Shaft sealing arrangement for a pump for delivering hot fluids

Abstract

A shaft sealing arrangement for a pump for delivering hot fluids includes a dynamic shaft seal (4), in particular a slide ring seal, in order to seal a rotatable shaft (2) relative to a housing (1), and a cooling ring (5) which is mounted in front of the dynamic shaft seal (4) in the direction of the pump interior and which surrounds the shaft (2) at a small spacing. The shaft sealing arrangement further includes an additional seal (8) which seals the shaft (2) in the region of the cooling ring (5) in order to reduce the feed of hot fluid into the gap between the shaft (2) and the cooling ring (5), with the additional seal (8) being formed as a brush seal.

Description

[0001] The invention relates to a shaft sealing arrangement for a pump for delivering hot fluids. The shaft sealing arrangement is arranged in a housing and includes a dynamic shaft seal, in particular a slide ring seal, to seal a rotatable shaft relative to the housing, and a cooling ring which is mounted in front of the dynamic shaft seal in the direction of the pump interior and which surrounds the shaft at a small spacing.

[0002] Centrifugal pumps are normally used to deliver hot fluids. Such a pump includes a pump shaft fitted with impellers which is rotatably arranged in a housing, and dynamic shaft seals in order to seal the shaft towards the housing. Pumps for delivering hot fluids further contain cooling stretches which are mounted in front of the dynamic shaft seals in the direction of the pump interior in order to lower the temperature so far that standard shaft seals can be used. In larger pumps such as in boiler feed pumps, mostly water-cooled cooling rings are found as the cooling stretches which surround the shaft at a small spacing. The gap between the shaft and the cooling ring is dimensioned such that normally no contact takes place between the shaft and the cooling ring. The gap is thus sufficiently wide that an exchange of fluid can take place between the gap and the adjoining pump interior. As long as the shaft rotates, the cooling action of the cooling ring is constant over the periphery of the shaft. However, if the shaft is stationary, a thermal flow is formed in the gap between the shaft and the cooling ring by hot fluid rising into the upper part of the gap and cooled fluid falling into the lower part. This effect, which is known as the thermosyphon circulation, results in a curving of the shaft as a consequence of the irregular temperature distribution. As a result of this, the strain of the bearing parts, such as of the relief piston for the compensation of the axial pressure, increases and additional contact points occur between rotating and non-rotating parts of the pump. The start-up of the pump is thereby made more difficult and an increased wear of the affected pump parts results. To avoid the above-described thermosyphon circulation during the standstill of the pump, intermediate insulation spaces are provided in the cooling ring and at the shaft periphery. For example, so-called thermo-sleeves are attached to the shaft periphery; these are shaft protection sleeves with an air gap between the shaft and the sleeve. The said intermediate insulation spaces, however, are frequently not sufficient to prevent the thermosyphon circulation.

[0003] It is the underlying object of the invention to completely prevent the mentioned thermosyphon circulation in the gap between the shaft and the cooling ring, which occurs during the standstill of the pump, and to avoid the disadvantages associated therewith.

[0004] This object is satisfied in accordance with the invention by the shaft sealing arrangements defined in independent claims 1 and 11.

[0005] The shaft sealing arrangement in accordance with the invention, which is arranged in a housing, includes—in a first embodiment—a dynamic wave seal, in particular a slide ring seal, to seal a rotatable shaft relative to the housing, and a cooling ring which is mounted in front of the dynamic shaft seal in the direction of the pump interior and which surrounds the shaft at a small spacing, as well as an additional seal between the housing and the shaft and/or between the housing and a relief piston for the axial pressure and/or between the cooling ring and a shaft to reduce the supply of hot fluid into the gap between the shaft and the cooling ring, with the additional seal being formed as a brush seal which includes a plurality of closely arranged fibres, bristles and/or wires as sealing elements which are distributed in a ring-like manner and are secured and extend towards the surface to be sealed with their free ends.

[0006] In an advantageous manner, the fibres, bristles and/or wires of the brush seal are flexible or are secured flexibly and are arranged at an acute angle to the shaft surface, with the tip of the angle pointing in the running direction. The length of the fibres, bristles and/or wires are advantageously pre-determined such that they are ground to a suitable length by the rotating shaft.

