Patent Grant
9427743
This application is a National Stage Application of PCT/EP2013/057881, filed 16 Apr. 2013, which claims benefit of Serial No. MI2012A000635, filed 17 Apr. 2012 in Italy, each of these applications being incorporated herein by reference. To the extent appropriate, a claim of priority is made to each of the above disclosed applications.
The present invention relates in general to the sector of devices and apparatus for grinding and crushing materials and products containing and formed by particles, such as, typically, powders, products and similar compounds in powdered form, into smaller particles, and in particular relates to an apparatus for the micronisation of a powdered product or similar substance comprising a micronising mill operating with high-energy jets of a gaseous fluid such as air, which said mill uses a novel, innovative system of dispensing the powdered material and product to be micronised and feeding it to the jet mill.
The present invention also relates to a corresponding process for the micronisation of a powdered product.
Current technology for crushing powders, such as powdered compounds for use in the pharmaceutical industry and powdered material in general, offers numerous solutions, some of which are alternative to one another, including powder micronisation systems based on the use of a high-energy gaseous-fluid-jet mill, also called a jet mill.
Said jet mills have a relatively simple construction and structure, normally comprising: a circular grinding or micronisation chamber wherein a series of high-energy jets, generated by a compressed gaseous fluid such as air, cause continuous collisions between the powdered product particles, and consequently their micronisation; a system of feeding and loading the powdered material into the micronisation chamber based on the use of a Venturi tube, also simply called a Venturi, namely a narrowing or throat in a pipe into which a gaseous fluid is conveyed so as to cause a negative pressure that attracts the powdered material; and a selection or classification system, of the static or dynamic type, associated with a central zone of the micronisation chamber and designed to classify the crushed and micronised particles and separate them selectively according to particle size.
The high-energy jets of gaseous fluid are inclined in relation to the radius of the micronisation chamber, with the result that said jets cause a fluid dynamic flow of gaseous fluid in said chamber that draws the particles of powdered material with it and presents two components: a first tangential component that rapidly moves the particles of powdered material in a vortex around the axis of the micronisation chamber, and a second radial component that tends to move the particles from the peripheral zone to the central zone of the micronisation chamber.
In this way, the powdered material or product is subjected, in said fluid dynamic flow in the micronisation chamber, to continual mixing and collisions between its particles.
Moreover, in the flow generated by the high-energy jets of gaseous fluid, the particles are subject to a centrifugal force that also leads to classification, whereby the finer and already micronised particles tend to move towards the central inner part of the micronisation chamber, from which they are evacuated, while the larger ones, not yet micronised, tend to remain in the peripheral outer zone of the micronisation chamber and to rotate around the axis on the periphery, thus undergoing further collisions.
The micronisation process is normally but not solely performed on powdered materials and practically dry powders.
Improvements over the years have led to optimisation of the configuration and geometry of the holes or nozzles through which the high-pressure jets of gaseous fluid are activated and created, both in the micronisation chamber and in the micronised particle classification system, where a dynamic classifier has been introduced in particular, already used in other types of apparatus, which uses a rotary element with peripheral wings that only allows micronised particles of the required size to pass through.
Nevertheless, current micronisation technology, including that based on the use of jet mills, still presents problems and limitations that need to be overcome and solved with further improvements, especially as regards feeding of the powdered material to be micronised to the micronisation chamber of the jet mill.
In particular, the current system of feeding the powdered material to be micronised, typically comprising a Venturi tube, as already stated, presents the following problems and drawbacks.
Furthermore, it is remarked that screw feeders, as those adopted in the actual technique, for feeding and transporting powders, have relevant problems related to the metal abrasion during the feeding, that can contaminate the final product.
Moreover screw type feeders cannot inject powders directly into a jet mill.
Indeed, as before discussed, in order to inject the powders an additional tool for acceleration and injection of the powders is required, as for example a Venturi type pneumatic feeder that aspirates the powder leaving the screw and finally blow it with high gas consumption into the spiral mill.
Beneath all mentioned disadvantages and limitations the screw feeder and the Venturi system underlay and imply strong wear if abrasive powders have to be transported.
