Abstract:
A process for producing LNG from high CO 2  natural gas. The process includes: separating methane from a hydrocarbon stream containing CO 2  to produce a methane-depleted hydrocarbon stream; subjecting the methane-depleted hydrocarbon stream to at least one separation process; and feeding at least one recycle stream from the at least one separation processes into the step for separating methane. The at least one separation process is selected from the group consisting of deethanizing, depropanizing, debutanizing and CO 2  separating.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to a process for producing liquefied natural gas (LNG) from high-CO 2  natural gas. More particularly, the present invention relates to a hybrid distillation process for producing multiple products from high-CO 2  natural gas, including LNG, ethane, propane, high-purity CO 2  product, and a hydrocarbon condensate stream. 
       BACKGROUND OF THE INVENTION 
       [0002]    Natural gas is a valuable, environmentally-friendly energy source. With gradually decreasing quantities of available or easily-refined crude oil, natural gas has become accepted as a cleaner alternative energy source. Natural gas may be recovered from natural gas reservoirs or as associated gas from crude oil reservoirs. Indeed, natural gas for use in the present process may be recovered from any process which generates light hydrocarbon gases. 
         [0003]    Natural gas can be found all over the world. Much of the natural gas reserves found around the world are separate from oil and as new reserves are discovered and processed, growth in the LNG industry will continue. Countries with large natural gas reservoirs include Algeria, Australia, Brunei, Indonesia, Libya, Malaysia, Nigeria, Oman, Qatar, Thailand, and Trinidad and Tobago. Countries that import significant quantities of LNG include China, France, India, Italy, Japan, Malaysia, South Korea, Spain, Taiwan, United Kingdom and United States. 
         [0004]    One of the key steps in producing liquefied natural gas (LNG) is the processing of natural gas to remove components such as CO 2 , H 2 S, H 2 O, Hg and aromatics (benzene, toluene, xylene) to ppm levels prior to gas liquefaction. The acid gas components from natural gas (CO 2 , H 2 S) are normally removed using an aqueous amine process. Amine processes are well known in the art, and typically involve one packed/trayed column for absorption of CO 2  and H 2 S into the amine solution and a separate packed/trayed column where CO 2  and H 2 S are stripped (via steam and/or pressure let-down) from the amine solution. Amine units operate only under a narrow range of concentrations and acid gas loadings (at a given CO 2  partial pressure in the gas phase) due to corrosion limitations. Because the required amine flowrate is proportional to the amount of CO 2  that needs to be removed, amine absorption plants become progressively larger and more expensive with higher CO 2  concentrations in the natural gas. 
         [0005]    Gas-permeation membranes are a well-known alternative to amine systems in selectively removing CO 2  from natural gas. Membranes rely on the pressure driving force of the permeating CO 2 , and does not require the use of solvents. Membranes however, have the similar disadvantage of amine systems in that the CO 2  is normally recovered at low pressure. Thus, in cases where CO 2  must be reinjected, the compression requirements would also be high for membranes. Further, membranes cannot make a perfect separation between CO 2 , and hydrocarbons; a small amount of hydrocarbon will always permeate with the CO 2 . Thus, the ultimate purity of the CO 2  rich product is limited to the order of 97% to perhaps 98%. Membranes are not able to produce a CO 2 -rich stream of ultra-high purity, such as on the order of 99.5+%. 
         [0006]    Once CO 2  is removed from the gas, the CO 2  must be captured, processed, sequestered or diverted to some end use. One option currently under study is the capture, compression and re-injection of the into a geologic formation (depleted reservoir, saline aquifer, coal beds, etc.). However, because the CO 2  recovered from the overhead of an amine stripping column is slightly above atmospheric pressure, recompression of that CO 2  to a state where it could be readily transported/reinjected may be economically impractical. 
         [0007]    It is possible to produce LNG from high-CO 2  gas using a combination of amine treating (with or without membranes) along with the other related separation processes known in the art (gas dehydration, mercury removal, scrub columns to remove heavy components) and liquefaction processes. Normally, each of these unit operations are conducted in series, with little or no process integration between them. Thus, there remains an opportunity for an improved, integrated process for making LNG, especially in cases where the natural gas contains high levels of CO 2  and in situations where it is highly desirable to produce said CO 2  at a suitable condition (pressure, purity) for reinjection/geologic sequestration. Further, there is an opportunity for being able to produce LNG with a range of heating values. In cases where the natural gas contains a significant fraction of ethane and propane, there may be an economic incentive to produce a separate, saleable high-purity ethane product instead of leaving most of the ethane into the final LNG product as is typically done in current art LNG production. Having a leaner (i.e., with a lower ethane and propane content) LNG product has several advantages: (1) Many LNG customers actually prefer to have leaner LNG, (2) Excess ethane and propane removed from the LNG may be sold as separate products at higher prices, (3) A greater proportion of the LNG ship&#39;s volume is made available for storing liquefied methane, and (4) LNG regasification terminals would not need to install ethane and propane removal units for heating value control. 
       SUMMARY OF THE INVENTION 
       [0008]    The present invention achieves the advantage of a process for producing LNG from high-CO 2  natural gas, with the flexibility of producing separated products such as ethane, propane, and a hydrocarbon condensate. 
