Solid acid fuel cells

Abstract

To provide a solid oxide type fuel cell capable of preventing occurrence of a sudden boiling phenomenon by suppressing an increase in temperature of a vaporizer.SOLUTION: A solid oxide type fuel cell comprises: reformed water supply means 14 for supplying reformed water; fuel gas supply means 22 for supplying a fuel gas; a vaporizer 2 that vaporizes the reformed water; a reformer 4 that reforms the fuel gas with a water vapor; and a cell stack 6 that generates power by a fuel battery reaction with a reformed gas with air. Cooling gas ejection means 48 for ejecting a cooling gas into the vaporizer 2 is provided, and temperature detection means for detecting a temperature in regard to the vaporizer is also provided. An ejection amount of the cooling gas ejected from the cooling gas ejection means 48 is controlled on the basis of a detection temperature of the temperature detection means. The temperature detection means is arranged at a drop region where the reformed water is dropped to the neighbor thereof at a bottom wall of the vaporizer 2. The cooling gas ejection means 48 ejects the cooling gas toward the drop region.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a solid oxide fuel cell (hereinafter also referred to as "SOFC") equipped with a vaporizer for vaporizing reformed water.

Background Art

[0002] As a solid oxide fuel cell (SOFC), for example, a fuel gas (e.g., city gas, etc.) is steam reformed to produce a reformed gas, this reformed gas is supplied to the fuel electrode (anode) side of the cell stack, and air as an oxidant is supplied to the oxygen electrode (cathode) side of the cell stack, and power generation is performed by a fuel cell reaction in this cell stack. Such a solid oxide fuel cell includes a vaporizer for vaporizing reformed water and a reformer for steam reforming the fuel gas, the reformed water is supplied to the vaporizer, and the water vapor vaporized in the vaporizer is fed to the reformer. Further, the fuel gas is supplied to the reformer (or the vaporizer), and steam reforming of the fuel gas is performed using water vapor in this reformer.

[0003] In such an SOFC, when steam reforming of a hydrocarbon-based fuel gas (e.g., methane) is performed with steam under a high-temperature situation in the reformer, the fuel gas is converted into hydrogen and carbon monoxide by the following reaction.

[0004] CH4 + H2O → CO + 3H2 ···(1) On the other hand, when the fuel gas (e.g., methane) is heated without steam, the following reaction (Boudouard reaction) proceeds and carbon is deposited.

[0005] CH4 → C + 2H2 ···(2) Also, using a metal such as nickel as a catalyst, carbon is deposited from carbon monoxide by the following reaction.

[0006] 2CO → C + CO2 ···(3) If carbon deposition progresses on the fuel electrode (anode) of the cell stack, it leads to a decrease in the power generation performance of the cell stack. Furthermore, if carbon deposition progresses in the reformer, it can cause blockage of the reformer and fouling of the reforming catalyst.

[0007] For these reasons, in order for steam reforming to occur as required in this reformer, a stable supply of steam is necessary. To achieve this, it is important that reformed water is supplied to the vaporizer to generate steam stably, and that the generated steam is then supplied to the reformer as required to react with the fuel gas.

[0008] Therefore, a SOFC has been proposed that stably generates water vapor in the vaporizer (evaporator) (see, for example, Patent Document 1). In this SOFC, the temperature is made to be high downstream of the fuel gas and vaporizer, while the temperature on the upstream side is not made to be excessively high, so that the temperature gradient in the vaporizer increases towards the downstream side. In such a vaporizer (evaporator), reformed water is supplied to the upstream side of the vaporizer, and the supplied reformed water flows downstream toward the high-temperature part, and by flowing in this manner, the reformed water is gradually heated and water vapor is generated. [Prior art documents] [Patent Documents]

[0009] [Patent Document 1] Patent No. 6848104 [Overview of the Initiative] [Problems that the invention aims to solve]

[0010] However, the following problems may arise in this SOFC. Generally, the amount of reformed water used to generate the steam used in steam reforming is small, while the inside of the vaporizer (evaporator) is at a high temperature of several hundred degrees. Therefore, when the reformed water supplied to the vaporizer (supplied in droplet form) drips onto the contact surface (evaporation surface) of the vaporizer, it may vaporize, become superheated, and cause sudden boiling.

[0011] Generally, the phenomenon in which bubbles are formed when a liquid reaches its boiling point is called boiling. However, there is a state in which bubbles are not formed even when a liquid reaches its boiling point. This state is called a superheated state, and if some stimulus (for example, vibration or the introduction of impurities) is applied to this superheated state, the liquid will suddenly boil explosively. This phenomenon is called bumping.

[0012] If the vaporizer becomes overheated, and some kind of stimulus acts on it in this overheated state, sudden boiling will occur inside the vaporizer. When this sudden boiling occurs, the pressure inside the vaporizer (evaporator) rises sharply, and fuel gas is not supplied to the vaporizer (evaporation chamber), which may lead to a phenomenon called fuel depletion.

