Method and apparatus for the coding and low temperature liquefaction of gaseous mixtures

Abstract

.Iadd.17. A process for totally liquefying a gaseous methane-rich feed stream comprising the steps of: a. supplying said methane-rich feed stream at a superatmospheric pressure and precooling said stream, b. providing a multicomponent refrigerant, c. compressing said multicomponent refrigerant to a superatmospheric pressure, d. cooling said multicomponent refrigerant and phase separating a single vapor fraction and a single liquid fraction from said cooled multicomponent refrigerant, e. subcooling said liquid fraction in heat exchange with itself after expansion to form a first subcooled liquid fraction, f. liquefying and subcooling all of said vapor fraction in heat exchange with said first subcooled liquid fraction, and with itself after expansion, to form a second subcooled liquid fraction, and g. totally liquefying said precooled methane-rich feed stream by further cooling said precooled methane-rich feed stream to at least its liquefaction temperature, at the superatmospheric pressure thereof, solely by progressive heat exchange steps with said first and second subcooled liquid fractions undergoing vaporization, said methane-rich feed stream and said multicomponent refrigerant being in indirect heat exchange with each other throughout the process..Iaddend. .Iadd.

I claim:  .[.1. Process for the liquefaction of a first gas mixture comprising passing said first gas mixture through a first liquefaction system in indirect contact with and in a direction opposite to a refrigerating liquid in a process of vaporization, said refrigerating liquid being admitted as a plurality of portions at several points in said first liquefaction system, said portions being increasingly more volatile in the direction followed by said first gas mixture and said portions of refrigerating liquid resulting from a liquefaction in successive stages in a second liquefaction system, of a second gas mixture obtained by vaporization of the refrigerating liquid in said liquefaction systems, said liquefaction in said second liquefaction system resulting from the vaporization with indirect contact of at least one part of the condensate of each previous stage, with the exception of the first condensate which is obtained by compression of said second gas mixture, the vaporization pressure of the refrigerating liquid in said first liquefaction system being lower than the vaporization pressure in said second liquefaction system, said first gaseous mixture flowing thru the first liquefaction system being out of contact with the fluid in the second liquefaction system throughout the process..].  .[.2. Process according to claim 1, wherein the absolute vaporization pressure in said first liquefaction system is between about 0.4 and about 3 atmospheres..]. .[.3. Process according to claim 1, wherein the absolute vaporization pressure in said first liquefaction system is between about 1 and about 1.5 atmospheres..]. .[.4. Process according to claim 1, wherein the absolute vaporization pressure in said second liquefaction system is between about 4 and about 8 atmospheres..]. .[.5. Process according to claim 1, wherein the absolute vaporization pressure in said second liquefaction system is between about 5 and about 7 atmospheres..]. .[.6. Process according to claim 1, wherein the absolute vaporization pressure is approximately 1.5-2 atmospheres in said first liquefaction system and approximately 3.5-4 atmospheres in said second liquefaction system..]. .[.7. Process according to claim 1, wherein the absolute liquefaction pressure of said second gas mixture is greater than about 31 bars..]. .[.8. Process according to claim 1, wherein the absolute liquefaction pressure of said second gas mixture is between about 31 and about 50 bars..]. .[.9. Process according to claim 1, wherein the absolute liquefaction pressure of said fitst gas mixture is between about 30 and about 100 bars..]. .[.10. Process according to claim 1, wherein said first gas mixture circulates upwardly from below and said refrigerating liquid downwardly from above, with indirect contact with said first gas mixture through the entire first liquefaction system..]. .[.11. Process according to claim 1, wherein said first gas mixture is a natural gas containing methane; and said second gas mixture contains approximately 0-3% by volume of gas having a volatility which is at least equal to that of nitrogen, 20-32% by volume of methane, 34-44% by volume of ethane, 12-20% by volume of propane, 8-15% by volume of butanes, and 3-8% by volume of hydrocarbons heavier than the butanes..]. .[.12. Process according to claim 1 wherein at least one of the liquefaction products of said second liquefaction system is sub-cooled before being utilized as a refrigerating liquid in one of said liquefaction systems..]. .[.13. Process according to claim 1, wherein the first at least partially liquified gas mixture is subjected to expansion permitting to recover a gas having a low liquefaction point, before being subjected to a final cooling..]. .[.14. Apparatus adapted for liquefaction of gaseous mixtures comprising: 
     
