US3437202A - Flow channel for zigzag classifiers - Google Patents

Description

April 8, 1969 w, KMSER 3,437,202

FLOW CHANNEL FOR ZIGZAG'CLASSIFIERS Filed April 4, 1967 Ill/1 Fig. 5

INVENTOR.

Fritz W. Kaiser ATTORNEYS.

United States Patent FLOW CHANNEL FOR ZIGZAG CLASSIFIERS Fritz W. Kaiser, Hammel, near Augsburg, Germany, as-

signor to Alpine Aktiengesellschaft, a company of Germany Filed Apr. 4, 1967, Ser. No. 628,497 Claims priority, applicafi5on0(82;rmany, Apr. 6, 1966, 2

Int. 01. B071) 7/12, 3/12 U.S. Cl. 209136 8 Claims ABSTRACT OF THE DISCLOSURE BACKGROUND OF THE INVENTION Field of the invention This material referes to a flow channel which conveys the material to be classified into a rising-tube classifier, particularly into a zigzag classifier, forwarding it in transverse direction to the rising classifying fluid stream, that ascends substantially from the bottom of said channel. As the fines are continuously carried out upwards, only a more or less clean coarse grain portion remains at the end of the flow channel.

The term flow channel indicates, as generally known, mostly slightly inclined channels, wherein dust fluidized by air blown in, is conveyed by gravity, this condition of dusts being named flow-bed. If operated in connection with a rising-tube classifier said flow-bed has to perform the following functions at a time:

(1) Conveying, in a channel 0.8 m. wide, very considerable amounts of material, which, under certain circumstances, may be as large as 200 tons per hour.

(2) Breaking-up of agglomerates or grains sticking together, while conveyed on the channel, with a view to obtaining a clean coarse prod-uct.

(3) Regular distribution of the required volume of classifying air over the entire separating area.

(4) Throwing at least the limit grains and fines upwards to a height where they are allowed to come into contact with the uniform classifying current that is initiated only on a certain level above the layer of material so that the fines are carried upwards by said current, whereas the coarse grains are dropped again.

Description of prior art Already known is the flow channel with a porous bottom through which air is blown, which channel conveys very large amounts of material, the volume of air, however, not being suflicient to achieve a clean coarse product and to perform good classification. For this reason it has already been suggested in German patent application No. A 47,159 to blow the required air through laterally arranged auxiliary nozzles into such a channel, their influence, however, being too irregularly distributed over the channel width.

In the known Vibro-Classifier the channel bottom consists of a screen with a hole width of -1-2 mm., blown through by air from below. To assist the conveying movement the screen is vibrated, but the flexible suspension Patented Apr. 8, 1969 as well as the sealing required involve considerable extra cost.

Screen holes must be small so as to prevent heavy grains of material from falling through. The emanating air jets are, therefore, too faint to produce an eflicient breaking-up of agglomerates. (Kirchberg, Aufbereitung bergbaulicher Rohstoffe, Gronau, January 1953, page 169.)

Vibration of the screen can be substituted, as already done in the so-called pulsating classifiers (ibid., page by pulsation of the air current. However, these classifiers did not give any better results.

Due to the low air velocities produced in the sieve holes of a sieve surface normally provided with about 40% of open area, both classifier types give a sharpness of separation which is not satisfactory.

During the initial periods of flow-bed construction, larger holes had been used. However, it had not been recognized that, with an adequately small open area in the sieve surface, the condition of the flying bed, as contemplated by the present invention, is obtained or that it would prove useful in separation processes.

In contrast with the foregoing prior structures, it is an object of the present invention to find a configuration of the flow-bed involving not only the accomplishment of the afore-mentioned four functions, but also simplicity and cheapness.

