JP2019079689A - Fuel cell system and control method of fuel cell system - Google Patents

Abstract

To prevent reduction in adiabatic flame temperature when the concentration of fuel containing water and oxygen reduces, thereby securing the heating value of a combustor.SOLUTION: A fuel cell system comprises: a fuel cell stack 1; a fuel tank 61 for storing an ethanol aqueous solution as fuel containing oxygen and water; a combustor 41; a fuel supply device (a second fuel injector 72) for supplying the combustor 41 with the ethanol aqueous solution; an oxidant gas supply device (an air compressor 81 and a flow control valve 82) for supplying the combustor 41 with air as oxidant gas; and a controller 51. The controller 51 detects a concentration Cof the ethanol aqueous solution and then adjusts a ratio (an excess air ratio) of the air to the ethanol aqueous solution inside the combustor 41 in accordance with the concentration Cthus detected.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a fuel cell system using a water-containing oxygenated fuel as a raw fuel and a control method thereof.

  Patent Document 1 includes an exhaust gas combustor and a start-up combustor, and when the system is started, the start-up combustor is supplied with the city gas which is the raw fuel and air which is the oxidant gas. And a fuel cell system configured to heat the fuel cell stack via the heat exchanger while heating the evaporator and the reformer using the heat quantity (paragraphs 0033, 0055 to 0058). . Patent Document 1 further discloses controlling the supply amount of the raw fuel or the oxidant gas to the start-up combustor based on the temperature of any one of the fuel cell stack, the evaporator and the reformer. There is. Specifically, when the temperature of the evaporator or reformer is equal to or higher than a predetermined value, the amount of oxidant gas supplied to the start-up combustor is reduced, while the temperature of the evaporator or reformer is lower than the predetermined value. In some cases, the supply of oxidant gas to the start-up combustor is increased (eg, paragraphs 0078, 0079 and 0081).

JP, 2012-221933, A

  However, when using a water-containing oxygenated fuel represented by an aqueous ethanol solution as the raw fuel, the following problems occur. The water-containing oxygenated fuel has the property that its concentration decreases with the passage of time. When the concentration decreases, the adiabatic flame temperature in the combustion of the water-containing oxygenated fuel decreases, and the calorific value of the catalyst for promoting combustion, that is, the calorific value of the combustor decreases. As a result, the heating by the combustor becomes insufficient, and therefore, when the combustor is used for warming up at the system startup, the time required for the startup may be prolonged or it may be difficult to achieve the startup itself. I am concerned. In Patent Document 1, city gas is used as a raw fuel, and no mention is made of these problems caused by the decrease in the concentration of the water-containing oxygenated fuel.

  An object of the present invention is to provide a fuel cell system and its control method in consideration of the above problems.

  A fuel cell system according to an aspect of the present invention includes a fuel cell, a fuel reservoir storing a water-containing oxygenated fuel that is a raw fuel of the fuel cell, and a catalyst having a catalyst that promotes the combustion of the water-containing oxygenated fuel. , A fuel supply device connected to the fuel reservoir for supplying water-containing oxygenated fuel to the combustor, an oxidant gas supply device for supplying oxidant gas to the combustor, and water-containing oxygenated fuel for the combustor And a control unit that controls the supply of the oxidant gas. In the present embodiment, the control unit detects the concentration of the water-containing oxygenated fuel, and the ratio of the oxidant gas to the water-containing oxygenated fuel in the combustor according to the concentration detected by the concentration detecting unit. And a ratio adjusting unit for adjusting.

  The present invention provides, in another form, a method of controlling a fuel cell system.

  The water-containing oxygenated fuel has the property that its concentration decreases with the passage of time. According to the present invention, by adjusting the ratio of the oxidant gas to the water-containing oxygenated fuel in the combustor with respect to the concentration decrease, the decrease in adiabatic flame temperature due to the concentration decrease is suppressed, and the calorific value of the combustor Can be secured.

FIG. 1 is an explanatory view conceptually showing the configuration of a fuel cell system according to an embodiment of the present invention. FIG. 2 is a block diagram showing a specific example of the fuel cell system according to the above embodiment. FIG. 3 is an explanatory view showing an operating state of the fuel cell system at the time of start-up. FIG. 4 is an explanatory view showing an operation state of the above fuel cell system at the normal time. FIG. 5 is an explanatory view showing the relationship between the excess air ratio and the adiabatic flame temperature of ethanol. FIG. 6 is an explanatory view showing a change in adiabatic flame temperature according to the excess air ratio. FIG. 7 is a flow chart showing the flow of activation control according to an embodiment of the present invention. FIG. 8 is an explanatory view showing a change of the combustor temperature after the supply of the aqueous ethanol solution is started. FIG. 9 is an explanatory view showing the relationship between the combustor temperature and the oxygenated fuel concentration (the concentration of the aqueous ethanol solution). FIG. 10 is an explanatory view showing the relationship between the oxygenated fuel concentration and the stack output. FIG. 11 is an explanatory view showing the relationship between the elapsed time after stop and the amount of concentration change. FIG. 12 is an explanatory view showing the relationship between the oxygenated fuel concentration and the inlet / outlet temperature difference of the reformer. FIG. 13 is an explanatory view showing a configuration of a fuel cell system according to another embodiment of the present invention. FIG. 14 is an explanatory view showing an operating state of the fuel cell system at the time of start-up. FIG. 15 is an explanatory view showing an operation state of the above fuel cell system at the normal time.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(Overall configuration of fuel cell system)
FIG. 1 conceptually shows the configuration of a fuel cell system S according to an embodiment of the present invention.

  A fuel cell system (hereinafter referred to as “fuel cell system” and may be simply referred to as “system”) S according to the present embodiment includes a fuel cell stack 1, a fuel processing unit 2, an oxidant gas heating unit 3, A combustor 4 and a control unit 5 are provided.

