WO2015071528A1 - Method for limiting an amount of its particle size smallest fraction which is generated in the counterjet grinding process of minerals - Google Patents
Method for limiting an amount of its particle size smallest fraction which is generated in the counterjet grinding process of minerals Download PDFInfo
- Publication number
- WO2015071528A1 WO2015071528A1 PCT/FI2014/000033 FI2014000033W WO2015071528A1 WO 2015071528 A1 WO2015071528 A1 WO 2015071528A1 FI 2014000033 W FI2014000033 W FI 2014000033W WO 2015071528 A1 WO2015071528 A1 WO 2015071528A1
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- WIPO (PCT)
- Prior art keywords
- grinder
- pairs
- crash
- amount
- fraction
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Classifications
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B02—CRUSHING, PULVERISING, OR DISINTEGRATING; PREPARATORY TREATMENT OF GRAIN FOR MILLING
- B02C—CRUSHING, PULVERISING, OR DISINTEGRATING IN GENERAL; MILLING GRAIN
- B02C19/00—Other disintegrating devices or methods
- B02C19/06—Jet mills
- B02C19/065—Jet mills of the opposed-jet type
Definitions
- the invention relates to a method for limiting an amount of its particle size smallest fraction which is generated in the counter] et grinding process of minerals so that the amount of the fine (overfine) fraction, whose particle size falls below the smallest aimed particle size, is reduced in the grinding.
- over fine fraction When generated in the mechanical grinding processes product, to which a certain maximum limit for particle size has been set, in all grinding processes also over fine fraction is generated belonging to the product.
- the over fine fraction is as its particle size below the smallest desired particle size. In the grinding process generated over fine fraction is useless energy cost.
- the overfine fraction causes problems and needless costs also for the end products in which products the ground material is used. The smallest particles including in said products are also threat for healthy and environment. Typically the production of this needless and plenty of energy used over fine fraction is limited by means of a closed grinding circulation, where by means of classification made after grinding end product having accepted fine level is removed from the circulation load.
- the efficiency coefficients of the classification devices or processes are, however, weak. Typically only 40 - 70 % of its particle size ready product, including in the circulation load, can be separated as an end product, wherein the other portion returns back into the grinding stage.
- the efficiency of the separation of its quality accepted end product is the weaker the smaller end product is desired to produce.
- the amount of the overfine fraction can be remarkably reduced, when it is obtained for the ground material by means of typical mechanical grinding methods as even as possible and of its particle size such a size, from which the grinding must be continued by means of counterjet grinding. It is used kinetic energy in the continued grinding i.e. 2-phase counterjet grinding technic based on the use of gas/solid suspension formed of powerful work gas and the material to be ground.
- the energy contents of the working gas is utilized so, that only necessary amount of energy is used when the material to be ground is transferred to the start portion of the special nozzles and the use of energy is applied as kinetic energy especially in the conical expanding portion after the throat of the acceleration nozzle.
- Characteristics for the method according to the invention is, that amount of the particle sizes which are smaller than the target size, is reduced by taking effect to crash into each other of the particles which crash happens in the counterjet grinder, wherein at least two side by side coupled grinder pairs are used, wherein the generated kinetic energies are arranged to differ from each other, said energies being calculated by means of crash diameters of grinder pairs per one mm2 of the crash cross-section area, wherein the run to crash situation of the particles of rougher fraction ground by means of one grinder of the mentioned grinder pair is improved and by means the other grinder of the pair the run of the smaller particles to crash situation is weakened.
- the size distribution of the particles becomes steeper in the area of smaller size, when a certain portion, for example half of the particles to be ground, is lead into such kind of grinder, by means of the kinetic energy of said grinder can hardly any overfine fraction be produced.
- the other grinder can be usual grinder and more effective, where also producing of overfine fraction is allowed.
- Fig. 1 shows side by side coupled grinders having different nozzle geometry
- Fig. 2 shows side by side coupled grinders having alternative nozzle geometry.
- Fig. 3 shows side by side coupled grinders having other alternative nozzle geometry.
- Fig. 4 shows schematically nozzles having directed to common grinder.
- Grinder unit of counterjet grinder in figure 1 is formed at least two pairs of acceleration nozzles 3 and 4, which pairs are directed to own grinder chambers 1 and 2, where crash of the opposite jets happens.
- Working gas including particle flow to be ground is distributed equally to nozzles 3 and 4 of both pairs.
- the narrowest portion or throat of all nozzles 3 and 4 has same diameter D.
- the nozzles 3 and 4 differ from each other only in then- widening angles, which is bigger in the nozzles 4. Due to the bigger widening angle the diameter d2 in the crash point has larger cross-section area than corresponding diameter dl of the grinder pair 1.
