U.S. patent application number 17/735909 was filed with the patent office on 2022-08-18 for alternative two column hru design with rich reflux.
The applicant listed for this patent is CONOCOPHILLIPS COMPANY. Invention is credited to Michael J. CALDERON, Paul R. DAVIES, Dale L. EMBRY, David W. LARKIN, Qi MA.
Application Number | 20220260311 17/735909 |
Document ID | / |
Family ID | |
Filed Date | 2022-08-18 |
United States Patent
Application |
20220260311 |
Kind Code |
A1 |
EMBRY; Dale L. ; et
al. |
August 18, 2022 |
ALTERNATIVE TWO COLUMN HRU DESIGN WITH RICH REFLUX
Abstract
The invention relates to a system, method and apparatus for
removing heavies from natural gas. Natural gas and an external rich
reflux gas feed are processed in a single column refluxed absorber.
A bottoms stream is routed to a first heat exchanger and then to a
stabilizer column where an overhead stream from the stabilizer
column is routed through a condenser for partial separation into an
overhead stream. A rich solvent may be introduced to the stabilizer
column. The overhead stream is routed through a condenser for
partial separation into a stabilizer reflux and a second overhead
stream lights. The second overhead stream lights is routed to a
heat exchanger and then routed to a partial condenser where the
stream is separated into a heavies rich reflux stream, a distillate
stream and heavies treated natural gas stream. The rich reflux is
routed through a heat exchanger and the rich reflux is pumped to
the single column refluxed absorber to be introduced into the
single column refluxed absorber as the external rich reflux gas
feed.
Inventors: |
EMBRY; Dale L.; (Houston,
TX) ; DAVIES; Paul R.; (Houston, TX) ; MA;
Qi; (Houston, TX) ; LARKIN; David W.;
(Houston, TX) ; CALDERON; Michael J.; (Houston,
TX) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
CONOCOPHILLIPS COMPANY |
Houston |
TX |
US |
|
|
Appl. No.: |
17/735909 |
Filed: |
May 3, 2022 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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15925873 |
Mar 20, 2018 |
11320197 |
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17735909 |
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62473701 |
Mar 20, 2017 |
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International
Class: |
F25J 3/02 20060101
F25J003/02; C10L 3/10 20060101 C10L003/10; C10G 5/06 20060101
C10G005/06; C10G 5/04 20060101 C10G005/04 |
Claims
1. A method for natural gas processing, the method comprising:
introducing a natural gas feed to a single column refluxed
absorber; introducing an external rich reflux gas feed to the
single column refluxed absorber; processing the natural gas feed
and the external rich reflux gas feed in the single column refluxed
absorber to produce a first bottoms stream and a first overhead
stream, wherein the first bottoms stream and the first overhead
stream are separate streams upon expulsion from the single column
refluxed absorber; and outputting the first bottoms stream from the
single column refluxed absorber to a heat exchanger.
2. The method of claim 1, wherein the first bottoms stream is
output from the heat exchanger to a stabilizer column.
3. The method of claim 2, wherein the first bottoms stream is
processed in the stabilizer column to produce a second bottoms
stream and a second overhead stream.
4. The method of claim 3, wherein a heavies rich reflux stream is
formed from the second overhead stream.
5. The method of claim 4, wherein the heavies rich reflux stream is
pumped to the single column refluxed absorber to be introduced into
the single column refluxed absorber as the external rich reflux gas
feed.
6. The method of claim 1, wherein a heavies rich reflux stream is
formed using the first bottoms stream downstream from the heat
exchanger, the heavies rich reflux stream being introduced into the
single column refluxed absorber as the external rich reflux gas
feed.
7. The method of claim 1, wherein the first overhead stream is
output from the single column refluxed absorber through a condenser
for partial separation of the first overhead stream into
heavies-treated natural gas.
