WO2015059591A1

WO2015059591A1 - Milling plant

Info

Publication number: WO2015059591A1
Application number: PCT/IB2014/064954
Authority: WO
Inventors: Mario DAZZI
Original assignee: Dazzi Mario
Priority date: 2013-10-21
Filing date: 2014-09-30
Publication date: 2015-04-30
Also published as: ITMO20130299A1; EP3060344A1

Abstract

A wet milling plant (1), in particular for milling clays and hard materials, comprises a plurality of continuous mills (4-4n), supplied with a water suspension (17) of materials to be milled, each continuous mill (4-4n) comprising a cylindrical body (23) inside which a respective milling chamber (5-5n) is defined, said cylindrical body (23) being rotatable around a longitudinal rotation axis (A), said milling chamber (5-5n) being provided with an inlet conduit (26) and with an outlet conduit (27), the outlet conduit (27) of a continuous mill (4-4n) of said plurality of continuous mills being able to be connected via a connecting conduit (10) to the inlet conduit (26) of another continuous mill (4-4n); said water suspension (17) is moved through said plurality of continuous mills (4-4n) via a single pump (8) the delivery of which is connected to the inlet opening of the first continuous mill (4a) of said plurality of continuous mills (4a-4n).

Description

Milling plant

The present invention relates to a wet milling plant, in particular a plant for milling clays and hard materials, such as, for example, feldspar, to produce ceramic products.

In the prior art, two milling processes are known, i.e. a discontinuous milling process and a continuous milling process.

In discontinuous milling, so-called discontinuous mills are used that comprise a rotating drum, inside which a milling chamber is defined. The rotating drum is provided with an upper opening through which water, the materials to be milled and the milling bodies generally consisting of alumina spheres are delivered into the milling chamber, where the first load is made with spheres with a diameter varying between 30 mm and 60 mm. The material to be milled varies in size, for example up to 15-20 cm for clays and up to 8 mm for hard materials. The rotating drum is further provided with a lower opening from which the milled material in a water suspension, the so-called slip, is extracted at the end of the milling process.

After the water, the materials to be milled and the milling bodies were loaded in the milling chamber, the drum is rotated at a preset speed according to the diameter thereof and kept rotating at a constant speed for a certain number of hours until the desired degree of milling fineness is reached, i.e. the desired granulometry of the materials subjected to milling. At the end of the cycle, the drum stops automatically in the discharge position and through gravity the slip is discharged into proper storage tanks through the lower opening of the drum. When emptying is complete, a subsequent operation of loading the materials to be milled and water and a subsequent milling cycle can be commenced.

The complete milling cycle consists of a first step of kneading the clays and of a second refining step. In fact, until the clays are kneaded and dissolved in water the step of crushing the hard materials does not begin because the latter, in the initial step, tend to be incorporated into the clays. Only in the second step of the cycle the milling and refining operation gradually start, which continues until the desired granulometry of the materials subjected to milling is obtained.

About 35% of the volume of the drum is normally loaded with the milling bodies consisting of alumina spheres and about 50% of the volume of the drum is loaded with the material to be milled and water. The drum is lined internally with wear-resistant rubber or with allumina. The milling bodies, as already said, have variable dimensions, generally milling bodies are used of three different diameters varying from a minimum of 30 mm to a maximum of 60 mm. This is because in the initial kneading step heavy milling bodies of a large diameter are required and in the final refining step milling bodies of small diameter with a great number of contact points between them are required. In order to enable kneading of the clays to be performed, it is necessary for the mill to be rotated at high peripheral speed (about 120 m/min) so that large-diameter spheres can then fall from top to bottom. This means that total milling efficiency is very low because not all the milling bodies are effective over the entire cycle because in the first step only the milling bodies of larger diameter would be required and in the final step only the milling bodies of smaller diameter. The energy consumption necessary to keep all the milling bodies rotating and moved over the entire cycle is thus significant and not optimised inasmuch as the centre of gravity of the mass is shifted very far from the centre of rotation and high torque is necessary for rotation.

