Note: Descriptions are shown in the official language in which they were submitted.
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HYDROGEN GENERATION SYSTEMS
Cross-reference to related applications
[001] This application claims priority to U.S. Patent Application No.
16/821,652, filed on
March 17, 2020, the entire contents of which are incorporated herein by
reference.
Background
[002] Hydrogen generation reactions convert hydrocarbons, such as methane,
into hydrogen
gas. Hydrogen gas can be used, e.g., as fuel for vehicles.
Summary
[003] We describe here systems for energy-efficient, low-emission
production of hydrogen
gas (H2) from hydrocarbons. The systems include a steam methane reactor (SMR)
having a
bayonet flow path in which incoming reactant fluid flowing along the flow path
is heated by
transfer of recovered heat from outgoing fluid flowing along the flow path.
Catalytic foam and
heat transfer foam disposed along the bayonet flow path catalyze a hydrogen
generation reaction
in the SMR and facilitate heat transfer to the incoming reactant fluid.
Product fluid from the SMR
is provided to a water gas shift (WGS) reactor. The fluid flows across one or
more WGS catalysts
and one or more heat transfer materials disposed along a reaction channel in
the WGS reactor.
The WGS catalysts and heat transfer material catalyze a hydrogen generation
reaction in the WGS
and facilitate removal of heat generated by the exothermic WGS hydrogen
generation reaction.
Cooling fluid heated by heat from the WGS hydrogen generation reaction can be
provided as
input into the SMR. The use of heat transfer among fluid streams in the SMR
enables energy
efficient production of hydrogen to be achieved.
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[004] In a general aspect, a system for production of hydrogen includes a
steam methane
reformer (SMR) including an outer tube, wherein a first end of the outer tube
is closed; and an
inner tube disposed in the outer tube, wherein a first end of the inner tube
is open. An SMR flow
channel is defined within the inner tube and an annular space is defined
between the outer tube
and the inner tube. The flow channel is in fluid communication with the
annular space. The SMR
includes a foam disposed in the annular space between the outer tube and the
inner tube. The
system includes a water gas shift (WGS) reactor including a reaction tube,
wherein a WGS
reaction channel is defined within the reaction tube, and wherein the WGS
reaction channel is in
fluid communication with the SMR flow channel; a heat transfer material
disposed in the WGS
reaction channel; and a WGS catalyst disposed in the WGS reaction channel.
[005] Embodiments can include one or any combination of two or more of the
following
features.
[006] An outlet of the SMR flow channel is in fluid communication with an
inlet of the
WGS reaction channel.
[007] The WGS reactor includes a housing, the reaction tube of the WGS
reactor being
disposed in the housing, and wherein a cooling fluid channel is defined
between the housing and
the reaction tube of the WGS reactor. An outlet of the cooling fluid channel
is in fluid
communication with an inlet of the annular space of the SMR. An inlet of the
WGS reaction
channel and an outlet of the cooling fluid channel are disposed at a first end
of the WGS reactor.
The WGS reactor includes a flow controller configured to control a flow rate
of cooling fluid
through the cooling fluid channel.
[008] The foam of the SMR includes an SMR catalyst. The SMR catalyst is
disposed on the
foam of the SMR. The SMR catalyst is configured to catalyze an SMR hydrogen
generation
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reaction in which hydrogen and carbon monoxide are produced. The SMR includes
an outer heat
exchange foam disposed in the annular space between the outer tube and the
inner tube, wherein a
distance between the outer heat exchange foam and a second end of the outer
tube is less than a
distance between the foam assembly and the second end of the outer tube.
[009] The SMR includes an inner heat exchange foam disposed in the SMR flow
channel.
[010] A bayonet flow path through the SMR is defined from an inlet at a
second end of the
outer tube, along the annular space between the outer tube and the inner tube
toward the first end
of the outer tube, along the SMR flow channel, and to an outlet at a second
end of the inner tube.
[011] The WGS catalyst includes a foam including a WGS catalyst material.
The WGS
catalyst material includes a foam substrate, wherein the WGS catalyst material
is disposed on the
foam substrate.
[012] The WGS catalyst includes: a first WGS catalyst disposed in the WGS
reaction
channel and configured to catalyze a hydrogen generation reaction in a first
temperature range;
and a second WGS catalyst disposed in the WGS reaction channel and configured
to catalyze the
hydrogen generation reaction in a second temperature range lower than the
first temperature
range. The heat transfer material is disposed in the WGS reaction channel
between the first WGS
catalyst and the second WGS catalyst.
[013] The heat transfer material disposed in the WGS reaction channel
includes a foam.
[014] The system includes a furnace, wherein a portion of the SMR is
disposed in the
furnace. The first end of the outer tube of the SMR is disposed in the
furnace. The system
includes an external heat transfer material disposed on an outer surface of
the outer tube of the
SMR.
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[015] In a general aspect, combinable with the previous aspect, a method
for producing
hydrogen includes flowing a first gas along a bayonet flow path of a steam
methane reformer
(SMR) to produce a first product, including flowing the first gas through a
foam disposed along
the bayonet flow path; providing the first product produced in the SMR to an
input of a water gas
shift (WGS) reaction channel defined within a reaction tube of a WGS reactor;
and flowing a
second gas including the first product through the WGS reaction channel to
produce a second
product. Flowing the second gas includes flowing the second gas across a heat
transfer material
disposed in the WGS reaction channel to reduce the temperature of the flowing
second gas; and
flowing the second gas across a WGS catalyst disposed in the reaction channel.
[016] Embodiments can include one or any combination of two or more of the
following
features.
[017] Flowing the first gas along the bayonet flow path of the SMR includes
flowing the first
gas from an annular space into an SMR flow channel, wherein the annular space
is defined
between an outer tube and an inner tube disposed within the outer tube and the
SMR flow channel
is defined within the inner tube. Flowing the first gas along the bayonet flow
path of the SMR
includes flowing the first gas from an inlet at a second end of the outer
tube, along the annular
space toward a first end of the outer tube, along the SMR flow channel defined
within the inner
tube, and to an outlet at a second end of the inner tube. The method includes
heating the first gas
flowing along the annular space with heat from the gas flowing along the flow
channel defined
within the inner tube.
[018] Flowing the first gas through a foam disposed along the bayonet flow
path includes
flowing the gas through a catalytic foam.
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[019] The method includes flowing a cooling fluid through a cooling fluid
flow pathway
defined between a housing of the WGS reactor and the reaction tube of the WGS
reactor.
Contacting the flowing second gas to the heat transfer material disposed in
the WGS reaction
channel includes transferring heat from the flowing second gas to the cooling
fluid. The method
includes heating the cooling fluid to a temperature of between 100 C and 300
C. The method
includes providing heated cooling fluid from the cooling fluid flow pathway to
an input of the
bayonet flow path of the SMR. The method includes providing heated cooling
fluid from the
cooling fluid flow pathway to an input of the WGS reaction channel. The method
includes
adjusting a flow rate of the cooling fluid through the cooling fluid flow
pathway based on a rate at
which the first product is provided to the input of the WGS reaction channel.
[020] The method includes providing the first product to the input of the
WGS reaction
channel at a temperature equal to or greater than a temperature at which the
WGS catalyst
structure catalyzes a hydrogen generation reaction. The method includes
providing the first
product to the input of the WGS reaction channel at a temperature of between
200 C and 450 C.
[021] Flowing the second gas across the WGS catalyst includes: flowing the
second gas
across a first WGS catalyst disposed in the WGS reaction channel, wherein the
first WGS catalyst
is configured to catalyze a hydrogen generation reaction in a first
temperature range; and flowing
the second gas across a second WGS catalyst disposed in the reaction channel,
wherein the second
WGS catalyst is configured to catalyze the hydrogen generation reaction in a
second temperature
range lower than the first temperature range. The method includes flowing the
second gas across
the heat transfer material after flowing the second gas across the first WGS
catalyst.
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[022] Flowing the second gas to the heat transfer material includes
reducing the temperature
of the flowing second gas to a temperature at which the WGS catalyst is
capable of catalyzing a
hydrogen generation reaction.
[023] The method includes flowing the first gas along the bayonet flow path
of the SMR to
produce carbon monoxide and hydrogen. Providing the first product to the input
of the WGS
reaction channel includes providing carbon monoxide to the input of the WGS
reaction channel.
[024] The method includes flowing the second gas along the WGS reaction
channel to
produce carbon dioxide and hydrogen.
[025] In a general aspect, combinable with any of the previous aspects, a
steam methane
reformer (SMR) system includes an outer tube, wherein a first end of the outer
tube is closed; an
inner tube disposed in the outer tube, wherein a first end of the inner tube
is open. A flow channel
is defined within the inner tube and an annular space is defined between the
outer tube and the
inner tube, the flow channel being in fluid communication with the annular
space. The SMR
system includes a catalytic foam disposed in the annular space between the
outer tube and the
inner tube, the catalytic foam including a catalyst.
[026] Embodiments can include one or any combination of two or more of the
following
features.
[027] The catalytic foam includes a foam substrate, wherein the catalyst is
disposed on the
foam substrate.
[028] The SMR system includes an outer heat exchange foam disposed in the
annular space
between the outer tube and the inner tube. A distance between the outer heat
exchange foam and a
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second end of the outer tube is less than a distance between the catalytic
foam and the second end
of the outer tube. The e outer heat exchange foam has an annular shape.
