US3157488A

US3157488A - Method for direct reduction of metal oxides

Info

Publication number: US3157488A
Application number: US58671A
Authority: US
Inventors: Charlton A Taylor
Original assignee: Individual
Current assignee: Individual
Priority date: 1960-09-27
Filing date: 1960-09-27
Publication date: 1964-11-17
Anticipated expiration: 1981-11-17

Description

Nov. 17, 1964 c. A. TAYLOR METHOD FOR DIRECT REDUCTION OF METAL OXIDES 6 Sheets-Sheet 1 Filed Sept. 27, 1960 m m T .Y m n V A N I n 2. o a h C 33. I\ 12%. mm wzfifizoim mm vn ozrswzwwu m 5 2 All V I N 2! 4 52E mm mm 6528 mm 7 F5235; E30: 5 M2105 98 SEER 202 $295350 m2 mwN mwziuo I N Q Q m 5 5 68 M2396 mm x23 wzF -585 oz 0v 525 6 m o NV his ATTORNEYS.

Nov. 17, 1964 c. A. TAYLOR 3,157,488

METHOD FOR DIRECT REDUCTION OF METAL OXIDES Filed Sept. 27, 1960 6 Sheets-Sheet 2 FIG.2.

IN VEN 70R Charton A.Taylor his ATTORNEYS Nov. 17, 1964 Filed Sept. 27, 1960 c. A. TAYLOR 3,157,488

METHOD FOR DIRECT REDUCTION OF METAL OXIDES 6 Sheets-Sheet 5 INVENTOR Charlton A. Taylor zz pwkw hi ATTORNEYS Nov. 17, 1964 c. A. TAYLOR METHOD FOR DIRECT REDUCTION OF METAL OXIDES Filed Sept. 27. 1960 6 Sheets-Sheet 4 l I II FIG .4.

INVENTOR Charlton A. Taylor ai his ATTORNEYS Nov. 17, 1964 c. A. TAYLOR mamas FOR DIRECT REDUCTION OF METAL oxmas 6 Sheets-Sheet 5 Filed Sept. 27. 1960 INVENTOR.

Cholfon. A. Taylor Pma uzdlq his ATTORNEYS.

Nov. 17, 1964 c. A. TAYLOR METHOD FOR DIRECT REDUCTION OF METAL OXIDES Filed Se t; 2'7. 1960 6 Sheets-Sheet 6 INVENTOR. Chalfon A. Taylor his ATTORNEYS.

United States Patent 7 O 3,157,488 varnon non nmncr REDUUEEQN or rvmrar. oxmns Charlton A. Taylor, Pfi. Box 435, Garrettsvliie, @hio Fiied Sept. 27, 19st), der. No. 53,671 3 Ciairns. (Q5. IS-34) The present invention is concerned with direct reduction of metallic oxides by reaction at suitable temperatures with hydrogen or other reducing gases to obtain substantially pure metal. The invention is further concerned with a batch process for such reduction, which process is low in cost, short in the length of time required for each batch and flexible as to quantities of oxides handled by a given size of apparatus used in practicing the process.

Various processes have been previously tried for direct reduction of metallic ores using a gas to convert the oxides of the metal to the metal itself. None, however, are commercially in use in the more industrially important countries because none have been found economically practical. This is chiefly caused by the fact that with such processes, the ores richest in the desired metallic oxides give the most eiiicient rate of production, and such ores can be more economically reduced by other processes.

Reduction of such metallic ores by hydrogen has long been known to be potentially most desirable but also the most difiicult process to use because of the heretofore unsolved problems of production in economical volumes, heating the ore to desired temperatures to obtain pure meta obtaining complete deomdization of the ore, the reversibility of the process in the presence of water vapor, and contamination by impurities found in the ore.

An object of the invention is to provide a batch type process for direct reduction of metal oxides with hydrogen gas producing substantially pure metal free from contamination by impurities which are removed by volatilization during the reduction process.

Another object of the invention is to provide a batch type process for direct reduction of metal oxides utilizing low temperatures and prevention of those conditions creating a state of equilibrium.

Another object of the invetnion is to provide a batch type process wherein substantially complete deoxidization of the oxide is obtained without the resultant metal becoming plastic or gummy.

Another object of the invention is to provide a batch type process for direct reduction of metal oxides by reaction with hydrogen wherein the metal oxide in finely divided form is maintained in constant agitation within a confined area for obtaining the desired reaction while maintaining control and removal of waste gaseous prod nets of the reaction.

