US3508846A - Hydraulic method and apparatus for metering molten alkali metals - Google Patents

Description

April 28, 1970 G. l. ADDIS E AL 3,508,846

HYDRAULIC METHOD AND APPARATUS FOR METERING MOLTEN ALKALI METALS Filed June 19. 1967 2 Sheets-Sheet 2 cu U1 QE 2 O L C x O E Sodlum Storage Chom ber (D 0) 8 m L o A 5 O O (\l W- 92 T 2 T L1.

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k. E E w 2 82 E 2 O Q. U) 106 m 5 N 2:- U Q INVENTORS 8 GILBERT I. ADDIS 2 (D THEODORE H. KELLY Q :1 BY 20 Mafia ATTORN EYS United States Patent O 3,508,846 HYDRAULIC METHOD AND APPARATUS FOR METERING MOLTEN ALKALI METALS Gilbert I. Addis, Plainfield, and Theodore H. Kelly,

Princeton, N.J., assignors to Union Carbide Corporation, a corporation of New York Filed June 19, 1967, Ser. No. 647,116 Int. Cl. F04b 19/22 U.S. Cl. 41765 5 Claims ABSTRACT OF THE DISCLOSURE Method and apparatus for metering a molten alkali metal wherein the molten alkali metal is transiently stored in and transferred or metered from one or more displacement chambers to an output line by hydraulic displacement at a substantially constant predetermined volume flow-rate with a liquid, such as mineral oil, that is inert to and immiscible with the molten alkali metal.

RELATED APPLICATIONS The method and apparatus of the present invention is particularly useful for, though not limited to, the metering of molten sodium to an extruding head used in the manufacture of electrical conductors in accordance with the product and process described respectively in pending applications Ser. No. 485,485 filed Sept. 7, 1965 entitled Electrical Conductor and Ser. No. 485,523 filed Sept. 7, 1965 entitled Method of Preparing Electrical Conductor. In this process, wherein a molten polymeric thermoplastic insulation is extruded in the form of a tubing and simultaneously filled with molten sodium, it is an important requirement that the liquid sodium be metered to the cross head die at a uniform volume flow-rate throughout the full length of -a cable run in order to avoid intolerable fiuctuations (both short-term and long-term) in the diameter of the conductor.

BACKGROUND OF INVENTION It is generally known and recognized that molten alkali metals are difiicult to transfer at a uniform rate by existing pumps because of the problems created by slag and the non-lubricating nature of the alkali metal itself. The inventors have tested both a constant head gravity feed system as Well as direct metering of the molten alkali metal with conventional constant displacement pumps and have found both to be generally unsatisfactory approaches for providing a uniform constant flow-rate. Using a constant head gravity feed system in a process for producing sodium core electrical conductor, accidental constrictions in the metering line produced by slag (i.e. oxides, hydroxides, carbonates etc.) were found to change sodium flow-rate and cable diameter. Both the non- Iubricating nature of sodium and the frequent occurrences of slag were found to cause troublesome jamming of conventional constant displacement pumps such as a gear pump with a consequent high incidence of ruined electrical cable.

SUMMARY OF THE INVENTION The aforementioned problems are effectively eliminated in accordance with the present invention by a method and apparatus which provide for a uniform continuous transfer or metering of the liquid alkali metal by hydraulic displacement from one or more displacement chambers which communicate with the output line. After the displacement chambers are loaded With molten alkali metal, at a rate, the uniformity of which is non-critical, the desired metering of the molten metal at a substantially constant volume flow-rate into the output line is achieved by pumping into the chamber at the desired flow-rate a liquid that is inert to and immiscible with the molten alkali metal and thereby hydraulically displacing the liquid metal into the line at the desired uniform rate. The hydraulic displacement liquid is of a type selected to be not only chemically inert to and immiscible with the molten alkali metal, but also one which separates readily from the molten alkali metal and which exhibits good lubricating and pumping qualities. Thus, during the course of the active metering operation, only the hydraulic displacement liquid (e.g. mineral oil) is directly pumped and since this liquid is free of slag contaminants and has good lubricating characteristics, it can be directly and reliably metered by conventional, constant displacement pumps at a uniform volume flow-rate. The abo-ve-enumerated problems encountered with prior art attempts to directly pump molten alkali metals are thus most effectively avoided.

DESCRIPTION OF DRAWINGS Operation of the invention will be explained in further detail in connection with the following descriptions of the accompanying drawings in which:

FIG. 1 illustrates one preferred embodiment of the invention method and apparatus for alternately and sequentially metering molten sodium at a substantially constant volume flow-rate from first and second displacement chambers to a process line; and

FIG. 2 illustrates a second preferred embodiment of the invention wherein molten sodium is continuously metered at a substantially constant volume flow-rate from a first displacement chamber and a second displacement chamber is provided for hydraulically replenishing the sodium supply in the first chamber.

