Note: Descriptions are shown in the official language in which they were submitted.
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SYSTEMS AND METHODS OF CONVERTING FUEL
The present invention is generally directed to systems and methods of
converting
fuel, and is generally directed to oxidation-reduction reactor systems used in
fuel
conversion.
There is a constant need for clean and efficient energy generation systems.
Most of
the commercial processes that generate energy carriers such as steam,
hydrogen, synthesis
gas (syngas), liquid fuels and/or electricity are based on fossil fuels.
Furthermore, the
dependence on fossil fuels is expected to continue in the foreseeable future
due to the
much lower costs compared to renewable sources. Currently, the conversion of
carbonaceous fuels such as coal, natural gas, petroleum coke is usually
conducted through
a combustion or reforming process. However, combustion of carbonaceous fuels,
especially coal, is a carbon intensive process that emits large quantities of
carbon dioxide
to the environment. Sulfur and nitrogen compounds are also generated in this
process due
to the complex content in coal.
Chemical reactions between metal oxides and carbonaceous fuels, on the other
hand, may provide a better way to recover the energy stored in the fuels.
Several processes
are based on the reaction of metal oxide particles with carbonaceous fuels to
produce
useful energy carriers. For example, Ishida et al. U.S. Pat. No. 5,447,024
describes
processes wherein nickel oxide particles are used to convert natural gas
through a
chemical looping process into heat, which may be used in a turbine. However,
recyclability of pure metal oxides is poor and constitutes an impediment for
its use in
commercial and industrial processes. Moreover, this technology has limited
applicability,
because it can only convert natural gas, which is more costly than other
fossil fuels.
Another well known process is a steam-iron process, wherein coal derived
producer gas is
reacted with iron oxide particles in a fluidized bed reactor to be later
regenerated with
steam to produce hydrogen gas. This process however suffers from poor gas
conversion
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rates due to improper contact between reacting solids and gases, and is
incapable of
producing a hydrogen rich stream.
As demands increase for cleaner and more efficient systems of converting fuel,
the
need arises for improved systems, and system components therein, which will
convert fuel
effectively, while reducing pollutants.
In one embodiment of the present invention, a system for converting fuel is
provided. The system comprises a first reactor comprising a plurality of
ceramic
composite particles, wherein the ceramic composite particles comprise at least
one metal
oxide disposed on a support. The first reactor is configured to reduce at
least one metal
oxide with a fuel to produce a reduced metal or a reduced metal oxide. The
system also
comprises a second reactor configured to oxidize the reduced metal or reduced
metal oxide
to produce a metal oxide intermediate, and a third reactor configured to
regenerate at least
one metal oxide by oxidizing the metal oxide intermediate.
In another embodiment of the present invention, a method of converting fuel to
hydrogen, CO, or syngas is provided. The method comprises the steps of:
reducing a metal
oxide in a reduction reaction between a fuel and a metal oxide to a reduced
metal or a
reduced metal oxide; oxidizing the reduced metal or reduced metal oxide with
an oxidant
to a metal oxide intermediate, while also producing hydrogen, CO, or syngas;
and
regenerating the at least one metal oxide by oxidizing the metal oxide
intermediate.
In yet another embodiment, a system comprising a Fischer-Tropsch reactor is
provided. The Fischer-Tropsch reactor is configured to produce hydrocarbon
fuel from a
feed mixture comprising gaseous fuel. The system also comprises a first
reactor
comprising a plurality of ceramic composite particles, wherein the ceramic
composite
particles comprise at least one metal oxide disposed on a support. The first
reactor is
configured to reduce the metal oxides with a gaseous fuel to a reduced metal
or a reduced
metal oxide, wherein the gaseous fuel comprises at least partially the
hydrocarbon fuel
produced by the Fischer-Tropsch reactor. The system also comprises a second
reactor
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configured to oxidize the reduced metal or reduced metal oxide with steam to
produce
=
metal oxide intermediates.
In another embodiment, a method of preparing ceramic composite particles is
provided. The method comprises reacting a metal oxide with a support material;
heat
treating the mixture of metal oxide and support material at temperatures of
between about
200 to about 1500 C to produce ceramic composite powders; converting the
ceramic
composite powders into ceramic composite particles; and reducing and oxidizing
the
ceramic composite particles prior to use in a reactor.
Additional features and advantages provided by embodiments of the present
invention will be more fully understood in view of the following detailed
description.
