Gas pressure balancing system for electrolysis systems

Abstract

A pressure regulation apparatus comprising a dome-loaded back pressure regulator having a dome, an inlet port configured to receive process fluid from a process pressure source, an outlet port, and a reference port in fluid communication with the dome. The apparatus includes a mechanical pilot valve having a diaphragm with a process side and a reference side, wherein the process side is in fluid communication with the process pressure source, and wherein the mechanical pilot valve includes a valve element and seat configured to modulate gas flow. A pressurized conduit connects the mechanical pilot valve to the dome of the back pressure regulator. A bleed orifice disposed in the pressurized conduit translates varying flow rate from the mechanical pilot valve into a pressure signal for the dome. A reference pressure source is in fluid communication with the reference side of the mechanical pilot valve.

Description

GAS PRESSURE BALANCING SYSTEM FOR ELECTROLYSIS SYSTEMSFIELD OF THE INVENTION

[0001] The present invention relates to pressure regulation, and more particularly to a diaphragm-type regulator with a mechanical pilot.BACKGROUND OF THE INVENTION

[0002] Electrolysis systems often require pressure balancing of two gases as part of level control of the gas / liquid interfaces due to the shared liquid source.

[0003] Back pressure regulators are often used to control gas pressure such that the level control of the liquids and the base pressure control of the system is maintained. In alkaline electrolysis systems, the manufacturers of separation membranes require tight pressure balance between the H2 and 02 sides, with ideal targets typically stated in the 10-50 mbar range (to prevent gas crossover), and absolute maximum limits typically in the 100-200 mbar range (also to prevent membrane damage).

[0004] Direct diaphragm sealing back pressure regulators with multiple orifices and dome loading, such as are offered by Equilibar of Fletcher, NC are often used in electrolysis systems due to the fast response time and the wider range of Valve Coefficient that is available (typically much higher than the 100: 1 turndown ratio with many solutions). A simplified diagram of this type of back pressure regulator is shown in FIG. 1.

[0005] Back pressure regulator 1 (alternative referred to as "BPR" herein) includes a body 2 including a process surface 6. A diaphragm 8 (also referred to interchangeably herein as a membrane) made of flexible material such as PTFE or fiber reinforced PTFE sheeting is disposed adjacent to the process surface 6. The diaphragm 8 has opposed sides referred to as reference and process sides, with the process side facing the process surface 6. The perimeter of the diaphragm 8 is securedagainst the body 2 by a reference housing 10 which is attached to the body 2.Collectively, a space defined between the diaphragm 8 and the reference housing 10 is referred to as a "dome" 1'. A reference port 12 is formed in the reference housing 10 and is disposed in fluid communication with the reference side of the diaphragm 8. Inlet and outlet ports 14 and 16 respectively, are also formed in the body 2. At least one inlet orifice 18 is disposed in fluid communication with the inlet port 14 and the process surface 6. At least one outlet orifice 20 is disposed in fluid communication with the outlet port 16 and the process surface 6. The outlet orifices 20 are small holes or small openings.

[0006] Another main advantage of using specialized dome-loaded BPRs is that there is very tight agreement between the pilot pressure and the process fluid inlet pressure. "OverPressure" will be used to define the differential pressure as Inlet -Pilot pressure, and % OverPressure will be OverPressure divided by Pilot Pressure. Whereas standard commercial models of these BPRs have OverPressure in the range of 2-4%, custom variants of these BPRs are available that can provide much more precision, down to 0.2 and even 0.1% OverPressure. These highly precise models are useful in the design of electrolysis systems.

[0007] The use of these sensitive BPRs is highly useful in the design of pressure control during the normal production process (for the reasons discussed above).Another key application for pressure control is that of "Emergency Shutdown" systems (ESD), whereby a separate pressure control system is provided to handle the safe depressurization of the system in the event of a failure of a key component, loss of electrical power or control, or the failure of the primary production pressure control system. Such ESD applications are becoming a standard feature of modern large-scale alkaline electrolysis systems.

[0008] For production pressure control systems, the use of electronic gas pressure regulators (EPR) is a convenient method of controlling the pilot pressure to the BPR. By monitoring key variable such as production gas differential pressure (H2 vs 02) and liquid level, the control system can steer the gas pressure by making slight adjustments (typically via PID control) to the EPR. The pilot pressure steers thesensitive BPR, which translates the slight changes to the gas pressure control.

[0009] FIG. 2 shows an implementation of such a production system, including a PEM electrolysis stack "S", water source "W", back pressure regulators "B", a PID / process controller "C", pressure transducers "PT", and electropneumatic controllers "E / P" . Such systems are capable of controlling differential gas pressures into the range < 10 mbar or < 0.1% of overall system pressure.

