EP3613508B1 - Method for discharging poorly grindable particles from a spiral jet mill - Google Patents

Description

The present invention relates to methods for removing particles that are difficult to grind from a spiral steel mill according to the features of claim 1.

State of the art

From the prior art, jet mills such as those from WO9601694 or DE 44 31 534 A1 known. These jet mills are used to crush various materials. The particles to be comminuted are accelerated using gas jets in order to be comminuted by mutual impact. Furthermore, shear forces occur at the points where the particles are accelerated by the gas jets, which additionally contribute to the size reduction process.

If feed material consists of different components, it may happen that only some of them can be ground using the steel mill. The sufficiently comminuted particles leave the grinding chamber in which the sufficiently comminuted particles, also referred to as fines, pass through a classifying device, for example a classifier wheel, and then leave the jet mill via a fines outlet. Components that have other properties, such as ductile behavior or higher hardness, can remain in the grinding chamber. These difficult-to-grind components, or even coarse particles, accumulate in the grinding chamber as the grinding process continues and thus reduce the volume of the grinding chamber that should actually be available for grinding, thereby significantly reducing the throughput of the jet mill.

It is known from jet mills from the prior art that these difficult-to-grind components are removed from the mill by reducing the classifier speed. The disadvantage of reducing the classifier speed is complete contamination of the system with coarse particles. The fluid bed must then be refilled again, which results in shifts in the grain distribution until the optimal filling level is reached and low throughput rates are also achieved. The system must also be flushed so that the coarse particles are removed from the system. This approach is very inefficient and takes a lot of time.

The object of the present invention is to optimize the grinding process in such a way that residues which remain within the grinding chamber during a grinding process can be removed from it more quickly and efficiently than is the case in the prior art.

The above tasks are achieved by the method according to claim 1. Further designs according to the invention can be found in the respective subclaims.

The invention relates to a method for grinding, separating and discharging difficult-to-grind components of a mixture of components with different grindability from a process space of a jet mill. Due to the different properties of the components contained in the good mixture, the sufficiently comminuted particles, also described as fines, leave the process room after classification via the fines outlet. The classification is carried out, for example, using a classifier wheel. The components that are difficult to grind, also described as coarse particles, are unable to overcome the classifying device and are therefore retained in the process space. In order to avoid an accumulation of coarse particles in the process space, the coarse particles are discharged using a fluid via at least one discharge nozzle. The opening of the discharge nozzle and the interruption of the feed of the regrind are carried out in a synchronized manner.

The fluid which removes the coarse particles from the process space is made available through the grinding nozzles protruding into the process space. During the grinding process, these nozzles provide the gas jets through which the particles of the feed material are comminuted. Due to the excess pressure or negative pressure that prevails in the process space, the coarse particles are discharged from the process space via the at least one discharge nozzle using the grinding gas.

In order to further optimize the process, the discharge nozzle is closed to the process space during the grinding process and is only opened manually or automatically during a coarse fraction discharge phase.

Another advantage of the method according to the invention is the manual or automatic interruption of the regrind feed. This prevents unground material from being fed into the grinding chamber via the ground material inlet during the emptying of the grinding chamber or during the discharge of the difficult-to-grind components from the grinding chamber. The feed of regrind via the regrind feed into the process space is carried out using a dosing unit, for example via a rotary valve, or a dosing pump.

The discharge nozzle and the feed of the ground material can be closed from the process space using closure elements. The closure elements can be designed, for example, as a flap, slide or rotary valve.

In order to be able to better regulate the interruption of the regrind feed, at least one operating parameter of the method is recorded via the at least one sensor. Important operating parameters include, for example, the filling level of the mill, the amount and speed of the grinding material feed, and the amount, pressure and speed of the grinding fluid used, the speed of the classifier wheel and the power consumption of the motor that drives the classifier wheel, as well as the grinding material throughput.

The various parameters interact with each other, in particular the degree of filling of the mill and the feed of the milled material. The filling level of the The mill is controlled via the power consumption of the classifying wheel. If ground material leaves the process space via the classifier wheel and the fine material outlet, there is less material to be ground in the process room, which means there are fewer collisions of particles of the material to be ground with the classifier wheel. As a result, the power required to maintain a constant speed of the classifier wheel decreases, and the power consumption of the motor that drives the classifier wheel decreases. If the current consumption leaves a defined minimum value, for example falls below 60% of the maximum power of the motor that drives the classifier wheel, regrind is fed into the process room via the regrind feed until the current consumption of the motor that drives the classifier wheel is reached, due to the now increasing number of collisions with ground material has again reached a defined maximum value, for example 65% of the maximum power of the motor that drives the classifier wheel. Depending on the material to be ground, the limits for the power consumption of the motor that drives the classifier wheel can vary. For example, values for the minimum value between 30% and 80%, in particular between 40% and 60%, are possible. The maximum value for the power consumption of the motor that drives the classifier wheel can be between 50% and 100%, in particular between 60% and 80%.