[029] The catalytic foam has an annular shape.
[030] The SMR system includes an inner heat exchange foam disposed in the
flow channel.
[031] The catalytic foam contacts the inner tube.
[032] A thickness of the catalytic foam is equal to a width of the annular
space.
[033] The catalytic foam has a porosity of between 10 pores per inch (ppi)
and 30 ppi.
[034] A length of the catalytic foam along the inner tube is between 10
inches and 5 feet.
[035] A length of the catalytic foam in an externally heated section of the
outer tube is
between 10% and 30% of a length of the outer tube.
[036] The catalytic foam includes a metal foam. The catalytic foam includes
nickel.
[037] The catalytic foam includes silicon carbide.
[038] A bayonet flow path through the SMR system is defined from an inlet
at a second end
of the outer tube, along the annular space between the outer tube and the
inner tube toward the
first end of the outer tube, along the flow channel, and to an outlet at a
second end of the inner
tube.
[039] A ratio between a cross-sectional area of the flow channel and a
cross-sectional area of
the annular space is between 1 and 5.
[040] The inner tube is coaxial with the outer tube.
[041] A width of the annular space between the outer tube and the inner
tube is between 0.2
inches and 4 inches.
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[042] A length of the outer tube is between 8 feet and 30 feet.
[043] The SMR system includes an elongated baffle disposed in the flow
channel.
[044] The SMR system includes a heat transfer material disposed on an outer
surface of the
first end of the outer tube. The heat transfer material includes a fin
disposed on the outer surface
of the first end of the outer tube. The heat transfer material includes a
baffle disposed on the outer
surface of the first end of the outer tube. The heat transfer material
includes a foam disposed on
the outer surface of the first end of the outer tube.
[045] In a general aspect, combinable with any of the previous aspects, a
method for
producing hydrogen in a steam methane reformer (SMR) system includes flowing a
gas along a
bayonet flow path of the SMR system. The bayonet flow path is defined by an
annular space
defined between an outer tube and an inner tube disposed in the outer tube,
wherein a first end of
the outer tube is closed and a first end of the inner tube is open; a flow
channel defined within the
inner tube, wherein the flow channel is in fluid communication with the
annular space. Flowing
the gas along the bayonet flow path includes flowing the gas through a
catalytic foam disposed in
the annular space between the outer tube and the inner tube.
[046] Embodiments can include one or any combination of two or more of the
following
features.
[047] Flowing the gas along the bayonet flow path includes flowing the gas
through an outer
heat exchange foam disposed in the annular space between the outer tube and
the inner tube.
[048] The method includes flowing the gas through the outer heat exchange
foam before
flowing the gas through the catalytic foam.
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[049] Flowing the gas along the bayonet flow path includes flowing the gas
through an inner
heat exchange foam disposed in the flow channel.
[050] Flowing the gas along the bayonet flow path includes flowing the gas
from the annular
space into the flow channel. The method includes flowing the gas from the
annular space at the
first end of the outer tube into the flow channel at the first end of the
inner tube.
[051] The method includes heating the gas flowing in the annular space with
heat from the
gas flowing in the flow channel defined within the inner tube.
[052] The method includes heating the gas in the annular space at the first
end of the outer
tube.
[053] The method includes flowing the gas along at least a portion of the
bayonet flow path
in turbulent flow.
[054] The method includes producing hydrogen from the gas flowing along the
bayonet flow
path.
[055] In an aspect, combinable with any of the previous aspects, a water
gas shift (WGS)
reactor system includes a housing; a reaction tube disposed in the housing,
wherein a reaction
channel is defined within the reaction tube and a cooling fluid channel is
defined between the
housing and the reaction tube; a catalyst disposed in the reaction channel,
the catalyst configured
to catalyze a hydrogen generation reaction; and a heat transfer material
disposed in the reaction
channel.
[056] Embodiments can include one or any combination of two or more of the
following
features.
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[057] The catalyst includes a first catalyst disposed in the reaction
channel and configured to
catalyze the hydrogen generation reaction in a first temperature range; and a
second catalyst
disposed in the reaction channel and configured to catalyze the hydrogen
generation reaction in a
second temperature range lower than the first temperature range. The heat
transfer material is
disposed in the reaction channel between the first catalyst and the second
catalyst. The first
catalyst is configured to catalyze the hydrogen generation reaction at a
temperature of between
200 C and 450 C. The second catalyst is configured to catalyze the hydrogen
generation reaction
at a temperature of between 180 C and 350 C.
[058] A distance between the heat transfer material and an inlet of the
reaction channel is
less than a distance between the catalyst structure and the inlet of the
reaction channel. The
catalyst includes a catalyst configured to catalyze the hydrogen generation
reaction at a
temperature of between 200 C and 450 C.
[059] The catalyst includes a foam including a catalyst material. The
catalytic foam includes
a foam substrate, wherein the catalyst material is disposed on the foam
substrate. The foam has a
porosity of between 5 pores per inch (ppi) and 30 ppi.
[060] The catalyst includes catalyst pellets.
[061] The heat transfer material includes a foam. The foam has a porosity
of between 5 ppi
and 30 ppi.
[062] The heat transfer material includes a fin.
[063] The WGS reactor system includes a cooling channel heat transfer
material disposed in
the cooling fluid channel. The cooling channel heat transfer material includes
a foam.
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[064] The housing includes a cylindrical housing, and wherein the reaction
tube is coaxial
with the cylindrical housing.
[065] The WGS reactor system includes an inner tube disposed in the
reaction tube, wherein
the reaction channel is defined by an annular space between the reaction tube
and the inner tube,
and wherein an inner cooling fluid channel is defined within the inner tube.
[066] The WGS reactor system includes multiple reaction tubes disposed in
the housing.
[067] An inlet of the reaction channel and an outlet of the cooling fluid
channel are disposed
at a first end of the WGS reactor.
[068] An inlet of the reaction channel is in fluid communication with an
outlet of the cooling
fluid channel.
[069] An outlet of the cooling fluid channel is configured to be in fluid
communication with
an inlet of a steam methane reformer (SMR).
[070] The WGS reactor system includes a flow controller configured to
control a flow rate of
cooling fluid through the cooling fluid channel.
[071] In a general aspect, a method for producing hydrogen in a water gas
shift (WGS)
reactor includes flowing a cooling fluid through a cooling fluid channel
defined between a
housing of a WGS reactor and a reaction tube disposed in the housing; and
flowing a gas
including carbon monoxide and steam through a reaction channel defined within
the reaction tube.
Flowing the gas through the reaction channel includes flowing the gas across a
heat transfer
material disposed in the reaction channel to transfer heat from the flowing
gas to the cooling fluid
in the cooling fluid channel; and flowing the gas across a catalyst disposed
in the reaction
channel, the catalyst configured to catalyze a hydrogen generation reaction.
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[072] Embodiments can include one or any combination of two or more of the
following
features.
[073] Flowing the gas across the heat transfer material includes reducing
the temperature of
the flowing gas to a temperature at which the catalyst structure catalyzes the
hydrogen generation
reaction. The method includes reducing the temperature of the flowing gas to
between 200 C and
450 C.
[074] Flowing the gas across the catalyst includes flowing the gas across a
first catalyst
disposed in the reaction channel, wherein the first catalyst is configured to
catalyze the hydrogen
generation reaction in a first temperature range; and flowing the gas across a
second catalyst
disposed in the reaction channel, wherein the second catalyst is configured to
catalyze the
hydrogen generation reaction in a second temperature range lower than the
first temperature
range. The method includes receiving the gas into the reaction channel at a
temperature within the
first temperature range. The method includes receiving the gas into the
reaction channel at a
temperature of between 200 C and 450 C. The method includes flowing the gas
across the heat
transfer material after flowing the gas across the first catalyst. Flowing the
gas across the heat
transfer material includes reducing the temperature of the flowing gas to
within the second
temperature range. The method includes reducing the temperature of the flowing
gas to between
180 C and 350 C.
[075] The method includes flowing cooling fluid through an inner cooling
fluid channel
defined within an inner tube disposed in the reaction tube.
[076] Flowing the gas through the reaction channel includes flowing the gas
from a first end
of the WGS reactor to a second end of the WGS reactor; and wherein flowing the
cooling fluid
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through the cooling fluid channel includes flowing the cooling fluid from the
second end of the
WGS reactor to the first end of the WGS reactor.
[077] The method includes adjusting a flow rate of the cooling fluid
through the cooling
fluid channel based on a flow rate of the gas through the reaction channel.
[078] The method includes outputting the cooling fluid from the cooling
fluid channel at a
temperature of between 100 C and 300 C.
[079] The method includes providing steam from the cooling fluid channel to
an input of the
reaction channel.
[080] The method includes providing steam from the cooling fluid channel to
an input of a
steam methane reformer.
[081] The approaches described here can have one or more of the following
advantages. The
use of recuperated heat to heat and cool fluid streams to target temperatures
enables the hydrogen
generation process to be an energy efficient, low-emission process. The
systems can be modular,
e.g., enabling a target throughput to be achieved by change in system
configuration or operation.
The systems can be scalable for large-scale, energy efficient hydrogen
generation.
