U.S. patent application number 11/691726 was filed with the patent office on 2009-11-05 for gas recovery system.
This patent application is currently assigned to PROTON ENERGY SYSTEMS, INC.. Invention is credited to Everett Bragg Anderson, Lawrence Clinton Moulthrop.
Application Number | 20090272271 11/691726 |
Document ID | / |
Family ID | 39792068 |
Filed Date | 2009-11-05 |
United States Patent
Application |
20090272271 |
Kind Code |
A9 |
Moulthrop; Lawrence Clinton ;
et al. |
November 5, 2009 |
GAS RECOVERY SYSTEM
Abstract
A gas recovery system is disclosed. The gas recovery system
includes a gas source productive of a gaseous stream comprising
moisture, a gas dryer in fluid communication with and downstream of
the gas source, and an electrochemical compressor in fluid
communication with and downstream of the gas dryer. The gas dryer
is disposed to receive the gaseous stream and produce a delivery
stream absent moisture and a slipstream comprising moisture. The
electrochemical compressor is disposed to receive the slipstream at
a first pressure and produce a compressed stream at a second
pressure greater than the first pressure.
Inventors: |
Moulthrop; Lawrence Clinton;
(Windsor, CT) ; Anderson; Everett Bragg;
(Glastonbury, CT) |
Correspondence
Address: |
CANTOR COLBURN, LLP - PROTON
20 Church Street, 22nd Floor
Hartford
CT
06103
US
|
Assignee: |
PROTON ENERGY SYSTEMS, INC.
Wallingford
CT
|
Prior
Publication: |
|
Document Identifier |
Publication Date |
|
US 20080236396 A1 |
October 2, 2008 |
|
|
Family ID: |
39792068 |
Appl. No.: |
11/691726 |
Filed: |
March 27, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11047119 |
Jan 31, 2005 |
7241522 |
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11691726 |
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09966727 |
Sep 28, 2001 |
6887601 |
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11047119 |
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60236278 |
Sep 28, 2000 |
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Current U.S.
Class: |
96/134 ;
429/411 |
Current CPC
Class: |
B01D 53/047 20130101;
C25B 9/19 20210101; B01D 53/261 20130101; B01D 2259/40052 20130101;
B01D 2259/402 20130101; C25B 1/04 20130101; H01M 8/241 20130101;
C01B 3/56 20130101; Y02E 60/50 20130101; C01B 2203/043 20130101;
C25B 9/00 20130101; Y02E 60/36 20130101; B01D 2256/16 20130101;
C01B 2203/0495 20130101; C25B 15/08 20130101; H01M 8/242
20130101 |
Class at
Publication: |
96/134 ; 429/13;
429/27 |
International
Class: |
B01D 53/02 20060101
B01D053/02 |
Claims
1. A gas recovery system comprising: a gas source productive of a
gaseous stream comprising moisture; a gas dryer in fluid
communication with and downstream of the gas source, the gas dryer
disposed to receive the gaseous stream and produce a delivery
stream absent moisture and a slipstream comprising moisture; and an
electrochemical compressor in fluid communication with and
downstream of the gas dryer, the electrochemical compressor
disposed to receive the slipstream at a first pressure and produce
a compressed stream at a second pressure greater than the first
pressure.
2. The system of claim 1, further comprising: a phase separator in
fluid communication with and downstream of the gas source, the
phase separator in fluid communication with and downstream of and
upstream of the electrochemical compressor, the phase separator in
fluid communication with and upstream of the gas dryer.
3. The system of claim 1, wherein: the gas source is an
electrochemical cell.
4. The system of claim 3, wherein: the electrochemical cell and the
electrochemical compressor are integrally arranged to define a
single cell stack.
5. The system of claim 4, further comprising: flow ports within the
single cell stack that control flow between the electrochemical
cell and the electrochemical compressor.
6. The system of claim 3, wherein: the electrochemical cell is an
electrolysis cell.
7. The system of claim 6, wherein: the gaseous stream, the delivery
stream, and the slipstream comprise hydrogen gas.
8. The system of claim 7, wherein: the electrochemical compressor
is disposed to recover the hydrogen gas from the slipstream to
increase a productive efficiency of the electrochemical cell
system.
9. The system of claim 6, wherein: the electrolysis cell produces
hydrogen gas near ambient pressure.
10. The system of claim 6, wherein: the electrolysis cell produces
hydrogen gas at a pressure less than or equal to 15 bar.
