Various embodiments of the present invention will be described with reference to the accompanying drawings. It is to be noted that same or similar reference numerals are applied to the same or similar parts and elements throughout the drawings, and the description of the same or similar parts and elements will be omitted or simplified.
Meanwhile, an air supply pipe 121 is connected to the cathode of the fuel cell 101 and serves as a cathode-side introducing passage. A compressor 122 (corresponding to the first air supply unit) is installed in the air supply pipe 121 and serves to compress the air supplied to the cathode. An air discharge pipe 123 is also connected to the cathode and serves as a cathode-side discharge passage. Oxidant gas supply valves 124 and 125 for controlling the flow rate of air supplied to the cathode are installed in the air supply pipe 121 and the air discharge pipe 123, respectively. The two flow rate control valves 124, 125 correspond to the second flow rate control valve. Although in this embodiment two flow rate control valves 124, 125 are provided as the second flow rate control valve, it is also acceptable to provide only one or the other of the flow rate control valves 124, 125. An air branch pipe 126 is connected to the air supply pipe 121 at a position upstream of the oxidant gas supply valve 124. The air branch pipe 126 serves as a branch passage and is connected to the discharged hydrogen combustor 115. The air supply valve 127 is installed in the air branch pipe 126. The air supply valve 127 corresponds to the first flow rate control valve and serves to control the flow rate of the air supplied to the discharged hydrogen combustor 115.
The discharged hydrogen combustor 115 treats the anode off gas introduced thereto by combusting the discharged hydrogen contained in the anode off gas. The anode off gas is discharged in order to discharge accumulated nitrogen and water from the system, but hydrogen is also contained in the anode off gas. Consequently, it is necessary to treat the discharged hydrogen. The discharged hydrogen combustor 115 includes a dilution element 1151, an auxiliary catalyst 1152, and a main catalyst 1153 arranged in order as listed from the inlet. The discharged hydrogen introduced into the discharged hydrogen combustor 115 is first mixed thoroughly with air by the dilution element 1151 and fed to the catalysts 1152, 1153 located downstream. The auxiliary catalyst 1152 is an electrically heated catalyst with self-heating and generates heat and, thereby, heat the inside of the discharge hydrogen combustor 115 when a voltage is applied to electrodes e1 and e2. Meanwhile, the main catalyst 1153 carries a precious metal such as platinum and its main function is to accelerate the combustion of the discharged hydrogen.
In this embodiment, an exhaust muffler 128 is installed in the air discharge pipe 123 to reduce the exhaust noise and lower the off gas temperature. The discharged hydrogen combustor 115 and the air discharge pipe 123 are connected together by a combustion gas discharge pipe 129 at a position upstream of the exhaust muffler 128. The combustion gas discharge pipe 129 corresponds to the connecting passage. A check valve 130 arranged to allow combustion gas to flow from the combustion gas discharge pipe 129 to the air discharge pipe 123 is installed in the combustion gas discharge pipe 129. A shut-off valve arrangement configured to merely open and close the passage or a proportional valve arrangement configured to operate according to the pressure difference across the valve can be used as the check valve 130.
A control unit 151 controls the operation of the fuel gas discharge valve 114, the oxidant gas supply valves 124, 125, and the air supply valve 127. The control unit 151 receives a detection signal indicating the operating conditions of the fuel cell 101 and a detection signal indicating the combustor internal temperature Tb (i.e., temperature inside the combustor 115) detected by a temperature sensor 161. The temperature sensor 161 detects the temperature of a combustion chamber in which the catalysts 1152, 1153 are installed as the combustor internal temperature Tb of the discharged hydrogen combustor 115. The operating conditions of the fuel cell 101 include the flow rate of hydrogen-containing fuel gas supplied to the anode, the flow rate of the oxidant gas (air in this embodiment) supplied to the cathode, and the electric current generated by the fuel cell 101. The flow rate of fuel gas to the anode is detected by a flow rate sensor 162 installed in the fuel gas supply pipe 111, the flow rate of oxidant gas is detected by a flow rate sensor 163 installed in the air supply pipe 121, and the electric current generated by the fuel cell 101 is detected by an electric current sensor 164 (measures electric current flowing to electrical load) installed in a circuit external to the fuel cell 101. The control unit 151 executes hydrogen discharge control and start-up combustion control (described later) based on the information that the control unit 151 receives from the input signals.
