Process for LPG recovery

Abstract

An improved process is described for the separation and recovery of substantially all the propane and heavier hydrocarbon components in a hydrocarbon gaseous feedstream. In this process, the vapor stream from a deethanizer is cooled to liquefaction and contacted with a vapor phase from the hydrocarbon gaseous feedstream. The contact takes place within a direct heat exchanger, and the resulting vapor fraction, which is essentially ethane and methane, is the gaseous product of the process.

We claim: 
     
       1. In a process for separating propane and heavier hydrocarbons from a gaseous feedstream containing hydrocarbon components of different boiling points wherein said feedstream is cooled and separated into a first vapor fraction and a first liquid fraction and said first liquid fraction is distilled in a deethanizer to form a second vapor fraction and a second liquid fraction, the improvement which comprises .[.expanding and.]. transferring said first vapor fraction to the lower portion of a direct heat exchanger, cooling .Iadd.at least a portion of .Iaddend.said second vapor fraction .Iadd.by passing it through an indirect heat exchanger .Iaddend.to form a substantially liquefied stream, .Iadd.partially flashing at least a portion of said liquefied stream and transferring .[.at least a portion of said liquefied stream.]. .Iadd.it .Iaddend.to the upper portion of said direct heat exchanger whereby said liquefied stream contacts said first vapor fraction to form a third vapor fraction and a third liquid fraction, .[.returning.]. .Iadd.transferring .Iaddend.said third liquid fraction to said deethanizer, .[.and.].  removing said third vapor fraction from said direct heat exchanger .Iadd.and passing said third vapor fraction through said indirect heat exchanger. .Iaddend. 
     
     
       2. A process as described in claim 1 wherein said direct heat exchanger is a packed column. 
     
     
       3. A process as described in claim 1 wherein said direct heat exchanger is a tray column. 
     
     
       4. A process as described in claim 1, .[.wherein.]. .Iadd.further comprising expanding .Iaddend.said first vapor fraction .[.is expanded.]. in a turboexpander .Iadd.prior to transferring it to the lower portion of said direct heat exchanger. .Iaddend. .[.5. A process as described in claim 1 further comprising partially flashing said liquefied stream prior 
     
     
        to transferring it to said direct heat exchanger..]. 6. A process for separating propane and heavier hydrocarbons from a gaseous feedstream containing hydrocarbon components of different boiling points which comprises: (a) cooling and separating said feedstream into a first vapor fraction and a first liquid fraction;   (b) distilling said first liquid fraction .[.is.]. .Iadd.in .Iaddend.a deethanizer to form a second vapor fraction and a second liquid fraction;   (c) removing said second liquid fraction from said deethanizer as a liquid product;   (d) .[.expanding said first vapor fraction and.]. transferring .[.it.]. .Iadd.said first vapor fraction .Iaddend.to the lower portion of a direct heat exchanger;   (e) cooling said second vapor fraction to form a third vapor fraction and a third liquid fraction;   (f) returning at least a portion of said third liquid fraction to said deethanizer as reflux;   (g) .[.further.]. cooling said third vapor fraction to form a .[.substantially liquefied.]. stream .Iadd.which is at least partially liquefied.Iaddend.;   (h) .[.transferring.]. .Iadd.partially flashing at least a portion of .Iaddend.said liquefied stream .Iadd.and transferring it .Iaddend.to the upper portion of said direct heat exchanger whereby said liquefied stream contacts said first vapor fraction to form a fourth vapor fraction and a fourth liquid fraction;   (i) removing said fourth vapor fraction from said direct heat exchanger .[.as a gaseous product.].; and   (j) .[.returning.]. .Iadd.transferring .Iaddend.said fourth liquid fraction   
     
     
        to said deethanizer. 7. A process as described in claim 6 wherein said 
     
     
        direct heat exchanger is a packed column. 8. A process as described in 
     
     
        claim 6 wherein said direct heat exchanger is a tray column. 9. A process as described in claim 6 .[.wherein.]. .Iadd.further comprising expanding .Iaddend.said first vapor fraction .[.is expanded.]. in a turboexpander .Iadd.prior to transferring it to the lower portion of said direct heat exchanger.Iaddend.. .[.10. A process as described in claim 6 further comprising partially flashing said liquefied stream prior to transferring 
     
     
        it to said direct heat exchanger..]. 11. A process as described in claim 6 further comprising combining at least a portion of said third liquid fraction with said third vapor fraction prior to .[.further.]. cooling 
     
     
        said third vapor fraction. 12. A process as described in claim 6 further comprising transferring at least a portion of said third liquid fraction 
     