8. A system for processing natural gas, the system comprising: a
single column refluxed absorber comprising a natural gas feed inlet
at a lower elevation than an external rich reflux gas feed inlet,
the single column refluxed absorber configured to expulse a bottoms
stream; and a heat exchanger downstream from the single column
refluxed absorber, such that the bottoms stream is output from the
single column refluxed absorber into the heat exchanger.
9. The system of claim 8, further comprising: a stabilizer column
downstream from the first heat exchanger, such that the bottoms
stream is output from the heat exchanger into the stabilizer
column, the stabilizer column configured to produce a natural gas
by processing the bottoms stream.
10. The system of claim 9, wherein the natural gas is further
produced by processing a rich solvent.
11. The system of claim 9, wherein a rich reflux is produced
downstream from the stabilizer column using the natural gas.
12. The system of claim 11, wherein the rich reflux is introduced
as an external rich reflux to the single column refluxed absorber
using the external rich reflux gas feed inlet.
13. The system of claim 8, wherein an external rich reflux is
pumped into the single column refluxed absorber using the external
rich reflux gas feed inlet.
14. A system for processing natural gas, the system comprising: a
single column refluxed absorber comprising a natural gas feed inlet
at a lower elevation than an external rich reflux gas feed inlet,
the single column refluxed absorber configured to expulse a bottoms
stream via a bottoms outlet, the bottoms stream produced by
processing natural gas received via the natural gas feed inlet and
an external rich reflux received via the external rich reflux gas
feed inlet; and a heat exchanger downstream from the bottoms outlet
of the single column refluxed absorber, such that the bottoms
stream is received by the first heat exchanger from the bottoms
outlet of the single column refluxed absorber.
15. The system of claim 14, wherein a stabilizer column is
downstream from the heat exchanger, the stabilizer column
configured to receive the bottoms stream from the heat
exchanger.
16. The system of claim 15, wherein the stabilizer column is
configured to produce a natural gas by processing the bottoms
stream.
17. The system of claim 16, wherein a rich reflux is formed from
the natural gas.
18. The system of claim 17, wherein the rich reflux is input as the
external rich reflux to the single column refluxed absorber.
19. The system of claim 16, wherein a heavies treated natural gas
is formed from the natural gas.
20. The system of claim 16, wherein the natural gas is further
produced using a rich solvent.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of and claims the benefit
of priority under 35 U.S.C. .sctn..sctn. 111 and 120 to U.S.
Non-Provisional application Ser. No. 15/925,873 entitled
"ALTERNATIVE TWO COLUMN HRU DESIGN WITH RICH REFLUX" filed on Mar.
20, 2018, which is a non-provisional application that claims
benefit under 35 USC .sctn. 119(e) to U.S. Provisional Application
Ser. No. 62/473,701 filed Mar. 20, 2017, entitled "ALTERNATIVE TWO
COLUMN HRU DESIGN WITH RICH REFLUX." Each of these applications is
incorporated in its entirety herein.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
[0002] None.
FIELD OF THE INVENTION
[0003] The present invention relates generally to a method and
apparatus for processing natural gas. In another aspect, methods
and apparatus are provided for removing heavies from natural gas
using a light oil reflux in a heavies removal unit.
BACKGROUND OF THE INVENTION
[0004] In the processing of natural gas there are several
challenges with the existing heavies removal processes. First, to
separate C6+ species from the natural gas feed the reboiled
absorber (i.e. the heavies removal column) requires a dual column
design which increases its capital and operating costs. In
addition, the absorber's two column geometry is quite sensitive to
both feed composition and conditions when sizing it. As a result,
the compositional feed range a specific design can run may be quite
limiting. Finally, in some cases when the absorber's diameters are
too significantly different (i.e. due to feed composition) a
superstructure is required. This results in an additional increase
in processing costs.
