TWO-STAGE METHOD FOR REMOVING CO2 FROM SYNTHESIS GAS

Abstract

A plant for removing CO.sub.2 from a fluid stream via an aqueous absorption medium contains a) a first absorption zone for treating the fluid stream with a partially regenerated absorption medium, b) a second absorption zone for treating the treated fluid stream with a regenerated absorption medium, c) a first flash vessel for depressurizing the loaded absorption medium, d) a second flash vessel for depressurizing the sub-partially regenerated absorption medium, e) a stripper for thermally regenerating the partially regenerated absorption medium, f) a conduit for feeding a substream of the partially regenerated absorption medium into the first absorption zone and a conduit for feeding a further substream of the partially regenerated absorption medium into a stripper, g) a conduit for recirculating the regenerated absorption medium to the second absorption zone, and h) a jet pump for compressing the water vapor-comprising, second CO.sub.2-comprising gas stream.

Claims

1-10. (canceled)

11. A plant for removing CO.sub.2 from a fluid stream with an aqueous absorption medium, the plant comprising: a) a first absorption zone for treating the fluid stream with a partially regenerated absorption medium, b) a second absorption zone for treating the treated fluid stream with a regenerated absorption medium, giving a fluid stream which has been freed of CO.sub.2 and a loaded absorption medium, c) a first flash vessel for depressurizing the loaded absorption medium to a pressure of from 1.2 to 3 bar absolute, giving a sub-partially regenerated absorption medium and a first CO.sub.2-comprising gas stream, d) a second flash vessel for depressurizing the sub-partially regenerated absorption medium to a pressure of from 1 to 1.2 bar absolute, giving the partially regenerated absorption medium and a water vapor-comprising, second CO.sub.2-comprising gas stream, e) a stripper for thermally regenerating the partially regenerated absorption medium, with the regenerated absorption medium and a third CO.sub.2-comprising gas stream being obtained, wherein the stripper is able to be operated at a pressure which is at least 0.9 bar higher than the pressure in the first flash vessel, f) a conduit for feeding a substream of the partially regenerated absorption medium into the first absorption zone and a conduit for feeding a further substream of the partially regenerated absorption medium into a stripper, g) a conduit for recirculating the regenerated absorption medium to the second absorption zone, and h) a jet pump for compressing the water vapor-comprising, second CO.sub.2-comprising gas stream and bringing it into direct heat exchange contact with the loaded absorption medium in the first flash vessel, wherein the jet pump is able to be operated with the third CO.sub.2-comprising gas stream.

12. A method of removing CO.sub.2 from a fluid stream via an aqueous absorption medium, the method comprising: removing CO.sub.2 from a fluid stream in the plant according to claim 11.

13. The plant according to claim 11, wherein the pressure of the water vapor-comprising, second CO.sub.2-comprising gas stream is increased by a blower before entry into the jet pump.

14. The plant according to claim 11, wherein the substream of the partially regenerated absorption medium which is fed into the stripper is preheated by indirect heat exchange with the regenerated absorption medium.

15. The plant according to claim 11, wherein the loaded absorption medium is depressurized to a pressure ranging from 6 to 10 bar absolute before depressurization thereof in the first flash vessel, giving a coabsorbate-comprising gas stream and the loaded absorption medium, which is free of coabsorbate and is fed into the first flash vessel.

16. The plant according to claim 11, wherein absorption medium constituents are condensed out from the first CO.sub.2-comprising gas stream, thereby giving a condensate, and wherein the condensate is recirculated into the first flash vessel.

17. The plant according to claim 16, wherein the condensate is recirculated via a backscrubbing zone into the first flash vessel.

18. The plant according to claim 11, wherein the fluid stream free of CO.sub.2 is conveyed through a backwashing zone, wherein the fluid stream free of CO.sub.2 is treated with an aqueous liquid.

19. The plant according to claim 18, wherein the aqueous liquid is water from an external source to make up for water losses.

20. The plant according to claim 11, wherein the aqueous absorption medium is an aqueous solution of an amine.

21. The plant according to claim 11, wherein the fluid stream is a synthesis gas or a shifted synthesis gas.

Description

EXAMPLE 1

[0063] The following abbreviations are used: [0064] T Temperature [0065] p Pressure [0066] V.sub.n Loading [0067] V Volume flow (on a water-free basis) [0068] ppm parts per million [0069] H Height [0070] D Diameter [0071] V.sub.pack Packing volume [0072] standard m.sup.3 Standard cubic meters (at p.sub.n=1.0 bar; T.sub.n=273.15 K)

[0073] The treatment of a shifted synthesis gas in a plant as shown in FIG. 1 was simulated. BASF's in-house software Chemasim was used for the simulation calculation (comparable results are obtained when using the commercially available software Aspen Plus (producer: AspenTech, Burlington/Mass., USA). The synthesis gas has the following composition (on a water-free basis): CO.sub.2 (17.87% by volume), CO (0.27% by volume), H.sub.2 (59.82% by volume), N.sub.2 (21.51% by volume), CH.sub.4 (0.53% by volume). The gas is saturated with water at 62.8° C. and 28.0 bar.

[0074] The absorption medium is: methyldiethanolamine MDEA (41.9% by weight), piperazine (8.1% by weight), water (50% by weight).

[0075] The following parameters of the plant were used as a basis:

TABLE-US-00001 # Component H [m] D [m] V.sub.pack [m.sup.3]  2 first absorption zone 5.35 4.77 95.6  3 second absorption zone 6.15 3.39 55.5  9 upstream flash vessel 2.00 4.15 27.1 13 first flash vessel 5.00 4.78 89.8 21 second flash vessel 2.00 4.74 35.3 29 stripper 10.00 3.08 74.3

[0076] Table 1 summarizes the essential properties and compositions for the various fluid, absorption medium and gas streams.

TABLE-US-00002 TABLE 1 V.sub.n V p [standard m.sup.3 V CO.sub.2 [standard # Designation of the stream T [° C.] [bar] of CO.sub.2/t]* [m.sup.3/h] [mol %]** m.sup.3/h] 1 CO.sub.2-comprising fluid stream 62.8 28.0 17.9 290529 36 Regenerated absorption medium after cooling 50.0 27.8 2.4 430.4 4 Fluid stream freed of CO.sub.2 50.0 27.8 <100 mol-ppm 238026 5 Make up water 50.0 27.8 1.0 6 Loaded absorption medium 87.1 28.0 49.8 2381.4 10 Coabsorbate-comprising gas stream 87.0 8.8 38.8 749 11 Loaded absorption medium which has been 87.0 8.8 2379.5 largely freed of coabsorbate 18 First CO.sub.2-containing gas stream 40.0 1.5 99.7 51756 20 Sub-partially regenerated absorption medium 82.3 1.65 38.5 2373.3 23 Water vapor-comprising, second CO.sub.2- 93.8 1.2 100.0 21385 comprising gas stream 24 Partially regenerated absorption medium 77.8 1.02 33.3 2353.9 30 Third CO.sub.2-comprising gas stream 114.1 2.5 100.0 14130 34 Regenerated absorption medium after regenerated/ 87.8 2.6 2.4 442.5 partially regenerated heat exchange *based on the absorption medium **water-corrected