     
        to said direct heat exchanger. 13. A process for separating propane and heavier hydrocarbons from a gaseous feedstream containing hydrocarbon components of different boiling points which comprises: (a) cooling and separating said feedstream into a first vapor fraction and a first liquid fraction;   (b) distilling said first liquid fraction in a deethanizer to form a second vapor fraction and a second liquid fraction;   (c) removing said second liquid fraction from said deethanizer as a liquid product;   (d) .[.expanding said first vapor fraction and.]. transferring .[.it.]. .Iadd.said first vapor fraction .Iaddend.to the lower portion of a direct heat exchanger;   (e) cooling said second vapor fraction to form a third vapor fraction and a third liquid fraction;   (f) removing said third vapor fraction as a gaseous product;   (g) returning 171 at least.]. a .Iadd.first .Iaddend.portion of said third liquid fraction to said deethanizer as reflux;   (h) .[.transferring at least.]. .Iadd.partially flashing .Iaddend.a .Iadd.second .Iaddend.portion of said third liquid fraction .Iadd.and transferring it .Iaddend.to the upper portion of said direct heat exchanger whereby said .Iadd.second portion of said .Iaddend.third liquid fraction contacts said first vapor fraction to form a fourth vapor fraction and a fourth liquid fraction;   (i) removing said fourth vapor fraction from said direct heat exchanger .[.as a gaseous product.].; and   
     
     
       (j) transferring said fourth liquid fraction to said deethanizer. 14. A process as described in claim 13 wherein said direct heat exchanger is a 
     
     
        packed column. 15. A process as described in claim 13 wherein said direct 
     
     
        heat exchanger is a tray column. 16. A process as described in claim 13 .[.wherein.]. .Iadd.further comprising expanding .Iaddend.said first vapor fraction .[.is expanded.]. in a turboexpander .Iadd.prior to transferring it to the lower portion of said direct heat exchanger.Iaddend.. .[.17. A process as described in claim 13 further comprising partially flashing said third liquid fraction prior to transferring it to said direct heat exchanger..]. .Iadd.18. The process as set forth in claim 1 wherein said second vapor fraction is cooled and separated into a fourth vapor fraction and a fourth liquid fraction upon removal from said distilling unit, said fourth vapor fraction constituting said portion of said second vapor 
     
     
        fraction. .Iaddend. .Iadd.19.  The process as set forth in claim 1 wherein said distilling unit is maintained at a substantially higher pressure than said direct heat exchanger. .Iaddend. .Iadd.20. The process as set forth in claim 18 wherein said distilling unit is maintained at a substantially higher pressure than said direct heat exchanger. .Iaddend. .Iadd.21. The process as set forth in claim 1 wherein said first vapor fraction and said first liquid fraction are passed through a separator prior to being transferred to said direct heat exchanger and said deethanizer, respectively. .Iaddend. .Iadd.22. The process as set forth in claim 6 wherein said deethanizer is maintained at a substantially higher pressure than said direct heat exchanger. .Iaddend. .Iadd.23. The process as set forth in claim 23 wherein said first vapor fraction and said first liquid fraction are passed through a separator prior to being transferred to said direct heat exchanger and said deethanizer, respectively. .Iaddend. .Iadd.24. The process as set forth in claim 22 wherein the step of cooling said third vapor fraction includes transferring heat from said third vapor 
     
     
        fraction to said fourth liquid fraction. .Iaddend. .Iadd.25.  The process as set forth in claim 13 wherein said deethanizer is maintained at a substantially higher pressure than said direct heat exchanger. .Iaddend. .Iadd.26. The process as set forth in claim 25 wherein said first vapor fraction and said first liquid fraction are passed through a separator prior to being transferred to said direct heat exchanger and said deethanizer, respectively. .Iaddend. .Iadd.27. A process for separating methane and ethane from the heavier components of a hydrocarbon feedstream, comprising the steps of: (a) separating said feedstream into a first vapor fraction and a first liquid fraction;   (b) transferring said first vapor fraction to a direct heat exchanger;   (c) transferring said first liquid fraction to a distilling unit;   (d) distilling the fluids introduced into said distilling unit to yield a second vapor fraction and a second liquid fraction;   (e) cooling and separating said second vapor fraction into a third layer fraction and a third liquid fraction;   (f) returning at least a portion of said third liquid fraction to said distilling unit;   (g) passing said third vapor fraction through an indirect heat exchanger to liquefy at least a portion of said third vapor fraction;   (h) decreasing the pressure of said at least partially liquefied third vapor fraction, whereby at least a portion of the liquid phase flashes;   (i) transferring said partially liquefied third vapor fraction to said direct heat exchanger whereby said partially liquefied third vapor fraction mixes with said first vapor fraction, yielding a fourth vapor fraction and fourth liquid fraction;   (j) transferring said fourth liquid fraction to said distilling unit whereby said fourth liquid fraction is distilled with said first liquid fraction; and,   (k) removing said fourth vapor fraction from said direct heat exchanger and passing it through said indirect heat exchanger to transfer heat from said   
     
     
        third vapor fraction to said fourth vapor fraction. .Iaddend. .Iadd.28. The process as set forth in claim 27 wherein said distilling unit is maintained at a substantially higher pressure than said indirect heat exchanger. .Iaddend. .Iadd.29. The process as set forth in claim 28 wherein said first vapor fraction is expanded in a turboexpander prior to transfer to said direct heat exchanger. .Iaddend. .Iadd.30. The process as set forth in claim 27 further comprising the step of transferring heat from said third vapor fraction to said fourth liquid fraction prior to 
     
