Improving the purity of a CO2-rich stream

Abstract

A process and plant for producing a high purity CO.sub.2 product, comprising: providing a CO.sub.2-rich stream containing hydrocarbons, hydrogen and/or CO, combining it with a stream rich in methane (CH.sub.4), and mixing it with oxygen, thereby forming a CO.sub.2/O.sub.2- mixture; subjecting the CO.sub.2/O.sub.2- mixture to a catalytic oxidation step, thereby producing a purified stream having a higher CO.sub.2 and/or H.sub.2O concentration; removing H.sub.2O from said purified stream, for producing said high purity CO.sub.2 product stream. The CO.sub.2-rich stream is for instance derived from the CO.sub.2-removal section of a plant for producing hydrogen.

Claims

1. A process for producing a high purity CO.sub.2 product, comprising the steps of: i) providing a CO.sub.2-rich stream containing hydrocarbons, hydrogen and/or CO; combining it with a stream rich in methane (CH.sub.4); and mixing it with oxygen, thereby forming a CO.sub.2/O.sub.2- mixture; ii) subjecting the CO.sub.2/O.sub.2- mixture to a catalytic oxidation step, thereby producing a purified stream having a higher CO.sub.2 and/or H.sub.2O concentration; iii) removing H.sub.2O from said purified stream, for producing said high purity CO.sub.2 product.

2. The process of claim 1, wherein the catalytic oxidation step is conducted in two or more steps with intermediate addition of oxygen.

3. The process of claim 1, wherein in step iii) the removing of H.sub.2O comprises passing the purified stream to a cooling train including one or more cooling units for thereby producing a cooled purified stream, and subsequently passing the cooled purified stream to a condensing step.

4. The process of claim 3, wherein the cooling train includes a cooling unit using N.sub.2 from an air separation unit (ASU).

5. The process of claim 1, wherein the oxygen is generated from an air separation unit (ASU) and/or a water/steam electrolysis unit.

6. The process of claim 1, wherein step iii) further comprises a drying step, preferably after conducting said condensing step.

7. The process of claim 6, wherein said drying step is conducted in a temperature swing adsorption unit.

8. The process of claim 1, wherein the CO.sub.2-rich stream of step i) is derived from a CO.sub.2-removal section, said CO.sub.2-removal section being arranged to receive a shifted synthesis gas stream, in which the CO.sub.2-removal section is an amine wash unit and comprises a CO.sub.2-absorber, a CO.sub.2-stripper and a low-pressure flash drum, from which said CO.sub.2-rich stream is separated.

9. The process of claim 8, wherein the CO.sub.2-removal section comprises a highpressure flash drum and the process further comprises adding hydrogen to said CO.sub.2-rich stream.

10. The process of claim 1, wherein step i) comprises: supplying a hydrocarbon feed to a reforming section, and converting it to a stream of synthesis gas; withdrawing a stream of synthesis gas from the reforming section and supplying it to a shift section, shifting the synthesis gas in a high temperature shift (HTS)-step, and optionally also in a medium temperature shift (MTS) and/or low temperature shift (LTS)-shit step, thereby providing a shifted synthesis gas stream; supplying the shifted synthesis gas stream from the shift section to a CO.sub.2 removal section, suitably said amine wash unit, and separating said CO.sub.2-rich stream from said shifted synthesis gas stream, thereby providing a H.sub.2-rich stream.

11. The process of claim 10, wherein the reforming section comprises autothermal reforming (ATR), and optionally also pre-reforming said hydrocarbon feed in one or more prereformer units prior to it being fed to the ATR.

12. The process of claim 10, further comprising preheating said hydrocarbon feed in one or more fired heaters and feeding at least a part of said H.sub.2-rich stream as hydrocarbon fuel to the at least one or more fired heaters.

