US3346368A - Heating metallic material for subhalide refining - Google Patents

Heating metallic material for subhalide refining Download PDF

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US3346368A
US3346368A US429826A US42982665A US3346368A US 3346368 A US3346368 A US 3346368A US 429826 A US429826 A US 429826A US 42982665 A US42982665 A US 42982665A US 3346368 A US3346368 A US 3346368A
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mass
particles
aluminum
particulate
converter
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US429826A
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Victor A Braunwarth
Nickle Alexander Gordon
Norman W F Phillips
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Alcan Research and Development Ltd
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Aluminium Laboratories Ltd
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Priority to US429826A priority Critical patent/US3346368A/en
Priority to GB1737/66A priority patent/GB1134171A/en
Priority to FR46090A priority patent/FR1469272A/fr
Priority to NO161327A priority patent/NO116141B/no
Priority to BE675576D priority patent/BE675576A/xx
Priority to OA52338A priority patent/OA01905A/xx
Priority to ES0322483A priority patent/ES322483A1/es
Priority to CH134066A priority patent/CH456164A/fr
Priority to NL6601343A priority patent/NL6601343A/xx
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    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
    • C22B21/00—Obtaining aluminium
    • C22B21/0038—Obtaining aluminium by other processes
    • C22B21/0046—Obtaining aluminium by other processes from aluminium halides

