JP7621766B2 - Solid fuel pulverizer, power generation plant, and method for operating the solid fuel pulverizer - Google Patents

Description

The present disclosure relates to a solid fuel pulverizer, a power generation plant, and a method for operating the solid fuel pulverizer.

Conventionally, solid fuels (carbon-containing solid fuels) such as coal and biomass fuels are pulverized into fine powder within a specified particle size range by a pulverizer (mill) and then supplied to a combustion device. In the mill, solid fuels such as coal and biomass fuels fed onto a pulverizing table are pinched between the pulverizing table and a pulverizing roller to pulverize them, and fine fuels within a specified particle size range are selected by a classifier from the pulverized solid fuel into fine powder form. The fine fuels are transported to a boiler by a carrier gas (primary air) supplied from the outer periphery of the pulverizing table, and are burned in a combustion device. In a thermal power plant, steam is generated by heat exchange with the combustion gas generated by burning the pulverized fuel in the boiler, and the steam is used to rotate and drive a steam turbine, which then rotates and drives a generator connected to the steam turbine to generate electricity.

Among carbon-containing solid fuels, biomass fuels such as wood-based fuels have the property of being difficult to pulverize, but have the property of being highly combustible and being able to be burned suitably even if the particle size is relatively large. Therefore, when using biomass fuel as a solid fuel, it is usually supplied from a mill to a combustion device installed in a boiler in a state of particle size about 5 to 10 times larger than that of coal.
Thus, since coal and biomass fuel have different particle sizes to be supplied to the combustion device, it is preferable that the mill for pulverizing and classifying the solid fuel is designed separately for biomass fuel pulverization and coal pulverization (e.g., housing shape, rotation speed of the pulverization table, and rotation speed of the classifier, etc.). However, from the viewpoint of equipment cost, installation space, etc., it is desirable to be able to use the same mill for both solid fuels, biomass fuel and coal, and to be able to use biomass fuel using the mill that can be used for both coal and biomass fuel.

However, because biomass fuel is fibrous, it is less easily pulverized by the crushing action of a mill than coal. Therefore, when using biomass fuel, it is necessary to use biomass pellets that have been pre-treated to finely cut the fibers of the biomass (the raw material for biomass fuel), or to mix a small amount of biomass chips, which are small pieces of biomass, into the coal and cut the fibers of the biomass chips using the grinding action of the coal, thereby pulverizing the biomass. For example, the device described in Patent Document 1 is known as an apparatus for pulverizing such biomass fuel.

Patent No. 4318259

Biomass chips and biomass pellets have different crushability and moisture content. It has been considered to mix biomass pellets and biomass chips, which have such different properties, and grind them in a mill. However, no consideration has been given to the appropriate operation of a mill when solid fuels with different properties are mixed.

The present disclosure has been made in consideration of these circumstances, and aims to provide a solid fuel pulverizing device and power generation plant, as well as a method for operating a solid fuel pulverizing device, that can be operated appropriately when solid fuels with different properties are mixed and pulverized.

In order to solve the above problems, the solid fuel pulverizing apparatus, the power generation plant, and the method of operating the solid fuel pulverizing apparatus of the present disclosure employ the following measures.
A solid fuel pulverization apparatus according to one aspect of the present disclosure includes a grinding table on whose upper surface a solid fuel mixed with a first solid fuel and a second solid fuel having a grindability and/or moisture content different from the first solid fuel is supplied, a grinding roller for pulverizing the solid fuel on the grinding table, a first solid fuel supply unit for supplying the first solid fuel onto the grinding table, a second solid fuel supply unit for supplying the second solid fuel onto the grinding table, and a control unit for adjusting the mixing ratio of the first solid fuel and the second solid fuel based on an operating condition.

A method of operating a solid fuel pulverizing device according to one aspect of the present disclosure is a method of operating a solid fuel pulverizing device including a pulverizing table on whose upper surface a solid fuel containing a mixture of a first solid fuel and a second solid fuel having a different pulverizability and/or moisture content from the first solid fuel is supplied, and a pulverizing roller for pulverizing the solid fuel on the pulverizing table, and includes a first solid fuel supplying step of supplying the first solid fuel onto the pulverizing table, a second solid fuel supplying step of supplying the second solid fuel onto the pulverizing table, and an adjustment step of adjusting the mixture ratio of the first solid fuel and the second solid fuel based on the operating state.

According to the present disclosure, the solid fuel pulverizing device can be operated appropriately when mixing and pulverizing solid fuels with different properties.

1 is a configuration diagram illustrating a power plant according to an embodiment of the present disclosure. FIG. 2 is a schematic vertical sectional view showing the solid fuel pulverizing apparatus of FIG. 1. FIG. 3 is an enlarged view of a main part of FIG. 2 . FIG. 3 is a block diagram showing a control unit of the solid fuel pulverizer of FIG. 2 . 5 is a flowchart showing a process performed by a control unit in FIG. 4 . 5 is a flowchart showing a process performed by a control unit in FIG. 4 . 1 is a graph showing the relationship between the lift amount of the crushing roller and the amount of biomass chips fed. 1 is a graph showing the relationship between the amount of vibration of the mill and the amount of biomass chips fed. 1 is a graph showing the relationship between inlet temperature and the amount of biomass chips fed. 1 is a graph showing the relationship between outlet temperature and the amount of biomass chips fed. 13 is a graph showing the relationship between table differential pressure and the amount of biomass chips fed. 1 is a graph showing the relationship between mill power and the amount of biomass chips fed. 1 is a graph showing the change over time in the amount of biomass pellets or biomass chips fed into the solid fuel pulverizer and the lift amount of the pulverizing roller when the solid fuel pulverizer is started up. 11 is a graph showing the change over time in the amount of biomass pellets or biomass chips fed and the lift amount of the grinding roller when the solid fuel grinding device is stopped.

Below, an embodiment of the solid fuel pulverizing device, power plant, and method of operating the solid fuel pulverizing device according to the present disclosure will be described with reference to the drawings.

First Embodiment
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will now be described with reference to the drawings. A power plant 1 according to this embodiment includes a solid fuel pulverizer 100 and a boiler 200.
In the following explanation, "upper" refers to the vertically upper direction, and "upper" in terms such as upper part and upper surface refers to the vertically upper part. Similarly, "lower" refers to the vertically lower part, and the vertical direction is not precise and may include errors.

The solid fuel pulverization device 100 of this embodiment is a device that pulverizes solid fuel (carbon-containing solid fuel) such as coal or biomass fuel, generates pulverized fuel, and supplies it to a burner (combustion device) 220 of a boiler 200.
The power plant 1 including the solid fuel pulverizer 100 and the boiler 200 shown in FIG. 1 is equipped with one solid fuel pulverizer 100, but it may also be a system equipped with multiple solid fuel pulverizers 100 corresponding to each of the multiple burners 220 of one boiler 200.

The solid fuel pulverizer 100 of this embodiment includes a mill (pulverizer) 10, a coal feeder (first solid fuel supply unit) 20, a blower (carrier gas supply unit) 30, a state detector 40, and a controller (determination unit) 50.

The mill 10, which pulverizes solid fuel such as coal or biomass fuel to be supplied to the boiler 200 into fine fuel, which is a finely powdered solid fuel, may be of a type that pulverizes only coal, may be of a type that pulverizes only biomass fuel, or may be of a type that pulverizes biomass fuel together with coal.
Here, biomass fuels are organic resources derived from renewable living organisms, such as thinned wood, waste wood, driftwood, grass, waste, sludge, tires, and recycled fuels (pellets and chips) made from these materials, but are not limited to the ones presented here.Biomass fuels are carbon neutral, meaning they do not emit carbon dioxide, a greenhouse gas, because they capture carbon dioxide during the biomass growth process, and various uses of biomass fuels are being considered.

The mill 10 comprises a housing 11, a grinding table (rotary table) 12, a grinding roller 13, a drive unit 14, a mill motor 15 connected to the drive unit 14 and driving the grinding table 12 to rotate, a rotary classifier 16, a fuel supply unit 17, and a classifier motor 18 that drives the rotary classifier 16 to rotate.
The housing 11 is formed in a cylindrical shape extending in the vertical direction, and is a case that accommodates the grinding table 12, the grinding rollers 13, the rotary classifier 16, and the fuel supply unit 17.
A fuel supply unit 17 is attached to the center of the ceiling portion 42 of the housing 11. This fuel supply unit 17 supplies solid fuel guided from the bunker 21 into the housing 11, and is disposed in the vertical direction at the center position of the housing 11 with its lower end extending into the interior of the housing 11.

A drive unit 14 is provided near the bottom surface 41 of the housing 11, and the grinding table 12 is rotatably disposed and rotated by the driving force transmitted from a mill motor 15 connected to the drive unit 14.
The grinding table 12 is a circular member in a plan view, and is disposed so as to face the lower end of the fuel supply unit 17. The upper surface of the grinding table 12 may have an inclined shape, for example, low at the center and high toward the outside, and the outer periphery may have a shape that is curved upward. The fuel supply unit 17 supplies solid fuel (for example, coal or biomass fuel in this embodiment) from above toward the grinding table 12 below, and the grinding table 12 grinds the supplied solid fuel between the grinding roller 13.

