Process for producing and purifying a synthesis gas

Abstract

A process for producing and purifying a synthesis gas stream that contains CO- and H.sub.2-produced from a hydrocarbon-containing feed in a gas production unit. CO.sub.2 is separated from the synthesis gas stream and CO is cryogenically separated from the synthesis gas stream. CO.sub.2 that makes up 5% to 30% by volume in the synthesis is reduced to less than 10 ppm by volume by temperature swing adsorption. The temperature swing adsorption takes place upstream of the cryogenic separation of CO. The CO.sub.2 is adsorbed using a disordered adsorbent bed wherein the adsorbent is cooled by means of indirect heat transfer from the adsorbent to the heat transfer medium during adsorption and the adsorbent loaded with CO.sub.2 is heated by indirect heat transfer from the heat transfer medium to the adsorbent to effect desorption of CO.sub.2.

Claims

1. A process for producing and purifying a synthesis gas stream, comprising: producing a CO- and H.sub.2-containing synthesis gas stream from a hydrocarbon-containing feed in a gas production unit, separating at least CO.sub.2 from the synthesis gas stream, and separating CO from the synthesis gas stream by cryogenic separation, wherein, prior to said separating of at least CO.sub.2, CO.sub.2 is present in said synthesis gas stream in a concentration in the range from 5% by volume to 30% by volume, and in said separating of at least CO.sub.2, CO.sub.2 is depleted to less than 10 ppm by volume in the synthesis gas stream by means of a first temperature swing adsorption upstream of said cryogenic separation, wherein, in said first temperature swing adsorption, CO.sub.2 is adsorbed on an adsorbent and the adsorbent is cooled by means of indirect heat transfer from the adsorbent to a heat transfer medium during adsorption of CO.sub.2, and the adsorbent loaded with CO.sub.2 is heated at least partly by indirect heat transfer from a heat transfer medium to the adsorbent to effect desorption of CO.sub.2; and in said first temperature swing adsorption CO.sub.2 is desorbed at a pressure in the range from 5 bar to 90 bar, and recirculated to the gas production unit as starting material for synthesis gas production.

2. The process as claimed in claim 1, wherein the adsorbent is configured as a disordered adsorbent bed.

3. The process as claimed in claim 1, wherein the CO.sub.2 is depleted by said first temperature swing adsorption to less than 1 ppm by volume in said synthesis gas.

4. The process as claimed in claim 1, wherein the synthesis gas stream is introduced under a pressure in the range from 10 to 50 bar into the temperature swing adsorption.

5. The process as claimed in claim 1, further comprising performing a second temperature swing adsorption, downstream of the first temperature swing adsorption, in order to separate CO.sub.2 still present in the synthesis gas stream from the synthesis gas stream, wherein is said second temperature swing adsorption CO.sub.2 is adsorbed on an adsorbent and the adsorbent loaded with CO.sub.2 is treated with a regenerating gas in such a way that heat of the regenerating gas is transferred directly to the absorbent to effect desorption of CO.sub.2.

6. The process as claimed in claim 3, wherein the CO.sub.2 in said synthesis gas is depleted by said first temperature swing adsorption to less than 0.1 ppm by volume.

7. The process as claimed in claim 1, wherein the adsorbed CO.sub.2 is desorbed at a pressure in the range from 15 bar to 60 bar.

8. The process as claimed in claim 1, wherein the synthesis gas stream is introduced into the temperature swing adsorption under a pressure in the range from 15 to 40 bar.

9. The process as claimed in claim 1, wherein said separating of at least CO.sub.2 does not involve the use a scrubbing operation.

10. The process according to claim 1, wherein the indirect cooling and heating of the adsorbent in said first temperature swing adsorption is provided by a heat transfer medium or thermofluid separated from the adsorbent by a dividing wall.

11. The process according to claim 5, wherein in said first temperature swing adsorption CO.sub.2 present in the synthesis gas is depleted to a concentration of less than 1 ppm by volume, and in said second temperature swing adsorption CO.sub.2 still remaining in the synthesis gas is depleted to less than 0.1 ppm by volume.

