Note: Descriptions are shown in the official language in which they were submitted.
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Membrane contactor for the transmission of water vapour between two gas flows
The invention relates to a membrane contactor for the transmission of water
vapour between
two gas flows. The membrane contactor can in particular be part of an air
conditioning system
or a fuel cell.
Technological background
In a large number of technical processes, gas flows have to be humidified or
dehumidified in a
controlled manner.
An example is the air-conditioning in stationary or mobile rooms. In
conventional air
conditioning systems, humid external air is cooled for example to 15 C in hot
seasons in order
to reduce the humidity to a desired value. The excess humidity condenses as
liquid water. The
heat of condensation thus arising increases the energy demand required for the
cooling. If the
excess humidity is reduced before the air flow is cooled, the air conditioning
requires much less
energy. This problem can be advantageously solved with the aid of a membrane
contactor.
The key component of the contactor is a membrane, which ideally is permeable
only for water
vapour, but not for oxygen, nitrogen and further components such as for
example odorous
substances. The humid external air flows over one side of the membrane and is
thereby dried,
since water vapour permeates through the membrane on account of a partial
pressure gradient.
The partial pressure gradient is maintained, whereby the drier external air is
guided as waste
air in the counterflow or crossflow via the rear side of the membrane. In cold
seasons, on the
other hand, the dry cold external is humidified by the humid, hot waste air
flow out of the internal
rooms. A heat exchange takes place at the same time via the thin membrane,
which further
reduces the energy expenditure. This mode of procedure is known in principle.
The production
complexity, the production time, the costs and installation size for
conventional flat membrane
contactors for the humidification and dehumidification, however, are high.
A further area of application for membrane contactors are polymer electrolyte
fuel cells. Fuel
cells, which are used for example to drive motor vehicles, use an
electrochemical reaction
between hydrogen and oxygen to generate electrical energy. The key component
of the fuel
cell is a polymer membrane, which has a high conductivity for protons; for
hydrogen and
oxygen, however, the membrane should be impermeable. The membrane must also be
an
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electrical insulator. On the anode side, hydrogen is fed to the fuel cell, a
catalyser bringing
about the splitting into protons and electrons. The protons migrate through
the membrane to
the cathode side and react there with supplied oxygen to form water. The
electrons required for
this are supplied by anode side via an external line. They thus generate an
electrical current,
which can be used for example to drive motor vehicles.
The polymer electrolyte membranes known today require moisture in order to
ensure a high
proton conductivity. The air flow compressed to 2 to 3 bar, which is fed to
the cathode side of
the fuel cell, contains only a small amount of moisture and leads to the
drying up of the
membrane, which would have as a consequence a marked performance loss of the
fuel cell.
The air flow therefore has to be humidified after the compression and before
entering into the
fuel cell.
The waste air flow on the cathode side contains large amounts of water vapour,
which have
been generated by the reaction of hydrogen and oxygen. This water vapour-
containing waste
air flow cannot simply be mixed with the dry supply air flow for the purpose
of humidification,
since the waste air flow from the fuel cell is highly enriched in its oxygen
content. A way
therefore has to be found of transmitting only the water vapour from the waste
air flow into the
supply air flow without reducing the oxygen content of the supply air. This is
precisely the task
of the fuel cell humidifier.
This problem can also be solved with the aid of a membrane contactor. The key
component of
the contactor is again a membrane, which ideally is permeable only for water
vapour, but not
for oxygen and nitrogen. If humid air flows over one side of the membrane and
dry air flows
over the other, preferably in the counterflow, water vapour from the humid gas
flow flows to the
dry gas flow. This happens, even though the compressed dry air flow is
normally under a higher
pressure than the humid waste air flow from the fuel cell. The water vapour
partial pressure
difference is decisive for the transport of water. Such membrane contactors
have long been
known as humidifiers for fuel cells. Suitable membranes can be produced as
thin hollow tubes
(hollow fibre membranes) or as flat sheet membranes. In the case of hollow
fibre membranes,
the implementation of a counterflow is in fact relatively simple, for example
humid gas outside,
dry gas in the tubes, but the production of hollow fibre modules is expensive.