         [0009]    In an aspect of the invention, a process for producing LNG from high-CO 2  natural gas includes the steps of: separating methane from a hydrocarbon feed stream containing CO 2  to produce a methane-depleted hydrocarbon stream; subjecting the methane-depleted hydrocarbon stream to at least one separation process to produce a hydrocarbon recycle stream; and combining the hydrocarbon recycle stream with the hydrocarbon feed stream prior to separating methane from the hydrocarbon feed stream, wherein the at least one separation process is selected from the group consisting of deethanizing, depropanizing, debutanizing and CO 2  separating. 
         [0010]    Optionally, in the above process, the step of separating methane includes conducting a full liquid reflux on the separated methane vapor product. 
         [0011]    Optionally, in the above process, the step of separating methane includes scrubbing and removing aromatics and heavy hydrocarbons from the hydrocarbon stream containing CO 2 . 
         [0012]    Optionally, the above process further includes the step of passing the methane to a liquefaction process. 
         [0013]    Optionally, the above process further includes the step of passing the methane to a main cryogenic heat exchanger of a liquefaction plant. 
         [0014]    Optionally, in the above process, the hydrocarbon recycle stream includes fractionated gas components passed from the at least one separation process. 
         [0015]    Optionally, in the above process, the hydrocarbon recycle stream includes a hydrocarbon stream from a front slug catcher. 
         [0016]    Optionally, in the above process, the methane contains less than about 100 ppm CO 2  and less than about 3 ppm H 2 S. 
         [0017]    Optionally, in the above process, the step of separating the methane from the hydrocarbon stream is conducted at a pressure in the range of about 38 to about 45 bar, and at a temperature in the range of about −91° C. to about −84° C. 
         [0018]    Optionally, in the above process, the step of deethanizing is conducted at a pressure in the range of about 35 to about 44 bar, and at a temperature in the range of about 4° C. at about 35 bar. 
         [0019]    Optionally, in the above process, the step of depropanizing is conducted at a pressure in the range of about 17 to about 27 bar, and at a temperature in the range of about −2° C. to about 67° C. 
         [0020]    Optionally, in the above process, the step of debutanizing is conducted at a pressure in the range of about 6 to 12 bar, and at a temperature in the range of about 40° C. to about 78° C. 
         [0021]    Optionally, in the above process, the step of CO 2  separating is conducted at a pressure in the range of about 28 to about 32 bar, and at a temperature in the range of about −6° C. to about −2° C. 
         [0022]    Optionally, in the above process, the step of subjecting the methane-depleted hydrocarbon stream to at least one separation process includes blending back at least one principal overhead product with the methane for heating value adjustment. 
         [0023]    Optionally, in the above process, the step of subjecting the methane-depleted hydrocarbon stream to at least one separation process includes feeding at least one principal overhead product stream to a fractionation train. 
         [0024]    Optionally, in the above process, the step of subjecting the methane-depleted hydrocarbon stream to at least one separation process includes feeding a principal overhead product of ethane and carbon dioxide to an azeotrope separation process. 
         [0025]    Optionally, in the above process, the step of subjecting the methane-depleted hydrocarbon stream to at least one separation process includes removing H 2 S via adsorption from the methane-depleted hydrocarbon stream. 
         [0026]    Optionally, in the above process, the step of removing H 2 S is conducted at a pressure in the range of about 17 to 27 bar, and at a temperature in the range of about −2° C. to 67° C. 
         [0027]    Optionally, in the above process, the step of subjecting the methane-depleted hydrocarbon stream to at least one separation process includes membrane-separating CO 2  from the methane-depleted hydrocarbon stream. 
         [0028]    Optionally, in the above process, the step of membrane-separating CO 2  is conducted to produce a stream containing about 98 vol % CO 2 . 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0029]      FIG. 1  illustrates an embodiment of the present invention. 
           [0030]      FIG. 2  illustrates another embodiment of the present invention. 
           [0031]      FIG. 3  illustrates another embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0032]    So that the above recited features and advantages of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to the embodiments thereof that are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments. 
         [0033]    Embodiments describing the process of the present invention are referenced in  FIGS. 1 to 3 . 
       First Embodiment 
       [0034]    In an embodiment of the invention illustrated in  FIG. 1 , a hydrocarbon feed stream  101 , having a composition as shown in TABLES 1 &amp; 2 (simulated data), is fed to a demethanizer (DeC 1 ) column  150 . The DeC 1  column  150  may be a packed or trayed-type distillation column equipped with a bottom reboiler, side reboilers, and a condenser, that is designed to process at least two feed streams: a light hydrocarbon feed gas stream and a heavy hydrocarbon liquid solvent stream. The operating pressure of the DeC 1  column is in the range of about 38 to about 45 bar. The operating temperature of the overhead condenser is in the range of about −91 to about −84° C. 
         [0035]    A hydrocarbon recycle stream  120  from the bottoms of a depropanizer (DeC 3 ) column  160  is also fed into the DeC 1  column  150 . Essentially, the hydrocarbon recycle stream  120  is fractionated gas components passed from the plurality of separation processes as further described below. The hydrocarbon recycle prevents the CO 2  from freezing and acts as a scrubbing agent to remove aromatics and other heavy hydrocarbons from the C1-rich product stream taken overhead. 
         [0036]    Although this embodiment shows the hydrocarbon recycle stream  120  being fed from the depropanizer  160 , it is also possible to feed a hydrocarbon recycle stream from a front slug catcher into the demethanizer  150 . An example of a front slug catcher includes a three phase separator required in the oil and gas industry at an upstream position (typically near a gas wellhead) to separate gas/oil/water. 
