Patent Application
20240301575
The invention relates to the field of hydrogen production plant, particularly to a method for producing hydrogen in the hydrogen production plant by using two different types of electrolysis systems. The invention further relates to a hydrogen production plant, to a program element, and to a computer-readable storage medium.
A hydrogen production plant is configured for producing hydrogen. In at least some cases, the hydrogen production plant (HPP) comprises a plurality of so-called “stacks”, e.g. by Nel Hydrogen. During production, the “stacks” and, accordingly, the rectifier modules, which deliver power for the “stacks”, need to be ramped-up and/or ramped-down, for example depending on production requirements and/or the currently available energy for the plant. Thus, it would make sense to use fully controllable rectifier modules (“active” rectifier) for this application, but active rectifier modules may be quite costly. On the other hand, a use of “passive” rectifier modules would be more cost-efficient, but their power output is uncontrolled, which may lead to an undesired behavior of the production plant.
The present disclosure describes a method for producing hydrogen in a hydrogen production plant.
One aspect of the present disclosure relates to a method for producing hydrogen in a hydrogen production plant. The plant comprises a first electrolysis system, comprising an active DC module and at least one first-type electrolyzer, which is configured for producing a first hydrogen output by using a first power from the active DC module, and a second electrolysis system, comprising a passive DC module and at least one second-type electrolyzer, which is configured for producing a second hydrogen output by using a second power from the passive DC module. The method comprises, in a ramp-up phase, increasing the first hydrogen output of the first electrolysis system; and when the first hydrogen output of the first electrolysis system crosses a first predefined hydrogen output threshold, switching on the second electrolysis system, and decreasing the first hydrogen output of the first electrolysis system to the first predefined hydrogen output threshold minus the second hydrogen output, so that an overall hydrogen output of the hydrogen production plant is a sum of the first hydrogen output and the second hydrogen output.
As explained in detail below, the first electrolysis system and the second electrolysis system differ in several aspects and/or features. The first electrolysis system and the second electrolysis system may use the same type of electrolyzer; however, at least in some embodiments, the first-type electrolyzer may be of a different type than the second-type electrolyzer. Each one of the electrolysis systems may comprise one or more electrolyzers. The first-type electrolyzer may get its power from a so-called active DC module, the second-type electrolyzer may get its power from a so-called passive DC module. The passive DC module may use diodes, e.g. high-performance diodes, whereas the active DC module may use controllable rectifiers. Although one embodiment of the hydrogen production plant may have only one first electrolysis system and several second electrolysis systems, alternative embodiments may have a different number of first and second electrolysis systems, for instance only one first electrolysis system and only one second electrolysis system, or several first electrolysis systems and several second electrolysis systems.
A ramp-up phase of HOtotal lasts from t0 to t1. At t1, when reaching or crossing a first predefined hydrogen output threshold HOthres1, the second electrolysis system ES2 is switched on. Also at t1, the first hydrogen output HO1 of the first electrolysis system ES1 is decreased to the first predefined hydrogen output threshold HOthres1 minus the second hydrogen output HO2. As a result, the overall hydrogen output at t1 is kept at (essentially) the same level. In
From t1 to t2, the overall hydrogen output HOtotal is kept unchanged. A ramp-down phase of HOtotal lasts from t2 to t4. At t3, when the first hydrogen output HO1 of the first-type electrolyzer E1 crosses a second predefined hydrogen output threshold HOthres2, the second electrolysis system ES2 is switched off. Also on t3, the first hydrogen output HO1 of the first electrolysis system ES1 is increased to the second predefined hydrogen output threshold HOthres2 plus the second hydrogen output HO2. Since HOthres2 is here greater than zero, the first hydrogen output HO1 is not reduced to zero at t3.
