Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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Description
The invention relates to an apparatus for the electrical production
of hydrogen from water.
It is counted as belonging to the state of the art, to apply
electrolysers for the production of hydrogen from water by way of
electrical energy. These exist in different constructional forms.
The subject matter of the present invention is an apparatus with an
electrolyser of the PEM construction type (polymer electrolyte
membrane), thus an electrolyser which operates with a proton-
permeable polymer membrane. Such electrolysers are typically
constructed in so-called stacks, in order to achieve an as high as
possible gas yield in an as small as possible space. Thereby water
is led to each membrane on one side, wherein a breakdown into
hydrogen and oxygen is effected by the electrodes which are
arranged on both sides of the membrane and which are supplied with
the electrolysis voltage, and the hydrogen arises at one side of
the membrane and the oxygen on the other side, to which the water
is supplied.
In order to ensure the proton permeability of the polymer
electrolyte membrane, it is necessary to constantly keep this
moist, which however leads to the fact that the produced hydrogen
is typically burdened with water vapour and/or water in droplet
form. This water load entrained in the hydrogen is not desirable
in many technical applications, which is why it is to be removed.
Thus for example with the storage of hydrogen in the metal
hydride storage means commonly used today, the contained or
entrained water load is to be removed before storage. Mechanical
water separators here as a rule are not sufficient, since they
are not in the position of adequately freeing the hydrogen flow
from water.
It is therefore counted as belonging to the state of the art, to
arrange a water separating device operating according to the
principle of pressure swing adsorption, downstream of the
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electrolyser at the exit side, for drying the hydrogen. Thereby,
the hydrogen flow which is enriched with water and water vapour and
exits the electrolyser is led over one or more molecular sieve beds
which bind the water. Such a binding however is effected only as
long as the molecular sieve beds are not saturated. The molecular
sieve beds must therefore be regenerated at regular intervals. In
practice therefore, two molecular sieve beds are provided in
parallel, and these are alternatingly subjected to through-flow,
wherein the non-active bed is regenerated by way of it being
flushed with dried hydrogen in a counter-flow. This method is
comparatively complicated and in particular worsens the efficiency
of the apparatus, since the hydrogen used for back-flushing usually
escapes without being used. The method in particular reaches its
limitations with an increasing water load in the hydrogen flow,
which is why these apparatus known from the state of the art are
relatively ineffective.
U.S.2009/263693A1 discloses an apparatus for the electrolytic
production of hydrogen from an electrolyte. The apparatus includes
a separating device in the form of condensation plates, on which
entrained moisture condensates and is separated from the hydrogen
stream. The apparatus appears to be designed for the limited
purpose of producing hydrogen from an electrolyte, since no mention
is given to the use of such apparatus for the production of
hydrogen from water.
JP8085892A discloses a device for the electrical generation of
hydrogen and oxygen from water using an electrolyser of the PEM
type. The electrolyser generates separate streams of oxygen and
hydrogen; for the purpose of removing the entrained water, each of
the two streams is further processed in a mechanical pre-separator
and in a thermal separation device which uses Peltier cooling
elements. An apparent limitation of the device is the fact that a
certain amount of residual moisture cannot be removed and remains
in the hydrogen end-product.
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Against this background, it is the object of the invention to
construct an apparatus of the known type for the electrical
production of hydrogen from water, such that it operates with an as
high as possible efficiency for producing dried hydrogen, i.e.
hydrogen freed from a large part of water.
According to the invention, this object is achieved by the features
specified in claim 1. Advantageous designs of the invention are to
be deduced from the dependent claims as well as from the subsequent
description.
The apparatus according to the invention for the electrical
production of hydrogen from water, comprises an electrolyser of the
PEM construction type, thus one which operates with a proton-
permeable polymer membrane. This electrolyser is provided with an
entry for feeding water and a first exit for hydrogen which is
enriched with water and/or water vapour and which is produced in
the electrolyser, as well as with a second exit for oxygen and
water. The apparatus moreover comprises a water separation device
whose entry is conductively connected to the first exit of the
electrolyser and whose gas-leading exit leads to a hydrogen removal
connection in or on the apparatus, wherein the water separation
device comprises one thermal separation stage.
The basic concept of the present invention is thus to provide an
electrolyser with a water separation device, within the apparatus,
wherein the water separation device has one thermal separation
stage. It is to be understood that a mechanical separation device
as a pre-separator, for example a cyclone separator or a gravity
separator is provided as part of the separation device or arranged
upstream of this. Such a separation device is not a separation
stage in the context of the invention. The water separation device
is, according to the invention, constructed in a two-stage or
multi-stage manner, wherein with regard to the first stage it is
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the case of a thermal separation stage, with which water is taken
from the hydrogen flow by way of cooling.
A water removal connection in the context of the invention is not
only to be understood as a connection in the actual sense, but also
a conduit within or outside the apparatus which leads the dried
hydrogen to the consumer or to a storage device. Thus a metal
hydride storage device likewise provided in the apparatus via a
conduit can be acted upon by such a water removal connection in the
apparatus.
