US1863185A - Metallurgical furnace - Google Patents

Description

Jam@ 14, 1932. E, H BUNCE ET AL 1,863,185

METALLURG I CAL FURNACE Filed March 24, 1950 INVEN OR I Wmv-s ATTORNEY Patented dune 14, 1932 Unirse stares EELH. BU'NCE, CLARENCE J. LENIZAND GEORGE T. MAHLER, 0F PALMERTON, :PENN- SYLVANIA, ASSIGNQRS TO THE NEW JERSEY ZINC COMPANY, OF NE'W RK, N. Y.,

CQRPGRTION OF NEW JERSEY METALLURGICAL FURNACE This invention relates to metallurgical Jfur-l heated reduction furnaces, such as are employed in the reduction of zinci'ferous `materials.

lt has heretoore been proposed to build-up externally heated chambers or retorts for the v1.0 reduction of zinciferous material with a multiplicity of pieces vof temperature-resistant material of good heat-conducting qualities. The pieces of temperature-resistant material usually consist of refractory material,

35 such as vdensely pressed silicon'carbide bricks,

copatentee.

whichare carefully assembled to form a rsuhstantially Zinc-vapor-tight chamber. Such a huilt-up retort is disclosed in United States Patent No. 1,680,726, of which one of us is a The patent more particularly discloses a vertically disposed and externally heated retort huilt-up ot a multiplicity of suitable refractory' brick fitted together with plain butt joints. Charge materials in 5 the form of agglomerates are progressively passed downwardly through the retort asthe zinc reduction step proceeds to completion. While such built-up retorts are a marked improvement over the monolithic and built-up retorts heretofore employed, in time they tend to rupture. This rupturing of the retorts takes place more particularly in 'their upper sections.r Considerable time, labor and expense are involved in repairing or re-buildin such ruptured retorts.

When employing a retort such as that disclosed in 'the above mentioned patent in the reduction of zinoiferous material, it is customary to maintain a temperature of anorexi- 40 mately 1250o C. throughout the heightl hf the 4.5 per end of the retort and they become hotter heating chamber. Since the charge materials .are progressively passed through the retort, as the reduction step proceeds to completion, the agglomerates are relatively cool in lthe up and hotter as they proceed through the retort. ,An externally applied temperature of approximately 1250" C., in the case of some zinc ores at least, seems necessary in order to drive suliicent heat into the core of the charge vset up to remove or eliminate the last traces of available zinc. This means that toward the end of the reduction process the charge materials will thus have risen to a temperature of close to 1250o C.

in the case of the charge materials confined in the upper section of the retort, it is to be noted that the cool charge takes on heat rapidly, thus tending quickly to ahstract a very large amount oi heat away 'from the inner face ofthe retort walls. As the heating operation continues, the agglomerates next to the inner retort walls gradually reach their temperature of reduction. The agglomerates close to the inner retort Walls are soon suliicientlyheated to reach their temperature of reduction. rThe resulting zinc reduction step is itself an endothermic reacmately 12500 C.) and the inside of the retort walls at its upper section (approximately OGOO C), numerous stresses and strains are' in the retort walls, which are proportional to the temperature diiierential, between the inside and the outside of the Walls. These stresses and strains intime tend 'to rupture the retort walls.

A different situation, however, exists in the lower section of the retort. By the time 'the agglomerated' charge materials have reached the lower section of the retort the reduction step itself will have proceed to, or almost to, completion. Since these agglomerates have been subjected to continuous heat- ,ing during their passage from the upper end to the lower end of the retort, the are no longer relatively, cool and have ta (en on a temperature substantially equal to that maintained at the outside of the retort walls. Furthermore,l since the reduction reaction has gone to substantial completion, `further amounts o heat are not taken up to el'eet the reduction reaction.

lIn other words, the charge materials confined in the lower section of the retort may be regarded as a substantially inactive or dead load that finally attains a temperature substantially equal to that provided on the inv G bebuilt in a. single section, itis readily sub- `lower end of the retort.

