SURGE Surge is defined as self oscillation of

. 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 min. flow beyond which it will surge. during surge there is actual reversal of flow accompanied by pressure drop.

. 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

COMPRESSOR OPERATING CURVE + VE SLOPE OF OPERATING CURVE Hp 3 MIN. STABLE FLOW POINT . DUE TO LOW FLOW , IT NO LONGER CAN ADHERE TO SUC. SIDE OF BLADE SO STALLING OF FLOW 2 1 MAX. STABLE COMP. FLOW POINT WHEN FLOW AT I/L REACHES SONIC VEL. NO FURTHER FLOW INCREASE IS POSSIBLE 1. 2. 3. STONEWALL POINT NORMAL POINT SURGE POINT Q

DEVELOPMENT OF SURGE CYCLE Pd R loss Pv Pd comp. Disch press. Pv vessel press. Pd=Pv+Rloss

DEVELOPMENT OF SURGE CYCLE . . B . pressure builds. resistancr goes up. comp. Rides the curve Pd . electro motor is started C. machine acc. to normal apeed. Comp. reaches performance curve. flow goes up faster becoz Press. Is integral Of flow A D Qs

DEVELOPMENT OF SURGE CYCLE . . Pd B C . COMP. REACHES SURGE POINT A. comp loses its ability to make pressure. suddenly Pd drops and Pv>Pd A D . because Pv>Pd The flow reverses. comp. Operating point goes. To B Qs

DEVELOPMENT OF SURGE CYCLE . . Pd B C . result of flow reversal Is that pressure goes down. presuure goes down ==less negative flow. operating pont goes to c A D Qs

. From A TO B From C TO D ABCDA . 20 -50 ms 20 -120 ms. 3 TO 3 sec B . comp. Starts to build pressure. comp rides curve toward surge. point A is reached. surge cycle is complete Pd C. system pressure is going down. comp is again able to overcome Pv. comp jumps back to performance curve to d. forward flow established A D Qs

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 LOAD DURING 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

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 SUCT DISCHARGE R R PROCESS +VALVE Q 2

SURGE LINES STOPPING SURGE REQUIRE THE ABILITY TO KNOW THE 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 SLL Hr SCL SLL SURGE LIMIT LINE SCL SURGE CONTROL LINE b b. Is the distance between two lines(margin of safety) Q 2

Protection 1 ANTISURGE CONTROLLER OPERATION CLOSE LOOP CONTROL PI WHEN OPERATING POINT CROSSES SCL, PI CONTROLLER WILL OPEN RECYCLE VALVE SLL B A SCL SUITABLE FOR SMALL DISTURBANCE AND STADY STATE

Protection 1 WHY CLOSE LOOP CONTROL IS INEFFECTIVE . 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 SLL b SCL Speed can also be increased by adding derivative value, but using. PID will open valve in response to any movement Toward surge, even if op. point Is away from limit.

Protection 1 ANTISURGE CONTROLER OPERATION ENHANCING THE EFFECTIVENESS OF PI CONTROLLER BY ADAPTIVE GAIN. WHEN THE OPERATING POINT MOVES FAST SLL TOWARD 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. b SCL

Protection 2 ANTISURGE CONTROLER OPERATION RECYCLE TRIP LINE. WHEN PI CONTROLLER IS TOO SLOW TO CATCH THE DISTURBANCE. OPERATING POINT HITS RTL. OPEN LOOP RESPONSE IS TRIGGERED RTL SLL C B SCL A TOTAL O/P VALVE PI RTL TIME

Protection 2 ANTISURGE CONTROLER OPERATION RECYCLE TRIP LINE. OPEWRATING POINT MOVES BACK TO SAFE SIDE OF RTL -RT FUNCTION DECAYS OUT STEP RESPONSE - PI CONTROLLER INTEGRATE TO STABILIZE ON SCL RTL SLL C B SCL . RESONSE OF CONTROLLER IS SUM OF PI CONTROLLER AND RTL ACTION A TOTAL O/P VALVE PI RTL TIME

Protection 3 ANTISURGE CONTROLER OPERATION SAFETY ON LINE (SOL) SOL SLL SCL RTL . IF OPERATING POINT CROSSES THE 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 SURGE MARGIN 2. ALARM OF SURGE IS PRODUCED(this has to reset for normalisation)

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. 8 Cv cal< Cv sel<2. 2 Cvcal correspond to point at intersection of mas speed curve to SLL . VALVE CHARACTERSTICS - it can operate anywhere between 0% to 100%. -linear characterstics is preffered.

Antisurge valve requirements STROKE SPEED -FAST STROKING SPEED IS VERY IMPORTANT recommended full stroke time size close to open 1” to 4” 1 sec 6 “to 12” 2 sec 16” up 3 sec open to close <3 sec <5 sec <10 sec MISCELLENEOUS. adequate air supply to power the valve. tubing run shuld be minimized to reduce lag time. One or more vol. booster are required to esure fast response and equal opening and closing time. fail position shuld be open.

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