US20050186458A1 - Electrolyzer cell stack system - Google Patents

Abstract

Some embodiments of the present invention provide a balance-of-plant system and apparatus suited for regulating the operation of an electrolyzer cell stack. Specifically, in some embodiments, a balance-of-plant system and apparatus is operable to regulate the respective pressures of at least two reaction products relative to one another. Various examples are provided to demonstrate how the respective pressures of two reaction products can be regulated in relation to one another in a pressure following configuration, thereby regulating the pressure differential across an electrolyte layer according to aspects of different embodiments of the invention. Some of the examples provided also include design simplifications and alternatives that may reduce production costs of electrochemical cells configured according to aspects of different embodiments of the invention.

Description

PRIORITY CLAIM
• This application claims the benefit, under 35 USC 119(e), of U.S. Provisional Application No. 60/504,227 that was filed on Sep. 22, 2003, and the entire contents of which is hereby incorporated by reference.
FIELD OF THE INVENTION
• The invention relates to electrolyzer cells and, in particular to a balance-of-plant system and apparatus suited for regulating the operation of an electrolyzer cell stack.
BACKGROUND OF THE INVENTION
• An electrolyzer cell is a type of electrochemical device that uses energy to dissociate a compound liquid into its components. For example, water can be dissociated into hydrogen and oxygen (e.g. H₂O→H₂+O₂).
• Generally, an electrolyzer includes an anode, a cathode and an electrolyte arranged between the anode and cathode. The specific arrangement of a particular electrolyzer cell is dependent upon the components, materials and technology employed. For example, a Proton Exchange Membrane (PEM) electrolyzer cell includes a thin polymer membrane arranged between an anode and a cathode.
• In practice, a number of electrolyzer cells are arranged into a stack to produce sizable amounts of one or more of the components of a compound liquid. To this end, the electrolyzer cell stack is included in a module that includes a suitable combination of supporting elements, collectively termed a balance-of-plant system, which is specifically configured to maintain operating parameters and functions for the electrolyzer cell stack. Example functions of a balance-of-plant system include the maintenance and regulation of various pressures, temperatures and flow rates.
SUMMARY OF THE INVENTION
• According to aspects of an embodiment of the invention there is provided a balance-of-plant system, suited for regulating the operation of an electrolyzer cell stack having at least one electrolyzer cell, including: a first pressure regulator for regulating a first pressure of a first reaction product; a pressure following device having: a pressure sensor for measuring the first pressure and providing a signal including information about a value of the first pressure; and, a second pressure regulator for regulating a second pressure of a second reaction product relative to the first pressure using the signal from the pressure sensor.
• In some embodiments, the first and second pressures correspond to pressures on respective anode and cathode sides of the electrolyzer cell.
• In some embodiments, the balance-of-plant system also includes: a hydrogen collection device; and, an oxygen collection device; wherein the first and second pressures correspond to pressures of hydrogen and oxygen produced by the electrolyzer cell stack.
• According to aspects of another embodiment of the invention there is provided a balance-of-plant system, suited for regulating the operation of an electrolyzer cell stack having at least one electrolyzer cell, including: a controller having a computer readable program code means for causing a first pressure of a first reaction product to be followed by a second pressure of a second reaction product, the computer readable code means including: instructions for regulating the first pressure; instructions for polling a pressure sensor operable to sense the first pressure; and, instructions for regulating the second pressure relative to the first pressure. In some embodiments the controller is comprised of at least one of a centralized control system and a distributed control system.
• In some embodiments the balance-of-plant system also includes: a first pressure regulator for regulating the first pressure; a pressure sensor for measuring the first pressure; and, a second pressure regulator for regulating the second pressure. In some embodiments, the first pressure regulator comprises a combination of valves, mechanical actuators and electronic actuators arranged to regulate the first pressure. In some embodiments, the second pressure regulator also comprises a combination of valves, mechanical actuators and electronic actuators arranged to regulate the second pressure.
• According to aspects of another embodiment of the invention there is provided an electrochemical cell stack module including: at least one electrochemical cell in which at least two pressures, of at least two respective gases, are controllable; and, a pressure following device that is operable to control one of the two pressures relative to the other. In some embodiments the pressure following device includes: a pressure sensor for measuring/sensing one of the two pressures and providing measured/sensed information; and, a pressure regulator connectable to accept measured/sensed information from the pressure sensor and to control the other of the two pressures relative to the measured/sensed information.
• According to aspects of another embodiment of the invention there is provided an electrolyzer cell module including: a controller having a computer readable program code means for causing a first pressure of a first reaction product to be regulated relative to a second pressure of a second reaction product, the computer readable code means including: instructions for regulating the second pressure; instructions for measuring/sensing the second pressure; and, instructions for regulating the first pressure relative to the second pressure.
• Other aspects and features of the present invention will become apparent, to those ordinarily skilled in the art, upon review of the following description of the specific embodiments of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
• For a better understanding of the present invention, and to show more clearly how it may be carried into effect, reference will now be made, by way of example, to the accompanying drawings that illustrate aspects of embodiments of the present invention and in which:
• FIG. 1 is a simplified schematic drawing of an electrolyzer cell;
• FIG. 2 is a simplified schematic drawing of an electrolyzer cell module according to aspects of an embodiment of the invention;
• FIG. 3 is a first detailed schematic drawing of an electrolyzer cell module according to aspects of an embodiment of the invention;
