0622457 - Sonatrach Antisurge.pdf

GE Oil & 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 

2.

3.

4.

Centrifugal compressor introduction

COMPRESSOR PERFORMANCE CURVES 

Introduction to Thermodynamic planes



Performance and system resistance curves theory



Operating Point and Conditions

ABNORMAL OPERATING CONDITIONS 

Centrifugal Compressor Unsteady Flows – Overview



Choking or Stonewall



Rotating Stall



Surge

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

GE Oil & 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

GE Oil & Gas

&HQWULIXJDO&RPSUHVVRU$QWLVXUJH TRAINING MANUAL

Customized for: SONATRACH (ALGERIA)

GE Oil & Gas

GE Oil & Gas

Customer Training Job: 0622457 Customer : SONATRACH (ALGERIA)

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 purchaser’s purpose, the matter should be referred to GE Oil & Gas.

Reviewed Massimiliano Romizi Manual Specialist /1/2013

Verified

Validate

Vito Antonio Tondolo

Sandro Fantini

Mechanical Instructor Leader

Customer Training Manager

/2/2013

/2/2013

GE Oil & Gas

GE Oil & Gas

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Customized for: SONATRACH (ALGERIA)

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GE Oil & Gas

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Customized for: SONATRACH (ALGERIA)

GE Oil & Gas Oil & Gas Industry Applications

Centrifugal Compressor Antisurge

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 pressure through the stator components, using the torque given by the driver

Why do I need to compress a gas?    

Transport Create chemical reactions Gas storage Enhance oil production

2 Antisurge

Centrifugal Compressor- Introduction Pipeline inspection device

Oil/Gas field Offshore production platform Re-injection plant

Oil / gas processing plant Subsea equipment

Gas boosting station

Power generation plant Oil boosting station

Natural Gas storage plant LNG liquefaction plant

LNG receiving plant Refinery / Petrochemical / fertilizer plant

3 Antisurge

Centrifugal Compressor- Introduction According to the section arrangement of a centrifugal compressor, the internal components can be resumed in different sections. This section nomenclature is used to identify the different areas where the gas passes and this is also called GAS PATH. The gas flows through the compressor along the gas path. A compression stage consists of the impeller, which is the rotating part, and the diffuser, which is the stationary part. We can split a compressor gas path into different main sections: • Suction stage • Discharge stage • Intermediate stage/s (multistage compressors)

4 Antisurge

Centrifugal Compressor- Introduction

5 Antisurge

Centrifugal Compressor- Introduction The gas flow from the pipe arrives at the suction stage traveling in a radial direction and must be reoriented into an axial direction to enter the impeller. The purpose of the suction stage is to convey the gas into the first impeller with low load losses and with uniform pressure and velocity. Usually, the suction stage has a fin positioned at the opposite side of the suction flange, which splits the flow of the gas to avoid gas recycling in the inlet volute.

Fin Casing Blade Impeller

Shaft Inlet Volute Suction Nozzle

Suction Pipe

6 Antisurge

Centrifugal Compressor- Introduction Gas inlet

Gas inlet

7 Antisurge

Centrifugal Compressor- Introduction The intermediate stages are the stages between the suction and the discharge; their number depends on how many impellers are installed on the shaft. Due to the fact that each compressor is fully customized, the geometry of the intermediate stages will change from compressor to compressor, according to operating specifications. Labirinth seals

Blades Diffuser Return channel

8 Antisurge

Centrifugal Compressor- Introduction A compressor stage consists of the impeller, the diffuser and the return channel. The impeller rotates with the shaft, increasing both the velocity and the pressure of the gas. Regarding the pressure increase, we can say that it occurs within the impeller and the diffuser, and that the magnitude of this increase depends on the design of both of these.

