Note: Descriptions are shown in the official language in which they were submitted.
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HUMID AIR TURBINE CYCLE WITH CARBON DIOXIDE RECOVERY
Field of The Invention
The field of the invention is carbon dioxide recovery, and especially carbon
dioxide
recovery from humid air turbine cycle.
Background of The Invention
Combustion gases, and especially flue gases from gas turbines often comprise a
substantial quantity of carbon dioxide, which is a known greenhouse gas. Thus,
isolation
and/or sequestration of carbon dioxide from combustion processes has gained
significant
attention over the last decade, and there are numerous configurations and
methods known in
the art to remove carbon dioxide from a flue gas.
For example, carbon dioxide may be removed from various gas streams with one
or
more membranes as described in U.S. Pat. No. 4,130,403 to Cooley et. al., U.S.
Pat. No.
4,639,257 to Duckett et. al., or U.S. Pat. No. 5,233,837 to Callahan. Membrane
processes
typically exhibit relatively high selectivity towards a particular gas
component. Moreover,
membrane processes can generally be operated without energy consuming
circulation (e.g.,
heating and/or cooling requirements that are often needed for solvent based
carbon dioxide
removal). However, and especially depending on the feed gas composition,
membrane life
time is less than desirable, or the feed gas requires pretreatment before
contacting the
membrane. Furthermore, membrane systems typically operate at a relatively high
pressure
differential, which either necessitates a blower or other pressure increasing
equipment for low
pressure feed gases or disqualifies membrane systems for such low pressure
feed gases.
Alternatively, carbon dioxide may be removed using physical or chemical
solvents,
and numerous process configurations for solvents are known in the art.
Physical solvent
processes are particularly advantageous where the acid gas partial pressure in
the feed gas is
relatively high. Thus, all, or almost all physical solvents exhibit only
limited usefulness for
the removal of carbon dioxide from flue gases which are typically near
atmospheric pressure,
and especially where the flue gas has a relatively low carbon dioxide content.
To circumvent problems associated with the use of physical solvents, chemical
solvents may be employed to scrub the feed gas, wherein the chemical solvent
is regenerated
downstream to recover the carbon dioxide. Scrubbing gases with chemical
solvents typically
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allows removal of carbon dioxide from a feed gas at relatively low pressure.
However, such
methods are often energy intensive as well as costly and problems with
corrosion and solvent
degradation frequently arise (see e.g., U.S. Pat. No. 2,065,112, U.S. Pat. No.
2,399,142, U.S.
Pat. No. 2,377,966, U.S. Pat. No. 4,477,419, or U.S. Pat. No. 3,137,654).
Moreover, as the
carbon dioxide partial pressure in the feed gas decreases (e.g., the exhaust
gas from a gas
turbine operated with relatively large amount of excess air, as well as that
from a HAT cycle),
the size of the recovery equipment as well as the power consumed by a blower
typically
increases substantially to overcome the pressure drop in the recovery
equipment.
Thus, although various carbon dioxide removal configurations and processes are
known in the art, all or almost all of them suffer from one or more
disadvantages, especially
where the partial pressure and/or concentration of the carbon dioxide in the
feed gas is
relatively low. Tllerefore, there is still a need to provide improved
configurations and
methods for carbon dioxide recovery from various gases, and especially gases
with relatively
low carbon dioxide partial pressure.
SumuaarV of the Invention
The present invention is directed to methods and configurations of carbon
dioxide
removal from flue gases in which at least part of the flue gas is compressed
to a higher
pressure thereby improving carbon dioxide removal efficiency.
In one aspect of the inventive subject matter, a plant will include a
combustor that
combusts a fuel in the presence of heated liuinid air to produce an exhaust
that is expanded in
an expander. A compressor (operationally coupled to the expander) conlpresses
air and at
least a portion of the exhaust from the expander to form a conipressed mixed
gas fiom which
carbon dioxide is removed in an acid gas removal unit, and a humidifier
humidifies the so
formed carbon dioxide depleted compressed mixed gas to produce the heated
humid air.
It is further particularly preferred that in such plants the heated humid air
is heated
using the exhaust as heat source, and that the humidifier uses water that is
heated by at least
one of the compressed mixed gas and the exhaust gas. While various methods of
acid gas
removal are contemplated, preferred acid gas removal units include a membrane
unit or
employ a solvent (e.g., an amine-based solvent). In alternative
configurations, it is
conteinplated that part of the compressed mixed gas may also be fed to the
combustor, and a
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cooler provides cooling for the expanded exliaust thereby condensing water
from the
expanded exhaust.