7 These and other objects of the invention will be made apparent from the following description and the drawings forming a part thereof. For purposes of illustration the process is described as applied to reduction of iron oxides, as this ore provides the largest volume of use at the present time and greatest economy over present conventional methods of converting iron ores to metal. The process is, however, equally adaptable to conversion to metal of any oxide which may be directly reduced by contact with hydrogen gas or other gases under suitable conditions conducive to the chemical reaction. The process and apparatus are useful for otherpurposes, such as in the titanium industry, mining and chemical industries and in production of powdered iron.

Referring now to the drawings, wherein:

FIG. 1 shows diagrammatically one form of suitable apparatus for practicing the process of the invention;

FIG. 2 shows in side elevation and partly in section 3,157,488 Patented Nov. 17, 1954 Ice the heating furnace or reaction chamber of the apparatus;

FIG. 3 shows a cross-section taken on lines IIIIII of FIG. 2 illustrating details of construction;

FIG. 4 shows a cross-section through the gas cleaner;

FIG. 5 shows a plan view of a modified form of apparatus for practicing the invention;

FIG. 6 shows a side elevation of the apparatus of FIG. 5;

FIG. 7 shows a side elevation partly in cross-section of only the furnace of FIG. 6;

FIG. 8 shows a cross-section on lines VIIVII of FIG. 7;

FIG. 9 shows a fragmentary enlarged cross-section through the periphery of the furnace showing details of construction.

One form of apparatus for practicing the invention is shown in diagrammatic form on FIG. 1 of the drawings, wherein the horizontal reaction chamber of furnace 1 is supported on hollow shafts 2, 3 extending partially into the furnace and mounted in suitable bearings 4, see FIG. 2. The furnace and shafts are oscillated through an arc of by suitable intermeshing gears 5 and 5a and electric motor 6 diagrammatically shown in FIG. 2. The furnace is heated to the several temperatures of the process by electrical resistance heaters 51 disposed within the reaction zone and electrical energy is supplied by conduits 7, 8 entering the furnace through hollow shaft 2 and connected with a suitable instrument and control panel 9. Pre-heated hydrogen is supplied to the reaction zone by a suitable gas line 10 entering through the hollow shaft 3 from a suitable pro-heater 11. A gas volume measuring flow meter 12 and thevalve 13 in gas line it) are electrically controlled through power lines 14 and 15 connected with the control panel 9. A suitable hydrogen generator 16 is connected by a gas line 17 to a gas holder 18 from which hydrogen gas is supplied through gas line 19 to the hydrogen preheater 1!. A gas flow meter 26 in gas line 17 is controlled from instrument panel 9 through power line 21 and measures the volume of hydrogen supplied to gas holder 18.

Suitable metal oxides, pulverized to a preferable fineness of to 500 mesh, are stored in storage bin 22 which is connected by a conduit 23 to a transfer box 24, and flow of oxides from bin to box is controlled by valve 25. A flexible conduit 26 connects transfer box 24- with the furnace 1 and a suitable pneumatic system 27 connects with transfer box 24 for charging ore through conduit 26 into the furnace and for removing the metal in finely divided for-m from the furnace through the same conduit. A conduit 28 connects the transfer box 24 with a cyclone cooler 29. Valve 39 in conduit 28 discharges the metal particles from the transfer box to the cooler 2). An air dehumidifier 31 supplies dry air to the cyclone cooler 29, for reducing the tempera ture of the metal particles passing through the cooler 29 and discharged into a storage bin 32. From the storage bin 32, the metal particles may be discharged through conduit 33 to a suitable melting furnace 34, or through conduit 35' to a briquetting machine 36. The gangue and metal particles when moving through conduit 26 are weighed by a suitable weight meter 37 connected by an electric line to the instrument panel 9.

Water vapor and other gaseous products are removed from furnace 1 through flexible conduit 39 to a gas cleaning and precipitation tank 44 Any free hydrogen passing into tank 4% is returned through conduit 41 to the hydrogen supply conduit 17. A valve 42 controls flow of hydrogen into conduit 41 and a flow meter 43 registers the amount of flow in conduit 41. Water vapor, volatilized sulphur, phosphorus, etc. are discharged from to metal.

Any suitable form of gas cleaner may be used. That shown in FIG. 4 of the drawings will give excellent results. The tank 49 is comprised of a cylindrical metal shell 60 supported upon a suitable foundation, such as 61. Within the shell 69 and supported by foundation 61 is' a lining of porous material, such as slag brick, having side walls 62 and connecting top wall 65 disposed in spaced relation tothe inner walls of the shell providing a space to receive water. The water seeps through the slag brick walls 62 and 65 for contacting the gases entering through conduit 39 and washes therefrom any suspended solids. The cleaned gas rises upwardly through top wall 63 and is removed through conduit 41. Preferably refrigerating coils 64 supported by suitable brackets retain the

