An Introduction to Compression Equipment

8/7/2019 An Introduction to Compression Equipment

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AN INTRODUCTION TO

COMPRESSION EQUIPMENT
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An Introduction to Compression Equipment

From the earliestrecorded times, man

has used the air

around him to drive

his sailing ships andturn the blades of his

windmills.


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Sailors and shipbuilders knewthrough countless years of

trial and error how to cut and

set a sail for maximum

efficiency. Why the pressureand flow of air made one

shape better than another was

of little interest to them.


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The air was then made to "magically open and close"

temple doors to the wonderments of the assembled rulers

and common people. Here again the why was no practicalvalue in the eyes of these people, and therefore did not

particularly interest them.

Early Egyptian writings tell of Priests using simple bellowsto compress air.


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It wasn't until the early to mid 17th century that manstarted to recognize the importance of the world around

him. At this time his knowledge of the air around him

began to increase significantly.

Spurred by the scientific awakening of the Renaissance,"natural philosophers" as scientists were then called,

began to dispel the errors and superstitions which for the

centuries had been divine truths.


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The Flemish Alchemist, Van Helmont,suspected from his study from the vapors

given off by fermenting fruit juices that the air

was not composed of a single element, but

that it might be a compound or mixture ofsubstances.

Henry Cavendish, was among the first to

establish that air was indeed a mixture of at

least 4 chemically different gases. In theprocess, he discovered hydrogen.


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Robert Boyle, an English physicist in the laterhalf of the 17th century, discovered the laws

governing the relationship between air

pressure to volume

The great Frensh chemist, AntoineLavoisier was set the proportions of oxygen

to nitrogen in air, and proved that the oxygen

content was essential to animal life.

Alexandre Charles discovered the laws governing the

relationship ofair pressure and temperature.


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Evangelista Torricelli in about 1630discovered the principle of the barometerby

being the first to measure the weight of the

atmosphere. In an elegant experiment, he

found it to be equivalent to a column of

mercury 30 inches high.


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Air, when compressed, represents apotential energy that can be used in a

tremendous variety of ways.

Man began to compress air and apply it

to a widespread and diverse uses about100 years ago.

Early compressors were steam driven, but in other respects

were essentially the same as today's models, differing only

in refinement of materials and tolerances.


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What is a compressor?


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A compressor is a device used to increase the pressure of acompressiblefluid.

In

letpressur e

-

0

+

Disch

argepressur

e

Sub atmospheric

Atmospheric

High level

Compressor


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Compressor


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The fluid can be any compressible fluid;

either gas or vapor and can have a wide

molecular weight range.

What does this mean?


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It means that, to selection and design of anycompressor, the fundamental is a knowledge of the basic

properties of the gas or gases being compressed.

2

352

Hydrogen

Uranium hexafluoride

Molecu

larwei g

htran

g


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Compressor

Station

Compressor

Station

Production32,000 Compressors

Processing5,000 Compressors

Transmission & Storage

8,500 Compressors

Distribution 0 Compressors

Compressor

Station


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For comparison, the different types of compressors canbe subdivided into two broad groups based on

compression mode.

There are two basic modes:

Intermittent .

Continuous.


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EjectorDynamic

Intermittent flow

COMPRESSORS

Continuous flow

An Introduction to Pumping Equipment

Positive displacement

Radial

flow

Mixed

flow

Axial

flow

RotaryReciprocating

Helical lobe

Straight lobe

Sliding vans

Liquid piston

Mechanical

piston


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EjectorDynamic

Intermittent flow

COMPRESSORS

Continuous flow



Radial

flow

Mixed

flow

Axial

flow

RotaryReciprocating

Helical lobe

Straight lobe

Sliding vans

Liquid piston

Mechanica

l piston

Intermittent mode ofcompression is cyclic

in nature, in that a

specific quantity of

gas is ingested by

compressor, actedupon and discharged,

before the cycle is

repeated.

Continuous compressionmode is one in which the

gas is moved into

compressor, is acted

upon, moved through the

compressor anddischarged without

interruption of the flow at

any point in the process.


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2

20

200

102 103 104 105 106

Multistage

Reciprocating

Single stage

Recip.

Flow rate (CFM

Pressurera

tio

Rotary

compressors

Multistage

Centrifugal

Single S Cen.

