US3190744A

US3190744A - Process for magnetic reduction of iron ore

Info

Publication number: US3190744A
Application number: US250386A
Authority: US
Inventors: Richard E King
Original assignee: Northern Natural Gas Co
Current assignee: Northern Natural Gas Co
Priority date: 1963-01-09
Filing date: 1963-01-09
Publication date: 1965-06-22
Anticipated expiration: 1982-06-22
Also published as: FR1378748A

Description

June 22, 1965 R, E, K|NG 3,190,744

PROCESS FOR MAGNETIC REDUCTION OF IRON ORE Filed Jan. 9, 1963 5 Sheets-Sheet l @i f3 18-` P27 sa /os 5oz /os F550 "jf g3 pas/Afef P --10 ,23 Il j/ June 22, 1965 R. E. KING 3,190,744

PROCESS FOR MAGNETIC REDUCTION OF IRON ORE Filed Jan. 9. 1963 3 Sheets-Sheet 2 TYP/au cam/f F02 Pgs/.s nwcf ro /J/,e How o/vz y @ffm/xga June 22, 1965 R. E. KING 3,190,744

PRocEss Fon MAGNETIC REDUCTION OF IRON ORE Filed Jan. 9, 1965 3 sheets-sheet 3 Pfff/aar Afm/cf com 57 65 jf; W

169 tuve "F MwST/rf 000 Fe Mfr/MUC l 1.o .9 .a .7 .5 .4 .3 .2 I.1 o

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United States Patent O 3,19%,74-4 PRGCESS FR MAGNETEC REDUCTN F IRUN GRE Richard E. King, Birmingham, Ala., assigner to Northern Naturai Gas Company, maha, Nehr., a corporation of Delaware, and W. S. Moore Company, Duluth, Minn.,

a corporation of Minnesota Filed `ian. 9, 1963, Ser. No. 250,386 14 ICiaims. (Cl. 75-26) This is a continuation-impart of the present inventors applications S.N. 89,984 tiled February 17, 1961, and now abandoned, and S.N. 113,854, filed May 3l, 1961.

This invention relates generally to a process for reducing small particle size ferruginous ore materials ina gaseous suspension and more particularly to a process for reducing a ferruginous ore material, having at least a portion of its iron content in the form of non-magnetic compounds, to convert a major portion of the non-magnetic compounds to magnetite.

In the accompanying diagrammatic drawings:

FIGURE l is a flow sheet illustrating an embodiment of a process in accordance with the present invention;

FIGURE 2 is a chart showing a graphic representation that the gas pressure developed at the bottom of an upwardly extending pipe by the liow of solids is directly proportional tothe length of the pipe and the pressure developed increases with the increasing rate of solids ow and decreasing pipe diameter; Y

FIGURE 3 is a liow sheet illustrating the complete treatment of the materials in a multi-stage system including one embodiment of a process in accordance with the present invention;

FIGURE 4 is an equilibrium diagram showing the wide l range of temperatures and concentrations of the reducing gases which may be employed; and

FIGURE 5 is a flow sheet illustrating another embodiment of a process in accordance with the present invention.

As is well known in the art to which my invention relates, there are many low-grade ores, such as Mesabi slaty ore, which cannot be smelted by the conventional type blast furnace ybecause the ore contains silica, alumina and other compounds (collectively called gangue) and the gangue causes the generation of a large volume of slag which increases the heat requirement in the furnace and lowers the yield of metallic iron. `Also, such ores are soft whereby upon handling or shipment, the ore disintegrates into small particles which are unsatisfactory for use in the blast furnace. Furthermore, the relatively low content of iron in such ores requires the shipment and handling of almost three parts by weight of ore to yield one part by weight of metallic iron.

When ore is magnetic, the quality of the ore can be improved by magnetic separation of the iron oxide from the gangue. There are large quantities of iron-bearing, low-grade ferruginous ores now available which could constitute a great potential source of iron, except for the fact that these low-grade ores occur largely as the oxide hematite (FezOa) or as hydrated oxides such as goethite or limonite, which in their naturally-occurring state are not adapted for magnetic separation in the usual manner. By roasting these iron oxides in a reducing atmosphere, the non-magnetic oxides can be converted into magnetite (Fe3O4) which is separable from a large part of the gangue by magnetic separation in a manner well understood in the art. The reducing gases usually employed are carbon monoxide (CO), hydrogen (H2) or mixtures of these two gases. The gases are generally used in a mixture of other gases which result from the partial combustion of fuel, such as natural gas, oil, coal or the like.

3,190,744 Patented June 22, 1965 This mixture of gases Valso contains other products of combustion including carbon dioxide (CO2) and water (H2O). t

Generally, a process in accordance with the present invention comprises the introduction of nely ground ferruginous ore material into an upwardly moving stream of pre-heated reducing gases free of uncombined oxygen, having a temperature subjacent the fusion point of the ore material and having sufficient velocity to maintain all the various particle sizes in suspension and to carry the particles through a reducing zone wherein the desired reduction takes place. Inrthe process of the present invention a number of factors must be controlled for optimum results, as will be set forth subsequently.

The simplified reaction of the reducing gas with the non-magnetic iron oxide may be represented by the following:

Due to the fact that these reactions are reversible, the accumulation of the gaseous products of reaction effect the rate of the reaction.

Where intimate contact of the reducing gas and the solid iron oxide is maintained at elevated temperatures, the reduction of the iron content of the ore from hematite to magnetite proceeds rapidly. Generally, the surfaces of large and small particles of ore and the interior of small particles are readily contacted by the reducing gases and the gaseous reaction products are easily removed so that reduction of oxides so located takes place rapidly. On the other hand, the iron oxides on the interior of a large particle of ore are not reduced as quickly because the reducing gas must diffuse through a greater volume of solid material before it contacts the iron oxide, and because the resulting gaseous reaction products must then diffuse outwardly through the greater volume of solid material to escape from the reaction area and be replaced by reducing gas so that the reaction may continue. Thus, the time required to reduce a particle a given amount varies with the particle size, generally in linear relation thereto.

It is desirable that ore particles of various sizes be re` duced uniformly.

