US2070237A - Production of sulphur dioxide - Google Patents

Description

Feb. 9, 1937. E. J. MULLEN PRODUCTION OF SULPHUR DIOXIDE Filed Dec. 3l, 1934 2 Sheets-Sheet 2 lNvEN'roR ATTORNEY idw/'n I Mul/en Patented Feb. 9, 1937 nntp stares aereas? -rnonuc'rron or simenon nroxmr. IEdwin l. Mullen, New Rochelle, N. Y., assigner to omer General Uhemical Company, New York, N." Y., a corporationof New York `milpilication Decennher 3l; 1934, Serial No. 759.375

Y 5 illaims. This invention is directed to methods and ap` paratus for roasting metal sulphides, and more I' and advantages thereof may be understood from hoppers 30.

a consideration of the following description taken in connection with the accompanying drawings,

in which Fig. l is a vertical section of a preferred form of burner for vcarrying out one embodiment of the improved process;

Fig. 2 is a vertical section of the lower por'` tion of a modied burner; f

Fig. 3 is a vertical section of the lower portion of another modined burner, and

' Fig. fl is a vertical section of a fines injector.

Referring particularly to Fig. l of the drawings, it designates a shaft burner comprising a steel shell or casing il within which is placed the furnace lining l2 made of suitable refractory material such as hrebrick. The upper part of the burner is formed by a crown l the top side of which forms a drying or preheating hearth il. The shell ll projects upwardly beyond the crown 4E55 and carries a framework it which in turn supports ore feeding and rabhling mecha- 30 'nisxn for the drying hearth.

The surface of hearth il is slightly coneshaped and slopes, downwardly toward the shell of the burner. Lying above the hearth are rabhle arms it having downwardly projecting plows o 2li pitched to work sulphides` gradually tpward the circumference of the drying hearth. Arms. l@ are rotated by a motor 22 through shaft 23 supported in bearings so as to maintain the iower ends of the plows 2@ spaced above the surface of the drying hearth. An ore bin 2t, mounted on framework it, discharges onreonto-a platform 2t from which the nes are -internnlttently dropped onto the center of hearth lli by a sweep El rotating Awith shaft 23.

Attached to shell il by suitable brackets, not shown, are hoppers at covered by sloping screens 3E. Oversized material discharged by screens 3l is collected by receptacles' -32 and conveyed by means not shown to a crush'er, or used in a bed roaster or otherwise disposed of. Cut through shell Il l near the upper end are downwardly .sloping passages or conduits 34. through which ore is passed from drying hearth ll into It will be understood the number of conduits 34 and hoppers 30 coniun- (ci. roma) i non with the burner correspond with. the mmrber ofy nes injectors employed. 0n rotation of rabble arms i9, the sulphide ines are' gradually fed through openings 34 into hoppers 3B, which discharge nes into feed pipes tti having at' their lower ends suitable means such as slide valves Bt for controlling flow of nues out of the lower ends of pipes 35. v 'The nes injectors, one of which is shown in vertical section in Fig. 4,'comprise principally an elongated pipe section or nozzle 38 providing an ore inlet conduit. A pipe 3Q, carrying on the upper end funnel do, is arranged to feed; nes into the lower end of nozzle or other gas used to injectv the nes intofthe burner is supplied from a bustle pipe t2 surrounding the lower 'end of the burner. Bustle d2 may be connected to a blower or other source of air through pipe lid.' Adjacent each injector, pipe t? is provided with a nipple t5 having a control valve fit., Numeral' il indicates a" exible hose connection attached at one end to nipple l5 andv at the other end to air jet it in the bottom of nozzle 3d. The upper end of each nozzle 3h extends through ari opening te and projects into 'the lower end of the burner.' Each injector unit, comprising a nozzle tt, feedpipe 39, funnel t@ and/connection dl, may be held approximately in the position shown in the drawings `by a suitable bracket not shown made in such a way as to permit adjustment of nozzle .fit toward and away from the vertical axis of the burner. Each open- 'ing di? is made sufficiently larger than the diameter of a nozzle to permit the vdesired adiustment. f"lihe burner may be provided with any desired number of injectors; in the embodiment of the burner illustrated in Fig. 1, two injectors are shown.

rlhe outer circular furnace lining i2 and casing il are carried bya plurality of pillars 52. A short cylindrical -wall tt, positioned concentrically with respect to outer casing li, forms a support for a vertically elongated), somewhat frusto-conical shaped shell 5 5 made of briclawork `of substantial thickness. The vertical lengths of shell 55 and outer furnace lining l2" are desirably about in the proportions shown in the drawings. Shell 55 provides on the inside thereof a. sedimentation chamber7 56. having a hoppershaped bottom formed by an inverted conelike hearth 5l terminating in a cinder discharge trough $8 provided with a. screw conveyor 59, or other suitable Ameans for discharging cinder from the burner.

