U.S. patent application number 14/520939 was filed with the patent office on 2016-04-28 for processes and systems for refining fuel gas.
The applicant listed for this patent is UOP LLC. Invention is credited to Luigi Laricchia, Jessy E. Trucko.
Application Number | 20160115409 14/520939 |
Document ID | / |
Family ID | 55791496 |
Filed Date | 2016-04-28 |
United States Patent
Application |
20160115409 |
Kind Code |
A1 |
Laricchia; Luigi ; et
al. |
April 28, 2016 |
PROCESSES AND SYSTEMS FOR REFINING FUEL GAS
Abstract
Processes and systems are provided for refining fuel gas. The
processes involve first and second water wash stages, before and
after a caustic wash stage, in which fuel gas is contacted with
water for removing amine and caustic compounds from the fuel gas.
The systems for refining LPG comprise a first water wash vessel and
a caustic wash vessel, followed by a second water wash vessel,
wherein the water wash vessels are each adapted for contacting the
LPG with water to remove amine and caustic compounds therefrom.
Inventors: |
Laricchia; Luigi; (Arlington
Heights, IL) ; Trucko; Jessy E.; (Lake Forest,
IL) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
UOP LLC |
Des Plaines |
IL |
US |
|
|
Family ID: |
55791496 |
Appl. No.: |
14/520939 |
Filed: |
October 22, 2014 |
Current U.S.
Class: |
585/836 ;
422/187 |
Current CPC
Class: |
C10L 2290/56 20130101;
C10L 3/12 20130101; C10L 2290/541 20130101; C10L 2290/545 20130101;
C10L 3/103 20130101; C10L 3/104 20130101 |
International
Class: |
C10L 3/12 20060101
C10L003/12 |
Claims
1. A process for refining fuel gas comprising: providing a fuel gas
comprising an amine compound; contacting the fuel gas with water in
a first water wash stage to remove at least a portion of the amine
compound therefrom and produce a washed fuel gas; contacting the
washed fuel gas with either a caustic to remove acid gas or a blend
of a caustic and an amine to remove both acid gas and carbonyl
sulfide (COS) from the washed fuel gas and produce a caustic
treated fuel gas comprising residual amine and residual caustic;
and contacting the caustic treated fuel gas with water in a second
water wash stage to remove residual amines and residual caustic
therefrom and produce a rewashed fuel gas substantially free of
amine and caustic.
2. The process of claim 1, wherein contacting the fuel gas with
water in a first water wash stage further comprises using a
coalescing material.
3. The process of claim 1, wherein contacting the caustic treated
fuel gas with water in a second water wash stage further comprises
using a coalescing material, which may be the same or different
from the coalescing material used in the first water wash
stage.
4. The process of claim 1, wherein providing the fuel gas comprises
contacting a fuel gas with an amine compound to remove hydrogen
sulfide (H.sub.2S), carbon dioxide (CO.sub.2), or both, therefrom
and produce an amine treated fuel gas comprising an amine compound,
and wherein the amine treated fuel gas is then contacted with
water.
5. The process of claim 4, wherein contacting the fuel gas with an
amine compound is performed by absorption with an aqueous solution
comprising the amine compound.
6. The process of claim 4, wherein providing the fuel gas comprises
providing liquefied petroleum gas (LPG).
7. The process of claim 1, wherein contacting the washed fuel gas
with caustic is performed using a strong base selected from sodium
hydroxide and potassium hydroxide as the caustic.
8. The process of claim 1, wherein a single vessel is used for
contacting the fuel gas with water to produce the washed fuel gas,
and for contacting the washed fuel gas with a caustic to produce
the caustic treated fuel gas comprising residual amine and residual
caustic, and for contacting the caustic treated fuel gas with water
in a second water wash stage to the rewashed fuel gas substantially
free of amine and caustic.
9. The process of claim 8, wherein the fuel gas is chosen from:
methane, ethane, propane, isobutene and mixtures thereof.
10. The process of claim 1, further comprising removing mercaptans
from the rewashed fuel gas.