water surrounding walls

62 and 63 at temperatures between 40 to 50 F. to cool the exhaust gases received through conduit 39 and precipitate therefrom all water vapor from the furnace 1. Water surrounding the

walls

62 and 63 is supplied by an inlet conduit 66 having a valve 67 associated therewith and controlled by a suitable float valve operating mechanism 6S,'well known in the art. At one side of the shell 60 a suitable conduit 72 extends through the shell and adjacent wall 62 and controlled by valve 73 to admit a cleaning water spray to remove any' scum or deposits which would impede passage of water through

walls

62 and 63. Water passing into tank 40 may be removed by gravity through a suitable opening 76 in the base of the shell '60 and foundation 61. If ,(lfiSlIBdythlS water may be re-cycled through tank 40 by means of a valved inlet 76, 71.

The furnace 1 is the heart of the process and is shown indetail in FIGS. 2 and 3 of the drawings. Such furnace is of generally cylindrical shape, comprising a cylindrical shell 45 having end closure walls 46. The cylindrical walls of the furnace are provided with a lining of suit- 7 able insulation and overlying layer of fire brick 47. The

end walls 46 are similarly insulated and have axial openings. 49 therein for reception of the hollow supporting shafts 2 and 3. The lined cylindrical space between the lining of the end walls of the cylinder define a reaction zone within which the pulverulent metal oxide is reduced Extending longitudinally of the reaction zone and spaced radially about the inner face thereof are a plurality of ore dividers 50 which assist in diffusing reduction gases through the ore. Electrical resistance heating elements 51 extend longitudinally of the reaction zone and are spaced radially thereof for radiantly heating the reaction zone to required temperatures. These heating elements 51 are connected with the instrument panel by power lines 8 extending through hollow shaft 2.

The furnace 1 is supported in horizontal position upon the hollow shafts 2 and 3 which in turn are journalled in suitable bearings forming part of the pedestals 4. The hollow shaft 2, outwardly of pedestal 4, has mounted thereon a'suitable gear 5 which is driven from a suitable reversing motor 6 having a driving gear 521 thereon. The motor oscillates furnace 1 through an arc of 180 and is controlled by a suitable time mechanism mounted on the instrument control panel 9. At the top of furnace,

L intermediate the ends thereof, are longitudinally spaced openings within which are secured the

conduits

52 and 53. Conduit 52 has a suitable flange 54 at the upper end thereof for attachment to a flexible conduit 26 (FIG. 1) for selective introduction of pulverized metal oxide into and removal of metal particles from the furnace reaction zone. Conduit 53 has a suitable flange 55 at the upper end thereof for attachment to the flexible conduit 39 (FIG. 1) for removal of water vapor and waste gases from the reaction zone. Extending through shaft 3 into the reaction zone of the furnace is a suitable thermocouple 56 for registering the temperature of the zone. The thermocouple 56 is connected with instrument panel 9 by power lines 57 for regulating supply of heat to the zone by heating elements 51.

enemas The process herein described may be manually controlled or made entirely automatic for processing each batch. Due to several variables, namely the water content of the pulverized oxide and the amount of oxide processed in each batch, it has been found desirable to provide manual control for both the ore loading and pre-heat cycles unless the variables referred to can be standardized.

For purposes of illustration of a preferred mode of operation of the apparatus in performing the method of the invention, iron ore is employed and the reaction zone of the furnace will be charged to its recommended maxi mum capacity for economical operation. The chemistry of direct reduction of iron ore by contact with hydrogen gas is well known. Hematite ores may be readily reduced according to the well known equation:

reacted with any given volume of ore is in excess of' the stoichiometric amount calculated to reduce such volume of ore to metal.

In the practice of one method of the present invention, 7

the iron ore is preferably pulverized to pass a screen of 100 to 500 mesh, 250 to 350 mesh gives good results. The heating elements 51 within the reaction zone are activated and the thermocouple set to cut 05 power to the heating elements when a temperature of 1000 F. within the zone is reached. After the temperature of the reaction zone reaches 212 F. the pulverized iron ore may be charged into furnace 1 by pneumatic means through

conduits

26 and 52 until the reaction zone is filled to adjacent, but slightly below, the axis of rotation of the furnace; The weight meter 37, recording the weight of ore passing therethrough will determine when the desired amount of ore is within the zone. Valve 25 in conduit 23 may then be closed and the motor 6 started to rock the furnace 180 in one direction and reversed to return the furnace to starting position. This completes one cycle of operation and a time interval of approximately seconds from start to completion of a cycle has been found to be satisfactory. A timing device (not shown) may be mounted on the control panel to provide a time interval between the completion of each two cycles of oscillation of the furnace. During this time interval while the furnace is positioned as in FIG. 3,

part thereof is utilizedto permit the ore within the furmice to settle and water vapor or other gases to rise to the top of the zone; Thereafter, the valve 58 in conduit 39 may be opened and water vapor and other gases" withdrawn from the reaction. zone through conduit'39 by fan 59 and discharged into the gas cleaning tank 40.

