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EP0362525A2 - Cold-grinding method and apparatus - Google Patents

Cold-grinding method and apparatus Download PDF

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Publication number
EP0362525A2
EP0362525A2 EP89115154A EP89115154A EP0362525A2 EP 0362525 A2 EP0362525 A2 EP 0362525A2 EP 89115154 A EP89115154 A EP 89115154A EP 89115154 A EP89115154 A EP 89115154A EP 0362525 A2 EP0362525 A2 EP 0362525A2
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EP
European Patent Office
Prior art keywords
refrigerant
grinding
sump
fluidized bed
grinding chamber
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Application number
EP89115154A
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German (de)
French (fr)
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EP0362525B1 (en
EP0362525A3 (en
Inventor
Klaus Bochmann
Hans Joachim Risto
Wolfgang Volker
Helmut Gursky
Dieter Steidl
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Messer Griesheim GmbH
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Messer Griesheim GmbH
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Priority to AT89115154T priority Critical patent/ATE103208T1/en
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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
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10S241/00—Solid material comminution or disintegration
    • Y10S241/37—Cryogenic cooling

Definitions

  • the invention relates to a method and a device for cold grinding in a fluidized bed counter jet mill.
  • Jet mills have long been known comminution machines in which the particles to be comminuted are accelerated by gas flows and comminuted by collision. There are a number of different jet mill designs. They differ in the type of gas flow, the type of Impact of the particles against each other or on an impact surface and thereby whether the particles to be comminuted are carried along in the gas jet or whether the gas jet hits the particles and entrains them. Air or superheated steam is usually used as the grinding gas.
  • the fluidized bed counter jet mill In the fluidized bed counter jet mill, freely expanding gas jets meet in a grinding chamber in which the material to be ground is in the form of a fluidized bed. The grinding is carried out practically exclusively by impact of the regrind particles against one another, the grinding is thus almost wear-free.
  • the fluidized bed counter jet mill is assigned a classifier, in which the fine material obtained is separated from the coarse material which has not yet been comminuted sufficiently. The coarse material is returned to the grinding chamber.
  • the propellant gas stream is therefore cooled, as described, for example, in DE-OS 21 33 019.
  • the cooling of the propellant gas stream makes it possible to grind materials that would not be grindable in jet mills under normal conditions.
  • intensive cooling for example with liquid nitrogen
  • the self-cooling of the propellant gas stream due to its expansion the achievable improvement in grindability leaves much to be desired.
  • fine Reach grain sizes but only with an extremely high expenditure of time and energy.
  • the invention is therefore based on the object of providing a method and a device for cold grinding which require little energy and refrigerant and at the same time enable the fine grinding of products to finest grain sizes which have hitherto been practically unattainable with a substantial increase in throughput.
  • the invention is therefore based on the idea of not cooling the propellant gas flow, but rather the coarse material circulating with a cryogenic refrigerant.
  • the measure according to the invention brings about a sudden improvement in the grinding results, as can be seen from the operating results set out below.
  • the invention enables a considerable increase in throughput to be achieved on fluidized bed counter-jet mills.
  • the end product is easy to pour and has a high bulk and bulk weight.
  • materials that are tough, rubber table, sticky or greasy can be excellently ground using the method according to the invention.
  • These are primarily natural products, many pharmaceutical products, thermoplastics, waxes and high-molecular plastics.
  • Liquefied gases, especially nitrogen, are primarily considered as refrigerants, but also carbon dioxide. In the simplest and in many cases the most practical case, these can be fed directly into the bottom of the mill. Indirect cooling of the coarse material is of course also possible. Indirect cooling can also take place using other refrigerants, for example brine baths.
  • the mill shows a fluidized bed counter jet mill in schematic form.
  • the mill consists of a housing 1 which comprises the grinding chamber 2 and the sump 3.
  • the propellant gas enters the grinding chamber 2 through the nozzles 4.
  • the classifier 5 connects to the housing 1.
  • the coarse material to be ground is in the form of a fluidized bed 6 in the grinding chamber.
  • the regrind is metered in through the lock 7.
  • the fine material 10 separated in the classifier 5 is drawn off through the fine material outlet 8, as indicated by the arrow 9, and fed to the filter system 15. This has a connection 16 for the exhaust gas and a removal lock 17 for the fine material 10 obtained.
  • the coarse material 11 flows from the classifier 5 back into the grinding chamber 2.
  • the propellant gas, with which the nozzles 4 are acted on, is brought in through the supply line 14.
  • the coarse material located in the sump 3 of the mill is cooled by liquid nitrogen. This is introduced through the line 12 and the porous entry body 13. Porous feed grains are particularly suitable for small mills. For grinders with larger diameters, other feed systems, for example nozzle plates, are preferred in order to be able to feed the nitrogen in as finely divided as possible.
  • the nitrogen supply through line 12 and the porous Entry body 13 takes place depending on the temperature control 18.
  • the regrind can be fed through the lock 7 directly into the sump 3.
  • the fine fraction of the fine material 10 is determined by the speed of the classifier 5.
  • the coarse material 11 flowing back from the classifier 5 forms, together with the mill material entering from the lock 7, the fluidized bed 6.
  • the liquid nitrogen entering through the porous feed body 13 evaporates and cools the sump of the mill, ie the coarse material 11 flowing back from the classifier 5 and possibly freshly applied mill material .
  • the evaporated cold nitrogen is drawn upwards through the material and enters the grinding zone.
  • Cold gas, coarse material and regrind form a first fluidized bed zone below the grinding chamber 2 in the sump 3.
  • FIG. 2 shows in schematic form the lower part of the fluidized bed counter-jet mill from FIG. 1, but with the lock 7 for the regrind arranged directly on the sump 3.
  • the arrows 19 illustrate the mixture of cold gas, propellant gas, coarse material and fine material which is drawn off towards the classifier.
  • the liquid nitrogen is supplied through lines 20 and 21.
  • the liquid nitrogen entering through line 21 passes into a double-walled tube 22 closed at the end faces.
  • This double-walled tube 22 has outlet openings 23 directed inwards.
  • the entire lower part of the mill housing is also designed as a double-walled chamber 24.
  • the line 20 opens into it.
  • the chamber 24 has outlet openings 25 arranged in the sump 3 for the nitrogen supplied through the line 20.
  • the coarse material 11 flowing back from the classifier is therefore first indirectly cooled in the area between the double-walled tube 22 and the chamber 24. Then there is direct cooling by the nitrogen emerging from the outlet openings 23 and 25. Depending on the mode of operation, this can still be liquid or already gaseous.
  • FIG. 4 shows an embodiment similar to FIG. 2, but with an elongated sump 3.
  • a certain flow form is impressed on the coarse material 11 and the cold gas by means of a tubular apron 26.
  • the apron 26 separates the grinding chamber into a central shaft 37, where the grinding process takes place, and into an annular shaft 38 for the coarse material flowing back.
  • the liquid nitrogen is supplied at two points, namely through line 12a directly into the sump 3 and through line 12b into a spray system 39 in the annular shaft 38.
  • the nitrogen introduced through line 12b therefore cools the coarse material flowing back from the classifier.
  • the invention is not limited to the embodiments described above, since there are numerous other possibilities for cooling the coarse material flowing back from the classifier by means of a refrigerant.
  • Several grinding zones with sump in the form of a cascade can also be connected in series. The mixture of fine and coarse material emerging from the grinding zone is separated from the exhaust gas in a filter and fed to the next grinding zone. The one under every meal zone swamp is cooled according to the invention. A sifter is only assigned to the last stage.
  • Hostalen (R) GUR 200 is a high-molecular polyethylene from Hoechst AG, Frankfurt. As the operating results show, the two investigated materials could not be ground to the finenesses that can be achieved with the method according to the invention under economic conditions.
  • the grain size analysis was determined using a commercially available laser granolaometer (Cilas). From the printed curve, the d10, d50 and d90 values were selected as representative values. For example, the d10 value of 10.2 ⁇ m in line 4 of the table means that 10% of the end product is grains with a size below 10.2 ⁇ m.

