Fuel cell device and related control method

A fuel cell device and related control method are disclosed wherein a water tank 5 is disposed downstream of a fuel cell stack 1 and a hot medium flow passage 25 is formed on an outer periphery of the water tank 5 to pass antifreeze solution. During cold start-up, a three-way vale 13 is switched over to allow antifreeze solution to flow through the fuel cell stack 1 and a heat exchanger 17, by which antifreeze solution is heated and supplied to the fuel cell stack 1 and the water tank 5 to heat these components, whereby the water tank 5 is heated to thaw frozen ice.

TECHNICAL FIELD

The present invention relates to a fuel cell device equipped with a water storage means that stores water required for a fuel cell.

BACKGROUND ART

In cases where water becomes frozen in a water tank during a cold time, to rapidly thaw such a frozen state needs for permitting water to be quickly supplied to the fuel cell.

In this respect, Japanese Application Laid-Open No. 2000-149970 discloses a fuel cell device which includes a water tank to supply water to the fuel cell, with the water tank employing a double-layer structure adapted to be heated by a heater.

DISCLOSURE OF THE INVENTION

However, although the heater of the fuel cell device is incorporated in a heat insulation material through which the water tank is heated, when thawing ice in the water tank a poor heat conductivity results in between the water tank and the heater, with a resultant inability caused in efficiently heating the water tank.

Therefore, it is an object of the present invention to provide a fuel cell device and a related control method for efficiently and rapidly thawing frozen ice in a water tank.

To achieve the object, a first aspect of the present invention is a fuel cell device comprising a fuel cell cooled by antifreeze solution, an antifreeze circulation flow passage to allow the antifreeze solution to be circulated, an antifreeze heater disposed in a midway of the antifreeze circulation flow passage to heat the antifreeze solution, a water storage unit that stores water to be supplied to the fuel cell, and a hot medium flow passage disposed in a water contact section of the water storage unit to allow the antifreeze solution, heated by the antifreeze heater, to flow.

A second aspect of the present invention is a method of controlling a fuel cell device, the method comprising preparing a fuel cell, preparing a water storage unit, to store water to be supplied to the fuel cell, that has a hot medium flow passage, circulating antifreeze solution to the fuel cell and the hot medium flow passage through an antifreeze circulation flow passage, and heating the antifreeze solution flowing through the antifreeze circulation flow passage for thereby heating the water in the water storage unit.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments according to the present invention are described with reference to the attached drawings.

FIG. 1is a system structural view of a fuel cell device illustrating a first embodiment according to the present invention. The fuel cell device, which is referred to here, is intended to be installed on a vehicle and includes an antifreeze circulation passage3, that circulates antifreeze solution to cool a fuel cell stack1, and a water tank5that serves as water storage means for storing water, to humidify air containing oxygen serving as oxidant to be supplied to the fuel cell stack1described above, or water to be mixed as steam with methanol to produce hydrogen in a structure equipped with a methanol reformer.

Water in the water tank5is drawn by a pump7and supplied to the fuel cell stack1for the purpose of humidifying the same as set forth above. Water expelled from the fuel cell stack1is returned to the water tank5through a return flow passage9.

Antifreeze solution, whose temperature is increased after having cooled the fuel cell stack1in which heat builds up, is cooled in a radiator11and fed through a three-way valve13to the fuel cell stack1.

Further, the antifreeze circulation passage3includes a heat-exchange bypass flow passage15, that bypasses the radiator11and has one end connected to the three-way valve13, in which a heat exchanger17is located which serves as an antifreeze heating means. The heat exchanger17is supplied with combustion gas generated in a hydrogen combustor19to heat antifreeze solution.

The hydrogen combustor19is supplied with hydrogen and air, which are combusted. The hydrogen results from hydrogen obtained in the methanol reformer stated above or hydrogen stored in a hydrogen tank, or excessive hydrogen expelled from the fuel cell stack1. Also, use is made for air that comes from air, diverged from an air flow passage, to be supplied to the fuel cell stack1.

As shown inFIG. 2andFIG. 3, the water tank5takes the form of a double-layer structure comprised of an inside tank component21, which serves as a water contact section, and an outside tank component23, with a spacing defined between the inside tank component21and the outside tank component23to form a hot medium flow passage25to allow the above-described antifreeze solution to flow.

Disposed in an upper area of the water tank5at right side thereof in the figure is an antifreeze solution inlet27that allows antifreeze solution to be admitted to the hot medium flow passage25from the antifreeze circulation passage3, and disposed in a lower area of the water tank5at left side thereof in the figure is an antifreeze solution outlet29that allows antifreeze solution prevailing in the hot medium flow passage25to be discharged into the antifreeze circulation passage3.

