US2670946A - Apparatus for magnetic roasting - Google Patents

Description

March 2, 1954 P. H. ROYSTER 2,670,946

APPARATUS FOR MAGNETIC ROASTING Filed Oct. 31, 1950 2 Sheets-Sheet l l ellf I 50 7mm l I NV EN TOR March 2, 1954 P. H. ROYSTER 2,670,946

APPARATUS FOR MAGNETIC ROAS TING Filed Oct. 31. 1950 2 Sheets-Sheet? 6 40 IN VEN TOR.

Patented Mar. 2, 1954 smart APPARATUS FOR MAGNETIC ROASTING Percy H.. Royster, Chevy Chase, Md., assignor to Pickands Mather & (30., Cleveland, Ohio, at

copartnership Application October 31, 1950, Serial No. 193,249

4 Claims. (01. 266-20) This invention relates to. the magnetic roasting or ferruginous ores and ore material initially containing substantial amounts of relatively non-magnetic oxidic' compounds of iron. The invention concerns a development related to the process described in my copending application Serial No. 695,914, filed September 10, 1946 (Patent No. 2,528,552), and Serial No. 710,747, filed November 19, 1946 (Patent No. 2,528,553), of which latter the present application is a continuation-in-part, In particular, the present invention is concerned with an improved apparatus for thermal treatment of iron ores as a preliminary: step in the magnetic concentration thereof. It is an object of the present invention to'provide a thermally eificient and economic apparatus for magnetically roasting low grade iron ores, and other related minerals, e. g., manganiferous iron ores, non-metallurgical chrome ores and other ores commonly designated as ferrous, the iron contents of which are relatively nonmagnetic. Theprimary objective of the heat treatment herein proposed is-to render naturally non-magnetic minerals adaptable to magnetic concentration. propose to remove not more than one-ninth of the oxygen occurring in ferric oxide. That is to say; I propose to reduce the initial ferric oxide largely to magnetite with the specific provision,

however, that I"cause a minimum of over rea diiction"by which term I mean the carrying' of the reduction to a lower state-of oxidation than FiezOr-i. e., to produce as little as possible FeO or metallic (sponge) iron.

According to the present invention, a body'of the mineral is caused gravitationally to descend through a first chamber and a second chamber in series. In its descent through the first chamber, the mineral is dehydrated and brought up to: reactive temperature, and thereupon all or substantially all of'its' content of relatively nonmagnetic oxidic compounds of iron is reduced to magnetite .by means of a current of reactive gas (the composition of which will be. described hereinafter, passed countercurrently through the body of mineral. The hot mineral discharged from the first chamber is passed to the second, wherein during its descent therethrough the hot mineral is cooled by means of a countercurrently moving initially relatively cool current of the aforesaid gas; Preferably, the aforesaid first second chambers are the .upper and: lower chambers. of 'a' substantially vertical shaft fur= nace--generally similar to thatdcscribed. and

illustrated: in my copending application Serial In attaining this objective, I

Nor-605,861 (Patent No. 2,533,152 )-characterized by an intermediate zone of' reduced cross-sectional area communicating between the upper and lower chambers.-

It is an essential feature of the present inventionthat the furnace structure is so arranged that a large part of the gas after its upward passage through the lower chamber is diverted from the latter and is caused to traverse a mixing chamber which receives hot combustion gases from a combustion chamber wherein fuel combustion is maintained. Heat is thus imparted to the gas stream in the mixing chamber, after which. thermal boosting and gas is introduced adjacent to the bottom of the upper chamber and passes upwardly in countercurrent thermal and chemical relationship with the ore materials de- 'scending therethrough.