side of the retort walls. The spent charge materials adjacent to the inside ofthe retort Vwalls thus serve to take 11p-the temperature shock that the inner walls of the retort are normally subjected to when fresh charge inan terials are being heated. This means 'that there is less temperature differential between the inside and thev `outside of the walls of the lt therefore follows that stresses and strains are not readily set up in the walls of the lower retort section, and therefore they are not as susceptible to rupture as are the .walls of the upper retort section. y

In copend'ing application, Serial. No. M8,- 914, filed February 17, 1927, there is disclosed an apparatus for smelting zinc coinprisin a vertically disposed metal retort adapted for external heating., The charge materials, preferably in an agglomerated form, may be progressively passed downwardly through the retort as the reduction operation proceeds to completion. Metal retorts offer a number of desirable advantages; especially over relarge quantities of heat ma torts built-up of refractory bricks. In the first place, a metal retort may have a wall of less thickness than that of a refractory brick/retort, therefore a considerable amount of heatmay more readily be passed through the. walls of such a metal retort and into the charge materials' confined therein', vand thus the temperature differential between the outside an the inside of the metal retort walls is very low. A s va consequence, less heat is required in the surrounding heating chamber to hold a given temperature within a metal retort. This means that a metal retort may be heated with less fuel consumption than in stituted as a unit -for one that has failed. In the case of a refractory brick retort, on the other hand, considerable time is required to tear down an old retort and .build up a new one. l t

Metals and alloys are well adapted to with stand the heat shocks produced by the in# sertion of' fresh batches of charge into the top of a verticle zinc retort of the type discussed here. The fresh charge at the top of the retort since the reaction between zinc oxide and carbonin the charge is endothermic, acts as a cooling agent and tends to keep the top of a metal retort from reaching a temperature at which it would soften to a dangerous de fictitious.

nasales degree ofheat. In the case of refractory retorts, the reverse is true: a refractory retort huilt of appropriate materials 'willstand the high bottom temperature to which it is subjected on account of the progressive elimination of Zinc from the charac better than the.

heat shocks produced at the top by the in sert-ion of fresh cha-nge;l

A. study of reducing operations conducted within a.vertically disposed and externally heated retort shows that `the ideal retort would be one constructed of materials which will at its top section deliver to the inside wall of the retort a large quantity of heat somewhat above the temperature of reduction (950 C.) with the least possible heat diderential across the thickness of the retort wall, ai1d which will, as the charge moves downwardly, deliver at thelinside wall of the retort the desired quantity of heat at a gradually 'increasing temperature; until at the lower section of the retort the inside wall temperature approximates 12500 C. l'hese 4conditions require that the heating chamber of the furnace be constructed or equipped Vwith devices capable of controlling the conibustion of fuel so that ythe heating chamber temperature rises from that required to deliver an inside wall temperature somewhat above 950 C. at the top section to an inside retort wall temperature of about 1250" C. at

the lower section of the retort,

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As a result of our investigations, we have ideal operating conditions just enumerated.

A combination retort has been developed which for the most part satisfies these speci- In the case of a vertically disposed and externally heated retort, we have found that avmetal upper section of suitable construction may advantageously be employed which will withstand temperatures of at least 1000O C, in a reducing atmosphere on the inside of the retort, and in a reducing or oxidizing atmosphere on the outside of the retort for a relatively long period of time without failure. l The lower section of the retort is constructed of suitable heat refractory material, such as brick, which will withstand a temperature 'of 1250 C. in the same atmosphere for a relatively long period of time without failure. We have also found that a oint may be provided between the refractory section and the metal section of the retort that is substantially zinc-vapor-tigbt.

