JP6089421B2 - Fuel cell system - Google Patents

Description

  The present invention relates to a fuel cell system, and more particularly to a technique for equalizing a temperature distribution in a stack at startup.

  Since a solid oxide fuel cell (SOFC) generates power at a high temperature, power generation is performed after the stack (fuel cell) is heated to a predetermined temperature during startup. As a method for heating the stack, a method is generally employed in which combustion gas is generated by a start-up combustor and the generated combustion gas is introduced into a cathode flow path in the stack.

  In addition, as another method, high temperature air obtained by heat exchange of combustion gas is introduced into the cathode channel and heated, or in addition to introduction of high temperature air into the cathode channel, gas generated by partial oxidation reaction or the like is used. In some cases, a method of introducing the anode into the anode of the stack, a method of heating the stack with a combustion type or electric surface heater, or the like may be used.

  Also, in recent years, it is required to start the stack from a cold state to generate power and improve the overall efficiency until the stack is stopped. For this purpose, it is used to heat the stack at startup. It is necessary to reduce energy as much as possible.

  Therefore, conventionally, it has been proposed to reduce the energy consumption at the time of start-up by stopping the start-up combustor when the stack temperature and the generated current value exceed the threshold values (see, for example, Patent Document 1). ).

JP 2009-146647 A

  However, in the conventional example described in Patent Document 1 described above, variation in the temperature distribution inside the stack is not considered, and when using a stack having a low heat capacity, the temperature distribution from the stack inlet to the stack outlet Changes could cause problems such as stack deterioration and damage.

  The present invention has been made to solve such a conventional problem, and an object of the present invention is to provide a fuel cell system capable of improving durability at the time of startup.

  In order to achieve the above object, the present invention supplies a combustion gas to the fuel cell in the startup mode in which the temperature of the fuel cell is raised to a predetermined temperature at startup, and when the temperature of the fuel cell reaches a set temperature, Reduce the flow rate of the combustion gas supplied to the fuel cell. As a result, the stack temperature is equalized before the power generation mode is started.

  In the fuel cell system according to the present invention, the combustion gas is supplied to the fuel cell to raise the temperature of the fuel cell. Further, when the temperature of the fuel cell reaches the set temperature, the flow rate of the combustion gas is reduced. , Make the fuel cell temperature uniform. Therefore, it is possible to prevent the temperature distribution in the fuel cell from changing greatly, and to prevent deterioration and damage of the fuel cell.

It is a block diagram which shows the structure of the fuel cell system which concerns on the 1st-4th embodiment of this invention. It is a flowchart which shows the process sequence at the time of starting of the fuel cell system which concerns on 1st Embodiment of this invention. It is a flowchart which shows the process sequence at the time of starting of the fuel cell system which concerns on 1st Embodiment of this invention. It is a characteristic view which shows the change of stack temperature, (a) shows the characteristic when this invention is applied, (b) shows the characteristic when this invention is not applied. It is a flowchart which shows the process sequence at the time of starting of the fuel cell system which concerns on 2nd Embodiment of this invention. It is a flowchart which shows the process sequence at the time of starting of the fuel cell system which concerns on 2nd Embodiment of this invention. It is a flowchart which shows the process sequence at the time of starting of the fuel cell system which concerns on 3rd Embodiment of this invention. It is a flowchart which shows the process sequence at the time of starting of the fuel cell system which concerns on 3rd Embodiment of this invention. It is a flowchart which shows the process sequence at the time of starting of the fuel cell system which concerns on 4th Embodiment of this invention. It is a characteristic view which shows the change of stack temperature of the fuel cell system which concerns on 4th Embodiment of this invention.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing a configuration of a fuel cell system according to first to fourth embodiments of the present invention.

  As shown in FIG. 1, the fuel cell system 100 supplies a fuel cell stack 11 (hereinafter abbreviated as “stack 11”) having a cathode 11a and an anode 11b, and air (oxidizing gas) to the cathode 11a. An air blower 12, an air preheating heat exchanger 13 for heating air sent from the air blower 12, a fuel pump 14 for supplying fuel such as hydrocarbon fuel to the anode 11b of the stack 11, and the fuel pump 14 An evaporator 25 that vaporizes the fuel to be sent out and a fuel reformer 15 that reforms the fuel vaporized by the evaporator 25 and supplies the reformed fuel to the anode 11b are provided.

  Further, a booster pump 17 that circulates the fuel gas discharged from the anode 11b to the fuel reformer 15 and an exhaust gas discharged from the cathode 11a to heat the fuel reformer 15 are used for heating the reformer. A burner 16, a branch valve 18 provided on the output side of the booster pump 17 and introducing part of the fuel gas discharged from the anode 11 b to the reformer heating burner 16, the fuel reformer 15, and the reformer And air blowers 26 and 27 for supplying air to the heating burner 16.

  In addition, a start-up combustor 21 that generates a combustion gas for raising the temperature of the cathode 11 a when the stack 11 is started up is provided. The start-up combustor 21 includes a part of the air sent from the air blower 12. The part is branched and supplied by the valve 22, and further, the fuel delivered from the fuel pump 23 is supplied after being vaporized by the evaporator 24. Then, combustion is performed with fuel and air, and combustion gas is supplied to the cathode 11 a to raise the temperature of the cathode 11 a when the stack 11 is activated.