The water tank5has a top portion that is formed with an opening portion, to which a lid31is mounted to cover the same. Connected to a lower end of the water pump7is a water suction conduit33that extends through the lid31and its distal end (lower end) reaches the vicinity of a bottom portion of the water tank5while carrying a strainer35. Also, the return flow passage9extends through the lid31and has its distal end exposed to an inside of the water tank5. Additionally, mounted on the water tank5are air bleeder37that suppresses increase in an internal pressure, a water level meter39that measures a water volume in the water tank5, and a water temperature gauge41that serves as a temperature detection means for measuring the temperature of water in the water tank5.

Now, operation of the fuel cell device of the presently filed embodiment is described.

During a normal traveling mode of a vehicle, the three-way valve13remains in a state to allow flow paths13a,13bto communicate one another and, hence, antifreeze solution flows through the fuel cell stack1and the radiator11so as to circulate through the antifreeze circulation passage3in a direction as shown by an arrow A. When this takes place, antifreeze solution absorbs heat from the fuel cell stack1, whose temperature is raised during operation, and dissipates the same in the radiator11, thereby adjusting the temperature of (cooling) the fuel cell stack1.

During a cold start-up mode, the three-way valve13remains in a state to allow flow paths13c,13bto communicate one another and, hence, antifreeze solution flows through the fuel cell stack1and the heat exchanger17so as to circulate through the antifreeze circulation passage3, involving the heat exchange bypass flow passage15, in a direction as shown by an arrow B.

When this takes place, the hydrogen combustor19is supplied with hydrogen for combustion, with resulting combustion gas being used as heating medium of the heat exchanger17by which antifreeze solution is heated. Heated antifreeze solution then passes through the fuel cell stack1to heat the same whereupon heated antifreeze solution flows through the antifreeze solution inlet27of the water tank5to the hot medium flow passage25.

Antifreeze solution, admitted to the hot medium flow passage25, thaws ice, that is formed when water is condensed in the water tank5, and, thereafter, flows out from the antifreeze solution outlet29to the antifreeze circulation passage3to be returned to the heat exchanger17. As far as hydrogen is supplied to the hydrogen combustor19, antifreeze solution is heated, with resulting heat medium heating the fuel cell stack1and the water tank5.

Thawed water in the water tank5is drawn by the water pump7and used for heating the fuel cell stack1. Also, combustion gas expelled from the heat exchanger17is exhausted to the outside of the vehicle.

Thus, according to the first embodiment set forth above, a heat value resulted in antifreeze solution heats ice (water) in the water tank5via the inside water tank component21which is held in contact with water inside the water tank5, thereby enabling a thawing phase to be efficiently completed in a rapid fashion.

Further, due to the presence of the antifreeze solution inlet27located in the water tank5at an area higher than the antifreeze solution outlet29, heat exchange takes place between water (ice), prevailing in an upper portion where temperature is relatively lower than that of a lower portion due to the existence of ice that is floating because of the small specific gravity during the thawing phase, and antifreeze solution prevailing closer to the antifreeze solution inlet27(with no drop in temperature) and, therefore, a temperature difference between two media relatively increases, resulting in a capability of efficiently and rapidly achieving the thawing phase.

Additionally, in such case, since the water tank5is heated using antifreeze solution, that is heated by the heat exchanger17, for heating the fuel cell stack1, no separate heating means, such as a heater, specific for heating the water tank5is required.

FIG. 4is a cross sectional view of a water tank5A illustrating a second embodiment of the present invention. Also, here, the same component parts as those of the first embodiment bear like reference numerals and only differing portions are described.

In the presently filed embodiment, a suction conduit heating section43through which antifreeze solution flows is located around a periphery of the water suction conduit33of the water pump7. The suction conduit heating section43takes the form of a cylindrical shape and is so configured as to extend from an upper end portion of the water suction conduit33toward a substantially central area thereof in a vertical direction, with one end of the antifreeze solution inlet27being connected to the vicinity of a lower end of the suction conduit heating section43. The other end of the antifreeze solution inlet27extends through the water tank5A to be taken out to the outside of the water tank5and is connected to the antifreeze circulation passage3as shown inFIG. 1as set forth above.