The fibres united
to form bundles are cast at the ends, usually with a polyurethane resin or an
epoxy resin. The
process is work- and time-intensive. In addition, large bonding blocks can
only be produced
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with difficulty on account of the reaction heat of the setting of the adhesive
components which
is poorly dissipated - heating as far as damaging the hollow fibres as
possible.
A further drawback with the use of hollow fibre membrane modules in mobile
systems is the
interface of the rigid adhesive bond with the flexible hollow fibre membrane.
With impact loads,
there is the risk of the membrane breaking at the adhesive bond. There are
applications in
which flat membrane modules have advantages on account of the conditions of
use.
The present invention is concerned solely with the use of flat membranes. Flat
membrane
contactors for the humidification of fuel cells are known. However, to a large
extent adhesive
bonds are also used here in most designs. This means a high production outlay,
the humidifier
cannot be dismantled without destruction and, as a result of this, a
replacement of defective
membranes or other components is not possible. The few contactor designs for
humidifiers
which largely dispense with adhesive bonds use a large number of seals.
A know membrane contactor for the humidification or dehumidification of gas
flows is described
for example in DE102009034095 Al. Here, a plurality of membranes lying above
one another
are combined to form a stack. Between each 2 membranes, there are alternately
flow channels
and sealing elements for the dry or the humid gas. The flow channels for the
moist or the dry
gas are arranged at right angles one another. The arrangement consists of a
large number of
planar elements, which are held together by adhesive bonding.
DE102016224475 Al also describes a membrane humidifier, which comprises a
plurality of
stack units placed above one another. Each individual stack unit consists of a
flow plate and a
diffusion unit. The diffusion unit consists of one or 2 diffusion layers and a
water vapour-
permeable membrane. Each diffusion unit further comprises two holding elements
lying
opposite. In a preferred design, the diffusion layer and the membrane are
folded at the edges,
in such a way that a groove is formed into which the flow plate is introduced.
DE102012008197 Al describes an exchange system for exchanging substances
between two
fluids, with a first space through which a first fluid can flow. A channel
labyrinth forms a second
space, which extends at least partially through the first space, through which
a second fluid can
flow. The channel labyrinth is formed by a first permeable membrane and a
membrane counter-
piece, wherein the latter are connected at predetermined lines and areas, so
that the channel
labyrinth arises between the first membrane and the membrane counter-piece.
Summary of the invention
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The flat membrane contactor according to claim 1 for the transmission of water
vapour between
two gases flows removes or at least minimises the drawbacks of the prior art.
To do this, the
flat membrane contactor comprises:
a) stack of membrane pockets arranged in a housing, wherein each membrane
pocket
comprises two membranes welded gas-tight at their edges, which are selectively
permeable
for water vapour;
b) guide structures for a first gas flow through the flat membrane contactor,
which is in a flow-
connection with the interior of the membrane pockets via openings in the
membrane pockets;
and
c) guide structures for a second gas flow through the flat membrane contactor,
which are
designed to guide the second gas flow past the membrane pockets on the
outside.
The membrane pockets are arranged in the stack in such a way that their
openings lie above
one another. The openings of the membrane pockets are provided with gas rings
and the first
gas flow is in a flow-connection with the interior of the membrane pockets via
the gas rings.
A further aspect of the invention relates to an air conditioning system or a
fuel cell with one
such flat membrane contactor.
Preferred embodiments can be found in the dependent claims and the following
description.
Brief description of the figures
The invention is explained in greater detail below with the aid of an example
of embodiment
and associated drawings. The figures show:
Figure 1 shows in a partial exploded representation an example of embodiment
of a flat
membrane contactor according to the invention.
Figure 2 shows a membrane pocket, which can be incorporated in the flat
membrane contactor
.. according to figure 1.
Figure 3 shows a distributor plate, which can be located in the interior of
the membrane pocket
from figure 2.
Figure 4 shows a distributor plate, which is arranged between the individual
membrane pockets
according to a further embodiment of the flat membrane contactor.
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Detailed description of the invention
General concept
The flat membrane contactor according to the invention for the transmission of
water vapour
5 between two gas flows comprises:
a) a stack of membrane pockets arranged in a housing, wherein each membrane
pocket
comprises two membranes welded at the edges, which are selectively permeable
for water
vapour;
b) guide structures for a first gas flow through the flat membrane contactor,
which are in a flow-
connection with the interior of the membrane pockets via openings in the
membrane pockets;
and
c) guide structures for a second gas flow through the flat membrane contactor,
which are
designed to guide the second gas flow past the membrane pockets on the
outside.
