U.S. patent application number 10/320912 was filed with the patent office on 2004-06-17 for method and system for producing dry gas.
Invention is credited to Murdoch, Karen E..
Application Number | 20040112741 10/320912 |
Document ID | / |
Family ID | 32506990 |
Filed Date | 2004-06-17 |
United States Patent
Application |
20040112741 |
Kind Code |
A1 |
Murdoch, Karen E. |
June 17, 2004 |
Method and system for producing dry gas
Abstract
A system and method for producing dry gas, such as methane or
carbon dioxide, incorporates an electrochemical device that removes
water and hydrogen from a mixed gas stream. The electrochemical
device uses one electrochemical cell to strip hydrogen and water
from the mixed gas stream and a second electrochemical cell,
combined with a dry feed stream, to remove any residual water from
the mixed stream and produce pure, dry gas.
Inventors: |
Murdoch, Karen E.; (Broad
Brook, CT) |
Correspondence
Address: |
CARLSON, GASKEY & OLDS, P.C.
400 WEST MAPLE ROAD
SUITE 350
BIRMINGHAM
MI
48009
US
|
Family ID: |
32506990 |
Appl. No.: |
10/320912 |
Filed: |
December 17, 2002 |
Current U.S.
Class: |
204/265 ;
204/266; 205/462; 205/555 |
Current CPC
Class: |
B01D 53/26 20130101;
C07C 1/12 20130101; B01D 53/326 20130101; C07C 1/12 20130101; C07C
9/04 20130101 |
Class at
Publication: |
204/265 ;
204/266; 205/462; 205/555 |
International
Class: |
C25B 003/00 |
Claims
What is claimed is:
1. An electrochemical device for a gas production system,
comprising: a first electrochemical cell that receives a mixed gas
stream containing at least a desired gas, hydrogen and water,
wherein the first electrochemical cell removes at least a portion
of the water from the mixed gas stream to form a mixed gas stream
having residual water; and a second electrochemical cell that
receives the mixed gas stream and a dry feed stream, wherein the
second electrochemical cell removes the residual water from the
mixed gas stream and wherein the dry feed stream absorbs the
residual water to obtain the desired gas.
2. The electrochemical device of claim 1, wherein the dry feed
stream is hydrogen.
3. The electrochemical device of claim 1, wherein the first
electrochemical cell removes the hydrogen from the mixed gas stream
along with said at least a portion of the water.
4. The electrochemical device of claim 1, wherein the
electrochemical device feeds the mixed gas stream on an anode side
of the second electrochemical cell and feeds the dry feed stream on
a cathode side of the second electrochemical cell.
5. The electrochemical device of claim 1, further comprising a
third electrochemical cell that receives the dry feed stream after
the dry feed stream has absorbed the residual water from the mixed
gas stream, wherein the third electrochemical cell outputs the dry
feed stream and the residual water in a metered fashion.
6. The electrochemical device of claim 1, wherein the desired gas
is one selected from the group consisting of methane and carbon
dioxide.
7. A methane production system, comprising: an electrolyzer that
receives a first stream containing carbon dioxide and water and
outputs a second stream containing carbon dioxide and hydrogen; a
Sabatier reactor that receives the second stream from the
electrolyzer and outputs a methane stream containing methane,
hydrogen and water; and an electrochemical device comprising a
first electrochemical cell that receives the methane stream,
wherein the first electrochemical cell removes at least a portion
of the water from the methane stream having residual water, and a
second electrochemical cell that receives the methane stream and a
dry feed stream, wherein the second electrochemical cell removes
the residual water from the methane stream and wherein the dry feed
stream absorbs the residual water.
8. The methane production system of claim 7, wherein the
electrochemical device feeds the methane stream on an anode side of
the second electrochemical cell and feeds the dry feed stream on a
cathode side of the second electrochemical cell.
9. The methane production system of claim 7, further comprising a
third electrochemical cell that receives the dry feed stream after
the dry feed stream has absorbed the residual water, wherein the
third electrochemical cell outputs the dry feed stream and the
residual water in a metered fashion to the electrolyzer.
10. A method for producing a dry desired gas, comprising: obtaining
a mixed gas stream containing the desired gas, hydrogen and water;
feeding the mixed gas stream and a dry feed stream into an
electrochemical device; removing the hydrogen and the water from
the mixed gas stream via the electrochemical device, wherein the
dry feed stream absorbs at least a portion of the water from the
mixed gas stream to produce the dry desired gas.
11. The method of claim 10, wherein the electrochemical device
comprises a first electrochemical cell and a second electrochemical
cell, and wherein the removing step comprises: removing at least a
portion of the water from the mixed gas stream via the first
electrochemical cell to form a gas stream having residual water;
sending the gas stream having residual water and the dry feed
stream to the second electrochemical cell, wherein the dry feed
stream absorbs the residual water to produce the dry desired
gas.
