PROCESS AND PLANT FOR PURIFYING CRUDE SYNTHESIS GAS

Abstract

The invention relates to a process for removal of unwanted, in particular acidic gas constituents, for example carbon dioxide and hydrogen sulfide, from a crude synthesis gas by gas scrubbing with a scrubbing medium. According to the invention the flash gases obtained during the decompression of the laden scrubbing medium are supplied to a recompressor in order to recycle these to the crude synthesis gas and thus utilize them materially after the recompression. Alternatively or in addition the flash gases may also be supplied to a decompression turbine to recover refrigeration and mechanical work. If the recompressor and/or the decompression turbine are/is designed to have multiple stages, the flash gases obtained at different pressure levels are preferably supplied to a corresponding pressure level of the recompressor and/or of the decompression turbine.

Claims

1-6. (canceled)

7. A process for purifying a crude synthesis gas by gas scrubbing with a scrubbing medium comprising: (a) providing and supplying the crude synthesis gas to a prescrubber for removal of trace components, (b) supplying a gaseous tops product from the prescrubber to an H.sub.2S scrubber for removal of H.sub.2S, (c) supplying a gaseous tops product from the H.sub.2S scrubber to a CO.sub.2 scrubber for removal of CO.sub.2, (d) discharging a purified synthesis gas stream as a gaseous tops product from the CO.sub.2 scrubber, (e) supplying a liquid bottoms product from the prescrubber to an intermediate-pressure prescrubbing flash vessel, supplying a gaseous tops product from the intermediate-pressure prescrubbing flash vessel to a recompressor, supplying a liquid bottoms product from the intermediate-pressure prescrubbing flash vessel to a low-pressure prescrubbing flash vessel, supplying a gaseous tops product from the low-pressure prescrubbing flash vessel to the recompressor, supplying a liquid bottoms product from the low-pressure prescrubbing flash vessel to at least one apparatus for flash regeneration and/or hot regeneration of the scrubbing medium, (f) supplying a liquid bottoms product from the H.sub.2S scrubber to an intermediate-pressure H.sub.2S flash vessel, supplying a gaseous tops product from the intermediate-pressure H.sub.2S flash vessel to the recompressor, supplying a liquid bottoms product from the intermediate-pressure H.sub.2S flash vessel to a low-pressure H.sub.2S flash vessel, supplying a gaseous tops product from the low-pressure H.sub.2S flash vessel to the recompressor, supplying a liquid bottoms product from the low-pressure H.sub.2S flash vessel to at least one apparatus for flash regeneration and/or hot regeneration of the scrubbing medium, (g) supplying a liquid bottoms product from the CO.sub.2 scrubber to an intermediate-pressure CO.sub.2 flash vessel, supplying a gaseous tops product from the intermediate-pressure CO.sub.2 flash vessel to the recompressor, supplying a liquid bottoms product from the intermediate-pressure CO.sub.2 flash vessel to a low-pressure CO.sub.2 flash vessel, supplying a gaseous tops product from the low-pressure CO.sub.2 flash vessel to the low-pressure H.sub.2S flash vessel and/or to the recompressor, supplying a liquid bottoms product from the low-pressure CO.sub.2 flash vessel to at least one apparatus for flash regeneration and/or hot regeneration of the scrubbing medium, (h) recycling the gas stream compressed by the recompressor to the prescrubber for the crude synthesis gas.

8. The process according to claim 7, wherein the scrubbing medium comprises one or more components selected from the group consisting of: methanol, N-methylpyrrolidone (NMP), secondary amines, diethanolamine, tertiary amines, methyldiethanolamine, polyethylene glycol dialkyl ethers, and polyethylene glycol dimethyl ether.

9. The process according to claim 7, wherein the recompressor is a multi-stage recompressor, wherein the gaseous tops products from the low-pressure flash vessels are supplied to the first stage and the gaseous tops products from the intermediate-pressure flash vessels are supplied to a subsequent stage of the multi-stage recom pressor.

