MILLING PLANT

Description

[0001] The invention relates to a grinding plant for crushing material to be ground, comprising at least one agitator ball mill and a separation unit.

[0002] Examples of materials used for grinding include limestone, dolomite, ores, clinker, fly ash, slag, and other cement clinker substitutes. A grinding plant for such materials is known from DE 10 2014 015 549 A1. To reduce the clinker factor in the cement industry and thus lower CO₂ emissions, efforts are being made to use cement clinker substitutes (such as calcined clays or slag) or more reactive clinkers for cement products. One way to increase the reactivity of clinker and cement clinker substitutes is to finely grind these materials. This fine grinding is implemented industrially, for example, using a dry-operated stirred ball mill.

[0003] Cement clinker substitutes often contain components that are difficult to grind. These components cannot be efficiently milled using conventional vertical roller mills and / or ball mills because the difficult-to-grind portion of the material accumulates in the mill's circulation and is thus primarily carried back to the mill via the classifier grit. This, in turn, leads to the more easily ground material being over-milled. As a result, the specific energy input increases and the throughput of the plant decreases. A further challenge is that the final product must not only have the desired fineness but also a specified particle size distribution.

[0004] A multi-stage grinding cycle is known from US 2020 / 261920 A1.

[0005] From EP 3 665 133 B1, a process and a plant for the production of cement are known, wherein cement feedstock is ground in at least one ball mill and subsequently separated into fines and coarses in a classifier, the coarses being fed back into the ball mill. The fines from the classifier are then divided by quantity into a first and a second batch, the first batch forming a first cement, while the second batch of fines is fed to a dry-operated agitated ball mill for further grinding, and the resulting second cement is optionally mixed with the first cement or used as a separate product.

[0006] From CN 113 976 277 B a vertical mill with external circulation for cement, combined with a high-performance grinding process system is known.

[0007] The invention is based on the objective of making the operation of the grinding plant with a stirred ball mill more efficient.

[0008] According to the invention, this problem is solved by a grinding system according to claim 1. Further embodiments of the invention are the subject of the dependent claims.

[0009] The grinding system according to the invention comprises a stirred ball mill with an inlet for material to be ground and an outlet for ground material, as well as a first separation unit arranged separately from the stirred ball mill. The first separation unit is connected to the outlet for ground material and has an outlet for a first fine product and an outlet for a first coarse product. Furthermore, a second separation unit is provided, arranged separately from the stirred ball mill, which is connected directly or indirectly to the outlet for ground material of the stirred ball mill and has an outlet for a second fine product and an outlet for a second coarse product.

[0010] According to the invention, the pulverized material can be fed onto two different or two identical separation units connected in parallel or in series. In a parallel connection, the product flow can be variably divided, for example 50 / 50, 80 / 20, etc., so that the load on each individual separation unit can be specifically adjusted. According to the invention, more than two separation units can also be used.

[0011] Furthermore, the two separation units can be variably adjusted, allowing the production of fines with different particle size distributions. These fines can then be selectively mixed to obtain a finished product with a predetermined fineness, particle size distribution, and distribution width. This allows for targeted control over the subsequent quality properties of the cement (such as water demand, slump, etc.).

[0012] Furthermore, independently adjustable separation units make it possible to selectively remove components that are difficult to grind. This can be achieved, for example, by setting a relatively coarse and broad particle size distribution on one of the separation units, allowing coarse, difficult-to-grind particles to leave the grinding circuit. To achieve the desired target fineness, the remaining separation unit(s) are adjusted accordingly to a finer setting.

[0013] The agitated ball mill used preferably has an agitator rotating about an axis, with the inlet for the material to be ground being located at one axial end of the agitator and the outlet for the ground material at the opposite axial end. Furthermore, the inlet of the agitated ball mill can be configured for feeding the material to be ground with or without air, while the outlet of the agitated ball mill has a pneumatic discharge opening for the pneumatic discharge of a first portion of the ground material together with air, and the outlet also provides a gravity discharge opening for the discharge of a second portion of the ground material by gravity, with the first separation unit being connectable to the pneumatic discharge opening and the second separation unit to the gravity discharge opening.Furthermore, the first and second separation units can each have a coarse material outlet that connects to the inlet of the stirred ball mill and / or another process unit (e.g., a peripheral grinding unit in a different grinding circuit; a mixer; a hopper / silo to utilize material for other products). It is also possible to feed one or both coarse materials (completely or partially) to another process step (e.g., storage, mixing, grinding in a different grinding circuit, thermal processes).

