EP3159061B1 - Ring ball mill with improved monitoring - Google Patents

Description

The invention relates to a ball mill with improved monitoring of Mahlkugelbewegung, and a corresponding method. Such a ball mill is from the document EP2075072 known. Ball mill mills have a grinder, which consists of a plurality of grinding balls, which are guided between a Mahlring and a pressure ring in a Mahlspur. Here, the grinding balls are set in motion by a difference in the rotational speeds of grinding and pressure ring. Through the running of the grinding balls on the lower Mahlring crushing of the ground material is carried out. The pressure ring, which is generally arranged at the top, serves to guide the grinding balls and transmits the grinding pressure built up by means of a hydraulic tensioning device or spring assemblies to the grinding balls. Ball ring mills are mainly used in the grinding of coarse-grained grinding material such as minerals, coal or gypsum. In particular, when used in large process plants considerable amounts of regrind can be enforced. Robust operation is expected here. This also applies to fluctuating properties in terms of the raw material supplied. Since these are often natural materials, variations in material properties are common. For example, in the case of gypsum, the moisture content can sometimes vary quite abruptly to a relevant extent.

Fluctuations in the raw material fed in can lead to too much or too little raw material being fed to the grinding path, which means that the grinding balls can no longer optimally roll on the grinding path. Thus, if the raw material is supplied too much or if the properties differ too greatly, for example excessively high humidity in the case of gypsum as the raw material, the grinding balls may become blocked. If this occurs, residence times increase as the ball mill loses efficiency. For a uniform process control, in particular downstream processes, this is extremely unfavorable.

The invention has for its object to provide an improved ball mill, which is more robust and less prone to blockages.

The inventive solution lies in the features of the independent claims. Advantageous developments are the subject of the dependent claims.

In a ball mill with a arranged in a mill housing grinder comprising a plurality of grinding balls in a grinding chamber, which are guided between a Mahlring and a pressure ring in a Mahlspur, a drive along the grinding balls due to a difference in the rotational speeds of the grinding and pressure ring moves the Mahlspur, a slip control system for the grinding balls is provided according to the invention, at the input of a arranged outside the grinding chamber sensor is connected to detect the ball and at the output at least one dynamically adjustable actuator is connected, which acts on the pressure ring and presses it against the guided on the Mahlring balls.

The invention thus achieves that when the slip is detected, the pressure acting on the pressure balls via the pressure ring increases or decreases, so as to reduce or increase the slippage of the grinding ball. Thus, the slip deviation can be compensated. With the slip control system according to the invention, the ball ring mill is thus more robust with regard to its operating behavior. Fluctuations, in particular varying properties of the raw material supplied, can be better compensated. Overall, a more sensitive control of the ball ring mill is achieved, which not only improves the reliability, but also increases the quality of the issued ground material. By placing the sensor to detect the actual recirculating ball outside the grinding chamber, it is not exposed to the critical, abrasive environmental conditions within the grinding chamber. This protects the sensor against harmful influences and therefore also robust in operation.

In most cases, the rotational speed of the drive is constant in the case of ball-type mills that are practically executed. Therefore, a measurement of the drive speeds is often unnecessary. However, it can also be provided that the actual drive speed is detected and fed to the slip control system as a further input signal. This offers the advantage that valid values for the slip control system are always available even in dynamically changeable situations (in particular when starting up the ball ring mill). Particularly useful here is when as a signal for the speed the speed difference between Mahlring and pressure ring is used.

The slip control system is preferably designed so that at a low ball circulation speed by lowering the pressure exerted by the pressure plate, the speed is increased and thus the slip is reduced. Thus, an optimization of the operation can be achieved, thanks to the achieved by the measurement of the invention high dynamics even with rapidly changing operating conditions.

The sensor for detecting the ball circulation is preferably designed as an acoustic sensor which measures the sound generated by the movement of the grinding balls in the grinding mechanism. Preferably, this sound measured by the acoustic sensor is evaluated by means of a frequency detector. Preferably, the frequency detector is designed for performing a real-time Fourier analysis. In this case, the frequency spectrum obtained by the Fourier analysis reproduces the real ball circulation frequency of the grinding balls. This is a non-invasive and easy to order and wear-free way a measure of the real ball screw frequency available. The Fourier transform can be done in real time, so that even with dynamic changes in the speed of the grinding ball quickly a corresponding measurement signal is available, without having to wait for complete rounds. The invention thus provides an improved measuring signal for the recirculating ball frequency on the one hand robust but on the other hand also in a very dynamic manner.

