U.S. patent application number 13/174002 was filed with the patent office on 2012-01-05 for methods and systems for recovering liquified petroleum gas from natural gas.
This patent application is currently assigned to BLACK & VEATCH CORPORATION. Invention is credited to Kevin L. Currence, Robert A. Mortko.
Application Number | 20120000245 13/174002 |
Document ID | / |
Family ID | 45398673 |
Filed Date | 2012-01-05 |
United States Patent
Application |
20120000245 |
Kind Code |
A1 |
Currence; Kevin L. ; et
al. |
January 5, 2012 |
Methods and Systems for Recovering Liquified Petroleum Gas from
Natural Gas
Abstract
A process and system is provided for separating a feed gas
stream containing methane, at least one C.sub.2 component, at least
one C.sub.3 component, and optionally heavier components, into a
volatile gas stream containing a major portion of the methane and
at least one C.sub.2 component and a less volatile stream
containing a major portion of the at least one C.sub.3 and heavier
components. The feed stream is cooled, at least partially
condensed, and fed to a fractionation column wherein the feed
stream is separated into an overhead vapor stream comprising
primarily the lighter components of the feed stream and a bottoms
liquid stream comprising primarily the heavier components of the
feed stream. The introduction of a reboiler onto the fractionation
column assists in removing co-absorbed C.sub.2 and lighter
components from the fractionation column bottoms thereby
facilitating more efficient operation of a downstream deethanizer
column. Addition of residue recycle can further supplement recovery
of desired components.
Inventors: |
Currence; Kevin L.; (Olathe,
KS) ; Mortko; Robert A.; (Olathe, KS) |
Assignee: |
BLACK & VEATCH
CORPORATION
Overland Park
KS
|
Family ID: |
45398673 |
Appl. No.: |
13/174002 |
Filed: |
June 30, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61360753 |
Jul 1, 2010 |
|
|
|
Current U.S.
Class: |
62/620 |
Current CPC
Class: |
F25J 2240/02 20130101;
F25J 3/0242 20130101; F25J 2205/04 20130101; F25J 2270/60 20130101;
F25J 2270/12 20130101; F25J 2200/74 20130101; F25J 2200/78
20130101; F25J 2200/04 20130101; F25J 2200/76 20130101; F25J
2235/60 20130101; F25J 3/0233 20130101; F25J 2245/02 20130101; F25J
3/0209 20130101 |
Class at
Publication: |
62/620 |
International
Class: |
F25J 3/08 20060101
F25J003/08 |
Claims
1. A process for separating a feed gas stream containing methane,
at least one C.sub.2 component, and at least one C.sub.3 component
into a volatile gas stream containing a major portion of the
methane and at least one C.sub.2 component and a less volatile
stream containing a major portion of the at least one C.sub.3
component, the process comprising: a) cooling the feed gas stream
to a temperature sufficient to condense the majority of the at
least one C.sub.3 component in the feed gas stream to produce a
cooled feed stream; b) introducing the cooled feed stream into a
separator vessel to separate the cooled feed stream into a
separator gas stream and a separator liquid stream; c) introducing
at least a portion of both of the separator gas and liquid streams
from the separator vessel into a fractionation column to produce a
fractionation column bottoms product and a fractionation column
overhead residue gas stream; d) introducing the fractionation
column bottoms product into a deethanizer tower and producing a
deethanizer bottoms stream comprising a majority of the at least
one C.sub.3 component and a deethanizer overhead gas stream; e)
cooling and at least partially condensing the deethanizer overhead
gas stream thereby producing a deethanizer liquid reflux stream and
a deethanizer residue gas stream; and f) introducing at least a
portion of the deethanizer liquid reflux stream into the
fractionation column.
2. The process according to claim 1, wherein the fractionation
column further includes a reboiler operable to vaporize at least a
portion of a fractionation column liquid, the vaporized
fractionation column liquid being reintroduced into the
fractionation column.
3. The process according to claim 1, further comprising: g)
combining the fractionation column overhead residue gas stream with
at least a portion of the deethanizer residue gas stream to form a
combined residue gas stream; h) compressing and cooling at least a
portion of the combined residue gas stream to produce a residue gas
reflux stream; and i) introducing the residue gas reflux stream
into the fractionation column.
4. The process according to claim 1, wherein the process further
comprises: g) compressing and cooling at least a portion of the
fractionation column overhead residue gas stream to produce a
residue gas reflux stream; and h) introducing the residue gas
reflux stream into the fractionation column.
