US3475304A - Cathodic protection of reinforcing metals in electrolytic cells - Google Patents

Description

Oct. 28, 1969 E, CURREY 3,475,304

CATHODiC PROTECTION OF REINFORCING METALS IN ELECTROLYTIC CELLS Filed March 28, 1966 2 Sheets-Sheet 1 Oct. 28, 1969 CATHODIC PROTECTION OF REINFORCING METALS IN ELECTROLYTIC CELLS Filed March 28, 1966 J. E. CURREY 2 Sheets-Sheet 2.

United States Patent 3,475,304 'CATI-IODIC PROTECTION OF REINFORCING METALS IN ELECTROLYTIC CELLS John E. Currey, Lewiston, N.Y., assignor to Hooker Chemical Corporation, Niagara Falls, N.Y., a corporation of New York Filed Mar. 28, 1966, Ser. No. 537,871 Int. Cl. -C23f 13/00 U.S. Cl. 204-147 12 Claims ABSTRACT OF THE DISCLOSURE Corrodible reinforcing metal members disposed at least partially within a component of an electrolytic cell are cathodically protected from the corrosive action of the cell contents and products by providing contact means external to said inert material of the cell component, said contact means being positioned in such manner as to directly contact alignment means positioned on the cathode of said cell. The cathode alignment means and the electrical contact for the reinforcing members of the cell component provide an integrated device which automatically provides cathodic protection for reinforcing metals at the time the electrolytic cell is installed and the cathode is aligned.

This invention relates to electrolytic cells such as those employed for the electrolysis of aqueous alkali metal chloride solutions. More particularly it relates to the cathodic protection of the reinforcing metal used in cell components of such electrolytic cells.

In the electrolysis processes such as those involving aqueous solutions of alkali metal chlorides, particularly sodium chloride, by means of diaphragm cells, the electrolytic cells utilized are, most commonly, at least partially constructed of inert materials such as concrete, Teflon, polyethylene, polyvinylidene chloride, and so forth, coated metals and the like. Concrete is particularly suited as a construction material for the cell tops and bottoms because of its ease of fabrication, low cost and inertness, but in utilizing its reinforcing means, such as ferrous metal rods, grids, wires or screens are preferably used to aid in sustaining the stresses and strains encountered in cell operations. Ferrous metals, such as mild steel, are normally employed as the reinforcing material. However, the use of reinforcing metal results in a disadvantage which, unless rectified, produces a premature end to the useful life of the cell bottom. Eventually, brine seeps through hairline cracks in the concrete or other inert material to corrode the reinforcing metals. In addition, when the anode blades are attached to a portion of the cell bottom, such as a lead conductor therein, current leakage from the anode through the seeping brine accelerates the corrosion rate of the reinforcing metal. This corrosion results in an expansion of the metal up to about ten times its original size, thereby further cracking and weakening the cell component until it becomes useless.

It has been previously suggested to protect the reinforcing metals in such concrete cell bottoms cathodically by electrically connecting the reinforcing metals through a copper wire to the cathode of the electrolytic cell. Such a method produces the desired protection but requires external wire connections which are undesirable. They are more susceptible to contacting a grounding means or otherwise becoming entangled in equipment, thus providing both a hazard and a ready path for unnecessary loss of electrical current. Further, additional connecting steps are required which add to the inconvenience of employing such previous protecting means.

It is an object of the present invention to provide a simplified method of efiecting electrical contact between the cathode and the reinforcing structure of cell components such as cell tops and cell bottoms. Another object of the present invention is to cathodically protect, in addition to the internal reinforcing metals, other, and preferably all of the metal parts associated with said cell bottom and top. It is a further object of the present invention to eliminate all extraneous connecting wires as well as additional connecting steps previously required to cathodically protect the reinforcing members, particularly those associated with concrete cell bottoms. These and other objects will become apparent to those skilled in the art from the description of the invention which follows.

