US2768813A - Heat exchangers - Google Patents

Description

Oct. 30, 1956 R. Q. BOYER HEAT- EXCHANGERS 2 Sheets-Shea+ 1 Original Filed March 51, 1944 CONOENJER DE-E'NTRA/NME/VT WAJH m4 TER ,FoR CALUTRONJ HEAD CALUTRO/V WAJH WATER INVENTOR. ROBERT Q. BOYER CALI/TRON WAJH JOLUT/O/V BY Wim- R. Q. BOYER HEAT EXCHANGERS Oct. 30, 1956 2 Sheets-Shee+ 2 Original Filed March 31, 1944 IN V EN TOR. E0550?- 4). EOYER United States Patent '0 HEAT EXCHANGERS Robert Q. BoyerQBerkeley, Calih, assignor to' the United States of America as'represented by the United States Atomic Energy Commission Original application March 31, 1944L Serial No. 529,012. Digidergl and this application May 28, 1945, Serial No, 59 ,22

3 Claims. (Cl. 257-224) The present invention relates to heat exchangers and more particularly to improvedevaporators that are especially adapted for use in conjunction with the concentration of wash solutions derived from calutrons employed in the calutron method of producing uranium enriched with U 5. This application is a division of the copending application of Robert Q. Boyer, Serial No. 529,012, filed March 31, 1944, now abandoned.

In the copending application of Ernest 0. Lawrence,

erial No. 557,784, filed October 9, 1944, now Patent No. 2,709,222, granted May 24, 1955, there is disclosed a calutron, a machine designed to separate the constituent isotopes of an element and, more particularly, to increase the proportion of a selected isotope in an element containing several isotopes, in order to produce the element enriched with the selected isotope. More specifically, the calutron mentioned is especially designed to produce uranium enriched with the thermal-neutron fissionable isotope U l In the copending application of James M. Carter and Martin D. Karnen, Serial No. 532,159, filed April 21, 1944, there is disclosed an improved process of producing uranium enriched with U 5 employing the calutron method and comprising first-stage and second-stage calutrons. In accordance with this process, uranium of natural or normal isotopic composition is treated in a first-stage calutron in order, to produce 'as a product uranium singly enriched with U ,which uranium singly enriched with U is treated in a second-stage calutron in order to produce as 'a product uranium doubly enriched with U which uranium doubly enriched with U may be used commercially. In the operation of either a first-stage calutron or a second-stage calutron the compound UC14 is treated, whereby a residue of the UCl4 is deposited on the parts of the calutron disposed in the source region thereof, metallic uranium enriched with U is deposited in the first pocket of the collector of the calutron, and metallic uranium impoverished with respect to U is deposited in the second pocket of the collector of the calutron. covered by a water wash step and the deposits of metallic uranium are separately recovered by acid wash steps; and the three wash solutions are separately purified, if required, to produce three separate batches of a standard compound of uranium, In this process, a first batch of the uranium compound mentioned, produced from the water wash derived from a first-stage'calutr-on, is then converted back to UC14 for re-treatment in the first-stage calutron, and a second batch of the uranium compound mentioned, produced from the water wash derived from a second-stage calutron, is then converted back to UCl4 for re-treatment in the second-stage calutron." g

In the copending application of Martin D. Kamen and Abel De Haan, 'SerialNo. 542,378, filed June27, 1944, there is disclosed an improved process of purifying a water wash solution of the character -mentioned in order to separate uranium from metallic impurities in the solution.

The deposit of UC14 is re- In accordance with this process, a water wash solution containing uranium, copper, nickel, iron and chromium in the form of chlorides is first concentrated; and the concentrated solution containing UOz++, Cu++, Ni++, Fe+++ and Cr+++ ions is then reduced electrolytically, whereby the uranyl ion, UO2++, and the ferric ion, Fe+++, are respectively reduced to the uranous ion, U++++, and the ferrous ion, Fe++. Thus, the reduced solution contains U++++, Cu++, Ni++, Fe++ and Cr++ ions; and to'this reduced solution there is added oxalic acid, whereby the uranium is precipitated as U(C2O4)z-6H2O away from the metal impurities in the solution. The solution is 'then filtered in order to separate the uranous oxalate precipitate, leaving the metal ions mentioned in the filtrate; which standard compound of uranium. is converted back to UCL; for further treatment in the appropriate one of the calutrons, as previously explained.