In continuous milling a single mill of large dimensions is used that has one or more internal chambers or a plurality of mills of reduced dimensions, each of which consists of a rotating drum inside which a milling chamber is defined. The drum is provided with an axial inlet opening of large diameter, about 30 cm, through which there can be delivered into the milling chamber water, the materials to be milled via the mechanical devices and the supplementary milling bodies, and with an outlet opening of the same dimensions as the inlet opening, which is also axial, through which the material milled in water suspension, the so-called slip, can be discharged.

In each mill a milling step is conducted, starting with a first coarse milling step, in which the clays are kneaded and pass into a water suspension, and subsequent steps in which the granulometry of the clays and of the other materials subjected to milling is progressively reduced to a desired value.

The slip can be transferred from one mill to the next by gravity, as disclosed, for example, in Italian patent application MO2008A000244.

Alternatively, the slip can be extracted from a mill and be poured into a storage tank from which, by a pump, it can be delivered to the next mill, as disclosed, for example, in Italian patent 1380382, or can be conveyed from one mill to the next by a conveying device, for example a screw feed device, arranged in a connecting conduit between the two mills, as disclosed, for example, in Italian patent 1361628. In the milling plants mentioned above, milling bodies of the same dimensions can be used in each mill, inasmuch as each mill does not have to run the entire milling cycle of the materials but only one step of said cycle.

Filling each mill is different from filling of the discontinuous mills, i.e. the milling chamber is filled to about 35% with the milling bodies. The level of materials to be milled and of the water (slip) is about the same level as that of the milling bodies inasmuch as everything must be at a lower level than the axial inlet opening in order not to obstruct the supply of materials to be milled.

The continuous milling plants mentioned above are inconvenient or complicated in transferring the slip between one mill and the next, sometimes requiring a rigid arrangement of the mills that does not enable the layout of the plant to be optimised. Further, the aforesaid plants have unsatisfactory energy efficiency because the centre of gravity of the mass is shifted far from the centre of rotation and needs great mechanical torque for rotation.

As the internal level of the slip is at a lower level than the axial discharge holes, the bottoms of the mills are assembled with rubber heads provided with peripheral pockets that collect the slip in the bottom part to then discharge the slip during rotation towards the axial outlet hole. Said pockets have calibrated holes that determine the flowrate of the mill. Obviously, both in the continuous and discontinuous mills, the worn milling bodies are always replaced by spheres of greater dimension.

The present invention proposes providing a milling plant for milling materials to produce ceramic products or to modify existing discontinuous mills by making a small hole in existing hubs and modifying the heads that permits a simple and easy transfer from one mill to the next of the water suspension of materials to be milled and optimises the energy efficiency of the plant.

The object of the present invention is achieved with a milling plant according to claim 1. Owing to the invention it is possible to transfer in a simple manner the material to be milled from one mill to the next without the position of one mill being constrained by the position of the other mills, so as to have maximum freedom in the spatial arrangement of the mills. Further, the plant according to the invention enables energy efficiency to be optimised, requiring, for the same productivity, lower energy consumption than that of prior art plants and also enabling the productivity thereof to be increased without increasing the number/volume of mills installed. Embodiments of the invention will be disclosed below merely by way of non-limiting example, with reference to the attached drawings, in which:

Figure 1 is a diagram of a milling plant according to the invention;

Figures 2 and 3 illustrate a discontinuous mill that is usable in the milling plant according to the invention;

Figure 4 is a schematic longitudinal section of a continuous mill used in the plant according to the invention;

Figure 5 is the V-V section of Figure 4; with the internal rubber heads shown that are set up for containing the milling bodies and the pockets with holes for the slip to enter/exit. Figure 6 illustrates an embodiment of a milling plant according to the invention that uses two serially arranged continuous mills;

Figure 7 illustrates a second embodiment of a milling plant according to the invention which uses three serially arranged continuous mills;

Figure 8 is a diagram of a third embodiment of a plant according to the invention comprising three continuous mills that can be connected to one another in series or in parallel, with the possibility of excluding one or two mills from the milling process without having to stop the plant;

Figure 9 is a diagram of a fourth embodiment of a plant according to the invention, comprising two groups of serially arranged continuous mills, each group comprising three continuous mills arranged parallel.

