Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
131~277
- PALLADIUM ALLOY AS CATALYST_FOR THE OXIDATION OF
HYDROGEN IN AN ATMOSPHERE CONTAINING HYDROGEN AIID OXYGEN
BACKGROUND OF THE INVENTION
-
5 1. Field of the Invention
-
The present invention relates to a palladium
alloy, which serves as a catalyst for the oxidation of
hydrogen in an atmosphere containing hydrogen and oxygen,
and moreover, relates to a safety installation for the
10 receiving of the palladium alloy.
The removal of hydrogen from a gas mixture which
contains hydrogen and oxygen and which, as a consequence
thereof, is explosive in nature, is of particular
significance with regard to nuclear reactor accidents. Such
15 gas mixtures can be encountered, above all, during core
melt-down accidents in light-water reactors.
2. Discussion of the Prior Art
For the removal of hydrogen from the atmosphere of
a safety containment for a nuclear reactor, it is known to
20 exhaust or suction off the gas mixture, and to convert or
decompose the latter externally of the safety containment with
copper oxide CuO2 at a temperature of 200C; as described by
W. Baukal, et al. "Moglichkeiten zur
Wasserstoffbeseitigung", BMI-1984-033, 1984. This procedure
25 is designated as the "non-reversible method", inasmuch as
the copper which is formed during the reaction must be - -
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13~427~
-2- 70577-55
replaced. Moreover, it is also considered to be a prerequisite
that, for the suctioning off of the hydrogen, energy must be
available for the operation of pumps.
It is also known from the publication by L. Thompson,
"Program Plan for ERRI Hydrogen Combustion and Control Studies",
ERRI, Palo Alto, November 1981; and from M. Berman, et al.,
"Hydrogen Behavior and Light-Water-Reactors", Nuclear Safety,
Vol. 25, No. 1, l984, to initiate a controlled ignition of the
gas mixture within the safety containment. For this purpose,
it is known to employ platinum as the catalyst in order to
initiate the ignition within a time interval of 20 seconds to
400 seconds in particular dependence upon the hydrogen and steam
concentration in the gas mixture, upon the velocity of the gas,
and upon the gas temperature; for instance, as described by L. R.
Thorne, et al., "Platinum Catalytic Igniters for Lean Hydrogen-
Air Mixtures", NRC FIN No. A-1336 (DOE 40-550-75), 1986. However,
the subsequent or secondary reactions which result from such
measures and the encountered forces acting on the safety con-
tainment are not yet clearly explained. In particular, the
occasionally higher than expected speed of propagation of the
flame front which is produced through turbulences in the gas
mixture, and the resultingly encountered danger of a detonation,
are viewed as being critical in nature.
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70577-55
In Canadian Patent Application Serial No. 529,438
(now Patent No. 1,271,619), which is assigned to the
Kernforschungsanlage Julich GmbH, Julich, West Germany, there
is described an arrangement for the removal of hydrogen which
is insertable into a safety container in which metals are
inserted for the take-up or absorption of the hydrogen, which
possess a high absorptive capacity for hydrogen even under a
low partial pressure of hydrogen in the gas mixture. In order
to prevent oxidizing, the metals are coated with a hydrogen-
permeable protective layer. As a protective layer, there is
also utilized palladium. Palladium-coated vanadium has
evidenced itself as being a catalyst for an effective
conversion of the hydxogen into water.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention
to find catalysts possessing the shortest possible response
time up to the initiation of the catalytic reaction.
Consequently, it i5 an intent to develop catalysts which react
insensitively with regard to catalyst toxicants, such as
chlorine, sulfur and carbon monoxide, in the gas mixture. The
catalytic conversion should also be as high as possible even
under temperatures at about 100C, in order to safely avoid any
oxyhydroge~n gas reactions within the safety containment.
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According to the invention, there is provided a
novel palladium alloy for the use of the above-mentioned purpose.
