JP7087341B2 - Fuel cell system and fuel cell system control method - Google Patents

Description

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

Patent Document 1 includes an exhaust gas combustor and a start-up combustor, and supplies city gas as a raw material and air as an oxidant gas to the start-up combustor when the system is started, and is generated by combustion of the raw material and fuel. A fuel cell system configured to heat an evaporator and a reformer using the amount of heat generated and to heat a fuel cell stack via a heat exchanger is disclosed (paragraphs 0033, 0055 to 0058). .. Patent Document 1 further discloses that the supply amount of raw fuel or oxidant gas to a starting combustor is controlled based on the temperature of any 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 the predetermined value, the supply amount of the oxidant gas to the starting 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 starting combustor is increased (eg, paragraphs 0078, 0079 and 0081).

Japanese Unexamined Patent Publication No. 2012-221933

However, when a water-containing oxygen-containing fuel typified by an aqueous ethanol solution is used as the raw material, the following problems arise. The water-containing oxygen-containing 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 oxygen-containing fuel decreases, and the calorific value of the catalyst for promoting combustion, that is, the calorific value of the combustor decreases. This causes a shortage of heating by the combustor, so when the combustor is used for warming up at system startup, the time required for startup may be prolonged or it may be difficult to achieve startup itself. I am concerned. Patent Document 1 uses city gas as a raw material, and does not mention any of these problems caused by a decrease in the concentration of water-containing oxygen-containing fuel.

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

The fuel cell system according to one embodiment of the present invention includes a fuel cell, a fuel reservoir for storing water-containing oxygen-containing fuel which is a raw material of the fuel cell, and a catalyst for promoting combustion of the water-containing oxygen-containing fuel. A fuel supply device connected to a container and a fuel reservoir to supply water-containing oxygen-containing fuel to the combustor, an oxidant gas supply device to supply the oxidant gas to the combustor, and a water-containing oxygen-containing fuel to the combustor. And a control unit that controls the supply of the oxidant gas. In the present embodiment, the control unit determines the ratio of the oxidant gas to the water-containing oxygen-containing fuel in the combustor and the concentration detection unit that detects the concentration of the water-containing oxygen-containing fuel stored in the fuel reservoir. It is provided with a ratio adjusting unit that adjusts according to the concentration detected by.

The present invention provides, in other embodiments, a method of controlling a fuel cell system.

The water-containing oxygen-containing 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 oxygen-containing fuel in the combustor with respect to the decrease in concentration, the decrease in the adiabatic flame temperature due to the decrease in concentration is suppressed, and the calorific value of the combustor is generated. Can be secured.

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

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.

The 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, and an oxidant gas heating unit 3. It includes a combustor 4 and a control unit 5.

The fuel cell stack (hereinafter, may be simply referred to as “stack”) 1 is configured by stacking a plurality of fuel cells or fuel cell unit cells, and each fuel cell as a power source is, for example, a solid oxide type. It is a fuel cell (SOFC). In the anode system, the fuel cell stack 1 has an anode gas passage 11 for supplying fuel gas to the anode electrode of the fuel cell and an anode off gas passage 11exh for flowing the anode off gas after the power generation reaction discharged from the anode electrode. In the cathode system, the cathode gas passage 12 for supplying the oxidizing agent gas to the cathode electrode of the fuel cell and the cathode off gas after the power generation reaction discharged from the cathode electrode are provided. It is provided with a cathode off gas passage 12ex (not shown) for flowing the fuel.

The fuel processing unit 2 processes the raw fuel, which is the primary fuel, to generate the fuel gas used for the power generation reaction in the fuel cell. The fuel processing unit 2 is interposed in the anode gas passage 11 and receives the supply of raw fuel (arrow A1). The raw material is a water-containing oxygen-containing fuel, and in this embodiment, an aqueous ethanol solution is adopted. 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 the oxidant gas (arrow B). The oxidant gas is, for example, air, and by supplying air in the atmosphere to the cathode electrode of the fuel cell, oxygen used for the power generation reaction can be supplied to the cathode electrode.

