[1]il@@'atenteel Mar. a ,all 19.30 197519142 UNITED STATES PATENT OFFICE W-DWARD J. FOWLER, DECEASED, LATE OF REDWOOD CITY, CALIFORNIA, BY EDITH MARY FOWLER, EXECUTRIX, OF REDWOOD CITY, CALIFORNIA, AND DUDLFY BAIRD, OF BER:KELEY, CALIFORNIA, ASSIGNORS TO 191CHOLS COPPER COMPANY, OF NEW YORK, N. Y., A CORPORATION OF NE-W YORX IDULTIPLE HEARTH FUFXACE Application filed llarch 8,19PS. Berial'LVo. 260,039. This invention relates to multiple hearth roasting furnaces and more particularly to methods and means for conti-olling temperature conditions at the various hearths 6f such furnaces. Also the inveiition as fo certain of its phases rela'es, to the construction and operation of furnaces having a substaiitially greater number of hearths than has heretofore been embodied in furnaces of this general type. The objects of the invention include the provision of furnace constructions of the class indicated, and also methods of operating such furnaces, which will be depenclable, relatively simple and efficient under various conditions, and in which the treatment of various kinds and grades of material may be accurately controlled. Various further and more specific objects. 20 featlires and advantages will clearly appear from the detailed description given below taken in connection -with the accompanying drawin(ys which form a part of this specification and illustrate merely by way of ex2r, ample one embodiment 6f the apparatus of the invention. The inverition consists in such novel fe,,itures, arrangements and combinations of parts as may be shown and described in con30 nection with the furnace liereiii disclosed by -%vay of example only @and as illustrative of a preferred emb ' odimeiit, together ivith stieli novel metbods aiid steps of processes as may be described herein. 35 The drawin(y comprises a vertical sectional view, partly broken away, through h furnace comprising one embodiment of the iiiveiition. The furnace a illustra'ted may be of the 4o s.ame general class as that shown in numerous patents to J. B. F. Herreshoff, as for example No. 976,175 of.-November 22, 1910, and may i--corporate if @desired various improvements such as for ena.mple the improved 45 shaft and rabble arm construction sliown in the copending application of Dudley Baird, Ser. No. 140.230, filed October 8, 1926. A pluraliiy of vertically spaced or superposed hearths is indicated and desio-nated 5o respectively by the numerals 1 to 12. These hearths may -be surrounded and supported iii the conventional ma-nner as by a cylindrical furnace wall'13. A rotatable and iiiternally cooled central shaft 14 extends verticall y up tlirough the center of the furnace and is provided with rabble arms as at 15 and 16. In the embodiment shown, two opposit ely directed rabble arms are provided to cooperate with each hearth area in the usual manner. Suitable rabble teeth as at 60 17 are provided along each of the rabble arms for advancing the material being treate d successively over each hearth down throug h the furnace. W hile in the drawing, 12 hearths only are 65 indicat ed for simplicity, it will be understood that various features of the invention are applicable alike to furnaces having a numbe r of heartbs in the nei(Yhborhood of 12 and to furnaces having a substantially 7( larger number of hearths, for example as many as 25. Th e central shaft 14 as here illustrated, may be provided with an i.nternal conduit as at 18, the rabble arms being also provided 75 with inner conduits of any desired well known form communicating With the condiiit 18, whereby cooling fluid such as air carrie d by the C'onduit, 18 may be allowed to pass through -the conduits of the various 50 rabble arms, and tbence back into an annular space 19 between the conduit 18 and the walls of the shaft 14. The cooling fltiid for example may be introduced through the usual adjustable damper intake at the end E;5 of the conduit 18 at the bottom of the f Lirnace and the same fluid or a poi,tion tliereof, after having circulated thr,ough the various rabble arms. may be discharged froin the top of the shaft 14 as through an adjlistabl@ go darnper 20. At various of the bearths. or if desired at all or substantially all of ihe besrths, the shaft 14 may be pr6vided with sockets or attaellill(y meaiis as at 21 clesifyned to receive 95 lieat absorbing or radiatizig arms as at 22. The sockets 21 as shown iiiay be conveniently located intei-niediate the rabl)le arnis 15 and 16. The ra(liating tinits 22 may be made commuiiicative through the sockets 21 with ioo
