Process and plant for producing a plurality of gas products from shifted and unshifted crude synthesis gas

Abstract

The invention relates to a gas scrubbing process and a corresponding plant for removal of acidic gas constituents from crude synthesis gas which make it possible by treatment of shifted and of unshifted crude synthesis gas in the gas scrubbing process and by combination of the thus-obtained partial product streams to produce a plurality of gas products having different compositions. In addition, the invention ensures that the flash gases obtained during decompression of the laden scrubbing medium are utilized materially and/or energetically in advantageous fashion.

Claims

1. A process for purifying a shifted crude synthesis gas and an unshifted crude synthesis gas by gas scrubbing with a scrubbing medium and for producing a plurality of synthesis gas product streams having different H.sub.2/CO ratios comprising: (a) providing and supplying the shifted crude synthesis gas and the unshifted crude synthesis gas to respective separate prescrubbers for removal of trace components (b) supplying the gaseous tops products from the prescrubbers to respective separate H.sub.2S scrubbers for removal of H.sub.2S, (c) supplying the gaseous tops products from the H.sub.2S scrubbers to respective separate CO.sub.2 scrubbers for removal of CO.sub.2, (d1) dividing the gaseous tops product stream from the CO.sub.2 scrubber for the unshifted crude synthesis gas into a first synthesis gas partial product stream and into a second synthesis gas partial product stream which for pressure reduction is passed through a multi-stage expander to recover mechanical work and refrigeration and to obtain an expanded second synthesis gas partial product stream, (d2) dividing the gaseous tops product stream from the CO.sub.2 scrubber for the shifted crude synthesis gas into a third synthesis gas partial product stream and into a fourth synthesis gas partial product stream, (e) supplying the liquid bottoms products from the separate prescrubbers to an intermediate-pressure prescrubbing flash vessel, supplying the gaseous tops product from the intermediate-pressure prescrubbing flash vessel to a recompressor, supplying the liquid bottoms product from the intermediate-pressure prescrubbing flash vessel to a low-pressure prescrubbing flash vessel, supplying the gaseous tops product from the low-pressure prescrubbing flash vessel to the recompressor, 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) supplying the liquid bottoms products from the separate H.sub.2S scrubbers to an intermediate-pressure H.sub.2S flash vessel, supplying the gaseous tops product from the intermediate-pressure H.sub.2S flash vessel to the recompressor, supplying the liquid bottoms product from the intermediate-pressure H.sub.2S flash vessel to a low-pressure H.sub.2S flash vessel, supplying the gaseous tops product from the low-pressure H.sub.2S flash vessel to the recompressor, 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) supplying the liquid bottoms products from the separate CO.sub.2 scrubbers to an intermediate-pressure CO.sub.2 flash vessel, supplying the gaseous tops product from the intermediate-pressure CO.sub.2 flash vessel to the recompressor, supplying the liquid bottoms product from the intermediate-pressure CO.sub.2 flash vessel to a low-pressure CO.sub.2 flash vessel, 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, 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) recycling the gas stream compressed by the recompressor to the prescrubber for the unshifted crude synthesis gas and/or the shifted crude synthesis gas.

2. The process according to claim 1, wherein the scrubbing medium comprises one or more components selected from the group consisting of: methanol, N-methylpyrrolidone (NMP), secondary amines, tertiary amines, and polyethylene glycol dialkyl ethers polyethylene glycol dimethyl ether.

3. The process according to claim 1, wherein the first and/or the third synthesis gas partial product stream are at least partially added to a methanol synthesis gas product stream or form a methanol synthesis gas product stream.

4. The process according to claim 3, wherein the first and the third synthesis gas partial product stream are at least partially added to a methanol synthesis gas product stream, wherein the particular proportion is chosen such that the H.sub.2/CO ratio required for methanol synthesis is established.

5. The process according to claim 1, wherein the second expanded synthesis gas partial product stream is added to a fuel gas product stream or forms a fuel gas product stream.

6. The process according to claim 1, wherein the fourth synthesis gas partial product stream is added to a hydrogen product stream or forms a hydrogen product stream.

7. The process according to claim 1, 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 recompressor.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) 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.

(2) FIG. 1 shows a schematic diagram of the process according to the invention/of the plant according to the invention in a first embodiment,

(3) 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

(4) 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 unshifted crude synthesis gas is supplied via conduit 1 and shifted crude synthesis gas is supplied via conduit 71 to two separate scrubbing apparatuses comprising the scrubbers 2, 4 and 6 and 72, 74 and 76 respectively. The individual scrubbers 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 apparatuses via conduits 98/99. 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).

