Dynamic Surge Curves - ccse.kfupm.edu.sa · PDF fileThe IGV and anti-surge controllers are all...

Dynamic Surge Curves

Ali Al Zahrani

Dhahran, 24/25.11.2008

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Table of Contents1 Basic Operation Concepts and Principles

• Theory of Operation• Theory of Operation

• Compressor Control Principle

2 Basic Definitions for the Surge Phenomena2 Basic Definitions for the Surge Phenomena • Definition of the Surge Limit• Major Process Parameters During the Surgej g g

• The Surge Cycle in on the Compressor Curve

• Causes of Premature Surge

3 Developing the Control Algorithms• Developing the Compressor Curve

• Demonstration for the Compressor Control

• Developing the Surge Control Algorithm

• Is the Curve Permanent?

24 Summary and Design Advices


Theory of OperationTheory of Operation

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Theory of OperationTheory of Operation

A compressor fundamentally comprises a rotor, flow conductinginternals and a casing. The gas enters the compressor throughthe inlet connections and is conducted axially to the inlet of thethe inlet connections and is conducted axially to the inlet of the1st stage impeller. The pressure and velocity of the gas becomeincreased as it flows through the impeller. On exiting, the gas is now at a higher pressure level and is guided to the inlet of the

h h b d Th b d fi d i hnext stage through a return bend. The return bends are fitted with guide vanes which conduct the radial outlet flow from the impellerinto an axial inlet flow to the next impeller.

The pressure increase from impeller to impeller stage. The dis –charge pressure is generated in the final impeller.

The working principle is based upon the conversion of kineticenergy into static energy, i.e. from velocity into pressure.

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Compressor Control PrincipleCompressor Control PrincipleThe compressor control is done by controlling the inlet flow, the inlet

pressure and the discharge pressure. This achieved by controlling the inlet

id (IGV) d th ti l ( bl ff l iguide vane (IGV) and the anti-surge valve (or blow off valve in some

compressors). The IGV and anti-surge controllers are all done in a

PLC or a DCS. Before the compressor starts, the IGV is fully closed and the anti-

surge valve is fully open When the compressor starts the IGV openssurge valve is fully open. When the compressor starts, the IGV opens

gradually and the anti-surge valve closes gradually. This works under a surge

control system that ensures that at any time the flow and the compressing ratio

(discharge pressure/suction pressure) will be in appropriate range (below the

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( g p p ) pp p g (

surge limits).

Definition of the Surge LimitDefinition of the Surge Limit

„Surging“ is the most well-known limit of compressorsand most important phenomenonand most important phenomenon.Reaching of the surge limit is signaled by a surge, whichcannot fail to be heard and which involves an abrupt reversalsal of the delivery flow from the discharge end to the suctionend. The surging process is initiated when the pressure levelpresent at the discharge end is higher than the pressure level which the compressor itself is able to attain at the smallest possible volume flowpossible volume flow.

The primary cause of the surging lies in the fact that the cha-racteristic curve begins to drop toward the zero capacity regi-

f hi k fons after reaching a peak of pressure.

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Definition of surge Limit ..Continued

When the capacity is reduced below this peak, the pressure in h di h li d h d d b hthe discharge line exceeds that produced by the compressor and the flow tends to reverse momentarily. However, as soonas the flow reverses, the system discharge pressure drops and the compressor resumes normal flow.the compressor resumes normal flow.

Surge will result in noisy operation and evidence of distress.Surge is an unstable condition, which should be avoided. The

ill ti i h f l t th boscillation is harmful to the compressor because:-rotor vibration may damage interstage labyrinth seals-reversal of flow will continously increase the temperature level,which may than lead to thermal overload of machine componentswhich may than lead to thermal overload of machine components-rapid changes in axial thrust may damage the thrust bearings-sudden changes in load may damage the driver as well as theimpellers.

To avoid damage of the compressor, it is necessary to avoidoperation of the compressor in the surge region.

9Therefore, compressors are safeguarded by means of antisurge control ,systems.

Major Process Parameters During the Surge

FLOW

the Surge

• Rapid flow oscillations1 2 3 oscillations

• Thrust reversalsP t ti l d

PRESSURE

TIME (sec.)

• Potential damage

1 2 3

TEMPERATURE

TIME (sec.)3

• Rapid pressure oscillations with process instability

10process instability

TIME (sec.)1 2 3

The Surge Cycle on the Compressor CurveThe Surge Cycle on the Compressor CurveThe Surge Cycle on the Compressor CurveThe Surge Cycle on the Compressor Curve

• Compressor reaches surge point A Pd

P• From A to B 20 - 50 ms Drop into surge• Compressor loses its ability to make pressure

• Suddenly Pd drops and thus Pv > Pd• Plane goes to stall - Compressor surges

PvRlosses

• Compressor starts to build pressure• Compressor “rides” curve towards surge• Point A is reached• The surge cycle is complete