Our invention therefore contemplates a metallurgical furnace comprising an externally heated reduction retort built-up in part of refractory material and in part of metal.,

In the present preferred practice of the in- Vention, the metallurgical furnace is provided with a vertically dispose-d and externally heated reduction retort, the lower section of which built up of a multiplicity of pieces of suitable heat refractory brick of good heat-conducting qualities, while the upper section is constructed of suitable metal, preferably an alloy, adapted to withstand the prevailing temperatures and atmospheres. A joint is provided bet-Ween the refractory brick section and the metal section that `is substantially zinc-vapor-tight. The retort is centrally disposed within an appropriate heating chamber. Suitable fuel may be introduced into and burned within the heating chamber to provide the 'desired temperatures and quantities of heat.

When operating the metallurgical furnace of the invention in the reduction of Zinciferyous materials, the heating chamber of the furnace is maintained at a temperature gradient of approximately 12500 C. at its lower end and about 10000 @-10509 C. at its upper end. Thus, the temperature at the bottom ofthe refractory brick retort may be maintained around 1250O C. The temperature at the joint between the refractory and metal sections of the retort is maintained at approximately 1100o C., and the temperature around the upper sect-ion of the metal retort is maintained at about 1000l050 C.

The gradual increase in the heating chamber temperature from the top to the bottom I of the retort may be brought about by the 5 burning ofthe fuel at the bottom of the heating chamber and cooling the products of combustion as they rise toward the top of the heating chamber. Thus, the hot combustion gases may be cooled by introducing a cooling agent, such as steam or air, into the central and/or upper sections ot the heating cham- 0r, in utilizing a down-drop, the combustion fuel may be introduced at or near the top'of the main heating chamber, and air maybe introduced at various points throughout the height of the chamber to regulate the combustion of the fuel to give the de sired temperature gradient; or, a separate DQ heating chamber may be provided for each retort section.

The novel features of the present invention, it is believed, will be better understood by J Fig. 2 is an enlarged sectional detail of a telescoping joint shown in Fig. 1.

The apparatus shown comprises a main furnace structure l0 resting ou concrete foundations 1l. The furnace structure comprises 3") a bottom 12, side walls 13 and an arched roof reference to the accompanying drawing, tak-` en in conjunction with the following descrip- 14C constructed of suitable refractory material, such as heat-resistant brick. These furnace linings (define a heating chamber 15.

A suitable number of ports 16 and 17, eX- tending completely through the side walls of the furnace structure are appropriately spaced throughout the height of the furnace structure. These ports are adapted to receive air and fuel, such as pulverized coal, oil, gas, etc., which may be burned within the heating chamber. Electrical energy may also be employed appropriately to heat the furnace and to eli'rct the desired reduction operation. Une or more port-s are preferably provided at or near the lower section and at or near the middle of the heating chamber. in outlet 18 is provided at or 'near the upper end ofthe heating chamber for the withdrawal of heating gases. This out-let preferably connects with a stack or chimney (not shown).

A number of relatively small openings 19 are Iprovided through the side walls of the furnace structure at spaced intervals throughout the height of the heating chamber for the taking of pyrometric readings. An outer metallic casing 20 completely surrounds the main furnace struct-ure. The space between. the top of the metallic casing and the arched Iroof is filled with suitable heat-insulating material 21, such as diatomaceous earth.

A. lvertically disposed retort extends centrally of and completely through the heating chamber. The retort shown comprises two connecting sections, a lower section 22 constructed of suitable refractory material, such as refractory brick, and an upper section 23 constructed of suitable metal, such as an alloy, that is adapted to withstand prevailing temperature and atmospheric conditions. lt is important that the two sections of the rctort be joined hermetically. That is to say, the joint between the two sections should be substantially zinc-vapor-tight. Moreover, the joint should be sufficiently tight to prevent retort gases from escaping into the heating chamber, or heating gases in the heating chamber from scoping` into the retort.

ln the construction shown in the drawing, the lower end of the upper (metal) section is flared out to form a lip, shoulder or flange 2li. This flanged section forms a base for the support of the metal section of the retort. A. suitable connector casting 25 is placed between the upper end of the lower retort (refractory) section and the lower end of the upper section. This connector casting base is circular in plan, with an opening in the center to conform to the configuration of the adjoining retort sections, and 'lA-shaped in crosssection. The lower half of the casting embraces the top of the refractory retort section and rests thereon. An intervening layer of silicon carbide fines is preferably provided on the upper face 26 of the refractory retort section, so that the casting may be non-leakably 5 of the refractory retort section, in order to provide as far as possible a non-leaking o int.