Further, here, the lid31is internally formed with a hot medium flow passage31a, through which antifreeze solution flows, that is in communication with the hot medium flow passage25and the suction conduit heating section43, respectively. That is, antifreeze solution flowing through the antifreeze circulation passage3shown inFIG. 1flows to the suction conduit heating section43from the antifreeze solution inlet27and, subsequently, flows into the hot medium flow passage25through the hot medium flow passage31ato reach the antifreeze solution outlet29. Consequently, the lid31is placed on the upper opening of the water tank5A to seal the upper opening watertight. Other structure is identical to that of the first embodiment.

According to the structure of the presently filed embodiment, heated antifreeze solution flows from the antifreeze solution inlet27into the suction conduit heating section43to heat water in the water suction conduit33and, thereafter, flows through the hot medium flow passage25between the inside water tank component21and the outer water tank component23, thereby heating ice (water). When this takes place, since it is possible to heat water being drawn by the water pump7, it is possible to prevent water from being frozen again in the water pump7where a high probability exists in the cold temperature condition below 0 C.

FIG. 5is a perspective view of a water tank5B showing a third embodiment of the present invention.FIG. 6is a cross sectional view of the water tank as viewed in a right direction inFIG. 5to show an outline of an internal structure of such a water tank5B. Also, although the water tank5B takes the form of a double-layer structure equipped with the inside tank component21and the outside tank component23like in the first embodiment shown inFIG. 1, the component elements, such as the lid31, the water pump7and the air bleeder37, which are mounted in the water tank5are omitted in a simplified form, and the same component parts as those of the first embodiment bear the same reference numerals to describe only differing portions.

In the presently filed embodiment, a spiral shaped antifreeze rectification plate45is disposed in the hot medium flow passage25between the inside tank component21and the outer water tank component23to guide antifreeze solution to the antifreeze solution outlet29through the antifreeze solution inlet27. The antifreeze rectification plate45has an inner periphery fixedly secured to an outer peripheral surface of the inside water tank component21. Meanwhile, in order for an edge portion of an outer peripheral side of the antifreeze rectification plate45to have less heat transfer with the outside of the water tank5B, the edge portion is out of contact with the inner periphery of the outside tank component23(seeFIG. 6).

With the structure of the presently filed embodiment, antifreeze solution introduced from the antifreeze solution inlet27into the hot medium flow passage25flows along the antifreeze rectification plate45and flows out from the antifreeze solution outlet29.

Accordingly, in such case, antifreeze solution substantially uniformly flows throughout an entire area of the hot medium flow passage25without depending upon the flow rate and temperature, enabling efficient heat exchange to take place.

FIG. 7is a perspective view illustrating an internal structure of a water tank5C of a fourth embodiment of the present invention. Also, here, the same component elements as those of the first embodiment set forth above bear the like reference numerals and differing portions are mainly described. Also, inFIG. 7, the component elements, such as the lid31, the water pump7and the air bleeder37, mounted in the water tank5are omitted.

In the presently filed embodiment, the water tank5C has no double-layer structure, and a plurality of annular conduits47(conduit components47a,47b,47c, . . . ,47g,47h), forming a hot medium flow passage that is disposed in an annular configuration along an inner wall of the water tank5C, are disposed in a stacked structure with a given distance prevailing in a vertical direction in the figure. Then, the antifreeze solution inlet27is connected to the uppermost annular conduit47a, and the antifreeze solution outlet29is connected to the lowermost annular conduit47h.

Here, the uppermost annular conduit47aand an adjacent lower annular conduit47bare connected at one side (on a left side wall inFIG. 7) of the water tank5opposite to the antifreeze solution inlet27and the antifreeze solution outlet29by means of a connecting conduit49. In addition, the third and fourth annular conduits47c,47dare mutually connected by means of a connecting conduit51, the fifth and sixth annular conduits47e,47fare mutually connected by means of a connecting conduit53, and the seventh and eight annular conduits47g,47hare mutually connected by means of a connecting conduit55, respectively, at the one side of the water tank5opposite to the antifreeze solution inlet27and the antifreeze solution outlet29.

Further, the second and third annular conduits47b,47c, the fourth and fifth annular conduits47d,47eand the sixth and seventh annular conduits47f,47gare mutually connected by means of connecting conduits57,59,61, respectively, on the other side of the water tank5at which the antifreeze solution inlet27and the antifreeze solution outlet29are located.

Thus, antifreeze solution, that enters from the antifreeze solution inlet25into the uppermost annular conduit47a, flows through the annular conduit47aleftward in the figure to enter from the connecting conduit49into the lower annular conduit47b, from which antifreeze solution then flows rightward in the figure to enter from the connecting conduit57into the lower annular conduit47c.