In accordance with this process the water wash solution derived from the second-stage calutron contains uranium which has been singly enriched with U?, due to the previous treatment thereof in the first-stage calutron, as well as the metal impurities mentioned. Accordingly, in the concentration of this wash solution prior to reduction electrolytically, it is essential that none of the contained valuable, singly enriched uranium be lost to the outside. Furthermore, it is highly desirable that this wash solution be not further contaminated with metal impurities incident to the concentration.

Accordingly, it is an object of the invention to provide an improved heat exchanger that is especially designed to concentrate a wash solution of the character and composition mentioned, whereby the wash solution is not further contaminated by metal impurities incident to the concentration.

Another object of the invention is to provide a heat exchanger of improved construction and arrangement, that is compact and efficient in operation.

Another object of the invention is to provide an improved evaporator that is lined throughout with tantalum.

Another object of the invention is to provide an evaporator, heated by a fluid under pressure and comprising relatively thin-walled tubes and sheets, that embodies an improved arrangement for preventing rupture of the joints between the tubes and sheets due to the pressure of the fluid mentioned.

A further object of the invention is to provide an improved evaporator that is especially designed to concentrate a calutron wash solution containing uranium and metal impurities as chlorides, wherein substantially none of the uranium is lost to the outside and substantially no metal impurities are introduced in the solution incident to the concentration.

The invention, both as to its organization and method of operation, together with further objects and advantages thereof, will best be understood by reference to the following specification taken in connection with the accompanying drawings, in which Figure l is a combined longitudinal sectional view of a heat exchanger and a diagrammatic illustration of the associated elements of the wash concentrating system, and embodying the present-invention, and in conjunction with which there may be carried out the method of the present invention; Fig. 2 is an enlarged fragmentary sectional view of the evaporator incorporated in the heat exchanger, taken along the line 2-2 in Fig. 1; Fig. 3 is an enlarged fragmentary sectional view of the evaporator, taken along the line 3-3 in Fig. 2, and illustrating the construction and arrangement of the header incorporated therein; and Fig. 4 is a further enlarged fragmentary sectional view of a portion of the header incorporated in the evaporator, taken alongthe line 4-4 in Fig. 2, illustrating the arrangement for preventing rupture of the joints between the thinwalled tubes and sheets supported by the header plate.

Referring now more particularly to Fig. 1 of the drawings, there is illustrated a heat exchanger that embodies the features of the present invention and comprises an evaporator 11 and a de-entrainment receiver 12. The heat exchanger 10 is supported in upstanding position by structure including a pair of spaced-apart channel shaped supports, the rear channel being illustrated at 13, and is operatively connected to other elements to form a Wash concentrating system, as explained more fully hereinafter. The evaporator 11 comprises upper and lower header plates 14 and 15, secured together by an upstanding cylindrical shell 16, all formed of steel or the like, to form a fluid-tight chamber 17 adapted to; receive steam under gauge pressure. One end of an inlet conduit 18, formed of steel or the like, is secured in an opening formed in the side wall of the shell 16 adjacent the upper end thereof, and the other end of the inlet conduit 18 carries a flange 19 which is adapted to be detachably connected to a source of steam, or other heating fluid, under pressure. One end of an outlet conduit 20, formed of steel or the like, is secured in an opening formed in the side wall of the shell 16 adjacent the lower end thereof, and the other end of the outlet conduit 29 carries a flange 21 which is adapted to be detachably connected to a fluid exhaust system, not shown.

