0622457 - Sonatrach Antisurge.pdf

8/11/2019 0622457 - Sonatrach Antisurge.pdf

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GEOil & Gas

Centrifugal Compressor Antisurge

Course Description

The training course provides control Eng. with the fundamentals of compressor anti surge control

system. Basics of Load Sharing concepts will be provided.

Prerequisite:Trainees must have already performed the Centrifugal Compressor Basic course.

Expected Audience: Control (ENG, Nouveaux & Anciens)

Course Content:

1.

GE OIL & GAS CENTRIFUGAL COMPRESSORS

Centrifugal compressor introduction

2. COMPRESSOR PERFORMANCE CURVES

Introduction to Thermodynamic planes

Performance and system resistance curves theory

Operating Point and Conditions

3. ABNORMAL OPERATING CONDITIONS

Centrifugal Compressor Unsteady Flows Overview

Choking or Stonewall

Rotating Stall

Surge

4.

ANTISURGE CONTROL AND PROTECTION

Control system introduction

Antisurge valve description

Antisurge block diagram sequence description

Antisurge control and protection philosophy

Antisurge control and protection operation


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GEOil & Gas

5. ANTISURGE SCREENS - BASED ON SPEEDTRONIC MARK FAMILY

Main screen field description

Auto/manual operation Antisurge control status description

6. LOAD SHARING AND BALANCING OVERVIEW

7. QUESTION AND ANSWER

Course Duration: 2 Days


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GE

Oil & Gas

TRAINING MANUAL


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GE Oil & Gas


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GE Oil & Gas

This manual contains proprietary information of GE Oil & Gas Nuovo Pignone

S.p.A. (GE Oil & Gas), and is furnished to its customers solely for customer

training courses purposes.

This manual shall not be reproduced in whole or in part nor shall its contents

be disclosed to any third party without the written approval of GE Oil & Gas.

The instructions and information contained in the manual do not purport to

cover all details or variations in equipment, or to provide for every possible

contingency to be met during installation, operation, and maintenance.

Should further information be desired or should particular problems arise that

are not covered sufficiently for the purchasers purpose, the matter should

be referred to GE Oil & Gas.

Reviewed Verified Validate

MassimilianoRomiziManual Specialist

/1/2013

Vito Antonio TondoloMechanical

Instructor Leader

/2/2013

Sandro FantiniCustomer Training

Manager

/2/2013

Customer Training Job:0622457

Customer : SONATRACH (ALGERIA)


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TRAINING MANUAL

INDEX

SEZ .1

SEZ .2


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TRAINING MANUAL

SEZ .1


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Centrifugal Compressor Antisurge

GE Oil & GasOil & Gas Industry Applications


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Centrifugal Compressor- Introduction

What is a compressor?

Driven machine Rotating machine Its duty is to increase the gas pressure

How it works?

Increase the kinetic energy throgh rotating components and converts it into static prescomponents, using the torque given by the driver

Why do I need to compress a gas?

Transport Create chemical reactions

Gas storage Enhance oil production


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Offshore production platform

Subsea equipment

Oil/Gas field

Re-injection plant

Oil / gas processing plant

LNG liquefaction plant

Gas boosting

Oil boosting station

Refinery / Petrochemical /fertilizer plant


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Shaft

Inlet Volute

Fin

Casing

Blade

Impeller

Suction Nozzle

Suction Pipe

The gas flow from the pipe arrives at the suction stage traveling in a radial direction and mu

direction to enter the impeller.

The purpose of the suction stage is to convey the gas into the first impeller with low load losand velocity.Usually, the suction stage has a fin positioned at the opposite side of the suction flange, whicavoid gas recycling in the inlet volute.


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Gas inle


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The intermediate stages are the stages between the suction and the discharge; their numbe

impellers are installed on the shaft.Due to the fact that each compressor is fully customized, the geometry of the intermediate scompressor to compressor, according to operating specifications.

Labirinth seals

Diffuser


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P2

P3

Increased velocity and pressure

A compressor stage consists of the impeller, the diffuser and the return

channel.The impeller rotates with the shaft, increasing both the velocity andthe pressure of the gas.Regarding the pressure increase, we can say that it occurs within theimpeller and the diffuser, and that the magnitude of this increasedepends on the design of both of these.


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432

Impeller Inlet BladeInlet

DiffuserInlet

DiffuserOutlet

Velocity

Pressure

Energy

1

As shown in this diagram: in the impeller both the velocity and pressure increase; in the diffuthe velocity decreases due to the convergent design; and in the return channel there is no in

convergent design is chosen only to avoid load losses.The return channel is bladed in order to more effectively convey the gas toward the next implosses, but there is no further increase of pressure downstream the diffuser outlet .We can state that all the pressure increase realized within a compressor stage is made betwdiffuser outlet.


