Increased energy efficiency of electrolyser units by using turboexpander for generation of electricity and cooling from pressurised oxygen

Field of the invention

Present invention relates to a novel system or apparatus set-up comprising a turboexpander unit and an electrolysis unit. Present invention also relates to an innovative method of utilizing the oxygen evolved during operation of the electrolysis unit.

Background of the invention

In electrochemical electrolysis of water, electricity is used to split water into its two elemental components - hydrogen and oxygen. It is a well-known technology that has been used industrially on a small scale for well over a century, but with the rapidly expanding supply of cheap, clean electricity, the production of hydrogen from electrolysis is expected to grow from a capacity of a few mega watts into tens of giga watts in the coming decade.

However, the upscaling of water electrolysis entails several challenges. Electrolysers have a very high energy conversion efficiency of approximately 70 % (based on chemical energy stored in the produced hydrogen).

However, the remaining energy is wasted. In order to make electrolysers a clearly sustainable option for hydrogen production, it is of great importance to make use of as much energy as possible. Most of the wasted energy is lost as heat and for very large electrolyser systems it could be beneficial to gather this heat for use in e.g. district heating and a similar manner to modern combined heat and powerplants (CHP). However, a more subtle yet useful source of energy is the potential energy from the pressurisation of the gasses produced by the electrolyser. Hydrogen, being the lightest of all elements, is one of the chemical compounds with the highest stored energy per weight, but at the same time it has the lowest energy per volume. Before there can be any practical use of hydrogen, it must be compressed to 50-700 bars before storage and transportation and for this reason, many electrolyser systems operate at elevated pressure. One example is pressurised alkaline electrolysis. The pressurisation of the electrolysis process comes with the major advantage that the produced hydrogen already is compressed, which makes is cheaper and easier for direct storage or further compression. Furthermore, it reduces the relative amount of water vapour which allows for operation at temperatures normally above the boiling point of water.

In alkaline water electrolysis, the pressure on the cathode and anode - the hydrogen and oxygen producing electrode respectively - must be equal to avoid gas crossover through the separating diaphragm. The produced oxygen is consequently also pressurised. However, this is without any particular benefit due to the high cost of transporting oxygen compared the value of the product itself, and the oxygen is for this reason simply expanded through a throttle and released into the air.

Present invention aims at taking advantage of the potential energy of the pressurised oxygen, which can be regarded as a source of waste energy that can be recovered and used in order to increase the overall efficiency of a pressurised electrolyser system. Present invention relates to the provision of an innovative apparatus or system set-up for taking advantage of the excess energy.

Summary of the invention

Present invention relates to a novel apparatus or system. Essentially, the system comprises the integration or combination of one or more turboexpanders with an electrolyser stack. Specifically, the turboexpander unit may be set in connection with the oxygen outlet of the electrolyser. By installing a turboexpander at the oxygen outlet of the electrolyser, the potential energy may be extracted and further converted into electricity in a generator. The turboexpander is in its most general form comparable or equivalent to a turbine used in a modern powerplants and is as such already a mature technology that may easily be coupled to an electrolyser with only minor configurations. A turboexpander has a high efficiency and may be operated autonomous together with the electrolyser system as a whole and therefore provides a source of highly useful energy.

The invention also enables using the cooling obtained in connection with the expansion of gasses for cooling the electrolyser unit. Consequently, present invention also relates to use of a system according to the invention for cooling of an electrolyser unit.

The size of the recovered energy is naturally on a smaller scale than the energy used by the electrolyser itself. However, the electrolyser operates with a multitude of auxiliary equipment such as pumps, sensors and electronic controlling devices that need a steady power supply, which ideally could be powered by this waste energy extracted by present invention.

Turboexpanders function with optimal efficiency within a well-defined pressure and flow range. Normally, turboexpanders are designed for high flow rates of approximately 1000 Nm ³ /h and above and the oxygen flow of a typical electrolyser unit does not suffice to this requirement. However, with the growing demand of hydrogen from electrolysers, it is expected that clustering of multiple electrolysers will demonstrate promising targets for a configuration producing well above 500-1000 Nm ³ /h. Furthermore, there is nothing fundamental that inhibits turboexpanders to function with lower flow rates so it is possible that specialised low flow turboexpanders could be developed for present invention.