  The air blower 12, the valve 22, the fuel pump 23, and the cathode 11 a (temperature sensor or the like) are each connected to the control unit 31. As will be described later, the control unit 31 adjusts the amount of fuel and the amount of air supplied to the start-up combustor 21 at the time of start-up, and the flow rate of the combustion gas output from the start-up combustor 21, and The temperature of the combustion gas is appropriately controlled so as to make the temperature in the cathode 11a uniform at the time of startup. Moreover, the control part 31 can be comprised as an integrated computer which consists of memory | storage means, such as central processing unit (CPU), RAM, ROM, a hard disk, for example.

[Description of Operation of First Embodiment]
Next, with reference to the flowchart shown in FIG. 2, the operation | movement at the time of starting of the fuel cell system which concerns on 1st Embodiment of this invention is demonstrated. When starting operation of the system, the stack 11 is first heated in the startup mode, and then the power generation mode is entered to generate power.

  When the start mode is started, in step S11, the control unit 31 ignites and burns the start-up combustor 21 with fuel and air supplied thereto. The combustion gas generated by the combustion is supplied to the cathode 11a of the stack 11, and the stack 11 is heated.

  In step S <b> 12, the control unit 31 measures the stack temperature Ts, and further calculates the change rate “dTs / dt” of the stack temperature Ts. It is desirable to set the stack temperature measurement location at the upstream portion of the stack 11 at which temperature fluctuations are likely to occur when starting power generation or switching from combustion gas to air. Therefore, in this embodiment, the stack temperature Ts is measured by a temperature sensor (not shown) provided in the upstream portion of the stack 11.

  In step S13, the control unit 31 determines whether or not the rate of change “dTs / dt” with respect to time of the stack temperature Ts is between the lower limit threshold Amin and the upper limit threshold Amax, and the stack temperature Ts is further equalized. It is determined whether or not a temperature T1 set in advance as a temperature for starting the warming process (set temperature; hereinafter referred to as “temperature equalization start temperature T1”) has been reached. When at least one of “Amin ≦ dTs / dt ≦ Amax” and “Ts ≧ T1” is negative (NO in step S13), the process proceeds to step S14.

  In step S14, the control unit 31 adjusts the amount of fuel and the amount of air supplied to the start-up combustor 21, and performs control so as to satisfy the condition of step S13.

  On the other hand, if “Amin ≦ dTs / dt ≦ Amax” and “Ts ≧ T1” (YES in step S13), the control unit 31 is output from the start-up combustor 21 in step S15. The flow rate Fb of the combustion gas is gradually reduced. By this process, the temperature in the cathode 11a is adjusted to be uniform. Specifically, when the combustion gas is introduced, the cathode 11a has a relatively higher temperature on the upstream side where the combustion gas is introduced than on the downstream side, so that the flow rate Fb of the combustion gas is gradually reduced. As a result, the temperature distribution from the upstream to the downstream of the cathode 11a is made uniform.

  In step S16, the control unit 31 determines whether or not the stack temperature Ts is within the range from the lower limit value T2min of the stack temperature during the temperature equalization process to the upper limit value T2max, and the combustion gas flow rate Fb is determined as follows. It is determined whether or not the preset flow rate Fb3 has been lowered. That is, it is determined whether or not “T2min ≦ Ts ≦ T2max”, and whether or not “Fb = Fb3”. If both of these determinations are negative (NO in step S16), in step S17, the control unit 31 adjusts the flow rate Fb of the combustion gas output from the start-up combustor 21, and then in step S16. Make sure the conditions are met.

  On the other hand, if “T2min ≦ Ts ≦ T2max” and “Fb = Fb3” (YES in step S16), the control unit 31 outputs the combustion gas output from the start-up combustor 21 in step S18. In addition, the air from the air blower 12 is introduced into the cathode 11a of the stack 11, and power generation by the stack 11 is started. The generated voltage Vs at this time is set as a target voltage V2. The target voltage V2 can gradually decrease the voltage and increase the amount of generated current according to a predetermined program. Further, the reforming off gas is introduced from the reformer 15 to the anode 11b during the heating temperature raising step until the stack temperature Ts reaches the temperature equalization start temperature T1 (between times t0 to t1 shown in FIG. 3 described later). Or in the middle of the temperature equalizing step for decreasing the combustion gas flow rate (between times t1 and t2 shown in FIG. 3).

  In step S19, the control unit 31 determines whether or not the stack temperature Ts is between the lower limit value T3min and the upper limit value T3max of the target temperature of the stack 11 in the power generation mode. If “T3min ≦ Ts ≦ T3max” is not satisfied (NO in step S19), the flow rate of air supplied to the cathode 11a is adjusted in step S20. For example, when the stack temperature Ts is lower than T3min, it is determined that the temperature of the stack 11 has decreased too much, and the air flow rate of the cathode 11a is decreased.

  On the other hand, if “T3min ≦ Ts ≦ T3max” (YES in step S19), in step S21, the control unit 31 determines whether or not the generated current Is has reached a target current value I1 for determining whether the generation mode can be started. to decide. That is, it is determined whether or not “Is = I1”. If “Is = I1” is not satisfied (NO in step S21), in step S22, the control unit 31 increases the flow rate of air supplied to the cathode 11a and reaches the allowable current value limit calculated from the cathode air flow rate. The generated current Is is increased by lowering the voltage a little so as to be within the range. In this case, the air flow rate increase amount and the voltage decrease amount per step can be set in advance. The target current value I1 is a generated current value for determining whether the power generation mode can be started. Thereafter, the process returns to step S19.