[0010] Emergency Shutdown Systems for Electrolysis Systems

[0011] With the increased demand for ESD systems that do not rely on computer or electrical control, there is a need to improve the sensitivity of these BPR systems to keep the differential pressure in the range of < 0.5%, and typically < 0.3% and in extreme cases down to 0.1% of overall system pressure.

[0012] A preferred method of using these precision BPRs for ESD is to utilize an inert gas pressure tank to pilot both the 02 and H2 BPR. The inert gas tank is allowed to decay in pressure during an ESD event, typically by blocking the supply pressure and allowing a bleed orifice to decay the tank, or by opening up a valve to a bleed orifice. However, standard precision BPRs are not suitable for using this method because varying OverPressure between the two BPRs would quickly exceed the target membrane dP for several reasons:

[0013] -Varying gas molecular weight (MW) between 02 and H2, including inert gas mixtures during start-up

[0014] -Varying pipe geometry

[0015] -Operational disruptions that may include closure of only one production gas valve

[0016] One method is to design the BPRs with extreme precision ratios, with very generous sizing ratios and with modified valve geometry. These BPRs have been able to have OverPressure ratios below 0.2% and < 0.15%. Note that there is a difference between membrane dP (02 vs H2) and BPR OverPressure. However, if thepiping and BPRs are properly sized, then two BPRs with a common pilot will be able to maintain very tight membrane dP if the OverPressures are very tight and in a similar range as the desired dP.

[0017] A typical schematic for this ESD system with common pilot is shown in FIG. 3 , including an alkaline electrolyser "A", back pressure regulators "B", and an N2 volume.

[0018] Need for Closed Loop Control in ESD Systems

[0019] The schematics shown in FIGS. 2 and 3 have been demonstrated as effective and precise for certain applications. However, with the advent of larger and larger electrolysis systems, and at higher pressures, the required valve size becomes large, cumbersome and expensive. For example, an electrolyser manufacturer increasing their pressure from < 20 bar to > 30 bar will typically maintain their target membrane dP in the ranges stated above. This means that extreme precision ratios are increased to and below 0.1% OverPressure. At the higher pressures, the valves much be heavier, and the Pressure Equipment Directive assigns higher quality control procedures for large, high pressure valves. Therefore, there is a need to develop an alternative method of controlling ESD that meets the following requirements:

[0020] -No electrical controls

[0021] -Very high precision ratios to < 0.1% OverPressure and to 0.1% membrane dP

[0022] -Is able to use commercial precision back pressure regulators with standard sizes

[0023] -Does not allow H2 and 02 to be in contact across a single diaphragm or seal

[0024] -Does not allow for the continuous bleed of any process or inert gas until initiation of an ESD event

[0025] Closed Loop Mechanical Pilot with Bleed Gas Control for ESD SystemsBRIEF SUMMARY OF THE INVENTION

[0026] According to an aspect of the present disclosure, a pressure regulation apparatus is provided. The apparatus comprises a dome-loaded back pressure regulator having a dome, an inlet port configured to receive process fluid from a process pressure source, an outlet port, and a reference port in fluid communication with the dome. The apparatus further comprises a mechanical pilot valve having a diaphragm with a process side and a reference side. The process side is in fluid communication with the process pressure source. The mechanical pilot valve includes a valve element and a seat configured to modulate flow of a gas. A pressurized conduit connects the mechanical pilot valve to the dome of the back pressure regulator. A bleed orifice is disposed in the pressurized conduit and configured to translate a varying flow rate from the mechanical pilot valve into a pressure signal for the dome of the back pressure regulator. A reference pressure source is in fluid communication with the reference side of the mechanical pilot valve.

[0027] According to other aspects of the present disclosure, the pressure regulation apparatus may include one or more of the following features. The apparatus may further comprise a vent valve disposed downstream of the bleed orifice and configured to bleed down pressure supplied by the reference pressure source in an open position. The vent valve may be a power-to-close, fail-to-open valve configured to provide automatic depressurization in the event of a power failure. The reference pressure source may be a tank containing a fixed volume of inert gas coupled to the reference port of the back pressure regulator through a rate setting orifice. The inert gas may be nitrogen. The mechanical pilot valve may further comprise a platen connected to the diaphragm. The valve element may comprise a valve stem having a groove formed therein to elongate an active valve stroke length of the mechanical pilot valve. The groove may incorporate shaping selected from the group consisting of ramps, tapers, and notches. The mechanical pilot valve may be constructed without sliding seals. The reference pressure source may be an electronic pressure regulator connected to the mechanical pilot valve and configured to provide a target pressure set-point, wherein the electronic pressure regulator is supplied by a pressure source. A ratio of a pilot valve seat effective cross-sectional area to a total free diaphragm areaof the mechanical pilot valve may be less than 0.1%.

