Method for supplying a compressed combined gas stream

Abstract

The present invention relates to a method for supplying a compressed combined gas stream comprising hydrogen and carbon dioxide for at least one downstream process, preferably for production of alcohols (e.g. methanol) or carbon fuels. More specifically, disclosed is a method wherein the hydrogen gas stream is dosed with a carbon dioxide gas stream and the combined gas stream is compressed in a multistage compression system.

Description

[0001] METHOD FOR SUPPLYING A COMPRESSED COMBINED GAS STREAM

[0002] TECHNICAL FIELD

[0003] The present invention relates to a method for supplying a compressed combined gas stream comprising hydrogen and carbon dioxide for at least one downstream process, preferably for production of alcohols (e.g. methanol) or carbon fuels. More specifically, disclosed is a method wherein the hydrogen gas stream is dosed with a carbon dioxide gas stream and the combined gas stream is compressed in a multistage compression system, wherein the multistage compression system comprises at least one compression stage.

[0004] BACKGROUND

[0005] Production of hydrogen gas using renewable energy is of high importance e.g . for Power-to-X technologies. This is because hydrogen gas produced from electrolysis can be converted into chemical compounds, such as alcohols, e.g . methanol or carbon fuels. Specifically for such processes, it may be advantages to be able to provide a gas stream of a specified pressure.

[0006] Compressors are mechanical devices used to increase the pressure of a gas by reducing its volume. They are used in a wide range of applications, from refrigeration and air conditioning systems to industrial processes. Several types of compressors exist. The most widely used types of compressors for pressurizing gases are centrifugal compressors, reciprocating compressors and screw compressors. Each type of compressor has its own advantages and disadvantages and is suited to specific types of applications. The choice of compressor depends on factors such as the required pressure, flow rate, and the nature of the gas being compressed .

[0007] Recently, it has been found to be possible to provide a suitably compressed gas stream comprising low molecular weight gases, however at this point, known methods using centrifugal or reciprocal or screw compression are not suitable for production of alcohols (e.g . methanol) or carbon fuels.

[0008] Centrifugal compressors are a type of dynamic compressor, wherein gas is compressed by mechanical action of rotating vanes or impellers imparting velocity to the gas. Typically, a gas stream enters at the centre of the impellers and is propelled out to the radial edges under rotary motion, hence gas is delivered at high velocity such to impact the casing . The velocity of the gas is converted to a static pressure to deliver high pressure gases. Centrifugal compressors have been known to be specifically suitable for handling large volumes of gases whereas for low molecular weight gases (e.g. hydrogen), it has been known to be difficult to establish sufficient centrifugal force due to the lower density of the gas, hence making high-pressure compression more difficult to achieve.

[0009] Reciprocal compressors, also known as piston compressors, are a type of dynamic compressor, wherein gas is compressed by mechanical action of pistons driven by a crank shaft. A gas stream is drawn through an inlet on the intake stroke of the piston and moved through a cavity or chamber that decreases in size on the upward stroke. This compresses the gas within the chamber, resulting in a pressure increase. Reciprocal compressors have been known to be suitable for high pressure application. However, it is known to be difficult to establish sufficient force when compressing low molecular weight gases (e.g. hydrogen) due to the lower density of the gas.

[0010] Rotary Screw Compressors use two meshing helical screws, known as rotors, which operate in opposite directions to compress the gas. This movement draws in gas that is compressed as the space between the rotors and their housing decreases. The compressed gas is then displaced to the outlet. Screw compressors have been known to be suitable for high pressure applications that continue over long period of time. However, it is known to be difficult to establish sufficient force when compressing low molecular weight gases (e.g. hydrogen) due to the lower density of the gas.

[0011] To evaluate if a specified pressure of a gas may be provided from the outlet of centrifugal, reciprocal or screw compressor, it is useful to consider the pressure ratio for a particular stage of compression. Said pressure ratio is defined as the discharge pressure divided by the inlet pressure, for said stage of compression. Using centrifugal, reciprocal or screw compression, the pressure ratio is highly sensitive to - and dependent on - the molecular weight of the gas being compressed. Hence it follows, compression of a gas with a low molecular weight may result in a discharge pressure at the outlet, which is lower than the specified pressure, unless additional impellers, pistons or screws are used. Typically, to compress a low molecular weight gas in a centrifugal compression system, such a system must be designed with many more impellers in series to accommodate the reduced gas density. This design substantially increases the cost of the compression system and is undesirable due to the inherent mechanical constraints of such a system. Some methods and systems have been provided in the art, however the provided compressed gas comprises nitrogen, which is not suitable for production of alcohols or carbon fuels.

[0012] There is therefore a need in the art to provide a solution suitable for production of alcohols or carbon fuels which will allow a compression system to maintain pressure ratios in an efficient way when used with low molecular weight gases, without dramatically increasing costs. Such a system and the development of a method for supplying a compressed combined gas stream comprising hydrogen and carbon dioxide would add significant value in production of specifically alcohols (e.g. methanol) or fuels.

[0013] SUMMARY

[0014] It has been found that a compressed combined gas stream comprising carbon dioxide and hydrogen can be provided when a hydrogen gas stream is dosed with a carbon dioxide gas stream and such combined gas stream is compressed in a multistage compression system comprising at least one compression stage.

[0015] So, in a first aspect the present invention relates to a method for supplying a compressed combined gas stream, the method comprising : electrolysing a water stream to provide a hydrogen gas stream; wherein the hydrogen gas stream is dosed with a carbon dioxide gas stream, to provide a combined gas stream; compressing the combined gas stream in a multistage compression system to provide a compressed combined gas stream; wherein the multistage compression system comprises at least one compression stage; such that a compressed combined gas stream comprising carbon dioxide and hydrogen is output from the multistage compression system.