The membrane pockets are arranged in the stack in such a way that their
openings lie above
one another. The openings of the membrane pockets are provided with gas rings
and the first
gas flow is in a flow-connection with the interior of the membrane pockets via
the gas rings.
The flat membrane contactor accordingly comprises as a key component a stack
of membrane
pockets. A first gas can flow through the membrane pockets on the inside,
whereas on the
outside, preferably in the counter-flow, the second gas flows along the
membranes of the
membrane pockets. The desired water-vapour exchange is enabled by the
membranes
selectively permeable for water vapour.
The flat membrane contactor comprises the guide structures required for
guiding the two gas
flows through the stack of membrane pockets. A first guide structure guides a
first gas through
a flow path, which runs through the interior of the membrane pockets. The
second gas, on the
other hand, follows a flow path which is predetermined by the second guide
structure and flows
along the membrane pockets on the outside. In the stack, the membranes of
adjacent
membrane pockets do not therefore lie directly against one another, but rather
enable the pass-
through of the second gas.
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The resultant very compact design consisting of few components reduces the
production outlay
and the production time considerably. In particular, bonding can be wholly or
largely dispensed
with.
It is particularly advantageous that, due to the modular design, the flat
membrane contactor
can be adapted with regard to the process parameters volume flow, pressure,
pressure loss
over the travel distance, overflow speed of the membrane, selectivity and
permeability of the
membrane.
The flow to the individual membrane pockets can be parallel, in series or in a
defined stack
formation. For example, in the case of a series connection of membrane
pockets, the flow can
pass successively through the membranes in a meandering manner. The individual
compartments of a stack formation can be provided with a different number of
membrane
pockets. For example, depending on the volume flow reduction, caused by the
membrane
permeability, a uniform flow over the membrane surface can thus also be
achieved, as the case
may be.
The water vapour-selective membrane used to produce the membrane pockets is
preferably a
multilayer membrane. The membrane can for example consist of polymer fabric
such as
polyester or polyphenylene sulphide and can consist in the second layer of a
porous polymer
such as polysulfone and polyimide. The typically 10 to 100 pm thick polymer
layer can comprise
pores, the pore diameter of which diminishes from one side to the other side,
wherein the
smaller pore diameters are located on the upper side of the membrane. The
water vapour-
permeable membrane can also consist of three or more layers. In this case, a
macroporous
polymer layer, for example polysulfone, is present on the fabric, which is
provided with a further,
largely pore-free layer. This pore-free layer can consist of one polymer layer
or of a composite
of a plurality of polymer layers.
The membrane pockets are produced, whereby two membrane sections are welded at
the
edges. This welding can take place thermally, by ultrasound or with the aid of
laser beams. The
membrane fabric can lie on the inside in the pockets or, if desired, can lie
on the outside. In the
case of a two-layer membrane consisting of a fabric and a nanoporous membrane,
the
preferred configuration is a fabric lying on the outside. The welding of the
membranes, whether
it be thermal, by ultrasound or by means of laser beams, is gas-tight. The
welding process can
easily be automated, is rapid and therefore suitable for mass production. In
many cases, the
welding of a pocket takes less than 30 seconds.
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The membrane pockets are arranged in the stack, in such a way that the
openings lie opposite
one another. In this way, the necessary guide structures can be implemented
especially easily
for the first gas. The openings in the individual membrane pockets are spaced
as far as possible
apart from one another, so that the gas can be guided over the entire width
and length of the
membrane pocket. As a rule, therefore, the openings for the entry and exit of
the gas lie at
opposite edges of the membrane pocket.
The openings of the membrane pockets are provided with gas rings and the first
gas flow is in
a flow-connection with the interior of the membrane pockets via the gas rings.
In other words,
the openings for the entry and exit of the gas into the membrane pocket have
an annular
structure bordering and surrounding the opening edge, which has flow channels
through which
the gas can flow in the radial direction. A height of the gas rings lying
above one another
preferably defines a spacing of the membrane pockets from one another. In this
way, a stack
with a defined distance between the individual membrane pockets can
particularly easily be
produced. For this purpose, the individual membrane pockets merely have to be
stacked and
braced with their gas rings lying above one another.