13. The process of claim 1, wherein the process is absent of a hydrogen purification step.

14. A plant for producing a high purity CO.sub.2 product, said plant comprising: a conduit for mixing an oxygen stream, preferably oxygen generated from an air separation unit (ASU) and/or a water/steam electrolysis unit, with a CO.sub.2-rich stream containing hydrocarbons, hydrogen and/or CO; and a conduit for combining a stream rich in methane (CH.sub.4), with said CO.sub.2-rich stream; thereby forming an inlet gas comprising a mixture of carbon dioxide and oxygen; a catalytic oxidation (CATOX) unit arranged to receive said inlet gas comprising a mixture of carbon dioxide and oxygen, said CATOX unit comprising an outlet for withdrawing an outlet gas as a purified stream having a higher CO.sub.2 and/or H.sub.2O concentration; a cooling train arranged to receive said outlet gas from the CATOX unit, said cooling train comprising one or more cooling units for cooling the outlet gas; a condensate separator arranged to receive the thus cooled outlet gas and for removing H.sub.2O, thereby forming an outlet product comprising said high purity CO.sub.2 product.

15. Use of a CATOX unit for purifying a CO.sub.2-rich stream containing hydrocarbons, hydrogen and/or CO, which is derived from a process or plant for producing hydrogen, in particular from a CO.sub.2-removal section thereof, while not increasing the carbon emission of the plant.

Description

[0021] In an embodiment according to the first aspect of the invention, the CATOX step is conducted in two or more steps with intermediate addition of oxygen. In a particular embodiment, the oxygen is provided by splitting an oxygen stream and feeding to the two or more steps, i.e. parallel feeding the oxygen to the CATOX units, for instance by mixing oxygen with a first stream exiting the first CATOX step prior to entering a subsequent or second CATOX step. This further enables better control of hydrogen and oxygen slip due to any excess of hydrogen and/or oxygen.

[0022] As used herein, the term “high purity CO.sub.2-product” means a CO.sub.2-product having a purity of as high as 99.8 vol.% CO.sub.2 or even higher, for instance 99.99 vol.%. It would be understood that the CO.sub.2 concentration of this high purity CO.sub.2-product is higher than the CO.sub.2 concentration of the CO.sub.2-rich stream containing hydrocarbons, hydrogen and/or CO.

[0023] As used, herein, the term “CO.sub.2-rich stream containing hydrocarbons, hydrogen and/or CO” means a stream with a significant content of CO.sub.2, for instance 98 vol.% or higher and which also contains hydrocarbons such as CH.sub.4, as well as CO and H.sub.2. For instance, less than 0.05 vol.% CH.sub.4, less than 0.05 vol.% CO, and less than 2 vol.% H.sub.2.

[0024] The CO.sub.2-rich stream is a stream having a significant content of CO.sub.2, in particular as explained farther below, a stream separated from the low-pressure flash step of a carbon dioxide removal section and having a CO.sub.2-concentration of 98 vol.% or higher such as 99 vol.%.

[0025] The invention enables the oxidation of H.sub.2 to H.sub.2O and subsequent removal of the H.sub.2O to reduce the H.sub.2 content in CO.sub.2 product, as well of the oxidation of other components like hydrocarbons.

[0026] In an embodiment according to the first aspect of the invention, in step iii) the removing of H.sub.2O comprises passing the purified stream to a cooling train including one or more cooling units for thereby producing a cooled purified stream, and subsequently passing the cooled purified stream to a condensing step, e.g. by passing the purified stream to a condensate separator, thereby separating water as a condensate phase. In a particular embodiment, the cooling train includes a first cooling unit for preheating said CO.sub.2/O.sub.2-mixture before the CATOX step, preferably in a feed/effluent heat exchanger. In a particular embodiment, the cooling train further includes a cooling unit using N.sub.2 from an air separation unit (ASU), such as a heat exchanger using N.sub.2 as the heat exchanging medium.

