US3400179A - Pellet manufacture - Google Patents

Description

Sept. 3, 1968 F. o. WIENERT PELLET MANUFACTURE 2 Sheets-Sheet 1 Filed April 2. 1965 INVENTOR.

21 55 0. u'ezzei'f ATTOI? p 3. 1968 F. o. WIENERT' 3,400,179

PELLET MANUFACTURE Filed April 2, 1965 2 Sheets-Sheet 2 OOOOOO I NVENTOR.

46 0; ZZ/ierzeri ATTOJ? EK United States Patent 3,400,179 PELLET MANUFACTURE Fritz 0. Wienert, Lewiston, N.Y. (394 Roosevelt Ave., Niagara Falls, N.Y.

Filed Apr. 2, 1965, Ser. No. 445,051 'Claims. (Cl. 264-) ABSTRACT OF THE DISCLOSURE This invention relates to the manufacture of pellets from finely divided materials and is particularly concerned with a process for producing such pellets from moist powders.

Hitherto the formation of pellets from moist powdered materials has most frequently been carried out by rolling small granules in fine powder under a spray of Water or an aqueous solution of a binding material. The rolling may be done with a variety of types of rotating apparatus including drums, truncated cones, and inclined discs. Such a process has a number of disadvantages. Among these are: (1) the difficulty in proper adjustment and control of the amount and distribution of the aqueous fluid which results in the production of pellets that frequently are deficient in strength or have an undesired size range; (2) the necessity of recirculating or otherwise disposing of pellets which are of unsuitable size; (3) the necessity of having a rather critical particle size distribution in the powdered material used; (4) the reduction of efliciency as the moist powder forms accretions on or in the apparatus; and (5) the reduction in production capacity of specific apparatus with increasing pellet size.

It is an object of the present invention to provide a process for producing rounded pellets from finely divided material which does not depend on agglomeration by rolling to form the pellets.

Another object of the invention is to provide a process by which pellets of the character described may be formed and shaped to very uniform size within a wide range of sizes.

Another object of the invention is to provide a process in which hard pellets can be produced from a mixture of particles of widely different sizes.

A further object of the invention is to provide a process by which pellets having concentric shells of varying compositions and/0r difierent particle size distribution may be conveniently produced.

Other objects and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings in which;

FIGURE 1 is a side elevational view, with some parts in section, of apparatus adapted to produce pellets according to the present invention;

FIGURE 2 is a transverse sectional view taken on line 2-2 of the apparatus illustrated in FIGURE 1;

FIGURE 3 is a detail view illustrating a modification of the apparatus illustrated in FIGURES 1 and 2;

FIGURE 4 is a fragmental, enlarged, sectional view illustrating a variation in mold shape; and

FIGURE 5 is a fragmental, enlarged, sectional View, illustrating a modified type of mold.

The above-mentioned objects, so far as the process is concerned, are achieved by a combination of steps which include the mixing together of particules of solid material with a liquid, and if desired, a binder, to produce a moist powder mixture depositing said mixture in molds having a volume approximately equal to the volume of the desired pellets and, by vibration of the molds, forming densely packed, plastic bodies; removing the plastic bodies from the molds; and thereafter rounding said bodies, while still plastic, into pellets by subjecting them to a rolling action. Preferably such rolling is carried out with the bodies in contact with a dry particulate material which may be the same as the particles of the body or may be different in composition and/ or particle size. The resultant rounded pellets which are preferably spheroidal are strong enough to resist ordinary handling and may be dried and used as desired.

The above-described process may be carried out in a number of ways. Many of these, however, are relatively inetiicient and uneconomic. The accompanying drawings illustrate a preferred embodiment of apparatus designed to produce rounded pellets according to the invention in an efiicient and convenient manner. It will be understood that the drawings are not to scale, portions thereof being exaggerated in size to make the construction and operation clearer.

