Patent Number: 042736706
Section: description

DETAILED DESCRIPTION OF THE DRAWINGS So far as it is practical, the same elements or parts which appear in the different views of the drawings will be identified by the same numbers. With reference to FIG. 1, the apparatus illustrated by this drawing is representative of those used to process low radioactive aqueous waste containing dissolved and dispersed solids to a concentrated liquor, or bottoms, containing 25% by weight or more of solids. Although the subject invention pertains to an improved apparatus and method for the withdrawal of bottoms from such a representative system, a clear understanding of a source of such bottoms is believed to facilitate an understanding of the invention. As shown in the attached drawing, an aqueous radioactive waste stream at 60.degree. F. and 50 psia of low radioactivity and low solids, such 0.35% solids by weight, is fed at 33 gallons per minute by conduit 10 to pipe 11 which feeds the stream to recirculation pump 12. Pipe 14 conveys the stream from pump 12 to the liquor box 16 at the bottom of two-pass heater 15. The stream flows upwardly through one-half of the number of tubes 17 in heater 15 to liquor box 18 from which the stream is fed downwardly through the other one-half of the number of tubes 17 into liquor box 19. Heater 15 is supplied on the shell side with stream at 298.degree. F. and 65 psia by conduit 20 and the condensed steam is removed by conduit 21. The heated liquor at about 252.degree. F. is withdrawn from liquor box 19 by pipe 25 which feeds it to vapor body 26. The liquor boils in vapor body 26 at 15 psia and 213.degree. F., producing vapor at 16,472 pounds per hour which is fed to and through entrainment separator 28 on the top of the vapor body. The liquor is removed from the bottom of vapor body 26 by pipe 11 and is recirculated at 6000 to 8000 gallons per minute as described. After the liquor has been reduced to the desired solids concentration, which will generally be 27% solids by weight or higher, the product is removed at 218.degree. F. from conduit 14 through ram valve 60 using the method and apparatus provided by this invention and which are described subsequently in more detail. As the vapor flows upwardly in entrainment separator 28 it contacts mesh pad 30 which separates entrained liquid drops or mist and solids. The vapor leaves separator 28 at 213.degree. F. and 15 psia through conduit 35 which delivers it to the shell side of condenser 37. The water formed by condensing the vapor is removed at 16,272 pounds per hour from condenser 37 by conduit 38 at 212.degree. F. and 14.7 psia which delivers it to the shell side of subcooler 40. The cooled water or distillate which results from the vapor condensation is removed at 120.degree. F. and 29.5 gallons per minute by conduit 41 from the shell side of subcooler 40. Conduit 41 can deliver it to any suitable destination, such as for reuse in the plant. Cold water at 100.degree. F. is fed by conduit 44 to water box 45 at the top of subcooler 40. The cold water flows downwardly through the tubes 46 into water box 47 at the bottom from which it flows through conduit 48 to water box 49 at the bottom of condenser 37. The water flows upwardly from water box 49 through one-half of the number of tubes 50 in condenser 37 to water box 51 at the top. The water then flows from water box 51 downwardly through the other one-half of tubes 50 into water box 52 from which the cooling water at 121.degree. F. is removed by conduit 53. Withdrawal of the bottoms from the evaporator according to the invention is achieved using the apparatus shown in FIG. 2. Fast acting ram valve 60 is connected to conduit 14 and provides access thereto for removal of bottoms from the evaporator system. Extending from ram valve 60 is drain conduit 63 which communicates with pump 64. Rinse water supply conduit 66 communicates with drain conduit 63 near ram valve 60 so as to facilitate rinsing the drain conduit as will be subsequently described. A rinse water conduit valve 67 is positioned in conduit 66, desirably close to its juncture with drain conduit 63. Extending from the outlet of pump 64 is a delivery conduit 69 which communicates with bottoms collecting tank 70. Valve 71 regulates flow of bottoms by conduit 69 to bottoms tank 70. Vent 72 in the top of tank 70 provides a means for withdrawal of separated gases which must, of course, be properly handled if they are radioactive. Conduit 74 and valve 75 provide means for removing