US3540711A

US3540711A - Apparatus for the reduction and purification of reactive metals

Info

Publication number: US3540711A
Application number: US786333A
Authority: US
Inventors: Stephen M Shelton; Henry Gordan Poole
Original assignee: Oregon Metallurgical Corp
Current assignee: Oregon Metallurgical Corp
Priority date: 1965-10-20
Filing date: 1968-12-23
Publication date: 1970-11-17
Anticipated expiration: 1987-11-17

Description

United States Patent [45] Patented [73] Assignee [54] APPARATUS FOR THE REDUCTION AND PURIFICATION OF REACTIVE METALS 4 Claims, 7 Drawing Figs.

[52] US Cl 266/19 [51] int. Cl. C22b 5/16 [50] Field of Search 266/19, 20,

Consulted; .23/Consulted: 210/130. 156, '45s 56] References Cited UNITED STATES PATENTS 1,071,791 9/1913 Pugsley 75/112 2,120,474 6/1938 Stimmel et a1. 266/20 Primary ExaminerJ. Spencer Overholser Assistant ExaminerR. Spencer Annear Attorney-Kolisch & Hartwell ABSTRACT: Apparatus for producing a reactive metal. A halide of the reactive metal is reduced with a reducing metal in a retort to form the reactive metal distributed as a bed on a grid within the retort. Such bed contains reducing metal and reducing metal halide as impurities. Such impurities are removed by heating the contents of the retort at an elevated temperature to vaporize the impurities. The retort is swept with an inert gas whereby the impurities in vaporous form are carried from the retort. A closed circulating system outside the retort including condenser means and filtering means is used to remove impurities from the inert gas prior to its being returned to the retort.

Patented Nov. '17, 1970 Sheet g of 2 atented Nov. 1 7, v

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APPARATUS FOR THE REDUCTION AND PURIFICATION OF REACTIVE METALS This application is a division of a copending application entitled Reduction and Purification of Reactive Metals", Ser. No. 498,500, filed Oct. 20, 1965 now US. Pat. No. 3,464,813, issued Sept. 9, 1969.

This invention relates to the production of reactive metals such as titanium, zirconium, hafnium, etc., and more particularly to a means for reducing a reactive metal halide and purifying the resulting product.

In the production of metals such as titanium, it is common to reduce a halide of the metal with a reducing metal such as magnesium, sodium, potassium, etc. Thus, titanium tetrachloride, a liquid, may be added over a period of time to a batch of molten magnesium contained in a closed retort, with a reduction reaction taking place according to the following equation:

In the reaction, a porous sponge is formed of titanium, and mixed with this sponge and beneath the sponge the byproduct magnesium chloride. Ordinarily, the reaction which takes place is not stoichiometric, and only a portion of the magnesium present in the retort is reacted, such as 75-85 percent of the magnesium. By reacting less than all of the magnesium it is possible to inhibit the formation of titanium subchlorides such as Ti C1 and Ti CI After the reduction reaction, therefore, there will be found in the reaction vessel in addition to titanium and magnesium chloride minor amounts of titanium subchlorides and magnesium. Much of the magnesium chloride may betapped off while in a molten state, but the titanium sponge that remains in the retort still contains a certain amount of entrapped magnesium chloride as well as pure magnesium. The sponge, therefore, must be subjected to a purification process to obtain a titanium metal product of high purity.

Further discussing general problems attending the manufacture of a reactive metal such as titanium, magnesium when it is reacted with titanium tetrachloride is in molten form and tends to float on the byproduct salt magnesium chloride produced by the reduction reaction. Liquid titanium tetrachloride is added to the magnesium by allowing the tetrachloride to fall from a pipe onto a pool of molten magnesium. To obtain a fast rate of reaction, and maximum production under controlled conditions, it is desirable to have as large an area as possible of molten magnesium exposed to the titanium tetrachloride dropping down thereon. It is also important that the titanium sponge which forms within the reactor be maintained in as shallow a bed as possible, in order that the separation of impurities from the sponge in a subsequent purification step be facilitated. The purification of titanium sponge is further promoted if the sponge is formed as a relatively porous nondense mass, as this results in a larger surface area being produced throughout the sponge, and greater exposure of the impurities soughtto be removed from within the sponge.

