PROCESS FOR GENERATING SYNGAS FROM A CO2-RICH HYDROCARBON-CONTAINING FEED GAS

Abstract

A process for generating a syngas from a CO.sub.2-rich and hydrocarbon-containing feed gas, wherein a CO.sub.2-rich and hydrocarbon-containing feed gas is provided and is reacted in a syngas generation step by means of partial oxidation or steam reforming to give an H.sub.2- and CO-comprising syngas. At least CO.sub.2 is removed from the feed gas in a scrubbing of the feed gas by means of a scrubbing medium, before the feed gas is fed to the syngas generation step.

Claims

1. Process for generating a syngas from a CO2-rich and hydrocarbon-containing feed gas, wherein a CO2-rich and hydrocarbon-containing feed gas is provided and is reacted in a syngas generation step by means of partial oxidation or steam reforming to give an H2- and CO-comprising syngas, characterized in that at least CO2 is removed from the feed gas in a scrubbing of the feed gas by means of a scrubbing medium, before the feed gas is fed to the syngas generation step, wherein, during the scrubbing, a CO2-rich stream is generated that has a pressure in the range from 20 bar to 100 bar, and wherein the CO2-rich stream is used as feed for a synthesis or to support the extraction of oil, wherein the CO2-rich stream is injected into an oil deposit in order to increase the pressure in the oil deposit.

2. Process according claim 1, characterized in that the feed gas is conducted downstream of the scrubbing through an adsorber unit, wherein one or more sulfur compounds that are still present in the feed gas are adsorbed in the adsorber unit and in this case removed from the feed gas.

3. Process according to claim 1, characterized in that the syngas that is generated is divided into first and second syngas substreams, wherein the first syngas substream is used as feed for a synthesis, and wherein the second syngas substream is subjected to a water-gas shift reaction, wherein CO of the second syngas substream is reacted with H2O to form H2 and CO2 in order to reduce the CO content in the second syngas substream and to increase the hydrogen content in the second syngas substream.

4. Process according to claim 1, characterized in that the reduction of the CO2 content in the feed gas in the scrubbing is set in dependence on a use of the syngas provided downstream of the syngas generation or in dependence on a desired ratio of CO to H2 in the syngas.

5. Process according to claim 3, characterized in that the second syngas substream is subjected after the water-gas shift reaction to a pressure-swing adsorption, wherein CO2 present in the second syngas substream is adsorbed to an adsorber at a first pressure and an H2-containing stream is generated, and wherein the adsorber is regenerated at a second pressure that is lower than the first pressure, wherein adsorbed CO2 is desorbed and wherein the adsorber is purged with H2, generating an H2-containing purge gas stream, to remove the desorbed CO2.

6. Process according to claim 5, characterized in that the purge gas stream is used as fuel, wherein the purge gas stream is burnt in a furnace to carry out the steam reformation or wherein the purge gas stream is burnt in a combustion furnace to generate or superheat steam.

7. Process according to claim 2, characterized in that oxygen is separated off cryogenically from air and used as oxidizing agent in the partial oxidation, wherein the oxygen is added to the feed gas downstream of the scrubbing, downstream of the adsorber unit and also upstream of the syngas generation step to the feed gas.

8. Process according to claim 5, characterized in that the synthesis is a Fischer-Tropsch synthesis, wherein the first syngas substream is reacted in the Fischer-Tropsch synthesis to form a crude product stream which comprises light hydrocarbons having four or fewer carbon atoms, heavy hydrocarbons having five or more carbon atoms, and also unreacted syngas.

9. Process according to claim 8, characterized in that a residual gas comprising light hydrocarbons and also unreacted syngas is separated off from the crude product stream and recirculated at least in part to the Fischer-Tropsch synthesis as feed, wherein some of the residual gas is recirculated as feed into the steam reformation or partial oxidation or is used as fuel.

10. Process according to claim 9, characterized in that hydrogen from the H2-containing stream is used for hydrogenation of heavy hydrocarbons of the crude product stream, wherein the crude product stream is divided hereinafter into one or more hydrocarbon-containing product streams.

11. Process according to claim 3, characterized in that the synthesis is a methanol synthesis, wherein the first syngas substream is reacted in the methanol synthesis to form a methanol-comprising crude product stream.

12. Process according to claim 11, characterized in that methanol present in the methanol-comprising crude product stream is separated from unreacted syngas present in the methanol-comprising crude product stream, generating a methanol product stream, wherein the unreacted syngas separated off is recirculated as feed to the methanol synthesis.

13. Process according to claim 1, characterized in that the syngas generated in the syngas generation step is cooled with water, wherein steam is generated that is used to generate electrical energy, wherein the steam is superheated in a furnace for carrying out the steam reformation or in another combustion furnace, and is then used in a steam turbine to generate electrical energy.

