Abstract:
An improved apparatus and process are disclosed for nitrogen rejection from a gaseous hydrocarbon stream recovered from an enhanced oil recovery project employing nitrogen for miscible flood of oil reservoirs. The process utilizes a modified dual distillation column arrangement including two fractionators which do not utilize overhead reflux condensers or reboilers for separating a nitrogen-methane mixture. Further, process conditions can be adjusted so as to provide efficient nitrogen rejection from a feedstream in which nitrogen content varies widely over a comparatively long period of time during enhanced recovery of oil.

Description:
This invention relates to separating nitrogen and hydrocarbons in a normally gaseous mixture containing nitrogen in variable amounts. In one aspect it relates to a process employing a modified dual distillation column arrangement for rejecting nitrogen from a gaseous stream. In another aspect it relates to an improved method for recovering nitrogen from a hydrocarbon stream containing Cz and heavier hydrocarbon components. 
     BACKGROUND OF THE INVENTION 
     Interest in separation and recovery of nitrogen from a hydrocarbon gas stream, which contains variable amounts of nitrogen, comes primarily from recovery of nitrogen from gas streams associated with enhanced oil recovery (EOR) projects employing nitrogen for miscible flood of oil reservoirs. In these miscible flooding projects a nitrogen rejection unit (NRU) for producing a nitrogen product pure enough to allow the recovered nitrogen to be reinjected into the oil reservoir is required. In addition, the NRU must have capacity for handling the gaseous feed mixture with a minimum of equipment changes while the nitrogen content of the recovered gas changes widely during the comparatively long life of the enhanced recovery project. 
     In response to the nitrogen recovery problem associated with enhanced oil recovery projects, several methods of separating nitrogen from the hydrocarbons have been developed. A commonly used method employs an integrated dual distillation column arrangement in which a high pressure column provides a rough nitrogen/methane split and a low pressure column makes the specification product. Generally these prior art methods have been designed for gaseous mixtures having a relatively low concentration of heavy hydrocarbons and/or a relatively unchanging nitrogen concentration in the gaseous mixture being processed, and would require equipment changes during the duration of the enhanced oil recovery project to accommodate the changing levels of nitrogen present in the gas to be processed. 
     Accordingly, it is an object of this invention to provide an improved integrated dual distillation apparatus and process for removing nitrogen from a gaseous mixture containing nitrogen and hydrocarbon components. 
     It is another object of this invention to provide an improved process for removing nitrogen from natural gas wherein the nitrogen concentration in the natural gas may vary from the naturally occurring concentration to as high as 75 mole-% or more. 
     It is yet another object of this invention to provide an improved process for removing nitrogen from natural gas wherein the natural gas also contains a relatively high concentration of heavy hydrocarbons. 
     It is yet another object of this invention to provide an improved method of recovering nitrogen from a miscible flooding project wherein the nitrogen is recovered as a substantially pure gaseous product. 
     It is yet another object of this invention to provide a process and apparatus for removing nitrogen from natural gas that is suitable for offshore operations. 
     BRIEF SUMMARY OF THE INVENTION 
     In treating a miscible flood gas stream, an improved process for separating gaseous nitrogen and methane is disclosed. As used herein a miscible flood gas is a mixture containing nitrogen, methane, ethane, and some heavier hydrocarbon components, wherein the nitrogen content can vary widely over the comparatively long life of an enhanced oil recovery project. 