11. The process of claim 10, wherein removing mercaptans from the
rewashed fuel gas comprises contacting the rewashed fuel gas with
an aqueous caustic solution in the presence of a catalyst to
produce a refined fuel gas product and an aqueous solution
comprising mercaptan derivatives; and heating and oxidizing the
aqueous solution comprising mercaptan derivatives to convert the
mercaptan derivatives to disulfides and regenerated caustic.
12. A process for refining fuel gas comprising: contacting a fuel
gas with an amine compound to remove hydrogen sulfide (H.sub.2S),
carbon dioxide (CO.sub.2), or both therefrom and produce an amine
treated fuel gas comprising an amine compound; contacting the amine
treated fuel gas with water to remove at least a portion of the
amine compound therefrom and produce a washed fuel gas; contacting
the washed fuel gas with a either a caustic to remove acid gas or a
blend of a caustic and an amine to remove both acid gas and
carbonyl sulfide (COS) from the washed fuel gas and produce a
caustic treated fuel gas comprising residual amine and residual
caustic; contacting the caustic treated fuel gas with water to
remove residual amines and residual caustic therefrom and produce a
rewashed fuel gas substantially free of amine and caustic; and
removing mercaptans from the rewashed fuel gas.
13. The process of claim 12, wherein contacting the fuel gas with
water in a first water wash stage further comprises contacting the
fuel gas and water with a coalescing material.
14. The process of claim 12, wherein contacting the caustic treated
fuel gas with water in a second water wash stage further comprises
contacting the caustic treated fuel gas with a coalescing material,
which may be the same or different from the coalescing material in
the first water wash stage.
15. The process of claim 12, wherein contacting a fuel gas with an
amine compound to remove hydrogen sulfide (H.sub.2S), carbon
dioxide (CO.sub.2), or both therefrom comprises selecting and
using, as the amine, one or more compounds chosen from:
monoethanolamine, diethanolamine, diglycolamine, methyl
diethanolamine (MDEA), MDEA-based solvents, and
diisopropylamine.
16. A system for refining liquefied petroleum gas (LPG) comprising:
a first water wash vessel; a caustic wash vessel in fluid
communication with, and located downstream of, the first water wash
vessel; and a second water wash vessel in fluid communication with,
and located downstream of, the caustic wash vessel.
17. The system of claim 16, wherein the first water wash vessel
comprises an interior and a coalescing material positioned within
the interior.
18. The system of claim 16, wherein the second water wash vessel
comprises an interior and a coalescing material positioned within
the interior, wherein the coalescing material may be the same or
different from the coalescing material of the first water wash
vessel.
19. The system of claim 16, further comprising an absorber wherein
the first water wash vessel is in fluid communication with, and
located downstream of, the absorber.
20. The system of claim 16, further comprising mercaptan removal
apparatus.
Description
TECHNICAL FIELD
[0001] The technical field generally relates to processes and
systems for refining fuel gas, and more particularly relates to
processes and systems for the removal of sulfur compounds from fuel
gas using an amine and a caustic to produce a refined fuel gas
substantially free of residual amine and residual caustic.
BACKGROUND
[0002] Fuel gases are a category of hydrocarbon mixtures in which
the hydrocarbons have from one to four carbons per molecule (i.e.,
C.sub.1-C.sub.4 hydrocarbons). Fuel gases are gaseous under normal
conditions and useful as sources of energy and light when burned.
In particular, natural gas is one type of fuel gas primarily
comprised of methane (C.sub.1 hydrocarbons). Mixtures containing
primarily C.sub.3-C.sub.4 hydrocarbons (i.e., propane and butane)
are also gaseous under normal conditions, but are sometimes
converted to liquefied petroleum gas (LPG) by pressurization to
convert them to liquid form, which reduces volume and facilitates
storage, delivery and use. LPGs are relatively clean burning fuels
useful for heating, cooking, and an alternative vehicle fuel, as
well as an aerosol propellant and a refrigerant.
