WO2025253086A1

WO2025253086A1 - Process for the production of hydrogen

Info

Publication number: WO2025253086A1
Application number: PCT/GB2025/051055
Authority: WO
Inventors: Peter Edward James Abbott; Majid SADEQZADEH BOROUJENI
Original assignee: Johnson Matthey Davy Technologies Ltd
Current assignee: Johnson Matthey Davy Technologies Ltd
Priority date: 2024-06-07
Filing date: 2025-05-15
Publication date: 2025-12-11
Anticipated expiration: 2026-12-07
Also published as: GB202507515D0; GB202408119D0

Abstract

A process for the production of hydrogen is described comprising the steps of: (i) reforming a gaseous mixture comprising a hydrocarbon and steam having a steam to carbon ratio in the range of 0.4:1 to 1.8:1, to in a reforming unit comprising an autothermal reformer to produce a reformed gas mixture, (ii) subjecting the reformed gas mixture to an isothermal water-gas shift reaction in an isothermal water-gas shift reactor using water as a heat exchange medium, thereby increasing the hydrogen content of the reformed gas mixture and producing a hydrogen-enriched reformed gas while raising steam, cooling at least some of the hydrogen-enriched reformed gas and separating condensed water therefrom to provide a de-watered hydrogen-enriched reformed gas, (iv) subjecting at least some of the de-watered hydrogen-enriched reformed gas to carbon dioxide separation by performing a reactive amine wash on the hydrogen-enriched reformed gas in a carbon dioxide separation unit to recover carbon dioxide gas and crude hydrogen gas, and (v) subjecting at least some of the crude hydrogen gas to purification in a hydrogen purification unit to produce a purified hydrogen gas and a tail gas, wherein a portion of the tail gas is recycled to the process.

Description

P102471 1 PROCESS FOR THE PRODUCTION OF HYDROGEN Field of the Invention This invention relates to a process for converting hydrocarbons to hydrogen (H₂) while _{maximising steam for export, carbon capture potential, and feedstock efficiency by recycling} _{a tail gas of the process to the process and operating a water gas shift reaction of the process} isothermally. Background to the Invention Processes for generating low carbon hydrogen, often referred to as “blue hydrogen”, are well- known. One major use of blue hydrogen is in the decarbonisation of refinery or petrochemicals _{facilities, which often comprise many fired heaters and fired boilers that use natural gas or} _{other fossil-derived fuels. Capturing carbon dioxide from the low pressure flue gases produced} _{by these sources may not be a cost effective solution for decarbonisation. Instead, for the} _{purpose of decarbonisation, it is more viable to use low carbon hydrogen as a fuel in the fired} heaters. However, greater efficiencies may be obtained if the steam produced in the fired _{boilers can be replaced with low carbon steam, thus reducing the need for, or entirely avoiding} _{use of, fired boilers for steam production. In these situations, therefore, there is a need for a} process to make blue hydrogen which not only has a high feedstock use efficiency, but which also exports a large quantity of low carbon (blue) steam. Generally, processes for the production of blue hydrogen include a steam reforming stage combined with a water-gas shift reaction stage. In the steam reforming stage, a feed stream of a gaseous mixture of hydrocarbon (predominantly methane) and steam is reformed (CnH2n+2 _{+ n H2O ^ n CO + (2n+1) H2) to produce a reformed gas mixture. The steam reforming stage} typically comprises an autothermal reformer (ATR), optionally after a step of adiabatic pre- _{reforming, so that most of the CO2 is formed in the reformed gas stream itself, rather than in} _{a low pressure flue gas stream. The CO2 can thus be removed more efficiently. In an ATR, a} _{portion of the hydrocarbon in the feed stream is typically combusted sub-stoichiometrically} _{with high purity oxygen to provide the heat required for steam reforming reactions for the} remainder of the feed stream adiabatically over a catalyst bed. _{The reformed gas, usually after cooling, is typically subjected to a water-gas shift stage. In} the water-gas shift stage, the H₂ content of the reformed gas mixture is increased using a P102471 2 _{water-gas shift reaction (CO +} _{CO2 + H2), to produce a hydrogen-enriched reformed} gas mixture, from which carbon dioxide (CO2) is then removed in a CO2 removal stage. The carbon dioxide can then be sequestered. The water-gas shift reaction is typically performed adiabatically in two sequential steps, respectively at a high temperature (typically above 320°C) and at a low temperature (below 230°C but typically above 190°C), to achieve a high overall conversion of the carbon monoxide (CO) in the reformed gas mixture. Thus, unconverted CO in the process is reduced, which _{also reduces the amount of unconverted CO that has to be recycled to the steam reforming or} _{water-gas shift stage and/or that is lost from the process, typically as a constituent of a low} pressure fuel stream. In addition to being driven by the steam demand of reforming, the total steam demand of such processes is also determined by the steam demand of the water-gas shift reaction, not only to maximise CO shift to H2 but also, in respect of the high temperature shift in particular, to prevent damage to conventional iron-containing high temperature water-gas shift catalysts through chemical over-reduction by CO and H2. Steam is typically added to the feed upstream of reforming. The amount of steam added is typically characterised by defining a steam to carbon ratio as the moles of steam in the gaseous mixture fed to the reforming divided by the moles of carbon in hydrocarbon compounds in the gaseous mixture. Unreacted steam in the reformed gas mixture will be available to participate in the water-gas shift reaction. Additional steam can also be added upstream of the water-gas shift reactor, after the reforming. The process steam demand of such processes, specifically for reforming and for the water- gas shift reaction, is typically for medium pressure steam, e.g. steam at a pressure of about 25-50 bar(a) and a boiling temperature of about 225-265°C. In some arrangements, superheated steam, i.e. steam above the boiling temperature is used to prevent water _{condensation on the catalyst particles and/or to heat up the process stream to the required} _{temperature. This demand is usually comfortably met by using process heat in boilers,} predominantly by cooling the reformed gas mixture that is produced in the steam reforming stage through heat exchange with water that is thus converted to steam. Excess high pressure steam (i.e. steam at a pressure or greater than 50 bar(a)) or medium pressure steam that is not used in the process can valuably be exported from the process as P102471 3 _{low carbon medium or high pressure steam, preferably being superheated to be exported as} superheated low carbon medium or high pressure steam. WO2022/003313 A1 discloses a process for the production of hydrogen comprising the steps of: subjecting a gaseous mixture comprising a hydrocarbon and steam, and having a steam to carbon ratio of at least 0.9:1, to adiabatic pre-reforming in a pre-reformer followed by autothermal reforming with an oxygen-rich gas in an autothermal reformer to generate a reformed gas mixture, optionally adding steam to the reformed gas mixture, increasing the hydrogen content of the reformed gas mixture by subjecting it to one or more water-gas shift stages in a water-gas shift unit to provide a hydrogen-enriched reformed gas, cooling the hydrogen-enriched reformed gas and separating condensed water therefrom, passing the resulting de-watered hydrogen-enriched reformed gas to a carbon dioxide separation unit to _{provide a carbon dioxide gas stream and a crude hydrogen gas stream, passing the crude} hydrogen gas stream to a purification unit to provide a purified hydrogen gas and a fuel gas, wherein the fuel gas is fed to one or more fired heaters used to heat one or more process streams within the process. In this process, the reformed gas mixture is cooled in a reformed gas boiler that raises high or medium pressure steam, and the cooled reformed gas mixture is subsequently subjected to a water-gas shift reaction in adiabatic reactors, sequentially at high and low temperatures, with inter-stage cooling, to produce a hydrogen-enriched reformed gas mixture. The hydrogen- _{enriched reformed gas mixture is further cooled before being sent to the CO2 removal stage.} CO2 in the hydrogen-enriched reformed gas mixture is then removed using a reactive amine wash system, before purification of the gas mixture by pressure-swing absorption that produces purified hydrogen gas and a low pressure hydrogen-lean CO and CH4 containing tail gas, that also comprises inert gases. The amine wash system typically requires a large amount of low temperature heat (for _{example around 130°C to separate absorbed CO2 from amine solution). This energy demand} is met by heat recovered, either directly, in exchangers downstream of the water-gas shift _{reaction, and/or via low pressure steam raised in a convenient location in the process.} _{The low-temperature heat demand of the amine wash system limits the extent to which the} process can be adapted to produce more high or medium pressure steam for export or to reduce the demand for medium pressure steam raised in the process, since a significant _{portion of heat recovered in the exchangers downstream of the water-gas shift reaction needs} P102471 4 to be used in the amine wash system and is, in any event, too cold for the raising of medium pressure steam. _{Moreover, in this process it is necessary to use all of the tail gas as fuel to raise additional} medium pressure steam for export, or to superheat excess medium pressure steam that is raised in the process for export. _{WO2023/148469 A1 discloses a process for the production of hydrogen comprising the steps} of: (i) subjecting a gaseous mixture comprising a hydrocarbon and steam to steam reforming in a gas-heated reformer or adiabatic pre-reformer followed by autothermal reforming with an oxygen-rich gas in an autothermal reformer to generate a reformed gas mixture, (ii) increasing the hydrogen content of the reformed gas mixture by subjecting it to one or more water-gas shift stages in a water-gas shift unit to provide a hydrogen-enriched reformed gas, (iii) passing _{the hydrogen- enriched reformed gas and an oxygen-rich gas to an oxidation unit containing} an oxidation catalyst that converts carbon monoxide present in the hydrogen-enriched reformed gas to carbon dioxide, to form a carbon-dioxide enriched gas mixture, (iv) cooling _{the carbon dioxide- enriched gas mixture and separating condensed water therefrom, and (v)} passing the carbon dioxide enriched gas mixture to a carbon dioxide separation unit to provide _{a carbon dioxide gas stream and a hydrogen product gas stream. In this process tail gases} from the separation unit are used only as fuel gases. It would be advantageous to increase the net high or medium pressure steam that is available _{for export from hydrogen production processes while maintaining a high feedstock efficiency} _{and increasing carbon capture potential.