         [0037]    Methane is taken as the principal overhead product, stream  103 , and has the composition as shown in TABLE 1. The separated methane contains less than about 100 ppm CO 2  and less than about 3 ppm H 2 S. Also, a full liquid reflux (not shown in figure) on the separated methane vapor product is fed back to the demethanizer  150 . 
         [0038]    The main portion of stream  103  is fed to a liquefaction process. Since the aromatics are reduced to such a low level and the temperature is very cold, the majority of stream  103  may be precooled further and eventually fed to a main cryogenic heat exchanger (MCHE)  170 , which is a specially-designed heat exchanger that may be of the spiral-wound type, plate-and-frame type, or any other type known in the LNG art. The purpose of the MCHE is to reduce the temperature of the C1-rich product to a point where it may be readily liquefied, stored, and shipped as LNG. The final steps of the liquefaction process includes nitrogen rejection via endflash or a stripping column. The nitrogen-depleted LNG final product is then pumped to storage and ready to be shipped. 
         [0039]    The bottoms product  102  will contain the ethane and heavier hydrocarbon liquids along with most of the CO 2  which is fed to a CO 2  column  155  (CO 2  separating). The bottoms product  102  has a composition as shown in TABLE 1. Two of the components in this stream form an azeotrope system: carbon dioxide and ethane. The CO 2  column  155  may be a packed or trayed-type distillation column equipped with a bottom reboiler, side reboilers, and a condenser, that is designed to process at least two feed streams: a hydrocarbon vapor stream and a hydrocarbon liquid stream. The operating pressure of the CO 2  column  155  is in the range of about 28 to about 32 bar. The operating temperature of the overhead condenser is in the range of about −6 to about −2° C. 
         [0040]    A hydrocarbon recycle stream  121  from the bottoms of the DeC 3  column  160  is also fed into the CO 2  column  155 . The hydrocarbon recycle breaks the azeotrope formed by the carbon dioxide and ethane. 
         [0041]    Carbon dioxide is taken as the principal overhead product, stream  105 , and has the composition as shown in TABLE 1. Since stream  105  is a high purity CO 2  stream, it is suitable for geologic reinjection or enhanced oil recovery (EOR). 
         [0042]    The bottoms product  104  is fed to the DeC 3  column  160 . The bottoms product  104  has a composition as shown in TABLE 1. The DeC 3  column  160  may be a packed or trayed-type distillation column equipped with a reboiler and condenser. The operating pressure of the DeC 3  column  160  is in the range of about 17 to about 27 bar. The operating temperature of the overhead condenser is in the range of about −2 to about 29° C. 
         [0043]    Ethane and propane are taken as the principal overhead product, stream  107 , and has the composition as shown in TABLE 1. 
         [0044]    Stream  107  is fed to an H 2 S separator  180 . The H 2 S separator may be a fixed bed adsorber that may be regenerative or non-regenerative, or any other process known in the art for selective-removal of H 2 S from hydrocarbon streams. An H 2 S-rich stream  123  may have several alternative destinations, depending on the design basis. For example, stream  123  may be fed to a Claus plant for further conversion to elemental sulfur, burned in a thermal or catalytic oxidizer, blended with the CO 2 -rich product for reinjection, or reinjected separately. The operating pressure of the H 2 S separator is in the range of about 17 to 27 bar, and the operating temperature is in the range of about −2 to 29° C. 
         [0045]    The principal overhead product output of the H 2 S separator  180 , stream  113 , is fed to a small fractionation train  175  to recover sufficient ethane and propane for sales and refrigerant makeup in a liquefaction process. A portion of the ethane and propane, stream  116 , from the small fractionation train  175  may be blended back with stream  103  for heating value adjustment. For example, in cases where it is desirable for the LNG product to have a higher heating value greater than that of pure methane (about 1000 BTU/SCF), additional ethane, propane, and/or butane may be added. 
         [0046]    For situations where C 2 , C 3 , and C 4  products are neither required for LNG heating value adjustment nor for refrigerant makeup, each of the components may be exported from the facility as separate, saleable products as shown in stream  114 ,  115 , and  125 . 
         [0047]    The bottoms product  106  is fed to the hydrocarbon recycle streams  120  and  121  via stream  119 , and to a debutanizer (DeC 4 ) column  165 , via stream  108 . The bottoms product is output as stream  110 . The DeC 4  column  165  may be a packed or trayed-type distillation column equipped with a reboiler and condenser. The operating pressure of the DeC 4  column  165  is in the range of about 6 to about 12 bar, and the operating temperature is in the range of about 40° C. to about 78° C. It is noted that the DeC 4  column is only necessary if a separate, C4-rich product stream is desired. If the DeC 4  column is omitted, a greater amount of C4 will be present in the hydrocarbon recycle streams  120 ,  121  and condensate export stream  108 . 
         [0048]    Butane is taken as the principal overhead product via stream  109 . 
         [0049]    Stream  109  is fed to an H 2 S separator  185 . The H 2 S separator  185  may be a fixed bed adsorber that may be regenerative or non-regenerative, or the separator may be any other process known in the art for selective-removal of H 2 S from hydrocarbon streams. An H 2 S-rich stream  111  may have several alternate destinations, depending on the design basis. For example, stream  111  may be fed to a Claus plant for further conversion to elemental sulfur, burned in a thermal or catalytic oxidizer, blended with the CO 2 -rich product for reinjection, or reinjected separately. The operating pressure of the H 2 S separator  185  is about 10 bar, and the operating temperature is up to 80° C. 
         [0050]    A portion (stream  117 ) of the output of the H 2 S separator  185 , stream  112 , is blended back with stream  103  for heating value adjustment, and the remainder, stream  125 , is fed to sales and refrigerant makeup of a liquefaction process. 
         [0000]    
       