In such a way, antifreeze solution sequentially flows through the respective annular conduits47, that are stacked up and down, and flows in a downward direction whereupon it finally flows out from the antifreeze solution outlet29, that is connected to the lower most annular conduit47h, to the outside. For this reason, with the presently filed embodiment, uniform flow of antifreeze solution can be obtained without depending upon the flow rate or the temperature thereof and a surface area between water (ice), forming a body to be heated, and the annular conduit47can be increased, enabling efficient heat-exchange.

Also, the annular conduit47of the presently filed embodiment does not need to be disposed in a substantially entire area of the water tank5C along a vertical direction thereof, but may be disposed only in a lower area where water is received.

Further, in place of the annular conduits47, a spiral shaped conduit may be provided which takes the form of a spiral configuration extending from an upper portion to a lower portion in the figure. In such case, no connecting conduits49to61are required. The presence of the flow passage formed in the spiral configuration to pass antifreeze solution provides a more simplified structure to be easily manufactured than that of the annular type, resulting in reduction cost.

FIG. 8is a perspective view illustrating an external structure of a water tank5D of a fifth embodiment of the present invention. Also, here, the same component parts as those of the first embodiment bear the same reference numerals and reference is mainly made in only differing portions. Further, inFIG. 8, the component elements, such as the water pump7and the air bleeder37, that are mounted in the water tank5are omitted.

The presently filed embodiment is configured to have a water tank5D that has a side wall by which a hot medium flow passage is formed. The hot medium flow passage in this case is comprised of a plurality of annular conduits47(conduit components47a,47b,47c, . . .47g,47h) that have the same structures as those shown inFIG. 7, with mutually adjacent portions being mutually joined by brazing to be stacked in sealed watertight state.

Further, communication ports49ato61a, that allow the adjacent annular conduits47to mutually communicate one another, are formed in the annular conduits, respectively, at positions corresponding to the connecting conduits49to61of the embodiment shown inFIG. 7.

Accordingly, in the presently filed embodiment, antifreeze solution sequentially flows downward through the respective annular conduits47stacked up and down and flows out to the outside from the antifreeze solution outlet connected to the lowermost annular conduit47h.

Furthermore, a lower portion of the lowermost annular conduit47his closed by brazing a tank bottom plate63. Meanwhile, a lid31is joined to or detachably placed on an upper portion of the uppermost annular conduit47a.

Consequently, in the presently filed embodiment, flow of antifreeze solution can be uniformed while constructing the side wall of the water tank5D enables production in light weight.

Also, the annular conduits47in the fifth embodiment set forth above does not need to be disposed in the substantially entire area of the water tank5D along the vertical direction thereof like in the fourth embodiment and may be disposed only in the lower area where water is received.

FIG. 9is a front view illustrating an external structure of a water tank5D showing a sixth embodiment of the present invention, andFIG. 10is a right side view ofFIG. 9. Also, here, the same component elements as those of the first embodiment bear the like reference numerals and reference is mainly made only in differing portions. Further, inFIGS. 9 and 10, the component elements, such as the water pump7and the air bleeder37, that are mounted in the water tank5are omitted.

In the presently filed embodiment, in place of the annular conduits47of the fifth embodiment shown inFIG. 8set forth above, a spiral shaped conduit65is provided which serves as a hot medium flow passage formed in a spiral configuration extending from an upper portion to a lower portion in the figure. In such case, mutually adjacent portions facing up and down of the spiral-shaped conduit65is sealed watertight, and no communication ports49ato61ashown inFIG. 8are required.

Disposed between the uppermost end of the spiral shaped conduit65and the lid31is a lid joint member67, for jointing or detachably mounting the lid31, that is joined in a watertight condition. Also, disposed between the lower most end of the spiral shaped conduit65and the tank bottom plate63is a lid joint member69, for jointing or detachably mounting the tank bottom plate63, that is joined in a watertight condition. The antifreeze solution inlet27is connected to the uppermost end of the spiral shaped conduit65, and the antifreeze solution outlet29is connected to the lowermost end of the spiral shaped conduit65.

Accordingly, in the presently filed embodiment, the presence of the hot medium flow passage formed in the spiral shape allows a structure to be further simplified to provide an ease of manufacturing than that of the case configured in the annular shape shown inFIG. 8, achieving reduction in cost.

FIG. 11is a system structural view of a fuel cell device illustrating a seventh embodiment of the present invention. Also, here, the same component elements as those of the first embodiment bear the same reference numerals and reference is mainly made only in differing portions.

In the presently filed embodiment, antifreeze solution is discharged from the hot medium flow passage25of the water tank5, and exhausted antifreeze solution is replaced with air that flows through the hot medium flow passage25.