5. A process for separating a feed gas stream containing methane,
at least one C2 component, and at least one C3 component into a
volatile gas stream containing a major portion of the methane and
at least one C2 component and a less volatile stream containing a
major portion of the at least one C3 component, the process
comprising: a) cooling the feed gas stream to a temperature
sufficient to condense the majority of the at least one C3
component in the feed gas stream to produce a cooled feed stream;
b) passing the cooled feed stream to a fractionation column to
produce a liquid fractionation column bottoms product and a
fractionation column overhead residue gas stream, the fractionation
column including a reboiler operable to vaporize at least a portion
of a fractionation column liquid, the vaporized fractionation
column liquid being reintroduced into the fractionation column; c)
introducing the fractionation column bottoms product into a
deethanizer tower and producing a deethanizer bottoms stream
comprising a majority of the at least one C.sub.3 component and a
deethanizer overhead gas stream; d) cooling and at least partially
condensing the deethanizer overhead gas stream thereby producing a
deethanizer liquid reflux stream and a deethanizer residue gas
stream; and e) introducing at least a portion of the deethanizer
liquid reflux stream into the fractionation column.
6. The process according to claim 5, wherein the process further
comprises: f) compressing and cooling at least a portion of the
fractionation column overhead residue gas stream to produce a
residue gas reflux stream; and g) introducing the residue gas
reflux stream into the fractionation column.
7. The process according to claim 6, wherein prior to step (b)
introducing the cooled feed stream into a separator vessel to
separate the cooled feed stream into a separator gas stream and a
separator liquid stream.
8. The process according to claim 6, wherein the process further
comprises, prior to step (f), combining at least a portion of the
deethanizer residue gas stream with the at least a portion of the
fractionation column overhead gas residue stream.
9. The process according to claim 9, wherein prior to step (b)
introducing the cooled feed stream into a separator vessel to
separate the cooled feed stream into a separator gas stream and a
separator liquid stream.
10. A process for separating a feed gas stream containing methane,
at least one C.sub.2 component, and at least one C.sub.3 component
into a volatile gas stream containing a major portion of the
methane and at least one C.sub.2 component and a less volatile
stream containing a major portion of the at least one C.sub.3
component, the process comprising: a) cooling the feed gas stream
to a temperature sufficient to condense the majority of the at
least one C.sub.3 component in the feed gas stream to produce a
cooled feed stream; b) passing the cooled feed stream to a
fractionation column to produce a liquid fractionation column
bottoms product and a fractionation column overhead residue gas
stream, c) introducing the fractionation column bottoms product
into a deethanizer tower and producing a deethanizer bottoms stream
comprising a majority of the at least one C.sub.3 component and a
deethanizer overhead gas stream; d) cooling and at least partially
condensing the deethanizer overhead gas stream thereby producing a
deethanizer liquid reflux stream and a deethanizer residue gas
stream; e) introducing at least a portion of the deethanizer liquid
reflux stream into the fractionation column; f) compressing and
cooling at least a portion of the fractionation column over-head
residue gas stream to produce a residue gas reflux stream; and g)
introducing the residue gas reflux stream into the fractionation
column.
11. The process according to claim 10, wherein prior to step (f),
at least a portion of the deethanizer overhead gas stream is
combined with the fractionation column overhead residue gas
stream.
12. A system for separating a feed gas stream containing methane,
at least one C.sub.2 component, and at least one C.sub.3 component
into a volatile gas stream containing a major portion of the
methane and at least one C.sub.2 component and a less volatile
stream containing a major portion of the at least one C.sub.3
component, the system comprising: a) a feed stream heat exchanger
configured to cool the feed gas stream to a temperature sufficient
to condense the majority of the at least one C.sub.3 component in
the feed gas stream to produce a cooled feed stream; b) a separator
vessel located downstream from the first heat exchanger and
configured to separate the cooled feed stream into a separator gas
stream and a separator liquid stream; c) a fractionation column
located downstream from the separator vessel and configured to
receive at least a portion of both the separator gas and liquid
streams and produce a fractionation column bottoms product and a
fractionation column overhead residue gas stream; d) a deethanizer
tower located downstream from the separator vessel and configured
to receive at least a portion of the fractionation column bottoms
product and produce a deethanizer bottoms stream comprising a
majority of the at least one C.sub.3 component and a deethanizer
overhead gas stream; e) a deethanizer heat exchanger configured to
receive and cool the deethanizer overhead gas stream; and f) a
deethanizer separation vessel configured to separate the cooled
deethanizer overhead gas stream into a deethanizer liquid reflux
stream and a deethanizer residue gas stream.
13. The system according to claim 12, wherein the fractionation
column further includes a reboiler configured to vaporize at least
a portion of a fractionation column liquid and reintroduce the
vaporized fractionation column liquid back into the fractionation
column.