The operation of the control unit 151 will now be described with reference to flowcharts shown in the figures.
In step S102, the control unit 151 reads in the supply flow rate of the fuel gas, the supply flow rate of the oxidant gas, the generated electric current of the fuel cell 101, etc., as parameters indicating the operating conditions of the fuel cell 101. The electrode temperatures of the anode and cathode, the supply pressures of the fuel gas and oxidant gas, and/or the voltage or power generated by the fuel cell 101 can be detected instead of or in addition to the parameters mentioned above.
In step S103, the control unit 151 determines if the conditions for hydrogen discharge are satisfied based on the operating conditions detected in the previous step. If so, the control unit 151 proceeds to step S104. If not, the control unit 151 ends the routine. The determination regarding the conditions for hydrogen discharge can be made, for example, by determining if the gas passage pressure inside the anode is equal to or above a prescribed pressure or determining if the electricity generating efficiency of the fuel cell 101 has declined to or below a prescribed efficiency.
In step S104, the control unit 151 executes the hydrogen discharge.
In step S203, the control unit 151 detects the combustor internal temperature Tb based on the output from the temperature sensor 161. In step S204, the control unit 151 determines if the discharged hydrogen combustor 115 is in such a state that it can ignite the discharged hydrogen. The determination regarding ignitability is accomplished by determining if the combustor internal temperature Tb has reached a prescribed ignitable temperature Tpre. The prescribed ignitable temperature Tpre can be set based on the ratio of the required air flow rate Qa to the hydrogen discharge flow rate Qh (i.e., the air-fuel ratio) and the gas space velocity inside the catalyst. In this embodiment, the prescribed ignitable temperature Tpre is set based on the air-fuel ratio and the gas space velocity and is contrived to be the minimum temperature at which ignition is possible. If ignitable conditions exist, the control unit 151 proceeds to step S206. Otherwise, the control unit 151 proceeds to step S205 to heat the catalyst and returns to step S204 to determine if ignitable conditions exist. In step S205, the control unit 151 applies a voltage to the electrodes e1, e2 of the auxiliary catalyst 1152 from a power source 171; the auxiliary catalyst 1152 emits heat and heats the discharged hydrogen combustor 115.
In step S206, the control unit 151 calculates the rotational speed of the compressor 122 and the opening degree of the air supply valve 127 to be used during hydrogen discharge based on the increased required air flow rate Qa and controls the compressor 122 and the air supply valve 127 based on the newly calculated compressor rotational speed and valve opening degree. In conjunction with the control of the air supply valve 127, the control unit 151 also controls the oxidant gas supply valves 124, 125 to adjust the flow rate ratio of the air supplied to the anode and the air supplied to the discharged hydrogen combustor 115.
In step S207, the control unit 151 calculates the opening degree of the fuel gas discharge valve 114 to be used during the hydrogen discharge based on the hydrogen discharge flow rate Qh and determines if the timing for opening the fuel gas discharge valve 114 (hereinafter called “hydrogen discharge timing”) has been reached. The hydrogen discharge timing is determined in relation to the opening timing of the air supply valve 127 and the operation timing of the compressor and is set such that the discharged hydrogen and the air are supplied to the discharged hydrogen combustor 115 substantially simultaneously. If the hydrogen discharge timing has been reached, the control unit 151 proceeds to step S208. If not, the control unit 151 repeats step S207 and waits until the hydrogen discharge timing is reached. It is also possible to set the hydrogen discharge timing such that the discharged hydrogen reaches the discharged hydrogen combustor 115 ahead of the air by advancing the hydrogen discharge timing with respect to the open timing of the air supply valve 127 or to set the hydrogen discharge timing such that the discharged hydrogen reaches the discharged hydrogen combustor 115 later than the air by retarding the hydrogen discharge timing with respect to the open timing of the air supply valve 127. The hydrogen discharge timing can also be switched (changed) in accordance with the state of the discharged hydrogen combustor 115. Supplying the hydrogen ahead of the air enables reliable ignition to be obtained and supplying the air ahead of the hydrogen enables excessive combustion of the hydrogen to be avoided. The hydrogen discharge timing can be set by reverse calculating based on the pipe diameters and pipe lengths of the fuel gas discharge pipe 112 and air branch pipe 126, the discharged hydrogen flow rate Qh, and the required air flow rate Qa.
