US2373845A - Metallic vessel for high temperature service - Google Patents

Description

3 shans- Sheet 1 c. L. NORTON,. JR METALLIC VESSEL FOR HIGH TEMPERATURE* SERVIGE April 17, 1945.

'Filed odt. 17, 1942 April c. NRTON'. JR z,373.845

v METALLIC VESSEL FOR HIGH TEMPERATURE SERVICE Filed Oct. 17, 1942 :5 Sheets-Sheet 2 I I 'f i E w. I

8 !Hr %lg I f 6) o u I Lum ?H L V I I N VEN TOK A Char/s L Norton, jk

` April 17, '1945. c. L'NQRTON. JR 373345: i

METALLIC VESSEL FOR'HIGH TEMPERATURE SERVICE Filed Oc't. 17, 1942 3 Sheets-Sheet 3 v INVENTR..

Patented Apr. 17, 3945 simas METALLIC VESSEL FOR HIGH 'remem- TUBE SEEVICE Charles Norton, Jr.-, New York, N. Y., assigno.- i

to The Babcock &a W

ilcox Company; Jersey City, N. J., a. corporation of New Jersey Application October 17, 1942, Serial No. 462,359

's Claims.

The present invention -relates in general to the construction of apparatus for heating material to a temperature aboveooo F. and including a 'container or pressure vessel adapted to contain thematerial to be heated 'and'formed of a metal subject to corrosion when exposed to corrosiv'e conditions at such temperatures. More particularly, my invention relates to the Construction oi apparatus for the production of metallic magnesium by the reduction of a charge of a magnesium-containing material in a furnace retort under a substantial vacuum. as disclosed in my prior joint application with James Fletcher, Serial No. 450372, filed July 10, 1942.

ordinary iron or steel having a melting point of 2700 F.-2900 F. oxidizes comparatively rapidiy at temperatures above 930 F. and for this reason ferrous structures are ordinarily limited to use under service temperatures below 900 F; For effective resistance to scaling at high temperatures, it is usually considered necessary to usea corrosive resistant alloy steel for at least the' exposd surface of the structure." Even such structures ,are

not wholly satisfacto ry for prolonged use at tem-V peratures above 2000 F. and moreover are expensive to manuiacture and require a substantial amount of alioy metal. The problem is further complicated by the loss of strength and increase of permeability of plain and alloy steelsat high temperatures. r

Thegeneral object of my invention is the pro- Vision of apparatus for heating a charge of material to a temperature substantially' above 1000 F. in a container or pressure vessel formed of a metal subject to rapid corrosion when exposed to Corrosive conditions at such tempefatures. A

-further and more specific object is the provision of a pressure vessei of non-alloy-ferrous metal with an external protective covering of a non-corrosive fluid or semi-fluid ceramic material permitting the use of the vessel for long periods under corrosive conditions. at temperatures substantially above the temperatures at which the vessel could safely be used in an exposed condition. A still further object is the provision of a furnace retort having a shell made of a non-alloy ferrous metal and protective means making it capable of use with a substantial vacuum therein under furnace tages and specific objects attained by I its use,

referenceshould be had to the accompanying drawings and descriptive matter in which .I have illustrated and described preferredembodiments of my invention.

. Of the drawings: l

Fig. 1 is a sectional elevation of a magnesum reduction furnace incorporating a retort con- 'structed in .accordance with my invention;

'Fig; 2 is a partial longitudinal section of the' furnace taken on the line 2--2 of Fig. 1; v I

Fig. 3 is a View similar to Fig. 1 illustratingu a modified furnace' and retort construction; and

Fig. 4 is a view similar to Fig. 2 taken on the line -A of Fig. 3.

'While the apparatus of my invention is adapted for a variety of uses where a vessel of corrodible or oxidizable metal is subjected to corrosive service conditions at temper'atures above 900 F., it'is particularly'designed for and especially useful in j the Construction of retorts for the production ofmetaliic magnesium by the reduction of -a' ma nesium containing materialet a temperature of 2100 12300 F. and under a substantial vacuum.