[082] The details of one or more implementations are set forth in the
accompanying
drawings and the description below. Other features and advantages will be
apparent from the
description and drawings, and from the claims.
Brief Description of Drawings
[083] Fig. 1 is a diagram of a hydrogen generation system.
[084] Fig. 2A is a cross sectional view of a steam methane reformer (SMR).
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[085] Fig. 2B is a cross-sectional view of the SMR of Fig. 2A along the
line A-A'.
[086] Fig. 2C is a cross-sectional view of the SMR of Fig. 2A along the
line B-B'.
[087] Fig. 3 is a diagram of a water gas shift (WGS) reactor.
[088] Fig. 4 is a diagram of a WGS reactor.
[089] Fig. 5 is a diagram of a WGS reactor.
[090] Fig. 6 is a diagram of a hydrogen generation system.
[091] Fig. 7 is a process flow chart.
[092] Fig. 8 is a plot of the temperature differential between the inner
and outer tubes of an
SMR.
[093] Figs. 9A and 9B are simulations of heat transfer in an SMR with and
without a foam,
respectively.
Detailed Description
[094] We describe here systems for energy-efficient, low-emission
production of hydrogen
gas (H2) from hydrocarbons. The systems include a steam methane reactor (SMR)
having a
bayonet flow path in which incoming reactant fluid flowing along the flow path
is heated by
transfer of recovered heat from outgoing fluid flowing along the flow path.
Catalytic foam and
heat transfer foam disposed along the bayonet flow path catalyze a hydrogen
generation reaction
in the SMR and facilitate heat transfer to the incoming reactant fluid.
Product fluid from the SMR
is provided to a water gas shift (WGS) reactor. The fluid flows across one or
more WGS catalysts
and one or more heat transfer materials disposed along a reaction channel in
the WGS reactor.
The WGS catalysts and heat transfer material catalyze a hydrogen generation
reaction in the WGS
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and facilitate removal of heat generated by the exothermic WGS hydrogen
generation reaction.
Cooling fluid heated by heat from the WGS hydrogen generation reaction can be
provided as
input into the SMR. The use of heat transfer among fluid streams in the SMR
enables energy
efficient production of hydrogen to be achieved.
[095] The hydrogen generation systems described here are modular and have a
small
footprint. The systems can be upgraded or turned down without significant
downtime. Elements
of the systems, such as tubes, manifolds, flanges, and catalysts, can be taken
apart or replaced
easily, enabling maintenance or operational adjustments with low downtime.
[096] Referring to Fig. 1, a schematic diagram of a hydrogen generation
system 100, shown
in an operational configuration, includes a steam methane reactor (SMR) 200
and a water gas shift
(WGS) reactor 300 that together generate hydrogen gas (H2) from hydrocarbons,
such as natural
gas, biogas, methane, methanol, or other suitable hydrocarbons. Fluid 102,
including
hydrocarbons and water vapor (steam) is input into the SMR and reacted in the
presence of a
catalytic foam. Recuperated heat from fluid flowing through the SMR 200 and
externally applied
heat raise the temperature of the reactants flowing through the SMR 200 to a
temperature at which
the SMR hydrogen generation reaction occurs. Heating of the reactants using
residual heat from
fluid flowing through the SMR reduces the heating load on an external heat
source, thereby
enabling energy efficient operation. Product gas 104 generated in the SMR
includes hydrogen gas
and carbon monoxide.
[097] At least a portion of the product gas 104 (e.g., hydrogen and carbon
monoxide), along
with steam, is provided as fluid input into the WGS reactor 300. For energy
efficient operation,
the product gas 104 is output from the SMR at a temperature appropriate for
input into the WGS
reactor 300, thereby enabling active heating or cooling of the fluid input
into the WGS reactor 300
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to be avoided. The fluid input into the WGS reactor 300 flows along a reaction
channel of the
WGS reactor 300 and reacts in the presence of a WGS catalyst, such as a
catalytic foam, to
produce hydrogen and carbon dioxide. A heat exchange material, such as a foam,
is disposed in
the reaction channel and transfers excess heat generated by the exothermic WGS
hydrogen
generation reaction to a cooling fluid 108 flowing through the WGS reactor
300. Cooling of the
fluid in the reaction channel by heat transfer facilitated by the heat
exchange material allows
active cooling in the WGS reactor 300 to be avoided, enabling energy efficient
operation. Product
gas 110 generated in the WGS includes hydrogen gas and carbon dioxide. Heated
cooling fluid
106, in the form of steam, can be provided as part of the fluid 102 input into
the SMR 200. In
some examples, additional steam is provided from an external water source,
e.g., for system
startup.
[098] Referring to Figs. 2A-2C, the SMR 200 includes two concentric tubes,
an outer tube
202 and an inner tube 204 disposed coaxially in the outer tube 202. A first
end of the outer tube
202 at a first end 206 of the SMR 200 is closed and a first end of the inner
tube 204 is open. An
annular space 210 is defined between the outer tube 202 and the inner tube
204. A flow channel
212 is defined within the inner tube 204 and is in fluid communication with
the annular space
210. An elongated baffle 213 is disposed along at least a portion of the
length of the inner tube
204.
[099] Fluid (e.g., gas) flowing through the SMR 200 follows a bayonet flow
path (indicated
by arrows in Fig. 2A) through the SMR 200 from an inlet 214 into the annular
space 210 at a
second end 216 of the SMR 200, along the annular space 210 toward the first
end of the outer
tube 202 at the first end 206 of the SMR, into the flow channel 212, along the
flow channel 212
toward a second end of the inner tube 204 at the second end 216 of the SMR,
and to an outlet 220
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at the second end of the inner tube 204. Reactants (e.g., hydrocarbons and
water) are input into the
bayonet flow path at the inlet 214. A hydrogen generation reaction occurs
toward the first end 206
of the outer tube in the presence of an SMR catalyst, generating products
(e.g., hydrogen gas and
carbon monoxide) that are output from the SMR 200 via the outlet 220. An
example hydrogen
generation reaction that occurs in the SMR 200 is represented as follows:
CH4 + H20 ¨> 3H2 + CO.
[0100] The hydrogen generation reaction is an endothermic reaction that
occurs above a
reaction temperature, such as between 600 C and 1000 C. An external heat
source 222 heats the
fluid flowing along the annular space 210 at the first end 206 of the SMR 200
to at least the
reaction temperature. The external heat source 222 can be driven by combustion
(e.g., a gas-
powered furnace), solar energy, or another appropriate energy source.
[0101] Fluid in the annular space 210 at the first end 206 of the SMR 200
is heated by the
external heat source 222. The heated fluid flows from the annular space 210 at
the first end 206 of
the SMR 200 into the flow channel 212, entering the flow channel at high
temperature. The
bayonet flow path of the SMR, in which the outer and inner tubes 202, 204 (and
hence the annular
space 210 and flow channel 212) are concentric, provides a configuration in
which heat from the
high-temperature fluid flowing along the flow channel 212 can be transferred
back to the lower-
temperature fluid flowing along the annular space 210. The inner tube 204 is
designed to facilitate
this heat transfer, e.g., the inner tube 204 can be formed of a material with
high thermal
conductivity, such as a metal or silicon carbide, and can have thin walls. The
use of recuperated
heat to raise the temperature of the fluid flowing along the annular space 210
lessens the load on
the external heat source 222, improving the energy efficiency of the hydrogen
generation reaction.
In addition, when the external heat source 222 is a combustion furnace, a
reduced load on the
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furnace reduces hydrocarbon consumption of the external heat source 222,
thereby reducing
emissions associated with the hydrogen generation reaction.
[0102] Referring specifically to Figs. 2A and 2B, a catalytic foam 230 is
disposed in the
annular space 210 between the outer tube 202 and the inner tube 204. The
catalytic foam 230
includes an SMR catalyst that catalyzes the hydrogen generation reaction
(e.g., the generation of
hydrogen and carbon monoxide from hydrocarbons and water). The hydrogen
generation reaction
occurs primarily in the portions of the bayonet flow path in which the
catalytic foam 230 is
disposed, and that are at a temperature at or above the reaction temperature.
For instance, the
hydrogen generation reaction occurs in portions of the bayonet flow path that
are heated by the
external heat source 222, such as in a heated portion 221 of the annular space
210 toward the first
end 206 of the SMR 200 and in an end space 223 at the first end 206 of the SMR
200. The
hydrogen generation reaction can also occur in regions outside the heated
portion 221, e.g.,
regions that are heated to or above the reaction temperature by heat transfer
from fluid flowing
along the flow channel 212 (discussed further below).
[0103] In some examples, the SMR catalyst is coated onto a foam substrate
to form the
catalytic foam 230. In some examples, the SMR catalyst is integrated or
impregnated into a foam
substrate to form the catalytic foam 230. The catalytic foam 230 is a porous
structure through
which one or more fluid flow paths are defined from an upstream side 232 to a
downstream side
234 of the catalytic foam 230. As fluid flows along the bayonet flow path
through the SMR 200,
the fluid flows through the fluid flow paths of the catalytic foam 230 and the
catalyst in the
catalytic foam 230 catalyzes the hydrogen generation reaction in the flowing
fluid. The porosity
of the catalytic foam 230 provides a high surface area for contact between the
catalytic foam 230
and the flowing fluid, which facilitates efficient catalysis of the hydrogen
generation reaction.