     In accordance with the present invention, there is provided an improved process and apparatus for an integrated dual distillation system which is advantageous for offshore operations. The process for separating nitrogen from methane in a distillation system employing a high pressure (HP) fractionator and a low pressure (LP) fractionator comprises the steps of: 
     (a) cooling a first portion of a first stream, essentially free of heavy hydrocarbons, and comprising a gaseous nitrogen-methane mixture at a pressure of at least 450 psia, so as to produce a partially condensed first portion of said first stream; 
     (b) separating said partially condensed first portion of said first stream in a first phase separator and withdrawing from said first separator a second stream having an actual temperature, comprising gaseous nitrogen-methane and a third stream comprising liquid nitrogen-methane, wherein said second stream is enriched in nitrogen and said third stream is enriched in methane; 
     (c) cooling said second stream sufficiently so as to produce a partially condensed second stream prior to introducing said partially condensed second stream into an upper portion of said HP fractionator; 
     (d) combining a second portion of said first stream with said third stream to form a fourth stream; 
     (e) feeding said fourth stream into a lower portion of said HP fractionator wherein said partially condensed second stream and said fourth stream are simultaneously fractionated in said HP fractionator to produce a fifth stream predominantly comprising gaseous nitrogen and a sixth stream predominantly comprising liquid methane; 
     (f) cooling said fifth stream sufficiently so as to produce a partially condensed condense fifth stream; 
     (g) separating said partially condensed fifth stream in a second phase separator and withdrawing from said second separator a seventh stream predominantly comprising liquid nitrogen and an eighth stream predominantly comprising gaseous nitrogen; 
     (h) feeding said seventh stream into a middle portion of said LP fractionator; 
     (i) expanding at least a portion of said eighth stream prior to feeding said eighth stream into an upper portion of said LP fractionator; 
     (j) combining a third portion of said first stream with said sixth stream to form a ninth stream; 
     (k) feeding said ninth stream into a lower portion of said LP fractionator and simultaneously fractionating said seventh stream, said eighth stream and said ninth stream in said LP fractionator under conditions sufficient to produce a high purity nitrogen overhead stream and a high purity methane bottom stream; 
     (l) recovering said overhead stream from said LP fractionator as a nitrogen product stream; and 
     (m) recovering said bottom stream from said LP fractionator as a gas product stream. 
     In a preferred embodiment of the present invention heavy hydrocarbons are removed from a miscible flood gas and the flood gas, essentially free of heavy hydrocarbons, is passed to a dual distillation system. The dual distillation system includes two fractionator columns which do not utilize overhead reflux condensers, or reboilers for separating the nitrogen-methane mixture. Further in accordance with the present invention certain process conditions can be adjusted so as to provide efficient nitrogen rejection from a feedstream whose nitrogen content may vary from a low of about 37 mole-% to a high of about 76 mole-%. 
    
    
     Further aspects and additional advantages of the invention will be apparent from the following detailed description of the preferred embodiment of the invention as illustrated by the drawings in which: 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic diagram illustrating process flow of the dual distillation column process for nitrogen rejection according to this invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     It will be appreciated by those skilled in the art that, since FIG. 1 is schematic only, many items of equipment which would be needed for successful operation of a commercial plant have been omitted for the sake of clarity. Such items of equipment would include, for example, additional temperature, flow and pressure measurement instruments and corresponding process controllers, pumps, compressors, additional heat exchangers, valves, etc. All these items would be provided in accordance with standard chemical engineering practice to maintain desired conditions throughout the process and are not necessary to describe the present invention. 
     The present invention is applicable to recovering nitrogen from a gaseous mixture in which the nitrogen content varies widely and wherein the gaseous mixture contains a significant concentration of C 2  and higher molecular weight hydrocarbon components. It is particularly applicable to treating miscible flood gas produced from enhanced oil recovery in an offshore operation. This flood gas recovery results in processing a gas having considerable nitrogen dilution, with a nitrogen concentration often in excess of 70 mole-%, and also having a significant concentration of C 2  and higher molecular weight hydrocarbons. 
     It should also be understood that the representative temperatures and pressures set forth herein, with relation to the description of the drawing and the examples, are illustrative only and are not to be considered as limiting. The particular temperatures and pressures utilized in a particular separation will be dependent upon the nature and composition of the feed stream, upon the particular heat exchange surface areas available and upon the initial temperatures and pressures of the feed stream. 
     Referring now to FIG. 1, a feed gas stream containing methane and nitrogen, and having a significant concentration of C 2  and heavier hydrocarbons, at a pressure above 450 psia and preferably at about 800 psia or more is fed to the nitrogen rejection system through conduit 1. The feed gas stream could have for its origin, for example, a gas stream produced in a miscible flooding for enhanced oil recovery, in which case it would contain a high and variable nitrogen loading, which could increase to 76 mole-% or more during the life of the EOR project, along with a significant concentration of C 2  and heavier hydrocarbons. In accordance with standard practice, other easily condensible contaminants such as CO 2  or H 2  S which may be found in a gas produced in a miscible flooding would be removed by, for example, an absorption process prior to entering the nitrogen rejection process via conduit 1. Generally the nitrogen concentration of the feed gas stream 1 varies from about 40 mole-% to about 70 mole-% over the life of the EOR project. 