Since the output of a turboexpander is proportional to the gas flow through it, multiple turboexpanders could be coupled in series and reduce the pressure in steps while maintaining a high flow through all turboexpanders in order to maintain an optimal pressure drop over the turboexpanders.

A thermodynamic side effect of a gas expansion in a turboexpander is a dramatic cooling of the gas itself. In this case, the cooling is highly useful since electrolysers with high power density need active cooling or it would otherwise overheat which could accelerate the degradation of components and ultimately it would destroy the electrolyser. The cooled gas could for this reason be used with a heat exchanger coupled to the electrolyser as autonomous cooling system. If the gas is expanded over multiple turboexpanders in series, heat exchangers between each turboexpander could be included as well. This will both make better use of the “cooling power” of the gas while heating the gas before entering the next turboexpander which will increase the overall efficiency of the expansion process.

In alkaline electrolysis, strong lye is used as an electrolyte and aerosols of such electrolyte would be present in the outlet gas. It is important to notice that present invention would require thorough removal of such corrosive chemicals that would be harmful to any components in the turboexpander module. Alternatively, turboexpanders could be designed with materials of extraordinary chemical resistance, but this would be expensive and could compromise mechanical performance of the turbine. Since the challenge of corrosive aerosols already are present in alkaline electrolysis, the cleaning of a gas with a scrubbing system is commonly included in the design of an electrolyser unit. It is therefore an aspect of the invention that such a scrubbing system is capable of operation at high pressures and is employed before the turboexpander module.

Another aspect of the turboexpander system is its handling of the fluctuating gas flow. The electrolyser is believed to operate entirely with electricity from renewable sources and varying output will thus be present. Functionality over a wide range of flow speeds is therefore mandatory and occasional shut down of the turbine unavoidable. It is however believed that these challenges are manageable and certainly outweighed by the advantages of regaining the energy from the depressurisation of the oxygen.

Consequently, present invention provides for several benefits and may comprise one or more of: a) a facile combination of compatible technologies, b) higher and more sustainable energy usage during electrolysis or in relation to any electrochemical reaction or application, c) employment of thermodynamic effects such as cooling, d) application in large up-scaled systems, etc.

Consequently, present invention relates to an apparatus or system, wherein the system comprises; a) one or more electrolysis units b) one or more turboexpander units, c) optionally one or more scrubber units.

In one aspect of the invention, the turboexpander is in connection with the oxygen outlet of the one or more electrolysis units.

In another aspect of the invention, the scrubber unit is placed in between the oxygen outlet of the electrolyser unit and the turboexpander, and consequently such that the oxygen outlet and the gas therefrom is passed through the scrubber unit prior to entering the turboexpander.

In yet a further aspect, present invention relates to a system comprising a turboexpander and an electrolyser unit, wherein the electrolyser unit as a whole is capable of producing approximately equal or more than about 1000 Nm ³ /h of oxygen.

In one aspect, the invention relates to a system comprising multiple turboexpanders/heat exchangers in any arrangement or cluster.

In yet a further aspect, the invention relates to a system wherein multiple turboexpanders/heat exchangers are present and alternatively or coupled to one another in series.

In one aspect, the system according to the invention relates to multiple turboexpanders and/or heat exchangers, such as two or more turboexpanders and/or heat exchangers, such as e.g. three or more, such as e.g. four or more, such as e.g. five or more, such as e.g. six or more, such as e.g. seven or more, such as e.g. eight or more, such as e.g. nine or more, such as e.g. ten or more turboexpanders and/or heat exchangers.

In one aspect, the gas, being primarily oxygen gas obtained from the electrolysis unit, is heated with dissipated heat from the system via the heat exchanger(s) of the system. The heated gas is subsequently led into the one or more turboexpander units. In a particular aspect, the turboexpanders and/or heat exchangers are coupled in series. This aspect is illustrated in e.g. Fig. 5A and 5B. Brief description of the drawings

Fig. 1 illustrates a system comprising a turboexpander that converts the energy from pressurised gas to kinetic energy that drives a turbine. For safe operation of the electrolyser stack, a regulator system is included for the gas to by-pass the turboexpander.

