Abstract:
Disclosed is a system with which fuel cell stacks can be tested automatically or manually so that production of pollutants and consumption of electricity are little. The system runs various analyses and tests on the fuel cell stacks and provides operative conditions such as temperatures and fluid flows needed in the tests.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to an environmentally friendly, energy-economic system for testing fuel cell stacks and, more particularly, to an environmentally friendly, energy-economic system for running various analyses and tests on fuel cell stacks and providing operative conditions such as temperatures and fluid flows needed in the tests so that consumption of electricity and production of pollutants are reduced. 
       DESCRIPTION OF THE RELATED ARTS 
       [0002]    Fuel cells are getting a lot of attention for being environmentally friendly and efficient regarding energy conversion. There are proton exchange membrane fuel cells (“PEMFC”), alkaline fuel cells (“AFC”), phosphoric acid fuel cells (“PAFC”), molten carbonate fuel cells (“MCFC”) and solid oxide fuel cells (“SOFC”). PEMFC, AFC and PAFC are classified in a low-temperature type. MCFC are classified in a intermediate-temperature type. SOFC are classified in a high-temperature type. Moreover, there are direct methanol fuel cell (“DMFC”) and metal-air hybrid cells. SOFC are getting more attention than other fuel cells for their high energy efficiencies, high-temperature waste heat and ability to use variety kind of fuels. 
         [0003]    Regarding operative principles of an SOFC, a fuel and an oxidizer such as air and oxygen are preheated to a temperature near an operative temperature (600 to 1000 degrees Celsius) of stacks of the SOFC before they are introduced into the anode and cathode of the SOFC respectively. Hydrogen is often used as the fuel. Alternatively, a hydrocarbon fuel such as natural gas may also be used as the fuel. In this case, a reformer can be used to convert the hydrocarbon into a hydrogen-rich gas for use in the SOFC. 
         [0004]    Unlike the fuel cells of the low-temperature type, SOFC require a high operative temperature of 600 to 1000 degrees Celsius. Moreover, an SOFC includes a membrane electrolyte assembly (“MEA”). At the cathode of the MEA, oxygen ions are formed. Then, the oxygen ions are transferred to the anode side of the MEA through a solid-state electrolyte. At the anode of the MEA, the oxygen ions react with hydrogen, carbon monoxide or a hydrocarbon fuel fuel. The products of the reaction are electrons, water and heat. Because the operative temperature of an SOFC is high, the temperature of the products near the anode and the temperature of the products near the cathode are close to the operative temperature of the stack. Therefore, the heat of the product gas can be recuperated for the pre-heating of the fresh reactants of the stack inlet. 
         [0005]    In the operation of the low-temperature type of fuel cells or the high-temperature type of fuel cells, not all of the fuels in the stack are used. Typically, about 60% to 85% of the fuels in the stack are used. That is, about 15% to 40% of the fuel is not consumed during the electrochemical reaction. A burner is often used to burn the residual fuel to release heat that can be recovered with a heat exchanger and used for preheating the fresh reactants. 
         [0006]    During development of SOFC, varieties of tests on the stacks are necessary. Generally, a test station is used to test the stacks. An example of a test station for the low-temperature type of fuel cells can be found in Taiwanese Patent M572462. The exemplary test station includes a gas supply unit, a stack load control unit, a system control unit and a human-machine interface. However, other test stations for the low-temperature type of fuel cells were seen before the filing of the Taiwanese patent and these test stations cannot be used for the high-temperature type of fuel cells. 
         [0007]    The present invention is therefore intended to obviate or at least alleviate the problems encountered in prior art. 
       SUMMARY OF THE INVENTION 
       [0008]    It is an objective of the present invention to provide a system with which fuel cell stacks can be tested automatically or manually. 
         [0009]    It is another objective of the present invention to provide an environmental friendly, energy-economic system for running various analyses and tests on fuel cell stacks and providing operative conditions such as temperatures and fluid flows needed in the tests. 