A number of upstanding thin-walled tubes 22, formed of tantalum, three being illustrated, are arranged within the shell 16 and extend between the header plates 14 and 15. The tubes 22 are arranged in a geometrical pattern within the shell 16, and the opposite ends of each tube are arranged in aligned openings formed in the header plates 14 and 15 and are secured in place in substantially fluid-tight relation with respect to the associated header plate. More specifically, the upper end of each tube 22 extends through one of the openings formed in the asso ciated header plate 14 and is surrounded by a bushing or ferrule 23, formed of copper or the like, and arranged between the adjacent surface of the tube 22 and the wall of the opening formed in the upper header plate 14, thereby to provide the substantially fluid-tight joint mentioned between the upper end of the tube 22 and upper header plate 14. Similarly, the lower end of each tube 22 extends through one of the openings formed in the associated header plate 15 and is surrounded by a bushing or ferrule 24, formed of copper or the like, and arranged between the adjacent surface of the tube 22 and the wall of the opening formed in the lower header plate 15, thereby to provide the substantially fluid-tight joint mentioned between the lower end of the tube 22 and the lower header plate 15.

The extreme upper end of each tube 22 is outwardly flared and arranged in an outwardly flared opening formed in a thin upper sheet 25, formed of tantalum, the sheet 25 being arranged on the outside of the upper header plate 14 and supported thereby, the adjacent outwardly flared edges of the tube 22 and the upper sheet 25 being welded together as at 25a in fluid-tight relation, The extreme lower end of each tube 22 is outwardly flared and arranged in an outwardly flared opening formed in a thin lower sheet 26, formed of tantalum, the sheet 26 being arranged on the outside of the header plate 15 and supported thereby, the adjacent outwardly flared edges of the tube 22 and the lower sheet 26 being welded together in fluid-tight relation.

The upper sheet 25 is substantially disk-shaped and extends over the outer surface of the upper header plate 14 some distance beyond the projection of the shell 16, and is secured in fluid-tight relation with respect to a thin-walled upper header 27, formed of tantalum, the header 27 being substantially cup-shaped, including a cylindrical side wall 28 having an outwardly flared rim 29 and an outwardly dished upper wall 30. The outwardly flared rim 29 of the header'27 is arranged over aperipheral portion of the upper sheet 25, a tantalum washer 31 being arranged between the parts mentioned in order to provide a fluid-tight joint therebetween. The outwardly flared rim 29 of the upper header 27 is secured to the peripheral portion of the upper sheet 25, with the tantalum washer 31 therebetween, by an arrangement including a clamping ring 32 surrounding the lower end of the cylindrical side wall 28 and detachably secured to the upper header plate 14 by a series of bolts 33 extending through'aligned openings formed in the clamping ring 32 and the upper header plate 14.

The lower sheet 26 is substantially disk-shaped and extends over the outer surface of the lower header plate 15 some distance beyond the projection of the shell 16, and is secured in fluid-tight relation with respect to a thinwalled lower header 34, formed of tantalum, the header 34 being substantially conical, including a conical side wall 35 having an outwardly flared upper rim 36 and an outwardly flared lower rim 37. The outwardly flared upper rim 36 of the header 34 is arranged below a peripheral portion of the lower sheet 26, a tantalum washer 33 being arranged between the parts mentioned in order to provide a fluid-tight joint therebetween. The outwardly flared upper rim 36 of the lower header 34 is secured to the peripheral portion of the lower sheet 26, with the tantalum washer 38 therebetween, by an arrangement including a clamping ring 39 surrounding the upper end of the conical side wall 35 and detachably secured to the lower header plate 15 by a series of bolts 4% extending through aligned openings formed in the clamping ring 39 and the lower header plate 15. The conical side wall 35 of the lower header 34 is supported by a substantially conical base plate 41, formed of steel or the like. The upper end of the base plate 41 is also secured to the clamping ring 39, and a clamping ring 42 is secured to the lower end of the base plate 41.

A horizontally disposed tube 43 is arranged below the base plate 41, and carries an upstanding communicating tube 44 arranged in alignment with the lower open end of the header 34, the tubes 43 and 44 being formed of tantalum and being of thin-walled construction. The upper end of the tube 44 is provided with an outwardly flared upper rim 45, arranged below the outwardly flared lower rim 37 ofthe header 34, a tantalum Washer 46 being arranged between the parts mentioned in order to provide a fluid-tight joint therebetween. The outwardly flared lower rim 37 of the lower header 34 is secured to the outwardly flared upper rim 45 of the tube 44, with the tantalum washer 46 therebetween, by an arrangement including a clamping ring 47 surrounding the upper end of the tube 44 and detachably secured to the clamping ring 42 by a series of bolts 48 extending through aligned openings formed in the clamping rings 42 and 47. The opposite ends of the tube 43 are outwardly flared and carry clamping rings 49 and 50 which are utilized for a purpose more fully explained hereinafter.

