EP0379711B1 - Method of sifting fine materials, and apparatus for carrying out the method - Google Patents

Method of sifting fine materials, and apparatus for carrying out the method Download PDF

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Publication number
EP0379711B1
EP0379711B1 EP89123623A EP89123623A EP0379711B1 EP 0379711 B1 EP0379711 B1 EP 0379711B1 EP 89123623 A EP89123623 A EP 89123623A EP 89123623 A EP89123623 A EP 89123623A EP 0379711 B1 EP0379711 B1 EP 0379711B1
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Prior art keywords
gas
drum
particles
speed
mass
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German (de)
French (fr)
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EP0379711A1 (en
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Roland Dr.-Ing. Nied
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B07—SEPARATING SOLIDS FROM SOLIDS; SORTING
    • B07B—SEPARATING SOLIDS FROM SOLIDS BY SIEVING, SCREENING, SIFTING OR BY USING GAS CURRENTS; SEPARATING BY OTHER DRY METHODS APPLICABLE TO BULK MATERIAL, e.g. LOOSE ARTICLES FIT TO BE HANDLED LIKE BULK MATERIAL
    • B07B7/00—Selective separation of solid materials carried by, or dispersed in, gas currents
    • B07B7/08—Selective separation of solid materials carried by, or dispersed in, gas currents using centrifugal force
    • B07B7/083—Selective separation of solid materials carried by, or dispersed in, gas currents using centrifugal force generated by rotating vanes, discs, drums, or brushes

