DE102018215372A1 - Humidifier and method of operating a humidifier - Google Patents

Abstract

The invention relates to a method for operating a humidifier (102) having at least one heating element (112) of a fuel cell system (100), with a stack-side cathode exhaust gas inlet (104) for a moist cathode exhaust gas, with a compressor-side cathode gas inlet (106) for dry cathode gas, with a stack-side cathode gas outlet (108) for humidified cathode gas and with a cathode exhaust gas outlet (110) for cathode exhaust gas, characterized by the steps:
- sensing a temperature at or near the cathode gas inlet (106) of the humidifier (102),
Detecting a temperature at or near the cathode gas outlet (108) of the humidifier (102),
- Determining a humidifier temperature by averaging all recorded temperatures, and
- Controlling a heating power of the at least one heating element (112) as a function of the humidifier temperature in such a way that the humidifier temperature is at least within a predetermined target temperature interval around a predetermined target temperature.
The invention also relates to a humidifier (102).

Description

The invention relates to a method for operating a humidifier of a fuel cell system having at least one heating element and a humidifier of a fuel cell system with a stack-side cathode exhaust gas inlet for a moist cathode exhaust gas, with a compressor-side cathode gas inlet for dry cathode gas, with a stack-side cathode gas outlet for humidified cathode gas exhaust and a cathode gas exhaust with humidified cathode gas exhaust . The humidifier also has at least one heating element.

Fuel cell systems serve to provide electrical energy in the context of an electrochemical reaction with the conversion of a fuel, usually hydrogen, with an oxygen-containing gas, usually air. There is the possibility of combining a plurality of fuel cells in a fuel cell stack in a fuel cell device, wherein there is a high power requirement in particular when the fuel cell device is used in a motor vehicle and a large number of fuel cells are therefore required in the fuel cell stack. Such polymer electrolyte membrane fuel cell systems, in particular those which have a high power density, require very good water management, the polymer electrolyte membrane having to be operated for high performance at a high moisture content. In order to adjust this moisture content, the cathode gas in particular is enriched with moisture in order to cause moisture saturation in the polymer electrolyte membrane, which improves the transport of hydrogen protons through the membrane. A humidifier is used to humidify the reactant gases, it being known that the introduction of moisture into a dry gas is favored by an elevated temperature.

A humidifier with a heating element, in particular with a heating wire, is for example in the DE 10 2005 056 833 B4 described, wherein the heating element is used to ensure a frost start ability of the fuel cell system to thaw any frozen water. Also in the DE 10 2013 021 506 A1 describes a fuel cell system in which the hose line is wrapped by a circuit which is used to heat the hose line in order also to avoid freezing of liquid water or to thaw frozen water. Ultimately it is also in the JP 2003 156 238 A described a humidifier that is equipped with a heating element in order to avoid damage from frozen water inside the humidifier.

Known humidifiers equipped with a heating element are therefore typically only operated with additional heating if any frozen water is to be thawed in order to ensure the mass flow through the humidifier or to enable it again at all. In known humidifiers, however, it has been found to be disadvantageous that, after the channels blocked by ice have been cleared, the temperature of the humidifier is reduced again or the heating element is switched off completely by means of the heating element. Setting the parameters of the humidifier for improved water transfer in normal operation is not possible or does not take place.

It is therefore the object of the present invention to develop a method for operating a humidifier and a humidifier of the type mentioned in the introduction in such a way that the efficiency of the water transfer within the humidifier into the cathode gas is improved.

This object is achieved by a method with the features of claim 1 and by a humidifier with the features of claim 7.

Advantageous refinements with expedient developments of the invention are specified in the dependent claims.

• - Erfassen einer Temperatur am oder nahe am Kathodengaseinlass des Befeuchters,
• - Erfassen einer Temperatur am oder nahe am Kathodengasauslass des Befeuchters,
• - Bestimmen einer Befeuchtertemperatur durch eine Mittelwertbildung aller erfassten Temperaturen, und
• - Regeln einer Heizleistung des mindestens einen Heizelements in Abhängigkeit der Befeuchtertemperatur derart, dass die Befeuchtertemperatur zumindest innerhalb eines vorgegebenen Zieltemperaturintervalls um eine vorgegebene Zieltemperatur liegt. Vorzugsweise wird die Heizleistung des mindestens einen Heizelements in Abhängigkeit der Befeuchtertemperatur derart geregelt, dass die Befeuchtertemperatur der Zieltemperatur entspricht.