} Summary of the Invention _{In the present invention, the inventors have unexpectedly found that by operating the water} _{gas shift reaction of a blue hydrogen production process isothermally and by operating the} synthesis gas generation at a reduced steam to carbon ratio, the process feedstock efficiency _{and carbon capture potential are improved whilst reducing process steam demand, leading to} an increase in steam export potential. In addition, all the heat generated by the water gas shift reaction can be used to raise steam _{to use in the process, and for export, which avoids the need for additional tail gas combustion} _{for process steam generation and further increases steam export potential.} P102471 5 _{In addition, the invention allows the extent of tail gas recycle to be conveniently adjusted to} _{balance the feedstock efficiency and capture rate vs steam export, such that if a higher} _{feedstock efficiency and capture rate is required, more tail gas can be directed to the process} rather than the fuel,hence reducing the fresh hydrocarbon flow required to produce the same blue hydrogen product throughput, and increasing the carbon capture rate as less CO and _{CH4 is combusted to CO2 and emitted from the process. Whilst a minimum amount of tail gas} _{needs to be purged from the system as a fuel to prevent the build-up of inert gases in the} _{process, and hence a maximum recycle rate, the invention permits a wider operability window} _{for the process, especially when there is a change in plant throughput or plant philosophy.} _{According to an aspect of the invention, there is provided a process for the production of} hydrogen comprising the steps of: _{(i) reforming a gaseous mixture comprising a hydrocarbon and steam having a steam to} _{carbon ratio in the range 0.4:1 to 1.8:1 in a reforming unit comprising an autothermal} reformer to produce a reformed gas mixture, _{(ii) subjecting the reformed gas mixture to an isothermal water-gas shift reaction in an} isothermal water-gas shift reactor using water as a heat exchange medium, thereby increasing the hydrogen content of the reformed gas mixture and producing a hydrogen- enriched reformed gas while raising steam, _{(iii) cooling at least some of the hydrogen-enriched reformed gas and separating condensed} water therefrom to provide a de-watered hydrogen-enriched reformed gas, _{(iv) subjecting at least some of the de-watered hydrogen-enriched reformed gas to carbon} dioxide separation by performing a reactive amine wash on the hydrogen-enriched reformed gas in a carbon dioxide separation unit to recover carbon dioxide gas and crude hydrogen gas, and _{(v) subjecting at least some of the crude hydrogen gas to purification in a hydrogen} purification unit to produce a purified hydrogen gas and a tail gas, _{wherein a portion of the tail gas is recycled to the process.} The tail gas may comprise hydrogen, thus being a hydrogen-containing tail gas. While hydrogen may be present in the tail gas, at least in trace amounts, the process may include increasing the concentration of hydrogen in the tail gas. For example, as disclosed herein, _{the process may include combining a hydrogen-containing flash gas with the tail gas, such} hydrogen-containing flash gas being obtained from the carbon dioxide separation unit. P102471 6 In the process, in contrast to the aforesaid WO2022003313 A1, a portion of the tail gas is _{recycled to the process, meaning that a portion of the tail gas is recycled to one or more of the} _{process steps for used the production of hydrogen. Recycling all of the tail gas is undesirable} _{because it results in a build-up of inert gases in the process. Therefore, in a preferred} _{arrangement the tail gas is divided and a portion of the tail gas is supplied to one or more tail} _{gas fuelled fired heaters, such that at least 10%vol, or at least 15% vol, or at least 20%vol, or} _{at least 30%vol of the total flowrate of inert gases present in the hydrogen enriched reformed} _{gas is present in the tail gas fuel supplied to the one or more tail gas fuelled fired heaters.} _{The portion of the tail gas may be compressed before it is recycled to the process.} _{Recycling of the tail gas to the process may be advantageously performed such that the} portion of tail gas is at least present in the feed to the autothermal reformer. _{As disclosed herein, recycling of the tail gas to the process may be to one or more of the} following locations: (_{a) to a hydrocarbon containing feed of the process, used to form the gaseous mixture} of hydrocarbon and steam; (_{b) to a desulphurised hydrocarbon feed stream downstream of a desulphurisation} _{unit, when included in the process,} _{(c) to a pre-reformer feed stream upstream of a pre-reformer, when included in the} process, (_{d) to the autothermal reformer, or to a feed of the autothermal reformer, downstream} _{of the pre-reformer when included in the process;} _{(e) to downstream of the autothermal reformer and upstream of the water-gas shift} reactor; (_{f) to downstream of the water-gas shift reactor and upstream of the carbon dioxide} separation unit; and (_{g) to downstream of the carbon dioxide separation unit and upstream of the hydrogen} purification unit. The Applicant has found that recycling tail gas to the pre-reformer outlet or autothermal _{reformer inlet (location (d)) can provide the highest carbon capture rate and greatest feedstock} efficiency, especially when the hydrocarbon feed comprises at least 50% vol methane and/or _{the tail gas comprises at least 80%vol H2 with some residual CO and methane. Recycling such} _{tail gases to the pre-reformer inlet may result in undesirable methanation, whilst sending it to} P102471 7 _{any other location downstream of autothermal reformer removes the possibility of converting} _{methane present in the tail gas to hydrogen and carbon oxides, meaning that the downstream} _{unit operations need to work harder to provide the same level of capture rate and feedstock} efficiency. _{In addition to recycling tail gas to the process, the process may include supplying a portion of} _{the tail gas to one or more tail gas fuelled fired heaters as a fuel gas and combusting the tail} _{gas to heat one or more process streams within the process and/or to generate steam.} The portion of the tail gas may be compressed before it is passed to the one or more fired heaters. _{In some arrangements, one tail gas fuelled fired heater may be used to preheat one or more} feeds to the process and also generate steam. In other arrangements, two tail gas fuelled fired heaters may be used; one to pre-heat one or more feeds to the process and one to _{generate steam. A tail gas fuelled fired heater may preferably heat a hydrocarbon-containing} _{feed. A tail gas fuelled fired heater may also, or alternatively, superheat steam that is} subsequently used to form the gaseous mixture comprising the hydrocarbon and steam. _{A tail gas fuelled fired heater may also be used to generate additional steam for use in the} _{process. The process may therefore include raising steam in the one or more tail gas fuelled} _{fired heaters. Optionally, at least some such steam may be combined with the hydrocarbon,} _{which is preferably mixed with a portion of the tail gas, to form the gaseous mixture comprising} the hydrocarbon and steam. _{If steam is raised in the one or more tail gas fuelled fired heaters, such raising of steam may} be by pre-heating boiler feed water in heat exchange with the hydrogen-enriched reformed _{gas and then further heating such pre-heated boiler feed water in a tail gas fuelled fired heater.} However in some arrangements, all of the boiler feed water pre-heating can be done in a tail gas fuelled fired heater. In some arrangements, the portion of the tail gas fed to the one or more fired heaters may be supplemented with alternative fuel sources e.g. a portion of the hydrocarbon feed. As disclosed herein, in one embodiment of the invention, the hydrocarbon may be mixed with a portion of the tail gas of the process upstream of forming the gaseous mixture comprising hydrocarbon and steam. The hydrocarbon may comprise any gaseous or low boiling P102471 8 hydrocarbon, such as natural gas, associated gas, biogas, liquid petroleum gas (LPG), liquified natural gas (LNG), petroleum distillate, diesel, naphtha, or hydrocarbon-containing off-gases from industrial chemical processes such as cracker off-gases from petrochemical _{facilities, refinery off-gases, or pre-reformed gases, etc. or mixtures of any two or more of such} _{gases .} _{The hydrocarbon preferably comprises a methane-containing gas. In an embodiment of the} invention, the methane-containing gas contains >30 vol. % methane. A lesser proportion of higher hydrocarbons may also be present. _{Typically, the methane-containing gas would comprise at least some natural gas.} _{Advantageously, the process of the invention can be employed using, as source of} _{hydrocarbon, an industrial off-gas, most typically that produced by a refinery, in which case} _{the gaseous mixture comprising hydrocarbon and steam would comprise at least some} _{methane-containing refinery off-gas, preferably mixed with natural gas.