INSTALLATION FOR PRODUCING NITRIC ACID WITH A SEALING DEVICE FOR SEALING A ROTATABLE SHAFT OF A NO COMPRESSOR AND/OR OF A RESIDUAL GAS EXPANDER

Abstract

A sealing device for sealing a rotatable shaft of a gas compressor and/or a gas expander may include first and second sealing chambers and an extraction unit. The first sealing chamber may surround the rotatable shaft and include an inlet for the supply of a sealing medium. The second sealing chamber may be separated from the first sealing chamber by a seal and may surround the rotatable shaft. The second sealing chamber may include an outlet for the discharge of the sealing medium. The extraction device may extract the sealing medium out of the second sealing chamber. The present disclosure also concerns a corresponding method. Still further, the present disclosure concerns an installation for producing nitric acid with a NO compressor and a residual gas expander as well as a corresponding method. The NO compressor and/or the residual gas expander may have such a sealing device.

Claims

1.-14. (canceled)

15. An installation for producing nitric acid with a NO compressor and a residual gas expander, wherein at least one of the NO compressor or the residual gas expander includes a sealing device for sealing a rotatable shaft of the NO compressor or the residual gas expander, the sealing device comprising: a first sealing chamber that surrounds the rotatable shaft and includes an inlet for supply of a sealing medium; a second sealing chamber that is separated from the first sealing chamber by a seal and surrounds the rotatable shaft, the second sealing chamber including an outlet for discharge of the sealing medium; and an extraction device for extraction of the sealing medium out of the second sealing chamber.

16. The installation of claim 15 wherein the extraction device comprises a jet pump.

17. The installation of claim 15 wherein the extraction device comprises an ejector.

18. The installation of claim 15 further comprising a third sealing chamber that surrounds the rotatable shaft and includes an outlet for discharge of the sealing medium, wherein the second sealing chamber is disposed between the first and third sealing chambers.

19. The installation of claim 18 wherein the extraction device is configured to extract the sealing medium out of the third sealing chamber.

20. The installation of claim 18 wherein the second and third sealing chambers are inlet-free.

21. The installation of claim 15 wherein the first sealing chamber is outlet-free.

22. The installation of claim 15 wherein the second sealing chamber is inlet-free.

23. The installation of claim 15 further comprising a joint extraction device for the NO compressor and the residual gas expander.

24. The installation of claim 15 wherein the extraction device is a joint extraction device for the NO compressor and the residual gas expander.

25. A method for operating an installation for producing nitric acid with a NO compressor and a residual gas expander and for sealing a shaft of at least one of the NO compressor or the residual gas expander, wherein the installation includes a sealing device that comprises a first sealing chamber surrounding the shaft and including an inlet for supply of a sealing medium and a second sealing chamber that is separated from the first sealing chamber by a seal, that surrounds the shaft, and that includes an outlet for discharge of the sealing medium, the method comprising: introducing the sealing medium into the first sealing chamber; and extracting the sealing medium out of the second sealing chamber.

26. The method of claim 25 further comprising extracting the sealing medium out of a third sealing chamber that surrounds the shaft and includes an outlet for discharge of the sealing medium, wherein the second sealing chamber is disposed between the first and third sealing chambers.

27. The method of claim 25 wherein the sealing medium is a sealing gas.

28. The method of claim 25 wherein the sealing medium is sealing air.

29. The method of claim 25 wherein the sealing medium is a working gas.

30. The method of claim 25 further comprising extracting the sealing medium with a jet pump that is operated with a jet stream form the sealing medium.

31. The method of claim 25 using part of a residual gas supplied to the residual gas expander as the sealing medium.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0024] FIG. 1 shows a schematic representation of a first exemplary embodiment of the installation according to the invention for nitric acid production,

[0025] FIG. 2 shows a schematic representation of a second exemplary embodiment of the installation according to the invention for nitric acid production,

[0026] FIG. 3 shows a schematic sectional representation of a sealing device according to the invention.

EMBODIMENTS OF THE INVENTION

[0027] Identical parts are always provided with the same reference numbers in the various figures and are therefore generally also only cited or mentioned once in each case.

