Electrolyser system and method of operation of electrolyser system

Abstract

An electrolyser system comprising at least one electrolyser cell comprising a first outlet for exhaust of off-gas from the first fluid volume at a relatively low pressure, a steam supply configured to supply steam at a relatively high pressure, means for mixing two fluids, a first heat exchanger; and a fuel supply. The means for mixing is configured to exhaust, at an intermediate pressure, an intermediate fluid comprising a mixture of steam from the supply and off-gas from the first fluid volume, and the system is configured to route said intermediate fluid to a first path of the first heat exchanger. The first heat exchanger is configured to transfer heat from the first path for the intermediate fluid to a second path for fuel from the fuel supply to separate water from the first product of the electrolyser reaction by condensing liquid water out of the intermediate fluid. The system is configured to route the first product of the electrolyser reaction out of the system at the intermediate pressure, and to route fuel from the second path of the first heat exchanger to a first inlet of the at least one electrolyser cell.

Description

[0001] ELECTROLYSER SYSTEM AND METHOD OF OPERATION OF ELECTROLYSER SYSTEM

[0002] Field of the Invention

[0003] The present invention relates to electrolyser systems and methods of operation of electrolyser systems, for producing pressurised product of electrolyser reaction.

[0004] Background to the Invention

[0005] Electrolyser cell units are typically operated to achieve the electrolysis of fuel (e.g., water and / or carbon dioxide) by input of electrical energy and using the solid oxide electrolyte to produce electrolysis products (e.g., hydrogen gas and / or carbon monoxide and oxygen, respectively).

[0006] Of the products, although the oxygen can be a valuable resource, the hydrogen and / or carbon monoxide is the main focus of the present invention. Particularly in the case of hydrogen, the collection and the subsequent storage and / or distribution of said product is commonly known to be difficult or costly, yet if achieved, the resulting pressurised product can be highly valuable as a fuel that can contribute towards achieving net zero or decarbonisation targets, either through combustion or the use of an electrolytic reaction in a fuel cell to recombine it with oxygen.

[0007] Most known hydrogen storage solutions are complex and expensive, due to the small size of the hydrogen particles, and their propensity to escape through the walls of conventional containers, and due to the need to compress them to great pressures, and / or to reduce their temperature to very low temperatures to liquefy the hydrogen. As a consequence, both the hydrogen storage containers and the filling equipment - in particular in respect of the processes and equipment required for compressing or liquefying the hydrogen ready for such storage or transportation - are costly to produce and use. For example, many hydrogen storage solutions require extremely low temperatures - known as cryogenic temperatures. Further, most hydrogen storage solutions require large levels of externally supplied energy - both to operate the electrolyser and to generate the high pressures and low temperatures required for liquefying (or sufficiently compressing) the hydrogen ready for loading into suitable storage vessels.

[0008] The present invention seeks to address, overcome or mitigate at least one of the prior art disadvantages.

[0009] Summary of the invention

[0010] In a first aspect there is provided an electrolyser system comprising: at least one electrolyser cell having a first inlet for supply of fuel to a first fluid volume (i.e., of the at least one electrolyser cell) and a first outlet for exhaust of off-gas from the first fluid volume at a relatively low pressure, the off-gas configured to comprise unused fuel and a first product of an electrolyser reaction; a steam supply configured to supply steam at a relatively high pressure; means for mixing two fluids; a first heat exchanger; and a fuel supply, wherein the means for mixing is configured to exhaust, at an intermediate pressure, an intermediate fluid comprising a mixture of steam from the supply and off-gas from the first fluid volume, and the system is configured to route said intermediate fluid to a first path of the first heat exchanger and wherein the first heat exchanger is configured to transfer heat from the first path for the intermediate fluid to a second path for fuel from the fuel supply, and wherein: the heat transfer from the first path is configured to separate water from the first product of the electrolyser reaction by condensing liquid water out of the intermediate fluid, the system is configured to route the first product of the electrolyser reaction out of the system at the intermediate pressure, and the system is configured to route fuel from the second path of the first heat exchanger to the first inlet of the at least one electrolyser cell (i.e., at the relatively low pressure).

[0011] In this way the first aspect allows an electrolyser cell (e.g., a cell unit, a stack of cell units, or a module containing a cell unit or stack thereof) to be operated at a relatively low pressure while the electrolyser system nevertheless produces the first product at a higher (intermediate) pressure. This reduces cost and regulatory burden of the electrolyser cell, since the cell need not operate at high pressure. At the same time, the first product is provided at the intermediate pressure which technically eases and reduces the cost of further pressurisation of the first product. Said first product is pressurised by the means for mixing alongside steam. Pressurisation of this mixed fluid is more efficient and easier to do than pressurisation of pure first product (especially when the first product is hydrogen). The pressure difference between paths of the first heat exchanger enables efficient energy transfer therein and the intermediate pressure of the first path leads to efficient separation of first product and water, by condensation of the latter. The steam at relatively high pressure is typically waste steam, which may be of low quality and can be "dirty" from other industrial processes. Industrial processes may produce low grade waste steam as a by-product. Such steam may be treated as waste due to impurities or contamination therein. Nonetheless, it may carry useful heat and is typically available at a pressure above ambient which reduces efficiency if wasted. The aspect enables use of such pressurised, often "dirty" steam comprising contaminants, in the electrolyser system to improve efficiency of the system without contamination of the at least one electrolyser cell. Meanwhile, any contaminants introduced to the product (e.g., hydrogen) stream may be acceptable in a downstream application therefor or removed in (downstream) hydrogen polishing systems.