At the end of the selected time interval, valve 53 is closed and the motor 6 turns the furnace 1 through another two cycles of rotation. During each said two cycles of oscillation of the furnace 1, the ore within the reaction zone is successively discharged over each ore divider or baflie into the adjacent space between baflies and in so doing the ore particles are tumbled about and spread apart. After about 8 said cycles of oscillation and 4 said time intervals, the ore has reached a temperature of about 1000 F. and most of the hydroscopic water, phosphorous and sulphur in the ore has volatilized, and

rising to the top of the reaction zone has been removed through conduit 39. At the end of the fourth time interval, the valve 58 having been closed, the thermocouple- 56 may be reset to about 750 F. and valve 13 in conduit 10 is opened admitting hot hydrogen gas in an amount less than the stoichiometric amount calculated to deoxidize the ore, through hollow furnace shaft 3 into the reaction zone where it mixes with the tumbling ore particles during the oscillation cycles and reacts therewith to form water vapor and substantially pure metal. Hydrogen is preferably continuously admitted throughout each two successive cycles of oscillation and thereafter the valve 13 is closed during the time interval following each cycle. The volume of hydrogen admitted to the reaction zone during each cycle is recorded by the flow meter 12. The valve 13 and flow meter 12 are connected with and controlled from the instrument panel 9, so that valve 13 may be closed during any cycle after the flow meter records a predete mined amount of hydrogen to be admitted between time intervals, thereby conserving hydrogen. At the end of each two cycles, the valve 13 is closed and valve 58 of conduit 39 is opened, after the ore has settled, and water vapor formed during the preceding two cycles of oscillation and any other gases present are removed before another cycle is commenced. After a predetermined number of cycles, and accompanying time intervals, during which an amount of hydrogen in stoichiometric excess of the amount necessary for reduction of ore has been admitted within the reaction chamber, the cycling of the furnace is stopped. Hydrogen valve 13 is held closed and valve es in conduit 26 is opened. The metal remaining in the furnace is pneumatically withdrawn through conduit 2% to transfer box 24, and valve 3 3 being open, is discharged into the cyclone cooler. Here dehumidified air from receptacle 31 cools the metal to a temperature of about 250 F. before it is discharged into the iron particle storage bin 32. From where it may be discharged into melting furnace 3d, briquetting machine 36 or otherwise disposed of. After the metal and any gangue is removed from the furnace, a new charge of oxide is introduced and the process is repeated.

The foregoing process provides a number of outstanding advantages over existing batch type processes. The ore is of such a small particle size that it may be readily brought to an anhydrous state when tumbled in the heated atmosphere of the reaction chamber. The low temperature at which the ore is reduced to metallic form prevents softening and adherence of the particles. The particle size of the ore and that of the resultant metal remains substantially constant. Since the ore, while being raced in an anhydrous state was heated to a temerature above the boiling points of water, phosphorus and sulphur, substantially none are present in the ore at the time when the reaction with hydrogen is begun. Much of the siiica, initially present in the ore, is also removed while the ore is being placed in an anhydrous state. Due to the small particle size of the ore, the silica present is in a substantially colloidal state and is carried off with the water vapor during removal thereof. Hence, even though the resultant metal particles are porous, only hydrogen can be found therein.

The time required to reduce a capacity charge of ore within the furnace is not subject to much change as the capacity of the furnace is increased or decreased. The ore is preferably in a substantially anhydrous state before reaction with hydrogen is begun. Due to the small particle size of the oxides being reduced, the reaction time for any particular particle after exposure to hydrogen is short. Oscillation plus the baffles within the furnace rapidly brings each particle into Contact with the hydrogen. Since the water vapor formed by the reaction is removed at frequent intervals and additional hydrogen supplied to the reaction zone, the reversibility of the reaction presents no problem. There are no problems added by combustion gases, as where a combustible fuel is used in heating the furnace. The heating elements are encased in plastic or other materials having no reaction with hydrogen. The furnace is well insulated and thus use of electric power for heating is economical.