• FIG. 4 is a second detailed schematic drawing of an electrolyzer cell module according to aspects of an alternative embodiment of the invention;
• FIG. 5 is a third detailed schematic drawing of an electrolyzer cell module according to aspects of another alternative embodiment of the invention that is similar to the electrolyzer cell module illustrated inFIG. 3;
• FIG. 6 is a fourth detailed schematic drawing of an electrolyzer cell module according to aspects of another alternative embodiment of the invention that is similar to the electrolyzer cell module illustrated inFIG. 4;
• FIG. 7A is a fifth detailed schematic drawing of a portion of an electrolyzer cell module according to aspects of another alternative embodiment of the invention that is similar to the electrolyzer cell module illustrated inFIG. 4;
• FIG. 7B is a sixth detailed schematic drawing of a portion of an electrotyzer cell module according to aspects of another alternative embodiment of the invention that is similar to the electrolyzer cell module illustrated inFIG. 3; and
• FIG. 7C is a seventh detailed schematic drawing of a portion of an electrolyzer cell module according to aspects of another alternative embodiment of the invention that is similar to the electrolyzer cell module illustrated inFIG. 3.
DETAILED DESCRIPTION OF THE INVENTION
• Some embodiments of the present invention provide a balance-of-plant system and apparatus suited for regulating the operation of an electrolyzer cell stack. Specifically, in some embodiments, a balance-of-plant system and apparatus is operable to regulate the respective pressures of at least two reaction products relative to one another. Various examples are provided below to demonstrate how the respective pressures of two reaction products can be regulated in relation to one another in a pressure following configuration, thereby regulating the pressure differential across an electrolyte layer. Some of the examples provided below also include design simplifications and alternatives that may reduce production costs of electrochemical cells configured according to aspects of different embodiments of the invention.
• There are a number of different electrochemical cell technologies and, in general, this invention is expected to be applicable to all types of electrochemical cells. Very specific example embodiments of the invention have been developed for use with Proton Exchange Membrane (PEM) electrolyzer cells. Various other types of electrolyzer cells also include, without limitation, Solid Polymer Water Electrolyzers (SPWE). Similarly, various types of fuel cells include, without limitation, Alkaline Fuel Cells (AFC), Direct Methanol Fuel Cells (DMFC), Molten Carbonate Fuel Cells (MCFC), Phosphoric Acid Fuel Cells (PAFC), Solid Oxide Fuel Cells (SOFC) and Regenerative Fuel Cells (RFC).
• Referring toFIG. 1, shown is a simplified schematic diagram of a Proton Exchange Membrane (PEM) electrolyzer cell, simply referred to aselectrolyzer cell100 hereinafter, that is described herein to illustrate some general considerations relating to the operation of electrochemical cells. It is to be understood that the present invention is applicable to various configurations of electrochemical cell modules that each include one or more electrochemical cells.
• Theelectrolyzer cell100 includes ananode electrode210 and a cathode electrode410. Theanode electrode210 includes awater input port220 and a water/oxygen output port240. Similarly, the cathode electrode410 includes awater input port420 and a water/hydrogen output port440. Anelectrolyte membrane300 is arranged between theanode electrode210 and the cathode electrode410.
• Theelectrolyzer cell100 also includes afirst catalyst layer230 arranged between theanode electrode210 and theelectrolyte membrane300, and asecond catalyst layer430 arranged between the cathode electrode410 and theelectrolyte membrane300.
• In order to energize theelectrolyzer cell100, avoltage source117 is coupled between the anode andcathode electrodes210,410.
• In operation, water is introduced into theanode electrode210 via thewater input port220. The water is dissociated electrochemically according to reaction (1), given below, in the presence of theelectrolyte membrane300 and thefirst catalyst layer230.
  H₂O→2H⁺+2e⁻+1/2O₂  (1)
  The chemical products of reaction (1) are hydrogen ions (i.e. cations), electrons and oxygen. The hydrogen ions pass through theelectrolyte membrane300 to the cathode electrode410 while the electrons are drawn through thevoltage source117. Water containing dissolved oxygen molecules is drawn out through the water/oxygen output port240.
• Simultaneously, additional water is introduced into the cathode electrode410 via thewater input port420 in order to provide moisture to the cathode side of themembrane300.
• The hydrogen ions (i.e. protons) are electrochemically reduced to hydrogen molecules according to reaction (2), given below, in the presence of theelectrolyte membrane300 and thesecond catalyst layer430. That is, the electrons and the ionized hydrogen atoms, produced by reaction (1) in theanode electrode210, are electrochemically consumed in reaction (2) in the cathode electrode410.
  2H₂⁺+2e⁻→H₂  (2)
• The water containing dissolved hydrogen molecules is drawn out through the water/hydrogen output port440. The electrochemical reactions (1) and (2) are complementary to one another and show that for each oxygen molecule (O₂) that is electrochemically produced two hydrogen molecules (H₂) are electrochemically produced.
• Although only one electrolyzer cell is illustrated inFIG. 1, it is commonly understood that in practice a number of electrochemical cells, all of one type, can be arranged in stacks having common elements, such as process gas/fluid feeds, drainage, electrical connections and regulation devices. That is, an electrochemical cell module is typically made up of a number of singular electrochemical cells connected in series to form an electrochemical cell stack. The electrochemical cell module also includes a suitable combination of structural elements, mechanical systems, hardware, firmware and software that is employed to support the function and operation of the electrochemical cell stack. Such items include, without limitation, piping, sensors, regulators, current collectors, seals, insulators, actuators, switches and electromechanical controllers.
• Referring now toFIG. 2, illustrated is a simplified schematic diagram illustrating anelectrolyzer cell module10athat is configured to dissociate water (H₂O) into hydrogen (H₂) and oxygen (O₂). Those skilled in the art will appreciate that an electrolyzer cell module includes a suitable combination of supporting elements, collectively referred to as a balance-of-plant system, and shown inFIG. 2 are only those balance-of-plant elements necessary to describe aspects of this embodiment of the invention.