  A fuel cell stack (hereinafter sometimes simply referred to as "stack") 1 is configured by stacking a plurality of fuel cells or fuel cell unit cells, and each fuel cell serving as a power source is, for example, a solid oxide type It is a fuel cell (SOFC). Fuel cell stack 1 includes, in an anode system, an anode gas passage 11 for supplying a fuel gas to the anode electrode of the fuel cell, and an anode off gas passage 11 exh for flowing an anode off gas after a power generation reaction discharged from the anode electrode. In FIG. 1, a cathode gas passage 12 for supplying an oxidant gas to the cathode electrode of the fuel cell in the cathode system, and a cathode off gas after power generation reaction discharged from the cathode electrode in the cathode system. And a cathode off gas passage 12 exh (not shown) for flowing the

  The fuel processing unit 2 processes a raw fuel which is a primary fuel, and generates a fuel gas used for a power generation reaction in a fuel cell. The fuel processor 2 is interposed in the anode gas passage 11, and receives the supply of raw fuel (arrow A1). The raw fuel is a water-containing oxygenated fuel, and in the present embodiment, an aqueous ethanol solution is employed. The fuel cell system S includes a fuel tank 6 in which an aqueous ethanol solution is stored. The fuel tank 6 is connected to the fuel cell stack 1 via the anode gas passage 11.

  The oxidant gas heating unit 3 is for heating the oxidant gas. The oxidant gas heating unit 3 is interposed in the cathode gas passage 12 and receives the supply of oxidant gas (arrow B). The oxidant gas is, for example, air, and oxygen used for a power generation reaction can be supplied to the cathode electrode by supplying air in the atmosphere to the cathode electrode of the fuel cell.

Here, the reaction involved in power generation at the anode and cathode of the solid oxide fuel cell can be represented by the following equation.
^{_{Anode: 2H 2 + 4O 2- → 2H}} 2 O + 4e - ... (1.1)
The ^{_{cathode: O 2 + 4e - → 2O}} 2- ... (1.2)

  The combustor 4 burns the raw fuel of the fuel cell to generate combustion gas. The combustor 4 receives supply of raw fuel from the fuel tank 6 (arrow A2) and also receives supply of oxidant gas (arrow C). The amount of heat generated by the combustion of the raw fuel or the amount of heat contained in the combustion gas can be supplied not only to the fuel cell stack 1 but also to the fuel processor 2 and the oxidant gas heater 3. FIG. 1 shows the transfer of heat from the combustor 4 to the fuel cell stack 1, the fuel processor 2 and the oxidant gas heater 3 by thick dotted lines.

  The control unit 5 controls the supply of the raw fuel and the oxidant gas to the fuel processing unit 2 and the oxidant gas heating unit 3 and controls the supply of the raw fuel and the oxidant gas to the combustor 4. The supply of the raw fuel to the combustor 4 is performed by the fuel supply device 7, and the fuel supply device 7 can be configured by a fuel injector. On the other hand, the supply of the oxidant gas to the combustor 4 is performed by the oxidant gas supply device 8, and the oxidant gas supply device 8 can be configured by an air compressor or a blower. The fuel supply device 7 and the oxidant gas supply device 8 operate in response to a command signal from the control unit 5 to supply a water-containing oxygenated fuel which is a raw fuel to the combustor 4 (arrow A2). Air, which is an oxidant gas, is supplied (arrow C).

  FIG. 2 shows a specific configuration of the fuel cell system S.

  The fuel cell system S includes a solid oxide fuel cell (SOFC) as a power source, and includes a fuel tank 61 that can be mounted on a vehicle. In the present embodiment, the raw fuel which is the primary fuel is a mixture of ethanol which is an oxygenated fuel and water, for example, an aqueous ethanol solution containing 45% by volume of ethanol. The fuel tank 61 and the fuel cell stack 1 are connected via the anode gas passage 11, and the evaporator 21, the fuel heat exchanger 22, and the reformer are connected to the anode gas passage 11 sequentially from the upstream side with respect to the flow direction. 23 are interspersed.

  On the other hand, a branch fuel passage 11sub branches from the anode gas passage 11 on the upstream side of the evaporator 21 and is connected to the combustor 41. A first fuel injector 71 is interposed in the anode gas passage 11 between the branch point of the branch fuel passage 11sub and the evaporator 21, and a second fuel injector 72 is interposed in the branch fuel passage 11sub. Thus, the flow of the raw fuel can be switched between the anode gas passage 11 and the branch fuel passage 11sub. The evaporator 21, the fuel heat exchanger 22, and the reformer 23 constitute the fuel processing unit 2 of the fuel cell system S, process the raw fuel, and generate the fuel gas of the fuel cell. The second fuel injector 72 constitutes a fuel supply device 7.

  The evaporator 21 receives a supply of an aqueous ethanol solution from a fuel tank 61, and heats and evaporates it to generate ethanol gas and water vapor.

  The fuel heat exchanger 22 receives the amount of heat generated by the combustion from the combustor 41 and heats the ethanol gas and the steam.

The reformer 23 incorporates a reforming catalyst, and generates hydrogen which is a fuel gas by steam reforming from ethanol which is an oxygenated fuel. Steam reforming can be represented by the following equation. Steam reforming is an endothermic reaction, and it is necessary to supply heat from the outside at the time of reforming. In the present embodiment, the remaining fuel in the anode off gas is burned by the combustor 41 also during reforming, and the heat generated by the combustion is supplied to the reformer 23.
C ₂ H ₅ OH + 3H ₂ O → 6H ₂ + 2CO ₂ (2)

  The oxidant gas heating unit 3 includes an air heat exchanger 31 and heats the oxidant gas flowing through the cathode gas passage 12 by heat exchange with the combustion gas supplied from the combustor 41 through the combustion gas passage 42. In the present embodiment, an air compressor 81 is installed near the open end of the cathode gas passage 12, and air in the atmosphere as the oxidant gas is drawn into the cathode gas passage 12 through the air compressor 81. The drawn air is heated from normal temperature (for example, 25 ° C.) when passing through the air heat exchanger 31, and is supplied to the fuel cell stack 1.

