FUEL CELL SYSTEM WITH EXHAUST GAS CONCENTRATION MONITORING

An electrolysis cell system includes a cathode portion configured to output a cathode exhaust stream, an anode portion configured to output an anode exhaust stream, a sensor configured to detect a concentration in an exhaust stream and to output sensor data, wherein the sensor is either a hydrogen concentration sensor configured to detect a hydrogen concentration in the cathode exhaust stream or a water concentration sensor configured to detect a water concentration of the anode exhaust stream, and a controller. The controller is configured to receive the sensor data from the sensor and, based on the sensor data, control at least one of (a) an air pressure adjustment device to adjust a pressure of air entering the anode portion or (b) a steam pressure adjustment device to adjust a pressure of steam entering the cathode portion.

BACKGROUND

The present disclosure relates generally to the field of electrochemical cells, such as fuel cells and electrolysis cells, and more particularly to pressure control of fuel cell inputs.

Generally, a fuel cell is a type of electrochemical cell that includes an anode, a cathode, and an electrolyte layer that together drive chemical reactions to produce electricity. Multiple fuel cells may be arranged in a stack to produce a desired amount of electricity. Fuel gas, such as hydrogen gas or hydrocarbon gas, is supplied to the anode, while oxidant gas is supplied to the cathode. The fuel gas and oxidant gas are used up by the electrochemical reactions as they flow over the anode and cathode, respectively.

A fuel cell may be operated in reverse as an electrolysis cell. In an electrolysis mode, an external power source provides an electric current to the cell, and water is supplied to the cathode as steam. Oxygen ions from the water molecules cross over the electrolyte to the anode while the hydrogen remains in the cathode. Thus, water molecules may be split into hydrogen gas and oxygen gas.

A difference in pressure between the reactants in the anode and cathode can cause the reactant gases to cross the electrolyte layer to the opposite electrode, a phenomenon called crossover. Crossover can result in reduced performance and efficiency, as the reactants that cross the electrolyte are not able to be utilized in the chemical reactions that generate electricity. Further, excessive differential pressure between the anode and cathode can impart stresses into the electrochemical cells.

SUMMARY

Systems and methods of the present disclosure relate to the monitoring of water and hydrogen concentration in fuel cell systems and electrolysis systems to monitor crossover of reactant gases. Reactant gas pressures can be adjusted to reduce or otherwise adjust the amount of crossover.

One embodiment relates to an electrolysis cell system including a cathode portion configured to output a cathode exhaust stream, an anode portion configured to output an anode exhaust stream, and a sensor configured to detect a concentration in an exhaust stream and to output sensor data. The sensor is either a hydrogen concentration sensor configured to detect a hydrogen concentration in the cathode exhaust stream or a water concentration sensor configured to detect a water concentration of the anode exhaust stream. The electrolysis cell system further includes a controller configured to receive the sensor data from the sensor and, based on the sensor data, control at least one of (a) an air pressure adjustment device to adjust a pressure of air entering the anode portion or (b) a steam pressure adjustment device to adjust a pressure of steam entering the cathode portion.

In one aspect, which is combinable with any other aspects or embodiments, the electrolysis cell system further includes a first pressure transducer configured to measure anode gas pressure in the anode portion and a second pressure transducer configured to measure cathode gas pressure in the cathode portion, wherein at least one of the air pressure adjustment device or the steam pressure adjustment device is controlled in part based on a comparison between the measured anode gas pressure and the measured cathode gas pressure.

In one aspect of the electrolysis cell system, which is combinable with any other aspects or embodiments, the controller is further configured to determine a differential pressure between the cathode portion and the anode portion based on the comparison between the measured anode gas pressure and the measured cathode gas pressure and the sensor data.

In one aspect of the electrolysis cell system, which is combinable with any other aspects or embodiments, the air pressure adjustment device is a back-pressure regulator configured to allow the anode exhaust stream to flow therethrough and the steam pressure adjustment device is a back-pressure regulator configured to allow the cathode exhaust stream to flow therethrough.

In one aspect of the electrolysis cell system, which is combinable with any other aspects or embodiments, the sensor is a hydrogen concentration sensor and the controller is configured to at least one of (a) control the steam pressure adjustment device to increase the pressure of steam entering the cathode portion when the sensor data indicates a decrease in the hydrogen concentration of the cathode exhaust steam or (b) control the air pressure adjustment device to decrease the pressure of air entering the anode portion when the sensor data indicates a decrease in the hydrogen concentration of cathode exhaust stream.

In one aspect of the electrolysis cell system, which is combinable with any other aspects or embodiments, the sensor is a water concentration sensor and the controller is configured to at least one of (a) control the steam pressure adjustment device to decrease the pressure of steam entering the cathode portion when the sensor data indicates an increase in the water concentration of anode exhaust stream or (b) control the air pressure adjustment device to increase the pressure of air entering the anode portion when the sensor data indicates an increase in the water concentration of anode exhaust stream.