In accordance with the present invention, ore particles are introduced downwardly into a rising stream of reducing gases, at a venturi, so that the ore particles have a downward velocity component. In order that the downward velocity of the particles be proportional to a function of the particle size, the particles are allowed to fall freely before introduction into the reducing gas whose upward velocity should be maintained at a rate sutlicient to offset the downward velocity of the largest particle at the time of introduction and to convey it upwardly. The linal upward velocity of any particle, so handled, depends upon the diiference between the upward gas velocity and the downward velocity for a freely falling particle which is generally proportional to a function of the particle size. Thus, the time a particle will spend in the reduction zone depends upon: its downward velocity at the time of introduction which, herein, is the downward velocity of a freely falling particle which is a function of the particle size; and the upward gas velocity.

Because the times required to reduce various particle sizes a uniform amount are dependent upon the respective particle sizes and because, in accordance with the present invention, the time a particle will spend in the re ducing zone is dependent upon velocities which are functions of the particle size, it is possible to achieve substantially uniform reduction among all particle sizes even when a relatively wide range of particle sizes are being reduced together.

Generally, the upward velocity of a reducing gas can be controlled to assure a predetermined reduction of the largest particle suspended therein but, if this is the only control exercised, the extent of reduction will not` be s ubstantially uniform over the entire range of particle sizes when the range of sizes varies considerably and there are substantial amounts of each of alarge number of different particle sizes in the range. However, substantially uniform reduction of different particle sizes can be obtained when the particles are introduced downwardly and have an initial downward velocity component as described.

The reduction of hematite ore is typical of the reduction of the various non-magnetic ferruginous ores. This reduction reaction will occur over a wide range of temperatures and concentrations of the reducing gas, as shown in the equilibrium diagram in FIGURE 4 of the drawing. At the right side of the diagram in FIGURE 4 of the drawing is shown an area representing the temperature and gas compositions which result in the production of magnetite. Any combination of conditions within the area shown may be employed to produce magnetite. The diagram in FIGURE 4 is for a gas consisting essentially of carbon monoxide and carbon dioxide. The temperature and the ratio of carbon monoxide to the sum of carbon monoxide plus carbon dioxide in the reducing gases must be maintained at a value below line Y-Z and to the right of the line X-Y respectively. That is, a relatively low ratio of CO2CO-l-CO2 and a relatively high temperature will normally produce magnetite, as is shown in FIGURE 4. However, if the ratio of carbon monoxide to the sum of carbon monoxide plus carbon dioxide in the reducing gases is too low, the conditions are oxidizing for magnetite, and hematite may exist. On the other hand, where the temperature and the ratio of carbon monoxide to the sum of carbon monoxide plus carbon dioxide in the reducing gases are maintained at a value above the line W-Y-Z, the conditions are reducing for magnetite and wustite may be formed, which is a nonmagnetic material. Temperature conditions and gas ratios below and to the left of line W-Y-X are fully reducing and will produce metallic iron.

A similarily shaped equilibrium diagram would exist where the reducing gases contain H2 and H2O. Generally, the ratio of H2 to Hzi-i-HgO and the temperature must both be controlled to provide conditions which will reduce hematite to magnetite without overly reducing to wustite or metallic iron.

A mixture of CO and CO2 and a mixture of HZ and H2O are both obtained together by the partial combustion of natural gas with air. mixture and HZ-HZO mixture exist in the same gas, other factors become significant which are not present when only one of the two gas mixtures is relied upon for reducing hematite. For example, a ratio of CO to CO-l-COz which would overly reduce in the absence of H2 and H2O may not do so in the presence of H2 and H2O in certain ratios, and vice versa.

Thus, if the ratios of H2 to HTI-H2O and CO to CO-l-COZ are each in an area on their respective equilibrium diagrams which will produce magnetite at the prevailing temperature, there is no difculty in maintaining magnetite. If the ratio of H2 to HLA-H2O is in an area which will overly reduce magnetite at the prevailing temperature, magnetite can still be maintained and over reduction be prevented because there are ratios of CO to CO-l-COz which will enable the production of magnetite in the presence of over-reducing ratios of H2:H2|-H2O. More specilically, referring to FIGURE 4, if the CO to CO-I-CO2 ratio is suiciently below and to the right of the line X-Y-Z at the particular reaction temperature, and the ratio of H2 to HTI-H20 is relatively high (in an area which would produce wustite if the gas contained only a mixture of H2-H2O), then overreduction would probably not occur and magnetite would probably be produced.

When both the CO-COZ r To prevent over-reduction, when the two gas mixtures are used together, it is necessary to maintain either the ratio of COzCO-I-CO2 or the ratio of HzzHz-l-HZO below the critical value which will enable the production of magnetite when the other ratio is over-reducing. One method of lowering these ratios is to increase the extent of partial combustion of the fuel (e.g., natural gas). However, this method generates too much heat, which is undesirable because it may cause fusion of the ore particles; and it requires a relatively large quantity of fuel to yield the quantity of reducing gases necessary for the amount of iron ore to be reduced.

In accordance with the present invention, fuel is burned with the least quantity of air necessary to obtain the desired quantity of reducing gases. The ratios of CO:CO2 and H22H2O are then adjusted by adding CO2 and/or water vapor until the resulting reducing gas contains a mixture of both CO-COz and P12-H2O which, together, will maintain magnetite and prevent over reduction at the temperature prevailing.

Another factor to be considered is that the reduction reactions occur in a rising stream of gas which is moving faster upwardly than the ore particles being reduced. Accordingly, at any location along the upwardly extending reduction path there will be a greater ratio of reducing gas to non-reducing gas (e.g., CO to CO2) than would be the case if the ore particles and the gas were moving at the same speed. Conversely, because the ore particles are moving at slower speeds than the gas, at any location along the upwardly extending reduction path an ore particle which is moving substantially slower than the gas will have undergone more reduction than it would have undergone had it moved at the same speed as the gas. Both of these factors tend to permit over-reduction.

To prevent over-reduction under these circumstances, the gas, upon initial commingling with the ore particles, should have a composition including ratios of COzCO-i-COz and H21H2-l-H2O which, for the prevailing temperature, will prevent over-reduction along the upwardly moving reduction path and which will assure that ore particles leaving the reduction zone will be magnetite rather than wustite or metallic iron.

