DE102022003499A1 - Process for reducing the specific energy consumption when comminuting material by combining good bed grinding and jet grinding - Google Patents

Abstract

In a method and a device for comminution of material by material bed grinding and jet grinding with air classification, the grinding of the material should be carried out as energy efficiently as possible. This is achieved by selecting the specific pressing force of the material bed grinding so that the specific total energy consumption for pre-grinding in the material bed, jet grinding and air classification is smaller than the specific total energy consumption for jet grinding and air classification without pre-grinding at the same grinding pressure and classifier speed.

Description

The invention is directed to a method of combined good bed and jet grinding and a device for this.

Jet grinding in spiral jet or fluid bed counterjet mills is ideal for grinding a wide variety of materials. Due to the high stress intensities and stress numbers, very fine powders can be produced. Due to the impact stress on the particles caused by particle-particle collisions and the lack of moving or stationary tools, grinding with very little wear and contamination is possible. Crushing is often combined with classification, so that the ground material is subjected to air sifting after grinding. Fine material is separated from coarse material and the fine material is removed from the mill as a product. The coarse material is rejected by the classifying wheel and subjected to grinding again, so that a product with the desired fineness can be produced.

A special form of jet mills are fluidized bed counterjet mills. In fluid bed counterjet mills, the air classifier is integrated into the mill.

In order for grinding to work in jet mills, compressed air or - more generally - compressed grinding gas must be expanded via nozzles. The compressed grinding gas required for this is compressed using compressors, which requires very high energy consumption. The reasons for this are the high energy requirement for compression and the poor efficiency of the compressors. Jet grinding is therefore associated with comparatively high specific energy consumption.

It is known to carry out two-stage or multi-stage comminution under certain conditions.

Multi-stage comminution is known from the processing of mineral materials, for example in ore processing or cement production.

For example, high-pressure material bed roller mills are used on a large scale in the cement industry for raw meal and clinker grinding in combination with ball mills.

The low-energy pre-shredding in the material bed using a high-pressure material bed roller mill leads to the formation of microcracks in the structure of the material to be ground and the subsequent comminution in ball mills results in energy-reduced fine comminution.

More recently, high-pressure material bed roller mills have also been used for pre-crushing for ore processing in combination with wet-operated ball mills or agitator ball mills.

The DE 41 37 901 C1 discloses a comminution of pigments in which compaction is carried out on a roller compactor with a defined line force before jet grinding, which means that the material can be dosed better and there is less dust. In addition, better product properties are achieved with the same amount of air in the jet mill. Disagglomeration occurs between the two process stages.

US 5,129,586 discloses a combination of a roller bowl mill with jet grinding and sifting in one machine. The material to be shredded is first shredded in the roller bowl mill and then fed to a classifier; the coarse material rejected by the classifier is fed to a jet mill for fine shredding.

The WO 93/08916 discloses a combination of pressure roller crusher and counter jet mill with downstream classifier.

At least the coarse material rejected by the classifier is re-ground in a roller mill, whereby the coarse particles are provided with cracks and micro-cracks and fed back to the counter-jet mill, so that re-grinding in the counter-jet mill becomes more efficient. This process can increase the capacity of the counterjet mill.

Furthermore, the reveals WO 93/08916 a process in which the material is additionally treated in a roller mill before counter-jet grinding.

The invention is therefore based on the object of creating a solution that makes it possible to carry out the grinding of material in a jet mill, in particular a fluidized bed counter-jet mill, as energy-efficiently as possible.

In a method of the type described above and a device for it, the object is achieved according to the invention by the characterizing part of claim 1.

