US1758188A - Method of roasting fines - Google Patents

Description

May 13, 1930. H. J. coRDY ET AL METHOD OF yROASTING FINES Filed Jan. 50, 1928` INVBNTORS H6075( J. Co rc/y W/'Y/ am J. 504g qyne IgA/# ATTOR mnixiiiiimlimv mim-1min@ Patented May 13, 1930 A UNITED STATES PATENT oFFlcr;

HENRY J. CORDY AND WILLIAM J; BURGOYNE, 0F SULPHIDE, ONTARIO, CANADA,

ASSIGNOBS TO GENERAL CHEMICAL COMPANY, 0F NEW YORK, N. Y., A CORPORA- TION 0F NEW YORK METHOD 0F ROASTIN' FINES Application ma January so, 192s. serial Nolasolc.

Our invention relates to the roasting of finely divided sulphide ores, flotation concentrates and the like, and more particularly to a method of roasting finely divided pyrites ores or flotation concentrates, to thoroughly desulfurize the same and to produce sulfur dioxide for use in the manufacture of sulfuric acid.

The present 'practice in pyrites fines roasting generally involves the use of mechanically operated multiple hearth constructions, such, for example, as the well known MacDougall, Herreshotf, and Wedge burners, and while these burners provide a very eii'ective roasting of the ines, their complicated construction and operation involves considerable initial and maintenance expense. As `distinguished from the bed roasting operation of these burners, it has been suggested to roast the iines while in gaseous suspension, wherein the fines are either injected v into a roasting chamber in suspension in the oxidizing gas, or are simply showered downwardlyinto the roasting chamber wherein they encounter cross or counter currents of the suspending gas.

This suspensionroasting is best applicable when the ines are in a very finely divided state, e. g. as flotation concentrates, and it presents the notable advantage over the mechanical multiple hearth operation of considerablyv lowering the cost of production, by reason of the elimination of the involved and expensive rabbling and other apparatus which distinguishes the construction and operation of the mechanical burners. In the practice of this suspension roasting, however, and .particularly as applied to roasting pyritic fines, difiiculties of some moment are presented which must be Overcome before the obvious theoretical advantages of this type of opera,- tion are practically available.

The most serious and perplexing diiiculty encountered in the suspension roasting of pyrites fines is the objectionable formation of vaccretions or scar onthe walls of the roasting chamber during the roasting operation. These scar masses assume imposing propor- 4tions with disconcerting rapldity, and in a relatively short time masses weighing several hundred pounds are commonly formed. Unless these masses are' removed, obstruction of the roasting passage willresult and the operation will be otherwise seriously hindered. The scar masses may be manually broken away, or barred down, from the walls periodically, but the frequency with which this operation must be repeated to keep the scar format-ion within reasonablel limits results in inordinate interruption of the operation, and, in addition, the wear and tear on the apparatus occasioned by the heavily falling masses raises even more serious objection to this manner of removal. Moreover, the problem of/incomplete desulphurization is not solved thereby, for the considerable amounts of undesulphurized material which in its transition from FeS2 to FezOs which would roiighly correspond to the oxidation of one atom of the sulphur in the FeS2, the partially desulphurized material sinters much more readily than at prior or subsequent stages in the desulphurization. This may be explained either on the basis that FeS is the major form existing at this particular stage and that the FeS per se sinters much more readily than any of the other transition or final products, or possibly that there is'a formation of a eutectic of FeS and Fe2O3.

Regardless of the exact reasons for this behavior, however, the results of our determinations have 'clearly indicated that the solution of this problem rests in so controlauv ling the operation that the pyrites being` roasted will not be permitted to contact with in the transitory sticky condition noted.

- constructed work holes 14,15 and 16 coveredl We have experimented with various methods of roasting the pyrites finesin suspension, in an endeavor to find a means of overcoming the effect of this transitorlyl' sintering condition, and we have found t at by injecting a quantity of the oxidizing as: adjacent the walls of the roasting cham er in the upper part thereof, that scarring 'of the chamber.. walls is eliminated, very thorough desulphurization of the nes is obtained, and concentrations of sulfur dioxide are obtainable which are very, suitable-for use in the manufacture of sulphuric acid. This action appears to be due to the interposition of a supplemental portion or blanket of the oxidizing 'gas between the walls of the roasting chamber and the main suspension of thev burning pyrites when the latter is in the state conducive to scar formation.

In the-following specification we have describedin detail1 a specific manner in which the invention may be applied, and one embodiment of the apparatus utilizable therein is shown in the accompanying drawing in which:

yFigure 1.` .isA a sectional elevation of a pyrites burner for caryingout oui` invention.