[0016] In a second aspect the present invention relates to a method of using a compressor for compressing hydrogen gas, the method comprising dosing hydrogen gas with carbon dioxide gas upstream of the compressor (which may be a centrifugal, reciprocal or screw compressor) to provide a combined gas stream and compressing the combined gas stream in the compressor.

[0017] The present inventor(s) have further developed a suitable apparatus for supplying a compressed combined stream. Hence, in a third aspect the present invention relates to an apparatus for supplying a compressed combined gas stream, the apparatus comprising : an electrolyser stage arranged to electrolyse a water stream to a hydrogen gas stream; a carbon dioxide gas source arranged to supply a carbon dioxide gas stream, wherein the source is arranged to dose the hydrogen gas stream with said carbon dioxide gas stream, to provide a combined gas stream; a multistage compression system, the multistage compression system comprising at least one compression stage arranged to compress the combined gas stream to a compressed combined gas stream, said at least one compression stage comprising a feed end, an outlet end and at least one compressor, the feed end being in fluid flow communication with the plurality of electrolysers via a feed header; and at least one downstream processing unit arranged to receive at least a portion of the compressed combined gas stream, from the multistage compression system.

[0018] Further details of the method and apparatus for supplying a compressed combined stream, are specified in the following detailed description, figures, and claims.

[0019] FIGURES

[0020] Fig. 1 shows a first schematic illustration of the method.

[0021] Fig. 2 shows a second schematic illustration of the method.

[0022] Fig. 3 shows a further schematic illustration of the method.

[0023] DETAILED DISCLOSURE

[0024] Unless otherwise specified, any given percentages for gas content are % by volume.

[0025] In a first aspect the present invention relates to a method for supplying a compressed combined gas stream, the method comprising : electrolysing a water stream to provide a hydrogen gas stream; wherein the hydrogen gas stream is dosed with a carbon dioxide gas stream, to provide a combined gas stream; compressing the combined gas stream in a multistage compression system to provide a compressed combined gas stream; wherein the multistage compression system comprises at least one compression stage; such that a compressed combined gas stream comprising carbon dioxide and hydrogen is output from the multistage compression system.

[0026] The hydrogen gas stream The term "hydrogen gas stream" refers to the hydrogen gas stream before it has been dosed with the carbon dioxide stream. The hydrogen gas stream may be provided from water electrolysis and will thus be saturated with water vapour at the temperature of the electrolyser system. Typically, said hydrogen gas stream comprises above 85 vol%, above 90 vol%, above 92 vol%, such as above 95 vol% or above 98 vol% hydrogen gas. The hydrogen gas stream may further comprise a portion of residual oxygen gas, such as 500, 1000, 2000 to 4000 ppmv and balance water vapour. Alternatively, said hydrogen gas stream may be further purified to remove at least a portion of the residual oxygen gas and / or at least a portion of the water.

[0027] The hydrogen gas stream may be provided from any suitable water electrolyser stage. Consequently, an apparatus for supplying a compressed combined stream may comprise an electrolyser stage arranged to electrolyse a water stream to a hydrogen gas stream. The water electrolyser stage may be arranged to receive a water stream, preferably a desalinated and demineralised water stream. Such desalinated and demineralised water stream may be provided by desalinating a sea water stream followed by further demineralisation. Preferably, the water electrolyser stage comprises at least one "low" pressure electrolyser such as an electrolyser operating at <5 bar g. Said at least one "low" pressure electrolyser may be either an alkaline water electrolyser, a Solid Oxide Electrolyser Cell (SOEC) or a Proton Exchange Membrane (PEM) electrolyser. Typically, the hydrogen gas stream from said electrolyser stage has a pressure of <5 bar g, preferably 0 - 3 bar g such as 0.5 bar g such as 0.3 bar g. The water stream may also be a steam stream.

[0028] The electricity for driving the water electrolysis may be generated by any source. However, preferably, at least one renewable energy source provides at least a portion of the electricity for the water electrolysis. Such renewable energy sources may be wind energy, solar energy, tidal energy, hydroelectric energy, or combinations hereof, most preferably wind energy and / or solar energy. In this way, renewable sources may provide power to the electrolyser(s). Most preferably, renewable sources such as wind energy and / or solar energy provides enough energy to cover the total electricity demand for driving the water electrolysis, hence the electrolysis is solely driven on renewable energy.

[0029] However, renewable energy sources are not always reliable, hence conditions where renewable energy source cannot sufficiently sustain the required electricity demand may occur. More specifically, such conditions may be during periods of high demand for product(s) from the downstream process(es) and / or during periods where the availability of said renewable energy sources is below the threshold to meet the demand such as when said renewable energy sources of wind and / or sun is / are not available. One solution to meet such conditions is to arrange for other energy sources may supplement with additional electricity / power. Additional electricity from other energy sources suitable for supplying may be provided from onsite battery storage and / or generated from one or more petrol-, diesel- or hydrogen-powered generator(s) including fuel cells. Alternatively, or additionally, additional electricity may be provided from the local or national grid.

[0030] The carbon dioxide gas stream

[0031] The carbon dioxide gas source may be a pipeline, a CO2 container or a carbon capture facility, hence the carbon dioxide gas stream may be provided from a pipeline, a CO2 container or carbon capture facility. The carbon capture facility may be direct air capture or point source. Typically, said carbon dioxide gas stream comprises above 80 vol% carbon dioxide gas, such as above 90 vol% carbon dioxide such as above 95 vol% carbon dioxide such as above 98 vol%. The carbon dioxide gas stream may further comprise carbon monoxide such as less than 50 ppmv such as 20 ppmv such as 10 ppmv.

[0032] The carbon dioxide gas stream may also comprise other contaminants such as N2, NH3, NOx, O2, SOx, VOC and H2O in the combined amounts of 0.1 to 5000 ppm.

