US1536702A - Method of and apparatus for roasting ores - Google Patents

Description

M. F. CHASE ET AL METHOD OF AND APPARATUS FOR ROASTING ORES Filed ma 4, 1925 Z3 13 I A- 9 I W 12 2. 4.

. I A- Z- 44- INVENTORS 3W MAM J; ATTO RNE Patented May 5, 1925.

UNITED STATES PATENT or F! C E YORK,

METHOD OF AND APPARATUS FOR ROASTING ORES.

Application filed May 4,

To all whom alt-may concern:

Be it known that we, (1) MARCH F. CHASE and (2) J OHN SKOGMARK, citizens of the United States, residing at (1) Ardsley-on- Hudson, (2) New York city, in the counties of 1) Westchester, (2) New York, and State of (1) and (2) New York, have invented certain new and useful Improvements in Methods of and Apparatus for Roasting Ores, of'which the following is a specification.

This invention relates to a method of and apparatus for contacting materials with each other, for instance for contacting a gas with a liquid, or'with a solid, or for contacting a liquid with a solid. Examples of I such processes are for instance, the absorption of a gas in a liquid, the roasting of an ore with an oxidizing gas, and the flotation of an orc in a liquid.

The invention broadly consists in passing the material to be treated, for instance the liquid or solid, downwardly step by step through a series of receptacles in each of which it is held by an upward flowing current of the treating gas or liquid and in dropping the material from receptacle to receptacle by control of the suspending current of gas or liquid.

The invention will be described and illustrated hereinafter by reference to the roast-' ing of sulfid ores.

Generally speaking it has not been found to be possible to smelt or otherwise treat sulfid ores for the purpose of extracting their metal values until a considerable portion of the sulfur has been removed. This necessary step of removing the sulfur before metallurgical treatment is usually done by roasting or calcining the ore.

The operation of roasting consists in burning the sulfur occuring in theore to sulfur dioxide and at the same time o'xidizing the metallic elements with which the sulfur was combined. Several well known types of furnaces or burners are used forthis purpose. In most furnaces the ore passes through-the furnace in a direction opposite to that taken by the air supplying the oxygen for reacting with sulfur, so that the percentage of sulfur in the ore as it passes through the furnace is constantly decreasing and the percentage of SO in the air is increasing and the percentage of oxygen is decreasing. In practically all apparatus used for the purpose of roasting sulfid ore,

1923'. Serial No. 636,652.

the ore is moved from one part of the furnaceto another by mechanical means which not only serve the purpose of moving the ore but also stir the ore so that fresh surfaces areconstantly exposed to the oxidizing effect of the gasor air passing through the furnace. This is an essential feature of roasting sulfid ores. If the ore is permitted to lie in a quiescent state the S0 content of the gas immediately in contact with the ore quickly reaches a concentration which prevents the rapid oxidation of the ore. To obtain the best results in roasting it is desirable (a) To move the air introduced into the furnace in a direction opposite to that in which the ore is moving;

(b) To constantly stir the fresh surfaces are exposed;

(0) To keep the gas stream moving at such a rate that the oxygen content of the gas in contact with the ore is not lowered materially below the average oxygen content of the gas in that particular part of the furnace.

It is to this method of roasting that our invention especially relates and, as will be seen from the description that follows we are able to roast, gaining the advantages enumerated above, without the employment of moving parts in the furnace proper.

In furnaces used for roasting ores requiring a high temperature the rabbles and arms moving the ore, being subjected to a high temperature, must, in order to withstand the destructive effect of the heat, be made of refractory materials, such as fire brick, or of metal, (usually iron). If made of refractory materials they are expensive to construct and maintain. they must be cooled by air or water. In this case if the roasting operation requires external heat, an additional fuel expense is incurred'to makeup for heat removed by the cooling.