The process for feeding the regrind explained in the paragraph above is expressed as a constant interval for regrind that does not contain any components that are difficult or impossible to grind. This means that the intervals between the stop of the regrind feed and the start of the regrind feed, as well as the duration of the regrind feed, behave almost periodically. This is not the case for ground material with components that are difficult or impossible to grind.

The enrichment of the components of the ground material that are difficult or impossible to grind means that fewer particles leave the process area than usual. For this reason, the current consumption of the motor that drives the classifier wheel does not fall below the defined minimum value so quickly, which is accompanied by a delay in the feed of the regrind. The components of the regrind that are difficult or impossible to grind and remain in the process space continue to put stress on the classifier wheel, but without passing through it. As a result, the power consumption of the motor that drives the classifier wheel does not decrease as with normal regrind without components that are difficult or impossible to grind, and the intervals between stopping the grinding material feed do not decrease and start of the regrind feed increase. The duration of the regrind feed, on the other hand, is reduced because once the current consumption of the motor that drives the classifier wheel falls below the defined minimum value, the corresponding maximum value is reached more quickly because a higher number of particles remain in the process space.

Due to the described behavior of grinding material with components that are difficult or impossible to grind, a significant reduction in throughput can be seen as the grinding time increases. This reduction in throughput can preferably be used as a control value for the discharge of the components that are difficult or impossible to grind from the mill.

If at least one defined value range of the at least one monitored operating parameter is exceeded, for example the throughput, the feed of the regrind is automatically stopped. Analogous to the regrind feed, i.e. also depending on the operating parameters, the opening and closing of the Discharge nozzle can be controlled. The interruption or start of the regrind feed and the opening or closing of the discharge nozzle can also be coordinated with one another. For example, it is possible to control only the regrind feed via at least one operating parameter. If at least one operating parameter, e.g. the throughput or the interval duration of the material supply, leaves the value range defined for it, the grinding material feed is interrupted. Depending on this, the opening of the discharge nozzle can be triggered at the same time or at a different time. The same is also conceivable if only the discharge nozzle is controlled via at least one operating parameter and the regrind feed reacts depending on this. This makes it possible to automatically create stable conditions for the grinding process that are adapted to the corresponding grinding material. The corresponding value ranges for the operating parameters must be selected depending on the material and grinding fluid.

Depending on the material to be ground, the opening time of the discharge nozzle and the interruption of the feed of the material to be ground are set individually. The opening time of the discharge nozzle is preferably 1 - 10 seconds. The interruption of the feed of the ground material is preferably 1 - 10 seconds.

In an advantageous version of the method, the opening of the discharge nozzle and the interruption of the regrind feed, as well as the closure of the discharge nozzle and the start of the regrind feed, are carried out in a coordinated manner. In order to avoid losses of the ground material, it is advantageous if the feeding of the ground material is interrupted before the discharge nozzle is opened. In this way, feed material that has not yet been ground can be ground and the particles still in the process space that have been ground to the target size can be discharged.

1. 1. Durch Anreicherung von schwer oder nicht mahlbaren Anteile des Mahlgutes im Prozessraum verlässt mindestens ein Betriebsparameter einen definierten Wertebereich.
2. 2. Unterbrechung der Mahlgutaufgabe.
3. 3. Vermahlung und Austrag des noch im Prozessraum befindlichen Mahlgutes.
4. 4. Öffnung des Austragsstutzens und Austrag der schwer oder nicht mahlbaren Anteile des Mahlgutes aus dem Prozessraum.
5. 5. Schließung des Austragsstutzens.
6. 6. Start der Mahlgutaufgabe und Weiterführung des Mahlprozesses.

An example of the process could be described as follows:

1. 1. Due to the accumulation of parts of the ground material that are difficult or impossible to grind in the process space, at least one operating parameter leaves a defined value range.
2. 2. Interruption of the regrind feed.
3. 3. Grinding and discharge of the ground material still in the process room.
4. 4. Opening the discharge nozzle and discharging the parts of the ground material that are difficult or impossible to grind from the process space.
5. 5. Closure of the discharge nozzle.
6. 6. Start of the grinding material feed and continuation of the grinding process.

