US2056564A - Apparatus for roasting ores - Google Patents

Description

@et 6, 1936. B, M CARTER 2,056,564

` APPARATUS FOR ROASTING GRES Original Filed Aug. 1l, 1950 2 Sheets-Sheet 1 INVENTOR JW. Carter v ATTORNEY Oct. 6, 1936. B M, CARTER v 2,056,564

APPARATUS FOR ROASTING ORES Original Filed Aug. ll, 1950 2 Sheets-Sheet 2 /dZ M3 INVENTOR Patented Oct. 6, 19536 PATENT 1 OFFICE APPARATUS FOR .ROASTING ORES Bernard M. Carter, Montclair, N. J., assigner to General Chemical Company, New York, N. Y., a corporation of New York Application August 11, 1930, serial No. 414,457

a Renewed June 9, 1934 1o claims. (01.' 26e-z8) This invention relates to an apparatus for roasting finely divided sulfide ores, flotation-concentrates and the'like, and more particularly to apparatus for roasting finely divided pyrites ores or` 5 otation concentrates, for the purpose of thoroughly desulfurizing the same and producing sulfur dioxide for `use in the manufacture of sulfuric y acid.

The present practice in pyrites Afines roasting generally involves the use of mechanically operated multiple hearth constructions, such, for example, as the well known MacDougall, Herreshoi, and Wedge burners, and while these burners provide a very eective roastingl of the fines, their complicated construction a-nd operation ins volve' considerable initial and maintenance ex pense. l

As distinguished lfrom the bed roasting operation of these burners, it has been suggested 20 to roast the iines while in gaseous suspension,

wherein the fines are either injected into a roasting chamber in suspension in an oxidizing gas, or are simply showered downwardly into the roasting chamber wherein they encounter cross or counter currents of the suspending gas.

This suspension roasting is best applicable when the ilnes are in a very-iinely divided state,v

y e. g. as notation concentrates, and presents the notable advantage over the mechanical multiple hearth operation of considerably lowering the cost of production, by reason of the elimination of the involved and expensive rabblingv and other apparatus which `distinguishes the construction and operation Aof the mechanical burners. In the practiceof this suspension roasting, however, and particularly as applied to roasting pyritie fines, difficulties of some moment are presented which must be overcomeI before the theoretical advantages of this type of operation are practi- 40 rcally available. r' As indicatedin U.v S. Patent No. 1,758,188, datedA May 13, 1930, toH. J. Cordy and W. J. Burgoyne, a. serious diiiiculty encountered in the suspension roasting of pyrites iines is-the objectionable y formation of accretions or scar on the walls lof the roasting chamber during the roasting operation. These scar masses rapidly assume imposing proportions, and in a relatively short time, masses weighing several hundred pounds are commonly formed. Unless these masses are removed, ob'struction of the roasting passage will result,I and the operation will be otherwise seriously hindered. The accretions may be manually broken away, or lbarred down from the walls periodically, but the frequency with which this' operation must be repeatedv to keep thescar formationwithin reasonable limits results in too frequent interruption of the operation and, in addition, the Wear and tear on the apparatus occasioned by the heavily falling masses raises 5 eveninore serious objection to this manner of removal. Moreover, the problem of incomplete desulphurization is not solved thereby for considerable amounts of undesulphurized material conned within the accretions pass l.oil inthe cinder 10 substantially unaiected.

The scarring problem noted has been previously extensively investigated and, while the exact reason for its occurrence is rather diicult to determine, it has appeared to be more or less ascribable to the pronounced tendency which sulde iines, particularlyiron pyrites, exhibits to sinters at a particular stage of its' desulphurization, at vwhich stage it readily adheres to the inner walls ofthe roasting chamber and builds up accretions thereon. Investigation of atypical iron-pyrites ore in this relation appeared to ind-icate that at a `point in its transition from Fe'Sz to FezOa which would roughly correspond to the oxidation of 'one atom of the sulphur in the'FeSz, the par- 25 tially de'sulphurized material sinters much more readily than at prior or subsequent stages in the desulphurization. This lmay perhaps be `explained either on the basis-that FeS is the major form existing at this particular stage, and that the FeSper sesinters much more readily than any of the other transition ornal products, or possibly that there is a formation of a eutectic [of FeS and FezOa. i

Various methods of roasting the pyrites nes in suspension have been heretofore investigated, in an endeavor to find a means of overcoming the eiect of this transitory sintering condition. It has previously been found (see U'. S'. Patent No. 1,758,188, )referred to above) that by injecting a 40 -quantity of the oxidizing gas adjacent the walls of theroasting chamber inthe upper part thereof, thatscarring of the chamber walls is largely eliminated, thorough desulphurization of the nes is obtained, and concentrationsl of sulfur dioxide'are obtainable whichare Very suitable for use in the manufacture of sulphuric acid.