[0027] In an embodiment according to the first aspect of the invention, the oxygen is generated from an air separation unit (ASU) and/or a water/steam electrolysis unit, Hence, the ASU provides preferably also for the oxygen being mixed with the CO.sub.2-rich stream prior to entering the catalytic oxidation step ii), as well as for the oxygen used in the reforming step where this reforming step includes autothermal reforming (ATR). Thereby, better integration and utilization of the streams produced in the ASU, i.e. not only O.sub.2 for the ATR but also N.sub.2 in the cooing train, is possible. In another embodiment, the oxygen being mixed with the CO.sub.2-rich stream prior to entering the catalytic oxidation step ii) is generated by providing a water feedstock and passing it through an electrolysis unit, i.e. a water/steam electrolysis unit. In a particular embodiment, the electrolysis unit is an alkali/polymer electrolyte membrane electrolysis unit i.e. alkali/PEM electrolysis unit (alkaline cells or polymer cells units). Such electrolysis unit utilizes water. In another particular embodiment, the electrolysis unit is a solid oxide electrolysis unit. Such electrolysis utilizes steam. Thereby, a more sustainable process and plant is possible, since the power required for electrolysis may be provided by renewable sources such as wind and solar energy.

[0028] It will be understood, that the term water feedstock includes water or steam. It would also be understood, that the term water/steam means water or steam.

[0029] In an embodiment according to the first aspect of the invention, step iii) further comprises a drying step, preferably after conducting said condensing step. This drying step enables a final water removal to provide a substantially water-free purified stream. In a particular embodiment, the drying step is conducted in a temperature swing adsorption unit. This enables to achieve the highest CO.sub.2 purity without increasing the carbon emission to the atmosphere. Temperature swing adsorption units are well-known in the art.

[0030] In an embodiment according to the first aspect of the invention, the CO.sub.2-rich stream of step i) is derived from a CO.sub.2-removal section, said CO.sub.2-removal section being arranged to receive a shifted synthesis gas stream, in which the CO.sub.2-removal section is an amine wash unit and comprises a CO.sub.2-absorber, a CO.sub.2-stripper and a low-pressure flash drum from which said CO.sub.2-rich stream is separated. Hence, according to this embodiment the CO.sub.2-rich stream is a product CO.sub.2-stream derived from the low-pressure flash step. For instance, the overhead stream from the low-pressure flash drum, mainly containing carbon dioxide, may be subjected to a separating step in a CO.sub.2-separator for thereby separate the CO.sub.2-rich stream and a condensate stream which may be recycled to the low-pressure flash drum. In a particular embodiment, this CO.sub.2-rich stream contains at least 98 vol.% CO.sub.2, such as 98.5 vol.% or 99 vol.% CO.sub.2.

[0031] In the CO.sub.2-removal section, in particular an amine wash unit, it is normally desirable to have a high-pressure flash step prior to the low-pressure flash step. Yet, in another particular embodiment according to the first aspect of the invention, the CO.sub.2-removal section is absent of a high-pressure flash step. This enables reduced complexity and costs associated with the CO.sub.2-removal section, as the high-pressure flash drum (HP flash drum) can be omitted. In addition, while it is possible, when operating a CO.sub.2 removal section with a HP flash drum, to recycle the HP flash gas back to the CO.sub.2 absorber column of the CO.sub.2 removal section, the rest of the impurities ends up in the CO.sub.2-rich stream separated from the low-pressure flash drum. This results in a lower purity of the CO.sub.2-rich stream than the one obtained by using CATOX in accordance with the present invention. The HP flash gas can also be burned releasing CO.sub.2 to atmosphere, but purity of CO.sub.2-rich stream will still be lower than with the present invention.

[0032] Hence, by using catalytic oxidation, the generated CO.sub.2 which otherwise would be carried over in the high-pressure flash gas of the CO.sub.2 removal section, is captured in the CO.sub.2-rich stream separated from the low-pressure flash drum, thus increasing the flow of the CO.sub.2-rich stream and avoiding the increase of CO.sub.2 emission to the atmosphere. This is especially of interest for blue hydrogen where CO.sub.2 emissions are required to be minimized. Other methods for purifying a CO.sub.2 stream such as pressure swing adsorption, membrane filtration or cryogenic, results in a purified stream and an off-gas stream. The off-gas stream is usually burned releasing CO.sub.2 to the atmosphere.