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  • Engineering & Computer Science (AREA)
  • Food Science & Technology (AREA)
  • Disintegrating Or Milling (AREA)
  • Mechanical Treatment Of Semiconductor (AREA)

Abstract

Fließbett-Gegenstrahlmühlen sind Gasstrahlmühlen, mit denen sich sehr hohe Mahlfeinheiten bei äußerst gerin­gem Verschleiß erreichen lassen. Eine Verbesserung des Mahlergebnisses läßt sich durch Abkühlung der Gasstrah­len mittels eines Kältemittels erreichen, jedoch ist die erreichbare Verbesserung nicht erheblich und der Kältemittelverbrauch sehr hoch. Zwecks Senkung des Kältemittelverbrauchs bei gleichzeitiger beträchtlicher Verbesserung der Mahlfeinheit wird das vom Sichter (5) der Mühle abgetrennte Grobgut (11) durch das Kältemittel innerhalb der Fließbett-Gegenstrahlmühle gekühlt und in die Mahlkammer (2) zurückgeführt. Als Kältemittel wird flüssiger Stickstoff bevorzugt, mit dem der Sumpf (3) der Mühle gekühlt wird.

Figure imgaf001
Fluidized bed counter-jet mills are gas jet mills with which very high finenesses can be achieved with extremely little wear. An improvement in the grinding result can be achieved by cooling the gas jets using a refrigerant, but the improvement that can be achieved is not significant and the refrigerant consumption is very high. In order to reduce the refrigerant consumption while at the same time considerably improving the grinding fineness, the coarse material (11) separated from the classifier (5) of the mill is cooled by the refrigerant inside the fluidized bed counter-jet mill and returned to the grinding chamber (2). Liquid nitrogen, with which the sump (3) of the mill is cooled, is preferred as the refrigerant.
Figure imgaf001

Description

Die Erfindung betrifft ein Verfahren und eine Vorrich­tung zum Kaltmahlen in einer Fließbett-Gegenstrahlmühle.The invention relates to a method and a device for cold grinding in a fluidized bed counter jet mill.

