PROCESS AND PLANT FOR REMOVAL OF ACIDIC GAS CONSTITUENTS FROM SYNTHESIS GAS CONTAINING METAL CARBONYLS

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 containing metal carbonyls by gas scrubbing with a scrubbing medium. According to the invention water is added directly into the feed conduit of the methanol water mixture containing metal sulfides before the introduction thereof into the methanol-water separating column and/or water is injected directly into the methanol-water separating column at at least one point. This avoids deposits or encrustations of metal sulfide particles in the methanol-water separating column.

Claims

1.-10. (canceled)

11. A process for removal of carbon dioxide and hydrogen sulfide from a crude synthesis gas containing CO.sub.2, H.sub.2S, water and metal carbonyls, with methanol as the scrubbing medium, comprising: a) supplying the crude synthesis gas to an absorption apparatus, b) contacting the crude synthesis gas with a cold methanol sub-stream and with at least one further methanol sub-stream recycled from downstream process stages in the absorption apparatus to obtain a product gas stream depleted in acidic gas constituents, water and metal carbonyls which is discharged from the process, and to obtain a methanol sub-stream laden with acidic gas constituents, water and metal carbonyls, c) multistage regeneration of the laden methanol sub-stream by pressure reduction and/or temperature elevation to obtain at least one regenerated methanol sub-stream which is recycled to process step b), to further obtain one or more carbon dioxide- and/or hydrogen sulfide-containing gas streams which are discharged from the process and to obtain a methanol sub-stream containing water and metal sulfides and depleted in acidic gas constituents, d) introducing the methanol sub-stream containing water and metal sulfides and depleted in acidic gas constituents into a methanol-water separating column, distillative fractionation thereof in the methanol-water separating column into a methanol-containing tops product that is at least partially recycled to process step b) and/or step c) and into a water-containing bottoms product that is discharged from the process, wherein e) water is added directly into the feed conduit of the methanol sub-stream containing water and metal sulfides and depleted in acidic gas constituents before the introduction thereof into the methanol-water separating column, and/or f) water is injected directly into the methanol-water separating column at at least one point.

12. The process according to claim 11, wherein in process step e) the addition of water is carried out such that the residence time of the obtained mixture in the feed conduit before introduction into the methanol-water separating column is sufficient to bring about a transferral of the metal sulfides from a methanol-rich environment to a water-rich environment of at least 50%.

13. The process according to claim 11, wherein in process step e) the addition point of the water into the feed conduit of the methanol sub-stream containing water and metal sulfides and depleted in acidic gas constituents is arranged such that a residence time of at least 5 s before entry into the methanol-water separating column is maintained, wherein the flow rate of the methanol-water mixture in the feed conduit is between 0.5 and 2.0 m/s.

14. The process according to claim 13, wherein in process step e) the addition point of the water into the feed conduit of the methanol sub-stream containing water and metal sulfides and depleted in acidic gas constituents is located at least 5 m upstream of the methanol-water separating column.

15. The process according to claim 11, wherein in process step f) the added amount of water is between 3% and 50% of the amount of feed to the methanol-water separating column.

16. The process according to claim 15, wherein at least 100 Vh of water are injected per injection point.

17. The process according to claim 11, wherein the metal sulfides are discharged from the process with the water-containing bottoms product of the methanol-water separating column.

18. The process according to claim 11, herein for the water addition in process step e) or f) at least one water-containing stream selected from the group of: water from a CO.sub.2 off-gas scrubber, bottoms product from the methanol-water separating column, fresh water, demineralized water is used.

19. The process according to claim 11, wherein the water stream used for the water addition in process step e) or f) has a temperature between 10 C. and 140 C.

20. A plant for removal of carbon dioxide and hydrogen sulfide from a crude synthesis gas containing CO.sub.2, H.sub.2S, water and metal carbonyls with methanol as the scrubbing medium, comprising the following constituents and assemblies in fluid connection with one another: a) a means for supplying the crude synthesis gas to an absorption apparatus, b) an absorption apparatus, means for supplying the crude synthesis gas, a cold methanol sub-stream and at least one further methanol sub-stream recycled from downstream process stages to the absorption apparatus, means for discharging a product gas stream depleted in acidic gas constituents, water and metal carbonyls and a methanol sub-stream laden with acidic gas constituents, water and metal carbonyls, c) one or more apparatuses for multi-stage regeneration of the laden methanol sub-stream by pressure reduction (flashing) and/or temperature elevation (hot regeneration), means for supplying the laden methanol sub-stream to the regeneration apparatuses, means for recycling at least one regenerated methanol sub-stream to the absorption apparatus, means for discharging one or more carbon dioxide- and/or hydrogen sulfide-containing gas streams from the regeneration apparatuses, means for discharging a methanol sub-stream containing water and metal sulfides and depleted in acidic gas constituents from the regeneration apparatuses, d) a methanol-water separating column, means for introducing the methanol sub-stream containing water and metal sulfides and depleted in acidic gas constituents into the methanol-water separating column, means for discharging and recycling a methanol-containing tops product to the absorption apparatus and/or to the regeneration apparatuses, means for discharging a water-containing bottoms product, further comprising a methanol-water separating column and means e) which allow addition of water directly into the feed conduit of the methanol sub-stream containing water and metal carbonyls and depleted in acidic gas constituents before the introduction thereof into the methanol-water separating column and/or which allow injection of water directly into the methanol-water separating column at at least one point.