  When the generated current Is reaches the target current value I1 (YES in step S21), in step S23, the control unit 31 shifts the process from the start mode to the generated mode. That is, the power generation mode is started, and the power generation output can be taken out from the fuel cell system.

  Next, the temperature change and flow rate change of each part by the above-described processing procedure will be described with reference to the characteristic diagram shown in FIG. As shown in FIG. 3, in this embodiment, the start-up combustor 21 (see FIG. 1) is operated, and the start-up mode until power generation by the stack 11 is started is changed to the entire system including the stack 11. Control is performed by distinguishing between two steps: a heating temperature raising step for raising the temperature, and a temperature equalizing step for equalizing the temperature of the entire stack 11 after the temperature is raised. And since it transfers to a power generation mode after completion | finish of a temperature equalization step, temperature distribution from the upstream part of the stack 11 along a downstream part is temperature-equalized, and the rapid thermal fluctuation of the stack 11 is prevented.

  In the heating and heating step, the start-up combustor 21 is started at time t0, combustion gas is output, the combustion gas is supplied to the stack 11, and the stack 11 is heated. At this time, the combustion gas temperature Tb gradually increases between the times t0 and t1. Accordingly, the stack temperature Ts (in this embodiment, the upstream temperature of the stack 11) gradually increases between time t0 and time t1. Furthermore, the downstream portion temperature q1 of the stack 11 gradually increases at a temperature slightly lower than the stack temperature Ts. At this time, the flow rate Fb of the combustion gas output from the start-up combustor 21 is controlled to be a substantially constant flow rate. This control can be performed by adjusting the fuel delivery amount of the fuel pump 23 by the control unit 31 and the air blower 12.

  Then, the control unit 31 detects that the stack temperature Ts has reached the preset temperature equalization start temperature T1 at time t1, and performs control so that the flow rate Fb of the combustion gas gradually decreases (in FIG. 3). Reference between t1 and t3, see step S15 in FIG. 2). Then, when the flow rate Fb of the combustion gas is reduced to the preset flow rate Fb3 set at time t2, the supply of the combustion gas from the start-up combustor 21 is stopped (see step S18 in FIG. 2). The combustion gas temperature Tb decreases.

  Further, the power generation air sent from the air blower 12 by switching the valve 22 at time t2 is preheated by the heat exchanger 13 and then introduced into the cathode 11a, so that the cathode air flow rate q3 increases, and The cathode air temperature q2 increases. Furthermore, power generation is started at time t2, and the generated current Is gradually increases.

  Thereafter, at the time t3 when the generated current value Is = I1 is reached at the stack temperature Ts at which it can be determined that the mode can be shifted to the power generation mode, the temperature equalizing step ends, and the stack 11 shifts to the power generation mode.

  Thus, when the start-up combustor 21 is activated to raise the temperature of the stack 11, the temperature from the upstream side to the downstream side of the cathode 11a is equalized by performing the temperature equalization step. It is possible to adjust the temperature and then shift to the power generation mode.

  FIG. 4 is a characteristic diagram showing the temperature distribution from the upstream side to the downstream side of the cathode 11a, and FIG. 4 (a) shows the characteristic when the temperature equalizing step according to this embodiment is adopted, and the curve n1 indicates the temperature distribution of the stack 11 at the end of the heating temperature raising step, the curve n2 indicates the temperature distribution of the stack 11 at the end of the temperature equalizing step, and the curve n3 indicates that power generation by the stack 11 is performed. The temperature distribution of the stack 11 is shown. That is, the combustion gas is supplied to the stack 11 when the warming temperature raising step is performed, so the upstream side has a higher temperature than the downstream side, and when the temperature equalizing step is being performed, the upstream side of the stack 11 is increased. The temperature is substantially uniform from the side to the downstream side. Moreover, since air is supplied to the stack 11 during the power generation mode, the downstream side has a higher temperature than the upstream side.

  On the other hand, FIG.4 (b) has shown the characteristic at the time of not employ | adopting the temperature equalization step which concerns on this embodiment, and the curves n11-n14 show in the stack 11 when changing from a starting mode to a power generation mode. The temperature distribution is shown.

  Since the power generation current and the heat generation amount proportional thereto are proportional to the temperature, when power generation is started from the state of the temperature distribution n11 by switching to the cathode air, the heat generation amount is greatest at the most upstream part where the temperature is high. On the other hand, since the most upstream part is cooled most by the cathode air having a temperature lower than the stack temperature, after a little time has elapsed, the temperature distribution becomes n12 where the temperature is slightly higher in the downstream part than the most upstream part. If power generation is continued in this state, the position indicating the maximum temperature shifts downstream with the passage of time, and shifts to the temperature distribution n14 in the power generation mode. Especially in a stack with a small heat capacity to reduce the temperature rise energy for startup, the effect of reducing the in-plane temperature distribution by heat transfer in the solid part of the separator or cell is small. Temperature fluctuations are noticeable. For this reason, in a low heat capacity stack with a small start-up energy and a fast start-up time, it is extremely important to suppress local temperature fluctuations.

  Therefore, local temperature fluctuations are applied to the stack 11, and there is a possibility that deterioration or damage of the stack 11 may occur due to stress caused by temperature deviation in the stack 11 or temporal fluctuation.