In the normal operation of this process do1o v mitic limestone is burned and pulverized to a nely temperature conditions maintaining a metal temdivided condition; it is then mixed with a predetermined amount of a pulverized reducing agent, preferabiy ferro-silicon. The pulverized dolomite and ferro-silicon in the form -of small briquets are charged into an externally heated metallic reto'rt which is kept under a, high vacuum by means of a suitable vacuum pump. The charge in the retort is heated to a temperature of approxi mately 2100-2300 F., i. e. above the vaporization temperature of magnesium which is usually considered as 1958-2048 F. A Chemical reaction cccurs between the burned dolomit'e and ferro.-

silicon V resulting in the reduction of the magnesium oxide and the formation' of magnesium, calcium silicate, and iron. .The Operating pressure within the retort is maintained as low as possible, preferably. at an absolute pressure of 0.1 'mini Hg. such a, high vacuum has been found to minimize wastage of the silicon by oxidation, formation of magnesium nitride, and discoloration and sponginess of the 'condensed magnesiu-m. The vaporized magnesium passes into the' condenser section of the retort where it is condensed and recovered in a solid dense crystalline mass99.98% pure. The condensed metal is removed from the retort, subsequently melted down under flux, and poured into ingots. v

In Figs. 1` and 2 I have illustrated afurnace designed for the' described process of reduction of magnesium ore. The furnace to is of sub- "stantially rectangular cross-section with an arched roof ll .containing spaed gas outlets l2.

the top of each partiton 5, and serve as supports for a corresponding horizontally elongated retort extending substantially the full width of the urnace chamber. Due to the high retort metal temperatures in operation, the Corrosive fu'nace atmosphere, and the high vacuum maintained within the retort, it has been considered essential to make such retorts of cast stainless steel, such as an 'alloy of chrome, 20% nickel, with the balance substantially all iron. .such alloy.

metal however is. expensive, and under war conditions relatively scarce, and such retorts normally have a relatively shortlife in service. In accordance with my invention, such stainless steel retorts 'can be economically replaced by retorts made of non-alloy ferrous metal having a protective covering preventing oxidation or corrosion of the'retort metal under the service conditions described. y

' Th retort 20 illustrated has a. body or shell 2! formed by an extra heavy pipe of mild steel. One end of the pipe is spun inwardly to form a rounded end portion '22 having a circular center opening which is closed by a metal plug 23'conforming in contour to the retort opening and welded therein to form a gas-tight closure. The opposite or outer end of the retort shell is provided with an external peripheral fiange 24 welded thereto. An end plate 25 is connected to the flange 24 in any suitable manner to form a gastight detach'able closure for the retort, adapted to be removed for the charging and discharging of the retort. The outer end portion of the retort is constructed to form a magnesium vapor condensing section by means of a .water cooled circumferential jacket 26 having water inlet and outlet connections 21 and 28 respectively. A cylindrical metallic sleeve 30 is arranged to closely fit within the condenser section of the shell with its outer end secured to the end plate 25 in any suitable manner. An outer section of the sleeve 30 is slotted as indic'ated at 3! to connect theinterier of the shell to a short pipe 32 to which a vacuum pump (not shown) is detachably connected. In operation the magnesium vapor condenses on the sleeve 30, whichis removed with the end plate 25 at the end of the heating period and the condensed magnesium removed. A fresh charge of briquets is then placed in the retort and the sleeve and end plate restored to their' rosion and scaling of the errous metal shell 2! under the contemplated service conditions.

In the embodiment illustrated in Figs. 1 and 2, the protective covering comprises an outer substantiallyfluid-tight container 35 o! similar shape but larger dimensions than the shell 2! and formed of high temperature refractory material which is not aflfected by the surrounding corrosivte furnace atmospheric conditions. tainer 35 can be made in a single piece, but more advantage'ously is made of overlapping sections of dense ceramic refractory material fired during its manufacture to a temperature above( the contemplated furnace temperature. A wide variety of compositions' are suitable for this purpose, such as silicon carbide or the ceramic mixes used for dense sewer pipe or Chemical stoneware. The sectionsare sealed at the overlap by a high temperature refractory cement.

The annular and end spaces between the shell 2 I and container 35 are filled with a scaling material 40 having a softening point several hundred deg'rees F. below the contemplated service temperatures and fluid enough at service temperatures to wet the metal surface of the shell. The sealing material must not -alloy with the metalof the shell or have a high vapor pressure at the contemplated service temperatures.

