US3082873A - Apparatus for classifying particulate material - Google Patents

Description

March 26, 1963 D. BARTELT 3,082,873

APPARATUS FOR CLASSIFYING PARTICULATE MATERIAL Filed Feb. 21, 1961 5 Shets-Sheet 1 By his af/omeys March 26, 1963 D. BARTELT 3,082,873

APPARATUS FOR CLASSIFYING PARTICULATE MATERIAL Filed Feb. 21, 1961 5 Sheets-Sheet 2 /n van/0r DEW/ch Bar/6W By his af/omeys March 26, 1963 D. BARTELT 3,032,873

APPARATUS FOR CLASSIFYING PARTICULATE MATERIAL Filed Feb. 21, 1961 5 Sheets-Sheet 5 5 Sheets-Sheet 4 March 26, 1963 D. BARTELT APPARATUS FOR CLASSIFYING PARTICULATE MATERIAL Filed Feb. 21, 1961 D. BARTELT I March 26, 1963 APPARATUS FOR CLASSIFYING PARTICULATE MATERIAL Filed Feb. 21, 1961 5 Sheets-Sheet 5 SW Q. Q QQ United States Patent 3,082,873 APPARATUS FOR CLASSHFYIN G PARTIQULATE MATERIAL Dietrich Bartelt, Essen, Germany, assignor to Marinesmann Aktiengesellschait, Dusseldorf, Germany Filed Feb. 21, 1061, Ser. No. 90,771 Claims priority, appiieation Germany Feb. 26, 1960 11 Claims. (Cl. 20941) This specification describes improvements in wet and dry jigs for classifying particulate material such as, for example, coal and ores. First the general nature of the improvements will be described and advantages pointed out and then'a few particular embodiments of them will be dealt with in more detail with reference to the at tached drawings.

In wet-jigging, for example in water, the material to be classified is made to form a bed on a submerged support. The water is pulsed by compressed air so that it moves in a vertical direction and dilates the bed. The bed is consequently divided into separate layers, mainly according to specific gravity with the lighter material on top and the denser below. The discrete lighter layer is removed from above through a draw-off device while the lower denser layer is drawn-cit from below. The rate of draw-off is regulated by sliding valves in some jigs while in others devices such as bucket wheels are used. The draw-off devices are controlled through a system responsive either to a float immersed in the bed or to the hydrostatic pressure below the bed. The use of a float, however, has the disadvantage that the density of the bed of water and particulate material is only sensed in a comparatively small volume overlying the float. Moreover, the response of the float is not only related to the density, but also to the inertia of the bed so that it not only senses the variations in density but also those in weight. The conditions are similar when a device sensitive to the hydrostatic pressure below the bed support is used to control the draw-off devices.

In a dry-jig, pulsed air for example is used for jigging the particles in a vertical direction so that, as in a wetjig, the denser material sinks to the bottom of the bed.

So far air-jigs have only been fitted with manuallycontrolled draw-off devices; determination of density by a float as in wet-jigging is not possible because there is no medium capable of supporting the float in an appropriate manner.

For this reason dry-jigs have only been used on a small scale in districts where water is scarce. Moreover, their efficiency or sharpness of separation is poor compared with wet-jigs. However, if these difficulties could be overcome there would be considerable advantages to be reaped not only in the form of savings in water costs but also in weight.

It has now been found that it is possible to carry out continuous measurement of the bed density in a jig by electromagnetic radiation. The radiation is arranged to extend from its source through a measurement zone stretching at right angles across the line of horizontal travel of the bed. The degree of absorption, depending on the density of the bed, of the radiation is determined by a radiation detector which produces an electrical signal corresponding to the radiation quanta received. This signal is used to direct a device controlling the draw-off device. Preferably the zone of measurement is triangular in plan and of small vertical thickness. It extends from a point source to a detector which is elongated in the direction of the horizontal flow of the bed. .The horizontal splaying-out of the zone means that the density variation is evaluated for a volume of the bed which is very much larger than that sensed by a float,

for in the latter case the geometrical form of the float is such that it can only sense the density of a comparatively small zone of bed vertically above it.

