PLANT AND METHOD FOR PRODUCING LIQUEFIED HYDROGEN

Abstract

The invention relates to a plant and a method for producing liquefied hydrogen comprising a hydrogen gas generator, a liquefier, a feed line connecting an outlet of the hydrogen gas generator to an inlet of the liquefier, the liquefier comprising a refrigerator having a cycle circuit to cool the hydrogen gas from the feed line, the plant comprising a buffer store configured to store the compressed hydrogen gas between the hydrogen gas generator and the liquefier, the liquefier being configured to supply a cooling power and/or the liquefaction capacity that can be modified between at least two levels, the plant comprising a means for determining the fill level of the buffer store, the plant being configured to modify the cooling power and/or liquefaction capacity of the liquefier as a function of the fill level of the buffer store determined by the determining means.

Claims

1. A plant for producing liquefied hydrogen the plant comprising: a hydrogen gas generator, for example an electrolyzer, configured to produce hydrogen gas, a liquefier, a feed line connecting a hydrogen gas outlet of the hydrogen gas generator to an inlet of the liquefier, wherein the liquefier further comprises a refrigerator having a cycle circuit configured to supply the cooling power and cool the hydrogen gas from the feed line, a buffer store configured to store the compressed hydrogen gas between the hydrogen gas generator and the liquefier, the liquefier being configured to supply a cooling power and/or the liquefaction capacity that can be modified between at least two levels, a means for determining the fill level of the buffer store, wherein the plant is configured to modify the cooling power and/or liquefaction capacity of the liquefier as a function of the fill level of the buffer store determined by the means for determining the fill level, wherein the plant is further configured to modify the cooling power and/or the liquefaction capacity of the liquefier as a function of the fill level of the buffer store determined by the means for determining after a given delay.

2. The plant as claimed in claim 1, wherein the means for determining the fill level of the buffer store is configured to determine the fill level of the buffer store from a plurality of predefined fill levels, and wherein the plant is configured to establish the cooling power and/or the liquefaction capacity of the liquefier at specific levels corresponding respectively to the fill levels of the predefined buffer store.

3. The plant as claimed in claim 1, wherein the plant is configured to relatively reduce the cooling power and/or the liquefaction capacity of the liquefier when the fill level of the buffer store decreases.

4. The plant as claimed in claim 1, wherein the plant is configured to relatively increase the cooling power and/or the liquefaction capacity of the liquefier when the fill level of the buffer store increases.

5. The plant as claimed in claim 1, wherein the means for determining the fill level of the buffer store comprises a pressure sensor.

6. The plant as claimed in claim 1, wherein the pressure sensor is configured to measure the pressure in the buffer store and/or in a line connected to an outlet of the buffer store.

7. The plant as claimed in claim 1, wherein the liquefier comprises a refrigerator with a cycle circuit in which a cycle gas flow is subjected to a given thermodynamic cycle, the plant being configured to modify the cooling power and/or liquefaction capacity of the liquefier by modifying the flow rate and/or quantity of cycle gas in the cycle circuit.

8. The plant as claimed in claim 1, wherein the plant is configured to decrease the cooling power and/or liquefaction capacity of the liquefier by decreasing the flow rate and/or the quantity of cycle gas in the cycle circuit via at least one of the following: a cycle gas discharge line to the feed line, a cycle gas discharge line to a discharge zone, a means for liquefying at least a portion of the cycle gas in the cycle circuit.

9. The plant as claimed in claim 1, wherein the liquefier comprises a refrigerator with a cycle circuit in which a cycle gas flow is subjected to a given thermodynamic cycle comprising a compression and an expansion, the plant being configured to modify the cooling power and/or liquefaction capacity of the liquefier by modifying the pressure level of the compression of the cycle gas in the cycle circuit.

10. The plant as claimed in claim 1, wherein the liquefier comprises several independent refrigerators with a cycle circuit each configured to supply the respective cooling power for cooling hydrogen gas from the feed line with a view to the liquefaction thereof, and in that the plant is configured to modify the cooling power and/or liquefaction capacity of the liquefier by differentially modifying the cooling power and/or liquefaction capacity of the various refrigerators.

11. The plant as claimed in claim 1, wherein the means for determining the fill level of the buffer store comprises a programmable electronic means for storing and processing data comprising a microprocessor, the means for determining the fill level being configured to receive operating data from the hydrogen gas generator and/or consumption data of the liquid hydrogen produced by the liquefier, and to use this data to predict a future fill level of the buffer store in a future time interval, for example between one and twenty-four hours, the plant being configured to modify the cooling power and/or liquefaction capacity of the liquefier as a function of the future fill level of the buffer store determined by the determining means.

