The present invention relates to improvements in a solid oxide fuel cell power generation apparatus and a method of operating the same.
A fuel cell power generation apparatus comprises an anode and a cathode on both sides of an electrolyte, wherein a fuel gas is supplied to the anode side and an oxidant gas (mainly air) is supplied to the cathode side so that the fuel and the oxidant are electrochemically reacted with each other via the electrolyte, thereby performing power generation. Researches toward practical use are now being conducted concerning a solid oxide fuel cell, which is one type of fuel cells. This is because in the solid oxide fuel cell, the operation temperature is high, i.e., about 700 to 1000° C. and the power generation efficiency is high, and the exhaust heat is also easily used.
Usually, a fuel cell constitutes an assembly (module) in which several tens of to several hundreds of cells are stacked in order to obtain electric power. Usually, in this module, power generation is performed after the temperature thereof is raised by an external heat source, such as a burner or a heater, to a predetermined temperature (e.g., around 600° C.) at which power generation is possible. However, in order to raise the temperature to this temperature, it takes time and energy loss is also high, which thereby reduces the usability of the solid oxide fuel cell.
Moreover, during power generation, these external heat sources can be stopped and the fuel cell system can be thermally self-sufficient by the power generation reaction of the fuel cell. However, in order to do this, the temperature of the supply gas during power generation needs to be properly controlled with the exhaust heat from the fuel cell. In other words, for the solid oxide fuel cell, there is a desire to achieve a reduction in the activation time, a reduction in the activation energy, as well as the temperature maintenance and performance improvements at the same time.
For the raising temperature of the modular, JP-A-2004-119299 discloses an example of disposing a heater in an air flow channel.
Moreover, for the temperature maintenance of the module, JP-A-2004-71312 discloses an example in which air is passed through a bypass path provided with a thermal storage medium during a partial load operation.
The problem here is that since a heating means used for activation such as an electric type air heater in JP-A-2004-119299 is disposed outside the module, heat will escape on the way, so that a high temperature gas can not be effectively supplied, which makes it difficult to facilitate the heating.
Moreover, since the heating means used for activation is disposed outside the modular, the whole system becomes large, so that the radiation amount becomes large, thereby reducing the efficiency.
Namely, in the prior art, the activation time is long and the activation energy loss is high. Moreover, the supply temperature of a gas required during power generation is difficult to maintain.
It is an object of the present invention to provide a solid oxide fuel cell power generation apparatus that reduces the activation time and improves the efficiency.
It is another object of the present invention to provide a solid oxide fuel cell power generation apparatus that achieves a reduction in the activation time and an improvement in the efficiency as well as the temperature maintenance and performance improvements during operation at the same time.
It is yet another object of the present invention to provide a power generation method of a solid oxide fuel cell power generation apparatus that achieves a reduction in the activation time and an improvement in the efficiency.
It is yet another object of the present invention to provide a power generation method of a solid oxide fuel cell power generation apparatus that achieves a reduction in the activation time and an improvement in the efficiency as well as the temperature maintenance and performance improvements during operation at the same time.
According to claim an aspect of the present invention, there is provided a modular structure wherein gas supply lines used for module heating (activation) and used for power generation are disposed independently from each other inside a fuel cell module.
Moreover, according to claim another aspect of the present invention, a fuel cell module includes a generator chamber in which a plurality of fuel cells are assembled, wherein gas supply lines used for module heating and used for power generation are switched and operated.
Moreover, according to claim yet another aspect of the present invention, a fuel cell module includes a distributor (header) of gasses supplied to the generator chamber, wherein the distributor includes two sets of gas supply ports for independently supplying gases used for activation and used for power generation.
Moreover, according to claim yet another aspect of the present invention, in the gas supply line to the generator chamber, a gas heating means used for activation is disposed close to the cell, and a gas preheater used for power generation is disposed further away from the fuel cell than this gas heating means used for activation is.
Moreover, according to claim yet another aspect of the present invention, a header for supplying a gas to the generator chamber and a preheater used for power generation are integrated into one.
According to claim a preferable embodiment of the present invention, by disposing gas supply lines used for activation and used for power generation separately from each other inside the fuel cell module, it is possible to achieve a reduction in the activation time and a reduction in the activation energy.
Moreover, according to claim a preferable embodiment of the present invention, by separating supply lines used for activation and used for power generation from each other, it is possible to achieve a reduction in the activation time, a reduction in the activation energy as well as the temperature maintenance and performance improvements during power generation at the same time. In the following description, a term “a solid oxide fuel cell” is used to indicate a solid oxide fuel cell power generation apparatus or to indicate a fuel cell unit 1 of solid oxide fuel cell power generation apparatus.
Other objects, features and advantages of the invention will become apparent from the following description of the embodiments of the invention taken in conjunction with the accompanying drawings.
Hereinafter, the preferable embodiments of the present invention will be described in detail with reference to the accompanying drawings.