11. The system of claim 6, wherein: the electrolysis cell produces
hydrogen gas at a pressure greater than 15 bar and less than or
equal to 30 bar.
12. The system of claim 6, wherein: the electrolysis cell produces
hydrogen gas at a pressure greater than 30 bar and less than or
equal to 200 bar.
13. The system of claim 1, wherein: the gas dryer comprises a
Pressure Swing Adsorption unit in fluid communication with and
upstream of and downstream of the electrochemical compressor.
14. The system of claim 1, wherein: the slipstream is greater than
about 5 percent and less than about 15 percent of the gaseous
stream.
15. A method to increase a productive efficiency of a gas
production system, the method comprising: producing a gaseous
stream comprising moisture by a gas source; obtaining the gaseous
stream and making available a dry delivery stream and a moist
slipstream via a gas dryer; recovering the moist slipstream from
the gas dryer by an electrochemical compressor and adding it to the
gaseous stream, thereby increasing the productive efficiency of the
gas production system.
16. The method of claim 15, wherein: the recovering comprises
obtaining the slipstream at a first pressure and in response
thereto, generating a compressed stream at a second pressure
greater than the first pressure.
17. The method of claim 15, further comprising: separating hydrogen
gas from liquid water in the gaseous stream and the moist
slipstream via a phase separator.
18. The method of claim 15, wherein the producing comprises:
producing a gaseous stream by an electrochemical cell.
19. The method of claim 15, wherein the producing comprises:
producing a gaseous stream comprising hydrogen gas by an
electrolysis cell.
20. The method of claim 19, wherein the producing comprises:
producing hydrogen gas near ambient pressure.
21. The method of claim 19, wherein the producing comprises:
producing hydrogen gas at a pressure less than or equal to 15
bar.
22. The method of claim 19, wherein the producing comprises:
producing hydrogen gas at a pressure greater than 15 bar and less
than or equal to 30 bar.
Description
BACKGROUND OF THE INVENTION
[0001] The present disclosure relates generally to gas recovery
systems, and particularly to gas recovery systems including an
electrochemical compressor.
[0002] Electrochemical cells are energy conversion devices, usually
classified as either electrolysis cells or fuel cells. A proton
exchange membrane electrolysis cell can function as a hydrogen
generator by electrolytically decomposing water to produce hydrogen
and oxygen gas, and can function as a fuel cell by
electrochemically reacting hydrogen with oxygen to generate
electricity. Referring to FIG. 1, which is a partial section of a
typical anode feed electrolysis cell 100, process water 102 is fed
into cell 100 on the side of an oxygen electrode (anode) 116 to
form oxygen gas 104, electrons, and hydrogen ions (protons) 106.
The reaction is facilitated by the positive terminal of a power
source 120 electrically connected to anode 116 and the negative
terminal of power source 120 connected to a hydrogen electrode
(cathode) 114. The oxygen gas 104 and a portion of the process
water 108 exit the cell 100 as byproducts 109, while protons 106
and water 110 migrate across a proton exchange membrane 118 to
cathode 114 where hydrogen gas 112 is produced.
[0003] Another typical water electrolysis cell using the same
configuration as is shown in FIG. 1 is a cathode feed cell, wherein
process water is fed on the side of the hydrogen electrode. A
portion of the water migrates from the cathode across the membrane
to the anode where hydrogen ions and oxygen gas are formed due to
the reaction facilitated by connection with a power source across
the anode and cathode. A portion of the process water exits the
cell at the cathode side without passing through the membrane.
[0004] A typical fuel cell uses the same general configuration as
is shown in FIG. 1. Hydrogen, from hydrogen gas, methanol, or other
hydrogen source, is introduced to the hydrogen electrode (the anode
in fuel cells), while oxygen, or an oxygen-containing gas such as
air, is introduced to the oxygen electrode (the cathode in fuel
cells). Water can also be introduced with the feed gas. Hydrogen
electrochemically reacts at the anode to produce protons and
electrons, wherein the electrons flow from the anode through an
electrically connected external load, and the protons migrate
through the membrane to the cathode. At the cathode, the protons
and electrons react with oxygen to form water, which additionally
includes any feed water that is dragged through the membrane to the
cathode. The electrical potential across the anode and the cathode
can be exploited to power an external load.
