Abstract:
A system and method for removing nitrogen from an intermediate stream in a gas subcooled process operation that processes natural gas into a sales gas stream and a natural gas liquids stream. The system and method of the invention are particularly suitable for use with gas subcooled process operations where the sales gas stream exceeds pipeline nitrogen specifications by up to about 3%, such as for reducing the nitrogen content of sales gas streams to levels permissible for pipeline transport.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    This invention relates to a system and method for separating nitrogen from methane and other components of natural gas streams being processed into a sales gas stream and a natural gas liquids (NGL) stream by the known gas subcooled/expander process (GSP/expander process or simply GSP). The system and method of the invention are particularly suitable for use in connection with natural gas streams where the processed sales gas stream contains nitrogen in an amount that exceeds pipeline specifications. 
         [0003]    2. Description of Related Art 
         [0004]    Nitrogen contamination is a frequently encountered problem in the production of natural gas. Transporting pipelines typically do not accept natural gas containing more than about 4 mole percent inerts, such as nitrogen. Estimates indicate that as much as 25% of natural gas in the United States exceeds a typical 4% pipeline specification. To correct this problem, the sales gas may be mixed or diluted with other gas to achieve the desired nitrogen specification. Alternatively, known methods of nitrogen removal such as a nitrogen rejection unit or NRU comprised of two cryogenic fractionating columns, as described in U.S. Pat. Nos. 4,451,275 and 4,609,390 or comprised of a single fractionating column, as described in U.S. Pat. Nos. 5,141,544, 5,257,505, and 5,375,422 may be used. However, dilution and full-blown NRU installation and operation are expensive for the gas processor. Additionally, a complete stand-alone NRU, which is capable of removing large percentages of nitrogen, may not be necessary or economically feasible for a gas subcooled process where the sales gas exceeds the nitrogen specification by only a small amount. 
       SUMMARY OF THE INVENTION 
       [0005]    The system and method disclosed herein facilitate the economically efficient removal of nitrogen from methane by modifying a conventional GSP system and its method of operation for nitrogen removal. The system and method of the invention are particularly suitable for use where the feed gas to a conventional GSP and expander system contains sufficient nitrogen and other inerts that the resultant sales gas contains a higher percentage of nitrogen (or inerts) than is permitted by the operating specifications of a particular pipeline. For example, conventional GSP processing of raw natural gas normally containing 3-10% nitrogen may produce a sales gas that exceeds the nitrogen specification set by the transporting pipeline by up to 3% (that is, sales gas nitrogen contents of about 6-7%, with a typical pipeline specification being around 3-4% nitrogen). Through use of the present invention, the nitrogen content of the sales gas can be reduced to levels that are acceptable for pipeline transport at a capital cost and with horsepower requirements that are significantly lower than those required by use of a conventional stand-alone NRU unit. 
         [0006]    According to one embodiment of the invention, a system and method are disclosed for strategically integrating an NRU into a typical GSP/expander operation. According to known GSP methods, a subcooler reduces the temperature of a process stream prior to feeding the top of a demethanizer column. Through use of this embodiment of the invention, a portion of the process stream that normally feeds the top of the demethanizer column after passing through the subcooler serves as the NRU feed gas stream. The NRU feed stream passes through a single fractionating column and other processing equipment to produce a treated gas stream with reduced nitrogen content. That treated gas stream is then reintroduced into the typical GSP operation as a portion of the feed to the top of the demethanizer column for further processing. The result is a processed sales gas (or residue gas) stream having a nitrogen content within typical pipeline specifications without adversely impacting the production of NGL product. 