As a system structure, in addition to the structure shown inFIG. 1set forth above, three-way valves71,73serving as hot medium switch-over means are disposed in the antifreeze solution flow passage3at upstream and downstream sides of the hot medium flow passage25of the water tank5, respectively.

Connected to the three-way valve71upstream of the water tank5is an air flow supply passage75through which air branched off from a flow path of air stream to be supplied to the fuel cell stack1is admitted, and connected to the three-way valve73downstream of the water tank5is one end of an antifreeze solution discharge flow passage77. The other end of the antifreeze solution discharge flow passage77is opened to an antifreeze drain tank79that serves as an antifreeze recovery means to allow antifreeze solution, expelled from the antifreeze drain tank79, to be returned thereto.

Next, operation of the fuel cell device of the presently filed embodiment during switch-over of antifreeze solution is described.

During switch-over of antifreeze solution, a situation wherein a flow path71aand a flow path71bof the three-way valve71communicate one another and a flow path73aand a flow path73bof the three-way valve73communicate one another is treated as an initial condition, and flow is proceeded in accordance with a flowchart ofFIG. 12.

That is, first, operation is implemented to read in switch-over flags (FLG) “1” and “0” indicative of switch-over to be carried out and switch-over not to be carried out, respectively (step1201). Next, judgment is made to find switch-over FLG=1 (step1203) and, if switch-over FLG=1, the flow paths71c,71bof the three-way valve71communicate one another while the flow paths73a,73cof the three-way valve73communicate one another (step1205). This allows air to be introduced from the supply flow passage75to the hot medium flow passage25, with introduced air stream causing antifreeze solution to be expelled from the hot medium flow passage25the antifreeze drain tank79for air purging.

After a sufficient time period has elapsed for recovering antifreeze solution to the antifreeze drain tank79, the respective flow paths71b,73aand the respective flow paths71c,73care closed to seal air introduced into the hot medium flow passage25(step1207). This antifreeze solution recovery time interval is appropriately determined based on experimental tests. If switch-over FLG≠1, the above-described initial states of the respective three-way valves71,73are continued (step1209).

This results in a capability of switching hot medium over from antifreeze solution to air with no disposal of antifreeze solution and, thus, if antifreeze solution includes 50% ethylene glycol aqueous solution, since a heat conductive rate is approximately 0.43 W/m/K whereas air has a heat conductive rate of approximately 0.024 W/m/K, a heat insulation property of the water tank5can be highly improved.

Also, in this case, as shown inFIG. 18which will be described later, due to provision of a bypass flow passage83that allows the upstream antifreeze circulation flow passage3of the three-way valve71and the antifreeze circulation flow passage3closer to the radiator11downstream of the three-way valve73, even if air is sealed in the hot medium flow passage25, it becomes possible to circulate antifreeze solution for cooling the fuel cell stack1.

Further, while the presently filed embodiment has been described with reference to the water tank5that has the structure to which the structure of the first embodiment is applied, the structure of the first embodiment may also be applied to the water tanks5of the fourth embodiment shown inFIG. 7, the fifth embodiment shown inFIG. 8and the six embodiment shown inFIG. 10such that the respective embodiments have the following features.

In the first embodiment, due to the presence of the water tank5formed in the double-layer structure, a significant advantage results in avoiding water from frozen. Especially, when use is made in a district where less frequency occurs in the ambient temperature dropping below freezing temperature, introducing air into the hot medium flow passage25allows a priority to be particularly given for a merit of preventing water from icing to permit water to be smoothly supplied during clod start-up.

In the fourth embodiment, due to the existence of the structure wherein the hot medium flow passage (composed of the annular conduits47) is piped in the inner wall of the water tank5, the peripheries of the annular conduits47are surrounded by water, resulting in an advantageous effect of efficiently achieving heat-exchange. That is, in a particular area, such as an extremely cold place (wherein no anti-freezing effect due to introduction of air is effectuated), where freezing frequently takes place, giving a top priority to thawing particularly enables heat-exchange to be efficiently performed, resulting in smooth operation to supply water during cold start-up.

In the fifth and six embodiments, due to the presence of the structure wherein the hot medium flow passage (comprised of the annular conduits47or the spiral shaped conduit65) forms the side wall of the water tank5, heat insulation effect is highly improved to enable efficient heat-exchange, thereby providing a compromise between block in freezing of water and efficient heat-exchange to some extent. If use is made in an intermediate district between an area to which the first embodiment is applied and another area to which the fourth embodiment is applied, the compromise between the effect of preventing water from being frozen and the effect in which efficient heat-exchange takes place is exhibited to some extent, thereby enabling water to be smoothly supplied during cold start-up.

