US2436157A

US2436157A - Metallurgical process and apparatus

Info

Publication number: US2436157A
Application number: US422930A
Authority: US
Inventors: Carl J Westling
Original assignee: MINERALS AND METALS CORP
Current assignee: MINERALS AND METALS Corp
Priority date: 1941-12-15
Filing date: 1941-12-15
Publication date: 1948-02-17
Anticipated expiration: 1965-02-17

Description

Feb. 17, 1948. C, 1 WESTLING A 2,436,157

METALLURGICAL PROCESS AND APPARATUS 5 sheets-sheet 1` Filed Dec. 15, 1941 cfr/PL, zwfszz/A/G' y Y 'ATT NEY Feb. 17, 1948. c. J. wl-:sTLlNG METALLURGICAL PROCESS AND APPARATUS Filed Dec.v 15, 1941 vI5 Sheets-Sheet 3 t Patented Feb. 17, 1948 Carl 1. Wstling,

'Animation December '15, 1941, serial Nol 4212.536

4 claims. 11123;1

isf-'divided metaniemfaterivls by -reductidngrastoi' :other n'iet'allurgical or *chemical process, and has 1:1articula'r""refererie` tomethods' and apparatusffor reducing metallio 'eornpouiids,l and "is so defsribedhereirias illustrative of the inventionfbfut it vis jto'beunderstood'tht the invention isf-,no tf'liini-t`edfto that use. l V l 111;;eepera1 the invention 'relates to ,treatment ofj-:tlie'lne-1ydividediehargeon" a hearth, prefer-v ably vho'riz'ontal,''by jineans yof' gases fvvhile` the charge i'scaused Vtofinove overthe hearth. iMov-A ingV charge l `hearths 4of t this general nature-have been 'known *heretoforeand' 'may be classiifed aeco'rding to "'theniode vof advano ernfent off'fthe r'zlh'ar'ge.,` Acooding'to `one Ine'thoiz, :the Ahearth is vibrateid in jsueh `a way that the shew-divided eharg'efadvaiie's thereoverfdurin'g lreduction,and Hardy` Batent No. 2.236.474 :and/ or Y'Brassert vPatent "No.j 2,296,498. disclose 'examples' ofthe appli*- c'ation j`of jthis inethod. Another nrietlrnxi involves propulsion 'of thephargealong fthe `hearth by directional "jets of y@as Lunder pressure and inlay be 'effected "by reduoing gas '-ipulses "as 'in Si'monds Patentv No. 1,'80 2959, "offloyicnstant fre#- du'cin'gprgas 'flwgimpring dirctipnal'movemrft to thejflnelyedivided foharg'egI and Brassertv Patent No. "2,296,498'a`nd/ or BrassertandfI-Iartley Patent No.v t 23131 62664 disclose "e'x'ar'np'les of the application o'fjthijs` method.

.Thse rtain'j I Conditions and aref vvexpensivet totA- manufacture, maintain' `land operate. Thus; the vibrating hearth-is expensive, 'Jbegausfe it lrequires ieostly' temperature-'resistant alloys 'and 'z'refractories, whilevin the gas propulsion'l'earthjthe vinetallic ar'tieles'fare likely tofw :ba'ckk'into and `thus clogf the gasl jet openings during` interruptions in operation,Y unless the'jet openings 'are Inade manier than the smallest particles oftheidrge, again 4Vre'c'luiring expensive Cheat-resistingalloys and. e'fraotoriesniorder to fobtain the accurate'- 1y4s`iz`edjet "openingsfrequired Also, where very' f lne materials are treated, which means10Qy to 200 mesh, the nu'rnbe'r offapertuijes' required `for the `[necessary vgas volume v'would be excessive;