When solid fuel is fed from the fuel supply unit 17 toward the approximate center region of the grinding table 12, the centrifugal force generated by the rotation of the grinding table 12 guides the solid fuel to the outer periphery of the grinding table 12, where it is pinched and ground between the grinding table 12 and the grinding rollers 13. The ground solid fuel is blown upward by the carrier gas (hereinafter referred to as primary air) guided from the carrier gas flow path (hereinafter referred to as primary air flow path) 100a, and is guided to the rotary classifier 16.
An outlet (not shown) is provided on the outer periphery of the grinding table 12, through which the primary air flowing in from the primary air passage 100a flows out into the space above the grinding table 12 in the housing 11. A swirling blade (not shown) is provided at the outlet, which applies a swirling force to the primary air blown out from the outlet. The primary air given a swirling force by the swirling blade becomes an airflow having a swirling velocity component, and conveys the solid fuel pulverized on the grinding table 12 to the rotary classifier 16 located at the upper part in the housing 11. Among the pulverized solid fuel, particles larger than a predetermined particle size are classified by the rotary classifier 16, or fall without reaching the rotary classifier 16, are returned to the grinding table 12, and are pulverized again between the grinding table 12 and the grinding roller 13.

The crushing roller 13 is a rotating body that crushes the solid fuel supplied onto the crushing table 12 from the fuel supply unit 17. The crushing roller 13 is pressed against the upper surface of the crushing table 12 and cooperates with the crushing table 12 to crush the solid fuel.
1 shows only one representative crushing roller 13, but multiple crushing rollers 13 are arranged at regular intervals in the circumferential direction so as to press against the upper surface of the crushing table 12. For example, three crushing rollers 13 are arranged at equal intervals in the circumferential direction on the outer periphery at angular intervals of 120°. In this case, the portions where the three crushing rollers 13 come into contact with the upper surface of the crushing table 12 (pressing portions) are equidistant from the central axis of rotation of the crushing table 12.

The crushing roller 13 can swing up and down by the journal head 45, and is supported so as to be able to move toward and away from the upper surface of the crushing table 12. When the crushing table 12 rotates, the crushing roller 13 receives a rotational force from the crushing table 12 and rotates with it, with the outer circumferential surface of the crushing roller 13 in contact with the solid fuel on the upper surface of the crushing table 12. When solid fuel is supplied from the fuel supply unit 17, the solid fuel is pressed between the crushing roller 13 and the crushing table 12 and crushed.

The support arm 47 of the journal head 45 is supported on the side of the housing 11 by a support shaft 48 whose middle part is aligned horizontally, allowing the crushing roller 13 to swing up and down around the support shaft 48. A pressing device 49 is provided on the upper end part vertically above the support arm 47. The pressing device 49 is fixed to the housing 11, and applies a load to the crushing roller 13 via the support arm 47 etc. so as to press the crushing roller 13 against the crushing table 12.

The drive unit 14 is a device that transmits a driving force to the grinding table 12 and rotates the grinding table 12 around its central axis. The drive unit 14 is connected to the mill motor 15 and transmits the driving force of the mill motor 15 to the grinding table 12.

The rotary classifier 16 is provided at the top of the housing 11 and has a hollow, generally inverted cone-shaped exterior. The rotary classifier 16 is provided with a plurality of blades 16a extending in the vertical direction at its outer periphery. The blades 16a are provided at predetermined intervals (equally spaced) around the central axis of the rotary classifier 16.
The rotary classifier 16 is a device that classifies the solid fuel pulverized by the pulverizing table 12 and the pulverizing rollers 13 (hereinafter, the pulverized solid fuel is referred to as "pulverized fuel") into fuel having a particle size larger than a predetermined particle size (for example, 70 to 100 μm for coal) (hereinafter, the pulverized fuel having a particle size larger than the predetermined particle size is referred to as "coarse pulverized fuel") and fuel having a particle size smaller than the predetermined particle size (hereinafter, the pulverized fuel having a particle size smaller than the predetermined particle size is referred to as "fine pulverized fuel"). The rotary classifier 16 that classifies by rotation is also called a rotary separator, and is given a rotational driving force by a classifier motor 18 controlled by a control unit 50, and rotates around a fuel supply unit 17 centered on a cylindrical axis (not shown) extending in the vertical direction of the housing 11.
The classifier may be a fixed classifier having a fixed hollow inverted cone-shaped casing and a plurality of fixed swirling vanes on the outer periphery of the casing instead of the blades 16a.

When the pulverized fuel reaches the rotary classifier 16, due to the relative balance between the centrifugal force generated by the rotation of the blades 16a and the centripetal force of the primary air flow, the large diameter coarse pulverized fuel is knocked down by the blades 16a and returned to the grinding table 12 where it is pulverized again, and the fine pulverized fuel is led to the outlet port (outlet portion) 19 in the ceiling portion 42 of the housing 11. The fine pulverized fuel classified by the rotary classifier 16 is discharged from the outlet port 19 together with the primary air into the fine fuel supply passage 100b and supplied to the burner 220 of the boiler 200. When the solid fuel is coal, the fine fuel supply passage 100b is also called a pulverized coal pipe.

The fuel supply unit 17 is attached with its lower end extending vertically into the interior of the housing 11 so as to penetrate the ceiling portion 42 of the housing 11, and supplies solid fuel fed from the top of the fuel supply unit 17 to the approximate center region of the grinding table 12. The fuel supply unit 17 is supplied with solid fuel (biomass pellets in this embodiment) from the charcoal feeder 20 (see arrow A3 in FIG. 2). The fuel supply unit 17 is also supplied with biomass chips from a biomass chip supply device 52 (described below) (see arrow A4 in FIG. 2).

The coal feeder 20 includes a transport unit 22 and a coal feeder motor 23. The transport unit 22 is, for example, a belt conveyor, and transports the solid fuel discharged from the lower end of a downspout 24 located directly below the bunker 21 to the top of the fuel supply unit 17 of the mill 10 by the driving force provided by the coal feeder motor 23, and inputs the solid fuel into the fuel supply unit 17.
Normally, primary air is supplied to the inside of the mill 10 to transport pulverized fuel to the burner 220, and the pressure therein is higher than that of the coal feeder 20 and the bunker 21. The downspout 24, which is a pipe extending in the vertical direction directly below the bunker 21, holds fuel in a layered state inside, and the solid fuel layers layered inside the downspout 24 ensure a sealing performance that prevents the primary air and pulverized fuel on the mill 10 side from flowing back to the bunker 21 side.
The amount of solid fuel supplied to the mill 10 is adjusted, for example, by the moving speed of the belt conveyor of the transport unit 22.

On the other hand, biomass fuel chips or pellets before crushing have a constant particle size (pellet size is, for example, about 6 to 8 mm in diameter and about 40 mm or less in length) and are lightweight compared to coal fuel (i.e., coal before crushing has a particle size of, for example, about 2 to 50 mm). Therefore, when biomass fuel is stored in downspout 24, the gaps formed between each biomass fuel in the solid fuel layer in downspout 24 are larger than in the case of coal fuel. Also, the state of the gaps formed between each biomass fuel in the solid fuel layer in downspout 24 is not necessarily constant and may fluctuate.
Therefore, compared to the case of coal fuel, relatively large gaps are formed between the biomass fuel chips and pellets in the downspout 24, and as a result, primary air and pulverized fuel from inside the mill 10 pass through the gaps formed in the solid fuel layer, causing a backflow of primary air and pulverized fuel from inside the mill 10 through the coal feeder 20 to the bunker 21, which can cause a drop in the pressure inside the mill 10, and this is more likely to occur than in the case of coal fuel.
In addition, if the primary air and pulverized fuel flow back toward the bunker 21 and the pressure inside the mill 10 drops, various problems may occur in the stable operation of the solid fuel pulverizing apparatus 100 and the boiler 200, such as a deterioration in the transportability of the pulverized fuel inside the mill 10, dust generation inside the coal feeder 20 and at the top of the bunker 21, ignition of the solid fuel inside the coal feeder 21, the bunker 21, and the downspout 24, and a reduction in the amount of pulverized fuel transported to the burner 220.
For this reason, in this embodiment, a rotary valve 51 is provided midway in the fuel supply section 17 leading from the coal feeder 20 to the inside of the mill 10 to suppress the occurrence of a backflow of the primary air and pulverized fuel leading from the inside of the mill 10 through the coal feeder 20 to the bunker 21. Note that in this embodiment, biomass pellets are stored in the bunker 21. Also, the rotary valve 51 does not have to be provided.

The blower 30 is a device that dries the pulverized fuel and blows primary air into the housing 11 for transporting the fuel to the rotary classifier 16. The primary air (see arrow A1 in FIG. 2) supplied from the blower 30 to the housing 11 transports the pulverized fuel (see arrow A2 in FIG. 2) on the pulverizing table 12 to the furnace 210 via the outlet port 19.
In order to appropriately adjust the flow rate and temperature of the primary air blown into the inside of the housing 11, in this embodiment, the blower section 30 is equipped with a primary air fan (PAF) 31, a hot gas flow path 30a, a cold gas flow path 30b, a hot gas damper 30c, and a cold gas damper 30d.

In this embodiment, the hot gas flow path 30a supplies a portion of the air (outside air) sent out from the primary air ventilator 31 as hot gas that has been heated by passing through a heat exchanger 34, such as an air preheater. A hot gas damper 30c is provided downstream of the hot gas flow path 30a. The opening degree of the hot gas damper 30c is controlled by the control unit 50. The flow rate of the hot gas supplied from the hot gas flow path 30a is determined by the opening degree of the hot gas damper 30c.

The cold gas flow path 30b supplies a portion of the air sent out from the primary air ventilator 31 as cold gas at room temperature. A cold gas damper 30d is provided downstream of the cold gas flow path 30b. The opening degree of the cold gas damper 30d is controlled by the control unit 50. The flow rate of the cold gas supplied from the cold gas flow path 30b is determined by the opening degree of the cold gas damper 30d.