  The combustor 41 incorporates a combustion catalyst composed of three elements of Pt (platinum), Pd (palladium) and Rh (rhodium), receives supply of an aqueous ethanol solution through the branch fuel passage 11sub, and burns combustion gas by catalytic combustion of ethanol. Generate In the present embodiment, the combustor 41 and the evaporator 21 are connected via the combustion gas passage 42, and the evaporator 21 is heated by the heat amount of the combustion gas. On the other hand, the fuel heat exchanger 22 and the reformer 23 are accommodated in a case shared with the combustor 41 (indicated by a two-dot chain line L), and the heat quantity of the combustion gas is transferred to the fuel heat exchanger in the shared case L. 22 and to the reformer 23.

  In the present embodiment, the combustor 41 is connected to a passage (hereinafter referred to as “branch air passage”) 12sub branched from the cathode gas passage 12 on the downstream side of the air compressor 81, and flows to the branch air passage 12sub through the passage 12sub. A flow control valve 82 is provided to control the flow of oxidant gas (air). Further, the combustor 41 is connected to an anode off gas passage 11 exh and a cathode off gas passage 12 exh extending from the fuel cell stack 1. As a result, when the fuel cell system S starts up, the air compressor 81 is operated, and the flow control valve 82 is opened, whereby the oxidant gas can be supplied to the combustor 41 through the branch air passage 12sub. In the present embodiment, after the reformer 23 reaches the reformable temperature, the flow control valve 82 is closed to stop the supply of the oxidant gas through the branch air passage 12sub, and the combustor 41 receives the cathode. An oxidant gas (remaining oxygen in the anode off gas) is supplied through the off gas passage 12exh. The air compressor 81 and the flow control valve 82 constitute an oxidant gas supply device 8.

Here, the reaction of ethanol in the combustor 41 can be expressed by the following equation.
C ₂ H ₅ OH + 3 / 2O ₂ → 2CO ₂ + 3H ₂ O (3)

  The above equation (3) is an exothermic reaction.

  The power generated by the fuel cell stack 1 can be used to charge a battery or drive an external device such as an electric motor or a motor generator. For example, the fuel cell system S can be applied to a drive system for a vehicle, and charges the battery with the power generated by the rated operation of the fuel cell stack 1 and travels the power according to the target driving force of the vehicle from the battery Supply to the motor generator for

(Configuration of control system)
The controller 51 controls the operation of the first fuel injector 71, the second fuel injector 72, the air compressor 81, the flow control valve 82, and various devices or components used to operate the fuel cell system S. In the present embodiment, the controller 51 is configured as an electronic control unit, and includes a microcomputer including a central processing circuit, various storage devices such as a ROM and a RAM, an input / output interface, and the like.

  The controller 51 sets the supply amount of the raw fuel required for the rated operation of the fuel cell stack 1, in other words, the operation at the maximum power generation output, at the normal time after the system start-up. The fuel is supplied to the fuel cell system S through the first fuel injector 71.

  On the other hand, the controller 51 performs start-up control to warm up the entire fuel cell system S at the time of start-up of the fuel cell system S, and the fuel cell stack 1 which was at low temperature (for example, normal temperature) during stop. Raise to operating temperature. The operating temperature of the solid oxide fuel cell is about 800 to 1000 ° C., and in the present embodiment, the temperature of the fuel cell stack 1 to the fuel cell is raised to 600 to 700 ° C. by start control.

The controller 51, as the information relating to the start control signal from the stack temperature sensor 101 for detecting the stack temperature T _stk, signals from the combustor temperature sensor 102 for detecting the combustor temperature T _cmb, the reformer temperature T _ref Besides inputting the signal from the reformer temperature sensor 103 to be detected, the signal from the concentration sensor 104 to detect the concentration of water-containing oxygenated fuel (hereinafter sometimes referred to as “oxygenated fuel concentration”) C _fuel is also inputted .

The stack temperature T _stk is an index indicating the temperature of the fuel cell stack 1 or the fuel cell, and in the present embodiment, the stack temperature sensor 101 is installed near the cathode off gas outlet of the fuel cell stack 1 and detected by the stack temperature sensor 101 _Let the stack temperature T _stk be the stack temperature.

The combustor temperature T _cmb is the temperature of the combustor 41. In the present embodiment, the combustor temperature sensor 102 is installed in the combustion gas passage 42 on the downstream side of the combustor 41, and the temperature detected by the combustor temperature sensor 102, that is, the outlet temperature of the combustor 41 T _cmb . It is also possible to use the catalyst bed temperature instead of the outlet temperature of the combustor 41 as the combustor temperature T _cmb .

The reformer temperature T _ref is the temperature of the reformer 23. In the present embodiment, the reformer temperature sensor 103 is installed in the anode gas passage 11 on the downstream side of the reformer 23, and the temperature detected by the reformer temperature sensor 103 is set as the reformer temperature T _ref .

The oxygen-containing fuel concentration C _fuel is the concentration of the water-containing oxygenated fuel stored in the fuel tank 61, specifically, the aqueous ethanol solution. In the present embodiment, the concentration sensor 104 is directly installed in the fuel tank 61, and the concentration detected by the concentration sensor 104 is set as the oxygenated fuel concentration C _fuel . However, the concentration sensor 104 is not limited to this, and may be installed in the anode gas passage 11 upstream of the evaporator 21 or in the branch fuel passage 11sub upstream of the second fuel injector 72. Good.