[0033] Particularly for hydrogen plants, where maximizing CO.sub.2 capture is important, such as when producing blue hydrogen, the CATOX process purifies the CO.sub.2 without increasing carbon emission. In all other processes, an off-gas stream is created which will lead to increased carbon emission if burned or it must be processed in some way.

[0034] Hence, the present invention uses CATOX to purify CO.sub.2 while not increasing carbon emissions in the plant.

[0035] At least part of the low-pressure flash gas, for instance in the form of a purge stream, is subjected to the catalytic oxidation, thereby also avoiding the build-up of impurities. In the catalytic oxidation step, the impurities are catalytically oxidized to CO.sub.2 and H.sub.2O. The oxidation of the hydrogen in the gas generates the necessary heat for the CATOX step. The H.sub.2O can be removed from the CO.sub.2 stream by condensation followed by optionally drying in a unit such a as a temperature swing adsorption unit, as explained above.

[0036] In another embodiment according to the first aspect of the invention, the CO.sub.2-removal section comprises a high-pressure flash drum, e.g. upstream said low-pressure flash drum, and the process further comprises adding hydrogen to said CO.sub.2-rich stream. This enables the provision of a CO.sub.2-removal section being able to generate the CO.sub.2-rich stream derived from the low-pressure drum as well as a high-pressure flash gas stream which may be used e.g. in fired heaters used to preheat the hydrocarbon feed in the reforming. The added hydrogen to the CO.sub.2-rich stream ensures thereby the provision of the necessary duty of the CATOX step(s). The hydrogen is suitably a stream derived from a H.sub.2-rich stream withdrawn from the CO.sub.2-removal section and/or a hydrogen stream derived from water/steam electrolysis

[0037] The high purity CO.sub.2 product obtained by the process is preferably captured and transported for e.g. sequestration in geological structures, thereby reducing the CO.sub.2 emission to the atmosphere.

[0038] Preferably, the CO.sub.2-removal section is comprised in a process or plant for producing hydrogen, whereby a synthesis gas generated by steam reforming (here interchangeably used with the term reforming) is subjected to water gas shift to form said shifted synthesis gas stream and subsequently to CO.sub.2-removal in a CO.sub.2-removal section.

[0039] Accordingly, in an embodiment according to the first aspect of the invention, step i) i.e. the step including providing a CO.sub.2-rich stream containing hydrocarbons, hydrogen and/or CO, comprises: [0040] supplying a hydrocarbon feed to a reforming section, and converting it to a stream of synthesis gas; [0041] withdrawing a stream of synthesis gas from the reforming section and supplying it to a shift section, shifting the synthesis gas in a high temperature shift (HTS)-step, and optionally also in a medium temperature shift (MTS) and/or low temperature shift (LTS)-shit step, thereby providing a shifted synthesis gas stream; [0042] supplying the shifted synthesis gas stream from the shift section to a CO.sub.2 removal section, suitably said amine wash unit, and separating said CO.sub.2-rich stream from said shifted synthesis gas stream, thereby providing a H.sub.2-rich stream.

[0043] Thus, from the CO.sub.2-removal section, not only a CO.sub.2-rich stream containing hydrocarbons, hydrogen and/or CO is generated, but also a H.sub.2-rich stream.

[0044] As used herein, the term H.sub.2-rich stream means a stream containing 95 vol.% or more, for instance 98 vol.% or more hydrogen, i.e. having a hydrogen purity of above 95 vol.%, with the balance being minor amounts of carbon containing compounds CH.sub.4, CO, CO.sub.2, as well as inerts N.sub.2, Ar.

