Patent ID: 12191542

DETAILED DESCRIPTION

Both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the features, as claimed. As used herein, the terms “comprises,” “comprising,” “has,” “having,” “includes,” “including,” or other variations thereof, are intended to cover a non-exclusive inclusion such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements, but may include other elements not expressly listed or inherent to such a process, method, article, or apparatus. In this disclosure, unless stated otherwise, relative terms, such as, for example, “about,” “substantially,” and “approximately” are used to indicate a possible variation of ±10% in the stated value.

FIG.1illustrates a system100for removing water from a PEMFC stack102including a plurality of PEMFCs104,104b,104c. The PEMFcs104band104cmay be substantially similar to the PEMFC104and details and description in reference to the PEMFC104herein may be applicable to the PEMFCs104b,104c, etc. The system100may further include a controller101configured to regulate an electrical power output from the PEMFC stack102as will be described in greater detail herein. The controller101may be configured to control an electrical distribution system122, an air management system126including a turbocompressor128, a coolant system144, and a dehumidifier134. The controller101and the various systems it is configured to control are explained in greater detail herein.

Each of the PEMFCs in the stack102receive hydrogen at their anode105from a hydrogen supply106that is fluidly coupled to an intake manifold108. The intake manifold108may be fluidly coupled to a recirculation line110which may include a recirculation pump112, a pressure regulator114, and a shutoff116. The recirculation line110may include a moisture separator118. The PEMFC stack102may further include an exhaust manifold120for removing water or other liquid from the cathodes107of the plurality of PEMFCs104. The exhaust manifold120may fluidly couple to the recirculation line110and to an output of the hydrogen supply106.

The PEMFCs104may be electrically coupled to an electrical distribution system122. The electrical distribution system122may be used to power, for example, one or more internal and external loads121associated with an earth moving machine (not depicted), another piece of heavy equipment, or other device configured to utilize electrical power. The electrical distribution system122may include, for example, a boost converter124for boosting a DC voltage, a DC power distribution123, and a battery127(e.g., a lithium iron phosphate (LFP) battery or other type of battery). The controller101may be configured to send and/or receive an electrical signal from the boost converter124or other component of the electrical distribution system122to regulate the electrical output of the PEMFC stack102. For example, the controller101may receive a stack voltage using a voltage detector125from the electrical distribution system122.

Additionally, the system100may include the air management system126for managing air flow through one or more of the intake manifold108and the exhaust manifold120. The air management system126may include the turbocompressor128. The turbocompressor128may be a motor-driven compressor/expander that pressurizes the PEMFC stack102with air (e.g., contamination free air) or other fluid and recovers energy from the high-pressure exhaust in the exhaust manifold120. The turbocompressor128may include, for example, a compressor129, a turbine131(which may be a variable nozzle turbine), and motor magnet rotor incorporated onto a common shaft, but other arrangements are possible. The turbocompressor128may receive air or other fluid from a fluid supply (not depicted) through a filter130and may compress the air or other fluid and deliver it to the stack102. The filter130may counteract cell voltage degradation and possible damage to the MEA by reducing air feed impurities.

The compressor129may be configured to provide a flow of oxygen to the stack102at the cathode catalyst reaction sites where the electrochemical reduction reaction may occur such that hydrogen protons and electrons combine with oxygen molecules to form water. As it is the hydrogen ions that provide the electrical current necessary to power the system100, the oxygen requirements (and thus compressor loads) may be dependent on the system electrical demands. The compressor129may generally be a parasitic load on the system100but may increase efficiency at high loading so as to justify its inclusion in the system100. The turbine131may use expansion to recover energy from the exhaust gases as explained in greater detail herein. The fluid in the exhaust manifold120may be used to expand through the turbine131and the resulting mechanical energy may be used to increase the overall efficiency of the system100.

