Gas separation process

Details Gas separation process Gas separation process

2001-06-06

2002-06-18

Capossela, Ronald (Department: 3744)

Refrigeration

Cryogenic treatment of gas or gas mixture

Separation of gas mixture

Reexamination Certificate

active

06405561

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to a process for the recovery of C
3
and heavier components from a natural gas stream or refinery gas stream.
BACKGROUND OF THE INVENTION
It is well known that natural gas streams can be separated into their component parts. Such processes involve a combination of chilling, expansion, distillation and/or like operations to separate methane and ethane from C
3
and heavier hydrocarbon components. Typically the separation made is of methane and ethane from propane and heavier components. If economically desirable, the ethane could also be recovered and similarly, it is desirable in many instances to further fractionate the recovered C
3
(or alternatively C
2
) and heavier components. Such variations are well known to those skilled in the art.
One such process is shown in U.S. Pat. No. 5,771,712 entitled “Hydrocarbon Gas Processing” issued Jun. 30, 1998, to Roy E. Campbell, John D. Wilkinsun and Hank M. Hudson. (the '712 Patent) This patent is hereby incorporated in its entirety by reference.
The '712 Patent demonstrates a typical process wherein an overhead stream from a deethanizer is passed into heat exchange with an exit stream from an absorber to cool the overhead stream from the deethanizer to a temperature at which it is partially liquefied. This partially liquefied stream is then introduced into the absorber wherein the liquid portion of the stream passes downwardly through the absorber to contact a gaseous stream passing upwardly through the absorber. While this processing system has been effective to separate C
2
and lighter components from C
3
and heavier components, it is relatively inefficient when processing lower pressure feed gas streams. It is also relatively inefficient when processing rich feed gas streams with respect to their C
3
and heavier content. It is particularly ineffective when large amounts of very light gases, such as hydrogen, may be present in the feed gas stream charged to the process. Hydrogen in gaseous streams recovered from refinery operations, which may be desirably separated in such processes, is not uncommon. While the occurrence of hydrogen in significant quantities in natural gas is rare, the presence of hydrogen in similar streams from refinery operations is common.
Accordingly, it is desirable that a more efficient and a more effective method be available for the separation of C
3
and heavier components from such refinery streams. It is also desirable that a more efficient and more effective method be available for the processing of natural gas streams.
SUMMARY OF THE INVENTION
According to the present invention, a more efficient and effective process is provided.
The invention comprises an improvement in a process for separating a feed gas stream containing methane, C
2
components, C
3
components and heavier components into a volatile gas stream containing a major portion of the methane and C
2
components and a less volatile stream containing a major portion of the C
3
and heavier components by adjusting the temperature and pressure of the feed gas stream to a suitable temperature for separation into an absorber gas stream and a first liquid stream in a separator/absorber with the absorber gas stream containing a major portion of the methane and C
2
components and the first liquid stream containing a major portion of the C
3
and heavier components, the first liquid stream being charged to a deethanizer from which a bottoms liquid product comprising primarily the C
3
and heavier components is recovered with the deethanizer overhead consisting primarily of C
2
and lighter components, the improvement comprising:
a) cooling the deethanizer overhead to produce a partially condensed stream;
b) separating the cooled deethanizer overhead stream into a liquid stream comprising principally C
2
components and a residue gas stream; and,
c) cooling a portion of the liquid stream by heat exchange with the absorber gas stream to produce a subcooled liquid stream and passing the subcooled liquid stream to an upper portion of the separator/absorber for contact with a gas stream rising through the separator/absorber to absorb C
3
and heavier components therefrom.
The invention further comprises a process for separating a feed gas stream containing methane, C
2
components, C
3
components and heavier components into a volatile gas stream containing a major portion of the methane and C
2
components and a less volatile stream containing a major portion of the C
3
and heavier components, the process comprising:
a) cooling the feed gas stream to a temperature sufficient to condense the majority of the C
3
components in the feed gas stream by heat exchange with at least one of a first liquid stream containing C
3
and heavier components and a refrigerant stream to produce a cooled feed gas stream;
b) passing the cooled feed gas stream to a separator/absorber to produce the first liquid stream as a bottoms product and a separator/absorber overhead residue gas stream;
c) passing the first liquid stream to a deethanizer tower operating at a pressure at least 25 psi (pounds per square inch) above the pressure in the separator/absorber;
d) separating the first liquid stream into a deethanizer bottoms stream containing a majority of the C
3
and heavier components and a deethanizer overhead gas stream;
e) cooling the deethanizer overhead gas stream to partially condense the deethanizer overhead gas stream by heat exchange with a refrigerant stream to produce a deethanizer liquid reflux stream, a second liquid stream and a deethanizer residue gas stream; and,
f) cooling the second liquid stream by heat exchange with the separator/absorber overhead residue gas stream to produce a subcooled second liquid stream and passing the subcooled second liquid stream into an upper portion of the separator/absorber.
The invention further comprises a process for separating a feed gas stream containing methane, C
2
components, C
3
components and heavier components into a volatile gas stream containing a major portion of the methane and C
2
components and a less volatile stream containing a major portion of the C
3
and heavier components, the process comprising:
a) cooling the feed gas stream to a temperature sufficient to condense the majority of the C
3
components in the feed gas stream by heat exchange with at least one of a first liquid stream containing C
3
and heavier components, a second liquid stream containing C
3
and heavier components, a residue gas stream, and a refrigerant stream to produce a cooled feed gas stream;
b) passing the cooled feed gas stream to a separator to produce a separator gas stream and the first liquid stream;
c) optionally further cooling the separator gas stream by heat exchange or expansion and passing it to a separator/absorber wherein a second liquid stream is produced as a bottoms stream and wherein a separator/absorber overhead residue gas stream is produced;
d) passing the first liquid stream and the second liquid stream to a deethanizer tower operating at a pressure at least 25 psi above the separator/absorber pressure;
e) separating the first and the second liquid streams into a deethanizer bottoms stream containing a majority of the C
3
and heavier components and a deethanizer overhead gas stream;
f) cooling the deethanizer overhead gas stream to partially condense the deethanizer overhead gas stream by heat exchange with a refrigerant stream to produce a deethanizer liquid reflux stream, a third liquid stream and a deethanizer residue gas stream; and,
g) cooling the third liquid stream by heat exchange with the separator/absorber overhead residue gas stream to produce a subcooled third liquid stream and passing the subcooled third liquid stream into an upper portion of the separator/absorber.
The invention further comprises a process for separating a feed gas stream containing methane, C
2
components, C
3
components and heavier components into a volatile gas stream containing a major portion of the methane and C
2
components and a less volatile strea

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