US2067027A - Production of sulphur dioxide - Google Patents

Description

Jan'. 5, 1937. c. F. slLsBY 2,067,027

Y. PRODUCTION OF, SULPHUR DIOXIDE Filed Sept. 20, 1954 y INVENTQR CFO/bes Siby ATTORNEY Patented Jan.. 5., 19137- NITED y-sl'i'rrra atentar raonUc'rroN or s Charles Forbes Silsby, te l signor to General @hemical Company, New York, N. Y., a corporation oil New York Application september zo, i934, son No. raar-7s This invention is directedto methods and ap-A paratus for roasting metal sulphides, and more particularly for roasting finely divided sulphidej consideration of the following description taken infconnection with the accom which Fig. 1 is a vertical section of a preferred burner for carrying'out the improved process; Fig. 2 is an enlarged vertical section of a preferred type ore feeding mechanism; and

nying drawing in r Fig. 3 is a horizontal section taken" approxi mately on the line 3 3 of Fig. 1.

i Referring particularly to Fig. 1l of the drawing, itdesignates a shaft burner, comprising a steel shell or casing lll within which is placed the -furnace lining i3.` constructed of suitable'refractory material such as lire-brick, and defining a roasting chamber l2 of cylindrical cross-section. The upper part of the combustion chamber is closed oif by a crown'l,A thetop side-of which' forms a drying or preheating hearth il. The shell il projects upwardly beyond the crown lo and carries a steel framework i8 which in turn supports ore 'feeding and rabbling mechanisml for the drying hearth.

The surface of the drying hearth l'l is slightly cone-shaped and slopes downwardly toward the shell of the burner. Lying above the hearth are. rabble arms l@ having downwardly projecting plows 2li pitched to work sulphides gradually tov ward Jthe circumference of the drying hearth.- Arms i9 are rotated by a motor 22 through shaft 23 supported in bearings so as to maintain the lower ends ofthe plows 2li spaced with respect to the surface of the drying hearth I1. An orey bi'n 2t, mounted on framework i8 discharges ore onto a platform 25 from which the n'es are intermittently dropped 'onto the center of hearth lll by .a sweep 21 rotating on shaft 23.. .v

Attached to shell Il by suitable brackets, not

shown, are hoppers 36 covered by sloping screens 3|. Cut through the steel shell II and also in the A upper edge of lining I3 are downwardly sloping passages or conduits 34 through which ore is passed from the drying hearth Il into hoppers 30. It Will'be understood the number of conduits and hoppers used in conjunction with the burner may correspond with the number of injectors 40 employed. On rotation of rabble arms I9, the sul v plaide fines in gradully fed through opening M into hoppers 3f which discharge nes into feed pipes 35 having control valves 36.

An ore injector, shown in-vertical section .in

Fig. 2 and also shown for convenience in vertical section in Fig. 1, comprises principally a metallic pipe section t2, the inner end of which is set into the shell of the burner in the lower .endvof the combustion chamber, tubeV t2 providing an ore] inlet conduit t3. v'llube t2 is held in position, as

indicated in Fig. 2, by a circular plate t5 and a flange 'i/bclted to the steel shell il. The axis of tube t2 is directed upwardly at a relatively sharp angle which may be about '75 from the horizontal.

Y As shown in Fig. 2, valve-controlled feed pipe 3b projects into the upper side of tube t?. A gas inlet pipe i@ passes through end plate 5@ closing the bottom of conduit di and terminates beneath the discharge end of pipe 35. Plug t2 provides a means. for cleaning out conduit to should the same become stopped up.

The burner maybe provided with anysuitable number of injectors. In the embodiment of the 4burner illustrated in the drawing four injectors 'are employed as shown in Fig. 3. The injectors air inlet header 5i provided with a control valve' 55. The rate of discharge'oiair into each conl duit 4t may be separately controlled by a valve 5t.