[0028] According to another aspect of the present disclosure, a method of regulating pressure in a process system is provided. The method comprises sensing a process pressure from a process pressure source on a process side of a diaphragm of a mechanical pilot valve. The method further comprises sensing a reference pressure on a reference side of the diaphragm of the mechanical pilot valve. The method comprises modulating, by the mechanical pilot valve, a flow of inert gas based on a pressure differential across the diaphragm. The method comprises directing the modulated flow of inert gas through a pressurized conduit to a dome of a dome-loaded back pressure regulator. The method comprises converting the modulated flow of inert gas into a dome pressure signal using a bleed orifice disposed in the pressurized conduit. The method comprises regulating, by the back pressure regulator, a pressure of the process tank based on the dome pressure signal. According to other aspects of the present disclosure, the method may include one or more of the following features. The method may further comprise opening a vent valve disposed downstream of the bleed orifice upon initiation of an emergency shutdown event to depressurize the process system. The vent valve may be a power-to-close, fail-to-open valve, and opening the vent valve may comprise automatically opening the vent valve in response to a power failure. The method may further comprise providing a target pressure set-point to the mechanical pilot valve using an electronic pressure regulator supplied by a pressure source.BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The invention may be best understood by reference to the following description taken in conjunction with the accompanying drawing figures in which:

[0030] FIG. 1 is a schematic cross-sectional view of a prior art pressure back pressure regulator;

[0031] FIG. 2 is a block diagram of a prior art electrolysis system having back pressure regulators connected thereto;

[0032] FIG. 3 is a block diagram of another prior art electrolysis system having back pressure regulators connected thereto;

[0033] FIG. 4 is a block diagram of a back pressure regulator with a mechanical pilot, connected to a fluid system;

[0034] FIG. 5 is a block diagram showing an alternate configuration of the system of FIG. 4; and

[0035] FIG. 6 is a schematic side view of a valve element.DETAILED DESCRIPTION OF THE INVENTION

[0036] Closed Loop Mechanical Pilot with Bleed Gas Control for ESD Systems

[0037] Described herein is a sensitive closed-loop mechanical pilot valve which senses the process tank pressure on one side of a diaphragm against an inert gas pilot pressure on the other side of the diaphragm. The pilot is capable of steering a back pressure regulator to maintain a Remote Sense pressure (connected to the process tank or membrane conduits) to a very tight agreement with an inert gas pilot source (as discussed above). This steering is done by lowering the pilot pressure slightly to compensate for the friction and "build" (OverPressure) inside of the BPR.

[0038] FIG. 4 shows an example system 100 incorporating the mechanical pilot. A process pressure source such as a process tank 102 (typically containing 02 or H2, but could be others) is connected to the inlet port 14 of a dome-loaded back pressure regulator 1, and the outlet port 16 is vented to atmosphere.

[0039] The process tank 102 is also is used to provide a remote sense signal to a mechanical pilot valve 104 which includes a diaphragm 106, platen 108, valve element 110, and seat 112. The connection could be in common with the inlet to the back pressure regulator 1, but the location should avoid nearly all friction losses (and pipe entrance losses are very significant in highly precise systems such as this).

[0040] A source containing a fixed volume of gas, such as tank 114 containing gas, preferably inert gas such as nitrogen (N2), is coupled to the reference port 12 ofthe regulator 1, through a rate setting orifice 116.

[0041] Any pressure differential (or change in pressure differential) across the diaphragm 8 of the regulator 1 is transferred to movement in the mechanical pilot valve 102 which adjusts the inert gas flow into a pressurized conduit 118 connected to the dome 1' of the regulator 1. A bleed orifice (or similar metering valve) 120 is present to translate the varying flow rate from the mechanical pilot control valve 104 into a pressure. The pilot valve system natively finds the correct pilot pressure for the dome of the pressure regulator 1 that balances the remote sense pressure to be nearly equal to the tank pressure.

[0042] To avoid wasted pilot gas, said bleed orifice 120 is prevented from flowing by a vent valve (or similar blocking method) 122 which is only opened by the initiation of an ESD event. A preferred vent valve style is power-to-close, fail-to-open, which provides for automatic de-pressurization in the event of a power failure.