In step S208, the control unit 151 opens the fuel gas discharge valve 114 and introduces discharged hydrogen into the discharged hydrogen combustor 115. In step S209, the control unit 151 determines if the hydrogen discharge is finished. If so, the control unit 151 proceeds to step S210. If not, the control unit 151 repeats step S209 and waits until the hydrogen discharge finishes.
In step S210, the control unit closes the fuel gas discharge valve 114 and stops the discharge of anode off gas to the outside of the system. In step S211, the control unit closes the air supply valve 127 and stops the supply of air to the discharged hydrogen combustor 115. Meanwhile, the control unit 151 returns the rotational speed of the compressor 122 and the opening degrees of the oxidant gas supply valves 124, 125 to values corresponding to the original operating conditions.
In step S305, the control unit 151 calculates the compressor rotational speed required to reach the required air flow rate and operates the compressor 122 at the calculated compressor rotational speed. In this embodiment, the oxidant gas supply valve 124 is closed fully so that all of the air exiting the compressor 122 is delivered to the discharged hydrogen combustor 115. In step S306, the control unit 151 determines if the open timing of the fuel gas discharge valve 114 (hereinafter also called “hydrogen supply timing”) has been reached. If the hydrogen supply timing has been reached, the control unit 151 proceeds to step S307. If not, the control unit 151 repeats step S306 and waits until the hydrogen supply timing is reached. Similarly to the aforementioned hydrogen discharge timing, the hydrogen supply timing is set in relation to the open timing of the air supply valve 127 and the operation timing of the compressor.
In step S307, the control unit 151 opens the fuel gas discharge valve 114 and supplies hydrogen to the discharged hydrogen combustor 115. Since the control unit 151 waits until the hydrogen supply timing is reached before opening the fuel gas discharge valve 114, the hydrogen and the air are delivered to the discharged hydrogen combustor 115 substantially simultaneously. In step S308, the control unit 151 determines if the startup combustion is finished. If so, the control unit 151 proceeds to step S309. If not, the control unit 151 repeats step S308.
In step S309, the control unit 151 closes the fuel gas discharge valve 114 and stops the supply of hydrogen to the discharged hydrogen combustor 115. In step S310, the control unit 151 closes the air supply valve 127 and stops the supply of air to the discharged hydrogen combustor 115. Meanwhile, the control unit 151 opens the oxidant gas supply valves 124, 125 and supplies air to the cathode of the fuel cell 101.
Although in this embodiment the oxidant gas supply valve 124 is closed fully during the startup combustion and the air supply valve 127 is closed fully when the startup combustion if finished, it is also acceptable to open the oxidant gas supply valves 124, 125 to the required opening degree when it is necessary to supply air to the cathode during startup combustion. Also, it is acceptable not to fully close the air supply valve 127 when it is necessary to continue combustion after startup combustion is finished.
Since the air supplied to the discharged hydrogen combustor 115 (“treatment unit”) through the air branch pipe 126 is drawn from the air supply pipe 121 at a position upstream of the cathode, the optimum quantity of air can be supplied to the discharged hydrogen combustor 115 regardless of the operating conditions of the fuel cell 101. Additionally, since the flow rate of the air supplied to the cathode is maintained both before and during the hydrogen discharge, the energy consumption can be prevented from increasing due to humidification and the balance between the intake and outlet of moisture can be prevented from degrading. Furthermore, since the air supplied to the discharged hydrogen combustor 115 has a higher oxygen concentration and a lower humidity than the cathode off gas, the ignitability of the discharged hydrogen in the discharged hydrogen combustor 115 can be improved and the treatment of the discharged hydrogen can be conducted in a stable manner.