14. The system according to claim 12, further comprising: g)
conduit configured to merge at least a portion of the deethanizer
residue gas stream with at least a portion of the fractionation
column overhead residue gas stream to form a combined residue gas
stream; h) a residue gas heat exchanger configured to receive at
least a portion of the combined residue gas stream and to produce a
residue gas reflux stream; and i) conduit configured to deliver at
least a portion of the residue gas reflux stream from the residue
gas heat exchanger to the fractionation column.
15. The system according to claim 12, further comprising: g) a
compressor located upstream from the residue gas heat exchanger and
configured to compress the combined residue gas stream.
16. A system for separating a feed gas stream containing methane,
at least one C.sub.2 component, and at least one C.sub.3 component
into a volatile gas stream containing a major portion of the
methane and at least one C.sub.2 component and a less volatile
stream containing a major portion of the at least one C.sub.3
component, the system comprising: a) a feed stream heat exchanger
configured to cool the feed gas stream to a temperature sufficient
to condense the majority of the at least one C.sub.3 component in
the feed gas stream to produce a cooled feed stream; b) a
fractionation column configured to receive the cooled feed stream
and produce a fractionation column bottoms product and a
fractionation column overhead residue gas stream, the fractionation
column including a reboiler configured to vaporize at least a
portion of a fractionation column liquid and reintroduce the
vaporized fractionation column liquid back into the fractionation
column; c) a deethanizer tower located downstream from the
fractionation column and configured to receive at least another
portion of the fractionation column bottoms product and produce a
deethanizer bottoms stream comprising a majority of the at least
one C.sub.3 component and a deethanizer overhead gas stream; d) a
deethanizer heat exchanger configured to receive and cool the
deethanizer overhead gas stream; and e) a deethanizer separation
vessel configured to separate the cooled deethanizer overhead gas
stream into a deethanizer liquid reflux stream and a deethanizer
residue gas stream.
17. The system according to claim 16, the system further
comprising: f) a residue gas heat exchanger configured to condense
at least a portion of the fractionation column overhead residue gas
stream to form a residue gas reflux stream; and g) conduit
configured to deliver at least a portion of the residue gas reflux
stream from the residue gas heat exchanger to the fractionation
column.
18. The system according to claim 16, further comprising: f) a
compressor located upstream from the residue gas heat exchanger and
configured to compress the fractionation column overhead residue
gas stream.
19. The system according to claim 16, further comprising: f)
conduit configured to merge at least a portion of the deethanizer
residue gas stream with at least the fractionation column overhead
residue gas stream to form a combined residue gas stream.
20. A system for separating a feed gas stream containing methane,
at least one C.sub.2 component, and at least one C.sub.3 component
into a volatile gas stream containing a major portion of the
methane and at least one C.sub.2 component and a less volatile
stream containing a major portion of the at least one C.sub.3
component, the system comprising: a) a feed stream heat exchanger
configured to cool the feed gas stream to a temperature sufficient
to condense the majority of the at least one C.sub.3 component in
the feed gas stream to produce a cooled feed stream; b) a
fractionation column configured to receive the cooled feed stream
and produce a fractionation column bottoms product and a
fractionation column overhead residue gas stream; c) a deethanizer
tower located downstream from the fractionation column and
configured to receive at least a portion of the fractionation
column bottoms product and produce a deethanizer bottoms stream
comprising a majority of the at least one C.sub.3 component and a
deethanizer overhead gas stream; d) a deethanizer heat exchanger
configured to receive and cool the deethanizer overhead gas stream;
e) a deethanizer separation vessel configured to separate the
cooled deethanizer overhead gas stream into a deethanizer liquid
reflux stream and a deethanizer residue gas stream; f) conduit
configured to deliver at least a portion of the deethanizer liquid
reflux stream to the fractionation column; g) a residue gas heat
exchanger configured to condense at least a portion of the
fractionation column overhead residue gas stream; and h) conduit
configured to deliver at least a portion of the condensed
fractionation column overhead residue gas stream to the
fractionation column.
21. The system according to claim 20, further comprising: i)
conduit configured to merge at least a portion of the deethanizer
residue gas stream with at least the fractionation column overhead
residue gas stream to form a combined residue gas stream.
Description
RELATED APPLICATION
[0001] This application claims the benefit of U.S. Provisional
Patent Application No. 61/360,753, filed Jul. 1, 2010, which is
incorporated by reference herein in its entirety.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention is directed toward processes and
systems for recovering liquefied petroleum gas (LPG) from a
hydrocarbon gas stream, especially a natural gas stream or a
refinery gas stream. Particularly, the processes and systems
described herein may be utilized to enhance LPG recovery,
particularly when processing higher pressure or leaner feed streams
thereby providing broader applicability compared to previous
processes.