In a method of the type described above, the object is achieved according to the invention in that a jet grinding is preceded by a pre-grinding in the material bed. By treating the material in the material bed, not only is the material crushed, but the material structure of the material to be ground is also additionally weakened so that the subsequent jet grinding can be carried out with lower specific energy consumption. Surprisingly, it has now been discovered in tests that a two-stage grinding of certain materials under certain operating conditions by means of a material bed grinding with a correspondingly selected specific pressing force followed by a jet grinding with integrated air sifting can be carried out with less energy overall than with pure jet grinding with sifting. The jet grinding and sifting were carried out both in the tests with pre-grinding and without pre-grinding at the same grinding pressure and sifter speed.

In order to carry out jet grinding in a fluidized bed counter-jet mill with an integrated classifying wheel in an energy-efficient manner, the feed material is pre-ground in the material bed in a material bed roller mill, especially in a high pressure material bed roller mill. In pilot plant trials it was shown that for brittle materials such as limestone or silicon carbide (SiC), the specific total energy consumption including grinding energy of the fluidized bed counterjet mill, grinding energy of the high-pressure material bed roller mill, blower energy of the system and visible energy can be reduced by 10 to 20%. This is also shown by the diagram in 2 using the example of SiC and the diagram in 3 using limestone as an example.

Specific total energy consumption means the energy consumption in kWh per t of material.

This effect is due to the low-energy pre-grinding in the material bed using the high-pressure material bed roller mill, which leads to the formation of microcracks in the structure. In the subsequent impact grinding in the fluidized bed counter-jet mill, this results in energy-reduced fine comminution.

By combining pre-grinding in the high-pressure material bed roller mill with fine grinding in the fluid bed counter-jet mill, a reduction in the specific total energy consumption of 10 to 20% is achieved. This also increases throughput by up to 20% or more. This is also shown for SiC in the diagram 4 clearly.

A fluidized bed counter-jet mill is preferably used for the jet mill. An air classifier is integrated into this mill, which makes it possible to produce material with a defined grain size distribution by rejecting coarse material from the air classifier and feeding it again for jet grinding. The fine material leaves the fluidized bed counterjet mill as a product. Laval nozzles or multiple nozzles are preferably used as grinding nozzles.

A good-bed roller mill, specifically a high-pressure material-bed roller mill, is used for good-bed grinding.

Through the combined good bed grinding and jet grinding with wind sifting, a saving in the specific total energy consumption of 5%, preferably 10, preferably 20% and particularly preferably greater than 20% can be achieved compared to pure jet grinding.

The process is suitable for materials with brittle behavior, e.g. minerals, chemical products and hard materials (e.g. silicon carbide (SiC)).

The invention is not limited to the number of respective process steps and devices shown. Additional steps such as dosing steps and corresponding silos can also be provided.

• 1 zeigt eine schematische Darstellung eines Anwendungsbeispiels mit Dosierung, Gutbettwalzenmühle, Fließbettgegenstrahlmühle, Filter und Gebläse
• 2 zeigt ein Diagramm für den spezifischen Gesamtenergieverbrauch über die Partikelgröße d₅₀ am Beispiel SiC ohne Vormahlung und mit Vormahlung in einer Hochdruckgutbettwalzenmühle
• 3 zeigt ein Diagramm für den spezifischen Gesamtenergieverbrauch über die Partikelgröße d₅₀ am Beispiel Kalkstein ohne Vormahlung und mit Vormahlung in einer Hochdruckgutbettwalzenmühle
• 4 zeigt ein Diagramm für den Durchsatz über der Partikelgröße d₅₀ am Beispiel SiC ohne Vormahlung und mit Vormahlung in einer Hochdruckgutbettwalzenmühle

Further details, features and advantages of the subject matter of the invention result from the subclaims and from the following description of the associated drawings, in which - by way of example - a preferred embodiment of the invention is shown. In the drawing shows:

