Field of the invention

[1] This invention relates to an attritor mill of the kind comprising a grinding container, which forms within itself a grinding chamber and a rotor arranged within said container wherein a plurality of arms extends radially from the rotor, and said arms are arranged to agitate a plurality of grinding free bodies mixed with the material to be processed.

[2] The invention furthermore relates to the application of such an attritor mill to the treatment and recycling of scraps such as, for example, urban solid waste, food scraps or more generally the so- called "wet waste", remains from mowing or pruning, vegetal residues from agricultural activity, waste similar to the urban ones, FOS ("dry organic fraction") of the urban waste, scraps from mechanical selection of the urban waste, silicate or carbonate-based inorganic materials.

State of the art

[3] It is currently known to treat the urban waste by grinding it in ball or pebble-type mills provided with a big drum rotating about a horizontal axis.

[4] The drum is charged with the waste to be treated mixed with a proper quantity of steel pebbles acting as grinding bodies.

[5] By making the drum rotate on itself about a horizontal axis, the steel pebbles grind, crush and mince the waste.

[6] By moving the steel pebbles at very low average speeds, this first type of ball mills is convenient and efficient if large-sized; for example, the city of Leicester (UK) uses, for the treatment of urban waste, a big horizontal axis ball-type mill charged with about 42 tons of steel pebbles .

[7] A second limit of this type of mills is the humidity content of the organic waste after the treatment, which remains in any way too high to allow the waste be treated in a waste to energy plant.

[8] Ball or pebble-type mills, often called attritor mills, are by the way known. These mills are provided with a grinding chamber wherein a rotor, by rotating about a vertical axis, randomly strikes a mass of steel pebbles mixed with other material to be treated.

[9] The latter material is mainly ground as a result of the repeated and very frequent impacts, crushing and rubbing among or anyway against the pebbles.

[10] Attritor mills having the aforementioned features are themselves already known, for example from US3131875, US3339896, US3084876, US3670970.

[11] The attritor mills described in the publication WO2013/167851 sought to provide an attritor mill improving the attritor mills previously known under various aspects and, for example, which would be more suitable for:

- grinding or anyway treating large amounts of materials, such as food scraps or waste with a high content of animal or vegetal tissues, relatively soft and humid or generally pasty solids, or relatively dry and brittle inorganic materials based for example on silicates or carbonates, operating with an efficiency acceptable in large mass productions and not only in small productions for laboratory activities or for relatively expensive products such as pigments;

-being used for the wide-scale processing of industrial waste or urban solid waste, even organic, such as for example food scraps (the so-called "wet fraction" of the urban waste) , scraps from mowing or pruning, vegetal residues from agricultural activity, waste similar to the urban ones, FOS ("dry organic fraction") of the urban waste, suitable for being made even as a small-sized plant;

treating the aforementioned urban solid waste, by producing a drier output material, and thus more suitable for being directly used as fuel or anyway less in need of further drying or sterilization treatments in order to reduce its bacterial load.

[12] The publication WO2013/167851 further aimed to: -provide an attritor mill more efficient than the known ones, especially capable of grinding greater amounts of materials with lower power consumption compared to the known attritor mills;

- provide a process for treating urban solid waste, even organic, of the aforementioned type, more suitable for being implemented with relatively small-sized plants .

[13] A purpose of the present invention is to provide an attritor mill or a process to treat waste and other scrape materials that is better than that described in publication WO2013/167851 , for example because it can treat a greater amount of material in the unit of time, substantially without, however, worsening the quality of the product obtained.

Summary of the invention

[14] In a first aspect of the invention, such object is achieved through an attritor mill having the features of claim 1.

[15] In a particular embodiment of the mill, the at least one compensation insert (200Ά, 200B, 200C, 200D) forms an edge that substantially extends along the external edges of the bottom wall (29) .

[16] In a particular embodiment, the mill is provided with a positioning system arranged to vary the position of at least one compensation insert (200A, 200B, 200C, 200D) adjusting the width (WR) of the clearance (203) .

[17] In a particular embodiment of the mill, the bottom wall (29) comprises a central portion (290) and one or more external inserts (292, 294) reversibly fixed to the central portion (292) so that the external edges (2920, 2940) of these external inserts form an overall external edge of the bottom wall (29) substantially broader than the external width (291) of the central portion (290) .

[18] In a particular embodiment, the mill comprises a rapid fastening system that reversibly fixes the central portion (290) to one or more external inserts (292, 294) and that, in turn, comprises one or more of the following elements: one or more screws (296), other threaded connections, snap connection elements, bayonet joints or other interlocking fasteners.

[19] In a particular embodiment, the mill is provided with a cooling system (30) arranged to spray a coolant on the material to be treated or treated in the grinding chamber (5) .

[20] In a particular embodiment of the mill, the cooling system (30) is arranged to cool the material to be treated or treated contained in the grinding chamber spraying liquefied gas, such as, for example, liquid nitrogen .

[21] In a second aspect, the invention relates to an attritor mill (1) comprising:

A) a grinding container (3) that forms within itself a grinding chamber (5) ; and

B) a rotor (7) housed within such container (3) and provided with a bottom wall (29) that delimits the bottom part of the grinding chamber (5) , substantially extends across the rotating axis (Al) of the rotor and on substantially at least half of the cross-section surface of the grinding chamber (5) in correspondence with the bottom wall (29) ;

and wherein:

C) a plurality of arms (9, 9', 9") extends radially from the rotor (7) and is arranged on one or more levels with reference to the distance from the bottom wall (29) , and the attritor mill (1) is arranged to grind, reduce, mince or micronize a material to be treated such as, for example, solid urban waste, food waste, mowing or pruning scraps, vegetable waste from agricultural activity, waste similar to urban waste, FOS ("dry organic fraction") of urban waste carrying out the following steps:

C.l) mixing the material to be treated with a plurality of grinding free bodies (11) in the grinding chamber; C.2) agitating the material to be treated and the plurality of grinding free bodies (11) by making the rotor rotate on itself so that its arms strike the grinding free bodies and at least a part of the latter bounce against the walls of the grinding chamber (5) and other grinding free bodies (11), and/or strike the material to be treated;

and the attritor mill 1 is provided with at least one compensation insert (200A, 200B _f 200C, 200D) inserted in a wall (13) of the grinding chamber (5) in such a way that it can reversibly and radially extend out of it and re-enter it by forming, in cooperation with the external edge of the bottom wall (29) , a variable width clearance (203) (WR) through which air and at least part of the particulate can exit from the grinding chamber (5) .

