Roller press to determine the filling level

Abstract

The invention relates to a roller press for crushing, compacting and briquetting material, in particular a material containing ore, comprising a press frame (1), two rollers (2) arranged side by side within the press frame (1) and forming a roller nip (3), and a feed shaft (4) arranged above the roller nip (3) through which material can be supplied to the roller nip (3), wherein the feed shaft (4) has one or more shaft walls (4a) which are vertical or curved so as to form a cross-section which is at least in parts of its height It is fixed or extends from top to bottom, and in which the feed shaft (4) has a measuring device (5) for determining the filling level in the feed shaft (4). A characteristic feature of this roller press is that the measuring device (5) is configured as a gravimetric measuring device.

Description

WO 2019 / 011626 A1ROLLER PRESS AND ME T HOD FOR DETERMINING THE FILLING LEVEL DESCRIPTIONThe invention relates to a roller press for the comminut i on, compacting or briquetting of material,with a press frame, two rollers arranged next to o n e another in the press frame forming a roller nip and a feed shaft which is arranged above the roller nip and via which the material can be supplied to the roller ni p ,wherein the feed shaft has one or more shaft walls which are orientated vertically or at an inclination to the vertical so as to form a cros s -section which over the height is at least in sections constant or widens from the top to the bottom,wherein the feed shaft is provided with a mea s uring device for determining the filling level in the feed shaft.In particular, such a roller press involves a material bed roller mill which is preferably u s e d for the comminution of material. However, the invention also encompasses roller presses or material bed roller mills for compacting or briquetting materials. The two pr e ss rollers are borne in a rotatingly driven manner in the press frame, wherein the rollers are driven in a counterrotating manner. As a rule, one of the two rolle r s is configured a s a fixed roller and the other roller as a loose roller (laterally displaceable), wherein a hydraulic system, supported on the press fram e , acts on this movable loose roller. Alternatively, however, two loose rollers or other frame designs can be realised. This principle according to the invention is not dependent on this. The material is supplied to the roller nip via the feed shaft solely w ith the aid of gravity.For efficient operation, roller presses (preferably material bed roller mills) are generally operated with a material template. This means that for continuous and thus faul t -free and cost-effective operation in t h e desired operati n g point of the roller press, there must always be a sufficient filling level of the material present to that there is always sufficient material available for drawing into the roller nip, because, as a rule, the effective roller nip between the rollers depends on the filling level of the material in the feed shaft, so that the filling level can have an effect on the throughput of the roller press, wherein this effect decreases with increasing filling level. In practice it is therefore often endeavoured to g uarantee a constant filling level in the feed shaft. For this reason, the determination of the filling level with the aid of a measuring device is of practical importance, wherein preferably the conveying means (e.g. conveyor belts) for filling the feed s h aft by way of 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 shaft.In practice, for measuring the filling level in the feed shaft a plurality of different meas u ring methods is available. If easily flowing material (with a high degree of flowability) is being worked with, funne l -shaped feed shafts with a downwardly narrowing cros s -section are generally used in practice. In the case of such funne l -shaped feed shafts gravimetric measuring device s , whereby the shaft stands on weighing cells, are used practice, as through the shaft walls running obliquely from top to bottom a force dependent on the filling level is exerted into the feed shaft and thereby onto the weig h ing cells so that via the signals of the weighing cell, the mass and hence (if the density is known) the filling level of the feed shaft can be deduced.However, when using not easily fl o wable material with a low degree of flowability the use of feed shafts with adownwardly narrowing cros s -section cannot always be considered, so that in practice feed shafts are used which have a constant cros s -section ov e r their height, or preferably a cros s -section widening from top to botto m . In practice, in the case of such designs radiometric filling level measurement is used in which the attenuation of radioactive radiation in the form of absorption and scattering through the filling material is utilised. A prerequisite for this is the use radioactive sources of radiation, which, however, are of course only permitted to be used under certain conditions. Overall, using such radiometric measuring methods is laborious. T h is is where the invention comes into its own, as the invention relates, in particular, to the processing of materials with low flowability, i.e. material containing ore, more particularly finely ground ores. Preferably a (moist) iron ore concentrate is processed for subsequent pelleting.The aim of the invention is therefore to create a roller press of the type described in the introduction which (even) when processing materials with a low degree of flowability (particularly in the case of moist or sticky feed materials) allows simple filling level measurement while dispensing with radiometric methods or other radiatio n -based methods.To solve this task, in a roller press of the type in question described in the introduction, the invention teaches that the measuring device is designed a s a gravimetric measuring device for gravimetric filling level measurement. In the context of the invention gravimetric filling level measurement means filling level m e asurement on a mechanical basis, dispensing with radiome t ric or radiatio n -based measurement, in which the filling level is determined by way of measuring the mass or the resulting weight force of the material.The invention is initially based on the knowledge that for certain application