Fuel cell system with co detector

A fuel cell system of the present invention includes: a hydrogen generator (1) having a reformer (1a) configured to generate a hydrogen-containing gas by a reforming reaction using a raw material; a fuel cell (2) configured to generate electric power using the hydrogen-containing gas supplied from the hydrogen generator (1); a combustor (3) configured to combust an anode off gas discharged from the fuel cell (2) to heat the reformer (1a); a CO detector (7) configured to detect a carbon monoxide concentration of a flue gas discharged from the combustor (3); an electric heater (8) configured to heat the CO detector (7); and a controller (19), and the controller (19) is configured to increase an amount of energization to the electric heater (8) in accordance with an increase in an amount of electric power generated by the fuel cell (2).

RELATED APPLICATIONS

This application is the U.S. National Phase under 35 U.S.C. §371 of International Application No. PCT/JP2009/000746, filed on Feb. 20, 2009, which in turn claims the benefit of Japanese Application No. 2008-038238, filed on Feb. 20, 2008, the disclosures of which Applications are incorporated by reference herein.

TECHNICAL FIELD

The present invention relates to a fuel cell system including a hydrogen generator having a combustor configured to supply heat for a reforming reaction.

BACKGROUND ART

As shown inFIG. 8, a conventional fuel cell system includes a hydrogen generator81and a fuel cell82. The hydrogen generator81generates a hydrogen-containing gas by a reforming reaction using as a raw material a hydrogen-containing organic compound, such as a city gas. The fuel cell82generates electric power using the hydrogen-containing gas supplied from the hydrogen generator81and an oxidizing gas. The fuel cell system is normally configured such that a combustible anode off gas discharged from the fuel cell82is combusted in a combustor, and heat necessary for the reforming reaction is supplied to the hydrogen generator81. A CO sensor85is normally used to confirm combustion stability of the combustor83. If moisture in a flue gas discharged from the combustor83condenses on the CO sensor85, detection failures occur. Therefore, proposed is to dispose a water discharging portion84, configured to discharge condensed water, on a flue gas channel in front of the CO sensor85(see Patent Document 1 for example).

Meanwhile, to solve the problem of the condensation with respect to the CO sensor, proposed is a combusting device in which an electric heater is disposed in the vicinity of the CO sensor (see Patent Document 2 for example).

Patent Document 1: Japanese Laid-Open Patent Application Publication 2006-213566

Patent Document 2: Japanese Laid-Open Patent Application Publication 8-035655

DISCLOSURE OF THE INVENTION

Problems to be Solved by the Invention

Here, in a case where the electric heater is disposed in the vicinity of the CO sensor as in Patent Document 2 to solve the problem of the condensation with respect to the CO sensor of the fuel cell system in Patent Document 1, the electric heater needs to heat the CO sensor to prevent the condensation on the CO sensor since the temperature of ambient surroundings of the fuel cell system including the CO sensor is low at the time of a start-up operation of the fuel cell system. In contrast, since the temperature is increased at the time of the start-up operation of the fuel cell system, the amount of heat for heating the CO sensor is normally reduced during an electric power generating operation. Here, the problem is that if the amount of electric power generated by the fuel cell is increased during the electric power generating operation, the condensation may occur on the CO sensor.

The present invention was made to solve the above problems, and an object of the present invention is to provide a fuel cell system which uses an electric heater configured to heat a CO sensor disposed on a passage of a flue gas of a combustor configured to combust an anode off gas of a fuel cell, and is capable of suppressing condensation with respect to the CO sensor during an electric power generating operation of the fuel cell as compared to before.

Means for Solving the Problems

As a result of diligent studies regarding the above problems, the present inventors have obtained findings as follows: even in a case where the amount of electric power generated by the fuel cell is large, i.e., the amount of combustible gas in the anode off gas may be large and the amount of moisture in the flue gas may be large, the condensation is unlikely to occur as long as the amount of electric power generated by the fuel cell is maintained at such high level, but the condensation with respect to the CO sensor tends to occur in a process in which the amount of electric power generated by the fuel cell is increasing. This may be because: in a case where the amount of electric power generated by the fuel cell is small, the amount of heat contained in the flue gas is small, so that the temperature of the CO sensor itself tends to become low; and if the amount of electric power generated by the fuel cell increases when the temperature of the sensor is low, the flue gas which is high in temperature and has a large amount of moisture contacts the CO sensor, and this tends to cause the condensation.