} _{It will be appreciated that the gaseous mixture comprising hydrocarbon and steam may} _{therefore be formed from one hydrocarbon containing feed that supplies the hydrocarbon of} the gaseous mixture comprising hydrocarbon and steam, or it may be formed from a mixture of various different hydrocarbon containing feeds. Hereinafter, reference is, for simplicity, _{made only to “hydrocarbon containing feed” which should be understood to include within its} _{scope both a single feed and a mixture of multiple different or similar feeds.} _{The hydrocarbon containing feed may be compressed to a pressure in the range 10-100} _{bar(a). The pressure of the hydrocarbon containing feed may usefully govern the pressure} throughout the process. Operating pressure is preferably in the range 15-50 bar(a), more preferably 25-50 bar(a) as this advantageously provides optimum overall economics for the process. The hydrocarbon containing feed may be pre-heated in one or more pre-heating stages. It _{may conveniently be pre-heated after compression. When the hydrocarbon containing feed} _{is desulphurised as disclosed herein, it may after desulphurisation be further heated before} being mixed with steam. P102471 9 _{Pre-heating of the hydrocarbon containing feed may conveniently exploit process heat,} including from the hydrogen-enriched reformed gas and from the reformed gas mixture. The process may therefore include pre-heating the hydrocarbon containing feed in heat exchange with at least one, and more preferably both, of the hydrogen-enriched reformed gas and the _{reformed gas mixture. A pre-heating stage using high or medium pressure steam may also be} _{provided to allow pre-heating when no hot reformed gas mixture or hydrogen-enriched} _{reformed gas is available.} Gases providing the hydrocarbon of the gaseous mixture may contain major or minor impurities, which could negatively affect the process efficiency or could have a deleterious effect on the catalysts utilised in the process. Such gases may be subject to upstream bulk purification steps. However, even after such bulk purification, it may still be advantageous to employ catalytic and absorption steps to remove trace impurities, such as sulphur compounds, to provide a purified hydrocarbon feed to the process and preferably to also react bulk levels of unsaturated hydrocarbons (e.g. ethylene or propylene) with hydrogen to form saturated hydrocarbons. The process may, in one embodiment thereof, include desulphurising the hydrocarbon by _{contacting the hydrocarbon, preferably as a hydrocarbon containing feed preferably mixed} with a portion of tail gas, with a desulphurisation catalyst at a desulphurisation temperature. _{The desulphurisation temperature may be in a range of from 200°C to 400°C, preferably in the} range of 200°C to 250°C. The hydrocarbon, preferably as a hydrocarbon containing feed preferably mixed with a portion of tail gas, is heated to the desulphurisation temperature in heat exchange with the hydrogen- enriched reformed gas and/or in heat exchange with the reformed gas mixture after cooling of _{the reformed gas mixture with water in a boiler to raise steam and/or in heat exchange with} high or medium pressure steam raised in the process. The desulphurisation may in particular comprise hydrodesulphurisation. For example, hydrodesulphurisation may be performed using CoMo or NiMo catalysts, and absorption of hydrogen sulphide using a suitable hydrogen sulphide adsorbent, e.g. a zinc oxide adsorbent. A hydrodesulphurisation catalyst may also be suitable to hydrogenate olefins present, P102471 10 provided that there is sufficient hydrogen present. Hydrodesulphurisation may be carried out before, or preferably after, compression of the hydrocarbon, if the hydrocarbon is compressed. An ultra-purification adsorbent may usefully be used downstream of the hydrogen sulphide _{adsorbent to protect the steam reforming and water gas shift catalysts further. Suitable ultra-} purification adsorbents may comprise copper-zinc oxide/alumina materials and copper-nickel- zinc oxide/alumina materials. _{To facilitate hydrodesulphurisation, hydrogen is preferably present in the hydrocarbon} containing feed. It may already be present in sufficient quantity as part of one or more of the individual hydrocarbon containing feeds, or it may be added or the concentration thereof may _{be increased by recycling a hydrogen containing process stream, such as a portion of the tail} gas. The amount of hydrogen in the resulting mixed hydrocarbon containing feed may be in the range 1-20 vol%, but is preferably in the range 1-10 vol%, more preferably in the range 1-5 vol% on a dry gas basis. This may be at the exit of the hydrodesulphurisation vessel. If olefins are present in the feed or mixture, the hydrogen content is preferably augmented to provide at least enough additional hydrogen for stoichiometric conversion of the olefin content. _{The hydrocarbon, or desulphurised hydrocarbon, is combined with steam to form the gaseous} mixture. The process may include forming the gaseous mixture comprising hydrocarbon and steam by mixing the hydrocarbon, typically as a hydrocarbon containing feed as disclosed herein, preferably having been pre-heated and having been subjected to desulphurisation as disclosed herein, with steam. _{The steam to carbon ratio is in the range of 0.4:1 to 1.8:1 and is preferably in the range of} _{0.4:1 to 1.6:1, more preferably in the range of 0.6:1 to 1.4:1 and most preferably in the range} _{of 0.8:1 to 1.2:1.} The steam that is used in forming the gaseous mixture is, preferably, medium pressure steam most preferably being steam that is raised in the process. In one embodiment of the invention, the steam may be steam that is raised in the isothermal water-gas shift reactor and/or in a _{reformed gas boiler used to cool the reformed gas mixture, as disclosed herein. Optionally,} _{the steam may also include steam raised in a fired heater, most desirably the tail gas fuelled} fired heater. P102471 11 In this specification, the term “medium pressure steam” is used to mean saturated or superheated steam at a boiling temperature that is in a range of from about 225°C to about 265°C and at a pressure that is in a range of from about 25 bar(a) to about 50 bar(a), for example steam that is at a temperature of about 255°C and at a pressure of about 43 bar(a). The term “high pressure steam” is used to mean saturated or superheated steam at a boiling _{temperature of above about 265°C and a pressure above about 50 bar(a). Any steam with a} _{temperature higher than the boiling temperature at the prevailing pressure may be defined as} superheated steam. _{Medium pressure steam used to produce the gaseous mixture comprising hydrocarbon and} _{steam is therefore at least partly, and more preferably fully, obtained from the steam that is} _{raised in the water-gas shift reactor and/or through cooling of reformed gas, which steam is} _{typically raised as high or medium pressure steam. As disclosed herein, if necessary, such} steam may be supplemented by additional steam raised in a fired heater, most typically the tail gas fuelled fired heater. _{In forming the gaseous mixture of hydrocarbon and steam, preference may be given to the} _{steam that is raised in the water-gas shift reactor. If such steam is insufficient to provide the} required steam to carbon ratio, it is preferably augmented by using a part of the steam produced in the reformed gas boiler. The steam may be produced in the reformed gas boiler at medium pressure, or it may be produced at high pressure in which case its pressure is preferably reduced before use as process steam to provide the required steam to carbon ratio for the autothermal reforming. In producing the gaseous mixture comprising hydrocarbon and steam, the hydrocarbon, as a _{hydrocarbon containing feed, may therefore be combined with medium pressure steam from} the high or, preferably, medium pressure steam that is raised in the process, more specifically in the in the water-gas shift reactor and/or in the reformed gas boiler, optionally also, if needed, _{with steam generated in a fired heater, most typically the tail gas fuelled fired heater.} _{Steam that is added to form the gaseous mixture comprising hydrocarbon and steam may} either be saturated steam or superheated steam. For instance, medium pressure steam raised in the isothermal water-gas shift reactor and/or in the reformed gas boiler may be superheated _{before mixing with the hydrocarbon containing feed. Such superheating is preferably} _{performed using a fired heater, most typically a tail gas fuelled fired heater. If export steam} P102471 12 from the process is superheated, superheating for process steam may preferably be carried _{out in a same fired heater.} In some arrangements, steam raised in the process, preferably high-pressure steam raised in a reformed gas boiler, is superheated and sent to a steam turbine generator (STG) to produce power and so reduce the power requirement of the process. The steam stream recovered from the STG is a superheated medium pressure steam that that may be either exported directly or mixed with other steam streams, e.g. from the isothermal water-gas shift reactor steam drum, before being exported. _{Introducing steam into the hydrocarbon containing feed, to produce the gaseous mixture} comprising hydrocarbon and steam, may be performed by direct injection of steam. _{The amount of steam introduced into the hydrocarbon containing feed is sufficient to give a} steam to carbon ratio in the range of from 0.4 to 1.8, preferably 0.4 to 1.6, more preferably 0.6 _{to 1.4 and most preferably 0.8 to 1.2.