The outer surface of shell -55 and the inner surface of the lower part of furnace lining l2 form an annular chamber 62 which together with the' space between the upper end of the shell 55 and the under'side of crown l5 constitute a combustion chamber designated generally by 53. The bottom of annular chamber 52 is formed by an inverted frusto-conical shaped wall section- 64 and the' upper end 65 of a cylindrical supporting wall 54. circumferentially spaced about the lower edge of wall i are several yopenings 68 through which lair is introduced into the air preheating chamber 69 'the air inlet ports formed bythe inner surface of circular wall 56 and the under side of sedimentation chamber hearth 57. In the upper edge of circular wall 54 are passages 1li aifording communication between chamber 59 and the lower end of annular chamber 62. Each opening 70 is of substantial size and is located in a vertical plane including a nozzle 38 and the vertical axis of the burner.

'I'he bulk of the air usedto support combustion in the burner is introduced through openings 58, chamber 69and passagesl. A gas main 'H "for withdrawing gaseous products of combustion from the burner opens into' the'up- ,per -end of the combustion chamber 63 at a` point preferably just beneath the under side of crown I5.

The burner shown in vertical section in Fig. 2 is in most respects the same asdescribed in connection with Fig. 1. The major diiferences of construction of the bumer of Fig. 2 are 'that l2 are circumferentially spaced about the lower end of outer casing l i y cation between ber Tl. In the is maintained in and lie in a horizontal plane positioned substantially above the upper end of nozzles 38 and also above the outlet ends of a plurality of openings 'M in shell 55' which openings afford communichamber 15 and tHe lower end of annular chamburner of Fig. 2, the gas main, for withdrawing gaseous products of combustion from the burner, 'opens into the top of the combustion chamber' as shown. in Fig.

i The construction of the burner of Fig. 3 is generally similar to that of Fig. 1. In Fig. 3, the.

air for. supporting oxidation of the nes passes into the lower end of annular chamber 'I9 through openings 8| in the lower edge of circular wall 54., chamber 69, and passages 82. The major structural difference between the burners of Fig. 3 and of Fig.31 is that in the furnace of Fig. 3, the combustion gas offtake conduit 85 passes through the lower ends of outer casing Il and lining i2, through thelower end of annular chamber 79, and opens into the bottom of sedimentation chamber 81 at aboutthe upper edge of hearth 88.

In the burners of both Figs. 2 and 3, it will be understood the relative proportions between the vertical lengths of the sedimentation chambers and the outer .burner casings il and linings i2 are substantially the saine as in Fig.

The invention is applicable to the roasting of nely divided metal sulphides such as iron pyzinc sulphide or arsenopyrite, but for convenience may bedescribed in ing of iron pyrites.

Referring to Fig. 1, a supply of sulphide nes the bin 24 by a suitable conmechanism not shown. Be-

connection with the roastveyor or elevator fore roasting is preheated te the ignition point df the particuface of 'the hearth il and into the the lower end of sedimentationthe operation of the process is begun, the-inside of the burnery lar ore to be roasted as by means of 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 2li onto platform 25, and on each revolution of shaft 23 a regulated quantity of nes is swept off the platform to approximately the center of hearth I1. During rotation of the rabble arms i9 the concentrates are gradually worked across the surseveral passages 341. The dry or dry and partly preheated ore runs onto sloping screens 3i, which remove Valves 36 in pipes 35 are adjusted so that substantially steady streams' of nes of required volumes run into the lower ends of nozzles 38 through funnels and pipes 39. Air, steam, or other gas, not adversely aecting oxidation of the sulphide, may bel employed to charge the rines into the combustion chamber. For this purpose, it is preferred to employ air which may be admitted to the lower endsA of nozzles 38 through jets 18 at pressures of, for example, about 5 pounds per 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. For

example, a combustible gas might be employed to inject the fines.