Strahlmühlen sind seit langem bekannte Zerkleinerungs­maschinen, in denen die zu zerkleinernden Teilchen durch Gasströme beschleunigt und durch Zusammenprall zerkleinert werden. Es gibt eine Anzahl unterschied­licher Strahlmühlenkonstruktionen. Sie unterscheiden sich durch die Art der Gasführung, durch die Art des Aufprallens der Teilchen gegeneinander oder auf eine Prallfläche und dadurch, ob die zu zerkleinernden Teil­chen im Gasstrahl mitgeführt werden oder ob der Gas­strahl auf die Teilchen auftrifft und sie mitreißt. Als Mahlgas wird gewöhnlich Luft oder Heißdampf verwendet.Jet mills have long been known comminution machines in which the particles to be comminuted are accelerated by gas flows and comminuted by collision. There are a number of different jet mill designs. They differ in the type of gas flow, the type of Impact of the particles against each other or on an impact surface and thereby whether the particles to be comminuted are carried along in the gas jet or whether the gas jet hits the particles and entrains them. Air or superheated steam is usually used as the grinding gas.

Bei der Fließbett-Gegenstrahlmühle treffen freiexpan­dierende Gasstrahlen in einer Mahlkammer aufeinander, in welcher sich das Mahlgut in Form eines Fließbettes befindet. Die Vermahlung erfolgt hierbei praktisch aus­schließlich durch Aufeinanderprall der Mahlgutteilchen gegeneinander, die Vermahlung ist somit nahezu ver­schleißfrei. Der Fließbett-Gegenstrahlmühle ist ein Sichter zugeordnet, in welchem das gewonnene Feingut vom noch nicht genügend zerkleinerten Grobgut abge­trennt wird. Das Grobgut wird in die Mahlkammer zurück­geführt.In the fluidized bed counter jet mill, freely expanding gas jets meet in a grinding chamber in which the material to be ground is in the form of a fluidized bed. The grinding is carried out practically exclusively by impact of the regrind particles against one another, the grinding is thus almost wear-free. The fluidized bed counter jet mill is assigned a classifier, in which the fine material obtained is separated from the coarse material which has not yet been comminuted sufficiently. The coarse material is returned to the grinding chamber.

Viele Stoffe, beispielsweise Kunststoffe, lassen sich wegen ihrer Zähigkeit nur schlecht oder überhaupt nicht auf feine Korngrößen vermahlen. Durch Kältezufuhr und die dadurch bewirkte Versprödung der Werkstoffe lassen sich die Mahleigenschaften derartig zäher Werk­stoffe verbessern. Bei Strahlmühlen kühlt man deshalb den Treibgasstrom ab, wie es beispielsweise in der DE-­OS 21 33 019 beschrieben ist. Die Abkühlung des Treib­gasstromes ermöglicht es, Materialien zu mahlen, die unter normalen Bedingungen in Strahlmühlen nicht mahlbar wären. Trotz intensiver Abkühlung, beispiels­weise mit flüssigem Stickstoff, und trotz der Eigenab­kühlung des Treibgasstromes infolge seiner Expansion, läßt die erreichbare Verbesserung der Mahlbarkeit jedoch sehr zu wünschen übrig. Zwar lassen sich feine Korngrößen erreichen, jedoch nur mit einem überaus hohen Zeit- und Energieaufwand.Many materials, such as plastics, are difficult or impossible to grind to fine grain sizes due to their toughness. The cooling properties and the resulting embrittlement of the materials can improve the grinding properties of such tough materials. In jet mills, the propellant gas stream is therefore cooled, as described, for example, in DE-OS 21 33 019. The cooling of the propellant gas stream makes it possible to grind materials that would not be grindable in jet mills under normal conditions. Despite intensive cooling, for example with liquid nitrogen, and despite the self-cooling of the propellant gas stream due to its expansion, the achievable improvement in grindability leaves much to be desired. Although fine Reach grain sizes, but only with an extremely high expenditure of time and energy.

Der Erfindung liegt daher die Aufgabe zugrunde, ein Verfahren und eine Vorrichtung zum Kaltmahlen zu schaffen, welche einen geringen Bedarf an Energie und Kältemittel erfordern und gleichzeitig die Feinstzer­mahlung von Produkten auf bisher praktisch nicht er­reichbare feinste Korngrößen bei wesentlicher Durch­satzsteigerung ermöglichen.The invention is therefore based on the object of providing a method and a device for cold grinding which require little energy and refrigerant and at the same time enable the fine grinding of products to finest grain sizes which have hitherto been practically unattainable with a substantial increase in throughput.

Ausgehend von dem im Oberbegriff des Anspruches 1 be­rücksichtigen Stand der Technik ist diese Aufgabe er­findungsgemäß gelöst mit den im kennzeichnenden Teil des Anspruches 1 angegebenen Merkmalen. Vorteilhafte Weiterbildungen der Erfindung sind in den Unteransprü­chen angegeben.Starting from the prior art taken into account in the preamble of claim 1, this object is achieved according to the invention with the features specified in the characterizing part of claim 1. Advantageous developments of the invention are specified in the subclaims.

Die Erfindung beruht daher auf der Überlegung, nicht den Treibgasstrom, sondern das umlaufende Grobgut mit einem kryogenen Kältemittel zu kühlen. Die erfindungs­gemäße Maßnahme bewirkt eine sprunghafte Verbesserung der Mahlergebnisse, wie aus den weiter hinten aufge­stellten Betriebsergebnissen ersichtlich ist.The invention is therefore based on the idea of not cooling the propellant gas flow, but rather the coarse material circulating with a cryogenic refrigerant. The measure according to the invention brings about a sudden improvement in the grinding results, as can be seen from the operating results set out below.