Where the acid gas removal unit comprises an autorefrigeration unit, it is
contemplated that the autorefrigeration unit removes carbon dioxide from a
first portion of
the conlpressed mixed gas, and that a humidifier humidifies a second portion
of the
compressed nuxed gas to form the heated humid air.
Thus, it is generally contemplated that a plant may include a turbine
combustor, and
particularly a humid air turbine combustor that receives fuel and humid carbon
dioxide
depleted air, wherein at least part of the humid carbon dioxide depleted air
is formed from an
exhaust gas of the humid air turbine combustor after a portion of the carbon
dioxide has been
removed for recoveiy. The carbon dioxide in such configurations is
adva.ntageously extracted
from the carbon dioxide containing air (mixture of fresh air and recycle flue
gas that contains
the carbon dioxide) using a membrane unit or a solvent. Viewed from another
perspective,
contemplated plants in twhicli carbon dioxide is remoired from an exhaust gas
of a turbine
conibustor may therefore include a compressor that compresses air and at least
a portion of
the exhaust gas (recycle gas) to form a conipressed mixed gas, wherein carbon
dioxide is
removed from the compressed mixed gas in an acid gas removal unit.
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According to one aspect of the present invention,
there is provided a plant comprising: a combustor that is
configured to combust a fuel in the presence of a humid gas
stream, wherein the combustor is configured to produce an
exhaust; an expander coupled to the combustor and configured
to expand the exhaust to form an expanded exhaust; a
compressor operationally coupled to the expander, wherein
the compressor is configured to compress air and at least a
portion of the expanded exhaust to form a compressed mixed
gas; an acid gas removal unit that is configured to remove
carbon dioxide from the compressed mixed gas to form a
carbon dioxide depleted compressed mixed gas; and a
humidifier that is configured to humidify the carbon dioxide
depleted compressed mixed gas to form the humid gas stream,
and wherein the combustor is further configured to receive
the humid gas stream.
According to another aspect of the present
invention, there is provided a plant comprising: a combustor
that is configured to combust a fuel in the presence of a
humid gas stream, wherein the combustor is further
configured to produce an exhaust; an expander coupled to the
combustor and configured to expand the exhaust to form an
expanded exhaust; a compressor operationally coupled to the
expander, wherein the compressor is configured to compress a
mixture of air and at least a portion of the expanded
exhaust to form a compressed mixed gas; an autorefrigeration
unit that is configured to remove carbon dioxide from a
first portion of the compressed mixed gas; a humidifier that
is configured to humidify a second portion of the compressed
mixed gas to form the humid gas stream; and wherein the
combustor is further configured to receive the humid gas
stream.
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According to still another aspect of the present
invention, there is provided a plant in which carbon dioxide
is removed from an exhaust gas of a turbine combustor
comprising a compressor that is configured to compress a
mixture of air and at least a portion of the exhaust gas to
form a compressed mixed gas, and further comprising an acid
gas removal unit that is configured to allow removing carbon
dioxide from the compressed mixed gas to thereby form a
treated air stream, and wherein the turbine combustor is
configured to allow feeding of the treated air stream to the
turbine combustor.
Various objects, features, aspects and advantages of the present invention
will become
more apparent from the following detailed description of preferred embodiments
of the
invention, along with the accompanying drawings in v.,hich like nunierals
represent like
components. -
Brief Description of The Dra-tvinas
Figure 1 is a schematic view of an exemplary configuration for carbon dioxide
recovery from exhaust gas using a membrane or solvent in the acid gas removal
unit.
Figure 2 is a schematic view of an exemplary configuration for carbon dioxide
recovery from exhaust gas using an autorefrigeration unit in the acid gas
removal unit.
Figure 3 is a scllematic view of another exemplary configuration for carbon
dioxide
recovery from exhaust gas using partial humidification.
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Detailed Description
The inventor has discovered that carbon dioxide contained in the exhaust gas
of a gas
turbine can be recovered at pressure by recycling at least part of the exhaust
gas back to a
compressor to increase the partial pressure of the carbon dioxide in the
compressed gas, and
to thereby facilitate removal of the carbon dioxide using appropriate acid gas
removal
technologies (e.g., using a physical or chemical solvent, a carbon dioxide
specific membrane,
or an autorefrigeration process).
