Abstract:
An anode stream recirculation system for a fuel cell, the fuel cell including an anode gas input and an anode gas output, the anode stream recirculation system comprising: an anode gas supply; a switch connected with the anode gas supply; a pressure regulating device connected between the switch and the anode gas input of the fuel cell; a diaphragm pump connected between the anode gas output and the anode gas input of the fuel cell thereby forming an anode gas recirculation; wherein the diaphragm pump has at least a sensor electrically connected with the switch.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
   Not Applicable 
   STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
   Not Applicable 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   This invention is related to a diaphragm pump and an anode stream recirculation system using such pump for a fuel cell, in particular, an anode stream recirculation system used in a proton exchange membrane fuel cell as well as the diaphragm pump used in such system, and most particularly, a hydrogen recirculation system and the diaphragm pump utilized in a proton exchange membrane fuel cell. The present invention eliminates certain elements required in the conventional anode stream recirculation system for a fuel cell and, thus reduces the cost for manufacture of the components of the fuel cell. Furthermore, this invention lowers the electrical energy required to operate the anode stream recirculation system so that the overall efficiency of electrical power generation for the fuel cell system can be promoted. 
   2. Description of the Related Art 
   With the rapid growth of civilization, the consumption of traditional energy resources, such as coal, oil and natural gas, increases rapidly. This results in serious environmental pollution and causes a series of environmental problems such as global warming and acid rain. It is now recognized that the existing natural energy resources are limited. Therefore, if the present rate of energy consumption continues, all existing natural energy resources will be exhausted in the near future. Accordingly, many developed countries are conducting research and development of new and alternative energy resources. The fuel cell is one of the most important and reasonably priced energy resources. Compared with traditional internal combustion engines, the fuel cell has many advantages such as high energy conversion efficiency, clean exhaust, low noise, and no consumption of traditional gasoline. 
   In brief, a fuel cell is an electrical power generation device powered by the electrochemical reaction of hydrogen and oxygen. Basically, the reaction is a reverse reaction of the electrolysis of water, to convert the chemical energy into electrical energy. The basic structure of a fuel cell, for example, a proton exchange membrane fuel cell, comprises a plurality of cell units. The structure of the cell unit generally illustrated in  FIG. 1  comprises a proton exchange membrane (PEM)  10  at the middle, with the two sides thereof provided with a layer of catalyst  12 , each of the two outsides of the catalyst  12  is further provided with a gas diffusion layer (GDL)  14 . An anode plate  16  and a cathode plate  18  are further provided at the outermost sides adjacent to the GDL  14 . After tightly combining all the above elements together, a cell unit is formed. For practical application of the fuel cell, a plurality of the above cell units are stacked and serially connected to provide sufficient power, as illustrated in FIG.  2 . Therefore, two adjacent cell units can share a common polar plate  20 , as illustrated in  FIG. 3 , which serves as the anode and the cathode for the two adjacent cell units, respectively. Accordingly, such a polar plate  20  is usually referred as a bipolar plate. Generally, as illustrated in  FIG. 3 , the two sides of the bipolar plate  20  are provided with many groove type gas channels  22  for transporting the gases for reaction, such as hydrogen and air (to provide oxygen), as well as transporting the reactants, such as water droplets or vapor, out of the bipolar plate  20 . 
   One conventional gas supply system for use in a fuel cell comprises: a cathode gas supply system (such as an oxygen supply), and an anode circulation system (such as a hydrogen circulation system), as illustrated in FIG.  4 . Atmospheric air may serve as a supply of the oxygen supply system  30 , where air is filtered by a filter  32  and than pumped into the fuel cell  50  through a blower  34 . Excessive air, upon reaction within the fuel cell  50 , is discharged through a water recuperator  36 . The water recuperator  36  may recuperate the minute amount of water contained within the discharged air, where the water is then directed to a cooling system  38 . The useless heat generated by the fuel cell  50  is also transmitted to the cooling system  38 . The coolant used in the cooling system  38  then re-enters the fuel cell  50  to provide sufficient cooling thereto. 