In Figure 1 a milling plant 1 according to the invention is illustrated schematically that comprises a discontinuous mill 2 (Figures 2 and 3) consisting of a cylinder inside which a milling chamber 3 is defined into which are loaded, via an upper opening 21, water, clays and hard materials, such as for example feldspar, to make mixtures to make ceramic products and milling bodies 15 consisting, for example, of allumina spheres all having the same diameter, for example of 60 mm to perform rapidly a first step of the milling process consisting of kneading the clays and coarse fragmentation of the hard materials, to enable the hard materials to be suspended in water together with the other materials to be milled. Milling is performed by rotating the cylinder 2 by means of a motor 19 and a transmission 20, for example a belt transmission.

At the end of this first milling step, the water suspension 17 of clays and hard materials is extracted by gravity from the milling chamber 3 via a lower opening 22 and conveyed to a storage tank 7 via an extracting conduit 6. The aforesaid water suspension is then removed from the storage tank 7 by a pump 8 and sent through a supply conduit 9 and a rotating joint to a first continuous mill 4a of a plurality of continuous mills 4a-4n serially connected to one another via respective connecting conduits 10 and rotating joints fixed to the inlet/outlet hubs.

In each continuous mill 4a-4n the milling bodies 16a- 16n have also been loaded beforehand, the milling bodies 16a-16n also consisting, for example, of allumina spheres. The milling bodies of the first load 16a-16n of each continuous mill 4a-4n all have the same diameter, which decreases progressively from one mill to the next until it reaches smaller dimensions, for example 20 mm, in the last mill 4n.

The level of the milling bodies can vary from mill to mill according to the raw materials to be milled and the final granulometry desired.

From the last mill 4n, the water suspension containing the milled materials, the so-called slip 18, is sent to a collecting tank 12, from which it can be subsequently removed for further processing.

The passage of the water suspension from the first continuous mill 4a to the subsequent continuous mills is ensured by the variable flow pump 8, which is chosen to provide sufficient head to overcome the load losses that occur along the path of the water suspension from the storage tank 7 to the collecting tank 12 and to reach the desired level inside the mills. The level of the slip inside the mills is adjusted by raising, in relation to the outlet hole, the level of a portion 36 of the last outlet conduit 11.

The quantity of the milling bodies 16a-16n in each continuous mill 4a-4n can be increased, with respect to mills used in prior art plants, until they occupy more than 50% of the usable volume of the respective milling chamber 5a-5n. Each milling chamber 5a-5n can be filled with the water suspension 17 up to about 80-90% of the usable volume thereof. In this manner, the milling bodies 16a-16n will always be immersed below the level of the water suspension 17 and all the milling bodies will contribute to the refining action.

As only the slip up to the desired values has to be refined, it will no longer be necessary to rotate the continuous mills 4a-4n at high speed to enable the large spheres to fall during the clays kneading step.

The mills can on the other hand be rotated at a reduced speed, equal for example to 50% of the speed required for the clays kneading step. Each mill can rotate at a different speed, depending on the milling load. The various mills can have milling loads that are different from one another. Reduced speed translates into a lower power requirement and thus a significant energy saving.

Further, by loading the milling bodies to more than 50% of the usable volume of the milling chamber 5a-5n and with a slip level up to 80-90% of the usable volume a shift is obtained of the centre of gravity of the materials loaded into each mill 4a-4n towards a rotation axis thereof with a consequent decrease of the eccentricity of the centre of gravity and consequently a reduction of the torque necessary to rotate the mill and thus a further reduction of the power required and of energy consumption.

Further with a load of the milling bodies that is greater than 50% of the usable volume of the milling chamber there is an approximately 50% increase of the pushing force between the points of contact between the milling bodies that causes more rapid milling and a reduction in the time required to obtain average preset granulometry of the milled materials, with a consequent further reduction in the energy consumption of the plant. Further, having only to refine the slip, the mills 4a-4n will be loaded with spheres of small diameter and for the same volume occupied a significant increase in the number of spheres will be obtained and thus of the points of contact (about 20 times). This entails a drastic decrease in the time required to reach the desired granulometry value and a further decrease in the energy consumption of the plant compared with discontinuous mills and continuous mills with several chambers.

