JP2006024478A - Operating method for fuel cell power generating system and fuel cell power generating system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an operating method for a fuel cell power generating system and the fuel cell power generating system not damaging a fuel cell even during low load operation while maintaining high generation efficiency. <P>SOLUTION: Provided with a utilization ratio lowering process lowering a utilization ratio of the fuel 42 in power generation only by a second prescribed time T2 shorter than a first prescribed time T1 when a low load operation continuation time a fuel cell 6 generating power by introducing a fuel 42 consisting essentially of hydrogen into a fuel electrode and introducing an oxidizing agent 32 into an oxidant electrode reaches the first prescribed time T1, the operating method for the fuel cell power generating system not damaging the fuel cell during the low load operation and the fuel cell power generating system can be provided. For example, the utilization ratio lowering process is at least a process selected from among a group comprising a hydrocarbon-type-fuel supply quantity variation process, a reforming temperature variation process, and a power generation load variation process. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a fuel cell operation method and a fuel cell power generation system, and more particularly to a fuel cell operation method and a fuel cell power generation system that do not damage the fuel cell even during low load operation.

  Conventionally, for example, a polymer electrolyte fuel cell has a low operating temperature of 100 ° C. or less, so that the start-up time can be shortened and the handling is easy, so that it is widely used for automobiles and households (cogeneration and cogeneration). Demand is expected. A polymer electrolyte fuel cell introduces a fuel such as hydrogen or methanol to the fuel electrode side sandwiched between solid polymer membranes, and an oxidant gas such as air or oxygen to the other oxidant electrode side. Is introduced to generate an electromotive force between the solid polymer films, and an electric power is generated by taking out electrons to an external circuit. At that time, heat is generated. A set of fuel electrode-solid polymer film-oxidant electrode is called a cell, and a stack of a plurality of cells is called a stack.

In a polymer electrolyte fuel cell cogeneration system that includes a polymer electrolyte fuel cell, the power output is extracted from the fuel cell stack and the exhaust heat from the fuel cell stack is recovered and used as the heat output. To do. The cogeneration system has a total thermal efficiency of about 80 to 90% (LHV), for example, combined with power output and heat output, and can provide high energy savings, reduce energy costs, and reduce CO ₂ emissions. It is expected as a distributed power source that can greatly contribute to environmental aspects such as suppression.

  On the other hand, for example, a small polymer electrolyte fuel cell cogeneration system with an output of about 0.5 to 2 kW assumes a general home as a market, but the power demand in a general home varies greatly depending on time zones. At the present time, no reverse power flow to the grid has been observed. For this reason, for example, in a time zone where the power demand at home is low, the fuel cell is often operated at a partial load and a low load (for example, 30% to 50% output) instead of the rated output of the fuel cell.

  In such partial load and low load operation of the fuel cell, for example, since the flow rate of fluid (for example, fuel gas, air) flowing through the fuel cell is small, it is generated in the fuel cell when the low load operation continues for a certain time or more. -The accumulated moisture (liquid) could not be discharged. At this time, if there is an excessive amount of water in the flow path for supplying fluid, liquid phase water is generated, and local flooding (flow path blockage due to moisture) occurs, and the electrode reaction area in the surrounding area. As a result, the reaction gas (hydrogen, oxygen) becomes insufficient, and battery performance, cell voltage, and the like may decrease.

  As measures to prevent this flooding, for example, when a drop in cell voltage is detected, the fuel utilization rate is lowered, the pressure loss of the fluid is increased, the condensed water is blown off, and the water is not stagnated in the fluid. There was a way.

  However, for example, when cell voltage decreases due to flooding on the air electrode side, it is effective to detect a decrease in cell voltage and increase the air flow rate to discharge moisture to the outside of the cell. At the time when the voltage dropped, the oxidant electrode catalyst was already permanently damaged.

  Accordingly, an object of the present invention is to provide a method of operating a fuel cell power generation system and a fuel cell power generation system that do not damage the fuel cell even during low load operation while maintaining high power generation efficiency.

  In order to achieve the above object, a method for operating a fuel cell power generation system according to the first aspect of the present invention includes, as shown in FIGS. 1 and 3, for example, introducing a fuel 42 mainly composed of hydrogen into a fuel electrode, When the low load operation continuation time of the fuel cell 6 that generates power by introducing the oxidizer 32 into the oxidizer electrode reaches the first predetermined time T1, the utilization rate of the fuel 42 in power generation is set to the first predetermined time. And a utilization rate lowering step S114 for lowering for a second predetermined time T2 shorter than T1.

  When configured in this manner, when the low load operation duration time of the fuel cell reaches the first predetermined time, the fuel utilization rate in power generation is reduced by a second predetermined time shorter than the first predetermined time, To increase the fuel flow rate in the fuel cell and discharge condensed water, and to provide a method for operating the fuel cell power generation system that does not damage the fuel cell even during low load operation while maintaining high power generation efficiency. it can.

  Further, as described in claim 2, in the operation method of the fuel cell power generation system according to claim 2, for example, as shown in FIG. 1, FIG. 3, FIG. 5, and FIG. And a reforming step (for example, S100 shown in FIG. 3) for supplying hydrocarbon material 40 to fuel 42 containing hydrogen as a main component. A hydrocarbon-based fuel supply amount changing step (for example, S114 shown in FIG. 3) for changing the supply amount of the hydrogen-based fuel 40, a reforming temperature changing step (for example, S214 shown in FIG. 5) for changing the reforming temperature, You may comprise so that it may be at least 1 process selected from the group which consists of the electric power generation load fluctuation | variation process (for example, S314 shown in FIG. 7) which fluctuates the electric power generation load of the fuel cell 6. FIG.

  With this configuration, the fuel utilization rate in the power generation is changed to the first by changing the supply amount of the hydrocarbon-based fuel to be supplied, changing the reforming temperature, or changing the power generation load of the fuel cell. It can be reduced for a second predetermined time shorter than the predetermined time, the fuel flow rate in the fuel cell can be increased, and condensed water can be discharged, so that the fuel cell can be maintained even during low load operation while maintaining high power generation efficiency. It is possible to provide a method of operating a fuel cell power generation system that does not cause damage.

  In order to achieve the above object, a fuel cell power generation system according to a third aspect of the present invention supplies a hydrocarbon fuel 40 and a reformer 41 to supply a hydrocarbon fuel 40 as shown in FIG. A fuel processing device 1 for reforming the fuel into a fuel 42 mainly composed of hydrogen; a fuel cell 6 for generating power by introducing the fuel 42 to the fuel electrode and introducing the oxidant 32 to the oxidant electrode; Utilization rate changing means for changing the utilization rate of the fuel 42 (for example, 7 or 27 or 28 shown in FIG. 1); the low load operation continuation time of the fuel cell 6 at a first predetermined time T1 (for example, see FIG. 2) When it reaches, the utilization rate changing means (for example, 7 or 27 or 28 shown in FIG. 1) is controlled, and the utilization rate of the fuel 42 in power generation is shorter than the first predetermined time T1 (for example, see FIG. 2). 2 for a predetermined time T2 (for example, see FIG. 2). Configured to include.

  With this configuration, when the low load operation duration time of the fuel cell reaches the first predetermined time, the control unit controls the utilization rate changing means to set the fuel utilization rate for power generation to the first predetermined time. Reduced by a second predetermined time shorter than the time, increases the fuel flow rate in the fuel cell, and discharges condensed water, thus maintaining high power generation efficiency and not damaging the fuel cell even during low load operation A fuel cell power generation system can be provided.

  Further, as described in claim 4, in the fuel cell power generation system described in claim 3, for example, as shown in FIG. 1, the utilization rate changing means supplies the hydrocarbon-based fuel 40 supplied to the fuel processing apparatus 1. A group consisting of a hydrocarbon-based fuel supply amount variation means 28 for varying the amount, a reforming temperature variation means 27 for varying the reforming temperature of the fuel processor 1, and a power generation load variation means 7 for varying the power generation load of the fuel cell 6. You may comprise so that it may be at least one means selected more.

  With this configuration, the supply amount of the hydrocarbon-based fuel 40 supplied to the fuel processing apparatus 1 is changed, the reforming temperature of the fuel processing apparatus 1 is changed, or the power generation load of the fuel cell 6 is changed. When the low load operation continuation time of the fuel cell reaches the first predetermined time, the fuel utilization rate in power generation is reduced by a second predetermined time shorter than the first predetermined time, and the fuel in the fuel cell is reduced. Since the flow rate can be increased and condensed water can be discharged, it is possible to provide a fuel cell power generation system that maintains high power generation efficiency and that does not damage the fuel cell even during low load operation.

  As described above, according to the present invention, the low-load operation continuation time of the fuel cell in which power is generated by introducing the fuel mainly composed of hydrogen into the fuel electrode and introducing the oxidant into the oxidant electrode is the first predetermined value. And a utilization rate lowering step of reducing the fuel utilization rate in power generation for a second predetermined time shorter than the first predetermined time when the time is reached, so that high power generation efficiency is maintained. On the other hand, it is possible to provide a method of operating the fuel cell power generation system that does not damage the fuel cell even during low load operation.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 to FIG. 7 are examples of embodiments for carrying out the invention. In the drawings, the same or similar reference numerals denote the same or equivalent parts, and duplicate descriptions are omitted. In the following description, unless otherwise specified, “connected” means that the two devices and the like are “connected”, including the case where they are directly connected and the case where they are connected via piping. A broken line represents an electric signal.

  FIG. 1 is a block diagram showing a schematic configuration of a fuel cell power generation system 101 according to the first embodiment of the present invention. The fuel cell power generation system 101 supplies a reforming raw material 40 as a hydrocarbon-based fuel and a process water 41 as a reforming agent, and uses the reforming raw material 40 as a fuel mainly composed of hydrogen. A solid polymer type fuel cell as a fuel cell for generating power by introducing the reforming gas 42 into the fuel electrode and introducing the stacking air 32 as the oxidant into the oxidant electrode. The fuel cell stack 6, the reforming material flow rate control valve 28 as a utilization rate changing means for changing the utilization rate of the reformed gas 42 in power generation, and the low-load operation duration time of the fuel cell stack 6 is a first predetermined value. When the low load flow rate standard time T1 (see FIG. 2) is reached, the reforming raw material flow rate control valve 28 is controlled, and the utilization rate of the reformed gas 42 in power generation is reduced to the low load flow rate standard time. A second predetermined time shorter than T1 (see FIG. 2) Of a control unit 4 to reduce only the low-load flow rate increase time T2 (see FIG. 2).

Here, the reforming raw material 40 as the hydrocarbon-based fuel is methane gas, which is a hydrocarbon-based gas in the present embodiment, but city gas, LPG (Liquid Petroleum Gas), digestion gas, methanol, GTL ( Gas to Liquid) or kerosene may be used. The reformed gas 42 as a fuel containing hydrogen as a main component is, for example, a gas having a hydrogen component of 40% or more, typically about 70 to 75% in terms of mol%. The low load operation is typically an operation at a load less than the rated load operation (partial load operation), and an operation at a load of 30% to 50% of the rated load operation. The utilization rate of the reformed gas 42 during power generation (hereinafter referred to as “fuel utilization rate” unless otherwise specified) is the ratio of the amount of fuel used for power generation out of the amount of fuel supplied to the fuel cell stack 6. Typically, it is defined by the following formula (1).
Fuel utilization rate (%) = Amount of fuel actually used for power generation / Amount of supplied fuel × 100 (1)

  The fuel processing apparatus 1 includes a reforming unit 18 having a reforming catalyst (not shown), a conversion unit 19 having a CO conversion catalyst (not shown), a selective oxidation unit 20 having a selective oxidation catalyst (not shown), It has a steam generation part 36 and a combustion part 10.

