WO2008104189A1

WO2008104189A1 - Process gas plant with a sensor for measuring a measured variable of a process gas

Info

Publication number: WO2008104189A1
Application number: PCT/EP2007/001661
Authority: WO
Inventors: Bernd Buchauer; Wolfgang Maurer; Klaus Scherrbacher
Original assignee: Daimler Ag; Ford Global Technologies, Llc
Priority date: 2007-02-27
Filing date: 2007-02-27
Publication date: 2008-09-04

Abstract

The problem addressed by the invention is that of providing a process gas plant, with a sensor for measuring a measured variable of a process gas, which ensures reliable functioning. Proposed is a process gas plant, preferably formed as a gas supply arrangement of a fuel cell device, with a sensor (1) for measuring a measured variable of a process gas, wherein the sensor comprises a sensor housing which has a gas connecting duct (6) with a gas-side opening (7) for conducting the process gas to a measured variable pickup, wherein the gas connecting duct (6) and/or the measured variable pickup have/has a surface which is provided with a hydrophilic (8) and/or a hydrophobic layer (9).

Description

Process gas system with a sensor for detecting a measured variable of a process gas

The invention relates to a process gas system, preferably designed as a gas supply arrangement of a fuel cell device, with a sensor for detecting a measured variable of a process gas, wherein the sensor comprises a sensor housing which has a gas connection channel with a gas-side opening for supplying the process gas to a Meßgrößenaufnehmer.

Such sensors are measuring instruments which measure a measurable physical quantity of a gaseous medium, such as e.g. the pressure of a gas or a gas mixture (pressure sensor) or a specific gas concentration of a gas in a gas mixture (gas sensor), with a suitable

Capture and use a transducer to convert into an electrical output. Measuring sensors and measured variable transducers are often protected in a sensor housing integrated, which has a one-sided open gas connection channel for supplying the gas to the Meßgrößenaufnehmer. The gas connection channel terminates at its closed end with the integrated Meßgrößenaufnehmer, which is separated for example in the design as a pressure sensor by a membrane or a plate from the sample gas to the sensitive micromechanical measuring device and the surrounding electronics to protect against external influences. For detecting the pressure, various physical effects can be used, after which a distinction is made between essentially piezoresistive, piezoelectric and capacitive pressure sensors. In the case of a gas sensor, the measuring sensor forms a contact surface to the measurement gas, which is usually formed from a semiconductor material, such as, for example, zinc oxide, titanium dioxide or from organic semiconductor material, such as MePTCDI. The semiconductor material changes its electrical conductivity as soon as a certain gas acts on it. Depending on the selectivity to specific gases different semiconductor materials are used. The output signals generated by the measured variable converter of the sensor are available in corresponding evaluation units for the control, regulation or monitoring of a technical functional unit, which are directly related to the measuring gas.

For example, such sensors are often used in gas supply arrangements of fuel cell systems in order to detect a system pressure or a gas concentration as measured variables of the process gas.

From the document DE 103 46 626 Al a pressure sensor with a pressure sensor housing for side impact detection in side doors of a vehicle is known, which detects the air pressure in an interior of the side door for side impact detection and thus absorbs measured variables of the ambient air. After this pressure sensor must work in an environmental atmosphere in which dirt, moisture, salt water and other more or less aggressive media may be present, parts of the pressure sensor housing, including the pressure inlet channel, provided with a water-repellent layer. This ensures that any moisture released from the environmental atmosphere, which is on the Pressure sensor housing condenses, due to the water-repellent layer from the pressure sensor housing rolls off. Likewise, contaminants will adhere less and will dissipate with the beading droplets.

Since the cited document deals with a pressure sensor which receives measured values of the ambient air and not of process gases, the known gas supply arrangements of fuel cell systems form the closest prior art.

The invention has for its object to provide a process gas system with a sensor for detecting a measured variable of a process gas, which ensures reliable operation.