P3,C3

P2,C2

P4,C4 P1,C1

Increased velocity and pressure 9 Antisurge

Centrifugal Compressor- Introduction Velocity Pressure

4

Energy

3

1 Impeller Inlet

1

Blade Inlet

2

Diffuser Inlet

3

Diffuser Outlet

4

2

As shown in this diagram: in the impeller both the velocity and pressure increase; in the diffuser the pressure increases and the velocity decreases due to the convergent design; and in the return channel there is no increase in pressure because the 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 impeller inlet, thus reducing load losses, 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 between the blade inlet and the diffuser outlet. 10 Antisurge

Centrifugal Compressor- Introduction The discharge section of the gas path is the connection between the inner parts of the compressor and the piping. The most important part is the Discharge volute. The discharge volute is installed after the last diffuser and convey the gas into the discharge piping. The volute has a variable section to impart low load losses to avoid decreasing the pressure. A fin is usually installed near the discharge flange to prevent gas recirculation within the volute

Last impeller

Discharge volute

11 Antisurge

Centrifugal Compressor- Introduction The performance curves are a graphical way to display the perfomance parameters, always related to Inlet flow. Each 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

12 Antisurge

Centrifugal Compressor- Introduction Maximum continuous speed (MCS)

Discharge pressure (bar a)

Normal operating point

105% 100% 98% 90% 80%

Minimum operating speed (MOS)

65%

Inlet capacity 13 Antisurge

Centrifugal Compressor- Introduction

Operating range

Surge Limit Line 105% 100% 98% 90% 80% 65%

Choking Area

14 Antisurge

Centrifugal Compressor- Introduction External system resistance curve



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.

105% 100% 98% 90% 80%

Operating point

65%

15 Antisurge

Centrifugal Compressor- Introduction 

The plant resistance curve can change during operation

105% 100% 98% 90% 80% 65%

16 Antisurge

Centrifugal Compressor- Introduction

105% 100% 98% 90% 80% 65%

Operating stability

Turndown Range 17 Antisurge

Centrifugal Compressor- Introduction Looking back at this performance curve diagram, the left and right limits for the perfomance map of a centrifugal compressor are called: Surge limit line and Choking area. To introduce the topic, choking is related to the maximum flow rate that the compressor can handle at a certain speed while surge is related to fluid dynamic instabilities that will occur if the flow rates decreases over a certain threshold at a certain speed.

Operating range

Surge Limit Line

105% 100% 98% 90% 80% 65%

Choking Area

18 Antisurge

Centrifugal Compressor- Introduction 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 of the impellers. Due to a change in system resistance, if the operating point reaches the choking limit, the flow remains constant but the discharge pressure will rapidly drop.

Rapid decrease in performances and efficiency. The increase of gas speed inside the compressor can lead to high vibrations alarms.

19 Antisurge

Centrifugal Compressor- Introduction 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

20 Antisurge

Centrifugal Compressor- Introduction

What is it surge? "Axis-symmetric stall", more commonly known as "compressor surge" or "pressure surge", is a complete breakdown in compression resulting in a reversal of flow. This phenomenon occurs when the machine operates at a compression ratio close the maximum that the compressor can furnish at the speed at which it is running. What is it due to? It’s due to the compressor's inability to continue working against the already-compressed gas behind it. What happens? The compressor either experiences conditions which exceed the limit of its pressure rise capabilities or is highly loaded such that it does not have the capacity to absorb a momentary disturbance, creating a rotational stall which can propagate in less than a second to include the entire compressor. Which are the main factors leading to Surge? During the normal operation: Increase of discharge pressure, downstream the compressor; decrease of suction pressure; increase of suction temperature. Due to high plant resistance, during Start up and Shutdown there’s a high risk of surge phenomenons.

21 Antisurge

Centrifugal Compressor- Introduction •

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 SLL;

22 Antisurge

Centrifugal Compressor- Introduction P2

P2 > P1

P1

Axial thrust

23 Antisurge

Centrifugal Compressor- Introduction

P2

P1 > P2

P1

Axial thrust

24 Antisurge

Centrifugal Compressor- Introduction Flow

Pressure

Time

Time Rapid pressure oscillations with process instability

Rapid flow oscillations Temperature

Rising temperatures inside the compressor

Time 25 Antisurge

Centrifugal Compressor- Introduction

•

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

26 Antisurge

Centrifugal Compressor- Introduction

• 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

27 Antisurge

Centrifugal Compressor- Introduction The purpose of the antisurge control system is to keep the operating point, at each respective speed, from surpassing the surge limit line SLL. At the same time, the antisurge control system allows the compressor to maintain a safe working range. The opening of the antisurge valve causes an increase of compressor suction flow that will reduce the slope of the external system resistance curve, so the working point of the machine remains safely on the right of the critical surge flow. External system resistance curve

In order to maintain the compressor operation within a safe operating range, all the centrifugal compressors are equipped with an antisurge system.