The palladium alloy contains at least 80% by weight of palladium,
a maximum of up to 19.9% by weight of a further metal of the
Group VIII of the Periodic System, especially nickel, and a
maximum of 10% by weight of copper. By means of palladium alloys
of this type, hydrogen is oxidized on the surface of the alloys
in the presence of oxygen in the gas mixture at temperatures at
about 100C. The response period up to the beginning of the
reaction, due to the toxicity of catalyst poisons, such as chlo-
rine, sulfur or carbon monoxide which are often present in the
gas atmosphere, is only a few minutes. It has been ascertained
that Pd-Ni-Cu alloys by far exceed the catalytic behavior or
activity of pure palladium under a gas atmosphere such as may be
realistically expected to be encountered during reactor accidents.
Minimum values should be maintained for the contents of Ni and
Cu; 1% by weight for Ni, and 0.1% by weight for Cu.
Preferably adapted are palladium alloys with at
least 89% by weight of Pd, a maximum of 10% by weight of Ni and
a maximum of 1% by weight of Cu. Found as being particularly
suitable has been an alloy with about 95% by weight of Pd, about
4% by weight of Ni and about 1% by weight of Cu. Alloys of
this type catalyze, with only a short delay, the oxidation of
hydrogen in gas mixtures which contain chlorine
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1 and sulfur compounds and carbon monoxide. The reactions
take place in a dependable manner.
In order to be able to absorb and then to conduct
off the heat which is produced during the catalytic
5 oxidation of the hydrogen, it is contemplated, pursuant to
further features of the invention, to apply the palladium
alloy on either one or both sides of a carrier plate or foil
which absorbs the heat of the reaction. Especially adapted
as the material for the carrier plate or foil is aluminum or
10 an aluminum alloy, or copper or a copper alloy.
For the utilization of the palladium alloy in a
safety installation for the catalytic oxidation of hydrogen,
pursuant to a further feature of the invention there is
provided a gas-tightly sealed catalyst chamber, which
15 contains a foil or a lattice, such as a meshwork,
constituted from the palladium alloy, or a metallic
substrate, such as a carrier plate or sheet which is coated
with the palladium alloy. The foil or lattice or carrier
~ plate is arranged within the catalyst~chamber in such a
20 manner, that upon the opening of the chamber in the case of
danger; in effect, when hydrogen penetrates into the oxygen-
containing gas atmosphere which surrounds the catalyst
chamber, it comes into contact with the gas atmosphere. In
order to avoid an ignition of the gas mixture upon coming
into contact with the gas atmosph~re, the entire catalyst
surface which stands available in the case of danger is so
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~ 31427~
1 configured, that the foil, lattice or carrier plate upon its
heating during the reaction is not heated to such an extent
through the absorption of the heat of the reaction so as to
cause the ignition temperature of the gas mixture to be
5 reached on the surface of the catalyst. A limiting
temperature is determined for the catalyst surface, which
temperature is located below the ignition temperature, and
the minimum surface of the foil or lattice or carrier plate
or rod or net provided for this purpose determines through
consideration, on one hand, of the expected quantity of
hydrogen, which can maximally penetrate into the gas atmo-
sphere and which prescribes the maximally developing reac-
tion heat; as well as, on the other hand, through consider-
ation of the possible emission of heat of the foil, lattice
or carrier plate to the environment whereby, the transfer
of heat between the catalyst surface and the gas atmosphere
is especially significant.
The foil, or lattice or the carrier plate are
preferably arranged in such a manner within the catalyst
20 chamber that they will extend into the surroundings upon the
opening of the catalyst chamber and thereby form a contact
surface. This is expediently provided under the action of
gravity such that, in the case of danger, no auxiliary
devices are necessary for the formation of the contact
surface. For this purpose, the foil, lattice or carrier
plate are folded within the catalyst chamber in a jalousie
or venetian blind-like manner, and are arranged so that
131~2~7
1 upon the opening of the safety container they will unfold
under the effect of gravity and rapidly extend into the
surroundlngs.
Independently of gravity, the foil or lattice or
5 carrier plate are also automatically extendable into the
surroundings without the use of auxiliary devices when they
are arranged wound like a roller shade and prestressed in
the interior of the catalyst chamber, such that after
opening of the catalyst chamber they will roll out into the --
10 surroundings under the action of a spring biasing force.