DESCRIPTION OF PREFERRED EMBODIMENTS As shown in the simplified drawing FIG. 1, the metering apparatus includes a pair of displacement chambers A and B each of which is adapted to transiently store a desired volume of molten sodium prior to and during its uniform metering to an output process line 50. Molten sodium is supplied by conventional means such as a pump or by gravity to the displacement chambers at any convenient temperature above the melting temperature of 97.8 C. for sodium, preferably between C. and C., from a make-up storage tank through line 40 and valves 24 and 34 respectively. The temperatures of the molten sodium in the A and B chambers are preferably maintained at substantially the same value by conventional controlled heating means 26 and 36 but not necessarily the same as the temperature of the make-up storage supply. In accordance with the invention, the molten sodium is hydraulically displaced from either the A or B chamber with mineral oil or other displacement fluid supplied at a predetermined constant volume flow-r-ate from pump system 10 through lines 11, 11A and valve 21 to chamber A or lines 11, 11B and valve 31 to chamber B. When the sodium has been displaced to the desired lower level, the oil flow is directed to the other chamber and the first chamber is refilled with molten sodium to the desired upper level. Since the displacement fluid is desirably chosen for excellent lubricating and handling characteristics, any one of a variety of well-known conventional constant-displacement pumps may be employed to supply the desired uniform flow of oil to line 11. The output flow from the selected pump should preferably be substantially free of pulsations.

In a preferred arrangement illustrated in FIG. 1, oil from a constant-head tank 14 is supplied to the input of a constant-displacement gear pump 12 having very low pulsation amplitude in the output which is connected to line 11. As shown, pump 12 is driven by a variable speed motor 13 controlled by a conventional speed regulator 13R, the latter being adjustable to give an operating speed which provides the desired oil volume rate-of-flow into either chamber A or B and in turn the desired uniform displacement volume flow-rate of molten sodium into process line 50. Desirably, a constant head of oil is maintained in tank 14 through line 19 by centrifugal pump 16 the oil input of which is supplied by line 18 from oil storage tank 17. The pumping rate of 16 is adjusted to be greater than that of pump 12 so that an over-flow return via 20 is continuously maintained and the desired constant head provided for the input of pump 12. If preferred, pump 16, constant head tank 14 and the accompanying lines may be eliminated and pump 12 supplied directly from oil storage tank 17. The temperature of the oil in storage tank 17 is preferably regulated by temperature regulator 17R to minimize variations in the density of the displacement oil and thereby minimize undesired changes in sodium volume flow-rate.

As indicated above, chambers A and B should preferably be controlled to substantially the same temperature to minimize differences in sodium density between the two chambers and thus minimize changes in metering rate with switch-over from one chamber to the other. The sodium displacement chambers A and B preferably should be free of trapped gas in order to avoid undesired variations due to gas compression with attendant change of flow-rate into line 50 during switch-over. To this end, the A and B displacement chambers should preferably be provided with conical tops and bottoms with the input and output lines connected near the respective crowns as shown to avoid undesired trapping of gas in the chambers during either the sodium filling or the sodium displacement operations.

The following is a description of an operation which required uninterrupted metering of molten sodium for lengthy periods of time, such as in the manufacture of long runs of sodium core electrical conductors. With valves 21, 31, 25 and 35 closed, the A and B chambers are initially filled with molten sodium to the desired level as indicated by level indicators 27 and 37 from a filtered storage supply via line 40 through opened valves 24 and 34, the oil being displaced through opened valves 22 and 32. Valves 24 and 34 are then closed and the sodiumis alternately metered from A and B chambers into line 50 with the chambers being alternately refilled from line 40. Starting first with the A chamber, valves 21 and 25 are both opened and valves 22, 31, 32 and 35 are all closed. Molten sodium is displaced into line 50 by the oil pumped into the top of the tank through 11, 11A and 21 by pump 12. The desired metering rate is established by adjusting the speed of motor 13 which is preferably maintained at the desired speed by 13R.

Before the molten sodium is completely displaced from tank A, transfer to tank B is effected by opening valves 31 and 35 and then closing valves 21 and 25. In this manner, an uninterrupted constant volume flow-rate is provided into line 50.