The combustion chamber is provided with a fire-brick partition orbridge wall'b sloping in-i wardly toward the vertical axis ofthe combustion chamber. The .wall 53, shown in vertical scetion and in plan in Figs. 1 and 3, is built arch` like across the combustion chamber, and is con-f structed so that. any horizontal section through the wall is more or less crescent-shaped. As seen f irrIgig. 3, the upper edge o@ is only slightly bent horizontally toward the burner wall, whereas the curvature of a horizontal section becomes more f pronounced toward the bottom of the wall, for

example as indicated lby 62, Fig. 3. The greater part of the air' used to support combustion in the roasting ychamber is introducedvthrough a main 6d opening into a chamber 65 formed by an arch '61, the partition' 58 and the inner burner wall.

Formed ,on th'e upper face of Wall 58 is a plurality of reiatively'small, diverging air ducts 'ill opening at the bottom into chamber 65 and terminating at the upper end short of the' top of wall 53. Duets 10 may be formed by suitably placed cover and spacer bricks 'li and 12 respectively. Air dispyrites.

charged from ducts 'I0 flows upwardly over the `surface of partition 58 to the top end thereof.

The bottom of combustion chamber I2 isA formed by a hopper-shaped, brick-faced hearth 'I5 terminating in an outlet II through which cinder continuously discharges into a conveyor. As desired, the surface of hearth I5 may be pitched'at an angle less or greater than the angle of repose of the cinder. A gas main 80, for withdrawing gaseous products of combustion from roasting chamber I2, opens into the latter at a point just above the hopper-shaped bottom as shown in Fig. 1. v

'I'he invention is applicable to the roasting of finely divided metal sulphides such as iron pyrites, pyrrhotite, zinc sulphide or arsenopyrite,but for convenience the operation of the process may -be described in connection with the roasting of iron A supply of sulphide fines is maintained in the bin 24 by a suitable conveyor or elevator mechanism not shown. Before roasting is begun, combustion chamber I2 is preheated to the ignition point of the particular ore to be roasted by means oi' oil burners inserted through conveniently located workholes, not shown.` When the desired degree of preheat is obtained, motor 22 is started, and rabble arms I9 and sweep 21 may be rotated at a rate of, say, one revolution in two minutes.

Fines run continuously out of hopper 24 onto platform 25, and on each revolution of shaft 23 a regulated Vquantity of nes is swept olf the platform toapproximately the center of hearth I'I.

as During rotation of the rabble arms I9 the sulphide fines are gradually worked across the surface of the hearth I1 and into the several passages 34, each of which communicates with a hopper 3U. 'I'he dry or dry and partly preheated ore runs Aonto sloping screens 3|, which remove lumps, and thence into hoppers 30 and feed pipes 36. Oversize material discharged by screens 3l is collected by receptacles 32 and conveyed by means not shown to a crusher, or used in a bed `roaster or otherwise disposed of.

Valves 36 in pipes 35 are adjusted so that a substantially steady stream oi' lines runs into feed conduits 43. Air,'ste`am, or other gas, not adversely affecting oxidation of the sulphide, may

be employed to charge the fines into the com-l bustion chamber.

For this purpose it is preferred to employ air which may be admitted to the lower` endsof conduits 42 through valvecontrolled jets 49 at pressures of, for example, about 5 poundsper square inch.

If the ore being roasted is of such nature that extraneous fuel is required to maintain proper roasting temperatures, such fuel in any suitable form may be introduced into the 'combustion chamber through the ore feed mechanism. kFor example, a combustible gas might be employed to inJect the fines.

The particular angle of the axes of conduits 4! .s dependent upon the size and type of combultion chamber which may be employed. The angles of the axes of conduits 42,.,the amountl of lines fed into the iniectors through pipes '35, and the air pressure in jets 49, adjusted by valves 56, are all regulated with respect to the particular size of the roasting chamber so that there is imparted to the ore particles from each injector sufllcient velocity to rise through the combus-`r tion chamber, away fromV thewalls thereof, to an elevation preferably just below the underside of crown I5. The angular -position of a particular conduit 42 and the rate of suppLv of we and air mately equal.

the dotted line 'I4 indicates the approximate path oi' travel of an ore particle of average size introduced through one of the injectors. Thus it will be seen the ore particles move in a, trajectory having initially a large vertical component, thenl a large horizontal component and thereafter' a large vertical component. In this manner the fines are caused to pass over substantially the longest possible path of travel considering the proportions of the combustion chamber. Aplurality of injectors are used preferably to effectively cover the area of the combustion-chamber. As previously mentioned, the outerl injectors are set at a somewhat higher elevation than the inner injectors, as the horizontal component of the arch of ore particles admitted through the outer injectors is less than in the case of the inner injectors.

