Vertical mill pulverization system

Abstract

To provide a vertical mill pulverization system which can suitably process a pulverization product as the control of a method for discharging the pulverization product modified according to the crushability of a pulverization stock material.SOLUTION: This system comprises a vertical mill which crushes a pulverization stock material and a hot gas supplier which supplies a hot gas into the vertical mill, where the vertical mill has the upper discharge port which discharges a pulverization product of a crushed pulverization stock material from above with the hot gas and the lower discharge port which discharges the crushed pulverization product from below. The vertical mill can switch the drive of the vertical mill between the first control for conveying the pulverization product under air streams with a hot gas, according to the crushability of the pulverization stock material, to discharge and recover the pulverization product out of the upper discharge port and the second control for conveying the pulverization product under no air streams with the hot gas to discharge and recover the pulverization material.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present application relates to a grinding system using a vertical mill. [Background technology]

[0002] Conventionally, vertical mills are used to pulverize raw materials such as limestone and fuels such as coal. Vertical mills are also used to pulverize woody biomass fuels. In the following explanation, "limestone," "coal," "biomass fuel," and the like are collectively referred to as "pulverized raw materials." Vertical mills can finely pulverize limestone, coal, and the like, but biomass fuels are difficult to pulverize finely, and there are documents that change the operation method of vertical mills depending on the material to be processed.

[0003] One such document is a pulverizer that allows the rotation direction of a rotary classifier equipped with multiple blades to be changed (see, for example, Patent Document 1). This pulverizer changes the rotation direction of the rotary classifier depending on the raw material to be pulverized, thereby changing the dischargeability of the pulverized material by the multiple inclined blades. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2019-84476 A Summary of the Invention [Problem to be solved by the invention]

[0005] In general, a grinding system for grinding raw materials using a vertical mill is configured such that hot gas is supplied to the vertical mill from a hot gas supplying device, and the ground material ground by the hot gas is air-transported from the top of the vertical mill. For this reason, in the case of raw materials with poor grindability, if the ground material that cannot be finely ground is air-transported by hot gas, it is difficult to extract it from the classifier provided above the vertical mill, which may lead to increased power consumption.

[0006] In the case of the above-mentioned document, the raw material is crushed in the crushing section and classified in the classifying section provided above, so that crushed material that cannot be crushed finely due to poor crushability remains in the crushing section.

[0007] Therefore, an object of the present application is to provide a vertical mill grinding system that can change the method of discharging the ground material depending on the grinding property of the raw material to be ground. [Means for solving the problem]

[0008] A vertical mill grinding system according to one embodiment of the present application comprises a vertical mill for grinding raw materials to be ground, and a hot gas supplier for supplying hot gas to the vertical mill. The vertical mill has an upper outlet for discharging the ground material obtained by grinding the raw materials together with the hot gas from above, and a lower outlet for discharging the ground material from below. Depending on the grindability of the raw materials to be ground, the operation of the vertical mill can be switched between a first control in which the hot gas transports the ground material with an air current and the ground material is discharged and recovered from the upper outlet, and a second control in which the hot gas does not transport the ground material with an air current and the ground material is discharged and recovered from the lower outlet. Effect of the Invention

[0009] According to the present application, it is possible to provide a vertical mill grinding system that can appropriately process the raw material by changing the discharge method of the ground material depending on the grinding property of the raw material. [Brief description of the drawings]

[0010] [Figure 1] FIG. 1 is an overall view showing the configuration of a vertical mill grinding system according to one embodiment of the present application. [Diagram 2] FIG. 2 is an overall view showing a case where a raw material having good grindability is ground in the vertical mill of the vertical mill grinding system shown in FIG. [Diagram 3] FIG. 3 is an overall view showing a case where a raw material having poor grindability is ground in the vertical mill of the vertical mill grinding system shown in FIG. [Figure 4]FIG. 4 is an overall view showing a different example of the case where the raw material having poor grindability shown in FIG. 3 is ground. [Diagram 5] FIG. 5 is an overall view showing an example of a vertical mill grinding system having a partly different configuration from that shown in FIG. [Figure 6] FIG. 6 is an overall view showing an example of a vertical mill grinding system of a different type from the vertical mill grinding system shown in FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] An embodiment of the present application will be described below with reference to the drawings. The vertical mill grinding system 1 of this embodiment will be described as an example of a negative pressure mill that grinds fuel used in cement manufacturing facilities as a grinding raw material. The vertical mill grinding system 1 in the following embodiment will be described as a preferred example of a configuration, but is not limited to the following configuration. The following embodiment is a diagram showing a case where the equipment is electrically controlled using a control device when controlling flow switching. The concepts of up, down, left, and right in this specification and claims are assumed to be consistent with the concepts of up, down, left, and right shown in FIG. 1.