In one particularly preferred configuration as depicted in Figure 1, an
exemplary
plant 100 includes a humid air turbine cycle for generation of power, wherein
at least part of
the expanded exhaust is recycled back to the compressor for carbon dioxide
recovery at
elevated pressure. More specifically, the combustor 110 receives fuel 112 and
heated humid
air 114' and produces exhaust 116 which is subsequently expanded in expander
120. The heat
in expanded exhaust 118 is then at least partially recovered in recuperator
170, which heats
humid air 114 from humidifier 180, which provides heat for a steam generator,
and which
further heats water for the humidifier 180 via economizer 170'.
One portion of the expanded a.nd cooled exhaust 11 8A is vented, while another
portion of the expanded and cooled exhaust 118B is cooled in cooler 140 to
form cooled
expanded exhaust stream 118' (while condensing and separating out a
substantial portion of
the water), which is combined with air 132 and conipressed in compressor 130
that is
operationally coupled to the expander 120. Thus, compressor 130 provides a
compressed
mixed gas 134 that is cooled in aftercooler 160, thereby heating at least a
portion of the water
employed in the humidifier. The so cooled compressed mixed gas 134 is then fed
to the acid
gas removal unit 150 (preferably a solvent based acid gas removal unit or a
membrane based
carbon dioxide removal unit). Carbon dioxide product stream 152 leaves the
plant (e.g., as
commercial product) while the carbon dioxide depleted compressed mixed gas 136
is fed to
the humidifier 180. Humidifier 180 produces humid gas streain 114 from the
carbon dioxide
depleted compressed mixed gas 136, wherein the humid gas stream 114 is heated
in the
recuperator 170 to form heated humid gas stream 114', which is fed into
combustor 110 (The
terms "humid gas stream" and "humid air" are used interchangeably herein).
Therefore, a plant may comprise a combustor that combusts a fuel in the
presence of
humid air, wherein the combustor produces an exhaust that is expanded in an
expander to
form an expanded exhaust; a compressor operationally coupled to the expander,
wherein the
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compressor compresses air and at least a portion of the expanded exhaust to
form a
compressed mixed gas; an acid gas removal unit that removes carbon dioxide
from the
compressed mixed gas to form a carbon dioxide depleted compressed mixed gas;
and a
humidifier that humidifies the carbon dioxide depleted compressed mixed gas to
form the
humid air.
Alternatively, and especially where carbon dioxide is removed in an
autorefrigeration
unit, an exeinplary configuration as depicted in Figure 2 may be employed. As
above, plant
200 includes a humid air turbine cycle for generation of power, wherein at
least part of the
expanded exllaust is recycled back to the compressor for carbon dioxide
recovery at elevated
pressure. In such configurations, the combustor 210 receives fuel 212 and
heated humid air
214' and produces exhaust 216, which is then expanded in expander 220. The
heat in
expanded exhaust 218 is then at least partially recovered in recuperator 270,
which heats
humid air 214 from humidifier 280, which provides heat for a steam generator
(not shown),
and which further heats water for the humidifier 280 via economizer 270'. The
expanded and
cooled exhaust 218 is cooled in cooler 240 to form cooled expanded exhaust
stream 218'
(while condensing and separating out a substantial portion of the water),
wliich is conibined
witli air 232 and compressed in compressor 230 that is operationally coupled
to the expander
220. Thus, compressor 230 provides a compressed niixed gas 234 that is cooled
in aftercooler
260, thereby heating at least a portion of the water employed in the
humidifier.
The so cooled compressed mixed gas 234 is then split into a first stream 234A
that is
fed to the humidifier 280 and a second stream 234B that is fed to the
autorefrigeration unit
250. Carbon dioxide product stream 2521eaves the plant (e.g., as commercial
product) while
the carbon dioxide depleted exhaust gas 2381eaves the plant as exhaust.
Humidifier 280
produces humid gas stream 214 from the first stream 234A, wherein the humid
gas stream
214 is heated in the recuperator 270 to form heated humid gas stream 214',
which is then fed
into combustor 210.
Thus, a plant may include a combustor that combusts a fu.el in the presence of
humid
air, wherein the combustor produces an exhaust that is expanded in an expander
to form an
expanded exhaust; a compressor operationally coupled to the expander, wherein
the
compressor compresses air and at least a portion of the expanded exhaust to
form a
compressed mixed gas; an autorefrigeration unit that removes carbon dioxide
from a first
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portion of the compressed mixed gas; and a humidifier that humidifies a second
portion of the
compressed mixed gas to form the humid air.