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  • This invention relates to the subhalide refining of aluminum wherein impure aluminum-containing material in particulate form is treated with normal aluminum halide gas, such as aluminum trichloride or aluminum tribromide, ⁇ at high temperature for conversion of the aluminum in the ycharge to gaseous aluminum monohalide which is thereafter decomposed to yield the purified aluminum metal and restored normal halide.
  • normal aluminum halide gas such as aluminum trichloride or aluminum tribromide
  • the invention is directed to improved procedure and apparatus in etfectuating the described conversion of aluminum in the charge material to monohalide, in operations where the heat for the reaction is supplied by electrical resistance heating, i.e. by passing electric current through the particulate material in the converter.
  • the present improvements are concerned with preheating the charge material prior to its introduction to the converting region, e.g., preheating the continuing 'supply of such material so that when it reaches the zone of electrical heating in the converter it is already characterized by a relatively high temperature.
  • bauxite with carbon as in an electric furnace, and is thus ordinarily a solid metallic composition containing aluminum (in proportion ranging downward and upward from 50%) with other elements such as iron and silicon, and usually some titanium and carbon, or further or other metals, depending on the composition of the original ore.
  • this material is supplied in particulate form, i.e. granular or as lumps or the like, such that it may be appropriately handled as a column or bed yet with sufficient interstices and exposed surfaces of the particles for efficient passage and reaction of the halide gas, eg. aluminum trichloride.
  • Suitable temperatures of operation in the converter are usually of the order of 1000 C. and above and preferably about l200 C. to 1300" C. or somewhat higher.
  • beds of alloys of this type may have a relatively high resistance at room temperatures and somewhat above, the resistivity drops at higher temperatures, to quite a low value at about 1000 C., and the problem of 2 electrically heating such beds is correspondingly acute through the indicated range, especially up to about 700 C.
  • the supply of fresh alloy should be preheated to temperatures near or at the desired reaction values, by other than electrical resistance procedure, i.e. by heat supplied from sources external to the particlesy themselves. If the body of material in the converting region is first established at a suitably high temperature, substantially in all its parts, and additions thereto are likewise made at such tem-perature, e.g. 1000 C. or above, further supply of heat for effectuating the reaction in this region is readily achieved by passage of electric current through the bed or body which then has a relatively low resistance, substantially uniformly throughout.
  • thermal conductivity of this material are relatively poor, and the formation, by surface fusion, of these agglomerated cores or masses is essentially intolerable and there is no practical way to get rid of them. As explained above, they clog the operation, an-dkmore Yso as they solidify; they tend to remain as preferential current paths, so that heating is non-uniform and efficiency of conversion, i.e. for treatment of an entire column, becomes poor; and they soon completely block the necessary movement of the column.
  • the present invention involves the discovery-that by appropriately moving the charge material, as down a vertical region or pipe which has a very substantially smaller cross-section than the columnar region inthe converter, so that the material advances at an'average rate which' is correspondingly greater than its slow travel through the converter and which is properly correlated with the rate of heating, such material can be effectively-preheated by passage of electric current through it Vin a direction coaxial with its path of advance, with an avoidance of serious current channeling and particularly with an avoidance of significant fusing of the particles or the consequent formation of elongated agglomerates or cores of the granular alloy.
  • the significant electrical resistance of the mass is mainly represented by the sum of (l) the contact resistance between particles, and (2) the resistance of the material in the region of highcurrent density (within the individual particles) close to the points ofcontact.
  • Heat is chiefly developed, by current flow, at the principal points of resistance, and thus at and near the localities of contact between particles. While heat is eventually transferred back into the body of each particle, the electrica-l properties of the mass are primarily defined by the temperature at and adjacent the contact localities.
  • beds of granular particles of these fusible metallic alloys show a negative temperature coeicient of resistivity even though the alloy in massive state may not: as the bed or column heats up, expansion causes an increase of contact pressure between particles reducing the resistance there, and as fusion begins and progresses, the local resistance decreases more and more, in the manner explained.
  • the size of the bed and its mode of advance must be such that all particles ⁇ are frequently disturbed, to avoid development of one or more hot channels.
  • These conditions, and likewise good current distribution, are facilitated or made possible by employing a column or other mass which has .a relatively small crosssectional area, a further important attribute of such dimensioning being that the length of heat diffusion paths through the body is then-short, as appropriate for material of relatively poorrthermal conductivity. In consequence there is fairly uniform heating throughout the whole cross-section.
  • a convenient, determining factor may therefore be deemed to reside in the pulse-type movement of the material, especially in the sense that with jerks of sufficient frequency, other necessary conditions can be readily determined to achieve the desired uniform heating by current flow.
  • the jerks or pulses of movement are ascertainable by electricial measurement, it being found that with a nominally constant voltage across the supply electrodes, there are distinct and frequent current fluctuations indicating changes in resistance of the moving column. These are understood to be representative of the pulses of movement, whereby simple experimental data can be obtained in any case for ready determination of conditions (especially a sufficiently rapid frequency of jerks) for the desired result of preheating without fusion.
  • the frequency of these cycles is such that the average time between jerks, i.e., the average period from one pulse of movement to another may range from about to about 100 seconds. It will be understood that the duration of the intervals of rest is not ordinarily uniform, even for a given average feed rate.
  • One convenient indication, however, of the condition of movement of a bed or column is the approximate maximum rest interval, which is defined below but which is exemplified, under certain tested circumstances of useful operation, by a value of about 30 seconds, or less, for rather high feed rates, and by values of about 60 to 100 seconds for considerably lower feed rates.
  • the dimensioning of the preheating column is to some extent related to the internal size of the converter, which in turn is designed to afford efficient performance of the reaction to produce monochloride from the alloy.
  • the dimensional proportions and the rate of alloy travel should be such that the alloy remains in the traversing ow of gaseous aluminum trichloride for a sufficient time to convert a suitably high percentage of the aluminum content.
  • the dimensions of the region are further governer by the requirements: that sufficient heat be generated by passage of electric current, to serve the endothermic reaction, and that the gas traverse the region in sufficient contact with the alloy, yet without such pressure drop as would unduly limit the rate of gas passage that would be practical.
  • an upright cylindrical converter should have an internal diameter of ⁇ at least about 5 feet, and preferably 7 feet Ior more, the ⁇ cross-sectional area of this or other configuration varying upward from a minimum of about 20 square feet or a preferred minimum of about 40 square feet.