[2]2 L,751,142 the coolirig fluid conduit 18 at their inlet ends and with the annular space 19 at their outlet ends, whereby a circulatory path is provided throtioh the radiatin- units, thus pei@mitting cont7rol or alteration'@of the teraperature condiiions on hearths which are provided Nvith such radiating means. In certain processes it may be desirable to maintain some of the hearths at a relatively low 10 temperature, or combustion conditiolas may be such as to require a considerable cooling effect on certain hearths. This may be generally accomplislied by using one or two of the radiating units as at 22 over such 15 hearths, or if these prove insufficient to accomplish the desired cooling, @either a greater number of these units may be applied at each hearth, or similar but larger units as at 23 may be I used. As indicated at 20 21', the su- porting sockets for the rftdiatin(y arms may be r.,.,.ord or less closely spaced so as to provide for the desired number of arms at each beartli. iVIthoLigh the radiatingr arms as here shown comprise a single 25 conduit, it will be understood that various other forms and shapes of radiating units pight be utilized to secure the desired cooling effect. Also it will be understood that the, invention is applicable equally to various 3o furnace constructions well known in the art, having central shaf t arrangements other than tho, particular double concentric wall construction shown. If for particular processes it is found to 35 be unnecessary to use radiating units as above described at certain,hearths, the socket. provisions such as at 21 may be still provided for manufacturinc, convenience and standardization of shaft7parts, the unu@ed 40 SOCkets being then covered either temporarily or permanently by cover plates as at 24. At other hearths, the lowermost hearths for example, it will not oiily be found to be undesikable to pro'vide coolin ' g means with 45 sses, but the efficie. . nace may be impro'ved by raisingr the temporature at such hearths. For this purpose "hot air arms" as at 25 may be p@ovided"to fiti if desired, sockets such as at 2.1 inter5o changeablv with th6 racliating units, S6 that sections of the shaft 14 may be standardized and still have provision for either tvpe of arm. The "hot air arms" 25 are ma(fe communicati-%,e with t)ie aianular space 19 sfo as 55 to dischargb a part of the air therefrom directly oti 'i@ the material under treatment at the hearths. The air or other fitiid medium th-us d@ischar@ed will -of course be preheated to a considerable extent b reason of 6o having previously passed through the radi@ at4ncr -Linit and the rabble arm cavities. A convenient means is therefore provided for reducing the temperature on certain hearths to the extent desired and for transferring o5 the heat thus acquired in the cooling-memany proe(@ ncy of the fur- , dium, to other hearths where the efficiency of operation may be enhanced by an increase over the temperature which would otherwise prevail. If desired, for certain roasting operations the furnace temper,atures at the 70 various hearths may be substtntially equalized in this manner. When "hot ait arms" as at 25 are used in lieu of radiating units at the sock-ets 21, the openings communicating with the, interior 7,5 shaft conduit 18 may be closed off as by plugs as at 26; similar pltigs of course may also be iised -vvhenen,er the plates 24 are necessary. In sbme instances it is desirable to provide at certain hearths, particularly at the lower 80 bearths, a greater amount of preheated air than cin be admitted by the arms 25. In tliat-event, one of the rabble arms at such liearths inay be replaced by a relatively large "h6t air arm" as at 27; 85 To achieve efficient roasting conditions, it is geiierally desirable to locate the openings of the -arms 25 at points where tlie- preheated air will engage the falling material as it passes from one hearth to the next. For i)o example, the arms 25 at hearth #10 may be placed so that the preheated air impinges directly tipoii the material droppino, from the hearth #9 through the central liearth - opening 28. The arms 27 if desired, may be 95 so @mewliat larger and longer than the arms 25 so as to widely distribute the preheated air over the heartli areas. As to the design and constructional details of other parts of the furnaci@ not specifically 100 referred to herein, the usual practice may be followed as in the construction of other well known furnaces of this general type. The above described radiating or heat absorbin@, arms are particularly useful in many 105 roasti@'g operations when placed at the interrnediate hearths, since there,is 6ften a tendeiicy for theii@termediate hearths to become overheated as a result of the rapid chemical actions taking place in the materials under 110 treatment when they arrive at the mid-portion of the ftirnace. On the other hand, as the ores,or other materials arrive at the lower hearths'of the furnace, there is often a tendency for the temperatures to liecome too low 115 to insure thorough treatment, inasm,uch as the heat of oxidation will Lisually be less at the lower hearths, the material havino, been previo-usl@ exhausted of most of its com,bus@tible or oxidizable substances in the upper or 120 intermediate heartbs. Thi invention therefore provides a convenient means for traiis, ferring the excess heat of the intermediate hearths to the lower hearths where such heat -is often needed to give the ores or other rna- 125 terial a COM'plete and final roasting. The heolt'absorbing arms embodyiria this invention sho-Lild of course be clo?@rly- distinguished from the mere use of air cooled@ rabble arms in which the Ttin-c.tion of the cir- 13C
