Fuel cell system for generating energy and water

Abstract

Fuel cell systems aboard means of transport can be used for generating energy and for producing water. In order to reduce the overall weight of the system, the fuel cell is controlled or regulated in dependence on a current fill level or a limit level of the water tank, as well as a predicted future water consumption. In this way, it may be possible to minimize the water quantity to be stored in the water tank.

Claims

1. A fuel cell system for generating electric energy and water for use aboard a means of transport, with the fuel cell system comprising: a fuel cell; a water tank for storing water delivered by the fuel cell; a control device configured to control operation of the fuel cell in dependence on a current fill level or limit level of the water tank and on a predicted future water consumption based on flight phase and remaining flight time.

2. The fuel cell system of claim 1, wherein the control device is further configured to control the fuel cell in dependence on a previous water consumption.

3. The fuel cell system of claim 1, wherein the control device comprises a fill level control device with a fill level sensor or a limit level sensor.

4. The fuel cell system of claim 1, further comprising: a condensation device configured to condense the water delivered by the fuel cell before the water is fed to the tank; wherein the control device is configured to control the fuel cell based on efficiency of the condensation device.

5. The fuel cell system of claim 4, wherein the control device comprises a performance demand signal control configured to determine a nominal value for the water production rate of the fuel cell based on efficiency of the condensation device.

6. The fuel cell system of claim 5, wherein a decrease of the efficiency of the condensation device leads to an increase of the nominal value.

7. The fuel cell system of claim 1, wherein the control device comprises a performance demand signal limiter configured to limit the nominal value for the performance of the fuel cell based on power consumption of electric consumers aboard the means of transport or fuel supply for the fuel cell.

8. A means of transport with a fuel cell system, the fuel cell system comprising: a fuel cell; a water tank for storing water delivered by the fuel cell; a control device configured to control the fuel cell in dependence on a current fill level or limit level of the water tank and on a predicted future water consumption based on flight phase and remaining flight time.

9. The means of transport of claim 8, wherein the means of transport comprises an aircraft.

10. A method for generating electric energy and water aboard a means of transport by a fuel cell system, with said method comprising: supplying fuel to a fuel cell; generating electric energy by the fuel cell; obtaining water from waste gas of the fuel cell; filling a water tank with the obtained water; controlling the fuel cell in dependence on a current fill level or limit level of the water tank and on a predicted future water consumption based on flight phase and remaining flight time.

11. The method of claim 10, further comprising: controlling the fuel cell based on previous water consumption.

12. The method of claim 10, further comprising: controlling or regulating the fuel cell based on efficiency of a condensation device.

13. The method of claim 10, further comprising: limiting a nominal value for the performance of the fuel cell based on power consumption of electric consumers aboard the means of transport or with consideration of a fuel supply for the fuel cell.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Exemplary embodiments of the invention are described below with reference to the figures.

(2) FIG. 1 shows a fuel cell system with a water supply according to an exemplary embodiment of the invention.

(3) FIG. 2 shows a fuel cell system with a power supply according to an exemplary embodiment of the invention.

(4) FIG. 3 shows a flow chart of a control or regulating process according to an exemplary embodiment of the invention.

(5) FIG. 4 shows the dependence of the maximum permissible water tank fill level, the upper limiting value of the water tank fill level and the lower limiting value of the water tank fill level on the time.

(6) FIG. 5 shows the dependence of the condensation efficiency on the temperature of the condenser.

(7) FIG. 6 shows a flowchart of a process for regulating the water tank fill level.

(8) FIG. 7 shows two tables for elucidating the characteristics of the fill level control or regulating process.

(9) FIG. 8A shows four tables for elucidating the characteristics of the performance demand signal control according to an exemplary embodiment of the invention.

(10) FIG. 8B shows a diagram for elucidating the characteristics of the performance demand signal control according to another exemplary embodiment of the invention.

(11) FIG. 8C shows a diagram for elucidating the characteristics of the performance demand signal control according to the exemplary embodiment of FIG. 8B.