A significant feature of the present invention is the realization of thermodynamically restrained reduction. The ferric oxide content of the mineral is subjected to chemical interaction with areactive gas, the composition of which is carefully controlled to present concentrations of CO2, CO, H2, and. H20 in such proportions that the only thermodynamically stable phase in the quartenary system Fe-CHO is F8304. When I start, therefore, with ferric oxide, the reducing action of the reactive gas can convert F6203 into FeaOi only, and over' reduction to-form FeO and Fe is chemically impossible regardless of the amount of reactive gas employed, the temperature of the gas or the time and intimacy of the contact between the gas and solid. In order to. achieve this desired result, a large portion of the gas discharging from the first or upper chamber (after passage through the two chambers in series) after the removal of suspended dust, the condensation of excess moisture and cooling, is caused to re-enter the system adjacent the bottom of the lower chamber. I: (1) bleed to waste a .part of this discharged gas, (2) introduce into it a controlled amount of reducing gas whereby to produce an enriched carrier gas, which I force upwardly through the lower chamber; (3) remove the major portion of the gas after passage through the lower chamber and transfer it into a mixing chamber connected with a combustionchamber into which (4) I inject a suitable fuel, e. g., oil, natural gas, powdered coke, blast. furnacegas, coke-ovengas, or other industrial fuel, while at the same time (5) introducing arestricted' amount .of draft air, controlled in amount toprovide, as nearly as possible, justenough oxygen to convert the combusti- 3 bles of the fuel into CO2 and H without causing a residual excess remanent amount of oxygen; and (6) reintroduce this gas from the mixing chamber into the bottom of the upper chamber.

A further object of the present invention is to provide for automatic control over the flow of the make-up reducing gas into the gas circulating system to the end that the circulating gas will be maintained at a substantially uniform richness in CO.

Yet another object is to provide automatic control of the combustion chamber unit so that a substantially uniform gas temperature is maintained as well as a constant ratio of fuel to combustion air which will assure complete combustion without any remnant free oxygen.

The novel apparatus for carrying out the process covered by the claims of my aforesaid parent application Serial 710,747, will be more readily understood by reference to the following specific description taken in conjunction with the appended drawings in which Fig. l is a somewhat diagrammatic representation of one embodiment with the furnace component shown in vertical central section. Fig. 2 is a view similar to Fig. 1 illustrating a modified construction for the furnace component and showing additional automatic controls for regulating admission of the make-up reducing gas and controlling the fuelair input to the combustion chamber.

- With reference now in particular to Fig. 1, the recirculating carrier gas is forced by a motordriven blower I, into which it is admitted by conduit 43, through cold gas inlet conduit 2 into bustle pipe 3 surrounding the second or lower cylindrical reaction chamber 5. Reducing gas, in amount controlled by the proper setting of valve 43a, enters inlet conduit 2 by way of conduit 3| from a source (not shown) of such reducing gas, comminglmg with the recirculating carrier gas to constitute the enriched carrier gas before its entrance into bustle pipe 3. A pinrality of openings spaced circumferentially about chamber 5 permits the flow of enriched carrier duit 9 into mixing chamber l0 wherein its temperature is raised in suitable amount by hot combustion gases produced in a combustion chamber 31 and delivered to the lower end of chamber [0. The resulting thermally enhanced enriched carrier gas discharges from mixing chamber In, through conduit I l into bustle pipe l2 positioned around upper cylindrical chamber [6 adjacent the bottom of the latter. A plurality of circumferentially spaced, thermally insulated blow pipes I3, l3 permit the entrance of gas from bustle pipe l2 into open space 14 positioned annularly about the lower perimeter of chamber Hi. The resulting spent gas passing from IT traverses the stockline 13 at the top of column l1, enters open space I 9 maintained at the top of, and serving as a gas-collecting space in, chamber 16.-

The spent carrier gas discharges from space l9 by way of exhaust main is stripped of entrapped solids (e. g., dust and fume) in passage through dust collector 26; and is transported through clean-gas line 21 into cooler or scrubber 28 wherein its temperature is reduced and excess moisture is removed. In treating ores which produce a large amount of extremely fine dust, it is or may be advantageous to install a Cottrell electrostatic precipitator in the return gas circuit 25, 26, 21, 28 and 29.

Cool, clean, spent carrier gas from scrubber 28 is carried through conduits 29 and 43 to the inlet of blower l. A sufiicient amount of the gas is bled through valved bleed-line 30 tapped from the exhaust main 25 to maintain continuously uniform pressure throughout the closed circuit.