c'I'he present invention relates generally tov methods of suspension roasting as outlined in the foregoingparagraphs. The general aim of4 50 the invention is directed toward the improvement of such processes with the particular object in view of increasing the ilexibility of operation oi.' such methods, and increasing the eiciency therelof. Ihe invention further contemplates the provision of improvements in apparatus for suspension roasting of sulide nes and broadly lncludes general improvements in several items of furnace construction, ore feed mechanism, and means for economically regulating the temperature of the combustion supporting gas in such a manner as to facilitate efcient roasting in the furnace or reaction chamber.

rhe invention accordingly comprises the several steps of the `process and the relation of one or more of such steps with respect to each of the others, and the apparatus embodying :features of construction, combination of elements and arrangements of parts which are adapted to carry out the' improved process, together with such other features of novelty which will appear from 'the following description taken in consideration with the accompanying drawings.

In the drawings- Fig. l is an elevation; mostly in section, of a preferred form of roasting furnace embodying the present invention; v f

Fig. 2 is an enlarged fragmental horizontal section on the line 2-2 of Figs. l and 3; f

Fig. 3 is a vertical section on the line 3--3 of Fig. 2;

Fig. 4 is a vertical section of the feed mechanism;

Fig. 5 is a horizontal section on the line 5 5 of Fig. 4;` l

Referring to the drawings, and particularly to Fig. 1, the reference numeral i8 indicates a shaft burner comprising a shell generally indicated at il, constructed of some suitable refractory material such as firebrick or the like,l which defines a roasting or reaction chamber I2 of cylindrical cross-section throughout the majorportion of its length. A casing I3 of steel or similar material about the sides of the shell II serves to 20 in the center of the burner crown 2|.

`top of the steel shell I3 is closed oi by the cover reinforce the same. It will be apparent that the height of the burner is several times greater than its cross-sectional dimension. For convenience in construction, the steel shell I3 may be made up of several cylindrical sections I4 suitably secured together at their contiguous edges byvbolts orrivets passing through flanges I5. The shaft burner as a whole .rests on a suitably constructedplatform I6 elevated by the supports I1 sufficiently vto permit the operation of the cinder cars I8 beneath the outlets of the'cinder pit of the burner and the dust chamber.

The chamber i2 is provided with a feed inlet The hole24 is shown. It Awill be understood that any number of such holes may be employed, ar-

vranged in any manner necessary or desirable to facilitate the proper operation of the burner.

.The lowerend of the roasting chamber I2, as

indicated on the drawings, is constructed Vto pro- 'vide a trough-like cinder pit 26, constituting the bottom of the chamber.v The cinder pit extends diametrically across the burner and terminates at the lower end in any suitable number of cinder outlets 21. The upper end of each outlet 21 is covered by a grate, not shown, which serves to prevent the passage of large chunks of cinder through the outlets 21. The lower end of the burner is equipped with work holes indicated at 28 and 29. While the burner is vin operation the Work hole 28 is closed off by the sliding door 3U constructed of a suitable steel frame enclosing a rebrick panel which, when the door is closed as shown in Fig. l, is directly in line with the opening t8. The door 38 is vertically movable in a frame 3i, but normally rests in lthe position shown in Fig. l. However, the closure may readily be moved upwardly in the frame 3I by movement of the counterweight 32 connected to the door 3D 4through thel cable 33 running over suitably arranged pulleys 554. Work hole 28 is generally for the purpose of inserting oil burners into' the chamber i2 to preheat the furnace before the roasting operation is initiated.

The work hole 28 is essentially for the purpose of affording access to the bottom of the cinder pit 26, so that any large accretions which may form on the walls of the roasting chamber and iail into the pit, may be broken up by sledges by workmen to such size as to permit passage through the grates covering the upper ends of theoutlets 21. The door 38 is constructed similarly to the door 38, and is arranged to slide vertically in the frame 39., The door 38 is counterbalanced by the weight 40 connected to the door 38 by the cable 4I passing over the pulleys 42.

it will be apparent from the drawings that the work hole 29 and the door 38 are arranged on the far side of the burner shaft. Any number of work holes 28 and Vsuitably arranged about the lower circumference of the burner may be employed as desired.

