US 2867513 A
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Jan. 6, 1959 L. D. BOYER PROCESS AND APPARATUS FOR PELLETING Filed Ja'n. 19, 1956 2 SheetsSheet 1 zuimwjo mm 530E mhjdn 596mm INVENTOR.
L. D. BOY E R BY I g ATTORNEYS x268. wOmDm mmwUOmm 20mm 204 5 w o O04 Jan. 6, 1959 L. D. BOYER PROCESS AND APPARATUS FOR PELLETING Filed Jan. 19, 1956 2 Sheets-Sheet 2 PRODUCT \TANK .54 TO OTHER I MILLs M26 PRODUCT PELLETS IO 12 I4 PELLET MILL FEED 24 ELEVATOR FIG. 2.
ELEVATOR ELEVATOR 64 so RECYCLE vEssEL o PRODUCT 42 6T6 TANK To OTHER PELLET MILLs J62 2 6 I I PRODUCT l2 l4 PELLETS I PELLET MILL 24 INVENTOR. L. D. BOYER FIG. 3.
ATTORNEYS PROCESS AND APPARATUS FOR PELLETING Lyndon D. Boyer, Norman, kla., assignor to Phillips Petroleum Company, a corporation of Delaware Application January 19, 1956, Serial No. 560,166
17 Claims. (Cl. 23314) This invention relates to an improved process and apparatus for pelleting pelletable powdered materials such as carbon black.
Powdered materials of various kinds, such as metal oxides and mixtures thereof suitable for adsorbent and catalytic uses, as well as carbon black for compounding rubber, are frequently and desirably pelleted into small pellets by rolling and/or tumbling the powdered materials in rotating horizontally elongated cylindrical drums or cylinders. The loose powdered material is fed into the drum or mill at or near one end and a bed of the tumbling material is maintained therein at a predetermined depth by disposition of weirs in the exit or delivery end of the mill or of a circular opening in the delivery end of the mill at a predetermined distance from the periphery of the mill. The pelleting process is generally effected with dry powder but may also be effected with the addition of a suitable liquid such as water whereby the material remains apparently dry but contains a substantial amount of the liquid. The latter technique is generally termed a semi-wet pelleting process as contrasted with a pelleting process using sufiicient water to render the powdered material visibly wet. In the pelleting of carbon black by semi-wet pelleting, usually up to about weight percent of water based upon the weight of the mixture is used, but up to 45 weight percent can be used and the resulting pellets are apparently dry.
Occasionally when pelleting powdered material such as carbon black, for causes known and unknown, a mill suddenly goes to the production of loose material instead of pellets and it is necessary to determine the cause, if possible, and get the mill back on production of suitable pellets. In other instances, a mill produces inferior pellets of low density for some unknown reason and it is essential to feed good quality pellets to the mill in order to bring the mill back into production. In conventional pelleting processes of this type, pellets are continuously recycled from the delivery end of a mill to the feed end so that recycle pellets are obtained from the mill product. Obviously, where production pellets are of inferior quality due to malfunction of the mill, recycle pellets are of no better quality and this poorer quality of the recycle pellets does not assist but rather obstructs returningthe mill to smooth operation with production of pellets of standard quality.
I have devised a process and apparatus which assures the recycle of good quality pellets to each pellet mill in a series, even though a portion of the mills are producing pellets below standard quality.
The invention has several objects which include the provision of an improved process and apparatus for pelleting powdered pelletable materials, such as'carbon black; the provision of a process and apparatus for pelleting carbon black which feed more nearly uniform recycle pellets to a plurality of pellet mills than conventional processes and apparatus; the provision of a process and apparatus which feed good quality recycle pellets to a mill in a series, even though that particular mill is producing below standard pellets or no pellets'at all; and, the pro- 2,867,513 Patented Jan. 6, 1959 vision of a process and apparatus which effect smoother operation of a series of pellet mills. ,Other objects of the invention will become apparent from a consideration of the accompanying disclosure.
The broadest aspect of the process of the invention comprises pelleting powdered pelletable material in admixture with pellets by tumbling the mixture in a series of horizontally elongated rotating pellet mills and recovering a representative composite pellet sample of the efiluent from all of the mills and recycling a portion of the composite sample to each mill. The ratio of recycle pellets to loose black feed is in the range of /z:1 to 5:1 by weight. The sample is obtained by combining the effluent from each of the mills to form a composite stream or mass and recycling a portion of this stream or mass to the feed end of each mill. Prior to recycling the representative composite sample, it is desirable to pass the combined product through a classifier means so as to separate fines and oversize particles of the material from the pellets of standard size, after which a portion of the relatively uniform pellets is recycled directly to the feed end of each mill and the fines are recycled to the loose black fed to the mills. It is also feasible to pass the combined fines and oversize materials to a pulverizer and thence to the loose black feed to the mills so that the fines and oversize particles are returned as feed in desirable form to the pelleting process. Thus, it can be seen that by operating in this manner, even though a portion of the mills are operating so as to produce below standard quality pellets, the recycle to all of the mills is of standard quality and this tends to effect smoother operation of the mills and more uniform pellet production than is permissible by recycling pellets from the delivery end of each mill, individually, to the feed end of the same mill.