Figure 2 is a plan view of a portion of the feeding mechanlsm for the same taken along the line 2-2, Figure 1, and

Figure 3 is a'plan view of another portion of the vfeeding mechanism taken along the line 3 3', Figure 1.

Referring to the drawing, and in particular to Figure 1, reference numeral 4 indicates a shaft burner comprisin a shell 5, constructed of a suitable re ractorymaterial such as fire brick or the like, which defines a roasting chamber 6 of cylindrical shape throughout the major portion of its length. A casin 7 .of steel or similar material is provided a out the sides of the shell 5 to suitably reinforce the same. Chamber 6 is provided, with a feed inlet 8 inthe center of the burner crown 9; a trough-like cinder pit 11, constituting the bottom of the chamber, which extends diametrically thereacross and is open at the base throughout its length to provide an elongated cinder outlet 12; and

a lateral gas outlet 13 in the wall of the chamber just above the cinder pit 11. Suitably by detachable external closures 17, 18 and 19 are also provided to afford access to the interior of the roasting chamber.

Terminating in the feed inlet 8 is afeed -mechanism 20 for introducing the fines and oxidizing gas into the roasting chamber.

This feed mechanism is constructed as .fol-v lows: A charging hopper 21, into which the finely divided material to be roasted is introduced in any suitable manner, is mounted above andterminates in a tubular charging conduit 22, which conduit discharges mto a cross 23. This cross comprises a lateral arm 24 to which is bolteda cap 25 provided with ,a suitable bore for the accommodation of conduit 22; a downwardly extending arm 26 above which the discharging end of thevconduit 22 terminates; a lateral arm 27 towhich' is bolted-a cap 28 having a bearing-29; and an .upwaldly extending arm 31 havlng a ca 32 detachably attached thereto in any wel knownmanner whereby access may be readily had to the interior of the cross. Within the conduit 22 is a helicoid' conveyor 33 whose shaft 34 is mounted for rotation in bearing 29 in c ap- 28 and bearing 35 provided in a plate 36 closing olie end ofthe conduit 22.

A cylindrical coupling 37 having `topland cured at its top flange' 38 to the fiangedbot:

. tom 41 of the arm 26 of lcossl23,and retained intermediate the joined flanges 38 and 441 is a baffle plate 42 which extends completely across the passage providedby coupling 37. Baffle plate 42 is-provided with a central orifice 43,'and below and in alignment with said orifice is a distributing cone 44 supported by a cross beam 45 which extends diametrically across and is boltedor `otherwise secured to the coupling 37 in any wellknown manner. A rod 46 depends from the cone 44, extending through a bore provided therefor in the cross beam 45,- and vvthis rod 56 of a cylindrical sleeve 57 which is set snugly into the feed inlet 8 and is supported therein by means of av circumferentlal projection 58 which abuts againstthe surface of the crown 9.

A terminal cylinder 59 is suspended by means of its top flange 59 gripped between the joined flanges 54 and 50, and terminates at a point below the base of the distributing cone 47 said cylinder fgrming a substantial continuation of the vertical passage provided by the su er- jacent couplings 48, 37 and the arm 26 o cross 23. I I

A cylindrical gas-distributing sleeve 60, havinga top flange 61 is carried onathe headed ends 62 of a number of-suspension rods -63 extending through said flange, atleast `terminates at its lower end in a larger dislas tained on the latter by means of adjustable nuts 64 on their threaded ends 65, whereby the sleeve 60 may be adjusted vertically of the cylinder 59 and the inlet sleeve 57. The sleeve 60 extends around the lower portion of the cylinder 59 in uniform radially'spaced rela,- t1on thereto whereb a narrow annular as passage 66 is provi( ed between the cylin er and the sleeve, and the clearance thereby presented will permit the sleeve to be readily adjusted vertically of the cylinder.Y The sleeve 60 is also posltioned in uniform radially spaced relation to a` portion of the casing 53 and the inlet sleeve 57, which members surround sleeve 60, and an additional annula1\ gas passage 67 is thereby provided between the sleeve 60 and these surrounding members. The annular mouth 68 of this latter passage 67 is defined by the rim of the flanged bottom 69 of sleeve 60 and the adjoining' inner surface of the inlet sleeve 57, and by suitable vertical adjustment of the sleeve 60 by means of the suspension rods 63 the size ofthe mouth 68 may be varied as desired, whereby a great` er or less amount of oxidizing gas may be admitted therethrough into the roasting chamv ber from the passage 67.