[0013] The object of the present invention is to provide a solid oxide fuel cell that can prevent the vaporizer from rising to a high temperature and thus prevent the occurrence of sudden boiling. [Means for solving the problem]

[0014] The solid oxide fuel cell according to claim 1 of the present invention comprises a reformed water supply means for supplying reformed water, a fuel gas supply means for supplying fuel gas, a vaporizer for vaporizing the reformed water into water vapor, a reformer for steam reforming by reacting the fuel gas from the fuel gas supply means with water vapor from the vaporizer, and a cell stack for generating electricity by a fuel cell reaction between the reformed gas from the reformer and air, The vaporizer is provided with a cooling gas ejection means for ejecting cooling gas, and a temperature detection means is provided for detecting the temperature in relation to the vaporizer, and the amount of cooling gas ejected from the cooling gas ejection means is controlled based on the temperature detected by the temperature detection means.

[0015] Furthermore, in the solid oxide fuel cell according to claim 2 of the present invention, the reformed water supply means includes a water supply pump for supplying reformed water and a water supply pipe for supplying reformed water from the water supply pump to the vaporizer, the tip of the water supply pipe protruding into the vaporizer, and the temperature sensing means is disposed in or near the dripping region on the bottom wall of the vaporizer where reformed water drips through the water supply pipe. Cooling gas ejection means The invention is characterized by injecting a cooling gas toward the dripping region of the vaporizer.

[0016] Furthermore, in the solid oxide fuel cell according to claim 3 of the present invention, the cooling gas injection means includes a cooling gas supply pipe that supplies cooling gas to the vaporizer, and the cooling gas is injected through the cooling gas supply pipe toward the dripping region of the vaporizer, and the reformed water supply period in which reformed water is supplied by the reformed water supply means and the cooling gas supply period in which cooling gas is supplied by the cooling gas injection means do not overlap.

[0017] Furthermore, in the solid oxide fuel cell according to claim 4 of the present invention, a gas flow rate adjustment valve for adjusting the flow rate of the cooling gas is provided in the cooling gas supply pipe of the cooling gas injection means, and furthermore, the cooling gas injection means and the Gas flow control valve A controller is provided for controlling the gas flow rate, and the controller includes a gas flow rate increase signal generating means for generating a gas flow rate increase signal and a gas flow rate decrease signal generating means for generating a gas flow rate decrease signal. When the temperature detected by the temperature detection means rises above the upper limit temperature value, the gas flow rate increase signal generating means generates the gas flow rate increase signal, and based on the gas flow rate increase signal, the gas flow rate control valve is controlled to open. Furthermore, when the temperature detected by the temperature detection means falls below the lower limit temperature value, the gas flow rate decrease signal generating means generates the gas flow rate decrease signal, and based on the gas flow rate decrease signal, the gas flow rate control valve is controlled to close.

[0018] Furthermore, in the solid oxide fuel cell according to claim 5 of the present invention, the controller further includes a gas ejection continuation signal generating means for generating a gas ejection continuation signal and a gas ejection stop signal generating means for generating a gas ejection stop signal, wherein when the temperature detected by the temperature detection means rises above the maximum upper limit temperature value, the gas ejection continuation signal generating means generates the gas ejection continuation signal, and based on the gas ejection continuation signal, the cooling gas ejection means continues to supply cooling gas during the reformed water supply period, and when the temperature detected by the temperature detection means falls below the maximum lower limit temperature value, the gas ejection stop signal generating means generates the gas ejection stop signal, and based on the gas ejection stop signal, the cooling gas ejection means stops ejecting cooling gas during the cooling gas supply period.

[0019] Furthermore, the solid oxide fuel cell according to claim 6 of the present invention is characterized in that the cooling gas supplied by the cooling gas injection means is an oxygen-free gas. [Effects of the Invention]

[0020] According to the solid oxide fuel cell described in claim 1 of the present invention, a cooling gas injection means is provided for injecting cooling gas into the vaporizer, and the amount of cooling gas injected from this cooling gas injection means is controlled based on the temperature detected by the temperature detection means. As a result, the temperature inside the vaporizer can be maintained at the required temperature by the injected cooling gas, and the required temperature can be maintained even if the supply amount of reformed water is small, thereby preventing the reformed water from boiling over inside the vaporizer.

[0021] Furthermore, according to the solid oxide fuel cell described in claim 2 of the present invention, reformed water is dripped into the dripping region of the vaporizer through a water supply pipe, and the temperature sensing means is disposed in or near the dripping region on the bottom wall of the vaporizer. Therefore, the amount of cooling gas ejected from the cooling gas ejection means can be controlled based on the temperature in or near the dripping region (also referred to as the "dripping region temperature" throughout this specification). Cooling gas ejection meansSince the cooling gas is jetted toward this dropping region, this dropping region can be effectively cooled, whereby even if the dropping amount of the reformed water is small, a rapid temperature rise can be suppressed and bumping of the reformed water in the vaporizer can be prevented.