Operating range Surge Limit Line 105% 100% 98% Operating 90% point 80% 65%

Choking Area

28 Antisurge

Centrifugal Compressor- Introduction 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 output of the machine. Recycles flow from discharge to suction in order to reduce system resistance. Cv of this valve, according to the stroke, is first equiexponential, for smooth regulation, then linear, for protection. Is a Failure Open valve and is equipped with a solenoid valve 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, a differential pressure transmitter across a calibrated orifice. In the last case we need also to measure the gas temperature to calculate the right density of the gas. 29 Antisurge

Centrifugal Compressor- Introduction Antisurge valve: Is a regulating valve, to avoid excessive recycles of flow that will reduce the output of the machine. Recycles flow from discharge to suction in order to reduce system resistance. Cv of this valve, according to the stroke, is first equiexponential, for smooth regulation, then linear, for protection. Is a Fail to Open valve and is equipped with a solenoid valve for quick opening. Antisurge valve fully open (ZSL XXX) is a permissive to start.

30 Antisurge

Centrifugal Compressor- Introduction 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, directly related to SLL. The relationship between SLL and SCL is the safety margin that we want to maintain, usually the points on SCL have 10% flow more 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, otherwise it will start to open. During the Start-up the antisurge valve remains fully open until the compressor reaches the MOS, once reached that speed 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 to prevent surge.

31 Antisurge

Centrifugal Compressor- Introduction AS control curves The actual “Surge Line” is the place in which the machine surge, it can change its position because can change the thermodynamic parameters of the gas. All the other curves are calculated using a specific thermodynamic condition so they can not change

.

SL

SPL

SCL

32 Antisurge

Centrifugal Compressor- Introduction AS control curves It is possible to have that after some change in the thermodynamic parameters, the surge line has moved while the surge protection line did not move (because set points must be inserted “manually”):

SPL

SL

SCL

33 Antisurge

Control system wiring and communication ways network command feedback

PDH HMI

UDH EXT. POWER

COMPRESSOR PLC

F&G SIS

Mark VI

MCC

BN

MP

AUXILIARY

TURBINE

GEAR BOX

COMPRESSOR

34 19/11/2013

Mark VI – Hardware Panel introduction Simplex

Main parts

2

2 1

1r

4 3

1s

1. VME rack r. Rack R s. Rack S t. Rack T 2. Protection Module 3. Terminal Boards 4. PDM

6

5. DACA1 (AC/DC) 6. Input filters

1t 5

35 19/11/2013

Mark VI – Hardware Panel introduction Simplex-TMR connections

I/O board I/O board

FIELD

I/O board I/O board I/O board I/O board

36 19/11/2013

Mark VI – Hardware Panel introduction Simplex-TMR connections

I/O board I/O board

FIELD

I/O board I/O board I/O board IONet (ethernet)

I/O board

37 19/11/2013

HMI Introduction

toolbox

The toolbox is a software for configuration of various control equipment. Therefore, each product package can consist of the toolbox, product files for the controller or drive, Trend Recorder, Data Historian, and product files for the System Database (SDB). To order the toolbox software and specific product support files.

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

cimplicity 38 19/11/2013

HMI Introduction

TCI

alarm

Mark VI feedbacks commands

cimplicity

EGD

toolbox 39 19/11/2013

Graphic pages - load

40 19/11/2013

Graphic pages - load

41 19/11/2013

Antisurge signals TEMPERATURE TRANSMITTER

PT-723: Surge pressure transmitter

PT-721

PT-723

FT-721

TT-715

TT

MKVI FV-722

PT-721: Discharge pressure transmitter

FT-721: Surge diff-pressure transmitter

TT-715: Surge temperature transmitter

42 19/11/2013

Antisurge signals Mark VI

Position L

Command: a20as

Position H :