Another embodiment relates to an electrolysis cell system including a cathode portion configured to output a cathode exhaust stream, an anode portion configured to output an anode exhaust stream, a first hydrogen concentration sensor configured to detect a hydrogen concentration in the cathode exhaust stream, a controller. The controller is configured to receive first hydrogen concentration sensor data from the first hydrogen concentration sensor and, based on the first hydrogen concentration sensor data, control at least one of (a) an air pressure adjustment device to adjust a pressure of air entering the anode portion or (b) a steam pressure adjustment device to adjust a pressure of steam entering the cathode portion.

In one aspect of the electrolysis cell system, which is combinable with any other aspects or embodiments, the controller is configured to, when the first hydrogen concentration sensor data indicates that the hydrogen concentration in the cathode exhaust stream has decreased below a predetermined threshold, control at least one of (a) the steam pressure adjustment device to increase the pressure of steam entering the cathode portion or (b) the air pressure adjustment device to decrease the pressure of air entering the anode portion.

In one aspect, which is combinable with any other aspects or embodiments, the electrolysis cell system further includes a second hydrogen concentration sensor configured to detect a hydrogen concentration of a cathode input stream, the cathode portion configured to receive the cathode input stream, and the controller is further configured to receive second hydrogen concentration sensor data from the second hydrogen concentration sensor, compare the first hydrogen concentration sensor data to the second hydrogen concentration sensor data, and control at least one of the air pressure adjustment device or the steam pressure adjustment device based on the comparison.

In one aspect, which is combinable with any other aspects or embodiments, the electrolysis cell system further includes a first pressure transducer configured to measure anode gas pressure in the anode portion and a second pressure transducer configured to measure cathode gas pressure in the cathode portion, wherein at least one of the air pressure adjustment device or the steam pressure adjustment device is controlled in part based on a comparison between the measured anode gas pressure and the measured cathode gas pressure.

In one aspect, which is combinable with any other aspects or embodiments, the electrolysis cell system further includes a first water concentration sensor configured to detect a water concentration of the anode exhaust stream, wherein the controller is configured to receive first water concentration sensor data from the first water concentration sensor, and based on both the first water concentration sensor data and the first hydrogen concentration sensor data, control at least one of (a) the air pressure adjustment device to adjust the pressure of air entering the anode portion or (b) the steam pressure adjustment device to adjust the pressure of steam entering the cathode.

In one aspect of the electrolysis cell system, which is combinable with any other aspects or embodiments, the controller is configured to, when the water concentration sensor data indicates that the water concentration in the anode exhaust stream has increased beyond a predetermined threshold, control at least one of (a) the air pressure adjustment device to increase the pressure of air entering the anode portion or(b) the steam pressure adjustment device to decrease the pressure of steam entering the cathode portion.

In one aspect, which is combinable with any other aspects or embodiments, the electrolysis cell system further includes a second hydrogen concentration sensor configured to detect a hydrogen concentration of a cathode input stream and a second water concentration sensor configured to detect a water concentration of an anode input stream, the cathode portion configured to receive the cathode input stream.

In one aspect of the electrolysis cell system, which is combinable with any other aspects or embodiments, the controller is further configured to receive second hydrogen concentration sensor data from the second hydrogen concentration sensor, receive second water concentration sensor data from the second water concentration sensor, perform a first comparison between the first hydrogen concentration sensor data and the second hydrogen concentration sensor data, perform a second comparison between the first water concentration sensor data and the second water concentration sensor data, and control at least one of the air pressure adjustment device or the steam pressure adjustment device based on the first comparison and the second comparison.

In one aspect of the electrolysis cell system, which is combinable with any other aspects or embodiments, the air pressure adjustment device is a back-pressure regulator configured to allow the anode exhaust stream to flow therethrough and the steam pressure adjustment device is a back-pressure regulator configured to allow the cathode exhaust stream to flow therethrough.

Another embodiment relates to an electrolysis cell system including a cathode portion configured to output a cathode exhaust stream, an anode portion configured to output an anode exhaust stream, a first water concentration sensor configured to detect a water concentration of the anode exhaust stream, and a controller. The controller is configured to receive first water concentration sensor data from the first water concentration sensor and, based on the first water concentration sensor data, control at least one of (a) an air pressure adjustment device to adjust a pressure of air entering the anode portion or (b) a steam pressure adjustment device to adjust a pressure of steam entering the cathode portion.

In one aspect of the electrolysis cell system, which is combinable with any other aspects or embodiments, the controller is configured to, when the first water concentration sensor data indicates that the water concentration of the anode exhaust stream has increased beyond a predetermined threshold, control at least one of (a) the steam pressure adjustment device to decrease the pressure of steam entering the cathode portion or (b) the air pressure adjustment device to increase the pressure of air entering the anode portion.

In one aspect, which is combinable with any other aspects or embodiments, the electrolysis cell system further includes a second water concentration sensor configured to detect a water concentration of an anode input stream, the anode portion configured to receive the anode input stream. The controller is further configured to receive second water concentration sensor data from the second water concentration sensor, compare the first water concentration sensor data to the second water concentration sensor data, and control at least one of the air pressure adjustment device or the steam pressure adjustment device based on the comparison.