To solve the above conventional problems based on the above findings, a fuel cell system of the present invention includes: a hydrogen generator including a reformer configured to generate a hydrogen-containing gas by a reforming reaction using a raw material; a fuel cell configured to generate electric power using the hydrogen-containing gas supplied from the hydrogen generator; a combustor configured to combust an anode off gas discharged from the fuel cell to heat the reformer; a CO detector configured to detect a carbon monoxide concentration of the flue gas discharged from the combustor; an electric heater configured to heat the CO detector; and a controller, wherein the controller is configured to increase an amount of energization to the electric heater in accordance with an increase in an amount of electric power generated by the fuel cell.

With this configuration, it is possible to suppress the possibility that when the amount of electric power generated by the fuel cell is increased, the moisture contained in the anode off gas of the fuel cell condenses on the CO detector. Thus, combustion stability of the combustor can be more stably monitored.

Moreover, the fuel cell system of the present invention may further include an electric power generation amount controller configured to control an amount of electric power obtained from the fuel cell, wherein the controller may be configured to increase the amount of energization to the electric heater in a case where the electric power generation amount command value given to the electric power generation amount controller increases.

Moreover, in the fuel cell system of the present invention, the controller may be configured to increase the amount of energization to the electric heater in a case where an amount of power consumption of an electric power load is larger than the amount of electric power generated by the fuel cell.

Moreover, in the fuel cell system of the present invention, the controller may be configured to increase the amount of energization to the electric heater in a case where the amount of electric power generated by the fuel cell increases.

Moreover, in the fuel cell system of the present invention, increasing the amount of energization to the electric heater may include turning the electric heater from off to on.

Moreover, in the fuel cell system of the present invention, the controller may control the electric heater such that in a case where the electric heater is turned on, the electric heater is maintained in an on state for a predetermined holding time, regardless of increase or decrease in the amount of electric power generated by the fuel cell after the electric heater is turned on.

With this configuration, the number of on-off operations of the electric heater is reduced, so that the durability of the electric heater improves.

Moreover, in the fuel cell system of the present invention, an average amount of energization to the electric heater during an electric power generating operation of the fuel cell system may be smaller than the average amount of energization to the electric heater during a start-up operation of the fuel cell system.

With this configuration, while suppressing a decrease in energy efficiency due to the electric power consumption of the electric heater, it is possible to suppress the possibility that the moisture contained in the anode off gas of the fuel cell condenses on the CO detector. Thus, the combustion stability of the combustor can be more stably monitored.

Moreover, in the fuel cell system of the present invention, an average amount of energization to the electric heater during an electric power generating operation of the fuel cell system may be smaller than a maximum amount of energization to the electric heater during a start-up operation of the fuel cell system.

Moreover, in the fuel cell system of the present invention, a base amount of energization to the electric heater which is an amount before the amount of energization to the electric heater during an electric power generating operation of the fuel cell system is increased may be smaller than the base amount of energization to the electric heater during a start-up operation of the fuel cell system.

With this configuration, while suppressing the decrease in the energy efficiency due to the electric power consumption of the electric heater, it is possible to suppress the possibility that the moisture contained in the anode off gas of the fuel cell condenses on the CO detector. Thus, the combustion stability of the combustor can be more stably monitored.

Moreover, in the fuel cell system of the present invention, the base amount of energization to the electric heater which is the amount before the amount of energization to the electric heater during the electric power generating operation of the fuel cell system may be zero.

Further, in the fuel cell system of the present invention, the controller may be configured to turn off the electric heater after the on state of the electric heater is continued for the predetermined holding time.

The above object, other objects, features and advantages of the present invention will be made clear by the following detailed explanation of preferred embodiments with reference to the attached drawings.

Effects of the Invention

In accordance with the fuel cell system of the present invention, it is possible to suppress the condensation of the moisture, contained in the flue gas, on the CO detector when the amount of electric power generated by the fuel cell is increased. Thus, the combustion stability of the combustor configured to heat the reformer can be more stably monitored.

EXPLANATION OF REFERENCE NUMBERS

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, best modes of the present invention will be explained in reference to the drawings. In the drawings, the same reference numbers are used for the same or corresponding portions, and a repetition of the same explanation is avoided.

FIG. 1is a diagram showing a schematic configuration of a fuel cell system of Embodiment 1 of the present invention.