The main gas outlet 44 is constructed in the wall of the burner immediately above the upper p edge of the sloping walls forming the cincler pit 26. The outlet 44 is of substantial cross-sectional dimensions, and serves to connect the roasting chamber l2 with the cinder pocket indicated at 45. The pocket 45 is a comparatively large chamber of substantial vertical length. The steel casing 46 forming the outer shell of the pocket is rigidly connected to the shell of the burner, and is supported in the position illustrated in Fig. 1

by suitable superstructure not shown in the drawings. f l

The cinder pocket is lined with rebrick 41, and is arranged with a vertically Adisposed wail 48 directly opposite the axis of the outlet 44. A stream of gas issuing from the burner through the outlet 44 strikes the vertical wall 45 at a right angle, thus abruptly changing the course Vof the gas stream and causing the gasstream to drop substantially all the heavy cindei` particles carried out of the reaction chamber in suspension in the exit gas. The pocket outlet terminates in an elbow 49, suitably lined with rebrick, and arranged to permit connection between the pocket `and the exit gas main, the latter including the the drawings by the numeral 55. The same construction is employed in the upper end of the shell from the point indicated by the numeral 56 upwardly to the crown 2|. That section of the shell I I disposed between the points 55 and 56 may be conveniently termed a heat transfer section. The heat transfer section comprises horizontal series of radially disposed rebrick indicated'at 58 in-Fig.v 3. The individual bricks each include a central passage 59, so arranged l that when the several horizontal series of bricks are superposed, and in position to form the shellv of the roaster, there are then provided wit the wallsof the transferrer section, the several vertical passages or conduits 66 which begin at the lower end of the tansferrer section at 55, and

terminate at the upper end thereof at 56.

' As shown in Fig. 3, two horizontal series of bricks 6| are arranged at the lower end of the transferrer section immediately within the cir- 25 cumference, the bustle pipe 62 surrounding vthe burner at the lower end of the transferrer` section. The bricks of both series 6| are provided with suitable openings 63, thus establislriingcommunication between the several vertical conduits 66 and the interior. of the bustle 62. The construction of the shell immediately adjacent the bustle 62 is clearly-shown in the enlarged' details in Figs. 2 and 3. In Fig. 2 it will be seen that the bricks constituting a series 6|, are each radially disposed with reference'to theA vertical axis of the'burner, and that each vertical conduit 66 is in direct communication with the bustle 62 by Areason of the openings 63 in each brick of a series 6|. A

The bustle 62 is suitably attached to the adjacent steel section of the shell i3 by flanges as indicated at 65 inlFig. 3. The bustle 62 is in. direct communication with the inlet pipe 66, Fig. 1, which is in turn connected through another pipe line, not shown, to the plant blowers.

, j arrangement by which the 4same is in communicationwith the upper ends of the vertical conduits 66 is in all respects the same` as that previously described in connection with Athe bustle 62, and illustrated in the enlargedl details in Figs. z

, y2 and 3.

The outlet 68 of the bustle 61 is. directly c'onnected to the short pipe section 69 which is'joined` at its opposite end to the main inlet pipe 16. The passage of gas through pipe 69 into the main vertical pipe 16 is controlled bythe valve 1|. The '60 lower end. of the vertical main 16 is connected t`o the inlet 66 as shown in Fig. 1, and the admission of gas fromthe inlet 66 to pipe 16 is controlled by valve 12. The pipe 69 is in communication with the plant stack and the latmosphere '65 through the pipe 13 which includes therein the control valves 14 and 15. The. upper end of thevertical main 16 yterminates ina 1 16. The T conduits 11 and 18 through pipes 82l and 83 respectively, each controlled by the valves 84 and 85. The pipe system just described supplies air, or other oxidizing gas to the ore feeding lsize of the cylinder and the' sleeve.

mechanismindicated generally by the numeral The feed mechanism, illustrated more or less diagrammatically in Fig.A 1, is shown in detail in the section of Fig. 4. In Fig. 4 the crown 2| oi.4

the burner, and the top plate22 are apparent. The cast iron cylindrical sleeve 68 is set into a circular opening in the crown 2|, and is held in the position shown by the horihontal flange 89. A ange 96 is formed on the upper edge of the sleeve 88 and is adapted to be bolted or otherwise attached to the bottom `flange -9| vmi casting or coupling member indicated generally at 92. The top ilange 93 on the`-upper end of the cylindrical portion 94 of the coupling 92 is similarly arranged to support and to be attached to the bottom ang'e .95 .on the lower edge of the4 primary gas linlet casting 96. The ange 91 on the casting 96 aiTords means for connecting the casting 96 to the inlet conduit 11, as indicated at 98 in Fig. 1.

