JP2016122629A - Fuel battery system and control method for the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a new control technique of suppressing deterioration of a fuel battery cell when a fuel battery system is started up.SOLUTION: In each of a period before raw fuel adsorbed to water vapor reforming catalyst is desorbed (period A), during a period when the raw fuel is being desorbed (period B) and a period from a time when a detector detects information correlated with a state that the desorption of the raw fuel has converged till a time when supply of reforming water to a reformer is started (period C), a controller executes a startup mode for controlling the supply amount of gas containing oxygen in an adjustment part to the extent that the ratio (air ratio) of an actually supplied oxygen amount to a theoretically required oxygen amount to perform perfect combustion on raw fuel supplied to an off-gas combustor does not fall below a predetermined threshold value and so that the air ratio during the period B is higher than the air ratio during the period A and the air ratio during the period C.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a fuel cell system.

  Conventionally, various fuel cell systems that generate power using fuel and air have been developed. Such a fuel cell system often includes a reforming unit that generates a hydrogen-containing gas necessary as fuel by reforming the raw fuel gas. For example, a reforming unit has been devised in which hydrocarbon-based raw fuel gas such as city gas or LPG is reformed using a catalyst to obtain a reformed gas mainly composed of hydrogen.

  The reforming unit may adsorb hydrocarbon as raw fuel gas to the catalyst depending on the combination of the catalyst and raw fuel gas used. When the adsorbed hydrocarbon is released from the catalyst as the temperature of the reforming unit rises at the start of the fuel cell system, the air-fuel ratio of the supplied raw fuel gas and air deviates from a desired value, There may be a problem that the combustion state in the heating means for heating the reforming section does not satisfy the required characteristics.

  Therefore, during the start-up operation of the fuel cell system, depending on the amount of the desorbed source gas desorbed from the components of the source gas adsorbed on at least one of the reforming catalyst and the carbon monoxide reducing catalyst, the source gas A fuel cell system that adjusts the amount of source gas supplied from a supply device has been devised (see Patent Document 1).

Japanese Patent No. 5121079

  By the way, as an example of the fuel cell system, a fuel cell using a solid oxide electrolyte is known. In such a fuel cell system, anode gas and cathode gas (hereinafter referred to as off-gas) that have not been used for power generation are combusted in a combustion portion in the vicinity of the fuel cell, and the heat of combustion is reformed at the time of startup. It is used for preheating and reforming reaction in the reforming section. Therefore, when the raw fuel gas adsorbed by the catalyst of the reforming unit is desorbed at the time of start-up and the amount of combustible gas burned in the combustion unit is larger than expected, the deterioration of the cell, particularly when the fuel cell and the combustion unit are in the vicinity. It will contribute.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a new control technique for suppressing deterioration of the fuel cell at the time of starting the fuel cell system.

  In order to solve the above problems, a fuel cell system according to an aspect of the present invention is provided between an anode to which a hydrogen-containing reformed gas is supplied, a cathode to which an oxygen-containing gas is supplied, and the anode and the cathode. A cell stack in which a plurality of cells having an electrolyte are stacked, a reforming section having a steam reforming catalyst that generates hydrogen-containing reformed gas to be supplied to the anode of the cell stack using raw fuel and steam, and reforming A hydrogen-containing reformed gas supply path for supplying hydrogen-containing reformed gas from the section to the anode, an oxygen-containing gas supply path for supplying oxygen-containing gas to the cathode, and a fuel for supplying raw fuel and reformed water to the reforming section An oxygen-containing gas provided above the cell stack and passed through the cathode without being used for power generation, and a hydrogen-containing reformed gas passed through the anode without being used for power generation, or An off-gas combustion unit that burns fuel, an adjustment unit that can adjust the amount of oxygen-containing gas supplied to the cathode, and whether or not the desorption of the raw fuel adsorbed on the steam reforming catalyst has converged in the reforming unit A detection unit that detects information correlated with the control unit, and a control unit that controls the supply amount of the oxygen-containing gas in the adjustment unit. The reforming unit is disposed above the off-gas combustion unit, and the control unit is before the raw fuel adsorbed on the steam reforming catalyst is desorbed (period A), while the raw fuel is being desorbed (period B), In each period from the detection of the information correlated with the state where the desorption of the raw fuel has converged in the detection unit to the start of the supply of reforming water to the reforming unit (period C), The ratio of the actually supplied oxygen amount (the air ratio) to the oxygen amount theoretically necessary for complete combustion of the raw fuel supplied to the combustion section is within a range that does not fall below a predetermined threshold, and in the period B The start-up mode for controlling the supply amount of the oxygen-containing gas in the adjustment unit is executed so that the air ratio becomes higher than the air ratio in period A and period C.

