U.S. patent application number 12/940621 was filed with the patent office on 2011-03-03 for self-concentrating absorbent for acid gas separation.
Invention is credited to Liang HU.
Application Number | 20110052458 12/940621 |
Document ID | / |
Family ID | 43032494 |
Filed Date | 2011-03-03 |
United States Patent
Application |
20110052458 |
Kind Code |
A1 |
HU; Liang |
March 3, 2011 |
Self-Concentrating Absorbent for Acid Gas Separation
Abstract
A process and systems for efficiently deacidizing a gaseous
mixture is described. The process and systems utilize a
self-concentrating absorbent that absorbs an acid gas at reduced
overall energy costs for the deacidizing operation.
Inventors: |
HU; Liang; (Hampton,
VA) |
Family ID: |
43032494 |
Appl. No.: |
12/940621 |
Filed: |
November 5, 2010 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
12430998 |
Apr 28, 2009 |
7846407 |
|
|
12940621 |
|
|
|
|
12250257 |
Oct 13, 2008 |
7718151 |
|
|
12430998 |
|
|
|
|
11279095 |
Apr 7, 2006 |
7541011 |
|
|
12250257 |
|
|
|
|
Current U.S.
Class: |
422/223 |
Current CPC
Class: |
B01D 2252/504 20130101;
B01D 2252/20484 20130101; B01D 53/1425 20130101; B01D 2252/20405
20130101; C10L 3/102 20130101; B01D 2252/202 20130101; B01D
2252/2023 20130101; B01D 53/1456 20130101; B01D 53/1493 20130101;
C10L 3/10 20130101; B01D 2252/20494 20130101 |
Class at
Publication: |
422/223 |
International
Class: |
B01J 20/34 20060101
B01J020/34 |
Goverment Interests
STATEMENT OF GOVERNMENT LICENSE RIGHTS
[0002] The U.S. Government has a paid-up license in this invention
and the right in limited circumstances to require the patent owner
to license others on reasonable terms as provided for by the terms
of National Science Foundation SBIR Award No. IIP-0839217.
Claims
1. A system for deacidizing a gaseous mixture comprising an acid
gas, comprising: an absorption unit adapted to allow contact
between the gaseous mixture and an absorbent comprising an amine
dissolved in a solvent at a first concentration, wherein the
absorbent absorbs the acid gas to form a concentrated-amine phase,
wherein the concentrated-amine phase is mechanically separable from
the remaining of the absorbent, and the concentrated-amine phase
comprises a concentrated amine at a concentration higher than the
first concentration and an absorbed acid gas, wherein the
concentrated amine comprises the amine or the amine having a
chemical modification, and the absorbed acid gas comprises the acid
gas or the acid gas having a chemical modification a separation
unit adapted to allow separation of the concentrated-amine phase
from the remaining of the absorbent; and a regeneration unit
adapted to allow regeneration of the concentrated-amine phase, so
as to obtain the acid gas and the concentrated amine.
2. The system of claim 1, wherein the separation unit is placed in
a position lower than the absorption unit, so that after the
absorbent absorbs the acid gas to form a gas-rich absorbent, the
gas-rich absorbent moves downward from the absorption unit to the
separation unit by gravity.
3. The system of claim 2, wherein the absorption unit, the
separation unit and the regeneration unit are placed in a single
tower, wherein the separation unit is placed in a position lower
than the absorption unit and the regeneration unit is placed in a
position lower than the separation unit, so that after the
absorbent absorbs the acid gas, the gas-rich absorbent moves
downward from the absorption unit to the separation unit by
gravity, and after the step of separation, the concentrated-amine
phase moves downward from the separation unit to the regeneration
unit by gravity.
4. The system of claim 1, wherein the regeneration unit is placed
in a position lower than the separation unit, so that after the
step of separation, the concentrated-amine phase moves downward
from the separation unit to the regeneration unit by gravity.