Multistage Axial


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50 60 70 80 90 100 110 120

60

80

100

120

140

Percent Flow

Pe

rcentPress

ure

Ra

tio

orHead

Positive

Displacement

Compressors

Axial-Flow

Compressor

Centrifugal

Compressors

Design Point

General Performance Curve


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EjectorDynamic

Intermittent flow

COMPRESSORS

Continuous flow



Radial

flow

Mixed

flow

Axial

flow

RotaryReciprocating

Helical lobe

Straight lobe

Sliding vans

Liquid piston

Mechanical

piston


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Intermittent mode compressorsReciprocating compressors


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It is a piston and

cylinder device with

(automatic) springcontrolled inlet and

exhaust valves the

reciprocating motion is

transmitted to a piston,which is free to move in

a cylinder.


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Delivery is usually to a receiver.

The receiver is effectively a store

of energy used to drive (eg)compressed air tools.

Pressure can be developed on one

or both sides of the piston ( double

acting ).


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When a single cylinder

is used or when multiple

cylinders on a commonframe are connected in

parallel, the

arrangement is referred

to as a single-stagecompressor.


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When multiple cylinders

on a common frame are

connected in series,usually through a cooler,

the arrangement is

referred to as a

multistage compressor.


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For large volumes of

compressed gas, they

are usually the mostexpensive to buy and

install, and require

greater maintenance,

however, they may belower cost at small

capacities.


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Due to their size and the

vibrations caused, they

require large foundationsand may not be suitable

where noise emissions are

an issue.

Nevertheless, they are the most energy efficient, both at fulland part loads.


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It is generally in the lower

flow end of the compressor

spectrum. Inlet flows rangefrom less than 100 to

approximately 10,000 cfm /

cylinder.

It is particularly well suited forhigh-pressure service.

The reciprocating compressor is one of the most efficient of

all the compressors.


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EjectorDynamic

Intermittent flow

COMPRESSORS

Continuous flow



Radial

flow

Mixed

flow

Axial

flow

RotaryReciprocating

Helical lobe

Straight lobe

Sliding vans

Liquid piston

Mechanical

piston


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Intermittent mode compressorsRotary Compressors

It consists of a single rotor

mounted eccentrically in a

cylinder slightly larger than

the rotor.

Sliding Vane Compressors

The rotor has a series ofradial slots, which hold a set

of vanes.


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The vans are free to move

radially within the rotor slots.

Sliding Vane Compressors

They maintain contact with

the cylinder wall by

centrifugal force generatedas the rotor turns.


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EjectorDynamic

Intermittent flow

COMPRESSORS

Continuous flow



Radial

flow

Mixed

flow

Axial

flow

RotaryReciprocating

Helical lobe

Straight lobe

Sliding vans

Liquid piston

Mechanical

piston


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Liquid Piston Compressors

It performs its compression

by use of liquid ring acting

as a piston.

The single rotor is located

eccentrically inside a

cylinder or stator.


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EjectorDynamic

Intermittent flow

COMPRESSORS

Continuous flow



Radial

flow

Mixed

flow

Axial

flow

RotaryReciprocating

Helical lobe

Straight lobe

Sliding vans

Liquid piston

Mechanical

piston


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Helical Lobe or Screw Compressors


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Screw (or rotary) compressors

use two meshing helical screws,

rotating in opposite directions to

compress air.

Oil Injected

These compressors are usually the lowest cost to install, for

large volumes of compressed gas.


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Variable output and variable

speed drives are usually available

from most suppliers.

Oil Injected


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Carry the same benefits as oil

injected screw compressors but

compress in two stages and have

no lubricant in contact with the

gas during its passage through

the compressor.

Oil free


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Water injected screw

compressors are also available

where oil free air is required.

Oil free


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EjectorDynamic

Intermittent flow

COMPRESSORS

Continuous flow



Radial

flow

Mixed

flow

Axial

flow

RotaryReciprocating

Helical lobe

Straight lobe

Sliding vans

Liquid piston

Mechanical

piston


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Intermittent mode compressors

Rotary Compressors

Straight Lobe Compressors

They are commonly called

blowers, and they are low-pressure machines.

The feature unique to these

compressors is that the machines

do not compress the gas

internally as do most of the other

rotaries.


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Rotary Compressors


The straight lobe compressor

uses two rotors, which inter-meshas they rotate.


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Rotary Compressors


The features rotary compressors

have in common are:They impart energy to the gas being

compressed by way of an input shaft

moving a single or multiple rotating

elements.

They perform the compression in an

intermittent mode.

They do not use inlet and discharge

valves.


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EjectorDynamic

Intermittent flow

COMPRESSORS

Continuous flow



Radial

flow

Mixed

flow

Axial

flow

RotaryReciprocating

Helical lobe

Straight lobe

Sliding vans

Liquid piston

Mechanical

piston


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Continuous compression compressors

Ejectors

The ejector can first be identified as having no moving parts .

it is used primarily for that feature as it is not as efficient as

most of the mechanical compressors.