As shown in Figs. l and 3, a series of suitably spaced apertures 71 for entrance of the oxidizing gas is punched inwardly in the wall of the sleeve at points therein below the bottom of cylinder 59, all of which apertures give access to the interior of the sleeve in substantially the same general direction as re-` frards the circumference of the sleeve. paced lower down in the wall of the sleeve is another seriesof similar inwardlypunched apertures v72 which give access to the interior of the sleeve in a direction substantially opposite to that of the upper series. A tangential extension 73 (Fig. 2) projects from the casing 53, and to the flanged end 74 of said extension is bolted the flanged end 75 of a pipe 76 leading from a suitable fan blower (not shown), whereby the oxidizing gas may be blown into the feed mechanism.

Beneath the cinder outlet 12 and extending in diametrical alignment therewith is a discharge conduit 7 7 -in which is mounted in any suitable fashion a helicoid conveyor 78 for continuously removing the cinder from theburner. A grate 79 1s mounted above the cinder outlet 12 leading into the discharge conduit, which grate may be supported at its sides by lugs 80 on the inclined walls 81 of the trough-like cinder pit 11, or in any other suitable fashion.A By means of the grate 79 pieces of cinder too large to be conveniently handled by the conveyor may be periodically broken up by a workman to permit their passage through the grate. Access to the grate for the operation noted is adorded by the work hole 14.

., The gas outlet 13 leadsto a dust chamber c .82 of any well-known type, part of which is well-known manner.

chambers, and this may be accomplished by maintaining a suitably reduced pressure at the outlet for the dust-free gases from the dust chambers (not shown), by any Wellknown means such as a fan blower.

The operation of ourinvention is substantially as follows: The furnace is first strongly preheated, for example by means ofone or more oil burners inserted. through the work hole 14, until a temperature is obtained in the chamber 6 substantially above the ignition point of the iron pyrites, for example, about 850 C. During the preheating operation work holes 15 and 16 are uncovered to provide flues for the escape of the products of combustion.

Finely divided iron pyrites, which has been dried until the moisture is not greater than 0.3% and preferably between 11% and .2%, and of a particle size such that 100% will pass a 6.0 mesh (to the inch) screen, is then fed into the hopper 21, in any suitable manner. From the hopper the lines are substantially continuously supplied to the helicoid conveyor 33 within the charge conduit 22, by means of which they are delivered into the passage in the arm 26 of cross 23. Some of the p rites fines will pass directly through the ori ce 43 in the' bafiie plate 42, and the remainder will pile up around the orifice until a funnel-like mass cffines is formed with the orifice 43 as its mouth, which mass will aid in directing subsequent portions of fines to the orifice and onto the distributing cone 44. Passing over the cone 44, the fines will be directed onto the sides of the funnel 52, and thence will proceed into the terminal cylinder 59, `at the lower portion of which they will be spread out by the distributing cone 47 into a somewhat 'cylindrical-shaped sheet, in which form they -the pipe 76 and tangentially into the space between the casing 53 and theV cylinder 59 (Figures-1 andv 2). The amount of air introduced will depend upon the amount of sulfur in the fines to be desulphurized, the concentration of SO2 'desired in the exit gases, and other factors evident to one skilled in the art, and the regulation of the air supply may be accomplished in any suitable and In practice, determination of the SO2 content of the exit gases and the character of the cinderwill usually indicate the necessary regulation of the air supply. to provide the desired results, the lines being supplied at a substantially regular rate. The pressure under which the air ly into the roasting chamber 6 throu h the mouth 68 of passage 67. ,The distri uting sleeve 60 should be so adjusted by means of its suspension rods 63 that the size of the mouth 68 is such that only suiicient air is admitted therethrough to prevent scar formation on the walls of the roasting chamber. This can be determined by varying the size of the mouth and observing the effect upon the chamber walls through one of the work holes'l or 16. The amount of scar inhibitjas ing air necessary is usually a minor proportion of the total amount of air admitted. The sheet of pyrites fines showering out of the terminal cylinder 59 will be swept up in the turbulent air pouring intothe sleeve 60 and the substantial suspension of the intimately mixed air and fines; obtained thereby, will pass on into the hot roasting chamber 6.

Upon entering the preheated chamber thev suspension of fines and air will be ignited and oxidation will thereafter proceed at a very rapid -rate.

The oxidation of the iron pyrites is a strongly exothermic reaction, to the extent that it is substantially self-sustaining, and other than the necessity of initiating the reaction, for example, by preheating the furnace to a suitable temperature above the ignition point of the pyrites, no auxiliary heat is required. y In operation the temperature will be quite high throughout the chamber 6 5 in the production of an approximately 10% SO2 gas, from a typical iron pyrites ore, for example, the temperature in the roasting chamber was in the neighborhood of 1000 C.