While the sodium in chamber B is being hydraulically displaced into line 50, chamber A is refilled with molten sodium by opening oil overflow valves 22 and 24. The oil used to displace the molten sodium from chamber A is then itself displaced through valve 22, line 60, oil cooler 61 and return line 62 back to oil storage tank 17. While cooler 61 may be eliminated from the oil return line, it is advantageous for more uniform operation to drop the return oil temperature from that of the molten sodium to say 50 C. and then reheat to the desired temperature of about C. to C. in tank 17. Following completion of the refilling operation, valves 22 and 24 are closed.

In like manner, transfer from chamber B back to A is effected by opening valves 21 and 25 and then closing valves 31 and 35. Valves 34 and 32 are opened to refill B with molten sodium and the displacement oil is returned to tank 17 via overflow valve 32, line 60, oil cooler 61 and return line 62. After tank B is refilled with molten sodium, valves 32 and 34 are again closed in readiness for the transfer from chamber A back to B.

Valves 21, 22, 24, 25, 31, 32, 34, 35 may be fitted with solenoid or other actuators and their opening and closing may be controlled in desired sequence by an appropriate controller actuated by level sensors, timing devices or other suitable control transducers.

A second preferred embodiment of the invention is illustrated in FIG. 2 wherein the molten sodium is continuously metered at the desired uniform flow-rate from only a single displacement chamber A to the output process line 50. In this embodiment of the invention, the sodium supply for chamber A is replenished as required in order to provide continuous uninterrupted output to line 50 by displacement of sodium from chamber B1 into A. The requirement of cyclically switching the output line 50 from one chamber to the other is thereby avoided. The operation of this embodiment will be described in further detail by reference to FIG. 2 in which like elements are identified by the same reference numerals as in FIG. 1.

Initially, chambers A and B1 are partially or completely filled with oil via oil supply line 11A. Molten sodium supplied via line 40 through opened valve 34, fills sodium storage chamber E1, the displaced oil returning to storage through line 60.

When sodium storage chamber B1 has been filled to the desired level, valve 34 is closed and valves 71 and 31B are opened, thus allowing sodium to flow from chamber B1 to sodium displacement chamber A. The sodium, being heavier than the mineral oil, displaces the oil from chamher A to chamber B1 through line 73 until the sodium levels are substantially equalized. The desired metering operation is initiated by closing valves 31B and 71, and opening valves 21 and 25, whereby molten sodium is displaced from tank A to the process line at a rate equivalent to the metered rate of oil input through line 11A. Sodium storage chamber B1 can be refilled with molten sodium during the metering operation by opening valves 32B and 34. Following the refilling operation, valves 32B and 34 are closed.

When the level of sodium in chamber A is displaced to a predetermined lower limit, valves 31B and 71 are opened to allow oil to flow from chamber A to chamber B1 and in turn allow sufficient molten sodium to flow from B1 to A until the sodium levels are substantially equal. Valves 31B and 71 are then closed and chamber B1 refilled as described above. The replenishment of both chambers with molten sodium is repeated as required to maintain an uninterrupted metering of sodium to line 50.

In an alternative operating arrangement, a pump may be installed in line 73 and the replenishment transfer of sodium from B1 to A may be effected by pumping oil from chamber A to chamber B1.

In the course of the replenishment transfer operation, the sodium-oil interfaces in the two chambers will reach the same level due to the force of gravity. At this stage of the operation, valves 71 and 313 may be left open so that sodium is displaced from both chambers into line 50 or these valves may be closed immediately and the sodium supply in chamber B1 replenished. In any event, valves 71 and 313 must be closed while sufiicient sodium remains in chamber A to supply the process during the period of time that is required to refill chamber B1 with molten sodium. Chamber B1 is preferably purged of any trapped gas after filling and the pressure in B1 is raised to equal the pressure in chamber A by admitting oil from any convenient source into chamber B1. Valves 71 and 3113 may then be opened to repeat the cycle of replenishing sodium in A.

The diameter of chamber B1 is preferably made larger than chamber A because, within limits, it is desirable that the level in chamber A be as high as possible after equalizing. Thus, if the diameter of B1 is twice the diameter of A, the level of sodium will rise four feet in chamber A for each one-foot fall of the level in B1. It should be understood that throughout the sodium replenishment operations described above, displacement oil is continuously pumped into chamber A via line 11A at a predetermined uniform floW-rate and molten sodium is continuously displaced at the desired uniform flow-rate into line 50. The displacement chambers and the inter-connecting lines in both embodiments must be heated to maintain the "sodium in a molten condition and the temperatures of the chambers preferably regulated as indicated above.