  • the alloy in utilizing an internally electrically heated body of particulate alloy in such a converter, for example with the arrangements and procedure just described as app-ropriate to function efficiently for conversion of aluminum to monohalide, the alloy must be preheated to a high value, e.g. 700 C. or above, and preferably near the conversion temperature (depending on the extent of other modes of preheating that may be inherently or specifically embodied in the converter), before feeding it to the converter, or difficulties of fusion between particles and of severe current channeling may arise.
  • a high value e.g. 700 C. or above
  • the preheating column should have a cross-section substantially smaller than that of the converter, indeed usually no greater in area than about half of the cross-sectional area of the converting region, and preferably considerably smaller, as in the case of a preheating column with a diameter of one-half to one-third that of the converter, or less.
  • a preheating column of particulate crude alloy, through which current is passed substantially parallel to the axis i.e.
  • a particularly useful size of preheating column is one having a diameter of about six to about eight times the average particle diameter.
  • a -suitable preheat column diameter, to feed a converter having a diameter of five feet, and utilizing a granular alloy having a nominal or average particle diameter of two inches (with individual particles ranging from one-half inch to two and one-half inches), is found to lie within a range of ten inches to twenty inches, and preferably fourteen to sixteen inches.
  • the converter is expected to handle an alloy feed in the range of 2000 to 6000 pounds per hour, or somewhat more, and effective preheating is then attained (using coaxial current flow in the preheating column) without appreciable fusion together of the feed particles.
  • the frequency of pulses or jerks of downward movement of the material, by gravity is adequate for the desired breaking of electrical contacts and re-orienting of the particles, and indeed lies within the limits in the above examples, whether determined by the average or by the approximate maximum rest interval.
  • FIG. 1 is an essentially diagrammatic view, in the nature of a vertical section, of a converter and a feeding and preheating system therefor, embodying the invention as an example of the apparatus thereof;
  • FIG. 2 is an enlarged view in vertical section of the preheating and certain associated portions of the system as shown in FIG. 1, with the structure illustrated in simplified form;
  • FIGS. 3 and 4 are respectively sections on lines 3-3 and 4 4 of FIG. 2.
  • the converter 10 which may be generally similar to the structures shown in the abovecited patent, is an upright cylindrical chamber or furnace having upper electrodes 12, 12', of carbon, graphite Aor the like extending through the walls at two or more localities, and the like lower electrodes 13, 13' whereby electric current, e.g. alternating current from a suitable source 14, may be passed between the electrodes 12, 12' and the electrodes 13, 13', through the contained mass of charge material 15.
  • the converter 10, and indeed all of the other structures hereinafter described which are intended to enclose the alloy material in a heated condition or while it is being heated, may be constructed with an external, sealed, steel shell (not shown for the converter in FIG. 1 but depicted for other vessels at 16, 17 in FIG.
  • the Zone defined between the upper and lower electrodes 12, 12 and 13, 13 represents the reaction region and is kept entirely filled with the granular alloy at all times, i.e. to a level above the upper electrodes.
  • Preheated aluminum trichloride gas enters through pipe 20 and is released within the converter by suitable distribution means 21, i.e. below the lowermost electrodes, and then flows upwardly through the bed of alloy, wherein by reason of heat energy from the current, the AlCl3 converts aluminum of the alloy to gaseous monochloride.
  • a refractory lined discharge conduit 22 carries the product gas, consisting of aluminum monochloride (AlCl) and unreacted aluminum trichloride, to the decomposer (not shown) where under the influence of appropriate cooling means, to extract heat, the monochloride decomposes to yield pure aluminum and aluminum trichloride.
  • Fresh alloy feed enters the converter at the top, i.e. through an inclined feed conduit 24, while the aluminum-depleted residue of granular solid leaves the bottom of the converter, as through a discharge conduit 25, advance of the spent alloy out of the converter being aided by suitable mechanical means, such as a conventional discharge cone 26, carried on and rotated by a vertical shaft 27.
  • the feed system which may be a long upright series of devices above the converter 10, includes a supply hopper 30, receiving the granular alloy and guiding it into the column structure shown below the hopper.
  • This column structure may include suitable lock or valve means whereby the alloy may advance downwardly, in successive increments, to a lower, enclosed feed hopper 32, without appreciable leakage of reactive chloride and monochloride gases and without appreciable access of air to the structures below.
  • Such lock or valve system may consist of a vertically spaced pair of valves 33, 34 in the feed column assembly 35, with an intermediate hopper 36 between them, the hopper 36 being arranged with a valved inlet pipe 37 for introduction of inert gas at desired times.
  • the valves 33, 34 may be of any appropriate character for interrupting the downward path of alloy and for essentially closing the path against liow of gas except when opened for alloy passage, they are shown as simple star valves, being known devices for this type of function.
  • the preheating section comprises an upper preheat column 40, a lower preheat column 41, and between them a mixing chamber or hopper 42 of substantially wider cross-section.
  • the column 40, chamber 42 and column 41 are kept filled with the downwardly traveling, granular alloy, means are provided below the column 41 for advancing or aiding the advance of the material into the inlet conduit 24 of the converter, such means 4being of appropriate sort, such as a table, cone, screw or other feeding device, the illustrated equipment specifically embodying a rotating circular table 43 for this purpose, within a lower feed chamber 44.
  • each of the preheating sections 40, 41 is an uprightV columnar chamber, refractory lined, having an internal, vertically elongated cylindrical configuration, and provided with electrode means for passage of current through the moving material.
  • the upper column 40 has vertically spaced sets of graphite, carbon or other suitable electrodes 45, 45 and 46, 46', which project to or into the enclosed feed path.
  • the lower column 41 has similar upper and lower sets of electrodes 47, 47 and 48, 48.
  • the mixing chamber 42 through which the material passes from the upper preheat column 40 to the lower preheat column 41 comprises an inner cylindrical section 50, from which a cone-shaped region 51 extends or tapers downwardly to the column 41, while an upper, flaring or cone-shaped region 52 extends from the lower end of the column 40 to the top of section 50,
  • the horizontal, circular, rotating table feeder 43 is disposed, being carried by a vertical shaft 53 below it, suitably driven -by means not shown.
  • a stationary scraping or pushing blade 54 may be mounted above the table at an outer part of its upper surface, e.g. on the side adjacent the conduit 24, so that as the table turns the material is pushed or aided in falling from the table into the latter conduit.
  • Coacting guide means may be carried by the lower side of the table 43, e.g. a chain structure 55 which aids in sweeping material into the duct 24.
  • Electric current for the preheating columns is furnished from a suitable source, for example an alternating current source 56.
  • a suitable source for example an alternating current source 56.
  • the upper pair of electrode sets 45, 45 and 46, 46 is supplied with current through a transformer 58, while the lower pair of electrode sets 47, 47 and 48, 48 is supplied through a like, similarly connected transformer 59.