The composition of the spent gas passing through cold gas main 2 generally exhibits a C02 content in the neighborhood of 20 to 25%. After passage through chamber 5, the gas exhausting through conduit 9 contains large amounts of CO2 and H20 which would tend to smother combustion if also done in mixing chamber 10. For this reason I prefer to combust the fuel and air in the separate chamber 31. I introduce draft air through draft main 32 into bustle pipe 33 from which the draft is conveyed through the plurality of conduits 34, 34 into the combustion chamber 31. Fuel is introducedinto chamber 3! by means of water-cooled burner 35. The relative amounts of fuel and draft air forced into chamber 31 are carefully controlled by regulating the opening of draft valve 4| and the opening of fuel valve 42 whereby, as exactly as possible, just sufiicient draft oxygen is introduced to effect the perfect combustion of the fuel. I prefer to employ an automatic control of these two valves actuated by orifices (not shown in Fig. l) positioned in-draft main 32 and fuel main 44.

The ore material to be magnetically roasted is charged into hopper 23 of the double bell-and hopper feed equipment illustrated at top of chamber 16. By opening the little bell 2!, charge material is introduced into gas seal 22, wherein it rests on the big bell 20. At suitable frequent intervals bell 20 is lowered, permitting the material in the gas seal to fall on the stockline (8 of the charge column I! in chamber IS. The big and little bells and gas seal illustrated in the drawings are of the type conventionally employed in blast furnace practice. I contemplate, in many instances, using in lieu of the illustrated bell-andhopper feed equipment any one or more of the conventional types of charging equipment employed in gas producers, which may variously be chain conveyors, belt conveyors, rotating. disks, star-gates, or the like. A

In describing the column of charge material contained in chambers *5 and it as continuously descending I construe the latter term specifically to include, of course, a downward motion of these charge columns taking place intermittently in recurrent steps, since the overall effect of such interrupted descent is identical with that experienced with an uninterrupted continuously downward flow of solids.

The provision of the gas-collecting plenum chamber 6 above the charge column in chamber 5 is an essential feature of the present apparatus. The volume of space 5 should be ample, in relation to the volume of gas discharging from the charge column in chamber 5, to promote maximum uniformity of flow of gas through this column. Such ample space can be provided by positioning the refractory tube 1 in the top of chamber 5, the length of conduit 1 being sufficient to maintain the upper free surface of the lower charge: columni ata suitable distance from the-conicalv top18 orchamber 5.. The connecting conduit: 1, which1I. term herein the-isthmus, should be relatively small. in cross secti'onal area compared with'the cross-sectional areas of chambers and 15. In order to reducethe amount of: gas flowing upwardly from chamber 5 to chamher-.16 by way of this isthmus, the major portion of this. gas stream may-be diverted through conduit 3 to combustion chamber 10.

It should be noted that if substantial amounts of, gas were to flow upwardly through conduit! intochamber Hi, this portion of the gas would arrive at' the bottom of the charge column I! with a gas composition which would difier from thecomposition ofthe gas' entering the column fromannular open space It. Were such short:- circuited gas to leak from chamber 5. through isthmus 1 into chamber I 6 in relatively large amount, objectionable irregularity in gas com-.- position would be encountered, which. irregularitywould have an adverse effect onthe emciency of reduction in chamber I 6. The exact dimensions. of isthmus. I would depend on the size of'the ore particles being treated and on their. physical characteristics: the diameter. of isthmus I should be suificiently large to avoid mechanical jamming of the material flowing therethrough.

In Fig. 1 of the drawing I haveshown a mechanism for; removing the finished solid product from the bottom of chamber 5. Ore leaves the inverted conicalbottom of chamber 5 through dischargev conduit 38, at a; rat controlled by the speed of revolution of the impeller in star-gate 48.. This star-gate-is preferably actuated bya variable speed geared motor. The rate at which the ore materialis moved through the duplex shaft furnace can thusibe controlled by suitable adjustment inithespeed of the star gate motor. Itis. convenient to provide a Sl'lllllrflfi va1ve39 positionedin discharge conduit 38 whereby the flow of material therethrough can be completely stopped.