The object is achieved by a process gas system having the features of patent claim 1. Advantageous embodiments and further developments of the invention are disclosed by the dependent subclaims, the following description and the attached drawings.

The process gas system according to the invention is suitable and / or designed to lead a process gas to a processing location and / or dissipate it from a processor, wherein the supplied or discharged process gas participates in the process location in a process engineering process and in particular at least partially implemented and / or consumed becomes. The conversion or consumption preferably takes place in a combustion process or in an electrochemical process. Preferably, the process gas system is designed to operate in operation with a normal pressure (1013 mbar) different pressure, which in particular as overpressure or Vacuum with at least 100 mbar, 200 mbar or 400 mbar difference to the normal pressure is formed.

For detecting a measured variable, a sensor with a gas connection channel is provided, which is in open communication with the process gas-carrying components of the process gas system and forms a supply line of the process gas to a sensor arranged in the Meßgrößenaufnehmer. The sensor is designed to detect measured variables of the process gas, which participates in the process engineering process, and is preferably designed as a pressure sensor, gas sensor, moisture sensor or gas concentration sensor. In alternative embodiments, this may also be implemented as a temperature sensor, flow sensor, mass flow sensor, conductivity sensor or the like.

According to the invention, it is proposed that the gas connection channel and / or the measured variable sensor of the sensor have / has a surface which is provided with a hydrophilic and / or a hydrophobic layer.

This coating ensures that even in closed systems, for example, condensate is reliably kept away from sensitive areas of the sensor and the functionality of the sensor and thus the operational safety of the process gas system can be increased. This is particularly advantageous in process gas plants, which are cooled to temperatures below freezing point, since in these process plants, the risk can not be ruled out that irreversible damage to the sensors can occur due to water condensate in the sensors. Preferably, the layer is formed as an additional applied coating and is in particular not formed by the base material of the gas connection channel and / or the Meßgrößenaufnehmers.

The respective coating influences the formation of droplets on condensing the moisture out of the process gas in such a way that no accumulations of liquid and dirt deposits in a shape and size that lead to the blockage of the gas connection channel or the freezing of the moisture to damage the sensor. Accordingly, the inner wall surface of the gas connection channel and, if appropriate, the surface of the measured variable receiver are also treated according to the inventive specification, depending on the application characteristics of the sensor.

The invention is based on the one hand that a hydrophobic, water-repellent layer has a high surface energy, so that the surface of the layer in relation to the surface tension of the condensing water, a contact angle of more than 90 °, preferably more than 130 °, in particular more than 160 ° generated. The angle of contact is the angle formed by the surface of an adherent liquid drop with respect to the adhesive surface. A contact angle of more than 90 ° means that the condensing water on the hydrophobic layer assumes a spherical shape, which easily bubbles off from this surface. A suitable hydrophobic layer is achieved, for example, by a coating with a perfluorinated polymer, such as polytetrafluoroethylene PTFE (also known as Teflon).

If the inner surface of the gas connection channel is provided with this hydrophobic layer, moisture from the process gas that enters or condenses in the gas connection channel can bead off early and out of the process gas entrain precipitating dirt particles, whereby a functionally impairing cross-sectional constriction or icing of the gas connection channel is avoided. This process is often referred to as "lotus effect" on technical surfaces, in which case the beading of the droplets is assisted by a favorable installation position of the sensor, preferably with a vertically downwardly directed gas connection channel.

On the other hand, it has also been found that with a hydrophilic, water-accepting coating, an advantageous effect in terms of reliable functional reliability of the sensor can be achieved. In the case of a hydrophilic layer, a contact angle with respect to water of less than 90 °, preferably less than 70 °, in particular less than 50 °, forms at low surface energy. Drops on the surface thus form a flat-domed cap or run at a contact angle against 0 ° almost flat on the surface. Hydrophilic properties include, for example, compounds with water-soluble salts, but also certain metallic layers.