In conjunction with other aspects, one of the important features of the invention relates to the relative proportions of the combustion chamber. In the speciiic embodiment of the burner illustrated in the drawing, the diameter and height of the combustion chamber are approxi- While this proportion is preferred, it is understood that the diameter of the chamber may in some instances desirably be less than or exceed the height by a substantial amount. In any event, to obtain the full benefits of the invention, the horizontal cross-section of the combustion chamber should be relatively large. The large diameter of the combustion chamber `in conjunction with the described manner of introducing the nes and combustion supporting air prevents contact between any substantial quantities of ore particles and the hot walls of the roasting chamber, thus avoiding accumulation of scar on the walls. As known to those skilled in the art, scar formation is one of the most serious operating diillculties encountered in suspension roasting.

The major portion of the total quantity of air or other oxidizing gas, necessary to support the oxidation reaction, is 'drawn into the combustion chamber at-the bottom through main 64 and ducts 'I0 and enters the combustion chamber at a velocity substantially less than the velocity of the ore particles introduced through the conduits 42. Where air is employed for injecting the fines through conduits 42, not more than about 10% of the total air required for oxidation would ordinarily be introduced through the several air iets 49, although larger amounts may be used if desired. In the preferred operation, where only a relatively small proportion of total air is introduced through the injectorait may be considered that substantially all the air is introduced into the combustion chamber through the main 64 and ducts III, and Initially flows upwardly through the combustion chamber. It should be noted that in accordance with the preferred construction ducts 'I0 are made of sunlciently restricted crosssection so that incoming air is flowed through` the ducts at a velocity sufcient to maintain a film of air over that portion of wall 58 above the ends of ducts 'Ill and to cause the air to rise substantially above the edge 60 of wall 58, but the velocity oir this main body sulphide nesandthe main stream of oxidizing' therair and or introduced through the ore jectors.

The method just described of introducing the gas at different velocities contributes materially to the successful operation of the present invention. By imparting to the ore particles, independently of the main stream of oxidizing gas, suflicient velocity to cause them to pass through the desired trajectory, the latter can be controlled and maintained as desired to avoid substantial contact of the ore particles with the walls of walls or other surfaces ofthe combustion chamber is minimized.

It is to be observed'during the latter part of the upward travel of the fines, the rate of vertical movement of the particles rapidly decreases to zero, and thereafter, during the initial part of the descent of the fines, the rate of downward movement of the lines is relatively small. Hence, while passing upwardly and downwardly through the upper zone of the combustion chamber, the average rate of movement o f the fines is low, and this slow rate of travel increases the time the, particles are in the roasting atmosphere, thereby giving a relatively long time for the reaction to proceed, thus permitting use of a roasting chamber of relatively short longitudinal dimension, the roasting of relatively coarse ore, and increased capacity of the burner.

'I'he sulphides are injected into the bottom of the combustion chamber through the several injectors IW, and, as substantially all of the air to support roasting is drawninto the'combustion chamberthrough ducts 10, it will be seen the fines are immediately charged into anf 'atmosphere relatively rich -in oxygen. Ignition of the upwardly moving ore particles takes place rapidly owing to the high temperatures existing in the combustion chamber. The large amount of air flowing upwardly 'over the upper surface of the baille 58, prevents contacting of any substantial quantity of `lines with the surface of bame 58 and accumulation of scar thereon is thus prevented. The fines, following ignition, continue to rise to approximaetly the top of the combustion chamber, the temperature of the particles increasing because of rapidly-progressing roasting. As previously explained, the average rate of travel of the ore particles upwardly and downwardly through, say, the upper half of the com- Y bustion chamber is` relatively low. Since the air for roasting is drawn into the combustion chamthe roasting chamber.- Hence, the ore particles,

