U.S. patent application number 11/276980 was filed with the patent office on 2006-07-13 for combustible gas detection system.
This patent application is currently assigned to Proton Energy Systems, Inc.. Invention is credited to Justin Baltrucki, Edward Demarest, John Koopman, Daniel Rabbett, Andrzej Stanek, Jeffrey Stull.
Application Number | 20060151332 11/276980 |
Document ID | / |
Family ID | 36652175 |
Filed Date | 2006-07-13 |
United States Patent
Application |
20060151332 |
Kind Code |
A1 |
Stull; Jeffrey ; et
al. |
July 13, 2006 |
COMBUSTIBLE GAS DETECTION SYSTEM
Abstract
A system is provided for monitoring the levels of combustible
gas in a gas stream. The system includes means for controlling the
relative humidity of the gas stream and maintain a humidity level
in the performance range of combustible gas sensors. A number of
methods are illustrated for achieving the humidity control
including secondary phase separations and the adjusting of the gas
stream temperature.
Inventors: |
Stull; Jeffrey; (Burlington,
CT) ; Baltrucki; Justin; (Marlborough, CT) ;
Stanek; Andrzej; (Meriden, CT) ; Demarest;
Edward; (Bristol, CT) ; Koopman; John;
(Colchester, CT) ; Rabbett; Daniel; (Ellington,
CT) |
Correspondence
Address: |
PROTON ENERGY SYSTEM
10 TECHNOLOGY DRIVE
WALLINGFORD
CT
06492
US
|
Assignee: |
Proton Energy Systems, Inc.
Wallingford
CT
|
Family ID: |
36652175 |
Appl. No.: |
11/276980 |
Filed: |
March 20, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10707324 |
Dec 5, 2003 |
|
|
|
11276980 |
Mar 20, 2006 |
|
|
|
Current U.S.
Class: |
205/335 ;
205/637 |
Current CPC
Class: |
Y02E 60/50 20130101;
C25B 15/02 20130101; Y02E 60/36 20130101; C25B 9/23 20210101; C25B
1/04 20130101; H01M 8/0656 20130101 |
Class at
Publication: |
205/335 ;
205/637 |
International
Class: |
C25B 1/02 20060101
C25B001/02 |
Claims
1. A system for generating hydrogen gas comprising: an
electrochemical cell stack; a phase separator fluidly coupled to
said electrochemical stack for receiving a water gas mixture; a
vent conduit fluidly connected and extending vertically from the
top of said phase separator; and, a combustible gas sensor coupled
to said vent conduit.
2. The system for generating hydrogen gas of claim 1 wherein said
vent conduit is metallic.
3. The system for generating hydrogen gas of claim 2 wherein said
combustible gas sensor is electrically grounded to said vent
conduit.
4. The system for generating hydrogen gas of claim 3 wherein said
vent conduit further comprises an exhaust outlet.
5. The system for generating hydrogen gas of claim 4 wherein said
combustible gas sensor is positioned adjacent to said exhaust
outlet.
6. A system for generating hydrogen gas comprising: an
electrochemical cell stack having and anode and electrode, said
electrochemical cell stack further having at least one gas outlet
and a means for electrolytically decomposing water to produce
hydrogen gas; a phase separator having a bottom and a top portion
thereon, said phase separator being fluidly coupled to said
electrochemical stack gas outlet for receiving a water gas mixture;
a vent conduit fluidly connected and extending from said phase
separator top portion; and, a catalytic bead type combustible gas
sensor coupled to said vent conduit, said combustible gas sensor
having sensing means for determining the lower explosive limit of
gas within said vent conduit.
7. The system for generating hydrogen gas of claim 6 wherein said
vent conduit comprises a body having a inlet fluidly coupled to
said phase separator top portion, an outlet positioned at a body
first end and perpendicular to said inlet, and a vent slot being
positioned at a body second end opposite said outlet.
8. The system for generating hydrogen gas of claim 7 wherein said
body is comprised of a housing portion mounted to a bracket
portion, said bracket portion having a first and second flange
wherein said body outlet is positioned in said first flange.