BRIEF DESCRIPTION OF THE DRAWINGS
-
Reference may now be had to the following detailed
description of further advantages and features of the
invention; illustrated on the basis of exemplary
15 embodiments, and taken in conjunction with the accompanying
drawings; in which~
Figure l generally illustrates the pressure
development in a reaction chamber with the catalytic
oxidation of hydrogen on a palladium alloy with a content of
95% by weight of palladium, 4% by weight of nickel, and 1%
by weight of copper; as well as the thereby encountered
temperature development in an aluminum carrier plate which
is coated on both sides thereof with the palladium alloy,
and the temperature development in the surroundings about
the carrier plate;
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1 Figure 2 graphically illustrates the pressure and
temperature developments as in Fig. l with catalytic
oxidation on a palladium alloy with a content of 90~ by
weight of palladium, 9.5% by weight of nickel, and 0.5% by
5 weight of copper;
Figures 3a and 3b rep~esent a tabulation of
various embodiments of the invention;
Figure 4 illustrates a perspective view of a
catalyst chamber with folded foil or carrier plate;
Eigures 5a and 5b respectively illustrate a
perspective longitudinal side view and transverse sectional
view of a catalyst chamber with a roller shade-like
tensioned foil or carrier plate;
Figure 6 graphically illustrates the minimum
15 catalyst surface in dependence upon the maximum
temperature in the foil or carrier plate.
DETAILED DESCRIPTION
EXAMPLE 1
Investigated in a reaction chamber is the
20 catalytic action of a palladium alloy which contains 95% by
weight of Pd, 4~ by weight of Ni, and 1% by weight of Cu,
and which is applied on both sides of a carrier plate which
is constituted from aluminum; in which chamber there is
introduceable a gas mixture which is correlatable with
realistic conditions encountered during reactor accidents.
In the reaction chamber there are presently arranged one or
~ 31~27~
1 more carrier plates with an exposed-remaining coated surface
in a manner whereby the two coated surfaces were accessible
to the gas mixture which is contained in the reaction
chamber. In total, pursuant to Example I, in the reaction
5 chamber which possessed a volume of 6.5 liters, there were
present carrier plates with an overall surface of 240 cm2
for the catalysis.
In Fig. 1 there is represented the pressure
distribution in the reaction chamber (identified by curve
10 plot I) after the introduction of hydrogen into a gas
atmosphere, which in partial pressures contained 1.3 bar
air, 1.6 bar steam, and 0.007 bar of C0. Into this gas
atmosphere there was introduced 0.4 bar of H2.
In addition thereto, in Fig. 1 there is also
15 represented the temperature development in the coated
carrier plate (the phantom-line curve plot II), as well as
the temperature development of the
coated carrier plate in the reaction chamber, in effect,
again represented the room temperature of the reaction
20 chamber (the dash-dot curve plot III).
After the introduction of the hydrogen into the
gas atmosphere, there initially reigns a pressure of above
3.3 bar in the reaction chamber. As a result of the
initiating catalytic oxidation of the hydrogen, the pressure
25 then dropped within the about first 3.5 minutes to a
pressure of about 3.15 bar. Thereafter, the pressure
1314277
1 remained constant, from which it is ascertainable that the
oxidation reaction was already essentially closed off after
this time interval and the hydrogen was presently bound into
water vapor or steam.
During the same time interval, the temperature in
the carrier plate increases within 1 minute from initially
120C up to a maximum temperature of 260C. The temperature
again rapidly attenuates after reaching this maximum
temperature. After 4 minutes the carrier plate again
10 reaches the initial temperature of 120C.
The fact that the heat which is produced during
the catalysis could be almost completely absorbed by the
carrier plate and then conducted off, is evidenced by the
slight temperature shading in the surroundings of the coated
15 carrier plates in the reaction chamber; in effect, the
temperature in the reaction chamber rose from 120C after
introduction of the hydrogen during the catalytic reaction
up to a maximum of 140C. This maximum temperature in the
reaction chamber was reached 2 minutes after the
20 commencement of the reaction. Thereafter the heat shading
in the reaction chamber attenuated again to its initial
value.