In one aspect, which is combinable with any other aspects or embodiments, the electrolysis cell system further includes a first pressure transducer configured to measure a pressure of anode gas in the anode portion and a second pressure transducer configured to measure a pressure of cathode gas in the cathode portion, wherein at least one of the air pressure adjustment device or the steam pressure adjustment device are controlled in part based on the measured anode gas pressure and the measured cathode gas pressure.

In one aspect of the electrolysis cell system, which is combinable with any other aspects or embodiments, the air pressure adjustment device is a back-pressure regulator configured to allow the anode exhaust stream to flow therethrough and the steam pressure adjustment device is a back-pressure regulator configured to allow the cathode exhaust stream to flow therethrough.

Another embodiment relates to a fuel cell system including a cathode portion configured to output a cathode exhaust stream, an anode portion configured to output an anode exhaust stream, a water concentration sensor configured to detect a water concentration of the cathode exhaust stream, and a controller. The controller is configured to receive water concentration sensor data from the water concentration sensor and, based on the water concentration sensor data, control at least one of (a) an oxidant gas pressure adjustment device to adjust a pressure of oxidant gas entering the cathode portion or (b) a fuel gas pressure adjustment device to adjust a pressure of fuel gas entering the anode portion.

In one aspect of the fuel cell system, which is combinable with any other aspects or embodiments, the controller is configured to, when the water concentration sensor data indicates that the water concentration of the cathode exhaust stream has increased beyond a predetermined threshold, control at least one of (a) the oxidant gas pressure adjustment device to increase the pressure of oxidant gas entering the cathode portion or (b) the fuel gas pressure adjustment device to decrease the pressure of fuel gas entering the anode portion.

In one aspect of the fuel cell system, which is combinable with any other aspects or embodiments, the cathode portion is configured to receive a cathode input stream, and the system further includes a second water concentration sensor configured to detect a water concentration of the cathode input stream. The controller is further configured to receive second water concentration sensor data from the second water concentration sensor compare the water concentration sensor data to the second water concentration sensor data, and control at least one of the oxidant gas pressure adjustment device or the fuel gas pressure adjustment device based on the comparison.

In one aspect, which is combinable with any other aspects or embodiments, the fuel cell system further includes a first pressure transducer configured to measure anode gas pressure in the anode portion and a second pressure transducer configured to measure cathode gas pressure in the cathode portion, wherein at least one of the oxidant gas pressure adjustment device or the fuel gas pressure adjustment device is controlled in part based on the measured anode gas pressure and the measured cathode gas pressure.

In one aspect, which is combinable with any other aspects or embodiments, the fuel cell system further includes a hydrogen concentration sensor configured to detect a hydrogen concentration of the anode exhaust stream The controller is configured to receive hydrogen concentration sensor data from the hydrogen concentration sensor, and based on both the water concentration sensor data and the hydrogen concentration sensor data, control at least one of the oxidant gas pressure adjustment device to adjust one or more of the pressure of oxidant gas entering the cathode portion or the fuel gas pressure adjustment device to adjust the pressure of fuel gas entering the anode portion.

In one aspect of the fuel cell system, which is combinable with any other aspects or embodiments, the controller is configured to, when the hydrogen concentration sensor data indicates that the hydrogen concentration of the anode exhaust stream has decreased below a predetermined threshold, control at least one of (a) the oxidant gas pressure adjustment device to decrease the pressure of oxidant gas entering the cathode portion or (b) the fuel gas pressure adjustment device to increase the pressure of fuel gas entering the anode portion.

Another embodiment relates to a fuel cell system including a cathode portion configured to output a cathode exhaust stream, an anode portion configured to output an anode exhaust stream, a hydrogen concentration sensor configured to detect a hydrogen concentration of the anode exhaust stream, and a controller. The controller is configured to receive hydrogen concentration sensor data from the hydrogen concentration sensor, and, based on the hydrogen concentration sensor data, control at least one of an oxidant gas pressure adjustment device to adjust a pressure of oxidant gas entering the cathode portion or a fuel gas pressure adjustment device to adjust a pressure of fuel gas entering the anode portion.

In one aspect of the fuel cell system, which is combinable with any other aspects or embodiments, the controller is configured to, when the hydrogen concentration sensor data indicates that the hydrogen concentration of the anode exhaust stream has decreased below a predetermined threshold, control at least one of (a) the oxidant gas pressure adjustment device to decrease the pressure of oxidant gas entering the cathode portion or (b) the fuel gas pressure adjustment device to increase the pressure of fuel gas entering the anode portion.

