US2113058A - Process for roasting ores - Google Patents

Description

Patented Apr. s, 1938 PATENT OFFICE raocEss roaaoAs'nNo oaEs Edwin J. Mullen, New Rochelle, N. Y., assignor to General Chemical Company, NewYork, N. Y., \a corporation oi' New York Application November 26, 1937, Serial No. 176,534

-10 Claims.

This invention is directed to methods for roast-V ing sulfide ores to desulfurize the same and to produce sulfur dioxide for use in the manufacture of sulfuric acid, or for any other purposes de- 5 sired. The invention is a development of my co-pending applications Serial Nos. 55,808 and 55,809, filed December 23, 1935.

To a substantial extent, present practice in roastingv of sulfidessuch as pyrites includes use l0 naces, such for example as the well-known Mac- Dougall, Herreshoff and Wedge burners. As distinguished from the' bed vor hearth vroasting operation of these burners, it has been suggested to roast finely divided sulfldes while in gaseous suspension. Suspension roasting processes such as shown for example in Burgoyne and Cordy U. S. Patent No. 1,758,188 of May 13, 1930 have been developed largely because of availability in re- U cent years of supplies of sulfldes, such as flotation concentrates, sulciently' nely dividedto permit roasting by suspension methods.

In the present state of the art of producing sulfur dioxide from sulfldes, it may be said that probably the major portion of the sulfur dioxide utilized in the manufacture of sulfur trioxide by the contact process is obtained by roasting what is known as pyrltes smal1s. The usual run-ofplle of pyrltes smalls has been crushed so that 100% passes about a half inch screen. A sub- :tantial portion of an ore of this type is sufficiently nely divided for suspension roasting if separated from the coarser material, although a large portion of the smalls, in many cases the V5;-, major portion, comprises ore too coarse for Suspension roasting by present methods. In the present specication, smalls is used in a generic sense to define a run-of-plle ore containing some ore fine enough for suspension roasting and some ore too coarse for suspension roasting. The term coarse is used to denote ore of too large parti# `cle size for roasting by suspension methods, and fines is utilized to designate sulfide ores sufficiently finely divided to permit roasting by suspension methods.

Since smalls usually contain a substantial portion of coarse ore, the smalls have heretofore been roasted as in a multi-hearth roaster. While multi-hearth furnaces such as the Wedge and Herreshoff burners provide effective roasting, use of burners of this type is objectionable principally on account of the low capacity per unit of apparatus per unit of time and because the complicated construction and operation involves substantial initial and maintenance expense. On

of mechanically operated multiple hearth furthe other hand, grinding of smalls by usual grinding operations, prior to roasting, to such degree of subdivision that all of the ore may beroasted in gaseous suspension is not desirable since, as

.well-known, fine grinding is one of the most expensive operations in metallurgical processes and in many instances grinding costs are prohibitive.

As disclosed in my earlier applications, I have previously found that when coarse ore is introduced into a combustion zone and suddenly sub jected to certain temperatures, preferably'not less than about 1300o F., the coarse ore particles are converted to a frangible, brittle condition which may be carried out in simple, rugged ap# paratus readily constructed and economically maintained.

The nature of the invention and the objects and advantages thereof may be fully understood from consideration of the following description taken in connection with the accompanying drawing illustrating in vertical longitudinal section a burner in which the improved process may be carried out. Referring to the drawing, I0 designates a burner comprising a steel shell or casing ll within which is placed the furnace lining I2 constructed of suitable refractory material, such as iirlebrick and dening a roasting chamber I4 of circular, horizontal cross-section.` The upper part of the. combustion chamber is closed'off by a crown I5 the top side of which forms a drying or preheating hearth I'I. 'I'he shell II projects upwardly beyond crown I5 and carries a steel framework i8 which in turnsupports ore feeding and rabbling mechanism for the drying hearth. The

-surface of hearth I1 is slightly cone-shaped and slopes downwardly toward the shell of the burner.