  Another aspect of the present invention is a control method for a fuel cell system. This method is a method for controlling a fuel cell system including a cell stack in which a plurality of cells each having an anode, a cathode, and an electrolyte provided between the anode and the cathode are stacked. The process of starting the supply of the oxygen-containing gas to the cathode and the supply of the raw fuel or hydrogen-containing reformed gas to the anode, and the raw fuel or hydrogen-containing reforming in the off-gas combustion section provided above the cell stack A step of burning the gas and the oxygen-containing gas, a step of heating the reforming unit having the steam reforming catalyst using the combustion heat of the off-gas combustion unit, and a raw material adsorbed on the steam reforming catalyst in the reforming unit A step of detecting information correlated with whether or not the desorption of the fuel has converged, and after detecting the information, the reforming reaction of the raw fuel using the catalyst causes the reformation of the hydrogen-containing reformed gas. And a step of initiating the formation, the. Before the raw fuel adsorbed to the steam reforming catalyst is desorbed (period A), the raw fuel is being desorbed (period B), and information that correlates with the state of desorption of the raw fuel converged is detected. The actual amount of oxygen that is theoretically required for complete combustion of the raw fuel supplied to the off-gas combustion section during each period until the start of the supply of reforming water to the mass section (period C) The amount of oxygen-containing gas supplied so that the ratio of the amount of oxygen supplied to the air (air ratio) does not fall below a predetermined threshold and the air ratio in period B is higher than the air ratio in periods A and C To control.

  ADVANTAGE OF THE INVENTION According to this invention, deterioration of the fuel cell at the time of starting of a fuel cell system can be suppressed.

It is the figure which showed typically schematic structure of the fuel cell system which concerns on embodiment. 1 is a block diagram of a fuel cell system according to an embodiment. It is a figure which shows the change of the air G1, the raw fuel gas G2, and the reforming water W1 which are supplied to each part in starting mode. It is a figure which shows the change of the raw fuel gas which detach | desorbs from a reforming part in starting mode. It is a figure which shows the temperature change of the predetermined area | region of a reforming part and a combustion part in starting mode. It is a figure which shows the change of the flow volume of the raw fuel gas actually injected | thrown-in to a reforming part, and the change of the flow volume of the raw fuel gas in consideration of the raw fuel gas which adsorb | sucks to a reforming part and desorbs | leaves. It is a figure which shows the change of the air ratio (The value which does not consider desorption gas, and the value which considers desorption gas) in starting mode. It is a flowchart which shows the starting mode which concerns on this Embodiment.

  A fuel cell system according to an embodiment of the present invention includes an anode to which a hydrogen-containing reformed gas is supplied, a cathode to which an oxygen-containing gas is supplied, and an electrolyte provided between the anode and the cathode. A cell stack having a plurality of stacked cells, a reforming unit having a steam reforming catalyst for generating hydrogen-containing reformed gas to be supplied to the anode of the cell stack using raw fuel and steam, and hydrogen from the reforming unit to the anode A hydrogen-containing reformed gas supply path for supplying the contained reformed gas, an oxygen-containing gas supply path for supplying the oxygen-containing gas to the cathode, a fuel supply path for supplying raw fuel and reformed water to the reforming section, and a cell An oxygen-containing gas that is provided above the stack and passes through the cathode without being used for power generation and a hydrogen-containing reformed gas or raw fuel that has passed through the anode without being used for power generation are burned. Information correlated with whether or not the desorption of the raw fuel adsorbed on the steam reforming catalyst has converged in the reforming unit, the adjustment unit that can adjust the supply amount of the oxygen-containing gas supplied to the cathode, and the off-gas combustion unit A detection unit for detecting, and a control unit for controlling a supply amount of the oxygen-containing gas in the adjustment unit.

  The reforming unit is disposed above the off-gas combustion unit, and the control unit is before the raw fuel adsorbed on the steam reforming catalyst is desorbed (period A), while the raw fuel is being desorbed (period B), In each period from the detection of the information correlated with the state where the desorption of the raw fuel has converged in the detection unit to the start of the supply of reforming water to the reforming unit (period C), The ratio of the actually supplied oxygen amount (the air ratio) to the oxygen amount theoretically necessary for complete combustion of the raw fuel supplied to the combustion section is within a range that does not fall below a predetermined threshold, and in the period B The start-up mode for controlling the supply amount of the oxygen-containing gas in the adjustment unit is executed so that the air ratio becomes higher than the air ratio in period A and period C.

  Thus, the control unit controls the supply amount of the oxygen-containing gas in a range in which the air ratio does not fall below a predetermined threshold in each of the period A, the period B, and the period C. Thereby, even if the supply amount of raw fuel fluctuates before and after the detachment of the raw fuel adsorbed on the catalyst, an appropriate amount of oxygen-containing gas can be supplied. In addition, the control unit causes the air ratio in the period B to be higher than the air ratio in the period A and the period C, so that the oxygen-containing gas (for example, air) at the stage where the raw fuel adsorbed on the catalyst is desorbed. ) Can be increased, for example, an increase in the temperature of the off-gas combustion section in period B is suppressed, and consequently an excessive increase in temperature near the tip of the cell stack is also suppressed. Therefore, it is possible to suppress the deterioration of the fuel cell at the time of starting the fuel cell system.

  The predetermined threshold may be an air ratio that does not misfire in the off-gas combustion section. Thereby, misfire can be suppressed in each of the periods A to C.