Preferably, some of the process steps described above have a defined duration. For example, the grinding and discharge of the portion of grindable portions of the ground material still in the process space takes between one second and five minutes, in particular between 1 and 60 seconds. The opening time of the discharge nozzle is between one second and one minute, in particular between 1 and 10 seconds. As soon as the discharge nozzle is closed, you can start feeding the ground material again. The time between these two process steps can be between 0.5 and 60 seconds, in particular between 0.5 and 5 seconds.

The process according to the invention is carried out by a spiral jet mill to act on material that can be partially comminuted and classified. Such spiral steel mills have a process space that is surrounded by a housing. At least two grinding nozzles protrude into the process space; the grinding fluid is passed into the process space through these grinding nozzles during the grinding process.

In spiral jet mills, the process space is rotationally symmetrical, flat and round, with a radial housing wall that is delimited by a circular surface at the top and bottom, with the height of the cylinder being smaller than the diameter. The grinding nozzles are arranged tangentially on the housing wall. Furthermore, the grinding nozzles are arranged on the same level as the classifier wheel, which is located in the middle of the process space. The classifier wheel is also rotationally symmetrical, flat and round, with radially extending slats, each of which is delimited at the top and bottom by a plate that forms a circular surface, whereby the height of the cylinder body is also smaller than the diameter.

Depending on the material to be ground and the grinding fluid, the set pressure at which the grinding fluid is fed through the grinding nozzles into the process space varies between 0.1 and 40 bar(g). Typical grinding fluids are air, nitrogen, water vapor and noble gases such as argon and helium.

The ground material introduced via a ground material inlet connected to the process space is captured by the grinding fluid jets, accelerated and comminuted by particle-particle collisions. It is therefore an autogenous grinding of the ground material. The stressed particles are transported from the grinding fluid to the classifier wheel, which is driven by a motor, for example a frequency-controlled motor. The desired target fineness of the fine material is preset via the speed of the classifier wheel. After passing the classifier wheel, the fine material is discharged from the machine via the fine material outlet. Particles that are too coarse or have not yet been ground sufficiently are rejected by the classifier wheel and thus find their way back into the product-laden grinding fluid jets for renewed stress. This creates a circular movement of the ground material in the process space.

In order to remove the components of the ground material that accumulate in the process space that are difficult to grind or cannot be ground, a discharge nozzle connected to the process space is provided. This discharge nozzle can be closed manually or automatically from the process space and is closed during the grinding process.

The machine, which acts on partially shredded and classifiable goods, has measuring instruments that record the operating parameters of the grinding process. Relevant operating parameters include, for example, the throughput of regrind per unit of time, the quantity and speed of the regrind feed, and the amount, pressure and speed of the grinding fluid used, the speed of the classifier wheel and the power consumption of the motor that drives the classifier wheel. The machine also includes a device with which the dosage of the ground material into the process space can be recorded and controlled.

As an alternative or in addition to the features described, the method may include one or more features and/or properties of the previously described device. The device can also alternatively or additionally have individual or multiple features and/or properties of the methods described.

It should be expressly mentioned at this point that all aspects and embodiment variants that were explained in connection with the starting mixture and the system for producing the starting mixture equally relate to or can be partial aspects of the method according to the invention. Therefore, if certain aspects and/or connections and/or effects are mentioned at one point in the description or in the claim definitions of the starting mixture and/or the system, this applies equally to the method according to the invention. The same applies in the opposite way, so that all aspects and embodiment variants that were explained in connection with the method according to the invention equally relate to or can be partial aspects of the starting mixture and the system. Therefore, if certain aspects and/or connections and/or effects are mentioned at one point in the description or in the claim definitions for the method according to the invention, this applies equally to the starting mixture and the system.

Character description

In the following, exemplary embodiments will explain the invention and its advantages in more detail using the attached figures. The proportions of the individual elements in the figures do not always correspond to the real proportions, as some shapes are simplified and other shapes are shown enlarged in relation to other elements for better illustration.

Identical reference numbers are used for elements of the invention that are the same or have the same effect. Furthermore, for the sake of clarity, only reference numbers that are necessary for the description of the respective figure are shown in the individual figures. The embodiments shown merely represent examples of how the device according to the invention or the method according to the invention can be designed and do not represent a final limitation.

Figure 1 shows a sectional view of a spiral jet mill (1), having a regrind feed (2) through which the regrind (10) is guided into the process space (3). The dosing, i.e. the feeding of the ground material (10), takes place via a dosing unit (not shown), for example a rotary valve or a pump device.