Further, the fuel cell power generation system 101 includes a desulfurizer 17, a reforming raw material blower 2, a process water pump 3, a recovered water tank 5, a humidified water pump 13, a stack air blower 15, and a humidifier. Appliance 16, first heat exchange unit 8, second heat exchange unit 9, third heat exchange unit 14,
A stack cooling water pump 12 and a steam / water separator 11 are provided.

  Furthermore, the fuel cell power generation system 101 includes pipes and flow paths connecting the above-described parts, that is, a raw material supply line 140, a combustion raw material supply line 130, a selective oxidation air supply line 134, and a process water supply line. 141, the steam supply line 141a, the stack air supply line 132, the reformed gas transfer line 142, the fuel electrode off-gas transfer line 143, the switching line 142a, the stack cooling water circulation line 160, and the combustion exhaust gas discharge line 150. And an oxidant electrode off-gas discharge line 133, a humidified water supply line 144, a heat recovery water circulation line 161, a drain water line 164, and a surplus water line 165.

  The reforming material blower 2 supplies the reforming material 40 to the reforming unit 18 via the material supply line 140 that connects the reforming material blower 2 and the reforming unit 18. A desulfurizer 17 and a reforming raw material flow rate control valve 28 are installed on the raw material supply line 140. In the present embodiment, the desulfurizer 17 is installed upstream of the reforming raw material flow rate control valve 28.

  The desulfurizer 17 is configured to desulfurize the reforming raw material 40 before the reforming raw material 40 is supplied to the reforming unit 18, and the desulfurized reforming raw material 40 is supplied to the reforming unit 18. Supplied.

  The reforming material flow rate control valve 28 is a two-way valve that controls the flow rate of the reforming material 40 supplied to the reforming unit 18 by a control signal i 28 from the control unit 4. The reforming material flow rate control valve 28 is configured to operate by a solenoid or a motor drive. When the reforming raw material flow control valve 28 is closed, the flow of fluid through the reforming raw material flow control valve 28 is interrupted. Therefore, in this case, the fluid in the reforming unit 18 does not leak through the reforming material flow rate control valve 28.

  The reforming raw material flow rate control valve 28 functions as a hydrocarbon-based fuel supply amount changing means for changing the supply amount of the reforming raw material 40 supplied to the fuel processing apparatus 1 and increases the supply amount of the reforming raw material 40. By doing so, the fuel utilization rate of the electric power generation in the fuel cell stack 6 mentioned later is reduced.

  Further, the raw material supply line 140 is connected with a combustion raw material supply line 130 that branches the raw material supply line 140 between the desulfurizer 17 and the reforming raw material flow rate control valve 28.

  The combustion raw material supply line 130 is configured to branch the flow of the reforming raw material 40. The other end of the combustion material supply line 130 opposite to the end connected to the material supply line 1 is connected to the combustion unit 10 via the combustion material flow rate control valve 27. The combustion raw material supply line 130 supplies the reforming raw material 40 as the combustion raw material 30 to the combustion unit 10, bypassing the reforming unit 18, the shift unit 19, the selective oxidation unit 20, and the like.

  The combustion material flow rate control valve 27 is a two-way valve that controls the flow rate of the combustion material 30 supplied to the combustion unit 10 by a control signal i 27 from the control unit 4. The combustion material flow rate control valve 27 is configured to operate by a solenoid or a motor. When the combustion raw material flow control valve 27 is closed, the flow of fluid through the combustion raw material flow control valve 27 is blocked. Therefore, in this case, the fluid in the combustion unit 10 does not leak through the combustion material flow rate control valve 27. In the present embodiment, the reforming material 40 and the combustion material 30 are gases.

  The combustion unit 10 is further connected to a combustion air supply line 131 that supplies combustion air 31, which is air containing oxygen consumed by combustion, to the combustion unit 10.

  The other end of the combustion air supply line 131 opposite to the end connected to the combustion unit 10 is connected to, for example, a combustion air blower (not shown). The combustion air supply line 131 supplies combustion air 31 supplied from a combustion air blower (not shown) to the combustion unit 10. Combustion air 31 is a reformed gas 42 that is produced by combustion of the raw material 30 for combustion in the combustion section 10 and reformed by the fuel processor, and the carbon monoxide gas in the gas is not sufficiently reduced. It is used for the combustion of the quality gas 42a or the combustion of the fuel electrode off-gas 43 described later.

  The combustion section 10 is supplied through a switching line 142a described later without being sufficiently reduced in carbon monoxide gas which is a reformed gas 42 reformed and generated by the combustion raw material 30 and the fuel processing device. The reformed gas 42a or the fuel electrode off-gas 43 of the fuel cell stack 6 to be described later is burned together with the combustion air 31, and the reforming section 18 is heated and used for the reforming reaction in the reforming section 18. It is configured to generate heat.

  Typically, the heat generated in the combustion unit 10 is also used to maintain each part of the fuel processor 1 at an appropriate temperature so that an efficient reaction is possible.

  Typically, the combustion unit 10 is configured to combust with the combustion air 31 using the reformed gas 42a in which the combustion raw material 30 or the carbon monoxide gas is not sufficiently reduced at the time of startup. Further, the combustion unit 10 is typically configured to burn with the combustion air 31 using the fuel electrode off-gas 43 as fuel during rated operation.

  The combustion exhaust gas 50 that is the exhaust gas after burning in the combustion unit 10 is discharged out of the system through a combustion exhaust gas discharge line 150 and the like to be described later.

In the reforming unit 18, a reforming reaction is performed in which the supplied reforming raw material 40 is reformed into a reformed gas 42 containing hydrogen as a main component. The reforming reaction is represented by the following formula (2) when the reforming raw material 40 is methane, for example.
CH ₄ + H ₂ O → CO + 3H ₂ (2)

  The reforming unit 18 includes a reforming catalyst (not shown). Any reforming catalyst (not shown) may be used as long as it promotes the reforming reaction. For example, a Ni-based reforming catalyst or a Ru-based reforming catalyst is used as the type of catalyst. The reforming unit 18 includes a temperature detection device 75 that detects the temperature of the reforming unit 18, and the detected temperature is transmitted to the control unit 4 as a temperature signal i 75.

  Since the reforming reaction represented by the formula (2) is an endothermic reaction, the higher the reaction temperature, the higher the reforming rate of the hydrocarbon and the faster the reaction rate. However, if the temperature is too high, the reforming catalyst (not shown) deteriorates, the requirement for the heat resistance specification of the reformer material becomes severe, and the thermal efficiency tends to decrease due to an increase in the dissipated heat of the fuel processing device 1. is there. Considering this point, the temperature of the reforming section 18 is preferably about 300 ° C. to 800 ° C., more preferably about 650 ° C. to 750 ° C.

The shift conversion unit 19 is connected to the reforming unit 18, and a CO shift reaction for reducing carbon monoxide gas in the reformed gas 42 generated by the reforming unit 18 is performed. The CO shift reaction is represented by the following formula (3), for example.
CO + H ₂ O → CO ₂ + H ₂ (3)

  The shift unit 19 includes a CO shift catalyst (not shown). The CO conversion catalyst (not shown) may be anything as long as it promotes the CO conversion reaction. For example, a Fe-Cr high temperature conversion catalyst, a Pt medium high temperature CO conversion catalyst, or a Cu-Zn low temperature CO conversion catalyst. And Pt low temperature CO conversion catalyst.

  Since the CO shift reaction shown in the formula (3) is an exothermic reaction, if the reaction temperature is lowered, there is an advantage that the CO concentration after the CO shift reaction is lowered, and a disadvantage is that the reaction rate is lowered. is there. Considering this point, the temperature of the shift part 19 during the CO shift reaction is preferably 180 ° C. to 500 ° C., more preferably about 200 ° C. to 350 ° C.

The selective oxidation unit 20 is connected to the shift unit 19, and a selective oxidation reaction of the carbon monoxide gas remaining in the reformed gas 42 subjected to the CO shift reaction is performed. The selective oxidation reaction is represented, for example, by the following formula (4).
CO + (1/2) O ₂ → CO ₂ (4)

  The selective oxidation unit 20 includes a selective oxidation catalyst (not shown). The selective oxidation catalyst is not particularly limited as long as it promotes a selective oxidation reaction, that is, has a high selective oxidation property with respect to CO, such as a Pt-based selective oxidation catalyst, a Ru-based selective oxidation catalyst, and a Pt-Ru-based selective oxidation catalyst There is. A selective oxidation air supply line 134 is connected to the selective oxidation unit 20, and the selective oxidation air supply line 134 selectively oxidizes the selective oxidation air 34 supplied from a selective oxidation air blower (not shown). To the unit 20.

  The temperature of the selective oxidation unit 20 at the time of the selective oxidation reaction represented by the formula (4) is preferably 80 ° C. to 250 ° C., more preferably about 120 ° C. to 200 ° C.

  The process water supply line 141 connects the recovered water tank 5 and the water vapor generating unit 36. On the process water supply line 141, the process water pump 3, the two-way valve 38, and the like are sequentially arranged from the recovered water tank 5 side. Is installed.

  The process water pump 3 supplies the recovered water in the recovered water tank 5 described later as process water 41 to the steam generation unit 36 via the process water supply line 141.

  The two-way valve 38 is set to open or closed by an open / close signal (not shown) from the control unit 4. When the two-way valve 38 is opened, the process water 41 can be supplied to the water vapor generation unit 36. The two-way valve 38 is configured to operate by solenoid or motor drive. When the two-way valve 38 is closed, the fluid flow through the two-way valve 38 is blocked. Therefore, in this case, the fluid in the water vapor generation part 36 does not leak through the two-way valve 38.

  In the water vapor generation part 36, the process water 41 is evaporated by the combustion heat of the combustion part 10 or the reaction heat of the shift part 19 and the selective oxidation part 20 to generate water vapor 41a. The steam generation unit 36 is connected to the reforming unit 18 via a steam supply line 141a.

  The steam supply line 141 a supplies the steam 41 a generated by the steam generating unit 36 to the reforming unit 18. The steam 41 a is used in the reforming reaction of the reforming raw material 40 in the reforming unit 18.

  The reformed gas transport line 142 connects the selective oxidation unit 20 of the fuel processing apparatus 1 and the fuel electrode side of the fuel cell stack 6, and transports the reformed gas 42 from the selective oxidation unit 20 to the fuel electrode side. A three-way switching valve 21 is installed on the reformed gas transfer line 142.

  One end of a switching line 142a is connected to the three-way switching valve 21, and the other end of the switching line 142a is connected to a fuel electrode off-gas transfer line 143 to be described later. A switching signal (not shown) for switching the three-way switching valve 21 is sent from the control unit 4 to the three-way switching valve 21. The three-way switching valve 21 is configured to operate by solenoid or motor drive.

  When the three-way switching valve 21 is set to the a side by a switching signal (not shown), the reformed gas 42 is supplied from the selective oxidation unit 20 to the reformed gas transport line 142, the three-way switch valve 21, the reformed gas transport line. 142 is conveyed to the fuel electrode side. On the other hand, when the three-way switching valve 21 is set to the b side by a switching signal (not shown), the reformed gas 42 is sent from the selective oxidation unit 20 to the reformed gas transfer line 142, the three-way switching valve 21, the switching line 142a, It is conveyed to the combustion unit 10 through the fuel electrode off-gas conveyance line 143.

