Gas-liquid separator for fuel cell system

A discharge port is located at a lower portion of the case of a gas-liquid separator. A discharge valve is located at the discharge port. A water retaining portion is located at the bottom of the case. The water retaining portion is located at a position lower than the discharge valve. An upward inclination surface is formed on the bottom of the water retaining portion. The upward inclination surface is inclined upward toward the discharge valve. A downward inclination surface is formed on the bottom of the water retaining portion. The downward inclination surface is inclined downward toward the upward inclination surface. A cover portion is located in an upper portion of the water retaining portion. The cover portion defines a gas passage in an upper portion of the water retaining portion. The gas passage is open at a portion closer to the inlet and connected to the discharge valve.

BACKGROUND OF THE INVENTION

The present invention relates to a gas-liquid separator that separates unreacted excess hydrogen discharged from a cell stack and product water from each other in a fuel cell system.

A typical fuel cell system has a gas-liquid separator located between the hydrogen outlet and the hydrogen inlet of the cell stack. Unreacted excess hydrogen and product water discharged from the cell stack are separated by a gas-liquid separator, so that the unreacted hydrogen is recovered to the cell stack and reused. The product water is discharged to the outside.

Conventionally, for example, Japanese Laid-Open Patent Publication No. 2006-49100 discloses such a gas-liquid separate used in such a fuel cell system. That is, as shown inFIG. 9, the gas-liquid separator111has ion-exchange resin112and a tank113located below the resin112. As the fuel cell system starts operating, hydrogen and product water discharged from the hydrogen outlet of the cell stack are conducted to the gas-liquid separator111through a circulation passage114. The hydrogen and product water are separated at the ion-exchange resin112, and the hydrogen is sent to the cell stack to be reused through a circulation passage115. The separated product water is received in the tank113, and discharged to the outside when a discharge valve116is open.

In the gas-liquid separator of Japanese Laid-Open Patent Publication No. 2006-49100, the discharge valve116is located below the tank113so that product water in the tank113can be discharged. When the fuel cell system is stopped, product water collected on the inner walls of the case of the gas-liquid separator111and product water remaining in the ion-exchange resin112drips and is stored in the tank113. When the fuel cell system is in the stopped state under a low-temperature environment, for example, in winter, such product water in the tank113may be frozen. In such a case, even when the fuel cell system is activated, the frozen water may hinder the opening and closing of the discharge valve116, and discharge of product water to the outside may be impossible. In some cases, the frozen water may damage the discharge valve116.

SUMMARY OF THE INVENTION

Accordingly, it is an objective of the present invention to provide a gas-liquid separator that is capable of allowing a discharge valve to operate normally even if product water dripped from the inner surfaces of a case and ion-exchange resin is frozen during the stopped state of a fuel cell system under a low-temperature environment.

To achieve the foregoing objective and in accordance with one aspect of the present invention, a gas-liquid separator of a fuel cell system is provided. The gas-liquid separator includes an inlet connected to a hydrogen discharge portion of a cell stack of the fuel cell system, an outlet connected to a hydrogen introduction portion of the cell stack, a product water separating member located between the inlet and the outlet, and a discharge port located below the product water separating member. The discharge port is used to discharge product water. The gas-liquid separator further includes a discharge valve for opening and closing the discharge port, a water retaining portion located at a position lower than the discharge valve, and a discharge portion. The water retaining portion is continuous to the discharge port. The discharge portion discharges product water retained in the water retaining portion.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

First, a fuel cell system will be roughly described with reference toFIG. 1. A cell stack1includes a plurality of single cells (not shown) and performs cell reaction. An air supply passage5is connected to the cell stack1to supply air, which is oxidation gas. Also, an air discharge passage6is connected to the cell stack1to discharge air and product water from the cell stack1. A hydrogen discharge portion (not shown) and a hydrogen introduction portion (not shown) of the cell stack1are connected to one end and the other end of a circulation path8aforming a hydrogen circuit8, respectively.

