Patent Publication Number: US-6336344-B1

Title: Dephlegmator process with liquid additive

Description:
REFERENCE TO PRIOR APPLICATIONS 
     This application incorporates by reference and claims the benefit of the filing date of U.S. Provisional Patent Application Ser. No. 60/135,969, filed May 26, 1999. 
    
    
     BACKGROUND OF THE INVENTION 
     A process known in the field as the Ryan-Holmes process employs the use of bottoms additives, such as a C 4 + stream into the upper portion of a distillation column or the reflux condenser of the column, to enhance distillation separation and to save energy. The Ryan-Holmes process and modifications are described in part in U.S. Pat. Nos. 4,293,322, issued Oct. 6, 1981; 4,318,723, issued Mar. 9, 1982; 4,350,511, issued Sep. 21, 1982; 4,428,759, issued Jan. 31, 1984, now Reissue Pat. No. 32,600, reissued Feb. 16, 1988; 4,451,274, issued May 29, 1984; 4,462,814, issued Jul. 31, 1984; and 5,345,772, issued Sep. 13, 1994. 
     The principles of continuous distillation are described in Perry&#39;s Chemical Engineer&#39;s Handbook, Seventh Edition, McGraw-Hill, Section 13. FIG. 13-1 shows a schematic diagram for a simple distillation column with one feed, a rectifying section above the feed containing multiple stages of vapor/liquid equilibrium, an overhead condenser at the uppermost stage where heat is removed, a stripping section below the feed also containing multiple stages of vapor/liquid equilibrium, and a reboiler at the lowermost stage where heat is added to the system. FIG. 13-3 illustrates a complex distillation process where heat is removed from each stage of the rectifying section and heat is added to each stage of the stripping section. 
     This process of removing heat from one or more stages of the rectifying section, in addition to the overhead condenser, is known dephlegmation. A dephlegmator is thus a device that enables more than one stage of distillative rectification with the simultaneous removal of heat from each of those stages, without the withdrawal of liquid or vapor streams from the column. It may be used over the whole length of the rectification zone in a distillation column or on a selected zone. 
     Dephlegmators, which operate as rectifying and heat transfer devices in the gas processing field are well-known, and for example, are employed to separate helium, nitrogen, or helium and nitrogen mixtures from a natural gas stream. Some examples of dephlegmators-heat exchangers used for such separation processes include: U.S. Pat. Nos. 5,011,521, issued Apr. 30, 1991; 5,017,204, issued May 21, 1991; and 5,802,871, issued Sep. 8, 1998. 
     SUMMARY OF THE INVENTION 
     The invention relates to a separation and rectification process employing a dephlegmator-heat exchanger device and introducing a liquid additive to improve the rectification process. 
     The invention comprises a dephlegmator-heat exchanger process for the separation of a light gas component from heavy components in a feed gas stream, which process comprises rectifying the feed gas stream in a dephlegmator-heat exchanger to provide a lean component overhead gas stream and a rich liquid stream. The invention comprises introducing, for example, injecting, during rectifying, a selected amount of a liquid hydrocarbon additive stream, for example, into the top or an upper portion of the dephlegmator-heat exchanger; withdrawing the rich liquid stream with the additive from a lower portion of the dephlegmator-heat exchanger; and withdrawing the lean overhead gas stream from an upper portion of the dephlegmator-heat exchanger. Optionally, the liquid hydrocarbon additive recycled may be recovered from the liquid stream. 
     It has been discovered that the use of a liquid hydrocarbon additive in a dephlegmator-type heat exchanger in place of a conventional reflux condenser, has two primary benefits: the quantity of liquid hydrocarbon injected is considerably reduced; and for the same liquid hydrocarbon injection flow rate, the condenser temperature is increased. These effects can also be combined at intermediate values of flow and temperature. 
     The introduction of a liquid additive stream, typically a hydrocarbon stream, such as a C 4 + stream, can increase the top or upper operating temperature of the dephlegmator-heat exchanger by at least 10° F., for example, increasing the top temperature to about −30 to −40° F. or more, rather than the usual temperature operating range of about −50 to −150° F., to achieve a given separation of a hydrocarbon feed stream. 
     In the process, the dephlegmator-heat exchanger device employed may be represented by a heat exchanger whose construction and design, for example, cross-sectional area, permits the device to act as a rectifying distillation column and heat transfer device, wherein vapor flows upwardly, while condensed liquid flows downwardly. The vapor and liquid are in equilibrium in the device, so that several stages of rectification are developed, while each step has heat removed, and in effect, nonadiabatic distillation occurs. 
