ga jdr anti-surge presentation [read-only] [compatibility mode][1]

Field-based Control for Compressor Anti-Surge

John RezabekProcess Control SpecialistProcess Control SpecialistISP Lima LLC

2009 General AssemblyYokohama, Japan

ObjectivesObjectivesObjectivesObjectives

• Provide efficient and reliable surge gcontrol to:• Prevent surge and consequent equipment e e t su ge a d co seque t equ p e t

damage• Prevent process downtimep• Improve process stability• Decrease blow offDecrease blow off• Reduce power consumption


© 1999 – 2009 Fieldbus Foundation2

IntroductionIntroduction• Compressor Anti-

surge requiressurge requires speed and reliability

• Can field-based control improve reliability and performance?

• How fast can we go ithwith newer

offerings?



What is Surge?What is Surge?What is Surge?What is Surge?ΔP

Surge Line Point where the flow pattern collapses

B Design Operating point

pattern collapses

Speed

A

D

105 %

100 %

C

95 %

Flow



Deep Surge!Deep Surge!Deep Surge!Deep Surge!ΔP

Surge LineCycle lasts 300 ms to 3 s

BC

Cycle lasts 300 ms to 3 s, depending on speed, compressor characteristics

A

E

Speed

100 %

DReverse flow finds blades resistance

Flow



Surge pathSurge pathSurge pathSurge path

• If the throughput is reduced from A, the compressor will follow the curve back to B.

• In B the flow collapses, going to zero at point C.With the head falling below the head capability of the• With the head falling below the head capability of the compressor, a new flow is produced (D).

• If the system load is the same, the compressor will y , pgo through A, B, C and back to D on and on.

• Each compressor speed has a point B, where the flow collapsesflow collapses

• The collection of these points is called Surge Curve.



What is Surge?What is Surge?What is Surge?What is Surge?ΔP

Surge Line Point where the flow pattern collapses

B Design Operating point

pattern collapses

Surge

Speed

ASurge Area

105 %

100 %

95 %

Flow



Consequences of SurgeConsequences of SurgeConsequences of SurgeConsequences of Surge

• During surge, the flow variation produces prominent axial oscillation.

• The frequency and displacement of this oscillation depends on the compressor speed among otherdepends on the compressor speed, among other factors.

• The oscillation can damage the bearings, impellers and labyrinth seals, causing parts of the rotor and stator to touch each other, resulting in serious damage or destruction.damage or destruction.

• Internal temperature can raise to dangerous levels.• Compressor life is shortened



Factors leading to SurgeFactors leading to SurgeFactors leading to SurgeFactors leading to Surge

• Load changes, start/stop• Gas Molecular Weight change• Upstream or downstream pressure changesp p g• Gas temperature changes



Surge controlSurge controlSurge controlSurge controlΔP PTSTTSFTSSurge Line

B' CompressorFIC

Driver

Speed

A

PTDTTD

Discharge Flow

105 %

100 %CalculatedSetpoint Line

95 %

Flow

Setpoint Line



Process Blower – Simpler with milder consequences

• Keeping the Blower out of the surge i t bl flregion means a more stable flow

• More stable flow allows running closer to constraintsconstraints

• Running closer to constraints means less fuel CO2fuel, CO2



Inside “peak pressure” line flow is unstableInside “peak pressure” line flow is unstableInside peak pressure line, flow is unstableInside peak pressure line, flow is unstable

Desired Operating Point

Peak Pressure



Field-based control of blow-off valveField-based control of blow-off valve

• Controls total flow• Allows operation• Allows operation

close to low-flow BMS trip pointp p

• Saves fuel costs and reduces CO2 emissions



Surge Control SchemeSurge Control SchemeSurge Control SchemeSurge Control Scheme

Discharge

C ff

Discharge Pressure SGCR SP

Blow-off Flow Σ FIC

(Total Flow)Blow-off

Valve

Flow to Burner

FIC Inlet Louvers



Louvers

Blower Anti-surge schemeBlower Anti-surge schemeFlow to BurnerFlow to Burner

Total Flow Setpoint

Total Flow Controller



Controller

Macrocycle ScheduleMacrocycle Schedule

Discharge PressureFlow to Burner

Blow-off Flow

Calculate SPSum Flows

“Fast” PID / AO would reduce

Burner Flow FIC

“Fast” PID / AO would reduce required macrocycle to 325 ms

or less

Burner Flow ValveTotal Flow FIC



Blow-off Valve

10,000 HP Turbine / Blower Anti-surge10,000 HP Turbine / Blower Anti-surge10,000 HP Turbine / Blower Anti surge10,000 HP Turbine / Blower Anti surge• Large critical