  The fuel cell stack 6 includes a fuel electrode and an oxidant electrode, and has a multiple structure in which solid polymer films (not shown) and separators (not shown) are alternately stacked (hereinafter, unless otherwise specified) -A set of solid polymer film-oxidant electrode is referred to as "cell", and a stack of a plurality of cells is referred to as "stack"). The reformed gas 42 is supplied to the fuel electrode side, and the oxidant electrode The stack air 32 is supplied to the side, and electric power is generated by an electrochemical reaction. From the fuel electrode side, the fuel electrode off-gas 43 (reformed gas remaining) is supplied to the fuel electrode off-gas transport line 143 and from the oxidant electrode side. The oxidant electrode off-gas 33 is discharged to the oxidant electrode off-gas discharge line 133 respectively.

The electrochemical reactions at the fuel electrode and the oxidant electrode of the fuel cell stack 6 can typically be expressed by the following equations (5) and (6), respectively.
Fuel electrode: H ₂ → 2H ++ 2e− (5)
Oxidant electrode: 2H ++ 2e − + (1/2) O ₂ → H ₂ O (6)

  As shown in the equation (6), when the fuel cell stack 6 is in operation, water is generated at the oxidizer electrode. A part of this water is back-diffused from the oxidizer electrode to the fuel electrode and is also discharged from the fuel electrode. That is, the fuel electrode off-gas 43 and the oxidant electrode off-gas 33 each contain moisture.

  The fuel electrode off gas transfer line 143 connects the fuel electrode side of the fuel cell stack 6 and the combustion unit 10, and supplies the fuel electrode off gas 43 from the fuel electrode to the combustion unit 10. As described above, the fuel electrode off-gas 43 is typically used in the combustion section 10 during rated operation. A two-way valve 23 is installed on the fuel electrode off-gas transfer line 143.

  The two-way valve 23 is set to open or closed by an open / close signal (not shown) from the control unit 4. The two-way valve 23 is configured to operate by solenoid or motor drive. When the two-way valve 23 is opened, the fuel electrode off-gas 43 can flow from the fuel electrode side through the two-way valve 23 to the combustion unit 10. When the two-way valve 23 is closed, the fluid flow through the two-way valve 23 is blocked. Therefore, in this case, the fluid does not flow to the fuel electrode side through the two-way valve 23, and the fluid on the fuel electrode side does not leak through the two-way valve 23.

  When the three-way switching valve 21 is set to the a side and the reformed gas 42 is supplied from the selective oxidation unit 20 to the fuel electrode side for power generation of the fuel cell stack 6, the two-way valve 23 is set to open. Thus, the fuel electrode off-gas 43 can be transported from the fuel electrode side to the combustion unit 10 through the fuel electrode off-gas transport line 143. When the three-way switching valve 21 is set to the b side, the two-way valve 23 is set to be closed, and the reformed gas 42 that has reached the fuel electrode off-gas transfer line 143 does not flow back to the fuel electrode side.

  The oxidant electrode of the fuel cell stack 6 is connected to the stack air blower 15 via the stack air supply line 132.

  The stack air blower 15 supplies the stack air 32 as the oxidant gas to the oxidant electrode side via the stack air supply line 132.

  On the stack air supply line 132, the humidifier 16 is installed between the oxidant electrode of the fuel cell stack 6 and the stack air blower 15.

  The humidifier 16 is connected to the recovered water tank 5 via the humidified water supply line 144. On the humidified water supply line 144, a humidified water pump 13 and a third heat exchanging section 14 to be described later are installed in order from the recovered water tank 5 side.

  The humidifier 16 is supplied with the humidified water 44 through the humidified water supply line 144 through the humidified water pump 13 and the third heat exchanging unit 14 described later in order, and the humidifier 16 is supplied with the humidified water 44 supplied thereto. Is used to humidify the stacking air 32. That is, the water stored in the recovered water tank 5 is used as the humidified water 44. The humidifier 16 is connected to a surplus water line 165 that delivers surplus water 65.

  The surplus water line 165 connects the bottom of the humidifier 16 and the ceiling of the recovered water tank 5, and the surplus water 65 that has not been used in the humidifier 16 out of the humidified water 44 supplied to the humidifier 16 is humidified. The excess water 65 is allowed to flow from 16 to the recovered water tank 5 and is recovered in the recovered water tank 5 as recovered water.

  The combustion exhaust gas discharge line 150 is connected to the combustion unit 10 and discharges the combustion exhaust gas 50 generated in the combustion unit 10 out of the system. The oxidant electrode off gas discharge line 133 described above discharges the oxidant electrode off gas 33 generated on the oxidant electrode side.

  The oxidant electrode off-gas discharge line 133 is connected to the combustion exhaust gas discharge line 150, and the oxidant electrode off-gas 33 that has passed through the oxidant electrode off-gas discharge line 133 is further discharged through the combustion exhaust gas discharge line 150. A check valve 25 is installed on the oxidant electrode off-gas discharge line 133. The check valve 25 allows the oxidant electrode off gas 33 to flow from the oxidant electrode side toward the combustion exhaust gas discharge line 150, and fluids such as the oxidant electrode off gas 33 and the combustion exhaust gas 50 move toward the oxidant electrode side. To block backflow.

  Further, on the combustion exhaust gas discharge line 150, the third heat exchange unit 14, the first heat exchange unit 8, and the steam / water separator 11 are arranged in this order on the downstream side of the connection portion of the oxidant electrode off-gas discharge line 133. It is installed at.

  A combustion exhaust gas discharge line 150 and the above-described humidified water supply line 144 are connected to the third heat exchanging unit 14, and the combustion exhaust gas 50, the oxidant electrode off-gas 33 (high temperature side) and the humidified water 44 (low temperature side) are connected. Heat exchange takes place between them. By the heat exchange, the combustion exhaust gas 50 and the oxidant electrode off-gas 33 are cooled and the temperature is lowered, and the humidified water 44 is heated and the temperature is raised.

  The first heat exchange unit 8 is disposed downstream of the third heat exchange unit 14. A combustion exhaust gas discharge line 150 and a heat recovery water circulation line 161 described later are connected to the first heat exchange unit 8 and circulates in the combustion exhaust gas 50, the oxidant electrode off-gas 33 (high temperature side), and the heat recovery water circulation line 161. Heat exchange is performed with the heat recovery water 61 (low temperature side). By the heat exchange, the combustion exhaust gas 50 and the oxidant electrode off-gas 33 are cooled and the temperature is lowered, and the heat recovery water 61 is heated and the temperature is raised.

  The steam separator 11 is installed on the combustion exhaust gas discharge line 150 on the downstream side of the first heat exchange unit 8. The steam separator 11 separates the combustion exhaust gas 50 and the oxidant electrode off-gas 33 from the condensed water contained in the combustion exhaust gas 50 and the oxidant electrode off-gas 33. The remaining combustion exhaust gas 50 and the oxidant electrode off-gas 33 from which moisture has been recovered by the steam separator 11 are exhausted out of the system. A drain water line 164 is connected to the bottom of the steam separator 11.

  The drain water line 164 connects the bottom of the steam / water separator 11 and the ceiling of the recovered water tank 5, and collects drain water 64 that is water collected by the steam / water separator 11 from the steam / water separator 11. Pour into water tank 5. The drain water 64 is stored in the recovered water tank 5 as the aforementioned recovered water.

  The heat recovery water circulation line 161 connects the heat recovery water 61 to the first heat exchange unit 8, the second heat exchange unit 9, the hot water tank 90, and a pump (not shown), and the heat recovery water 61 is connected to the first heat exchange unit 8. , A circulation flow path that circulates through the second heat exchange unit 9, the hot water storage tank 90, and a pump (not shown) in this order. On the warm heat recovery water circulation line 161, the second heat exchange unit 9 is disposed on the downstream side of the first heat exchange unit 8 and on the upstream side of the hot water storage tank 90.

  The hot water storage tank 90 temporarily stores the heat recovery water 61 circulating through the heat recovery water circulation line 161. The pump (not shown) raises the pressure in the heat recovery water circulation line 161 and circulates the heat recovery water 61 in the heat recovery water circulation line 161.

  A stack cooling water circulation line 160 and a hot heat recovery water circulation line 161 described below are connected to the second heat exchanging section 9, and between the stack cooling water 60 (high temperature side) and the heat recovery water 61 (low temperature side). Heat exchange takes place. By the heat exchange, the stack cooling water 60 is cooled and the temperature is lowered, and the hot heat recovery water 61 is heated and the temperature is raised.

  The stack cooling water circulation line 160 connects the stack cooling water pump 12, the second heat exchange unit 9, and the fuel cell stack 6, and the stack cooling water 60 is used as the stack cooling water pump 12, the second heat exchange unit 9, and the fuel cell. This is a circulation channel that circulates through the stack 6 in order.

  The stack cooling water pump 12 circulates the stack cooling water 60 through the stack cooling water circulation line 160. When the stack cooling water 60 is circulated through the stack cooling water circulation line 160 and introduced into the fuel cell stack 6, the stack cooling water 60 absorbs heat generated by the electrochemical reaction of the fuel cell stack 6 to cool the fuel cell stack 6. Then, as described above, heat exchange is performed with the heat recovery water 61 in the second heat exchange unit 9, and the temperature is lowered by cooling.

  The hot water tank 90 is connected to a device (not shown) that supplies heat to the heat demand outside the system by supplying or circulating the heat recovery water 61. For example, the hot heat recovery water 6 stored in the hot water tank 90 circulates outside the system and supplies exhaust heat, and then is returned to the hot water tank 90. That is, the exhaust heat recovered in the warm heat recovery water 61 is effectively used as a heat source. That is, the fuel cell power generation system 101 according to the embodiment of the present invention can also be used as a fuel cell power generation cogeneration system.

  The power conditioner 7 includes a DC / DC converter and a DC / AC inverter (not shown), adjusts the voltage of DC power (stack voltage) generated by the fuel cell stack 6, and further converts DC to AC. The power conditioner 7 receives the control signal i74 from the control unit 4 and outputs AC power having a power value required by the control signal i74.

  In the wiring connecting the fuel cell stack 6 and the power conditioner 7, a voltage detection device 68 for detecting the stack voltage, a current detection device 69 for detecting the stack current, and a relay 67 are installed. The voltage detection device 68 sends a voltage signal (not shown) representing the detected stack voltage to the control unit 4, and the current detection device 69 sends a current signal (not shown) representing the detected stack current to the control unit 4. The relay 67 is opened / closed by an open / close signal (not shown) sent from the control unit 4. When the relay 67 is closed, power is output from the fuel cell stack 6. When the relay 67 is opened, the fuel cell stack 6 is opened. Will not output power.

  Stack air blower 15, reforming raw material blower 2, selective oxidation air blower (not shown), combustion air blower (not shown), process water pump 3, humidified water pump 13, stack cooling water pump 12 Are driven by an electric motor (not shown) as a prime mover.

  The rotation speed of each electric motor is controlled by a control signal (not shown) from the control unit 4, and stack air 32, reforming raw material 40, selective oxidation air 34, combustion air 31, process water 41, humidification The flow rates of water 44 and stack cooling water 60 are controlled. Each electric motor stops when each control signal is not sent from the control unit 4.

