DE102020206898A1 - Method for determining the gas temperature in an anode path of a fuel cell system, control device and computer program product - Google Patents

Abstract

The invention relates to a method for determining the gas temperature in an anode path (1) of a fuel cell system, via which an anode gas is fed to at least one fuel cell (2) of the fuel cell system during operation of the fuel cell system (1) arranged, is heated by a coolant of an external cooling circuit (4) flowing through the heat exchanger (5). According to the invention, the gas temperature is determined in the area of the gas outlet from the heat exchanger (5) and an energy balance of the cooling circuit (4) is carried out to determine the gas temperature. The invention also relates to a control device (7) and a computer program product for executing the method according to the invention.

Description

The invention relates to a method for determining the gas temperature in an anode path of a fuel cell system according to the preamble of claim 1. Furthermore, the invention relates to a control device and a computer program product.

State of the art

Fuel cell systems are used in stationary and mobile applications to generate electrical energy. You need hydrogen and oxygen for this. The required oxygen is supplied in the form of air that is taken from the environment. The hydrogen that is also required is held in special storage facilities. These can be pressurized gas storage tanks or so-called cryotanks, in which hydrogen is stored at low temperatures, i.e. at temperatures down to -252 ° C. The gas temperature in a pressurized gas storage tank is usually between -40 ° C and + 85 ° C.

To optimize the operation of a fuel cell system and to protect the following components, the hydrogen taken from a storage tank or tank is usually heated with the help of a heat exchanger so that the temperature is between 60 ° C and 85 ° C. In a mobile application, a heat exchanger that is integrated into a vehicle cooling system can be used for this purpose. This is because the temperature of the working fluid in a vehicle cooling system is between 40 ° C and 90 ° C during normal operation. Compliance with the hydrogen temperature in the hydrogen supply of a fuel cell system is usually monitored with the help of suitable sensors. However, it proves to be disadvantageous that suitable sensors are expensive. In addition, an additional interface is created in an anode path of the fuel cell system, via which the hydrogen supply takes place. The additional interface increases the risk of leakage.

The present invention is therefore based on the object of providing a method and a device for determining the gas temperature in an anode path of a fuel cell system, which do not require any additional sensors, so that the above-mentioned disadvantages are avoided.

To achieve the object, the method with the features of claim 1 is proposed. Advantageous further developments of the invention can be found in the subclaims. In addition, a control device and a computer program product for executing the method are specified.

Disclosure of the invention

The proposed method is used to determine the gas temperature in an anode path of a fuel cell system, via which an anode gas is fed to at least one fuel cell of the fuel cell system during operation of the fuel cell system, which anode gas is taken from a gas reservoir and with the aid of a heat exchanger arranged in the anode path and through which a coolant of an external cooling circuit flows is heated. According to the invention, the gas temperature in the region of the gas outlet from the heat exchanger is determined and an energy balance of the cooling circuit is carried out to determine the gas temperature.

The gas temperature is therefore not determined directly, but indirectly via the energy balance of the cooling circuit. This means that there is no need to intervene in the anode path. In particular, an additional sensor and thus a further interface in the anode path can be omitted. In this way the risk of leakage is minimized. At the same time, the number of parts is reduced, so that costs and space requirements are reduced.

The heat flow Q that is transferred from the coolant to the gas is preferably determined within the framework of the energy balance. Because when the gas in the anode path is heated, heat is withdrawn from the coolant, so that the heat flow Q and thus the heating of the gas in the anode path can be determined on the basis of the temperature difference between the coolant inlet temperature and the coolant outlet temperature. If the gas inlet temperature and the gas mass flow through the heat exchanger are known, the gas outlet temperature can be determined with knowledge of the heat flow Q.

worin
m = Massenstrom
c_p = spezifische Wärmekapazität
T_ein = Eintrittstemperatur
T_aus = AustrittstemperaturThe following formula is preferably used to determine the heat flow Q: $$\dot{Q}={\dot{m}}_{Gas}\ast c_{p,Gas}\ast \left(T_{Gas,ein}-T_{Gas,aus}\right)={\dot{m}}_{K\mathrm{M.}}\ast c_{p,K\mathrm{M.}}\ast \left(T_{K\mathrm{M.},ein}-T_{K\mathrm{M.},aus}\right)$$

wherein
m = mass flow
c _p = specific heat capacity
T _a = inlet temperature
T _off = outlet temperature

The "Gas" index relates to the gas in the anode path, the "KM" index to the coolant in the cooling circuit.

