METHOD FOR REMOVING INERT GAS FROM LIQUID AMMONIA

Abstract

A method of removing inert gas dissolved in liquid ammonia involves evaporating, compressing, and then condensing the liquid ammonia together with the inert gas dissolved therein. Thereby, a product stream of warm liquid ammonia that has been freed of the inert gas is obtained, which is under elevated pressure relative to standard pressure and hence suitable for immediate use in methods in which pure liquid pressurized ammonia is required. If, by contrast, the ammonia is cooled first, for example, below the boiling temperature for ammonia and expanded to standard pressure to store it in tanks as liquid ammonia at low temperatures, it is necessary first to reheat and compress it for further processing operations. Thus the disclosed methods lead to significant energy savings.

Claims

1.-15. (canceled)

16. A method of removing inert gas dissolved in liquid ammonia, the method comprising evaporating, compressing, and then condensing the liquid ammonia and the inert gas dissolved therein.

17. The method of claim 16 wherein the inert gas consists of a noble gas.

18. The method of claim 16 wherein the inert gas consists of at least one of helium, argon, or methane.

19. The method of claim 16 comprising condensing the ammonia at an elevated pressure and at a temperature above +10° C.

20. The method of claim 16 comprising condensing the ammonia at an elevated pressure in a range from 10 bar to 30 bar.

21. The method of claim 16 comprising cooling a process stream with heat that is absorbed by the ammonia during the evaporation.

22. The method of claim 21 comprising using the heat that is absorbed by the ammonia during the evaporation for condensation of ammonia in an ammonia synthesis plant.

23. The method of claim 16 wherein evaporated ammonia is compressed together with the inert gas dissolved in the ammonia.

24. The method of claim 16 wherein compressed ammonia is condensed with the aid of cooling water.

25. The method of claim 16 comprising drawing off gases that are insoluble in ammonia during the condensation from an apparatus used for the condensation.

26. The method of claim 25 comprising recycling the drawn off gases into a plant for preparing ammonia.

27. The method of claim 16 wherein a first substream of a reactant stream of the liquid ammonia is evaporated, compressed, condensed, and then removed from a system as ammonia that has been freed of the inert gas in a liquid pressurized warm stream, the method comprising branching off a second substream from the reactant stream and from the system as a cold liquid stream.

28. The method of claim 27 wherein the first substream is a main stream of the ammonia removed from the system.

29. The method of claim 27 comprising: feeding the second substream to a tank and expanding the second substream to a standard pressure in the tank; and drawing off the inert gas from the tank while expanding the second substream.

30. A plant for removing inert gas dissolved in liquid ammonia, the plant comprising: a conduit for supplying the liquid ammonia to an ammonia evaporator; an ammonia compressor operatively connected to the ammonia evaporator; an ammonia condenser operatively connected to the ammonia compressor and including means for removing a stream of the inert gas separated off in the ammonia condenser; and a collecting vessel that is operatively connected to the ammonia condenser and is for receiving the liquid ammonia that has been freed of the inert gas.

31. The plant of claim 30 wherein the inert gas is a noble gas consisting of at least one of helium, argon, or methane.

32. The plant of claim 30 wherein the conduit is or is connected to an output conduit of a plant for preparation of ammonia.

33. The plant of claim 30 comprising a vessel for receiving the liquid ammonia with the dissolved inert gas, with the conduit leading from the vessel to the ammonia evaporator, wherein a branch conduit that branches off from the conduit is used to remove a substream of cold liquid ammonia from the plant and supply the cold liquid ammonia to a tank where the cold liquid ammonia is expanded.

Description

[0029] The present invention is elucidated in detail hereinafter by a working example with reference to the appended drawing. The drawing shows:

[0030] FIG. 1 a schematically simplified flow diagram of an illustrative plant of the invention.

[0031] A possible working example of the present invention is elucidated in detail hereinafter with reference to FIG. 1. The diagram shows a simplified flow diagram of an illustrative plant of the invention for removal of gases dissolved in liquid ammonia from the ammonia. The diagram is highly schematically simplified, and only the plant components that are essential in the context of the present invention are shown.

[0032] A process stream 10 of liquid ammonia which comprises dissolved gases such as inert gases and possibly further gases and which comes from a plant for preparation of ammonia (this ammonia plant is not shown here) is fed via the conduit 11 to a vessel 12 in which liquid ammonia can optionally be stored intermediately before the processing of the invention. Liquid ammonia is removed from this vessel 12 via the conduit 13, and this conduit divides downstream of a branch 14, giving rise to two substreams of liquid ammonia. A first, smaller substream flows through conduit 15 and is supplied as a cold substream of liquid ammonia to a further tank 16. The ammonia can be expanded to standard pressure therein, in which case gases dissolved in the ammonia outgas and can be removed via conduit 17. The cold liquid ammonia can be removed via conduit 18 and, for example, exported or, after heating and compression, fed to a urea plant via conduit 17.

[0033] Proceeding from the branch 14, by contrast, the predominant substream is processed by the method of the invention, for which purpose it is fed via conduit 19 to an ammonia evaporator 20. After being evaporated, the process stream is fed via conduit 21 to an ammonia compressor 22. After the compression, the process stream passes through conduit 23 to an ammonia condenser 24. The compressed ammonia can be condensed therein with the aid of cooling water. The temperature of the ammonia after the condensation is, for example, about 30° C., and the condensed liquid ammonia is accordingly under elevated pressure. This condensation causes the gases to be separated from the ammonia to escape, and they can therefore be drawn off from the condenser in gaseous form via conduit 25 and removed from the plant via the output conduit 26.

[0034] The purified liquid ammonia can optionally be stored intermediately under pressure at the appropriate temperature in a tank 27. From this tank, it is then possible to feed a warm stream of liquid pressurized ammonia via conduit 28 to a further plant, for example a urea plant. It is also possible to dispense with the intermediate storage in the tank 27 when, for example, there is an immediate need for an appropriate amount of “warm” liquid ammonia for a further process in which the ammonia is required as a warm pressurized stream and hence can be processed further directly without intermediate cooling.

[0035] The advantage of the method of the invention is thus that it can be used to produce a purified “warm” substream of liquid ammonia on the one hand and optionally also a “cold” substream of liquid ammonia that does not require any separate processing.

LIST OF REFERENCE NUMERALS

[0036] 10 process stream

[0037] 11 conduit

[0038] 12 vessel

[0039] 13 conduit

[0040] 14 branch

[0041] 15 conduit

[0042] 16 tank

[0043] 17 conduit

[0044] 18 conduit

[0045] 19 conduit/first substream

[0046] 20 ammonia evaporator

[0047] 21 conduit

[0048] 22 ammonia compressor

[0049] 23 conduit

[0050] 24 ammonia condenser

[0051] 25 conduit

[0052] 26 output conduit

[0053] 27 tank

[0054] 28 conduit