Grinding nozzles (4), which are positioned at a suitable distance from one another, protrude into the process space (3). This suitable distance varies depending on the number of grinding nozzles (4) and should be chosen so that the grinding nozzles (4) are evenly distributed over the circular path that describes the housing (5) which encloses the process space (3), in the example Figure 1 The grinding nozzles (4) are each arranged 90° offset and their respective longitudinal axes (41) close with an im The tangent (13) created in the area of the respective grinding nozzle attachment in the housing (5) forms an angle alpha (α) which should be in the range of 10° and 60°. Depending on the application, the grinding nozzles (4) can also be arranged irregularly on the housing (5).

The grinding nozzles (4) supply the grinding fluid (6) to the process space (3). This grinding fluid (6) is used to stress and shred the ground material (10) that is dispensed. Depending on the application and the feed (10), the parameters such as pressure, quantity, temperature and spray angle for the grinding fluid (6) must be adjusted. For example, gases come into consideration as grinding fluid (6), in particular protective gases such as argon and helium and nitrogen.

The fine material outlet (7) is located in the middle of the process space (3). This leads particles out of the process space (3) through the lid or bottom of the housing (5). The particles that have achieved the necessary fineness through grinding in the process space (3), i.e. the ground portions of the ground material (11), are removed through the fine material outlet (7). A classifier wheel (8) is positioned around the fine material outlet (7) so that only particles with the necessary fineness can leave the process space (3). The classifier wheel (8) rotates and is operated at a variable speed. The necessary fineness for the ground portions of the ground material (11) can thus be set. If a particle that is too large wants to pass through the rotating classifier wheel (8), it is thrown back into the process space (3) by the safety wheel (8) and stressed again. If the particle is ground finely enough, i.e. it has a sufficiently small particle or grain size, it can leave the process space (3) through the fine material outlet (7) with the fluid flow of the ground parts of the ground material (11).

The parts of the ground material (12) that are difficult or impossible to grind remain in the process space (3) and accumulate there during the grinding process. In order to remove these particles from the process space (3), the regrind feed (2) is closed relative to the process space (3). At the same time, or with a defined time offset, the discharge nozzle (9) opens. This is closed during the grinding process by a closure element (14), for example a flap, or a slide relative to the process space (3). This closure element (14) can be positioned anywhere in the discharge nozzle (9), for example the closure element (14) can rest flush against the outer shell of the housing (5), or can be mounted inside the housing (5) and be flush with the process space (3). . Due to the overpressure or negative pressure of -500 mbar(g) to +600 mbar(g) prevailing in the process space (3), all particles located in the process space (3) are now flushed out of the process space (3) via the discharge nozzle (9).

After a period of, for example, 1 to 60 seconds or a message from a sensor that monitors the degree of filling in the process space (3) and thus checks whether all parts of the ground material (12) that are difficult or impossible to grind have been discharged from the process space, the discharge nozzle (9 ), closed again by means of the closure element (14). The grinding material feed (2) is then opened or started again and the grinding process is continued.

Optionally, it can also be provided to close the regrind feed (2) with a further closure element (15), analogous to the closure element (14) in the discharge nozzle (9) relative to the process space (3).

Reference symbol list

1

Spiral steel mill

2

Grinding material feed

3

Process room

4

grinding nozzles

5

Housing

6

grinding fluid

7

Fines outlet

8th

sifter wheel

9

discharge nozzle

10

Ground material

11

Ground portions of the ground material

12

parts of the ground material that are difficult or impossible to grind

13

tangent

14

Closure element

41

Longitudinal axis of the grinding nozzles

Claims (9)

1. A method for grinding, separating, and discharging hard to grind parts of a material mixture of components with different grindability from a process chamber of a spiral steel mill, from which the easily grindable parts are discharged via a fine material outlet, and the hard to grind parts are discharged from the process chamber via at least one additional discharge nozzle by means of a fluid, characterized in that the opening of the discharge nozzle and the interruption of the grinding material feeding is performed in a synchronized manner.
2. The method according to claim 1, wherein the hard to grind parts are discharged from the process chamber by means of a grinding fluid.
3. The method according to claim 1 or 2, wherein the discharge nozzle and/or the grinding material feeding is closed during the grinding process.
4. The method according to one of claims 1 to 3, wherein the discharge nozzle can be opened automatically.
5. The method according to one of claims 1 to 4, wherein the grinding material feeding can be interrupted automatically.
6. The method according to one of claims 1 to 5, wherein different operating parameters of the method are detected during the grinding process.
7. The method according to claim 6, wherein the grinding material feeding is interrupted when a defined value range of the detected operating parameters is left.
8. The method according to claim 6 or 7, wherein the discharge nozzle is opened when a defined value range of the detected operating parameters is left.
9. The method according to one of claims 1 to 8, wherein the opening time of the discharge nozzle is 1 - 10 seconds and/or the interruption of the grinding material feeding is 1 - 10 seconds.

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