Problems and solutions (1) There are a multitude of conditions in which a flow-bed may occur (see, e.g., VDI Forschungshaft 509/ 1965). Optimum separation is achieved by a flow-bed condition not described as yetat least in connection with this particular applicationhere named flying bed, in which the flow-bed is so largely flufled-up, for instance, to 50100% of the bed volume, that considerable distances are covered by the single grains wirled forward in free flight, chiefly in vertical direction. The flow-bed has no longer the otherwise known properties of liquids as it is, for instance, exempt from floating bodies. If putting the hand in the bed, one feels no longer the resistance of inertia characteristics of liquids, but only the repeated shocks or impacts of the individual grains, the condition resembles the movement of molecules of gas. It differs from that of dust conveyed in flight by the fact that in the flying bed an equal amount of material is, on average, carried forward in the same and in the opposite direction to the flow of the current, whereas all of the material conveyed in flight is substantially moved forward in the current direction. Frequent collisions occur in the flowbed between the grains and especially between the grains and the bottom of the flow channel so that an eflicient breakup of agglomerates is obtained.

For producing a flow-bed the bottom of the channel must be provided with individual nozzles through which air is introduced and which are so designed that the emanating jets carry the grains of the flow-bed. To accomplish this purpose, two conditions must be fulfilled as follows.

(a) The jet diameter must at least be of the same dimensional order as the grain, rather be larger so as to ensure that the single grains are suspended by the jets without requiring the pressure-consuming initiation of a jet velocity higher than the speed needed according to condition (b).

(b) The impetus of the jets must be so high that they are able to keep all of the grains in suspension. From this condition results the equation:

channel bottom, 5 the density of air and AP the pressure drop at the screen, converted to jet velocity. If v =3m./sec. of air velocity and AP=100 mm. WG, G/F would be 15 kg./m. as permissible charge in the channel; thus, the feed rate would be rather small. This requires a jet velocity of 40 m./sec. and an open sieve area of 7.5%. The test confirms approximately this equation, that does not, however, give any definite limits for the initiation of the flow-bed.

The flow-bed condition is easy to check either visually or by putting the hand in and to adjust by a pressure drop large enough in relation to the level of material, such adjustment possibly requiring adaptation of the open sieve area in the channel bottom.

(2) The small charge in the flow channel, the importance of which is emphasized in the preceding section, requires, with large throughlput rates a high velocity of conveyance. The invention contemplates several means to achieve this speed rate.

For the initiation of the flow bed conditions immediately behind the beginning of the flow-bed, the invention equally provides several means.

The goal aimed at is attained according to the inven tion by operation of the flow-bed in flying bed condition. As described before, adjustments to obtain said conditions can easily be made during operation.

For producing the flow-bed, the flow channel bottom comprises a plate wherein several nozzles are fitted, this plate being most simply designed as a perforated sheet provided with round or otherwise shaped holes. I

Precondition of the flow-bed condition is that the individual jets are strong enough to carry the single grains. This is mostly achieved by providing a perforated bottom with holes the diameter of which is equal to or larger than the diameter of the largest grains conveyed. A few oversize grains in the material are negligible.

The necessary impetus of the jets is obtained by calculating the number of holes and the open sieve area, respectively, in such a way that the pressure drop at the perforated bottom corresponds at least to the equation:

Explication of the symbols are given above.

To keep G/F small, that means, to keep the layer of material thin, a relatively high velocity of the material being conveyed is required. This can be achieved by one or several of the following measures: M ost essential is a certain inclination of the channel; a minimum inclination of 9 has proven eflicient.

Another feature is to make the individual air jets inclined in flow direction. Even to avoid any braking effect on the flow of material, they must have a forward component of a value at least equal to the flow speed of the material. A larger forward component exerts a propelling action. These oblique jets are produced by nozzles inclined in direction of conveyance. Regarding the large number of nozzles, a low-cost manufacture is mandatory. This can easily be achieved by deforming the holes of the perforated sheet, subsequently, for instance, by pushing through a mandrel or when punching the holes.

In order to obtain a high velocity of the material in the channel, this velocity must already exist at the entry of material. This speed is most simply imparted to the material by a gravity chute with deflection in direction of conveyance prior to feeding the material into the channel. Dependent on flow speed, the height of fall provided by this chute may vary from a few decimeters up to a few meters.