- the kinetic energies of the flows per mm2 of the cross-section area at crash point are thus different and energies are smaller in the grinder pair 2.
- the grinder 2 works by means of smaller kinetic energy than the grinder 1 observed per mm2 at the point d1.
- the grinder 2 produces essentially less overfine fraction than the grinder 1.
- the construction of the grinder units 1, 2 is arranged so that the start portion of the special nozzle is formed of narrowing conical part, which ends at the point of the throat part D, when arrived said part the speed of the material has been increased from typical speed of pneumatic transfer 15 - 30 m/s to over 100 m/s which is near the speed which is needed in grinding. After the throat part D of the nozzle there is widening conical part which ends in the grinding chamber.
- the used base level of the kinetic energy is elected based on pressure and flow volume of the working gas and amount of the solid material.
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- Engineering & Computer Science (AREA)
- Food Science & Technology (AREA)
- Disintegrating Or Milling (AREA)
Abstract
Method for limiting an amount of its particle size smallest fraction which is generated in the counterjet grinding process of minerals so that the amount of the fine (overfine) fraction, whose particle size falls below the smallest aimed particle size, is reduced in the grinding. Amount of the particle sizes which are smaller than the target size, is reduced by taking effect to crash into each other of the particles which happens in the counterjet grinder, wherein in the method at least two side by side coupled grinder pairs (1, 2) are used, wherein the generated kinetic energies are arranged to differ from each other, said energies being calculated by means of crash diameters (d1,- d4) of grinder pairs (1, 2) per one mm2 of the crash cross-section area, wherein the run to crash situation of the particles of rougher fraction ground by means of one grinder of the mentioned grinder pair is improved and by means of the other grinder of the pair the run of the smaller particles to crash situation is weakened.
Description
METHOD FOR LIMITING AN AMOUNT OF ITS PARTICLE SIZE SMALLEST FRACTION WHICH IS GENERATED IN THE COUNTERJET GRINDING
PROCESS OF MINERALS
The invention relates to a method for limiting an amount of its particle size smallest fraction which is generated in the counter] et grinding process of minerals so that the amount of the fine (overfine) fraction, whose particle size falls below the smallest aimed particle size, is reduced in the grinding.
In many product applications where solid pulverized materials are used as raw materials, for example minerals, a steep distribution of the particle sizes are presupposed.
These kind of typical mineral based product applications and materials are talc, kaoline in plastic industry used woUastonite and other heavy auxiliary materials.
When fine raw material powders have steep and narrow particle distribution, it is possible by means of this property to take effect positively to the manufacturing process of the actual end product and to its properties. When a steep particle distribution exists in the lower portion of the size class, it follows that viscosity of paste or other sludge-like end product will go down. This is remarkable advantage for example in the manufacturing of paste for paper industry.
When coating paper or cardboard their gloss can be improved and drying costs also can be reduced. In the applications, where this kind of material is used as filler material, the strength of the end product increases and amount of the binding materials decreases.
When generated in the mechanical grinding processes product, to which a certain maximum limit for particle size has been set, in all grinding processes also over fine fraction is generated belonging to the product. The over fine fraction is as its particle size below the smallest desired particle size. In the grinding process generated over fine fraction is useless energy cost. The overfine fraction causes problems and needless costs also for the end products in which products the ground material is used. The smallest particles including in said products are also threat for healthy and environment.
Typically the production of this needless and plenty of energy used over fine fraction is limited by means of a closed grinding circulation, where by means of classification made after grinding end product having accepted fine level is removed from the circulation load.
The efficiency coefficients of the classification devices or processes are, however, weak. Typically only 40 - 70 % of its particle size ready product, including in the circulation load, can be separated as an end product, wherein the other portion returns back into the grinding stage.
The efficiency of the separation of its quality accepted end product is the weaker the smaller end product is desired to produce. The amount of the overfine fraction can be remarkably reduced, when it is obtained for the ground material by means of typical mechanical grinding methods as even as possible and of its particle size such a size, from which the grinding must be continued by means of counterjet grinding. It is used kinetic energy in the continued grinding i.e. 2-phase counterjet grinding technic based on the use of gas/solid suspension formed of powerful work gas and the material to be ground.
In this solution the particles of the material to be ground are accelerated to have high speed in special nozzles. This speed and amount of particles can be accurately adjusted and also geometry of nozzles and pressure and temperature of working gas and by this way controlled the crash situation, where particles breaks up.
