US2797987A - Process for roasting of sulfide ores - Google Patents

Description

July 2, 1957 A. A. J. QUINTIN 2,797,987

PROCESS FOR ROASTING 0F SULFIDE ORES Filed Feb. 26. 1954 PRIOR ART INVENTOR I MPH-11.11 [IL-Mira 341N 09 PRGESS FOR .RDASTING OF SULFI DE ORES" Albert Andrel'osepli Quintin, Overpelt, Belgium, assignor to Compagnie des Metaux dOverpelt-Lommel et de Corphalie, Overpelt-lez-Neerpelt; Belgium, a- Belgian body corporate Application Februaryl, 1954,.Serial No. 412,892

4 'GliiimS. (Cl; 759) This invention-relates to a process for' roasting sulfide TSl- I It is-ltn'own'to' roast sulfide ores-by a process of semi'- suspension, or fluidiza'tion, of the ore: in a current of air or oxidizing gas; the ore may be in the form of nat-. ural grains; orthese grains; may havezbeentmanufactured by; any method of sintering; and. granulation; or theme may-beintheform of a-fine powder: Useis: made for the'roasting of an.enclosure-which generally has a" height which is' greater than; its width, and at: the lower part of. which at perforated diaphragm" is-- provided, through which air or'ant oxidizing; gas is blown; Afterv theen-z closurehasbeen heated tothe. temperature of reaction, raw-ore'issfed above the diaphragm andthe amount of oxidizing. gas orair admitted through the. diaphragmis regulatedsothat its speed immediately. above the dia-. phragm shallbe sufficientr to place the orein arstate of. semiasuspension. and agitation generally called fluidiza tion similar tothatof. boiling water, but insufficient. to carry. over. the major part of the ore outside the roasting enclosure.

The ore which accumulates in the roasting enclosureor furnace is removed, in a continuous or discontinuous manner, generally by overflow, through suitable outlets provided for thatpurpose in the side wall of the enclosure.v

In the accompanying. drawings,. Figure 1 shows diagrammatically"a known device for carrying out a process" of" the above kind. In Figure 1,, the'referencenw meral 1 showsthe roasting enclosure, 2' is'the perforated diaphragm; 3 is a wind box which is fed -by airor'oxidizing gas under pressure through an' orifice' ll Theoverflow of the ore takes" place through-an orifice 5 and through a pipe 6 intoahopper 7"havinga tight jointfit from which it can'be removed by means of adamper 8, The reference numeral 9" shows an outlet forrthe roasting gases; 10"is a pipe for feeding=rawore into the enclosure, theorebeing fed by a screw 11 from a hopper 12'l The screw 11" is driven by a motor 13-.

The above system has two important drawbacks; when applied to ore in the form of grains:

(1) The removed material represents practically? an average sampling of the material which is fluidized in the enclosure 1'. Itcontains a certain proportion of grains whichhave remained too short a time inside the enclosure to be completely desulfurized.

(2') The speed of the oxidizing gas or air blown through the diaphragm 2 must be chosen so asto maintain the larger grains in. suspension and to avoid the carrying over of smaller grains as. much as possible. This requires a very precise sizing of the grains, thus limiting .within narrow limits the difierence in-size between the largest. grain andthe smallest grain if it is desired. to avoid either a. carrying over of too large quantities. of materials together with the oxidizing gas through the orifice 9, oran accumulation of the larger grains at the lower part of the-roasting enclosure where they would be insufliciently roasted owing to their. lack of mobility.

rates Patent The present invention has for its obpject to avoid the above drawbacks.

With this object in view, the invention consists in a process for the roasting of sulfide ores in which the roasting is mainly carried out in a state of fluidization, that is in a state of. semi-suspension of the mass of ore, by means of a current. offair or oxidizing gas (hereinafter called sometimes oxidizing gas alone or air alone) andi'n such a'processdividing the amount of oxidizing gasnecessary'for the roasting into various portions,.infooting the said portions at various points of the mass of the ore subjected'to-roasting to produce an intermediate zone of intense turbulence of the OIC"WhlCl'1 separates anupper zone in' which theore is fluidized, that is in which ore isin a state of semi-suspension, and a lower zonein which the grains'of'ore are at rest relatively to each other; causing the mass of ore in which the grains are" at rest relatively to each other toadvance downwards=ina regular manner by gravity, removing substantia'llytherentire' m'ass of roasted ore at the lower part of ther'roastingxenclosure; ands causing a slow current of air on of: oxidizingrgas to passthroughthe mass of ore in which: the grains: are 'at' rest relatively to each other'fo'r completing: the; roasting. of the grains without agitating them;

The air or gas required for completing-the: roasting operation, is caused totpass' in acountercurrent direction through-theiroastedt material of the zone where. the grains are comparatively at rest relatively to each other.