This hydrophilic coating causes a reduction of the water droplet size up to a uniform distribution of the condensing water in a thin film of water on the surface of the thus treated gas connection channel or Meßgrößenaufnehmers. The layer thickness that forms the water is so small that even with a considerable amount of condensate, the cross-section of the gas connection channel is narrowed only insignificantly and when freezing of the extremely thin layer no such tension forces occur that can cause damage to the sensor. In addition, a hydrophilic coated draws Surface of the resulting moisture from the process gas, so that in a differentiated coating, for example, only the inner surface of the gas connection channel, the moisture is deflected by the particularly sensitive surface of the Meßgrößenaufnehmers. The effect of differentiated moisture absorption increases when a partial hydrophilic coating is combined in direct proximity with a partial hydrophobic coating, for example in a hydrophobic coating of the surface of the hydrophilic coating

Meßgrößenaufnehmers next to a hydrophilic coating of the inner surface of the gas connection channel or vice versa or in an alternating coating of the inner surface of the gas connection channel with hydrophilic and hydrophobic coating or an alternating coating of the Meßgrößenaufnehmers.

As a result, the process gas system according to the invention designed with the sensor has a lower susceptibility to the resulting condensate and contaminants of the process gas and is suitable for use under freezing conditions, which is also referred to as freezing ability.

A preferred application relates to the use of the process gas system as a gas supply system in a fuel cell device. Here are the sensors under the conditions of the dynamic process parameters and the associated variable gas properties and composition particularly high demands placed on an accurate and reliable mode of action.

In the fuel cell device, a plurality of fuel cells are combined as a fuel cell stack to the required electrical power, for example, to drive a vehicle to provide. In preferably used fuel cells (PEMFC), an anode space and a cathode space of the fuel cells are separated from each other by a proton-conducting polymer membrane. The taking place in the fuel cell electrochemical process between a recorded on the anode side fuel, for example hydrogen, and recorded on the cathode side of the oxidant, usually oxygen, in which electrical energy is generated to form water, requires on the cathode side, as well as on the anode side a metered supply of process gases to the fuel cell by means of a regulated gas supply. On the cathode side, ambient air, as a carrier of the oxygen content necessary for the process, is usually conveyed via a supply line to the fuel cell stack. After passing through the cathode space, the only partially consumed air, optionally in a closed recirculation circuit with the addition of fresh air again supplied to the cathode side or discharged via an exhaust pipe to the environment, which can be contained in the recirculation circuit, as well as in the exhaust line, the water formed , On the anode side of the fuel cell stack, an anode gas containing the fuel gas, promoted, wherein the fuel gas is also not completely consumed in the passage through the anode compartment and optionally conveyed in a closed recirculation, with unused fuel gas is admixed. The pressure or the gas concentration or the water concentration of the process gas in the anode and cathode-side gas supply arrangement of the fuel cell device, in particular during the supply and / or discharge of the process gas is detected by means of at least one of the sensors, which to the line components of the gas supply arrangement be connected gas-tight, for example by means of a threaded flange with integrated gas connection channel, so that a gas-side connection between the process gas line and the gas connection channel of the sensor is realized. The pressure measured value is supplied as a measurement signal to a control unit in order to regulate the pressure in the fuel cells or the cathode and / or anode-side gas volume flow in adaptation to the electrical power requirement of the fuel cell device. For a sufficient humidification of the polymer membrane also a certain relative humidity of the process gases in the fuel cell stack is required, which requires a corresponding gas supply management, controllable via the gas pressure or the gas concentration of the process gases.