10. A process for purifying a crude synthesis gas by gas scrubbing with a scrubbing medium comprising: (a) providing and supplying the crude synthesis gas to a prescrubber for removal of trace components such as NH.sub.3 and HCN, (b) supplying a gaseous tops product from the prescrubber to an H.sub.2S scrubber for removal of H.sub.2S, (c) supplying a gaseous tops product from the H.sub.2S scrubber to a CO.sub.2 scrubber for removal of CO.sub.2, (d) introducing at least a portion of a gaseous tops product from the CO.sub.2 scrubber into a multi-stage expander to recover mechanical work and refrigeration and to discharge an expanded, purified synthesis gas stream from the multi-stage expander, (e) supplying a liquid bottoms product from the prescrubber to an intermediate-pressure prescrubbing flash vessel, supplying a gaseous tops product from the intermediate-pressure prescrubbing flash vessel to a recompressor, supplying a liquid bottoms product from the intermediate-pressure prescrubbing flash vessel to a low-pressure prescrubbing flash vessel, supplying a gaseous tops product from the low-pressure prescrubbing flash vessel to the recompressor, supplying a liquid bottoms product from the low-pressure prescrubbing flash vessel to at least one apparatus for flash regeneration and/or hot regeneration of the scrubbing medium, (f) supplying a liquid bottoms product from the H.sub.2S scrubber to an intermediate-pressure H.sub.2S flash vessel, supplying a gaseous tops product from the intermediate-pressure H.sub.2S flash vessel to the first stage or a subsequent stage of the multi-stage expander or into the conduit downstream of the expander, supplying a liquid bottoms product from the intermediate-pressure H.sub.2S flash vessel to a low-pressure H.sub.2S flash vessel, supplying a gaseous tops product from the low-pressure H.sub.2S flash vessel to the recompressor, supplying a liquid bottoms product from the low-pressure H.sub.2S flash vessel to at least one apparatus for flash regeneration and/or hot regeneration of the scrubbing medium, (g) supplying a liquid bottoms product from the CO.sub.2 scrubber to an intermediate-pressure CO.sub.2 flash vessel, supplying a gaseous tops product from the intermediate-pressure CO.sub.2 flash vessel to the first stage or a subsequent stage of the multi-stage expander or into the conduit downstream of the expander, supplying a liquid bottoms product from the intermediate-pressure CO.sub.2 flash vessel to a low-pressure CO.sub.2 flash vessel, supplying a gaseous tops product from the low-pressure CO.sub.2 flash vessel to the low-pressure H.sub.2S flash vessel and/or to the recompressor, supplying a liquid bottoms product from the low-pressure CO.sub.2 flash vessel to at least one apparatus for flash regeneration and/or hot regeneration of the scrubbing medium, (h) recycling the gas stream compressed by the recompressor to the prescrubber for the crude synthesis gas.

11. The process according to claim 10, wherein the scrubbing medium comprises one or more components selected from the group consisting of: methanol, N-methylpyrrolidone (NMP), secondary amines, diethanolamine, tertiary amines, methyldiethanolamine, polyethylene glycol dialkyl ethers, and polyethylene glycol dimethyl ether.

12. The process according to claim 10, wherein the recompressor is a multi-stage recompressor, wherein the gaseous tops products from the low-pressure flash vessels are supplied to the first stage and the gaseous tops products from the intermediate-pressure flash vessels are supplied to a subsequent stage of the multi-stage recom pressor.