[0003] Particularly when derived from petroleum, fuel gases often
contain undesirable components including sulfur compounds and
carbon dioxide, among others, which adversely affect various
refining steps and end use application. More particularly, for
example, fuel gases are often treated with an amine compound to
remove hydrogen sulfide (H.sub.2S) and carbon dioxide (CO.sub.2),
followed by removal of carbonyl sulfide (COS) and possibly
additional H.sub.25 by contact with caustic in a prewash unit.
After removal of H.sub.2S, CO.sub.2, and COS, mercaptans (R-SH) are
removed from the fuel gas, such as by extraction in the presence of
caustic, followed by conversion of the extracted mercaptans to
organic disulfides and regenerated caustic that can be recycled and
reused.
[0004] Amine solubility in fuel gases, as well as amine entrainment
in the process streams of fuel gas refinement processes, results in
the presence of amines in the effluent of the amine treatment stage
as well as in subsequent process stages, which is often referred to
as amine carryover. Amine carryover in fuel gas refining processes
is one of the major causes of amine losses and serious problems in
stages downstream of the amine treatment stage. For example, when
amines are mixed with caustic solutions in the presence of
hydrocarbons, emulsions are formed that adversely affect the
composition of the final fuel gas product, cause higher caustic
consumption and corrosion of carbon steel in downstream process
units, and require operation at lower hydrocarbon flow rates that
decreases production. Additionally, any amines remaining in the
effluent of the caustic prewash stage, when fed to the mercaptan
extraction stage, reduces the capability of the mercaptan
extraction stage to produce refined fuel gas having the required
low nitrogen content. Amine carryover is often exacerbated when
refining LPG derived from fluid catalytic cracking processes or
from the coker units of atmospheric or vacuum distillation
processes.
[0005] Following amine treatment for removal of H.sub.2S and
CO.sub.2, but prior to contact with caustic for removal of COS,
fuel gas is sometimes subjected to a water wash to remove soluble
amines and reduce formation of unwanted emulsions during the
caustic prewash step. However, amine carryover remains an issue
even in processes that include a water wash stage prior to caustic
prewash, or knockout (KO) drums for removing entrained amines, or
both, since such apparatus typically does not include internal
features to enhance separation between amine and spent water from
the hydrocarbons.
[0006] Accordingly, it is desirable to develop processes for
refining fuel gas that provide improved removal of unwanted
compounds. In addition, it is desirable to provide processes for
refining fuel gas wherein substantially all the amine is removed
prior to subjecting the fuel gas to treatment for mercaptan
removal. Furthermore, other desirable features and characteristics
of the present invention will become apparent from the subsequent
detailed description of the invention and the appended claims,
taken in conjunction with the accompanying drawings and this
background of the invention.
BRIEF SUMMARY
[0007] Processes and systems are provided for refining fuel gas. An
exemplary embodiment of the process comprises: providing a fuel gas
comprising an amine compound; contacting the fuel gas with water in
a first water wash stage to remove at least a portion of the amine
compound therefrom and produce a washed fuel gas; contacting the
washed fuel gas with either a caustic to remove acid gas (H.sub.2S,
CO.sub.2, or both) or a blend of a caustic and an amine to remove
both acid gas and carbonyl sulfide (COS) from the washed fuel gas
and produce a caustic treated fuel gas comprising residual amine
and residual caustic. The process further comprises contacting the
caustic treated fuel gas with water in a second water wash stage to
remove residual amines and residual caustic therefrom and produce a
rewashed fuel gas substantially free of amines and caustic.
[0008] In another exemplary embodiment, a process for refining fuel
gas comprising: contacting a fuel gas with an amine compound to
remove hydrogen sulfide (H.sub.2S), carbon dioxide (CO.sub.2), or
both, therefrom and produce an amine treated fuel gas comprising an
amine compound; and contacting the amine treated fuel gas with
water to remove at least a portion of the amine compound therefrom
and produce a washed fuel gas. The process further comprises,
contacting the washed fuel gas with either a caustic to remove acid
gas or a blend of a caustic and an amine to remove both acid gas
and carbonyl sulfide (COS) from the washed fuel gas and produce a
caustic treated fuel gas comprising residual amine and residual
caustic; contacting the caustic treated fuel gas with water to
remove residual amines and residual caustic therefrom and produce a
rewashed fuel gas substantially free of amines and caustic; and
removing mercaptans from the rewashed fuel gas.