In accordance with the invention, an electrolytic cell component is provided comprising a substantially inert material at least partially internally reinforced with reinforcing means made of a corrodible metal, said reinforcing means having connected thereto an externally positioned metal contact means positioned to electrically contact alignment means positioned on the cathode of said cell. The invention further provides for a method of assembling and aligning the cathode and cell bottom of an electrolytic cell while simultaneously electrically contacting the reinforcing metals associated with the cell bottom with the negative electrical potential of the cathode.

The present invention provides a marked improvement in the method of cathodically protecting metal reinforcing associated with cell parts, particularly concrete cell bottoms in a manner whereby the electrical connection for cathodic protection of the reinforcing members is effected in aligning the cathode means on the cell bottom. In the same manner, the cell top can be cathodically protected. Thus, no additional wires or other connections need be made which may require additional steps in the assembly of the cell. Further, extraneous wires, clips, and the like, are eliminated from exposure on the cell where they might restrict the working area around the cell. Also, by the present method, the cathodic protection device is automatically connected during the cell assembly and, as such, it cannot be inadvertently overlooked.

The invention will be further described by reference to the drawing in which:

FIG. 1 is a partially exposed perspective view of a concrete cell bottom for an electrolytic cell, as seen from above;

FIG. 2 is a partial sectional view in elevation of the lower assembly (primarily the cell bottom) of 'an electrolytic cell along plane 22 of FIG. 3;

FIG. 3 is another partial sectional elevation, the section being along plane 33 of FIG. 2 of the lower assembly (primarily the cell bottom) of an electrolytic cell of this invention.

The electrolyte cell bottom 10 of the present invention is constructed of an exterior material inert to the reaction conditions such as concrete or synthetic organics having reinforcing means 12, such as rods, bars, cables, wires, screens or plates of a ferrous metal, such as steel, or other suitable conductive metal, imbedded in the inert material. Since the inert material most often used is concrete, the description will be directed more particularly to concrete structures. However, in describing concrete structures, it is implied that other inert materials can also be us ed and are included. Reinforcing means 12 can be any of the numerous strong, relatively high tensile strength metals and alloys, the most frequently used metals being those subject to both chemical and a combination of chemical and electrical corrosion. Such metals are normally ferrous metals and alloys. Mild steel is usually preferred but other rigid, high tensile strength metals can also be used. The parts of reinforcing means 12 are welded or otherwise attached together as a single unit (unitized) in a manner such that electrical contact may be made with all the reinforcing metal by contacting any part thereof. If, as in an alternate embodiment of the present invention, a unitized reinforcing means is not used, more than one electrical contact can be made with the cathode as described hereafter. Attached to the reinforcing metal is stud connector 16 on which is attached an external metal contact plate 14. Metal contact plate 14 can be of the same metal as reinforcing means 12 or, more preferably, it is a relatively soft metal such as copper or lead which, on contacting with the alignment means, the alignment bolt 33 partially pentrates the metal thereby improving the electrical contact. On forming the inert material or casting the concrete about the reinforcing means 12, metal contact plate 14 remains exposed at the surface of the concrete.

In addition to ordinary methods of reinforcing unstressed concrete, the cell bottom can be prestressed or post-tensioned as by placing the reinforcing metals under a high tensile stress up to within about 80 percent of the metals ultimate strength and retaining such a tensile stress while concrete is cast about the reinforcement. After the concrete cures, the stress is transferred to the concrete as a compressive force. Such prestressing and post-tensioning reduce the formation of hairline cracks and in so doing, further extend the useful life of the cell part.

Base plates 20 and 22 are also fastened, as by welding, to the reinforcing means 12, thereby providing electrical contact with the rest of the reinforcing structure. Base plates 20 and 22 provide a means for electrically connecting lifting angle iron 18, which is attached to the exterior of the concrete through connecting bolt assembly 24, to the unitized internal reinforcing means. Thus, in the assembled cell, lifting iron 18 is also cathodically protected by electrically contacting the internally positioned reinforcing metal 12. Base plate 22 is also in electrical contact with metal reinforcing channel 28, thereby electrically contacting metal base plate 20 and metal external reinforcing channel 28 by means of connecting bolt assembly 26. By unitizing all of the metal parts of the cell bottom by welding or bolt assemblies, electrical contact is made with all the metal and thus, substantially all of the internal and exposed metal parts of the cell bottom are cathodically protected.