Upon the entry of the turbulent gaseous suspension into the enlarged space presented by the roasting chamber, expansion of the suspension takes place, and this expansion is enhanced by the-large amount'of heat sup-u chamber.

rnvmrse lin thetransitoryfsticky condition hereinbefore discussed would under ordinary circumstances tend to adhere to the walls upon contactin therewith and rapidly build up accretions-t ereon.

The portion of air, however, lwhich enters .the roasting chamber throu h the annular mouth 68, slmultaneously wit the introduction of the main body of the suspension from the sleeve 60 serves to inhibit throughout the.

operation the usually inescapable scar formation.-.

The initial stages of the roasting o eration are the mostintense andnormally ta e place 'in the upper part of the roasting chamben It 1s'in this upper part of the chamber that the tendency toward scar formation appears to be most marked, and it seems robable that as the proportion of the FezO, increases, the tendency toward scarring decreases. On that basis it would seem that the provision of the air blanket between the walls of the chamber and the burning suspension need only be conlined to the upper part of the chamber in order to prevent scar'formation, and itv may be that such is theI case in the operation of the present method as noted, although the particular path of the air blanket is more ditlicult to trace the greater its penetration into the furnace. On the other hand it is quite possible that the gaseous sus ension of fines could be introduced under suc pressure, forp example, that t-heV scar forming stage would occur at a point considerably lower down in the roasting chamber,in which event it would be necessary to run the air blanket substantially throughout the length of the In view of these considerations it is essential primarily that the air blanket be interposed between the walls of the chamber and vertically the position of the flanged sleeve 60, and thereby the volume and direction of the air blanket admitted through the mouth 68, the formation of scar under such variations of the roasting operation as are involved in ordinaryiindustrial practice can be eliminated. a

Whether the scar inhibiting action of the air blanket is due Vto an oxidizing effect, whereby the particles in the sticky stage are oxidized past that stage prior to contacting with the chamber walls, or to a physical effect involving entrainment of the particles, whereby they are prevented from contacting with the walls, or toa combination of both effects, is practically indeterminate and not particularly material. Regardless of the exact explanation it is certaln that this auxildenced by the fact that by suitably varying nasales.

iary portion of the oxidizing gas is inter-I posed in the upper ortion of the furnace between the walls of t e chamber-and the burning fines while they are in a state conducive to the formation of scar on the walls.

The length of the roasting chamber and the speed of introduction and travel of the fines and airl should be such that a thorough desulphurization is obtained in the passage through the roasting chamber, as is obvious to one skilled in the art.

By conducting the operation in accordance with the foregoing principles, the nes in suspension are quite thoroughly desulphurized by the time the cinder and as outlets are reached, and by regulation o the pres.- sure as hereinbefore noted, the major portion of the desulfurized particles, mainly in the form of iron oxide collects in the cinder pit l1 whence it is conducted away by the helicoid conveyor 78. The gases containing the SO2 passin into the dust chambers 82 carry entrained t erein an appreciable portion of the finest particles, i. e. dust, which dust,`con

sisting mainly of iron oxide is collected in the dust chambers, and the dust-free gases containing the SO2 are drawn from the chamber and conducted away for utilization in the production of sulphuric acid.

The roasting of pyritic fines in suspension according to our invention provides an operation which, in practice, presents numerous advantages over the various methods of burning such fines'heretofore suggested.

Its most important accomplishment is the removal of the obstacle to eiiicient practical operation presented by the formation of the o jectiona le scar. .The sulde fines are, moreover, very thoroughly desulphurized, a very desirable feature from an eiciency standpoint; this very thorough desulphurization being also ascribable in the main to the elimination of the scar formation which rites ore and flotation concentrates of the same are characterized by a similar action, and the same is also trueof pyrrhotite although to a less marked degree.

We claim as our invention:

1. The method of roasting a finely dividedv sulphide ore which comprises forming a suspension of said ore in an oxidizing gas, and

burning said suspended ore in a roastin chamber while maintaining a ortion of sai gas between the walls ofsai chamber and said burning ore while the latter isin a state conducive to scar formation on said walls, whereby said scar formation is avoided.