[0012] The separated water is typically liquid water - separable as a result of condensation of steam in the first heat exchanger. The fuel for use in the at least one electrolyser cell may comprise at least one of steam, carbon dioxide, and nitrogen dioxide. Preferably, the said fuel is steam. In such cases, the fuel supply may be a supply of (liquid) water to be routed as fuel (steam) to the first inlet of the at least one electrolyser cell. Said steam may be raised from liquid water supplied to the second path of the first heat exchanger. Preferably the at least one electrolyser cell comprises an electrolyte that conducts oxygen ions (for example, a solid oxide electrolysis cell, SOEC) and so the first product comprises hydrogen when the fuel comprises steam (or CO, NO if the fuel is CO2,NO2, respectively). The first fluid volume of the at least one electrolyser cell is for fuel and the first product of the electrolysis reaction. The at least one electrolyser cell may comprise a second fluid volume for second product of the electrolysis reaction (e.g., oxygen if the electrolyte conducts oxygen ions) and, optionally, a sweep gas.

[0013] The off-gas from the first fluid volume typically comprises first product and unused fuel. The heat transfer from the first path is configured to separate water from the first product of the electrolyser reaction by condensing liquid water out of the intermediate fluid, the intermediate fluid comprising steam from the steam supply, first product, and unused fuel from the first fluid volume (which may itself comprise steam). It will be understood that there may not be complete separation of water from the first product. For example, heat transfer may result in a stream that comprises at least 60% first product at least 70% first product, preferably at least 80% first product, more preferably at least 90% first product by weight. In other words, the stream may be wet hydrogen, which may be subsequently further dried.

[0014] It will be appreciated that the intermediate pressure is between that of the steam supply at relatively high pressure and the relatively low pressure in the first fluid volume or at first outlet of electrolyser cell. The relatively high pressure may at least 5 barg, preferably at least 8 barg, more preferably at least 10 barg. The relatively high pressure may be no more than 20 barg, preferably no more than 15 barg. The relatively low pressure may be no more than 3 barg, preferably no more than 2 barg, no more than 1.5 barg, preferably no more than 1.0 barg, more preferably less than 0.5 barg such that the at least one electrolyser cell need not be capable of operation at elevated pressures. The relatively low pressure is typically not less than ambient. It will be appreciated that the intermediate pressure at which the first product of the electrolyser reaction is routed out of the system may be the same as, but typically smaller than, the intermediate pressure of the intermediate fluid output from the means for mixing due to pressure loss in pipes and the first heat exchanger, but nonetheless between the relatively low and relatively high pressures.

[0015] The first heat exchanger may be referred to as a two-phase or condenser-evaporator heat exchanger. The first path is for separation of water and first product. The second path may be for production of steam from liquid water by heat transfer from the first path. The first heat exchanger is configured to transfer heat to the second path for fuel. Said heat may raise steam. Said heat is also configured to raise the temperature of the fuel for use in the at least one electrolyser cell. The first heat exchanger is preferably a counter-flow heat exchanger. The ejector may be referred to as a compressor since it acts to compress the off-gas from the first fluid volume. The at least one electrolyser cell may be a solid oxide electrolyser cell, SOEC, a molten carbonate cell, or an alkaline electrolyte cell, but preferably a SOEC and may be a metal-supported SOEC in which the electrochemically active area (fuel electrode, electrolyte, air electrode) are coated on and supported by a metal support plate. The at least one electrolyser cell may operate at a first temperature, for example between 400 and 700 degrees C, preferably between 450 and 600 degrees C, in other words an operating temperature of an intermediate temperature electrolyser cell. The intermediate temperature electrolyser cell may be a solid oxide electrolyser cell (SOEC), and may comprise a ceria-based electrolyte.

[0016] Preferably, the means for mixing comprises an ejector configured to eject, at the intermediate pressure, the intermediate fluid comprising the mixture of steam from the supply and off-gas from the first fluid volume. An ejector is an efficient component for mixing two fluids at different pressures and exhausting a mixed fluid at intermediate pressure.

[0017] Preferably, the electrolyser system comprises a heat source configured to transfer heat to the fuel routed from the first heat exchanger to the at least one electrolyser cell. Said heat source may further raise the temperature of the fuel for use in the at least one electrolyser cell. Said heat source may comprise a heat exchanger or heater configured to transfer heat to fuel.

[0018] Preferably, the electrolyser system comprises a second heat exchanger configured to transfer heat from the off-gas from the first fluid volume to the fuel routed from the first heat exchanger to the at least one electrolyser cell. The second heat exchanger enables efficient recovery of heat from the off-gas to the fuel, and so improves efficiency of the electrolyser system. The second heat exchanger may be located on the path of off-gas from the first fluid volume upstream of the means for mixing (e.g., ejector) and downstream of first outlet of the at least one electrolyser cell. The second heat exchanger may be located on the path of fuel upstream of the first inlet of the at least one electrolyser cell and downstream of the first heat exchanger. The second heat exchanger is preferably a counter-flow heat exchanger.