Of unreacted excess hydrogen (gas) and product water discharged from the cell stack1, the circulation path8acirculates the hydrogen and supplies the hydrogen, together with new hydrogen, to the cell stack1. The circulation path8adischarges the product water to the outside. A circulation pump3, a gas-liquid separator10, a hydrogen tank2, and a pressure-regulating valve4are provided in the hydrogen circulation path8a. The circulation pump3applies circulating force to fluid in the circulation path8a. The gas-liquid separator10receives hydrogen and product water from the cell stack1through the circulation path8a, separates the hydrogen and product water. The hydrogen tank2supplies new hydrogen to the cell stack. The pressure-regulating valve4regulates the pressure of hydrogen supplied from the hydrogen tank2to the cell stack.

The gas-liquid separator10will now be described. As shown inFIG. 2, the case11of the gas-liquid separator10is formed of a lower case member12, which has a closed lower end and an open upper end, and an upper case member13, which has an open lower end and a closed upper end. An inlet14is formed in a peripheral wall of the lower case member12. The inlet14conducts gas-liquid mixture containing hydrogen and product water discharged from the cell stack1into the case11. A filter15is attached to the inner opening of the inlet14. The filter15is made of woven fabric or nonwoven fabric, and removes foreign matter from hydrogen and product water drawn into the case11.

In the case11, ion-exchange resin16is located between the lower case member12and the upper case member13. The ion-exchange resin16serves as a product water separating member portion, which separates gas-liquid mixture supplied through the inlet14into hydrogen and product water. A discharge port17is formed in a lower portion of the peripheral wall of the lower case member12, at a position opposite to the inlet14. The discharge port17discharges separated product water to the outside along a substantially horizontal direction. An electromagnetic discharge valve18is located in the discharge port17. Opening and closing of the discharge valve18is controlled by a control circuit (not shown).

An outlet19is formed in the upper wall of the upper case member13, at a position opposite to the discharge port17with respect to the ion-exchange resin16. The outlet19discharges the separated hydrogen and supplies the hydrogen to the cell stack1.

A water retaining portion20is formed in the bottom of the lower case member12, at a position below the discharge valve18. The water retaining portion20has a storage capacity capable of retaining product water that drips from the inner wall of the case11and the ion-exchange resin16during the stopped state of the fuel cell system. Specifically, the capacity of the water retaining portion20is set to such a value that, when a maximum credible amount of dripped product water is stored in the water retaining portion20, the level of the water is below the discharge valve18.

An upward inclination surface20ais formed in a portion of the bottom of the water retaining portion20closer to the discharge valve18. The upward inclination surface20ais inclined upward from the side closer to the inlet14toward the discharge valve18. Also, a downward inclination surface20bis formed in a portion of the bottom of the water retaining portion20closer to the inlet14. The downward inclination surface20bis inclined downward from the side closer to the inlet14toward the upward inclination surface20a. The inclination angle α1of the upward inclination surface20arelative to the horizontal plane is less than the inclination angle α2of the downward inclination surface20brelative to the horizontal plane. In the present embodiment, the inclination angle α1of the upward inclination surface20ais 20 degrees, and the inclination angle α2of the downward inclination surface20bis 30 degrees.

A cover portion21that covers the upper portion of the water retaining portion20is formed on the inner surface of the lower case member12. The cover portion21defines a gas passage22in an upper portion of the water retaining portion20. The gas passage22has an opening22aat a position closer to the inlet14, and is connected to the discharge valve18. The gas passage22, the upward inclination surface20a, and the downward inclination surface20bform a discharge portion. When the discharge valve18is open and hydrogen is supplied into the case11through inlet14, the hydrogen flows into the gas passage22through the opening22a.

An operation of the gas-liquid separator10thus constructed will now be described.

When the fuel cell system having the gas-liquid separator10is operated, the pump3is activated. This supplies unreacted hydrogen and product water discharged from the cell stack1to the case11of the gas-liquid separator10through the inlet14. Then, the ion-exchange16separates the hydrogen and the product water in the case11. The hydrogen is sent to the circulation path8athrough the outlet19to be supplied to and reused in the cell stack1.

