Process and plant for the purification of raw synthesis gas

Abstract

A process for the stepwise separation of accompanying gases from a raw synthesis gas stream by a liquid absorbent countercurrently guided through all process steps and circulated via regeneration plants, wherein either the accompanying gases H.sub.2S, COS and CO.sub.2 are separated in a common absorption step or, in one of the selective absorption steps chiefly H.sub.2S and COS are separated and in the next step in flow direction of the gas chiefly CO.sub.2 is separated, and in the last step a separation of accompanying gas residues (fine wash) is effected, wherein before the separation of H.sub.2S and COS an absorption step chiefly for the separation of aromatics and subsequently an absorption step chiefly for the separation of methyl mercaptan is carried out.

Claims

1. A process for the stepwise separation of accompanying gases from a raw synthesis gas stream by a liquid absorbent countercurrently guided through all process steps and circulated via regeneration plants, the process comprising the steps of: separating H.sub.2S, COS and CO.sub.2 in an absorption step; and separating accompanying gas residues, wherein before the separation of H.sub.2S, COS and CO.sub.2 , the process further comprises an absorption step configured for the removal of aromatics followed by an absorption step configured for the separation of methyl mercaptan.

2. The process according to claim 1, wherein the contact between the raw synthesis gas and the absorbent is effected via packed beds and/or via structured packings.

3. The process according to claim 1, wherein methanol is used as absorbent.

4. The process according to claim 1, wherein the absorption is carried out at a pressure between 20 and 40 bar.

5. The process according to claim 1, wherein the separation of CO.sub.2 in the regeneration plants is effected by lowering the pressure in the absorbent and/or by stripping with nitrogen.

6. The process according to claim 1, wherein the separation of the mercaptans, the H.sub.2S and COS from the absorbent loaded in the step for the separation of mercaptan and in the step for the separation of H.sub.2S and COS is effected by hot regeneration.

7. The process according to claim 1, wherein the absorbent loaded in the aromatics separation step is washed with water for regeneration, then liberated from gases by rectification with water and then by pressure reduction and subsequent heating.

8. The process according to claim 1, wherein the quantity of the absorbent used in the absorption step for the separation of aromatics is smaller than the quantity of the absorbent used in the absorption step for the separation of methyl mercaptan.

9. The process according to claim 1, wherein the raw synthesis gas stream is obtained by fixed-bed pressure gasification of coal.

10. A process for the selective and stepwise separation of accompanying gases from a raw synthesis gas stream by a liquid absorbent countercurrently guided through all process steps and circulated via regeneration plants, the process comprising the steps of: removing H.sub.2S and COS from the raw synthesis gas in an absorption step followed by removal of CO2 in the next step in flow direction; and separating of accompanying gas residues, wherein before the separation of H.sub.2S and COS, the process further comprises an absorption step configured for the separation of aromatics and followed by an absorption step configured for the separation of methyl mercaptan.

11. The process according to claim 10, wherein the contact between the raw synthesis gas and the absorbent is effected via packed beds and/or via structured packings.

12. The process according to claim 10, wherein methanol is used as absorbent.

13. The process according to claim 10, wherein the absorption is carried out at a pressure between 20 and 40 bar.

14. The process according to claim 10, wherein the separation of CO.sub.2 in the regeneration plants is effected by lowering the pressure in the absorbent and/or by stripping with nitrogen.

15. The process according to claim 10, wherein the separation of the mercaptans, the H.sub.2S and COS from the absorbent loaded in the step for the separation of mercaptan and in the step for the separation of H.sub.2S and COS is effected by hot regeneration.

16. The process according to claim 10, wherein the absorbent loaded in the aromatics separation step is washed with water for regeneration, then liberated from gases by rectification with water and then by pressure reduction and subsequent heating.

17. The process according to claim 10, wherein the quantity of the absorbent used in the absorption step for the separation of aromatics is smaller than the quantity of the absorbent used in the absorption step for the separation of methyl mercaptan.

18. The process according to claim 10, wherein the raw synthesis gas stream is obtained by fixed-bed pressure gasification of coal.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Further features, advantages and possible applications of the invention result from the subsequent description of the drawings and the exemplary embodiments. In this case, all described and/or pictorially presented features, alone or in any combination, are the subject matter of the invention, independently of the summary thereof in the claims and the dependency reference thereof.

(2) The Figure shows a flow diagram of an exemplary aspect of the process according to the invention and the plant according to the invention

DETAILED DESCRIPTION OF THE INVENTION

(3) Further features, advantages and possible applications of the invention can also be taken from the following description of an exemplary embodiment and the drawing. All features described and/or illustrated form the subject-matter of the invention per se or in any combination, independent of their inclusion in the claims or their back-reference.

(4) With reference to the Figure, the invention will now be explained in detail. The plant represents an implementation of the selective absorption process and comprises the two-stage pre-scrubber 1 and the three-stage main scrubber 2 as main components. The washing and absorption stages each substantially consist of a packed bed which is irrigated with the absorbent methanol. In each of these stages an absorption step is carried out. Via conduit 3, raw synthesis gas is introduced into the pre-scrubber 2 via a cooler 4 with a temperature in the range from 5 to 30 C. and with a pressure in the range from 25 to 33 bar. The first stage 5 of the pre-scrubber 1 on the gas side is designed such and, by adjustment of the process parameters, in particular of the supplied absorbent mass flow 11, operated such that chiefly aromatics are absorbed from the gas. The second stage 6 on the gas side is designed for the separation of mercaptans. In the second stage 6 a partial stream 7 of the absorbent loaded in the main scrubber 2 is used as absorbent. After passing through the packed bed of the second stage 6, the methanol is collected at the column bottom 8. A partial stream 9 thereof is passed into the hot regeneration plant 10 and a partial stream 11 is guided through the first stage 5 for further loading and then, through conduit 12, into the regeneration plant 13. Here, the hydrocarbons first are extractively separated by means of water 14 and as naphtha product 15 supplied to a further, non-illustrated treatment. In a further step, water and absorbent then are separated by means of rectification. The separated water 16 is supplied to a waste water treatment, the regenerated absorbent is supplied to the hot regeneration plant 10 via conduit 17. The gases 18 obtained during the rectification in the regeneration plant 13 contain sulfur compounds and are supplied to a non-illustrated sulfur recovery plant.