In this embodiment, the flow rate of the primary air is the sum of the flow rate of the hot gas supplied from the hot gas flow path 30a and the flow rate of the cold gas supplied from the cold gas flow path 30b, and the temperature of the primary air is determined by the mixing ratio of the hot gas supplied from the hot gas flow path 30a and the cold gas supplied from the cold gas flow path 30b, and is controlled by the control unit 50.
In addition, the oxygen concentration of the primary air blown from the primary air passage 100a to the inside of the housing 11 may be adjusted by introducing a portion of the combustion gas discharged from the boiler 200 via a gas recirculation fan (not shown) into the hot gas supplied from the hot gas passage 30a and mixing it.

In this embodiment, the state detection unit 40 of the mill 10 transmits measured or detected data to the control unit 50. The state detection unit 40 of this embodiment is, for example, a differential pressure measurement means, and measures the differential pressure between the pressure at the portion where the primary air flows into the inside of the housing 11 from the primary air flow passage 100a and the pressure at the outlet port 19 where the primary air and the pulverized fuel are discharged from the inside of the housing 11 to the pulverized fuel supply flow passage 100b as the differential pressure of the mill 10. An increase or decrease in this differential pressure of the mill 10 corresponds to an increase or decrease in the amount of pulverized fuel circulating between the vicinity of the rotary classifier 16 inside the housing 11 and the vicinity of the grinding table 12 due to the classification effect of the rotary classifier 16. In other words, by adjusting the rotation speed of the rotary classifier 16 in accordance with the pressure difference of the mill 10, the amount of pulverized fuel discharged from the outlet port 19 can be adjusted in relation to the amount of solid fuel supplied to the mill 10.Therefore, within the range in which the particle size of the pulverized fuel does not affect the combustibility of the burner 220, an amount of pulverized fuel corresponding to the amount of solid fuel supplied to the mill 10 can be stably supplied to the burner 220 provided in the boiler 200.
The state detection unit 40 in this embodiment is, for example, a temperature measuring means, which detects the temperature of the primary air supplied to the inside of the housing 11 (the temperature of the primary air at the mill inlet) and the temperature of the primary air from the space above the grinding table 12 inside the housing 11 to the outlet port 19, and controls the blower unit 30 so that the temperature does not exceed the upper limit temperature. The upper limit temperature is determined taking into consideration the possibility of ignition of the solid fuel, etc. The primary air is cooled inside the housing 11 by transporting the pulverized fuel while drying it, and the temperature of the primary air at the outlet port 19 is, for example, about 60 to 90 degrees.

The control unit 50 is a device that controls each part of the solid fuel pulverization device 100 .
The control unit 50 may, for example, transmit a drive command to the mill motor 15 to control the rotation speed of the grinding table 12 .
The control unit 50, for example, transmits a drive command to the classifier motor 18 to control the rotational speed of the rotary classifier 16 to adjust the classification performance, and optimizes the differential pressure of the mill 10, i.e., the circulation amount of pulverized fuel inside the mill 10, within a predetermined range, thereby enabling a stable supply of pulverized fuel to the burner 220.
In addition, the control unit 50 can adjust the amount of solid fuel supplied (coal supply amount) that the conveying unit 22 conveys and supplies to the fuel supply unit 17 by, for example, transmitting a drive instruction to the coal supply motor 23 of the coal supply unit 20.
Furthermore, the control unit 50 can adjust the flow rate and temperature of the primary air by controlling the opening of the hot gas damper 30c and the cold gas damper 30d by transmitting an opening instruction to the blower unit 30. Specifically, the control unit 50 controls the opening of the hot gas damper 30c and the cold gas damper 30d so that the flow rate of the primary air supplied to the inside of the housing 11 and the temperature of the primary air at the outlet port 19 become predetermined values set in accordance with the amount of coal feed for each type of solid fuel.

The control unit 50 is composed of, for example, a CPU (Central Processing Unit), a RAM (Random Access Memory), a ROM (Read Only Memory), and a computer-readable storage medium. A series of processes for realizing various functions is stored in a storage medium or the like in the form of a program, and the CPU reads this program into the RAM or the like and executes information processing and arithmetic processing to realize various functions. The program may be pre-installed in a ROM or other storage medium, provided in a state stored in a computer-readable storage medium, or distributed via wired or wireless communication means. Examples of computer-readable storage media include magnetic disks, magneto-optical disks, CD-ROMs, DVD-ROMs, and semiconductor memories. The HDD 140 may also be replaced with a solid-state disk (SSD) or the like.

Next, we will explain the boiler 200, which generates steam by burning the pulverized fuel supplied from the solid fuel pulverizer 100. The boiler 200 is equipped with a furnace 210 and a burner 220.

The burner 220 is a device that burns pulverized fuel to form a flame using primary air containing pulverized fuel supplied from the pulverized fuel supply passage 100b and secondary air supplied by heating air (outside air) sent out from a forced draft fan (FDF: Forced Draft Fan) 32 in a heat exchanger 34. The pulverized fuel is burned in the furnace 210, and the high-temperature combustion gas is exhausted to the outside of the boiler 200 after passing through heat exchangers (not shown) such as an evaporator, a superheater, and a coal economizer.

The combustion gas discharged from the boiler 200 undergoes a predetermined treatment in an environmental device (such as a denitration device or an electric dust collector, not shown), and then undergoes heat exchange between the air discharged from the primary air fan 31 and the air discharged from the forced draft fan 32 in a heat exchanger 34, such as an air preheater, and is then guided to a chimney (not shown) via an induced draft fan (IDF) 33 and released into the outside air. The air discharged from the primary air fan 31, heated by the combustion gas in the heat exchanger 34, is supplied to the above-mentioned hot gas flow path 30a.
The water supplied to each heat exchanger of boiler 200 is heated in a coal economizer (not shown), and then further heated by an evaporator (not shown) and a superheater (not shown) to generate high-temperature, high-pressure steam. This is then sent to the steam turbine (not shown), which is the power generation section, to rotate the steam turbine, which in turn rotates a generator (not shown) connected to the steam turbine to generate electricity, thereby constituting power generation plant 1.

In this embodiment, a mixture of biomass pellets (first solid fuel) and biomass chips (second solid fuel) is pulverized in a mill 10. The biomass pellets and biomass chips are described below.

Biomass pellets are produced by shaping and granulating wood powder such as sawdust using a pelletizer. Specifically, biomass pellets are produced by compressing and molding biomass particles that have been crushed to about 0.6 mm to 1 mm, and then compacting them into a size of about 10 mm x 40 mm. As such, biomass pellets are more expensive than biomass chips because they require processing such as compression molding.
Furthermore, biomass pellets have a lower moisture content than biomass chips. The moisture content of biomass pellets is, for example, 0 wt % or more and 10 wt % or less. If the moisture content of biomass pellets becomes high, they may ferment or expand and lose their shape.
Biomass pellets have short fibers and are more easily crushed than biomass chips. In other words, biomass pellets are easy to crush. Therefore, when crushing biomass pellets, the lift amount of the crushing roller 13 tends to decrease. Accordingly, the amount of pulverized fuel circulating in the mill 10 decreases, and the differential pressure of the mill 10 also tends to decrease.

Biomass chips are, for example, cut wood such as green wood or waste wood. Specifically, they are cut so that the long side is about 50 mm or less. As such, biomass chips do not require complicated processing, so they are less expensive than biomass pellets.
Furthermore, biomass chips have a higher moisture content than biomass pellets. The moisture content of biomass chips is, for example, 8 wt % or more and 75 wt % or less. Preferably, the moisture content of biomass chips is 12 wt % or less.
In addition, biomass chips have low pulverizability because the fibers remain long. In other words, biomass chips are difficult to pulverize. Therefore, when pulverizing biomass chips, the lift amount of the pulverizing roller 13 tends to increase. Accordingly, the amount of pulverized fuel circulating in the mill 10 also increases, so the differential pressure of the mill 10 also tends to increase.

Next, the biomass chip supplying device 52 and other components provided in the mill 10 will be described in detail.
As shown in FIG. 2 , a biomass chip supplying device (second solid fuel supplying section) 52 is provided downstream of the coal supplying machine (first solid fuel supplying section) 20 .
The biomass chip supplying device 52 is disposed downstream of the bunker 21 and upstream of the rotary valve 51. In detail, the biomass chip supplying device 52 is provided vertically above the fuel supplying unit 17. The biomass chip supplying device 52 drops the biomass chips to directly supply the biomass chips to the fuel supplying unit 17. The biomass chip supplying device 52 is configured to be switchable between a state in which biomass chips are supplied to the fuel supplying unit 17 and a state in which they are not supplied. The biomass chip supplying device 52 is also provided with an adjustment function for adjusting the amount of biomass fuel supplied to the fuel supplying unit 17.