        .[.  .  Apparatus according to claim 14 wherein the heat exchange systems comprise internal piping adapted for the circulation of said refrigerating liquids by gravity..]. .[.16. Apparatus according to claim 14, wherein an expansion and separation means for gas and liquid is interposed in said first exchange system on the path followed by the first gas mixture..]. .Iadd. 17. A process for totally liquefying a gaseous methane-rich feed stream comprising the steps of: a. supplying said methane-rich feed stream at a superatmospheric pressure and precooling said stream,   b. providing a multicomponent refrigerant,   c. compressing said multicomponent refrigerant to a superatmospheric pressure,   d. cooling said multicomponent refrigerant and phase separating a single vapor fraction and a single liquid fraction from said cooled multicomponent refrigerant,   e. subcooling said liquid fraction in heat exchange with itself after expansion to form a first subcooled liquid fraction,   f. liquefying and subcooling all of said vapor fraction in heat exchange with said first subcooled liquid fraction, and with itself after expansion, to form a second subcooled liquid fraction, and   g. totally liquefying said precooled methane-rich feed stream by further cooling said precooled methane-rich feed stream to at least its liquefaction temperature, at the superatmospheric pressure thereof, solely by progressive heat exchange steps with said first and second subcooled liquid fractions undergoing vaporization, said methane-rich feed stream and said multicomponent refrigerant being in indirect heat exchange with each other throughout the process. .Iaddend.     
     
     
        .Iadd. 18.  The process as claimed in claim 17, wherein both of said vaporized liquid fractions are recycled for recompression to said superatmospheric pressure. .Iaddend..Iadd. 19. The process as claimed in claim 18, wherein said totally liquefied methane-rich feed stream is expanded. .Iadd. 20. The process as claimed in claim 17, further including the step of maintaining a multicomponent refrigerant composition comprising   ______________________________________                                    
                    % by volume                                           
______________________________________                                    
N.sub.2 and more highly volatile gases                                    
                      0-3                                                 
methane               20-32                                               
ethane                34-44                                               
propane               12-20                                               
butanes                8-15                                               
pentanes and heavier fluids                                               
                      3-8                                                 
______________________________________                                    
  .Iadd. 21. The process as claimed in claim 17, wherein said
 multicomponent refrigerant is compressed to a superatmospheric pressure
 between about 31 and about 50 bars. .Iaddend..Iadd. 22. A process for
 liquefying the major portion of a gaseous, methane-rich feed stream
 comprising the steps of
     a. supplying said methane-rich feed stream at a superatmospheric pressure and precooling said stream,   b. providing a multicomponent refrigerant at a superatmospheric pressure,   c. cooling said multicomponent refrigerant and phase separating a single vapor fraction and a single liquid fraction from said cooled multicomponent refrigerant,   d. subcooling said liquid fraction in heat exchange with itself after expansion to form a first subcooled liquid fraction,   e. liquefying and subcooling all of said vapor fraction in heat exchange with said first subcooled liquid fraction, and with itself after expansion, to form a second subcooled liquid fraction, and   f. liquefying at least the major portion of said methane-rich feed stream by further cooling said precooled methane-rich feed stream to a temperature below about -143° C. solely by progressive heat exchange with said first and second subcooled liquid fractions undergoing vaporization, said methane-rich feed stream and said multicomponent refrigerant being in indirect heat exchange with each other throughout the process. .Iaddend. .Iadd. 23. The process as claimed in claim 22, wherein both of said vaporized liquid fractions are recycled for recompression to said superatmospheric pressure. .Iaddend..Iadd. 24. The process as claimed in claim 23, wherein said liquefied methane-rich feed stream is expanded. .Iaddend. .Iadd. 25. The process as claimed in claim 22, wherein said multicomponent refrigerant is compressed to a superatmospheric pressure between about 31 and about 50 bars. .Iaddend. .Iadd. 26. A refrigeration system for totally liquefying a gaseous methane-rich feed stream at superatmospheric pressure comprising in combination     a. a first multi-stage heat exchanger means connected to said free stream for precooling said feed stream,   b. means for supplying a multicomponent refrigerant,   c. a compressor for compressing said multicomponent refrigerant to a superatmospheric pressure,   d. a second multi-stage heat exchanger means for cooling and for partially condensing said multicomponent refrigerant,   e. a phase separator connected to said second multi-stage heat exchanger means for separating said partially condensed multicomponent refrigerant into a vapor fraction and a condensed liquid fraction,   f. third heat exchange means connected to said phase separator and including expansion means for subcooling said condensed liquid fraction in heat exchange with itself, after expansion in said expansion means, to form a first subcooled liquid fraction,   g. fourth heat exchanger means connected to said phase separator means and including expansion means for liquefying and subcooling said vapor fraction in heat exchange with said first subcooled liquid fraction, and with itself after expansion in said expansion means, to form a second subcooled liquid fraction, and   h. fifth heat exchanger means for further cooling said precooled stream to at least its liquefaction temperature, at the superatmospheric pressure thereof, and totally liquefying said precooled feed stream by passing said feed stream in heat exchange with said first subcooled liquid fraction undergoing vaporization and then in heat exchange with said second subcooled liquid fraction undergoing vaporization, said methane-rich feed stream and said multicomponent refrigerant being in indirect heat exchange with each other throughout the process. .Iaddend. .Iadd. 27. A refrigeration system as claimed in claim 26 further including conduit means connected to said fifth heat exchanger means and to said compressor for returning said vaporized first and second fractions to said compressor as said multicomponent refrigerant. .Iaddend..Iadd. 28. A refrigeration system as claimed in claim 27 further including conduit means connected to said fifth heat exchanger means for withdrawing said totally liquefied feed stream from said fifth heat exchanger means. .Iaddend..Iadd. 29. A refrigeration system as claimed in claim 28 including expansion means in said conduit means for expanding said totally liquefied feed stream. .Iaddend. .Iadd. 30. A refrigeration system for liquefying the major portion of a gaseous methane-rich feed stream at a superatmospheric pressure comprising in combination     a. a first multi-stage heat exchanger means for precooling said feed stream,   b. means for supplying a multicomponent refrigerant,   c. a compressor for compressing said multicomponent refrigerant to a superatmospheric pressure,   d. a second multi-stage heat exchanger means for cooling and to partially condense said multicomponent refrigerant,   e. a phase separator connected to said second multistage heat exchanger means for separating said partially condensed multicomponent refrigerant into a single vapor fraction and a single condensed fraction,   f. third heat exchanger means connected to said separator and including expansion means for subcooling said condensed liquid fraction in heat exchange with itself, after expansion in said expansion means, to form a first subcooled liquid fraction,   g. fourth heat exchanger means connected to said separator and including expansion means for liquefying and subcooling said vapor fraction in heat exchange with said first subcooled liquid fraction, and with itself, after expansion in said expansion means, to form a second subcooled liquid fraction, and   h. fifth heat exchanger means connected to said first heat exchanger means for further cooling said feed stream to at least -143° C. solely by heat exchange with said first and second subcooled liquid fractions undergoing vaporization, said methane-rich feed stream and said multicomponent refrigerant being in indirect heat exchange with each other throughout said system. .Iaddend.     
     
