Compressors, an introduction Dynaflow 2009-09-10 Transport, Storage, Liquefaction Upstream Oil exploration and production Downstream Processing Applications LPG LNG, Boil off gas GTL

© Siemens AG 2008. All rights reserved.

Compressors, an introduction

Dynaflow

2009-09-10

Agenda

1. Introduction.

2. Applications

3. Compressor Types

4. Centrifugal compressorworking principles

5. Compressor selection

6. Mechanical design

7. Aerodynamics

8. Rotordynamics

EnergyOil&Gas SolutionsRotating equipment

Steam turbine Gas turbine Electric motor

Compressor

MidstreamTransport, Storage, Liquefaction

UpstreamOil exploration and production

DownstreamProcessing

Applications

LPGLNG,

Boil off gasGTLCNG

Gas GatheringGas field depletion

Gas–Oil Separation GOSPGas (re)Injection

Gas LiftExport

Gas transmissionGas transport (pipeline)

Gas storage

Refineries

Petrochemical

General chemical

STC-GV STC-GC STC-GV

Compressors

STC-SX STC-SR STC-SH STC-SV STC-SP STC-SI

DisplacementDynamic

AxialIntegrally Geared

Radial

Rotarytwo rotorsone rotor

Liquid ringVane Screw RootsLabyrinth Diaphragm

Reciprocating

Single Shaft

Others

Compressor types

Overview Compressor Working Principles

Reciprocating

V1

V2

P2

p1

V1

V2

( )=

Positive Displacement

volume reduction

χ

Overview Compressor Working Principles

Tip diameter

Blade inlet diameter

Eye diameter

Hub diameter

Centrifugal

Velocity increase

1

11

http://www.geocities.com/mojju/me797/Compressors101.swf

2 Compressors types animation.swf

Reciprocating

DynamicCompressor Types

Single shaft compressors

Axial/axial-radialcompressors Integrally geared compressors

Performance characteristic for various compressor types

Application range of different types of compressors

Reciprocating

Screw / Rotary vane / Roots

Turbo radial

Turbo axial-(radial)

Actual suction volume [m3/h]

Dis

char

ge p

ress

ure

[bar

]

MD experimental

Naptha Cracking (Ethylene)

Gaslift

Ammonia Synthesis, Hydrocracking

Reinjection

Polyethylene

No pulsations

Lower foundation cost and civil cost

Minimum weight and space

No wearing parts

Reliability and availability

Low noise emission

Smooth start up and control

Total Cost of Ownership

Turbocompressor

compared to reciprocating

Advantages Disadvantages

Efficiency

CAPEX

Operating range

Delivery time

BEST WORST

Capital Cost Screw Axial

Maintenance Centrifugal Reciprocating

Efficiency Reciprocating Screw

Flexibility Reciprocating Axial

Comparative evaluation of compressor types

Agenda

1. Introduction.

2. Applications

3. Compressor Types




7. Aerodynamics

8. Rotordynamics

Working principle

▲

▲

▲

▲▲

Discharge Suction

Work is done by rotating impellers, increasing the velocity of the gas

Diffusers convert velocity into

pressure

Return vanes guide the flow to the next impeller

Performance curve

0

5

10

15

20

25

30

35

40

45

50

2,000 4,000 6,000 8,000 10,000 12,000 14,000M3/HR

Poly

trop

ic H

ead

[kJ/

kg]

Head is the amount of work necessary to move one unit of mass through the system

⎪⎭

⎪⎬⎫

⎪⎩

⎪⎨⎧

−⎟⎟⎠

⎞⎜⎜⎝

⎛−

=

−

11

1

1

21

nn

pol pp

nnzRTH

Actual volumetric inlet flow

performance curve

compressor characteristic

The final shape of the performance curve is determined by various losses. These losses and the final curve are indicated in the figure below.

THEO RETIC AL C HARAC TERISTIC

D ISK FRIC TIO N & LEA KA G E LO SSESFRIC TIO N LO SSES

SH O C KLO SSES

SHO C KLO SSES

FLOW

HEA

D

SPEED = CONSTANT

Stable performancecurve

Performance map

Agenda

1. Introduction.

2. Applications

3. Compressor Types




7. Aerodynamics

8. Rotordynamics

What is the basic function of a compressor?Move a quantity of gas against the head dictated by the system characteristics

p1

T1

gas composition

p2 (p2 > p1)

m•

Selection

Casing/frame size

Impeller diameter, type, flow coefficient

Rotational speed

Number of impellers

Required power

Performance Map

FlowPressureTemperature CompositionProcess variation

Volume flowHead

Mechanical constraints Available drivers

Selection

OutputInput

Impellers

Master blade contour

SmallerFlow

or lowertemperature

Larger Hub to Tip ratio

LargerPressure ratio

or larger Mol weight

Impellers

Q.H. OPERATING POINTS + ESTIMATED IINITAL + INTERMEDIATE + FUTURE COMPRESSOR CURVE

lc17

lc18

lc6

2002

2002

+1.52004

2004

(60)

