METHOD AND DEVICE FOR PRODUCING SYNTHESIS GAS WITH CARBON DIOXIDE RETURN

Abstract

A method and to a device for producing a synthesis gas, which contains carbon monoxide and hydrogen, wherein natural gas having a first carbon dioxide partial pressure (CO.sub.2 pressure) is provided and is processed inter alia by means of a pressure increase to form a natural gas input for a thermochemical conversion, in which a synthesis raw gas having a second CO.sub.2 pressure greater than the first CO.sub.2 pressure is produced, from which synthesis raw gas at least carbon dioxide is subsequently separated in order to obtain the synthesis gas and carbon dioxide, at least some of which is returned and is used in the thermochemical conversion of the natural gas input. To separate carbon dioxide, the synthesis raw gas is conducted across the one membrane on the retentate side, which membrane is permeable to carbon dioxide and is flushed on the permeate side by the provided natural gas.

Claims

1. A method for producing a synthesis gas, which contains carbon monoxide and hydrogen, wherein natural gas having a first carbon dioxide partial pressure (CO.sub.2 pressure) is provided and is processed inter alia by means of a pressure increase to form a natural gas input for a thermochemical conversion, in which a synthesis raw gas having a second CO.sub.2 pressure greater than the first CO.sub.2 pressure is produced, from which synthesis raw gas at least carbon dioxide is subsequently separated in order to obtain the synthesis gas and carbon dioxide, at least some of which is returned and is used in the thermochemical conversion of the natural gas input, wherein, in order to separate carbon dioxide, the synthesis raw gas is conducted across the one membrane on the retentate side, which membrane is permeable to carbon dioxide and is flushed on the permeate side by the provided natural gas.

2. The method according to claim 1, wherein carbon dioxide is largely selectively separated from the synthesis raw gas via the membrane.

3. The method according to claim 1, wherein carbon dioxide and hydrogen are largely selectively separated from the synthesis raw gas via the membrane.

4. The method according to claim 1, wherein the thermal conversion of the natural gas input takes place by steam reforming or autothermal reforming or partial oxidation.

5. A device for producing a synthesis gas, which contains carbon monoxide and hydrogen, with a processing apparatus comprising a compressor for processing a natural gas provided with a first carbon dioxide partial pressure (CO.sub.2 pressure) to form a natural gas input; a converter, in which the natural gas input may be thermochemically converted to obtain a synthesis raw gas having a second CO.sub.2 pressure greater than the first CO.sub.2 pressure; and a separating apparatus, in which the synthesis gas may be obtained from the synthesis raw gas at least by the separation of carbon dioxide, wherein the separating apparatus is connected to the converter in such a way that carbon dioxide separated from the synthesis raw gas may be returned and used in the thermochemical conversion of the natural gas input, wherein the processing apparatus is connected to the separating apparatus via a membrane module having a membrane which is largely permeable to carbon dioxide and to which the synthesis raw gas may be fed on the retentate side, while the natural gas provided may be used as purge gas on the permeate side.

6. The device according to claim 5, wherein the membrane is largely selectively permeable to carbon dioxide.

7. The device according to claim 5, wherein the membrane is largely selectively permeable to carbon dioxide and hydrogen.

8. The device according to claim 5, wherein the membrane consists of a rubber- or glass-like polymer material or is constructed as a composite membrane with active components.

9. The device according to claim 5, wherein the thermal converter is a steam reformer or an autothermal reformer or a POX reactor.

Description

[0025] The invention is explained in more detail below using an exemplary embodiment schematically illustrated in FIG. 1.

[0026] FIG. 1 shows the invention in a first and a second preferred variant.

[0027] In both preferred variants, natural gas is provided via line 1 in order to convert it to a synthesis raw gas 2 containing hydrogen and carbon monoxide, in which synthesis raw gas carbon dioxide is present at a higher partial pressure than in the provided natural gas 1. Both the provided natural gas 1 and the synthesis raw gas 2 are introduced into the membrane module Z, in which a membrane M that is selectively permeable to carbon dioxide is arranged, the retentate side of which is swept by the synthesis raw gas 2 and the permeate side of which is swept by the provided natural gas 1. Due to its greater partial pressure on the permeate side, carbon dioxide 3 is separated from the synthesis raw gas 2 via the membrane M and transferred into the natural gas 1 acting as a purge gas, which, enriched with carbon dioxide, leaves the membrane module Z via line 4. In the processing apparatus A, the natural gas 4 enriched with carbon dioxide is first compressed via the compressor P and then supplied via line 5 to the desulfurization apparatus E in order to obtain a largely sulfur-free natural gas input 6. Together with steam 7, the natural gas input 6 is fed to the converter K, which is, for example, an SMR reactor or an ATR reactor, and thermally converted to a synthesis raw gas 8 rich in carbon monoxide and containing hydrogen, water and carbon dioxide, which, after cooling and the removal of water, is conducted from the cooling apparatus C arranged in the separating apparatus T, via line 2 into the membrane module Z for the separation of carbon dioxide. In the acid gas scrubbing S, the synthesis gas 10 consisting largely of hydrogen and carbon monoxide is finally obtained from the carbon-dioxide-depleted synthesis raw gas 9, in particular by the removal of remaining carbon dioxide.

[0028] In order to increase the carbon monoxide content in the synthesis gas 10, in the second preferred variant of the invention, the carbon dioxide 11 separated in the acid gas scrubbing S from the carbon-dioxide-depleted synthesis raw gas 8 is compressed via the compressor P′ and subsequently admixed via line 12 to the natural gas 4 already enriched with carbon dioxide.