Satisfactory results have been obtained in reducing a capacity charge of oxides every hour, regardless of furnace capacity, using the following sequence of operation:

Min. (1) Charge the furnace to capacity 5 (2) Start motor at speed to complete 2 cycles of os cillation every 60 seconds. (3) Dehydrate ore in 4 one-minute periods of operation spaced 4 5-minute time intervals 24 (4) Reduce ore in 4 one-minute periods of operation spaced 4 5-minute time intervals 24 (5) Unload metal from furnace 5 The volume of hydrogen necessary to reduce one ton of iron oxides is readily calculated on the basis that theoretically 16,000 cu. ft. of hydrogen will reduce one ton f iron oxides to metal. The reduced particles are somewhat porous, so as to retain within their pores a substantial amount of hydrogen. It is recommended a 25% excess of hydrogen be used making 20,000 cu. ft. for each ton of iron oxides. Some of this excess may be recovered as hereinbefore discussed. The presence of hydrogen in the metal particles causes them to become pyrophoric upon contact with air, necessitating storage in an oxygen free atmosphere. This condition may be overcome by purging the hydrogen from the metal particles by a suitable inert gas placed in the furnace before the metal is unloaded therefrom. Due to the low temperature at which the reduction of the oxides is carried out, the metal particles are not plastic and have no tendency to adhere to each other. This condition facilitates purging and, in fact, the entire operation.

This latter condition makes the process highly desirable for the powdered iron industry. The present practice is to use substantially pure iron oxide in producing powdered metal. The metal produced by the process of the invention will provide porous particles free of impurities, except for such hydrogen gas as is lodged in the pores of the metal. After the oxide is completely reduced and before removal from the reaction zone, all hydrogen may be readily removed by purging the reaction zone with its content through injection of an inert gas, such as argon gas.

A portion of the apparatus herein described could advantageously be used as a roasting or calcining furnace. This could be readily accomplished by shutting off the hydrogen from the reaction zone and continue removal of vapors driven ofi through the water vapor and waste gas conduit of the apparatus.

The apparatus of FIGS. 1 to 4 inclusive broadly describes apparatus which may advantageously be used to practice the method herein described. The apparatus of FIGS. 5 to 9 inclusive disclose a preferred form of furnace which may be used to directly reduce metal oxides by means of any suitable gaseous reductant to provide metal in finely divided form and free of substantially all contaminants which may be displaced by volatilization, including silica. This latter apparatus may also be used as an effective roasting or dehydration means independently of the direct reduction features.

Due to the rapidly approaching depletion of the all lmown large deposits of lump magnetite ores, the steel industry is extensively engaged in searching for means whereby the remaining large quantities of high grade ore fines of both magnetite and hematite can be' utilized in the production of iron for steel manufacture and to meet the increasing demands for high purity powdered iron. Likewise many low grade ore fines are available for these purposes, but must be beneficiated in some manner to be usable. Many new processes have been developed to both beneficiate the low grade ores by removal of has beenbeneficiated and oxide particle size, to mention the most important of such variables.

Due to the observed elficiency of the present type apparatus, larger particle sizes in the range from to -l00 can be economically processed in the furnace of FIG; 7, although possibly of lesser purity and freedom from contaminants than in the case of smaller particle sizes of to 500 mesh sizes. In these latter particle sizes much of the silica is of such small size as to pass ed with the water vapor and substantially all of the sulphur and phosphorous is removed before reduction. As shown in FIGS. 5 and 9, a cylindrical furnace 101 is suspended for rotation upon hollow stub axles 102 and 163 suitably journaled in bearings 194 mounted upon suitable bearing stands 105. Rotary motion is imparted to the furnace by any suitable means such as motor 136 and speed reducer 107. Suitable sprockets 108 on the speed reducer and 1119 on the shaft 1% may be connected by a suitable drive chain 110.

Adjacent the furnace shaft 102 may be provided suitable storage of reducing gases and purging gases, for purposes of illustration, portable gas storage cylinders 111 of H 112 of N and 113 ofA are shown. Both nitrogen and argon gases have been selected as inert gases for purging purposes, either may be used as desired. Suitable piping may be provided to discharge the stored gas from the cylinders into the furnace 101 through shaft 1132. As shown, a pipe 114 extending transversely of

cylinders

111, 112 and 113 has another pipe 115 connected thereto and branch pipes 115, 117 and 118 extending from 114 to connection with said cylinders. Each branch pipe has intermediate its ends a suitable flow meter 119 and a suitable valve 120 for registering flow of gas from its respective cylinder. Pipe 115 has a suitable check valve 121 intermediate its ends. The free end of pipe 115 is provided with a suitable elbow 122 and an extension therefrom into adjacent shaft 102. The extension of pipe 115 has a suitable swing joint connection 123 with the opening end of shaft 102 which serves to close the end of the shaft and permit relative rotary movement between the shaft'lfil and pipe extension therein. At the opposite end of furnace 101, the shaft 103 has its outer end closed by a swivel joint member 124 having extending therethrough an exhaust pipe 125 having connected therewith an exhaust means (not shown). The exhaust pipe 125 has its inner end extending within the shaft 1153 in communication with the interior of furnace 101. The outer end of the exhaust pipe 125 has a suitable flow meter 126 mounted therein for registering the volume of gas and vapors removed from the furnace by an exhaust means (not shown). I,

