EP2326857A1

EP2326857A1 - Arrangement comprising a shaft seal

Info

Publication number: EP2326857A1
Application number: EP09782564A
Authority: EP
Inventors: Ludger Alfes
Original assignee: Siemens AG
Current assignee: Siemens AG
Priority date: 2008-09-25
Filing date: 2009-09-03
Publication date: 2011-06-01
Also published as: WO2010034605A1; CN102165229A; DE102008048942B4; EP2326858A1; EP2169282A1; DE102008048942A1; US20110189013A1; US8714907B2; CN102165228A; CN102165228B; US8647052B2; WO2010034601A1; US20110255966A1

Abstract

The invention relates to a shaft seal (SS) which comprises more than one sealing module (SM), at least one fluid supply (FF) and one fluid outlet (FS), an inner main seal (MS1) and an outer main seal (MS2) and a fluid outlet (FS1) between the two main seals (MS1, MS2). Conventional shaft seals of the above type require significant amounts of additional barrier fluid (SF) in regular intervals to ensure suitable pressure gradients. According to the invention, the inner main seal (MS1) is designed as a radial double seal (RDS) which is defined by two gas seals (DGS) having respective rotating sealing surfaces (RSS) and stationary sealing surfaces (SSS), said pair of sealing surfaces (SSP) being opposite each other in a sealing plane (SEP), and the two sealing planes extending relative to the shaft (S) in a substantially radial manner.

Description

description

Arrangement with a shaft seal

The invention relates to a shaft seal for sealing a gap of a passage of a shaft through a housing, wherein in the interior of the housing, a process fluid under a sealing pressure and outside of the housing is an ambient fluid under an ambient pressure, wherein the shaft seal more than a sealing module, at least one fluid supply and a fluid discharge, wherein the sealing modules comprise at least one inner main seal and an outer main seal and between the two main seals at least one fluid discharge is provided, by means of which a first discharge fluid is discharged. In addition, the invention also relates to an arrangement with a shaft seal of the aforementioned type.

Shaft seals of the aforementioned type are frequently used, in particular, on turbomachines which have a shaft led out of the housing, which allows the connection of a drive or driven-down drive. It is in the nature of the shaft seal that due to the relative movement of the shaft surface to the adjacent housing, a hundred percent tightness can not be achieved. Particularly in the case of toxic or explosive process fluids which are to be kept away from the environment by means of the shaft seal, the leakages must be carefully deduced. Also, for example, in steam or gas turbines, the process fluid is prevented by means of such a shaft seal to escape into the environment and the leakage of the shaft seal or the quantum of the suction has a direct impact on the resulting thermal efficiency. Minimizing the leaks of a

Shaft sealing is one of the most important tasks in the design of such machines. In turbocompressors, so-called tandem gas seals often take over the task of sealing the pressure chamber within the housing to the atmosphere. The tandem gas seals are non-contact seals and are lubricated with dry filtered barrier fluid.

A conventional arrangement with a shaft seal of the type mentioned above is shown schematically in FIG. A shaft S extends through a passage PT of a housing C. Inside the housing C is a process fluid PF under a sealing pressure PPF. The process fluid PF is conveyed to the sealing pressure PPF by means of a compressor CO. Outside the housing C, air AM is below an ambient pressure PAM. A gap G between the shaft S and the housing C in the region of the passage PT is sealed by means of a shaft seal SS. The shaft seal SS comprises a plurality of sealing modules SM, including two main seals, a first main seal MS1 and a second main seal MS2. The two main seals MS1, MS2 are designed as gas seals DG1, DG2 or dry gas seals DGS. Starting from the interior of the housing C, two labyrinth seals are initially provided, a first labyrinth seal LS1 and a second labyrinth seal LS2, between which a pressure increase blocking fluid SFP is introduced. The purpose of the labyrinth LS1 and the pressure-increasing blocking fluid SFP is to increase the sealing pressure to an at least required pressure level and are only required if the existing pressure in the compressor is lower than the minimum required pressure level. In addition, a barrier fluid is fed into the gap G between the first main seal MS1 and the second, outer labyrinth seal LS2. As a result of the feed line of the barrier fluid SF results through the first main seal MSL a mass flow to the outside and a mass flow through the labyrinth LS2 towards the compressor. This mass flow is usually relatively low and builds up no significant differential pressure in the labyrinth LS2. The mass flow of the pressure increase blocking fluid SFP is sized to coincide with the mass flow of the barrier fluid SF flowing through the labyrinth LS2, accumulates a differential pressure in the labyrinth LS1, which corresponds to the minimum required pressure level in addition to the pressure in the compressor. This mass flow flows back into the interior of the housing C. Between the first main seal MS1 and the second main seal MS2, a third labyrinth seal LS3 is provided. Between the third labyrinth seal LS3 and the second main seal MS2, an intermediate blocking fluid ISF is introduced into the gap G. While the barrier fluid SF is process fluid PF, the intermediate barrier fluid ISF is either an inert or inert gas or the surrounding medium, usually nitrogen.