(12) FIG. 9 shows a flow chart of a performance demand signal limiting process according to an exemplary embodiment of the invention.

(13) FIG. 10 shows an aircraft according to an exemplary embodiment of the invention.

DETAILED DESCRIPTION

(14) The figures show schematic illustrations that are not true-to-scale.

(15) In the following description of the figures, identical or similar elements are identified by the same reference symbols.

(16) FIG. 1 shows a fuel cell system 100 according to an exemplary embodiment of the invention. The power supply system for distributing the electric energy generated by the fuel cell 101 to the on-board loads, i.e. consumers, is not illustrated (in this respect, see FIG. 2).

(17) A water generation system 102 featuring, for example, one or more condensers and a water separator is arranged downstream of the fuel cell 101. The water obtained from the waste gas of the fuel cell 101 in this fashion is then fed to a water tank 103 and stored therein.

(18) The water consumers 104 are connected to the water tank 103 by means of a corresponding pipe system. A drain valve 105 is also provided on the water tank 103 in order to prevent the water tank 103 from being overfilled. The excess water may be discharged, for example, into the surroundings of the means of transport.

(19) Several sensors 106 to 111 are provided and measure, for example, the fill level or limit level of the water tank 103 (sensor 110), the efficiency of the water generation system 102 (sensor 108) and/or certain parameters of the fuel cell 101 (sensor 106). The waste gas rate of the fuel cell 101 can also be measured, for example, with the sensor 107. The sensor 109 measures the actual water production rate, for example, by measuring the flow through the water pipe between the water generation system 102 and the tank 103.

(20) Other sensors 111 may be provided in order to measure the water demand and/or the energy demand of the on-board loads 104.

(21) The control or regulating device 115 is supplied with the sensor data from the sensors 106 to 111 via a data bus 112 and controls the fuel cell 101 based on the sensor data of one or more of these sensors. For this purpose, a control line 113 is provided and connects the control or regulating device 115 to the fuel cell 101. The control or regulating device 115 can also control the drain valve 105 via the control line 114.

(22) It should be noted that it would also be possible to provide more or fewer sensors. In a simple scenario, only a limit level sensor is provided in order to detect a limit level of the water tank 103.

(23) The control or regulating device 115 can adjust the operating point of the fuel cell 101. The fuel cell system delivers electric energy to the on-board electrical system together with other energy generators (see FIG. 2) while the water production system delivers water into the tank 103, from which the water consumers 104 aboard the means of transport are supplied.

(24) At this point, it should be noted that a plurality of fuel cells 101 may also be provided.

(25) According to FIG. 2, additional energy generators 202 for generating electric energy may be provided and connected to the electrical network 203 of the means of transport analogous to the fuel cell 101. The electric loads 204 are supplied with electric energy via this electrical network 203.

(26) FIG. 3 shows a flow chart of a regulating process according to an exemplary embodiment of the invention. The control or regulating device 115 features a tank fill level control or regulating device 301, a downstream performance demand signal control 302, a performance demand signal limiter 303 arranged downstream thereof and a fuel cell performance regulator 304 arranged downstream of the performance demand signal limiter.

(27) The tank fill level control or regulating device 301 comprises, for example, a two-position controller that detects limit fill levels. If the lower limiting value of the water tank fill level V.sub.Tu is not reached, the device 301 sends a demand signal for the production of water to the performance demand signal control 302. The demand signal is once again reset once the water level in the tank rises and the upper limiting value V.sub.To is exceeded (see FIG. 4). If the maximum permissible fill level V.sub.Tmax is exceeded, a drain valve 105 opens and discharges the excess water outward into the surroundings of the means of transport (for example, of the aircraft).