2006

2009

2012

2013

lc2

lc3

lc4

lc5

lc7lc8

lc9lc1

0

lc11

lc12

lc13

lc14

lc15lc1

6lc1

9lc2

0

ec2

ec2

ec3

ec4

ec5

ec6

ec7

ec8ec9

ec10

ec11

ec12

ec13

ec14

ec15

ec16

ec17

ec18

hc3 hc3

hc4

hc5

hc6

105100

90

70

50

SURGE

657072

7374

74.5

68.5

0.00

25.00

50.00

75.00

100.00

125.00

150.00

175.00

200.00

0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000

Q volume [m^3/hr]

Poly

trop

ic H

ead

[kJ/

kg]

INITIAL ROTOR2 + 2 impellers parallel

FUTURE ROTOR3 + 3 impellers in series

INITIAL ROTOR2 + 2 impellers in series - SAME ROTOR

- CHANGE PIPING

- NEW ROTOR- SAME PIPING

Agenda

1. Introduction.

2. Applications

3. Compressor Types




7. Aerodynamics

8. Rotordynamics

Page 2 E O OS REDynaflow: 10/09/2009

Compressor Mechanical designExploded view


Compressor Mechanical design Main parts

1 Casing:The casing is designed towithstand the pressure inside the compressor and contains the basic compressor components.

2 Inner barrel:The inner barrel contains the aero assembly and the rotor.


Compressor Mechanical design Main parts

5 Bearing brackets:Supports the axial and radial bearings

4 End Sealing:Makes the compressorgas tight.

3 Rotor:A shaft with impellers and a balance drum

6 Probes:Measure vibration level and axial displacements.


Compressor Mechanical design Compressor Casing

SV-B SH-B


Compressor Mechanical design Flowpath in the compressor

Inlet Plenum

Volute

Inlet Nozzle

DischargeNozzle

Compressor Stage

Spool Piece (not standard in every compressor)

Inner assembly

DiaphragmsRotor

Aero AssemblyInner assembly

Inner barrel


Compressor Mechanical design Inner assembly of bundle

rotor

aero assembly

Inner assembly


Compressor Mechanical design Aero assembly

Diaphragms

Aero Assembly

Inner barrel


Compressor Mechanical design Diaphragms

The main function of diaphragms is to guide gas to the next compressor stage.

A diaphragm consists of 2 parts, a front plate and a back plate. The front plate of the first (1) and the back plate of a second (2) diaphragm together form the vanelessdiffuser and the return passage to the inlet of the next impeller.

Complete Diaphragmassembly

Return Channel Blades

11 2

The diffusers are usual vaneless, but for some applications LSVs are applied.


Compressor Mechanical design Diffuser types

Diffussor types and differences:

-Vaneless-Lower Head and efficiency

-Wider flow range

-Vaned-Higher Head and efficiency

-Smaller flow range


Compressor Mechanical design Return vanes


Compressor Mechanical design Return vanes

Flow


Typical compressor partsFlow distribution of Inlet plenum with spoolpiece


Typical compressor partsMilled volute


Typical compressor partsRotor

The rotor assembly consists of a shaft fitted with the following parts:1 Thrust collar2 Balance drum3 Coupling hub4 Impeller(s) 5 Shaft

Back-to-back Rotor

123

5

4 In-line Rotor

The impellers are shrunk on to the shaft and positioned by a locating ring.


Typical compressor partsLabyrinths

Labyrinth seals can be found:

- 2 at each impeller.

- Between the end sealing and the impellers

- On the balance drum

- Where the shaft protrudes from the bearingbracket

Function:

- Minimizing recycle lossesSeal

GasShaft


Compressor Mechanical design Impeller manufacturing

1. BrazingBrazingmaterial

ShroudBladeDisc

2. Inside weldingWeldingseam

3. Slot weldingSlot seam


Compressor Mechanical design Compressor End

Bearing bracketRadial and Axial Oil bearings

End SealingDry Gas seal, Barrier seal, Labyrinth

Probes


Compressor Mechanical design Active Magnetic Bearings

Dry gas seal cartridge

Rotor

Sensor

Auxiliary bearing

Magnetic radial bearing

Auxiliary bearing

Sensor

ImpellerDry gas seal cartridge

Technical Data:Type: STC-SV-08-3-APower: 5186 kWn: 12128 1/min P1: 32 bar gP2: 56 bar gMedium: Natural Gas


Compressor Mechanical design ECO type compressor

Compressor section

Compressor / motor rotor

Motorsection

Motor casing

Bottom end radial AMB

Bottom back-up bearing

Top end radialAMB

Compressor casing

Axial AMB

Top back-upbearingDue to integral design:

-No protruding shaft

-No end sealing

-No lube oil


1. Introduction.

2. Applications

3. Compressor Types




7. Aerodynamics

8. Rotordynamics

Agenda


Compressor aerodynamicsInstabilities

The following instabilities occur in a compressor:

SurgePhenomenonProtection

StallPhenomenonImpeller stallDiffuser stall

Noise


Aerodynamic instabilities1. Surge

FLOW

TIME (sec.)1 2 3

PRESSURE

TIME (sec.)1 2 3

TEMPERATURE

TIME (sec.)1 2 3

Major process parameters during surge

Rapid flow oscillations Thrust reversalsPotential damage

Rapid pressure oscillations with process instability

Rising temperatures inside compressor


Aerodynamic instabilities1. Surge

Factors leading to onset of surge:Start-upShutdownOperation related:

Surge is harmful to the compressor:Oscillating flow causes rotor vibrationsReversed flow with heats up the gas in the impellers. Rapid changes in axial thrust may damage the thrust bearings. Sudden changes in load may damage the internals as well as the driver.Instable flow and pressure causes problems in process control and equipment.Operating a compressor in surge will reduce its life time.

