DE3136323A1 - METHOD FOR OPERATING A BALL MILL AND CORRESPONDING BALL MILL - Google Patents

Abstract

1. An agitator ball mill comprising a mill container (12) surrounding a mill space (34) in which at least one agitator element (32) rotatable relative to the mill container (12) is arranged, and further comprising at least one lock means (60) in a line (68) for feeding milling balls (36) from a reservoir (64) into the mill space (34) during operation, characterized in that a valve (70) and upstream of if a nozzle means (74, 78) are provided in the line (68) between the reservoir (64) and the mill space (34) through which a fluid may be discharged under pressure in the direction of the desired ball flow to transport the milling balls (36) into the mill space (34).

Description

BOEHRINGER MANNHEIM GMBH int.no.2398

Method of operating a ball mill and corresponding ball mill

The invention relates to a method for operating a ball mill, in particular for the digestion of biomass, in which the material to be ground is fed to a grinding chamber containing grinding balls and in the grinding chamber by the rotary movement grind by at least one rotating grinding media and the resulting movement of the grinding balls will.

The invention is also directed to a ball mill which is particularly suitable for carrying out the method is and has a grinding chamber surrounding a grinding chamber, in which at least one relative to the Housing rotatable grinding media is provided.

Ball mills have become increasingly important in a number of industrial processes in recent years. An example of this is the paint industry, where it is particularly important to use the pigments in the paints Distribute as evenly as possible to ensure a good dispersion effect to achieve.

Another example of the advantageous use of the Ball mills are the digestion of biomass from fermentative processes in order to obtain enzymes in biochemical ones Operated. Here it comes first of all

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on achieving the best possible digestion of the cells of the biomass, i.e. as high as possible Percentage of the cell content, such as enzymes, to be released in order to be able to isolate them in the subsequent processing steps.

The effect of ball mills in general and in particular the digestion of biomass is illustrated by a number of influenced by various parameters. For a given mill size, this includes, in particular, the stirring speed, the throughput rate and the size of the grinding balls used, which are generally made of glass, Consist of metal or aluminum oxide.

In a special embodiment, the width of the gap between the grinding body and the grinding container is also important for the grinding effect essential. In DE-OS 28 11 899 a gap ball mill is therefore proposed in which the gap width can be changed in that the distance between Grinding body and grinding container is set by means of an exchangeable spacer ring between the grinding processes can be exchanged in order to adapt the gap width to the respective requirements.

Another important influencing factor is the degree of ball filling, which is generally expressed as the ratio between the actually used and the maximum possible ball filling quantity is defined. In principle, an increased Ball filling level usually improves the grinding effect. It should be noted, however, that the increase the degree of ball filling also brings problems,

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that set limits. The wear on the mill and on the balls increases as the filling level increases to. The energy consumption increases because the grinder harder turns. This is related to the corresponding increase in the frictional heat in the ball mill, which can lead to cooling problems. Finally, especially with biomass, digestion is optimal to achieve, in which a maximum breakdown of the enzyme (s) is achieved, but at the same time the cells are not damaged so much that the subsequent processing is made more difficult.

In the known ball mills, the degree of filling can be determined before the start of a grinding process by filling in a precisely defined amount of balls. However, this filling level is not retained during the grinding process. Rather, it changes as a result of the wear of the balls and the wall and stirring parts in contact with them. In a ten-hour long-term test, for example, wear of 2.5 % was found. On the one hand, this changes the grinding behavior of the ball mill during the grinding process. Perhaps even more important, however, is that in the known ball mills or in the known methods of operating ball mills, there is no possibility of varying the degree of ball filling during operation of the ball mill so that the optimum operating conditions are achieved, which vary greatly depending on the product.

The object of the present invention is therefore to provide a method for operating a ball mill and to provide a corresponding ball mill, with which a uniform and optimized Grinding effect is achieved during the entire grinding process.

In a method of the type mentioned at the outset, this object is achieved in that the degree of ball filling regulated in the grinding chamber during the grinding process to adapt to the respective operating conditions

The device according to the invention of the type indicated at the outset is characterized by devices by which controls and continuously changes the degree of ball filling in the grinding chamber during operation of the ball mill is.

While in the known ball mills, because of the above-mentioned limitations, a relatively low degree of ball filling of a maximum of 80 % had to be used, it has surprisingly been found that by checking and regulating the degree of filling during operation, i.e. without interrupting the grinding process, considerably higher degrees of ball filling and so that improved grinding properties can be achieved without excessive wear or the ground material occurring

, and. cfeschäcfiqt, too much heated / effective The grinding process can, for example be controlled so that a relatively low level of ball filling is used in the start-up phase of the mill, see above

that the starting resistance is relatively easily overcome by the mill motor. The filling level then slowly increases to that which is optimal for normal operation Filling level increased.