Because some CO2 and some H2O will be generated along the reduction path, and because over-reduction is not a problem at initial portions of the reduction path (inasmuch as the ore is virtually all hematite at said initial portions) the ratios of COrCO-l-COZ and HzzHz-l-HZO, upon initial commingling, need not neces- -sarily be those which will maintain magnetite. However, at subsequent portions of the reduction path these ratios must be such that there is enough CO2 and/ or H2O (both initially added and subsequently generated) to prevent over-reduction and maintain magnetite.

At the end of the reduction path, the particles are separated from the gas. The gas is hot and may be recycled to earlier stages of the `system for preheating purposes.V The gas may also be mixed with gas from the combustion furnace to increase the CO2 and H2O in the gas mixture entering the reduction path.

Referring now to the drawings for a better understanding of my invention, I show a two-stage system in FIG- `URE l which comprises a first upwardly extending riser 10 and a second upwardly extending riser 11. A gas inlet 12 is provided at the lower end of riser 10 while the upper end of riser 10 communicates with a cyclone separator 13 which separates the gas from the solid particles. The Vsolid particles are discharged from cycline separator 13 through a discharge conduit 14. Communicating with the gas discharge of separator 13 is a downwardly extending conduit 17 which in turn communicates with the lower end of second riser 11 whereby the stream of gases indicated by the dotted arrow 18 are conveyed upwardly through second riser 11. The upper end of riser 11 cornmunicates with a cyclone separator 19 having a gas out-` let 2l and an outlet 22 for discharging solid particles.

The lower ends of

risers

10 and 11 are provided with venturi throats 23 and 24 respectively. Communicating with venturi 24 is a downwardly extending inlet conduit 25 for supplying the small particle size materials to be roasted. The materials thus introduced through conduit 26 are conveyed upwardly by the upwardly moving stream of gases, the flow of the solid particles being indicated by the solid arrows 2.7. As the concurrently flowing stream of gas and solid particles pass through separator 19, the gases are discharged through outlet 21 while the solid particles are discharged downwardly through outlet 22.

Communicating with solid discharge outlet 22 is the upper end of a downwardly extending conduit 28. The lower end of conduit 28 communicates with venturi 23 whereby the solid particles are introduced into the lower end of rst riser 10.

From the foregoing description, the operation of the process illustrated in FIGURE 1 will be readily understood. Preheated, hot reducing gases are continuously introduced through inlet 12 at venturi 23 whereby they ow upwardly through riser 10 and separator 13 and then flow downwardly through conduit 17 to venturi 24 at the lower end of second riser 11. After passing through venturi throat 20.1, the gaseous stream passes upwardly through riser 11 and is finally discharged through outlet 21 or" separator 19. The solid materials are fed into venturi 2d through conduit 2.6 whereby they are conveyed upwardly and flow concurrently with the stream of gas to separator 19. The solid particles are discharged from separator 19 through outlet 22 into yconduit 2S whereupon the solids are introduced into venturi 23 of riser liti. The solid particles then flow upwardly and concurrently with the hot reducing gases introduced through inlet 12 to separator 13. The solid particles are discharged from separator 13 through outlet 14. The volumev of gases introduced into riser 1@ and the size of riser 1@ is such that the velocity of the gas .stream will suspend theine particle size materials and convey them to separator 13. This velocity is dependent largely upon the particle size and density of the ne ore. ln actual practice, I have found that a velocity greater than l feet per second is usually required to prevent particles of ferruginous ore .from settling out of the gas stream due to the forces of gravity;

It will thus be seen that the solid particles and reducing gas flow concurrently as they pass upwardly through risers 1@ and 11 whereby the solid particles are suspende-d in the moving gases. However, the overall ow of the solids is countercurrent to the flow of gases. That is to say, the solid particlesare introduced into the lower end of second riser 11 and are then passed through first riser 11D before being discharged. Accordingly, second riser 411 serves as a preheater while first riser serves` as a reactor. Because down ilow of solid materials in conduit A28 is essential to the maintenance of pressure balance and proper direction of gas flow, the introduction of solids at 26 must be started at a relatively low rate and -gradually increased to the proper operating level. Also,

if desired, a suitable Valve may be provided in conduit Z8 whereby the ow of gas through conduit 2S is restrained until the system is `placed. in operation. That is, valve 25 would be gradually moved to open position after a solids feed rate has been established. Also, solids discharge outlet 14 is connected to a solids discharge system which restricts the flow of gas into and out of the system. As the solids ow upwardly concurrently with the gas stream, gravity restrains upward movement of the larger particle size materials more than it restrains upward movement of the smaller particle size materials `whereby the larger particle size materials are subjected to longer exposure to the hot gases thereby bringing about the required minimum amount of reduction of the larger particle size materials.

Unless counteracted, the gas introduced at inlet 12 will tend to pass upwardly through solids downcomer 28 to separator 19, .thereby short-circuiting the reaction zone and greatly lowering the separating efficiency of separator 19. That is, because of frictional losses in the system, the gas at the inlet will be at a higher pressure than the gas within separator 19, unless counter-acted. The desired flow of gas is through venturi 23 and upwardly through first riser 1t) to separator 13 and then downwardly through conduit 17 .to the lower end of second riser 11 where the gas ows upwardly therethrough and is finally discharged through outlet 21. This problem cannot be solved by providing a mechanical air-lock device, such as a rotary feeder or `a gravity trickle valve due to the fact that such devices would not be satisfactory for use at temperatures employed for the reduction of iron.

Proper flow of the gases and solids is provided without the use of mechanical devices. When gas alone is flowing through the system the pressure drop of the gas flowing through the desired path in my apparatus is almost completely equalled by the venturi pressure change so that essentially no pressure exists Ito cause flow of gas upwardly through the conduit or solids downcomer 28. In actual practice, when solids are being conveyed by gas in the illustrated system, the pressure drop through the desired path is increased while the differential of pressure brought about by the venturi may be reduced by the presence of solids. By proper choice of the diameter and length of solids downcomer 28, the solids failing down the solids downcomer 28 will increase the gas pressure near the bottom of the downcomer and short-circuiting of gas, when the system `is conveying solids, can be prevented.