[0007] In a preferred variant, the brush seal is arranged close to the side boundary of the cooling ring, towards the pump interior. In a further preferred embodiment, the cooling ring is integrated in the housing. In a further preferred embodiment, the shaft is provided with a thermo-sleeve in the region of the cooling ring and/or in the region of the brush seal.

[0008] A pump for delivering hot fluid having a shaft sealing arrangement in accordance with the present invention is the object of claims 8 and 15. The invention is advantageously used with boiler feed pumps which are designed, for example, for fluid temperatures from 150 to 250° C. and for pressures of 60 to 360 bar.

[0009] In a variant, the shaft sealing arrangement for a pump for delivering hot fluids includes a dynamic shaft seal to seal a rotatable shaft relative to a housing and a cooling ring which is mounted in front of the dynamic shaft seal in the direction of the pump interior and which surrounds the shaft at a small spacing. The shaft sealing arrangement furthermore includes an additional seal which seals the shaft in the region of the cooling ring in order to reduce the supply of hot fluid into the gap between the shaft and the cooling ring, with the additional seal being formed as a brush seal.

[0010] In a second embodiment, the shaft sealing arrangement in accordance with the invention is arranged in a housing and includes a dynamic shaft seal in order to seal a rotatable shaft relative to the housing, with the dynamic shaft seal being designed as a brush sealing arrangement which includes a plurality of individual brush seals. The brush seals include a plurality of closely arranged fibres, bristles and/or wires as sealing elements which are distributed and secured in a ring-like manner and extend towards the surface to be sealed with their free ends. The brush sealing arrangement advantageously includes a section in which a barrier liquid and/or a flushing liquid is fed. The barrier liquid and/or flushing liquid advantageously has a lower temperature than the delivered fluids to achieve a cooling action. Advantageously, a plurality of ring-like brush seals of the brush sealing arrangement are arranged next to one another as a packing.

[0011] Further advantageous embodiments can be seen from the dependent claims and the drawing.

[0012] The invention will be explained in more detail in the following with reference to the embodiments and to the drawing. There are shown:

[0013] FIG. 1 a longitudinal section through a boiler feed pump;

[0014] FIG. 2 a longitudinal section through a shaft sealing arrangement in accordance with a first embodiment of the present invention; and

[0015] FIG. 3 a cross-section through a shaft sealing arrangement in accordance with the first embodiment, with the sectional plane having been laid in the brush seal;

[0016] FIG. 4 a longitudinal section through a shaft sealing arrangement in accordance with a second embodiment of the present invention; and

[0017] FIG. 4a a cross-section through a brush seal (detailed view).

[0018] FIG. 2 shows a longitudinal section through a shaft sealing arrangement in accordance with a first embodiment of the present invention. In FIG. 2, the reference numeral 1 designates a housing and the reference numeral 2 a shaft which is rotatably arranged in the housing 1. The bearings required for this are not shown in FIG. 2. The shaft sealing arrangement in accordance with the present embodiment includes a dynamic shaft seal 4 to seal the shaft 2 relative to the housing 1. The dynamic shaft seal 4 can, for example, be designed as a single-action or double-action slide ring seal, as a balanced slide ring seal, as a floating seal, as a brush sealing arrangement which includes a plurality of individual brush seals, or as a fixed restrictor or the like. In addition to the actual shaft seal, a quench seal can be used, that is a sealing section through which a barrier liquid or a flushing liquid flows and which is sealed, for example, by simple radial sealing rings. The shaft sealing arrangement in accordance with the present embodiment furthermore includes a cooling ring 5 which is mounted in front of the dynamic shaft seal 4 in the direction of the pump interior, that is towards the hot part of the pump, and which surrounds the shaft 2 at a small spacing in order to reduce the temperature so far, for example to approximately 60° C., that the dynamic shaft sealing 4 can be designed as a standard seal for medium temperatures. In the embodiment, the cooling ring 5 is integrated in the housing 1 and includes a ring-like, water-cooled chamber 6 and a ring-like air gap 7 for the thermal insulation of the cooling ring 5. The shaft sealing arrangement in accordance with the present embodiment furthermore includes an additional seal 8 which can be arranged at the hot side of the cooling ring 5, for example close to the side boundary of the cooling ring 5, towards the pump interior in order to reduce the feed of hot fluid into the gap between the shaft 2 and the cooling ring 5.

