Absorption process for hydrogen and ethylene recovery

In a process for recovering substantially all ethylene and heavier hydrocarbons and a selected proportion of hydrogen within a gas stream selected from the group consisting of refinery off-gases and cracked hydrocarbon gases containing said ethylene and heavier hydrocarbons and said hydrogen, said gas stream having been sweetened, compressed, and dehydrated, the improvement comprising:

• A. feeding said gas stream to an intercooled and reboiled demethanizing absorber which produces an overhead stream and a rich solvent bottom stream;
• B. selectively splitting said overhead stream of Step A into a hydrogen portion stream which is fed to a methane absorber and a fuel portion stream which is fed to an auto refrigerated recovery unit;
• C. feeding said rich solvent bottom stream of Step A to a solvent regenerator which produces an overhead stream of said ethylene and heavier hydrocarbons and a bottom stream of lean solvent;
• D. selectively splitting said bottom stream of Step C into a methane portion stream which is fed to said methane absorber and an ethylene portion stream which is fed to said demethanizing absorber;
• E. producing from said methane absorber an overhead stream containing said selected proportion of hydrogen and a rich solvent bottom stream;
• F. selectively splitting said rich solvent bottom stream of Step E into an absorber portion stream which is fed to said demethanizing absorber and a stripper portion stream which is fed to a methane stripper;
• G. producing from said methane stripper an overhead stream which is fed to said auto refrigerated recovery unit and a bottom stream which is fed to said methane absorber;
• H. producing from said auto refrigerated recovery unit a stream of fuel gases, a recovered solvent stream which is recycled to said demethanizing absorber, and a stream of ethylene and heavier hydrocarbons;
• and
• I. combining said overhead stream of said ethylene and heavier hydrocarbons of Step C with said stream of said ethylene and heavier hydrocarbons of Step H to form an ethylene and heavier product stream.

A process for recovery of up to 100% of the hydrogen and substantially all of the ethylene and heavier hydrocarbons from a cooled, sweetened, and compressed hydrocarbon gas stream containing hydrogen, methane, carbon monoxide, ethane, ethylene, acetylene, and the C.sub.3 and heavier hydrocarbons characteristic of an ethylene plant cracked gas and/or a refinery off-gas stream, said stream having been additionally pretreated through a heat-pumped front-end deethanizer or depropanizer and selectively catalytically hydrogenated to significantly reduce the acetylene and diolefins content thereof and then dehydrated, said process comprising:

• A. feeding said gas stream to an intercooled and reboiled demethanizing absorber and producing therefrom a bottom stream of rich solvent containing most of said ethylene and heavier hydrocarbons present in said treated gas stream and an overhead stream containing said hydrogen, said methane, said carbon monoxide, and the remainder of said ethylene and heavier hydrocarbons;
• B. feeding said rich solvent bottom stream of Step A to a solvent regenerator and obtaining therefrom a bottom stream of lean solvent and an overhead hydrocarbon stream of said ethylene and heavier hydrocarbons;
• C. selectively splitting said overhead stream of Step A into a hydrogen portion stream and a fuel portion stream;
• D. feeding said hydrogen portion stream to a methane absorber and feeding said fuel portion stream to an auto refrigerated recovery unit;
• E. producing from said methane absorber a hydrogen product overhead stream and a rich solvent bottom stream;
• F. selectively splitting said rich solvent bottom stream of Step E into an absorber portion stream and a stripper portion stream;
• G. feeding said absorber portion stream to said demethanizing absorber and feeding said stripper portion stream to a methane stripper;
• H. producing from said methane stripper an overhead stream which is fed to said auto refrigerated recovery unit and a bottom stream which is fed to said methane absorber;
• I. producing from said auto refrigerated recovery unit a fuel gas stream of hydrogen, methane, and carbon monoxide having less than 0.5 mol % of said ethylene in said treated gas stream, a recovered solvent stream which is recycled to said demethanizing absorber, and a stream containing substantially all of said remainder of ethylene and heavier hydrocarbons;
• J. combining said ethylene and heavier hydrocarbons stream of Step I with said overhead hydrocarbon stream of Step B to form an ethylene and heavier product stream;
• K. selectively splitting said lean solvent bottom stream of Step B into a methane portion stream and an ethylene portion stream;
• and
• L. feeding said ethylene portion stream of Step K to said demethanizing absorber and feeding said methane portion stream of Step K to said methane absorber.