The coolant inlet temperature T _KM , in and the coolant outlet temperature T _{KM, out} are preferably measured. The cooling circuit is equipped with suitable sensors for this purpose. From the measured temperatures T _{KM, KM,} and _{T, from} the temperature difference .DELTA.T is then determined.

According to the above formula, the heat flow Q is not only _{dependent on the temperature difference between T KM, on} and T _{KM, off} , but also on the coolant mass flow ṁ _KM and that of the specific heat capacity c _{p, KM of} the coolant. The specific heat capacity c _{p, KM of} the coolant can be assumed to be known. The coolant mass flow ṁ _KM , however, must be determined. Various methods are suitable for this.

According to a first method, the coolant mass flow ṁ _{KM is} modeled. The heat exchanger was advantageously measured beforehand so that the coolant mass flow ṁ _KM can be modeled on the basis of the measurement data. The coolant inlet pressure applied to the heat exchanger is required as a further variable. This can be derived, for example, from the speed of an electrically driven coolant pump or - alternatively - from the control data and the pump characteristics of an electrically driven auxiliary pump.

The speed of an electrically driven coolant pump is usually known, so that the coolant inlet pressure and the coolant mass flow can be derived from it, depending on the operating point of the coolant pump. If the cooling circuit is not supplied with coolant via its own coolant pump, but rather via an electrical auxiliary pump, the control data of the auxiliary pump can be used as the basis for determining the coolant inlet pressure and the coolant mass flow.

Knowing the coolant mass flow, the specific heat capacity of the coolant and the temperature difference ΔT in the coolant, the amount of energy transferred can now be balanced on the basis of the above formula. The gas inlet _{temperature T gas, in} other words the gas temperature when the gas enters the heat exchanger, depends, among other things, on the temperature in the gas reservoir. The specific heat capacity c _{p, gas of} the gas is again known. The gas mass flow through the heat exchanger can be calculated on the basis of the gas consumption, so that the gas outlet temperature T _gas can be determined on the basis of all these data.

worin
α = Wärmeübergangskoeffizient
T_ein = Eintrittstemperatur
ṁ = MassenstromAccording to a second method, the heat flow Q can be determined approximately. The following formula is preferably used here: $$\dot{Q}~\propto \ast T_{K\mathrm{M.},ein}\ast {\dot{m}}_{K\mathrm{M.}}$$

wherein
α = heat transfer coefficient
T _a = inlet temperature
ṁ = mass flow

The heat transfer coefficient α characterizes the thermal behavior of the heat exchanger and can be stored in a characteristic curve or a characteristic map, for example in a control unit for controlling the cooling circuit. The heat transfer coefficient α is preferably determined by means of the similarity theory and stored for a relevant operating range of the heat exchanger. With the knowledge of the coolant inlet temperature T _{KM, a} and the coolant mass flow ṁ _KM , the amount of heat transferred to be determined. _{The gas outlet temperature T gas} can in turn be deduced from the amount of heat transferred.

The advantage of the second method is in particular that a maximum of one temperature sensor is required in the cooling circuit, with the aid of which the coolant inlet temperature T _{KM, on is} measured.

The coolant mass flow (ṁ _KM ) can be modeled analogously to the first method for determining the heat flow Q, preferably taking into account the coolant inlet pressure applied to the heat exchanger. This in turn can - analogously to the first method - be derived from the speed of an electrically driven coolant pump or from the control data and the pump characteristics of an electrically driven auxiliary pump.

Any calculation errors that occur when using the method according to the invention, specifically according to the first and / or second method, can be corrected with a system-related dead time via the necessary gas temperature sensor. This gas temperature sensor is usually indispensable and is arranged further downstream in the anode path.

If the determination of the gas temperature in the area of the gas outlet from the heat exchanger shows that it deviates from a target value, the coolant mass flow in the cooling circuit can be varied via an actuator.

In addition, a control device is proposed which is set up to carry out the method according to the invention. In particular, the data required to carry out the method can be stored in the control device or transmitted to the control device during operation so that the energy balance of the cooling circuit required to determine the gas temperature can be carried out with the aid of the control device.

• - die spezifische Wärmekapazität des Gases
• - die Gastemperatur im Gasspeicher zur Ermittlung der Gas-Eintrittstemperatur,
• - der aktuelle Gasverbrauch im Betrieb des Brennstoffzellensystems,
• - die spezifische Wärmekapazität des Kühlmittels,
• - die Drehzahl einer Kühlmittelpumpe des Kühlkreises,
• - die Ansteuerdaten und die Pumpencharakteristik einer Nebenpumpe, die der Versorgung mit Kühlmittel dient, und/oder
• - die Messdaten mindestens eines am Kühlkreis angeordneten Temperatursensors zur Bestimmung der Kühlmittel-Eintrittstemperatur und/oder der Kühlmittel-Austrittstemperatur.

