US20050183948A1

US20050183948A1 - Apparatus and method for reducing instances of pump de-priming

Info

Publication number: US20050183948A1
Application number: US10/944,868
Authority: US
Inventors: Ali Rusta-Sallehy; Michael Vale
Original assignee: Hydrogenics Corp
Current assignee: Hydrogenics Corp
Priority date: 2003-09-22
Filing date: 2004-09-21
Publication date: 2005-08-25
Also published as: WO2005028713A1; US7353085B2; US20050197743A1; WO2005028714A1; WO2005028715A1

Abstract

Abruptly shutting down an electrolyzer cell module during normal operation may, in some instances, be necessary when one or more process and operating parameters uncontrollably deviate into an unsafe range. However, abruptly shutting down an electrolyzer cell module may have residual effects that make it difficult to restart the electrolyzer cell module. In particular, in some instances a circulation pump is de-primed by the accumulation of gas bubbles within the circulation pump, which normally do not exist during normal operation since a fluid containing dissolved gas molecules is pressurized to ensure that the gas remains dissolved. In some embodiments of the invention there is provided a modified safety system that can controllably shutdown an electrolyzer cell module in an emergency situation so as to prevent instances of pump de-priming.

Description

PRIORITY CLAIM

This application claims the benefit, under 35 USC 119(e), of U.S. Provisional Application No. 60/504,218 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 an apparatus and method suited for controlling an electrolyzer cell module.

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).
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 related to the operation of the stack.
Typically, during the normal operation of an electrolyzer cell module, process gases and fluids are pressurized. For example, the water within the electrolyzer cell module is pressurized so that oxygen produced in the stack remains dissolved within the water, since large gas bubbles will reduce efficiency. In some emergency situations, the operation of an electrolyzer cell module is abruptly halted and power provided to the balance-of-plant elements is cut-off. As a result, the pressure in the various gas/fluid lines is released, which causes the formation of relatively large gas bubbles that sometimes make it difficult to restart the electrolyzer cell module.

SUMMARY OF THE INVENTION

According to aspects of an embodiment of the invention there is provided an electrolyzer cell module having: an electrolyzer cell stack for electrolysing a compound liquid to produce at least one gas; a plurality of balance-of-plant elements connected to the electrolyzer cell stack, for regulating the operation of the electrolyzer cell stack; a safety system connected to at least some of the balance-of-plant elements and the electrolyzer cell stack, for monitoring at least one process and operating parameter related to the operation of the electrolyzer cell module and evaluating whether or not at least one alarm threshold has been violated by the at least one process and operating parameter; a computer usable medium, in communication with the safety system, having computer program readable code means embodied therein for emergency stoppage of the normal operation of the electrolyzer cell module when the at least one alarm threshold has been violated, the computer program readable code means including: instructions for stopping the electrolysis of the compound liquid within the electrolyzer cell stack, thereby stopping the production of the at least one gas; instructions for operating the electrolyzer cell module so as to flush out residual amounts of the at least one gas dissolved in the compound liquid over a time period; and, instructions for cutting-off power, at the end of the time period, to all of the elements included in the electrolyzer cell module required for flushing out residual amounts of the at least one gas dissolved in the compound liquid, to shut-down the electrolyzer cell stack.
In some embodiments the computer program readable code means also includes: instructions for cutting-off power to some of the balance-of-plant elements included in the electrolyzer cell module, while continuing to provide power to other balance-of-plant elements required to flush out the residual amounts of the at least on gas dissolved in the compound liquid within the electrolyzer cell module. In some related embodiments the balance-of-plant elements that continue to receive power during an emergency stoppage include a circulation pump and pressure regulating devices.
In some embodiments the electrolyzer cell module also includes a pressure release means that is operable to slowly and controllably release the pressure within the electrolyzer cell module as it is being turned off. In some specific instances the pressure release means in comprised of a combination of valves that includes, without limitation, a need/orifice valve and a second valve connected in series, wherein the second valve is opened when the electrolyzer cell module is shut down.
According to other aspects of an embodiment of the invention there is provided an emergency stoppage method of operating an electrolyzer cell module that includes a number of balance-of-plant elements and an electrolyzer cell stack, the method including: stopping electrolysis of a compound liquid, thereby stopping the production of at least one gas dissolved in the compound liquid; flushing out residual amounts of the at least one gas evolved from the compound liquid by operating some of the balance-of-plant elements included in the electrolyzer cell module and not others; and, cutting-off power, to all of the elements included in the electrolyzer cell module required for flushing out the residual amounts of the at least one gas dissolved in the compound liquid, to shut-down the operation of the electrolyzer cell stack.
In some embodiments the method also includes a step of controllably releasing the pressure within the electrolyzer cell module as the residual amounts of the at least one gas are flushed from the electrolyzer cell module. In some specific instance the method also includes the step of cutting-off power to some of the balance-of-plant elements included in the electrolyzer cell module, while continuing to provide power to other balance-of-plant elements required to flush out the residual amounts of the at least on gas dissolved in the compound liquid within the electrolyzer cell module.
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 first detailed schematic drawing of an electrolyzer cell module according to aspects of an embodiment of the invention;
FIG. 3 is a second detailed schematic drawing of an electrolyzer cell module according to aspects of an alternative embodiment of the invention;
FIG. 4 is a flow chart illustrating a high-level method of operating an electrolyzer cell module according to aspects of an embodiment of the invention; and
FIG. 5 is a flow chart depicting the general steps provided in an emergency stop program according to an embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