[0043] Alternatively, the pilot bleed orifice 120 could discharge directly to the atmosphere if waste of inert gas is not a concern.

[0044] The ESD vent valve 122 should be sized adequately to easily exceed the capacity of all the orifices feeding into it.

[0045] In the illustrated example, both orifices 116 and 120 are shown being tied together upstream of vent valve 122. Alternatively, these orifices could be separately vented to atmosphere.

[0046] Alternate Embodiment: Closed-Loop Mechanical Pilot for Steady State Pressure Control

[0047] An alternate use for the mechanical pilot is to replace the need for an external PID system to keep the pressure of an electrolysis process very close to the target pressure. As shown in the modified system 200 of FIG. 5, an electronic pressure regulator (EPR) (or other suitable manual pressure regulator if no automation is required) 130, supplied by a pressure source 132 such as inert gas supply or shop air, can be used to provide the target pressure set-point to the mechanical closed-looppilot valve 104. In this system, the pilot serves to keep the inlet of the pressure regulator 1 very close to target system pressure, replacing the external PID.

[0048] In FIG. 5, an optional vent valve 122 is shown to prevent inert gas leakage when no flow is required through the pressure regulator 1.

[0049] In one optional configuration, not illustrated, the parallel process tank may share in the use of the common pilot system (including pilot bleed vents and vent valves).

[0050] Mechanical Valve Design

[0051] The mechanical pilot control valve 104 contains a valve seat 112 which decreases the pilot control valve flow when the diaphragm 106 moves in the direction away from the process side, such as when the process gas exceeds the pilot pressure, or when the process gas pressure increases relative to the pilot pressure. With this decrease in pilot flow towards the pressure regulator dome 1', the bleed orifice equilibrates the conduit to a lower pressure, which steers the pressure regulator 1 to lower the control pressure of the process gas.

[0052] Mechanical valve features

[0053] A preferred embodiment is to design valve 104 with no sliding seals to improve the precision (avoid "stiction" or friction). Because of the presence of the bleed orifice 120 and the vent valve 122, there is no need for complete shut-off of the pilot control valve 104 under any circumstance. Therefore, the mechanical pilot can be constructed with a design avoiding friction.

[0054] In one embodiment (see FIG. 6), the valve 104 is provided with a valve stem 300 that is cylindrical with a small groove 302 machined into the stem to elongate the active valve stroke length. Said elongation can improve system tuning and prevent cycling in some circumstances. (Elongating the control valve stroke length is a mechanical analog to adjusting the proportional gain in PID control systems). The groove 302 may incorporate shaping such as ramps, tapers, or notches to modify its performance.

[0055] Altering the volume of the pilot pressure conduit (the volume of gas that is connected to the dome of the BPR) is another means of controlling the tuning of the system and preventing oscillations. Increasing the pilot volume is a mechanical analogue to slowing the integral action of a PID controller.

[0056] In simpler implementations, the valve seat could be a simpler or more traditional cone shape, such as in more traditional globe control valves. For convenience, FIG. 6 shows only a cone indicating the sense of the control, but not the detailed method of the valve seat design.

[0057] The capacity of the Pilot Vent Valve should have a maximum capacity (Valve Coefficient) far in excess of the capacity that of the Pilot Bleed Orifice so that the system is capable of generating a pilot pressure nearly equal to the N2 Tank pressure.

[0058] Use of bias springs or gravity

[0059] While the mechanical pilot valve functions without the use of springs, an optional implementation is to add a small biasing feature to allow for slight adjustments to the pressure balance. The insertion of a small spring to bias the force on the diaphragm (not shown) would provide for said bias. Said spring could easily be adjusted using an adjustment screw, as is common for mechanical pressure regulators.

[0060] Another method of providing a bias is to orient the valve in a vertical axis such that the movement of the diaphragm is aligned with the force of gravity. This will provide a small pressure bias which can be useful to system designers. The diaphragm platen (shown as rectangle in center of diaphragm) could be enlarged to have more mass, thereby altering the gravity bias.

[0061] One use of said bias is to minimize the leak flow from the BPR during normal production, highly precise BPRs sometimes require a slightly negative OverPressure to close off flow adequately.

[0062] Performance and Valve System Design

[0063] Closed-loop remote sense pilots are demonstrated to dramatically reduce the residual error (defined as the dP between the target pressure and the remote sense pressure). One way to look at the performance is the "residual error %" divided by the total valve system dP (Target pressure - downstream valve pressure [typically 0 gauge pressure],

[0064] Similar closed-loop pilot systems have demonstrated residual error % down to 0.1% and even down to 0.02%. For example, controlling a 55 bar gas system, the equilibrium was maintained within 11 mbar. However, a key design consideration how fast the pilot pressure needs to change to adapt to changing process parameters. To adapt very quickly changing parameters, both the control valve and bleed orifice need to be sized larger than for slower reacting systems. The size of the control valve orifice must be extremely small, as the area ratio between the control valve seat area and the mechanical pilot diaphragm area is the primary factor controlling this residual error %.