Between the first main seal MS1 and the second main seal MS2, in particular the third labyrinth seal LS3, the mixture collecting there from the barrier fluid SF and the interlocking fluid ISF or from the process fluid and the inert fluid or ambient fluid becomes a subsequent treatment, not shown derived. The preparation can also be a torch, by means of which the mixture is flared. Outside the second main seal MS2 is often still an additional tandem arrangement of a labyrinth seal, consisting of two seals LS4, LS5, between which a separation fluid SPF is initiated. A mixture of the separation fluid SPF and the interstitial fluid ISF, which flows in the outward direction through the second main seal MS2 as a leak, is led by means of a second discharge EX2 to a treatment or also to a torch.

Below the seal arrangement, Fig. 1 shows the Durckverlauf over the axial direction, from which results the flow directions through the seals. The dry gas seals are not arbitrarily reversible in terms of flow. In this respect, under certain operating conditions, an increased amount of Druckanhebesperrfluid SFP must be supplied. The arrangement of the gas seal shown in Figure 1 is also referred to as a tandem gas seal. In the design of the tandem gas seal, with or without a labyrinth between the two main seals, the intermediate barrier fluid is only needed in the labyrinth type. An intermediate barrier fluid is normally nitrogen from an external source. Both subsets of the barrier fluid SF between the main seal MSL and the auxiliary shaft seal LS2 and subsets of the

Interlocking fluid ISF between the main seal MS2 and an adjacent additional shaft seal LS3 are supplied to the first derivative EXl, wherein the pressures, as in the pressure curve shown in Figure 1 below the schematic representation are selected such that the majority of the supplied fluid quantity passes into the first derivative EXl , A smaller part of the intermediate blocking fluid passes through the second main seal MS2 into the second outlet EX2. The auxiliary shaft seals LS4 and LS5 with the supplied separation fluid SPF essentially serves to shield the outer main seal MS2 from contamination of the surroundings AM, which may be contaminated by, for example, oil mist from an adjacent bearing. The separation fluid partly exits into the environment AM and partly it is discharged in the second discharge EX2. For the sealing module SM consisting of the

Additional shaft seals LS4, LS5 can also be used for coal rings or other types of seals.

At low sealing pressures it happens that the sealing pressure must be increased by means of the additional Druckanhebesperrfluids SFP in the first additional shaft seal LSL, so that a pressure gradient to the first derivative EXI is present. This is particularly because the first main seal MS1 designed as a gas seal always requires a pressure gradient of the space to be sealed or the sealing pressure in the outward direction so as not to interfere with the rotation of the shaft to be destroyed. Depending on how high the pressure has to be increased, this considerable amounts of Druckanhebesperrfluid SFP are required. This in turn significantly deteriorates the efficiency of the overall system.

The invention has therefore taken on the task of improving the arrangement with the shaft seal of the type mentioned in such a way that the need for sealing fluids decreases without resulting in losses in terms of tightness and safety of operation.

To solve the object of the invention, an arrangement of the type mentioned is proposed with the features of the characterizing part of claim 1.

Whenever the terms inward or outward, inside or outside are used, this directional indication refers to an increasing or decreasing proximity to the interior of the housing or the exterior of the housing.