[0009] In still another embodiment, a system for refining LPG
comprising: a first water wash vessel capable of receiving and
contacting LPG with water to remove an amine compound from the LPG
and produce a washed LPG; a vessel capable of receiving and
contacting the washed LPG with either a caustic to remove acid gas
or a blend of a caustic and an amine to remove both acid gas and
carbonyl sulfide (COS) from the washed fuel gas and produce a
caustic treated LPG comprising residual amine; and a second water
wash vessel capable of receiving and contacting the caustic treated
LPG with water to remove residual amine therefrom and produce a
rewashed LPG substantially free of amines.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] The present invention will hereinafter be described in
conjunction with the following drawing figures, wherein like
numerals denote like elements, and wherein:
[0011] FIG. 1 is a block diagram showing an exemplary embodiment of
a refining system including first and second water wash stages that
are vertically oriented; and
[0012] FIG. 2 is a block diagram showing another exemplary
embodiment of a refining system including first and second water
wash stages that are horizontally oriented.
DETAILED DESCRIPTION
[0013] The following detailed description is merely exemplary in
nature and is not intended to limit the processes and systems
contemplated herein, or the application and uses thereof.
Furthermore, there is no intention to be bound by any theory
presented in the preceding background or the following detailed
description.
[0014] The processes and systems contemplated and described herein
are directed to removal of unwanted compounds, including one or
more of H.sub.2S, CO.sub.2, COS, and mercaptans, from fuel gas, as
well as removing amine compounds and caustic that are often used to
remove the aforesaid unwanted compounds but which interfere with
other refining stages. The processes and systems contemplated and
described herein are suitable for refining any fuel gas, including
natural gas (methane), ethane, mixtures of methane and ethane
(i.e., mixtures of C.sub.1-C.sub.2 hydrocarbons), propane, butane,
mixtures of propane and butane (i.e., mixtures of C.sub.3-C.sub.4
hydrocarbons), and LPG (liquefied mixtures of C.sub.3-C.sub.4
hydrocarbons). More specifically, the processes and systems
described hereinbelow are suitable for refining liquid phase fuel
gases such as LPG, as well as fuel gases that are in gaseous form
such as the others types of fuel gases listed above. The fuel gas
may be derived from any one or more of various sources including,
without limitation, fractionation processes and apparatus, straight
run petroleum refining processes and apparatus, fluidized catalytic
cracking processes and apparatus, and thermal cracking processes
and apparatus (e.g. coker units).
[0015] Additionally, the refining of fuel gas generally involves
various treatments, operations, stages, techniques and methods for
achieving various goals, all of which are ultimately aimed at
producing pure hydrocarbon products having desired characteristics
for particular end uses. Accordingly, it should be understood that
the processes and systems contemplated and described herein may
exist, and be performed or operated, within the context of larger
refining processes and systems, or more complex refining processes
and systems, or both.
[0016] In an exemplary embodiment, the process for refining fuel
gas contemplated and described herein comprises providing a fuel
gas comprising an amine compound, and contacting that fuel gas with
water in a first water wash stage to remove at least a portion of
the amine compound therefrom and produce a washed fuel gas. In the
first water wash stage, after contacting the fuel gas and water,
the amine compound migrates from the fuel gas (organic phase) and
is dissolved into the water (aqueous phase) and aqueous and organic
phases are separated, such as by gravity separation where both
phases are liquid (as when refining LPG), or liquid-gas phase
separation where the aqueous phase is liquid and the organic phase
is gaseous (as when refining a gaseous fuel gas). The resulting
organic phase is the washed fuel gas that is subjected to further
processing, and the resulting aqueous phase can be processed or
recycled, or both, as desired.