[0005] In other embodiments, one or more electrochemical cells can
be used within a system to both electrolyze water to produce
hydrogen and oxygen, and to produce electricity by converting
hydrogen and oxygen back into water as needed. Such systems are
commonly referred to as regenerative fuel cell systems.
[0006] Electrochemical cell systems typically include a number of
individual cells arranged in a stack, with the working fluids
directed through the cells via input and output conduits or ports
formed within the stack structure. The cells within the stack are
sequentially arranged, each including a cathode, a proton exchange
membrane, and an anode. The cathode and anode may be separate
layers or may be integrally arranged with the membrane. Each
cathode/membrane/anode assembly (hereinafter "membrane-electrode
assembly", or "MEA") typically has a first flow field in fluid
communication with the cathode and a second flow field in fluid
communication with the anode. The MEA may furthermore be supported
on both sides by screen packs or bipolar plates that are disposed
within, or that alternatively define, the flow fields. Screen packs
or bipolar plates may facilitate fluid movement to and from the
MEA, membrane hydration, and may also provide mechanical support
for the MEA.
[0007] In order to maintain intimate contact between cell
components under a variety of operational conditions and over long
time periods, uniform compression may be applied to the cell
components. Pressure pads or other compression means are often
employed to provide even compressive force from within the
electrochemical cell.
[0008] It is often desired for an electrochemical cell system to
deliver hydrogen absent water or moisture vapor. Dryers, including
Pressure Swing Adsorption (PSA) units, are used to remove moisture
from the hydrogen produced by the electrolysis cell. To maintain
functionality, the PSA used in existing systems is regenerated, or
purged with a slipstream of dry hydrogen. Because the slipstream
purge, which can be about 5 to 15 percent of the hydrogen produced
by the cell includes moisture, it is typically vented, or
discarded. Accordingly, the electrolysis cell must produce about 5
to 15 percent more hydrogen than is actually delivered to an end
user or end user system, reducing an overall productive efficiency
of the electrochemical cell system. Additionally, it is desired to
deliver the hydrogen with a pressure that is higher than that
provided by the electrolysis cell. Mechanical compressors are often
used to increase the pressure of the hydrogen. However, mechanical
compressors consume power, and use moving parts that may require
maintenance, thereby reducing an overall reliability and efficiency
of the electrochemical cell system. Furthermore, mechanical
compressors are not tolerant of moisture within the hydrogen.
Accordingly, there is a need in the art for a hydrogen generation
arrangement that overcomes these drawbacks.
BRIEF DESCRIPTION OF THE INVENTION
[0009] An embodiment of the invention includes a gas recovery
system. The electrochemical cell system includes a gas source
productive of a gaseous stream comprising moisture, a gas dryer in
fluid communication with and downstream of the gas source, and an
electrochemical compressor in fluid communication with and
downstream of the gas dryer. The gas dryer is disposed to receive
the gaseous stream and produce a delivery stream absent moisture
and a slipstream comprising moisture. The electrochemical
compressor is disposed to receive the slipstream at a first
pressure and produce a compressed stream at a second pressure
greater than the first pressure.
[0010] Another embodiment of the invention includes a method to
increase a productive efficiency of a gas production system. The
method includes producing a gaseous stream comprising moisture by a
gas source, obtaining the gaseous stream and making available a dry
delivery stream and a moist slipstream via a gas dryer, and
recovering the moist slipstream from the gas dryer by an
electrochemical compressor and adding it to the gaseous stream,
thereby increasing the productive efficiency of the gas production
system.
[0011] These and other advantages and features will be more readily
understood from the following detailed description of preferred
embodiments of the invention that is provided in connection with
the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] Referring to the exemplary drawings wherein like elements
are numbered alike in the accompanying Figures:
[0013] FIG. 1 depicts a schematic diagram of a partial
electrochemical cell in accordance with embodiments of the
invention;
[0014] FIG. 2 depicts an exploded cross-section schematic diagram
of an electrochemical cell for use in embodiments of the
invention;
[0015] FIG. 3 depicts a gas recovery system in accordance with
embodiments of the invention;
[0016] FIG. 4 depicts a gas recovery system in accordance with
embodiments of the invention;
[0017] FIG. 5 depicts an electrochemical cell in accordance with
embodiments of the invention; and
[0018] FIG. 6 depicts a flowchart of process steps for increasing a
productive efficiency of a gas production system in accordance with
embodiments of the invention.