         [0007]    There are several advantages to the system and method disclosed herein not previously achievable by those of ordinary skill in the art using existing technologies. These advantages include, for example, an ability to produce sales gas meeting typical pipeline specifications for nitrogen content without diluting the sales gas prior to transport and without requiring any additional dehydration or carbon dioxide removal prior to processing the gas for removal of nitrogen. Although the present system and method has the disadvantage of higher capital costs associated with additional equipment for the NRU and higher operating costs for that equipment, compared to a GSP operation without an NRU, the costs of such are sufficiently offset by the savings in having sales gas within pipeline specification and savings in operating costs achieved by strategically placing the NRU within the GSP operation to take advantage of inter-operational efficiencies, such as heat exchange between process stream. Additionally, the costs of the NRU according to the present system are reduced as compared to either a two-column or single column NRU operated externally to the GSP system. Such known NRU systems have higher capital and operating costs associated with various pieces of equipment typically used in such systems, such as the additional fractionating column (in the two-column system), equipment to remove water and carbon dioxide, and multiple heat exchangers. The capital costs and operating expenditures for implementing the system and method of the present invention are believed to be around 25-50% of the costs of conventional full-blown, stand-alone NRU systems. Additionally, the NRU system and method of the present invention do not substantially interfere with NGL production and may enhance NGL recovery over a GSP system without the NRU system and method of the present invention. 
         [0008]    Those of ordinary skill in the art will appreciate upon reading this disclosure that references to separation of nitrogen and methane used herein refer to processing NRU feed gas to produce various multi-component product streams containing large amounts of the particular desired component, but not pure streams of any particular component. One of those product streams is a rejected nitrogen stream, which is primarily comprised of nitrogen but may have small amounts of other components, such as methane and ethane. Another product stream is an intermediate stream, which is primarily comprised of methane but may have small amounts of other components, such as nitrogen, ethane, and propane, that feeds the GSP demethanizer column to produce a sales gas stream within pipeline specifications. 
         [0009]    Those of ordinary skill in the art will also appreciate upon reading this disclosure that additional processing sections for removing carbon dioxide, water vapor, and possibly other components or contaminants that are present in the GPS feed stream or NRU feed stream, can also be included in the system and method of the invention, depending upon factors such as, for example, the origin and intended disposition of the product streams and the amounts of such other gases, impurities or contaminants as are present in the GSP feed stream or NRU feed stream. However, additional removal of carbon dioxide and water vapor from the NRU feed stream are not needed to achieve a sales gas stream within pipeline specifications and the system and method of the invention will not be adversely impacted by the presence of small amounts of such contaminants in the NRU feed stream. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    The system and method of the invention are further described and explained in relation to the following drawings wherein: 
           [0011]      FIG. 1  is a simplified process flow diagram illustrating principal processing stages of a typical prior art GSP/expander operation; 
           [0012]      FIG. 2  is a simplified process flow diagram illustrating principal processing stages of an embodiment of a system and method for separating nitrogen from process streams in a GSP/expander operation; 
           [0013]      FIG. 3  is a simplified process flow diagram illustrating principal processing stages of the NRU portion of an embodiment of a system and method for separating nitrogen from process streams in a GSP/expander operation; 
           [0014]      FIG. 4  is a more detailed process flow diagram illustrating the processing stages of the simplified process flow diagram of  FIG. 2 ; 
           [0015]      FIG. 5  is a more detailed process flow diagram illustrating the NRU processing stage of the simplified process flow diagram of  FIG. 3 ; 
           [0016]      FIG. 6  is a simplified process flow diagram illustrating principal processing stages for another embodiment of the system and method for separating nitrogen from process streams in a GSP/expander operation. 
       