Still, screw type feeders cannot feed sticky powders or powders with low or no flowing behavior (e.g. flake like powders, short fibres or most of powders with average particle size below 10 microns down to nanometers) and cleaning is very difficult and time consuming.
It is also remarked that the nowadays increasing demand of powders with submicron and nanometre sized particles requires efficient production methods, and the actual state of the art of jet milling technologies appears as not being capable of completely fulfilling this task, as above outlined.
For instance, blocky shape abrasive diamond powders with a particle size below 10 microns cannot be efficiently transported by using a screw type feeder, as those adopted at present in the technique.
Moreover also the methods for producing powders, in particular with low impurities, to be used in application involving grinding or lapping, as diamond powders, SiC (Silicon Carbide), WC (Tungsten Carbide), CBN (Cubic Boron Nitride) and B4C (Boron Carbide) powders, appear to require further improvements.
A first purpose of the present invention is therefore to provide a novel apparatus for micronisation of powders, in particular of the type comprising a high-energy fluid-jet mill, which eliminates the above-mentioned drawbacks present in the prior art, and above all can control and precisely dispense the quantity of powdered material fed to the micronisation apparatus, i.e. to the corresponding jet mill, to be micronised.
A further more general purpose of the present invention is also to increase the overall efficiency of the micronisation process used for powders and similar materials, by means of precise control and dispensing of the quantity of powdered material fed to the zone in which said material will be micronised.
A third purpose of the present invention is to find a solution that allows the jet mill to be fed with low flow rates and quantities of material to be micronised, at the same time operating with high operating pressures to generate the fluid jets in the mill, as required to obtain optimum micronisation of superior quality with given types of powdered materials.
Finally, a fourth purpose of the present invention is to improve and make even more efficient and controllable the micronisation of powders and powdered compounds specifically designed for use and application in the pharmaceutical field, an industry in which said needs for increasing efficiency of the micronisation process and increasingly high quality of the micronised product are particularly felt.
Moreover another possible purpose of the invention can be directed to improve the actual technique for producing powders, in particular with low impurities, and thereby produce improved and more efficient powders, to be used in application involving grinding or lapping, as diamond powders, SiC (Silicon Carbide), WC (Tungsten Carbide), CBN (Cubic Boron Nitride) and B4C (Boron Carbide) powders, and other types of powder.
Said purposes can be deemed to be fully achieved by the powder micronisation apparatus having the characteristics defined in independent claim 1.
Particular forms of embodiment of the present invention are defined by the dependent claims.
In the powdered material micronisation apparatus of the present invention the jet-mill is specifically of the spiral type, that means that the nozzles are forming a circle, and are not all directed towards one point, as in other micronization systems, like for instance the fluidized bed jet-mills with opposite nozzles, and thereby with jet trajectories incident in a common point.
Moreover an essential feature of this proposed powdered material micronisation apparatus, compared to the systems at present known, is the combination of a spiral jet-mill, instead of a opposite jet mill, with a new generation of powder feeders, of the type of a powder pump, implying better milling results at higher efficiencies and lower impurities level, as those caused by wear, without limitations of powders to be handled.
Even flakes or fibres can be precisely injected into the mill.
In particular the system or apparatus here proposed is composed by only one single feeding step, and the feeder is a so called powder pump without any mechanical moving parts in contact with the powder.
The feeding of the powder is made in a volumetric way and in a dense phase mode instead of the traditional mechanical and pneumatic transport of the powder.
Therefore the powder is flowing at low speed to the milling chamber (normally by the factor 3 to factor 10 lower particles speeds compared to pneumatic powder feeding). This reduce dramatically the wearing, and makes easy the control of final feed-rates. No limitations are indentified by the applicant regarding the powders to be handled. With multiple feeding parts in series the synchronization is fundamental to avoid clogging or emptying of the feeding line
There are numerous advantages, some of which have been implicitly stated above, associated with the novel powder micronisation apparatus according to the present invention, such as those listed in below by way of example:
These and other purposes, characteristics and advantages of the present invention will clearly appear from the following description of a preferred embodiment thereof, given by way of example but not of limitation, by reference to the annexed drawings, wherein:
With reference to the drawings, an apparatus or unit, conforming to the present invention, for grinding or micronisation of a material containing and formed by particles to be micronised, typically constituted by a product, compound, substance or powdered material P in general, is indicated as a whole as 10, and comprises in particular:
In detail, feed system 13 operates so as to aspirate and attract powdered product P from container 11, along a first transport or entrance line 14, and then feed it to jet mill 12, along a second transport or exit line 16.