[22] In a third aspect, the invention relates to an attritor mill (1) comprising:

A) a grinding container (3) that forms within itself a grinding chamber (5) ; and

B) a rotor (7) housed within said container (3) and provided with a bottom wall (29) that delimits the bottom part of the grinding chamber (5) , substantially extends transversally to the rotation axis (Al) of the rotor itself and substantially over at least half of the surface of the cross-section of the grinding chamber (5) in correspondence to the bottom wall (29) itself;

and wherein:

C) a plurality of arms (9, 9', 9") extends radially from the rotor (7) and is arranged on one or more levels with reference to the distance from the bottom wall (29) , and the attritor mill (1) is arranged to grind, reduce, mince or micronize a material to be treated such as, for example, solid urban waste, food waste, mowing or pruning scraps, vegetable waste from agricultural activity, waste similar to urban waste, FOS ("dry organic fraction") of urban waste carrying out the following steps:

C.l) mixing the material to be treated with a plurality of grinding free bodies (11) in the grinding chamber; C.2) agitating the material to be treated and the plurality of grinding free bodies (11) by making the rotor rotate on itself so that its arms strike the grinding free bodies and at least a part of the latter bounce against the walls of the grinding chamber (5) and other grinding free bodies (11), and/or strike the material to be treated;

and wherein the bottom wall (29) comprises a central portion (290) and one or more external inserts (292, 294) fixed reversibly to the central portion (292) so that the external edges (2920, 2940) of these external inserts form an overall external edge of the bottom wall (29) that is substantially broader than the external edge (291) of the central portion (290) .

[23] In a fourth aspect of the invention, this object is achieved through a process having the features according to claim 14.

[24] In a particular embodiment, the process according to the invention comprises the step of spraying a coolant on the material treated or to be treated contained in the grinding chamber (5) , in order to cool such material.

[25] In a particular embodiment of the process according to the invention, the organic solid waste to be treated have a humidity content equal to or greater than 60 % by weight.

[26] In a particular embodiment of the process according to the invention, the organic solid waste to be treated are fed in continuous into the grinding chamber (5) and after having been treated they are extracted in continuous from the grinding chamber (5) , for example in the form of powder, granules, shavings, flakes, sticks, small cylinders, pellets.

[27] In a particular embodiment, the process according to the invention comprises the step of turning the rotor (7) during grinding at a speed of between 500 and 1500 revolutions/minute.

[28] In a fifth aspect, the invention relates to a procedure to disassemble an attritor mill, comprising the following operations in order:

-remove the one or more external inserts (292, 294) from the central portion (290) of the bottom wall (29) ; -remove at least the part of the rotor (7) comprising the pivot or central shaft (70) from the rest of the mill (1) extracting said part of the rotor (7) from the upper open end of the grinding chamber (5) , without having previously removed the walls (13) of the grinding chamber from the rest of the mill (1) .

[29] The dependent claims are directed to further optional features of the attritor mill and of the process according to the invention.

[30] The advantages achievable through the present invention will be more apparent, to the person skilled in the field, from the following detailed description of some particular embodiments provided as non-limiting examples, described with reference to the following schematic figures.

List of figures

Figure 1 shows a perspective view of an attritor mill according to a first particular embodiment of the invention ; Figure 2 shows a first side view, partially sectioned according to plane II-II, of the attritor mill of Figure 1;

Figure 3 shows a top view, partially sectioned according to plane III-III, of the attritor mill of Figure 1;

Figure 4 shows a perspective view of the bottom wall of the rotor of an attritor mill according to a second particular embodiment of the invention;

Figure 5 shows a second side view, partially sectioned according to plane II-II, of the attritor mill of Figure 1;

Figure 6 shows a perspective view of the dirt scraping protrusions present at the bottom of the grinding chamber of the attritor mills of Figures 1, 4, 7-12;

Figure 7 shows a side view, partially sectioned according to plane VII-VII of an attritor mill according to a third particular embodiment of the invention;

Figure 8 shows a section detail according to a section plane passing through the rotation axis Al of the clearance between the edge of the bottom wall and the wall of the grinding chamber of the attritor mills of the Figure 7 or 12;

Figure 9 shows a partially sectioned view according to an observation direction parallel to the rotation axis Al , of the grinding chamber and the compensation inserts of the mill of Figure 7;

Figure 10 shows a partially sectioned view according to an observation direction parallel to the rotation axis Al , of the central portion and external inserts of the bottom wall of the mill of Figure 7; Figure 11 shows a section view according to a section plane passing through the rotation axis Al of the central portion and of the external inserts of the bottom wall of the mill of Figure 10;

Figure 12 shows a first side view, partially sectioned according to a section plane XII-XII passing through the rotation axis Al of a fourth embodiment of an attritor mill according to the invention.

Detailed description

[31] Figures 1-6 relate to an attritor mill, indicated with the overall reference 1, according to a first particular embodiment of the invention.

[32] The attritor mill 1 comprises a grinding container 3 which forms in its inside a grinding chamber 5 and a rotor 7 housed inside said chamber (Figure 2) .

[33] The grinding container 3 can be made up of, or any way can comprise a metal sheet shell, preferably in a cylindrical shape.

[34] Preferably the grinding chamber 5 has a substantially cylindrical shape.

[35] The ratio between the height HC and the diameter DC of the cylindrical grinding chamber 5 is preferably greater than 0.8, more preferably greater than 1 and for example comprised between 0.8 and 1.3.

[36] The rotor 7 preferably comprises a pivot or central shaft 70 and can be fixed to the rest of the mill 1 through a bearing inserted on the rotor itself (Figure 2, 5) .

[37] The rotor 7 is provided with a bottom wall 29 that delimits and closes the bottom part of the grinding chamber 5 and is arranged to protect the bearing from dust, granules or other particles coming from the grinding chamber itself.