The Fourier analysis is preferably carried out as a discrete Fourier analysis. This offers the advantage of fast measured value processing, which in particular serves to achieve greater dynamics. Preferably, the Fourier analysis is performed as a Fast Fourier Analysis (FFT). This also improves the dynamics of measured value acquisition.

The acoustic sensor may be implemented as a conventional microphone. However, it can also be provided that the acoustic sensor is designed as a structure-borne sound sensor. The latter has the advantage that the structure-borne noise generated by the movements of the grinding balls in the grinder is measured directly, so that an impairment of the measurement is reduced by ambient noise.

Appropriately, more than one structure-borne sound sensor is provided on the mill housing. This not only improves the acquisition of the measurement signal for structure-borne noise, since now two signals are available and thus increases the power of the desired signal so far. The provision of a second structure-borne sound detector also has the advantage that it creates a reference, whereby interference from external components, which are expected to act on both structure-borne sound sensors, can be more easily detected and taken into account in the subsequent processing of the measurement signals. Since structure-borne sound sensors are extremely inexpensive available and the location of their attachment to the mill housing is not critical, a considerable improvement in the quality of measurement is achieved in this way with little additional effort.

Additionally or alternatively, a second correction circuit may be provided, which includes the slip meter and the drive. This correction circuit is designed in such a way that if the slip is too great, a correction signal is output to the drive for changing the rotational speed of the drive. This is expediently carried out in such a way that the rotational speed of the grinding ring is reduced in the event of too great a slip by lowering the drive speed. As a result, the balls no longer need to rotate so fast around the mill axis, whereby the slip is reduced. By acting on the drive, the ball mill according to the invention can be better adapted in changing operating conditions, in particular fluctuations in the amount of ground material supplied.

The invention further extends to a corresponding method for monitoring the ball circulation.

Fig. 1:

eine schematische Ansicht eines Ausführungsbeispiels einer erfindungsgemäßen Kugelringmühle;

Fig. 2:

ein Blockschaltbild zu einem Schlupfkontrollsystem gemäß dem Ausführungsbeispiel;

Fig. 3 a,b:

Signalkurven eines akustischen Sensors und deren Darstellung als Frequenzspektrum; und

Fig. 4 a-d:

Diagramme zu einigen Betriebsparametern der Erfindung.

The invention will now be described by way of example with reference to the accompanying drawings. Show it:

Fig. 1:

a schematic view of an embodiment of a ball mill according to the invention;

Fig. 2:

a block diagram of a slip control system according to the embodiment;

3 a, b:

Signal curves of an acoustic sensor and their representation as a frequency spectrum; and

Fig. 4 ad:

Diagrams of some operating parameters of the invention.

An embodiment of a ball mill according to the invention is shown schematically in FIG Fig. 1 shown. The ball ring mill 1 comprises a mill housing 10 with a grinder 2, which is arranged in a grinding chamber 11. The grinder 2 comprises a grinding ring 21, which is offset by a drive motor 23 in rotary motion. In the embodiment, five grinding balls 3 are provided, of which three in the illustration in accordance with Fig. 1 are visible. From above, a pressure ring 22 acts on the grinding balls 3, so that the grinding balls 3 are held between the pressure ring 22 and the grinding ring 21. By pressing the pressure plates 24, the pressure ring 22 presses the grinding balls 3 into the grinding track 27 at the top of the grinding ring 21. The grinding ring 21 is rotated by the drive motor 23, and the grinding balls roll both on the grinding ring 21 and on the pressure ring 22 off. In the undisturbed state, they move approximately at half the differential rotational speed between pressure ring 22 and Mahlring 21. If, as in the illustrated embodiment, the pressure ring 22 stationary and only the Mahlring 21 driven, the Mahlkugeln 3 run at about half the rotational speed of the Mahlrings 22. The regrind, in Fig. 1 represented by black dots 9, is fed from above into the grinding chamber 11 and passes between the grinding balls 3 and the grinding ring 21 and is there comminuted and, if it has reached a sufficient grinding fineness, under the action of an air flow 80 exiting from a fan 8 transported away from the top of the grinding chamber 11 (see dotted arrows).