The ore inlet chamber casing |66 having the vinlet connection 10| secured thereto rests on the top of the casting 96. The upper end of the pipe |62 is threaded into the lower end of vthe chamber casing |66. Theexterior threads on the upper end of the pipe |62 extend downwardly far enough to thread into the opening inthe top of casting 96, thus retaining casing |66 and pipe |62 in-place. The fuiste-'conical shaped oriilce plate terminates in a curved rimv |68, the Lfunction of which will hereinafter appear. The dispersion cones 6 and are fixed to the adjusting rod ||2 which extends upwardly through the center of the terminal cylinder v| 66, through the ore feed pipe |62, through the ore inlet chamber and projects through" the cap in the top of casing |66. The upper end of` the rod |I2 is threaded to receive the adjusting and lock nuts ||3. The dispersion cone has fastened to its base and, to the spindle projecting downwardly therefrom several radially disposed vanes ||5 which serve to center the dispersion cones ||6 and and maintain the same in a relatively xed position in the center of the terminal cylinder |66.

The numeral ||6 indicates `what may be generally designated as a gas mixing sleeve. The

sleeve ||6 is supported in the position shown in Fig. 4 by vertical rods I1, the lower ends of which are welded or otherwise rigidly fastened lto the upper edge of the sleeve ||6. The free ends of rods ||1 pass through suitable `openings in the annular top ||8 `of the casting 92. vThe upper ends of the rods I|1 are threaded to receive the adjusting and lock nuts I9. The lower end of the sleeve |6 is bent inwardly to form a funnelshaped deiiecting or mixing portion ||8./ The short cylindrical member I9 isxed to the lower end of the cylindrical portion of the sleeve I6 in such manner as to form substantially a. continuation thereof.. The lower edge of member ||9 is bent to-provlde `an outwardly directed ilange |26. The arrangement of the sleeve ||6 and the cylinder is such as to constitute between these two members an annular passage 2| the dimensions and capacity of which depend upon the relative It will be understood that the cross-sectional dimension of both cylinder |06 and sleeve i |6, together providing a sectional feed conduit, may be subject to variation.

The horizontal flange |22 of the sleeve |23 is clamped between flanges 90 and 9|, and thus supports sleeve |23 in the position shown. The lower edge of sleeve |23 isk bent outwardly to form a flange |23 shaped similarly to ange |20. The relation of sleeve |23 and sleeve ||6 is such as to provide between these members 'an annular chamber |24 terminating in an annular mouth or passage i25. Sleeve H6, cylinder |06, together with that portion of the oreinlet passage above cylinder i6, may be said to constitute a sectional ore inlet conduit.

The interior of the casting or coupling 92 includes a vertically extending ring imember 326 which is so formed as to constitute in effect an upwardly directed continuation of the inner surface of the sleeve 88. The upper edge of the ring |26 stops short of the under side of the horizontal portion ||8, and thus provides an anlnular passage |21 which affords communication between the interior of the bustle |28, and the gas r underside of the annular top ||8, and a series lof perforations provided near theupper end of ring |26 to establish communication between bustle |28 and inlet chamber 29.

For convenience, the operation of the invention will be described in connection with the roasting of iron pyrites. The operation of the invention is substantially as follows.' j

'I'he furnace is first preheated, for example by means f of one or more oil burners inserted through workholes 28, until a temperature isv obtained in the chamber |2 of for example about 425 C. #During the preheating operation the work holes 24 in the crown of the chamber are uncovered to. provide flues for escapeof the products of combustion. u A

Finely divided iron pyrites which has been dried until the moisture is not greater than about 0.3% and preferably between 0.1% and 0.2%, and of a particle size' such that 100% will pass a 60 mesh screen, is `fed into the feed mechanism re v inlet The ore may be continuously' supplied to the inlet |0| by a chute from suitable hoppers or by means of a screw conveyor or any other desirable feed mechanism. The finely divided ore passes downwardly through the ore inlet feed pipe |02 into the 'interior of the terminal cynic,4

der |06. I i

Air or oxygen may be used as the oxidizing gas, preferably the former for economic reasons, and either at atmospheric temperature or preheatedI to anydesired degree as will be hereinafter more fullyexplained. The oxidizing -gas enters the feed mechanism 01 through the conduits 11 and 18 connected respectively to the inlet casting 96 and the inlet |30 of the bustle |28 of the feed mechanism. For operation under usual conditions, about to 15% of the total air required. for the complete combustion of the ore in the roasting chamber is introduced into the feed mechanism through the conduit 11 and the inlet casting 96. For the purpose of this description the air introduced into the roasting chamber through the conduit 11 and the casting 96 may be termed primary air, and that introduced into the roasting chamber through the conduit 18 and the bustle |28 may be considered secondary air.

