Multiple reflux stream hydrocarbon recovery process

Abstract

Systems herein separate an inlet gas stream containing methane, C2 components, C3 components and optionally heavier hydrocarbons into a volatile gas fraction containing methane and a less volatile hydrocarbon fraction containing C2+ components. The system may include piping, valving, and controls configured to flexibly allow the system to operate in a high ethane recovery mode, a high throughput mode, or in some embodiments, a high propane recovery mode.

What is claimed: 
     
         1 . A system for separating an inlet gas stream containing methane, C2 components, C3 components and optionally heavier hydrocarbons into a volatile gas fraction containing methane and a less volatile hydrocarbon fraction containing C2+ components, the system comprising:
 a splitter for dividing the inlet gas stream into a first feed stream and a second feed stream, the first feed stream and second feed stream having substantially the same composition as the inlet gas stream;   a first heat exchanger for cooling the first feed stream to form a cooled first feed stream;   a second heat exchanger for cooling the second feed stream to form a cooled second feed stream;   a separator for separating the cooled first feed stream and cooled second feed streams into a first vapor stream and a first liquid stream;   a flow line for feeding the first vapor stream to a demethanizer tower;   a flow line for feeding the first liquid stream to the demethanizer tower;   the demethanizer tower for separating the feed streams into a demethanizer overheads stream and a demethanizer bottoms stream;   one or more compressors for compressing the demethanizer overheads stream to form a residue gas stream;   a demethanizer tower line for providing a demethanizer tower stream to a top of the demethanizer tower;   a flow line for providing a portion of the residue gas stream to the demethanizer tower line;   a flow line for providing a third portion of the inlet gas stream to the demethanizer tower line, the third portion having substantially the same composition as the inlet gas stream;   a first valve for permitting or stopping a flow of the portion of the residue gas stream to the demethanizer tower line; and   a second valve for permitting or stopping a flow of the third portion of the inlet gas stream to the demethanizer tower line.   
     
     
         2 . The system of  claim 1 , further comprising a control system configured for controlling a position of the first and second valves. 
     
     
         3 . The system of  claim 1 , wherein the first heat exchanger comprises a gas-gas heat exchanger for exchanging heat between one or more of the first feed stream, the demethanizer tower overheads stream, and the demethanizer tower stream. 
     
     
         4 . The system of  claim 1 , wherein the second heat exchanger comprises a reboiler for exchanging heat between one or more side draws from the demethanizer tower and the second feed stream. 
     
     
         5 . A method for operating the system of  claim 1 , comprising
 closing the first valve and opening the second valve, and operating the system for a period of time in a high throughput mode; and   closing the second valve and opening the first valve, and operating the system for a period of time in a high ethane recovery mode.   
     
     
         6 . A system for separating an inlet gas stream containing methane, C2 components, C3 components and optionally heavier hydrocarbons into a volatile gas fraction containing methane and a less volatile hydrocarbon fraction containing C2+ components, the system comprising:
 a splitter for dividing the inlet gas stream into a first feed stream and a second feed stream;   a gas-gas heat exchanger for cooling the first feed stream and producing a cooled first feed stream;   a second heat exchanger for cooling the second feed stream and producing a cooled second feed stream;   a first separator for separating the cooled first feed stream and cooled second feed stream into a first vapor stream and a first liquid stream;   a splitter for dividing the first vapor stream into a first portion and a second portion;   an expander for expanding the first portion of the first vapor stream and for extracting work from the first portion of the first vapor stream;   a flow line for cooling the second portion of the first vapor stream in the gas-gas heat exchanger;   a flow line for feeding the first liquid stream to a demethanizer tower as a first tower feed stream;   a flow line for feeding the expanded first portion of the first vapor stream to the demethanizer tower as a second tower feed stream;   a flow line for feeding the second liquid stream to the demethanizer tower as a third feed stream;   a flow line for feeding the second vapor stream to the demethanizer tower as a fourth feed stream;   the demethanizer tower for separating the first and second feed streams into a demethanizer overheads stream and a demethanizer bottoms stream;   a flow line for warming the demethanizer overheads stream in the gas-gas exchanger;   one or more compressors for compressing the warmed demethanizer overheads stream to form a residue gas stream, at least one of the one or more compressors driven by the work extracted in the expander;   a fifth tower feed stream configured for receiving (i) a portion of the residue gas stream, (ii) a third portion of the inlet gas stream, or (iii) a mixture of (i) and (ii), and cooling the received (i), (ii), or (iii) in the gas-gas exchanger;   a flow line for providing a demethanizer tower stream to a top of the demethanizer tower, wherein valving and piping are configured such that the demethanizer tower stream comprises either (i), (ii), or (iii) as provided from the fifth tower feed stream;   a first valve for controlling or stopping a flow of the portion of the residue gas stream to the fifth tower feed line; and   a second valve for controlling or stopping a flow of the third portion of the inlet gas stream to the fifth tower feed line.   
     
     
         7 . The system of  claim 6 , further comprising
 a second separator for separating the cooled second portion of the first vapor stream into a second vapor stream and a second liquid stream;   a flow line for feeding the second liquid stream to the demethanizer tower as a third feed stream; and   a flow line for feeding the second vapor stream to the demethanizer tower as a fourth feed stream;   wherein the demethanizer tower is configured to separate the first, second, third, and fourth feed streams into the demethanizer overheads stream and the demethanizer bottoms stream; and   wherein the demethanizer tower stream optionally comprises the second vapor stream.   
     
     
         8 . The system of  claim 7 , further comprising a flow line for cooling the second vapor portion in the gas-gas exchanger. 
     
     
         9 . The system of  claim 6 , wherein the first tower feed stream is fed to a lower portion of the demethanizer tower than the second tower feed stream, the second tower feed stream is fed to a lower portion of the demethanizer tower than the third tower feed stream; and the third tower feed stream is fed to a lower portion of the demethanizer tower than the fourth tower feed stream. 
     
     
         10 . The system of  claim 9 , wherein, in a first configuration, the fourth tower feed stream is the reflux stream and wherein the fifth tower feed stream is fed to a portion of the demethanizer tower higher than the third tower feed stream but lower than the demethanizer tower stream, and, in a second configuration, the fifth tower feed stream is the reflux stream and wherein the fourth tower feed stream is fed to a portion of the demethanizer tower lower than the reflux stream. 
     
     
         11 . The system of  claim 6 , further comprising a flow line configured to provide at least a portion of the first liquid stream to the second heat exchanger. 
     
     
         12 . The system of  claim 6 , wherein the second heat exchanger comprises a reboiler for exchanging heat between one or more side draws from the demethanizer tower and the second feed stream. 
     
     
         13 . The system of  claim 6 , further comprising, upstream of the first separator, a mixer for mixing the cooled first and second feed streams, producing a mixed cooled feed stream, and an exchanger for further cooling the mixed cooled feed stream.