The upper half of the connector casting.

serves to receive the flanged portion'of the lower end of the upper metal retort section. The space 27 between the outer wall of the end of the metal retort and the inner upper portion o f the connector casting ring is filled with silicon carbide fines, sand or similar material to act as a seal. y

Batlle walls 28 are advantageously built into the side walls ofthe furnace structure. These bailles extend laterally across the heating chamber and are so positioned with respect to the ports located about Iridway up the heating chamber that heating gases or fuel introduced therethrough may be deviateed from and `kept substantially out of immediate Contact with the retort. The ports in question are shown in the side walls of the furnace substantially on the same level as the joint between the upper and lower sections of the retort. The baiiies are advantageously placed close to the joint in order to protect the same from direct contact with heating gases at their hottest zone introduced through the immediate ports. In fact, steam and/'or airmay be introduced through these ports to cool the heating gases thus protecting the metal retort section against over-heating.

Similar protecting baffles 29 are constructed in the bottom of the furnace in order to protect the lower retort section from immediate contact with combustion gases resulting from the burning of fuel introduced through the lower ports. fThe Vbailles may of course likewise be fastened into the side walls, or a combination of the two types of constructionmay be employed.

While the retort, or its sections, mav have any desired configuration, in the present preferred practice of the invention the retort is circular in outline, having an internal diameter of 15%E inches. The passageways of both sections of the retort are in substantial alignment with one another. ln order that the retort may expand and contract independent of the furnace structure, it is preferred that the retort be supported by the In the present instance, the lower section of the refractory retort is supported by the botfurnace structure at not more than one point.y

height of 9 feet 11 inches, and the metal retort section has an overall height of 10 feet 1 inch.

The lower end of the refractory retort section terminates with a sleeve member 30 which acts as an extension thereof. This sleeve is attached to the underside of the bottom of the furnace structure, and its passageway is in substantial alignmentwith the passageway of the retort. Arevolving platform 31, moving about a vertical axis 32, is locatedA immediately below the lower end of the retort and sleeve. It is adapted to receive spent residues or agglomerates 33 and 'to discharge them as the platform isl revolved. l The upper end of/the metal retort section -movabl connectswith a metal prolongation 34, which may be constructed 0f wrought iron, into which the metal retort section advantageously telescopes (see 2), This metal prolongation preferably extends a convenient distance above the furnace structure.

The telescoping joint provided between the l upper end of the metal retort section and the metal prolongation comprises an annular band 35 of'flat iron, 21/2 inches wide by l@ inch thick, riveted along the inside of the lower end of the metal prolongation. The inside diameter of the annular band is suf- `icien'tly large to permit of the entry of the metal retort section, so that any expansion or contraction of the metal retort section may easily take place within the fixed metal pro.

longation. One or more layers of asbestos wick packing 36 are snugly fitted into the space provided between the upper periphery vwhich rests an eliminator structure B9 adapted to support and contain an eliminator 40. This eliminator structure comprises an outer metallic casing /ll that completely surrounds the eliminator, leaving a space adapted to receive heat-insulating material 42, such as coal dust. One or more doors e3 are provided at or near the lower end of the metal casing for the'remcval of dust coal in order to regulate thetemperature of the eliminator during reduction operations. The outermetallic casing may be of any size adapted to give an intervening layer of heat-insulating material of desired thickness. The metal casing is preferably open at Ithe top, or has an opening at or'near the top, for the introduction of heat-insulating material.