     The feed gas flowing in conduit 1 is divided so that a portion of the feed gas is cooled in chiller 100 by heat exchange with cooled exiting gas streams. Chiller 100 is bypassed, and the warm feed gas flowing in the bypass conduit is combined with the gas cooled in chiller 100 to form a combined stream in conduit 2 which is blended to a temperature of about -60° F. The cooled and partially condensed gas flowing in conduit 2 is passed through valve 102 and is then passed to a liquid/vapor phase separator 104 and separated into a vapor phase and a liquid phase. From separator 104 a liquid stream containing heavy hydrocarbons is withdrawn through conduit 5 and a vapor stream is withdrawn through conduit 4. The liquid discharged from separator 104 is preferably manipulated by liquid level control valve 103 in response to the actual liquid level in separator 104. The condensed heavy hydrocarbon stream flowing in conduit 5 is combined with the predominantly methane stream exiting the nitrogen rejection system in conduit 43 as will be explained more fully hereinafter. The uncondensed vapor stream in conduit 4, essentially free of heavy hydrocarbons, is the feedstream to the dual distillation system. This feedstream is divided so that a portion of the vapor flowing in conduit 4 is passed to conduit 6 and is cooled and partially condensed by heat exchange with cooled exiting gas streams in chiller 106. 
     The temperature of the cooled and partially condensed gas exiting chiller 106 in conduit 10 is reduced when the nitrogen content of the feed gas increases as will be further described hereinafter. The cooled and partially condensed gas flowing in conduit 10 is passed to a phase separator 108 and separated into a vapor phase and a liquid phase. From separator 108 a condensed liquid stream is withdrawn through conduit 12 and passed through expansion/control valve 115 to a lower portion of the high pressure (HP) fractionator 110 An uncondensed vapor stream is withdrawn from separator 108 through conduit 11. The liquid discharged from separator 108 is preferably manipulated through control valve 115 in response to the actual liquid level in separator 108. The uncondensed vapor stream flowing in conduit 11 is cooled in chiller 112 by heat exchange with cooled exiting gas streams. The cooled and partially condensed gas stream exiting chiller 112 in conduit 13 is further cooled in passing through an expansion device, such as expansion valve 113, and into conduit 14 from where the partially condensed gas is fed to a tray in the upper portion of the HP fractionator 110. 
     Chillers 106 and 112 and separator 108 are bypassed by the combination of conduits 7, 8, and 16 and expansion valve 114. A portion of the uncondensed vapor flowing in conduit 4, which is passed through expansion valve 114 via conduits 7 and 8 is cooled and partially condensed in passing through valve 114, or other similar expansion device, into conduit 16. The predominantly vapor stream flowing in conduit 16 is combined with the liquid stream flowing in conduit 15 and enters the bottom of the HP fractionator in mixture with the liquid supplied in conduit 15 via conduit 17. The predominantly vapor stream is provided via conduit 8 to the lower portion of HP fractionator 110 so as to increase stripping vapors provided to HP fractionator 110 thereby increasing the amount of nitrogen rejected by the fractionator 110. 
     The HP fractionator 110 produces an overhead fraction of nitrogen-enriched gas which is withdrawn through conduit 18, and a bottoms fraction of methane-enriched liquid which is withdrawn through conduit 19. The nitrogen enriched vapor stream flowing in conduit 18 is cooled sufficiently in chiller 116 by heat exchange with cooled exiting streams so as to partially condense the gaseous nitrogen flowing in conduit 18. The thus cooled and partially condensed gas exits chiller 116 via conduit 23 and is passed to phase separator 122 and separated into a vapor phase and a liquid phase. A liquid stream is withdrawn from separator 122 through conduit 25 and passed through control/expansion valve 128 into conduit 26 where the pressure is reduced so as to effect flashing of the liquid which is fed to a tray at or near the middle tray of the LP fractionator 118. The liquid discharged from separator 122 is preferably manipulated by liquid level control/expansion valve 128 in response to the actual liquid level in separator 122. 