(28) The control or regulating device may be expanded in order to achieve a more precise control or regulation of the fill level in the tank V.sub.T and to operate the fuel cell at the optimal operating point, i.e., in the partial-load range, for as long as possible. In this case, the water quantity V.sub.V consumed in the last time interval and/or the current flight phase are taken into consideration. It is checked if the consumed water quantity V.sub.V exceeds a critical limiting value V.sub.Vkrit and if the catering for the passengers and the higher water consumption associated therewith (e.g., for the preparation of coffee or tea) will take place in the near future. A demand signal for the water quantity V.sub.Gsoll to be produced in the next time interval is output with the aid of a suitable calculation method in dependence on the three influencing variables tank fill level V.sub.T, water consumption V.sub.V and flight phase. In this case, the signal V.sub.Gsoll can assume the three states no water production, water production at optimal operating point or maximum water production. One possible method is illustrated in an exemplary fashion in FIGS. 6 and 7.

(29) The consumed water quantity can be measured, e.g., with a flow sensor in the supply pipe on the water tank outlet. Another option consists of calculating the water consumption from the opening times of the individual consumers (e.g., water faucets and flushing valves in the toilets) and the water pressure in the system.

(30) The flight phase or the elapsed and the remaining flying time are known from the on-board computer that is also connected to the control or regulating device 115. The termination of the catering phases may either be preadjusted or input by the cabin crew during the flight.

(31) According to FIG. 3, sensor measurement data with respect to the water tank fill level V.sub.T and the current water consumption rate V.sub.V, as well as information on the flight phase, is fed to the tank fill level control or regulating device 301.

(32) The device 301 calculates the water generation rate V.sub.Gsoll thereof in the form of a nominal value.

(33) For example, information on the cooling temperature of the condenser T.sub.K, the ambient pressure P.sub.U and the air inflow velocity v.sub.L may be fed to the performance demand signal control 302.

(34) The performance demand signal control 302 translates the output signal V.sub.Gsoll of the tank fill level regulating device 301 into a performance demand signal P.sub.Wsoll for the fuel cell that is required for the water production, for example, with consideration of the efficiency of the condensation K of the condenser. The signal V.sub.Gsoll may assume, for example, three values that represent no water production, average water production and maximum water production.

(35) The condensation efficiency K describes the proportion of the water actually produced in the water production system in relation to the absolute water quantity in the fuel cell waste gas. Due to the characteristics of the system, it is not possible to use the entire water quantity contained in the waste gas for the water system. The exhaust air exiting the water separator contains a residual quantity of water. The cooling temperature of the condenser T.sub.K can have the most significant operational influence on the condensation efficiency (see FIG. 5). A very high condensation efficiency is achieved at cruising altitudes and the correspondingly low outside temperatures, wherein the condensation efficiency is much lower on the ground and the correspondingly high outside temperatures. A mathematical model of the condensation efficiency K as a function of different physical parameters such as, e.g., the cooling temperature T.sub.K, the ambient pressure P.sub.U and the air inflow velocity v.sub.L is stored in the performance demand signal control 302 and serves for calculating the instantaneous condensation efficiency.

(36) Two options for calculating the performance demand for the water generation (nominal value) P.sub.Wsoll are described below:

(37) 1. It is determined if the instantaneous condensation coefficient K has fallen short of a limiting value K.sub.krit. The performance demand signal P.sub.Wsoll required for the water production is generated in the increments no performance demand, performance demand at optimal operating point P.sub.Bzopt and maximum performance demand P.sub.BZmax in dependence on the result of the aforementioned determination and in connection with the output signal V.sub.Gsoll of the tank fill level regulating device (see FIG. 8A).

(38) 2. In case the tank fill level regulating device 301 outputs the value water production at optimal operating point for the signal V.sub.Gsoll, the output signal of the performance demand signal control P.sub.Wsoll may alternatively be variably adjusted between the fuel cell performance at optimal operating point P.sub.Bzopt and the value maximum performance demand P.sub.BZmax in accordance with the following equation (see also FIG. 8B):

(39) $P_{\mathrm{Wsoll}}=\frac{1}{K}{P}_{\mathrm{BZopt}}$

(40) An advantage may be that the performance demand signal is not increased erratically, but rather continuously as the condensation efficiency decreases and the maximum value may not be reached as often.