[3]1,751,142 3 culated air- is to merely maintain the rabble arms and teeth at temperatures which will prevent their deterioration or distortion. While the rabble arms at the various hearths may ordinarily be madesubstantially alike as to form, number and arraiigement, in order to insiire a uniform flow through the furnace of the material under treatment, on the other hand the heat absorbin(y arms at 10 each hearth may, of course, be n@ade independent of such arms on the other hear@lis, as to form, number, and arrangement. The cooling arms provide a coolino, effect substantially in excess of any normal cooling 15 effect ar'lsing from the use of the usual air cooled rabble arms, since the heat absorbed from the furnace through the necessarily relatively thick walls of the rabble arms is small as compared -with the heat which,,may be 20 transferred through. cooling arins a's at 22 designecl particularly for that purpose. Although for convenience and for obtaining substantial uniformity of cooling effects throughout the area, of the hearths it is de25 sirable to arrange the, rabble arms and cooling arms alternately as shown, it will be uiiderstood that approximately equivalent results might be obtained by other arran-ements or by providing the radiatino,, units-as 30 substantially unitary structures in con]iinc_ tion with the rabble arms. Accordino, to this invention, the circulating. coolini'fluid serves as many as three functions; namely, the necessary cooling of 3:, the rabble arms and shaft is accomplished, temperature conditions throughout the furnace may be equalized or controlled with a wide ranoe of fleicibility, an.d a sotirce of preheated air is provi(led at certain hearths 40 -Lor iii-,iiring a, very effective supply of oxidizin(y fluid siifficient for proper cornpletion of t,h@ roasting processes. At the same tiiiie the beat available tbroughout the furnace is. econotnically utilized. 45 In i-ecent times it has. become the practice with furnaces of this general type to treat materials embodying. large quantities of finely divided flotation concentrates. Because of their fineness such mixtures ofteii 53 do not oxidize readily on, the 1-iearths; tliei-e bein(y few voids in such fine matei-ial, the oxiilizin(y action tends to become smothered. We liave found that this effect may be oiei-come in a desirable manner by providing a subs il.3 tantially larger numbei- of beartbs witli a consequent correspondingly large jiumbelOf "material drops" or places where the material dro' s froin one hearth to the text through the aseendina liot oxidizing gases. (;o At these "material drops" the multitudes of finely divided paiticles have ample oppor_ tunity f@r sufficient contact with the oxidiz_ ing gases notwithstanding the degree of finetemp erature conditions throughout the rnace becomes more difficult, but any difficulties in that respect may be readily met by the heat transferring means provided-in the man ner above dese'ribed. With ma-ny roast- 7,3 ing operations it is desirable to provide relativel y cool hearths at the top of the furnace (the top fou@ or six hearths for example), and also a number of relatively cool hearths at the very bottom of the furnace, (as many 75 as four or six hearths) and this is ordinarily per missible only where the numbe@ of hearths is increased to in the neighborhood of 12 or more. According to our inventibn these cool er hearths may be maintained at tem- '30 pera tures in the neighborhoo-d-lof'SOO' F. to 1000 0 F. for example. On the other hand, in certain roasti - ng operati ons as above indicated, it is desirable to have hot discharge calcines and in connection 85 with acid manufacture, particularly chamber acid, it is aesirable to have a hot gas disc harge and cool cinder discharge. With som e sulphide ores the free sulphur ignites at the top hearth, resulting in h - .igh tempera- .0.1) tures at the upper hearths. It is obvious, how ever, that a furnace with a large number of hearths as above described, particularly if equipped with the heat absorbing arms and hot air arms, will permit operating 9r3 cond itions satisfactory for all of these vaiious processes and at the same timp, provide a sufficient number of "material drops" to insu"e rapid and thorough i)rocessinlr notwitlistaia ding the fineness of tfle material. 100 I n the treatment of zinc ores where the furn ace is fired on the lower hearths, furnace s as above described are pai-ticularly desirab le in tfiatoxidationmiiybegraduallyearried out on several or numerous of the hearths 105 inste ad of largely on one or two heatths, as has generally occurred in practice. Furnace s embodying this invention are adaptable - to a wide variety of other uses such as calcinin g of fuller's earth, filteting clays, filtrol, 110 limes tone, dolomite, mercury ores, soda compou nds, copper, iron, zinc, tin, antimony and arse nic ores, drying operations, etc. In thes e various operations the' temperature co'n ditions -within the furnace may be so con- 115 troll ed as to'support combustion from tlip'ores br material treated, or of course, the furnace may be fired externally. Whilo the invention has been Glescribed with respect to certain particular preferred 1!.10 examples which, give satisfactory results, it will be understood by thos6 skilled in the art after understanding tlle invention, that various changes and modifications may be made 12'5 without departing from the spirit and scope of the invention and it is intended 'therefore in the appended claims to cover all iiess of the material. Howe'ver, as the num- such changes @and modificaiions. G3 ber of hearths is increased, the control of What is claimed as new and desired to be 130