         
               
             
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Summary of Major Streams Only (Compositions in mol %) 
               
             
          
           
               
                 Stream No. 
                   
                   
                   
                   
                   
                   
                   
                   
               
               
                 (FIG. 1) 
                 C 1   
                 C 2   
                 C 3   
                 C 4   
                 C 4 + 
                 CO 2   
                 N 2   
                 H 2 S 
               
               
                   
               
             
          
           
               
                 101 
                 77.8 
                 3.2 
                 0.9 
                 0.3 
                 0.1 
                 14.7 
                 3.0 
                 0.003 
               
               
                 102 
                 0.1 
                 10.8 
                 5.8 
                 15.9 
                 18.2 
                 49.2 
                 0 
               
               
                 103 
                 96.3 
                 0 
                 0 
                 0 
                 0 
                 0 
                 3.7 
               
               
                 104 
                 0 
                 7.6 
                 9.1 
                 38.3 
                 45 
                 0 
                 0 
               
               
                 105 
                 0.2 
                 0.4 
                 0.6 
                 0 
                 0 
                 98.8 
                 0 
               
               
                 106 
                 0 
                 0 
                 8 
                 42.1 
                 49.9 
                 0 
                 0 
               
               
                 107 
                 0 
                 76.4 
                 18.9 
                 4.6 
                 0.01 
                 0.04 
                 0 
                 0.07 
               
               
                 108 
                 0 
                 0 
                 8 
                 42.1 
                 49.9 
                 0 
                 0 
               
               
                 120 
                 0 
                 0 
                 8 
                 42.1 
                 49.9 
                 0 
                 0 
               
               
                 121 
                 0 
                 0 
                 8 
                 42.1 
                 49.9 
                 0 
                 0 
               
               
                   
               
             
          
         
       
     
         [0000]    
       
         
               
             
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 2 
               
             
             
               
                   
               
               
                 Summary of Major Streams Only 
               
             
          
           
               
                   
                 Stream No. 
                 Flowrate 
                 Pressure 
                 Temp 
               
               
                   
                 (FIG. 1) 
                 (kgmole/hr) 
                 (bar) 
                 (° C.) 
               
               
                   
                   
               
             
          
           
               
                   
                 101 
                 59,770 
                 41 
                 −67 
               
               
                   
                 102 
                 17,870 
                 39 
                 22 
               
               
                   
                 103 
                 48,250 
                 38 
                 −91 
               
               
                   
                 104 
                 24,860 
                 33 
                 141 
               
               
                   
                 105 
                 8,890 
                 33 
                 −2 
               
               
                   
                 106 
                 22,380 
                 17 
                 117 
               
               
                   
                 107 
                 2,477 
                 17 
                 −3 
               
               
                   
                 108 
                 153 
                 43 
                 18 
               
               
                   
                 120 
                 6,350 
                 42 
                 −62 
               
               
                   
                 121 
                 15,880 
                 43 
                 18 
               
               
                   
                   
               
             
          
         
       
