surging one of the above

7/27/2019 Surging one of the above

1/21

SURGE

Surge is defined as self oscillation of pressure and flow,

often including a flow reversal

Every centrifugal or axial comp has a characteristics

combination of max.head and and min.flow beyond

which it will surge.during surge there is actual

reversal of flow accompanied by pressure drop .

.


2/21

SURGE DESCRIPTION

. Flow reverses in 20 to 50 milisec.

.Surge cycle at a rate of .3 to 3 sec.

.Comp. Vibrates

. Temperature rises.

.Whooshing noise

.trips may occur

.


3/21

COMPRESSOR OPERATING CURVE

Hp

Q

1

2

3

1. STONEWALL POINT

2. NORMAL POINT

3. SURGE POINT

.

+ VE SLOPE OF OPERATING CURVE

MAX.STABLE COMP. FLOW POINT

MIN.STABLE FLOW POINT

WHEN FLOW AT I/L REACHES SONIC

VEL.NO FURTHER FLOW INCREASE

IS POSSIBLE

DUE TO LOW FLOW ,IT NO LONGER

CAN ADHERE TO SUC. SIDE OF BLADE

SO STALLING OF FLOW


4/21

Pv

Pd

R loss

DEVELOPMENT OF

SURGE CYCLE

Pd comp. Disch press.

Pv vessel press.

Pd=Pv+Rloss


5/21

.

.

AB

C D

Pd

Qs

DEVELOPMENT OF

SURGE CYCLE

.electro motor is started

.machine acc.to normal apeed.

Comp.reaches performance curve

.flow goes up faster becoz

Press. Is integral Of flow

.pressure builds

.resistancr goes up

.comp. Rides thecurve


6/21

.

.

AB

C D

Pd

Qs

.COMP. REACHES

SURGE POINT A

.comp loses its ability to make

pressure

.suddenly Pd drops and Pv>Pd

.because Pv>Pd

The flow reverses

.comp. Operating

point goesTo B

DEVELOPMENT OF

SURGE CYCLE


7/21

.

.

AB

C D

Pd

Qs

.result of flow reversal

Is that pressure goes down

.presuure goes down ==lessnegative flow

.operating pont goes to c

DEVELOPMENT OF

SURGE CYCLE


8/21

.

.

AB

C D

Pd

Qs

.system pressure is going down

.comp is again able to overcome Pv

.comp jumps back to performance

curve to d

.forward flow established

.comp. Starts to build pressure

.comp rides curve toward surge

.point A is reached

.surge cycle is complete

From A TO B 20-50 ms

From C TO D 20-120 ms

ABCDA .3 TO 3 sec


9/21

EFFECTS OF SURGING

1. RAPID FLOW OSCILLATION AND PRESSURE

OSCILLATION CAUSES PROCESS IN STABILITY

2. RISING TEMP. INSIDE COMPRESSOR

3. TRIPPING OF COMP.

4. MECHANICAL DAMAGE

A. RADIAL BEARING LOADDURING INITIAL PHASE OF SURGING SIDE LOAD

IS PLACED ON ROTAR WHICH ACT PERPENDICULAR TO AXIS

B. THRUST BEARING LOAD

DUE TO LOADING AND UNLOADING

C. SEAL RUBBING

D.STATIONARY AND ROTATING PART CONTACT

IF THRUST BEARING OVERLOADED


10/21

DISCHARGE

SUCT

BASIC ANTISURGE CONTROL SYSTEM

.ANTISURGE CONTROLLER PROTECT

THE COMP AGAINST SURGE BY

OPENING RECYCLE VALVE

.THIS REDUCES RESISTANCE

(BACK PRESS)