In roasting certain sulfid, ores the heat liberated by the oxidation of the constituents of the ore is more than sufficient to maintain the temperature of the air and the gas in contact with it at a point where the roasting action will continue; When roasting other sulfid ores the quantity of heat liberated While theoretically sufiicient to maintain a roasting temperature is not sufficient to do so in the ordinary roasting furore' so that If made of metalnace because of the loss of heat due to radiation and the cooling of the arms and rabbles moving the ore. Zinc sulfid is an example of this class of ore. The heat of sufiicient to maintain a temperature that excess of that used in the first case due to the will permit the roasting to proceed provided that the ratio of air to ore is kept within certain definite limits. It is difiicult, if not impossible, in present types of furnaces to maintain this roper ratio of air to ore. For this reason it is almost always necessary to provide heat from an external source. This'is done in two ways- (a) By assing the air for roasting the ore througli a fire box where it is mixed with the gases of combustion of fuel used, to provide the excess heat needed for the roasting process;

' (b) By heating the hearth where the ore is roasted by passingcombustion gases from an external fire box underneath or around it but not mixing the combustion gases with the gases passing over the ore.

In the first case the gases coming from the roasting furnace in addition to being contaminated by the products of combustion from the burning fuel are so low in percentage volume of SO as to make them unsuitablefor use in sulfuric acid manufacture.

In the second case are suitable for malnng sulfuric acid, the amount of fuel used for roasting 1s much-1n inefficiency of transferring the heat of combustion gases through the brick work of the hearths and mufiies to the ore and roaster gases. 1 i

- Whenroasting various classes'of ores it is advantageous to make .the best possible use of the heat generated in the combustion of the ores, provided the method employed to do this does not decrease the percentage volume of SO in the roaster gases below that obtained when roasting in ordinary types of muffle roasters, as under these circumstances'not only will fuel be saved but a waste gas will be obtained suitable for the manufacture of sulfuric acid (a by-product of value).

The object of the present invention, therefore, is to rovi'de as follows:

(a) A conditlon in roasting sulfid ores where the particles of ore are completely surrounded by' gases containing oxygen, thus intensif ing the reaction;

(b) .movement of the ore through the furnace without employing movin parts in the path of the ore, thus avoi ing high maintenance expense and the cooling effect attendant on such use; i i

(c) A process which, while it has the advantage-of surrounding the particles of ore while the roaster gases with the gas, provides for the general movement of the ore against the current of the gas,

thus getting the ore with the lowest sulfur content in contact with gas of highest oxy- (d) A method of roasting sultid ores in which the heat in the roasted ore is utilized 'to heat the air used for roasting.

In the accompanying drawing we have shown diagrammatically one form of apparatus embodying'our invention and suitable for carrying out the process thereof.

Figure 1 is a vertical section; and

Figure 2 is a horizontal section of the apparatus.

Referring to the drawings:

1 is a feed hopper or bin having a valve or feeder 2 for regulating the quantityvof ore charged to the furnace.

3, 4, 5, 6 and 7 designate what we shall hereafter term combustion chambers.

8, 9, 10 and 11 represent control valves located in a passage 22 communicating with the combustion chambers through openings 23, 24, 25 and 26.