In contrast, the separated product water drips from the ion-exchange resin16and moves to the water retaining portion20of the lower case member12via the opening22ato be retained there. During the operation of the fuel cell system, the discharge valve18is opened at a predetermined interval. Also, during the operation of the fuel cell system, the pressure in the circulation path8a, which includes the gas-liquid separator10, is maintained at a high level by the circulation pump3. Thus, when the discharge valve18is opened, hydrogen is spurted through the inlet14and flows into the gas passage22through the opening22a. The hydrogen then quickly flows through the gas passage22. The momentum of the hydrogen flow moves the product water in the water retaining portion20toward the discharge valve18in a drifting manner. Further, the hydrogen flow waves the surface of the water retaining portion20or increases the level of the water as indicated by chain double-dashed line inFIG. 2, so that the opening area of the gas passage22is reduced. This further increases the velocity of the hydrogen flow. In this state, the hydrogen flows at a high velocity from the downward inclination surface20bto the upward inclination surface20a, while sweeping the product water.

Almost the whole product water in the water retaining portion20is instantly discharged to the outside through the discharge port17and the discharge valve18. The discharge valve18is closed when the product water is discharged. The open time of the discharge valve18is relatively short and the same as the time required for discharging the product water. Since the circulation pump3is connected to the downstream side of the outlet19, backflow of hydrogen from downstream of the circulation pump3is prevented. Therefore, when the discharge valve18is open, little hydrogen is spurted into the case11from the outlet19.

Thereafter, when the fuel cell system is stopped, the discharge valve18is opened for a short time as described above. The timing at which the discharge valve18is opened may be immediately before, simultaneous with, or immediately after stopping of the fuel cell system. As in the case described above, the opening of the discharge valve18causes hydrogen to quickly move from the inlet14into the gas passage22through the opening22a, and the product water in the water retaining portion20is instantly discharged.

Since the filter15is provided at the inlet14, foreign matter contained in hydrogen and product water is removed by the filter15. This prevents foreign matter from clogging the ion-exchange resin16. The gas-liquid separation efficiency is therefore maintained. Also, since foreign matter is not incorporated in the product water in the water retaining portion20, the discharge valve18is prevented from being clogged.

As described above, the product water in the water retaining portion20is discharged during the stopped state of the fuel cell system, which empties the water retaining portion20. Thus, even if product water drips from the inner wall of the case and the ion-exchange resin16after the fuel cell system is stopped, the dripped water is retained in the water retaining portion20and does not enter the discharge valve18.

The first embodiment has the following advantages.

(1) During the stopped state of the fuel cell system under a low-temperature environment, even if product water that has dripped from the inner wall of the case11and the ion-exchange resin16is frozen, the discharge valve18is operated normally without being incapable of opening and closing. When starting the fuel cell system, the discharge valve18is operated to open and close without any trouble. Thus, when the fuel cell system restarted, discharge failure does not occur. Further, the discharge valve18is prevented from being damaged by frozen water.

(2) To prevent the discharge valve18from being frozen, the water retaining portion20and the gas passage22are simply formed in the case11. No dedicated component, such as a suction pump to draw in dripped product water is provided. This simplifies the structure.

(3) The water retaining portion20includes the downward inclination surface20bformed at a portion closer to the inlet14and the upward inclination surface20aformed at a portion closer to the discharge port17. Therefore, when the discharge valve18is opened and hydrogen starts being supplied into the case11, the momentum of the hydrogen smoothly moves the product water in the water retaining portion20along the upward inclination surface20atoward the discharge valve18. The product water in the water retaining portion20is thus discharged out of the discharge valve18, and the water retaining portion20is emptied. Gas that is supplied to the case11through the inlet14is directed to the product water in the water retaining portion20along the downward inclination surface20b. The product water in the water retaining portion20is thus reliably discharged through the discharge valve18. Further, the inclination angle α1of the upward inclination surface20arelative to the horizontal plane is less than the inclination angle α2of the downward inclination surface20brelative to the horizontal plane. This allows the product water in the water retaining portion20to be smoothly swept toward the discharge port17by the flow of hydrogen.