After introduction of the air from the conduit 11 into the inlet casting 96, the same passes into the terminal cylinder |06 through the annular passage betweenthe edge of the orifice plate |03 and the lower end of the feed inlet pipe |02. On account of the funnel-like shape of the orice plate |03, the air passing therethrough is deflected to a certain degree toward the vertical axis of the cylinder |06. 'I'his causes an initial mixing of air andere dropping out of the lower end of the feed pipe |02. A further advantage of this arrangement is that the air enters the upper end of the terminal cylinder |06 with something of an injector action which aids in drawing in the ore from the pipe |02, and at the same time tends to prevent the escape of any gas from the roasting chamber upwardly through the ore inlet pipe |02.

The initial mixture of ore and gas drops down- ,wardly through the upper endof the terminal cylinder |06, and the greater part of the mixture strikes the upper surface of the dispersion cone The falling mixture leaves the lower edge of the cone in a sheet resembling the surface of a cone, and strikes against the inner wall Yof the cylinder |06 at a point somewhat-below the lower edge of the dispersion cone On so striking the inner surface of the .cylinder |06, the particles of ore are for the most part deflected back toward the axis of the cylinder, i. e., towards the adjusting stem |2, and in so doing become more thoroughly mixed with the air which is not deflected from the inner walls of the cylinder |06 in essary for the combustion of the ore in the roasting chamber is, as previously mentioned, admitted to the feed mechanism through the conduit 18.

Air entering the inletv |30 of'the bustle |28 from the conduit 18 immediately lls the bustle', and

passes therefrom through the annular passage before anyI appreciable-quantity of the air leaves' vthe same through the annular passage |21 into the gas inlet chamber |29. It will be apparent that this arrangement is such that the 'air is caused to enter the inlet chamber |29 from -all points on the circumference of the upper edgefof the ring |26. This radial introduction of air from f the bustle |28 intothe gas inlet chamber |29 is such that undesirable turbulent airzmcurrents arel not created'within the inlet chamber |29. It has been found that in certain instances where too great a turbulent action is set up in the gas inlet chamber |29, and accordingly in the feed mechaand air issuing from the lower ends of the cylinnism as whole, certain strong currents are set up which tend to carry large portions of ore against some particular spot on the interior of the reaction chamber wall. These undesirable eddy currents are prevented by the construction justl described.

About 85 to 95% of the total quantity of oxidizing gas necessary for the roasting of the ore in the reaction chamber isintroduced into the re' K action chamber by .way ofthe gas inletI chamber H29. In the neighborhood of to 10% 'of/the total air utilized in the roasting operation is introduced into the reaction chamber through the annular passage" H24 between the sleeve S23 and the outer surface of the distributing sleeve M6. This air passes through the annular mouth l25, and forms a gas blanket between the walls of the reaction chamber and the burning gaseous suspension therein. The remaining quantity of air in the gas inlet chamber |29 passes into the annular space [2l between the inner surface of the sleeve ll i6 and the outer surface of the cylinder G06. It will be observed that the lower end of the cylinder B06 is bent up to form the curved rim 1 08. Air passing downwardly through the annular passage l2l strikes the sloping surface of the rim M8 and is deflected outwardly fromA the vertical axis of the feed mechanism and impinges upon the inwardly directed funnel-shaped deecting portion H8 of the sleeve M6. Y This rapid change in the direction of the gas stream serves to further increase the mixing ofthe ore der '|66 and the annular passage i2 I.

" The total amount o f air introduced into the feed mechanism 81 will depend upon the amount of sulfur in the nes to be desulfurized, the concentration of the sulfur dioxide desired in the exit quantity may be accomplished in any suitable and hot roasting chamber I2.

well known manner. In practice, determination of the sulfur dioxide content of theexit gas and the character of the cinder. will usually indicate the necessary regulation of the air supply to provide the desired results, the fines being supplied at a substantially constant rate. The pressure under which the air is introduced may be regulated to suit operating conditions, although it is usually desirable that a pressure approximately atmospheric is obtained over the 4c'inder outlet.

When the furnace is in operation, the sleeve M6' should be so adjusted. by means of the suspension rods H1 andthe associated regulating and set. nuts that the size of the mouth 25 is such that only sufflcient air is admitted thereto to prevent scar formation on the walls of the roasting chamber.' This may be determined by varying the size of the mouth l25, and observing the effect upon the chamber walls through one of the sights in a work hole cover 25. The amount of scar inhibiting air necessary is usually a minor proportion of the total amount of air admitted and, as previously noted, ranges generally from 5 to 10% of the total quantity of air necessary for combustionin the furnace. The sheet of pyrites iines issuing from the lower end of the B2i, and the suspension ofl intimately mixed air and n'es thus obtained is. introduced into the 12inl entering the preheated chamber, ithe suspension of fines in air will be'igmted and oxidauoawiu thereafter proceed at a very 'rapid rate.