In low power load mode, as well as after a shutdown of the fuel cell device cool under unfavorable environmental conditions of

Fuel cell device, the process gases containing water vapor down to a lower temperature level and condense water in the process gas lines. Deposits of water droplets and entrained dirt particles endanger the functionality of the known sensors, since the deposits easily get into the gas connection channel of the sensor and narrow or even clog the channel cross-section. In the case of weather conditions below 0 °, the gas supply channel can also freeze, resulting in a temporary impairment of the measuring capability (measured value error or measured value failure) and irreversible damage to components of the sensor. This source of error is excluded or at least reduced by the inner coating of the sensor on the surfaces leading the process gas. In an advantageous embodiment, the gas connection channel has a guide element. The guide element causes the surfaces additionally created an advantageous increase in surface area of the gas connection channel at approximately constant cross-section of the gas connection channel and thus serves to further absorption and distribution of the resulting condensate and any dirt particles in the manner of a moisture or mud trap. If the guide element is additionally provided with a hydrophilic or a hydrophobic layer, a further possibility results in the gas connection channel of the combination of differentiated layers on the one hand for the gas connection channel and on the other hand for the guide element with the aforementioned advantages.

The advantageous effect of the guide element is increased by the fact that a free end of the guide element projects beyond the gas-side opening of the gas connection channel. Vertically draining droplets, which adhere to the surface of the guide element at the free end of the guide element due to the existing adhesion forces, do not cause a reduction in the cross section of the gas connection channel at this point.

In a particularly advantageous embodiment, the hydrophobic layer is formed from nanostructured fluoropolymers. In addition, the water-repellent fluorinated polymers are additionally hardened with tiny ones

Provided particle structures in the nanometer range, so that the surface with Nanofeiner roughness reaches a superhydrophobic, extremely water-repellent property. Superhydrophobic surfaces have contact angles of much more than 90 °. At a contact angle of about 160 °, the spherical water droplets are almost round and there is hardly any wetting of the surface, so that the water at The smallest inclination of the surface unrolls, whereby it attaches dirt particles on the surface of the drop and entrains. This effect corresponds to the self-cleansing effect of the lotus leaf, which is why it is also called the lotus effect. Such a hydrophobic layer with superhydrophobic properties increases the self-protection and reliability of the sensor to a further.

The process gas system embodied according to the invention is not only excellently suitable for use in a gas supply arrangement of a fuel cell device in which moist process gases such as hydrogen gas or air-water vapor mixture are operated, but is also potentially suitable for use in an exhaust system of an internal combustion engine because of the described advantages the heavily polluted process gases, such as Diesel exhaust, happen.

Further features and advantages of the invention will become apparent from the following description of a preferred embodiment and the accompanying drawings. The two figures show:

Fig. 1 shows a sensor as a pressure sensor with a

Sensor housing in a side view for a process gas plant according to the invention and

Fig. 2 shows a sensor in the same view as in Figure 1 with an additional guide element, also for a process gas plant according to the invention.

Like reference numerals designate like or corresponding parts. In Figs. 1 and 2, a pressure sensor 1 is shown in each case, as it can be used in a gas supply arrangement in a fuel cell device for measuring the gas pressure of fuel-containing anode gas or air-containing cathode gas, as the process gases of the electrochemical fuel cell process.

In a sensor housing 2, the sensitive mechanical and electronic components of a non-visible pressure transducer and transducer are integrated. The sensor housing 2 has a port 3 for connecting the sensor housing 2 to a gas line carrying process gas, e.g. an exhaust duct, or to a process gas tank, e.g. a compressed air tank, on, said connection possibilities are not shown. In port 3, which in addition to a screw 4 comprises a connection piece 5, a hollow cylindrical gas connection channel 6, is formed. Of course, another channel shape of the gas connection channel 6, e.g. as a cone, possible. For better clarification of the gas connection channel 6, the connecting piece 5 is shown cut.