In the drawings, the numeral 11 indicates generally an endless belt which passes around and is carried by horizontally spaced rollers or pulleys 12 and 13 thereby forming an upper belt span 14 and a lower belt span 15 between said pulleys, said spans being preferably generally horizontal and vertically aligned. The pulleys or rollers 12 and 13 are rotatably mounter, respectively, on upwardly extending posts 16 and 17 of a frame designated generally by the numeral 18. Suitable gear mechanism 20, which may be driven by an adjustable speed electric motor 21, is provided for rotation of the pulley 12. The belt 11 moves in the direction of the arrow shown and is, as shown in FIGURES 2 and 3, provided with a plurality of apertures or holes 23, preferably arranged regularly in a plurality of rows and columns, extending through said belt.

Referring again to FIGURE 1, the numeral 24 indicates a feeding hopper extending transversely across the upper span 14 of the belt 11 and arranged to deposit a moist powder mixture 25, containing material to be formed into pellets, substantially evenly over the width of the span 14 above the supporting plate 26. The plate 26 together with the supporting plates 27 and 28, which are arranged below the span 14 and in sequential, spaced relation longitudinally thereof in the direction of travel of the belt 11, support the span 14 between the rollers 12 and 13 and maintain it substantially fiat. The plate 28 is rigidly mounted adjacent the roller 13 by brackets 29 on a platform 31 that constitutes a part of the frame 18, and extends longitudinally between spans 14 and 15 of the belt 11. The plate 26 is carried on the platform 31, adjacent the pulley 12, by springs 32 or equivalent resilient means and is provided with suitable vibrating means 33, such as an electromagnetic vibrator. The plate 27, located intermediate the plates 26 and 28, is carried on the platform 31 by resil ient means such as springs 34 and like the plate 26 is also provided with suitable vibrating means 35. The vibrating means 33 and 35 are attached to the plates in any desired or convenient manner.

Above the supporting plate 26 there is provided means for filling the holes 23 in the belt 11 with mixture 25. This filling means comprises one or more blades 38 positioned transversely across the width of the span 1.4 in contact with the belt. The blade or blades 38 are mounted on a transverse girder 39 carried by flexible side plates 40 attached in any desired and suitable manner to the platform 31. Preferably, the girder 39 and blade or blades 38 are vibrated by means such as an electromagnetic vibrator 42 carried by the girder.

A hood 46 is suspended, by suitable means such as hangers 47, which are preferably adjustable in length, from the platform 31 over the upper face of the span 15 of the belt 11 adjacent the pulley 13. The hood extends transversely across the width of the belt and preferably comprises a top 49, side walls 50, end walls 51, and a plurality of internal partitions 52 which may be integral with the top 49, and which extend longitudinally of the hood and across the belt 11. The lower edges of the walls of the hood 46 and of the partitions 52 are provided with flexible, resilient, sealing strips 54, which may conveniently be formed of rubber. The interior of the hood 46 is divided by the partitions 52 into a plurality of compartments to which air or other gaseous fluid under pressure, for example steam, may be supplied from the supply line 58, through the valved branch lines 59 which are connected by suitable means such as nipples or the like to the top 49 of the hood through which communicating ports (not shown) are provided to the interior of the hood.

Below the hood 46 the belt span 15 is supported by a grid 61. The latter is flexibly and resiliently mounted at its sides, as by the springs 62, on stands 63 that extend upwardly from the frame 18 on the sides thereof. The grid 61 is preferably, as best shown in FIGURE 2, somewhat wider than the belt 11 and provided with a plurality of parallel slots 64 that extend longitudinally thereof for the major portion of its length. The slots 64 are laterally spaced whereby each slot registers with one of the several columns of holes 23 provided in the belt 11, although the slots 64 are wider than the diameter of the holes and the walls thereof preferably flare outwardly toward the bottoms thereof. The grid 61 is also provided with vibrating means therefor such as electromagnetic vibrators 65.

Between the stands 63 there is provided a shaking table 67 which extends longitudinally under the span 15 of the belt 11 and the grid 61. The shaking table is provided with suitable, preferably conventional, means 68 for imparting reciprocation thereto and is mounted for such reciprocation on flexible supports 69. The actuating means 68 and supports 69 may be carried by the frame 18 in any convenient manner. The table 67 is preferably inclined with its left end, as viewed in FIGURE 1, slightly lower than its right end. As best seen from FIGURE 2, the upper surface of the shaking table 67 is formed as a series of smooth parallel grooves or channels 71 with curved bottoms, said channels extending longitudinally for the length of thetable.

