GE centrifugal compressors.pdf

Introduction
General description and main features
GE Oil & Gas
Oil & Gas Industry Applications

Customer Training
2
Centrifugal Compressor Training Course
22/11/2012
What is a Compressor?
A machine used to increase the
pressure of a GAS
Introduction Customer Training

Customer Training
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What is a Gas?
Gas is one of the three classical states of
matter characterized by molecular weight
(MW), pressure (p) and temperature (T)
Introduction Customer Training

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Customer Training
Gas compression
Gas
ps
Gas
pd
Mechanical
power
Introduction

Customer Training
5
22/11/2012
What we need to compress a gas?
For many reasons: to transport it,
to enhance an oil field production, etc…
Introduction

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Customer Training
Compression Services
Pipeline inspection device
Offshore production platform
Subsea equipment
Oil/Gas field
Re-injection plant
Oil / gas processing plant
LNG receiving plant
LNG liquefaction plant
Gas boosting station
Oil boosting station
Power generation plant
Natural Gas storage plant
Refinery / Petrochemical /
fertilizer plant

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Customer Training
Compression Services
Distribution
Midstream Downstream
Upstream
• Exploration &
Production
 Re-injection
 Gas Lift
 Gas Gathering
 Export Gas
•Gas Plants
 Feed Gas
 Gas Treatment
• LNG
 Mixed Refrigerant
 Propane
• Pipelines
 Gas Boosting
 HP Transport
 Gas Storage (Injection +
withdrawal)
• Refinery
 HCU, HDT, HDS
 Recycle
 Air Feed
 FCC
• Petrochemical/
Fertilizers
 Syngas
(Ammonia, Methanol)
 Refrigeration
 CO2 Compression
(Urea)
 Feed Gas
 Charge Gas
 Ethylene & derivatives
• NGV Re-fuelling
 Cubogas

Nuovo Pignone Compressors
GE Oil & Gas

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Customer Training
Vertically split
Compressors overview

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Customer Training
Horizontally split

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Customer Training
Single Volute

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Customer Training
Nuovo Pignone TAGs
BCL 406
2

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Customer Training
Nuovo Pignone TAGs
BCL 406
Casing
B=barrel
P=pipeline
M=Middle Split
S=single volute
Impeller design
C=closed
R=open
Diffuser
L=free vortex (not vaned)
2
Literal Part

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Customer Training
2 BCL 406
BCL 406 /A
Casing design pressure rating
 N p<150 bar
 A p<200 bar
 B p<300 bar
 C p<400 bar
 D p<550 bar
 E p up to 1000 bar
Barrel Type

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Customer Training
 Pipeline compressors are designed to maximize compression efficiency over the broad range of
operating conditions required by gas pumping stations;
 Suction and discharge nozzles for gas transportation are generally located opposite each other to
meet station layout requirements.
pmax 150 bar
PCL 406
Pipeline Type

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Customer Training
Low pressure applications
2 MCL 406
Middle Split Type

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Customer Training
SRL
Integrally geared
Single stage
 Impeller overhung mounted on the shaft;
 Each impeller has the discharge volute.
Single Volute Type

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Customer Training
IMPELLERS design
R= open type
C= closed type
2 BCL 406

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Customer Training
Free vortex DIFFUSER
Diffuser
No fixed blades
2 BCL 406

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Customer Training
Nuovo Pignone TAGs
BCL 406
n. of
impellers
Nominal diameter of the
impeller
Section arrangment
2
Numerical Part

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Customer Training
Nominal size (mm)
400 mm
BCL 406
2

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Customer Training
BCL...MCL...
Section arrangment
suction discharge
 One compression section;
 In line configuration.

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Customer Training
2 BCL... 2 MCL...
Section arrangment
1 st
suction
1 st
discharge
2 nd
suction
2 nd
discharge
 Two compression sections in a single
casing;
 Back to back configuration;
 Cooling of the gas;
 Tmax 250°C.