[0014] The first and second separation units can be formed, in particular, by sieves, static classifiers, electrostatic sifters, or dynamic classifiers. According to the invention, however, airflow classifiers, especially cross-flow rotary basket classifiers, are used for both separation units. These are particularly efficient for medium particle sizes in the range of 0.5 µm to 30 µm. The separation limit of this type of classifier is essentially determined by the centrifugal acceleration at the outer rotor diameter. Therefore, very high centrifugal accelerations are required to achieve very fine products (medium particle size < 10 µm, possibly < 5–7 µm). Furthermore, higher peripheral speeds are required for a constant centrifugal acceleration with increasing rotor diameter (aZF = u2 / rrotor). Due to this relationship and design constraints, classifiers for fine grinding should not exceed a certain size.Since preferably at least two air classifiers are provided, the grinding plant can be implemented with correspondingly higher throughputs. Furthermore, if the air classifiers are operated independently of each other, for example by adjusting their airflow rates independently, both types of fines produced can be specifically controlled.

[0015] If the separation units are designed as airflow classifiers, a first separator is connected to the first fines outlet of the first separation unit to separate the first fines from the classifying air, and a second separator is connected to the second fines outlet of the second separation unit to separate the second fines from the classifying air. In this way, two different types of fines can be produced.

[0016] The two resulting fines can be fed into separate or a shared fines silo. Furthermore, it may be advantageous to feed one or both fines into another processing unit (e.g., a separate milling unit).

[0017] In a further embodiment of the invention, a mixing device is provided for mixing the first fine material with the second fine material. This allows a finished product with a desired particle size distribution to be specifically produced.

[0018] Further embodiments of the invention are explained with reference to the following description of some exemplary embodiments and the drawing.

[0019] The drawing shows Fig. 1 a schematic representation of a grinding plant according to the invention according to a first embodiment, Fig. 2 a schematic representation of a grinding plant according to the invention according to a second embodiment, Fig. 3 a schematic representation of a stirred ball mill, Fig. 4 a schematic representation of a grinding plant according to the invention according to a third embodiment, Fig. 5 a schematic representation of a grinding plant according to the invention according to a fourth embodiment, Fig. 6 a schematic representation of a grinding plant according to the invention according to a fifth embodiment and Fig. 7 a schematic representation of a grinding plant according to the invention according to a sixth embodiment.

[0020] The in Fig.1 The depicted grinding plant comprises a stirred ball mill 1, a first separation unit 2 designed as an air classifier, and a second separation unit 3 also designed as an air classifier. The stirred ball mill 1 has an inlet 1.1 for material to be ground 4 and an outlet 1.2 for ground material 4'. The material to be ground 4 consists of one or more components 4.1, 4.2 held in storage silos 5, 6, as well as recycled coarse material, and is fed to the inlet 1.1 of the stirred ball mill 1 via at least one conveying element 7.

[0021] The agitated ball mill 1 used has an agitator 1.3 rotating about an axis, with the inlet 1.1 for the material 4 to be ground being located at one axial end of the agitator 1.3 and the outlet 1.2 for the ground material 4' being located at the opposite axial end of the agitator 1.3. Furthermore, the inlet 1.1 of the agitated ball mill 1 can be configured to feed the material 4 to be ground with or without conveying air. The grinding action is carried out by the agitator 1.3 in conjunction with grinding balls 1.4 within the grinding chamber 1.5. A separating device 1.6 is provided at the end of the grinding chamber 1.5 facing the outlet, which allows the sufficiently ground material 4' to pass through and retains the grinding balls 1.4 in the grinding chamber 1.5. The crushed material 4' is conveyed to the outlet 1 via a conveying device 1.7, for example a screw conveyor.2, from where it is transported either pneumatically and / or mechanically to the two separation units 2, 3.

[0022] In the first embodiment, the material 4' ground in the stirred ball mill 1 is divided into two partial streams 4.1' and 4.2', with one partial stream 4.1' being fed to the first separation unit 2 and the second partial stream 4.2' to the second separation unit 3. Both separation units 2, 3 are thus in direct communication with the outlet 1.2 of the stirred ball mill 1.

[0023] The first separation unit 2 has an outlet 2.1 for a first fines 8 and an outlet 2.2 for a first coarses 9. Similarly, the second separation unit 3 has an outlet 3.1 for a second fines 10 and an outlet 3.2 for a second coarses 11. While the two coarses 9 and 11 are conveyed back to the inlet 1.1 of the agitator ball mill for further comminution, the two fines 8 and 10, together with the classifying air, enter a separator 12 or 13, where the fines 8 and 10 are separated from the classifying air. The adjustment of the sight air volume flow of the two separation units 2, 3 is effected by a fan 14, 15 downstream of the respective separator 12, 13. In principle, it is also conceivable that only one common fan is provided, whereby, if necessary, the volume flow control of the sight air in the two separation units 2, 3 can be effected, for example, by dampers.

