Download - Centrifugal Compressors Overview

Centrifugal Centrifugal CompressorsCompressors

OverviewOverview

By / Eng. Alaa E. Omar

Content

•Applications

•Design Features

•Casing

•Barrel and internals

•Rotor and Impellers

•Sealing and sealing gas system

•Lube oil system and bearing

Centrifugal CompressorsCentrifugal Compressors

Definition:

A compressor is a device that transfers energy to a gaseous fluid for the purpose of raising the pressure of the fluid.


Application:

-Prime mover of fluid through the process.

-Gas transportation.

-Rise gas temperature to enhance the chemical reaction.


The centrifugal compressor system consist of:

-The compressor.

- Driver( Steam or Gas turbine Elect. motor ).

-Lube oil and seal oil system.


Vertically split / multistage / barrel type

Vertically split barrel type.


•Vertically split casing has a cylindrical shape, its open ends are covered by head covers sealed with O-rings.

•Is suitable for high pressure operation.

Theory of Operation A centrifugal

compressor acts on a gas by means of blades on a rotating impeller.

The rotary motion of the gas results in an outward velocity due to centrifugal forces.

The tangential component of thus outward velocity is then transferred to pressure by means of a diffuser.

Standard Compressor Series

Main Elements Consist of :

Inlet nozzle Inlet guide

vanes. Impellers Radial diffuser. Return channel. Collector volute Discharge

nozzle.

Main Elements

Casing The inlet nozzle

accelerates the gas stream and directs it into the inlet guide vanes which may be fixed or adjustable.

Impeller Design

Consist of a series of blades and attached to the shaft.

As the shaft rotates the centrifugal force generated by the rotating impeller forces gas to flow outward.

Impellers

Impeller types

Kinetic energy is imparted to the gas via the impeller by centrifugal forces.

The diffuser then reduces the velocity and converts the kinetic energy to pressure energy

Diffusers

Because of the rotational effects of the impeller, the gas travels through the diffuser in a spiral manner.

Therefore, before entering the next impeller, the flow must be straightened out by the return channel vanes.

Inter-stage Seal

Inter-stage seal:

Due to the pressure rise across successive compression stages, seals are required at the impeller eye and rotor shaft to prevent gas backflow from the discharge to inlet end of the casing

Rotor

•The shaft transmits the mechanical energy from the driver to the compressor.

Bundle

Shaft ends : Labyrinth seal Gas seal Oil seal Bearing


Shaft Sealing Shaft sealing is provided to

minimize the gas leakage along the shaft.

Shaft seal types: Labyrinth seal Fluid film seal Mechanical seal Dry gas seal

Labyrinth Seal Consist of a series of

a sharp edged circular fins generating flow resistance for rotating gas inside the casing.

The labyrinth seal has a small clearance along the rotating shaft and therefore a minute amount of gas does escape.

Oil Film Seal The seal oil enters the seal

between bushings, flow around the shaft and forms an oil film. This oil film prevents gas from escaping.

Dry Gas Seal Consists of a

static carbon ring located in a steel retainer and spring loaded against rotating tungsten carbide seal rings.

Dry Gas seal

•Sealing of the gas is achieved at the radial interface of the rotating and the stationary rings in a unique way.

•The sealing surfaces are lapped to a very high degree of flatness while the rotating ring has a series of spiral grooves machined into it’s running face.

Dry Gas Seal

Dry Gas Seal

Principle of Seat and Face

Dry Gas Seals

Grooves on rotating seat

Dry Gas Seal

Principle of Seat and Face

Lube Oil System The lube oil system consists of :

Oil reservoir. Oil pump. Oil cooler. Oil filter. Bearing. Overhead tank. Pressure regulator. Sight glass.

Fluid Film Bearing

Tilting pad journal bearing

The pads are fitted in a two piece bearing housing which positions them radially and axially.

The pads are held in the journal bearing housing by special pad stops.

Fluid Film Bearing

•The bearings are lubricated by oil from the main oil system.

•The oil is supplied via an hole in the pad stop pins into the spaces between the pads.

•Most of the oil is picked up by the rotating movement of the shaft and enters the space between the pads and the rotating shaft.The rest of the oil leaves the bearing housing axially and flows into the oil drain line.

Fluid Film Bearing

• Through the tilting action of the pads, oil wedges will be built up between the rotating shaft and the stationary bearing pads.

Fluid Film Bearing

Fluid Film Bearing

Thrust bearing

Is a double acting thrust bearing of the multiple pad, self aligning and equalizing type.

Fluid Film Bearing

The rotor is axially positioned by the thrust bearing, which also serves to absorb any axial force on the compressor.

The thrust bearing consists of:

-a steel rotating member ( thrust collar )

- -two sets of stationary pivoted Babbitt-faced segments ( thrust pads)

-load equalizing leveling plate