As shown inFIG. 1, a fuel cell system100of Embodiment 1 includes: a hydrogen generator1having a reformer1aconfigured to generate a hydrogen-containing gas by a steam-reforming reaction using a raw material supplied from a material supplier12and water supplied from a water supplier13; a fuel cell2configured to generate electric power using the hydrogen-containing gas supplied from the hydrogen generator1and an oxidizing gas supplied from an oxidizing gas supplier14; a combustor3configured to combust an anode off gas discharged from the fuel cell2to supply heat to the reformer1afor the steam-reforming reaction; a flue gas passage4through which a flue gas discharged from the combustor3flows; a first heat exchanger5configured to condense moisture in the flue gas flowing through the flue gas passage4; a condensed water tank6configured to store condensed water condensed by the first heat exchanger5; a CO detector7configured to detect a carbon monoxide concentration of the flue gas from which the moisture is removed by the first heat exchanger5; an electric heater8disposed in the vicinity of the CO detector7to suppress the condensation on the CO detector7; a cooling water passage9through which cooling water for cooling down the fuel cell2flows; a second heat exchanger10configured to recover heat from the cooling water; a hot water tank11configured to store as hot water the heat recovered by the first heat exchanger5and the second heat exchanger10; an electric power generation amount controller15configured to control the amount of electric power obtained from the fuel cell2; a first current detector16disposed between a system power supply and an interconnection point located between the fuel cell2and the system power supply; a second current detector17configured to detect the amount of current output from the electric power generation amount controller15; a switching unit18configured to switch a supply destination of the hydrogen-containing gas generated in the hydrogen generator1, between the fuel cell2and a passage bypassing the fuel cell2; and a controller19configured to control operations of devices in the fuel cell system100.

The hydrogen generator1includes not only the reformer1abut also a shift converter (not shown) configured to reduce, by a shift reaction, carbon monoxide in the hydrogen-containing gas generated by the reformer1aand a CO remover (not shown) configured to reduce the carbon monoxide by an oxidation reaction. The material supplier12supplies the hydrogen-containing organic compound, such as a city gas, as the raw material to the hydrogen generator1. The electric power generation amount controller15includes an inverter as an AC/DC inverter configured to convert DC power of the fuel cell2into AC power. The controller19outputs an electric power generation amount command value to the electric power generation amount controller15based on power consumption of an electric power load so as to follow the power consumption of the electric power load. In the fuel cell system100of Embodiment 1, the controller19controls on and off of the electric heater8based on the electric power generation amount command value. Moreover, for example, a sheath heater or the like is utilized as the electric heater8. An installation mode of the electric heater8is not especially limited as long as the electric heater8can heat the CO detector7.

Next, operations of the fuel cell system100of Embodiment 1 will be explained.

FIG. 2is a diagram showing time-lapse changes of the power consumption of the electric power load, time-lapse changes of the amount of electric power generated by the fuel cell2of the fuel cell system100of Embodiment 1 with respect to the above time-lapse changes of the power consumption of the electric power load, and control of on-off operations of the electric heater8with respect to the amount of electric power generated by the fuel cell2.

As shown inFIG. 2, by turning on the electric heater8in the case of increasing the amount of electric power generated by the fuel cell2, the fuel cell system100of Embodiment 1 suppresses the condensation on the CO detector7in a process in which a temperature of the flue gas discharged from the combustor3and an amount of moisture in the flue gas increase. Whether or not the amount of electric power generated by the fuel cell2is increased is determined based on the electric power generation amount command value output from the controller19to the electric power generation amount controller15. Moreover, once the electric heater8is turned on, the on operation is continued for a predetermined holding time T1or more, regardless of increase or decrease in the electric power generation amount command value of the fuel cell2after the electric heater8is turned on. Thus, frequent on-off operations of the electric heater8are suppressed, and this leads to suppression of deterioration of the electric heater8.

More specific operations of the electric heater8will be explained in reference to the flow chart shown inFIG. 3. First, when a start-up operation of the fuel cell system100is started, the controller19turns on the electric heater8to suppress the condensation on the CO detector7. Then, when a step of increasing the temperature of the hydrogen generator1is completed, and the carbon monoxide in the hydrogen-containing gas generated by the hydrogen generator1is adequately reduced, the controller19switches the switching unit18such that the supply destination of the hydrogen-containing gas supplied from the hydrogen generator1is switched from a bypass passage to the fuel cell2side, and the start-up operation of the fuel cell system100is terminated. Then, an electric power generating operation of the fuel cell2is started.

Then, during the electric power generating operation of the fuel cell2, the electric power generation amount command value is output from the controller19to the electric power generation amount controller15for every predetermined time. Whether or not the amount of change of the current electric power generation amount command value with respect to the previous electric power generation amount command value (output the predetermined time ago) is a positive value is determined, to be specific, whether or not the amount of electric power generated by the fuel cell2is increased by the controller19is determined (Step S31). In a case where it is determined in Step S31that the electric power generation amount command value of the fuel cell2is increased, the electric heater8is turned on (Step S32). In a case where it is determined that the amount of electric power generated is not increased, the process returns to Step S31, and whether or not the amount of electric power generated by the fuel cell2is increased is determined for every predetermined time.