(5) The raw synthesis gas treated in the pre-scrubber 1 is passed into the main scrubber 2 via conduit 19. Here, the raw synthesis gas one after the other traverses the absorption stage 20 for the separation of H.sub.2S and COS, subsequently the absorption stage 21 for the separation of CO.sub.2, and finally the absorption stage 22 for the fine wash.

(6) The fine wash in stage 22 exclusively is carried out with absorbent treated in the hot regeneration plant 10, which is introduced into the stage 22 via conduit 23. The absorbent partly loaded in stage 22 subsequently is used for the CO.sub.2 absorption in stage 21. The absorbent partly loaded in stage 21 is collected at the column bottom 24. From the column bottom 24 a partial stream is supplied to the further loading in stage 20 via conduit 25. The remaining part of the absorbent collected at the bottom 24 is charged into the regeneration plant 27 via conduit 26. Via conduit 28, CO.sub.2 is separated there from the absorbent by depressurization and supplied to the further, non-illustrated treatment. Via conduit 29, a part of the absorbent regenerated in plant 27 is introduced into stage 21 for reloading, the other part is transferred into the regeneration plant 31 via conduit 30. A partial stream of the absorbent loaded in the three absorption stages of the main scrubber 2 likewise is introduced into the regeneration plant 31 via conduit 32 and, together with stream 30, is liberated there from CO.sub.2 by depressurization, which CO.sub.2 is discharged from the regeneration plant 31 as stream 33 for the further treatment. When particularly low CO.sub.2 values are to be achieved in the absorbent, stripping of the absorbent for example with nitrogen additionally is carried out in plant 31. In the regeneration plant 31 sulfur-containing components, in particular H.sub.2S and COS, are not removed from the absorbent; this will only be done in the hot regeneration plant 10 into which the absorbent is transferred via conduit 34. The sulfur-containing gases, in particular H.sub.2S, COS and mercaptans, are supplied to the further treatment, preferably in a non-illustrated sulfur recovery plant, as stream 35.

(7) At the head of the main scrubber 2, the purified synthesis gas is discharged as stream 36 and supplied to the further use.

INDUSTRIAL APPLICABILITY

(8) The invention provides an advantageous process which produces less environmental problems due to mercaptans and achieves a longer service life of the absorbent by separation of aromatics and higher hydrocarbons from the absorbent. The invention therefore is industrially applicable. These advantages are obtained in particular in the treatment of raw synthesis gas which has been produced by fixed-bed pressure gasification of coal.

(9) While the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications, and variations will be apparent to those skilled in the art in light of the foregoing description. Accordingly, it is intended to embrace all such alternatives, modifications, and variations as fall within the spirit and broad scope of the appended claims. The present invention may suitably comprise, consist or consist essentially of the elements disclosed and may be practiced in the absence of an element not disclosed. Furthermore, if there is language referring to order, such as first and second, it should be understood in an exemplary sense and not in a limiting sense. For example, it can be recognized by those skilled in the art that certain steps can be combined into a single step.

(10) The singular forms a, an and the include plural referents, unless the context clearly dictates otherwise.

(11) Comprising in a claim is an open transitional term which means the subsequently identified claim elements are a nonexclusive listing (i.e., anything else may be additionally included and remain within the scope of comprising). Comprising as used herein may be replaced by the more limited transitional terms consisting essentially of and consisting of unless otherwise indicated herein.

(12) Providing in a claim is defined to mean furnishing, supplying, making available, or preparing something. The step may be performed by any actor in the absence of express language in the claim to the contrary.

(13) Optional or optionally means that the subsequently described event or circumstances may or may not occur. The description includes instances where the event or circumstance occurs and instances where it does not occur.

(14) Ranges may be expressed herein as from about one particular value, and/or to about another particular value. When such a range is expressed, it is to be understood that another embodiment is from the one particular value and/or to the other particular value, along with all combinations within said range.

(15) All references identified herein are each hereby incorporated by reference into this application in their entireties, as well as for the specific information for which each is cited.

LIST OF REFERENCE NUMERALS

(16) 1 pre-scrubber 2 main scrubber 3 conduit for raw synthesis gas 4 cooler 5 first stage of the pre-scrubber 6 second stage of the pre-scrubber 7 partial stream of the absorbent loaded in the main scrubber 8 column bottom 9 partial stream absorbent 10 hot regeneration plant 11 partial stream absorbent 12 partial stream absorbent 13 regeneration plant 14 water 15 naphtha product 16 waste water 17 conduit for absorbent 18 sulfur-containing gases 19 raw synthesis gas after pre-wash 20 first absorption stage of main scrubber 21 second absorption stage of main scrubber 22 third absorption stage of main scrubber (fine wash) 23 absorbent 24 column bottom 25 partial stream absorbent 26 partial stream absorbent 27 regeneration plant 28 CO.sub.2 stream 29 absorbent 30 absorbent 31 regeneration plant 32 absorbent 33 CO.sub.2 stream, possibly also containing N.sub.2 34 absorbent 35 sulfur-containing gases 36 purified synthesis gas