US2770364A - Alkali metal purification device - Google Patents

Description

av. 13, 1956 J 5 HQNEA ALKALI METAL PURIFICATION DEVICE Filed Oct. 14, 1954 tec -1 FIG. 4

FIG. 2

United States Patent ALKALI METAL PURIFICATION DEVICE John S. Honea, Baton Rouge, La., assignor to Ethyl Corporation, New York, N. Y., acorporation of Delaware Application October 14, 1954, Serial No. 462,235

2 Claims. (Cl. 210-525) This invention relates to cells for the production of alkali metals by the electrolysis of fused salts. More particularly, the invention relates to an improved discharge device incorporated in cells of the stated class, the discharge device being for discharge of liquid metal product from the cell, and for concurrently purifying same.

The most successful cells for the production of alkali metals by the electrolysis of fused salts are, basically, cells of the Downs type, such as are disclosed in Downs U. S. Patent 1,501,756. The characteristic of this cell is the employment of a centered bottom mounted carbon anode surrounded by a ferrous metal cathode, the two electrodes thus defining an annular electrolysis Zone. A diaphragm of cylindrical shape is inserted in this electrolysis zone and in effect provides a partition for segregating the products of the electrolysis, e. g. liquid sodium metal and chlorine gas. The catholyte, or metal product, and the anolyte or gaseous chlorine product rise in the fused electrolysis medium or bath in the electrolysis zone and in the sub Zones defined by the electrodes and the diaphragm. Suitable collection devices above .the electrodes provide for retention of the gaseous halogen product and the liquid alkali metal product.

It is customary in the electrolytic production of alkali metals to employ electrolytic bath mixtures including not only an alkali metal halide, but an additional component. In the case of the most significant commercial metal, sodium, an appreciable amount of calcium chloride is maintained in the bath. This component provides for a lower melting point of the electrolyte without allowing, to too great an extent, decomposition or electrolysis of the added component. Unfortunately, in practice, an appreciable amount of calcium metal is concurrently released, so that catholyte as deposited comprises sodium metal plus minor amounts of calcium. In discharging fromthe hot interior of a cell to the cooler external conduits; calcium metal is precipitated andconstitutes a heterogeneous impurity in the product.

r This precipitationof calcium impurity adeompanying a ,dropin the temperatureof the cell catholyte productjhas long been utilized in effecting; a partial purification of the product before dischafge toexternal vessels or conduits.

The discharge line from a sodium cell normally a verticalipipe, termed'a riser pipe,.projecting upwardly from the sodium collector. Owingto the difference in density of the. cell bath and the sodium metal pro d uct, sufiicient hydrostatic head is availableto .transport this sodium an appreciable distance above thebath level andhence. into space outside thelcell proper. 1 The riser pipe has therefore been available for and has been usedas a heat transfer device for radiating heat from the catholyte product and allowing precipitation of solid calcium metal particles which are. heavier than the sodium properl These precipitated particles tcndto settle back through the slowly rising stream of sodium and t o be returned to the cell interior. Unfortunately, the calcium is precipitated. predominantly at the riser pipe wall; at which point, of

'ice

course the temperature is lowest and the heat transfer occurs. To prevent adhesion and eventual plugging of the riser pipe by these calcium particles, manually operated devices termed ticklers have been built into the riser pipes. These are elongated shafts, concentric with and coextensive with the riser pipe and having paddles or blades attached thereto at right angles and sweeping a short segment of the riser pipe wall. In operation, such ticklers were rotated and vertically oscillated through a. limited path by cell' operators.

It has been customary to operate these ticklers by hand. In a given operation of a large bank or series of cells, an operator would usually be assigned a specific num ber of cells and be responsible for their performance. It is customary to agitate these ticklers at regular intervals and thereby to keep the riser pipe walls clean and prevent pluggage and maintain product purity. This system is, of course, adequate in theory but because of normal human frailties, it sometimes happens that the required tickling is inadvertently omitted from the sched: ule sequence. In addition, the manual tickling operation is an onerous task inasmuch at is requires standing above an operating cell, the interior of which is at a temperature of over 500 C. Manual operation has also been found to be limited in practice to non-integrated motion, i. e., without the correlation of movement provided by the present invention. Frequently calcium deposits do build up in the riser pipe. Then, when operation does take place, the mechanical strain results in bending or breakage, and frequently the riser pipe can also not be effectively cleaned. In consequence, the industry has been accustomed to change tickiers at frequent intervals.