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[0104] The catalytic foam 230 includes a thermally conductive material such
that the catalytic
foam 230 also facilitates heat transfer to the fluid flowing through the
catalytic foam 230 from the
external heat source 222, the fluid flowing along the flow channel 212 in the
inner tube 202, or
both. Physical contact between the catalytic foam 230 and the outer tube 202
enables transfer of
heat from the external heat source 222 to the fluid flowing through the
catalytic foam. Physical
contact between the catalytic foam 230 and the inner tube 204 enables transfer
of heat from the
fluid flowing along the flow channel 212 to the fluid flowing through the
catalytic foam. The high
surface area of the catalytic foam 230 facilitates heat transfer. The porosity
of the catalytic foam
230 also can lead to turbulent fluid flow in at least a portion of the annular
space 210, further
facilitating heat transfer to the fluid flowing along the annular space 210
and enhancing the
energy efficiency of the hydrogen generation process.
[0105] The catalytic foam 230 has an annular shape. As shown in Figs. 2A
and 2B, a
thickness t, of the annulus of the catalytic foam 230 (referred to simply as
the thickness of the
catalytic foam 230) is equal to the radial distance between the outer wall of
the inner tube 204 and
the inner wall of the outer tube 202 (referred to as the width of the annular
space 210) such that
the catalytic foam 230 is in physical contact with both the outer tube 202 and
the inner tube 204.
Contact between the catalytic foam 230 and the outer and inner tubes 202, 204
enables heat
transfer from the external heat source 222 and the fluid flowing along the
flow channel 212 in the
inner tube 202 to the fluid flowing through the catalytic foam 230. In some
examples, the
thickness t, of the catalytic foam 230 is less than the width of the annular
space 210 and the
catalytic foam 230 is in physical contact with only one of the tubes, such as
with only the outer
tube 204 or only the inner tube 204.
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[0106] The porosity of the catalytic foam 230 (e.g., pores per inch) and
length of the catalytic
foam 230 (referring to the length of the catalytic foam along the axis of the
outer tube 202 from
the upstream side 232 to the downstream side 234 of the catalytic foam 230)
affect the surface
area of the catalytic foam 230, thus affecting the efficiency of catalysis and
heat transfer.
Increased porosity and length both increase the opportunity for contact
between the flowing fluid
and the catalytic foam 230, thereby enhancing the efficiency of both catalysis
and heat transfer.
The length of the catalytic foam 230 also affect the drop in fluid pressure
that occurs across the
catalytic foam 230 as fluid flows through the catalytic foam 230. Increased
porosity and length
both cause increased pressure drop across the catalytic foam 230, which can
slow fluid flow along
the bayonet flow path, reducing throughput of the SMR 200. The porosity and
length of the
catalytic foam 230 can be selected to achieve efficient catalysis and heat
transfer with low
pressure drop across the catalytic foam 230. For instance, the catalytic foam
230 can have a
porosity of between 10 pores per inch (ppi) and 30 ppi. In some examples, the
catalytic foam 230
is entirely within the heated portion 221 of the outer tube 202 (as in the
example of Fig. 2A), e.g.,
the length /, of the catalytic foam 230 is between 10% and 30% of the length
of the heated portion
221 of the outer tube 202, such as between 10 inches and 5 feet in length. In
some examples, the
catalytic foam 230 extends beyond the heated portion 221 of the outer tube 202
and can extend up
to the entire length of the outer tube. In some examples, the porosity and
length of the catalytic
foam 230 can be selected such that a fluid pressure drop of less than 1 pound
per square inch (psi)
occurs across the catalytic foam 230.
[0107] The catalytic foam 230 includes a material (e.g., the foam
substrate) having a thermal
conductivity sufficient to facilitate heat transfer to fluid flowing through
the catalytic foam 230,
e.g., heat transfer from the fluid flowing along the flow channel 212, heat
transfer from the
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external heat source 222, or both. The material of the catalytic foam 230 is
non-reactive to the
fluid (e.g., the reactants and products of the hydrogen generation reaction)
flowing along the
bayonet flow path of the SMR 200 in the temperature range at which the SMR 200
is operated.
The material of the catalytic foam 230 can be thermally compatible with, e.g.,
have a similar
thermal expansion coefficient as, the material of the outer tube 202, the
inner tube 204, or both,
e.g., to avoid delamination of the catalytic foam 230 from the tubes 202, 204.
For instance, the
foam can be a metal foam, such as a nickel or stainless steel foam, or a
silicon carbide foam; or
another suitable material.
[0108] Referring to Fig. 2A, an outer heat exchange foam 250 formed of a
thermally
conductive material is disposed in the annular space 210 between the outer
tube 202 and the inner
tube 204. A distance between the outer heat exchange foam 250 and the inlet
214 at the second
end 216 of the outer tube 202 is less than a distance between the catalytic
foam 230 and the inlet
214, such that fluid flowing along the annular space 210 flows through the
outer heat exchange
foam 250 prior to flowing through the catalytic foam 230. The outer heat
exchange foam 250 is in
physical contact with the inner tube 204 and facilitates heat transfer from
the fluid flowing along
the flow channel 212 to the fluid flowing through the outer heat exchange foam
250.
[0109] Referring also to Fig. 2C, an inner heat exchange foam 252 formed of
a thermally
conductive material is disposed in the flow channel 212 defined within the
inner tube 204. The
inner heat exchange foam 252 is in physical contact with the inner tube 204
and facilitates heat
transfer from fluid flowing through the inner heat exchange foam 252 to the
fluid flowing along
the annular space 210. The porosity of the outer and inner heat exchange foams
250, 252 provide
a high surface area for contact between the foams 250, 252 and the fluid
flowing through the
respective foam, which facilitates efficient heat transfer. The porosity of
the outer and inner heat
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exchange foams 250, 252 also can lead to turbulent fluid flow in at least a
portion of the annular
space 210 or the flow channel 212, respectively, further facilitating heat
transfer. In some
examples, a catalytic foam can be disposed in the flow channel 212, e.g., in
addition to or instead
of the inner heat exchange foam 252.
[0110] The heat transfer enabled by the outer and inner heat exchange foams
250, 252 enables
the fluid in the annular space 210 to be preheated before the fluid reaches
the catalytic foam 230,
using excess heat recovered from the higher temperature fluid flowing along
the flow channel
212. The use of recuperated heat to preheat the fluid flowing along the
annular space 210 can
reduce the amount of heat provided by the external heat source 222 to heat the
fluid flowing along
the annular space 210 to the reaction temperature, thereby enhancing the
efficiency of the SMR
200.
[0111] The outer heat exchange foam 250 has an annular shape. A thickness
of the annulus of
the outer heat exchange foam 250 (referred to as the thickness of the outer
heat exchange foam
250) is equal to the width of the annular space 210 such that the outer heat
exchange foam 250 is
in physical contact with both the outer tube 202 and the inner tube 204. In
some examples, the
thickness of the outer heat exchange foam 250 is less than the width of the
annular space 210 and
the outer heat exchange foam 250 is in physical contact with only one of the
tubes, such as with
only the inner tube 204.
[0112] The inner heat exchange foam 252 also has an annular shape. A
thickness t, of the
annulus of the inner heat exchange foam 252 is equal to the radial distance
between the inner tube
204 and the elongated baffle 213 such that the inner heat exchange foam 252 is
in physical contact
with the inner tube 204. In some examples, the thickness t, of the inner heat
exchange foam 252 is
less than the radial distance and the inner heat exchange foam 252 is in
physical contact with the
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inner tube 204 but not with the elongated baffle 213. In some examples, the
elongated baffle 213
is not present, and the inner heat exchange foam 252 is annular or
cylindrical, with a thickness
that is equal to or less than the radius of the flow channel 212.
[0113] The porosity and length of each of the outer heat exchange foam 250
and the inner
heat exchange foam 252 can be selected to achieve efficient heat transfer with
low pressure drop
across the respective heat exchange foam 250, 252. For instance, each of the
heat exchange foams
250, 252 can have a porosity of between 10 pores per inch (ppi) and 30 ppi.
The length of the
outer heat exchange foam 250 can be as small as, e.g., 4 inches, and as long
as the distance
between the inlet 212 and the upstream side 232 of the catalytic foam 230. The
length of the inner
heat exchange foam 252 can be as small as, e.g., 4 inches, and as long as the
distance between the
first end 208 of the inner tube 204 and the outlet 220 at the second end 218
of the inner tube 204.
In some examples, the porosity and length of the outer and inner heat exchange
foams 250, 252
can be selected such that a pressure drop of less than 1 pound per square inch
(psi) occurs across
the each of the outer and inner heat exchange foams 250, 252. In some
examples, the outer heat
exchange foam 250, the inner heat exchange foam 252, or both are not present.
[0114] The outer and inner heat exchange foams 250, 252 are formed of a
material having a
thermal conductivity sufficient to facilitate heat transfer to the fluid
flowing along the annular
space 210. The material of the heat exchange foams 250, 252 is non-reactive to
the fluid (e.g., the
reactants and products of the hydrogen generation reaction) flowing along the
bayonet flow path
of the SMR 200 in the temperature range at which the SMR 200 is to be
operated. The material of
the outer and inner heat exchange foams 250, 252 can be thermally compatible
with, e.g., have a
similar thermal expansion coefficient as the inner tube 204, e.g., to avoid
delamination. For
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instance, the heat exchange foams 250, 252 can be metal foams, such as nickel
or stainless steel
foams; or silicon carbide foams; or another suitable material.