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Ejectors

The ejector is operated directly by a motive gas or vapor

source. Air and steam are probably the two most common of

motive gases.


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Ejectors

The ejector uses a nozzle to accelerate the motive gas into

the suction chamber where the gas to be compressed is

admitted at right angles to the motive gas direction.


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Ejectors

In the suction chamber, also referred to as the mixture

moves into a diffuser where the high velocity gas is gradually

decelerated and increased in pressure.


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Ejectors

The ejector is widely used as a vacuum pump, where it is

staged when required to achieve deeper vacuum levels.


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Ejectors

If the motive fluid pressure is sufficiently high, the ejector can

compress gas to a slightly positive pressure.


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Ejectors

Ejector are used both as subsonic and supersonic devices.

The design must incorporate the appropriate nozzle and

diffuser compatible with the gas velocity.


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Ejectors

The ejector is one of the few compressors immune to liquid

carryover in the suction gas.


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EjectorDynamic

Intermittent flow

COMPRESSORS

Continuous flow



Radial

flow

Mixed

flow

Axial

flow

RotaryReciprocating

Helical lobe

Straight lobe

Sliding vans

Liquid piston

Mechanical

piston


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Dynamic compressors

In dynamic compressors energy is transferred from a moving

set of blades to the gas.

Because of the dynamic nature of these compressors, the

density and molecular weight have an influence on the

amount of pressure the compressor can generate.

The energy takes the form of velocity and pressure in therotating element, with further pressure conversion taking

place in the stationary elements.


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Dynamic compressors

The dynamic compressors are further subdivided into three

categories, based primarily on the direction of flow through

the machine.These are radial, axial and mixed flow.


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EjectorDynamic

Intermittent flow

COMPRESSORS

Continuous flow



Radial

flow

Mixed

flow

Axial

flow

RotaryReciprocating

Helical lobe

Straight lobe

Sliding vans

Liquid piston

Mechanical

piston


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Dynamic compressors

Radial flow or centrifugal compressor


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Dynamic compressors


It is a widely used compressor and is

probably second only to the reciprocatingcompressor in usage in the process

industries.

The compressor uses an impeller consisting

of radial or backward-leaning blades and afront and rear shroud.


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Dynamic compressors


The front shroud is optionally rotating or

stationary depending on the specific design.

As the impeller rotates gas is moved between

the rotating blades from the area near the

shaft and radially outward to discharge into a

stationary section, called a diffuser.


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Dynamic compressors


Diffuser

Impeller


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Dynamic compressors


Another feature of the centrifugal is its ability

to admit or extract flow to or from the mainflow stream, at relatively close pressure

intervals, by means of strategically located

nozzles.


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EjectorDynamic

Intermittent flow

COMPRESSORS

Continuous flow



Radial

flow

Mixed

flow

Axial

flow

RotaryReciprocating

Helical lobe

Straight lobe

Sliding vans

Liquid piston

Mechanical

piston


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Dynamic compressors

Axial compressors


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Dynamic compressors

Axial compressors are large-volume

compressors that are characterized by theaxial direction of the flow passing through the

machine, .

Typically, the rotor consists of multiple rows of

unshrouded blades. Before and after eachrotor row is a stationary (stator) row.

Axial compressors


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Dynamic compressors

A gas particle passing through the machine

alternately moves through a stationary row,then a rotor row, then another stationary

blades row, until it completes the total gas

path.

Pair of rotating and stationary blades rowsdefines a stage.

Axial compressors
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Dynamic compressors

Axial compressors

Stage Stage Stage


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Dynamic compressors

One common arrangement has the energy

transfer arranged to provide 50% of thepressure rise in the rotating row and the other

50% in the stationary row. This design is

referred to as 50% reaction.

Axial compressors are smaller and aresignificant more efficient than centrifugal

compressors when a comparison is made at

an equivalent flow rating.

Axial compressors


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Dynamic compressors

The axial compressor, because of a low

pressure rise per stage, is exclusivelymanufactured as a multistage machine.

Axial compressors

Axial compressors are an integral part of

large gas turbines where the pressure ratios

normally are much higher. In gas turbineservice, discharge pressures up to 50 psi are

utilized.


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Dynamic compressors

Mixed flow compressor


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Dynamic compressors


A bladed impeller is used, but

the flow path is angular indirection to the rotor; that is, it

has both radial and axial

components .

Because the stage spacing is wide, the compressor is usedalmost exclusively as a single-stage machine.


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Dynamic compressors


The compressor size is flexible

and covers the centrifugalcompressor flow range, generally

favoring the higher flow rates.

The head per stage is lower than available in the centrifugal.

An Introduction to Compression Equipment

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