  The control unit 4 includes a low-load flow rate standard time measurement timer C1 (see FIG. 3) and a low-load flow rate increase time T2 (see FIG. 2) for measuring a later-described low-load flow rate standard time T1 (see FIG. 2). A low load flow rate increase time measurement timer C2 (see FIG. 3) to be measured is included. The control unit 4 typically measures a high load time T3 (see FIG. 3), which is a duration of an operation that is not a low load operation (hereinafter referred to as “high load operation” unless otherwise specified). A time measurement timer C3 (see FIG. 3) is included.

  As will be described later with reference to FIG. 2, when the low load operation continuation time of the fuel cell stack 6 reaches the low load flow rate standard time T <b> 1 (see FIG. 2), the control unit 4 performs the reforming material flow rate control valve 28. By controlling the flow rate and increasing the supply amount of the reforming raw material 40, the fuel utilization rate of power generation in the fuel cell stack 6 is shorter than the low load flow rate standard time T1 (see FIG. 2), and the low load flow rate increase time is shorter. It is configured to decrease by T2 (see FIG. 2).

  A signal cable for transmitting control transmitted from the control unit 4 is wired to each unit in the control unit 4. Typically, the control unit 4 controls the opening and closing of the combustion raw material flow rate control valve 27 as described above to control the flow rate of the combustion unit 10 supplied to the combustion unit 10, and the reforming raw material flow rate. The control signal i28 for controlling the opening and closing of the control valve 28 and the flow rate of the reforming raw material 40 supplied to the reforming unit 18 and the power conditioner 7 are controlled, and the output of the electric power generated by the fuel cell stack 6 is controlled. Each of the control signals i74 is transmitted to control the combustion raw material flow rate control valve 27, the reforming raw material flow rate control valve 28, and the power conditioner 7.

Furthermore, the control unit 4 typically controls each unit by transmitting a control signal (not shown) to each unit in addition to the control signal described above, so that the start-up operation, steady operation, and partial load operation of the fuel cell power generation system 101 are performed. Also controls low load operation, stop operation, etc. As a result, the fuel cell power generation system 101 can have a more rational configuration, and the operation of the fuel cell power generation system 101 can be controlled quickly, reliably, and with no human error.
Hereinafter, the operation of the fuel cell power generation system 101 under the control of the control unit 4 will be described.

  Next, with reference to FIG. 1, the operation at the time of starting the fuel cell power generation system 101 according to the first embodiment of the present invention will be described. At the time of the previous stop operation, the three-way switching valve 21 is finally set to the position b, and the combustion raw material flow control valve 27, the reforming raw material flow control valve 28, and the two-way valves 23 and 38 are set to the closed positions. Therefore, immediately before activation, the three-way switching valve 21 is in the position b, and the combustion raw material flow control valve 27, the reforming raw material flow control valve 28, and the two-way valves 23 and 38 are in the closed position.

  First, the combustion air 31 is supplied to the combustion section 10 for purging a burner (not shown), the reforming material blower 2 is started, the combustion material flow rate control valve 27 is set to the open position, and the reforming material 40 is supplied as a raw material 30 for combustion. At this time, the reforming material flow rate control valve 28 is in the closed position and the combustion material flow rate control valve 27 is in the open position, and the flow rate control of the combustion material 30 is performed by the combustion material flow rate control valve 27. At this time, supply of the reforming raw material 40 to the reforming unit 18 is not performed.

  When the supply of the combustion air 31 and the combustion raw material 30 is started, the combustion exhaust gas 50 is discharged from the combustion section 10 when the burner is ignited and combustion in the combustion section 10 is started at the same time.

  Next, the reforming material flow rate control valve 28 is opened and the reforming material 40 is desulfurized by passing through the desulfurizer 17 and then supplied to the reforming unit 18. At the same time, the humidifying water pump 13 is activated to supply the humidifying water 44 to the humidifier 16. At this time, the stack air 32 is not supplied, and the humidified water 44 supplied to the humidifier 16 is sent to the recovered water tank 5 via the surplus water line 165 and circulates.

  When the humidifying water pump 13 is activated, the humidifying water 44 can be heated by the combustion exhaust gas 50 in the third heat exchanging section 14, and the temperature of the humidifying water 44 is sufficiently increased by the start of power generation, so that the stack air 32 The lack of humidification can be avoided.

  In the initial stage of start-up, the reforming reaction in the reforming unit 18 does not occur because the temperature of the reforming unit 18 has not reached a temperature suitable for the reforming reaction. The reforming material 40 passes through the reforming unit 18, the shift unit 19, and the selective oxidation unit 20, and is sent to the combustion unit 10 via the reformed gas transfer line 142, the switching line 142a, and the fuel electrode off-gas transfer line 143. The combustion of the reforming raw material 40 in the combustion unit 10 is started. Due to the combustion in the combustion unit 10, the temperatures of the reforming unit 18, the transformation unit 19, and the selective oxidation unit 20 rise.

  When the temperature of the reforming unit 18, the temperature of the transformation unit 19, and the temperature of the selective oxidation unit 20 all exceed 100 ° C., the process water pump 3 is started and the process water 41 is supplied to the steam generation unit 36. Steam 41a is supplied to the reforming unit 18. The flow rate of the process water 41 is determined based on a predetermined S (water vapor 41a) / C (carbon in reforming raw material) ratio (molar ratio).

  After a lapse of a predetermined time (for example, 10 minutes) after the supply of the process water 41 is started, the selective oxidation air 34 is supplied to the selective oxidation unit 20 based on a predetermined molar ratio with the reforming raw material 40. When the catalyst temperature in the fuel processor 1 reaches a predetermined temperature (for example, when the temperature of the reforming section is 670 ° C., the temperature of the shift section 19 is 250 ° C., and the temperature of the selective oxidation section 20 is 120 ° C.) ), The three-way switching valve 21 is switched to the position on the a side, and at the same time, the two-way valve 23 is opened, and the reformed gas 42 rich in hydrogen and containing about 10 ppm or less of carbon monoxide is supplied to the fuel electrode side.

  After a predetermined time (for example, 2 minutes) has elapsed from the start of supply of the reformed gas 42, the stack air blower 15 is started, the stack air 32 is supplied to the oxidizer electrode, and the fuel cell stack 6 starts generating power. To do. At this time, the stack voltage of the fuel cell stack 6 becomes an open circuit voltage. However, since the hydrogen-rich reformed gas 42 is supplied to the fuel electrode side first, this causes an instantaneous potential increase on the oxidant electrode side. It is possible to start without damaging the fuel cell stack 6 without causing deterioration due to electrode corrosion. Therefore, high durability of the fuel cell stack 6 can be realized.

  The internal auxiliary machine power of the fuel cell power generation system 101 is switched from the system side (partially not shown) to the fuel cell stack 6 side so that it can be operated independently. At the same time, the relay 67 is changed from open to closed, the power conditioner 7 is activated, and output of electric power to an external load (not shown) is started. The internal auxiliary machine of the system means, for example, a rotary auxiliary machine such as a blower and a pump, sensors such as a thermocouple and a pressure gauge, and the control unit 4 (partially not shown). The power output of the power conditioner 7 is increased, and at the same time, the flow rates of the reforming raw material 40, the selective oxidation air 34, the stack air 32, the process water 41, and the combustion air 31 are increased so that the fuel reaches the target output (rated output). The power output of the battery stack 6 is increased.

  Further, with reference to FIG. 1, the operation of the fuel cell power generation system 101 according to the first embodiment of the present invention during power generation (rated power output state) will be described.

  As described above, the reforming raw material 40 is supplied from the reforming raw material blower 2 to the desulfurizer 17 and the deodorizing agent containing the sulfur content in the reforming raw material 40 is removed and desulfurized. The desulfurized reforming raw material 40 passes through the reforming raw material flow rate control valve 28 and is supplied to the reforming unit 18 of the fuel processing apparatus 1. At this time, the reforming material flow rate control valve 28 is in the open position, and the reforming material flow rate control valve 28 controls the flow rate of the reforming material 40.

  The process water 41 is supplied from the recovered water tank 5 to the water vapor generating unit 36 of the fuel processing apparatus 1 by the process water pump 3. At this time, the two-way valve 38 is in the open position, and the electric motor (not shown) that drives the process water pump 3 is controlled in rotational speed, and the flow rate of the process water 41 is controlled.

  Water vapor 41a is generated in the water vapor generating unit 36, and the generated water vapor 41a is supplied to the reforming unit 18 and used as reforming water vapor. That is, in the reforming unit 18, the reforming catalyst (not shown) performs the steam reforming reaction that can be expressed by the above-described equation (2), and the reformed gas 42 is generated.

    The reformed gas 42 is supplied from the reformer 18 to the shifter 19, and the shifter 19 performs a shift reaction that can be expressed by the above-described equation (3) by a CO shift catalyst (not shown). The carbon monoxide gas in the quality gas 42 is removed.

  Further, the reformed gas 42 is sent from the shift unit 19 to the selective oxidation unit 20. The selective oxidation air 34 is supplied to the selective oxidation unit 20. At this time, the rotational speed of an electric motor (not shown) that drives a selective oxidation air blower (not shown) is controlled, and the flow rate of the selective oxidation air 34 is controlled. The carbon monoxide gas remaining in the reformed gas 42 is selectively oxidized by the selective oxidation air 34 in the selective oxidation unit 20, and the selective oxidation reaction shown in (4) above is performed.

  The reformed gas 42 from which the carbon monoxide gas has been removed by the selective oxidation unit 20 is supplied to the fuel electrode side of the fuel cell stack 6. At this time, the three-way switching valve 21 is at the position a.

  The stack air 32 is supplied from the stack air blower 15 to the humidifier 16, humidified by the humidifier 16, and supplied to the oxidant electrode side of the fuel cell stack 6. At this time, an electric motor (not shown) that drives the stack air blower 15 is controlled in rotational speed, and the flow rate of the stack air 32 is controlled.

  An electric motor (not shown) that drives the humidifying water pump 13 is controlled in rotational speed, and the flow rate of the humidifying water 44 is controlled. The humidified stack air 32 is supplied to the oxidizer electrode side in order to maintain durability and realize high power generation efficiency in terms of the characteristics of the solid polymer type fuel cell stack 6. This is because (not shown) needs to be in a sufficiently humidified state.

  In the fuel cell stack 6, the reformed gas 42 is supplied to the fuel electrode side, the stack air 32 is supplied to the oxidant electrode side, and direct current is generated by an electrochemical reaction using the reformed gas 42 and the stack air 32. Electric power is generated, voltage conversion and DC / AC conversion are performed by the power conditioner 7, and AC power is output to an external load (not shown).

  When DC power is generated by an electrochemical reaction in the fuel cell stack 6, the fuel electrode off-gas 43 is discharged from the fuel electrode side, and the oxidant electrode off-gas 33 is discharged from the oxidant electrode side. At this time, since the two-way valve 23 is in the open position, the fuel electrode off-gas 43 can be discharged.

  The fuel electrode off-gas 43 is supplied to the combustion unit 10 of the fuel processing apparatus 1 and is combusted in the combustion unit 10. The combustion exhaust gas 50 is generated by this combustion, and the combustion exhaust gas 50 is discharged from the combustion unit 10. The oxidant electrode off-gas 33 joins the combustion exhaust gas 50 and is discharged.