In order to attain maximum thermal efliciency for the present process, it is essential to realize a maXimum.l.lniformity of flow both in regard to the upward flow of ga in chambers 5 and I6 and .in'regard to the downward flow of solids in these chambers. Since the finishedproduct moving" through the hopper-bottom of chamber 5' is at a. relatively low temperature, I generally prefer to install adjacent this hopper-bottom a plurality of inverted truncated cones '45, 45; made of sheet steel or: of cast iron. These conical baflies are dimensioned, and positioned concentrically with respect to the cone of the hopper-bottom, where: by to promote uniformity of flow of solids in chamber. 5. The device has long beenknown and its use .is conventional. 'I have not .shown' S mir larconical .baifies positioned in the'conical bottom of upper chamber I6 since,'in.the.more usual case. 'I do not recommend theiru'se there. Itv is truethat increased uniformity of solid flow (and "Examples? v The starting materialis a. lean hematite; ore which exhibits the following analysis; on a dry basis:

This ore contains 15. 5% moisture as charged. The apparatus as shown in the accompanying drawing has the following dimensions: upper chamber Hi has inside diameter of"20 feet andla vertical'height between open space I4 and stocke line It of'l6' feet. Ore is chargedat the rate of 1596 gross tOIlS(Cz: T.) per24-hour day. Blower l forces 14,430 cu. ft./min. (standardconditions; F., 29.92 inches Hg) of cold,: clean'spent carrier gas through cold gas conduit 2., Thiswgas has the following composition:

CO2 21.68 CO 0157 Hz 0:06 H2O 4.05 Hz .73.64

Reducing gas is forced through' valved conduit 31 into conduit 2 This'gas hasthefollowing composition: v

CO2. 0.62 CO .*4.-.28 Hz.. 1:84 H20 0.36 N2 62.80

The above reducing gas may be, and preferably is, producedin a slagging type gas producer.

The recirculating carrier gas and'the reducing gas commingle and. flow" into thebustl'e pipe3 with. the .following. gas. composition.

C0 6355 H2 0.3 6 H50 3.416 Na" 71.51

C02 16;71 oo. 4.67 0'.2 6

flows into bustle pipel 'lZ-atthe rate of 23,630 cu. ft/min" and passes by way of blowpipes l3, [3 into open space I! and thence "entersj charge column I! by passage under the inverted truncated concentric conical shield 05. As this gas ascends the descending ore column 11, reduction is effected in the lower portion of chamber l6, and the spent gas" resulting from this reduction in passing through the ore in the neighborhood of stockline l8 dehydrates the combined water associated with the Fezoa and evaporates the moisturecontent of the ore. The water vapor removed in the present case is 9700 cu. ft./min. (measured at 60 F. and 29.92 in. Hg). The resulting wet spent gas discharging through open space [9 and discharge conduit has the following analysis:

CO2 14.83 CO 0.16 Hz 0.02 H2O 34.48 N2 50.51

This gas, after passage through dust collector 26, is cooled to about 85 F. by passage through scrubber 28 and the large amount of water evaporated from the ore is condensed therein and removed from the gas.

Before cleaning and cooling the spent gas, I bleed through bleed main 30 about 8600 cubic feet per minute of such gas and return the remainder through conduit 43 to blower l.

The evaporation of moisture from the ore and the dehydration of the material therein, in the present instance, absorb a large amount of heat, viz., 455,000 B. t. u. per minute. To a large ex tent, this absorption of heat is compensated by the production of 310,000 B. t. 11. per minute of heat generated bythe exothermic reduction of F6203 to FesOi-by the combined action ofthe CO and the H2 of the enriched carrier gas. The net thermal effect of thesetwo factors, however, is that 145,000 B. t. u. per minute of heat are absorbed.

The fuel requirements of the process are largely dominated by the loss of heat experienced from discharging the spent gas through conduit 25, and the finished solid product through conduit 38, at temperatures above atmospheric.

The spent gas discharges from open space [9 at ments of the process up to 526,000 B. t. u./min.

A considerable loss of heat through the bricklining of the two chambers and the combustion zone is experienced, amounting to 19,000 B. t. u./ min.- The total thermal input required to maintain the apparatus at a steady state is, therefore, 545,000 B. t. u./min.