The regulation of the degree of filling can, as in the example described above, be designed so that the degree of filling is varied during operation of the ball mill. According to a particularly preferred embodiment of the method according to the invention, however, the ball mill is operated in such a way that the degree of ball filling is kept essentially constant during most of the grinding process. In the context of the present invention it was found that the range of optimal ball filling, in particular when digesting biomass, is relatively narrow. A change in the degree of filling of the balls of 5 % can result in a change in the enzyme content of the product emerging from the ball mill by 20 % . If one compares this numerical value with the above-mentioned fact that 2.5% wear on the ball filling and mill is already possible after ten hours of operation and with the additional requirement that the ball mill should be operated continuously for a long time as possible without interruption, one recognizes that longer operation in the optimal range is only possible if the filling volume, which is decreasing due to wear, is compensated in such a way that the degree of filling of the balls remains constant.

The regulation of the degree of filling of the balls can be done manually. However, it is particularly preferably carried out automatically., Wherein according to a preferred embodiment, the performance

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recording of the ball mill motor is used as a measure for regulating the degree of ball filling. It has been found that the load on the motor and thus its power consumption depends very much on the degree of filling of the sphere. With a certain ball mill and a certain type of grist (and otherwise the same boundary conditions such as temperature etc.), the power consumption of the motor can be clearly assigned to the degree of ball filling. In this case, the power consumption fluctuates in the limit range which is essential for an optimal grinding effect in a certain ball mill, for example by 20 % if the ball filling is only changed by 1%. On the basis of this knowledge, it is sufficient for a specific application to determine the power consumption of the motor corresponding to a specific filling level in order to then use this value as a setpoint for keeping the ball filling level constant.

The regulation according to the invention of the degree of filling of the balls can be carried out according to a preferred embodiment of the invention Carry out the process by adding or removing grinding balls during the grinding process. For this, only relatively minor measures are necessary on the corresponding ball mill, so that even existing ball mills can be converted to this process relatively easily. The addition of balls can be done in relatively small amounts, so that a sensitive dosage is possible. A removal of balls must only be provided if operating conditions can occur in which the degree of ball filling, for example, due to momentary overloading of the machine, should be reduced relatively quickly

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Another preferred method proposal is in particular in connection with specifically for this purpose designed ball mills and suggests the volume of the grinding chamber during the grinding process to be controlled in such a way that the desired regulation of the degree of filling of the balls is achieved. Such a one Solution allows a particularly quick reaction to the given circumstances by means of a corresponding one rapid change of the grinding chamber volume and thus the degree of filling.

In the following, the invention will be described in greater detail using an exemplary embodiment shown in the drawing explained, the advantages of the device according to the invention will also be discussed in more detail. Show it:

Figure 1 shows a ball mill according to the invention with devices for adding and removing balls during the grinding process in section;

Figure 2 shows an embodiment of the invention Ball mill with a grinding chamber that is variable with the help of a bellows in section;

FIG. 3 shows a ball mill according to the invention with two displaceable relative to one another for the purpose of varying the grinding chamber volume Housing parts in section.

The essential parts of a ball mill can be seen in FIG 10, wherein, for the sake of clarity, the parts that are not essential to the invention, such as the Machine stand, the drive motor and the operating parts are omitted in the cross section shown.

The part shown consists essentially of the Grinding container 12, which is designed as a circular cylinder in the ball mill shown here, which with. a base plate 14 is completed on one side. On the side opposite the base plate of the grinding container 12 is the grinding container closure j on the motor side, which in its entirety with the Reference numeral 16 is provided. Kr essentially consists from a grinding chamber cover 18, which is connected via a connecting flange 20 to a corresponding flange 22 with in Screws not shown in the drawing are screwed on »There is a seal between the two flanges In the center of the Mahlraumdeclcels 18 is a break through 26, which is not described in detail here, since it is completely identical to that of the known ball mills can correspond to the bushings used.

With the drive shaft penetrating the shaft bushing 26 28, the agitator shaft 30 is connected, which carries the agitator disks and is driven by the not shown Motor in the grinding container 12 can rotate.

The grinding container 12 and the agitator shaft 30 with the agitator disks 32, which are also generalized as entrainment bodies can denote, delimit the grinding chamber 34, which during operation the grinding balls 36 of preferably about 1-3 mm Diameter and the grist 38 contains.

The grinding container 12 is surrounded by a cooling jacket 40 with two connecting pieces for coolant 44 and 46.

