WO2021083776A1 - Green method for the preparation of synthesis gas - Google Patents

Green method for the preparation of synthesis gas Download PDF

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WO2021083776A1
WO2021083776A1 PCT/EP2020/079701 EP2020079701W WO2021083776A1 WO 2021083776 A1 WO2021083776 A1 WO 2021083776A1 EP 2020079701 W EP2020079701 W EP 2020079701W WO 2021083776 A1 WO2021083776 A1 WO 2021083776A1
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steam
stream
autothermal
gas
reforming
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French (fr)
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Peter Mølgaard Mortensen
Kim Aasberg-Petersen
Pat A Han
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Haldor Topsøe A/S
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    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B3/00—Hydrogen; Gaseous mixtures containing hydrogen; Separation of hydrogen from mixtures containing it; Purification of hydrogen
    • C01B3/02—Production of hydrogen or of gaseous mixtures containing a substantial proportion of hydrogen
    • C01B3/32—Production of hydrogen or of gaseous mixtures containing a substantial proportion of hydrogen by reaction of gaseous or liquid organic compounds with gasifying agents, e.g. water, carbon dioxide, air
    • C01B3/34—Production of hydrogen or of gaseous mixtures containing a substantial proportion of hydrogen by reaction of gaseous or liquid organic compounds with gasifying agents, e.g. water, carbon dioxide, air by reaction of hydrocarbons with gasifying agents
    • C01B3/38—Production of hydrogen or of gaseous mixtures containing a substantial proportion of hydrogen by reaction of gaseous or liquid organic compounds with gasifying agents, e.g. water, carbon dioxide, air by reaction of hydrocarbons with gasifying agents using catalysts
    • C01B3/382—Multi-step processes
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
    • C25B1/00—Electrolytic production of inorganic compounds or non-metals
    • C25B1/01—Products
    • C25B1/02—Hydrogen or oxygen
    • C25B1/04—Hydrogen or oxygen by electrolysis of water
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
    • C25B15/00—Operating or servicing cells
    • C25B15/08—Supplying or removing reactants or electrolytes; Regeneration of electrolytes
    • C25B15/081—Supplying products to non-electrochemical reactors that are combined with the electrochemical cell, e.g. Sabatier reactor
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B2203/00—Integrated processes for the production of hydrogen or synthesis gas
    • C01B2203/02—Processes for making hydrogen or synthesis gas
    • C01B2203/0205—Processes for making hydrogen or synthesis gas containing a reforming step
    • C01B2203/0227—Processes for making hydrogen or synthesis gas containing a reforming step containing a catalytic reforming step
    • C01B2203/0233—Processes for making hydrogen or synthesis gas containing a reforming step containing a catalytic reforming step the reforming step being a steam reforming step
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B2203/00—Integrated processes for the production of hydrogen or synthesis gas
    • C01B2203/02—Processes for making hydrogen or synthesis gas
    • C01B2203/0205—Processes for making hydrogen or synthesis gas containing a reforming step
    • C01B2203/0227—Processes for making hydrogen or synthesis gas containing a reforming step containing a catalytic reforming step
    • C01B2203/0244—Processes for making hydrogen or synthesis gas containing a reforming step containing a catalytic reforming step the reforming step being an autothermal reforming step, e.g. secondary reforming processes
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B2203/00—Integrated processes for the production of hydrogen or synthesis gas
    • C01B2203/06—Integration with other chemical processes
    • C01B2203/061—Methanol production
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B2203/00—Integrated processes for the production of hydrogen or synthesis gas
    • C01B2203/08—Methods of heating or cooling
    • C01B2203/0805—Methods of heating the process for making hydrogen or synthesis gas
    • C01B2203/0811—Methods of heating the process for making hydrogen or synthesis gas by combustion of fuel
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B2203/00—Integrated processes for the production of hydrogen or synthesis gas
    • C01B2203/08—Methods of heating or cooling
    • C01B2203/0805—Methods of heating the process for making hydrogen or synthesis gas
    • C01B2203/085—Methods of heating the process for making hydrogen or synthesis gas by electric heating