The troughs or grooves 71 are so shaped and spaced as to register with, i.e. lie vertically under, the slots 64 of the grid 61, whereby a body falling through one of the slots 64 will be caught in the associated channel of the shaking table 67.

A stop or end wall 72 extends upwardly at the right end of the table 67 closing the channels or grooves 71 at that end of the table. At the left end of the table 67 there is provided a receiving hopper 73, which extends transversely of the table beneath the end thereof.

Nozzles 75 and 76 are provided above the shaking table 67 and are connected by suitable piping to sources (not shown) of suitable gas and liquid, respectively. Also provided above the table 67 is the sieve 77 which is suspended by suitable resilient means such as spring arms 78 from the cross girder 79 attached to the side plates 40, and has connected thereto vibrating means 80 which may be of conventional design. A feed distributor 81 is provided in association with the sieve 77 whereby to feed fine particulate material evenly across the width of the table 67. Liquid from nozzle 76 and particulate material from distributor 81 will provide a thicker coating on the pellets. Above the shaking table 67 at its right end (FIGURE 1) powder distributing means 83 is provided to supply powdered material to the grooves or channels 71 to prevent uncoated pellets from sticking.

The following example illustrates the use of the apparatus shown in FIGURES 1 and 2 in carrying out the novel pelletizing process of the present invention.

Example 1 A mixture is formed from parts of Brazilian hematite ore and 9.5 parts of a 10% aqueous solution of sodium silicate. The ore contains substantial proportions of both coarse and fine particles the sieve analysis (Tyler Standard Screens) being:

Percent: Mesh 24.1 20+35 12.3 35+100 2.8 l00+150 5.0 -+20O 55.8 -200 The mixture is fed from the feed hopper 24 onto the surface of the belt 11, which is preferably formed of rubber and is continuously moved by the roller or pulley 12 in the direction indicated by the arrows in FIGURE 1. In passing under the blades 38 the mixture is forced into the holes 23 of the belt 11, these holes serving as molds for forming bodies of approximately the same volume as the desired pellets. Filling of these molds is facilitated by vibration of the moving belt by the supporting plate 26 and vibration of the blades 38.

Further vibration of the bodies in the molds of the belt 11 produced by the vibrating support 27 results in compaction of the bodies as evidenced by the exudation of liquid at the exposed surfaces of the bodies. If desired, suitable means (not shown) may be provided for removing excess exuded liquid.

Removal of the compacted bodies from the molds formed by the holes 23 of the belt is accomplished by passing the belt in its lower, inverted span over the vibrating grid 61. The vibration imparted thereby to the belt makes it relatively easy to expel the compacted plastic bodies from the molds by gas pressure in the hood 46 located above the grid 61. Normally air pressure of about 25 cm. of water is sufiicient.

The bodies which have a diameter of about 1.7 cm. and a length of about 1.4 cm. drop through the slots 64 of the grid 61 into the corresponding grooves or channels 71 of the shaking table 67. This table has a reciprocating motion which results in the bodies being rounded into pellets as they roll back and forth in the grooves 71. A reciprocating travel of the table of about 7 cm. with a cycle time of about /2 second is ordinarily suflicient to obtain good rounding before the pellets roll off the lower end of the table. Additional fine hematite ore, 91.2% passing a 200 mesh Tyler screen, is spread thinly in the grooves 71 by the distributor 83. During a shaking period of about 6 seconds the pellets pick up a surface coating of this fine material, about 11 parts of hematite per 109.5 parts of the original mixture being incorporated in such coatings on the pellets of this batch. The pellets, after drying, weigh approximately 15 grams each and have a diameter of about 1.8 cm.

As shown by the following examples, the process is adopted for use with other particulate material.

Example 2 A mixture is formed from 79 parts of chromite ore ground so that 90% passes a 325 mesh Tyler screen, 21 parts of bituminous coal ground to pass 100% through a 200 mesh Tyler screen, and 27 parts of water containing 1 part of dissolved sodium silicate.