   The conventional anode circulation system includes: a hydrogen source  40  which regulates hydrogen input through a pressure regulator  42 ; a hydrogen pump  44  being provided at the other end of the fuel cell  50  for discharging excessive hydrogen, upon reaction within the fuel cell, and for pumping the hydrogen source  40  into the fuel cell  50 . The excessive hydrogen is discharged through a humidifier  46 , such as a bubbler, for increasing the humidity of the excessive hydrogen, then flows back into the piping of the hydrogen supply to be mixed with fresh hydrogen, and then repeats the same circulation. The water within the cooling system  38  can be transmitted to the water within the humidifier  46 . 
   The hydrogen within the bipolar plate of the fuel cell must have adequate humidity such that the hydrogen ions (H + ) after reaction can be carried through the PEM by the water vapor. The hydrogen ions then react with the oxygen at the other side of the PEM and the electrons provided from the outer circuit, to establish proton conduction. Generally, if the humidity of the hydrogen is too low, the PEM will be dehydrated, thus, the electrical resistance of the fuel cell will increase and the voltage of the fuel cell will decrease, which will result in the working life of the fuel cell being significantly shortened. If, on the other hand, the humidity of the hydrogen is too high, the channels for transporting the gases within the bipolar plate may be clogged by water droplets, which will stop the reaction of gases within the fuel cell and the performance of the fuel cell will be seriously impaired. Accordingly, in the anode stream recirculation system, a humidifier to adjust the humidity of the hydrogen is generally required. 
   BRIEF SUMMARY OF THE INVENTION 
   A primary objective of this invention is to improve the conventional anode stream recirculation system by utilizing a diaphragm pump for continuously collecting the excessive hydrogen discharged from the fuel cell, and then directing the collected hydrogen back into the fuel cell for reaction. Therefore, the conventional hydrogen pump may be eliminated, the parasitic loss of electrical energy of the fuel cell itself can be reduced, and the overall efficiency of electrical power generation by the fuel cell system can be promoted. 
   Another objective of this invention is that the anode stream recirculation system and the diaphragm pump can be further connected with a water circulation system. As a result, the water in the water circulation system can be driven by the diaphragm pump simultaneously. Therefore, the driving pump necessary for conventional water circulation system of the fuel cell may also be eliminated and thus, the parasitic loss of electrical energy of the fuel cell can be further reduced and the overall efficiency of electrical power generation by the fuel cell system is further promoted by this invention. 
   A further objective of this invention is to automatically clear out the gas channels of the bipolar plates within the fuel cell by the pressure pulses introduced from intermittently switching on/off the hydrogen source so that no water droplet will stay within the gas channels to impair the power generation efficiency of the fuel cell. 
   The primary technical contents of this invention are related to an anode stream recirculation system for a fuel cell, the fuel cell including an anode gas input and an anode gas output, the anode stream recirculation system comprising: an anode gas supply; a switch connected with the anode gas supply; a pressure regulating device connected between the switch and the anode gas input of the fuel cell; a diaphragm pump connected between the anode gas output and the anode gas input of the fuel cell thereby forming an anode gas recirculation; wherein the diaphragm pump has at least a sensor electrically connected with the switch. 
   Another important feature of this invention is the diaphragm pump utilized in the anode stream recirculation system for the fuel cell. The diaphragm pump has a wall defining an interior space, a piston provided in the interior space, and a diaphragm assembly sealing with the piston and the wall of the diaphragm pump thereby dividing the interior space into two portions. 
   The structures and characteristics of this invention can be realized by referring to the appended drawings and explanations of the preferred embodiments. 