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0017]      FIG. 1  (prior art) depicts the basic processing stages of a known GSP/expander system  10 . GSP feed gas  12  is fed through GSP primary heat exchange and primary separation block  14  and exits as streams  16  and  36 . GSP primary heat exchange and primary separation block  14  contains one or more separators, one or more heat exchangers, a compressor for compressing the sales gas  50  and other equipment (such as valves, splitters, and mixers), which are known to those of ordinary skill in the art. Stream  36  feeds a demethanizer column  40  and stream  16  passes through a GSP subcooler  26 , exiting as stream  32  which also feeds demethanizer column  40 . Stream  22 , split off from stream  16  passes through expander  24 , exiting as stream  28  which also feed demethanizer column  40 . The demethanizer column  40  produces an NGL product stream  42  and an overhead stream  44 . Overhead stream  44  passes through GSP subcooler  26 , exiting as stream  46 , which then passes through the heat exchangers and compressor in block  14 , exiting as sales gas stream  50 , containing primarily methane. Depending on the composition of the GSP feed stream  12 , the resulting sales gas stream  50  may contain too much nitrogen to meet pipeline specifications. For example, a GSP feed stream  12  containing 4% nitrogen would result in a sales gas stream  50  with a nitrogen content in excess of 4%, requiring further processing or dilution to meet pipeline specifications. 
         [0018]      FIG. 2  depicts the basic processing stages of the system and method according to a preferred embodiment of the invention. The system  100  comprises processing equipment typically found in GSP operations, with a few modifications to permit insertion of NRU system  300  in the process as described more fully below. System  100  of the invention includes processing block  114 , which contains the GSP primary heat exchanger(s) (one or more) and primary separators(s) (one or more) and a compressor, as well as other equipment (such as valves, splitters, and mixers), known to be used in a typical GSP operation. GSP feed stream  112  passes through GSP primary processing block  114 , exiting as streams  116 ,  118 ,  222 ,  136 , and  138 . Streams  116  and  118  pass through GSP subcooler  126 , exiting as cooled streams  122  and  124 . Stream  122  is the feed stream for NRU system  300 . Two streams, treated gas stream  128  and refrigerant recycle stream  130 , are returned to system  100  after processing in NRU system  300 , as depicted in  FIG. 3 . Cooled stream  124  is mixed with treated gas stream  128  to form stream  132 , which feeds a demethanizer column  140 . Stream  228  mixes with refrigerant recycle stream  130  to form stream  134 , which also feeds demethanizer column  140 . Streams  136  and  138  also feed demethanizer column  140 . The demethanizer column  140  produces an NGL product stream  142  and an overhead stream  144 . The overhead stream  144  passes through GSP subcooler  126 , exiting as stream  146 , which then passes through the heat exchanger(s) and compressor in block  114 , exiting as sales gas stream  150 , containing primarily methane. For a GSP feed stream containing around 4% nitrogen, the sales gas stream  150  will only contain around 3% nitrogen, which is within typical pipeline specifications. 
         [0019]      FIG. 3  depicts the basic processing stages of the NRU portion of the system and method according to a preferred embodiment of the invention. The NRU system  300  comprises a heat exchanger  302 , a nitrogen rejection column  310 , and a refrigerant recycle block  356 , as well as other equipment (such as valves, separators, and mixers, which are not depicted in  FIG. 3 ). Stream  122  exiting GSP subcooler  126 , (depicted in  FIG. 2 ) feeds the NRU heat exchanger  302  and exits as cooled stream  308 , which feeds nitrogen rejection column  310 . Nitrogen rejection column  310  produces overhead stream  318  and bottom stream  322 . Overhead stream  318  passes through heat exchanger  302 , exiting as warmed nitrogen vent stream  320 . Bottom stream  322  is split into streams  354  and  340 , both of which pass through heat exchanger  302 . Stream  354  is warmed, exiting as treated gas stream  128 , which is returned to system  100  for further processing. Stream  340  is also warmed, exiting as stream  342 , which passes through refrigerant recycle block  356  before returning to heat exchanger  302  as stream  350  and exits as refrigerant recycle stream  130 . The cooled refrigerant recycle stream is returned to system  100  for further processing. 
         [0020]    Systems  100  and  300  are depicted in greater detail in  FIGS. 4 and 5 . Referring to  FIG. 4 , a 100 MMSCFD GSP feed stream  112  containing approximately 4% nitrogen and 70% methane at 120° F. and 750 psig is split into streams  152  (67.5%) and  158  (32.5%) by splitter  151 . Stream  152  passes through heat exchanger  154  from which it emerges as stream  156 , having been cooled to 72° F. This cooling is the result of heat exchange with another process stream,  230 , discussed later. Stream  158  passes through heat exchanger  160  and exits as stream  162 , having been cooled to 30.6° F. Streams  156  and  162  are mixed together by mixer  164  to form stream  166  at 57.3° F. and 743 psig. 