         [0010]    To achieve the foregoing objectives, the system includes a system control unit, a temperature control unit, a fluid supply unit, a heat recovery unit, a gas-preheating and reforming unit, a furnace and compressive load unit, an electrical load and performance measurement unit, a gas/pressure analysis unit, a gas-cooling and vapor-condensing unit, a security unit and a human-machine interface. The system control unit includes a controller, a signal acquisition device, an industrial computer and a signal-and-power line. The temperature control unit is connected to the system control unit, and includes a temperature sensor and a temperature controller. The fluid supply unit provides fluid that includes a fuel, an oxidizer and water. The fluid supply unit is connected to the system control unit, and includes mass flow controllers, a gas humidifier and a set of piping. The heat recovery unit is connected to the system control unit, the fluid supply unit and the fuel cell, and includes a rear-part heat exchanger for recovering heat of hot gas released from the fuel cell. The gas-preheating and reforming unit is connected to the fuel cell, and includes a heater and a reformer. The heater executes a second phase of heating the fluid provided from the fluid supply unit. The reformer reforms the fuel to hydrogen-rich gas. The furnace and compressive load unit is connected to the temperature control unit, and includes a furnace and a compressive load element. The furnace heats up the fuel cell under the control of the temperature controller. The compressive load element exerts a compressive load on the fuel cell. An electrical load and performance measurement unit is connected to the system control unit and the fuel cell, and includes an electrical load instrument and an AC impedance analyzer. The AC impedance analyzer measures the internal impedance of the fuel cell. The gas/pressure analysis unit is connected to the system control unit, the fluid supply unit, the heat recovery unit, the preheating and reforming unit and the fuel cell, and includes a gas analyzer and an absolute/differential pressure sensor. The gas analyzer analyzes gases released from the reformer, the burner and the fuel cell to evaluate performance of the units. Sampling of the gases is executed under the control of the system control unit. The absolute/differential pressure sensor monitors pressure in a middle segment of the system. The gas-cooling and vapor-condensing unit is connected to the fluid supply unit and the gas/pressure analysis unit, and includes a gas-cooling and vapor-condensing module and a condensed water filter and storage tank. The gas-cooling and vapor-condensing module cools the hot gas in a rear segment of the system. The condensed water filter and storage tank filters and collects the water for use in the fluid supply unit. The security unit monitors security in the system and triggers a security procedure in the system control unit. The security unit is connected to the system control unit, and includes a programmable logic controller operable independent of the system control unit, a hazardous gas sensor and an uninterrupted power supply. The human-machine interface is connected to the system control unit, and includes a display and a command output device. The display shows numbers, charts and tables of data processed in the industrial computer. The command output device is operable for giving commands to the system control unit. The controller of the system control unit is used as a control center for the temperature control unit, the fluid supply unit, the heat recovery unit, the load control and performance measurement unit, the gas/pressure analysis unit, the security unit and the human-machine interface. 
         [0011]    Other objectives, advantages and features of the present invention will become apparent from the following description referring to the attached drawings. 
     
    
     
       BRIEF DESCRIPTIONS OF THE DRAWINGS 
         [0012]    The present invention will be described via the detailed illustration of two embodiments referring to the drawings. 
           [0013]      FIG. 1  is a block diagram of a system for testing fuel cells according to the first embodiment of the present invention. 
           [0014]      FIG. 2  is a block diagram of a first fluid loop of the system shown in  FIG. 1 . 
           [0015]      FIG. 3  is a block diagram of a second fluid loop of the system shown in  FIG. 1 . 
           [0016]      FIG. 4  is a block diagram of a third fluid loop of the system shown in  FIG. 1 . 