The energy contents of the working gas is utilized so, that only necessary amount of energy is used when the material to be ground is transferred to the start portion of the special nozzles and the use of energy is applied as kinetic energy especially in the conical expanding portion after the throat of the acceleration nozzle.
Characteristics for the method according to the invention is, that amount of the particle sizes which are smaller than the target size, is reduced by taking effect to crash into each other of the particles which crash happens in the counterjet grinder, wherein at least two
side by side coupled grinder pairs are used, wherein the generated kinetic energies are arranged to differ from each other, said energies being calculated by means of crash diameters of grinder pairs per one mm2 of the crash cross-section area, wherein the run to crash situation of the particles of rougher fraction ground by means of one grinder of the mentioned grinder pair is improved and by means the other grinder of the pair the run of the smaller particles to crash situation is weakened.
By means of this method the size distribution of the particles becomes steeper in the area of smaller size, when a certain portion, for example half of the particles to be ground, is lead into such kind of grinder, by means of the kinetic energy of said grinder can hardly any overfine fraction be produced. The other grinder can be usual grinder and more effective, where also producing of overfine fraction is allowed.
In the following the invention is described by referring to the attached drawings where
Fig. 1 shows side by side coupled grinders having different nozzle geometry
Fig. 2 shows side by side coupled grinders having alternative nozzle geometry.
Fig. 3 shows side by side coupled grinders having other alternative nozzle geometry.
Fig. 4 shows schematically nozzles having directed to common grinder.
Grinder unit of counterjet grinder in figure 1 is formed at least two pairs of acceleration nozzles 3 and 4, which pairs are directed to own grinder chambers 1 and 2, where crash of the opposite jets happens. Working gas including particle flow to be ground is distributed equally to nozzles 3 and 4 of both pairs. The narrowest portion or throat of all nozzles 3 and 4 has same diameter D. The nozzles 3 and 4 differ from each other only in then- widening angles, which is bigger in the nozzles 4. Due to the bigger widening angle the diameter d2 in the crash point has larger cross-section area than corresponding diameter dl of the grinder pair 1. The kinetic energies of the flows per mm2 of the cross-section area at crash point are thus different and energies are smaller in the grinder pair 2. The smallest particles in the particle flow ground in the grinder 2 will easily turn sidewards, are retarding and do not hit opposite particles as well as do not take part the crashs. Due to this hardly any overfine fraction is generated in the grinder 2. Possibility to generate overfine fraction is bigger in the grinder 1. As a whole the method, however, produces essentially less overfine fraction compared with known grinders.
In the figure 2 the difference is location of the throat part (diameter D) of the nozzles in the grinder 2, which location is essentially farther from the end of the nozzles 5 than in the grinder 1. This causes between nozzle geometries of the grinders 1 and 2 a difference, which produces different kinetic energy values at crash points (diameters d1 and d2) calculated per mm2.
In the figure 3 there is shown correspondingly nozzles 3, as in the figures 1 and 2, but the nozzles 6 has been transferred nearer to each other in the grinder 1 so, that the free distance L1 is essentially smaller than the free distance L2 in the grinder 2. In this the grinder 2 works by means of smaller kinetic energy than the grinder 1 observed per mm2 at the point d1. The grinder 2 produces essentially less overfine fraction than the grinder 1. The construction of the grinder units 1, 2 is arranged so that the start portion of the special nozzle is formed of narrowing conical part, which ends at the point of the throat part D, when arrived said part the speed of the material has been increased from typical speed of pneumatic transfer 15 - 30 m/s to over 100 m/s which is near the speed which is needed in grinding. After the throat part D of the nozzle there is widening conical part which ends in the grinding chamber.
The widening conical part, its length as welt as widening angle all have very remarkable meaning concerning grinding grade and generation of overfine fraction. The influence of the kinetic energy to grinding grade and to amount of overfine fraction are adjusted conclusively in the widening portion after the throat of the acceleration nozzle. Also common grinder chamber 8 according to figure 4 is possible.
By means of dimensioning the nozzle part is defined:
- how much kinetic energy /mm2 is used in the grinding section, which is at points of the diameters d1- d2. The used base level of the kinetic energy is elected based on pressure and flow volume of the working gas and amount of the solid material.
- Experimentally has been shown that grinding effect and result will change when the cross-section area D of the acceleration nozzle and widening part of the nozzle are changing.
The grinding process and grinding effect can be controlled by observing pressure of the as a constant flow functioning powerful working gas, pressure in the grinding chamber and observing the mass flow of the material to be ground. These process values are signal of the grinding result and of that how much kinetic energy is used in the grinding process.