  When information correlating with the state in which the desorption of the raw fuel has converged is detected, the control unit sets the flow rate F1 of the oxygen-containing gas supplied to the cathode to the flow rate of the oxygen-containing gas that has been supplied to the cathode so far. You may control an adjustment part so that it may become a value lower than F2. As a result, it is possible to prevent excessive oxygen from being supplied after the desorption of the raw fuel from the catalyst has converged.

  The control unit may execute the start-up mode without supplying steam to the reforming unit. Thereby, the control part can perform the starting mode which controls supply_amount | feed_rate of the oxygen containing gas in an adjustment part in the state in which the steam reforming in a reforming part does not arise.

  The fuel supply path may supply raw fuel containing hydrocarbons having 2 or more carbon atoms or alcohols. Examples of the raw fuel include LPG (liquefied petroleum gas) and kerosene (kerosene) mainly composed of propane and butane. In the raw fuel containing a substance having 2 or more carbon atoms, adsorption to the steam reforming catalyst tends to occur. Therefore, in the fuel cell system using LPG or the like as the raw fuel, the effect of the above-described start mode is greater.

  The detection unit detects information correlated with the temperature of the reforming unit as information correlated with whether or not the desorption of the raw fuel has converged, and the control unit detects the temperature of the reforming unit detected by the detection unit. May reach the predetermined temperature Tr, the supply amount of the oxygen-containing gas in the adjustment unit may be changed. Thereby, it is possible to determine the timing for changing the supply amount of the oxygen-containing gas in the startup mode with a simple configuration.

  The detection unit detects information correlated with the temperature of the off-gas combustion unit as information correlated with whether or not the desorption of the raw fuel has converged, and the control unit detects the temperature of the off-gas combustion unit detected by the detection unit. When the amount of change of Tb per unit time becomes a predetermined value or less, the supply amount of the oxygen-containing gas in the adjustment unit may be changed. Thereby, it is possible to determine the timing for changing the supply amount of the oxygen-containing gas in the startup mode with a simple configuration.

  When the temperature Tb becomes equal to or lower than the predetermined temperature Tb1 after the change amount per unit time of the temperature Tb of the off-gas combustion unit detected by the detection unit has turned negative, the control unit detects the oxygen-containing gas in the adjustment unit. The supply amount may be changed. Thereby, it is possible to determine the timing for changing the supply amount of the oxygen-containing gas in the startup mode with a simple configuration.

  The control unit, when the change amount per unit time of the temperature Tb of the off-gas combustion unit detected by the detection unit turns negative at the temperature Tb0, the temperature Tb becomes equal to or lower than the temperature Tb1 ′ lower than the temperature Tb0 by a predetermined temperature. The supply amount of the oxygen-containing gas in the adjustment unit may be changed. Thereby, it is possible to determine the timing for changing the supply amount of the oxygen-containing gas in the startup mode with a simple configuration.

  Another aspect of the present invention is a control method for a fuel cell system. This method is a method for controlling a fuel cell system including a cell stack in which a plurality of cells each having an anode, a cathode, and an electrolyte provided between the anode and the cathode are stacked. The process of starting the supply of the oxygen-containing gas to the cathode and the supply of the raw fuel or hydrogen-containing reformed gas to the anode, and the raw fuel or hydrogen-containing reforming in the off-gas combustion section provided above the cell stack A step of burning the gas and the oxygen-containing gas, a step of heating the reforming unit having the steam reforming catalyst using the combustion heat of the off-gas combustion unit, and a raw material adsorbed on the steam reforming catalyst in the reforming unit A step of detecting information correlated with whether or not the desorption of the fuel has converged, and after detecting the information, the reforming reaction of the raw fuel using the catalyst causes the reformation of the hydrogen-containing reformed gas. And a step of initiating the formation, the.

  The fuel cell system correlates with the state in which the raw fuel is desorbed (period A), the raw fuel is being desorbed (period B), and the desorption of the raw fuel has converged. In order to completely burn the raw fuel supplied to the off-gas combustion section in each period from the detection of information to the start of the supply of reforming water to the reforming section (period C) So that the ratio of the actually supplied oxygen amount to the oxygen amount required for the air (air ratio) does not fall below a predetermined threshold, and the air ratio in period B is higher than the air ratio in period A and period C. The supply amount of the oxygen-containing gas is controlled.

  Thereby, in each of period A, period B, and period C, the supply amount of the oxygen-containing gas is controlled in a range where the air ratio does not fall below a predetermined threshold. Thereby, even if the supply amount of raw fuel fluctuates before and after the detachment of the raw fuel adsorbed on the catalyst, an appropriate amount of oxygen-containing gas can be supplied. Further, by making the air ratio in period B higher than the air ratio in period A and period C, the supply amount of oxygen-containing gas (for example, air) at the stage where the raw fuel adsorbed on the catalyst is desorbed Therefore, for example, an increase in the temperature of the off-gas combustion section in the period B is suppressed, and thus an excessive increase in the temperature near the tip of the cell stack is also suppressed. Therefore, it is possible to suppress the deterioration of the fuel cell at the time of starting the fuel cell system.