Definitions

  • Comminution machines are known in which the particles to be comminuted are accelerated in a rapid gas flow and comminuted by colliding with one another or by impact on a target.
  • these constructions known as jet mills
  • jet mills put great effort into reducing the inherently higher energy requirements.
  • jet mills developed from this point of view result e.g. from TIZ departments, Vol. 109, No. 1, 1985.
  • Impact grinding is a widespread comminution process when the finest subtleties are to be achieved or the hardest materials are to be processed.
  • the rotor impact mills and the jet mills are available ("Speech Hall", Vol. 119, No. 7, 1986).
  • the drum speed cannot be increased arbitrarily.
  • the drum stands still and the gas carrying the good is introduced into the drum via nozzles with high energy so that forms a rotating flow with respect to the drum wall, which allows a separation between coarse and fine material in the mill, so that only finely ground material is discharged with the gas and through the discharge nozzle, which is fed to a classifier, classified and partly as fine material to be separated from the gas in a filter while the material rejected in the classifier is repeatedly treated until it has the mass of the fine material.
  • one way or the other should be aimed at defining the boundary between coarse and very fine material in such a way that the gas leaving the classifier via the discharge nozzle contains only solid particles with the lowest possible mass, while particles are still rejected, if they have already reached a relatively low mass in a less specific way.
  • a known spiral jet mill in which the material to be comminuted is held in a circular motion by means of propellant jets in a round grinding chamber and the finely ground material exits the chamber near the chamber axis in order to be fed to a classifier, is characterized in that material which has already been largely comminuted is given an increased rotational speed by additional blowing agent jets in a viewing zone lying between the outer grinding zone and the exit points, as a result of which the larger particles are returned to the grinding zone (DE-C-921 970).
  • the aim of this solution is to remove only very finely ground material from the mill and also to leave relatively finely ground particles as coarse material in the grinding process or to feed it to a new grinding process.
  • it is essential that the classification is within a mill and not a classification downstream of the mill and that the particles are accelerated exclusively with gas jets, that is to say exclusively pneumatically.
  • the parts of the material that still have a relatively large mass are first separated out from the material introduced into the classifier before the particles with a relatively low mass floating in the air flow as fine material enter a discharge nozzle by means of a classifying wheel, through which they are fed to a filter be, which holds back the fine material parts and allows the cleaned air to pass for reuse or further use.
  • the invention is now concerned with a classifier, that is to say a device connected downstream of a mill of any type. It is based on the object of making it possible for only very fine material with extremely low mass to be discharged from the classifier and for “fine material” to be rejected as belonging to the coarse material even if it is already regarded as fine material in current solutions and is fed to the filter .
  • the invention is intended to be one possibility show how a higher circumferential speed can be achieved for the gas rotating in the drum than is the case with the solutions with fixed or rotating drum, which are regarded as alternatives today, in order to have a relatively extremely small mass due to the centrifugal force that is developing Do not allow solid particles to emerge from the classifier, but instead again to the mass-reducing treatment.
  • the circumferential speed associated with the centrifugal force should be generated as rationally as possible.
  • the principle of the invention is the invention
  • the aim is to combine the two solution principles, which until now have only been viewed as alternatives, by first mechanically pre-accelerating a gas containing small particles to a certain circumferential speed, as is already the only measure for rotating drums, but that this acceleration involves a pulse transition between an additional one , faster gas flow and the pre-accelerated gas-good mixture. This results in a significant energy supply to the pre-accelerated good-gas mixture, the flow rate is increased and a fine-gas mixture is fed to the fine substance filtering, which contains particles with a much smaller mass than was previously achievable. The fine sighting is therefore significantly improved.
  • FIG. 1 a schematic side view
  • FIG. 2 an equally schematic top view.
  • An upright, cylindrical drum 1 can be driven with a suitable drive at high speed around its vertical longitudinal axis 2.
  • the desired target speed is 2000 rpm.
  • blades 3 are assigned in a constant division, which first deflect a gas flow radially introduced into the drum from any mill and enriched with fine dust, first deflecting it in the circumferential direction of the drum and then accelerating it on the way to the center of the drum. Concentric to the axis of rotation, the material discharge is guided into the classifier wheel from drum 1 and blading 3, which can be stationary or rotate with the drum.
  • the flow or peripheral speed of the good-gas mixture is now increased significantly beyond the value that can be achieved mechanically with the rotating drum, in that a certain number of nozzles 5, which are arranged tangentially and somewhat inclined downwards, correspond to this Gas-jet mixture already rotating at high speed are superimposed on gas jets, the raw gas flow being reduced by the volume fraction of the secondary air. It follows the mechanical acceleration of the raw gas flow, its pneumatic acceleration in the circumferential direction of the drum. The total acceleration is therefore much higher than with mechanical or pneumatic acceleration alone and only mass particles with extremely low mass are entrained in the material discharge.
  • the number of nozzles 5 provided depends on the circumstances of the individual case, but it is understandable that if a smaller nozzle cross section is selected, the number of nozzles can be larger than in the case of appropriately larger nozzle cross sections.
  • the mouths of the acceleration nozzles, which cause the at least approximately tangential gas outlet, lie in the virtual cylinder surface, which continues at the gas outlet into the interior of the drum.
  • the acceleration that can be achieved by the gas jets should be as high as possible, i.e. the gas jets should be blown into the drum at the highest possible speed.
  • the upper limit is the speed of sound, which is different for individual gases.
  • a medium should therefore preferably be used as the gas which only reaches the speed of sound at high speed, i.e. whose speed of sound has the highest possible value in order to impair the achieved values as little as possible by the compression of the gas. This is why air with an increased temperature of e.g. 200 ° C or superheated steam of 400 ° is an example of a guideline.
  • superheated steam is therefore also a gas.
  • a gas or a gas state comes into question in which the speed of sound is significantly higher than that of air at ambient temperature.
  • the proportion of gas should be at least about a quarter of the amount of output air, and it can be up to a factor of 2 larger.