  On the other hand, as can be understood from the curves n1 to n3 of the respective temperature distributions shown in FIG. 4A, the temperature on the inlet side of the cathode 11a is high at the time when the heating and heating step is completed, and The temperature is low, and the temperature of the entire cathode 11a is made uniform by executing the temperature equalization step. After that, by starting power generation, the temperature on the inlet side of the cathode 11a is high, and the temperature on the outlet side is increased. It changes so that temperature becomes low.

  In this case, the temperature change of the stack 11 is a linear change as a whole, and no local temperature fluctuation is applied to the stack 11, so that the deterioration of the stack 11 due to the temperature deviation in the stack 11 Damage can be prevented.

  Thus, in the fuel cell system according to the first embodiment of the present invention, when the temperature of the stack 11 is raised using the start-up combustor 21, the combustion is performed by the temperature equalization step at the end of the heating temperature raising mode. Since the gas flow rate is gradually decreased (that is, the combustion gas flow rate Fb is gradually decreased between t1 and t2 in FIG. 3), the stack before the start of power generation by the stack 11 is performed. 11 is capable of equalizing the entire temperature from the upstream side to the downstream side.

  Therefore, power generation can be started after the temperature distribution in the cathode flow direction is reduced by raising the cell temperature on the downstream side of the cathode without increasing the cell temperature on the upstream side of the cathode. Since power generation can be started, local temperature changes can be suppressed. As a result, it is possible to prevent the stack 11 from being deteriorated or damaged.

  In addition, since the power generation is started when the combustion gas flow rate Fb is lower than the set flow rate Fb3, it is easy to balance the amount of heat generated by the power generation of the cells in the stack 11 and the cooling or heating of the cells by the combustion gas, and the heat capacity is small. Also in the stack, a local temperature distribution change from the upstream side to the downstream side in the stack 11 can be suppressed.

  In the first embodiment, the combustion gas flow rate Fb is controlled to gradually decrease to a flow rate Fb3 by a predetermined program, but in addition to this, it corresponds to the cathode flow channel upstream portion and the cathode flow channel downstream portion. A temperature sensor is also set near the gas manifold where the heat capacity is large and the heat capacity is large, and the combustion gas flow rate Fb is controlled to decrease based on the temperature difference information of the two points together with the temperature information of the upstream portion, and lowered to Fb3 You can also.

  The optimum way of reducing the combustion gas flow rate Fb depends on the shape of the cell, the heat capacity ratio between the cell and the metal support part supporting the cell and the gas manifold part, and the cathode gas flow structure. It is possible to reduce the number in steps and hold it, or to decrease it a plurality of times.

  Further, the combustion gas flow rate Fb is decreased based on a program set so that the temperature fluctuation from the upstream to the downstream falls within an allowable range based on the heating temperature increase map at each cell point designed or measured in advance. Can do. Further, the stop timing of the combustion gas can be determined based on the temperature signal of the air preheating heat exchanger 13 in addition to the stack temperature and the generated current value.

[Description of Operation of Second Embodiment]
Next, with reference to the flowchart shown in FIG. 5, the operation | movement at the time of starting of the fuel cell system which concerns on 2nd Embodiment is demonstrated. Similar to the first embodiment described above, when starting the operation of the system, the temperature of the stack 11 is first raised in the startup mode, and then the power generation mode is entered to generate power.

  When the start mode is started, in step S31, the control unit 31 ignites and burns the start-up combustor 21 in a state where fuel and air are supplied. The combustion gas generated by the combustion is supplied to the cathode 11a of the stack 11, and the stack 11 is heated.

  In step S <b> 32, the control unit 31 measures the stack temperature Ts, and further calculates a change rate “dTs / dt” of the stack temperature Ts. Here, as in the first embodiment, the stack temperature Ts is measured by a temperature sensor (not shown) installed upstream of the stack 11.

  In step S33, the control unit 31 determines whether or not the rate of change “dTs / dt” of the stack temperature Ts is between the lower limit threshold Amin and the upper limit threshold Amax, and the stack temperature Ts is equalized. It is determined whether or not a temperature equalization start temperature T1 set in advance as a temperature for starting the process has been reached. When at least one of “Amin ≦ dTs / dt ≦ Amax” and “Ts ≦ T1” is negative (NO in step S33), the process proceeds to step S34.

  In step S34, the control unit 31 adjusts the amount of fuel and the amount of air supplied to the start-up combustor 21, and performs control so as to satisfy the condition of step S33.

  On the other hand, if “Amin ≦ dTs / dt ≦ Amax” and “Ts ≦ T1” (YES in step S33), the control unit 31 is output from the start-up combustor 21 in step S35. A process for reducing the temperature Tb of the combustion gas and reducing the flow rate Fb of the combustion gas is performed. Specifically, when the temperature of the combustion gas when the stack temperature Ts reaches the temperature equalization start temperature T1 is Tb1, and the flow rate of the combustion gas is Fb1, the temperature of the combustion gas is set to Tb2 lower than Tb1. And set the flow rate of the combustion gas to Fb2 which is smaller than Fb1. That is, “Tb = Tb2 ≦ Tb1” and “Fb = Fb2 ≦ Fb1”. The flow rate Fb2 is set higher than the air flow rate Fc supplied to the cathode 11a in the power generation mode, and the temperature Tb2 is set higher than the air temperature Tc supplied to the cathode 11a in the power generation mode (see FIG. 6 described later).

