Grinding System

Abstract

To improve operation stability of a pulverization system including a vertical type roller mill when the pulverization system pulverizes a raw material.SOLUTION: A pulverization method includes: performing primary classification on a raw material into coarse powder and fine powder while heating the raw material by using carrier gas; supplying the coarse powder to a vertical type roller mill to pulverize the coarse powder, and mixing the pulverized product discharged from the vertical type roller mill into a raw material that is subjected to the primary classification. A temperature of the carrier gas used for the primary classification is higher than that of the raw material and a mixture of the raw material and the pulverized product.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a grinding system and method including a vertical roller mill. [Background technology]

[0002] Conventionally, vertical roller mills have been known as a type of grinding machine that dries and grinds various raw materials such as cement raw materials and calcium carbonate. In general, vertical roller mills are equipped with a rotary table and grinding rollers provided in a grinding chamber formed in a housing, and are configured to grind raw materials by pinching them between the rotary table and the grinding rollers while drying them with hot air. The ground raw materials are discharged from an outlet below the rotary table, and gas accompanied with fine powder generated by grinding is discharged from an exhaust port above the rotary table. Patent documents 1 and 2 disclose grinding systems including this type of vertical roller mill.

[0003] Patent Document 1 shows a grinding system for grinding raw materials that are dry and contain a large amount of fine particles. This grinding system includes a vertical roller mill for performing primary grinding of the raw materials, and a secondary grinder for performing secondary grinding of the raw materials. The raw materials are classified in advance by an air classifier, and the coarse particles after classification are supplied to the vertical roller mill, while the fine particles after classification are supplied directly to the secondary grinder without passing through the vertical roller mill.

[0004] Patent Document 2 shows a grinding system for grinding raw materials with low grindability. This grinding system includes a vertical grinder (vertical roller mill) that pre-grinds the raw materials, and a finish mill that finish-grinds the pre-grinded raw materials. A classification chute is provided immediately before the vertical grinder, and the raw materials are classified into fine particles and coarse particles by this classification chute. The fine particles are forwarded to the finish mill, and only the coarse particles are pre-grinded by the vertical grinder and then sent to the finish mill. The pulverized material that is finish-grinded by the finish mill is separated into crushed materials by a cyclone separator, and the remaining crushed material is returned to the finish mill to be pulverized again. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 7-848 [Patent Document 2] Japanese Patent Application Publication No. 7-313897 Summary of the Invention [Problem to be solved by the invention]

[0006] It is known that in a vertical roller mill, operation is stable when the temperature of the raw material caught between the rotating table and the grinding rollers (hereinafter referred to as the "grinding temperature") is at a suitable grinding temperature. The suitable grinding temperature varies depending on the properties of the raw material and the characteristics of the vertical roller mill. When the temperature of the raw material supplied to the vertical roller mill is lower than the suitable grinding temperature or when the moisture content is high, the temperature and amount of hot air introduced into the grinding chamber is adjusted to raise the temperature of the raw material caught between the grinding rollers to the suitable grinding temperature.

[0007] However, the hot air introduced into the grinding chamber is also used for airflow transport of the ground material, so there is a limit to the amount of hot air. In addition to the raw materials newly fed, the vertical roller mill also receives coarsely ground material to be returned to the vertical roller mill. Since there is a difference in temperature and moisture content between the raw materials and the coarsely ground material, there is a risk of unevenness in the temperature of the mixture of the raw materials and the coarsely ground material fed to the rotary table. In view of this, it is considered effective to preheat the raw materials before feeding them into the vertical roller mill in order to heat the materials to a suitable grinding temperature before they are caught in the grinding rollers. In Patent Document 2, since the exhaust gas from the vertical roller mill is used in the classification chute, it is presumed that the raw materials fed to the vertical roller mill are preheated to some extent by heat exchange with the exhaust gas. However, in Patent Document 2, the ground material of the vertical roller mill is not returned to the vertical roller mill, so the unevenness in temperature of the materials of the vertical roller mill is not taken into consideration. Furthermore, since the exhaust gas from the vertical roller mill is directly used as the carrier gas in the classifying chute, the mill exhaust volume and the carrier gas flow rate cannot be adjusted independently.