In one aspect, which is combinable with any other aspects or embodiments, the fuel cell system further includes a second hydrogen concentration sensor configured to detect a hydrogen concentration of an anode input stream, the anode portion configured to receive the anode input stream. The controller is further configured to receive second hydrogen concentration sensor data from the second hydrogen concentration sensor, compare the hydrogen concentration sensor data to the second hydrogen concentration sensor data, and control at least one of the oxidant gas pressure adjustment device or the fuel gas pressure adjustment device based on the comparison.

In one aspect, which is combinable with any other aspects or embodiments, the fuel cell system further includes a first pressure transducer configured to measure anode gas pressure in the anode portion and a second pressure transducer configured to measure cathode gas pressure in the cathode portion, wherein the oxidant gas pressure adjustment device and/or the fuel gas pressure adjustment device are controlled in part based on the measured anode gas pressure and the measured cathode gas pressure.

It will be appreciated that these and other aspects and/or features may be used in any combination.

It will be recognized that the Figures are schematic representations for purposes of illustration. The Figures are provided for the purpose of illustrating one or more implementations with the explicit understanding that the Figures will not be used to limit the scope of the meaning of the claims.

DETAILED DESCRIPTION

In fuel cell systems, a fuel gas stream comprising hydrogen is supplied to the anode of each fuel cell, and an oxidant gas stream comprising air is supplied to the cathode of each fuel cell. If the pressure in the cathode exceeds the pressure in the anode, nitrogen and other gases in the oxidant gas stream may cross over the electrolyte into the anode by diffusing through the electrolyte, passing through small cracks that form in the electrolyte over time. Similarly, if the pressure in the anode exceeds the pressure in the cathode, hydrogen may cross over the electrolyte into the cathode. The hydrogen that crosses over may react with the oxygen in the cathode to form water (e.g., steam). Accordingly, a method of monitoring this crossover so that the input pressures of the fuel gas and oxidant gas can be adjusted and balanced is desirable.

Referring toFIG.1, a fuel cell system10according to an exemplary embodiment is shown. A fuel cell module40may include one or more fuel cells arranged in one or more fuel cell stacks. The fuel cell module40includes an anode portion42and a cathode portion44. Each fuel cell in the module40includes an electrolyte sandwiched between an anode and a cathode. The fuel cells may be, for example, solid oxide fuel cells or molten carbonate fuel cells. Fuel gas, such as hydrogen gas or hydrocarbon fuel gas, is supplied from a fuel gas supply12to the anode portion42via anode input stream32and distributed to the anodes of the fuel cells. Fuel gas back-pressure regulator22controls the pressure in the anode portion42by controlling the pressure required for fuel gas to flow therethrough. For example, the fuel gas back-pressure regulator22may include a spring that holds a valve closed, and fuel gas may only be able to pass through the valve when the pressure in the anode portion42overcomes the spring force. The pressure in the anode portion42can be increased or reduced by adjusting the spring such that more or less pressure is required to overcome the spring force. In some embodiments, other types of back-pressure regulators, flow regulators, compressors, blowers, or valve assemblies may be used to adjust the pressure in the anode portion42.

Oxidant gas is supplied from an oxidant gas supply14to the cathode portion44via cathode input stream34and distributed to the cathodes of the fuel cells. Oxidant gas back-pressure regulator24controls the pressure in the cathode portion44by controlling the pressure required for oxidant gas to flow therethrough. For example, the oxidant gas back-pressure regulator24may include a spring that holds a valve closed, and oxidant gas may only be able to pass through the valve when the pressure in the cathode portion44overcomes the spring force. The pressure in the cathode portion44can be increased or reduced by adjusting the spring such that more or less pressure is required to overcome the spring force. In some embodiments, other types of back-pressure regulators, flow regulators, compressors, blowers, or valve assemblies may be used to adjust the pressure in the anode portion42. Oxygen ions from the cathode input stream34cross over the electrolyte and bond to hydrogen ions at the anode to form water molecules. Electrons produced in the oxidation reaction travel through an external circuit to generate electricity. Water formed at the anode, as well as unreacted hydrogen, exits the anode portion42via the anode exhaust stream52. Unreacted oxidant gas exits the cathode portion44via the cathode exhaust stream54.

When the pressure of the anode portion42exceeds that of the cathode portion44, hydrogen gas molecules can pass through the electrolytes of the fuel cells from the anode to the cathode. The hydrogen molecules may react with oxygen in the cathode to form water (e.g., steam). The fuel cell system10includes a water concentration sensor64(e.g., a dew point sensor, a humidity sensor, etc.) positioned in the cathode exhaust stream54. The water concentration sensor64is configured to measure the concentration of water in the cathode exhaust stream54. The concentration of water in the cathode exhaust stream54can be used to detect changes in the amount (quantity, percentage, etc.) of the hydrogen molecules in the anode input stream32that are crossing over the electrolyte. An increase in the concentration of water detected in the cathode exhaust stream54by the water concentration sensor64indicates an increase in the number of hydrogen molecules crossing over the electrolyte, which indicates an increase in the relative pressure of the anode portion42compared to the cathode portion44. In some embodiments, the air supplied in the cathode input stream34contains little to no water. Thus, any water detected in the cathode exhaust stream54will likely be due to hydrogen crossover. In some embodiments, the cathode input stream34may comprise a certain concentration of steam. The water concentration detected by the sensor64may be compared to the concentration of steam in the cathode input stream34to determine how much of the water in the cathode exhaust stream54is due to hydrogen crossover. The concentration of steam in the cathode input stream34may be measured, for example, by an additional water concentration sensor65.