A product feed 48 is provided for feeding in the ground material, after the grinding process, the grist flows

continuously through the separating gap 50, the annular channel and the product drain 54. The separation gap is through a cutting disk 5 3 rotating with the agitator shaft 30 and a stationary cutting disk 55 are formed and are so narrow that the balls conveyed on with the product cannot pass it and thus remain in the grinding chamber 34.

In this respect, the ball mill shown here corresponds to one of a number of known ball mill types and other types could be used with the invention. The peculiarity of the ball mill shown consists in the fact that devices for continuous and controlled change in the degree of filling of the balls are present in the grinding chamber, and in the embodiment shown in FIG. 1, a lock device 60 is provided for adding and a drain valve 62 for removing grinding balls.

The lock device 60 comprises a storage container 64, which is connected to the grinding chamber 34 via a line 68. In the case shown, the product feed 48 is on the line 68 is connected. On the facing away from the grinding chamber 34 On the side of the line 68 there is a valve, which in the illustrated embodiment is a rubber bellows valve 70 is formed, which can be actuated via a line with compressed air. In the storage container a nozzle device 74 opens with a valve 76, which can be a conventional flap valve, and an injector nozzle 78, which is arranged in the center of the storage container 64 and oriented towards the line 68. The reservoir 64 can be tightly closed with a cover 80.

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The entire lock device is stable under pressure designed that the pressures occurring in ball mills in operation of, for example, 0.5 bar to 2 bar can easily absorb.

The drain valve 62 is connected to the grinding chamber 34 via a line 82 and also has a compressed air line 84 for actuating the rubber bellows, not shown in the figure, located in the valve 62 on"

The ball filling level of the ball mill shown in FIG. 1 is now in operation, i. H. while the agitator shaft 30 rotates, controlled by the fact that, as required, 60 grinding balls are supplied via the lock device or the grinding balls can be drained via the drain valve 62. For this purpose, the storage container 64 is provided with grinding balls filled and hermetically sealed with the cover 80. If the degree of filling is to be increased, these are preferred at the same time the valve 76 of the nozzle device 74 and the rubber bellows valve 70 are opened. As shown in the preferred embodiment of the storage container 04 is arranged vertically above the grinding chamber 34, the balls fall down into the

Mahlraum »To accelerate this process, the nozzle device 74 a liquid or a gas in the flow direction of the grinding balls 36 through the injector nozzle 78 injected. This enables a sufficiently fast and easily metered addition of grinding balls and thus with With a constant volume of the grinding chamber 34, an increase in the degree of filling of the balls is achieved.

The rubber bellows valve 70 is particularly well suited for this purpose, since it is also here hardly avoidable contamination with the grinding balls 36 still closes reliably. The product feed 48 can also be provided separately from the line 68. The actuation of the valves 76 and 70 and thus the supply of grinding balls can in the device according to the invention can be done both manually and automatically. In the case of the automatic embodiment, there are corresponding Actuators and electronic circuitry are provided by which the valves are operated when an increase the ball filling level is necessary. Such devices are known and are not described in detail here.

If the ball filling level is to be reduced at a certain moment, the drain valve 62 is simply opened, so that, driven by the pressure prevailing in the ball mill and due to the effect of gravity, a low pressure Amount of the ground material 38 together with the grinding balls 36 located therein leaves the grinding chamber 34. Because such a draining of balls is rarely necessary in practical operation, the drain valve 6 2 can also be omitted. In each In this case, it only has to be actuated rarely, so that the loss of grist that is associated therewith can be tolerated.

Figure 2 shows another embodiment of the invention Ball mill, the corresponding parts with the same reference characters, but provided with a line are designated. The main difference compared to the embodiment shown above is that here a variation of the ball filling degree not by adding or

Removal of grinding balls 36 ', but by variation
of the volume of the grinding chamber 34 * is reached. For this purpose, on the inner surface of the base plate 14 '
a bellows 86 is provided, which can consist of a suitable rubber-elastic material or of metal. Its interior is sealed off from the grinding chamber 34 'and connected via the connection piece 88 to an external source, not shown in the drawing, for a pressure medium, preferably hydraulic oils, so that the bellows is in its
Volume can be reduced or increased. In the preferred embodiment shown, a cover plate 90 is located on the grinding chamber-side surface of the bellows, which is sealed against the inner wall 93 'of the cylindrical part of the grinding container 12 with the aid of an annular seal 92, for example an O-ring seal. This prevents the ground material 38 'and grinding balls 36' from penetrating into the gaps present between the bellows 86 and the inner wall 93 'and then no longer being conveyed in the desired uniform manner in the direction of the product outlet 54' Other embodiments of the invention are also conceivable in which a bellows is used in the grinding chamber, which is located more in the product flow, so that a seal of the type shown here is not necessary in such cases.