Lying above the hearth arerabble arms I9 having downwardly projecting plows 20 pitched to work suldes gradually toward the circumference of the drying hearth. Arms I9 are rotated by motor 22 through shaft 23 supported in bearings so as to maintain the lower ends of plows 20 -spaced with respect to the surface of hearth I1.

An ore bin 24, mounted on framework I8, disl charges ore onto a platform 25 from which the from shaft 63 through gear 64.

smalls are intermittently dropped to the center of drying hearth I1 by a sweep 21 rotating with shaft 23.:l

Cut through shell and also through the up- .per edge of lining I2 is a. passage 34 through which smalls are passed from hearth I1 into a conduit thru which the smalls are transferred to hopper 36. On rotation of rabble arms I9, the sulfide ore is gradually fed through opening 34 into conduit 35.

The bottom of the combustion chamber is formed by a cone-shaped hearth or hopper 40, of substantial vertical length, terminating in a cinder discharge opening 42 which may if desired be provided with a gas lock mechanism through which cinder may bevdischarged without permitting gas to escape from the combustion chamber.

Part of the air needed to effect roasting is drawn into chamber |4 thru ports 45, 46, and 41, each provided with a damper or door 49 by means of which the amount of entering air may be regulated.

Numeral 55 indicates a grinder-burner com-f prising a steel shell 56 having a suitable refractory lining 51 and-forming a preliminary grinding-roastlng chamber 58. Furnace 55 is rotatably mounted on bearings 60 and 6| and is driven One end of furnace 55 is provided with a fixed head 66, supported by framework not shown and arranged in relatively gas-tight relationship with the end 'of the shell 56. The opposite end of furnace 55 projects through opening 68 in the lower portion f ol the vertical wall of the combustion chamber I4. Smalls are fed into furnace 55 from hopper 36 through conduit 31 controlled by valve 38.

pheric air into pipe 15 by means of an air inlet l f 11 having a regulating damper 18. Air-line 80 is connect-cd at one end to the outlet side of blower` 16 and projects thru fixed head 66 into the grinding and preliminary combustion chamber 58.

A gas main 85 for withdrawing gaseous products of combustion from the burner opens into combustion chamber I4 at a point just below crown I5. Main 85 conducts such gases into a waste heat boiler 81 in which steam drum 89, headers 90, and water tubes 9| may be of standard construction. Gases from combustion chamber I4 are discharged through line 85 into a chamber 94, formed partly by vertical lire-wall 95, in which dust entrained in the gases settles out and collects in hopper 91 preferably provided with an air-lock 98 `through which dust may be withdrawn without admitting air to chamber 94.- After contacting water tubes 9| the gases pass downwardly through chamber |00 in which further settling out of entrained solid particles is effected. Chamber |00 is likewise similarly provided at the bottom with` an air-lock discharge |02. Movement of the gases through the system is largely controlled by a blower. not shown, to the inlet side of which gas-line |03 is connected.

The invention is applicable to the roasting of sulfide ores such as iron pyrites, pyrrhotite, zinc sulfide or arsenopyrlte, but for convenience operation of the process will be described in connection with the roasting of iron pyrltes smalls.

In the following discussion it may be assumed the ore referred to is a run-of-pile or pyrites "smalls" ore, 100% passing a. half inch screen and containing about 50% coarse ore insufficiently finely divided for suspension roasting, and about. 50% fines le. g. 30 mesh or finer) of such size as to permit roasting in suspension.

A supply of pyritcs smalls is maintained in bin 24 by suitable conveyor or elevator, not shown. Before roasting is begun, grinding and preliminary roasting chamber 58 and combustion chamber I4 are preheated to temperatures above the ignition point of the ore to be roasted, as by oil burners inserted through conveniently located work-holes .not shown. When the desired degree of preheat is obtained, motor 22 is started, and rabble arms I9 and sweep y21 may be rotated at a rate of say one revolution in two minutes. Smalls run continuously out of 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 drying hearth I1. During rotation of arms I9, the sulfide smalls are gradually worked across the surface of hearth I1, into passage 34, and thence thru conduit 35 into hopper 36. During movement of the smalls over hearth I1, the fines and the coarse ore are thoroughly dried and may be preheated as a rule to about 250 F. and generally not in excess of about G-500 F.