12. The method of claim 10, further comprising directing the dry
feed stream to an electrolyzer after the dry feed stream has
absorbed the residual water.
Description
TECHNICAL FIELD
[0001] The invention relates to methane gas production, and more
particularly to a system and method that obtains pure, dry gas by
removing hydrogen and water from a mixed gas stream.
BACKGROUND OF THE INVENTION
[0002] Sabatier reactors are known in the art for converting carbon
dioxide (CO2) and hydrogen (H2) into methane (CH4) and water (H2O).
These reactors can be used to obtain pure methane for use in other
applications, such as fuel. Known methane production systems
include an electrolyzer, which separates water into gaseous
hydrogen and oxygen, a Sabatier reactor that receives the carbon
dioxide, carbon monoxide, hydrogen and water and converts them into
methane and water, forming a "wet" methane stream, where methane
gas is intermingled with water vapor. Excess hydrogen left over
from the Sabatier reaction may also be mixed into the wet methane
stream.
[0003] Although an electrochemical separator can be used to easily
remove the excess hydrogen from the wet methane stream, it is
difficult to completely remove the residual water from the stream.
Currently known water pumps remove less than all of the water from
the stream and do not produce pure, dry methane as a final product.
If the methane will later be cooled in a liquefaction process, any
residual water will form undesirable ice crystals before the
methane gas condenses to liquid. Thus, any methane gas to be
liquefied in a later process must be absolutely dry, with no
residual water. Currently known systems, however, have been able to
remove only a portion of the water from the methane gas stream.
Other gas production systems (e.g., carbon dioxide gas production
systems) encounter similar difficulties in forming a completely
pure, dry gas.
[0004] There is a desire for a gas production system that can
produce pure, dry gas.
SUMMARY OF THE INVENTION
[0005] The present invention is directed to a system and method
that removes water from a mixed gas stream containing a desired
gas, hydrogen, and water via an inventive electrochemical device
acting as a pump and a separator that removes both excess hydrogen
and water from the stream. In one embodiment, the electrochemical
device includes two electrochemical cells. Hydrogen and water are
removed from the mixed gas stream as the stream passes through the
first electrochemical cell. As the mixed gas stream passes the
anode of the second electrochemical cell, a dry feed stream, such
as a hydrogen stream, is fed to the cathode side of the second
electrochemical cell. The dry feed stream creates a partial
pressure differential with respect to the mixed gas stream, causing
the dry feed stream to absorb any residual water from the mixed gas
stream. Further, the potential applied across the second
electrochemical cell prevents any portion of the dry feed stream
from diffusing into the mixed gas stream. As a result, the gas
stream that is output from the second electrochemical cell is pure,
dry gas, with virtually no water mixed into the desired gas.
[0006] An alternative embodiment incorporates a third
electrochemical cell that act as metering device to send the dry
feed gas stream back to the electrolyzer after the stream has
absorbed excess water from the mixed gas stream. The third
electrochemical cell can be controlled to feed the feed hydrogen in
a metered fashion as needed to maintain sufficient reduction of
carbon dioxide in a methanation reactor.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] FIG. 1 is a block diagram illustrating a gas production
system incorporating an electrochemical pump and separator device
according to one embodiment of the invention; and
[0008] FIG. 2 is a representative diagram of the electrochemical
device used in the system shown in FIG. 1.
DETAILED DESCRIPTION OF THE EMBODIMENTS
[0009] FIG. 1 illustrates one embodiment of an overall gas
production system 100 that incorporates a novel electrochemical
device to obtain pure, dry gas. Note that although the example
described below focuses on removing hydrogen and water from a wet
methane stream, the invention can be applied to any gas production
system requiring removal of water and hydrogen from a mixed gas
stream.
[0010] In the example shown in FIG. 1, the system 100 includes an
electrolyzer 102, a Sabatier reactor 104, and an electrochemical
device 106 that acts as a water pump and a hydrogen separator. To
produce methane, a stream 108 containing carbon dioxide, hydrogen
gas, and water is fed into the electrolyzer 102. As is known in the
art, the electrolyzer 102 separates the water into hydrogen and
oxygen gases. The oxygen gas is then output from the electrolyzer
102 as a separate product that may be captured and used in a
separate application.
[0011] In addition to outputting oxygen, the electrolyzer 102 sends
carbon dioxide, carbon monoxide, hydrogen and water to the Sabatier
reactor 104. The Sabatier reactor 104 reduces the hydrogen and
carbon dioxide into methane gas and water vapor. Extra hydrogen may
be sent to the Sabatier reactor 104 to ensure that all of the
carbon dioxide it receives is converted to methane. Any excess,
unconverted water from the electrolyzer 102 is fed to the Sabatier
reactor 104 along with the hydrogen and carbon dioxide.
