US2075823A - Production of sulphur dioxide - Google Patents

Description

April 6, 1937. E, J MULLEN-ET 2,075,823

PRODUCTION OF SULPHUR DIOXIDE Filed April 26, 1935 Fig.4! a? 82 IINVENTORS f. 1/. Mal/en 63/7. Gal/0y! 83 BY ATTORNEY Patented Apr. 6, 1937 PRODUCTION or SULPHUR moxmn Edwinv J. Mullen, New Rochelle, N. Y., and Charles A. Gallagher, California, Pa., assignors to General Chemical Company,

New York,

N. Y., a corporation of New York I Application April 26, 1933, Serial No. 667,950

6 Claims.

This invention is directed to methods and apparatus for roasting metallic sulphides, and more particularly for roasting finely divided sulphide ores, to desulphurize the same and to produce sulphur dioxide for use in the manufacture of sulphuric acid, or for any other purpose desired.

As a general rule, to a large extent present practice in roasting sulphide fines includes the use of mechanically operated multiple hearth 10 constructions, such, for example, as the well known MacDougal, Herreshofiand Wedge burners, and while such burners provide effective roasting, the complicated construction and operation thereof involve considerable initial and main- -tenance expense.

As distinguished from bed roasting carried out in such burners, it has been previously suggested to roast fines while in gaseous suspension, in operations in which the fines are either injected into a roasting chamber in suspension in the oxidizing gas, or are showered downwardly into a roasting chamber wherein the fines encounter cross or countercurrents of oxidizing and/or suspending gas.

5 Suspension roasting is best applicable when the fines ores are in a relatively finely divided state, and this method presents the notable advantage over the mechanical multiple hearth operation of considerably lowering the cost of production, by

reason of the elimination of complicated and moving parts, expensive rabbling and other apparatus inherent in the construction and opera tion of mechanical burners. Inthe practice of suspension roasting, however, and particularly as applied to roasting metallic sulphide fines, difliculties are encountered which must be overcome before theoretical advantages of this type of roasting are made practicably available.

One of the problems presented by suspension roasting involves preliminary treatment of the fines, particularly drying, prior to introduction of fines into the combustion chamber, and the formation of a uniform dispersion of ore particles therein. This phase of the process usually requires, for efiicient conduct thereof, a relatively dry ore, substantially free from lumps and extraneous foreign material. Damp or wet ore tends to clog feed pipes and injector mechanisms thus interfering with operations in this respect.

Furthermore, damp fines do not ignite readily on introduction into the combustion chamber, and

thus prevent efiicient roasting. To avoid such difiiculties, it is desirable to feed into the furnace, dry, or dry and preheated ore.

55 In the prior practice, it has been generally customary to dry the fines away from the burner, with conventional drying apparatus, before the ore is fed into the combustion chamber. This procedure is not satisfactory for several reasons including dust loss, nuisance arising from dust- 5 ing, absorption of moisture from the air after drying but before charging the ore into the furnace, and particularly the expenseinvolved by installation and maintenance of the drying ap-' paratus, and in the provision of extraneous heat 10 needed to effect drying.

To overcome disadvantages of this nature, it has been suggested to employ waste heat of the roaster to accomplish preliminary drying of the ore. It has also been proposed to dry fines ores 15 prior to injection into the combustion chamber by causing the ore to pass in heat exchange relation over the top and sides of the combustion chamber thus utilizing radiated and conducted heat to dry the ore. 2

It is one of the principal objects of the invention to provide improved apparatus to effect preliminary drying, or drying and preheating of the metallicsulphide fines before introducing the fines into the furnace, by utilization of heat which, 25 according to usual prior practice, would normally be lost to the atmosphere by conduction and radiation from the top and sides of the shell forming the roasting chamber. 1

The improved apparatus of the invention for 30 drying, or drying and preheating the fines prior to feeding into the injector mechanism, includes a jacket, surrounding the burner, constructed in such manner as to permit free flow of wet or damp fines ore along the exterior walls of the -35 burner, and to. make provision for the ready escape of water vapor from the body of fines being dried.