} _{As disclosed herein, medium pressure steam demand to produce the gaseous mixture} _{comprising hydrocarbon and steam fed to the reforming unit, and to perform the water-gas} shift reaction, would typically, as a feature of the invention, be met fully by high or medium pressure steam that is generated in the reformed gas boiler and the medium pressure steam that is generated in the isothermal steam raising water-gas shift reactor, and would leave an excess of such high or medium pressure steam. At least a major portion, e.g. above 90 vol%, or all, of the excess medium pressure or high _{pressure steam that remains after utilisation of the steam in producing the gaseous mixture} comprising hydrocarbon and steam and, if applicable, in supplying steam to the feed to the water gas shift reactor, may be exported from the process, i.e. is not utilised in the process. It will be appreciated that there are often a number of other minor flow uses of medium pressure steam within the hydrogen production process. Examples include (i) preheating of process _{feed streams or regeneration gas streams and (ii) stripping of organic contaminants from} process condensate streams. A small proportion of the excess medium pressure steam is preferably therefore used for such minor flow uses, with the remainder being exported. P102471 13 The process preferably includes superheating the excess high or medium pressure steam that would be exported from the process, such that the exported excess high or medium pressure steam is superheated high or medium pressure steam. Superheating the excess high or medium pressure steam that would be exported from the _{process may include using hydrocarbon feed, purified hydrogen gas and/or tail gas as fuel in} _{a fired heater in which such superheating is performed, preferably being solely a tail gas} fuelled fired heater as disclosed herein. The process may include heating the gaseous mixture of hydrocarbon and steam upstream of the reforming unit. This may be performed using the one or more tail-gas fuelled fired heaters. When the process includes heating the gaseous mixture upstream of the reforming unit, which _{is preferred, such heating may alternatively be in heat exchange with the reformed gas mixture} after cooling of the reformed gas mixture with water in a boiler to raise steam. _{The gaseous mixture of hydrocarbon and steam is passed to a reforming unit comprising the} _{autothermal reformer where it is reformed to produce the reformed gas mixture. The gaseous} mixture of hydrocarbon and steam may be passed directly to the autothermal reformer, but in _{some arrangements, it may be advantageous to feed the gaseous mixture to an adiabatic pre-} _{reformer upstream of the autothermal reformer. The reforming unit may then include one or} _{more pre-reformers arranged in series or in parallel depending on the composition of} hydrocarbon feed, upstream of the autothermal reformer. In the pre-reformer, the gaseous _{mixture may be subjected to adiabatic pre-reforming such that a pre-reformed gas mixture is} fed to the autothermal reformer. Thus, the optionally pre-heated gaseous mixture comprising hydrocarbon and steam is either fed to the autothermal reformer or, preferably, is subjected to a step of adiabatic steam reforming in one or more pre-reformer vessels (“pre-reforming”) before being subjected to autothermal reforming in the autothermal reformer. The pre-reformer and autothermal reformer are, in such an embodiment, preferably operated in series. The process may include that at least a portion of the tail gas is recycled to a hydrocarbon- containing feed to the pre-reformer, or one of the pre-reformers if multiple pre-reformers are present. P102471 14 In pre-reforming, the gaseous mixture comprising hydrocarbon and steam is preferably passed at an inlet temperature in the range of 300-650°C, preferably 380-450°C, adiabatically through a bed of a steam reforming catalyst, usually a steam reforming catalyst having a high nickel content, for example above 40% by weight. During such an adiabatic pre-reforming step, hydrocarbons higher than methane (e.g. ethane, propane) react with steam in equilibrium to give a mixture of methane, carbon oxides and hydrogen. According to the design conditions of the ATR, this advantageously reduces or eliminates the potential to form soot in the combustion of the gaseous mixture comprising hydrocarbon and steam with oxygen. _{All of the preferably pre-reformed gaseous mixture comprising hydrocarbon and steam is} preferably fed to the autothermal reformer. It will be appreciated that, if the process includes pre-reforming, then the feed to the autothermal reformer would be the pre-reformed gaseous mixture of hydrocarbon and steam, whereas the feed would otherwise be the gaseous mixture of hydrocarbon and steam, in each case preferably being mixed with tail gas. If desired, the temperature and/or pressure of the pre-reformed gaseous mixture comprising hydrocarbon and steam may be adjusted before feeding it to the autothermal reformer. In a _{preferred embodiment of the invention, the pre-reformed gaseous mixture comprising} hydrocarbon and steam is heated before feeding it to the autothermal reformer, for example _{by passing it through a fired heater, most typically a tail gas fuelled fired heater. Desirably,} _{the pre-reformed gaseous mixture is heated to 450-700°C, preferably 550-650°C.} The autothermal reformer may comprise a burner disposed at the top of the reformer, to which the gaseous mixture comprising hydrocarbon and steam, or the pre-reformed gaseous mixture _{comprising hydrocarbon and steam, and an oxygen-rich gas are fed, a combustion zone} beneath the burner through which a flame extends, and a fixed bed of particulate steam reforming catalyst disposed below the combustion zone. In autothermal reforming, the heat for the endothermic steam reforming reactions is provided by combustion of a portion of hydrocarbon in the gaseous mixture with oxygen-rich gas. _{The gaseous mixture comprising hydrocarbon and steam, or the pre-reformed gaseous} _{mixture comprising hydrocarbon and steam, is typically fed to the top of the autothermal} reformer and the oxygen-rich gas is fed to the burner, mixing and combustion occur downstream of the burner generating a heated gas mixture the composition of which is brought to equilibrium as it passes through the steam reforming catalyst. P102471 15 The autothermal steam reforming catalyst may comprise nickel supported on a refractory support such as rings or pellets of calcium aluminate, magnesium aluminate, alumina, titania, zirconia and the like. In a preferred embodiment, the autothermal steam reforming catalyst comprises a layer of a catalyst comprising Ni and/or Ru on zirconia over a bed of a Ni on alumina catalyst to reduce catalyst support volatilisation that can result in deterioration in performance of the autothermal reformer. The oxygen-rich gas may comprise at least 90% vol O₂, still more preferably at least 95% vol O₂, most preferably at least 98% vol O₂, or at least 99% vol O₂, e.g. a pure oxygen gas stream, which may be obtained using a vacuum pressure swing adsorption (VPSA) unit or, more typically, an air separation unit (ASU). When an ASU is used, the ASU may be electrically driven and is desirably driven using renewable electricity to further improve the efficiency of the process and minimise CO2 emissions. Preferably, the amount of oxygen added is such that the reformed gas mixture leaves the autothermal reforming catalyst at a temperature in the range 900-1100°C. The reformed gas mixture recovered from the reforming unit is preferably cooled, for example in a reformed gas boiler with water as a coolant. This brings the temperature of the reformed gas down to a more suitable inlet temperature for the isothermal water-gas shift reaction in _{the isothermal water-gas shift reactor and usefully raises steam for the process.} Typically, the reformed gas mixture would leave the autothermal reformer at a much higher temperature than the temperature at which the water-gas shift reaction would take place, e.g. at a temperature in a range of from about 900°C to about 1100°C. The process therefore preferably includes cooling the reformed gas mixture that leaves the autothermal reformer, before feeding the reformed gas mixture to the water-gas shift reactor. Cooling the reformed gas mixture is suitably performed in a reformed gas boiler, through heat exchange with water as a coolant, raising high or medium pressure steam. The reformed gas mixture may optionally also be further cooled by providing heat to preheat other streams such as boiler feed water or the gaseous mixture comprising hydrocarbon and steam, or the hydrocarbon containing feed to the process. _{At least a portion of the tail gas may be recycled to the isothermal water gas shift reactor, e.g.} to an inlet of the water gas shift reactor, or to a feed of the water gas shift reactor. P102471 16 The isothermal water gas shift reaction is performed isothermally at a temperature of at least _{225°C or at least 240°C but below 300°C.} In relation to the water gas shift reaction and reactor, the skilled person will appreciate that, when the term “isothermal” is used herein, this is because the temperature profile in the catalyst is constrained by heat transfer to the boiling water, which is at almost constant temperature. The inlet temperature of the cooled reformed gas to the water-gas shift reactor may be lower or higher than the boiling water temperature and there may be a small increase or decrease in gas temperature between an inlet and an outlet of the water-gas shift reactor, so that the temperature of the hydrogen-enriched reformed gas stream at the outlet of the water-gas shift reactor may be between 0°C and 40°C higher than the boiling water temperature. To operate isothermally, the water-gas shift reactor would be configured to provide for heat exchange in the reactor such that the water-gas shift reaction in the water-gas shift catalyst bed occurs in contact with heat exchange surfaces. Thus, in such a reactor, the water-gas shift catalyst may be provided in tubes surrounded by coolant, or coolant may be provided in tubes surrounded by the catalyst. A suitable reactor may, for example, be an axial flow reactor in which the water-gas shift catalyst is provided inside the tubes of the reactor and coolant is provided outside the tubes, _{or an axial or radial flow reactor in which coolant is provided inside the tubes of the reactor} and the water-gas shift catalyst is provided outside the tubes. ‘Axial’ flow defines the predominant gas flow in a cylindrical reactor as being parallel to the cylindrical axis, while ‘radial’ flow defines the predominant gas flow in a cylindrical reactor as being in a radial direction, either passing from the outside cylindrical wall of the reactor to an inner collector positioned at the central, cylindrical axis or vice versa. Radial flow reactors may advantageously have a low gas side pressure drop. The isothermal steam-raising water-gas shift reactor may be coupled with a steam drum. The water and steam mixture, which is