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Last impeller Discharge volute

The discharge section of the gas path is the connection between the

inner parts of the compressor and the piping. The most important partis the Discharge volute.The discharge volute is installed after the last diffuser and convey thegas into the discharge piping.The volute has a variable section to impart low load losses to avoiddecreasing the pressure.A fin is usually installed near the discharge flange to prevent gasrecirculation within the volute


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The performance curves are a graphical way to display the perfomance parameters, always relEach of the curves is related to a certain fixed speed.The parameters shown are:

Polytropic Head

Polytropic Efficiency

Pressure Ratio

Power

Discharge Temperature

Discharge Pressure


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Minimumoperating speed

(MOS)

Discharge

pressure(bara)

Inlet capacity

65%

80%

90%

9

Normal operating point


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Surge LimitLine

Chokin65%

80%

90%

98

Operating range


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65%

The plot represents the envelope of all thepossible operating conditions relevant tothe given suction parameter.

The actual operating point is unique and

it is always the intersection between thecompressor curve at the given speedand the plant resistance curve.


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65%

The plant resistance curve can change

during operation


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65%

80%

90%

98%

100

Operatingstability

Turndown Range


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Surge LimitLine

Cho65%

80%

90%

Operating range

Looking back at this performance curve diagram, the left and right limits for the perfomancecompressor are called: Surge limit line and Choking area.

To introduce the topic, choking is related to the maximum flow rate that the compressor cansurge is related to fluid dynamic instabilities that will occur if the flow rates decreases over aspeed.


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Rapid decrease in performaThe increase of gas speed ihigh vibrations alarms.

Choking rapresents the right limit of the perfomance curves.

It is the maximum flow that the compressor can handle at that speed, given by the geometry Due to a change in system resistance, if the operating point reaches the choking limit , the flowdischarge pressure will rapidly drop.


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Choking is a physical limit of the compressor but it will mostly affect only the output.

No detection or protection system is required to provide choking.

What happens if the compressor chokes:

The flow reaches M=1 at the inlet of the impeller (restricted section);

Shock wave causes a dicontinuity of p and T.

Maximum flow rate;

Flow rate remains constant

Discharge pressure will drop

Gas velocity will increase

Shock wave


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What is it surge?

"Axis-symmetric stall", more commonly known as "compressor surge" or "pressure surge", compression resulting in a reversal of flow. This phenomenon occurs when the machine operamaximum that the compressor can furnish at the speed at which it is running.

Its due to the compressor's inability to continue working against the already-compressed ga

What is it due to?

The compressor either experiences conditions which exceed the limit of its pressure rise capabthat it does not have the capacity to absorb a momentary disturbance, creating a rotational stthan a second to include the entire compressor.

What happens?

During the normal operation: Increase of discharge pressure, downstream the compressor; de

increase of suction temperature.Due to high plant resistance, during Start up and Shutdown theres a high risk of surge phenom

Which are the main factors leading to Surge?


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Surge is the left limit of performance curve, on the left of this line the compressor opera

Represents the maximum polytropic head of the curve;

All surge points, defined for different speeds represent the Surge Limit Line SLL;


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P2

P1

P2 >

Axial thrust


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P2

P1

Axial thrust


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Rapid flow oscillations Rapid press

Flow Pressure

Temperature

Time

Time


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Flow reverses in 20 to 50 milliseconds

Surge cycles at a rate of 0.3 sec to 3 sec per cycle

Compressor vibrates, shakes

Temperature rise

Whooshing noise or clanking noise

Conventional instruments and human operators may fail to recognize surge


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Unstable flow and pressure

Damage increasing with severity to seals, bearings, impellers and shaft

Increased seal clearances and leakage

Lower efficiency

Trips

Reduced compressor life


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The purpose of the antisurge control system is to keep the operating point, at each respectiv

surge limit line SLL.At the same time, the antisurge control system allows the compressor to maintain a safe wo

The opening of the antisurge valve causes an increase of compressor suction flow that will rsystem resistance curve, so the working point of the machine remains safely on the right of t

Surge LimitLine

65%

Operating range

In order to maintain the compressoroperation within a safe operating range, allthe centrifugal compressors are equippedwith an antisurge system.


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The Antisurge System is composed by:

Antisurge Valve

Instrumentation:

Flow indicator trasmitter

Pressure indicator trasmitter

Electronic controller

Antisurge valve: Is a regulating valve, to avoid excessive recycles of flow that will reduce the flow from discharge to suction in order to reduce system resistance. Cv of this valve, accordiequiexponential, for smooth regulation, then linear, for protection. Is a Failure Open valve anvalve for quick opening. Antisurge valve fully open (ZSL XXX) is a permissive to start.

Instrumentation: The flow transmitter can be a rotameter, an annubar or, more commonly, aacross a calibrated orifice. In the last case we need also to measure the gas temperature to gas.


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Antisurge valve: Is a regulating valve, to avoid excessive recycles of flow that will reduce the ouflow from discharge to suction in order to reduce system resistance. Cv of this valve, accordingequiexponential, for smooth regulation, then linear, for protection. Is a Fail to Open valve and is

valve for quick opening. Antisurge valve fully open (ZSL XXX) is a permissive to start.