[0028] FIG. 1 schematically represents an installation for the production of nitric acid (HNO3). The installation has a low-pressure part 1 in which an ammonia/air mixture is oxidized by means of a catalytic converter to form nitrogen monoxide (NO) and water. Gaseous nitrogen monoxide 2 is conducted into a NO compressor 3 in which the nitrogen monoxide is compressed. Compressed nitrogen monoxide 4 exiting from NO compressor 3 is moved into a high-pressure part 5 of the installation in which oxidation of NO to form nitrogen dioxide (NO.sub.2) and absorption of nitric acid (HNO.sub.3) take place. Unabsorbed residual gas 6 is conducted via a heat exchanger 7 to a residual gas expander 11 in order to reduce it to ambient pressure in order to obtain energy and discharge it into an exhaust gas flow 20.

[0029] Since the escape of gases containing nitrogen can lead to irritation or damage of the respiratory passages, particular precautions are taken in the case of NO compressor 3 and residual gas expander 11 of the installation in order to prevent the undesirable escape of the gases introduced into NO compressor 3 and residual gas expander 11. Both NO compressor 3 and residual gas expander 11 comprise two sealing devices 24 via which rotatable shafts 26 of NO compressor 3 or residual gas expander 11 are sealed and which shall be explained in greater detail below on the basis of the representation in FIG. 3.

[0030] FIG. 3 shows a cross section through a shaft 26 of NO compressor 3 or residual gas expander 11, which shaft 26 is mounted about a rotational axis 23 rotatably with respect to a fixed housing 27. An impeller 37, which, in the case of NO compressor 3, contributes to the compression of the conveyed gas or, in the case of residual gas expander 11, is driven by the introduced gas, is arranged on shaft 26 in inner space 25 of NO compressor 3 or of residual gas expander 11. A multi-stage sealing device 24 is provided to seal off the inner space from the surroundings. Sealing device 24 comprises a first sealing chamber 51 which entirely surrounds shaft 26. First sealing chamber 51 is formed to be annular. It is separated from inner space 25 by a seal 40.

[0031] Seal 40 is formed as a labyrinth seal which has a certain degree of porosity as a result of its design. First sealing chamber 51 comprises an inlet 44 through which a sealing medium formed as a sealing gas can be introduced into first sealing chamber 51.

[0032] Sealing device 24 furthermore comprises a second sealing chamber 52 which has an annular design and surrounds shaft 26. Second sealing chamber 52 is arranged directly adjacent to first sealing chamber 51. It is separated from first sealing chamber 52 by a seal 41. Seal 41 is also formed as a labyrinth seal. There is provided in second sealing chamber 52 an outlet 45 via which gas can escape out of second sealing chamber 52. First sealing chamber 51 is arranged between inner space 25 of NO compressor 3 or residual gas expander 11 and second sealing chamber 52.

[0033] A third sealing chamber 53 is also provided which is likewise configured to be annular and surrounds shaft 26. Third sealing chamber 53 is arranged directly adjacent to second sealing chamber 52 and separated from the second sealing chamber by a seal 42. On its side opposite second sealing chamber 52, a further seal 43 is provided via which third sealing chamber 53 is sealed off from the surroundings. Both seals 42, 43 which delimit third sealing chamber 53 are configured as labyrinth seals.

[0034] First sealing chamber 51 is formed to be outlet-free so that the sealing gas introduced via inlet 44 can leave the first sealing chamber exclusively through both seals 40 and 41 which delimit first sealing chamber 51 from inner space 25 and second sealing chamber 52. Second sealing chamber 52 and third sealing chamber 53 are formed to be inlet-free. That is to say that gases can arrive at second sealing chamber 52 solely via seals 41 and 42, which seals 41 and 42 delimit second sealing chamber 52 from first sealing chamber 51 and third sealing chamber 53. Gases can arrive at third sealing chamber 53 exclusively through both seals 42 and 43 which delimit third sealing chamber 53 from second sealing chamber 52 and the surroundings.

[0035] In order to improve the safety of sealing device 24, outlet 45 of second sealing chamber 52 is connected to extraction device 29, 31. A vacuum can be generated by extraction device 29,31 in second sealing chamber 52 so that gas is extracted out of second sealing chamber 52. Even in the case of failure of the sealing medium, gas collecting in second sealing chamber 52 is extracted and cannot escape into the surroundings. As a result of this, the release of hazardous gases can be prevented and thus the safety of NO compressor 3 or expander 11 can be improved. Gas 32, 33 extracted by extraction device 29, 31 is supplied to exhaust gas flow 20 of residual gas expander 11.

[0036] As is apparent from the representation in FIG. 3, outlet 46 of third sealing chamber 53 is also connected to extraction device 29, 31 so that gas can also be extracted out of third sealing chamber 53. In this regard, second sealing chamber 52 and third sealing chamber 53 are connected to a joint extraction device 29, 31.