DETAILED DESCRIPTION OF THE INVENTION
[0019] An embodiment of the invention provides an electrochemical
compressor (ECC) capable of accepting a mixture of hydrogen and
water to recover wet hydrogen used as a purge for dryers, such as
the PSA. Accordingly, use of the ECC within an electrochemical cell
system eliminates the venting loss of wet hydrogen, and thereby
increases a productive efficiency of the electrochemical cell
system. In an embodiment, the ECC increases the pressure of the
hydrogen provided by the electrolysis cell, thereby eliminating the
need to use mechanical compressors. In another embodiment, hydrogen
and water vapor from a hydrogen/water phase separator is introduced
to the ECC, thereby increasing the useful pressure of the supplied
hydrogen.
[0020] Referring to FIG. 2, an electrochemical cell 200 that may be
suitable for operation as an anode feed electrolysis cell, cathode
feed electrolysis cell, fuel cell, or regenerative fuel cell, is
depicted schematically in an exploded cross section view. Thus,
while the discussion below may be directed to an anode feed
electrolysis cell, cathode feed electrolysis cells, fuel cells, and
regenerative fuel cells are also contemplated. Cell 200 is
typically one of a plurality of cells employed in a cell stack as
part of an electrochemical cell system. When cell 200 is used as an
electrolysis cell, voltage inputs are generally between about 1.48
volts and about 3.0 volts at current densities between about 50
A/ft2 (amperes per square foot) and about 4,000 A/ft2. When used as
a fuel cell, voltage outputs range between about 0.4 volts and
about 1 volt, at current densities of about 0.1 A/ft2 and about
10,000 A/ft2. The number of cells within the stack, and the
dimensions of the individual cells is scalable to the cell power
output and/or gas output requirements. Accordingly, application of
electrochemical cell 200 may involve a plurality of cells 200
arranged electrically either in series or parallel depending on the
application. Cells 200 may be operated at a variety of pressures,
such as up to or exceeding 50 psi (pounds-per-square-inch), up to
or exceeding about 100 psi, up to or exceeding about 500 psi, up to
or exceeding about 2500 psi, or even up to or exceeding about
10,000 psi, for example.
[0021] In an embodiment, cell 200 includes a membrane 118 having a
first electrode (e.g., an anode) 116 and a second electrode (e.g.,
a cathode) 114 disposed on opposite sides thereof. Flow fields 210,
220, which are in fluid communication with electrodes 116 and 114,
respectively, are defined generally by the regions proximate to,
and bounded on at least one side by, each electrode 116 and 114
respectively. A flow field member (also herein referred to as a
screen pack) 228 may be disposed within flow field 220 between
electrode 114 and, optionally, a pressure pad separator plate 222.
A pressure pad 230 is typically disposed between pressure pad
separator plate 222 and a cell separator plate 232. Cell separator
plate 232 is disposed adjacent to pressure pad 230. A frame 224,
generally surrounding flow field 220 and an optional gasket 226, is
disposed between frame 224 and pressure pad separator plate 222
generally for enhancing the seal within the reaction chamber
defined on one side of cell system 200 by frame 224, pressure pad
separator plate 222 and electrode 114. Gasket 236 may be disposed
between pressure pad separator plate 222 and cell separator plate
232 enclosing pressure pad 230.
[0022] Another screen pack 218 may be disposed in flow field 210.
Optionally, screen packs 218, 228 may include a porous plate 219 as
depicted. The porous plate 219 shall preferably be of conductive
material, and may be included to provide additional mechanical
support to the electrodes 116, 114. A frame 214 generally surrounds
screen pack 218. A cell separator plate 212 is disposed adjacent
screen pack 218 opposite oxygen electrode 116, and a gasket 216 may
be disposed between frame 214 and cell separator plate 212,
generally for enhancing the seal within the reaction chamber
defined by frame 214, cell separator plate 212 and the oxygen side
of membrane 118. The cell components, particularly cell separator
plates 212, 232, frames 214, 224, and gaskets 216, 226, and 236 are
formed with the suitable manifolds or other conduits as is
conventional.
[0023] In an embodiment, membrane 118 comprises electrolytes that
are preferably solids or gels under the operating conditions of the
electrochemical cell. Useful materials include proton conducting
ionomers and ion exchange resins. Useful proton conducting ionomers
include complexes comprising an alkali metal salt, an alkali earth
metal salt, a protonic acid, or a protonic acid salt. Useful
complex-forming reagents include alkali metal salts, alkaline metal
earth salts, and protonic acids and protonic acid salts.