[0115] The presence of the catalytic foam 230 and the outer and inner heat
exchange foams
250, 252 along the bayonet flow path enables both high throughput through the
SMR 200 and
energy efficient operation of the SMR 200. For instance, heating the fluid
flowing along the
annular space 210 with recuperated heat from the higher temperature fluid
flowing along the flow
channel 212 enables the reaction temperature to be reached with less input of
heat from the
external heat source 222, providing for energy efficient SMR operation. In
addition, by heating
the fluid flowing along the annular space 210 with recuperated heat, the
annular space 210 can be
made relatively wide, such as between 0.2 inches and 4 inches, which can
accommodate relatively
high volume gas flow.
[0116] Referring to Fig. 2A, a heat transfer material 258 is disposed on an
outer surface of the
first end 206 of the outer tube 202 to facilitate heat transfer from the
external heat source 222 to
the fluid flowing along the bayonet flow path of the SMR 200. In the example
of Fig. 2A, the heat
transfer material 258 is a fin; in some examples, the heat transfer material
258 can be a baffle, a
foam, or another structure suitable for facilitating heat transfer. The heat
transfer material 258
enhances the efficiency of heat transfer from the external heat source 222 to
the fluid flowing
along the annular space 210, contributing to the energy efficient operation of
the SMR by
increasing the amount of heat produced by the external heat source 222 that is
used to heat the
fluid in the bayonet flow path.
[0117] The locations, lengths, and properties (e.g., porosity, thermal
conductivity) of the
catalytic foam 230 and the inner and outer heat exchange foams 250, 252 can be
selected to
achieve a desired temperature at one or more points along the bayonet flow
path. For instance, the
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foam locations, lengths, and properties can be selected to achieve a target
temperature at the
catalytic foam 230 to facilitate a high efficiency hydrogen generation
reaction. In some examples,
fluid output from the SMR is provided to a WGS reactor to act as a reactant in
a further hydrogen
generation reaction, and the foam locations and lengths can be selected to
achieve a target
temperature of fluid output from the outlet 220 of the flow channel 212, such
as a target
temperature for input into the WGS reactor. By outputting fluid from the SMR
200 at the target
temperature for input into the WGS reactor, the use of external heat sources
for preheating WGS
reactor inputs can be reduced or eliminated, enhancing the overall efficiency
of the system.
[0118] The catalytic foam 230 and outer and inner heat transfer foams 250,
252 can be
removed from the SMR 200 and replaced, e.g., with foams of different
characteristics (e.g.,
different porosity, length, thermal conductivity, or other characteristics).
For instance, exchanging
one or more of the foams can help a desired performance to be achieved, such
as a target
throughput or a target temperature of the output fluid from the SMR 200.
[0119] In some examples, the length of the outer tube 202 is between 8 feet
and 30 feet, e.g.,
for a modular hydrogen generation system. In some examples, the outer tube 202
can be longer,
e.g., for an industrial plant scale hydrogen generation system. The width of
the annular space can
be between 0.2 inches and 4 inches. The ratio between a cross-sectional area
of the flow channel
212 and a cross-sectional area of the annular space 210 (see Fig. 2B) is
greater than one, e.g.,
between 1 and 5, to accommodate the increase in moles of gas resulting from
the hydrogen
generation reaction.
[0120] In some examples, the catalytic foam 230, outer heat transfer foam
250, inner heat
transfer foam 252, or a combination of any two or more of them is a non-
uniform structure, e.g.,
having a non-uniform porosity or a multimaterial composition. For instance, in
locations at which
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fluid pressure drop across a foam is less important, the foam can be
configured with smaller pores
to enhance heat transfer. The foam can be a multimaterial foam, e.g., a foam
having an outer shell
of nickel for chemical compatibility with an inner shell of aluminum or copper
for heat transfer
efficiency. In some examples, the outer heat transfer foam 250, the inner heat
transfer foam 252,
or both can be replaced by a solid, cylindrical tube.
[0121] Heat transfer in the SMR (e.g., heat transfer from fluid flowing
along the flow channel
to fluid flowing along the annular space 210) is related to the pressure of
the flowing fluid.
Increased fluid pressure generally results in increased heat transfer. The
walls of the inner and
outer tubes 202, 204 for an SMR operating at high pressure are thicker than
the walls of the inner
and outer tubes 202, 204 for an SMR operating at lower pressure. The increased
wall thickness
can reduce heat transfer. SMR components (e.g., wall thickness for the inner
and outer tubes) and
operating parameters (e.g., fluid pressure) can be designed to balance such
competing factors.
[0122] In the example of Figs. 2A-2C, the SMR 200 includes a single set of
tubes that
includes the outer tube 202 and the inner tube 204. In some examples, an SMR
includes multiple
sets of tubes, each set having an outer tube and an inner tube. The multiple
sets of tubes can be
operated in parallel for increased throughput and can be heated by a single
external heat source
222 sized to generate sufficient heat for the multiple sets of tubes.
[0123] The products of the hydrogen generation reaction in the SMR 200,
including hydrogen
gas and carbon monoxide, along with excess steam, are output from the SMR 200
via the outlet
220. The SMR output is provided as input to a water gas shift (WGS) reactor,
where carbon
monoxide and water (e.g., steam) are reacted in the presence of a WGS catalyst
to generate
hydrogen gas and carbon dioxide.
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[0124] The output from the SMR 200 is at a temperature sufficient for input
into the WGS
reactor. The WGS reactor includes one or more WGS catalysts, each of which
operates in a
respective temperature range, and the SMR output is at a temperature at or
above the temperature
range of the WGS catalyst such that external, active heating of the SMR output
does not occur
prior to input into the WGS reactor. The temperature of the SMR output is
controllable by
adjustment of parameters that affect heat transfer between the fluid flowing
along the flow
channel 212 and the fluid flowing along the annular space 210 of the SMR,
e.g., characteristics of
the outer heat transfer foam 250, the inner heat transfer foam 252, diameters
and materials of the
outer and inner tubes 202, 204, flow rate of fluid along the bayonet flow
path, or other factors.
[0125] Referring to Fig. 3, an example WGS reactor 300 includes a housing
302 and a
reaction tube 304 disposed in the housing 302. A reaction channel 306 is
defined within the
reaction tube 304. For instance, the housing 302 and the reaction tube 304
both can be cylindrical
tubes, with the reaction tube 304 coaxial with the cylindrical housing 302. In
the example of Fig.
3, the reaction channel 306 is an annular space defined between the reaction
tube 304 and an inner
tube 308 disposed in the reaction tube 304. In some examples, the reaction
channel 306 is
cylindrical and no inner tube is disposed in the reaction tube 304.
[0126] Reactant fluid, such as the fluid output from the SMR, enters into
an inlet 305 of the
reaction channel 306 at a first end 310 of the WGS reactor 300 and flows along
the reaction
channel 306. A hydrogen generation reaction occurs along the reaction channel
306 in the
presence of a WGS catalyst that is disposed in the reaction channel 306. The
hydrogen generation
reaction generates products (e.g., hydrogen gas and carbon dioxide) that are
output from the
reaction channel 306 via an outlet 307 at a second end 312 of the WGS reactor.
For instance, the
inlet 305 of the reaction channel 306 at the first end 310 of the WGS reactor
300 is in fluid
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communication with the outlet 220 of the SMR 200 (see Fig. 2A), and fluid
output from the SMR
is provided into the reaction channel 306 of the WGS 300. An example of the
WGS hydrogen
generation reaction is represented as follows:
CO + H20 ¨> H2 + CO2.
[0127] The hydrogen generation reaction in the WGS 300 is an exothermic
reaction. Heat
generated by the hydrogen generation reaction in the WGS 300 is removed by
cooling fluid, such
as water, flowing along a cooling fluid channel 314 defined between the
housing 302 of the WGS
and the reaction tube 304. Cooling fluid can also flow through an inner
cooling fluid channel 316
defined within the inner tube 308. The cooling fluid enters into an inlet of
each the cooling fluid
channel 314 and the inner cooling fluid channel 316 at the second end 312 of
the WGS reactor
300, and exits from an outlet of each the cooling fluid channel 314 and the
inner cooling fluid
channel 316 at the first end 310 of the WGS reactor. The direction of flow of
the fluid in the
reaction channel 308 is from the first end 310 to the second end 312 of the
WGS reactor 300; the
direction of flow of the cooling flow is the opposite, from the second end 312
to the first end 310
of the WGS reactor 300. As the cooling fluid flows along the cooling fluid
channel 314 and the
inner cooling fluid channel 316, the cooling fluid is heated with heat from
the fluid flowing along
the reaction channel 308. In some examples, the cooling fluid is liquid water
at the inlets and is
heated such that the cooling fluid is steam, or a mixture of liquid water and
steam, at the outlets.