     Unlike a process using a condenser where heat is removed from the uppermost rectifying stage only, in the process of this application the dephlegmator is removing heat from more than the uppermost stage of a rectifying zone. The dephlegmator may remove heat from anywhere between two to every stage in the rectifying zone. 
     The process of the invention may be usefully employed in a variety of processes in the separation of gas feed streams, such as, but not limited to: the separation of acid gases, like carbon dioxide and hydrogen sulfide from methane; the recovery of ethane (C 2 H 6 ) and propane (C 3 H 8 ) from natural gas streams; the recovery of ethylene (C 2 H 4 ) and propylene (C 3 H 6 ) from refinery offgas streams; the recovery of ethylene or propylene in ethylene or propylene production plants; and the separation of hydrogen and carbon monoxide by liquid methane. 
     In many of the processes, the product to be recovered may be from either the overhead (lean) gas stream or the bottoms (rich) liquid stream from the dephlegmator-heat exchanger. The liquid additive may be removed from the bottoms liquid stream and recycled for use in the dephlegmator-heat exchanger, or alternatively, the bottoms liquid stream with the liquid additive may be directed for further processing or use. The illustrative process, as described, employs a single dephlegmator-heat exchanger; however, one or more dephlegmators-heat exchangers of the same or different design may be employed in series or parallel in any process, provided at least one of the dephlegmators-heat exchangers employs a liquid hydrocarbon additive stream. For example, with two dephlegmators-heat exchangers in series, the liquid additives of the same or different hydrocarbon compositions may be injected into one or both dephlegmators-heat exchangers to increase the temperature in each device and to aid the rectification and separation in each dephlegmator-heat exchanger. 
     The liquid additive introduced into the dephlegmator-heat exchanger may vary in composition and concentration, as required, to increase the dephlegmator-heat exchanger temperature levels and separation efficiency, depending on the particular rectification process carried out. For example, where the process is a carbon monoxide-hydrogen separation, the additive may comprise methane, while with other C 2 -C 3  hydrocarbon separations, the liquid additive may comprise liquid hydrocarbon, or particularly, bottoms recovery products, like C 4 + hydrocarbons, i.e., C 4 -C 8 , with C 4 , as the primary component preferred. 
     Generally, the liquid additive comprises a higher molecular weight hydrocarbon additive stream, which is generated in the particular process, or a by-product of the process, or is separately supplied. Usually, the liquid additive is introduced at the top or directly into an upper section of the dephlegmator-heat exchanger and may be introduced as a separate stream or be sprayed in particulate form into the rising vapor and falling liquid of the dephlegmator-heat exchanger. The amount of the liquid additive may range from about 200 mole percent of the feed gas, such as, from about 5 to 100 mole percent and at temperatures varying from up to 0° F., e.g., −320 to −35° F. 
     The process will be described for the purpose of illustration only in connection with certain illustrated embodiments; however, it is recognized that various changes, modifications, additions and improvements may be made by those persons skilled in the art of the invention, as described and disclosed, without departing from the spirit and scope of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a general schematic representation of the use of a dephlegmator-heat exchanger in the process of the invention; 
     FIG. 2 is a schematic representation of the process of the invention in the recovery of olefins from a Coker or Fuel Catalatic Cracker Unit (FCCU) offgas source; and 
     FIG. 3 is a schematic representation of a prior art process (FIG. 3A) and a process of the invention (FIG. 3B) in the separation of hydrogen and carbon monoxide. 
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     With reference to FIG. 1, there is shown a process  50  employing a brazed aluminum dephlegmator-heat exchanger  52  having a plurality of vertical passages  54  (only one passage is illustrated), with one or a plurality of passages  56  for a refrigerating stream to cool and condense the upward flowing vapors. The dephlegmator-heat exchanger  52  includes an inlet  58  for the lower introduction of an upward flowing feed gas stream an outlet  60  for the upper withdrawal of a gas component lean stream, a lower discharge outlet  62  for the withdrawal of a liquid rich component stream, and a liquid additive injection inlet  64  for the introduction of the liquid additive hydrocarbon stream to the top or upper portion of the dephlegmator-heat exchanger  52 . Representative flow arrows are illustrated in the drawing. A collection vessel  66  located at the lower end of the dephlegmator passages permits the distribution of the vapors in the inlet  58  to each passage and also collects the liquid draining from each passage  54  to discharge the combined liquid flow. Both this vessel  66  and the hydrocarbon liquid additive injection inlet  64  avoid reentrainment of the liquid in the vapor stream at each location. 