The air management system126may further include an air conditioner132, a dehumidifier134, an isolation valve136, and a water separator138. In some embodiments, an exhaust temperature140, exhaust pressure143, and a relative humidity145of the cathode exhaust may be measured at an exhaust line142from the exhaust manifold120to the turbine of the turbocompressor128. One or more of the sensed exhaust temperature140, the sensed exhaust pressure143, and the sensed relative humidity145may serve as an input to the controller101to affect the power output of the stack102as described in greater detail herein.

The dehumidifier134may be fluidly coupled to the compressor129and the turbine131of the turbocompressor128. The turbine131may receive an input from the exhaust line142through the dehumidifier134such that the humidifier removes moisture from the exhaust fluid before entering the turbine131for expansion. The compressor129may send compressed fluid through the dehumidifier134to the intake manifold108to control the flow and humidity of compressed fluid to the PEMFC stack102. In some embodiments, the controller101may be configured to activate the humidifier134based on the relative humidity of the exhaust fluid in the exhaust manifold120as described in greater detail herein. The water separator138may be used to separate a water-fluid mixture (e.g., a water-oil mixture) into multiple component fluids.

Additionally, the system100may include a coolant system144for providing a flow of coolant to the stack102. The coolant system144may include a coolant supply149and a coolant return147. The coolant supply149may be configured to provide a flow of coolant to the intake of the PEMFCs104. The coolant return147may be configured to receive heated coolant from the PEMFCs104at the exhaust manifold120. In some embodiments, the individual PEMFCs104within the stack102may include cooling channels within one or more of their component parts. For example, the PEMFCs104may include coolant channels integrated into their bipolar plates (not shown). The coolant may be, for example, a liquid coolant, such as refrigerant, water, a water-glycol mixture, or another liquid coolant. In some embodiments, the coolant system may include a deionizer (not shown). The coolant system144may include one or more pumps for increasing the pressure in a coolant supply of the coolant system144.

The relative humidity145may be measured using any device capable of measuring relative humidity such as, for example, a sling psychrometer, a capacitive hygrometer, a resistive hygrometer, a thermal hygrometer, a gravimetric hygrometer, an optical hygrometer, or other device capable of measuring a humidity. The relative humidity145may be measured using one or more sensors at one or more locations. For example, the relative humidity may be measured at an inlet or outlet of the exhaust manifold120, at the outlets of the channels in the individual PEMFCs104, at the exhaust line142from the exhaust manifold120to the turbine131, or at another location. The relative humidity145may serve as an input to the controller101as described in greater detail herein.

The exhaust pressure143at the cathode exhaust may be measured using one or more of a pressure transducers, pressure transmitters, pressure senders, pressure indicators, piezometers, and manometers to generate exhaust pressure system data as described herein. The exhaust pressure143may serve as an input for, among other things, the controller101to determine whether to take one or more actions based on the relative humidity at the cathode exhaust as described in greater detail herein.

The exhaust temperature140may be measured using one or more temperature detectors, such as, for example, one or more thermocouples, liquid expansion thermometers, resistance temperature detectors, pyrometers, Langmuir probes, infrared sensors, and other devices for measuring temperature to generate exhaust temperature system data as described herein. The exhaust temperature140may serve as an input for, among other things, the controller101to determine whether to take one or more actions based on the relative humidity at the cathode exhaust as described in greater detail herein. In some embodiments, the plurality of PEMFCs102may be configured such that a temperature profile is substantially uniform across the plurality of PEMFCs. That is, the PEMFC stack102may be configured such that an individual cell temperature of each of the cells is substantially equivalent to the other cells.