In this way, powdered product P is conveyed along the first transport line 14 installed upstream of feed system 13, and subsequently conveyed along the second transport line 16, installed downstream of feed system 13, from container 11 to jet mill 12, where powdered product P is micronised.
As jet mill 12 possesses substantially known characteristics, it is only schematically illustrated in the drawings, and will not be described in detail.
It will merely be mentioned that jet mill 12 comprises an annular outer pressure chamber 12a and a circular inner micronisation chamber 12b, separated from one another by an annular intermediate wall 12c in which are drilled a plurality of channels or through holes 12e, suitably inclined relative to the radius of micronisation chamber 12b, which place the two chambers 12a and 12b in communication.
In operation, jet mill 12 is supplied with a fluid F, in particular air, at high pressure, which is introduced into outer pressure chamber 12a, and emerges, in jet form, in inner micronisation chamber 12b through channels 12e, formed in annular separation wall 12c between the two chambers 12a and 12b.
In this way a system of high-energy jets G is generated, which are inclined and tangential to an imaginary circle, and which cause a vortical motion and an air spiral around the axis of micronisation chamber 12b, converging towards a central area 12b′ thereof.
Powdered material P in turn is fed by feed system 13 to inner micronisation chamber 12b of jet mill 12, with the result that particles of powdered material P are drawn by the vortical motion generated by jets G in micronisation chamber 12b, and are consequently liable to collide continually with each other and be crushed, so as to micronise powdered material P.
In particular, in the micronisation chamber, due to said vortical motion, the particles of powdered product P are subject to a centrifugal force that tends to move them towards annular wall 12c, so that they remain in the micronisation zone until the particles exceed a given size or have not yet been sufficiently crushed.
When said particles have been completely crushed, they are subjected to a radial force that tends to move them towards central zone 12b′ of micronisation chamber 12b, whence they are evacuated.
The vortical motion in the micronisation chamber therefore acts in such a way as to classify the particles and determine their evacuation, once micronised.
Micronisation apparatus 10 also contains an evacuation system, schematically illustrated with a pipe 18 and fitted at the outlet of jet mill 12, which has the function of evacuating from micronisation chamber 12b the gaseous flow consisting of fluid F and the material, indicated as P′, containing the particles of micronised powder, and conveying them to a separation system with known characteristics not shown in the drawings, designed to separate and collect the micronised particles from gaseous fluid F.
Optionally, micronisation apparatus 10 can also be fitted with an auxiliary exit, schematically illustrated by arrow 19, to recover the powder from jet mill 12.
Optionally, micronisation apparatus 10 can also contain, along transport line 16 fitted downstream of microdispenser device 20, a coaxial disperser 15 with known characteristics, schematically illustrated with an arrow in
According to one characteristic of the present invention, feed system 13 of micronisation apparatus 10 comprises, alternatively to conventional feed systems usually based on a Venturi tube, a microdispenser device 20, which dispenses powdered product P micrometrically, and feeds it or injects it directly into micronisation chamber 12b of jet mill 12.
Due to said microdispenser device 20, and unlike conventional Venturi type feed systems, which do not usually allow precise dispensing and control of the quantity of powdered material introduced into the jet mill to be micronised, in micronisation apparatus 10 according to the present invention the quantity or flow rate of powdered material P which is fed into jet mill 12 to be micronised is dispensed and determined precisely and kept constantly under control.
For this purpose, microdispenser device 20, which is an essential part of micronisation apparatus 10 according to the invention, transfers and feeds powdered product P from container 11 into micronisation chamber 12b of jet mill 12 in a way totally different from and alternative to Venturi type feed systems based on the creation, in a narrow section of a boundary layer, of a negative pressure designed to attract and feed the powdered material from the outside to the micronisation area.