Here, the reaction related to power generation at the anode electrode and the cathode electrode of the solid oxide fuel cell can be expressed by the following equation.
Anode pole: 2H ₂ + 4O ^2- → 2H ₂ O + 4e-... ⁽ 1.1)
Cathode pole: O ₂ + ^4e- → 2O ^2- … (1.2)

The combustor 4 burns the raw fuel of the fuel cell to generate a combustion gas. The combustor 4 is supplied with raw fuel from the fuel tank 6 (arrow A2) and is supplied with 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 processing unit 2 and the oxidant gas heating unit 3. FIG. 1 shows the transfer of heat from the combustor 4 to the fuel cell stack 1, the fuel processing unit 2, and the oxidant gas heating unit 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 also controls the supply of the raw fuel and the oxidant gas to the combustor 4. The supply of raw fuel to the combustor 4 is executed by the fuel supply device 7, and the fuel supply device 7 can be configured by the 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 oxygen-containing fuel as a raw material to the combustor 4 (arrow A2). Air is supplied as an oxidant gas (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 a fuel tank 61 that can be mounted on a vehicle. In the present embodiment, the raw material as the primary fuel is a mixture of ethanol as an oxygen-containing 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 to each other via the anode gas passage 11, and the anode gas passage 11 has an evaporator 21, a fuel heat exchanger 22, and a reformer in order from the upstream side with respect to the flow direction. 23 is intervening.

On the other hand, a branched 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. The first fuel injector 71 is interposed in the anode gas passage 11 between the branch point of the branched fuel passage 11sub and the evaporator 21, and the second fuel injector 72 is interposed in the branched fuel passage 11sub. This makes it possible to switch the flow of raw fuel between the anode gas passage 11 and the branched 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 raw fuel, and generate fuel gas for the fuel cell. The second fuel injector 72 constitutes the fuel supply device 7.

The evaporator 21 receives a supply of an aqueous ethanol solution from the fuel tank 61, heats it to evaporate it, and produces ethanol gas and steam.

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

The reformer 23 has a built-in reforming catalyst and generates hydrogen, which is a fuel gas, from ethanol, which is an oxygen-containing fuel, by steam reforming. Steam reforming can be expressed by the following equation. Steam reforming is an endothermic reaction, and it is necessary to supply heat from the outside during reforming. In the present embodiment, the combustor 41 burns the residual fuel in the anode off-gas even during reforming, and the amount of 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 is composed of 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, the air compressor 81 is installed near the open end of the cathode gas passage 12, and air in the atmosphere as an oxidant gas is sucked into the cathode gas passage 12 through the air compressor 81. The sucked air is heated from room temperature (for example, 25 ° C.) as it passes through the air heat exchanger 31 and is supplied to the fuel cell stack 1.

The combustor 41 has a built-in combustion catalyst composed of three elements of Pt (platinum), Pd (palladium) and Rh (lodium), is supplied with an ethanol aqueous solution through the branched fuel passage 11sub, and is a combustion gas by catalytic combustion of ethanol. To 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 amount of heat possessed by the combustion gas. On the other hand, the fuel heat exchanger 22 and the reformer 23 are housed in a case shared with the combustor 41 (indicated by the two-point chain line L), and the calorific value of the combustion gas is inside the shared case L. It is configured to be transmitted to 22 and the reformer 23.

In the present embodiment, the combustor 41 is connected to a passage (hereinafter referred to as “branched air passage”) 12sub that branches from the cathode gas passage 12 on the downstream side of the air compressor 81, and flows through the passage 12sub in the branched air passage 12sub. A flow control valve 82 for adjusting the flow rate of the oxidant gas (air) is installed. Further, the combustor 41 is connected to an anode off-gas passage 11ex and a cathode off-gas passage 12ex extending from the fuel cell stack 1. Thereby, when the fuel cell system S is started, the air compressor 81 is operated and the flow control valve 82 is opened, so that the oxidant gas can be supplied to the combustor 41 through the branched air passage 12sub. In the present embodiment, after the reformer 23 reaches the reformable temperature, the flow control valve 82 is closed, the supply of the oxidant gas through the branched air passage 12sub is stopped, and the cathode is directed to the combustor 41. Oxidizing agent gas (residual oxygen in the anode off-gas) is supplied through the off-gas passage 12ex. The air compressor 81 and the flow rate 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 generated power of the fuel cell stack 1 can be used to charge the 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, charges the battery with the electric power generated by the rated operation of the fuel cell stack 1, and runs the electric power corresponding to the target driving force of the vehicle from the battery. Supply to the motor generator for.