the collected bottoms from tank 70 for subsequent disposal. A branch conduit 77 having valve 78 therein communicates with feed tank 80. Low radioactive aqueous waste, collected from various sources, can be fed to feed tank 80 by conduit 82 through valve 83. Vent 85 in the top of feed tank 80 provides a means for removal and entry of air and other gases during filling and emptying of feed tank 80. Feed liquor withdrawal conduit 10 communicates with feed tank 80 through valve 87. Although not an essential part of the bottoms withdrawal apparatus, it is very advisable to position a block valve 91 in drain conduit 63 upstream but close to pump 64, and to position a block valve 92 in delivery conduit 69 downstream but close to pump 64. The block valves 91 and 92 can be used to isolate pump 64 thereby permitting its removal in case of failure. Although the apparatus as illustrated in FIG. 2 can be operated manually, it is clearly far more practical for it to be operated by automatic controls, including timers, electrically operated solenoid valves and such other conventional instrumentation as may be appropriate considering the radioactivity of the product being handled. Accordingly, the subsequent additional discussion of FIG. 2 will be as an automatic system. When the bottoms removal apparatus illustrated by FIG. 2 is not in operation it is maintained full of rinse or wash water which can be, if desired, the low radioactive liquor fed to the evaporator. When the density of the concentrated radioactive waste material or bottoms in the evaporator apparatus shown in FIG. 1 reaches a predetermined level, based on observation or according to a time cycle, the process sequencer 100 initiates control operations. At time zero, a 24-hour timer, which is part of the sequencer, sends a signal by line 110 which simultaneously opens block valves 91 and 92 and starts pump 64, and a signal by line 120 which opens ram valve 60 permitting bottoms to flow from conduit 14 to drain conduit 63. The 24-hour timer simultaneously also energizes a 0 to 30 minute timer and a separate 0 to 1 minute timer A. The 0-30 minute timer and timer A are part of the process sequencer. The valve 78 to the feed tank is simultaneously opened by a signal delivered to the valve by line 130. With pump 64 running, bottoms are withdrawn from the evaporator while simultaneously the wash or rinse water initially in conduits 63 and 69 is fed to feed tank 80. Timer A then times out in about 30 seconds, causing valve 78 to close and sending a signal by line 140 to valve 71, leading to bottoms tank 70, to open. Bottoms are removed from the evaporator for a 30 minute period, or such time as considered appropriate in view of the size of the evaporator, the concentration of the bottoms and the capacity of the bottoms withdrawal system. For a particular evaporator, a 30 minute cycle may cause the liquid level in the evaporator to drop 2 feet upon withdrawal of 400 to 600 gallons of bottoms with 2 inch diameter conduits 63 and 69. After 30 minutes, the 30 minute timer times out and a 0 to 10 minute timer is energized. The 0 to 10 minute timer sends a signal by line 150 to wash conduit valve 67, which is thereby opened. Wash water at about 40 to 50 psig thereby flows into conduits 63 and 69 while simultaneously bottoms are back flushed from the fast acting ram valve 60 into conduit 14 for a short time, i.e. 30 seconds, due to the lower pressure (25 psig) in conduit 14. At the same time, 0 to 1 minute timer A, as well as a 0 to 1 minute timer B, which are part of the sequencer, are energized. The 0 to 1 minute timer A times out in 30 seconds and bottoms tank valve 71 closes and valve 78 to the feed tank opens. In this way the bottoms at the front of the stream are directed to bottoms tank 70 and once that has been almost completed the flow is redirected to the feed tank which receives whatever small amount of bottoms are in the conduits as well as the conduit wash stream. The 0 to 1 minute timer B then times out in five seconds thereby sending a signal by line 120 to close ram valve 60. Subsequently, the 0 to 10 minute timer times out resulting in a signal being sent by line 150 to close wash conduit valve 67, a signal being sent by line 130 to close valve 78 leading to the feed tank 80, and a signal being sent by line 110 to shut off pump 64 and close block valves 91 and 92. At that point, the bottoms removal cycle is completed and remains on hold, ready for the next bottoms removal at a predetermined time.