Fig. 2 illustrates a system of turboexpander on the oxygen outlet of an electrolyser: Oxygen of initial pressure P, and temperature T, enters the expander system from the right. A programmable valve (1) controlling the flow. A heat exchanger (2) heating the gas with heat from the electrolyser stack. The turboexpander (3) which converts the potential energy in the high- pressure gas into work, W. The work, W, is transferred via a crankshaft to a generator (4). The expanded and cooled gas is used to cool the stack via another heat exchanger (5). A regulator valve (6), optionally equipped with gas throttling, where the gas can bypass the turboexpander system and expand freely. A further heat exchanger (7) coupled to the electrolyser stack may be further employed in cooling the stack. Gas of final pressure P _f and temperature T _f exits to the right. Fig. 3 illustrates a system according to the invention comprising a turbo expander on the oxygen outlet of an electrolyser: Oxygen of initial pressure P, and temperature T, enters the expander system from the right. 1) Control valve. 2) Fleat exchanger coupled to the electrolyser. 3) Turboexpander. 4) Generator driven by the work, W, from the turboexpander. 5) Another heat exchanger coupled to the electrolyser. 6) A regulator valve with gas throttling. 7) Heat exchanger coupled to the electrolyser stack. Gas of final pressure P _f and temperature T _f exits to the right. 8) The components in the dashed box may be repeated multiple times in series and thus illustrates having multiple turboexpanders/heat exchangers in series. Fig. 4 illustrates one example of a complete electrolyser stack with turboexpander system. 1) Electrolyser unit. 2) Water and electricity fed to the electrolyser. 3) Scrubber system for both Fh and O2 outlet. 4) Rinsed H2 to further compression and/or storage. 5) Turbo-expander system (see next/previous figure) 6) Heat exchange system 7) Electricity produced by turbo-expander system. 8) Exhaust O2 at atmospheric pressure.

Fig. 5A and 5B illustrate a system according to the invention. In Fig. 5A illustrates the electrolysis part/unit of the system from which the obtained oxygen gas (02-gas seen in separator vessel) is collected and further transferred into the turboexpander units seen in Fig. 5B. Fig. 5A illustrates a cluster of four cell stacks and which is regarded as the electrolyser unit, wherein each stack have in- and outlets, each with inlets having a Ti _n temperature and Tout temperature. For example, Cell stack 3 has two illustrated inlets having a T, _n temperature and two illustrated outlets of T3 _,out temperature; Cell stack 2 has two illustrated inlets having a T, _n temperature and two illustrated outlets of T2 _, out temperature and so on. Fig. 5A further illustrates heat exchangers (A) and (B).

Fig. 5B illustrates the turboexpander units coupled in series (3 in total), and into which the obtained oxygen gas from the electrolyser units is transferred into the turboexpander units. Fig. 5B further illustrates heat exchangers (2), (5), and (7). The obtained heat from heat exchangers (A) and/or (B) seen in Fig. 5A is transferred to the one or more of heat exchangers (2), (5), or (7) seen in Fig. 5B.

Definitions

In the context of the invention, the terms “system”, apparatus”, “device”, “module” or “set-up” is intended to mean the collective elements of the invention and may be used interchangeably. The term “turboexpander” or “turboexpander unit” is intended to mean a turbine that may be employed in converting potential energy (such as e.g. pressurized gas) into kinetic energy. The term is intended to mean an expansion turbine, which may be a centrifugal or axial-flow turbine, through which a high-pressure gas is expanded to produce work where energy may be conveyed to a generator etc.

The term “scrubber” or “scrubber unit” or a “scrubber system” is intended to mean a device that may be e.g. chemical scrubbers, gas scrubbers etc, that are a diverse group of air pollution control devices that can be used to remove some particulates and/or gases from industrial exhaust streams. The aim with the scrubber is to remove corrosive components from the gas stream before the gas stream enters the turboexpander unit. As is known in the art, usually, the scrubber unit is an integral part of the electrolyser.

The term electrolyser unit or electrolysis unit is intended to mean a complete and independent electrolyser system capable of converting water into hydrogen and oxygen through the process of electrolysis. Each unit may consist of any number electrochemical cells where the electrolysis takes place. The wording “stack” as in electrolysis or electrolyser stack is intended to mean a unit as seen in element (1) seen in Fig. 4. The vertical lines in element (1) may denote single cells which are assembled into one stack.