The process is characterized in particular by the following steps:

• Sensing a temperature at or near the humidifier cathode gas inlet,
• Sensing a temperature at or near the humidifier cathode gas outlet,
• - Determining a humidifier temperature by averaging all recorded temperatures, and
• - Controlling a heating power of the at least one heating element as a function of the humidifier temperature such that the humidifier temperature is at least within a predetermined target temperature interval around a predetermined target temperature. The heating power of the at least one heating element is preferably regulated as a function of the humidifier temperature in such a way that the humidifier temperature corresponds to the target temperature.

The improved method for operating a humidifier can react particularly to fluctuating inlet temperatures, which have a significant influence on the transfer behavior of the liquid into the cathode inlet. In particular, the use of the humidifier or the fuel cell system comprising the humidifier in a motor vehicle leads to strongly fluctuating Entry temperatures that negatively affect the transfer behavior of the liquid. This problem resolves this problem. In addition, the temperature within the humidifier can be set very high, so that good liquid absorption into the cathode gas takes place and in particular the cathode gas leaves the humidifier saturated with moisture before it is fed to the fuel cell stack of a fuel cell system.

In order to be able to set and / or regulate the humidifier temperature even better, it has proven to be advantageous if a temperature at or near the cathode exhaust gas inlet is also taken into account when averaging. The temperature and thus the amount of heat that is introduced into the humidifier by the cathode exhaust gas are thus also taken into account.

In order to be able to reliably take into account the amount of heat emitted by the cathode exhaust gas, it is advantageous if a temperature at or near the cathode exhaust gas outlet is also taken into account when averaging.

There is the possibility that when determining the humidifier temperature, in addition to averaging the recorded temperatures, a quantity of heat introduced into the humidifier by at least one heating element and the specific heat capacity of the humidifier are also taken into account. The specific heat capacity of the humidifier is defined as the amount of heat or energy that must be supplied to the humidifier to raise its temperature by one Kelvin (K). When determining the humidifier temperature, a conclusion can be drawn based on the specific heat capacity of the humidifier on the heating power to be used by the at least one heating element.

The efficiency of the humidifier can also be increased by reducing the heating output to zero as long as the specific humidifier temperature corresponds to or exceeds the target temperature. In addition, this configuration sensibly prevents the at least one heating element from additionally raising the humidifier to a temperature range which is damaging to individual components, for example damaging its membrane.

In order to be able to set the target temperature of the humidifier depending on the current or future expected operating point and the resultant necessary water transfer, it has proven to be advantageous if the target temperature or the target temperature interval of the humidifier which is around the target temperature is dependent on forecast or expected load points of the fuel cell system can be specified or adjusted. For this purpose, the method is therefore provided with a predictive component which gives the humidifier an operating mode in which it is adapted more quickly — and therefore more dynamically — to an upcoming required liquid transfer.

The advantages described in connection with the method apply mutatis mutandis to the humidifier, which is distinguished in particular by the fact that a first temperature sensor for detecting a temperature at or near the cathode gas inlet is present, and that a second temperature sensor is available for detecting a temperature at or near the cathode gas outlet and that there is a control device which is designed to determine a humidifier temperature by averaging all the recorded temperatures and to regulate a heating output of the at least one heating element as a function of the humidifier temperature in such a way that the humidifier temperature is at least within a predeterminable target temperature interval around a predetermined target temperature lies. The heating power is preferably regulated in such a way that the humidifier temperature corresponds to the target temperature.

This design of the humidifier has accelerated operability at low temperatures. In addition, due to the increased temperature inside the humidifier, an improved water transfer and overall a smaller design of the humidifier can be realized.

In addition, there is the possibility that a third temperature sensor is present at or near the cathode exhaust gas inlet and / or a fourth temperature sensor at or near the cathode exhaust gas outlet, and that the control device is designed to also form a temperature at or near the cathode exhaust gas inlet when averaging and / or at or near the cathode exhaust outlet. By using additional temperature sensors and taking their values into account when determining the humidifier temperature, an even more robust humidifier can be realized which has a more uniform operating behavior.

In order to make the humidifier particularly compact and to realize an even more efficient water transfer in the humidifier, it has proven to be advantageous if a water vapor permeable membrane is present and if the at least one heating element is integrated into the water vapor permeable membrane, in particular sewn into the membrane, is.

The at least one heating element is preferably designed as a PTC heater (English: “positive temperature coefficient”) or as a PTC resistor, since this acts as a function of temperature and can be adapted to the water transfer behavior. As an alternative or in addition, the at least one heating element can also be formed as a heating spiral, and consequently as an electrical heating wire, which, due to its flat design, can be easily introduced or sewn into the water vapor-permeable membrane, for example.