Mechanically operated ticklers have been heretofore proposed, but none has ever been provided which meets the requirements of simple operation, longevity, low cost of construction and operation, and effective cleaning of the riser pipe Walls to permit extended cell operation and release an adequately purified sodium product.

The object of the present invention is to provide a new and improved mechanically operated tickler and operating mechanism therefor for use in a sodium cell or the like. A further object is to provide a tickler assembly in a cell providing substantially increased usefullife, thus reducing substantially interruptions to cell operation for replacements. A further object is to provide improved cell operations without increase in operating labor. Still another object is to provide a mechanically operated tickler which provides automatically repetitive movement of a single cycle, or portion thereof, ifsevere. deposits must be cleared from the riser pipe wall in that cycle, without jamming and becoming inoperative. A further object is toprovide apparatus capable of fully automatic operation even in plant installations on a large number of cells. Yet another object is to provide a tickler apparatus which accomplishes a hitherto unavailable motion sequence, and not only; cleans the riser pipe ,wall, but also i movement along a generally predetermined path. The tickler proper is mounted concentrically and approximately coextensivelywithin the riser pipe of a cell, and

is adapted for limited vertical movement and for-rotation within the riser pipe. The actuating means for lowering and raising the tickler proper maybe of several varieties, e. g., a pneumatic piston-cylinder combination operatively connected to the tickleiyor an electrical means such as a solenoid. The guiding means includes a cylindrical cam and: a cam follower, the follower being operatiyely connected to thetickler proper. The ac;

tuating means and guiding means concurrently provide for a repetitive series of motion cycles which provide a sweep or cleaning of substantially the entire riser pipe wall in one revolution, and also provide for cleaning of the tickler proper as hereafter explained.

As heretofore mentioned, the guiding and actuating means must provide a combination of multi-component sequential motions, certain limitations having been found essential on the several components and the combination thereof. These requisites include the following. Firstly, the entire interior surface or substantially all of the surface of the riser pipe must be periodically cleaned by wiping or near wiping with sufficient force to dislodge solidified calcium particles from the pipe wall. Secondly, not only must the calcium be dislodged from the riser pipe wall, but substantially concurrently it must be removed from the dislodging elements, i. e., the tickler assembly itself. In addition, if the effective motion includes vertical travel components, the extent should be limited to less than about one-half a foot, not only because of mechanical design limitations, but also because vertical movement of greater amplitude than, roughly, six inches (regardless of the diameter of the riser pipe) will tend to unduly agitate the sodium stream within the riser pipe and cause highly undesirable back mixing.

Accordingly, the present invention in operation provides a sequence of repetitive, equivalent cycles of the tickler assembly. Each cycle includes up and down vertical components of from about two to about six inches. In addition, each vertical component has superimposed upon at least a portion thereof a rotation component. The relation of this component to the portion of the vertical component upon which it is superimposed is conveniently expressed as degrees per inch. This ratio is preferably of the order of to per inch, and should not exceed about per inch. In order to provide self cleaning of the tickler parts, it has also been discovered that the total downward thrust, including the weight of moving parts, in each cycle must be above a certain level, which has been found to be about ten pounds per pound of the moving assembly. It is preferred, however, to provide a downward thrust in the range of 12 to 15 pounds per pound although a downward thrust as high as 20 pounds per pound may be employed in embodiments having a smaller amplitude of vertical path. In the event that the'actuating means employed is unable to dislodge particularly hard and adherent calcium particles in any particular cycle, the cycle must be reinitiated automatically, and until the calcium is dislodged and the riser pipe wall is clean, before the next cycle. is initiated. The requirements of new upward thrust are less rigorous, but it should be of the same order of magnitude.

The apparatus of the present invention provides these requisites as will be seen from the description following. The details of the apparatus and of preferred embodiments. will be more readily understood from the following description and by reference to the accompanying Figures 1 4, where in Figure 1 is a generalized elevation illustrating the relation of the assembly of the present invention to the fused salt electrolysis cell for which it is intended,

Figure 2 is an elevation, ona somewhat larger scale, and in partial cross section of the riser pipe of the cell having the apparatus and operating means incorporated therein, and l Figure 3, which is a developed schematic diagram of a typical and preferred guiding or cam means, and Figure 4, which is a schematic representation illustrating the tickler movement guided by the cam means shown 'in Figure 3.