Theintermediate zoneof. intenseturbulence may consist" of. a. plurality of convergent-divergent. spaces into which air or. oxidizing gasris blown.

Theinjection chair. or oxidizing gasintothesaid: intermediate. zone. may be efiected. by means of perforated hollow bars immersed. into. the. mass. of ore and having a shape such asto-offer. aminimum section of. passage to the ore at approximately, the level wherethe main blowing of air. or oxidizing, gas takes place. The main portion of air or. oxidizing gas-(primary air) is blown at high speed, for instance 15 to 30 meters peresecond, through the holes of the bars so. that the material shall be maintained at that. level. between the bars in a state offluidization withviolent whirling or turbulence. A secondary and much smaller amount of air oroxidizing gas (secondary air) is blown intothemass of meat a lower level of the bars, in" the zone of relative rest where there areno movements of'the grains relatively-to eachother.

According to another characteristic feature of the invention, another small amount of air or oxidizing gas (tertiary air) is injectedjust above the level of theout let of'ore from the lower part of the roasting enclosure.

The total amount of secondary'plus tertiary air'iscarefully chosensmall enough so-that it does not agitate the grains relatively to each other in the zone' of" relative rest that extends from about" the level of the primary injection to" the outlet ofthe roasted are.

The secondary" air, assisted' by'the' tertiary air; has for its' main'obiect, to complete the combustion of the" sulfur inflsulfidetorm, before the'mass of material=has been appreciably cooled. The: tertiary air fiowingina countercurrent:direction'has for its first object-torecover: the heat of the "roasted oreand tobring' it'into the reaction zone,- whilstpreventing the formation of. sulfates.

The-hollow bars for theinjection of primary and'sec ondary air-may have a cross-section formed of two tr-iangles joined by their: bases; I

Fig. Zin-the a'ccompanyingdrawings shows-in-elevation diagrammaticallyand by" way ofexample: one mode of carrying: theinvention into= effect, which-has been. applied in practicetothe roasting of raw blende: (impure zinc sulfide.) which originally was he a finelyr dividec lr state, and which was granulated by a suitable process and sized, for instance between /2 mm. and 4 mm., prior to its being roasted.

In Figure 2, the reference numeral 1 shows the furnace enclosure, 2 are hollow bars, made of a material which is fire-resistant and preferably good conductor of heat, for instance of stainless steel.

The bars 2 have two independent chambers, an upper chamber 3 from which air or gas passes through nozzles 4, and a lower chamber 5 from which air or gas passes through nozzles or slots 6. All the chambers 3 are connected with a feeding pipe (not shown) for primary air under pressure. All the chambers 5 are connected with a second feeding pipe (not shown) for secondary air, also under pressure. 7 is a hopper, which preferably is heat-insulated. 8, 8 are wind boxes which feed nozzles or slots 9. They are connected with a third feeding pipe (not shown) for tertiary air, also under pressure.

10 is a feeding screw driven by a motor 11 with a change speed gear, which screw removes roasted material to an extent such as to maintain the material in state of semisuspension up to a constant level 17 inside the upper part of the reaction enclosure. 12 is a hopper with a tight joint fit in which roasted material accumulates. 13 is a hopper containing raw material, 14 is a feeding screw driven by a motor 18 having a change speed gear. 15 is a pipe for feeding raw material into the reaction enclosure, preferably made of stainless metal. 16 is an orifice for the escape of roasting gases.