It should be observed that the cooling effect of the enriched carrier gas ascending through the column in reaction chamber 5 is insuiiicient to cool the solid particles to a nearer approach to atmospheric temperature than the 510 F. indicated above, due to the excess heat capacity of the solids above the 17,000 cu. ft./min. of gas ascending therethrough. It is, of course, possible to increase the amount of recirculating carrier gas, thereby reducing the temperature of the solids discharged through conduit 38 and 'therebydecreasin'g the loss of heat due to the discharge of heated solids. However, whenthe yolume. of recirculated gas is increased-With. the

same ,fiow of solids through the'apparatus-thci heat capacity of the gas traversing upper chamber 16 exceeds the amount of heat re-, quired to heat the solids descending therethrough and the temperature of the gas discharging from stockline I8 is increased. Considerable latitude is permissible in regulating the amount of carrier gas which is recirculated per ton of ore charged. The requirements for maximum thermal efficiency are: (l) the amount of reducing gas introduced through conduit. 3i shall be proportioned with respect to the iron content of charged material and to the degree of conversion from FezOa to F8304 which is desired, whereby to attain a high efficiency of ultilization of the reducing gas; and (2) the amount of fuel introduced through burner 35 and of draft through bustle pipe 33 shall be proportioned so that complete combustion of the fuel will be realized without remanent excess of oxygen or of unburned combustibles.

. With regard to requirement 1 above, if more C0 and/or H2 is introduced through conduit 3| in enriching the carrier gas than is required to effect the conversion of all the ferric oxide in the ore to magnetite, the excess C0 and H2 will remain unoxidized and will be discharged through exhaust conduit 25, thus wasting the excess reducing agent.

In the above illustration, the reducing gas employed is the product of a slagging type gas producer and the fuel is a petroleum liquid. This selection of reducing gas and fuel is appropriate to operations carried out at an iron mine, e. g., in the Lake Superior region, distant from sources of natural gas, coal and coke and other industrial fuels. Whenever the ore mine is located near a blast furnace and steel plant, it ma be advantageous to use producer gas both as reducing agent and as fuel. Where natural gas is available, this natural gas may readily enough be used as fuel, and the reducing gas may readily enough be relative pure H2 obtained by the thermal decomposition of the natural gas. Innumerable combinations of reducing gas and fuel appear appropriate, depending on the geographical location and character of the ore to be treated.

A modified construction for the furnace apparatus and controls is illustrated in Fig. 2 and, for convenience in comparison with the construction of Fig. 1, those components which are of like construction in both Figs. 1 and 2 bear like reference numerals.

With reference now to Fig. 2, the ore treating furnace proper from a viewpoint of construction principles is basically the same as that shown in Fig. 1, the principal differences between the two residing in the configuration of the sectionor isthmusof restricted cross-section connecting the upper and lower furnace chambers, the arrangement for admitting carrier gas to such chambers, and the arrangement of the combustion chamber.

In Fig. 2, the vertical furnace includes an upper chamber 50, a lower chamber 5|, and a chamber 52 intermediate the upper and lower chambers all being in vertical alignment and preferably cylindrical in transverse section. The wall of upper chamber 50 preferably has-a slight, diverging taper in the downward direction and ore I! to be treated is admitted intc'thetop of chamber 50 by way of hopper 23 and double bells 20, 2! as previously described with reference 110, the Fig. 1 furnace.

The intermediate chamber :52 :is generally conical with the wall preferably converging (as measured in the downward direction) at an angle of not more than 15 from vertical to assurefree'flow of the ore along the wall and thus eliminate the possibility of forming stagnantore. The upper end of intermediate chamher 52' is larger in diameter than the lower, discharge end of upper chambergSilat the junction between the two thus establishing an upper-"annular plenum space '53 into whichthe hot carriergases are delivered from conduit leading from the-vertically disposed mixing chamber '53.

.At the discharge end of chamber :52 thereisprovided a' conical "shell 54 preferably made from agood heat resisting material such as Inconel," a-high nickel ferrous alloythat will retain its shape and strength under the temperatures and loading conditions encounteredin the furnace. The wall of. insert 54, which forms a continuation of the brickword wall portion 55' of chamber 52,.extends for a .considerabledistance into thelower chamber 5| and since the lower-discharge end of .shelllit is of smaller diameter than that of lower chamber 5|, a second, intermediate annular plenum space 56 is established at the upper end of chamber 5|. for collecting and discharging enriched carrier gases preheated by the ore charge in chamberBl into agas diverting conduit. 59 which leads to the lower entrance end of mixing chamber 58.