The gas rings lying above one another preferably constitute distributors
channels, which
represent the part of the guide structure for the first gas flow in the stack
that produces the flow
connection with the interior of the membrane pockets. The gas rings of the
entry and exit
openings of the stacked membrane pockets thus create a distributor channel,
via which the first
gas is supplied and discharged. The gas rings abut gas-tight against one
another, so that the
first gas cannot escape at the side. The distributor channels of the first
guide structure as a rule
merge in connection points, which are accommodated in the cover of the
housing.
Particularly preferably, the aforementioned distributor channels are
continuously open or the
flow path of the first gas flow through the membrane pockets is predetermined
by deflection
plates in the distributor channels. According to the first alternative, the
flow takes place parallel
through all the membrane pockets, which enables a very straightforward
implementation of the
flat membrane contactor. The second alternative provides a deflection of the
gas flow, so that
the flow takes place for example through all the membrane pockets in series.
The deflection
structures can however also be constituted in such a way that individual
blocks of a plurality of
membrane pockets arise, the flow to which is in fact parallel, but inside
which the flow takes
place through the membrane pockets in series.
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A further preferred embodiment makes provision such that a distributor plate
is present in the
interior of the membrane pockets and this distributor plate comprises webs on
its upper and
lower side, which predetermine a flow path for the first gas flow. The inner
distributor plate
serves not only for a mechanical stabilisation of the membrane pocket. On the
contrary, the
webs on the surface provide for the more uniform distribution of the gas flow
in the interior of
the membrane pocket and for the formation of turbulence. The latter leads to a
reduction of the
interface at the membrane arising through laminar flow, which hinders the
exchange of water
vapour. As an alternative to the inner distributor plate, distance-keeping and
flow-influencing
elements, such as polymer spacers, can be provided in the membrane pocket, for
example net-
like spacers of polypropylene.
Furthermore, it is preferable if the guide structures for the second gas flow
comprise distributor
plates, which are arranged alternately with the membrane pockets in the stack.
Each distributor
plate in particular comprises webs on the upper and lower side, which
predetermine a flow path
for the second gas flow via the distributor plate. In other words, distributor
plates are located
between the membrane pockets, over the upper and lower side of which the
second gas flow
is guided. The mechanical stability of the stack is thus further increased. In
addition, the
distributor plates enable a more uniform distribution of the gas flow over the
outer sides of the
membrane pockets, so that the water vapour exchange is expedited. The
separating result of
the membrane unit is also dependent on the fact that, when the flow takes
place over the
membrane surface, the laminar interface between the gas flow and the membrane
surface is
kept small. The formation of turbulence and thus a reduction of the interface
can in particular
be assisted by the geometry of the webs. As an alternative to the distributor
plate, distance-
keeping and flow-influencing elements, such as polymer spacers, can be present
between the
membrane pockets, for example net-like spacers of polypropylene.
The stack of membrane pockets and, as the case may be, distributor plates
arranged in
between are accommodated in a housing. Advantageously, a cover plate of the
housing
comprises the connections for the guide structures of the first gas flow and
the connections for
the guide structures of the second gas flow, so that the production process is
greatly simplified
and a particularly compact flat membrane contactor in terms of installation
space is produced.
The stack is introduced in particular into the housing in such a way that two
spaces separated
from one another result, which are connected solely by the free spaces present
between the
membrane pockets. A connection for the second gas flow is provided in the
cover plate above
the one space, whilst a second corresponding outlet is integrated in the cover
plate above the
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second space. With this construction, the guide structure for the second gas
flow can
accordingly already be implemented to a large extent by the housing itself, so
that the
production costs are particularly low.
The use of the previously described flat membrane contactors in air-
conditioning systems or
.. fuel cells, for example polymer fuel cells for motor vehicles, is
particularly advantageous on
account of its compact structure.
The invention is explained in greater detail below with the aid of an example
of embodiment.