Each unit may be clustered together with any number of other units to increase the production capacity of hydrogen and, thereby, also the flow of oxygen. The internal structure and design of the electrolyser unit is not of interest for present invention unless the electrolyser unit separately outputs high pressure oxygen and hydrogen. Thus, present invention relates only to pressurized electrolyser unit(s). In the context of present invention “high pressure” is intended to mean a pressure of about at least 30 bar, such as e.g. at least about 50 bar, such as e.g. at least about 70 bar, such as e.g. at least about 90 bar, such as e.g. at least about 110 bar etc.

Detailed description of the invention

As is apparent from the above, present invention relates to a novel innovative system set-up comprising; a) one or more electrolysis units, b) one or more turboexpander units, c) optionally, one or more scrubber units.

In one aspect of the invention, the turboexpander unit is connected to the one or more electrolysis units, via the oxygen outlet of the one or more electrolysis units, such that the formed oxygen gas may pass through the turboexpander.

In yet a further aspect, present invention also relates to a novel innovative system set-up comprising; a) one or two or more pressurized electrolysis units, b) two or more turboexpander units, c) optionally, one or more scrubber units, wherein the turboexpander units are connected to the electrolysis units, via the oxygen outlet of the two or more electrolysis units, such that the formed oxygen gas may pass through the turboexpander, and further characterised in that the two or more turboexpanders are coupled in series to one another. As is clear from the description of the invention, the electrolysis unit is capable of, or configured to converting water into hydrogen and oxygen. Moreover, the electrolysis unit is capable of, or configured to separately outputting high pressure oxygen and hydrogen.

Thus, present invention relates to a novel innovative system set-up comprising; a) one, or two or more pressurized electrolysis units wherein the pressure is of about at least 30 bar, b) two or more turboexpander units, c) optionally, one or more scrubber units, wherein the turboexpander units are connected to the electrolysis units, via the oxygen outlet of the two or more electrolysis units, such that the formed oxygen gas may pass through the turboexpander, and further characterised in that the two or more turboexpanders are coupled in series to one another, and wherein the one or more electrolysis units are capable of, or configured to converting water into hydrogen and oxygen, and separately outputting high pressure oxygen and hydrogen.

In one aspect, the incoming oxygen gas has a high initial pressure P, and an initial temperature T,. P, may be in range of about 30 bar to about 100 bar, such as e.g. about 35 bar. In another aspect, the pressure P, may be about 40 bar, such as e.g. about 45 bar, such as e.g. about 50 bar, such as e.g. about 55 bar, such as e.g. about 60 bar, such as e.g. about 65 bar , such as e.g. about 70 bar, such as e.g. about 75 bar , such as e.g. about 80 bar , such as e.g. about 85 bar, such as e.g. about 90 bar such as e.g. about 95 bar etc. The initial temperature T, may be in range of about 20°C to about 100°C, such as e.g. about 50°C. In another aspect, the temperature T, may be about e.g. about 25°C, or about 30°C, about 35°C, about 40°C, about 45°C, about 50°C, about 55°C, about 60°C, about 65°C, about 70°C, about 75°C, about 80°C, about 85°C, about 90°C, or e.g. about 95°C.

In one aspect, the gas inlet may be regulated via a regulator valve (1) and as illustrated in Fig. 1 prior to entering the turboexpander/turbine (3).

In another aspect, optionally, the incoming oxygen gas at pressure P, and an initial temperature T, may be wholly or partially be passed by the turbine/turboexpander in a separate stream, such that this stream does not enter the turboexpander/turbine unit. The bypassed stream may be passed through a regulator valve (6) where the gas can bypass the turboexpander system and expand freely. The regulator valve may optionally also be equipped with a gas throttling device (thorough which the gas expands). This aspect is exemplified in Fig. 2.

The bypassed stream may optionally further be equipped with a heat exchanger (7) which may be in connection with the stack and may be employed to cool the stack from the expanding gas. This aspect is exemplified in Fig. 2.

According to the invention, the heat from the stack may be utilised to heat the incoming gas stream and before entering the turboexpander/turbine (3). This may be executed via a heat exchanger unit (2) as exemplified in Fig. 2.