The general disposition of the apparatus of the present invention and asodium cell is illustrated by Figure 1 as above mentioned. Referring to Figure 1, the principal componentsof a cell include a cell body 11 comprising an external steel shell lined with refractory brick or lining.

A centrally mounted carbon anode 12 is surrounded by' a cylindrical cathode 13, having lugs 14 projecting through the cell walls and providing for connection to bus bars 15 supplying the electric current. Similarly the current is fed to the anode 12 by an anode bus bar 16. A dome and collector assembly 17 is mounted centrally above the anode-cathode electrodes and includes a chlorine dome 18 in the form of an inverted generally conical member and a sodium collecting conduit 19. The chlorine dome terminates in a chlorine discharge line 20 to transfer the gaseous chlorine to subsequent operations. The sodium collecting conduit 19 meets and is connected to the riser pipe 21. The riser pipe, here shown only in external view, is an elongated steel tube provided with fins 22 on at least a portion of the external portion. Surmounting the riser pipe is the guiding and actuating assembly discussed and described in detail hereafter. The fins 22 on the exterior portion of the riser pipe improve the dissipation of heat from the interior of the pipe and its contents. Sodium discharge from the cell is discharged through a connecting line 25 from the riser pipe and feeds a receiving box 26 which is a container for temporary hold up of the sodium, the sodium being then passed through a discharge spout 27 to a transfer vessel or container.

In operation, the cell contains, up to a level approximately intermediate the full vertical elevation of the chlorine dome 18, fused electrolyte chlorides or a bath 31. This molten bath includes not only sodium chloride but appreciable quantities of calcium chloride. The sodium and chlorine are released in the annular space between the anode 12 and cathode 13 and rise on opposite sides of a diaphragm 32. The sodium collects in the channel 19 and flows to the entrance of the riser pipe 21. It then rises in the riser pipe 21 and is discharged through line 25 to the receiver 26 and thence through the nozzle to a transfer container, not shown. The heat loss from the riser pipe through the fins 22 results in precipitation of calcium at and on the interior Wall of the riser pipe 21.

The details of construction and operation of the improved tickler, and guiding and actuating assembly, will be most readily understood by reference to Figures 2, 3, and 4, these latter two figures illustrating explicitly a preferred embodiment of the present invention. 'Iurning firstly to Figure 2, this is an elevation, on a larger scale than Figure 1 and in partial cross section showing the relation of a typical tickler assembly within the riser pipe 21. The tickler includes a central shaft 41 upon which are mounted a plurality of tickler blades 42 at regular intervals through its vertical length. The blades are generally rectangular steel blades of approximately the proportions 4:1 to 6:1, length: width, the length of the blades being only'a fraction of an inch lessin length than the diameter of the riser pipe at the particular location. The blades are joined by sweep bars 43 to the adjacent paddles, the connection being alternated only, thus creating-in effect a-zig-zag pattern in plan as shown in Figure 2. The tickler shaft 41 projects through the riser pipe cover 23 into the guiding and actuating assembly 51 and connects thereto. This assembly comprises two principal sub-assemblies, namely, means for guiding and providing rotative as well as vertical movement for the tickler assembly, and'actuating means for applying vertical movements. In the'preferred apparatus of the invention as shown herein the first of the said two sub-assemblies is a cylindrical multi-lobe cam 53 engaging with and guiding a follower 54 operatively' connected to the tickler shaft 41. An extension 55 concentric with and attached to the tickler shaft 41 projects through the cam arrangement into'means 56 for providing vertical movements.

The operating means in the present embodiment is a pneumatic actuated piston-cylinder combination, a compressed gas for operating the piston and the related and V fconnected components being provided through lines 57.

In operation, cyclic transmission of gas pressure to the s operating; piston-cylinder 56 through lines 57 results in alternating upward-downward movement of the piston, the shaft extension 55, cam follower 54, and the tickler assembly including the shaft and blades 41, 42. Concurrently with the upward or downward movement, radial motionis impartedby cam 53 and follower 54. As explained in more detail hereafter, it has been found that rotatative movement should be imparted in at least a portion of each vertical path, and, further, that such rotation should not be in excess of 30 per inch of vertical travel. The apparent reason for this requisite is described hereafter. Generally, therefore, it is desired that the cam will provide a path having not less than five lobes and preferably from six to eight lobes. Generally, an even number of lobes is preferable, primarily for economy of fabrication.

