METHOD FOR AVOIDING VOC AND HAP EMISSIONS FROM SYNTHESIS GAS-PROCESSING SYSTEMS

Abstract

Systems and methods for the synthesis of ammonia includes a reformer; a carbon monoxide converter; a carbon dioxide scrubber unit with recovery; a methanation unit; and an ammonia synthesis unit; wherein the carbon dioxide scrubber unit with recovery is connected to at least one fired auxiliary steam boiler.

Claims

1.-14. (canceled)

15. A plant for ammonia synthesis, at least comprising: a reformer; a carbon monoxide converter; a carbon dioxide scrubber unit with regeneration; a methanization unit; and an ammonia synthesis unit; wherein the carbon dioxide scrubber unit with regeneration is connected to at least one fired auxiliary steam boiler.

16. The plant of claim 15 wherein the fired auxiliary steam boiler is connected to a waste air apparatus.

17. The plant of claim 15 wherein the reformer comprises a steam reformer with or without secondary reformer, and/or an autothermal reformer.

18. The plant of claim 15 wherein an air separation plant is included and/or the nitrogen is provided from the process air treated in a secondary reformer.

19. The plant of claim 15 wherein connected in the process direction and in series are the reformer, the carbon monoxide converter, the carbon dioxide scrubber unit with regeneration, the methanization unit and ammonia synthesis unit, and the carbon dioxide scrubber unit with regeneration has an additional connection to at least one fired auxiliary steam boiler.

20. The plant of claim 15 wherein the fired auxiliary steam boiler has supply lines for air and supply lines for fuel.

21. The plant of claim 20 wherein the supply lines for air are connected to the carbon dioxide scrubber unit with regeneration.

22. The plant of claim 15 wherein the fired auxiliary steam boiler has a capacity of 10 tonnes to 200 tonnes of steam per hour.

23. A process for ammonia synthesis, comprising: introducing an alkane-containing gas into a reformer and obtaining a first synthesis gas mixture; introducing the first synthesis gas mixture into a carbon monoxide converter and obtaining a second synthesis gas mixture; introducing the second synthesis gas mixture into a carbon dioxide scrubber unit with regeneration and obtaining a third synthesis gas mixture and an offgas containing carbon dioxide; introducing the third synthesis gas mixture into a methanization unit and obtaining a fourth synthesis gas mixture; introducing the fourth synthesis gas mixture into an ammonia synthesis unit and obtaining ammonia; wherein the offgas containing carbon dioxide from said introducing the second synthesis gas mixture is introduced wholly or partly into a fired auxiliary steam boiler, and, by oxidation in the auxiliary steam boiler, obtaining an offgas free of or low in volatile hydrocarbons.

24. The process of claim 23 wherein the reformer comprises a steam reformer with or without secondary reformer, and/or an autothermal reformer.

25. The process of claim 23 wherein the ammonia and a major part of the offgas containing carbon dioxide or offgas free of or low in volatile hydrocarbons are reacted in a urea plant to form urea.

26. The process of claim 23 wherein the fired auxiliary steam boiler is operated at 170° C. to 550° C. on a steam generation side.

27. The process of claim 23 wherein the fired auxiliary steam boiler is operated at 5 bar to 150 bar on the steam generation side.

Description

[0047] Additionally the invention is elucidated in more detail by means of the following figures. These figures do not limit the scope of protection of the invention, instead serving only for illustrative elucidation. The figures are not to scale.

[0048] FIG. 1 shows a schematic flow diagram of a plant for ammonia synthesis, and

[0049] FIG. 2 shows a schematic flow diagram of a plant of the invention for ammonia synthesis.

