Compressors - Training sessions

COMPRESSORS- TRAINING SESSION

WHAT IS A COMPRESSOR?

A device used for pumping compressible fluids.

i.e. Air , gas and Steam

Compressor is a mechanical device that increases the pressure

by reducing volume.

Compressors are similar to pumps: both increase the pressure

on a fluid and both can transport the fluid through a pipe. As

gases are compressible, the compressor also reduces the volume

of a gas. Liquids are relatively incompressible, the main action

of a pump is to pressurize and transport liquids

COMPRESSOR

PRESSURE RATIO

GAS

Suction Pressure = PsSuction Temperature = TsSuction Velocity = Us

GAS

Discharge Pressure = PdDischarge Temperature = TdDischarge Velocity = Ud

Compressor = Black Box to increase Gas Pressure

a) Principle of operation

b) Type of construction

c) Staging

d) Service duty

e) Lubricated/ non lubricated

Compressor ClassificationBased on

Types of Compressors

• Reciprocating

• Rotary

• Centrifugal

• Axial

Rotary Compressors

Screw

Sliding Vane

Twin Lobe

Liquid Ring

Selection of compressors

Parameters for selection of compressor- Application:

Gas handled:

Gas analysis:

Flow rate:

Suction Pressure :

Suction Temperature:

Mol wt. of Gas:

Compressibility

Discharge Pressure:

Drive System:

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Selection of compressor

Typical Reciprocating Compressor

Centrifugal Compressor

AXIAL COMPRESSORS

Cut-view of Screw Compressor

HOW

COMPRESSORS

WORK?

Reciprocating Compressor

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Centrifugal Compressor

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Casing

Diaphragm

Impellers

Sealing Elements

Balancing drum

Bearings

Parts of centrifugal compressor

Casing:

It is the housing of the compressor, in which all components were intacted.

There are two types of casing

1. Horizontal Split

2. Vertical Split

Horizontal Split:

Centrifugal compressors with horizontal split casings typically permit internal

of around 700psi (70 bars) with flow rate of around 300,000 Nm3/hr at low

pressure.

Vertical split or Barrel type compressor

Above 700psi horizontal split casing lose their sealing capability, resulting in an

increased in potential for the escape of process gas. Hence vertical casing is more

preferred for high pressure application.

Based on the nozzle arrangement:

Straight through:

It is the general arrangement of compressor. In which the casing consisting of two

nozzles, one is inlet and the other one is outlet. gas enters at the inlet nozzle passes

through one or more stages of compression and leave through the discharge nozzle in

to the piping system.

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Impeller:

Impeller is the heart of the compressor. In which the mechanical energy (rotary motion)

of the rotor is converted in to kinetic energy of the process fluid (compressing fluid

There are three types of impellers

Open impeller

Semi open impeller

Closed impeller

Open impellers have the vanes positioned radial direction and have no enclosing covers

on either front or back side.

Semi open impellers have the vanes positioned in a radial or backward leaning direction

and have a cover on the back side with extended to the periphery of the vanes.

Closed impellers have enclosed cover on both front and back side. this is the most

common type in large processing compressors. The blades are usually backward leaning

and in some special cases radial curved vanes

Diaphragm:

It is the stationary component of the centrifugal compressor. It consisting of two

parts one is the diffuser and the return guide vanes. Normally around 2/3 of

kinetic of gas is converted in to pressure energy in the impeller itself and the

remaining 1/3 of energy conversion is takes place in the diffuser as shown below.

Cross section view of Diaphragm

After conversion of kinetic energy in to pressure energy in the

diffuser the gas pass through the return guide vanes. The function

of return guide vanes is to guide the gas to the next stage of

impeller with laminar flow.

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Radial Bearing:

Radial bearing of the centrifugal compressor are force lubricated. For the

ease of maintenance the bearing are horizontal split with replaceable

Babbitt lined pads. Number of pad in the radial bearing is depending

upon the speed and load condition of the compressor.

Thrust bearing:

The main purpose of the bearing is to take the thrust load produced in

the rotor. Tilting pad is the most common type of bearing used in

centrifugal compressor. Flat land, tapper land , kingsbury and Michel

bearings are used by most of the manufacture , the selection of bearing

is depend up the thrust load produced by the rotor.

Sealing system

Types

1.Liquid film seals

2.Labyrinth Type seals

3.Mechanical seals

4.Injection &Extraction seals

5.Dry gas seals

1. Liquid film seals: This system is used when the gas medium is poisonous,

inflammable and expensive and no external leakage is permitted. The principle of this sealing is that high pressure oil is injected in between a set of close clearance seal rings mounted on shaft ends. The seal rings are free floating type with white metalled bore. The oil leakage through LP side is recirculated through the oil system and HP leakage is recovered by automatic traps are re-used after separating dissolved gases.

This system is employed for gases like Air, Nitrogen. The amount of gas

leaking to ambient is reduced by selecting adequate number of

labyrinth fins. Some of the developments in a labyrinth type seals are

stepped type seals, honey comb type and turbine type.

LABYRINTH SEALS

In this type of seals the carbon-rings forming part of stator part

is kept in continuous contact with a rotating collar. The contact

surfaces are lubricated either by a cool buffer gas or

lubricating oil. These seals are very effective means of

providing shaft sealings.

Mechanical Seals

For gases like oxygen, raw gas and other explosive, corrosive, media the

sealing has to be perfect and where sealing medium like oil cannot be

used, the above sealing system is selected. The principle of this sealing is

that vacuum is created by a ejector at the shaft ends which sucks the

gases and thus prevents any outward leakage of the contained gas.

INJECTION EXTRACTION SEALS

Today the preferred choice is the dry-running, gas-lubricated seal over

conventional seals. A gas-lubricated mechanical seal necessarily needs a

gas supply system to ensure pressurizations of the seal with clean process

gas or external gas.

Dry gas seals

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Single seal arrangement

Single seal is used for the compressors, which have lower sealing pressures

and where a small leakage of gas medium can be tolerated. The single seal is

particularly advantageous as they occupy less space at compressor ends.

Double arrangement

A double arrangement is a sealing system, which reliably prevents product gas

escaping to the surroundings. It involves feeding a buffer gas, e.g. nitrogen,

between the seals at a higher pressure than the product pressure.

Any questions?

THANK YOU ALL THE BEST