         [0021]    Stream  166  feeds a first separator  168  to produce a first overhead vapor stream  174  and a first bottom liquid stream  170 . Bottom stream  170  has a flow rate of approximately 1.9 MMSCFD at 738 psig and 57° F., which drops to 265 psig and 31.2° F. after exiting Joule-Thomson (JT) valve  172  as stream  138 . Stream  138 , containing 0.52% nitrogen, feeds a lower stage of demethanizer column  140 . JT valve  172  is capable of cooling by the well-known Joule-Thomson effect, but in post-start up, steady state operation the valve provides less actual thermal cooling, but does provide the necessary pressure reduction for stream  138  prior to feeding demethanizer column  140 . Overhead stream  174  has a flow rate of approximately 98 MMSCFD at 738 psig and 57° F. before passing through heat exchanger  176  to exit as stream  178  at −40° F. This cooling is the result of heat exchange with process streams  146  (discussed below) and stream  258 , which originates from a second process feed stream  240 . Stream  240  contains 97% propane at 36° F. and 60 psig and passes through JT valve  242 , exiting as stream  244  having been cooled by expansion to −35° F. and a pressure of 3.6 psig. Stream  244  feeds a vertical stand pipe  246 , where the vapor rises and exits as stream  248  and the liquid exits the bottom of stand pipe  246  as stream  254 . Stream  254  has a volumetric flow rate of 276.7 sgpm as it passes through a length of vertical pipe  256  exiting as stream  258 , with a slight increase in pressure. Stream  258  passes through heat exchanger  176  and exits as stream  260 , having been warmed to 10° F. Stream  260  mixes with vapor stream  248  in mixer  250  forming stream  252  at −9.5° F. and 3.6 psig. 
         [0022]    After exiting heat exchanger  176 , stream  178  feeds a second separator  180  to produce a second overhead vapor stream  196  and a second bottom liquid stream  182 . Second bottom stream  182 , with a flow rate of approximately 31 MMSCFD at 733 psig and −40° F., is split into stream  136  (99.99%) and  186  (0.01%) by splitter  184 . Stream  136 , containing 1% nitrogen, feeds demethanizer column  140 . Stream  186  passes through GSP subcooler  126 , exiting as stream  188 . Stream  188 , at 728 psig and −97.7° F., passes through a second JT valve  190 , exiting as stream  124 , at 215 psig and −121° F. Stream  124  mixes with treated gas stream  128  (from NRU system  300 ) in mixer  192  to form stream  132 . Stream  132 , at a flow rate of 26.6 MMSCFD and containing around 0.5% nitrogen, feeds the top of demethanizer column  140  at 210 psig and −162.2° F. 
         [0023]    Second overhead stream  196  exits second separator  180  with a flow rate of approximately 67.2 MMSCFD at 733 psig and −40° F. Stream  196  is split into stream  202  (45%) and stream  116  (55%) by splitter  198 . Stream  116  passes through GSP subcooler  126 , exiting as NRU feed stream  122 . Stream  202  may be split into stream  206  and stream  218  by splitter  204 ; however, in this example of a preferred embodiment of the system and method of according to the invention, the entirety of stream  202  is directed to stream  218 . Valve  220  controls stream  218 , but stream  220  exits valve  220  as stream  222  at substantially the same temperature and pressure as stream  218 . Stream  222  passes through expander  224  and exits as stream  226 , with the pressure having dropped from 730 psig to 225 psig. If stream  206  is used, it passes through a third JT valve  208 , exiting as stream  210 . Stream  210  would then be mixed with stream  226  in mixer  212  to form stream  214 . Stream  214  flows through a length of pipe (depicted as  216 ), over which there is a slight pressure drop, becoming stream  228 . Stream  228 , at a flow rate of 30.2 MMSCFD and containing around 5.5% nitrogen, mixes with refrigerant recycle stream  130  (from NRU system  300 ), at a flow rate of 8.2 MMSCFD and containing around 0.5% nitrogen, in mixer  194  to form stream  134 . Stream  134 , at a flow rate of 38.4 MMSCFD and containing around 4.4% nitrogen, feeds demethanizer column  140 . 
         [0024]    Demethanizer column  140  separates feed streams  132 ,  134 ,  136 , and  138  into overhead stream  144  and bottoms stream  264 . Stream  264  from the bottom of the demethanizer column  140  is directed to reboiler  266  that receives heat (designated as energy stream Q- 110 ) from heat exchanger  160 . Stream  264  is at approximately 15.4° F. and 206 psig and contains a negligible amount of nitrogen, 2.6% methane, 58.3% ethane, and 29.6% propane. The demethanizer column  140  also receives heat from heat exchanger  176 , designated by energy stream Q- 114 . Liquid stream  270  exits reboiler  266  and feeds separator  272  where it is separated into an NGL stream  274  and a vapor stream  278 . Stream  274  passes through pump  276 , exiting as an NGL product stream  142  at approximately 49° F. and 1200 psig and 470 sgpm. NGL product stream  142  contains a negligible amount of nitrogen, 52.8% ethane, 34% propane, and 1% methane, and is suitable for sale or further processing. Pump  276  requires an energy input, designated as Q- 118 . Vapor stream  278  at 0.035 MMSCFD, 34.2° F., 205 psig and containing 7.9% methane is recycled to the bottom of demethanizer column  140 . Vapor stream  268 , containing 7.9% methane, exits reboiler  266  at 34.4° F., 206 psig and is also recycled to the bottom of demethanizer column  140 . 