[0017] The washed fuel gas from the first water wash stage is then
contacted, in a caustic wash stage, with either a caustic to remove
acid gas (i.e., H.sub.2S, CO.sub.2, or both) or a blend of a
caustic and an amine to remove both acid gas and carbonyl sulfide
(COS) from the washed fuel gas and produce a caustic-treated fuel
gas. In either case, suitable caustic includes sodium hydroxide
(NaOH) and potassium hydroxide (KOH), with NaOH being the more
common choice. Where a blend of caustic and amine is used, the
amine is comprised of primary amines, secondary amines, or mixtures
thereof. Since undesirable emulsions are formed when amines are
mixed with caustic solutions in the presence of hydrocarbons,
removal of residual amine compounds in the fuel gas before
contacting the fuel gas with caustic to remove COS improves the
effectiveness and efficiency of the COS removal during the caustic
wash stage. However, the first water wash stage removes a majority
of the amine compound which improves performance of the caustic
wash stage, but the caustic treated fuel gas still contains
residual amine compound, as well as residual caustic from the
caustic wash stage. Furthermore, additional amine compound may be
added during the caustic wash stage to assist in removal of
unwanted compounds, such as H.sub.2S, in the washed fuel gas, which
consequently increases the total amine compound content of the
caustic treated fuel gas. Any additional amine compound used in the
caustic wash stage may be the same or different from the amine
compound present in the fuel gas prior to the first water wash
stage.
[0018] Removal of substantially all residual amine compounds is
important for today's refining processes to produce hydrocarbon
streams having the required low levels of unwanted compounds to
avoid downstream operational and product quality issues where the
fuel gas will undergo further refinement stages. Consequently, the
caustic treated fuel gas containing residual amine compound is
contacted with water in a second water wash stage to remove
residual amine therefrom and produce a rewashed fuel gas
substantially free of amine compounds. The second water wash phase
operates substantially the same as the first water wash stage,
except that in the second water wash stage, the caustic also
migrates from the fuel gas (organic phase) to the water (aqueous
phase) so that when the aqueous and organic phases are formed and
separated, the aqueous phase contains amine compound and
caustic.
[0019] "Substantially free of amine compounds," means that any
amines present in the rewashed fuel gas are below the amount that
causes downstream operational and product quality issues. For
example, "substantially free of amine compounds" as used herein,
means that the rewashed fuel gas comprises no more than about 60
parts per million by weight (ppm) total amine compound. For
example, without limitation, the rewashed fuel gas may comprise no
more than about 50 ppm total amine compound, or no more than about
30 ppm total amine compound, or even no more than about 10 ppm
total amine compound.
[0020] Similarly, "substantially free of caustic compounds," means
that any caustic present in the rewashed fuel gas are below the
amount that cause downstream operational and product quality
issues. More particularly, and independently of the amine content,
"substantially free of caustic compounds" as used herein, means
that the rewashed fuel gas comprises no more than about 60 ppm
total caustic compound. For example, without limitation, the
rewashed fuel gas may comprise no more than about 50 ppm total
caustic compound, or no more than about 30 ppm total caustic
compound, or even no more than about 10 ppm total caustic
compound.
[0021] In some embodiments, such as when the fuel gas being refined
is LPG, during either the first water wash stage or the second
water wash stage, or both, the fuel gas (or caustic treated fuel
gas, as applicable) and water are also contacted with coalescing
material to enhance aqueous-organic phase separation and removal of
the amine compound from the fuel gas. More particularly, the
coalescing material may be any material known now or in the future
to be hydrophilic and facilitate aqueous-organic phase separation.
For example, without limitation, the coalescing material may be
mesh made of metal such as stainless steel, and may further be
coated with a hydrophilic material such as a polymer. The
coalescing material may be present in a layer that is from about
15.24 centimeters (cm) (6 inches) to about 60.96 cm (24 inches)
thick. Additionally, the coalescing material used in each of the
first and second water wash stages may be the same or different
from one another, in composition as well as physical form and
size.