The details of construction of furnace 101 are best shown in FIGS. 7, 8 and 9 of the drawing. The inner peripheral shell 127 is preferably of suitable material, 'such as a high nickel content steel, tostand temperatures up to 1200 to 1500 Hand is closed by suitable end walls 128 of similar metal. Preferably the joints between them are welded. Each end wall 128 is preferably reinforced by a suitable spider 129 through which end walls 128 extend the shafts 192 and 103. Enclosing the furnace inner'shell is a similarly shaped jacket member 130 dis posed in spaced relation to the inner shell providing a heating zone 131 therebetween. Mounted within the heating zone 131 and in spaced relation to both the jacket 130 and furnace inner shell 127 are electrical heating elements 132.

These are preferably angularly spaced about the furnace inner shell so as to provide substantially uniform heating of the periphery of the furnace inner shell. One form of suitable heating elements are shown in FIGS. 8 and 9 wherein the element is of elongated U-shape with the free ends 133 angularly olfset and extending through the jacket. Suitable means such as 134 may be employed to secure the heating elements in fixed relation to the jacket 13%. Enclosing the jacket 13% and in spaced relation thereto is a furnace outer shell 135 comprised of cylindrical side walls and circular end walls. Between the jacket and outer shell is placed a suitable layer of insulation 136 so as to retain the heat from the heating elements within the heating zone 131. It will be noted that the ends 133 of the. heating elements extend outwardly beyond the outer shell. Adjacent each outer shell end wall and surrounding the adjacent shafts 11l2and 103 may be suitable water cooling jackets 137. These jackets .137 retard transmission of heat through the shafts by conduction.

A suitable opening 138 is provided in the top wall of furnace 101 for admission of metal oxide to the furnace. A suitable circular collar 139 is mounted in opening 138 and provided with a central opening 141) which is closed by a movable closure member 141. A suitable stand 142 is mounted on collar 139 and is provided with a top Wall 143. A suitable air cylinder 144 is mounted on top wall 143 and is provided with a depending piston 145 connected with closure member 141 for raising and lowering the latter. Above furnace 101 and adjacent the filling opening may be mounted any suitable form of ore storage. bin 155 (FIG. 6) equipped with any well known form of vibrator, for feeding measured quantities of metal oxide into the furnace, after closure member 141 is raised for this purpose. 7

Within furnace 10 1 are mounted suitable .baflle members for lifting and spreading the metal oxide as the furnace is rotated to insure rapid and efifective particle contact with the gaseous reductant. Within and adjacent the top of furnace 101 and surrounding the filling opening is a bafiie 146 which extends longitudinally and transversely of the furnace. Such bafile 146 is comprised of longitudinally V, extending, angularly disposed portions 147 each having their opposite ends connected with the inner shell end walls 128 and their longitudinal lower edge connected to the periphery of the inner shell side walls .127 at opposite sides of the vertical center line of the furance. The inner free ends of bafile portions 147 have connected thereto upwardly and inwardly triangular portions 148'which preferably connect with the furnace opening collar 1351. These bafile portions 148 at opposite sides of the longitudinal center line of the furnace have their edge portions149 and 150 connected by

flat plate portions

151 and 152. In this manner the bathe 146 not only serves to turn and spread the oxide as the furnace rotates, but also provides a chute which discharges all the reduced oxide from the furnace through opening 141) after the furnace is stopped in an inverted position relative to that shown in FIG. 7

and the closure member 141 retracted from opening 140.

At opposite sides of the longitudinal center line of furnace 1111 and adjacent the bottom of the inner shell side wall I 127 are triangular shaped baffles 153 and 154. These latter baflles are suitably connected to the inner face of the side wall 127 and preferably extend continuously between the inner shell end walls 128.

The apparatus of FIGS. 5 to 9 is intended to be equipped with suitable forms of well known types of controls to 7 provide complete automatic control of temperature within the heating zone between the furnace inner shell and the jacket and also within the inner shell of the furnace. After a charge of metal oxide within the furnace has been'sufi'iciently dehydrated the subsequent sequence of step's'of semi-reduction, removal of water vapor, completion of reduction and purging of the reduced metal and furnace interior as well as discharge of the furnace contents, may be automatically carried out.