[0033] The hydrogen gas stream being dosed with the carbon dioxide gas stream

[0034] The hydrogen gas stream is dosed with a carbon dioxide gas stream, to provide a combined gas stream. Herein, "dosed with" is used to describe that carbon dioxide gas is fed to the hydrogen gas in small amounts to provide a combined gas stream comprising hydrogen and carbon dioxide, wherein the majority of the combined gas is hydrogen gas. In this way, the term "combined gas" specifically refers to hydrogen gas after it has been dosed with carbon dioxide.

[0035] The combined gas stream may comprise carbon dioxide in an amount up to about 30 mol % such as up to 25 mol % such as up to 20 mol % such as up to 10 mol % such as up to 5 mol%. Additionally, the combined gas stream may comprise carbon dioxide in an amount of at least about 0.05 mol % such as at least of about 0.1 mol %, such as at least of about 0.5 mol %, such as at least of about 1 mol %, e.g. at least of about 2 mol %. Preferably, the combined gas stream may comprise carbon dioxide in an amount in a range from about 0.5 mol % to about 20 mol %. More preferably, the combined gas stream may comprise carbon dioxide in an amount ranging from about 1 mol % to about 10 mol %, such as from about 2 mol % to about 4 mol %, most preferably of about 3 mol %.

[0036] The effect of the hydrogen gas being dosed with carbon dioxide is that it provides an increase in the apparent molecular weight of the combined gas stream relative to the hydrogen gas stream. The apparent molecular weight of the combined gas stream is important to the performance of centrifugal compression. Herein, the apparent molecular weight is used to describe the molecular weight of a gaseous medium having an admixture of low and high molecular weight constituents. The apparent molecular weight of a gas mixture can be measured or alternative estimated by calculating the sum of the products of the mole fraction of each component times the molecular weight of that component, i.e. Mapp= (MA X YA + MB x yB+...) for a mixture of gasses comprising component gas A and component gas B and..., where Mxis the molecular weight of a component gas X and yxis the mole faction of the component gas X.

[0037] Typically, the hydrogen gas stream will have an increased apparent molecular weight compared to pure hydrogen gas due to water being present in the hydrogen steam. The hydrogen gas stream will have an apparent molecular weight of between 2.016 being the molecular weight of pure hydrogen gas and 18.015 being the apparent molecular weight of wet hydrogen gas saturated with water. In this way, the hydrogen gas may have an apparent molecular weight of from about 2.5 to about 4, or from about 2.5 to about 3.5, such as of about 3. Typically, the carbon dioxide gas stream will have a decreased apparent molecular weight compared to pure carbon dioxide due to the presence of additional compounds / gases in the stream.

[0038] The combined gas stream may have an apparent molecular weight in a range from about 2.05 to about 7. However, as the combined gas stream may be compressed over a plurality of stages and further be dosed one or more times, the apparent molecular weight of the combined gas stream may vary throughout the system.

[0039] To dose said hydrogen gas steam, an apparatus for supplying a compressed combined stream may comprise a carbon dioxide gas source arranged to supply a carbon dioxide gas stream, wherein the source is arranged to dose the hydrogen gas stream with said carbon dioxide gas stream, to provide a combined gas stream. The flow of carbon dioxide gas may be controlled such that a suitable amount of carbon dioxide gas is provided from said carbon dioxide gas source. Such suitable amount may be selected base on the amount of hydrogen gas generated by electrolysis as this may be dependent on the renewable energy source. According, the method may further provide that the amount of hydrogen gas being provided by the electrolysis of water is variable, and the hydrogen gas is dosed with the carbon dioxide gas in an amount determined based upon the amount of hydrogen gas being provided by the electrolysis. Specifically, the amount of carbon dioxide used to dose the hydrogen gas stream may be controlled such that the concentration of carbon dioxide in the combined gas stream is constant. Additionally, such control allows for specific selection of the carbon dioxide concentration in said combined gas stream. Additionally, or alternatively, said suitable amount may be selected based on the amount of water present in the hydrogen gas stream. If the hydrogen gas stream is a wet hydrogen stream less carbon dioxide gas may be added (such as upstream an initial compression stage, followed by additional dosing upstream a downstream compression stage), whereas if the hydrogen gas stream is dry more carbon dioxide may be added such to provide a hydrogen gas of having an apparent molecular weight such as of above 2.05.

[0040] The increase in the apparent molecular weight of the combined gas stream specifically improves the performance of the centrifugal compression stage (specifically of the compressor within said stage) comprised in the multistage compression system. Generally, a compression stage is responsible for compressing a stream having a first pressure being the inlet pressure to said stream having a second pressure being the discharge pressure. The compression stage may comprise a centrifugal, reciprocal or screw compression stage or a combination of such stages. Specifically for a centrifugal, reciprocal or screw compression stage, said increase in the apparent molecular weight results in a discharge pressure at the outlet which may be within a specified pressure range, and such allows for a suitable pressure ratio (the discharge pressure divided by the inlet pressure, for a particular stage of compression). Consequently, adequate compression can be achieved for low molecular weight gases.

[0041] More specifically, the increase in apparent molecular weight of the combined gas stream caused by the presence of carbon dioxide has the advantage that the apparent molecular weight of said combined gas stream stays above a threshold value (e.g. about 2.05). This is of significance as the temperature of a gas increases when compressed. Additionally, a multistage compression system may comprise additional cooling arrangements providing temperature control. Consequently, the combined gas may be exposed to a temperature range. The fact that said apparent molecular weight of said combined gas stream stays above a threshold value over a temperature range allows for a suitable discharge pressure in the centrifugal, reciprocal or screw compression stage (thus also in the multistage compression stage) such that a suitable pressure ratio may be provided.