Abruptly shutting down an electrolyzer cell module during normal operation may, in some instances, be necessary when one or more process and operating parameters uncontrollably deviate into an unsafe range. However, abruptly shutting down an electrolyzer cell module may have residual effects that make it difficult to restart the electrolyzer cell module. In particular, in some instances a circulation pump is de-primed by the accumulation of gas bubbles within the circulation pump, which normally do not exist during normal operation since a fluid containing dissolved gas molecules is pressurized to ensure that the gas remains dissolved. In some embodiments of the invention there is provided a modified safety system that can controllably shut down an electrolyzer cell module in an emergency situation so as to prevent instances of pump de-priming.
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 to FIG. 1, shown is a simplified schematic diagram of a Proton Exchange Membrane (PEM) electrolyzer cell, simply referred to as electrolyzer cell 100 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.
The electrolyzer cell 100 includes an anode electrode 210 and a cathode electrode 410. The anode electrode 210 includes a water input port 220 and a water/oxygen output port 240. Similarly, the cathode electrode 410 includes a water input port 420 and a water/hydrogen output port 440. An electrolyte membrane 300 is arranged between the anode electrode 210 and the cathode electrode 410.
The electrolyzer cell 100 also includes a first catalyst layer 230 arranged between the anode electrode 210 and the electrolyte membrane 300, and a second catalyst layer 430 arranged between the cathode electrode 410 and the electrolyte membrane 300.
In order to energize the electrolyzer cell 100, a voltage source 117 is coupled between the anode and cathode electrodes 210, 410.
In operation, water is introduced into the anode electrode 210 via the water input port 220. The water is dissociated electrochemically according to reaction (1), given below, in the presence of the electrolyte membrane 300 and the first catalyst layer 230.
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 the electrolyte membrane 300 to the cathode electrode 410 while the electrons are drawn through the voltage source 117. Water containing dissolved oxygen molecules is drawn out through the water/oxygen output port 240. The water is pressurized to ensure that the oxygen molecules remain dissolved in the water and do not form relatively large gas bubbles.
Simultaneously, additional water is introduced into the cathode electrode 410 via the water input port 420 in order to provide moisture to the cathode side of the electrolyte membrane 300.
The hydrogen ions (i.e. protons) are electrochemically reduced to hydrogen molecules according to reaction (2), given below, in the presence of the electrolyte membrane 300 and the second catalyst layer 430. That is, the electrons and the ionized hydrogen atoms, produced by reaction (1) in the anode electrode 210, are electrochemically consumed in reaction (2) in the cathode electrode 410.
2H₂ ⁺+2e ³¹→H₂ (2)
The water containing dissolved hydrogen molecules is drawn out through the water/hydrogen output port 440. 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 in FIG. 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 to FIG. 2, illustrated is a simplified schematic diagram illustrating an electrolyzer cell module 10 a that is configured to dissociate water (H₂O) into hydrogen (H₂) and oxygen (O₂). The electrolyzer cell module 10 a includes an electrolyzer cell stack 11, a power supply 117, a hydrogen collection device 39, an oxygen collection device 20, a water supply tank 16 and a suitable combination of balance-of-plant elements.
Those skilled in the art will appreciate that shown in FIG. 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 to FIG. 2, the electrolyzer cell module 10 a includes a controller 90 that is used to manage the operations of the electrolyzer cell module 10 a. Although the controller 90 is not shown specifically connected to any of the other elements included in the electrolyzer cell module 10 a of FIG. 2, those skilled in the art will generally appreciate that a controller can be connected to any suitable combination of elements included in an electrolyzer cell module.
The controller 90 includes a modified safety system 93, an emergency stop program 97 and at least one application program 95 used to manage the normal operations of the electrolyzer cell module 10 a. To that end, in the present embodiment of the invention, the controller 90 includes a memory for storing a computer program readable code means having instructions for the modified safety system 93, the emergency stop program 97 and the at least one application program 95.