The drive motor 23 is actuated by a control unit 25. The control unit 25 sets a number of revolutions n of Drive motor 23 and the grinding ring 21 a. Usually, the number of revolutions n of the grinding ring 21 is constant, but it is also possible for deviations Δn to be predetermined. The pressure ring 21 is acted upon by the hydraulically operated pressure plate 24 with a force acting on Mahlring 21 force. The pressure plates 24 are actuators of a pressure control loop implemented in the pressure controller 26.

According to the invention, an acoustic sound sensor 40 is provided. It is arranged outside at the height of the grinding balls 3 on the mill housing 10. However, the arrangement at this position is not mandatory, it may also be located at other locations, also outside the mill and be located, for example, at the position indicated by the reference numeral 40 'position. The acoustic sensor 40 receives the circulating noise caused by the grinding balls 3 in the mill housing 10. The signal measured by the acoustic sensor 40 is added to an evaluation unit 41. In this a module for a fast Fourier transformation (FFT) is implemented. This is expediently realized in the form of a discrete FFT, which is particularly suitable for implementation in a computer-aided system. At the output of the evaluation unit 41, a signal ω for the recorded by the sound sensor 50 actual rotational frequency of the grinding balls 3 is output. This signal is applied to an input of a slip control system 5. At a further input of the slip control system 5, a signal for the rotational speed n of the grinding ring 21 is applied. A computing unit 51 of the slip control system 5 determines from the applied values for the rotational frequency ω of the grinding balls 3 on the one hand and the rotational speed n of the grinding ring (in FIG Revolutions per minute), on the other hand, the actually occurring slip s according to the relationship: $$s=\frac{120}{5\mathrm{}n}\omega -1$$

Here, the number "5" stands for the number of grinding balls 3, which rotate on the grinding ring 21. The thus obtained signal s for the slippage of the grinding balls 3 is output by the arithmetic unit 51 and applied to the input of a control unit 52. The control unit 52 is designed to modify the pressure acting on the pressure plate 24 hydraulic pressure generated by a hydraulic unit 28 in response to the slip signal s. For this purpose, a servo valve 54 is arranged between the hydraulic unit 28 and the pressure plate 24, which is controlled by a control signal at the output of the control unit 52. For example, the control unit 52 may be implemented as a P or PI controller. It is designed so that with increasing slip s the pressure acting on the pressure plate 24 hydraulic pressure is increased by means of the servo valve 54. Thus, the pressure plate 24 exert a greater compressive force on the pressure ring 22, so that the grinding balls 3 are pressed firmly against the grinding ring 21. Thus, the force acting as a driving force for the grinding balls 3 Reibschlusskraft between Mahlring 21 and the surface of the grinding balls 3, whereby the slippage of the grinding balls 3 decreases. For a small slip s, the procedure is reversed.

Apart from the first correction circuit formed by the control unit 52, a second correction circuit 6 may be provided, which includes its own speed correction unit 60. At an input of the speed correction unit 60 is also the signal s for the slip applied. It determines a need for a change in the rotational speed n with which the drive motor 23 drives the grinding ring 21. As a rule, this speed n should be kept constant and not be changed. However, in particular, if the slip deviates too much and the first correction circuit comprising the action on the pressure adjusting device 24 is no longer sufficient for correction, the correction member 60 can generate a speed correction signal Δn which is applied to the drive control unit 25 as an additional input signal. In this way, the drive control unit 25 with the drive 23 of the grinding ring 21 can make a contribution to the stabilization of the slip s and thus to safe mill operation. Appropriately, a tolerance band member 62 is provided for the correction member 60 thereto. It is thereby achieved that, with slight slip, the first correction circuit alone operates via the pressure actuator 24, while in the case of greater slip, intervention is still effected by the second correction circuit 6 generating a speed change value Δn for the speed control 25 of the drive motor 23.

It should be noted that the acoustic sensor 40 may, for example, also be embodied as a structure-borne sound sensor. This can be arranged arbitrarily on the mill housing. A possible location is 40 'in place Fig. 1 shown. This stands by way of example for any desired location, in particular outside the actual plane of the grinding balls 3. Furthermore, it can also be provided that two or more acoustic sensors are arranged. In such a case, for example, an acoustic sensor 40 in the plane of the grinding balls 3 and another outside Mahlkugele be arranged, as symbolized by the reference numeral 40 '.