  That is, the combustion exhaust gas 50 is discharged from the combustion unit 10 and mixed with the oxidant electrode off gas 33, and the humidified water 44 is heated from 40 ° C. to 65 ° C., for example, at the third heat exchange unit 14. The heat recovery water 61 is cooled to, for example, 20 ° C. to 28 ° C. and is cooled to, for example, 55 ° C. to 22 ° C. by the heat recovery water 61. Further, the steam is separated and exhausted by the steam separator 11.

  The water, that is, the drain water 64 separated by the steam separator 11 is sent to the recovered water tank 5 and recovered as recovered water.

  The humidified water 44 supplied to the humidifier 16 raises the stacking air 32 to, for example, 55 ° C. and humidifies it to RH 95% or more in the humidifier 16. The hot heat recovery water 61 is heated from 28 ° C. to 64 ° C., for example, by the stack cooling water 60 in the second heat exchange unit 9 and returned to the hot water tank (not shown), and the amount of heat is stored in the hot water tank.

  The stack cooling water 60 supplied to the fuel cell stack 6 cools the fuel cell stack 6, and the stack cooling water 60 itself is heated from 55 ° C. to 65 ° C. by the fuel cell stack 6 and exits the fuel cell stack 6. After passing through the cooling water pump 12, the second heat exchanging unit 9 cools the heated heat recovery water 61 from 65 ° C. to 55 ° C., and supplies the fuel cell stack 6 again to circulate.

  An electric motor (not shown) that drives the stack cooling water pump 12 is controlled in rotational speed, and the flow rate of the stack cooling water 60 is controlled. The power generation efficiency of the fuel cell stack 6 is normally 50 to 70% (LHV), and the loss is consumed as heat generated by the fuel cell stack 6, and this heat generated is removed by the stack cooling water 60.

The control unit 4 supplies two control signals i27 and i28 for controlling the flow rate to the combustion raw material flow rate control valve 27 and the reforming raw material flow rate control valve 28, and two open / close signals (not shown) for opening or closing the opening position. A control signal (not shown) for controlling the rotation speed of each electric motor (not shown) is transmitted to each of the electric motors 23 and 38.

  Further, the control unit 4 sends a switching signal (not shown) for switching the three-way switching valve 21 to the a side before the power generation is started, and outputs power to the external load (not shown) to the power conditioner 7 when the power generation is started. A control signal i74 for controlling is sent. Further, a temperature signal i75 from the temperature detection device 75 is transmitted to the control unit 4.

  When the fuel cell power generation system 101 has a constant load operation value of 100%, the value of 100% is, for example, a generated power of 1.3 kW, a reforming raw material 40 flow rate of 4.2 L / min (NTP), The flow rate of process water 41 is 11 cc / min, the flow rate of selective oxidation air 34 is 1.5 L / min (NTP), the flow rate of stack air 32 is 60 L / min (NTP), and the temperature of the reforming unit 18 is 700 ° C. This will be described below.

  Next, with reference to FIG. 2 and FIG. 3, an operation method during low load operation of the fuel cell power generation system 101 according to the first embodiment of the present invention will be described. The following operation is performed under the control of the control unit 4. Note that FIG. 1 is appropriately referred to for the reference numerals of the constituent elements of the fuel cell power generation system 101.

  FIG. 2 is a graph showing an example of operating parameters during low load operation of the fuel cell power generation system 101 according to the first embodiment of the present invention. In the figure, the horizontal axis represents time, and the vertical axis represents operating parameters, that is, the fuel utilization rate (%) and the flow rate of the reforming raw material 40 (L / min (NTP)). This figure is a graph showing when the output power of the fuel cell stack 6 is constant (for example, 440 W) for easy theoretical explanation.

  When the fuel cell power generation system 101 is in a low load operation, for example, the control unit 4 prevents the flooding caused by the flow rate of the fluid (reformed gas 42, stack air 32) flowing through the fuel cell stack 6 is small. Thus, when the low load operation duration time of the fuel cell stack 6 reaches the low load flow rate standard time T1, the reforming raw material flow rate control valve 28 is controlled to increase the supply amount of the reforming raw material 40. Thus, the flow rate of the reformed gas 42 generated in the fuel processing device 1 is increased, and the fuel utilization rate of power generation in the fuel cell stack 6 is decreased by the low load flow rate increase time T2 shorter than the low load flow rate standard time T1. Let

  The low load flow rate increase time T2 is, for example, half or less of the low load flow rate standard time T1 (for example, if the low load flow rate standard time T1 is 20 minutes, the low load flow rate increase time T2 is 10 times. Less than a minute). If the low load flow rate increase time T2 is more than half of the low load flow rate standard time T1, depending on the setting when the fuel utilization rate is reduced, for example, the low load flow rate standard time T1, low This is because the average fuel utilization rate through the on-load flow rate increase time T2 decreases too much, and the average power generation efficiency decreases. That is, when the low load flow rate increase time T2 is less than or equal to one half of the low load flow rate standard time T1, the average fuel utilization rate does not decrease too much and the average power generation efficiency hardly decreases. Further, the low load flow rate increase time T2 may be, for example, at least 1/40 of the low load flow rate standard time T1. If the low load flow rate increase time T2 is too short with respect to the low load flow rate standard time T1, the moisture accumulated during the low load flow rate standard time T1 cannot be discharged sufficiently.

  Further, the low load flow rate increase time T2 is preferably not more than one fifth of the low load flow rate standard time T1 (for example, if the low load flow rate standard time T1 is 50 minutes, the low load flow rate increase time T2 is 10 minutes or less, or if the low load flow rate standard time T1 is 25 minutes, the low load flow rate increase time T2 is 5 minutes or less). The operation when the fuel utilization rate is lowered is slightly more complicated than when the fuel utilization rate is constant (for example, when the fuel utilization rate is constantly reduced during low-load operation). When the low load flow rate increase time T2 is 1/5 or more of the low load flow rate standard time T1, the operation when the fuel utilization rate is reduced is compared with the case where the fuel utilization rate is kept constant. For example, there is little improvement in the average fuel utilization rate through the low load flow rate standard time T1 and the low load flow rate increase time T2, and the increase in average power generation efficiency is also reduced. That is, when the low load flow rate increase time T2 is 1/5 or less of the low load flow rate standard time T1, the average fuel utilization rate is sufficiently improved as compared with the case where the fuel utilization rate is kept constant. However, the increase in average power generation efficiency will be sufficient. The low load flow rate increase time T2 is preferably set to be 1/25 or more of the low load flow rate standard time T1.

  Further, in general, it is preferable that the fuel cell power generation system 101 is operated at a high fuel utilization rate because hydrogen produced by the fuel processing apparatus 1 can be used effectively, and power generation efficiency is increased. Therefore, it is desirable that the low load flow rate standard time T1 be as long as possible, the fuel utilization rate at that time be as high as possible, the low load flow rate increase time T2 be as short as possible, and the fuel utilization rate at that time be as high as possible. However, in the present embodiment, in order to contribute to stable operation of the fuel cell stack 6, a decrease in power generation efficiency due to a decrease in the fuel utilization rate during the low load flow rate increase time T2 is allowed.

  On the other hand, if the fuel utilization rate in the fuel cell stack 6 is set low, surplus hydrogen in the fuel cell stack 6 returns to the combustion unit 10 of the fuel processing apparatus 1 as the fuel electrode off gas 43 and is combusted there. If the fuel utilization rate is set too low in order to shorten the low load flow rate increase time T2, the amount of combustion in the combustion section 10 becomes excessive, the fuel processing apparatus 1 overheats, and the temperature balance cannot be achieved. Examples of the influence of the fuel processing apparatus 1 due to excessive temperature rise include deterioration of the combustion unit 10, catalyst deterioration of the reforming unit 18, and the shift unit 19.

  More specifically, considering the above power generation efficiency, the temperature balance of the fuel processing apparatus 1, etc., the low load flow rate standard time T1 and the low load flow rate increase time T2 are, for example, the low load flow rate standard time. T1 is about 30 to 180 minutes, low load flow rate increase time T2 is about 5 to 20 minutes, preferably low load flow rate standard time T1 is about 60 to 180 minutes, and low load flow rate increase time T2 is 5 to 10 It should be about minutes. In this embodiment, the low load flow rate standard time T1 is about 120 minutes, and the low load flow rate increase time T2 is about 10 minutes.

  For example, in the figure, the low load operation of the fuel cell stack 6 is continued from t4 to t5 with the flow rate of the reforming raw material 40 and the like being the standard flow rate. For example, the flow rate of the reforming raw material 40 at this time is 1.4 L / min (NTP), and the fuel utilization rate is 67.5%.

  When the low load operation time of the fuel cell stack 6 reaches t5, the reforming material flow rate control valve 28 is controlled by the control by the control unit 4 between t5 and t6. The flow rate is increased to 1.6 L / min (NTP) and the fuel utilization rate is decreased to 62.5%.

  Thereafter, the flow rate of the reforming raw material 40 is maintained at 1.6 L / min (NTP) and the fuel utilization rate is 62.5% from t6 to t7, and the reforming is performed again from t7 to t8. The flow rate of the raw material 40 is reduced to 1.4 L / min (NTP) and returned to the standard flow rate, and the fuel utilization rate is increased to 67.5%. The average fuel utilization rate through the low load flow rate standard time T1 and the low load flow rate increase time T2 is about 66.25%.

  That is, here, the time from t4 to t5 is the low load flow rate standard time T1 = 120 minutes in which the flow rate of the reforming raw material 40 and the like is the standard flow rate, and the time from t5 to t8 after t6, t7, The low load flow rate increase time T2 = 10 minutes when the flow rate of the reforming raw material 40 or the like is increased. In this figure, the time from t1 to t4 after passing through t2 and t3 indicates the low load flow rate increase time T2 before the low load flow rate increase time T2 starting from t5.

  Note that, as described above, this diagram is a graph showing the time when the output power of the fuel cell stack 6 is constant (for example, 440 W) for easy theoretical explanation. However, in practice, the control unit 4 controls the stack current density of the fuel cell stack 6, the flow rate of the reforming raw material 40, and the like following the change in the load of the fuel cell stack 6. Output power is controlled.

  Therefore, the flow rate of the reforming raw material 40 actually varies as the load of the fuel cell stack 6 varies. For example, when the load of the fuel cell stack 6 increases and the output power of the battery stack 6 increases during the low load flow rate increase time T2, the reforming raw material 40 follows the output power of the battery stack 6. The flow rate also increases. When the flow rate of the reforming raw material 40 increases to a predetermined amount (standard flow rate), the high load time T3 (see FIG. 3) is measured, and the high load time T3 is determined to be a predetermined time ( 10 minutes), the low load flow rate increase time T2 may end without waiting for a predetermined time (10 minutes). By doing in this way, the driving | operation of the fuel cell stack 6 suitable for a condition can be performed.

  Here, when the load of the fuel cell stack 6 is low, that is, when the load is low, the stack current density of the fuel cell stack 6 becomes low, and the cell average voltage increases. In the present embodiment, it is determined whether or not the fuel cell power generation system 101 is in a low load operation based on the stack current density.

  As described above, the low load operation is an operation with a load that does not satisfy the rated load operation (partial load operation), and is an operation when the load is small or absent. This means an operation with a load of 30% to 50%. In the present embodiment, the operation is performed when the stack current density of the fuel cell stack 6 is below a reference value.