When starting up the process, in addition to preheating preliminary grinding and roasting chamber ,58, and suspension roasting chamber I4 to temperatures in excess of the ignition t em` perature of the particular sulfide ore being treated, chamber 58 is preheated to temperatures not less than about 1300 F. As will hereinafter appear', during course of operations the extent of combustion of sulfur in chamber 58 is controlled so that such chamber is maintained at temperatures preferably not less than about 1300 F. Owing to the existence of such temperatures in chamber 58 the coarse ore particles charged thereto are very suddenly subjected to relatively high temperatures. Experience indicates the loosely combined sulfur of the coarse ore is practically instantaneously volatillzed on sudden introduction of the coarse ore into the high temperature atmosphere in chamber 58, and on account of such sudden exposure to these temperatures and consequent differential expansion, strains are set up in the coarse ore particles thus disrupting and converting the ore particles to a porous condition. When the coarse ore is introduced suddenly into chamber 58 the resulting differential expansion and rapid volatilization ofthe loosely combined sulfur appears to exert within the lumps of the coarse ore. explosive forces which open up the ore rendering the particles porous and converting the same to a frangible condition offering very little resistanee to crushing. It will be appreciated that this makes possible easier and more economical grinding'of the coarse fraction and greatly simregulation of blower 18, damper 12 in the prenot in excess of about 40o-500 TF. and collecting in hopper 38 run through conduit 31 into chamber 58, rate of feed of sulildes being controlled by a suitable valve Il. As explained above, when these coarse ore particles are suddenly subjected ore to a. particle size suitable for. suspension' roasting is very rapid.

In the present example approximately half of.

the air needed to eil'ect oxidation of the total sul-` iur and the iron of the initial ore is fed into lchamber 58 through pipe 88. Appreciable roasting of both fines and coarse ore takes place, such roastinghowever probably comprising principally oxidation of loosely combined sulfur of both lines and coarse ore. Part `or all of the air needed in chamber 58 may be drawn into the system through the inlet 1I in the lower end of air preheating jacket 1I)V surrounding the suspension Y process are controlled so as to maintain in chamber 58 temperatures of not less than about 1300 F., and passage of a gas current of sufficient `velocity to sweep up and carry out of chamber 58 and into suspension roasting chamber I4 those particles which are suillciently fine, e. g., 30-35 mesh and smaller. to permit roasting in gaseous suspension. l

The present improvements relate primarily to suspension roasting and it is the object to eiect as much roasting as possible in suspension and thereby make use of the economic advantages of suspension roasting, principally simple apparatus. Hence, the purpose of grinder-burner 55 is only to eilect subdivision of coarse ore to suspension roasting particle size, and no particular advantage is to be gained by maintaining temperatures in chamber 58 much in excess of i300-1400 F. To obtain the best economic advantages, preferably temperatures should not be permitted to appreciably exceed l550 because at higher temperatures fusion (conversion to magnetic FeaOl) begins to take place. Fused particles are hard and not `readily grindable, and hence formation of appreciable amounts of fused particles defeats the primary purpose (conversion to readily grindable form) of the coarse ore treatment in grinder-burner 55. When proceeding so as to maintain the temperatures described tests show that-the coarse ore particles for the most part are so frangible aste be crushable by pressure of the hand, this indicating how little attrition and .consumption of power are needed to pulverize the coarse ore. tenance of proper temperatures, the extent of sul'- iur combustion, the rapidity of grinding of the frangible coarse ore, and the velocity of the gas current in chamber 58 may be readily obtained by control of feed of smalls from hopper 36, rate of rotation of shell 56, and temperature and amount of air introduced into chamber 58 through pipe 80. It will be appreciated that by The mainheating jacket air inlet pipe 1I, and damper 18 in cold'air inlet pipe 11, the quantity and temperature of the air entering chamber 58 may be very closely controlled. The result of operation of ,the preliminary grinding-roasting phase of the process is such as to quickly and cheaply reduce all of the coarse ore particles to suspension roasting particle size and to etlect some roasting oi.' all of the ore with consequent production of some sulfur dioxide. No particular economies are to be gained by conducting operations in chamber 58 in any way other than to accomplish these ends.