Next, in a case where the electric heater8is turned on, the electric heater8is maintained in an on state until the predetermined holding time T1elapses (Step S33). After that, the electric heater8is turned off (Step S34). Then, in a case where the fuel cell2is carrying out the electric power generating operation, the process returns to Step S31, and the above operations are repeated.

The foregoing has explained that in the fuel cell system100of Embodiment 1, the on-off operations of the electric heater8are controlled based on whether or not the amount of electric power generated by the fuel cell2is increased. However, the fuel cell system100of Embodiment 1 may be configured such that during the electric power generating operation of the fuel cell system100, the on operation of the electric heater8is continuously carried out, and the amount of energization to the electric heater8is increased or decreased in accordance with the increase or decrease in the amount of electric power generated by the fuel cell2(increase or decrease in the electric power generation amount command value or increase or decrease in a current value detected by the second current detector17). To be specific, in a case where the electric power generation amount command value of the fuel cell2increases or in a case where the start of the increase in the amount of electric power generated by the fuel cell2is detected by the current value detected by the second current detector17, it is estimated that the temperature of the flue gas passing through the CO detector7and the amount of moisture in the flue gas increase. Therefore, the amount of energization to the electric heater8is increased to increase the amount of heat generated by the electric heater8. Moreover, in a case where the electric power generation amount command value of the fuel cell2decreases, it is estimated that the temperature of the flue gas passing through the CO detector7and the amount of moisture in the flue gas decrease. Therefore, the amount of energization to the electric heater8is reduced. The above phrase “amount of energization” denotes the amount of electric power supplied to the electric heater8per unit time. The amount of heat generated by the electric heater8may be increased or decreased by the increase or decrease in the amount of energization to the electric heater8. Therefore, the fuel cell system100may adopt a mode in which the voltage applied to the electric heater8is consecutively increased or decreased. Moreover, so called “Duty control” may be carried out, i.e., a predetermined voltage pulse which is periodically turned on and off may be applied to the electric heater8to increase or decrease the amount of energization based on the ratio of an on time per one cycle. For example, in a case where the controller19applies a voltage pulse of one-second cycle to the electric heater8so as to turn on the electric heater8for 100 milliseconds and turn off for remaining 900 milliseconds, the amount of energization can be decreased by setting the on time in one-second cycle to 50 milliseconds, and the amount of energization can be increased by setting the on time in one-second cycle to 150 milliseconds.

Moreover, the controller19controls the electric heater8based on whether or not the amount of electric power generated by the fuel cell2is increased. However, the present embodiment is not limited to this, and the controller19may control the electric heater8based on a control value (a control value of the amount of raw material supplied to the hydrogen generator1, a control value of the amount of water supplied to the hydrogen generator1, a control value of the amount of air supplied to a cathode of the fuel cell2, or the like) of a physical quantity controlled in accordance with the increase or decrease in the amount of electric power generated by the fuel cell2or based on a detected value of each detector (a detector configured to detect the flow rate of raw material supplied from the material supplier12to the hydrogen generator1, a detector configured to detect the amount of water supplied to the hydrogen generator1, a detector configured to detect the amount of air supplied to the cathode of the fuel cell2, or the like), not shown, of a physical quantity controlled in accordance with the increase or decrease in the amount of electric power generated by the fuel cell2.

Here, as described above, the fuel cell2generates electric power by the hydrogen-containing gas generated by the hydrogen generator1using the raw material supplied from the material supplier12and the water supplied from the water supplier13, and the oxidizing gas (herein, air) supplied from the oxidizing gas supplier14, and the controller19increases or decreases the amounts of these in accordance with the amount of electric power generated by the fuel cell2. Therefore, instead of the amount of electric power generated by the fuel cell2used in Embodiment 1, the controller19may control the electric heater8based on a raw material flow rate, a water flow rate, or an air flow rate detected by each detector, or a flow rate command value to each supplier. To be specific, in a case where the raw material flow rate, the water flow rate, or the air flow rate detected by each detector, or the flow rate command value to each supplier increases, the controller19may adopt a mode in which the electric heater8is turned on or a mode in which the amount of energization to the electric heater8which is continuously carrying out the on operation even during the electric power generating operation is increased.