The de-entrainrnent receiver 12 comprises an upstanding upper cylindrical tube 51 of relatively large diameter, an upstanding lower cylindrical tube 52 of relatively small diameter, and an intermediate upstanding conical element 53 disposed between the tubes 51 and 52, the tubes 51 and 52 and the element 53 being formed of tantalum and being of thin-walled construction. The upper end of the tube 51 is provided with an outwardly flared rim 54, carrying a clamping ring 55 which is utilized for a purpose more fully explained hereinafter; while the lower end of the tube 51 is provided with an outwardly flared rim 56 carrying a clamping ring 57. Also, the intermediate portion of the tube 51 is connected to the cylindrical side wall 28 of the upper header 27 by a horizontally disposed tube 58, formed of tantalum and of thin-walled construction, whereby the interior of the header 27 is arranged in communication with the interior of the tube 51 through the tube 58.

Thev upper end of the element 53 is provided with an. outwardly flared rim 59 carrying a clamping ring 60,

while the lower end of the element 53 is provided with an outwardly flared rim 61 carrying a clamping ring 62. The outwardly flared lower rim 56 of the tube 51 overlies the outwardly flared upper rim 59 of the element 53, a tantalum washer 63 being arranged between the parts mentioned in order to provide a fluid-tight joint therebetween, these parts being retained in fluid-tight relation by the clamping rings 57 and 60, a series of bolts 64 extending through aligned openings formed in the clamping rings mentioned. The upper end of the tube 52 is provided with an outwardly flared rim 65 carrying a clamping ring 66, while the lower end of the tube 52 is provided with an outwardly flared rim 67 carrying a clamping ring 68. The outwardly flared lower rim 61 of the element 53 overlies the outwardly flared upper rim 65 of the tube 52, a tantalum washer 69 being arranged between the parts mentioned in order to provide a fluid-tight joint therebetween, these parts being retained in fluid-tight relation by the clamping rings 62 and 66, a series of bolts 70 extending through aligned openings formed in the clamping rings mentioned.

A horizontally disposed tube 71 is arranged below the tube 52 in alignment with the tube 43, and carries an upstanding communicating tube 72 arranged in alignment with the lower end of the tube 52, the tubes 71 and 72 being formed of tantalum and being of thin-walled construction. The upper end of the tube 72 is provided with an outwardly flared upper rim 73, arranged below the outwardly flared lower rim 67 of the tube 52, a tantalum washer 74 being arranged betweenthe parts mentioned in order to provide a fluid-tight joint therebetween. The outwardly flared lower rim 67 of the tube 52 is secured to the outwardly flared upper rim 73 of the tube 72, with the tantalum washer 74 therebetween, by an arrangement including a clamping ring 75 surrounding the upper end of the tube 72 and detachably secured to the clamping ring 68 by a series of bolts 76 extending through aligned openings formed in the clamping rings 68 and 75. The opposite ends of the tube 71 are outwardly flared and carry clamping rings 77 and 78 which are utilized for'a purpose more fully explained hereinafter.

More particularly, the adjacent outwardly flanged ends of the tubes 43 and 71 are secured together with a tantalum washer 79 therebetween by the clamping rings 49 and 75, a series of bolts 80 extending through aligned openings formed in the clamping rings mentioned. Accordingly, the tubes 43 and 71 are detachably secured together in fluid-tight relation; while the tubes 44 and 72 are respectively detachably secured to the lower header 34 and the tube 52 in fluid-tight relation. Similarly, the element 53 is detachably secured between the tubes 51 and 52 in fluid-tight relation, While the tube 51 is arranged in direct communication through the tube 58 with the upper header 27. Finally, the upper header 27 is detachably secured to the upper sheet 25 in fluidtight relation, while the lower header 34 is detachably secured to the lower sheet 26 in fluid-tight relation, the tubes 22 being secured between the upper sheet 25 and the lower sheet 26 by fluid-tight joints. Hence, the heat exchanger constitutes a vessel lined throughout with thinwalled expensive metal, tantalum, tubes and sheets, for a purpose more fully explained hereinafter.