The modified safety system 93, in accordance with an embodiment of the invention, is capable of calling an alarm recovery sequence and/or calling the emergency stop program 97, in the event that an alarm threshold has been violated. Details relating to various embodiments of modified safety programs are provided in the applicant's co-pending U.S. patent application Ser. No.______[Attorney Ref: 9351-493], which was filed on the same day as this application and is hereby incorporated by reference.
The electrolyzer cell stack 11 shown in FIG. 2 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 in FIG. 1. The electrolyzer cell stack 11 has a cathode outlet port 28, an anode inlet port 202 and an anode outlet port 27. The cathode outlet port 28 is fluidly connected to each of the respective cathode electrodes included in the electrolyzer cell stack 11. Similarly, the anode inlet and outlet ports 202, 27 are fluidly connected to each of the respective anode electrodes included in the electrolyzer cell stack 11. The electrolyzer cell stack 11 also includes respective electrical connections 12, 13 to the anode and cathode terminals of the electrolyzer cell stack 11.
The power supply 117 is coupled to the electrical connections 12, 13 of the electrolyzer cell stack 11 to energize the electrolyzer cell stack 11. A stack disconnect device 48 is also coupled between the electrical connections 12, 13 of the electrolyzer cell stack 11 and the power supply 117. Additionally, a current 15 and a voltage sensor 14 are appropriately arranged between the stack disconnect device 48 and the power supply 117 to measure the current drawn by the electrolyzer cell stack 11 and the voltage across the electrical connections 12, 13.
The stack disconnect device 48 is operable between two states. In a first state, the stack disconnect device 48 electrically couples the power supply 117 to the electrolyzer cell stack 11. In a second state, the stack disconnect device 48 electrically isolates the power supply 117 from the electrolyzer cell stack 11. In some embodiments, switching the stack disconnect device 48 between the two states is, for example, controlled by a central and/or local distributed control system, which may use readings from the current and voltage sensors 15, 14 in this process.
The hydrogen collection device 39 includes an output port 5; another output port and an input port. In some embodiments, the output port 5 serves as a tap for hydrogen collected by the hydrogen collection device 39, and is also connectable to other downstream components (not shown). The input of the hydrogen collection device 39 is coupled to the cathode outlet port 28 to accept a combination of water and hydrogen from the electrolyzer cell stack 11. The other output port is coupled to the water supply tank 16 to return water separated from hydrogen during operation.
The oxygen collection device 20 includes an output port 4; another output port and two input ports. In some embodiments, the output port 4 serves as a tap for oxygen collected by the oxygen collection device 20, and is also connectable to other downstream components (not shown). The other output port is coupled to provide water to the anode inlet port 202, and one of the input ports is coupled to receive a combination of water and oxygen from the anode outlet port 27. The other input port is coupled to receive water from the water supply tank 16. That is, according to this specific example, water is provided to the electrolyzer cell stack 11 from the water supply tank 16 via the oxygen collection device 20, which also recycles water received back from the electrolyzer cell stack 11.
Optionally, in other embodiments, the water supply tank 16 is also coupled to a cathode inlet port of the electrolyzer cell stack 11 to hydrate the respective cathode sides of the membranes included in the electrolyzer cell stack 11.
In some embodiments, the hydrogen and oxygen collection devices 39, 20 each include a condenser, such as, for example, the apparatus described in the applicant's issued U.S. Pat. No. 6,619,054, which is hereby incorporated by reference.
In some embodiments, the hydrogen collection device 39 has a volume that is about twice the volume of the oxygen collection device 20. This difference in size accommodates the relative rates of hydrogen and oxygen evolution that will occur according to reactions (1) and (2) described above.
