EP Description
[0001] The invention relates to a roller press for the comminution, compacting or briguetting of material with a press stand, two rollers arranged in the press stand that form a roller gap, and a feed chute arranged above the roller gap, via which the material can be supplied to the roller gap, wherein the feed chute comprises one or more chute walls that are orientated in an inclined manner to the vertical, forming a cross-section which over its height is constant, at least in sections, or widens from the top downwards, wherein the feed chute is provided with a measuring device for determining the filling level of the material in the feed chute.
[0002] Such a roller press 1s particularly preferably a material bed roller mill, which preferably serves to comminute materials. However, the invention also includes roller presses or material bed roller mills for compacting or briquetting material. In the press stand, the two press rollers are borne in a borne in a driven rotating manner, wherein the two press rollers are driven in opposite directions. As a rule, one of the two rollers is borne as a fixed roller and the other as a loose roller (laterally displaceable), wherein a hydraulic system supported on the press stand acts on this moveable loose roller. Alternatively, however, two loose rollers or other frame concepts can be implemented . The principle according to the invention does not depend on this. The material is only supplied to the roller gap via the feed chute with the aid of gravity.
[0003] For efficient operation, roller presses (preferably material bed roller mills) are generally operated with a head of material. This means that for continuous and thereby fault-free and cost-effective operation at the desired operating point of the rollers, there must always be an adequate filling level of material in the feed chute, so that there always sufficient material for supplying to the roller gap available. This is because the effective roller gap between the rollers depends on the filling level of the material in the feed chute so that the filling level can influence the throughput of the roller press, whereby this influence decreases with increasing filling level height. In practice it is therefore often endeavoured to ensure a constant filling level in the feed chute. For this reason, determination of the filling level with a measuring device is of practical importance, wherein preferably the conveying means (e.g. conveyor belts) for filling the feed chute via a suitable control or regulator (e.g. speed control/regulation of the conveyor belts) can be connected to a filling level signal in the feed chute.
[0004] In practice, there are a number of different measuring techniques available for measuring the filling level in the feed chute. If easily flowing materials (with a high flowability) are being worked with, funnel-shaped feed chutes with a downwardly narrowing cross-section are generally used in practice. In such funnel-shaped feed chutes, gravimetric measuring devices are used in practice in which the chute stands on load cells, as through the inclined chute walls that converge downwards, a force dependent on the filling level is transmitted into the feed chute and thus to the load cells, so that via the signal of the load cells, the mass of the material and from this (if the density is known) the filling level of the feed chute can be determined.
[0005] However, when processing material with a low flowability that does not flow easily the use of feed chutes with a cross-section narrowing towards the bottom cannot always be considered, so that in practice feed chutes are used which have constant cross-section over their height, or, preferably, a cross-section that widens towards the bottom. In the case of such designs, in practice, for example, radiometric filling level measurement is used, in which the attenuation of radioactive radiation in the form or absorption and scattering through the filling material is utilised. A precondition for this is the use of radioactive radiation sources, which of course may only be used under certain conditions. Overall, using such radiometric measuring methods is costly. This is where the invention comes in, as the invention relates in particular to the processing of material with a low flowability, e.g. material containing ore, more particularly finely ground ore, known as fine ores. Preferably a (damp) iron ore concentrate is processed for subsequent pelleting.
[0006] From (WO 2013/115747 Al) a device is known with several roller presses according to the introductory section of claim 1, which are supplied by a feed chute, wherein the feed chute can widen from the top towards the bottom. The filling level within the feed chute can be monitored, for example, with a capacitively operating filling level sensor which is arranged inside the fall chute. Alternatively, the possibility is also mentioned of using a weight sensor, which is also arranged inside the fall chute and on which the material acts.
[0007] The invention is therefore based on the task of creating a roller press of the type described in the introduction, which (even) in the processing of materials with low flowability (in particular in the case of damp and sticky input materials), makes simple filling level measurement possible without radiometric or other radiation-
based methods. To solve this task, the invention discloses a roller press with the features of claim 1 and a method with the features of claim 7. It is envisaged that the measuring device is designed as a gravimetric measuring device for gravimetric filling level measurement. In the context of the invention, gravimetric filling level measurement means filling level measurement on a mechanical basis, dispensing with radiometric or radiation-based measurements, in which the filling level is determined by way of measurement of the mass or the resulting weight force of the material.
[0008] The invention is initially based on the knowledge that for certain applications, more particularly for the processing of materials with a low flowability, it is indispensable to work with a feed chute that does not narrow towards the bottom, but has a downwardly-widening cross- section. The invention also includes forms of embodiment in which the feed chute only has a constant cross-section in sections, so that, in particular, feed chutes are also included that widen downwards in a stair or step-like manner. Surprisingly, the invention has now found that that even in the case of such a geometry of the feed chute in which adhesion of the feed material on the chute walls is to be avoided and thus a constant material flow is to be achieved, gravimetric filling level measurement can be worked with.