Furthermore! even if jetopenitrigsof suffcientlyl small* sie* could beV economically praeticable, Ait would Abe diiicultto keep them V"openjeoau`se `of the tendency toward carbon deposit andcorrosion under v'the rigorousl operating conditions' to 'which the' hearth would be subjedted, Y Also, `it'is dini'- oult to supply sufficient vheat vby;'means''of the preheated reducing gases without liability'of fritaeneral Charge propulsion iiaye'ifourid this relation pfe'cmderenenheiing for t A afpelyfingh gas l pressure ate vthe b'ed With/resultant gas lovy lit afstate -sirnilar-r wie "afijssd'vantages y1'rmere'nv Another object is the provision of a hearth structure wherein gas openings of desirable width may be sealed against back leakage of a nelydivided charge,

but without an attendant formation of pockets wherein the charge may frit or obstruct flow or prevent any cleaning.

pressure, correlated to the particle size and Weight of the charge, so that a state of fluency is imparted thereto resembling fluidity, with the result that the entire charge will progress with a flowing motion at predetermined speed from one end of the hearth to the other While the particles thereof are being reduced to metal., The gas openings are relatively Wide and horizontally-directed and are not necessarily designed to impart directional propulsion to the charge, the permeation of the charge and the construction and arrangement of the hearth causing the natural now of the ne materials without the provision of positive or directional means urging the charge in the desired direction. With this arrangement, preheated reducing gas may be employed Without liability of fritting or sintering of the charge in or near the'gas openings, and the horizontal dis- Another object is the provision of a hearth structure in which gas slots and preheat passages may be laidopen and madeaccessible for periodic inspection and cleaning, if desired, by a simple removal of the hearth surface structure.

t. Another object is the provision of a furnace structure in vwhich the completely attained, not ,only in metal construction but with equal safetyand facility in refractory materials.

' Another object primary heating means and substructure whereby the hearth and the reducing gas for individual slot connections may at the same time be efficiently. preheated between the inlet at which the cold gas volume is controlled audits exit to the individual slot sections. Y

Another object is to provide a reducing furnace in which speed of reduction is made possible by the use of a reducing gas very low in N2, together with satisfying a peak portion of the heat demand throughout the length ofr the charge, by supplying radiant heat from direct partial combustion of spent reducing gases blowing up from and protecting the charge/against reoxidation.

Another object is to provide a safe method of` supplying secondary heat-by direct partial combustion, preferably of spent reducing gases, above thecharge wherebyl the radiantheat created is transferred directly into the charge in the furnace while the sensible heat of the gases is exchanged to the ore ahead of the furnace, thereby obtaining high overall efficiency.

Another object is to provide a controllable secondary heat source by which heat input can be varied throughout the length ofthe furnace to suit the demands of the reducing charge, or as may be desired to modify or control the rate of reaction throughout the charge. j

YAnother object is to provide-a method and means whereby part of the dust loss in the dirty exit reducing gas from the furnace is trapped in the ore drying operation by these gases and thus also to make one set of gas cleaning apparatus take care of both reducing furnace and ore drying'apparatus requirements.

These and other objects ofthe invention are obtained in a furnace of the horizontal hearth type, as distinguished from vertical shaft or roand in which the hearth tary kiln type furnaces, contains' a series of adjacent parallel, preferably v-shaped longitudinal troughs through which the material flows from the charging to the discharging end of thevfurnace, and from the bottom of each of which the-permeating reducing gas issues with suicient volume and under sufficient above objectives may beA is'to provide a furnace hearth high in H2 and CO and Aa secondary heating means,`

cold charge, including a gas cleaning system for,

' rials. Its construction enables compact arrange-S position i of the latter precludes back flow and clogging of the gas passages for any reason. Also, since the gas is not employed for direct or positive propulsion of the charge, the pressures neednot be great, no greater than is necessary to olil tain the fluid simulation of the charge which is a concomitant of the desired .thorough permeation.

of the charge bythe reducing gas. In conjunction with the hearth, primary indirect heating` means and secondary heating means for the charge are provided,.as well as means for transferrine the sensible heat in the spent gases to the the spent gases, which are recovered and regenerated for reuse.