[0024] The maximum size of an air classifier for the desired fineness, particularly < 6 µm, is limited, whereas the stirred ball mill 1 can certainly be designed for higher throughputs. By providing two separation units 2, 3 and thus being able to divide the ground material 4' between the two units, a grinding plant with higher throughputs can be realized. Furthermore, it is possible to produce two different fine materials 8, 10, which can be used individually or mixed together.

[0025] In the following descriptions of exemplary embodiments, the same reference numerals are used for identical components.

[0026] While the two separating units 2, 3 of the first embodiment are arranged parallel to each other, shows Fig. 2 A second embodiment with a series connection of the two separation units 2, 3. Here, all the material 4' ground in the stirred ball mill 1 is fed to the first separation unit 2, which is again designed as an air classifier. There, in combination with the separator 12, the first fines 8 are separated. All the coarse material 9 from the first separation unit 2 is fed to the second separation unit 3, which, in combination with the separator 13, produces the second fines 10. The coarse material 11 from the second separation unit 3 is returned to the inlet 1.1 of the stirred ball mill 1 and fed in together with the freshly ground material from the storage silos 5, 6.

[0027] This grinding system efficiently removes fine particles from the ground material (4') through double screening, thus largely preventing over-grinding. Furthermore, different materials suitable for grinding can be selectively removed. The system's circulation rate can also be optimized for energy-efficient operation.

[0028] The embodiments described below ( Fig. 4 bis 7 The stirred ball mill 1 used is in Fig. 3 depicted and differs only in the design of outlet 1.2 from that shown in the Fig. 1 and 2 agitated ball mill 1 is used. However, these embodiments could in principle also be carried out with an agitated ball mill 1 according to Fig. 1 be carried out.

[0029] In all embodiments, it is also possible to discharge or recirculate crushed material in a defined ratio.

[0030] The outlet 1.2 has a discharge housing 1.2.1 with a pneumatic discharge opening 1.2.2 for the pneumatic discharge of a first partial stream 4.1' of the comminuted material 4' together with air 16 introduced either into the discharge housing 1.2.1 or supplied via the inlet 1.1 of the stirred ball mill. Furthermore, a gravity discharge opening 1.2.3 is provided for the discharge of a second partial stream 4.2' of the comminuted material 4' by gravity. Thus, a pre-classification of the comminuted material 4' takes place in the discharge housing 1.2.1, such that the pneumatically discharged partial stream 4.1' contains a finer component and the gravity-discharged partial stream 4.2' contains a coarser component. This has the advantage that the two separation units 2, 3 can be adjusted in a more targeted manner, thus enabling more efficient screening.Optimal coordination of the milled product and the two vision circuits is also possible.

[0031] The third embodiment according to Fig. 4 This essentially corresponds to the first embodiment, however, the division of the mass in the stirred ball mill 1 (according to Fig. 3 The discharge of the crushed material 4' is not quantitative, but rather occurs via pneumatic discharge for partial flow 4.1' and gravity discharge for partial flow 4.2', with partial flow 4.1' being fed to the first separation unit 2 and partial flow 4.2' to the second separation unit 3. Furthermore, a preliminary classification of the crushed material 4' takes place in the discharge housing 1.2.1 of the agitator ball mill 1. Here, too, optimal coordination of the milled product and the two classification circuits is possible.

[0032] Fig. 5 shows an optional variant of the third embodiment according to Fig. 4 , by feeding the fine material 10 from the second separation unit 3, either wholly or partially, to the first separation unit 2. Furthermore, only one fan 14 is used for both separation units 2 and 3. However, separate fans for each separation unit would also be conceivable.

[0033] In this grinding plant, it is particularly suitable to design the first separation unit 2 as an ultra-fine classifier for separating a mean particle size of less than 6 µm, while the second separation unit 3 can be designed as a conventional classifier for separating a mean particle size of greater than 6 µm.

[0034] This circuit is particularly suitable for producing the largest possible quantity of fines with an average particle size of less than 6 µm. Furthermore, it allows for an optimized selection of the classifier with regard to the mill's material discharge.