[0012] <Configuration of vertical mill grinding system> FIG. 1 is an overall view showing the configuration of a vertical mill grinding system 1 according to one embodiment. The vertical mill grinding system 1 of this embodiment includes a vertical mill 10 for grinding a grinding raw material, a hot gas supplier 20 for supplying hot gas 21 to the vertical mill 10 from a gas supply line 22, and a raw material supplier 30 for supplying the grinding raw material to the vertical mill 10. The hot gas supplier 20 may produce the hot gas 21 by itself, or may use exhaust gas discharged from a factory as the hot gas 21. The gas supply line 22 has a gas amount adjustment damper 23, which is a gas amount regulator for adjusting the flow rate of the hot gas 21. The supply amount of the hot gas 21 may be adjusted by the hot gas supplier 20. The raw material supplier 30 of this embodiment includes a first raw material supplier 31 for supplying a first raw material 41, which is a grinding raw material with good grindability, and a second raw material supplier 32 for supplying a second raw material 42, which is a grinding raw material with poor grindability. The first raw material supplying machine 31 may be, for example, a feeder that feeds out a predetermined amount of the first raw material 41 from the first raw material hopper 33. The second raw material supplying machine 32 may be, for example, a feeder that feeds out a predetermined amount of the second raw material 42 from the second raw material hopper 34. The hot gas from the hot gas supplying machine 20 may be exhaust gas discharged from a factory. The number of raw material supplying machines and raw material hoppers may increase depending on the type of input raw material.

[0013] The vertical mill 10 has a pulverizer 11 for pulverizing the raw material at the bottom, and a classifier 12 for classifying the pulverized material pulverized by the pulverizer 11 at the top. The vertical mill 10 may have a classifier 12 as a separate component. When the raw material to be pulverized is the first raw material 41 having good pulverizability, the vertical mill 10 has an upper discharge port 15 for discharging the pulverized material pulverized by the pulverizer 11 from above together with the hot gas 21 supplied from the hot gas supplying device 20. The first raw material 41 having good pulverizability is a raw material that is air-transported together with the hot gas 21, and the upper discharge port 15 is an outlet for discharging the pulverized material of the raw material having good pulverizability together with the hot gas 21 by air-transport. In addition, when the raw material to be pulverized is the second raw material 42 having poor pulverizability, the vertical mill 10 has a lower discharge port 16 for discharging the pulverized material pulverized by the pulverizer 11 from below. The second raw material 42, which has poor grindability, is a raw material that is not transported by air current from the upper discharge outlet 15 together with the hot gas 21, and the lower discharge outlet 16 is an outlet for discharging the pulverized material that has poor grindability and is not transported by air current from the upper discharge outlet 15 together with the hot gas 21.

[0014] The grindability of the raw material to be pulverized can be determined, for example, such that mineral raw materials are raw materials with good grindability, and non-mineral raw materials are raw materials with poor grindability. The first raw material 41, which is a raw material with good grindability, is a raw material that discharges pulverized material together with the hot gas 21 supplied from the hot gas supplier 20. Examples of the first raw material 41 include coal, limestone, clay, and silica. The second raw material 42, which is a raw material with poor grindability, is a raw material that does not discharge pulverized material together with the hot gas 21 supplied from the hot gas supplier 20. Examples of the second raw material 42 include woody biomass fuel. Woody biomass fuel is a raw material that contains fibers and is difficult to make into a fine particle size.

[0015] The vertical mill grinding system 1 of this embodiment has a dust collector 60 and a first product hopper 61 downstream of the upper discharge port 15 of the vertical mill 10. The ground material discharged from the upper discharge port 15 enters the dust collector 60 together with the hot gas 21 and is collected. The gas discharged from the dust collector 60 is discharged to the atmosphere via a fan 62. The ground material separated by the dust collector 60 is sent to the first product hopper 61 by a first conveyor 63 and stored therein. The vertical mill grinding system 1 of this embodiment has a bypass path 24 between the upstream of the dust collector 60 and the gas supply path 22. The bypass path 24 has an opening / closing damper 25 as a switch that opens and closes the flow path. The opening / closing damper 25 may be one whose opening degree can be adjusted.