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Customer Training
3 BCL... 3 MCL...
Section arrangment
 More than two compression sections
in a single casing;
 Sidestreams.
suction discharge
sidestreams

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Customer Training
D BCL... D MCL...
Section arrangment
suction
discharge
 Two compression sections in parallel in the
same casing;

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Customer Training
Technology Selection Map

Compressor rotating parts
GE Oil & Gas

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Customer Training
Rotating parts
Shaft
Thrust Collar
Impellers
Spacers
Balance drum
Coupling hub

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Customer Training
Thrust Collar
 Transmits the rotor thrust to the thrust bearing;
 Fixes the axial position of the rotor;
 Hydraulically shrink-fitted to the shaft;

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Customer Training
Impeller
The function of the
impeller is to add
energy to the gas.

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Customer Training
Impeller
In order to minimize erosion and corrosion effects on impeller due to pitting or fouling phenomenon
related to gas composition, it is possible to use special stainless steel alloy with Ni-Cr-Mo or apply a
specific protective coating.

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Customer Training
The blades are bended
Impeller
The blades are bended and twisted
Impellers are fully customized

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Customer Training
Balancing Drum
 Balances part of the axial thrust;
 Interference fitted and keyed;
 Positioned after the last impeller;
 Holes for rotor balancing.

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Customer Training
Coupling
FLEXIBLE DRY type design is mostly used by NP
HUB
No lubrication is needed
Connects elements between compressor and the remaining equipment of a compressor
train.

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Customer Training
Coupling
Basically a flexible coupling has the following functions:
2. Accommodate Parallel Offset and/or Angular misalignment
1. Physically connect two rotating shafts
3. Compensate for axial movement of coupled shafts

Compressor stator parts
GE Oil & Gas

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Customer Training
Stator parts
Diaphragms
Bearings
Seal
End cover
Flanges and Nozzles
Bearings

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Customer Training
Stator parts

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Customer Training
BCL: Casing-Diaphragms
LOWER HALF
UPPER HALF

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Customer Training
Casing-Diaphragms: bundle
Diaphragms

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Customer Training
Labyrinth
seals
Diffuser
Return channel
Blades
Impeller

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Customer Training
Suction volute Discharge volute
In new barrel compressors the inlet and disharge volutes are separated from the inermediate
diaphragms.

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Customer Training
The upper half of the bundle is lowered on the lower
half.

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Customer Training
Horizontally split
The diaphragms are installed in the casing without a countercasing

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Customer Training
Flanges and nozzles
Discharge Sideflow Suction
Discharge
Suction

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Customer Training
Flanges and nozzles
In the barrel type for high or very high pressure, piping is directly connected to the casing
without nozzles;

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Customer Training
Shear and Shim rings
Shear ring
Shim ring
Locking system using
shear and shim rings

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Customer Training
Head cover
The functions of the head cover are:
 Close the bundle inside the casing;
 Guide the flow;

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Customer Training
Bearings
Thrust bearing
 Direct Lubricated: lube oil is provided for each pad
through a groove manufactured on the pads
 Flooded: Oil fills the bearing assembly and drains
from the top through a flow control orifice
Tilting pads type are adopted. The function of the thrust
bearing is to compensate part of the axial thrust.

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Customer Training
Thrust Bearings Components
Thrust bearing are self equalizing: the bearing distributes the load equally between all pads.
Thrust shoes
Base ring
Leveling plates
Thrust collar
Pivot

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Customer Training
Journal Bearing
Jourbal bearing
Tilting pads type are adopted.
The functions of the journal bearing are:
 Support the rotor weight
 Create a lifting effect
 Damping effect
Two types of possible lubrication:
 Direct lubrication: Lube oil is provided for each pad through a
groove manufactured on the pads
 Flooded lubrication: The oil enter from an orifice in the upper
part of the bearing and exits in the lower part after the
lubriction of pads.

