Passive Dual Modulation Regulator for Hydrogen Generation

Abstract

A passive dual modulation regulator is provided that responds to a pressure differential between the hydrogen and oxygen sides of one or more proton exchange membrane (PEM) cells. The passive dual modulation regulator includes a flexible diaphragm clamped along its periphery between hemispherical chambers. A bidirectional valve assembly extends through the flexible diaphragm and includes opposing valve plugs for selectively closing the exhaust ports of each hemispherical chamber. Large or sustained pressure imbalances between the hydrogen and oxygen sides of the hydrogen generation system are avoided without any type of active control input, and as a result, PEM rupture is generally avoided.

Description

[Technical field]

[0001] The present invention relates to water electrolysis for the production of hydrogen fuel using proton exchange membrane stacks. [Background technology]

[0002] Water electrolysis is a process in which water is separated into hydrogen and oxygen through the application of electrical energy. In existing electrolysis technologies, proton exchange membrane (PEM) electrolyzers use a proton exchange membrane as the ion conductor. A proton exchange membrane consists of a thin, solid, ion-conducting membrane rather than the aqueous solution found in alkaline electrolyzers. The membrane is + Ions (ie, protons) are transported from the anode to the cathode, separating hydrogen and oxygen gases.

[0003] PEM electrolysis is preferred over alkaline electrolysis because no corrosive electrolyte is used in PEM electrolysis. In addition, PEM electrolysis has a thinner membrane (e.g., DuPont's Nafion) which allows for faster ion transport, which is important under variable conditions. In addition, alkaline cells have cross-contamination challenges because both gas (hydrogen and oxygen) and alkaline substances are present in the exhaust gas, requiring scrubbers to remove oxygen and alkaline contaminants from the hydrogen gas. This is especially important because as little as 3% oxygen in hydrogen is enough to form an explosive mixture.

[0004] PEM electrolyzers include differential pressure and balanced pressure designs. In either differential pressure or balanced pressure designs, pressure regulation of hydrogen and oxygen gases is critical to the efficiency and lifespan of the PEM electrolyzer. Thus, there remains a need for improved pressure regulators for PEM electrolyzers. In particular, there remains a need for improved pressure regulators to balance hydrogen and oxygen gases without cross-contamination. Summary of the Invention

[0005] A passive dual modulation regulator is provided that responds to pressure differences between the hydrogen and oxygen sides of one or more PEM cells. The passive dual modulation regulator includes a flexible diaphragm clamped along its periphery between hemispherical chambers. A bidirectional valve assembly extends through the flexible diaphragm and includes opposing valve plugs for narrowing and eventually closing the exhaust ports of each hemispherical chamber. A sustained pressure imbalance between the hydrogen and oxygen sides of the hydrogen generation system is avoided without any type of active control input, and as a result, electrolyzer membrane rupture is generally avoided.

[0006] In one embodiment, the opposing ends of the bidirectional valve assembly include an alignment rod, a valve plug, a valve stem, and a fender washer. The alignment rod has external threads at one end for attachment to the valve stem and secures the valve plug relative to the valve stem. The valve plug includes an angled washer formed from silicone rubber and includes an angled engagement surface for engaging a corresponding valve seat machined into the concave inner surface of each hemispherical chamber. The valve stem has internal threads at a distal end for attachment to the alignment rod and internal threads at a proximal end for attachment to a headless screw that joins the sides of the valve assembly together.

[0007] The flexible diaphragm is sensitive to even small pressure differences, so when the high pressure side pushes the diaphragm towards the low pressure side, the exhaust port on the low pressure side is closed. The pressure on the low pressure side slowly rises because the exhaust port is closed while gas is continuously produced in the PEM cell. When the pressures equalize, the exhaust port is gradually opened. As a result, the thin polymer membrane in each PEM cell is balanced on both sides, preventing rupture of the thin polymer electrolyte membrane.