[0016] Meanwhile, the vertical mill grinding system 1 of this embodiment has a second product hopper 71 downstream of the lower discharge port 16 of the vertical mill 10. The ground material discharged from the lower discharge port 16 is sent to the second product hopper 71 by a second conveyor 72 and stored therein. In this embodiment, the conveyor 72 is used to transport the ground material discharged from the lower discharge port 16 of the vertical mill 10, but the ground material may be transported by air conveyance or the like.

[0017] The vertical mill grinding system 1 can switch between a flow in which raw materials with good grindability are ground in the vertical mill 10 and discharged from the upper discharge port 15 by air current transport and collected, and a flow in which raw materials with poor grindability are ground in the vertical mill 10 and discharged from the lower discharge port 16 and collected. In this specification and claims, the flow in which raw materials are discharged from the upper discharge port 15 and collected is referred to as "first control", and the flow in which raw materials are discharged from the lower discharge port 16 and collected is referred to as "second control". The switching between the first control and the second control may be performed manually by a human being or by the control device 80.

[0018] The control device 80 is electrically connected to the first raw material supplying device 31, the second raw material supplying device 32, the vertical mill 10, the hot gas supplying device 20, and the fan 62. FIG. 1 illustrates the connection between these main components. The control device 80 is also electrically connected to the gas amount adjusting damper 23 of the gas supplying path 22, the opening and closing damper 25 of the bypass path 24, the first conveyor 63, and the second conveyor 72. The control device 80 controls the amount of hot gas supplied by the hot gas supplying device 20 and the opening degree of the dampers 23 and 24, thereby switching between a first control for pulverizing and recovering raw materials with good pulverizability and a second control for pulverizing and recovering raw materials with poor pulverizability. When switching the control, the control device controls the necessary equipment. When controlling, an operator may operate manually, or the control device 80 may be used for electrical control.

[0019] <Grinding of raw materials with good grinding properties> FIG. 2 is an overall view showing a case where a first raw material 41, which is a raw material having good grindability, is ground in the vertical mill 10 of the vertical mill grinding system 1 shown in FIG.

[0020] When a pulverized raw material 41 having good pulverizability is fed into the vertical mill 10, the control device 80 switches to the first control in which the pulverized material is discharged from the upper discharge port 15 of the vertical mill 10. The control device 80 supplies the necessary hot gas 21 from the hot gas supplier 20 to the pulverized material pulverized by the vertical mill 10. The control device 80 then feeds the first raw material 41 from the first raw material hopper 33 from the first raw material supplier 31 to the input conveyor 35, and supplies the first raw material 41 from the input conveyor 35 to the vertical mill 10 via the rotary valve 36. The first raw material 41 supplied to the vertical mill 10 is pulverized by the pulverizer 11 of the vertical mill 10. The first raw material 41 is pulverized to a predetermined size by the pulverizer 11 to become the first pulverized material 51. The first pulverized material 51 passes through a classifier 12 provided at the top of the vertical mill 10 and is discharged from the upper discharge port 15 by air current together with the hot gas 21. The first pulverized material 51 discharged from the upper discharge port 15 is collected by a dust collector 60, and the first pulverized material 51 collected by the dust collector 60 is transported by a first conveyor 63 to a first product hopper 61 and stored therein. The hot gas 21 is released into the atmosphere via a fan 62.

[0021] <Crushing of raw materials with poor grindability> Fig. 3 is an overall view showing a case where a second raw material 42, which is a raw material having poor grindability, is ground in the vertical mill 10 of the vertical mill grinding system 1 shown in Fig. 1. Fig. 4 is an overall view showing a different example of a case where the second raw material 42, which is a raw material having poor grindability, shown in Fig. 3 is ground.

[0022] In the example shown in FIG. 3, the control device 80 switches to the second control in which the pulverized material is discharged from the lower outlet 16 of the vertical mill 10. When maintaining the state in which the hot gas 21 is supplied from the hot gas supplier 20 to the vertical mill 10, the control device 80 closes the gas amount adjustment damper 23 of the gas supply path 22 that supplies the hot gas 21 from the hot gas supplier 20 to the vertical mill 10, and opens the opening and closing damper 25 of the bypass path 24. As a result, the hot gas 21 supplied from the gas supplier flows downstream of the upper outlet 15 of the vertical mill 10 and is released into the atmosphere via the dust collector 60 and the fan 62. Note that the hot gas 21 may be prevented from being supplied from the hot gas supplier 20 to the vertical mill 10.