• Those skilled in the art will appreciate that shown inFIG. 2 are only those balance-of-plant elements necessary to describe aspects of this example embodiment of the invention. Generally, balance-of-plant elements can be roughly divided into two groups. A first group may be defined as a suitable combination of supporting apparatus and electromechanical systems that includes, without limitation, elements such as heaters, filters, pumps, humidifiers, valves and the like. A second group may be defined as a suitable combination of control and sensor systems that includes, without limitation, sensors, switches, valves, hardware, software, firmware and the like.
• In some embodiments, the control and sensor systems include a centralized control system including for example a microcontroller and/or a computer program readable code means for monitoring and regulating the operation of an electrolyzer cell module, including portions of the supporting apparatus and electromechanical systems. In alternative embodiments, distributed control systems/controllers are provided along with or in place of a centralized control system. Generally, the sensors and the switches are electronically coupled to the aforementioned centralized and/or distributed control systems, which process sensor readings and signal the switches and other electromechanical devices accordingly in order to regulate and in some cases shut down an electrolyzer cell module.
• With specific reference toFIG. 2, theelectrolyzer cell module10aincludes acontroller90 that is used to manage the operations of theelectrolyzer cell module10a.Although thecontroller90 is specifically shown to be connected to a number of elements included in theelectrolyzer cell module10aofFIG. 2, those skilled in the art will appreciate that a controller can be connected to any suitable combination of elements included in an electrolyzer cell module. Moreover, as also shown inFIG. 2, thecontroller90 includes a modifiedsafety system93 and at least oneapplication program95 used to manage the normal operations of theelectrolyzer cell module10a.Specifically, in the present embodiment of the invention thecontroller90 includes memory storing a computer program readable code means having instructions for the modifiedsafety system93 and the at least oneapplication program95.
• Theelectrolyzer cell module10ahas anelectrolyzer cell stack11 that includes one or more PEM electrolyzer cells (not shown). Each PEM electrolyzer cell includes an electrolyte membrane arranged between an anode electrode and a cathode electrode as schematically illustrated inFIG. 1. Theelectrolyzer cell stack11 has acathode inlet port204, acathode outlet port28, ananode inlet port202 and ananode outlet port27. The cathode inlet andoutlet ports204,28 are fluidly connected to each of the respective cathode electrodes included in theelectrolyzer cell stack11. Similarly, the anode inlet andoutlet ports202,27 are fluidly connected to each of the respective anode electrodes included in theelectrolyzer cell stack11. Theelectrolyzer cell stack11 also includes respectiveelectrical connections12,13 to the anode and cathode terminals of theelectrolyzer cell stack11.
• With further reference toFIG. 2, theelectrolyzer cell module10aalso includes apower supply117, awater supply tank16, ahydrogen collection device39, anoxygen collection device20 and apressure following device34.
• Thepower supply117 is coupled across theelectrical connections12,13 to energize theelectrolyzer cell stack11, as described above. In some embodiments, thepower supply117 is, without limitation, one of a voltage source and a current source.
• Theoxygen collection device20 includes anoutput port4; another output port and two input ports. In some embodiments, theoutput port4 serves as a tap for oxygen collected by theoxygen collection device20, and is also connectable to other downstream components (not shown). The other output port is coupled to provide water to theanode inlet port202, and one of the input ports is coupled to receive a combination of water and oxygen from theanode outlet port27. The other input port is coupled to receive water from thewater supply tank16. That is, according to this specific example, water is provided to theelectrolyzer cell stack11 from thewater supply tank16 via theoxygen collection device20, which also recycles water received back from theelectrolyzer cell stack11. Optionally, as is illustrated inFIG. 2, thewater supply tank16 is also coupled to thecathode inlet port204 of theelectrolyzer cell stack11 to hydrate the respective cathode sides of the membranes included in theelectrolyzer cell stack11. This optional connection is not provided in the examples described below with reference toFIGS. 3-7C.
• Thehydrogen collection device39 includes anoutput port5; another output port and an input port. In some embodiments, theoutput port5 serves as a tap for hydrogen collected by thehydrogen collection device39, and is also connectable to other downstream components (not shown). The input of thehydrogen collection device39 is coupled to thecathode outlet port28 to accept a combination of water and hydrogen from theelectrolyzer cell stack11. The other output port is coupled to thewater supply tank16 to return water separated from hydrogen during operation.
• In some embodiments, the hydrogen andoxygen collection devices39,20 each include a condenser, such as, for example, the apparatus described in the applicant's issued U.S. patent application Ser. No. 6,619,054, which is hereby incorporated by reference.
• In some embodiments, thehydrogen collection device39 has a volume that is about twice the volume of theoxygen collection device20. This difference in size accommodates the relative rates of hydrogen and oxygen evolution that will occur according to reactions (1) and (2) described above.
• With further reference toFIG. 2, thepressure following device34 is coupled between thehydrogen collection device39 and theoxygen collection device20. The pressure of the oxygen is a reasonable approximation of the pressure on the respective anode sides of the membranes included in theelectrolyzer cell stack11; and, similarly, the pressure of the hydrogen is a reasonable approximation of the pressure on the respective cathode sides of the membranes included in theelectrolyzer cell stack11. Thepressure following device34 measures/senses pressure in one and adjusts the pressure in the other relative to measured/sensed pressure, thereby regulating the pressure differential across the respective membranes within theelectrolyzer cell stack11. Moreover, although thepressure following device34 is specifically coupled between the hydrogen andoxygen collection devices39,20, in alternative arrangements thepressure following device34 can be placed between at any two points around theelectrolyzer cell stack11 that provide a reasonable measure of the internal pressures within theelectrolyzer cell stack11 and a control point for those pressures so that the pressure differential across the membranes can be regulated. Various configurations and alternative arrangements for thepressure following device34 are described in detail below with reference toFIGS. 3-7C.
