Separation sequence for hydrocarbons from a gentle thermal cleavage

1. A method for separating hydrocarbons generated from a hydrocarbonaceous feed by cleavage, wherein said method comprises:

compressing ( 2 a ) and drying ( 5 a , 5 b ) a raw gas ( 1 ) from the cleavage of said hydrocarbonaceous feed, said raw gas ( 1 ) containing gaseous hydrocarbons,

introducing said raw gas ( 1 ) into a front end C3/C4 separation stage,

separating the raw gas ( 1 ) in said front end C3/C4 separation stage into a hydrocarbon fraction of hydrocarbons having a maximum of 3 carbon atoms ( 15 ) and a hydrocarbon fraction of hydrocarbons having at least 4 carbon atoms ( 17 ), said front end C3/C4 separation stage comprises a C4 separator ( 6 ), a depropanizer ( 8 ), and a C2/C4 separation stage ( 7 ),

removing a bottom product stream from said C4 separator ( 6 ) and introducing said bottom product stream into said C2/C4 separation stage ( 7 ), and

removing a liquid stream ( 18 ) from said C2/C4 separation stage ( 7 ) and introducing said liquid stream into said depropanizer ( 8 ),

wherein said hydrocarbon fraction of hydrocarbons having a maximum of 3 carbon atoms is obtained as a gaseous overhead product ( 15 ) from said C4 separator ( 6 ),

wherein said hydrocarbon fraction of hydrocarbons having at least 4 carbon atoms is obtained as a bottom liquid product ( 17 ) from said depropanizer ( 8 ), and

wherein said C2/C4 separation stage ( 7 ) is operated at a higher pressure than said C4 separator ( 6 ).

2. The method as claimed in claim 1 , wherein said C2/C4 separation stage ( 7 ) is a C2/C4 separation column ( 7 ), and said C4 separator ( 6 ) and said C2/C4 separation column ( 7 ) are operated at a pressure between 18 bar and 20 bar.

3. The method as claimed in claim 1 , wherein said C4 separator ( 6 ) and said C2/C4 separation stage ( 7 ) are combined in one column.

4. The method as claimed in claim 3 , further comprising

removing an overhead stream from said C2/C4 separation stage ( 7 ) and introducing said overhead stream into said C4 separator ( 6 ).

5. The method as claimed in claim 4 , wherein said C2/C4 separation stage ( 7 ) has a top condenser.

6. The method as claimed claim 1 , wherein said C4 separator ( 6 ) and said C2/C4 separation stage ( 7 ) are different columns.

7. The method as claimed in claim 6 , further comprising

removing an overhead stream from said C2/C4 separation stage ( 7 ) and introducing said overhead stream into said C4 separator ( 6 ).

8. The method as claimed in claim 7 , wherein said C2/C4 separation stage ( 7 ) has a top condenser.

9. The method as claimed in claim 1 , wherein said depropanizer ( 8 ) is operated at a pressure between 10 bar and 12 bar.

10. The method as claimed in claim 1 , wherein said raw gas ( 1 ) contains ethylene and propylene at an ethylene to propylene weight ratio of 1.5 or less than 1.

11. The method as claimed in claim 1 , wherein the cleavage is performed under conditions to achieve a propylene to ethylene ratio from 0.65 to 1.5 kg/kg.

12. The method as claimed in claim 1 , wherein the cleavage is performed under conditions to achieve a propylene to ethylene ratio from 0.7 to 1.3 kg/kg.

13. The method as claimed in claim 1 , wherein the cleavage is performed under conditions to achieve a propylene to ethylene ratio from 0.8 to 1.2 kg/kg.

14. The method as claimed in claim 1 , further comprising,

after said compressing ( 2 a ) of the raw gas and prior to said drying ( 5 a , 5 b ) of the raw gas, subjecting said raw gas to a precooling stage,

removing a condensate and overhead gas from said precooling and separately sending said condensate and overhead gas to said drying ( 5 a , 5 b ), and

thereafter sending said overhead gas to said C4 separator ( 6 ), and sending said condensate to said C2/C4 separation stage ( 7 ).

15. The method as claimed in claim 14 , further comprising

removing an overhead stream from said C2/C4 separation stage ( 7 ) and introducing said overhead stream into said C4 separator ( 6 ).

16. The method as claimed in claim 1 , further comprising

removing an overhead stream from said C2/C4 separation stage ( 7 ) and introducing said overhead stream into said C4 separator ( 6 ).

17. A method for separating hydrocarbons generated from a hydrocarbonaceous feed by cleavage, wherein said method comprises:

compressing ( 2 a ) and drying ( 5 a , 5 b ) a raw gas ( 1 ) from the cleavage of said hydrocarbonaceous feed, said raw gas ( 1 ) containing gaseous hydrocarbons,

introducing said raw gas ( 1 ) into a front end C3/C4 separation stage, and

separating the raw gas ( 1 ) in said front end C3/C4 separation stage into a hydrocarbon fraction of hydrocarbons having a maximum of 3 carbon atoms ( 15 ) and a hydrocarbon fraction of hydrocarbons having at least 4 carbon atoms ( 17 ),

wherein the front end C3/C4 separation stage comprises a C4 separator ( 6 ) and a depropanizer ( 8 ),

wherein said hydrocarbon fraction of hydrocarbons having a maximum of 3 carbon atoms is obtained as a gaseous overhead product ( 15 ) from said C4 separator ( 6 ),

wherein said hydrocarbon fraction of hydrocarbons having at least 4 carbon atoms is obtained as a bottom liquid product ( 17 ) from said depropanizer ( 8 ),

wherein the front end C3/C4 separation stage further comprises a C2/C4 separation stage ( 7 ),

wherein the C2/C4 separation stage ( 7 ) is arranged between said C4 separator ( 6 ) and said depropanizer ( 8 ), and wherein a stream from a bottom region of said C4 separator ( 6 ) is introduced into said C2/C4 separation stage ( 7 ), and a stream from a bottom region of said C2/C4 separation stage ( 7 ) is introduced into said depropanizer ( 8 ), and

wherein said C2/C4 separation stage ( 7 ) is operated at a higher pressure than said C4 separator ( 6 ).