during the relatively long time of suspension in the upper half of thecombustion chamber, are

in an atmosphere relatively rich in oxygen. The air current from ducts 1li, iiowing upwardly underneath the stream of fines, tends to forma support or cushion for the fines and aids in dispersing the iines in the upper part of the combustion chamber beyond the top edge of the baille. During the fall of the particles through the lower half of the combustion chamber roasting proceeds to completion, the`v cinder collecting on Conduit 80 preferably communicates with the inlet side of a blower so that the burner operates under a slightly negative pressure. When so operating, it is desirable to have partition 58 extend a substantial distance toward the top of the combustion chamber so as to canse the incom- .ing air stream from ducts 10 to flow initially upward a substantial distance to insure the presence of a relatively large amount of oxygen in the top of the combustion chamber. If itis desired to operate the burner under a positive pressure, the cinder discharge 61 may be provided with an air lock. If desired, the air introduced through main 64 may be preheated.

The iron oxide cinder falling on hopper-shaped hearth 'l5 is free-flowing and continuously runs out through opening 'il into a suitable conveyor. The sulphur dioxide gas withdrawn through gas main 80 may be used in the manufacture of sulphuric acid. The sulphur dioxide content of the burner gas may be regulated as desired by adjusting the amount of air fed into the corn-i bustion chamber as is known by those skilled in the art. Gases containing 10.0-12.5 per cent sulphur dioxide may be readily made by this process.

- ly co-currently through the roasting zone, con-v trolling introduction into and passage of the fines through the enlarged chamber so that the fines do not contact the roasting chamber walls, and withdrawing gaseous combustion products from the bottom ofthe roasting chamber, the invention provides a high capacity suspension roasting process in which the iines are passed over a long path of travel and maintained in the roasting atmosphere for a maximum period of time, scar formation on the roasting4 chamber walls is avoided. One of the important advantages of the invention is the provision of a large capacity process aording' roasting of large quantities of fines per unit of time per unit of apparatus. This advantage and that of avoiding scar formation on the burner walls may not be had Awhen operating in accordance with other generally similar prior proposed methods in which iines and air are introduced into and gaseous combustion products withdrawn from the bottom of theroasting chamber.` y

, In th above description and in the appended claims the term fines is intended to designate material in such a degree of subdivision as may be roasted while suspended in oxidizing gas.

I claim:

l. The method of roasting nely divided metal sulphides to produce sulphur dioxide which comprises introducing sulphide ines into the lower portion of a combustion chamber of relatively large horizontal cross-section at a velocitysuch as to carry the lines particles into the upper portion of the combustion chamber, then causing the said fines to pass downwardly through the said combustion chamber while out of contact with the walls of said combustion chamber, separately introducing a stream of combustion supporting gas moving-at a velocity less than that of ,said lines particles into the portion of the combustion chamber adjacent the Vpoint of introduction of the nes, and passing the combusiid wall and also the base portion of a substantially unobstructed combustion chamber of relatively largehorizontal cross-section and heated to a emperatureabove the ignition point of the nes by means of a stream of air under superatmospherlc pressure, causing the fines to pass upwardly and away from said wall, thenl causing the said lines to pass downwardly through the said combustion chamber while out of contact with f the walls of said combustion-chamber, separately introducing a stream of combustion supporting gas moving at a'velocity less than thatc of said iines particles into the portion of the combustion chamberadjacent the point of introduc` tionoi the fines and passing the oxygen-contaming gas upwardly and then downwardly through the combustion chamber in substantial co-current now with the fines, discharging the cinder from the bottom portion of the combustion chamber, and separately withdrawing sulphur dioxide-containing gases from the bottom portion ofthe combustion chamber.