• In some embodiments, the pressure following device includes, without limitation, a pressure sensor, a dome-loaded pressure valve, a negative bias regulator, a positive bias regulator and an electronically actuated pressure regulator.
• The operation of the electrolyzer cell module11 (inFIG. 2) is similar to that of the electrolyzer cell100 (inFIG. 1). To briefly reiterate, thepower supply117 supplies the requisite energy for reactions (1) and (2). Oxygen is produced in the anode electrodes according to reaction (1) and then a combination of water and oxygen flows out of theanode outlet port27 into theoxygen collection device20 where the oxygen is separated from the water. Hydrogen is produced in the cathode electrodes according to reaction (2) and then a combination of water and hydrogen flows out of thecathode outlet port28 into thehydrogen collection device39 where the hydrogen is separated from the water.
• Thepressure following device34 is operable in at least two modes of operation. In a first mode of operation, the hydrogen pressure is measured/sensed by thepressure following device34 and the oxygen pressure is regulated to a relative value of the hydrogen pressure. In a second mode of operation, the oxygen pressure is measured/sensed by thepressure following device34 and the hydrogen pressure is regulated to a relative value of the oxygen pressure.
• In either mode of operation, a pressure, hereinafter referred to as a set pressure, that is set relative to a measured/sensed pressure, can be regulated to be higher than the measured/sensed pressure, lower than the measured/sensed pressure or approximately equal to the measured/sensed pressure. In some embodiments, a set pressure is regulated to be slightly lower than a corresponding measured/sensed pressure. For reasons described in further detail below, this is preferable in situations where the measured/sensed pressure is of a reaction product that is to be generated in a relatively pure form. Those skilled in the art will also appreciate that the measured/sensed pressure is not left unregulated but is regulated independently of the set pressure. That is, respective pressures related to various reaction products are set relative to one independently regulated pressure of the system.
• For example, if theelectrolyzer cell module10ashown inFIG. 2 is operated to produce relatively pure hydrogen, then the hydrogen pressure in the cathode electrodes is regulated to be slightly greater than the oxygen pressure in the anode electrodes. This can be accomplished by at least two different methods according to aspects of various embodiments of the invention. In a first method the hydrogen pressure is regulated independently (e.g. to approximately 100 psig) and thepressure following device34 measures/senses the hydrogen pressure and regulates the oxygen pressure accordingly to a lower value (e.g. to approximately 98 psig). In a second method the oxygen pressure is regulated independently (e.g. to approximately 97 psig) and thepressure following device34 measures/senses the oxygen pressure and regulates the hydrogen pressure accordingly to a higher value (e.g. to approximately 99 psig). Both methods are examples of respective pressure following configurations according to aspects of various embodiments of the invention.
• In an alternative example, if the electrolyzer cell module shown inFIG. 2 is operated to produce relatively pure oxygen, then the hydrogen pressure in the cathode electrodes is regulated to be slightly lower than the oxygen pressure in the anode electrodes. To that end, this may be accomplished by at least two different methods according to aspects of various embodiments of the invention. In a third method, the hydrogen pressure is regulated independently and the oxygen pressure follows at a higher value via the operation of thepressure following device34. Similarly, in a fourth method, the oxygen pressure is regulated independently and the hydrogen pressure follows at a lower value via the operation of thepressure following device34. Again, both the third and fourth methods are examples of respective pressure following configurations according to aspects of various embodiments of the invention.
• In another alternative example, the hydrogen and oxygen pressures can be regulated to be approximately equal to one another as well. To that end, this may be accomplished by at least two different methods according to aspects of various embodiments of the invention. In a fifth method, the hydrogen pressure is regulated independently and the oxygen pressure follows via the operation of thepressure following device34. Similarly, in a sixth method, the oxygen pressure is regulated independently and the hydrogen pressure follows via the operation of thepressure following device34. Again, both the fifth and sixth methods are examples of respective pressure following configurations according to aspects of various embodiments of the invention.
• With respect to PEM electrolyzer cells, regardless of which pressure is higher, the relative differential pressure across a membrane is preferably regulated to be small. In theory, a high differential pressure may be useful in some instances, however, since the membrane for a PEM electrolyzer cell is very thin, the membrane is susceptible to rupturing if the differential pressure is too high. Moreover, a relatively high-pressure differential will typically have an adverse effect on the durability and lifetime of a membrane, even if it does not cause a rupture or tear.
• In some circumstances relatively pure production of gases is not absolutely required and an electrolyzer cell module can be adapted to reduce costs by replacing some elements with cheaper complementary elements.
• For example, an electrolyzer cell module can be simplified and its total cost may be reduced if one of an oxygen detector and a hydrogen detector can be left off the list of elements included in the balance-of-plant system. By employing at least one of these detectors, a balance-of-plant system can be configured to check for irregularities, such as leaks of one reactant product into a second reactant product stream. However, both types are detectors are not required in an electrolyzer cell module to accomplish this diagnostic function. If the hydrogen pressure is normally regulated to be higher than the oxygen pressure, then, even if there is an irregularity (e.g. a leak), a detectably large amount of hydrogen will leak into the oxygen stream before oxygen leaks into the hydrogen stream. Such an electrolyzer cell module may only require a hydrogen detector somewhere along the oxygen lines, as long as the hydrogen pressure is slightly higher than the oxygen pressure.
