that in the embodiment shown in FIG. In addition, C/A can be increased from 0.5 to 0.71 without requiring any improvement in the performance of the mill 5, and the amount of air for conveying pulverized coal can be reduced by 30%.

Furthermore, in the embodiment shown in FIG. 3, high C/A fuel can be supplied even if the collection efficiency of the cyclone separator 9 etc. is reduced from 85% to 55%, and the performance of the mill 5 needs to be improved. C/A can be increased from 0.5 to 0°63,
Furthermore, the amount of air used to convey pulverized coal can be reduced by 20%.

In the embodiments described above, the configuration of a single mill, a cyclone separator, and a set of concentration burners has been described for one furnace. However, in the case of a boiler, the larger the boiler, the more multiple burner systems are installed.

In this case, pulverized coal fuel is fed to a plurality of mills and cyclone separators and is burned by one or two divided groups of burners.

Therefore, in the embodiment shown in FIG. 1, two or more cyclone separators 9 are provided for one mill 5, and a high C/A fuel pipe 11 is branched for each cyclone separator 9. one or more rich fuel burners 8,8.・
・Pulverized coal fuel may be introduced into.

Furthermore, in the embodiment shown in FIG. 3, the same number of lean fuel burners as rich fuel burners can be provided.

Furthermore, in the above-mentioned embodiments, a cyclone was used as the pulverized coal separator, but the solid-gas concentrator is capable of separating a fluid containing pulverized coal into a fluid with a high pulverized coal concentration and a fluid with a low pulverized coal concentration. Any container is fine.

[Effects of the Invention] As described above, according to the present invention, high C/A pulverized coal fuel can be used in the burner regardless of the separation efficiency of pulverized coal in the separator and without improving the performance efficiency of the mill. The pulverized coal can be supplied to combustion devices such as the following, and stable combustion of pulverized coal can be achieved.

[Brief explanation of the drawing]

Fig. 1 is a system diagram showing one embodiment of the pulverized coal fuel supply device of the present invention, Fig. 2 is a system diagram of main parts of the device of Fig. 1, and Fig. 3 is a system diagram showing an embodiment of the pulverized coal fuel supply device of the present invention. FIG. 4 is a system diagram showing the main parts of the device shown in FIG. 3, FIG. Figure 7 is a diagram showing the relationship between mill load and C/A.
9 is a diagram showing the relationship between the fuel ratio and C/A, and FIG. 9 is a diagram showing the relationship between the outlet pipe diameter of the cyclone separator, the critical particle diameter, and the collection efficiency. ■・・・Coal bunker, 3・・・Measuring feeder, 5・・・Mill, 6・・・Mill outlet fuel supply pipe, 6a・・・Branch Pipe, 8... burner for rich fuel, 9... cyclone separator 9.
10...Ejector, 11...High C/
A Fuel piping, 12... Lean fluid outlet duct, 1
2a... Branch pipe, 14... Mill return duct, 15... Flow rate adjustment damper, 16...
...Combustion air duct, 18a, 18b...Air preheater, 21...Primary air duct, 31...
...Rotary seal, 32...Flow I adjustment damper. Agent Patent Attorney Masaru Nishimoto - Figure 6 Figure 7 Mill load (%) Figure 8 j, r Fees (-)

Claims (6)

[Claims] (1) After supplying coal and air to the mill and introducing the pulverized coal pulverized in the mill together with conveying air from the mill outlet fuel pipe to the solid gas concentrator, the concentrated pulverized coal flow is transferred to the solid gas concentrator. A pulverized coal fuel supply device that supplies fuel to a combustor via an outlet fuel pipe, characterized in that it is provided with a lean fluid pipe that returns lean fluid from the air outlet side of the solid gas concentrator to the mill. (2) The pulverized coal fuel supply device according to claim (1), wherein the mill outlet fuel pipe is branched, and the branch pipe is connected to the concentrated fluid outlet side of the solid gas concentrator. (3) The dilute fluid piping that returns the dilute fluid from the air outlet side of the solid gas concentrator to the mill is branched, and the branch pipe is connected to the dilute fuel combustor installed in the combustor. The pulverized coal fuel supply device according to claim (1). (4) Coal and air are supplied to the mill, and the pulverized coal pulverized in the mill is introduced together with conveying air from the mill outlet fuel pipe to the solid gas concentrator, and then combusted via the solid gas concentrator outlet fuel pipe. A method for supplying pulverized coal fuel to a mill, characterized in that during operation of the combustor, a diluted fluid from the air outlet side of the solid gas concentrator is continuously returned to the mill. (5) The mill outlet fuel pipe is branched, and the pulverized coal fuel at the mill outlet is continuously supplied to the concentrated fluid outlet side of the solid gas concentrator through the branch pipe. 4) The pulverized coal fuel supply operation method described above. (6) A diluted fluid pipe that returns diluted fluid from the gas outlet side of the solid gas concentrator to the mill is branched, and diluted fluid is installed in the combustor from the solid gas separator via the branched pipe. The pulverized coal fuel supply operation method according to claim 4, characterized in that the pulverized coal is continuously supplied to a combustor for lean fuel.