FIG. 13is a system structural view of a fuel cell device illustrating an eighth embodiment of the present invention. The presently filed embodiment contemplates to introduce combustion gas, expelled from the hydrogen combustor19through the heat exchanger17, into the hot medium flow passage25in place of air to be introduced to the hot medium flow passage25of the fourth embodiment shown inFIG. 11set forth above. Other structures are similar to those of the seventh embodiment.

That is, a three-way valve87is disposed in an exhaust gas exhaust flow passage85connected to the heat exchanger17, with the three-way valve87and the three-way valve71disposed in the antifreeze circulation flow passage3disposed upstream of the water tank5being connected to one another by means of a combustion gas supply flow passage89.

Now, operation of the fuel cell device of the presently filed embodiment during switch-over of antifreeze solution is described.

During switch-over of antifreeze solution, a situation wherein a flow path87aand a flow path87bof the three-way valve87communicate one another and the flow path71aand the flow path71bof the three-way valve71communicate one another while, further, the flow path73aand the flow path73bof the three-way valve73communicate one another is treated as an initial condition, and flow is proceeded in accordance with a flowchart ofFIG. 14.

That is, first, operation is implemented to read in switch-over flags (FLG) “1” and “0” indicative of switch-over to be carried out and switch-over not to be carried out, respectively (step1401). Next, judgment is made to find whether switch-over FLG=1 (step1403) and, if switch-over FLG=1, the flow paths87a,87cof the three-way valve87communicate one another while the flow paths71c,71bof the three-way valve71communicate one another and, further, the flow paths73a,73cof the three-way valve73communicate one another (step1405).

This allows combustion gas to be admitted to the hot medium flow passage25through the combustion gas supply flow passage89to expel antifreeze solution from the hot medium flow passage25to the antifreeze drain tank79for gas purging.

After a sufficient time period has elapsed for recovering antifreeze solution to the antifreeze drain tank79, the respective flow paths87a,87bcommunicates one another while the respective flow paths71b,73aand the respective flow paths71c,73care closed, respectively, to seal combustion gas introduced into the hot medium flow passage25(step1407). This antifreeze solution recovery time interval is appropriately determined based on experimental tests. If switch-over FLG≠1, the above-described initial states of the respective three-way valves71,73,87are continued (step1409).

Consequently, with the presently filed embodiment, due to an ability of high temperature combustion gas being introduced into and sealed in the hot medium flow passage25, as the temperature of the sealed combustion gas drops, pressure reduction occurs in the hot medium flow passage25, enabling the water tank5to have a highly improved heat insulation property.

FIG. 15is a system structural view of a fuel cell device illustrating a ninth embodiment of the present invention. The presently filed embodiment contemplates to incorporate an air tank91, serving as an air storage means, that stores combustion gas, into the combustion gas flow passage89in the structure of the eighth embodiment shown inFIG. 13set forth above. Other structures are similar to those of the eighth embodiment.

When storing combustion gas in the air tank91, the flow path87aand the flow path87cof the three-way valve87communicate one another and the flow path71cof the three-way valve71is closed. Under such condition, combustion gas generated in the hydrogen combustor19passes through the combustion gas exhaust passage85and the combustion gas supply flow passage89from the heat exchanger17and stored in the air tank91.

During switch-over of antifreeze solution, a situation wherein the flow path87aand the flow path87bof the three-way valve87communicate one another (with the flow path87cbeing closed) and the flow path71aand the flow path71bof the three-way valve71communicate one another while, further, the flow path73aand the flow path73bof the three-way valve73communicate one another is treated as an initial condition, and flow is proceeded in accordance with a flowchart ofFIG. 16.

That is, first, operation is implemented to read in switch-over flags (FLG) “1” and “0” indicative of switch-over to be carried out and switch-over not to be carried out, respectively (step1601). Next, judgment is made to find whether switch-over FLG=1 (step1603) and, if switch-over FLG=1, the flow paths71c,71bof the three-way valve71communicate one another while the flow paths73a,73cof the three-way valve73communicate one another (step1605).

This allows combustion gas in the air tank91to be introduced into the hot medium flow passage25through the combustion gas supply flow passage89and the three-way valve71to expel antifreeze solution from the hot medium flow passage25to purge antifreeze solution into the drain tank79.