THIS TAKES THE COMP.AWAY

FROM SURGE

R

Q2

R PROCESS

R PROCESS

+VALVE


11/21

SURGE LINES

STOPPING SURGE REQUIRE THE ABILITY TO KNOWTHE IMPENDING SURGE

WHICH MEANS KNOWING WHERE IS THE OPERATING POINT

RELATIVE TO SURGE POINT

SO SURGE CONTROL LINE IS DEFINED FOR SET POINT OF

ANTISURGE CONTROLLER

Q2

HrSLL

SCL SLL SURGE LIMIT LINE

SCL SURGE CONTROL LINE

b b. Is the distance between

two lines(margin of safety)

P i 1


12/21

ANTISURGE CONTROLLER OPERATION

SLL

SCL

AB

CLOSE LOOP CONTROL PI

WHEN OPERATING POINT CROSSES

SCL,PI CONTROLLER WILL OPEN

RECYCLE VALVE

SUITABLE FOR SMALL DISTURBANCE

AND STADY STATE

Protection 1


13/21

WHY CLOSE LOOP CONTROL IS INEFFECTIVE

b

. Since surging is fast so for PI controller to be fast

b shuld be high.. But increasing b will limit comp. Operation in lower

thruput and unnecessary will recycle

Speed can also be increased

by adding derivative value,but usingPID will open valve

in response to any movement

Toward surge,even if op. point

Is away from limit.

SLL

SCL

Protection 1


14/21

ANTISURGE CONTROLER OPERATION

ENHANCING THE EFFECTIVENESS OF PI CONTROLLER

BY ADAPTIVE GAIN

.WHEN THE OPERATING POINT MOVES FASTTOWARD SCL ,(by calculating time derivative

of operating point)ADAPTIVE GAIN MOVES

THE SCL TOWARD OPERATING POINT

.THIS ALLOWS THE PI CONTROLLER TO

REACT EARLIER

.AS A RESULT SMALL B CAN BE ACHIEVED

WITHOUT SACRIFICING RELIABILITY.

SLL

SCL

b

Protection 1

P i 2


15/21

Protection 2 ANTISURGE CONTROLER OPERATION

RECYCLE TRIP LINE

SLL

SCL

RTL

ABC

.WHEN PI CONTROLLER IS TOO SLOWTO CATCH THE DISTURBANCE

.OPERATING POINT HITS RTL

.OPEN LOOP RESPONSE IS TRIGGERED

O/PVALVE

TIME

TOTAL

RTL

PI

P t ti 2


16/21

Protection 2 ANTISURGE CONTROLER OPERATION

RECYCLE TRIP LINE

SLL

SCL

RTL

ABC

.OPEWRATING POINT MOVES BACKTO SAFE SIDE OF RTL-RT FUNCTION DECAYS OUT STEP RESPONSE

- PI CONTROLLER INTEGRATE TO STABILIZE

ON SCL

.RESONSE OF CONTROLLER IS SUM OF

PI CONTROLLER AND RTL ACTION

O/PVALVE

TIME

TOTAL

RTL

PI


17/21

Protection 3ANTISURGE CONTROLER OPERATION

SAFETY ON LINE (SOL)

SOLSLL

RTL

SCL

. IF OPERATING POINT CROSSESTHE SOL LINE THE COMP IS IN SURGE

.SO RESPONSE SHIFTS THE SCL AND

RTL TO RIGHT

.SO ADDITIONAL SURGE MARGIN IS

ADDED

.

BENEFITS OF SO

1.ADDITIONAL SURGING IS

AVOIDED BY LARGE SURGEMARGIN

2.ALARM OF SURGE IS

PRODUCED(this has to reset

for normalisation)


18/21

Antisurge valve requirements

.VALVE SIZING-must be large enough to prevent surge under all possible

operating condition

- excessive large valve will provide poor control precision

and lead to stonewall.

- 1.8Cv cal< Cv sel


19/21

Antisurge valve requirements

STROKE SPEED-FAST STROKING SPEED IS VERY IMPORTANTrecommended full stroke time

size close to open open to close

1 to 4 1 sec


20/21


21/21

THANKS

surging one of the above

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