[0045] Synthesis gas is typically produced by reforming a hydrocarbon feed either by steam reforming (SMR), secondary reforming, such as autothermal reforming (ATR) and two-step reforming with SMR and ATR in series. The SMR is advantageously an electrically heated steam reformer (e-SMR, or interchangeably, e-reformer), as for instance disclosed in applicant’s Patent Application WO 2019/228797A1 . A stand-alone ATR which may also include the use of a pre-reformer, is particularly suitable for the production of a H.sub.2-rich stream in accordance with the invention.

[0046] Accordingly, in a particular embodiment, the reforming section comprises autothermal reforming (ATR). In another particular embodiment, the reforming section further comprises pre-reforming said hydrocarbon feed in one or more prereformer units prior to it being fed to the ATR.

[0047] Thus, preferably the process or plant is without i.e. is absent of, a steam methane reformer unit (SMR) upstream the ATR. Accordingly, the reforming may include prereforming, yet it is conducted without primary reforming i.e. without a primary reforming unit. Thereby, a reduction in plant size is achieved.

[0048] In a particular embodiment, the process further comprises preheating said hydrocarbon feed in one or more fired heaters and feeding at least a part of said H.sub.2-rich stream as hydrocarbon fuel to the at least one or more fired heaters.

[0049] By using part of the H.sub.2-rich stream as fuel, i.e. as low carbon hydrogen fuel, it is possible, in a simple manner, to decarbonize the hydrocarbon feed, this for instance being natural gas, whereby at least 95% of the carbon is captured, while still achieving a high hydrogen purity in the H.sub.2-rich stream.

[0050] In an embodiment according to the first aspect of the invention, the process further comprises providing a hydrogenation unit and a sulfur absorption unit for conditioning the hydrocarbon feed, e.g. for sulfur removal, prior to said prereforming or prior to passing to said ATR, and mixing a portion of the H.sub.2-rich stream, i.e. as H.sub.2-recyle, with the hydrocarbon feed before being fed to the hydrogenation unit.

[0051] It would be understood that the reforming section is the section of the plant comprising units up to and including the ATR, i.e. the ATR, or the one or more pre-reformer units and the ATR. The reforming section may also comprise a hydrogenation unit and sulfur absorber upstream the one or more pre-reformer units and ATR.

[0052] The air separation unit (ASU) is arranged for receiving an air stream and produce an oxygen comprising stream which is then fed through a conduit to the ATR. Preferably, the oxygen comprising stream contains steam added to the ATR in accordance with the above-mentioned embodiment. Examples of oxidant comprising stream are: oxygen; mixture of oxygen and steam; mixtures of oxygen, steam, and argon; and oxygen enriched air. In the ASU, a nitrogen stream is also produced, which advantageously may also be used in the process and plant of the invention, as explained above.

[0053] The temperature of the synthesis gas at the exit of the ATR is between 900 and 1100° C., or 950 and 1100° C., typically between 1000 and 1075° C. This hot effluent synthesis gas which is withdrawn from the ATR (syngas from the ATR) comprises carbon monoxide, hydrogen, carbon dioxide, steam, residual methane, and various other components including nitrogen and argon.

[0054] Autothermal reforming (ATR) is described widely in the art and open literature. Typically, the ATR comprises a burner, a combustion chamber, and catalyst arranged in a fixed bed all of which are contained in a refractory lined pressure shell. ATR is for example described in Chapter 4 in “Studies in Surface Science and Catalysis”, Vol. 152 (2004) edited by Andre Steynberg and Mark Dry, and an overview is also presented in “Tubular reforming and autothermal reforming of natural gas - an overview of available processes”, lb Dybkjær, Fuel Processing Technology 42 (1995) 85-107.

[0055] Preferably steam is added upstream the HTS unit. Steam may optionally be added after the high temperature shift step such as before one or more following MT or LT shift and/or HT shift steps in order to maximize the performance of said following HT, MT and/or LT shift steps. The catalysts and process for conducting HTS, MTS and LTS are well known in the art.