The operation of the invention will be described with reference to Fig. 4 ad explained. It shows the course of some parameters over time. Thus, assuming stable operation, it is assumed that at the time t = t0 the consistency of the feedstock 9 fed changes, for example as a result of a considerable increase in the moisture content of coal as regrind. This has an effect on the operation of the grinder 2, so that there is an increase in the slip s of the grinding balls 3. This is visualized in a conventional grinder 2 by the dashed line from the time t = t0. It can be seen that the slippage increases considerably and permanently assumes an excessive value after an overshoot (from t = t2). Due to the slippage, the efficiency of the grinder 2 is reduced, so that the throughput of material to be ground 9 by the ball ring mill 1 decreases. This is in Fig. 4c by the flow rate expressed as mass flow m (also shown by dashed line). The fluctuations of the mass flow are unfavorable and can lead to an unstable operation of the ball mill 1 and in particular also downstream process stages.

To avoid this, the effect of the invention is shown by solid lines. Again, at the time t = t0, the moisture of the supplied coal 9 increases abruptly as regrind. Initially, the slip s also increases, but this is detected by the slip control system 5 according to the invention and, after a short time, there is an increase in the hydraulic pressure p _D acting on the pressure platens 24, as in FIG Fig. 4d is shown. This increases the contact pressure of the grinding balls 3 on the grinding ring 21, so that the short-term increase of the slip is limited and finally reduced until the slip s again reaches its original value (from t = t1) stationary. As a result, the throughput drops hardly noticeably as a result, since the slip s is reduced thanks to the increase in the contact pressure p _D caused by the slip control system 5. Thus, the throughput again reaches its original value very quickly stationary. The operating behavior of the ball ring mill is significantly more robust according to the invention.

Claims (12)

1. Ring ball mill having a grinding mechanism (2) which is arranged in a mill housing (10) and which comprises a plurality of grinding balls (3) in a grinding chamber (11), which are guided between a grinding ring (21) and a pressure ring (22) in a grinding track (27), a drive (23) moving the grinding balls (3) on account of a difference in the speeds of revolution of grinding and pressure ring (21, 22),
   characterized in that
   a slip monitoring system (5) for the grinding balls (3) is provided, on the input of which there is arranged a sensor (40) arranged outside the grinding chamber for detecting the ball circulation, and on the output of which there is arranged at least one dynamically adjustable actuator (24), which acts on the pressure ring (22) and presses the latter against the grinding balls (3) guided on the grinding ring (21).
2. Ring ball mill according to Claim 1, characterized in that the slip monitoring system (5) comprises a control unit (52) which is designed such that, in the event of a rise in the slip s of the grinding balls (3), an actuating signal is output which acts on the actuator (24) in a pressure-increasing manner.
3. Ring ball mill according to one of the preceding claims, characterized in that the slip monitoring system (5) has a further input, to which a signal for the rotational speed n of the drive (23) is applied.
4. Ring ball mill according to one of the preceding claims, characterized in that the sensor for detecting the circulation of the grinding balls (3) is embodied as an acoustic sensor (40) .
5. Ring ball mill according to Claim 4, characterized in that a frequency detector (41) is provided, which evaluates the signal from the sensor (40).
6. Ring ball mill according to Claim 5, characterized in that a Fourier analysis is implemented in the frequency detector (41), preferably as a discrete Fourier analysis.
7. Ring ball mill according to one of the preceding claims, characterized in that the sensor is embodied as a structure-borne sound sensor.
8. Ring ball mill according to one of the preceding claims, characterized in that more than one sensor is provided.
9. Ring ball mill according to one of the preceding claims, characterized in that a second correction loop (6) is provided, which comprises the slip monitoring system (5) and the drive (23).
10. Ring ball mill according to Claim 9, characterized in that the second correction loop (6) is formed in such a way that, in the event of excessively high slip s, a correction signal Δn which effects a reduction in the speed of revolution Δn is output to the drive (23).
11. Method for operating a ring ball mill having a grinding mechanism which is arranged in a mill housing and which comprises a plurality of grinding balls in a grinding chamber, which are moved between a grinding ring and a pressure ring in a grinding track, a drive moving the grinding balls along the grinding track on account of a difference between grinding and pressure ring, the following being provided in accordance with the invention:

    I. detection of ball circulation of the grinding balls, characterized by

    II. determination of a slip of the grinding balls and actuation of a pressure actuator to change the contact pressure of the pressure ring in such a way that, in the event of increased slip, the pressure is increased via the pressure ring to the pressure exerted by the grinding balls.
12. Method according to Claim 11, characterized by use of a slip monitoring system according to one of Claims 2-10.

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