[0008] The present invention has been made in consideration of the above circumstances, and an object of the present invention is to improve the operational stability of a grinding system that includes a vertical roller mill and a classifier connected by a circulation path when grinding raw materials. [Means for solving the problem]

[0010] In addition, a grinding system according to another aspect of the present invention includes: a vertical roller mill having a rotary table arranged in a grinding chamber and at least one grinding roller whose peripheral surface is pressed against the rotary table, and configured to grind materials supplied to the rotary table by pinching them between the rotary table and the grinding roller while blowing hot air into the grinding chamber, discharge the ground material, and discharge fine powder particles generated by the grinding by carrying them on an air current; a primary classifier configured to primarily classify a raw material into coarse powder and fine powder while heating the raw material using a carrier gas; A first conveying unit that conveys the coarse powder discharged from the primary classifier to the vertical roller mill as the material to be crushed; A return unit that conveys the pulverized material discharged from the vertical roller mill to the primary classifier so as to mix the pulverized material with the raw material to be primarily classified; A first hot gas supply unit that supplies hot gas from a hot gas source to the vertical roller mill as the hot air; A second hot gas supply unit that supplies hot gas from the hot gas source to the primary classifier as the carrier gas without passing through the vertical roller mill. Preparation, The temperature of the carrier gas is higher than that of the raw material and the mixture of the raw material and the pulverized material.

[0011] In the above-mentioned grinding method and grinding system, a mixture of the raw material and the ground material returned from the vertical roller mill is roughly classified and heated in a primary classifier. The material whose particle size and temperature have been adjusted in this manner by primary classification is supplied to the vertical roller mill. This reduces temperature unevenness of the material caught in the grinding rollers, making it possible to uniformly heat the material to a suitable grinding temperature. By making the temperature of the material caught in the grinding rollers uniform and stable, stable grinding can be maintained, improving the grinding efficiency of the vertical roller mill. Furthermore, by maintaining good grinding in the vertical roller mill, the operational stability of the grinding system can be improved.

[0012] In addition, in the above-mentioned crushing method and crushing system, since the mixture of the raw material and the returned crushed material is preheated in the primary classification, it is possible to raise the temperature of the material to be crushed between the crushing rollers to a suitable crushing temperature even if the raw material has a relatively large temperature difference from the returned crushed material (e.g., raw material at room temperature). Therefore, the above-mentioned crushing method and crushing system are suitable for crushing raw materials having a relatively large temperature difference from the returned crushed material (e.g., raw material at room temperature). Effect of the Invention

[0013] According to the present invention, when a raw material is pulverized in a pulverization system including a vertical roller mill and a classifier connected by a circulation path, the operational stability of the system can be improved. [Brief description of the drawings]

[0014] [Figure 1] FIG. 1 is a diagram showing the overall configuration of a grinding system according to one embodiment of the present invention. [Diagram 2] FIG. 2 is a partially enlarged view of FIG. 1 showing the configuration of a static classifier and a dynamic classifier. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] Next, an embodiment of the present invention will be described with reference to the drawings. Fig. 1 is a diagram showing the overall configuration of a grinding system 1 according to one embodiment of the present invention. The grinding system 1 shown in Fig. 1 includes a vertical roller mill 2, a ground material circulation system 3 for circulating ground material to the vertical roller mill 2, and a gas circulation system 4 for circulating gas within the system.

[0016] [Vertical roller mill 2] The vertical roller mill 2 includes a housing 21, a rotary table 22, at least one crushing roller 23, and a motor 24. The housing 21 of the vertical roller mill 2 does not include a classifier.

[0017] A crushing chamber 20 in which crushing takes place is formed within the housing 21. A rotating table 22 and a crushing roller 23 are disposed within the crushing chamber 20. The rotating table 22 is configured to be rotatable about a vertical rotation axis. Rotational power of a motor 24 is transmitted to the rotating table 22 via a reduction gear mechanism 25. The peripheral surface of the crushing roller 23 is pressed against the rotating table 22 by a pressing means (not shown). When the rotating table 22 rotates, the crushing roller 23 is rotated accordingly.