  It should be noted that any combination of the above-described constituent elements and a representation of the present invention converted between a method, an apparatus, a system, etc. are also effective as an aspect of the present invention.

  The present invention will be described below based on preferred embodiments with reference to the drawings. The same or equivalent components, members, and processes shown in the drawings are denoted by the same reference numerals, and repeated descriptions are omitted as appropriate. Further, the embodiments do not limit the invention but are exemplifications, and all features and combinations thereof described in the embodiments are not necessarily essential to the invention. In this embodiment, a solid oxide fuel cell system (SOFC) will be described as an example. Also, the description of the structure and operation that are not different from those of a general solid oxide fuel cell system will be omitted as appropriate.

[Fuel cell system]
FIG. 1 is a diagram schematically showing a schematic configuration of a fuel cell system according to the present embodiment. FIG. 2 is a block diagram of the fuel cell system according to the embodiment. The fuel cell system 100 includes a fuel cell module 10, an oxygen-containing gas supply path 12 that supplies air G1 that is an oxygen-containing gas to the fuel cell module 10, a reformed water supply path 13 that supplies reformed water W1, Hydrogen supply path 14 for supplying raw fuel gas G2 such as LPG, exhaust gas path 15 for discharging exhaust gas G3 generated by combustion in the fuel cell module 10 to the outside, and hydrogen content from the reforming unit 40 to the anode A hydrogen-containing reformed gas supply path 16 that supplies the reformed gas and a control unit 18 that controls a control valve and a pump provided in each path are provided.

  The oxygen-containing gas supply path 12 is provided with an oxygen-containing gas supply unit 20 that adjusts the amount of oxygen-containing gas (oxidant) supplied to the cathode. The control unit 18 adjusts the supply amount of the air G1 to the fuel cell module 10 by controlling the driving of the oxygen-containing gas supply unit 20. The oxygen-containing gas supply unit 20 may include a flow meter and a control valve in order to improve the accuracy of the supply amount of the oxygen-containing gas. The reforming water supply path 13 is configured such that the flow rate of the reforming water W1 can be controlled by a water supply unit 52 (see FIG. 2) that includes an adjustment valve, a pump, a flow meter, and the like. The oxygen-containing gas may be appropriately selected from gases containing oxygen atoms in addition to air.

  The fuel supply path 14 is provided with a hydrogen-containing fuel supply unit 54 (see FIG. 2) including a supply valve 22, a flow meter 24, a pressure gauge 28, a feed pump 30, and the like. The control unit 18 controls the operation of the supply valve 22 and the feed pump 30 based on the information acquired from the flow meter 24 and the pressure gauge 28, so that the supply amount of the raw fuel gas G2 to the fuel cell module 10 is appropriate. Adjust to. A reforming water supply path 13 is connected in the middle of the fuel supply path 14, and the fuel supply path 14 supplies the raw fuel gas G2 and the reforming water W1 to the reforming unit 40. The reforming water supply path 13 and the fuel supply path 14 may be connected to the reforming unit 40 without joining (see FIG. 2). Further, a water vaporization unit 56 may be provided on the upstream side of the reforming unit 40.

  In the present embodiment, LPG is used as the raw fuel gas G2. LPG is mainly composed of butane and propane. Usually, LPG contains an odorant as a measure against gas leakage. Since the odorant contains a sulfur component, if the gas containing the odorant is supplied to the reforming part of the fuel cell as it is, the reforming catalyst is poisoned and the performance is deteriorated. Therefore, a desulfurization unit 50 that desulfurizes the hydrogen-containing fuel supplied to the reforming unit 40 is further connected to the fuel supply path 14. Note that the hydrogen-containing gas may be appropriately selected from hydrogen gas, hydrocarbon gas, gas containing hydrogen atoms, and the like.

[Fuel cell module]
The fuel cell module 10 includes a reforming unit 40 that generates a reformed gas using a hydrogen-containing fuel such as LPG, a cell stack 42 that generates power using the reformed gas, and a cathode used as a cathode of the cell stack 42. A cathode gas path 44 for supplying air G1 as a gas, and an oxygen-containing gas (cathode off-gas) that is provided above the cell stack 42 and passes through the cathode of the cell stack and a hydrogen-containing reformed gas that passes through the anode of the cell stack And a combustion unit 46 that heats the reforming unit 40 by burning raw fuel gas or the like (anode off gas), a casing 48 that houses the reforming unit 40, the cell stack 42, and the combustion unit 46, and the interior of the casing 48 And an exhaust gas passage 49 for discharging off-gas combustion exhaust gas to the outside. The reforming unit 40 has a steam reforming catalyst that generates hydrogen-containing reformed gas to be supplied to the anode of the cell stack 42 using raw fuel and steam. The combustion unit 46 according to the present embodiment is an off-gas combustion unit that burns cathode off-gas that has passed through the cathode without being used for power generation and anode off-gas that has also passed through the anode without being used for power generation. Further, the reforming unit 40 is disposed above the combustion unit 46.