produced in the reactor, may then be conveniently separated into steam and boiling water at its bubble point within the drum. Furthermore, make- up boiler feed water to replenish the water removed through steam raising can either be added to the steam drum or to a circulating coolant water line to the isothermal steam raising water- P102471 17 gas shift reactor. This make-up boiler feed water has preferably been heated, for example by process streams, so that it is already at, or close to, such as within 20°C of, its boiling point. The water that is used as the coolant in the isothermal steam raising water-gas shift reactor is preferably passed from the steam drum to the isothermal steam raising water-gas shift reactor. One option is to use a pump to supply the motive power. Another option is to use natural circulation, whereby a density difference (brought about by reduced density of mixed steam and boiling water leaving the isothermal steam raising water-gas shift reactor, compared to the water entering the isothermal steam raising water-gas shift reactor) causes water to flow through the isothermal steam raising water-gas shift reactor. Preferably, the water that is used as coolant in the isothermal steam raising water-gas shift reactor is a mixture of water at its bubble point and make-up boiler feed water. At a waterside inlet of the isothermal steam raising water-gas shift reactor the water is preferably at a temperature that is in a range of from about 0°C to 20°C below the temperature at which water boils at the pressure at the shell inlet. The water that is used as coolant in the water-gas shift reactor may be pressurised water, preferably pressurised boiling water. Preferably, as the water is heated it reaches its boiling point and then an increasing fraction becomes steam, such that the water leaves the water- gas shift reactor as a two-phase mixture of medium pressure steam and water. Preferably, the water that is used as coolant in the water-gas shift reactor may, typically at an exit therefore from the reactor, be at a temperature that is in a range of from about 225°C to about 265°C and at a pressure that is in a range of from about 25 bar(a) to about 50 bar(a). The water-gas shift reaction taking place in the water-gas shift reactor is exothermic, and there would therefore continuously be heat available for transfer to the coolant while the reaction is taking place. Such transfer would, in accordance with the invention, at least partially vaporise the coolant, thus producing medium pressure steam. _{The water-gas shift catalyst would typically not be an iron-based high temperature water-gas} _{shift catalyst. More typically, the water-gas shift catalyst would be a medium- or low-} temperature water-gas shift catalyst, for example a copper-based catalyst, such as a _{copper/zinc oxide/alumina catalyst, preferably doped with Si and/or Mg. Such a catalyst does} not suffer from over reduction leading to side reactions in the same way as an iron-based catalyst and it can advantageously operate at lower temperatures. P102471 18 The water-gas shift catalyst would typically be provided in the water-gas shift reactor in a conventional configuration, i.e. in particulate format as a bed of catalyst particles, either inside of the tubes of the reactor or outside of the tubes of the reactor, if the reactor is configured as disclosed herein. _{The process may include combining medium pressure steam, raised in the process, with the} reformed gas mixture, typically with the cooled reformed gas mixture, upstream of the water- gas shift reactor. Such medium pressure steam may be obtained from the high or medium pressure steam that is raised in the reformed gas boiler and/or from the medium pressure steam that is raised in the water-gas shift reactor. Such combining may increase the conversion of CO in the isothermal water-gas shift reaction, which may advantageously reduce the amount of CO that needs to be recycled and the power consumption of the process. It may also advantageously reduce the exotherm in the isothermal steam raising water-gas shift reactor. However, it will be appreciated that such combining may also reduce the amount of medium pressure steam that is raised by the isothermal water-gas shift reactor, which may be _{disadvantageous depending on the specific requirement for steam export in a given project.} _{The isothermal water-gas shift reactor produces a hydrogen enriched reformed gas mixture.} The hydrogen-enriched reformed gas mixture is cooled to produce a de-watered hydrogen- enriched reformed gas. Cooling of the hydrogen-enriched reformed gas mixture in order to _{produce the de-watered hydrogen enriched reformed gas mixture, involves cooling it to a} temperature below its dew point, so that the steam content thereof condenses to produce a liquid water condensate, which is then desirably separated from the hydrogen-enriched reformed gas mixture in a gas-liquid separator, to produce the de-watered hydrogen enriched reformed gas mixture. To cool the hydrogen-enriched reformed gas mixture, any coolant may be used in one or more stages. Preferably, heat from cooling is used to heat process water streams (such as boiler feed water, process condensate and demineralised water), which are subsequently used in producing steam, for example in the reformed gas boiler and/or in the isothermal water-gas shift reactor. Cooling may also be accomplished by producing low pressure steam or by rejection of heat to the atmosphere, for example by using an air cooler or by using cooling _{water. In a preferred embodiment cooling may also be accomplished by regeneration of a} carbon dioxide absorbent liquid recovered from the downstream carbon dioxide separation unit. P102471 19 In separating the liquid water condensate from the hydrogen-enriched reformed gas mixture to produce the de-watered hydrogen enriched reformed gas mixture, one or more, preferably two or three, stages of condensate separation may be used. Condensed water that is recovered from the process may be used to provide at least a portion of the steam in the gaseous mixture fed to the reforming unit. This may be achieved by passing the condensate to a saturator unit through which the hydrocarbon (gas) is passed, or by stripping the condensate with steam and using the stripping steam in the generation of the gaseous mixture. Therefore, if desired, a portion or all of the condensate, preferably treated as disclosed herein, may be used to generate steam for the process, e.g. in the reformed gas boiler and/or in the _{water-gas shift reactor. Preferably, some or all of the condensate is treated by contacting with} medium pressure steam to volatilise compounds dissolved in the condensate. One such dissolved compound may be methanol, which may form as a byproduct in the water-gas shift reactor. The medium pressure steam, together with the volatilised compounds may then be added to _{the hydrocarbon containing feed. In this way, organic compounds, dissolved process gases} and other impurities in the condensate may be returned to the process and thus increase the process efficiency and reduce the burden on any aqueous effluent treatment. The treated _{condensate may be used as boiler feed water, for the generating of steam. Any condensate} not used to generate steam may be sent to water treatment as effluent. The tail gas may comprise a portion of the crude hydrogen gas recovered from the carbon dioxide separation unit. Such portion of the crude hydrogen gas may be obtained by withdrawing a hydrogen-containing flash gas from the carbon dioxide separation unit and mixing it with tail gas from the hydrogen purification unit, such hydrogen-containing flash gas bypasses the hydrogen purification unit. This may usefully reduce the size of the purification unit. _{The process may further include recycling at least a portion of the tail gas to the carbon dioxide} _{removal unit or to the hydrogen-enriched reformed gas feed to the carbon dioxide removal} unit. P102471 20 _{The reactive amine wash may be performed as an acid gas recovery (AGR) process. In the} AGR process, the de-watered hydrogen-enriched reformed gas stream is contacted with a _{stream of a suitable absorbent liquid, which is typically an amine, particularly methyl} _{diethanolamine (MDEA) solution, so that the carbon dioxide is absorbed by the liquid to give} a laden absorbent liquid and a gas stream having a decreased content of carbon dioxide. The laden absorbent liquid is then regenerated by heating and/or reducing the pressure, to desorb the carbon dioxide and to give a regenerated absorbent liquid, which is then recycled to the carbon dioxide absorption stage. Alternatively, methanol or a glycol may be used to capture the carbon dioxide in a similar manner as the amine. In a preferred arrangement, at least part of the heating to regenerate the absorbent liquid is _{performed using the hydrogen-enrich reformed gas leaving the isothermal shift reactor. If the} carbon dioxide separation step is operated as a single pressure process, i.e. essentially the same pressure is employed in the absorption and regeneration steps, only a little recompression of the recycled carbon dioxide will be required. The recovered carbon dioxide, e.g. from the AGR, may be compressed and used for the manufacture of chemicals, sent to storage or sequestration, used in enhanced oil recovery (EOR) processes or used in the production of other chemicals. Compression may be accomplished using an electrically driven compressor powered by renewable electricity. In cases where the CO2 is to be compressed for storage, transportation or use in EOR processes, the CO2 may be dried to prevent liquid water present in trace amounts, from condensing. For _{example, the CO2 may be dried to a dew point below -10°C by passing it through a bed of a} suitable desiccant, such as a zeolite, or contacting it with a glycol in a glycol drying unit. _{Upon the separation of the carbon dioxide, the process provides the crude hydrogen gas. The} _{crude hydrogen gas may comprise 85-99% vol hydrogen, preferably 90-99% vol hydrogen,} more preferably 95-99% vol hydrogen, with the balance comprising methane, carbon _{monoxide, carbon dioxide and inert gases. Whereas this hydrogen gas may be pure enough} _{for several duties, in the present invention, the crude