9. The system for generating hydrogen gas of claim 8 wherein said
body is made from stainless steel.
10. The system for generating hydrogen gas of claim 7 wherein said
combustible gas sensor is electrically connected to said vent
conduit.
11. The system for generating hydrogen gas of claim 10 wherein said
electrical connection is an electrical ground.
12. The system for generating hydrogen gas of claim 6 wherein said
vent conduit further comprises an exhaust outlet.
13. The system for generating hydrogen gas of claim 12 wherein said
sensing means is positioned adjacent to said exhaust outlet.
14. A system for generating hydrogen gas comprising: a water
conduit; an electrochemical cell stack having an inlet connected to
said water conduit and a gas outlet, said cell stack further having
a membrane electrode assembly comprising an anode and cathode with
a solid membrane arranged in between, said membrane electrode
assembly being arranged to allow electrolytic decomposion of water
received from said water conduit to produce hydrogen gas wherein
said hydrogen exits said gas outlet; a phase separator having an
inlet coupled to said cell stack outlet and a water outlet fluidly
coupled to said water conduit, said phase separator further having
a vent outlet arranged opposite said water outlet; a vent conduit
fluidly connected and extending from said phase separator vent
outlet, said vent conduit having an inlet and an outlet being
arranged perpendicular to said inlet; and, a combustible gas sensor
having a monitoring unit and a sensor unit, said sensor unit being
operably coupled to said vent conduit.
15. The system for generating hydrogen gas of claim 14 wherein said
sensor unit is mounted to said vent conduit opposite said vent
conduit outlet.
16. The system for generating hydrogen gas of claim 15 wherein said
sensor unit is a catalytic bead type sensor.
17. The system for generating hydrogen gas of claim 15 wherein said
vent conduit is comprises: a housing having an opening coupled to
said phase separator vent outlet; and, a bracket coupled to said
housing and having a wall portion positioned opposite to and
generally perpendicular to said housing opening.
18. The system for generating hydrogen gas of claim 17 wherein said
housing has a pair of tabs extending therefrom, and said bracket
has at least one pair of slots sized and positioned to receive said
housing tabs.
19. The system for generating hydrogen gas of claim 18 wherein said
bracket further includes a first and second flange extending
perpendicular to said bracket wall portion, said first and second
flanges being arranged on opposite ends of said bracket.
20. The system for generating hydrogen gas of claim 19 wherein said
first flange has an opening sized to receive said sensor unit.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. patent
application Ser. No. 10/707,324 which was filed on Dec. 5, 2003
FIELD OF THE INVENTION
[0002] This disclosure relates generally to the detection of
combustible gases, and especially relates to the detection of
hydrogen in a vent gas stream.
BACKGROUND OF THE INVENTION
[0003] Hydrogen gas is used and produced in many applications.
Since the amount of hydrogen in a gas stream produced by a given
process may be an indicator of system efficiency, the systems
typically utilize sensors, such as combustible gas sensors to
determine the level of hydrogen. An example of a prior art system
having an arrangement for monitoring combustible gas is shown in
FIG. 1A. The electrochemical system 12 receives water from an
external source 14 and passes it through a deionizing bed 16. Once
the water has been properly conditioned, it is supplied to an
electrochemical cell 18 which disassociates the water into hydrogen
and oxygen gas.
[0004] One example of an electrochemical cell 18 is a proton
exchange membrane electrolysis cell which 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. 1B, which is a partial section of a
typical anode feed electrolysis cell 100, conditioned 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 103 and a portion of the process
water 108 exit cell 100, while protons 106 and water 110 migrate
across a proton exchange membrane 118 to cathode 114. At cathode
114, hydrogen gas 112 is formed and removed. Water is also removed
from cathode 114.
[0005] A typical fuel cell uses the same general configuration as
is shown in FIG. 1B. Hydrogen gas 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. The hydrogen gas for fuel cell operation can
originate from a pure hydrogen source, hydrocarbon, methanol, or
any other hydrogen source that supplies hydrogen at a purity
suitable for fuel cell operation (i.e., a purity that does not
poison the catalyst or interfere with cell operation). Hydrogen gas
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 cathode can
be exploited to power an external load.