[0023] The control device 80 then causes the second raw material 42 in the second raw material hopper 34 to be fed to the feeding conveyor 35 by the second raw material feeder 32, and supplies the second raw material 42 from the feeding conveyor 35 to the vertical mill 10 via the rotary valve 36. The second raw material 42 fed to the vertical mill 10 is pulverized by the pulverizer 11 of the vertical mill 10. When pulverizing the second raw material 42 that is poorly pulverizable, the pulverizer 11 may reduce the rotation speed of the mill table 13 to extend the pulverization time of the second raw material 42, or may operate by increasing the roller pressure.

[0024] The second raw material 42 is pulverized to a predetermined size by the pulverizer 11 to become the second pulverized material 52. The second pulverized material 52 is discharged from the lower discharge port 16 provided at the bottom of the vertical mill 10 to the second conveyor 72, and is transported by the second conveyor 72 to the second product hopper 71 and stored therein. The second pulverized material 52 stored in the second product hopper 71 is used as fuel for the burner 100.

[0025] In the example shown in Fig. 4, a cyclone 65 and a dust collector 60 are provided downstream of the upper discharge outlet 15 of the vertical mill 10. The product collected by the cyclone 65 is stored in a first product hopper 61 by a third conveyor 66. The product collected by the dust collector 60 is stored in the first product hopper 61 by a first conveyor 63.

[0026] The example shown in FIG. 4 is an example in which the control device 80 switches to the second control in which the ground material is discharged from the lower outlet 16 of the vertical mill 10, and the amount of hot gas 21 supplied from the hot gas supplier 20 to the vertical mill 10 is adjusted by the opening degree of the gas amount adjustment damper 23 of the gas supply path 22. In this embodiment, the gas supplier 22 uses exhaust gas from the factory as the hot gas 21. The opening and closing damper 25 of the bypass path 24 is in a closed state. In this embodiment, the vertical mill grinding system 1 adjusts the opening degree of the gas amount adjustment damper 23 of the gas supply path 22 by the control device 80 to adjust the amount of hot gas 21 supplied from the hot gas supplier 20 to the vertical mill 10 to a predetermined amount. The supply amount of hot gas 21 may be adjusted to a predetermined amount required for drying the second raw material 42 inside the vertical mill 10 by the hot gas 21. In the case of the second control, regardless of whether hot gas is introduced into the vertical mill 10, dust generated inside the vertical mill 10 may be collected by the dust collector 90. The predetermined amount of hot gas 21 in the second control is a predetermined amount that is less than the amount of airflow transport in the first control shown in Fig. 2. In addition, the second raw material collected by the dust collector 90 may be merged with the classifier 70 or the hopper 71.

[0027] The control device 80 then causes the second raw material 42 in the second raw material hopper 34 to be fed to the feeding conveyor 35 by the second raw material feeder 32, and supplies the second raw material 42 from the feeding conveyor 35 to the vertical mill 10 via the rotary valve 36. The second raw material 42 fed to the vertical mill 10 is pulverized by the pulverizer 11 of the vertical mill 10. When pulverizing the second raw material 42 that is poorly pulverizable, the pulverizer 11 may reduce the rotation speed of the mill table 13 to extend the pulverization time of the second raw material 42, or may operate by increasing the roller pressure.

[0028] The second raw material 42 is pulverized to a predetermined size by the pulverizer 11 to become the second pulverized material 52. The second pulverized material 52 is discharged from the lower discharge port 16 provided at the bottom of the vertical mill 10 to the second conveyor 72. In this embodiment, the second pulverized material 52 is fed from the second conveyor 72 to the bucket elevator 73, and then fed from the bucket elevator 73 to the classifier 70. The classifier 70 classifies the second pulverized material 52 into a predetermined size, and the second pulverized material 52 smaller than the predetermined size is stored in the second product hopper 71. The second pulverized material 52 stored in the second product hopper 71 is used as fuel for the burner 100. The second pulverized material 52 classified by the classifier 70 and larger than the predetermined size is returned to the feed conveyor 35, fed again to the vertical mill 10, and pulverized by the pulverizer 11.

[0029] On the other hand, a predetermined amount of hot gas 21 is supplied to the vertical mill 10 from a hot gas supplier 20. This hot gas 21 is used to dry the second raw material 42 inside the vertical mill 10. When the second raw material 42, which is poorly grindable, is, for example, a biomass fuel, it may be dried by the heat of the hot gas 21 at the same time as grinding. In addition, dust generated during grinding may be collected by a dust collector 90.