The radiation detector is arranged to control the drawoif device through the agency of a rapidly responding control device. In practice, electrohydraulic control devices have been found to have a shorter time lag than pneumatic ones. It is also desirable to use a draw-off device which responds quickly, for example a mushroom valve or a bucket wheel or other device whose mode of operation exploits the weight of the bed. A mushroom valve or a bucket wheel can be placed below the bed support; the bed material passes down from the rest of the bed under its own weight so that there is no pile-up or damming of dense matter on the bed support, and removal is therefore rapid.

The zone of the measurement of the bed is located in that part of the bed where stratificationis most nearly complete. By moving the source and detector vertically and horizontally in the bed it is possible, for the first time, to locate part of the bed whence measurement will be the most reliable during operation. The draw-off device should also be at this position. This method of loeating the draw-oil device at the position of most nearly completed stratification is a considerable improvement over the previous more approximate empirical methods. The ability to examine a given layer in the bed, whether it is in the middle or at the bottom, by means of radiation, for example from a radio-isotope source, enables the accuracy of the measurement and of the control to be increased considerably over those possible with known wet-jigging techniques.

In the case of through the screen jigging, the signals derived from the radiation detector can be used to control the amplitude of pulsation of the bed-dilating medium, for example water. The rate of passage of bed .through the screen increases with increasing pulsation amplitude because of the increased dilation of the bottom part of the bed, for example felspar'in the-case of coal jigging. It is also possible in theory to influence the rate of draw-oil of the denser particles by varying the pulsation frequency.

Y The improvements enable theefliciency of a through the sieve jig to be increased markedly; forthe main weak point of this type of jig, the sensitivity to changes in the rate and composition of the feed is practically removed owing to the increase in the size of the-zone of density measurement and the smaller time lag in eifecting variations in draw-off rate.

It has been found that there is an optimal length of measurement zone, i.e. in the direction from the source to the detector, since measurements become inaccurate owing to dispersal effects if the zone is too long, while if the zone is too short, the amount of bed examined is so' small that itdoes not give a good result for the average density of the bed. The optimum distance is found to be between 30 and cms. in a bed under water. Good results can be achieved with a source of low activity so. that an elaborate code of safety measures is not necessary to assure full protection of personnel. -Measurements at the operator position have shown that, even in unfavourable conditions, the random radiation is less than 0.1 rnr./h., considerably below permitted levels. When it is also considered that the jig can run without supervision,

it will be recognised that there can be no serious objection in responsible professional circles to isotopes in jigs.

One of the most significant practical advantages of jigs embodying the above improvements is that'the jig is capable of dealing with substantialchanges in the rate of feed and the composition of, feed. As the draw-oft the use of radiowill be smaller.

aosasvs V 3 rate is so rapidly adjusted in response to changes in density, it is usually possible to do without a mixing holder. Saving in both the price and size of jigs are also brought in many cases owing to the fact that the optimum length of the bed can be calculated exactly to requirements. Another contribution to a saving in the length of the bed isdue to the 'fact that with conventional jigs a certain length is added as a safety measure to the bed in order to compensatefor damming of the dense material.

It is found to be advantageous if the radiation source and the radiation detector are arranged so that they can be moved in a direction along the direction of horizontal movement of the bed and can also be moved vertically. For this purpose a transverse beam can be provided.

In certain circumstances it may be advantageous to provide a further detector above the detector already mentioned. In this case the electrical signals from both the radiation detectors are led to the rapid-acting control device for the draw-off device. A signal is then derived from the difference between the measurements given by the two radiation detectors and this signal is used to change the target value of the control device. For instance if the density of the bed in the zone of the radiation rises owing to the presence of more heavy material from below (refuse in the case of coal), say, the difierence between the values of the signals given by the detectors produced and consequently a change in the target value of the control device and therefore more of the denser material is drawn oil from below so that the imaginary plane on which the bed .is' to be divided is lowered.