[38] The bottom wall 29 can be obtained, for example, from a more or less planar disk (Figure 2, 3, 5) .

[39] The bottom wall 29 preferably lies in a plane substantially perpendicular to the rotation axis Al of the rotor itself, is integrally fixed to the rest of the rotor 7 and rotates together with it.

[40] Preferably the bottom wall 29 substantially covers at least half of the bottom surface or of the cross section of the grinding chamber.

[41] From the central pivot or central shaft 70, or more in general from the rotor 7, a plurality of arms 9, 9', 9" extends radially; such arms are arranged above the plate 29 and on one or more determined levels with reference to their distance from the plate 29 itself according to the direction of the rotation axis Al of the rotor.

[42] The attritor mill is arranged to grind, crush, mince or micronize a material to be treated, such as for example urban solid waste, food scraps, waste with a high content of animal or vegetal tissues, remains from mowing or pruning, vegetal residues from agricultural activity, waste similar to the urban ones, FOS ("dry organic fraction") of the urban waste, by actuating the following steps:

- mixing the material to be treated with a plurality of grinding free bodies 11 in the grinding chamber 5;

agitating the material to be treated and the plurality of grinding free bodies 11 by making the rotor 7 rotate on itself so that its arms 9, 9', 9" strike the grinding free bodies 11 and at least a part of the latter bounce against the walls 13 of the grinding chamber, against other grinding free bodies 11, and/or strike the material to be treated.

[43] The wording "free bodies" in the present description indicates bodies not directly fixed or anyway mechanically constrained to other parts of the mill 1.

[44] These free bodies are therefore free to move and to bounce in the grinding chamber, hampered in this substantially by the same material to be treated only.

[45] The grinding free bodies 11 can be for example spheres, pebbles, pellets, balls, cobbles, granules of materials such as steel, copper or other metals, metal materials, stones.

[46] The grinding free bodies 11 can also be other bodies having various and more sharp-cornered shape, such as for example waste and metal scraps, nails, screws and bolts; however, these grinding free bodies as well, after a certain permanence in the grinding chamber, assume shapes even and even more rounded and more similar to pebble, cobbles or bullets.

[47] Preferably the mill 1 is arranged to rotate the rotor 7 on itself, during the normal operation, about a substantially vertical axis Al, or at least having an inclination with respect to the vertical not greater than about 45° .

[48] The mill 1 is also provided with one or more first extraction openings 10 each arranged to allow the exit of material treated in the chamber itself and possibly withholding the grinding free bodies 11 within the grinding chamber 5.

[49] In an aspect of the invention, the one or more extraction openings 10 are located at least in the lower portion of the grinding chamber 5, this expression meaning the lower half of the chamber 5.

[50] To this end, the upper edge of each first extraction opening 10, in particular of the topmost opening, is preferably located at a height HI equal to or lower than:

- the centre line of the part of the rotor contained in the grinding chamber; and/or

-the height of the fourth or fifth level, if any, of the arms starting from the bottom wall 29; and/or

-0.6 times the average or maximum internal diameter (DC) of the grinding chamber.

[51] The height HI is measured with reference to the lower zones of the bottom surface 29.

[52] The height HI of the upper edge of the topmost first extraction opening 10 is preferably less than or equal to 0.2 times the internal average or maximum diameter DC of the grinding chamber; more preferably, less than or equal to 0.1 times the diameter DC and even more preferably equal to the height HP described further below.

[53] As in the embodiment of Figure 2, the bottom wall 29 can extend radially at least so as to reach the one or more lateral walls 13.

[54] Preferably, the bottom wall 29 extends radially beyond the one or more lateral walls 13 and even outside of them (Figures 2, 5) .

[55] Thus, the author of the invention was able to increase the capacity of the ground material by 30-40%.

[56] This measure also allow a significant reduction of the wear and tear of both the grinding bodies and the grinding chamber 5 and of the risks of rotor 7 jams caused by grinding bodies or other foreign bodies that are stuck between the bottom wall 29 and the lower edge of chamber 5.

[57] Preferably, the bottom wall 29 extends radially beyond the one or more lateral walls 13 for a length greater than or equal to 2 millimetres and/or 0.002 times the DC diameter of the chamber 5.

[58] More preferably, the bottom wall 29 extends radially beyond the one or more lateral walls 13 for a length greater than or equal to 0.003 times the diameter DC and even more preferably greater than or equal to 0.01 times the diameter DC.

[59] As, for example, in the embodiment of Figures 2-5, one or more of the first extraction openings 10 can have the form of a perimeter slit that extends around the lateral walls 13 of the grinding chamber 5.

[60] More particularly, as for example in the embodiment of Figure 2, the mill 1 can be provided with just one first extraction opening 10 located substantially in correspondence or in proximity to the external edge of the disk that forms the bottom wall 29; the first extraction opening 10 is in practice a slit formed by the bottom wall 29 and by the lower edge of the lateral wall 13 that ends slightly above the bottom wall 29.

[61] Each of the first openings 10 has a height HP clearly shorter than the diameter or the minimum linear dimension of the grinding masses.

[62] To this end, the height HP is preferably comprised between 0.05-50 millimetres and more preferably comprised between 1-10 millimetres or between 2-5 millimetres . [63] Alternatively or in combination, the ratio HP/DC between the height HP of the first opening 10, and the diameter DC of the chamber 5 is preferably comprised between 0.002-0.07 times, more preferably between 0.005-0.02 times or between 0.002-0.006 times.

[64] Alternatively or in combination, the ratio SA1/SPL between area SA1, that is the total area of the all the first openings 10, and the SPL area of the wall or of the lateral walls 13 of the chamber 5 is preferably comprised between 0.001-0.08 times, more preferably between 0.001-0.02 times and, for example, between 0.003-0.008 times.

[65] Even the slit 10 or the other first extraction opening 10 contributes to increasing the capacity of ground material up to 30-40% and significantly reducing the wear and tear both of the grinding bodies and the grinding chamber 5 and the risks of jamming of rotor 7 caused by the grinding bodies or other extraneous bodies, so that the author of the present invention was able to extract up to about 70% of the total capacity of ground material from the hole 10 or the other first extraction opening 10 located at the height of the bottom wall 29, probably aided by the fact that the ground material is generally more rarefied in the upper part of chamber 5 and denser and more concentrated in the lower part of chamber 5.