[0004] 2. Description of the Prior Art
[0005] Natural gas comprises primarily methane, but can also
include varying amounts of heavy hydrocarbon components such as
ethane, propane, butane, and pentane, for example. It is well known
that natural gas streams can be separated into their respective
component parts. Such processes involve a combination of chilling,
expansion, distillation and/or like operations to separate methane
and ethane from C.sub.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.sub.3 (or alternatively
C.sub.2) and heavier components.
[0006] One process that has been devised for separating a natural
gas stream into light and heavy component streams is shown in U.S.
Pat. No. 5,771,712, incorporated by reference herein its entirety.
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.sub.2 and lighter components from C.sub.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.sub.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.
[0007] U.S. Pat. No. 6,405,561 discloses a process for recovering
C.sub.3 and heavier components from low-pressure natural gas or
refinery gas streams. The '561 patent teaches the improvement of
cooling and partially condensing a deethanizer overhead gas stream
to produce a deethanizer liquid stream that is further cooled and
directed into an upper portion of a separator/absorber, which
separates the inlet feed stream into a liquid bottoms stream
comprising primarily C.sub.3 and heavier components and an overhead
gas stream comprising primarily C.sub.2 and lighter components. The
process of the '561 patent is particularly effective for treatment
of feed gas streams at lower pressure that contain substantial
amounts of very light components, including hydrogen that is often
found in refinery applications. The process of the '561 patent is
also effective for treatment of feed gas streams rich with respect
to recoverable C.sub.3 and heavier components.
[0008] However, as feed gas pressure increases, or if feed gas
streams with higher quantities of C.sub.2 and lighter components
are used, the process of the '561 patent becomes less effective due
to co-adsorption of these lighter components in the
separator/absorber bottoms stream. As a result, these lighter
components tend to reduce the temperature required to partially
condense the deethanizer overhead gas stream. Thus, the refrigerant
medium used in this condensation operation must be changed from
propane to a colder, more horsepower-intensive refrigeration media.
As a result, the investment in equipment and operating cost is
increased substantially.
SUMMARY OF THE INVENTION
[0009] In one embodiment of the present invention, there is
provided a process for separating a feed gas stream containing
methane, at least one C.sub.2 component, and at least one C.sub.3
component into a volatile gas stream containing a major portion of
the methane and at least one C.sub.2 component and a less volatile
stream containing a major portion of the at least one C.sub.3
component. The process comprises first cooling the feed gas stream
to a temperature sufficient to condense the majority of the at
least one C.sub.3 component in the feed gas stream to produce a
cooled feed stream. The cooled feed stream is introduced into a
separator vessel to separate the cooled feed stream into a
separator gas stream and a separator liquid stream. At least a
portion of both of the separator gas and liquid streams from the
separator vessel is introduced into a fractionation column to
produce a fractionation column bottoms product and a fractionation
column overhead residue gas stream. The fractionation column
bottoms product is introduced into a deethanizer tower which
produces a deethanizer bottoms stream comprising a majority of the
at least one C.sub.3 component and a deethanizer overhead gas
stream.
[0010] In another embodiment of the present invention, there is
provided a process for separating a feed gas stream containing
methane, at least one C.sub.2 component, and at least one C.sub.3
component into a volatile gas stream containing a major portion of
the methane and at least one C.sub.2 component and a less volatile
stream containing a major portion of the at least one C.sub.3
component. The process comprises cooling the feed gas stream to a
temperature sufficient to condense the majority of the at least one
C.sub.3 component therein to produce a cooled feed stream. The
cooled feed stream is passed to a fractionation column to produce a
liquid fractionation column bottoms product and a fractionation
column overhead residue gas stream. The fractionation column
including a reboiler operable to vaporize at least a portion of the
fractionation column liquid which is taken from the bottom or near
the bottom of the column. The vaporized portion is then
reintroduced into the fractionation column. The fractionation
column bottoms product is introduced into a deethanizer tower which
produces a deethanizer bottoms stream comprising a majority of the
at least one C.sub.3 component and a deethanizer overhead gas
stream. The deethanizer overhead gas stream is cooled and at least
partially condensed thereby producing a deethanizer liquid reflux
stream and a deethanizer residue gas stream. Optionally, the
deethanizer residue gas stream is combined with at least a portion
of the overhead residue gas stream to form a combined residue gas
stream. At least a portion of the combined residue gas stream is
compressed and cooled to produce a residue gas reflux stream. The
residue gas reflux stream is introduced into the fractionation
column.