' service temperatures inthe range of 2100-2300 original position.`

With a retort metal temperature of 2100-2300 F. and'a corrosive atmosphere, a non-alloy. ferrous metal shell has been found to have a service life of only a relatively few hours before the oxidation and scaling of the metal progresses to tective material which efl'ectively prevents cor- F. I have found various mixtures of ceramic materials, such as sodium silicate, raw clay, calcined clay, and silica sand highly effective protecting In preparing each of such mixtures, water equal to about 19% of the weight of the dry ingredients was added and the space between the shell and container filled with the inixture. Small refractory blocks 42 were used at intervals between the shell and container to center the shell within the container. The retort was then heated in a drying chamber until most of the mositure and gaseous constituents of the scaling layer had been driven oil; The retort is then ready for service in the reduction urnace.

In operation, the retort is rapidly heated up to the service temperature with the ceramic sealing layer, 40 gradually softening to a viscous bubbly mass filling the .space between the shell and container. l Under service conditions this viscous layer of ceramic material acts as a gas-tight impervious seal, preventing any furnace gases penetrating the refractory container wall from coming into contact with the shell metal, even with the described substantial pressure differential between the inside and outside of the retort. The shell metal thus remains uncorroded and capableof withstanding for long periods the high temperatures to which it must be heated for reduction of its magnesium ore charge.

In Figs. 3 and 4, I have illustrated another embodiment of my invention in which the container for. the 'retort shell protecting layer of ceramic material is iormed by the fumace walls and floor. In this construction the lower part of the furnace is lined with dense refractories of substantially the 'same composition as that suitable for glas The con- For " tani: blocks to form a series' ot' Sdee-bY Sde elongated chambers 50 extending the tull width.

of the furnace. Each' chamber has refractory side walls l extending upwardly fromthe fur-'.

nace floor '52 and formedof' 'glass tank blocks. The bottom 53 of each .chamber is' formed of simfilar reiractories shaped to slope downwardly J from 'the walls SI and side walls M of the fur-j nace to-'a central discharge opening 54 above a larger opening 55 in the iurnace floor. A In operation.- the hole 54' is closed 'by a' suitable cay plug 56, which can be removed to drain the correspondingchamber 50. Refractory tile blocks .58 extend'between the ide walls sl. at spaced points' and are cut away on their upper'sides to receive and support the non-alloy' fe'rousretort shell-zl. 4 I -The chambers'o form containers for a bath or batch of ceramic protective material `60 of the same 'general character. as, but preferably'more fluidat the contemplated service temperatures than' the. ceramic material 40 used in' the construction shown in Figs. 1 and 2.. ordinary sodalime glass, such as'73% SiOz, 5% Cao, and 22% `Na2O, is quite satsfactory for service :temperatures in the 2l00-2300 F. range, but anymaterial which will not alloy and coribine with the retort shell metal'and has a low vapor pressure and is sufficiently fluid at the service temperatures can be used. Baths of fused borax, barium chloride, sodium fluoride, or sodiuin disili'cate are also considered suitable for this purpose. In starting-up, the chambers 50 are filled with sub flcient protective' material, such `as`-'-'.broke`n or powdered siass, to provide an amount when fused sufllcient to immerseor submerge the retort as shown in Figs. 3 and l. In this construction the. fue] burners |3 are alternately arranged at op posite sides 'of the furna'ce. above the correspond-.

ing chambers ill to provide asub'sta'ntially uniormheatingjefiect throughout the width of the. che.m`b'ers. x

In operation the. retortsare charged aspreviously described and the reducing operation takes place. at a temperature in the 2100 -2300 F.

range.- The bath material provides an 'eflicie'nt heat conducting medium to the reto't s ell and included charge. 'A high fluidity of the* ,bath

material and the'se'ctioning of 'the fu'rnae tends 4 to promote acirculation ot the' ceramic'- bath material 'around the immersedretorts withoutpermitting contact -between the corrosive .con-

stituents-of the rumace atmos'phereand the re-' tort shell; If desired; the walls "separating the chambers illcan be omitt'ed to' provide a' common bath 'of protecting material 'for the retorts.