[66] In order to increase the bouncings upwards of the grinding free bodies 11 or the average height - both in time and number of various grinding bodies 11 - at which the various grinding free bodies 11 fly during normal operation, and in order to reduce the amount of grinding bodies 11 that lie on the bottom wall 29 or however in the lower part of the grinding chamber 11, advantageously on the lower wall 29 at least a supporting protrusion 19 and preferably a plurality of supporting protrusions 19 are provided, each of which is arranged to deviate mainly upwards the grinding free bodies 11, which substantially randomly hit the projection 19 itself (Figures 2-5) .

[67] Each supporting protrusion 19, 19' preferably has a shape selected from the following group: semi- spherical, spherical cap (Figures 2, 3, 5), stud-like or other round protrusion, in the shape of a smooth crest or rib such as, for example, a cylinder-shaped surface portion (Figure 4) .

[68] Protrusions 19, 19' having a substantially rounded plan such as semispherical-, spherical cap- or stud ^¬ like protrusions can be fixed more easily to the bottom wall 29.

[69] When they have a substantially oblong form, the supporting protrusions 19 can extend radially relative to the rotation axis Al of the rotor (Figure 4) .

[70] Alternatively the supporting protrusions 19 can extend from the centre outwards of the grinding chamber, even though not in radial directions and extend, for example, in a spiral manner.

[71] Thanks to their very smooth shape, the protrusions 19, 19' are much less worn and wear much less the grinding bodies 11 compared, for example, to the supporting protrusions 19 with sharper edges described in the publication WO2013/167851A1.

[72] The supporting protrusions 19 have a height HB preferably comprised between 1-8 centimetres, and more preferably between 3-6 centimetres (Figure 2) . [73] Alternatively or in combination, the ratio HB/DC is preferably comprised between 0.01-0.07 times and more preferably between 0.02-0.04 times and, for example, equal to 0.03 times wherein HB is the height by which each supporting protrusion 19 extends beyond and above the rest of the bottom wall 29.

[74] Preferably, when they have semi-spherical, spherical cap- or stud-like shape, the supporting protrusions 19 are placed close one to another and in groups of three and substantially placed at the vertexes of an equilateral triangle (Figure 2) .

[75] Said provision allow the ground free bodies 11 be sustained very efficiently, in particular making them speed up without hampering one another and distributing their trajectories more uniformly within the whole volume of the grinding chamber 5.

[76] When the supporting protrusions 19 have semi- spherical, spherical cap- or smooth stud-like shape, they have a maximum diameter or width in a plan view preferably comprised between 5-15 centimetres, and even more preferably between 7-13 centimetres and, for example, equal to 10 centimetres.

[77] Alternatively or in combination, when the supporting protrusions 19 have a semi-spherical, spherical cap- or smooth stud-like shape, the ratio DB/DC is preferably comprised between 0.05-0.2 times and more preferably comprised between 0.08-1.4 times, where DB is the maximum diameter or length of a stud in a plan view and DC is the internal average or maximum diameter of the grinding chamber 5.

[78] When they are grouped in equilateral triangles, the centres of two adjacent semi-spheres, spherical- caps or smooth studs 19 are located preferably 20 - 40 millimetres from one another.

[79] On the bottom wall 29 four triangle groupings of protrusions 19 can be provided, preferably located near the external edge of the bottom wall 29.

[80] The four groupings are preferably and substantially located at the ends of a cross having substantially orthogonal arms (Figure 3) .

[81] Said rounded shapes of the supporting protrusions 19 allow the mill 1 to grind predominantly by impact or by friction depending on the rotation speed of the rotor 7.

[82] During the grinding mainly by impact the material is mostly crushed, while in the grinding mainly by friction the materials are vigorously exfoliated and delaminated .

[83] Indicatively, with a rotor 7 rotation speed for about 1000-1200 revolutions per minute, there is grinding by attrition while grinding by impact takes place at a speed of about 800 revolutions/minute.

[84] In combination with the first extraction openings 10, the mill 1 can be provided with at least a second extraction opening 17 arranged at least in the upper part of the grinding chamber 5 and arranged to allow for the material treated into the chamber itself to exit and/or retain the grinding free bodies 11 inside the grinding chamber 5, wherein the lower edge 170 of the at least a second extraction opening 17 is located at a height H3 same as or lower than:

- the centre line of the portion of the rotor contained in the grinding chamber; and/or

- at the height of the third or fourth level of the arms starting from the bottom of the grinding chamber (5) ; and/or

- at a height less than or equal to 0.6 times the average or maximum internal diameter DC of the grinding chamber 5.

[85] Said heights are measured with reference to the lowest zones of the bottom surface 29.

[86] Preferably, the lower edge 170 of the at least one second extraction opening 17 is located at a height H3 lower than or equal to 0.5 times the average or maximum internal diameter DC of the grinding chamber 5.

[87] Advantageously, the at least one second extraction opening 17 extends for a height H2 greater than or equal to 0.5 times, more preferably greater than or equal to 0.6 times or even more preferably greater than or equal to 0.75 times the average or maximum internal diameter DC of the grinding chamber 5.

[88] The heights HI, H2 , H3 are measured with reference to the direction of the rotation axis Al of the rotor.

[89] Preferably the grids or other second extraction openings 17 extend over at least one third of the perimeter of the cross-section of the walls 13 of the grinding chamber 5, wherein these cross sections are the ones wherein the openings 17 are present and are considered perpendicular to the rotation axis Al of the rotor 7.

[90] More preferably the grids or other extraction openings 17 extend over at least half and, more preferably, over at least one three fourths of the perimeter of the cross-section of the walls 13 of the grinding chamber 5.

[91] Thanks to the size or to the size ratio previously described, the second opening 17 or the second extraction openings 17 resulted to be particularly efficient to increase flow rate of the air and particulate removed from the chamber 5 during the grinding, increasing accordingly the efficiency of the mill 1.

[92] Moreover, by increasing the flow rate of the air removed from the grinding chamber 5, the first 10 and the second evacuation openings 17 contribute to lowering the temperature within the chamber 5.