Considering now the wash concentration system in which the heat exchanger 10 is incorporated, the outer end of the tube 43 is connected to a source of calutron wash water which is to be concentrated by a conduit system including a valve 101, the conduit system mentioned being connected to the tube 43 by an arrangement including the clamping ring 50. The outer end of the tube 71 is connected to a storage tank, not shown, adapted to receive concentrated calutron Wash solutions, by a conduit system including a valve 102, the conduit system mentioned being connected to the tube 71 by an arrangement including the clamping ring 77. The tie-entrainment receiver 12 communicates with a de-entrainment head 103, of any suitable type, disposed thereabove, the deentrainment head 103 being detachably secured to the tube 51 by an arrangement including the clamping ring 55. Further, the de-entrainment head 103 is suitably connected by a conduit system 104 to a condenser 105 of any suitable type; while the condenser 105 is suitably connected to a storage tank, not shown, adapted to receive condensate from the condenser 105, which condensate is adapted for re-use as calutron wash water.

As previously explained, steam under pressure is admitted into the chamber 17 through the inlet conduit 18 and is exhausted therefrom through the outlet conduit 20, whereby calutron wash water standing in the tubes 22 is heated and evaporated, as explained more fully hereinafter. In order to insure substantially uniform distribution of the steam entering the chamber 17 through the inlet conduit 13, a deflector plate 81 is arranged over the inner end of the inlet conduit 18 in spaced relation thereto, within the chamber 17, and is secured to the cylindrical side wall 16. In the present embodiment of the heat exchanger 10, the steam admitted through the inlet conduit 18 into the chamber 17 is under a pressure of about pounds per square inch gauge, corresponding to a temperature of 353 F., whereby the tubes 22 are heated to a corresponding relatively high temperature. With valve 102 initially closed, the calutron wash water from the source is admitted by way of the associated conduit system including the valve 101 into the tube 43, whereby the communicating tubes 44, 71 and 72, the lower header 34, the extreme lower ends of the tubes 22, and the lower portion of the tube 52 are substantially completely filled with the wash water. The wash water filling the lower header 34 and rising into the extreme lower ends of the tubes 22 is heated and boiled, whereby the boiling wash water rises in the hot tubes 22, causing a portion of the wash water to be flashed into steam, the evaporator 11 operating in eflect as a flash boiler. Accordingly, the steam generated in the tubes 22 carries forward with it a great amount of unvaporized wash v water which is thrown rather violently into the upper header 27 and through the communicating tube 58 into the tube 51 of the de-entrainment receiver 12. In view of the fact that the tube 51 of the de-entrainment receiver 12 is of relatively large diameter, the slight pressure of the steam or vapor is immediately reduced, causing substantially all of the unvaporized wash water to fall from the tube 51 into the element 53, whereby it is drained into the tube 52. 'A column of the wash water stands in the tube 52 and, due to the hydrostatic head, it is in large part returned via the tubes 72, 71, 43 and 44 into the lower header 34 to be re-circulated. In the normal operation of the evaporator 11, more than three hundred gallons of wash water per hour are circulated or pumped therethrough due to the action explained above, whereas only about ten percent of this wash water pumped is actually flashed into steam, whereby a great volume of wash water is continuously re-circulated between the evaporator 11 and the de-entrainment receiver 12.

The steam or vapor in the wash water delivered to the tube 51 of the de-entrainment receiver 12 rises into the de-' entrainment head 103, carrying with it small amounts of entrained wash water. Substantially all of the entrained wash water in the vapor rising into the de-entrainment head 103 is trapped out therein and returned to the tube 51 by gravity to be re-circulated. The vapor or steam, substantially free of entrained wash water, passes from the de-entrainment head 103 via the conduit system 104 into the condenser 105, in which it is condensed, this condensate being returned to the associated storage tank, not shown, to be again utilized as water for washing calutrons.