-While'l'n ambulance with 'the provisions of the patent statutes' I`have illustrated and described' heroin' the best iorms or" the invention now knownto me, those skilled in the art .will under- V stand that changes may be 'made in the' form of the apparatus'disclosed without'departing from the spirit of the invention covered by my claims, and that certain-features or the invention may.

sometimes be used to advantage without a corresponding use of other features.

Iclaim; a 1. Apparatus for heating peratures above 1000" F. which comprises a'body member adapted 'to 'contain the material to be heated and formedof a metal'subjct torrapid corrosion when expsed'to corrosive conditions at said temperatures, a 'heat resistant protective covering for said body member com'prising a layer of ceramic material chemically inert relative to a material to' 'tem- 3 said metal and in a* sumciently fluid condition when heated to said temperatures to wet the surface of said body member, and ceramic refractory' means Iorming a container for holding said cer- -5 amic material in contact with said body mem.-

ber.

member adapted to contain the material to be heated and formed of a non-alloy ferrous metal subject to rapid corrosion when exposed to corrosive conditions at said temperatures, a heat resistant protective covering for said body member comprising a layer ofceramic material chem-, icallyinert relative to said metal and in a sufficiently fluid condition when heated to said temperatures to wet the surface of said body member, and ceramic refractory means forming a container for holding said ceramic material in contact zog with said body member.

3. Apparatus for heating a material to temperv atures-ab'ove 2000" F."wh ich comprises a hollow body member adapted to. containthe material to beheated and formed of 'a metal subject to rapid corrosion when exposed to Corrosive conditions at" 'said temperatures, means fo'rming' a heat resistant protective'covering for said body member -conprising a layer of ceramic materialin contact with the 'outer surface ot said body-member, said ceramic material being' viscous when heated to said temperatures and chemically inert relativeto said metal, and ceramic refractory means forming a container for' 'holding said ceramic material in contact with said body member.

' vacuum therein and temperatures above '2000 F. whieh'comprises .a hollow body member adap'ted' to contain a material to be heated and ormed of a non-alloy erous metal subject to rapid cor- 4o rosion' when exposed to Corrosive conditions at formed; of 'a metal subject to 'rapid corrosion when exposed to Corrosive conditions at said temperatures, a heat resistant protectivecovering for said shell including a layer of ceramic material contacting with the outer surface of said shell, i said ceramicmaterial being viscous when heated to ,said temperatures and chemically inert relative to saidametal, and ceramic refractory means forming a container for holding said ceramic materialincontact with said shell. I

6. Apparatus for heating a material to tem 'peratures above 2000 F. which comprises a shell' I adapted to contain the material 'to be heated and f formed of a' non-alloy ferrousmetal subject to rapid corrosion when exposed'to Corrosive condition's at said temperatures, a heat resistant protective covering for said shell includinga layer of ceramic material contactng with and in a sufliciently fluidcondition when heated to said temperatures to wet'the outer surface of 'said shell, and ceramic refractory means forming a container for holding said ceramic material in contact with said shell.

2. Apparatus tor heating a material to temper-- j atures above 1000 F. which comprises a body 4. A pressure vessel capable of use under a high 5. Apparatus for heating a material to tem-' ing a container with said shell. w

7. A furnace retort capable of use under corrosive conditions at metal temperatures above 2000 F which comprises a shell otnon-alloy ferrous metal subject to rapid corrosion when exposed'to said service conditions, a heat resistant protective covering for said shell including a layer I 'of chemically inert ceramic material Contacting withand in a sufiiciently fluid condition when heated to said temperatures to wet the outer surface of said shell, and ceramic refractory means forming a container for holding said; ceramic material in contact with said shell. I

high vacuum'comprlsing a !umace' bottom con- V structed to receive a pool of ceramic material chemically inert relative to ferrous metal and in a viscous condition when heated to said temperatures; a fuel burner above the level of said pool of ceramic'` material,'and a retort for 'said magnesium ore having a body of 'a -non-alloy ferrous metal subject to rapid corrosion when exposed to 8. A furnace retort capable of use under corrosive conditions at temperatures above 1000 F.

which comprises a shell of metal subject to rapid corrosion when exposed to said service conditions, and a heat resistant protective covering for said shell including an inner layer of ceramic material neutral relative to said shell 'metal and Contacting with the outer surface of said shell, and an outer member of refractory material forming a container holding said viscous inner layer in contact with said shell;

9. A furnace retort capable of use under corrosive conditions at temperatures above 2000? F. which comprises a shell of ferrous metal subject to rapid corrosion when exposed to said ser' ce corrosive conditions at temperatures above 2000 F. and immersed in said pool ofceramic material.