A process for recovering up to 50 per cent of the hydrogen and substantially all of the olefins from a sweetened, compressed, and dried hydrocarbon gas stream containing hydrogen, methane, carbon monoxide, ethane, ethylene, acetylene, and the C.sub.3 and heavier hydrocarbons characteristic of an ethylene plant cracked gas and/or a refinery off-gas stream, said process comprising:

• A. feeding said gas stream to an intercooled and reboiled demethanizing absorber and producing therefrom a bottom stream of rich solvent containing most of said ethylene and heavier hydrocarbons present in said treated gas stream and an overhead stream containing said hydrogen, said methane, said carbon monoxide, and the remainder of said ethylene and heavier hydrocarbons;
• B. selectively splitting said overhead stream into a hydrogen portion stream and a fuel portion stream;
• C. feeding said hydrogen portion stream to a methane absorber and feeding said fuel portion stream to an auto refrigerated recovery unit and producing therefrom a fuel gas stream of hydrogen, methane, and carbon monoxide having less than 0.5 mol % of said ethylene, a recovered stream of lean solvent which is recycled to said demethanizing absorber, and a stream containing substantially all of said ethylene and heavier hydrocarbons in said fuel portion stream;
• D. feeding said rich solvent bottom of Step A to a solvent regenerator and obtaining therefrom a bottom stream of lean solvent which is fed to said methane absorber and an overhead hydrocarbon stream of said ethylene and heavier hydrocarbons;
• E. combining said product stream of Step C with said overhead hydrocarbon stream of Step D to form an ethylene and heavier product stream;
• F. producing a hydrogen product overhead stream and a rich solvent bottom stream from said methane absorber;
• and
• G. feeding said rich solvent bottom stream of Step F to the top of said demethanizing absorber.

A process for recovering from 20% to 100% of the hydrogen and substantially all of the ethylene from a sweetened, compressed, and dried hydrocarbon gas stream containing hydrogen, methane, carbon monoxide, ethylene, ethane, acetylene, and the C.sub.3 and heavier hydrocarbons characteristic of an ethylene plant cracked gas and/or a refinery off-gas, said process comprising:

• A. feeding said treated gas stream to an intercooled and reboiled demethanizing absorber and producing therefrom a bottom stream of rich solvent containing most of said ethylene and heavier hydrocarbons present in said treated gas stream and an overhead stream containing said hydrogen, said methane, said carbon monoxide, and the remainder of said ethylene and heavier hydrocarbons;
• B. feeding all of said overhead stream to a methane absorber which produces an overhead stream as hydrogen product and a rich solvent bottom stream;
• C. splitting said rich solvent stream of Step B into an absorber portion stream and a stripper portion stream;
• D. feeding said stripper portion stream to a methane stripper which produces an overhead stream and a bottom stream;
• E. feeding said bottom stream of Step D to said methane absorber and feeding said overhead stream of Step D to an auto refrigerated recovery unit which is internally refrigerated and producing therefrom a fuel gas stream of methane and carbon monoxide having less than about 0.5 mol % of said ethylene, a stream containing substantially all of the remainder of said ethylene and heavier hydrocarbons, and a stream of recovered solvent which is recycled to said demethanizing absorber;
• F. feeding said rich solvent bottom stream of Step A to a solvent regenerator and obtaining therefrom a bottom stream of lean solvent which is recycled to the top of said methane absorber and an overhead stream of said ethylene and heavier hydrocarbons;
• and
• G. combining said overhead hydrocarbon stream of Step F with said stream of Step E containing substantially all of the remainder of said ethylene and heavier hydrocarbons to form a combined ethylene and heavier product stream.