As described above, in this embodiment, biomass pellets are stored in the bunker 21. Therefore, only biomass pellets are transported by the coal feeder 20. The biomass pellets transported by the transport section 22 of the coal feeder 20 drop from the downstream end of the transport section 22 as shown by arrow A3, and are supplied onto the crushing table 12 via the rotary valve 51 provided in the fuel supply section 17.
In addition, the biomass chips dropped from the biomass chip supplying device 52 are supplied onto the grinding table 12 via the rotary valve 51 provided in the fuel supplying section 17, as shown by the arrow A4.
That is, the biomass pellets and biomass chips are mixed in the rotary valve 51. As a result, a layer of solid fuel containing a mixture of biomass pellets (see symbol P) and biomass chips (see symbol C) is formed on the grinding table 12 as shown in Figures 2 and 3. The grinding roller 13 presses the layer of solid fuel formed on the grinding table 12 from above, thereby grinding the solid fuel containing the mixture of biomass pellets and biomass chips. As described above, the ground solid fuel is guided to the outlet port 19 by the primary air (see arrows A1 and A2 in Figure 2).
In addition, if the rotary valve 51 is not provided, the biomass pellets and biomass chips are mixed on the grinding table 12.

The mixing ratio of biomass pellets and biomass chips is appropriately set depending on the operating state of the solid fuel pulverizer 100. For example, when the solid fuel pulverizer 100 is operating normally (pulverizing solid fuel and transporting the pulverized solid fuel to the furnace 210), a small amount of biomass chips is mixed with the biomass pellets. Specifically, for example, the biomass pellets and biomass chips are mixed so that the calorific value of the biomass chips is 2% to 3% or less of the calorific value of the biomass pellets. Note that the mixing ratio of biomass pellets and biomass chips may be different when the solid fuel pulverizer 100 is started or stopped. The start-up and stop-up of the solid fuel pulverizer 100 will be described later.

As shown in FIG. 4, the mill 10 of this embodiment is equipped with a lift amount detection unit 61 that detects the lift amount of the grinding roller 13, a vibration detection unit 62 that detects the vibration of the mill 10, an outlet temperature detection unit 63 that detects the temperature of the pulverized fuel discharged from the mill 10, an inlet temperature detection unit 64 that detects the temperature of the primary air supplied into the mill 10, a power detection unit 65 that detects the power of the mill 10, and a table differential pressure detection unit 66 that detects the table differential pressure of the mill 10.

The lift amount detection unit 61 continuously or intermittently detects the lift amount of the crushing roller 13. The lift amount detection unit 61 transmits the detected lift amount to the control unit 50. For example, the lift amount detection unit 61 detects the lift amount of the crushing roller 13 by detecting the rotation angle of the support shaft 48 from a no-load state (when no solid fuel exists on the crushing table 12) as a reference.
The lift amount of the grinding roller 13 is the thickness t of the powder layer to be ground (the layer of solid fuel on the grinding table 12) minus the distance (gap amount, which may be zero) between the outer circumferential surface of the grinding roller 13 and the surface (upper surface) of the grinding table 12 in an unloaded state (when no solid fuel exists on the grinding table 12). In other words, it represents the amount by which the grinding roller 13 is lifted by the powder layer, and is used as an index representing the grinding load of the mill 10.

The vibration detection unit 62 detects the amount of vibration of the mill 10 continuously or intermittently. The vibration detection unit 62 transmits the detected amount of vibration to the control unit 50. The vibration detection unit 62 is provided, for example, in the housing 11, and detects the vertical amplitude of the housing 11.

The outlet temperature detection unit 63 is provided, for example, near the outlet port 19 of the pulverized fuel supply passage 100b. The outlet temperature detection unit 63 detects the temperature of the primary air at the outlet port 19 and/or the pulverized fuel transported to the primary air (hereinafter referred to as the "outlet temperature"). The outlet temperature detection unit 63 transmits the detected temperature to the control unit 50.

The inlet temperature detection unit 64 is provided, for example, near the housing 11 in the primary air flow path 100a. The inlet temperature detection unit 64 detects the temperature of the primary air supplied to the inside of the housing 11 (hereinafter referred to as the "inlet temperature"). The inlet temperature detection unit 64 transmits the detected temperature to the control unit 50.

The power detection unit 65 detects the power of the mill 10, for example, by detecting the power of the mill motor 15 that rotates the grinding table 12. The power detection unit 65 transmits the detected power to the control unit 50.

The table differential pressure detection unit 66 detects the difference between the pressure above the grinding table 12 and the pressure below the grinding table 12. The table differential pressure detection unit 66 transmits the detected differential pressure to the control unit 50. The table differential pressure is correlated with the amount of grinding fuel circulating within the mill 10, and is used as an index representing the grinding load of the mill 10.

The control unit 50 is equipped with an adjustment unit 53 that adjusts the mixing ratio of biomass pellets and biomass chips based on the operating state of the solid fuel pulverizing device 100. In detail, the adjustment unit 53 adjusts the mixing ratio based on the lift amount of the pulverizing roller 13, the vibration of the mill 10, the outlet temperature, the inlet temperature, the power of the mill 10, and the table differential pressure. The adjustment unit 53 adjusts the mixing ratio of biomass pellets and biomass chips by controlling the biomass chip supply device 52.

Specifically, the adjustment unit 53 mixes a predetermined amount of biomass chips into the biomass pellets to achieve a predetermined mixing ratio during normal operation of the solid fuel pulverization device 100. The predetermined mixing ratio is, for example, as described above, a mixing ratio in which the calorific value of the biomass chips is about 2% to 3% of the calorific value of the biomass pellets. The adjustment unit 53 stops the supply of biomass chips when a change occurs in the operating state of the solid fuel pulverization device 100 while a predetermined amount of biomass chips has been supplied.

Next, the process performed by the control unit 50 will be described in detail with reference to the flowcharts in FIG. 5 and FIG. 6. Note that the process described below is an example, and the process performed by the control unit 50 is not limited to this.

First, in step S1, the control unit 50 determines whether the power of the mill 10 detected by the power detection unit 65 is excessive. Whether or not it is excessive may be determined based on whether or not it exceeds a predetermined threshold value. If it is determined that the power of the mill 10 is excessive, the process proceeds to step S2 and records an abnormality signal. After recording an abnormality signal, the process proceeds to step S11. If it is determined that the power of the mill 10 is not excessive, the process proceeds to step S3.

In step S3, the control unit 50 determines whether the table differential pressure detected by the table differential pressure detection unit 66 is excessive. If it is determined that the table differential pressure is excessive, the process proceeds to step S4 and records an abnormality signal. If an abnormality signal is recorded, the process proceeds to step S11. If it is determined that the table differential pressure is not excessive, the process proceeds to step S5.
In step S5, the control unit 50 judges whether the lift amount of the crushing roller 13 detected by the lift amount detection unit 61 is excessive or not. If it is judged that the lift amount is excessive, the process proceeds to step S6 and records an abnormality signal. If an abnormality signal is recorded, the process proceeds to step S11. If it is judged that the lift amount is not excessive, the process proceeds to step S7.

In step S7, the control unit 50 determines whether the inlet temperature detected by the inlet temperature detection unit 64 is excessively high. If it is determined that the inlet temperature is excessively high, the process proceeds to step S8 and records an abnormality signal. After recording the abnormality signal, the process proceeds to step S11. If it is determined that the inlet temperature is not excessively high, the process proceeds to step S9.
In step S9, the control unit 50 judges whether the outlet temperature detected by the outlet temperature detection unit 63 is excessively high. If it is judged that the outlet temperature is excessively high, the process proceeds to step S10 and records an abnormality signal. After recording the abnormality signal, the process proceeds to step S11. If it is judged that the outlet temperature is not excessively high, the process returns to step S1.

In step S11, the control unit 50 stops the input of biomass chips. That is, the control unit 50 controls the biomass chip supplying device 52 so that the biomass chip supplying device 52 does not supply biomass chips. After completing step S11, the process proceeds to step S12.

In step S12, the control unit 50 determines whether the abnormal signal has recovered. If it is determined that the abnormal signal has recovered, the abnormal signal is reset and normal operation is resumed. In other words, the process returns to step S1. If it is determined that the abnormal signal has not recovered, the process proceeds to step S13. In step S13, the rotation speed of the rotary classifier 16 is reduced. After step S13 is completed, the process proceeds to step S14.

In step S14, the control unit 50 judges whether the abnormal signal has been recovered. If it is judged that the abnormal signal has been recovered, the abnormal signal is reset and normal operation is resumed. That is, the process returns to step S1. If it is judged that the abnormal signal has not been recovered, the process proceeds to step S15. In step S15, the hydraulic pressure of the pressing device 49 is reduced. That is, the pressing force with which the crushing roller 13 presses the solid fuel is reduced. After step S15 is completed, the process proceeds to step S16.

In step S16, the control unit 50 judges whether the abnormal signal has recovered. If it is judged that the abnormal signal has recovered, it resets the abnormal signal and returns to normal operation. In other words, it returns to step S1. If it is judged that the abnormal signal has not recovered, it proceeds to step S17. In step S17, the rotation speed of the grinding table 12 is reduced. After completing step S17, it proceeds to step S18.

In step S18, the control unit 50 determines whether the abnormal signal has recovered. If it is determined that the abnormal signal has recovered, it resets the abnormal signal and returns to normal operation. In other words, it returns to step S1. If it is determined that the abnormal signal has not recovered, it proceeds to step S19. In step S19, it increases the flow rate of primary air. After completing step S19, it proceeds to step S20.

In step S20, the control unit 50 determines whether the abnormal signal has recovered. If it is determined that the abnormal signal has recovered, it resets the abnormal signal and returns to normal operation. In other words, it returns to step S1. If it is determined that the abnormal signal has not recovered, it proceeds to step S21. In step S21, it reduces the supply amount of biomass pellets. After completing step S21, it proceeds to step S22.