(Control system configuration)
The operation of the first fuel injector 71, the second fuel injector 72, the air compressor 81, the flow control valve 82, and other various devices or parts used for operating the fuel cell system S is controlled by the controller 51. In the present embodiment, the controller 51 is configured as an electronic control unit, and includes a central arithmetic circuit, various storage devices such as ROM and RAM, an input / output interface, and the like.

The controller 51 sets the rated operation of the fuel cell stack 1 in the normal time after the system is started, in other words, the supply amount of the raw fuel required for the operation at the maximum power output, and uses the raw material of the normal supply amount as the raw fuel. It is supplied to the fuel cell system S through the first fuel injector 71.

On the other hand, the controller 51 executes start control for warming up the entire fuel cell system S when the fuel cell system S is started, and puts the fuel cell stack 1 which was at a low temperature (for example, normal temperature) during the stoppage. Raise the temperature to the 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 or the fuel cell is raised to 600 to 700 ° C. by start control.

The controller 51 receives a signal from the stack temperature sensor 101 that detects the stack temperature T _stk , a signal from the combustor temperature sensor 102 that detects the combustor temperature T _cmb , and a reformer temperature T _ref as information related to the start control. In addition to inputting the signal from the reformer temperature sensor 103 to be detected, the concentration of water-containing oxygen-containing fuel (hereinafter sometimes referred to as "oxygen-containing fuel concentration") is input from the concentration sensor 104 to detect C _fuel . ..

The stack temperature T _stk is an index indicating the temperature of the fuel cell stack 1 or the fuel cell. 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. The stack temperature is T _stk .

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 combustor temperature is the temperature detected by the combustor temperature sensor 102, that is, the outlet temperature of the combustor 41. Let T _cmb . As the combustor temperature T _cmb , it is also possible to adopt the catalyst bed temperature instead of the outlet temperature of the combustor 41.

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 defined as the reformer temperature T _ref .

The oxygen-containing fuel concentration C _fuel is the concentration of the water-containing oxygen-containing fuel stored in the fuel tank 61, specifically, the ethanol aqueous 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 used as the oxygen-containing fuel concentration C _fuel . However, the concentration sensor 104 may be installed in the anode gas passage 11 on the upstream side of the evaporator 21 or in the branch fuel passage 11sub on the upstream side of the second fuel injector 72. good.

(Explanation of operation of fuel cell system)
3 and 4 show the operating state of the fuel cell system S, FIG. 3 shows the operating state at the time of starting the fuel cell system S, and FIG. 4 shows the operating state at the normal time after the system is started. There is. Of the anode system and cathode system passages, the passages through which gas actually flows are shown by thick solid lines, and the passages through which gas flow is stopped are shown by thin dotted lines.

At the time of start-up, the supply of raw fuel through the first fuel injector 71 is stopped, and the raw fuel required for warming up 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 rate control valve 82, the oxidant gas (air) is supplied to the combustor 41 through the branched 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. This heats the evaporator 21, the fuel heat exchanger 22, the reformer 23, and the air heat exchanger 31 to promote warming up of the fuel cell system S.

In the normal state, the raw fuel of the normal supply amount required for the 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 the rated output (FIG. 4). .. On the other hand, the residual fuel in the anode off-gas is burned in the combustor 41 to supply the reformer 23 with the amount of heat required for reforming, and the combustion gas of the residual fuel is used in the air heat exchanger 31 and the evaporator 21. And keeps the entire fuel cell system S at the temperature required for operation.

Here, in the present embodiment, the following problems become a problem by using an aqueous ethanol solution as a raw material and fuel.

If the water-containing oxygen-containing fuel represented by the aqueous ethanol solution is left unattended, its concentration will decrease. When the concentration decreases, the adiabatic flame temperature of the oxygen-containing fuel (ethanol) decreases, the calorific value of the combustor 41 decreases, and the transport heat amount of the combustion gas also decreases, so that the heating by the combustor 41 becomes insufficient. Not only does the time required to start the fuel cell system S become longer, but in some cases it becomes difficult to achieve the start-up itself.

