Selective plugging of broken fibers in tubesheet-hollow fiber assemblies

• US 4,226,921 A
• Filed: 07/16/1979
• Issued: 10/07/1980
• Est. Priority Date: 07/16/1979
• Status: Expired due to Term

• Current Assignee: The Dow Chemical Company (Dow, Inc.)
• Original Assignee: The Dow Chemical Company (Dow, Inc.)
• Inventors: Tsang, Floris Y.
• Primary Examiner(s): Skapars, Anthony
• Application Number:
  US06/057,926
• Time in Patent Office: 449 Days
• Field of Search: 429/104, 429/193, 429/191, 429/31, 429/102, 429/218, 264/36
• US Class Current: 429/104
• CPC Class Codes: B01D 65/106 Repairing membrane apparatus or modules
• CPC Class Codes: H01M 10/3918 characterised by the electrolyte
• CPC Class Codes: H01M 50/466 U-shaped, bag-shaped or folded
• CPC Class Codes: Y02E 60/10 Energy storage using batteries

Abstract

There is disclosed a method of selectively plugging broken fibers included in a bundle of hollow fibers having open ends terminating in or protruding from one face of a tubesheet and closed ends or loops depending from the other face of the tubesheet. The open ends are covered with a curable and flowable sealant and a pressure differential is utilized to draw the sealant into the broken fibers. The resistance to compression of the gases in the unbroken fibers is such that the sealant does not move into them a substantial distance. The sealant is diluted and another pressure differential employed to expel the sealant from the good fibers. The diluted sealant is removed and the plugs in the broken fibers are cured. This method is of particular value in preparing tubesheet-fiber assemblies for use in high temperature alkali metal-sulfur battery cells, wherein the hollow fibers function as an electrolyte separator, but also has utility for remedying leaks in devices employing hollow fibers as separatory membranes.

Claims

1. The method of treating a tubesheet/hollow fiber assembly to ensure that any defective fibers and/or tubesheet channels included therein will be selectively plugged, said method comprising

A. providing as said assembly one which comprises a bundle of gas-filled, hollow fiber lengths passing through and sealingly engaged with a rigid, relatively thin wall-member of tubesheet having first and second generally parallel faces, each of said lengths having an open end terminating in or protruding from said first face and at least a majority of said lengths having portions depending from said second face which have closed ends or are generally U-shaped loops having second open ends terminating in or protruding from said first face,

B. covering said first face with a body of a flowable, curable sealant and developing a pressure differential between said body and the exteriors of said dependent fiber portions, thereby

(1) causing said sealant to flow into the defective fibers and/or tubesheet channels and to displace therefrom at least a portion of the gas contained therein, and

(2) causing said sealant to flow into the open ends of the non-defective fibers to a limited extent determined by the resistance to compression of the gas they contain,

C. diluting the sealant external to the fibers,

D. subjecting the exteriors of said dependent fiber portions and the diluted sealant body to essentially the same reduced pressure, with the results that:

the gas in the non-defective fibers expands until the pressure inside them is the same as the pressure outside them,

the undiluted sealant in the non-defective fibers is expelled and the diluted sealant intrudes slightly into them,

the column of sealant in each defective fiber and tubesheet channel remains in place and no more than a small terminal portion of it is diluted,

E. While maintaining the pressure equilibrium established in step D, removing the main body of the diluted sealant from contact with the tubesheet,

F. optionally, rinsing said first face and open fiber ends with a diluent, and

G. curing the sealant in the defective fibers and/or tubesheet channels, thereby plugging them,

said sealant being so composed as to be convertible, in-situ in said defective fiber lengths or channels and at a temperature below the distortion temperature of said fibers, to plugs of a solid, non-porous material sealingly bonded to the fiber or channel walls and having a coefficient of expansion substantially matching that of the fiber material.

2. The method of claim 1 wherein:

said fiber lengths are adapted to function as the electrolyte/separator in a high temperature battery cell,

said sealant is a suspension, in an inert volatilizeable liquid, of glass or ceramic particles which have a maximum diameter of about 1/3 or less of the inner diameter of said fiber lengths and will fuse together to form said plugs when heated to a temperature, T₁, which is less than the distortion temperature of said lengths, and

said assembly is heated to T₁, thereby devolatilizing said suspension in said defective fibers and/or tubesheet channels and converting said particles to said plugs.

3. The method of claim 1 when carried out after said assembly has been incorporated in a casing adapted to function as a component of a complete hollow fiber device.

4. The method of claim 2 wherein said cell is an alkali metal/sulfur battery cell.

5. The method of claim 4 wherein said alkali metal is sodium.

6. The method of claim 2 wherein said tubesheet and said particles have essentially the same composition.

7. The method of claim 2 wherein said assembly additionally comprises a perforated metallic sheet disposed therein as a plurality of generally concentric wraps spiralled about the central axis of said bundle and separated by intervening, generally concentric layers of said fiber lengths.

8. The method of claim 1 or 2 wherein said open ends terminate in said first face.

9. A tubesheet and hollow fiber assembly treated by the method of claim 1.