[0018] A supply port 26 (or a supply chute) and an exhaust port 27 are provided at the upper part of the housing 21. Materials to be crushed are supplied to the upper surface of the rotary table 22 through the supply port 26. Finely pulverized material produced by the pulverization of the materials to be crushed is discharged from the exhaust port 27 on the air current.

[0019] A discharge outlet 28 (discharge chute) is provided below the turntable 22. From the discharge outlet 28, the crushed material that has spilled over the outer periphery of the turntable 22 is discharged to the outside of the vertical roller mill 2. In addition, a hot air outlet 29 is provided around the outer periphery of the turntable 22. The hot air outlet 29 is connected to a hot air inlet 29a through which hot air is supplied, and hot air is blown upward from the hot air outlet 29 into the grinding chamber 20.

[0020] In the vertical roller mill 2 configured as described above, the inside of the crushing chamber 20, including the turntable 22 and the crushing rollers 23, is preheated by hot air blown up from the hot air outlet 29, and then the material to be crushed is supplied onto the rotating turntable 22. The material to be crushed is caught between the turntable 22 and the crushing rollers 23, where it is crushed and crushed. The crushed material (i.e., the crushed material) spills over the periphery of the turntable 22 and is discharged outside the machine through the discharge port 28. Furthermore, the finely crushed material produced by the crushing is blown up by the blown up hot air, and is carried by the air current and discharged from the exhaust port 27.

[0021] [Ground material circulation system 3] The pulverized material circulation system 3 is configured to separate the highly fine powder that will become the pulverized product from the pulverized material discharged from the vertical roller mill 2, and to return the pulverized product from which the highly fine powder has been separated to the vertical roller mill 2. The highly fine powder separated in the pulverized material circulation system 3 is recovered as the pulverized product.

[0022] The pulverized material circulation system 3 is provided with a pulverized material circulation path 30 that returns the pulverized material discharged from the discharge port 28 of the vertical roller mill 2 to the supply port 26 of the vertical roller mill 2 via classifiers 7, 8. The pulverized material circulation path 30 according to this embodiment is provided with two-stage classifiers 7, 8, a primary classifier 8 and a secondary classifier 7. The pulverized material circulation path 30 is made up of the vertical roller mill 2, a bucket elevator 31, the primary classifier 8, and the secondary classifier 7, as well as conveying sections 32-35 that connect these in a circular fashion. The conveying sections 32-35 may be formed by piping, conveyors, or the like.

[0023] The discharge outlet 28 of the vertical roller mill 2 is connected to the first inlet 31a of the bucket elevator 31 via the conveying section 34. In this embodiment, since the raw material inlet 82 of the primary classifier 8 is located higher than the discharge outlet 28 of the vertical roller mill 2, the bucket elevator 31 is provided in the pulverized material circulation path 30. However, a vertical conveyor or other vertical conveyor may be used instead of the bucket elevator 31. The bucket elevator 31 has a plurality of buckets (not shown), and conveys the pulverized material fed into the buckets through the first inlet 31a and the second inlet 31b upward and discharges it from the outlet 31c. The outlet 31c of the bucket elevator 31 is connected to the raw material inlet 82 of the primary classifier 8 via the conveying section 35. The conveying section 34, the bucket elevator 31, and the conveying section 35 form a return section R that returns the pulverized material discharged from the vertical roller mill 2 to the raw material inlet 82 of the primary classifier 8.

[0024] The pulverized material sent through the return section R and the unpulverized raw material are fed into the raw material inlet 82 of the primary classifier 8. In the primary classifier 8, the mixture of the raw material and the pulverized material (hereinafter referred to as the "raw material mixture") is classified into fine powder and coarse powder. The coarse powder is sent as the pulverized material to the supply port 26 of the vertical roller mill 2 through the conveying section 32 connected to the raw material outlet 83 of the primary classifier 8. The fine powder flows into the secondary classifier 7 accompanied by the carrier gas passing through the primary classifier 8. In the secondary classifier 7, the fine powder accompanied by the carrier gas is classified into fine powder and the remaining powder and granular material. In other words, in the secondary classifier 7, the fine powder is separated from the fine powder accompanied by the carrier gas. The fine powder is discharged from the gas outlet 77 of the secondary classifier 7 accompanied by the carrier gas and collected by the collector 6. The remaining powder (ie, fine powder from which the fine powder has been removed) is sent as material to be ground to the supply port 26 of the vertical roller mill 2 through the conveying section 33 connected to the raw material outlet 78 of the secondary classifier 7 .