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Customer Training
Journal Bearing
Bearings pad
Bearings casing
Pivot

Centrifugal Compressor Gas Path
GE Oil & Gas

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Customer Training
SUCTION DISCHARGE
Gas Path

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Customer Training
Shaft
Inlet Volute
Fin
Casing
Blade
Impeller
Suction Nozzle
Suction Pipe
Suction
The gas flow is directed towards the
eye of the first impeller.

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Customer Training
Suction

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Customer Training
Labyrinth
Seal
Suction
diaphragm
Labyrinth
Seal
Shaft
Key
Disk
Suction

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Customer Training
Intermediate stages

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Customer Training
Single stage
Labirinth
seals
Diffuser
Return channel
Blades

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Customer Training
C3=C1
optimal condition
Gas Inlet
Increased
velocity
P4,C4
P1,C1
P2,C2
P3,C3
+ +
+
++ +
Single stage

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Customer Training
Single stage
Impeller
Inlet
Blade
Inlet
Diffuser
Inlet
Diffuser
Outlet
Velocity
Pressure
Energy
1 2 3 4
1
2
3
4

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Customer Training
Last impeller
Discharge volute
Discharge

Centrifugal Compressor Axial Thrust
GE Oil & Gas

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Customer Training
Axial Thrust
Axial thrust
P2 > P1
P2
P2
P1

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Customer Training
Axial Thrust
Balancing Drum
The BALANCE DRUM is a disk installed after the last impeller in order to balance part of the axial
thrust (80÷85%).

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Customer Training
Axial Thrust
P2
P1
P2
Ps
R1 R2 Rd
Axial Force Drum Force

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Customer Training
Axial Thrust
Balancing
Line
Ps Pd Ps+ΔP
Ps= Suction Pressure
Ps = Discharge Pressure
ΔP= Pressure Drop on balancing line
Axial Force Drum Force

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Customer Training
Balancing line

Centrifugal Compressor
Performance Curves
GE Oil & Gas

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Customer Training
Performance Curves
 Polytropic Head
 Polytropic Efficiency
 Pressure Ratio
 Power
 Discharge Temperature
 Discharge Pressure
Performance curves describe the relation of the centrifugal compressor operating
parameter and the inlet capacity.
The performance curves are valid ONLY for the condition specified in the performance diaghram...
Qinlet

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Customer Training
Operating Range Maximum
continuous speed
(MCS)
Minimum
operating speed
(MOS)
Discharge
pressure
(bar
a)
Normal operating
point
Qinlet
Choking Area
Surge Limit
Line

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Customer Training
Operating point Plant
resistance curve
Operating
point
 The plot represents the
envelope of all the possible
operating conditions relevant
to the given suction parameter.
 The actual operating point is
unique and it is always the
intersection between the
compressor curve at the given
speed and the plant
resistance curve.
Qinlet

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Customer Training

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Customer Training
Off-design conditions
Discharge
pressure
MW
MW
Qinlet
Ts
Ts
Ps
Ps

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Customer Training
Other map variation cause:
Normal working
graph
Internal recycles
effect
Discharge
pressure
Qinlet

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Customer Training
According to API 617 the following regulating methods are defined:
 Speed Variation
 Suction throttling
 Variable inlet guide vanes (VIGV)
 Discharge blowoff
 Cooled bypass
Regulation

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Customer Training
Discharge
pressure
Regulation
Qinlet

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Customer Training
Discharge
pressure
Regulation
Qinlet

Choke, Stall, Surge and
Anti-surge Control System
GE Oil & Gas

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Customer Training
Choking
Choking Area
Choke rapresents the right limit of performance
curve.
Rapid decrease in performances and
efficiency.
Discharge
pressure
Qinlet

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Customer Training
Surge
 Surge is the left limit of performance curve, on the left of this line the compressor operates in
unstable condition;
 Represents the maximum polytropic head of the curve;
 All surge points, defined for different speeds represent the Surge Limit Line;
Surge Limit
Line
Discharge
pressure
Qinlet

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Customer Training
Surge
P2
P1
P2 > P1
Flow inside the impeller
Axial thrust
Normal operating
conditions

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Customer Training
Surge
P2
P1
Flow inside the impeller
Axial thrust
P1 > P2
Surge condition

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Customer Training
Factors leading to surge
During NORMAL OPERATION:
 High discharge pressure (Increase of plant resistance);
 Reduction of suction pressure;
 Increase of suction temperature.

