Control method for a fuel cell system, and fuel cell system

Abstract

To provide a control method for a fuel cell system which improves power generation output by improving heat exchange efficiency of an oxidant gas, and a fuel cell system.SOLUTION: The present invention relates to a control method for a fuel cell system which comprises a combustor 5 for generating a combustion gas by combusting a mixed gas of an anode off-gas and a cathode off-gas exhausted from a fuel cell stack 1 and a heat exchanger 4 for heating air by the combustion gas and in which the combustor 5 and the heat exchanger 4 are formed integral and a circulation direction of air and a circulation direction of the combustion gas are set reverse to each other. A flow rate of at least one of the combustion gas and air is controlled so as to provide the mixed gas to be a target composition (a composition of the mixed gas in which a moisture concentration is a target moisture concentration (X0)) at a time when a temperature of air is a predetermined target temperature (T0), the target composition of the mixed gas being calculated based on correlations (Fig. 5, Fig. 6 and Fig. 8) between the temperature of air and the composition of the mixed gas just after heat exchange in the heat exchanger 4.SELECTED DRAWING: Figure 4

Claims

1. A fuel cell that generates electricity by being supplied with fuel gas and oxidizer gas, A combustor that burns a mixed gas of fuel off-gas and oxidizer off-gas discharged from the fuel cell to generate combustion gas, The system comprises a heat exchanger capable of exchanging heat with the combustion gas and heating the oxidizing gas, A control method for a fuel cell system in which the combustor and the heat exchanger are integrally formed, and the flow direction of the oxidizer gas and the flow direction of the combustion gas are set to be opposite to each other, A control method for a fuel cell system, comprising controlling the flow rate of at least one of the fuel gas and the oxidizer gas so that the mixed gas contains moisture generated in the fuel cell, and the mixed gas reaches a target moisture concentration calculated based on the correlation between the temperature of the oxidizer gas immediately after heat exchange in the heat exchanger and the moisture concentration of the mixed gas, which is the target moisture concentration when the temperature of the oxidizer gas reaches a predetermined target temperature.

2. The control method for a fuel cell system according to claim 1, wherein the moisture concentration is detected by a sensor.

3. A control method for a fuel cell system according to Claim 1, wherein the moisture concentration is estimated from the power generation current of the fuel cell, the flow rate of the fuel gas, and the flow rate of the oxidizer gas.

4. The flow rate of the fuel off-gas and the water flow rate in the fuel off-gas are estimated by estimating the equilibrium composition of the fuel off-gas from the power generation current of the fuel cell and the outlet temperature of the fuel off-gas of the fuel cell, The flow rate of the oxidizer off-gas is estimated based on the power generation current of the fuel cell. A control method for a fuel cell system according to claim 1, wherein the water concentration is estimated based on the flow rate of the fuel off-gas, the flow rate of the oxidizer off-gas, and the water flow rate in the fuel off-gas.

5. A control method for a fuel cell system according to Claim 1, wherein the flow rate of the fuel gas is increased and / or the flow rate of the oxidizer gas is decreased when the moisture concentration is reduced to reach the target moisture concentration.

6. When the temperature of the oxidizing gas immediately after heating by the heat exchanger is determined by a monitor temperature represented by the outlet temperature of the oxidizing gas of the heat exchanger or the inlet temperature of the oxidizing gas of the fuel cell, the monitor temperature when the temperature of the oxidizing gas is the target temperature is set as the target monitor temperature, and the difference between the estimated temperature of the oxidizing gas calculated from the moisture concentration and the correlation and the target monitor temperature is calculated, A control method for a fuel cell system according to claim 1, wherein the flow rate of the fuel gas is increased and / or the flow rate of the oxidizer gas is decreased as the aforementioned difference increases.

7. A control method for a fuel cell system according to claim 6, in which the flow rate of the fuel gas is increased as the difference increases, the amount of increase in the flow rate of the fuel gas is calculated based on the required heat amount to increase the flow rate of the fuel gas by the difference and the lower heating value of the fuel gas.

8. A control method for a fuel cell system according to claim 7, wherein the required heat quantity is calculated based on the difference, the specific heat of the fuel gas, the heat exchange efficiency of the integrated heat exchanger and combustor, and the amount of heat dissipated by the integrated.

9. When controlling at least one of the flow rates of the fuel gas and the oxidizer gas using a second correlation between the oxygen excess ratio of the oxidizer gas relative to the fuel gas and the adiabatic flame temperature when the fuel gas and oxidizer gas with said oxygen excess ratio are mixed and burned adiabatically, The first adiabatic flame temperature is estimated using the current oxygen excess rate, which is the first oxygen excess rate, and the second adiabatic flame temperature is calculated based on the second correlation, which is a second adiabatic flame temperature that is higher than the first adiabatic flame temperature by the difference. A method for controlling a fuel cell system according to claim 6, wherein the flow rate of the fuel gas and the flow rate of the oxidizer gas are controlled such that the oxygen excess rate becomes the second oxygen excess rate.

10. A fuel cell that generates electricity by being supplied with fuel gas and oxidizer gas, A fuel gas supply unit that supplies the fuel gas to the fuel cell, An oxidant gas supply unit that supplies the oxidant gas to the fuel cell, A combustor that burns a mixed gas of fuel off-gas and oxidizer off-gas discharged from the fuel cell to generate combustion gas, A heat exchanger capable of heat exchange with the combustion gas and heating the oxidizing gas, A fuel cell system comprising a fuel gas supply unit and a control unit for controlling the oxidizer gas supply unit, The combustor and the heat exchanger are formed as a single unit, and the flow direction of the oxidizer gas and the flow direction of the combustion gas are set to be opposite to each other. The control unit, A fuel cell system that controls the flow rate of at least one of the fuel gas and the oxidizer gas so that the mixed gas contains moisture generated in the fuel cell and the flow rate of at least one of the fuel gas and the oxidizer gas is such that the mixed gas has a target moisture concentration calculated based on the correlation between the temperature of the oxidizer gas immediately after heat exchange in the heat exchanger and the moisture concentration of the mixed gas, and the target moisture concentration is reached when the temperature of the oxidizer gas reaches a predetermined target temperature.

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