[0035] The fifth embodiment according to Fig. 6 Figure 1 again shows a series connection of the two separation units 2, 3, whereby all the pulverized material 4' (partial streams 4.1' and 4.2') is fed to the first separation unit 2. Although here a stirred ball mill 1 is used according to... Fig. 3 A stirred ball mill can also be used, according to the Fig. 1 and 2 The fines 8 from the first separation unit 2 are fed wholly or partially to the second separation unit 3. The coarses 9 from the first separation unit 2 enter a third separation unit 17, which is formed, for example, by a screen or a static classifier, whereby the fines from the third separation unit 17 are also fed to the second separation unit 3, while the coarses 18 from the third separation unit 17 are discharged or, together with the coarses 11 from the second separation unit 3, are fed back into the stirred ball mill 1.

[0036] In this circuit, the second separation unit 2 is expediently designed as an ultrafine classifier for separating particles with a mean size of less than 6 µm. The first separation unit can be configured as a conventional airflow classifier or as an ultrafine classifier for separating particles with a mean size of less than 6 µm. Furthermore, more efficient loading of the ultrafine classifier is possible. The resulting intermediate products can be used for various types of cement (clinker reduction / CO₂ reduction / cements of the future).

[0037] The milling plant according to Fig. 7 essentially corresponds to the grinding plant according to Fig. 4 , wherein only a mixing device 19 is provided for mixing the first fine material 8 with the second fine material 10 to produce a finished product 20. The desired particle size distribution in the finished product 20 can be set by adjusting the mixing ratio.

[0038] With this grinding system, the particle size distribution of the finished product 20 (mixture of the two fine materials 8, 10) can be adjusted very precisely with regard to fineness, particle size distribution and distribution width, which makes it possible to influence the later quality properties of the cement (water requirement, spread, etc.).

Claims

1. Grinding plant with an agitator ball mill (1) with an inlet (1.1) for material to be ground (4) and an outlet (1.2) for ground material (4'), as well as a first separating unit (2) arranged separately from the agitator ball mill (1), which is connected to the outlet (1.2) for crushed material (4') and has an outlet (2.1) for a first fine material (8) and an outlet (2.2) for a first coarse material (9), a second separating unit (3) being provided which is arranged separately from the agitator ball mill (1), which is connected directly or indirectly to the outlet (1.2) for comminuted material (4') of the agitator ball mill (1) and has an outlet (3.1) for a second fine material (10) and an outlet (3.2) for a second coarse material (11), wherein the first separating unit (2) and the second separating unit (3) are designed as air flow separators and a first separator (12) is connected to the first fine material outlet (2.1) of the first separating unit (2) and a second separator (13) for separating the second fine material (10) from the air stream is connected to the second fine material outlet (3.1) of the second separating unit (3).

2. Grinding plant according to claim 1, wherein the agitator ball mill (1) has an agitator (1.3) rotating about an axis and the inlet (1.1) for material (4) to be ground is arranged at one axial end of the agitator (1.3) and the outlet (1.2) for ground material (4') is arranged at an opposite axial end of the agitator (1.3).

3. Grinding plant according to one of the preceding claims, wherein the inlet (1.1) of the agitator ball mill (1) is designed for feeding the material (4) to be ground, and the outlet (1.2) of the agitator ball mill has a pneumatic discharge opening (1.2.2) for the pneumatic discharge of a first partial flow (4.1') of the crushed material (4') together with air, and the outlet (1.2) further provides a gravity discharge opening (1.2.3) for discharging a second partial stream (4.2') of the crushed material (4') by means of gravity.

4. Grinding plant according to one of the preceding claims, wherein the first separating unit (2) and the second separating unit (3) each have a coarse material outlet (2.2; 3.2) which is connected to the inlet (1.1) of the agitator ball mill (1) and / or another process unit.

5. Grinding plant according to one of the preceding claims, wherein the first separating unit (2) and the second separating unit (3) are designed as air flow separators whose separating air volume flows are independently adjustable.

6. Grinding plant according to one of the preceding claims, wherein a common or two separate fine material silos are provided for the first fine material (8) and the second fine material (10).

7. Grinding plant according to one of the preceding claims, wherein at least one further process unit is provided for further processing of the first and / or second fine material (8, 10).

8. Grinding plant according to one of the preceding claims, wherein a mixing device (19) is provided for mixing the first fine material (8) with the second fine material (10) to produce a finished product (20) with an adjustable particle size distribution.

9. Grinding plant according to one of the preceding claims, wherein the first separating unit (2) and the second separating unit (3) are arranged in a series connection or a parallel connection.