The following detailed description of the illustrative embodiments of the
present
invention can be best understood when read in conjunction with the following
drawings,
where like structure is indicated with like reference numerals and in which:
Fig. 1 is a schematic illustration of a system for producing hydrogen from
coal
according to one or more embodiments of the present invention;
Fig. 2 is a schematic illustration of another system for producing hydrogen
from
coal according to one or more embodiments of the present invention;
Fig. 3 is a schematic illustration of another system for producing hydrogen
from
coal using direct chemical looping and sieves for ash separation according to
one or more
embodiments of the present invention;
Fig. 4 is a schematic illustration of another system for producing hydrogen
from '
coal using direct chemical looping and cyclones for ash separation according
to one or
more embodiments of the present invention;
Fig. 5 is a schematic illustration of another system for producing hydrogen
from
coal, wherein the system utilizes a third reactor for heat recovery according
to one or more
embodiments of the present invention;
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Fig. 6 is a schematic illustration of another system for producing hydrogen
from
coal, wherein the system utilizes a sorbent in the first reactor for sulfur
removal according
to one or more embodiments of the present invention;
Fig. 7 is a schematic illustration of system for producing hydrogen from
syngas
according to one or more embodiments of the present invention;
Fig. 8 is a schematic illustration of another system for producing hydrogen
from
coal, wherein carbon dioxide produced in the first reactor is recycled back to
the second
reactor according to one or more embodiments of the present invention;
Fig. 9 is a schematic illustration of another system for producing steam from
coal
according to one or more embodiments of the present invention;
Fig. 10 is a schematic illustration of yet another system for producing
hydrogen
from syngas according to one or more embodiments of the present invention;
Fig. II is a schematic illustration of another system for producing hydrogen
from
syngas, wherein the system comprises pollutant control components according to
one or
more embodiments of the present invention;
Fig. 12 is a schematic illustration of a system of chemical looping in
conjunction
with Fischer-Tropsch (F-T) synthesis according to one or more embodiments of
the
present invention;
Fig. 13 is a schematic illustration of another system of chemical looping in
conjunction with Fischer-Tropsch synthesis according to one or more
embodiments of the
present invention;
Fig. 14 is a schematic illustration of another system of chemical looping in
conjunction with Fischer-Tropsch synthesis according to one or more
embodiments of the
present invention;
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Fig. 15 is a schematic illustration of yet another system of chemical looping
in
conjunction with Fischer-Tropsch synthesis, wherein the system comprises
pollutant
control components according to one or more embodiments of the present
invention;
Fig. 16 is a schematic illustration of another system of chemical looping in
conjunction with Fischer-Tropsch synthesis, wherein the system operates
without the use
of a gasifier according to one or more embodiments of the present invention;
Fig. 17 is a schematic illustration of a system of chemical looping for
onboard H2
storage on a vehicle according to one or more embodiments of the present
invention;
Fig. 18(a) is a schematic illustration of a reactor cassette used in the
onboard H2
storage system of Fig. 17, wherein the reactor cassette comprises Fe
containing media and
a packed bed of small pellets according to one or more embodiments of the
present
invention;
Fig. 18(b) is a schematic illustration of another reactor cassette used in the
onboard
H2 storage system of Fig. 17, wherein the reactor cassette comprises Fe
containing media
and a monolithic bed with straight channels for steam flow according to one or
more
embodiments of the present invention;
Fig. 18(c) is a schematic illustration of yet another reactor module used in
the
onboard H2 storage system of Fig. 17, wherein the reactor cassette comprises
Fe
containing media and a monolithic bed with channels for steam and air flow
according to
one or more embodiments of the present invention;
Fig. 19 is a schematic illustration of a reactor cassette used in the onboard
H2
storage system of Fig. 17, wherein the reactor cassette utilizes a series of
monolithic bed
reactors with air injection to provide heat for steam formation according to
one or more
embodiments of the present invention;
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Fig. 20 is a schematic illustration of a system of chemical looping in
conjunction
with a solid oxide fuel cell according to one or more embodiments of the
present
invention;
Fig. 21 is a schematic illustration of a reactor utilized in the system of the
present
invention, wherein the reactor is a moving bed reactor comprising an annular
region
disposed near a fuel feed location according to one or more embodiments of the
present
invention;
Fig. 22 is a schematic illustration of a reactor utilized in the system of the
present
invention, wherein the reactor is a moving bed comprising a annular region as
well as a
cone inserted into the moving bed according to one or more embodiments of the
present
invention; and
Fig. 23 is a schematic illustration of another reactor utilized in the system
of the
present invention, wherein the reactor is a moving bed reactor comprising an
annular
region according to one or more embodiments of the present invention.
Referring generally to Fig. 1, the present invention is directed to systems
and
methods for converting fuel by redox reactions of ceramic composite particles.
As shown
in Fig.1, the system comprises two primary reactors, as well as additional
reactors and
components, which will be described in detail below. The first reactor 1,
which is
configured to conduct a reduction reaction, comprises a plurality of ceramic
composite
particles having at least one metal oxide disposed on a support. As would be
familiar to
one of ordinary skill in the art, the ceramic composite particles may be fed
to the reactor
via any suitable solids delivery device/mechanism. These solids delivery
devices may
include, but are not limited to, pneumatic devices, conveyors, lock hoppers,
or the like.
Ceramic composite particles are described in Thomas et al. U.S. Published App.
No.
2005/0175533 Al. In addition to the particles and particle synthesis methods
disclosed in
Thomas, the Applicants, in a further embodiment, have developed alternative
methods of
making the ceramic composite, which may improve the efficacy and activity of
the
ceramic composite
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particles in the present system. Two of these alternative methods are co-
precipitation and
spray drying.