Counter-ions useful in the above salts include halogen ion,
perchloric ion, thiocyanate ion, trifluoromethane sulfonic ion,
borofluoric ion, and the like. Representative examples of such
salts include, but are not limited to, lithium fluoride, sodium
iodide, lithium iodide, lithium perchlorate, sodium thiocyanate,
lithium trifluoromethane sulfonate, lithium borofluoride, lithium
hexafluorophosphate, phosphoric acid, sulfuric acid,
trifluoromethane sulfonic acid, and the like. The alkali metal
salt, alkali earth metal salt, protonic acid, or protonic acid salt
is complexed with one or more polar polymers such as a polyether,
polyester, or polyimide, or with a network or cross-linked polymer
containing the above polar polymer as a segment. Useful polyethers
include polyoxyallcylenes, such as polyethylene glycol,
polyethylene glycol monoether, and polyethylene glycol diether;
copolymers of at least one of these polyethers, such as
poly(oxyethylene-co-oxypropylene)glycol,
poly(oxyethylene-co-oxypropylene)glycol monoether, and
poly(oxyethylene-co-oxypropylene)glycol diether; condensation
products of ethylenediamine with the above polyoxyallcylenes; and
esters, such as phosphoric acid esters, aliphatic carboxylic acid
esters or aromatic carboxylic acid esters of the above
polyoxyallcylenes. Copolymers of, e.g., polyethylene glycol with
diallcylsiloxanes, maleic anhydride, or polyethylene glycol
monoethyl ether with methacrylic acid are known in the art to
exhibit sufficient ionic conductivity to be useful.
[0024] Ion-exchange resins useful as proton conducting materials
include hydrocarbon- and fluorocarbon-type resins. Hydrocarbon-type
ion-exchange resins include phenolic resins, condensation resins
such as phenol-formaldehyde, polystyrene, styrene-divinyl benzene
copolymers, styrene-butadiene copolymers,
styrene-divinylbenzene-vinylchloride terpolymers, and the like,
that are imbued with cation-exchange ability by sulfonation, or are
imbued with anion-exchange ability by chloromethylation followed by
conversion to the corresponding quaternary amine.
[0025] Fluorocarbon-type ion-exchange resins may include hydrates
of tetrafluoroethylene-perfluorosulfonyl ethoxyvinyl ether or
tetrafluoroethylene-hydroxylated(perfluoro vinyl ether) copolymers.
When oxidation and/or acid resistance is desirable, for instance,
at the cathode of a fuel cell, fluorocarbon-type resins having
sulfonic, carboxylic and/or phosphoric acid functionality are
preferred. Fluorocarbon-type resins typically exhibit excellent
resistance to oxidation by halogen, strong acids and bases. One
family of fluorocarbon-type resins having sulfonic acid group
functionality is NAFION (TM) resins (commercially available from E.
I. du Pont de Nemours and Company, Wilmington, Del.).
[0026] Electrodes 116 and 114 may comprise a catalyst suitable for
performing the needed electrochemical reaction (i.e., electrolyzing
water and producing hydrogen). Suitable catalyst include, but are
not limited to, materials comprising platinum, palladium, rhodium,
carbon, gold, tantalum, tungsten, ruthenium, iridium, osmium,
alloys thereof, and the like. Electrodes 116 and 114 may be formed
on membrane 118, or may be layered adjacent to, but in contact
with, membrane 118.
[0027] Screen packs 218, 228 support membrane 118, allow the
passage of system fluids, and preferably are electrically
conductive. The screen packs 218, 228 may include one or more
layers of perforated sheets or a woven mesh formed from metal or
strands.
[0028] Pressure pad 230 provides even compression between cell
components, is electrically conductive, and therefore generally
comprises a resilient member, preferably an elastomeric material,
together with a conductive material. Pressure pad 230 is capable of
maintaining intimate contact to cell components at cell pressures
up to or exceeding about 100 psi, preferably about 500 psi, more
preferably about 2,500 psi, or even more preferably about 10,000
psi. The pressure pads can thus be introduced into a high-pressure
electrochemical cell environment. The foregoing is intended for
illustration, and not limitation.