     This process can be integrated into a variety of cryogenic distillative or absorption processes. The reason for its effectiveness is that the heat of absorption in the process is absorbed over several theoretical stages of distillation or absorption. Thus, it functions as multiple intermediate condensers, which results in the beneficial effects described above. 
     The processes can be compared to prior art patents describing the Ryan-Holmes process. Both the prior art processes and the process of the current application may utilize a distillation column with a rectification zone, containing multiple vapor/liquid contact stages. In the prior art process, heat is removed from a single equilibrium condensing stage using a single condenser. In the process of the current invention, utilizing the dephlegmator-heat exchanger  52 , heat is able to be removed from two or more (up to every stage of the process) equilibrium stages. The resulting increased efficiency means that in the Ryan-Holmes process the flow rate of the additive hydrocarbon stream (such as C 4 +) may be reduced while achieving equivalent results compared to the prior art processes. This, in turn, results in reduced system refrigeration and reboiler heat loads. 
     Some examples of the application of this FIG. 1 process are illustrated in FIGS. 2 and 3. 
     In FIG. 2, process steps are designated by the  10 ,  11 ,  12 , and  13  series. Process equipment within step  13  is designated by the  20 ,  21  . . . series. Process streams within FCCU step  13 , are designated by the  31 ,  32  . . . through  42  series. 
     The refinery offgases feed considered in this described embodiment are combined FCCU and Coker gases. The gases are at lower pressure, i.e., near atmospheric pressure, and are compressed to about 270 psig in compressor  10 , cooled in exchanger  11  to 100° F., and then processed in stages in a pretreatment step  12 . These stages may be comprised of a waterwash; an amine contactor column for H 2 S removal or other acid gas removal; and a dehydration stage for water vapor removal. The treated gas stream now enters the single column process  13 . 
     The following is a description of the single column process  13  for ethylene recovery, incorporating a dephlegmator-heat exchanger with a liquid hydrocarbon additive. The feed vapor  31  is introduced into column  20 . The dephlegmator  21  is mounted overhead the column  20 . Vapor  40 , from the column  20  (without a reflux condenser), flows directly to the dephlegmator  21 . The condensed liquid  37  is returned to the top stage of the column  20 . The recycle hydrocarbon stream  35 , is chilled in heat exchanger  28  and one passage of dephlegmator  21 , and stream  42  is injected into the top of the dephlegmator  21  passages. Propylene refrigerant is used to provide the dephlegmator duty and the recycled liquid hydrocarbon duty in dephlegmator  21 . The lean overhead vapor  41  is reheated in heat exchanger  28  and exported as the ethylene lean product stream  32 . 
     The column  20  has a side reboiler  23  for heat conservation purposes. A side vapor draw, stream  38 , is extracted from the column  20  at this stage. The side reboiler  23  employs liquid from an intermediate tray of the column  20 , below the point of introduction of the feed stream  31 , and then after reboiling, returning the reboiled liquid to the tray below the tray from which the liquid is withdrawn. The use of a column intermediate side reboiler  23  enhances the concentration of the olefin component in the vapor side draw stream  38 . The vapor side draw stream  38  is withdrawn from between the two intermediate trays used for the side reboiler  23 . 
     The bottom reboiler is  25 . The bottoms liquid, stream  39 , is pumped by pump  27 , then cooled in exchanger  26  and split into two streams  34  and  35 . Stream  35  is cooled and recycled to the dephlegmator  21 . 
     The vapor phase side draw, stream  38 , is cooled and condensed in exchanger  24 , and stream  33  is then withdrawn as the olefin rich liquid stream  33 . The split off stream  34  is exported as the heavy liquid bottoms stream  34 . The reheated vapor stream  32  may go to the refinery fuel gas stream. 
     The operating conditions for the column  20 , with the dephlegmator-heat exchanger  21 , are listed in Table 1. The overall material balance and the recycle stream flow and composition is given in Table 2. For comparison purposes, the conditions for the same process using a conventional condenser are also listed in the same table. For these cases, the recycle liquid flow has been kept constant, while the condenser temperature has been raised from −114° F. (conventional condenser) to −50° F. (dephlegmator-heat exchanger). 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 Comparison of Column Conditions 
               