In step S22, the control unit 50 judges whether the abnormal signal has recovered. If it is judged that the abnormal signal has recovered, the abnormal signal is reset and normal operation is resumed. In other words, the process returns to step S1. If it is judged that the abnormal signal has not recovered, the process proceeds to step S23. In step S23, the solid fuel pulverization device 100 is stopped. When the solid fuel pulverization device 100 is stopped, this process ends.

The determinations in steps S1, S3, S5, S7, and S9 (hereinafter referred to as "abnormal state determinations") may be performed simultaneously.
Moreover, the countermeasure operations in steps S11, S13, S15, S17, S19 and S21 may be performed simultaneously.
In addition, the judgments in steps S12, S14, S16, S18, S20 and S22 (hereinafter referred to as "recovery judgments") may be made during or after a specified time by setting a timer for the time required for recovery.
Furthermore, each countermeasure action and recovery judgment may be provided for each abnormal state judgment.

The control unit 50 may adjust the mixing ratio of biomass pellets and biomass chips based on one or more of the lift amount of the grinding roller 13, the vibration of the mill 10, the outlet temperature, the inlet temperature, the power of the mill 10, and the table differential pressure. Specifically, for example, the mixing ratio of biomass pellets and biomass chips may be adjusted by adjusting the input amount of biomass chips based on each parameter acquired by the control unit 50. The control based on each parameter is described below.

For example, the amount of biomass chips to be fed may be adjusted based on the lift amount of the grinding roller 13. When the lift amount is large, the amount of biomass chips to be fed is reduced, and when the lift amount is small, the amount of biomass chips to be fed is increased. Specifically, for example, the amount of biomass chips to be fed may be adjusted as shown in FIG. 7. In FIG. 7, the horizontal axis indicates the lift amount of the grinding roller 13, and the vertical axis indicates the amount of biomass chips to be fed per unit time. In the example of FIG. 7, when the lift amount of the grinding roller 13 detected by the lift amount detection unit 61 is equal to or less than a predetermined value 1 (e.g., 30 mm), a predetermined amount of biomass chips is fed. When the lift amount is greater than the predetermined value 1 (e.g., 30 mm), the amount of biomass chips to be fed is adjusted so that the amount of biomass chips to be fed decreases as the lift amount increases. In other words, the amount of biomass chips to be fed is adjusted so that the mixing ratio of biomass chips to biomass pellets decreases as the lift amount increases. When the lift amount is equal to or greater than a predetermined value 2 (e.g., 50 mm), the amount of biomass chips to be fed is set to zero. That is, the feeding of biomass chips is stopped. In addition, the predetermined value 2 is usually set to a value larger than the predetermined value 1.
As the layer of solid fuel on the grinding table 12 becomes thinner, the lift amount of the grinding roller 13 becomes smaller. On the other hand, as the layer of solid fuel on the grinding table 12 becomes thicker, the lift amount of the grinding roller 13 becomes larger. Therefore, by adjusting the input amount of biomass chips based on the lift amount of the grinding roller 13, the thickness of the layer of solid fuel on the grinding table 12 can be set within a predetermined range.

Also, for example, the amount of biomass chips fed may be adjusted based on the vibration amount of the mill 10. When the vibration amount is large, the amount of biomass chips fed is increased, and when the vibration amount is small, the amount of biomass chips fed is decreased. Specifically, for example, adjustment may be performed as shown in FIG. 8. In FIG. 8, the horizontal axis indicates the vibration amount of the mill 10, and the vertical axis indicates the amount of biomass chips fed per unit time. In the example of FIG. 8, a predetermined amount of biomass chips are fed until the vibration amount detected by the vibration detection unit 62 reaches a predetermined value (P1). When the vibration amount is larger than the predetermined value, the amount of biomass chips fed is adjusted so that the greater the vibration amount, the greater the amount of biomass chips fed.
As the layer of solid fuel on the grinding table 12 becomes thinner, the vibration absorbing effect of the solid fuel layer decreases, and the vibration amount of the mill 10 increases. On the other hand, as the layer of solid fuel on the grinding table 12 becomes thicker, the vibration absorbing effect of the solid fuel layer increases, and the vibration amount of the mill 10 decreases. Therefore, by adjusting the input amount of biomass chips based on the vibration amount of the mill 10, the vibration amount of the mill 10 can be kept within a predetermined range.
Since noise is generated due to the vibration of the mill 10, the volume of the noise emitted from the mill 10 may be detected, and the amount of biomass chips added may be adjusted based on the volume of the noise instead of the amount of vibration of the mill 10. In this case as well, a predetermined amount of biomass chips is added until the volume of the noise reaches a predetermined value. If the volume of the noise is greater than the predetermined value, the amount of biomass chips added is adjusted so that the larger the noise, the greater the amount of biomass chips added.

Also, for example, the amount of biomass chips to be fed may be adjusted based on the inlet temperature of the mill 10. When the inlet temperature is high, the amount of biomass chips to be fed is reduced, and when the inlet temperature is low, the amount of biomass chips to be fed is increased. Specifically, for example, the amount of biomass chips to be fed may be adjusted as shown in FIG. 9. In FIG. 9, the horizontal axis indicates the inlet temperature of the mill 10, and the vertical axis indicates the amount of biomass chips to be fed per unit time. In the example of FIG. 9, a predetermined amount of biomass chips is fed until the inlet temperature detected by the inlet temperature detection unit 64 reaches a predetermined value (P2). When the inlet temperature is higher than a predetermined value, the amount of biomass chips to be fed is adjusted so that the amount of biomass chips to be fed decreases as the inlet temperature increases. Also, when the inlet temperature reaches a predetermined temperature, the amount of biomass chips to be fed is set to zero. That is, the feeding of biomass chips is stopped. When the moisture content of the fuel fed to the mill 10 increases, the required heat quantity used for drying in the mill 10 increases, so that the mill inlet temperature rises, the opening degree of the hot gas damper (30c) increases, and the opening degree of the cold gas damper (30d) decreases. Conversely, when the moisture content of the fuel fed to the mill 10 decreases, the required heat quantity used for drying in the mill 10 decreases, so that the mill inlet temperature drops, the opening degree of the hot gas damper (30c) decreases, and the opening degree of the cold gas damper (30d) increases.
Therefore, by adjusting the amount of biomass chips fed based on the inlet temperature of the mill 10, the inlet temperature of the mill 10 can be kept within a predetermined range, and the opening degree of the hot gas damper (30c) and cold gas damper (30d) can be kept within a control range.
In addition, by setting the amount of biomass chips fed in to zero when the inlet temperature of the mill 10 exceeds a predetermined temperature, the inlet temperature of the mill can be prevented from rising above an upper limit, thereby improving safety against mill fires.

Also, for example, the amount of biomass chips to be fed may be adjusted based on the outlet temperature. When the outlet temperature is high, the amount of biomass chips to be fed is increased, and when the outlet temperature is low, the amount of biomass chips to be fed is reduced. Specifically, for example, the amount of biomass chips to be fed may be adjusted as shown in FIG. 10. In FIG. 10, the horizontal axis indicates the outlet temperature of the mill 10, and the vertical axis indicates the amount of biomass chips to be fed per unit time. In the example of FIG. 10, the amount of biomass chips to be fed is adjusted so that the amount of biomass chips to be fed increases as the outlet temperature increases, until the outlet temperature detected by the outlet temperature detection unit 63 reaches a predetermined temperature. However, when the outlet temperature is higher than the predetermined temperature, the amount of biomass chips to be fed is not increased any more, and the amount of biomass chips to be fed is maintained.
Usually, the mill outlet temperature is fed back to the mill inlet temperature, and is controlled so that the mill outlet temperature is constant. When the moisture content of the fuel fed into the mill 10 increases, the heat requirement used for drying in the mill 10 increases, so feedback is applied to increase the mill inlet temperature, but the mill inlet temperature response is slow, so the mill outlet temperature temporarily drops. Therefore, when the mill 10 outlet temperature drops, the amount of biomass chips fed into the fuel is reduced to reduce the moisture content of the fuel fed into the mill 10, suppress the drop in the mill 10 outlet temperature, and stabilize the mill outlet temperature.
Conversely, when the moisture content of the fuel fed to the mill 10 decreases, the required heat amount used for drying in the mill 10 decreases, and the mill outlet temperature increases. Therefore, when the outlet temperature of the mill 10 increases, the amount of biomass chips fed can be increased to increase the moisture content of the fuel fed to the mill 10, suppress the increase in the outlet temperature of the mill 10, and stabilize the mill outlet temperature.
On the other hand, when the outlet temperature of the mill 10 is higher than a predetermined temperature, by maintaining the amount of biomass chips fed into the mill 10, the moisture contained in the fuel fed into the mill 10 is stabilized and the required amount of heat used for drying within the mill 10 is stabilized, thereby suppressing disturbances to the drop in the mill outlet temperature due to feedback to the mill inlet temperature, ensuring a reliable drop in the mill outlet temperature, and preventing mill fires, etc.

Also, for example, the amount of biomass chips fed may be adjusted based on the table differential pressure. When the table differential pressure is high, the amount of biomass chips fed is reduced, and when the table differential pressure is low, the amount of biomass chips fed is increased. Specifically, for example, adjustment may be made as shown in FIG. 11. In FIG. 11, the horizontal axis indicates the table differential pressure, and the vertical axis indicates the amount of biomass chips fed per unit time. In the example of FIG. 11, the amount of biomass chips fed is adjusted so that the greater the table differential pressure, the smaller the amount of biomass chips fed.
As the layer of solid fuel on the grinding table 12 becomes thinner, the amount of pulverized fuel circulating within the mill 10 decreases, and the table differential pressure also tends to become smaller. On the other hand, as the layer of solid fuel on the grinding table 12 becomes thicker, the amount of pulverized fuel circulating within the mill 10 increases, and the table differential pressure also tends to become larger. Therefore, by adjusting the amount of biomass chips fed based on the table differential pressure, the table differential pressure can be kept within a predetermined range.