The anode and cathode outlet ports 27, 28 of the electrolyzer cell stack 11 are respectively connected to the oxygen and hydrogen collection devices 20, 39 through respective combinations of balance-of-plant elements.
Specifically, in this example embodiment, there is a second pressure sensor 30, a first pressure safety switch 33, a first temperature sensor 36 and a first heat exchanger 38 arranged along the fluid pathway from the cathode outlet port 28 to the hydrogen collection device 39. The first pressure safety switch 33 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 the cathode outlet port 28 reaches a predetermined high value. In some embodiments, the first pressure safety switch 33 is configured to override and halt the operation of the electrolyzer cell module 10 a in the event that the pressure is too high, which may imply that there is a severe problem with the electrolyzer cell module 10 a.
The first temperature sensor 36 is coupled to provide the first heat exchanger 38 with a regulation signal. Using the regulation signal from the first temperature sensor 36, the first heat exchanger 38 is operable to cool the stream of hydrogen and water exiting the cathode outlet port 28, thereby initiating condensation of the water to separate it from the hydrogen within the hydrogen collection device 39.
Similarly, in this example embodiment, there is a first pressure sensor 29, a second temperature sensor 31 and a first temperature safety switch 32 arranged along the fluid pathway from the anode outlet port 27 to the oxygen collection device 20. The first temperature safety switch 32 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 the anode outlet port 27 reaches a predetermined high value. In some embodiments, the first temperature safety switch 32 is configured to override and halt the operation of the electrolyzer cell module 10 a in the event that the temperature is too high, which may imply that there is a severe problem with the electrolyzer cell module 10 a.
The anode inlet port 202 of the electrolyzer cell stack 11 is connected to receive water from the oxygen collection device 20 through a respective combination of balance-of-plant elements as well. Specifically, a circulation pump 23, a second heat exchanger 22, a resistivity meter 24, a flow switch 25 and preferably a de-ionizing filter 26 are arranged along the fluid pathway to the anode inlet port 202 from the oxygen collection device 20. The second heat exchanger 22 is also coupled to receive a regulation signal from the second temperature sensor 31 arranged on the fluid pathway originating from the anode outlet port 27.
The circulation pump 23 is operable to force the flow of water into the electrolyzer cell stack 11. 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 the second temperature sensor 31, the second heat exchanger 22 is operable to adjust the temperature of the water stream entering the electrolyzer cell stack 11. The resistivity meter 24 is operable to measure the resistivity of the water flowing into the electrolyzer cell stack 11. The flow switch 25 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, the de-ionizing filter 26 incorporates organic and particulate filtering functions.
As a side note, in different embodiments the first and second heat exchangers 38, 22 are made up of different components. For example, in one embodiment the first and second heat exchangers 38, 22 include fans for temperature regulation by air-heating/cooling, whereas in other embodiments the first and second heat exchangers 38, 22 include pumps and coolant fluids for temperature regulation by liquid-heating/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 the water supply tank 16 to the oxygen collection device 20. Specifically, the water supply tank 16 is connected to the oxygen collection device 20 through a fill pump 17, an organic filter 18, a particulate and a de-ionizing filter 19, a check valve 47 and a three-way valve 21. An output of the three-way valve 21 is also coupled back to the water supply tank 16. The check valve 47 is arranged to prevent back flow of water through the fill pump 17 and filters 18, 19.
A first water level indicator 37 is coupled to the oxygen collection device 20 and to the fill pump 17 and the three-way valve 21. The first water level indicator 37 is operable to measure the water level in the oxygen collection device 20 and provide a feedback control signal to the fill pump 17 and the three-way valve 21. For example, when the water level in the oxygen collection device 20 is higher than a pre-set high level value, the three-way 21 valve is set to re-circulate water back to the water supply tank 16; or, when the water level is lower than a pre-set low level value, the fill pump 17 is signalled to increase the rate of water flow.