           [0017]      FIG. 5  is a block diagram of a system for testing fuel cells according to the second embodiment of the present invention. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0018]    Referring to  FIG. 1 , a solid oxide fuel cell (“SOFC”)  16  is tested with an environmentally friendly, energy-economic system according to a first embodiment of the present invention. The system includes a system control unit  10 , a temperature control unit  11 , a fluid supply unit  12 , a heat recovery unit  13 , a preheating and reforming unit  14 , a furnace and compressive load unit  15 , an electrical load and performance measurement unit  17 , a gas/pressure analysis unit  18 , a gas-cooling and vapor-condensing unit  19 , a security unit  20  and a human-machine interface  21 . In operation of the system, consumption of energy and production of pollutants are minimized. 
         [0019]    The system control unit  10  includes a controller, a signal acquisition device, an industrial computer and a signal-and-power line. The controller may be a programmable logic controller (“PLC”) or a controller including a microprocessor. The system control unit  10  controls all statuses of the system. The controller of the system control unit  10  is used as a control center for the temperature control unit  11 , the fluid supply unit  12 , the heat recovery unit  13 , the electrical load and performance measurement unit  17 , the gas/pressure analysis unit  18 , the security unit  20  and the human-machine interface  21 . 
         [0020]    The temperature control unit  11  is connected to the system control unit  10 . The temperature control unit  11  includes a temperature sensor and a temperature controller. The temperature sensor may be a thermocouple. The temperature controller controls the output power of the preheating and reforming unit  14  and the furnace and compressive load unit  15  to achieve temperature increasing rates and target temperatures required for tests. The temperature controller may be a PID controller. 
         [0021]    The fluid supply  12  is connected to the system control unit  10 . The fluid supply  12  includes mass flow controllers  121 , a gas humidifier  122  and a piping  123 . The fluid supply  12  supplies fluid that includes a fuel, an oxidizer and water. The fuel and oxidizer may be in the form of gas or liquid. 
         [0022]    The heat recovery unit  13  is optional, i.e., the system is workable with or without the heat recovery unit  13 . The heat recovery unit  13  is connected to the system control unit  10  and the fluid supply unit  12 . The heat recovery unit  13  is used for a first phase of heating the fluid provided from the fluid supply unit  12 . 
         [0023]    There are three layouts for the heat recovery unit  13 . In the first layout as shown in  FIG. 2 , the heat recovery unit  13  includes a burner  131 , a front-part heat exchanger  132  and a rear-part heat exchanger  133 . The burner  131  may be a porous medium burner or catalyst burner. Hot exhaust is released from the burner  131  into the rear-part heat exchanger  133  for heat recovery. 
         [0024]    In the second layout as shown in  FIG. 3 , the heat recovery unit  13  includes a burner  131  and a rear-part heat exchanger  133 . Hot exhaust is released from the burner  131  into the atmosphere without heat recovery. The burner  131  may be a porous medium burner or catalyst burner. 
         [0025]    In the third layout as shown in  FIG. 4 , the heat recovery unit  13  only includes a rear-part heat exchanger  133 . 
         [0026]    The gas-preheating and reforming unit  14  is connected to the temperature control unit  11 , the fluid supply unit  12  and the heat recovery unit  13 . The gas-preheating and reforming unit  14  includes a heater  141  and a reformer  142 . The heater  141  executes a second stage of heating the fluid provided from the fluid supply unit  12 . The reformer  142  reforms the fuel provided from the fluid supply unit  12 . 
         [0027]    The mass flow controllers  121  control flow rates of the fluid required in the SOFC  16 , the reformer  142  and the burner  131 . 
         [0028]    The furnace and compressive load unit  15  is connected to the temperature control unit  11 . The furnace and compressive load unit  15  includes a furnace and a compressive load element so that it can heat and exert a compressive load on the SOFC  16 . The furnace is operable under the control of the temperature control unit  11 . 
         [0029]    During the testing, the SOFC  16  is located in the furnace and compressive load unit  15 . The SOFC  16  is connected to the heat recovery unit  13  and the gas-preheating and reforming unit  14 . The SOFC  16  includes at least on stack for generating electricity via a chemical reaction of the fuel and the oxidizer. 