[0025] In the above, "highly fine powder" is defined as an aggregate of particles in a particle size range determined according to the particle size of the crushed material. Also, "fine powder" is defined as an aggregate of particles in a particle size range equal to or larger than the particle size range of the high-fine powder. In other words, the particle size of the high-fine powder is equal to or smaller than that of the fine powder, and the fine powder classified by the primary classifier 8 includes the high-fine powder. "Coarse powder" is defined as an aggregate of particles larger than the particle size range of the fine powder.

[0026] [Gas Circulation System 4] The gas circulation system 4 is provided with a mill exhaust gas circulation path 40 and a carrier gas circulation path 50. The mill exhaust gas circulation path 40 and the carrier gas circulation path 50 are connected by a connection part 53.

[0027] The mill exhaust circulation path 40 is formed so as to return the gas (hereinafter, "mill exhaust") discharged from the exhaust port 27 of the vertical roller mill 2 to the hot air inlet 29a. The mill exhaust circulation path 40 is composed of the vertical roller mill 2, a dust collector 41, a second fan 42, and air supply units 40a, 40b that connect these in a circular manner. The air supply units 40a, 40b may be composed of piping, valves, etc.

[0028] The exhaust port 27 of the vertical roller mill 2 is connected to the inlet of the dust collector 41 via the air supply section 40a. The exhaust port of the dust collector 41 and the hot air inlet 29a of the vertical roller mill 2 are connected by the air supply section 40b. A second fan 42 is provided in the air supply section 40b. The powder and granular material outlet of the dust collector 41 and the second inlet 31b of the bucket elevator 31 are connected by the conveying section 38.

[0029] The mill exhaust air coming out of the exhaust port 27 of the vertical roller mill 2 flows into the dust collector 41 by the attraction of the second fan 42. In the dust collector 41, fine pulverized material accompanying the mill exhaust air is separated from the mill exhaust air. The fine pulverized material separated in the dust collector 41 is sent to the second inlet 31b of the bucket elevator 31 through the conveying section 38 and merges with the flow of pulverized material in the pulverized material circulation system 3. In this embodiment, a cyclone type dust collector that utilizes the suction action of the second fan 42 is used as the dust collector 41. However, the dust collector 41 is not limited to this embodiment as long as it can separate fine pulverized material from the mill exhaust air.

[0030] A hot gas generator 43 is connected to the air supply section 40b of the mill exhaust circulation passage 40. As a result, a first hot gas supply section F1 is formed between the hot gas generator 43 and the hot air inlet 29a of the vertical roller mill 2, which supplies hot gas from the hot gas generator 43 to the hot air inlet 29a. The temperature and flow rate of the hot gas supplied from the hot gas generator 43 to the vertical roller mill 2 may be adjusted according to the temperature inside the vertical roller mill 2. The hot gas generator 43 is, for example, a hot air generating furnace that generates hot air of a desired temperature. However, the hot gas generator 43 is not limited to a hot air generating furnace, and for example, when a high-temperature gas source such as a kiln (cement firing furnace) exists around the vertical roller mill 2, the high-temperature gas source may be used as the hot gas generator 43. The hot gas supplied from the hot gas generator 43 to the mill exhaust gas circulation passage 40 is sent to the hot air inlet 29a of the vertical roller mill 2 together with the mill exhaust gas.

[0031] The carrier gas circulation path 50 is formed to circulate the carrier gas to the primary classifier 8, the secondary classifier 7, and the collector 6. The carrier gas circulation path 50 is composed of the primary classifier 8, the secondary classifier 7, the collector 6, and the first fan 66, as well as air supply units 51, 64, 65, and 52 that connect these in a circular manner. The air supply units 51, 64, 65, and 52 may be composed of pipes, valves, and the like.