Es ist überraschend, daß sich dies allein durch die er­findungsgemäße Maßnahme, nicht den Treibgasstrom, son­dern das umlaufende Grobgut zu kühlen, erreichen läßt. Die Erfinder folgerten dies aus Betriebsversuchen mit einer Fließbett-Gegenstrahlmühle, bei der sich trotz intensiver Abkühlung des Treibgasstromes mit flüssigem Stickstoff für das umlaufende Grobgut im Sumpf der Müh­ le nur eine geringe Abkühlung ergab. Die Erfinder schlossen hieraus, daß die Kühlung am Grobgut selbst erfolgen müsse, um die Mahlleistung zu verbessern.It is surprising that this can be achieved solely by the measure according to the invention, not to cool the propellant gas stream, but rather the coarse material circulating. The inventors concluded this from operational trials with a fluidized bed counter-jet mill, in which despite the intensive cooling of the propellant gas stream with liquid nitrogen, the coarse material circulating in the bottom of the mill was bothered le only showed a slight cooling. The inventors concluded from this that the cooling of the coarse material itself had to take place in order to improve the grinding performance.

Spätere theoretische Überlegungen bestätigten die Rich­tigkeit dieser Folgerung.Later theoretical considerations confirmed the correctness of this conclusion.

Wesentlich hierbei ist, daß dann, wenn mit einem ge­kühlten Treibgasstrom gemahlen wird, die in Wärme umge­wandelte Stoßenergie eines Teilchens nur unvollkommen auf den kalten Gasstrom übergeht. Dies hat mehrere Ur­sachen. So ist die Zeit für den Wärmeübergang vom Teil­chen auf das Gas extrem kurz. Da die Wärmekapazität mit sinkender Temperatur kleiner wird, ist die Temperatur­erhöhung durch einen Stoß bei tiefen Temperaturen grö­ßer als bei höheren Temperaturen. Die Relativbewegung zwischen Teilchen und kaltem Treibgas ist gering, so daß die Werte für den Wärmeübergang ebenfalls abfallen. Hinzu kommt, daß die Wärmeleitfähigkeit vieler Mahlgü­ter an sich schon niedrig ist und mit sinkender Tempera­tur noch schlechter wird. Ferner ist die Beschleuni­gungsenergie von kaltem Gas schlechter als von warmem Gas. Je feiner die angestrebten Korngrößen werden, um so schlechter werden daher die Mahlbedingungen beim Mahlen mit einem gekühlten Treibgasstrom. Dies trifft besonders auf Thermoplaste zu, die einen sehr niedrigen Kristallisationsbereich haben. Deren Mahlung wird völ­lig unwirtschaftlich.It is essential here that when grinding with a cooled propellant gas stream, the impact energy of a particle converted into heat is only incompletely transferred to the cold gas stream. There are several reasons for this. The time for heat transfer from the particle to the gas is extremely short. Since the heat capacity decreases with falling temperature, the temperature increase due to a shock at higher temperatures is greater than at higher temperatures. The relative movement between the particles and the cold propellant gas is low, so that the values for the heat transfer also drop. In addition, the thermal conductivity of many regrinds is already low and gets worse with falling temperature. Furthermore, the acceleration energy of cold gas is worse than that of warm gas. The finer the desired grain sizes, the worse the grinding conditions become when grinding with a cooled propellant gas stream. This is especially true for thermoplastics that have a very low crystallization range. Grinding them becomes completely uneconomical.

Durch die Erfindung läßt sich auf Fließbett-Gegen­strahlmühlen eine beträchtliche Durchsatzsteigerung erreichen. Es lassen sich Teilchen höchster Feinheit mit entsprechender Oberflächenvergrößervng und glatter Oberflächenstruktur herstellen. Das Endprodukt wird gut rieselfähig und besitzt ein hohes Schütt- und Rüttge­wicht. Insbesondere Werkstoffe, die zäh, gummielstisch, klebrig oder schmierig sind, lassen sich mit dem er­findungsgemäßen Verfahren hervorragend mahlen. Hierbei handelt es sich vor allem um Naturstoffe, viele Pharma­produkte, Thermoplaste, Wachse und hochmolekulare Kunststoffe. Als Kältemittel kommen in erster Linie verflüssigte Gase, insbesondere Stickstoff, infrage, aber auch Kohlendioxid. Diese können im einfachsten und in vielen Fällen zweckmäßigsten Fall direkt in den Sumpf der Mühle eingespeist werden. Selbstverständlich ist auch eine indirekte Kühlung des Grobgutes möglich. Eine indirekte Kühlung kann auch durch andere Kältemit­tel, beispielsweise Solebäder, erfolgen.The invention enables a considerable increase in throughput to be achieved on fluidized bed counter-jet mills. There are particles of the finest fineness with a corresponding surface enlargement and smooth surface structure. The end product is easy to pour and has a high bulk and bulk weight. In particular, materials that are tough, rubber table, sticky or greasy can be excellently ground using the method according to the invention. These are primarily natural products, many pharmaceutical products, thermoplastics, waxes and high-molecular plastics. Liquefied gases, especially nitrogen, are primarily considered as refrigerants, but also carbon dioxide. In the simplest and in many cases the most practical case, these can be fed directly into the bottom of the mill. Indirect cooling of the coarse material is of course also possible. Indirect cooling can also take place using other refrigerants, for example brine baths.