Since the initiation of the flow-bed, with no especial expedients, requires a certain amount of time and a certain distance on the flow channel, it is essential to make special provisions to obtain, immediately at the beginning of the flow channel, at least part of said flow-bed. It is already known to introduce at this point a larger amount of air through one or several enlarged nozzles arranged 4 immediately behind the intake. They can be spaced regularly across the channel width or concentrated at individual spots in order to effect a splitting of the film of material emanating from the gravity chute.

The same purpose is accomplished by means of perturbing bodies fitted on the bottom of the gravity channel immediately in front on the intake. They can be arranged so as to either break-up the film of material into several strands or throw-up the material for mechanical initiation of the flow-bed.

With certain materials it has been found that, independent of any length of the flow channel, a dwell time of about 1 second, during which the material is retained in the flow channel, is required and suflicient to obtain a clean separation. With other products this period of time may be different, notwithstanding, it is characteristic of a large variety of materials, particularly of the iron ore Minette.

In case of a rising-tube classifier which is not free of internal structures above the flow channel, but sub-divided into several small tubes, especially zigzag tubes, it is es sential to provide above said flow channel a defined headroom. Too small a headroom makes it diflicult for the non-entrapped material to fall again out of the classifying tube so that material would accumulate inside the tubes. With too large a headroom, on the other hand, the flow-bed would not extend to the tubes so that the latter would be fed with an amount of material not large enough to allow them to be utilized completely. From experience, a headroom of 70-200 mm., reaching to any existing subdivisions of the rising tube or tubes of the classifier should be provided.

In order to increase the flow speed in the channel, it is of assistance to make the lower end portions of the rising-tube subdivisions, also called aprons, to face the direction of flow. For better adaptation to the service conditions that, under certain circumstances, require a headroom variable along the flow-bed length, it is advantageous to make the length of the aprons adjustable.

Should the rate of material flowing through be too large or the flow speed be too low to operate a flow-bed all over the sieve area, it may be helpful to set up small single flow-beds at least in the voids around the individual perturbing bodies regularly spaced on the channel bottom.

Since one cannot avoid that; for instance, when shutting-down or if temporary overloads occur, material falls through the holes in the perforated plate, it would sometimes be advisable to build in the space beneath the plate a worm conveyor or any other conveying means that discharges the fallen material, which is most simply carried out through a swing flap into the coarse product line.

Cleanness of the coarse product is increased by extending the flow channel beyond the classifying chamber towards the coarse product side. This effect is particularly obtained by a flow path of the fines-laden air in counterdirection to the stream of coarse product so that fines that may be precipitated again are settling down in front of the spot where they have been whirled up, thus, they are given the chance of being whirled up once again.

With a very small open sieve area, it may be advantageous to provide a porous sieve surface so as to prevent the fine material from settling down between the individual nozzles.

It has shown that, when classifying materials containing very fine or sticky dust, the sieve surface adds to the tendency of the material to form deposits under as well as on the sieve. To eliminate this inconvenience, it has proven efficient to provide a flexible suspension of the sieve and to tap it, at certain intervals of time, with a compressed air device of any known design. Also other knocking or shaking means are likely to prove more or less successful. The rapper presents the advantage that the flexible suspension of the sieve can be rather rigid and, therefore, inexpensive.

SUMMARY OF INVENTION The invention covers improvements in rising-tube classifiers and more particularly to a flow channel therefor, comprising the features described above, for conveying material to be classified at an incline downwardly across the classifier, the flow channel comprising a perforated plate provided with air flow nozzles pointing in the direction of flow and the other features associated therewith arranged to provide for a clean separation of fines from clean coarse material.