It will be seen that the present invention provides a very simple and effective method of pro.

curing continuous and economical reduction ofv finely-divided ores or other reducible metallic4 compounds of a wide range of particle sizes, since .l the pressures and volume of gas can be adjusted to suit reducing and charge permeation require--l1 ments without regard'to forcible directional pro-p pulsion requirements of the moving charge methods heretofore known, the gas pressure andvol' urne being merely correlated to the weight of theA column of charge above the gas openings. The'.

apparatus in which this method is practiced hasy no moving parts and is extremely simple in con.

struction, and may be made of inexpensive matement. over a heat exchanger structure whereby minimum heat losses and maximum neat recovery are provided.v The hearth maybe readily ree4 moved, section by section, for repair inspection and replacement, and remains clean at all times.V It may be cleared ofthe charge for inspection` without manual effort and when cleared will bev clean and ready for reuse in a short time.

For a more complete understanding of the in-.

vention, reference may be had to the accompanying drawings, irrwhlch:Y

Figure 1 is a. vertical longitudinal section matically;

Fig. 2- is a vertical section through the furnace; including the reducing gas preheater, as seen along the line 2-2 of Fig. 1;

Fig. ;3 is a plan view of the hearth as seen along.

the line 3-3 of Fig. 1;

preheating flues;

'Fi'gzf isranz-enlarg'edwerticai transvmfsesetation-f through fthe hearth oorvandithef" upper' portioni.

othe-.reducingjgas preheaterfas seen.along..their;`

liiigiz .65" is.' an enlarged`- longitudinal.. se'cticur.l

throughithez. dischargefend ofthe-hearth.; as seen.

hearth providing;.means.for-rapid removal. ofthe entire` chargez'.l

structurefasiabwe presenmeauiesffrminganea reducing igasfiprelieatingiilueSpassages i225?? Th ribsi i l Sacs are fpreferablggy:` made. in' sections. corre sponding t'o=..i,l'ref:spaci'ngi' of.' flues 22? :orf multiples s@ thereof The'ierrdsfof fthe 'irib sections'. l 9a=l havej naceofthisinvention isscontained in asuitablel.` casingf l supportedfbyfbottomisbeams 2, .buckstayf beamsz3granditop tie beams. 4.' The-casing l 'cone tains \the combustion char'nber.;y Stand: air` preheate ing recuperator-; and :is preferably madey pressure-tight' toy-permit .thencombustion .chamberf 51 i andi.r the.' gas.. preheatingf. structure under the.. hearth; asv described 1 later, to: be .put under. an'. equali'zing pressurefif desired; Any. variation required in the pressure of the reducing gas sup.'- plied to the hearthzmaythus-be offset byvarying thewaste gas .pressuresor aste-reduce the differ-` ent-iai pressureacross. thegas. preheating `structure practically to .zero,.: whereby the dangerof leakage losses4 or pressure ...damage Vcan .be-.elimi-v mated?.

Thev furnace casing: is' provided `witnan insulation-lining r1 andrefractory'walls disposedinte` riorlyof .the insulation. Theabottomof the furnace consists fof sa suitable -refractory basev Il);V resting` ori-anl insulating .concrete slab .8,` and .the4 toproftheufurrrace comprises a "series sof'. arches` I I,- preferably ofkth'e suspended type of construction.. I Theroof arches-:l I-arealso preferably fin-"r ish'ed-with the insulationl but do not necessarily.-

need pressure tight casing cover,l since .the reducingigas. above-l the icharge on: the- 'hearth may.

loe-maintained substantially atatmospheric pressure:v

Alrefractory arch IZLJforms: the bottom" of the combustion chamber 5 andsthe topzof theair.

preheater chamber'. The topfof thev combustion chamber preferably iconsistsfof. a1 suspended arch l3- placed atfor belowl the level of the furnace hearth, thereby permittingithe use of access doors lil-fat the feed end of the furnace hearth. Similar access doors 1| l arerprovidedr at the dischargeend offth'e'- furnace. Near the'dischargeend of the Thespa'cingoof :thehearth channels l 9v is tde'- v pendent :onfathe spacingtof gasl supplyues. 22; cr-"f vicerversan. Preferably the :hearth .channel spacaing-.Willbe madetoi'suit the uerspacing of stand#v with .fgasr'm'ani-fold': .piping`r space?. requirements underf.` the: furnacerl The minimum'V Width` and spacing-r provides. a, maximum chargefvolume:.andr'-v iggtherleast dea-d Lsp`ace;ras.frepresentedk :byithearea of? rib i sections: |917., .forf any given.' total Width.

hearth with` .atgivenf depth of charge.