Electrical contact is made with the external metal plate 14 through alignment bolt 33 and alignment lug 32. Alignment lug 32 is attached to cathode 35 by rivets, bolts or preferably by welding. Gasket means 36 forms an electrical and water-tight seal between the concrete cell bottom and the cathode 35. Since it is normally preferred to use four alignment lugs for positioning the cathode 35 on the concrete cell bottom 10 in proper alignment with the anode blades 40 and cathode fingers 41, electrical contact can be made through any one of more of these alignment lugs and alignment bolts as with alignment lug 31 and alignment bolt 34. However, under most conditions, a single contact point is sufiicient to provide the needed protection. Anode blades 40 are held securely in position by means of conductive base 38 which may be of lead or other suitable metal or material cast around the blades in a configuration which fits securely in the cell bottom. Sealing compound 39 is normally placed over conductive base 38 to keep it from functioning as an anode during cell operations.

In addition to cathodically protecting the reinforcing metals and external metals, the cell bottom legs 42 can also be cathodically protected. However, in such an instance, it is desirable to provide insulating means in said legs so that the negative potential does not become grounded through the legs thereby resulting in the loss of electrical current.

In a further aspect of the present invention, a method of assembling an electrolytic cell, particularly a chloralkyli diaphragm cell, is provided. Such a cell is normally composed of a cell bottom having positioned therein graphite or carbon anodes secured to a conductive base material, a cathode section comprised of a plurality of foraminous screen fingers and a cell top. The cell is assembled by placing a gasket 36 on the cell bottom 10 and then lowering the cathode section 35 over the anode blades 41 thereby positioning the cathode fingers 41 between the anode blades 40. Accurate alignment of the anode blades 40 an equal distance between the cathode fingers 41 is obtained by drawing cathode section 35 to either side by tightening alignment bolts 33 or 34 on alignment lugs 31 and 32 thereby centering the anode blades between the cathode fingers. Alignment bolt 33 is tightened so that it fits into alignment point 15 on contact plate 14 thereby making electrical contact between cathode section 35 and reinforcing means 12. When the anode blades are centered between the cathode fingers, all of the alignment bolts are tightened to thereby secure and hold the cathode section in a fixed position. In this manner, the position of the cathode section with respect to the anode blades is retained even though the cell might be subsequently jarred or otherwise moved during startup operations. Finally, the cell top is placed on top of the cathode section and if desired, cathodic protection is provided to the reinforcing means therein in the same manner as that of the cell bottom.

Thus, the cathodic connecting means of the present invention provides a means for performing a dual function of both aligning the cathode in relation to the anode blades while at the same time making the electrical connection for cathodic protection of the metallic parts of the concrete cell bottom.

It will be readily recognized by those skilled in the art that other alignment means than those specifically illustrated herein can be used with correspondingly good results. Thus, the alignment means can be attached to the cell bottom in electrical contact with the reinforcing means and the alignment lugs brought to bear on the cathode thereby aligning it while electrically contacting it. Further, the externally positioned contact means can be positioned on the top edge of the cell bottom on the surface thereof where the gasket is positioned between the cell bottom and the cathode section and electrical contact made therewith by alignment means.

The method and apparatus of the present invention are suited for many electrolytic processes such as the electrolysis of alkali-metal chlorides in aqueous solutions. Such uses include cathodically protecting all of the reinforcing metals associated with the cell parts including both cell tops and cell bottoms. Electrolytic cells in which the present method and apparatus are used include chlor-alkali cells, alkali-metal chlorate cells, alkalimetal perchlorate cells, HCl electrolytic cells which utilize brine solutions in their electrolytic operations and the like.