• Moreover, such an electrolyzer cell module will produce a relatively pure hydrogen stream since during normal operation oxygen will be less likely to diffuse into the hydrogen stream because the hydrogen pressure is normally higher than the oxygen pressure. By contrast, the oxygen stream will likely contain trace amounts of hydrogen during normal operation since some hydrogen will diffuse into the oxygen stream as a result of the aforementioned pressure differential. However, oxygen containing trace amounts of hydrogen is not harmful in some hydrogen fuel cells and, thus, the oxygen stream can be used for such applications without further processing. Alternatively, an electrolyzer cell module that is configured to provide relatively pure oxygen may have a preferably higher oxygen pressure than a hydrogen pressure, which would in turn reduce the need for a hydrogen detector.
• Continuing with the same example, the pressure differential can be regulated by employing a pressure following configuration according to aspects of an embodiment of the invention. In some embodiments, a positive bias pressure regulator is employed when the set pressure is higher than the measure/sensed pressure. Alternatively, in other embodiments, a negative bias pressure regulator is employed when the set pressure is lower than the measured/sensed pressure.
• Referring now toFIG. 3, illustrated is a first detailed schematic drawing of anelectrolyzer cell module10baccording to aspects of an embodiment of the invention. Theelectrolyzer cell module10b(shown inFIG. 3) is configured to dissociate water (H₂O) into hydrogen (H₂) and oxygen (O₂), and includes the same elements as the simplifiedelectrolyzer cell module10a(shown inFIG. 2). In particular, theelectrolyzer cell module10bincludes theelectrolyzer cell stack11 with the various aforementioned various inlet andoutlet ports202,27,28 and the respectiveelectrical connections12,13 to the anode and cathode terminals of theelectrolyzer cell stack11. Theelectrolyzer cell module10balso includes thepower supply117, thewater supply tank16, thehydrogen collection device39, theoxygen collection device20 and thepressure following device34. However, these elements are not directly connected to one another as described above. Instead, a number of balance-of-plant elements are connected between each of the aforementioned elements. Those skilled in the art will appreciate that theelectrolyzer cell module10balso includes a controller (not shown) similar to thecontroller90 illustrated inFIG. 2, which is connected to a suitable combination of elements; however, this controller has not been illustrated for the sake of simplicity.
• The balance-of-plant elements, introduced inFIG. 3, can be roughly divided into two groups. A first group may be defined as a suitable combination of supporting apparatus and electromechanical systems that includes, without limitation, elements such as heaters, filters, pumps, humidifiers, valves, and the like. A second group may be defined as a suitable combination of control and sensor systems that include, without limitation, sensors, switches, valves, hardware, software, firmware and the like.
• In some embodiments, the control and sensor systems include a centralized control system (not shown) including for example a microcontroller and/or a computer program readable code means for monitoring and regulating the operation of an electrolyzer cell module, including portions of the supporting apparatus and electromechanical systems. In alternative embodiments, distributed control systems/controllers are provided with or in place of a centralized control system. Generally, the sensors and the switches are electronically coupled to the aforementioned centralized and/or distributed control systems, which process sensor readings and signal the switches and other electromechanical devices accordingly in order to regulate and in some cases shut down the electrolyzer cell module.
• Again, thepower supply117 is coupled to theelectrical connections12,13 of theelectrolyzer cell stack11 to energize theelectrolyzer cell stack11. Astack disconnect device48 is also coupled between theelectrical connections12,13 of theelectrolyzer cell stack11 and thepower supply117. Additionally, a current15 and a voltage sensor14 are appropriately arranged between thestack disconnect device48 and thepower supply117 to measure the current drawn by theelectrolyzer cell stack11 and the voltage across theelectrical connections12,13.
• Thestack disconnect device48 is operable between two states. In a first state, thestack disconnect device48 electrically couples thepower supply117 is to theelectrolyzer cell stack11. In a second state, thestack disconnect device48 electrically isolates the power supply from theelectrolyzer cell stack11. In some embodiments, switching thestack disconnect device48 between the two states is, for example, controlled by a central and/or local distributed control system, which may use readings from the current andvoltage sensors15,14.
• The anode andcathode outlet ports27,28 of theelectrolyzer cell stack11 are respectively connected to the oxygen andhydrogen collection devices20,39 through respective combinations of balance-of-plant elements.
• Specifically, in this example embodiment, there is afirst pressure sensor29, atemperature sensor31 and a firsttemperature safety switch32 arranged along the fluid pathway from theanode outlet port27 to theoxygen collection device20. The firsttemperature safety switch32 is operable to send an alarm signal to a centralized and/or distributed control system if the temperature of the stream of oxygen and water exiting theanode outlet port27 reaches a predetermined high value. In some embodiments, the firsttemperature safety switch32 is configured to override and halt the operation of theelectrolyzer cell module10ain the event that the temperature is too high, which may imply that there is a severe problem with theelectrolyzer cell module10a.
• Similarly, in this very specific example embodiment, there is asecond pressure sensor30, a firstpressure safety switch33 and afirst heat exchanger38 arranged along the fluid pathway from thecathode outlet port28 to thehydrogen collection device39. The firstpressure safety switch33 is operable to send an alarm signal to a central and/or distributed control system if the pressure of the stream of hydrogen and water exiting thecathode outlet port28 reaches a predetermined high value. In some embodiments, the firstpressure safety switch33 is configured to override and halt the operation of theelectrolyzer cell module10ain the event that the pressure is too high, which may imply that there is a severe problem with theelectrolyzer cell module10a.Thefirst heat exchanger38 is used to cool the stream of hydrogen and water exiting thecathode outlet port28, thereby initiating condensation of the water to separate it from the hydrogen within thehydrogen collection device39.
• Theanode inlet port202 of theelectrolyzer cell stack11 is connected to receive water from theoxygen collection device20 through a respective combination of balance-of-plant elements as well. Specifically, acirculation pump23, asecond heat exchanger22, aresistivity meter24, aflow switch25 and preferably ade-ionizing filter26 are arranged along the fluid pathway to theanode inlet port202 from theoxygen collection device20. Thesecond heat exchanger22 is also coupled to receive a regulation signal from thefirst temperature sensor31 arranged on the fluid pathway originating from theanode outlet port27.