Theobjects and advantages of the invention may be more clearly understood from a consid- 40 eration of the following description taken in connection with the accompanying drawing, in which Fig. 1 is a vertical section of a burner in connection with which the improvements of the in- 4 vention may be advantageously employed;

Fig. 2 is an enlarged, vertical section of a fines ore injector mechanism;

Fig. 3 is a development, on a reduced scale, of the ore drying and heating jacket surrounding the walls of the burner of Fig. 1; and

Fig. 4 is adevelopment, ona reduced scale of a modified form of jacket.

Referring particularly to Fig. 1 of the drawing,

numeral l0 designates generally a shaft burner 5.

comprising a shell ll constructed of suitable refractory 'material, such as firebrick, and defining a roasting or combustion chamber 12 of cylindrical cross-section. Surrounding the shell H is a steel casing I3, acting as a protective reinforcement for the furnace. The upper end of the combustion chamber is closed off by a crown l5, the top side of which forms a drying and preheating hearth M. The cylindrical shell M and casing l3 project upwardly beyond the crown, and carry a framework l8 which in turn supports ore feeding and rabbling mechanism for hearth ll.

The surface of hearth ll is slightly cone-shaped and slopes downwardly toward the shell of the burner, Lying above the hearth are rabble arms l9, having downwardly projecting plows 2U pitched. to work sulphide fines gradually toward the circumference of the drying hearth. Arms iii are rotated by a motor 22 through shaft 23, supported in bearings so as to maintain the lower ends of the plows 20 properly spaced with respect to the surface of the drying hearth ll. An ore bin 23, mounted on frame work iii, discharges ore onto a platform 25 from which fines are intermittently dropped onto approximately the center of hearth ll by a sweep Zll rotating with shaft 23.

Surrounding the major portion of easing l3 are a plurality of louvers 30 which with casing I3 form an ore drying and preheating jacket designated generally by reference numeral 32, enveloping asubstantial portion of the vertical walls of the burner. Cut in shell ll, near the upper end, are downwardly sloping ore supply passages 34 through which ore is passed, from the dry-- ing hearth l'l, through a sloping screen 35 into the. topmost louver 36 constituting the upper edge of jacket 32. The drawing shows, in section, two passages 34. may pass through the top of shell It at spaced points about the circumference of the burner so that, on rotation of the rabble arms l3, lines are gradually fed through the openings 38, through the screen and into the top of the drying 1 jacket.

In the embodiment of the apparatus shown in Fig. l the jacket 32 is provided at the bottom with three outlets, indicated at' 38, through which fines are fed into the relatively small subjacent hoppers or bins, designated by reference numeral 40. As shown in section at the left of Fig. 1 immediately above bin 40, and also in elevation in (Fig. 3, sloping side 42 of lowermost louver 43 is of greater length than the sides of other louvers so as to provide small hoppers terminating in discharge openings 38. ,The bottom of jacket 32 is formed by sloping edges 45 which intersect lower louvers 43, several of the upper louvers 30, and are attached to steel casing IS. A development of the louvers is shown in Fig. 3. Edges 45 of the jacket are sloped at an angle greater than the angle of repose of the sulphide fines, so that the latter run freely toward outlets 38 through which the material is fed into the hopper 40. The louvers are supported by ledge-like projections 48 of verticals 49 which in turn may be suspended from frame work l8. The louvers rest loosely on the projections, this arrangemen permitting repair or replacement. Hoppers 40 terminate at the bottom in an outlet pipe 5! for feeding material into an observation funnel 52 on the top end of an injector feed pipe 53 having a control valve 54.

Referring particularly to Figs. land 2, the inlfreferably, several such conduitsjectors for introducing fines into the furnace comprise a pipe section 60, the inner end of which isset into the shell of the burner atthe lower end of the combustion chamber, pipe 60 providing an ore inlet 6|. Tube 60 is held securely in position by a circular plate 62 and a flange 63 bolted to steel shell l3. In the preferred construction, the axis of tube 60 is directed upwardly at a relatively sharp angle, for example about 75 to the horizontal.

