US1810070A - Preparation of coked agglomerates - Google Patents

Description

matted June 1 .1931

UNITED- STAresf PATENT OFFICE mar. HAML N Burton, on. remnnroiv, rnmvsynvam assrenon? TO THE New JERSEY zmc country, or new YORK,

N. Y., A CORPORATION or NEW mass? 4 rmnm'rron or coxnn 'aeenomnrns no Drawing. 7

This invention relates to the reduction of zinciferous material and is more especially concerned with that method of reduction in WlllCh the charge consists of coked agglomerates of mixed zin'ciferous material and carbonaceous materials The invention aims to provide certain improvements in the preparation of such coked agglomerates.

It has heretofore been found that coked agglomerates of mixed zinciferous and carbonaceous materials constitute a peculiarly advantageous char e for vertica l zinc distillation retortsuch agglomerates must not s lit up during coking and must possess satis actory residue strength, i. e., 'suflicient strength to pass progressively through the vertical retort without breaking down or sanding, thereby preserving throughout the entire reducing operation that desirable uniform porosity of the charge which enables economic andeflicient transfer of heat by hot gases fromthe hot wall of the retort to the center or core of the charge.

These agglomeratesare prepared by first crushing the ore .and coal separately, then kneading-them together, in a Chilean mill orv edge-runner tov form a mixture that is suitable for agglomerating. The. Chilean mill .or edge-runner isfrequentIy referred to as a chaser, itsv o ration as chasing, and

the treated material as having been chased. j

A binder, if necessary, such as sulfite liquor, may be added .durin the treatment in the edge-runner. The the/edge-runner is then agglomerated and coked, at temperatures insufficient to cause an'y'substantial loss of zinc.

The appropriate control of the preparation of the charge for ag lomeration involves a proper adjustment 0 'at least the following three factors: (1) nature of the coal with articular reference to its coking characteristics; (2) particle size .of (a) the zinc ore. and (b) the coal, before they are kneaded together in the ed -runner; 8). particle size of the mixture 0 zinc ore an coal, after treatment in the edge-runner, in the final stage of its preparation for agglomeration. These three factors may be appropriately controlled in co'mbinatiomto secure a firm ixture thus prepared in...

capacity of compacting Application filed November 15, 1928. Serial m5. 319,735.

agglomerate consisting of a coke; structure .mtlmately bonded with and enveloping the particles of zinc-ore, so asto prevent both splitting up of the agglomerates during' cokmg and disintegration during the subsequent distillation: or reduction step.

- The carbonaceous material-used to prepare the agglomerates' should be composed in part.

ofa so-called free-flowing? coal, i'. e., a coal that during coking softens to a great extent, wetting the individual particles of ore, so that'when the coke hardens substantially eachore particle is enveloped in and in intimate contact with coke; and, when the ore particles are later disintegrated by the expulsion of their zinc content during the distillation theg'aps left in the structure are as small as possible, so that. the strength of the residue is preserved. However, such free-flowing .coals'as a rule'swell'or pufl up when heated to coking temperatures, and are then known asswelling coals. This property'of swelling is undesirable in the preparation of coked agglomerat'es'of zinc ore and coal, since the swelling tends to split up the agglomeratesv during the coking operation.. This tendency of the'swelling free-flowing coal to spllt up the briquettes may be overcome by appropriate blending with a coal that does not swell during coking. This non-swell ng coal. need not necessarily be free-flowing; mdeed,

even non-coking carbonaceous material, such as anthracite coal dust and. coke-breeze or "the like may advantageously form part of the blend. I

The inclusionof anthracite dust coal in the agglomerate mixture servesto maintain the coke structure and give residuestrength during the zinc distillation operation. Crushed coke,coke breeze, and similarnon-coking carbonaceous materials may be substituted forthe anthracite dust coal.

The particle size ofboth 't-he ore and the coal afi'ects the intimacy of contact of the ore and coal brought about by the subsequent treatment in the edge-runner, as well as the thus brought about.

In general, at least 50% ofboth the zinciferone material and the carbonaceous material concentrates.