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  • Combined Means For Separation Of Solids (AREA)
  • Analysing Materials By The Use Of Radiation (AREA)

Abstract

The subject of the invention is a method of screening particle-shaped material with an extremely low mass in a gas stream which, originating from a mill, is introduced into a sifting drum (1) with a preferably vertical axis (2) and rotates in the latter. Under the effect of the centrifugal force which is formed, material particles from a specific mass upwards are separated out as coarse material whilst gas with particles of material with a lower mass, so called fine-grade material, is fed to a tubular material discharge (4) arranged concentrically with respect to the drum axis in order to pass into a filter where a separation into gas and fine-grade material occurs. The material/gas mixture introduced into the drum is initially preaccelerated mechanically to a specific circumferential speed and, subsequently, the preaccelerated material/gas mixture is accelerated to the final circumferential speed by means of high-speed gas jets additionally introduced approximately tangentially into the drum. <IMAGE>

Description

Es sind Zerkleinerungsmaschinen bekannt, bei denen die zu zerkleinernden Teilchen in einem schnellen Gasstrom beschleunigt und durch gegenseitiges Zusammenprallen oder den Prall auf ein Target zerkleinert werden. Bei diesen im Gegensatz zu den mechanischen Mühlen als Strahlmühlen bezeichneten Konstruktionen wurde große Mühe darauf verwandt, den von Haus aus höheren Energiebedarf zu senken. Insbesondere unter diesem Gesichtspunkt entwickelte Strahlmühlen ergeben sich z.B. aus TIZ-Fachbereichte, Vol. 109, No. 1, 1985. Die Prallmahlung ist ein weit verbreitetes Zerkleinerungsverfahren, wenn höchste Feinheiten erreicht oder härteste Materialien verarbeitet werden sollen. Unter diesem Gesichtspunkt stehen je nach Aufgabenstellung zwei Maschinentypen, die Rotorprallmühlen und die Strahlmühlen, zur Verfügung ("Sprechsaal", Vol. 119, No. 7, 1986). Bei den Rotorprallmühlen entspricht es der Gesetzmäßigkeit, daß die Zerkleinerung umso besser gelingt, je schneller die Trommel sich dreht und je größer die demzufolge sich ausbildende Fliehkraft ist. Andererseits kann die Trommeldrehzahl nicht beliebig gesteigert werden.Comminution machines are known in which the particles to be comminuted are accelerated in a rapid gas flow and comminuted by colliding with one another or by impact on a target. In contrast to the mechanical mills, these constructions, known as jet mills, put great effort into reducing the inherently higher energy requirements. In particular, jet mills developed from this point of view result e.g. from TIZ departments, Vol. 109, No. 1, 1985. Impact grinding is a widespread comminution process when the finest subtleties are to be achieved or the hardest materials are to be processed. From this point of view, depending on the task, two machine types, the rotor impact mills and the jet mills, are available ("Speech Hall", Vol. 119, No. 7, 1986). In the case of rotor impact mills, it is the law that the faster the drum rotates and the greater the resulting centrifugal force, the better the size reduction. On the other hand, the drum speed cannot be increased arbitrarily.

Bei Spiralstrahlmühlen als einem Typ der Strahlmühlen steht die Trommel still und das Gut tragende Gas wird über Düsen mit hoher Energie in die Trommel eingebracht, so daß sich eine gegenüber der Trommelwand rotierende Strömung ausbildet, die in der Mühle eine Trennung zwischen Grob- und Feingut zuläßt, so daß mit dem Gas und durch den Austragstutzen nur fein gemahlenes Gut ausgetragen wird, das einem Sichter zugeführt wird, um klassiert und zum Teil als Feinstgut in einem Filter vom Gas getrennt zu werden, während das im Sichter abgewiesene Gut wiederholt solange behandelt wird, bis es die Masse des Feinstgutes hat.In spiral jet mills as a type of jet mill, the drum stands still and the gas carrying the good is introduced into the drum via nozzles with high energy so that forms a rotating flow with respect to the drum wall, which allows a separation between coarse and fine material in the mill, so that only finely ground material is discharged with the gas and through the discharge nozzle, which is fed to a classifier, classified and partly as fine material to be separated from the gas in a filter while the material rejected in the classifier is repeatedly treated until it has the mass of the fine material.