[0019] Preferably, the electrolyser system further comprises a heater for heating fuel upstream of the first inlet of the at least one electrolyser cell. The heater is preferably downstream of the second heat exchanger, where present. In such cases, the heater may be referred to as a topping heater. The heater may be an electrical heater. Said heater may enable control of temperature of the electrolyser cell.

[0020] Preferably, the at least one electrolyser cell has a second outlet for exhaust of second off-gas from a second fluid volume of the at least one electrolyser cell, the second off-gas configured to comprise a second product of the electrolyser reaction, the system further comprising a third heat exchanger configured to transfer heat from the second off-gas from the second fluid volume to the fuel routed from the first heat exchanger to the at least one electrolyser cell. In cases where the electrolyte conducts oxygen ions, the second product is oxygen. Preferably, the second off-gas at second outlet comprises at least 50%, more preferably at least 70%, more preferably at least 90% of second product of the electrolyser reaction by weight - the remainder being an optional sweep gas (which may be air). In some cases there may be no sweep gas and the off-gas at the second outlet consists of the second product. The third heat exchanger may be located on the path of the second off-gas upstream of an outlet from system and downstream of second outlet of the at least one electrolyser cell. The third heat exchanger may be located on the fuel path upstream of the second heat exchanger and downstream of the first heat exchanger. The third heat exchanger is preferably a counter-flow heat exchanger. Said location for the third heat exchanger may maximise heat transfer and so system efficiency.

[0021] Preferably, the at least one electrolyser cell has a second inlet for supply of sweep gas to the second fluid volume of the at least one electrolyser cell, the system further comprising a fourth heat exchanger configured to transfer heat to the sweep gas routed to the at least one electrolyser cell. The sweep gas may be or comprise air, oxygen, or nitrogen. The fourth heat exchanger may be configured to transfer heat from the second off-gas from the second fluid volume to the sweep gas routed to the at least one electrolyser cell. The fourth heat exchanger may be located on the path for second off-gas upstream of the third heat exchanger and downstream of second outlet of the at least one electrolyser cell. The fourth heat exchanger may be located on the path for sweep gas upstream of the second inlet and downstream of a supply of sweep gas. The fourth heat exchanger may be a counter-flow heat exchanger. Said location for the fourth heat exchanger may maximise heat transfer and so system efficiency.

[0022] Preferably, the electrolyser system comprises a second heater for heating sweep gas upstream of second inlet of the at least one electrolyser cell. The second heater is preferably downstream of the fourth heat exchanger, where present. In such cases, the second heater may be referred to as a topping heater. The second heater may be an electrical heater. Said second heater may enable control of temperature of the electrolyser cell.

[0023] Preferably the fuel comprises steam. The fuel may be at least 75% steam, preferably at least 90% steam by weight, more preferably consist of steam. In such cases, where the electrolyte is an oxygen ion conducting electrolyte, the first product comprises H2, the second product is 02, and unused fuel - steam - is configured to be condensed out at the first heat exchanger. In such cases, the first path of the first heat exchanger is preferably configured to produce said steam for supply of fuel to the first inlet of the at least one electrolyser cell. In such cases, heat transfer from the first path to the second path of the first heat exchanger is configured to raise steam from liquid water in the second path. Preferably, the first heat exchanger is configured to produce at least 50%, preferably at least 70 %, more preferably at least 90%, even more preferably all of the steam for use by the at least one electrolyser cell.

[0024] Preferably, the electrolyser system comprises a boiler (sometimes referred to as a vaporiser) configured to produce steam for supply of fuel to the first inlet of the at least one electrolyser cell. The boiler may be fed liquid water from the same source as that configured to feed the first heat exchanger. The boiler may be an electrical boiler. The system is configured to combine steam raised by the boiler with steam raised by the first heat exchanger. Said combining may be upstream of the second and / or third heat exchanger. Said boiler may improve flexibility of the electrolyser system and may enable resilience of the system against variability of the relatively high pressure steam supply. In steady state use, at least 50%, preferably at least 70%, preferably at least 90% by weight, preferably all of the steam supplied as fuel to the at least one electrolyser cell may be raised by the first heat exchanger (the balance from the boiler).

[0025] According to a second aspect there is provided a method of operating an electrolyser system, the method comprising: supplying steam at a relatively high pressure from a steam supply; supplying off-gas from a first fluid volume of an electrolyser cell at a relatively low pressure; mixing of steam from the supply and off-gas from the first fluid volume to form an intermediate fluid at a first temperature; supplying a fuel from a fuel supply; transferring heat from a first path of a first heat exchanger for the intermediate fluid to a second path for fuel, wherein said transferring heat separates water from a first product of the electrolyser reaction by condensing liquid water out of the intermediate fluid routing the first product of the electrolyser reaction out of the system at the intermediate pressure; routing fuel from the second path of the first heat exchanger to a first inlet of the at least one electrolyser cell, the first inlet an inlet to the first fluid volume; and using said fuel in the at least one electrolyser cell.