[0006] 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.
[0007] After the electrochemical cell 18 disassociates the water,
oxygen and hydrogen gas exit the cell 18 through conduits 20 and 22
respectively. As mentioned herein above, in addition to the gas
products, water entrained in the gases exits with the oxygen and
hydrogen. The hydrogen conduit 22 typically connects with a
hydrogen phase separator 24 which extracts most of the water from
the gas, with the water exiting the phase separator 24 through a
valving arrangement which recycles the water back into the
electrochemical cell water feed conduit. Depending on the needs of
the application, additional water may be removed from the hydrogen
gas by passing through an optional desiccant gas dryer 26 before
exiting the process for use in the application.
[0008] The oxygen gas stream 20 also enters into a phase separator
28 with a majority of the water separating from the gas stream and
dropping to the bottom of the separator 28. As with the hydrogen
separator 24 this water is removed and recycled into the
electrochemical cell water feed conduit. The separated hydrogen gas
exits the phase separator 28 via a conduit 32 to exit the process.
Since it is desirable to monitor for the presence of hydrogen gas
in the oxygen gas stream through an orifice 40 to a combustible gas
sensor 36. A gas dryer 38, such as a NAFION tube dryer, is usually
placed in line between the phase separator 28 and the sensor 36 to
remove water still entrained in the gas. Unfortunately, since the
gas stream can still have a relative humidity greater than 95%.
This high relative humidity results in lower monitoring performance
than is desired.
[0009] Accordingly, what is needed in the art is a system for
monitoring combustible gas levels in a gas stream that reduces or
eliminates the effects of relative humidity on the combustible gas
sensor.
SUMMARY OF INVENTION
[0010] A system for monitoring combustible gas includes a phase
separator having a first outlet, a conduit having an inlet
connected to said phase separator and an exhaust outlet, and a
combustible gas sensor adjacent said exhaust outlet and connected
to said conduit. The combustible gas sensor is generally mounted
perpendicular to either the gas stream exhaust or the gas inlet
exhaust. The conduit is generally made of a metal composition or
from a conductive polymer.
[0011] An alternate embodiment of the system for monitoring
combustible gas includes a bracket having a main body and a first
flange on one end of said body and a second flange on an end of
said body opposite said first flange. A housing is mounted to the
bracket, and the housing has an opening to receive a gas stream. A
combustible gas sensor mounted to the first flange.
[0012] A system for generating hydrogen gas includes an
electrochemical cell stack having a phase separator fluidly coupled
to the electrochemical stack for receiving a water gas mixture. A
vent conduit fluidly connected and extending vertically from the
top of the phase separator, and a combustible gas sensor coupled to
the vent conduit.
BRIEF DESCRIPTION OF DRAWINGS
[0013] Referring now to the drawings, which are meant to be
exemplary and not limiting, and wherein like elements are numbered
alike:
[0014] FIG. 1A is a schematic drawing of an electrochemical system
having a combustible gas detection system used in the prior
art;
[0015] FIG. 1B is a schematic diagram of a partial prior art
electrochemical cell showing an electrochemical reaction;
[0016] FIG. 2 is an illustration of an exemplary embodiment of a
oxygen-water phase separator having a combustable gas detector
incorporated into the gas vent stream;
[0017] FIG. 3 is an illustration of an alternate embodiment of a
combustible gas sensor arrangement;
[0018] FIG. 4 is a simplified cross-section view of the of the
combustible gas sensor arrangement of FIG. 3;
[0019] FIG. 5 is an exploded view of the assembly of the
combustible gas sensor arrangement of FIG. 3.
DETAILED DESCRIPTION
[0020] Hydrogen gas is a versatile material having many uses in
industrial and energy application ranging from the production of
ammonia, to power vehicles being propelled into space. Since the
hydrogen molecule is one of the smallest known particles,
containing and controlling leaks of hydrogen gas is very difficult.
Monitoring of these leaks is important as it is typically an
indicator of performance degradation and or component wear.