hydrogen gas is passed as a feed to the} hydrogen purification unit to provide a purified hydrogen gas and the tail gas, so that the tail gas may be used in the process as disclosed herein. P102471 21 _{The hydrogen purification unit may suitably comprise a hydrogen selective membrane unit, a} temperature swing adsorption system, or a pressure swing adsorption system, or a combination thereof. Such systems are commercially available and are not described in detail. _{The hydrogen purification unit preferably comprises one or more, most preferably at least two,} pressure swing adsorption units. Such systems comprise regenerable porous adsorbent materials that selectively absorb gases other than hydrogen and thereby produce products enriched in hydrogen. The purified hydrogen gas may have a purity of 95% or higher. The purified hydrogen gas _{produced by the hydrogen purification unit preferably has a purity greater than 98 vol%, more} preferably greater than 99.5 vol%, even more preferably greater than 99.9 vol% or yet more preferably greater than 99.99 vol%. _{As has been referenced earlier herein, the tail gas is produced in the hydrogen purification} _{unit, optionally being combined with hydrogen-containing flash gas such that the tail gas is} provided with a (increased) hydrogen content. The process may include recycling at least a portion of the tail gas to the hydrogen purification unit or to the crude hydrogen gas feed of the hydrogen purification unit. _{The tail gas is preferably enriched in inert gas content (such as nitrogen and argon) and} optionally comprises such content of CO, CH4 and CO2 as is acceptable to allow a combustion product of the impure hydrogen fuel gas to pass to atmosphere while still meeting the carbon footprint specification of the low carbon hydrogen process or the target carbon capture efficiency. _{The composition of the tail gas that is produced in the hydrogen purification unit depends on} _{the extent of the purification. The tail gas may, for example, comprise 80 to 90 vol% hydrogen,} _{with the balance comprising methane, carbon monoxide, carbon dioxide, residual steam and} _{inert gases. The methane content may be in the range 1 to 10 vol%, preferably 2 to 5 vol%.} _{The carbon monoxide content may be in the range 0 to 10 vol%, preferably 0 to 8 vol%. The} _{carbon dioxide content may be in the range 0 to 1.5 vol%. There may also be traces of steam,} _{nitrogen and argon in the range 0 to 5 vol%.} P102471 22 The process may include compressing the purified hydrogen gas, for example using an electrically driven compressor, preferably being powered by renewable electricity. This also applies to compression of the tail gas and of the hydrocarbon containing feed of the process, which may be compressed by similar means. The purified hydrogen gas may be used in downstream power or heating processes, for example by using it as fuel in a gas turbine or by injecting it into a domestic or industrial _{networked gas piping system. The purified hydrogen gas may also be used as a fuel for} vehicles using fuel cells. The purified hydrogen gas can also be stored in a convenient form as an energy carrier and optionally transported. For example, it can be stored as compressed hydrogen or liquid hydrogen, or it can be reacted with another compound (such as reaction with benzene to form cyclohexane) to enable easier transport to another geographic location. The purified hydrogen gas may alternatively be used in a downstream chemical synthesis process. Thus, the purified hydrogen gas may be used to produce, for example, ammonia by reaction with nitrogen in an ammonia synthesis unit. It is also possible for the purified hydrogen gas to be used to upgrade hydrocarbons, e.g. by hydro-treating or hydro-cracking hydrocarbons in a hydrocarbon refinery, or in any other process where pure hydrogen may be used. Such hydrocarbons can be fossil fuel derived or may be biogenic, such as in the hydrogenation of vegetable oils. In such cases, it could be advantageous to use the off-gas and/or a low value stream from the hydrocarbon upgrading _{process as one or more of the hydrocarbon containing feeds to the process of this invention.} Detailed Description of and Embodiment of the Invention _{The invention is illustrated by way of example with reference to the accompanying drawing in} which: Figure 1 is a diagrammatic flowsheet showing one embodiment of a process according to the invention. In the illustrated embodiment of the process of the invention, a portion of a tail gas that is _{produced by the process, as disclosed herein, is recycled to the process, while another portion} P102471 23 _{thereof is combusted as fuel gas in a tail gas fuelled fired heater, to heat certain process} _{streams and to produce and superheat medium pressure steam.} _{It will be understood by those skilled in the art that the drawing is diagrammatic and that further} items of equipment such as reflux drums, pumps, vacuum pumps, temperature sensors, pressure sensors, pressure relief valves, control valves, flow controllers, level controllers, holding tanks, storage tanks, and the like may be required in a commercial plant. The provision of such ancillary items of equipment forms no part in the present invention and is in accordance with conventional chemical engineering practice. _{In Figure 1, a gaseous hydrocarbon containing feed stream 10 is formed by combining a} _{natural gas stream 12 with an industrial off-gas stream 14, e.g. wherein the industrial off-gas} _{stream comprises off-gas from an oil refining operation.} In an alternative embodiment of the process, the gaseous hydrocarbon containing feed stream _{10 may consist of natural gas only.} _{The off-gas stream 14 is produced by subjecting raw off-gas along line 15 to bulk sulphur and} _{acid gas removal in a purification unit 16, upstream of being combined with the natural gas} _{stream 12. Bulk sulphur removal is performed at a temperature of around 20°C to 100°C, e.g.} _{around 30°C to 50°C and an acid gas stream containing high levels of sulphur is recovered} along line 17 and is sent to a sulphur recovery plant. _{Although not illustrated as such, in one embodiment of the process, upstream of being} subjected to bulk sulphur and acid gas removal, the off-gas in line 14 or line 15 may be combined with a portion of a hydrogen-containing tail gas of the process that is produced as _{disclosed herein and that is recycled to be combined with the off-gas.} Although not illustrated as such, in one embodiment of the process, upstream of being _{subjected to bulk sulphur and acid gas removal in purification unit 16, the off-gas in line 15} may be subject to a mercury removal stage. _{The hydrocarbon gas feed stream 10 is mixed with a portion of the hydrogen-containing tail} _{gas of the process, which is recycled to the hydrocarbon containing feed stream from} _{downstream in the process along line 18. Thus, a hydrogen-containing hydrocarbon gas} P102471 24 _{stream 20, comprising a portion of the tail gas of the process, is formed as a feed to the} process. _{The hydrogen-containing hydrocarbon gas stream 20 is fed to a heat exchanger 22 where it} _{is heated in heat exchange with a partially cooled hydrogen-enriched reformed gas stream 25} _{which is produced in the process as disclosed herein.} _{The hydrogen-containing hydrocarbon gas stream 20 is further heated in heat exchange with} _{a reformed gas stream 26 in a heat exchanger 42. The reformed gas stream is produced in} _{the process as disclosed herein.} _{The now pre-heated, hydrogen-containing hydrocarbon gas stream 29 is then passed to a} _{hydrodesulphurisation (HDS) vessel 30 containing a bed of hydrodesulphurisation catalyst.} _{In the HDS vessel 30, organic sulphur compounds in the pre-heated hydrogen-containing} _{hydrocarbon gas stream 29 are converted to hydrogen sulphide by reacting with hydrogen} over the hydrodesulphurisation catalyst. _{The resulting hydrogen sulphide containing gas is then passed long line 32 to an absorber} _{vessel 34 in which the hydrogen sulphide is removed in a bed of zinc oxide adsorbent and a} _{bed of copper-zinc oxide-alumina ultra-purification adsorbent, thus producing a desulphurised} hydrocarbon gas stream 36. _{If desired, a portion of the hydrogen sulphide containing gas in line 32 may be cooled,} _{compressed, and recycled via line 33 to the inlet of the HDS vessel 30 in order to control the} exotherm over the HDS catalyst caused when the hydrocarbon feed contains olefins. _{The desulphurised hydrocarbon gas stream 36 is combined with steam that is raised in the} _{process as disclosed herein and supplied along stream 38, to provide a hydrocarbon gas and} steam mixture along line 40. The gaseous mixture of hydrocarbon gas and steam has a steam to carbon ratio of at least 0.4:1. P102471 25 _{The hydrocarbon gas and steam mixture is heated in heat exchange with the reformed gas} _{stream 26 in a heat exchanger 28 that is upstream of the heat exchanger 42, and is then fed} _{along line 44 to a first adiabatic pre-reformer 46.} _{The pre-reformer 46 contains a bed of pelleted nickel-based steam reforming catalyst. In the} pre-reformer 46, higher hydrocarbons in the hydrocarbon gas and steam mixture are converted to methane and are partially steam reformed as the mixture passes over the pre- _{reforming catalyst, to produce a partially pre-reformed gas mixture containing hydrogen.} Upstream of the pre-reformer 46, the hydrocarbon gas and steam mixture is optionally _{combined along line 48 with a portion of the hydrogen-containing tail gas of the process that} is recycled along line 49, such that the hydrocarbon gas and steam mixture that is supplied to _{the pre-reformer 46 and is subjected to pre-reforming contains a portion of the hydrogen-} _{containing tail gas.} _{A partially pre-reformed gas mixture from the first pre-reformer 46 is then passed to a second} _{pre-reformer 50 along line 52, in which it is subjected to further pre-reforming, in combination} with a portion of the hydrocarbon gas and steam mixture optionally comprising hydrogen- containing tail gas that is supplied to the second pre-reformer from line 44 along line 54. _{Thus, a pre-reformed gas mixture is produced along line 55.