Labyrinth compressors

The labyrinth compressor is suitable for gases of higher density (molecular mass > 15 kg / kmol). The labyrinth-seal of the piston (see Section 4.1.5 ) is non-contacting, operates without... 

Labyrinth compressors are normally built vertical, with a multistage (4 stages up to around 200 bar) arrangement and with separate open- or closed- (flushed) lantern housings, for... 

The leakage-flow of non-contact gap and labyrinth seals can be considerable, and must be recycled internally. It should be noted that labyrinth compressors use this type of seal on the rods, also. 

Nitrous gas compressor with air-sealed labyrinth shaft seals... 

Gas compressor steam cleaning facility with steam injection in the compressor suction main and in the discharge-side labyrinth shaft seal... 

Obviously, oil leakage may be caused by leaking mechanical seals. In turboexpander compressors, however, the most common cause is improperly designed labyrinth seals. Tapered labyrinth designs seem more prone to suffer from this defect. 

Damage to the labyrinth requires replacement of the expander heat barrier or compressor shaft seal. A replacement design (Figure 5-6) uses a replaceable stainless-steel labyrinth mounted on the shaft. Because the seal is not tapered, axial movement of the shaft has little or no measurable effect on seal gas flowrates. Each labyrinth has an integral oil slinger incorporated into the design. Also, each rotating... 

Figure 6-20. Cross-section of turboexpander compressor with AMB and labyrinth seal.

Gas compressors operating on highly toxic or flammable gases may require redundant systems to assure no leakages. In many applications, such as refrigeration gas, buffer seals are required with the liquid-buffered face seal. A popular technique is to use a buffered labyrinth seal with a liquid seal. 

An unusual nonlubed compressor is a labyrinth piston compressor, shown in Figure 3-1. The piston does not touch the sides of the cylinder... 

Figure 3-1. Labyrinth piston compressor. This non-iubed piston s circumferential labyrinths operate with a close clearance to the cylinder wall instead of rubbing. Courtesy of Sulzer)...

In dry compressors, shaft end seals are generally one of five type.s. These are labyrinth, restrictive ring, mechanical contact, liquid film, and dry gas seal. The labyrinth type is the most simple but has the highest leakage. The labyrinth seal is generally ported at an axial point between the seals in order to use an eductor or ejector to control leakage and direct it to the suction or a suitable disposal area. Alternatively, a buffer gas is used to prevent the loss of process gas. Appendix D presents a calculation method for use with labyrinth seals. 

Figure 5-48, J-strip type labyrinth seal. Courtesty ofA-C Compressor Corpmtiofi)...

Because most axial compressors are in air service, most are equipped with labyrinth type end seals. There are no interstage seals in the machines with unshrouded stator blades. The balance piston seal, a labyrinth type, is the only internal seal. There is no reason that axials cannot use some of the other seals as described in Chapter 5, such as the controlled leakage or the mechanical contact type, if the gas being handled by the compressor needs a more positive seal. If there is any prob-... 

When oil buffered seals are used, oil will move past an inner seal toward the process side of the compressor. The oil is prevented from moving into the compressor by a set of labyrinths and is captured in an inner drain cavity. From the cavity, it is piped to the outside where it is collected in either a pot or trap. Figure 8-13 shows several alternative arrangements and equipment. The user must choose between automatic or manual drainers. If the gas from the top of the drainers is to be directly returned to the compressor, it is important that mist eliminators be used. The oil collected in the drainers is reclaimed or disposed of, based on the level of contamination and the user s disposal practices. 

Figure D-4. Residual energy factors for straight labyrinths. (Reprinted by permission and courtesy of A-C Compressor Corporation)...

As the result of some problems with a compressor, changes were made to the design of a shaft labyrinth. A new one was ordered and installed, but a spare of the old design was left in the store. Eight years later, after the staff had changed, the part had to be replaced. You ve guessed what happened the old spare was withdrawn from the store and installed. 

Finally, there are many opportunities in the typical process for air or nitrogen to enter the gas stream. These have been described elsewhere [1], and here we mention by way of example the gas (nitrogen or dry air) used to pad the labyrinth seals on the typical centrifugal chlorine compressor. 

Rotor Thrust Problems Thrust loads in compressors due to aerodynamic forces are affected by impeller geometry, by pressure rise through the compressor, and by internal leakage due to labyrinth clearances. The impeller thrust is calculated by using correction factors to account for internal leakage, and a balance piston size is selected to compensate for the impeller thrust load. The common assumptions made in the calculation are... 

Fig. 4.1-29. Power range of various compressor types for high-pressure [24], D, Diaphragm compressor PI, Piston compressor, dry running (piston ring, labyrinth) P2, Piston compressor, lubricated (piston ring) P3, Ultra-high-pressure compressor, lubricated (plunger piston) TR, Radial turbo-compressor TA, Axial turbo-compressor S, Screw compressor.

Fig. 4.1-30. Vertical labyrinth piston compressor, longitudinal section (adopted from SUL-ZER)...

Non-contact seals with defined narrow clearances, such as labyrinth seals in turbo-machines (Fig. 4.1-47 A), are less problematic owing to the relatively low differential pressures however, the fluid should not have an erosive effect. Differential pressures up to several hundred bar occur at the axial-thrust compensation pistons of centrifugal pumps and compressors, but the fluid expansion is distributed over the many labyrinth stages. 

With dry-running, or sparsely lubricated piston compressors, the use of piston rings made of PTFE composites (Fig. 4.1-49) has proved to be effective as an alternative to non-contact labyrinth seals, but without any limitations with regard to the gas properties. 

Sel iiion of Compressor Equipment, Compressors for such gas processes as liquid-air separation, hydrogenation, and desulfurization must be non-lubricated to avoid possible explosive reaction with lubricating oils. Graphite rings are used in reciprocating compressors, and labyrinth or... 

Three different compressors have been used with the refrigerator, with varying results. Two of the compressors used were horizontal machines with glass- and carbon-impregnated Teflon rings and packings, while the third compressor is a vertical machine using a labyrinth... 

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