[93] The first extraction openings 10 can also be provided with grids or can form the grids themselves or other filtering barriers having analogous function as of the grids or other second extraction openings 17.

[94] Advantageously the arms of the rotor 9 which are more distant from the bottom of the grinding chamber 5 are substantially shorter than the arms 9', 9" which are closer to the bottom of the grinding chamber (5) ; in this way the rotating arms 9, 9', 9" tend to rise, and to maintain more raised, the bulk of the grinding free bodies 11, thus increasing the efficiency of the grinding .

[95] Preferably the length LB of the arms 9, 9', 9" of the rotor progressively reduces by moving away ideally from the bottom of the grinding chamber 5 (Figure 2); thus the ability of the mill 1 of rising and of maintaining raised the bukl of the grinding free bodies 11 increases .

[96] The various arms 9, 9', 9" can be fixed to the rotor so as to substantially lie in two ideal mutually orthogonal planes.

[97] The rotor 7 can be driven for example by a proper electric motor, not shown, arranged below the grinding chamber 5.

[98] The attritor mill 1 is arranged to make the rotor 7 rotate on itself, for example through the aforementioned electric motor, at a speed preferably comprised between 500 and 1500 rev/min, and more preferably comprised between 800 and 1200 rev/min.

[99] Preferably the length LB of the arms 9, 9', 9" of the rotor progressively reduces according to a linear law by moving away ideally from the bottom of the grinding chamber 5.

[100] Preferably the waste or other material to be treated are introduced into the grinding chamber from the top, for example through the supplying duct 15 which preferably is substantially vertical (Figure 1) .

[101] However the wet fraction of the urban organic waste, which can contain up to 80% by weight of humidity, often tends to form a pasty mass which advances with a relative difficulty in possible ducts and does not lend itself to be introduced into the mill 1 by simple gravity.

[102] Therefore the attritor mill 1 is advantageously provided with a feeder (not shown) arranged to push the material to be treated into the grinding chamber 5.

[103] Such a feeder can comprise or consist of a screw or Archimedean screw feeder, a piston, a hydraulic or mechanical pusher, a volumetric pump.

[104] Such a screw, Archimedean screw or hydraulic pusher can be housed for example in the same supplying duct 15.

[105] Each arm 9, 9' , 9" can have for example substantially circular cross sections, and more in particular can be in the shape of a cylindrical rod.

[106] In many cases, through a proper choice of the rotational speed of the rotor 7 and of other operating parameters, such as for example the ratio between the amount of waste or other material to be treated and of grinding free bodies 11 present in the grinding chamber 5, it is possible to bring the temperature of the material to be treated and of the grinding bodies 11 in the chamber 5 at sufficiently high values, for example comprised between 60° and 100° Celsius degrees so as to quickly desiccate the material to be treated and reduce it, at the end of the treatment, in the form of granules or relatively dry powder that can be extracted from the grinding chamber 5 through the first 10 and the second extraction opening 17.

[107] The second extraction openings 17 are preferably closed by appropriate grids, sieves, filters in general or other filtering elements that can be crossed by the outgoing air flow from the grinding chamber but hold the solid particles larger than a pre-determined granulometry .

[108] Advantageously the extraction grid or grids 17 have holes or meshes of dimensions such as to let the particles of treated material of the desired dimensions pass, and on the other hand to retain the grinding free bodies 11 inside the grinding chamber 5; preferably the holes or meshes of each of the extraction grids 17 have a diameter, or anyway a maximum length or width, equal to or less than 2 cm, more preferably comprised between 3 mm and 9 mm and even more preferably equal to about 6 mm .

[109] Adopting holes or meshes of the extraction grids of about 6 mm treating organic waste and/or urban solid waste the particle size of the extracted waste ranges from 100 microns to 5 mm.

[110] Preferably the attritor mill 1 comprises a suction system arranged to suction and extract the powders or other particles of treated material from the grinding chamber 5, and the suction system comprises a fan or other aspirator 21 located outside the grinding chamber itself (Figure 5) .

[111] To this end, the grinding container 3 can be enclosed in an external casing 23 capable of assuring a proper pneumatic seal, and the inside of the casing 23 can be fluidically connected to the fan or other suction 21 through a collecting duct 25 in order to create a pneumatic depression in the internal space 22 of casing 23 and outside of the mill 1.

[112] The fan or other suction 21 is preferably motorized, for example driven by an electric motor.

[113] Advantageously the attritor mill 1 is provided with a grid cleaning system arranged to keep clean the at least one extraction grid 17 or at least to reduce its clogging.

[114] To this end, the grid cleaning system comprises at least one nozzle 27 arranged to emit air jets towards the at least one extraction grid.

[115] Preferably the grid cleaning system comprises a plurality of nozzles 27.

[116] Preferably the attritor mill 1 is furthermore provided with a logic unit programmed or anyway arranged to activate in sequence, for example one at a time, the nozzles 27; the fewer nozzles are simultaneously activated, the less the flow set between the grinding free bodies 11 and the material to be treated breaks .

[117] As already previously explained, under proper operating conditions the mass of material to be treated and the grinding free bodies 11 heat reaching even high temperatures, that can advantageously be exploited to desiccate the material to be treated and favouring its transformation into dusty or granular material.

[118] To this end, advantageously the attritor mill 1 is provided with a temperature control and adjusting system arranged to detect the temperature in the grinding chamber 5 during the functioning of the mill and to control it, preferably in real time, keeping it within a desired range of values, for example between 50-90 degrees C.

[119] Besides proper sensors, the control and adjusting system of the temperature can comprise one or more of the following subsystems:

- a measuring device for controlling with an adequate precision the amount - or the capacity - of material to be treated that is fed into the grinding chamber 5;

- a cooling system of the grinding chamber that can be for example a water-, air- or other thermovector liquids or aeriforms ;

- a logic unit arranged to control and vary the rotation speed of the rotor 7, the aforementioned measuring device and/or cooling system.

[120] More precisely, the cooling system can comprise one or more conduits lapping the walls of the grinding chamber 5 and crossed by suitable cooling liquid.