Ersichtlich sollte bei allen diesen Lösungen auf die eine oder andere Weise angestrebt werden, die Grenze zwischen Grob- und Feinstgut so festzulegen, daß das den Sichter über den Austragstutzen verlassende Gas nur Feststoffpartikel mit möglichst geringer Masse enthält, während Partikel auch dann noch abgewiesen werden, wenn sie in weniger spezieller Betrachtungsweise schon eine relativ geringe Masse erreicht haben.Obviously, with all of these solutions, one way or the other should be aimed at defining the boundary between coarse and very fine material in such a way that the gas leaving the classifier via the discharge nozzle contains only solid particles with the lowest possible mass, while particles are still rejected, if they have already reached a relatively low mass in a less specific way.

Eine bekannte Spiralstrahlmühle, bei der das zu zerkleinernde Gut mit Hilfe von Treibmittelstrahlen in einer runden Mahlkammer in kreisender Bewegung gehalten wird und das fein gemahlene in der Nähe der Kammerachse aus der Kammer austritt, um einem Sichter zugeführt zu werden, ist dadurch gekennzeichnet, daß dem bereits weitgehend zerkleinerten Gut in einer zwischen der außenliegenden Mahlzone und den Austrittsstellen liegenden Sichtzone durch zusätzliche Treibmittelstrahlen eine erhöhte Rotationsgeschwindigkeit erteilt wird, wodurch die größeren Teilchen in die Mahlzone zurückgeführt werden (DE-C-921 970). Ziel dieser Lösung ist es, nur feinstgemahlenes Gut aus der Mühle abzuführen und auch bereits relativ fein gemahlene Partikel als Grobgut im Mahlprozeß zu belassen bzw. einem erneuten Mahlprozeß zuzuführen. Im Hinblick auf die Erfindung ist bei diesem Stand der Technik wesentlich, daß es sich um die Klassierung innerhalb einer Mühle und nicht um eine der Mühle nachgeschaltete Sichtung handelt und daß die Beschleunigung der Partikel ausschließlich mit Gasstrahlen, also ausschließlich pneumatisch erfolgt.A known spiral jet mill, in which the material to be comminuted is held in a circular motion by means of propellant jets in a round grinding chamber and the finely ground material exits the chamber near the chamber axis in order to be fed to a classifier, is characterized in that material which has already been largely comminuted is given an increased rotational speed by additional blowing agent jets in a viewing zone lying between the outer grinding zone and the exit points, as a result of which the larger particles are returned to the grinding zone (DE-C-921 970). The aim of this solution is to remove only very finely ground material from the mill and also to leave relatively finely ground particles as coarse material in the grinding process or to feed it to a new grinding process. With regard to the invention In this prior art, it is essential that the classification is within a mill and not a classification downstream of the mill and that the particles are accelerated exclusively with gas jets, that is to say exclusively pneumatically.