Description

[0041] Further features and advantages of the invention will be explained hereinafter in the description of the figures of exemplary embodiments of the invention with reference to the figures.

[0042] FIG. 1 shows a schematic depiction of a process according to the invention for producing a syngas from a CO.sub.2-rich feed gas, wherein the syngas produced is used in a Fischer-Tropsch synthesis.

[0043] FIG. 2 shows a schematic depiction of a process according to the invention for producing a syngas from a CO.sub.2-rich feed gas, wherein the syngas produced is used in a methanol synthesis.

[0044] FIG. 1 shows a schematic depiction of a plant 1 and of a process for generating a syngas from a CO.sub.2-rich and hydrocarbon-rich feed gas FG, in particular natural gas, which according to an example, in addition to CO.sub.2 at a content of 10% by volume to 70% by volume and possibly one or more sulfur compounds, such as e.g. H.sub.2S, CS.sub.2, COS and/or HCN, each at a content in the range of up to 5% by volume, comprises at least one of the following hydrocarbons or substances: 25% by volume to 95% by volume CH.sub.4, 5% by volume to 75% by volume CO.sub.2, up to 5% by volume: ethane, up to 3% by volume propane, up to 2% by volume butane, up to 3% by volume pentane, up to 5% by volume nitrogen.

[0045] The feed gas stream FG, before a reaction to form syngas (comprising H.sub.2 and CO) is subjected according to the invention to a scrubbing in order to remove at least CO.sub.2 and sulfur components possibly present such as e.g. H.sub.2S, CS.sub.2, COS from the feed gas FG. In this scrubbing 10 also designated acid gas scrubbing (in particular Rectisol process), CO.sub.2 and any sulfur components possibly present are preferably separated off from the feed gas FG as described above, wherein preferably CO.sub.2 and those sulfur components are separated off separately. A CO.sub.2-rich stream or a CO.sub.2 stream K (in particular having up to 75% by volume C).sub.2) is generated hereby, which has a pressure in the range from 15 bar to 100 bar.

[0046] The CO.sub.2-rich stream K can be used, e.g. as feed for a synthesis, e.g. for a methanol synthesis 81 according to FIG. 2, or e.g. for supporting the extraction of oil, wherein the CO.sub.2-rich stream K can be injected, e.g. into an oil deposit E in order to increase the deposit pressure.

[0047] Downstream of the acid gas scrubbing 10, the feed gas stream FG, in addition, is freed from traces of CO.sub.2 and/or sulfur compounds still present, preferably in an adsorber unit 30, wherein the content of sulfur components is reduced to below 10 ppb, for example by means of a guard bed.

[0048] Hereafter, the feed gas stream is reacted in a syngas generation step 50 to form syngas (containing H.sub.2 and CO). For this purpose, a partial oxidation or a steam reformation can be used.

[0049] In the steam reformation, the prepurified feed gas stream FG is mixed as described above with steam and reacted to syngas in reactor tubes, in which a suitable catalyst is arranged, at a temperature in the range from, e.g. 700 C. to 950 C and also a pressure in the range from, e.g. 20 bar to 50 bar, which syngas is then cooled and dried.

[0050] Alternatively, or supplementally, a partial oxidation can also be used, in which the feed gas FG is reacted, as described above, with oxygen at a temperature in the range from, e.g., 1100 C. to 1300 C., and a pressure in the range from, e.g., 20 bar to 100 bar, to form syngas. As oxidizing agent, preferably pure oxygen is used, which is generated by cryogenic air separation 20 and is added to the feed gas FG downstream of the acid gas scrubbing 10, downstream of the adsorber unit 30 and also upstream of the syngas generation step 50.

[0051] The syngas generated is divided into first and second syngas substreams S. S wherein the first syngas substream S (85 to 95% by volume) is fed as feed to a Fischer-Tropsch synthesis 80, and wherein the second syngas substream S (5 to 15% by volume) is subjected to a water-gas shift reaction 120 in which CO of the second syngas substream S is reacted with H.sub.2O to form H.sub.2 and CO.sub.2 in order to reduce the CO content in the second syngas substream S and to increase the hydrogen content in the second syngas substream S

[0052] After the water-gas shift reaction 120, the second syngas substream S is subjected to a known pressure-swing adsorption 121, wherein CO.sub.2 present in the second syngas substream S is adsorbed to at least one adsorber 122 at a first pressure (e.g. in the range from 15 bar to 35 bar), and also a temperature in the range from 20 C. to 80 C. and an H.sub.2-containing stream W (in particular having an H.sub.2 content from 85 to 97% by volume) is generated, and wherein the adsorber 122 is regenerated at a second pressure (e.g. in the range from 20 bar to 35 bar) and also a temperature in the range from 40 C. to 120 C., wherein adsorbed CO.sub.2 is desorbed and wherein the adsorber 122 is purged with H.sub.2, generating an H.sub.2-containing purge gas stream T, to remove the desorbed CO.sub.2 (and also any other desorbed components). Preferably, a plurality of, in particular, two or four, adsorbers, are used in the pressure-swing adsorption, in order that as far as possible one adsorber can always be operated in the adsorption mode in such a manner that hydrogen can be delivered semicontinuously. The purge gas stream T can, e.g., be burnt as fuel in a furnace 51 to carry out the steam reformation and/or can be used as fuel to generate and/or superheat steam.