[121] Advantageously, the cooling system comprises one or more cooling nozzles 30 (Figure 1) , each of which are arranged to sprinkle for the materials contained in grinding chamber 5 with the appropriate coolant (Figure 1) .

[122] More in particular, the nozzle or nozzles 30 can be arranged to give out liquid nitrogen jets that, becoming gaseous, cool the contents of the grinding chamber, both the waste yet to be ground or partially ground and the waste already ground.

[123] The liquid nitrogen is easy to manage and apply.

[124] The injection of liquid nitrogen or another cryogenic liquid or coolant directly in the material to be ground is useful to grind, for example, waste with a high content of light plastic, or in all cases in which there is not sufficient space to mount the cooling coils on the walls of the grinding chamber 5, for example due to the presence of very large extraction openings 10, 17 or the heating resistors 33 as the described below.

[125] By cooling the content of chamber 5 by sprinkling coolant on it - for example, simply a much cooler substance - it is possible to control the temperature in the chamber with remarkable accuracy, keeping it preferably between 80-100° C so as to dry and exsiccate the ground materials as fast as possible, keeping them below their ignition temperature at the same time.

[126] Instead, when other materials, such as, for example, waste with a moisture content between 45%-80%, are introduced into the grinding chamber 5, they will excessively cool its content; the only heat produced from impact and friction with the free bodies 11 does not heat and dries the material to be ground fairly quickly . [127] The grinding is therefore too slow and inefficient .

[128] Therefore, the attritor mill 1 can be advantageously provided with one or more heating elements 33 that provide additional heat to the material to ground contained in chamber 5 (Figure 5) .

[129] The heating elements 33 can comprise one or more of the following elements: Joule effect heating resistors, infrared ray lamps, heat exchangers internally crossed by a gas or a thermovector liquid that transfers heat to the material to be ground, and electrical resistance with a ceramic band.

[130] The heating elements 33 are preferably arranged on the lateral walls 13 of the grinding chamber 5 (Figure 5) , even if they can clearly be arranged even on or at the bottom 29 of the chamber 5, in arms 9, 9', 9" or in other parts of the rotor 7.

[131] Advantageously, on the sub-floor 8 of the grinding chamber, near the shaft the arms 9 of the rotor are assembled with, one or more dirt scraping protrusions 31 are present that serve to clean off any build-up of materials to be ground, ground materials or other dirt, if any, that is deposited on the lower side of the bottom wall 29, thus reducing the maintenance needs of the mill and lengthening its operative life (Figure 6) .

[132] The protrusions 31 can be shaped, for example, as ribs or studs, the top of which forms a crest that preferably has a sharp edge.

[133] Some constructional measures are described below that are particularly suited for the embodiments of a mill 1' , 1" according to the invention in which the bottom wall 29 does not extend radially beyond the one or more lateral walls 13.

[134] As shown in Figure 7, 12, one or more of the first extraction openings 10 are located below the bottom wall 29.

[135] The first openings 10 can also be on the sub- floor 8, if any, of the grinding chamber below the bottom wall 29, such as, for example, in the embodiment of Figure 12.

[136] Alternatively, the sub-floor 8 can also be completely absent (Figure 7) ; in this case, the mill 1 is provided with the only opening 10 delimited by the simple extension of the walls 13 of the grinding chamber below the bottom wall 29.

[137] As shown in Figure 7, 8, 12, one or more first extraction openings 10 can advantageously form an overall pass-through section -wherein such expression means the flow area of the opening 10 if just one of such opening is present, or the sum of the pass-through sections of all the first openings 10 if more than one opening is present - greater than or equal to 0.2 times and even more preferably greater than or equal to 0.8 times, the cross-section area of the grinding chamber 5 at the height of the bottom wall 29.

[138] These relatively high values of the total pass- through section of the first openings 10 allow for an efficient downward evacuation of the heaviest particulates produced in the grinding chamber.

[139] In order to enhance the downwards extraction of the particulates from the grinding chamber 5, the mill 1' , 1" is advantageously provided with a suction conduit 110 arranged to suck air from the grinding chamber 5 toward an area located below the bottom wall 29 (Figure 7) .

[140] Advantageously, this suction conduit 110 extends for at least 10 cm, more preferably for at least 20 centimetres, more preferably for at least 30 centimetres, and even more preferably for 100 centimetres downwards with reference to a direction parallel direction to the rotation axis Al .

[141] Alternatively or in combination, this suction conduit 110 preferably extends advantageously downward for a height of at least 0.2 times, 0.5 times, once, 2 times the average or maximum diameter DC of the grinding chamber 5.

[142] The conduit 110 can be in fluidic communication with the pneumatic depression ambient 22, with a vacuum pump or any other pneumatic depression generators.

[143] As shown for example in Figures 8, 9, the bottom wall 29 can have advantageously such an extension that the radial clearance WR between its peripheral edge and the grinding chamber walls 5 has a width WR of between one and five times the diameter or however maximum width or length of the aforementioned holes or meshes of each of the extraction grids 17.

[144] More preferably the distance between its peripheral edge of the bottom wall 29 and the walls of the grinding chamber 5 are comprised between 3 and 3.5 times the diameter, or anyway a maximum length or width, of the aforementioned holes or meshes of each of the extraction grids 17.

[145] Alternatively or in combination, the radial clearance 203 WR is preferably between 0.1-1 millimetres, or between 0.2-0.8 millimetres or between 0.3-0.6 millimetres.

[146] Advantageously the peripheral edge of the bottom wall 29 is flared so that the distance between the edge of the plate and the walls of the grinding chamber 5, according to a radial direction with respect to the rotation axis Al of the rotor, increases by ideally moving towards the bottom of the grinding chamber, preventing the particles coming from the grinding chamber 5 from getting stuck between the edge of the bottom wall 19 and the walls of the grinding chamber 5 and permitting instead their outflow through proper drains downstream of the bottom wall 29 itself.

[147] Because of wear and tear during its operation, it was observed that a groove progressively forms on the grinding chamber wall 5, in front of the edge of the bottom wall 29, which expands the radial clearance 203 between plate 29 and wall 13.

[148] This widening is undesired since it excessively increases the air flow rate and the granulometry of the particulate extracted from the grinding chamber 5 beyond the project conditions, also making it more difficult to extract the rotor 7 together with the plate 29 from the grinding chamber for maintenance operations .