[0042] Considering the apparent molecular weight of a wet hydrogen gas stream, such apparent molecular weight may not stay above a threshold value. Such wet hydrogen gas stream may have an increased apparent molecular weight caused by the presence of the gaseous water. Accordingly, a wet hydrogen gas stream, such the hydrogen gas stream may have an apparent molecular weight of around 3, such as from about 2.5 to about 4, or from about 2.5 to about 3.5. If such hydrogen gas stream is passed through the multistage compression system, water will be removed from the hydrogen gas due to condensation of the gaseous water and phase separation of liquid water. Such removal of water from the hydrogen gas stream results in a reduced apparent molecular weight of the hydrogen gas i.e. approaching 2.016, and hence significantly effect on the discharge pressure in the centrifugal compression stage causing insufficient compression. In contrast to this, any water optionally present in the combined gas stream, said water and removal of water does not significantly affect the apparent molecular weight as that the apparent molecular weight of said combined gas stream stays above a threshold value (e.g. about 2.05). Hence, the impact of reduced apparent molecular weight on the discharge pressure caused by lose of water in the centrifugal compression stage (hence, in the multistage compression stage) is of no significant importance. Consequently, the performance of the at least one compression stage is not affected. This is a significant advantage over conventional compression systems as the need for mitigating pressure drops is eliminated.

[0043] Compression and arrangements suitable for hydrogen gas stream being dosed with the carbon dioxide gas stream

[0044] The hydrogen gas stream may be dosed with the carbon dioxide stream at various steps within said method for supplying a compressed combined gas stream, hence before or during compression of the gas.

[0045] Herein, a multistage compression system is responsible for compressing the combined gas stream, such as to increase the pressure of the hydrogen gas stream and / or the combined gas stream to the pressure of the compressed combined gas stream. The multistage compression system may comprise one or a plurality of compression stages and associated coolers may be arranged between or after such compression stage(s). The multistage compression system may comprise any type of compression stage(s) such as one or more reciprocal compression stage i.e. a stage comprising at least one reciprocal compressor, however the multistage compression system comprises at least one compression stage. The plurality of compression stages may all be centrifugal compressor stages, alternatively at least a portion of the plurality of compression stages may be centrifugal compressor stages or alternatively, one compressor stage comprised in the multistage compression system is a centrifugal compressor stage. The at least one compression stage may comprise a feed end, an outlet end and at least one centrifugal, screw or reciprocal compressor, wherein said at least one compressor may comprise rotating vane(s), impeller(s) or pistons.

[0046] The plurality of compression stages comprised in the multistage compression system may be arranged such that compression is performed in parallel and / or in series. Accordingly, the multistage compression system may comprise an initial compression stage and an intermediate compression stage. The intermediate compression stage may be arranged in series and downstream the initial compression stage. Additionally, the multistage compression system may comprise one or more sections. Herein, a section comprises one or more compression stages, and each section may comprise a specific arrangement of compression stages. Accordingly, the multistage compression system may further comprise a first section and at least one further section downstream of the first section. Consequently, the multistage compression system may comprise at least one initial compression stage, such as one or more initial compression stages for a first section and for any further sections. Preferably, at least the first or an initial compression stage of said multistage compression system comprises a centrifugal or reciprocal compression stage.

[0047] Specifically, the method comprises a step of compressing the combined gas stream in a multistage compression system to provide a compressed combined gas stream; wherein the multistage compression system comprises at least one compression stage such that at least one compression stage is arranged to compress the combined gas stream to a compressed combined gas stream such that the compressed combined gas stream comprising carbon dioxide and hydrogen is output from the multistage compression system.

[0048] Preferably, said hydrogen gas stream is dosed with the carbon dioxide stream at least in one step of the method upstream the compression step. In this way, the apparent molecular weight of the hydrogen gas stream is increased before compression and thus allow for a multistage compression system comprising smaller, more cost-effective compression stages in addition to further requiring fewer compression stages. Suitably, the hydrogen gas stream or the combined gas stream may further be dosed with carbon dioxide one or more times. The following sections disclose suitable method steps and arrangements of the multistage compression system for dosing the hydrogen gas stream with the carbon dioxide gas stream.

[0049] The multistage compression system may comprise an initial compression stage, wherein said initial compression stage may be any type of compression stage such as preferably at least one centrifugal, reciprocal or screw compression stage. Preferably, the at least one initial compression stage e.g. such as the feed end of the at least one centrifugal, reciprocal or screw compression stage, may be arranged to receive the combined gas stream. In this way, the method may further comprise that the hydrogen gas stream is dosed with the carbon dioxide gas stream upstream of an initial compression stage of the multistage compression system. It is particularly advantageous to have the hydrogen gas stream dosed with the carbon dioxide before any compression of the hydrogen gas stream such as before the multistage compression system, as this ensures a suitable apparent molecular weight before any compression, and such allows for all compression stages being the same centrifugal, reciprocal or screw compression stages. The multistage compression system may comprise an initial compression stage and an intermediate compression stage, wherein the intermediate compression stage is arranged downstream the initial compression stage. The initial compression stage may be any compression such as a centrifugal, reciprocal or screw compression stage and said intermediate stage may be any compression stage such as a centrifugal, reciprocal or screw compression stage. Preferably, the multistage compression system may have at least one centrifugal, reciprocal or screw compression stage in combination with at least one further centrifugal, reciprocal or screw compression stage. In this way, additionally or alternatively, the method may further comprise that the hydrogen gas stream or the combined gas stream is dosed with the carbon dioxide gas stream downstream of an initial compression stage of the multistage compression system and upstream of an intermediate compression stage of the multistage compression system. Said method may be particularly suitable when the compression in the initial stage result in gaseous water being condensed followed by separation of liquid water. In such case, the performance of the intermediate compression stage is improved because of the increased apparent molecular weight of the combined gas stream upstream of an intermediate compression stage. In a specific embodiment, an initial compression stage is not a centrifugal compression stage and said initial compression stage receives the hydrogen gas stream, compresses said hydrogen gas stream followed by said stream being dosed with the carbon dioxide stream upstream of the intermediate compression stage, wherein said intermediate stage comprises a centrifugal compression stage. In another specific embodiment, the initial compression stage is a centrifugal compression stage and said initial compression stage receives the combined gas stream, compress said combined gas stream followed by said stream being further dosed with additional carbon dioxide stream upstream of the intermediate compression stage, said intermediate stage comprising a centrifugal compression stage. In this way, this method allows for the hydrogen gas stream to be dosed followed by said combined gas stream being dosed in one or more steps. The suitable number of dosing steps may depend on the number of intermediate compression stages, the pressure ratio across each of the compression stages and / or water content of the hydrogen gas stream. In methods comprising more than one dosing, said method may further comprise that the carbon dioxide stream is further pressurised before the combined gas stream is dosed with said carbon dioxide stream. Preferably, the combined gas stream is dosed with a carbon dioxide gas stream of similar pressure, such as the same pressure, as that of the combined gas stream.