[0128] A WGS catalyst and a heat transfer material are disposed in the
reaction channel 306
of the WGS reactor 300. The configuration of the WGS catalyst and the heat
transfer material can
be adjusted, e.g., to achieve a target throughput or hydrogen generation
efficiency, to achieve
operation in a target temperature range, or to achieve another goal. For
instance, the position of
the WGS catalyst and the heat transfer material along the reaction channel 306
can be adjusted.
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The structure and extent of the WGS catalyst and the heat transfer material
can be adjusted. In the
example of Fig. 3, the WGS reactor 300 is configured as a two-catalyst system
with a heat transfer
material 334 disposed between two WGS catalysts 330, 332. In the example of
Fig. 4, the WGS
reactor 300 is configured as a one-catalyst system, with a heat transfer
material 434 and a single
WGS catalyst 430. Other configurations of WGS catalysts and heat transfer
materials are also
possible.
[0129] In the two-catalyst configuration of the WGS reactor 300 shown in
Fig. 3, a first WGS
catalyst 330 and a second WGS catalyst 332 are disposed in the reaction
channel 306. The first
WGS catalyst 330 catalyzes the WGS hydrogen generation reaction in a first
temperature range,
e.g., between 200 C and 450 C. The first WGS catalyst 330 can be a high
temperature WGS
catalyst that catalyzes the WGS hydrogen generation reaction at temperatures
of, e.g., between
310 C and 450 C. The first WGS catalyst 330 can be a medium temperature WGS
catalyst that
catalyzes the WGS hydrogen generation reaction at temperatures of, e.g.,
between 200 C and 350
C. The reactants are input into the reaction channel 306 at a temperature
within the first
temperature range such that the first WGS catalyst 330 can catalyze the
hydrogen generation
reaction in the gas flowing across the first WGS catalyst 330.
[0130] The second WGS catalyst 332 is disposed further along the reaction
channel 306 such
that the distance between the first WGS catalyst 330 and the inlet 305 of the
reaction channel 306
is less than the distance between the second WGS catalyst 332 and the inlet
305 of the reaction
channel 306. Gas flowing along the reaction channel 306 flows across the first
WGS catalyst 330
before flowing across the second WGS catalyst 332. The second WGS catalyst 332
catalyzes the
WGS hydrogen generation reaction in a second temperature range that is lower
than the first
temperature range. For instance, the second WGS catalyst 332 catalyzes the WGS
hydrogen
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generation reaction in a temperature range of, e.g., between 180 C and 350
C. When the first
WGS catalyst 330 is a high temperature WGS catalyst, the second WGS catalyst
332 can be a
medium temperature WGS catalyst; or the second WGS catalyst 332 can be a low
temperature
WGS catalyst that catalyzes the WGS hydrogen generation reaction at
temperatures of, e.g.,
between 180 C and 250 C. When the first WGS catalyst 330 is a medium
temperature WGS
catalyst, the second catalyst 332 can be a low temperature WGS catalyst.
[0131] A heat transfer material 334 is disposed in the reaction channel 306
between the first
WGS catalyst 330 and the second WGS catalyst 332, with the distance between
the heat transfer
material 334 and the inlet 305 of the reaction channel 306 being less than the
distance between the
second WGS catalyst 332 and the inlet 305 of the reaction channel 306. Fluid
flowing along the
reaction channel 306 first flows across the first WGS catalyst 330, then
across the heat transfer
material 334, and then across the second WGS catalyst 332. The heat transfer
material 334 is in
physical contact with the reaction tube 304, the inner tube 308, or both. The
heat transfer material
334 facilitates in-situ transfer of heat from the fluid flowing along the
reaction channel 306 (e.g.,
heat generated by the exothermic hydrogen generation reaction that occurs at
the first catalyst
330) to the cooling fluid flowing along the cooling fluid channel 314, the
inner cooling fluid
channel 316, or both. This heat transfer reduces the temperature of the gas
flowing along the
reaction channel to the temperature range at which the second WGS catalyst 332
can catalyze the
hydrogen generation reaction.
[0132] In some examples, an input side heat transfer material (not shown)
is disposed in the
reaction channel 306 such that fluid received into the reaction channel 306
flows across the input
side heat transfer material prior to flowing across the first catalyst 330.
This input side heat
transfer material reduces the temperature of the fluid to the temperature
range at which the first
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WGS catalyst 330 can catalyze the hydrogen generation reaction. For instance,
when fluid from
the SMR 200 (Fig. 2) is provided as input into the WGS 300 at a temperature
that is too high for
the first WGS catalyst 330, the input side heat transfer material reduces the
temperature of the
input fluid to the temperature range of the first WGS catalyst 330. In some
examples, an output
side heat transfer material (not shown) is disposed in the reaction channel
306 such that fluid
flows across the output side heat transfer material after flowing across the
second catalyst 332.
This output side heat transfer material facilitates recovery of heat into the
cooling fluid after
completion of the WGS hydrogen generation reaction, enhancing the energy
efficiency of the
WGS reactor.
[0133] Heat transfer materials 336, 338 are disposed in the cooling fluid
channel 314 and in
the inner cooling fluid channel 316, respectively. Cooling fluid flowing along
the cooling fluid
channel 314 and the inner cooling fluid channel 316 flows across the heat
transfer materials 336,
338, respectively. The heat transfer material 336 is in physical contact with
the reaction tube 304
to facilitate transfer of heat from the fluid flowing along the reaction
channel 306 to the cooling
fluid flowing along the cooling fluid channel 314. The heat transfer material
338 is in physical
contact with the inner tube 308 to facilitate transfer of heat from the fluid
flowing along the
reaction channel 306 to the cooling fluid flowing along the inner cooling
fluid channel 316.
[0134] As the cooling flow flows along the cooling fluid channels 314, 316,
the cooling fluid
is heated by heat transfer from the fluid flowing along the reaction channel.
In some examples, the
heated cooling fluid is provided as input to the SMR 200 or returned as input
to the reaction
channel 306 of the WGS 300. For instance, the heated cooling fluid can be
saturated water or two-
phase water (liquid/steam) produced at a temperature and flow rate appropriate
for input into the
SMR.
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[0135] In the configuration of the WGS reactor 300 shown in Fig. 3, the
heat transfer
materials 336, 338 are aligned with the heat transfer material 334. In some
examples, the heat
transfer materials 336, 338 are not aligned with the heat transfer material
334. The heat transfer
materials 336, 338 can extend along some or all of the length of the cooling
fluid channel 314 and
inner cooling fluid channel 316, respectively. In some examples, only one of
the heat transfer
materials 336, 338 is present, or neither of the heat transfer materials 336,
338 is present.
[0136] The catalyst arrangement in the WGS reactor 300 enables activation
and reduction of a
single catalyst without affecting the other catalyst. In general, the
catalyst(s) in the WGS reactor
300 are activated by slowly flowing a reducing gas across the catalyst at a
slightly elevated
temperature to reduce the catalyst to a metallic, active form. In some
examples, the WGS
catalyst(s) are activated externally prior to connection of the WGS to the
SMR.
[0137] Referring to Fig. 4, the WGS reactor 300 is configured as a single-
catalyst system in
which a single WGS catalyst 430 is disposed in the reaction channel 306 of the
WGS reactor 300.
The WGS catalyst 430 catalyzes the WGS hydrogen generation reaction at
temperatures of, e.g.,
between 200 C and 450 C. The WGS catalyst 430 can be a high temperature WGS
catalyst or a
medium temperature WGS catalyst.
[0138] A heat transfer material 434 is disposed in the reaction channel 306
such that a
distance between the heat transfer material 434 and the inlet 305 of the
reaction channel 306 is
less than the distance between the WGS catalyst 430 and the inlet 305 of the
reaction channel 306.
Fluid flowing along the reaction channel 306 first flows across the heat
transfer material 434 and
then flows across the WGS catalyst 430. The heat transfer material 434 is in
physical contact with
the reaction tube 304, the inner tube 308, or both, and facilitates the
transfer of heat from the fluid
received into the reaction channel 306 to the cooling fluid flowing along the
cooling fluid channel
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314, the inner cooling fluid channel 316, or both. This heat transfer reduces
the temperature of the
fluid to within a temperature range at which the WGS catalyst 430 can catalyze
the WGS
hydrogen generation reaction. For instance, when carbon monoxide output from
the SMR 200
(Fig. 2) is provided as input into the WGS 300 at a temperature that is too
high for the WGS
catalyst 430, the heat transfer material 434 reduces the temperature of the
input fluid to the
temperature range of the catalyst 430.
[0139] Heat transfer materials 436, 438 are disposed in the cooling fluid
channel 314 and in
the inner cooling fluid channel 316, respectively, and facilitate heat
transfer from the fluid
flowing along the reaction channel 306 to the cooling fluid flowing along the
cooling fluid
channel 314 and the inner cooling fluid channel 316. In the configuration of
the WGS reactor 300
shown in Fig. 4, the heat transfer materials 436, 438 are aligned with the
heat transfer material
434. In some examples, the heat transfer materials 436, 438 are not aligned
with the heat transfer
material 434. The heat transfer materials 436, 438 can extend along some or
all of the length of
the cooling fluid channel 314 and inner cooling fluid channel 316,
respectively. In some
examples, only one of the heat transfer materials 436, 438 is present, or
neither of the heat transfer
materials 436, 438 is present.