     An uncondensed vapor stream is withdrawn from separator 122 via conduit 24 and is passed to an expander, or similar expansion means, 130. The thus expanded and partially condensed vapors are withdrawn from expander 130 via conduit 31 and introduced into an upper portion of LP fractionator 118 as the main feed stream for LP fractionator 118. The bottoms stream from HP fractionator 110 is withdrawn in conduit 19 and expanded across control/expansion valve 111 into conduit 20 and then combined with a third portion of the feedstream flowing in conduit 4 which flow through the combination of conduits 4, 7, 9, and 21, and expansion/control valve 117. Preferably the bottoms temperature of LP fractionator 118 is controlled by manipulating valve 117. The thus combined stream flowing in conduit 22 is fed to a lower portion of the LP fractionator 118. The feed entering fractionator 118 via conduits 31, 26, and 22 is simultaneously fractionated under conditions sufficient to produce a high purity nitrogen stream withdrawn in conduit 32 and a high purity methane stream withdrawn in conduit 33. 
     The high purity overhead nitrogen product stream and the high purity methane product are withdrawn from LP fractionator 118 at a pressure level of about 50 psia via conduits 32 and 33 respectively. The high purity methane stream flowing in conduit 33 is elevated in pressure and provided to conduit 34. The liquid discharged from LP fractionator 118 is preferably manipulated by liquid level control valve 119 in response to the actual liquid level in fractionator 118. 
     In a preferred embodiment of the invention, the cooled exiting streams flowing in conduits 32 and 34 are utilized to provide the refrigeration necessary in the separation steps by countercurrent flow heat exchange with incoming or internal streams in the nitrogen rejection system. Additional cooling for the feed streams in chillers 106 and 100 is provided by depressurizing the portion of the LP fractionator 118 bottoms stream flowing in conduit 37, as will be described more fully hereinafter. 
     The high purity nitrogen stream flowing from LP fractionator 118 in conduit 32 is heated in chiller 116 by countercurrent flow heat exchange with the overhead nitrogen stream from HP fractionator 110 which is flowing in conduit 18. The high purity nitrogen stream exits chiller 116 in conduit 36 and is then further heated in chillers 112, 106 and 100. 
     The high purity methane stream from LP fractionator 118 flowing in conduit 34 is heated by countercurrent flow heat exchange with an internal stream in chillers 116 and 112. After exiting chiller 112 via conduit 37 the high purity methane stream is divided. A portion of the stream flowing in conduit 37 is supplied to conduit 39 and is depressurized and cooled in passing through control/expansion valve 119 which is operably connected between conduits 39 and 41. The thus expanded stream enters chiller 106 via conduit 41 where it is further heated and passed to chiller 100 via conduit 42 where it is still further heated and essentially vaporized in chiller 100 before exiting chiller -00 in conduit 47 as the low pressure gas product stream. 
     The remaining portion of the stream flowing in conduit 37 is supplied to conduit 40 and enters chiller 106 where it is heated and partially vaporized by countercurrent flow heat exchange with the feed stream flowing in conduit 6. On exiting chiller 106 in conduit 43, this stream is combined with the heavy hydrocarbon liquid stream discharged from separator 104 via conduits 5 and 45. The liquid discharged from separator 104 is preferably manipulated by a liquid level control valve 103 which is operably located between conduits 5 and 45. The thus combined stream flowing in conduit 46 is heated and essentially vaporized in chiller 100, and on exiting chiller 100 is provided as a high pressure gas product stream via conduit 48. 
     Further in accordance with the present invention the temperature of the vapor stream withdrawn from separator 108 in conduit 11 is controlled to a desired value. Specifically, as illustrated in the examples set forth hereinafter, the desired value for the temperature of the vapor flowing in conduit 11 will decrease as the nitrogen content of the feed gas increases during the life of the EOR project. 
     A specific temperature control loop is set forth in FIG. 1 for illustration. The invention extends, however, to different types of control configurations which accomplish the purpose of the invention. Dash lines designated as signal lines in the drawing are electrical or pneumatic in this preferred embodiment. 
     The temperature controller 129 illustrated in FIG. 1 may utilize the various modes of control such as proportional, proportional-integral, or proportional-integral-derivative. In this preferred embodiment, proportional-integral modes are preferred but any controller having the capacity for accepting two input signals and providing a scaled output signal representative of a comparison of the two input signals is within the scope of this invention. 
     The scaling of a controller output signal is well known in the control system art. Essentially, the output of a controller may be scaled to represent any desired factor or variable. An example of this is where a desired temperature and an actual (measured) temperature are compared by a controller. The controller output could be a signal representative of a change in the flow rate of some gas stream necessary to make the desired and actual temperatures equal. On the other hand, the same output signal could be scaled to represent a percentage change. If the controller output can range from 0 to 10 volts, which is common, then the output signal could be scaled so that an output signal having a voltage level of 5 volts corresponds to 50 percent, some specific flow rate or some specific temperature. 