12. The process according to claim 1, further comprising, downstream of the first temperature swing adsorber, separating hydrogen from the synthesis gas stream by a pressure swing adsorber.

Description

(1) The above-described invention is explained in detail below in the light of the relevant technical background with reference to the accompanying drawings which show preferred embodiments. The invention is not restricted in any way by the purely schematic drawings, and it may be stated that the drawings are not to scale and are not suitable for defining size ratios.

(2) FIG. 1 is: a block diagram of a process known from the prior art for producing/purifying a synthesis gas.

(3) FIG. 2 is: a block diagram of a first embodiment of the process of the invention or the synthesis gas plant of the invention.

(4) FIG. 3 is: a block diagram of a second embodiment of the process of the invention or the synthesis gas plant of the invention.

(5) FIG. 1 shows a conventional synthesis gas plant 11 in which a hydrocarbon-containing feed (e.g. natural gas) is firstly converted in a unit for synthesis gas production into a synthesis gas stream S containing at least CO and H.sub.2 and also CH.sub.4 and possibly traces of N.sub.2. The synthesis gas S is fed to a scrub 9 in which CO.sub.2 and water are separated off. Trace amounts of CO.sub.2 and possibly water or methanol are subsequently separated off from the synthesis gas stream S in a conventional temperature swing adsorber 3 in which a hot regenerating gas is contacted with the adsorbent in order to carry out direct heat transfer to the adsorbent so as to regenerate the adsorbent. Finally, carbon monoxide and possibly a tailgas 8 (containing, for example, CO, CH.sub.4 and possibly H.sub.2 and N.sub.2) are separated off from the synthesis gas stream S in a cryogenic separation unit (also referred to as cold box) 6. Downstream, furthermore, hydrogen 7a and a tailgas 8a (containing, for example, CO, CH.sub.4 and possibly H.sub.2 and N.sub.2) are separated off from the synthesis gas stream S by pressure swing adsorption in a pressure swing adsorber 7. Furthermore, the carbon dioxide which has been separated off in the scrub 9 is recirculated via the return line 14 to the synthesis gas production 4, for which a multistage compressor 10 is necessary because of the pressure drop required for the scrub 9. By means of this conventional synthesis gas plant, the concentration of carbon dioxide in the synthesis gas stream is decreased from 10% by volume to less than 50 ppm by volume.

(6) FIG. 2 shows a first embodiment of a process according to the invention or a corresponding plant 12 as per the above description. Here, the scrub 9 and the conventional temperature swing adsorber 3 (see FIG. 1) are replaced by a rapid temperature swing adsorber 1 which is alone able to separate off a large amount of carbon dioxide and water. In the temperature swing adsorption 1, the adsorbent in the form of a disordered bed is regenerated by being heated by indirect heat transfer. The heat is provided here by a fluid heat transfer medium which is spatially separated from the adsorbent. The carbon dioxide recovered in this way at a high gas pressure can thus be recirculated immediately, with merely a blower 2 compensating for the pressure drop due solely to hydrodynamic effects. By means of this process, the concentration of carbon dioxide in the synthesis gas stream is decreased from, for example, 5% by volume to 30% by volume to less than 10 ppm by volume, in particular to at least 0.1 ppm by volume or less than 0.1 ppm by volume.

(7) FIG. 3 shows a second embodiment of a process according to the invention or a synthesis gas plant 13 according to the invention which resembles the synthesis gas plant 12 in FIG. 2. Here, the rapid temperature swing adsorber 1 is followed by an additional conventional temperature swing adsorber 3 which is regenerated by means of direct heat transfer (see above) and assumes the task of removing trace amounts of CO.sub.2 and possibly water.

(8) TABLE-US-00001 List of reference symbols 1 Temperature swing adsorber (RTSA) 2 Blower 3 Temperature swing adsorber (TSA) 4 Reactor or synthesis gas production 5 Feed 6 Cold box or cryogenic separation unit 7 Pressure swing adsorber 7a Crude hydrogen stream 8, 8a Tailgas 9 Scrub for removal of CO.sub.2 10 Multistage compressor 11 Conventional synthesis gas plant 12 First synthesis gas plant 13 Second synthesis gas plant 14 Return line S Synthesis gas stream