Einige Ausführungsbeispiele der Erfindung sollen anhand der beigefügten Zeichnungen erläutert werden.Some embodiments of the invention will be explained with reference to the accompanying drawings.

Es zeigen:

  • Fig.1 eine Fließbett-Gegenstrahlmühle in schematischer Form,
  • Fig.2 die Kühlung des Sumpfes der Fließbett­Gegenstrahlmühle von Fig.1,
  • Fig.3 eine Mischform aus direkter und indirekter Kühlung des Sumpfes,
  • Fig.4 eine Ausführungsform ähnlich Fig.3, jedoch mit ausschließlich direkter Kühlung.
Show it:
  • 1 shows a fluidized bed counter jet mill in schematic form,
  • 2 the cooling of the sump of the fluidized bed counter-jet mill from FIG. 1,
  • 3 shows a mixed form of direct and indirect cooling of the sump,
  • 4 shows an embodiment similar to FIG. 3, but only with direct cooling.

In der nachfolgenden Beschreibung sind für gleiche Tei­le in allen Figuren die gleichen Bezugszeichen verwen­det worden.In the following description, the same reference numerals have been used for the same parts in all figures.

Fig.1 zeigt eine Fließbett-Gegenstrahlmühle in schema­tischer Form. Die Mühle besteht aus einem Gehäuse 1, welches die Mahlkammer 2 und den Sumpf 3 umfaßt. Das Treibgas tritt durch die Düsen 4 in die Mahlkammer 2 ein. An das Gehäuse 1 schließt sich der Sichter 5 an. Das zu mahlende Grobgut befindet sich in Form eines Fließbettes 6 in der Mahlkammer. Das Mahlgut wird durch die Schleuse 7 zudosiert. Das im Sichter 5 abgetrennte Feingut 10 wird durch den Feingutaustritt 8 abgezogen, wie durch den Pfeil 9 angegeben, und der Filteranlage 15 zugeführt. Diese besitzt einen Stutzen 16 für das Abgas und eine Entnahmeschleuse 17 für das gewon­nene Feingut 10. Das Grobgut 11 strömt vom Sichter 5 zurück in die Mahlkammer 2. Das Treibgas, mit dem die Düsen 4 beaufschlagt werden, wird durch die Zufuhrlei­tung 14 herbeigeführt.1 shows a fluidized bed counter jet mill in schematic form. The mill consists of a housing 1 which comprises the grinding chamber 2 and the sump 3. The propellant gas enters the grinding chamber 2 through the nozzles 4. The classifier 5 connects to the housing 1. The coarse material to be ground is in the form of a fluidized bed 6 in the grinding chamber. The regrind is metered in through the lock 7. The fine material 10 separated in the classifier 5 is drawn off through the fine material outlet 8, as indicated by the arrow 9, and fed to the filter system 15. This has a connection 16 for the exhaust gas and a removal lock 17 for the fine material 10 obtained. The coarse material 11 flows from the classifier 5 back into the grinding chamber 2. The propellant gas, with which the nozzles 4 are acted on, is brought in through the supply line 14.

Erfindungsgemäß wird das sich im Sumpf 3 der Mühle be­findende Grobgut durch flüssigen Stickstoff abgekühlt. Dieser wird durch die Leitung 12 und den porösen Ein­tragkörper 13 eingeleitet. Poröse Eintragkörner eignen sich besonders für kleine Mühlen. Für Mühlen mit grö­ßeren Durchmessern sind andere Eintragsysteme, bei­spielsweise Düsenplatten, vorzuziehen, um den Stick­stoff möglichst feinzerteilt eintragen zu können. Die Stickstoffzufuhr durch die Leitung 12 und den porösen Eintragkörper 13 erfolgt in Abhängigkeit von der Temperaturregelung 18. Die Mahlgutaufgabe durch die Schleuse 7 kann auch direkt in den Sumpf 3 erfolgen. Die Feinfraktion des Feingutes 10 wird durch die Drehzahl des Sichters 5 bestimmt. Das vom Sichter 5 zurückstromende Grobgut 11 bildet zusammen mit dem aus der Schleuse 7 eintretenden Mahlgut das Fließbett 6. Der durch den porösen Eintragkörper 13 eintretende flüssige Stickstoff verdampft und kühlt den Sumpf der Mühle, d.h. das vom Sichter 5 zurückstromende Grobgut 11 und gegebenenfalls frischaufgegebenes Mahlgut. Der verdampfte kalte Stickstoff zieht nach oben durch das Gut ab und tritt in die Mahlzone ein. Kaltgas, Grobgut und Mahlgut bilden unterhalb der Mahlkammer 2 im Sumpf 3 eine erste Fließbettzone.According to the invention, the coarse material located in the sump 3 of the mill is cooled by liquid nitrogen. This is introduced through the line 12 and the porous entry body 13. Porous feed grains are particularly suitable for small mills. For grinders with larger diameters, other feed systems, for example nozzle plates, are preferred in order to be able to feed the nitrogen in as finely divided as possible. The nitrogen supply through line 12 and the porous Entry body 13 takes place depending on the temperature control 18. The regrind can be fed through the lock 7 directly into the sump 3. The fine fraction of the fine material 10 is determined by the speed of the classifier 5. The coarse material 11 flowing back from the classifier 5 forms, together with the mill material entering from the lock 7, the fluidized bed 6. The liquid nitrogen entering through the porous feed body 13 evaporates and cools the sump of the mill, ie the coarse material 11 flowing back from the classifier 5 and possibly freshly applied mill material . The evaporated cold nitrogen is drawn upwards through the material and enters the grinding zone. Cold gas, coarse material and regrind form a first fluidized bed zone below the grinding chamber 2 in the sump 3.