BRIEF SUMMARY OF THE DISCLOSURE
[0005] The invention more particularly relates to a system, method
and apparatus for removing heavies from natural gas. Natural gas
and an external rich reflux gas feed are processed in a single
column refluxed absorber. A bottoms stream is routed to a first
heat exchanger and then to a stabilizer column where an overhead
stream from the stabilizer column is routed through a condenser for
partial separation into an overhead stream. A rich solvent may be
introduced to the stabilizer column. The overhead stream is routed
through a condenser for partial separation into a stabilizer reflux
and a second overhead stream lights. The second overhead stream
lights is routed to a heat exchanger and then routed to a partial
condenser where the stream is separated into a heavies rich reflux
stream, a distillate stream and heavies treated natural gas stream.
The rich reflux is routed through a heat exchanger and the rich
reflux is pumped to the single column refluxed absorber to be
introduced into the single column refluxed absorber as the external
rich reflux gas feed.
BRIEF DESCRIPTION OF THE DRAWINGS
[0006] A more complete understanding of the present invention and
benefits thereof may be acquired by referring to the follow
description taken in conjunction with the accompanying drawings in
which:
[0007] FIG. 1 illustrates a simplified diagram of a heavies removal
process using an external lean reflux;
[0008] FIG. 2 illustrates a conventional two-column heavies removal
unit design using an external rich reflux; and
[0009] FIG. 3 illustrates an alternative two-column heavies removal
unit design using an external rich reflux.
DETAILED DESCRIPTION
[0010] Turning now to the detailed description of the preferred
arrangement or arrangements of the present invention, it should be
understood that the inventive features and concepts may be
manifested in other arrangements and that the scope of the
invention is not limited to the embodiments described or
illustrated. The scope of the invention is intended only to be
limited by the scope of the claims that follow.
[0011] The following examples of certain embodiments of the
invention are given. Each example is provided by way of explanation
of the invention, one of many embodiments of the invention, and the
following examples should not be read to limit, or define, the
scope of the invention.
[0012] To address issues with heavies removal, an alternative two
column heavies removal unit (HRU) design with rich reflux with a
refluxed absorber and stabilizer can be used. As compared to a
reboiled absorber HRU design with rich reflux, methods and
apparatus provided with this disclosure provide for a refluxed
absorber with a shorter single column diameter unit with a
condenser, but no reboiler. This results in reducing the system's
overall capital and operating expenditures. It also increases its
operational feed flexibility as a result of column dimensions that
are not as sensitive to feed composition. Further, the absorber's
condenser helps reduce the system's C6+ loss and external solvent
loss to the overheads as well as increases its C6+ separation
efficiency.
[0013] The Liquefied Natural Gas (LNG) Optimized Cascade Process
uses a heavies removal distillation column to eliminate C6+
hydrocarbons (i.e. heavy components) from the natural gas prior to
condensing the gas to LNG. In the usual case gas has already been
amine treated and dehydrated prior to heavies removal. Heavies
removal is done in order to prevent freezing from occurring in the
liquefaction heat exchangers and to moderate the heating value of
the LNG.
[0014] As illustrated in FIG. 1, the existing heavies removal
process includes feeding chilled external lean reflux natural gas
103, which has been piped through heat exchanger 101 to the top of
the dual column reboiled absorber 105 where most of the C6+
components are removed. The dual column reboiled absorber 105 also
receives a natural gas feed 104. The heavies liquid bottom stream
106, passes through reboiler 107, is then sent 109 to a stabilizer
column 111 where it is stabilized as the heaviest components are
removed as condensate 115. The lighter components are separated
with condenser 116 into a methane rich recycle stream and external
lean reflux stream 118 sent to compressors 140 and sent to heat
exchanger 101 for delivery as external lean reflux 103 to the
heavies removal column 105. The heavies treated natural gas 124
feed exits the top of the heavies removal column 105. This overhead
stream 124 can now be further cooled by one or more heat exchangers
126 and optional heat exchanger 127, pass into flash drum 128 and
be separated as overhead 129 to deliver lean reflux to compressors
140, or exit bottom outlet as distillate 130 and be pumped 132 to
LNG storage/tankage 134.