purposes, in particular for the processing of material with low flowability, it is absolutely necessary to work with a feed shaft that does not narrow from top to botto m , but either has a constant cros s -section over its height or, preferably has a cros s -section that widens in the downward direction. The invention also comprises forms of embodiment which widen from top to bottom in a step-like manner. Surprising the invention has now found that gravimetric filling le v el measurement can also be used with such a geometry of the feed s haft in which adhesion of the feed material on the shaft wa l ls is avoided and thereby a constant material flow should be able to be achieved.The flow behaviour of bulk materials in a shaft results in stresses in the bulk material and, taking into account the wall friction and properties of t h e bulk materials, in wall stresses. Due to the bulk material horizontal stresses act in a shaft cross - section and through supporting on the inner walls of the shaft these result in weight forces on the bearing points of the feed shaft. The material thus produces a surprisingly high force transmission onto the s haft wall in the form of a relevant mass or relevant vertical force component which can be measured. Depending on the material properties and geometry this is of a magnitude of 35 % to45 % of the applied mass. The embodiment according to the invention is particularly suitable in the case of processing materials with a low flowability, especially as such material allows particularly effective force transmission onto the shaft walls. Interesting here is the fact that in this way filling level measurement is poss i ble both statically (e.g. after filling the feed shaft) and also dynamically (e.g. for continuously sliding material during pressing operatio n ).Preferably, as part of the invention a feed shaft which widens from top to bottom is used. This comprises one or more shaft walls which (at least in sections) are orientatedat a (negative) angle of, for example, 0.1° to 10°, preferably for example 0.5° to 5° to the vertical. In practice relatively small angles of inclination are used, which however even with poorly flowing bulk materials already ensure improved feeding of materials to the roller press and in the case of which, surprisingly, gravimetric filling level measurement can nevertheless be implemented.The measuring device comprises one or more measuring cel l s which support the feed shaft. By means of the weighing cells weight force produced through the total mass of the feed shaft is measured, wherein in the manner according to the invention this is dependent on the filling level of the material in the feed shaft. In a preferred embodiment the feed shaft stands on one or more weighing cells wherein, for example, the feed shaft is arrang e d on the press frame with the weighing cells arranged in between. The feed shaft can have a lower frame or be connected to a lower frame, wherein this lower frame is arranged on the press frame with the interspersion of the weighing cells. As the feed shaft has to be arranged in the vertical di r ection on the press frame with the weighing cells in between, it is expedient to connect the feed shaft to the press frame with the interspersion of a (fram e -like) compensator that is elastic in the vertical direction. Such a compensator can, for example have an upper flange for conne c tion to the feed shaft or its lower frame and a lower fl a nge for connection to the press frame, wherein between the u pper flange and the lower flange an elastic and / or displaceable frame is provided which can be made of, for example of elastomer material, for example of rubber or vertically arranged shaft elements that can be displaced vertically against each other and / or with each other. The weighing cells can th e n, for example, be arranged between the upper flange and the lower flange of the compensator.In the case of the weighing cell, commercially available weighing cells can be used which, for example, are designed as electromechanical weighing cells. Here, through the elastic deformation of a deformat i on element the electrical resistance of one or m o re integrated strain gauges changes. Via, for example, a bridge circuit the change in resistance can be shown in a voltage signal proportional to the weight. Fundamentally, however, differently designed weighing cells can also be used.Preferably the already described standing measurement of the feed shaft takes place. However, suspension of the container with integrated weighing cells can also imp l emented as part of the invention.The feed shaft is generally made of metal, e.g. steel, and tests have shown that for different materials, e.g. materia l s containing ore, e.g. fine ore, sufficient force transmission to the container wall for reliable gravimetric measurement takes place. Optionally, however, as part of the invention the inside of the shaft walls (in sections or preferably entirely) can be provided with a coating (for protection against wear, for example), e.g. a plastic coating. In this way the shaft walls can on the inside b e covered with, for example, plastic panels, e.g. of polyethylene of sim i lar material. The invention can also be realised with such coatings.The subject matter of the invention is not just the described roller press but also a method of determining the filling level of material in a shaft, and in particular during the course of loading a roller press o f the initially described type. The method according to the invention is consequently also protected independently of t h e specific area of use of the roller presses. This method is characterised in that the shaft, e.g. feed shaft, comprises one or more shaft wal l s which are orientated vertically or inclined to the vertical,forming a cross-section constant over the height or a cros s - section wideningfromtoptobotto m .Themethodis characterised in that the filling level is determined by weighing cells on which the shaft acts, in that the weighing cells measure a weight force or m a ss from which the filling level is calculated. This method is preferred during the course of loading a roller press of the described type so that that shaft is formed as a feed shaft of a roller press.Particularly preferably the method according to the invention relates to the processing of materials with low