(41) The performance demand signal limiter 303 limits the performance demand signal P.sub.Wsoll required for the water production to an actual performance demand for the fuel cell P.sub.BZsoll.

(42) The output signal of the performance demand signal control P.sub.Wsoll is based exclusively on the water demand and only limited with respect to its peak value by the design-related maximum performance of the fuel cell system P.sub.BZmax. The performance demand signal limiter 303 may receive measured values that concern the fill level of the supply tank for the fuel cell. This fill level consists, for example, of the fill level of the hydrogen tank m.sub.H2. It may also receive data with respect to the current power demand of the loads P.sub.V and data with respect to the current flight phase and the remaining flying time.

(43) The electric power of the fuel cell associated with the required water production is fed into the on-board network of the aircraft. In order to prevent more power than that currently consumed from being generated, the performance demand signal P.sub.Wsoll can be compared with the current power consumption P.sub.V. If the current power consumption is exceeded, the performance demand signal for the fuel cell P.sub.BZsoll is limited to the actual power demand of the loads P.sub.V (see also FIG. 9).

(44) In addition, the demand signal can be set to zero or at least reduced if the supply of fuel for the fuel cell falls short of a minimum supply, e.g., with consideration of the still remaining flying time. In this way, the availability of the fuel cell system as an energy supplier (e.g., an emergency power system) is ensured up to the end of the flight (see, for example, FIG. 9).

(45) Since other energy generators also feed power into the on-board network, the performance demand signal for the fuel cell P.sub.BZsoll can be used for limiting the power to be delivered by the other energy generators to the differential amount between the instantaneous power consumption P.sub.V and the performance demand P.sub.BZsoll.

(46) The thusly calculated and, if applicable, limited fuel cell performance is forwarded to the fuel cell performance regulating device 304 in the form of a nominal value P.sub.BZsoll.

(47) FIG. 4 shows an example of the maximum permissible tank fill level 403, the upper limiting value for the tank fill level 404 (that lies below the maximum permissible tank fill level) and the lower limiting value for the tank fill level 405 (that lies below the upper limiting value) as a function of the time. According to the exemplary embodiment shown in FIG. 4, these three fill level limiting values are not time-variant. However, it would be possible, for example, that the lower limiting value decreases over time because the remaining traveling time become shorter and shorter.

(48) FIG. 5 shows the dependence of the condensation efficiency K 502 on the cooling temperature of the condenser T.sub.K 501. According to the curve 504, the condensation efficiency drops in a non-linear fashion as the temperature increases and has a value that is lower than the limiting value of the condensation efficiency K.sub.krit 503 above a limiting temperature.

(49) FIG. 6 shows a flow chart of a process for controlling or regulating the tank fill level. The tank fill level is measured in step 601 and it is determined if the measured tank fill level is higher than the upper limiting value for this fill level in step 602. If this is the case, no water generation takes place (step 603). If this is not the case, it is determined if the measured tank fill level is lower than the lower limiting value for the tank fill level in step 604.

(50) If this is the case, it is determined if the water consumption (or the water consumption rate) in the interval in question is higher than a limiting value for the water consumption in step 605. If this is the case, the command for maximizing the water generation is output (step 606).

(51) If this is not the case, it is determined if catering of the passengers is imminent in step 607.

(52) If this is the case, the command for increasing the water generation to a maximum value is output (step 608).

(53) If this is not the case, the water generation is adjusted to an average value (step 609).

(54) If it is determined that the tank fill level does not lie below the lower limiting value in step 604, the next step to be carried out is step 610, in which it is determined if the water consumption in the interval in question is higher than a limiting value for the water consumption.

(55) If this is the case, it is determined if catering is imminent in step 611. If this is the case, the water generation is increased to a maximum value in step 612. If this is not the case, the water generation is set to an average value in step 613.

(56) However, if it is determined that the water consumption in the interval in question does not lie above the limiting value for the water consumption in step 610, the next step to be carried out is step 614, in which it is determined if a catering phase is imminent. If this is the case, the value for the water generation is set to an average value (see step 613). If this is not the case, it is determined that no water generation should take place in step 615.