  • the heating current circuit of the electrodes of each column includes an inductive reactance coil, e.g. the coil 60 in the upper circuit and the coil 61 in the lower, which substantially stabilizes the operation. Without these coils, there may be large fluctuations in power input, that may create some difficulty, although not insuperable, in control of the operation.
  • Electrical balancing means may also be employed in order to distribute the current between the electrodes .and thereby avoid any preferential passage of current through one electrode or the other with corresponding tendency to non-uniformity of current flow through the column, such balancing coils being shown at 62, 62', ⁇ 63 and 63.
  • the two electrodes 45, 45 are respectively conncted to the ends of the coil 672 which has its mid-point connected to one Side of the secondary of the transformer 58, and in this instance through the stabilizing coil 60.
  • the remaining balancing coils 62', 63 and 63 are similarly connected to the remaining pairs of electrodes, respectively 4646, 4747 and 48-48.
  • transformers 58, 59 are designed or adjusted (as by tapped or other variable windings, e.g. a tapped primary winding, as shown) to afford desired voltages respectively for the upper and lower heating columns and also for appropriate regulation of power inputs to these columns.
  • alternating current is of special advantage for energizing the several heating circuits shown, direct current (under suitable controls) can be used if available and desired.
  • the resistivity of the feed alloy in the columns 40, 41 decreases as its temperature rises, it is usually necessary, especially for good electrical eiiiciency, to apply different voltages to the respective column sections.
  • the voltage between the electrodes of column 40 is conveniently substantially higher than that applied across the electrodes of column 41.
  • the resistance of the body of material in column ⁇ 40, considered as a unitary mass, is correspondingly higher than that of the hotter body in column 41, making the above difference of voltages requisite or at least desirable to achieve high power input and maximum heating in both columns.
  • a suitable two-sta-ge heater such as shown in the drawings, for supply of granular alloy to a cylindrical converter 10 having an internal diameter of 5 feet and a vertical'distance between upper and lower electrodes 12, 12 and 13, 13 of about 25 feet.
  • Each of the columns 40, 41 in this example, has an internal diameter of 14 inches Iand a vertical distance between upper and lower electrodes (center to center) of 93 inches.
  • the intermediate mixing chamber 42 has a diameter at its maximum width region 50 of 39 inches, and a total capacity, between columns, of about 27.5 cubic feet.
  • the alloy entered the top of the first-stage heater, column 40, at approximately room temperature and was there heated to 400-500 C. under an Iapplied Voltage of 70 to 140 volts.
  • the 4alloy was carried from the above terminal temperature of the first stage, to a substantially higher value, i.e. ⁇ 700 C. and above, by current at a voltage of 40 to 70 volts.
  • valves 33, 34 are closed and hoppers 36, 32 are considered empty, the top hopper 30 being full of carbothermic alloy, e.g. irregular particles or fragments as resulting from breaking or crushing largerV pieces, and having particle size characteristics as elsewhere herein explained.
  • the top valve 33 is first opened and simultaneously a stream of inert gas is supplied through the pipe 37, venting through the top valve and hopper 30 as alloy descends into the hopper 36.
  • the valve 33 is then closed and the lower valve 34 opened allowing alloy to descend into the third hopper, and thence to the lower shaft system, i.e. the preheating column 40, chamber 42 and column 41.
  • the hopper 32 is lreiilled as necessary so that a continuous supply of feed is maintained for the system.
  • the speed of rotation of the table 43 bears a relationship to the rate of removal of alloy from the column and can be employed, within limits, to govern the general or average rate of downward travel of alloy under the force of gravity, i.e. the through-put.
  • This rate should be selected to agree with the desired through-put in the converter 10, the latter being chosen for desired results and being adjusted or controlled, not only in accordance with the gravity head of the material in the converter but also by varying the speed of the discharge device, e.g. cone 26, utilized for aid in removal of spent charge.
  • the following table sets forth typical electrical characteristics for various feed rates of an aluminum-containing carbothermic alloy, expressed in pounds per hour.
  • the composition of the alloy was: aluminum, 5053%; iron, 28- 3l%; carbon, 3.5-4.5 silicon 8.5-9.5 titanium, 3.3- 3.6%.
  • the moving alloy was raised from room temperature to .an average of about 500 C. and from the latter value to an average of about 700 C.
  • the power supplied in the respective stages is given as kilowatts required, the average power density (kw.
  • each stated value of nequired power included about 20 kilowatts of heat loss.
  • the table also sets forth the total resistance and the bulk resistivity (averaged ⁇ over the column) of the body of particulate lalloy in each stage, for the stated conditions of feed rate and current ow.
  • the resistan-ce of a column means the bulk resistance of the entire mass of particles in the column, as compacted by their own weight; resistivity of a column or bed similarly means the average bulk resistivity of the mass of particles; and each reference herein to a temperature coefficient of resistivity is characterized explicitly or by context, to have a selected one of two meansings, viz (a) a property of the column or bed in bulk, or (b) a property of the solid material itself, e.g. of massive alloy, as in the body of a single particle.
  • this alloy in particulate form, and indeed in the particle size ranges mentioned above, may be readily heated by operations of the type described and with apparatus as shown in the drawing, to bulk temperatures of more than l000 C. without diculty from fusing. Indeed experience indicates that up to temperatures near the softening point of the alloy (for example, about 1300J C. in the alloys treated above), the higher the temperature, i.e. temperature reached at the outlet of the preheater, the better the system performs.
  • the columns employed had an inside diameter of 14 inches and a length of 7 feet between electrodes.
  • the carbothermic alloy used had a particle size range between about one-fourth inch and about two and one-half inches, being regarded as a nominal or Iaverage particle size of about one and one-half to two inches. Feed rates of 1500 to 6000 Apounds per hour were utilized, being equivalent to about 135 to 550 cubic feet per hour of the ybulk material as it descended under gravity in the columns.
  • chart records of the current through a preheating column of the sort here shown show a continuing sequence of current fluctuations, with sharp decreases and gradual rises.
  • these sharp decreases regarded as major current iiuctuations, are understood to correspond to the pulses of downward movement of the alloy, when the particles shift and are re-oriented with fresh, relatively cooler points of contact and thus relatively hi-gher regions of electrical resistance.
  • the following table derived from counts of these major current fluctuations over a considerable number of r-uns of successful opera- TABLE I KW required Typical Feed Rate, (includes lb./hr. 20 kw. heat l 105s Current, Volts Resistance Resistivity,
  • the percentages at the head of each of the columns of time values refer to a measure of averaging or of numerically characterizing the rest periods: e.g. at 2000 pounds per hour, 50% of the intervals .between fluctations were 26 seconds or less, and 99% of such intervals were 93 seconds or less.
  • the greater or greatest intervals between downward jerks or pulses were about 75 to 100 seconds at the lowest of the feed rates and about 25 to 30 seconds at the highest.