13. A plant for purifying a crude synthesis gas by gas scrubbing with a scrubbing medium comprising: (a) a means for providing and supplying the crude synthesis gas to a prescrubber for removal of trace components, (b) a means for supplying the gaseous tops product from the prescrubber to an H2S scrubber for removal of H.sub.2S, (c) a means for supplying the gaseous tops product from the H.sub.2S scrubber to a CO.sub.2 scrubber for removal of CO.sub.2, (d) a means for discharging a purified synthesis gas stream as a gaseous tops product from the CO.sub.2 scrubber, (e) a means for supplying the liquid bottoms product to an intermediate-pressure prescrubbing flash vessel, a means for supplying the gaseous tops product from the intermediate-pressure prescrubbing flash vessel to a recompressor, a means for supplying the liquid bottoms product from the intermediate-pressure prescrubbing flash vessel to a low-pressure prescrubbing flash vessel, a means for supplying the gaseous tops product from the low-pressure prescrubbing flash vessel to the recompressor, means for supplying the liquid bottoms product from the low-pressure prescrubbing flash vessel to at least one apparatus for flash regeneration and/or hot regeneration of the scrubbing medium, (f) a means for supplying the liquid bottoms product from the H.sub.2S scrubber to an intermediate-pressure H.sub.2S flash vessel, a means for supplying the gaseous tops product from the intermediate-pressure H.sub.2S flash vessel to the second stage or to a subsequent stage of the multi-stage recompressor, a means for supplying the liquid bottoms product from the intermediate-pressure H.sub.2S flash vessel to a low-pressure H.sub.2S flash vessel, a means for supplying the gaseous tops product from the low-pressure H.sub.2S flash vessel to the recompressor, a means for supplying the liquid bottoms product from the low-pressure H.sub.2S flash vessel to at least one apparatus for flash regeneration and/or hot regeneration of the scrubbing medium, (g) a means for supplying the liquid bottoms product from the CO.sub.2 scrubber to an intermediate-pressure CO.sub.2 flash vessel, a means for supplying the gaseous tops product from the intermediate-pressure CO.sub.2 flash vessel to the recompressor, a means for supplying the liquid bottoms product from the intermediate-pressure CO.sub.2 flash vessel to a low-pressure CO.sub.2 flash vessel, a means for supplying the gaseous tops product from the low-pressure CO.sub.2 flash vessel to the low-pressure H.sub.2S flash vessel and/or to the recompressor, a means for supplying the liquid bottoms product from the low-pressure CO.sub.2 flash vessel to at least one apparatus for flash regeneration and/or hot regeneration of the scrubbing medium, and (h) a means for recycling the gas stream compressed by the recompressor to the prescrubber for the crude synthesis gas.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Further features, advantages and possible applications of the invention are also apparent from the description of working examples which follows and the drawings. All the features described and/or depicted, on their own or in any combination, form the subject-matter of the invention, irrespective of their combination in the claims or their dependency references.

[0041] FIG. 1 shows a schematic diagram of the process according to the invention/of the plant according to the invention in a first embodiment,

[0042] FIG. 2 shows a schematic diagram of the process according to the invention/of the plant according to the invention in a second embodiment.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0043] In the schematic diagram shown in FIG. 1 of the process according to the invention/of the plant according to the invention according to a first embodiment crude synthesis gas is supplied via conduit 1 to a scrubbing apparatus comprising the scrubbers 2, 4 and 6. The individual scrubbers 2, 4, 6 may be separate devices or else regions of an integrated scrubbing/absorption column. The scrubbing medium employed in the present working example is cold methanol which is passed to the scrubbing apparatus via conduit 98. Usually a plurality of methanol streams of different degrees of purity/regeneration are supplied to the scrubbing apparatus at various points in a manner known to those skilled in the art (not shown).

[0044] Via conduit 1 the crude synthesis gas enters the prescrubber 2 for removal of trace components such as NH.sub.3 and HCN with a typical pressure of 20 to 70 bar(a) and is therein scrubbed by means of methanol partially laden with acidic gas constituents which is supplied via conduit 48. Via conduit 3 the tops product from the prescrubber 2 is supplied to the H.sub.2S scrubber 4 and therein likewise scrubbed with partially laden methanol. The tops product from the H.sub.2S scrubber 4 is supplied via conduit 5 to the CO.sub.2 scrubber 6 and therein scrubbed with methanol of high-purity which is supplied via conduit 98 and is formed by hot-regenerated methanol, fresh pure methanol or mixtures thereof. Via conduit 7 the tops product from the CO.sub.2 scrubber 6 is supplied to an expander in the form of a two-stage decompression turbine comprising the coolers 8, 12, 16, the turbine stages 10, 14 and the internal conduits 9, 11, 13, 15. Therein the purified synthesis gas is decompressed to a pressure of typically 5 bar(a), thus recovering refrigeration and mechanical work. Condensate separators are typically present after each decompression stage but are not shown. Condensate collected here is recycled to a part of the plant in which liquids are processed at similar pressure; these are usually flash vessels. Via conduit 17 the decompressed pure synthesis gas is discharged from the process and sent for further treatment or processing.