The features according to the invention result in particular advantages. The amount of barrier fluid is greatly reduced since, compared to the conventional arrangement shown in FIG. 1, a labyrinth seal is no longer directly loaded with the barrier fluid, but the barrier fluid must first pass through a sealing surface pair. In addition, it can be dispensed with a pressure increase by means of Druckanhebesperrfluids at low sealing pressures, since the radial double seal a pressure drop of the entering barrier fluid needed on both sides, or generated. Due to the elimination of the pressure increase, the internal circulating amounts of fluid to be compressed are reduced and the volumetric efficiency of, for example, a compressor is improved. Finally, it becomes possible to realize sealing pressures below the ambient pressure. Since the radial double seals require only little axial space and in addition the option is opened to allow previously required additional shaft seals, can the rotor dynamics of the shaft are improved as a result of the shortening.

Furthermore, it is possible to select the pressure level in the first derivative EX1 so that a return of the fluid from the first derivative EXl back into the compressor process can be realized.

Preferably, the stationary support of the radial double seal is biased by means of an elastic element in the direction of the rotating carrier. In this way, the centrifugal force exposed construction of the rotor is less complicated.

The sealing surface pairs are preferably arranged coaxially, so that there is a simple and space-saving design.

An optimal operation of the invention

Sealing arrangement provides that the inner main seal is acted upon by process fluid as a barrier fluid.

The outer main seal may be formed as a simple dry gas seal. However, it is also preferable to use a radial double seal for the outer main seal, which is acted upon by an intermediate blocking fluid as barrier fluid. Depending on the type of medium to be compressed, the intermediate blocking fluid may be identical to the barrier fluid of the inner main seal or another fluid, for example nitrogen. Decisive is the guarantee that the outer main seal in each

Operating point on both sides has a positive pressure difference and thus results in a stable fluid film between the opposite sealing surfaces of the sealing surface pairs. Thus eliminates the need to accumulate a corresponding pressure in the first derivative, so that there is a minimum pressure difference to the outer main seal. An advantageous embodiment of the invention, in particular when the second main seal MS2 is designed as a simple dry gas seal, provides that between the two main seals MSl and MS2 an additional first additional shaft seal LS3 preferably a

Labyrinth shaft seal is arranged. In this way, it is ensured that no leaks of the first main seal MS1 reach the second derivative EX2 via the second main seal MS2. In the embodiment with this first additional shaft seal, it is expedient if the first barrier fluid drain is arranged on the inward side of this additional shaft seal between the two main seals.

An advantageous development of the invention provides that a supply of an intermediate blocking fluid ISF is provided between the outer main seal MS2 and this aforementioned additional shaft seal LS3.

For the same reasons as the first additional shaft seal between the two main seals can be arranged with advantage, it is expedient to provide a second additional shaft seal, preferably designed as a labyrinth shaft seal, inwardly of the inner main seal MS1. If the process fluid is loaded with particles or other dirt, it is expedient to provide a supply of a rinsing fluid, which is preferably purified process fluid, between the inner main seal and the second auxiliary shaft seal. This flushing fluid preferably has an overpressure of preferably 5 to 20 mbar compared to the process fluid.

For foreclosure of the sensitive shaft seal system, it may also be expedient if, in addition, two shaft seals, preferably labyrinth shaft seals, are arranged in succession outside the outer main seal, an inner third auxiliary shaft seal and an outer fourth additional shaft seal. The foreclosure becomes special effective when a supply of a separation fluid is provided between these two additional shaft seals. This separation fluid may be filtered ambient medium. Such an arrangement is particularly interesting if the whole of the outside

Sealing arrangement, for example, an oil storage is provided from the leaking oil mist can get into the seal assemblies and would lead to possibly dangerous fluid mixtures.

The supplied separation fluid can be conveniently derived between the outer main seal and the two successively arranged third and fourth additional shaft seals by means of a second derivative.

If necessary, the discharges can be supplied to a combustion in a common flare.

In the following the invention with reference to embodiments with reference to drawings is described in detail. In addition to the embodiments of the invention listed in the exemplary embodiments, the description of additional possible embodiments also results for the person skilled in the art. Show it:

Figure 1 is a schematic representation of a conventional arrangement.

FIG. 2 shows an exemplary representation of a radial double seal,

Each of an embodiment of an inventive arrangement in a schematic representation.