The: ore,;.or^other.i1 metallic compound to bef-1 reduced,rwith.or without admixed carbon', is `sup` plied'to the furnace atth'e feed end of Ltheh'earth". through 1 aafeed .chute..29, which is adapted'tow spread the; ore. to. lall: the channels l 9 across :the ff width for.theffurnace-1v Anradjustable gate'. means'.

.1i operated Lby; suitable 4adjusting lmeans 23 l, is:

theproductldischarge. This gate may be. opere.

' 4matediby-suitable .regulating means. 361 extending;- through a gas tight connection 31 to cooperate with the .gate 35. on the inside of the furnace.

The-supply; of gasto the individual sets of slots.` 20.1-is admittedfbyfindividual.connections 43 be- 45.l lowthe furnace through'inlet pipes 42 to the prefurnacel the lroofv structure is arranged to form,

anioutlet l5 '-for'the spent reducing gas Which is.

removed from-the furnace as later described,` through the finsulatedduot .l 6. Peepfsight connections I8 are -providecl-along-the sides of the:

furnace V vlto fen'able the f operatorv to. observe the action'pf the charge. on `the hearth.

-In its preferred form therefractory hearthconsists ofa series of parallel ribs .I 9a oftriangu-v larI vsection* forming V-shaped longitudinal channels IS, -although they mayhave any other suitable'contour; disposed side by sideacross the widthlof `thefurnace hearth; as vshown in Figs..

2and'3i Horizontal slot openings 20.at the bottom of `eachheartl'r channel introduce preheated reducing'gas intd the cha-rgeon the hearth. The gas 'slots 20; narrow vertically and wide horizontally, are suitably i spaced longitudinally of the hearth and are staggeredwith -respect to the slots in fthe'adjacent row. as indicated'in Fig. 4. Each slot `is supplied withxpreheatedgas from a corre-'- spondinggflue'passage22 toinsure uniform gasf distribution with resultant complete agitationin thelch'arge from' end to end of-'the hearth chanheatingfflues22. The gasis suppliedtoeach pair;

oftransversetrows of flues122 through a manifoldi.

44 and,is metered z to inlet pipes 42;through an xed orvariable orifice A45 set to a desired maximum .rate of gas-flow'. Each of the several mani-5 y folds 44`extends acrossthe width ofthe furnace andlisxsupplied from av longitudinal-supply manif fold. liexten'ding alongthe entire length of. the.V furnace.-k Each'transverse manifold 44 is equippedr l' with a regulating valve 41 for control of total gas flow'. to. corresponding length sections of the hearth'. The sectional,regulatingzvalves 41 are!l preferably all disposed outr beyond one side vof the furnace .to permit' key-'manipulation by means of handlesA 41a by'fansoperator standing on a plat;- form-abovenand alongside .the furnace, ,Where he: may at the same; time observe` the effectA of the volume. regulation .through :the peep-sights I8.-

The -iiues 22 .may be lled with a series of rsuit'- ablyfshapedlrefractory llers-'22a to increase the velocity and lcreatel turbulence in the risinggases l1 and `therebyimprove the rate of heat transfer to.

them, similar'to thev practice in modern blast furnace stoves.