[0030] <Other embodiments> Fig. 5 is an overall view showing an example in which the vertical mill grinding system 1 shown in Fig. 1 has a different configuration. Only the configuration of the vertical mill grinding system 1 shown in Fig. 5 that is different from that of the vertical mill grinding system 1 shown in Fig. 1 will be described, and the same configuration will be given the same reference numerals and will not be described. The vertical mill grinding system 1 shown in Fig. 5 has a configuration in which the gas supply path 22 does not have a gas amount adjustment damper 23, which is a gas amount adjuster, and does not have a bypass path 24. In this configuration, the supply amount of the hot gas 21 supplied from the hot gas supplier 20 to the vertical mill 10 is adjusted to a predetermined amount in the hot gas supplier 20, or is controlled so as not to be supplied from the hot gas supplier 20.

[0031] 6 is an overall view showing an example of a vertical mill grinding system of a different type from the vertical mill grinding system 1 shown in FIG. 6, only the configuration different from the vertical mill grinding system 1 shown in FIG. 1 will be described, and the same configuration will be given the same reference numerals and description will be omitted. The vertical mill grinding system 1 shown in FIG. 6 is an example in which the ground material discharged from the upper outlet 15 of the vertical mill 10 is used as fuel for the burner 100. The vertical mill grinding system 1 can also be applied to a positive pressure mill that grinds fuel used in power plant facilities, etc., and is not limited to a negative pressure mill that grinds fuel used in cement manufacturing facilities, etc., as in the above-mentioned embodiment.

[0032] In the above embodiment, coal is used as an example of a pulverized raw material having good pulverizability, and woody biomass fuel is used as an example of a pulverized raw material having poor pulverizability. However, the pulverized raw material having good pulverizability may be limestone, etc., and the pulverized raw material having poor pulverizability is not limited to woody biomass fuel, and the pulverized raw material is not limited to the above-mentioned raw materials.

[0033] The above-described embodiment shows one example of a preferred configuration, and the processing of the pulverized material discharged from the lower discharge port 16 of the vertical mill 10 is not limited to the above-described embodiment. For example, a configuration not including the classifier 70 is also possible, and various configuration changes may be made without departing from the gist of the present application, and the present application is not limited to the above-described embodiment.

[0034] As described above, according to the vertical mill grinding system 1, when the raw material to be ground is the first raw material 41 having good grindability, the first control is switched to in which the first ground material 51 ground by the vertical mill 10 is discharged and collected from the upper discharge port 15. Also, according to the vertical mill grinding system 1, when the raw material to be ground is the second raw material 42 having poor grindability, the second control is switched to in which the second ground material 52 ground by the vertical mill 10 is discharged and collected from the lower discharge port 16. Therefore, the vertical mill grinding system 1 can appropriately process both the first raw material 41 having good grindability and the second raw material 42 having poor grindability in a single vertical mill grinding system 1.

[0035] Each of the following sections is a disclosure of a preferred embodiment. [Item 1] A vertical mill grinding system comprising: a vertical mill for grinding a raw material to be ground; and a hot gas supplier for supplying hot gas to the vertical mill, wherein the vertical mill has an upper discharge outlet for discharging the ground material obtained by grinding the raw material together with the hot gas from above, and a lower discharge outlet for discharging the ground material from below, and the operation of the vertical mill can be switched between a first control in which the hot gas transports the ground material with an air current and the ground material is discharged and recovered from the upper discharge outlet, and a second control in which the hot gas does not transport the ground material with an air current and the ground material is discharged and recovered from the lower discharge outlet, depending on the grindability of the raw material to be ground.

[0036] With this configuration, when a pulverized raw material with good pulverizability is supplied to the vertical mill, the pulverized material can be discharged and collected from the upper discharge port together with the hot gas supplied from the hot gas supplier to the vertical mill by the first control, in which the discharge direction of the pulverized material is switched to the upper discharge port. When a pulverized raw material with poor pulverizability is supplied to the vertical mill, the pulverized material can be discharged and collected from the lower discharge port by the second control, in which the discharge direction of the pulverized material is switched to the lower discharge port. Thus, the vertical mill can appropriately collect the pulverized material depending on the pulverizability of the supplied pulverized raw material.