[0140] The WGS catalysts 330, 332, 430 of Figs. 3 and 4 can be pellets,
beads, saddles, rings,
or other structures formed of a catalyst material. The WGS catalysts 330, 332,
430 can be
catalytic foams, foils, fins, or other structures that include a substrate and
a catalyst material, e.g.,
with the catalyst material disposed on or integrated into the substrate. A
catalytic foam is a porous
structure through which one or more flow paths are defined. The porosity of
the catalytic foam
can be selected to achieve a high surface area, enabling efficient catalysis,
as well as a low
pressure drop across the catalytic foam, enabling efficient fluid flow along
the reaction channel
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306. For instance, the catalytic foam can have a porosity of between 5 ppi and
30 ppi. The
material of the catalytic foam is non-reactive to the fluid (e.g., the
reactants and products of the
WGS hydrogen generation reaction) flowing along the reaction channel 306 in
the temperature
range at which the WGS 300 is operated. For instance, the catalytic foam can
be a metal foam,
such as copper or aluminum, or a silicon carbide film, or another suitable
material. In the two-
catalyst configuration of Fig. 3, the first and second WGS catalysts 330, 332
both can have the
same structure, or each of the first and second WGS catalysts 330, 332 can
have a distinct
structure.
[0141] The heat transfer materials 334, 336, 338, 434 are materials having
a thermal
conductivity sufficient to enable heat transfer from the fluid flowing along
the reaction channel
306 to the cooling fluid flowing along the cooling fluid channel 314 or the
inner cooling fluid
channel 316 or both. The heat transfer materials 334, 434 disposed in the
reaction channel 306 are
non-reactive to the fluid (e.g., the reactants and products of the WGS
hydrogen generation
reaction) flowing along the reaction channel 306 in the temperature range at
which the WGS 300
is operated. For instance, the heat transfer materials 334, 434 can be a
metal, such as copper or
aluminum, or silicon carbide, or another suitable material.
[0142] The heat transfer materials 334, 336, 338, 434 can be foams, fins,
foils, rings, saddles,
beads, or pellets, or other structures capable of heat transfer. In the
example of a foam, the
porosity and length of the foam can be selected to achieve a high surface
area, enabling efficient
heat transfer, as well as a low pressure drop across the foam, enabling
efficient fluid flow along
the reaction channel 306. For instance, the heat transfer materials 334, 336,
338, 434 can be foams
having a porosity of between 5 ppi and 30 ppi.
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[0143] Referring to Figs. 3 and 4, the flow rate of cooling fluid along the
cooling fluid
channels 314, 316 is controlled by a flow controller 340. The flow rate can be
selected or adjusted
based on the temperature of the fluid input into the reaction channel 306, the
temperature of the
cooling fluid input into the cooling fluid channels 314, 316. The flow rate
can be selected or
adjusted based on a target output temperature of the fluid output from the
reaction channel 306, a
target output temperature of the cooling fluid, or both. The flow rate can be
selected or adjusted
based on the catalyst configuration, the type of catalyst(s) (e.g., high-,
medium-, or low-
temperature WGS catalyst), or both. The flow rate can be selected or adjusted
based on an actual
or desired throughput.
[0144] Cooling of the fluid in the reaction channel 306 of the WGS reactor
300 enables the
WGS hydrogen generation reaction to be carried out at high energy efficiency.
The transfer of
heat from the fluid in the reaction channel 306 to the cooling fluid cools the
fluid in the reaction
channel 306, e.g., removing heat generated during the exothermic hydrogen
generation reaction
and reducing the temperature of the fluid to an appropriate temperature range
for the WGS
catalyst(s), with no energy-intensive active cooling of the fluid. Moreover,
the heat transfer in the
WGS reactor enables isothermal conditions to be achieved, improving the
conversion efficiency
of the WGS hydrogen generation reaction.
[0145] Referring to Fig. 5, a WGS reactor 500 includes multiple reaction
tubes 504a-504c
disposed in a housing 502. A reaction channel 506a-506c is defined within each
reaction tube
504a-504c (collectively referred to as reaction tubes 504). Reactant gas flows
into the reaction
channels 506a-506c (collectively referred to as reaction channels 506) at a
first end 510 of the
WGS reactor 500, and product gas exits the reaction channels 506 at a second
end 512 of the
WGS reactor 500.
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[0146] A cooling fluid channel 514 is defined in the space between the
housing 502 and the
reaction tubes 504. Cooling fluid enters into the cooling fluid channel 514 at
the second end 512
of the WGS reactor and exits from the cooling fluid channel at the first end
510 of the WGS
reactor 500.
[0147] In the example of Fig. 5, the WGS reactor 500 is a single-catalyst
system, with a single
catalyst 522, such a high temperature WGS catalyst or a medium temperature WGS
catalyst,
disposed in each reaction channel 506. A heat transfer material 524 is
disposed in each reaction
channels 506 to facilitate heat transfer from the gas in the reaction channel
508 to the cooling
fluid in the cooling fluid channel 514. In some examples, the WGS reactor 500
including multiple
reaction tubes can be configured as a two-catalyst system.
[0148] Referring to Fig. 6, the SMR 200 and WGS 300 are integrated into a
system 600 for
production of hydrogen gas (H2) from hydrocarbons. A combustion furnace 602 as
the external
heat source heating the first end of the SMR 200. The system 600 also can be
implemented with
the WGS 500, with an SMR including multiple sets of outer and inner tubes, or
both.
[0149] The hydrogen generation reaction in the SMR 200 produces hydrogen
gas (H2) and
carbon monoxide (CO) from reactants including hydrocarbons and water vapor
(steam) in the
presence of a catalytic foam including an SMR catalyst. The hydrogen gas and
carbon monoxide
are output from the flow channel defined within the inner tube of the SMR onto
an SMR product
line 604 along with excess steam. The fluid (e.g., hydrogen gas, carbon
monoxide, and steam)
from the SMR 200 are provided as input to the reaction channel of the WGS 300.
The outlet of
the SMR 200 is in fluid communication with the inlet of the WGS 300 via the
SMR product line
604. In some examples, additional steam is provided into the reaction channel
of the WGS 300,
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e.g., from a water storage 614 (discussed infra) or from a cooling fluid
output line 620 from the
WGS 300 (discussed infra) to achieve a target ratio of steam to carbon
monoxide.
[0150] As discussed supra, the fluid flowing along the flow channel toward
the outlet of the
SMR 200 is cooled by heat transfer with the incoming fluid flowing along the
annular space of the
SMR. The temperature of the fluid at the outlet of the SMR is thus at least
partially controllable
by the extent of heat transfer with the fluid in the annular space. The heat
transfer, and thus the
outlet fluid temperature, is affected by the configuration of the SMR 200
(e.g., the position,
length, porosity, or other characteristics of the catalytic foam and the heat
exchange foams) and
by the operation of the SMR (e.g., the flow rate of fluid along the bayonet
flow path of the SMR
200). The configuration, operation, or both of the SMR 200 can be adjusted to
achieve heat
transfer such that the fluid output from the SMR 200 is at a temperature
appropriate for input into
the reaction channel of the WGS 300. For instance, when the WGS 300 is
configured with a high-
or medium-temperature WGS catalyst toward the input of the reaction channel,
the SMR 200 can
be configured such that the carbon monoxide and steam arrive at the reaction
channel of the WSG
300 with a temperature in the range at which the WGS catalyst is active. By
making use of heat
transfer within the SMR 200 to achieve a target temperature for fluid output
from the SMR,
external, active cooling devices are not used between the SMR 200 and the WGS
300, and the
role of external, active heating devices (e.g., the furnace 602) can be
reduced, thus contributing to
high energy efficiency of the system-level hydrogen generation process.
[0151] The hydrogen generation reaction in the WGS 300 produces hydrogen
gas and carbon
dioxide (CO2), which are output from the reaction channel of the WGS 300 onto
a WGS product
line 608 along with excess steam. The excess steam is removed from the fluid
on the WGS
product line 608 in a vapor liquid separator (VLS) 610. The remaining hydrogen
gas and carbon
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dioxide are sent downstream 611 for separation, with the carbon dioxide
discarded (e.g., via a flue
stack, discussed infra) and the hydrogen gas removed to a hydrogen storage,
e.g., for use as fuel.
The separated steam flows along a steam line 612 to a water storage 614, which
also stores water
provided from an external water source 616. The separated steam on the steam
line 612, the water
from the external water source 616, or both can be treated before storage in
the water storage 614.
[0152] Water from the water storage 614 is provided along a cooling fluid
line 618 as cooling
fluid input into the WGS 300. The heated cooling fluid output from the WGS
300, which is a
mixture of liquid water and steam, flows along a cooling fluid output line
620. The heated cooling
fluid will ultimately be provided as an input reactant into the SMR 200. The
temperature of the
heated cooling fluid output from the WGS 300 is affected by the configuration
of the WGS 300
(e.g., the type, position, or other characteristics of the WGS catalyst and
the heat transfer
material(s)) and by the operation of the WGS 300 (e.g., the flow rate of fluid
along the reaction
channel and the flow rate of cooling fluid). The configuration, operation, or
both of the WGS 300
can be adjusted such that the heated cooling fluid is output at a target
temperature, such as a
temperature sufficient for input into the SMR 200. By heating the cooling
fluid to a target
temperature using recovered heat from the fluid in the WGS 300 reaction
channel, external, active
heating elements to heat the SMR input fluid are not used. In addition,
external, active cooling are
not used to remove heat from the exothermic WGS hydrogen generation reaction.