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Customer Training
The Antisurge System is composed by:
 Antisurge Valve
 Instrumentation:
 Flow indicator trasmitter
 Pressure indicator trasmitter
 Electronic controller
Antisurge system

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Customer Training
Antisurge system
PRESSURE
TRANSMITTER
ANTISURGE VALVE
COMPRESSOR
FT PT PT
ANTISURGE
CONTROL
FLOW
TRANSMITTER
PRESSURE
TRANSMITTER
The opening of the Antisurge Valve increases the suction flow moving the operating point along the
speed.
The purpose of the Antisurge Control System is to avoid that the operating point reaches the SLL.

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Customer Training
…just a clarification:
The systems work together but are separately.
Antisurge system
The anti-surge controller is a special electronic device that interacts with the
main control panel but is not depending from it.

Lube Oil System
GE Oil & Gas

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Customer Training
Lube Oil System
The function of the lube oil system is to provide the
right amount of lube oil to bearings with the desired
viscosity by regulating pressure and temperature.

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Customer Training
Lube Oil System P&ID
Tank

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Customer Training
Main
pump
Auxiliary pump Emergency pump

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Customer Training
PCV

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Customer Training
TCV

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Customer Training
Filters

Dry Gas Seals System
GE Oil & Gas

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Customer Training
Sealing systems
The function of the sealing system is to avoid gas leakages
Statoric part
Rotating part
Gap
 Gas property is to occupy all the available volume
 Gas moves from high pressure sections to low pressure ones

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Customer Training
Sealing systems
The function of the sealing system is to avoid two types of leakage
Process gas leakages between the
compression stages
Process gas leakages towards the
atmosphere

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Customer Training
Types of seals:
 Fluid dynamic seals
 Labyrinth seals
 O-Ring gaskets

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Customer Training
Labyrinth Seals
Plain Stepped Abradable
A labyrinth seal is a type of mechanical seal that minimize the gas leakages. Labyrinth seals on
rotating shafts provide non-contact sealing action by controlling the passage of fluid through a
series of teeth.
Efficiency
Main purpose is to minimize internal leakages
close to the impellers due to different
pressure value at inlet and discharge.
 Eye of the impeller
 Foot of the impeller
 Balance drum

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Customer Training
Balancing Line
Shaft End Seal Shaft End Seal
Balancing Drum
Shaft end sealing

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Customer Training
Dry gas seal system
Mechanical dry gas seal are
supplied as cartridges.

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Customer Training
DGS: main components
Stationary ring
Rotating ring
Spring
Seal gas
SHAFT
Process
side
Athmosphere
side

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Customer Training
Operating conditions
Static Pressure +
Spring Thrust
Dynamic
Pressurization
Process Side
Stationary ring Rotating ring
Seal
gas
Seal
gas
The pressure profile at the
interface is self adjuxting to
restore to a position of equilibrium
 Gas enters the groove moving towards the center;
 Gas is compressed and pressure increases setting the gap between the rings.

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Customer Training
Shaft rotation Shaft rotation
Dry gas seal

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Customer Training
Gas source

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Customer Training
Intermediate Labyrinth
Product side
Outboard seal
Inboard seal
Seal gas STREAM 1
Primary vent (leakage from inbord seal
+ intermediate buffer gas - to flare) STREAM 2
Intermediate buffer
gas (N2)
STREAM 3
Secondary vent (leakage from Outbord seal
+ separation gas - atmospheric) STREAM 4
Separation gas (N2)
STREAM 5
Atmosphere
(Bearing chamber)
Separation seal
Inner seals
Carbon rings
Face
Seat
Seat
Face
Nomenclature TANDEM type:

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Customer Training
Process gas
side
Bearings
side
Buffer-Process gas
supply
Seal
gas supply
N2
Seal gas
leakage Separation gas
N2
Inner seal Inboard seal Outboard seal Separation seal
Dry gas seal: DOUBLE type

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Customer Training
Tertiary seal
The function of the tertiary seal is to avoid the oil vapours entering into the dry gas seal.