After a sufficient time period has elapsed for recovering antifreeze solution to the antifreeze drain tank79, the respective flow paths71b,73aand the respective flow paths71c,73care closed to seal introduced combustion gas in the hot medium flow passage25(step1607). This antifreeze solution recovery time interval is appropriately determined based on experimental tests. If switch-over FLG≠1, the above-described initial states of the respective three-way valves71,73,87are continued (step1609).

Consequently, with the presently filed embodiment, even if the fuel cell electric generation system remains in a halt condition, antifreeze solution in the hot medium flow passage25of the water tank3can be replaced with combustion gas by using combustion gas stored in the air tank91, enabling the water tank5to have a highly improved heat insulation property.

Also, the structure in which the air tank91is provided can be applied to the seventh embodiment ofFIG. 11set forth above. That is, in such case, the air tank91is disposed in the air supply flow passage75shown inFIG. 11and the three-way valve may be disposed in the supply flow passage upstream of the air tank91for storing air in the air tank91.

FIG. 17is related to a tenth embodiment of the present invention and shows a flowchart for setting the switch-over flag for use in antifreeze switch-over in the seventh embodiment (FIGS. 11,12), the eighth embodiment (FIGS. 13,14) and the ninth embodiment (FIGS. 15,16).

First, the antifreeze temperature T1of the hot medium flow passage25in the water tank5is measured by an antifreeze temperature gage92serving as a temperature detection means (step1701). Next, the antifreeze temperature T1is compared with 0 C and αC (step1703). Here, α designates a temperature with which reference is made for the heat capacity of antifreeze solution to act on block of freezing of water in the water tank5.

Stated another way, since air has less coefficient of thermal conductivity than antifreeze solution, even at the same temperature of 0 C, air is harder to be cooled than antifreeze solution and, so, there is a probability in which it is preferable for antifreeze solution to be replaced with air at a timing with antifreeze solution remaining at a high temperature above 0 C to enable water to be avoided from being frozen in the water tank5as a whole. Thus, an upper limit of the high temperature above 0 C is determined as αC.

In the above step1703, if 0≦T1≦α, it is supposed for switch-over FLG=1 (step1705). If a situation does not stand for 0≦T1≦α, it is supposed for switch-over FLG=0 (step1707). Since α varies in dependence upon the atmospheric temperature and the heat dissipating condition of the water tank5, it is possible to employ a method wherein this value may be clear from experimental tests for each condition as data base for control in terms of parameters of the atmospheric temperature and the heat dissipating condition.

In response to this switch-over FLG, operation is executed to switch antifreeze solution, in the hot medium flow passage25in the water tank5, over to air as shown in the seventh, eighth and ninth embodiments.

Replacing antifreeze solution inside the hot medium flow passage25with air in such a way allows the heat capacity of antifreeze solution to be used to its maximum while preventing waste of an operating performance of the fuel cell electric power generation system (to improve an efficiency), and combining this advantage with heat insulating action of air enables water in the water tank5from being efficiently prevented from being frozen.

FIG. 18is a system structural view of a fuel cell device illustrating an eleventh embodiment of the present invention. The presently filed embodiment contemplates to incorporate a bypass flow passage83, in the structure of the seventh embodiment shown inFIG. 11set forth above, for bypassing the water tank5. The bypass flow passage83has one end connected to a three-way valve93, that is disposed in the antifreeze circulation flow passage3upstream of the three-way valve71, and the other end connected to the antifreeze circulation flow passage3upstream of the radiator11and downstream of the heat exchanger bypass flow passage15. Other structures are similar to those of the seventh embodiment.

In such case, an initial condition is set a situation where flow paths93a,93cof the three-way valve93communicate one another, that is, a situation where antifreeze solution is admitted through the bypass flow passage83, and operations are executed in accordance with a flowchart ofFIG. 19.

That is, first, the water (or ice) temperature T3of the water tank5is measured by the temperature gage41(step1901).

Next, resulting detected temperature T3is compared with the bypass judgment temperature T30(step1903) and, if T3>T30, judgment is made that there is no need for heating the water tank S on the supposition that the water temperature of the water tank5exceeds a prescribed value whereupon the flow paths93a,93ccontinues to communicate one another while antifreeze solution is passed to the bypass flow passage83so as to bypass the water tank5(step1905).

Meanwhile, if no situation stand for T3≧T30, judgment is made that there is a need for heating the water tank5on the supposition that the water temperature of the water tank5is below the preset value, and the flow paths93a,93bof the three-way valve93communicate one another to allow antifreeze solution to be supplied to the hot medium flow supply passage25of the water tank5.