5. A system for deacidizing a gaseous mixture comprising an acid
gas, comprising: an absorption unit adapted to allow contact
between the gaseous mixture and an absorbent comprising an agent
dissolved in a solvent at a first concentration, wherein the agent
is selected from the group consisting of amino-acid salts, amides,
alkaline salts, alkaline-earth salts, ammonium salts, ureas,
alkaline metal phosphates, carbonates, borates, acid phosphites,
phosphites, phosphonite, phosphinate, phosphonate, acid phosphates,
pyrophosphites, bicarbonates, metaborates, diborates, tetraborates,
pentaborates, and combinations thereof; wherein the absorbent
absorbs the acid gas to form a concentrated-agent phase, the
concentrated-agent phase is mechanically separable from the
remaining of the absorbent, and the concentrated-agent phase
comprises a concentrated agent at a concentration higher than the
first concentration and an absorbed acid gas, wherein the
concentrated agent comprises the agent or the agent having a
chemical modification, and the absorbed acid gas comprises the acid
gas or the acid gas having a chemical modification; a separation
unit adapted to allow separation of the concentrated-agent phase
from the remaining of the absorbent; and a regeneration unit
adapted to allow regeneration of the concentrated-agent phase, so
as to obtain the acid gas and the concentrated agent.
6. The system of claim 5, wherein the solvent comprises water, an
aqueous solution containing one or more salts selected from
alkaline salts, ammonium salts, alkanolamine salts, alkaline-earth
salts, phosphates, acid phosphites, phosphites, phosphonite,
phosphinate, phosphonate, acid phosphates, pyrophosphites,
carbonates, bicarbonates, borates, metaborates, diborates,
tetraborates, or pentaborates.
Description
REFERENCE TO RELATED APPLICATIONS
[0001] This application is a division of Application U.S. patent
application Ser. No. 12/430,998 filed Apr. 28, 2009, published Oct.
22, 2009 as U.S. patent publication No. 20090263302 A1, which is a
continuation-in-part patent application of U.S. patent application
Ser. No. 12/250,257, filed on Oct. 13, 2008, issued as U.S. Pat.
No. 7,718,151 on May 18, 2010, titled "Methods and Systems For
Deacidizing Gaseous Mixtures," which is a continuation-in-part
patent application of U.S. patent application Ser. No. 11/279,095,
filed on Apr. 7, 2006, issued as U.S. Pat. No. 7,541,011 on Jun. 2,
2009, titled "Phase Transitional Absorption Method," all of which
are hereby incorporated by reference herein in their entirety.
FIELD OF THE INVENTION
[0003] The present invention relates to a process for deacidizing a
gaseous mixture using a self-concentrating absorbent. More
particularly, the present invention relates to a method for the
separation of an acid gas from a gaseous mixture using a
self-concentrating absorbent, which reduces the overall energy
costs for such deacidizing operation.
BACKGROUND OF THE INVENTION
[0004] Removal of acid gas from gas mixture is required for many
processes, such as, deacidization of a raw natural gas or any other
gaseous mixture that contains significant amounts of an acid gas,
e.g., hydrogen sulfide (H.sub.2S), carbon dioxide (CO.sub.2), or
similar contaminants. The deacidization process reduces the acid
gas impurity in the gaseous mixture to acceptable levels. This is
commonly done with an amine gas treatment process. Amine gas
treatment processes are common in various types of industrial
settings, such as refineries, natural gas processing plants, and
petrochemical plants. Amine gas treatment processes include the
processes utilizing aqueous solutions of amines to remove acid gas,
such as H.sub.2S and CO.sub.2.
[0005] A common deacidization process is gas-liquid absorption.
Such process typically involves contacting a gaseous mixture
containing an acid gas to be removed with an aqueous amine
solution, whereby the amine solution is an absorbent that absorbs
the acid gas. In industrial settings, the most commonly used amines
are alkanolamines, such as monoethanolamine (MEA) and
diethanolamine (DEA). The use of the alkanolamine
methyldiethanolamine (MDEA) for CO.sub.2 separation has recently
become notable for use in industrial settings. Diisopropanolamine
(DIPA) is currently used in the Sulfinol process and in the SCOT
process for Claus plant tail acid gas purification.
[0006] In the typical gas-liquid absorption process, after an acid
gas is absorbed into the absorbent in an absorption unit, the
gas-rich absorbent is sent to a regeneration unit, where the
gas-rich absorbent is treated and separated to regenerate the
absorbed gas and the gas-lean absorbent. The regenerated gas-lean
absorbent is then recycled back into the absorption unit and the
acid gas is either collected or discharged, depending on the
purpose of the user. In this type of gas-liquid absorption, the
regeneration process accounts for greater than 80% of the total
energy costs because the entire volume of the absorbent effluent
must be regenerated in order to be reused in the absorption unit.