Therefore, in the present embodiment, as a part of the start control of the fuel cell system S, when the concentration of the water-containing oxygen-containing fuel decreases, the calorific value of the combustor 41 is reduced by executing the control to raise the adiabatic flame temperature. Maintain and ensure the startability of the fuel cell system S. Specifically, when the concentration of the ethanol aqueous solution stored in the fuel tank 61 decreases, the ratio of the air in the combustor 41 to the ethanol aqueous 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 of change with respect to the air excess rate λ at the boundary of the air excess rate λ = 1, and when the air excess rate λ is less than 1, air. While the excess rate λ tends to increase, when the excess air rate λ is 1 or more, the excess rate λ tends to increase due to the decrease in the excess air rate λ. FIG. 5 shows the relationship when a 45% by volume ethanol aqueous solution is used, but the tendency of the adiabatic flame temperature _Taft to change with the air excess ratio λ = 1 is a concentration other than 45% by volume or The same applies when other types of water-containing oxygen-containing fuels are used.

FIG. 6 shows changes in the adiabatic flame temperature _Taft when the concentration C _fuel of the ethanol aqueous solution decreases, when the air excess rate λ is less than 1 (a) and when the air excess rate 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 ethanol aqueous solution decreases, the adiabatic flame temperature _{Taft decreases, so that the target adiabatic flame temperature T afttrg can} not be achieved while the excess air ratio λ0 is maintained, and the combustor 41 There is a shortage of calorific value. Here, the adiabatic flame temperature _{Taft is increased by adjusting the air excess rate λ. However, in order to achieve the target adiabatic flame temperature T afttrg regardless} of the decrease in the concentration C _fuel , the air excess rate λ is 1. If it is less than, as shown in FIG. 6A, it is necessary to increase the air excess rate λ to λ1a that is larger than λ0, and if the air excess rate λ is 1 or more, it is shown in FIG. 6B. As shown, it is necessary to reduce the excess air ratio λ to λ1b, which is smaller than λ0. That is, the excess air ratio λ should be adjusted so as to approach 1 with respect to the decrease in the concentration C _fuel of the ethanol aqueous solution. In other words, when the excess air ratio λ is smaller than 1, the excess air ratio λ should be 1. When the excess air ratio λ is larger than 1, the excess air ratio λ is decreased toward 1 to raise the adiabatic flame temperature _Taft and 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.

(Explanation of start control)
FIG. 5 shows a basic flow of start control of the fuel cell system S according to the present embodiment by a flowchart.

The controller 51 is programmed to execute the start control of the fuel cell system S according to the procedure shown in the flowchart of FIG. 7 when a 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 upon inputting the start request signal, and ends this when it is determined that the fuel cell stack 1 or the fuel cell warm-up is completed.

In S101, various sensor outputs related to activation control are read. Specifically, the stack temperature T _stk , the combustor temperature T _cmb , the reformer temperature T _ref , and the oxygen-containing fuel concentration C _fuel are read.

In S102, a basic value (hereinafter referred to as “basic air excess rate”) λ0 of the air excess rate λ in the combustor 41 is set. The basic air excess ratio λ0 takes a different value 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 modification, it is permissible to set it to a value smaller than 1. In the present embodiment, since the combustor 41 provided with the combustion catalyst is targeted, the basic air excess rate λ0 is set to a value larger than 1.

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

In S104, it is determined whether or not the oxygen-containing fuel concentration C _fuel is lower than the predetermined value C _fuel 1. That is, it is determined whether or not the concentration C _fuel of the aqueous ethanol solution has decreased to such an extent that the time required for warming up the fuel cell system S is excessively prolonged. The predetermined value C _fuel 1 is set to a value smaller than the 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, proceed to S105 to adjust the excess air ratio λ, and if it is equal to or higher than the predetermined value C _fuel 1, adjust the excess air ratio λ. The basic air excess rate λ0 is maintained and the process proceeds to S108.

In S105, it is determined whether or not the basic air excess rate λ0 is less than 1. This is because, as described above, the tendency of the adiabatic flame temperature _Taft to change with respect to the air excess rate λ differs depending on whether the air excess rate λ is less than 1 or 1 or more.

In S106, a correction is performed to increase the excess air ratio λ. Specifically, the estimated reached value T _aftest of the adiabatic flame temperature is calculated from the actual oxygen-containing fuel concentration C _fuel , and the difference DEF (= T _afttrg- ) between the target value T _afttrg of the adiabatic flame temperature and the estimated reached value T _aftest . The correction amount Δλa (= f (DEF)) according to _Taftest ) is added to the basic air excess rate λ0 (λ1a = λ0 + Δλa). The estimated reached value _Taftest of the adiabatic flame temperature can be calculated by a calculation formula that models the combustion reaction of the ethanol aqueous solution, and the relational expression f between the difference DEF and the correction amount Δλa is more approximate than the adaptation through experiments and the like. It is possible to ask for. By creating table data in which the correction amount Δλa is assigned to the oxygen-containing fuel concentration C _fuel and storing it in the controller 51 in advance, this table data is referred to by the oxygen-containing fuel concentration C _fuel during actual operation. You may do so. The correction amount Δλa when the air excess rate λ is less than 1 tends to increase with respect to the decrease in the concentration C _fuel , and the corrected air excess rate λ1a approaches 1.