A gas-side opening 7 of the gas connection channel 6 creates the connection, via which the process gas can act on the integrated pressure sensor, which closes off the gas connection channel 6 in the interior of the sensor housing 2. The surface of the gas connection channel 6 -according to the exemplary embodiment the inner cylinder jacket surface of the hollow-cylindrical gas connection channel 6 -is provided with a hydrophilic layer 8. Alternatively, the surface may also be provided with a hydrophobic layer 9, preferably of nanostructured fluoropolymers with lotus effect. Both types of coating effect in different ways that when condensing the Water vapor from the process gas can not form droplets or accumulations of dirt in a shape and size that lead to blockage of the gas connection channel 6 and at low gas temperatures, such as during standstill of the fuel cell device in cold environment, frost damage to the connection piece 5 or the pressure transducer.

Thus, the hydrophilic coating 8 causes a uniform distribution of the water on the surface of the

Gas connection channel 6 at the lowest layer thickness, whereas the (super) hydrophobic coating 9 reaches an early beading of the spherical water droplets, which is supported by an alignment of the connected pressure sensor 1 with vertically downwardly directed opening 7 of the gas connection channel 6. In both types of layers 8, 9, the cross-section of the gas connection channel 6 is largely kept free of accumulations of water and dirt, so that no measurement value falsification or even a measured value failure occurs during the pressure measurement of the process gas. At the same time, the remaining gossamer thin film of water on the hydrophilic layer 8 does not develop any such dangerous tension forces upon solidification that can cause freezing damage to the pressure sensor 1.

In a further design of the pressure sensor 1 according to FIG. 2, an axially directed guide element 10 is integrated in the gas connection channel 6, which projects beyond the gas-side opening 7 of the gas connection channel 6 with its free end 11. The two-sided surfaces of the guide element 10 are provided, for example, with the hydrophobic layer 9. In contrast, the inner cylinder jacket surface of the gas connection channel 6 is provided with the hydrophilic layer 8. The condensing water is particularly attracted to this layer 8 and forms a thin on her Water film. Condensing water on the hydrophobic layer 9 of the vertically oriented surfaces of the guide element 10, however, rolls off as spherical droplets on this and thereby entrains the collected from the guide element 10 dirt particles. If the droplets adhere to the free end 11 of the guide element 10 because of the existing minimum adhesion forces, they do not form any disturbing cross-sectional constriction of the gas connection channel 6.

As a further alternative embodiment, the inner cylindrical surface of the gas connection channel 6 with the hydrophobic layer 9 and the guide element 10 may be coated with a hydrophilic layer 8 in order to ensure an advantageous condensate drainage.

Claims

claims

1. process gas system, preferably designed as a gas supply arrangement of a fuel cell device, with a sensor (1) for detecting a measured variable of a process gas, wherein the sensor comprises a sensor housing (2) having a gas connection channel (6) with a gas-side opening (7) to the supply line of the process gas to a sensor,

characterized in that

the gas connection channel (6) and / or the Meßgrößenaufnehmer have a surface which is provided with a hydrophilic (8) and / or a hydrophobic layer (9).

2. Process gas system according to claim 1, characterized in that the sensor is designed as a pressure sensor (1) for detecting an absolute or differential pressure of the process gas or as a gas sensor for detecting a gas concentration of the process gas.

3. Process gas system according to claim 1 or 2, characterized in that the gas connection channel (6) has a guide element (10).

4. Process gas installation according to claim 3, characterized in that a surface of the guide element (10) with a hydrophilic (8) or a hydrophobic layer (9) is provided.

5. Process gas system according to claim 3 or 4, characterized in that the guide element (10) has a free end (11) which projects beyond the gas-side opening (7) of the gas connection channel (6).

6. Process gas installation according to one of claims 1 to 5, characterized in that the hydrophilic layer (8) is formed from hydrophilic polymers.

7. Process gas installation according to one of claims 1 to 5, characterized in that the hydrophobic layer (9) is formed from one or more nanostructured fluoropolymers.

8. Process gas installation according to one of claims 1 to 7, characterized in that the gas supply system as a cathode-side gas supply arrangement or as an anode-side gas supply arrangement of

Fuel cell device is formed.

9. Process gas installation according to one of claims 1 to 7, characterized by a design as an exhaust system of an internal combustion engine.