Note that a control of the hydrogen output delivery system bears a risk to produce oscillations of switching on and off the passive DC modules, particularly when the ramping up and down is done around one of the thresholds HOthres1 and HOthres2. This risk may be reduced by a hysteresis strategy. In
In the other direction, after Mp2 was turned on, the power of the active DC module has to fall until Pthres2, before Mp2 is turned off and the active DC module power rises along the arrow “turn off Mp2”. To prevent rapid oscillations between turning on and off passive DC modules, a ΔPH difference is designed. This implies that the width, Pthres1 minus Pthres2 is wider than power of Mp2, and results in ΔPH, equals Pthres1 minus Pthres2 minus power of Mp2. The overall ramp up and down related to time is shown in
The envelope curve HOtotal shows a ramp-up phase between t0 and t5, a constant phase between t5 and t6, and a ramp-down phase between t6 and to. The maximum hydrogen output HO1max of the first electrolysis system (ES11) is shown as dotted line. Each one of the hydrogen outputs HO22 to HO25 is either zero or HO2max; in the example shown, each one of the second hydrogen outputs HO22 to HO25 is the same. In some other embodiments, the value of the single baseload powers may be different for each one of the second hydrogen outputs and/or the second-type electrolyzers.
During the ramp-up phase of the hydrogen production plant, the first hydrogen output HO11 always changes its actual operating point from zero slowly to its maximum hydrogen output HO1max. The first electrolysis system (ES11) must be able to deliver at least the hydrogen output HO2max of one of the second electrolysis systems (ES22 to ES25), i.e. HO1max needs to be greater than or equal to HO2max. As soon as the envelope curve HOtotal reaches, at t1, the HO2max output value, i.e. the first predefined hydrogen output threshold HOthres1, the second electrolysis system (ES22), is switched on, thus producing at t1 a hydrogen output HO22=HO2max. Also at t1, the first hydrogen output HO11 of the first electrolysis system (ES11) is decreased to the predefined hydrogen output threshold minus the second hydrogen output, i.e. to an output value of HOthres1−HO22. Since, in the case shown, HOthres1=HO22, the hydrogen output HO22 is reduced to zero at t1. Note that, for real-world electrolysis systems, the switching on of the second electrolysis system and/or the decreasing the first hydrogen output of the first electrolysis system may take a while, e.g. a few minutes, caused, e.g., by internal time constants of the electrolysis systems. On the electronics' side, there may be a much faster reaction speed, e.g. due to the fast control speed of active rectifiers based on power electronics.
This procedure is repeated at t2, t3 and t4, thus leading to a linear hydrogen output increase of the overall hydrogen output HOtotal. The ramp-up of HOtotal is continued until t5, between t4 and t5 only caused by an output increase of HO11. During the constant phase of HOtotal, i.e. between t5 and t6, no changes need to be done by the control units of the active and passive DC modules . . . . Possibly except compensating fluctuations coming from the grid and influencing the passive power supply (not shown here).
During the ramp-down phase of the hydrogen production plant, starting with to, the first electrolysis system (ES11) decreases (in this embodiment) its hydrogen output HO11 to HOthres2, which is zero in this embodiment, until t7. At t7, a second predefined hydrogen output threshold HOthres2 is reached. At t7, the second electrolysis system (ES22), is switched off. Also at t7, the first hydrogen output HO11 of the first electrolysis system (ES11) is increased to the second predefined hydrogen output threshold plus the second hydrogen output, i.e. to an output value of HOthres2+HO22. Then, the ramp-down of the overall hydrogen output HOtotal continues until to. At t8 and t9, HO23 and HO24 are turned off, thus reducing their hydrogen output to zero. From to, the overall power Ptotal is kept constant, and the overall hydrogen output HOtotal is delivered by the modules ES11 and ES22.
Furthermore, the defined control of the stack temperature could be used to control the production of hydrogen in the second electrolysis systems (e.g. using passive rectifier), and therefore also the grid power consumption.
The ramp-up phase starts at a step 106, where a first hydrogen output of the active DC module Ma is increased. A step 108 checks if the power output ramping-up of the of the active DC module Ma crosses (or just has crossed) a first predefined hydrogen output threshold HOthres1. If yes, the second electrolysis system ES2 is switched on (step 110), and the first hydrogen output HO1 of the first electrolysis system ES1 is decreased to the first predefined hydrogen output threshold HOthres1 minus the second hydrogen output HO2 (step 112). In (optional) cases when a plurality of second electrolysis systems ES2 are in the hydrogen production plant, the ramping-up may be continued, i.e. this is checked in step 114, and is branched to step 106, again. Otherwise, the ramp-up phase ends at a step 116.