               
                 Dephlegmator vs. Conventional Condenser, 
               
               
                 Both With Liquid Hydrocarbon Injection 
               
               
                 Ethylene Recovery 
               
               
                 Column Pressure = 250 PSIG 
               
            
           
           
               
               
               
            
               
                 HEATER/COOLER 
                 TEMPERATURE (° F.) 
                 DUTY (MMBTU/HR) 
               
               
                   
               
               
                 Condenser 
                 −50 (Dephlegmator) 
                 12.0 
               
               
                 and Chiller 
                 −114 (Condenser) 
               
               
                 Feed 
                  17 
               
               
                 Side Reboiler 
                 155 
                 13.9 
               
               
                 Reboiler 
                 337 
                 20.1 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 2 
               
             
            
               
                   
               
               
                 Single Column Material Balance Ethylene Recovery 
               
            
           
           
               
               
            
               
                   
                 Stream ID 
               
            
           
           
               
               
               
               
               
               
            
               
                   
                 31 
                   
                 33 
                 34 
                 35 
               
            
           
           
               
               
            
               
                   
                 Name 
               
            
           
           
               
               
               
               
               
               
            
               
                   
                 Feed 
                 Fuel Gas 
                 Light Liquid 
                 Heavy Liquid 
                 Recycle 
               
            
           
           
               
               
            
               
                   
                 Phase 
               
            
           
           
               
               
               
               
               
               
            
               
                 Fluid Rates, lb/mol/hr 
                 Mixed 
                 Dry Vapor 
                 Mixed 
                 Dry Liquid 
                 Dry Liquid 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
            
               
                  1 
                 H 2 O 
                 .0000 
                 .0000 
                 .0000 
                 .0000 
                 .0000 
               
               
                  2 
                 H 2 S 
                 .0295 
                 9.5482E−08 
                 .0295 
                 2.4110E−09 
                 2.9808E−07 
               
               
                  3 
                 N 2   
                 101.0916 
                 101.0915 
                 7.9409E−07 
                 .0000 
                 .0000 
               
               
                  4 
                 CO 
                 15.3521 
                 15.3520 
                 5.1159E−07 
                 .0000 
                 .0000 
               
               
                  5 
                 CO 2   
                 14.7452 
                 8.9584 
                 5.7869 
                 5.7701E−11 
                 7.1338E−09 
               
               
                  6 
                 H 2   
                 287.0592 
                 287.0588 
                 1.3279E−11 
                 .0000 
                 .0000 
               
               
                  7 
                 C 1   
                 1108.8446 
                 1107.0658 
                 1.7770 
                 6.5158E−15 
                 8.0558E−13 
               
               
                  8 
                 Ethylene 
                 302.8797 
                 30.3389 
                 272.5427 
                 1.8621E−07 
                 2.3022E−05 
               
               
                  9 
                 C 2   
                 486.4302 
                 8.4172E−04 
                 486.4327 
                 1.1531E−05 
                 1.4257E−03 
               
               
                 10 
                 Propylene 
                 254.2555 
                 .5378 
                 253.6669 
                 .0525 
                 6.4968 
               
               
                 11 
                 C 3   
                 138.7629 
                 .7325 
                 137.9453 
                 .0860 
                 10.6346 
               
               
                 12 
                 Isobuten 
                 18.1834 
                 .4979 
                 17.4023 
                 .2832 
                 35.0071 
               
               
                 13 
                 1Butene 
                 25.3941 
                 .6988 
                 24.2896 
                 .4056 
                 50.1500 
               
               
                 14 
                 T2Butene 
                 17.9134 
                 .4453 
                 17.1102 
                 .3578 
                 44.2330 
               