According to the invention, the system may comprise a turbine/turboexpander (3) being equipped with a crank shaft which conveys the generated work, (W), to a generator (4). The output stream from the turbine/turboexpander may be passed through a heat exchanger which may be employed for cooling the stack. This aspect is exemplified in Fig. 1 and 2.

The output stream has a final pressure P _f and a final temperature T _f. The final pressure P _f may be in range of e.g. about 1 bar and the final temperature (T _f ) will be around - 100°C before entering the heat exchanger which works with heat from the electrolyser unit. The exhaust temperature will be close to ambient conditions. Alternatively, the pressure can be reduced over multiple turboexpanders in series, each with a subsequent heat exchanger.

According to one aspect of the invention, the system may be equipped with a scrubber system. The scrubber system is arranged such that the gas stream is chemically scrubbed prior to entering the turbine/turboexpander unit. The aim with the scrubber is to remove as much as possible of any corrosive elements that may otherwise damage the turbine/turboexpander unit or any other mechanical parts of the system. The scrubber may be any suitable type of scrubber known in the art.

In another aspect, the invention may include any operation or device in order to clean the oxygen gas from the electrolyser unit from any corrosive elements before being further led to the one or more turboexpanders. In another aspect, the system may include any operation or device in order to reduce the amount of any corrosive elements from the oxygen gas from the electrolyser unit before being further led to the one or more turboexpanders.

As mentioned herein, such device may be a scrubber unit.

Thus, in one aspect the invention relates to a system essentially exemplified in Fig. 1. In a further aspect, the invention relates to a system essentially exemplified in Fig. 2. In a further aspect, the invention relates to a system essentially exemplified in Fig. 3.

In a further aspect, the invention relates to a system essentially exemplified in Fig. 4.

In a further aspect, the invention relates to a system essentially exemplified in Fig. 5A and Fig. 5B.

Present invention also relates to a method for cooling an electrolysis device, the method comprising; i) obtaining a gas stream from the oxygen outlet of the electrolyser device having a high initial pressure P, and an initial temperature T,, ii) passing the gas stream from i) through a regulator valve or an expansion valve, thereby regulating the gas flow, iii) optionally passing the gas stream from ii) through a heat exchanger, wherein the heat exchanger is in connection with the electrolysis device and whereby heat from the electrolysis device is employed to heat the gas stream, iv) passing the gas stream obtained from ii) or optionally from iii), to a turbine unit/turboexpander, and allowing said stream to pass through the turbine/turboexpander, thereby creating a work which is passed on to a generator via a crank shaft, v) passing the stream obtained from iv) i.e. the stream exiting the turbine/turboexpander, through a heat exchanger which is in connection with the electrolyser device, thereby cooling said device with the aid of the heat exchanger, vi) allowing the gas stream obtained from v) to pass out of the turboexpander/electrolysis device with a final pressure P _f and a final temperature T _f.

Optionally, the method according to the invention may comprise leading the stream obtained in i), wholly or partially, through a separate loop which bypasses the turboexpander/turbine. This stream may be passed through a regulator valve, optionally equipped with a gas throttle device. The stream may be further passed through a heat exchanger which may be in connection with the electrolysis device, and thereby cooling said electrolysis device.

A further optional method feature is that the gas stream provided for in i), is passed through a scrubber system prior to entering the turboexpander/turbine unit in order to remove any corrosive elements that would otherwise damage or degrade the turboexpander/turbine unit.

The initial pressure P, and an initial temperature T,. P, may be in range of about 30 bar to about 100 bar, such as e.g. about 35 bar. In another aspect, the pressure P,may be about 40 bar, such as e.g. about 45 bar, such as e.g. about 50 bar, such as e.g. about 55 bar, such as e.g. about 60 bar, such as e.g. about 65 bar , such as e.g. about 70 bar, such as e.g. about 75 bar , such as e.g. about 80 bar , such as e.g. about 85 bar, such as e.g. about 90 bar such as e.g. about 95 bar etc.

The initial temperature T, may be in range of about 20°C to about 100°C, such as e.g. about 50°C. In another aspect, the temperature T, may be about e.g. about 25°C, or about 30°C, about 35°C, about 40°C, about 45°C, about 50°C, about 55°C, about 60°C, about 65°C, about 70°C, about 75°C, about 80°C, about 85°C, about 90°C, or e.g. about 95°C. The final pressure P _f and a final temperature T _f. The final pressure P _f may be in range of e.g. about 1 bar and final temperature T _f around -100°C before it enters any heat exchanger coupled to the electrolyser unit. The heat exchanger will increase the temperature of the exhaust gas close to ambient temperatures.