[0065] Additional factors would be stiffness of diaphragm (which limits free movement) and presence of any friction or spring forces. Practical design considerations, including economy of valve body size, will tend to limit the precision in real-world applications.

[0066] In a preferred embodiment, the ratio of the (pilot valve seat effective cross sectional area [the area generating the pressure thrust inside the valve seat]) to the (total free diaphragm area) is less that 0.1% and in a highly preferred embodiment the ratio is less than 0.02%.

[0067] All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and / or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and / or steps are mutually exclusive.

[0068] Each feature disclosed in this specification (including any accompanying claims, abstract and drawings) may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unlessexpressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

[0069] The invention is not restricted to the details of the foregoing embodiment(s). The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

Claims

WHAT IS CLAIMED IS:

1. A pressure regulation apparatus, comprising:a dome-loaded back pressure regulator having a dome, an inlet port configured to receive process fluid from a process pressure source, an outlet port, and a reference port in fluid communication with the dome;a mechanical pilot valve having a diaphragm with a process side and a reference side, wherein the process side is in fluid communication with the process pressure source, and wherein the mechanical pilot valve includes a valve element and a seat configured to modulate flow of a gas;a pressurized conduit connecting the mechanical pilot valve to the dome of the back pressure regulator;a bleed orifice disposed in the pressurized conduit and configured to translate a varying flow rate from the mechanical pilot valve into a pressure signal for the dome of the back pressure regulator; anda reference pressure source in fluid communication with the reference side of the mechanical pilot valve.

2. The pressure regulation apparatus of claim 1, further comprising a vent valve disposed downstream of the bleed orifice and configured to bleed down pressure supplied by the reference pressure source in an open position.

3. The pressure regulation apparatus of claim 2, wherein the vent valve is a power-to-close, fail-to-open valve configured to provide automatic depressurization in the event of a power failure.

4. The pressure regulation apparatus of claim 1, wherein the reference pressure source is a tank containing a fixed volume of inert gas coupled to the reference port of the back pressure regulator through a rate setting orifice.

5. The pressure regulation apparatus of claim 4, wherein the inert gas is nitrogen.

6. The pressure regulation apparatus of claim 1, wherein the mechanical pilot valve further comprises a platen connected to the diaphragm.

7. The pressure regulation apparatus of claim 1, wherein the valve element comprises a valve stem having a groove formed therein to elongate an active valve stroke length of the mechanical pilot valve.

8. The pressure regulation apparatus of claim 7, wherein the groove incorporates shaping selected from the group consisting of ramps, tapers, and notches.

9. The pressure regulation apparatus of claim 1, wherein the mechanical pilot valve is constructed without sliding seals.

10. The pressure regulation apparatus of claim 1, wherein the reference pressure source is an electronic pressure regulator connected to the mechanical pilot valve and configured to provide a target pressure set-point, wherein the electronic pressure regulator is supplied by a pressure source.

11. The pressure regulation apparatus of claim 1, wherein a ratio of a pilot valve seat effective cross-sectional area to a total free diaphragm area of the mechanical pilot valve is less than 0.1%.

12. A method of regulating pressure in a process system, comprising: sensing a process pressure from a process is your source on a process side of a diaphragm of a mechanical pilot valve;sensing a reference pressure on a reference side of the diaphragm of the mechanical pilot valve;modulating, by the mechanical pilot valve, a flow of inert gas based on a pressure differential across the diaphragm;directing the modulated flow of inert gas through a pressurized conduit to a dome of a dome-loaded back pressure regulator;converting the modulated flow of inert gas into a dome pressure signal using a bleed orifice disposed in the pressurized conduit; andregulating, by the back pressure regulator, a pressure of the process tank based on the dome pressure signal.

13. The method of claim 12, further comprising opening a vent valve disposed downstream of the bleed orifice upon initiation of an emergency shutdown event to depressurize the process system.

14. The method of claim 13, wherein the vent valve is a power-to-close, fail-to-open valve, and wherein opening the vent valve comprises automatically opening the vent valve in response to a power failure.

15. The method of claim 12, further comprising providing a target pressure set-point to the mechanical pilot valve using an electronic pressure regulator supplied by a pressure source.

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