The precise mode of operation of the operating assembly 51 will be more readily apparent from Figure 3 which is a developed enlargement showing the cylindrical cam outline, and from Figure 4, showing schematically the cam follower path for the cam of Figure 3. Referring to Figure 3, developed elevations of matching cylindrical cam segments 53a and 53b are shown, these cams defining a circumferential oscillating path including six up and six down strokes, each of said strokes being accompanied by a uni-directional rotation component equivalent to 30. In addition, the total amplitude of vertical motion should not exceed a distance of the order of approximately one-half foot, a preferred range being about 2 to 4". It will be seen that each cam segment provides six lobes 58 having a vertical side and an inclined side. The spacing of the lobes is, of course, 60, but the apposition of the corresponding valley in the opposite cam, results in operation of the inclined portion of the lobe on the cutter 54 to provide rotation through 30 by each of said lobes.

It will be noted that the crest 59 of each lobe 58 of each cam segment is staggered circumferentially from the valley 60 of the opposite segment. This has an important practical significance, inasmuch as it provides (a) normally unidirectional rotation and (b) and also opportunity for reinitiation of a cycle, or a portion of a cycle, if unexpectedly severe fouling is encountered. Thus, if, for example, the tickler becomes jammed while on any particular segment, the follower 54 will remain stationary until reversal of the vertical movement. The follower will then return to the bottom of the valley and the same cycle movement will be reinitiated on the next reversal of the actuating mechanism. This sequence, in effect, amounts to providing repetitive striking of a particularly adherent chunk or deposit of calcium, automatically and when necessary. I

Figure 4 illustrates the motion sequence somewhat more clearly than apparent from Figure 3, the figure showing the progression of the center line of the follower 54 in making one full revolution. It will be seen that the full revolution includes six cycles of degree rotation each, and each cycle includes four substantially lineal segments a, b, c, d. In this embodiment the first portion, a, of a cycle is an upward thrust for a distance of approximately one-half the total vertical movement, thus, from about one to three inches. The next component is a continuation of the upward movement and an accompanying or superimposed rotation of 30 degrees. Following these two components, the pattern is reversed with a downward thrust, c, and a final component, d, which includes a 30 degree rotation. As a typical variation, the inclined segment of each cam lobe may be a concave curve segment, so that, upon changing from a solely vertical path to a helical path, sharp impact is avoided between the follower and the cam lobe. Thus, in effect, the vertical downward motion, 0 (Figure 4), may merge gradually into the component, d, by design of the latter portion as a tangential curve to the straight vertical section.

In addition to variations in path of this general character, it is not essential that corresponding components of upward and downward travel be exactly equal even if in the same cycle. Thus, referring to Figure 4, the straight upward motion, a, may be considerably less in magnitude than the straight downward component, 0. Successive cycles, are of course usually and desirably identical, but even here there may be certain variations within the limits already defined.

It will be evident to those skilled in the art that the general requisites of the sequential movement heretofore stated can be accomplished with appreciable variation of the cycle specifically illustrated.

As has heretofore been discussed, the number of lobes can of course be varied providing that the desired ranges of ratio components is maintained; thus it is quite practical to utilize five lobes in each cam element or as many as eight lobes. The larger number of lobes will permit application of greater torque on the tickler assembly proper upon a definite downward thrust component and will be considered advantageous in riserpipes of larger diameters. Normally, six lobes and a vertical path, total, of about threeto four inches is ample for most purposes.

The apparatus is fully capable of being continuously operated if desired, but in practice this has been found nonessential and in fact it is preferred to operate on an intermittent basis. Generally, it is found preferable that the apparatus be operated for short duration at intervals of about fifteen minutes to about one hour. By operation for short duration is meant that it is operated to provide a total of about two to five complete revolutions. The particular means of providing for such intermittent and repetitive automatic operation can be widely varied. In the embodiment illustrated by Figure 2 wherein the actuating mechanism is a pneumatic piston-cylinder combination, the cycling of the compressed gas through lines 57, to the top or bottom face of the operating piston within the cylinder 56 is accomplished by any appropriate timing-valving combination. The apparatus is not restricted specifically to pneumatic actuating devices, however, and in some instances it will be found highly advantageous to employ an electric solenoid type of actuator. The problem of timing and sequential intermittent operation of a large plurality of these apparatuses is essentially the same for an electrical actuating device as for a pneumatic device.