Bei Windsichtern wird aus dem in den Sichter eingebrachten Gut zunächst die noch mit relativ großer Masse behafteten Teile des Gutes ausgesondert, ehe die mit relativ geringer Masse behafteten Teilchen im Luftstrom schwebend als Feinstgut mittels eines Sichtrades in einen Austragstutzen gelangen, durch den sie einem Filter zugeführt werden, der die Feinstgutteile zurückhält und die gereinigte Luft zur Wieder- oder Weiterverwendung passieren läßt. Dabei ist es bekannt, eine um eine vertikale Achse drehende Trommel zu verwenden, die auf ihrer Innenwand mit Schaufeln versehen ist, die den in die Trommel eingebrachten, mit Gut beladenen Gasstrom radial ins Trommelzentrum führen, wo in Richtung der Drehachse der Trommel der Austragstutzen für die mit Feinstgut befrachtete Luft angeordnet ist, während infolge der aus der Umdrehung der Trommel resultierenden Fliehkraft Feststoffpartikel abgewiesen werden, deren Masse größer ist als die Masse der Partikel, die mit dem Gas durch den Austragstutzen den Sichter als Feinstgutpartikel verlassen.In air classifiers, the parts of the material that still have a relatively large mass are first separated out from the material introduced into the classifier before the particles with a relatively low mass floating in the air flow as fine material enter a discharge nozzle by means of a classifying wheel, through which they are fed to a filter be, which holds back the fine material parts and allows the cleaned air to pass for reuse or further use. It is known to use a drum rotating about a vertical axis, which is provided on its inner wall with blades which lead the gas stream, which is introduced into the drum and is loaded with gas, radially into the center of the drum, where in the direction of the axis of rotation of the drum the discharge nozzle for the air loaded with fine material is arranged, while due to the centrifugal force resulting from the rotation of the drum, solid particles are rejected, the mass of which is greater than the mass of the particles which leave the classifier as fine material particles through the discharge nozzle.

Mit einem Sichter, also einer einer Mühle beliebiger Art nachgeschalteten Vorrichtung befaßt sich nun die Erfindung. Ihr liegt die Aufgabe zugrunde, es zu ermöglichen, daß nur Feinstgut mit extrem geringer Masse aus dem Sichter abgeführt wird und "Feingut" auch dann noch als zum Grobgut gehörig abgewiesen wird, wenn es bei heutigen Lösungen bereits als Feinstgut angesehen und dem Filter zugeführt wird. Verkürzt ausgedrückt soll die Erfindung eine Möglichkeit aufzeigen, wie für das in der Trommel rotierende Gas eine höhere Umfangsgeschwindigkeit erzielt werden kann, als es bei den heute als Alternativen angesehenen Lösungen mit feststehender oder mit drehender Trommel der Fall ist, um mittels der sich ausbildenden Fliehkraft auch schon mit relativ extrem kleiner Masse behaftete Feststoffpartikel nicht aus dem Sichter austreten zu lassen, sondern nochmals der die Masse vermindernden Behandlung zuzuführen. Dabei soll die mit der Fliehkraft einhergehende Umfangsgeschwindigkeit möglichst rationell erzeugt werden können.The invention is now concerned with a classifier, that is to say a device connected downstream of a mill of any type. It is based on the object of making it possible for only very fine material with extremely low mass to be discharged from the classifier and for “fine material” to be rejected as belonging to the coarse material even if it is already regarded as fine material in current solutions and is fed to the filter . In short, the invention is intended to be one possibility show how a higher circumferential speed can be achieved for the gas rotating in the drum than is the case with the solutions with fixed or rotating drum, which are regarded as alternatives today, in order to have a relatively extremely small mass due to the centrifugal force that is developing Do not allow solid particles to emerge from the classifier, but instead again to the mass-reducing treatment. The circumferential speed associated with the centrifugal force should be generated as rationally as possible.