EXAMPEE 2
In Fig. 2 there is represented the reaction
cycle for a catalytic oxidation of hydrogen for a palladium
alloy which contains 90% by weight of Pd, 9.5~ by weight of
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1 Ni, and 0.5% by weight of Cu. The palladium alloy is
sputtered onto both sides of a carrier plate which is
constituted from aluminum. The carrier plate is O.l mm
thick. A total of 80 cm2 catalytic surface area is
5 available for the catalysis.
Also represented in Fig. 2, in the same manner as
in Fig. l, is the pressure development in the reaction
chamber, as well as the temperature development in the
carrier plate; reference numeral I representing the curve
10 plot for the pressure develGpment in the reaction chamber,
and reference numeral II the temperature development in the
carrier plate. In Fig. 2, the temperature development in
- the surroundings of the carrier plate is not represented;
however, the heat shading in the reaction chamber, in this
15 instance also minor. The heat which is produced during the
catalysis is absorbed by the carrier plate and conducted
off.
In the exemplary embodiment pursuant to Fig. 2,
the reaction chamber contained a gas atmosphere with the
following gas components (given in partial pressures):
air at 1.3 bar, water vapor or steam at 1.6 bar, C0 at 0.005
bar. Into this gas atmosphere there was introduced hydrogen
at 0.4 bar.
As in the example of Fig. l, in the palladium
alloy employed herein, the catalytic reaction also takes
place immediately after the introduction of the hydrogen
13142~7
1 into the gas atmosphere. With an increasing pressure in the
reaction chamber at the addition of the hydrogen, there also
increases the temperature in the carrier plate. The
catalytic oxidation of the hydrogen leads to a pressure
5 drop-off, the pressure in the reaction chamber falls from
about 3.4 to 3.1 bar. The temperature in the carrier plate
increases rapidly commencing from 120C, and rises within
the first minute up to about a maximum of about 240C.
Thereafter it again drops, and after already 3 minutes again
10 reaches its initial value of 120C. The hydrogen is
completely converted into steam.
On the basis of these investigations, for suitable
alloys there was only determined the commencement of the
oxidation reaction; in effect~ the time at which there took
15 place a temperature rise in the carrier plate through the
absorption of the heat of the reaction.
EXAMPLE 3
A palladium alloy with a content of 90% by weight
of Pd, 9.5% by weight of Ni, and 0.5% by weight of Cu was
20 employed in the form of a sheet (rolled-out foil). A
separate carrier plate was not employed. The dimensions of
the foil consisted of 200 x 20 x 0.1 mm3. In the reaction
chamber possessing a volume of 6~5 liters there was
available a total of 80 cm2 of catalyst surface area.
Contained in the reaction chamber was a gas
mixture with 1.3 bar air, 0.005 bar CO, and 1.6 bar steam.
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In addition thereto, the gas atmosphere was contaminated with
traces of contaminants of chlorine, sulfur, phosphorus, iodine,
water-soluble aerosols (silver and boron nitrate) and oil, so
as to create the possibly most unsatisfactory condition of the
gas atmosphere for the catalytic reaction, such as could be
encountered in the reactor safety containment during reactor
accidents. The initial temperature in the foil consisted of
120C
Introduced into the reaction chamber were 0.4 bar
H2. The catalytic action of the palladium alloy commenced in
the absence of any noticeable delay, the temperature rise in the
foil began spontaneously. The temperature in the Pd-foil rose
to a maximum of 500C.
EXAMPLE 4
The palladium alloy described in Example 3, with a
content of 90% by weight of Pd, 9.5% by weight of Ni and 0.5%
by weight of Cu, was applied onto a carrier plate constituted of
aluminum.
Introduced into the reactor chamber were carrier
plates with a catalytically-effective total surface of 120 cm2.
A gas atmosphere reigned which contained 1.6 bar oE air, and
0.005 bar of carbon monoxide. Introduced into this gas
atmosphere were 0.4 bar of H2. The initial temperature in the
carrier plate was 120C.
The pressure drop-off and the temperature rise
commenced after 1 minute. The temperature in the carrier plate
rose to a maximum of 325C.