Typically, prior art systems have used combustible gas sensors to
monitor levels of combustible gas in the system. When unacceptable
levels of hydrogen are detected in the system, the system is either
shut down, or the operator is alerted that preventative maintenance
is required.
[0021] Commercial combustible gas sensors typically use a
technology referred to as a "catalytic bead" type sensor, such as
the Detcon, Inc. Model FP-524C. These sensors monitor the
percentage of lower explosive limit ("LEL") of combustible gas in a
product gas stream. This LEL measurement represents the percentage
of a combustible gas, such as hydrogen, propane, natural gas, in a
given volume of air. One limitation of catalytic bead sensors is
their sensitivity to moisture in the gas they are monitoring. Once
the gas reaches 95% relative humidity, the ability of the sensor to
detect combustible gas deteriorates resulting in less than
desirable life and reliability. Many hydrogen applications,
including but not limited to electrochemical cells, electrolyzers,
fuel cells and methane steam reformers, also utilize water in their
processes which tends to effect the relative humidity of the
product gas stream being monitored. It should be appreciated that
while the examples described herein typically refer to
electrochemical systems such as electrolyzers or fuel cells, the
present invention can be equally applied in any application where a
combustible gas needs to be monitored.
[0022] Referring to FIGS. 1A and 1B, and electrochemical system 12
of the present invention is shown. Electrochemical cells 18
typically include one or more individual cells arranged in a stack,
with the working fluids directed through the cells within the stack
structure. The cells within the stack are sequentially arranged,
each including a cathode, proton exchange membrane, and an anode
(hereinafter "membrane electrode assembly", or "MEA" 119) as shown
in FIG. 1B. Each cell typically further comprises a first flow
field in fluid communication with the cathode and a second flow
field in fluid communication with the anode. The MEA 119 may be
supported on either or both sides by screen packs or bipolar plates
disposed within the flow fields, and which may be configured to
facilitate membrane hydration and/or fluid movement to and from the
MEA 119.
[0023] Membrane 118 comprises electrolytes that are preferably
solids or gels under the operating conditions of the
electrochemical cell. Useful materials include, for example, proton
conducting ionomers and ion exchange resins. Useful proton
conducting ionomers include complexes comprising an alkali metal
salt, alkali earth metal salt, a protonic acid, a protonic acid
salt or mixtures comprising one or more of the foregoing complexes.
Counter-ions useful in the above salts include halogen ion,
perchloric ion, thiocyanate ion, trifluoromethane sulfonic ion,
borofuoric 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
can be 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 polyoxyalkylenes, 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 polyoxyalkylenesl; and
esters, such as phosphoric acid esters, aliphatic carboxylic acid
esters or aromatic carboxylic acid esters of the above
polyoxyalkylenes. Copolymers of, e.g., polyethylene glycol
monoethyl ether with methacrylic acid 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,
styrene-divinylbenzene-vinylchloride terpolymers, and the like,
that can be imbued with cation-exchange ability by sulfonation, or
can be imbued with anion-exchange ability by chloromethylation
followed by conversion to the corresponding quaternary-amine.
[0025] Fluorocarbon-type ion-exchange resins can include, for
example, hydrates of tetrafluoroethylene-perfluorosulfonyl
ethoxyvinyl ether or tetrafluoroethylene-hydroxylated
(perfluorovinylether) copolymers and the like. When oxidation and
or acid resist is desirable, for instance, at the cathode of a fuel
cell, fluorocarbon-type resins having sulfonic, carboxylic and/or
phosophoric 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.RTM.resins (commercially available from E.I. du Pont de
Nemours and Company, Wilmington, Del.).
[0026] Electrodes 114 and 116 comprise catalyst suitable for
performing the needed electrochemical reaction (i.e. electrolyzing
water to produce hydrogen and oxygen). Suitable electrodes
comprise, but are not limited to, platinum, palladium, rhodium,
carbon, gold, tantalum, tungsten, ruthenium, iridium, osmium, and
the like, as well as alloys and combinations comprising one or more
of the foregoing materials. Electrodes 114 and 116 can be formed on
membrane 118, or may be layered adjacent to, but in contact with or
in ionic communication with, membrane 118.