• From A to B 20 - 50 ms Drop into surge• From C to D 20 - 120 ms Jump out of surge• A-B-C-D-A 0.3 - 3 seconds Surge cycle

PdAB

Pd = Compressor discharge pressurePv = Vessel pressureRlosses = Resistance losses over pipe

• Pressure builds• Resistance goes up• Compressor “rides” the curve• Pd = Pv + Rlosses

CD • System pressure is going down

• Compressor is again able to overcome Pv• Compressor “jumps” back to

performance curve and goes to point D• Electro motor is started• Machine accelerates to nominal

speed• Compressor reaches performance

curve

• Because Pv > Pd the flow reverses• Compressor operating point goes to point B• Result of flow reversal is that pressure goes

down• Pressure goes down => less negative flow• Operating point goes to point C

• Forward flow is re-established

Machine shutdown

curve• Note: Flow goes up faster because

pressure is the integral of flow

• Operating point goes to point C

Flow

11no flow, no pressure

Causes of Premature SurgeCauses of Premature Surge

DIRTY INTERCOOLERS:INCREASED AIR TEMPERATURE REDUCES AIR DENSITY INTO THE COMPRESSION STAGE RESULTING IN REDUCED STAGE PRESSURE RATIO AND REDUCED RISE TOSTAGE, RESULTING IN REDUCED STAGE PRESSURE RATIO AND REDUCED RISE TO SURGE.

DIRTY INLET FILTER:REDUCES THE PRESSURE INTO THE FIRST STAGE, RESULTING IN A LOWER NATURAL SURGE POINT. A LOWER NATURAL SURGE POINT REDUCES THE THROTTLE RANGE.

HOT COOLANT:INCREASED AIR TEMPERATURE REDUCES AIR DENSITY INTO THE COMPRESSION STAGE RESULTING IN REDUCED STAGE PRESSURE RATIO AND REDUCED RISE TOSTAGE, RESULTING IN REDUCED STAGE PRESSURE RATIO AND REDUCED RISE TO SURGE.

HOT INLET AIR:INCREASED AIR TEMPERATURE TO THE FIRST STAGE REDUCES AIR DENSITY INTO THAT STAGE RESULTING IN REDUCED STAGE PRESSURE RATIO SINCE PRESSURE ISTHAT STAGE, RESULTING IN REDUCED STAGE PRESSURE RATIO. SINCE PRESSURE IS MULTIPLIED AS AIR MOVES THROUGH A MULTISTAGE COMPRESSOR, THE FIRST STAGE HAS THE MOST DRAMATIC EFFECT ON RISE TO SURGE.

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Developing the compressor curveDeveloping the compressor curveDeveloping the compressor curveDeveloping the compressor curve

Pprocess limit

Pd

maximum IGVsurge limit

adding control margins

surge limit

power limit

stonewall orchoke limit

minimum IGV

choke limit

stable zonestable zoneof operationof operationActual available

operating zone

Flow

minimum IGV

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Demonstration for Compressor Control

Baustellen-Kalibrierung / Site calibration sheet DTC- Regelung / DTC Control system

Auftrags / Order No.:Compressor :

2451 1600Kennwort / Code : Geprüft / Checked :Compr. type : von / by :Compr. No.: Date :Customer Tag No. Name :

Regellinie für / Antisurge control line for : Druckbegrenzung für / Max. Press. control line for := 31.0 °C ¤ P atm = 1.000 bar a Pd max = 3.2 bar g

Reihe 1 : Reihe 2 Reihe 3 Reihe 4 : Reihe 5 Reihe 6 Ventilkennlini Pumplinie / S Regellinie / C DruckbegrenzIGV: 20°<; ts : 310 IGV: 35°<; ts : 310 IGV: 50°<; ts : 310 IGV: °<; ts : 0 IGV: °<; ts : 0 IGV: °<; ts : 0

x y x y x y x y x y x y x y x y x y x y x y

3K-2731 A

AL JubailCVK 20 / 210022

3 Points for Simulation

28/04/2004

TS 0Andere / different temperature -> Seite / page 1 : Parameters -> Seite / page 2 :Pumpversuch / Surgetest