Here, the reference value of the stack current density is, for example, about 0.07 A / cm ² to about 0.2 A / cm ² , preferably about 0.07 A / cm ² to about 0.09 A / cm ² , where 0 .About.08 A / cm ² . Note that the reference value of the stack current density depends on the internal flow path design of the fuel cell stack 6, the design of the electrode diffusion layer, the number of cells, and the like. This is often a trade-off with the pressure loss of the fuel cell stack 6 and may be set as appropriate according to the design concept.
Next, an example of a specific operation method in the low load operation of the fuel cell power generation system 101 according to the first embodiment of the present invention will be described with reference to FIG.

  FIG. 3 is a flowchart showing an operation method during low load operation of the fuel cell power generation system 101 according to the first embodiment of the present invention. The following operation is performed under the control of the control unit 4.

  First, the fuel cell power generation system 101 is in a rated power output state with the flow rate of the reforming raw material 40 set as standard (S100). When the load of the fuel cell stack 6 fluctuates, the control unit 4 controls the stack current density of the fuel cell stack 6, the flow rate of the reforming raw material 40, and the like. Controls output power.

  At this time, in the fuel processing apparatus 1, as a reforming step, the reforming raw material 40 and the process water 41 are supplied as described above, and the reforming raw material 40 is reformed gas containing hydrogen as a main component. A process of reforming to 42 is performed.

When the flow rate and the like of the reforming material 40 are set as standard (S100), the control unit 4 detects the stack current density during the operation of the fuel cell stack 6 (S102). The stack current density is detected by the control unit 4 dividing the stack current value measured by the current detection device 69 by the cell cross-sectional area (cm ² ).

Next, the control unit 4 determines whether or not the detected stack current density is less than the reference value 0.08 A / cm ² (S104). If the stack current density is smaller than the reference value 0.08 A / cm ² (S104: Yes), it is determined that the load operation is low, and the process proceeds to S106. When the stack current density is larger than the reference value 0.08 A / cm ² (S104: No), it is determined that the operation is high load, and the process proceeds to S126.

  When it is determined that the operation is low load (S104: Yes), the control unit 4 once clears the high load time measurement timer C3 of the control unit 4 (S106), and the flow rate of the reforming raw material 40 is set to increase. It is determined whether or not (S108).

  When it is determined that the flow rate of the reforming raw material 40 is not set to increase (S108: No), the control unit 4 adds the low load flow rate standard time measurement timer C1 to the low load flow rate standard time T1 (120 Minute) is measured (S110). If the measurement of the low load flow rate standard time T1 (120 minutes) has not started, the addition here starts the addition of the low load flow rate standard time measurement timer C1, and the low load flow rate standard time T1 (120 minutes). Is started, it means that the addition of the low load flow rate standard time measurement timer C1 is continued.

  Subsequently, the control unit 4 determines whether or not the count of the low load flow rate standard time measurement timer C1 has reached the low load flow rate standard time T1 (120 minutes) (S112). When it is determined that the low load flow rate standard time T1 (120 minutes) has been reached (S112: Yes), the supply rate of the reforming raw material 40 supplied to the fuel processing apparatus 1 in this embodiment, the utilization rate lowering step. As the reforming raw material supply amount fluctuation step as the hydrocarbon fuel supply amount fluctuation step for varying the fuel, the control unit 4 controls the reforming raw material flow rate control valve 28 to increase the flow rate of the reforming raw material 40. Set (S114). Thereby, the fuel utilization rate in the fuel cell stack 6 decreases. Then, the low load flow rate standard time measurement timer C1 is cleared (S116). Then, it returns to S102 and repeats the subsequent processes. Even when it is determined that the low load flow rate standard time T1 (120 minutes) has not been reached (S112: No), the process returns to S102 and the subsequent processing is repeated.

  When it is determined that the flow rate of the reforming raw material 40 is being set to increase (S108: Yes), the control unit 4 adds a low load flow rate increase time measurement timer C2 and adds a low load flow rate increase time T2 ( 10 minutes) is measured (S118). The addition here is similar to the addition of the low load flow rate standard time measurement timer C1, and if the low load flow rate increase time T2 (10 minutes) has not been started, the low load flow rate increase time measurement timer C2 If the addition is started and the measurement of the low load flow rate increase time T2 (10 minutes) is started, this means that the addition of the low load flow rate increase time measurement timer C2 is continued.

  Subsequently, the control unit 4 determines whether or not the count of the low load flow rate increase time measurement timer C2 has reached the low load flow rate increase time T2 (10 minutes) (S120), and the low load flow rate increase. When it is determined that the time T2 (10 minutes) has been reached (S120: Yes), the control unit 4 controls the reforming material flow rate control valve 28 to decrease the flow rate of the reforming material 40 and set the standard. (S122), the low load flow rate increase time measurement timer C2 is cleared (S124). Then, it returns to S102 and repeats the subsequent processes. Even when it is determined that the low load flow rate increase time T2 (10 minutes) has not been reached (S120: No), the process returns to S102 and the subsequent processing is repeated.

When the stack current density is larger than the reference value 0.08 A / cm ^{2 in} S104 and it is determined that the operation is a high load operation (S104: No), the control unit 4 adds the high load time measurement timer C3 to increase the load. Time T3 (10 minutes) is measured (S126). The addition here is similar to the addition of the low load flow rate standard time measurement timer C1 and the low load flow rate increase time measurement timer C2, and if the measurement of the high load time T3 (10 minutes) has not started, the high load time If the addition of the measurement timer C3 is started and the measurement of the high load time T3 (10 minutes) is started, it means that the addition of the high load time measurement timer C3 is continued.

  Subsequently, the control unit 4 determines whether or not the count of the high load time measurement timer C3 has reached the high load time T3 (10 minutes) (S128), and has reached the high load time T3 (10 minutes). (S128: Yes), the control unit 4 clears the low load flow rate standard time measurement timer C1 (S130), clears the low load flow rate increase time measurement timer C2 (S132), and the high load time measurement timer. C3 is cleared (S134). Then, it returns to S102 and repeats the subsequent processes. Even when it is determined that the high load time T3 (10 minutes) has not been reached (S128: No), the process returns to S102 and the subsequent processing is repeated.

  Here, in each process after S126, for example, even when the flow rate of the reforming raw material 40 is increased at S114 and the low load flow rate increase time T2 is measured at S118 and S120, the fuel cell. When the load of the stack 6 rises and the output power increases, that is, when the operation shifts to a high load operation, the stack current density of the fuel cell stack 6 and the flow rate of the reforming raw material 40 increase accordingly. Therefore, the flow rate of the fluid (reformed gas 42, stack air 32) flowing through the fuel cell stack 6 is sufficient to prevent flooding. Therefore, if the high load time T3 reaches 10 minutes, substantially the same effect as when the low load flow rate increase time T2 is continued for 10 minutes can be obtained. Therefore, in this embodiment, when the high load time T3 reaches 10 minutes, the low load flow rate standard time T1 and the low load flow rate increase time T2 are once cleared.

  According to the fuel cell power generation system 101 or the operation method of the fuel cell power generation system 101 according to the first embodiment of the present invention described above, the low load operation duration of the fuel cell stack 6 during low load operation. When the low-load flow rate standard time T1 is reached, the reforming material flow rate control valve 28 is controlled to increase the supply amount of the reforming material 40, whereby the reforming produced by the fuel processing apparatus 1 is achieved. Since the flow rate of the gas 42 is increased and the fuel utilization rate of power generation in the fuel cell stack 6 is decreased by the low load flow rate increase time T2 shorter than the low load flow rate standard time T1, the fluid flow is maintained while maintaining high power generation efficiency. The pressure loss increases, and the condensed water and moisture are blown away, so that the water does not stagnate in the fluid of the fuel cell stack 6. As a result, flooding on the oxidant electrode side and fuel electrode side is prevented, the electrode reaction area is reduced, and the reaction gas (hydrogen, oxygen) becomes insufficient, so that there is no decrease in battery performance, cell voltage, and the like.

  Further, since the flow rate of the reformed gas 42 is increased based on the duration of the low load operation, for example, the cell voltage decreases due to flooding on the fuel electrode side, and the oxidant electrode catalyst is permanently damaged. Not receive.

  Further, for example, even when the fuel cell power generation system 101 is used at home, flooding on the fuel electrode side of the fuel cell stack 6 even in a low load operation that is considered to be a dominant operation pattern among the operation patterns of the fuel cell stack 6. Therefore, it is possible to avoid the shortage of hydrogen due to the above, to prevent the oxidant electrode catalyst from being damaged, and to achieve high durability of the fuel cell stack 6. In other words, the fuel cell power generation system 101 and the fuel cell power generation system 101 can be operated without damaging the fuel cell stack 6 even during low load operation.

  Further, since the time for reducing the fuel utilization rate, that is, the time for increasing the flow rate of the reformed gas 42 can be shortened as much as possible, it is not always necessary to supply a larger amount of the reformed gas 42, and the fuel processing apparatus 1 is always provided. In addition, since it is not necessary to supply a large amount of the reforming raw material 40, it is possible to minimize a decrease in power generation efficiency of the fuel cell power generation system. That is, the power generation efficiency of the fuel cell power generation system 101 can be kept relatively high.

  Next, a fuel cell power generation system 201 and a method for operating the fuel cell power generation system 201 according to the second embodiment of the present invention will be described with reference to FIGS. In the description of the fuel cell power generation system 201 and the operation method of the fuel cell power generation system 201 according to the second embodiment, the description common to the first embodiment is omitted as much as possible. The same applies to the description of the third embodiment.

  In the fuel cell power generation system 201 according to the second embodiment of the present invention, the utilization rate changing means for changing the utilization rate of the reformed gas 42 in the power generation of the fuel cell stack 6 is modified in the first embodiment. It is different from the first embodiment in that it is a raw material flow rate control valve 27 for combustion but a raw material flow rate control valve 27 for combustion.

  The combustion raw material flow rate control valve 27 is a two-way valve that controls the flow rate of the combustion raw material 30 supplied to the combustion unit 10 by the control signal i27 from the control unit 4 as described above. Further, the combustion raw material flow rate control valve 27 functions as a reforming temperature changing means for changing the reforming temperature of the fuel processing apparatus 1.

  Specifically, the control unit 4 increases the supply amount of the combustion raw material 30 to the combustion unit 10 by controlling the opening degree of the combustion raw material flow rate control valve 27 and raises the combustion temperature of the combustion unit 10. . Thereby, the temperature of the reforming part 18 heated by the combustion heat of the combustion part 10 is raised.

  When the temperature of the reforming unit 18 rises, the reforming temperature also rises. Since the reforming reaction represented by the formula (2) is an endothermic reaction, when the reforming temperature rises, the conversion rate in the reforming unit 18 also increases. That is, when the temperature of the reforming unit 18 increases, the conversion rate of the reformed gas 42 in the fuel processing apparatus 1 increases. Accordingly, when the temperature of the reforming unit 18 rises, the supply amount and flow rate of the reformed gas 42 to the fuel electrode of the fuel cell stack 6 increase, and the fuel utilization rate of power generation in the fuel cell stack 6 decreases.

  Note that if the temperature of reforming in the reforming unit 18 is too high, the reforming catalyst (not shown) deteriorates or the requirements for the heat resistance specifications of the reformer material become severe. The temperature of the reforming is preferably detected by a temperature detecting device 75 in which the temperature sensing portion is embedded, and the flow rate of the combustion raw material 30 is controlled so as not to become too high.