         [0025]    Overhead stream  144  exits demethanizer column  140  at −147.5° F. and 200 psig, with a volumetric flow rate of 73.4 MMSCFD, and containing approximately 2.9% nitrogen, 94.5% methane, and 2.5% ethane. Stream  144  passes through subcooler  126 , exiting as stream  146 , having been warmed to −50° F. Stream  146  then passes through heat exchanger  176 , exiting as stream  230 , having been warmed to 44.5° F. Stream  230  then passes through heat exchanger  154 , exiting as stream  232 , having been warmed to 109.7° F. Stream  232  passes through a JT valve  234 , exiting as stream  236  having a slight drop in pressure. Stream  236  passes through compressor  238  (powered by energy from expander  224 , designated by energy stream Q- 116 ) exiting as sales gas stream  150 . Sales gas stream is at 133° F. and 207.7 psig and contains 2.9% nitrogen, making it suitable for sale within typical pipeline specifications. In a typical GSP operation, a feed stream nitrogen content of around 4% would result in a sales gas nitrogen content greater than 4%, falling outside most pipeline specifications. In this preferred embodiment of the invention, the sales gas stream  150  nitrogen content is reduced from the feed stream nitrogen content by slightly more than 1%. This reduction in nitrogen is possible by the addition of the NRU system  300 , depicted in  FIG. 5 . 
         [0026]    Referring to  FIG. 5 , NRU feed stream  122 , containing 5.5% nitrogen and having a temperature of −97.7° F. and a pressure of 728 psig enters NRU system  300 . According to this embodiment of the present invention, it is not necessary to remove water vapor or carbon dioxide from the NRU feed stream  122 , although additional steps and equipment may be added to do so if desired. Methods for removing water vapor, carbon dioxide, and other contaminants are generally known to those of ordinary skill in the art and are not described herein. NRU feed stream  122  passes through heat exchanger  302  exiting as stream  304 , having been cooled to −185° F. Stream  304  passes through JT valve  306 , reducing the pressure of exiting stream  308  to 250 psig. Stream  304  feeds nitrogen rejection column  310 . Stream  322  exits the bottom of nitrogen rejection column  310 , containing 1% nitrogen, and feeds virtual reboiler  324 . Although depicted in  FIG. 5  as a separate piece of equipment, preferably virtual reboiler  324  is part of other process equipment as will be understood by those of ordinary skill in the art. Vapor stream  326 , containing 2.8% nitrogen and 96.6% methane, exits virtual reboiler  324  and is fed back into the bottom of nitrogen rejection column  310 . Liquid stream  328 , containing 0.5% nitrogen, 87% methane and 9.9% ethane exits virtual reboiler  234  at −159° F. and 253 psig. Stream  328  is split into stream  332  (23.5%) and stream  334  (76.5%) by splitter  330 . 
         [0027]    Stream  332  passes through JT valve  335  and exits as stream  336  having been cooled by expansion to −240° F., with a pressure of 12 psig. Stream  336  passes through virtual condenser  338  and exits as stream  340 , warmed to −210° F. Stream  340  passes through heat exchanger  302  and exits as stream  342  warmed to 90° F. Stream  342  feeds a refrigerant recycle system  356 , first passing through compressor  344  (supplied by energy stream Q- 318 ) and exiting as stream  346  at a temperature of 573° F. and a pressure of 225 psig. Stream  346  passes through cooler  348  (releasing energy stream Q- 316 ) and is cooled to 120° F. as exiting stream  350 . Stream  350  passes through heat exchanger  302 , exiting as refrigerant recycle stream  130  at −90° F. and 215 psig. Refrigerant recycle stream  130  is returned to system  100  for further processing as described above. 
         [0028]    Stream  334  passes through JT valve  352 , with a pressure drop of 38 psig and a decrease in temperature of around 7° F. as it exits as stream  354 . Stream  354  passes through heat exchanger  302 , exiting as treated gas stream  128 . Treated gas stream  128  contains only 0.5% nitrogen, compared to the 5.5% nitrogen in NRU feed stream  122 . Treated gas stream  128  is returned to system  100  for further processing as discussed above. 
         [0029]    Vapor stream  312  exits the top of nitrogen rejection column  310 , having a temperature of −203° F. and a pressure of 250 psig and containing 57.5% nitrogen. Stream  312  feeds internal condenser  314  (which is depicted as exterior to NRU column  310 ). Heat released from internal condenser  314  (designated as energy stream Q- 314 ) supplies virtual condenser  338 . Liquid stream  316  exits internal condenser  314  and is feed back into NRU rejection column  310 . Vapor stream  318 , at −232° F., passes through heat exchanger  302 , exiting as rejected nitrogen stream  320 , warmed to 90° F. Rejected nitrogen stream  320  contains 85% nitrogen, 15% methane, and negligible amounts of ethane and propane. The heat released from heat exchanger  302  supplies heat to nitrogen rejection column  310  (designated as energy stream Q- 312 ) and virtual reboiler  324  (designated as energy stream Q- 310 ). 
       EXAMPLE 
       [0030]    The flow rates, temperatures and pressures of various flow streams referred to in connection with the discussion of the system and method of the invention in relation to  FIGS. 4 and 5 , for a GSP feed stream flow rate of 100 MMSCFD and containing 4% nitrogen, 70% methane, 14.7% ethane, and 8.4% propane appear in Table 1 below. The values for the energy streams referred to in connection with the discussions of the system and method of the invention in relation to  FIGS. 4 and 5  appear in Table 2 below. The values discussed herein and in the tables below are approximate values. 
         [0000]    
       