  In step S36, the control unit 31 waits for a predetermined time to elapse (between times t1 and t2 in FIG. 6 described later).

  In step S38, the control unit 31 determines whether or not the stack temperature Ts is within the range of the lower limit value T2min and the upper limit value T2max of the stack temperature during the temperature equalization process. If it is not within this range (NO in step S38), in step S39, the control unit 31 extends the predetermined time used in the process of step S36.

  On the other hand, when it is determined that the stack temperature Ts falls within the range of the lower limit value T2min and the upper limit value T2max of the stack temperature during the temperature equalization process (YES in step S38), in step S40, the control unit 31 stops the combustion gas output from the start-up combustor 21 (time t2 in FIG. 6), and further supplies air to the cathode 11a of the stack 11. Further, the generated voltage Vs by the stack 11 is set to the target voltage V2. It is desirable that V2 ≦ V1.

  In step S41, the control unit 31 determines whether or not the stack temperature Ts is between the lower limit value T3min and the upper limit value T3max of the target temperature of the stack 11 in the power generation mode. If “T3min ≦ Ts ≦ T3max” is not satisfied (NO in step S41), the flow rate of air supplied to the cathode 11a is adjusted in step S42. For example, when the stack temperature Ts falls below T3min, it is determined that the temperature of the stack 11 has dropped too much, and the air flow rate of the cathode 11a is reduced.

  On the other hand, if “T3min ≦ Ts ≦ T3max” (YES in step S41), in step S43, the control unit 31 determines whether or not the generated current Is has reached the target current value I1 in the power generation mode. That is, it is determined whether or not “Is = I1”. If it is not “Is = I1” (NO in step S43), in step S44, the control unit 31 increases the air flow rate supplied to the cathode 11a and reaches the allowable current value limit calculated from the cathode air flow rate. The generated current Is is increased by lowering the voltage a little so as to be within the range. In this case, the air flow rate increase amount and the voltage decrease amount per step can be set in advance. The target current value I1 is a generated current calculated from the system request output. Thereafter, the process returns to step S41.

  If the generated current Is has reached the target current value I1 (YES in step S43), in step S45, the control unit 31 shifts the process from the start mode to the generated mode. That is, the power generation mode is started, and the power generation output can be taken out from the fuel cell system.

  Next, the temperature change and flow rate change of each part by the above-described processing procedure will be described with reference to the characteristic diagram shown in FIG. In the second embodiment, similarly to the first embodiment described above, the heating mode in which the startup mode until the start-up combustor 21 is operated and the power generation mode is reached increases the temperature of the entire system including the stack 11; The control is performed by distinguishing between two steps, a temperature equalizing step for equalizing the temperature of the entire stack 11 after the temperature is raised.

  In the heating temperature raising step, the start-up combustor 21 is started at time t0, combustion gas is output, the combustion gas is supplied to the stack 11, and the stack 11 is heated. At this time, the combustion gas temperature Tb gradually increases between the times t0 and t1. Along with this, the stack temperature (stack upstream temperature) Ts gradually rises between times t0 and t1. Furthermore, the downstream portion temperature q1 of the stack 11 gradually increases at a temperature slightly lower than the stack temperature Ts. At this time, the flow rate Fb of the combustion gas output from the start-up combustor 21 is controlled to be a substantially constant flow rate Fb1.

  When the control unit 31 detects that the stack temperature Ts has reached the preset temperature equalization start temperature T1 at time t1, the control unit 31 sets the combustion gas temperature Tb to the preset temperature Tb2 (combustion gas temperature at time t1). (Temperature lower than Tb1) is adjusted to decrease, and then this temperature Tb2 is maintained. Similarly, the flow rate Fb of the combustion gas is adjusted to decrease to a preset value Fb2 (a flow rate smaller than the combustion gas flow rate Fb1 at time t1), and then this flow rate Fb2 is maintained. Specifically, as shown between times t1 and t2 in FIG. 3, the control is performed to slightly reduce the combustion gas temperature Tb and the combustion gas flow rate Fb and then maintain them at a constant value. During this time, the temperature of the entire stack 11 from the upstream side to the downstream side is equalized.

  At a time t2 when a predetermined time has elapsed from the time t1, the combustion gas from the start-up combustor 21 is stopped, and air is introduced into the cathode 11a to start power generation by the stack 11. Thereafter, when the generated current Is reaches the target current value I1 at time t3, the mode shifts to the power generation mode.

  Here, in the temperature equalization step, the time (between t1 and t2) for holding the combustion gas temperature Tb and the combustion gas flow rate Fb can be a predetermined time, or two temperatures in the stack 11. Based on the difference information ΔTs, it can be determined that ΔTs <C (where C is a constant). Then, power generation by the stack 11 is started at time t2 after being held for a certain time. That is, power is generated by introducing air into the cathode 11a of the stack 11.

  Thus, when starting up the combustor 21 and raising the temperature of the stack 11, the temperature from the upstream side to the downstream side of the stack 11 is equalized by performing the temperature equalization step. It will be possible to adjust and then shift to the power generation mode.

  As described above, in the fuel cell system according to the second embodiment of the present invention, similarly to the first embodiment described above, after the stack 11 is heated to reach the set temperature T1, the process by the temperature equalizing step is performed. Since the temperature of the entire stack 11 can be equalized by executing the above, the temperature difference generated in the stack 11 can be reduced, and deterioration and damage of the stack 11 due to local temperature fluctuations can be prevented. It becomes possible.