[0011] In a further embodiment of the present invention, there is
provided a process for separating a feed gas stream containing
methane, at least one C.sub.2 component, and at least one C.sub.3
component into a volatile gas stream containing a major portion of
the methane and at least one C.sub.2 component and a less volatile
stream containing a major portion of the at least one C.sub.3
component. The process comprises cooling the feed gas stream to a
temperature sufficient to condense the majority of the at least one
C.sub.3 component in the feed gas stream to produce a cooled feed
stream. The cooled feed stream is passed to a fractionation column
to produce a liquid fractionation column bottoms product and a
fractionation column overhead residue gas stream. The fractionation
column bottoms product is introduced into a deethanizer tower,
which produces a deethanizer bottoms stream comprising a majority
of the at least one C.sub.3 component and a deethanizer overhead
gas stream. The deethanizer overhead gas stream is cooled and at
least partially condensed thereby producing a deethanizer liquid
reflux stream and a deethanizer residue gas stream. At least a
portion of the fractionation column overhead residue gas stream is
compressed and cooled to produce a residue gas reflux stream. The
residue gas reflux stream is then introduced into the fractionation
column.
[0012] In yet another embodiment of the present invention, there is
provided a system for separating a feed gas stream containing
methane, at least one C.sub.2 component, and at least one C.sub.3
component into a volatile gas stream containing a major portion of
the methane and at least one C.sub.2 component and a less volatile
stream containing a major portion of the at least one C.sub.3
component. The system comprises a feed stream heat exchanger
configured to cool the feed gas stream to a temperature sufficient
to condense the majority of the at least one C.sub.3 component in
the feed gas stream to produce a cooled feed stream. A separator
vessel is located downstream from the first heat exchanger and
configured to separate the cooled feed stream into a separator gas
stream and a separator liquid stream. A fractionation column is
located downstream from the separator vessel and configured to
receive at least a portion of both the separator gas and liquid
streams and produce a fractionation column bottoms product and a
fractionation column overhead residue gas stream. A deethanizer
tower is located downstream from the separator vessel and
configured to receive at least a portion of the fractionation
column bottoms product and to produce a deethanizer bottoms stream
comprising a majority of the at least one C.sub.3 component and a
deethanizer overhead gas stream.
[0013] In still another embodiment of the present invention, there
is provided a system for separating a feed gas stream containing
methane, at least one C.sub.2 component, and at least one C.sub.3
component into a volatile gas stream containing a major portion of
the methane and at least one C.sub.2 component and a less volatile
stream containing a major portion of the at least one C.sub.3
component. The system comprises a feed stream heat exchanger
configured to cool the feed gas stream to a temperature sufficient
to condense the majority of the at least one C.sub.3 component
therein to produce a cooled feed stream. A fractionation column is
located downstream from the feed stream heat exchanger and is
configured to receive the cooled feed stream and produce a
fractionation column bottoms product and a fractionation column
overhead residue gas stream. The fractionation column includes a
reboiler configured to vaporize at least a portion of the
fractionation column liquid and reintroduce the vaporized
fractionation column liquid back into the fractionation column. A
deethanizer tower is located downstream from the fractionation
column and configured to receive at least another portion of the
fractionation column bottoms product and produce a deethanizer
bottoms stream comprising a majority of the at least one C.sub.3
component and a deethanizer overhead gas stream. A deethanizer heat
exchanger is provided and configured to receive and cool the
deethanizer overhead gas stream. A deethanizer separation vessel is
located downstream from the deethanizer heat exchanger and is
configured to separate the cooled deethanizer overhead gas stream
into a deethanizer liquid reflux stream and a deethanizer residue
gas stream. Optionally, the system further includes a conduit
configured to merge at least a portion of the deethanizer residue
gas stream with at least a portion of the fractionation column
overhead residue gas stream to form a combined residue gas stream.
A residue gas heat exchanger is provided and configured to condense
at least a portion of the combined residue stream to form a residue
gas reflux stream. Conduit is configured to deliver at least a
portion of the residue gas reflux stream from the gas condensation
unit to the fractionation column.
[0014] In even a further embodiment, there is provided a system for
separating a feed gas stream containing methane, at least one
C.sub.2 component, and at least one C.sub.3 component into a
volatile gas stream containing a major portion of the methane and
at least one C.sub.2 component and a less volatile stream
containing a major portion of the at least one C.sub.3 component.
The system comprises a feed stream heat exchanger configured to
cool the feed gas stream to a temperature sufficient to condense
the majority of the at least one C.sub.3 component in the feed gas
stream to produce a cooled feed stream. A fractionation column is
located downstream from the heat exchanger and is configured to
receive the cooled feed stream and produce a fractionation column
bottoms product and a fractionation column overhead residue gas
stream. A deethanizer tower is located downstream from the
fractionation column and configured to receive at least a portion
of the fractionation column bottoms product and produce a
deethanizer bottoms stream comprising a majority of the at least
one C.sub.3 component and a deethanizer overhead gas stream. A
deethanizer heat exchanger is provided and configured to receive
and cool the deethanizer overhead gas stream. A deethanizer
separation vessel is provided and configured to separate the cooled
deethanizer overhead gas stream into a deethanizer liquid reflux
stream and a deethanizer residue gas stream. Conduit is provided
and configured to deliver at least a portion of the deethanizer
liquid reflux stream to the fractionation column. A residue gas
heat exchanger is provided and configured to condense at least a
portion of the fractionation column overhead residue gas stream.