[0022] Further, according to the solid oxide fuel cell described in claim 3 of the present invention, since the supply period of the reformed water supplied through the water supply pipe and the supply period of the cooling gas supplied through the cooling gas supply pipe do not overlap, the cooling gas is not supplied when the reformed water dropped from the water supply pipe is evaporating. By controlling the supply in this way, the dropping region of the vaporizer is not supercooled, and the delay in the generation of water vapor can be prevented.

[0023] Further, according to the solid oxide fuel cell described in claim 4 of the present invention, the cooling gas jetting means and Gas flow control valve the controller for controlling include a gas flow rate increase signal generation means and a gas flow rate decrease signal generation means. When the detected temperature of the temperature detection means becomes higher than the upper limit temperature value, based on the gas flow rate increase signal generated by the gas flow rate increase signal generation means, the gas flow rate adjustment valve is controlled in the opening direction and the jetting amount of the cooling gas increases. When the detected temperature of the temperature detection means becomes lower than the lower limit temperature value, based on the gas flow rate decrease signal generated by the gas flow rate decrease signal generation means, the gas flow rate adjustment valve is controlled in the closing direction and the jetting amount of the cooling gas decreases. By adjusting the jetting amount of the cooling gas in this way, the temperature of the dropping region of the vaporizer can be maintained within a predetermined temperature range.

[0024] Furthermore, according to the solid oxide fuel cell described in claim 5 of the present invention, the controller includes a gas injection continuation signal generating means and a gas injection stop signal generating means. When the temperature detected by the temperature detection means rises above the maximum upper limit temperature value, the cooling gas injection means continues to supply cooling gas during the reformed water supply period based on the gas injection continuation signal generated by the gas injection continuation signal generating means. During this reformed water supply period, reformed water and cooling gas are supplied to the dripping area of ​​the vaporizer, thereby preventing this dripping area from becoming abnormally hot. Also, when the temperature detected by the temperature detection means falls below the maximum lower limit temperature value, the cooling gas injection means stops ejecting cooling gas during the cooling gas supply period based on the gas injection stop signal generated by the gas injection stop signal generating means. During this cooling gas supply period, reformed water and cooling gas are not supplied to the dripping area of ​​the vaporizer, thereby preventing this dripping area from becoming abnormally cold.

[0025] Furthermore, according to the solid oxide fuel cell described in claim 6 of the present invention, since the cooling gas is an oxygen-free gas, oxidation of the fuel electrode of the cell stack can be prevented. [Brief explanation of the drawing]

[0026] [Figure 1] A simplified diagram showing a first embodiment of a solid oxide fuel cell according to the present invention. [Figure 2] A partial cross-sectional view showing the vaporizer and related components of a solid oxide fuel cell according to the first embodiment. [Figure 3] Figure 3(a) shows the supply pattern when the amount of treated water supplied is small, Figure 3(b) shows the supply pattern when the amount of treated water supplied is moderate, and Figure 3(c) shows the supply pattern when the amount of treated water supplied is large. [Figure 4] A simplified block diagram showing the control system of a solid oxide fuel cell according to the first embodiment. [Figure 5] A flowchart showing the control flow by the control system in Figure 4. [Figure 6]A simplified block diagram showing the control system of a second embodiment of a solid oxide fuel cell according to the present invention. [Figure 7] A flowchart showing the control flow by the control system in Figure 6. [Modes for carrying out the invention]

[0027] Hereinafter, embodiments of a solid oxide fuel cell according to the present invention will be described with reference to the attached drawings. First, a first embodiment of a solid oxide fuel cell according to the present invention will be described with reference to Figures 1 to 5.

[0028] In Figure 1, the illustrated solid oxide fuel cell (SOFC) comprises a vaporizer 2 that vaporizes reformed water, a reformer 4 that steam reforms fuel gas (e.g., city gas), and a solid oxide cell stack 6 that generates electricity through a fuel cell reaction. In this embodiment, a water supply source 8, which is composed of, for example, a water tank, is connected to the vaporizer 2 via a water supply pipe 10 (which constitutes a water supply channel), and a water supply pump 12 and a water flow rate detection means 13 are installed in this water supply pipe 10. When the water supply pump 12 is activated, water from the water supply source 8 is supplied to the vaporizer 2 as reformed water through the water supply pipe 10. The water supply source 8, water supply pump 12, and water supply pipe 10 (water supply channel) constitute a water supply means 14 that supplies reformed water to the vaporizer 2, and the water flow rate detection means 13 (e.g., a water flow rate detection sensor) detects the amount of reformed water supplied from this water supply means 14.