     
       Second Embodiment 
       [0051]    In another embodiment of the invention as illustrated in  FIG. 2 , a hydrocarbon feed stream  201 , having a composition as shown in TABLES 3 &amp; 4 (simulated data), is fed to a DeC 1  column  250 . The DeC 1  column  250  is similar to that described above. The operating pressure of the DeC 1  column  250  is in the range of about 38 to about 45 bar. The operating temperature of the overhead condenser is in the range of about −91 to about −84° C. 
         [0052]    A hydrocarbon recycle stream  228  from the bottoms of a DeC 3  column  260  is also fed into the DeC 1  column  250 . The hydrocarbon recycle prevents the CO 2  from freezing and acts as a scrubbing agent to remove aromatics and other heavy hydrocarbons from the C1-rich product stream taken overhead. 
         [0053]    Methane is taken as the principal overhead product, stream  203 , and has the composition as shown in TABLE 3. The separated methane contains less than about 100 ppm CO 2  and less than about 3 ppm H 2 S. Also, a full liquid reflux on the separated methane is fed back to the demethanizer  250 . 
         [0054]    The main portion of stream  203  is fed to a liquefaction process. Since the aromatics are reduced to such a low level and the temperature is very cold, the majority of stream  203  may be fed to a MCHE  270 . The MCHE  270  is similar to that described above. 
         [0055]    The bottoms product  202  is fed to a deethanizer (DeC 2 ) column  255 . The bottoms product  202  has a composition as shown in TABLE 3. The DeC 2  column  255  may be a packed or trayed-type distillation column equipped with a reboiler and condenser. The operating pressure of the DeC 2  column  255  is in the range of about 35 to about 44 bar. The operating temperature of the overhead condenser is in the range of about −4° C. (at 35 bar). 
         [0056]    Ethane and carbon dioxide are the main components of the overhead product, stream  205 , and has the composition as shown in TABLE 3. 
         [0057]    The overhead product stream  205  is mixed with stream  216  and is fed to a CO 2  membrane  290 , via stream  213 , at a pressure of about 34 bar. In the membrane unit  290 , the gases pass over a semi-permeable membrane through which the carbon dioxide passes much more readily than ethane. The surface area of the membrane available and residence time are controlled so that a stream containing up to about 98 vol % CO 2 , at a pressure of about 2 bar, is produced. It is well known in the art that the operating parameters of gas-separation membranes (e.g., membrane area, feed and downstream pressure, temperature, and degree of staging) may be varied to yield any desired combination of (CO 2 ) product purity and (C2) recovery. 
         [0058]    The gas exiting the membrane system rich in ethane, stream  215 , is fed to a Azeo column  295  at a pressure of about 25 bar. The overhead product stream  216  from the Azeo column  295 , substantially the binary azeotrope of ethane and carbon dioxide, is returned to the entrance of the membrane unit  290 . A bottoms product  217 , which is substantially ethane, is blended back with stream  203 , via stream  218 , for LNG heating value adjustment, fed to sales (stream  219 ), and/or supplied to the refrigerant makeup of a liquefaction process. 
         [0059]    A bottoms product  204  is fed to a DeC 3  column  260  (depropanizer). The bottoms product  204  has a composition as shown in TABLE 3. The DeC 3  column  260  is similar to that described above. The operating pressure of the DeC 3  column  260  is in the range of about 17 to about 27 bar. The operating temperature of the overhead condenser is in the range of about −2 to about 67° C. 
         [0060]    Propane is taken as the principal overhead product, stream  207 , and has the composition as shown in TABLE 3. 
         [0061]    Stream  207  is fed to an H 2 S separator  280 . The H 2 S separator  280  is similar to that described above. An H 2 S stream  220  is Fed to a Claus plant to produce sulfur if the sulfur (tonne/day) is sufficiently high, or disposed of using alternatives known in the art such as reinjection as a separate stream, reinjection as a mixed stream with the CO 2  (stream  214 ), or burned in a thermal or catalytic oxidizer. The operating pressure of the H 2 S separator  280  is in the range of about 17 to about 27 bar. The operating temperature of separator  280  is in the range of about −2 to about 67° C. 
         [0062]    A portion of the output of the H 2 S separator  280 , stream  221 , is blended back with stream  203 , via stream  223 , for heating value adjustment. The remainder of the output is fed to sales (stream  222 ) and refrigerant makeup in a liquefaction process. 
         [0063]    A bottoms product  206  is fed to the hydrocarbon recycle stream  228 , and to a DeC 4  column  265 , via stream  208 . The bottoms product  206  has a composition as shown in TABLE 3. The DeC 4  column  265  is similar to that described above. The operating pressure of the DeC 4  column  265  is in the range of about 6 to about 12 bar. The operating temperature of column  265  is in the range of about 40° C. to about 78° C. The bottoms product is output as stream  210 . 
         [0064]    Butane is taken as the principal overhead product, stream  209 , and has the composition as shown in TABLE 3. 
         [0065]    Stream  209  is fed to an H 2 S separator  285 . The H 2 S separator  285  is similar to that described above. An H 2 S stream  224  is fed to a Claus plant to produce sulfur, or any of the other alternatives for managing H 2 S known in the art as described previously. The operating pressure of the H 2 S separator is in the range of about 11 bar, and the operating temperature is up to about 78° C. 
         [0066]    A portion of the output of the H 2 S separator  285 , stream  225 , is blended back with stream  203 , via stream  227 , for heating value adjustment, and the remainder of the stream is fed to sales (stream  226 ) and refrigerant makeup of a liquefaction process. 
         [0000]    
       
         
               
             
               
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 3 
               
             
             
               
                   
               
               
                 Summary of Major Streams Only (Compositions in mol %) 
               
             
          
           
               
                 Stream 
                   
                   
                   
                   
                   
                   
                   
                   
                   
               
               
                 No. 
               
