US1524268A - Electrolyzing fused baths - Google Patents

Description

Jan, 27, 1925. 1,524,268

R. J. MCNITT ELECTROLY ZING FUSED BATHS I Original Filed Feb. 2, 1921 2 Sheets$heet l J 27, 1925. 1,524,268 R. J. MCNITT BLECTROLYZING FUSED BATHS Original Filed Feb. 2, 1921 2 Sheets-Sheet 2.

be mentioned the following:

Patented Jan. 27, 192 5.

UNITED STATES PATENT oi-"Pica.

ROBERT J. MGNITT, OF PERTH AMBOY, NEW JERSEY.

ELECTROLYZING FUSED BATES.

Application filed February 2, 1921, Serial No. 441,921. Renewed April 4, 1924.

and State of New Jersey, have invented certain new and useful Improvements in Electrolyzing Fused Baths, of which the following is a specification.

My invention pertains to electrochemical processes operating with fused electrolytes, and has for its purpose the elimination or reductionof imperfections existing in such processes. Among these imperfections may 1st. The application of heat from external sources is not advantageously made, and in attempting to maintain thermal equilibrium by -means of the electrolytic current there occur excessive energy losses, and those conditions favorable to high yields (current density and electrode spacing) are sacrificed. Where units are operated electrically in series as is customary, the'cur rent isadjusted to maintain a favorable temperature in the coldest unit, that is the unit operating with highest energy efliciency; and in order to prevent excessive temperature in other units, it is customary to shunt a portion of the current around these units through an external resistance, to! disconnect the hot units from the circuit from time to time, to change the electrode spacing, to circulate cooling fluids through ducts in the electrolyte or furnace walls, or to vary the rate of heat radiation from external surfaces. These methods of control'result in loss of power, loss of production, unfavorable conditions for high average yields, and high costs for attendance and maintenance 2nd. In the operation of units connected electrically in multiple, it is difficult to maintain proper division of the electric current, on account of the temperature resistance characteristic of-the fused electrolyte.

After the current has been carefully ad justed, owing to a slight change in radiation constant or operating efficiency one unit may tend to Cl'llll ofl' w1th consequent 1ncrease in the electrolyte resistance and a diversion of current to other units. One or more of these other units will warm up under the additional current with corresponding reduction in the resistance of their electrolytes. Hence more and more of the current will be divertedfrom'the cold unit electrodes with larger surfaces and low re-' sistance it has been considered impracticable to operate more than one electrochemical unit in a single cell, or to operate individual cells in multiple except in a multiple series arrangement, where a sufficient number of units are in series, so that the average resistance characteristics of all parallel branches shall be approximately the same.

3rd. The electrolye is not maintained in such condition as to uniformity of constituents, temperature and purity as is necessary to lnsure uniformly high ampere yields. It is customary to allow impurities to accumulate until the yield falls below i the economic limit, whereupon the electrolyte is removed, and the cell cleaned and refilled with fresh electrolyte; a method of operation which is costly in both labor and materials, and which results in relatively low average yields. Also, due to the tendency to accumulation of impurities, all materials put into the bath must be as pure as possible. l/Vhere mixed baths or fluxing agents are used it is difficultto maintain in all units the most favorable mixtures of constituents. Generally it is necessary to make frequent analyses of the bath in. each unit, and, treating each unit separately, to add such amounts of the various materials as are determined to be necessary.

4th. On account of structural limitations and operating difliculties the size of the individual unit used in these processes is small, and the energy lost through radiation and conduction is great in comparison with the energy consumed in useful work. Also the cost of operating and maintaining numerous small units is high.

Now the improvement which I have made reduces or eliminates these imperfections and consists in its preferred embodiment:

In causing the fused electrolyte of proper (constitution, temperature, and purity to flow to each electrochemical unit, in excess of the amount required for electrolytic deoutside the zone of elctrolyticaction, and

2 cell wall are made of graphite and are re- I trolyzing units; and

submitting same to purification, replenishment, the application of heat, cold, or such I additional treatment as may be necessary totproduce an electrolyte of proper constitution, temperature and purity; and cansing the latter to again flow in excess to each unit as described before.

By way of illustration I shall describe my invention asapplied to a process of electrolyzing fused sodium chloride in units consisting of vertical electrodes separated by a porous partition or diaphragm, and for assistance to a clear understanding of the invention reference is made to the accom panying drawings, in which the figures are diagrammatic in character and wherein:

Fig. 1 is a vertical longitudinal view,

partly in section along line 11 of Fig. 2,

I of a typical installation for the above pur- )oses. 1 Fig. 2 is a plan view of the same;

Fig. 3 is a partly sectional View along the central line 3-3 of Fig. 2;

Fig. 4 is a transverse vertical section on line 4-4 of Fig. 2; v

Fig. 5 is a transverse vertical section on a somewhat larger scale of one of the elec- Fig. 6 is a longitudinal vertical section on a somewhat enlarged scale of one ofthe electrolyzing units.