12. The plant as claimed in claim 1, wherein the hydrogen gas generator comprises an intermittent electrical supply supplied by a renewable energy source, for example solar, and in that the means for determining the fill level is configured to receive weather forecast data and to predict, including from this data, the future fill level of the buffer store.

13. A method for producing liquefied hydrogen using a plant, the method comprising the steps of: providing the plant as claimed in claim 1; determining the fill level of the buffer store; and regulating the cooling power and/or liquefaction capacity of the liquefier as a function of the determined fill level of the buffer store.

14. The method as claimed in claim 13, wherein the determination of the fill level of the buffer store is measured, and/or estimated and/or predicted from operating data from the plant, which includes: hydrogen production capacity per hydrogen gas generator, historical hydrogen production capacity per hydrogen gas generator, meteorological data, current and future consumption of liquid hydrogen produced by the liquefier.

15. The method as claimed in claim 13, wherein the step of regulating the cooling power and/or liquefaction capacity of the liquefier comprises a modification of the cooling power and/or liquefaction capacity of the liquefier which is performed in response to a change in the fill level of the buffer store, the modification of the cooling power and/or liquefaction capacity being carried out concomitantly and/or before and/or after the change in the determined fill level of the buffer store.

16. The method as claimed in claim 13, wherein the liquefier comprises a refrigerator having a cycle circuit in which a cycle gas flow is subjected to a given thermodynamic cycle, the step of regulating the cooling power and/or the liquefaction capacity of the liquefier comprising at least one of the following: a modification of the flow rate and/or the quantity of cycle gas in the cycle circuit, for example a discharge of cycle gas from the cycle circuit, a decrease in the quantity of gas in the cycle circuit by partial liquefaction of the cycle gas in a separator vessel, a modification of the pressure of the compression of the cycle gas in the cycle circuit.

17. The method as claimed in claim 13, further comprising a step of stopping the plant in which the liquefier is stopped, followed by a step of restarting the plant and the liquefier, the method comprising, after restarting and before a step of regulating the cooling power and/or liquefaction capacity of the liquefier, a given delay, for example between two and twelve hours, and/or a delay until the fill level of the buffer store reaches a predetermined threshold.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The invention will be understood better from reading the following description and from studying the accompanying figures. These figures are given only by way of illustration and do not in any way limit the invention.

[0033] FIG. 1 is a schematic and partial view illustrating the structure and the operation according to a first exemplary embodiment of the invention,

[0034] FIG. 2 is a schematic and partial view illustrating the structure and the operation according to a second exemplary embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0035] Throughout the figures, the same references relate to the same elements.

[0036] In this detailed description, the following embodiments are examples. Although the description refers to one or more embodiments, this does not mean that the features apply only to a single embodiment. Individual features of different embodiments can also be combined and/or interchanged to provide other embodiments.

[0037] The plant 1 for producing liquefied hydrogen that is illustrated in FIG. 1 comprises a hydrogen gas generator 2, for example an electrolyser 2, configured to produce hydrogen gas, a liquefier 7 and a feed line 6 connecting a hydrogen gas outlet of the hydrogen gas generator 2 to an inlet of the liquefier 7.

[0038] The plant 1 comprises a buffer store 9 configured to store the compressed hydrogen gas between the hydrogen gas generator 2 and the liquefier 7. In this example, the buffer store 9 is arranged in series between the hydrogen gas generator 2 and the liquefier 7.

[0039] As illustrated, the plant 1 may comprise at least one compressor 10 for compressing the hydrogen gas produced by the hydrogen gas generator 2 with a view to filling the buffer store 9.

[0040] The liquefier 7 comprises a refrigerator 8 having a cycle circuit 18 configured to supply the cooling power and cool the hydrogen gas from the feed line 6 with a view to the liquefaction thereof.

[0041] The liquefier 7 is configured to supply a cooling power and/or the liquefaction capacity that can be modified between at least two distinct levels (N1, N2).

[0042] The plant 1 comprises a means 3 for determining the fill level of the buffer store 9, and the plant 1 is configured to modify the cooling power and/or liquefaction capacity of the liquefier 7 as a function of the fill level of the buffer store 9 determined by the determining means 3.

[0043] For example, the means 3 for determining the fill level of the buffer store 9 is configured to determine the fill level of the buffer store 9 from a plurality of predefined fill levels, and the plant 1 is configured to establish the cooling power and/or the liquefaction capacity of the liquefier 7 at specific levels corresponding respectively to the fill levels of the predefined buffer store 9.