12 represents the pipe which conducts the air used for roasting from the blower (16) to the furnace. This air may all be admitfed at the bottom ofthe-passage 22, or part may be admitted at other points in the passage 22 as indicated by inlets (20) and (21) 'centigrade by means of oil burners or gas burners (notshown). Then with all of the valves 8, 9, 10 and 11 closed,-the blower or fan 16 is started and a charge of ore is supplied to the combustion chamber 3 through feeder 2. The blast of air passes upwardly through the combustion chambers 7, 6; 5, 4 and 3 successively and its strength through the contraction at the base of combustion chamber 3 is so adjusted that it is suflicient to prevent the ore from passing to the next combustion chamber 4, below. The valve 8 is now opened thus permitting the air to pass at low speed from the combustion chamber 4 through the opening 23 to the dust chamber 13. As a result of the bypassing of thecombustion chamber 3 the speed of the air'through the aperture at the bottom of this-chamber is reduced and the ore is permitted-to pass by gravity to combustion chamber 4. The valve 8 is only kept open for approximately the time necessary for the charge of ore in combustion chamber 3 to fall to combustion chamber 4 and is then closed and a new charge is supplied to combustion chamber 3., The valve 9 is next opened which by-passes the gas from the combustion chamber 5 around combustion chamber 4 to combustion chamber 3; thus allowing the ore in combustion chamber 4 to fall into combustion chamber 5. Valve 9 is then closed and valve 8 is operated and the charge in combustion chamber 3 is passed on to combustion chamber 4. Valve 8 is then closed and chamber 3 recharged 311d thenrvalve '10 is operated which brings the charge from combustion chamber 5 to combustion chamber 6. Valves 9 and 8 are operated as described above to pass the charges in" chambers 3 and 4 into chambers 4 and 5 and chamber 3 is again charged. Next "valve 11 is op. erated, bringing the ore down to combus: tion chamber 7 where it is accumulated in the bottom and is finally drawn ofi' through valve 15, and the charges in chambers 3, 4 and 5. are passed to chambers 4, 5 and 6 and chamben 3 recharged as described.

From this period on, the operation will consist in operating valves 11, 10, 9 and 8 in sequence, each time dropping a charge from one combustion chamber to the one next below. The time needed to 'keep' the valves open for passing ofthe ore from one combustion chamber to the next is of the magnitude of-two or three seconds and the time for the ore to pass through the furnace will be determined by the frequency of the operation of the'valves, thus, if one minute passes between each time a certain valve in the series is operated the ore will remain in each combustion chamber for that period of.time. It may, under some circumstances, be desirable to supplement the supply of air to the upper combustion chambers 5, 4 and 3 from the' lower chambers -7 and6. This is accomplished by supplying regulated quantities of air through the openin 20 and 21.

he action of this method of roasting is as follows:

The ore which is fed into combustion chamber 3 encounters the hot gases from the lower. chambers and is ignited so that when it passes on to combustion chamber 4 its temperature is elevated and with this higher temperature the roasting action is intensified. Similarly the ore passing to combustion chamber 5 is of a still higher temperature and in encountering a gas current with a higher oxygen content will be chamber, and other conditions may of course be made to suit the requirements of each particular installation.

.'The reason this furnace is adapted for complete roasting is that the ore charge in each combustion chamber is suspended in the rapid air current issuing from the bottom of the combustion chamber by which it is carried up a certain height and then falls down tothe slope at the bottom of the chamber and at the bottom of the slope it is again caught by this air current. The particles of ore consequently -are surrounded by the gas which provides a much more eflicient action than is possible in a, roasting furnace as constructed according to present practice Where the ore generally is present in each combustion chamber except the f lower ones whichperform an entirely different function from that of roasting. Thus, the ore treated in any combustion chamber except the lower ones has less percentage of sulfur in it than the ore. in the chamber immediately above it. As the ore progres-' 'sively passes throughthe furnace it is subjected to the oxidizing eflect of the gas in the successive stages or ste s. mits of obtaining a more uniform temperature throughout the roasting than if the entire oxidation was completed in one stage.

As the ore enters each combustion chamher or stage of roastingit meets the ascend ing gas current where the action is as described so that it is subjected while in a combustion chambertoperiods of suspension in the as current and in the intervals" between suc periods of suspension it is still in motion so that it is always presenting fresh surfaces tothe atmosphere through which it is moving. 4 In the foregoing specification we have described in detail an application of the invention for the roasting of sulfid ores. It is clear, however, that the same .principles ma be applied for other treatments of completely roasted. The ore passing from solids with gases, for instance, for chloridiz- 5 to 6 is still heated, but, since the sulfur is ing ores, etc, and for the treatment of SOlldS substantially all removed and" the metals with liquids mstead ofwith gases and for oxidized in thechambers above,

there'is no contacting gases with liquids, for instance further reaction taking place, and this ore for scrubbing the gas or for absorbing the This per gas or a component thereof in the liquid.