[0053] In the said Fischer-Tropsch synthesis 80, the first syngas substream S is reacted in a known manner to form a crude product stream R which comprises light hydrocarbons having four or fewer carbon atoms, heavy hydrocarbons having five or more carbon atoms, and also unreacted syngas. Water B required for the synthesis 80 is provided by means of a water supply 70. From the crude product stream R, a residual gas F comprising the light hydrocarbons and also unreacted syngas is separated off, wherein at least a part of the residual gas F, after compression in a compressor 101 (e.g. to a pressure in the range from 15 bar to 35 bar), is recirculated as feed to the Fischer-Tropsch synthesis 80. A further part F of the residual gas F can, after compression in a compressor 100 (e.g. to a pressure in the range from 20 bar to 50 bar), be recirculated as feed into the steam reformation 50 and/or be used as fuel 140.

[0054] The H.sub.2-containing stream W generated in the pressure-swing adsorption 121, in addition, is used e.g. for hydrogenation (130) of heavy hydrocarbons of the crude product stream R of the Fischer-Tropsch synthesis. The treated crude product stream R is divided into one or more hydrocarbon-containing product streams P that can have different hydrocarbon fractions.

[0055] FIG. 2 shows a further exemplary embodiment of the invention, in which, in contrast to FIG. 1, a Fischer-Tropsch synthesis is not carried out, but rather a methanol synthesis 81. In this case, the first syngas substream S is compressed in a compressor 101 (e.g. to a pressure in the range from 20 bar to 100 bar) and reacted in the methanol synthesis 81 to form a methanol-comprising crude product stream R, wherein methanol present in the crude product stream R is separated 91 from the unreacted syngas S present in the crude product stream R, wherein a methanol product stream P is generated. The unreacted syngas S separated off is compressed in a compressor 100 (e.g. to a pressure in the range from 40 bar to 100 bar) and recirculated as feed to the methanol synthesis 81, more precisely via the other compressor 101 (wherein, in particular, a pressure elevation to a pressure in the range from 40 bar to 100 bar proceeds). The H.sub.2-containing stream W obtained in the pressure-swing adsorption 121 can be provided, e.g. as hydrogen product.

[0056] In addition, in the embodiment according to FIG. 2, the CO.sub.2-rich stream K can also be used as feed for the methanol synthesis 81 (cf. FIG. 1), wherein the stream K is conducted to the methanol synthesis via the compressor 101 and in this case is compressed to a pressure in the range from 40 bar to 100 bar.

[0057] In the embodiments according to FIGS. 1 and 2, in each case the syngas generated in the syngas generation step 50 is cooled with water B of the water supply 70, wherein steam D is generated that can be used to generate electrical energy 60. In this case, the steam D can be superheated, e.g. in the furnace 51 of the steam reformation 50, or in another combustion furnace 52, and then used for generating electrical energy, e.g. in a steam turbine 61.

[0058] Ultimately, the teaching according to the invention permits a comparatively low inert content or CO.sub.2 content to be obtained in the syngas stream, wherein the plant can overall be made smaller, manages with a lower energy consumption and the process streams that are to be recirculated are advantageously comparatively smaller. In the POX, a lower oxygen consumption becomes possible.

LIST OF REFERENCE SIGNS

[0059]

TABLE-US-00001 1 Plant for syngas production and also synthesis of hydrocarbons 10 Scrubbing for CO.sub.2 removal 20 Air separation unit 30 Adsorber unit for desulfurization 50 Syngas generation step and also syngas cooling 51 Furnace for steam reformation 52 Combustion furnace 60 Energy generation 61 Steam turbine 70 Water supply 80 Fischer-Tropsch synthesis 81 Methanol synthesis 90, 91 Separation 100, 101 Compressor 120 Water-gas Shift reaction 121 Pressure-swing adsorption 130 Product workup 140 Fuel system or fuel supply B Water E Oil deposit F, F Residual stream K CO.sub.2-rich stream L Air FG Feed gas P, P Product stream R, R Crude product stream S First syngas substream S Second syngas substream S Unreacted syngas T Purge gas W Hydrogen-containing stream