[0044] The means 3 for determining the fill level of the buffer store 9 may for example comprise a pressure sensor measuring the pressure in the buffer store 9.

[0045] The pressure sensor 3 is for example configured to measure the pressure in the buffer store 9 and/or in a line connected to an outlet of the buffer store 9.

[0046] A fill level may be determined as a function of the measured pressure value.

[0047] For example, a fill level of 0% can be set for a minimum pressure upstream of an inlet valve of the liquefier (for example 20 to 40 bar).

[0048] A fill level of 100% can be set for a maximum pressure upstream of an inlet valve of the liquefier (for example 40 to 100 bar).

[0049] Thus, for example, the plant can be configured to relatively reduce the cooling power and/or the liquefaction capacity of the liquefier 7 when the fill level of the buffer store 9 decreases.

[0050] Similarly, the plant can be configured to relatively increase the cooling power and/or the liquefaction capacity of the liquefier 7 when the fill level of the buffer store 9 increases.

[0051] Thus, the running rate of the liquefier 7 can be set as a function of the fill level of the buffer store 9 (fill level measured for example by the pressure thereof) with set action levels that do not depend on the actual production characteristics of the liquefier 7. For example, all or some of the following configurations are possible, for example with the following actions on the liquefier:

[0052] If the fill level of the buffer store or stores 9 is 70% or more, the running rate of the liquefier 7 can be set at 100%.

[0053] If the fill level of the buffer store or stores 9 is 50% or more, the running rate of the liquefier 7 can be set at 75%.

[0054] If the fill level of the buffer store or stores 9 is 35% or more, the running rate of the liquefier 7 can be set at 50%.

[0055] If the fill level of the buffer store or stores 9 is 10% or more, the running rate of the liquefier 7 can be set at 25%.

[0056] If the fill level of the buffer store or stores 9 is 2% or less, the running rate of the liquefier 7 can be set at 0%.

[0057] The plant can be configured to limit the frequency or number of changes to the running rate of the liquefier, for example to avoid cycling about an operating point.

[0058] For example, the plant can be configured to modify the cooling power and/or the liquefaction capacity of the liquefier 7 only after a given delay, for example between one and ten hours (following a change in the fill level of the buffer store 9).

[0059] For example, a minimum delay of six hours may be provided between two changes.

[0060] Similarly, if the plant 1 is started (starting and cooling the liquefier 7), such starting may only be possible after a delay of 6 hours and if the fill level of the buffer store 9 is greater than or equal to a threshold, for example 50%.

[0061] The liquefier 7 for example comprises at least one refrigerator 8 with a cycle circuit 18 in which a cycle gas flow is subjected to a given thermodynamic cycle comprising an expansion. The plant 1 can be configured to modify the cooling power and/or liquefaction capacity of the liquefier 7 by modifying, for example, the flow rate and/or the quantity of cycle gas in the cycle circuit 18.

[0062] For example, the plant can be configured to reduce the cooling power and/or liquefaction capacity of the liquefier 7 by reducing the flow rate and/or the quantity of cycle gas in the cycle circuit 18. This can for example be achieved via at least one of the following: a cycle gas discharge line to the feed line 6, a cycle gas discharge line to a discharge zone, a means for liquefying at least a portion of the cycle gas in the cycle circuit 18.

[0063] In the case where the liquefier 7 comprises a refrigerator 8 with a cycle circuit 18 in which a cycle gas flow is subjected to a given thermodynamic cycle comprising a compression 80 and an expansion, the plant can be configured to modify the cooling power and/or liquefaction capacity of the liquefier 7 by modifying the pressure level of the compression 80 of the cycle gas in the cycle circuit 18.

[0064] Similarly, the liquefier may comprise several independent refrigerators 8 with a cycle circuit 18 (i.e. several trains in parallel) each configured to supply the respective cooling power for cooling hydrogen gas from the feed line 6 with a view to the liquefaction thereof. In this case, the plant 1 can be configured to modify the cooling power and/or liquefaction capacity of the liquefier 7 by differentially modifying the cooling power and/or liquefaction capacity of the various refrigerators 8.

[0065] Thus, for example, in the case of a liquefier with several trains of refrigerators in parallel (for example three trains), the plant can be configured to modify control of the running rate of one or more trains, for example, by lowering, for example, the power to 25% if the fill level of the buffer store falls below 20%.