BRIEF DESCRIPTION OF THE DRAWING An embodiment of the invention is shown by way of example on the drawing in which:

FIG. 1 is a sectional diagrammatic view showing in elevation the flow channel arranged beneath the tubes of a rising-tube zigzag classifier according to the invention;

FIG. 2 is a plan view of the flow channel taken on the line IIII of FIG 1;

FIG. 3 is a broken sectional view on a large scale of the perforated plate and its nozzle structure;

FIG. 4 is a detail view showing the arrangement of a compressed-air rapper; and

FIG. 5 is a detail view of a flexible suspension means for a perforated bottom plate.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The essential parts of the classifier as shown in FIG. 1, are the zigzag shaped rising tubes 1, of which only the lower portion is shown, the flow channel 2 conveying the material to be classified in transverse direction to the possibly upwardly ascending air current. The material to be classified is fed at point A into gravity chute 3, wherein it attains a certain velocity. Deflection part 4 of the channel bottom 5 directs it subsequently onto the perforated bottom of the flow channel on which it is carried forward at rather high speed until the coarse product G leaves the classifier at the end of the flow channel through coarse product duct 6. The classifying air, produced by a suitable pneumatic installation, enters through a flanged pipe socket 7 into a distributing box 8, passes through bottom plate 5, ascends into the zigzag tubes 1 and, laden with the classified fines, it is discharged at the top of the tube unit 1 to be freed from dust in another pneumatic installation such as a cyclone separator.

The number and size of holes in the bottom 5, which, in correlation with the volume of air, determine the pressure differential at the perforated plate 5, as well as the level where classification takes place and which is dependent upon the quantity and velocity of the material being separated are matched so as to obtain the flow-bed condition of the material in the channel. The material is constantly flung upwards and lifted to the classifying tubes 1, which, according to their separation boundary, carry all of the fines they can entrap upwards so that, atthe end of the flow-bed, only a more or less clean coarse product G remains.

In order to speed-up initiation of the flow-bed at the inlet end of the channel 2, several protruding bodies 11 are arranged at the end 9 of the gravity chute 3 to subdivide the film of material into several strands or streams between which the thickness of the layer is so small that the material can be immediately whirled up. A similar purpose is accomplished by air flow slot 10 provided at the inlet end of the perforated bottom 5 and acting as a nozzle through which a strong jet of air blows upwards. Should the layer of material, while following its path in the flow channel, be too thick to provide a flowbed, the latter can, at least locally, be obtained in the voids around the individual bodies 11.

The drawing indicates different means to impart to the material a high flow velocity: Bottom 5 is inclined by the angle 12, a high rate of fall is imparted to the material by gravity chute 3; the lower portions of zigzag tubes 1 have the aprons 13 inclined in flow direction so as to give the non-entrapped material falling down a certain forward component of velocity; the individual nozzles in the perforated bottom 5 are inclined in forward direction so as to give the issuing jets a forward component of impetus. The headroom 14 above the flow channel is so largely dimensioned that only a very small portion of the forward impetus is destroyed by the impact action of aprons 13 against which the whirled-up ma terial is flung.

The inclination of the nozzles in the perforated bottom 5 is, as shown on FIG. 3, achieved in a simple manner by deforming the holes 15 in a normal perforated plate 5 with the aid of a mandrel 16 pushed through holes 15 to bend the forward edge down. If high wear is expected, a shape like that of hole 17 may prove advantageous.

The flow channel 5 is extended by measure or amount 18 beyond the end 19 of the rising tube or tubes. The air escaping from 5 in the space 18 travels a certain distance in counter-direction to the stream of material which it frees, in a very eflicient manner, from the fines entrapped, without requiring any additional channel surface or extra air. The same may be achieved to a certain extent by an air flow opening 22, so that air flows upwardly through the coarse material in duct 6.

Should material fall through the relatively large holes 15 in the perforated bottom 5, when stopping or if temporary overloads occur, it is directed by worm conveyor 20 and swing flap 21 into the coarse product duct 6.

FIG. 4 shows the arrangement of a known type of compressed-air rapper or vibrator 26, the interior design of which corresponds to that of a pneumatic hammer. This rapper taps bedplate 27. To fasten it, the upper end of bottom 5 passes through the rear side of the air distributing box 8, stiffened by means of welded-on straps 23 and connected to flange 24 carrying plate 27 of rapper 26. The passage zone is sealed with soft rubber sections 25.

