Plant and Method for Producing Liquefied Hydrogen

This application claims the benefit of priority under 35 U.S.C. § 119 (a) and (b) to European patent application No. EP2403073, filed Mar. 27, 2024, which is herein incorporated by reference in its entirety.

The invention relates to a plant and a method for producing liquefied hydrogen.

Liquefiers have a relatively limited ability to change operating point (or “running rate”). That is to say, the cooling power and/or the liquefaction capacity of the liquefier is difficult to modify.

One solution for handling fluctuations in the intermittent energy sources (and therefore in the production of hydrogen to be liquefied) therefore involves providing buffer stores of hydrogen gas to feed the feed circuit of the liquefier.

These buffer stores can be arranged in series between the electrolyser and the liquefier and/or connected in parallel with the liquefier at the outlet of the electrolyser.

The control solutions for these plants are unsatisfactory.

One aim of the present invention is to overcome all or some of the aforementioned drawbacks of the prior art.

In certain embodiments, the invention relates more particularly to a plant for producing liquefied hydrogen comprising a hydrogen gas generator, for example an electrolyser, 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, the liquefier comprising a refrigerator having a cycle circuit configured to supply the cooling power and cool the hydrogen gas from the feed line with a view to the liquefaction thereof, the plant comprising a buffer store configured to store the compressed hydrogen gas between the hydrogen gas generator and the liquefier.

In certain embodiments, the invention relates, for example, to the production of hydrogen with electrolysers electrically powered by renewable energy sources. This type of plant can be connected downstream to a gas network, a liquefier, an ammonia or methanol production unit. These plants must be controlled as a function of the electricity generation capacity of the renewable energy source. Such control makes it possible in particular to reduce investments related to buffer stores or additional equipment required to manage the intermittent power supply. Such control can also improve production capacity by avoiding losses and reduce production costs by limiting the use of the electricity grid.

In an effort to overcome the deficiencies of the prior art discussed, supra, the plant according to the invention, which otherwise corresponds to the general definition given in the preamble above, is configured such that the liquefier is 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.

In addition, embodiments of the invention can comprise one or more of the following features:

The invention also relates to a method for producing liquefied hydrogen using a plant according to any one of the features above or below comprising the following steps: 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.

According to other possible specific features:

The invention can also relate to any alternative device or method comprising any combination of the features above or below within the scope of the claims.

Further distinctive features and advantages will become apparent on reading the description below, provided with reference to the figures, in which:

Throughout the figures, the same references relate to the same elements.

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.

The plantfor producing liquefied hydrogen that is illustrated incomprises a hydrogen gas generator, for example an electrolyser, configured to produce hydrogen gas, a liquefierand a feed lineconnecting a hydrogen gas outlet of the hydrogen gas generatorto an inlet of the liquefier.

The plantcomprises a buffer storeconfigured to store the compressed hydrogen gas between the hydrogen gas generatorand the liquefier. In this example, the buffer storeis arranged in series between the hydrogen gas generatorand the liquefier.

As illustrated, the plantmay comprise at least one compressorfor compressing the hydrogen gas produced by the hydrogen gas generatorwith a view to filling the buffer store.

The liquefiercomprises a refrigeratorhaving a cycle circuitconfigured to supply the cooling power and cool the hydrogen gas from the feed linewith a view to the liquefaction thereof.

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

The plantcomprises a meansfor determining the fill level of the buffer store, and the plantis configured to modify the cooling power and/or liquefaction capacity of the liquefieras a function of the fill level of the buffer storedetermined by the determining means.

For example, the meansfor determining the fill level of the buffer storeis configured to determine the fill level of the buffer storefrom a plurality of predefined fill levels, and the plantis configured to establish the cooling power and/or the liquefaction capacity of the liquefierat specific levels corresponding respectively to the fill levels of the predefined buffer store.

The meansfor determining the fill level of the buffer storemay for example comprise a pressure sensor measuring the pressure in the buffer store.

The pressure sensoris for example configured to measure the pressure in the buffer storeand/or in a line connected to an outlet of the buffer store.

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

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).

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).

Thus, for example, the plant can be configured to relatively reduce the cooling power and/or the liquefaction capacity of the liquefierwhen the fill level of the buffer storedecreases.

Similarly, the plant can be configured to relatively increase the cooling power and/or the liquefaction capacity of the liquefierwhen the fill level of the buffer storeincreases.

Thus, the running rate of the liquefiercan be set as a function of the fill level of the buffer store(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. For example, all or some of the following configurations are possible, for example with the following actions on the liquefier:

If the fill level of the buffer store or storesis 70% or more, the running rate of the liquefiercan be set at 100%.

If the fill level of the buffer store or storesis 50% or more, the running rate of the liquefiercan be set at 75%.

If the fill level of the buffer store or storesis 35% or more, the running rate of the liquefiercan be set at 50%.

If the fill level of the buffer store or storesis 10% or more, the running rate of the liquefiercan be set at 25%.

If the fill level of the buffer store or storesis 2% or less, the running rate of the liquefiercan be set at 0%.

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.

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

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

Similarly, if the plantis started (starting and cooling the liquefier), such starting may only be possible after a delay of 6 hours and if the fill level of the buffer storeis greater than or equal to a threshold, for example 50%.

The liquefierfor example comprises at least one refrigeratorwith a cycle circuitin which a cycle gas flow is subjected to a given thermodynamic cycle comprising an expansion. The plantcan be configured to modify the cooling power and/or liquefaction capacity of the liquefierby modifying, for example, the flow rate and/or the quantity of cycle gas in the cycle circuit.

For example, the plant can be configured to reduce the cooling power and/or liquefaction capacity of the liquefierby reducing the flow rate and/or the quantity of cycle gas in the cycle circuit. This can for example be achieved 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.

In the case where the liquefiercomprises a refrigeratorwith a cycle circuitin which a cycle gas flow is subjected to a given thermodynamic cycle comprising a compressionand an expansion, the plant can be configured to modify the cooling power and/or liquefaction capacity of the liquefierby modifying the pressure level of the compressionof the cycle gas in the cycle circuit.

Similarly, the liquefier may comprise several independent refrigeratorswith a cycle circuit(i.e. several “trains” in parallel) each configured to supply the respective cooling power for cooling hydrogen gas from the feed linewith a view to the liquefaction thereof. In this case, the plantcan be configured to modify the cooling power and/or liquefaction capacity of the liquefierby differentially modifying the cooling power and/or liquefaction capacity of the various refrigerators.

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%.

To reduce the running rate, the plantcan for example be designed to switch off the trains gradually and sequentially in order to maintain liquefaction capacity.

For example, if the fill level of the buffer storefalls 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.

Similarly, if the fill level of the buffer storefalls 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.

Similarly, if the fill level of the buffer storefalls 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.