Comparatively, the balance-of-plant setup between the hydrogen collection device 39 and the water supply tank 16 is quite simple. A second water level indicator 45 is coupled to the hydrogen collection device 39 and a purge valve 46 is connected between the hydrogen collection device 39 and the water supply tank 16. The purge valve 46 is operated by a control signal received from the second water level indicator 45 coupled to the hydrogen collection device 39. When the water level in the hydrogen collection device 39 is higher than a pre-set level value, the purge valve 46 opens after receiving the control signal from the second water level indicator 45. Once the purge valve 46 is opened, water can flow from the hydrogen collection device 39 to the water supply tank 16. Alternatively, the purged water can be dumped out of the system or used for other purposes (i.e. as a coolant).
The hydrogen collection device 39 also has a safety valve 44 that automatically vents gas from the hydrogen collection device 39 when the pressure inside reaches a pre-set upper threshold. Accordingly, the safety valve 44 aids in the regulation of the hydrogen pressure, which in this embodiment, is followed by the oxygen pressure via the operation of the pressure following device 34.
In this particular embodiment, the output port 5 of the hydrogen collection device 39 is coupled to a combination of valves. Specifically, the output port 5 is coupled to a backpressure valve 40 that is in parallel with a normally open venting valve 41 that is arranged in series with a needle/orifice valve 42. The outputs of the backpressure valve 40 and the needle/orifice valve 42 are coupled in parallel into a check valve 43.
The backpressure valve 40 is arranged to regulate the hydrogen pressure within the hydrogen collection device 39 during the operation of the electrolyzer cell module 10 b. 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 combination of the normally open valve 41 and the needle/orifice valve 42 cooperate to controllably release the pressure within the electrolyzer cell module 10 a when it is shut down. The normally open venting valve 41 is preferably closed during start-up and opens when the electrolyzer cell module 10 b shuts down. The normally open valve 41 also functions as an emergency pressure relief path when the electrolyzer cell module 10 b is suddenly stopped in emergency situations, which reduces the chances that any of the pumps in the electrolyzer cell modules 23 will be de-primed by the sudden formation of gas bubbles in the system. The needle/orifice valve 42 is arranged after the normally open valve 41 to slowly lower the hydrogen pressure to the ambient pressure, after the electrolyzer cell module 10 b is shut down, again, in order not to de-prime any of the circulation pumps.
The check valve 43 is arranged to prevent back flow into the hydrogen collection device 39 and isolate the hydrogen pressure from pressures downstream.
A hydrogen gas sensor 35 is arranged on the output port 4 of the oxygen collection device 20 to detect irregularly high levels of hydrogen in the oxygen stream, which may indicate that there is a leak somewhere in the system. The oxygen collection device 20 also has a safety valve 49 arranged to vent oxygen should the pressure inside reach a pre-set high value.
With continued reference to FIG. 3, the pressure following device 34 is arranged between the output port 4 of the oxygen collection device 20 and the hydrogen collection device 39. Specifically, the pressure following device 34 includes a pressure sensor connected to measure the hydrogen pressure in the hydrogen collection device 39, and a dome-loaded pressure valve, which is configured as a negative bias pressure regulator, that is connected to the output port 4 of the oxygen collection device 20. The pressure following device 34 measures/senses the hydrogen pressure and sets the oxygen pressure via control of the dome-loaded pressure valve. Aspects of pressure following arrangements according to aspects of embodiments of the invention are described in greater detail in the applicant's co-pending U.S. patent application Ser. No.______ [Attorney Ref. No: 9351-460], which was filed on the same day as this application and is hereby incorporated by reference.
During an emergency shutdown process it is preferable that the pressure following device 34 continues operation so as to permit the circulation pumps to flush out gases dissolved in the water so that they do not accumulate in relatively large bubbles within the electrolyzer cell module 10 a. This is desirable since the accumulation of relatively large gas bubbles within the electrolyzer cell module 10 a may lead to a de-priming of the circulation pumps.