In the basic structure of a solid oxide fuel cell 1, as illustrated in
On the cathode 103 side of the fuel cell 1, an oxidant gas (air or a combustion gas) is flown as cathode gases 2, 9. Among these, the cathode gas 2 used for activation is supplied from a gas supply port 21 used for activation, while the cathode gas 9 used for power generation is supplied from a gas supply port 91 used for power generation. These cathode gases 2, 9 pass through a header 3 for equally distributing the cathode gas to an air inlet pipe 4 to each fuel cell 1 inside a generator chamber 10, and reach the cathode 103 of each fuel cell 1.
In a preferable embodiment of the present invention, a burner 7 used for activation is disposed close to the air header 3 inside the fuel cell module 30, as shown in
Now, during activation, prior to power generation, firstly, the temperature of the fuel cell is raised to about 600 to 700° C., which is the minimum temperature at which power generation can be started. From a cathode gas line 20 used for activation, fuel 5 and air 6 are supplied to the burner 7 used for activation to produce the high temperature cathode gas 2 used for activation, and the heating is continued using this high temperature gas.
At this time, since the burner 7 used for activation is disposed close to the air header 3, the cathode gas 2 used for activation heated by the burner 7 used for activation is less likely to be cooled in the middle of the supply to the header 3. Therefore, the high temperature cathode gas 2 used for activation can be effectively supplied to the fuel cell 1 inside the generator chamber 10, and heating the module can be effectively promoted. Note that the burner 7 used for activation described here is just an example, and the bottom line is that a heating means for supplying a high temperature gas to the fuel cell 1 and thereby raising the temperature thereof is required.
Thereafter, upon reaching a temperature at which power generation can be started, the supply of the fuel 5 used for activation is cut off and the burner 7 used for activation is stopped, and at the same time a fuel gas from an anode gas line 8 and the cathode gas 9 used for power generation are supplied to the solid oxide fuel cell 1 to start power generation.
As the fuel gas supplied from the anode gas line 8, a reformed gas obtained by steam-reforming a part or whole of a mixed gas of a hydrocarbon-based fuel such as a town gas, LNG, or LPG, and water vapor by means of a reformer is used. Since the fuel cell 1 generates heat during power generation, the system is thermally independently operated at about 700-1000° C. using this heat. The anode gas and cathode gas that did not cause power generation (chemical) reaction are burned into an exhaust gas 81 on the outlet side of the fuel cell 1.
Now, the air distribution header 3 has two supply ports, i.e., a supply port 21 to which the high temperature cathode gas 2 used for activation is supplied, and a supply port 91 to which the cathode gas 9 used for power generation is supplied, and has a system configuration in which the cathode gas line 20 used for activation and a cathode gas line 90 used for power generation are separately formed. A supply port 91 of this cathode gas line 90 used for power generation is provided via a preheater 11 by means of a metal pipe. This preheater 11 to operate during power generation is also disposed inside the fuel cell module 30. Accordingly, the cathode gas 9 used for power generation heated by the preheater 11 is less likely to be cooled in the middle of the supply to the header 3. Therefore, the high temperature cathode gas 9 used for power generation can be supplied to the fuel cell 1 inside the generator chamber 10 and highly efficient power generation can be promoted.
According to this embodiment, during activation, the fuel 5 and air 6 are supplied to the burner 7 used for activation disposed close to the header 3 and then are burned to thereby produce the high temperature cathode gas 2. Then, the high temperature cathode gas 2 is supplied to the closest cell 1 to thereby facilitate raising the temperature of the whole fuel cell module 30. It is therefore possible to achieve a reduction in the activation time and a reduction in the activation energy.
In this system, at a time point t1, the burner 7 is ignited to start raising temperature, and the module 30 is heated with the cathode gas 2 used for activation. Then, at a time point t2, if the temperature T1 of the generator chamber 1 exceeds the minimum temperature at which power generation is possible, e.g., Tu=600° C., then this fact is detected, and at a time point t3, the burner 7 used for activation is stopped and at the same time a supply of the fuel gas is started from the anode gas line 8 to start power generation.
Conventionally, at this time, if the burner 7 is stopped at the time point t3, a temperature T9c of the cathode gas 9 used for power generation decreases abruptly and a temperature T1c of the generator chamber 10 also decreases abruptly as shown in
In contrast thereto, in Embodiment 1 of the present invention, the cathode gas line 90 used for power generation including the preheater 11 is provided independently of the cathode gas line 20 used for activation. For this reason, after the stop of the burner 7 used for activation, the cathode gas 9 used for power generation preheated by recovering the heat of the exhaust gas 81 can be supplied to the fuel cell 1 inside the generator chamber 10, so that a low-temperature gas will not be directly supplied to the fuel cell 1. Accordingly, as shown in
The high temperature cathode gas 2 used for activation during activation can be produced by supplying the fuel 5 and air 6 from the gas supply port 21 used for activation to the burner 7 used for activation and by burning the same. Then, this high temperature cathode gas 2 used for activation can be supplied to the closest fuel cell 1. Accordingly, raising the temperature of the module 30 becomes easy, so that a reduction in the activation time and a reduction in the activation energy can be attained. Moreover, independently of this line used for activation, the cathode gas line 90 used for power generation is provided and the preheater 11 is provided, so that after the stop of the burner 7, the air preheated by recovering the heat of the exhaust gas 81 can be supplied to the fuel cell 1 as the cathode gas 9 used for power generation. For this reason, a low-temperature gas will not be directly supplied to the inside of the generator chamber 10, so that the temperature maintenance of the module 30 and a reduction of the temperature distribution thereof can be attained and the power generation performance can be improved.