[0032] An air supply unit 51 is connected to a gas inlet 81 of the primary classifier 8. A gas outlet 77 of the secondary classifier 7 and an inlet of the collector 6 are connected by an air supply unit 64. An air supply unit 65 connected to an exhaust port of the collector 6 is connected to the air supply unit 51 by an air supply unit 52. This allows a part or all of the carrier gas discharged from the collector 6 to be returned to the gas inlet 81 of the primary classifier 8 through the air supply units 65, 52, 51. A flow rate adjustment valve 56 is provided in the air supply unit 65 (or the air supply unit 52). The flow rate adjustment valve 56 allows the flow rate of the carrier gas returned to the primary classifier 8 to be adjusted.

[0033] The connection part 53 connects a portion of the mill exhaust gas circulation path 40 downstream of the second fan 42 and upstream of the hot air inlet 29a of the vertical roller mill 2 to a portion of the carrier gas circulation path 50 downstream of the first fan 66 and upstream of the gas inlet 81 of the primary classifier 8. The connection part 53 is provided with a flow rate control valve 55. The flow rate control valve 55 adjusts the amount of mill exhaust gas flowing from the mill exhaust gas circulation path 40 through the connection part 53 into the air supply section 51 of the carrier gas circulation path 50, thereby adjusting the amount of mill exhaust gas circulated.

[0034] Between the hot gas generator 43 and the gas inlet 81 of the primary classifier 8, a second hot gas supply section F2 is provided which supplies hot gas directly from the hot gas generator 43 (i.e., without passing through the vertical roller mill 2) to the gas inlet 81 of the primary classifier 8. The second hot gas supply section F2 is mainly formed of the air supply section 51. In this way, the carrier gas flowing into the gas inlet 81 of the primary classifier 8 is a mixture of the hot gas supplied from the hot gas generator 43, the carrier gas circulating through the carrier gas circulation path 50, and the mill exhaust gas flowing from the mill exhaust gas circulation path 40 into the carrier gas circulation path 50.

[0035] In order to efficiently heat and dry the raw materials, it is desirable for the relationship T1>T2>T3>T4>T5 to hold, where T1 is the temperature of the gas flowing into the hot air inlet 29a through the air supply section 40b, T2 is the temperature of the gas discharged from the vertical roller mill 2 to the air supply section 40a, T3 is the temperature of the gas flowing through the connection section 53, T4 is the temperature of the gas flowing into the gas inlet 81 of the primary classifier 8 through the air supply section 51, and T5 is the temperature of the gas discharged from the collector 6 to the air supply section 52.

[0036] Here, a detailed description will be given of the configurations of the primary classifier 8 and the secondary classifier 7. Fig. 2 is a partially enlarged view of Fig. 1 showing the configurations of the primary classifier 8 and the secondary classifier 7.

[0037] [Primary classifier 8] As shown in FIG. 2, the primary classifier 8 is a static classifier (airflow type classifier) ​​that does not require power. The primary classifier 8 includes a casing 80 having a gas inlet 81, a raw material inlet 82, and a gas outlet 84 formed at the top and a raw material outlet 83 formed at the bottom. A carrier gas flow path that flows in a V-shape from the gas inlet 81 to the gas outlet 84 is formed inside the casing 80. A first baffle plate row 89a and a second baffle plate row 89b are provided in this carrier gas flow path. Each of the baffle plate rows 89a and 89b is formed of a plurality of baffle plates arranged in the vertical direction. The raw material inlet 82 opens upward between the first baffle plate row 89a and the second baffle plate row 89b.

[0038] In the primary classifier 8 having the above-mentioned configuration, carrier gas is introduced into the casing 80 from the gas inlet 81, and the raw material and the pulverized material carried through the pulverized material circulation path 30 are fed into the raw material inlet 82 of the primary classifier 8. The raw material mixture falls between the first baffle plate row 89a and the second baffle plate row 89b due to gravity. The carrier gas passes through the first baffle plate row 89a and the second baffle plate row 89b in this order, and flows out from the gas outlet 84.