The third alternative method includes the step of physically mixing a metal
oxide
with a ceramic support material. Optionally, a promoter material may be added
to the
mixture of metal oxides and support material. After mixing, the mixture is
heat treated at
temperatures of between about 200 to about 1500 C to produce ceramic
composite
powders. Heat treating may occur in the presence of inert gas, steam, oxygen,
air, H2, and
combinations thereof at a pressure of between vacuum pressure and about 10
atm. The
method may also include a chemical treatment step, wherein the mixture of
metal oxides
and support material are treated with an acid, base, or both to activate the
ceramic
composite powder. After powder production, the ceramic composite powders may
be
converted into ceramic composite particles by methods known to one of ordinary
skill in
the art. These methods may include, but are not limited to, extrusion,
granulation, and,
pressurization methods such as pelletization. The particle may comprise
various shapes
and forms, for example, pellets, monoliths, or blocks.
The method then includes the step of reducing and oxidizing the ceramic
composite
particles prior to use in a reactor. This cycle is important for the ceramic
composite
particles because this mixing process may produce a particle with increased
activity,
strength and stability. This cycle is important for the ceramic composite
particles to
increase their activity, strength and stability. This treatment also leads to
a reduced
porosity (0.1-50 m2/g) as well as crystal structure changes that make the
particle readily
reducible and oxidizable without loosing its activity for multiple such
reaction cycles. The
porosity in Thomas patent is not reported but it is stated that the particle
was porous and
had mesopores. Although the description of particle synthesis in this
application is limited
to spray dry, co-precipitation, and direct mixing approach, ceramic composite
particles
produced by other techniques such as sol-gel, wet impregnation, and other
methods known
to one of ordinary skill in the art are also operable in the reactors of the
present system.
The metal oxide of the ceramic composite comprises a metal selected from the
group consisting of Fe, Cu, Ni, Sn, Co, Mn, and combinations thereof. Although
various
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compositions are contemplated herein, the ceramic composite typically
comprises at least
40% by weight of the metal oxide. The support material comprises at least one
component
selected from the group consisting of SiC, oxides of Al, Zr, Ti, Y, Si, La,
Sr, Ba, and
combinations thereof. The ceramic composite comprises at least 5 4 by weight
of the
support material. In further embodiments, the particle comprises a promoter
material. The
promoter comprises a pure metal, a metal oxide, a metal sulfide, or
combinations thereof.
These metal based compounds comprise one or more elements from the group
consisting
of Fe, Ni, Sn, Li, Na, K, Rb, Cs, Be, Mg, Ca, Sr, Baõ B, P. V, Cr, Mn, Co, Cu,
Zn, Ga,
Mo, Rh, Pt, Pd, Ag, and Ru. The ceramic composite comprises up to 40% by
weight of the
promoter material. In an exemplary embodiment of the ceramic composite, the
metal
oxide comprises Fe203 supported on a TiO2 support, and specifically a support
comprising
a mixture of TiO2 and A1203. In another exemplary embodiment, the ceramic
composite
may also comprise Fe203 supported on an YSZ (Yittria stabilized Zirconia)
support.
Referring back to the reduction reaction of the first reactor 1, the first
reactor 1
receives a fuel, which is utilized to reduce the at least one metal oxide of
the ceramic
composite to produce a reduced metal or a reduced metal oxide. As defined
herein, "fuel"
may include: a solid carbonaceous composition such as coal, tars, oil shales,
oil sands, tar
sand, biomass, wax, coke etc; a liquid carbonaceous composition such as
gasoline, oil,
petroleum, diesel, jet fuel, ethanol etc; and a gaseous composition such as
syngas, carbon
monoxide, hydrogen, methane, gaseous hydrocarbon gases (C1-C6), hydrocarbon
vapors,
etc. For example, and not by way of limitation, the following equation
illustrates possible
reduction reactions:
Fe203 + 2C0 4 2Fe + 2CO2
16 Fe203 + 3 C5H12 4 32 Fe + 15C0-, + 18H20
In this example, the metal oxide of the ceramic composite, Fe203, is reduced
by a
fuel, for example, CO, to produce a reduced metal oxide, Fe. Although Fe is
the
predominant reduced composition produced in the reduction reaction of the
first reactor 1,
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FeO or other reduced metal oxides with a higher oxidation state are also
contemplated
herein.
=
The first reactor 1 and second reactor 2 may include various suitable reactors
to
allow an overall countercurrent contacting between gas and solids. Such may be
achieved
using a moving bed reactor, a series of fluidized bed reactors, a rotatory
kiln, a fixed bed
reactor, combinations thereof, or others known to one of ordinary skill in the
art.
As shown in Figs. 21- 23, the first reactor 1 may comprise a moving bed
reactor
with an annular region 8 created around the moving bed. Although various
orientations for
the annulus 8 are possible, the annulus 8 is typically located at a region
where a reducing
fuel is being introduced. As shown in Fig. 22, the moving bed reactor may also
include a
mixing device, e.g. a cone 9, inserted in the moving bed to radially
distribute the ceramic
composite particles and mix unconverted fuel with the ceramic composite
particles.