[0015] One of the main issues with the current heavies removal
system is that the lean reflux rate to the heavies removal column
has to be considerably increased as the natural gas feed becomes
leaner in C2 through C5 components, but not in C6+ components. The
increase in rate allows the system to still be able to remove the
heavy components from the lean feed, but also increases its
compression costs (i.e. capex and opex due to gas compression
requirements).
[0016] An alternative HRU design as illustrated in FIG. 2,
Conventional Two Column HRU Design with Rich Reflux 200, replaces
the lean reflux stream (LNG) 103 with a rich one 203 comprised of
C2s through C5s. As illustrated in FIG. 2, the rich reflux stream
203 is fed to the column 205 (i.e. a reboiled absorber) to remove
C6+ components within the natural gas feed 204. After the bottom
liquid stream 206 passes through reboiler 207, the resulting liquid
bottom product stream 209 passes through heat exchanger 210 and is
then fed to the stabilizer 211 to produce condensate 215 from
reboiler 213 for sale. The overhead 217 in the stabilizer 211 is
partially condensed as overhead with condenser 216, then routed
through heat exchanger 226 and into partial condenser 228 in order
to produce 1) heavies treated natural gas to send through
compressor 240 to heavies treated natural gas 250, and 2)
distillates that may be pumped 242 to storage with heavies treated
natural gas 250 and 3) the rich reflux 203, routed through heat
exchanger 230 and pumped 232 as external rich reflux 203 to the
heavies removal column 205.
[0017] Since the reflux 203 is a liquid, the alternative design
does not need gas compression, but instead uses a pump 232 to set
the reflux flowrate (i.e. lower capex and opex requirements). In
addition, the rich reflux flowrate requirement is lower than the
lean one as a result of the higher separation efficiency of heavy
components within the HRU 205. In cases where the HRU wetting rate
from the rich reflux is too low (i.e. natural gas feed is too
lean), the design utilizes an external rich solvent 212 to maintain
an adequate rate. This rich solvent 212 (also referred as purchased
solvent) can be input into the process via the stabilizer 211 or
the recycle. The external solvent 212 is preferentially composed of
hydrocarbons ranging from ethane to pentane. Mixtures that are
predominately composed of isopentane and/or normal pentane are
preferred due to lower usage and improved performance in removal of
the heavies.
[0018] Although the conventional two column HRU rich reflux design
200 addresses the issue with lean feeds, there are several
additional challenges with a heavies removal system that neither it
nor the lean reflux design 100 addresses. First, to separate C6+
species from the natural gas feed the reboiled absorber 205 (i.e.
the heavies removal column) requires a dual column design which
increases its capex. In addition, the absorber's two column
geometry is quite sensitive to both feed composition and conditions
when sizing it. As a result, the compositional feed range a
specific design can run is quite limiting. Finally, in some cases
when the absorber's diameters are too significantly different (i.e.
due to feed composition) a superstructure is required. This results
in an additional increase in process capex.
[0019] To address these issues, as illustrated in FIG. 3 with the
Alternative Two Column HRU Design with Rich Reflux 300, the
methods, apparatus and systems provided herein replaces the dual
column reboiled absorber 205 in the conventional two column HRU
design with rich reflux 200, with a single column refluxed absorber
305. As illustrated in FIG. 3, the single column refluxed absorber
305 may be a shorter single column diameter unit with a condenser
307, with no reboiler. This results in reducing the system's
overall capital expenditures and operating expenditures. The
methods, apparatus and systems provided also increases the
operational feed flexibility as a result of column dimensions that
are not as sensitive to feed composition, making the system and
method especially favorable for use with highly variable
feedstocks. Further, the absorber's condenser 307 helps reduce the
units C6+ loss and external solvent 312 loss to the overheads as
well as increase its C6+ separation efficiency. Finally, the
stabilizer 311 provided with this system functions as the bottom
half of the previous 105 and 205, as well as 111 and 211.