In addition, the typical gas-liquid absorption process is limited
to the use of an absorbent in the form of one liquid phase.
BRIEF SUMMARY OF THE INVENTION
[0007] It is now discovered that a method for deacidizing a gaseous
mixture involving a self-concentrating absorbent increases the
absorption rate of an acid gas from the gaseous mixture and reduces
the overall energy costs for such deacidizing operation.
[0008] In one general aspect, embodiments of the present invention
relate to a method for deacidizing a gaseous mixture comprising an
acid gas. The method comprises:
[0009] contacting the gaseous mixture with an absorbent in an
absorption unit, wherein the absorbent comprises an amine dissolved
in a solvent at a first concentration;
[0010] allowing the absorbent to absorb the acid gas to form a
concentrated-amine phase, wherein the concentrated-amine phase is
mechanically separable from the remaining of the absorbent and
comprises a concentrated amine at a concentration higher than the
first concentration and an absorbed acid gas, wherein the
concentrated amine comprises the amine or the amine having a
chemical modification, and the absorbed acid gas comprises the acid
gas or the acid gas having a chemical modification;
[0011] separating the concentrated-amine phase from the remaining
of the absorbent;
[0012] cycling the remaining of the absorbent back into the
absorption unit;
[0013] providing the concentrated-amine phase to a regeneration
unit, so as to obtain the acid gas and the concentrated amine;
and
[0014] cycling the regenerated concentrated amine back into the
absorption unit.
[0015] In an embodiment of the present invention, the absorbent and
the absorbed acid gas move downward from the absorption unit to the
separation unit by gravity, and the separated concentrated-amine
phase moves downward from the separation unit to the regeneration
unit by gravity.
[0016] In another general aspect, embodiments of the present
invention relate to a system for deacidizing a gaseous mixture
comprising an acid gas. The system comprises:
[0017] an absorption unit adapted to allow contact between the
gaseous mixture and an absorbent comprising an amine dissolved in a
solvent at a first concentration, wherein the absorbent absorbs the
acid gas to form a concentrated-amine phase, wherein the
concentrated-amine phase is mechanically separable from the
remaining of the absorbent, and the concentrated-amine phase
comprises a concentrated amine at a concentration higher than the
first concentration and an absorbed acid gas, wherein the
concentrated amine comprises the amine or the amine having a
chemical modification, and the absorbed acid gas comprises the acid
gas or the acid gas having a chemical modification
[0018] a separation unit adapted to allow separation of the
concentrated-amine phase from the remaining of the absorbent;
and
[0019] a regeneration unit adapted to allow regeneration of the
concentrated-amine phase, so as to obtain the acid gas and the
concentrated amine.
[0020] In an embodiment of the present invention, the absorption
unit, the separation unit and the regeneration unit are in a single
tower, wherein the separation unit is placed in a position lower
than the absorption unit and the regeneration unit is placed in a
position lower than the separation unit, so that after the gas
absorption, the absorbent and the absorbed acid gas move downward
from the absorption unit to the separation unit by gravity, and the
concentrated-amine phase moves downward from the separation unit to
the regeneration unit by gravity.
[0021] In yet another general aspect, embodiments of the present
invention relate to a method for deacidizing a gaseous mixture
comprising an acid gas. The method comprises:
[0022] contacting the gaseous mixture with an absorbent in an
absorption unit, wherein the absorbent comprises an agent dissolved
in a solvent at a first concentration, wherein the agent is
selected from the group consisting of amino-acid salts, amides,
alkaline salts, alkaline-earth salts, ammonium salts, ureas,
alkaline metal phosphates, carbonates, borates, acid phosphites,
phosphites, phosphonite, phosphinate, phosphonate, acid phosphates,
pyrophosphites, bicarbonates, metaborates, diborates, tetraborates,
pentaborates, and combinations thereof;
[0023] allowing the absorbent to absorb the acid gas to form a
concentrated-agent phase, wherein the concentrated-agent phase is
mechanically separable from the remaining of the absorbent and
comprises a concentrated agent at a concentration higher than the
first concentration and an absorbed acid gas, wherein the
concentrated agent comprises the agent or the agent having a
chemical modification, and the absorbed acid gas comprises the acid
gas or the acid gas having a chemical modification;
[0024] separating the concentrated-agent phase from the remaining
of the absorbent;
[0025] cycling the remaining of the absorbent back into the
absorption unit;
[0026] providing the concentrated-agent phase to a regeneration
unit, so as to obtain the acid gas and the concentrated agent;
and
[0027] cycling the regenerated concentrated agent back into the
absorption unit.