[0050] Additionally or alternatively, the feed end of the at least one compression stage may be arranged to receive the hydrogen gas stream and the carbon dioxide gas stream or the combined gas stream and an additional carbon dioxide stream. In this way, the method may further comprise that the compression stage has a feed end and the hydrogen gas is dosed with the carbon dioxide gas at the feed end of the compression stage or wherein the compression stage has a feed end and the combined gas stream is dosed with a second carbon dioxide gas stream at the feed end. Preferably, the feed end is in fluid flow communication with at least one or a plurality of electrolysers via a feed header. Said feed end may further be arranged such that the hydrogen gas stream is dosed with the carbon dioxide gas stream at said feed end such to provide a combined gas stream. The compressor is then arranged to compress the combined gas stream such to provide a compressed combined gas stream. In this way, the hydrogen gas stream or the combined gas stream is dosed with the carbon dioxide stream at least in one step of the method upstream the compression. Again, this might be specifically relevant if water has been separated from the hydrogen gas stream or the combined gas stream in a previous compression stage.

[0051] The multistage compression system may further comprise a first section and at least one further section downstream of the first section. Preferably, the first section and the at least one further section each comprises at least one initial compression stage. In this way, the method may further comprise, wherein the multistage compression system comprises a first section and at least one further section downstream of the first section, the hydrogen gas stream or the combined gas stream may be dosed with the carbon dioxide gas stream upstream of an initial compression stage of the first section of the multistage compression system. Additionally or alternatively, the hydrogen gas stream or the combined gas stream may be dosed with the carbon dioxide gas stream downstream of the first section and upstream of an initial compression stage of the at least one further section of the multistage compression system. In this way, this method allows for the hydrogen gas stream may be dosed followed by said combined gas stream being dosed in one or more steps. A preferred arrangement suitable for such method may comprise that a first header may be arranged to collect combined gas stream from each compressor in the first section and feed the combined gas stream to the compressors of the second section such to provide a compressed combined gas stream. More preferably, carbon dioxide gas source may be arranged to feed carbon dioxide gas to the feed header to dose the hydrogen gas or the combined gas stream with carbon dioxide gas. The suitable number of dosing steps may depend on the number of section, the pressure ratio across each of the compression stages and / or water content of the hydrogen gas stream. In methods comprising more than one dosing, said method may further comprise that further carbon dioxide stream(s) is / are further pressurised before the combine gas stream is dosed with said carbon dioxide stream. Preferably, the combined gas stream is does with a carbon dioxide gas stream of similar pressure, such as the same pressure, as that of the combined gas stream.

[0052] In a specific embodiment of the method, in a first section the hydrogen gas stream is dosed with a carbon dioxide gas stream upstream a compression stage comprised in said first section and in a second section the combined gas stream is dosed with a further carbon dioxide gas stream upstream a compression stage comprised in said second section. In a more specific embodiment, the hydrogen gas stream is dosed with a carbon dioxide gas stream at the initial compression stage of the first stage in the first section and the combined gas stream is dosed with a further carbon dioxide gas stream at the initial compression stage of at least one further section downstream of the first section. In specific embodiments, the multistage compression system comprises two sections, a first section in which the hydrogen gas is compressed from the feed pressure to a first increased pressure, wherein feed pressure is the pressure of the hydrogen gas stream when it is fed to the multistage compression system, and a second section in which the hydrogen gas stream is compressed from the first increased pressure to a final increased pressure desired for the downstream processes. Preferably, the first section is a low-pressure section, wherein the hydrogen gas stream is compressed from the feed pressure to a first increased pressure of about 2 bar to about 6 bar and the second section is a medium pressure section, wherein the hydrogen gas stream is compressed from the about 2 bar to about 6 bar to the final increased pressure. More specifically, the first increased pressure may be of about 2 bar to about 3 bar, such as 2.5 bar. Alternatively, the first increased pressure may be of about 4 bar to about 6 bar, such as 5 bar.

[0053] At the step where the hydrogen stream is dosed with said carbon dioxide stream, the pressure of the carbon dioxide stream should preferably be the same as that of the hydrogen gas stream as provided from the electrolyser stage such as ranging from 0 to < 10 bar g, preferably 0 - 5 bar g such as 0.5 bar g such as 0.01 bar g. Alternatively, if the carbon dioxide stream is used to dose a hydrogen gas stream or a combined gas stream that has been through an initial compression stage the further carbon dioxide stream has to be further pressurised before the hydrogen gas stream or the combined gas stream is dosed with said further carbon dioxide stream. The overall pressure ratio across each of the plurality of compression stages comprised in said multistage compression system is suitably 1.5 to 2.5 such as 2 to 2.5. The advantage of such pressure ratios is that such ratios allow for limiting the temperature increase of the compressed combined gas. Additionally, the multistage compression system may require one or more cooler(s), such as between adjacent stages i.e. inter-coolers and / or such as after the final compression stage i.e. after-coolers. In this way, excess heat resulting from compression may be removed from the combined gas stream.