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The goal of this system is to maintain the operating point within a safe operating area.

But we have to avoid to reach the SLL, surge limit line.

For this reason, inside the controller, is stored another curve called SCL, surge control line, di

The relationship between SLL and SCL is the safety margin that we want to maintain, usuallymore than the points on the SLL at the same rotational speed.

If the operating point remains on the right of the SCL, the antisurge valve will remain closed,

During the Start-up the antisurge valve remains fully open until the compressor reaches the the valve turns in control, according to where the operating point is.As soon as the Shutdown sequence begins, antisurge valve becomes immediately fully open


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SL

SPL SCL

AS control curves

The actual Surge Line is the place in which the machine surge, it can change itsthermodynamic parameters of the gas. All the other curves are calculated using a specif

can not change.


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AS control curves

It is possible to have that after some change in the thermodynamic parameters, the surgesurge protection line did not move (because set points must be inserted manually):

SL

SPL SCL


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Control system wiring and communic

TURBINE GEAR BOXAUXILIARY

MCC

Mark VI

F&G

HMI

SIS

UDH

EXT.POWER

PDH


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Main parts

Mark VI Hardware Panel introduction

1

2

3

1r

1s

1t

2

Simplex


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Simplex-TMR connections

I/O board

I/O board

I/O board

I/O board

I/O board

I/O boar



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I/O board

I/O board

I/O boar

I/O board

I/O board

I/O boIONet (ethernet)

Simplex-TMR connections



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HMI Introduction

The toolbox is a software for configuration Therefore, each product package can consisfor the controller or drive, Trend Recorder, Dfor the System Database (SDB). To order theproduct support files.

toolbox

The Cimplicity is a software for the definition and visualization of the HMIscreens for real time control of power-plant, processes and equipment.In addiction, throught the Cimplicity software the operator can issuecommands to the selected turbine or driven devices.


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co

cimplicity

Mark VI

EGD

TCIalarm

toolbox

HMI Introduction


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Graphic pages - load


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Graphic pages - load


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MKVI

TT

Antisurge signals

FV-722

PT

-723

PT-72

PT

-721

PT-72FT-721

FT-72

TEMPERATURETRANSMITTER

TT-715

TT-71


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Antisurge signals

Mark VI

PositionH:

Command:a20as

ON/OFF signal


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AS Sequence in MKVI

Antisurge master enabling signal

L3: READY TO LOAD

L94X: NO SHOUT DOWN

L33CDMN: MIN. COMPRESSOROPERATIVE SPEED

L4: MASTER OPERATIVE SIGNAL

L14LS: MINIMUM OPERATIVE SPEED


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AS Sequence in MKVI

Start/Purge sequenceL4AS = 0A20as = 0%

A20as = 10closed) to p

L1X = 1 (auxiliaries ON)And:

No Water WashNo AS manual control

No Compressor pressuruzed

stopped

Compressorpurge

a20as = 0%to purge th

AS purge

accelerationProtection

From L14LR = 1 (shaftrevolution)

to L3=1 (ready to load) LoadL4AS = 1 (Aa20as = 0-


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AS Sequence in MKVI

Antisurge control Loop

A PI controller regulates antisurge valveposition in order to maintain theoperative point on the control line (SCL).

A20AS_MAR

A20AS_PARM

a20a


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AS Sequence in MKVI


A20AS_MAR

A20AS_PARM

a20a

DEAD BAND: to PI error is added to avoidthat measurement noise acts directly onPI output when operative point is nearcontrol line.The dead band is defined by 2 constantK20AS_DB_L and K20AS_DB_H.


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AS Sequence in MKVI


A20AS_MAR

A20AS_PARM

a20a

RATE LIMITER: PI controller output rate is limited by thfunction. Two ramps are defined:

Opening rate is limited K20AS_ARATO (30% Closing rate is limited by K20AS_ARATC (1.5


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AS Sequence in MKVI

Antisurge specific funtions

SLOW OPENING (L20AS_SO):It is activated in case of engineshoutdown.The valve, starting from tha actualposition, is opened at a slow rate(K20AS_ARASO = 0.5%/s). All othercomtrols remain active and, ifrequired, the valve can be openedfaster.When the function is deactivated,the valve is closed using theautomatic closing rate(K20AS_ARRATC = 1.5%/s) until thenormal activation controller actiontakes back the control.


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AS Sequence in MKVI


TRANSIENT ABSORPTION(L20AS_TA):It is activated in case of rapidapproaching to surge line.

Detection: threshold K20AS_TA(510) is reached andoverride by derivative parameterA20AS_PARAM.

Action: the setpoint A20AS_MAR isincreased by multiplying factorK20AS_TA_G (1.15).The original setpoint is thanrestored when the derivative

parameter returns below the slowrate threshold K20AS_TA_R(510).


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AS Sequence in MKVI


SAFETY CORRECTION (L20AS_COR):It is activated if operating pointapproches surge line more thancorrection line (COR).

Detection: AS parameter

0622457 - Sonatrach Antisurge.pdf

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