[0028] In another general aspect, embodiments of the present
invention relate to a system for deacidizing a gaseous mixture
comprising an acid gas. The system comprises:
[0029] an absorption unit adapted to allow contact between the
gaseous mixture and an absorbent comprising an agent dissolved in a
solvent at a first concentration, [0030] wherein the agent is
selected from the group consisting of amino-acid salts, amides,
alkaline salts, alkaline-earth salts, ammonium salts, ureas,
alkaline metal phosphates, carbonates, borates, acid phosphites,
phosphites, phosphonite, phosphinate, phosphonate, acid phosphates,
pyrophosphites, bicarbonates, metaborates, diborates, tetraborates,
pentaborates, and combinations thereof; [0031] wherein the
absorbent absorbs the acid gas to form a concentrated-agent phase,
the concentrated-agent phase is mechanically separable from the
remaining of the absorbent, and the concentrated-agent phase
comprises a concentrated agent at a concentration higher than the
first concentration and an absorbed acid gas, [0032] wherein the
concentrated agent comprises the agent or the agent having a
chemical modification, and the absorbed acid gas comprises the acid
gas or the acid gas having a chemical modification;
[0033] a separation unit adapted to allow separation of the
concentrated-agent phase from the remaining of the absorbent;
and
[0034] a regeneration unit adapted to allow regeneration of the
concentrated-agent phase, so as to obtain the acid gas and the
concentrated agent.
[0035] Other aspects, features and advantages of the invention will
be apparent from the following disclosure, including the detailed
description of the invention and its preferred embodiments and the
appended claims.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
[0036] The foregoing summary, as well as the following detailed
description of the invention, will be better understood when read
in conjunction with the appended drawings. For the purpose of
illustrating the invention, there are shown in the drawings
embodiments which are presently preferred. It should be understood,
however, that the invention is not limited to the precise
arrangements and instrumentalities shown.
[0037] In the drawings:
[0038] FIG. 1 is a flow diagram showing the steps of the
deacidization process according to an embodiment of the present
invention; and
[0039] FIG. 2 is a flow diagram showing the steps of the
deacidization process according to another embodiment of the
present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0040] Unless defined otherwise, all technical and scientific terms
used herein have the same meaning as commonly understood to one of
ordinary skill in the art to which this invention pertains.
Otherwise, certain terms used herein have the meanings as set in
the specification. All patents, published patent applications and
publications cited herein are incorporated by reference as if set
forth fully herein. It must be noted that as used herein and in the
appended claims, the singular forms "a," "an," and "the" include
plural reference unless the context clearly dictates otherwise.
[0041] In one general aspect, the present invention relates to a
process of deacidizing a gaseous mixture using a self-concentrating
amine absorption, while minimizing energy costs and maximizing
absorption rates.
[0042] According to an embodiment of the present invention, an
absorbent and a gaseous mixture containing an acid gas to be
removed are contacted in an absorption unit. The absorbent
comprises an amine or an agent dissolved in a solution at a first
concentration. During the absorption, amine or the agent in the
absorbent is spontaneously concentrated into a concentrated-amine
or concentrated-agent phase. After the absorption is complete, the
concentrated-amine or concentrated-agent phase is mechanically
separable from the remaining of the absorbent, i.e., the
concentrated-amine or concentrated-agent phase does not form a
solution with the remaining of the absorbent.
[0043] The acid gas to be removed can be, for example, one or more
acid gases selected from the group consisting of carbon dioxide
(CO.sub.2), sulfur dioxide (SO.sub.2), sulfur trioxide (SO.sub.3),
hydrogen sulfide (H.sub.2S), carbon oxysulfide (COS), carbon
disulfide (CS.sub.2), mercaptans (RSH), nitric oxide (NO), nitric
dioxide (NO.sub.2), fluorides, HCl, and a combination thereof.