Referring now toFIG.2, the controller101may receive multiple inputs201and send various outputs202and may include a memory203. The controller101may comprise a data processor, a microcontroller, a microprocessor, a digital signal processor, a logic circuit, a programmable logic array, or one or more other devices for controlling the system100in response to one or more of the inputs201. Controller101may embody a single microprocessor or multiple microprocessors that may include one or more features (e.g., hardware and/or software) for automatically reducing a relative humidity in a PEMFC stack exhaust by controlling one or more associated systems. For example, the controller101may include a memory, a secondary storage device, and a processor, such as a central processing unit or any other means for accomplishing a task consistent with the present disclosure. The memory or secondary storage device associated with controller101may store data and/or software routines that may assist the controller101in performing its functions, such as the functions of the exemplary control process300described inFIG.3. Further, the memory or secondary storage device associated with the controller101may also store data received from various inputs associated with the system100. Numerous commercially available microprocessors can be configured to perform the functions of the controller101. It should be appreciated that controller101could readily embody a general machine controller capable of controlling numerous other machine functions. Alternatively, a special-purpose machine controller could be provided. Further, the controller101, or portions thereof, may be located remote from the system100. Various other known circuits may be associated with the controller101, including signal-conditioning circuitry, communication circuitry, hydraulic or other actuation circuitry, and other appropriate circuitry.

The memory203may store software-based components to perform various processes and techniques described herein of the controller101. The memory203may store one or more machine readable and executable software instructions, software code, or executable computer programs, which may be executed by a processor of the controller101. The software instructions may be further embodied in one or more routines, subroutines, or modules and may utilize various auxiliary libraries and input/output functions to communicate with other equipment, modules, or aspects of the system100. In some embodiments, the memory203may include exhaust system temperature data, exhaust pressure system data, exhaust relative humidity system data, or voltage system data which may be used to enact one or more of the steps of the control process300described herein or another control process.

The inputs201to the controller101may include, among other things, exhaust temperature system data205, exhaust pressure system data207, relative humidity system data209, and voltage system data211. The system data may be measured or sensed at various components in the system100. For example, the exhaust temperature system data205may come from a temperature of the cathode exhaust as measured at the exhaust temperature140. The exhaust pressure system data207may be measured as exhaust pressure143, and the relative humidity system data209may be measured as cathode relative exhaust humidity145. The voltage system data211may be based on, for example, a signal from the voltage detector125. Each of the inputs201may serve to help regulate the relative humidity at the cathode exhaust by generating the controller output signals as described in greater detail herein. The outputs202from the controller101may include a power control signal206, a turbine signal208, a coolant flow control signal210, and a humidity control signal212. The power control signal206, turbine signal208, coolant flow control signal210, and humidity control signal212may be generated in a power module214, an air flow module216, a coolant flow module218, and a humidity control module220, respectively. Additionally, the controller101may include a flooding probability module222for calculating a probability of flooding at the cathode105of the PEMFC stack102as described in greater detail herein.

The power control signal206may control one or more components within the electrical distribution system122. For example, the power control signal206may be configured to change one or more settings within the boost converter124to reduce the voltage applied from the PEMFC stack102. The turbine signal208may be configured to control air flow to the intake manifold108by controlling operation of the turbocompressor128. The coolant flow control signal210may be configured to control a speed, pressure, and/or volumetric or mass flow rate of coolant in the coolant supply system122for example, by increasing the speed of the pumps at the coolant supply. The humidity control signal212may be configured to control the operation of the humidifier134in order to control a humidity at the exhaust manifold120, thus controlling a relative humidity at the cathode exhaust and decreasing the power reduction of the stack102due to cathode flooding.

INDUSTRIAL APPLICABILITY

The disclosed aspects of the system100of the present disclosure may be used to control the relative humidity at the exhaust manifold120or the cathode of the PEMFC stack102. Controlling the relative humidity may be beneficial to operation of the system because, as described herein, the capacity for electrical power output of the PEMFC stack102may decrease with increasing current density based on flooding at the cathode(s) of the PEMFCs104.

Referring toFIG.3, an exemplary control process300for controlling the relative humidity at the cathode of the PEMFC stack102ofFIG.1is shown. The exemplary control process300could be implemented using, for example, a controller such as the controller101ofFIGS.1and2receiving the inputs201and generating the outputs202shown inFIG.2.