[0008] In another embodiment, a hydrogen generation system is provided. The hydrogen generation system includes one or more PEM cells, an oxygen-water separator, a hydrogen-water separator, a hydrogen storage tank, and a passive dual modulation regulator. The hydrogen-water separator receives hydrogen gas and trace amounts of water from the cathode side of the PEM cells, and the hydrogen gas is drawn off to a hydrogen exhaust line. The oxygen-water separator acts as a primary water reservoir for the PEM cells and collects excess water carried along with the oxygen from the anode side of the PEM cells. Oxygen gas is then drawn off from the oxygen-water separator to an oxygen exhaust line. The passive dual modulation regulator is disposed between the hydrogen exhaust line and the oxygen exhaust line to maintain a pressure balance between the hydrogen and oxygen sides of the PEM cell(s). The hydrogen exhaust line is coupled to a pressurized hydrogen storage tank, and the oxygen exhaust line is coupled to an oxygen valve and gauge to safely vent the oxygen gas to the atmosphere.

[0009] In some embodiments, the hydrogen fuel is routed to a gas grill having one or more hydrogen burners. The gas grill may be suitable for personal applications or commercial applications such as a restaurant or cafeteria. A gas grill that runs on hydrogen gas is environmentally friendly in that it produces no carbon emissions and can run directly from renewable energy such as solar energy collected by solar cells. The hydrogen generation system and passive dual modulation regulator are not limited to cooking applications and can be used in other systems, including emergency backup power systems, transportation systems, and propulsion systems, if desired.

[0010] These and other features and advantages of the present invention will become apparent from the following description of embodiments of the invention when viewed in accordance with the accompanying drawings and the appended claims. [Brief description of the drawings]

[0011] [Figure 1]FIG. 1 is a schematic diagram of a hydrogen production system according to one embodiment. [Diagram 2] 2 shows a PEM cell for use in the hydrogen generation system of FIG. 1. [Diagram 3] FIG. 2 is a first exploded view of a passive dual modulation regulator for use in the system of FIG. 1. [Figure 4] FIG. 2 is a second exploded view of a passive dual modulation regulator for use in the system of FIG. 1. [Diagram 5] FIG. 5 is an exploded side view of a diaphragm and valve assembly for the passive dual modulation regulator of FIGS. 3-4. [Figure 6] FIG. 13 is a first exploded view of a passive dual modulation regulator according to a further embodiment. [Figure 7] FIG. 7 is a second exploded view of the passive dual modulation regulator of FIG. 6. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] This embodiment includes a passive dual modulation regulator that responds to the pressure difference between the hydrogen and oxygen sides of one or more PEM cells, thereby ensuring that the PEM cells do not explode. Large or sustained pressure imbalances between the hydrogen and oxygen sides are avoided without any type of active control input. However, before discussing the passive dual modulation regulator in detail, an exemplary hydrogen storage system having two PEM cells is described below. This system is described below as producing hydrogen fuel for cooking applications, although the passive dual modulation regulator is in no way limited to such systems and can be used in other systems as desired.

[0013] 1, a hydrogen generation system 10 according to an exemplary embodiment includes a distilled or deionized water source 12, an oxygen-water separator 14, a hydrogen-water separator 16, two PEM cells 18, 20, a hydrogen storage tank 22, a passive dual modulation regulator 24, an oxygen valve 26, and a gauge 28. The PEM cells 18, 20 may include any of the commercially available PEM cells having a proton exchange membrane 32, an anode 34, and a cathode 36, as shown diagrammatically in FIG. 2. At the anode 34 of each PEM cell, the feed water is electrochemically converted into protons (H + ), electron (e - ), and oxygen (O 2 ) The protons are transported through the proton exchange membrane 32 to the cathode 36. The electrons exit the anode 34 through an external power circuit and provide the driving force (cell voltage) for the reaction. At the cathode 36, the protons and electrons combine to produce hydrogen. Although not shown, the hydrogen production system 10 includes an energy source that generates a cell voltage for the series connected PEM cells 18, 20. The energy source can be, by way of non-limiting example, solar cells, solar heat, or geothermal heat.