3. Apparatus for roasting finely divided metal sulphides comprising 'a shell forming a. substanvtially cylindrical, vertically disposed, substantially unobstructed combustion chamber of relatively large horizontal cross-section, a nes ore feeding conduit in the periphery of the shell adjacent the base thereof, said conduit being inclined at'a relatively high angle to the horizontal and opening into the combustion chamber at a point higher than the inlet end of the said ore feeding conduit, means for feeding lnes ore into the feed conduit to charge ore into the combustion clfamber in an upwardly direction, a gas inlet port in the periphery adjacent the base of the shell and the ore feeding conduit, a baille in the combustion chamber arranged to direct gas introduced through said port in an upward direction substantially co-current with the nes ore, means for discharging cinder from the bottom of the combustion chamber, and a gas outlet at the bottom for withdrawing ygaseous products of combustion. .l l

4. Apparatus for roasting finely divided metal sulphides comprising'a shell forming a substantially cylindrical, vertically disposed, substantially unobstructed combustion chamber of relatively' large horizontal cross-section, a plurality o1' adjacently disposed fines ore feeding conduits in the periphery of the shell near the base thereof,

'said conduits being inclined at a relatively high angle to the horizontal and opening lnto'thec'ombustion chamber at points higher than the inlet ends of the said ore feeding conduits, means for i feeding nes ore into the feed conduits to charge ore into the combustion chamber in a plurality of upwardly directed streams, a gas inlet port inthe periphery adjacent the base of the shell-and the ore feeding conduits, means comprising a relatively vertically disposed partition extending across a portion of the combustion chamber and sloping toward the center thereofA for directing gas introduced through said port in an upward direction substantially co-currently with the nes me, means for discharging cinder from the bottom of the combustion chamber, and a gas outlet at the bottom for withdrawing gaseous products of combustion.

5. The method of roasting ilnely divided metal sulphides which comprises introducing sulphide fines adjacent a side wall and also the base portion of a substantially unobstructed combustion chamber of relatively large horizontal-cross-section and heated to a temperature above the ignition point of the nes, introducing said fines by means of a stream of gas of such superatmospheric pressure and so directed as to cause the fines to pass upwardly away from said wall over a path having ahorizontal component and to points adjacent the top of the combustion zone and to then cause the said fines to pass downwardly through the said combustion zone while l out of contact with the walls of said combustion chamber, separately introducing oxidizing gas in quantity sufcient to support combustion of the ines into the portion of theacombustion chamber adjacent the point of introduction of the tlnes and passing the combustion supporting gas`up wardly and vthen downwardly through lthe combustion chamber in substantially co-ourrent iiow 4with the iines, maintaining the fines 'in suspension in the oxidizing gas for a period of time sufiicient to yeffect substantially complete desulphur-A gas of such superatmospheric pressure and so dil rected as to cause the fines to,pass upwardly away from said wall over a path having a horizontal component 'and to points adjacent the top of the combustion zone and to then cause the said fines to pass downwardly through the said combustion zone while out of contact with the walls ofsaid combustion chamber, introducing oxidizing gas in quantity suiilcient' to support combustion of the fines into the portion of the Ac,-: mb'ustion chamber adjacent the point. o1' introduction of the iines and passing the combustion `supporting gas upwardly and then down'- wardly through the combustion chamber in substantially' co-current flow with the fines, malntaining the `nes in suspension in the oxidizing gas for a period of .time suiliicient toeffect substantially complete desulphurization of the nesf withdrawing sulphur# dioxide gases from the bottom of the combustion zone, vand discharging from the bottom ofthe colnl nieta] oxide cinder bustion zone.

. 7The method of roasting finelyy divided metal sulphides to produce sulphur dioxide which com- ,prises introducing sulphide fines into a combustion chambery of relatively large horizontal crosssection, ycausing the .sulphide iines to move ythrough a trajectory having initially a large hor-,- izontal 'and a large vertical component, then a predominatinghorizontal component and therei after'a large vertical component, said trajectory being such as to avoid substantial contact of the sulphide nes with surfacesin the combustion chamber throughout the movement of the sulphide lines. introducing a stream of oxygen congen concentration in the upper portion of the combustion chamber for a. maximum period of time, and maintaining the ines in suspension in the oxidizing gas for aperiod of time sufcient to eiect substantially complete desulphurization 5 of the nes.

CHARLES FORBES SILSBY.

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