Conclusion:The message is to avoid surge.Therefore a Anti Surge Control System is installed at each compressor.


Aerodynamic instabilities1. Surge: Control

Typical Anti Surge control

FT TT PT PT

Cooler Controller

FCV

Obtains: Pd/Ps, Ts, V

Stored: Surge controllinePd/Ps = f (V, Ts)

Compressor


Aerodynamic instabilities2. Rotating stall: Phenomenon

Smooth flow

v1, P1

V2, P2

Lift

a

As angle (a) of attack increases:

- Lift increases

- Break away starts

If angle (a) of attack > critical angle:

- Break down of flow

- Lift collapses STALL

aa

Lift (Bernoulli):

- V1 > V2

- P1 < P2


Aerodynamic instabilities2. Rotating stall: Impeller stall

1. Due to low flow separation on the blade suction side causing flow blockage and flow reversal.

2. Flow moves out of this passage into the next passage and creates separation at the discharge side of this passage

Dis

char

ge s

ide

Suct

ion

side

3. Flow increases due to reversal flow helps to re-establish the normal flow conditions.

4. In the re-established flow the boundary layer is developing again at the blade suction side, till separation occurs. The whole cycle starts again.

The stall appears to be moving in the direction of the rotor rotation, at a Sub synchronous vibration at 5–20% of the compressor speed.


Aerodynamic instabilities2. Rotating stall: Vaneless diffuser stall

Diffuser stall is induced by friction:• Friction decreases the gas velocity.

• Mainly effecting radial component.

• Gas stays longer in diffuser.

• Result instable flow = STALL

• Sub synchronous vibration at

7–15% of compressor speed.

Counter measure:• Narrowing diffuser width

Efficiency will drop with increasing flow.

• Apply vaned diffuser

U2

C2 β2W2α2

tang.

rad.

velocityStream lines between stall cells

stall cell

stall cell

stall cell


Aerodynamic instabilitiesNoise

Noise:

SourceAny flow instability causes pressure variations and results is increased noise levels.Especially flow incidence at vanes at high velocity can cause (tonal) noise.

Impeller vanesStator vanesRotor-stator interaction

Counter measuresApply noise-enclosures around the equipment that makes the most noise. This is often a gearbox or a gas turbine.The compressor it selves produces less noise due to the rather thick casing, but the generated noise will be transported forward into the downstream piping.

Movie to visualize rotating stall in a laboratory? (takes few minutes)


1. Introduction.

2. Applications

3. Compressor Types




7. Aerodynamics

8. Rotordynamics

Agenda


Rotor dynamicsVibrations:

Rotor Vibrations

Lateral Torsional

Self-Excited:

• Oil Whirl

• Labyrinth Induced Whirl

• Thermal Instability

• Aerodynamic Whirl

Rotor Vibrations

Lateral Torsional

Rotor Vibrations

Lateral Torsional

Forced:

• Unbalance

• Rotating Stall

• Surge

• Pressure Pulsation’s

Rotor Vibrations

Lateral Torsional


Rotor dynamicsLateral vibrations

Dynaflow: 10/09/2009

Lateral vibrations

Synchronous Asynchronous

Sub-synchronous

Super-synchronous


RotordynamicsLateral analysis

Lateral Rotor Model

Bearing Span OverhungDE

Overhung NDE



Undamped Lateral Critical Speed Map

Operating Speed Range

Undamped Lateral Critical Speeds



Undamped Lateral Critical Speed Mode Shapes


RotordynamicsTorsional analysis

0 5000 10000 15000 20000Operating Speed [RPM]

1/Rev

3097

8918

17080

2/Rev

Tors

iona

l Crit

ical

Spee

d [R

PM]

4/Re

v

3/Rev

10000

20000

30000

40000

0

Torsional Critical Speed

Excitation Frequency

Gas Turbine Operating Speed Range

Compressor Operating Speed Range

Campbell Diagram for System Torsional Natural Frequencies

For a torsion analysis the whole rotating string has to be taken into account!


RotordynamicsTorsional analysis

Rotor Configuration with Relative Angular Amplitude

Most Sensitive Element


Rotor dynamicsVibrations:

So far the Rotor dynamics

Proceed with Noise and Mechanical response by Dynaflow

Thank you

Documents

Compressors, an introduction Dynaflow 2009-09-10 Transport, Storage, Liquefaction Upstream Oil exploration and production Downstream Processing Applications LPG LNG, Boil off gas GTL