flowability. In the context of the invention low flowability means materials with a flowa b ility f f c of less than 10, preferably less than 4. The flowability f f c is the ratio of the consolidation stress and compression strength. The consolidation stress is the stress required to consolidate a bulk material sample in a hollow cylinder. I f the lo a d in the vertical direction and the hollow cylinder is removed and a compression stress acts on the cylindrical bulk material sample, on reaching the compression strength the sample breaks or flows. Materials with lower flowability have a high degree of internal friction so that they also transmit friction to vertically or negatively se t -up shaft walls. This effect is utilised in a preferred embodiment as part of the invention.Of particular importance is also the fact that the method according to the inv e ntion allows not only static filling level measurement, but also dynamic filling level measurement and consequently filling level measurement in continuous operation of the roller mill.The fact must be taken into account that the transmission of the weight force of the material in the feed shaft to the shaft wall depends on various factors, wherein the weight force, which also results from the walls stress, is n o t linearly dependent on the filling level. On this basis it isenvisaged by the invention that the filling level is determined using one or more conv e rsion functions which are provided for the relevant shaft geometry and / or the relevant material. Influences come from the material properties, including the flowability f f c and material moisture content, the wall inclination / the shaft angle as well as the coefficient of friction between the material and the shaft wall. Overall, in the evaluation (e.g. with a computer) corresponding and possibly also no n -linear conversion of the measuring signal of the weighing cells at a particular filling level then takes place, namely with the inclusion of the aforementioned material and design parameters.Primarily the invention relates to 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 utilizing the described filling level measurement. This makes it possible to use the determined filling level or the signal measured with the weighing cells in order to control or regulate the filling assemblies and / or the roller press. Thus, as a rule, the feed shaft is filled by one of more filling assemblies (e.g. conveyor belts) and according to the invention such filling assemblies can be controlled or regulated t aking into account the determined signals or filling levels. The same applies to the operation of the roller press, e.g. the control or regulation of the speed of the rollers or the roller nip or other press parameters. Below the invention is shown in more detail by way of drawing showing just one example of embodiment. HereFig. 1 schematically shows a side view of a roller press in a very simplified mannerFig. 2 shows a perspective view of a roller press.In the figure a roller press in t h e form of e m bodiment of a material bed roller mill is shown. In the example ofembodiment this is used for the comminution of material, e.g. material containing ore. Particularly preferably this involves fine ore (e.g. iron ore concentrate) which due to its moisture content can have a relatively low flowability.The roller press comprises a press frame 1 , and in the press frame 1 two rollers 2 arranged next to each other between which a roller nip 3 is formed. The two rollers 2 are driven in a counter-rotating manner by actuators which are not shown. Arranged above the roller nip 2 is a feed shaft 4 via which the material is fed to the roller nip 3. In the example of embodiment, the feed shaft comprises at least two opposing shaft walls 4a which are each vertical or inclined at an angle α to the vertical so that the feed shaft 4 has a cros s - section widening from the top to the bottom. The ( n egative) angle α can be around 0.1° to 10°, preferably only 0.5° to5°, e.g. 0.5° to 2°.The roller press is equipped with a measuring device 5 with which the filling level of the ma t erial in the feed shaft 4 can be determined and monitored. A ccording to the invention this measuring device 5 is configured so that gravimetric filling level measurement can take place. In the example of embodiment, the gravimetric measuring device comprises several weighing cells 5 on which the feed shaft acts. In the shown example of embodiment this is realised in that the feed shaft 4 stands on the weighing cells 6. For this, the feed shaft in the example of embodiment has a lower frame 7, wherein this lower frame 7, with the inte r spersion of the weighing cells 6 is arranged on the press frame 1. Otherwise, the feed shaft 4 can be connected to the press frame 1 with the intermediate placement of a compensator which is elastic or displaceable in the vertical direction.By way of the weighi n g cells 6, in the context of the invention the filling level of the material in the feed shat4 can not only determined and monitored statically (e.g.after filling or emptying), but also dynamically and consequently continuously during filling and also (simultaneous) emptying during the operation of the roller press. Hitherto such gravimetric filling level measurement was only used in the case of funne l -like, downwardly tapering feed shafts, in which, particular l y because of the geometry the weight force o f the material is transmitted into the side walls. In accordance with the invention it has, surprisingly, now also been established that even with the geometry of the feed shaft shown in the figures with a cross- section widening from top to bottom, sufficient force introduction is possible as in this case too as the feed material is supported on the cont a iner wall too which leads to a weight force measurable with the weighing cell. Even continuously flowable power bulk m aterial is supported to a considerable degree on the container wall, in order to derive a dependence of the measured weight fo r ce on the filling level. In this way, even in the processing of fine and moist and sticky filling material which for perfect operation presupposes a falling shaft, open i ng out towards the bottom it is simple to determine t he filling levels gravimetrically so that the radiatio n -based measuring methods known from the prior art can be dispensed with.