  Further, by reducing both the combustion gas temperature Tb and the combustion gas flow rate Fb to equalize the stack temperature, the temperature equalization required from the end of the temperature increase of the stack 11 to the start of power generation. The step time can be shortened.

  Further, after the combustion gas temperature Tb and the combustion gas flow rate Fb are lowered, the temperature and the flow rate are maintained for a certain time, so that the temperature rise on the downstream side can be promoted, and the stack temperature can be more stably leveled. Can be warmed.

  In addition, since power generation is started after a lapse of a predetermined time between time t2 when the combustion gas temperature and flow rate are reduced and time t3 when air is introduced, the temperature of the downstream portion is not increased excessively. Since the increase is promoted, the output current of the fuel cell can be made to reach the desired output current immediately in a state where the stack temperature is equalized, and the time required for starting can be shortened.

  Furthermore, since the power generation air is supplied to the cathode 11a after the supply of the combustion gas is stopped, it is not necessary to control both the combustion gas and the power generation air at the same time, and the control load can be reduced.

[Description of Operation of Third Embodiment]
Next, with reference to the flowchart shown in FIG. 7, the operation | movement at the time of starting of the fuel cell system which concerns on 3rd Embodiment is demonstrated. In FIG. 7, the processing from step S31 to S35 is the same as the processing from step S31 to S35 shown in FIG. 5, and thus the same step number is assigned and description thereof is omitted. When the process of step S35 ends, the process of step S51 is performed.

  In step S <b> 51, the control unit 31 starts power generation by the stack 11. The generated voltage Vs at this time is set to the voltage V1. Then, the voltage V1 is gradually decreased.

  In step S52, the control unit 31 determines whether or not the stack temperature Ts is within the range of the lower limit value T2min and the upper limit value T2max of the stack temperature during the temperature equalization process. Further, it is determined whether or not the elapsed time since the start of power generation has reached a preset time P1. If the determination in step S52 is NO, in step S53, the control unit 31 adjusts the power generation voltage of the stack 11 so that the condition of step S52 is satisfied.

  On the other hand, when the determination in step S52 is YES, in step S54, the control unit 31 stops the combustion gas output from the start-up combustor 21, and further introduces air into the cathode 11a of the stack 11, The power generation voltage Vs generated by the stack 11 is set to the target voltage V2. Note that V2 ≦ V1 is desirable.

  In step S55, the control unit 31 determines whether or not the stack temperature Ts is between the lower limit value T3min and the upper limit value T3max of the target temperature of the stack 11 in the power generation mode. If “T3min ≦ Ts ≦ T3max” is not satisfied (NO in step S55), the air flow rate supplied to the cathode 11a is adjusted in step S56. For example, when the stack temperature Ts is lower than T3min, it is determined that the temperature of the stack 11 has decreased too much, and the air flow rate of the cathode 11a is decreased.

  On the other hand, if “T3min ≦ Ts ≦ T3max” (YES in step S55), in step S57, the control unit 31 determines whether or not the generated current Is has reached the target current value I1 in the power generation mode. That is, it is determined whether or not “Is = I1”. If “Is = I1” is not satisfied (NO in step S57), in step S58, the control unit 31 increases the air flow rate supplied to the cathode 11a and reaches the allowable current value limit calculated from the cathode air flow rate. The generated current Is is increased by lowering the voltage a little so as to be within the range. In this case, the air flow rate increase amount and the voltage decrease amount per step can be set in advance. The target current value I1 is a generated current that determines whether the power generation mode can be started. Thereafter, the process returns to step S55.

  When the generated current Is has reached the target current value I1 (YES in step S57), in step S59, the control unit 31 shifts the process from the start mode to the generated mode. That is, the power generation mode is started, and the power generation output can be taken out from the fuel cell system.

  Next, the temperature change and flow rate change of each part by the above-described processing procedure will be described with reference to the characteristic diagram shown in FIG. In the third embodiment, as in the first and second embodiments described above, the start-up mode from when the start-up combustor 21 is operated to the power generation mode is changed to the heating increase in which the entire system including the stack 11 is heated. A temperature step and a temperature equalizing step for equalizing the temperature of the entire stack 11 after the temperature is raised are distinguished.

  In the heating temperature raising step, the start-up combustor 21 is started at time t0, combustion gas is output, the combustion gas is supplied to the stack 11, and the stack 11 is heated. At this time, the combustion gas temperature Tb gradually increases between the times t0 and t1. Along with this, the stack temperature (stack upstream temperature) Ts gradually rises between times t0 and t1. Furthermore, the downstream portion temperature q1 of the stack 11 gradually increases at a temperature slightly lower than the stack temperature Ts. At this time, the flow rate Fb of the combustion gas output from the start-up combustor 21 is controlled to be a substantially constant flow rate Fb1.

  When the control unit 31 detects that the stack temperature Ts has reached the preset temperature equalization start temperature T1 at time t1, the control unit 31 decreases the combustion gas temperature Tb to the preset temperature Tb2 (<Tb1). Further, the flow rate Fb of the combustion gas is adjusted so as to decrease to a preset Fb2 (<Fb1).

  At time t2 when the combustion gas temperature Tb and the combustion gas flow rate Fb decrease, the stack 11 starts power generation (see step S51 in FIG. 7). Then, the generated voltage Is is gradually increased until time t3 by holding the generated voltage by the stack 11 at a predetermined value or by gradually decreasing it according to a preset program.