[0020] As illustrated in FIG. 3, the rich reflux stream 303 is fed
to the single column refluxed absorber 305 to remove C6+ components
within the natural gas feed 304. After the bottom liquid stream 309
passes through heat exchanger 310 it is then fed to the stabilizer
311 to produce condensate 315 from reboiler 313 for sale. The
overhead 317 from the stabilizer 311 is partially condensed with
condenser 316, then routed to heat exchanger 326 and into partial
condenser 328 in order to produce 1) heavies treated natural gas to
send to compressor 340 and on to heavies natural gas storage 350,
and 2) distillates that may be pumped 342 to storage with heavies
treated natural gas storage 350, and 3) the rich reflux 303 routed
through heat exchanger 330 and pumped 332 as external rich reflux
303 to the heavies removal column 305.
[0021] Since the reflux 303 is a liquid, the alternative design
does not need gas compression, but instead uses a pump 332 to set
the reflux flowrate (i.e. lower capex and opex requirements). In
addition, the rich reflux flowrate requirement is lower than the
lean flowrate requirement as a result of the higher separation
efficiency of heavy components. In cases where the HRU wetting rate
from the rich reflux is too low (i.e. natural gas feed is too
lean), the design utilizes an external rich solvent 312 to maintain
an adequate rate. This rich solvent 312 (also referred as purchased
solvent) can be input into the process via the stabilizer 311 or
the recycle. The external solvent 312 is preferentially composed of
hydrocarbons ranging from ethane to pentane. Mixtures that are
predominately composed of isopentane and/or normal pentane are
preferred due to lower usage and improved performance in removal of
the heavies.
[0022] A nonlimiting method provided herein comprises introducing a
natural gas feed 304 to a single column refluxed absorber 305,
introducing an external rich reflux gas feed 303 to the single
column refluxed absorber 305, processing the natural gas feed 304
and the external rich reflux gas feed 303 in the single column
refluxed absorber 305 to produce a first bottoms stream 308 and a
first overhead stream 306, wherein the first bottoms stream 308 and
the first overhead stream 306 are separate streams upon expulsion
from the single column refluxed absorber 305, wherein the first
bottoms stream 308 is routed to a first heat exchanger 310 and then
to a stabilizer column 311 and the first overhead stream 306 is
routed through a condenser 307 for partial separation of the first
overhead stream into heavies-treated natural gas 324. The heavies
treated natural gas may then be routed to storage of heavies
treated natural gas. A rich solvent (C2 to C5) 312 may be
introduced to the stabilizer column 311. The first bottoms stream
308 and the rich solvent 312 is processed in the stabilizer column
311 to produce a second bottoms stream 314 and a second overhead
stream 317, wherein the second bottoms stream 314 and the second
overhead stream 317 are separate streams upon expulsion from the
stabilizer column 311, wherein the second bottoms stream 314 is
routed to a reboiler 313 and then the reboiler bottom stream
product is expelled as stabilized condensate 315, which may be
stored, and the second overhead stream 317 is routed through a
condenser 316 for partial separation of the second overhead stream
317 into a stabilizer reflux and a second overhead stream lights
325. The second overhead stream lights 325 is routed to a heat
exchanger 326 and then routed to the to a partial condenser 328. In
the partial condenser 328, the second overhead stream lights 325 is
separated into a heavies rich reflux stream 303, a distillate
stream 329 and heavies treated natural gas stream 339. The rich
reflux 303 is routed through a heat exchanger 330 and the rich
reflux 303 is pumped 332 to the single column refluxed absorber 305
to be introduced into the single column refluxed absorber 305 as
the external rich reflux gas feed 303.
[0023] In other aspects, the heavies treated natural gas is routed
from partial condenser to a compressor for storage of heavies
treated natural gas. The distillate stream may be routed from the
partial condenser through a pump for storage with heavies treated
natural gas. The external rich reflux feed inlet may be positioned
on the single column refluxed absorber at a higher elevation than
the natural gas feed inlet. In still another aspect, the rich
solvent comprises ethane, propane, butane and pentane. In addition,
the rich solvent may predominantly be composed of isopentane,
normal pentane, or both.