Conduit is provided and configured to deliver at least a portion of
the condensed fractionation column overhead residue gas stream to
the fractionation column.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] FIG. 1 is a schematic diagram of a process according to one
embodiment of the present invention; and
[0016] FIG. 2 is a schematic diagram of a process according to
another embodiment of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0017] Turning to FIG. 1, an embodiment of the present invention is
shown that is particularly adapted for the recovery of C.sub.3 and
heavier components from a hydrocarbon-containing gas stream, such
as a natural gas or refinery gas stream. In particular embodiments,
the inlet feed gas stream 10 comprises methane, at least one
C.sub.2 component, at least one C.sub.3 component, and optionally
heavier components. In still other embodiments, inlet feed gas
stream 10 comprises methane as the predominant component, with
C.sub.2, C.sub.3, and heavier components being present in lesser
amounts. In refinery applications, the feed may also contain
significant quantities of lighter components such as hydrogen.
Particularly, in certain applications, the feed stream may comprise
as much as 10%, or even as much as 50%, hydrogen.
[0018] The present invention exhibits the flexibility to
accommodate a wide variety of feed pressures. In one embodiment,
the feed stream 10 can be supplied at a pressure of at least 300
psi, or particularly, between about 350 psi to about 700 psi.
Typically, feed stream 10 will be supplied at a temperature that is
above the condensation point for the C.sub.3 components present
therein; therefore, feed stream will need to be cooled in order to
condense these components. In this embodiment, feed gas stream 10
is passed through a heat exchanger 12 where it is cooled to a
temperature sufficient to condense the majority of the at least one
C.sub.3 component in the feed gas stream to produce a cooled gas
feed stream. Note, the use of the word "gas" in the term "cooled
gas feed stream" should not be taken as implying that the entirety
of the stream is present in the gaseous state. Certain components,
particularly the heavier components may be present as liquids. The
cooling streams used in heat exchanger 12 are discussed in greater
detail below. It will be understood that the heat exchange function
shown schematically in heat exchanger 12 may be accomplished in a
single or a plurality of heat exchange vessels.
[0019] The cooled inlet gas is passed via a line or conduit 14 to a
separation vessel 16 where it is separated into a vapor stream 18
and a bottoms stream 20. Vapor stream 18 is directed toward an
expander 22 to reduce the pressure of and further cool the stream.
The expanded vapor stream is passed via a line 24 to a
fractionation column 26 containing one or more theoretical stages
of mass transfer. In certain embodiments, the fractionation column
26 is a conventional distillation column containing a plurality of
vertically spaced trays, one or more packed beds, or some
combination of trays and packing.
[0020] The bottoms stream 20 recovered from separator vessel 16
contains primarily C.sub.3 and heavier components, although the
bottoms stream 20 will also contain quantities of lighter
materials. As explained further below, ultimately these lighter
components will be separated from the C.sub.3 and heavier
components in subsequent processing steps. In order to maximize the
efficiency of those subsequent processing steps, the present
embodiment seeks to control the levels of C.sub.2 and lighter
components contained in the liquid, predominantly C.sub.3 stream
that will be further processed. Thus, bottoms stream 20 is also
passed to fractionation column 26. Generally, bottoms stream 20 is
introduced into fractionation column 26 below the introduction
point for the expanded vapor stream carried by line 24, although
the arrangement of the introduction points for the various streams
fed to fractionation column 26 can be varied as deemed appropriate.
This step of introducing bottoms stream 20 into fractionation
column 26 provides an opportunity for the lighter materials
co-absorbed in liquid bottoms stream 20 to be separated therefrom.
Fractionation column 26 is equipped with an optional reboiler 28 to
assist with separation of the C.sub.2 and lighter components from
the bottoms of the fractionation column. A portion of the
fractionation column liquids taken from the bottom or near the
bottom of column 26 are directed to reboiler 28 and at least
partially vaporized and then reintroduced into the fractionation
column 26. Accordingly, as the liquid stream exiting fractionation
column 26 contains fewer C.sub.2 or lighter components, it has
higher condensation temperature than the stream 20. This permits a
propane refrigerant, or similar refrigerant, to be used to condense
the overhead stream from a deethanizer 36, which is discussed in
greater detail below. Otherwise, if the bottoms product from
fractionation column 26 contained a higher level of C.sub.2 or
lighter components, a colder and therefore more expensive
refrigeration system would need to be employed.