When the pressure of the cathode portion44exceeds that of the anode portion42, oxidant gas molecules can pass through the electrolytes of the fuel cells from the cathode to the anode. The oxidant gas molecules exiting the anode portion42via the anode exhaust stream52dilute the steam and unreacted hydrogen in the anode exhaust stream52. The fuel cell system10includes a hydrogen concentration sensor62positioned in the anode exhaust stream52. The hydrogen concentration sensor62is configured to measure the concentration of hydrogen in the anode exhaust stream52. The concentration of hydrogen in the anode exhaust stream52can be used to detect changes in the amount (quantity, percentage, etc.) of oxidant molecules in the cathode input stream34that are crossing over the electrolyte to the anode portion42. A decrease in the concentration of hydrogen detected in the anode exhaust stream52by the hydrogen concentration sensor62indicates an increase in the number of oxidant molecules crossing over the electrolyte, which indicates an increase in the relative pressure of the cathode portion44compared to the anode portion42. When the anode input stream32comprises fuel gas other than pure hydrogen, for example, a mixture of hydrogen and methane, or when there are minor impurities in the hydrogen stream, hydrogen concentration sensor data may be compared to the concentration of hydrogen in the anode input stream32. The concentration of hydrogen in the anode input stream32may be measured, for example, by an additional hydrogen concentration sensor63. In some embodiments, the amount of oxidant crossover can be determined by condensing and removing water formed in the fuel cell reactions from the anode exhaust stream52before measuring the hydrogen concentration using the hydrogen concentration sensor62. The volumetric flow rate and hydrogen concentration in the anode input stream32can then be compared to the volumetric flow rate and hydrogen concentration of the dried anode exhaust gas, and the amount of oxidant that crossed over to the anode and further diluted the hydrogen can thereby be determined.

The hydrogen concentration sensor62and the water concentration sensor64are communicatively coupled to a controller70. The controller70is configured to receive hydrogen concentration sensor data from the hydrogen concentration sensor62and water concentration sensor data from the water concentration sensor64. The controller70is configured to determine, based at least in part on the hydrogen concentration sensor data and/or the water concentration sensor data, the differential pressure in the fuel cell module40. In some embodiments, the system10may include only the hydrogen concentration sensor62without the water concentration sensor64. In other embodiments, the system10may include only the water concentration sensor64without the hydrogen concentration sensor62. In still other embodiments, the system10may include both the water concentration sensor64and the hydrogen concentration sensor62. The fuel cell system10may also include pressure transducers72configured to respectively measure the pressure of oxidant entering the cathode portion44from the oxidant gas supply14and the pressure of fuel entering the anode portion42from the fuel supply10, thus indirectly measuring the pressures in the cathode portion44and the anode portion42. In some embodiments, the pressure transducers72may be directly coupled to the fuel cell module40and may directly measure the pressure in the cathode portion44and the anode portion42. The controller70may use pressure measurements from the pressure transducers72along with the hydrogen concentration data and/or water concentration data to determine the differential pressure in fuel cell module40. For example, the pressure measurements from the pressure transducers72may be used to establish a baseline differential pressure between the anode portion42and the cathode portion44. Because the pressures of the gases entering the anode portion42and cathode portion44may differ from the pressures of the gases inside the anode portion42and cathode portion44, the measurements from the pressure transducers72may not provide the most accurate pressure information to minimize crossover. The hydrogen concentration data and/or water concentration data may be used to adjust and improve the calculation of differential pressure.

In a system that includes only a hydrogen concentration sensor62and does not include a water concentration sensor64, the controller70is configured to determine changes in the differential pressure between the anode portion42and the cathode portion44using the hydrogen concentration sensor data. For example, if the hydrogen concentration sensor data indicates a decrease in the hydrogen concentration in the anode exhaust stream52, the controller70may determine that the pressure in the cathode portion44has increased relative to the pressure in the anode portion42. As discussed above, this may indicate that oxidant gas from the cathode input stream34is crossing over the electrolytes in the fuel cells to the anodes and diluting the unreacted hydrogen in the anode exhaust stream52. If the hydrogen concentration sensor data indicates an increase in the hydrogen concentration in the anode exhaust stream52, the controller70may determine that the pressure in the cathode portion44has decreased relative to the pressure in the anode portion42. This may indicate that less oxidant gas or no oxidant gas is crossing over the electrolytes of the fuel cells to the anode portion42. It may also indicate that hydrogen is crossing over the electrolyte to the cathode portion44.