- and preheated therein,

The oxidation of the iron pyrites is a strongly exothermic reaction, to the extent that itis substantially self-sustaining, and other than the necessity of initiating thereaction, for example by .preheating the furnace to a suitable temperature y amount of heat supplied by the combustion of the fines in addition to that emanating from the heated walls of the roasting chamber. This expansion tends to cause an appreciable proportion of the suspended particles to be drawn toward the chamber wall, and such particles as are in the transitory sticky stage -hereinbefore discussed would under ordinary circumstances tend to 'adhere to the walls upon contacting therewith and rapidlybuild up accretions thereon.

In the roasting of different grades of -pyrite' and p yrrhotite ores and sulde flotation concentrates from various sources, it is highly desirable to be able to control to a certain' degree the temehamber i 2 and to a corresponding degree the temperatures obtainable within the roasting chamber are 'thus regulated. Such desired control may beobtained by suitable manipulations of .the several valves in the piping system between the inlet of the main pipe 66 and the feed mecha- -nisni 81, and by controlling the quantity of air circulated through the conduits 60.

If it is desired yto supply air of ordinary temperature to the feed mechanism 81, the valve 1l in the line 69 is closed, and the valve 12 in pipe 10opened sufficiently to permit the passage of the required4 amount oi air to support the combustion in the reaction Ichamber i2. When proceeding under this mode of operation, the valves 19 and 80 in the lines 11 vand 18 are so adjusted to permit the admission of the desired proportions of primary and secondary air to the feed mechanism through the inlet casting 96 and the bustle 128. Further, ifit is desired at the same time to circulate air through the vertical conduits 60 for the purpose of cooling the walls of the reaction chamber,` the necessary quantity of air may be admitted to the passages 6l) from pipe perature ,of the mixture entering the Iroasting*- 66 throughthe bustle 62. After passing. through Y the transferrer section and cooling the burner walls, and thus further serving to control the temperature .of the-reaction within the roasting chamber, the heated air leaves through the bustle 61 and is vented to the 'atmosphere through the line 13. In such situation, 'are opened, and the valves B4 and 85 are closed.

When yit is desired to preheat the primary air andthe secondary air to the same degree, cold air is circulated through the transferrer section and is then mixed with the main stream of cold air entering the apparatus through themain' vertical pipe 16. To ac 'complish this mixing of cold and heated air, the

valve 1l is openedv as required and the valve 14- In this manner, the air in the 10 beyond the connection the valves 14 and 15 of preheat, and this heated stream of air is then divided and passed into the feed mechanism through the conduits 11 and 18. It will thus be seen that under such operation the primary and secondary air for the feed mechanism 81 is preheated to the same degree. The degree of preheat is regulated by the proportions of cool and heated air mixed at the connection between pipes 69 and 1G. l

There may also be encountered in practice, situations where it will be desired to preheat the primary and secondary air to different degrees. Assuming that it is required to preheat the primary air and not the secondary air, the valves 1| and 19 are closed. The 'cold air passes upwardly through the main line 10, through the conduit 18 and into the bustle |28. By regulation of the valve 12, the quantity of air required to be preheated is admitted to the bustle 62, and passed through the transferrer section. On leaving the latter through the bustle 61, vthe stream of preheated air passes through the open valve 14, into the pipe 13 and through the open valve 84 through pipe 82 and then into the conduit 11. In this instance the valve 85 is closed, and the valve 15 is closed to such an'extent as may be required by 4the quantity of gas required to be passed into the conduit 11.

. Where it is desiredto preheat the secondary air and not the primary air, the valve 19 is opened andthe valve 80 is closed. Unheated air is supplied to the conduit 11 from the main line 18. Air preheated in the transferrer section passes through the pipe 69, through the open valve 14 into pipe 13, thence through the open valve 85, through pipe 83 to conduit 18. In this instance, the valve- `84 is closed and the valve 15 closed to such a degree as may be necessary. Intermediate temperature adjustments of primary and secondary air maybe obtained by suitable manipulation of the several valves in the piping system.

Referring to the roasting of the ore, the initial stages of the roasting operation are the most intense and normally take place in the upper part of the roasting chamber. It is in this upper par.v of the chamber that the tendency toward scar formation appears to be most marked, and it seems probable thatv as the proportion of the FezOa increases, the tendency toward scarring decreases. On that basis it would appear that the provision of the air blanket between the walls of the chamber and the burning suspension need only be conned to the upper part of the chamber in order to 4prevent scar formation, vand it may be that such is the case in the operation of the present method as noted, although the particular path of the air blanket is more difcult to trace the greater its penetration into the furnace. On the other hand it is quite possible that the gaseous suspension of nes could. be introduced under such pressure, for example, that the 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 chamber.