2. The method of roasting a finely divided sulfide ore which comprises forming a suspension of said ore in an oxidizing gas, '1ntroducing said suspension into a roasting chamber at a temperature sufficient to ignite said suspended ore and to permit substantial f complet-.ion .of the desulfurization thereof, and maintaining a supplemental portion of said gas between the walls of said chamber and said burning ore while the latter is in a state conducive to scar formation on said walls. e f

3. The method of roasting a finely divided sulfide ore which comprises dividing a body of oxidizing gas into two portions, suspending said finely divided ore in one of said portions, introducing said suspension into a roasting chamber at a temperature sufficient to cause ignition of said ore, and introducing the other portion of said oxidizing gas into said chamber between the walls thereof and the burning ore in suspension when in a state conducive to scar formation on said walls.

p 4. The method of roasting a finely divided sulfide ore which comprises forming a suspension of said ore in an oxidizing gas, burning said suspended ore in a chamber, and maintaining a portion of said gas between the walls of said chamber and said burning ore toa point in said chamber where sufficient oxidation of said or'e has taken place to inhibit the subsequent formation of scar on said walls.

5. The method of roasting a finely divided sulfideV ore which comprises contacting said inel divided ore with a turbulent portion of a bo y of air whereby said ore is substantially suspended in said portion, passing said suspended ore into a roastingchamber, igniting said suspended ore therein, and simultaneously with the resultant combustion of said ore passing another portion of said body of air between the walls of said chamber and that portion of theburnin'g ore which vis in a state conducive to the formation of scar on said walls. l.

6. The method of roastin a finely divided sulfide ore which comprises orming a suspension of said ore in air, passing said ore into a roasting chamber at a' temperature at which self sustaining combustion ofthe same will" be initiated and maintained, maintaining a blanket of air between the walls of said chamber and said burning ore while in a state conducive to scar formation on said walls, retaining said suspension in said roasting chamber a 'sufficient period toresult in substantial desulphurization of the sulfide ore, and separating the desulfurized ore from the gases.

. 7. The method of roastin a iinely divided sulfide ore which com rises ringin said ore in contact with a tur ulent bodyv o air ata temperature below theignition point of said ore to forml a substantial suspension of the ore in the air, passing said suspension into a roasting chamber at a temperature above the i 'tion point of said' ore whereby combustion of said suspended ore will be initiated, and simultaneousl passing a blanket of air completely aroun and in contact with said suspension and between said burning suspension and the walls of said chamber, said air blanket being in suiicient quantity and of such extent of intervening contact with said. suspension and said walls to inhibit the formation of scar on said walls by portions of said burning ore throughout the passageof said Ore through said chamber. 8. The method of roasting a finely divided sulide ore which comprises Iforming a sus- -pension of said ore in an oxidizing gas, introducing said suspension into' a roasting chamber at a temperaturesuicient' to ignite said suspended ore,vand enveloping said suspension at the point of introduction into said chamber in a supplemental portion of said oxidizing gas, whereby scar formation on the walls of said chamber is avoided. 9. The method of roasting a finely divided sulfide ore which comprises forming a suspension of said ore in an oxidizing gas, introducing said sus ension hinto the upper vpart of a roasting cham er at a temperature above the ignition point of said sus ended ore, en-

veloping said. suspension at t e point of in-` troduction of said suspension into said chamber in a Vdownwardly moving supplemental portion of said oxidizing as, and passing saidburning ore downwar y through said chamber until substantial desulphurization of said ore is obtained.

10. The method of roasting a finely divided sulfide ore which comprises forming a suslpension of said ore in an oxidizing gas, in-

troducing said suspension into a roasting chamber at the upper part thereof, simultaneously introducing a supplemental portion of Y said oxidizing a gas adjacent the W ls of said chamber at t e upperpart thereof, igniting said suspended ore substantially'upon its in-. troduction, and lpassing said burning ore downwardly through said chamber until the desired degree of desulphurization is obtained. 'p

11. The method of roasting a finely divided formation of scar on sai insens sulfide ore which comprises forming asuspension of said ore .in an oxidizing gas, introducing said suspension into a roasting chamber at a temperature suicient to ignite said susppnded ore, and enveloping said sus ension at t e point of introduction into said c amber in a supplemental portion of gas, whereby scar formation on the walls of said chamber is avoided'. f/

13. The method of roasting a nely divided sulfide ore which comprises forming a suspension of said ore in an oxidizing gas, burning said suspended ore iii a chamber, maintainin an enve ope of. gas between the walls of said chamber and said burning ore to a point'in the chamber where suicient oxidation of'said ore has taken place to cprevent subsequent walls.V

In testimony whereof, we aix our lsignatures.

HENRY J. CORDY. WILLIAM J BURGOYNE.

sulfide o re which comprises forming a susy ension of said ore in an oxidizing gas, and

urning said suspended ore in a roasting chamber while maintaining a"layer of gas vbetween the walls of said chamber and said burning ore while the latter is in a state conducive to scar formation onsaid walls, whereby 'said scar formation is avoided.

12. The method of roasting a finely divided

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