In a system that includes only a water concentration sensor64and does not include a hydrogen concentration sensor62, the controller70is configured to determine the differential pressure between the anode portion42and the cathode portion44using the water concentration sensor data. For example, if the water concentration sensor data indicates an increase in the concentration of water in the cathode exhaust stream54, the controller70may determine that the pressure in the anode portion42has increased relative to the pressure in the cathode portion44. As discussed above, this may indicate that more hydrogen from the anode input stream32is crossing over the electrolytes in the fuel cells to the cathodes and bonding with oxygen from the cathode input stream34to form water. If the water concentration sensor data indicates a decrease in the concentration of water in the cathode exhaust stream54, the controller70may determine that the pressure in the anode portion42has decreased relative to the pressure in the cathode portion44. This may indicate that less hydrogen or no hydrogen is crossing over the electrolytes of the fuel cells to the cathode portion44. It may also indicate that oxidant gas is crossing over the electrolyte to the anode portion42.

In systems that include both a water concentration sensor64and a hydrogen concentration sensor62, the controller70is configured to determine the differential pressure between the anode portion42and the cathode portion44using both the hydrogen concentration sensor data and the water concentration sensor data. For example, if the water concentration sensor data indicates an increase in the concentration of water in the cathode exhaust stream54and the hydrogen concentration sensor data indicates an increase in the concentration of hydrogen in the anode exhaust stream52, the controller70may determine that the pressure in the anode portion42has increased relative to the pressure in the cathode portion44. If the water concentration sensor data indicates a decrease in the concentration of water in the cathode exhaust stream54and the hydrogen concentration sensor data indicates a decrease in the concentration of hydrogen in the anode exhaust stream52, the controller70may determine that the pressure in the anode portion42has decreased relative to the pressure in the cathode portion44.

When the controller70determines that the differential pressure between the anode portion42and the cathode portion44exceeds a predetermined value, the controller70is configured to adjust the pressure of fuel gas in the anode input stream32and/or the pressure of the oxidant gas in the cathode input stream34from the oxidant gas supply14. The controller70is configured to send signals instructing the gas back-pressure regulators22,24to adjust the respective pressures of the fuel gas in the anode input stream32and/or the oxidant gas in the cathode input stream34by, for example, increasing or decreasing the spring force sealing the respective valve. For example, if the controller70determines that the pressure in the anode portion42is too low relative to the pressure in the cathode portion44, the controller70may instruct the fuel gas back-pressure regulator22to increase the spring force sealing the valve to increase the fuel gas pressure in the anode portion42. Additionally or alternatively, the controller70may instruct the oxidant gas back-pressure regulator24to decrease the spring force sealing the valve to decrease the pressure of oxidant gas in the cathode portion44. If the controller70determines that the pressure in the anode portion42is too high relative to the pressure in the cathode portion44, the controller70may instruct the fuel gas back-pressure regulator22to decrease the spring force sealing the valve to decrease the fuel gas pressure in the anode portion42. Additionally or alternatively, the controller70may instruct the oxidant gas back-pressure regulator24to increase the spring force sealing the valve to increase the pressure of oxidant gas in the cathode portion44. Advantageously, the fuel cell system10allows continuous monitoring of hydrogen concentration in the anode exhaust stream52and water in the cathode exhaust stream54, as well as real-time back-pressure regulator22,24adjustments to balance pressure and minimize crossover. This can increase fuel gas utilization and minimize stresses in the fuel cells.

It should be understood that some amount of crossover is possible even when the pressures of the anode portion42and the cathode portion44are balanced, and that the methods described herein may be used to minimize crossover without eliminating crossover. In some embodiments, some pressure differential between the anode portion42and the cathode portion44may be desirable. In these embodiments, the water concentration data and hydrogen concentration data may be used by the controller70to achieve the desired differential pressure.

Referring toFIG.2, a process90(e.g., a method) for controlling the pressures of reactant gases in a fuel cell system (e.g., fuel cell system10) to achieve a desired pressure balance is shown. The process90may be performed, for example, by controller70in the fuel cell system10. The process90begins at operation91with the receipt of hydrogen concentration data. The hydrogen concentration data includes the hydrogen concentration of the anode exhaust stream52of the fuel cell system10, measured by the hydrogen concentration sensor62. At operation92, water concentration data is received. The water concentration data includes the water concentration of the cathode exhaust stream54, measured by the water concentration sensor64. At operation93, changes in the differential pressure between the anode portion42and the cathode portion44are determined based on the hydrogen concentration data and the water concentration data. For example, as described above, a decrease in the hydrogen concentration of the anode exhaust stream52may indicate that the pressure in the cathode portion44has increased relative to the pressure in the anode portion42. An increase in the water concentration of the cathode exhaust stream54may indicate that the pressure in the anode portion42has increased relative to the pressure in the cathode portion44. Additional data may be used to determine changes in the differential pressure in addition to the hydrogen concentration data and the water concentration data. For example, direct pressure readings from pressure transducers72and gas concentration data from other sensors may be used to measure changes in the differential pressure.