The particular angle with respect to the horizontal of the axes of nozzles 38 is dependent upon such features as the sizeof the burner, the height of the combustion chamber, the height of shell 55 and the distance between shell 55 and the furnace lining l2. The angle of the axes of nozzles 38, the amount of iines fed into the injectors through pipes 35, and the air pressure inl jets 48, adjusted by valves 13S, are all regulated with respect to the proportions of the particular roasting chamber sol that there is imparted to the sulphideflnes particles from each injector suicient velocity to rise through the combustion chamber, away from the walls thereof, to an elevation preferably just below the underside of crown l5. The angular position of a particular' nozzle 38 and the rate of supply of nes and air thereto are likewise controlled so that the'horizontal travel of the ore particles while reaching the top of the combustion chamber and after dropping to the bottom of sedimentation chamber '56, does not exceed, say, two-thirds and preferably about one-half thediameter of the burner. 'I'he dotted line 95 of Fig. 1 indicates the approximate path of travel of an ore particle of average size introduced through one of the injectors. Thus it will be seen the ore particles move first over a trajectory having an initially short horizontal component and a relatively large vertical component, then a relatively large horizontal component and a short vertical component, and

' less than or exceed the height by a substantial amount.V In any event, to obtain the full bene-` ts of the invention, the horizontal cross-sectionv of the burner should be relatively large. The large diameter of the combustion chamber in commotion with the desired manner of introducing the nes preventsv contact between any substantial quantities of ore particles and the hotwalls of the roasting chamberthus avoid- `ing accumulation of scar on the walls. As

known to those skilled in the art, scar forma' tion is one of the most serious operating diculties encountered in suspension roasting. The process of the invention alsof permits use of burners of relatively low height `which is an important feature with respect to cost reduc. tion bothwith respect to the burner and the building within which it is housed.

A major `portion of the total-quantity `oi air or other oxidizing gas-necessary to support the oxidation reaction is drawn into the combustion chamber 63 at the bottom through ports 68, chamber be, and passages l0. air enters the combustion chamber at 'a velocity substantially less than the velocity of the ore particles introduced through nozzles 3B. Where air is employed for injecting the fines through The incoming nozzles 38, not more than about 10% of thel total air required for oxidation would ordinarily be introduced through the several air jets 43,.

although larger amounts may be used if desired. In the preferred operation, .where only a relatively small proportion oftotalair is introduced through the injectors, it may be considered that substantially all the air is introduced into the combustion chamber preheating chamber E@ as described, and initially flows upwardly through the combustion chamber.

The described method of introducing the sulphide iines and the main stream of oxidizing gas into ,the burner at different velocities is a feature of,l relative importance. By imparting to the ore particles, independently of the main stream of oxidizing gas, sulcient velocity to cause them to pass over-a trajectory such as described, the path of the ore particles can be controlled and maintained as desired to substantially avoid contact of ore particles with the hotfurnace walls to which the ore particles migiht adhere with resulting scar formation. Inasmuch as the ore particles have a velocity greater than that of the main air stream, the tendency of the latter to interrupt the desired path of travel of the ore 'particles and cause them to impinge onthe walls'or other surfaces of the combustion chamber is reduced.

It is to beobserved that during the latter Vpart of the upward travel/of the nes and during that portion of downward travel say prior to entry into the top of subsidence chamber 56, the rate of rvertioal 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 ,movef ment of 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 oi relatively shortv vertical dimension, the roasting of relatively coarse ore,` and increased capacity of thel ber, it will be seen the nes are immediately charged intoan atmosphere rich in oxygen. Ig-

nition of the upwardly moving ore particles takes place rapidly owing to the'high temperatures existing in the combustion chamber.

Prompt ignition of the nes is also facilitated by heat contained in the incoming air which is preheated to a substantial extent in chamber 59 surrounding hearth 51. The nes, following ignition, continue to rise to approximately the top of the combustion chamber, the temperature of the particles increasing because of rapidly progressing roasting. Part of the air stream entering the combustion chamber from openings 'lll imoves upwardly generally between .the fines and the outer surfacemof shell 55 and aids in preventing scarring on the outer surface and top edge of shell 55. Combustion of the nes particles is substantially complete by the time the particles fall back and enter the top of sediof sulphur dioxide may be made by this process.

Cinder particles drop through a quiescent zone ings i0 at the bottom of the combustion chammaintained in sedimentation chamber 56, the

cinder collecting in a free-flowing condition on hearth 51' and running continuously into trough 58 from which the cinderl is removed by conveyor 59.