     
        .Iadd. 31.  A refrigeration system as claimed in claim 30 including passage means connected to said fifth heat exchanger means for returning said vaporized fractions to said compressor. .Iaddend..Iadd. 32. A refrigeration system as claimed in claim 31 including expansion means connected to said fifth heat exchanger means for reducing the pressure of said cooled feed stream to a reduced pressure. .Iaddend. .Iadd. 33. A refrigeration system for liquefying the major portion of a methane-rich feed stream comprising the combination a. means supplying a multicomponent refrigerant including one component having a boiling point substantially below that of methane,   b. first heat exchanger means for precooling and partially condensing a substantial portion of said multicomponent refrigerant,   c. a phase separator connected to said first heat exchanger means for separating said partially condensed multicomponent refrigerant into a vapor fraction and a condensed liquid fraction,   d. second heat exchanger means connected to said separator for subcooling said condensed liquid fraction in heat exchange with itself after expansion to form a first subcooled liquid fraction,   e. third heat exchanger means connected to said separator for liquefying and subcooling said vapor fraction in heat exchange with said first subcooled liquid fraction, and with itself after expansion, to form a second subcooled liquid fraction, and   f. fourth heat exchanger means for liquefying the major portion of said precooled feed stream in heat exchange with said first and second subcooled liquid fractions undergoing vaporization, said methane-rich feed stream and said multicomponent refrigerant being in indirect heat exchange with each other throughout the process.     
     
     
        .Iaddend..Iadd. 34.  In a refrigeration process wherein a multicomponent refrigerant is in indirect heat exchange throughout the process with a methane-rich feed stream and is partially condensed to form a single vapor fraction and a single liquid fraction, the improvement which comprises a. subcooling said liquid fraction in heat exchange with itself after expansion to form a first subcooled liquid fraction, and   b. liquefying and subcooling all of said vapor fraction in heat exchange with said first subcooled liquid fraction, and with itself after expansion, to form a second subcooled liquid fraction. .Iaddend.