The illustrated installation comprises a multiplicity of electrolyzing units 10 arranged in multiple electrical connection with a source of current 11, and are grouped together to reduce the external heat radiating andconducting surfaces. The walls of the cells l2 inwhlch'the units are located are preferably constructed of refractory brick and fireclay shapes and are preferably surrounded by thermal insulating material, as Ifor-example bricks 13 made from kieselu r.

O The anodes 14 which form part of the spectively connected with the source of electrical energy 11 through graphite conhoods 21 surmounting the cathodes. In turn these hoods are supported by pipes 22 through which the metallic sodium which collects in Lhe hoods in operation may be withdrawn. Inwardly extending collars 21 centrally of the hood provide passages between the upper and lower levels of the cells.

The chlorin gas develo ed in the electrol sis is removed throng pipes 23. p

The bottoms 24 of the cells converge as shown and open into a duct or trough 2b running lengthwise of the installation, there being shown one of these ducts for each of the two rows of cells. Each duct 25 opens at one end thereof into an electrolyte reservoir 26 and the two reservoirs 26 are in c0mmunication at or near their bottoms through a cross-passage 27 (Fig. 4). In each reservoir 26 a pump 28 is provided,

the outlet passage whereof leads to respective filter chambers 29. Each filter 29 has an outlet pipe 30 communicating with a central reservoir 31.

A suitable pump 32 in reservoir 31 has its inlet side open to the electrolyte in the reservoir while its outlet connects through pipe 33 with acell-supply duct or manifold 34 which lies in a channel in the top of the brickwork between and above the two rows of cells. Branch pipes 35 distribute the ,electrolyte to the individual cells, regulation of the flow through the respective branch pipes being effected by means of the valves 36. The electrolyte is preferably introduced into the cell at two points on each side thereof, a portion entering at the top of the anode 14 through pipes 37 (Fig. 6) and a portion entering near the top of the bath through the pipes 38. The relative flow through pipes 37 and 38 is adjusted by suitable devices, not shown, such as deflectors in the branch pipes 35.

For supplying additional heat to the electrolyte flowing to the units, each of the individual feed pipes 37 may be provided with an electrical resistor 39. For the purpose of extracting heat from the electrolyte as it passes through the branch ducts, the latter are provided at their upper portions with suitable water-jackets 40 (Fig. 5)

Beyond the branch pipes of the last cells the manifold 34 makes a return bend, and extends rearwardly beneath the cell-supof gas or oil burners 47.

plying portion of the same, through the central reservoir 31 and into an electrolyteheating retort 41. The heating means for this retort may be a gas or an oil burner, indicated at 42. Through a valved outlet 43 the electrolyte which "is not diverted to the cells 10 is returned. to the reservoir 31- :tor recirculation, valve 44 in the section of the manifold extending into the retort 41 being partly orentirely closed. It substantial reheatingot the electrolyte is necessary, valve 44 is opened and valve 43 is partly or entirely closed.

Arranged near the reservoirs 26 and communicating respectively therewith are retorts 45 into which the solid replenishing materials, for example common salt with small quantities of fluxing agents, are introduced through hoppers 46, and in which such materials are fused and purified. The retorts may be externally heated by means For purilying the materials, the latter in a fused state are passed through special low-voltage electrochemical units 48, shown submerged in the fused baths in retonts 45, and provided with insoluble or removable anodes. .The fused replenishing materials are discharged from units 48 through pipes 49 into reservoirs 26 where they mingle with the residual portion of the electrolyte therein, and are filtered with the latter.- 1

For maintaining an elevated temperature in the fused electrolyte in the reservoirs 26, an electrical resistor 50 maybe located along the bottoms thereof andthe bottom of the cross duct'27ewhich connects the reservoirs 26. The terminals of the resistor are indicated at 51. Similarly, the duct 25 -may be provided with an electrical resistor 52 for maintaining the fused electrolyte therein at an elevated temperature.

In using the apparatus described for carrying out my process, a fused'electrolyte of proper temperature, purity and constitution, for example sodium chloridand such fluxing agents as may be preferred, is pumped from reservoir 31 through the manifold 34 to each unit, in excess of the amount required for electrolytic decomposition. The flow of the electrolyte to the various units 10 is regulated by the valves 36 in the branch ducts 35, and the temperature of the entering electrolyte is regulated by means of the respective electric heating elements 39 (Fig; 5). By this regulation the tem- V perature ofthe electrolyte undergoing electrolysis is held at the point favoring highest yields. Also a proper division of electric current is maintained between the various units connected in multiple.

The electrolyte is circulated through the units in such manner (see arrows in Figs.