Pressure transducers, however, may not provide a complete picture of the differential pressure in the fuel cell system10or the electrolysis cell system110(described below). As the chemical reactions occur in the fuel cells, ions are transported across the electrolytes and form gas molecules at the opposite electrode. Thus, the gas pressures in the anode portion42and the cathode portion44are often different proximate the gas inlets than proximate the outlets. There may be a point in the gas flow path, between the inlet and the outlet, at which crossover may be minimized by minimizing the differential pressure. However, the pressure transducers may be positioned outside the fuel cells themselves and not positioned precisely at that point. The pressure transducers may thus provide a baseline differential pressure, and fine pressure adjustments can be made based on the monitored crossover. For example, if the pressure transducers indicate that the pressure in the anode portion42is roughly equal to the pressure in the cathode portion44, but the sensor data indicates that crossover from the anode portion42to the cathode portion44is still occurring, this may indicate that the pressure transducers are not positioned at the precise point at which crossover is minimized by minimizing the differential pressure.

The changes in differential pressure determined at operation93may be used to adjust the pressure of fuel gas and oxidant gas in the fuel cells. For example, it may be desired that the pressure in the anode portion42is equal to the pressure in the cathode portion44. A baseline hydrogen concentration in the anode exhaust stream52and a baseline water concentration in the cathode exhaust stream54that correspond to equal pressure in the anode portion42and the cathode portion44may be determined. The water concentration data may be compared to the desired or baseline water concentration, and the hydrogen concentration data may be compared to the desired or baseline hydrogen concentration in order to determine how to adjust the pressures of fuel gas and oxidant gas. At operation94, the pressure of fuel gas in the anode portion42is adjusted, and at operation95, the pressure of oxidant gas in the cathode portion44is adjusted. For example, if it is determined at operation93that the hydrogen concentration in the anode exhaust stream52has decreased or is lower than a desired or baseline hydrogen concentration, which may indicate that the pressure in the anode portion42is too low relative to the pressure in the cathode portion44, the fuel gas pressure may be increased and/or the oxidant gas pressure may be decreased until the desired or baseline concentrations are achieved. As discussed above, the pressures may be adjusted by controlling the valves of the back-pressure regulators22,24. If it is determined at operation93that the water concentration in the cathode exhaust stream54has increased or is higher than a desired or baseline concentration, which may indicate that the pressure in the anode portion42is too high relative to the pressure in the cathode portion44, the fuel gas pressure may be decreased and/or the oxidant gas pressure may be increased until the desired or baseline concentrations are achieved. The desired or baseline concentrations of water and hydrogen may each be a range of concentrations with a predetermined upper threshold concentration and a predetermined lower threshold concentration. The gas pressures can be adjusted when one or both of the hydrogen concentration or water concentration exceeds the predetermined upper threshold or falls below the predetermined lower threshold.

Referring now toFIG.3, an electrolysis cell system110is shown in accordance with an exemplary embodiment. The electrolysis cell system110includes an electrolysis cell module140. The electrolysis cell module140may be the fuel cell module40of fuel cell system10run in electrolysis mode. The anode of each fuel cell acts as a cathode in electrolysis mode, while the cathode of each fuel cell acts as an anode. The electrolysis cell module140may be described as having one or more stacks of electrolysis cells or one or more stacks of fuel cells operated in electrolysis mode. In electrolysis mode, steam is provided via the steam supply112and the steam flow controller122to the cathode portion142via the cathode input stream132. An electrical current is applied to the cells in the module140, which electrolyzes the water molecules. The electrical current causes oxygen ions from the steam to cross the electrolytes from the cathodes to the anodes and exit the anodes as oxygen gas, while hydrogen in the steam does not cross the electrolyte and instead exits the cathodes as hydrogen gas. Air from an air supply114is provided to the anode portion144of the electrolysis cell via the air flow controller124and the anode input stream134to dilute the oxygen gas in the anode exhaust stream154and to balance the pressure in the electrolysis cell module140.

When the pressure of the anode portion144increases relative to the pressure in the cathode portion142, the amount of nitrogen gas and other gases in the air crossing over the electrolytes increases, diluting the hydrogen in the cathode exhaust stream152. When the pressure of the cathode portion142increases relative to the pressure in the anode portion144, water molecules may cross over the electrolytes of the cells from the cathodes to the anodes. The hydrogen concentration sensor62is configured to measure the hydrogen concentration of the cathode exhaust stream152and the water concentration sensor64is configured to detect the concentration of water in the anode exhaust stream154. Thus, the pressures of steam and air input into the electrolysis cell module140can be controlled similarly to the pressures of fuel gas and oxidant gas in the fuel cell module40. The hydrogen concentration sensor62and the water concentration sensor64each send data to the controller170. The controller170determines, based on the received data, changes in differential pressure between the cathode portion142and anode portion144and instructs the flow controllers122,124to adjust the input pressures from the steam supply112and/or the air supply114. The electrolysis cell system110may also include pressure transducers72respectively configured to measure the pressure of the steam entering the cathode portion142and the pressure of air entering the anode portion144. In some embodiments, the electrolysis system may include an additional hydrogen concentration sensor63configured to measure the hydrogen concentration in the cathode input stream132and/or an additional water concentration sensor65configured to measure the water concentration in the anode input stream134. The measurements can be compared to the measurements from the hydrogen concentration sensor62and the water concentration sensor64to determine how much crossover is occurring. As discussed above with respect to the fuel cell system10, measurements from the sensors62,64may provide a more accurate measurement of differential pressure than the pressure transducers72alone.