[0039] The carrier gas flowing into the gas inlet 81 of the primary classifier 8 contains hot gas supplied directly from the hot gas generator 43. The temperature of the carrier gas flowing into the gas inlet 81 (inlet temperature) is higher than the temperature of the raw material and the mixture of the raw material and the pulverized material (raw material mixture). As a result, the raw material mixture is heated by heat exchange with the carrier gas. For reference, as an example, when the moisture content of the raw material mixture is about 2 mass%, the temperature of the raw material input into the raw material inlet 82 of the primary classifier 8 is about 30°C, and the temperature of the pulverized material input into the raw material inlet 82 is about 73°C, the temperature of the carrier gas flowing into the gas inlet 81 of the primary classifier 8 (inlet temperature) is about 85°C.

[0040] The flow path of the carrier gas and the flow of the raw material mixture intersect. The raw material mixture is heated by heat exchange with the carrier gas. In addition, the aggregated particles of the raw material mixture moving through the chute 85 are broken down and dispersed by the carrier gas. The fine powder contained in the raw material mixture moving through the casing 80 is transported by the airflow of the carrier gas and separated from the raw material mixture, and the fine powder is carried by the carrier gas to the gas outlet 85. The raw material mixture from which the fine powder has been removed in this manner (i.e., the coarse powder) is discharged from the raw material outlet 83 and sent to the supply port 26 of the vertical roller mill 2 by the conveying section 32.

[0041] In the above-mentioned grinding system 1, since the raw materials are fed directly into the primary classifier 8, wear of the components of the primary classifier 8 (e.g., each baffle plate row 89a, 89b) is expected. However, since the primary classifier 8 is a static classifier with no moving parts, maintenance can be easily performed.

[0042] [Secondary classifier 7] The secondary classifier 7 is a dynamic classifier equipped with a motor 73 as a power source. The secondary classifier 7 includes a casing 75, a chute 74 arranged in the casing 75, a classification rotor 71 arranged above the chute 74, a motor 73 that rotates and drives the classification rotor 71, and a classification vane 72 arranged around the classification rotor 71. A gas inlet 76 is provided at the bottom of the casing 75, and a gas outlet 77 is provided at the top of the casing 75. In this embodiment, the gas inlet 76 is directly connected to a gas outlet 84 of the primary classifier 8. A raw material outlet 78 is provided at the bottom of the chute 74.

[0043] The carrier gas carrying fine powder from the primary classifier 8 flows into the gas inlet 76 of the secondary classifier 7 configured as above. Raw materials having a relatively large particle size fed into the system are separated as coarse powder by the primary classifier 8 and do not flow into the secondary classifier 7. This allows the secondary classifier 7 to obtain a stable and high classification efficiency, suppresses fluctuations in the rotational torque of the motor 73, and further suppresses wear on the classifying rotor 71.

[0044] The carrier gas flowing upward from the gas inlet 76 of the secondary classifier 7 is blown up between the casing 75 and the chute 74, and the fine powder accompanying the carrier gas is classified into high-fine powder and the remaining powder and granules by the action of the classification vane 72. The remaining powder and granules (i.e., the fine powder from which the high-fine powder has been removed) falls down the chute 74 and is discharged from the raw material outlet 78, and is sent to the supply port 26 of the vertical roller mill 2 by the conveying section 33. The high-fine powder flows out from the gas outlet 77 accompanied by the carrier gas, and flows into the collector 6 through the air sending section 64. The collector 6 collects the high-fine powder accompanying the carrier gas discharged from the secondary classifier 7 and recovers it as a crushed product. The collector 6 according to this embodiment is a bag filter, but the collector 6 is not limited to a bag filter as long as it can collect the high-fine powder accompanying the carrier gas.