[0056] In an embodiment according to the first aspect of the invention, the process is absent of a hydrogen purification step, such as pressure swing adsorption (PSA). Thereby there is no need for handling off-gas, e.g. a PSA off-gas, by for instance burning-off or flaring, thereby further reducing CO.sub.2-emissions. In a particular embodiment, the process is absent of a hydrogen purification step such as pressure swing adsorption (PSA) after said CO.sub.2-removal section. Thereby, the process and/or plant is further simplified, and plant size being reduced.

[0057] In a second aspect of the invention, there is also provided a plant, i.e. process plant, for producing a high purity CO.sub.2 product stream, said plant comprising: [0058] a conduit for mixing an oxygen stream, preferably oxygen generated from an air separation unit (ASU) and/or a water/steam electrolysis unit, with a CO.sub.2-rich stream containing hydrocarbons, hydrogen and/or CO; and a conduit for combining a stream rich in methane (CH.sub.4), such as a natural gas stream, with said CO.sub.2-rich stream; thereby forming an inlet gas comprising a mixture of carbon dioxide and oxygen; [0059] a catalytic oxidation (CATOX) unit arranged to receive said inlet gas comprising a mixture of carbon dioxide and oxygen, said CATOX unit comprising an outlet for withdrawing an outlet gas as a purified stream having a higher CO.sub.2 and H.sub.2O concentration; [0060] a cooling train arranged to receive said outlet from the CATOX unit, said cooling train comprising one or more cooling units for cooling the outlet gas; [0061] a condensate separator arranged to receive the thus cooled outlet gas and for removing H.sub.2O, thereby forming an outlet product comprising said high purity CO.sub.2 product stream.

[0062] In a third aspect of the invention, there is also provided the surprising use of a CATOX unit for purifying a CO.sub.2-rich stream containing hydrocarbons, hydrogen and/or CO, which is derived from a process or plant for producing hydrogen, in particular from a CO.sub.2-removal section thereof, while not increasing the carbon emission of the plant

[0063] In an embodiment according to the third aspect of the invention, said process comprises: [0064] supplying a hydrocarbon feed to a reforming section, and converting it to a stream of synthesis gas; [0065] withdrawing a stream of synthesis gas from the reforming section and supplying it to a shift section, shifting the synthesis gas in a high temperature shift (HTS)-step, and optionally also in a medium temperature shift (MTS) and/or low temperature shift (LTS)-shit step, thereby providing a shifted synthesis gas stream; [0066] supplying the shifted synthesis gas stream from the shift section to said CO.sub.2 removal section, suitably an amine wash unit, and separating said CO.sub.2-rich stream from said shifted synthesis gas stream, thereby providing a H.sub.2-rich stream.

[0067] In another embodiment according to the third aspect of the invention, the invention encompasses also a plant for carrying out said process, i.e. the plant comprises a reforming section, a shift section and said CO.sub.2-removal section.

[0068] Suitably also, the process or plant is absent of a hydrogen purification unit, such as pressure swing adsorption (PSA) unit, for instance a PSA unit downstream the CO.sub.2-removal section.

[0069] It would be understood that any of the embodiments and associated benefits of the first aspect of the invention may be used in connection with any of the embodiments of the second and third aspect of the invention, and vice versa.

[0070] The accompanying figure illustrates a layout of an ATR-based hydrogen process and plant with further purification of a CO.sub.2-rich stream according to one embodiment of the invention.