In S107, a correction is performed to reduce the excess air ratio λ. Similar to in S106, the correction amount Δλb according 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 Δλb is calculated from the basic air excess rate λ0 for the subtraction correction. Subtract (λ1b = λ0-Δλb). It is advisable to create table data in which the correction amount Δλb is assigned to the oxygen-containing fuel concentration C _fuel and store it in the controller roller 51 in advance. The correction amount Δλb (> 0) when the air excess rate λ is 1 or more. Also, like the correction amount Δλa, it has a tendency to increase with a decrease in the concentration C _fuel , and is reduced from the basic air excess rate λ0 to bring the corrected air excess rate λ1b closer to 1.

In S108, the supply amount (fuel supply amount) Qf of the raw material and fuel according to the corrected air excess rate λ1 (λ1a, λ1b) is calculated.

In S109, the supply amount (air supply amount) Qa of the oxidant gas capable of achieving the corrected air excess rate λ1 is calculated with respect to the fuel supply amount Qf. In the present embodiment, the adjustment of the air excess rate λ with respect to the decrease in the oxygen-containing 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 for the air excess rate λ, and is decreased when the decrease correction is performed. Then, in order to increase the air supply amount Qa, the rotation speed of the air compressor 81 is increased or the opening degree of the flow rate control valve 82 is increased. However, the present invention is not limited to this, and it is also possible to adjust the air excess rate λ by changing the fuel supply amount Qf or changing the air supply amount Qa and the fuel supply amount Qf at the same time.

In S110, it is determined whether or not the warm-up of the fuel cell stack 1 is completed. Specifically, it is determined whether or not the stack temperature T _stk has reached the predetermined temperature T _stkwup for determining the completion of warm-up, and if the stack temperature T _stk reaches the predetermined temperature T _stkwup , the fuel cell system Assuming that the warm-up of S is completed, the start control is terminated, and if the predetermined temperature T _stkwup is not reached, it is assumed that the warm-up has not been completed yet, the start control is continued, and the stack temperature T _stk is continuously monitored. .. When the start control is finished, the normal control is executed according to another routine (not shown), and the fuel cell stack 1 is operated at the rated output. Here, if the reformer 23 (specifically, the reforming catalyst provided in the reformer 23) reaches the reformable temperature before the warm-up of the fuel cell system S is completed, the first fuel By starting the supply of raw fuel through the injector 71 and supplying the fuel gas (hydrogen) and the oxidizing agent gas to the fuel cell stack 1, the fuel cell stack 1 is started to generate power. As a result, the fuel cell stack 1 is heated by using the oxidant gas as a medium, and the warming up of the entire fuel cell system S is promoted by power generation.

In the present embodiment, the fuel tank 61 is a "fuel reservoir", the combustor 41 is a "combustor", the second fuel injector 72 is a "fuel supply device", and the air compressor 81 is an "oxidizer gas supply device". The controller 51 constitutes a "control unit", respectively. Then, among the processes performed by the controller 51 regarding the activation control, the process of S103 shown in FIG. 7 corresponds to the function of the "concentration detection unit", and the process of S104 to 107 corresponds to the function of the "ratio adjustment unit".

(Explanation of action and effect)
The fuel cell system S according to the present embodiment is configured as described above, and the actions 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 oxygen-containing 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 oxidizing agent gas to the water-containing oxygen-containing fuel in the combustor 41, that is, the excess air ratio λ is adjusted with respect to the decrease in the oxygen-containing fuel concentration C _fuel . This makes it possible to suppress a decrease in the adiabatic flame temperature _Taft and maintain the calorific value of the combustor 41 as much as possible. As a result, the adiabatic flame temperature _Tafttrg can be brought close to the target value, the required calorific value of the combustor 41 can be obtained, and the startability of the fuel cell system S can be ensured.