A second embodiment of the present invention will now be described. The differences from the first embodiment will mainly be discussed in the second and subsequent embodiments and modifications below.

In the second embodiment, a forcing mechanism25is provided at the bottom of the water retaining portion20as shown inFIGS. 3 and 4. That is, a water impermeable sheet26is laid on the inner bottom surface of the water retaining portion20. In the lower case member12, an air impermeable pressure receiving ribbon27is provided at the downstream side of the filter15. The pressure receiving ribbon27is supported with a support frame28and guide rollers29a,29b,29c. One end of the pressure receiving ribbon27is integrally connected to the sheet26.

When the discharge valve18is closed, that is, when hydrogen is not being spurted through the inlet14, the sheet26is laid on and conforms to the shape of the bottom surface of the water retaining portion20due to the own weight as shown inFIG. 3. Thus, product water that drips from the ion-exchange resin16and the inner wall of the case11is retained on the sheet26in the water retaining portion20. In contrast, when the discharge valve18is open and hydrogen is spurted through the inlet14, the pressure receiving ribbon27receives the spurting pressure of the hydrogen from the inlet14, and is curved to bulge inward of the case11. The bulging pulls the sheet26toward the inlet14, so that the sheet26is tense. This pulls up the sheet26from the bottom of the water retaining portion20, and force toward the discharge valve18is applied to the product water on the sheet26.

Thus, as in the case of the first embodiment, the momentum of the hydrogen flow from the opening22ainto the gas passage22generates force that moves the product water on the sheet26in the water retaining portion20toward the discharge valve18. At the same time, the tension of the sheet26generates a force that send the product water toward the discharge valve18.

In addition to the advantages (1) and (3) of the first embodiment, the second embodiment provides the following advantage.

(4) The product water in the water retaining portion20is positively moved toward the discharge valve18by means of the sheet26, so that the water retaining portion20is more reliably emptied. Therefore, after the fuel cell system is stopped, dripped product water can be retained in the water retaining portion20without overflowing.

A third embodiment of the present invention will now be described.

According to the third embodiment, a drain port31, which serves as a drain portion, is provided at the bottom of the water retaining portion20. An electromagnetic drain valve32is located in the drain port31. When the fuel cell system is stopped, the drain valve32is opened, so that product water in the water retaining portion20is discharged to the outside through the drain port31and the water retaining portion20is emptied.

The third embodiment provides the same advantages as the advantages (1) and (3) of the first embodiment.

In addition, the third embodiment provides the following advantage.

(5) Since the product water in the water retaining portion20is moved downward and discharged, the water retaining portion20is more reliably emptied.

The present invention is not limited to the above illustrated embodiments, but may be modified as follows.

As shown inFIG. 6, the opening22aof the gas passage22may be widened, and the gas passage22may be gradually narrowed toward the discharge port17. This structure allows a great amount of hydrogen to be drawn into the gas passage22, and increases the flow rate of hydrogen in the gas passage22toward the discharge port17. Thus, the product water in the water retaining portion20is efficiently discharged.

As shown inFIG. 7, a guide wall33may be provided between left and right side walls of the case11to face the inlet14. The guide wall33is designed to guide spurted hydrogen toward the opening22aof the gas passage22. This allows a great amount of hydrogen to flow into the gas passage22, thereby efficiently discharging product water.

As shown inFIG. 8, the bottom wall of the case11of the gas-liquid separator10may be formed as a large arc. This increases the amount of product water retained in the water retaining portion20.

A check valve preventing backflow of hydrogen from the circulation pump3to the outlet19may be located between the outlet19and the circulation pump3. This almost certainly prevents hydrogen from flowing from the outlet19to the case11, allowing hydrogen to be spurted from the inlet14at a high pressure.