Further, the reduced rotation speed will prevent the milling bodies falling on to those underneath, decreasing wear thereof. There will be only the reciprocal rolling movement of the spheres, with consequent significant reduction in wear of the milling bodies.

In Figures 4 and 5 there is illustrated a continuous mill 4 that is usable in a plant according to the invention. Figure 4 is a longitudinal section of the continuous mill 4, whereas Figure 5 is the V-V section of Figure 4.

The continuous mill 4 has a cylindrical body 23, inside which a milling chamber Sis defined, into which the milling bodies are loaded through an upper opening, which is not shown.

The body 23 can be rotated around a longitudinal axis A thereof.

The milling chamber 5 is provided with an inlet conduit 26, through which the water suspension 17 can be delivered to the milling chamber 5, and an outlet conduit 27, through which the water suspension 17 can be extracted from the milling chamber 5. The inlet conduit 26 and the outlet conduit 27 are both formed in respective hubs 26a and 26b of the cylindrical body 23 and both have an axis substantially coinciding with said longitudinal axis A.

The milling chamber 5 is provided with an internal coating 25 made of wear-resistant material.

Further, the cylindrical body 23 is provided with a first diaphragm 29, interposed between the inlet conduit 26 and the milling chamber 5 and with a second diaphragm 30 interposed between the milling chamber 5 and the outlet conduit 27. The first diaphragm 29 and the second diaphragm 30 are provided with respective openings 28, through which the water suspension 17 coming from the inlet conduit 26 can enter the milling chamber 5 and can pass from the milling chamber 5 into the outlet conduit 27. The dimensions of the openings 28 are chosen in such a manner as to enable the milling bodies in the milling chamber 5 to go past the diaphragms 29 and 30 and possibly obstruct the inlet and outlet conduits 26 and 27.

In Figure 6 an embodiment of a plant according to the invention is illustrated comprising a discontinuous mill 2 (not visible in the figure) and two continuous mills 4a and 4b that are arranged serially. A water suspension 17 of clays and hard materials, which has undergone an initial coarse milling in the discontinuous mill 2, is removed from the storage tank 7 and delivered by the variable flow pump 8 to the milling chamber 5a of the first continuous mill 4a, via a first rotating joint 31 and the inlet conduit 26. Subsequently, the water suspension 17 is delivered to the milling chamber 5b of the second continuous mill 4b, via the outlet conduit 27, a second rotating joint 32 and the connecting conduit 10. Lastly, at the end of the milling process the water suspension 17, i.e. the so-called slip 18, is sent to the collecting tank 12 via the outlet conduit 11.

As already disclosed previously, the milling bodies 16a, 16b can occupy a volume that is greater than 50% the volume of the milling chamber 5a, 5b, i.e. can reach a level that is greater than the level of the rotation axis A of each mill 4a, 4b. The level of the water suspension 17 in both mills is determined by the level of the upper portion 36 of the outlet conduit 11 and can correspond to a degree of filling of the milling chambers 5a, 5b that is equal to about 80-90%.

The connecting conduit 10 is provided with a syphon 37 that is used to discharge into a collecting container 35, via a drainage conduit 33, provided with a valve 34, possible fragments of the milling bodies that have passed through the second diaphragm 30 and the outlet conduit 27 of the first mill 4a, or is able to collect a sample of water suspension 17, to conduct checks on the degree of milling obtained in the respective mill. Also the second rotating joint 32 of the second mill 4b is provided with a drainage conduit 33, provided with a valve 34, to discharge into a collecting container 35 possible fragments of the milling bodies that have passed through the second diaphragm 30 and the outlet conduit 27 of the second mill 4b.

In Figure 7 there is illustrated a second embodiment of a plant according to the invention that differs from the embodiment illustrated in Figure 6 by the fact that it comprises three continuous mills 4a, 4b, 4c arranged serially.

