Chemistry: electrical current producing apparatus – product – and – With pressure equalizing means for liquid immersion operation
Reexamination Certificate
1999-09-07
2002-12-31
Brouillette, Gabrielle (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
With pressure equalizing means for liquid immersion operation
C429S006000
Reexamination Certificate
active
06500573
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a humidifier device for use in fuel cells and an operating system thereof in entire fuel cell systems. In particular, the present invention relates to a humidifier device for use in fuel cells and a water control device for use in fuel cell systems, which are suitable as a humidifier device and a water control device for humidifying process gases supplied to fuel cells used as onboard power sources or fixed-type small sized electric generators.
2. Description of the Related Arts
Fuel cells are adapted to supply fuels and discharge reaction products continuously and convert chemical energy possessed in fuels directly into electric energy, and have various advantages features such as high energy conversion efficiency, less emission of atmospheric contaminants, low noises and optional choice of scales. The fuel cells are classified in accordance with the kind of electrolytes used into solid polymeric type, phosphate type, alkali type, molten carbonate type and solid oxide type.
Among the fuel cells, solid polymer fuel cells, phosphoric acid fuel cells and alkaline fuel cells generate electromotive force by proton-conducting from an anode to a cathode and it is in common with them that control of a wet state of electrolytes is essential for normal operation of electrolytes.
For example, in a solid polymer fuel cell, a solid polymer electrolyte membrane having a proton conductivity is used as the electrolyte. Specifically, fluoro polymer electrolyte membrane typically represented by a perfluoro sulfonic acid membrane is used generally which is known under the trade name of Nafion (registered trade mark for products manufactured by Du Pont Co.).
The fluoro polymer electrolyte membrane is excellent in oxidation resistance and show good proton conductivity in a wet state but the electric resistance is increased as the water content lowers and can no longer function as the electrolyte membrane. Accordingly, the fluoro polymer electrolyte membrane is usually used in a saturated wet state.
However, since the operation temperature of a solid polymer fuel cell is about 80° C., water evaporates from the electrolyte membrane during operation of the fuel cell, and water content in the electrolyte membrane lowers gradually. Further, when proton-conducting from the anode to the cathode, since molecules of water transfer simultaneously, the area for the anode tends to be drying-out particularly. If the situation is left as it is, the electric resistance of the electrolyte membrane increases to generate heat, which lowers the electric power or causes failure.
In view of the above, in the solid polymer fuel cell, process gases supplied to a gas diffusion electrode is generally humidified for properly controlling the wet state of the electrolyte membrane for operating the electrolyte normally.
Further, a phosphoric acid fuel cell uses as an electrolyte, a concentrated aqueous solution of phosphoric acid impregnated in an SiC matrix and the operation temperature is about 200° C. Further, an alkaline fuel cell includes a matrix type and a free electrolyte type, in which the matrix type is a fuel cell using, as an electrolyte, an aqueous solution of potassium hydroxide at a concentration of 30 to 45% impregnated into asbestos and operated at a temperature of about 100° C.
Also in the phosphoric acid fuel cell and the alkaline fuel cell, it is necessary to properly control the wet state of the electrolyte membrane in order to operate the electrolyte normally and process gases are humidified if the output voltage is lowered or temperature elevation occurs in the fuel cell.
As a humidifier device for humidifying process gases supplied to fuel cells, a humidifier device using steams for humidification and a humidifier device using mists for humidification are known. In the humidifier device using steams, process gases are passed in a humidifying tank (so-called bubbling tank) kept at a high temperature for humidification corresponding to saturated steam pressure, which has a merit capable of stable humidification.
In the humidifier device using mists, finely atomized mists are added to process gases. For example, Japanese Published Unexamined Patent Application Hei 5-54900 discloses a solid polymer fuel cell having a humidifier device for process gases of adding mists finely atomized to 300 &mgr;m or less to at least one of fuels or oxidants by using a mist atomizer having a spray nozzle or an ultrasound atomizer apparatus.
In the humidifier device using mists, since sprayed mists are transferred as they are to the electrode on the process gases as a carrier, it provides a merit capable of quantitatively controlling the amount of humidifying water. Further, since the process gases are deprived of latent heat of evaporation when the mists atomize into steams, it has a merit capable of expecting a cooling effect for the process gases.
However, since the humidifier device of humidifying process gases by steams consumes a great amount of energy for generating steams, which causes lowering of energy conversion efficiency of the fuel cell. In addition, since it is necessary to keep the water source at a high temperature to always generate steams during operation of a fuel cell, heating is necessary also for unconsumed water content to further increase the energy loss.
Further, for always generating steams a bubbling bath of a large capacity is required and since a bubbling bath of a large capacity has a large heat capacity, a time constant regarding the change of temperature is increased. Therefore, it requires a long time for elevating the temperature of the bubbling bath and water to a predetermined level to bring about a problem in view of the starting property.
Further, since the time constant relative to the change in temperature is large, the response characteristic is poor, which leads to difficulty in transient control. That is, if a load changes abruptly to require a large amount of process gases and, correspondingly, a great amount of steams, since the amount of humidification cannot be increased abruptly, the water content in the electrolyte membrane becomes insufficient to lower the output.
On the other hand, if an excessive amount of steams is sent to the electrode, so-called flooding in which a gas flow channel is closed by liquid water is caused to lower the output and make the operation state of the fuel cell instable. Particularly, since water is produced by electrode reactions on the cathode, flooding is liable to be caused.
On the contrary, the humidifier device for humidifying process gases by mists as disclosed in Japanese Published Unexamined Patent Application Hei 5-54900 consumes less electric power for the spray nozzle or ultrasound atomizer apparatus and, accordingly, it is efficient. Further, since it is not necessary to wait for the elevation of water temperature for atomizing water, there is no problem for the starting property. Further, since the increase/decrease for the amount of humidification can be controlled irrespective of the water temperature, it is highly responsive.
However, even in a case of a mist humidifier using a spray nozzle or ultrasound atomizer apparatus, it is necessary to change the addition amount of the mists to the process gases continuously corresponding to the change of load for stable operation of the fuel cell. However, Japanese Published Unexamined Patent Application Hei 5-54900 describes only for the control corresponding to the output power but discloses nothing at all for concrete means of continuously changing the addition amount of mists in accordance with change of load.
Further, the spray nozzle or the ultrasound atomizer apparatus has only a small control range for the performance of supplying mists and cannot change the addition amount of mists greatly. For example, in a case of atomizing mists by using a spray nozzle, the addition amount of mists to the process gases can be controlled by a primary air flow rate.
However, a minimum flow rate is present in t
Aoki Hiroshi
Asaoka Takahiko
Hiroshima Kazutaka
Ohya Yutaka
Simazu Takashi
Brouillette Gabrielle
Kabushiki Kaisha Toyota Chuo Kenkyusho
Wills Monique
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