(Description of fuel cell system operation)
3 and 4 show the operating state of the fuel cell system S, FIG. 3 shows the operating state at the time of startup of the fuel cell system S, and FIG. 4 shows the operating state at the normal time after system startup. There is. Of the anode and cathode channels, the channel through which the gas actually flows is indicated by a thick solid line, and the channel through which the gas flow is stopped is indicated by a thin dotted line.

  At the time of startup, the supply of the raw fuel through the first fuel injector 71 is stopped, and the raw fuel required for the warm-up of the fuel cell stack 1 is supplied to the combustor 41 through the second fuel injector 72 (FIG. 3). On the other hand, by operating the air compressor 81 and opening the flow control valve 82, the oxidant gas (air) is supplied to the combustor 41 through the branch air passage 12sub. The fuel heat exchanger 22 and the reformer 23 are heated by the amount of heat generated by the combustion of the raw fuel, and the combustion gas is supplied to the air heat exchanger 31 and the evaporator 21 through the combustion gas passage 42. Thereby, the evaporator 21, the fuel heat exchanger 22, the reformer 23, and the air heat exchanger 31 are heated, and the warm-up of the fuel cell system S is promoted.

  Under normal conditions, the raw fuel of normal supply amount required for rated operation of the fuel cell stack 1 is supplied to the fuel cell system S through the first fuel injector 71, and the fuel cell stack 1 is operated at rated output (FIG. 4) . On the other hand, the remaining fuel in the anode off gas is burned by the combustor 41, and the heat required for reforming is supplied to the reformer 23, and the combustion gas of the remaining fuel is supplied to the air heat exchanger 31 and the evaporator 21. , And maintain the entire fuel cell system S at a temperature required for operation.

  Here, in the present embodiment, the following problems are caused by using an aqueous ethanol solution as the raw fuel.

  The concentration of the water-containing oxygenated fuel represented by the aqueous ethanol solution decreases when it is allowed to stand. When the concentration decreases, the adiabatic flame temperature of the oxygenated fuel (ethanol) decreases, the calorific value of the combustor 41 decreases, and the heat transfer of the combustion gas also decreases, so that the heating by the combustor 41 becomes insufficient. Not only does it take a long time to start up the fuel cell system S, in some cases, it may be difficult to achieve the start up.

  Therefore, in the present embodiment, as part of the start control of the fuel cell system S, when the concentration of the water-containing oxygenated fuel decreases, the heat generation amount of the combustor 41 is increased by executing control to raise the adiabatic flame temperature. Maintain the startability of the fuel cell system S. Specifically, when the concentration of the aqueous ethanol solution stored in the fuel tank 61 decreases, the ratio of the air in the combustor 41 to the aqueous ethanol solution, that is, the excess air ratio λ in the combustor 41 is adjusted.

FIG. 5 shows the relationship between the excess air ratio λ and the adiabatic flame temperature _{Taft of} ethanol. As shown in the figure, the adiabatic flame temperature _Taft has a different tendency to change with respect to the excess air ratio λ at the excess air ratio λ = 1, and when the excess air ratio λ is less than 1, the air While there is a tendency to increase as the excess rate λ increases, if the air excess rate λ is 1 or more, it tends to increase as the air excess rate λ decreases. FIG. 5 shows the relationship when 45% by volume ethanol aqueous solution is adopted, but the tendency of the change of the adiabatic flame temperature _Taft bordering on the excess air ratio λ = 1 is a concentration other than 45% by volume or The same applies to the case where another kind of water-containing oxygenated fuel is employed.

FIG. 6 shows the change in the adiabatic flame temperature _Taft when the concentration C _{fuel of the} aqueous ethanol solution decreases, when the excess air ratio λ is less than 1 (a) and when the excess air ratio λ is 1 or more (b) It shows about each of. In the figure, the dotted line shows the characteristic line before the concentration C _fuel decreases, and the solid line shows the characteristic line after the concentration C _fuel decreases.

When the concentration C _{fuel of the} aqueous ethanol solution decreases, the adiabatic flame temperature T _aft decreases. _Therefore , the target adiabatic flame temperature T _afttrg can not be achieved while maintaining the excess air ratio λ 0. Insufficient heat is generated. Here, the adiabatic flame temperature T _aft is raised by adjusting the excess air ratio λ, but in order to achieve the target adiabatic flame temperature T _afttrg regardless of a decrease in the concentration C _fuel , the excess air ratio λ is 1 In the case of less than 1, as shown in FIG. 6A, it is necessary to increase the excess air ratio λ to λ1a larger than λ0, and in the case where the excess air ratio λ is 1 or more, FIG. As shown, it is necessary to reduce the excess air ratio λ to λ 1 b which is smaller than λ 0. That is, the excess air ratio λ is adjusted to be close to 1 with respect to the decrease in the concentration C _fuel of the aqueous ethanol solution, in other words, the excess air ratio λ is set to 1 when the excess air ratio λ is smaller than 1. To increase the adiabatic flame temperature _Taft by securing the excess air ratio λ to 1 when the excess air ratio λ is larger than 1, and to secure the calorific value of the combustor 41. Is possible.

  The start control of the fuel cell system S will be specifically described below with reference to the flowchart.

(Description of start control)
FIG. 5 is a flowchart showing the basic flow of start control of the fuel cell system S according to the present embodiment.

  The controller 51 is programmed to execute start control of the fuel cell system S according to the procedure shown in the flowchart of FIG. 7 when the start request signal is input from the start switch 105 based on the operation of the start switch 105 by the driver. . The controller 51 starts the start control in response to the input of the start request signal, and ends the determination that the fuel cell stack 1 or the fuel cell has been warmed up.

In S101, various sensor outputs related to start control are read. Specifically, stack temperature T _stk, combustor temperature T _cmb, the reformer temperature T _ref and oxygenated fuel concentration C _Fuel load.