• Thecirculation pump23 is operable to force the flow of water into theelectrolyzer cell stack11. In some embodiments, the circulation pump is of a high-temperature/high-pressure type, and is constructed with materials such as Teflon® or Peek®. Using the regulation signal from thefirst temperature sensor31, thesecond heat exchanger22 is operable to adjust the temperature of the water stream entering theelectrolyzer cell stack11. Theresistivity meter24 is operable to measure the resistivity of the water flowing into theelectrolyzer cell stack11. Theflow switch25 is operable to send an alarm signal to a central and/or local distributed control system if the water level is too low. In some embodiments, thede-ionizing filter26 incorporates organic and particulate filtering functions.
• As a side note, in different embodiments the first andsecond heat exchangers38,22 are made up of different components. For example, in one embodiment the first andsecond heat exchangers38,22 include fans for temperature regulation by air-cooling, whereas in other embodiments the first andsecond heat exchangers38,22 include pumps and coolant fluids for temperature regulation by liquid-cooling. Those skilled in the art will generally appreciate that a heat exchanger can be embodied in a number of different forms, but in each embodiment the function of a heat exchanger is to serve as a temperature regulation means.
• There are also a number of balance-of-plant elements arranged along the fluid pathway from thewater supply tank16 to theoxygen collection device20. Specifically, thewater supply tank16 is connected to theoxygen collection device20 through afill pump17, anorganic filter18, a particulate and ade-ionizing filter19, acheck valve47 and a three-way valve21. An output of the three-way valve21 is also coupled back to thewater supply tank16. Thecheck valve47 is arranged to prevent back flow of water through thefill pump17 and filters18,19.
• A firstwater level indicator37 is coupled to theoxygen collection device20 and to thefill pump17 and the three-way valve21. The firstwater level indicator37 is operable to measure the water level in theoxygen collection device20 and provide a feedback control signal to thefill pump17 and the three-way valve21. For example, when the water level in theoxygen collection device20 is higher than a pre-set high level value, the three-way21 valve is set to re-circulate water back to thewater supply tank16; or, when the water level is lower than a pre-set low level value, thefill pump17 is signalled to increase the rate of water flow.
• Comparatively, the balance-of-plant setup between thehydrogen collection device39 and thewater supply tank16 is quite simple. A secondwater level indicator45 is coupled to thehydrogen collection device39 and apurge valve46 is connected between thehydrogen collection device39 and thewater supply tank16. Thepurge valve46 is operated by a control signal received from the secondwater level indicator45 coupled to thehydrogen collection device39. When the water level in thehydrogen collection device39 is higher than a pre-set level value, thepurge valve46 opens after receiving the control signal from the secondwater level indicator45. Once thepurge valve46 is opened, water can flow from thehydrogen collection device39 to thewater supply tank16. Alternatively, the purged water can be dumped out of the system or used for other purposes (i.e. as a coolant).
• Thehydrogen collection device39 also has asafety valve44 that automatically vents gas from thehydrogen collection device39 when the pressure inside reaches a pre-set upper threshold. Accordingly, thesafety valve44 aids in the regulation of the hydrogen pressure, which in this embodiment, is followed by the oxygen pressure via the operation of thepressure following device34.
• In this particular embodiment, theoutput port5 of thehydrogen collection device39 is coupled to a combination of valves. Specifically, theoutput port5 is coupled to abackpressure valve40 that is in parallel with a normally open ventingvalve41 that is arranged in series with a needle/orifice valve42. The outputs of thebackpressure valve40 and the needle/orifice valve42 are coupled in parallel into acheck valve43.
• Thebackpressure valve40 is arranged to regulate the hydrogen pressure within thehydrogen collection device39 during the operation of theelectrolyzer cell module10b.The hydrogen is preferably stored in a large low-pressure (e.g. around 100 psi) tank having water drainage to remove whatever small amount of water that could still be present with the hydrogen. Alternatively, the hydrogen could be stored in low-pressure storage devices such as metal hydrides. The hydrogen could also be further compressed into higher-pressure storage vessels.
• The normally open ventingvalve41 is preferably closed during start-up and opens when theelectrolyzer cell module10bshuts down. The normallyopen valve41 also functions as an emergency pressure relief path when theelectrolyzer cell module10bis suddenly stopped in emergency situations, which reduces the chances that any of the pumps in theelectrolyzer cell modules23 will be de-primed by the sudden formation of gas bubbles in the system.
• The needle/orifice valve42 is arranged after the normallyopen valve41 to slowly lower the hydrogen pressure to the ambient pressure, after theelectrolyzer cell module10bis shut down, again, in order not to de-prime any of the circulation pumps. This is described in greater detail in the applicant's co-pending U.S. Patent Application [Attorney Ref No. 9351-514], which was filed on the same day as this application, and is hereby incorporated by reference.
• Thecheck valve43 is arranged to prevent back flow into thehydrogen collection device39 and isolate the hydrogen pressure from pressures downstream.
• Ahydrogen gas sensor35 is arranged on theoutput port4 of theoxygen collection device20 to detect irregularly high levels of hydrogen in the oxygen stream, which may indicate that there is a leak somewhere in the system. Theoxygen collection device20 also has asafety valve36 arranged to vent oxygen should the pressure inside reach a pre-set high value.
• With continued reference toFIG. 3, thepressure following device34 is arranged between theoutput port4 of theoxygen collection device20 and thehydrogen collection device39. Specifically, thepressure following device34 includes a pressure sensor connected to measure the hydrogen pressure in thehydrogen collection device39, and a dome-loaded pressure valve, which is configured as a negative bias pressure regulator, that is connected to theoutput port4 of theoxygen collection device20. Thepressure following device34 measures/senses the hydrogen pressure and sets the oxygen pressure via control of the dome-loaded pressure valve.