As shown in Fig. 2, the valve-{controlled pipe 53 projects into the upper side of tube 60. A gas inlet pipe or jet 65 passes through end plate 68 and terminates beneath the discharge end of pipe 53. Admission of air or other gas to jet 65 is controlled by a valve M. A plug 69 affords means for cleaning out conduit 6i should the same become stopped up.

Surrounding the burner near the injectors is a bustle Ill for supplying gas to injector jets 65, the bustle being connected to a gas supply through a pipe ll controlled by valve 72. Oxidizing gas to support the roasting operation is introduced into the shell I2 through circumferentially spaced ports 13, positioned adjacent the ore injectors, and connected through short pipe sections, not shown, with a bustle 14. The bustle i l may be provided with an inlet pipe connection, having a control valve, either open to the atmosphere orconnected to a blower when it is desired to operate the burner under positive presder is continuously discharged into a conveyor.

A gas main 11 for withdrawing gaseous products of combustion from the chamber 12 opens into the latter just beneath the crown l5. It will be understood provision is made for passage of the gas main through the adjacent section of the drying jacket.

In the specific embodiment of the invention described, the height and diameter of the combustion ohamber are about the same. While such particular proportion of the combustion chamber is preferred when carrying out the roasting operation per se in a burner of the general type illustrated in the drawing, it is to be understood that the diameter of the chamber may in some instances, advantageously exceed the height by a substantial amount, and may also be less than the vertical dimension. Prefjerably the diameter of the chamber is not less than the height. It will be understood, however, that the apparatus of the invention for drying or drying and preheating the fines, prior to introduction into the combustion chamber may be employed in connection with any kind of roasting chamber.

Fig. 4 shows, in elevation, a development of a modified type of drying jacket. This construction comprises a series of horizontally disposed louvers, spaced apart as in the apparatus of Fig. 1. In Fig. 4, however, the louvers are arc-like in plan, and are of limited horizontal length, the ends of the louvers being welded or otherwise attached to vertical sidemembers 32 and the sloping lower edges 83. Any desired number of units, of the type shown in Fig. 4, may be attached to the burner shell l3, each unit forming above each ore injector. When operating with this construction, it will be understood that fines are fed from the deck I1, through suitably spaced passages 34 into the top of the several individual jackets, the fines gradually dropping through the jackets, and being directed by sloping edges 83 toward outlets 38.

In the construction of Fig. 4, the louvers between the vertical edges 82 may be of any desired length, preferably such that a plurality of jackets attached to the shell [3 would cover at least a major portion of the burner. Where the louvers are of substantial length, the edges of the louvers intermediate the verticals 82 may be supported by hangers such as 49 shown in Fig. 1. In some instances the individual units of Fig. 4 may be preferable, for convenience in construction and repairs, to the arrangement disclosed in Fig. 1.

The invention is applicable to the roasting of metallic sulphide fines such as iron pyrites, pyrrhotite, zinc sulphide or arsenopyrite, but for convenience, and by way of illustration only, the operation of the process maybe described in connection with the roasting of iron pyrites. A supply of finely divided pyrites is maintained in the bin 24 by suitable conveyor or elevator mechanism, not shown. Before roasting is begun, combustion chamber I2 is preheated to tem: peratures above the ignition point of the particular ore to be roasted, as by the use of oil burners inserted through conveniently located workholes, not shown. When the desired degree of preheat is obtained in the combustion chamber, the motor 22 is started, and rabble arms 59 and sweep 21 may be rotated at a rate of say one revolution in two minutes. Fines run continuously out of the bin 24 onto platform 25, and, on each revolution of shaft 23, a regulated quantity of ore is swept off the platform to approximately the center of hearth ll.