Bituminous coal hammer mill crushed Per cent Per cent on through 8 mesh screen 4. 3 95. 7 14 mesh screen.. 11. 8 83. 9 20 mesh screen.. 10. 6 73. 3 28 mesh screen- 9. 6 63. 7 35 mesh screen-. 11. 8 51. 9 48 mesh screen- 8. 9 43. 0 65 mesh screen.. 7. 5 35. 5 80 mesh screen.. 3. 6 31. 9 100 mesh screen. 4. 6 27. 3 150 mesh screen--- 5.8 21.5 200 mesh screen 5. 0 16. 5

It is desirable, but not necessary, that the non-coking carbonaceous material of the agglomerate mixture be of the aforementioned graded particle size, and the closer this is approximated the more closely will the coked agglomerates approximate the optimum desired properties. Coke crushed to pass through 8 mesh has, however, been successfully used for the non-coking carbonaceous material. 1

The present invention is primarily concerned with the production of coked agglomerates from such finely divided zinciferous material as roasted flotation concentrates and the like, which have, prior to flotation and roasting, been crushed to a size that is too fine forsecuring the appropriate treatment in the edge-runner. If such extremely fine material, e. g., a roasted concentrate with 30 to 40% through a 200 mesh screen, be sub ected to the edge-runner treatment together with the requisite coal, the resulting briquettes will be too dense and will tend to split up during the subsequent coking (by the method heretofore indicated) unless the coking is carried out at an uneconomically slow rate.

I have found that coked agglomerates of improved physical properties can be secured by sintering the roasted zinciferous flotation Accordingly, my present invention involves sintering the very finely divided zinciferous material as a preparatory step to the production of coked agglomerates therefrom. Where the finely divided zinciferous material is a zinc flotation concentrate, it is first roasted. The roasting operation may beconductedv in any appropriate manner as, for example, in a furnace of the multiple hearth type, in a Hegeler furnace, or the like. Preferably, the roasting is carried on until the sulfur content of thecon fur, or a combination of both, should be as-" sociated or admixed with the roasted concentrate. Where the sulfur content of the roasted concentrate is around 23%, I preferably mix therewith from 4 to 12% of anthracite coal dust, coke breeze, or the like, to supply the necessary fuel for the sintering operation.

The roasted concentrate and associated combustible agent is then subjected to a sintering operation preferably by blast roasting. This operation I prefer to conduct on a Dwight-Lloyd sintering machine of the down-draft type. The sintering temperature is sufficiently high to break down the metal sulfates present in the concentrate, such, for example, as magnesium sulfate, calcium .sulfate, zinc sulfate, etc. These sulfates are reactive towards the carbonaceous material of the agglomerate mixture during coking and therefore deleteriously affect the coking operation. Accordingly, their elimination in the course of the sintering operation is one of the advantages of the invention.

If the roasted zinc flotation concentrate has been sintered only once, the sinter cake may be fed directly to the edge-runner without preliminary crushing. In case the material has been given a double sintering treatment, that is sintered twice, it is advantageous, before feeding it to the edge-runner, to crush it to approximately the following screen analysis:

Screen analysis of twice sintered roasted concentrate after once through a set of rolls Per cent Per cent on through 8 mesh screen 1. 2 98. 8 14 mesh screen 8. 3' 90. 5 20 mesh screen... 8. 2 82. 3 28 mesh screen... 8. 5 73. 8 35 mesh screen... 11. 9 61. 9 48 mesh screen... 10. 3 51. 6 65 mesh screen-.. 13. 3 38. 3 mesh screen... 5. 0 33. 3 100 mesh screen-. 7. 1 26. 2 150 mesh screen 8. 3 17. 9 200 mesh screen. 5. 7 12. 2

The porous ore particles produced by sintering are blended by the edge-runner with the coal in such a manner that briquettes formed from the mixture are not so dense as to split up during the subse uent coking operation, and yet the contact etween the ore and coal is sufficiently intimate to prevent disintegration of the briquettes during the subsequent distillation or reduction step.

The particle size of the mixture of ore and coal after treatment in the edge-runner is also of importance- The chased material should have aparticle size that is consistent with the formationof anagglomerate of optnnum or at least adequate coking and residue strengths. Thus, if the particle size of the chased material is too fine, the agglomerates will be relatively dense andzcompact. During the subsequent coking, the-volatile constltuents will tend to split up the agglomerates when-they are volatilized." In order to drive the volatile hydrocarbons from the agglomerate, considerable pressure will be set up within the agglomerate. Stresses and strains take place within and the agglomerate will usually rupture and disintegrate. Such a result works away from porosity of the charge, is therefore harmful,and should be avoided. i

On the other hand, if the particle size'of the chased material is toocoarse, the agglomerates will not be as dense and compact as they should be to insure adequate, let alone optimum, coking and residue strengths. In other words, there appears to be a happy mean of particle size for the chased material which is compatible with the formation of an- I agglomerate that will have adequate or op- .timum coking and residue strengths.