'The reducing gasv in iiues 22. is preheated by.

hotf gases vfiowingaroundv `thern from the com. bustion vchamberthrough-a series offhorizontal-r' The capi structurer 38ffor the gas 'vpreheateron which thefhearth-'rib sections IQal-restis' pflfrefra'ctory materia'hand passes,j 25,126,121; andi-'28.

gard heat vexchange;structures,zlcut'irr any'- eventl will be made tliefminiium dimensionziconsistent" of such thickness that the rateY of heat transmis-V sion "through the hearthv to theribs 18a and channels I9 supporting the' charge can be `heldv at substantially' the same temperature as that'.

of the reducing gas entering'the charge'. This is for the reason thatin order toeffect rapid heat transfer, a temperature 'differentialof several hundred degrees may be necessary vbetween vthe waste'gases surrounding the upper ends 4of 'the preheating ilues, and the temperature of the 'reducing gas leaving the fiue's.I VIt vwouldbe a. disadvantage to allow the top ofthe hearth 'struc-A ture to reach a temperature very muchv higher y than that of the reducing gas or the desired temperature in the charge, since there is danger of sticking or fritting to the hot surfaces.

4The heating gases flowing around reducing gas ues 22 are supplied by combustion 'chamber 5 as an integral part of the furnace support structure by 'extending the function of the top tie beams 4 which, by proper disposition will serve to provide framing for the manifolds 62, as shown; Each connection 63 is equipped with regulating means 64 which may consist of a butterfly or other suitable type of valve, by which the volume of air admitted to the manifold and consequently the degree of combustion of the' combustible excess reducing gas and gaseous vreduction'products can be controlled. The furnace roofarches l I are so arranged that the low .v-point cf'each succeeding arch is higher than that which is preferably fired byA cleaned spent reducing gas from the furnace.' Air vand gas are introduced under controlled pressure@ throughv suitable burners 56. The hot products of combustion pass from the combustion chamber 5 through the opening 51 directly into the waste gas passages 25 circulating backl and forth throughthe preheater courses around flues 22 as described previously, whereby the column of reducing gas rising in flues 22 is first heatedby the cooler combustion products and nally by the hottest gases immediately before it is projected into the charge, meanwhile increasing its pressure as it is heated. From the last course 28.' thev combustion gases pass vdown into the air preheater 6 after which they Vexhaust to a stack flue 58. The stack flue 58 is preferably equipped with a regulating damper59 for the purpose of maintaining the required back pressure of waste gases all the way back to the furnace combustion chamber 5. Wastev gases are discharged to the atmosphere through a suitable stack 50.

The air preheater 6 is preferably built as an integral part of the reducing furnace to simplify the construction requirements necessary Afor hclding'the unit at a controlled pressure above atmospheric to minimize leakage losses, as previously mentioned. In the preferred'formshown, air preheater 6 consists of suitable vertical metal tubes 48'supported between upper and'lower deck plates 49 and 56. The deck plates 49 and 50 are provided with vertical of the tubes with sealing collars 52 so that by lling the deck plates with a layer Of'sand or other suitable material, the connections may be sealed against leakage. Y

The furnace waste gas passes down through the air preheatertubes 48, and the space around the tubes is preferably divided into a number of passes for the air by means of horizontal bales 53. Air is supplied to the bottom pass from a blower 54 and leaves the preheater from the top pass to enter an insulated air duct 55, which ex-` tends along the length of the furnace to supply air for supporting gas combustion at the burners 56 of the preliminary for the secondary partial combustion under the furnace roof arches il, as will be described later;

The furnace top or roof construction consists f a series of nat sloping arches H each so inclined as to reflect heat diagonally downwardly toward the charging end ofthe hearth. Pre-` heated air from preheater 6 may be introduced under each arch Il from manifold duct 55 through supply ducts 63 and S2 to multiple ports or openings Si.' A series Yof theset openings 6l.

thimbles l, and the top Y combustion chamber 5 andV of the'previous arch, thereby preventing undueincrease in the velocity of the gas flowing toward gthe gas outlet l5 near the discharge end of the furnace.