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B2203/00—Integrated processes for the production of hydrogen or synthesis gas
    • C01B2203/08—Methods of heating or cooling
    • C01B2203/0805—Methods of heating the process for making hydrogen or synthesis gas
    • C01B2203/0866—Methods of heating the process for making hydrogen or synthesis gas by combination of different heating methods
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B2203/00—Integrated processes for the production of hydrogen or synthesis gas
    • C01B2203/12—Feeding the process for making hydrogen or synthesis gas
    • C01B2203/1205—Composition of the feed
    • C01B2203/1211—Organic compounds or organic mixtures used in the process for making hydrogen or synthesis gas
    • C01B2203/1235—Hydrocarbons
    • C01B2203/1241—Natural gas or methane
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B2203/00—Integrated processes for the production of hydrogen or synthesis gas
    • C01B2203/12—Feeding the process for making hydrogen or synthesis gas
    • C01B2203/1205—Composition of the feed
    • C01B2203/1211—Organic compounds or organic mixtures used in the process for making hydrogen or synthesis gas
    • C01B2203/1235—Hydrocarbons
    • C01B2203/1247—Higher hydrocarbons
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B2203/00—Integrated processes for the production of hydrogen or synthesis gas
    • C01B2203/12—Feeding the process for making hydrogen or synthesis gas
    • C01B2203/1258—Pre-treatment of the feed
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B2203/00—Integrated processes for the production of hydrogen or synthesis gas
    • C01B2203/14—Details of the flowsheet
    • C01B2203/141—At least two reforming, decomposition or partial oxidation steps in parallel
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B2203/00—Integrated processes for the production of hydrogen or synthesis gas
    • C01B2203/14—Details of the flowsheet
    • C01B2203/142—At least two reforming, decomposition or partial oxidation steps in series
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/30—Hydrogen technology
    • Y02E60/36—Hydrogen production from non-carbon containing sources, e.g. by water electrolysis
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P20/00—Technologies relating to chemical industry
    • Y02P20/10—Process efficiency
    • Y02P20/133—Renewable energy sources, e.g. sunlight

Definitions

  • the present application is directed to the preparation of synthesis gas. More particular, the invention combines electrolysis of water, electrical heated steam reforming and autothermal reforming and optionally additionally heat exchange reforming of a hydrocarbon feed stock in the prep aration of a hydrogen and carbon oxides containing synthe sis gas.
  • emission of greenhouse gas ses is reduced to a minimum by applying renewable power in all principal process steps.
  • Production of synthesis gas e.g. for the methanol synthesis with natural gas feed is typically carried out by steam re forming.
  • the steam reforming catalyst is typically loaded in a plurality of reformer tubes arranged within a reformer house.
  • the reformer tubes are heated by radiant heat produced by burning fuel gas in a plurality of burners arranged either at sidewall or top in the reformer house.
  • the product gas will comprise hy drogen, carbon monoxide, and carbon dioxide as well as other components normally including methane and steam.
  • SMR steam methane reformer
  • the ATR in the 2-step reforming concept requires oxygen. Today this is typically produced in a cryogenic air separation unit (ASU). The size and cost of this ASU is large. If the oxygen could be produced by other means, this would be desirable.
  • flue gas from the burners in tubular steam reformers in one of the main by-products in the preparation of synthesis gas and the amount of flue gas representing undesirable greenhouse gasses should be re Jerusalem to produce.
  • the present invention provides a method to reduces produc- tion of flue gas to an absolute minimum by integrating electrical powered unit operations in the synthesis gas production, that is electrolysis and electrically heated primary steam reforming.
  • the concept utilizes a layout where a fired heater is used to process any off-gases from the plant and provide preheating to the process side - this heater is the only source of flue gas emissions.
  • the process gas from the electrical heated primary steam reforming is sent to a secondary reformer together with ox- ygen to burn part of the gas and supply the remaining en ergy for the reforming.