   
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       FIG. 1  is a schematic cross sectional view showing the structure of a cell unit of a conventional fuel cell; 
       FIG. 2  is a schematic cross sectional view showing the structure of combining a plurality of the conventional cell units; 
       FIG. 3  is a schematic cross sectional view showing a portion of the conventional fuel cell; 
       FIG. 4  is a schematic view showing a gas supply of a conventional fuel cell; 
       FIG. 5  is a schematic view showing a preferred embodiment of an anode gas recirculation system of this invention; 
       FIG. 6  is a schematic cross sectional view showing the diaphragm pump of this invention; and 
       FIG. 7  schematically illustrates the anode gas recirculation system and the diaphragm pump being further connected with a water circulation system according to a preferred embodiment of this invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   This invention is related to an anode stream recirculation system for a fuel cell, in particular, a hydrogen recirculation system utilized in a proton exchange membrane (PEM) fuel cell. One preferred embodiment of this invention is substantially shown in  FIG. 5 , which includes an anode gas supply  60  to provide the anode gas required for the reaction proceeded in the fuel cell  80 . For the present embodiment of the proton exchange membrane fuel cell, the anode gas is hydrogen. The anode gas flows through a switch  62  and a pressure regulating device  64  before entering the fuel cell  80  through an anode gas input  82 . The switch  62  can be a solenoid valve which is used to control the open/close of the gas flow in the piping and to determine whether fresh anode gas should be released from the anode gas supply  60 . The pressure regulating device  64  is used to adjust the pressure of the anode gas flowing therethrough. Generally, the flowing amount of the anode gas is set to be higher than the required Stoichiometric amount for a specific electrical power generation of the fuel cell so as to ensure that the electrochemical reaction takes place completely within the fuel cell  80 . The fuel cell  80  also has an anode gas output  84 . The anode stream recirculation system further comprises a diaphragm pump  70  connected with both the anode gas output  84  and the anode gas input  82  of the fuel cell  80  thereby forming an anode gas recirculation as illustrated in FIG.  5 . The anode stream recirculation system further comprises two check valves  72  and  74  with one provided between the anode gas input  82  of the fuel cell  80  and the diaphragm pump  70 , and the other provided between the anode gas output  84  of the fuel cell  80  and the diaphragm pump  70 . In this preferred embodiment, the check valves  72  and  74  are mounted on the two sides of the diaphragm pump  70 . 
   According to the preferred embodiment of this invention, the diaphragm pump  70  has a wall  76  defining an interior space and a piston  90  is provided in the interior space. A diaphragm  92  is attached over the piston  90  and is sealing with the wall  76  of the diaphragm pump  70 . The diaphragm  92  can be made of rubber and divides the interior space into two portions  102  and  104 . The wall  76  of the diaphragm pump  70  further comprises an opening  96  for atmosphere. Thus, the portion  102  of the interior space is adjoined with the anode stream recirculation system, and the other portion  104  of the interior space is communicated with atmosphere. Furthermore, the piston  90  lies on an elastic device, such as a spring  94 . In the preferred embodiment, such as that shown in  FIGS. 5 and 6 , the diaphragm pump  70  has two Hall effect sensors  106  and  108  mounted on the top side and bottom side of the diaphragm pump  70 , respectively. The Hall effect sensor may be model No. HAL504UA-E produced by Micronas Company, or model No. DN6848-ND produced by Panasonic Company, or any other types of sensors that can perform a similar function as described below. A magnetic member, such as a magnet  110 , is mounted on the piston  90 . The piston  90  can move up and down, depending on variation of the pressure of the portions  102  and  104  on the two sides of the diaphragm  92 , as well as the elastic force provided by the spring  94 . 