  Further, after time t2, the combustion gas temperature Tb maintains Tb2, and the combustion gas flow rate Fb maintains Fb2. Then, when the predetermined time P1 has elapsed from time t2 (time t3), the supply of combustion gas is stopped (see step S54 in FIG. 7), air is introduced into the cathode 11a, and the power generation voltage is set to V2. Start power generation. The air flow rate and the generated voltage are adjusted so that the stack temperature Ts becomes equal to or higher than T3min and equal to or lower than T3max, and the generated current Is becomes the target current I1, and then, at time t4, the generated current Is reaches the target current value I1, Migrate to As a result, the temperature of the entire downstream side from the upstream side of the stack 11 is equalized between times t1 and t4.

  Thus, when starting up the combustor 21 and raising the temperature of the stack 11, the temperature from the upstream side to the downstream side of the stack 11 is equalized by performing the temperature equalization step. It can be adjusted and then shifted to the power generation mode.

Thus, in the fuel cell system according to the third embodiment of the present invention, after the stack temperature Ts reaches the temperature equalization start temperature T1, power generation is started by reducing the combustion gas flow rate and temperature. too raised the temperature of the section, while stabilized without excessive Gitari reduced, it is possible to raise the temperature of the downstream portion, faster time Atsushi Nobori step in addition to the shortening of HitoshiAtsushika step Can also be performed, and the startup time can be shortened.

  Further, the flow rate of the combustion gas at the time of the temperature equalizing step can be reduced, and the power of the fuel and the air blower to be input to the start burner required for executing the temperature equalizing step can be reduced. Energy can be reduced.

  Here, as in the third embodiment, when power generation for raising the temperature of the stack 11 is started at time t2 immediately after the heating temperature raising step is completed, it is advantageous for a stack having a relatively large heat capacity. is there. In the case of a stack having a relatively large heat capacity, the energy required for temperature increase increases, so reduction of the startup energy is an important issue. However, the closer the power generation start time is to time t2, the greater the effect of reducing the startup energy. On the other hand, power generation will start before the temperature inside the stack is sufficiently equalized, but in a stack with a large heat capacity, local temperature fluctuations due to local heat generation are likely to be suppressed, so transition from startup mode to power generation mode Therefore, the temperature distribution of the stack 11 can be made uniform.

[Description of Operation of Fourth Embodiment]
Next, a fourth embodiment of the present invention will be described. The fuel cell system according to the fourth embodiment starts power generation during the temperature equalizing step, and performs the temperature equalizing step to reduce the temperature difference between the upstream portion and the downstream portion while increasing the temperature of both the upstream portion and the downstream portion. As a result, the startup energy is reduced and the time required to start power generation is shortened.

  The operation of the fuel cell system according to the fourth embodiment will be described below with reference to the characteristic diagram shown in FIG. In the heating temperature raising step shown in FIG. 9, the start-up combustor 21 is started at time t <b> 0 and combustion gas is output, and the combustion gas is supplied to the stack 11 to heat the stack 11. At this time, the combustion gas temperature Tb gradually increases between the times t0 and t1. Along with this, the stack temperature (stack upstream temperature) Ts gradually rises between times t0 and t1. Furthermore, the downstream portion temperature q1 of the stack 11 gradually increases at a temperature slightly lower than the stack temperature Ts. At this time, the flow rate Fb of the combustion gas output from the start-up combustor 21 is controlled to be a substantially constant flow rate Fb1.

  When the control unit 31 detects that the stack temperature Ts has reached the preset temperature equalization start temperature T1 at time t1, the control unit 31 decreases the combustion gas temperature Tb to the preset temperature Tb2 (<Tb1). Further, the flow rate Fb of the combustion gas is adjusted so as to decrease to a preset Fb2 (<Fb1).

  Thereafter, power generation by the stack 11 is started at time t2 when the combustion gas temperature Tb and the combustion gas flow rate Fb decrease. When the power generation voltage Vs is set to the voltage V1, heat generation accompanying power generation is first started in the upstream portion of the stack 11, and the temperature in the upstream portion continues to increase although the rate of temperature increase decreases. As the power generation possible area spreads downstream, the temperature of the downstream part continues to rise. Since power generation is started by reducing the flow rate and temperature of the combustion gas, the temperature rise rate at the upstream portion can be reduced to raise the temperature gently. As a result, only the most upstream part is prevented from suddenly rising in temperature and causing thermal runaway. Since the temperature of the downstream portion is also raised and reaches the power generation possible temperature, heat is generated, so that the temperature increase rate in the downstream portion continues to increase. After the generated current reaches I2, the voltage Vs is gradually increased from the temperature rise rate at the upstream portion, and control is performed so that the increase rate of the current value accompanying the temperature rise at the downstream portion is slow. At time t3 when the generated current reaches I2, most of the stack reaches the power generation possible temperature, and the temperature rise rate in the downstream portion starts to exceed the temperature rise rate in the upstream portion.

  Thereafter, when the generated current Is reaches the preset upper limit current value I3 at time t4, the generated voltage Vs is increased from time t4 to gradually decrease the generated current Is. As a result, the temperature increase rate in the downstream portion is reduced, and the temperature difference between the upstream portion and the downstream portion is small and stable. At time t4, the stack temperature Ts is higher than the temperature T1 at the start of the temperature equalization step. When the stack temperature Ts becomes equal to or higher than T2min and equal to or lower than T2max and a predetermined time P1 elapses, supply of the combustion gas is stopped and air is supplied to the cathode 11a. The air flow rate and the power generation voltage are adjusted so that the stack temperature Ts becomes equal to or higher than T3min and equal to or lower than T3max, and the power generation current Is becomes I1.