[0019] The seal 8 can also be arranged between the shaft 2 and a projecting part of the housing 1 which is mounted in front of the cooling ring or, if a relief piston for the axial pressure is present, between the relief piston and the housing 1. It is furthermore possible to provide a plurality of seals 8. In the shaft sealing arrangement in accordance with the invention, the additional seal 8 is formed as a brush seal which includes a plurality of closely arranged fibres, bristles and/or wires as sealing elements which are distributed and secured in a ring-like manner and extend with their free ends towards the surface of the shaft 2 to be sealed. The shaft 2 is expediently provided with a thermo-sleeve 9 in the region of the additional seal 8 and/or in the region of the cooling ring 5. An air gap can be provided between the thermo-sleeve 9 and the shaft 2 for the thermal insulation.

[0020] FIG. 3 shows a cross-section through a shaft sealing arrangement in accordance with the embodiment, with the sectional plane having been placed in the brush seal. As can be seen from FIG. 3, a thermo-sleeve 9 is arranged on a shaft 2. An additional seal 8, which is let into a cooling ring 5, surrounds the thermo-sleeve 9 such that the shaft 2 is sealed towards the cooling ring 5. In the shaft sealing arrangement in accordance with the invention, the additional seal 8 is formed as a brush seal which includes a plurality of closely arranged fibres, bristles and/or wires, which are distributed and secured in ring-like manner and which extend with their free ends towards the surface to be sealed, that is, in the present embodiment, towards the surface of the thermo-sleeve 9. The section in FIG. 3 has been laid such that the fibres, bristles and/or wires of the seal 8 are visible. The fibres, bristles and/or wires of the brush seal are advantageously flexible and/or flexibly secured and arranged at an acute angle to the shaft surface, with the tip of the angle extending in the running direction 12 of the shaft 2. The length of the fibres, bristles and/or wires is advantageously pre-determined such that they are ground to a suitable length by the rotating thermo-sleeve 9 and/or the shaft 2 and/or a relief piston 10 drawn in FIG. 1.

[0021] Trials with pumps for delivering hot fluids such as boiler feed pumps have shown that the thermosyphon circulation, which otherwise occurs in the gap between the shaft and the cooling ring during the standstill of the hot pump, can be practically fully suppressed with the aid of the shaft sealing arrangement described above. The disadvantages associated with the said thermosyphon circulation such as curving of the shaft at standstill, startup problems and increased wear at the contact points between rotating and non-rotating parts of the pump are thus also avoided. The use of the shaft sealing arrangement in accordance with the invention is a simple and cost-favourable measure to prevent the said thermosyphon circulation.

[0022] FIG. 4 shows a longitudinal section through a shaft sealing arrangement in accordance with a second embodiment of the present invention. In FIG. 4, the reference numeral 21 designates a housing and the reference numeral 22 a shaft which is rotatably arranged in the housing 21. The bearings required for this are not shown in FIG. 4. The shaft sealing arrangement in accordance with the present embodiment includes a dynamic shaft seal to seal the shaft relative to the housing 21, with the dynamic shaft seal being designed as a brush seal arrangement 28 which includes a plurality of individual brush seals 28′. A detailed view of a cross-section through an individual brush seal 28′ is shown in FIG. 4a. The brush seals 28′ include a plurality of closely arranged fibres, bristles and/or wires 28a as sealing elements which are distributed and secured in ring-like manner and extend with their free ends towards the surface to be sealed. In addition to the individual brush seals, the brush seal arrangement 28 can include a quench seal, that is a seal section through which a barrier liquid or a flushing liquid flows. For this purpose, the brush sealing arrangement 28 in the present embodiment includes a feed line 26a and a discharge line 26b for the barrier liquid and/or flushing liquid. The barrier liquid and/or flushing liquid advantageously has a lower temperature than the delivered fluids in order to achieve the cooling action. A plurality of ring-like brush seals 28′ of the brush sealing arrangement 28 are advantageously arranged next to one another as a packing. The shaft 22 is expediently provided with a thermo-sleeve 29 in the region of the brush sealing arrangement 28. An insulation gap can be provided between the thermo-sleeve 29 and the shaft 22 for the thermal insulation.