[0045] As described above, the crushing system 1 according to the embodiment is as follows: a vertical roller mill 2 having a rotary table 22 arranged in a grinding chamber 20 and at least one grinding roller 23 whose peripheral surface is pressed against the rotary table 22, and configured to grind materials supplied to the rotary table 22 by biting them between the rotary table 22 and the grinding roller 23 while blowing hot air into the grinding chamber 20, discharge the ground material, and discharge fine powder particles generated by the grinding by carrying them on an air current; a primary classifier 8 configured to primarily classify the raw material into coarse powder and fine powder while heating the raw material using a carrier gas; A first conveying section 32 that conveys the coarse powder discharged from the primary classifier 8 to the vertical roller mill 2 as a crushed material; A return section R is provided for conveying the pulverized material discharged from the vertical roller mill 2 to the primary classifier 8 so as to mix the pulverized material with the raw material to be primarily classified. The temperature of the carrier gas is higher than that of the raw material and the mixture of the raw material and the pulverized material.

[0046] In addition, the pulverization method according to the above embodiment includes the steps of: The raw material is heated using a carrier gas while being primarily classified into coarse and fine powders. Supplying the coarse powder to a vertical roller mill 2 for pulverization; and Mixing the pulverized material discharged from the vertical roller mill 2 with the raw material to be primarily classified; The temperature of the carrier gas is higher than that of the raw material and the mixture of the raw material and the pulverized material.

[0047] In the above-mentioned grinding method and grinding system 1, the raw material mixture in which the raw material and the returned ground material are mixed and dispersed is roughly classified and heated in the primary classifier 8. The material to be ground, the particle size and temperature of which have been adjusted in this manner by the primary classification, is supplied to the vertical roller mill 2. This reduces temperature unevenness in the material to be ground that is caught in the grinding roller 23, and makes it possible to uniformly heat the material to a suitable grinding temperature. By making the temperature of the material to be ground that is caught in the grinding roller 23 uniform and stable, stable grinding can be maintained, and the grinding efficiency of the vertical roller mill 2 can be improved. Furthermore, by maintaining good grinding in the vertical roller mill 2, the operational stability of the grinding system 1 can be improved.

[0048] Furthermore, in the above-described crushing method and crushing system 1, the amount of heat required to raise the temperature to the same level can be reduced compared to when the raw material and the crushed material returned to the primary classifier 8 are classified and heated separately, thereby reducing fuel costs.

[0049] Furthermore, in the above-mentioned crushing method and crushing system 1, since the raw material mixture of the raw material and the returned crushed material is preheated in the primary classification, it is possible to heat the material to be crushed that is caught in the crushing roller 23 to a suitable crushing temperature even if the raw material is at a lower temperature than the returned crushed material (e.g., raw material at room temperature). Therefore, the above-mentioned crushing method and crushing system 1 are suitable for crushing raw materials at a lower temperature than the returned crushed material (e.g., raw material at room temperature). In this specification, "raw material at room temperature" refers to raw material stored in a state exposed to the outside air, and may include raw material at a temperature ranging from below freezing to about 50°C depending on the outside air temperature.

[0050] The grinding system 1 according to the embodiment further includes a first hot gas supplying section F1 that supplies the hot gas sent from the hot gas source as hot air to the vertical roller mill 2, and a second hot gas supplying section F2 that supplies the hot gas sent from the hot gas source as carrier gas to the primary classifier 8 without passing through the vertical roller mill 2. The grinding system 1 according to the embodiment includes a hot gas generator 43 as a hot gas source, but the hot gas source is not limited to the hot gas generator 43 and may be a facility (e.g., a combustion furnace) adjacent to the grinding system 1, and the exhaust gas from that facility may be used as the hot gas.

[0051] In this way, the hot gas sent from the hot gas source is sent to both the vertical roller mill 2 and the primary classifier 8. Therefore, it is possible to introduce a carrier gas at a higher temperature than the mill exhaust gas of the vertical roller mill 2 into the primary classifier 8. Furthermore, since the flow rate of the hot air of the vertical roller mill 2 and the flow rate of the carrier gas of the primary classifier 8 can be controlled independently, the flow rate of the hot air and the flow rate of the carrier gas can be set to suitable values ​​without being influenced by each other. This improves the operational stability of the grinding system 1.