It should be noted that the connecting conduits 10 are provided with a respective syphon 37 in order to prevent possible fragments of the milling bodies 16a-16n that have gone beyond the second diaphragms 30 being able to pass from one mill to the next. The fragments of the milling bodies 16a-16n that go beyond the second diaphragms 30 are discharged via the drainage conduits 33 of the respective syphons 37.

In Figure 8 an example of the layout of a milling plant according to the invention is illustrated schematically.

In addition to a discontinuous mill that is not shown, the plant comprises three continuous mills 4a, 4b, 4c that can be connected in series or in parallel. Further, each of the continuous mills 4a, 4b, and 4c can be excluded from the plant in the event of a fault or stop to restore the milling bodies, without this causing the other mills to stop. The first mill 4a is connected to the delivery of the pump 8, via a supply conduit C and a first on-off valve VI. The first mill 4a is further connected to the second mill 4b via a first connecting conduit D, provided with a second on-off valve V2 and with a third on-off valve V3.

The second mill 4b is connected to the third mill 4c via a second connecting conduit E provided with a fourth on-off valve V4 and with a fifth on-off valve V5. Lastly, the third mill 4c is connected to the collecting tank 12 via a discharge conduit F, provided with a sixth on-off valve V6.

The supply conduit C is connected to the first connecting conduit D via a first connecting conduit G, provided with a seventh on-off valve V7 and a second connecting conduit H, provided with an eighth on-off valve V8.

The first connecting conduit G is further connected to the second connecting conduit E via a third connecting conduit I provided with a ninth on-off valve V9.

The second connecting conduit E is connected to the discharge conduit F via a fourth connecting conduit L provided with a tenth on-off valve V10. Lastly, the first connecting conduit D is connected to the fourth connecting conduit L via a fifth connecting conduit M provided with an eleventh on-off valve.

To connect together serially the mills 4a, 4b and 4c, it is necessary to keep the valves VI, V2, V3, V4, V5 and V6 open and keep the remaining valves V7-V11 closed.

To exclude the mill 4a from the connection in series, the valves VI and V2 have to be closed and the valves V7 and V8 have to be opened.

To exclude the mill 4b from the connection in series, the valves V3 and V4 have to be closed and the valves V 8 and V 9 have to be opened.

Lastly, to exclude the mill 4c from the connection in series, the valves V5 and V6 have to be closed and the valve V10 has to be opened.

To connect the mills 4a, 4b and 4c together in parallel, it is necessary to keep all the valves open except for valves V8 and V10.

To exclude from the connection in parallel the mill 4a it is sufficient to close the valves VI and V2.

To exclude from the connection in parallel the mill 4b it is sufficient to close the valves V3 and V4.

Lastly, to exclude from the connection in parallel the mill 4c, it is sufficient to close the valves V5 and V6.

In Figure 9 there is illustrated schematically another embodiment of the layout of a milling plant according to the invention.

The plant comprises, in addition to a discontinuous mill, which is not shown, a first group Gl of continuous mills comprising a first continuous mill 4a, a second continuous mill 4b and a third continuous mill 4c that are connectable together in parallel and a second group G2 of continuous mills comprising a fourth continuous mill 4d, a fifth continuous mill 4e and a sixth continuous mill 4f that are connectable together in parallel. The second group G2 of continuous mills is connectable in series to the first group Gl of continuous mills. The first continuous mill 4a is connectable to the delivery of the pump 8, via a first supply conduit C and a first on-off valve Wl.

The second continuous mill 4b is connectable to the delivery of the pump 8 via the first supply conduit C, a second supply conduit CI, connected to the first supply conduit C and a second on-off valve W2. The third continuous mill 4c is connectable to the delivery of the pump 8 via the first supply conduit C, the second supply conduit CI, a third supply conduit C2, connected to the second supply conduit CI and a third on-off valve W3.

The first continuous mill 4a is connectable, via a first outlet conduit O, to a first connecting conduit P and to a second connecting conduit Q that connect the first group Gl of continuous mills to the second group G2 of continuous mills. The first outlet conduit O is provided with a fourth on-off valve W4.