During rotation of rabble arms 59, the fines are gradually worked across the heated surface of the hearth it into passages M. The dry or partly dry ore then runs over' and through screens 35, which separate lumps, and into the louver 36 and the top of jacket 32. The louvers 38 are spaced sufiiciently close sothat material, while running from one louver into the one immediately below does not overflow the upper horizontal edge of the lower louver, that is, the surface of material between the lower edge of a louver and the upper edge of a subjacent louver, for example, as indicated at 80, is substantially at the angle of repose. The numerous exposed surfaces of the fines between the several louvers permit intermittent exposure to the atmosphere of at least some of the fines and thereby provides for the ready escape of water vapor formed during drying or'drying and preheating of the fines.

When roasting is under way, hearth l1, and the vertical Walls of the combustion chamber become relatively highly heated, and sulphide fines are dried and preheated to some extent during movement over the drying hearth l1 and through jacket 32 surrounding preferably at least a major portion of the burner shell. This operation blankets the top and sides of the burner with ore which acts as aheat 'insulaton'retaining heat in the combustion chamber, and em-- ploying heat which is transmitted through shell H, to'the ore, to dry and heat the latter. This preliminary heating serves to dry the fines, thus facilitating the formation of more satisfactory T5 dispersion of ore in the combustion chamber,

and at the same time preheats the fines to temperatures such as to promote ignition shortly after introduction into the combustion chamber. In accordance with the invention, by causing the fines to be roasted to pass over the top and substantially all of the sides of the roasting chamber, a large amount of heat formerly lost to the atmosphere is retained either in the combustion chamber, thus increasing the temperature therein, or is utilized to dry and preheat the fines, some of the heat transmitted outwardly through the walls of the burner being returned to the combustion chamber as preheat in the fines. Furthermore, inasmuch as the area of heated surface available for drying is largely increased by this procedure, it will be seen that relatively large quantities of ore may be dried and preheated, to

say 300 to 400 F., prior to introduction into the combustion chamber.

Fines ores are usually in a wet or damp condition, and hence preferably require drying before roasting by suspension methods. Generally, in prior methods for suspension roasting of fines, it has been necessary to provide elaborate additional apparatus to dry the fines sufiiciently to permit formation of a good suspension in the roasting chamber. By the present method, the wet fines are dried and after drying, preheated to substantially elevated temperatures. It will be seen the capacity of a burner unit of given size is largely increased, inasmuch as one operating limitation of the burner is the amount of ore which can be dried and preheated per unit of time.

The fines dried, or dried and preheated, by passage through jacket 32 are directed by sloping edges 45 toward outlets 38 through which the material is fed to the subjacent hoppers and thence into funnels 52.

Valves 56in feed pipes 53 are adjusted so that a substantially steady stream of fines runs into feed conduits 6i The fines are then injected into the combustion chamber i2 by means of air, steam, or other gas not adversely affecting oxidation of the sulphide. It is preferred to employ air for this purpose, and when using the latter, air may be introduced into the lower ends of conduits 69 through valve-controlled jets at pressures of about 5 pounds per square inch.

The axes of inlet conduits 6 l Fig. 1, the amount of fines fed into the injectors through pipes 53, and the air pressure in jets 65, regulated by valves 67, are all adjusted with respect to the particular size of the roasting chamber so that the ore particles from each injector rise through the combustion chamber to an elevation just below the underside ,of crown l5. Ore particles then fall to hearth I5, and while passing through an atmosphere increasingly rich in oxygen, oxidation of the fines is completed. It will be understood in the embodiment of the invention shown in Fig. 1, the major portion of the air for roasting is drawn into the combustion chamber through ports 13 by a suction fan in the gas outlet conduit I1 through which the gaseous products or roasting are withdrawn. The roasting operation per se is no part of the present invention, and hence need not be further detailed.

The sulphur dioxide gases produced may be used, for example, in the manufacture of sulphuric acid. Thesulphur dioxide content of the burner gas may be regulated as desired by adjusting the amount of air fed into the combustion chamber as is known by those skilled in the Gil art. Gases containing say about -13% sulphur dioxide may be readily made by the present process.