The pressure developed by solids falling in a standpipe is important in the function of the illustrated multi-stage system due to the fact that the solid particles ow down the downcomer 28. The gas pressure developed at the bottom of a standpipe by the ow of -solids is directly proportional to the length of the standpipe. FIGURE 2 of the drawings shows that the pressure developed also increases with the increasing rate of solids flow and decreasing pipe diameter. The iron ore employed in obtaining the results shown in FIGURE 2 was minus 2O mesh iron ore. The curves show that the pressure devel# oped is much reduced in larger diameter pipe, such as would be used in commercial operation. However, a compensating factor is that the resistance offered to gas flow in the riser and other parts of the system will also be reduced in larger diameter pipes, as shown by the dashed line in FIGURE 2. Accordingly, the pressure developed by falling solids would be'equally useful in a large commercial system to prevent upward iiow of gas through the solids downcomer 25. The pressure developed is indicated in FIGURE 2 by inches of water, on the water gauge, over the length of the conduit, measured in feet.

Referring now to FIGURE 3 of the drawings, I show the complete treatment of the materials in a multi-stage system. The crushed ore is stored in a suitable bin 29 and is transferred to a dry-grinding system indicated generally at 31 whereby the ore is pulverized and dried simultaneously. The particle size to which the ore must be crushed to effect rapid reaction is determined by the physical characteristics of the natural ore. That is, some natural ores have a porous structure which permits some penetration of gas into the interior of the particles. T-hese ores will reduce rapidly at a much coarser size than will an ore having a dense structure. In actual practice, many ores can be reduced in the illustrated system by crushing the ores to a particle size whereby the largest particles will pass a standard l0 mesh testing sieve. Y

The finely pulverized ore passes from the grinding system 31 to an air classiiier 32 and then Ato a cyclone separator 33 Where exhaust gases are removed as at 34. The pulverized ore is stored .in a bin 36 and is then con- Veyed through a supply line 37 to an upwardly extending riser 38 which communicates at its Yupper end with a cyclone separator 39. The exhaust gases from separa-tor 39 are removed through a conduit 41 where they are conveyed through grinding system 31, air classifier 32 and separator 33 whereby the gases dry the ore introduced into the grinding system. The fine particle size materials introduced into riser 38 thus move concurrently and in suspension with the gaseous stream to separator 39.

The gaseous stream supplied to line 38 comes from the exhaust of a cyclone separator 42. The tine particle size ore materials discharged from the lower end of cyclone separator 39 enter a line 43 and are then discharged into a riser 44 which communicates the gas exhaust of a cyclone separator 45 with cyclone separator 42. The upwardly moving stream of gas in riser 44 picks up the tine particle size ore materials whereby they are suspended in the gas and conveyed concurrently therewith to separator 42.

Communicating with cyclone separator 45 is the upper end of riser 46. The lower end of riser 46 communicates with a line 47 which supplies the gaseous stream from a gas generator 48. Solid materials discharged from separator 42 are introduced into the lower end of riser 46 by a line 49 whereby they move upwardly and concurrently in suspension with the gaseous stream to separator 45. The reducing gases formed in gas generator 48 may be provided by introducing air through a conduit 51 and natural gas through a conduit 52 whereby they are mixed and partially burned in gas generator 48 prior to being introduced into riser 46. The composition and temperature of the gases leaving the generator 48 may be controlled by recycling a portion of the gaseous stream exhausted from cyclone separator 42 (and containing CO2 and H2O) through a line 53 to air supply line 51. As an alternative embodiment H2O and/or CO2 from an outside source may be introduced linto conduit 47 through a line 60.

The movement of the tine particle size ore materials through

risers

38 and 44 serves as a temperature preparation whereby the ore is preheated prior to being introduced into riser 46 carrying the hot reducing gases. The tine particle size materials to be roasted are fed through the apparatus at a suitable rate whereby the particles are freely suspended completely or fully in the reducing gases while passing through riser 46. Riser 46 thus serves as a reaction zone whereby the ine particle size materials are not only suspended in this zone but flow concurrently with the reducing gases to separator 45. The volume of the reducing gases introduced in riser 46 and the size of riser 46 is such that the velocity of the gas stream will suspend the ne particle size materials and convey them to separator 45. As the ore particles pass through separator 45, they are separated and are discharged into a cooler 54.

From cooler 54, the reduced or passes to suitable magnetic separators indicated generally at 56 whereby the magnetic materials are separated from the non-magnetic materials. The magnetic ore may then pass to suitable briquetting or pelletizing apparatus 57 in a manner well understood in the art.

Another embodiment is illustrated in FIGURE and is similar in many respects to that illustrated in FIGURE 3. However, in addition to the two preheating stages consisting of separators 3-9, 42 and their associated downcomers and risers, and the reducing stage consisting of separator 45, etc., the embodiment of FIGURE 5 also includes a c-ooling stage comprising a cyclone separator 160.

Reduced ore particles leave reducing zone separator through a downcomer 162 and are fed into an upwardly moving stream of gas in a riser 161. The bottom of riser 161 communicates with the top of first preheat stage separator 39 through a conduit 141 which also communicates with a conduit 171 leading to a vent (not shown). The gases in riser 161 have previously passed through two preheat stages (i.e., at separators 42 and 39) where much of the heat of the gases has been transferred to the iron ore particles to preheat the latter. Accordingly, the gas in riser 161 is substantially cooler than the reduced iron Cil ore particles introduced into riser 161 from downcomer 162, .and the gas will cool the iron ore particles suspended therein. Iron ore particles from cooling stage separator 16) pass downwardly through a conduit 163 to a quench tank 165. Gases from separator 160, now substantially hotter after the exchange of heat with the ore particles, pass into a conduit 164 which communicates with the bottom of riser 44, at the second preheat stage, via a blower 166 and a conduit 167.