   In this preferred embodiment, the two sensors  106  and  108  sense the position of the piston  90  by the magnet  110  thereon. The flowing rate and the pressure of the anode gas supply  60  are set to be higher than the required Stoichiometric amount for a specific electrical power generation of the fuel cell  80  so as to ensure that the electrochemical reaction takes place completely within the fuel cell  80 . Accordingly, excessive anode gas will be discharged into the output piping and be collected in the portion  102  of the diaphragm pump  70  through the anode gas output  84 . As the other portion  104  of the diaphragm pump  70  is communicated with the atmosphere by the opening  96 , the pressure of the portion  104  remains at a constant atmospheric pressure. When the switch  62  is switched on, the anode gas from the anode gas supply  60  with significantly higher pressure will thrust into the whole system, the pressure of the portion  102  thus increases and thereby moves the piston  90  downwardly and compresses the spring  94 . When the piston  90  downwardly moves to a predetermined position, the sensor  108  senses the position of the approaching magnet  110  on the piston  90  and transmits a signal to switch off the switch  62 . At this time, no more fresh anode gas is supplied. As the electrochemical reaction within the fuel cell  80  proceeds, the anode gas will be consumed and the pressure in the system decreases. Therefore, the piston  90  is forced upwardly by the elastic force of the spring  94  and the atmospheric pressure to further expel the anode gas stored in the portion  102  into the fuel cell  80 . As the electrochemical reaction within the fuel cell  80  continues, the anode gas within the portion  102  will be consumed progressively, and the excessive anode gas discharged from the fuel cell  80  keeps decreasing. Accordingly, the pressure in the portion  102  keeps decreasing and the pump  90  keeps moving upwardly. When the piston  90  upwardly moves to another predetermined position, the sensor  106  senses the approaching magnet  110  on the piston  90  and thus, transmits another signal to switch on the switch  62 . As a result, fresh anode gas is again supplied from the anode gas supply  60  and thrusts into the whole system, and the piston  90  is therefore compressed downwardly. 
   By the above design, the anode recirculation system of this invention can recycle excessive anode gas that has not been reacted, and automatically redirect this gas back into the fuel cell for reaction. Thus, the hydrogen pump  44  required in the conventional technique for gas recirculation is utterly unnecessary. This invention therefore reduces the parasitic loss of electrical energy of the fuel cell itself. For this preferred embodiment, about 5% of the generated electrical power from the fuel cell can be saved and thus, the overall efficiency of electrical power generation by the fuel cell system is promoted. 
   According to another preferred embodiment of this invention, as shown in  FIG. 7 , the diaphragm pump  70  may not be communicated with atmosphere, instead, it is communicated with a water circulation system. The water circulation system further comprises a reservoir  122  to contain the circulation water and a radiator  124  to lower the water temperature. The circulation water may also be directed to the fuel cell  80  to cool it. The water circulation system is connected with the diaphragm pump  70  through check valves  126  and  128  for input and output of the circulation water. Thus, the portion  104  of the diaphragm pump  70  is now filled with water instead of air. When the piston  90  of the diaphragm pump  70  moves up and down according to the same manner described above, the water is driven and circulated within the water circulation system simultaneously. Therefore, the driving pump necessary for conventional water circulation system of the fuel cell  80  may also be eliminated and thus, the parasitic loss of electrical energy of the fuel cell can be further reduced and the overall efficiency of electrical power generation by the fuel cell system is further promoted by this invention. 
   The diaphragm pump according to this invention involves simple construction with low manufacture costs, and it does not need to consume any energy during operation. In addition, every time the switch  62  is switched on, the anode gas with significantly higher pressure will thrust into the whole system, especially into the fuel cell  80 . As a result, any water droplet condensed from the reaction of the fuel cell  80  or any undesired particle existing within the gas channels  22  of the bipolar plate  20  will be shattered and/or expelled out of the gas channels  22  by such intermittent high-pressure thrust gas. Thus, this invention also provides a function of intermittently and automatically clearing out the gas channels within the fuel cell. 
   This invention is related to a novel creation that makes a breakthrough to conventional art. Aforementioned explanations, however, are directed to the description of preferred embodiments according to this invention. Various changes and implementations can be made by persons skilled in the art without departing from the technical concept of this invention. Since this invention is not limited to the specific details described in connection with the preferred embodiments, changes to certain features of the preferred embodiments without altering the overall basic function of the invention are contemplated within the scope of the appended claims.