[0022] When the fuel gas being refined is a gaseous fuel gas such
as including natural gas (methane), ethane, propane, butane, or
mixtures of two or more of these hydrocarbons, the fuel gas (or
caustic treated fuel gas, as applicable) and water forms a
liquid-gas system for which coalescing material is less
advantageous. Accordingly, in embodiments where the fuel gas is a
gaseous type of fuel gas, the fuel gas (or the caustic treated fuel
gas, if applicable) and water may also be contacted with an
internal device positioned within one or both of the first and
second water wash stages, for enhancing aqueous-organic phase
separation and removal of the amine compound from the gaseous
organic phase fuel gas. The internal device is not particularly
limited and may be any internal device known now or in the future
that facilitates phase separation in liquid-gas systems. Suitable
internal devices include, for example, one or more bubble trays,
sieve trays, packed beds and other contacting devices.
[0023] Furthermore, it is noted that when the fuel gas is a gaseous
type of fuel gas that is being refined, contacting the fuel gas
with water in the first water wash stage, contacting the resulting
washed fuel gas with caustic in a caustic wash stage, then
contacting the resulting caustic treated fuel gas with water in the
second water wash stage may all be performed in the same vessel,
such as a single vertical column A suitable single vessel would, of
course, be capable of allowing the gaseous fuel gas to flow from
one end to an opposite end of the vessel, while also allowing the
fuel gas to sequentially contact the water, caustic and then water
again to produce a rewashed fuel gas suitable for further
refinement. In some embodiments, the vessel is capable of also
contacting the liquid-gas mixture comprising gaseous fuel gas and
water with internal devices positioned within the vessel to enhance
phase separation during the first water wash stage, caustic wash
stage, and second water wash stage occurring therein.
[0024] In another exemplary embodiment, regardless of whether the
fuel gas is gaseous or LPG, providing a fuel gas comprising an
amine compound includes first providing a fuel gas comprising
unwanted compounds including hydrogen sulfide (H.sub.2S), carbon
dioxide (CO.sub.2), and carbonyl sulfide (COS) and contacting that
fuel gas with an amine compound to remove hydrogen sulfide
(H.sub.2S), carbon dioxide (CO.sub.2), or both, therefrom.
Contacting the fuel gas with an amine compound produces an amine
treated fuel gas comprising an amine compound. Contacting the fuel
gas with an amine compound may, for example, be performed by
absorption with an aqueous solution comprising the amine compound.
Where the fuel gas is LPG, the absorption will occur as a
liquid-liquid absorption process. In such embodiments where fuel
gas containing unwanted compounds is contacted with an amine
compound, the resulting amine treated fuel gas, which consequently
comprises an amine compound, is contacted with water in the first
water wash stage. The amine compound may be any amine compound
known now or in the future to be a good solvent for H.sub.2S and
CO.sub.2 and at least partially soluble in aqueous solution.
Suitable amine compounds include one or more compounds chosen from,
for example without limitation, monoethanolamine (MEA),
diethanolamine (DEA), diglycolamine (DGA), methyl diethanolamine
(MDEA), MDEA-based solvents, and diisopropylamine (DIPA), among
others.
[0025] In still another exemplary embodiment, the process further
comprises removing mercaptans from the rewashed fuel gas. Removal
of mercaptans may be accomplished by any technique known now or in
the future. For example, mercaptans (RSH) may be removed from the
rewashed fuel gas by a two stage process in which the first stage
involves contacting the rewashed fuel gas with caustic (MOH, where
M is sodium, Na, or potassium, K) in the presence of a catalyst
capable of catalyzing the conversion and extraction of the
mercaptan in metal salt form (M-SR) into an aqueous caustic
solution. Suitable catalysts are commercially available, for
example, from UOP LLC of Des Plaines, Ill., USA. In addition to the
aqueous caustic solution containing the mercaptan derivatives
(M-SR), the first stage also produces a refined fuel gas product.
In the second stage, generally referred to as regeneration, the
aqueous caustic solution containing the mercaptan derivatives
(M-SR) is heated and oxidized to form insoluble disulfides (RSSR)
and regenerated caustic (MOH). Moreover, in some embodiments such
as where the fuel gas is a gaseous phase material, the
above-described three contacting steps (first water wash, caustic
wash, and second water wash), as well as removing mercaptans from
the rewashed fuel gas, may all be performed in the same vessel as
described earlier hereinabove.