The arrows under sealing modules SM each indicate the flow direction which sets in nominal operation. Figure 2 shows a schematic representation of a radial double seal RDS, which seals a gap G between a shaft S and a housing C. In the region of a passage PT of the shaft S through the housing C, the shaft S is provided with a circumferential shoulder SC, which carries a rotating part of the radial double seal RDS. The radial double seal consists essentially of two radially successively arranged gas seals DGSl, DGS2, each having a rotating sealing surface RSS and a stationary sealing surface SSS, the corresponding two

Sealing surface pairs SSP result. Between the two sealing surface pairs SSP, a blocking fluid SF is fed into a circumferentially extending chamber SFC located there, which escapes due to the overpressure between the rotating sealing surface RSS and the stationary sealing surface SSS of the two sealing surface pairs SSP. The rotating sealing surfaces RSS and the stationary sealing surfaces SSS of the two sealing surface pairs SSP are firmly connected to each other by means of a common carrier RSUP, SSUP. The stationary carrier SSUP is biased by means of an elastic element EEL against the rotating carrier RSUP.

FIG. 3 shows an inventive construction of an arrangement comprising a shaft S, a housing C and a shaft seal SS comprising a plurality of sealing modules SM. The sealing modules include, starting from the interior of the housing C, a first auxiliary shaft seal LS1 designed as a labyrinth shaft seal, a main seal MS1, designed as a radial double seal according to FIG. 2, a second main seal MS2, designed as a simple dry gas seal and an arrangement of two additional shaft seals LS4, LS5, which as

Labyrinth shaft seals are arranged one behind the other. Inside the housing C there is a sealing pressure PPF of a process fluid PF. Between the first additional shaft seal

LS1 and the first main seal MS1, a barrier flushing fluid SPF is supplied, which is purified process fluid PF having an overpressure against the sealing pressure of 5 to 20 mbar. This supply prevents contamination of the entire seal assembly from a loaded with dirt process fluid PF. If the process fluid should be sufficiently clean, this additional shaft seal LS1, LS2 can be omitted. In the first main seal MS1 blocking fluid SF is supplied in the form of purified process fluid PF with an overpressure, so that an outflow through the two sealing surface pairs SSP of the radial double seal results both inward and outward. Between the first main seal MS1 and the second main seal MS2 is a first one

Discharge EXl, which derives the flowing out of the first main view MSl outward process fluid PF. Opposite the gap between the second main seal MS2 and the outward seals, the gap between the first main seal MSl and the second

Main seal MS2 on an overpressure, which is further reduced by the second main seal MS2, which is designed as a simple gas seal. Between the second main seal MS2 and the outermost seals there is a second drain EX2, which discharges a mixture of process fluid PF and fluid originating from the outwardly following seal combination. Outside the housing, the environment AM is under an ambient pressure PAM. Between the two additional shaft seals LS4 and LS5 at the outer end of the

Arrangement is a separation fluid SPPF supplied, which escapes in both directions and to prevent any contamination from the outside at the entrance to the assembly. The separation fluid SPPF is either the purified medium of the environment or an inert fluid, for example nitrogen.

In the figure 4, the arrangement of Figure 3 is supplemented by a third additional shaft seal LS3, which is designed as a labyrinth seal, between the two main seals MSL, MS2. The first derivative EX1 is located inwardly of this additional third auxiliary shaft seal LS3. Between the additional third additional shaft seal LS3 and the second main seal MS2, an intermediate blocking fluid ISF, for example nitrogen, is introduced. This ensures that no barrier fluid SF of the first main seal MSl can get to the second main seal MS2 and can be discharged as leakage in the derivative EX2.

5 shows an embodiment of the invention is shown, in which the second main seal MS2 is formed as a radial double seal RDS.

FIG. 6 shows the arrangement of FIG. 5 with a supplement to a third additional shaft seal LS3 between the two main seals MS1, MS2. The pressure curve shown in Figure 6 over the axial extent of

Sealing arrangement shows that the pressure P of the barrier fluid used SF is higher than the other pressures and accordingly always ensures a safe sealing effect in an operating condition. In particular, no pressure raising blocking fluid SFP is required.