[0037] [Item 2] 2. The vertical mill grinding system according to item 1, wherein in the second control, a rotation speed of the mill table of the grinder of the vertical mill is slowed down relative to a rotation speed of the mill table of the grinder of the vertical mill in the first control.

[0038] With this configuration, when grinding raw material that is difficult to grind, the rotation speed of the mill table of the grinding machine can be slowed down to extend the grinding time.

[0039] [Item 3] 3. The vertical mill grinding system according to claim 1, wherein in the second control, a predetermined amount of the hot gas is supplied from the hot gas supplying machine to the vertical mill, the amount being smaller than the amount of the hot gas supplied from the hot gas supplying machine to the vertical mill in the first control, or the hot gas is not supplied from the hot gas supplying machine.

[0040] With this configuration, during the second control for grinding raw materials that have poor grindability, a predetermined amount of hot gas that is less than the amount of hot gas during the first control can be supplied to the vertical mill, and the hot gas can be used to dry the raw materials.

[0041] [Item 4] 4. The vertical mill grinding system according to any one of items 1 to 3, further comprising a gas amount regulator between the hot gas supplier and the vertical mill, and controls an opening degree of the gas amount regulator to switch between the first control and the second control.

[0042] With this configuration, when grinding raw materials with good grindability, the opening of the gas regulator can be increased to discharge the ground material from the upper discharge port, and when grinding raw materials with poor grindability, the opening of the gas regulator can be decreased or closed to discharge the ground material from the lower discharge port.

[0043] [Item 5] 5. The vertical mill grinding system according to item 4, further comprising a bypass passage between a gas supply passage between the hot gas supplier and the vertical mill and a flow passage in a downstream direction of the upper discharge port, the bypass passage having a switch, and the control device, in the second control, closes the gas amount regulator and opens the switch.

[0044] With this configuration, when grinding raw materials with poor grindability, a predetermined amount of hot gas can be supplied to the vertical mill, and the raw materials can be dried and discharged using the hot gas. The predetermined amount of hot gas can be controlled to an appropriate amount by adjusting the opening of the gas amount regulator and the opening of the switchgear by the control device. [Explanation of symbols]

[0045] 1 Vertical mill grinding system 10 Vertical Mill 11 Crusher 12 Classifier 13 Mill Table 15 Upper outlet 16 Lower outlet 20. Hot gas supply machine 21 Hot Gas 22 Gas supply line 23 Gas volume adjustment damper (gas volume regulator) 24 Bypass Road 25 Opening and closing damper (switch) 30 Raw material feeder 31 1st raw material feeder 32 Second raw material feeder 36 Input hopper 41 First raw material 42 Second raw material 51 First crushed material 52 Second crushed material 60 Cyclone 61 First product hopper 70 Classifier 71 Second product hopper 80 Control device 90 Dust collector 100 Burner

Claims

1. The present invention comprises a vertical mill for pulverizing a raw material to be pulverized, and a hot gas supplier for supplying hot gas to the vertical mill, The vertical mill has an upper discharge port through which the pulverized material obtained by pulverizing the pulverized raw material is discharged from above together with the hot gas, and a lower discharge port through which the pulverized material is discharged from below, A vertical mill grinding system in which the operation of the vertical mill can be switched between a first control in which the hot gas is used to air-transport the ground material and the ground material is discharged and recovered from the upper discharge outlet, and a second control in which the hot gas is not used to air-transport the ground material and the ground material is discharged and recovered from the lower discharge outlet, depending on the grindability of the raw material.

2. 2. The vertical mill grinding system according to claim 1, wherein in the second control, a rotation speed of the mill table of the grinder of the vertical mill is slowed down relative to a rotation speed of the mill table of the grinder of the vertical mill in the first control.

3. A vertical mill grinding system as described in claim 1 or 2, wherein in the second control, a predetermined amount of hot gas that is smaller than the amount of hot gas supplied from the hot gas supplier to the vertical mill in the first control is supplied from the hot gas supplier to the vertical mill, or the hot gas is not supplied from the hot gas supplier.

4. A gas amount regulator is provided between the hot gas supplier and the vertical mill, The vertical mill grinding system according to claim 1 , wherein the first control and the second control are switched by controlling an opening degree of the gas amount regulator.

5. A bypass is provided between a gas supply path between the hot gas supplier and the vertical mill and a flow path in a downstream direction of the upper discharge port, The bypass path has a switch, 5. The vertical mill grinding system according to claim 4, wherein in the second control, the gas regulator is closed and the switch is opened.

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