[0044] The absorption unit according to embodiments of the present
invention can be, for example, an absorption column or a membrane
contractor, or any other gas-liquid contacting units that are known
to those skilled in the art.
[0045] It is readily appreciated by those skilled in the art that
the absorbent can comprise one or more amines dissolved in a
solvent. Examples of the amines include, but are not limited to
monoethanolamine, diethanolamine, triethanolamine, ethanolamines,
isopropanolamines, ethyleneamines, alkyl alkanolamines,
methyldiethanolamine, piperidine, dibutylamine, diisopropylamine,
derivatives thereof, or mixtures thereof.
[0046] The solvent can be aqueous or organic. For example, the
aqueous solvent can be water, an aqueous solution of one or more
salts, including, but not limited to, alkaline salts, ammonium
salts, alkanolamine salts, alkaline-earth salts, or derivatives
thereof. The organic solvent can comprise one or more components,
including, but not limited to, alcohols, glycols, alkanes,
unsaturated hydrocarbon, ethers, esters, aldehyde, ketones, glycol
ethers, alkylene carbonates, dialkyl carbonates, sulfolane, and
derivatives thereof, such as ionic liquids, polymers. The solvent
can further be a combination of an aqueous solution and an organic
solvent.
[0047] In a preferred embodiment, the organic solvent comprises a
C.sub.8 to C.sub.12 alcohol.
[0048] The solvent can also be water insoluble or slightly water
soluble solvent, such as water insoluble alcohol, glycol, or glycol
ether. The solvent can further be ionic liquids or polymers.
[0049] In an embodiment of the present invention, the absorbent
comprises an amine solution, including, but not limited to an
alcohol, glycol or glycol ether solution of monoethanolamine,
diethanolamine, triethanolamine, ethanolamines, isopropanolamines,
ethyleneamines, alkyl alkanolamines, methyldiethanolamine,
piperidine, dibutylamine, diisopropylamine, derivatives thereof, or
mixtures thereof.
[0050] In an embodiment of the present invention, the amine can be
another agent instead, the other agent can be amino-acids,
amino-acid salts, amides, alkaline salts, ammonium salts, ureas,
alkaline metal phosphates, carbonates, borates, acid phosphites,
phosphites, phosphonite, phosphinate, phosphonate, acid phosphates,
pyrophosphites, bicarbonates, metaborates, diborates, tetraborates,
pentaborates, derivatives thereof, or combinations thereof. The
solvent can be water, an aqueous solution of one or more salts,
including, but not limited to, alkaline salts, ammonium salts,
alkanolamine salts, alkaline-earth salts, ureas, alkaline metal
phosphates, acid phosphites, phosphites, phosphonite, phosphinate,
phosphonate, acid phosphates, pyrophosphites, carbonates,
bicarbonates, borates, metaborates, diborates, tetraborates,
pentaborates, or derivatives thereof. The organic solvent can
comprise one or more components, including, but not limited to,
alcohols, glycols, alkanes, unsaturated hydrocarbon, ethers,
esters, aldehyde, ketones, glycol ethers, alkylene carbonates,
dialkyl carbonates, sulfolane, and derivatives thereof, such as
ionic liquids, polymers, such as, the absorbent comprises a
carbonates or borates aqueous solution.
[0051] In an embodiment of the present application, the absorbent
comprises a solution of an amine at a concentration selected from
the group consisting of 0.1%, 1%, 5%, 10%, 15%, 20%, 25%, 30%, 35%,
40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, etc.
[0052] According to embodiments of the present invention, when the
acid gas contacts with the absorbent, the acid gas can be absorbed
physically, chemically, or both physically and chemically. After
physical absorption, the acid gas is absorbed in the absorbent,
mainly in the concentrated-amine phase, without being chemically
modified. After chemical absorption, however, the acid gas is
absorbed in the absorbent, mainly in the concentrated-amine phase,
after being chemically modified, e.g., in a reaction product of the
amine and the acid gas.
[0053] In one embodiment of the present invention, the reaction
product of the amine with the acid gas is substantially insoluble
in the solvent.