[0052] The grinding system 1 according to the above embodiment further includes a secondary classifier 7 for secondarily classifying the fine powder classified by the primary classifier 8 into fine powder having the same or smaller particle size as the fine powder and the remaining powder and granular material, a collector 6 for collecting the fine powder discharged from the secondary classifier 7, and a second conveying section 33 for conveying the remaining powder and granular material discharged from the secondary classifier 7 to the vertical roller mill 2 as material to be ground. A carrier gas circulation path 50 may be formed to circulate the carrier gas through the primary classifier 8, the secondary classifier 7, and the collector 6.

[0053] Similarly, the grinding method according to the above embodiment further includes secondary classification of the fine powder into fine powder having the same or smaller particle size as the fine powder and remaining powder and granular material, supplying the remaining powder and granular material to a vertical roller mill 2 to grind it together with the coarse powder, and recovering the fine powder as a ground product.

[0054] In general, a dynamic classifier including a rotating part is used to obtain precisely classified powder to be the crushed product. According to the crushing method and crushing system 1 described above, the fine powder from which the coarse powder has been removed in the primary classification is subjected to secondary classification in the secondary classifier 7, so that even when a dynamic classifier is used as the secondary classifier 7, wear of the rotating part (e.g., the classifying rotor 71) can be suppressed. Furthermore, since the fine powder from which the coarse powder has been removed in the primary classification is subjected to secondary classification in the secondary classifier 7, good classification performance can be obtained in the secondary classifier 7, and a crushed product with high accuracy can be obtained.

[0055] Although the preferred embodiment of the present invention has been described above, the present invention also includes modifications of the specific structure and / or details of the above embodiment without departing from the spirit of the present invention. The above configuration can be modified, for example, as follows.

[0056] For example, the grinding system 1 according to the above embodiment is suitable for grinding raw materials (e.g., raw materials at room temperature) that have a relatively large temperature difference from the ground material returned from the vertical roller mill 2, but the temperature of the raw materials is not limited to this.

[0057] Also, for example, in the grinding system 1 according to the above embodiment, hot gas is sent from one hot gas generator 43 to both the vertical roller mill 2 and the primary classifier 8, but a hot gas generator 43 may be provided for each of the vertical roller mill 2 and the primary classifier 8. [Explanation of symbols]

[0058] 1: Grinding system 2: Vertical roller mill 3: Grinding material circulation system 30: Crushed material circulation path 4: Gas circulation system 40: Mill exhaust circulation path 50: Carrier gas circulation path 6: Collection machine 7:Secondary classifier 8:Primary classifier 20: Crushing chamber 22: Rotating table 23: Crushing roller 32~38: Transport section 43: Hot gas generator 50: Carrier gas circulation path R: Return section F1: First hot gas supply section F2: Second hot gas supply section

Claims

1. a vertical roller mill having a rotary table arranged in a grinding chamber and at least one grinding roller whose peripheral surface is pressed against the rotary table, and configured to grind materials supplied to the rotary table by being caught between the rotary table and the grinding roller while blowing hot air into the grinding chamber, discharge the ground material, and discharge fine powder particles generated by the grinding by carrying them on an air current; a primary classifier configured to primarily classify a raw material into coarse powder and fine powder while heating the raw material using a carrier gas; a first conveying unit that conveys the coarse powder discharged from the primary classifier to the vertical roller mill as the material to be crushed; A return unit that conveys the pulverized material discharged from the vertical roller mill to the primary classifier so as to mix the pulverized material with the raw material to be primarily classified; a first hot gas supplying section that supplies hot gas from a hot gas source to the vertical roller mill as the hot air; a second hot gas supply unit that supplies hot gas from the hot gas source to the primary classifier as the carrier gas without passing through the vertical roller mill; The temperature of the carrier gas is higher than that of the raw material and the mixture of the raw material and the pulverized material. Grinding system.

2. a secondary classifier for secondarily classifying the fine powder into fine powder having a particle size equal to or smaller than that of the fine powder and the remaining powder and granular material; A collector that collects the fine powder discharged from the secondary classifier; A second conveying unit that conveys the remaining powder discharged from the secondary classifier to the vertical roller mill as the crushed material. The grinding system of claim 1 .

3. A carrier gas circulation path through which the carrier gas circulates through the primary classifier, the secondary classifier, and the collector. The grinding system according to claim 2.

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