[0021] In fractionation column 26, a liquid bottoms stream
comprising primarily C.sub.3 and heavier components plus some light
components is recovered via a line 30 and a pump 32 and pumped via
a line 34 to heat exchanger 12 where it is used to cool the inlet
gas stream in line 10. The stream in line 34 is then passed to a
deethanizer 36. In deethanizer 36 the stream from line 34 is
separated by conventional distillation techniques as well known to
the art for deethanizers into an overhead vapor stream 38 and a
bottoms stream 40. Deethanizer 36 also comprises a conventional
reboiler 42. The stream recovered from deethanizer 36 through line
40 comprises primarily C.sub.3 and heavier components. An overhead
stream is recovered from the deethanizer via line 38, which is rich
in C.sub.2 and lighter components and is passed to a heat exchanger
44 where it is partially condensed and then through a line 46 to a
separator 48. From separator 48, a liquid stream is withdrawn via a
line 50 and passed to a pump 52 from which a portion of the liquid
stream is passed via a line 54 into an upper portion of deethanizer
36 as a reflux. The vapor stream recovered from separator 48 is
passed via a line 56.
[0022] Deethanizer 36 is maintained at a higher pressure than
fractionation column 26. The increased pressure for deethanizer 36
is supplied by pump 32 and maintained by a valve 57 disposed in
line 56. In certain embodiments, the pressure in deethanizer 36 is
at least 25 psi, or at least 100 psi, or at least 200 psi greater
than the pressure in fractionation column 26.
[0023] A second portion of the liquid stream from separator 48 is
passed via a line 58, through a heat exchanger 60, and into an
upper portion of fractionation column 26. An overhead vapor stream
recovered from the upper portion of fractionation column 26 is
passed via a line 62, through heat exchanger 66 and then combined
with the stream in line 56. It is noted that the stream carried by
line 56 is flashed across valve 57. The combined stream contains a
residue gas that comprises a major portion of the C.sub.2 and
lighter components from the inlet gas feed stream. This stream is
passed via line 64 through heat exchanger 12 so as to provide
cooling for feed stream 10. Alternatively, stream 56 and stream 62
can be passed separately through heat exchanger 12 such that stream
56, which contains a significant quantity of C.sub.2 components,
would be available for internal use thus reducing the C.sub.2
content of the residue gas.
[0024] The cooling to heat exchanger 12 provided by the materials
carried by lines 34 and 64 can be supplemented by a refrigerant,
such as propane, supplied to heat exchanger 12 by line 76. Next,
the residue gas carried by line 64 is passed through a compressor
66. The residue gas exits compressor 66 via line 68. Optionally, a
portion of the residue gas carried by line 68 is passed via a line
70 to a heat exchanger 72 where it is cooled and condensed. In the
embodiment illustrated, the chilled portion of residue gas exiting
heat exchanger 72 is refluxed to the top of fractionation column
26. The other portion of residue gas from line 68 is withdrawn from
the system via line 74. In those embodiments in which streams 56
and 62 are not combined and an additional reflux is desired for
column 26, a portion of the contents of stream 62 are compressed,
condensed and refluxed to the column.
[0025] In an illustrative embodiment of the process shown in FIG.
1, a dehydrated gas stream is charged to the process at 340 psia
and 114.degree. F. The gas stream is cooled in heat exchanger 12 to
a temperature of -66.degree. F and 330 psia and charged to
separation vessel 16. In separation vessel 16, gaseous overhead
stream 18 is produced and passed through expander 22 and is carried
by line 24 at -99.degree. F. and 150 psia to fractionation column
26. The liquid stream recovered via line 20 at -1.5.degree. F. and
145 psia and directed through pump 32 where its pressure is
increased to 360 psia. The stream carried by line 34 is used to
provide refrigeration to heat exchanger 12 and then directed to
deethanizer 36 at a temperature of 74.degree. F. and 355 psia.
[0026] In deethanizer 36, a bottoms liquid stream composed
primarily of C.sub.3 and heavier components is recovered via a line
40 at a temperature of 173.degree. F. at 350 psia. The vapor stream
recovered via line 56 is at a temperature of 24.degree. F. at 335
psia. In the current simulation, the vapor stream recovered via
line 56 was withdrawn from the system and used as fuel gas.
However, as illustrated in FIG. 1, this stream can be flashed
across valve 57 and combined with the gas carried by line 62. A
liquid reflux stream carried by line 58 is withdrawn from the
deethanizer at a temperature of 24.degree. F. and 335 psia. This
stream is cooled, expanded, and refluxed to fractionation column 26
at -111.degree. F. and 145 psia.