[0029] Referring now to FIG. 3, an embodiment of a gas recovery
system 300, such as an electrochemical cell system for example, is
depicted. The system 300 includes a gas source 200, such as an
electrochemical cell 200, for example, an electrochemical
compressor (ECC) 305, a phase separator 310, and a gas dryer 315
(also herein referred to as a dryer). An exemplary electrochemical
cell 200 is an electrolysis cell.
[0030] The electrochemical cell 200 produces a stream 326, such as
a gaseous stream including hydrogen 112 and water 110 (best seen in
reference to FIG. 1) in response to a supply of process water 102
and electrical power via the power source 120. The water 110 within
the gaseous stream 326 produced by the electrochemical cell 200 is
at least one of liquid water and water vapor. The electrochemical
cell 200 is in fluid communication with and upstream of the phase
separator 310. The gaseous stream 326 is provided to the phase
separator 310, which separates hydrogen gas from liquid water. It
will be appreciated that while the phase separator 310 separates
hydrogen gas from liquid water, the hydrogen gas may still include
water vapor.
[0031] While an embodiment of the invention has been described as a
gas recovery system 300 with an electrochemical cell 200 as a gas
source, it will be appreciated that the scope of the invention is
not so limited, and that the invention will also apply to other
sources of the gaseous stream including water, such from
hydrocarbon reforming, cellulose digestion, and hydrogen production
from biomass, for example.
[0032] The ECC 305 is in fluid communication with and downstream of
the phase separator 310 and the dryer 315 (as will be described
further below). The ECC 305 receives hydrogen and water vapor as an
input 320. In response to a supply of electrical power via a power
source 325, the ECC 305 is configured to produce a compressed
stream 327 that has a pressure of hydrogen greater than a pressure
of hydrogen at the input 320. The compressed stream 327, having the
pressure of hydrogen greater than the pressure of hydrogen at the
input 320, (and also including water) is provided to the phase
separator 310.
[0033] Hydrogen, including water vapor (but absent liquid water) is
transported to the dryer 315 in fluid communication with and
upstream of the electrochemical cell 200 via the phase separator
310. The dryer 315 receives the gaseous stream 326 provided by the
electrolysis cell 200 and processed by at least one of the phase
separator 310 and the ECC 305. The dryer 315 produces a dry
delivery stream 335 of hydrogen gas absent moisture for use by an
end user or an end user system. An absorption unit 330 of the gas
dryer 315 removes water vapor from the hydrogen, to produce the dry
delivery stream 335. A transfer unit 340 of the dryer 315, such as
a PSA, utilizes a slipstream 345, or portion of the delivery stream
335 provided by the absorption unit 330 to absorb moisture from and
regenerate the absorption unit 330. That is, the transfer unit 340
uses the slipstream 345 to regenerate the absorption unit 330 to
prevent saturation, or an inability to remove additional water
vapor from the gaseous stream 326 provided by the electrolysis cell
200. The slipstream 345 represents about 5 to 15 percent of the
hydrogen within the gaseous stream 326 produced by the electrolysis
cell 200 (and processed through the phase separator 310 and
absorption unit 330) to regenerate the absorption unit 330. Dry
hydrogen from the delivery stream 335 is provided at the desired
delivery pressure at a product output 350.
[0034] The ECC 305 is disposed downstream of the dryer 315 and
recovers from the transfer unit 340 the hydrogen gas from the
slipstream 345, thereby increasing a productive efficiency of the
electrochemical cell system 300. That is, use of the ECC 305 as
described herein eliminates the venting (loss) of the hydrogen in
the slipstream 345. Additionally (as described above), a mixture of
hydrogen and water vapor from the phase separator 310 may also be
provided to the ECC 305. Furthermore, the ECC 305 receives the
slipstream 345 (including water vapor) and the hydrogen gas from
the phase separator 310 (collectively indicated as input 320) at a
first pressure, and in response to the supply of electrical power
via the power supply 325, produces the compressed stream 327 at a
second pressure greater than the first pressure. It will be
appreciated that this will continue as necessary to provide the
desired delivery pressure at the product output 350. Liquid water
separated from by the phase separator 310 is returned to the
electrolysis cell 200 via a water conduit 352 as an input for
subsequent electrolysis. In an alternate embodiment, (as depicted
by the dashed line in FIG. 3), the transfer unit 340 provides the
slipstream 345 to the phase separator 310 before the ECC 305, to
separate any liquid water from the slipstream 345. In further
embodiments, more than one phase separator 310 is utilized to
individually separate liquid water 110 from hydrogen 112 from more
than one stream, such as one or more of the gaseous stream 326, the
slipstream 345, and the compressed stream 327, for example. As
compared with a mechanical compressor, the ECC 305 is cleaner,
quieter, and has no moving parts. Accordingly, it is contemplated
that the ECC 305 will enhance a reliability of the electrochemical
cell system 300.