Although Fig. 22 illustrates the cone 9 in conjunction with the annulus 8, it
is
contemplated that the moving bed reactor may incorporate a cone 8, but not an
annulus in
some embodiments. The annular region 8 allows the first reactor 1 to introduce
solid and
liquid fuels into the middle of a moving bed of solids ceramic composites. In
one
embodiment, the fuel may be introduced pneumatically and then partially
combusted in
the annulus 8. The unburnt fuel drops down onto the heap of ceramic composites
in the
annulus 8 and is mixed with them for further reactions. Figures 21, 22 and 23
show some
of the different methods to form the annular region 8. Fig 21 uses an internal
hopper to
create the annular region. Fig. 23 uses an internal hopper along with a rotary
valve to
create an even larger annular region with better control over the flow of
ceramic
composite particles. Fig 22 creates an external annular region for the flow of
the moving
bed and uses a mixing device, e.g. a cone 9 to disperse the solids axially so
that
unconverted fuel may be distributed uniformly over the entire cross section of
the moving
bed.
The first reactor 1 may be constructed with various durable materials suitable
to
withstand temperatures of up at least 1200 C. The reactor may comprises
carbon steel
with a layer of refractory on the inside to minimize heat loss. This
construction also allows
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the surface temperature of the reactor to be fairly low, thereby improving the
creep
resistance of the carbon steel. Other alloys suitable for the environments
existing in
various reactors may also be employed, especially if they are used as internal
components
configured to aid in solids flow or to enhance heat transfer within a moving
bed
embodiment. The interconnects for the various reactors can be of lock hopper
design or
rotary/star valve design to provide for a good seal. Other interconnects as
can be
determined easily by a person skilled in the art may also be used.
After reduction in the first reactor 1, the reduced metal or reduced metal
oxide
particles are then delivered to the second reactor 2 to undergo an oxidation
reaction. The
second reactor 2, which may comprise the same reactor type or a different
reactor type
than the first reactor 1, is configured to oxidize the reduced metal or
reduced metal oxide
to produce a metal oxide intermediate. As used herein, "metal oxide
intermediate" refers to
a metal oxide having a higher oxidation state than the reduced metal or metal
oxide, and a
lower oxidation state than the metal oxide of the ceramic composite. For
example, and not
by way of limitation, the following equation illustrates possible oxidation
reactions:
3 Fe + 4 H20 .3 Fe304 + 4 H2
3 Fe + 4CO2 ---> Fe304 + 4 CO
In this example which centers on ceramic composites that utilize Fe203 as the
metal
oxide, oxidation in the second reactor using steam will produce a resultant
mixture that
includes metal oxide intermediates comprising predominantly Fe304. Fe203 and
FeO may
also present. Furthermore, although H20, specifically steam, is the oxidant in
this example,
numerous other oxidants are contemplated, for example, CO, 02, air, and other
compositions familiar to one of ordinary skill in the art.
Referring to the solid fuel conversion embodiment of Fig. 1, the system
comprises
25. two moving bed reactors 1 and 2. The first reactor 1, which defines a
moving bed, operates
by having the solids (Fe203 and coal) moving downwards in a densely packed
mode, while
the gases, for example, H2, steam, CO, CO2, or combinations thereof move
upwards. This
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movement of solids and gases is defined as a countercurrent contacting
pattern. The Fe203
containing ceramic composite particles are introduced from the top via a
gravitational
feeder while solid fuel, e.g. coal is introduced at a region of the first
reactor 1 lower than
the feed location of the ceramic composite particles. Typically, the reactors
operate at a
temperature in the range of about 400 to about 1200 C and a pressure in the
range of
about 1 to about 150 atm; however, one of ordinary skill in the art would
realize that
temperatures and pressures outside these ranges may be desirable depending on
the
reaction mechanism and the components of the reaction mechanism. In the
embodiment of
Fig. 1, coal is introduced in pulverized form by pneumatically conveying with
oxygen or
carbon dioxide or steam. The oxygen may be separated in the air separation
unit 24 as
illustrated in Figures 2-6, 9 and 20. After the coal is delivered to the first
reactor 1, coal
will devolatilize and form char. The volatiles may also react with Fe203 to
form CO2 and
water. The outlet gas composition of the first reactor 1 may contain
predominantly CO2
and steam. Subsequently, the CO2 and steam may be fed to a condenser 4 to
separate the
steam and the CO2. The CO2 obtained after condensation of water will be
relatively pure
and may be sequestered under the ocean or in geological formations or enhanced
oil
recovery without emitting to the atmosphere and contributing to green house
warming of
the earth.
The char formed on devolatilization of coal will then react with partially
reduced
iron oxide as it flows downwardly in the first reactor 1. To enhance the char
reaction with
iron oxide, a small amount of hydrogen is introduced at the bottom of the
moving bed to
result in the formation of H20 on its reaction with partially reduced iron
oxide. The 1120
produced will react with downwardly flowing char leading to its gasification
into H2 and
CO. The hydrogen formed will then react with the partially reduced iron oxide
in order to
further reduce the reduced iron oxide, thereby enhancing the char-iron oxide
reaction
rates. The hydrogen introduced at the bottom of the reactor will also ensure
that the iron
oxide particles are greatly reduced to Fe as they exit the first reactor 1. In
some cases,
some carbon is intentionally left unconverted in the particle to generate CO
using steam in
the second reactor. In yet some other cases, an excess of ceramic composite
particles
comprising Fe2O3 may be inserted into the first reactor 1 in order to enhance
reaction rates.