The system as a whole has under normal operating conditions an evaporating capacity of approximately thirty gallons of wash water per hour, this volume of wash water being delivered as condensate from the condenser 105 to the associated storage tank. Under these conditions, the valve 101 is opened sufiiciently to supply approximately thirty-three gallons of wash water per hour, corresponding to about three gallons of liquid in excess of the thirty gallons of wash water which is effectively vaporized and transferred to the storage tank, not shown, associated with the condenser 105. Also, the valve 102 is opened sufficiently to allow approximately three gallons of concentrated calutron Wash solution per hour to be delivered from the heat exchanger 10 to the associated storage tank, not shown. Accordingly, an approximately constant amount of concentrated wash water is retained in the heat exchanger 10 and about thirtythree gallons of calutron wash water is concentrated into about three gallons of concentrated wash solution per hour by the system.

In view of the fact that the heat exchanger 10 is lined throughout with tantalum, the calutron wash water contacts only this material incident to the concentration, which material is particularly advantageous in that it is not attacked by the corrosive wash water containing metal chlorides as well as some free hydrochloric acid. Thus, incident to the concentration of the approximately thirty-three gallons of wash water into three gallons of wash solution per hour, as explained above, substantially no additional metal impurities are introduced therein and substantially none of the contained uranium and metal impurities are lost to the outside. Thus the concentration of the uranium and the originally contained copper, nickel, iron and chromium impurities in the wash water is increased by a factor of about ten due to the treatment in the heat exchanger 10, whereby the concentrations of the metals mentioned in the concentrated wash solution are sutiiciently high to render efficient the subsequent electrolytic reduction in accordance with the process disclosed in the previously mentioned application of Kamen and De Haan.

It is noted that the concentrated wash solution conducted from the heat exchanger 10 into the associated storage tank via the conduit system including the valve 102, is taken from the outer end of the tube 71 substantially continuously; and in view of the fact that a much larger volume of wash water is returned from the tube 52 through the tubes 72 and 71 into the tube 43, the flow of wash water from the d e-entrainment receiver 12 into the evaporator 11 effectively blocks the passage of wash water from the outer end of the tube 43 to the outer end of tube 71. Accordingly, there is substantially no possibility that dilute calutron wash water from the source is conducted directly through the communicating tubes 43 and 71 to the storagetank for the concentrated wash solution; and in the ordinary course of events, all of the concentrated wash solution conducted to the associated storage tank has passed through the evaporator 11 and the de-entrainment receiver 12 in the previously described cycle in the heat exchanger 10 approximately ten times, due to the high rate of re-circulation between the evaporator 11 and the de-entrainment receiver 12.

in the embodiment of the heat exchanger disclosed, having the capacities noted, some of the pertinent dimensions of the elements are as follows: the tubes 43 and 71 are of about 1% l. D.; the tubes 44, 72, 52 and 22 are of about I" I. D.; the tubes 22 are about 48 long; the upper end of the lower header 34 is about 4" I. D.; the lower end of the lower header 34 is about 1 I. D.'; and the length of the lower header 34 is about 2%. During the normal operation of the heat exchanger 19, wash water stands in the tube 52 about 18 above the lower header plate 15; the wash water filling the extreme lower ends of the tubes 22 begins to flash to steam immediately at the entrance of the chamber 17; and the lower header 34, as well as the tubes 44, 43, 71 and 72 are completely filled with the wash water, as previously noted; whereby the total volume of the wash water in the heat exchanger 10 at any time is approximately one quart. Also, throughout the heat exchanger 10 the tantalum tubes and sheets are of approximately 0.013" stock; the opposite ends of the tubes 22 are rolled into the copper ferrules 23 and 24; and the tubes 22 are bowed slightly between the upper and lower header plates 14 and 15 to accommodate unequal expansion of the tubes 22 and the shell 16 incident to heating by the steam in the chamber 17.