The solution according to the invention is particularly
advantageous, since the electrolyser can be operated with a
comparatively high temperature and thus with a high efficiency.
With regard to the efficiency, favourable operating conditions
result if the electrolyser is operated in regions of 70 C to 80 C or
more, since for an effective operation of the electrolyser, the
temperature should be as high as possible, but on the other hand
the proton-exchange membrane must constantly be held moist. The
operating temperature is limited to the top by the boiling point of
water, which cannot be reached under any circumstances. However,
the water load carried by the hydrogen roughly doubles every 11 C.
If therefore the operating temperature is increased from 60 C to
70 C, then almost double the quantity of water to be led away
results. The separation of such a quantity of water is not a
problem with the solution according to the invention, specifically
with a thermal separation stage, and in particular is completely
without any hydrogen loss. The electrolyser of the apparatus
according to the invention can thus be operated significantly more
effectively, since one operates with a greater temperature. The
energy to be applied for cooling is accordingly significantly
lower.
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According to the invention, the water separation is effected in two
stages, but one can also provide more than two stages. The second
separation stage is, according to the invention, effected by a
pressure swing adsorption device. A pressure swing adsorption is
considered as a second stage, since here only a little water is yet
to be removed from the hydrogen, but it is the case of an as
complete as possible water removal. The molecular sieve beds can be
used for a comparatively long period of time before a back-flushing
is necessary, since very small quantities of water are still
entrained in the hydrogen.
According to the invention, a mechanical pre-separator is
arranged between the electrolyser and the thermal separation
stage, for example a gravity water separator or a cyclone water
separator. A part of the entrained water load can be separated
away almost without losses in such a pre-separator. Thereby, it
is particularly advantageous, with regard to the conduit system,
to integrate the pre-separator such that it can simultaneously
serve for receiving the water lead back out of the separation
stage. For this, the pre-separator is usefully able to be shut-
off on the entry side as well as exit side of its gas-leading
conduits, by way of gas valves, and able to be bridged via a
bypass conduit which can likewise be shut off by way of a bypass
valve. If then the return conduit of the thermal separation stage
which can likewise be shut off via a return valve, run out into
the pre-separator, then by way of shutting off the gas-leading
conduits of the pre-separator and opening the bypass conduit, the
water to be led back can be pressed via the pressure in the
hydrogen conduit which is present in any case, into the pre-
separator, on opening the valves in the return conduits. Thereby,
it is not a problem if gas in the form of hydrogen goes through
the return conduits into the pre-separator, since this can later
be led back to the separation steps.
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Advantageously, according to a further development of the
invention, a water-leading exit of the thermal separation stage
is conductively connected to the entry of the electrolyser for
leading back the water. The conduit connection is effected at
least for a time, i.e. suitable valves are provided in the
conduit, which when necessary are suitably activated, in order to
lead the water collected in the thermal separation stage back to
the entry of the electrolyser. The system conduit pressure within
the apparatus i.e. the hydrogen pressure can serve for the
transport of this water. Usefully, a bypass conduit with a valve
is to be provided for this, and specifically between the first
exit of the electrolyser, thus the exit leading hydrogen and the
separator to be emptied, amid the bridging of the separator or
separators lying therebetween.
The entry of the electrolyser in the context of the present
invention is to be understood as any water-leading conduit which
leads thereto and which for example is fed from a reservoir within
or outside the apparatus. This water can thus either be led back
into this conduit or advantageously into the reservoir.
The pre-separator likewise comprises a return conduit which can be
shut off by way of a closure valve and via which the hydrogen
collected in the pre-separator can be fed to the entry of the
electrolyser or to the water tank arranged upstream. The return of
the water can be effected in a quasi automatic manner by way of the
application of a float valve, as long as the shut-off valve in the
return conduit leading to the water tank is open.
The thermal separation stage is advantageously provided with an
electrically operated common cooling device. Such cooling devices
are comparatively inexpensive, efficient and available with a small
construction size. A compressor cooling device is advantageously
applied with larger apparatus. Alternatively, in particular with
smaller apparatus, one can also apply an absorber cooling device or
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a cooling device operating with Peltier elements. It is
particularly advantageous if the thermally operating separation
stage is designed such that the hydrogen coming from the
electrolyser and enriched with water and/or water vapour is cooled
down to a temperature slightly above the freezing point, thus
preferably between 0 1: and 5 C. A large part of the water entrained
in the hydrogen flow condenses in this temperature range. The
remaining water load in the hydrogen is comparatively small. Since
a cooling is effected above the freezing point, no particular
provisions need to be made concerning the removal of the condensed
water with regard to the formation of ice.
The apparatus according to the invention operates in a particularly
effective manner if the electrolyser, water separation device as
well as any auxiliary apparatus, connection conduits, valves and
likewise are designed such that the hydrogen is produced and held
at a pressure of 20 bar or more, preferably about 30 bar. The
operation of the apparatus at this pressure is particularly
advantageous, since then no separate pressure increase installation
is required for the storage of the hydrogen in metal hydride
storage devices. The apparatus thus provides the dry hydrogen at
the required pressure.