It is also possible to provide sources of radiation on each side of the bed. The source or sources of radiation can be placed in or outside the bed.

Though it is usually convenient to use a point-like source of radiation, it may under certain circumstances be desirable to use one which extends in the direction of travel of the bed, for example, when it is desired to use irradiated cobalt.

The improvements will now be further explained with reference to the schematic drawings forming part of this specification. What the various figures of the drawings show is as 'follows:

FIGURE 1, a wet-jig in longitudinalv section;

FIGURE 2, a section on the 'line A-A of FIGURE 1;

FIGURES 3 to ,5, another wet-jig in longitudinal, in cross section (on the line A A of FIGURE 3), and in plan view; 7

FIGURES 6 and 7, an air-operated, jig, FIGURE 6 being a longitudinal section and FIGURE 7 a transverse section on the line A-A;

FIGURES 8 and 9, a longitudinal section and a plan .view respectively of another wet-jig; and

2. The water in the wet-jigs whose level lies above the bed 2 is pulsed by a compressed air valve 4. denotes a radiation detector in the form of acounter tube in a waterrtight casing. It is adjustably mounted on the crossbeam 6. 7 The source of radiation? is mounted outside the bed 2 on the side of the hutch 1." The electrical signals from the detectors 5 are fed to a control device 8 which isacaused to alter the aperture of an outlet opening or V the bed correspondingly. This control device acts as' 7 'means for influencing the treatment of the bed and also This causes a stronger current to be density of the bed is also measured in a zone at the other outlet aperture.

In the jig shown in FIGURES 6 and 7 the bed is dilated by pulsed air fed from a blower 11 through several ducts through regulating valves 12 under the bed support 3. The latter is driven by a vibrator 10. With this dry jig it is naturally essential to use material which will not agglomerate.

It is preferable to arrange the detector 5 in the middle of the bed while the sources 7 are placed outside and on each side of the'hutch. In this manner it is possible to create a measuring zone which extends right across the bed, thus making possible a more accurate determination of the density of the bed. It would ofcourse be possible to use the present arrangement of the sources 7 in wet-jigs as well. 7

In the coal separating jig shown in FIGURES 8 and 9, besides means for continuously measuring the density of the bed and adjusting a regulating device for a drawoff device, there is also a device for continuously measuring the ash content. This latter device is denoted by 14 and is placed by a drying sieve 13 on the outlet side of the jig. The signal from this ash content determining device is arranged to vary the target value of the device controlling the draw-oil device.

This jig can be regarded as being mainly concerned with the separation of the coal and refuse according to density; however it must be remembered that the ash content of the washed coal should be kept as constant as possible. If the division line between the layers in the bed, that is to say the line along which the bed is to be as means controlling the jigging. The control device can for .exampleibe a so-called rocking-coil controller.

In the jig shown in FIGURES 3 to 5, 'two detectors and S' are adjustably mounted on the cross beam 6 for controlling the second draw-elf device'9 aperture; The

divided as jigging is. completed, remains in the same position so that the, target setting of the control device also remains the sanre-the refuse content of the coal will vary according to the proportions of refuse fed in. This leads to substantial variations in the ash content of the coal. Furthermore there are also likely to be variations in ash content owing to changes in the mineral in the coal substance itself.

The use of the device for constantly measuring the ash content enables variations in ash content due to these two causes to be held in within certain limits. This setting of the target value of the control device offers a great advantage over previous plant in which the control device was merely set permanently for coal with the most uniavourable composition, so that the ash limit was never exceeded. With the novel jig the ash content can be kept practically constant over long periods of time, while the yield of coal is greater.

The zone of measurement of density is comparatively .deep in the bed, that is to say in a region in which the volumetric ratio solids; water remains practically constant despite changes in the rate of feed. If this were not so, variations in the amount of water would cause errors in the measurement of density. On the other hand, no method has yet been found of'determining ash content under water. Consequently the "ash determination is carried out downstream from the draw-oil from the jig in a position wheresthe coal is already more or less free of Water. The water is in fact removed by using the stationary or moving sieve 13.