[0026] In this way the method allows an electrolyser cell (e.g., a cell unit, a stack of cell units, or a module containing a cell unit or stack thereof) to be operated at a relatively low pressure while the electrolyser system nevertheless produces the first product at a higher (intermediate) pressure. This reduces cost and regulatory burden of the electrolyser cell, since the cell need not operate at high pressure. At the same time, the first product is provided at the intermediate pressure which technically eases and reduces the cost of further pressurisation of the first product. The steam at relatively high pressure is typically waste steam, which may be of low quality and can be "dirty" from other industrial processes. Said "dirty" steam, comprising contaminants is used without contamination of the electrolyser cell. The first temperature may be the intermediate temperature described above.

[0027] Preferably, the method comprises transferring heat to the fuel routed from the first heat exchanger to the at least one electrolyser cell. Said transferring of heat may be via one or more of the heat exchangers and heater described above for the first aspect.

[0028] Preferably, the method comprises removing of second off-gas from a second fluid volume of the at least one electrolyser cell, the second off-gas comprising a second product of the electrolyser reaction.

[0029] Preferably, the method comprises supplying a sweep gas to the second fluid volume of the at least one electrolyser cell. Preferably, the method comprises transferring heat to the sweep gas to be routed to the second fluid volume of the at least one electrolyser cell.

[0030] Preferably, the fuel comprises steam, wherein steam is raised from water on the second path of the first heat exchanger.

[0031] Preferably, the off-gas from the first fluid volume comprises hydrogen. In such cases, the fuel typically comprises steam.

[0032] Preferably the method of the second aspect is a method of operation of the electrolyser system of the first aspect, and includes components described with respect to the first aspect. Preferably, the electrolyser system referred to in the second aspect is the electrolyser system of the first aspect.

[0033] Particular and preferred aspects of the invention are set out in the accompanying independent claims. Combinations of features from the dependent claims may be combined with features of the independent claims as desired and appropriate and not merely as explicitly set out in the claims. The term "comprising" as used herein to specify the inclusion of components also includes embodiments in which no further components are present.

[0034] An enabling disclosure of the present invention, to one of ordinary skill in the art, is provided herein. Reference now will be made in detail to embodiments of the invention, one or more examples of which are set forth below. Each example is provided by way of explanation of the invention, and not limitation of the invention.

[0035] Brief Description of the Drawings

[0036] Features of the present invention will now be described in further detail, by way of various embodiments, and just by way of example, with reference to the accompanying drawings (which drawings are not to scale, in which:

[0037] Figure 1 is a schematic view of a first example electrolyser system.

[0038] Figure 2 is a schematic view of a second example electrolyser system.

[0039] Figure 3 is a schematic view of a third example electrolyser system.

[0040] Figure 4 is a schematic view of a fourth example electrolyser system.

[0041] Figure 5 depicts an example method of operation of an electrolyser system.

[0042] In the following figures and description like reference numerals will be used for like elements in different figures.

[0043] Detailed Description Referring to Fig. 1, a schematic view of an example electrolyser system 100 is shown. The electrolyser system 100 includes a stack comprising at least one electrolyser cell 120 (also referred to as a cell unit), a steam supply 105, an ejector 115, a first heat exchanger 125, a fuel supply 106, an optional heat source 140, a first product outlet 112 (e.g., for hydrogen), a condensate outlet 111, an optional sweep gas supply 107, and a second product outlet 110 (e.g., for oxygen).

[0044] The at least one electrolyser cell 120 will be described as a cell which has an oxygen-conducting electrolyte. The at least one electrolyser cell 120 and / or the stack thereof provides a first fluid volume for fuel supplied via first inlet 121 and a first product of the electrolysis reaction exhausted (along with unused fuel) from the first fluid volume by first outlet 122. First product and any unused fuel exhausted from the first fluid volume, via outlet 122, are together referred to as off-gas exhausted from the first fluid volume. The at least one electrolyser cell 120 and / or the stack thereof provides a second fluid volume for optional sweep gas (e.g., air, oxygen, or nitrogen) supplied from a supply 107 via optional second inlet 123 and a second product of the electrolysis reaction exhausted (along with sweep gas, if present) from the second fluid volume by second outlet 124 to second product outlet 110. Second product and sweep gas, if present, exhausted from the second fluid volume, via outlet 124, are together referred to as off-gas exhausted from the second fluid volume.

[0045] The ejector 115 serves as a means for mixing two fluids of differing pressures. The ejector 115 has a first inlet 116a fluidically connected to the first outlet 122 of the at least one electrolyser cell 120, a second inlet 116b fluidically connected to a steam supply 105, and an outlet 117 fluidically connected to the first heat exchanger 125. In this way, the ejector 115 is configured to receive, at inlet 116a, relatively low pressure off-gas from the first fluid volume of the at least one electrolyser cell 120 and to receive relatively high pressure steam at inlet 116b from a steam supply 105. The ejector is configured to mix the fluids from its two inlets 116a, b and eject the mixed fluid at outlet 117. The fluid ejected from the outlet 117 is referred to as an intermediate fluid herein since it is configured to have an intermediate pressure, i.e., a pressure between that of the fluids supplied to the inlets 116a, b of the ejector 115.