[0054] The concentrated-amine phase comprises a concentrated amine
at a concentration higher than the first concentration and an
absorbed acid gas. The concentrated amine can be the amine or the
amine having a chemical modification, for example, a reaction
product resulting from a chemical reaction between the amine and
the acid gas. The absorbed acid gas can be the acid gas or the acid
gas having a chemical modification, for example, a reaction product
resulting from a chemical reaction between the amine and the acid
gas. The concentrated-amine phase can exist as a single phase,
e.g., a solution of amine. The concentrated-amine phase can also
contain multiple phases.
[0055] Because the absorbent forms the concentrated-amine phase
spontaneously upon absorption of the acid gas, the absorbent is
also referred to as the self-concentrating amine absorbent.
[0056] The absorbed acid gas accumulates in the concentrated-amine
phase.
[0057] After the absorbent absorbs the acid gas, the purified
gaseous mixture, with the acid gas being removed or significantly
reduced, is released from the absorption unit. The released
purified gaseous mixture can be collected or disposed of, depending
on the user's purpose.
[0058] After the absorbent absorbs the acid gas, the contents of
the absorption unit are provided to a separation unit to separate
the concentrated-amine phase from the remaining of the absorbent.
The formation of the concentrated-amine phase can proceed before,
simultaneously, or after the contents of the absorption unit are
provided to the separation unit.
[0059] In one embodiment of the present invention, the contents of
the absorption unit are provided to the separation unit after the
complete formation of the concentrated-amine phase.
[0060] In another embodiment of the present invention, the contents
of the absorption unit are provided to the separation unit before
the complete formation of the concentrated-amine phase.
[0061] The separation can be achieved using phase separation
methods known to those skilled in the art in view of the present
disclosure. For example, the concentrated-amine phase can be
separated based on the density of the phase, e.g., by a separating
drum. The concentrated-amine phase can also be separated based on
other properties of the phase, e.g., by a membrane that has
different permeability to the concentrated-amine phase and the
remaining of the absorbent.
[0062] The separating step of the present invention can be
accomplished utilizing one or more types of phase settlers or phase
separation units known in the art as suited for separation of bulk
liquid phases. Some examples include simple settlers, filtration,
centrifugation, membrane, etc.
[0063] After the separation, the remaining of the absorbent
contains mostly the solvent. It can also contain the amine at a
concentration much lower than the first concentration. The
remaining of the absorbent can further contain a small amount of
the absorbed acid gas. After the separation, the remaining of the
absorbent is cycled back into the absorption unit for reuse.
[0064] The separated concentrated-amine phase is routed to a
regeneration unit, where the concentrated-amine phase is treated to
produce or regenerate the amine and the acid gas. The regeneration
process according to embodiments of the present invention can be
accomplished by regeneration methods known to those skilled in the
art in view of the present disclosure. Exemplary regeneration
methods include, but are not limited to, thermal decomposition, gas
stripping, steam stripping, distillation, treatment through a
membrane contractor, pervaporization, pressure differential
treatment, and a combination thereof.
[0065] The regenerated acid gas is collected or disposed of
depending on the purpose of the user. The regenerated amine is
cycled back into the absorption unit for reuse.
[0066] In an embodiment of the present invention, the contents of
the absorbent are transferred from one unit to another unit by a
pump. In other embodiments of the present invention, the contents
of the absorbent are transferred between at least some of the units
by gravity.
[0067] In an embodiment of the present invention, the contents of
the absorbent move downward from the absorption unit to the
separation unit by gravity.
[0068] In another embodiment of the present invention, the
separated concentrated-amine phase moves downward from the
separation unit to the regeneration unit by gravity.
[0069] In still another embodiment of the present invention, the
contents of the absorbent move downward from the absorption unit to
the separation unit, and the separated concentrated-amine phase
moves downward from the separation unit to the regeneration unit,
all by gravity.
[0070] In another general aspect, the present invention relates to
a system for deacidizing a gaseous mixture comprising an acid gas.
The system comprises an absorption unit, a separation unit and a
regeneration unit as those described herein.
[0071] In an embodiment of the present invention, the separation
unit is placed in a position lower than the absorption unit, so
that the contents of the absorbent move downward from the
absorption unit to the separation unit by gravity.
[0072] In another embodiment of the present invention, the
regeneration unit is placed in a position lower than the separation
unit, so that the separated concentrated-amine phase moves downward
from the separation unit to the regeneration unit by gravity.