               
                 15 
                 C2Butene 
                 12.9536 
                 .3002 
                 12.3737 
                 .2796 
                 34.5641 
               
               
                 16 
                 13Butd 
                 .3810 
                 .0102 
                 .3645 
                 6.3586E−03 
                 .7861 
               
               
                 17 
                 IC 4   
                 31.2459 
                 .9798 
                 29.8409 
                 .4252 
                 52.5700 
               
               
                 18 
                 NC 4   
                 23.5549 
                 .6275 
                 22.4764 
                 .4509 
                 55.7502 
               
               
                 19 
                 3M 1 Butene 
                 .3733 
                 7.1252E−03 
                 .3528 
                 .0134 
                 1.6516 
               
               
                 20 
                 1Pentene 
                 6.1519 
                 .0909 
                 5.7766 
                 .2843 
                 35.1454 
               
               
                 21 
                 2M1Butene 
                 3.1259 
                 .0436 
                 2.9350 
                 .1472 
                 18.2015 
               
               
                 22 
                 2M2Butene 
                 5.7787 
                 .0617 
                 5.3698 
                 .3470 
                 42.9030 
               
               
                 23 
                 T2Pentene 
                 5.0993 
                 .0620 
                 4.7608 
                 .2764 
                 34.1734 
               
               
                 24 
                 C2Pentene 
                 2.9111 
                 .0347 
                 2.7166 
                 .1598 
                 19.7527 
               
               
                 25 
                 IC 5   
                 17.3760 
                 .2799 
                 16.3346 
                 .7611 
                 94.1029 
               
               
                 26 
                 NC 5   
                 8.2941 
                 .1068 
                 7.7517 
                 .4354 
                 53.8301 
               
               
                 27 
                 1Hexene 
                 22.9652 
                 .1430 
                 20.3361 
                 2.4847 
                 307.1939 
               
               
                 28 
                 NC 6   
                 14.8743 
                 .0752 
                 12.9524 
                 1.8457 
                 228.1893 
               
               
                 29 
                 NC 7   
                 5.6047 
                 9.9184E−03 
                 4.2342 
                 1.3599 
                 168.1266 
               
               
                 30 
                 NC 8   
                 1.1669 
                 6.2739E−04 
                 .6831 
                 .4830 
                 59.7093 
               
               
                 31 
                 NC 9   
                 .1702 
                 2.1248E−05 
                 .0663 
                 .1037 
                 12.8183 
               
               
                 32 
                 NC 10   
                 .0463 
                 1.0473E−06 
                 .0105 
                 .0356 
                 4.3988 
               
            
           
           
               
               
               
               
               
               
            
               
                 Total Rate, lb − mol/hr 
                 2933.0148 
                 1551.6116 
                 1366.3190 
                 11.0842 
                 1370.3901 
               
               
                 Temperature, ° F. 
                 100.0000 
                 85.5957 
                 100.0000 
                 100.0045 
                 100.5957 
               
               
                 Pressure, psig 
                 270.5000 
                 246.0000 
                 249.5559 
                 247.0000 
                 280.0000 
               
               
                 Enthalpy, mm btu/hr 
                 11.5129 
                 2.4138 
                 6.9835 
                 .3000 
                 3.7577 
               
               
                 Molecular Weight 
                 26.2661 
                 14.8964 
                 38.7783 
                 79.5827 
                 79.5827 
               
               
                   
               
            
           
         
       
     
     In both instances, the ethylene recovery is 90 percent, while the C 1 /C 2  ratio is 0.0025 in the product. 
     In Table 3, the performance features of the process of the invention include: a single fluid refrigeration cycle; a significant reduction in refrigeration compressor power consumption; and elimination of the stainless steel reflux drum and pumping station. 
     