[0023] In a preferred variant, the shaft sealing arrangement in accordance with the second embodiment, and in particular the dynamic shaft seal, that is the brush sealing arrangement 28 or parts thereof, acts as a cooling stretch. Brush seals are exceptionally suitable for the dissipation of heat both from the shaft to be sealed and from fluids inside the seal, if the fibres, bristles and/or wires of the brush seal consist of material such as metal with good thermal conductive properties. The fibres, bristles and/or wires in this case form a large metallic surface which is opposite a small fluid volume inside the seal. A thermosyphon circulation is practically suppressed under these circumstances and the problems associated with the thermosyphon circulation are avoided.

Claims

1. A shaft sealing arrangement for a pump for delivering hot fluids, wherein the shaft sealing arrangement is arranged in a housing (1) and includes a dynamic shaft seal (4), in particular a slide ring seal, in order to seal a rotatable shaft (2) relative to the housing (1), and a cooling ring (5) which is mounted in front of the dynamic shaft seal (4) in the direction of the pump interior and which surrounds the shaft (2) at a small spacing, characterized in that the shaft sealing arrangement includes an additional seal (8) between the housing (1) and the shaft (2) and/or between the housing (1) and a relief piston (10) for the axial pressure and/or between the cooling ring (5) and the shaft (2) in order to reduce the feed of hot fluid into the gap between the shaft (2) and the cooling ring (5); and in that the additional seal (8) is formed as a brush seal which includes a plurality of closely arranged fibres, bristles and/or wires as sealing elements which are distributed and secured in ring-like manner and extend with their free ends towards the shaft surface to be sealed.

2. A shaft sealing arrangement in accordance with claim 1, wherein the fibres, bristles and/or wires of the brush seal (8) are flexible and/or are flexibly secured.

3. A shaft sealing arrangement in accordance with claim 1 or claim 2, wherein the fibres, bristles and/or wires of the brush seal (8) are arranged at an acute angle to the shaft surface and the tip of the angle extends in the running direction (12) of the shaft (2).

4. A shaft sealing arrangement in accordance with any one of claims 1 to 3, wherein the length of the fibres, bristles and/or wires of the brush seal (8) is pre-determined such that they can be ground to a suitable length by the rotating shaft (2).

5. A shaft sealing arrangement in accordance with any one of claims 1 to 4, wherein the brush seal (8) is arranged close to the side boundary of the cooling ring (5), towards the pump interior.

6. A shaft sealing arrangement in accordance with any one of claims 1 to 5, wherein the cooling ring (5) is integrated in the housing (1).

7. A shaft sealing arrangement in accordance with any one of claims 1 to 6, wherein the shaft (2) is provided with a thermo-sleeve (9) in the region of the cooling ring (5) and/or in the region of the brush seal (8).

8. A pump for delivering hot fluids having a shaft sealing arrangement in accordance with any one of claims 1 to 7.

9. A pump in accordance with claim 8, wherein the pump is designed as a boiler feed pump.

10. A pump in accordance with claim 8 or claim 9, wherein the pump is designed for fluid temperatures from 150 to 250° C. and for pressures from 60 to 360 bar.

11. A shaft sealing arrangement for a pump for delivering hot fluids, wherein the shaft sealing arrangement is arranged in a housing (21) and includes a dynamic shaft seal in order to seal a rotatable shaft (22) relative to the housing (21), characterised in that the dynamic shaft seal is designed as a brush sealing arrangement (28) which includes a plurality of individual brush seals (28′), wherein the brush seals (28′) include a plurality of closely arranged fibres, brushes and/or wires (28a) which are distributed and secured in ring-like manner and which extend with their free ends towards the shaft surface to be sealed.

12. A shaft sealing arrangement in accordance with claim 11, characterised in that the brush sealing arrangement (28) includes a section through which a barrier liquid and/or a flushing liquid flow.

13. A shaft sealing arrangement in accordance with claim 12, wherein the barrier liquid and/or the flushing liquid has a lower temperature than the delivered fluids to achieve a cooling action.

14. A shaft sealing arrangement in accordance with any one of claims 11 to 13, wherein a plurality of ring-like brush seals (28′) of the brush sealing arrangement are arranged next to one another as a packing.

15. A pump for delivering hot fluids having a shaft sealing arrangement in accordance with any one of claims 11 to 14.