Example of embodiment
.. Figure 1 shows in a partial exploded representation an exemplary embodiment
of a flat
membrane contactor 100. Flat membrane contactor 100 comprises a module housing
10, which
is closed by a cover plate 20. A stack 40 of individual membrane pockets 50 is
accommodated
in the interior of the housing.
A membrane pocket 50 is represented in greater detail in figure 2. According
to the present
.. embodiment, membrane pocket 50 has a hexagonal elongated basic shape,
wherein the width
is selected such that stack 40 abuts largely in a sealing manner against the
side walls of
housing 10. Membrane pocket 50 comprises two membranes, which are welded
together at
the edges 54. Membranes 52 are selectively permeable for water vapour.
Each membrane pocket 50 comprises two openings 56, 58, which enable the inlet
and outlet
.. of a gas flow. Inlet and outlet openings 56, 58 are provided with seals 60
and gas rings 62,
which define the distance from adjacent membrane pockets 50, wherein seals 60
and gas rings
62 can also be constituted as one part. The gas can pass through a plurality
of radial drill-holes
64 of gas rings 62 into the interior of membrane pockets 50. Gas rings 62 can
be formed from
metal or hard plastic.
A distributor plate 70, for example made of metal, can be embedded in the
interior of membrane
pocket 50. The surface of inner distributor plate 70 is structured on both
sides by a number of
webs 72. Webs 72 serve to provide the uniform distribution of the gas flow in
the interior of
membrane pocket 50 and are intended at the same time to create turbulence,
which
counteracts the formation of a laminar boundary film at membranes 52 and thus
facilitates the
.. exchange of water vapour through membrane 52.
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A plurality of membrane pockets 50 are stacked above one another in flat
membrane contactor
100 according to figure 1, wherein openings 56, 58 lying above one another.
Inlet and outlet
openings 56, 58 form an inlet and outlet distributor channel either for the
first gas or the second
gas.
5 Stack 40 thus constituted is located in module housing 10 with cover
plate 20. Membrane stack
40 is held in the distributor channels by in each case two diagonally offset
tie rods - which each
comprise a rod 90 and an end piece 92. Cover plate 20 comprises a peripheral
seal and can
also be reinforced by snap-in links. It is provided with an inlet opening 21
and an outlet opening
22 for the second gas and an inlet opening 23 and an outlet opening 24 for the
first gas.
10 In flat membrane contactor 100 represented by way of example, a first
guide structure for a first
gas flow accordingly comprises both inlet and outlet openings 23, 24 in cover
plate 20, the
continuous distributor channels resulting from openings 56, 58 of membrane
pockets 50 lying
above one another as well as the inner path sections in the individual
membrane pockets 50.
A second guide structure for the second gas flow comprises both inlet and
outlet openings 21,
22 in cover plate 20 and the adjoining spaces in the interior of module
housing 10, which in the
example are bounded by walls of module housing 10 and stack 40. Furthermore,
these spaces
lie beneath one another in a flow connection via stack 40, i.e. the second gas
flow entering
through opening 21 is guided between module pockets 50 along membranes 52
through stack
40. Accordingly, water vapour can be exchanged between the two gas flows.
In an embodiment, the gas containing much water vapour flows for example
through the interior
of membrane pockets 50. The flow path for the humid gas thus follows the first
guide structure.
Gas containing little or no water vapour, on the other hand, follows a flow
path in the counter-
flow, which is predetermined by the second guide structure. The dry gas flows
past membranes
52 of membrane pockets 50 on the outside and absorbs moisture. Also
conceivable, however,
is an operation in which the dry gas flows through the interior of membrane
pockets 50 and the
humid gas in the counter-flow between membrane pockets 50.
In a further embodiment, a distributor plate 80 can be arranged between each
of membrane
pockets 50 of stack 40. Distributor plate 80 provides for the more uniform
distribution of the gas
flow flowing along membranes 52 of membrane pockets 50. For this purpose, the
upper and
lower side of distributor plate 80 comprises a plurality of webs 82, which
define channels for
the gas flow. The channels at the same time increase the turbulence and thus
minimise the
extent of the concentration polarisation at membranes 52, so that the exchange
of water vapour
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is improved. Furthermore, a (two-sided) edge seal 84 is provided, which
prevents potential
losses due to an edge flow.
Date Recue/Date Received 2023-05-09