According to the invention, and is apparent from the above, the electrolysis device or unit is pressurised and consequently operates above normal pressure, such as e.g. about 30 bar to about 100 bar, such as e.g. about 35 bar. The electrolysis device or stack may be a device used for water splitting, i.e. to obtain hydrogen and oxygen from water. Moreover, the electrolysis device may be employing alkaline electrolysis, wherein the electrolyte may be e.g. an aqueous solution of KOH at a concentration of about 3 wt% to about 30 wt%.

In specific embodiment, present invention also relates to the following items;

1. A system comprising the following elements; a) one or more electrolysis units, b) one or more turboexpander units, c) optionally, one or more scrubber units.

2. The system according to item 1, wherein the turboexpander unit is connected to the one or more electrolysis units, via the oxygen outlet of the one or more electrolysis units, such that the formed oxygen gas may pass through the turboexpander.

3. The system according to any of the preceding items, wherein the multiple electrolysis units form one electrolysis unit and may thus be regarded as a cluster of several units. 4. The system according to any of the preceding items, wherein the gas inlet is in connection with a regulator valve (1 ) placed prior to the turboexpander/turbine (3).

5. The system according to any of the preceding items, wherein the system comprises a by-passing loop, consequently bypassing the turboexpander unit and further comprising a regulator valve (6), where the gas can bypass the turboexpander system and expand freely, and wherein, the regulator valve optionally also comprises a gas throttling device.

6. The system according to item 5, wherein the bypassing loop further comprises a heat exchanger (7), which is in connection with the one or more electrolysis units.

7. The system according to any of the preceding items, wherein the oxygen gas is passed through the scrubber unit prior to entering the turboexpander unit (3).

8. The system according to any of the preceding items, wherein the system comprises a heat exchanger (2), which is in connection with the one or more electrolysis units.

9. The system according to any of the preceding items, wherein the turboexpander (3) is equipped with a crank shaft which conveys the generated work, (W), to a generator (4).

10. The system according to any of the preceding items, wherein the system comprises a heat exchanger (5), which is in connection with the one or more electrolysis units. 11. A system, wherein the system is essentially according to any one of Fig. 1 , or Fig. 2 or Fig. 3, or Fig. 4.

12. A method for cooling an electrolysis device, the method comprising; i) obtaining a gas stream from the oxygen outlet of the electrolyser device having a high initial pressure P, and an initial temperature T,, ii) passing the gas stream from i) through a regulator valve, thereby regulating the gas flow, iii) optionally passing the gas stream from ii) through a heat exchanger, wherein the heat exchanger is in connection with the electrolysis device and whereby heat from the electrolysis device is employed to heat the gas stream, iv) passing the gas stream obtained from ii) or optionally from iii), to a turbine unit/turboexpander, and allowing said stream to pass through the turbine/turboexpander, thereby creating a work which is passed on to a generator via a crank shaft, v) passing the stream obtained from iv) i.e. the stream exiting the turbine/turboexpander, through a heat exchanger which is in connection with the electrolyser device, thereby cooling said device with the aid of the heat exchanger, vi) allowing the gas stream obtained from v) to pass out of the turboexpander/electrolysis device with a final pressure P _f and a final temperature T _f , and wherein the method optionally comprises passing the gas stream provided for in i), through a scrubber system prior to entering the turboexpander/turbine unit in order to remove any corrosive elements that would otherwise damage or degrade the turboexpander/turbine unit.