Also, for example, the amount of biomass chips fed may be adjusted based on the power of the mill 10. When the power is large, the amount of biomass chips fed is reduced, and when the power is small, the amount of biomass chips fed is increased. Specifically, for example, adjustment may be made as shown in FIG. 12. In FIG. 12, the horizontal axis indicates the power of the mill 10, and the vertical axis indicates the amount of biomass chips fed per unit time. In the example of FIG. 12, the amount of biomass chips fed is adjusted so that the greater the power, the smaller the amount of biomass chips fed.
When the layer of solid fuel on the grinding table 12 becomes thinner, the amount of solid fuel pulverized decreases, and therefore the power of the mill 10 becomes smaller. On the other hand, when the layer of solid fuel on the grinding table 12 becomes thicker, the amount of solid fuel pulverized increases, and therefore the power of the mill 10 becomes larger. Therefore, by adjusting the amount of biomass chips fed based on the power of the mill 10, the power of the mill 10 can be kept within a predetermined range.

In addition, the control unit 50 may perform control different from that during normal operation when starting and stopping the solid fuel pulverizer 100.

The control at the start-up of the solid fuel pulverizer 100 will be explained using FIG. 13. In FIG. 13, the vertical axis indicates the input (supply) amount of biomass pellets or biomass chips and the lift amount of the pulverizer roller 13, and the horizontal axis indicates time. That is, FIG. 13 shows the change over time in the input (supply) amount of biomass pellets or biomass chips and the lift amount of the pulverizer roller 13.

As shown in FIG. 13, when the solid fuel pulverizer 100 is stopped (t0), the input (supply) amount of biomass pellets or biomass chips and the lift amount of the pulverizing roller 13 are both zero. In other words, there is no solid fuel on the pulverizing table 12.

When the solid fuel pulverizer 100 is started, first, biomass chips are loaded onto the pulverizing table 12. The amount of biomass chips loaded is increased, and the increase in the amount of biomass chips loaded is stopped at timing t1. In other words, the amount of biomass chips loaded is set to a constant amount. The amount of biomass chips loaded at this time is set to be greater than the amount of biomass chips loaded during normal operation. Also, at this time, biomass pellets are not loaded onto the pulverizing table 12.
Next, at time t2, the introduction of biomass pellets is started. In response to this, the introduction amount of biomass chips is reduced. Thereafter, the control unit 50 transitions to control for normal operation.
The timing t2 is the timing at which a layer of solid fuel having a predetermined thickness t is formed on the grinding table 12 by the biomass chips.

By controlling in this manner, a large amount of biomass chips with low grindability are supplied onto the grinding table 12 at the time of startup, making it easier for a layer of solid fuel to form on the grinding table 12. Therefore, a layer of solid fuel can be quickly formed on the grinding table 12 after the solid fuel pulverizing device 100 is started, making it possible to quickly suppress vibrations that tend to occur immediately after the solid fuel pulverizing device 100 is started. In addition, damage and wear to the grinding roller 13 and grinding table 12 caused by foreign matter that tends to occur immediately after the solid fuel pulverizing device 100 is started can be quickly suppressed.

The control when stopping the solid fuel pulverizer 100 will be explained using FIG. 14. In FIG. 14, the vertical axis indicates the input amount (supply amount) of biomass pellets or biomass chips and the lift amount of the pulverizer roller 13, and the horizontal axis indicates time. That is, FIG. 14 shows the change over time in the input amount (supply amount) of biomass pellets or biomass chips and the lift amount of the pulverizer roller 13.

As shown in Fig. 14, when the solid fuel pulverizing device 100 is stopped, a constant amount of biomass chips continues to be fed even during the period (between t4 and t5) during which the amount of biomass pellets fed is reduced. In addition, even after the amount of biomass pellets fed is reduced to zero (after t6), biomass chips are fed intermittently. By controlling in this manner, the layer of solid fuel on the pulverizing table 12 (lift amount of the pulverizing roller 13) is prevented from becoming completely zero. Therefore, it is possible to suppress, reduce, or delay the generation of vibrations of the mill 10 and noises caused by the vibrations when the device is stopped.
Furthermore, when the mill is stopped, a small amount of solid fuel may remain on the grinding table 12, but when the above-mentioned stop control is implemented, the small amount of solid fuel remaining on the grinding table 12 is generally replaced with biomass chips. Biomass chips have a smaller surface area per volume than biomass pellets. Therefore, they are less likely to naturally oxidize and heat up than biomass pellets. Biomass chips also have a higher moisture content than biomass pellets. Therefore, even if a small amount of biomass chips remains in the mill 10, they are less likely to cause a fire. This improves safety when the mill 10 is stopped.

According to this embodiment, the following advantageous effects are obtained.
In this embodiment, a control unit 50 is provided that adjusts the mixing ratio of the biomass pellets and the biomass chips based on the operating state. Therefore, when biomass pellets and biomass chips having different properties are mixed and pulverized, the mixing ratio of the biomass pellets and the biomass chips can be set according to the operating state of the solid fuel pulverization device 100.

The lift amount of the grinding roller 13 varies depending on the grindability of the solid fuel to be ground. Specifically, the lift amount of the grinding roller 13 tends to be small when grinding a solid fuel with high grindability (solid fuel that is easy to grind), and tends to be large when grinding a solid fuel with low grindability (solid fuel that is difficult to grind). This is because a solid fuel with high grindability is ground to a predetermined particle size or less in a short time and is easily discharged from the solid fuel grinding device 100, so the amount of solid fuel remaining in the solid fuel grinding device 100 is small, and the layer of solid fuel formed between the grinding table 12 and the grinding roller 13 is thin. In addition, a solid fuel with low grindability is difficult to discharge from the solid fuel grinding device 100, unlike a solid fuel with high grindability, so the layer of solid fuel formed between the grinding table 12 and the grinding roller 13 is thick.

In this embodiment, the control unit 50 adjusts the mixing ratio of biomass pellets and biomass chips, which have different crushability, based on the lift amount of the grinding roller 13 detected by the lift amount detection unit 61. Therefore, by adjusting the mixing ratio of the biomass pellets and biomass chips so that the lift amount of the grinding roller 13 is within a predetermined range, the thickness of the layer of solid fuel on the grinding table 12 can be made to be within a predetermined range.
As the layer of solid fuel becomes thinner, the vibration absorbing effect of the solid fuel layer decreases, and the amount of vibration of the solid fuel pulverization device 100 increases. Therefore, by setting the thickness of the layer of solid fuel on the pulverization table 12 within a predetermined range, the vibration of the solid fuel pulverization device 100 can be suppressed. This makes it possible to suppress damage to the solid fuel pulverization device 100 and extend the life of the solid fuel pulverization device 100. In addition, since the vibration of the solid fuel pulverization device 100 can be suppressed, the noise generated by the solid fuel pulverization device 100 can be reduced.
Furthermore, by setting the thickness of the layer of solid fuel on the grinding table 12 within a predetermined range, even if a foreign object e (see FIG. 3) such as metal is mixed into the solid fuel, the foreign object e is likely to be covered by the layer of solid fuel. This makes it difficult for the foreign object e to come into contact with the grinding table 12 and/or the grinding roller 13. This makes it possible to suppress damage and wear to the grinding roller 13 and the grinding table 12 caused by the foreign object e, thereby extending the lifespan of the grinding roller 13 and the grinding table 12.
In this way, by mixing biomass chips, which are difficult to crush, the layer of solid fuel can be maintained at a predetermined thickness, and the crushing load can be increased compared to when only biomass pellets are crushed. Therefore, more biomass pellets can be crushed by the mill 10, and the capacity of the mill 10 can be increased.

The temperature of the pulverized solid fuel also changes depending on the moisture content of the solid fuel being pulverized. Specifically, when the moisture content of the solid fuel being pulverized is high, the temperature of the pulverized solid fuel is low. This is because the higher the moisture content of the solid fuel, the more heat is consumed for drying, and thus the temperature rise is suppressed. If the temperature of the pulverized solid fuel is low, the solid fuel may not be burned properly. On the other hand, in contrast, if the solid fuel has a low moisture content, the less heat is consumed for drying, and therefore the temperature becomes high. If the temperature of the pulverized solid fuel is high, there is a possibility that abnormal combustion of the pulverized fuel may occur inside the mill 10.
In this embodiment, the mixing ratio of biomass pellets and biomass chips having different moisture contents is adjusted based on the temperature of the solid fuel detected by the outlet temperature detection unit 63. Therefore, by adjusting the mixing ratio of biomass pellets and biomass chips so that the temperature of the solid fuel discharged from the outlet port 19 is within a predetermined range, the temperature of the solid fuel discharged from the outlet port 19 can be kept within a predetermined range. Therefore, the pulverized solid fuel discharged from the outlet port 19 can be suitably combusted in the furnace 210. Furthermore, the occurrence of abnormal combustion of the pulverized fuel in the mill 10 can be suppressed.