Wenn nun mit der Erfindung ein deutlich besseres Ergebnis in der Weise erzielt werden soll, daß im Sichter auch Feinstaub abgeschieden werden kann, der wegen seiner geringen Masse bisher nicht auf diesem Wege ausgeschieden werden konnte, sondern ins Filter gelangte, so liegt der Erfindung das Prinzip zugrunde, die beiden bisher ausschließlich als Alternativen angesehenen Lösungsprinzipien zu vereinigen, indem ein kleinmassiges Partikel enthaltendes Gas zunächst mechanisch auf eine bestimmte Umfangsgeschwindigkeit vorbeschleunigt wird, wie es bei rotierenden Trommeln als alleinige Maßnahme bereits üblich ist, daß sich jedoch dieser Beschleunigung ein Impulsübergang zwischen einem zusätzlichen, schnelleren Gasstrom und dem bereits vorbeschleunigten Gut-Gas-Gemisch überlagert. Hierdurch tritt eine deutliche Energiezufuhr zu dem vorbeschleunigten Gut-Gas-Gemisch auf, die Strömungsgeschwindigkeit wird erhöht und der Feinststofffilterung wird ein Gut-Gas-Gemisch zugeführt, das Partikel mit wesentlich kleinerer Masse enthält, als es bisher erzielbar war. Die Feinstsichtung wird also deutlich verbessert.If a significantly better result is to be achieved with the invention in such a way that fine dust can also be separated in the classifier, which, because of its low mass, could not previously be eliminated in this way, but instead got into the filter, the principle of the invention is the invention The aim is to combine the two solution principles, which until now have only been viewed as alternatives, by first mechanically pre-accelerating a gas containing small particles to a certain circumferential speed, as is already the only measure for rotating drums, but that this acceleration involves a pulse transition between an additional one , faster gas flow and the pre-accelerated gas-good mixture. This results in a significant energy supply to the pre-accelerated good-gas mixture, the flow rate is increased and a fine-gas mixture is fed to the fine substance filtering, which contains particles with a much smaller mass than was previously achievable. The fine sighting is therefore significantly improved.

In der Zeichnung ist das Prinzip der Erfindung, diese erläuternd dargestellt, und zwar in Fig. 1 als schematische Seiten-, in Fig. 2 als ebenso schematische Draufsicht.In the drawing, the principle of the invention is illustrated, this being illustrated, in FIG. 1 as a schematic side view, in FIG. 2 as an equally schematic top view.

Eine aufrechtstehende, zylindrische Trommel 1 ist mit einem geeigneten Antrieb in hochtouriger Umdrehung um ihre vertikale Längsachse 2 antreibbar. Bei einem äußeren Trommeldurchmesser von etwa 460 mm und einer Trommelhöhe von etwa 130 mm liegt die angestrebte Solldrehzahl bei 2000 min⁻¹. Auf der Innenseite des Trommelmantels sind dieser in gleichbleibender Teilung Schaufeln 3 zugeordnet, die einen aus einer beliebigen Mühle kommenden radial in die Trommel eingeführten Gasstrom, der mit Feinstaub angereichert ist, zunächst in Umfangsrichtung der Trommel umlenken und dann auf dem Weg zur Trommelmitte beschleunigen. Konzentrisch zur Drehachse ist in das Sichterrad aus Trommel 1 und Beschaufelung 3 der Gutaustrag hineingeführt, der feststehen oder mit der Trommel umlaufen kann. Die Strömungs- bzw. Umfangsgeschwindigkeit des Gut-Gas-Gemisches wird nun dadurch deutlich über den mechanisch mit der drehenden Trommel erzielbaren Wert hinaus erhöht, daß über eine bestimmte Anzahl von Düsen 5, die tangential und etwas nach unten geneigt angeordnet sind, dem mit entsprechend hoher Geschwindigkeit bereits rotierenden Gut-Gas-Gemisch Gasstrahlen überlagert werden, wobei der Rohgasstrom um den Volumenanteil der Zweitluft verringert wird. Es folgt also auf die mechanische Beschleunigung des Rohgasstromes dessen pneumatische Beschleunigung im Umfangsrichtung der Trommel. Die Gesamtbeschleunigung ist dadurch wesentlich höher als bei allein mechanischer oder allein pneumatischer Beschleunigung und es werden nur noch Massepartikel mit extrem geringer Masse in den Gutaustrag mitgerissen.An upright, cylindrical drum 1 can be driven with a suitable drive at high speed around its vertical longitudinal axis 2. With an outer drum diameter of approximately 460 mm and a drum height of approximately 130 mm, the desired target speed is 2000 rpm. On the inside of the drum shell, blades 3 are assigned in a constant division, which first deflect a gas flow radially introduced into the drum from any mill and enriched with fine dust, first deflecting it in the circumferential direction of the drum and then accelerating it on the way to the center of the drum. Concentric to the axis of rotation, the material discharge is guided into the classifier wheel from drum 1 and blading 3, which can be stationary or rotate with the drum. The flow or peripheral speed of the good-gas mixture is now increased significantly beyond the value that can be achieved mechanically with the rotating drum, in that a certain number of nozzles 5, which are arranged tangentially and somewhat inclined downwards, correspond to this Gas-jet mixture already rotating at high speed are superimposed on gas jets, the raw gas flow being reduced by the volume fraction of the secondary air. It follows the mechanical acceleration of the raw gas flow, its pneumatic acceleration in the circumferential direction of the drum. The total acceleration is therefore much higher than with mechanical or pneumatic acceleration alone and only mass particles with extremely low mass are entrained in the material discharge.