  • the procedure and apparatus herein described are concerned with beds of fusible conductive material, e.g. solid metallic material in divided, i.e. particulate form (usually having particle diameters from about one-fourth inch to about five inches, and an average particle -diameter selected in the range from about one inch to about four inches), which have a negative coefficient of resistivity over a range of elevated temperatures (e.g. at least several lhundred degrees C.), it being desired -to heat the material over a substantial part of such range.
  • fusible conductive material e.g. solid metallic material in divided, i.e. particulate form (usually having particle diameters from about one-fourth inch to about five inches, and an average particle -diameter selected in the range from about one inch to about four inches), which have a negative coefficient of resistivity over a range of elevated temperatures (e.g. at least several lhundred degrees C.), it being desired -to heat the material over a substantial part of such range.
  • the invention is particularly concerned with alloyed r otherwise inseparablymixed or aggregated metals, including a substantial but not necessarily major content of aluminum, being material, such as the described carboA thermic alloy, utilized for separation of aluminum therefrom in the monohalide refining process.
  • alloys which remain essentially in solid state at the temperatures, i.e. upwards of 1000" C., employed for conversion.
  • a negative temperature coeicient of resistivity, over a range approaching conversion temperatures is charactertistic of massive bodies of most of such alloys or crude metals, e.g.V as given below, and of granular beds or columns of all of them, i.e. including compositions having relatively high aluminum content, single .pieces of which may show little change of resistance with temperature.
  • the carbothermic alloys employed, in granular, solid form generally had compositions within the following range (excluding slight or trace amounts of other metals):
  • Beds of granular alloys of this character have a resistivity at C. within the range of about 50 to 5000 ohmcentimeters.
  • the resisitivity drops yrapidly with increasing temperature to a value of about 0.1 ohm-centimeter at 1000" to 1100" C., and thereafter decreases only very slowly (indeed relatively insignificantly) to a value notV lower than about 0.05 at 1400" to 1500" C.
  • the electrical preheating operations can also .be employed in conjunction with other modes of preheating, for instance in that the function of the column or columns above the converter may be limited to reaching some temperature well below 1000" C., and one or moreother preheating practices, eg., as disclosed in the aforesaid U.S. Patent No. 2,937,082 and performed in upper zones of the converter vessel itself, may be utilized to get the granular charge material into a highly heated state, even to l200 C. or above, as it reaches the uppermost electrodes 12, 12' of the converter.
  • the present invention affords an effective and reliable mode of heating the fusible metallic material, utilizing the passage ofV electric current through suchmaterial, and particularly being able to take advantage of the efficient manner of operation wherein the current travels along ya path or paths coaxial with, i.e. the same as or parallel to, the path of movement of the material, whether the latter is directly vertical, or in some other direction, e.g. downward at an incline. Indeed notably in an upright column, this mode of current supply has special significance in aid of avoiding fused linkages of particles.
  • the equalization or mixing chamber 42 is of material consequence in the process, alfording not only some further, considerable shifting of contacts among the particles, but also providing equalization of temperature, both by distribution of the more highly heated granules and also by increased opportunity for conduction of heat throughout the mass.
  • the time of retention of a given particle i.e. its time of passage through the chamber, depends obviously on the rate of feed, Ait being found that as a very rough approximation, a typical and suitable time of retention for particles in this chamber 42 was about three times the interval of retention between electrodes in each of ,the columns 40 above and 41 below.
  • some further equalization, as well as redistribution occurs as the heated material traverses the chamber 44, and is advanced by the table feeder 43 down through the chute 24.
  • the number and dimensions of the preheat columns, and likewise of intermediate equalization chambers can be selected to suit any desiredcircumstances.
  • a single column may suflice, and in others two or more columns of equal size, preferably separated by an intermediate chamber, may be employed.
  • any desired number of stages can be used, with any desired temperature rise in each.
  • the process may be carried out with other means, even such equipment as a very slowly rocking or rotating, cylindrical rotary kiln, suitably inclined and refractory-lined and having embedded ring or other electrodes for passing current through the contained moving mass, or indeed with other suitable apparatus involving a bed of particles having appreciable, even though slight, freedom of movement relative to Veach other in consequence of advance of the bed or major portions of it, the use of upright columns (or a plurality of column systems in parallel) through which the bed of particulate material travels downward under the influence of gravity, is especially effective in achieving the desired character of motion .and reorientation of contacts (by virtue of such freedom of movement) while maintaining sufficient pressure between particles to assure a large multiplicity of current-carrying contacts ⁇ at all times.
  • a major but easily determined factor is the speed of movement of the material, epecially the rate at which particle-to-particle contacts are broken and the particles re-oriented, i.e. the frequency of pulsations or jerks in the downward travel of the bed.
  • the heating rate appropriately selected to suit the characteristics of the material (as explained), the desired results are easily achieved by designing the system and operation to have a suitable frequency of movement of the particulate mass.
  • the heating rate can be taken, for a given material, as power density, i.e. supplied power (including that required to account for heat losses) per cubic foot, averaged over the height of the column.
  • a method of heating a continuing feed of a mass which is composed of particulate, solid metallic material and which has a negative temperature coefficient of resistivity over a range of elevated temperatures, for raising the ltemperature of said particulate material to a predetermined value at least substantially higher than the lower limit of said range, from a value substantially below said predetermined value, comprising advancing said mass of metallic particles along a predetermined downward path while passing electric current through said mass to generate heat therein, said advance of the mass of particles including imparting pulsations of movement, through the mass, which produce mutual displacement of individual particles, and said pulsations being effected with sufficient frequency to prevent substantial mutual adhesion of particles in the mass by vfusion under the heating influence of the current, said mass being advanced by moving it under gravity along said downward path in a confined, columnar region, said downward movement being effectuated with the aforesaid pulsations by discharging the material of the mass at a locality below said region at a rate selected to impart said pulsations with the a
  • moving the mass of the material through the preheating zone comprises moving said mass downward by pulses under gravity through said Zone of columnar configuration, while passing said last-mentioned electric current through paths parallel tothe axis of the column between upper and lower electrodes exposed to said mass, said downward gravity movement and said cross-sectional area of the preheating zone being respectively controlled and selected for displacing the mass by said pulses of movement having a frequency to disturb the particles relative to each other to provide the aforesaid sufiicient mutual displacement ⁇ of the particles.