[0009] The flow behaviour of bulk materials in a chute leads to strains in the bulk material and, taking into account wall friction and the bulk material properties, to wall stresses. In a chute cross-section, due to the bulk material, horizontal stresses are exerted and through supporting on the inner walls of the chute these result in weight forces on the bearing points of the feed chute. Consequently, the material produces a surprising high force transmission onto the chute wall in the form of a relevant mass or a relevant vertical force component which can be measured. Depending on
- 5 = the material properties and the geometry, this corresponds to magnitude of 35 % to 45 % of the feed-in mass. The embodiment according to the invention is particularly suitable for the processing of material with a low flowability, particularly if such material allows particularly effective force transmission onto the chute walls. Interesting here is the fact that in this way filling level measurement is possibly both statically (e.g. after filling of the feed chute) and also dynamically (e.g. for continuously sliding material during operation of the press).
[0010] Preferably, in the context of the invention a feed chute widening from the top downwards is used. This has one or more chute walls which (at least in sections) are orientated at a (negative) angle of, for example 0.1° to 10°, preferably, for example, 0.5° to 5° to the vertical. Thus, in practice, relative small angles of inclination are worked with, which, however, even with poorly flowing bulk goods already ensure improved material supply to the roller press and in the case of which, surprisingly, gravimetric filling level measurement can nonetheless be implemented in the manner described above.
[0011] The measuring device comprises one or preferably more load cells which support the feed chute. Consequently the weight force produced by the total mass of the feed chute is weighed, wherein in the manner according to the invention this is dependent on the filling level of the material in the feed chute. In a preferred embodiment the feed chute stands on one or more load cells, in that, for example, the feed shaft is arranged on the press stand with the interposition of the load cells. For this the feed chute can have a lower frame or be connected to a lower frame, wherein this lower frame is arranged on the press stand with the interposition of the load cells. As the feed chute has to be arranged moveably in the vertical direction on the press stand with the interposition of the load cells, it is expedient to connect the free chute to the press stand with the interposition of an elastic (frame-like) compensator that is moveable in the vertical direction. Such a compensator can, for example, have an upper flange for connection to the feed chute or its lower frame, and a lower flange for connection to the press stand, wherein provided between the upper flange and the lower flange there is an elastic and/or displaceable frame, that can be made, for example, of an elastomer material, e.g. rubber, or chute elements that are arranged vertically displaceable contrary to each other and/or with each other. The load cells can the, for example, be arranged between the upper flange and the lower flange of the compensator.
[0012] For the load cells, commercial available load cells can be use, which can, for example, be designed as electromechanical load cells. Through elastic deformation of a deformation body, the electrical resistance of one of more strain gauge(s) integrated therein changes. Via, for example, a bridge circuit, the change in resistance can be shown in the form of a voltage signal that is proportional to the weight. In principle, however, otherwise designed load cells can be used.
[0013] Preferably the already described standing weighing of the feed chute takes place. Alternatively, however, within the scope of the invention it is also possible to suspend the container with integrated load cells.
[0014] The feed chute is generally made of metal, e.g. of steel, and tests have shown that for various materials, e.g. material] containing ore, e.g. fine ore, adeguate force transmission to the container well for reliable gravimetric filling level measurement takes place. Optionally, however, it is within the scope of the invention to provide the container walls (in parts or preferably fully) with a coating
- J] -
(e.g. for the purpose of protection against wear). On the inside, the chute walls can thus be coated with, for example, plastic panels, made, for example, of polyethylene or suchlike. The invention can also be implemented with such coatings.
[0015] The subject matter of the invention is not only the described roller press, but also a method of determining the filling level of material in a chute, more particularly during the course of supplying a roller press of the type described in the introduction. The method according to the invention is thus also placed under protection independently of the specific area of application of roller presses. This method is characterised in that the chute, e.g. feed chute, comprises one or more chute walls that are vertical or inclined to the vertical forming a cross section that is constant in height or widens from the top downwards. The method is characterised in that the filling level is determined gravimetrically by the load cells on which the chute acts, in that with the load cells a weight force or mass introduced into the container walls is measured and from this the filling level is determined. Preferably, this method is used during the course of supplying a roller press of the described type, so that chute is designed as a feed chute of a roller press.