     In a preferred embodiment for a closed temperature control loop, a temperature transducer 125 in combination with a temperature measuring device such as a thermocouple which is operably located in conduit 11 provides an output signal 127 which is representative of the actual temperature of the vapor stream flowing in conduit 11. Signal 127 is provided from the flow transducer 125 as the process variable input to the PID (proportional-integral-derivative) temperature controller 129. The PID temperature controller 129 is also provided with a set point signal 131 which is representative of the desired temperature of the vapor flowing in conduit 11. Signal 131 may be an operator entered temperature value for a temperature which is substantially constantly maintained for the vapor flowing in conduit 11, or the signal 131 may be provided from a supervisory control computer, not illustrated in FIG. 1. 
     In response to signals 127 and 131 the temperature controller 129 provides an output signal 133 which is representative of the difference between signals 127 and 131. Signal 133 is scaled so as to be representative of the position of control valve 119 which is operably located between between conduits 39 and 41 required to maintain the actual temperature of the vapor flowing in conduit 11 substantially equal to the desired temperature represented by signal 131. Signal 133 is provided from temperature controller 129 as a control signal to control valve 119, and the control valve 119 is manipulated in response thereto. 
     In this manner the desired temperature of the vapor in conduit 11 is maintained by manipulating the division of the gas product between the low pressure gas product provided via conduit 47 and the high pressure gas product provided via conduit 48. As has been previously stated the desired temperature for the vapor in conduit 11 is generally reduced as the nitrogen content of miscible flood gas increases during the life of the EOR project. 
     The following examples are presented in further illustration of the invention and are not to be considered as unduly limiting the scope of this invention. 
     EXAMPLE 1 
     This example illustrates nitrogen rejection from a gaseous stream containing about 40 mole-% nitrogen according to the improved process of this invention. The feed stream 1 is a gaseous stream having a composition which might be found in a gas stream actually produced in a reservoir flood during a relatively early stage of an EOR project. 
     Table 1, below, shows the composition, temperature, pressure, vapor fraction and mass flow rate which were calculated from heat and material balance considerations. The numbers in the left hand column of Table 1 refer to the reference numerals of the conduits (or equivalently streams) illustrated in the drawing FIG. 1. 
     
                                           TABLE 1__________________________________________________________________________Conduit/Mole Fraction     °F.                      psia                         lb/day                               VaporStreamN2 C1 C2 C3 i-C4               n-C4                  Temp                      Press                         Flow  Fraction__________________________________________________________________________ 1   0.360   0.556      0.055         0.020            0.002               0.005                   -80                      880                         .569E+07                               1.0 2   0.360   0.556      0.055         0.020            0.002               0.005                   -60                      880                         .569E+07                               0.963 3   0.360   0.556      0.055         0.020            0.002               0.005                   -70                      700                         .569E+07                               0.957 4   0.374   0.567      0.047         0.010            0.001               0.001                   -70                      700                         .531E+07                               1.0 5   0.050   0.307      0.235         0.249            0.041               0.089                   -70                      700                         .380E+06                               0 6   0.374   0.567      0.047         0.010            0.001               0.001                   -70                      700                         .531E+07                               1.0 7   0  0  0  0  0  0   -70                      700                         --    1.0 8   0  0  0  0  0  0  --  -- --     -- 9   0  0  0  0  0  0  --  -- --     --10   0.374   0.567      0.047         0.010            0.001               0.001                  -169                      700                         .531E+07                               011   0.602   0.392      0.006         0  0  0  -169                      690                         .253E+06                               1.012   0.364   0.575      0.049         0  0.001               0.001                  -169                      690                         .505E+07                               013   0.602   0.392      0.006         0  0  0  -207                      690                         .255E+06                               014   0.602   0.392      0.006         0  0  0  -230                      290                         .253E+06                               0.25615   0.364   0.575      0.049         0.011            0.001               0.001                  -203                      290                         .505E+07                               0.36616   0  