  In S102, a basic value (hereinafter referred to as a "basic air excess rate") λ0 of the air excess rate λ in the fuel tank 41 is set. The basic air excess rate λ0 takes different values depending on the type or function of the catalyst provided in the combustor 41, and is set to a value larger than 1 when the catalyst is for combustion, for example. On the other hand, for example, when the catalyst is for reforming, setting to a value smaller than 1 is permitted. In the present embodiment, since the combustor 41 including the combustion catalyst is targeted, the basic air excess rate λ0 is set to a value larger than one.

In S103, based on the signal from the concentration sensor 104, the oxygen-containing fuel concentration C _fuel is detected.

In S104, it is determined whether the oxygen-containing fuel concentration C _fuel is lower than a predetermined value C _fuel 1 or not. That is, it is determined whether or not the concentration C _fuel of the aqueous ethanol solution has decreased enough to cause an excessively long time required for warming up the fuel cell system S. The predetermined value C _fuel 1 is set to a value smaller than a specified value (for example, 45% by volume) of the oxygen-containing fuel concentration. If the oxygen-containing fuel concentration C _fuel is lower than the predetermined value C _fuel 1, the process proceeds to S 105 to execute the adjustment of the excess air ratio λ, and when it is the predetermined value C _fuel 1 or more, the adjustment of the excess air ratio λ The basic air excess rate λ0 is maintained without performing the process, and the process proceeds to S108.

In S105, it is determined whether the basic air excess rate λ0 is less than one. As described above, the tendency of the change of the adiabatic flame temperature _Taft to the excess air ratio λ differs depending on whether the excess air ratio λ is less than 1 or greater than or equal to 1.

In S106, correction is performed to increase the excess air ratio λ. Specifically, the actual from oxygenated fuel concentration C _Fuel calculates the estimated arrival value T _Aftest adiabatic flame temperature, the difference DEF target value T _Afttrg adiabatic flame temperature and the estimated arrival value _T aftest (= T afttrg - A correction amount Δλa (= f (DEF)) according to T _aftest ) is added to the basic air excess ratio λ0 (λ1a = λ0 + Δλa). The estimated ultimate value T _aftest of the adiabatic flame temperature can be calculated by a calculation formula that models the combustion reaction of the aqueous ethanol solution, and the relational expression f between the difference DEF and the correction amount Δλa is approximate by fitting through experiments etc. It is possible to ask for By creating table data in which the correction amount Δλa is allocated to the oxygenated fuel concentration C _fuel and storing it in the controller 51 in advance, this table data is referred to by the oxygenated fuel concentration C _{fuel in} actual operation. You may do so. The correction amount Δλa in the case where the excess air ratio λ is less than 1 tends to increase with the decrease in the concentration C _fuel , and the excess air ratio λ1a after correction approaches 1.

In S107, correction is performed to reduce the excess air ratio λ. As in S106, the correction amount Δλb corresponding to the difference DEF between the target value T _afttrg of the adiabatic flame temperature and the estimated arrival value T _aftest is calculated, but the correction amount Δλ b is calculated from the basic air excess rate λ 0 for the decrease correction. Subtract (λ 1 b = λ 0 −Δλ b). It is recommended to create table data in which the correction amount Δλb is allocated to the oxygen-containing fuel concentration C _fuel and store in advance in the controller roller 51. The correction amount Δλb (> 0) when the excess air ratio λ is 1 or more Similarly to the correction amount Δλa, it tends to increase with the decrease of the concentration C _fuel , and is reduced from the basic air excess rate λ0, thereby bringing the corrected air excess rate λ1b closer to one.

  In S108, the supply amount (fuel supply amount) Qf of the raw fuel is calculated according to the excess air ratio λ1 (λ1a, λ1b) after correction.

In S109, with respect to the fuel supply amount Qf, the supply amount (air supply amount) Qa of the oxidant gas capable of achieving the excess air ratio λ1 after correction is calculated. In the present embodiment, the adjustment of the excess air ratio λ with respect to the decrease of the oxygenated fuel concentration C _fuel is achieved by changing the air supply amount Qa. Specifically, the air supply amount Qa is increased when the increase correction is performed on the excess air ratio λ, and is decreased when the decrease correction is performed. Then, in order to increase the air supply amount Qa, the rotational speed of the air compressor 81 is increased or the opening degree of the flow control valve 82 is increased. However, it is also possible to adjust the excess air ratio λ by changing the fuel supply amount Qf or simultaneously changing the air supply amount Qa and the fuel supply amount Qf.

In S110, it is determined whether the warm-up of the fuel cell stack 1 is completed. Specifically, when the stack temperature T _stk it is determined whether or not has reached a predetermined temperature T _Stkwup for determining the completion of warming up, the stack temperature T _stk has reached the predetermined temperature T _Stkwup, the fuel cell system _Assuming that warm-up of S is completed, start-up control is terminated, and if the predetermined temperature T _stkwup is not reached, start-up control is continued as warm-up is not yet completed, and stack temperature T _stk is continuously monitored. . When the start control is finished, the normal control is executed according to another routine not shown to operate the fuel cell stack 1 at the rated output. Here, when the reformer 23 (specifically, the reforming catalyst included in the reformer 23) reaches the reformable temperature before the warm-up of the fuel cell system S is completed, the first fuel is Supply of the raw fuel through the injector 71 is started, and fuel cell (hydrogen) and oxidant gas are supplied to the fuel cell stack 1 to cause the fuel cell stack 1 to start power generation. Thus, the fuel cell stack 1 is heated using the oxidant gas as a medium, and the warm-up of the entire fuel cell system S is promoted by power generation.