[0024] In another nonlimiting embodiment, an apparatus for
processing natural gas is provided, the apparatus comprises a
single column refluxed absorber 305 with a first condenser 307 and
a natural gas feed 304 inlet at a lower elevation than an external
rich reflux gas feed 303 inlet, a first heat exchanger 310
downstream from the bottoms outlet of the single column refluxed
absorber 305, a stabilizer column 311 downstream from the first
heat exchanger 310, the stabilizer column 311 comprising a second
condenser 316 and a reboiler 313, wherein the stabilizer column 311
has an inlet for a rich solvent 312 feed and wherein the second
condenser 316 partially separates a natural gas overhead 317 into
overhead stream lights 325 and a second heat exchanger 326
downstream of the second condenser 316. A partial condenser 328 is
downstream from the second heat exchanger 326 and is configured to
separate, from the overhead stream lights 325, heavies treated
natural gas 339 expelled though the overhead outlet, distillates
329 and rich reflux 303 expelled from the bottoms outlet. A third
heat exchanger 330 is downstream from the bottoms outlet of the
partial condenser and a first pump 332 is downstream from the third
heat exchanger 330 to pump the rich reflux 303, as an external rich
reflux, to the single column refluxed absorber 305. The distillate
stream 329 may be pumped 342 to heavies treated natural gas.
[0025] In another aspect the apparatus further comprises a heavies
treated natural gas storage downstream from the first condenser, a
compressor downstream from an overhead outlet for compressing
overhead vapor from the partial condenser, a stabilized condensate
storage downstream from the reboiler of the stabilizer and a second
pump downstream from the bottoms outlet of the partial condenser,
to pump distillates to a heavies treated natural gas storage.
[0026] In still another nonlimiting embodiment, a system for
processing natural gas comprises a single column refluxed absorber
305 with a first condenser 307 and a natural gas feed 304 inlet at
a lower elevation than an external rich reflux gas feed 303 inlet,
a first heat exchanger 310 downstream of a bottoms outlet of the
single column refluxed absorber 305, a stabilizer column 311
downstream from the first heat exchanger 310, the stabilizer column
305 comprising a second condenser 316 and a reboiler 313, wherein
the stabilizer column has an inlet for a rich solvent feed 312 and
wherein the second condenser 316 partially separates a natural gas
overhead 317 into overhead stream lights 325. A second heat
exchanger 326 is downstream of the second condenser 316. A partial
condenser 328 is downstream from the second heat exchanger 326 and
is configured to separate, from the overhead stream lights, heavies
treated natural gas 339 that is expelled though the overhead
outlet, distillates 329 and rich reflux 303 expelled through a
bottoms outlet, and a third heat exchanger 330 is downstream from
the bottoms outlet of the partial condenser 328 to cool the rich
reflux 303. A first pump 332 is downstream from the third heat
exchanger 330 to pump the rich reflux 303, as an external rich
reflux, to the single column refluxed absorber 305. Additionally,
there may be a compressor 340 downstream from the partial condenser
328 overhead outlet, in order to compress the heavies treated
natural gas, and a second pump 342 may be downstream from the
bottoms outlet of the partial condenser to pump distillates 329 to
a heavies treated natural gas storage.
[0027] In closing, it should be noted that the discussion of any
reference is not an admission that it is prior art to the present
invention, especially any reference that may have a publication
date after the priority date of this application. At the same time,
each and every claim below is hereby incorporated into this
detailed description or specification as a additional embodiments
of the present invention.
[0028] Although the systems and processes described herein have
been described in detail, it should be understood that various
changes, substitutions, and alterations can be made without
departing from the spirit and scope of the invention as defined by
the following claims. Those skilled in the art may be able to study
the preferred embodiments and identify other ways to practice the
invention that are not exactly as described herein. It is the
intent of the inventors that variations and equivalents of the
invention are within the scope of the claims while the description,
abstract and drawings are not to be used to limit the scope of the
invention. The invention is specifically intended to be as broad as
the claims below and their equivalents.
* * * * *