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The exiting reduced Fe containing particles may then be introduced into the
second
reactor 1. Like in the first reactor 1, the second reactor 2 may also comprise
a moving bed
with a countercurrent contacting pattern of gas and solids. Steam is
introduced at the
bottom of the reactor and it oxidizes the reduced Fe containing particles as
the particles
move downwardly inside the second reactor 2. In this embodiment, the product
formed is
hydrogen, which is subsequently discharged from the top of the second reactor
2. It will be
shown in further embodiments that products such as CO and syngas are possible
in
addition to hydrogen. Though Fe203 formation is possible in the second reactor
2, the
solid product from this reactor is expected to be mainly metal oxide
intermediate, Fe304.
The amount of Fe203 produced in the second reactor 2 depends on the oxidant
used, as
well as the amount of oxidant fed to the second reactor 2. The steam present
in the
hydrogen product of reactor 2 may then be condensed with condenser 5 in order
to provide for
a hydrogen rich stream. At least part of this hydrogen rich stream may be
recycled back to
the first reactor 1 as described above. In addition to utilizing the same
reactor type as the
first reactor 1, the second reactor 2 may similarly operate at a temperature
between about
400 to about 1200 C and pressure of about 1 to about 150 atm.
To regenerate the metal oxide of the ceramic composite, the system utilizes a
third
reactor 3, which is configured to oxidize the metal oxide intermediate to the
metal oxide of
the composite. Referring to the embodiment Fig. 1, the third reactor 3 may
comprise an
_________________________________________ air filled line or tube used to
oxidize the metal oxide intei mediate. Referring to the Fig. 5
embodiment, the oxidation of the metal oxide intermediate may be conducted a
heat
recovery unit 3. The following equation lists one possible mechanism for the
oxidation in
the third reactor 3:
2 Fe304 + 0.5 02 4 3 Fe2O3
Referring to the embodiment of Fig. 1, the Fe304 product may be oxidized to
Fe203
in solid conveying system 6. Different mechanisms can be used for solid
transportation.
Figure 1 shows it as a transport system using pneumatic conveyor driven by
air. Belt
conveyors, bucket elevators, screw conveyors, moving beds and fluidized bed
reactors
may also be used to transport the solids. The resultant depleted air stream is
separated
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from the particles and its high-grade-heat content recovered for steam
production. After
regeneration, the ceramic composite particle is not degraded and maintains
full particle
functionality and activity. In further embodiment, the particle may undergo
numerous
regeneration cycles, for example, 10 or more regeneration cycles, and even
greater than
100 regeneration cycles, without losing its functionality. This system can be
used with
existing systems involving minimal design change, thus making it economical.
The iron particles exiting the first reactor 1 may also contain ash and other
unwanted byproducts. If the ash is not removed after the first 1 or second
reactor 2 stages,
the ash may keep building up in the system. Numerous devices and mechanisms
for ash
removal would be familiar to one of ordinary skill in the art. For example,
ash may be
removed based on the size of ash with respect to the iron oxide particles from
any of the
solid streams in the system. If pulverized coal is used as the fuel source, it
will yield fine
ash particles, typically lower than 100 1.im in size. The size of the ceramic
composite
particles may vary based on the metal components used and the oxidation-
reduction
reaction in which the ceramic composite is utilized. In one embodiment, the
particle
comprises a size between about 0.5 to about 50 mm. As a result, simple
sieving, for
example, simple sieving at high temperatures, may result in removal of ash.
Simple
sieving uses the size and density differences between the wanted and unwanted
solid
particles in the separation process. Other methods, for example, mechanical
methods, and
methods based on weight, or magnetic properties, may be used to separate ash
and
unwanted materials. Separation devices, such as cyclones, will be further
discussed in later
embodiments.
Heat integration and heat recovery within the system and all system components
is
highly desirable. Heat integration in the system is specifically focused on
generating the
steam for the steam requirements of the second reactor 2. This steam can
easily be
generated using the high grade heat available in the hydrogen, CO2 and
depleted air
streams exiting reactors 1, 2, 3, respectively. In the process described
above, there is also
a desire to generate pure oxygen. To generate this pure oxygen, at least part
of the
hydrogen may be utilized.
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The residence time in each reactor is dependent upon the size and composition
of
individual ceramic composite particles, as would be familiar to one or
ordinary skill in the
art. For example, the residence time for a reactor comprising Fe based metal
oxides may
range from about 0.1 to about 20 hours.
As stated above, additional unwanted elements may be present in addition to
ash.
Trace elements like Hg, As, Se are not expected to react with Fe203 at the
high
temperatures of the process. As a result they are expected to be present in
the CO2 stream
produced. If CO2 is to be used as a marketable product, these trace elements
must be
removed from the stream. Various cleanup units, such as mercury removal units
are
contemplated herein. Similar options will need to be exercised in case the CO2
stream is
let out into the atmosphere, depending upon the rules and regulations existing
at that time.
If it is decided to sequester the CO2 for long term benign storage, e.g. in a
deep geological
formation, there may not be a need to remove these unwanted elements.
Moreover, CO2
may be sequestered via mineral sequestration, which may be more desirable than
geological storage, because it is safer and more manageable. Additionally
sequestering
CO2 has an economic advantage for global CO2 credit trading, which may be
highly
lucrative.