[0035] Recovery of the slipstream 345 of hydrogen (which has
typically been vented) increases a proportion of hydrogen available
for delivery at the product output 350 relative to the amount of
hydrogen 112 produced by the electrolysis cell 200. Accordingly,
recovery of the slipstream 345 of hydrogen increases a productive
efficiency of the system 300 and is estimated to reduce an
electrical power consumption of the system 300 by about 2 to 10
kilowatt-hours per kilogram of hydrogen delivered at the product
output 350.
[0036] Inefficiencies associated with operation of the electrolysis
cell 200 and the ECC 305 include a back diffusion of hydrogen (I
loss) component that is related to pressure, and an electrical
resistance (R loss) component that is related to the electrical
power provided to the cell 200 and the ECC 305 via the power
supplies 120, 325.
[0037] In an embodiment, the electrolysis cell 200 is a
low-pressure electrolysis cell 200, such as to produce hydrogen 112
gas near ambient pressure for example. Use of the low pressure
electrolysis cell 200 can represent a low cost, high efficiency
stage, which exhibits only the electrical resistance (R loss)
component. The ECC 305 will compress, or increase the pressure of
hydrogen 112 provided by the low-pressure electrolysis cell 200 to
the desired delivery pressure. Therefore, because of the pressure
differential across the ECC 305, it will exhibit an I loss as well
as an R loss. Accordingly, because all of the gas produced by the
low-pressure electrolysis cell 200 will need to be compressed by
the ECC 305 to the desired delivery pressure, an overall
inefficiency for operation of the system 300 using the low-pressure
electrolysis cell 200 can be represented as 2R+I. Use of the
low-pressure electrolysis cell 200 significantly reduces a
likelihood of mixture of oxygen and hydrogen. As used herein, the
term "near ambient pressure" shall represent the low-pressure
electrolysis cell 200 productive of hydrogen gas at such a pressure
that a contribution of inefficiency due to back diffusion (I loss)
of hydrogen can be considered to be negligible.
[0038] In another embodiment, the electrolysis cell 200 is a
high-pressure electrolysis cell 200, which produces hydrogen 112
at, or very near, the desired delivery pressure. In an embodiment,
the high-pressure electrolysis cell 200 produces hydrogen gas 112
up to about 15 bar. In another embodiment, the high-pressure
electrolysis cell 200 produces hydrogen gas 112 between about 15
bar and 30 bar. In yet another embodiment, the electrolysis cell
200 produces hydrogen gas 112 between about 30 bar and 200 bar.
[0039] Because the high-pressure electrolysis cell 200 produces
hydrogen 112 (along with water 110) at or near the desired delivery
pressure, the ECC 305 is contemplated to perform much less work to
increase the pressure of the hydrogen 112 to the desired delivery
pressure. Accordingly, a flow through the input 320 to the ECC 305
is contemplated to be reduced substantially to that of the
slipstream 345 from the transfer unit 340, for recovery of the
slipstream 345 hydrogen. In an exemplary embodiment, the system 300
incorporating a high-pressure electrolysis cell is contemplated to
incorporate an ECC 305 that is approximately one-tenth the capacity
of an ECC 305 used by the system 300 that incorporates a
low-pressure electrolysis cell.
[0040] Because the compression performed by the ECC 305, in
conjunction with the high-pressure electrolysis cell 200, is
reduced, the power input 325 and accompanying electrical resistance
(R loss) is reduced. Further, the reduced pressure differential
across the ECC 305 results in a reduced back diffusion (I loss).
However, the increased pressure differential across the
high-pressure electrolysis cell 200 results in an increased I loss
as compared to use of the low-pressure electrolysis cell. Use of
the high-pressure electrolysis cell 200 results in an inefficiency
for operation of the system 300 using the high-pressure
electrolysis cell 200 that is represented as 1.1R+1.1I.