[0046] The ejector 115, which may also be referred to as a steam ejector, is configured to entrain low- pressure off-gas at first inlet 116a into relatively high-pressure steam at second inlet 116b while preventing backflow and pressure fluctuations upstream. An ejector sends high-pressure (motive) steam through a reduced passageway (nozzle), accelerating it and converting its pressure energy to velocity. This high velocity energy in turn creates a suction effect that will draw the low- pressure stream into the mixing chamber and entrain it into the motive flow. The increased mass of the mixed / combined stream flow causes velocity to decrease, and as the flow expands again through a diffuser section, the velocity energy is converted back to pressure energy. In other words, an ejector uses thermocompression to mix flows of two different pressures and output steam at a mid-level pressure somewhere between those of the composite flows. This is what makes it possible to raise the relatively low pressure off-gas to usable levels (i.e., the intermediate pressure of the intermediate fluid or composite flow). The outlet of the ejector 115 is f I uidically connected to a first inlet 126 of the first heat exchanger 125. The first heat exchanger 125 is a two-phase heat exchanger, and has a counter-flow configuration. The first inlet 126 is an inlet to a first path in the first heat exchanger 125. Said first path has two outlets: an outlet 127a for liquid and an outlet 127b for gas (including vapour). A second path of the first heat exchanger has a second inlet 128 and a second outlet 129. The second inlet 128 is fluidically connected to a fuel source, specifically a source of water (usually liquid water). The second outlet 129 is fluidically connected to the first inlet 121 of the at least one electrolyser cell 120. The first heat exchanger is configured for heat exchange (transfer) between the first and second paths, particularly from the first path to the second path. In use, said heat exchange results in raising steam from liquid water on the second path, such that fluid at the second outlet 129 is or comprises steam. Said heat exchange cools the fluid in the first path, and is configured to condense liquid water out of the intermediate fluid provided to the first path at the inlet 126 (water from steam from the steam supply 105 and unused fuel from the first outlet 122 of the at least one electrolyser cell 120). Said liquid water is removed from the first heat exchanger 125 at the outlet 127a and may be removed from the system at condensate drain 111. Other components of the intermediate fluid, typically first product (e.g., hydrogen) of the electrolyser reaction, are removed from the first heat exchanger 125 at outlet 127b and routed to first product outlet 112. Condensation may not be complete, in which case the first product may be a "wet" first product, e.g., the stream routed to first product outlet 112 may be at least 60% first product, preferably at least 70% first product, preferably at least 80% first product, more preferably at least 90% first product by weight. In other words, the stream may be wet hydrogen, which may be subsequently further dried.

[0047] The second outlet 129 of the first heat exchanger 125 is fluidically connected to the first inlet 121 of the at least one electrolyser cell 120, optionally via a heat source 140. Heat source 140 may be provided to raise the temperature of the fuel for use in the at least one electrolyser cell 120. Heat source 140 may be an electrical heater. In some cases, fuel, in particular comprising steam, output from the first heat exchanger 125 (at second outlet 129) may have a temperature of 120 to 300 degrees C, and the heat source 140 may increase the temperature of the fuel to an operating temperature of the at least one electrolyser cell 120, for example between 400 and 700 degrees C, preferably between 450 and 600 degrees C. In other examples, the fuel output from the first heat exchanger may be at a suitable temperature for provision to the at least one electrolyser cell 120 as a result of the steam supply 105 supplying the majority or all of the required heat for the fuel. Preferably the first heat exchanger 125 is a single heat exchanger, however, in some implementations of Fig. 1 is may be necessary to provide a series of heat exchangers dependent on maximum temperature differentials within said heat exchanger.

[0048] The sweep gas source 107 may be fluidically connected to the second inlet 123 of the at least one electrolyser cell 120 via a heat source (e.g., an electrical heater, not shown) in order that temperature gradients are minimised and operating temperatures of the at least one electrolyser cell are maintained.

[0049] In use, fuel supplied by the supply 106 to the first heat exchanger 125 is heated in the second path of the first heat exchanger by heat exchange from the first path. When the fuel is water, liquid water is vaporized to steam in this process. Fuel may be further heated by heat source 140. Heated fuel is routed to the first inlet 121 of the at least one electrolyser cell 120, specifically the first fluid volume thereof. Electrical power is also supplied to the at least one electrolyser cell. The at least one electrolyser cell converts the fuel to a first product, released into the first fluid volume, and a second product, released into the second fluid volume. In an example where the electrolyte of the at least one electrolyser cell conducts oxygen ions and the fuel is steam, the first product is hydrogen and the second product is oxygen.

[0050] Sweep gas from the sweep gas source 107 may be supplied to the second fluid volume (optionally via a heat source to heat the sweep gas) via second inlet 123 in order to drive flow in said second fluid volume to the second outlet 124. Second product and, where present, sweep gas is removed from the second fluid volume at the second outlet 124 and routed to the second product outlet 110.