Furthermore, sulfur may constitute another unwanted element, which must be
accounted for in the system. In a solid fuel conversion embodiment, sulfur,
which is
present in coal, is expected to react with Fe203 and form FeS. This will be
liberated on
reaction with steam in reactor 2 as H2S and will contaminate the hydrogen
stream. During
the condensation of water from this steam, most of this H2S will condense out.
The
remaining H2S can be removed using conventional techniques like amine
scrubbing or
high temperature removal using a Zn, Fe or a Cu based sorbent. Another method
for
removing sulfur would include the introduction of sorbents, for example, CaO,
MgO, etc.
Additionally, as shown in the embodiment of Fig. 6, sorbents may be introduced
into the
first reactor 1 in order to remove the sulfur and to prevent its association
with Fe. The
sorbents may be removed from the system using ash separation device.
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Although the embodiments of the present system are directed to producing
hydrogen, it may be desirable for further treatment to produce ultra-high
purity hydrogen.
As would be familiar to one of ordinary skill in the art, some carbon or its
derivatives may
carry over from reactor 1 to 2 and contaminate the hydrogen stream. Depending
upon the
purity of the hydrogen required, it may be necessary to use a pressure swing
adsorption
(PSA) unit for hydrogen to achieve ultra high purities. The off gas from the
PSA unit may
comprise value as a fuel and may be recycled into the first reactor 1 along
with coal, in
solid fuel conversion embodiments, in order to improve the efficiency of
hydrogen
production in the system.
Referring to Fig. 2, the hydrogen produced in the second reactor 2 may provide
additional benefits to the system. For instance, the hydrogen may be fed a
power
generation section 10 configured to produce electricity from a hydrogen
product of the
second reactor 2. As would be familiar to one of ordinary skill in the art,
the power
generation section 10 may comprise air compressors 12, gas turbines 14, steam
turbines,
electric generators 16, fuel cells, etc. In another embodiment, unconverted H2
from fuel
cell can be recycled to the middle region of reactor 2, this helps to increase
fuel cell
efficiencies while reducing the fuel cell size. Thus improve the overall
system efficiency.
Referring to Fig. 3, another coal conversion system similar to Fig. 1 is
provided.
Part of the CO2 is recycled back as carrier gas for the injection of coal.
Both of the reactors
operate under 400-1200 C and the reduced metal particles would be transported
to the
second reactor 2 by an inert gas such as N2 from the air separation unit. The
hydrogen
produced in second reactor 2 may also be used for transportation of reduced
metal oxide
particles. The reduced metal will be separated out from the nitrogen gas and
fed into the
second reactor 2 to react with steam to generate 112. The 112 generated would
contain H2S
due to the sulfur inside the coal, and would attach to the particle to form
MeS. As shown, a
traditional sulfur scrubbing unit 22 may be used to remove H2S and generate
pure H2. The
oxidized particles from the outlet of the second reactor 2 would go through an
ash
separation system 28 using a sieve. In this embodiment, most of the ash and
metal oxide
particles, as a result of attrition, would be separated out for regeneration,
while the rest of
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the metal oxide particles would be introduced back into the inlet of the first
reactor 1 using
a feed device, for example, a pneumatic conveyor by air, where the makeup
ceramic
composite would also be fed. As used herein, makeup ceramic composite
particles refer to
fresh particle used to replace the fines or ceramic composite particles
rendered too small
or ineffective due to attrition and deactivation. The typical makeup ceramic
composite rate
would be less than 2% of the particle flow rate in the system.
Referring to Fig. 4, a different solid conveying system, as well as a
different ash
separation unit, may be used for coal direct reactor system. Here, the reduced
metal
particles are transferred to the second reactor 2 using a bucket elevator in
an N2
environment. After being oxidized in the second reactor 2 to metal oxide
intermediates,
the metal oxide intermediates are sent to a cyclone 3 using a pneumatic
conveyor with air
so that the particle is already oxidized by the time it reaches the cyclone.
The fines due to
attrition and the coal ash may be removed along with air while the particles
will be
separated out with the cyclone and fed into the first reactor along with the
makeup metal
oxide particles. The makeup rate is again less than 2% of the particle flow
rate in the
system. Other devices like a particle classifier or other devices commonly
known to one of
ordinary skill in the art may also be used for ash separation.
Referring to the Fig. 5 embodiment, a third reactor 3 in form of a fluidized
bed is
utilized to recover the heat for further oxidation of the particles exiting
the second reactor /
i.e. the metal oxide intermediates, such as Fe304. In other embodiments and
figures this
reactor was shown as the transport line from the second reactor 2 to first
reactor 1 where
air or oxygen is introduced. It will be a transport reactor, a fast fluidized
bed, a fluidized
bed, a riser or pneumatic conveying system. Here, the metal oxide
intermediates, e.g.
Fe304, from the outlet of the second reactor 2 are injected into a heat
recovery unit 3 where
oxygen or air is introduced to oxidize the particles back into their highest
oxidation state
i.e. the metal oxide of the ceramic composite, e.g. Fe203. In addition to the
oxidation
conversion, heat is generated in this process, and the particles' temperature
may also
increase drastically. The particles with significantly higher temperature may
be introduced
back into the first reactor 2 and the heat stored in the particle would
provide, at least in
=
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part, the heat required for reduction reactions. For particles with high heat
capacity, it may
desirable, in one exemplary embodiment, to utilize a support such as SiC,
which has high
thermal conductivity.