         [0030]    The electrical load and performance measurement unit  17  is connected to the system control unit  10  and the SOFC  16 . The electrical load and performance measurement unit  17  includes an electrical load machine and an AC impedance analyzer for measuring the performance of the SOFC  16 . The electrical load machine is serially connected to the SOFC  16  to automatically adjust internal resistance to measure the voltage to current performance of the SOFC  16  under various loads. The AC impedance analyzer is connected to the SOFC  16  in parallel for providing AC signals of various frequencies to measure the impedance performance of the SOFC  16 . 
         [0031]    The gas/pressure analysis unit  18  is connected to the system control unit  10 , the fluid supply unit  12 , the heat recovery unit  13 , the gas-preheating and reforming unit  14  and the SOFC  16 . The gas/pressure analysis unit  18  includes a gas analyzer and an absolute/differential pressure sensor. The gas/pressure analysis unit  18  analyzes the composition of gas leaving the reformer  142 , the SOFC  16  and the burner  131 , evaluates emissions of the units, and monitors the pressure drops across the system. The sequence of sampling the gases leaving the units connected to the gas/pressure analysis unit  18  is under the control of the system control unit  10 . The gas analyzer may be a gas chromatograph, an on-line gas analyzer or a flue gas analyzer. 
         [0032]    The gas-cooling and vapor-condensing unit  19  is connected to the fluid supply unit  12  and the gas/pressure analysis unit  18 . The gas-cooling and vapor-condensing unit  19  includes a gas-cooling and vapor-condensing module  191  and a condensed water filter and storage tank  192 . The gas-cooling and vapor-condensing module  191  cools the hot exhaust released from the burner  131  and condenses vapor into water. The condensed water filter and storage tank  192  filters and collects the condensed water for use in the fluid supply unit  12 . 
         [0033]    The security unit  20  is connected to the system control unit  10 . The security unit  20  includes a programmable logic controller (“PLC”) operable independent of the system control unit  10 , a hazardous gas sensor and an uninterrupted power supply. The security unit  20  monitors the security of the system and triggers a security procedure in the system control unit  10 . 
         [0034]    The human-machine interface  21  is connected to the system control unit  10 . The human-machine interface  21  includes a display and a command output device such as a mouse, a keyboard and a touch panel. The human-machine interface  21  provides numbers, charts and tables of data processed in the industrial computer of the system control unit  10 . Moreover, the display and the command output device are used together to give commands to the system control unit  10 . 
         [0035]    In the first layout, the reformer  142 , the burner  131  and the rear-part heat exchanger  133  are connected to check valves  30 . Each of the check valves  30  is connected to a related one of the mass flow controllers  121 . The mass flow controllers  121  are connected to solenoid valves  40 . 
         [0036]    In operation, the PLC (or the controller including the microcontroller) of the system control unit  10  is used as a control center to execute an automatic control procedure. At first, the signal acquisition device acquires signals from the units and sensors, and sends the signals to the PLC. Then, the PLC relays the data to the industrial computer for processing and storage of the data. The signals are transferred to the PLC and the industrial computer from the sensors and the units through the signal-and-power line. After the processing of the data in the industrial computer is complete, results are provided in numbers, charts and tables through the human-machine interface  21 . At this instant, a user can give commands to control the units through the human-machine interface  21 . The flow path of the commands sending is a reverse way mentioned above. The system control unit  10  communicates analog signals with the temperature sensor and the absolute/differential pressure sensor, but communicates digital signals with the other units and sensors. The signals may be communicated according to a digital communication protocol such as RS-323, RS-485, RS-422 and GPIB or an internet communication protocol such as TCP/IP. 
         [0037]    To test the performance of the SOFC  16 , the fluid supply unit  12  provides a fuel, an oxidizer and water. The fuel includes hydrogen, natural gas and/or a hydrocarbon fuel. The oxidizer is pure oxygen or air. The fuel, the water and the oxidizer are transferred into the heat recovery unit  13  through the piping  123 . 