[0066] To reduce the running rate, the plant 1 can for example be designed to switch off the trains gradually and sequentially in order to maintain liquefaction capacity.

[0067] For example, if the fill level of the buffer store 9 falls below a first threshold (for example 15%), the trains (for example three) can each be set to a running rate of 25% of the maximum cooling power thereof.

[0068] Similarly, if the fill level of the buffer store 9 falls below a second threshold (for example 10%), one train can be stopped and the other trains (for example two) can each be set to a running rate of 25% of the maximum cooling power thereof.

[0069] Similarly, if the fill level of the buffer store 9 falls below a third threshold (for example 2%), a second train can be stopped and the remaining train can be set to a running rate of 25% of the maximum cooling power thereof.

[0070] A gradual restart of the plant can be carried out in reverse by gradually starting the liquefaction trains.

[0071] FIG. 2 illustrates a variant with a buffer store 9 connected in parallel to the liquefier 7.

[0072] For example, a fill level of 0% can be set for a minimum pressure in the buffer store 9 (20 to 40 bar, for example).

[0073] A fill level of 100% can be set for a maximum pressure in the buffer store 9 (40 to 250 bar for example). Operating cases can be predefined (50%, 75%, 100% of fill level or running rate, for example). This enables the control values of the plant 1 to be modified automatically to ensure efficient operation.

[0074] For example, the decrease in cooling power produced by the liquefier (running rate) can be controlled with the following measures, preferably taken individually or in combination or sequentially in this order: [0075] decreasing the cycle gas flow in the cycle of the refrigerator or refrigerators, [0076] decreasing the quantity of cycle fluid in the cycle circuit to reduce the high pressure in the cycle circuit (while maintaining the low pressure after expansion).

[0077] For example, in the case of a cycle gas consisting of or comprising hydrogen, a fraction of this cycle gas can be transferred into the feed circuit 6.

[0078] In the case of a cycle gas consisting of or comprising nitrogen (nitrogen cycle refrigerator), a fraction of this cycle gas may be discharged to the outside (for example venting).

[0079] In the case of a modification of the pressure within the refrigerator cycle, for example in the case of a nitrogen cycle and/or a hydrogen cycle, the corresponding refrigerator may be controlled to modify at least one pressure value (relatively low, medium or high) in the cycle.

[0080] For example, the means for determining the fill level of the buffer store 9 may comprise a programmable electronic means 4 for storing and processing data comprising a microprocessor.

[0081] Similarly, the control (modification) of the running rate of the refrigerator 8 as described above can be carried out by this programmable electronic data storage and processing means 4 (and/or another means of the same type).

[0082] For example, such an electronic means can implement the actions for controlling the plant 1 that are described above.

[0083] The means 3 for determining the fill level can be configured to receive operating data from the hydrogen gas generator 2 and/or data on consumption of the liquid hydrogen produced by the liquefier 7 and to use these data to predict a future fill level of the buffer store 9 in a future time interval, for example between one and twenty-four hours. The plant 1 may be configured to modify the cooling power and/or liquefaction capacity of the liquefier 7 as a function of the future fill level of the buffer store 9 determined by the determining means 3.

[0084] According to this predictive approach, the running rate of the liquefier 7 can be set as a function of the fill level of the buffer store 9 in a given future, for example in 12 hours. The filling state of the buffer store 9 can for example be calculated based on the production of hydrogen by the electrolyser in the next 12 hours by estimating the future production using various parameters, for example the weather or any other forecasting and/or historical method.

[0085] The quantity of hydrogen available can be calculated from the available electricity and the efficiency of the electrolyser and the compression of this hydrogen produced by the electrolyser.

[0086] Similarly, the consumption of hydrogen gas by downstream user units can be estimated. For example, the quantity of liquefied hydrogen consumed (and/or used to produce ammonia or methanol) can be calculated as a function of a current load level.

[0087] The plant 1 can for example be controlled in the following manner.

[0088] If the fill level of the buffer store 9 in a predefined future (for example 12 hours) is greater than a maximum threshold (for example 100% or more), the cooling power and/or the liquefaction capacity of the liquefier 7 is increased (in advance). A new prediction/simulation can be performed with these new operating conditions.

[0089] On the other hand, if the fill level of the buffer store 9 in a predefined future (for example 12 hours) is less than a minimum threshold (for example 0%), the cooling power and/or the liquefaction capacity of the liquefier 7 is reduced (in advance). A new prediction/simulation can be performed with these new operating conditions.