[0029] Furthermore, a fuel gas supply source 16, which consists of, for example, a fuel tank and buried pipes, is connected to a reformer 4 via a fuel gas supply pipe 18 (which constitutes a fuel gas supply path), and a fuel gas supply pump 20 and a fuel gas flow rate detection means 21 (for example, a fuel gas flow rate detection sensor) are installed in this fuel gas supply pipe 18. When the fuel gas supply pump 20 is activated, fuel gas from the fuel gas supply source 16 is supplied to the reformer 4 through the fuel gas supply pipe 18. The fuel gas supply source 16, fuel gas supply pump 20, and fuel gas supply pipe 18 (fuel gas supply path) constitute a fuel gas supply means 22 that supplies fuel gas to the reformer 4, and the fuel gas flow rate detection means 21 detects the amount of fuel gas supplied from this fuel gas supply means 22.

[0030] The vaporizer 2 vaporizes the reformed water into steam, and the steam generated in the vaporizer 2 is supplied to the reformer 4 through the steam supply channel 24 (which consists of, for example, a steam supply pipe). The reformer 4 is filled with a reforming catalyst, and in this reformer 4, the steam from the vaporizer 2 is used to steam reform the fuel gas supplied from the fuel gas supply means 22.

[0031] The reformed gas, steam reformed in the reformer 4, is supplied to the fuel electrode (anode) side of the cell stack 6 through the reformed gas supply channel 26 (for example, consisting of a reformed gas supply pipe). In addition, air is supplied to the oxygen electrode (cathode) side of the cell stack 6 as an oxidizing gas. An air supply pipe 28 (which constitutes an air supply channel) is connected to the oxygen electrode side of the cell stack 6, and an air blower 30 and an air flow rate detection means 31 (for example, an air flow rate detection sensor) are installed in this air supply pipe 28. When the air blower 30 is activated, air from the atmosphere is supplied to the cell stack 6 through the air supply pipe 28. The air blower 30 and the air supply pipe 28 constitute an air supply means 32 that supplies air to the cell stack 6, and the air flow rate detection means 31 detects the supply flow rate of the air supplied from this air supply means 32.

[0032] In the cell stack 6, electricity is generated by a fuel cell reaction between the reformed gas (reformed fuel gas) from the reformer 4 and the air (oxygen contained in the air) from the air supply means 32. The reformed gas (fuel off-gas) that flows through the fuel electrode of the cell stack 6 and the air (air off-gas) that flows through its oxygen electrode flow to the fuel region 34 above the cell stack 6, where the fuel off-gas (containing fuel gas) is burned by the air off-gas (containing air).

[0033] In this SOFC, the vaporizer 2, reformer 4, and cell stack 6 are housed within an insulated module 36, with the vaporizer 2 and reformer 4 positioned above the cell stack 6. With this configuration, the vaporizer 2 and reformer 4 are heated by combustion in the combustion zone 34 and kept at a high temperature, and this combustion heat is used to keep the inside of the insulated module 36 at a high temperature as well.

[0034] The combustion exhaust gas from within the insulated module 36 is discharged through a combustion gas discharge channel 38 (which consists of, for example, a combustion gas discharge pipe). The combustion gas discharge channel 38 is provided with a combustion section 40, which is equipped with, for example, a combustion catalyst. The combustion exhaust gas from within the insulated module 36 is completely combusted by the catalytic reaction in the combustion section 40 before being discharged to the outside through the combustion gas discharge channel 38.

[0035] In this SOFC, to prevent the reformed water from boiling over in the vaporizer 2, it is further configured as follows: Referring to Figure 2 as well as Figure 1, the water supply pipe 10 penetrates the side wall 42 of the vaporizer 2 and protrudes inward. The reformed water supplied through this water supply pipe 10 is dripped from its tip toward the dripping area S of the bottom wall 44 of the vaporizer 2, as indicated by arrow 46, and the dripped reformed water spreads along the surface of this bottom wall 44 and evaporates.

[0036] At this time, if the dripping region S of the vaporizer 2 is at a high temperature (for example, 120°C or higher) due to the combustion heat from the combustion region 34, the reformed water dripped from the tip of the water supply pipe 10 into the dripping region S may be rapidly heated and become overheated. Therefore, in order to prevent this overheating, a cooling gas injection means 48 is provided to inject cooling gas into the vaporizer 2.

[0037] To explain further, the illustrated cooling gas injection means 48, as shown in Figure 1, comprises a cooling gas supply source 50, which is for example composed of a cooling tank, and a cooling gas supply pipe 52 (which constitutes a cooling gas supply path) that supplies cooling gas from the cooling gas supply source 50 to the vaporizer 2. A cooling gas supply pump 54 and a gas flow rate control valve 55 are installed in this cooling gas supply pipe 52. When the cooling gas supply pump 54 is activated, cooling gas from the cooling gas supply source 50 is supplied to the vaporizer 2 through the cooling gas supply pipe 52, and the gas flow rate control valve 55 adjusts the amount of cooling gas supplied through the cooling gas supply pipe 52 as will be described later.

[0038] It is preferable to use an oxygen-free gas as the cooling gas, as this prevents oxidation of the fuel electrode of the cell stack 6. For example, nitrogen gas can be used as the cooling gas.