As above, the above “case where the increase in the amount of electric power generated by the fuel cell starts” defined in the present invention includes both a case where the amount of electric power generated by the fuel cell2is increased, i.e., a case where the increase in the control value (the electric power generation amount command value, the control value of the amount of raw material supplied, the control value of the amount of water supplied, the control value of the amount of air supplied, or the like) of the physical quantity directly or indirectly correlated to the amount of electric power generated by the fuel cell2starts and a case where the increase in the detected value (the detected value of the amount of current, the raw material flow rate, the water flow rate, the air flow rate, or the like) of the physical quantity directly or indirectly correlated to the amount of electric power generated by the fuel cell2starts.

Moreover,FIG. 2shows that the on operation of the electric heater8in a certain period is longer than the predetermined holding time T1. This period is a period in which although the electric heater8is turned off once as above, it is determined in second or later Step S31that the amount of change of the electric power generation amount command value of the fuel cell2increases, and the electric heater8is quickly turned on again. Therefore, the on operation of the electric heater8in this period becomes practically longer than the holding time T1.

In accordance with the fuel cell system100of Embodiment 1 explained as above, while suppressing the decrease in the energy efficiency due to the electric power consumption of the electric heater8, the condensation of the moisture contained in the anode off gas of the fuel cell2with respect to the CO detector17can be suppressed, and the combustion stability of the combustor3can be more stably monitored. Moreover, once the electric heater8is turned on, the controller19causes the electric heater8to continue the on operation for the predetermined holding time T1, regardless of the increase or decrease of the electric power generation amount command value of the fuel cell2after the electric heater8is turned on. Thus, frequent on-off operations of the electric heater8are suppressed, so that the deterioration of the electric heater8can be suppressed.

Next, the fuel cell system of Embodiment 2 of the present invention will be explained.

The fuel cell system100of Embodiment 2 is the same in configuration as the fuel cell system100of Embodiment 1 but is different from the fuel cell system100of Embodiment 1 in how the controller19controls on and off of the electric heater8. This difference will be explained in detail.

FIG. 4is a diagram showing time-lapse changes of the power consumption of the electric power load, time-lapse changes of the amount of electric power generated by the fuel cell2of the fuel cell system100of Embodiment 2 with respect to the above time-lapse changes of the power consumption of the electric power load, and control of the on-off operations of the electric heater8with respect to the amount of electric power generated by the fuel cell2.

As shown inFIG. 4, in a case where the power consumption of the electric power load is larger than the amount of electric power generated by the fuel cell2, the fuel cell system100of Embodiment 2 controls the amount of electric power generated by the fuel cell2such that the amount of electric power generated by the fuel cell2follows the power consumption of the electric load. Therefore, the electric power generation amount command value of the fuel cell2output from the controller19is likely to increase, and the electric heater8is turned on. To be specific, the above “case where the increase in the amount of electric power generated by the fuel cell starts” defined in the present invention includes a case where the increase in the amount of electric power generated by the fuel cell2is predicted. However, even in a case where the power consumption of the electric power load is larger than the amount of electric power generated by the fuel cell2, but a difference therebetween is small, the amount of electric power generated by the fuel cell2is unlikely to continuously increase. Therefore, it is preferable that the fuel cell system100be configured such that the electric heater8is turned on in a case where ΔW1that is the difference between the power consumption of the electric power load and the amount of electric power generated by the fuel cell2is equal to or more than a first threshold by which the amount of electric power generated by the fuel cell2is likely to continuously increase.

Hereinafter, details of the above control operation of the electric heater8of the fuel cell system100of Embodiment 2 will be explained based on the flow chart shown inFIG. 5. First, the electric power generating operation of the fuel cell2is started through the same start-up operation as explained in Embodiment 1, and whether or not ΔW1that is the difference between the power consumption of the electric power load and the amount of electric power generated by the fuel cell2is 150 W or more is determined by the controller19(Step S51). Here, the power consumption of the electric power load is a sum of the electric power generation amount command value output from the controller19and the current value detected by the first current detector16, and the amount of electric power generated by the fuel cell2is the electric power generation amount command value output from the controller19. In this case, the controller19and the second current detector17constitute a load power detector of the present invention, and the controller19also functions as an electric power generation detector of the fuel cell of the present invention. Instead of the electric power generation amount command value, the current value detected by the second current detector17disposed on an electric wiring extending between the electric power generation amount controller15and the interconnection point may be used to calculate the power consumption of the electric power load, and the calculated power consumption of the electric power load may be used as the amount of electric power generated by the fuel cell2. In this case, the first current detector16and the second current detector17constitute the load power detector of the present invention, and the second current detector17constitutes the electric power generation detector of the fuel cell of the present invention.