In accordance with the present invention, provision of inner shell 55 and the associated chamber 56 provide several operating advantages, some of which are as follows:

In the preferred construction, shell 55 is made of such height and diameter as to provide about 25 to 40% more wall surface within the burner than would be the casein the absence of the shell. As has been noted, the preferred relative proportions between the shell 55 and the outer walls of the burner are about as illustrated in the drawings in which instance the outside face bustion zone above those which would exist in the absence of shell 5 5. Temperatures prevailing in the combustion zone may be of the order of 1700 to 1900 F. Higher temperatures in chamber 62 wd in the combustion zone as a whole in turn cause. more rapid ignition of nes and insure substantially 'completev combustion and desulphurization before thev nesenter the toprof sedimentation chamber 56. The presence orf the added heart reflecting surface afforded by the shell 55 materially enhances rapidity of ignition and/completion of combustion and desulphurization whichare to a large dehence the cinder reaches the bottom gree dependent upon the amount o f radiant heat emanating from the heated walls.

Introduction of air through chambers such as 69 of Fig. l absorbs heat from hearth: 5l and preheats the incoming combustion supporting air. Admission of this preheated air into the zone of initial introduction of the nes aids in rapid ignition and completion of combustion of the nes.

yIn the embodiment of thev burner illustrated, refractory shell 55 is made about eight to ten inches thick, and consequently is a poor conductor of heat from chamber 62 to sedimentation chamber 56 which thus forms a zone substantially insulatedA fromthe high combustion temperatures in the burner. Shell 55 accordingly provides the further important advantage of shielding the burnt-out or desulphurized ore particles from the radiant heat and high temperatures of vthe combustion zone outside sedimentation chamber 56. Cinder produced in the process is an excellent absorber vof radiant heat beingabout 95% as effective as lamp black. After desulphurization and entry lof the cinder into the top of chamber 56, shell 55 protects the iron oxidecinder from a great part of the heat radiated in the combustion-chamber, and of the sedimentation chamber at considerably lower temperature than if exposed to Aintense radiant heat on its downward path yi-n the absence of refractory shell 55, thus resulting in prevention of clinkering of cinder on hearth 51 and facilitating removal of cinder from the burner in a free-flowing condition. Onfaccount of the insulating .effects of shell .55, the temperatures in sedimentation chamber 56 may be of the order of about` 250 to 400 F. less than those prevailing in the hottest of the combustion zone.

In suspension roasting, a condition of turbulence tends to exist in the combustion chamber caused by rapid burning of the ore particles and changes in air and gas volumes by abrupt changes in temperature. This tends to 'maintain burnt ore particles in suspension and to interfere with settling of such some instances this may cause suspension of cinder,V particles. In

substantial quantities of cinder andcdust in the sulphur dioxide` gas stream Such condition is prevented to a" large extent by sedimentation chamber 56 which provides a )quiescent zone in which the cinder is not influenced by gas movements in the ore burning zone. Provision of chamber 56 permits ne burnt ,ore particles to readilyv settle out of the th roasting ore particles.

combustion zone inthe burner.

In addition to theabove advantages outlined .in connection with theapparatus of Fig. l, in

the burner of Fig. 2, thereare -provided in the lower end of sedimentation chambers 15 ports 14`which permit relatively .slow circulation of hot sulphur dioxide gases through the vsedimentation chamber 15 and annular chamber Tl. The comparatively slow downward gas movement in chamber'15 prolongs the time of contact of the ore particles with a. more or less oxidizing atmosphere thus creating a condition conducive to complete desulphurization. down-flow of Vgas in chamber15 aids in settling The induced upward now through annular chamber 1l of sulphur dioxide bearing gases from the lower part -of sedimentation chamber l5 operates to transfer some of the heat from the iron oxide particles terial leaving the burner.

I eating at the top The same slow adidas? in zone 'i5 to the lower end of chamber 'E'Lthus further aiding in avoiding clinkering of cinder in sedimentation chamber l5, and enhancing the 'rapidity and completeness of roasting of ore introduced into the lower end of chamber Ti.

In the burner of Fig. '3 in which the sulphur dioxide combustion gases are withdrawn through conduit, 65 from the lower end of vsedimentation A metal sulphide material to produce sulphur dioxide which lcomprises injecting -the sulphide material upwardly atv the outer periphery and at the base po'rtion of a combustion zone by means of air at superatmospheric pressure, introducing a stream of oxidizing gasinto'the base portion of the combustion zone; roasting the material in material and the gas upwardly in co-current iow.v relation, withdrawing sulphur dioxide from the top4 of the combustion zone, passing the material, `while suspended, downwardly through an inner sedimentation zone communicating at the top with and arranged concentrically with respect to the outer terial is shielded, while suspended, from high combustion temperatures and absorption of heat by the material is minimized, and discharging solid material from the bottom of the sedimentation zone.