in view of the foregoing explanation of the mode of operation of the heat exchanger 10, it will be understood that the pressure of the steam in the chamber 17, exerted upon the exterior of the tubes 22, the header plates 14 and 15 and the shell 16, is of the order of 125 pounds per square inch; whereas the pressure of the vapor or steam in the tubes 22, as well as in the upper header 27, is only slightly greater than atmospheric pressure, in view of the fact that the tube 51 of the de-entrainment receiver 12 is directly connected to the de-entrainment header 103 and the condenser 105, which are maintained substantially at atmospheric pressure. Accordingly, it will be understood that for all practical purposes the pressure exerted upon the interior of the tubes 22 may be considered to be atmospheric. Thus it will be appreciated that in the event there is any leakage between the tubes 22 and the ferrules 23 and 24 or between the ferrules 23 and 24 and the associated upper and lower header plates 14 and 15, the respective joints between the ends of the tubes 22 and the upper and lower sheets 25 and 26 will be subjected to a pressure of approximately 125 pounds per square inch. Accordingly, in this event the upper sheet 25 or the lower sheet 26 will be blown away from the associated upper header plate 14 or lower header plate 15, and torn loose from the associated end of the tube 22, in view of the fact that the peripheral portion of the upper and lower sheets 25 and 26 are respectively retained in place by the clamping rings 32 and 39. In order to prevent this danger, both the upper header plate 14 and the lower header plate 15 incorporate improved arrangements for relieving any pressure between the header plate and the associated sheet.

The arrangements incorporated in the upper and lower header plates 14 and 15 are substantially identical for practical purposes, and only that incorporated in the upper header plate 14- will be described in detail, in the interests of brevity. Referring now more particularly to Figs. 2 to 4, inclusive, illustrating the upper portion of the evaporator 11, it will be observed that in the outer surface of the upper header plate 14 three annular recesses 91 are provided, respectively surrounding the ends of the associated tubes 22. More particularly, each of the annular recesses 91 surrounds the outer end of the associated ferrule 23 immediately below the upper sheet 25. Also, a large annular recess 92 is formed in the outer surface of the upper header plate 14, surrounding the three tubes 22 are communicating with each of the three recesses 91 individually surrounding the three tubes 22. Further, an annular channel 93 is formed in the upper surface of the upper header plate 14 adjacent the periphery thereof and beyond the perimeterof the upper sheet 25, the channel 93 communicating with the atmosphere. Three substantially equally spaced apart radially extending holes 94'are drilled in the upper header plate 14 from the peripheral edge thereof and extend below the annular recess 92, the holes 94 intersecting the channel 93. The channel 93 forms a flange 95 disposed about the peripheral edge of the upper header plate 14, and the openings formed in this flange by the holes 94 mentioned are plugged by three plugs 96, whereby the holes 94 communicate with the channel 93. Finally, three holes 97 are drilled in the upper header plate 14- communicating between the annular recess 92 and the ends of the holes 94. Accordingly, it will be understood that the three annular recesses 91 surrounding the three ferrules 23 communicate with the annular recess "92, which latter recess communicates through the connected holes 97 and 94 with the channel 93, and consequently with the atmosphere.

Thus it will be understood that in the event any of the steam under relatively high gauge pressure in the chamber 17 leaks between one of the tubes 22 and the associated ferrule 23 or between one of the ferrules 23 and the upper header plate 14, it will flow into the associated annular recess 91 and escape via the annular recess 92, the holes 97 and 94, and the channel 93 to the atmosphere, whereby no substantial pressure is exerted on the welded joint between the end of the associated tube 22 and the upper sheet 25, thereby to prevent rupture of this joint or the end of the tube 22 or the upper sheet 25, all of the tantalum elements mentioned being of the thin-walled 0.013" stock, as previously explained. Any of the steam condensing in the annular recesses 91 and 92 or the holes 97 and 94 is drained into the channel 93 and then conducted to a suitable sump by a piping system including an elbow 98, threaded in an opening formed in the flange 95 and communicating with the lower portion of the channel 93.