  FIG. 4 is a graph showing an example of operation parameters at the time of low load operation of the fuel cell power generation system 201 according to the second embodiment of the present invention. In the figure, the horizontal axis represents time, and the vertical axis represents operating parameters, that is, the fuel utilization rate (%), the reforming temperature (° C.), and the flow rate (L / min (NTP)) of the combustion raw material 30. As in the case of FIG. 2, this figure is a graph showing when the output power of the fuel cell stack 6 is constant (for example, 440 W) for easy theoretical explanation.

  When the fuel cell power generation system 201 is operated at a low load, for example, the control unit 4 prevents the flooding caused by the flow rate of the fluid (reformed gas 42, stack air 32) flowing through the fuel cell stack 6 is small. Thus, when the low load operation duration time of the fuel cell stack 6 reaches the low load flow rate standard time T1, the combustion raw material flow rate control valve 27 is controlled, and the supply amount of the combustion raw material 30 to the combustion unit 10 is reduced. By increasing the temperature, the temperature of the reforming unit 18 is increased, the flow rate of the reformed gas 42 generated by the fuel processing apparatus 1 is increased, and the fuel utilization rate of power generation in the fuel cell stack 6 is reduced to a low load flow rate standard. Decrease by a low load flow rate increase time T2 shorter than the time T1.

  For example, in the figure, during the period from t4 to t5, the low load operation of the fuel cell stack 6 is continued while the flow rate of the raw material for combustion 30 is a standard flow rate. For example, the flow rate of the combustion raw material 30 at this time is 0.05 L / min (NTP), the reforming temperature is 640 ° C., and the fuel utilization rate is 67.5%.

  When the low load operation time of the fuel cell stack 6 reaches t5, the control of the controller 4 controls the opening / closing of the combustion material flow rate control valve 27 between t5 and t6. The flow rate is increased to 0.4 L / min (NTP), the reforming temperature is increased to 680 ° C., and the fuel utilization rate is decreased to 62.5%.

  Thereafter, during the period from t6 to t7, the flow rate of the combustion raw material 30 is continued at 0.4 L / min (NTP), the reforming temperature is 680 ° C., the fuel utilization rate is 62.5%, and the period from t7 to t8 Again, the flow rate of the combustion raw material 30 is reduced to 0.05 L / min (NTP) and returned to the standard flow rate, the reforming temperature is lowered to 640 ° C., and the fuel utilization rate is increased to 67.5%. The average fuel utilization rate through the low load flow rate standard time T1 and the low load flow rate increase time T2 is about 66.25%.

  That is, here, the time from t4 to t5 is a low load flow rate standard time T1 = 120 minutes, where the flow rate of the raw material for combustion 30 is a standard flow rate, and the time from t5 to t8 after passing through t6 and t7 is Low load flow rate increase time T2 = 10 minutes in which the flow rate of the raw material 30 is increased. In this figure, the time from t1 to t4 after passing through t2 and t3 indicates the low load flow rate increase time T2 before the low load flow rate increase time T2 starting from t5.

  Note that, as described above, this diagram is a graph showing the time when the output power of the fuel cell stack 6 is constant (for example, 440 W) for easy theoretical explanation. However, in practice, the control unit 4 controls the stack current density of the fuel cell stack 6, the flow rate of the combustion raw material 30, the reforming raw material 40, etc. following the change in the load of the fuel cell stack 6, The output power of the fuel cell stack 6 is controlled.

  Accordingly, the flow rate of the combustion raw material 30 or the like actually varies with the variation of the load of the fuel cell stack 6, and the reforming temperature also varies. Further, the control unit 4 controls the combustion air blower (not shown) in accordance with the change in the flow rate of the combustion raw material 30 to control the flow rate of the combustion air 31 including oxygen consumed by the combustion in the combustion unit 10. There are also fluctuations.

  Next, an example of a specific operation method in the low load operation of the fuel cell power generation system 201 according to the second embodiment of the present invention will be described with reference to FIG.

  FIG. 5 is a flowchart showing an operation method during low-load operation of the fuel cell power generation system 201 according to the second embodiment of the present invention. Also here, the description overlapping with the first embodiment is omitted as much as possible. The difference of the second embodiment from the first embodiment is, for example, each process performed in S200, S208, S214, and S222. The following operation is performed under the control of the control unit 4.

  S100 (see FIG. 3) of the first embodiment is processed as S200 in the second embodiment. That is, the fuel cell power generation system 201 is in the rated power output state with the combustion raw material 30 flow rate and the like set as standard (S200). At this time, in the fuel processing apparatus 1, as a reforming step, the reforming raw material 40 and the process water 41 are supplied as described above, and the reforming raw material 40 is reformed gas containing hydrogen as a main component. A process of reforming to 42 is performed.

  S108 (see FIG. 3) of the first embodiment is processed as S208 in the second embodiment. That is, in the first embodiment, it is determined whether or not the flow rate of the reforming raw material 40 is set to increase (S108, see FIG. 3), whereas in the second embodiment, combustion is performed. It is determined whether or not the flow rate of the raw material 30 is being set to increase (S208). If the flow rate of the combustion raw material 30 is set to increase (S208: Yes), the process proceeds to S118. If the flow rate of the combustion raw material 30 is not set to increase (S208: No), the process proceeds to S110.

  S114 (see FIG. 3) of the first embodiment is processed as S214 in the second embodiment. That is, in the utilization rate lowering step, in this embodiment, as a reforming temperature fluctuation step for changing the reforming temperature of the fuel processing apparatus 1, the control unit 4 controls the combustion raw material flow rate control valve 27 to perform combustion. The raw material 30 flow rate is set to increase (S214).

  S122 (see FIG. 3) of the first embodiment is processed as S222 in the second embodiment. That is, the control unit 4 controls the combustion raw material flow rate control valve 27 to reduce the flow rate of the combustion raw material 30 to a standard setting (S222).

  In the fuel cell power generation systems 101 and 201, the combustion unit 10 typically includes combustion air using the reformed gas 42a, in which the raw material for combustion 30 or the carbon monoxide gas has not been sufficiently reduced at the time of startup, as fuel. It is comprised so that it may burn with 31 and it is comprised so that it may burn with the combustion air 31 by making the fuel electrode off gas 43 into a fuel at the time of rated operation (at the time of normal operation).

  Therefore, as described in the first embodiment, the supply amount of the reforming raw material 40 to the fuel processing apparatus 1 is increased, the flow rate of the generated reformed gas 42 is increased, and the fuel cell stack 6 If the fuel utilization rate of power generation in this is reduced, the amount of reformed gas 42 not used in power generation also increases, and the amount of hydrogen in the fuel electrode off-gas 43 increases. Therefore, when the fuel electrode off gas 43 is combusted, the combustion heat in the combustion unit 10 also increases, and as a result, the reforming temperature in the reforming unit 18 also increases.

  That is, the method of raising the reforming temperature of the reforming unit 18 and lowering the fuel utilization rate of power generation in the fuel cell stack 6 is the same as the combustion in the combustion unit 10 as shown in the second embodiment. This is not limited to the method of increasing the supply amount of the raw material 30, and can also be achieved, for example, by increasing the supply amount of the reforming raw material 40 to the fuel processing apparatus 1 as shown in the first embodiment. .

  According to the fuel cell power generation system 201 or the operation method of the fuel cell power generation system 201 according to the second embodiment of the present invention described above, the low load operation duration time of the fuel cell stack 6 during low load operation. Is controlled by the combustion raw material flow rate control valve 27 when the low load flow rate standard time T1 is reached, and the supply amount of the combustion raw material 30 is increased, so that the reforming temperature is raised and generated by the fuel processing device 1. Since the flow rate of the reformed gas 42 is increased and the fuel utilization rate of power generation in the fuel cell stack 6 is decreased by the low load flow rate increase time T2 shorter than the low load flow rate standard time T1, high power generation efficiency is maintained. However, the pressure loss of the fluid rises, and the condensed water and moisture are blown away, so that the water is not stagnated in the fluid of the fuel cell stack 6. As a result, flooding on the oxidant electrode side and fuel electrode side is prevented, the electrode reaction area is reduced, and the reaction gas (hydrogen, oxygen) becomes insufficient, so that there is no decrease in battery performance, cell voltage, and the like.

  Next, the fuel cell power generation system 301 and the operation method of the fuel cell power generation system 301 according to the third embodiment of the present invention will be described with reference to FIGS.

  In the fuel cell power generation system 301 according to the third embodiment of the present invention, the utilization rate changing means for changing the utilization rate of the reformed gas 42 in the power generation of the fuel cell stack 6 is modified in the first embodiment. The raw material flow rate control valve 28, which is the combustion raw material flow rate control valve 27 in the second embodiment, differs from the first and second embodiments in that it is a power conditioner 7.

  As described above, the power conditioner 7 adjusts the voltage (stack voltage) of the DC power generated by the fuel cell stack 6, further converts the DC into AC, receives the control signal i74 from the control unit 4, and receives the control signal. AC power having a power value required by i74 is output to an external load (not shown). That is, the power conditioner 7 functions as a power generation load changing unit that changes the power generation load of the fuel cell stack 6.

  Specifically, the power conditioner 7 reduces the power generation output of the fuel cell stack 6 by reducing the external load (not shown) of the fuel cell stack 6 to reduce the fuel utilization rate of power generation in the fuel cell stack 6. Reduce. In this case, by keeping the flow rate of the reforming raw material 40 and the like constant without following the output power of the fuel cell stack 6, the fuel utilization rate of power generation in the fuel cell stack 6 with respect to the flow rate of the reformed gas 42 is Relatively decreases. By increasing the flow rate of the reformed gas 42 that is not used for power generation in the fuel cell stack 6, flooding can be prevented.

  FIG. 6 is a graph showing an example of operation parameters at the time of low load operation of the fuel cell power generation system 301 according to the third embodiment of the present invention. In the figure, the horizontal axis represents time, and the vertical axis represents operating parameters, that is, fuel utilization rate (%) and fuel cell stack output power (W). As in the case of FIG. 2, this figure excludes the low load flow rate increase time T2 (time during which the power conditioner 7 is controlled to reduce the fuel utilization rate) in order to facilitate the theoretical explanation. The graph shows when the output power of the fuel cell stack 6 is constant (for example, 440 W).

  When the fuel cell power generation system 301 is operated at a low load, for example, the control unit 4 prevents the flooding caused by the flow rate of the fluid (reformed gas 42, stack air 32) flowing through the fuel cell stack 6 is small. Thus, when the low load operation continuation time of the fuel cell stack 6 reaches the low load flow rate standard time T1, the power conditioner 7 is controlled to reduce the output power of the fuel cell stack 6 and the flow rate of the reformed gas 42. Is relatively increased, and the fuel utilization rate of power generation in the fuel cell stack 6 is decreased by a low load flow rate increase time T2 shorter than the low load flow rate standard time T1.

  For example, in the figure, the low load operation of the fuel cell stack 6 is continued while the output power of the fuel cell stack 6 is a standard power from t4 to t5. For example, the output power of the fuel cell stack 6 at this time is 440 W, and the fuel utilization rate is 67.5%.

  When the low load operation time of the fuel cell stack 6 reaches t5, the power conditioner 7 is controlled by the control of the control unit 4 between t5 and t6, for example, the output power of the fuel cell stack 6 is reduced to 375W. And reduce the fuel utilization rate to 60%.