A device similar to the invention is hereinafter explained in more
detail by way of an example shown in the drawing. The single figure
shows an illustratory picture of one variant similar to the
apparatus according to the invention. Similarly, the list of
reference numerals refers to an illustratory variant similar to the
apparatus according to the invention.
The apparatus represented in the figure is arranged in an
essentially closed housing which is not shown, but does not
necessarily need to be constructed in such a manner, but in
particular, with integration into an installation, can also be
integrated with its components into the installation.
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The apparatus comprises an electrolyser 1 of the PEM construction
type, which is constructed as a stack in the usual manner, but can
basically be constructed in any other suitable shape and form. The
electrolyser has an entry 2 for feeding water. A first exit 3 of
the electrolyser 1 is envisaged for leading away the hydrogen
produced in the electrolyser 1, which is typically laden with water
and water vapour. Moreover, the electrolyser 1 comprises a second
exit 4 which is envisaged for leading away the oxygen arising in
the electrolyser 1.
With the represented embodiment, the apparatus comprises a
reservoir 5 in the form of a water tank which is connected by water
conduit via a pump 6 to the entry 2 of the electrolyser. The second
exit 4 runs out via a conduit in the upper region of the water tank
5. The first exit 3, thus the exit 3 of the electrolyser 1 which
leads hydrogen, is conductively connected which is to say connected
by conduit, to a water separation device 7.
The water separation device 7 comprises a gravity water separator 8
whose gas-leading conduit 9 is conductively connected to a first
thermal water separation stage 10. The hydrogen flow laden with
water and coming from the gravity water separator 8 is cooled down
to a temperature of about 4 C in this first thermal separation stage
10 which is formed of a closed container 11 with a coolant conduit
12 integrated therein. The coolant conduit 12 in the region of the
container is designed as an evaporator. A condenser is provided
outside the container. These components are connected in a manner
known per se via a throttle location and a compressor to a cooling
circuit. The water condensing on the evaporator 12 collects at the
base of the container 11.
The gas exiting from the first thermal separation stage 10 gets via
a conduit 13 into a second thermal separation stage 14 which is
formed from two containers 15 with coolant conduits 16 as
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evaporators, arranged therein. The coolant conduits 16 are designed
in the same manner as described with the first thermal separation
stage 10 and connected to a condenser. The cooling circuits each
have a compressor and a condenser for all evaporators together and
a throttle location and are provided for alternating operation. The
separation stages 10 and 14 can advantageously be fed via a common
cooling circuit, so that only one compressor is necessary, wherein
the different temperatures are set in each case via the assigned
throttle locations.
The hydrogen with the residual water which is still entrained
therein is cooled down to -36 C in this second thermal separation
stage 14. Thereby, the remaining residual water resublimes or
solidifies on the evaporator 16. The hydrogen exiting from the
second thermal separation stage 14 is present at the hydrogen
removal connection 17 and is dry, thus practically water-free. The
containers 15 can be alternatingly operated via exit-side valves
18, i.e. one of the containers serves for cooling whilst the other
container is thawed, and the water collecting on the container base
is led via a conduit 20 which can likewise be shut-off by way of a
valve 19, into the gravity water separator 8.The valve 19 in a
return conduit 20 is opened in each case only briefly, wherein the
valve 18 belonging to the container 15 at the exit side is
activated to block until the thawed water is led out of the
container 15 over into the gravity water separator 8.
A corresponding device is provided for the container 11, and there
the water can be transferred from the container 11 into the gravity
water separator 8 via the conduit 21 connecting there on the base
side and the shut-off valve 22 arranged downstream. For this, the
gravity water separator 8 is to be bridged via a bypass conduit 23
and to be blocked off by way of the valves 24 and 25, so that the
container 11 is impinged by pressure after opening a valve 26 in
the bypass conduit 23, and the water located at the base is pressed
via the conduit 21 into the gravity water separator 8.
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Alternatively, this return conduit can also run out directly into
the water tank 5.
In the present embodiment example, a water return conduit 27 which
can be connected via a valve 28 to the water tank 5 connects on the
base of the gravity water separator 8. The water separated in the
water separation device 7 is thus led back completely into the
water tank 5. The device is thus typically operated such that the
hydrogen is present with a pressure of 20 - 30 bar at the exit side
of the electrolyser. The electrolyser is thereby operated at a
temperature of between 70 and 80 C.
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List of reference numerals
1 - electrolyser
2 - entry of 1
3 - first exit of 1
4 - second exit of 1
5 - water tank
6 _ pump
7 - water separation device
8 - gravity water separator
9 - gas-leading conduit
10 - first thermal separation stage
11 - container of 10
12 - coolant conduit, evaporator of 14
13 - conduit
14 - second thermal separation stage
15 - container of 14
16 - coolant conduit, evaporator of 14
17 - hydrogen removal connection
18 - valve at the exit
19 - valves in the conduit
20 - return conduit of 16
21 - return conduit of 11
22 - valve in 21
23 - bypass conduit
24 - valve
25 - valve
26 - valve in the bypass conduit
27 - water return conduit
28 - valve in the water return conduit