The discharge end of. lower chamber 5| is fitted with a tapered metallic shell 68, converging in the downward direction which discharges into a larger convergingly tapered shell 63 to thereby establish a third, lower annular plenum space. as into which relatively. cool enriched carrier gas is delivered for flow upwardly through the downwardly descending ore column "in chamber 5|.

The lower verticaldischarge mouth d5 of shell BBempties the ore onto a horizontal-plate 66 supported-directly beneath mouth 65 by the side walls of a discharge-chamber '61, the plate 66 being provided with a plurality of apertures 68 through. which ore dropsint'othe lower end of shell-67 for final discharge through star gate 40. A rake 69 is arranged to reciprocate across the upperfaceof plate. 66. by. means of a. motorized driveconsisting of a variable speed motor Ill drivingan. eccentric plate H to which is coupled one end o'f.crank.'|2, the. other end of crank l2...being connectedtothe rake. handle 13' which .slidesin bearing sleeve 14. Eccentric plate .'II is preferably provided with a pluralityofapertures Ha at different radial distances from.the center of rotation usable selectively to receive thecoupling pinl'lZa of crank 12 so. that the stroke of the rake can be correspondingly adjusted, and motor is ,provided with a variable resistance 75 inits armature circuit so that the frequency with which rake ea reciprocates can also be adjusted, These two controls for the rake are used to regulate the rate at which the ore column will be permitted to descend through the furnace structure, and the comiderable heightv of the ore; column below plenumispace 64 in combination with .the air tightshell Stand chamber 6! set upa baclcpres sure sufficient to prevent any appreciable. loss of enriched carrier gas entering chamber. downwardly through the discharge gate 40.

addition to. introduction of enriched carrier gas. into plenum space 64, such. gas isalso: introduced directly into the body of ore chamber 5-|-.by means of .a pipe: 16 arranged verticallyand centrally within chamber .5,|,\ a conical .shield H 10 beingzprovided over the. outlet .endof the pipe to facilitate distribution of the gas and preventing clogging of the pipe by ore.

As-in-the; Fig.1 construction, spent carrier gas discharges from the upper end of upper chamber Ell-by waylof exhaust conduit 25,-stripped of solids incdust .collector;25, transported through conduit 2lzinto coolererscrubber Ztwhere its temperature is reduced and excess moisture isxremoved, thence delivered through conduit 43 to the suction; side of lower Also as in Fig. 1, a sufficient amount of the -carriergas is bled through the bleedconduit 33 tapped from exhaust conduit- 25 to maintain continuously .unifor-m pressures throughout the closed circuit.

From-the pressure side of blower cool and clean-carrier gas is transported through conduit 2rand distributed by a "Yioint to a branch conduit l8 leacling .to plenum chamber 64 and branch conduit"!!! leadingto the vertical pipe 15. Pref erably adjustable valves Stare interposedin the conduits l8, 19 to adjustthe division of the total gaszin'conduit 2 between branch conduits 18, (9.

Reducing gas (rich in CO), in sufficient quantityto replacethat used in the reduction of the manganeseand iron oxides and the small amount lostthrough the bleed 1ine'30 to the end that the carriergas will always :be of the same richness when-enteringthe furnace is admitted to conduitz through-supply pipe 3l in which is located a valveziikcontrolled by solenoid 85.