         [0038]    In the first phase of heating, the gas is transferred into the front-part heat exchanger  132  from the fluid supply unit  12  through a proportional control valve  50  while hot gas, if any, is transferred into the front-part heat exchanger  132  from the cathode outlet of the SOFC  16 . In the front-part heat exchanger  132 , the gas receives heat from the hot gas. Hence, the hot gas from the cathode of the SOFC  16  is cooled before it is transferred into the burner  131 . On the other hand, gas from the fluid supply unit  12  is preheated. 
         [0039]    The preheated gas is sent from the front-part heat exchanger  132  into the rear-part heat exchanger  133  while hot exhaust is released from the burner  131  into the rear-part heat exchanger  133  where the preheated gas receives heat from the hot exhaust. Now, the first phase of preheating is complete. The heat for the first phase of preheating is recovered with the heat recovery unit  13 . 
         [0040]    If there is any need to humidify the anode inlet gas of the SOFC  16 , the fuel can be humidified in the gas humidifier  122  before it is transferred into the SOFC  16 . 
         [0041]    The second layout of the heat recovery unit  13  shown in  FIG. 3  does not include any proportional control valve, nor does the third layout of the heat recovery unit  13  shown in  FIG. 4 . 
         [0042]    After the first phase of heating, the fluid goes into the gas-preheating and reforming unit  14  for a second phase of heating and reforming. The heater  141  preheats the gases before they are transferred into the cathode and anode of the SOFC  16  to compensate the inadequacy of heat in the heat recovery unit  13 . The reformer  142  reforms the natural gas, water and air into hydrogen-rich gas. The hydrogen-rich gas is transferred into the SOFC  16  for reaction, thus generating electricity. 
         [0043]    After the second phase of heating, the piping  123  sends the fluid into the cathode and anode of the SOFC  16  which is inside the furnace and compressive load unit  15 . The furnace and compressive load unit  15  heats the SOFC  16  to 700 to 1000 degrees Celsius to facilitate stable operation of the SOFC  16 . A compressive load may be applied on the SOFC  16  via providing a heavy refractory metal block. Instead of the heavy refractory metal block, hydraulic device may be used. A ceramic or metal column may be provided between the hydraulic device and the SOFC  16  to ensure air-tightness and electrical isolation of the SOFC  16 . 
         [0044]    The performance of the SOFC  16  is measured with the load control and performance measurement unit  17 . A conventional electrical load machine and an AC impedance analyzer can be connected to SOFC  16  in series and parallel respectively to measure voltage, current and power curves and impedance performance of the SOFC  16 . 
         [0045]    In the first layout shown in  FIG. 2 , as the SOFC  16  performs the electrochemical reaction of the hydrogen-rich gas, and the cathode and anode thereof respectively release residual fuel and air into the burner  131  for combustion, the temperature sensor of the temperature control unit  11  monitors the operative temperatures of the SOFC  16  and the burner  131 . As the temperature sensor detect high temperature, the hot gas is transferred from the cathode of the SOFC  16  into the front-part heat exchanger  132  where the cold-end gas is used to cool the hot gas before it is mixed and combusted in the burner  131 . Heat generated from the combustion is transferred into the rear-part heat exchanger  133  to heat the fluid provided from the fluid supply unit  12  to significantly reduce the electricity consumed by the preheating and reforming unit  14 . The cold-end gas is transferred into the front-end heat exchanger  132  under the control of the system control unit  10 . 
         [0046]    In the second layout shown in  FIG. 3 , the cathode and anode of the SOFC  16  respectively release residual fuel and air into the burner  131  for mixing and combustion to reduce pollution. Exhaust is released from the burner  131  into the atmosphere. No heat from burned gas is recovered. 
         [0047]    In the third layout shown in  FIG. 4 , residual fuel is simply released into the atmosphere from the anode outlet of the SOFC  16 . The cathode outlet of the SOFC  16  releases hot air into the rear-part heat exchanger  133  for heat recovery. 