A more complete understanding of the invention may be obtained by reference to the accompanying schematic drawing of which Figure 1 presents a flow or plan of an arrangement of apparatus in accordance with the invention; Figure 2 is an elevation showing an arrangement of apparatus for returning or recycling pellets to a series of pelleting mills;; and Figure 3 is an elevation showing another arrangement of apparatus for returning or recycling pellets to a series of pellet mills. Corresponding parts of various figures are correspondingly numbered.
Referring to Figure 1, the apparatus shown comprises a series of rotatable horizontally elongated cylindrical pellet mills Ill, providing with inlet lines 12 and eflluent lines 14. Inlet lines 12 may be of any suitable type but generally comprise horizontal conduits containing rotatable feed screws. A conveyor system 16 is connected with a surge tank (not shown) which receives carbon black from a series of carbon black furnaces by conventional means. Conveyor system 16 passes in front of pelleting mills 1t) and delivers loose carbon black in conventional manner to each of feed lines 12. A return conveyor system 18 returns feed in excess of that delivered to feed lines 12 so that the excess feed is recycled through the system. A micro-pulverizer 20 or other disintegrating device forms finely powdered material of carbon black aggregates fed to it. This device is positioned in conveyor line 16 in order to assure the delivery of the feed material in powdered form to the pelleting mills.
Efiluent lines 14 frompellet mills 10 may comprise sloping chutes or any other suitable conveyor means which pick up pellets andfines from the delivery end of the mills and convey the same to a common conveyor line 22. Conveyor 22 delivers the combined product from the several mills to a conveyor belt 24 or other suitable conveyor, preferably of the enclosed type, which connects with the lower end of an elevator 26. Elevator 26, which may be of any suitable type, elevatesthe combined product to adesir'ed, level from which themiaterial gravitates to a product classifier 28 via chute or other conveyor 30. Product classifier 28 is provided with screens 32 and 34 for separating the feed thereto into three components comprising fines,'oversize pellets and irregular particles, and standard size pellets. Classifier 32 may also comprise an air type classifier or other suitable classifying device. 7
Oversize pellets and irregularly shaped large particles of carbon black, such as scale fromthe mills, is passed via line 36 to conveyor line 38 in which fines are transferred to the feed conveyor system 16upstream of the pulverizer. The oversize material may be'transferred separately to the micro-pulverizer and the fines may be transferred to conveyor 16 downstream of the pulverizer or directly to the feed end of the mill, if desired. Product pellets are passed via line 40 into pellet storage vessel 42 from which pellets are passed via line 44 to product conveyor 46 and to recycle conveyor'48 which transfers the recycle pellets to inlet conveyors 50 to each of mills 10. Where desired, a conveyor line 51 may be used as an alternative route for recycle pellets from line 40 to feeder conveyors 50 via line 48. Recycle line 52 connecting conveyor 24 with conveyor 48 may be used to recycle a portion of the composite pellet mass passing over conveyor 24 directly there from to conveyor means 48 from which recycle pellets are delivered to the feed end of the mills via conveyors 50.
Referring to Figure 2, the arrangement of apparatus shown is 'for applications where the product storage tank is located close to the mills. In this arrangement, elevator 26 leads into pellet storage vessel 42 which is disposed sufiiciently close and at such an elevation above "mills 10 that chutes 50 gravitate recycle pellets directly to the feed end of the mills. Suitable flow control means 54, such as rotary variable-speed valves are positioned in chutes 50 to regulate the rate of flow of recycle pellets to the several mills. Line 44 leading out of the bottom of pellet vessel 42 feeds product pellets to packaging or shipping facilities. The classifier is omitted from the arrangement of apparatus shown in Figure 2 but may be positioned at any suitable location, such as in conveyor line 24 or in eflluent line 30 from the upper end of elevator 26.
In Figure 3, pellet storage vessel 42 is positioned at such a distance from mills 10 that the gravitation of recycle pellets from storage vessel 42 to the feed end of the mills is impossible and, instead, recycle pellets are transferred by a conveyor 60, such as an enclosed belt conveyor to an elevator 62 postioned close to the mills and fromwhich the elevated pellets are delivered via conduit 64 to recycle vessel 66 which feeds recycle pellets into chutes 50 for delivery'into the mills.
