Anti Surge Control

March 29, 2018 | Author: gopinath87 | Category: Valve, Gas Compressor, Control System, Machines, Gas Technologies



ANTI-SURGE CONTROLSYSTEM M.S.MANI , CES-INSTS. 1 CONTROL PHILOSOPHY I n c a s e o f a P r o c e s s U n it s t h e e m p h a s is is o n s a f e o p e r a t io n a n d p r e c is e c o n t r o l In c a s e o f R o ta ry M /C s th e e m p h a s is is o n s a f e o p e r a tio n a n d m o n it o r in g . 2 Measurements : Health of a Rotary machine is best monitored by measuring and monitoring the following machine parameters :     Vibration levels of casing and / or shaft Shaft RPM Relative location of the shaft with respect to a predetermined mark ( e.g.-Key phasor ) Axial shift of shaft 3 Measurements     ( CONTINUED): Temperature of thrust bearing pads Temperature of bearing housing Temperature of lube oil return line Oil/gas flow/pressure to seals 4 . Lube Oil / Seal Oil back up system Sequential start / stop (speed ramping of turbines) to avoid human error Capacity control Surge control system 5 .Major control system      Auto start of stand by lube oil pump. CONTROL SYSTEMS BLOCK DIAGRAM : UCP MCMS B -N 3 3 0 0 /3 5 0 0 S E R IE S ALLEN BRADLEY P L C -5 /4 0 DCS C C C /T U R B O L O G FOXBORO I/A S E R IE S W OOD W ARD 505 BY E L E C T R IC A L (A S A P P L IC A B L E ) ESD MCC PROTECH 203 T R IC O N E X TM R LO CAL IN D IC A T O R (M T L M A K E ) LO CAL CO NTRO L PANEL (IN F IE L D ) 6 . What is “Surge” ? SURGING IS AN UNSTABLE OPERATING CONDITION THAT CAUSES ERATIC COMPRESSOR PERFORMANCE 7 . WHERE AND WHEN SURGE EVERY AXIAL AND CENTRIFUGAL OCCURS ? COMPRESSOR WILL EXPERIENCE A DAMAGING PHENOMENON KNOWN AS SURGE WHEN THE FLOW THROUGH THE COMPRESSOR DROPS BELOW A CERTAIN LEVEL 8 . Why surge Occurs ? Surge can be induced by low suction pressure. high discharge pressure and reduction of speed of the compressor 9 . this leads to a very rapid pulsating flow backward and forward through the internals of compressor.How Compressor is affected due to Surging ? Compressor damage results from repetitive or frequent surging  During Surge momentary flow reversal takesplace. resulting in SEVERE VIBRATION and consequent damage  10 . 3 s to 3 s per cycle Compressor vibrates Temperature rises “Whooshing” noise Trips may occur Conventional instruments and human operators may fail to recognize surge 11 .What happens during Surge ?        Flow reverses in 20 to 50 milliseconds Surge cycles at a rate of 0. shaft • Increased seal clearances and leakage • Lower energy efficiency • Reduced compressor life 12 .impellers.bearings.Some surge consequences • Unstable flow and pressure resulting in process upset • Damage in sequence with severity to seals. there is a risk of machine damage and downtime costs Adequate protection is defined as protecting the compressor but not at the cost of unnecessary upset to the process The job of the antisurge system is to detect the potential upset and automatically compensate for it by maintaining a flow through the compressor in excess of the surge condition 13 .Anti-Surge control system     To prevent Surge. Surge protection systems are required If adequate protection against Surge is not provided. the control system should be tailored to open the surge control valve only when and as far as necessary to stop surge 14 .Anti-surge Control system-(contd)  The chief drawback of this approach is the efficiency penalty  The energy that was used to compress the recycled will go to waste  So. ASPECTS OF SURGE CONTROL SYSTEM Compressor Flow path has probability of sudden flow reduction  Is the Compressor provided with Variable Speed Drive?  Is the Compressor provided with IGV ?  Molecular Weight Changes  Manufacturer’s Surge curve and tested surge Points  Safety Margin  15 . Limited stroke speed of Blow-off valve .REQUIREMENTS FOR ANTI-SURGE CONTROL    API asks for 10% safety distance between Surge line and control line.Anti surge controller response time .Compressor fouling and changes in gas composition 16 .Measuring errors when the location of the surge line is determined . referred to surge flow This corresponds to 4 to 8% referred to full range flow This safety distance need to cover: .Transmitter accuracy and drift . SURGE DETCTION METHODS DCS-Minimum Flow controller(On spill back)  Mechanical Minimum stopper on suction Valve  Operating Point proximity to “Surge control Line”  Flow reversal detection . Pr and Diff Temp.Diff.  