} In an alternative embodiment of the invention, the second pre-reformer 50 may be omitted, in which case the partially pre-reformed gas mixture along line 52 would be the pre-reformed gas mixture along line 55. _{The pre-reformed gas mixture is optionally combined with a portion of the hydrogen-containing} _{tail gas from line 49 along line 56, thus forming a mixture of pre-reformed gas and hydrogen-} _{containing tail gas, which is passed to a fired heater 58 along line 59.} _{In the fired heater 58, the pre-reformed gas mixture, optionally comprising hydrogen-} _{containing tail gas, is heated by combusting a portion of the hydrogen-containing tail gas of} _{the process that is supplied to the fired heater 58 along line 60. The fired heater 58 is therefore} _{a tail gas fuelled fired heater. Such heating of the pre-reformed gas mixture, is to an inlet} temperature for an autothermal reformer 62, to which the pre-heated pre-reformed gas P102471 26 mixture, optionally comprising hydrogen-containing tail gas, is subsequently supplied along line 64. _{Feeding of the pre-reformed gas mixture, comprising hydrogen-containing tail gas, from the} _{fired heater 58 along line 64 is to the burner region 63 of the autothermal reformer 62, where} _{the pre-reformed gas mixture, optionally comprising hydrogen-containing tail gas, is partially} _{combusted with oxygen that is supplied to the autothermal reformer 62 along line 65, such} _{oxygen having been produced in an air separation unit 66 and pre-heated in a heat exchanger} _{68 in heat exchange with steam along line 80 which is generated as disclosed herein.} _{The hot combusted gas mixture is then brought towards equilibrium inside the autothermal} reformer 62 over a fixed bed of pelleted nickel-based secondary reforming catalyst 69, _{disposed below the combustion zone 63 in the autothermal reformer 62.} _{A resulting hot reformed gas mixture thus produced is fed from the autothermal reformer 62} _{along line 70 to the tube-side of a steam-raising boiler 72, which is coupled to a steam drum} _{74. The reformed gas mixture boils water that is fed to the shell side of the boiler 72 from the} _{steam drum 74 along line 76 and returns steam from the boiler 72 to the steam drum 74 along} line 78. Preheated boiler feed water may be fed to steam drum 74 via line 89 heated by heat exchanger 94. _{Steam drum 74 coupled to the boiler 72 generates medium pressure steam which is recovered} _{from the steam drum 74 along line 82 and is used in the process, including as a heat exchange} _{medium to pre-heat oxygen from the Air Separation Unit 66 in the heat exchanger 68 to which} steam is supplied along line 80 from line 82. As the hot reformed gas passes through the boiler 72, it is cooled. The resulting cooled reformed gas mixture 26 is heat exchanged in heat exchangers 28 and _{42 as described above, before being passed along line 27 to an isothermal water-gas shift} vessel 86. _{The water-gas shift vessel 86 contains a cooled fixed bed of particulate copper-based} isothermal-temperature shift catalyst. In passing over the catalyst, carbon monoxide in the _{reformed gas mixture that is fed to the shift vessel 86 is converted to carbon dioxide while the} P102471 27 hydrogen content of the reformed gas is increased, thus producing hydrogen-enriched _{reformed gas that is withdrawn along line 24.} _{The shift vessel 86 is configured for isothermal operation, such that the water-gas shift reaction} taking place over the water-gas shift catalyst takes place isothermally, using water as a heat _{exchange medium. Such water is supplied to the shift vessel 86 from steam drum 88 along} _{line 90 and returned to steam drum 88 along line 92, as steam.} _{Steam drum 88 is supplied with fresh boiler feed water along line 93, after pre-heating such} _{water in heat exchanger 94 in heat exchange with hydrogen-enriched reformed gas produced} _{in the shift vessel 86 and withdrawn along line 24. Fresh boiler feed water is supplied to heat} _{exchanger 94 along feed line 96.} _{As mentioned above, in being used as heat exchange medium in the isothermal shift vessel} _{86, water supplied along line 90 is converted to steam which is passed along line 92 to steam} _{drum 88. From steam drum 88, steam is withdrawn along line 98 and is combined with steam} _{from steam drum 74 along line 84 and is passed to the fired heater 58 along line 100 to be} _{superheated in the fired heater 58.} A portion of the pre-heated fresh boiler feed water in line 93 is fed along line 200 to a steam drum 202 that is connected to the fired heater 58. Pre-heated fresh boiler feed water is supplied from the steam drum 202 to the fired heater 58 along line 204 and recovering steam _{along line 206. Steam from the steam drum 202 is withdrawn along line 208 and is divided} _{along line 210 to be used as heat exchange medium for pre-heating process streams in} _{heating train 211, and along line 212 to be combined with steam in line 100 that is used to} _{provide the superheated steam in the fired heater 58.} _{The process also provides an export stream 214 of superheated steam, which is divided from} _{the heated steam stream produced in the fired heater 58.} In an alternative embodiment of the invention, the steam drum 202 and its ancillary piping are omitted from the process. _{In addition to being supplied with the reformed gas mixture along line 26, the shift vessel 86} _{is optionally supplied with a portion of the superheated steam that is generated in the fired} _{heater 58, such steam being supplied along line 102, and optionally fed with a portion of the} P102471 28 _{hydrogen-containing tail gas from line 49 along line 104, both of these being combined with} the reformed gas mixture along line 26 downstream of heat exchangers 42 and 28 and upstream of the shift vessel 86. Thus, the feed to the shift vessel 86 may comprise the _{reformed gas mixture 26, steam 102, and tail gas 104.} In another embodiment of the process, supply of superheated steam and tail gas to the water _{gas shift reactor 86 are omitted.} _{After exchanging heat with the fresh boiler feed water in heat exchanger 94 and before} _{exchanging heat with the hydrogen-containing hydrocarbon gas in heat exchanger 22, the} _{hydrogen-enriched reformed gas is used to provide a portion of heat required for regenerating} _{amine in a stripper reboiler of CO2 removal stage in heat exchanger 106.} After having been used for heat exchange in heat exchanger 22, the hydrogen-enriched _{reformed gas is supplied along line 108 to heat exchanger 110 in which the hydrogen-enriched} _{reformed gas is cooled with water to lower the temperature of thereof to below the dew point,} causing water to condense. _{In another embodiment of the process, heat exchanger 110 uses other coolants such as} process streams thereby increasing heat recovery, or cooling air. _{The cooled hydrogen-enriched reformed gas is then fed from the heat exchanger 110 along} _{line 114 to a gas-liquid separator 112, in which the condensate is separated from the} hydrogen-enriched reformed gas mixture, thus dewatering the reformed gas mixture. _{The condensate is recovered from the separator 112 along line 116 and a partially de-watered} _{hydrogen-enriched reformed gas mixture is recovered from the separator 112 along line 118.} _{The partially de-watered hydrogen-enriched reformed gas mixture is further cooled in heat} _{exchange with water in heat exchanger 120. The cooled gas is then passed to a second gas-} _{liquid separator 122 to recover further condensate along line 124. The condensate recovered} _{along lines 116 and 124 are combined into a combined stream 128 and is supplied to a storage} drum 130. _{A de-watered hydrogen-enriched reformed gas mixture is recovered from the second} _{separator 122 along line 126.} P102471 29 _{In another embodiment of the process, additional cooling and condensate separation stages} _{are employed.} The vapour fraction of condensate from streams 116 and 124 is flashed in drum 130 and _{supplied to the de-watered hydrogen-enriched reformed gas mixture in line 126 along line 132} _{to increase the recovery of volatile components such as hydrogen and carbon dioxide, thereby} increasing the feedstock efficiency and carbon capture potential. _{The liquid fraction of the combined condensate is passed from storage drum 130 along line} _{134 to a process condensate stripper 136 in which the condensate is contacted with a portion} _{of the superheated steam from line 38 generated in the fired heater 58, along line 138, to} _{produce a stripped condensate steam stream 142 comprising steam and volatile organic} _{compounds such as methanol, which is combined with the remainder of the superheated} _{steam withdrawn from the fired heater 58 along line 38, to be combined with the desulphurised} _{hydrocarbon gas along line 36, to produce the hydrocarbon and steam mixture along line 40.} A stripped condensate 140 is recovered from near the bottom of the stripping vessel 136. In another embodiment of the process, the process condensate stripper 136 uses saturated _{steam to strip volatile organic compounds from the condensate feed 134.} In another embodiment of the process, stripped condensate steam stream 142 is mixed with _{saturated steam withdrawn from the heating train 211.} _{The de-watered hydrogen-enriched reformed gas mixture in line 126 is optionally combined} _{with a portion of the hydrogen-containing tail gas of the process, such tail gas being supplied} along line 144 from line 18. The de-watered hydrogen-enriched reformed gas mixture _{optionally comprising tail gas is then passed to a carbon dioxide removal unit 146.} The carbon dioxide removal unit 146 is an acid gas recovery unit operating with an amine liquid absorbent wash system that absorbs carbon dioxide from the hydrogen-enriched _{reformed gas mixture 126 that is fed to it.} Absorbed carbon dioxide is recovered from the carbon dioxide-laden absorbent liquid in the _{unit 146 by heating it in heat exchange with hot hydrogen-enriched reformed gas in exchanger} P102471 30 106 and steam supplied along line 127 and reducing the pressure. Steam condensate is _{recovered from the removal unit 146 along line 129.