Also communicating with the bottom of riser 44, in series, are

conduits

173 and 168, the latter communicating with the top of reducing stage separator 45. Hot reaction gases pass from separator 45 through

conduits

168, 173 to riser 44 to assist in the preheating. Gases from conduit 168 also pass through a conduit 172 into riser 46. The gases from 172 mingle with the reducing gases from furnace 48 to help adjust the CO:CO-}CO2 and HgzHz-l-HzO ratios to .the desired levels, as discussed with respect to the function of conduit 53 in the embodiment of FIGURE 3.

Gases from separator 42 pass through a conduit 170 to the bottom of riser 38, into separator 39, and from there .to cooling riser 161 via conduit 141.

A second or preheat stage furnace 14S effects a substantial combustion of natural or combustible gas with air and feeds the resulting gases through .a conduit 169 and conduit 173 into riser 44 of the second preheat stage. Thus, riser 44 contains a commingling of gases from reducing separator 45, from furnace 148 and from cooling separator 160.

Because the gases in riser 44 are eventually introduced into cooling stage riser 161 (after having passed through both preheat

separators

42, 39 in that order), and because riser 161 conveys ore particles which have already been reduced, it is important that the gas introduced into riser 161 be of a composition which will maintain a particle composition of magnetite. Therefore, the gases in riser 161 should contain no free oxygen and be slightly reducing, but, also, not over-reducing.

Gases such as CO2 and H2O have a higher heat capacity and permit transfer of a greater quantity of heat with a smaller volume of gas then do gases such as CO or H2. Accordingly, it is desirable that the gases passing through the preheat stages have as much CO2 and H2O as is possible without creating conditions which are oxidizing to the reduced ore particles in cooling riser 161 into which the gases from the preheat stages eventually ow. Some of the desired H2O and CO2 are provided by the exhaust gases from the reducing stage (i.e., through

conduits

168 and 173 to preheat riser 44). Additional CO2 and H2O is provided by combustion of fuel in furnace 148, communicating with riser 44 through

conduits

169, 173. To the extent that large quantities of heat are generated in furnace 148, this is acceptable during the preheat stages where fusion of the as yet unheated or slightly heated ore particles is not a problem as it is in the reducing stage.

Therefore, furnace 148 is controlled to produce a gas for mixture with other gases entering riser 44 to give a composition having as high a content of CO2 and H2O which can be tolerated and still prevent oxidation of reduced ore particles in cooling riser 161.

In order to convert one pound of hematite to magnetite, approximately 0.8 cubic foot of either carbon monoxide or hydrogen (dry basis, 60 F., 29.92 inches of mercury) is required. Where the reducing gas contains 15% carbon monoxide or hydrogen at a temperature of approximately 1400 F. and atmospheric pressure, the gas volume required for one pound of hematite is approximately 19 cubic feet. Approximately this volume of gas is required to suspend one pound of hematite and the other materials associated therewith in the natural ore.

The suspension of fine particle size materials in reducing gases is maintained at an elevated temperature which is below the fusion point of the various components of the material. That is, it is desirable to prevent the par- 9 yticles from passinginto the liquid or melted state during the reaction.

Increasing the ytemperature increases the reaction rate. As an example, an iron ore containing 50% iron was crushed to pass a 30 mesh testing sieve. This ore was reduced in a stream of reducing gas having approximately 8.8% carbon monoxide.

At a temperature of approximately 1090 F., the ore was 68% reduced to magneti-te in 3 seconds.

At a temperature of approximately 1250 F., the ore Was 82% reduced to magnetite in 3 seconds; and,

At .approximately 1375 F., maximum reduction to magnetite was obtained in 3 secondsg As another' example, iron ore containing 57% iron was crushed to pass a 30 mesh sieve and was treated with the Same gas composition listed in theexample hereinabove for 3 seconds at approximately '1240 F. The ore was 82% reduced to magnetite in the 3 seconds.

The relationsihp of the size of the tine particle size materials to the velocity of the reducing gases is maintained at or above a value which prevents any particles of the ore from settling out of the gaseous stream'due solely to the action of gravity.

As an example of the operation of the process, an iron ore containing 43.6% iron was crushed to pass a 14 mesh testing sieve. Thisore was reduced in a two-stage apparatus similar to that shown in FIGURE 1 in which the risers were of standard 1% inch pipe approximately 7 feet long. lThe reducing gas contained 16.5% carbon monoxide and hydrogen. The measured temperature of the gas was maintained at approximately 1540J F. Essentially complete reduction of the iron oxide to magnetite was obtained at an ore rate of approximately 188 pounds per hour and a gas rate of l standard (60 F., 29,92 inches of mercury) cubic feet per minute.

The foregoing describes an improved process for treating ore-like materials, such as ferruginous ores. While the described process is particularly adapted for use in treating ferruginous ores, it will be apparent `that it is also adaptable generally for roasting other materials, such as pyrite and the like. By roasting the ine particle size materials while they are in complete suspension in the hot gases, the roasting or reduction takes place in a' minimum of time. Also, by constructing and arranging the appartus whereby the pressure drop of gas flowing through the risers and the equipment associated therewithis substantially equal to the change of pressure at the venturi in the first riser and that created by solids flowing down the solids downcomer, there is substantially no pressure drop across the solids downcomer to cause flow of gas directly from the gas inlet to the separator associated with the second riser.

The foregoing detailed description has been given for clearness of understanding only, and no unnecessary limitations should be understood therefrom, as modications will be obvious to those skilled in the art.