Titanium sponge which forms within a retort clings to the sides of the retort introducing a problem of the-removal of the sponge after the process is completed. It is advantageous, therefore, in apparatus used to produce titanium, that a con struction be selected for the reaction retort that permits easy loosening of the sponge from the retort walls.

As a way of purifying titanium sponge, it has been proposed that impurities be distilled off by heating the sponge in a closed retort for a period of time while maintaining a vacuum .in the retort. A number of problems are introduced by such a procedure, however, since distillation is done at elevated temperatures, with weakening of the walls of the retort, and the usual retort must be heated within a special vacuum furnace if the retort is to be prevented from collapsing. Furthermore. there IS always the danger of a leak developing in the equipment, with the loss of the batch of titanium sponge being processed.

An object is to provide improved apparatus for preparing and purifying a reactive metal.

A more specific object is to provide improved means for producing a reactive metal, which features the use of the same retort for the reduction of the metal and for its purification, and the same furnace for heating the retort to produce the operating temperatures required within the retort. A further feature is the maintenance of a pressure condition within the retort which is atmospheric or nearly atmospheric pressure, whereby the furnace employed for heating need not be a vacuum furnace, and assurance is had that the retort will not collapse during the manufacturing process.

A further object is the provision of a means for producing reactive metals characterized by the use of an inert gas stream passed through a retort at substantially atmospheric pressure, for removing vaporized impurities, and a novel method of removing impurities from this inert gas stream upon such leaving the retort.

Another object is to provide an improved means of the type above indicated wherein an inert gas is circulated through a retort with heating of the retort to remove vaporized impurities, the circulated gas is cooled in a region outside of the retort, and a portion of the cooled gas is mixed with hot gas flowing from the return for the purpose of initially cooling the hot gas. Using the means outlined, solidification of impurities takes place in a novel manner which facilitates the removal of these impurities from the inert gas stream. 7

A still further object is to provide novel apparatus for reacting a reactive metal halide and a reducing metal such as magnesium wherein a large area of the reducing metal in molten form is provided during the reaction, and a relatively shallow bed of reactive metal is produced during the process facilitating subsequent purification of the metal by vaporization of impurities. Using the apparatus contemplated, a relatively porous sponge product may be produced, having a relatively large exposed surface area distributed through the sponge exposing impurities contained in the sponge.

These and other objects and advantages are attained by the invention, which is described hereinbelow in conjunction with specific illustrations of the invention and the accompanying drawings, wherein:

FIG. 1 is a side elevation, somewhat simplified, showing a retort such as may be used in the process of the invention, with the retort mounted within a furnace;

FIG. 2 is an end elevation, taken along the line 2-2 in FIG. 1;

FIG. 3 is a top plan view, somewhat simplified, showing apparatus for cleansing gas which is circulated in the process of the invention;

FIG. 4 is a side elevation, with portions broken away along the line 4-4 in FIG. 3, illustrating in simplified form a cooler unit in the cleansing apparatus;

FIG. 5 is a slide elevation, with portions broken away along the line 55 in FIG. 3, illustrating in simplified form a filter unit in the cleansing apparatus;

FIG. 6 is a cross-sectional view, taken along the line 6-6 in FIG. 5; and

FIG. 7 (first sheet of drawings) is a cross-sectional view,

somewhat enlarged, taken along the line 7-7 in FIG. 1.

In apparatus according to a preferred embodiment of the'invention, an iron retort is employed for reducing and then purifying the reactive metal halide taking the form of an elongated hollow cylinder, closed at opposite ends, and disposed with the axis thereof horizontal. In the drawings this retort is in-;.

dicated at I0, and comprises a cylindrical shell 12 and end walls l4, 16 closing off ends of the shell. Slightly above the base of the shell and within the retort is a horizontal, perforated iron plate or reactor grid 18. Titanium sponge forms over this reaction grid upon the reaction of metal halide and reducing metal.

Retort 10 is supported on cradle structure 20 mounted on car hearth 22. The car hearth has wheels 24 disposed under it,

riding on rails 26. Thus the retort is movable into and out of a' furnace indicated generally at 28.