Additionally, the hydrogen discharge control executed in this embodiment can be applied to situations in which the gas inside the anode is replaced with a filler gas when the fuel cell 101 is stopped (i.e., when stop control is executed). More specifically, when the gas inside the anode is discharged and replaced with a filler gas as part of the stop control, the hydrogen discharge control of this embodiment can be used to introduce the discharged hydrogen into the discharged hydrogen combustor 115 while simultaneously introducing the quantity of air required to combust the hydrogen into the discharged hydrogen combustor 115 and combusting the hydrogen. If the combustor internal temperature Tb is below the prescribed ignitable temperature Tpre, the inside of the discharged hydrogen combustor 115 can be heated with the auxiliary catalyst 1152 to ensure the ignitability before the hydrogen discharge is executed.
The power generating system 1B can accomplish hydrogen discharge control and startup combustion control by replacing the control of the compressor 122, air supply valve 127, and oxidant gas supply valves 124, 125 used in the first embodiment with a control of the compressor 182. The hydrogen discharge control and startup combustion control of the second embodiment will now be explained while indicating the corresponding steps of the flowcharts shown in
Meanwhile, in the startup combustion control, the inside of the discharged hydrogen combustor 115 is preheated with the auxiliary 1152 as required (steps S301 to S303) and, after the ignition conditions are satisfied, the compressor 182 is operated (step S305). When the hydrogen supply timing is reached, the fuel gas discharge valve 114 is opened and the hydrogen is supplied to the discharged hydrogen combustor 115 (steps S306 and S307). After the startup combustion is finished, the fuel gas discharge valve 114 is closed and the compressor 182 is stopped (steps S308 to S310).
Also, similarly to the first embodiment, the hydrogen discharge control of the second embodiment can be applied to the stop control of the fuel cell 101.
With the second embodiment, a dedicated compressor 182 is provided for supplying air to the discharged hydrogen combustor 115 and, thus, a small compressor can be used for each of the compressors 122, 182. As a result, vibrations can be reduced and the components of the power generating system 1B can be arranged in an efficient fashion. Also, since the compressors 122, 182 can be operated independently of each other, the optimum quantity of air can be supplied to the discharged hydrogen combustor 115 without supplying an excessive amount of air to the cathode and thereby degrading the balance between the intake and outlet of moisture to and from the cathode.
With this embodiment, the hydrogen discharge control and the startup combustion control can be executed in the same manner as the first embodiment (excluding the steps S203 to S205 (
It is also acceptable to connect an air supply pipe (181) serving as a “supply passage” to the dilution mixer 115A and provide a compressor (182) serving as a “second air supply unit” so that a compressor that is separate from the compressor (122) supplying air to the cathode is used to supply air to the dilution mixer 115A. An off gas treatment device employing the dilution mixer 115A can also be used to execute stop control of fuel cell 101.
With the third embodiment, the quantity of air required to dilute the discharged hydrogen can be supplied to the dilution mixture 115A regardless of the operating conditions of the fuel cell 101. As a result, the dilution of the discharged hydrogen can be conducted in a stable manner.
As explained previously, when a fuel cell power generating system in accordance with the present invention is used, the optimum quantity of air can be supplied to the anode off gas treatment unit regardless of the operating conditions of the fuel cell 101 because the air to be supplied to the treatment means is either drawn from a position upstream of where the air is supplied to the cathode of the fuel cell 101 or drawn from a separate source. Furthermore, since the air supplied to the treatment means has a higher oxygen concentration and a lower humidity than the cathode off gas, the ignitability of the anode off gas can be improved in cases where the anode off gas is treated by means of combustion.
The entire contents of Japanese patent application P2004-222830 filed Jul. 30, 2004 are hereby incorporated by reference.
The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiment is therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.
The following are examples of applications in which the present invention can be applied: fuel cell automobiles, railroad vehicles capable of traveling through areas where electric power service is not available, and stationary fuel cell systems.
Number | Date | Country | Kind |
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2004-222830 | Jul 2004 | JP | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/JP05/12972 | 7/7/2005 | WO | 00 | 1/30/2007 |