         
               
             
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 FLOW STREAM PROPERTIES 
               
             
          
           
               
                 Stream 
                   
                   
                   
                   
                   
                 Temper- 
                   
               
               
                 Reference 
                 % 
                 % 
                 % 
                 % 
                 Flow Rate 
                 ature 
                 Pressure 
               
               
                 Numeral 
                 N 2   
                 CH 4   
                 C 2 H 6   
                 C 3 H 8   
                 (lbmol/h) 
                 (deg. F.) 
                 (psig) 
               
               
                   
               
             
          
           
               
                 112 
                 4 
                 69.9 
                 14.8 
                 8.4 
                 10979.8 
                 120 
                 750.3 
               
               
                 116 
                 5.5 
                 82.8 
                 9.3 
                 2.2 
                 4057.2 
                 −40 
                 733.3 
               
               
                 122 
                 5.5 
                 82.8 
                 9.3 
                 2.2 
                 4057.2 
                 −97.7 
                 728.3 
               
               
                 124 
                 1 
                 44.8 
                 46.4 
                 20.6 
                 0.34 
                 −121.1 
                 215 
               
               
                 128 
                 0.5 
                 87 
                 9.9 
                 2.3 
                 2919.1 
                 −162.2 
                 210 
               
               
                 130 
                 0.5 
                 87 
                 9.9 
                 2.3 
                 899.6 
                 −90 
                 215 
               
               
                 132 
                 0.5 
                 87 
                 9.9 
                 2.4 
                 2919.5 
                 −162.2 
                 210 
               
               
                 134 
                 4.4 
                 83.7 
                 9.4 
                 2.2 
                 4219.1 
                 −109.5 
                 215 
               
               
                 136 
                 1 
                 44.8 
                 26.4 
                 20.6 
                 3395.2 
                 −40 
                 733.3 
               
               
                 138 
                 0.5 
                 22.4 
                 18.8 
                 26.7 
                 207.6 
                 31.2 
                 265 
               
               
                 142 
                 neg. 
                 1 
                 52.8 
                 34.1 
                 2686 
                 49.1 
                 1200 
               
               
                 144 
                 2.9 
                 94.5 
                 2.5 
                 0.04 
                 8055.4 
                 −147.5 
                 200 
               
               
                 146 
                 2.9 
                 94.5 
                 2.5 
                 0.04 
                 8055.4 
                 −50 
                 195 
               
               
                 150 
                 2.9 
                 94.5 
                 2.5 
                 0.04 
                 8055.4 
                 133.4 
                 207.8 
               
               
                 152 
                 4 
                 69.9 
                 14.8 
                 8.4 
                 7412.6 
                 119.9 
                 748.3 
               
               
                 156 
                 4 
                 69.9 
                 14.8 
                 8.4 
                 7412.6 
                 72 
                 743.3 
               
               
                 158 
                 4 
                 69.9 
                 14.8 
                 8.4 
                 3567.3 
                 119.9 
                 748.3 
               
               
                 162 
                 4 
                 69.9 
                 14.8 
                 8.4 
                 3567.3 
                 30.6 
                 743.3 
               
               
                 166 
                 4 
                 69.9 
                 14.8 
                 8.4 
                 10979.8 
                 57.3 
                 743.3 
               
               
                 170 
                 0.5 
                 22.4 
                 18.8 
                 26.7 
                 207.61 
                 57 
                 738.3 
               
               
                 174 
                 4.1 
                 70.8 
                 14.7 
                 8 
                 10772.2 
                 57 
                 738.3 
               
               
                 178 
                 4.1 
                 70.8 
                 14.7 
                 8 
                 10772.2 
                 −40 
                 733.3 
               
               
                 182 
                 1 
                 44.8 
                 26.4 
                 20.6 
                 3395.56 
                 −40 
                 733.3 
               
               
                 188 
                 1 
                 44.8 
                 26.4 
                 20.6 
                 0.34 
                 −97.7 
                 728.3 
               
               
                 186 
                 1 
                 44.8 
                 26.4 
                 20.6 
                 0.34 
                 −40 
                 733.3 
               
               
                 196 
                 5.5 
                 82.8 
                 9.3 
                 2.2 
                 7376.6 
                 −40 
                 733.3 
               
               
                 202 
                 5.5 
                 82.8 
                 9.3 
                 2.2 
                 3319.5 
                 −40 
                 733.3 
               
               
                 214 
                 5.5 
                 82.8 
                 9.3 
                 2.2 
                 3319.5 
                 −113.1 
                 225 
               
               
                 218 
                 5.5 
                 82.8 
                 9.3 
                 2.2 
                 3319.5 
                 −40 
                 733.3 
               
               
                 222 
                 5.5 
                 82.8 
                 9.3 
                 2.2 
                 3319.5 
                 −40.2 
                 730.3 
               
               
                 226 
                 5.5 
                 82.8 
                 9.3 
                 2.2 
                 3319.5 
                 −113.1 
                 225 
               