Fig.2 zeigt in schematischer Form den unteren Teil der Fließbett-Gegenstrahlmühle von Fig.1, jedoch mit der Schleuse 7 für das Mahlgut direkt am Sumpf 3 angeordnet. Die Pfeile 19 verdeutlichen das nach oben zum Sichter hin abziehende Gemisch aus Kaltgas, Treibgas, Grobgut und Feingut.2 shows in schematic form the lower part of the fluidized bed counter-jet mill from FIG. 1, but with the lock 7 for the regrind arranged directly on the sump 3. The arrows 19 illustrate the mixture of cold gas, propellant gas, coarse material and fine material which is drawn off towards the classifier.

Fig.3 zeigt eine Variante mit indirektem und direkten Wärmeaustausch zwischen zugeführtem Stickstoff und Mahlgut. Die Zufuhr des flüssigen Stickstoffes erfolgt durch die Leitungen 20 und 21. Der durch die Leitung 21 eintretende flüssige Stickstoff gelangt in ein an den Stirnflächen geschlossenes doppelwandiges Rohr 22. Die­ses doppelwandige Rohr 22 besitzt nach innen gerichtet Austrittsöffnungen 23. Der gesamte untere Teil des Mühlengehäuses ist ebenfalls als doppelwandige Kammer 24 ausgebildet. In sie mündet die Leitung 20. Die Kammer 24 besitzt im Sumpf 3 angeordnete Austrittsöffnungen 25 für den durch die Leitung 20 zugeführten Stickstoff. Das vom Sichter zurückströmende Grobgut 11 wird daher zunächst in dem Bereich zwischen dem doppelwandigen Rohr 22 und der Kammer 24 indirekt gekühlt .Anschließend erfolgt eine direkte Kühlung durch den aus den Aus­trittsöffnungen 23 und 25 austretenden Stickstoff. Je nach Betriebsweise kann dieser noch flüssig oder be­reits gasförmig sein.3 shows a variant with indirect and direct heat exchange between the nitrogen supplied and the regrind. The liquid nitrogen is supplied through lines 20 and 21. The liquid nitrogen entering through line 21 passes into a double-walled tube 22 closed at the end faces. This double-walled tube 22 has outlet openings 23 directed inwards. The entire lower part of the mill housing is also designed as a double-walled chamber 24. The line 20 opens into it. The chamber 24 has outlet openings 25 arranged in the sump 3 for the nitrogen supplied through the line 20. The coarse material 11 flowing back from the classifier is therefore first indirectly cooled in the area between the double-walled tube 22 and the chamber 24. Then there is direct cooling by the nitrogen emerging from the outlet openings 23 and 25. Depending on the mode of operation, this can still be liquid or already gaseous.

Fig.4 zeigt eine Ausführungsform ähnlich Fig.2, jedoch mit einem verlängerten Sumpf 3. Durch eine rohrförmige Schürze 26 wird hierbei dem Grobgut 11 und dem Kaltgas eine bestimmte Strömungsform aufgeprägt. Die Schürze 26 trennt die Mahlkammer in einen zentralen Schacht 37, wo der Mahlvorgang stattfindet, und in einen ringförmigen Schacht 38 für das zurückströmende Grobgut. Die Zufuhr des flüssigen Stickstoffes erfolgt an zwei Stellen, nämlich durch die Leitung 12a direkt in den Sumpf 3 und durch die Leitung 12b in ein Einsprühsystem 39 im ring­förmigen Schacht 38. Der durch die Leitung 12b einge­leitete Stickstoff kühlt demnach unmittelbar das vom Sichter zurückströmende Grobgut.FIG. 4 shows an embodiment similar to FIG. 2, but with an elongated sump 3. A certain flow form is impressed on the coarse material 11 and the cold gas by means of a tubular apron 26. The apron 26 separates the grinding chamber into a central shaft 37, where the grinding process takes place, and into an annular shaft 38 for the coarse material flowing back. The liquid nitrogen is supplied at two points, namely through line 12a directly into the sump 3 and through line 12b into a spray system 39 in the annular shaft 38. The nitrogen introduced through line 12b therefore cools the coarse material flowing back from the classifier.