By reason of the insulated heating zone 131 and uniform heating of the furnace inner shell, the metal oxide within the inner shell may be rapidly raised to temperatures up to about 1000 F. to drive off Water from the oxide and remove game through exhaust pipe 125 prior to beginning the reduction cycle. During such initial heating the sulphur and phosphorus within the oxide is :V latilized and removed with the water vapor before reduction begins, thereby preventing these contaminants from being reabsorbed by the newly reduced metal. Preferably, in addition to automatic controls, thermocouples placed in the heating zone and within the furnace may be used to actuate the controls to maintain a high temperature within the furnace during oxide dehydration and a reaction t mperature of about 750 F. before reduction is commenced. The bafiies Within the furnace, during reverse rotation thereof, spread and tumble the ore about for contact with the reducing gas. The baffles also serve to turn and spread the ore over and adjacent heated inner walls of the shell. The bafies themselves are also heated by conduction due to attachment to the inner shell walls.

The furnace 191 has advantages over the furnace of FIGS. 1 to 3 which result from the details of construction thereof. The

inner shell walls

127 and 128 due to their uniform heating and the heated battles provide for rapid heating of the ore therein. The additional mixing and turning of the ore due to the shape of the top bafile collecting the ore and discharging it over the two lower bafiles, during forward and reverse rotation of the furnace through an arc of 360, provides excellent and complete gas to ore contact. A furnace designed as 101 does I1 need pro-heating of the reducing gas before introduction into the furnace.

Preferably the apparatus of FIGS. to 9 should be equipped with automatic controls which govern a complete cycle of reduction of ore to metal. A complete cycle of loading, dehydration, reduction, purging and unloading can be accomplished in one hour or less depending upon the ore particle size and moisture content. For ore particle sizes between 100 to 500 mesh the time cycle can be correspondingly reduced.

A suitable sequence of operation comprises:

(1) Positioning the furnace with the filling opening adjacent the ore storage bin and energize the heating elements to effect an initial furnace interior temperature of 250 F.

(2) Raise closure member 143 and charge the furnace with a quantity of ore of a particle size of 100 to 500 mesh to about the level of the longitudinal center line of the inner shell, then lower member 143 to seal the charging opening.

(3) Initially rotate the furnace 180 on the axles thereof, then alternately rotate the furnace through an arc of 360 in opposite directions at a speed of between 1 to 5 r.p.m. while raising the temperature of the furnace interior and contained ore particles to about- 1000 R, then discontinue rotation and remove Water and other vapors from the furnace.

(4) Continue alternate rotation of furnace and withdrawal of water and other vapors until ore is dried and volatile matter exhausted.

(5) Reset thermostat control for 750 F. and charge furnace interior with hydrogen or other reducing gases in a measured amount less than the stoichiometric amount to reduce the ore to metal, while continuing alternate rotation through the 360 cycle for about 2 to 5 minutes.

(6) Stop motor at end of one 360 cycle and rotate furnace 180 to upright position.

(7) Stop motor and furnace rotation for about 3 minutes allowing ore and fine particles to settle.

(8) Withdraw water vapor from furnace and recharge with a measured amount of reducing gas, as in step 5.

(9) Rotate furnace to inverted position and resume reversing 360 cycle of rotation for 2 to 5 minutes.

return furnace to inverted position and resume 360.

cycles of reverse rotation until ore particles are fully reduced.

(12) Stop furnace rotation, return to upright position,

hold to settle dust.

(13) Withdraw spent reducing gases and purge furnace interior with an inert gas.

(14) Invert furnace and discharge contents.

(15) Right furnace and recharge with ore to commence a new cycle.

The foregoing proposed cycle of operations can be extended or shortened in time, depending upon the grade and particle size of ore used. Such a method can reduce a suitable amount of ore to gangue and metal. When purged of hydrogen with an inert gas before discharge from the furnace, the reduced metal may be stored and handled Without danger since it is the residual hydrogen which causes the well known pyrophoric reaction. The metal can readily be separated from the gangue by any well known magnetic means.

This application is a continuation-in-part of my copending application Serial No. 746,820, filed July 7, 1958, and now abandoned.

I claim:

1. A batch method :of direct reduction of metal oxides within a heated closed chamber rotatable about its horizontal axis, comprising the steps of:

(a) charging a measured batch of pulverized metal oxides into the chamber, not in excess of about onehaif the capacity thereof,

(b) rotating the chamber in alternate opposite directions while raising the temperature of the interior thereof and its contents to about 1000 F. for removing moisture and other volatizable matter from the oxides,

(c) discontinuing rotation of the chamber and withdrawing the volatile matter therefrom,

(d) charging a measured volume of a gaseous reductant therein which is less than that to reduce the oxide to metal and resuming rotation of the chamber in alternate opposite directions while maintaining a chamber interior temperature and its contents above the temperature of reaction and below a temperature causing tackiness of the surface of the oxide particles to efiect at least partial reduction thereof,