  The fuel cell system 100 according to the present embodiment includes a temperature detection unit 32 that detects the temperature of a predetermined region of the reforming unit 40, and a temperature detection unit 34 that detects the temperature of a predetermined region of the combustion unit 46. In addition. Regardless of the contact method or the non-contact method, the temperature detection unit 32 may be any device that can directly or indirectly detect information correlated with the temperature of the reforming unit. Moreover, the temperature detection part 34 should just be able to detect the information correlated with the temperature of a combustion part directly or indirectly irrespective of a contact system and a non-contact system. Specifically, for example, a thermocouple or a radiation thermometer can be used. Thus, the temperature detection unit 32 and the temperature detection unit 34 function as detection units that detect information correlated with whether or not the desorption of the raw fuel adsorbed on the steam reforming catalyst in the reforming unit 40 has converged. To do.

  As shown in FIG. 2, the cell stack 42 includes an anode 102 to which a hydrogen-containing gas is supplied, a cathode 104 to which an oxygen-containing gas is supplied, and an electrolyte 106 provided between the anode 102 and the cathode 104. Are connected in series and / or in parallel. Electricity generated by the cell stack 42 is output to the outside via the power conditioner 58.

[Startup mode]
Next, the operation of each part in the startup mode of the fuel cell system 100 according to the present embodiment will be described using a timing chart and a flowchart. FIG. 3 is a diagram showing changes in the air G1, the raw fuel gas G2, and the reformed water W1 supplied to each part in the startup mode. FIG. 4 is a diagram showing changes in the raw fuel gas desorbed from the reforming section in the start-up mode. FIG. 5 is a diagram illustrating a temperature change in a predetermined region of the reforming unit and the combustion unit in the startup mode. FIG. 6 is a diagram illustrating a change in the flow rate of the raw fuel gas that is actually input to the reforming unit and a change in the flow rate of the raw fuel gas in consideration of the raw fuel gas that is adsorbed and desorbed to the reforming unit. . FIG. 7 is a diagram illustrating changes in the air ratio (a value not considering desorption gas and a value considering desorption gas) in the startup mode.

  In the fuel cell system 100, the activation mode is executed by the control unit 18 when the apparatus is activated. Specifically, the control unit 18 controls the oxygen-containing gas supply unit 20 to start supplying the air G1 to the cathode of the cell 110 at time t1, as indicated by a line L1 in FIG. Next, as shown by a line L2 in FIG. 3, the control unit 18 controls the supply valve 22, the feed pump 30, and the like so as to start supplying the raw fuel gas G2 to the reforming unit 40 at time t2. Further, as shown by a line L3 in FIG. 3, the control unit 18 sets each unit so that the supply of the reforming water W1 is started at a time t5 when the steam reforming reaction in the reforming unit 40 is appropriately possible. Control.

  Here, when the raw fuel gas G <b> 2 starts to be supplied to the reforming unit 40, the raw fuel gas is adsorbed on the steam reforming catalyst of the reforming unit 40. Therefore, for a while after the supply of the raw fuel gas G2 to the reforming unit 40 is started, the raw fuel gas G2 coming out of the reforming unit 40 becomes zero or much less than the amount of the supplied raw fuel gas. . When the adsorption of the raw fuel gas G2 to the catalyst of the reforming unit 40 approaches saturation, the raw fuel gas G2 is supplied to the combustion unit 46. Thereafter, combustion of off-gas in the combustion section 46 starts slightly before time t3, and the temperature in a predetermined region of the combustion section 46 begins to rise (see line L4 in FIG. 5). As the temperature of the combustion section 46 rises, the temperature of the reforming section 40 also rises, so that the raw fuel gas G2 once adsorbed to the catalyst of the reforming section 40 begins to desorb, and the amount gradually increases (in FIG. 4). Before and after time t3).

  For a while from time t3, the amount of raw fuel gas (line L5 in FIG. 6) is equal to the amount of raw fuel gas supplied to the reforming unit 40 (line L6 in FIG. 6) until then. The amount obtained by desorbing the raw fuel gas adsorbed on the catalyst (line L7 in FIG. 6) is added. Therefore, if the amount of the raw fuel gas supplied to the reforming unit 40 remains the same as before, the raw fuel gas used for combustion in the combustion unit 46 becomes excessive. As a result, the temperature at the tip of the cell 110 in the lower part of the combustion part 46 may exceed the desired range and become a high temperature, which causes a deterioration of the cell.

  Therefore, in the present embodiment, suppression of deterioration of the fuel cell is realized by appropriately controlling the supply amounts of the raw fuel gas G2 and the air G1 in the startup mode.

  Specifically, as shown in FIG. 3, the control unit 18 decreases the supply amount of the raw fuel gas G2 and increases the supply amount of the air G1 at time t3. Thereafter, the supply amount of air G1 is decreased again at time t4. Further, as shown in FIG. 7, the supply amounts of the raw fuel gas G2 and the air G1 are controlled so that the air ratio does not fall below a predetermined threshold. The predetermined threshold value may be a value of an air ratio that does not misfire in the combustion unit 46 (for example, an arbitrary value of 1.3 or more). Thereby, misfire can be suppressed in each period from the start of the fuel cell system 100 to the time t5. 7 is a theoretical air ratio calculated from the amount of air G1 supplied to the combustion section and the amount of raw fuel gas G2 supplied to the reforming section 40, and the line L9 is This is the actual air ratio in consideration of the raw fuel gas desorbed from the reforming unit 40. Hereinafter, the air ratio indicated by the line L9 will be described as an example.