Die Erfindung ist nicht auf die vorstehend beschriebe­nen Ausführungsformen beschränkt, da zahlreiche weitere Möglichkeiten für die Abkühlung des vom Sichter zurück­strömenden Grobgutes durch ein Kältemittel bestehen. Es können auch mehrere Mahlzonen mit Sumpf in Form einer Kaskade hintereinander geschaltet werden. Hierbei wird das aus der Mahlzone austretende Gemisch aus Feingut und Grobgut in einem Filter vom Abgas abgetrennt und der nächsten Mahlzone zugeführt. Der unter jeder Mahl­ zone befindliche Sumpf wird hierbei gemäß der Erfindung gekühlt. Erst der letzten Stufe wird ein Sichter zuge­ordnet.The invention is not limited to the embodiments described above, since there are numerous other possibilities for cooling the coarse material flowing back from the classifier by means of a refrigerant. Several grinding zones with sump in the form of a cascade can also be connected in series. The mixture of fine and coarse material emerging from the grinding zone is separated from the exhaust gas in a filter and fed to the next grinding zone. The one under every meal zone swamp is cooled according to the invention. A sifter is only assigned to the last stage.

Nachstehende Betriebsergebnisse zeigen den Fortschritt des erfindungsgemäßen Verfahrens gegenüber der herkömm­lichen Betriebsweise. Produktbezeichnung Korngrößen Produktdurchsatz Gasdurchsat Aufgabegut Endprodukt Kg/h Luft N₂ d₁₀ µm d₅₀ µm d₉₀ µm d₁₀ µm d₅₀ µm d₉₀ µm m³/h m³/h Hostalen(R) GUR 200 30,3 82,2 127,3 17,5 32,1 85,3 2,0 850 ohne Hostalen(R) GUR 200 30,3 82,2 127,3 14,3 23,6 38,6 13,0 850 200 Polyamid 70 130 200 keine Mahlwirkung 850 ohne Polyamid 70 130 200 10,2 26,5 41,6 3 850 300 The following operating results show the progress of the method according to the invention compared to the conventional mode of operation. Product name Grain sizes Product throughput Gas throughput Feed End product Kg / h air N₂ d₁₀ µm d₅₀ µm d₉₀ µm d₁₀ µm d₅₀ µm d₉₀ µm m³ / h m³ / h Hostalen (R) GUR 200 30.3 82.2 127.3 17.5 32.1 85.3 2.0 850 without Hostalen (R) GUR 200 30.3 82.2 127.3 14.3 23.6 38.6 13.0 850 200 polyamide 70 130 200 no grinding effect 850 without polyamide 70 130 200 10.2 26.5 41.6 3rd 850 300

Hostalen(R) GUR 200 ist ein hochmolekulares Polyethylen der Hoechst AG, Frankfurt. Wie die Betriebsergebnisse zeigen, konnten beide untersuchten Materialien unter wirtschaftlichen Bedingungen nicht auf solche Feinhei­ten gemahlen werden, wie sie mit dem erfindungsgemäßen Verfahren erreichbar sind.Hostalen (R) GUR 200 is a high-molecular polyethylene from Hoechst AG, Frankfurt. As the operating results show, the two investigated materials could not be ground to the finenesses that can be achieved with the method according to the invention under economic conditions.

Die Korngrößenanalyse wurde mit einem handelsüblichen Lasergranolometer (Cilas) ermittelt. Aus der ausge­druckten Kurve wurden die d₁₀-, d₅₀- und d₉₀-Werte als repräsentative Werte ausgewählt. Zum Beispiel bedeutet der d₁₀-Wert von 10,2 µm in Zeile 4 der Tabelle, daß 10% des Endproduktes Körner mit einer Größe unter 10,2µm sind.The grain size analysis was determined using a commercially available laser granolaometer (Cilas). From the printed curve, the d₁₀, d₅₀ and d₉₀ values were selected as representative values. For example, the d₁₀ value of 10.2 µm in line 4 of the table means that 10% of the end product is grains with a size below 10.2 µm.

Besonders überraschend ist die Steigerung des Produkt­durchsatzes bei Hostalen(R)GUR 200 von 2,0 auf 13,0 kg/h bei gleichzeitig wesentlich engerem Kornband. Durch die damit verbundene signifikante Vergrößerung der spezi­fischen Oberfläche eröffnen sich neue Anwendungsmög­lichkeiten.The increase in product throughput for Hostalen (R) GUR 200 from 2.0 to 13.0 kg / h with a significantly narrower grain band is particularly surprising. The associated significant increase in the specific surface area opens up new application possibilities.

Claims (7)