Finally, FIG. 3 shows a further embodiment of the invention in which, as in the embodiment according to Figure 2 shows the change in the degree of ball filling by a corresponding Change in the grinding chamber volume is achieved. Here the corresponding components are with the same reference

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characters in Figures 1 and 2, but with two Marked with lines.

The grinding container 12 'comprises, in the illustrated embodiment, two housing portions 94 and 96 sealed to each other by means of a ring seal ^98! And are guided by the guide rings 100 concentric with each other. The side facing away from the shaft passage 26 housing part 96 is relatively by means of hydraulic cylinders 102 the housing part 94. The hydraulic rods 104, cross members 106 and 108 and corresponding joint flanges 110 and 112 serve as mechanical connecting parts the respective operating conditions.

In order to enable automatic regulation of the degree of filling, a A series of preliminary tests was carried out to determine the degree of ball filling at which the optimum grinding effect was achieved will. In the case of the digestion of biomass from fermentative processes for the production of enzymes can Use ultrasound digestion as a benchmark, which is carried out in parallel on the same sample. the parallel determination of the enzymatic activity on the sample digested with ultrasound on the one hand and on the with The sample digested by the ball mill, on the other hand, then enables the degree of digestion to be determined very precisely with the aid the ball mill. In these tests, the power consumption of the ball mill motor is measured at the same time, i. H. at

constant voltage its power consumption. If now With the help of these preliminary tests, the optimal operating conditions and in particular the optimal ball filler wheel are specified, the current consumption of the motor under these operating conditions can be used as a benchmark use for the ball filling level. A completely automatic control can then be achieved very easily if one is familiar with the control technology Set the motor current as the ACTUAL value for the degree of ball filling used and then with the help of a suitable electronic control and the device according to the invention Ball filling level changed in each case so that the desired Ball filling degree corresponding amperage is achieved. Normally, such a control will be desirable in the start-up phase with a relatively low Kugelfüllgrad is worked, which is then continuously increased up to the value corresponding to the opt imalcn digestion, which is then above the at by far the largest part of a grinding process is kept constant.

Claims (12)

Expectations .. Process for operating a ball mill, in particular for the digestion of biomass, in which the Grist fed to a grinding chamber containing grinding balls and in the grinding chamber by the rotary movement of at least one rotating driver body and the resulting movement of the grinding balls is ground, characterized in that the degree of filling of the balls is regulated in the grinding chamber during the grinding process to adapt to the respective operating conditions « 2. The method according to claim 1> characterized in that the degree of filling of the ball is kept essentially constant at least during the greater part of the grinding process 3. The method according to any one of claims 1 or 2, characterized characterized in that the power consumption of the ball mill as a measure for regulating the degree of ball filling is used » Method according to one of Claims 1-3, characterized in that the degree of filling of the balls by adding or Removal of grinding balls is controlled during the grinding process. 5. The method according to any one of claims 1 - 3, characterized in that the ball filling level by changing of the grinding chamber volume during the grinding process is controlled. 6. Ball mill, in particular for performing the method according to claim I ^ with a grinding chamber (34) surrounding grinding container (12) in which at least one entrainment body rotatable relative to the grinding container (12) per (30, 32), characterized in that devices (60, 62; 86, 90; 94, 96) are present by which the degree of ball filling in the grinding chamber (34) is controlled during operation of the ball mill (10) and is continuously changeable. 7. Ball mill according to claim 6, characterized by at least one lock device (60) for adding and / or removing grinding balls (36) during operation. 8. Ball mill according to claim 7, characterized in that the lock device (60) for adding grinding balls (36) includes a pressure-tight storage container (64) for grinding balls (36), which via a line (68) is connected to the grinding chamber (34), wherein in the line (68) between the pressure-tight storage container (64) and the grinding chamber (34) a valve (70) is provided and in front of the valve (70), directed towards this, a Nozzle device (74, 78) is arranged through which a Can be carried in the grinding chamber fluid escape in the direction of the desired Kugelfliisses under pressure _s the grinding balls (36). 9. Ball mill according to claim 8, characterized in that that the valve (70) is a rubber bellows valve. 10. Ball mill according to claim 6, characterized in that the volume of the grinding chamber (34) can be changed. 11. Ball mill according to claim 9, characterized in that that in the grinding chamber (34) a bellows (86) is arranged, the interior of which is sealed off from the grinding chamber (84) and is connected to an external source of pressure medium so that the bellows volume during the operation of the ball mill (10) hydraulically or pneumatically is changeable. 12. Ball mill according to claim 10, characterized in that the grinding container (12) includes at least two mutually displaceable and sealed housing parts (94, 96), which can be adjusted relative to one another in such a way that the volume of the grinding chamber (34) can thereby be changed in a controlled manner is.