At step302, the system100may be started. The system100may be a PEMFC stack that is used to power a mobile machine or other heavy equipment (e.g., an earth moving machine, etc.) The mobile machine may be manually operated or have varying levels of autonomy and the mobile machine may be started manually or automatically. Once the mobile machine is started, the system100will begin to supply hydrogen to the anode105of the PEMFC stack102and oxygen (e.g., in air) to the cathode107.

At step304, the load on the system100may be increased. For example, a demand on the system100may be increased by increasing the speed of the mobile machine or, for example, increasing the amount of substance moved with the mobile machine (e.g., excavating more earth) or taking some other action to increase the load of the mobile machine or system100. As the load increases the amount of water generated at the cathode increases for reasons explained herein.

At step306, the controller may calculate a probability of flooding (FP). The flooding probability may be based on the inputs to the controller101. Specifically, the flooding probability may be based on the exhaust temperature system data205, the exhaust pressure system data207, the exhaust relative humidity system data209, and the voltage system data211. The flooding probability may be calculated in the flooding probability module222. To calculate the probability of flooding, the controller101may determine the water saturation within the cathode exhaust based on one or more of the temperature at the cathode exhaust and the pressure at the cathode exhaust. Additionally, the controller101may determine the water saturation directly by measuring the relative humidity at the cathode exhaust. The water saturation may correspond to the extent of flooding. In general, as relative humidity at the cathode approaches 100% (i.e., saturation conditions), decreases in temperature and pressure at the cathode may cause the water vapor at the cathode to condense, flooding the cathode. Accordingly, the controller may take one or more actions to increase the temperature and/or pressure at the cathode105in response to a relative humidity above 90% to prevent cathode flooding.

As discussed otherwise herein, flooding in a PEMFC may occur at high current densities when the generation rate of by-product water exceeds the removal rate of residual water from the cell. Flooding can be detected using one or more of the systems described herein (e.g., directly sensing the humidity and other aspects of the air at the cathode exhaust) or by monitoring electrical characteristics of the membrane (e.g., ohmic resistance).FIG.4shows a chart400including an actual voltage402and a reference voltage404. The actual voltage402and reference voltage are plotted on a chart showing cell potential (V) for a given PEMFC v. current density (A/cm2). A sudden drop in the actual voltage402of the cell may be a sign of flooding in PEMFC. Blockage by residual water of the access of reactant gases to the catalyst sites means the electrochemical reaction of the cell will stop. A sharp voltage decline (e.g., large delta between actual voltage402and reference voltage404) may occur at a limiting current density of the cell, this limiting current density may be referred to as a cut-off current density406. The various systems and methods for removing water from the cathode of the PEMFC discussed herein may help increase the value of the cutoff voltage.

The flooding probability calculation may be based on, for example, an input of one or more of exhaust temperature system data205, exhaust pressure system data207, relative humidity system data209, and voltage system data211.

At step308, the controller may take an action in response to the potential cathode flooding. For example, the controller101may reduce a voltage at the electrical distribution system122in order to reduce the rate of the chemical reaction within the PEMFCs104based on a high system voltage as measured with the voltage system data215. The controller101may receive a voltage as measured at an anode105of one or more of the proton exchange membrane fuel cells with the voltage detector125. The voltage may be measured at one or more of the anodes105of the various PEMFCs104in the stack102. While the particular arrangement shown inFIG.1shows the voltage being measured at the output of the stack102, embodiments are not limited to this arrangement, and system voltage could be measured at various locations within the electrical distribution system122and this voltage could be used as an input to the controller101. For example, the voltage may be measured at an output of the boost converter124or at other locations of the electrical distribution system122.