The second continuous mill 4b is connectable to the first connecting conduit P and to the second connecting conduit Q, via a second outlet conduit 01 provided with a fifth on-off valve W5.

The third continuous mill 4c is connectable to the first connecting conduit P and to the second connecting conduit Q, via a third outlet conduit 02 provided with a sixth on-off valve W6.

The fourth continuous mill 4d is connectable to the second connecting conduit Q, via a third connecting conduit R and a fourth supply conduit S, provided with a seventh on-off valve W7.

The fifth continuous mill 4e is connectable to the second connecting conduit Q, via the third connecting conduit R and a fifth supply conduit S I, provided with an eighth on-off valve W8.

The sixth continuous mill 4f is connectable to the second connecting conduit Q, via the third connecting conduit R and a sixth supply conduit S2, provided with a ninth on-off valve W9.

The fourth continuous mill 4d is connectable via a fourth outlet conduit T to a first discharge conduit U and to a second discharge conduit X, through which the water suspension containing the milled materials, the so-called slip 18, is sent to a collecting tank 12, from which it can be subsequently removed for further processing. The fourth outlet conduit T is provided with a tenth on-off valve W10.

The fifth continuous mill 4e is connectable to the first discharge conduit U and to the second discharge conduit X through a fifth outlet conduit Tl provided with an eleventh on- off valve Wl l.

The sixth continuous mill 4f is connectable to the first discharge conduit U and to the second discharge conduit X through a sixth outlet conduit T2 provided with a twelfth on- off valve W 12. The first supply conduit C is connectable to the second connecting conduit Q through a first branch conduit Y provided with a thirteenth on-off valve W13. Further, on the first supply conduit C, downstream of the first branch conduit Y, a fourteenth on-off valve W14 is arranged.

Lastly, the second connecting conduit Q is connectable to the second discharge conduit X, through a second branch conduit Z, provided with a fifteenth on-off valve W15. A sixteenth on-off valve W16 is provided on the second connecting conduit Q, to exclude from the plant the second group G2 of continuous mills as explained in greater detail below.

The plant illustrated in Figure 9 is very versatile, because, by keeping the plant in operation, it is possible to exclude therefrom one or more mills, or one of the two groups of mills. This brings the significant advantage of not having to interrupt production when maintenance, repair or restoration of the milling bodies on one or more mills or groups of mills of the plant has to be performed.

To exclude from the plant a single mill it is sufficient to close the on-off valves located on the supply conduit and on the outlet conduit of the mill.

For example, if it is wished to exclude the first mill 4a from the plant, it is sufficient to close the first on-off valve Wl on the first supply conduit C and the fourth on-off valve W4 on the first outlet conduit O. If it is desired to exclude the fifth mill 4e from the plant, it is sufficient to close the eighth on-off valve W8 on the fifth supply conduit S 1 and the eleventh on-off valve Wl 1 on the fifth outlet conduit Tl.

If it is wished to exclude the first group Gl of continuous mills, it is sufficient to close the fourteenth on-off valve W 14 on the supply conduit C, so as to interrupt the supply to the continuous mills of the first unit Gl and open the thirteenth on-off valve W 13 to supply only the continuous mills of the second group G2.

If it is wished to exclude the second group G2 of continuous mills, it is sufficient to close the on-off valve W13 and the sixteenth on-off valve W16 on the second connecting conduit Q, so as to interrupt the supply to the continuous mills of the second group G2 and open the fifteenth on-off valve W15 on the second branch conduit Z, to place in communication the outlets of the continuous mills of the first group Gl directly with the second discharge conduit X and the collecting tank 12.

Owing to the fact that the water suspension of materials to be milled is moved through the mills of the plant according to the invention only via the pump 8, a great variety of plant patterns is possible, in addition to those illustrated, to meet the most varied productive needs and to obtain maximum production flexibility.

Further, the plant according to the invention, in the event of the stop of one or more mills, can continue to operate at a reduced flowrate, but with constant final granulometry of the milled materials in the exiting water suspension, because the plant is supplied by the variable flow pump 8. A further advantage of the plant according to the invention is the fact that it is possible to make the plant by modifying already existing discontinuous mills by making a small hole in existing hubs and modifying the heads by inserting diaphragms 29 and 30. This enables the cost of making a plant according to the invention to be reduced significantly.