  • an electrolysis unit provides hydrogen to bal ance the module from the reforming section to the desired level - CO2 can also be imported both upstream one of the reformers, or downstream the reformers for the same pur pose. Oxygen from the electrolysis is used for the second ary reformer.
  • this invention provides a method for the preparation of synthesis gas comprising the steps of
  • step (c) steam reforming at least a part of the hydrocarbon feed stock from step (a)to a steam reformed gas;
  • step (f) withdrawing the synthesis gas, wherein the steam re- forming in step (c)is performed in an electrical heated re former.
  • the oxygen prepared by electrolysis of water introduced into the autothermal reformer in step (d) can additionally be supplemented by oxygen prepared by air separation in an (ASU).
  • the method accord ing to the invention comprises the further step of separat- ing air into a separate stream containing oxygen and into a separate stream containing nitrogen and introducing at least a part of the separate stream containing oxygen into the autothermal reformer in step (d).
  • the air sepa ration unit can preferably be powered by renewable energy.
  • a part of the hydrocarbon feed stock from step (a) can bypass the steam reforming in step (c) and be introduced into the autothermal reformer in step (d).
  • the method comprises the further step of steam reforming a part of the hydrocarbon feed stock in indirect heat transfer relationship with the process stream leaving the autothermal reforming step (d) and mixing the heat exchange steam reformed process gas stream with autothermal reformed process gas stream up stream step (e).
  • heat exchange steam re forming is performed in series with the autothermal reform ing step.
  • all the hydrocarbon feedstock is passed through the heat exchange reformer where it is heated and partially converted.
  • the partially converted feedstock is then fed to the autothermal reformer where the final conversion takes place.
  • the hot process stream from the autothermal reformer is passed through heat exchange reformer in indirect heat exchanging relationship with the hydrocarbon feedstock and provides the necessary heat for the endothermic steam re forming reaction.
  • the method comprises the further step of heat exchange steam reforming the hydrocarbon feed stock in indirect heat transfer rela tionship with the process stream leaving the autothermal reforming step (d) and passing the heat exchanged steam re formed hydrocarbon feed stock to step (d).
  • the amount of hydrogen added to the reformed gas downstream step (d) can be tailored such that when the hydrogen is mixed with the process gas generated by the reforming steps, the desired value of M of between 1.90 and 2.20 or preferably between 2.00 and 2.10 is achieved.
  • the module can additionally be adjusted to the desired value by introducing substantially pure carbon dioxide up stream step (c), and/or upstream of step (d) and/or down stream step d.
  • the carbon dioxide stems optionally from the flue gas generated when burning off-gases and purified by known means.
  • the electrolysis unit is operated such that all the hydrogen produced in this unit is added to the reformed gas downstream step (d) and the module of the re sulting mixture of this hydrogen and the process gas is be tween 1.9 and 2.2 or preferably between 2 and 2.1.
  • step (d) some or preferably all the oxygen from the electrolysis unit is added to the autothermal reformer in step (d). Additional oxygen from an air separation unit can be added to the autothermal reformer in this embodi ment.
  • suitable hydrocarbon feed stocks to the re former and/or the heat exchange reformer(s) for use in the invention comprise natural gas, methane, LNG, naphtha or mixtures thereof either as such or pre-reformed and/or desulfurized.
  • the hydrocarbon feed stocks may further comprise hydrogen and/or steam as well as other components.
  • the electrolysis can be performed by various means known in the art such as by solid oxide based electrolysis or elec trolysis by alkaline cells or polymer cells (PEM). If the power for the electrolysis is produced (at least in part) by sustainable sources, the CC ⁇ -emissions is per unit of product produced by the method is further reduced.
  • the method according to the invention is preferably em- ployed for the production methanol by conversion of the synthesis gas withdrawn in step (f).
  • the method according to the invention can also be employed for producing synthesis gas for other applications where it is desirable to increase the hydrogen concentra tion in the feed gas and where part of the oxygen and hy drogen needed for synthesis gas production is favorably produced by electrolysis.