13. The method according to item 12, wherein the method comprise leading the stream obtained in i), wholly or partially, through a separate loop which bypasses the turboexpander/turbine, and wherein said stream is passed through a regulator valve, optionally equipped with a gas throttle device, and further passed through a heat exchanger which is in connection with the electrolysis device, and thereby cooling said electrolysis device. 14. The method according to any one of items 12-13, wherein P, is in range of 30 bar to about 100 bar, such as e.g. about 35 bar, or the pressure P, may be about 40 bar, such as e.g. about 45 bar, such as e.g. about 50 bar, such as e.g. about 55 bar, such as e.g. about 60 bar, such as e.g. about 65 bar , such as e.g. about 70 bar, such as e.g. about 75 bar , such as e.g. about 80 bar , such as e.g. about 85 bar, such as e.g. about 90 bar such as e.g. about 95 bar etc., and wherein the initial temperature T, is in range of about 20°C to about 100°C, such as e.g. about 50°C, or about e.g. about 25°C, or about 30°C, about 35°C, about 40°C, about 45°C, about 50°C, about 55°C, about 60°C, about 65°C, about 70°C, about 75°C, about 80°C, about 85°C, about 90°C, or e.g. about 95°C,and the final pressure P _f is e.g. about 1 bar, and wherein the final temperature (T _f ) is about -100°C. Examples

Present invention will be further illustrated in the below non-limiting examples. It is to be noted that the examples are mere illustrations of the invention and a person skilled in the art will be able to exercise the full scope of the invention based on the examples.

A single modular electrolyser unit can be coupled together with multiple other electrolyser units to increase total production of hydrogen which is the main product. Oxygen is due to its lower value considered as a by-product and is therefore just discarded. A cluster of 20 electrolyser units could produce up towards 1800 Nm ³ /h of pure hydrogen and 900 Nm ³ /h of pure oxygen and both gasses are compressed to a pressure of 35 bar from the electrolysis process. The process will in total consume approximately 8,68 MW at maximum load which is expected to be supplied in the form of electricity produced from sustainable energy sources (e.g. wind turbines or solar panels). The electrolysers operate at 90°C and is heated by intrinsic loss mechanisms of the electrolysis process.

The 900 Nm ³ /h of oxygen is rinsed from any aerosols of the electrolyte (lye) and is fed to the turboexpander system. The turboexpander system comprises three turboexpanders in series. Heat exchangers are placed after each turboexpander and a single one before the first turboexpander. The expansion process functions as follows:

• The oxygen exhaust gas is heated in first heat exchanger to 90°C.

• The gas enters the first turboexpander. The pressure drops from 35 bar to 12 bar over the turboexpander. This process extracts approximately 31 ,1 kW of energy which is converted into electricity in a generator. The gas is cooled to -5°C in the process.

• The gas enters the next heat exchanger where it is heated to 90°C again. The heat it supplied from the electrolyser unit. This intentionally cools the unit which already needs cooling.

• The gas enters the second turboexpander. The pressure drops from 12 bar to 3.5 bar over the turboexpander. This process extracts approximately 35,0 kW of energy which is converted into electricity in a generator. The gas is again cooled to below -5°C in the process.

• The gas enters the third heat exchanger where it is heated to 90°C again. Same heating procedure as previous heat exchanger.

• The gas enters the third and final turboexpander. The pressure drops from 3.5 bar to 1 bar over the turboexpander. This process extracts approximately 35,0 kW of energy which is converted into electricity in a generator. The gas is again cooled to below -5°C in the process.

• The gas enters the fourth and final heat exchanger where it is heated to 90°C again. Same heating procedure as previous heat exchanger. The system as mentioned above is illustrated in Fig. 5A and 5B. In total, over 100 kW is extracted from pressurized oxygen which otherwise would have been wasted. This amounts to 1.2 % of the total energy consumption and is thus a significant energy saving. The generated electricity is inputted directly into the auxiliary equipment that controls the operation of the electrolyser units.

The cooling of the electrolyser units also contributes a significant energy saving. The total oxygen mass flow rate is 0.35 kg/s. This gas has at least been heated three times from below -5°C to 90°C and the total “heat energy” extracted from the system amounts to 30.6 kW of cooling which otherwise should have been supplied from elsewhere. In case of issues and/or maintenance on the turboexpanders, these can be by-passed and regular a regular valve coupled to an expansion throttle expands the gas from 35 bar to 1 bar over several steps. As with the system with turboexpanders, several heat exchangers are coupled to the expansion throttle, and a similar amount of heat (30.6 kW) can be extracted from the electrolyser unit to heat the cold gas.

The system thus demonstrates a subtle but significant source of potentially saved energy in an otherwise energy intensive process. With the growing market for electrolysers and sustainable hydrogen production, present invention will illustrate an important step add-on to an already mature technology.