         [0048]    In the first layout shown in  FIG. 2 , the exhaust is transferred from the burner  131  into the rear-part heat exchanger  133  before it is sent into the gas/pressure analysis unit  18 . Not only the heat recovery unit  13  is connected to the gas/pressure analysis unit  18 , but also the fluid supply unit  12 , the preheating and reforming unit  14  and the SOFC  16  are connected to the gas/pressure analysis unit  18  through gas-sampling pipes. The sampling is executed in order under the control of the system control unit  10 . Via the analysis of the gas samples, the properties of the gases generated from the reformer  142 , the SOFC  16  and the burner  131  are obtained. Based on data related to the properties of the gases, the pollution generated by and operative efficiencies of the units are evaluated. The absolute/differential pressure sensor of the gas/pressure analysis unit  18  monitors the pressure in selected segment of the system. Via measuring a value of pressure at a single point or the differential pressure between two points along the flow path, a pressure drop is learned. The system control unit  10  uses the pressure drop to determine whether there is clogging or deposition of carbon in the units and whether to take actions to remove such clogging or carbon deposition. 
         [0049]    After the gas/pressure analysis unit  18 , the exhaust is transferred into the gas-cooling and vapor-condensing unit  19 . The gas-cooling and vapor-condensing module  191  of the gas-cooling and vapor-condensing unit  19  cools the exhaust at a rear end of the system so that vapor in the exhaust condenses into water for recovery. The condensed water filter and storage tank  192  of the gas-cooling and vapor-condensing unit  19  collects and filter the water so that the water can be transferred into the fluid supply unit fore reuse. Thus, the demand for pure water in the system is significantly reduced. 
         [0050]    Because the fuel for the SOFC  16  is explosive, the PLC (or the controller including the microcontroller) of the security unit  20  is operated independently of the system control unit  10 . When there is leak or an event that could endanger operative personnel, the PLC of the security system stops the supply of all gases except nitrogen. The uninterrupted power supply of the security unit  20  connected to the system control unit  10  and the fluid supply unit  12  provides a buffer period long enough for executing a fuel cell-protecting procedure and an urgent shut-down procedure after the interruption of the mains power. For example, the supply of the fuel is interrupted, and the nitrogen is used to purge the anode of the SOFC  16 . The hazardous gas sensor of the security unit  20  determines whether there is leakage of the fuel or hazardous gas such as carbon monoxide. The hazardous gas sensor is located in the security unit  20  for local monitoring or a laboratory for overall monitoring. The hazardous gas sensor is connected to the security unit  20  and the system control unit  10 . When the concentration of such hazardous gas reaches a predetermined value, the system control unit  10  executes a system-level urgent shut-down procedure. For example, all valves for supplying the fuel are closed. 
         [0051]    Referring to  FIG. 5 , there is shown an environmentally friendly, energy-economic system according to a second embodiment of the present invention. The second embodiment is like the first embodiment except that the fluid supply  12  includes blowers  124 . The mass flow controllers  121  and the blowers  124  together control flow rates of the fluid required in the SOFC  16 , the reformer  142  and the burner  131 . With the use of the blowers  124 , there is no need for air compressors. 
         [0052]    As described above, with the system, high-temperature fuel cells can be tested manually or automatically. The system provides the operative conditions such as temperatures and the flow rates of the fluid required during the testing of the fuel cells. The units ensure the stability and security of the testing that lasts for long. With the heat recovery, the consumption of energy and the production of pollutants are significantly reduced. Hence, the system is energy-economic and environmentally friendly. Accordingly, the cost in the development and testing of the fuel cells are reduced. 
         [0053]    The present invention has been described via the detailed illustration of the embodiments. Those skilled in the art can derive variations from the embodiments without departing from the scope of the present invention. Therefore, the embodiments shall not limit the scope of the present invention defined in the claims.