[0016] Particularly preferably the method according to the invention relates to the processing of materials with low flowability. In accordance with the invention, low flowability means materials with a flowability ff. of less than 10, preferably less than 4. Flowability ff. is the ratio of consolidation stress and compressive strength. Consolidation stress is the stress required to consolidate a bulk material sample in a hollow cylinder. If the load in the vertical direction and hollow cylinder are removed and the cylindrical bulk material sample subjected to compressive stress, on reaching the compressive strength the sample fractures or flows. Materials with a low flowability have high internal friction so that they also transmit friction onto vertical or negatively orientated chute walls. This effect is utilised in a preferred embodiment of the invention.
[0017] Of particular importance is also the fact that the method according to the invention not only makes static filling level measurement, but also dynamic filling level measurement, and thereby filling level measurement in continuous operation of the roller press possible.
[0018] The fact should be taken into account that the transmission of the weight force of the material in the feed chute onto the chute wall depends on various factors, wherein the weight force, which also results from the wall stress, does not depend linearly on the filling level. On the basis of this, in accordance with the invention it is envisaged that the filling level is determined using one or more conversion functions provided for the respective chute geometry and/or the respective material. Influencing this are the material properties, including the flowability ff. and the material moisture content, the wall inclination/chute angle as well as the coefficient of friction between the material and the chute wall. Overall, during the evaluation (e.g. with a computer), corresponding and possibly also non-linear conversion of the measuring signal of the weight cell measuring signals into a corresponding filling level takes place, also with the inclusion of the aforementioned material and design parameters.
[0019] The invention primarily concerns the filling level measurement taking into account the described aspects. However, the subject matter of the invention is also a method of operating a roller press utilising the described filling level measurement. In doing so, it is possible to use the determined filling level, or the signals measured by the load cells, to control or regulate the filling units and/or the roller press. Thus, as a rule, filling of the feed chute takes place with one or more filling units (e.g. conveyor belts), and in accordance with the invention such filling units can be controlled or regulated taking into consideration the determined signals or filling levels. The same applies for the operation of the roller press, e.g. the control or regulation of the roller speed or the roller gap or other press parameters. The invention will be described below with the aid of a drawing showing only one example of embodiment. In these:
Fig. 1 schematically shows a greatly simplified side view of a roller press,
Fig. 2 shows a perspective view of a roller press.
[0020] Shown in the figures is a roller press in the form of embodiment of a material bed roller mill. In the example of embodiment, this is for the comminution of material e.g. material containing ore. Particularly preferably this is fine ore (e.g. an iron ore concentrate) which on the basis of its moisture content can have a relatively low flowability.
[0021] The roller press comprises a press stand 1 and two rollers 2 arranged next to each other on the press stand 1, between which a roller gap 3 is formed. The two rollers 2 are driven in a counter-rotating manner by drives which are not shown. Arranged above the roller gap 3 is a feed chute 4, via which the material is supplied to the roller gap 3. In the example of embodiment, the feed chute comprises two opposite chute walls 4a, which are each vertically inclined at an angle of o to the vertical so that the feed chute 4 has a cross-section that widens from the top downwards. The
(negative) angle o can be between around 0.1° to 10°, preferably 0.5° to 5°, for example 0.5° to 2°.
[0022] The roller press is equipped with a measuring device 5, with which the filling level of the material in the feed chute 4 can be determined and monitored. According to the invention this measuring device 5 is designed as a gravimetric measuring device so that gravimetric filling level measurement takes place. In the example of embodiment, this gravimetric measuring device 5 comprises several load cells 6 on which the feed chute 4 acts. In the shown example of embodiment this is implemented in that the feed chute 4 stands on the load cells 6. For this, in the example of embodiment, the feed chute has a lower frame 7, wherein this lower frame 7 is arranged on the press stand 1 with the interposition of the load cells 6. Otherwise, the feed chute 4 can be connected to the press stand 1 with the interposition of elastic or displaceable compensators. Details of the compensators are not shown.
[0023] With the help of the load cells 6, in the context of the invention the filling level of the material in the feed chute 4 can not only be statically (e.g. after filling or emptying), but also dynamically determined and monitored, and therefore continuously during filling and also (simultaneous) emptying during operation of the roller press. Hitherto, such gravimetric filling level measuring has been used in the case of funnel-shaped, downwardly converging feed chutes, in which due to the geometry the weight force of the material is transmitted into the chute wall. According to the invention, it has now surprisingly been found that sufficient force transmission is also possible in the case of the geometry of the feed chute shown in the figure with a cross-section that widens downwards, as in this case too the supplied material is decisively supported on the container wall which results in a weight force measurable with the load cells. Even continuously flowing bulk material is supported on the container wall to a considerable extent, in order to derive therefrom a dependency of the measure weight force on the filling level.
In this way, even when processing damp and sticky bulk materials, which for smooth operation require a downwardly widening fall chute, the filling levels can easily be determined in a gravimetric manner, so that the radiation- based measuring methods known from the prior art can be dispensed with.