Provision is made in Fig. 2 for-continuously analyzing the enriched carrier gas just prior to en-teringthe furnace,- and automatically regulating-the flow ofreducing'gas into the gas systemat'this ,pointiin accordance with the gas analysis so. that a substantially uniform degree of richness is maintained. .For this purpose-I preferablyv-use an industrial type of gas analyzer known to the trade as a Bailey meter. The-construction ofithe meteris well. known and hence in the. interest of simplifying the drawings has been illustrated simply by-box 86. The (JO-zenriched carrier gas is tapped from, the circulating system, just =prior-to entering the furnace by a T connection 81 andcarried through conduit 88, which may i include .a shut-01f cook .93, to the analyzer .86; TheCO' contentof the enriched carrier gas canbe recorded or as shown registered-v on HIEtBIh-Ql. For automatic control purposes, therev'is also produced a control voltage variable inversely with, the departure of the CO content of theenriched carrier gasfrom the pre-' determined degree of richness desired to be maintained. andisuch voltage is applied over line 94 tothesolenoid-85 controlling the degree of opening of. the-:valve- 84 in the (10- gas. supply lineal. Hence valve 84 will be moved to a more open positionwith increased energization of solenoid Baas: the CO content of the enriched carrier gas drops below the predetermined value desired to be maintained, and conversely, valve 84 will move to -amore closedposition whenever the CO content rises above v the predetermined value.

Provision is also made for continuously analyzing-and indicating the CO content of the minor fractionof spent gasvented to waste through pipe 30. To, thisend there is provided a conduit 89 extendingifromT connection 90 in pipe 30 to the analyzer 86, and the CO. content is read on meter 95. Conduit 89 may also includea shutoifcock 92.

- For heatingthe enrichedcarrier-gas where, the larger portionof it leaves .the; lower chamber 5| (since: plenum.,chamber. 56- and. conduit 59 offer a path far less resistant to gas now than the ore column restricted in cross sectional area at the relatively small discharge end of cone 54) I provide a combustion chamber I disposed horizontally. Fuel and combustion air enter chamber I00 from the right end as viewed in the drawing, and the hot combustion gas leaves chamber I00 through a constricted outlet Illl that discharges into the lower end of mixing chamber 58 opposite the discharge end of conduit 59. The enriched carrier gas entering chamber 58 through conduit 59 thus mingles intimately With and is heated by the combustion gases discharged through the restricted outlet The restriction IOI assures complete combustion within the combustion chamber proper and prevents the flame from being blown out by the carrier gas sweeping into mixing chamber 58.

; As previously expained with respect to the Fig. 1 construction, it is most desirable to maintain such a ratio between fuel and combustion air that just enough oxygen is introduced to convert all the combustibles of the fuel into CO2 and H without causing any residual excess of free oxygen. To this end I have shown gear actuated valves I02, I03 in the fuel and air conduits I04, (05 respectively, the gear I06 of valve I02 being meshed with the gear I01 of valve I03, and the two gears being so sized as to maintain the desired ratio of fuel-to-air flow into combustion chamber I00 throughout the range of fuel and air adjustment. g

It is also preferable to maintain the thermally enhanced enriched carrier gas discharging through conduit 51 into plenum chamber 53 at a constant temperature. To this end, a temper ature sensing device such as thermocouple I08 placed in conduit 51 is electrically connected by wires I09 to a control unit N0 of conventional design and which therefore has been illustrated only in block form. Control unit [I0 trans lates departures in temperature in conduit 51 measured by thermocouple Hi8 from a predetermined temperature level into control voltages which feed over wires III to motor I I2 and cause the shaft of the latter to rotate in one direction or the other dependent upon the sense of the departure in temperature of the gas in conduit 51 from the predetermined value desired to be maintained. The shaft of motor H2 drives gear H3 which meshes with gear I06 and hence valves I92, I03 controlling flow of fuel and air, respectively will be regulated simultaneously and automatically to vary the fuel and air as may be necessary to maintain constant gas temperature in conduit 5?. Basically, the modified'furnace construction shown in Fig. 2 operates in the same manner as has already been explained in connection with the Fig. 1 embodiment and hence no further description of operational details is deemed necessary.

In conclusion, I wish it to be understood that the two embodiments of the improved furnace structure which have been described and illustrated are to be considered as typical rather than limitative and hence may be subjected to various changes in the construction and arrangement of component parts without departing from the spirit and scope of the invention as defined in the appended claims.