What is claimedV is:

1. The process of treating a ferruginous ore material having a-t least a portion of its iron content in the form of non-magnetic oxygen-containing compounds reducible to magnetite, said process comprising the steps of:

providing said ore material as iinely divided particles;

providing a stream of heated gases consisting essen- 'tially of at least one gas selected from a first group consisting of carbon monoxide (CO) and hydrogen (H2) and at least one gas selected from a second group consisting of carbon dioxide (CO2) and water vapor (H2O), with said stream of gases being free of uncombined oxygen and at a temperature below the fusion point of said ore material;

providing said stream of gases With a ratio of iirstgroup gases to second-group gases which is reducing to said ore material at said temperature;

introducing said stream of gases into one end of a closed, longitudinally extending reaction zone and moving the stream of gases through said reaction zone;

introducing said particles of ore material into said one end of said reaction zone with the particles having a downward velocity component at the time of said introduction;

forming a free suspension of said particles in said stream ot gases, with said suspension moving through the reaction zone from said one end to the other end thereof;

reducing said non-magnetic oxygen-containing compounds in said particles to magnetite, during movement of the suspension rthrough said reaction zone, to render said particles magnetic;

controlling the ratio of first-group gases to second-group gases and the temperature of said stream of gases in the reaction zone to prevent over-reduction of the ore particles to metallic iron or to wustite and to maintain magnetite at the other end of the reaction zone; separating said ore particles at said other end of the reaction zone from lsaid stream of gases; the movement of said stream of gases, from the time the ore particles become suspended in the stream of gases until the stream of gases reaches the other end of the reaction zone, consisting of movement in a direction having an upward component; and magnetically separating the magnetic particles from the non-magnetic particles in said ore material, without further reduction of the ore material. Z. The process of claim 1 wherein the largest of said ore particles is smaller than a standard l() mesh.

3. The process of claim l wherein said stream of gases is heated to a temperature between 1090 F. and 1540 F. 4. VThe process of treating a ferruginous ore material having at least a portion of its iron content in the form of non-magnetic oxygen-containing compounds reducible to magnetite, said process comprising the steps of:

providing said ore material as iinely divided particles; providing a stream of heated gases consisting essentially of at least one gas selected from a first group consisting of carbon monoxide (CO) and hydrogen (H2) and at least one gas selected from a second group consisting of carbon dioxide (CO2) and water vapor (H2O), with said stream of gases being free of uncombined oxygen and at a temperature below the fusion point of said ore material; providing said stream of gases with a ratio of iirstgroup gases to second-group gases which is reducing to said ore material at said temperature; introducing said stream of gases into a closed, upwardly extending reaction zone and moving said stream upwardly through said reaction zone; introducing said particles of ore material into said upwardly moving stream of gases at the bottom of said reaction zone; forming, in said closed reaction zone, an upwardly moving free suspension of said particles in said stream of gases; reducing said Vnon-magnetic oxygen-containing cornpounds in said particles to magnetite, during movement of the suspension through said reaction zone, to render said particles magnetic; controlling the ratio of iirst-group gases to secondgroup gases and the temperature in said stream of gases in the reaction zone to prevent over-reduction of the ore particles to metallic iron or wustite and to maintain magnetite at the top of the reaction zone; separating said ore particles at said top of the reaction zone from said stream of gases; magnetically separating the magnetic particles from the non-magnetic particles in said ore material, without further reduction ofthe ore material; introducing said ore particles, before introduction thereof into said reaction zone, into one end of a longitudinally extending, closed preheating zone;

introducing hot preheating gases into said one end of the preheating zone, and moving said gases upwardly through the preheating zone;

forming a free suspension of said ore particles in said preheating gases with said suspension moving through the preheating zone from said one end to the other end thereof;

said ore parlicles and said hot preheating gases undergoing a mutual heat transfer during movement of the suspension through said preheating zone to provide heated ore particles and cooled gases; and separating the heated ore particles at said other end of the preheating zone from said cooled gases;

the movement of said preheating gases, from the time the ore particles become suspended in the preheating gases until the stream of gases reaches the other end of said preheating zone, consisting of movement in a direction having an upward component;

' at least part of lthe volume of said hot preheating gases being provided by circulating gases from said stream of gases a-t the top of said reaction zone to the one end of said preheating zone.

5. A process as recited in claim 4 wherein:

another part of the volume of said hot preheating gases is provided by effecting combustion of combustible gases with air at a location outside the reaction zone, between one end of the preheating zone and the top of said reaction zone, to produce a mixture of gases free of uncombined oxygen and including at least one of said second-group gases;

and circulating said mixture of gases to the one end of the preheating zone.

6. A process as recited in claim 4 and comprising:

controlling the ratio of said second-group gases to said iirst-group gases in said preheating zone so that said ratio is as high as is possible without causing oxidation of magnetite at the temperature prevailing in the o re material separated at the other end of said reaction zone.

7. The process of treating a ferruginous ore material having at least a portion of its iron content in the form of non-magnetic oxygen-containing compounds reducible to magnetite, said process comprising the steps of:

providing said ore material as linely divided particles in a relatively wide range of particle sizes each having a substantial amount, by weight;

providing a stream of heated gases consisting essentially of at least one gas selected from a first group consisting of carbon monoxide (CO) and hydrogen (H2) and at least one gas selected from a second group consisting of carbon dioxide (COZ) and water vapor (H2O), with said stream of gases being free'of uncombined oxygen and a temperature below the fusion point of said ore material;

providing said stream of gases with a ratio of firstgroup gases to second-group gases which is reducing to said ore material at said temperature;

permitting said particles to fall freely, due to the action of gravity alone, until introduction thereof into the reaction zone, whereby the particles have a downward velocity component proportional to a function of the particle size;

forming a free suspension of said ore particles in said stream of gases, with said suspension moving through the reaction zone from sai-d one end to the other end thereof;

reducing said non-magnetic oxygen-containing cornpounds in said particles to magnetite, during movement of the suspension through said reaction zone, to render said particles magnetic;

maintaining the largest of said particles in said reaction zone until it has been reduced to the extent desired, whereby each of the particle sizes is subjected to substantially uniform reduction on the basis of weight percent undergoing reduction;

controlling the ratio of first-group gases to secondgroup gases and the temperature of said stream of gases in the reaction zone to prevent over-reduction of the ore particles to metallic iron or to wustite and to maintain magneti-te at the other end of the reaction zone;

separating said ore particles at said other end of the reaction zone from said stream of gases;

the movement of said stream of gases, from the time the ore particles become suspended in the stream of gases until the stream of gases reaches the other end of the reaction zone, kconsisting of movement in a direction having an upward component;

and magnetically separating the magnetic particles from the non-magnetic particles in said ore material, without further reduction of the ore material.