[0090] In other cases, the fill level of the buffer store 9 in a predefined future (for example 12 hours) is within an acceptable range (for example 5-80%), the cooling power and/or the liquefaction capacity of the current liquefier 7 is unchanged.

[0091] Different cooling power and/or liquefaction capacity values of the liquefier 7 can be predefined, for example 25%, 50%, 75% and 100%. Using such predefined load levels allows for fast and efficient changes of running rate.

[0092] Similarly, a minimum stoppage time of the plant 1 can be provided to avoid stop/restarts and limit the impact on critical equipment.

[0093] For example, notably after stoppage of the liquefier, a given delay can be provided before a new restart, for example 24 hours.

[0094] Moreover, such a restart may be subject to at least one essential precondition. For example, a minimum stoppage time (for example 6 hours) and a sufficient fill level of the buffer store 9 (for example at least 25% for a future duration, for example 12 hours).

[0095] The following condition may also be provided: the future hydrogen production by the source 2 is at least a fraction (for example 50%) of the quantity of hydrogen required to operate the plant 1 (for example, the cooling power and/or the liquefaction capacity of the liquefier 7 at a specific level, for example 25% for a given future period, for example 16 hours or 6 hours).

[0096] The plant 1 can also operate in a mixed or hybrid mode. That is to say, a prediction of hydrogen gas production can be used to control the plant (the running rate of the liquefier), but the operating parameters are re-evaluated and modified if necessary on the basis of actual fill data from the buffer store 9. This helps to limit stoppages.

[0097] For example, a six-hour hydrogen production prediction can be made to calculate the available hydrogen and add it to the quantity. A backup reserve (for example 10% of the maximum fill level) can be subtracted from the quantity available in the buffer store 9.

[0098] The average value obtained for the quantity of hydrogen available determines the new running rate of the liquefier (for example, 25%, 50%, 75%, 100%). Preferably, the change of running rate is carried out after a delay (for example 6 hours).

[0099] The invention allows efficient adaptation of the plant to handle fluctuations in the intermittent energy sources (and therefore the production of hydrogen to be liquefied).

[0100] Preferably, high-load operation of the liquefier (close to the maximum power) is only permitted if the fill level of the buffer store 9 is sufficient (for example at least 90%).

[0101] Starting from high or maximum power, if the fill level of the buffer store 9 falls below a level (for example 50%), the running rate of the liquefier can be reduced (for example to 75%) until the fill level recovers (for example above 95%).

[0102] If the plant 1 is operating at reduced load (for example minimum) and the fill level is below a level required to ensure a specified hydrogen supply time (for example one hour), the plant may be stopped.

[0103] Restarting can for example only be effected if the following conditions are met: the fill level is sufficient for operation for a given period (for example 12 hours) at a given running rate (for example minimum or reduced) and the predicted quantity of hydrogen to be produced by the source 2 in the future (for example the following 6 hours) is greater (for example by 50%) than the quantity required for this operation at reduced running rate.

[0104] An example of operation may include the following steps: [0105] estimating hydrogen production in the following hours (for example 12 hours), this estimate can be based on meteorological data and a current or historic state of electricity generation by one or more renewable energy sources [0106] measuring or calculating the fill level of the buffer store 9.

[0107] While the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications, and variations will be apparent to those skilled in the art in light of the foregoing description. Accordingly, it is intended to embrace all such alternatives, modifications, and variations as fall within the spirit and broad scope of the appended claims. The present invention may suitably comprise, consist or consist essentially of the elements disclosed and may be practiced in the absence of an element not disclosed. Furthermore, if there is language referring to order, such as first and second, it should be understood in an exemplary sense and not in a limiting sense. For example, it can be recognized by those skilled in the art that certain steps can be combined into a single step.

[0108] The singular forms a, an and the include plural referents, unless the context clearly dictates otherwise.

[0109] Comprising in a claim is an open transitional term which means the subsequently identified claim elements are a nonexclusive listing (i.e., anything else may be additionally included and remain within the scope of comprising). Comprising as used herein may be replaced by the more limited transitional terms consisting essentially of and consisting of unless otherwise indicated herein.

[0110] Providing in a claim is defined to mean furnishing, supplying, making available, or preparing something. The step may be performed by any actor in the absence of express language in the claim to the contrary.

[0111] Optional or optionally means that the subsequently described event or circumstances may or may not occur. The description includes instances where the event or circumstance occurs and instances where it does not occur.

[0112] Ranges may be expressed herein as from about one particular value, and/or to about another particular value. When such a range is expressed, it is to be understood that another embodiment is from the one particular value and/or to the other particular value, along with all combinations within said range.