Process and apparatus for the cryogenic separation of air

Abstract

Air is separated in a cryogenic distillation system operating a dual reboiler/condenser cycle. Refrigeration for the system is usually provided by expanding a process stream. In the present invention, refrigeration is provided by introducing from an external source at least one refrigerant.

1 . A process for cryogenically separating air in a cryogenic distillation system comprising a higher pressure (“HP”) distillation column and a lower pressure (“LP”) distillation column, a first reboiler/condenser, a second reboiler/condenser and heat exchange means, said process comprising: 
 separating feed air in the HP column into nitrogen-rich overhead vapour and crude liquid oxygen (“CLOX”);    separating at least a portion of said CLOX or crude oxygen vapour derived therefrom in the LP column to produce nitrogen overhead vapour and liquid oxygen (“LOX”);    at least partially condensing air by indirect heat exchange against LOX in said first reboiler/condenser to produce oxygen vapour and at least partially condensed air;    at least partially condensing at least a portion of said nitrogen-rich overhead vapour by indirect heat exchange against an oxygen-rich liquid in said second reboiler/condenser to produce oxygen-rich vapour and at least partially condensed nitrogen-rich overhead vapour;    vaporising LOX from said LP column by indirect heat exchange against compressed air in said heat exchange means to produce gaseous oxygen (“GOX”) and cooled compressed air; and    using at least a portion of said at least partially condensed nitrogen-rich overhead vapour and/or at least a portion of said at least partially condensed air as reflux in the distillation system;    wherein the required refrigeration duty for the process is provided by introducing into the distillation system from an external source at least one refrigerant.    
     
     
         2 . The process according to  claim 1 , wherein the or at least one refrigerant is selected from liquid nitrogen (“LIN”) or LOX.  
     
     
         3 . The process according to  claim 1 , wherein the or at least one refrigerant is LOX.  
     
     
         4 . The process according to  claim 3 , wherein at least a portion of the required refrigeration duty for the process is provided by feeding LOX from an external source to the sump of the LP column.  
     
     
         5 . The process according to  claim 1 , wherein at least a portion of the required refrigeration duty for the process is provided by vaporising LOX from an external source by indirect heat exchange against compressed air in the heat exchange means to produce cooled compressed air and vaporised LOX refrigerant.  
     
     
         6 . The process according to  claim 5  further comprising combining at least a portion of said vaporised LOX refrigerant with said GOX produced by vaporising LOX from the LP column to produce combined GOX product.  
     
     
         7 . The process according to  claim 1  wherein the or at least one refrigerant is LIN.  
     
     
         8 . The process according to  claim 7 , wherein LIN from an external source is introduced into the distillation system at a location having high nitrogen concentration.  
     
     
         9 . The process according to  claim 7 , wherein LIN from an external source is introduced into the distillation system at the top of the LP column.  
     
     
         10 . The process according to  claim 7 , wherein LIN from an external source is introduced into the distillation system at the top of the HP column.  
     
     
         11 . The process according to  claim 1 , wherein the first reboiler/condenser is located in the sump of the LP column, said process comprising at least partially condensing air by indirect heat exchange against LOX produced in the LP column to produce said oxygen vapour and said at least partially condensed air.  
     
     
         12 . The process according to  claim 1  wherein the second reboiler/condenser is located at an intermediate location in the LP column, said process comprising at least partially condensing said nitrogen-rich overhead vapour by indirect heat exchange against oxygen-rich liquid descending the LP column to produce said oxygen-rich vapour and said at least partially condensed nitrogen-rich overhead vapour.  
     
     
         13 . The process according to  claim 1 , wherein the second reboiler/condenser is located outside the LP column, said process comprising at least partially condensing said nitrogen-rich overhead vapour by indirect heat exchange against CLOX produced in the HP column to produce said crude oxygen vapour and said at least partially condensed nitrogen-rich overhead vapour.  
     
     
         14 . The process according to  claim 1 , wherein said feed air comprises at least a portion of said cooled compressed air.  
     