Mit im Sinne der bisherigen Technologien nur geringe Masse aufweisende Partikel, die bei den bisherigen Lösungen ebenfalls in den Gutaustrag gelangen, werden dagegen abgewiesen und einer erneuten, ihre Masse nochmals verringernden Behandlung zugeführt.On the other hand, particles which have only a low mass in the sense of the previous technologies and which also get good discharge in the previous solutions are rejected and subjected to a further treatment which further reduces their mass.

Die Anzahl der vorgesehenen Düsen 5 hängt von den Umständen des Einzelfalles ab, es ist aber verständlich, daß bei Auswahl eines geringeren Düsenquerschnittes die Anzahl der Düsen größer sein kann als bei entrsprechend größeren Düsenquerschnitten. Die Mündungen der Beschleunigungsdüsen, die den zumindest etwa tangentialen Gasaustritt bewirken, liegen in der virtuellen Zylinderfläche, die sich an den Gasaustrag in das Trommelinnere fortsetzt.The number of nozzles 5 provided depends on the circumstances of the individual case, but it is understandable that if a smaller nozzle cross section is selected, the number of nozzles can be larger than in the case of appropriately larger nozzle cross sections. The mouths of the acceleration nozzles, which cause the at least approximately tangential gas outlet, lie in the virtual cylinder surface, which continues at the gas outlet into the interior of the drum.

Die Beschleunigung, die durch die Gasstrahlen erzielt werden kann, soll möglichst hoch sein, d.h. die Gasstrahlen sollen mit möglichst hoher Geschwindigkeit in die Trommel eingeblasen werden. Die Obergrenze ist die Schallgeschwindigkeit, die bei einzelnen Gasen unterschiedlich ist. Es soll deshalb als Gas ein Medium bevorzugt verwendet werden, das erst bei hoher Geschwindigkeit Schallgeschwindigkeit erreicht, d.h. dessen Schallgeschwindigkeit einen möglichst hohen Wert hat, um die erzielten Werte in möglichst geringem Maße durch die Kompression des Gases zu beeinträchtigen. Es kommt deswegen Luft erhöhter Temperatur von z.B. 200°C oder Heißdampf von 400° als beispielsweisem Richtwert in Frage. Im Sinne der Erfindung ist demzufolge auch überhitzter Wasserdampf ein Gas. Generell gesprochen kommt ein Gas oder ein Gaszustand in Frage, bei dem die Schallgeschwindigkeit deutlich höher liegt als die von Luft bei Umgebungstemperatur.The acceleration that can be achieved by the gas jets should be as high as possible, i.e. the gas jets should be blown into the drum at the highest possible speed. The upper limit is the speed of sound, which is different for individual gases. A medium should therefore preferably be used as the gas which only reaches the speed of sound at high speed, i.e. whose speed of sound has the highest possible value in order to impair the achieved values as little as possible by the compression of the gas. This is why air with an increased temperature of e.g. 200 ° C or superheated steam of 400 ° is an example of a guideline. For the purposes of the invention, superheated steam is therefore also a gas. Generally speaking, a gas or a gas state comes into question in which the speed of sound is significantly higher than that of air at ambient temperature.