Secondly, the tendency of the change of the adiabatic flame temperature _Taft changes according to the air excess rate λ, and specifically, it changes with 1 indicating the equivalent as a boundary. Therefore, in adjusting the excess air ratio λ, by making this close to 1, the adiabatic flame temperature _Taft can be surely increased regardless of the excess air ratio λ, and the calorific value of the combustor 41 can be secured. Can be done.

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) is used to determine the supply amounts Qf and Qa of the ethanol aqueous solution or air to the combustor 41. By changing it, the excess air ratio λ can be easily adjusted.

Fourth, by providing the concentration sensor 104 for detecting the oxygen-containing fuel concentration C _fuel , accurate detection of the oxygen-containing fuel concentration C _fuel becomes possible.

(Explanation of other embodiments)
In the above description, the concentration sensor 104 is installed to detect the oxygen-containing fuel concentration C _fuel , and the oxygen-containing fuel concentration C _fuel is directly detected by the concentration sensor 104. However, not limited to this, the oxygen-containing 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 oxygen-containing fuel. Is.

FIG. 8 shows the change of the combustor temperature T _cmb with respect to time t after starting the supply of the ethanol aqueous solution, and FIG. 9 shows the relationship between the combustor temperature T _cmb and the oxygen-containing 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 (reached temperature) is an adiabatic flame according to the oxygen-containing fuel concentration C _fuel . Due to the difference in temperature, it differs depending on the oxygen-containing fuel concentration C _fuel , and the lower the oxygen-containing fuel concentration C _fuel , the smaller the gradient of change and the lower the ultimate temperature. In FIG. 8, the combustor temperature T cmb when the oxygen-containing fuel concentration C _fuel is high (C _fuel 0) is shown by a thick solid line, and the combustor temperature T _cmb when the oxygen-containing fuel concentration C fuel is low (C _fuel 1) is shown by a thin solid line. .. Therefore, by grasping the relationship between the combustor temperature T _cmb and the oxygen-containing fuel concentration C _fuel in advance through experiments or the like, combustion at time t1 after the time t0 when the supply of the water-containing oxygen-containing fuel to the combustor 41 is started is started. It is possible to estimate the oxygen-containing fuel concentration C _fuel based on the vessel temperature T _cmb 0 and T _cmb 1.

By creating the table data of the tendency shown in FIG. 9 and storing it in the controller 51 in advance, the oxygen-containing fuel concentration C _fuel can be referred to by the combustor temperature T _cmb at time t1 during the actual operation. To 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 oxygen-containing fuel concentration C _fuel and the output P _stk of the fuel cell stack 1.

In the reformer 23, fuel gas is generated by steam reforming of ethanol, which is an oxygen-containing fuel. Here, steam reforming becomes more predominant when the concentration of the aqueous ethanol solution is low, in other words, when the water content of the water-containing oxygen-containing fuel is high, and more fuel gas (specifically, hydrogen) is generated. It tends to make you. Since the output of the fuel cell stack 1 increases as the amount of fuel gas increases, the output of the fuel cell stack 1 (hereinafter sometimes referred to as "stack output") P _stk correlates with the concentration of the ethanol aqueous solution. Has. With a predetermined amount of ethanol aqueous solution supplied to the reformer 23, the relationship between the oxygen-containing fuel concentration C _fuel and the stack output P _stk is acquired and stored in the controller 51 in advance as table data. Therefore, it is possible to estimate the oxygen-containing fuel concentration C _fuel based on the stack output P _stk during operation of the fuel cell stack 1.

Here, at the time of system startup, the temperature of the reformer 23 is low unlike the normal time after startup, so that steam reforming does not proceed satisfactorily, and the fuel cell stack 1 itself is also at a low temperature. In consideration of this, 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 as of the time when the system is started this time. In the present 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 P _stk and measures the elapsed time Δt.

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

The concentration change amount ΔC tends to increase as a longer time elapses from the system shutdown.

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

FIG. 12 shows the relationship between the oxygen-containing 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 at the same time. The reaction that occurs in the reformer 23 can be expressed by the following equations (4.1) to (4.7). Here, which of the endothermic reaction and the exothermic reaction is predominant depends on the conditions, but when the endothermic reaction is predominant, the outlet temperature T _ref of the reformer 23 decreases, and the temperature difference between the inlet and the outlet The ΔT _ref (hereinafter referred to as “inlet / outlet temperature difference”) expands. On the other hand, when the exothermic reaction is predominant, the outlet temperature T _ref of the reformer 23 increases, and the inlet / outlet temperature difference ΔT _ref decreases. As described above, the inlet / outlet temperature difference ΔT _ref of the reformer 23 has a correlation with the concentration C _fuel of the water-containing oxygen-containing 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 inlet / outlet temperature difference ΔT _ref of the reformer 23.