[0041] While embodiments of the invention have been described
having a low-pressure electrolysis cell 200 producing hydrogen 112
at ambient pressure and a high-pressure electrolysis cell 200
producing hydrogen 112 at, or near, the desired delivery pressure,
it will be appreciated that the scope of the invention is not so
limited, and that the invention will also apply to electrochemical
cell systems 300 that include electrolysis cells 200 that produce
hydrogen gas 112 at any pressure between ambient and the desired
delivery pressure. It will be further appreciated that a required
capacity of the ECC 305 (and a corresponding system 300
inefficiency representation) will be determined, in part, on the
relationship between the pressure output of the electrolysis cell
200, the desired delivery pressure, and a quantity of the flow of
the hydrogen slipstream.
[0042] FIG. 4 depicts an exemplary arrangement of a gas recovery
system 302 including the components described above. In an
embodiment of the system 302 depicted in FIG. 4, the electrolysis
cell 200 provides the stream 326 (including hydrogen 112 and water
110) directly to the ECC 305 without passing through the phase
separator 310. That is, the ECC 305 processes both hydrogen 112 and
water 110 without phase separation. It will be appreciated that in
the system 302, the ECC 305 directly receives the slipstream 345
from the transfer unit 340.
[0043] FIG. 5 depicts an alternate embodiment in which the
high-pressure electrolysis cell 200 and the ECC 305 are integrally
arranged as sub-sections of a single cell stack 355. Flow ports
within the stack 355 control flow between the subsections 200,
305.
[0044] Referring now to FIG. 6, a flowchart 400 of process steps
for increasing a productive efficiency of a gas production system,
such as facilitated by the gas recovery system 300 is depicted.
[0045] The process begins with producing at Step 410 the gaseous
and liquid stream 326 comprising water and hydrogen by the
electrolysis cell 200. The process continues by obtaining at Step
420 the stream 326 and making available the dry delivery stream 335
and the moist slipstream 345 via the gas dryer 315. The process
proceeds by recovering at Step 430 the moist slipstream 345 from
the gas dryer 315 by an electrochemical compressor 305, thereby
increasing the productive efficiency of the electrochemical cell
system 300. In an embodiment, the recovering at Step 430 includes
recovering hydrogen gas.
[0046] In an embodiment, the recovering at Step 430 includes
obtaining the slipstream 345 at a first pressure. In response to
the recovering at Step 430, the process further includes generating
a compressed stream at a second pressure greater than the first
pressure. In an embodiment, the process further includes separating
hydrogen gas from liquid water via the phase separator 310.
[0047] In an embodiment, producing the gaseous stream 326 includes
producing hydrogen gas by the electrolysis cell 200. In one
embodiment, the electrolysis cell 200 produces hydrogen gas near
ambient pressure. In another embodiment, the electrolysis cell 200
produces hydrogen gas at a pressure less than or equal to 15 bar.
In another embodiment, the electrolysis cell 200 produces hydrogen
gas at a pressure greater than 15 bar and less than or equal to 30
bar. In further embodiments, the electrolysis cell 200 produces
hydrogen gas at a pressure greater than 30 bar and less than or
equal to 200 bar.
[0048] As disclosed, some embodiments of the invention may include
some of the following advantages: the ability to recover hydrogen
from a slipstream used to regenerate a gas dryer; the ability to
increase a productive efficiency of an electrochemical cell system;
the ability to reduce an overall power consumption of an
electrochemical cell system; and the ability to increase a
reliability of an electrochemical cell system.
[0049] While the invention has been described with reference to
exemplary embodiments, it will be understood by those skilled in
the art that various changes may be made and equivalents may be
substituted for elements thereof without departing from the scope
of the invention. In addition, many modifications may be made to
adapt a particular situation or material to the teachings of the
invention without departing from the essential scope thereof.
Therefore, it is intended that the invention not be limited to the
particular embodiment disclosed as the best or only mode
contemplated for carrying out this invention, but that the
invention will include all embodiments falling within the scope of
the appended claims. Also, in the drawings and the description,
there have been disclosed exemplary embodiments of the invention
and, although specific terms may have been employed, they are
unless otherwise stated used in a generic and descriptive sense
only and not for purposes of limitation, the scope of the invention
therefore not being so limited. Moreover, the use of the terms
first, second, etc. do not denote any order or importance, but
rather the terms first, second, etc. are used to distinguish one
element from another. Furthermore, the use of the terms a, an, etc.
do not denote a limitation of quantity, but rather denote the
presence of at least one of the referenced item.
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