The following table gives data illustrating the proper size of a chased mix of 60% sintered roasted zinc flotation concentrate, 20% free-flowing coal of bituminous rank mined series in. the Preston-Taylor Mining. District, Taylor County, West Virginia, and 20% anthracite dust coal: 7

Screen analysis of chased Per cent on t Very satisfactory agglomeratesv have also been obtained with the following mixtures:

I. 50% sintered roasted zinc flotation concentrate 33% Preston-Taylor coal 417% anthracite dustcoal 54% sintered roasted zinc flotation concentrate a 28% Preston-Taylor coal 18% anthracite dust coal In general, the mixture may vary within .the following limits: i

Sinteredroasted zinc 05- 50-60% flotation concentrate of the agglomerate mixture insures such vof the zinciferous and carbonaceous mateor optimum from the Pittsburg seam of the Monongahela 'Free-flowing coal, such as Preston-Taylor 35-20% Anthracite dust coal 15-20% The graded particle size of the ingredients density of the mixture as will give adequate if not maximum strength of the coked agglomerate. This graded, particle size furthermore promotes the desired intimate mixture 0 rials and insures better compacting of these materials by briquetting, extrusion and like operations. Where the agglomerate mixture is too dense, cracking or rupturing of the agglomerates is liable to take placeduring the coking operation, and if the mixture is not dense enough the coked agglomerates are deficient in strength, particularly in residuestrength during the subsequent reduction operation. The graded particle sizes herein contemplated dproduce a mixture of adequate sired ultimate properties of the coked agglomerates.

The chased material is suitably agglomerated by briquetting, extrusion, or the like. In this connection, it may be advisable to use a bimder in appropriate amounts. The agglomerates may be formed in various sizes and shapes and with varying degrees of densit and compactness. Such factors as size, s a e and density of the agglomerates.

will be argely governed by the particular I coking and reduction operations to be employed. Other conditions being equal, the lon r the column of agglomerates placed in a co and in a reduction retort, the stronger sho d be the agglomerates near the bot:

tom of the column to "avoid breaking downby compressive forces. Any suitable a paratus may be employed for-both the co in and reduction operations. In the presen preferred practice of the invention, the agglomerates are coked bydirect heatmg and the coked xagglomerates' are then smelted for the recovery of their zinc content in an externally heated vertical retort.

I claim I .1. The method of preparing coke agglomerates of finely divided zinciferous material and carbonaceous material which comprises subjecting. the zinciferous material to a sintering operation, intimately mixing the sin-'.

teredzinciferous material with the carbonaceous material, forming the resulting mixture into agglomerates, and subjecting the agglomeratesto a coking operation.

2. The method of preparing coked agglomerates of roasted zinc flotation concentrates and carbonaceous material which comprises subjecting the concentrate to a 'sintering operation, intimately mixing the sintered concentrate with the carbonaceous material, formensity with respect to the deing the resulting mixture by pressure into 1 agglomerates, and subjecting the agglomerates to a coking operation.

3. The method of preparing coked agglomerates of finely divided zinciferous material and carbonaceous material which comprises subjecting the zinciferous material to a sintering operation, intimately mixing the sintered zinciferous material with the carbothe sintered zinciferous m'aterial adapted to provide agglomerates that willnot swell and disintegrate when heated, and subjecting the .ag lomerates to a coking o eration. testimony whereof I a x mggsi EARL HAMLIN U ature. 1. CE.

and carbonaceous material which comprises subjecting the zinciferous material to a sintering operation, intimately mixing the sintered zinciferous material with the carbonaceous material, the carbonaceous material being made up of a substantial proportion of a free-flowing coal of good coking quality, forming the resulting mixture by pressure into agglomerates, and subjecting the agglomerates to a coking operation.

5. The method of preparing coked agglom-' erates of finely divided zinciferous material and carbonaceous material which comprises subjecting the zinciferous material to a sintering operation, intimately mixing the sintered zinciferous material with the carbonaceous material, the carbonaceous material being made up of a substantial proportion of a free-flowing coal of good coking quality and at least of both the sintered zinciferous material and the carbonaceous material being of a graded particle size between 14 and 100 mesh, forming the resulting mixture by pressure into ag'glomerates, and subjecting the agglomerates to a coking operation. a

6. The method of preparing coked agglomerates of roasted zinc flotation concentrates and carbonaceous material which comprises subjecting the concentrate to a sintering operation, intimately mixing the sintered concentrate. with the carbonaceous material, the

carbonaceous material being made up of about equal arts by weig'ht of a free-flowing coal of goo coking quality and an non-coka 111%(2filb0118080118 material and at least 50% of 'oth the sintered concentrate and the carbonaceous material being of a graded particle size between 14 and 100 mesh, forming the resulting mixture by pressure into agglomerates, and subjecting the agglomerates to a coking operation.

7 The method of preparing coked agglomerates of finely divided zinciferous material and carbonaceous material which-comprises agglomerating an intimate admixture of sintered zinciferous materialand coal, said coal consisting of a blende of free-flowing coking coal and non-coking coal in conjunction with