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Customer Training
Dry Gas Seal System P&ID
Seal Gas Filters
Buffer Gas Filters

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Customer Training
Buffer Gas
PCV
Seal Gas
PCV

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Customer Training
Primary Vent

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Customer Training
Secondary Vent

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Customer Training
Seal Gas
Heater

Vibrations Overview
GE Oil & Gas

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Customer Training
The measure of the mechanical behavior of a compressor is given by the amplitude
and frequency of the rotor vibrations.
The rotor vibration amplitude must not cause:
 Contact between rotating and stator parts;
 Dry gas seals overloading;
 Fatigue in the bearings.
Mechanical behavior

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Customer Training
The typical vibrations of the centrifugal compressors can be classified with reference to
the frequency and the nature of the force causing vibrations.
According to the first classification (frequency) the vibration may be:
 Synchronous
The vibration frequency corresponds to the machine rotation speed (ωR)
 Asynchronous
The vibration frequency is different from the machine rotation speed (ω R)
Vibrations classification

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Customer Training
Syncronous vibrations
𝜔 = 𝜔𝑅
The most common causes are:
 Unbalance in the rotor system;
 Rotor and stator parts contact;
 Fouling deposit.

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Customer Training
Asyncronous vibrations
It is necessary to do another distinction between frequency of the vibration and
machine rotational speed
 Frequency of the vibration multiple of ωR
 Frequency of the vibration lower or higher than ωR
𝜔 = 𝐾𝜔𝑅

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Customer Training
Asyncronous vibrations
Frequency of the vibration multiple of ωR
𝜔 = 𝐾𝜔𝑅
 Coupling misalignment;
 Loose of interference in some rotor components.
𝜔 = 2𝜔𝑅

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Customer Training
Asyncronous Vibrations
Frequency of the vibration lower or higher than ωR
 High clearance in journal bearings
 Oil whip;
 Aerodynamic effects
(rotating stall in diffusers)
 Cross - coupling
𝜔 = 0.5 𝜔𝑅
𝜔 = ( 0.4 − 0.5 ) 𝜔𝑅
𝜔 = ( 0.1 − 0.2 ) 𝜔𝑅
𝜔 = 0.2 𝜔𝑅

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Customer Training
What are the problems?
The main problem that we have to consider when a rotor-bearing system is
subjected to a periodic force is the phenomenon of RESONANCE.
 A system is in resonance when vibration amplitude becomes maximum;
 This occurs when the frequency of a periodic force (excitation frequency), applied to a rotor-
bearing system, corresponds to a natural frequency of that system.
A centrifugal compressor has many natural frequencies that are colled Critical
Speeds;The most important are the first and the second; It is necessary to determine the
field operation speeds that avoid the resonance.

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Customer Training
NC1 = Rotor first critical, center frequency, cycles per minute
Ncn = Critical speed, n th
Nmc = Maximum continuous speed, 105 percent
N1 = Initial (lower) speed at 0,707 x peak amplitude (critical)
N2 = Final (higher) speed at 0,707 x peak amplitude (critical)
SM = Separation margin
API 617
𝑁1 𝑁2
𝑁𝑐1
0.707 𝑝𝑒𝑎𝑘
𝑆𝑀
𝑜𝑝𝑒𝑟𝑎𝑡𝑖𝑛𝑔
𝑠𝑝𝑒𝑒𝑑𝑠
𝑁𝑐𝑛
𝑁𝑚𝑐
𝑉𝑖𝑏𝑟𝑎𝑡𝑖𝑜𝑛
𝑙𝑒𝑣𝑒𝑙
𝐴𝐹 =
𝑁𝑐𝑖
𝑁2 − 𝑁1
𝑆𝑀

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