We claim:

5 1. Apparatus for treating material comprising a shell forming a reaction chamber having a substantially flat top, means for passing material to be treated over the top, means for subsequently passing said material over at least a substantial l0 portion of the walls of the reaction chamber including means for intermittently exposing a large portion of the said material to the atmosphere while passing over the walls, and means for feeding said material after passage over said walls into the reaction chamber.

2. Apparatus for roasting finely divided metal sulphides comprising a vertically disposed shell forming a combustion chamber, said chamber having a relatively flat top, a plurality of spaced louvers forming with the outer walls of the shell a jacket covering at least a substantial portion of the side walls of the shell, means for feeding finely divided sulphide onto the center of the top, means for working the material over the top of the shell and into the top of the jacket, an outlet for fines at the bottom of the jacket, means for feeding fines into the combustion chamber, means between the outlet of the jacket and the feeding means for introducing material into the latter, means for discharging cinder from the combustion chamber, and means for withdrawing gases therefrom.

3. Apparatus for roasting finely divided metal sulphides comprising a vertically disposed shell iorming a combustion chamber having a relatively ilat top, a plurality of spaced louvers forming with the outer surface of the shell 9. jacket covering at least a substantial portion of the side walls of the shell, means for feeding sulphides onto the center of the top, means for gradually working the sulphides over the top of the shell and into the top of the jacket, means for withdrawing sulphides from the bottom of the jacket, an injector adjacent the base of the combustion chamber having an upwardly directed inlet conduit, means for feeding sulphides into the injector, means for charging the sulphides into the combustion chamher and forming therein a suspension of sulphides in an oxidizing gas, means for discharging cinder from the bottom of the combustion chamber, and

' means for withdrawing sulphur dioxide containing gases therefrom.

4. Apparatus for roasting finely divided metal sulphides comprising a vertically disposed shell forming a combustion chamber having a relatively iiat top, a plurality of spaced louvers forming with the outer surface of the shell a jacket covering at phides over the top of the shell and into the top of the jacket, a plurality of peripherally spaced outlets for the fines at the bottom of the jacket,

a plurality of peripherally spaced injectors adjacent the base of the combustion chamber, each having an upwardly directed inlet conduit, means between the jacket outlets and the injectors for feeding sulphides into the injectors, means for charging the sulphides into the combustion chamber in such manner as to approach the top of the combustion chamber, means for passing a stream of oxidizing gas upwardly through the chamber, and means for withdrawing sulphur dioxide containing gases therefrom.

5. Apparatus for treating material comprising a vertically disposed shell forming a treating chamber, said chamber having a relatively fiat top, a plurality of spaced louvers forming with the outer walls of the shell a jacket covering at least a substantial portion of the side walls of the shell, means for feeding material to be treated onto the center of the top, means for working the material over the top of the shell and into the top of the jacket, an outlet for material at the bottom of the jacket, means for feeding material into the treating chamber, means between the outlet of the jacket and the feeding means for introducing material into the latter, means for discharging solid residue from the treating chamber, and means for withdrawing gas therefrom.

6. Apparatus for treating material comprising a vertically disposed shell forming a treating chamber, said chamber having a relatively flat top, means forming with walls of the shell 2. jacket through which material to be treated is adapted to be passed, said means being constructed so as to cause intermittent exposure of at least a substantial portion of the material to the atmosphere and efiect escape from the material of vapor substantially as soon as generated while the material passes through the jacket, means for feeding material to be treated onto the center of the top, means for gradually working the material over the top of the shell and into the top of the jacket, an outlet for material at the bottom of the jacket, means for feeding the material into the treating chamber, means between the outlet of the jacket and the feeding means for introducing material into the latter, means for discharging solid residue from the treating chamber, and means for withdrawing gas therefrom.

EDWIN J. MULLEN.

t CHARLES A. GALIAGHER.

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