(5) Via conduit 1 the unshifted 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 with 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 a portion of 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 the flash vessels for example. Via conduit 17 the decompressed pure synthesis gas is discharged from the process and sent for further treatment or processing. The thus-obtained pure synthesis gas may be utilized as fuel gas for example. Via conduit 7 and, after combination with the gas supplied via conduit 77, via conduit 79 the remaining portion of the tops product from the CO.sub.2 scrubber for the unshifted crude synthesis gas 6 is discharged from the process as methanol synthesis gas.

(6) Via conduit 71 the shifted crude synthesis gas enters the prescrubber 72 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 with methanol partially laden with acidic gas constituents which is supplied via conduit 84. Via conduit 73 the tops product from the prescrubber 72 is supplied to the H.sub.2S scrubber 74 and therein likewise scrubbed with partially laden methanol. The tops product from the H.sub.2S scrubber 74 is supplied via conduit 75 to the CO.sub.2 scrubber 76 and therein scrubbed with methanol of high-purity which is supplied via conduit 99 and is formed by hot-regenerated methanol, fresh pure methanol or mixtures thereof. The tops product from the CO.sub.2 scrubber 76 is discharged via conduit 77 and divided into two portions. Via conduit 78 a first portion is discharged from the process as a crude hydrogen product and sent for further processing/treatment (not shown). A second portion is discharged via conduit 77 and combined with the remaining proportion of the tops product from the CO.sub.2 scrubber 6 and discharged from the process via conduit 79.

(7) The methanol scrubbing medium laden with trace components such as NH.sub.3 and HCN in the prescrubbers 2, 72 is supplied via conduits 19, 81 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. Conduits inside the recompressor have not been marked with dedicated reference numerals. 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.

(8) The methanol scrubbing medium laden with hydrogen sulfide in the H.sub.2S scrubbers 4, 74 is supplied via conduits 39, 82 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.

(9) The methanol scrubbing medium laden with carbon dioxide in the CO.sub.2 scrubbers 6, 76 is supplied via conduits 49, 83 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.

(10) 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.

(11) 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 conduits 98, 99 to the CO.sub.2 scrubbers 6, 76. 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).

(12) 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.

INDUSTRIAL APPLICABILITY

(13) 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 by treatment of shifted and of unshifted crude synthesis gas in the gas scrubbing process and by combination of the thus-obtained partial product streams to produce a plurality of gas products having different compositions. In addition, the invention ensures that the flash gases obtained during decompression of the laden scrubbing medium are utilized materially and/or energetically in advantageous fashion.

LIST OF REFERENCE NUMERALS

(14) 1 Conduit

(15) 2 Prescrubber

(16) 3 Conduit

(17) 4 H.sub.2S scrubber

(18) 5 Conduit

(19) 6 CO.sub.2 scrubber

(20) 7 Conduit

(21) 8 Cooler

(22) 9 Conduit

(23) 10 Turbine stage

(24) 11 Conduit

(25) 12 Cooler

(26) 13 Conduit

(27) 14 Turbine stage

(28) 15 Conduit

(29) 16 Cooler

(30) 17 Conduit

(31) 19 Conduit

(32) 20 Intermediate-pressure prescrubbing flash vessel

(33) 21 Conduit

(34) 22 Conduit

(35) 24 Low-pressure prescrubbing flash vessel

(36) 25 Conduit

(37) 26 Conduit

(38) 30 Separator

(39) 31 Compressor stage

(40) 32 Cooler

(41) 33 Separator

(42) 34 Compressor stage

(43) 35 Cooler

(44) 36 Conduit

(45) 39 Conduit

(46) 40 Intermediate-pressure H.sub.2S flash vessel

(47) 41 Conduit

(48) 42 Conduit

(49) 45 Low-pressure H.sub.2S flash vessel

(50) 46 Conduit

(51) 47 Conduit

(52) 49 Conduit

(53) 50 Intermediate-pressure CO.sub.2 flash vessel

(54) 51 Conduit

(55) 52 Conduit

(56) 55 Low-pressure CO.sub.2 flash vessel

(57) 56 Conduit

(58) 57 Conduit

(59) 60 Conduit

(60) 71 Conduit

(61) 72 Prescrubber

(62) 73 Conduit

(63) 74 H.sub.2S scrubber

(64) 75 Conduit

(65) 76 CO.sub.2 scrubber

(66) 77 Conduit

(67) 78 Conduit

(68) 79 Conduit

(69) 81 Conduit

(70) 82 Conduit

(71) 83 Conduit

(72) 84 Conduit

(73) 90 Flash regeneration apparatus

(74) 91 Conduit

(75) 92 Conduit

(76) 93 Conduit

(77) 94 Hot regeneration apparatus

(78) 95 Conduit

(79) 96 Conduit

(80) 98 Conduit

(81) 99 Conduit

(82) 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.