  Thereafter, the output power of the fuel cell stack 6 is maintained at 375 W and the fuel utilization rate is 60% from t6 to t7, and the output power of the fuel cell stack 6 is increased to 440 W again from t7 to t8. Return to standard output power and increase fuel utilization to 67.5%. The average fuel utilization rate through the low load flow rate standard time T1 and the low load flow rate increase time T2 is about 65%.

  That is, here, the time from t4 to t5 is the low load flow rate standard time T1 = 120 minutes where the output power of the fuel cell stack 6 is the standard power, the time from t5 to t8 after t6, t7, The low load flow rate increase time T2 in which the output power of the battery stack 6 is reduced is T2 = 10 minutes. In this figure, the time from t1 to t4 after passing through t2 and t3 indicates the low load flow rate increase time T2 before the low load flow rate increase time T2 starting from t5.

  Note that, as described above, in this figure, in order to facilitate the theoretical explanation, except for the low load flow rate increase time T2 (time during which the power conditioner 7 is controlled to decrease the fuel utilization rate), The graph shows a time when the output power of the fuel cell stack 6 is constant (for example, 440 W). However, in practice, during the time excluding the low load flow rate increase time T2, the control unit 4 follows the fluctuation of the load of the fuel cell stack 6 and the control unit 4 performs the stack current density of the fuel cell stack 6, the combustion raw material 30, The flow rate of the reforming raw material 40 is controlled, and the output power of the fuel cell stack 6 is controlled.

  Next, an example of a specific operation method in the low load operation of the fuel cell power generation system 301 according to the third embodiment of the present invention will be described with reference to FIG.

  FIG. 7 is a flowchart showing an operation method during low-load operation of the fuel cell power generation system 301 according to the third embodiment of the present invention. Also here, the description overlapping with the first embodiment is omitted as much as possible. The third embodiment is different from the first embodiment in, for example, each process performed in S300, S308, S314, and S322. The following operation is performed under the control of the control unit 4.

  S100 (see FIG. 3) of the first embodiment is processed as S300 in the third embodiment. That is, in the fuel cell power generation system 301, the output power of the fuel cell stack 6, the reforming raw material 40 flow rate, and the like are set as standard, and are in a rated power output state (S300). At this time, in the fuel processing apparatus 1, as a reforming step, the reforming raw material 40 and the process water 41 are supplied as described above, and the reforming raw material 40 is reformed gas containing hydrogen as a main component. A process of reforming to 42 is performed.

  S108 (see FIG. 3) of the first embodiment is processed as S308 in the third embodiment. That is, in the first embodiment, it is determined whether or not the flow rate of the reforming raw material 40 is being set to increase (S108, see FIG. 3), whereas in the third embodiment, the fuel cell It is determined whether or not the output power of the stack 6 is being set to decrease (S308). If the output power of the fuel cell stack 6 is set to decrease (S308: Yes), the process proceeds to S118, and if the output power of the fuel cell stack 6 is not set to decrease (S308: No), the process proceeds to S110.

  S114 (see FIG. 3) of the first embodiment is processed as S314 in the third embodiment. That is, in the utilization rate lowering step, in the present embodiment, as a power generation load changing step for changing the power generation load of the fuel cell stack 6, the control unit 4 controls the power conditioner 7 to reduce the output power of the fuel cell stack 6. Decrease setting is made (S314). Thereby, the flow rate of the reformed gas 42 is relatively increased, and the fuel utilization rate of power generation in the fuel cell stack 6 is decreased.

  S122 (see FIG. 3) of the first embodiment is processed as S322 in the third embodiment. That is, the control unit 4 controls the power conditioner 7 to set the output power of the fuel cell stack 6 as a standard setting (S322).

  In the third embodiment described above, similarly to the first embodiment, when the fuel utilization rate of power generation in the fuel cell stack 6 is reduced, the reformed gas 42 not used in power generation is used. The amount of hydrogen also increases, and the amount of hydrogen in the anode offgas 43 increases. Therefore, when the fuel electrode off gas 43 is combusted, the combustion heat in the combustion unit 10 also increases, and as a result, the reforming temperature in the reforming unit 18 also increases.

  That is, the method of increasing the reforming temperature of the reforming unit 18 described in the second embodiment and reducing the fuel utilization rate of power generation in the fuel cell stack 6 is, for example, in the third embodiment. As shown, this can also be achieved by reducing the output power of the fuel cell stack 6.

  According to the fuel cell power generation system 301 or the operation method of the fuel cell power generation system 301 according to the third embodiment of the present invention described above, the low load operation duration of the fuel cell stack 6 during low load operation. When the low load load flow standard time T1 is reached, the power conditioner 7 is controlled, the output power of the fuel cell stack 6 is decreased, the flow rate of the reformed gas 42 is relatively increased, and the fuel cell stack 6 The fuel usage rate of power generation is reduced by a low load flow rate increase time T2, which is shorter than the low load flow rate standard time T1, so that while maintaining high power generation efficiency, the fluid pressure loss increases, and condensed water and moisture are blown away. Water is not stagnated in the fluid of the fuel cell stack 6. As a result, flooding on the oxidant electrode side and fuel electrode side is prevented, the electrode reaction area is reduced, and the reaction gas (hydrogen, oxygen) becomes insufficient, so that there is no decrease in battery performance, cell voltage, and the like.

  Note that the operation method of the fuel cell power generation systems 101, 201, 301 or the fuel cell power generation systems 101, 201, 301 according to the first, second, and third embodiments of the present invention described above is the same as that described above. The present invention is not limited to this form, and various modifications can be made within the scope described in the claims.

  For example, the utilization rate changing means is a modification of the reforming raw material flow rate control valve 28 as the hydrocarbon fuel supply amount changing means for changing the supply amount of hydrocarbon fuel supplied to the fuel processing apparatus 1 and the fuel processing apparatus 1. At least one selected from the group consisting of a combustion raw material flow rate control valve 27 as a reforming temperature changing means for changing the temperature of the quality, and a power conditioner 7 as a power generation load changing means for changing the power generation load of the fuel cell stack 6. Any means may be used, and the combustion raw material flow rate control valve 27, the reforming raw material flow rate control valve 28, and the power conditioner 7 may be provided.

  Further, the hydrocarbon-based fuel supply amount fluctuation means, the reforming temperature fluctuation means, and the power generation load fluctuation means are not limited to the above-described forms. For example, as described above, the reforming raw material flow control valve 28, the power The conditioner 7 can also function as a reforming temperature changing means. Furthermore, the reforming material blower 2 that supplies the reforming material 40 may be used as a hydrocarbon-based fuel supply amount variation unit or a reforming temperature variation unit.

  Similarly, the utilization rate lowering step includes a hydrocarbon fuel supply amount changing step for changing the supply amount of hydrocarbon fuel supplied to the fuel processing apparatus 1, a reforming temperature changing step for changing the reforming temperature, a fuel cell. It may be at least one process selected from the group consisting of a power generation load fluctuation process that fluctuates the power generation load of the stack 6, and includes a hydrocarbon fuel supply amount fluctuation process, a reforming temperature fluctuation process, and a power generation load fluctuation process, respectively. May be.

1 is a block diagram showing a schematic configuration of a fuel cell power generation system according to a first embodiment of the present invention. It is a graph which shows an example of the operation parameter at the time of low load operation of the fuel cell power generation system concerning a 1st embodiment of the present invention. It is a flowchart which shows the driving | operation method in the low load driving | running of the fuel cell power generation system which concerns on the 1st Embodiment of this invention. It is a graph which shows an example of the operation parameter at the time of low load operation of the fuel cell power generation system concerning a 2nd embodiment of the present invention. It is a flowchart which shows the driving | operation method in the low load driving | running of the fuel cell power generation system which concerns on the 2nd Embodiment of this invention. It is a graph which shows an example of the operation parameter at the time of low load operation of the fuel cell power generation system concerning a 3rd embodiment of the present invention. It is a flowchart which shows the driving | operation method in the low load driving | running of the fuel cell power generation system which concerns on the 3rd Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Fuel processing apparatus 2 Raw material blower for reforming 3 Process water pump 4 Control part 5 Recovery water tank 6 Fuel cell stack 7 Power conditioner 8 1st heat exchange part 9 2nd heat exchange part 10 Combustion part 11 Air-water separator 12 Stack cooling water pump 13 Humidification water pump 14 Third heat exchanging unit 15 Stack air blower 16 Humidifier 17 Desulfurizer 18 Reforming unit 19 Transformation unit 20 Selective oxidation unit 27 Combustion raw material flow control valve 28 Reforming raw material Flow control valve 30 Combustion raw material 31 Combustion air 32 Stack air 33 Oxidant electrode off gas 34 Selective oxidation air 36 Water vapor generating part 40 Reforming raw material 41 Process water 42 Reformed gas 43 Fuel electrode off gas 44 Humidified water 50 Combustion Exhaust gas 60 Stack cooling water 61 Heat recovery water 64 Drain water 65 Surplus water 90 Hot water storage tanks 101, 201, 301 Fuel cell power generation system 130 Combustion raw material supply line 131 Combustion air supply line 132 Stack air supply line 133 Oxidant electrode off-gas discharge line 134 Selective oxidation air supply line 140 Raw material supply line 141 Process water supply line 141a Steam supply line 142 Reformed gas Transfer line 142a Switching line 143 Fuel electrode off-gas transfer line 144 Humidified water supply line 150 Combustion exhaust gas discharge line 160 Stack cooling water circulation line 161 Heat recovery water circulation line 164 Drain water line 165 Surplus water line C1 Low load flow time standard time measurement timer C2 Low Load increase flow time measurement timer C3 High load time measurement timer T1 Low load flow standard time T2 Low load flow increase time T3 High load times i27, i28, i74 Control signal i75 Temperature signal

Claims (4)

When the low load operation continuation time of the fuel cell that introduces the fuel containing hydrogen as the main component into the fuel electrode and generates power by introducing the oxidant into the oxidant electrode reaches the first predetermined time, A utilization rate lowering step of reducing the fuel utilization rate of the fuel for a second predetermined time shorter than the first predetermined time;
Operation method of fuel cell power generation system. Comprising a reforming step of supplying a hydrocarbon fuel and a reforming agent to reform the hydrocarbon fuel into the fuel containing hydrogen as a main component;
The utilization rate lowering step includes a hydrocarbon fuel supply amount changing step for changing the supply amount of the hydrocarbon fuel to be supplied, a reforming temperature changing step for changing the reforming temperature, and a power generation load of the fuel cell. At least one process selected from the group consisting of a fluctuating power generation load fluctuation process;
The operation method of the fuel cell power generation system according to claim 1. A fuel processor for supplying a hydrocarbon fuel and a reformer to reform the hydrocarbon fuel into a fuel mainly composed of hydrogen;
A fuel cell that introduces the fuel into the fuel electrode and introduces an oxidant into the oxidant electrode to generate electric power;
Utilization rate variation means for varying the utilization rate of the fuel in the power generation;
When the low load operation continuation time of the fuel cell reaches a first predetermined time, the utilization rate changing means is controlled, and the fuel utilization rate in the power generation is set to a second value shorter than the first predetermined time. And a control unit that lowers for a predetermined time;
Fuel cell power generation system. The utilization rate changing means includes a hydrocarbon fuel supply amount changing means for changing the supply amount of the hydrocarbon fuel supplied to the fuel processing apparatus, and a reforming temperature for changing the reforming temperature of the fuel processing apparatus. Fluctuating means, at least one means selected from the group consisting of power generation load fluctuation means for fluctuating the power generation load of the fuel cell;
The fuel cell power generation system according to claim 3.

Images