0  0  0  0  0  --  290                         --     --17   0.364   0.575      0.049         0.001            0.011               0.001                  -203                      290                         .505E+07                               0.36618   0.674   0.326      0  0  0  0  -209                      290                         .220E+07                               1.019   0.198   0.709      0.075         0.016            0.001               0.001                  -203                      290                         .311E+07                               020   0.198   0.709      0.075         0.016            0.001               0.001                  -248                       50                         .311E+07                               0.26421   0  0  0  0  0  0  --   50                         --     --22   0.198   0.709      0.075         0.016            0.001               0.001                  -274                       50                         .311E+07                               0.26423   0.674   0.326      0  0  0  0  -228                      290                         .220E+07                               0.52924   0.832   0.168      0  0  0  0  -228                      280                         .136E+07                               1.025   0.463   0.537      0  0  0  0  -228                      280                         .843E+06                               026   0.463   0.537      0  0  0  0  -277                       50                         .843E+06                               0.31131   0.832   0.168      0  0  0  0  -280                       50                         .136E+07                               0.85832   0.843   0.157      0  0  0  0  -270                       50                         .258E+07                               1.033   0.060   0.842      0.079         0.017            0.001               0.001                  -248                       50                         .272E+07                               034   0.060   0.842      0.079         0.017            0.001               0.001                  -250                      540                         .272E+07                               035   0.060   0.842      0.079         0.017            0.001               0.001                  -213                      540                         .272E+07                               036   0.843   0.157      0  0  0  0  -213                       50                         .258E+07                               1.037   0.060   0.842      0.079         0.017            0.001               0.001                  -207                      540                         .272E+07                               038   0.843   0.157      0  0  0  0  -207                       50                         .258E+07                               1.039   0.060   0.842      0.079         0.017            0.001               0.001                  -207                      540                         .136E+07                               040   0.060   0.842      0.079         0.017            0.001               0.001                  -207                      540                         .136E+07                               041   0.060   0.842      0.079         0.017            0.001               0.001                  -206                      190                         .136E+07                               042   0.060   0.842      0.079         0.017            0.001               0.001                   -92                      190                         .136E+07                               0.98743   0.060   0.842      0.079         0.017            0.001               0.001                   -92                      540                         .136E+07                               0.89544   0.843   0.157      0  0  0  0   -92                       50                         .258E+07                               1.045   0.050   0.307      0.235         0.249            0.041               0.089                   -75                      510                         .379E+06                               0.07746   0.059   0.772      0.099         0.047            0.006               0.013                   -86                      510                         .174E+07                               0.75747   0.060   0.842      0.079         0.017            0.001               0.001                    54                      190                         .146E+07                               1.048   0.059   0.772      0.099         0.047            0.006               0.013                    54                      510                         .174E+07                               1.049   0.843   0.157      0  0  0  0    54                       80                         .258E+07                               1.0__________________________________________________________________________ 
    
     EXAMPLE 2 
     This example illustrates nitrogen rejection from a gaseous stream containing about 76 mole-% nitrogen according to the improved process of this invention. The feed stream 1 is a gaseous stream having a composition which might be found in a gas stream actually produced in a reservoir flood during a relatively late stage of an EOR project. 
     Table 2 shows the composition, temperature, pressure, vapor fraction and mass flow rate which were calculated from heat and material balance considerations. The numbers in the left hand column of Table 2 refer to the reference numerals of the conduits (or equivalently streams) illustrated in the drawing FIG. 1. 