[0054] The compressed combined gas stream

[0055] The compressed combined gas stream comprising carbon dioxide and hydrogen is output the multistage compression system. The compressed combined gas stream may be collected from one or more compressors comprised in said multistage compression system, such be collected from the outlet end of the multistage compression system. Typically, the pressure of said compressed combined gas stream is from about 50 bar to about 150 bar. Specifically, the pressure of said compressed combined gas stream may be from about 60 bar to about 145 bar, preferably 80 bar to about 140 bar. Alternatively, the pressure of said compressed combined gas stream may be from about 90 bar to about 130 bar, preferably 100 bar to about 120 bar. The pressure of the compressed combined gas stream is preferably at least a little higher than the feed pressure of the downstream process.

[0056] Preferably compressed combined gas stream comprises carbon dioxide in an amount in a range from about 0.5 mol % to about 30 mol %. Said compressed combined stream may further comprise residual oxygen gas and / or water. The compressed combined gas stream may further have an apparent molecular weight in a range from about 2.0 to about 16. More specifically, the compressed combined gas stream may have an apparent molecular weight in a range from about 2.1 to about 17, such as from about 2.5 to about 16, most preferably from about 2.5 to about 15.5. In this way, the compressed combined gas stream has an increased apparent molecular weight relative to a pure hydrogen gas stream of 2.06.

[0057] Typically, the compressed combine gas stream has an apparent molecular weight ranging from 0.1 to 8.06. times the apparent molecular weight of the hydrogen gas stream, such as 0.5 to 7.6 times, such as 1.0 to 7.0 times the apparent molecular weight of the hydrogen gas stream.

[0058] The method may further comprise a step of feeding at least a portion of the compressed combined gas stream to a downstream process(es). The method may further comprise that said downstream process(es) consumes carbon dioxide. A specific advantage of downstream process(es) consuming carbon dioxide is that the carbon dioxide gas used to dose the hydrogen gas stream does not need to be removed at a later step, hence no additional equipment is need for such removal. Said downstream process(es) may be process(es) for synthesis of alcohols (e.g. methanol) or carbon fuels, said process(es) being known in the art. Suitably, at least one downstream processing unit may be arranged to receive at least a portion of the compressed combined gas stream, from the multistage compression system. Within said downstream processing unit the compressed combined gas stream may be reacted with addition carbon dioxide gas, typically at temperatures of 150 to 400 C and pressures in the range from about 100 bar to about 200 bar.

[0059] The method may further comprise that further carbon dioxide gas is added as required to the compressed combined gas stream upstream of the downstream process(es). The amount of added carbon dioxide may depend on the amount of carbon dioxide already comprised in said compressed combined gas stream. This may be advantageous to provide a compressed combined gas steam of a specific composition suitable for a specific carbon dioxide consuming downstream process(es). In this way, the method may comprise adding carbon dioxide gas two or more times such as least one time in a dosing step upstream the at least one compression stage and further adding additional carbon dioxide to the compressed combined gas stream.

[0060] As previously discussed, the availability of energy from the renewable sources may vary e.g. be dependent on weather conditions. Consequently, conditions and periods may occur where more hydrogen gas is produced by the electrolysis than is required for the downstream process(es). Under such conditions it is advantageous that at least a portion of the additional hydrogen i.e. a portion of the hydrogen produces in excess, is used to provide additional compressed combined gas stream and that said additional compressed combine gas stream can be stored. Storage of such compressed combined gas is suitably achieved at a further increased pressure. Additionally or alternatively, the at least a portion of the more hydrogen may be used elsewhere such as in a plant. Conditions and periods may also occur where the amount of hydrogen gas produces by electrolysis is not sufficient to reach the required amount for the downstream process(es) i.e. more compressed combined gas stream is required for the downstream process(es). Under such conditions it is advantageous to withdraw compressed combined gas from storage. Withdrawing such compressed combined gas may require suitable pressure reduction followed by feeding the reduced pressure combined gas stream to a compression stage of the multistage compression system, hence said pressure is reduced to an appropriate level having regard to the inlet pressure of the compression stage to which the carbon dioxide gas stream is fed.

[0061] Having the possibility of supplying a compressed combined gas stream from storage when an insufficient amount of hydrogen gas is produced by electrolysis has the advantage that the carbon dioxide gas stream and carbon dioxide gas source does not have to be shot down, when hydrogen is not being produced. Hence the arrangement for storage, provide a more robust production line (i.e. potential saves significant costs as starting up and shutting down parts of production lines are time consuming and may result in a decrease of product production). Accordingly, the method may further comprise, that, during periods when more hydrogen gas is produced by the electrolysis than is required for the downstream process(es), the method comprises feeding excess compressed combined gas stream to storage, optionally after further compression; wherein during periods when more combined gas stream is required for the downstream process(es) than is produced by the electrolysis, the method comprises withdrawing compressed combined gas stream from storage and, after suitable pressure reduction, feeding the reduced pressure combined gas stream to a stage of the multistage compression system. Preferably the method further comprises that the hydrogen gas is dosed with the carbon dioxide gas upstream of the stage of the multistage compression system to which the reduced pressure combined gas stream is fed during periods when more combined gas stream is required than is produced by the electrolysis. Method of using a centrifugal compressor for compressing hydrogen gas

[0062] In a second aspect, the present invention relates to a method of using a compressor for compressing hydrogen gas, the method comprising dosing hydrogen gas with carbon dioxide gas upstream of the compressor to provide a combined gas stream and compressing the combined gas stream in the compressor. In this method, the compressor may be a centrifugal, reciprocal or screw compressor.