A substantial operating advantage afforded by the preliminary oxidation taking place in chamber 58 is that since substantial quantities of sultur are burned in chamber 58 corresponding amounts of heat are generated most oi.' which heat is dissipated by radiation from the walls of the rotating shell 58. This leaves less heat to be generated in the suspension roasting zone with the result that the tendencies to slag up and agglomerate the suspension roasting zone cinder are appreciably reduced.

The velocityof gas movement through chamber 58 and suspension roasting zone I4 are controlled by the blower, not shown, in gas main |03, and the auxiliary blower 18 ahead .of the grinderburner 55. By regulation of these two blowers velocity of gas movement to chamber 58 is controlled so as to be just suillciently high to sweep` more injectors 13 a small part of, the air to be charged into chamber I4. Such air would aid in carrying the lines particles to the top of chamber I4.

The reason for limiting the amount of air entering chamber 58 is to facilitate maintenance therein of temperatures only suillclently high to bring about the described relative explosion of the coarse ore particles, and not to effect any this purpose. In the'present example, using the particular ore comprising about @50% coarse ore and 50% fines, lroughly about -half of the total amount of air required to combust all of the ore is introduced into chamber 58. Hence,v further amounts of-air or other oxidizing gas are needed to effect roasting, vand such air is drawn into the suspension roasting zone I4 through vports 45, 46, and 41. The rate of movement of the upwardly flowing gas stream in chamber I4 is such that the ore particles are carried upwardly well toward the top of chamber I4. However, sincethe rate of gas movement upwardly t rough chamber I4 is appreciably less, on account f the relatively large cross-section ofchamber I4,'than the velocity of the gas stream passing thru chamber 58, the fines particles soon lose their initial momentum'and for the most part drop more or less vertically through chamber I4, dotted line |05 on the drawing 4indicating the general course of a fines particle through chamber I4.

On introduction of the fines into chamber I4 flash vroasting of` the nes commences and/or further combustion of sulfur than is necessary for Al..A

increases with o great rapidity. relatively. large amounts of heat are generated, and ,during the upward and downward course of travel oi.' the ilnes particles through chamber I4 roasting proceeds to completion. Gas temperatures prevailing in chamber I4 are comparable with those existing in known suspension roasting methods, e. g., of the order of 180o-2000 F. In general, the roasting of the fines particles in chamber I4 is similar to that disclosed in my U. S. Patent No. 2,070,236, o i February 9, 1937. The resulting iron oxide cinder drops onto hearth 40 and is discharged from the furnace as required.

In the modification illustrated in the drawing, opening 68 into .which the outlet end of grinderburner' 55 projects is relatively in the lower end of the suspension roaster. Gas movement in chamber I4 is in an upwarddirection, the sulfur dioxide gases being withdrawn from the top oi' the combustion zone. I f desired, opening 60 may be adjacent the top of chamber I4 and grinderburner 55 mounted in a similarly elevated position. In such modified apparatus, air inlets corresponding with ports 45, 46, and 49 may be 1ocated in the upper periphery ofthe walls ot chamber I4 just beneath crown I5. Sulfur dioxide gas outlet 05 would then be located near the bottomI of the combustion chamber. In this modication, the travel of the lines and gas in chamber I4 would be in a downward direction only and the suspension roasting-phase wouldv be a co-current operation similar to that shown in Burgoyne et al. patent previously mentioned. l The sulfur dioxide gases produced .enter waste heat boiler 81 at temperatures of around 1800- 2000 F. Heat is recovered in the form of steam and entrained dust settles out and'v collects in chambers 94 and |00. The gas stream enters line |03 at temperatures of say 50B-600 F., and may be purified if desired for use, e. g. in the manufacture of sulfuric acid bythe contact process.