14. A furnace for the reduction of magnesium ore at temperatures above 2 000 F. and under a high vacuun comprising' a furnace bottom con-. tructed to receive a pool of ceramic material chemically inert; relative to ferrous-metal `and'in a'viscous condition when heated to,said temperatures, auel bu'rner above the level of said pool of ceramic'material, a retort for said magnesium or having a body of a non-alloy ferrous metal subjectto. rapid corrosion when ;exposed to cor-' rosive conditions at temperatures above 2000 F.

and immersed in said pol of cer'amic material,

conditions, and a heat' resistant protective covering for said shell including an inner layer of ceramic material viscous when heated to said temperatures and neutral relative tosaid shell .meta and -contacting with the outer 'surface of said hell, and an outer layer of dense refractory material covering said viscous inner layer and forming a container holding the same in contact said vessel. 11. A furnace for heatingmaterial to temperatures abov 1000 F. comprising a iurnace bottom 'construc d to receiv e a body of ceramic material chemically inert relative to 'ferrous metal, a fuel' burner above the level of said'body of ceramiqmaterial, and a retort for said material having a body of a errous metal subject torapid corrosion when exposed to Corrosive conditions at temperatures above 1000 F..and submerged in said body of refractory material. v v 12. A.furnac e !or heating material to temperatures above 200091 1. comprising a furn ace bottom constructed to receive 'a poolof ceramic material chemically inert relativeto ferrous .metal and in a viscous condition when heated to said temholding the same in contact with -tures and extending through one of said side walls peratures, a rue burner above the level of said v 'pool of. ceramic material, and a pressure -vessel for said material having a body ot a ferrous met-' al subject to rapid corrosion when exposed to corrosive conditions at temperatures above 2000 F. immersed in said pool of ce'ramic material.

' 13. A Iurnace !or the reduc'tion of magn'esium i' ore at temperature above 2000? F. and under a external gonden'sin'g section and an:

I terial and meansfor charging 'said-tetori; with 'magnesium ore and -a reducing agent. I

15. A; urnace for heating material to temperatures above.1000 F. comprising a me'tallic tubular-container for the material to be heated formed ctmetal subject to corrosion when exposed to cor rosive conditions at said temperatures, ceramic refractory means forming a containerfor a bath cf protective material in which said tubular con- .tainer is immersed, said protective material being chemically inert relative to said metal andin a viscous condition whenheated to said temperatures, and means "for heating said bath of rotective material. I c 4 16. 'A furnace for heating material to temper atures above 1000 F. comprising means forming a ceramic refractory container 'for 'a 'bath of molten ceramic material chemically inert relative to ferrous metal and in a viscous. condition' when heated to said temperatures, means for heating said bath of ceramic material, and a tubularcontamer for the material to be heated iormed of w ferrous, metal and immersed in said bath ot *ceramic material. v

17 A furnae' for heating material to temperatures above 1000 F. comprising refractory sidewalls and a bottom forming a container for a bath of molten protective material chemically inert v relative to ferrous metal and in a viscous condition when heated to said temperatures, means for heating said bath of protective material, and atubular container for the material to be heated: formed of. ferrous metal subject to corrosion when exposed-to corrosive conditions at said temperabelow the' upper level or and immersed in said 'bath of protective material. I a

18. A .iurnace for the reduction oti a metallic ore at' temperatures above 1000 F. comprisig means forming a container tor a bath of mplten ceramic material chemically-inert relative to ferrous metal and in a viscous condition when beat:

ed to said temperatures, means for heating said bath of ceramic material, and a retort tor said metalliqor'e having a body of ferrous metal subject to, corrosion when exposed ta'corrosive conditions at said temperatures and h ving an lulzu' heating section immersed in said bath of cera'nic -ma-

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