[0063] Apparatus

[0064] In a third aspect, the present invention relates to an apparatus for supplying a compressed combined gas stream, the apparatus comprising : an electrolyser stage arranged to electrolyse a water stream to a hydrogen gas stream; a carbon dioxide gas source arranged to supply a carbon dioxide gas stream, wherein the source is arranged to dose the hydrogen gas stream with said carbon dioxide gas stream, to provide a combined gas stream; a multistage compression system the multistage compression system comprising at least one compression stage arranged to compress the combined gas stream to a compressed combined gas stream, said at least one compression stage comprising a feed end, an outlet end and at least one compressor, the feed end being in fluid flow communication with the plurality of electrolysers via a feed header; and at least one downstream processing unit arranged to receive at least a portion of the compressed combined gas stream, from the multistage compression system.

[0065] Said apparatus may further comprise that the carbon dioxide gas source is arranged to feed carbon dioxide gas stream to the feed header to dose the hydrogen gas stream with carbon dioxide gas, and the multistage compression system contains a single section, the section comprising a plurality of compression stages arranged in parallel, each compression stage comprising at least one centrifugal and / or reciprocating compression stage; the apparatus further comprising a header to collect compressed combined gas stream from each compression stage and feed the compressed combined gas stream to the downstream processing unit(s), or to a purification system upstream of the downstream process unit(s).

[0066] The apparatus may further comprise that the multistage compression system further comprises: a first section comprising a plurality of compression stages arranged in parallel; and a second section downstream of said first section, said second section comprising a plurality of compression stages arranged in parallel; the apparatus comprising : a first header to collect compressed combined gas stream from each compression stage in the first section and feed the compressed combined gas stream to the compression stage of the second section; and a second header to collect compressed combined gas stream from each compression stage in the second section and feed the compressed combined gas stream to the downstream processing unit(s), or to a purification system upstream of the downstream processing unit(s), wherein the carbon dioxide gas source is arranged to feed the carbon dioxide gas stream to the feed header to dose the hydrogen gas stream with carbon dioxide gas.

[0067] The apparatus may further comprise a control system for controlling flow of carbon dioxide gas stream from the carbon dioxide gas source, the flow being determined based on the level of production of hydrogen gas by the electrolyser stage. Such control may further be provided from a feedback loop, which takes into account information about the concentration of carbon dioxide in the combined gas stream.

[0068] The apparatus may further comprise a storage system for storing compressed hydrogen gas comprising the carbon dioxide gas, the storage system being in fluid flow communication with the outlet end of the multistage compression system and at least one compression stage of the multistage compression system, and the carbon dioxide gas source may be arranged to dose the hydrogen gas stream with carbon dioxide gas upstream of the point at which the storage system is in fluid flow communication with the at least one centrifugal compression stage of the multistage compression system.

[0069] In the apparatus described herein, the compression stage may comprise a centrifugal, reciprocal or screw compression stage or a combination of such stages.

[0070] Specific embodiments

[0071] Figure 1 illustrates a method or a layout for an apparatus according to the invention. A water stream (1) is electrolysed in electrolyser stage (10) to provide a hydrogen gas stream (11). The hydrogen gas stream (11) is dosed with a carbon dioxide gas stream (2), to provide a combined gas stream (5). The combined gas stream (5) is compressed in a multistage compression system (20) to provide a compressed combined gas stream (21). The multistage compression system (20) comprises at least one compression stage (20A). A compressed combined gas stream (21) comprising carbon dioxide and hydrogen is output from the multistage compression system (20).

[0072] Figure 2 illustrates a method or layout as per figure 1, in which the combined gas stream (5) is dosed with the carbon dioxide gas stream (2) at the feed end (22) of the compression stage (20).

[0073] Figure 3 illustrates a multistage compression system (20) responsible for compressing the combined gas stream (5), such as to increase the pressure of the hydrogen gas stream (11) and / or the combined gas stream (5) to the pressure of the compressed combined gas stream (21). The multistage compression system may comprise one or a plurality of compression stages (25, 29) and associated coolers (30) may be arranged between or after such compression stage(s). The multistage compression system may comprise any type of compression stage(s) (25, 29) such as one or more reciprocal compression stage i.e. a stage comprising at least one reciprocal compressor, however the multistage compression system comprises at least one compression stage. The plurality of compression stages may all be centrifugal compressor stages, alternatively at least a portion of the plurality of compression stages may be centrifugal compressor stages or alternatively, one compressor stage comprised in the multistage compression system is a centrifugal compressor stage. The at least one compression stage may comprise a feed end (22, 26), an outlet end (24, 28) and at least one centrifugal, screw or reciprocal compressor (23, 27), wherein said at least one compressor (23, 27) may comprise rotating vane(s), impeller(s) or pistons.

Claims

CLAIMS1. A method for supplying a compressed combined gas stream, the method comprising : electrolysing a water stream (1) to provide a hydrogen gas stream (11); wherein the hydrogen gas stream (11) is dosed with a carbon dioxide gas stream (2), to provide a combined gas stream (5); compressing the combined gas stream (5) in a multistage compression system (20) to provide a compressed combined gas stream (21); wherein the multistage compression system (20) comprises at least one compression stage (25); such that a compressed combined gas stream (21) comprising carbon dioxide and hydrogen is output from the multistage compression system (20).

2. The method according to claim 1, further comprising a step of feeding at least a portion of the compressed combined gas stream (21) to a downstream process(es);3. The method according to any one of the preceding claims, the compressed combined gas stream (21) comprises carbon dioxide in an amount in a range from about 0.5 mol % to about 30 mol %.

4. The method according to any one of the preceding claims, the compressed combined gas stream (21) has an apparent molecular weight in a range from about 2.05 to about 16.