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Abstract

Method for the preparation of synthesis gas comprising the steps of (a) providing a hydrocarbon feed stock; (b) preparing a separate hydrogen containing stream and a separate oxygen containing stream by electrolysis of water and/or steam; (c) steam reforming at least a part of the hydrocarbon feed stock from step (a) to a steam reformed gas; (d) autothermal reforming in an autothermal reformer the steam reformed gas with at least a part of the oxygen containing stream obtained by the electrolysis of water and/or steam in step (b) to an autothermal reformed gas stream comprising hydrogen, carbon monoxide and carbon dioxide; (e) introducing at least part of the separate hydrogen containing stream from step (b) into the autothermal reformed gas stream from step (d); and (f) withdrawing the synthesis gas,wherein the steam reforming in step (c) is performed in an electrical heated steam reformer.

Description

Title: Green method for the preparation of synthesis gas
The present application is directed to the preparation of synthesis gas. More particular, the invention combines electrolysis of water, electrical heated steam reforming and autothermal reforming and optionally additionally heat exchange reforming of a hydrocarbon feed stock in the prep aration of a hydrogen and carbon oxides containing synthe sis gas.
By the method of the invention, emission of greenhouse gas ses is reduced to a minimum by applying renewable power in all principal process steps. Production of synthesis gas e.g. for the methanol synthesis with natural gas feed is typically carried out by steam re forming.
Optimal production of synthesis gas requires an integration of the process with the entire chemical plant, wherefore by-products will need to be handled properly a balanced reasonably. In a modern reforming plant, unprocessed off gas, in particular flue gas is one of the biggest by-prod uct, because it has little value.
The principal reaction of steam reforming is (given for me thane):
CH4 + H20 ¾ 3H2 + CO
Similar reactions occur for other hydrocarbons. Steam re- forming (SMR) is normally accompanied by the water gas shift reaction:
CO + H20 ¾ C02 + H2 Steam reforming is a strongly endothermic process and heat must be provided to the process. In the known fired tubular steam reformers, the steam reforming catalyst is typically loaded in a plurality of reformer tubes arranged within a reformer house. The reformer tubes are heated by radiant heat produced by burning fuel gas in a plurality of burners arranged either at sidewall or top in the reformer house. Regardless of whether stand-alone SMR, 2-step reforming, or stand-alone ATR is used, the product gas will comprise hy drogen, carbon monoxide, and carbon dioxide as well as other components normally including methane and steam. Methanol synthesis gas has preferably a composition corre sponding to a so-called module (M= (H2-C02)/(C0+C02)) of 1.90-2.20 or more preferably slightly above 2 (eg.2.00- 2.10). In 2-step reforming the steam methane reformer (SMR) must be large and a significant amount of heat is required to drive the endothermic steam reforming reaction. Hence, it is desirable if the size and duty of the steam reformer can be reduced. Furthermore, the ATR in the 2-step reforming concept requires oxygen. Today this is typically produced in a cryogenic air separation unit (ASU). The size and cost of this ASU is large. If the oxygen could be produced by other means, this would be desirable. As mentioned hereinbefore, flue gas from the burners in tubular steam reformers in one of the main by-products in the preparation of synthesis gas and the amount of flue gas representing undesirable greenhouse gasses should be re duced to a minimum.
The present invention provides a method to reduces produc- tion of flue gas to an absolute minimum by integrating electrical powered unit operations in the synthesis gas production, that is electrolysis and electrically heated primary steam reforming. The concept utilizes a layout where a fired heater is used to process any off-gases from the plant and provide preheating to the process side - this heater is the only source of flue gas emissions.
The process gas from the electrical heated primary steam reforming is sent to a secondary reformer together with ox- ygen to burn part of the gas and supply the remaining en ergy for the reforming.