• 1 eine schematische Darstellung eines Befeuchters mit einem Heizelement,
• 2 der in ein Brennstoffzellensystem eingebundene Befeuchter aus 1, und
• 3 eine zeitabhängige Gegenüberstellung der Befeuchtertemperatur T des Befeuchters gegenüber der zeitabhängigen Darstellung der Leistung des Heizelements P_H des Befeuchters.

Further advantages, features and details of the invention result from the claims, the following description of a preferred embodiment, and with reference to the drawings. Show:

• 1 1 shows a schematic representation of a humidifier with a heating element,
• 2nd the humidifier integrated in a fuel cell system 1 , and
• 3rd a time-dependent comparison of the humidifier temperature T of the humidifier compared to the time-dependent representation of the performance of the heating element P _H of the humidifier.

In 1 is essentially the cathode side of a fuel cell system 100 to recognize. In addition, there is a fuel cell stack comprising several fuel cells 130 shown. Fuel cells serve to provide electrical energy in a chemical reaction between a fuel, usually hydrogen, and an oxygen-containing oxidizing agent, usually air. If the power requirement exceeds the power provided by the fuel cell, there is the possibility of several fuel cells in series with the fuel cell stack 130 to summarize, whereby, however, the need for the reactants involved in a chemical reaction increases and on the cathode side there is the need to use the cathode gas in a compressor 126 to compress. As a result of this compression, the cathode supply line contains highly heated, dry cathode gas after compression, which is for direct use in the fuel cell stack 130 is not suitable since sufficient moisture is required for the proton exchange membrane given in the fuel cell. The cathode supply line is therefore usually downstream of the compressor 126 a charge air cooler 128 and again a humidifier downstream of it or combined with it 102 Arranged in which the cathode gas is humidified by the product water resulting from the chemical reaction via a cathode exhaust line to the humidifier 102 is fed.

The humidifier 102 itself is present with a heating element 112 Mistake. There can be multiple heating elements 112 be present, which is then preferably distributed in the humidifier 102 are arranged. The humidifier 102 has a stack-side cathode exhaust inlet 104 for the moist cathode exhaust, a compressor-side cathode gas inlet 106 for dry cathode gas, a stacked cathode gas outlet 108 for humidified cathode gas and a cathode exhaust outlet 110 for cathode exhaust. The heating element 112 is provided to a temperature of the humidifier 102 to increase or adjust to a desired level at which the transfer of liquid from the moist cathode exhaust gas into the dry supplied cathode gas is optimized. In addition, the fluid transfer from the humid side of the humidifier 102 through a membrane 124 to the dry side of the humidifier 102 be optimized by an adapted temperature.

To control the temperature of the humidifier at hand 102 is a first temperature sensor 114 for sensing a temperature at or near the cathode gas inlet 106 available. There is also a second temperature sensor 116 for sensing a temperature at or near the cathode gas outlet 108 available. There is also a third temperature sensor 118 at or near the cathode exhaust inlet 104 and a fourth temperature sensor 120 at or near the cathode exhaust outlet 110 available.

As can be seen from the broken line, the temperature sensors are located 114 , 116 , 118 , 120 in a communication link with a control unit 122 . With the control unit 122 it can preferably be the control unit 122 of the fuel cell system 100 or the fuel cell stack 130 act. This control unit 122 is designed in the present case to determine a humidifier temperature by averaging all recorded temperatures and a heating power of the at least one heating element 112 to be regulated as a function of the determined humidifier temperature in such a way that the humidifier temperature is at least within a predeterminable target temperature interval around a predetermined target temperature.

The target temperature is therefore a temperature of the humidifier 102 , in which the liquid transfer from the moist fluid into the dry cathode gas is optimized. The control unit 122 can also be connected to a temperature sensor (not shown) which measures the ambient temperature in order to be able to take this into account when determining the humidifier temperature.

The control unit 122 is also with a switch 142 communicative so that the control unit 122 the switch depending on the humidifier temperature and the target temperature 142 actuated a circuit in which the heating element 112 is involved or available. The heating element 112 is formed here as a heating wire and preferably in one or more of the membranes 124 of the humidifier 102 integrated or sewn. The humidifier 102 with the temperature sensors 114 , 116 , 118 , 120 and the heating element 112 have a configuration such that the heating element 112 at least between two of the temperature sensors 114 , 116 , 118 , 120 is positioned. If the control unit 122 the switch 142 closes, a current flows through the heating element formed as a heating wire 112 , causing the temperature inside the humidifier 102 is raised to improve fluid transfer. The circuit in which the heating element 112 is present, has a power source that when the switch is closed 142 with the heating element 112 is connected and this is energized. But it should be mentioned that the control unit 122 can also be designed, one from the fuel cell stack 130 to conduct current generated in the circuit in which the heating element 112 is present, so that no separate power source for this heating element 112 necessary is. This can be done between the circuit and the fuel cell stack 130 there is also a converter to adjust the current accordingly.