• 1 shows a schematic representation of an application example with metering, good bed roller mill, fluid bed counterjet mill, filter and blower
• 2 shows a diagram for the specific total energy consumption over the particle size d ₅₀ using the example of SiC without pre-grinding and with pre-grinding in a high-pressure material bed roller mill
• 3 shows a diagram for the specific total energy consumption over the particle size d ₅₀ using the example of limestone without pre-grinding and with pre-grinding in a high-pressure material bed roller mill
• 4 shows a diagram for the throughput over the particle size d ₅₀ using the example of SiC without pre-grinding and with pre-grinding in a high-pressure material bed roller mill

The 1 shows schematically a system for carrying out the method according to the invention from combined good bed grinding and jet grinding with wind sifting. The material to be shredded is metered into a high-pressure material bed roller mill 2 via a metering device 1. The high-pressure roller bed mill 2 pulls the material via the counter-rotating rollers 3. A bed of material is formed in the nip 4 by grinding the particles, which also leads to the formation of microcracks in the structure of the particles. The specific pressing force is selected depending on the material. The material from the material bed roller mill is fed into the fluidized bed counterjet mill 6 via a metering device 5. This is where the fine comminution takes place. Jet grinding occurs in the fluidized bed of the mill through particle-particle collisions caused by gas jets. The grinding pressure is selected depending on the material to be ground. The shredded material is fed to the classifying wheel 7 of the fluidized bed counter-jet mill 6, which is located above the grinding zone. This sets the final fineness of the product. The coarse material is rejected by the classifying wheel and falls back into the grinding zone to be shredded again. The fine material leaves the fluidized bed counter-jet mill 6 via the classifying wheel 7 and is separated from the grinding fluid in a filter 8 and leaves the system as a product. The blower 9 ensures that the material is transported through the system.

List of reference symbols

1

Dosing device

2

High pressure material bed roller mill

3

rollers

4

Roll gap

5

Dosing device

6

Fluidized bed counterjet mill

7

sifting wheel

8th

filter

9

fan

QUOTES INCLUDED IN THE DESCRIPTION

This list of documents listed by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 4137901 C1 [0010]
• WO 9308916 [0012, 0014]

Claims (8)

Method for comminuting material comprising the steps - feeding material into a pre-grinding - pre-grinding the material by means of good bed grinding - grinding the pre-ground material by means of jet grinding - classifying the ground material by means of wind sifting - returning the coarse material resulting from the wind sifting to jet grinding and - discharging the fine material with a defined particle size, characterized in that the specific pressing force of the good bed grinding is selected so that in jet grinding with a specified grinding pressure and in wind sifting with a given classifier speed, the specific total energy consumption of the combined good bed grinding and jet grinding with wind sifting is smaller than in jet grinding with wind sifting without Upstream good bed grinding with the same grinding pressure of the jet grinding and the same classifier speed. Procedure according to Claim 1 characterized in that the specific total energy consumption of the jet grinding and wind sifting includes the grinding energy of the jet grinding, the fan energy of the system and the sifting energy. Procedure according to Claim 1 characterized in that the specific total energy consumption of the good bed grinding, jet grinding and wind sifting includes the grinding energy of the jet grinding, the grinding energy of the good bed grinding, the blower energy of the system and the sifting energy. Procedure according to Claim 1 until 3 characterized in that the jet grinding and the air sifting are carried out on a fluidized bed counter-jet mill (6) with an integrated sifting wheel (7). Procedure according to Claim 1 until 4 characterized in that the material bed grinding is carried out in a material bed roller mill, preferably in a high-pressure material bed roller mill (2). Method according to one of the preceding claims, characterized in that the combined good bed grinding and jet grinding with wind sifting enables a saving in the specific total energy consumption compared to jet grinding with wind sifting of 5%, preferably 10%, preferably 20% and particularly preferably more than 20%. Method according to one of the preceding claims, characterized in that the material to be shredded is materials with brittle behavior such as minerals, chemical products and hard materials. Device for carrying out the method according to Claims 1 until 7 , characterized in that the device comprises a high-pressure material bed roller mill (2), a fluidized bed counter-jet mill (6) with an integrated air classifier and a blower (9).

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