In parallel an electrolysis unit provides hydrogen to bal ance the module from the reforming section to the desired level - CO2 can also be imported both upstream one of the reformers, or downstream the reformers for the same pur pose. Oxygen from the electrolysis is used for the second ary reformer. Thus, this invention provides a method for the preparation of synthesis gas comprising the steps of
(a) providing a hydrocarbon feed stock;
(b) preparing a separate hydrogen containing stream and a separate oxygen containing stream by electrolysis of water and/or steam;
(c) steam reforming at least a part of the hydrocarbon feed stock from step (a)to a steam reformed gas; (d)autothermal reforming in an autothermal reformer the steam reformed gas with at least a part of the oxygen con taining stream obtained by the electrolysis of water and/or steam in step (b) to an autothermal reformed gas stream comprising hydrogen, carbon monoxide and carbon dioxide;
(e) introducing at least part of the separate hydrogen con taining stream from step (b) into the autothermal reformed gas stream from step (d);and
(f) withdrawing the synthesis gas, wherein the steam re- forming in step (c)is performed in an electrical heated re former.
In some applications, the oxygen prepared by electrolysis of water introduced into the autothermal reformer in step (d) can additionally be supplemented by oxygen prepared by air separation in an (ASU).
Thus in an embodiment of the invention, the method accord ing to the invention comprises the further step of separat- ing air into a separate stream containing oxygen and into a separate stream containing nitrogen and introducing at least a part of the separate stream containing oxygen into the autothermal reformer in step (d). Like the electrolysis of water and/or steam, the air sepa ration unit can preferably be powered by renewable energy.
In all of the above embodiments, a part of the hydrocarbon feed stock from step (a) can bypass the steam reforming in step (c) and be introduced into the autothermal reformer in step (d). In an embodiment of the invention, the method comprises the further step of steam reforming a part of the hydrocarbon feed stock in indirect heat transfer relationship with the process stream leaving the autothermal reforming step (d) and mixing the heat exchange steam reformed process gas stream with autothermal reformed process gas stream up stream step (e).
In another type of such a process, heat exchange steam re forming is performed in series with the autothermal reform ing step. In the serial heat exchange steam reforming pro cess, all the hydrocarbon feedstock is passed through the heat exchange reformer where it is heated and partially converted. The partially converted feedstock is then fed to the autothermal reformer where the final conversion takes place. The hot process stream from the autothermal reformer is passed through heat exchange reformer in indirect heat exchanging relationship with the hydrocarbon feedstock and provides the necessary heat for the endothermic steam re forming reaction.
Thus in another embodiment of the invention, the method comprises the further step of heat exchange steam reforming the hydrocarbon feed stock in indirect heat transfer rela tionship with the process stream leaving the autothermal reforming step (d) and passing the heat exchanged steam re formed hydrocarbon feed stock to step (d).
The amount of hydrogen added to the reformed gas downstream step (d) can be tailored such that when the hydrogen is mixed with the process gas generated by the reforming steps, the desired value of M of between 1.90 and 2.20 or preferably between 2.00 and 2.10 is achieved.
The module can additionally be adjusted to the desired value by introducing substantially pure carbon dioxide up stream step (c), and/or upstream of step (d) and/or down stream step d. The carbon dioxide stems optionally from the flue gas generated when burning off-gases and purified by known means.
In one embodiment, the electrolysis unit is operated such that all the hydrogen produced in this unit is added to the reformed gas downstream step (d) and the module of the re sulting mixture of this hydrogen and the process gas is be tween 1.9 and 2.2 or preferably between 2 and 2.1.
In this embodiment, some or preferably all the oxygen from the electrolysis unit is added to the autothermal reformer in step (d). Additional oxygen from an air separation unit can be added to the autothermal reformer in this embodi ment.
In general suitable hydrocarbon feed stocks to the re former and/or the heat exchange reformer(s) for use in the invention comprise natural gas, methane, LNG, naphtha or mixtures thereof either as such or pre-reformed and/or desulfurized.
The hydrocarbon feed stocks may further comprise hydrogen and/or steam as well as other components. The electrolysis can be performed by various means known in the art such as by solid oxide based electrolysis or elec trolysis by alkaline cells or polymer cells (PEM). If the power for the electrolysis is produced (at least in part) by sustainable sources, the CC^-emissions is per unit of product produced by the method is further reduced.
The method according to the invention is preferably em- ployed for the production methanol by conversion of the synthesis gas withdrawn in step (f).