FIG. 5 illustrates a structure for arranging the lengthwise, flexible suspension of the perforated bottom 5. Since, due to the high impact frequency of the rapper, the vibration paths are short, said suspension may be rather rigid. Here, the perforated sheet 5 is interposed between three soft rubber sections 28.

The measures as contemplated by the invention present, singly and in combination, the advantage that the rising-tube classifiers, particularly zigzag classifiers of the special design incorporating a flow channel allowing large feed rates to be handled and to be separated cleanly. The equipment needed to achieve this is inexpensive and very simple. The example below shows the results obtained.

Example Minette was separated, with 30% residue on a 315 micron sieve in a rising-tube classifier similar to that of FIG. 1, having a cross section of 0.8 m. and being subdivided into ten classifying zigzag tubes. The flow channel, 500 mm. wide, had an inclination of 9 and was filtted with a perforated bottom with alternately ar ranged holes of 8 and 10 mm. diameter, 13% of the total sieve area being open. The pressure drop at these holes was about 70 mm. water gauge. Feeding 10 tons per hour, the fines yield was 6.2 tons per hour with 5% residue on a 315 micron sieve; 81% of the product smaller than 315 microns entered the fines fraction. A classification could still be achieved at a feed rate of 40 tons per hour, with the fines yield being corresponding smaller.

Regardless of the fact that, in the foregoing description, air was consitently used as the operating fluid of the classifier, any other gas or steam may be used; also warm air for drying as operating fluid may be used. If

7 the usual provisions are made for the use of liquids, the flow channel can be operated with them.

What is claimed is:

1. In a rising-tube classifier of the type including a zigzag rising-tube unit, a flow channel extending laterally across the unit for conveying material to be classified, means for supplying material onto one end of the flow channel, a discharge duct evacuating coarse material at the other end of the flow channel, and means for delivering classifying medium to the classifier to flow up through the flow channel and the material thereon, wherein the improvement comprises a flow-channel including a perforated bottom plate provided with individual air-flow nozzles, the diameter of the nozzles and the pressure drop therein being so rated that the individual jets from said nozzles are strong enough to carry the single grains of said material along and upwardly.

2. A classifier as claimed in claim 1, wherein the airflow nozzles in the perforated bottom plate are at least as large as the largest grains of material to be classified.

3. A classifier as claimed in claim 2, wherein means additional to said air-flow nozzles is provided for increasing the initial rate of flow of material on the inlet end of the flow channel 4. A classifier as claimed in claim 1, wherein means additional to said air-flow nozzles is provided for increasing the initial rate of flow of material on the inlet end of the flow channel.

5. A classifier as claimed in claim 4, wherein said increasing means comprises at least one enlarged nozzle (10).

6. A classifier as claimed in claim 4, wherein said increasing means is a steeply down-inclined gravity chute (3) the bottom of which is deflected at its lower end in the direction of the channel giving velocity to the material as it flows onto the flow channel.

7. A classifier as claimed in claim 1, wherein said rising tube unit includes a series of rising tubes, and wherein a headroom (14) of to 200 mm. is provided reaching from the bottom plate of the flow-channel to any existing subdivision of any rising tube of the classifier.

8. A classifier as claimed in claim 7, wherein the flow channel extends beyond the last tube of the series where it adjoins the discharge chute.

References Cited UNITED STATES PATENTS 187,193 2/1877 Stanley 209506 1,720,861 7/1929 Stebbins 209139 X 2,106,027 1/1938 Guest 209-506 X 2,258,789 10/ 1941 Morgan 209504 X 2,279,590 4/ 1942 Haworth 209466 2,743,817 5/1956 Musgrave et al. 209474 2,815,858 12/1957 Rich 209138 FOREIGN PATENTS 380,196 9/ 1932 Great Britain. 1,014,723 12/ 1965 Great Britain.

969,075 7/1949 Germany.

TIM R. MILES, Primary Examiner.

U.S. Cl. X.R.

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