While preferred embodiments have been describd for metering molten sodium by displacement with mineral oil, it will be appreciated and understood by those skilled in the art that the invention may also be used to meter any molten alkali metal having an atomic weight below 40 such as lithium and potassium. It will also be appreciated that any other displacement fluid which is inert to the alkali metal may be substituted for mineral oil, as for example, kerosene, naphtha, or inert synthetic oils. Alternatively, if desired, displacement fluids having a density greater than that of the molten metal may be used with the molten metal then being displaced out of the tops of the chambers. Additionally, it will be apparent that while it is advantageous to employ a plurality of two or more displacement chambers for operations using the embodiment illustrated in FIG. 1 which may require a continuous uniform output over a relatively long, indefinite period of time, for known shorter term applications, a single displacement chamber may be satisfactorily employed.

What is claimed is:

1. Apparatus for hydraulically metering a molten alkali metal from a supply source to an output line at a substantially constant flow-rate, said apparatus comprising:

(a) a hydraulic displacement chamber for receiving and transiently storing a supply of molten alkali metal, said chamber having an input for receiving a displacement liquid and an output connected to said output line,

(b) a constant head tank connected to the input of said displacement chamber for supplying thereto, from a supply source, said displacement liquid which is inert to and immiscible with the molten alkali metal, and in series,

(c) a first pumping means for pumping said displacement liquid to said constant head tank and a second pumping means for pumping said displacement liquid to said displacement chamber from said constant head tank, wherein said first pumping means is capable of pumping displacement liquid to said constant head tank at a rate greater than the rate at which the said displacement liquid is pumped to said displacement chamber,

(d) and means to feed the excess displacement liquid from said constant head tank to the supply source therefor whereby a desired constant head can be provided in said constant head tank with the result that the displacement liquid can be fed at a substantially constant volume flow-rate to the input of said displacement chamber and displace molten alkali therefrom.

2. Apparatus in accordance with claim 1 wherein said displacement liquid is mineral oil and said alkali metal is sodium.

3. Apparatus for hydraulically metering a molten alkali metal from a supply source to an output line at a substantially constant volume flow-rate, said apparatus comprising:

(a) a plurality of displacement chambers for receiving and transiently storing molten alkali metal, each of said chamber having an input for receiving a displacement liquid and an output for delivering metered amounts of molten alkali metal,

(b) a constant head tank,

(c) an input line, having separate control valves, connecting the respective inputs of said displacement chambers to said constant head tank, for supplying said displacement liquid, which is inert to and immiscible With the molten alkali metal, to said 'displacement chambers and in series,

((1) a first pumping means for pumping said displacement liquid to said constant head tank, from a supply source, at a rate greater than the rate at which said displacement liquid is pumped to said displacement chambers, and

(e) a second pumping means for pumping said displacement liquid from said constant head tank, through said input line, to said displacement chambers,

(f) means to feed the excess displacement liquid from the said constant head tank to the supply source therefor whereby a desired constant head can be provided in said constant head tank with the result that a substantially constant volume flow-rate displacement liquid can be fed to the input of said displacement chambers and displace molten alkali therefrom,

(g) and separate valve means connecting each of said displacement chamber outputs to said output line, so that displacement of alkali metal can be alternately effected from said displacement chambers.

4. Apparatus in accordance with claim 3 characterized in that means are provided for controlling the temperature of the molten alkali metal in each of the plural displacement chambers.

5. Apparatus for hydraulically metering a molten alkali metal from a supply source to an output line at a substantially constant flow-rate, said apparatus comprising:

(a) a hydraulic displacement chamber for receiving and transiently storing a supply of molten alkali metal, said chamber having an input for receiving a displacement liquid and an output connected to said output line,

(b) a constant head tank connected to the input of said displacement chamber and connected to a supply source containing a displacement liquid which is inert to and immiscible with the molten alkali metal, and in series,

(c) a first pumping means for pumping said displacement liquid to said constant head tank at a rate greater than the rate at which the displacement liquid is supplied to said displacement chamber, and

(d) a second pumping means for pumping said displacement liquid from said constant head tank to said displacement chamber,

(e) means for feeding the excess displacement liquid from said constant head tank to the supply source therefor whereby a desired constant head can be provided in said constant head tank, with the result that the said displacement liquid can be fed, at a substantially constant volume flow-rate, to the input of said displacement chamber and displace molten 2,310,377 2/1943 Voorhees 103-165 X alkali therefrom, 2,704,034 3/1955 Jones 103- 165 (f) and means for maintaining said displacement liquid at a substantially constant temperature. WILLIAM L. FREEH, Primary E a I References Cited 5 U.S. Cl. X.R. UNITED STATES PATENTS 417 249 755,722 3/1904 Stroh 103-165 X 2,246,594 6/ 1941 Kinsella 103-465

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