' Iclaim:

1. Apparatus for treating ferruginous ore material, wherein the iron content consists mainly of a non-magnetic oxidic compound of iron, with reducing gas to render the are material adaptable for magnetic concentration, said'apparatus comprising, a pair of superposed ore treating chambers, gas-tight means for feeding ore to be treated to the upper end of said upper chamber, gas-tight means for extracting treated ore from the bottom of said lower chamber, means adjacent the lower ends of said chambers to provide lower openspaces adjacent lower free surfaces of a column of ore therein,-a passageway conduit connecting the lower end of said upper chamber with the upper end of said lower chamber for gravitational feed of ore from the upper to the lower chambers, the relationship between the lower end of said passageway conduit and the upper walls of said lower chamber being such as to define an upper open space of substantial extent above the upper free surface of a bed of ore in said lower treating chamber when the latter is filled to the highest level attainable by gravitational feed of ore through said passageway conduit, means for feeding a reducing gas to the lower open space of said lower chamber for upward flow through and extraction of heat from the bed of ore contained therein, a mixing chamber, a conduit leading from the upper open space of said lower chamber to the inlet end of said mixing chamber, a conduit leading from the outlet end of said mixing chamber to the lower free space of said upper chamber for delivering thermally enhanced reducing gas to the latter for passage upwardly through a bed of ore in said upper chamber to effect the conditioning, heating and reduction thereof, a combustion chamber disposed adjacent said mixing chamber and adapted to supply hot combustion gases to said mixing chamber, a' conduit leading from the upper end of said upper chamber for exhausting spent reducing gas and entrained moisture therefrom, a scrubber for said spent reducing gas connected to the last mentioned conduit, means in said last mentioned conduit for bleeding on spent reducing gas, a conduit connecting said scrubber with said gas feeding means, and means for adding replenishment reducing gas to the gas fed to the lower open space of said lower chamber by the aforementioned reducing gas feeding means. g

2. Apparatus for treating ferruginous ore material, wherein the iron content consists mainly of a non-magnetic oxidic compound of iron, with reducing gas to render the or material adaptable for magnetic concentration, said apparatus comprising interconnected upper, intermediate and lower ore treating chambers arranged in vertical superposed relation and adapted to be substantially filled with a column of the ore, said intermediate chamber having a converging taper as measured in the downward direction of not more than 15 from vertical, the upper inlet end of said intermediate chamber being larger than the adjacent outlet end of said upper chamber to thereby establish a first plenum space at the junction of said upper and intermediate chambers, and the lower outlet end of said intermediate chamber being smaller than and penetrating the inlet end of said lower chamber to thereby establish a second plenum space between the walls of the intermediate and lower chambers, gas-tight means for feeding ore to be treated onto the stockline of the ore column in said upper chamber, gas-tight means for extracting treated ore from the bottom of said lower chamber whereby said ore column will be caused to descend gravitationally through said chambers, gas conduit means interconnecting the top of said upper chamber and the bottom of said lower chamber, a vertical mixing chamber, gas conduits connecting said first and second plenum spaces respectively with the upper outlet and lower inlet ends of said mixing chamber, a horizontal combustion chamber disposed adjacent the lower end of said mixing chamber, the combustion gases passing to said mixing chamber from said combustion chamber through an outlet of restricted area, means admitting fuel and air to said combustion chamber in a predetermined ratio for producing combustion gases without an excess of oxygen, said ore treating chambers, said mixing chamber, said gas conduits and said gas conduit means forming a substantially closed circuit for the circulation of reducing gas upwardly through said chambers, a recirculating pump in said gas circuit, means for bleeding spent gas from said gas circuit at a locus adjacent the top of said upper chamber, and means for admitting replenishment gas to said gas circuit at a locus intermediate the pressure side of said pump and the bottom of said lower chamber.

3. Apparatus for treating ore material as defined in claim 2 wherein a third plenum space is also provided adjacent the bottom end of said lower chamber, and which further includes a branch conduit discharging a portion 01 the gas 14 from said conduit means into said third plenum space and a second branch conduit discharging the remainder of the gas from said conduit means directly within said lower chamber.

4. Apparatus for treating iron ore material as defined in claim 2 and which further includes means for extracting and analyzing a sample of the gas in said circuit at a locus adjacent said spent gas bleeding means, and means-controlled by said analyzing means for regulating admission of replenishment gas into said gas circuit.

PERCY H. ROYSTER.

References Cited in the file of this patent Norton, Jr., Chemical and Metallurgical Engineering, July 1946, page 117.

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