5. The method according to any one of the preceding claims, wherein the hydrogen gas stream (11) is dosed with the carbon dioxide gas stream (2) upstream of an initial compression stage of the multistage compression system.

6. The method according to any one of the preceding claims, wherein the hydrogen gas stream (11) or the combined gas stream (5) is dosed with the carbon dioxide gas stream (2) downstream of an initial compression stage of the multistage compression system and upstream of an intermediate compression stage of the multistage compression system.

7. The method according to any one of the preceding claims, wherein the compression stage has a feed (22) end and the hydrogen gas stream (11) or the combined gas stream (5) is dosed with the carbon dioxide gas stream (2) at the feed end (22) of the compression stage (20) or wherein the compression stage has a feed end (22) and the combined gas stream (5) is dosed with a second carbon dioxide gas stream (2b) at the feed end.

8. The method according to any one of the preceding claims, wherein the downstream process(es) consumes carbon dioxide.

9. The method according to any one of the preceding claims, wherein further carbon dioxide gas is added as required to the compressed combined gas stream (21) upstream of the downstream process(es).

10. The method according to any one of the preceding claims, wherein the multistage compression system comprises a first section and at least one further section downstream of the first section, and wherein the hydrogen gas stream (11) or the combined gas stream (5) is dosed with the carbon dioxide gas stream (2) upstream of an initial compression stage of the first section of the multistage compression system or wherein the hydrogen gas stream (11) or the combined gas stream (5) is dosed with the carbon dioxide gas stream (2) downstream of the first section and upstream of an initial compression stage of the at least one further section of the multistage compression system.

11. The method according to any one of the preceding claims, wherein during periods when more hydrogen gas is produced by the electrolysis than is required for the downstream process(es), the method comprises feeding excess compressed combined gas stream (21B) to storage, optionally after further compression. wherein during periods when more combined gas stream is required for the downstream process(es) than is produced by the electrolysis, the method comprises withdrawing compressed combined gas stream from storage (21B) and, after suitable pressure reduction, feeding a reduced pressure combined gas stream (21C) to a compression stage of the multistage compression system.

12. The method according to claim 11, wherein the hydrogen gas stream (11) or the combined gas stream (5) is dosed with the carbon dioxide gas stream (2) upstream of the compression stage of the multistage compression system to which the reduced pressure combined gas stream is fed during periods when more combined gas stream is required than is produced by the electrolysis.

13. The method according to any one of the preceding claims, wherein the amount of hydrogen gas being provided by the electrolysis of water is variable, and the hydrogen gas stream (11) or the combined gas (5) is dosed with the carbon dioxide gas in an amount determined based upon the amount of hydrogen gas being provided by the electrolysis.

14. A method of using a compressor for compressing hydrogen gas, the method comprising dosing hydrogen gas with carbon dioxide gas upstream of the compressor to provide a combined gas stream and compressing the combined gas stream in the compressor.

15. Apparatus for supplying a compressed combined gas stream, the apparatus comprising : an electrolyser stage (10) arranged to electrolyse a water stream (1) to a hydrogen gas stream (11); a carbon dioxide gas source arranged to supply a carbon dioxide gas stream (2), wherein the source is arranged to dose the hydrogen gas stream (11) with said carbon dioxide gas stream (2), to provide a combined gas stream (5); a multistage compression system (20) the multistage compression system (20) comprising at least one compression stage (25) arranged to compress the combined gas stream (11) to a compressed combined gas stream (21), said at least one compression stage comprising a feed end, an outlet end and at least one compressor, the feed end being in fluid flow communication with the plurality of electrolysers via a feed header; and at least one downstream processing unit arranged to receive at least a portion of the compressed combined gas stream, from the multistage compression system.

16. The apparatus according to claim 15, wherein the carbon dioxide gas source is arranged to feed carbon dioxide gas stream (2) to the feed header to dose the hydrogen gas stream (11) with carbon dioxide gas, and the multistage compression system contains a single section, the section comprising a plurality of compression stages arranged in parallel, each compression stage comprising at least one compressor; the apparatus further comprising a header to collect compressed combined gas stream from each compression stage and feed the compressed combined gas stream (21) to the downstream processing unit(s), or to a purification system upstream of the downstream process unit(s).

17. The apparatus according to any one of claims 15-16, wherein the multistage compression system comprises:a first section comprising a plurality of compression stages arranged in parallel; and a second section downstream of said first section, said second section comprising a plurality of compression stages arranged in parallel; the apparatus comprising : a first header to collect compressed combined gas stream from each compression stage in the first section and feed the compressed combined gas stream to the compression stage(s) of the second section; and a second header to collect compressed combined gas stream from each compression stage in the second section and feed the compressed combined gas stream to the downstream processing unit(s), or to a purification system upstream of the downstream processing unit(s), wherein the carbon dioxide gas source is arranged to feed the carbon dioxide gas stream (2) to the feed header to dose the hydrogen gas stream (11) with carbon dioxide gas.

18. The apparatus according to any one of claims 15-17, comprising a control system for controlling flow of carbon dioxide gas stream from the carbon dioxide gas source, the flow being determined based on the level of production of hydrogen gas by the electrolyser stage (10).

19. The apparatus according to any one of claims 15-18, comprising a storage system for storing compressed hydrogen gas comprising the carbon dioxide gas, the storage system being in fluid flow communication with the outlet end of the multistage compression system and at least one compression stage of the multistage compression system, and wherein the carbon dioxide gas source is arranged to dose the hydrogen gas stream (11) with carbon dioxide gas upstream of the point at which the storage system is in fluid flow communication with the at least one centrifugal compression stage of the multistage compression system.

20. The method according to any one of claims 1-13 or the apparatus according to any one of claims 15-19, wherein the compression stage comprises a centrifugal, reciprocal or screw compression stage or a combination of such stages.

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