In yet another contemplated configuration, as depicted in Figure 3, an
exemplary
plant 300 includes a gas turbine (e.g., the large scale General Electric
7FA+e) with a
capability of up to 20 to 30% air extraction in a humid air turbine cycle for
generation of
power, wherein at least part of the expanded exhaust is recycled back to the
compressor for
carbon dioxide recovery at elevated pressure. Here, combustor 310 receives
fuel 312 and
heated humid air 314' to produce exhaust 316 which is expanded in expander
320. The heat in
expanded exhaust 318 is at least partially recovered in heat recovery steam
generator 370.
One portion of the expanded and cooled exhaust 318A is vented, while another
portion of the expanded and cooled exhaust 318B is cooled in cooler 340 to
form cooled
expanded exhaust stream 318' (while condensing and separating out a
substantial portion of
the water), which is combined with air 332 and compressed in compressor 330
that is
operationally coupled to the expander 320. Thus, compressor 330 provides a
compressed
mixed gas 334. One portion of the compressed mixed gas 334A is directly fed to
the
combustor 310 (in a manner similar to what is practiced in conventional gas
turbines), while
another portion of the compressed mixed gas 334B is cooled in aftercooler 360,
thereby
heating at least a portion of the water employed in the humidifier. The so
cooled compressed
mixed gas 334B is then fed to the acid gas removal unit 350 (preferably a
solvent based acid
gas removal unit or a membrane based carbon dioxide removal unit). Carbon
dioxide product
stream 3521eaves the plant (e.g., as commercial product) while the carbon
dioxide depleted
conipressed mixed gas 336 is fed to the humidifier 380. Humidifier 380
produces humid gas
stream 314 from the carbon dioxide depleted conipressed mixed gas 336, wherein
the humid
gas stream 314 is heated in the aftercooler 360 to form heated humid gas
stream 314', which
is fed into coinbustor 310.
Thus, it should be recognized that contemplated configurations significantly
facilitate
recovery of carbon dioxide contained in flue gas with relatively low carbon
dioxide partial
pressure, which is particularly desirable in the case of a gas turbine where a
large amount of
excess air is employed. Consequently, the size of the carbon dioxide recovery
equipment as
well as the power consumed by the blower to overcome the pressure drop of the
carbon
dioxide recovery equipment (e.g., direct contact cooler and the absorber) may
be significantly
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reduced in configurations according to the inventive subject matter when
compared to
numerous known configurations.
While exhaust gas recycling may be employed in numerous configurations that
include a turbine driving a load (e.g., generator or compressor), it is
generally preferred that
plant configurations in which exhaust is at least partially recycled are
plants that include a
humid air turbine (HAT), and an exemplary plant that includes a HAT is
described in U.S.
Pat. No. 4,829,763 to Rao. Where contemplated
configurations include a HAT cycle, it should be especially appreciated that
previously
existing difficulties of known HAT cycles may be overcome by contemplated
carbon dioxide
removal configurations. Aniong other things, previously known HAT cycle
configurations
typically required customized turbo machinery in vvhich the compressor of the
gas turbine
needed to be significantly smaller than the expander. By removing carbon
dioxide from the
system in case of solvent based processes, or by removing carbon dioxide and
other gaseous
components in case of the membrane or autorefrigeration based processes
upstream of the
expander, additional water vapor can be supplied to the combustor and/or
expander without
significantly changing the relative flow of gas through the compressor and the
expander of
the engine. Therefore, contemplated configurations are not only expected to
improve the
economics of carbon dioxide recovery in gas turbine based plants, but also to
implement
carbon dioxide recovery to existing recuperated gas turbines (e.g.,
recuperated gas turbines
210 commercially available fronl Sulzer Turbo or MAN GHH Borsig).
Furtliermore, it is contemplated that configurations and methods according to
the
inventive subject matter may also be utilized in relatively small power plants
with a capacity
of 101VIW or less to recover carbon dioxide from the combustion gases.
Alternatively,
contenlplated configurations and methods may be included in all plants in
which a gas turbine
are eniployed to drive a compressor or generator.
It is still further contemplated that the so isolated carbon dioxide may be
utilized in a
variety of processes, and particularly contemplated processes include urea
plants, and
enhanced oil recovery. Alternatively, isolated carbon dioxide may be sold for
medical or
nutritional use, employed in freezing processes, or pumped into mines, the
ocean, or other
locations where carbon dioxide may be at least temporarily sequestered. The
makeup water to
the humidifier in contemplated configurations may be provided by various
sources, including
waste water (e.g., fiom within the plant), recycled water, or fresh water.