               
                 228 
                 5.5 
                 82.8 
                 9.3 
                 2.2 
                 3319.5 
                 −113.7 
                 221.7 
               
               
                 230 
                 2.9 
                 94.5 
                 2.5 
                 0.04 
                 8055.4 
                 44.5 
                 190 
               
               
                 232 
                 2.9 
                 94.5 
                 2.5 
                 0.04 
                 8055.4 
                 109.7 
                 185 
               
               
                 236 
                 2.9 
                 94.5 
                 2.5 
                 0.04 
                 8055.4 
                 109.4 
                 180 
               
               
                 240 
                 0 
                 0 
                 1.5 
                 97 
                 2861.9 
                 36.3 
                 60.3 
               
               
                 244 
                 0 
                 0 
                 1.5 
                 97 
                 2861.9 
                 −35 
                 3.6 
               
               
                 248 
                 0 
                 0 
                 2.8 
                 96.6 
                 1276.4 
                 −35 
                 3.6 
               
               
                 252 
                 0 
                 0 
                 1.5 
                 97 
                 2861.9 
                 −9.5 
                 3.6 
               
               
                 254 
                 0 
                 0 
                 0.5 
                 97.3 
                 1585.5 
                 −35 
                 3.6 
               
               
                 258 
                 0 
                 0 
                 0.5 
                 97.3 
                 1585.5 
                 −35 
                 4.8 
               
               
                 260 
                 0 
                 0 
                 0.5 
                 97.3 
                 1585.5 
                 10.2 
                 3.8 
               
               
                 264 
                 neg. 
                 2.6 
                 58.3 
                 29.6 
                 3495.3 
                 15.4 
                 206 
               
               
                 268 
                 neg. 
                 8 
                 76.3 
                 14.4 
                 805.4 
                 34.5 
                 206 
               
               
                 270 
                 neg. 
                 1 
                 52.9 
                 34.1 
                 2689.9 
                 34.5 
                 206 
               
               
                 274 
                 neg. 
                 1 
                 52.8 
                 34.1 
                 2686 
                 34.2 
                 205 
               
               
                 278 
                 neg. 
                 7.9 
                 76.3 
                 14.4 
                 3.9 
                 34.2 
                 205 
               
               
                 304 
                 5.5 
                 82.8 
                 9.3 
                 2.2 
                 4057.2 
                 −185 
                 723.3 
               
               
                 308 
                 5.5 
                 82.8 
                 9.3 
                 2.2 
                 4057.2 
                 −184.4 
                 250.3 
               
               
                 312 
                 57.6 
                 42.4 
                 neg. 
                 neg. 
                 968.3 
                 −203 
                 249.8 
               
               
                 316 
                 48.6 
                 51.4 
                 neg. 
                 neg. 
                 729.9 
                 −232.2 
                 249.8 
               
               
                 318 
                 85 
                 15 
                 neg. 
                 neg. 
                 238.4 
                 −232.2 
                 249.8 
               
               
                 320 
                 85 
                 15 
                 neg. 
                 neg. 
                 238.4 
                 90 
                 244.8 
               
               
                 322 
                 1 
                 89.3 
                 7.7 
                 1.8 
                 4981.2 
                 −162.2 
                 252.8 
               
               
                 326 
                 2.8 
                 96.6 
                 0.6 
                 0.02 
                 1162.4 
                 −159.1 
                 252.8 
               
               
                 328 
                 0.5 
                 87 
                 9.9 
                 2.3 
                 3818.8 
                 −159.1 
                 252.8 
               
               
                 332 
                 0.5 
                 87 
                 9.9 
                 2.3 
                 899.6 
                 −159.1 
                 252.8 
               
               
                 334 
                 0.5 
                 87 
                 9.9 
                 2.3 
                 2919.1 
                 −159.1 
                 252.8 
               
               
                 336 
                 0.5 
                 87 
                 9.9 
                 2.3 
                 899.6 
                 −239.9 
                 12 
               
               
                 340 
                 0.5 
                 87 
                 9.9 
                 2.3 
                 899.6 
                 −210 
                 10 
               
               
                 342 
                 0.5 
                 87 
                 9.9 
                 2.3 
                 899.6 
                 90 
                 5 
               
               
                 346 
                 0.5 
                 87 
                 9.9 
                 2.3 
                 899.6 
                 573.1 
                 225 
               
               
                 350 
                 0.5 
                 87 
                 9.9 
                 2.3 
                 899.6 
                 120 
                 220 
               
               
                 354 
                 0.5 
                 87 
                 9.9 
                 2.3 
                 2919.1 
                 −466 
                 215 
               
               
                   
               
             
          
         
       
     
         [0000]    
       
         
               
             
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 2 
               
             
             
               
                   
               
               
                 ENERGY STREAM REPORT 
               
             
          
           
               
                 Energy 
                   
                   
                   
                   
               
               
                 Stream 
                 Energy 
               
               
                 Reference 
                 Rate 
                 Power 
               
               
                 Numeral 
                 (Btu/h) 
                 (hp) 
                 From 
                 To 
               
               
                   
               
             
          
           
               
                 Q-110 
                 5.27E+06 
                 2070.3 
                 Heat 
                 Reboiler 
               
               
                   
                   
                   
                 Exchanger 
                 266 
               
               
                   
                   
                   
                 160 
               
               
                 Q-114 
                   4E+06 
                 1572.1 
                 Heat 
                 Demeth. 
               