[0027] Flow field members (not shown) and support membrane 118,
allow the passage of system fluids, and preferably are electrically
conductive, and may be, for example, screen packs or bipolar
plates. The screen packs include one or more layers of perforated
sheets or a woven mesh formed from metal or strands. These screens
typically comprise metals, for example, niobium, zirconium,
tantalum, titanium, carbon steel, stainless steel, nickel, cobalt
and the the like, as well as alloys and combinations comprising one
or more of the foregoing metals. Bipolar plates are commonly porous
structures comprising fibrous carbon, or fibrous carbon impregnated
with polytetrafluoroethylene or PTFE (commercially available under
the trade name TEFLON.RTM. from E.I. du Pont de Nemours and
Company).
[0028] After hydrogen and oxygen have been disassociated from the
water, the hydrogen exits the electrochemical cell 18 as described
herein above via the separator 24 and an optional dryer 26. The
oxygen gas and excess process water exit the electrochemical cell
through a conduit 20 which carries the oxygen and water into a
phase separator 50 and exits the system through exhaust outlet 54.
It should be noted that while the phase separator 50 removes water
from the gas stream, the oxygen gas typically exits the separator
50 in a saturated condition with a relative humidity in excess of
95%.
[0029] Since high relative humidity has undesirable effects, the
present invention addresses these issues by either controlling the
temperature of the gas stream or by controlling the pressure of the
gas stream. Referring to FIGS. 2-5, two different types of
combustible gas sensor arrangements are shown. As will be described
in more detail herein, the arrangement of the gas sensor in
combination with other components reduce the relative humidity of
the sampled gas to increase the performance of combustible gas
measurements.
[0030] The combustible gas ("CG") sensor arrangement utilized by
the prior art is shown in FIG. 1A. In this arrangement, the CG
sensor device 36 includes a CG sensor 42 and a housing 44. The
housing 44 is typically tubular in shape and attaches to the sensor
42 by any convenient means such as a thread (not shown). The CG
sensor 42 also includes a sensing face 43 which detects the levels
of combustible gas, this face 43 is located opposite a housing open
end 46. A gas sample tube 48 is inserted into the open end 46.
During operation, the saturated gas stream 49 exits the sample tube
48 and mixes with the air in the housing allowing some drying of
the saturated gas.
[0031] An exemplary embodiment of the CG sensor of the present
invention is shown in FIG. 2. In this embodiment, the CG sensor 36
is mounted to one end of a vent conduit 52 adjacent a vent exhaust
54. The conduit 52 is vertically connected to above a water-gas
phase separator 50. The separator 50 is a large container which
receives water from an upstream process such as an electrochemical
cell 18 through tubes 56, 58. The separator may also utilize other
components such as filters 60, water lines 62, level sensors 64,
and overflow drain 66.
[0032] In operation, the separator 50 receives the process water
which may contain entrained gases, including oxygen and possibly
combustible gas, from tube 58. As the water mixture enters the
separator 50 it experiences a slight pressure drop causing some of
the water entranced in the stream to condense and drop to the
bottom of the phase separator. The separated water exits via a
conduit 68 to be either recycled back into the process or is
otherwise disposed of. The liberated gases, exit through conduit 52
and exit the system through exhaust outlet 54. As the gas
vertically ascends conduit 52, additional water is separated from
the gas stream through condensation on the side walls of conduit
52. In the preferred embodiment, the conduit 52 is made from a
metal such as stainless steel to enhance the condensation of water
out of the gas. By knowing the operating conditions of the process
and the temperature of the environment, the conduit 52 may be sized
appropriately to dry the gas to desired relative humidity level to
allow the CG sensor 36 to function as desired. A conductive
metallic conduit 52 also provides additional benefit in providing
an electrical ground for the sensor 36. It should be noted that the
electrical grounding provides a further benefit of eliminating a
possible voltage potential between the sensor and the conduit. By
eliminating the voltage potential, the possibility of an electrical
arc forming between the sensor 36 and the conduit 52 is also
eliminated, which is advantageous when operating in an environment
which may contain combustible gases. Alternatively to the metallic
conduit, a conductive polymer could also be used to achieve the
appropriate grounding. The CG sensor 36 being positioned adjacent
and perpendicular to the exhaust port 54 allows the monitoring of
the gas to ensure that any combustible gases present are maintained
at appropriate levels.