Next, in a case where it is determined in Step S51that ΔW1is 150 W or more, the electric heater8is turned on (Step S52). In a case where it is determined in Step S51that ΔW1is less than 150 W, the process returns to Step S51, and whether or not ΔW1is 150 W or more is determined for every predetermined time. Next, in a case where the electric heater8is turned on, the electric heater8is maintained in an on state until the predetermined holding time T1elapses (Step S53). After that, the electric heater8is turned off (Step S54). Then, in a case where the fuel cell2is carrying out the electric power generating operation, the process returns to Step S51, and the above operations are repeated.

The foregoing has explained that in the fuel cell system100of Embodiment 2, the on-off operations of the electric heater8are controlled based on whether or not the difference ΔW1between the power consumption of the load power and the amount of electric power generated by the fuel cell2is 150 W or more. However, as with the fuel cell system100of Embodiment 1, the fuel cell system100of Embodiment 2 may be configured such that after the electric heater is once turned on, the amount of energization to the electric heater8may be increased or decreased in accordance with the increase or decrease in the amount of electric power generated by the fuel cell2(increase or decrease in the electric power generation amount command value or the detected current of the second current detector17) after the electric heater is turned on.

In accordance with the fuel cell system100of Embodiment 2 explained as above, the decrease in the energy efficiency due to the electric power consumption of the electric heater8can be further suppressed as compared to the fuel cell system100of Embodiment 1. To be specific, in a case where it is assumed that the amount of electric power generated by the fuel cell2continuously increases and becomes a high output, the fuel cell system100of Embodiment 2 causes the electric heater8to be turned on. Therefore, after that, the on operation of the electric heater8is carried out only when it is required, as compared to Embodiment 1 in which the electric heater8is turned on in a case where the electric power generation amount command value of the fuel cell2increases regardless of whether or not the continuous increase in the output of the fuel cell is expected. On this account, an operating frequency of the electric heater8decreases, and this leads to the increase in efficiency of the fuel cell system100and the improvement in durability of the electric heater8.

Next, the fuel cell system of Embodiment 3 of the present invention will be explained.

The fuel cell system100of Embodiment 3 is the same in configuration as the fuel cell system100of Embodiment 1 but is difference from the fuel cell system100of Embodiment 1 in how the controller19controls on and off of the electric heater8. Therefore, this difference will be explained.

FIG. 6is a diagram showing time-lapse changes of the power consumption of the electric power load, time-lapse changes of the amount of electric power generated by the fuel cell2of the fuel cell system100of Embodiment 3 with respect to the above time-lapse changes of the power consumption of the electric power load, and control of the on-off operations of the electric heater8with respect to the amount of electric power generated by the fuel cell2.

As shown inFIG. 6, in the fuel cell system100of Embodiment 3, in a case where the amount of electric power generated by the fuel cell2continuously increases, the amount of increase in the amount of moisture in the flue gas passing through the CO detector7increases, and this increases the possibility of the occurrence of the condensation on the CO detector7. On this account, the electric heater8is turned on. To be specific, it is preferable that the fuel cell system100of Embodiment 3 be configured such that the electric heater8is turned on in a case where an increased amount ΔW2of the amount of electric power generated by the fuel cell2within a predetermined time is a second threshold or more. It is preferable that the second threshold be a predetermined value equal to or lower than an upper limit of the increased amount of the amount of electric power generated by the fuel cell2at which limit the condensation on the CO detector7does not occur. Moreover, the case where the amount of electric power generated by the fuel cell2continuously increases includes not only a case where the amount of electric power generated by the fuel cell2consecutively increases but also a case where the amount of electric power generated by the fuel cell2is increasing within the entire predetermined time even if it may increase or decrease to some extent within the predetermined time.

Hereinafter, details of the above control operation of the electric heater8of the fuel cell system100of Embodiment 3 will be explained based on the flow chart shown inFIG. 7. First, the electric power generating operation of the fuel cell2is started through the same start-up operation as explained in Embodiment 1, and whether or not ΔW2that is the increased amount of the amount of electric power generated by the fuel cell2within the predetermined time is 150 W or more is determined by the controller19(Step S71). Here, used as the amount of electric power generated by the fuel cell2is the electric power generation amount command value output from the controller19or the current value detected by the second current detector17disposed on the electric wiring extending between the electric power generation amount controller15and the interconnection point. In this case, the controller19also functions as the electric power generation detector of the fuel cell2of the present invention, or the second current detector17constitutes the electric power generation detector of the fuel cell of the present invention.