` 1'~1~ 2 7 ~
1 EXAMPLE 5
A palladium alloy consisting of 94% by weight of
Pd, 5% by weight of Ni and l~ by weight of Cu was vapor
deposited onto both sides of a carrier plate constituted of
5 aluminum. The thickness of the palladium alloy on both
sides of the carrier plate was 3000 A. A carrier plate
evidenced the following dimensions: 200 x 30 x O.l mm3. In
this exemplary embodiment, in the reaction chamber there was ~~
available a total of 240 cm of catalyst surface area. It
10 is self-understood that the catalytic reation would take
place the more rapidly the greater the catal~st surface
which is inserted into the reaction chamber. However, it is
important for the determination of the catalyst surface,
its maximum permissible heating up to the pregiven limiting
15 temperature below the temperature of the ignition for the
gas mixture. Inasmuch as, for this purpose, there is
decisive the heat transfer from the foil or the carrier
plate to the surroundings, this then relates to the given
specific heat transfer, (heat-transfer coefficient in
20 J/m2Ks). In order to achieve a high degree of safety, it is
consequently intended to afford the gas atmosphere in the
reactor safety containment, in the case of any accident,
the greatest amount catalyst surface and this as rapidly as
possible.
In this exemplary embodiment, the gas atmosphere
contained in the reaction chamber possessed the following
2 7 ~
1 composition in partial pressures: air 1.3 bar, steam 1.6
bar, and C0 0.007 bar. The initial temperature in the
carrier plate consisted of 120C. Introduced into the
reaction chamber were 0.4 bar of H2.
The catalytic reaction commenced without any
noticeable delay, the maximum temperature in the carrier
plate was 280C.
EXAMPLE 6
A palladium alloy with a content of 94% by weight
10 of Pd, 5% by weight of Ni, and 1~ by weight of Cu. was
applied onto both sides of a carrier plate constituted of
aluminum and possessing a dimension of 145 x 28 x 0.1 mm3.
Inserted into the reaction chamber were carrier plates with
a catalyst surface area of a total of 180 cm2. The gas
15 atmosphere which was present in the reaction chamber
evidenced the following gas components in partial pressures:
air 1.3 bar, steam 1.6 bar, C0 0.006 bar. The initial
temperature in the carrier plate consisted of 120C.
Introduced were 0.4 bar of H2.
The reaction commenced spontaneously, the maximum
temperature in the carrier plate consisted of 305~C.
EXAMPLE 7
A palladium alloy with a content of 95% by weight
of Pd, 4~ by weight of Ni, and 1% by weight of Cu were
25 vapor-deposited onto both sides of a carrier plate
constituted of copper. Available in the reaction chamber
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1 were 240 cm2 of catalyst surface area. Introduced into the
air atmosphere of 1.9 bar present in the chamber were 0.08
bar of hydrogen (4% by volume). The initial temperature in
the carrier plate was about 100C.
Notwithstanding the lower hydrogen concentration,
also in this instance there commenced the reaction
immediately after the introduction of the hydrogen; the
maximum temperature in the carrier plate was 130C.
The essential data of the above-mentioned
10 exemplary embodiment 1 through 9 are elucidated in tabular
form in Figs. 3a and 3b.
Referring now to Fig. 4, there is generally
diagrammatically illustrated a gas-tightly sealed catalyst
chamber 1 with a jalousie or venetian blind-like folded
carrier plate 2, the latter of which is coated with a
palladium alloy. The catalyst chamber is arranged with its
ceiling or cover wall 3 being hangingly suspended from a
support 4. On the cover wall 3, in two chamber spaces la,
lb which are separated by a partition wall 5, there are
20 presently fastened the uppermost foil or plate components 2a
of the carrier plate along one edge 6. The support 4 can be
anchorPd, for example, on the ceiling or cover of the
reactor safety container in such a manner that an open space
remains below the catalyst chamber 1 for the extension of
the carrier plate 2 after the opening of the catalyst
chamber.
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1 The catalyst chamber l is constituted of aluminum
walls 7, which are soft-soldered to the cover wall 3 and
with each other. The soft solder is so selected that the
catalyst chamber will open at the encountering of a
5 pregiven temperature in the case of danger, through the
softening of the connecting seams along the aluminum wall 7
and the falling apart of the walls, and thereby release the
carrier plate 2. The carrier plate then extends under its
.. ..~ ~,
own weight into the space below the catalyst chamber l. The
10 catalyst surface is brought into contact with the gas
atmosphere.