The use of
recovered heat to heat the SMR input fluid and the cooling of the exothermic
WGS hydrogen
generation reaction contributes to high system-level energy efficiency.
[0153] The heated cooling fluid output from the WGS 300 flows along the
cooling fluid
output line 620 to an accumulator 622. The accumulator 622 also receives
additional water from
the water storage 614 along a water line 624. Steam and water output from the
accumulator 622
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onto an accumulator output line 626 is heated in a heat exchanger 634 with
heat from flue gases
636 from the combustion furnace 602. Hydrocarbons provided via a hydrocarbon
line 630 are
heated in a heat exchanger 635 with heat from the flue gases 636. The heated
steam and
hydrocarbons 632, 633, respectively, are mixed in a mixer 628 and output onto
an SMR input line
638, which feeds the heated steam and hydrocarbons to the inlet of the outer
tube of the SMR 200.
The use of recovered heat from the flue gases 636 to heat the mixture of steam
and hydrocarbons
to a temperature sufficient for input into the SMR contributes to high system-
level energy
efficiency. In this configuration, the outlet of the WGS cooling fluid flow
channels is in fluid
communication with the inlet of the SMR 200 such that the heated WGS cooling
fluid ultimately
is provided as a component of the fluid input into the SMR 200. The flue gases
636, after passing
through the heat exchanger 634, are discarded to a flue gas stack 640.
[0154] Referring to Fig. 7, in operation of a hydrogen generation system
including an SMR
and a WGS reactor, a fluid (e.g., a gas) including reactants is provided as
input (700) to an SMR.
Specifically, the fluid is provided into an inlet of an annular space of the
SMR at a second end of
the SMR, with the annular space being defined between an outer tube and an
inner tube of the
SMR. The fluid provided to the inlet includes hydrocarbons, e.g., methane,
natural gas, biogas,
methanol, or other hydrocarbons. The fluid provided to the inlet also includes
steam.
[0155] The fluid flows along a bayonet flow path of the SMR. Specifically,
the fluid flows
(702) along the annular space from the second end to the first end of the SMR.
Along the annular
space, the fluid flows through an outer heat exchange foam (704) that
facilitates heat transfer from
high-temperature fluid flowing along a flow channel defined in the inner tube
of the SMR to the
lower-temperature fluid flowing along the annular space. The outer heat
exchange foam also can
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induce turbulent flow in the fluid flowing along the annular space, enhancing
the heat transfer
efficiency.
[0156] The fluid flowing along the annular space is heated (706) by an
external heat source,
such as a combustion furnace, toward the first end of the SMR. In the heated
region of the SMR,
the fluid flows through a catalytic foam (708), which catalyzes the SMR
hydrogen generation to
produce hydrogen gas and carbon monoxide from the hydrocarbon and steam
reactants (710). The
catalytic foam facilitates heat transfer to the gas flowing therethrough,
e.g., heat transfer from
higher-temperature product fluid flowing along the flow channel within the
inner tube of the SMR
and heat transfer from the external heat source.
[0157] The fluid, now at higher temperature and including hydrogen and
carbon monoxide,
flows (712) from the annular space into the flow channel at the first end of
the SMR. The fluid in
the flow channel flows from the first end of the SMR toward the second end of
the SMR, opposite
the direction of flow of fluid in the annular space. The fluid in the flow
channel flows through an
inner heat exchange foam (714) that facilitates heat transfer from high-
temperature fluid flowing
along the flow channel to the lower-temperature fluid flowing along the
annular space. The inner
heat exchange foam also can induce turbulent flow in the fluid flowing along
the flow channel,
enhancing the heat transfer efficiency. The presence of an elongated baffle in
the inner tube also
enhances heat transfer efficiency.
[0158] When the fluid flowing along the flow channel reaches the SMR
outlet, the fluid
(including hydrogen gas, carbon monoxide, and steam) is output from the SMR
(716) at the
second end of the SMR. The SMR output fluid is provided as input into a
reaction channel of a
WGS reactor (720). The heat transfer between fluid flowing along the annular
space and fluid
flowing along the flow channel in the SMR can result in the carbon monoxide
being at a
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temperature sufficient for input into the WGS reactor, such as a temperature
in or above a
temperature range at which a WGS catalyst can catalyze the WGS hydrogen
generation reaction.
For instance, the fluid output from the SMR and provided as input into the
reaction channel of the
WGS reactor is at a temperature of between 200 C and at least 450 C.
[0159] Fluid including carbon monoxide and steam flow along the reaction
channel of the
WGS reactor (722), flowing across one or more WGS catalysts and one or more
heat transfer
materials. Cooling fluid, such as water, flows along one or more cooling fluid
channels (724). The
direction of fluid flow along the reaction channel is opposite the direction
of fluid flow along the
cooling fluid channels. The flow rate of the cooling fluid can be adjusted
(726), e.g., based on a
flow rate of the fluid flow along the reaction channel (e.g., which is based
on throughput of the
SMR), based on a target output temperature for the cooling fluid, or based on
a configuration or
operation of the WGS.
[0160] In the example of Fig. 7, the WGS reactor is configured as a two-
catalyst system, e.g.,
as shown in Fig. 3. The fluid in the reaction channel flows across a first WGS
catalyst (728), e.g.,
a high-temperature or medium-temperature WGS catalyst. The first WGS catalyst
catalyzes the
WGS hydrogen generation reaction in a first temperature range (730), e.g.,
between 200 C and
450 C, to produce hydrogen gas and carbon dioxide. The fluid in the reaction
channel then flows
across a heat transfer material disposed in the reaction channel (732). The
heat transfer material
reduces the temperature of the fluid to a second temperature range in which a
second WGS
catalyst operates by heat transfer to the cooling fluid flowing in the cooling
fluid channel(s). The
heat transfer raises the temperature of the cooling fluid, e.g., to between
100 C and 300 C. The
fluid in the reaction channel, now in the second temperature range, flows
across a second WGS
catalyst (734), e.g., a medium-temperature or low-temperature WGS catalyst.
The second WGS
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catalyst catalyzes the WGS hydrogen generation reaction in a second
temperature range (736)
lower than the first temperature range, e.g., between 180 C and 250 C. to
produce hydrogen gas
and carbon dioxide.
[0161] Fluid, including hydrogen gas, carbon dioxide, and excess steam, is
output from the
reaction channel of the WGS reactor (738). The excess steam is separated (740)
and the separated
steam, along with cooling fluid (e.g., a mixture of steam and liquid water)
from the WGS reactor,
are recycled (742) to be used, e.g., as input into the WGS reaction channel or
as input into the
SMR.
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[0162] Examples
[0163] Simulations and experiments of heat transfer in an SMR were
performed to evaluate
the role of catalytic foam in transferring heat from the external heat source
to the fluid flowing
along the annular space of the SMR.
[0164] Referring to Fig. 8, foams of differing porosities were disposed in
the annular space of
an SMR. For each foam type, the SMR was heated to 400 C and the temperature
differential
between the outer tube and the inner tube was measured by thermocouple. The
temperature
differential for each of three foams (10 ppi, 20 ppi, and 30 ppi), and the
temperature differential
for an empty annular space (no foam) is shown in Fig. 8. A lower temperature
differential
indicates temperature equilibration due to heat transfer. The measured
temperature differential
between outer and inner tubes was about 50 C greater when no foam was used
than when a foam
was present, indicating lack of heat conduction without foam and effective
heat conduction with
foam.
[0165] Referring to Figs. 9A and 9B, the heat transfer characteristics of
an SMR 150 were
simulated to demonstrate the effect of foam on heat transfer from an external
heat source into the
SMR. The SMR 150 has an outer tube 152 and an inner tube 154, with an annular
space 160
defined between the outer tube 152 and the inner tube 154, and a flow channel
162 defined within
the inner tube 152. Figs. 9A and 9B show a cross section of only half of the
SMR; the axis X-X'
is the axis along the center of the flow channel 162. An external heat source
172 supplies heat to a
heated portion 171 of the SMR. In Fig. 9A, a foam 180 is disposed in the
annular space 160. In
Fig. 9B, no foam is present in the annular space (Fig. 9B). Other parameters,
including inlet fluid
flow rate, inlet fluid temperature, annular width, and tube dimensions, were
the same. The heat
source 172 was simulated as a section of the outer tube 152 maintained at 875
C. As can be seen
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from Figs. 9A and 9B, with the foam 180 present in the annular space 130 (Fig.
9A), the fluid in
the annular space 160 reached a temperature of over 760 C, while in the SMR
without foam (Fig.
9B), the fluid in the annular space 160 reached a temperature of only 450 C.
The foam 180
present in the annular space also resulted in increased temperature of the
fluid in the flow channel
162 within the inner tube 152, e.g., by heat transfer and by flow of heated
fluid from the annular
space 160 into the flow channel 162. These results demonstrate the effective
heat transfer
provided by foam disposed in the annular space of an SMR.
[0166] Particular embodiments of the subject matter have been described.
Other
embodiments are within the scope of the following claims.
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