[0045] The methanol scrubbing medium laden with trace components such as NH.sub.3 and HCN in the prescrubber 2 is supplied via conduit 19 to the intermediate-pressure prescrubbing flash vessel 20 and therein decompressed to typically 15 to 40 bar(a). The thus-obtained gaseous tops product is passed via conduit 21 to the second stage of a recompressor which comprises the coolers 32, 35, the compressor stages 31, 34 and the separators 30, 33. The liquid bottoms product from the intermediate-pressure prescrubbing flash vessel 20 is passed via conduit 22 to a low-pressure prescrubbing flash vessel 24 and therein decompressed to typically 1.5 to 15 bar(a). The thus-obtained gaseous tops product is passed via conduit 25 to the first stage of the recompressor and therein introduced into the separator 30. The liquid bottoms product from the low-pressure prescrubbing flash vessel 24 is passed via conduit 26 to a hot regeneration apparatus 94.

[0046] The methanol scrubbing medium laden with hydrogen sulfide in the H.sub.2S scrubber 4 is supplied via conduit 39 to an intermediate-pressure H.sub.2S flash vessel 40 and therein decompressed to typically 15 to 40 bar(a). The thus-obtained gaseous tops product is passed via conduits 41, 51, 60 and 21 to the second stage of the recompressor. The liquid bottoms product from the intermediate-pressure H.sub.2S flash vessel 40 is passed via conduit 42 to a low-pressure H.sub.2S flash vessel 45 and therein decompressed to typically 1.5 to 15 bar(a). The thus-obtained gaseous tops product is passed via conduit 47 to the first stage of the recompressor and therein introduced into the separator 30, The liquid bottoms product from the low-pressure H.sub.2S flash vessel 45 is passed via conduit 46 to a flash regeneration apparatus 90.

[0047] The methanol scrubbing medium laden with carbon dioxide in the CO.sub.2 scrubber 6 is supplied via conduit 49 to an intermediate-pressure CO.sub.2 flash vessel 50 and therein decompressed to typically 15 to 40 bar(a). The thus-obtained gaseous tops product is passed via conduits 51, 60 and 21 to the second stage of the recompressor. The liquid bottoms product from the intermediate-pressure CO.sub.2 flash vessel 50 is passed via conduit 52 to a low-pressure CO.sub.2 flash vessel 55 and therein decompressed to typically 1.5 to 15 bar(a). The thus-obtained gaseous tops product is passed via conduit 57 to the low-pressure H.sub.2S flash vessel 45 and therein combined with the tops product therefrom. The liquid bottoms product from the low-pressure CO.sub.2 flash vessel 55 is passed via conduit 56 to the flash regeneration apparatus 90.

[0048] The gas streams entering into the two-stage recompressor are in two pressure stages compressed to the pressure level of the crude synthesis gas and via conduits 36 and 1 recycled to the prescrubber 2. It is also possible for conduit 36 to pass directly into the prescrubber 2.

[0049] The laden methanol scrubbing medium introduced into the flash regeneration apparatus 90 is decompressed therein. The decompression is carried out in a plurality of stages (not shown) and finally a CO.sub.2 product stream of high CO.sub.2 purity and a CO.sub.2 exhaust gas stream of lower CO.sub.2 purity are obtained and discharged from the process via conduits 91 and 92. The procedure required here and the employed pressure stages are known per se to those skilled in the art. Also obtained is a methanol scrubbing medium laden essentially with hydrogen sulfide which is passed via conduit 93 to the hot regeneration apparatus 94. This too is a multi-stage apparatus (shown only schematically) and the individual process steps and process conditions of the hot regeneration are known to those skilled in the art. Obtained as the product of the hot regeneration is a methanol scrubbing medium stream of high purity (so-called fine scrubbing methanol) which—optionally after further treatment steps and with addition of fresh methanol—is recycled via conduit 98 to the CO.sub.2 scrubber 6. Also obtained as a further product of the hot regeneration is an acidic gas stream which contains hydrogen sulfide and further sulfur components and via conduit 95 is discharged from the process and sent for further treatment or processing. The acidic gas stream is typically supplied to a sulfur recovery plant operating according to the Claus process for example (not shown).