In this particular embodiment, the hydrogen side of the electrolyzer cell stack 11 does not include a pump, and, accordingly the hydrogen pressure is primarily established using the backpressure valve 40. 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 the electrolyzer cell stack 11. Having smaller hydrogen bubbles improves efficiency and counteracts any decrease in efficiency caused by the relatively high pressure(s) of the system.
The operation of the electrolyzer cell stack 11 (in FIG. 2) is similar to that of the electrolyzer cell module 100 (in FIG. 1). To briefly reiterate, the power supply 117 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 the anode outlet port 27 into the oxygen collection device 20 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 the cathode outlet port 28 into the hydrogen collection device 39 where the hydrogen is separated from the water.
Referring now to FIG. 3, shown is an electrolyzer cell module 10 b, which includes an alternative pressure following arrangement to that included in the electrolyzer cell module 10 a shown in FIG. 2. Specifically, the electrolyzer cell module 10 b is configured so that the hydrogen pressure follows the oxygen pressure, but remains higher. To this end, a pressure following device 34′ is arranged between the output port 5 of the hydrogen collection device 39 and the oxygen collection device 20. The pressure following device 34′ includes a pressure sensor connected to measure the oxygen pressure in the oxygen collection device 20, and a dome-loaded pressure valve, which is configured as a positive bias pressure regulator, that is connected to the output port 5 of the hydrogen collection device 39. As described above, the pressure following device 34′ measures/senses the oxygen pressure and sets the hydrogen pressure via control of the dome-loaded pressure valve. Again, aspects of pressure following arrangements according to aspects of embodiments of the invention are described in greater detail in the applicant's co-pending U.S. patent application Ser. No.______[Attorney Ref. No: 9351-460], which was incorporated by reference above.
During an emergency shutdown process it is preferable that the pressure following device 34′ continues operation so as to permit the circulation pumps to flush out gases dissolved in the water so that they do not accumulate in relatively large bubbles within the electrolyzer cell module 10 b. This is desirable since the accumulation of relatively large gas bubbles within the electrolyzer cell module 10 b may lead to a de-priming of the circulation pumps.
Moreover, the output port 5 of the hydrogen collection device 39 is now only connected to the normally open venting valve 41 that is arranged in series with the check valve 43. The normally open venting valve 41 and the check valve 43 operate as described above. Additionally, the output port 4 of the oxygen collection device 20 is connected to a needle/orifice valve 42′ that is further connected in series to another normally open valve 41′. The needle/orifice valve 42′ and the normally open valve 41′ operate to regulate the oxygen pressure during the operation of the electrolyzer cell module 10 c.
The combination of the normally open valve 41′ and the needle/orifice valve 42′ cooperate to controllably release the pressure within the electrolyzer cell module 10 b when it is shut down, in a similar manner to the combination of the normally open valve 41 and the needle/orifice valve 42 descrfibed above. The normally open venting valve 41 is preferably closed during start-up and opens when the electrolyzer cell module 10 b shuts down. The normally open valve 41 also functions as an emergency pressure relief path when the electrolyzer cell module 10 b is suddenly stopped in emergency situations, which reduces the chances that any of the pumps in the electrolyzer cell modules 23 will be de-primed by the sudden formation of gas bubbles in the system. The needle/orifice valve 42 is arranged after the normally open valve 41 to slowly lower the hydrogen pressure to the ambient pressure, after the electrolyzer cell module 10 b is shut down, again, in order not to de-prime any of the circulation pumps.
FIG. 4 is a flow chart illustrating a high-level method of operating an electrolyzer cell module according to aspects of an embodiment of the invention. At step 4-0, the electrolyzer cell module is energized and an initialization sequence, including basic checks, occurs at step 4-1. The basic checks include, without limitation, checks for control system readiness, the presence of electric power and pneumatic air pressure.