For instance if the ash content of the drawn ofl coal rises, the signal from the ash content-determining device changes and'causes the output current from the control devices to be increased in such a manner that the level of the boundary between the coal and refuse layers is lowered somewhat; more of the refuse, which is denser than the coal, is drawmofi. from below. The adjustment of the boundary level is in the'opposite direction when the density of the bed in the measuring zone is increased.

Use is made of a rapid-responding ash content determining device which, by transmitting different signals 7 causes the levellof the division line between the layers in the bed to be changed immediately when variations occur in the ash content. The known devices used up till now,

working for instance by X-rays deliver too few values per unit of time and are not suitable for the rapid control required in practice. It is therefore preferred to use for ash determination devices in which, for instance, reflected neutrons and rays such as gamma rays are measured. Such devices have in the past been used for measuring the wall thickness of conduits and other articles which are only accessible from one side.

However, as an alternative method of determining ash content in the novel jigs, it is also possible to use devices in which the absorption of radiation with an energy below 0.2 mev. is measured since they respond rapidly.

In the case of a jig for hard coal, it is preferred to provide two bottom draw ofi devices, one in the first half of the bed for shale and the other for middlings. In this case each bottom draw-cit the bed is measured in two zones with independently working devices. It is found that the ash content of the coal obtained from the jig can be controlled as desired by varying the rate of draw-01f from the middle of the bed. Consequently, the ash-determining device is only arranged to influence the device controlling draw-off at the middle of the bed.

FIGURE shows an arrangement that can be incorporated in any one of the novel jigs already discussed. The arrangement includes a time-switch which is in circuit with the control device 8. The outlet opening is here controlled by a valve in the form of a plane slide 9.

The reason for providing this switch 15 is that it is found that when jigging coarse granular material extra large particles such as :16 in FIGURE 10 block the slide 9' of the draw-off as it is being closed and jam it, so that coal particles from the less dense layer pass through the draw-01f device intended for the dense layer and are lost. In known devices it was diflicult to recognise this trouble when it occurred and it could not be put right without some delay; for the draw-off device was under surface of the water under the bed and was therefore difiicult to see. Losses of coal could therefore only be prevented by continual inspection of the dense material as it was carried away, for instance in a bucket conveyor.

In order to get over this difiiculty the draw-0E device was in previous devices coated with rubber or the fiat movable part of the draw-ofl valve was divided into segments so that only one or two of the segments would be blocked by a coarse particle instead of the whole slide. However, these contrivances did not satisfactorily solve the problem.

It has now been found that a better solution is provided by the use of the current or voltage time switch 15 which brings about the opening of the draw-off device for a short, adjustable period if the current or voltage rises above a certain adjustable value for more than an interval which is also adjustable. Thus if the pnoportion of dense refuse particles in the feed to the jig decreases, there will be an increase in the less dense material in the measuring zones, and owing to the decreased absorption of radiation in the measuring zones, the signal from the radiation detector will increase. This results in the control device causing the draw-01f device to be closed somewhat. However, if during this closing movement of the outlet valve a coarse particle gets in the way, there will be an undesirable loss of coat from the less dense layers. At the same time still lighter strata will pass into the measuring zone and bring about a considerable deviation of the current signal from the radiation detector from the target value. If this current exceeds a predetermined value the time switch is actuated. If it continues to exceed the value for a preset interval, a contact is closed and the draw-off valve is opened. The coarse particle is now released. The valve only remains open a short while in order to minimise loss of coal.

Therefore the currentor voltage-responsive delay switch 15 is used. It can for instance be set, according to the conditions, so that it responds when the actual should be limited to under 2 to 5 seconds according to the construction.

The improvements described above enable a jig run fully automatically.

It will of course be understood that the above novel devices have been described merely for the sake of example and that various modifications can be made in them without departing from what is now claimed in the following patent claims which are taken to cover all equivalents.

I claim:

1. Apparatus for controlling the draw-01f of material from a bed in a settling tank in jigs for coal or ore, comprising a source of penetrating nadiation, a detector determining the strength of said radiation after having passed through a layer of said bed, the distance between said source and said detector being between substantially 30 and centimetres, and means for controlling the draw-off of material from said bed in correlation with said absorption.