[0073] In still another embodiment of the present invention, the
absorption unit, the separation unit and the regeneration unit are
placed in a single tower, wherein the separation unit is placed in
a position lower than the absorption unit and the regeneration unit
is placed in a position lower than the separation unit, so that the
gas-rich absorbent moves downward from the absorption unit to the
separation unit by gravity, and the separated concentrated-amine
phase moves downward from the separation unit to the regeneration
unit by gravity.
[0074] The deacidization process according to embodiments of the
present invention can be used to remove an impurity acid gas from a
gaseous mixture, in which case the impurity acid gas can be
disposed of, with improved efficiency. Alternatively, the
deacidization process according to embodiments of the present
invention can be used to collect an acid gas of interest from a
gaseous mixture, with improved efficiency.
[0075] In one embodiment of the present invention, the solvent in
an absorbent according to an embodiment of the present invention
serves to increase the absorption rate of the acid gas. The acid
gas is absorbed into the absorbent at a rate greater than that if
it were directly absorbed by the amine.
[0076] In an aspect of the present invention, the energy to be
expended for the regeneration process is reduced because only part
of the absorbent, the concentrated-amine phase, needs to be
regenerated, while the remaining of the absorbent can immediately
be recycled for reuse in the absorption unit.
[0077] In yet another aspect of the present invention, the energy
to be expended for the deacidization process is further reduced by
incorporating two or more of the units used in the process in a
single tower, so that the various components can be transferred
between some of the units by gravity, instead of pumping. The use
of multiple units in a single tower is enabled and becomes
practical, because of the relatively smaller size of the
concentrated-amine phase that needs to be regenerated. In a
conventional liquid-gas separation process, the volume of the
gas-rich absorbent that needs to be regenerated is significantly
larger than that of the concentrated-amine phase according to
embodiments of the present invention. Thus, in the conventional
methods, a single tower containing the absorption unit and the
regeneration unit would be too tall to be practical.
[0078] FIG. 1 illustrates a particular embodiment of the present
invention. A gaseous mixture 1 containing an acid gas to be removed
and an absorbent 3 are provided into an absorption unit 10. The
gaseous mixture 1 and the absorbent 3 contact with each other in
the absorption unit 10. After the acid gas is absorbed in the
absorbent 3 in the absorption unit 10, the purified gaseous mixture
2 is released from the absorption unit 10. The gas-rich absorbent 5
is sent to a separation unit 20, such as a gravity settler tank,
for separating the concentrated-amine phase 6 from the remaining of
the absorbent 4. After the separation, the remaining of the
absorbent 4, comprising most or all components of the solvent and
little or none of the amine and little or none of the absorbed acid
gas, is cycled back into the absorption unit 10 for reuse, with or
without further treatment. The separated concentrated-amine phase
6, containing most or all of the amine and the absorbed acid gas,
both with or without chemical modification, optionally one or more
components of the solvent, is provided for regeneration.
[0079] Referring to FIG. 1, the separated concentrated-amine phase
6 is routed to a regeneration unit 30, where the concentrated-amine
phase 6 is treated to separate the absorbed acid gas 12 from the
rest of the concentrated-amine phase, which is the gas-lean phase
14. The absorbed acid gas 12 is further treated to separate the
acid gas 18 from the rest 16, which may contain the amine and one
or more components of the solvent that react with the acid gas
during the absorption of the acid gas and/or the transfer of the
absorbed acid gas. The separated acid gas 18 can be disposed of or
collected, depending on the user's purpose. The rest 16 is
regenerated as part of the gas-lean phase 14. The gas-lean phase
14, which contains the regenerated amine and optionally one or more
components of the solvent, is cycled back into the absorption unit
10 for reuse, with or without further treatment.
[0080] As shown in FIG. 1, the remaining of the absorbent 4 from
the separation unit 20 and the gas-lean phase 14 from the
regeneration unit 30 are mixed together in a mixer 40. The
resulting absorbent 3 is then cycled back into the absorption unit
10 for reuse. According to other embodiments of the present
invention, the remaining of the absorbent 4 and the gas-lean phase
14 can each be cycled back into the absorption unit 10 for reuse
without being first mixed together.