Conversely, microdispenser device 20, as more particularly specified below, is designed to attract and feed powdered product P from container 11 to jet mill 12 via a series of high-frequency pulses imparted to the valves of said microdispenser device 20, which generate pneumatic microtransport of powdered material P along transport lines 14 and 16, and at the same time precisely dispense the quantity transported and fed.
In more detail, microdispenser device 20, which is an integral part of micronisation apparatus 10 according to the invention, is as described in the international patent applications published as WO 03/029762 A1 and WO 2010/11881 A2.
For all further details and clarifications not expressly described herein regarding microdispenser device 20, an essential part of micronisation apparatus 10, reference should therefore be made to said applications, the content of which must be deemed to be incorporated in the description of the present invention.
However, for the sake of clarity and completeness information, microdispenser device 20 is schematically illustrated in
As already stated, microdispenser device 20 is designed to receive powdered material P from container 11 along inlet line 14 and to feed it, in batched form, through outlet line 16 to micronisation chamber 12b of jet mill 12, where powdered material P will be micronised by the effect of high-energy air jets G, acting in said micronisation chamber 12b.
In particular, microdispenser device 20 comprises one or more dispensing units or sections, indicated as 21, associated with a suction line 22, wherein a vacuum or negative pressure is created, for example through a suction pump 23, and a pressure line 24, in which a pressure is generated, for example through a pressure pump 25.
A plurality of control valves 26 and 27 are fitted to place each dispensing unit 21 selectively in communication with suction line 22 and pressure line 24 respectively.
The various dispensing units 21 are designed to receive powdered material P from container 11 via transport line 14 and to dispense it, after measuring, to outlet line 16, so that it feeds jet mill 12.
A plurality of control valves 28 and 29 are fitted to place each dispensing unit 21 selectively in communication with inlet line 14 and outlet line 16 respectively.
It is therefore clear that the dispensing process, which is performed with microdispenser device 20 and allows jet mill 12 to be fed with an exactly determined quantity and at an exactly determined flow rate of powdered material, is basically the volumetric/quantitative type.
This dispensing process, as first illustrated, is based on filling dispensing units 21, which in turn define a given volume and consequently a given quantity of powdered material with which they are filled, and subsequent emptying of said dispensing units 21 so as to dispense the powdered material, after measuring, to jet mill 12.
In the operation of micronisation apparatus 10, the operator sets microdispenser 20, via setting and control means and taking account of the characteristics of powdered material P to be micronised, to feed jet mill 12 in the time unit with the desired quantity of powdered material P.
Said setting and control means in turn control the various control valves 26, 27, 28 and 29, namely their opening and closing, via suitable high-frequency pulses so as to cause each dispensing unit 21 to be filled, cyclically and alternately, with powdered material P originating from container 11, and subsequently emptied, thus feeding jet mill 12 with the quantity of powdered material P set by the operator.
In this way powdered material P, which is fed to micronisation chamber 12b where it will be micronised, is precisely measured, and its quantity is precisely determined, and kept constantly under control over time.
Microdispenser device 20 presents a special configuration and comprises suitable control and dispensing means, fully and clearly described in the above-mentioned patent applications WO 03/029762 A1 and WO 2010/11881 A2, which have the effect that microdispenser device 20 micrometrically dispenses and measures, in response to suitable commands issued at high frequency to control valves 26, 27, 28 and 29 associated with the various lines 14, 16, 22 and 24 connected with dispensing units 21, the quantity of powdered material P which is introduced into the pipe of outlet line 16 and consequently feeds micronisation chamber 12b of jet mill 12.
Powder P, originating from container 11, is therefore suitably micrometrically measured, while it passes through microdispenser device 20, from which it is introduced into the pipe of outlet line 16, so as to feed micronisation chamber 12b of jet mill 12.
Powdered material P is also fed to micronisation chamber 12b by pneumatic micrometric transport, due to the effect of the high-frequency pulses that control the opening and closing of the various control valves 26, 27, 28 and 29.
