Compressors Compressors

What are compressors ?What are compressors ?

What is their significance/role in What is their significance/role in continuous process industries?continuous process industries?

• Compressors :Compressors :– Handles compressible fluid like air, Handles compressible fluid like air,

gases, vapours etc.gases, vapours etc.

COMPRESSORS

POSITIVE DISPLACEMENT(COMPRESSING FLUID BY REDUCINGVOLUME OF COPRESSION CHAMBER)

DYNAMIC TYPE(ACCELERATING AND

DECLERATING OF FLUID)

RECIPROCATING ROTARY TYPECENTRIFUGALCOMPRESSORS

AXIALCOMPRESSORS

HELICALSCREW

SPIRALAXIAL

STRAIGHTLOBE

SLIDEVANE

Types of CompressorsTypes of Compressors

Selection Criterion :Selection Criterion :

• Application range.Application range.

• Reliability criterion.Reliability criterion.

• Operational range requirements.Operational range requirements.

Inlet Flow Atm.cfm

Dis

char

ge

Pre

ssu

re P

sia

Reciprocating

Axial

102 103 104 105 106

101

102

103

104

105

Centrifugal

Application RangeApplication Range

Characteristic CurveCharacteristic Curve

Head

Capacity

Axial

Positive Displacement

Centrifugal

• Therefore at constant speed–Therefore at constant speed–– A Centrifugal compressor is A Centrifugal compressor is

essentially a variable capacity, essentially a variable capacity, constant pressure ( relatively ) constant pressure ( relatively ) machine.machine.

– While axial flow & positive While axial flow & positive displacement compressors are displacement compressors are constant capacity variable constant capacity variable pressure machines.pressure machines.

(This is an important factor in the (This is an important factor in the selection of type of compressor )selection of type of compressor )

• Reliability, operating Reliability, operating characteristics and a very wide characteristics and a very wide operating range – all favors a operating range – all favors a centrifugal compressor for centrifugal compressor for industrial use in most of the industrial use in most of the cases.cases.

CentrifugalCentrifugal CompressorCompressor

Centrifugal compressor Centrifugal compressor selectionselection

• At constant speed : At constant speed : – A positive displacement A positive displacement

compressor will always impart to compressor will always impart to working fluid a predetermined working fluid a predetermined constant reduction in volume.constant reduction in volume.

– While a centrifugal compressor will While a centrifugal compressor will always impart a constant change always impart a constant change in velocity of the fluidin velocity of the fluid

C

α

CCww

CCff

u

CCrr

Q = CCff *A

H e= 1/g ( u2 Cw2 – u1 Cw1 )

For reduced capacity

Cf will decrease

&

Cw will increaseC

α

CCww

CCff

u

CCrr

Head

Capacity

Centrifugal compressor

Actual

Ideal

Because of this reason for a centrifugal compressor (with backward curved vane) following head-capacity curve is obtained

SurgeSurge– As we have seen in above theory that as As we have seen in above theory that as

flow is reduced, the velocity of the fluid flow is reduced, the velocity of the fluid jet leaving the vane is increased and jet leaving the vane is increased and hence head is also increased. Also due hence head is also increased. Also due to reduction in flow the fluid channel to reduction in flow the fluid channel between two vanes is not completely between two vanes is not completely filled up which causes localized flow re-filled up which causes localized flow re-circulation. A more decrease in flow circulation. A more decrease in flow results in unstable operation and is results in unstable operation and is called “Surging of compressor”.called “Surging of compressor”.

Horizontal split casingHorizontal split casing

Barrel type casingBarrel type casing

Main PartsMain Parts

• Stator :Stator :– Casing Upper HalfCasing Upper Half– Casing Lower Half Casing Lower Half – ( Or Casing Barrel & counter ( Or Casing Barrel & counter

casing in case of Barrel type casing in case of Barrel type compressor )compressor )

– Diaphragms ( Suction, discharge Diaphragms ( Suction, discharge and intermediate diaphragms )and intermediate diaphragms )

Main PartsMain Parts• StatorStator(contd…)(contd…)

– SealSeal• Seal for individual impellerSeal for individual impeller• Seal on balancing drumSeal on balancing drum• End gas seal ( labyrinth )End gas seal ( labyrinth )• End oil seal or dry gas seal or End oil seal or dry gas seal or

injection sealinjection seal– Bearing HousingBearing Housing

• Incorporates radial bearing on one Incorporates radial bearing on one side and radial and thrust bearing on side and radial and thrust bearing on another side.another side.

• Instruments on bearing housing :Instruments on bearing housing :1.1.For Temperature : Thermocouple on For Temperature : Thermocouple on

bearing pads for direct measurement of bearing pads for direct measurement of bearing tempbearing temp

2.2.Axial position indicating probeAxial position indicating probe3.3.Radial vibration probesRadial vibration probes4.4. Speed probe is generally mounted on Speed probe is generally mounted on

gas /steam turbine if the compressor is gas /steam turbine if the compressor is turbo driven, but if compressor is motor turbo driven, but if compressor is motor driven then a key phasor probe is installed driven then a key phasor probe is installed for analysis of vibration readings.for analysis of vibration readings.