The spent gases from the furnace leave at the outlet l5, thence out through a duct I6 and through a blower 65 `exhausting to the rotary iore dryer 66. The gases are exhausted from the dryer 66 through the fan El and pass on to the gas cleaning equipment 58 for removal ofl entrained 'dust and to cool the gas and condense moisture from the reaction and partial combus- `tion. Part of the gas from the cleaning equipe ment 68 is supplied by pipe 1l to the burners 55` of the'combustion chamber 5 as previously described, and the remainder to meet the heat requirements of the gas reforming apparatus 69.

1A portion of the cleaned gas may also be rccircu lated Vback to the furnace through the reducing gas main 10 to supply the manifolds 48 and 44. The spent gas main 10 will preferably be connected to, and supply, about the first third of the -*length of the hearth, where it may be desired to use clean spent gas or an admixture of spent gas to fresh reducing gas.

The ore for the reduction process may be fed in finely-divided state to the dryer B6 through a feeder'12 from astorage bin 13.' If desired, a aid.-

small percentage of finely-divided carbon to inthe reduction of the metal may be admixed with the ore in the bin 13.

of air or the escape of spent reducing gases frorn the dryer E6, and may be driven by a variablel speed gear and motor unit 14, which may be con-'= trolled to hold the rate of the ore feed at a vol-2 innel in accordance with taking place in the furnace. The dried ore discharges from dryer 66 through the distributing chute 29 to feed all the channels I9 across the width of the furnace. A small percentage of carbon may also be added at dition to or instead of at the bin 13.

The product from the furnace hearth falls. through the discharge opening or duct 33 as pre-i viously described, thence out through the bottom of the furnace, and through a connecting chute 15 to suitable briquetting machine or other compact chine 16'is equipped with a sealed discharge 11 to prevent the permit pressing preferably quenched and discharged through a conveyor 18. l

In operation of the apparatus ofthis invention The feeder 12 is preferably arranged to provide a seal against ingress the rate of reduction 29a if desirable, in ad.-4

escape of reducing gases and to" or working the powder in a hot; reducing atmosphere. The compacted productiemosphere." In `any case, only 'part 'ofthe spent gases may be used foi-one preparation, the'rbalance may be taken directly to the cleaning apparatus for use .in preheating the fresh reducing gas and air, The ore feed to the dryer Gnis maint'ainedby the feeder 'l2 at Ia rate which can be set or varied in accordancewith thefurnace capacity kas affected by theraw materials -used and the product tcjbe 'madal The hct'ore4V from the dryer dropsdown through the shortest posisible chute 29 directly into the-furnace.V ,"I'hu's, the lengthof hot gas vand ofv hot ore 4paths is reduced to the minimum by the flow clrcuitsmade possible with the furnace andI drying-reduction gas cycle according to the present invention, resulting in proportionately decreased heat losses.

In the present invention there is thus provided a permeable hearth, -Which permits controllable charge movement induced by reducing'g'as'agitation producing a state equal to fluidity; which is not restricted as to'width of gas slotopening; which can use a varying depth of charge which will allow rabbling if desired';` which will not permit charge backflow; which is cleanable and 'may with reasonable ease-bel opened-for'inspection; which is not restricted to metallic construction; and wherein the method of heating Aeliminates excessively hot surfaces'incontact Withthe re,-

ducing charge gasegV .,..Y

The present inventiomby taking advantage of the'continuous stream-of reducing gas? blowing and" excessive preheat in reducing up from the charge lande-creating a 'protective blanket above it; making use of `indirect'partial combustion of this gas under radiant archesfthus provides an eiiicient direct secondary heat source to supply any deiiciency'from an indirect'primary heating means, whereby the total-heat rey quirementof the reducing'- operation can-be -met with goodeconomy, especially as the gas cycle preferably also includesa subsequent means (for transfer of the exit spent gas sensible heat to raw gre,

It wm be evident that bythe cycle of gases provided only one gas cleaning system lis re.- quired, whereas if the ore'were preheated by hot gases from some other source, it would be necessary to provide Yseparate sets of vcleaning appara- 'tus for both furnace and dryer with proportionately higher installation, maintenance` and operating costs. At the' sameV time a certain portion of the entrainedldirt'fin theexit spentgas from. the furnace will be trapped by the charge in the dryer and thus be recycled directly to the furnace with'the-net dust loss lowered accordingly.