[0051] First product (e.g., hydrogen) and unused fuel is removed from the first fluid volume at the first outlet 122 and routed to the first inlet 116a of the ejector 115. The fuel (as routed through the first heat exchanger and the at least one electrolyser cell) and first product are at a relatively low pressure. Relatively high pressure steam from steam supply 105 is routed to the second inlet 116b of the ejector 115. Said steam supply is advantageously waste steam, which may be dirty or contaminated, from other industrial processes, and typically has a temperature of 120-700 degrees C. The pressure of steam supplied by the steam supply may be at least 5 barg, preferably at least 8 barg, more preferably at least 10 barg. Typically it will be at most 15 barg since higher pressure steam would typically be used elsewhere. Steam temperatures of at least 300 degrees C may be preferred in this example. The ejector 115 combines streams from the first inlet 116a and second inlet 116b to eject a intermediate fluid at the outlet 117 of the ejector 115. The intermediate fluid is at an intermediate pressure as a mixture of steam from the steam supply 105, first product and unused fuel (which may be further steam) from the first outlet 122 of the at least one electrolyser cell 120.

[0052] The intermediate fluid is routed to the first inlet 126 of the first heat exchanger 125, and on the first path of the first heat exchanger, exchanges heat with (transfers heat to) the fuel on the second path. As the intermediate fluid is cooled by heat exchange, liquid water is condensed therefrom and removed via the outlet 127a to a condensate outlet 111. As a result, remaining species in the first path is first product (e.g., hydrogen) of the electrolyser reaction, that first product is routed out of the first heat exchanger 125 via the outlet 127b and routed to the first product outlet 112 - where the first product may be stored or otherwise used.

[0053] As a result of the electrolyser system 100, the at least one electrolyser cell can be operated at a relatively low pressure while the electrolyser system nevertheless produces the first product at a higher (intermediate) pressure. This reduces cost and regulatory burden of the electrolyser cell, since the cell need not operate at high pressure. At the same time, the first product is provided at the intermediate pressure which technically eases and reduces the cost of further pressurisation of the first product. The steam at relatively high pressure is typically waste steam, which may be of low quality and can be "dirty" from other industrial processes. Said "dirty" steam, comprising contaminants is used without contamination of the electrolyser cell. Referring to Fig. 2, a schematic view of an example electrolyser system 200 is shown. Electrolyser system 200 includes various similar components and functions to electrolyser system 100, those having similar reference numerals, and will not be described further. Electrolyser system 200 comprises a second heat exchanger 230 and a third heat exchanger 235. The system need not include both second and third heat exchangers. It will also be appreciated that where both second and third heat exchangers are present their order on the fuel path (i.e., between second outlet 129 of the first heat exchanger 125 and the first inlet 121 of the at least one electrolyser cell 120) may be reversed relative to that of Fig. 2. Each of the second and third heat exchangers work to recover heat from the off-gasses from the at least one electrolyser cell 120 and thereby increase efficiency of the electrolyser system 200 relative to electrolyser system 100.

[0054] The third heat exchanger 235 is configured to transfer heat from the off-gas from the second fluid volume (on a second path through the third heat exchanger) to fuel (on a first path through the third heat exchanger), and may be a counter-flow heat exchanger. With regard to the fuel path, the third heat exchanger 235 is downstream of the first heat exchanger 125, upstream of the at least one electrolyser cell 120, and upstream of the second heat exchanger 230 and heat source 140. A first inlet 236 of the third heat exchanger 235 is f I uidically connected to the second outlet 129 of the first heat exchanger. Accordingly, fuel from the second outlet 129 of the first heat exchanger 125 is routed to the first inlet 236 of the third heat exchanger 235. The first inlet 236 is fluidically connected to a first outlet 237 via a first path of the third heat exchanger 235. The first outlet 237 is fluidically connected to the first inlet 121 of the at least one electrolyser cell 120 (in some examples via the second heat exchanger 230 and / or heat source 140). Fuel on the first path is heated by heat exchange with the second path of the third heat exchanger 235. With regard to the off-gas path from the second fluid volume, the third heat exchanger 235 is downstream of the at least one electrolyser cell 120 and upstream of the second product outlet 110. Second outlet 124 of the at least one electrolyser cell 120 is fluidically connected to a second inlet 238 of the third heat exchanger 235. The second path through the third heat exchanger connects the second inlet 238 and a second outlet 239. The second outlet 239 is fluidically connected to the second product outlet 110, and configured to route off-gas from the second fluid volume thereto. The third heat exchanger 235 is configured to exchange heat between the second path and the first path. In use, heat in the off-gas from the second fluid volume is recovered by transfer to fuel at the third heat exchanger 235 before the off-gas is routed to the second product outlet 110.