[0026] Amines entering the mercaptan removal phase of the refining
process are generally not removed or otherwise altered and,
therefore, often cause fuel gas products having unacceptably high
nitrogen content, as well as potential process upsets in stages
downstream of the mercaptan removal phase. Thus, employing the
second water wash stage to remove additional residual amine
compounds prior to subjecting the caustic treated and rewashed fuel
gas to mercaptan removal processes improves the effectiveness and
efficiency of the mercaptan removal process as well as downstream
refining stages.
[0027] A system for refining LPG will now be described in detail
with reference to FIGS. 1 and 2 which provide schematic diagrams of
such systems. In an exemplary embodiment, the system 10, 110 for
refining LPG comprises a first water wash vessel 12, 112, a caustic
wash vessel 14, 114 and a second water wash vessel 16, 116. More
particularly, the first water wash vessel 12, 112 is capable of
receiving and contacting LPG 18, 118 with water (provided via lines
46, 48, 146, 148, respectively) to remove an amine compound from
the LPG 18, 118 and produce a washed LPG 20, 120.
[0028] The caustic wash vessel 14, 114 is in fluid communication
with, and located downstream of, the first water wash vessel 12,
112. The caustic wash vessel 14, 114 is capable of receiving and
contacting the washed LPG 20, 120 with a caustic to remove acid
gas, or a blend of caustic and amine (provided via line 15, 115,
respectively) to remove both acid gas and carbonyl sulfide (COS)
from the washed LPG and produce a caustic treated LPG 22, 122
comprising residual amine. In either case, the caustic is a strong
base selected from sodium hydroxide (NaOH) and potassium hydroxide
(KOH). Where a blend of caustic and amine is used, the amine is
comprised of primary amines, secondary amines, or mixtures thereof.
The second water wash vessel 16, 116 in fluid communication with,
and located downstream of, the caustic wash vessel 14, 114. The
second water wash vessel 16, 116 is capable of receiving and
contacting the caustic treated LPG 22, 122 with water (not shown)
to remove residual amine and residual caustic therefrom and produce
a rewashed LPG 24, 124 substantially free of amine and caustic
compounds. The first water wash vessel 12 and second water wash
vessel 16 may each be oriented vertically as shown in FIG. 1, or
they 112, 116 may be oriented horizontally as shown in FIG. 2.
"Substantially free of amine compounds" has the same meaning as
stated hereinabove.
[0029] As mentioned above in connection with the first and second
water wash stages, coalescing material may also be contacted with
the LPG and water to facilitate aqueous-organic phase separation.
Accordingly, as shown in each of FIGS. 1 and 2, either or both of
the first and second water wash vessels 12, 112, 16, 116 may
include coalescing material 26, 126, 28, 128 in the interiors
thereof, respectively. Suitable coalescing materials are as
described above. The coalescing material 26, 126 in the interior of
the first water wash vessel 12, 112 may be the same or different,
in composition as well as physical form and size, from the
coalescing material 28, 128 in the interior of the second water
wash vessel 16, 116. As shown in FIG. 1, when the first and second
water wash vessels 12, 16, are oriented vertically, the coalescing
material 26, 28 is oriented horizontally. When the first and second
water wash vessels 112, 116 are oriented horizontally, as shown in
FIG. 2, the coalescing material 126, 128 is oriented
vertically.
[0030] Regardless of whether they are oriented vertically or
horizontally, or whether the include coalescing material, each of
the first and second water wash vessels 12, 112, 16, 116 produces
spent wash water 42, 142, 44, 144, respectively. The spent wash
water 42, 142, 44, 144 may be sent for further processing, or
recycled to one or both of the first and second water wash vessels
12, 112, 16, 116, as shown in FIGS. 1 and 2. Furthermore, fresh
water may be provided to one or both of the first and second water
wash vessels 12, 112, 16, 116 via fresh water inlets 46, 146, 48,
148, respectively, which are in direct or indirect fluid
communication with the first and second water wash vessels 12, 112,
16, 116, respectively.