The ramp-down phase starts at a step 118, where a first power output of the first electrolysis system ES1 is decreased. A step 120 checks if the ramping-down continues (in step 118), or if it crosses (or just has crossed) a predefined second hydrogen threshold HOthres2. If yes, the second electrolysis system ES2 is switched off (step 122), and the first hydrogen output HO1 of the first electrolysis system ES1 is increased to the second predefined hydrogen output threshold HOthres2 plus the second hydrogen output HO2. In (optional) cases when a plurality of second electrolysis systems ES2 are in the hydrogen production plant, the ramping-down may be continued, i.e. this is checked in step 126, and is branched to step 106, again. Otherwise, the ramp-down phase ends at a step 128.
The so-called passive DC module may comprise rectifiers that use diodes, e.g. high-performance diodes, for rectifying an AC input. The active DC module may use SCRs (Silicon Controlled Rectifiers, or thyristors), IGBTs (Insulated-Gate Bipolar Transistors) and/or other types of controllable rectifiers for rectifying the AC input. Hence, costs for an active DC module may be higher, e.g. caused by more expensive components (e.g. for the rectifiers) and by an additional effort for controlling the SCRs. Hence, the method described above and/or below, where two types of electrolysis systems are used, makes the overall hydrogen output of the hydrogen production plant well controllable, but may reduce the cost for its components significantly.
The power delivery system of the plant comprises several DC modules each connected to one or more electrolyzer stacks (e.g. E11a and E11b in
The electrolysis systems may get its power-depending on its specified power output-from, e.g., a so-called “medium voltage grid” (MV grid), typically with voltages from about 1 kV to about 50 kV. Alternatively, a “high voltage grid” (HV grid) may be used, e.g. for very large hydrogen production plant. Note that the method described above and/or below also works for voltages below 1 kV. Thus, at least some of the methods described above and/or below may be applied to a broad range of AC sources, e.g. having one phase, three phase or any other AC source.
When running the hydrogen production plant, there may be a need to ramp-up the hydrogen production, e.g. caused by a higher demand for the overall hydrogen output and/or caused by more currently available energy for the plant. This may particularly the case for a so-called “green hydrogen production plant”, which may get its energy, e.g., from solar panels and/or wind-driven generators. Hence, the “stacks” and, accordingly, the rectifier modules, which deliver power for the “stacks”, need to be ramped-up. There may be also a need for ramping-down the hydrogen production, and/or for running the hydrogen production plant in a ramp-up and ramp-down mode. Thus, during production, the hydrogen production plant may be in a constant phase, in a ramp-up phase, or in a ramp-down phase. In the constant phase, no control interventions may be necessary. Also during the constant phase, the control system may still react on grid voltage fluctuations, which may influence the power supplied, e.g., by the passive DC modules, and/or on hydrogen output changes, e.g. caused by temperature or other variations in the stacks.
In the ramp-up phase, the overall hydrogen output needs to be increased. For this, the first hydrogen output of the first electrolysis system is increased, up to a first predefined hydrogen output threshold. When the first hydrogen output crosses the first predefined hydrogen output threshold, the second electrolysis system can be switched on. For keeping, in this transition phase, the overall hydrogen output at the same level, the first hydrogen output of the first electrolysis system is decreased to the first predefined hydrogen output threshold minus the second hydrogen output. This may include zero hydrogen output of the first electrolysis system (at least at this level), depending on the definition of the “first predefined hydrogen output threshold” and of the “second hydrogen output”. In at least some cases, the second electrolysis system may be operated on two levels only, i.e. at zero power or at a maximum power, for example because the diodes are not controllable. In at least some cases, the second electrolysis system may comprise a device—e.g. a tap changer-that is configured for changing the second power of the passive DC module, which is the electrical power input for the second-type electrolyzer, thus changing the second hydrogen output.
It may be noted that the (first as well as the second) predefined hydrogen output threshold may not necessarily be a fixed threshold, but may be varied, depending on several influencing factors, such as power level of the plant's input power, degradation of the modules, and/or further factors.
For real-world electrolysis systems, the switching on of the second electrolysis system and/or the decreasing the first hydrogen output of the first electrolysis system may take a while, e.g. more than 1 min, more than 5 min, more than 10 min, caused, e.g., by internal time constants (or “inertia”) of the electrolysis systems. It may make sense to consider these time constants in the control module of the hydrogen production plant.