Der Gasanteil soll zumindest etwa ein Viertel der Ausgangsluftmenge sein, und er kann bis zum Faktor 2 größer sein.The proportion of gas should be at least about a quarter of the amount of output air, and it can be up to a factor of 2 larger.

Claims (4)

1. A method of grading material in the form of particles of extremely low mass in a current of gas which, coming from a mill, is introduced into a sifting drum of preferably vertical axis, and rotates therein so that in response to the centrifugal force developing particles of the material as from a given mass are separated as coarse material while gas containing particles of material of lower mass, i.e. micro-material, is fed to a tubular material outlet disposed concentrically in relation to the drum axis to pass to a filter where separation into gas and micro-material takes place, characterised in that the mixture of material and gas introduced into the drum is initially accelerated mechanically to a given circumferential speed and then, as a result of pulse exchange between high-speed gas streams additionally introduced substantially tangentially into the drum and pre-accelerated mixture of material and gas, the said mixture is accelerated to the final circumferential speed.
2. A method according to claim 1, characterised by a type of gas or a gas in a condition such that the speed of sound of the gas is much higher than that of air at ambient temperature.
3. A method according to claim 1 or 2, characterised in that the amount of acceleration gas is at least approximately 1/4 of the volume of gas originally in the drum and no more than substantially twice said volume.
4. Apparatus for performing the method according to any one of claims 1 to 3, characterised by a bladed sifting wheel in the form of a drum, which rotates about the drum axis as a means of pre-accelerating the mixture of material and gas, and acceleration nozzles for introducing additional gas streams at least substantially tangentially into the rotating drum in the region of the virtual cylinder surface forming the continuation of the gas outlet into the interior of the drum.
EP89123623A 1988-12-27 1989-12-20 Method of sifting fine materials, and apparatus for carrying out the method Expired - Lifetime EP0379711B1 (en)

Priority Applications (1)

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AT89123623T ATE73694T1 (en) 1988-12-27 1989-12-20 PROCESS FOR FINE VISION AND DEVICE FOR CARRYING OUT THE PROCESS.

Applications Claiming Priority (4)

Application Number Priority Date Filing Date Title
DE3844008 1988-12-27
DE3844008 1988-12-27
DE3915552 1989-05-12
DE19893915552 DE3915552A1 (en) 1989-05-12 1989-05-12 Fine sifting of light, granular material

Publications (2)

Publication Number Publication Date
EP0379711A1 EP0379711A1 (en) 1990-08-01
EP0379711B1 true EP0379711B1 (en) 1992-03-18

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Family Applications (1)

Application Number Title Priority Date Filing Date
EP89123623A Expired - Lifetime EP0379711B1 (en) 1988-12-27 1989-12-20 Method of sifting fine materials, and apparatus for carrying out the method

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EP (1) EP0379711B1 (en)
AT (1) ATE73694T1 (en)
DE (1) DE58900995D1 (en)
ES (1) ES2030258T3 (en)

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
AU3909693A (en) * 1993-04-16 1994-11-08 Sigurd Fongen Means for filtering and fractionation of suspensions containing fibres, fibre fragments, fines and other particles

Family Cites Families (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE921970C (en) * 1952-02-21 1955-01-07 Basf Ag Grinding device
DE2651383A1 (en) * 1976-11-11 1978-05-18 Krauss Maffei Ag Centrifugal disc pneumatic classifier - has circumferential gap formed by cover through which are discharged centrally supplied material and air
DE3303078C1 (en) * 1983-01-29 1984-05-30 Alpine Ag, 8900 Augsburg Air classifier for the fine area

Also Published As

Publication number Publication date
EP0379711A1 (en) 1990-08-01
DE58900995D1 (en) 1992-04-23
ES2030258T3 (en) 1992-10-16
ATE73694T1 (en) 1992-04-15

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