'5 and '6) that solid impurities such as particles of carbon, carbides, iron, calcium, magnesium, copper, sand 'and fireclay, as well as impurities in solution, such as the metallic chlorids, are taken up by the residual portion of the electrolyte (i. e. the portion not decomposed) and removed from the Zone of electrolytic action. This residua1 portion of the electrolyte laden with impurities passes through the open "bottom of each unit into one of the ducts 25 where it unites with the residual portions from the other units, and by these ducts 25 the electrolyte is conveyed to the reservoirs 26. In the latter are facilities toixremoving impurities from the electrolyte. Purification may consist in chemical treatment, or electrolysis in a specially designed unit, to separate out impurities from solution, or it may consist merely in settling or filtering out of the solid impurities. The detailed method of purification depends on the nature of the impurities, which in turn depends upon the purity of the materials used for replenishment, and the nature of the materials used in the construction of the supporting structure and linings of the cell surrounding the unit, as well as upon the skill of the operator. In general, mechanical treatment is sutficient and accordingly I have shown a filter 29 in each reservoir 26 through which the electrolyte is forced by the pumps 28. The filters may beconstructed of wire cloth, perforated metal, coke, charcoal and similar materials. From the filters 29 the purified electrolyte passes into the central reservoir 31 for recirculation.

The facilities for fusing and mixing the materials supplied as requ1red for replenishing the electrolyte are preferably grouped together with the units as shown, and where the number of units is suflticient there may be facilities for purifying these materials. In the example described the replenishing materials, mostly common salt with small quantities of fluxing agents are fused in the'retorts 45, being fed solid thereto from thehopper46 (Fig.1). The purification treatment of the replenishing materials is. here illustrated as effected by electrolyzing the fused material in a special low voltage unit 48, the anodes of which are insoluble or removable. By this treatment oxygen bearing impurities are broken down and prevented from entering the regular process and attacking the permanent graphite electrodes. The units 48 are shown sub merged in the tusedbaths in retorts 45.

The fused replenishing materials are discharged trom the units 48 through the conduits 49 into the reservoirs 26 where they mingle with the residual portion of the electrolyte and are filtered with the latter. The temperature of the fused electrolyte in the reservoirs 26 is maintained at a suitable point by the generation of heat in the electrical resistors 50 and 52 located at the bottoms" of the reservoirs and the ducts 25 and 27 The purified and replenished electrolyte is discharged from the filters 29' into the discharged through valve 44 into retort 41 (Figs. 2 and 3) where heat is added, and the hot electrolyte discharged by pipe 53 into reservoir 31 from which it is again pumped to the various units through the manifold 34.

By the addition of heat to the electrolyte in retorts 45 and 41 and the resistor in duct 27, it is possible to maintain thermal equilibrium in the system and still opcrate the units with a current density and electrode spacing most favorable for'maximum yields. This additional heat replaces a considerable portion of the total energy losses and results in 'a saving in electrolytic power by reducing the operating voltage to a point as near as possible to the decomposition voltage.

Where heat is added by the combustion of fuels, retorts 45-and 41 should be made wholly or as to linings from calorized steehmiekel-chromium or other suitable alloys. As the quantity of exit gases from the retorts may be considerable and as they leave the heating surfaces at a high temperature it is economical to pass them through some form of economizer (not shown), as for example a steam boiler.

If the cost of electrical power' is relatively low, heat may be obtained for fusing the replenishing materials and maintaining temperature equilibrium by applying the power directly or indirectly through resistors in retorts 45 and 41 or in the reservoirs 26 and 31-. I The regulation oftemperature of the electrolyte entering each unit is brought about by adding or extracting heat at some point between the control cock 36 of each unit and the point where the electrolyte enters the chamber surrounding the unit. This heat is added by applying auxiliary electric power, or by the combustion-of gas or oil. In the embodiment illustrated in the drawings, it is obtained through the electrical resistors 39 -.(Fig,- 5) in each branch duct 35 whichconnects each cock 36 with the chamber surrounding the unit. Where oil or gas fuel is used a .small'coil or r e.-'

tort (not shown) of sufiicient heating surface is inserted between each cock and the corresponding branch duct, and the entering electrolyte is made to flow through this coil or retort while flames are projected against the external surface. Heat is extracted by wa ter-cooling. In the example illustrated, the upper portion of each branch duct 35 is surrounded by a Water-jacket 40 (Fig. 5) so proportioned that the temperature of the flowing electrolyte may be reduced without risk of freezing or solidification.

By the manner of flow through manifold 34, the electrolyte enters the control cook 36 of each unit at practically the same temperature. Also the constitution of the electrolyte is practically uniform in all units. These two facts make it possible to control most units by merely regulating the rate of flow of the entering electrolyte. In units having abnormal radiation or efiicien'cy characteristics, however, it is advantageous to be able to regulate the temperature of the entering electrolyte.