Numerous variations in the apparatus and process are permissible and within the scope of the invention, it being essential that a representative sample of the composite r product from the various pellet mills be recycled to each of'the mills ofthe series in operation. The process and apparatus of the invention provides a plentiful supply of uniform'recycle pellets which is necessary for smooth pelleting operations. tern provides the same high quality pellets for all of the mills regardless of the quality of pellets being produced by an individual mill. When the product density of a particular m'ill drops below standard quality, good recycle pelletsare readily available to assist in bringing up the quality of the pellets being produced by the mill without the usual recharge screw arrangement currently utilized. In addition, when a mill is down for repairs and empty, it is readily brought back on stream very quickly by simply feeding loose :black and readily available recycle pellets of good quality to the mill. 7 Certain modifications of the invention willbecome ap- 'parent'to those skilled in the art and the illustrative details disclosed are'not toi'beconstrued as imposing unnecessary limitations on the invention.
The centralized pellet recycle sys- I claim:
1. A process for pelleting powdered pelletable material which comprises pelleting said material in a plurality of rotating pellet mills; collecting effiuent pellets from said mills in a common mass; recycling a portion of the pellets from said mass to each of said mills; and recovering another portion of pellets from said mass as product.
2. The process of claim 1 wherein said pellets'from said common mass are passed thru a classifying zone to remove fines and oversize particles before recycling the classified pellets to said mills.
3. The process of claim 2 including the step of separately recycling fines to said mills.
4. The process of claim 2 including the steps of pulverizing said oversize particles and recycling same together with said fines to said mills.
5. A process for pelleting loose carbon black which comprises separately feeding'said black'to one end of each of a plurality of horizontally elongated rotating pellet mills so as to form pellets therein; simultaneously feeding recycle pellets to the feed end of each mill; passing efiluent pellets from said mills to a common collecting system; separating fines and oversize particles'from the collected pellets to provide classified pellets-of more uniform size; recycling a portion of the classified pellets as said recycle pellets to each said mill; and recovering the remainder of the classified pellets as product.
6. The process of claim 5 wherein the recycle ratio of pellets to product pellets is in the range of /2 :1 to 5:1.
7. A process for pelleting powdered pelletable material which comprises simultaneously tumbling said powdered material in admixture with pellets thereof in a plurality of horizontally elongated rotating pellet mills so as to form additional pellets therein; recovering a representative composite pellet sample'of the efiluents from all of said mills and recycling same'as a portion of the feed to each mill.
8. The process of claim 7 wherein said sample is obtained from the combined effluents from said mills'after removing therefrom fines and oversize particles; i
9. The process of claim 8 wherein said material comprises carbon black.
10. Apparatus for pelleting powdered pelletable material comprising in combination a plurality of separate, independently rotatable pelleting mills each having a eed line leading into one end'and an efiluent'pellet line leading from the other end; common pellet collecting means connectedwith each said efiinent line; and pellet recycle conveyor means connecting said common pellet collecting means to the feed end of each said mill.
ll. Apparatus for pelleting carbon black comprising in combination a' plurality of rotatable 'pellet'ing mills each having a loose-black feed line leading into one end and an efiluent pellet line leading from the other end; commonconveyor collecting means connecting-said efiluent pellet lines with a classifier for the efiluent pellets, said classifier comprising means for separating fines, oversize particles, and standard size pellets into separate streams; and conveyor means to recycling pellets from said classifier to the feed end of each mill.
12. The apparatus of claim 11 including a pulverizer; conveyor means for passing fines and oversize particles tosaid pulverizer; and means for passing the pulverized material to the feed lines to said mills.
13. Apparatus for pelleting carbon. black comprising in combination a plurality of rotatable pelleting mills each having a ioose-black feed line leading into one end and an effluent pellet line leading from the other end; common pellet collecting means connected with each said efi'luent lineielevatofmeins in saidcollecting'means downstream or said eiliuent lines for elevating said pellets to a level substantially above said mills; a surge vessel connected with the delivery 'end'ofsaid elevator means; conveyor means connecting said surge vessel with the 5 feed end of each mill; and flow-control means in said conveyor means for controlling the flow to each mill.
14. The apparatus of claim 13 wherein said conveyor means comprises a chute from each mill connected with said surge vessel for gravitation of pellets to each mill.
15. The apparatus of claim 14 wherein said flowcontrol means comprises a rotary, variable-speed valve in each said chute.
16. Apparatus for pelleting carbon black comprising in combination a plurality of rotatable pelleting mills each having a loose-black feed line leading into one end and an efiluent pellet line leading from the other end; common pellet collecting means connected with each said eflluent line; elevator means in said collecting means downstream of said eflluent lines for elevating said pellets to a level substantially above said mills; a pellet storage tank connected with the delivery end of said elevator means; a recycle surge vessel disposed above and close to said mills so as to permit gravitation of pellets to said 17. The apparatus of claim 16 wherein last said conveyor means comprises a chute from each mill connected with said surge vessel for gravitation of pellets to each mill; and wherein said flow control means comprises a rotary, variable-speed valve in each chute.
References Cited in the file of this patent UNITED STATES PATENTS 1,261,398 Janney Apr. 2, 1918 2,164,164 Price June 27, 1939 2,327,016 Carney Aug. 17, 1943 2,503,361 Studebaker Apr. 11, 1950