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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
• 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.
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”.
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
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
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
Labyrinth Sealing With Gas Labyrinth Sealing With Gas Ejector Recovery SystemEjector Recovery System
• 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