It is of course evident that the apparatus,

although of the same general character, will be modified as to size, shape, materials, kinds of valves and conduits, etc., to suit the materials under treatment.

The terms and expression which we have employed are used as terms of description and not of limitation, and we have no intention in the use of such terms and expressions of excluding any mechanical equivalent of the features shown and described or portions thereof, but recognize that various modifications are possible within the scope of the invention claimed.

WV e claim- 1. Process of subjecting mobile material to the action of a fluid, which consists in passing the mobile material downwardly through a closed passage way, passing the fluid upwardly through the passage way under conditions to normally hold the column of mobile material suspended and intermittently varying the action of the fluid pressure upon the mobile material to allow the latter to descend in successive stages.

2. Process of subjecting mobile material to the action of a fluid, which consists in passing the mobile material downwardly through a closed passage way, passing the fluid upwardly through the passage way under conditions to normally hold the column of mobile material suspended and intermittently by-passing part of the fluid to different points of the passage way to allow the material to descend in successive stages.

3. Process of subjecting mobile material to the action of a fluid, which consists in passing the mobile material downwardly through a plurality of receptacles, passing a fluidupwardly through the receptacles under conditions to normally hold the mobile material in suspension and successively bypassing part'of the fluid around the different receptacles to allow the material to descend in successive stages.

4. Process of roasting sulfur-bearing ores which comprises providing an upward flowing current of gas through a plurality of receptacles,maintaining a charge of the sulfur-bearing material in each of said receptacles by the force of said gas current, and progressing the material downwardly through said receptacles by by-passing said current of gas around each of said receptacles successively from top to bottom.

5. Process of roasting sulfur-bearing materials which comprises establishing a plurality of superposed separate bodies of the material in subdivided condition in suspension in an upwardly flowing current of an oxidizing gas, supplying gas to said current intermediate at least two adjacent bodies of said material, progressing said bodies downwardly by successively reducing the strength of said current of gas suspending each of said bodies, the roasting operation being so regulated that the oxidation of the ore is completed before it reaches the position of the lowermost body whereby the current of gas supplied to the ore in the upper bodies is preheated by contact with the hot roasted ore in said lowermost body.

6. Apparatus for treating a mobile material with a fluid, comprising a plurality of superposed chambers, each of said chambers communicating with the chamber next beneath through a restricted passage, means for supplying the uppermost chamber with the mobile material, pressure means for passing the fluid into the lowermost chamber and means for independently by-passing the fluid around some of said chambers.

7. Apparatus for roasting ores, comprising a plurality of superposed chambers, each of said chambers communicating with the chamber next beneath through a restricted passage, means for supplying the uppermost chamber with ore in subdivided condition, means for supplying the lowermost chamber with an oxidizing gas, and means for by-passing theoxidizing gas around each of said chambers independently.

8. Apparatus for roasting ores as defined in claim 7 in which the means for by-passing the oxidizing gas around each of said chambers independently comprises a vertical conduit communicating with the upper part of each of said chambers; and valves 1n said conduit for controlling the passage of gas therethrough.

9. Apparatus according to claim 7 in which the means for independently by-passing the oxidizing gas around each of said chambers comprises a conduit communieating with the upper part of each of said chambers; valves in said conduit for controlling the' passage of gas therethrough, and means for supplying the oxidizing gas to the said conduit.

10. Apparatus according to claim 7 in which the means for independently by-passing the oxidizing gas around each of said chambers comprises a conduit communicating with the upper part of each of said chambers: valves in said conduit for controlling the passage of gas therethrough, means for supplying the oxidizing gas to the said conduit and a dust settling chamber in communication with the said uppermost chamber and the said conduit.

In testimony whereof, we afiix our signatures.

MARCH F. CHASE. JOHN SKOGMARK.

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