x y x y x y x y x y x y x y x y x y x y x y5.50 2.70 v 8.50 3.24 v 10.00 3.50 v 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 5.5 2.7 4.4 4 0.0 1.0 0.0 4.25.20 2.90 v 8.00 3.50 v 9.70 4.00 v 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 8.5 3.24 7.2 4.4 0.0 1.0 10.0 4.2 4.4 3.15.10 3.26 v 7.80 3.70 v 8.80 4.40 v 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 10 3.5 8 4.6 3.6 2.7 5.8 3.64.90 3.50 v 7.50 4.00 v 8.20 4.60 v 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 #N/A #N/A #N/A #N/A 5.1 3.4 7.8 3.94.70 3.70 v 7.20 4.40 p 8.00 4.60 p 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 #N/A #N/A #N/A #N/A 6.5 3.74.40 4.00 p 7.20 4.40 0.00 8.00 4.60 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 #N/A #N/A #N/A #N/A 9.0 4.04.40 4.00 0.00 7.20 4.40 0.00 8.00 4.60 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 10.0 4.14.40 4.00 0.00 7.20 4.40 0.00 8.00 4.60 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Patm 1.0 bar a4.40 4.00 0.00 7.20 4.40 0.00 8.00 4.60 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Maxp(bar 3.2 bar g4.40 4.00 0.00 7.20 4.40 0.00 8.00 4.60 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Max_Xac 10.0 dP/Ps4 40 4 00 0 00 7 20 4 40 0 00 8 00 4 60 0 00 0 00 0 00 0 00 0 00 0 00 0 00 0 00 0 00 0 00 PT 01 0 04.40 4.00 0.00 7.20 4.40 0.00 8.00 4.60 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 PT 01 0 05.5 2.7 1 8.5 3.24 1 10 3.5 1 #N/A #N/A #N/A #N/A #N/A #N/A #N/A #N/A #N/A TS 0 = 31 °C4.4 4 6 7.2 4.4 5 8 4.6 5 #N/A #N/A #N/A #N/A #N/A #N/A #N/A #N/A #N/A TS Fak 1

6 9 10 0 0 0 9.0 T KorrPs bara1

1

Characteristic

4 50

5.00

IGV: 20°<; ts : 310

IGV: 35°<; ts : 310

2 50

3.00

3.50

4.00

4.50

Pd / Ps

IGV: 50°<; ts : 310

IGV: °<; ts : 0

IGV: °<; ts : 0

IGV: °<; ts : 0

151.00

1.50

2.00

2.50

0.00 2.00 4.00 6.00 8.00 10.00 12.00dP / Ps

Ventilkennlinie / Valvecharacteristic

Pumplinie / Surge line

Regellinie / Control line

Druckbegrenzung / Max. press.Control

Developing the Surge Control Algorithm

Perform Physical Test for the CompressorDraw the surge control curveCut the curve into straight lines (4 to 8 lines) Get the slope of each lineGet the slope of each lineIn every scanning cycle, read the discharge pressure from the pressure transmitter, the

suction pressure from the pressure transmitterThe valve opening is calculated in a PLC (or a DCS) written program code as shown in the following steps:1. The values of the inlet flow, the inlet pressure and the discharge pressure are read from the transmitters.2 The discharge pressure to inlet pressure ratio (the compression ratio) is calculated2. The discharge pressure to inlet pressure ratio (the compression ratio) is calculated.3. The PLC (or the DCS) takes the ratio and then depending on the performance curves, it estimates the value of the flow (interpolation of the line).4. The PLC reads the value of the flow (actual value from transmitter) and compares it to the estimated value of flow. 5. If the value of flow (actual) is less than the estimated value, the controller stops the valve from opening more in order not to fall in the surge zone. Otherwise, it opens the IGV more.

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Is the Curve Permanent?Is the Curve Permanent?

Characteristic at Tcorr=1

00

IGV: 20°<; ts : 310

IGV: 35°<; ts : 310

4 00

4.50

5.00;

IGV: 50°<; ts : 310

3 00

3.50

4.00

Ps

IGV: °<; ts : 0

IGV: °<; ts : 0

2 00

2.50

3.00

Pd /

IGV: °<; ts : 0

Ventilkennlinie / Valve

1 00

1.50

2.00 characteristic

Pumplinie / Surge line

R lli i / C t l li

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1.000.00 2.00 4.00 6.00 8.00 10.00 12.00

dP / Ps


Druckbegrenzung / Max. press.Control

Is the Curve Permanent?Is the Curve Permanent?Ch t i ti t T 0 5 IGV: 20°<; ts : 310Characteristic at Tcorr=0.5

6.00

IGV: 20 <; ts : 310

IGV: 35°<; ts : 310

4 50

5.00

5.50 IGV: 50°<; ts : 310

IGV: °<; ts : 0

3.50

4.00

4.50

d / P

s IGV: °<; ts : 0

IGV °< t 0

2 00

2.50

3.00Pd IGV: °<; ts : 0

Ventilkennlinie / Valvecharacteristic

1.00

1.50

2.00Pumplinie / Surge line


180.00 2.00 4.00 6.00 8.00 10.00 12.00

dP / Ps Druckbegrenzung / Max. press.Control

Summary and Design AdviceSummary and Design AdviceTh i t lid t diff t t tThe curve is not valid at different temperaturesThe vendors tend to increase the safety margin (surge control curve)(surge control curve)Adaptive surge control curves is the solutionThe technique is provided by some vendors inThe technique is provided by some vendors in the world (patents)The technique is implemented in SABICThe technique is implemented in SABIC (SHARQ Project) without open source code Researches shall be executed to reveal the relationship jointly between the universities and SABIC/ARAMCO

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Thanks for your attention

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Dynamic Surge Curves - ccse.kfupm.edu.sa · PDF fileThe IGV and anti-surge controllers are all...

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