It may be advantageous that the method described above and/or below may combine benefits of active and passive DC modules. Generally, a benefit of having a passive rectifier configuration, i.e. a diode-based configuration of the rectifier as described, is that a diode rectifier creates substantially less harmonics on both the DC-side and on the AC-side and, hence, requires less harmonics-filters and/or control effort to achieve a certain voltage and/or current quality. Furthermore, a passive rectifier needs no control units, because it simply rectifies the input voltage and therefore needs no drivers for the semiconductors; this may result in higher mean time between failures (MTBF) as well as in fewer failures of the components. Additionally, further cost savings may be achieved, because some components-i.e. a control system, harmonic filters, semiconductor drivers, etc.—are less costly, or simply not required for passive DC modules. Moreover, in most cases passive components are cheaper. The active DC modules, on the other hand, are fully controllable, but may require further components and may be quite costly. Hence, the method described above and/or below may combine at least some of their benefits, leading to well-controllable and cost-efficient hydrogen production plants.
In various embodiments, the method further comprises the steps of: In a ramp-down phase, decreasing the first hydrogen output of the first electrolysis system; and when the first hydrogen output of the first-type electrolyzer crosses a second predefined hydrogen output threshold, switching off the second electrolysis system, and increasing the first hydrogen output of the first electrolysis system to the second predefined hydrogen output threshold plus the second hydrogen output. The ramp-down phase may be controlled in a quite analogous way than the ramp-up phase, thus leading to a consistent overall control of the hydrogen production, with positive effects on controllability and/or maintenance. Moreover, the analogous way of controlling the ramp-down phase may open up further possibilities, e.g. a control mechanism that comprises a hysteresis.
In various embodiments, the first and/or the second predefined hydrogen output threshold is greater than or equal to the second hydrogen output. This may contribute to a better controllability of the overall system.
In various embodiments, the first predefined hydrogen output threshold is higher, e.g. 10% higher, 20% higher, 30% higher, 50% higher, 70% higher, 100% higher, 150% higher, 200% higher, than the second hydrogen output, and/or the second predefined hydrogen output threshold is higher than zero and/or lower than the second hydrogen output.
In various embodiments, the first predefined hydrogen output threshold minus the second electrolyzer output is greater than or equal to the second predefined hydrogen output threshold. This feature enables a control that comprises a hysteresis. This may advantageously lead to reducing or even preventing an effect of fast switching on and off (“oscillations”) the second electrolysis system around certain points, e.g. around the first and/or the second predefined hydrogen output threshold. Since switching on and off the second electrolysis system may, in at least some cases, lead to stress on some components of the electrolysis systems, reducing the number of on-and-off-switching may lead to higher reliability of the systems and/or longer maintenance intervals.
In various embodiments, the hydrogen production plant comprises a plurality, N2, of second electrolysis systems, so that the overall hydrogen output of the hydrogen production plant is a sum of the first hydrogen output plus a sum of the N2 second maximum hydrogen outputs. Such systems may be even very cost-effective, because far less (e.g. only one) first electrolysis system is needed, whereas a plurality of-less expensive-second electrolysis system may be used.
The second electrolysis systems may have different performances, operation range, efficiency, cost, lifetime and/or different manufacturers. However, in at least some embodiments, each one of the N2 second electrolysis systems, and/or of the second-type electrolyzers, may have essentially the same maximum second hydrogen output.
In some embodiments, the hydrogen production plant comprises a plurality, N1, of first electrolysis systems. This may, e.g., contribute to a higher power of the first electrolysis system. Additionally or as an alternative, this may be used to implement a redundancy concept of the first electrolysis systems, for example a warm redundancy concept.
In various embodiments, the first-type electrolyzer is designed as a polymer electrolyte membrane, PEM, electrolysis system, and/or the second-type electrolyzer is designed as an alkaline water electrolysis system. This selection may support the characteristics of the first or the second electrolysis system, respectively.
In some embodiments, the passive DC module can be operated at zero power or at a maximum power. This may be a highly cost-effective DC module, because it only uses diodes for rectifying and does not need further components for controlling the input power of the passive DC module.
In some embodiments, the passive DC module can be operated at zero power, at the maximum power, or at a low power, and/or the passive DC module can be operated at three or more power levels, particularly by means of a tap changer. This provides a higher degree of flexibility for the passive DC modules, wherein the diodes for rectifying still can be used. In all these embodiments—may it have two, three or even more power levels—, the second hydrogen output can be produced by using the second power from the passive DC module at any one of the above power levels except zero.