.A base plate 44 rests on the I-beams, which is adapted to support the eliminator struc- 'fractory material, such as heat-resistant brick. These brick are preferablv of the same general type as that employed in the building-up of the eliminator, i. e., silicon carbidey brick. The desired telescoping elfect may be obtained by arranging the joint brick in the form of inverted steps, as shown in the drawing.

It will be seen that the telescoping joint may be so constructed as toyprovide an eliminator of any desired cross-sectional configuration; The brick going into the joint are advantageously kept in alignment by means of a circumferential steel band 47.

An olf-take pipe 48 is provided at or near the upper end of the eliminator forthe withdrawal of zinc vapor and retort gases. It communicates with a zinc vapor treatment device 49. If zinc metal is to be produced, this device consists of a condenser. If, on the other hand,zinc oxide is to be manufactured, the device is one adapted to eil'ect the oxidation of the incoming zinc vapor. In the case of the manufacture of zinc dust, the device consists of a canister designed for the condensation of the zinc vapor into minute zinc particles.

Tlie upper end of the eliminator is provided with a charge feedin g device 50 that extends downwardly in the eliminator to a distance slightly below the gas and vapor olftake pipe, so that charge materials 51 may be kept therefrom; thus leaving a free passageway to and through the .olf-take pipe. A removable cap 52 lits over the mouth of the charging device.

The above described apparatus may be operated as follows in the reduction of zinciferous material, and more particularly with respect to zinciferous material containing objectionable amounts of lead and the like:

The cap 52`is removed and an appro riately agglomerated charge of mixed zinclferous material and oarbonaceous reducing agent is` fedinto the charging device 50. A suiiicient amount of the agglomerates are thus introduced until the communicating passageways yof the retortsections, the eliminator and the charging device itself are substantially lilled. The cap 52 is then returned.

Air and fuel, such as oil, are introduced Se through the ports 16 and 17.' As the combustion gases circulate around both the lower and upper retort sections, spent gases ultimately iind their way through the opening 18 and into the stacker chimney (not shown).

53 The highly heated combustion gases formed by the fuel introduced through the lower ports 16 strike the baille walls 29, kthus protecting the retort section 22 from immediate contact therewith. In a similar manner, the baiie walls 28 protect the joint between the lower and upper retort sections from immediate contact with the combustion gases resulting from fuel introduced through the ports 19.

Pyrometric temperature readings are periodically or continuously taken through the openings 19. Temperature conditions within the heating chamber are suitably regulated in accordance with the temperature gradients to be maintained.' In order to have a temperature gradient increasing from the upper end of the heatingl chamber to the lower end ofthe heating chamber, the hottest gases are preferably introduced through the ower ports. Asthe heating gases rise upwardly through the heating chamber, while swirling around the retort, they are gradually cooled. If additional cooling effects are desired, steam and/or air may be suitably introduced at various points ythroughout the height of the heating chamber. Thus, steam may advantageously be introduced through the ports 19. The relatively cooler steam contacts with the rising heated gases and tends effectively to lower their temperature. A cooling medium may also advantageously be introduced through openings 19, or similar openings provided in the side walls of the furnace structure for that purpose. As 100 pointed out above, it is preferred to maintain a temperature of approximately 1250 C. in the lower part of the heating chamber, and a temperature of approximately 1000-1050 C. in the upper end of the heatchamber.

The heat externally applied to both the lower and upper sections of the retort is ultimately driven through the retort walls and into the charge conlined therein. Since the upper metal retort section has a relatively 'thin wall, heat is readily transferred through its vwalls into the charge. As pointed out above, under ideal operating conditions it is preferred to have large quantities of heat transferred to the charge materials in the upper section of the retort. This desirable result is obtained with the metal retort section, while yielding a relatively small temperature diiierential between its outer and inner wall surface. On the other hand, it is also preferred to deliver the desired amount of heat into the charge materials in the lower end of the retort at increasing temperatures. This advantageous result is obtained when employing a lower retort section constructed of refractory brick, the walls ci which are suciently thick to withstand the elevated temperature.