[149] Therefore, to reduce this phenomenon, the attritor mill 1', 1" is advantageously provided with one or more compensation inserts 200A-200D inserted in corresponding slots provided in the walls that delimit the grinding chamber 5 (Figures 8, 9), so as to be able to radially slide into said slots.

[150] Inserts 200A-200D can be present, for example, in the number four and can be arranged so that their internal edge is at the height of the external edge of the bottom wall 29 and is substantially facing and overlapping it .

[151] Through appropriate positioning systems, such as, for example, mechanisms with adjustment screws or eccentric devices (not shown) , the inserts 200A-200D can be moved radially (Arrows F1-F4) in order to move the internal edge closer to the edge of the bottom wall 29 and restore the original value of the width WR of the radial clearance 203 as the edge gets worn.

[152] Each compensation insert can have the form of a simple flat plate in an arch-shape.

[153] Advantageously, each compensation insert 200A- 200D is made of a relatively hard material, such as an appropriately treated steel.

[154] Because of the reduced radial clearance 203 between the plate 29 and the wall 13, it is sometimes relatively difficult to remove the rotor 7 from the grinding chamber 5 to clean and maintain the mill 1.

[155] In order to avoid having to disassemble the wall 13 of the grinding chamber before being able to remove rotor 7, the bottom wall 29 advantageously comprises a central portion 290 and one or more external inserts 292, 294 reversibly fastened to the central portion 292 so that their external edges 2920, 2940 form an overall external edge of the bottom wall 29 that is broader than the external edge 291 of the central portion 290 (Figures 10, 11) .

[156] Preferably, the overall external edge formed by edges 2920, 2940 contains the external edge 291 of the central portion 290.

[157] Preferably, the overall external edge formed by edges 2920, 2940 is substantially circular.

[158] Preferably, there are at least two inserts 292 _f

294.

[159] Each external insert 292, 294 can substantially have the form of a substantially flat plate, even if it has a variable thickness and a curved overall shape.

[160] Each external insert 292, 294 is fastened to the central portion 292 through appropriate quick fastening systems 296 in order to be easily and quickly disassembled and, for example, they are screwed, hooked or somehow fastened to the lower side of the central portion 292 (Figure 11) .

[161] The aforementioned quick fastening systems can clearly comprise systems different from the screws 296 or snap systems, and can comprise, for example, other threaded, bajonet or eccentric connections.

[162] To clean or maintain the mill 1, first the external inserts 292, 294 are disassembled and removed from the bottom; after that, the rest of the rotor 7, or the parts of it, such as the pivot or central shaft 70, along with the central portion 290 of the bottom wall 29 can be more easily and quickly extracted from above through an upper opening of the grinding chamber 5, with no need of disassembling the walls 13 of the grinding chamber and dramatically reducing the maintenance times:

in fact, the central portion 290 lacking external inserts 292, 294 has coupling clearances with walls 13 of chamber 5 that are much greater and looser than the bottom wall 29 provided with the external inserts 292, 294.

[163] The external inserts 292, 294 allowed the author of the present invention to also reduce the mill maintenance time by 2-3 hours, disassembling and reassembling the rotor 7.

[164] In a second aspect, the invention relates to a process for treating organic solid waste such as for example urban solid waste, food scraps, remains from mowing or pruning, vegetal residues from agricultural activity, waste materials similar to the urban ones, FOS ("dry organic fraction") of the urban waste, comprising the following steps:

- providing an attritor mill 1, 1' , 1" in its turn comprising a grinding container 3 which forms a grinding chamber 5 in its inside and a rotor 7 housed inside said container 3, wherein a plurality of arms 9, 9', 9" radially protrudes from the rotor 7;

- mixing the organic solid waste to be treated with a plurality of grinding free bodies 11 in the grinding chamber 5;

- agitating the organic solid waste to be treated and the plurality of grinding free bodies 11 making the rotor 7 rotate on itself so that its arms 9, 9', 9" strike the grinding free bodies 11, and at least a part of the latter bounce against the walls of the grinding chamber 5 and other grinding free bodies, and/or strike the organic solid waste to be treated, so as to grind, crush or mince the latter.

[165] In general the use of an attritor mill 1, 1' , 1" having pebbles or other grinding free bodies agitated by a vertical axis rotor permits to efficiently treat urban organic waste of the previously exemplified types, desiccating and transforming them into a dry granular or dusty material or anyway with much smaller humidity contents and a much greater calorific power, and thus ready to be directly used as fuel.

[166] Thanks to the high average speeds of the grinding free bodies 11 during the functioning of the attritor mill 1, 1' , 1" , even if the latter is substantially modest-sized, it is capable of treating high amounts of urban organic waste, having a humidity content up to about 80%, quickly and with a good energetic and mechanical efficiency; for example, a single attritor mill 1, 1', 1" having a cylindrical grinding chamber with a diameter DC of about 80-90 cm and a height HC of about 90 cm is capable of treating, by reducing it into dust or dry granulate, an average capacity of 1300-1800 kg/hour of urban organic waste that is "wet" with a humidity content of about 80%, against an electric energy consumption of about 20 kW/h.

[167] This makes the attritor mill 1, 1' , 1" particularly suitable for making plants for treating waste or other materials, relatively small-sized, hence particularly suitable for being installed on islands, mountain zones or other places difficult to be reached or with scarce energetic availability, or again particularly suitable for being supplied with solar, aeolic energy or with other alternative energies.

[168] Advantageously the organic solid waste to be treated are introduced in continuous into the grinding chamber 5 and after being treated they are extracted in continuous from the same grinding chamber 5.

[169] It is now described a possible example of functioning and use of the previously described attritor mill 1 with reference to Figures 1-6.

[170] The urban organic solid waste, or other material to be treated, possibly after preventive grosser screening or grinding, are introduced into the grinding chamber 5 through the supplying duct 15, for example through the aforementioned Archimedean screw or pusher and mixed with the grinding free bodies 11 and with the mass of waste - or other material to be treated - already present in the chamber 5 and already partially ground .