     
        step (g). .Iaddend. .Iadd.31.  The process as set forth in claim 27 wherein said distilling unit is a deethanizer. .Iaddend. .Iadd.32. The process as set forth in claim 27 wherein said first vapor fraction and said first liquid fraction are passed through a separator prior to being transferred to said direct heat exchanger and said distilling unit, respectively. .Iaddend. .Iadd.33. A process for separating methane and ethane from the heavier components of a hydrocarbon feedstream, comprising the steps of: (a) separating said feedstream into a first vapor fraction and a first liquid fraction;   (b) transferring said first vapor fraction to a direct heat exchanger;   (c) transferring said first liquid fraction to a distilling unit;   (d) distilling the fluids introduced into said distilling unit to yield a second vapor fraction and a second liquid fraction;   (e) passing said second vapor fraction through a first indirect heat exchanger to cool it;   (f) separating said cooled second vapor fraction into a third vapor fraction and a third liquid fraction;   (g) returning at least a first portion of said third liquid fraction to said distilling unit;   (h) partially flashing a second portion of said third liquid fraction and transferring it to said direct heat exchanger whereby said partially flashed second portion of said third liquid fraction contacts said first vapor fraction to establish a fourth vapor fraction and a fourth liquid fraction;   (i) transferring said fourth liquid fraction to said distilling unit whereby said fourth liquid fraction is distilled with said first liquid fraction; and,   (j) removing said fourth vapor fraction from said direct heat exchanger and passing it through said indirect heat exchanger to transfer heat from said   
     
     
        second vapor fraction to said fourth vapor fraction. .Iaddend. .Iadd.34. The process as set forth in claim 33 wherein said distilling unit is maintained at a substantially higher pressure than said indirect heat exchanger. .Iaddend. .Iadd.35. The process as set forth in claim 34 wherein said first vapor fraction is expanded in a turboexpander prior to transfer to said direct heat exchanger. .Iaddend. .Iadd.36. The process as set forth in claim 33 wherein step (e) includes transferring heat from said second vapor fraction to said fourth liquid fraction. .Iaddend. .Iadd.37. The process as set forth in claim 33 wherein said distilling 
     
     
        unit is a deethanizer. .Iaddend. .Iadd.38.  The process as set forth in claim 33 wherein said third and fourth vapor fractions are removed as the gas product of the process and said second liquid fraction is removed as the liquid product of the process, said gas product being substantially free from propane and heavier hydrocarbons and said liquid product being substantially free from methane and ethane. .Iaddend. .Iadd.39. The process as set forth in claim 33 wherein said first vapor fraction and said first liquid fraction are passed through a separator prior to being transferred to said direct heat exchanger and said distilling unit, respectively. .Iaddend. .Iadd.40. A process for separating a hydrocarbon feedstream into a first portion predominantly composed of methane and ethane, and a second portion predominantly composed of propane and heavier hydrocarbons, said process comprising the steps of: (a) cooling and separating said feedstream into a first vapor fraction and a first liquid fraction;   (b) expanding said first vapor fraction and transferring it to a direct heat exchanger;   (c) transferring said first liquid fraction to a deethanizer, said deethanizer being effective to convert the fluids introduced therein into a second vapor fraction and a second liquid fraction, said deethanizer being maintained at a higher pressure than said direct heat exchanger;   (d) removing said second liquid fraction as a product predominantly composed of propane and heavier hydrocarbons;   (e) removing and cooling said second vapor fraction to yield a third vapor fraction and a third liquid fraction;   (f) returning at least a portion of said third liquid fraction to said deethanizer;   (g) passing said third vapor fraction through an indirect heat exchanger to remove heat from and liquefy at least a portion of said third vapor fraction;   (h) decreasing the pressure of said third vapor fraction to flash at least a portion of the liquefied gases within said third vapor fraction whereby said third vapor fraction is further cooled;   (i) introducing said third vapor fraction into said direct heat exchanger, whereby said third vapor fraction and said first vapor fraction come into contact to form a fourth vapor fraction and a fourth liquid fraction;   (j) removing said fourth vapor fraction as a product predominantly composed of methane and ethane;   (k) passing said fourth vapor fraction through said indirect heat exchanger to transfer heat from said third vapor fraction to said fourth vapor fraction; and   (l) transferring said fourth liquid fraction to said deethanizer. .Iaddend.   
     
     
        .Iadd.41.  The process as set forth in claim 40 wherein the expansion of 
     
     
        step (b) is conducted in a turboexpander. .Iaddend. .Iadd.42.  The process as set forth in claim 40 further including the step of passing said third vapor fraction and said fourth liquid fraction through a second indirect heat exchanger to transfer heat from said third vapor fraction to said fourth liquid fraction. .Iaddend. .Iadd.43. The process as set forth in claim 40 wherein said first vapor fraction and said first liquid fraction are passed through a separator prior to being transferred to said direct heat exchanger and said deethanizer, respectively. .Iaddend. .Iadd.44. The process as set forth in claim 40 wherein at least a portion of said third liquid fraction is added to said third vapor fraction prior to passing said third vapor fraction through said indirect heat exchanger.