Piping of various types is shown communicating with the interior of retort 10. Specifically, pipe 30 projecting from rear end wall 14 of the retort adjacent its base, and connecting with the inside of the retort at a point located beneath grid 18, is provided for tapping the retort and removing salt byproduct produced in the reduction reaction. Connecting with the retort at points 32a. 32b and 34a, 34b are pipes 32, 34, both of which connect with a common pipe 33, utilized in circulating gas through the inside of the retort. Pipe 35 isa blowoff pipe,

and at 37 is shown a pipe used in evacuating and backfilling the retort. Extending from end wall 16 is an outlet pipe 36 through which gas flows on leaving the retort. A pipe 38 communicates with the retort adjacent the top of shell 12, and this comprises a feed pipe for feeding reactive metal halide to the retort.

Furnace 28 comprises sides 52 and a top 54 made of refractory furnace lining. The sides are apertured as at 56 to accommodate gas burners which supply the heat for the furnace. Furnace doors 58,60 (see FIG. 2), slidable laterally of the furnace, and suitably apertured to accommodate the pipes extending out the back end of the retort, are provided adjacent the back end of the furnace to close this end off. Similar furnace doors such as the one shown at 64 (see FIG. 1) close off the front end of the furnace.

According to this invention, purification of the reduced reactive metal produced in the retort by the reduction reaction is carried out with atmospheric or close to atmospheric pressure within the retort whereby a vacuum furnace is not required and the same furnace may be used to heat the retort during purification as was used in the reduction process. Purification is performed by vaporizing impurities, and then sweeping them from the retort by circulating an inert gas such as argon therethrough. The invention also contemplates a novel method of cleansing the argon or other inert gas used in the sweep process, with impurities being condensed and forming as solid particles which are collected. In the drawings, the apparatus producing circulation of gas through the retort while the same is in the furnace, and cleansing of the gas with removal of impurities, is shown in plan in FIG. 3, and is designated generally at 70.

More specifically, suitably supported on a platform, 72 which is outside the furnace, are three cyclone filter units, given the reference numerals 74, 76 and 78, and a cyclone cooler unit, given the reference numeral 80. Platform 72 has wheels 82 underneath it supporting it on rails 26, enabling movement of the platform along the rails. Thus, the filter units and cooler unit may be moved bodily together with the retort on moving of the retort out of the furnace.

Referring to FIG. 1, outlet pipe 36 which gas flows through on leaving the retort is jacketed directly adjacent the retort, at 86, to permit the circulation of cold water around the pipe whereby a water-cooled condenser section is formed. A water inlet and water outlet for the condenser section are shown at 86a, 86b. Progressing from condenser section 86, outlet pipe 36 connects with a valve 84 which connects with the top of cyclone cooler unit 80 by way of pipe 85.

Connecting with pipe 36 between where the condenser section is located and retort I is a pipe 88 for feeding cool gas into outlet pipe 36. As will be described in greater detail later, by feeding cool gas into the gas leaving the retort, and by the provision of the condenser section for further cooling of the gas leaving the retort, a temperature is produced in the gas mixture flowing through pipe 36 low enough to produce solidification of impurities in the gas stream with such being carried along as particles entrained in the gas stream.

Cyclone cooler unit 80 comprises a hollow cylindrical casing portion 80a forming the top ofthe unit, and a hollow conically shaped casing portion 80b forming the bottom of the unit. Flow into the unit through pipe 85 is against the inner surface of cylindrical casing portion 80a. Cooling water may be circulated about the outside of easing portion 8012, with such water flowing through a cooling line 800 extending in helical turns about casing portion 80b. Additional cooling in the unit may be brought about by including a jacket such as that shown at d about cylindrical casing portion 80a permitting cooling water to be circulated about the outside of the casing portion. 5

The cyclone cooler unit and cyclone filter unit 74 are interconnected by a pipe 90. A cooling water coil 92 intermediate the ends of pipe provides additional cooling of gas flowing to the filter unit. Such cooling is desirable in order that gas entering the filter unit be at a low enough temperature so as not to burn up or otherwise damage filter cloths provided in the filter unit. I

The various filter units are similar in construction. Thus, and referring to FIGS. 5 and 6, each includes a casing having a conical base such as the one shown at 740 for unit 74, and also a cylindrical top such as the one shown at 74b for filter unit 74. Within the hollow casing is a leaf-type filter made of folds ofa filter cloth, such as the one shown at 74c, depending from a shield such as the one shown at 74d. Flow of gas out of the unit can take place only through the folds of the leaf-type filter and thence out through an outlet such as is provided by pipe 94. Material filtered out by the filter unit collects at the base ofthe unit in housing portion 74a earlier described.