In the illustrated embodiment, the carrier plate 2
is inserted merely folded into the catalyst chamber. Should
there be produced the most possibly planar or flat, rapidly
15 unfolding surface, then it is expedient to interconnect the
individual carrier plates along their edges through the
intermediary of hinges, such that the joined-together
carrier plates are easily movable with respect to each
other. Carrier plates which are lnterconnected by means of
20 hinges are not illustrated in Fig. 4.
In Fig. 5 of the drawings there i5 illustrated a
drum-shaped catalyst chamber 8, in which a carrier plate or
foil 9 which is coated with a palladium alloy is rolled
up roller shade-like onto a shaft lO which is pretensioned
25 by a coil spring. After the opening of one bottom flap ll
which, in the same manner as in the exemplary embodiment
~0
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131~2~7
1 pursuant to Fig. 4 is soft soldered in the drum-shaped
catalyst chamber 8, the carrier plate 9 will unroll under
the action of the spring force into the surroundings, and
release the catalyst surface for contact with the gas
5 atmosphere which is produced in the reactor safety
container. The catalytic oxidation of the hydrogen then
commences within a few minutes.
Both catalyst chambers 1 and 8 are filled with an
inert gas in the closed conditions thereof; for example,
10 with Argon. The inert gas stands under a super-
atmospheric pressure in order to prevent the penetration of
foreign gas from the external space. In order to be able to
maintain with assurance the catalytic quality of the
palladium alloy over a lengthier period of time, the inert
15 gas-atmosphere possesses 1 to 2~ by volume of hydrogen.
In the catalyst chambers which are illustrated in
- Figs. 4 and 5, instead of carrier plates which are coated
with palladium alloys, there can also be utilizable sheets
or lattices or meshes of palladium alloys, for example,
20 which are rolled out into foils. When foils are employed,
then for their extension into the surroundings provision is
made, for example, through the application of a bar
weighting the foil along the outer edge of the foil, which
will drop down first upon the opening of the catalyst
chamber. A bar 12 of this type is illustrated in Fig. 5.
3~
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1 In Fig. 6, for a reactor safety containment with a
total volume of 80,000 m3, there i5 given the necessary
catalyst surface with the following assumptions:
1.) streaming into the reactor safety containment,
5 in the case of a reactor accident, within a period of 1000
seconds (16.6 minutes) are 800 kg of hydrogen;
2.) the catalyst surface, at a 3 bar pressure in
the reactor safety containment, is not allowed to reach
ignition temperature of 600C for the gas mixture containing
10 hydrogen and oxygen.
With consideration given to the heat of the
reaction which is encountered at the complete conversion of
the hydrogen, and with consideration given to the
experimentally determined heat-transfer coefficiencies of
15 the coated carrier plates, there is computed the heat
development in the carrier plate during the catalytic
oxidation. ~ereby, it is presumed that the heat of the
exothermic reaction is completely absorbed by the carrier
plate. This heat is then to be again conducted into the
atmosphere of the reactor safety containment. To that extent,
in the same manner as already with the assumption of the
hydrogen quantity streaming into the reactor safety
container, there are presumed to be unsatisfactory
preconditions present at the site of the reactor accident.
With respect to Fig. 6, across the minimum surface
for the catalyst surface measured in m2, there is plotted
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1 the temperature increase in K, which occurs to a maximum
extent in the carrier plate at the above assumed hydrogen
penetration. The temperature development in the carrier
plate is determined through the thermal equilibrium between
5 the heat development resulting from the oxidation reaction
and the heat emission from the carrier plate to the
surroundings. The maximum temperature in the catalyst
surface reduces with an increasing surface area. At a
surface size of 5000 m2, the maximum temperature increase
10 remains below 300 K; meaning, at an initial temperature of
120 the temperature in the carrier plate rises to about
400C. This temperature lies far below the ignition
temperature and, even under realistic conditions, provides
an adequate safety zone to the ignition temperature.
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