Furthermore, if biomass pellets absorb a large amount of moisture, this can lead to the pellets spoiling, the accumulation of fermentation heat causing fires, or the loss of shape, which can result in the generation of combustible dust and deterioration of handling.
In this embodiment, the biomass pellets and biomass chips are mixed immediately before being crushed on the crushing table 12. This allows the biomass pellets to be crushed before the moisture contained in the biomass chips is absorbed by the biomass pellets. This prevents the biomass pellets from absorbing too much moisture. This prevents the pellets from spoiling.

In addition, biomass chips are less expensive than biomass pellets. Therefore, by mixing in inexpensive biomass chips, it is possible to reduce fuel costs compared to using only biomass pellets as fuel while maintaining the biomass co-firing ratio.

In the solid fuel pulverization device 100, the temperature of the primary air is adjusted by adjusting the opening of the hot gas damper 30c and the opening of the cold gas damper 30d so that the temperature is the temperature required by the mill 10. Therefore, in a high temperature situation such as summer, when the heat amount of the primary air required by the mill 10 is low, the opening of the hot gas damper 30c may be in a minimum state (a state in which the opening cannot be reduced any further). In such a state, there is a possibility that the temperature of the primary air cannot be suitably adjusted. In particular, since biomass pellets have a low moisture content, the amount of heat required for drying is small. Therefore, when only biomass pellets are pulverized, the opening of the hot gas damper 30c is particularly likely to be in a minimum state.
In this embodiment, biomass chips with a high moisture content are fed. Therefore, the amount of heat required for drying in the mill 10 increases. Therefore, even under high temperature conditions such as summer, the opening degree of the hot gas damper 30c is unlikely to be at the minimum. Therefore, the temperature of the primary air can be suitably adjusted. In addition, since the proportion of hot air in the primary air increases, the exhaust heat recovery in the heat exchanger 34 is promoted, which can contribute to improving the energy efficiency of the entire power plant 1.

Biomass chips are difficult to pulverize using the mill 10, and require fiber cutting through a grinding action, but biomass pellets cannot be expected to have the same grinding action as coal. For this reason, it takes longer to pulverize biomass chips in the mill 10 than coal. Therefore, if the amount of biomass chips mixed with the biomass pellets is increased too much, the biomass chips may be excessively retained in the mill 10, resulting in overloading the mill 10.
In this embodiment, the biomass pellets and the biomass chips are mixed so that the calorific value of the biomass chips is 2% to 3% or less of the calorific value of the biomass pellets. This makes it possible to prevent the biomass chips from being excessively retained. In addition, since the adjustment unit 53 adjusts the amount of biomass chips mixed, it is possible to prevent the biomass chips from being excessively retained.

Note that this disclosure is not limited to the above-described embodiments, and can be modified as appropriate without departing from the spirit of the disclosure.

For example, in the above embodiment, an example of using biomass fuel as solid fuel has been described, but the present disclosure is not limited to this. For example, the solid fuel may be coal or PC (Petroleum Coke) fuel generated during oil refining, or a combination of these fuels may be used.

In the above embodiment, an example in which only biomass pellets are stored in the bunker 21 has been described, but the present disclosure is not limited thereto. For example, the bunker 21 may store a biomass fuel that is a mixture of biomass pellets and biomass chips. In this case, the biomass chips need to be dried so that their moisture content is approximately the same as that of the biomass pellets. The mixing ratio of the biomass chips and the biomass pellets is the same as that described above. In this case, it is desirable to thoroughly mix the biomass pellets and the biomass chips so that there is no bias in density or heat generation. In this case, the biomass chip supply device 52 is not provided, and the solid fuel that is a mixture of the biomass pellets and the biomass chips is supplied to the mill 10 by the coal feeder 20.

In addition, in the above embodiment, an example has been described in which the biomass chip supplying device 52 supplies biomass chips to the biomass pellets upstream of the rotary valve 51, but the present disclosure is not limited to this. For example, the biomass chip supplying device 52 may supply biomass chips to the biomass pellets downstream of the rotary valve 51. This is particularly suitable when applied to a negative pressure mill.

It is desirable for the biomass chip supplying device 52 to be inserted from a position that does not contact the weighing section of the coal supplying machine 20.
In order to reduce the contact time between the biomass chips and the biomass pellets and to reduce the transfer of moisture, a partition may be provided between the path through which the biomass chips flow from the biomass chip supply device 52 to the top of the grinding table 12 and the path through which the biomass pellets flow. Specifically, a partition plate may be provided inside the fuel supply unit 17.
In addition, the biomass chips and the biomass pellets may be supplied through separate routes. Specifically, two fuel supply units may be provided, one of which is dedicated to the biomass chips and the other is dedicated to the biomass pellets.

The biomass chip supplying device 52 may supply biomass chips continuously while changing the input amount. It may also supply biomass chips intermittently, for example by monitoring the lift amount of the mill 10 and inputting a fixed amount when it detects that the lift amount has decreased.

The biomass chips fed in may also be weighed and their heat value may be included in the heat input to the boiler. It is desirable for a weighing device for weighing the biomass chips to be installed, for example, immediately before the chip feed port and to measure the mass flow rate of the feed material. However, the amount of biomass chips may also be estimated from the volumetric flow rate, the transport conveyor speed, the amount of chips received, etc.

The size of the biomass chips to be fed is preferably equal to or smaller than the maximum particle size of coal that can be fed into the mill 10. If the biomass chips are plate-like or string-like, they may get caught on the unevenness inside the mill 10, so it is preferable to feed them in a shape that gives the smallest surface area relative to the volume (i.e., a sphere), if possible.

The mixing ratio of biomass pellets and biomass chips should be planned at the design stage based on the properties of the biomass pellets and biomass chips, and should be determined by gradually increasing the mixing ratio during trial operation and conducting actual machine verification.

In addition, in the above embodiment, an example has been described in which the control unit 50 detects fluctuations in the lift amount, outlet temperature, inlet temperature, power of the mill 10, and table differential pressure of the grinding roller 13, and automatically performs corrective action by the control unit 50, but the present disclosure is not limited to this. For example, the detection of fluctuations in the lift amount, outlet temperature, inlet temperature, power of the mill 10, and table differential pressure of the grinding roller 13 may be performed manually, and corrective action such as stopping the input of biomass chips or reducing the rotation speed of the rotary classifier 16 may be performed manually.

The biomass chip supplying device 52 may also be provided with a moisture adjustment device. The biomass chip supplying device 52 may also be provided with a pre-crushing device to adjust the particle size of the chips before feeding them. The biomass chip supplying device 52 may also be provided with a chip particle size sorting device such as a sieve and a foreign matter removal device.

The solid fuel pulverizing apparatus, the power plant, and the method of operating the solid fuel pulverizing apparatus described in the above-described embodiments can be understood, for example, as follows.
A solid fuel pulverization device (100) according to one embodiment of the present disclosure includes a grinding table (12) on whose upper surface a solid fuel mixed with a first solid fuel and a second solid fuel having a grindability and/or moisture content different from the first solid fuel is supplied, a grinding roller (13) for pulverizing the solid fuel on the grinding table (12), a first solid fuel supply unit (20) for supplying the first solid fuel onto the grinding table (12), a second solid fuel supply unit (52) for supplying the second solid fuel onto the grinding table (12), and a control unit (50) for adjusting the mixing ratio of the first solid fuel and the second solid fuel based on an operating state.

The above configuration includes a control unit that adjusts the mixing ratio of the first solid fuel and the second solid fuel based on the operating state. Therefore, when the first solid fuel and the second solid fuel, which have different properties, are mixed and pulverized, the mixing ratio of the first solid fuel and the second solid fuel can be set to a mixing ratio that corresponds to the operating state of the solid fuel pulverization device.

The lift amount of the grinding roller varies depending on the grindability of the solid fuel to be ground. Specifically, the lift amount of the grinding roller tends to be small when grinding a solid fuel with high grindability (solid fuel that is easy to grind), and tends to be large when grinding a solid fuel with low grindability (solid fuel that is difficult to grind). This is because a solid fuel with high grindability is ground to a predetermined particle size or less in a short time and is easily discharged from the solid fuel grinding device, so the amount of solid fuel remaining in the solid fuel grinding device is small, and the layer of solid fuel formed between the grinding table and the grinding roller becomes thin. In addition, a solid fuel with low grindability is difficult to discharge from the solid fuel grinding device, unlike a solid fuel with high grindability, so the layer of solid fuel formed between the grinding table and the grinding roller becomes thick.
Therefore, in the above configuration, for example, when the grindability of the first solid fuel and the second solid fuel differs, the thickness of the layer of solid fuel on the grinding table can be made to be within a predetermined range by adjusting the mixing ratio of the first solid fuel and the second solid fuel so that the lift amount of the grinding roller is within a predetermined range.
When the layer of solid fuel becomes thin, the vibration absorbing effect of the layer of solid fuel decreases, and the amount of vibration of the solid fuel pulverizer increases. Therefore, by setting the thickness of the layer of solid fuel on the pulverization table to within a predetermined range, the vibration of the solid fuel pulverizer can be suppressed. This can suppress damage to the solid fuel pulverizer and extend the life of the solid fuel pulverizer. In addition, since the vibration of the solid fuel pulverizer can be suppressed, the noise generated by the solid fuel pulverizer can be reduced.
Furthermore, by setting the thickness of the layer of solid fuel on the grinding table within a predetermined range, even if foreign matter such as metal is mixed into the solid fuel, the foreign matter is less likely to come into contact with the grinding table and/or the grinding roller, and therefore damage and wear to the grinding roller and the grinding table due to the foreign matter can be suppressed, thereby extending the life of the grinding roller and the grinding table.