After the basic system checks are complete, the electrolyzer cell module enters a standby mode in step 4-2. During the standby mode, the control system waits for a start-up command from an operator or another automated machine.
Once a start-up command has been received, a start-up sequence is commenced at step 4-3. During the start-up sequence the electrolyzer cell module is readied for normal operation. Examples of operations that occur during a start-up sequence include, without limitation, a water fill process, priming of pumps, water polishing, pressurization, and hydrogen purging.
After the start-up sequence 4-3, a run mode is started at step 4-4. The run mode can end in at least three different ways, which include, without limitation, normal shutdown initiated by an operator or another automated machine, through an alarm recovery sequence at steps 4-5 and 4-6, and by an emergency stoppage at step 4-7. The alarm recovery sequences and emergency stoppages result from safety system logic that is included in the control system for an electrolyzer cell module. Examples describing how the safety system logic can be incorporated into the control system for an electrolyzer cell module are described in the applicant's copending U.S. patent application Ser. No.______[Attorney Ref: 9351-493], which was incorporated by reference above. It is worth noting here that an alarm recovery sequence is only followed by an emergency stoppage if the alarm recovery sequence is not effective correcting the conditions that called for the alarm recovery sequence in the first place.
In some embodiments a control system is provided with a computer program readable code means that has instructions that mirror the method steps described below. Moreover, those skilled in the art will appreciate that these methods may be modified without departing from the scope of the inventive aspects specifically described herein.
Referring now to FIG. 5, illustrated is a flow chart depicting the general steps provided in an emergency stop program according to one embodiment of the invention. Once a safety system concludes that an emergency stoppage is the only way left to deal with violated alarm conditions within an electrolyzer cell module the emergency stop program is started at step 5-1.
With further reference to FIGS. 2 and 3, at step 5-2 the electrolyzer cell stack 11 is disconnected from the power supply 117. Then at step 5-3, power supplied to the balance-of-plant elements not related to the circulation pump 23 and the pressure following devices 34 and 34′ is cut-off. That is, the circulation pump 23 and the pressure regulation of the line is maintained until gases dissolved in the water within the electrolyzer cell module (10 a or 10 b) can be flushed from the system, leaving the behind relatively pure water. This process will take some finite amount of time, depending upon the exact configuration of an electrolyzer cell module. Simultaneously, pressure is slowly released by way of the normally open valve 41 and the needle/orifice valve 42 (in FIG. 2) or the normally open valve 41′ and the needle/orifice valve 42′. Normally open valves require power to close the valve, but are normally open when no power is supplied. Accordingly, during an emergency stoppage power does not need to be supplied to the normally open valve 41 or 41′. However, if the normally open valves were replaced with normally closed valves, power would be required for these valves to remain open during an emergency stoppage.
At step 5-4 it is determined whether or not an emergency timer has expired. The emergency timer provides a count down period that has a duration that is about as long as the finite amount of time it takes to flush out the gases from the electrolyzer cell module. If the emergency timer has not expired (no path, step 54), then the balance-of-plant elements, such as the circulation pump 23, required to flush the residual gas from the electrolyzer cell module continue to be powered at step 5-5 while the emergency timer is checked again at step 5-4, after a short delay. On the other hand, if the emergency timer has expired (yes path, step 54), then it is assumed that the most of the residual gas left in the electrolyzer cell module has been expelled and the entire electrolyzer cell module is shut down, including elements such as the circulation pump 23 and the pressure following devices 34 and 34′.
While the above description provides examples according to aspects of embodiments of the invention, it will 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