[0081] Although not shown in FIG. 1, in view of the present
disclosure, it is readily appreciated by those skilled in the art
that, in addition to the cycled back components of the absorbent 3,
additional one or more components of the absorbent 3 can be added
to compensate for the loss of the one or more components during the
deacidizing process.
[0082] FIG. 2 illustrates another particular embodiment of the
present invention. In this process, the absorption unit 10,
separation unit 20 and regeneration unit 30 are grouped inside a
single tower 100. The gas-rich absorbent from the absorption unit
10 flows downward into the separation unit 20 by gravity, so as to
separate the concentrated-amine phase and the remaining of the
absorbent 4. After separation, the concentrated-amine phase flows
downward into the regeneration unit 30, by gravity, where the
regenerated acid gas 18 and the gas-lean phase 14 are obtained. The
remaining of the absorbent 4 and the gas-lean phase 14 further flow
downward into the mixer 40, and are mixed in the mixer 40 to obtain
the absorbent 3. The absorbent 3 is pumped back into the absorption
unit 10, where it forms contact with the gaseous mixture 1, to
start another cycle.
[0083] According to other embodiments of the present invention, the
remaining of the absorbent 4 and the gas-lean phase 14 can each be
pumped back into the absorption unit 10 for reuse without being
first mixed together.
[0084] Again, in addition to the cycled back components of the
absorbent 3, additional one or more components of the absorbent 3
can be added to compensate for the loss of the one or more
components during the deacidizing process.
[0085] In this embodiment, no pumping energy is required for liquid
transfer from the absorption unit 10 to the regeneration unit 30,
thus achieves further energy saving.
[0086] The following examples illustrate the invention but are in
no way intended to limit the scope of the present invention.
Example 1
[0087] The absorbent was made of 20% by volume of the amine,
monoethanolamine (MEA), and 80% by volume of the solvent,
iso-octanol. The absorbent was contacted with a gaseous mixture
containing an acid gas, carbon dioxide (CO.sub.2), in a stirring
cell absorption unit at about 25-45.degree. C., 1 atm. MEA in the
absorbent was concentrated spontaneously into a concentrated-amine
phase, which contained MEA and the reaction product of MEA and
CO.sub.2.
[0088] After the absorption, the absorbent was settled to separate
by gravity the concentrated-amine phase from the remaining of the
absorbent. After the separation, the remaining of the absorbent,
which contains most of the iso-octanol and optionally some MEA and
absorbed CO.sub.2, was cycled back into the absorption unit for
reuse. In the concentrated-amine phase, the concentration of the
total MEA, which includes the chemically unmodified MEA and the
reaction product of MEA and CO.sub.2, was about 70% by volume.
[0089] The separated concentrated-amine phase was forwarded to a
regenerator and was treated to obtain the regenerated MEA and
CO.sub.2. by the method of heating the concentrated-amine phase.
The regenerated MEA was mixed with the remaining of the absorbent.
The mixture was cycled back to the stirring cell absorption unit to
complete the cycle.
[0090] The CO.sub.2 released from the regeneration process was
collected.
Example 2
[0091] This example illustrates the absorption of CO.sub.2 by a
carbonate aqueous solution.
[0092] An absorbent is made of carbonate aqueous solution. The
absorbent is contacted with a gas mixture containing acid gas,
carbon dioxide (CO.sub.2), in a stirring cell absorption unit at
50.degree. C., 1 atm.
[0093] During the absorption, carbonate in aqueous solution reacts
with CO.sub.2 to form bicarbonate. After absorption, the absorbent
is cooled to 25.degree. C. and the bicarbonate is crystallized. The
bicarbonate solid phase is separated from the absorbent. It is then
forwarded to a regeneration section and is treated to obtain the
regenerated carbonate and CO.sub.2 by the method of heating the
solid phase of bicarbonate. The regenerated carbonate is dissolved
in aqueous solution and cycled back to the stirring cell absorption
unit to complete the cycle.
[0094] It will be appreciated by those skilled in the art that
changes could be made to the embodiments described above without
departing from the broad inventive concept thereof. It is
understood, therefore, that this invention is not limited to the
particular embodiments disclosed, but it is intended to cover
modifications within the spirit and scope of the present invention
as defined by the appended claims.
* * * * *