When the electrolytic cell used with the present invention is one utilizing brine, the brine solutions used include alkali-metal chloride solutions of a concentration approaching the saturation point of the particular alkali-metal chloride at the operating temperature of the cell. Although such solutions are most frequently sodium chloride solutions, the alkali-metal chloride can also be potassium chloride, lithium chloride, rubidium chloride and cesium chloride. Depending on the particular electrolysis being effected, the cells on which the present invention is best utilized can be of either the diaphragm type or those without diaphragms. When a diaphragm is utilized, it is of a fluid permeable type such as asbestos, synthetic fiber such as after-chlorinated polyvinyl chloride, polyvinylidene chloride, polypropylene, and the like.

The importance of the present invention is greatly increased as the size and electrical capacity of the particular cell increases. With large chlor-alkali cells such as those of 60,000 amperes and higher current capacities,

reinforcing of concrete cell bottoms becomes more critical because of the much greater weight being supported. Such larger cell bottoms encounter greater stresses and are more expensive to construct-Because of the more critical and higher fabrication costs, the cell bottoms become less expendable and further increase the desirability of means such as the.present invention for extending the useful life of such cell bottoms.

In the operation of the present invention, the electrical energy expended is very nominal. Under ordinary operating conditions, the current expenditure is less than about one ampere per cell. This current flow will of course vary with the cell. For new cell bottoms, the current expenditure will normally be considerably less than one ampere while with older cell bottoms wherein current leakage from the anode structure secured in the concrete cell bottom increases as brine seepageincreases, the current expenditure may increase slightly above about one ampere. Such-a loss is of an extremely low cost compared to the increased life expectancy of the cell bottom.

While there have been described various embodiments of the present invention, the methods and apparatus described are not intended to be understood as limiting the scope of the invention. It is realized that changes therein are possible and it is further intended that each element recited in any of the following claims is to be understood as referring to all equivalent elements for accomplishing substantially the same results in substantially the same or equivalent manner. It is intended to cover the invention broadly in whatever form its principles may be utilized.

What is claimed is:

1. An electrolytic cell comprising a cathode, alignment means positioned on said cathode in electrical contact therewith, and a cell component comprising a substantially inert material at least partially internally reinforced with reinforcing means made of a corrodible material, said reinforcing means having connected thereto an electrical contact means directly contacting said alignment means to complete an electrical circuit between said cathode and said reinforcing means.

2. The cell of claim 1 wherein the reinforcing means is electrically unitized.

3. The cell of claim 1 wherein the cell component is a concrete cell bottom reinforced with a ferrous metal.

4. The cell of claim 1 wherein the reinforcing means is in electrical contact with an externally positioned corrodible metal part.

5. The cell of claim 4 wherein said metal part is an externally positioned metal lifting iron.

6. The cell of claim 4 wherein said metal part is an externally positioned metal reinforcing channel.

7. The cell of claim 1 wherein the externally positioned metal contact means is a metal plate wherein said metal is a softer metal than that of the reinforcing means.

8. The cell of claim 1 wherein the cell component is a concrete cell bottom having therein a conductive base material in which is positioned an anode, said concrete being internally reinforced with reinforcing means of a ferrous metal, said reinforcing means being electrically unitized and having connected thereto an externally positioned metal contact means positioned on an exposed surface of said cell bottom.

9. The cell of claim 1 wherein more than one metal contact means is provided for electrical contact with the alignment means.

10. The cell of claim 1 wherein the cell component is prestressed concrete.

11. The cell of claim 1 wherein the cell component is post-tensioned concrete.

12. A method for assembling an electrolytic cell com prising securing an anode in a cell bottom having corrodible reinforcing means, placing a cathode over said anode on said cell bottom and aligning with an alignment means said anode with said cathode while simultaneously electrically contacting the reinforcing means in said cell bottom with the cathode through said alignment means.

References Cited UNITED STATES PATENTS 101,248 3/1870 Fisher 204196 822,109 5/1906 Gabriel 204266 1,341,516 5/1920 Patterson 204266 1,866,065 7/1932 Stuart 204262 2,834,728 5/1958 Gallone 204147 2,890,157 6/1959 Raetzsch 204196 3,081,252 3/1963 Preiser et al. 204196 JOHN H. MACK, Primary Examiner T. TUNG, Assistant Examiner US. Cl. X.R.

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