[0055] The second heat exchanger 230 is configured to transfer heat from the off-gas from the first fluid volume (on a second path through the second heat exchanger) to fuel (on a first path through the second heat exchanger), and may be a counter-flow heat exchanger. With regard to the fuel path, the second heat exchanger 230 is downstream of the first heat exchanger 125, upstream of the at least one electrolyser cell 120, downstream of the third heat exchanger 235, and upstream of the heat source 140. A first inlet 231 of the second heat exchanger 230 is fluidically connected to the second outlet 129 of the first heat exchanger (in some examples, as shown in Fig. 2, via the third heat exchanger and so fluidically connected to the first outlet 237 of the third heat exchanger). Accordingly, fuel from the second outlet 129 of the first heat exchanger 125 is routed to the first inlet 231 of the second heat exchanger 230. The first inlet 231 is fluidically connected to a first outlet 232 via a first path of the second heat exchanger 230. The first outlet 232 is fluidically connected to the first inlet 121 of the at least one electrolyser cell 120 (in some examples via the heat source 140). Fuel on the first path is heated by heat exchange with the second path of the second heat exchanger 230. With regard to the off-gas path from the first fluid volume, the second heat exchanger 230 is downstream of the at least one electrolyser cell 120 and upstream of the ejector 115. First outlet 122 of the at least one electrolyser cell 120 is f I uidically connected to a second inlet 233 of the second heat exchanger 230. The second path through the second heat exchanger 230 connects the second inlet 233 and a second outlet 234. The second outlet 234 is fluidically connected to the first inlet 116a of the ejector 115, and configured to route offgas from the first fluid volume thereto. The second heat exchanger 230 is configured to exchange heat between the second path and the first path. In use, heat in the off-gas from the first fluid volume is recovered by transfer to fuel at the second heat exchanger 230 before the off-gas is routed to the ejector 115.

[0056] Referring to Fig. 3, a schematic view of an example electrolyser system 300 is shown. Electrolyser system 300 includes various similar components and functions to electrolyser system 200, those having similar reference numerals, and will not be described further. Electrolyser system 300 comprises a fourth heat exchanger 345 and a heat source 350. The system need not include both fourth heat exchanger 345 and heat source 350. Indeed, heat source 350 is a depiction of the optional heat source previously described with respect to sweep gas which may be provided to the second inlet 123 of the at least one electrolyser cell 120. The fourth heat exchanger 345 works to recover heat from the off-gas from the second volume of the at least one electrolyser cell 120 and thereby increase efficiency of the electrolyser system 300 relative to electrolyser system 200.

[0057] The fourth heat exchanger 345 is configured to transfer heat from the off-gas from the second fluid volume (on a second path through the fourth heat exchanger) to sweep gas (on a first path through the fourth heat exchanger), and may be a counter-flow heat exchanger. With regard to the sweep gas path, the fourth heat exchanger 345 is downstream of the sweep gas source 107, upstream of the at least one electrolyser cell 120 (second inlet 123 thereof), and upstream of the heat source 350. Accordingly, sweep gas from the sweep gas source 107 is routed via the first path of the fourth heat exchanger 345 to the at least one electrolyser cell 120 (second inlet 123 thereof). With regard to the path of off-gas from the second fluid volume, the (second path of the) fourth heat exchanger 345 is downstream of the at least one electrolyser cell 120 (fluidically connected to the second outlet 124 thereof) and upstream of the third heat exchanger 235 (fluidically connected to the second inlet 238 thereof). Sweep gas on the first path is heated by heat exchange with the second path of the fourth heat exchanger 345. In use, heat in the off-gas from the second fluid volume is recovered by transfer to sweep gas at the fourth heat exchanger 345 before the off-gas is routed to the third heat exchanger 235 for further heat recovery from the off gas, transferred to the fuel as described with reference to Fig. 2.

[0058] Referring to Fig. 4, a schematic view of an example electrolyser system 400 is shown. Electrolyser system 400 includes various similar components and functions to electrolyser system 300, those having similar reference numerals (some of which have been redacted for clarity), and will not be described further. Electrolyser system 400 comprises a boiler 455 for raising additional steam for use as fuel in the at least one electrolyser cell 120 and may be used for start-up of the system or otherwise in situations where the steam supply 105 cannot be used or cannot meet demand from the at least one electrolyser cell 120. In steady state use, at least 50%, preferably at least 70%, preferably at least 90% by weight, preferably all of the steam supplied as fuel to the at least one electrolyser cell may be raised by the first heat exchanger (the balance from the boiler). Boiler 455 may be an electrical boiler. Boiler 455 may alternatively be provided with heat from an external source. The boiler 455 may be supplied with liquid water from the supply 106. An outlet of boiler 455 is fluidically connected to the first inlet 121 of the at least one electrolyser cell 120 (for example via the first inlet 236 to the third heat exchanger, and / or via the first inlet 231 to the second heat exchanger, and / or via the heat source 140), such that steam raised by the boiler 455 may be routed to and used as fuel in the at least one electrolyser cell 120. It will be understood that boiler 455 may be added to the electrolyser systems 100 or 200 (of Figs. 1, 2) in the same manner and for the same reasons as described above.

[0059] Referring to Fig. 5, a method 500 of operating an electrolyser system is depicted. The method 500 may be carried out using the electrolyser system described with reference to any of the preceding figures. At step 505, the method comprises supplying steam at a relatively high pressure from a steam supply. At step 510, the method comprises supplying off-gas from a first fluid volume of an electrolyser cell at a relatively low pressure. At step 515, the method comprises mixing of steam from the supply and off-gas from the first fluid volume to form an intermediate fluid at an first (or intermediate) temperature. At step 520, the method comprises supplying a fuel from a fuel supply. At step 525, the method comprises transferring heat from a first path of a first heat exchanger for the intermediate fluid to a second path for fuel, wherein said transferring heat separates water from the first product of the electrolyser reaction by condensing liquid water out of the intermediate fluid. At step 530, the method comprises routing the product of the electrolyser reaction out of the system at the intermediate pressure. At step 535, the method comprises routing fuel from the second path of the first heat exchanger to a first inlet of the at least one electrolyser cell, the first inlet an inlet to the first fluid volume. At step 540, the method comprises using said fuel in the at least one electrolyser cell.