Consequently, with the presently filed embodiment, if there is no need for heating water in the water tank5, since no antifreeze solution is required to flow through the hot medium flow passage25, a pressure loss in the flow passage due to flow of antifreeze solution can be minimized and a load of an antifreeze pump, which is not shown, can be decreased, resulting in improvement in an efficiency of a whole system.

FIG. 20is a cross sectional view of a water tank5F for use in a fuel cell device of a twelfth embodiment of the present invention. The water tank5F of the presently filed embodiment takes the form of a double-layer structure, comprised of the inside tank component21and the outside tank component23, like the one of the first embodiment shown inFIGS. 1 to 3, between which the hot medium flow passage25is defined to allow antifreeze solution to flow.

The hot medium flow passage25accommodates therein a heat insulation member95which is shown in a perspective view inFIG. 22. The heat insulation member95has a center formed with a through-bore95a, so that it is accommodated in a space (hot medium flow passage25) between a peripheral side wall of the inside tank component21and a peripheral side wall of the outside tank component23, and is formed of material with a specific gravity greater than that of air but less than that of antifreeze solution to be moveable in the vertical direction.

For this reason, inFIG. 20, the heat insulation member95is floating upward in antifreeze solution and, inFIG. 21, the heating insulation member95in air is located downward in the hot medium flow passage25.

A stopper member97is mounted in the inside tank component21to support the heat insulation member95during downward movement of the heat insulation member95. Outer peripheral sides of the stopper member97are positioned apart from opposing inner peripheral walls of the outside tank component23, thereby allowing antifreeze solution or air to flow out of the antifreeze solution outlet29. The heat insulation member95is made of material such as styrol foam and evacuated heat insulation material with core material composed of silica powder.

As shown inFIG. 20, if antifreeze solution is introduced into the hot medium flow passage25, the heat insulation member95moves upward (floats) and prevents heat from escaping to the space (an upper area above a water level L) in the inside tank component21, thereby promoting thawing or heating.

Meanwhile, if air is introduced into the hot medium flow passage25as shown inFIG. 21, the heat insulation member95moves downward to decrease the degree of heat dissipation from water, thereby improving a heat dissipating effect.

Consequently, according to the presently filed embodiment, it is possible to improve a thawing property, a heating property and a heat insulation property.

FIGS. 23 and 24are cross sectional views of a water tank5G for use in a fuel cell device of a thirteenth embodiment of the present invention. The water tank5G of the presently filed embodiment takes the form of a double-layer structure, comprised of the inside tank component21and the outside tank component23, like the one of the first embodiment shown inFIGS. 1 to 3, between which the hot medium flow passage25is defined to allow antifreeze solution to flow.

In place of the heat insulation member95of the twelfth embodiment shown inFIG. 22set forth above, a plurality of spherical heat insulation members99, that form a plurality of members smaller than the flow sectional area of the hot medium flow passage25between the inside tank component21and the outside tank component23, are accommodated in the hot medium flow passage25.

These heat insulation members99are formed of material with a specific gravity greater than that of air but less than that of antifreeze solution like the heat insulation member95ofFIG. 22set forth above. Accordingly, when antifreeze solution is introduced in the hot medium flow passage25, the heat insulation members99take a state wherein they are floating upward as shown inFIG. 23and, when air is introduced in the hot medium flow passage25, the heat insulation members99take a sinking state as shown inFIG. 24. To prevent the heat insulation members99from escaping from the antifreeze solution outlet29in such a case, the inside tank component21is provided at its lower portion with a heat-insulation member escape block member101. The heat-insulation member escape block member101may be comprised of a net-like configuration.

Accordingly, the heat insulation members99of the presently filed embodiment are able to move upward when antifreeze solution is introduced and to move downward when air is introduced even in a case where the spiral shaped antifreeze rectification plate45as in the embodiment shown inFIG. 5set forth above, thereby enabling a compromise between an improved heat exchange efficiency of the antifreeze rectification plate45and a thawing property, humidifying property and a heat insulation improvement of the heat insulation members99.

INDUSTRIAL APPLICABILITY

As set forth above, according to the present invention, due to an ability of antifreeze solution, heated by the antifreeze heating means, permitted to flow through the hot medium flow passage located in the water storage means, even if water stored in the water storage means is frozen, frozen water can be rapidly thawed by heated antifreeze solution in an efficient manner.

The entire content of Japanese Application No. P2002-246873 with a filing date of Aug. 27, 2002 is herein incorporated by reference.

Although the present disclosure has been described above by reference to certain embodiments of the invention, the invention is not limited to the embodiments described above and modifications will occur to those skilled in the art, in light of the teachings. The scope of the invention is defined with reference to the following claims.