8. The process of treating a ferruginous ore material,

having at least a portion of its iron content in the form of non-magnetic oxygen-containing compounds reducible to magnetite, said process comprising the steps of:

providing said ore material as inely divided particles;

providing a stream of heated gases consisting essentially of at least one gas selected from a iirst group consisting of carbon monoxide CO) and hydrogen (H2) and at least one gas selected from a second group consisting of carbon dioxide (CO2) and water vapor (H2O), with said stream of gases being free of uncombined oxygen and at a temperature below the fusion point of said ore material;

introducing said stream of gases into one end of a closed, longitudinally extending reaction zone having a pair of ends, and moving said stream through said reaction zone;

introducing said particles of ore material into said moving stream of gases at one end of said reaction zone;

forming, in said closed reaction zone, a free suspension of said particles and said stream of gases, and moving said suspension through said reaction zone;

reducing said non-magnetic oxygen-containing compounds in said particles to magnetite, during movement of the suspension through said reaction zone, to render said particles magnetic;

controlling the ratio of first-group gases to secondgroup gases and the temperature in said stream of gases in the reaction zone to prevent over-reduction of the ore particles to metallic iron or wustite and to maintain magnetite at the other end of the reaction zone;

magnetically separating the magnetic particles from the non-magnetic particles in said ore material, without further reduction of the ore material;

introducing said ore particles, before introduction thereof into said reaction zone, into one end of a longitudinally extending, closed preheating zone having a pair of ends;

introducing hot preheating gases into the one end of the preheating zone, and moving said gases through the preheating zone;

heating gases and ore particles, with the suspension moving through the preheating zone;

said ore particles and said hot preheating gases undergoing a mutual heat transfer during movement ot` the suspension through said preheating zone to provide heated ore particles and cooled gases;

separating the heated ore particles at the other end of the preheating zone from said cooled gases;

ing stream of gases at one end of said reaction zone; forming, in said closed reaction zone, a free suspension of said particles and said stream of gases, `with said suspension moving through the reaction zone; reducing said non-magnetic oxygen-containing compounds in said particles to magnetite, during movement of the suspension through said reaction zone, to render said particles magnetic; controlling the ratio of rst-group gases to secondat least part of the volume of said hot preheating gases group gases and the temperature in said stream of being provided by circulating gases from said stream gases in the reaction zone to prevent over-reduction c of gases at the other end of said reaction zone to of the ore particles to metallic iron or wustite and the one endof said preheating zone; to maintain magnetite at the other end of the reintroducing said magnetite-containing ore particles, action zone;

after said separation thereof from said stream of 15 separating said ore particles at said other end of the gases, into one end of a closed longitudinally extendreaction zone from said stream of gases; ing cooling zone having a pair of ends; magnetically separating the magnetic particles from circulating said cooled preheating gases from said the non-magnetic particles in said ore material, withother end of said preheating zone into said one end out further reduction of the ore material; of said cooling zone, suspending said ore particles introducing said ore particles, before'introduction therein said cooled gases in the cooling zone, and conof into said reaction zone, into one end of a longiveying said ore particles in suspension with said tudinally extending, closed preheating zone having cooled preheating gases through said cooling zone to a pair of ends; the other elld thereof, Wherehy the ore material is introducing hot preheating gases into said one end of Cooled and the gases are heated; the preheating zone, and moving said gases through separating said cooled ore particles at said other end the preheating zone;

of the COOlihg Zone from Said heated gases; forming, in said preheating zone, a suspension of preand controlling the composition of Said preheating heating gases and ore particles, with the suspension gases, before introduction thereof into said cooling moving through the preheating zone; zone, to eXcludc uncombined oxygen and to provide ao :said cre particles and said hot preheating gases undera ratio of iirst-group gases to second group gases going a mutual heat transfer during movement of the which Will maintain magnetite at the temperatures Suspension through the preheating zone to provide prevailing in said cooling zone. heated ore particles and cooled gases; 9. A process as recited in claim 8 and comprising: separating the heated ore particles at the other end of circulating heated gases from said other end of the the preheating zone from said cooled gases;

cooling zone to said one end of the preheating zone. at least part of the volume of said hot preheating gases 10- A Process as recited iu claim s Wherein being provided by circulating gases from said stream another part of the volume of said hot preheating gases of gases at the other end of said reaction zone to the is provided by effecting partial combustion of comone end of said preheating zone; bustible gas With air, at a locatioI1 outside the reac- 40 another part of the volume of said hot preheating gases tion zone between said one end of the preheating being provided by effecting Combustion of com- Zone and Said Other end 0f the reaction Zone, t0 bustible gases with air, at a location outside the reproduce a mixture of gases free 0f uricoihhirled action zone between one end of the preheating zone oxygen and including at least ohe of said secoudand the other end of said reaction zone, to produce group gases; amixture of hot gases free of uncombined oxygen and c1rculat1ng said mixture of gases to said one end and including at least one of Said Second-group gases; of said preheating zone. commingling said other part of said hot gases with said 11- A Process as recited irl claim 8 arid corhPrisiug hot gases circulated from the other end of Isaid recohtrolllug the ratio of said secoi1d-grouP gases to said action zone, before introduction of the hot gases into iirst-group gases in said preheating zone so that said o the preheating zone; ratio is as high as is Possible Without causing oXi d and controlling the composition of said hot preheating datioii of Inagile-tite at the temperature prevailing iii gases to exclude uncombined oxygen and provide, at the ore material separated at the other end of said said other end of said preheating Zone, a ratio 0f reaction Zone first-group gases to second-group gases which will 12- The Process 0f treating a ferruglnous Ore material 5,- maintain magnetite at the temperature prevailing in having at least a portion of its iron content in the form o the ore material Separated at the other end of Said of non-magnetic oxygen-containing compounds reducible reaction Zone. to magnetite, said Process comprising the steps of: 13. A process as recited in claim 12 and comprising: ProVidihg Said ore material as hely diVided Particles? controlling the ratios of said second-group gases to Providing a Stream of heated gases consisting essen' l60 said rst-group gases in said preheating zone so that tially of at least one gas selected from a first group said ratios are as high as is possible Without causing Consisting of Carbon monoxide (C0) and hydrogen oxidation of magnetite at the temperature prevailing (H2) arid at least ohe gas selected from a second in the ore lnaterial separated at the other end of said group consisting of carbon dioxide (CO2) and Water reaction zone Vapor (H2O), With said stream of gases being frcc 65 14. A process for treating ore material, said process of uncombined oxygen and at a temperature below Comprising the steps of; the fusioh Point of said ore material; providing said ore material as finely divided particles; Providing said stream of gases With a ratio of iirstproviding a stream of heated gases reactive with said group gases to second-group gases which is reducing ore material, said stream of gases having a temperato said ore material at said temperature; ture below the fusion point of said ore material; introducing said stream of gases into one end of a introducing said stream of gases into a closed, longiclosed, longitudinally extending reaction zone having tudinally extending reaction zone having a pair of a pair of ends, and moving said stream through said ends, and moving said stream through said reaction reaction zone; zone; introducing said particles of ore material into said movintroducing said particles of ore material into said moving stream of gases at one end of said reaction zone;