(e) discontinuing chamber rotation and withdrawing the spent gaseous reductant and other volatiles from the chamber interior,

(1) charging an additional measured volume of gaseous reductant into the chamber interior in an amount raising the total volume thereof applied to the batch of oxides to an amount in excess of the stoichiometric amount to reduce all the oxide to metal,

(g) resuming rotation of the chamber in alternate opposite directions and maintaining the reducing temperature to expose all the oxides to the reductant and reduce them to metal,

(h) discontinuing chmber rotation and withdrawing therefrom the spent reductant and other volatiles, then purging the chamber interior and the fully re duced oxides with an inert gas to cool and remove reductant therefrom before discharging the reduced metal particles from the chamber.

2. The method as defined in claim 1, wherein the reductant is hydrogen and the oxides are iron oxides.

3. The method of direct reduction of iron oxides to 1 1 metal in batch amounts within a closed heated chamber provided with baffies alternately aggregating and spreading the oxide in the presence of hydrogen while the chamber is rotating in alternate opposite directions upon its horizontal axis, comprising the steps of: v

- (a) charging the chamber with a measured amount of pulverulent iron oxides,

(b) heating the interior of the chamber and contained oxides to a temperature above 250 F. to vaporize water and other volatile substances in the oxide while rotating the chamber upon its horizontal axis and alternately in opposite directions, 7

(c) stopping rotation of the chamber, withdrawing the volatile matter and charging the chamber with a 7 measured volume of hydrogen,

(d) resuming alternate rotation of the chamber in opposite directions While raising the temperature of the chamber interior and contents to the temperature of reaction between the oxide and hydrogen and below that at which the oxide particles tend to cohere upon contact,

(e) alternately stopping rotation of the chamber, withdrawing the gaseous products of reduction, recharg- 12 ing with measured amounts of hydrogen and resuming alternate rotation of the chamber until the total hydrogen charged to the chamber to reduce the oxide is inrexcess of the stoichiometric amount necessary to reduce the charge to metal,

(f) thereafter stopping the chamber rotation, withdrawing the spent hydrogen and gaseous products of reduction thenfilling the chamber with an inert gas to purge the hydrogen therefrom,

(g) then resuming rotation of the chamber to purge the hydrogen from the reduced oxides before discharging the metal to storage.

References ited in the file of this patent UNITED STATES PATENTS 1,275,232 Edison Aug. 13, 1918 2,236,474 Hardy Mar. 25, 1944 2,414,718 Christensen Jan. 21, 1947' 2,648,535 Ramsay et a1 Aug. 11, 1953 2,689,715 Ericson Sept. 21, 1954 2,818,328 Francis Dec. 31, 1957 2,927,016 Francis Mar. 1, 1960 2,964,309 Rouaux Dec. 13, 1960

Claims

1. A BATCH METHOF DIRECT REDUCTION OF METAL OXIDES WITHIN A HEATED CLOSED CHAMBER ROTATABLE ABOUT ITS HORIZONTAL AXIS, COMPRISING THE STEPS OF: (A) CHARGING A MEASURED BATH OF PULVERIZED METAL OXIDES INTO THE CHAMBER, NOT IN EXCESS OF ABOUT ONEHALF THE CAPACITY THEREOF, (B) ORTATING THE CHAMBER IN ALTERNATE OPPOSITE DIRECTIONS WHILE RAISING THE TEMPERATURE OF THE INTERIOR THEREOF AND ITS CONTENTS TO ABOUT 1000*F. FOR REMOVING MOISTURE AND OTHER VOLATIZABLE MATTER FROM THE OXIDES, (C) DISCONTINUING ROTATION OF THE CHAMBER AND WITHDRAWING THE VOLALTILE MATTER THEREFROM, (D) CHARGING A MEASURED VOLUME OF A GASEOUS REDUCTANT THEREIN WHICH IS LESS THAN THAT TO REDUCE THE OXIDE TO METAL AND RESUMING ROTATION OF THE CHAMBER IN ALTERNATE OPPOSITE DIRECTIONS WHILE MAINTAINING A CHAMBER INTERIOR TMEPERATURE AND ITS CONTENTS ABOVE THE TEMPERATURE OF REACTION AND BELOW A TEMPPERATURE CAUSING TACKINESS OF THE SURFACE OF THE OXIDE PARTICLES TO EFFECT AT LEAST PARTIAL REDUCTION THEREOF, (E) DISCONTINUING CHAMBER ROTATION AND WITHDRAWING THE SPENT GASEOUS REDUCTANT AND OTHER VOLATILES FROM THE CHAMBER INTERIOR,