               
                 (FIG. 2) 
                 C 1   
                 C 2   
                 C 3   
                 C 4   
                 C 4 + 
                 CO 2   
                 N 2   
                 H 2 S 
                 BTEX 
               
               
                   
               
             
          
           
               
                 201 
                 77.9 
                 3.3 
                 0.9 
                 0.3 
                 0.2 
                 14.8 
                 2.5 
                 0.003 
                 0.06 
               
               
                 202 
                 0.01 
                 14 
                 4.1 
                 7.7 
                 9.7 
                 62.7 
                 0 
                 0.01 
                 1.8 
               
               
                 203 
                 96.9 
                 0 
                 0.01 
                 0.04 
                 0.01 
                 0 
                 3.1 
                 0 
                 0 
               
               
                 204 
                 0 
                 0.01 
                 17.7 
                 33 
                 41.5 
                 0 
                 0 
                 0.01 
                 7.8 
               
               
                 205 
                 0.01 
                 18.2 
                 0.03 
                 0 
                 0 
                 81.8 
                 0 
                 0.01 
                 0 
               
               
                 206 
                 0 
                 0 
                 2 
                 39.3 
                 49.4 
                 0 
                 0 
                 0 
                 9.3 
               
               
                 207 
                 0 
                 0.03 
                 0.99 
                 0.5 
                 0 
                 0.02 
                 0 
                 0.05 
                 0 
               
               
                 208 
                 0 
                 0 
                 2 
                 39.3 
                 49.4 
                 0 
                 0 
                 0 
                 9.3 
               
               
                 209 
                 0 
                 0 
                 4.9 
                 95.1 
                 0.04 
                 0 
                 0 
                 0 
                 0 
               
               
                 210 
                 0 
                 0 
                 0 
                 0.07 
                 84 
                 0 
                 0 
                 0 
                 15.9 
               
               
                 213 
                 0.2 
                 23.3 
                 0.02 
                 0 
                 0 
                 76.5 
                 0 
                 0.01 
                 0 
               
               
                 214 
                 0.01 
                 1.6 
                 0 
                 0 
                 0 
                 98.4 
                 0 
                 0.01 
                 0 
               
               
                 215 
                 0.4 
                 49.8 
                 0.04 
                 0 
                 0 
                 49.7 
                 0 
                 0.01 
                 0 
               
               
                 216 
                 0.6 
                 33.2 
                 0 
                 0 
                 0 
                 66.3 
                 0 
                 0 
                 0 
               
               
                 217 
                 0 
                 99.8 
                 0.2 
                 0 
                 0 
                 0.01 
                 0 
                 0.02 
                 0 
               
               
                 228 
                 0 
                 0 
                 2 
                 39.3 
                 49.4 
                 0 
                 0 
                 0 
                 9.3 
               
               
                   
               
             
          
         
       
     
         [0000]    
       
         
               
             
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 4 
               
             
             
               
                   
               
               
                 Summary of Major Streams Only 
               
             
          
           
               
                   
                 Stream No. 
                 Flowrate 
                 Pressure 
                 Temp 
               
               
                   
                 (FIG. 2) 
                 (kgmole/hr) 
                 (bar) 
                 (° C.) 
               
               
                   
                   
               
             
          
           
               
                   
                 201 
                 58,550 
                 45 
                 −49 
               
               
                   
                 202 
                 13,760 
                 45 
                 19 
               
               
                   
                 203 
                 47,090 
                 44.5 
                 −84 
               
               
                   
                 204 
                 3,209 
                 35 
                 178 
               
               
                   
                 205 
                 10,560 
                 34.5 
                 −4 
               
               
                   
                 206 
                 2,693 
                 25 
                 175 
               
               
                   
                 207 
                 516 
                 24.5 
                 67 
               
               
                   
                 208 
                 393 
                 25 
                 175 
               
               
                   
                 209 
                 162 
                 10.5 
                 78 
               
               
                   
                 210 
                 231 
                 11 
                 171 
               
               
                   
                 213 
                 16,000 
                 34.5 
                 0.2 
               
               
                   
                 214 
                 8,801 
                 2.1 
                 0.2 
               
               
                   
                 215 
                 7,200 
                 34.5 
                 0.2 
               
               
                   
                 216 
                 5,401 
                 24 
                 −19 
               
               
                   
                 217 
                 1,799 
                 24.5 
                 0.9 
               
               
                   
                 228 
                 2,300 
                 45 
                 −32 
               
               
                   
                   
               
             
          
         
       