[0060] The present invention is not limited to the above examples only, and other examples will be readily apparent to one of ordinary skill in the art without departing from the scope of the appended claims.

[0061] These and other features of the present invention have been described above purely by way of example. Modifications in detail may be made to the invention within the scope of the claims.

Claims

Claims1. An electrolyser system comprising: at least one electrolyser cell having a first inlet for supply of fuel to a first fluid volume and a first outlet for exhaust of off-gas from the first fluid volume at a relatively low pressure, the off-gas configured to comprise unused fuel and a first product of an electrolyser reaction; a steam supply configured to supply steam at a relatively high pressure; means for mixing two fluids; a first heat exchanger; and a fuel supply, wherein the means for mixing is configured to exhaust, at an intermediate pressure, an intermediate fluid comprising a mixture of steam from the supply and off-gas from the first fluid volume, and the system is configured to route said intermediate fluid to a first path of the first heat exchanger and wherein the first heat exchanger is configured to transfer heat from the first path for the intermediate fluid to a second path for fuel from the fuel supply, and wherein: the heat transfer from the first path is configured to separate water from the first product of the electrolyser reaction by condensing liquid water out of the intermediate fluid, the system is configured to route the first product of the electrolyser reaction out of the system at the intermediate pressure, and the system is configured to route fuel from the second path of the first heat exchanger to the first inlet of the at least one electrolyser cell.

2. The electrolyser system of claim 1, further comprising a heat source configured to transfer heat to the fuel routed from the first heat exchanger to the at least one electrolyser cell.

3. The electrolyser system of claim 1 or 2, further comprising a second heat exchanger configured to transfer heat from the off-gas from the first fluid volume to the fuel routed from the first heat exchanger to the at least one electrolyser cell.

4. The electrolyser system of any preceding claim, further comprising a heater for heating fuel upstream of the first inlet of the at least one electrolyser cell.

5. The electrolyser system of any preceding claim, wherein the at least one electrolyser cell has a second outlet for exhaust of second off-gas from a second fluid volume of the at least one electrolyser cell, the second off-gas configured to comprise a second product of the electrolyser reaction, the system further comprising a third heat exchanger configured to transfer heat from the second off-gas from the second fluid volume to the fuel routed from the first heat exchanger to the at least one electrolyser cell.

6. The electrolyser system of claim 5, wherein the at least one electrolyser cell has a second inlet for supply of sweep gas to the second fluid volume of the at least one electrolysercell, the system further comprising a fourth heat exchanger configured to transfer heat to the sweep gas routed to the at least one electrolyser cell.

7. The electrolyser system of claim 6, further comprising a second heater for heating sweep gas upstream of second inlet of the at least one electrolyser cell.

8. The electrolyser system of any preceding claim, wherein the fuel comprises steam.

9. The electrolyser system of claim 8, wherein the first path of the first heat exchanger is configured to produce said steam for supply of fuel to the first inlet of the at least one electrolyser cell.

10. The electrolyser system of claim 8 or 9, further comprising a boiler configured to produce steam for supply of fuel to the first inlet of the at least one electrolyser cell.

11. The electrolyser system of any preceding claim, wherein the means for mixing comprises an ejector configured to eject, at the intermediate pressure, the intermediate fluid comprising the mixture of steam from the supply and off-gas from the first fluid volume.

12. A method of operating an electrolyser system, the method comprising: supplying steam at a relatively high pressure from a steam supply; supplying off-gas from a first fluid volume of an electrolyser cell at a relatively low pressure; mixing of steam from the supply and off-gas from the first fluid volume to form an intermediate fluid at a first temperature; supplying a fuel from a fuel supply; transferring heat from a first path of a first heat exchanger for the intermediate fluid to a second path for fuel, wherein said transferring heat separates water from a first product of the electrolyser reaction by condensing liquid water out of the intermediate fluid; routing the first product of the electrolyser reaction out of the system at the intermediate pressure; routing fuel from the second path of the first heat exchanger to a first inlet of the at least one electrolyser cell, the first inlet an inlet to the first fluid volume; and using said fuel in the at least one electrolyser cell.

13. The method of claim 12, further comprising transferring heat to the fuel routed from the first heat exchanger to the at least one electrolyser cell.

14. The method of claim 12 or 13, further comprising removing of second off-gas from a second fluid volume of the at least one electrolyser cell, the second off-gas comprising a second product of the electrolyser reaction.

15. The method of claim 14, further comprising supplying a sweep gas to the second fluid volume of the at least one electrolyser cell.

16. The method of claim 15, further comprising transferring heat to the sweep gas to be routed to the second fluid volume of the at least one electrolyser cell.

17. The method of any one of claims 12 to 16, wherein the fuel comprises steam, wherein steam is raised from water on the second path of the first heat exchanger.

18. The method of any one of claims 12 to 17, wherein the off-gas from the first fluid volume comprises hydrogen.

19. The method of any one of claims 12 to 18, wherein the electrolyser system is the electrolyser system of any one of claims 1 to 11.

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