Pipe 94 which provides an outlet for gas from the first filter unit extends from the first unit to the second filter unit 76. Gas flow out from this unit is through outlet pipe 96 which extends to the third filter unit 78. The outlet from the third filter unit is provided by a pipe 98.

Downstream from the third filter unit pipe 98 connects with the inlet side of an impeller pump 100 driven by a motor 102. Gas exhausted from the pump passes through a pipe 104, which pipe branches into two

pipes

105, 106. One of these, namely, pipe 105, which constitutes a bypass conduit joins with pipe 88 previously described in connection with the fceding of cool gas to outlet pipe 36 extending from the retort. Pipe 106 connects with pipe 33 provided for circulating gas through the retort. Flow meters for indicating the rate of flow through the pipes are indicated at 108 and 110 (see FIG. 3),

and valves controlling-flow through the pipes are shown at 112 and 114 (see FIG. 1).

The feeding of cool gas into pipe 36 for producing initial cooling of the gas coming from the'retort and condensing of impurities contained in such gas is an'important feature of this invention. The cool gas, as should be apparent from the above description of the apparatus, is obtained by diverting part of the inert gas circulated by the pump after such gas has been cleaned so that while much of the gas after cleaning passes through the retort to sweep it and remove impurities, a good proportion of the gas bypasses the retort to return to the gas flowing from the retort in pipe 36 at a point located in advance of the condenser section provided at 86. The gas is introduced to outlet pipe 36 in a special manner, moreover, whereby a film of moving gas, at a relatively low temperature, is produced which extends about the inside of pipe 36 to envelope hot gas flowing from the retort. Thus, and referring to FIG. 7, pipe 88 which connects with pipe 36 extends in a tangential direction from its point of joinder with pipe 36, and gas flowing into pipe 36 from pipe 88 tends to flow around the inner wall of pipe 36 to produce a spiraling flow of cool gas within pipe 36 as indicated by the arrow in FIG. 7.

The result of the construction above described, and the process by which a portion of the gas after cleaning and cooling is bypassed to. cool gas flowing from the retort, is that impurities condense as particles entrained in the gas stream, and these particles are carried along pipe 36 without collecting on the wall of the pipe thereby to clog it. Put in another way, what the invention envisions is a system of cooling wherein condensed particles are formed, and these are formed in a traveling gas stream in a region away from the wall of the pipe confining the gas. The particles once solidified are carried by the gas stream into the cooler and filter units to be separated, and thence collect in the bases of these units.

In the case of the manufacture of reactive metals such as zirconium and hafnium, the halide is a solid, the retort is initially The operation of the apparatus described and the method of the invention contemplated will now be explained with reference to the production of titanium from titanium tetrachloride and using magnesium as the reducing metal.

800 pounds of magnesium was first charged in a retort 3 feet in diameter and approximately 6 feet in length. The retort was mounted as pictured with its longitudinal axis horizontal. The retort was closed after charging with magnesium, by welding the end walls in placeover shell 12. Cleansing and circulating apparatus 70 was suitably joined with the retort, and the retort was then evacuated and filled with argon to produce a pressure of l p.s.i.g. within the retort. Evacuating and filling with argon was performed using pipe 37. This pressure was maintained throughout the reduction and purification steps.

The retort was then mounted within furnace 28, and the furnace doors then closed. The gas burners of the furnace were ignited, and the retort was heated with the temperature of the walls of the retort rising to about 800C. (l472F.). Titanium tetrachloride was then fed to the retort through pipe 38, at a rate of about 600800pounds per hour, until 3000 pounds of the tetrachloride had been added over a period of about 4% hours. During the reduction reaction, the temperature of the walls of the retort was maintained within the range of about 5.9 0. (1 2Z-l7 l -l Arena washes. 995121259: tort through pipe 35 so as to maintain the pressure within the retort constant. After about 60 percent of the titanium tetrachloride had been added (and the lapse of about 2% hours time), byproduct magnesium chloride formed in the reduction reaction was drained from the retort through pipe 30. The reduction reaction was about 75 percent efficient, and resulted in the production of about 600 pounds of titanium sponge. Estimated to be contained in the sponge was about 80 pounds of unreacted magnesium and 85 pounds of magnesium chloride and subchlorides.