[0039] In this embodiment, as shown in Figure 2, the tip end (downstream end) of the cooling gas supply pipe 52 penetrates the side wall 42 of the vaporizer 2 and protrudes inward, protruding somewhat further inward than the tip end of the reformed water pipe 10, and this tip end extends downward toward the dripping region S of the bottom wall 44 of the vaporizer 2. With this configuration, the cooling gas supplied through the cooling gas supply pipe 10 is ejected toward the dripping region S, as indicated by arrow 56, and this ejected cooling gas can effectively cool the dripping region S of the vaporizer 2.

[0040] In this embodiment, a temperature detection means 58 is further provided to detect the temperature of the dripping region S or its vicinity on the bottom wall 44 of the vaporizer 2 (i.e., the dripping region temperature). This temperature detection means 58 is composed of, for example, a temperature sensing sensor such as a thermocouple. The temperature detection means 58 is attached to the outer surface of the dripping region S on the bottom wall 44, as shown in Figure 2, for example. However, instead of this configuration, it may be attached to the outer surface near the dripping region S, or it may be embedded within the bottom wall 44. The amount of cooling gas ejected from the cooling gas ejection means 48 is controlled based on the temperature detected by the temperature detection means 58, as will be described later.

[0041] In this embodiment, the reformed water supplied from the water supply means 14 and the cooling gas supplied from the cooling gas injection means 48 are supplied at the timings shown in Figure 3. For example, when the supply amount of reformed water is small, as shown in Figure 3(a), the reformed water is supplied only once in the time X of one cycle T, and the cooling gas is supplied during the period when reformed water is not supplied (one period). When the supply amount of reformed water is moderate, as shown in Figure 3(b), the reformed water is supplied twice in the time X of one cycle T, and the cooling gas is supplied during the periods when reformed water is not supplied (two periods). Furthermore, when the supply amount of reformed water is large, as shown in Figure 3(c), the reformed water is supplied four times in the time X of one cycle T, and the cooling gas is supplied during the periods when reformed water is not supplied (four periods), as described above.

[0042] By timing the supply of reformed water and cooling gas in this way, during the period when reformed water is supplied, the dripping region S of the vaporizer 2 is cooled by the vaporization of the reformed water, and during the period when reformed water is not supplied, it is cooled by the cooling gas ejected from the cooling gas ejection means 48. Therefore, it is possible to prevent the dripping region S of the vaporizer 2 from becoming hot and to prevent the occurrence of super-boiling of the reformed water inside the vaporizer 2. Furthermore, since the reformed water supply period and the cooling gas supply period do not overlap, the dripping region S of the vaporizer 2 is not cooled simultaneously by the reformed water and cooling gas, thereby preventing the dripping region S from being supercooled.

[0043] This solid oxide fuel cell is controlled by the control system shown in Figure 4. This solid oxide fuel cell includes a controller 62, which is composed of, for example, a microprocessor. This controller 62 includes a fuel gas supply amount calculation means 64, a reformed water supply amount calculation means 66, an air supply amount calculation means 68, a cooling gas supply amount calculation means 70, and an operation control means 71.

[0044] The fuel gas supply amount calculation means 64 calculates the amount of fuel gas to be supplied according to the power output of the cell stack 6, and the operation control means 71 controls the rotation speed of the fuel gas supply pump 20 based on this supply amount, thereby controlling the amount of fuel gas supplied from the fuel gas supply means 22. The reformed water supply amount calculation means 66 calculates the amount of reformed water to be supplied according to the power output of the cell stack 6, and the operation control means 71 controls the rotation speed of the water supply pump 12 based on this supply amount, thereby controlling the amount of reformed water supplied from the water supply means 14.

[0045] Furthermore, the air supply amount calculation means 68 calculates the amount of air to be supplied according to the power generation output of the cell stack 6, and the operation control means 71 controls the rotation speed of the air blower 30 based on this supply amount, thereby controlling the amount of air supplied from the air supply means 32. In addition, the cooling gas supply amount calculation means 70 calculates the amount of cooling gas to be supplied, and the operation control means 71 controls the rotation speed of the cooling gas supply pump 54 and the opening degree of the gas flow rate adjustment valve 55 based on this supply amount, thereby controlling the amount of cooling gas ejected from the cooling gas ejection means 8.

[0046] The controller 62 further includes a temperature comparison means 72, a temperature determination means 74, a gas flow rate decrease signal generation means 76, a gas flow rate increase signal generation means 78, and a memory means 80. In this embodiment, detection signals from the fuel gas flow rate detection means 21, the reformed water flow rate detection means 13, and the air flow rate detection means 31 are sent to the controller 62, and a detection signal from the temperature detection means 58 is also sent to the controller 62. The memory means 80 stores an upper limit temperature value (for example, about 120°C) that serves as a reference for the upper limit temperature range of the temperature range of the dripping region temperature of the vaporizer 2, and a lower limit temperature value (for example, about 80°C) that serves as a reference for the lower limit temperature range.