Next, in a case where it is determined in Step S71that ΔW2is 150 W or more, the electric heater8is turned on (Step S72). In a case where it is determined in Step S71that ΔW2is less than 150 W, the process returns to Step S71, and whether or not ΔW2is 150 W or more is determined for every predetermined time. Next, in a case where the electric heater8is turned on, the electric heater8is maintained in an on state until the predetermined holding time T1elapses (Step S73). After that, the electric heater8is turned off (Step S74). Then, in a case where the fuel cell2is carrying out the electric power generating operation, the process returns to Step S71, and the above operations are repeated.

The foregoing has explained that in the fuel cell system100of Embodiment 3, the on-off operations of the electric heater8are controlled based on whether or not the increased amount ΔW2of the amount of electric power generated by the fuel cell2within the predetermined time is 150 W or more. However, as with the fuel cell system100of Embodiment 1, the fuel cell system100of Embodiment 3 may be configured such that after the electric heater is once turned on, the amount of energization to the electric heater8may be increased or decreased in accordance with the increase or decrease in the amount of electric power generated by the fuel cell2(increase or decrease in the electric power generation amount command value or the detected current of the second current detector17) after the electric heater is turned on.

In accordance with the fuel cell system100of Embodiment 3 explained as above, the decrease in the energy efficiency due to the electric power consumption of the electric heater8can be further suppressed as compared to the fuel cell system100of Embodiment 2. To be specific, the fuel cell system100of Embodiment 3 causes the electric heater8to be turned on after it has confirmed that the amount of electric power generated by the fuel cell2has been continuously increased. Therefore, the on operation of the electric heater8is carried out only when it is required, as compared to Embodiment 2 in which the electric heater8is turned on just because the output of the fuel cell2is likely to continuously increase. On this account, the number of unnecessary on operations of the electric heater8is reduced, and this lead to the increase in efficiency of the fuel cell system100and the improvement in durability of the electric heater8.

Moreover, in accordance with the fuel cell system100of Embodiment 2, even in a case where the amount of electric power generated by the fuel cell2actually increases continuously, and there is a possibility that the condensation occurs on the CO detector17, ΔW1does not become the first threshold or more, so that the electric heater8is not turned on, and the condensation with respect to the CO detector17may not be prevented. However, in accordance with the fuel cell system100of Embodiment 3, since the on-off operations of the electric heater8are controlled based on the actual amount of electric power generated by the fuel cell2, the condensation with respect to the CO detector17can be more surely suppressed. The fuel cell system100may be configured to be able to carry out as the control of the operations of the electric heater8both the control of the operations of the electric heater of the fuel cell system100of Embodiment 2 and the control of the operations of the electric heater8of the fuel cell system100of the present embodiment.

Next, the fuel cell system of Embodiment 4 of the present invention will be explained.

The fuel cell system100of Embodiment 4 is the same in configuration as the fuel cell system100of Embodiment 1, and is characterized in that the controller19controls such that an average amount of energization to the electric heater8during the electric power generating operation of the fuel cell system100becomes smaller than the average amount of energization to the electric heater8during the start-up operation of the fuel cell system100.

The temperatures of respective devices, such as the CO detector7, before the start-up operation of the fuel cell system100are lower than those during the electric power generating operation, and they may be lowered to about an outside air temperature depending on the length of a standby time from when the operation of the fuel cell system100stops until when the next start-up operation of the fuel cell system100starts. Therefore, at the time of the start-up of the fuel cell system100, the condensation on the CO detector7is likely to occur. On this account, the CO detector7needs to be heated by the electric heater8. In contrast, since the temperatures of respective devices, such as the CO detector7, are already increased in the start-up operation of the fuel cell system100, it is unnecessary to heat the CO detector7during the electric power generating operation of the fuel cell system100by the same amount of heat as in the start-up operation of the fuel cell system100to suppress the condensation with respect to the CO detector7. Therefore, to suppress the decrease in the energy efficiency due to the electric power consumption of the electric heater8, the electric heater8is controlled by the controller19such that the average amount of energization to the electric heater8during the electric power generating operation of the fuel cell system100becomes smaller than the average amount of energization to the electric heater8during the start-up operation of the fuel cell system100.

Here,FIG. 9is a diagram showing time-lapse changes of the power consumption of the electric power load, time-lapse changes of the amount of electric power generated by the fuel cell2of the fuel cell system100of Embodiment 4 with respect to the time-lapse changes of the power consumption of the electric power load, and control of the operations of the electric heater8during the start-up operation and electric power generating operation of the fuel cell system100.