The A invention by its combination heating method eliminates asfar'asvpossible the losses connected with indirect firing Vwhere the gas must first be cleaned, cooled and rehandled. At

the' same time it avoids'the retarding effect assodated with` ccrit'acunguthe cnargebyhign nitro-y gen gas or by excess CO2 and H2O-products of l combustion, such.A as',V much" slower operation, lower output and proprtionately 'higher heatv consumption.V r 'Y It will also be evident that the heat'input throughout the length of the furnace may in the present .inventionV be adjusted by regulating the admission ofr combustion air to the different arches so a's to releasejradiant heat into the charge as desired tom'eetV or modify the requirements Aof "the Yreaction1 zones throughout the lengthk of the hearth. Bye-thus using a responsive secondary heating means, a degree Of QODEIQI.

gaseous reductants.

While a preferred embodiment of the invention has been illustrated and described herein, itis to be understood that the invention is not limited to structural details of apparatus or to the-reduction of ores, but is applicable to the treatment of finely-divided materials While aerated in the manner described. vFor example, the process is equally applicable to, and the apparavtus may be used for other metallurgical orchemical treatments, such asroasting fine ores, the various steps involved in nickel carbonyl treatment, and the like.

I claim: Y

'1.- The method of treating finely-divided material, which comprises feeding a layer of vthe material upon a horizontally placed hearth provided with V-shapedV troughs extending from the feed end to the discharge end of the hearth, so injecting astream of fluidizing gas into and transversely of'the bottom of the trough at spaced points along the length of the trough and into the layer from'below the'same that the interstices between the particles on the hearth are permeatedbyv the gas and the particles in the layer are suspendedttherein and by so injectingy the gas, causing said 4particles Y so' suspended therein to describe a circular path beginning approximately at the bottom of the layer, progressing upwardly toward the top thereof, there dividing into two streams moving oppositely in adi- `rection transverse to the hearth, and then descending independently toward the gas stream `for merging near the source of gas injection to orifices in the bottom portion of said troughs, a hood over said hearth comprising` a plurality of reversed arches extending transversely of the troughs, inlets for the admission of a combustion supporting gas between the arches at high points inthe hood, and an outlet for gases in the hood in the end portion of the furnace.

3. In apparatus for treating finely divided material with lheated gases, the combination of a chamber, a substantially horizontal hearth comprising a trough, gas inlet nozzles in the bottom of said trough horizontally Adirected into said trough soas to direct the gases against the walls thereof` and thenupwardly through the finely dividedmaterial in said trough, feeding means in one portion of said chamber and discharge means in another portion of saidV chamber, said hearth feeding means, and discharge means being so constructed that said nely divided material will comprising'a trough, gas inlet nozzles in the' bottom of said troughand horizontally directed into said trough, some of said nozzles being directe'd in one direction andothers being directed in substantially the opposite direction, so as to direct the gas in generally opposite directions and then upwardly through thev material in the trough, feeding means'in vone portion of said divided machamber and discharge means in another portion of said chamber, said hearth feeding means, andV discharge means being so constructed that said finely divided material will ow through said chamber by gravity.

CARL J. WESTLING.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Number 14 I Name Date Vogel-Jorgensen June 17, 1941 Chance Feb. 29, 1916 Ridge May 13, 1930 Richardson May 21, 1940 Ahlman Nov. 5, 1940 Morton et al Sept. 7, 1937 Fitch Mar. 28, 1939 Brasseit June 23, 1942 Hartley Sept. 22, 1942 Brassert et al. Apr. 13, 1943 Huppke Feb. 11, 1941 Odell Dec.l 18, 1934 Toogood Dec. 21, 1909 Rudbach Jan. 27, 1942 FOREIGN PATENTS Country Date Great Britain Dec. 22, 1932 Germany Sept. 5, 1930