CA3201325A1

CA3201325A1 - Membrane contactor for transferring water vapor between two gas flows

Info

Publication number: CA3201325A1
Application number: CA3201325A
Authority: CA
Inventors: Thomas Beeskow; Klaus Ohlrogge; Klaus-Viktor Peinemann; Rudolf Waldemann
Original assignee: Gmt Membrantechnik GmbH
Current assignee: Gmt Membrantechnik GmbH
Priority date: 2020-11-09
Filing date: 2021-10-22
Publication date: 2022-05-12
Also published as: EP4240519A2; DE102020129403A1; WO2022096287A2; WO2022096287A3

Abstract

The invention relates to a membrane contactor for transferring water vapor between two gas flows. The membrane contactor can, in particular, be part of an air-conditioning system or a fuel cell. The flat membrane contactor comprises: a) a stack of membrane pockets disposed in a housing, each membrane pocket having two membranes which are welded gas tight at their edges and which are selectively permeable to water vapor; b) guide structures for a first gas flow through the flat membrane contactor, which guide structures are fluidically connected to the interior of the membrane pockets by means of openings in the membrane pockets; and c) guide structures for a second gas flow through the flat membrane contactor, which guide structures are designed to guide the second gas flow past the outside of the membrane pockets. The membrane pockets are arranged in the stack in such a way that their openings lie one above the other. The openings of the membrane pockets are provided with gas rings, and the first gas flow is fluidically connected to the interior of the membrane pockets by means of the gas rings.

Description

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 Date Recue/Date Received 2023-05-09

2 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 Date Recue/Date Received 2023-05-09

3 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 Date Recue/Date Received 2023-05-09

4 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.
Date Recue/Date Received 2023-05-09 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.
Date Recue/Date Received 2023-05-09

6 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.
Date Recue/Date Received 2023-05-09

7 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.
Date Recue/Date Received 2023-05-09

8 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 Date Recue/Date Received 2023-05-09

9 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.
Date Recue/Date Received 2023-05-09 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 Date Recue/Date Received 2023-05-09

11 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

Claims

1. A flat membrane contactor (100) for the transmission of water vapour between two gases, comprising:
a) a stack (40) of membrane pockets (50) arranged in a housing (10), wherein each membrane pocket (50) comprises two membranes (52) 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 (100), which are in a flow-connection with the interior of the membrane pockets (50) via openings (56, 58) in the membrane pockets (50); and c) guide structures for a second gas flow through the flat membrane contactor (100), which are designed to guide the second gas flow past the membrane pockets (50) on the outside, wherein the membrane pockets (50) are arranged in the stack (40), in such a way that their openings are (56, 58) lie above one another, characterised in that the openings (56, 58) of the membrane pockets (50) are provided with gas rings (62) and the first gas flow is in a flow-connection with the interior of the membrane pockets (50) via the gas rings (62).

2. The flat membrane contactor according to claim 1, characterised in that a height of the gas rings (62) lying above one another defines a spacing of the membrane pockets (50) from one another.

3. The flat membrane contactor according to claim 1 or 2, characterised in that the gas rings (62) lying above one another constitute distributors channels, which represent the part of the guide structure for the first gas flow in the stack (40) which produces the flow connection with the interior of the membrane pockets (50).

4. The flat membrane contactor according to claim 3, characterised in that distributor channels are continuously open or the flow path of the first gas flow through the Date Recue/Date Received 2023-05-09 membrane pockets (50) is predetermined by deflection plates in the distributor channels.

5. The flat membrane contactor according to any one of the preceding claims, characterised in that a distributor plate (70) is present in the interior of the membrane pockets (50) and this distributor plate (70) comprises webs (72) on its upper and lower side, which predetermine a flow path for the first gas flow.

6. The flat membrane contactor according to any one of the preceding claims, characterised in that the guide structures for the second gas flow comprise distributor plates (80), which are arranged alternately with the membrane pockets (50) in the stack (40).

7. The flat membrane contactor according to claim 6, characterised in that each distributor plate (80) comprises webs (82) on the upper and lower side, which predetermine a flow path for the second gas flow via the distributor plate (80).

8. An air conditioning system or fuel cell with a flat membrane contactor (100) according to any one of the preceding claims.
Date Recue/Date Received 2023-05-09