  Next, a change in the temperature distribution of the stack 11 will be described with reference to a characteristic diagram shown in FIG. In this embodiment, as shown by the curve n21 in the heating temperature raising step, the lowest power generation temperature has been reached on the upstream side of the stack 11, but the lowest power generation temperature has not been reached on the downstream side of the stack 11. . Then, by performing the temperature equalization step, the temperature on the downstream side rises and the temperature distribution of the stack 11 is made uniform as shown by the curve n22. That is, the temperature on the upstream side also rises, and the temperature on the downstream side of the stack 11 reaches the lowest power generation possible temperature. Thereafter, when the mode is shifted to the power generation mode, the temperature on the downstream side of the stack 11 becomes higher than the temperature on the upstream side, as indicated by a curve n23.

  Thus, after the temperature equalization step is started and the combustion gas temperature Tb is reduced and the combustion gas flow rate Fb is reduced, the power generation by the stack 11 is started and the power generation current Is is increased, whereby the upstream portion of the cathode 11a, It is possible to raise the temperature of both the downstream portions so that the entire stack 11 reaches the target temperature in the power generation mode.

  In this manner, in the fuel cell system according to the fourth embodiment, the stack 11 is heated by performing power generation by the stack 11 in the temperature equalization step in which the flow temperature of the combustion gas is lowered. It is possible to reduce energy applied to the starting burner for producing combustion gas from an early stage when the temperature of the downstream portion does not reach the power generation possible temperature. Further, since the temperature can be equalized while raising the average temperature from the upstream to the downstream, the activation time can be shortened and the energy required for activation can be reduced.

  Although the fuel cell system of the present invention has been described based on the illustrated embodiment, the present invention is not limited to this, and the configuration of each part is replaced with an arbitrary configuration having the same function. Can do.

  For example, in each of the embodiments described above, an example using a solid oxide fuel cell has been described. However, the present invention is not limited to a solid oxide fuel cell, and a proton conductive electrolyte layer operating at a high temperature is used. It can also be used for the fuel cell used. The fuel cell may be a tube type in addition to the flat plate stack type.

  The present invention can be used to equalize the temperature of the fuel cell when the fuel cell is started.

DESCRIPTION OF SYMBOLS 11 Stack 11a Cathode 11b Anode 12 Air blower 13 Heat exchanger for air preheating 14 Fuel pump 15 Fuel reformer 16 Reformer heating burner 17 Booster pump 18 Partial pressure valve 21 Start-up combustor 22 Valve 23 Fuel pump 24, 25 Evaporator 26, 27 Air blower 31 Control unit 100 Fuel cell system

Claims (9)

In a fuel cell system comprising at least a fuel cell and a start-up combustor that raises the temperature of the fuel cell during start-up,
The fuel cell is operated in a startup mode in which the temperature of the fuel cell is raised during startup, and in a power generation mode in which power generation is performed in response to an output request after the temperature of the fuel cell is raised,
In the start-up mode, the combustion gas from the start-up combustor is supplied to the fuel cell to raise the temperature of the fuel cell, and then the temperature of the fuel cell reaches a preset set temperature . fuel cell system characterized by comprising a control means for decreasing the flow rate of the previous SL combustion gas performs control for supplying to the fuel cell. When the fuel cell reaches the set temperature , the control means reduces the flow rate of the combustion gas and supplies the fuel cell to the second set temperature range lower than the set temperature. The fuel cell system according to claim 1, wherein power generation in the power generation mode is performed after the arrival. The control means performs control for reducing the temperature of the combustion gas in addition to reducing the flow rate of the combustion gas after the temperature of the fuel cell reaches the set temperature in the start-up mode. The fuel cell system according to claim 1 or 2, characterized in that The control means reduces the flow rate of the combustion gas and reduces the combustion gas temperature, holds the reduced flow rate for a certain period of time, and holds the reduced combustion gas temperature for a certain period of time. The fuel cell system according to claim 3 . 5. The control device according to claim 1, wherein the control unit stops the combustion gas after reducing the flow rate of the combustion gas, and then supplies air to the cathode in the power generation mode. The fuel cell system according to item. Wherein, after reducing the flow rate of the supplied combustion gas to the fuel cell, if a value below the set flow rate set in advance, according to claim 1 to claim 5, characterized in that makes starting the generator The fuel cell system according to any one of claims. Wherein, after reducing the flow rate of the supplied combustion gas to the fuel cell, when a predetermined time has elapsed, according to claim 1 to claim 5, characterized in that to start the power generation by the fuel cell The fuel cell system according to any one of claims. Wherein, after reducing the flow rate of the supplied combustion gas to the fuel cell starts power generation by the fuel cell immediately after reaching the target current value generated current is preset to the generator mode The fuel cell system according to any one of claims 1 to 5, wherein the fuel cell system is shifted. The control means starts power generation by the fuel cell immediately after reducing the flow rate of the combustion gas supplied to the fuel cell, and decreases the generated current after the generated current reaches a preset upper limit current value. 9. The fuel cell system according to claim 8, wherein the fuel cell system is shifted to the power generation mode after reaching the target current value.

Images