  In the present embodiment, the fuel tank 61 is a "fuel storage device", the combustor 41 is a "combustor", the second fuel injector 72 is a "fuel supply device", and the air compressor 81 is an "oxidant gas supply device" The controller 51 configures the "control unit". Then, among the processes performed by the controller 51 regarding activation control, the process of S103 shown in FIG. 7 corresponds to the function of the “density detection unit”, and the processes of S104 to S107 correspond to the function of the “ratio adjustment unit”.

(Description of function and effect)
The fuel cell system S according to the present embodiment is configured as described above, and the operation and effects obtained by the present embodiment will be described below.

First, in the present embodiment, an aqueous ethanol solution, which is a water-containing oxygenated fuel, is stored in the fuel tank 61. Here, the concentration of the aqueous ethanol solution (oxygen-containing fuel concentration C _fuel ) has a property of changing with the passage of time. On the other hand, the oxygen-containing fuel concentration C _fuel is detected, and the ratio of the oxidant gas to the water-containing oxygen-containing fuel in the combustor 41 with respect to the decrease in the oxygen-containing fuel concentration C _fuel , that is, the excess air ratio λ is adjusted. Thus, it is possible to suppress the decrease in adiabatic flame temperature _Taft and maintain the calorific value of the combustor 41 as much as possible. As a result, the adiabatic flame temperature T _afttrg can be made close to the target value to obtain the necessary amount of heat generation of the combustor 41, and the _startability of the fuel cell system S can be secured.

Second, the tendency of the adiabatic flame temperature T _aft to change changes according to the excess air ratio λ, specifically, changes at 1 which indicates the equivalent. Therefore, in adjusting the excess air ratio λ, the adiabatic flame temperature _Taft is surely increased and the calorific value of the combustor 41 is secured regardless of the excess air ratio λ by making the ratio close to 1. Can.

  Thirdly, when adjusting the excess air ratio λ, the fuel supply device (second fuel injector 72) or the oxidant gas supply device (air compressor 81) supplies the supply amounts Qf and Qa of the aqueous ethanol solution or air to the combustor 41. By changing the ratio, the excess air ratio λ can be easily adjusted.

Fourth, the provision of the density sensor 104 for detection of oxygenated fuel concentration C _Fuel, it is possible to accurately detect the oxygenated fuel concentration C _Fuel.

(Description of Other Embodiments)
In the above description, it established the density sensor 104 for detection of oxygenated fuel concentration C _Fuel, and the oxygenated fuel concentration C _Fuel and be directly detected by the concentration sensor 104. However, the present invention is not limited to this, and the oxygenated fuel concentration C _fuel can be indirectly detected or estimated based on the behavior of the combustor 41, the reformer 23 or the fuel cell stack 1 with respect to the supply of the water-containing oxygenated fuel. It is.

FIG. 8 shows the change with time t of the combustor temperature T _cmb after the supply of the aqueous ethanol solution is started, and FIG. 9 shows the relationship between the combustor temperature T _cmb and the oxygenated fuel concentration C _fuel .

As shown in FIG. 8, the change of the combustor temperature T _cmb with respect to time t, specifically, the gradient of the change and the temperature after reaching the equilibrium point ( _final temperature) are adiabatic flames according to the oxygenated fuel concentration C _fuel the difference in temperature varies depending on oxygenated fuel concentration C _fuel, small slope changes as at low oxygenated fuel concentration C _fuel, having reached the temperature also becomes low tendency. FIG. 8 shows the combustor temperature Tcmb when the oxygen-containing fuel concentration C _fuel is high (C _fuel 0) by a thick solid line, and the combustor temperature T _cmb when it is low (C _fuel 1) by a thin solid line. . Therefore, the combustion at time t1 after time t0 after the supply of the water-containing oxygenated fuel to the combustor 41 is started by grasping the relationship between the combustor temperature T _cmb and the oxygen-containing fuel concentration C _{fuel in} advance through experiments etc. It is possible to estimate the oxygen-containing fuel concentration C _fuel based on the unit temperatures T _cmb 0 and T _cmb 1.

By creating table data of the tendency shown in FIG. 9 and storing it in the controller 51 in advance, this table data is referred to by the combustor temperature T _cmb at time t1 in actual operation, and the oxygenated fuel concentration C _fuel Estimate In the present embodiment, the function of the “temperature detection unit” is realized by the processing of the controller 51 that detects the combustor temperature T _cmb .

According to this embodiment, the oxygen-containing fuel concentration C _fuel can be detected without using a dedicated component such as a concentration sensor.

FIG. 10 shows the relationship between the oxygenated fuel concentration C _fuel and the output P _stk of the combustion cell stack 1.

In the reformer 23, fuel gas is generated by steam reforming of ethanol which is an oxygenated fuel. Here, the steam reforming becomes dominant as the concentration of the aqueous ethanol solution is lower, in other words, as the water content of the water-containing oxygenated fuel increases, and more fuel gas (specifically, hydrogen) is generated. Tend to If the amount of fuel gas is large, the output of the fuel cell stack 1 also increases accordingly, the output of the fuel cell stack 1 (hereinafter sometimes referred to as “stack output”) P _stk is correlated with the concentration of the aqueous ethanol solution Have. In a state where a predetermined amount of aqueous ethanol solution is supplied to the reformer 23, obtain the relationship between the oxygen-containing fuel concentration C _fuel and the stack output P _stk and store it in the controller 51 in advance as table data. Then, it is possible to estimate the oxygen-containing fuel concentration C _fuel based on the stack output P _stk during the operation of the fuel cell stack 1.

Here, at the system startup, unlike the normal time after startup, the temperature of the reformer 23 is low, so the steam reforming does not proceed well, and the fuel cell stack 1 itself is also at a low temperature. Taking this into consideration, the oxygen-containing fuel concentration C _fuel before the previous system shutdown is detected from the stack output P _stk, and this is determined by the decrease ΔC of the concentration C _fuel according to the elapsed time Δt after the previous system shutdown. By correcting (C _fuel = C _fuel −ΔC), it is possible to detect the oxygen-containing fuel concentration C _fuel at the current system startup. In this embodiment, the functions of the “output detection unit” and the “time measurement unit” are realized by the processing of the controller 51 that detects the stack output _Pstk and measures the elapsed time Δt.