In 2nd is the fuel cell system 100 with the humidifier explained above 102 shown. The humidifier 102 is with its cathode-side cathode gas outlet 108 via a cathode supply line with cathode spaces of a fuel cell stack 130 connected. In addition, the humidifier 102 with its cathode exhaust gas inlet 104 also connected to the cathode compartments via a cathode exhaust gas line, via which unreacted cathode gas or moist cathode exhaust gas to the humidifier 102 is returned. The cathode gas becomes the cathodes of the majority in the fuel cell stack via the cathode spaces 130 arranged fuel cells supplied. Proton-conductive membranes separate the cathodes from the anodes of the fuel cells, and fuel (eg hydrogen) can be fed to the anodes via anode spaces. The anode compartments are connected via an anode feed line with a fuel reservoir that provides the fuel 132 connected. Via an anode recirculation line 138 Unreacted fuel can be fed back to the anode compartments at the anodes. In this case, the anode recirculation is preferably assigned a recirculation blower (not shown in more detail) or fluid mechanically into the anode recirculation line 138 coupled. The anode supply line is a fuel actuator for regulating the supply of fuel 134 assigned or arranged in the anode supply line. This fuel actuator 134 is preferably formed as a pressure control valve. Upstream of the pressure control valve is a heat exchanger 136 , preferably provided in the form of a recuperator for (pre) heating the fuel.

A separator is present in the anode circuit 140 , preferably a water separator through which liquid can be accumulated. The drain of the separator 140 can be connected to a liquid line leading the separator 140 with a humidifier fluid supply, not shown 102 connects to the liquid in the anode circuit for humidifying the cathode gas in the humidifier 102 to be able to use. In other words, the liquid generated on the anode side can thus be used to dispense it on the cathode side for moistening the cathode gas in the humidifier 102 to use. To the amount of in the humidifier 102 In order to be able to adjust the guided liquid, the liquid line can be assigned a liquid actuator, also not shown, in particular a valve, or can be fluid mechanically coupled into it. The liquid actuator then enables the preferably preferably controllable supply of the liquid from the separator 140 to the humidifier present in the cathode circuit 102 .

From the representation of the 3rd it can be seen that at the beginning the humidifier temperature of the humidifier 102 far below a target temperature shown in dashed lines ( T _G ) lies and therefore a great achievement ( P _H ) from the heating element 112 is applied to the temperature of the humidifier 102 to raise. Once the humidifier temperature of the humidifier 102 the target temperature T _G the achievement is reached or exceeded P _H of the at least one heating element 112 reduced to zero. If the humidifier temperature falls below the target temperature again T _G , so will the performance P _H of the heater increased again.

The following describes how the humidifier 102 with its heating element 112 is operated. First, the temperature at or near the cathode gas inlet 106 of the humidifier 102 by means of the first temperature sensor 114 detected. Then or at the same time the temperature at or near the cathode gas outlet 108 of the humidifier 102 with the second temperature sensor 116 detected. Subsequently or simultaneously, the temperature at or near the cathode exhaust gas inlet is also measured 104 by means of the third temperature sensor 118 detected. Subsequently or at the same time, the temperature at or near the cathode exhaust outlet is also increased 110 by means of the fourth temperature sensor 120 detected.

Then a humidifier temperature is obtained by averaging all the recorded temperatures determines after which a regulation of the heating power of the at least one heating element 112 as a function of the determined humidifier temperature, the humidifier temperature is at least within a predetermined target temperature interval around the predetermined target temperature T _G lies.

When determining the humidifier temperature, in addition to averaging the recorded temperatures, one from the heating element is also preferred 112 in the humidifier 102 heat introduced and the specific heat capacity of the humidifier 102 considered. Should the humidifier temperature be the target temperature T _G reach or exceed this, the heating power of the at least one heating element 112 reduced to zero and held there until the humidifier temperature reaches the target temperature T _G falls below again.

It should be noted that the humidifier 102 can also be used in a predictive operation, with the target temperature T _G or the target temperature T _G lying target temperature interval of the humidifier 102 can be moved depending on the forecast or expected load points of the fuel cell system 100 .