In various embodiments, the first hydrogen output is a function of the first power from the active DC module, and of a temperature and a pressure of the at least one first-type electrolyzer, and/or the second hydrogen output is a function of the second power from the passive DC module, and of a temperature and a pressure of the at least one second-type electrolyzer. Considering these dependencies may lead to an improved controlling of the plant, particularly of the electrolyzers. Additionally or as an alternative, the controlling may consider influencing factors like heat cycling and/or cooling set-points, which may lead to less degradation of the electrolyzers and/or the electrolysis systems
In various embodiments, the first hydrogen output is a function of a degradation of the first electrolysis system, and/or the second hydrogen output is a function of a degradation of the second electrolysis system. Considering these dependencies may lead to an improved controlling of the plant, particularly of the electrolyzers.
An aspect relates to a hydrogen production plant, comprising: a first electrolysis system, comprising an active DC module and at least one first-type electrolyzer, which is configured for producing a first hydrogen output by using a first power from the active DC module, a second electrolysis system, comprising a passive DC module and at least one second-type electrolyzer, which is configured for producing a second hydrogen output by using a second power from the passive DC module, wherein a maximum of the second hydrogen output is less than or equal to a maximum of the first hydrogen output, and a control module, configured for controlling the passive DC module and the active DC module according to a method as described above and/or below.
In various embodiments, the controlling the passive DC module and the active DC module is dependent on a requested overall hydrogen output of the hydrogen production plant, and/or the controlling the passive DC module and the active DC module is dependent on an available power from a power source, which delivers a sum of the first power for the active DC module and the second power for the passive DC module. Shortly spoken, the controlling may be driven by an output demand, and/or by input factors. The input factors may, for instance, take into account that the input may fluctuate on a long-term or mid-term range, e.g. caused by the energy source (solar or wind power), and/or on a short-term range main, for example power fluctuations.
In various embodiments, the passive DC module comprises uncontrolled rectifiers, and/or the active DC module comprises controlled rectifiers. The uncontrolled rectifiers may use rectifying diodes, e.g. high-performance diodes, for rectifying an AC input. The active DC module may use SCRs (Silicon Controlled Rectifiers, or thyristors), IGBTs (Insulated-Gate Bipolar Transistors) and/or other types of controllable rectifiers for rectifying the AC input.
An aspect relates to a computer program product comprising instructions, which, when the program is executed by a control module of a hydrogen production plant and/or on another processing unit, cause the control module and/or the processing unit to carry out the method as described above and/or below.
An aspect relates to a computer-readable storage medium where a computer program or a computer program product as described above is stored on.
All references, including publications, patent applications, and patents, cited herein are hereby incorporated by reference to the same extent as if each reference were individually and specifically indicated to be incorporated by reference and were set forth in its entirety herein.
The use of the terms “a” and “an” and “the” and “at least one” and similar referents in the context of describing the invention (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. The use of the term “at least one” followed by a list of one or more items (for example, “at least one of A and B”) is to be construed to mean one item selected from the listed items (A or B) or any combination of two or more of the listed items (A and B), unless otherwise indicated herein or clearly contradicted by context. The terms “comprising,” “having,” “including,” and “containing” are to be construed as open-ended terms (i.e., meaning “including, but not limited to,”) unless otherwise noted. Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided herein, is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention.
Preferred embodiments of this invention are described herein, including the best mode known to the inventors for carrying out the invention. Variations of those preferred embodiments may become apparent to those of ordinary skill in the art upon reading the foregoing description. The inventors expect skilled artisans to employ such variations as appropriate, and the inventors intend for the invention to be practiced otherwise than as specifically described herein. Accordingly, this invention includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the invention unless otherwise indicated herein or otherwise clearly contradicted by context.
| Number | Date | Country | Kind |
|---|---|---|---|
| 21209367.8 | Nov 2021 | EP | regional |
The instant application claims priority to International Patent Application No. PCT/EP2022/081059, filed Nov. 8, 2022, and to European Patent Application No. 21209367.8, filed Nov. 19, 2021, each of which is incorporated herein in its entirety by reference.
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/EP2022/081059 | Nov 2022 | WO |
| Child | 18667600 | US |