The pipes of lines 14 and 16 for the transport of powdered material P to and from microdispenser device 20 respectively are dimensioned on the basis of the maximum flow rates allowable to feed jet mill 12 via feed system 13.
Starting material P, containing the particles to be micronised, which is fed and dispensed through microdispenser 20, can consist of dry powders, a liquid solution or a paste, or a mixture often described by the English term “slurry”.
It will also be appreciated that the microdispencer device 20, differently from the traditional pumps, performs the feeding step without any mechanical moving parts in contact with the powdered material.
Still the feeding is made in a dense phase mode, instead of the traditional mechanical and pneumatic transport of the powder.
In this way the powder is flowing at low speed to the milling chamber (normally by the factor 3 to factor 10 lower particles speeds compared to pneumatic powder feeding), with the effect of reducing considerably the wearing.
Experimental Tests
Micronisation apparatus 10 according to the invention, including microdispenser 20, has been subjected to detailed experimental tests with the following purposes:
In particular the experimental tests were performed on a micronisation unit or apparatus comprising the following components:
The plant was tested with a powdered product consisting of lactose.
A first series of experimental tests was performed under the following conditions in the test unit:
In this first series of tests the spiral or jet mill, in combination with the pneumatic microdispenser, always operated correctly.
For the sake of completeness and to demonstrate said correct operation, the results of the particle-size analysis of the micronised powder output by the jet mill in this first series of tests are specified in the test report shown in
A second series of tests was performed under the following operating conditions in the test unit:
The above operating conditions used in said second series of tests, corresponding to a relatively low flow rate, namely 20 [g/h], of powdered material to the jet mill where it is to be micronised, and a relatively high operating pressure, namely 9 [barg], in the jet mill, designed to generate high-energy fluid jets, are not usually obtainable with conventional micronisation systems, wherein the jet mill is fed with Venturi type feed systems.
Also in this second series of tests the spiral mill or jet mill, in combination with the pneumatic microdispenser, always operated correctly, providing a micronised product complying with the desired quality requirements.
For the sake of completeness and to demonstrate said correct operation, the results of the particle-size analysis of the micronised powder output by the jet mill in this second series of tests are specified in the test report shown in
Briefly, these tests clearly demonstrate that the spiral mill or jet mill, in combination with the pneumatic microdispenser, always operates correctly, under all the operating conditions tested, confirming the innovative characteristics of micronisation apparatus 10 according to the invention.
Also for the sake of completeness, the photographic images in
From the above description, it is therefore clear that the present invention fully achieves the intended purposes.
In particular it provides a novel micronisation apparatus or unit which presents significant improvements and better performance compared with the apparatus currently known and used to micronise powders, in particular apparatus designed for use in the pharmaceutical industry, and also allows the quantity of powdered material to be introduced into the micronisation chamber for micronising to be controlled and dispensed with great precision, leading to significant favourable effects on the micronisation process as a whole.
Variations
Variations on micronisation apparatus 10 described above are obviously possible, and also fall within the scope of the present invention.
For example, more than one microdispenser device can be fitted to feed jet mill 12 with different materials containing particles, or different products in powdered form.
| Number | Date | Country | Kind |
|---|---|---|---|
| MI2012A0635 | Apr 2012 | IT | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2013/057881 | 4/16/2013 | WO | 00 |
| Publishing Document | Publishing Date | Country | Kind |
|---|---|---|---|
| WO2013/156465 | 10/24/2013 | WO | A |
| Number | Name | Date | Kind |
|---|---|---|---|
| 5992773 | Schwechten | Nov 1999 | A |
| Number | Date | Country |
|---|---|---|
| 1135274 | Aug 1962 | DE |
| 03029762 | Apr 2003 | WO |
| 2010011881 | Jan 2010 | WO |
| Entry |
|---|
| International Search Report and Written Opinion for International Application No. PCT/EP2013/057881 mailed Aug. 19, 2013 (10 pages). |
| Number | Date | Country | |
|---|---|---|---|
| 20150083830 A1 | Mar 2015 | US |