  • the preheating method includes moving said last-mentioned mass of particulate material from the aforesaid enclosed preheating zone through an enclosed region, for equalizing temperature throughout the material, and then through a second enclosed zone, for further preheating, said movement of thematerial through said second preheating zone being effected at a substantially faster average speed lof the particles than the advance of material through the converting region, while passing electric current through the moving material in said second preheating Zone to supply heat energy thereto, the said faster speed of movement of the material and the said smaller cross-sectional area of said second preheating zone cooperating to provide sufficient mutual displacement of particles of the material to prevent substantial mutual adhesion of said particles by, fusion while heating the material by said current in the second preheating zone to a temperature :substantially higher than the temperature to which the material is heated in the first preheating zone.
  • Vparticles of material have size characteristics within a range of about 1/2-inch to aboutl 4 inches and an average size selected in the range of 1 to 3 inches, said material having a negative temperature coefficient of resistivity through a temperature range from about 400 C. to at least about 1000" C., each ofsaid columnar preheating zQIfleS having a vertical distance of at least several feet between electrodes through which distance the mass is moved downwardly, said heating by the current in each said preheating zone being effected at a selected power density, of at least about 5 kilowatts per cubic foot,'to raise the temperature of the material in the first zone by at least 200 C.
  • said method including controlling the descent of material through the zones so that the mass is advanced in each Zone by pulsations having an approximate maximum interval between them sufficiently less than three minutes to provide the aforesaid sufficient disturbance of the particles to prevent appreciable particle fusion under the selected power density in each zone.
  • a method as defined in claim 8, which includes displacing the material transversely during its advance between said preheating Zones by moving it through an enclosed region, as aforesaid, having a cross-sectional area substantially larger than both of said preheating zones, to enhance equalization of temperature and uniformity of heating of the material by re-distributing the particles among Veach other for modifying their mutual contacts while slowing their advance between Zones for enhanced diffusion ofl heat.
  • a method as defined in claim 10, which includes continuously displacing the particles of material from a locality below the second preheating zone to advance the material into the conversion zone, for effectuating the downward movement of the mass through the first preheating zone, the ⁇ intermediate enclosed region and the second preheating zone by pulses of movement, said displacement of the particles being effected at a rate selected to provide the aforesaid frequency of pulses for said sufficient disturbance of the particles in each of Vsaid preheating zones.
  • a method as defined in claim 12, wherein the advance of the material through the preheating zone comprises advancing said last-mentioned mass of the material downward by gravity through said preheating zone while controlling discharge of said material below said preheating zone into the conversion zone, to maintain the aforesaid rate of said pulsations.
  • a converter comprising an upright columnar vessel adapted to receive a continuing downwardly traveling mass of said material, having vertically spaced electrode means for passage of current through the material in the vessel for supply of heat therein, said vessel having gas inlet and outlet means at respectively opposite ends thereof, and having a predetermined internal cross-sectional area, and means for preheating the particulate material for supply into said converter, comprising upright columnar structure above the converter vessel, to receive a continuing mass of said particulate material for downward advance, vertically spaced electrode means in said columnar structure for passage of current through the material to preheat the same, said columnar structure having an internal cross'- sectional area substantially smaller than the aforesaid cross-sectional area of the converter vessel, to provide substantially more rapid downward advance of the pafticulate mass in the columnar structure than in the converter, and means providing a path for said particulate material between said columnar structure and the converter vessel.
  • the upright columnar structure comprises va plurality of vertically successive columns each adapted to be filled with the descending particulate material and each having vertically spaced electrodes for passage of current through the material, each of said columns having an internal cross-sectional area substantially smaller than said area of the converter vessel, Iand enclosed means intermediate and communicating with the columns, providing enclosed space for travel of material between successive columns, having a cross-sectional area substantially wider than the columns adjoining said space, for slower travel of material than in the columns, to equalize the temperature of particles across the mass.
  • a converter comprising an upright refractory-lined columnar vessel adapted to receive a continuing downwardly traveling mass of said material, having vertically spaced electrode means for passage of current through the material in the vessel for supply of heat therein, said vessel having gas inlet means at a lower part thereof and gas outlet means at an upper part thereof, and said vessel having an internal crosssectional area of at least about 20 square feet, and means for preheating the particulate material for supply into said converter, comprising upright refractory-lined columnar structure above the -converter vessel, to receive a continuing mass of said particulate material for downward gravitation-al advance, vertically spaced electrode means in said columnar structure for passage of current through the material to preheat the same, said columnar structure having an internal cross-sectional area of less than one-third the aforesaid cross-sectional area of the converter vessel, means providing a path for said particulate material between said
  • the upright columnar structure comprises two vertically spaced refractory-lined columns each ladapted to be filled with the particulate material for movement downwardly by gravity
  • said apparatus including means providing a temperature-equalizing enclosed region between and communicating with said columns, which is substantially wider than the columns and is adapted to be filled with material moving from the upper column to the lower column, each of said columns having vertically spaced electrode means therein for passage of heating current through the body of material in the column along paths parallel to the axis thereof, said feeding means being constructed and arranged for controlling the downward travel of the material through the columns and the aforesaid intermediate equalizing zone, at the aforesaid desired speed in both of the columns.
  • Apparatus for preheating particulate metallic aluminum-containing material for continuing supply of successive quantities thereof to a converter of a system for producing purified aluminum by subhalide distillation from the Iaforesaid material comprising vertically spaced refractory-lined columns adapted tobe lled with such particulate material for movement downwardly by gravity, means providing a temperature-equalizing enclosed region betweenand-communicating with said columns, which is adapted to be iille'dvwith material moving from the upper column to the lower column, vertically spaced electrode means in each of the columns for passing current through the body of material in the column along paths parallel to the axis thereof, and feeding means arranged at the lower end of the lower column to receive the material, coacting with the'gravitational advance of material in the columns, and adapted for communication with a converter 4to feed the material thereto, for Icontrolling the downward travel of the material at a desired rate through the columns and the aforesaid intermediate equalizing zone.