               
                   
                   
                   
                 Exchanger 
                 Column 140 
               
               
                   
                   
                   
                 176 
               
               
                 Q-116 
                 1.65E+06 
                 649.2 
                 Expander 
                 Compressor 
               
               
                   
                   
                   
                 224 
                 238 
               
               
                 Q-118 
                 967034 
                 380.1 
                 — 
                 Pump 276 
               
               
                 Q-310 
                 3.05E+06 
                 1200 
                 Heat 
                 Virtual 
               
               
                   
                   
                   
                 Exchanger 
                 Reboiler 
               
               
                   
                   
                   
                 302 
                 324 
               
               
                 Q-312 
                 500000 
                 196.5 
                 Heat 
                 N 2  Reject. 
               
               
                   
                   
                   
                 Exchanger 
                 Column 310 
               
               
                   
                   
                   
                 302 
               
               
                 Q-314 
                  1.8E+06 
                 706.4 
                 Internal 
                 Virtual 
               
               
                   
                   
                   
                 Condenser 
                 Condenser 
               
               
                   
                   
                   
                 314 
                 338 
               
               
                 Q-316 
                 4.75E+06 
                 1865.7 
                 Cooler 348 
                 — 
               
               
                 Q-318 
                 4.88E+06 
                 1918.7 
                 — 
                 Compressor 
               
               
                   
                   
                   
                   
                 344 
               
               
                   
               
             
          
         
       
     
         [0031]    Those of ordinary skill in the art will appreciate upon reading this disclosure that the values discussed above are based on the particular parameters and composition of the feed stream in the Example, and that the values can differ depending upon differences in operating conditions and upon the parameters and composition of the GSP feed stream  112  and the NRU feed stream  122 . 
         [0032]      FIG. 6  depicts the basic processing stages of another embodiment of the invention, wherein the NRU processing stage  600  is located in an alternate location compared to the NRU processing stage  300  as depicted in  FIGS. 2 and 4 . The system  400  comprises processing equipment typically found in GSP operations, with a few modifications to permit insertion of system  600  in the process, as will be understood by those of ordinary skill in the art. System  400  of the invention includes processing block  414 , which contains the GSP primary heat exchanger(s) (one or more) and primary separator(s) (one or more) and a compressor, as well as other equipment (such as valves, splitters, and mixers), known to be used in a typical GSP operation. GSP feed stream  412  passes through GSP primary processing block  414 , exiting as streams  416  and  436 . A portion of stream  436  is split off into stream  486 , with the remainder of stream  436  feeding demethanizer column  440 . A portion of stream  116  is split off into stream  522 , which passes through expander  524  exiting as stream  528 . Stream  528  also feeds demethanizer column  440 . The remainder of stream  116  is mixed with stream  486  before passing through GSP subcooler  426 , exiting as cooled stream  432 , which also feeds demethanizer column  440 . The demethanizer column  440  produces an NGL product stream  442  and an overhead stream  444 . The overhead stream  444  feeds NRU processing stage  600 . Treated gas stream  428  and a nitrogen reject stream  620  exit NRU processing stage  600 . Treated gas stream  428  passes through subcooler  426 , exiting as stream  446 . Stream  446  then passes through the heat exchanger(s) and compressor in block  414 , exiting as sales gas stream  450 , containing primarily methane. For a GSP feed stream containing around 4% nitrogen, the sales gas stream  450  will only contain around 3% nitrogen, which is within typical pipeline specifications. NRU processing stage  600  is similar to NRU processing stage  300  depicted in  FIG. 5 . 
         [0033]    Those of ordinary skill in the art will appreciate upon reading the disclosure in light of the accompanying drawings that the system and method of the present invention can be used with expander configurations known to be used in GSP operations other than those depicted in the drawings and described herein. Other alterations and modifications of the invention will likewise become apparent to those of ordinary skill in the art upon reading this specification in view of the accompanying drawings, and it is intended that the scope of the invention disclosed herein be limited only by the broadest interpretation of the appended claims to which the inventor is legally entitled.