• In this particular embodiment, the hydrogen side of theelectrolyzer cell stack11 does not include a pump, and, accordingly the hydrogen pressure is primarily established using thebackpressure valve40. It is beneficial to the overall system efficiency to keep the hydrogen pressure relatively high in order to reduce the size of hydrogen gas bubbles, which will in turn increase the active reaction area and reduce the amount of current fed to theelectrolyzer cell stack11. Having smaller hydrogen bubbles improves efficiency and counteracts any decrease in efficiency caused by the relatively high pressure(s) of the system.
• Referring now toFIG. 4, shown is anelectrolyzer cell module10c,which includes an alternative pressure following arrangement to that included in theelectrolyzer cell module10bshown inFIG. 3. Specifically, theelectrolyzer cell module10cis configured so that the hydrogen pressure follows the oxygen pressure, but remains higher. To this end, apressure following device34′ is arranged between theoutput port5 of thehydrogen collection device39 and theoxygen collection device20. Thepressure following device34′ includes a pressure sensor connected to measure the oxygen pressure in theoxygen collection device20, and a dome-loaded pressure valve, which is configured as a positive bias pressure regulator, that is connected to theoutput port5 of thehydrogen collection device39. As described above, thepressure following device34′ measures/senses the oxygen pressure and sets the hydrogen pressure via control of the dome-loaded pressure valve.
• Again, those skilled in the art will appreciate that theelectrolyzer cell module10balso includes a controller (not shown) similar to thecontroller90 illustrated inFIG. 2, which is connected to a suitable combination of elements; however, this controller has not been illustrated for the sake of simplicity.
• Moreover, theoutput port5 of thehydrogen collection device39 is now only connected to the normally open ventingvalve41 that is arranged in series with thecheck valve43. The normally open ventingvalve41 and thecheck valve43 operate as described above. Additionally, theoutput port4 of theoxygen collection device20 is connected to a needle/orifice valve42′ that is further connected in series to another normallyopen valve41′. The needle/orifice valve42′ and the normallyopen valve41′ operate to regulate the oxygen pressure during the operation of theelectrolyzer cell module10c.
• Referring now toFIG. 5, shown is anelectrolyzer cell module10d,which includes another alternative pressure following arrangement to that included in theelectrolyzer cell module10b(shown inFIG. 3). Theelectrolyzer cell module10d(shown inFIG. 5) is almost identical to theelectrolyzer cell module10b(shown inFIG. 3), except that thepressure following device34 includes a dome-loaded pressure valve that is configured as a positive bias pressure regulator, as opposed to the negative bias pressure regulator included inFIG. 3. Thepressure following device34 measures/senses the hydrogen pressure and sets the oxygen pressure via control of the dome-loaded pressure valve. However, since the dome-loaded pressure valve is a positive bias pressure regulator the resulting oxygen pressure will be set higher than the measured/sensed hydrogen pressure.
• Additionally, theoxygen collection device20 includes an output connected to another normallyopen valve41″ that is further connected in series to anothercheck valve43″. The normallyopen valve41″ and thecheck valve43″ are used to regulate the oxygen pressure during the operation of theelectrolyzer cell module10d.
• Referring now toFIG. 6, shown is anelectrolyzer cell module10e, which includes an alternative pressure following arrangement to that included in theelectrolyzer cell module10cshown inFIG. 4. Theelectrolyzer cell module10eis configured so that the hydrogen pressure follows the oxygen pressure. To this end, apressure following device34′ is arranged between theoutput port5 of thehydrogen collection device39 and theoxygen collection device20. Thepressure following device34′ includes a pressure sensor connected to measure the oxygen pressure in theoxygen collection device20, and a dome-loaded pressure valve, which is configured as a negative bias pressure regulator, that is connected to theoutput port5 of thehydrogen collection device39. As described above, thepressure following device34′ measures/senses the oxygen pressure and sets the hydrogen pressure via control of the dome-loaded pressure valve.
• Additionally, theoutput port4 of theoxygen collection device20 is coupled to a combination of valves. Specifically, theoutput port4 is coupled to abackpressure valve40′ that is in parallel with a needle/orifice valve42′ that is arranged in series with a normally open ventingvalve41′. The outputs of thebackpressure valve40′ and the normally open ventingvalve41′ are coupled in parallel into acheck valve43′. This combination of valves connected to theoutput port4 operates in a similar manner to combination of valves connected to theoutput port5 of theelectrolyzer cell module10bshown inFIG. 3.
• It was noted above that a pressure following device can be placed between at any two points around an electrolyzer cell stack that provide a reasonable measure of the internal pressures within the electrolyzer cell stack and a control point for those pressures so that the pressure differential across the membranes can be regulated.FIGS. 7A, 7B,7C show partial detailed schematic drawings ofelectrolyzer cell modules10f,10gand10h,respectively, that illustrate alternative pressure following arrangements according to aspects of different embodiments of the invention.
• Referring specifically toFIG. 7A, theelectrolyzer cell module10f,is similar to theelectrolyzer cell module10cillustrated inFIG. 4. However, thepressure following device34′ is connected between theoutput port5 and theanode outlet port27 of theelectrolyzer cell stack11, and not to theoxygen collection device20. In particular, a pressure sensor is arranged to measure/sense the pressure at theanode outlet port27 instead of within theoxygen collection device20.
• Referring now toFIGS. 7B and 7C, the respectiveelectrolyzer cell modules10gand10h,are similar to theelectrolyzer cell module10billustrated inFIG. 3. However, the respectivepressure following devices34 are connected between theoutput port4 and respective points before and after thefirst heat exchanger38, and not to thehydrogen collection device39. In particular, respective pressure sensors are arranged to measure/sense the pressure at respective points following thecathode outlet port28 instead of within thehydrogen collection device39.
• While the above description provides examples according to aspects of embodiments of the invention, it wilt be appreciated that the present invention is susceptible to modification and change without departing from the fair meaning and scope of the accompanying claims. Accordingly, what has been described is merely illustrative of the application of some aspects of embodiments of the invention. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described herein.