This mix is filled into the molds in the belt 11 and the molds are vibrated to compact the bodies in the same way as the mixture of Example 1. After removal from the molds by air pressure in the hood 46 and vibration, the compacted bodies are rolled in the grooves of the shaking table 67, which are supplied with additional powdered coal, while blowing warm air over the table. The bodies are thus rounded into pellets and pick up as concentrate shells on their surfaces about 2 parts of coal per 100 parts of ore-coal mixture used.

The pellets obtained are about 1.8 cm. in diameter. They are strong enough to resist breaking during handling whereas quite soft pellets were obtained using the same ore-coal mix with prior art balling devices even when using a 15% sodium silicate solution.

In the foregoing examples aqueous liquid binders are employed in forming bodies for the production of pellets. However, not only may other liquid binders such, for example, as oils, thin tars, and liquid resins be used instead of aqueous binders but also, where their presence in the pellet is desired or will be unobjectionable, solid binders such as clays may be used with a suitable liquid to give a plastic coherent mass. This is illustrated in the following examples.

Example 3 A plastic mixture is formed from 57 parts of limestone ground to pass a 100 mesh Tyler screen, 19 parts of clay ground to pass a 200 mesh Tyler screen, and 16 parts of water. This mix is molded and vibrated as described above in Examples 1 and 2. The molded bodies, after removal from the molds formed in the belt 11, are formed into spheroidal pellets by rolling them in the grooves of the shaking table in which there is provided by the feeder 83 a thin layer of finely powdered limestone. The pellets obtained are well formed with a smooth, non-sticky surface.

Example 4 100 parts of the same hematite ore as used in Example 1 are mixed with 0.8 part of bentonite and then with 11 parts of water. The mixture is molded into bodies in the same way as in Example 1. The bodies may be removed from the molds by air pressure in the hood 46 alone, no vibration being required, and may be rounded into spheroidal pellets either on a shaking table as described above or by rolling them in a cylinder rotating around an axis inclined about 5 to the horizontal. The loading of the cylinder is restricted to permit substantially all of the plastic bodies to lie in contact with or adjacent to the cylindrical surface and fine, e.g. 200 mesh (Tyler), dry hematite ore is spread or sprinkled over the bodies as the cylinder rotates. The bodies assume a spheroidal shape and pick up from the dry, finely divided ore a coating weighing about of the original dry weight. The pellets are separated from any excess dry ore by screening and may be dried in any suitable manner.

It will be understood that apparatus for producing pellets according to the present invention may assume other forms and that the apparatus illustrated herein may be modified, all without departing from the invention. One possible apparatus modification is shown in FIGURE 3.

Sometimes it may be desired to extend the lentgh of the shaking table used for rounding the pellets so as to permit faster belt speeds wtihout crowding the grooves or troughs of the table with pellets. In such cases, as illustrated in FIGURE 3, the shaking table 86 may be arranged at an angle, 90 being preferred, to the direction of travel of the belt 11. The plastic bodies are freed from the molds comprised by the holes or apertures 23 by air under pressure supplied to the angularly disposed, compartmented hood 88 so as to be distributed in the troughs 87 of the table. The construction of the belt, its drive, the mold filling mechanism, and/ or other portions of the apparatus may be identical with the construction shown in FIGURES 1 and 2 or may be modified as desired, or as required by the angular disposition of the shaking table.

It should also be particularly mentioned that the molds used in forming the pellet bodies may be of different shapes and/ or construction. Thus, as shown in FIGURE 4, the holes or apertures 91 formed in the belt 11 may be tapered to facilitate ejection of shaped bodies from the molds formed by said apertures. Further, as shown in FIGURE 5, liners or inserts 92 may be provided in the holes or apertures 23. The liners 92 may be of any desired and suitable size and shape and may be formed of any convenient and suitable material. In some cases the use of silicone rubber or fluorocarbon polymers may be desired for such liners or inserts because the non-sticking surface characteristics of such materials will facilitate removal of molded bodies therefrom. The provision of inserts or liners as molds permits convenient adjustment of the size of the pellets and easy correction thereof when the molds become worn. The liners may be fastened in place in any desired way.