[0047] As described later, the temperature comparison means 72 compares the temperature detected by the temperature detection means 58 with the upper temperature limit (e.g., 120°C) and lower temperature limit (e.g., 80°C) registered in the memory means 80. When the detected temperature is higher than the upper temperature limit (120°C), the temperature determination means 74 determines that the temperature is high, and based on this high temperature determination, the gas flow rate increase signal generation means 78 generates a gas flow rate increase signal to increase the flow rate of the cooling gas. When the detected temperature is lower than the lower temperature limit (80°C), the temperature determination means 74 determines that the temperature is low, and based on this low temperature determination, the gas flow rate decrease signal generation means 76 generates a gas flow rate decrease signal to decrease the flow rate of the cooling gas.

[0048] The control system in Figure 4 is performed, for example, following the flowchart shown in Figure 5. Referring mainly to Figures 4 and 5, in the power generation operation of the solid oxide fuel cell, the fuel gas supply amount calculation means 64 calculates the amount of fuel gas to be supplied to the reformer 4 (see Figure 1), the reformed water supply amount calculation means 66 calculates the amount of reformed water to be supplied to the vaporizer 2 (see Figure 1), the air supply amount calculation means 68 calculates the amount of air to be supplied to the oxygen electrode side of the cell stack 6 (see Figure 1), and the cooling gas supply amount calculation means 70 calculates the amount of cooling gas to be injected into the vaporizer 2 (step S1).

[0049] Once the supply amounts are calculated in this way, the fuel gas supply pump 20 is controlled so that the amount of fuel gas supplied through the fuel gas supply pipe 18 is the calculated amount, the water supply pump 12 is controlled so that the amount of reformed water supplied through the water supply pipe 10 is the calculated amount, the air blower 30 is controlled so that the amount of air supplied through the air supply pipe 28 is the calculated amount, and the cooling gas supply pump 54 and gas flow control valve 55 are controlled so that the amount of cooling gas supplied through the cooling gas supply pipe 52 is the calculated amount (step S2). Once the fuel gas, reformed water, air, etc. are supplied in this way, electricity is generated in the cell stack 6 by the fuel cell reaction (step S3).

[0050] During power generation in the cell stack, the temperature detection means 58 detects the temperature of the dripping region S (or its vicinity) of the vaporizer 2, and the flow rate of the cooling gas is controlled based on this detected temperature (step S4). This cooling gas flow rate control is performed based on the temperature of the dripping region of the vaporizer 2 detected by the temperature detection means 58. The temperature detection means 58 detects the temperature of the dripping region (step S4-1), the temperature comparison means 72 compares the temperature detected by the temperature detection means 58 with the upper and lower temperature limits registered in the memory means 80 (step S4-2), and the temperature determination means 74 makes a determination based on this comparison result.

[0051] For example, if the detected temperature is higher than the upper temperature limit (e.g., 120°C), the process proceeds from step S4-3 to step S4-4, where the temperature determination means 74 makes a high temperature determination, and based on this high temperature determination, the gas flow rate increase signal generation means 78 generates a gas flow rate increase signal (step S4-5). In this way, the operation control means 71 adjusts the operation of the gas flow rate adjustment valve 55 to the open direction (step S4-6), thereby increasing the amount of cooling gas ejected into the dripping area S of the vaporizer 2 through the cooling gas supply pipe 52. Thus, the cooling effect of the cooling gas is enhanced, and the temperature rise in the dripping area S of the vaporizer 2 is suppressed and maintained within a predetermined temperature range.

[0052] When this detected temperature is lower than the lower limit temperature value (for example, 80°C), the process proceeds from step S4-3 through step S4-7 to step S4-8, where the temperature determination means 74 makes a low temperature determination, and based on this low temperature determination, the gas flow rate reduction signal generation means 78 generates a gas flow rate reduction signal (step S4-9). Thus, the operation control means 71 adjusts the operation of the gas flow rate adjustment valve 55 in the closing direction (step S4-10), thereby reducing the amount of cooling gas ejected into the dripping region S of the vaporizer 2 through the cooling gas supply pipe 52. In this way, the cooling effect of the cooling gas is weakened, and the temperature drop in the dripping region S of the vaporizer 2 is suppressed and maintained within a predetermined temperature range.

[0053] Furthermore, when the detected temperature is within the temperature range between the lower and upper temperature limits (i.e., the appropriate temperature range), the process proceeds from step S4-3 through step S4-7 to step S5, and power generation continues without adjusting the flow rate of the gas flow control valve 55. This adjustment of the cooling gas supply is carried out until the operation of the solid oxide fuel cell is completed.

[0054] Next, a second embodiment of the solid oxide fuel cell according to the present invention will be described with reference to Figures 6 and 7. In this second embodiment, the cooling gas injection is configured to be temporarily continued or temporarily stopped. In this second embodiment, components that are substantially the same as those in the first embodiment described above are given the same reference numerals, and their descriptions are omitted.