Description

BRIEF DESCRIPTION OF THE DRAWING

[0043] Further features, advantages and possible applications of the invention are also apparent from the following description of a working and numerical example and the drawing. All described and/or depicted features on their own or in any desired combination form the subject matter of the invention, irrespective of the way in which they are combined in the claims and the way in which said claims refer back to one another.

[0044] FIG. 1 is a schematic representation of an exemplary embodiment of the process according to the invention/the plant according to the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0045] FIG. 1 is a schematic diagram of a methanol-water separating column 1 inside the scrubbing medium workup of a plant for gas scrubbing of crude synthesis gas with cryogenic methanol operating according to the Rectisol process.

[0046] Via conduit 10, control valve 11 and conduit 12, regenerated methanol scrubbing medium from the methanol hot regeneration (not depicted in the FIGURE) is supplied to the separating column and applied thereto in the upper part thereof in proximity to the column top via liquid distributor 78. In addition separating column 1 is supplied via conduit 20, control valve 21 and conduit 22 with a methanol-water mixture likewise originating from the methanol hot regeneration which is applied thereto in the middle column region via liquid distributor 75.

[0047] In the present working example the separating column 1 is fitted with structured packing segments 70, 71, 72, 73 which are used to adjust the vapour-liquid equilibrium of the components involved. The separating column may alternatively be fitted with trays or dumped random packing bodies; this has no substantial effect on the functioning of the invention. The energy input required for distillative fractionation of the methanol-water mixture is provided via reboiler 60 in which a portion of the bottoms product supplied via conduit 66 evaporates and the vapour/the heated vapour-liquid mixture is recycled to the separating column via conduit 65. The heating of the reboiler is effected by means of steam applied to the reboiler via conduit 61. The condensate thus generated is discharged via conduit 62.

[0048] Methanol vapour depleted in water is withdrawn from the top of the separating column and recycled to the methanol hot regeneration via conduit 50. Discharging of bottoms product enriched in water is effected via conduit 40, control valve 41 and conduit 42. The bottoms product is supplied to a workup not depicted in the FIGURE or is removed from the process.

[0049] According to the invention demineralized water is now additionally supplied via conduit 30. In the present example this originates from a gas scrubber by means of which methanol traces were removed from the CO.sub.2 stream discharged from the Rectisol plant before discharge thereof to the atmosphere. The demineralized water is supplied via conduit 34, control valve 35, conduit 36, shutoff valve 37 and conduit 38 to the separating column 1 and applied thereto via liquid distributor 77.

[0050] Alternatively or in addition the entirety of the water stream supplied via conduit 30 or a substream thereof may be sent via conduit 31, control valve 32 and conduit 33 to the methanol-water mixture supplied via conduit 20 and combined therewith in conduit 22. The water stream or a substream then enters the separating column together with the methanol-water mixture via liquid distributor 75.

[0051] It is also possible by appropriate opening/closing of the shutoff valves 24, 27, 37 to introduce into the separating column a substream or the entirety of the water stream via conduit route 30, 34, 36, 23, 25 and liquid distributor 76. Water input via conduit route 26, 28, 22 is also possible. In order to allow finer control/better distribution of the water on the liquid distributors it is also possible to replace one or more shutoff valves with control valves.

[0052] The choice of water addition points via liquid distributors 75, 76, 77 will depend in particular on which parts of the separating column are particularly severely affected by deposits or encrustations of metal sulfide particles. This is based on relevant operating experience or may be determined by corresponding experiments without water addition.

INDUSTRIAL APPLICABILITY

[0053] The invention provides a gas scrubbing process for removal of acidic gas constituents from synthesis gas containing metal carbonyls which makes it possible to reliably discharge the metal sulfide particles formed from the metal carbonyls via the column bottom of the methanol-water separating column without encrustations or obstructions occurring therein and without additional equipment parts such as for example precipitation vessels being required.

LIST OF REFERENCE NUMERALS

[0054] 1 separating column [0055] 10 conduit [0056] 11 control valve [0057] 12 conduit [0058] 20 conduit [0059] 21 control valve [0060] 22 conduit [0061] 23 conduit [0062] 24 shutoff valve [0063] 25 conduit [0064] 26 conduit [0065] 27 shutoff valve [0066] 28 conduit [0067] 30 conduit [0068] 31 conduit [0069] 32 control valve [0070] 33 conduit [0071] 34 conduit [0072] 35 control valve [0073] 36 conduit [0074] 37 shutoff valve [0075] 38 conduit [0076] 40 conduit [0077] 41 control valve [0078] 42 conduit [0079] 50 conduit [0080] 60 reboiler [0081] 61 conduit [0082] 62 conduit [0083] 65 conduit [0084] 66 conduit [0085] 70 structured packing [0086] 71 structured packing [0087] 72 structured packing [0088] 73 structured packing [0089] 75 liquid distributor [0090] 76 liquid distributor [0091] 77 liquid distributor [0092] 78 liquid distributor

[0093] 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.