By virtue of the control obtained through regulation of the temperature and rate of fiow of the entering electrolyte, it is possible to adjust the electrolytic current for average conditions and to run for a long period without readjustment. The excess heat developing in any unit tendin to run warm is carried by a relatively arge flow of slightly superheated electrolyte into the duct 25, where it warms up the chilled elec trolyte returning from units which tend to run cold. This thermal equalizing effect is most advantageous in saving energy and in stabilizing the system, thus reducing the attendance required.

The circulation of the electrolyte through each unit should be such as to insure that the purest electrolyte shall always be present in the electrolytic zone, that im urities shall be prevented from entering t e electrolytic zone and shall be removed to the reservoirs 26 with the residual electrolyte. The circulation should also facilitate the temperature control of the electrolyte of each unit. In the example described, this is accomplished by causing a portion of the electrolyte to enter at the top of the anode and a portion to enter near the top of the bath (Figs. 5 and 6). By adjusting. the relative flow entering at these ints, which is accomplished by suitable de ectors in the ducts 35 leading from the cocks 36 to each electrolytic chamber, and by properly proportioning the various openings and passages this method of circulation is very satisfactory.

The auxiliary electric heat is adVa'ntn-' geously applied in the manifold 34 and in the duct 25 to-facilitate starting up of the system and to maintain it in smooth operation.

The application of my invention to the process described above carries the following improvements:

(l) A large reduction in energy losses is effected;

(2) The electrolytic power: used per lb. of product is reduced;

(3) The current density, electrode spacing, and the condition of the electrolyte as to constituents, temperature and purity are ideal for uniform and continuous high yields;

(4) The units are operated entirely satisfactorily in multiple, which in turn permits them to be grouped in the compact simple system illustrated;

(5)The interruptions required for chang-' ing the diaphragm and for cleaning are materially reduced;

(6) The labor and attendance required in the operation are minimized;

(7 By continuous operation under uniform conditions there is less wear and tear,

and by fusing the replenishing materials in one place and handling the molten bath mechanically both labor and energy are re;

duced. I

I do not limit my invention to the arrangement and details described, as it may be applied with advantage to any arrangement of units or to a single isolated unit. The electrochemical units may be located in a common bath or separated by cell partitions. Likewise the purifying and treating equipment may be contained in a common bath with the electrochemical unit or units, or may be located in a separate compartment as described above.

The operation of purification and treatment of the electrolyte may be divided, a part of the operation, as for example settling and filtering, being carried on in connection with the units, while special treatment is carried on continuously or in batches, in a special purification plant isolated from the units. Likewise the preparation of the re plenishing materials may be? carried on in connection with the units .as described or may be done in a separate plant. v

' The circulation of the electrolyte may be continuous or intermittent. Each unit may have an independent circulation and purification system, or a number of units may be connected to a common system. The electrolyte may be made to flow to two or more units simultaneously or 'to one after the other in succession. The various units may receive electrolyte from separate branches of the main duct, or the electrolyte may pass through one unit after the other in series.

In the latter case the regulation of rate of flow through any unit is secured by passing more or less of the main stream around the unit through a by-pass.

Where units are in series electrical con- .nection and receive electrolyte from a common source it may be necessary to avoid annoyance from cross currents by breaking the continuity of the electrolyte stream flowing to and from the units by means of a cock with an oscillating deflecting vane, a rotating disk or screw, a duplex tilting bucket, or other appropriate device.

I claim 1. The hereindescribed process of electrolyzing fused baths, comprising causing a fused electrolyte to flow in excess through an electrochemical unit; controlling the operating temperature of said unit by regulating the temperature and rate of flow of the electrolyte; regenerating the undecomposed portion of the electrolyte at a point outside the zone, of electrolytic action, and returning the same to the electrochemical unit.

2. Process according to claim 1 in which the electrolyte is caused to flow repeatedly through a plurality of electrochemical units in the same electrical circuit.

3. Process according to claim 1 in which the electrolyte is caused to flow repeatedly through a plurality of electrochemlcal units I electrically connected in multiple.

4. The hereindescribed process of electrolyzin fused baths, comprising grouping a plurality of electrochemical units in close proximity to each other to minimize loss of heat by radiation; causing a fused electrolyte to flow in excess through said units; collecting the excess electrolyte at a common point outside the zone of electrolytic action; supplying heat to the electrolyte at the said point; and returnin the electrolyte to the said units in cyclic ow.

5. The hereindescribed process of electrolyzing fused baths, comprising grouping a plurality of electrochemical units in close proximity to each other to minimize loss of heat by radiation; causing a fused electrolyte to flow in excess through said units; 001- ROBERT J. MoNITT.

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