Claims
1. Method for limiting an amount of its particle size smallest fraction which is generated in the counterjet grinding process of minerals so that the amount of the fine (overfine) fraction, whose particie size falls below the smallest aimed particle size, is reduced in the grinding, characterized in that amount of the particle sizes which are smaller than the target size, is reduced by taking effect to crash into each other of the particles which crash happens in the counterjet grinder,
- at least two side by side coupled grinder pairs (1, 2) are used, wherein the generated kinetic energies are arranged to differ from each other, said energies being calculated by means of crash diameters (d1,- d4) of grinder pairs (1, 2) per one mm2 of the crash cross- section area, wherein the run to crash situation of the particles of rougher fraction ground by means of one grinder of the mentioned grinder pair is improved and by means of the other grinder of the pair the run of the smaller particles to crash situation is weakened.
2. Method according to claim 1, characterized in that one grinder of the grinder pairs (1, 2) is equipped with larger widening angle in the nozzle (4) than in the nozzles (3) in another pair.
3. Method according to claim 1, characterized in that one grinder of the grinder pairs (1, 2) is equipped with longer widening length in the nozzle (5) than in the nozzles (3) in another pair.
4. Method according to claim 1, characterized in that one grinder of the grinder pairs (1, 2) is equipped with shorter free nozzle distance (L1) than the nozzle distance (L2) in another pair.
5. Method according to claim 1, characterized in that there are lead to the grinder pairs (1, 2) of their pressure and mass flows equal working gas flows and the throat diameter (D) is same for all nozzles of the grinder pairs.
6. Method according to claim 1, characterized in that equal amount of the working gas flows lead to the grinder pairs (1, 2) are controlled by measuring surface temperatures of the nozzles.
7. Method according to claim 1, characterized in that the grinder pairs (1, 2) are fitted into common grinding chamber (8).
8. Method according to claim 1, characterized in that the grinder pairs (1, 2) are fitted into common grinding chamber (8), wherein from different directions extending nozzles are directed essentially to the same point.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| FI20130338 | 2013-11-14 | ||
| FI20130338 | 2013-11-14 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| WO2015071528A1 true WO2015071528A1 (en) | 2015-05-21 |
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| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| PCT/FI2014/000033 WO2015071528A1 (en) | 2013-11-14 | 2014-11-14 | Method for limiting an amount of its particle size smallest fraction which is generated in the counterjet grinding process of minerals |
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN106060516A (en) * | 2015-04-17 | 2016-10-26 | 丰田自动车株式会社 | Stereoscopic object detection device and stereoscopic object detection method |
Citations (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US2704635A (en) * | 1951-06-02 | 1955-03-22 | Conrad M Trost | Pulverizing mill having opposed jets and circulatory classification |
| EP0488637A2 (en) * | 1990-11-27 | 1992-06-03 | Xerox Corporation | A fluidized bed jet mill |
| WO1992011090A1 (en) * | 1990-12-19 | 1992-07-09 | Oy Finnpulva Ab | A pulverizing chamber of a counterjet pulverizer |
| WO2001024935A2 (en) * | 1999-10-06 | 2001-04-12 | Cornerstone Technologies, L.L.C. | High pressure mill and method of creating ultra-fine particles of materials using the same |
| WO2007060283A1 (en) * | 2005-11-28 | 2007-05-31 | Micropulva Ltd Oy | Method for industrial production of especially fine powders |
| JP2009106839A (en) * | 2007-10-29 | 2009-05-21 | Sunrex Kogyo Kk | Jet mill |
-
2014
- 2014-11-14 WO PCT/FI2014/000033 patent/WO2015071528A1/en active Application Filing
Patent Citations (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US2704635A (en) * | 1951-06-02 | 1955-03-22 | Conrad M Trost | Pulverizing mill having opposed jets and circulatory classification |
| EP0488637A2 (en) * | 1990-11-27 | 1992-06-03 | Xerox Corporation | A fluidized bed jet mill |
| WO1992011090A1 (en) * | 1990-12-19 | 1992-07-09 | Oy Finnpulva Ab | A pulverizing chamber of a counterjet pulverizer |
| WO2001024935A2 (en) * | 1999-10-06 | 2001-04-12 | Cornerstone Technologies, L.L.C. | High pressure mill and method of creating ultra-fine particles of materials using the same |
| WO2007060283A1 (en) * | 2005-11-28 | 2007-05-31 | Micropulva Ltd Oy | Method for industrial production of especially fine powders |
| JP2009106839A (en) * | 2007-10-29 | 2009-05-21 | Sunrex Kogyo Kk | Jet mill |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN106060516A (en) * | 2015-04-17 | 2016-10-26 | 丰田自动车株式会社 | Stereoscopic object detection device and stereoscopic object detection method |
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