ON/OFF signal

43 19/11/2013

AS Sequence in MKVI Antisurge master enabling signal

L3: READY TO LOAD L94X: NO SHOUT DOWN L33CDMN: MIN. COMPRESSOR OPERATIVE SPEED

L4AS Antisurge master enabling signal

L4: MASTER OPERATIVE SIGNAL L14LS: MINIMUM OPERATIVE SPEED

44 19/11/2013

AS Sequence in MKVI Start/Purge sequence

L1X = 1 (auxiliaries ON) And: No Water Wash No AS manual control No Compressor pressuruzed

stopped Compressor purge

AS purge From L14LR = 1 (shaft revolution)

to L3=1 (ready to load)

acceleration

Load

L4AS = 0 A20as = 0% (AS valve completely opened) A20as = 100% (AS valve completely closed) to purge the compressor

a20as = 0% (AS valve completely opened) to purge the AS line

Protection mode (a20as = 0% (closed) L4AS = 1 (AS enabledl) a20as = 0-100% (AS valve in control)

45 19/11/2013

AS Sequence in MKVI Antisurge control Loop

A20AS_MAR

a20as

A20AS_PARM

A PI controller regulates antisurge valve position in order to maintain the operative point on the control line (SCL).

46 19/11/2013

AS Sequence in MKVI Antisurge control Loop

A20AS_MAR

a20as

A20AS_PARM

DEAD BAND: to PI error is added to avoid that measurement noise acts directly on PI output when operative point is near control line. The dead band is defined by 2 constant K20AS_DB_L and K20AS_DB_H. 47 19/11/2013

AS Sequence in MKVI Antisurge control Loop

A20AS_MAR

a20as

A20AS_PARM

RATE LIMITER: PI controller output rate is limited by the «rate limiter» function. Two ramps are defined: • Opening rate is limited K20AS_ARATO (30%/s) • Closing rate is limited by K20AS_ARATC (1.5%/s)

48 19/11/2013

AS Sequence in MKVI Antisurge specific funtions

SLOW OPENING (L20AS_SO): It is activated in case of engine shoutdown. The valve, starting from tha actual position, is opened at a slow rate (K20AS_ARASO = 0.5%/s). All other comtrols remain active and, if required, the valve can be opened faster. When the function is deactivated, the valve is closed using the automatic closing rate (K20AS_ARRATC = 1.5%/s) until the normal activation controller action takes back the control.

49 19/11/2013

AS Sequence in MKVI Antisurge specific funtions

TRANSIENT ABSORPTION (L20AS_TA): It is activated in case of rapid approaching to surge line. Detection: threshold K20AS_TA (5 10 ) is reached and override by derivative parameter A20AS_PARAM. Action: the setpoint A20AS_MAR is increased by multiplying factor K20AS_TA_G (1.15). The original setpoint is than restored when the derivative parameter returns below the slow rate threshold K20AS_TA_R (5 10 ).

50 19/11/2013

AS Sequence in MKVI Antisurge specific funtions

SAFETY CORRECTION (L20AS_COR): It is activated if operating point approches surge line more than correction line (COR). Detection: AS parameter < K20AS_COR Action: set point is increased at fixed time (2.2s). Integral time is divided for 4 to uncrease integral action and, as consequence, speeding the valve opening.

51 19/11/2013

AS Sequence in MKVI Antisurge specific funtions SAFETY PROTECTION (L20AS_SPR): It is activated if operating point approches surge line more than protection line (SPR). Detection: AS parameter < K20AS_SPR Action: recycling valve fast opening ramp is initiated. Than safety protaction terminate when operating point parameter is above safety protection SPR line with hysteresis K20AS_SPRH. If the situation is not OK in 10s an alarm indicates a problem in the AS valve opening. Safety protection is also active during START/STOP sequence. 52 19/11/2013

AS Sequence in MKVI Antisurge specific funtions PROTECTIONS DISABLING When unit is operative (L4AS = 1), safety protection and correction can be disabled (normally to allow surge zone exploration) by the override command L43AS_O_CMD. In this case alarm L43AS_O_ALM is generated.

DANGER !!!

53 19/11/2013

AS Sequence in MKVI Antisurge specific funtions MANUAL OPERATION (L43AS_CMD) Manual operation can be selected if at least one of the following condition is verified: • Safety protection od safety correction not active • Antisurge master enabing signal disabled (L4AS = 0) • Protections disabled (L43AS_O_CMD) If MANUAL OPERATION is selected, recycling valve positio n is managed by five pushbuttons (with a ramp of ±1%/s): 1.