Claims

claims

Shaft seal (SS) for sealing a gap (G) of a passage (PT) of a shaft (S) through a housing (C), wherein in the interior (IN) of the housing (C), a process fluid (PF) under a sealing pressure (PPF) and outside the housing (C) is an ambient fluid (AF) under an ambient pressure (PAF), wherein the shaft seal (SS) more than one sealing module (SM), at least one fluid supply (FF) and a

Fluid discharge (FS), wherein the sealing modules (SM) at least one inner main seal (MSL) and an outer main seal (MS2) and between the two main seals (MSL, MS2) at least one fluid discharge (FSL) is provided, by means of which a first Derivative fluid (FLEXI) is discharged, characterized in that at least the inner main seal (MSl) as a radial double seal (RDS) is formed, which is determined by two gas seals (DGS), each with a rotating sealing surface (RSS) and a stationary Sealing surface (SSS), which sealing surface pair (SSP) in each case in a sealing plane (SEP) is opposite, wherein the two sealing planes have a substantially to the shaft (S) radial extent, wherein a first

Sealing surface pair (SSP) of the two sealing surface pairs (SSP) is located on a larger radius than the second sealing surface pair (SSP) and wherein the standing sealing surfaces (SSS) and rotating sealing surfaces (RSS) of the two sealing surface pairs (SSP) in each case on a common carrier (RSUP, SSUP), namely a stationary carrier (SSUP) and a rotating carrier (RSUP), and the sealing surfaces (RSS, SSS) of the sealing surface pairs (SSP) are elastically braced against each other by either at least the stationary carrier (SSUP) or the rotating support (RSUP) is biased by means of an elastic element (EEL), wherein between the two sealing surface pairs (SSP) one in the circumferential direction extending barrier fluid chamber (SFC) is provided, which by means of a barrier fluid supply line (SFS) with barrier fluid (SF) can be acted upon.

Second shaft seal (SS) according to claim 1, wherein the stationary support (SSUP) is biased by means of the elastic element (EEL).

3. shaft seal (SS) according to claim 1 or 2, wherein the sealing surface pairs (SSP) are arranged coaxially to the axial extent of the shaft.

4. Shaft seal (SS) according to one of the preceding claims 1 to 3, wherein the inner main seal (MSL) with process fluid (PF) is acted upon as a barrier fluid (SF).

5. shaft seal (SS) according to at least one of the preceding claims 1 to 4, wherein the outer main seal (MS2) is formed as a simple dry gas seal.

Shaft seal (SS) according to one of the preceding claims 1 to 4, wherein the outer main seal (MS2) as a radial double seal (RDS) is formed, which is acted upon with an intermediate blocking fluid (ISF) as a barrier fluid (SF).

7. shaft seal (SS) according to at least one of the preceding claims 1 to 6, wherein between the two main seals (MSL, MS2), a third additional shaft seal (LS3) is arranged.

8. shaft seal (SS) according to claim 7, wherein the first fluid drain (EXL) on the inside of the third additional shaft seal (LS3) is arranged.

Shaft seal (SS) according to at least one of the preceding claims 1 to 8, wherein between the outer main shaft seal (MSL) and the third auxiliary shaft seal (LS3) is provided with the supply of an intermediate blocking fluid (ISF).

10. Shaft seal (SS) according to at least one of the preceding claims 1 to 9, wherein the inside of the inner main shaft seal (MSL) a second additional shaft seal (LSL LS2) is arranged.

Shaft seal (SS) according to claim 10, wherein between the inner main seal (MSL) and the second auxiliary shaft seal (LSL), a supply of a flushing fluid (SPF) is provided.

12. shaft seal (SS) according to at least one of the preceding claims 1 to 11, wherein externally the outer main seal (MSL) two additional shaft seals, (LS4, LS5) are arranged one behind the other, an inner fourth additional shaft seal (LS4) and an outer fifth additional shaft seal (LS5 ).

13. Shaft seal (SS) according to claim 12, wherein between the fourth additional shaft seal (LS4) and the fifth additional shaft seal (LS5), a supply line of a separation fluid (SPPF) is arranged.

14 shaft seal (SS) according to at least one of the preceding claims 12 or 13, wherein between the outer main seal (MSL) and the fourth auxiliary shaft seal (LS4), a second discharge line (EX2) is provided.

15. shaft seal (SS) according to at least one of the preceding claims 1 to 14, wherein the first derivative (EXl) and the second derivative (EX2) in a common discharge (EX) open.

16. Arrangement with a shaft seal (SS) according to at least one of the preceding claims.