     
       Third Embodiment 
       [0067]    In another embodiment of the invention as illustrated in  FIG. 3 , a hydrocarbon feed stream  301 , having a composition as shown in TABLES 5 &amp; 6 (simulated data), is fed to a DeC 1  column  350 . 
         [0068]    The DeC 1  column  350  is similar to that described above. The operating pressure of the DeC 1  column  350  is in the range of about 38 to about 45 bar. The operating temperature of the overhead condenser is in the range of about −91 to about −84° C. 
         [0069]    A hydrocarbon recycle stream  312  from the bottoms of a DeC 3  column  360  is also fed into the DeC 1  column  350 . The hydrocarbon recycle prevents the CO 2  from freezing and acts as a scrubbing agent to remove aromatics and other heavy hydrocarbons from the C1-rich product stream taken overhead. Also, a full liquid reflux on the separated methane is fed back to the demethanizer  350 . 
         [0070]    Since the aromatics are reduced to such a low level and the temperature is very cold, the majority of stream  303  may be fed to a MCHE  370 . The MCHE is similar to that described above. 
         [0071]    In stream  303 , the separated methane contains less than about 100 ppm CO 2  and less than about 3 ppm H 2 S. 
         [0072]    A bottoms product  302  is fed to a DeC 2  column  355  at a pressure of about −40 bar. The bottoms product  302  has a composition as shown in TABLE 5. 
         [0073]    The DeC 2  column  355  is similar to that described above. The operating pressure of the DeC 2  column  355  is in the range of about 35 to about 44 bar, and the operating temperature of the overhead condenser is in the range of about 4° C. (at  35 , bar). 
         [0074]    Ethane and carbon dioxide are major components in the principal overhead product, stream  305 , and has the composition as shown in TABLE 5. 
         [0075]    The overhead product stream  305  is fed to an Azeo column  375  at a pressure of about 25 bar. The overhead product  318  from the Azeo column  375 , which is substantially a binary azeotrope of ethane and carbon dioxide, is mixed with stream  321  and is fed to the entrance of a CO 2  removal membrane  395  via stream  322 . A bottoms product  319 , which is substantially carbon dioxide, is sent to a re-injection process. In the membrane unit  395 , the gases pass over a semi-permeable membrane through which the carbon dioxide passes much more readily than ethane. The surface area of the membrane available and residence time are controlled so that a stream containing about 98 vol % CO 2 , at a pressure of about 2 bar, is produced. The membrane unit  395  is similar to that described above. The permeate output (stream 323) from the CO 2  membrane  395  is fed to a compressor  380  and output as a vapor stream  320 . The vapor stream  320  is recycled back to the Azeo column  375 . 
         [0076]    The gas (stream  324 ) exiting the membrane unit  395  rich in ethane is fed to an ethane recovery (C 2  Rec) column  396  at a pressure of about 24 bar. The overhead product  321  from this C 2  Rec column  396 , substantially the binary azeotrope of ethane and carbon dioxide, is returned to the entrance of the membrane unit  395 . A bottoms product  325 , which is ethane, is blended back with stream  303  for heating value adjustment, fed to sales, and/or refrigerant makeup of a liquefaction process. 
         [0077]    A bottoms product  304  is fed to a DeC 3  column  360  at a pressure of about 25 bar. The bottoms product  304  has a composition as shown in TABLE 5. The DeC 3  column  360  is similar to that described above. The operating pressure of the DeC 3  column  360  is in the range of about 17 to about 27 bar. The operating temperature of the overhead condenser is in the range of about −2 to about 67° C. 
         [0078]    Propane is taken as the principal overhead product, stream  307 , and has the composition as shown in TABLE 5. 
         [0079]    Stream  307  is fed to an H 2 S separator  385 . The H 2 S separator  385  is similar to that describe above. An H 2 S stream  327  is fed to a Claus plant to produce sulfur, or any of the other H 2 S mitigation processes as described above. The operating pressure of the H 2 S separator  385  is in the range of about 17 to about 27 bar. The operating temperature of the overhead condenser is in the range of about −2 to about 67° C. 
         [0080]    A portion of the output of the H 2 S separator  385 , stream  326 , is blended back with stream  303  for heating value adjustment. The remainder of the output is fed to sales and/or refrigerant makeup in a liquefaction process. 
         [0081]    A bottoms product  306  is fed to the hydrocarbon recycle stream  312 , and to a DeC 4  column  365 , via stream  309 , at a pressure of about 11 bar. The bottoms product  306  has a composition as shown in TABLE 5. 
         [0082]    The DeC 4  column  365  is similar to that described above. The operating pressure of the DeC 4  column  365  is in the range of about 6 to about 12 bar, and the operating temperature of the overhead condenser is in the range of about 40° C. to about 78° C. The bottoms product is output as stream  310 . 
         [0083]    Butane taken as the principal overhead product, stream  311 , and has the composition as shown in TABLE 5. 
         [0084]    A portion of the stream  311 , is blended back with stream  303  for heating value adjustment, and the remainder of stream is fed to sales and/or refrigerant makeup of a liquefaction process. 
         [0000]    
       
         
               
             
               
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 5 
               
             
             
               
                   
               
               
                 Summary of Major Streams Only (mol %) 
               
             
          
           
               
                 Stream 
                   
                   
                   
                   
                   
                   
                   
                   
                   
               
               
                 No. 
               