1. An electrolyzer cell module comprising:

an electrolyzer cell stack for electrolysing a compound liquid to produce at least one gas;

a plurality of balance-of-plant elements connected to the electrolyzer cell stack, for regulating the operation of the electrolyzer cell stack;

a safety system connected to at least some of the balance-of-plant elements and the electrolyzer cell stack, for monitoring at least one process and operating parameter related to the operation of the electrolyzer cell module and evaluating whether or not at least one alarm threshold has been violated by the at least one process and operating parameter;

a computer usable medium, in communication with the safety system, having computer program readable code means embodied therein for emergency stoppage of the normal operation of the electrolyzer cell module when the at least one alarm threshold has been violated, the computer program readable code means including:

instructions for stopping the electrolysis of the compound liquid within the electrolyzer cell stack, thereby stopping the production of the at least one gas;

instructions for operating the electrolyzer cell module so as to flush out residual amounts of the at least one gas dissolved in the compound liquid over a time period; and

instructions for cutting-off power, at the end of the time period, to all of the elements included in the electrolyzer cell module required for flushing out residual amounts of the at least one gas dissolved in the compound liquid, to shut-down the electrolyzer cell stack.

2. An electrolyzer cell module according to claim 1, wherein the computer program readable code means further comprises:

instructions for cutting-off power to some of the balance-of-plant elements included in the electrolyzer cell module, while continuing to provide power to other balance-of-plant elements required to flush out the residual amounts of the at least on gas dissolved in the compound liquid within the electrolyzer cell module.

3. An electrolyzer cell module according to claim 2, wherein the balance-of-plant elements that continue to receive power during an emergency stoppage include a circulation pump and pressure regulating devices.

4. An electrolyzer cell module according to claim 1 further comprising a pressure release means that is operable to slowly and controllably release the pressure within the electrolyzer cell module as it is being turned off.

5. An electrolyzer cell module according to claim 4, wherein the pressure release means in comprised of a combination of valves.

6. An electrolyzer cell module according to claim 5, wherein the combination of valves is comprised of a need/orifice valve and a second valve connected in series, wherein the second valve is opened when the electrolyzer cell module is shut down.

7. An electrolyzerr cell module according to claim 6, wherein the second valve is one of a normally open valve and a normally closed valve.

8. An electrolyzer cell module according to claim 4 further comprising a hydrogen collection device and an oxygen collection device.

9. An electrolyzer cell module according to claim 8, wherein the pressure release means is connected to one of the hydrogen collection device and the oxygen collection device.

10. An emergency stoppage method of operating an electrolyzer cell module that includes a number of balance-of-plant elements and an electrolyzer cell stack, the method comprising:

stopping electrolysis of a compound liquid, thereby stopping the production of at least one gas dissolved in the compound liquid;

flushing out residual amounts of the at least one gas evolved from the compound liquid by operating some of the balance-of-plant elements included in the electrolyzer cell module and not others; and

cutting-off power, to all of the elements included in the electrolyzer cell module required to flush out the residual amounts of the at least one gas dissolved in the compound liquid, to shut-down the operation of the electrolyzer cell stack.

11. A method according to claim 10 further comprising:

controllably releasing the pressure within the electrolyzer cell module as the residual amounts of the at least one gas are flushed from the electrolyzer cell module.

12. A method according to claim 11 further comprising:

cutting-off power to some of the balance-of-plant elements included in the electrolyzer cell module, while continuing to provide power to other balance-of-plant elements required to flush out the residual amounts of the at least on gas dissolved in the compound liquid within the electrolyzer cell module.