As shown in the embodiment of Fig. 6, sorbent materials, such as modified
calcium
carbonate or calcium oxide or calcium hydroxide, may be injected into the
first reactor 1
to remove the sulfur from the coal. The CaCO3 injection rate will range from
about 1% to
about 15% of the metal oxide flow rate in the system; however, the injection
rate varies
depending on the cornposition of the coal used. Magnesium oxide may also be
used as a
sorbent. Generally, the size of the sorbent particle is smaller than the
ceramic composite
particles, and may in some exemplary embodiment, comprises a particle size
ranging from
about 100 p.m to about 1 mm depending on the size of the ceramic composite
particle in
the system. The spent sorbent, after sulfur capture, would be separated out
with ash and
regenerated afterwards for further use in the first reactor 1. In this
embodiment, pure H2
may be produced without the need of a scrubber.
Referring generally to Figs. 7-9, system embodiments for converting gaseous
fuels
are provided. As shown in Fig. 9, part of the CO2 produced in the first
reactor 1 may be
split and introduced into second reactor 2 along with steam. By controlling
the feed rates
of steam and CO2, syngas having a different H2 and CO ratio can be obtained.
The syngas
can be introduced to a gas turbine to generate electricity or it can be used
for
chemical/liquid fuel synthesis. In order to generate syngas with an H2/C0
ratio of about
2:1 for Fischer-Tropsch synthesis to produce liquid fuel, a typical steam and
CO2 feed rate
ratio should be around 2:1. The present system in conjunction with Fischer-
Tropsch
synthesis will be discussed in greater detail below. The output ratio of H2/C0
may also be
varied by recycling part of the output after condensation of water to a middle
section of
the second reactor 2. This will allow more water gas shift reaction to convert
unconverted
CO2 into CO.
As shown in the Fig. 9 embodiment of syngas conversion, reduced metal
particles
are burnt with air in the second reactor 2. The heat generated may be
extracted using water
to generate high temperature steam. The steam can then be either used for
electricity
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generation or it can be used to extract heavy oil from oil shale. In the
embodiment of Fig.
10, the system must account for the fact that H2S in raw syngas would react
with metal to
form metal sulfide. Reduced metal and metal sulfide would be introduced to the
second
reactor 2 to react with steam. The product stream in this system would contain
Hy and
H2S. H2S may be taken out using traditional scrubber technology and a Hy rich
stream
would be achieved. By using gaseous fuel, e.g. syngas, instead of solid fuel,
the ash
separation process may be avoided.
Referring to the Fig. 11 embodiment, a hot gas sulfur removal unit using
sorbents
such as CaO is utilized to remove bulk quantities of H2S in raw syngas to
below 100 ppm.
The pretreated syngas is then mixed with steam and CO2 of appropriate
quantity, typically
< 15% and introduced to the bottom of the first reactor 1. Due to the
equilibrium between
1-12S and steam/CO2, H2S as well as Hg will not react with the particles
inside the first
reactor I. As a result, the pollutant will come out of the first reactor 1
along with CO2 and
can be sequestrated together. Only pure metal particles will enter the second
reactor 2 and
therefore, Hy rich streams may be generated without using low temperature
sulfur and
mercury removal units. Additionally, ceramic composite particles with degraded
activity
or size, which are no longer effective in the processes of the first and
second reactor, may
be used instead of CaO to remove the H2S, for example, to a level below 30
ppm.
Referring generally to Fig. 13, the chemical looping system, as a hydrogen
generator, may be coupled with Fischer-Tropsch (F-T) synthesis system,
directed to
producing chemicals or liquid fuels. Syngas from modem gasifiers usually fail
to provide
enough Hy concentration to meet the requirements of F-T synthesis (H2/C0 =
2:1). The
feedstock for the first reactor 1 is part of the byproduct from the F-T
reactor 100 and
unconverted syngas. In a further embodiment, the feedstock may include part of
the
product from the refining system. The rest of the byproduct and unconverted
syngas is
recycled to the F-T reactor 100 to enhance the conversion, or, it can also be
recycled to the
gasifier to make more syngas. Moreover, steam for the second reactor can be
obtained
from both the gasifier and the F-T reactor 100, as F-T reactions are usually
highly
exothermic. The Hy product of the second reactor I, which may contain some CO
and
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which is generated from chemical looping reactors is recycled back to adjust
the H2/C0
ratio of the F-T feed to about 2:1. This adjustment may occur, in some
embodiments, after
the clean syngas exits the gasifier 30 and is delivered to gas cleanup units
22. In this case,
a stoichiometric amount of byproducts and unconverted syngas are used to
generate H2 for
gas tune up i.e., adjustment of the ratio to about 2:1, while the rest of the
gas stream is
recycled back into the F-T reactor 100. By converting the CI-C4 byproducts and
unconverted syngas into H2, which is the feedstock of F-T reactor 100, system
efficiency
and product selectivity can be greatly improved. The operating pressure for
the chemical
looping system would be similar to the F-T process, for example, around 20 atm
for
medium pressure synthesis.