As shown inFIG. 9, the fuel cell system100of Embodiment 4 is configured such that only on-off control is executed as the control of the operations of the electric heater8, and the amount of energization to the electric heater8is controlled depending on the length of the on time per unit time. Here, the controller19controls such that an average energization time (on operation time) per unit time of the electric heater8during the electric power generating operation of the fuel cell system100becomes shorter than the average energization time (on operation time) per unit time of the electric heater8during the start-up operation of the fuel cell system100. With this, the controller19controls such that the average amount of energization to the electric heater8during the electric power generating operation of the fuel cell system100becomes smaller than the average amount of energization to the electric heater8during the start-up operation of the fuel cell system100.

Specifically, in the fuel cell system100, the on operation of the electric heater8is started with the start of the start-up operation of the fuel cell system100, and the on operation of the electric heater8is continued until a step of increasing the temperature of the hydrogen generator1is completed during the start-up operation of the fuel cell system100, and the switching unit10is switched to allow the hydrogen-containing gas to be supplied to the fuel cell2. Then, as with Embodiment 1 or 2, in a case where the increase in the amount of electric power generated by the fuel cell2starts, the on operation of the electric heater8is suitably carried out for the predetermined holding time T1. Herein, the controller19controls such that the average amount of energization to the electric heater8during the electric power generating operation of the fuel cell system100becomes smaller than the average amount of energization to the electric heater8during the start-up operation of the fuel cell system100. However, the present embodiment is not limited to this, and the controller19may control such that the average amount of energization to the electric heater8during the electric power generating operation of the fuel cell system100becomes smaller than a maximum amount of energization to the electric heater8during the start-up operation of the fuel cell system100.

With this, in accordance with the fuel cell system100of Embodiment 4, while suppressing the decrease in the energy efficiency due to the electric power consumption of the electric heater8during the electric power generating operation, the condensation with respect to the CO detector7can be suppressed.

Modification Example

FIG. 10is a diagram showing time-lapse changes of the power consumption of the electric power load, time-lapse changes of the amount of electric power generated by the fuel cell2of the fuel cell system100of Modification Example with respect to the time-lapse changes of the power consumption of the electric power load, control of the operations of the electric heater8during the start-up operation and electric power generating operation of the fuel cell system100, and the amount of energization to the electric heater8.

Unlike the fuel cell system of Embodiment 4, the fuel cell system100of Modification Example is configured such that as the control of the operations of the electric heater8, the controller19can control not only the on-off operations of the electric heater8but also the amount of energization to the electric heater8during the on operation. Then, as shown inFIG. 10, unlike Embodiment 4, the on operation of the electric heater8is carried out during the electric power generating operation in not only a case where the increase in the amount of electric power generated by the fuel cell1starts but also the other cases. Here, the amount of energization to the electric heater8in a case other than the case where the increase in the amount of electric power generated by the fuel cell1starts is controlled to be a certain amount of energization (W2) that is smaller than the amount of energization to the electric heater8in the case where the increase in the amount of electric power generated by the fuel cell1starts. The certain amount of energization in a case other than the case where the increase in the amount of electric power generated by the fuel cell2starts is called a first base amount of energization. Moreover, in Modification Example, the controller10controls the operation of the electric heater8such that the amount of energization to the electric heater8in the start-up operation of the fuel cell system100becomes a second base amount of energization W1that is larger than the first base amount of energization W2. With this, as with Embodiment 4, while suppressing the decrease in the energy efficiency due to the electric power consumption of the electric heater8during the electric power generating operation, the condensation with respect to the CO detector7can be suppressed.

The fuel cell system100of each of Embodiment 4 and Modification Example has adopted a mode in which in a case where the increase in the amount of electric power generated by the fuel cell2starts, the fuel cell system100executes such control that the amount of energization to the electric heater8is increased, as with Embodiments 1 and 2. However, the fuel cell system100of each of Embodiment 4 and Modification Example may adopt a mode in which in a case where the amount of electric power generated by the fuel cell2is continuously increasing, the amount of energization to the electric heater8increases, as with Embodiment 3.

From the foregoing explanation, many modifications and other embodiments of the present invention are obvious to one skilled in the art. Therefore, the foregoing explanation should be interpreted only as an example, and is provided for the purpose of teaching the best mode for carrying out the present invention to one skilled in the art. The structures and/or functional details may be substantially modified within the spirit of the present invention.

INDUSTRIAL APPLICABILITY

In accordance with the fuel cell system of the present invention, when the amount of electric power generated by the fuel cell is increased, the condensation of moisture in the flue gas with respect to the CO detector can be suppressed, and the combustion stability of the combustor can be more stably monitored. Therefore, the fuel cell system of the present invention is useful as, for example, a domestic fuel cell system.