[0033] An alternate embodiment of combustible gas sensing
arrangement is shown in FIGS. 3-5. This embodiment comprises a
sensor assembly 70 having a housing 76 secured to a bracket 72 by a
pair of fasteners 90 which thread into corresponding holes 92. A
set of tabs 82 in housing 76 are sized and positioned to fit into
corresponding slots 84 in the bracket 72. To connect the vent
conduit 52 to the assembly 70 a coupling 88 secures the conduit 52
to a hole 86 in the housing 76. The housing 76 further includes
projections 94 on one end which provide for venting of the enclosed
space created by the assembly. To provide for flexibility in
manufacturing of the assembly 70, the bracket 72 includes a first
flange 78 and second flange 79 for the mounting of the CG sensor
42. CG sensors 42 from different manufacturers may be of different
sizes. To accommodate this variation, the CG sensor mounting holes
96 and 97 are of different sizes. To switch from one CG sensor
manufacturer to another simply requires the bracket 72 to be
rotated 180.degree., orienting the flange 79 on top and mounting
the CG sensor 42 to the flange 79. A cable 98 connected to CG
sensor 42 carries signals generated by the sensor 42 to a
monitoring unit 99.
[0034] In this embodiment, which may be preferred in applications
where a vertical conduit is undesirable, the conduit 52 is
connected to a sensor assembly 70 by coupling 88. As best shown in
FIG. 4, the oxygen gas stream enters the assembly 70 through a
housing 76 and impinges on bracket 72. As with the phase separator
50, as the stream enters the assembly 70, it experiences a further
pressure drop which causes the relative humidity to less than 95%.
The dried gas and any water exit through the open bottom portion
74. Due to the mixing of the gas stream within the assembly 70 when
the stream contacts the bracket 72, the CG sensor 36 is able to
monitor for levels of combustible gas. By arranging the sensor
vertically above the entrance of the gas stream, the sensor 42 can
be protected from liquids in the stream and providing a drier gas
for monitoring. Since combustible gases such as hydrogen are
lighter than air, any hydrogen mixed with the oxygen gas stream
will disperse vertically toward the CG sensor 42, to prevent the
accumulation of combustible gases in the assembly 70 which would
result in faulty measurements, a set of vent openings formed
between the housing and the flange 78 by the projections 94
adjacent to the CG sensor 42.
[0035] It should be appreciated that the flanges 78, 79 for
mounting the CG sensor 42 may alternatively be located on the
housing 76. Additional advantages in calibration of the sensor 42
are achieved by positioning the flanges 78, 79 as shown in the
preferred embodiment. CG sensors such as those which are described
herein require a periodic calibration to ensure proper
measurements. These calibration procedures typically involve using
a canister of premixed combustible gas having a predetermined LEL
and introducing the gas to the sensor. For accurate results to be
achieved, the premixed gas must be introduced directly adjacent the
sensor. To calibrate the system as shown in the preferred
embodiment, the user simply needs to remove the housing 76 by
removing bolts 90 without disturbing the CG sensor. The premixed
gas can then be introduced to the sensor 42 without any physical
hindrances to the procedure.
[0036] While preferred embodiments have been shown and described,
various modifications and substitutions may be made thereto without
departing from the spirit and scope of the invention. For example,
while the embodiments shown referred specifically to an
electrochemical system generating hydrogen, this invention would
apply equally to any system where there is a potential for mixing
hydrogen with air or oxygen including, but not limited to
photolysis, fuel cells, steam methane reformers or hydrocarbon
reformers. Accordingly, it is to be understood that the present
invention has been described by way of illustrations and not
limitation.
* * * * *