} _{The recovered carbon dioxide from the carbon dioxide removal unit 146 is sent via line 148} for compression using a compressor 150, and storage along a product stream 152. CO₂ compressor may include multi-stage compression with intermediate cooling and condensate separation. Any condensate recovered in the CO₂ compressor may be sent to the condensate drum 130 (not shown). Further water removal from the CO₂ product may be carried out depending on the required CO₂ specification. _{A crude hydrogen gas stream is recovered from the carbon dioxide removal unit 146 and is} _{optionally combined with a portion of the hydrogen-containing tail gas of the process, and the} _{combined stream is then fed along line 154 to a pressure swing adsorption unit 156 containing} _{a porous adsorbent that traps carbon oxides, methane and inert gases in the crude hydrogen} _{gas stream, thereby producing purified hydrogen gas.} _{The purified hydrogen gas is recovered from the pressure swing adsorption unit 156. At least} _{some of the tail gas produced in unit 156 may be subjected to secondary purification stage in} _{a purification unit 158, such as a secondary pressure swing adsorption unit, to recover some} _{of residual hydrogen present in the tail gas from unit 156 thereby maximising hydrogen} recovery to hydrogen product and minimising hydrogen losses to the tail gas. _{Purified hydrogen gas from the secondary purification stage 158 along line 160 is combined} _{with purified hydrogen gas that is produced in the pressure swing absorption unit 156 along} _{line 162 and is sent along line 164 to a compressor 166 for compression and storage or the} generation of power of heat, or for the production or conversion of chemicals, as a product stream 168. _{In the hydrogen purification units 156 and 158, carbon oxides and methane are separated to} _{produce a tail gas that is recovered from the units 156 and 158 along line 170.} _{The recovered tail gas along line 170 is combined with a portion of a hydrogen-containing} _{flash gas produced in the carbon dioxide removal unit 146 along line 172, which bypasses the} _{hydrogen purification units 156 and 158. This increases the hydrogen content to the tail gas} and thus produces the hydrogen-containing tail gas that is recycled to the process as disclosed herein. P102471 31 _{The tail gas containing the hydrogen-containing flash gas is compressed in a compressor 192} and a portion thereof is the supplied along line 60 as fuel to the fired heater 58. In another embodiment of the process, the compressor 192 can be omitted. The remainder is passed to a further compressor 174, compressed further, and then divided into streams 18 and 49 to be used in the process as disclosed herein. _{In the process depicted in Figure 1, the tail gas recycle to the process is preferably provided} _{via line 56 to the pre-reformed gas upstream of the fired heater 58. In alternative embodiments} _{of the invention, one or more of the tail gas recycle streams 18, 48, 56, 104, 144, and 153 may} be omitted, provided that at least one thereof remains in the process, to recycle at least a _{portion of the tail gas to the process.}

Claims

P102471 32 Claims _{1. A process for the production of hydrogen comprising the steps of:} _{(i) reforming a gaseous mixture comprising a hydrocarbon and steam having a steam} _{to carbon ratio in the range of 0.4:1 to 1.8:1, to in a reforming unit comprising an} autothermal reformer to produce a reformed gas mixture, (_{ii) subjecting the reformed gas mixture to an isothermal water-gas shift reaction in an} isothermal water-gas shift reactor using water as a heat exchange medium, thereby increasing the hydrogen content of the reformed gas mixture and producing a hydrogen-enriched reformed gas while raising steam, (_{iii) cooling at least some of the hydrogen-enriched reformed gas and separating} condensed water therefrom to provide a de-watered hydrogen-enriched reformed gas, (_{iv) subjecting at least some of the de-watered hydrogen-enriched reformed gas to} carbon dioxide separation by performing a reactive amine wash on the hydrogen- enriched reformed gas in a carbon dioxide separation unit to recover carbon dioxide gas and crude hydrogen gas, and (_{v) subjecting at least some of the crude hydrogen gas to purification in a hydrogen} purification unit to produce a purified hydrogen gas and a tail gas, w_{herein a portion of the tail gas is recycled to the process.} _{2. The process according to claim 1, wherein the steam to carbon ratio is in a range of from} _{0.4:1 to 1.6:1, preferably in the range of 0.6:1 to 1.4:1 and more preferably in the range} _{of 0.8:1 to 1.2:1.} _{3. The process according to claim 1 or claim 2, wherein the hydrocarbon is a methane-} containing gas, preferably containing >30 vol. % methane. _{4. The process according to any one of claims 1 to 3, wherein the hydrocarbon is natural} gas, preferably being mixed with an industrial methane-containing off-gas, e.g. from an oil refining process. _{5. The process according to any one of claims 1 to 4, wherein at least a portion of the tail} _{gas is recycled to a hydrocarbon containing feed of the process.} P102471 33 _{6. The process according to any one of claims 1 to 5, wherein the reforming unit includes} _{one or more pre-reformers in which the gaseous mixture is subjected to adiabatic pre-} reforming such that a pre-reformed gas mixture is fed to the autothermal reformer. _{7. The process according to claim 6, wherein at least a portion of the tail gas is recycled to} a hydrocarbon-containing feed to the pre-reformer. _{8. The process according to any one of claims 1 to 7, wherein at least a portion of the tail} gas is recycled to the autothermal reformer, or to a feed of the autothermal reformer. _{9. The process according to any one of claims 1 to 8, wherein at least a portion of the tail} gas is recycled to the inlet of the isothermal water gas shift reactor. _{10. The process according to any one of claims 1 to 9, wherein the isothermal water gas} _{shift reactor contains a copper/zinc oxide/alumina catalyst promoted with MgO and/or} SiO2. _{11. The process according to any one of claims 1 to 10, which includes desulphurising the} hydrocarbon by contacting the hydrocarbon, preferably mixed with a portion of the tail gas, with a desulphurisation catalyst at a desulphurisation temperature. _{12. The process according to claim 11, wherein the desulphurisation temperature is in a} _{range of from 200°C to 400°C, preferably in the range of 200°C to 250°C.} _{13. The process according to claim 11 or claim 12, wherein the hydrocarbon, preferably} mixed with a portion of the tail gas, is heated to the desulphurisation temperature in heat exchange with the hydrogen-enriched reformed gas and/or in heat exchange with the reformed gas mixture after cooling of the reformed gas mixture with water in a boiler to r_{aise steam and/or in heat exchange with high or medium pressure steam raised in the} process. _{14. The process according to any one of claims 11 to 13, wherein the hydrocarbon is} desulphurised by hydrodesulphurisation. _{15. The process according to any one of claims 1 to 14, wherein the gaseous mixture} comprising the hydrocarbon and steam is formed by mixing the hydrocarbon, preferably P102471 34 mixed with a portion of the tail gas, with steam that is raised by cooling the reformed gas mixture with water in a boiler and/or that is raised in the isothermal water gas shift reactor. _{16. The process according to any one of claims 1 to 15, which includes heating the gaseous} mixture upstream of the reforming unit, in heat exchange with the reformed gas mixture after cooling of the reformed gas mixture with water in a boiler to raise steam. _{17. The process according to any one of claims 1 to 16, wherein condensed water recovered} from the process is used to provide at least a portion of the steam in the gaseous mixture fed to the reforming unit. _{18. The process according to any one of claims 1 to 17, which includes supplying a portion} _{of the tail gas to one or more fired heaters as a fuel gas and combusting the tail gas to} heat one or more process streams within the process. _{19. The process according to claim 18, wherein the tail gas is supplied to the tail gas fuelled} _{fired heater(s), such that at least 10% vol, or at least 15% vol, or at least 20% vol, or at} _{least 30% vol of the total flowrate of inert gases in the hydrogen enriched reformed gas} _{is present in the tail gas fuel fed to the one or more fired heaters.} _{20. The process according to claim 18 or claim 19, wherein the one or more fired heaters} heats a hydrocarbon-containing feed of the autothermal reformer. _{21. The process according to any one of claims 18 to 20, wherein the one or more fired} _{heaters superheats steam that is subsequently used to form the gaseous mixture} comprising the hydrocarbon and steam. _{22. The process according to any one of claims 18 to 21, which includes raising steam in} _{the one or more fired heaters and optionally combining at least a portion of such steam} _{with the hydrocarbon, preferably mixed with a portion of the tail gas, to form the gaseous} mixture comprising the hydrocarbon and steam. _{23. The process according to claim 22, wherein steam is raised by pre-heating boiler feed} water in heat exchange with the hydrogen-enriched reformed gas and then further heating such pre-heated boiler feed water in the one or more fired heaters. P102471 35 _{24. The process according to any one of claims 1 to 23, wherein the tail gas further} comprises a portion of the crude hydrogen gas from the carbon dioxide separation unit. _{25. The process according to claim 24, which includes withdrawing a hydrogen-containing} flash gas from the carbon dioxide separation unit and mixing it with tail gas from the hydrogen purification unit, such hydrogen-containing flash gas bypasses the hydrogen purification unit. _{26. The process according to any one of claims 1 to 25, which includes recycling at least a} _{portion of the tail gas to the hydrogen-enriched reformed gas feed of the carbon dioxide} removal unit. _{27. The process according to any one of claims 1 to 26, which includes recycling at least a} _{portion of the tail gas to the crude hydrogen gas feed of the hydrogen purification unit.} _{28. The process according to any one of claims 1 to 27, wherein the isothermal water gas} _{shift reaction is performed isothermally at a temperature of at least 225°C but below} 300°C.