       
         
           
               
             
               
                 TABLE 3 
               
             
            
               
                   
               
               
                 Comparison of Processes 
               
            
           
           
               
               
               
            
               
                   
                 CONVENTIONAL 
                   
               
               
                 REFRIGERATION 
                 CONDENSER 
                 DEPHLEGMATOR 
               
               
                   
               
               
                 Cycle Type 
                 Cascade 
                 Single Loop 
               
               
                   
                 Ethylene/Propylene 
                 Propylene 
               
               
                 Compressor Power 
                 8660 HP 
                 5400 HP 
               
               
                 Relative Power 
                 160 
                 100 
               
               
                 Equipment 
                 Stainless Steel 
                 No Reflux Drum 
               
               
                   
                 Reflux Drum, Pumps 
                 or Pumps 
               
               
                   
                 Column Section 
                 Carbon Steel 
               
               
                   
                   
                 Column 
               
               
                   
               
            
           
         
       
     
     In the case where propylene recovery is required from refinery offgas, with the ethylene rejected to the fuel gas, a similar design can be illustrated. In this case, the condenser temperature is kept the same at −35° F. for both options, and the recycled hydrocarbon liquid flow is reduced from 538 to 136 pound moles per hour by the application of the dephlegmator design, i.e., by a factor of four. In both cases, the propylene recovery is maintained at 98 percent and the C2/C3 equals 0.005 in the recovered product. 
     The invention can also be applied to ethylene recovery from the synthesis gas produced by cracking furnaces for the production of ethylene. 
     The invention provides benefits in the distillative separation of CO 2  and CH 4 , where a liquid hydrocarbon additive is employed to overcome the potential solids formation, as shown in the following example: 
     EXAMPLE 
     With a feed gas containing 24% CO 2  and CH 4  at −55° F., 525 psig fed to a column having specifications 3% CO 2  in the overhead vapor and 2% CH 4  in the bottoms stream, and having a C 5 + injected to the condenser, the results are listed below: 
     
       
         
           
               
               
               
             
               
                   
                   
               
               
                   
                 CONVENTIONAL 
                   
               
               
                   
                 CONDENSER 
                 DEPHLEGMATOR 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                 Additive rate with 
                 1159 
                 661 
               
               
                 overhead at −55° F. 
               
               
                 lb. moles/hr. 
               
               
                 Overhead 
                 −92 
                 −55 
               
               
                 temperature (° F.) 
               
               
                 additive rate = 661 lb. 
               
               
                 moles/hr. 
               
               
                   
               
            
           
         
       
     
     Thus, the dephlegmator can be utilized to either reduce the liquid hydrogen injection flow or raise the condenser temperature with the same hydrocarbon injection flow. 
     The liquid may be injected at many levels over the height of the dephlegmator. This modifies the duty at each theoretical stage and the technique may be used to make more equal refrigeration load at each stage. Also, from a mechanical aspect, it may offer advantages to spread the injection devices over an extended zone of the dephlegmator passages. 
     FIG. 3 illustrates the application of the invention in a H 2 /CO separation. The invention may be used for the methane wash process. In the prior art, FIG. 3A, liquid methane stream  100  is subcooled with liquid nitrogen stream  101  in heat exchanger  150  and fed to the top stage of absorption column  151 . 
     The feed gas, stream  102 , containing H 2 , CO and CH 4 , is fed to below the lowest stage of column  151 . The objective of this process is to absorb the gaseous CO in the liquid methane  100 . One or more heat exchanger devices  152  are spaced out over the height of the column  151  between the stages, to remove the heat of absorption. Liquid nitrogen  101  is the refrigerating fluid. The hydrogen product, stream  103 , is the overhead vapor stream, and the CO absorbed is in the bottoms liquid stream  104 . 
     The improved inventive process is illustrated in FIG.  3 B. The dephlegmator  256  is immersed in a pool of liquid nitrogen  253  in vessel  254 , which is introduced by stream  201 . The liquid nitrogen  253  circulates through passages  252  and is partially vaporized to provide refrigeration. Thus, the whole height of the dephlegmator  256  is at constant temperature. The liquid methane  200  is subcooled in passages  250  and injected to the top of the dephlegmator passages  251 . The feed gas  202  enters the separator  255  at the base of these passages. The liquid product  204  is extracted from the separator  255  at this point. The hydrogen product  203  exits at the top. Thus, this device is now a an isothermal cryogenic absorption tower. A prime feature of this invention is that the liquid methane absorption fluid flow rate is minimized, since the temperature excursions over the stages between the cooling devices of the prior art FIG. 3A are eliminated. 
     Those skilled in the art will recognize this invention is applicable to many cryogenic absorption processes.