These two effects can be achieved by firstly the fact that as shown in
Furthermore, as describes below, the present invention also facilitates to perform power generation during combustion of the burner 7 used for activation.
In order for the solid oxide fuel cell to perform power generation, a specified amount of air is required. However, even if attempting to supply this specified amount of air for power generation from the same gas line for the burner during combustion of the burner 7, unless the ratio of the fuel 5 and air 6 and the temperature thereof are kept in an appropriate range in order for the burner 7 to stably burn the mixture of the fuel and air, the burner will misfire or backfire. For example, the mole ratio (equivalent ratio) of the fuel to air when the burner 7 burns the mixture of the fuel and air is typically in the range of about 0.5 to 0.8. Accordingly, if the equivalent ratio is reduced from this range by increasing air in order to generate power, the burner 7 will misfire.
Alternatively, if the amount of fuel supply is reduced to increase the amount of air, the supply flow rate of the fuel decreases or the fuel temperature increases, which will increase the likelihood of backfire. It is therefore difficult to supply the gas used for power generation from an identical line during combustion of the burner 7.
Then, in a preferable embodiment of the present invention, the cathode gas line 20 used for activation and the cathode gas line 90 used for power generation are separated from each other, so that the gas required for power generation can be supplied independently of the gas supply port used for power generation 91 without being aware of the combustion state of the burner 7.
As shown in
Since this operation method can gradually switch to power generation without completely stopping the combustion of the burner 7, this method also provides the effect that, as compared with the operation method shown in
Furthermore, a large amount of heat of the exhaust gas 81 that is conventionally discarded during combustion of the burner is recovered by the preheater 11 and supplied to the generator chamber in this embodiment, so that the heat loss is reduced, the activation energy is reduced, and an efficient system can be obtained.
Information of the temperature T1 of the generator chamber is inputted as the detection signal 12S to the system controller 13 by the temperature sensor 12. In response to this, the system control device 13 functions so as to optimize the temperature raising speed of the generator chamber 10.
Referring to
If at the time point t2 the signal 12S from the temperature sensor 12 detects that the generator chamber temperature T1 exceeded the minimum temperature Tu at which power generation is possible, then at the time point t3, the supply of the fuel 5 used for activation is cut off and the burner 7 is stopped by the control signal 131S. On the other hand, by means of a control signal 132S, the cathode gas line 20 used for power generation is activated to start a supply of the cathode gas 9 used for power generation and at the same time the anode gas supply line 8 is activated to start a supply of the fuel for power generation. The temperature of the gas 9 used for power generation in this case is as shown in
A reduction in the activation time, a reduction in the activation energy as well as the temperature maintenance and performance improvements during power generation can be achieved at the same time by such control.
Note that although this embodiment showed an example of control based on the temperature signal 12S from the temperature sensor 12, the control system is not limited to this. For example, it is also possible to switch over to power generation by counting sufficient time after igniting the burner 7.
In this structure, a container plane constituting the header 3 and the preheater 11 are in contact with each other over a wide area between metals. For this reason, more heat of the exhaust gas 81 can be conducted to the preheater 11 by heat conduction through the header 3, so that the preheating performance is improved than in the embodiment of
Note that the present invention, although illustrated as a cylindrical shape in the above embodiments, can be applied, of course, to the case of a solid oxide fuel cell having a flat shape other than the cylindrical shape.
Furthermore, in the above embodiments, a system configuration has been described in which only the gas supply line on the cathode side is separated during activation and during power generation, however, also with the same configuration on the anode side, the effects of the present invention can be obtained, of course.
Since the present invention can achieve a reduction in the activation time of a solid oxide fuel cell, a reduction in the activation energy thereof as well as the temperature maintenance and performance improvements thereof at the same time, the solid oxide fuel cell of the present invention can be used as an earth environment-friendly distributed power supply system.
It should be further understood by those skilled in the art that although the foregoing description has been made on embodiments of the invention, the invention is not limited thereto and various changes and modifications may be made without departing from the spirit of the invention and the scope of the appended claims.
Number | Date | Country | Kind |
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2007-101797 | Apr 2007 | JP | national |
The present application relates to subject matters described in a co-pending patent application Ser. No. 11/835,454 filed on Aug. 8, 2007 entitled “FUEL CELL POWER GENERATION SYSTEM AND METHOD OF OPERATING THEREOF” by Shin Takahashi, et al. and assigned to the assignee of the present application. The disclosures of this co-pending application are incorporated herein by reference.