[0055] In Figure 6, in this second embodiment, the controller 62A includes, in addition to the gas flow rate decrease signal generating means 76 and the gas flow rate increase signal generating means 78, a gas ejection stop signal generating means 82 for generating a gas ejection stop signal and a gas ejection continuation signal generating means 84 for generating a gas ejection continuation signal. In connection with this, the memory means 80A stores, in addition to the upper and lower temperature limits, the maximum upper temperature limit value that serves as a reference for the maximum upper temperature of the maximum temperature range (for example, around 140°C) and the maximum lower temperature limit value that serves as a reference for the maximum lower temperature of the maximum temperature range (for example, around 60°C). The other configurations in this second embodiment are the same as those in the first embodiment described above.

[0056] In this second embodiment, the flow rate control of the cooling gas based on the detected temperature is performed, for example, according to the flowchart shown in Figure 7. Referring to Figures 6 and 7, in this cooling gas flow rate control, the temperature detection means 58 detects the temperature of the dripping region of the vaporizer 2 (step S4a-1), the temperature comparison means 72 compares the temperature detected by the temperature detection means 58 with the upper limit temperature value, maximum upper limit temperature value, lower limit temperature value, and maximum lower limit temperature value registered in the memory means 80A (step S4a-2), and the temperature determination means 74 makes a determination based on the comparison result with the temperature detected by the temperature detection means 58.

[0057] For example, when the temperature detected by the temperature detection means 58 is higher than the upper limit temperature value (e.g., 120°C) and less than or equal to the maximum upper limit temperature value (e.g., 140°C), the process proceeds through steps S4a-3 and S4a-31 to step S4a-4, where the temperature determination means 74 determines that the temperature is high, the gas flow rate increase signal generation means 78 generates a gas flow rate increase signal (step S4a-5), and the operation control means 71 adjusts the operation of the gas flow rate adjustment valve 55 in the open direction (step S4a-6). These operations from steps S4a-4 to S4a-6 are the same as the operations from steps S4-4 to S4-6 in the first embodiment.

[0058] Furthermore, for example, if the detected temperature is lower than the lower limit temperature value (e.g., 80°C) and greater than or equal to the maximum lower limit temperature value (e.g., 60°C), the process proceeds through steps S4a-3 and S4a-31, steps S4a-7 and S4a-71 to step S4a-8, where the temperature determination means 74 determines that the temperature is low, the gas flow rate reduction signal generation means 76 generates a gas flow rate reduction signal (step S4a-9), and the operation control means 71 adjusts the operation of the gas flow rate adjustment valve 55 in the closing direction (step S4a-10). These operations from steps S4a-8 to S4a-10 are the same as the operations from steps S4-8 to S4-10 in the first embodiment.

[0059] Furthermore, if the detected temperature is higher than the maximum upper limit temperature value (for example, 140°C), the process proceeds through steps S4a-3 and S4a-31 to step S4a-11, where the temperature determination means 74 determines that the temperature is abnormally high, the gas ejection continuation signal generation means 84 generates a gas ejection continuation signal (step S4a-12), and the operation control means 71 operates the cooling gas ejection means (cooling gas supply pump 54) to continue ejecting cooling gas even during the reformed water supply period when reformed water is supplied (step S4a-13). Consequently, at this time, reformed water from the reformed water supply means (water supply pump 12) is dripped into the dripping area of ​​the vaporizer, and cooling gas from the cooling gas ejection means (cooling gas supply pump 54) is ejected towards this dripping area, further enhancing the cooling effect of this dripping area and suppressing further temperature increases in this area, causing the temperature to decrease. At this time, the abnormal lamp 86 lights up (step S4a-14), indicating that the dripping area of ​​the vaporizer is in an overheated state.

[0060] Furthermore, if the detected temperature is lower than the maximum lower limit temperature (for example, 60°C), the process proceeds through steps S4a-3, S4a-7, and S4a-71 to step S4a-15, where the temperature determination means 74 determines that the temperature is abnormally low, the gas ejection stop signal generation means 82 generates a gas ejection stop signal (step S4a-16), and the operation control means 71 stops the operation of the cooling gas ejection means (cooling gas supply pump 54) during the cooling gas supply period in which cooling gas is ejected, thereby stopping the ejection of cooling gas (step S4a-17) (reformed water is not supplied during this cooling gas supply period). Consequently, at this time, the ejection of cooling gas from the cooling gas ejection means (cooling gas supply pump 54) is stopped, the cooling effect on the dripping area of ​​the vaporizer is further weakened, and further temperature drops in this dripping area are suppressed, causing the temperature to rise. In this case as well, the abnormality lamp 86 lights up (step S4a-18), indicating that the vaporizer's dripping area is in a supercooled state.