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

When the system is started, 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. Therefore, the previous system is stopped due to the inlet / outlet temperature difference ΔT _ref . By detecting the previous oxygen-containing fuel concentration C _fuel and correcting this by the decrease ΔC of the concentration C _fuel according to the elapsed time Δt after the previous system shutdown, the current oxygen-containing fuel at the time of the system startup this 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.

In this way, 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 oxygen-containing fuel concentration C _fuel is dedicated to the concentration sensor and the like. It can be detected regardless of the parts of.

In the above description, the combustor 41 is positioned as a "combustor", and the fuel processing unit 2 (evaporator 21, fuel heat exchanger 22, reformer) is determined by the amount of heat generated by the combustion of raw fuel or the amount of heat possessed by the combustion gas. 23) and the air heat exchanger 31 are heated, and the fuel cell stack 1 is heated to promote warming up of the entire fuel cell system S. However, the present invention is not limited to this, and the reformer 23 can be positioned as a “combustor”. For example, when the system is started, an aqueous ethanol solution and air are supplied to the reformer 23, and the calorific value is obtained by the reaction of both on the reforming catalyst to raise the temperature of the reformer 23 or the reforming catalyst. It is.

FIGS. 13 to 15 show an example in that case.

13 shows the configuration of the fuel cell system S1 according to another embodiment of the present invention, FIG. 14 shows the operating state of the fuel cell system S1 at the time of system startup, and FIG. 15 shows the normal operation state after the system startup. It shows the operating state at the time.

Explaining mainly the differences from the system S (FIG. 2) according to the previous embodiment, as shown in FIG. 13, in the present embodiment, the passage 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 the flow rate of the oxidizing agent gas (air) flowing through the passage 12subb is adjusted in the second branch air passage 12subb. A flow control valve (second flow control valve) 83 for this purpose is installed. As a result, as shown in FIG. 14, when the fuel cell system S1 is started, air is supplied not only to the combustor 41 but also to the reformer 32 to obtain a calorific value due to the reaction between ethanol and oxygen. Combined with the heating by the combustion gas supplied from the combustor 41, it is possible to raise the temperature of the reformer 23 more quickly. 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 time required for startup is expected to be prolonged, the combustor 41 and The excess air ratio λ in the combustor 23 is adjusted. In the present embodiment, the basic air excess rate λ0 is set to a value larger than 1 for the combustor 41, and the air excess rate λ is reduced in order to raise the adiabatic flame temperature _Taft with respect to the decrease in the concentration C _fuel . Let me. 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 in order to raise the adiabatic flame temperature _Taft . Then, after the warm-up of the fuel cell system S is completed, 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. Then, the reformed fuel gas (hydrogen) is supplied to the fuel cell stack 1 through the anode gas passage 11, and the heated air 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 form an "oxidizer gas supply device". ”.

Although the embodiment of the present invention has been described above, the above-described embodiment shows only a part of the application example of the present invention, and the technical scope of the present invention is limited to the specific configuration of the above-mentioned embodiment. Not the purpose. Various changes and amendments can be made to the above embodiments within the scope of the matters described in the claims.

S ... Fuel cell system 1 ... Fuel cell stack 2 ... Fuel processing unit 21 ... Evaporator 22 ... Fuel heat exchanger 23 ... Reformer 3 ... Oxidizing agent gas heating unit 31 ... Air heat exchanger 4, 41 ... Combustor 5 , 51 ... Controller (control unit)
6, 61 ... Fuel tank (fuel storage)
7 ... Fuel supply device 71 ... 1st fuel injector 72 ... 2nd fuel injector 8 ... Oxidizing agent gas supply device 81 ... Air compressor 82 ... Flow control valve (1st flow control valve)
83 ... Second flow rate control valve 11 ... Anode gas passage 12 ... Cathode gas passage

Claims (12)