Upon the completion of the reduction reaction, and the draining of all free magnesium chloride and magnesium from the retort, motor 102 was energized to start pump 100. Cleansing and circulating apparatus 70, which previously had been evacuated and back filled with argon, was placed in operation by adjusting of the valves controlling the flow of gas through pipe 33 and bypass pipe 88, to produce a sweep of argon gas through the retort with such then being recirculated through the filter units. Gas flowed through the retort at the rate of approximately 50 cubic feet per minute, and the same rate of gas flow was maintained through the bypass pipe. A pressure on the downstream side of the pump of about 5 p.s.i.g. was sufficient to produce proper circulation of gas through the equipment.

During the circulation of gas through the equipment, the furnace was operated and a temperature of from about 950- IQS Q C. $1742 7 l922F.) maintained in the walls of the re-' tort.- Water was circulated through the various cooling coils 1 and condenser sections described. Gas flowing from the retort had an average temperature of about 1000C. A temperature of about 600C. was noted in the gas traveling into the cyclone cooler unit, and gas traveling into the first cyclone filter unit had a temperature of about 150C. With some additional ,cooling of the gas occurring as the same traveled through the other filter units, and some heating of the gas occurring on such passing through the compressor (ZS-30C.), temperature of from (SO-70C. was noted in the gas which flowed through bypass pipe into condenser section 86. 7

Purification by vaporization and sweeping of the retort was continued .for approximately 48 hours. During this time magnesium, magnesium chloride, and subchloride impurities collected in the bottoms of the various units as particles. At the conclusion of the purification process, the furnace was shut sponge was relatively easily removed by forcing the web of sponge upwardly toward the middle of the retort (note that the sides of the retort diverge from each other progressing upwardly toward the middle of the retort promoting loosening of the web). A relatively porous pure titanium sponge product resulted, containing not more than 0.1 percent chlorine.

in the process of manufacturing titanium just set forth, argon was employed as the inert gas. Titanium has also been prepared employing a process similar to the one just set forth save that the inert gas helium was substituted for argon. The use of helium as the inert gas has some particular advantages.

For one thing, having a lower density than argon, less power is required in pumping the gas whereby it circulates through the system. Furthermore, helium being less dense than argon there is more mobility of the molecules within the system which results in such advantages as the minimizing of hot spotsin the retort during the reduction reaction.

The method of; the invention features a number of advantages contributing to the relatively efficient production of large quantities of titanium sponge, of requisite purity, which method is reliable, and economical to perform.

Thus, of particular importance is the fact that the retort used in the reduction reaction and .in the purification step is the same retort, and this retort is heated to operating temperatures while residing in the same furnace. Removal of impurities during the purification step is produced by vaporizing of these impurities, and relies upon sweeping of the retort with an inert gas at approximately atmospheric pressure (which may be defined herein as within the range of from atmospheric pressure to about 10 p.s.i.g. above atmospheric pressure) for bringing of the impurities out of the .retort. Because of the pressure condition in the retort, heating during the reduction and purification steps need not be done in a vacuum furnace, but a conventional furnace may-be used. It should be remembered thatwith operating temperatures close to 2000F., the.

side of the retort of a pressure condition similar to the one inside.

Furthermore, by utilizing a vaporization process wherein the impurities are swept from the retort with gas at close to atmospheric pressure, chances of inadvertent leakage both inside the furnace, and in the purification equipment outside the furnace, are sharply minimized. In a process where large pressure differentialsexist, chances ofinadvertent leaks occurring are ever present, and should a leak develop, the result is the loss of the entire charge of metal being produced.

With the elongated cylindrical retort employed positioned with the longitudinal axis thereof horizontal, a relatively large area of molten magnesium extends over the top of the molten pool of the metal. This promotes the reaction of the magnesi um with the titanium tetrachloride introduced to the retort. Further explaining, and referring to FIG. 2, it will be noted that the cross-sectional area within the retort of a plane such as plane A paralleling the longitudinal axis of the retort is substantially greater than the cross-sectional area within the retort ofa plane at right angles to the retort's longitudinal axis. Coupled with the advantage of obtaining a large exposed area for reaction, is the feature that a relatively shallow bed of sponge is formed for a given, amount of reactants. The shallow product is below a horizontal plane passing through the mid dle of the retort, it is easily removed by being forced upwardly into a region of wider dimension than the region the product originally occupied.