[0050] FIG. 1 shows a schematic flow diagram of a plant for ammonia synthesis. Serving for the provision of hydrogen is a reformer (1), preferably a primary reformer and a secondary reformer and/or an autothermal reformer. Hydrogen is formed here in principle according to equation [4]. The plant additionally comprises a carbon monoxide (CO) converter (2). In this converter, the carbon monoxide (CO) formed in equation [4] and not needed in the ammonia synthesis itself is converted into carbon dioxide with further formation of hydrogen, in accordance with equation [5]. Following the carbon monoxide (CO) converter (2) there is a carbon dioxide (CO.sub.2) scrubber unit with regeneration (3). The carbon dioxide (CO.sub.2) scrubber unit may be configured, for example, as a known apparatus/arrangement wherein carbon dioxide is dissolved in a suitable solvent—potassium carbonate or amines, for example—under pressure in an absorber and is subsequently expanded again (“flash”) separately from the synthesis gas. The solvent can then be reheated and regenerated in a stripping column (desorber). A methanization unit (4) allows for the further abatement of oxides of carbon (CO.sub.x). This is accomplished in accordance with equations [6] and [7], for example. The plant additionally comprises an ammonia synthesis unit (5) connected to the methanization unit (4). The ammonia synthesis unit (5) comprises the actual ammonia synthesis reactor for the reaction of hydrogen and nitrogen in accordance with equation [3]. Nitrogen may be provided preferably from the process air processed (i.e., burned) in the secondary reformer. The ammonia synthesis unit (5) is connected to apparatuses for purification, compression and/or liquefaction (9). Connected in the process direction and in series are the reformer (1), the carbon monoxide (CO) converter (2), the carbon dioxide (CO.sub.2) scrubber unit with regeneration (3), the methanization unit (4), the ammonia synthesis unit (5), and the apparatuses for purification, compression and/or liquefaction (9). The carbon dioxide (CO.sub.2) scrubber unit with regeneration (3) has an additional removal line (8c) for the offgases (6a) that are not required further (primarily CO.sub.2), leading to a waste air plant (7). In the waste air plant (7), the offgases arising in the carbon dioxide (CO.sub.2) scrubber unit (primarily CO.sub.2) and volatile organic hydrocarbons are emitted as offgas (6a) to the surrounding environment. The expression “connected” in the sense of the invention embraces suitable pipes, connectors, pumps, compressors, etc., which are suitable for the transport of liquids and gases even at subatmospheric (less than 1 bar) and superatmospheric (greater than 1 bar) pressures. Disposed between the aforesaid elements there may be further elements such as heat exchangers, pumps, compressors, heaters, etc.

[0051] FIG. 2 shows a schematic flow diagram of the plant of the invention for ammonia synthesis. The basic construction corresponds to the construction described in FIG. 1. The plant of the invention is characterized in that the carbon dioxide (CO.sub.2) scrubber unit with regeneration (3) is connected to a fired auxiliary steam boiler (6). The volatile hydrocarbons (VOCs and HAPs) arising in the carbon dioxide (CO.sub.2) scrubber unit with regeneration (3), with the carbon dioxide in the carbon dioxide-containing offgases (6a), methanol for example, are burned in the fired auxiliary steam boiler and converted into carbon dioxide and water. The auxiliary steam boiler (6) is fed with air via a first supply line (8a) and with fuel gas via a second supply line (8b). The first supply line (8a) here is connected to the removal line (8c) from the scrubber unit with regeneration (3), and so the volatile hydrocarbons arising in the carbon dioxide (CO.sub.2) scrubber unit with regeneration (3) with the CO.sub.2 are premixed with atmospheric oxygen. Via the waste air apparatus (7), offgas (6b) free of or low in volatile hydrocarbons (VOC and HAP) passes into the atmosphere.

LIST OF REFERENCE SYMBOLS

[0052] (1) Reformer [0053] (2) Carbon monoxide (CO) converter [0054] (3) Carbon dioxide (CO.sub.2) scrubber unit with regeneration [0055] (4) Methanization unit [0056] (5) Ammonia synthesis unit [0057] (6) Fired auxiliary steam boiler [0058] (6a) The carbon dioxide (CO.sub.2)-containing offgas [0059] (6b) Offgas free of or low in volatile hydrocarbons (VOC and HAP) [0060] (7) Waste air plant [0061] (8a) First supply line [0062] (8b) Second supply line [0063] (9) Apparatuses for purification, compression and/or liquefaction