When the charge materials confined within the retort are heated to their temperature of reduction, zinc vapor is liberated and retort` gases are evolved. Due to the natural buoyancy of the hot vapor and gases, theyV tend to rise upwardly. rIhis upward movement ofthe vapor and gases is preferably assisted by providing and maintaining a stack draft throughout the system. For this purpose, it is advantageous to have a retort of substantial height. Moreover, in the preferred practice of the invention, regulated amounts of gases, such as air, are admitted into the lower end of the retort.

As reduction proceeds to completion, the spent residues or agglomerates 33 are removed from the lower end of the retort by setting the revolving platform 31 in motion. The movement of the platform tends to withdraw spent residues. As fast as spent residues are removed, the inner column of agglomerates within the retort section tends to lower itself. thus effecting a progressive movement of theagglomerates downwardly through theretort. The cap 52 is again removed and further amounts of fresh charge materials are introduced into the charging device, to compensate for the spent residues that have been withdrawn from the lower end of the retort. If the process is to be operated substantially continuously, the cap may be removed and connection made with a source of material adapted to feed fresh agglomerates into the system as fast as spent residues are removed therefrom.

The liberated zinc vapor and evolved retort gases rise upwardly through the passageways of the retort sections, as agglornorates move downwardly. rlhe mixture of zinc vapor and retort gases ultimately finds its way into the eliminator 40, where it contacts with the hot body of agglomerates confined therein, and which agglomerates are aboutto be subjected to the reduction operation.

If the zinc vapor is contaminated with objectionable amounts of lead, dust, or the like, and it is desired to eliminate the same. the temperature of the agglomerates confined i within the eliminator must be carefully controlled. ln other words, under appropriate temperature conditions, the hot agglomerates confined within the eliminator are adapted to filter out the lead and dust without undue condensation of zinc vapor, while permitting the purified vapor to pass on. If the temperature of the agglomerates is too hot, provision should be made for removing the excess heat. This may be accomplished by lowering'the amount of heat-insulating material 42 in the metal casing al. Coal dust may readily be removed from the door or doors 43. On the other hand, if the agglomerates are not suficiently hot to avoid the condensation of-appreciable amounts of zinc vapor, additional heat-insulating material should be provided around the eliminator to inhibit dissipation of heat. This result may be accom- Lacasse fect the oxidation of the Zinc vapor. Fur` thermore, if zinc dust is to be made, the device consists of a canister adapted to condense theincoming zinc vapor into minute particles of zinc. v

A consideration ofthe structural features of the above describedvapparatus will readily indicate that the metallurgical furnace of the invention is 'peculiarly adapted for the reduction of zinciferous materials. The relative advantages and disadvantages of refractory retorts and of metal retorts lare so balanced against one another in the combined retort of the invention that the old disadvantages are minimized while practically all of the advantages of both types of construction are retained.

We claim:

1. An apparatus for the reduction' of zinciferous material comprising a vertically disposed and externally heated reduction retort, the lower section being built-up of a multiplicity -ofrefractory brick, the upper section being formed of suitable metal, the two sections being joined by an intervening casting vadapted to make a substantially zinc-vapor-tight joint..-

2. An apparatus according to claim l, in which the upper end of the metal retort section movably connects with a fixed 'metal prolongation.

3. An apparatus according to claim l, in which the upper end of the metal retort section telescopes into a fixed metal prolonga-` tion whereby expansion and contraction of the metal retort may freely take place within the metal prolongation.

4.A.n apparatus according to claim 1, in which the intervening casting is T-shaped in cross-section so that the lower half of the casting embraces the top lof the refractory retort section and rests thereon, and so that the upper half of the casting supports a ianged portion of the lower end of the metal retort section.

'5. An apparatus according to claim l, in which the joints between the retort sections and the intervening casting 'are sealed with an appropriate agent.

ln testimony whereofwe aiiix our signatures. l

EARL H. BUNCE. CLARENCE J. LENTZ. GEGRGE T. MAHLER.

EGG

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