[0031] In some embodiments, as shown in FIGS. 1 and 2, the system
10, 110 also comprises an absorber 30, 130 capable of receiving and
contacting LPG 32, 132 with an amine compound (not shown) to remove
H.sub.2S, CO.sub.2, or both, from the LPG 32, 132 and produce an
amine treated LPG 34, 134 comprising residual amine compounds. In
such embodiments, the first water wash vessel 12, 112 is in fluid
communication with the absorber 30, 130 for receiving and
contacting the amine treated LPG 34, 134 with water (not shown).
Suitable amine compounds are as described above. In such
embodiments, i.e., systems that include an absorber upstream of the
first water wash stage, the amine treated LPG 34, 134 serves as the
LPG 18, 118 that is provided to the first water wash stage for
contacting with water.
[0032] In still other embodiments, the system 10, 110 for refining
LPG further comprises apparatus capable of removing mercaptans from
the rewashed LPG 24, 124. For example, as shown in FIGS. 1 and 2,
such apparatus may comprise an extractor 36, 136 capable of
receiving and contacting the rewashed LPG 24, 124 with caustic
(MOH, where M is sodium, Na, or potassium, K). The extractor 36,
136 generally comprises a catalyst (not shown per se) capable of
catalyzing the conversion and extraction of the mercaptans, as
described above. The extractor 36, 136 produces an LPG product 38,
138 and an aqueous caustic solution 40, 140 comprising the
mercaptan in metal salt form, as also previously described above.
The system 10, 110 may further comprise a regeneration vessel (not
shown) capable of receiving the aqueous caustic solution 40, 140
from the extractor 36, 136 and heating and oxidizing the aqueous
caustic solution 40, 140 to form insoluble disulfides and
regenerated caustic (not shown).
[0033] Although not shown in the figures, it should be appreciated
that the system 10, 110 shown in FIGS. 1 and 2 may be modified for
refining fuel gas in gaseous form, such as natural gas (methane),
ethane, mixtures of methane and ethane (i.e., mixtures of
C.sub.1-C.sub.2 hydrocarbons), propane, butane, mixtures of propane
and butane (i.e., mixtures of C.sub.3-C.sub.4 hydrocarbons), and
mixtures of C.sub.1-C.sub.4 hydrocarbons. Such modifications to the
system 10 shown in FIG. 1 will now be discussed in further detail.
More particularly, in an exemplary embodiment of a modified system
(not shown per se) for refining fuel gas, the first water wash
vessel 12, the caustic wash vessel 14, and the second water wash
vessel 16 are instead replaced by a vessel, such as a multi-stage
column, capable of receiving fuel gas in a bottom portion thereof
and allowing the fuel gas to flow upward through the column
Furthermore, the multi-stage column comprises a first water wash
zone located proximate the bottom portion of the column, a caustic
(or caustic-amine blend) wash zone located in a middle portion of
the column, and a second water wash zone located an upper portion
of the column Instead of coalescing material (see 26, 126, 28, 128
in FIG. 1), the first and second water wash zones of the
multi-stage column may each include internal devices such as bubble
trays (not shown per se) to facilitate contact between the gaseous
fuel gas and water in each water wash stage and, thereby enhance
phase separation. Additionally, a system (not shown) for refining
gaseous fuel gas may include an absorber adapted for receiving and
contacting gaseous fuel gas with a liquid aqueous solution
containing an amine compound. For example, such an absorber may
comprise a plurality of trays to increase gas-liquid phase contact
between the gaseous fuel gas and the aqueous amine solution.
[0034] While at least one exemplary embodiment has been presented
in the foregoing detailed description of the invention, it should
be appreciated that a vast number of variations exist. It should
also be appreciated that the exemplary embodiment or exemplary
embodiments are only examples, and are not intended to limit the
scope, applicability, or configuration of the invention in any way.
Rather, the foregoing detailed description will provide those
skilled in the art with a convenient road map for implementing an
exemplary embodiment of the invention. It being understood that
various changes may be made in the function and arrangement of
elements described in an exemplary embodiment without departing
from the scope of the invention as set forth in the appended
claims.
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