The following data and / or values are preferably available to the control unit for the required energy balance:

• - the specific heat capacity of the gas
• - the gas temperature in the gas storage tank to determine the gas inlet temperature,
• - the current gas consumption in the operation of the fuel cell system,
• - the specific heat capacity of the coolant,
• - the speed of a coolant pump in the cooling circuit,
• - The control data and the pump characteristics of a secondary pump that is used to supply coolant, and / or
• - The measurement data of at least one temperature sensor arranged on the cooling circuit for determining the coolant inlet temperature and / or the coolant outlet temperature.

With the help of these data and / or values, the determination of the heat flow Q required for energy balancing can be carried out according to the first method. In order to be able to correct the gas temperature determined in this way if necessary, it is also proposed that the control device be aware of the sensor data of a gas temperature sensor present further downstream in the anode path.

In order to be able to determine the heat flow Q according to the second method, at least one characteristic curve / map of the heat exchanger describing the thermal behavior of the heat exchanger is preferably stored in the control device - as an alternative or in addition.

The control device is also preferably connected in a data-transferring manner to an actuator for regulating the coolant mass flow in the cooling circuit, so that this can be varied as a function of the gas temperature in the region of the gas outlet from the heat exchanger.

Computer program product with a program code which executes the method according to the invention when the computer program runs on a computer and / or control device.

• 1 eine schematische Darstellung des Anodenpfads eines ersten zur Durchführung des erfindungsgemäßen Verfahrens geeigneten Brennstoffzellensystems und
• 2 eine schematische Darstellung des Anodenpfads eines zweiten zur Durchführung des erfindungsgemäßen Verfahrens geeigneten Brennstoffzellensystems.

The invention is explained in more detail below with reference to the accompanying drawings. These show:

• 1 a schematic representation of the anode path of a first fuel cell system suitable for carrying out the method according to the invention and
• 2 a schematic representation of the anode path of a second fuel cell system suitable for carrying out the method according to the invention.

Detailed description of the drawings

The Indian 1 shown anode path 1 serves to supply an anode of at least one fuel cell 2 a fuel cell system with an anode gas, which in the present case is hydrogen, which is stored in a gas storage tank 3 is stored. The anode path 1 thus connects the gas storage tank 3 with the anode of the at least one fuel cell 2 .

In the anode path 1 is a shut-off valve 8th to enable the extraction of gas from the gas storage tank 3 arranged. Furthermore, upstream and downstream of a heat exchanger 5 is a pressure regulator 9 intended. Downstream of the heat exchanger 5 is a metering valve 10 for pressure control in the anode path 1 arranged. With the help of the heat exchanger arranged in between 5 the gas can be brought to a suitable operating temperature, in particular heated. Further downstream is a temperature sensor 11th in the anode path 1 arranged.

worin
ṁ = Massenstrom
c_p = spezifische Wärmekapazität
T_ein = Eintrittstemperatur
T_aus = AustrittstemperaturThe heat exchanger 5 is in a cooling circuit 4th integrated in which a coolant circulates. Since the gas temperature is below the temperature of the coolant, the coolant in the heat exchanger is used 5 a heat flow Q is given off to the gas so that the gas flows through the heat exchanger 5 is heated. This means that the gas temperatures on the inlet and outlet sides are different in relation to the heat exchanger 5 differentiate. The same applies to the inlet and outlet temperatures of the coolant. The relationship can be shown using the following formula: $$\dot{Q}={\dot{m}}_{Gas}\ast c_{p,Gas}\ast \left(T_{Gas,ein}-T_{Gas,aus}\right)={\dot{m}}_{K\mathrm{M.}}\ast c_{p,K\mathrm{M.}}\ast \left(T_{K\mathrm{M.},ein}-T_{K\mathrm{M.},aus}\right)$$

wherein
ṁ = mass flow
c _p = specific heat capacity
T _a = inlet temperature
T _off = outlet temperature

Via the heat flow Q or the coolant mass flow through the heat exchanger 5 the gas outlet temperature can thus be influenced. In order to vary the coolant mass flow, if necessary, is on the cooling circuit 4th an actuator 6th provided via a control unit 7th is controllable. To determine whether the coolant mass flow has to be varied, the gas outlet temperature must be monitored. This can be done with the help of another temperature sensor. However, this is expensive and requires further intervention in the anode path 1 so that the risk of leakage increases.