2. In combination with a jig in which a bed of particulate material is being stratified substantially in accordance with density, an apparatus for influencing the quality of material drawing off from said bed, said apparatus comprising; a radiation detector in said bed, sources of penetrating radiation to each side of said detector, in combination with means for influencing the quantity of material removed in correspondence with signals from said detector related to the sum of radiation reaching it from both said sources.

3. Apparatus for controlling the draw-oflf of material from a bed in a settling tank in apparatus for jigging coal or ore by a pulsed fluid, comprising a source of electromagnetic radiation, projecting such radiation through a zone of the bed for the continuous measurement of density, there being a source of rays on at least one side of the settling tank, in combination with a discharge device, at least one detector to produce a signal in correspondence with the radiation absorbed in said zone of the bed, said source of rays and at least one detector being located near the discharge device, control means electrically connected with said detector and adapted to influence the draw oflf by the discharge device, whereby any variation in the absorption or" radiation in the zone in said bed causes the said control device to alter the rate of draw-off by said discharge device.

4. Apparatus for controlling the draw-ofl of material in accordance with claim 3 in which the source of electromagnetic radiation is adapted to be projected through a zone of maximum Stratification according to density in said bed, and the said source of electromagnetic radiation and the detector are displaceable horizontally and adjustable in height, whereby the measurement can be located where it will give the most reliable operation.

5. Apparatus for controlling the draw-01f of material according to claim 3 in which there are two detectors one above the other measuring the radiation, any difierence in the signals from the two detectors influencing the nominal value of the signal to the control device.

6. Apparatus tor controlling the draw-off of material in accordance with claim 3, in which the source of electromagnetic radiation is elongated in the direction of horizontal travel of said bed, and the source is activated cobalt.

7. Apparatus for controlling the draw-off of material in accordance with claim 3, in which there is a vibrator and screen driven by the vibrator for dry jigging the to be particulate material.

8. Apparatus for controlling the draw-oif of material in accordance with claim 3 in Which the discharge device is a valve in combination with electrical means for opening and closing the valve, and means for opening said valve for a predetermined interval when any variation in the absorption rate shows a predetermined variation from a preset target value. v

'9. Apparatus fior controlling the draw-otf of materia in accordance with claim 3, in combination with a continuous ash content determining device whose electrical impulses atfeet the control device for the discharge device.

10. Apparatus for controlling the draw-off of material in accordance with claim 9 in which there are means for draining the material after removal from the bed and quickaacting means determining the ash content of said removed material and means influencing the rate of drawotf :of material in response to changes in ash content; whereby both the separation of coal and refuse and the ash content can be kept independently within pre-set limits.

11. Apparatus for controlling the drawofl of material from a bed of particulate coal or ore being stratified substantially according to density in la settling tank in apparatus forjigging said material, said apparatus comprising a radiation detector in said bed, in combination with a source of penetrating radiation on each side of the settling material outside thereof and control means electrically connected with said detector and adapted to influence the draw-ofi by the discharge device, whereby any variation in the absorption of radiation in the zone in said bed causes the said control device to alter the rate of draw-0E by said discharge device.

References Cited in the file of this patent UNITED STATES PATENTS 2,132,750 Muller Oct. 11, 1938 2,316,239 Hare Apr. 13, 1943 2,737,186 Molins Mar. 6, 1956 2,861,188 Dijkstra Nov. 18, 1958 2,883,053 Smith Apr. 21, 1959 2,958,777 Sieswerda et a1 Nov. 1, 1960 FOREIGN PATENTS 793,301 Great Britain Apr. 16, 1958

Claims (1)

1. APPARATUS FOR CONTROLLING THE DRAW-OFF OF MATERIAL FROM A BED IN A SETTLING TANK IN JIGS FOR COAL OR ORE, COMPRISING A SOURCE OF PENETRATING RADIATION, A DETECTOR DE-

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