Sudden Drop in Motor current  17 . The locus of all such points defines a curve known as surge line 18 .Compressor Performance Map For any operating curve the point of minimum flow and maximum pressure is known as the Surge limit point. SURGE CONTROL LINE 4. SKETCH .3 1 2 3 Pd -----Ps 4 3 FLOW 1.OPERATING POINT 19 . SURGE LIMIT LINE 3.Surge control Diagram: The diagram below shows the performance map of a compressor with the surge control lines .PERFORMANCE CURVES 2. Effect of Gas composition on Surge 2 1.6 M2 new M28 1.6 1.4 0.8 1.6 0.2 0 0 0.8 0.2 1 0.4 M7.2 0.8 M4.4 0.8 1 20 .6 0. Antisurge Control System Anti surge system achieve this By manipulating the positions of Recycle valve (Normally for Hazardous Gas) By using a Blow off valve (Normally for Air or Non hazardous applications) in order to maintain the volumetric flow rate above a safe. minimum level. Compressor Antisurge Valve FT PT TT TT PT FT FY ANTI SURGE CONTROLLER 21 .  Open the vent or Blow off valves in a controlled way . 22 .Surge Control Techniques :  Calculate and Monitor the "Operating Point " of the Compressor.  In variable speed machines . reduce the speed.  Open the recycle valve( Between the discharge and suction of the compressor) in a controlled way. Surge control line at normal operating pressure 4. Surge control line at maximum speed and total recycle 3. The design capacity of the machine Normally point 1 is the governing case (i. Surge control line at minimum speed and total recycle 2. lowest flow and lowest delta P) and the valve usually pass flow the machine design capacity 23 .e.Surge Control Valve  SURGE CONTROL VALVE SIZING Surge control valves should be sized for each of the following 1. Surge control Valve(contd..)   VALVE CHARACTERISTICS The installed characteristics of the surge control valve should be linear. This can be accomplished by either a linear trim characteristic control valve or line arising an equal percentage valve in the controller SPEED OF RESPONSE: The Valve is designed to “Open fully” from “full close” with in 2 seconds. This is accomplished by proper punematic accessories with Valve Actuator 24 . SERIES 4  GHH.CONTROL SYSTEMS INSTALLED AT JG CCC .BROSIG .SERIES 3+.PROTRONIC  25 .TURBOLOG  HARTMANN.BRAUN .COMPRESSOR CONTROLS CORPORATION . SURGE PROTECTION/CAPACITY CONTROL FOR CRITICAL COMPRESSORS IN JAMNAGAR  HEAT PUMP COMPRESSOR  MIN FLOW CONTROLLER IN DCS WITH OPERATOR ENTERED SET POINT  MANUAL SPEED CONTROL THROUGH DCS  PLAT FORMER/ISOMAR GAS COMPRESSORS  MIN MECHANICAL STOP IN SUCTION VALVES 26 . TAIL GAS COMPRESSOR  DEDICATED CONTROL SYSTEM "TURBOLOG" FROM GHH BASED ON COMPRESSOR PERFORMANCE MAP  SURGE CONTROL BY RECYCLE VALVE  MIN OPENING BY OPERATOR  SUCTION PRESSURE CONTROL BY IGV IMPLEMENTED IN GHH  TRIP ON SURGE 27 . COKER GAS COMPRESSOR  DEDICATED MULTI VARIABLE CONTROL CCC SEREIS 3+ CONTROLLER  SURGE CONTROL BY RECYCLE VALVE SEPARATELY FOR FIRST AND SECOND STAGE  ASC HAS PRESSURE OVERRIDE CONTROL(POC) FOR THE FIRST STAGE DISCHARGE PRESSURE  AUTO CAPACITY CONTROL BY SPEED VARIATION BASED ON SUCTION PRESSURE/COLUMN OVERHEAD PR.  DECOUPLING BETWEEN PERFORMANCE AND ANTI SURGE CONTROLLER 28 . VGO HT COMPRESSOR  DEDICATED CONTROL SYSTEM "TURBOLOG" FROM GHH BASED ON COMPRESSOR PERFORMANCE MAP  SURGE CONTROL BY RECYCLE VALVE  TO HASNDLE DIFFERENT PROCESS CONDITIONS (MOL WT CHANGE) SELECTION SWITCH IS PROVIDED IN THE UCP.3.2 28  VISUALIZATION IS PROVIDED IN THE PIB.0.7. MOL WT-2.4.  MIN OPENING BY OPERATOR  CAPACITY CONTROL IS BY SPEED CONTROL BY OPERATOR. 29 . PRT  DEDICATED CONTROL SYSTEM FROM CCC SERIES 4 SYSTEM  CONTROL SYSTEM IS DUAL REDUNDANT AND FAULT TOLERANT  FALL BACK STRATEGY IS IMPLEMENTED  PRT CONTROLS ARE VERY COMPLEX DUE TO MULTIPLE INTERACTING CONTROLS SUCH AS EXPANDER CONTROL DELTA P CONTROL RX/RG STEAM TURBINE CONTROLS BLOWER CAPACITY CONTROL LOAD SHARING CONTROL M/G CONTROL( LIMIT CONROL)  GHH TURBOLOG CONTROL SYSTEM FOR START UP AND MACHINE PROTECTION  GHH SPECIAL SURGE DETECTOR BASED ON DP REVERSAL/ 'T' REVERSAL( FAST T/C) ACROSS SUCTION AND DISCHARGE OF THE BLOWER 30 . Turbine / Compressor Control System Concept 31 . Compressor surge control systems  Shell Dep 16GS-600 .Turbolog operation manual  32 .Design requirements for compressor surge control systems  CCC Publication for Accurately defining surge control line  GHH-BORSIG .References Shell Dep 16ES-600 . THANK YOU 33 .
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