[0014] Referring again to FIG. 1, a source of distilled or deionized water 12, for example distilled city water, is fed to an oxygen-water separator 14. The feed water from the oxygen-water separator 14 is fed by gravity via a feed line 30 to the anode sides of the first and second PEM cells 18, 20 where it is separated into oxygen and hydrogen as described above. The oxygen-water separator 14 acts as a primary water reservoir for the PEM cells 18, 20 and collects excess water carried along with the oxygen from the anode sides of the PEM cells 18, 20 via the oxygen line 30. Oxygen gas is then drawn off from the oxygen-water separator 14 into an oxygen exhaust line 44. The hydrogen-water separator 16 receives hydrogen gas and trace amounts of water from the cathode sides of the PEM cells 18, 20 via the hydrogen line 38. Hydrogen gas is drawn off into a hydrogen exhaust line 42. A passive dual modulation regulator 24 is disposed between a hydrogen exhaust line 42 and an oxygen exhaust line 44 to maintain pressure balance between the hydrogen and oxygen sides of the PEM cells 18, 20. The hydrogen exhaust line 42 is coupled to a pressurized hydrogen storage tank 22, and the oxygen exhaust line 44 is coupled to an oxygen valve 26 and gauge 28 to safely vent the oxygen gas to the atmosphere. Although two series connected PEM cells 18, 20 are shown in Figure 1, other embodiments may include a greater or lesser number of PEM cells, such as a single PEM cell or three or more PEM cells.

[0015] As hydrogen is produced, it is stored in a pressurized hydrogen storage tank 22. No compressor is required to pressurize the hydrogen storage tank 22. The PEM cells 18, 20 produce gas continuously until a pressure limit is reached, prompting activation of a shutoff switch. Hydrogen is produced twice as fast as oxygen, but the hydrogen side has a large storage tank 22 for filling, while the oxygen side does not, and the oxygen gas is released to the atmosphere. When there is even a small amount of hydrogen pressure, the oxygen side begins to modulate the release of gas to maintain equal pressure on both sides. Hydrogen fuel can be routed to a gas grill with one or more hydrogen burners. This gas grill can be suitable for personal applications or commercial applications such as restaurants or cafeterias. Gas grills that run on hydrogen gas (as opposed to propane gas) are environmentally friendly in that they do not produce carbon emissions and can run directly from renewable energy, such as solar energy collected by solar cells. The hydrogen generation system and passive dual modulation regulator are not limited to cooking applications, but may also be used in other systems, including emergency back-up power systems, transportation systems, and propulsion systems, if desired.

[0016] 3-5, an exemplary embodiment of a passive dual modulation regulator 24 is shown. The regulator 24 includes an outer housing formed by first and second end caps 50, 52 that cooperate to define a spherical internal cavity separated into a hydrogen chamber and an oxygen chamber. The first end cap 50 includes an inlet 54 for receiving hydrogen gas from the hydrogen exhaust line 42 and an outlet 56 for discharging hydrogen gas to the hydrogen storage tank 22. Similarly, the second end cap 52 includes an inlet 58 for receiving oxygen gas 60 from the oxygen exhaust line 44 and an outlet 60 for discharging oxygen gas to the outlet valve 26. The inlets 54, 58 are each formed in a side opening in a rectangular flange 62, and the outlets 56, 60 are each formed in a central opening in a hemispherical end wall 64. As a result, the hydrogen inlet 54 is in fluid communication with the hydrogen outlet 56 via the hemispherical hydrogen chamber 66 , and the oxygen inlet 58 is in fluid communication with the oxygen outlet 60 via the hemispherical oxygen chamber 68 .

[0017] The regulator 24 also includes a flexible diaphragm 70 sandwiched between the first and second end caps 50, 52 for separating the spherical interior cavity into a hemispherical hydrogen chamber 66 and a hemispherical oxygen chamber 68. A series of bolt openings 72 around the periphery of the flexible diaphragm 70 are aligned with bolt openings 74 in the first and second end caps 50, 52. The flexible diaphragm 70 is optionally formed from silicone rubber or other gas impermeable membrane material and includes a central aperture. The regulator 24 further includes a valve assembly 76 extending from the central aperture in the flexible diaphragm 70 for selectively closing the exhaust ports 56, 60 of the hydrogen chamber 66 and the oxygen chamber 68. As best seen in FIG. 5, the opposing ends of the valve assembly 76 are joined by a headless screw 78 and include an alignment rod 80, a valve plug 82, a valve stem 84, and a fender washer 86. The alignment rod 80 is externally threaded on one end for attachment to the valve stem 84 and functions to (a) maintain the alignment of the valve assembly 76 and (b) secure the valve plug 82 relative to the valve stem 84. The valve plug 82 includes an angled washer formed from silicone rubber and includes a 60 degree engagement surface 88 for engaging a corresponding 60 degree valve seat machined into the concave inner surface of each hemispherical end wall 64. The valve stem 84 is internally threaded on a distal end for attachment to a threaded portion 90 of the alignment rod 80 and internally threaded on a proximal end for attachment to the headless screw 78 that joins the two sides of the valve assembly 76 together.