[171] As the rotor 7 quickly rotates on itself about the axis Al, the arms 9, 9', 9" repeatedly and randomly strike the grinding free bodies 11 more or less like baseball bats, throwing the bodies 11 one against the other, against the semi-ground mass of waste or against the walls of the grinding chamber 5.

[172] A good part of the mechanical energy provided by the rotor 7 directly or through the grinding bodies is converted into thermal energy that heats the chamber 5 and its content, in particular the grinding free bodies 11 and the waste - or other material to be treated - ground or semi-ground.

[173] As a consequence, the ground or semi-ground wastes, even if originally partly decomposed and putrefying, dry and desiccate, generally becoming more fragile and breaking up into granules, scales, dust, shavings or other particles substantially dry and anyway more volatile compared with the waste entering the chamber 5.

[174] Since they are generally more volatile than the incoming waste, both due to the motion of the grinding free bodies 11 and thanks to the pneumatic suction, that, as mentioned, is advantageously created in the space 22 within the casing 23 and outside of mill 1, part of the dry particles of the waste tends to rise to the upper part of the grinding chamber 5 until they exit through the extraction grids 17, which grids limit the maximum dimension of the exiting particles withholding the grinding free bodies 11 in the grinding chamber .

[175] Another part of the ground particles, basically their less volatile fraction, flows down to the bottom wall 29 and therefore exits radially through one or more of the first extraction openings 10 in the lower part of the grinding chamber 5, for example sucked thanks to the pneumatic depression present in the space 22 and/or launched by centrifugal force.

[176] The edge of the bottom surface 29 protruding from the slit - or the first opening- 10 facilitates the downward exit of the ground material and increases the quantity of the material that can be ground for the unit of time.

[177] Periodically, for example after a few days, the attritor mill 1 can be stopped and a user, for example through the door 28 can reach the grinding chamber 5, clean it from possible encrustations or dirt and extract the grinding free bodies (Figure 1) .

[178] The grinding free bodies 11 can thus be sieved eliminating those that became too small due to wear and tear, afterwards they can be re-introduced into the chamber 5 possibly together with fresh grinding free bodies 11.

[179] Both the first extraction openings 10 and the new sizes of the extraction grids 17, determined by the heights HI and H2 increase the overall flow area through which the ground product is extracted from the grinding chamber, increasing the quantity of materials that the mill 1 is able to treat in comparison with the known mills.

[180] Thanks to the previous teachings, the author of the invention was able to increase up to 30-45% the capacity of the ground material compared to other known attrition mills.

[181] The first extraction openings 10 located by the bottom wall 29 also allow the heavier and less volatile ground particles to be extracted more quickly, reducing the formation of particle deposits and crusts at the same time in the space between any sub-floor 8 and the bottom wall 29.

[182] When, as shown in Figure 2, the bottom wall 29 radially extends beyond the lateral walls 13 and outside of them or the disk that forms the bottom wall 29 has a diameter greater than the grinding chamber 5, the material ground that exits the slit 10 follows radial trajectories that are almost all horizontal and does not reach, or however reaches at a minimum extent, the bearings and other mechanical parts located on the disk of wall 29.

[183] In addition, when, as shown in Figure 2, the bottom wall 29 extends radially beyond the lateral walls 13 and outside of them, the problems previously described are completely eliminated of the wear and tear of the lateral walls 13 of the chamber 5 or the obstruction of light between the disk of the bottom wall 29 and the lateral walls 13, lengthening the operative life of the machine and reducing the failures and maintenance interventions.

[184] In the embodiments shown in Figures 7-12, instead, a part of the ground particles - mdicatively up to about 70% - basically their less volatile fraction, flows down to the bottom wall 29 through the radial gap present between the external edge of the wall and the walls of the grinding chamber 5 and then possibly through one or more of the first extraction openings 10' , 10" in the lower part of the grinding chamber 5, for example sucked by the pneumatic depression present in space 22 or in any case downwards through the suction conduit 110.

[185] In other words, the first extraction openings 10' , 10" located in below the bottom wall 29 and/or the suction conduit 110 allow the heavier and less volatile ground particles to be extracted quicker, reducing the formation of particle deposits and crusts at the same time in the space between the sub-floor 8 and the bottom wall 29.

[186] From the previous description it is moreover clear how a mill 1, 1' , 1" according to the invention is particularly suitable for operating in continuous, with a continuous inflow of waste or other materials to be treated into the grinding chamber 5 and a continuous outflow of desiccated particles from the grids 17, requiring technologies relatively simple in order to automate the process.

[187] The aforementioned use of Archimedean screws or other feeders in continuous, and of the fan or other sucker or blower 21 helps automating and making the functioning in continuous of the mill 1, 1', 1" possible .

[188] The use of the heat produced by the transformation of the mechanical power provided by the rotor 7 or by the heating elements 33 to desiccate or anyway to dry the organic solid waste helps increasing the energetic efficiency of the attritor mill and of the process for treating the organic solid waste according to the invention.

[189] Furthermore, the combined action of the temperature and of the repeated and violent impacts with the grinding free bodies 11 helps destroying a great part of the bacteria initially present in the waste, thus in particular destroying the resistant shells that protect such microorganisms, disinfecting and by the way making the product exiting from the mill biologically more stable.

[190] The previously described examples of embodiments can undergo various changes and variations yet without coming out of the scope of protection of the present invention .

[191] For example an attritor mill according to the invention can also operate discontinuously, for example by supplying the material to be treated and extracting the treated material according to the batch modality.

[192] The supporting protrusions 19 can be shaped of not only as rectilinear oblong ribs, but for example have also curved shapes.

[193] When they have the shape of semi-spheres, spherical-caps or studs and are in groups of three, the supporting protrusions 19 can be clearly placed at the vertexes even of a non-equilateral triangle or other types of geometric figures or be arranged for example in a star-like, spiral-, staggered arrangements or concentric circles .

[194] Moreover, all details are replaceable with technically equivalent elements.

[195] For example the used materials, as well as their dimensions, can be any according to the technical needs .

[196] It is to be intended that an expression such as "A comprises B, C, D" also comprises and describes even the particular case wherein "A consists of B, C, D" .

[197] The examples and lists of the possible variations of the present application are to be intended as non exhaustive lists.