un-sparedun spared asset

• Typically runs yp yat 5000 to 7000 RPM

• Expensive to repair; lost

d tiproduction even more expensive



expensive

Discharge Flow / Pressure / T t M tDischarge Flow / Pressure / T t M tTemperature MeasurementTemperature Measurement

• Venturi Flow meter on discharge

• Pressure and Temperature Compensationp

• Discharge and suction converted to ACFMconverted to ACFM



Control Scheme – FF for IO onlyControl Scheme – FF for IO onlyControl Scheme FF for IO onlyControl Scheme FF for IO only




CALC Block 2:

CALC Block:1) Corrects SCFM2) C d

1) Calculates Theoretical Surge Curve

2) Converts corrected SCFH to Suction and Discharge

2) Calculates % Over Surge

3) Adds 5 10%gACFM

3) Converts PSIG to PSIA

3) Adds 5 – 10% “Bump” when surge is approachedPSIA



Macrocycle Schedule – no FF controlMacrocycle Schedule – no FF controlMacrocycle Schedule no FF controlMacrocycle Schedule no FF control



With Core Calculations in Field:With Core Calculations in Field:With Core Calculations in Field:With Core Calculations in Field:• Keep same “look and

feel” for operatorfeel” for operator• “Percent over Surge”

calculation does notcalculation does not fit nicely in standard FF blocks

• CALC blocks will not run in H1 card



With Core Calculations in Field:With Core Calculations in Field:Converts Mass Flow to ACFM With Core Calculations in Field:With Core Calculations in Field:

at Suction Conditions

New DP cell does

Mass Flow



internally

With Core Calculations in Field:With Core Calculations in Field:With Core Calculations in Field:With Core Calculations in Field:Derives

Discharge ACFM Asynchronously



With Core Calculations in Field:With Core Calculations in Field: TRK VAL is aWith Core Calculations in Field:With Core Calculations in Field: TRK_VAL is a constant 100%

Sets “TRK IN D”ARTHMHOST still2009 General Assembly

Yokohama, Japan


Sets TRK_IN_D if Suction Flow <

Surge Flow

ARTHM calculates % over

Surge

HOST still calculates surge

curve

Macrocycle Schedule – FF controlMacrocycle Schedule – FF controlMacrocycle Schedule FF controlMacrocycle Schedule FF control

Di h PDischarge PressureSuction Temperature 1

Discharge FlowDischarge Flow

Disch. Press. PushISEL’ d i H t B’ISEL’s doing Hot B’up

Disch. Temp. Push

Calc % Over Surge

Check if < 0%2009 General Assembly

Yokohama, Japan


Check if < 0%Blow-off Valve

Business Results AchievedBusiness Results Achieved

• Data from CCC talks about 100K yearly energy savings for a compressor about the same size used in process air.

• Control in the field responds within the macrocycle whereas in the DCS takes longer.

• Proven availability and fault tolerance with physical layer diagnostics.



SummarySummary

• Anti-surge control is of great benefit, if not a necessity

• Unless there is great economic benefit for running close to surge, extraordinary cycle times are not required

• Intelligent devices and field-based deterministic control can be superior to host-solved schemessolved schemes

• Newer devices have increasingly fast and efficient function blocks



efficient function blocks

About the PresenterAbout the Presenter

• John Rezabek, Process Control Specialist, ISP Lima LLC

• Began with Standard Oil and later BP, working in refineries and chemical plants. After 27+ years, still pulls into a process plant and sits at DCS engineering consoleplant and sits at DCS engineering console nearly every day.



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