  As described above, the control unit 18 of the fuel cell system 100 according to the present embodiment allows the raw fuel gas adsorbed to the steam reforming catalyst of the reforming unit 40 to desorb (period A: FIGS. 3, 4, 7), when the raw fuel is being desorbed (period B: the same as above), the detection unit detects information correlated with the state where the desorption of the raw fuel has converged, and then supplies reformed water to the reforming unit In each period of time until the start of the operation (period C: the same as above), the oxygen amount actually supplied with respect to the oxygen amount theoretically necessary for completely burning the raw fuel gas supplied to the combustion section 46 The amount of air G1 supplied from the oxygen-containing gas supply unit 20 is controlled within a range where the ratio (air ratio) does not fall below a predetermined threshold. Thereby, even if the supply amount of the raw fuel gas to the combustion unit 46 fluctuates before and after the desorption of the raw fuel gas adsorbed on the steam reforming catalyst, an appropriate amount of air can be supplied.

  In addition, the control unit 18 controls the supply amount of the oxygen-containing gas in the oxygen-containing gas supply unit 20 so that the air ratio in the period B is higher than the air ratio in the period A and the period C. The period B is a timing at which combustion by the combustion unit 46 is performed. If the supply amount of the raw fuel gas does not change even in the period B in which the raw fuel gas is desorbed, the temperature at the tip of the cell 110 is excessive. May become hot. Therefore, in the present embodiment, the air ratio is increased by increasing the supply amount of the air G1 in the period B. Thereby, since the air which is not used for combustion increases, the cell 110 front-end | tip can be cooled with the air. In the present embodiment, the supply amount of the raw fuel gas G2 is reduced at time t3.

  As described above, the control unit 18 controls each unit so that the air ratio in the period B is higher than the air ratio in the period A and the period C, so that the raw fuel gas adsorbed on the steam reforming catalyst is desorbed. The amount of air supply can be increased at the stage where Therefore, the temperature rise of the combustion unit 46 in the period B is suppressed, and consequently, an excessive temperature rise near the tip of the cell stack 42 is also suppressed. Therefore, it is possible to suppress the deterioration of the cell 110 when the fuel cell system 100 is activated.

  Thereafter, when information correlating with the state in which the desorption of the raw fuel gas has converged is detected, the control unit 18 sets the flow rate F1 of air supplied to the cathode to the cathode at time t4 shown in FIG. The oxygen-containing gas supply unit 20 is controlled so as to have a value lower than the flow rate F2 of the air supplied to the air. As a result, it is possible to prevent excessive oxygen from being supplied after the desorption of the raw fuel gas from the steam reforming catalyst has converged.

  Here, the information correlated with the state where the desorption of the raw fuel gas has converged includes, for example, the case where the temperature of the predetermined region of the reforming unit 40 has reached the predetermined temperature Tr. The outlet temperature of the reforming unit 40 gradually increases with the start of combustion in the combustion unit 46. At that time, desorption of the raw fuel gas in the reforming unit 40 is also progressing. That is, by measuring the outlet temperature of the reforming unit 40 with the temperature detecting unit 32, it is possible to estimate how much the raw fuel gas is desorbed. Therefore, it is possible to estimate whether or not the desorption of the raw fuel gas has converged by obtaining the relationship between the temperature of the reforming unit 40 and the progress of the desorption of the raw fuel gas in advance. The progress of desorption of the raw fuel gas is not an increase or decrease of the desorption amount per unit time, but the desorption of the raw fuel gas desorbed from the catalyst with respect to the total raw fuel gas adsorbed on the catalyst. It can be regarded as an index indicating how much the amount has been accumulated.

  Note that the state in which the desorption of the raw fuel gas has converged is, for example, a case where the desorption of the raw fuel gas is not completely generated or a result of the balance between the adsorption and desorption of the raw fuel gas, This includes cases where it appears to be zero. In addition, a state where the amount of desorption of the raw fuel gas has peaked out and has become less than X% of the peak is also included. Here, X% may be appropriately selected within a range of 60% or less, preferably 50% or less, and more preferably 30% or less.

  When the temperature detection unit 32 detects that the temperature Tr of the reforming unit 40 has reached 70 degrees (line L10 in FIG. 5), the control unit 18 according to the present embodiment desorbs the raw fuel gas. Since it is estimated that the air has converged, the oxygen-containing gas supply unit 20 is controlled so that the supply amount of the air G1 once increased is reduced again at time t4. Thus, the control unit 18 can determine the timing for changing the air supply amount in the start-up mode with a simple configuration such as the temperature detection unit 32. The temperature Tr may be set in the range of 40 to 100 ° C. Further, the temperature Tr may be set in a range of 50 to 90 ° C. Moreover, the temperature Tr may be set in the range of 60-80 degreeC.