Additionally, the controller101may cause the system100to reduce a load on the PEMFC stack102based on an input of one or more of exhaust temperature system data205, exhaust pressure system data207, relative humidity system data209, and voltage system data211. The controller101may, for example, send a control signal (e.g., the power control signal206) to the DC/DC converter124to reduce an output voltage at the output of the DC/DC converter124. In other embodiments, the controller101may send a control signal to the DC power distribution123to secure power supply to one or more loads or may send a control signal to the internal and external loads121directly to secure one or more of the internal and external loads.

Additionally, the controller101may send a turbine control signal208to the turbocompressor128based on an input of one or more of exhaust temperature system data205, exhaust pressure system data207, relative humidity system data209, and voltage system data211. The turbine signal208may cause the turbocompressor128to change speeds (thus changing the speed of both the compressor129and the turbine131, which may be on a common shaft), to change a geometry of the turbine (e.g., change the nozzle throat area), and/or make one or more other changes to the operation of the turbocompressor128to increase air flow through the exhaust manifold120or the cathode exhaust of the PEMFCs104. In some embodiments, the cathode air flow control signal208may change the back pressure in the exhaust manifold120from the turbine131, thus changing fuel cell operating pressure. The compressor129may be configured to send compressed air or other gas to one or more of the intake manifold108and the exhaust manifold120of the PEMFC stack102to change the pressure within the stack102. Changing the operating pressure within the stack102may increase the saturation pressure within the cathode exhaust, reducing the probability of flooding, as described herein. Additionally, increasing the air flow may remove saturated or humid air from the stack102. With higher gas mass flow, the oxygen partial pressure may increase at the cathode107of the stack102increasing the voltage of the stack102, especially at higher power outputs. Additionally, because a significant portion of the cathode exhaust flow is water vapor, the turbine131may increase efficiency of the system through energy recovery as the turbocompressor128operates, which may partially account for the added energy consumption of operating the compressor129.

Additionally, in response to an increased load condition in which the system100calculates a flooding probability of greater than 90% based on an input of one or more of exhaust temperature system data205, exhaust pressure system data207, relative humidity system data209, and voltage system data211, the controller may generate the coolant flow control signal210. The coolant flow control signal210may travel from the controller101to one or more components of the cooling system144causing an increased mass or volumetric flow rate of coolant to the cooling channels in the PEMFCs104. The increased coolant flow may reduce cell temperatures by absorbing the latent heat of vaporization of the water in the cathode exhaust channels, condensing the water in the PEMFC cathode channels more quickly and reducing back pressure within the channel, thereby increasing the flow of protons across the MEA and increasing cell electrical power output.

In some embodiments, the system100may include the dehumidifier134and the dehumidifier may be used to control the humidity levels at the cathode exhaust120using a humidity control signal212. The humidity control signal212may be generated in the controller101and may be used to dehumidify the PEMFC cathode by removing fluid at the cathode exhaust line142. In some embodiments, the dehumidifier134may be operable to increase the humidity levels (i.e., act as a humidifier) in order to keep the fuel cell stack at the proper level of moisture in the case of overly dry fuel cells. The dehumidifier134may operate based on a signal from the controller101or other signal and may remove moisture from air at the PEMFC exhaust or add moisture to, for example, air at an exhaust of the compressor129.

It should now be understood that measuring and controlling the relative humidity at a cathode exhaust can be advantageous to proper operation of a PEMFC stack. By controlling one or more of a power output of a PEMFC stack, an airflow to the exhaust of the PEMFC stack, a coolant flow to coolant channels within the fuel cell stack, and a humidity at the exhaust of the one or more cells, a system can reduce a voltage drop that is generally otherwise seen as current densities increase throughout the stack.

It will be apparent to those skilled in the art that various modifications and variations can be made to the disclosed system without departing from the scope of the disclosure. Other embodiments of the system will be apparent to those skilled in the art from consideration of the specification and practice of the system disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope of the disclosure being indicated by the following claims and their equivalents.