The temperature of the pulverized solid fuel also changes depending on the moisture content of the solid fuel being pulverized. Specifically, when the moisture content of the solid fuel being pulverized is high, the temperature of the pulverized solid fuel is low. This is because the higher the moisture content of the solid fuel, the more heat is consumed for drying, and thus the temperature rise is suppressed. If the temperature of the pulverized solid fuel is low, the solid fuel may not be burned properly. On the other hand, in contrast, if the solid fuel has a low moisture content, the less heat is consumed for drying, and therefore the temperature becomes high. If the temperature of the pulverized solid fuel is high, there is a possibility that abnormal combustion of the pulverized fuel may occur inside the mill 10.
In the above configuration, for example, when the moisture content of the first solid fuel is different from that of the second solid fuel, the mixing ratio of the first solid fuel and the second solid fuel can be adjusted so that the temperature of the pulverized solid fuel is within a predetermined range. Therefore, the solid fuel can be burned suitably. In addition, the occurrence of abnormal combustion of the pulverized fuel in the mill 10 can be suppressed.

The first solid fuel may be, for example, biomass pellets. The second solid fuel may be, for example, biomass chips.

The solid fuel pulverization device (100) according to one embodiment of the present disclosure further includes a lift amount detection unit (61) that detects the lift amount of the pulverization roller (13), the second solid fuel has lower pulverizability than the first solid fuel, and the control unit (50) adjusts the mixture ratio of the first solid fuel and the second solid fuel based on the lift amount detected by the lift amount detection unit (61).

In the above configuration, the control unit adjusts the mixture ratio of the first solid fuel and the second solid fuel based on the lift amount of the pulverizing roller detected by the lift amount detection unit. By adjusting the mixture ratio of the first solid fuel and the second solid fuel so that the lift amount of the pulverizing roller is within a predetermined range, the thickness of the layer of the solid fuel on the pulverizing table can be set within a predetermined range. Therefore, the vibration of the solid fuel pulverizing device can be suppressed. Therefore, damage to the solid fuel pulverizing device can be suppressed and the life of the solid fuel pulverizing device can be extended. Furthermore, since the vibration of the solid fuel pulverizing device can be suppressed, the noise generated by the solid fuel pulverizing device can be reduced.
In addition, by setting the thickness of the layer of solid fuel on the grinding table within a predetermined range, damage and wear to the grinding roller and the grinding table due to foreign matter can be suppressed, thereby extending the life of the grinding roller and the grinding table.

Also, a solid fuel pulverization device (100) according to one aspect of the present disclosure includes a housing that houses the crushing table (12) and the crushing roller (13) therein, a carrier gas supply unit (30) that supplies a carrier gas to the inside of the housing (11) for transporting the solid fuel pulverized on the crushing table (12) to an outlet portion (19) provided in the housing (11), and a temperature detection unit (63) that detects the temperature of the solid fuel discharged from the outlet portion (19);
The second solid fuel has a higher water content than the first solid fuel, and the control unit (50) adjusts the mixing ratio of the first solid fuel and the second solid fuel based on the temperature of the solid fuel detected by the temperature detection unit (63).

In the above configuration, the mixing ratio of the first solid fuel and the second solid fuel is adjusted based on the temperature of the solid fuel detected by the temperature detection unit. This allows the temperature of the solid fuel discharged from the outlet of the solid fuel pulverizer to be within a predetermined range. Therefore, the pulverized solid fuel discharged from the outlet of the solid fuel pulverizer can be burned appropriately. In addition, the occurrence of abnormal combustion of the pulverized fuel in the mill can be suppressed.

In addition, in the solid fuel pulverization device (100) according to one embodiment of the present disclosure, the second solid fuel has lower pulverizability than the first solid fuel, and the control unit (50) adjusts the mixing ratio so that the second solid fuel is greater than the first solid fuel when starting the solid fuel pulverization device (100).

In the above configuration, when the control unit starts the solid fuel pulverizing device, it adjusts the mixing ratio so that the second solid fuel is greater than the first solid fuel. As a result, a large amount of the second solid fuel, which has low pulverizability, is supplied onto the pulverizing table at the time of startup, making it easier for a layer of solid fuel to form on the pulverizing table. Therefore, after the solid fuel pulverizing device is started, a layer of solid fuel can be quickly formed on the pulverizing table, making it possible to quickly suppress vibration of the solid fuel pulverizing device. In addition, damage and wear to the pulverizing roller and pulverizing table caused by foreign objects can be quickly suppressed.

In addition, in the solid fuel pulverization device (100) according to one embodiment of the present disclosure, the second solid fuel has lower pulverizability than the first solid fuel, and the control unit (50) adjusts the mixing ratio so that the second solid fuel is greater than the first solid fuel when the solid fuel pulverization device (100) is stopped.

In the above configuration, when the solid fuel pulverizer is stopped, the control unit adjusts the mixing ratio so that the second solid fuel is greater than the first solid fuel. This makes it easier for a layer of solid fuel to form on the pulverization table when the solid fuel pulverizer is stopped. Therefore, when the solid fuel pulverizer is stopped, a layer of solid fuel can be formed on the pulverization table, so vibration of the solid fuel pulverizer can be suppressed.

A power generation plant (1) according to one embodiment of the present disclosure includes any one of the solid fuel pulverizers (100) described above, a boiler (210) that burns the solid fuel pulverized by the solid fuel pulverizer (100) to generate steam, and a power generation unit that generates power using the steam generated by the boiler (210).

In addition, a method of operating a solid fuel pulverizing device (100) according to one aspect of the present disclosure is a method of operating a solid fuel pulverizing device having a pulverizing table to the upper surface of which solid fuel is supplied, and a pulverizing roller for pulverizing the solid fuel on the pulverizing table, and includes a first solid fuel supplying step of supplying a first solid fuel onto the pulverizing table, a second solid fuel supplying step of supplying a second solid fuel onto the pulverizing table, the second solid fuel having a pulverizability and/or content different from that of the first solid fuel, and an adjustment step of adjusting the mixture ratio of the first solid fuel and the second solid fuel based on the operating state.

1: Power plant 10: Mill 11: Housing 12: Grinding table 13: Grinding roller 14: Drive unit 15: Mill motor 16: Rotary classifier 16a: Blade 17: Fuel supply unit 18: Classifier motor 19: Outlet port 20: Coal feeder 21: Bunker 22: Conveyor unit 23: Coal feeder motor 24: Downspout 30: Blower unit 30a: Hot gas flow path 30b: Cold gas flow path 30c: Hot gas damper 30d: Cold gas damper 31: Primary air ventilator 32: Forced draft fan 34: Heat exchanger 40: Status detection unit 41: Bottom surface unit 42: Ceiling unit 45: Journal head 47: Support arm 48: Support shaft 49: Pressing device 50: Control unit 51: Rotary valve 52: Biomass chip supply device 53 : Adjustment section 61 : Lift amount detection section 62 : Vibration detection section 63 : Outlet temperature detection section 64 : Inlet temperature detection section 65 : Power detection section 66 : Table differential pressure detection section 100 : Solid fuel pulverizer 100a : Primary air flow path 100b : Pulverized fuel supply flow path 140 : HDD
200: boiler 210: furnace 220: burner

Claims (7)

A grinding table on whose upper surface a solid fuel containing a mixture of biomass pellets and biomass chips is supplied;
a grinding roller for grinding the solid fuel on the grinding table;
A first solid fuel supply unit that supplies the biomass pellets onto the grinding table;
a second solid fuel supply unit that supplies the biomass chips onto the grinding table;
A control unit that adjusts a mixing ratio of the biomass pellets and the biomass chips based on an operating condition. a lift amount detection unit for detecting a lift amount of the crushing roller,
The biomass chips are less pulverizable than the biomass pellets ;
The solid fuel pulverizer according to claim 1 , wherein the control unit adjusts a mixing ratio of the biomass pellets and the biomass chips based on the lift amount detected by the lift amount detection unit. a housing that houses the grinding table and the grinding roller therein;
a carrier gas supply unit that supplies a carrier gas into the housing so as to transport the solid fuel pulverized on the grinding table to an outlet unit provided in the housing;
a temperature detection unit that detects a temperature of the solid fuel discharged from the outlet,
The biomass chips have a higher moisture content than the biomass pellets ,
The solid fuel pulverizer according to claim 1 , wherein the control unit adjusts a mixing ratio of the biomass pellets and the biomass chips based on the temperature of the solid fuel detected by the temperature detection unit. The biomass chips are less pulverizable than the biomass pellets ;
The solid fuel pulverizer according to claim 1 , wherein the control unit adjusts a mixing ratio such that the biomass chips are greater than the biomass pellets when starting the solid fuel pulverizer. The biomass chips are less pulverizable than the biomass pellets ;
The solid fuel pulverizer according to claim 1 , wherein the control unit adjusts a mixing ratio such that the biomass chips are greater than the biomass pellets when the solid fuel pulverizer is stopped. A solid fuel pulverizer according to any one of claims 1 to 5,
a boiler for burning the solid fuel pulverized by the solid fuel pulverizer to generate steam;
a power generation unit that generates electricity using the steam generated by the boiler. A grinding table on whose upper surface a solid fuel containing a mixture of biomass pellets and biomass chips is supplied;
and a grinding roller for grinding the solid fuel on the grinding table.
a first solid fuel supplying step of supplying the biomass pellets onto the grinding table;
a second solid fuel supply step of supplying the biomass chips onto the grinding table;
and an adjusting step of adjusting a mixing ratio of the biomass pellets and the biomass chips based on an operating condition.

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