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  • Engineering & Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Manufacturing & Machinery (AREA)
  • Materials Engineering (AREA)
  • Mechanical Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Manufacture And Refinement Of Metals (AREA)
  • Vaporization, Distillation, Condensation, Sublimation, And Cold Traps (AREA)
  • Paper (AREA)
  • Furnace Details (AREA)
US429826A 1965-02-02 1965-02-02 Heating metallic material for subhalide refining Expired - Lifetime US3346368A (en)

Priority Applications (9)

Application Number Priority Date Filing Date Title
US429826A US3346368A (en) 1965-02-02 1965-02-02 Heating metallic material for subhalide refining
GB1737/66A GB1134171A (en) 1965-02-02 1966-01-13 Heating metallic material for sub-halide process of refining aluminium
FR46090A FR1469272A (fr) 1965-02-02 1966-01-17 Raffinage aux sous-halogénures de l'aluminium
NO161327A NO116141B (US07709020-20100504-C00068.png) 1965-02-02 1966-01-19
BE675576D BE675576A (US07709020-20100504-C00068.png) 1965-02-02 1966-01-25
OA52338A OA01905A (fr) 1965-02-02 1966-01-29 Matériel de chauffage métallique pour le procédé de raffinage aux sous-halogénures de l'aluminium.
ES0322483A ES322483A1 (es) 1965-02-02 1966-02-01 Un procedimiento para la recuperacion de aluminio a partir de aleaciones que contienen aluminio.
CH134066A CH456164A (fr) 1965-02-02 1966-02-01 Procédé pour extraire l'aluminium d'alliages contenant de l'aluminium
NL6601343A NL6601343A (US07709020-20100504-C00068.png) 1965-02-02 1966-02-02