In view of these considerations it is of importance that the air blanket be interposed between the walls of the chamber and the burning pyrites while the latter is in a state conducive to scar formation, regardless of its lrelative location in the roasting chamber while in thatstate. That such is the case in the operation of the present method is evidenced by the fact that by suitably varying vertically the position of the ange i211,

and thereby the volume and to a limited degree the direction of the air blanket admitted through the mouth |25, the formation of scar under such variations of the roasting operation as are involved in4 ordinary industrial practice can be eliminated. i

Further improvements in the roasting operation arise from the particular structure of the feed mechanism and the arrangement of the piping system in association with the heat transferrer section of the burner. In regard to the former, the provision of a feed mechanism whereby the oxidizing gas is radially'introduced therein serves to avoid the setting up of strong eddy currents which in some instances, as hereinbefore mentioned, tend to direct pronounced streams of ore against some particular portion of the roasting chamber wall. In the present mechanism, the mixing of gas and ore is such that the mixture formed, on leaving the feed mechanism and after the initial expansion of the mixture has taken place, passes vertically through the shaft. Small individual streams of ore do not assume an inclined course, and hence clinkering is reduced to a minimum.

Additionally, by manipulation of the valves in the piping system as described, the temperature lil of the oxidizing gas entering the feed mechanismV may be controlled. The control of the temperature of the oxidizing gas permits control of the temperature within the roasting chamber. This renders the process applicable to the burning of a wide variety of sulfide ores, and permits the maintenance of temperatures within the roasting chamber most favorable for the eilicient roasting of a particular sulfide ore.

The length `of the -roasting chamber and the speed of introduction and travel of the fines and air should vbe such that a thorough desulphurization is obtained in the passage through the roast ing chamber.

By conducting the roasting operation as deoughly desulphurized by the time the cinder and gas outlets are reached, and by proper regulation of the oxidizing gas pressure, the major portion of the desulphurized particles, mainly in the form of iron oxide collects in the cinder pit 28 whence it is withdrawn through the outlets 21. The gases containing the sulfur dioxide passing into the dust chamber 45 carry entrained therein an appreciable portion of solid particles, consisting mainly of iron oxide which are collected in the dust chamber 45. The gases containing the sulfur dioxide are drawn from the chamber 55 and conducted away for utilization in the production of sulphuric acid, or for other purposes.

While the invention has been specifically described in connection with the roasting of nely divided iron pyrites ore or flotation concentrate, the invention is not confined to the use of that particular material but is applicable generally to the roasting of a wide range of sulde ores where undesirable sintering is involved-and where it is desirable to control the temperature of the roasting operation. '.[he invention contemplates the treatment of diiferent grades of iron and copper pyrites, pyrrhotite, zinc blend and similar ores and flotation concentrates of the same.

the mixture a secondary volume of gas and forming a suspension of said material therein including a gas inlet chamber surrounding the conduit, a bustle encircling the inlet chamber, an annular passage between the bustle and the chamber whereby a secondary volume of gas is introduced radially into the inlet chamber, a sleeve forming a passage communicating with the inlet chamber and projecting beyond the primary conduit, and means in said sleeve for delecting gas passing through the passage toward the axis of the primary conduit.

2. Apparatus ofthe character described comprising a primary conduit, means for forming in said conduit a mixture of a finely divided material in a primary volume of gas, means for adding to the mixture a secondary volume of gas including a gas inlet chamber surrounding the conduit, a bustle encircling the inlet chamber, an annular passage between the bustle and the chamber whereby a secondary volume of gas is introduced radially into the inlet chamber, a sleeve forming a passage communicating with the inlet chamber and s projecting beyond the primary conduit, means in said sleeve for deflecting gas passing through the sleeve toward the axis of the primary I for forming a suspension of said material therein including a gas inlet chamber surrounding thev conduit, a bustle encircling the inlet chamber, an annular connection between the bustle and the chamber `whereby a secondary volume of gas is peripherally introduced radially into the inlet chamber, and a sleeve surroundingat least a portion of the primary conduit andforming a passage communicating with the inlet chamber and projecting beyond the outlet end of the primary conduit for introducing 'into the mixture formed in and discharged from the primary conduit a secondary volume of gas.

i. Apparatus of the character described comprising a primary conduit, means for introducing iinely divided material into said conduit, means for adding to the material a volume of gas for forming a suspension of said material. therein including a gas inlet chamber surrounding the conduit, a bustle encircling the inlet chamber, an annular connection between the bustle and the chamber whereby a volume of gas is peripherally introduced radially into the inlet chamber, and a sleeve surrounding at least a portion of the primary conduit and forming a passage communicating with the inlet chamber and propecting beyond the outlet end of the primary conduit for introducing into, the material discharged from the primary conduit a volume of gas. v