Claims

1. Milling plant (1) comprising a plurality of continuous mills (4-4n), supplied with a water suspension (17) of materials to be milled, each continuous mill (4-4n) comprising a cylindrical body (23) inside which a respective milling chamber (5- 5n) is defined, said cylindrical body (23) being rotatable around a longitudinal rotation axis (A), said milling chamber (5-5n) being provided with an inlet conduit (26) and an outlet conduit (27), the outlet conduit (27) of a continuous mill (4-4n) of said plurality of continuous mills being able to be connected via a connecting conduit (10) to the inlet conduit (26) of another continuous mill (4-4n), characterised in that said water suspension (17) is moved through said plurality of continuous mills (4-4n) via a single pump (8) the delivery of which is connected to the inlet opening of the first continuous mill (4a) of said plurality of continuous mills (4a-4n).

2. Plant (1) according to claim 1, wherein said variable flow pump (8) removes said water suspension (17) from a storage tank (7).

3. Plant (1) according to claim 1, or 2, wherein the outlet conduit (27) of a last continuous mill (4n) of said plurality of continuous mills (4-4n) discharges said water suspension (17) into a collecting tank (12).

4. Plant (1) according to any preceding claim, wherein in the milling chamber (5-5n) of each continuous mill (4-4n) a plurality of milling bodies (16a-16n) is arranged, said milling bodies occupying a volume that is greater than 50% of the volume of said milling chamber (5-5n).

5. Plant (1) according to claim 4, wherein into said milling chamber (5-5n) a quantity of said water suspension (17) is delivered that is such as to occupy, together with said milling bodies (16a-16n) a volume equal to about 80% of the volume of said milling chamber (5-5n).

6. Plant (1) according to any preceding claim, wherein the milling chamber (5-5n) of each of said continuous mills (4-4n) is provided with an internal coating (25) made of wear-resistant material, with a first diaphragm (29), interposed between said inlet conduit (26) and said milling chamber (5-5n) and with a second diaphragm (30) interposed between said milling chamber (5-5n) and said outlet conduit (27); the first diaphragm (29) and the second diaphragm (30) are provided with respective openings (28) sized so as to prevent the milling bodies (16a- 16n) located in the milling chamber (5-5n) passing beyond said diaphragms (29, 30).

7. Plant (1) according to any preceding claim, wherein said connecting conduit (10) is provided with syphon (37).

8. Plant (1) according to claim 7, wherein said syphon (37) is connected to a drainage conduit (33).

9. Plant (1) according to any preceding claim, wherein a first rotating joint (31) is associated with said inlet conduit (26) and a second rotating joint (32) is associated with said outlet conduit (27), the second rotating joint (32) of the last continuous mill (4n) being connected to a drainage conduit (33).

10. Plant (1) according to any one of claims 5 to 9, further comprising an outlet conduit (11) through which said water suspension (17) is discharged into said collecting tank (12), said outlet conduit (11) comprising an upper portion (36) that determines a filling level of said milling chamber (5-5n), in each of said continuous mills (4- 4n).

11. Plant (1) according to any preceding claim, wherein said continuous mills (4a-4c) are connected together so as to be able to be connected together in series or in parallel.

12. Plant (1) according to any one of claims 1 to 10, wherein said continuous mills (4a- 4f) are divided into a first group (Gl) and into a second group (G2), the mills (4a- 4c) of said first group (Gl) and the mills (4d-4f) of said second group (G2) being connected to one another in parallel, said first group (Gl) and said second group (G2) being connected to one another in series.

13. Plant (1) according to claim 11, or 12, wherein each of said continuous mills (4a-4f) can be excluded from the plant without it being necessary to interrupt the operation of the plant.

14. Plant (1) according to claim 12, or 13, wherein said first group (Gl) or said second group (G2) can be excluded from the plant without it being necessary to interrupt the operation of the plant.