Main PartsMain Parts• Rotor: As name implies it Rotor: As name implies it

consists of all rotating parts of consists of all rotating parts of the compressor like :the compressor like :– ImpellersImpellers– ShaftShaft– Balancing drumBalancing drum– Coupling hubCoupling hub– Thrust discThrust disc

Protective DevicesProtective Devices

• Emergency Stop Devices.Emergency Stop Devices.• Alarm Devices.Alarm Devices.• Safety Valves.Safety Valves.• Anti Surge By-pass ValveAnti Surge By-pass Valve

Emergency StopEmergency Stop• The conditions causing emergency stop may The conditions causing emergency stop may

be following ( only indicative and may vary be following ( only indicative and may vary from case to case )from case to case )– Low lube oil pressure.Low lube oil pressure.– Low level in seal oil tank ( if compressor Low level in seal oil tank ( if compressor

incorporates seal oil system )incorporates seal oil system )– Over speed.Over speed.– Low control oil pressure ( for turbo driven )Low control oil pressure ( for turbo driven )– High differential pressure / high axial thrustHigh differential pressure / high axial thrust– High radial vibrationHigh radial vibration– In some cases high temperature after inter cooler or In some cases high temperature after inter cooler or

after coolerafter cooler

Alarm EventsAlarm Events• All emergency stop conditions All emergency stop conditions

will first generate alarm.will first generate alarm.• Temperature ( of bearing, Temperature ( of bearing,

process fluid, lube oil etc. )process fluid, lube oil etc. )• Pressure.Pressure.• Suction flow Suction flow • Low / high oil level in reservoirLow / high oil level in reservoir• Low level in seal oil tankLow level in seal oil tank

Typical Bypass Anti Surge SystemTypical Bypass Anti Surge System

Compressor Performance Compressor Performance CurveCurve

P1

Q1

P

Q

Anti Surge Line

Compressor Surge Line

surge

Qsurgereq.

Quantity Bypassed

Design Point

Flow

Pre

ssu

r e

Typical Compressor Performance Map And Surge Control

Thrust BalancingThrust Balancing

Labyrinth Sealing Labyrinth Sealing

Floating Oil SealsFloating Oil Seals

Oil Mechanical SealsOil Mechanical Seals

Air Injection Sealing SystemAir Injection Sealing System

Injection / Extraction SealingInjection / Extraction Sealing

Dry Gas SealsDry Gas Seals

Types of Compressor EndTypes of Compressor EndSealing SystemsSealing Systems

Gas Mechanical Sealing Gas Mechanical Sealing SystemSystem

Labyrinth Sealing With Steam Labyrinth Sealing With Steam EjectorEjector

Labyrinth Sealing With Gas Labyrinth Sealing With Gas Ejector Recovery SystemEjector Recovery System

Labyrinth Sealing With Labyrinth Sealing With Air InjectionAir Injection

Floating oil sealFloating oil seal

Dry Gas SealDry Gas Seal

Dry Gas SealDry Gas Seal

• Atmospheric leakages are very lowAtmospheric leakages are very low

• Oil free operation hence no oil Oil free operation hence no oil

contamination to process gascontamination to process gas

• Minimum auxiliary equipmentMinimum auxiliary equipment

• Reduction in power lossReduction in power loss

• Extremely compact and trouble freeExtremely compact and trouble free

Advantages of Dry Gas SealAdvantages of Dry Gas Seal

Seal Gas Skid System Seal Gas Skid System for Dry Gas Sealsfor Dry Gas Seals

• Supply Clean gasSupply Clean gas• Monitor Seal Monitor Seal

LeakageLeakage• Supply Buffer GasSupply Buffer Gas• Initiate alarms & Initiate alarms &

shutdowns when shutdowns when necessarynecessary

• API 610 Centrifugal PumpsAPI 610 Centrifugal Pumps

• API 611 Auxiliary Steam TurbinesAPI 611 Auxiliary Steam Turbines

• API 612 Drive Steam TurbinesAPI 612 Drive Steam Turbines

• API 613 GearboxAPI 613 Gearbox

• API 614 Oil SystemsAPI 614 Oil Systems

• API 616 Drive Gas turbinesAPI 616 Drive Gas turbines

• API 617 Centrifugal CompressorsAPI 617 Centrifugal Compressors

Applicable StandardsApplicable Standards

• API 670 InstrumentationAPI 670 Instrumentation

• API 671 CouplingsAPI 671 Couplings

• API 672 Packaged, Integrally Geared API 672 Packaged, Integrally Geared

Compressors Compressors

• API 676 Positive Displacement PumpsAPI 676 Positive Displacement Pumps

• IS 325 Auxiliary Electric MotorsIS 325 Auxiliary Electric Motors

• ASME PTC 10 Performance TestASME PTC 10 Performance Test

• ASME Sec. VIII & IX Heat ExchangersASME Sec. VIII & IX Heat Exchangers

Applicable StandardsApplicable Standards

Compressors require the following sub-Compressors require the following sub-systems for their reliable, safe and systems for their reliable, safe and efficient operation;efficient operation;

• Lube oilLube oil• Anti-surge and performance control Anti-surge and performance control

systemsystem• Sealing (oil, DGS, ejector etc.) systemSealing (oil, DGS, ejector etc.) system• Instrumentation and monitoring systemInstrumentation and monitoring system• Coolers and separators.Coolers and separators.

Auxiliaries & SubsystemsAuxiliaries & Subsystems