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

Abstract

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.

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, wherin 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 first 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: (a) a first indirect heat exchange system for counterflow of a first gas mixture and a refrigerating liquid, said first exchange system comprising a plurality of feed conduits for said refrigerating liquid arranged along said first exchange system and an outlet conduit for vaporized refrigerating liquid, inlet means at one end for said first gas mixture and outlet means at the opposite end for liquified first gas mixture;   (b) a second indirect heat exchange system for counterflow comprising a refrigerating liquid feed pipe system and outlet means for vaporized refrigerating liquid, on one side, inlet means at one end for a second gas mixture and a plurality of outlet conduits for partial condensates of said second gas mixture occurring through stepwise liquefaction, on the other side;   (c) means for compressing vapors of the refrigerating liquids issued from said first and said second exchange system, and means for passing the resulting compressed vapors into said second exchange system as a second gas mixture; and   (d) conduits for passing condensates resulting from the stepwise liquefaction of said second gas mixture toward the corresponding inlet means in refrigerating liquid of the two exchange systems through respective expansion means flowing the first gaseous mixture through the first liquefaction system out of contact with the fluid in the second liquefaction system throughout the process, and means for maintaining the vapor pressure of the refrigerating liquid in the first indirect heat exchange system at a lower pressure than the vaporizing pressure of the refrigerating liquid in said second indirect heat exchange system.   
     
     
       15. 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.