[0061] Although embodiments of solid oxide fuel cells according to the present invention have been described above, the present invention is not limited to these embodiments, and various changes and modifications are possible without departing from the scope of the present invention.

[0062] For example, in the above-described embodiment, the vaporizer 2 and the reformer 4 are configured separately, but the invention is not limited to this configuration and can be similarly applied to a configuration in which the vaporizer 2 and the reformer 4 are configured as a single unit.

[0063] Furthermore, in the embodiment described above, the cooling gas supply means 48 includes a cooling gas supply pump 54. However, if, for example, cooling gas at a predetermined pressure can be supplied from a cooling gas supply source 50, a supply shut-off valve (not shown) may be provided instead of the cooling gas supply pump 54. In this case, when the supply shut-off valve is opened, cooling gas is supplied through the cooling gas supply pipe 52, and when the supply shut-off valve is closed, the supply of cooling gas is stopped. [Explanation of Symbols]

[0064] 2. Vaporizer 4. Reformer 6-cell stack 10 Water supply pipes 14 Water supply means 22 Fuel gas supply means 32 Air supply means 48 Cooling gas ejection means 52 Cooling gas supply pipe 55 Gas flow control valve 58 Temperature detection means 62, 62A Controller 66. Means for calculating the amount of treated water supplied 70 Cooling gas supply amount calculation means 72 Temperature comparison means 74 Temperature determination means 76 Gas flow rate reduction signal generation means 78 Gas flow rate increase signal generation means 82 Gas ejection stop signal generation means 84 Gas ejection continuation signal generation means S Dripping area

Claims

1. A solid oxide fuel cell comprising: a reformed water supply means for supplying reformed water; a fuel gas supply means for supplying fuel gas; a vaporizer for vaporizing the reformed water into water vapor; a reformer for steam reforming by reacting the fuel gas from the fuel gas supply means with water vapor from the vaporizer; and a cell stack for generating electricity through a fuel cell reaction between the reformed gas from the reformer and air, A solid oxide fuel cell is provided, characterized in that a cooling gas injection means for injecting cooling gas into the vaporizer is provided, and a temperature detection means for detecting the temperature in relation to the vaporizer is provided, and the amount of cooling gas injected from the cooling gas injection means is controlled based on the temperature detected by the temperature detection means.

2. The solid oxide fuel cell according to claim 1, wherein the reformed water supply means includes a water supply pump for supplying reformed water and a water supply pipe for supplying reformed water from the water supply pump to the vaporizer, the tip of the water supply pipe protruding into the vaporizer, the temperature sensing means is disposed in or near the dripping region on the bottom wall of the vaporizer where reformed water drips through the water supply pipe, and the cooling gas ejection means ejects cooling gas toward the dripping region of the vaporizer.

3. The solid oxide fuel cell according to claim 2, wherein the cooling gas ejection means includes a cooling gas supply pipe that supplies cooling gas to the vaporizer, and the cooling gas is ejected through the cooling gas supply pipe toward the dripping region of the vaporizer, and the reformed water supply period during which reformed water is supplied by the reformed water supply means and the cooling gas supply period during which cooling gas is supplied by the cooling gas ejection means do not overlap.

4. The cooling gas supply pipe of the cooling gas ejection means is provided with a gas flow rate control valve for adjusting the flow rate of the cooling gas, and further, a controller is provided for controlling the cooling gas ejection means and the gas flow rate control valve, the controller includes a gas flow rate increase signal generating means for generating a gas flow rate increase signal and a gas flow rate decrease signal generating means for generating a gas flow rate decrease signal, and when the temperature detected by the temperature detection means rises above the upper limit temperature value, the gas flow rate increase signal generating means generates the gas flow rate increase signal, and based on the gas flow rate increase signal, the gas flow rate control valve is controlled to open, and when the temperature detected by the temperature detection means falls below the lower limit temperature value, the gas flow rate decrease signal generating means generates the gas flow rate decrease signal, and based on the gas flow rate decrease signal, the gas flow rate control valve is controlled to close, characterized in that the solid oxide fuel cell according to claim 3.

5. The controller further includes a gas ejection continuation signal generating means for generating a gas ejection continuation signal and a gas ejection stop signal generating means for generating a gas ejection stop signal, wherein when the temperature detected by the temperature detection means rises above the maximum upper limit temperature value, the gas ejection continuation signal generating means generates the gas ejection continuation signal, and based on the gas ejection continuation signal, the cooling gas ejection means continues to supply cooling gas during the reformed water supply period, and when the temperature detected by the temperature detection means falls below the maximum lower limit temperature value, the gas ejection stop signal generating means generates the gas ejection stop signal, and based on the gas ejection stop signal, the cooling gas ejection means stops ejecting cooling gas during the cooling gas supply period, characterized in that the solid oxide fuel cell according to claim 4.

6. The solid oxide fuel cell according to claim 1, characterized in that the cooling gas supplied by the cooling gas injection means is an oxygen-free gas.

Images