When the hydrogen concentration sensor62detects a decrease in the concentration of hydrogen in the cathode exhaust stream152, indicating an increase in pressure of the anode portion144relative to the cathode portion142, the controller170may instruct the steam flow controller122to increase the flow of steam from the steam supply112to the cathode input stream132and/or may instruct the air flow controller124to decrease the flow of air from the air supply114to the anode input stream134. When the water concentration sensor64detects an increase in the concentration of water in the anode exhaust stream154, indicating an increase in the pressure of the cathode portion142relative to the anode portion144, the controller170may instruct the steam flow controller122to decrease the flow of steam from the steam supply112to the cathode input stream132and/or may instruct the air flow controller124to increase the flow of air from the air supply114to the anode input stream134. Like in the fuel cell system10described above, the electrolysis cell system110may include one or both of the hydrogen concentration sensor62or the water concentration sensor64, and the controller170may receive and use data from one or both of the sensors62,64. The electrolysis cell system110allows continuous monitoring of the hydrogen concentration in the cathode exhaust stream152and the water concentration in the anode exhaust stream154and real-time reactant flow adjustments to balance pressure and minimize crossover. This can increase hydrogen production and purity and can minimize stresses in the electrolysis cells.

Referring toFIG.4, a process190(e.g., a method) for controlling the pressures of reactant gases in an electrolysis cell system (e.g., electrolysis cell system110) to achieve a desired pressure balance is shown. The process190may be performed, for example, by controller170in the electrolysis cell system110. The process190begins at operation191with the receipt of hydrogen concentration data. The hydrogen concentration data includes the hydrogen concentration of the cathode exhaust stream152of the electrolysis cell system110, measured by the hydrogen concentration sensor62. At operation192, water concentration data is received. The water concentration data includes the water concentration of the anode exhaust stream154, measured by the water concentration sensor64. At operation193, changes in differential pressure between the cathode portion142and the anode portion144are determined based on the hydrogen concentration data and the water concentration data. For example, as described above, a decrease in the hydrogen concentration of the cathode exhaust stream152may indicate that the anode portion144has increased relative to the pressure in the cathode portion142. An increase in the water concentration of the anode exhaust stream154may indicate that the pressure in the cathode portion142has increased relative to the pressure in the anode portion144. Additional data may be used to determine changes in the differential pressure in addition to the hydrogen concentration data and the water concentration data. For example, direct pressure readings from pressure transducers and gas concentration data from other sensors may be used to determine changes in the differential pressure.

The changes in differential pressure determined at operation193may be used to adjust the pressures of steam and air to the electrolysis cells. For example, it may be desired that the pressure in the anode portion144is equal to the pressure in the cathode portion142. A baseline hydrogen concentration in the cathode exhaust stream152and a baseline water concentration in the anode exhaust stream154that correspond to equal pressure in the cathode portion142and the anode portion144may be determined. The water concentration data may be compared to the desired or baseline water concentration, and the hydrogen concentration data may be compared to the desired or baseline hydrogen concentration in order to determine how to adjust the pressures of steam and air. At operation194, the air pressure in the anode portion144is adjusted, and at operation195, the steam pressure in the cathode portion142is adjusted. For example, if it is determined at operation193that the water concentration in the anode exhaust stream154has decreased or is lower than a desired or baseline water concentration, which may indicate that the pressure in the anode portion144is too low relative to the pressure in the cathode portion142, the air pressure may be increased and/or the steam pressure may be decreased until the desired or baseline concentrations are achieved. If it is determined at operation193that the hydrogen concentration in the cathode exhaust stream152has decreased or is lower than a desired or baseline concentration, which may indicate that the pressure in the anode portion144is too high relative to the pressure in the cathode portion142, the air pressure may be decreased and/or the steam pressure may be increased until the desired differential pressure is achieved. The desired or baseline concentrations of water and hydrogen may each be a range of concentrations with a predetermined upper threshold concentration and a predetermined lower threshold concentration. The gas pressures can be adjusted when one or both of the hydrogen concentration or water concentration exceeds the predetermined upper threshold or falls below the predetermined lower threshold.

Configuration of Exemplary Embodiments

Although the figures and description may illustrate a specific order of method steps, the order of such steps may differ from what is depicted and described, unless specified differently above. In some embodiments, methods may include additional steps or may omit recited steps. Also, two or more steps may be performed concurrently or with partial concurrence, unless specified differently above.