In view of the foregoing, it will be understood that there has been provided an improved method of and system for concentrating calutron wash water containing uranium and metal impurities in the form of chlorides, whereby substantially none of the uranium is lost to the outside incident to the concentration, and substantially no additional metal impurities are introduced in the concentrated wash solution incident to the concentration. Also an improved heat exchanger has been provided which is lined throughout with tantalum, which is particularly resistant to corrosion by metal chlorides and hydrochloric acid, thereby insuring that the wash water is not contaminated by additional metal impurities incident to the concentration, as previously noted, and also lending long life and efiicient operation to the heat exchanger. Finally, the heat exchanger comprises an improved arrangement for preventing blowout or rupture of the relatively thin tantalum tubes and sheets due to the relatively high gauge pressure encountered in the evaporator and the inherent weakness of the tubes and sheets in view of their thinwalled construction. Further, it will be understood that the last-mentioned arrangement is of general utility in evaporators employing relatively thin expensive metal sheets, whereby a considerable saving is effected in the manufacturing cost of the evaporator.

While there has been described what is at present considered to be the preferred embodiment of the invention, it will be understood that various modifications may be made therein and it is intended to cover in the appended claims all such modifications as fall within the true spirit and scope of the invention.

What is claimed is:

1. In a tube and shell heat exchanger adapted to concentrate a hot corrosive solution, the combination comprising a rigidly mounted aperture tube sheet, a second apertured tube sheet, a plurality of tubes formed of corrosion-resistant material, said tubes having a coefficient of expansion difierent from that of the non-corrosion-resistant portions ofthe structure and being bowed intermediate their ends, a plurality of bushings supporting said tubes adjacent their respective ends within said apertured tube sheets, first and second sheets of corrosion-resistant material covering the external surfaces of said respective tube sheets and welded to the projecting ends of said tubes in overlying relation to said bushings, a shell surrounding said tubes and joined at its ends to said tube sheets, means supplying a corrosive solution to one end of said tubes, and means supplying a heating medium under pressure to the interior of said shell, whereby upon operation of the heat exchanger the expansion of the shell away from the rigidly mounted tube sheet is accommodated by the flexing of said bowed tubes thereby to avoid rupture of the tube and attached sheets of corrosionresistant material.

2. Apparatus as defined in claim 1, wherein said tubes and said first and second sheets provide a unitary corrosion-resistant liner formed of tantalum.

3. In a tube and shell heat exchanger adapted to concentrate a hot corrosive solution, the combination comprising a rigidly mounted apertured tube sheet, a second apertured tube sheet, a plurality of tubes formed of corrosion-resistant material, said tubes having a coeflicient of expansion different from that of the noncorrosion-resistant portions of the structure and being bowed intermediate their ends, a plurality of bushings supporting said tubes adjacent their respective ends within said apertured tube sheets, first and second sheets of corrosion-resistant material covering the external surfaces of said respective tube sheets and welded to the projecting ends of said tubes in overlying relation to said bushings thereby to form a unitary liner, a shell surrounding said tubes and joined at its ends to said tube sheets, means supplying a corrosive solution to one end of said tubes, means supplying a heating medium under pressure to the interior of said shell, leakage collecting recesses disposed between the tube sheets and the respective corrosion-resistant sheets adjacent the junction of said sheets and bushings, and drain passages connect ing said recesses to the exterior of the heat exchanger, whereby upon operation of the heat exchanger the expansion of the shell away from the rigidly mounted tube sheet is accommodated by the flexing of the bowed tubes and any leakage of heating medium into said recesses is passed to the exterior without permitting pressure to develop between the tube sheets and the unitary liner.

References Cited in the file of this patent UNITED STATES PATENTS 1,614,159 Smith Ian. 11, 1927 1,856,618 Brown May 3, 1932 1,948,550 Voorheis Feb. 27, 1934 1,962,170 Blennerhassett June 12, 1934 1,987,891 Cattanach Jan. 15, 1935 1,991,194 Child Feb. 12, 1935 2,336,879 Mekler Dec. 14, 1943 FOREIGN PATENTS 208,822 Great Britain Ian. 3, 1924 OTHER REFERENCES Publication, The Metal Tantalum, published by Fansteel Metallurgical Corp, North Chicago, illinois. Copyright December 1939.

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