[0012] Once the carbon dioxide has been converted to methane and
water, the methane, water and any excess hydrogen gas is sent as a
wet methane stream 110 to the electrochemical device 106. The
device 106 acts as both a water pump and a hydrogen separator. As
is known in the art, the excess hydrogen can be easily separated
from the stream using an electrochemical cell because there is a
direct relationship between current and the number of protons
pumped through the electrochemical cell.
[0013] To remove excess water from the wet methane stream 110, the
electrochemical device 106 incorporates a second electrochemical
cell that acts as a pump to send the water in the stream 110 into a
dry hydrogen feed stream 112 via a partial pressure differential
between the two streams 110, 112. The dry hydrogen feed stream 112
is supplied from a separate hydrogen gas source (not shown).
[0014] FIG. 2 illustrates one embodiment of the electrochemical
device 106 and the flow path of the wet methane stream 110 in more
detail. As noted above, the device 106 receives a wet methane
stream 110 containing methane, hydrogen, and water from the
Sabatier reactor 104. The wet methane stream 110 is introduced to
an anode of a first electrochemical cell 200. The cell voltage
applied to the first electrochemical cell 200 is kept at a level
that is sufficient to move protons through the cell 110 while still
low enough to avoid electrolyzing the water in the methane stream
110. This first electrochemical cell 200 will be able to transfer
some of the water and virtually all of the hydrogen in the methane
stream 110 to the cathode of the cell 200, but the methane stream
110 may still contain significant amounts of remaining water that
need to be removed to obtain pure, dry methane. The residual water
occurs when there is too much water in the methane stream 110
relative to the hydrogen protons needed to carry the water away
from the stream 110. In some cases, the methane stream 110 may
still contain as much as 10% hydrogen and 50-100% water
saturation.
[0015] After being sent past the first electrochemical cell 200,
the methane stream 110 is diverted to the anode side of a second
electrochemical cell 202. Dry hydrogen gas is sent to the device
106 as a feed stream 112 on the cathode of the second cell 202.
When a potential is applied across the second cell 202, any
remaining hydrogen in the methane stream 110 is pumped to the
cathode of the second cell 202 along with more of the water vapor
from the methane stream 110. The dry hydrogen feed stream 112 on
the cathode of the second cell 202 helps remove even more water
from the methane stream 110 by creating a partial water pressure
differential between the hydrogen feed stream 112 and the methane
stream 110. More particularly, water molecules in the wet methane
stream 110 will be pulled by protons in the hydrogen feed stream
112, drawing water molecules away from the methane stream 110.
[0016] The potential applied across the second cell 202 prevents
hydrogen from the hydrogen feed stream 112 from diffusing into the
methane stream 110 as the hydrogen feed stream 112 absorbs the
excess water from the methane stream 110 by driving protons back to
the hydrogen feed stream 112. Once the excess water has been
removed from the methane stream 110 in the second cell 202, pure,
dry methane gas 114 is output from the device 106.
[0017] The hydrogen feed stream 112, which has now absorbed water
from the methane stream 112, is routed to a third electrochemical
cell 204. The current through the third cell 204 is controlled via
any known manner so that the third cell 204 acts as a metering
device, outputting controlled amounts of hydrogen and water to the
electrolyzer 102. This information is used to control the rate at
which hydrogen is generated in the electrolyzer 102. As a result,
the moisture in the hydrogen/water feed stream 112 sent to the
electrolyzer 102 allows control over the moisture content in the
hydrogen electrolyte.
[0018] The inventive system and method therefore provides higher
water removal efficiency than currently known systems by
incorporating additional at least one additional electrochemical
cell and a dry feed gas to extract additional water from a mixed
gas stream via partial pressure driving force. By sending the mixed
gas stream, such as a wet methane stream, through more than one
drying stage, the inventive system can generate a pure, dry desired
gas without adding undue complexity to the system. Further, by
recycling the dry feed gas after it has absorbed water from the
mixed gas stream and sending it back to the electrolyzer in the
system, the system can use the output of the electrochemical device
to maintain the moisture level in the electrolyzer. Regardless of
the type of gas sent through the inventive system, an
electrochemical device according to the present invention can
reliably remove excess water and hydrogen from a mixed gas stream
containing the desired gas.
[0019] It should be understood that various alternatives to the
embodiments of the invention described herein may be employed in
practicing the invention. It is intended that the following claims
define the scope of the invention and that the method and apparatus
within the scope of these claims and their equivalents be covered
thereby.
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