[0018] As pressure builds up from the PEM cells 18, 20, hydrogen and oxygen enter the regulator 24, but hydrogen is produced at twice the rate of oxygen. The hydrogen side has a large storage tank 22 for filling, while the oxygen side does not have a storage tank, and oxygen gas is released to the atmosphere without restriction from the start. When there is even a small amount of hydrogen pressure, the oxygen side starts to modulate the release of gas to maintain equal pressure on both sides. The diaphragm 70 is sensitive to even small pressure differences, so when the hydrogen side pushes the diaphragm 70 towards the oxygen side, the oxygen exhaust port 60 is closed while hydrogen gas is allowed to pass through to the hydrogen storage tank 22. The pressure on the oxygen side slowly rises (and matches the pressure on the hydrogen side) because oxygen is continuously produced in the PEM cells 18, 20 while the oxygen exhaust port 60 is closed. When the pressure on the oxygen side reaches the pressure on the hydrogen side, the valve assembly is centered, allowing gas flow at each exhaust port 56, 60. The thin polymer membrane 32 in each PEM cell 18, 20 is balanced on both sides to prevent rupture of the membrane 32. Excess oxygen is vented through the outlet valve 26 to maintain pressure balance between the hydrogen and oxygen sides.

[0019] The passive dual modulation regulator is not limited to the valve assemblies of Figures 3-5 and may include other configurations as desired. For example, as shown in Figures 6-7, the valve assembly may include a valve plug 82 extending from a flexible diaphragm 70 to alignment rods 80 on either side of the flexible diaphragm. In this embodiment, the valve plug 82 is conical and has a frusto-conical geometry for closing off either of the exhaust ports 56, 60. For example, the valve plug 82 may include a 60 degree cone that matches a 60 degree valve seat machined into the concave inner surface of each hemispherical end wall 64.

[0020] Below, a practical example of the hydrogen generation system of FIGS. 1-2 including the passive dual modulation regulator of FIGS. 3-5 is described. The hydrogen generation system included two series connected PEM cells powered by a 100 W solar panel. The passive dual modulation regulator included a valve assembly with a machined brass stem 0.5 inches (12.7 mm) in diameter and 0.625 inches (15.875 mm) long. The stem had internal threads on both ends. The valve assembly also included a brass alignment rod 1.1 inches (27.94 mm) long and 0.25 inches (6.35 mm) in diameter with one end machined to 0.19 inches (4.826 mm) and externally threaded. The alignment rod was threaded onto the brass stem with a rubber angled washer between them. Two such assemblies were coupled to 0.25 inch (6.35 mm) x 28 headless screws that extended through 0.25 inch (6.35 mm) openings in the silicone rubber diaphragm. Two steel 1.5 inch (38.1 mm) fender washers were used on either side of the diaphragm to prevent it from bursting. This hydrogen generation system achieved hydrogen delivery pressures in excess of 200 PSI (approximately 1379 kPa) at flow rates between 320 ml / min and 400 ml / min. In contrast, commercially available hydrogen generators contain hydrogen delivery pressures between 5 and 100 PSI (approximately 34 to 689 kPa) at flow rates of only 160 ml / min, and cost several times the cost of the hydrogen generation system of the present invention. Thus, the present invention provides a commercially viable hydrogen fuel source that can run on renewable energy, such as solar power, and has delivery pressures and flow rates that are significantly improved over those found in existing systems.

[0021] It should be noted that the numerical values ​​in the above examples are illustrative and are not intended to be limiting. For example, the 200 psi in the above examples was selected based on economic and practical considerations because existing propane tanks are typically 200 psi. Hydrogen generation systems may be configured to operate at higher supply pressures, including pressures in excess of 5000 psi, with only an order of magnitude decrease in efficiency.

[0022] The above description is provided for illustrative purposes and should not be construed as an exhaustive description of all embodiments of the present invention, nor should it be construed as limiting the scope of any claims to the specific elements illustrated or described in connection with the present embodiments. References to elements in the singular, such as the use of articles "a," "an," "the," or "said," should not be construed as limiting the element to the singular. Additionally, the use of terms such as "upper," "lower," "upper," and "lower," in describing the embodiments shown in the figures, is intended for clarity of information and should not be construed as limiting the relationship between geometric features of the present invention.