[0071] With reference to the figure, there is shown a plant/process 100 in which a hydrocarbon feed 1, such as natural gas, is passed to a reforming section comprising a pre-reforming unit 140 and ATR 110. The reforming section may also include a hydrogenator and sulfur absorber unit (not shown) upstream the pre-reforming unit 140. Prior to entering the hydrogenator, the hydrocarbon steam 1 is mixed with a hydrogen-recycle stream 8‴ diverted from a H.sub.2-rich stream 8 produced in downstream CO.sub.2-removal section 170. Prior to entering the pre-reforming unit 140, the hydrocarbon feed 1 is also mixed with steam 13 and the resulting prereformed hydrocarbon feed 2 is fed to the ATR 110, as so is an oxidant stream formed by mixing oxygen 15 and steam 13. Steam may also be added separately, as also shown in the figure. The oxygen stream 15 is produced by an air separation unit (ASU) 145 to which air 14 is fed. In the ATR 110, the hydrocarbon feed 2 is converted into a stream of synthesis gas 3, which is withdrawn from the ATR 110 and passed to a shift section. This syngas exits the ATR through a refractory lined outlet section and transfer line to waste heat boilers (not shown) in the syngas i.e. process gas cooling section.

[0072] The shift section comprises a high temperature shift (HTS) unit 115 where additional or extra steam 13′ also may be added upstream. Additional shift units, such as a low temperature shift (LTS) unit 150 may also be included in the shift section. Additional or extra steam may also be added downstream the HTS unit 115 yet upstream the LTS unit 150 for increasing the steam-to-carbon ratio. From the shift section, a shifted synthesis gas stream 5 enriched in hydrogen is produced which is then fed to a CO.sub.2-removal section 170. The CO.sub.2-removal section 170 comprises a CO.sub.2-absorber and a CO.sub.2-stripper (regenerator), which separates a CO.sub.2-rich stream 10 derived from a low-pressure flash drum (not shown) and which contains e.g. more than 99 vol.% CO.sub.2, and hydrocarbons such as CH.sub.4, as well as CO and H.sub.2. A H.sub.2-rich stream 8 containing e.g. 98 vol.% hydrogen or higher is also withdrawn from the CO.sub.2-removal section 170. Optionally, a high-pressure flash gas 12 from a high-pressure flash drum (not shown) of the CO.sub.2-removal section 170 may be generated. The plant 100, as illustrated in the figure,is absent of a hydrogen purification unit, such as a PSA.

[0073] The H.sub.2-rich stream 8 is divided into a H.sub.2-product 8′ for supplying to end customers such as refineries, a low carbon hydrogen fuel 8″ which is used in fired heater unit(s) 135, and a hydrogen-recycle 8‴ for mixing with the hydrocarbon feed 1. The fired heater 135 provides for the indirect heating of hydrocarbon feed 1 and optionally also hydrocarbon feed 2.

[0074] The CO.sub.2-rich stream 10 is compressed (not shown), combined e.g. mixed with a portion of natural gas being feed in line 1 (not shown) or a separate natural gas stream (not shown), and mixed with oxygen stream 15 from the ASU, thereby forming a CO.sub.2/O.sub.2-mixture stream 17. The CO.sub.2/O.sub.2-mixture is preheated in a CATOX feed/effluent heat exchanger 180, thus forming a preheated stream 18 which is then passed to the CATOX unit 190. From the CATOX unit 190, catalytic oxidation over e.g. a fixed bed of catalyst, as is well known in the art, is conducted thereby producing a purified stream 19 having a higher CO.sub.2 and H.sub.2O concentration than the CO.sub.2-rich stream 10 stream prior to or after combining with the stream rich in methane, or higher than in the CO.sub.2/O.sub.2-mixture stream 17 and 18. This purified stream 19 is withdrawn and used as heat exchanging medium in the feed/effluent heat exchanger 180. The thus cooled purified stream 20 is further cooled in cooling train 200, which may comprise a CO.sub.2 air cooler and CO.sub.2 water cooler (not shown) as well as a heat exchanger using nitrogen 16 from the ASU as cooling medium. The nitrogen is then withdrawn as stream 21, while water is removed from the further cooled purified stream 22 as condensed stream 23 in condensate separator 210, thereby forming a high purity CO.sub.2 product stream 24 having a CO.sub.2 concentration of e.g. 99.9 vol.% or 99.99 vol.% or even higher.