5. Apparatus of the character described comprising a primary conduit, means ior forming in said conduit a mixture of a nely divided material in a primary volume of gas, means for adding to the mixture a secondary volume of gas ior forming a suspension of said material therein including a gas inlet chamber surrounding the conduit, a bustle encircling the inlet chamber, an annular connection between the bustle and the chamber whereby a secondary volume of gas is peripherally introduced radially inte the inlet chamber and e sieeve adjustable axially of the conduit, forming a passage communicating with the inlet chamber and projecting beyond'the outlet end of the primary ccnduit for introducing into the mixture formed in and discharged from the primary conduit a secondary volume of gas.

6. Apparatus of the character described comprising a primary conduit, means for forming in said conduit a mixture of a iinely divided material in a primary volume of gas, means for adding to -the mixture a secondary volume of gas for forming a suspension lof said material therein including a gas inlet chamber surrounding the conduit, a bustle encircling the inlet chamber, an annular connection between the bustle and the chamber whereby a secondary volume of gas'is peripherally introduced radially into the inlet chamber; a sleeve, adjustable axially vof the conduit, surrounding at least a portion of the primary conduit and forming a passage communicating with the inlet chamber and projecting beyond the outlet end of the primary conduit and means in said sleeve beyond said end of the primary conduit for deflecting gas passing through the passage toward the axis of the conduit to thereby introduce into the mixture formed in andy discharged from the primary conduit a. secondary volume oi' gas.

il. Apparatus of the character described comprising in combination a reaction chamber, feed mechanism therefor comprising a primary conduit, means for introducing finely divided material into said conduit, means for adding to the material a volume of gas for forming a suspension of said material therein including a gas inlet chamber surrounding the conduit, a bustle encircling the inlet chamber, a connection between the bustle and the chamber whereby a volume of gas is introduced radially into the inlet chamber; a sleeve, adjustable axially of the conduit, forming a passage communicating with the inlet chamber and projecting beyond the outlet end of the primary conduit, means in said sleeve beyond the end of the conduit for deflectinggas passing through the passage toward the axis ofthe conduit, and means associated with said sleeve for maintaining a layer of gas between the walls of the reaction chamber and the material therein.

8. Apparatus oi the character described comprising in combination a reaction chamber, heat transfer means associated with said chamber, means for circulating gas through said fheat transfer means, reaction chamber feed mechafor introducing into the primary volume of gas a given quantity of gas circulated through the heat transfer means to preheat the primary vol=` ume of gas to a given degree, means for introducing into the secondary volume of gas a diiierent quantity of gas circulated through the heat transfer means to preheat the secondary volume of gas to a dierent degree to thereby provide different degrees ofpreheat in the primary and secondary volumes of gas, and means for ininto the reaction transfer vmeans associated with said chamber,-

means for circulating gas through said lheat transfer means, reaction chamber feed mecha# nism including means for introducing into the feed mechanism a primary volume of gas and for forming a mixture of finely divided material in said primary volume of gas, means for introducing into the feed mechanism a secondary volume of gas and for adding to the said mixture a secondary volume of gas, thereby forming asuspension of material in the gas; means for introducing into the primary volume of gas a given quantity of gas circulated through the heat transfer means to preheat the primary volume of gas to a given degree, means for' introducing into the secondary volume of gas a diierent quantity of gas circulated through the heattransfer meansto preheat the secondary volume of gas to a different degree to thereby provide different degrees of preheat in the primary and secondary volumes of gas,`me`ans for introducing the suspension into the reaction chamber, and means for maintaining a layer of gas between the walls of the reaction chamber and the gaseous suspension therein.

10. Apparatus of the character described comprising in combination a reaction chamber, heat transfer means associated in heat transfer relation with said chamber, means for circulating oxidizing gas through said transfer means in quantity to remove variable amounts of heat fromthe reaction chamber to control tl e temperature thereof, reaction chamber feed mechanism including means forintroducing into the feed mechanism a primary volume of gas and for forming a mixture of finely divided material .in said primary volume of gas, means for introducing into the feed mechanism a secondary volume of gas and for adding to the said mixture a secondary volume of gas, thereby forming a suspension of material `in the oxidizing gas; means for introducing into the primary volume of gas a given quantity of gas circulated through the heat transfer means to preheat the primary volume lof gas to a given degree, meansy for introducing into the secondary volume of gas a y different quantity of gas circulated through the

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