  When the supply amount of the air G1 decreases, the reforming water W1 is supplied to the sufficiently heated reforming unit 40 via the reforming water supply path 13 and the fuel supply path 14 at time t5 shown in FIG. Thus, the control unit 18 executes the start-up mode in a state where the steam (reformed water W1) is not supplied to the reforming unit 40.

  The fuel cell system 100 includes a temperature detection unit 34 that detects the temperature Tb of a predetermined region of the combustion unit 46 as information correlated with whether or not the desorption of the raw fuel gas has converged. When the amount of change per unit time of the temperature Tb of the combustion unit 46 detected by the temperature detection unit 34 is below a predetermined value, that is, when the temperature of the combustion unit 46 is stabilized, the control unit 18 increases the temperature once. Then, the oxygen-containing gas supply unit 20 is controlled so as to reduce the supply amount of the air G1 again. Thus, the control unit 18 can determine the timing for changing the air supply amount in the start-up mode with a simple configuration such as the temperature detection unit 34. The temperature Tb is, for example, a value in the range of 400 ° C to 900 ° C.

  As a modified example, the control unit 18 changes the temperature Tb of the combustion unit 46 detected by the temperature detection unit 34 per unit time, and then the temperature Tb becomes equal to or lower than a predetermined temperature Tb1. The oxygen-containing gas supply unit 20 may be controlled so as to reduce the supply amount of the air G1 once increased. Thereby, the supply amount of air can be changed at an appropriate temperature after the temperature of the combustion section 46 has peaked out. That is, it is possible to suppress malfunctions such as changing the air supply amount at the timing when the temperature of the combustion unit 46 continues to rise.

  As another modification, the control unit 18 changes the temperature Tb of the combustion unit 46 per unit time detected by the temperature detection unit 34 to minus at the temperature Tb0, and then the temperature Tb is changed from the temperature Tb0 to a predetermined value. The oxygen-containing gas supply unit 20 may be controlled so that the supply amount of the air G1 once increased is reduced again when the temperature becomes lower than the temperature Tb1 ′. Thereby, even if the maximum temperature of the combustion unit 46 in the start-up mode varies due to individual differences in the system, the supply amount of the air G1 can be changed at an appropriate timing according to the individual.

  FIG. 8 is a flowchart showing a start mode according to the present embodiment. When the start-up mode is started (S10), supply of air G1 to the cathode and supply of raw fuel gas G2 to the anode are started (S12, S14). Thereafter, the raw fuel gas G2 and air G1 are combusted in the combustion section 46 provided above the cell stack, and the reforming section 40 is heated using the combustion heat (S16). Immediately thereafter, control is performed to increase the air ratio by increasing the supply amount of the air G1 to the cathode and reducing the supply amount of the raw fuel gas G2 to the reforming unit 40 (S18).

  Thereafter, the temperature Tr of the reforming unit 40 is detected by the temperature detection unit 32 (S20), and it is determined whether or not the temperature Tr is 70 ° C. or higher (S22). When the temperature Tr is less than 70 ° C. (No in S22), the process returns to step S20. On the other hand, when the temperature Tr is 70 ° C. or higher (Yes in S22), the air ratio is controlled by reducing the supply amount of the air G1 to the cathode (S24), and the start-up mode ends. Thereafter, the reforming water W1 is supplied to the reforming unit 40 at a predetermined timing, and power is generated in the cell stack 42 using hydrogen generated by steam reforming.

  As described above, the present invention has been described with reference to each of the above-described embodiments, but the present invention is not limited to the above-described embodiments, and those in which the configurations of the embodiments are appropriately combined or replaced. Are also included in the present invention. In addition, it is possible to appropriately change the combination and processing order in the embodiment based on the knowledge of those skilled in the art and to add various modifications such as various design changes to the embodiment. The described embodiments can also be included in the scope of the present invention.

  F1 flow rate, G1 air, W1 reformed water, F2 flow rate, G2 raw fuel gas, G3 exhaust gas, 10 fuel cell module, 12 oxygen-containing gas supply route, 13 reformed water supply route, 14 fuel supply route, 15 exhaust gas route, 16 Hydrogen-containing reformed gas supply path, 18 control section, 20 oxygen-containing gas supply section, 32, 34 temperature detection section, 40 reforming section, 42 cell stack, 44 cathode gas path, 46 combustion section, 100 fuel cell system, 102 anode, 104 cathode, 106 electrolyte, 110 cell.