2. The method for roasting nely divided metal sulphide material to producesulphur dioxcombustion zone, said sedimentation zone being relatively insulated from. high combustion temperatures whereby the masuspension in the oxidizing gas while passing'the w ide which comprises injecting the sulphide maupwardly at the base portion of a combustion zone so as to cause thematerial -to move upwardly through, the combustion zone to av point approaching the upper endthereof, introducing a stream of oxidizing gas into the base portion of thev combustion zone, roasting the material in' suspension in the oxidizing gas while passing the material and the gas upwardly in co-current flow relation, withdrawing sulphur dioxide from the `top of the combustion zone, wardly through a sedimentation zonecommunily concentrically with respect to the'combustion passing the material, while suspended, downwith and arranged substantialzone, said sedimentation zone being relatively insulated from high combustion temperatures whereby the material is'shielded, while suspended, from high combustion temperaturesfabsorption of heat by whereby the material is permitted to settle through a zone substantially undisturbed by the gas currents of the combustionfizone; and discharging solid material from the bottom'of the sdimentation zone.

3. The method for roasting lnely divided metal sulphide material to produce sulphur dioxide which comprises injecting the sulphide material upwardly at the base portion of a combustion zone so as to cause the material to move upwardly through the combustion zone to'a point approaching the' upper end thereof, introducing a stream of oxidizing gas, moving at a velocity the material is minimized, and.

lil

substantially less then that of the initial rate o movement of the fines materiel, into the hase portion oi the combustion zone, roasting the mu-A teriel in suspension in the 'i' wlw. ges while poss the materiel and the gas upwardly in cri-current new relation, withdrawing sulphur dioxide from the top of the combustion zone, passing the materiel, While susded, "dowm wardly throughl o sedimentation zone oo noting et the top with and arranged substantielly eoncentrically with respect to the combustion zone, seid sedimentation zone heine relatively insulated from high combustion temperatures whereby the materiel is shielded, while suspended, from high combustion tei'nperuizures,` absorption oi heut by the materiel is v und whereloy the materiel is permitted to settle through e,

zone substantially undisturmd hy the guscurrents of the combustion zone; end discharging solid materiel from the bottom of the seentetion zone.

d. The method for roest ilnely divided f metal sulphide teriai to produce sulphur dioxide which comprises injecting the sulphide nieteriei upwardly et the outer periphery :tw et the hose portion of e. ycomhustion zone hy ineens oi gos et superatmospheric pressure, introducing e stream of oxidi eas, moving et o Velocity substantially less than that oi the initial rete oi movement oi the iines materiel, into the hustion zone, seid sedimentation ione '1- tively insulated from high combustion temlaeru tures whereby the materiel is shielded, while suspended, from high combustion temperatures, absorption oi heet by the materiel is :Il f ,1f A--.. und whereby the materiel is permitted to settle through e zone substantially undisturbed by ges currents oi theeomioustion zone; undoiischeise-I ing 'solid muteriel from the bottom oi the sedimentation sone.,

The method for roasting nely dividedmetal sulphide materiel to produce sulphurdioxide which comprises injecting the sulphide matenel upwardly et the outer periphery end et the hase portion of a combustion zone hy means of ges et super-atmospheric pressure, introducing e. stream of oxidizing gos moving et e velocity snhstentiully less n that of the initial rete oi movement of the nes materiel into the hase portion of the combustion zone, roasting the materiel in suspension in the oxidizing gas while pussingthe materiel end the ges upwardly in co-current dow relation, withdrawing sulphur dioxide from the top of the combustion zone, passing lthe materiel, while suspended, downwerdly through en inner sedimentation zone counieetine et the top with and arranged concentricelly with respect to theouter `combustion zone, seid sedimentation zone being rela,- tively insulated from high combustion tempera.- tures whereby the materiel is shielded, while suspended, from high combustion temperatures, uhsorption of heet by the materiel is minimized, and whereby the material is permitted to settle through e zone substantially undisturbed by ees currents oi the combustion zone; und dischargine solid materiel from the bottom oi the sedimentution zone.

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