L5AS_C_CPB: AS valve close PB (fine tuning)

2.

L5AS_O_CPB: AS valve ope PB (fine tuning)

3.

L5AS_FC_CPB: AS valve close PB (latched till valve completely closed or L5AS_S_CPB is received)

4.

L5AS_FO_CPB: AS valve open PB (latched till valve completely closed or L5AS_S_CPB is received)

5.

L5AS_S_CPB: stop AS valve stroking 54 19/11/2013

Graphic pages - load

55 19/11/2013

Graphic pages - load

56 19/11/2013

Graphic pages - load

57 19/11/2013

Load sharing theory Regulation of the operating point of a compressor

The operating point of a compressor can be changed (regulated) by means mainly two ways: •

Speed variation

The operating point can be changed changing the shaft speed.

105% 100% 98% 90% 80%

NPT  = Pout  and Qin  NPT  = Pout  and Qin 

65%

58 19/11/2013

Load sharing theory Regulation of the operating point of a compressor

The operating point of a compressor can be changed (regulated) by means mainly two ways: •

Cooled bypass

The operating point can be changed throught the managing of the antisurge valve.

105% 100% 98% 90% 80%

AS Closing = Pout  and Qin  AS Opening = Pout  and Qin 

65%

59 19/11/2013

Load sharing theory Regulation of the operating points of 2 compressors in PARALLEL

Pout

Qin1

DRIVER 1

Collector

Pout1

C1

Qin2 Pout2 DRIVER 2

The goal is to share the load in equal parts on the two compressor trains, 50% on C1 and 50% on C2.

Pout = Pout1 = Pout2

C2 60 19/11/2013

Load sharing theory Regulation of the operating points of 2 compressors in PARALLEL

Train 1

Train 2

105%

105%

100% 98%

100% 98%

90%

90%

80% 65%

80% 65%

If Driver1 increases its rpm, Pout1 increases. Pout = Pout1 =Pout2, so also Pout2 increases changing the resistance curve of the second compressor. For that reason the working point 2 goes closer the surge limit. When a train in a parallel configuration changes its speed, also the speed of the other train must be changed in the same way. 61 19/11/2013

Load sharing theory Regulation of the operating points of 2 compressors in SERIES

Pout

Qin2

Qin1 Pout1

C1

DRIVER 2

C2

Collector

DRIVER 1

Pout2

Pout = Pout1 + Pout2 The goal, in this configuration, is the managing of the requested Pout. An increasing of te Pout is implemented increasing the revolution speed.

62 19/11/2013

Load sharing theory Regulation of the operating points of 2 compressors in SERIES

Pout

Qin2

Qin1 Pout1

C1

DRIVER 2

C2

Collector

DRIVER 1

Pout2

Pout = Pout1 + Pout2 If the Pout needs to be increased, Driver2 can increase the speed. But, if only Driver2 increases the speed, this variation determines the lowering of the resistance curve of the Compressor1 that generates a decresing of Pou1; and finally the consequent new decreasing of Pout. When a train of a series changes its speed, also the speed of the other train must be changed in the same way. 63 19/11/2013

Load sharing theory Regulation of the operating points of 2 compressors.

AS valve

Qin

Pout DRIVER

C

Fine regulation through the antisarge valve:

Because the 2 compressors cannot be perfectly equal (for costruction tolerances, dirty...) even if they are revolving a the same speed, they will work a little bit differently one by the other. In consideration of that: speed regulation is not enoght .

A fine regulation of the load sharing, both for series and parallel configurations, needs to be implemented by means of Cooled bypass method.

64 19/11/2013

Centrifugal Compressor- Introduction

65 Antisurge

GE Oil & Gas

&HQWULIXJDO&RPSUHVVRU$QWLVXUJH TRAINING MANUAL

SEZ . Drawings

Customized for: SONATRACH (ALGERIA)

GE Oil & Gas

Drawings Index BCL505/N assembly drawing

SOS9929211

Performancecurves

SOS9983763

Piping and instrument diagram

SOM5081477

Instrument list

SOM6609947

Control system functional description

SOM6670429

Antisurge Valve

SOS7248866

Antisurge valve data sheet

RV 28465

Antisurge write-up

SOS9983403

Performance curves

SOS9983763