Claims (11)

A cell stack in which a plurality of cells having an anode supplied with a hydrogen-containing reformed gas, a cathode supplied with an oxygen-containing gas, and an electrolyte provided between the anode and the cathode,
A reforming section having a steam reforming catalyst for generating hydrogen-containing reformed gas to be supplied to the anode of the cell stack using raw fuel and steam;
A hydrogen-containing reformed gas supply path for supplying the hydrogen-containing reformed gas from the reforming section to the anode;
An oxygen-containing gas supply path for supplying an oxygen-containing gas to the cathode;
A fuel supply path for supplying raw fuel and reformed water to the reforming section;
An off-gas that is provided above the cell stack and burns oxygen-containing gas that has passed through the cathode without being used for power generation and hydrogen-containing reformed gas or raw fuel that has passed through the anode without being used for power generation. A combustion section;
An adjustment unit capable of adjusting the amount of oxygen-containing gas supplied to the cathode;
A detection unit for detecting information correlated with whether or not the desorption of the raw fuel adsorbed on the steam reforming catalyst has converged in the reforming unit;
A control unit for controlling the supply amount of the oxygen-containing gas in the adjustment unit,
The reforming unit is disposed above the off-gas combustion unit,
The controller is
There is a correlation with the state in which the desorption of the raw fuel is converged in the detection unit before the raw fuel adsorbed on the steam reforming catalyst is desorbed (period A), during the desorption of the raw fuel (period B). In each period between the detection of information and the start of supply of the reforming water to the reforming unit (period C),
The ratio of the actually supplied oxygen amount (the air ratio) to the oxygen amount theoretically necessary for complete combustion of the raw fuel supplied to the off-gas combustion unit is within a range that does not fall below a predetermined threshold value, and A fuel cell system that executes a start-up mode that controls the supply amount of the oxygen-containing gas in the adjustment unit so that the air ratio in the period B is higher than the air ratio in the period A and the period C. .   The fuel cell system according to claim 1, wherein the predetermined threshold is an air ratio that does not cause misfire in the off-gas combustion unit.   When the information correlated with the state in which the desorption of the raw fuel has converged is detected, the control unit sets the flow rate F1 of the oxygen-containing gas supplied to the cathode to the oxygen-containing gas supplied to the cathode so far. 3. The fuel cell system according to claim 1, wherein the adjustment unit is controlled to have a value lower than a gas flow rate F <b> 2. 4.   2. The fuel cell system according to claim 1, wherein the control unit executes the start-up mode in a state where steam is not supplied to the reforming unit.   The fuel cell system according to any one of claims 1 to 3, wherein the fuel supply path supplies a raw fuel containing a hydrocarbon having 2 or more carbon atoms or an alcohol. The detection unit detects information correlated with the temperature of the reforming unit as information correlated with whether or not the desorption of raw fuel has converged,
The control unit, when the temperature of the reforming unit detected by the detection unit reaches a predetermined temperature Tr, changes the supply amount of the oxygen-containing gas in the adjustment unit. The fuel cell system according to any one of 5.   The fuel cell system according to claim 6, wherein the temperature Tr is set in a range of 40 to 100 ° C. The detection unit detects information correlated with the temperature of the off-gas combustion unit as information correlated with whether or not the desorption of raw fuel has converged,
The control unit changes the supply amount of the oxygen-containing gas in the adjustment unit when the change amount per unit time of the temperature Tb of the off-gas combustion unit detected by the detection unit becomes a predetermined value or less. The fuel cell system according to any one of claims 1 to 5, wherein:   When the temperature Tb becomes a predetermined temperature Tb1 or less after the amount of change per unit time of the temperature Tb of the off-gas combustion unit detected by the detection unit has turned negative, the control unit The fuel cell system according to claim 8, wherein the supply amount of the oxygen-containing gas is changed.   After the amount of change per unit time of the temperature Tb of the off-gas combustion unit detected by the detection unit turns negative at the temperature Tb0, the control unit detects that the temperature Tb is lower than the temperature Tb0 by a predetermined temperature Tb1 ′. 9. The fuel cell system according to claim 8, wherein the supply amount of the oxygen-containing gas in the adjustment unit is changed in the following cases. In a control method of a fuel cell system comprising a cell stack in which a plurality of cells each having an anode, a cathode, and an electrolyte provided between the anode and the cathode are stacked,
Starting a fuel cell system and then starting supplying oxygen-containing gas to the cathode and supplying raw fuel or hydrogen-containing reformed gas to the anode;
A step of combusting the raw fuel or the hydrogen-containing reformed gas and the oxygen-containing gas in an off-gas combustion section provided above the cell stack;
Heating the reforming section having a steam reforming catalyst using the combustion heat of the off-gas combustion section;
Detecting information correlated with whether or not the desorption of the raw fuel adsorbed on the steam reforming catalyst has converged in the reforming unit;
After detecting the information, starting production of a hydrogen-containing reformed gas by a reforming reaction of the raw fuel using the catalyst,
Before the raw fuel adsorbed on the steam reforming catalyst is desorbed (period A), information correlated with the state in which the desorption of the raw fuel is converged is detected while the raw fuel is desorbing (period B). In each period from the start to the start of supply of reforming water to the reforming section (period C),
The ratio of the actually supplied oxygen amount (the air ratio) to the oxygen amount theoretically necessary to completely burn the raw fuel supplied to the off-gas combustion unit is within a range that does not fall below a predetermined threshold, and the period A control method for a fuel cell system, wherein the supply amount of the oxygen-containing gas is controlled so that the air ratio in B is higher than the air ratio in the period A and the period C.

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