In connection with the belt 11, it may be explained that although it is preferred for the belt to be actually endless and formed of rubber or other suitable elastomer or flexible plastic material it may be, if desired, formed in sections which are fastened together to form a belt that is endless for the purpose of this application. If sections are used they may be of other suitable materials with flexible connections therebetween. The holes in the belt which serve as molds or as holders for mold inserts are, as mentioned above, preferably arranged regularly in a plurality of rows and columns. However, other arrangements may be contrived and in some cases, if desired, the holes or apertures in some columns or rows may be of different size and/or shape than those in other rows or columns.

Among other possible modifications and variations of the apparatus usable in carrying out the present invention there may be mentioned the omission of vibrating means for the blades 38 and/or the supporting plate 26 and/or 27. In some cases less vibration may be necessary to produce dense packing of the material in the molds. Also, as an alternative means for packing the material into the molds or for emptying them, there may be employed mechanical fingers or pins suitably arranged to cooperate with the holes in the belt.

Substantially any particulate material may be formed into pellets by the process of the present invention with a suitable liquid and in some cases a binder. Among the large variety of such materials which are particularly useful in pellet form are magnetite ore and ore concentrates, ilmenite, alumina, silica-alumina mixtures, silicacoke mixtures, iron oxide-silica-carbon mixtures, and magnesia. Pellets of many of these and other materials with outer layers of coke, for use as a reducing agent, or of a flux such as lime will also be of practical interest. While best results are obtained when the material used for forming pellets has a particle size distribution favorable to dense packing the process is of value even with unfavorable particle size distribution since in many such cases it is impossible to make pellets at all by methods other than the one described herein.

The liquid phase of the plastic mass from which pellets are formed should exceed the amount of liquid which can be absorbed by the mass of particles when it is densely packed. The excess may be from about /z% to not, more than 20%. As mentioned above, the exudation of excess liquid as the molds are vibrated is an indication of the obtaining of dense packing of the particles. The time required for vibrating will depend on the intensity and amplitude of the vibration and other factors such as the design of the apparatus and the amount of excess liquid present. With respect to the last mentioned factor, it may be mentioned as exemplary that if only 9 parts of the aqueous silicate solution is used in the procedure of Example 1 instead of 9.5 parts the required vibration time is increased more than 100%.

As mentioned above, a soluble silicate, a clay such as bentonite, and other materials may be used as binders when a binder is desired. Other water-solube binders such as starch, glue, and certain cellulose derivatives may also be employed. The amount of binder used may vary depending upon the materials involved. In many cases a binder is unnecessary and in most instances no more than about 0.2% to 1% on the dry basis in the pellet is required, although more can be used if desired. Whether the binder is added as a solid or liquid is a matter of choice.

In removing the pellet bodies from their molds, vibration may not, as pointed out above, be required, the gas pressure in the hood 46 often being sufficient to force the bodies from the molds. The hood is preferably formed with compartments, as shown in FIGURE 1, with a valved gas supply to each compartment so that the pressure drop in the last compartment, (i.e. the last one encountered by a specific point on the moving belt) when there may be none or only a few bodies remaining in the molds, will not seriously affect the pressure in the other compartments. Any suitable gas may be employed in the hood 46. Air is preferred in most cases but steam, nitrogen, carbon dioxide, and other gases or vapors may be used when desired.

As described above, the bodies coming from the molds are preferably rounded by rolling them in longitudinally extending, arcuate troughs or grooves provided in a shaking table to form spheroidal pellets. Best results are obtained if the bottoms of the grooves or troughs has a radius of curvature r such that when V is the volume of a single pellet. A larger or smaller radius tends to cause the pellets to have ellipsoidal shapes. The operation of the shaking table will vary with the size of the pellets, the materials used, and other factors. Ordinarily the time for satisfactory rounding will range between about seconds and seconds for bodies of the stiffness of those obtained in Example 1.

It has been previously mentioned that the plastic bodies in rolling on the shaking table in contact with fine dry powder pick up a coating on the surface thereof. Since this coating has a drying and stiffening effect the thickness of coating that can be obtained without further treatment is limited. Where it is desired to obtain a thicker coating a suitable liquid, which may contain additional binder, may be sprayed on the pellets through the nozzle 76 and finely divided material may be sifted on them from the vibrating screen 77. Of course, the same procedure may be used to obtain outer coatings of a different material on the pellets. On the other hand, blowing warm air or other suitable gas over the table through the nozzle 75 will tend to dry the surfaces of the pellets and reduce the pick-up of dry powder.