With a fuel cell
A fuel reservoir for storing water-containing oxygen-containing fuel, which is the raw material of the fuel cell, and
A combustor having a catalyst that promotes the combustion of the water-containing oxygen-containing fuel, and
A fuel supply device connected to the fuel reservoir and supplying the water-containing oxygen-containing fuel to the combustor.
An oxidant gas supply device that supplies oxidant gas to the combustor,
A control unit that controls the supply of the water-containing oxygen-containing fuel and the oxidant gas to the combustor,
It is a fuel cell system equipped with
The control unit
A concentration detection unit that detects the concentration of the water-containing oxygen-containing fuel stored in the fuel reservoir, and
A ratio adjusting unit that adjusts the ratio of the oxidant gas to the water-containing oxygen-containing fuel in the combustor according to the concentration detected by the concentration detecting unit.
Equipped with a fuel cell system. The ratio adjustment unit
The adiabatic flame temperature of the water-containing oxygen-containing fuel is estimated based on the detected concentration.
The ratio of the oxidant gas to the water-containing oxygen-containing fuel in the combustor is adjusted so that the estimated adiabatic flame temperature approaches a target value corresponding to the calorific value of the combustor required. The fuel cell system described in. The ratio adjusting unit increases the ratio when the ratio is smaller than 1 in terms of equivalent ratio with respect to the decrease in the concentration of the water-containing oxygen-containing fuel, and when the ratio is larger than 1 in terms of equivalent ratio. Brings the ratio closer to 1 in terms of equivalent ratio by reducing the ratio.
The fuel cell system according to claim 1 or 2. 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 any one of claims 1 to 3. The concentration detecting unit includes a concentration sensor arranged so as to be able to detect the concentration of the water-containing oxygen-containing fuel supplied to the combustor.
The fuel cell system according to any one of claims 1 to 4. The control unit further includes a temperature detection unit that detects the temperature of the combustor.
The concentration detecting unit detects the concentration of the water-containing oxygen-containing fuel based on the temperature detected by the temperature detecting unit after starting the supply of the water-containing oxygen-containing fuel to the combustor.
The fuel cell system according to any one of claims 1 to 4. The fuel cell system according to any one of claims 1 to 4, further comprising a reformer that produces fuel gas for the fuel cell by treating the water-containing oxygen-containing fuel.
The control unit further includes an output detection unit that detects the output of the fuel cell.
The concentration detecting unit detects the concentration of the water-containing oxygen-containing fuel based on the output detected by the output detecting unit.
Fuel cell system. The control unit further includes a time measurement unit that measures the elapsed time from the previous system stop to the current startup.
The concentration detection unit is the water-containing oxygen-containing fuel based on the output detected by the output detection unit before the previous system stop at the time of system startup and the elapsed time measured by the time measurement unit. Detects the concentration of
The fuel cell system according to claim 7. The fuel cell system according to any one of claims 1 to 4, further comprising a reformer that produces fuel gas for the fuel cell by treating the water-containing oxygen-containing fuel.
The control unit further includes a temperature difference detecting unit that detects a temperature difference between the inlet and outlet of the reformer as an inlet / outlet temperature difference.
The concentration detecting unit detects the concentration of the water-containing oxygen-containing fuel based on the inlet / outlet temperature difference detected by the temperature difference detecting unit.
Fuel cell system. The control unit further includes a time measurement unit that measures the elapsed time from the previous system stop to the current startup.
The concentration detection unit is based on the inlet / outlet temperature difference detected by the temperature difference detection unit before the previous system stop at the time of system startup and the elapsed time measured by the time measurement unit. Detect the concentration of oxygen-containing fuel contained,
The fuel cell system according to claim 9. The water-containing oxygen-containing fuel is an aqueous ethanol solution.
The fuel cell system according to any one of claims 1 to 10. It is a control method of a fuel cell system that controls a fuel cell system that supplies fuel gas generated by processing a water-containing oxygen-containing fuel to a fuel cell.
At the time of starting the fuel cell system,
The water-containing oxygen-containing fuel is burned on the catalyst to be burned.
Using the combustion gas generated by combustion as a heat source, the fuel cell system is warmed up.
The concentration of the water-containing oxygen-containing fuel stored in the fuel reservoir is detected, and the concentration is detected.
The ratio of the oxidant gas to be used for combustion to the water-containing oxygen-containing fuel is adjusted according to the detected concentration of the water-containing oxygen-containing fuel.
How to control the fuel cell system.

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