(57) FIG. 7 shows two tables for elucidating the characteristics of the tank fill level control process. If the current tank fill level lies above the upper limiting value for the tank fill level (value 0), the command that no water should be produced is output.

(58) If the current tank fill level lies between the lower limiting value and the upper limiting value (value 1), the water consumption in the interval in question lies below the corresponding limiting value (value 0) and no catering is planned in the near future (value 0), the command that no water should be produced is output (see second line of the first table). Accordingly, it is also determined if the command for producing water should be output with an average production rate or a maximum production rate as already described above with reference to FIG. 6.

(59) FIG. 8A shows several tables that elucidate how the performance demand signal control according to the exemplary embodiment described above under option 1 can be operated. In this case, the determination of the performance demand signal P.sub.Wsoll required for the water production takes place erratically. In column 1 of the upper table, the value 0 means that the nominal value for the water production is 0. The value 1 means that the nominal value for the water production assumes an average value, and the value 2 means that the nominal value for the water production assumes a maximum value. In the second column, the value 0 means that the condensation efficiency lies below a limiting value and the value 1 means that the condensation efficiency lies above this limiting value.

(60) In the third column, the value 0 means that the performance demand signal P.sub.Wsoll required for the water production is 0, the value 1 means that the performance demand signal has an average value (at which the fuel cell operates at the optimal operating point) and the value 2 means that the performance demand signal has a maximum value, at which the fuel cell delivers maximum power.

(61) For example, if the nominal value for the water production is set to an average value (V.sub.Gsoll=1) and the condensation efficiency lies below the critical value (K =0), the performance demand signal is set to its maximum (P.sub.Wsoll=2).

(62) FIG. 8B shows the dependence of the performance demand signal 802 on the cooling temperature of the condenser 801. In this case, the erratic curve 804 corresponds to the first exemplary embodiment and the curve 805 corresponds to the second exemplary embodiment, in which P.sub.Wsoll is continuously adjusted.

(63) The curve 803 shows the dependence of the condensation efficiency on the cooling temperature of the condenser.

(64) FIG. 8C shows the dependence of the performance demand signal 811 on the condensation efficiency 810. The curve 812 shows the erratic dependence according to exemplary embodiment 1 and the curve 813 shows the continuous dependence according to exemplary embodiment 2 (see above).

(65) FIG. 9 shows a flow chart of a performance demand signal limiting process. The performance demand signal P.sub.Wsoll required for the water production is output in step 901 and this signal is compared with the instantaneous power consumption of the electric loads in step 902. If P.sub.Wsoll is higher than the instantaneous power consumption P.sub.V, the actual performance demand for the fuel cell is set to the instantaneous power consumption in step 903. If this is not the case, the actual performance demand for the fuel cell is set to P.sub.Wsoll in step 904.

(66) It can furthermore be determined if a critical hydrogen supply has been reached in step 905. If this is the case, P.sub.BZsoll (i.e., the actual performance demand for the fuel cell) is set to 0 in step 906. If this is not the case, P.sub.Wsoll is compared with the instantaneous power consumption P.sub.V in step 907. If P.sub.Wsoll is higher than P.sub.V, the actual performance demand for the fuel cell is set to the instantaneous power consumption P.sub.V in step 908. If this is not the case, the actual performance demand for the fuel cell is set to P.sub.Wsoll in step 909.

(67) FIG. 10 shows an aircraft 1000 according to an exemplary embodiment of the invention. The aircraft 1000 features a fuselage 1001, into which a fuel cell system 100 is installed.

(68) As a supplement, it should be noted that comprising and featuring do not exclude any other elements or steps, and that a or an does not exclude a plurality. It should furthermore be noted that characteristics or steps that were described with reference to one of the above exemplary embodiments can also be used in combination with other characteristics or steps of other above-described exemplary embodiments. Reference symbols in the claims should not be interpreted in a restrictive sense.