However, the method according to the invention can also be employed for producing synthesis gas for other applications where it is desirable to increase the hydrogen concentra tion in the feed gas and where part of the oxygen and hy drogen needed for synthesis gas production is favorably produced by electrolysis. Example
In the below table a comparison between conventional 2-step reforming and 2-step reforming + electrolysis according to the invention is provided.
Comparison Table
Figure imgf000008_0001
Figure imgf000009_0001
Figure imgf000010_0001
* Included in product gas ** Included in oxidant to ATR
As apparent from the Comparison Table above, the required duty for the reformer can be significantly reduced by the current invention. This duty will in practice translate in to less use of electricity for heating.

Claims

Claims
1. Method for the preparation of synthesis gas comprising the steps of
(a) providing a hydrocarbon feed stock;
(b) preparing a separate hydrogen containing stream and a separate oxygen containing stream by electrolysis of water and/or steam; (c) steam reforming at least a part of the hydrocarbon feed stock from step (a)to a steam reformed gas;
(d)autothermal reforming in an autothermal reformer the steam reformed gas with at least a part of the oxygen con taining stream obtained by the electrolysis of water and/or steam in step (b) to an autothermal reformed gas stream comprising hydrogen, carbon monoxide and carbon dioxide;
(e) introducing at least part of the separate hydrogen con taining stream from step (b) into the autothermal reformed gas stream from step (d); and (f) withdrawing the synthesis gas, wherein the steam reforming in step (c) is performed in an electrical heated steam reformer.
2. The method of claim 1, comprising the further step of separating air into a separate stream containing oxygen and into a separate stream containing nitrogen and introducing at least a part of the separate stream containing oxygen into the autothermal reformer.
3. The method of claim 1 or 2, wherein a part of the hy drocarbon feed stock from step (a) is bypassed the steam reforming in step (c) and introduced to the autothermal re former in step (d).
4. The method of any one of claims 1 to 3, wherein the hydrocarbon feed stock comprises natural gas, methane, LNG, naphtha or mixtures thereof either as such or pre-reformed and/or desulfurized.
5. The method of any one of claims 1 to 4, wherein the electrolysis of water and/or steam in step (b) is powered at least in part by renewable energy.
6. The method of any one of claims 2 to 5, wherein the separating of air is powered at least in part by renewable energy.
7. The method of any one of claims 1 to 6, wherein the electrical heated reformer is powered at least in part by renewable energy.
8. The method of any one of claims 1 to 7, comprising the further step of introducing substantially pure carbon diox ide upstream step (c), and/or upstream of step (d), and/or downstream step (d).
9. The method of any one of claims 1 to 8, wherein the electrolysis is operated such that all the hydrogen pro duced by the electrolysis is added to the reformed gas downstream step (d) to provide a module M= (H2-CO2)/(CO+CO2) in the synthesis gas withdrawn from step (f) of between 1.9 and 2.2, preferably between 2 and 2.1.
10. The method of claim any one of claims 1 to 9, wherein the module M=(H2-CC>2)/(CO+CO2) in the synthesis gas with drawn in step (f) is in the range from 2 to 2.1.
11. The method of any one of claims 1 to 10, wherein the synthesis gas withdrawn in step (f) is in a further step converted to a methanol product.
12. The method of any one of claims 1 to 11, wherein wherein off-gas generated in process steps is burnt to pre heat the hydrocarbon feedstock and/or steam generation.
13. The method of any one of claims 1 to 12, comprising the further step of steam reforming a part of the hydrocar- bon feed stock in indirect heat transfer relationship with the process stream leaving the autothermal reforming step (d) and mixing the heat exchange steam reformed process gas stream with autothermal reformed process gas stream up stream step (e).
14. The method of any one of claims 1 to 12, comprising the further step of heat exchange steam reforming the hy drocarbon feed stock in indirect heat transfer relationship with the process stream leaving the autothermal reforming step (d) and passing the heat exchanged steam reformed hy drocarbon feed stock to step(d).
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