1. Verfahren zum Kaltmahlen in einer Fließbett-­Gegenstrahlmühle mit einer von Gasstrahlen beauf­schlagten Mahlkammer (2), einer Mahlgutaufgabeein­richtung, einem Sichter (5) zur Trennung von Grob­(11) und Feingut (10) und einem Sumpf (3) unterhalb der Mahlkammer für zudosiertes Mahlgut und vom Sich­ter zurückströmendes Grobgut,
dadurch gekennzeichnet,
daß das vom Sichter zurückströmende Grobgut inner­halb der Fließbett-Gegenstrahlmühle durch ein kryogenes Kältemittel gekühlt wird.1. A method for cold grinding in a fluidized bed counter-jet mill with a grinding chamber (2) acted upon by gas jets, a grist feed device, a sifter (5) for separating coarse (11) and fine material (10) and a sump (3) below the grinding chamber for dosed regrind and coarse material flowing back from the classifier,
characterized,
that the coarse material flowing back from the classifier is cooled within the fluidized bed counter jet mill by a cryogenic refrigerant. 2. Verfahren nach Anspruch 1,
dadurch gekennzeichnet,
daß das kryogene Kältemittel in feinzerteilter Form mit dem Grobgut in Berührung gebracht wird.2. The method according to claim 1,
characterized,
that the cryogenic refrigerant is brought into contact with the coarse material in finely divided form. 3. Verfahren nach Anspruch 1 oder 2,
dadurch gekennzeichnet,
daß das kryogene Kältemittel in den Sumpf eingetra­gen wird.3. The method according to claim 1 or 2,
characterized,
that the cryogenic refrigerant is introduced into the sump. 4. Vorrichtung zur Durchführung des Verfahrens nach Anspruch 2 oder 3
gekennzeichnet durch eine im Sumpf einer Fließbett­Gegenstrahlmühle angeordnete Eintragvorrichtung für ein kryogenes Kältemittel, welche als an den Stirn­flächen geschlossenes doppelwandiges Rohr (22) aus­gebildet ist, das in axialer Richtung mit Abstand zu den zylindrischen Wänden der Mahlkammer angeord­net ist und auf die Rohrachse gerichtete Austritts­ öffnungen (23) für das Kältemittel aufweist.4. Apparatus for performing the method according to claim 2 or 3
characterized by an inlet device for a cryogenic refrigerant arranged in the sump of a fluidized bed counter-jet mill, which is designed as a double-walled tube (22) closed on the end faces, which is arranged in the axial direction at a distance from the cylindrical walls of the grinding chamber and has an outlet directed towards the tube axis has openings (23) for the refrigerant. 5. Vorrichtung nach Anspruch 4,
dadurch gekennzeichnet,
daß die dem doppelwandigen Rohr zugeordneten Wände der Mahlkammer doppelwandig ausgebildet sind, mit kryogenem Kältemittel beaufschlagbar sind und in den Sumpf gerichtete Austrittsöffnungen (25) für das Kältemittel besitzen.5. The device according to claim 4,
characterized,
that the walls of the grinding chamber assigned to the double-walled tube are double-walled, can be charged with cryogenic refrigerant and have outlet openings (25) for the refrigerant directed into the sump. 6. Vorrichtung zur Durchführung des Verfahrens nach einem der Ansprüche 1 bis 3,
gekennzeichnet durch eine konzentrische rohrförmige Schürze (26) welche die Mahlkammer in einen zentra­len Schacht (37) und einen ringförmigen Schacht (38) trennt.6. Device for carrying out the method according to one of claims 1 to 3,
characterized by a concentric tubular skirt (26) which separates the grinding chamber into a central shaft (37) and an annular shaft (38). 7. Vorrichtung nach Anspruch 6,
gekennzeichnet durch eine Einsprühvorrichtung (39) für das kryogene Kältemittel im ringförmigen Schacht.7. The device according to claim 6,
characterized by a spray device (39) for the cryogenic refrigerant in the annular shaft.
EP89115154A 1988-10-05 1989-08-17 Cold-grinding method and apparatus Expired - Lifetime EP0362525B1 (en)

Priority Applications (1)

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AT89115154T ATE103208T1 (en) 1988-10-05 1989-08-17 METHOD AND DEVICE FOR COLD GRINDING.

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DE3833830A DE3833830A1 (en) 1988-10-05 1988-10-05 METHOD AND DEVICE FOR COLD GRINDING
DE3833830 1988-10-05

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EP (1) EP0362525B1 (en)
JP (1) JPH02227148A (en)
AT (1) ATE103208T1 (en)
DE (2) DE3833830A1 (en)
ES (1) ES2052845T3 (en)
ZA (1) ZA897535B (en)

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EP0377170A3 (en) * 1988-12-31 1991-05-02 Hoechst Aktiengesellschaft Method for the manufacture of fine-grained polyester ketone powder and its use
US5247052A (en) * 1988-12-31 1993-09-21 Hoechst Aktiengesellschaft Fine-grained polyether-ketone powder, process for the manufacture thereof, and the use thereof
US5887803A (en) * 1995-09-07 1999-03-30 Messer Griesheim Gmbh Process and apparatus for grinding and sifting a product
WO2007008480A1 (en) * 2005-07-07 2007-01-18 Nanotherapeutics, Inc. Process for milling and preparing powders and compositions produced thereby

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US5247052A (en) * 1988-12-31 1993-09-21 Hoechst Aktiengesellschaft Fine-grained polyether-ketone powder, process for the manufacture thereof, and the use thereof
US5887803A (en) * 1995-09-07 1999-03-30 Messer Griesheim Gmbh Process and apparatus for grinding and sifting a product
WO2007008480A1 (en) * 2005-07-07 2007-01-18 Nanotherapeutics, Inc. Process for milling and preparing powders and compositions produced thereby

Also Published As

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DE3833830A1 (en) 1990-04-12
ATE103208T1 (en) 1994-04-15
EP0362525B1 (en) 1994-03-23
US4962893A (en) 1990-10-16
EP0362525A3 (en) 1991-01-16
ES2052845T3 (en) 1994-07-16
DE3833830C2 (en) 1991-11-07
DE58907281D1 (en) 1994-04-28
JPH02227148A (en) 1990-09-10
ZA897535B (en) 1990-06-27

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