In Examples 1 and 4 the rounding of the molded pellet bodies on a shaking table and in a rotating cylinder, respectively, were described. It will be understood that other apparatus in which the plastic bodies may be rolled on a smooth surface in contact with dry particulate material, for example rotating disc apparatus such as an inclined disc pelletizer, may also be employed for such rounding. Generally, however, the most uniform and satisfactory results are obtained with a shaking table.

It will be evident from the foregoing description that the present invention provides a novel process and novel apparatus that are very effective and convenient for producing spheroidal pellets from particulate material. A

wide variety of materials may be used and the pellets obtained may have different structures and characteristics. It will be understood that in addition to the modifications of and variations from the preferred apparatus and process described herein other changes may be made without departing from the spirit of the invention. Accordingly, it is intended that the invention shall not be considered as limited by the foregoing disclosure but shall be interpreted as broadly as permitted by the appended claims.

Except as otherwise stated parts and percentages set forth herein are parts and percentages by weight.

What is claimed is: 1. A process for producing rounded pellets which comprises mixing together particles of solid material having a particle size distribution favorable to dense packing and a predetermined quantity of a liquid; filling molds with said mixture, each mold having a volume approximately equal to the volume of the desired pellet; subjecting said mixture to vibration in the mold to obtain dense packing of said particles into plastic bodies; removing said bodies from said molds; and thereafter rolling said plastic bodies on a moving surface to form said plastic bodies into rounded pellets.

2. A process for producing rounded pellets which comprises mixing together particles of solid material having a particle size distribution favorable to dense packing and a predetermined quantity of an aqueous liquid; charging said mixture into molds having a volume slightly less than the volume of the desired pellets; subjecting said mixture to vibration in the mold to obtain dense packing of said mixture into plastic bodies; removing said plastic bodies from said molds and dropping them onto a moving surface; and thereafter rounding said plastic bodies by rolling said plastic bodies in contact with a dry particulate material on said surface to produce pellets, said pellets being maintained sufiiciently damp as to become coated to a substantial thickness with said dry particulate material.

3. A process as set forth in claim 2 in which said plastic bodies are rounded by imparting thereto a reciprocating motion on a smooth surface which is arcuate in crosssection.

4. A prooess as set forth in claim 2 in which said plastic bodies are removed by gas pressure.

5. A process as set forth in claim 4 in which said plastic bodies are removed with the aid of vibration.

6. A process as set forth in claim 2 in which said plastic bodies are moistened during rounding.

7. A process as set forth in claim 2 in which said plastic bodies are partially dried during rounding.

8. A process as set forth in claim 2 in which the particulate material in the coating on said bodies is different from the material of which said bodies are principally composed.

9. A process as set forth in claim 2 in which said aqueous liquid comprises a binder.

10. process for producing dense, round, pellets which comprises:

mixing together particles of a solid material having a particle size distribution favorable to dense packing and a quantity of a liquid suitable'for the formation of a plastic mass to produce a moist powder mixture;

filling said mixture into mold cavities of a desired size, said mold cavities being located in an endless belt traveling in an upper span and a lower span between a pair of horizontally spaced rollers, said filling taking place in said upper span;

vibrating said filled mold cavities and said mixture con tained therein during horizontal travel on said upper and lower spans to densely pack said particles and form plastic bodies, a small portion of liquid being exuded during said vibration;

expelling said plastic bodies from said mold cavities and causing said plastic bodies to drop onto a moving surface; and

rolling said plastic bodies in contact with dry partic- 9 ulate material on said moving surface to coat said 2,813,299 bodies with said particulate material and form said 3,005,420 bodies into round pellets. 3,006,291 3,233,022 References Cited 5 UNITED STATES PATENTS 2,304,382 12/1942 Shoeld 26415 2,543,898 3/1951 DeVaney 26415 Massey 18-1 Wiklund et a1 1078.2

Montez 107-8.95 Henry et a1 264-123 ROBERT F. WHITE, Primary Examiner.

I. R. HALL, Assistant Examiner.

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