[0037] Extraction device 29, 31 is formed as a jet pump, in particular as an ejector. Extraction device 29, 31 is operated with a jet stream 28, 30. A flow from the sealing medium can be used as the jet stream.

[0038] In the case of the installation represented in FIG. 1 for nitric acid production, two separate extraction devices 29, 31 are provided, wherein a first extraction device 29 is connected to NO compressor 3 and a second extraction device 31 is connected to residual gas expander 11. Extraction flow 18, which is extracted out of second sealing chamber 52 of NO compressor 3, is supplied together with extraction flow 22, which is extracted out of the third sealing chamber of the NO compressor, to first extraction device 29. Exhaust gas flow 19, which is extracted out of second sealing chamber 52 of residual gas expander 11, is supplied together with extraction flow 39, which is extracted out of third sealing chamber 53 of residual gas expander 11, to second extraction device 31.

[0039] In contrast to the first exemplary embodiment, second sealing chambers 52 and third sealing chambers 53 of NO compressor 3 and residual gas expander 11 can be connected to a joint extraction device.

[0040] In the case of the installation according to the first exemplary embodiment, a sub-flow 17, 21 of residual gas 8 supplied to residual gas expander 11 is used as the sealing medium. For this purpose, residual gas flow 8 coming from heat exchanger 7 is divided into two sub-flows 9, 10, wherein a first sub-flow 9 is supplied to residual gas expander 11. A second sub-flow 10 is divided into two sub-flows 17, 21, wherein a first sub-flow 17 is supplied to residual gas expander 11 and a second sub-flow 21 is supplied to compressor 3. Alternatively or additionally, the residual gas can be removed from an intermediate stage of residual gas expander 11. The residual gas removed from the intermediate stage is represented by the reference number 16 in the representation in FIG. 1.

[0041] The installation represented in FIG. 2 for nitric acid production is formed to be substantially identical to the installation according to the first exemplary embodiment. In contrast to the first exemplary embodiment, a sealing gas flow 36 is supplied to the installation from the outside. Sealing gas flow 36 is guided through a heat exchanger 38 and then divided into two sub-flows 34 and 35, wherein a first sub-flow 34 is supplied to NO compressor 3 and a second sub-flow 35 is supplied to residual gas expander 11. Sealing gas flow 36 can be formed from primary air, secondary air, instrument air or installation air. Alternatively, an inert gas can be used as the sealing gas.

[0042] The installations described above for nitric acid production with an NO compressor 3 and a residual gas expander 11 comprise in each case sealing devices 24 for sealing rotatable shafts 26 of NO compressor 3 and of residual gas expander 11. The sealing devices encompass a first sealing chamber 51, which surrounds shaft 26 and comprises an inlet 44 for the supply of a sealing medium, and a second sealing chamber 52, which is separated from first sealing chamber 51 by a seal 41 and surrounds shaft 26 and comprises an outlet 45 for the discharge of the sealing medium, wherein the sealing medium is discharged out of second sealing chamber 52 by an extraction device 29, 31.

LIST OF REFERENCE NUMBERS

[0043] 1 Low-pressure part [0044] 2 Nitrogen monoxide [0045] 3 NO compressor [0046] 4 Compressed nitrogen monoxide [0047] 5 High-pressure part [0048] 6 Residual gas [0049] 7 Heat exchanger [0050] 8 Residual gas [0051] 9 Residual gas sub-flow [0052] 10 Residual gas sub-flow [0053] 11 Residual gas expander [0054] 16 Residual gas flow from intermediate stage [0055] 17 Residual gas sub-flow [0056] 18, 19 Extraction flow [0057] 20 Exhaust gas flow [0058] 21 Residual gas sub-flow [0059] 22 Extraction flow [0060] 23 Rotational axis [0061] 24 Sealing device [0062] 25 Inner space [0063] 26 Shaft [0064] 27 House [0065] 28 Jet stream [0066] 29 Extraction device [0067] 30 Jet stream [0068] 31 Extraction device [0069] 34, 35 Sub-flow [0070] 36 Sealing gas flow [0071] 37 Impeller [0072] 38 Heat exchanger [0073] 39 Extraction flow [0074] 40, 41, 42, 43 Seal [0075] 44 Inlet [0076] 45, 46 Outlet [0077] 51 First sealing chamber [0078] 52 Second sealing chamber [0079] 53 Third sealing chamber