The method according to the invention therefore sees no further temperature measurement on the anode path 1 , but on the cooling circuit 4th before. With the help of at least one on the cooling circuit 4th arranged temperature sensor 12th the coolant inlet temperature and the coolant outlet temperature are measured. The measurement data are transmitted via a data line 13th to the control unit 7th transmitted, which uses this data to carry out an energy balance. The control unit 7th not only are the measurement data from the at least one temperature sensor 12th before, but also the respective specific heat capacities of the gas and the coolant. The respective mass flows through the heat exchanger are also known 5 or they are determined. The coolant mass flow can, for example, be derived from the speed of an electric coolant pump (not shown) that is supplied to the control unit 7th is known. Alternatively, the control data and pump characteristics of a secondary pump (not shown) replacing the coolant pump can be used, which in this case is the control unit 7th are also known.

worin
α = Wärmeübergangskoeffizient
Tein = Eintrittstemperatur
m = MassenstromTo just take a temperature measurement at one point in the cooling circuit 4th must be made, the calculation of the heat flow Q can also be based on the following relationship: $$\dot{Q}~\propto \ast T_{K\mathrm{M.},ein}\ast {\dot{m}}_{K\mathrm{M.}}$$

wherein
α = heat transfer coefficient
Tein = inlet temperature
m = mass flow

As exemplified in the 2 shown, in this case only the coolant inlet temperature or the coolant outlet temperature with the aid of the temperature sensor 12th measured and the control unit 7th made available. The thermal behavior of the heat exchanger 5 or the heat transfer coefficient α can already be used as a characteristic curve or map in the control unit 7th be stored, for example in a data memory 14th . The coolant mass flow can be determined using the method described above.

If the gas outlet temperature deviates from a target value, the control unit can be used 7th via a control line 15th the actuator 6th be controlled to the coolant mass flow through the heat exchanger 5 to vary. The gas outlet temperature in the anode path rises or falls accordingly 1 .

The calculated gas outlet temperature can be checked using the measurement data from the temperature sensor 11th be made to the control unit 7th via a data line 13th to provide.

Claims (10)

Method for determining the gas temperature in an anode path (1) of a fuel cell system, via which an anode gas is fed to at least one fuel cell (2) of the fuel cell system during operation of the fuel cell system, which anode gas is taken from a gas reservoir (3) and arranged with the aid of an anode path (1) , is heated by a coolant of an external cooling circuit (4) flowing through the heat exchanger (5), characterized in that the gas temperature is determined in the region of the gas outlet from the heat exchanger (5) and an energy balance of the cooling circuit (4) is carried out to determine the gas temperature . Procedure according to Claim 1 , characterized in that the heat flow (Q) that is transferred from the coolant to the gas is determined as part of the energy balance. Procedure according to Claim 2 , characterized in that the following formula is used to determine the heat flow (Q): $$\dot{Q}={\dot{m}}_{Gas}\ast c_{p,Gas}\ast \left(T_{Gas,ein}-T_{Gas,aus}\right)={\dot{m}}_{K\mathrm{M.}}\ast c_{p,K\mathrm{M.}}\ast \left(T_{K\mathrm{M.},ein}-T_{K\mathrm{M.},aus}\right)$$

wherein M = mass flow _p c = specific heat capacity of _a T = inlet temperature T _off = outlet temperature Procedure according to Claim 2 , characterized in that the following formula is used to determine the heat flow (Q): $$\dot{Q}~\propto \ast T_{K\mathrm{M.},ein}\ast {\dot{m}}_{K\mathrm{M.}}$$

where α = heat transfer coefficient Tein = inlet temperature m = mass flow Procedure according to Claim 3 or 4th Characterized in that at least the coolant inlet temperature (T _{KM, a),} preferably the coolant inlet temperature (T _{KM, a)} and the coolant outlet temperature (T _{KM, off)} is measured or are. Method according to one of the Claims 3 until 5 , characterized in that the coolant mass flow (ṁ _KM ) is modeled, preferably taking into account the coolant inlet pressure applied to the heat exchanger (5). Procedure according to Claim 6 , characterized in that the coolant inlet pressure is derived from the speed of an electrically driven coolant pump or from the control data and the pump characteristics of an electrically driven auxiliary pump. Method according to one of the preceding claims, characterized in that if the gas temperature in the area of the gas outlet from the heat exchanger (5) deviates from a setpoint value, the coolant mass flow (ṁ _KM ) in the cooling circuit (4) via an actuator (6 ) is varied. Control device (7) which is set up to carry out a method according to one of the preceding claims. Computer program product with a program code, which a method according to one of the Claims 1 until 8th executes when the computer program product runs on a computer and / or control device (7).

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