Claims (30)

1. A balance-of-plant system, suited for regulating the operation of an electrolyzer cell stack having at least one electrolyzer cell, comprising:

a first pressure regulator for regulating a first pressure of a first reaction product;

a pressure following device having:

a pressure sensor for measuring the first pressure and providing a signal including information about a value of the first pressure; and

a second pressure regulator for regulating a second pressure of a second reaction product relative to the first pressure using the signal from the pressure sensor.

2. A balance-of-plant system according toclaim 1, wherein the first and second pressures correspond to pressures on respective anode and cathode sides of the electrolyzer cell.

3. A balance-of-plant system according toclaim 1, wherein the balance-of-plant system further comprises:

a hydrogen collection device; and

an oxygen collection device;

wherein the first and second pressures correspond to pressures of hydrogen and oxygen produced by the electrolyzer cell stack.

4. A balance-of-plant system according toclaim 3, wherein the pressure sensor is operable to measure/sense the oxygen pressure and the second pressure regulator is operable to set the hydrogen pressure.

5. A balance-of-plant system according toclaim 4, the second pressure regulator is one of a negative bias pressure regulator and a positive bias pressure regulator.

6. A balance-of-plant system according toclaim 5, wherein the pressure sensor is connectable to measure the oxygen pressure between the electrolyzer cell stack and the oxygen collection device.

7. A balance-of-plant system according toclaim 5, wherein the pressure sensor is connectable to measure the oxygen pressure inside the oxygen collection device.

8. A balance-of-plant system according toclaim 3, wherein the pressure sensor is operable to measure/sense the hydrogen pressure and the second pressure regulator is operable to set the oxygen pressure.

9. A balance-of-plant system according toclaim 8, the second pressure regulator is one of a negative bias pressure regulator and a positive bias pressure regulator.

10. A balance-of-plant system according toclaim 9, wherein the pressure sensor is connectable to measure the hydrogen pressure between the electrolyzer cell stack and the hydrogen collection device.

11. A balance-of-plant system according toclaim 9, wherein the pressure sensor is connectable to measure the hydrogen pressure inside the hydrogen collection device.

12. A balance-of-plant system, suited for regulating the operation of an electrolyzer cell stack having at least one electrolyzer cell, comprising:

a controller having a computer readable program code means for causing a first pressure of a first reaction product to be followed by a second pressure of a second reaction product, the computer readable code means including:

instructions for regulating the first pressure;

instructions for polling a pressure sensor operable to sense the first pressure; and

instructions for regulating the second pressure relative to the first pressure.

13. A balance-of-plant system according toclaim 12, wherein the controller is comprised of at least one of a centralized control system and a distributed control system.

14. A balance-of-plant system according toclaim 12, wherein the second pressure is set relative to the first pressure such that the second pressure is one of greater than, less than and approximately equal to the first pressure.

15. A balance-of-plant system according toclaim 12 further comprising:

a first pressure regulator for regulating the first pressure;

a pressure sensor for measuring the first pressure; and

a second pressure regulator for regulating the second pressure.

16. A balance-of-plant system according toclaim 15, wherein the first pressure regulator comprises a combination of valves, mechanical actuators and electronic actuators arranged to regulate the first pressure.

17. A balance-of-plant system according toclaim 15, wherein the second pressure regulator also comprises a combination of valves, mechanical actuators and electronic actuators arranged to regulate the second pressure.

18. A balance-of-plant system according toclaim 12, wherein the first and second pressures correspond to pressures of hydrogen and oxygen produced by the electrolyzer cell stack.

19. A balance-of-plant system according toclaim 18, wherein the hydrogen pressure is set relative to the oxygen pressure.

20. A balance-of-plant system according toclaim 18, wherein the oxygen pressure is set relative to the hydrogen pressure.

21. An electrochemical cell stack module comprising:

at least one electrochemical cell in which at least two pressures, of at least two respective gases, are controllable; and

a pressure following device that is operable to control one of the two pressures relative to the other.

22. An electrochemical cell stack according toclaim 21, wherein the pressure following device comprises:

a pressure sensor for measuring/sensing one of the two pressures and providing measured/sensed information; and

a pressure regulator connectable to accept measured/sensed information from the pressure sensor and to control the other of the two pressures relative to the measured/sensed information.

23. An electrochemical cell stack according toclaim 21, wherein the at least one electrochemical cell is an electrolyzer cell and the at least two pressures correspond to hydrogen and oxygen pressures.

24. An electrochemical cell stack according toclaim 23, wherein the hydrogen pressure is set relative to the oxygen pressure.

25. An electrochemical cell stack according toclaim 23, wherein the oxygen pressure is set relative to the hydrogen pressure.

26. An electrolyzer cell module comprising:

a controller having a computer readable program code means for causing a first pressure of a first reaction product to be regulated relative to a second pressure of a second reaction product, the computer readable code means including:

instructions for regulating the second pressure;

instructions for measuring/sensing the second pressure; and

instructions for regulating the first pressure relative to the second pressure.

27. An electrolyzer cell module according toclaim 26, wherein the controller is comprised of at least one of a centralized control system and a distributed control system.

28. An electrolyzer cell module according toclaim 26, wherein the first pressure is set relative to the second pressure such that the second pressure is one of greater than, less than and approximately equal to the first pressure.

29. An electrolyzer cell module according toclaim 26 wherein the first and second pressures correspond to hydrogen and oxygen pressures.

30. An electrolyzer cell module according toclaim 26 wherein the controller is comprised of at least one of a central control system and a distributed control system.

Images