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With respect to contemplated acid gas removal units, it should be recognized
that all
known processes for isolating carbon dioxide from a gas are suitable in
conjunction with the
teachings presented herein. However, particularly preferred methods and
configurations
include pllysical solvent based processes (see e.g., U.S. Pat. No. 2,863,527,
U.S. Pat. No.
2,926,751, U.S. Pat. No. 3,505,784, U.S. Pat. Nd,. 2,649,166,
or U.S. Pat. No. 3,773,896), chemical solvent based
processes (see e.g., U.S. Pat. No. 3,563,695, or U.S. Pat.
No. 2,177,068), membrane processes (see e.g., U.S. Pat.
No. 4,705,540 or U.S. Pat. No. 4,741,744), and
autorefrigeration (see e.g., U.S. Pat. No. 6,301,927).
Where carbon dioxide removal includes a membrane or solvent based process as
shown in Figure 1, it should be recognized that the quantity of recycled
expanded exhaust
118B may vary considerably and will depend, among other factors, on the
particular carbon
dioxide removal unit and/or partial pressure of the carbon dioxide in the
compressed mixed
gas. Thus, it is generally contemplated that the amount of recycled expanded
exhaust 118B
may be within the range of 0 vol% and 100 vol% of the total expanded exhaust
118.
However, and particularly where the exhaust gas has a relatively low carbon
dioxide partial
pressure, it is preferred that the amount of recycled expanded exhaust 118B is
between about
vol% and 75 vol% of the total expanded exhaust 118.
20 Similarly, where a.utorefrigeration is employed as depicted in Figure 2, it
should be
recognized that depending on the particular operational parameters the amount
of compressed
mixed gas stream 234B that is fed to the autorefrigeration unit may vary
considerably.
However, under most operating conditions, suitable quantities of compressed
niixed gas
stream 234B will be in the range between about 20 vol% and 80 vol%. Where
contemplated
25 configurations include a partial HAT configuration as depicted in Figure 3,
the quantity of
mixed compressed gas 334A that is directly routed to the combustor may
advantageously be
between about 5 vol% and 50 vol%. However, depending on the particular
configuration, the
quantity of mixed compressed gas 334A may also be higher than 50 vol%. With
respect to
the cooled expanded exhaust gas stream 318B that is recycled back to the
compressor, it is
contemplated that suitable amounts will vary considerably. However, it is
generally preferred
that the amount of cooled expanded exhaust gas stream 318B will be in the
range between
about 25 vol% to about 75 vol%.
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Mixing of the recycled cooled expanded exhaust gas stream may be performed in
numerous manners, and all known manners of mixing are contemplated suitable
herein. For
example, where an existing plant is retrofitted to a configuration according
to the inventive
subject matter, mixing may be performed in a mixing vessel upstream of the
compressor
inlet. On the other hand, wliere a configuration according to the inventive
subject matter is
built from scratch, mixing may be performed by supplying recycled gas to the
compressor
inlet along with fresh air.
Therefore, the inventor generally contemplates that a plant may include a
humid air
turbine combustor that receives fuel and humid carbon dioxide depleted gas
stream, wherein
at least part of the humid carbon dioxide depleted gas stream is formed from
an exhaust gas
of the humid air turbine combustor. Such plants may advantageously fitrther
comprise a
humidifier, wherein water used in the humidifier is heated by at least one of
the compressed
mixed gas and the exhaust gas. The term "carbon dioxide depleted gas streanl"
as used herein
refers to any gas from which at least a portion of the carbon dioxide has
previously been
removed.
Viewed from another perspective, a plant in which carbon dioxide is removed
from an
exhaust gas of a turbine combustor will comprise a compressor that compresses
air and at
least a portion of the exhaust gas to form a compressed mixed gas, wherein
carbon dioxide is
removed from the compressed mixed gas in an acid gas removal unit.
Thus, specific embodiments and applications of liurnid air turbine cycles with
carbon
dioxide recovery have been disclosed. It should be apparent, however, to those
skilled in the
art that many more modifications besides those already described are possible
without
departing from the inventive concepts herein. The inventive subject matter,
therefore, is not
to be restricted except in the spirit of the appended claims. Moreover, in
interpreting both the
specification and the claims, all terms should be interpreted in the broadest
possible manner
consistent with the context. In particular, the terms "comprises" and
"comprising" should be
interpreted as referring to elements, components, or steps in a non-exclusive
manner,
indicating that the referenced elements, components, or steps may be present,
or utilized, or
combined with other elements, components, or steps that are not expressly
referenced.
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