The invention has been described in connection with roasting of smalls containing about 50% coarse ore and 50% lines because the usual run of smalls contains coarse ore and fines in approximately these proportions. It will be understood, however, that the process of the invention is readily adaptable to handle smalls containing less or greater quantities of coarse ore. In the case of smalls containing less amount of coa-rse ore, the smalls may be fed to grinderburner 55 at a greater rate, and-where the smalls contain greater quantities of coarse ore rate of introduction of smalls may be correspondingly reduced. Regulation of control conditions in accordance with the nature of the smalls used will be apparent to the skilled operator. The invention presents several substantial operating advantages. For example, when working with pyrites smalls passing a half inch screen as mentioned, it would ordinarily be necessary to roast this type of ore in a multi-hearth burner or go to the expense of grinding the ore to a sufficient degree of fineness to permit roasting bysuspension methods. In accordance with the present process, on account of the exceedingly frangible condition to which the coarse ore is rapidly converted, whatever grinding is necessary may be accomplished with much less expenditure o! power than would be the case if the o coarse ore constituents were pulverized in usual grinding operations.v By the present method,

' smalls maybe roasted in a way much more eilicient than could be accomplished in a multiu hearth roaster. An outstanding advantage afforded by the invention is that operations may b e carried out in simply constructed and ecov nomlcally maintained apparatus.` l'

I claim:

1. The method for roastingl coarse metal sulde ore which comprises maintaining avzone at temperatures not less than about 1300 F., introducing the coarse ore into said zone whereby the ore is suddenly subjected to temperatures of the combustion zone and converted to a relatively porous frangible condition, subjecting the ore while in said zone to attrition suiicient to reduce the coarse ore to nnes, then introducing said ilnes into a combustion zone, forming therein a suspension of lines in oxidizing gas, roasting the fines while in suspension in the oxidizing gas to produce sulfur dioxide, and recovering sulfur dioxide.

2. 'I'he vmethod for roasting coarse metal sulfide ore which comprises maintaining an oxygen-containing combustion zone at temperatures not less than about 1300 F.,introducing the coarse ore into said zone whereby the ore is suddenly subjected to temperatures of the combustion zone, converted to a relatively porous frangible condition and partially roasted, subjecting the ore while in said'zone to attrition sufficient to reduce the ore to fines, then introducing said fines into a second combustion zone, forming therein a suspension of fines in oxidizing gas, roasting the fines while in suspension in the oxidizing gas to oxide.

3. The method for roasting coarse metal sulfide A ore which comprises introducing the coarse ore into an oxygen-containing combustion zone heated to temperatures not less than about 1300 F. whereby the ore is suddenly subjected to temperatures of the combustion zone, converted to a relatively porous Irangible condition and partially roasted, maintaining such temperatures by at least partial combustion of some of said ore, subjecting the ore while in said zone to attrition sufcient to reduce the ore to lines, then introducing said nes into a second combustion zone, forming therein a suspension of iines ,in oxidizing gas, roasting the fines while in suspension in the oxidizingl gas to produce sulfur dioxide, and recovering sulfur dioxide.

4. The method for roasting metal sulfide smalls containing coarse sulde ore and initial sulfide fines which comprises maintaining an oxygencontaining combustion zone at temperatures not `less than about 1300 F., introducing the smalls `containing coarse sulildeore and initial sulde nes which comprises introducing the smalls into an oxygen-containing combustion zone heated to temperatures not less than about 1300 F. whereby 'the smalls are suddenly subjected to temperatures of the combustion zone and the coarse ore is converted to a relatively porous frangible condition and partially roasted, mainroasting the fines while in suspension in the oxi-l dizing gas to produce sulfur ering sulfur dioxide.

6. The v method for roasting metal sulfide dioxide, and recovsmalls containing coarsesuliide ore and initial sulfide nes which comprises maintaining-an oxygen-containing combustion zone at temperatures not less than about 1300 F. and not substantially in excess of about 1550 F., introducing the smalls into said zone whereby the smalls are suddenly subjected to` temperatures of the combustion zone and the coarse ore is converted to a relatively. porous frangible condition and partially roasted, sub- `iecting the coarse ore while in said zone to attrition sufiicient to reduce the same to iines, then introducing such resulting iines together with `said initial nes into a second combustion zone,

forming therein a suspension of fines in oxidizing gas, roasting the nes while in suspension in the oxidizing gas .to produce sulfur dioxide, and recovering sulfur dioxide.