Claims

1. 1. A passive dual modulation regulator, comprising: a first housing section and a second housing section, each of the first housing section and the second housing section including a gas inlet and a gas outlet; a diaphragm clamped along its periphery between the first housing section and the second housing section, a first chamber disposed on a first side of the diaphragm and a second chamber disposed on a second side of the diaphragm; and a valve assembly, the valve assembly including a first valve plug extending through the diaphragm and aligned with a valve seat in the first housing section and a second valve plug aligned with a valve seat in the second housing section, wherein a pressure differential between the first chamber and the second chamber causes the diaphragm to deflect toward an area of ​​lower pressure and the valve assembly narrows and thus seals the gas outlet for the first chamber or the second chamber, equalizing the pressure in the first chamber and the second chamber.

2. 2. The regulator of claim 1, wherein the first housing section includes a first hemispherical end wall and the second housing section includes a second hemispherical end wall.

3. 3. The regulator of claim 2, wherein the gas outlet for the first housing section extends through the first hemispherical end wall and the gas outlet for the second housing section extends through the second hemispherical end wall.

4. 2. The regulator of claim 1, wherein the first housing section and the second housing section each include a flange plate defining the gas inlet for the corresponding housing section.

5. 2. The regulator of claim 1, wherein the first valve plug comprises a first angled washer and the second valve plug comprises a second angled washer.

6. The valve assembly includes: a first alignment rod extending from the first valve plug; a second alignment rod extending from the second valve plug.

7. 2. The regulator of claim 1, wherein the valve assembly includes a first fender washer on a first side of the diaphragm and a second fender washer on a second side of the diaphragm.

8. 2. The regulator of claim 1, wherein the diaphragm and the valve plug are each formed from an elastomeric material.

9. 2. The regulator of claim 1, wherein the diaphragm is gas impermeable and includes a central aperture for the valve assembly.

10. 10. The regulator of claim 9, wherein the valve assembly includes a headless screw extending through the central aperture for attachment to the first and second valve stems.

11. 1. A system for producing hydrogen, comprising: a proton exchange membrane (PEM) cell; an oxygen-water separator for receiving oxygen-containing water from the anode side of the PEM cell and having an outlet; a hydrogen-water separator for receiving hydrogen-containing water from the cathode side of the PEM cell and having an outlet; a passive dual modulation regulator coupled to the outlet of the oxygen-water separator and the outlet of the hydrogen-water separator, the passive dual modulation regulator comprising: a diaphragm clamped between the first housing section and the second housing section; a bidirectional valve assembly comprising a first valve plug extending through the diaphragm and aligned with a valve seat in the first housing section and a second valve plug aligned with a valve seat in the second housing section, wherein a pressure imbalance across the diaphragm causes the diaphragm to deflect toward either the first valve seat or the second valve seat to equalize pressures in the passive dual modulation regulator; and

12. 12. The system of claim 11, further comprising a storage tank in fluid communication with the outlet of the hydrogen-water separator through the passive dual modulation regulator.

13. The system of claim 11 , further comprising a source of distilled or deionized water in fluid communication with the PEM cell.

14. the first housing section includes a first flange and a first hemispherical end wall; and The system of claim 11 , wherein the second housing section comprises a second flange and a second hemispherical end wall.

15. 12. The system of claim 11, wherein the first valve plug comprises a first angled washer and the second valve plug comprises a second angled washer.

16. The bidirectional valve assembly includes: a first alignment rod extending from the first valve plug; a second alignment rod extending from the second valve plug.

17. 12. The system of claim 11, wherein the valve assembly includes a first fender washer on a first side of the diaphragm and a second fender washer on a second side of the diaphragm.

18. The system of claim 11 , wherein the diaphragm and the valve plug are each formed from an elastomeric material.

19. 12. The system of claim 11, further comprising an exhaust valve in fluid communication with the exhaust of the oxygen-water separator through the passive dual modulation regulator.

20. 12. The system of claim 11, wherein the PEM cell is a first PEM cell, and the system further includes a second PEM cell connected in series with the first PEM cell.

Images