The humidifier 102 and the method of operating the humidifier 102 are characterized by an efficient transfer of the liquid into the dry cathode gas. The humidifier 102 is operational more quickly at low outside temperatures. The humidifier can also 102 due to the heating element used 112 be structurally smaller, since an increased water transfer can be achieved due to the adjustable temperatures. Overall, the humidifier points 102 a robust design and more uniform operating behavior.

Reference list

100

Fuel cell system

102

Humidifier

104

Cathode exhaust inlet

106

Cathode gas inlet

108

Cathode gas outlet

110

Cathode exhaust outlet

112

Heating element

114

first temperature sensor

116

second temperature sensor

118

third temperature sensor

120

fourth temperature sensor

122

Control unit

124

membrane

126

compressor

128

Intercooler

130

Fuel cell stack

132

Fuel storage

134

Fuel

136

Heat exchanger

138

Recirculation line

140

Separator

142

switch

QUOTES INCLUDE IN THE DESCRIPTION

This list of documents listed by the applicant has been generated automatically and is only included for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent literature cited

• DE 102005056833 B4 [0003]
• DE 102013021506 A1 [0003]
• JP 2003156238 A [0003]

Claims (10)

Method for operating a humidifier (102) of at least one heating element (112) of a fuel cell system (100), with a stack-side cathode exhaust gas inlet (104) for a moist cathode exhaust gas, with a compressor-side cathode gas inlet (106) for dry cathode gas, with a stack-side cathode gas outlet (108 ) for humidified cathode gas and with a cathode exhaust gas outlet (110) for cathode exhaust gas, characterized by the steps: - detecting a temperature at or near the cathode gas inlet (106) of the humidifier (102), - detecting a temperature at or near the cathode gas outlet (108) of the Humidifier (102), - determining a humidifier temperature by averaging all recorded temperatures, and - regulating a heating output of the at least one heating element (112) as a function of the humidifier temperature such that the humidifier temperature is at least within a predetermined target temperature interval by a predetermined target temperature lies. Procedure according to Claim 1 , characterized in that a temperature at or near the cathode exhaust gas inlet (104) is also taken into account when averaging. Procedure according to Claim 1 or 2nd , characterized in that a temperature at or near the cathode exhaust outlet (110) is also taken into account when averaging. Method according to one of claims 1 to 3, characterized in that, when determining the humidifier temperature, in addition to averaging from the recorded temperatures, a quantity of heat introduced into the humidifier (102) by at least one heating element (112) and the specific heat capacity of the humidifier (102 ) are taken into account. Method according to one of claims 1 to 4, characterized in that the heating power is reduced to zero as long as the determined humidifier temperature corresponds to or exceeds the target temperature. Method according to one of Claims 1 to 5, characterized in that the target temperature or the target temperature interval of the humidifier (102) which is around the target temperature is predetermined or set as a function of predicted or expected load points of the fuel cell system (100). Humidifier (102) of a fuel cell system (100) for carrying out the method according to one of claims 1 to 6, with at least one heating element (112), with a stack-side cathode exhaust gas inlet (104) for a moist cathode exhaust gas, with a compressor-side cathode gas inlet (106) for dry Cathode gas, with a stack-side cathode gas outlet (108) for humidified cathode gas and with a cathode exhaust gas outlet (110) for cathode exhaust gas, characterized in that a first temperature sensor (114) for detecting a temperature at or near the cathode gas inlet (106) is present, that a second There is a temperature sensor (116) for detecting a temperature at or near the cathode gas outlet (108), and that a control device (122) is provided, which is designed to determine a humidifier temperature by averaging all the recorded temperatures and a heating power of the at least one heating element (112) depending on the humidification to regulate the temperature such that the humidifier temperature is at least within a predefinable target temperature interval around a predetermined target temperature. Humidifier (102) after Claim 7 , characterized in that there is a third temperature sensor (118) at or near the cathode exhaust gas inlet (104) and / or a fourth temperature sensor (120) at or near the cathode exhaust gas outlet (110), and in that the control device (122) is designed at the averaging also takes into account a temperature at or near the cathode exhaust gas inlet (104) and / or at or near the cathode exhaust gas outlet (110). Humidifier (102) after Claim 7 or 8th , characterized in that a water vapor permeable membrane (124) is present and that the at least one heating element (112) is integrated in the water vapor permeable membrane (124). Humidifier (102) according to one of claims 7 to 9, characterized in that the at least one heating element (112) is formed as an electrical PTC heater or as an electrical heating wire.

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