7. The method for roasting metal -sulilde smalls containing coarse sulilde ore and initial suliide` lines which comprises introducing the smalls in' to a combustion zone heated to temperatures not less than about 1300 F. whereby the smalls are suddenly subjected to temperatures of the combustion zone and the coarse ore is converted to a relatively' porous frangible condition and partially roasted, passing through said zone a gas stream containing oxygen in amount less than that needed to support complete oxidation of said smalls but in quantity suilicient to maintain such temperatures by at least partial combustion of some of saidsmalls, subjecting the coarse ore while in said zone to attrition suiiicient to reduce the same to ilnes, regulating ,the velocity of the gas stream passing through said zone so as to sweep out of said zone fines resulting from such attrition together with said initial fines, introducing the gas stream containin-g such iines into a second combustion zone. forming therein a suspension of `lines in oxidizing gas in amount suillcient to eil'ect substantially complete oxidation of said nes, roastingthe fines while in suspension in the oxidizing gas to produce sulfur dioxide, and recovering sulfur dioxide.

8. The method for roasting metal sulilde smalls containing coarse sulfide ore and initial sulde lines which comprises introducing the smalls into a combustion zone heated to temperatures not less than about 1300 F. whereby the smalls are suddenly subjected to temperatures of the combustion zone and the coarse ore is converted to a relatively porous frangible condition and partially roasted, passing through said zone a gas stream containing oxygen in amount less than that needed to support complete oxidation of said 'smalls and in quantity restricted to maintain such temperatures not substantially in excess of .about 1550 F., subjecting the coarse ore while in said zone to attrition suiiicient to reduce the same to lines. maintaining the velocity-of the gas stream through said zone high lenough but not substantially in excess of that required to sweep out of said zneviines resulting from l such attrition together with said initial fines. in-

troducing the gas stream containing such fines a suspension oi' fines in oxidizing gas in amount sufficient to eilect substantially complete oxidation oi' said lines, roastingy the nes while in suspension in theroxidizing gas to Produce sulfur di oxide, andrecovering sulfur dioxide. y

9. The method for roasting metal sulfide smalls containing coarse sulilde ore and initial i into a second combustion zone, forming therein sulde Viines which comprises introducing the of the combustion zone and the coarse ore is Y converted to a relatively porousfranglble condition and partially roasted, passing through saidv zone a gas stream containingoxygen in amount less than that needed to support complete oxidation of said smalls but in quantity sumcient to maintain such temperatures by at least partial combustion of some of said smalls, subjecting the coarse ore while in said zone to attrition sutiicient to -reduce the same to nes, regulating the velocity of the gas streampassing through said zone so as to sweep out of said vzone iines resulting from such attrition together with said initial'nes, introducing the gas stream containing such lines into the lower portion.v of a second combustion zone. forming therein a. suspension vof fines in an upwardly-'moving stream of gas containing oxygen in amount sumcient to effect substantially complete oxidation of saidnes,

smalls containing coarse sulilde ore and initial sulfide lines which comprises introducing the smalls into a combustion z 'one heated to* temperatures not less than-about l300 F. whereby the smalls are suddenly subjected to temperatures of the combustion zone and the coarse' ore is converted to a relatively porous trangible-y condition and partially roasted, passing through said zone a gas stream containing oxygen in amount less than that needed to support complete oxidation of said smalls and in quantityrestricted to maintain such temperatures not'substantially in excess of about l550 1"., subjecting the coarse ore while in said 'zone to attrition suilicient to reduce the same to nes, maintaining the velocity oi' the gas stream passing through said zone -high enough but not substantially in excess of that. re-

quired to sweep out of said zone lines resulting produce sulfur dioxide, and withdrawing sulfur dioxide from' the upper end of said second combustion zone. f

Images