Considerable variation of the specific esign of the tickler proper is permissible, subject to the limitation that substantially all the riser pipe wall is wiped by one revolution. Thus, as an alternative to the tickler assembly shown in Figure 2, install blades and sweep bars defining an alternating plan, one full length sweep bar the full height of the tickler would suflice. Such a design, would, however, be open to the objection that some bottom bearing would be necessary for the shaft 41, whereas, with alternately positioned sweep bars 43, the riser pipe itself, in effect, forms a journal for the movement of the ticlrler assembly.

As illustrative of the efiicieucy of the apparatus in commercial installations, in a typical sodium cell shop, a battery of the automatic ticklers herein described was placed in operation and carefully observed for an extended period, while concurrently the remaining cells of the shop Were operated in the conventional manner, i. e., with manual tickling. The experience of the operation was that highly effective purification of sodium was obtained in all instances, and that the average duration of life of the automatic ticklers of the present invention was four times or greater than the average duration of manually operated ticklers.

Having fully described the apparatus of my invention and the manner of its employment, what I desire to claim 1s:

1. An automatic tickler assembly for use in a substantially vertical riser pipe of a fused salt electrolysis cell,

said assembly including a tickler for insertion within the riser pipe, the tickler having elements for sweeping substantially the entire riser pipe internal wall area by movement hereafter defined, and being adapted for limited vertical movement and for rotation, means for applying solely vertical reciprocating force to the tickler independent of rotation thereof, said force including a downward thrust of at least 10 pounds for pound of the tickler weight; and guiding means, said guiding means including a stationary, two element, cylindrical cam and a follower operatively attached to the tickler, the cam defining a repetitive series of cycles for the tickler, each cycle c011- sisting of vertical upward and downward movements of equal amplitude of from about two to about six inches and unidirectional rotation in a portion of each vertical movement, the ratio of rotation to the concurrent vertical movement being not greater than about 30 degrees per inch.

2. An automatic tickler assembly for use in a substantially vertical riser pipe of a fused salt electrolysis cell, said assembly including a tickler for insertion within the riser pipe, the tickler having elements for sweeping substantially the entire riser pipe internal Wall area by movement hereafter defined, and being adapted for limited vertical movement and for rotation, means for applying solely vertical reciprocating force .to the tickler independent of rotation thereoflsaid force including a downward thrust of from 12 to 15 pounds per pound of the tickler weight, and guiding means, said guiding meansuineluding a stationary, two element, cylindrical cam and a follower operatively attached to the tickler, the cam defining a repetitive series of cycles for the tickler, each cycle consisting of vertical upward and downward movements of equal amplitude of from about two to about four inches and unidirectional rotation in a portion of each vertical movement, the ratio of rotation to the concurrent vertical movement being from about 15 to about 20 degrees per inch, and each cycle providing a rotation of 60 degrees.

References Cited in the file of this patent UNITED STATES PATENTS 230,917 Baum Aug. 10, 1880 1,228,496 Turner June 5, 1917 1,387,101 Candee Aug. 9 1921 2,286,397 Weiss et a1 June 16, 1942 2,390,115 McNitt Dec. 4, 1945 2,454,884 Peadon Nov. 30, 1948 2,472,093 Cournoyer et a1. June 7, 1949

Claims (1)

1. AN AUTOMATIC TICKLER ASSEMBLY FOR USE IN A SUBSTANTIALLY VERTICAL RISER PIPE OF FUSED SALT ELECTROLYSIS CELL, SAID ASSEMBLY INCLUDING A TICKLER FOR INSERTION WITHIN THE RISER PIPE, THE TICKLER HAVING ELEMENTS FOR SWEEPING SUBSTANTIALLY THE ENTIRE RISER PIPE INTERNAL WALL AREA BY MOVEMENT HEREAFTER DEFINED, AND BEING ADAPTED FOR LIMITED VERTICAL MOVEMENT AND FOR ROTATION, MEANS FOR APPLYING SOLELY VERTICAL RECIPROCATING FORCE TO THE TICKLER INDEPENDENT OF ROTATION THEREOF, SAID FORCE INCLUDING A DOWNWARD THRUST OF AT LEAST 10 POUNDS FOR POUND OF THE TICKLER WEIGHT; AND GUIDING MEANS, SAID GUIDING MEANS INCLUDING A STATIONARY, TWO ELEMENT, CYLINDRICAL CAM AND A FOLLOWER OPERATIVELY ATTACHED TO THE TICKLER, THE CAM DEFINING A REPETITIVE SERIES OF CYCLES FOR THE TICKLER, EACH CYCLE CON-

Images