  FIG. 11 shows the relationship between the elapsed time Δt after stopping the system and the concentration change amount ΔC.

  The concentration change amount ΔC tends to increase as a longer time after system stoppage.

Thus, based on the stack output P _stk before the previous system stop and the elapsed time Δt after the previous system stop, the oxygen-containing fuel concentration C _fuel is detected without using a dedicated component such as a concentration sensor can do.

FIG. 12 shows the relationship between the oxygenated fuel concentration C _fuel and the inlet / outlet temperature difference ΔT _ref of the reformer 23.

In the steam reforming reaction of ethanol generated in the reformer 23, the endothermic reaction and the exothermic reaction proceed simultaneously. The reaction generated in the reformer 23 can be represented by the following formulas (4.1) to (4.7). Here, although which of the endothermic reaction and the exothermic reaction is dominant depends on the conditions, when the endothermic reaction is dominant, the outlet temperature T _ref of the reformer 23 decreases, and the temperature difference between the inlet and outlet (Hereinafter referred to as "inlet / outlet temperature difference") ΔT _ref is expanded. On the other hand, when the exothermic reaction is dominant, the outlet temperature T _ref of the reformer 23 rises and the inlet / outlet temperature difference ΔT _ref decreases. Thus, the inlet / outlet temperature difference ΔT _ref of the reformer 23 has a correlation with the concentration C _fuel of the water-containing oxygenated fuel.
C ₂ H ₅ OH + 3H ₂ O → 6H ₂ + 2CO ₂ (4.1)
C ₂ H ₅ OH → CH ₃ CHO + H ₂ (4.2)
CH ₃ CHO → CH ₄ + CO (4.3)
_{CH 3 CHO + H 2 O →} 3H 2 + 2CO ... (4.4)
CO + H ₂ O ⇔ CO ₂ + H ₂ ... (4.5)
C ₂ H ₅ OH → C ₂ H ₄ + H ₂ O (4.6)
CH ₄ + H ₂ O ⇔ 3H ₂ + CO (4.7)

FIG. 12 shows the relationship between the concentration C _{fuel of the} aqueous ethanol solution and the temperature difference ΔT _ref of the reformer 23.

The difference in inlet / outlet temperature difference ΔT _ref of the reformer 23 tends to increase because the outlet temperature T _ref decreases as the steam reforming reaction becomes dominant as the oxygen-containing fuel concentration C _fuel decreases. . The table data of the tendency shown in FIG. 12 is created and stored in the controller 51 in advance.

Then, at the time of system startup, the temperature T _ref of the reformer 23 is low, and the steam reforming reaction does not proceed well even if the water content is sufficient, so the previous system stop from the inlet / outlet temperature difference ΔT _ref By detecting the oxygen-containing fuel concentration C _fuel before and correcting it with the decrease ΔC of the concentration C _fuel according to the elapsed time Δt after the previous system shutdown, the oxygen-containing fuel at the current system startup time The concentration C _fuel is detected. In the present embodiment, the functions of the “temperature difference detection unit” and the “time measurement unit” are realized by the processing of the controller 51 that detects the inlet / outlet temperature difference ΔT _ref and measures the elapsed time Δt.

Thus, based on the inlet / outlet temperature difference ΔT _ref of the reformer 23 before the previous system shutdown and the elapsed time Δt after the previous system shutdown, the oxygenated fuel concentration C _{fuel is set} to Can be detected independently of

  In the above description, the combustor 41 is regarded as a "combustor", and the fuel processing unit 2 (the evaporator 21, the fuel heat exchanger 22, the reformer) is generated by the amount of heat generated by combustion of the raw fuel or the amount of heat possessed by the combustion gas. 23) The air heat exchanger 31 is heated, and the fuel cell stack 1 is heated to promote the warm-up of the entire fuel cell system S. However, the invention is not limited to this, and it is also possible to position the reformer 23 as a "combustor". For example, at the time of system startup, an aqueous ethanol solution and air are supplied to the reformer 23, and the calorific value is obtained by the reaction of the two on the reforming catalyst to raise the temperature of the reformer 23 or the reforming catalyst. It is

  13 to 15 show an example in that case.

  FIG. 13 shows the configuration of a fuel cell system S1 according to another embodiment of the present invention, FIG. 14 shows the operation state of the fuel cell system S1 at system startup, and FIG. It shows the operating state at the time.

To explain mainly the difference from the system S (FIG. 2) according to the previous embodiment, as shown in FIG. 13, in the present embodiment, it is connected to the combustor 41 as a passage branching from the cathode gas passage 12. In addition to the first branch air passage 12suba, a second branch air passage 12subb connected to the reformer 32 is provided, and in the second branch air passage 12subb, the flow rate of oxidant gas (air) flowing through the passage 12subb is adjusted. A flow control valve (second flow control valve) 83 for the purpose is provided. Thereby, as shown in FIG. 14, when the fuel cell system S1 starts up, air is supplied not only to the combustor 41 but also to the reformer 32, and the calorific value due to the reaction between ethanol and oxygen is obtained, In combination with the heating by the combustion gas supplied from the combustor 41, it is possible to achieve quicker temperature rise of the reformer 23. Here, as in the previous embodiment, when the concentration C _fuel of the aqueous ethanol solution is detected and this is lower than the predetermined value C _fuel 1 and the prolongation of the time required for starting is predicted, the combustor 41 and The excess air ratio λ in the reformer 23 is adjusted. In the present embodiment, the basic excess air ratio λ0 is set to a value larger than 1 for the combustor 41, and the excess air ratio λ is decreased to increase the adiabatic flame temperature _Taft with respect to the decrease in the concentration C _fuel. Let On the other hand, for the reformer 23, the basic air excess rate λ0 is set to a value smaller than 1, and the air excess rate λ is increased to increase the adiabatic flame temperature _Taft . Then, after the fuel cell system S is completely warmed up, as shown in FIG. 15, the supply of air to the combustor 41 and the reformer 23 through the first and second branch air passages 12suba and 12subb is stopped. The reformed fuel gas (hydrogen) is supplied to the fuel cell stack 1 through the anode gas passage 11 and the air after heating is supplied through the cathode gas passage 12.