The magnesium chloride is not drained from the retort until at least about 60 percent of the titanium tetrachloride has been added. This tends to produce a more porous sponge product. If the magnesium chloride is drained earlier, the level of liquid magnesium in the reactor (which floats on magnesium chloride) tends to remain low, and new sponge tends to be produced on the addition of titanium tetrachloride in the interstices of already formed sponge to produce a dense product. With a more porous product, vaporization of impurities during the purification step is facilitated.

Although vaporization of impurities is promoted by heating the products in the retort, the walls of the retort must be maintained below a temperature of about 2000F. This follows from the fact that iron and titanium form a eutectic at a temperature only slightly under 2000F. (approximately 1085C.), and ifthe reactor walls exceed this temperature, undesirable reaction of the retort walls with titanium results. It should be noted that with a reactor of the type contemplated positioned with the longitudinal axis thereof horizontal, there i is a maximum of wall surface bounding the region where a high temperature reaction occurs during the reduction part of the process available to dissipate heat. This is an additional feature of the invention.

The invention further contemplates, in combination with the sweep system of withdrawing vaporized impurities from the retort, a uniquemethod of removing impurities as particles from the gas utilized to sweep the retort. Thus, cyclone units have been described where the impurities separate as particles and collect at the bases of the units. Note also that a novel bypass of cool gas into the gas emanating from the retort is contemplated, producing initial cooling of the gas mixture and condensation of the impurities in such a manner that clogging ofthe outlet pipe for the retort is inhibited.

Earlier the use of helium was described as preferred where it is desired to minimize the power used by the pump in circulating the gas and .where it is desired to have the most even temperature conditions within the system. It should be pointed out here that the sweep evaporation contemplated herein, whether it be performed by argon, helium or other inert gas, promotes better efficiency in the system wherever heating or cooling is a factor than ispossible with a system which relies on vacuum conditions. Because of the presence of the gas, the transfer of heat is not entirely the result of radiation as is the case where a vacuum is present, but also takes place by reason ofconvection.

While an embodiment of the invention has been described together with a working example, it is appreciated that changes and variations are possible without departing from the invention. It is desired to cover all modifications and variations of the invention as would be apparent to one skilled in the art, and that come within the scope of the appended claims.

We claim:

1. Apparatus for producing and then purifying a reactive metal by the steps of first reducing a halide of the metal with a reducing material, and then vaporizing and removing from the reactive metal impurities in the form of the halide of the reducing material and unreacted reducing material, the ap paratus comprising:

a closed stationary retort;

a furnace for heating the retort having the retort received therewithin;

a gas inlet pipe connecting with one region of the retort for introducing inert gas used in sweeping the retort to remove vaporized impurities and a gas outlet pipe connecting with another region of the retort for withdrawing such inert gas;

a closed circulating system connecting said gas outlet and gas inlet pipes disposed outside the retort and furnace for circulating inertgas between said outlet and said inlet pipe; and

said system including condenser means where vaporized impurities carried in the inert gas being circulated are reduced to solid particles, gas-filtering means toward the inlet pipe from the condenser means for filtering out such solid particles carried in such inert gas, and means for producing a flow of such inert gas in a direction extending from said outlet to said inlet pipe.

2. The apparatus of claim 1, wherein said circulating system includes a bypass conduit diverting a portion of the gas flowing from the filtering means from flowing back into the retort through said inlet pipe and directing such gas into the path of gas flowing from the retort through said outlet pipe directly adjacent said condenser means.

3. The apparatus of claim 2, wherein said bypass conduit directs gas carried therein into the path of gas flowing from the retort in a manner producing envelopment of the gas glowing from the retort by the gas flowing in said bypass conduit.

4. The apparatus of claim 1, wherein the retort comprises an elongated shell with the longitudinal axis-thereof substantially horizontal, a grid is provided in said retort below said longitudinal axis,'said shell includes walls defining a region in the re-. tort above said. grid where the reactive metal collects on reduction of the halide ofthe metal, and said walls where they' define said region and immediately above such region diverge from each other progressing upwardly in the retort in a direction extending transversely of the longitudinal axis of the retort.