As shown in the drawing, the whole of the tertiary, secondary and primary air passes through the fluidized material above the nozzles 4, 4. The total amount of air is so chosen as to obtain, in the section of the furnace extending from above the hollow bars 2, 2 up to the level 17, a speed which at the roasting temperature (950 to 1050 C. for blende) will maintain the material in a state of fluidization with moderate whirling. The said speed, calculated for cold air and for an empty furnace, is of the order of 50 cm. per second. The primary air, injected under pressure into the chambers 3 of the bars 2, represents about 80% of the total amount of air.. The nozzles 4, which are spaced at regular intervals along the bars, have orifices of a size such that the escaping air has a speed of the order of 15 to 30 metres per second (calculated with regard to cold air). The bars 2 have a double prismatic shape, upwards and downwards from the nozzles 4, so that the minimum passage section for the ore between the bars is located at or about the level of the nozzles 4. This minimum section represents about 50 to 70% of the total horizontal section of the furnace at the level 17. The distance between the primary nozzles 4 and the secondary nozzles or slots 6 is about 30 to 50 cm. The amount of air injected through the nozzles or slots 6 is about 10 to 15% of the total air. The amount of air injected through the nozzles or slots 9 is of the order of 10 to 5% of the total air. The nozzles or slots 6 and 9 have a sufiiciently large section to impart a small speed to the outflowing air, for instance about 5 metres per second, so as not appreciably to disturb the state of relative rest of the grains inside the lower part of the enclosure.

It follows that below the level of the nozzles 4, the speed of the air is considerably lower than that which would be required to produce a turbulence in the material. This speed, calculated for cold air and the horizontal section of the furnace supposed empty does not exceed some 10 cm. per second. The grains of material therefore remain at rest relatively to each other, and the mass of grains goes downwards by gravity in a regular manner between the bars and through the hopper 7 according as the removal of roasted material by means of the feeding screw 10 proceeds, the movement of latter screw being regulated so as to remove the amount of roasted blende or other ore corresponding to the amount of raw blende or other ore which is fed by the screw 14. It follows that the small amount of sulfur in the state of sulfide which is still contained in certain grains at the level of the nozzles 4 is systematically burned by the two countercurrent air currents injected through the nozzles 6 and 9, the first current being heated by the heat recovered from the roasted ore in the hopper 7, the second current being heated by conductivity from the walls of the chambers 5. It may also be useful, but not indispensable, to preheat the air in any suitable manner before it enters the chambers 5, for instance by a heat exchange with the roasting gases which leave at 16.

A complete roasting can thus be obtained. The percentage of sulfur in sulfide form is reduced to less than 0.05% and the percentage of sulfur in sulfate form is practically equal to the amount of sulfur already combined with calcium and with barium in the form of fixed sulfates; moreover, there is no re-formation of zinc sulfate, below the level of the nozzles 4, since the combustion of the small amount of sulfide remaining in the material is effected above 900 C., after which the subsequent cooling takes place in a current of pure air, free from S02 and S03.

On the other side, the gas or air passing through the nozzles 4 into a greatly reduced section of the furnace gives a largely increased air speed per unit of cross-section. Moreover, there is a state of intense turbulence in that part due to the opposed nozzles which blow air or gas at a high speed. It follows that the larger grains are all lifted by the rapid current and are completely roasted without injecting an amount of air which would lead to a high vertical velocity in the section of the furnace above the bars, which would carry over too large quantities of material through the outlet 16. The practice has shown that it is possible under the above conditions to obtain that and more of the roasted material is removed at the lower part of the reaction enclosure, less than 5% of the material being carried over with the roasting gases, because in a very fine state.

I claim:

1. An apparatus for the roasting of sulfide ore in grain form, comprising an enclosure the upper part of which has a conical shape with the smaller section situated below, means for the admission of the ore and means for the removal of gases at the upper part of said enclosure, the upper part being followed by a cylindrical part at about the lower end of which a plurality of hollow bars are arranged, each having a section resembling two triangles joined by their bases and provided with means for the injection of air from the hollow bars into the space comprised between the latter, the said cylindrical portion being followed by a part of truncated conical shape with the smaller section situated below, means being provided at the lower part of the latter truncated conical part for the injection of air, and means for the removal of ore at the lower part of the enclosure, as set forth.