  In the present embodiment, the first fuel injector 71 and the second fuel injector 72 constitute a "fuel supply device", and the air compressor 81, the first flow control valve 82 and the second flow control valve 83 are "oxidizer gas supply device Configure

  As mentioned above, although embodiment of this invention was described, the said embodiment showed only a part of application example of this invention, and limits the technical scope of this invention to the specific structure of the said embodiment. It is not the purpose. Various changes and modifications can be made to the above embodiment within the scope of the claims.

S ... fuel cell system 1 ... fuel cell stack 2 ... fuel processing unit 21 ... evaporator 22 ... fuel heat exchanger 23 ... reformer 3 ... oxidant gas heating unit 31 ... air heat exchanger 4, 41 ... combustor 5 , 51 ... controller (control unit)
6, 61 ... fuel tank (fuel storage unit)
DESCRIPTION OF SYMBOLS 7 ... Fuel supply apparatus 71 ... 1st fuel injector 72 ... 2nd fuel injector 8 ... Oxidizer gas supply apparatus 81 ... Air compressor 82 ... Flow control valve (1st flow control valve)
83 ... 2nd flow control valve 11 ... anode gas passage 12 ... cathode gas passage

Claims (11)

With fuel cells,
A fuel reservoir for storing a water-containing oxygenated fuel which is a raw fuel of the fuel cell;
A combustor having a catalyst that promotes the combustion of the water-containing oxygenated fuel;
A fuel supply device connected to the fuel reservoir for supplying the water-containing oxygenated fuel to the combustor;
An oxidant gas supply device for supplying an oxidant gas to the combustor;
A control unit that controls the supply of the water-containing oxygenated fuel and the oxidant gas to the combustor;
A fuel cell system comprising
The control unit
A concentration detection unit that detects the concentration of the water-containing oxygenated fuel;
A ratio adjustment unit configured to adjust a ratio of the oxidant gas to the water-containing oxygenated fuel in the combustor according to the concentration detected by the concentration detection unit;
A fuel cell system comprising: The ratio adjusting unit increases the ratio when the ratio is smaller than 1 in terms of equivalent ratio conversion with respect to the decrease in the concentration of the water-containing oxygenated fuel, and the ratio is larger than 1 in equivalent ratio conversion Decreases the ratio to bring the ratio closer to 1 in terms of equivalent ratio,
The fuel cell system according to claim 1. The ratio adjusting unit controls the operation of the fuel supply device or the oxidant gas supply device to adjust the ratio.
The fuel cell system according to claim 1. The concentration detection unit includes a concentration sensor disposed to be able to detect the concentration of the water-containing oxygenated fuel supplied to the combustor.
The fuel cell system according to any one of claims 1 to 3. The control unit further includes a temperature detection unit that detects a temperature of the combustor.
The concentration detection unit detects the concentration of the water-containing oxygenated fuel based on the temperature detected by the temperature detection unit after starting the supply of the water-containing oxygenated fuel to the combustor.
The fuel cell system according to any one of claims 1 to 3. The fuel cell system according to any one of claims 1 to 3, further comprising a reformer that generates a fuel gas of the fuel cell by processing the water-containing oxygenated fuel.
The control unit further includes an output detection unit that detects an output of the fuel cell,
The concentration detection unit detects the concentration of the water-containing oxygenated fuel based on the output detected by the output detection unit.
Fuel cell system. The control unit further includes a time measurement unit that measures an elapsed time from the previous system stop to the current start,
The concentration detection unit is configured to receive the water-containing oxygenated fuel based on an output detected by the output detection unit before the previous system stop and a lapse time measured by the time measurement unit at the time of system startup. To detect the concentration of
The fuel cell system according to claim 6. The fuel cell system according to any one of claims 1 to 3, further comprising a reformer that generates a fuel gas of the fuel cell by processing the water-containing oxygenated fuel.
The control unit further includes a temperature difference detection unit that detects a temperature difference between the inlet and outlet of the reformer as the inlet and outlet temperature difference,
The concentration detection unit detects the concentration of the water-containing oxygenated fuel based on the inlet / outlet temperature difference detected by the temperature difference detection unit.
Combustion cell system. The control unit further includes a time measurement unit that measures an elapsed time from the previous system stop to the current start,
The water concentration detector detects the water based on an inlet / outlet temperature difference detected by the temperature difference detector before the previous system stop at the time of system startup and an elapsed time measured by the time measuring unit. Detect the concentration of oxygen-containing fuel
The fuel cell system according to claim 8. The water-containing oxygenated fuel is an aqueous ethanol solution,
The fuel cell system according to any one of claims 1 to 9. A control method of a fuel cell system, which controls a fuel cell system for supplying a fuel cell with a fuel gas generated by processing of a water-containing oxygenated fuel, comprising:
At the start of the fuel cell system,
Burning the water-containing oxygenated fuel on a catalyst;
Warming up the fuel cell system using the combustion gas generated by the combustion as a heat source,
Detecting the concentration of the water-containing oxygenated fuel;
The ratio of the oxidant gas to be supplied to the combustion to the water-containing oxygenated fuel is adjusted according to the concentration of the water-containing oxygenated fuel.
Control method of fuel cell system.

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