     
                                           TABLE 2__________________________________________________________________________Conduit/Mole Fraction     °F.                      psia                         lb/day                               VaporStreamN2 C1 C2 C3 i-C4               n-C4                  Temp                      Press                         Flow  Fraction__________________________________________________________________________ 1   0.763   0.201      0.021         0.009            0.001               0.003                    80                      880                         .507E+08                               1.0 2   0.763   0.201      0.021         0.009            0.001               0.003                   -60                      880                         .507E+08                               0.993 3   0.763   0.201      0.201         0.009            0.001               0.003                   -68                      700                         .507E+08                               0.992 4   0.768   0.202      0.020         0.007            0.001               0.001                   -68                      700                         .499E+08                               1.0 5   0.069   0.093      0.114         0.245            0.078               0.227                   -68                      700                         .772E+06                               0 6   0.768   0.202      0.020         0.007            0.001               0.001                   -68                      700                         .434E+08                               1.0 7   0.768   0.202      0.020         0.007            0.001               0.001                   -68                      700                         .648E+07                               1.0 8   0.768   0.202      0.020         0.007            0.001               0.001                   -68                      700                         .195E+07                               1.0 9   0.768   0.202      0.020         0.007            0.001               0.001                   -68                      700                         .454E+07                               1.010   0.768   0.202      0.020         0.007            0.001               0.001                  -183                      700                         .434E+08                               0.95011   0.798   0.195      0.007         0  0  0  -183                      690                         .410E+08                               1.012   0.209   0.337      0.278         0.137            0.013               0.023                  -183                      690                         .238E+07                               013   0.798   0.195      0.007         0  0  0  -194                      690                         .410E+08                               1.014   0.798   0.195      0.007         0  0  0  -230                      290                         .410E+08                               0.80915   0.209   0.331      0.278         0.137            0.013               0.023                  -197                      290                         .238E+07                               0.16916   0.768   0.202      0.020         0.007            0.001               0.001                   -92                      290                         .195E+07                               0.99817   0.472   0.273      0.157         0.076            0.007               0.013                  -173                      290                         .433E+07                               0.63118   0.868   0.131      0  0  0  0  -230                      290                         .385E+08                               1.019   0.282   0.545      0.118         0.043            0.004               0.007                  -222                      290                         .682E+07                               020   0.282   0.545      0.118         0.043            0.004               0.007                  -263                       50                         .682E+07                               0.26121   0.768   0.202      0.020         0.007            0.001               0.001                  -112                       50                         .454E+07                               1.022   0.462   0.418      0.082         0.030            0.003               0.005                  -251                       50                         .114E+08                               0.62823   0.868   0.131      0  0  0  0  -237                      290                         .385E+08                               0.86324   0.896   0.104      0  0  0  0  -237                      280                         .350E+08                               1.025   0.621   0.377      0.002         0  0  0  -237                      280                         .347E+07                               026   0.621   0.377      0.002         0  0  0  -287                       50                         .347E+07                               0.30931   0.896   0.104      0  0  0  0  -289                       50                         .350E+08                               0.84232   0.963   0.037      0  0  0  0  -289                       50                         .413E+08                               1.033   0.095   0.773      0.091         0.032            0.003               0.005                  -260                       50                         .856E+07                               034   0.095   0.773      0.091         0.032            0.003               0.005                  -261                      540                         .856E+07                               035   0.095   0.773      0.091         0.032            0.003               0.005                  -239                      540                         .856E+07                               036   0.963   0.037      0  0  0  0  -239                       50                         .413E+08                               1.037   0.095   0.773      0.091         0.032            0.003               0.005                  -205                      540                         .856E+07                               038   0.963   0.037      0  0  0  0  -205                       50                         .413E+08                               1.039   0.095   0.773      0.091         0.032            0.003               0.005                  -205                      540                         .299E+07                               040   0.095   0.773      0.091         0.032            0.003               0.005                  -205                      540                         .556E+07                               041   0.095   0.773      0.091         0.032            0.003               0.005                  -204                      190                         .299E+07                               0.00742   0.095   0.773      0.091         0.032            0.003               0.005                   -97                      190                         .299E+07                               0.93443   0.095   0.773      0.091         0.032            0.003               0.005                   -97                      540                         .556E+07                                .78844   0.963   0.037      0  0  0  0   -97                       50                         .413E+08                               1.045   0.069   0.093      0.114         0.245            0.078               0.227                   -68                      510                         .772E+06                               0.03746   0.094   0.737      0.092         0.044            0.007               0.017                   -94                      510                         .633E+07                                .73747   0.095   0.773      0.091         0.032            0.003               0.005                    44                      190                         .299E+07                               1.048   0.094   0.737      0.092         0.044            0.007               0.017                    44                      510                         .633E+07                                .99049   0.963   0.031      0  0  0  0    44                       80                         .413E+08                               1.0__________________________________________________________________________ 
    
     The results indicated in Tables 1 and 2 show that the process of this invention maintains sufficient separation for feed streams widely varying in nitrogen content by maintaining the indicated process conditions, and that the inventive process will allow the use of nitrogen rejection units for providing sufficiently pure nitrogen for reinjecting in an EOR project. Further, the elimination of overhead reflux condensers and reboilers on the fractionators make them extremely simple to operate and therefore more suitable for offshore operations. 
     It is to be understood that reasonable variations and modifications for various usages and conditions are possible by those skilled in the art, and such modifications and variations are within the scope of the described invention and the appended claims.