forming, in said closed reaction zone, a moving free suspension of said particles and said stream of gases;

reacting said ore material with said gases during movement of the suspension through said reaction zone;

introducing hot preheating gases into said one end of the preheating zone, and moving said gases through lthe preheating zone;

forming, in said preheating zone, a moving suspension of preheating gases and ore particles;

said ore particles and said hot preheating gases undergoing a mutual heat transfer in said preheating zone to provide heated ore particles and cooled gases;

and separating the heated ore particles at the other end of the preheating zone from said cooled gases;

i at least part of the volume of said hot preheating gases being provided by circulating gases from said stream of gases at the other end of said reaction zone to the one end of said preheating zone;

recycling at least part of said cooled preheating gases to said stream of gases introduced into the one end of said reaction zone;

and subjecting said recycled cooled preheating gases to at least two stages of separation from said ore material before said recycling of said cooled preheated gases. l

References Cited by the Examiner UNITED STATES PATENTS 2,343,780 3/ 44 Lewis 75--26 2,399,984 5/ 46 Caldwell 75-26 2,870,003 1/59 Cavanagh 75-26 FOREIGN PATENTS 690,527 4/ 53 Great Britain.

DAVID L. RECK, Primary Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE 0E CORRECTION Patent No. 3,190, 744 June 22, 1965 Richard E. King It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column l, line 54, after "When" insert iron column 4, line 67, for "cycline" read cyclone column 7, line 52, for "or" read ore column 8, line 4l, for "then" read than column 9, line 19, for "relationsihp" read relationship U column Il, line l0, for "parlicles" read particles line 55, before "a" insert at column 13, line 3l, for "second group" read second-group Signed and sealed this 21st day of December 1965.

(SEAL) Attest:

ERNEST W. SWIDER EDWARD J. BRENNER Attesting Officer Commissioner of Patents

Claims

1. THE PROCESS OF TREATING A FERRUGINOUS ORE MATERIAL HAVING AT LEAST A PORTION OF ITS IRON CONTEND IN THE FORM OF NON-MAGNETIC OXYGEN-CONTAINING COMPOUNDS REDUCIBLE TO MAGNETITE, SAID PROCESS COMPRISING THE STEPS OF: PROVIDING SAID ORE MATERIAL AS FINELY DIVIDED PARTICLES; PROVIDING A STREAM OF HEATED GASES CONSISTAING ESSENTIALLY OF AT LEAST ONE GAS SELECTED FROM A FIRST GROUP CONSISTING OF CARBON MONOXIDE (CO) AND HYDROGEN (H2) AND AT LEAST ONE GAS SELECTED FROM A SECOND GROUP CONSISTING OF CARBON DIOXIDE (CO2) AND WATER VAPOR (H2O), WITH SAID STREAM OF GASES BEING FREE OF UNCOMBINED OXYGEN AND AT A TEMPERATURE BELOW THE FUSION POINT OF SAID ORE MATERIAL; PROVIDING SAID STREAM OF GASES WITH A RATIO OF FIRSTGROUP SAID ORE MATERIAL AT SAID TEMPERATURE; INTRODUCING SAID STREAM OF GASES INTO ONE END OF A CLOSED, LONGITUDINALLY EXTENDING REACTION ZONE AND MOVING THE STREAM OF GASES THROUGH SAID REACTION ZONE; INTRODUCING SAID PARTICLES OF ORE MATERIAL INTO SAID ONE END OF SAID REACTION ZONE WITH PARTICLES HAVING A DOWNWARD VELOCITY COMPONENT AT THE TIME OF SAID INTRODUCTION; FORMING A FREE SUSPENSION OF SAID PARTICLES IN SAID STREAM OF GASES, WITH SAID SUSPENSION MOVING THROUGH THE REACTION ZONE FROM SAID ONE END TO THE OTHER END THEREOF; REDUCING SAID NON-MAGNETIC OXYGEN-CONTAINING COMPOUNDS IN SAID PARTICLES TO MAGNETITE, DURING MOVEMENT OF THE SUSPENSION THROUGH SAID REACTION ZONE, TO RENDER SAID PARTICLES FMAGNETIC; CONTROLLING THE RATIO OF FIRST-GROUP GASES TO SECOND-GROUP GASES AND THE TEMPERATURE OF SAID STREAM OF GASES IN THE REACTION ZONE TO PREVENT OVER-REDUCTION OF THE ORE PARTICLES TO METALLIC IRON OR TO WUSTITE AND TO MAINTAIN MAGNETITE AT THE OTHER END OF THE REACTION ZONE; SEPARATING SAID ORE PARTICLES AT SAID OTHER END OF THE REACTION ZONE FROM SAID STREAM OF GASES; THE MOVEMENT OF SAID STREAM OF GASES, FROM THE TIME THE ORE PARTICLES BECOME SUSPENDED IN THE STREAM OF GASES UNTIL THE STREAM OF GASES REACHES THE OTHER END OF THE REACTION ZONE, CONSISTING OF MOVEMENT IN A DIRECTION HAVING AN UPWARD COMPONENT; AND MAGNETICALLY SEPARATING THE MAGNETIC PARTICLES FROM THE NON-MAGNETIC PARTICLES IN SAID ORE MATERIAL, WITHOUT FURTHER REDUCTION OF THE ORE MATERIAL.