The embodiments of Fig. 12 and 14 are similar to the one described in figure
13;
with one major difference being that all the byproducts are used to generate
H2. The
excessive amount of H2 can be used for hydrocracking of the wax product from
the F-T
reactor 100. If an excessive amount of H2 remains after hydrocracking, a
combustion
turbine or a fuel cell can be utilized to generate electricity for plant use
or for the energy
market in general.
In the F-T embodiment of Fig. 15, hot gas cleanup is used before the first
reactor 1
and the rest of the pollutants would come out from the first reactor 1 without
attachment to
the particles. Here, part of the CO2 generated from the first reactor 1 is
introduced to a
product cleanup unit or a CO2 separation unit to extract substantially pure
CO2 from the
exhaust gas stream of the first reactor 1. The substantially pure CO2 is then
introduced into
second reactor 2 along with steam to form clean syngas with a H2/C0 ratio of
about 2:1.
The syngas is then used in F-T reactor 100 to produce liquid fuels or
chemicals. The
byproduct stream from the F-T reactor 100 would also be recycled back to first
reactor to
further increase the syngas production rate of the chemical looping system.
Referring to
Fig. 16, the F-T system may be combined with a coal converting system instead
of syngas.
In this embodiment, sorbents may be fed into the system to take out sulfur.
Byproducts of
F-T synthesis may also be fed into the first reactor 1 to make more syngas. In
this solid
fuel conversion embodiment, a gasifier is not needed; consequently, the system
may
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comprise less equipment, thereby lowering costs and capital investment while
improving
system efficiency.
In all the F-T embodiments, part of the steam generated in the F-T reactor may
be
superheated by high temperature streams from the chemical looping system of
the present
invention or gasifiers. The superheated steam may comprise various uses, for
example,
driving a steam turbine for parasitic energy or as a feed stock in reactor 2.
In the embodiment of Fig. 17, an additional use for the present system is
provided.
In this example, metal oxide particles such as Fe203 are processed into a
packed bed or
monolith in a module or cartridge for onboard H2 storage in a vehicle 230.
Here, the
modules are processed in a central facility 210 (including a gasifier 220) to
get reduced to
its metal form using carbonaceous fuel such as syngas. The reduced modules are
then
distributed to fuel stations 200 and installed into a car 230 to replace the
spent modules.
Steam would be obtained from the PEM fuel cell or Hydrogen Internal Combustion
Engine and would be introduced into the model to react with the reduced
particles to
generate H2 to drive the car. The typical temperature for the reaction would
be around
250-700 C, as the reaction is exothermic. The temperature in the module can
either be
maintained by well designed insulations or the heat recovery in other areas of
the system.
The modules would consist of different individual enclosures and each
enclosure can
either be a packed bed of pellets or it can be monolith. In one exemplary
embodiment, the
monolith may comprises small channels with diameter of 0.5-10 mm while the
thickness
of the wall that is made of particles are kept below 10 mm. Figs. 18(a)-(c),
and Figs 18
illustrates some examples of the modules, i.e. reactors with Fe containing
media having:
(a) a packed bed of small pellets; (b) a monolithic bed with straight channels
for steam;
and (c) a monolithic bed with channels for steam and air
Figs 18c and Fig. 18b show that air will flow through some of the channels
while
steam flows through the rest of the channels. By this kind of flow
arrangement, the
channels with air going through would generate heat for the adjacent channels
keeping
them at desirable temperature (250-700 C) for hydrogen production. Figure 19
shows one
possible arrangement using the enclosure design shown in figure 18(c). Here,
different
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enclosures are packed into a module and connected with one another to
consistently
generate H2 for a fuel cell or an internal combustion engine in the car 230.
The air and
steam channels may be strictly separated from one another using the special
monolith
design and connection scheme.
Referring to Fig. 20, the present system may also be utilized in fuel cell
technologies. In this exemplary embodiment of Fig. 20, reduced metal particles
are
directly fed into a solid oxide fuel cell that can process solid fuels
directly. In effect, the
solid oxide fuel cell acts the second reactor 2 in the oxidation reduction
system. Particles
are reduced in the fuel reactor and then introduced to the fuel cell to react
with oxygen or
air under 500-1000 C to produce electricity. The oxidized particle is recycled
back to the
fuel reactor to be reduced again. Because of the applicability of the present
system, it is
contemplated that the present invention may be incorporated in numerous other
industrial
processes.
It is noted that terms like "preferably," "generally", "commonly," and
"typically"
are not utilized herein to limit the scope of the claimed invention or to
imply that certain
features are critical, essential, or even important to the structure or
function of the claimed
invention. Rather, these terms are merely intended to highlight alternative or
additional
features that may or may not be utilized in a particular embodiment of the
present
invention.
For the purposes of describing and defining the present invention it is noted
that the
term "substantially" is utilized herein to represent the inherent degree of
uncertainty that
may be attributed to any quantitative comparison, value, measurement, or other
representation. The term "substantially" is also utilized herein to represent
the degree by
which a quantitative representation may vary from a stated reference without
resulting in a
change in the basic function of the subject matter at issue.
While particular embodiments of the present invention have been illustrated
and
described, it would be obvious to those skilled in the art that various other
changes and
modifications can be made. The scope of the claims should not be limited by
the preferred
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embodiments set forth in the examples, but should be given the broadest
interpretation
consistent with the description as a whole.