[0050] The schematic representation of the process according to the invention/of the plant according to the invention in a second embodiment shown in FIG. 2 corresponds largely to the embodiment of FIG. 1. In contrast to the latter, the tops products from the intermediate-pressure H.sub.2S flash vessel 40 and from the intermediate-pressure CO.sub.2 flash vessel 50 are passed via conduits 41 and 51 to the second stage of the two-stage expander. Accordingly, in this specific embodiment only a portion of the flash gases from the intermediate-pressure H.sub.2S flash vessel and the intermediate-pressure CO.sub.2 flash vessel is utilized materially by recompressing and recycling to the crude synthesis gas entering into the gas scrubbing process while the remaining proportion of the flash gases is used for recovery of refrigeration and mechanical work and is thus utilized energetically. This achieves an advantageous compromise between utilization of the flash gases materially and energetically.

[0051] It is also possible to pass only a portion of the tops product from the intermediate-pressure H.sub.2S flash vessel 40 and the intermediate-pressure CO.sub.2 flash vessel 50 to the second stage of the two-stage expander via conduits 41 and 51 while the remaining proportion is passed to the recompressor. This allows adjustability between material and energetic utilization of the flash gases.

INDUSTRIAL APPLICABILITY

[0052] The invention provides a gas scrubbing process and a corresponding plant for removal of acidic gas constituents from crude synthesis gas which make it possible to utilize the flash gases obtained during decompression of the laden scrubbing medium materially and/or energetically in advantageous fashion, namely for recovery of refrigeration and mechanical work.

LIST OF REFERENCE NUMERALS

[0053] 1 Conduit

[0054] 2 Prescrubber

[0055] 3 Conduit

[0056] 4 H.sub.2S scrubber

[0057] 5 Conduit

[0058] 6 CO.sub.2 scrubber

[0059] 7 Conduit

[0060] 8 Cooler (heat exchanger)

[0061] 9 Conduit

[0062] 10 Turbine stage

[0063] 11 Conduit

[0064] 12 Cooler (heat exchanger)

[0065] 13 Conduit

[0066] 14 Turbine stage

[0067] 15 Conduit

[0068] 16 Cooler (heat exchanger)

[0069] 17 Conduit

[0070] 19 Conduit

[0071] 20 Intermediate-pressure prescrubbing flash vessel

[0072] 21 Conduit

[0073] 22 Conduit

[0074] 24 Low-pressure prescrubbing flash vessel

[0075] 25 Conduit

[0076] 26 Conduit

[0077] 30 Separator

[0078] 31 Compressor stage

[0079] 32 Cooler (heat exchanger)

[0080] 33 Separator

[0081] 34 Compressor stage

[0082] 35 Cooler (heat exchanger)

[0083] 36 Conduit

[0084] 39 Conduit

[0085] 40 Intermediate-pressure H.sub.2S flash vessel

[0086] 41 Conduit

[0087] 42 Conduit

[0088] 45 Low-pressure H.sub.2S flash vessel

[0089] 46 Conduit

[0090] 47 Conduit

[0091] 49 Conduit

[0092] 50 Intermediate-pressure CO.sub.2 flash vessel

[0093] 51 Conduit

[0094] 52 Conduit

[0095] 55 Low-pressure CO.sub.2 flash vessel

[0096] 56 Conduit

[0097] 57 Conduit

[0098] 60 Conduit

[0099] 90 Flash regeneration apparatus

[0100] 91 Conduit

[0101] 92 Conduit

[0102] 93 Conduit

[0103] 94 Hot regeneration apparatus

[0104] 95 Conduit

[0105] 96 Conduit

[0106] 98 Conduit

[0107] It will be understood that many additional changes in the details, materials, steps and arrangement of parts, which have been herein described in order to explain the nature of the invention, may be made by those skilled in the art within the principle and scope of the invention as expressed in the appended claims. Thus, the present invention is not intended to be limited to the specific embodiments in the examples given above.