2. In a process for the roasting of sulfide ores, the steps comprising admitting the sulfide ore in grain form at the upper part of a vertical enclosure, causing the sulfide ore to move downwards in the said enclosure for a substantial portion of the height of the vertical enclosure in a continuous manner in a state of quiet fluidization in a current of oxidizing gases, mechanically supporting the grains at a plurality of points throughout the cross-section of the said enclosure, injecting an oxidizing gas through the grains of ore at the said points of mechanical support to create a zone of intense turbulence while leaving at the points where the oxidizing gas is injected a plurality of substantially vertical passages for the grains moving downwards, then allowing the grains to move in a downward direction in a defluidized non-expanded condition and therefore in a state of practical immobility relatively to each other, and removing the grains in a practically completely oxidized state, at the lower end of the said vertical enclosure.

3. In a process for the roasting of blende in grain form, the steps comprising admitting the blende at the upper part of an enclosure, causing it to move downward in a continuous manner for a substantial portion of the height of the vertical enclosure causing air to move upwards through the grains in the upper part of the enclosure with a speed of the order of 50 cm. per second (calculated for cold air and for an empty space), thus causing the grains in the upper part of enclosure to move in a state of quiet fluidization, mechanically supporting the grains at a plurality of points throughout the cross-section of the enclosure, then injecting air at the said supporting points with a speed of the order of to 30 metres per second (calculated with regard to cold air) to produce a zone of intense turbulence while leaving at the points where the air is injected a plurality of substantially vertical passages for the grains moving downwards, causing a current of oxidizing gas of slow velocity to pass in an upward direction through the grains in the lower part of the enclosure while leaving the grains in a defluidized non-expanded condition and therefore in a state of practical immobility relatively to each other, and removing the grains, in a practically completely oxidized state, at the lower part of the said enclosure.

4. In a process for the roasting of blende in grain form, the steps comprising admitting the blende at the upper part of a vertical enclosure and causing it to move downwards in a continuous manner for a substantial portion of the height of the vertical enclosure in a continuous manner, causing air to move upwards through the grains in the upper part of the said enclosure with a speed of the order of cm. per second (calculated for cold air and for an empty space), then restricting the section of passage of the grains in the enclosure by means of a plurality of mechanical points of support throughout the cross-section of the enclosure with formation of a plurality of substantially vertical passages and injecting air into the latter passages with a speed of the order of 15 to 30 metres per second (calculated with regard to cold air) to produce a zone of intense turbulence therein, while allowing the grains of ore to move downwards in a plurality of substantially parallel streams, causing a current of oxidizing gas of slow velocity representing 5 to 15% of the total air to pass in an upward direction through the grains in the lower part of the enclosure underneath the mechanical points of support while leaving the grains in a defluidized non-expanded condition and removing the grains in a practically completely oxidized state at the lower part of the said enclosure.

References Cited in the file of this patent UNITED STATES PATENTS 1,885,998 Edholm Nov. 1, 1932 2,386,670 Evans 1 Oct. 9, 1945 2,465,410 White Mar. 29, 1949 2,560,175 Kalbach July 10, 1951 2,612,438 Murphree Sept. 30, 1952 2,621,118 Cyr et a1 Dec. 9, 1952 2,665,899 Fassotte Ian. 12, 1954 FOREIGN PATENTS 519,869 Belgium May 30, 1953

Claims (1)

1. AN APPARATUS FOR THE ROASTING OF SULFIDE ORE IN GRAIN FORM, COMPRISING AN ENCLOSURE THE UPPER PART OF WHICH HAS A CONICAL SHAPE WITH THE SMALLER SECTION SITUATED BELOW, MEANS FOR THE ADMISSION OF THE ORE AND MEANS FOR THE REMOVAL OF GASES AT THE UPPER PART OF SAID ENCLOSURE THE UPPER PART BEING FOLLOWED BY A CYLINDRICAL PART AT ABOUT THE LOWER END OF WHICH A PLURALITY OF HOLLOW BARS ARE ARRANGED, EACH HAVING A SECTION RESEMBLING TWO TRIANGLES JOINED BY THEIR BASES AND PROVIDED WITH MEANS FOR THE INJECTION OF AIR FROM THE HOLLOW BARS INTO THE SPACE COMPRISED BETWEEN THE LATTER, THE SAID CYLINDRICAL PORTION BEING FOLLOWED BY A PART OF TRUNCATED CONICAL SHAPE WITH THE SMALLER SECTION SITUATED BELOW, MEANS BEING PROVIDED AT THE LOWER PART OF THE LATTER TRUNCATED CONICAL PART FOR

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