               
                 (FIG. 3) 
                 C 1   
                 C 2   
                 C 3   
                 C 4   
                 C 4 + 
                 CO 2   
                 N 2   
                 H 2 S 
                 BTEX 
               
               
                   
               
             
          
           
               
                 301 
                 77.9 
                 3.3 
                 0.9 
                 0.3 
                 0.2 
                 14.8 
                 2.5 
                 0.003 
                 0.06 
               
               
                 302 
                 0.01 
                 14 
                 4.1 
                 7.7 
                 9.7 
                 62.7 
                 0 
                 0.01 
                 1.8 
               
               
                 303 
                 96.9 
                 0 
                 0.01 
                 0.04 
                 0.01 
                 0.01 
                 3.1 
                 0 
                 0 
               
               
                 304 
                 0 
                 0.01 
                 17.7 
                 33 
                 41.5 
                 0 
                 0 
                 0.01 
                 7.8 
               
               
                 305 
                 0.01 
                 81.8 
                 0.03 
                 0 
                 0 
                 18.2 
                 0 
                 0.01 
                 0 
               
               
                 306 
                 0 
                 0 
                 2 
                 39.3 
                 49.4 
                 0 
                 0 
                 0 
                 9.3 
               
               
                 307 
                 0 
                 0.03 
                 99.5 
                 0.4 
                 0 
                 0.02 
                 0 
                 0.05 
                 0 
               
               
                 309 
                 0 
                 0 
                 2 
                 39.3 
                 49.4 
                 0 
                 0 
                 0 
                 9.3 
               
               
                 310 
                 0 
                 0 
                 0 
                 0.07 
                 84.2 
                 0 
                 0 
                 0 
                 15.9 
               
               
                 311 
                 0 
                 0 
                 4.9 
                 95.1 
                 0.04 
                 0 
                 0 
                 0 
                 0 
               
               
                 312 
                 0 
                 0 
                 2 
                 39.3 
                 49.4 
                 0 
                 0 
                 0 
                 9.3 
               
               
                 318 
                 0.09 
                 26.1 
                 0 
                 0 
                 0 
                 73.9 
                 0 
                 0 
                 0 
               
               
                 319 
                 0 
                 0.1 
                 0.03 
                 0 
                 0 
                 99.8 
                 0 
                 0.02 
                 0 
               
               
                 320 
                 0.1 
                 2 
                 0 
                 0 
                 0 
                 97.9 
                 0 
                 0 
                 0 
               
               
                 321 
                 2.7 
                 34.5 
                 0 
                 0 
                 0 
                 62.8 
                 0 
                 0 
                 0 
               
               
                 322 
                 1.5 
                 30.4 
                 0 
                 0 
                 0 
                 68.2 
                 0 
                 0 
                 0 
               
               
                 323 
                 0.1 
                 2 
                 0 
                 0 
                 0 
                 97.9 
                 0 
                 0 
                 0 
               
               
                 324 
                 2.2 
                 46.8 
                 0 
                 0 
                 0 
                 51.0 
                 0 
                 0 
                 0 
               
               
                 325 
                 0 
                 99.9 
                 0 
                 0 
                 0 
                 0.01 
                 0 
                 0 
                 0 
               
               
                   
               
             
          
         
       
     
         [0000]    
       
         
               
             
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 6 
               
             
             
               
                   
               
               
                 Summary of Major Streams Only 
               
             
          
           
               
                   
                 Stream No. 
                 Flowrate 
                 Pressure 
                 Temp 
               
               
                   
                 (FIG. 3) 
                 (kgmole/hr) 
                 (bar) 
                 (° C.) 
               
               
                   
                   
               
             
          
           
               
                   
                 301 
                 58,550 
                 45 
                 −49 
               
               
                   
                 302 
                 13,760 
                 45 
                 19 
               
               
                   
                 303 
                 47,090 
                 44.5 
                 −84 
               
               
                   
                 304 
                 3,209 
                 35 
                 178 
               
               
                   
                 305 
                 10,560 
                 34.5 
                 −4 
               
               
                   
                 306 
                 2,693 
                 25 
                 175 
               
               
                   
                 307 
                 516 
                 24.5 
                 67 
               
               
                   
                 309 
                 393 
                 11 
                 40 
               
               
                   
                 310 
                 231 
                 11 
                 171 
               
               
                   
                 311 
                 162 
                 10.5 
                 78 
               
               
                   
                 312 
                 2,300 
                 45 
                 −32 
               
               
                   
                 318 
                 7,779 
                 24.6 
                 −17 
               
               
                   
                 319 
                 8,632 
                 25 
                 −11 
               
               
                   
                 320 
                 5,856 
                 25 
                 40 
               
               
                   
                 321 
                 8,208 
                 24.7 
                 −18 
               
               
                   
                 322 
                 15,990 
                 24.7 
                 −18 
               
               
                   
                 323 
                 5,846 
                 24.2 
                 −4 
               
               
                   
                 324 
                 10,140 
                 24.2 
                 −4 
               
               
                   
                 325 
                 1,898 
                 24.3 
                 0