[0027] The overhead vapor from fractionation column 26 carried by
line 62 is at a temperature of -117.degree. F. and a pressure of
140 psia and is heat exchanged with the stream carried by line 58
and emerges from heat exchanger 60 at -99.degree.F. and 135 psia
and directed to heat exchanger 12 via line 64. This residue gas
stream exits heat exchanger 12 at 95.degree. F. and 125 psia and is
directed toward compressor 66 (in this simulation a series of
compressor stages with intercooling) where it is boosted to 1265
psia and its temperature raised to 115.degree. F. A portion of this
compressed stream is withdrawn via line 70, cooled and condensed by
heat exchanger 72 and refluxed to fractionation column 26 at a
temperature of -112.degree. F. and pressure of 1255 psia.
[0028] While specific temperatures have been referred to in
connection with the embodiment illustrated in FIG. 1, it should be
understood that a wide range of temperature and pressure variations
are possible within the scope of the present invention. Such
temperature and pressure variations are readily determined by those
skilled in the art based upon the composition of the specific feed
streams, the desired recoveries and the like within the scope of
the processes disclosed above.
[0029] FIG. 2 illustrates another embodiment of a process in
accordance with the present invention. Note, when applicable, the
same reference numerals used in the description of FIG. 1 have been
used to identify comparable lines or equipment. In the process of
FIG. 2, the inlet gas stream is charged to the process via a line
10. The inlet feed gas is cooled in a heat exchanger 12 and
thereafter passed via a line 14 to a heat exchanger 15 where it is
further cooled to a selected temperature and passed via line 17 to
a fractionation column 26 containing one or more theoretical stages
of mass transfer. Fractionation column 26 is equipped with a
reboiler 28 to assist with separation of the C.sub.2 and lighter
components from the bottoms of the fractionation column. A portion
of the tower liquid from fractionation column 26 is directed to
reboiler 28 and at least partially vaporized and then reintroduced
into the bottom of fractionation column 26.
[0030] In fractionation column 26, a liquid bottoms product
comprising primarily C.sub.3 and heavier components plus some light
components is recovered via a line 30 and a pump 32 and pumped via
a line 34 to heat exchanger 12 where it is used to cool the inlet
gas stream in line 10. The stream in line 34 is then passed via to
a deethanizer 36. In deethanizer 32 the stream from line 34 is
separated by conventional distillation techniques into an overhead
vapor stream 38 and a bottoms stream 40. A conventional reboiler 42
is shown for with-drawing a portion of the deethanizer tower
liquid, at least partially vaporizing the withdrawn portion, and
returning the at least partially vaporized stream back to
deethanizer 36. The stream recovered from deethanizer 36 through
line 40 comprises primarily C.sub.3 and heavier components. An
overhead stream is recovered from the deethanizer via line 38,
which is rich in C.sub.2 and lighter components and is passed to a
heat exchanger 44 where it is at least partially condensed and then
through a line 46 to a separator 48. From separator 48, a liquid
stream is withdrawn via a line 50 and passed to a pump 52 from
which a portion of the liquid stream is passed via a line 54 into
an upper portion of deethanizer 36 as a reflux. The vapor stream
recovered from separator 48 is passed via a line 56 and through an
expansion valve 57. The vapor stream is then combined with the
residue gas from line 62 and directed toward a compressor 66 via
line 64.
[0031] A second portion of the liquid stream from separator 48 is
passed via a line 58 and a heat exchanger 60 into an upper portion
of fractionation column 26. An overhead vapor stream recovered from
the upper portion of fractionation column 26 is passed via a line
62 through heat exchanger 60 to combination with the stream in line
26. The combined stream carried by line 64 contains a major portion
of the C.sub.2 and lighter components from the inlet gas feed
stream. As noted above, the stream in line 64 is compressed by
compressor 66 and passed into line 68. A portion of the compressed
residue gas carried by line 68 is passed via a line 70 to a heat
exchanger 72 where it is cooled and condensed. In the embodiment
illustrated, the condensed portion of residue gas exiting heat
exchanger 72 is refluxed to the top of fractionation column 26. The
other portion of residue gas from line 68 is withdrawn from the
system via line 74.
[0032] It is noted that, as discussed above with respect to FIG. 1,
in certain embodiments, streams 56 and 62 may be kept separate.
When an additional reflux is desired for column 26, a slip stream
of the material carried by line 62 can be compressed, condensed,
and refluxed to the column. It is also noted that for any
embodiment discussed above, it is within the scope of the present
invention for the residue gas reflux carried by line 70 to be used
without equipping fractionation column 26 with a reboiler 28.
[0033] While the present invention has been described by reference
to certain of its preferred embodiments, it is respectfully pointed
out that the embodiments described are illustrative rather than
limiting in nature and that many variations and modifications are
possible within the scope of the present invention.
* * * * *