     
         15 . The process according to  claim 1 , wherein said feed air comprises at least a portion of said at least partially condensed air.  
     
     
         16 . The process according to  claim 1  for the production of GOX.  
     
     
         17 . The process according to  claim 1  wherein GOX is produced having a purity from about 80 to about 98 vol %.  
     
     
         18 . The process according to  claim 1  wherein GOX is produced at a pressure of from about 0.15 MPa to about 0.5 MPa.  
     
     
         19 . The process according to  claim 1  wherein there is no expansion of a process stream to provide refrigeration.  
     
     
         20 . The process according to  claim 1  comprising using at least partially condensed air as reflux to the HP column and/or the LP column.  
     
     
         21 . The process according to  claim 1  comprising using condensed nitrogen-rich overhead vapour as reflux at the top of the HP column.  
     
     
         22 . Apparatus for cryogenically separating air comprising: 
 an HP distillation column for separating feed air into nitrogen-rich overhead vapour and CLOX;    an LP distillation column in fluid flow communication with said HP column for separating at least a portion of said CLOX or crude oxygen vapour derived therefrom to produce nitrogen overhead vapour and LOX;    a first reboiler/condenser for at least partially condensing air by indirect heat exchange against LOX to produce oxygen vapour and at least partially condensed air;    a second reboiler/condenser in fluid flow communication with said HP column for at least partially condensing at least a portion of said nitrogen-rich overhead vapour by indirect heat exchange against an oxygen-rich liquid to produce oxygen-rich vapour and at least partially condensed nitrogen-rich overhead vapour;    heat exchange means in fluid flow communication with said LP column for vaporising LOX from said LP column by indirect heat exchange against compressed air to produce GOX and cooled compressed air;    at least one reflux conduit means in fluid flow communication with said HP column and/or said LP column for feeding at least a portion of said at least partially condensed air and/or at least a portion of said at least partially condensed nitrogen-rich overhead vapour as reflux to the distillation system; and    at least one refrigerant conduit means in fluid flow communication with said distillation system for introducing into said distillation system from an external source at least one refrigerant,    wherein the apparatus is without an expansion turbine to expand a process stream to provide refrigeration.    
     
     
         23 . Apparatus according to  claim 22  wherein the or at least one refrigerant conduit means is adapted to carry LOX and is in fluid flow communication with the sump of the LP column.  
     
     
         24 . Apparatus according to  claim 22  wherein the or at least one refrigerant conduit means is adapted to carry LOX and is in fluid flow communication with the cold end of the heat exchange means.  
     
     
         25 . Apparatus according to  claim 24  further comprising GOX conduit means for combining said GOX produced by vaporising LOX from the LP column and GOX produced by vaporising said LOX refrigerant.  
     
     
         26 . Apparatus according to  claim 22  wherein the or at least one refrigerant conduit means is adapted to carry LIN and is in fluid flow communication with a location of the distillation system having high nitrogen concentration.  
     
     
         27 . Apparatus according to  claim 26  wherein the or at least one refrigeration conduit means is in fluid flow communication with the top of the LP column.  
     
     
         28 . Apparatus according to  claim 26  wherein the or at least one refrigeration conduit means is in fluid flow communication with the top of the HP column.  
     
     
         29 . Apparatus according to  claim 22  wherein the first reboiler/condenser is located in the sump of said LP column.  
     
     
         30 . Apparatus according to  claim 22  wherein the second reboiler/condenser is located at an intermediate location in said LP column.  
     
     
         31 . Apparatus according to  claim 22  wherein the second reboiler/condenser is located outside said LP column.  
     
     
         32 . Apparatus according to  claim 31  further comprising conduit means for feeding crude oxygen vapour from said second reboiler/condenser to said LP column.  
     
     
         33 . Apparatus according to  claim 22  further comprising conduit means for feeding at least a portion of said partially condensed air as feed air to said HP column.  
     
     
         34 . Apparatus according to  claim 22  further comprising conduit means for feeding at least a portion of said cooled compressed air as feed air to said HP column.