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
US429826A US3346368A (en) 1965-02-02 1965-02-02 Heating metallic material for subhalide refining

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US3346368A true US3346368A (en) 1967-10-10

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US429826A Expired - Lifetime US3346368A (en) 1965-02-02 1965-02-02 Heating metallic material for subhalide refining

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US (1) US3346368A (US07709020-20100504-C00068.png)
BE (1) BE675576A (US07709020-20100504-C00068.png)
CH (1) CH456164A (US07709020-20100504-C00068.png)
ES (1) ES322483A1 (US07709020-20100504-C00068.png)
FR (1) FR1469272A (US07709020-20100504-C00068.png)
GB (1) GB1134171A (US07709020-20100504-C00068.png)
NL (1) NL6601343A (US07709020-20100504-C00068.png)
NO (1) NO116141B (US07709020-20100504-C00068.png)
OA (1) OA01905A (US07709020-20100504-C00068.png)

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3384475A (en) * 1965-09-08 1968-05-21 Aluminum Lab Ltd Aluminum refining
US4522589A (en) * 1983-08-31 1985-06-11 Larson Ulf R Apparatus for discharging liquid-covered particles from a reaction chamber and subsequent drying of said particles
US5974076A (en) * 1998-02-09 1999-10-26 Brassey; John Michael Apparatus for activation of carbonaceous char or reactivation of spent carbon by electrical resistance heating

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
None *

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3384475A (en) * 1965-09-08 1968-05-21 Aluminum Lab Ltd Aluminum refining
US4522589A (en) * 1983-08-31 1985-06-11 Larson Ulf R Apparatus for discharging liquid-covered particles from a reaction chamber and subsequent drying of said particles
US5974076A (en) * 1998-02-09 1999-10-26 Brassey; John Michael Apparatus for activation of carbonaceous char or reactivation of spent carbon by electrical resistance heating

Also Published As

Publication number Publication date
CH456164A (fr) 1968-05-15
ES322483A1 (es) 1966-11-16
OA01905A (fr) 1970-02-04
BE675576A (US07709020-20100504-C00068.png) 1966-07-25
NO116141B (US07709020-20100504-C00068.png) 1969-02-03
FR1469272A (fr) 1967-02-10
NL6601343A (US07709020-20100504-C00068.png) 1966-08-03
GB1134171A (en) 1968-11-20

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