Dynamic Analysis of a Multi-Stage Compressor Train Augusto Garcia-Hernandez, Jeffrey A. Bennett, and Dr. Klaus Brun
Slide 2: Presenter/Author Bios Augusto Garcia-Hernandez Group Leader, Pipeline Simulation, Southwest Research Institute 14 years experience modeling pipelines and associated machinery MS Petroleum Engineering, University of Tulsa BS Mechanical Engineering, Universidad Central de Venezuela Jeffrey A. Bennett (Presenter) Research Engineer, Southwest Research Institute Experienced in thermal fluid network modeling MSc Turbomachinery Aeromechanics, KTH/Université de Liège BS Mechanical Engineering, Virginia Tech Dr. Klaus Brun Program Director, Southwest Research Institute Highly experienced in Rotating machinery, energy generation, power cycles, and fluids Ph.D., Mechanical and Aerospace Engineering, University of Virginia, 1996 M.S., Mechanical and Aerospace Engineering, University of Virginia, 1993 B.S.E., Aerospace Engineering, University of Florida-Gainesville, 1991 Dynamic Analysis of a Multi-Stage Compressor Train 2
Short Abstract A complex multiple-stage compressor train which is part of an off-shore booster installation was facing process and mechanical related problems. The frequency of these problems has increased lately leading to frequent trips and shut downs. These interruptions affect the operation of the plant and resulted in a loss in production and a subsequent loss of revenue to the company. The platform contains two similar compressor trains consisting of a four-stage compressor with a gas turbine driver. Each train is fitted with an integrated turbine compressor control panel. Thus, a detailed dynamic system simulation of the subject compressor trains was performed in order to provide a series of recommendations that would improve the safe operation and increase the reliability of the compression systems. Thus, results of the analysis and some of the recommendations obtained are presented in this case study. Dynamic Analysis of a Multi-Stage Compressor Train 3
Presentation Overview Background and Introduction Case Study Computational Model Dynamic Simulation Analysis Summary and Conclusions Dynamic Analysis of a Multi-Stage Compressor Train 4
Background Process and mechanical related problems on the multiple-stage compressor trains Machine frequent trips and shut downs Several surge events in the past two years and a catastrophic machine failure Loss in production and consequences of lost revenue for the company Dynamic Analysis of a Multi-Stage Compressor Train 5
Introduction A four-stage centrifugal compressor is driven by a gas turbine Each stage has its own dedicated antisurge loop and cooling system The trains are fed with gas from different production fields Compressor trains are used to boost the pressure of natural gas coming from off-shore production fields to an onland processing facility Dynamic Analysis of a Multi-Stage Compressor Train 6
Case Study Analyze an existing compressor train A site visit was performed to review and understand the existing antisure control system Build an accurate model of the compression train anti-surge system Evaluate different scenarios to provide recommendations to improve the system operation and reliability Parametric studies of Anti-Surge Valves (ASVs), Non-Return Valves (NRVs), Emergency ShutDowns (ESDs) Dynamic Analysis of a Multi-Stage Compressor Train 7
Compression System Two booster platforms Two four-stage centrifugal compressors on each platform The compressor trains have low pressure (LP1 & LP2), medium pressure (MP) and high pressure (HP) stages Each stage includes a suction scrubber, cooler, recycle loop, and blowdown line Each train is fitted with an integrated turbine compressor control panel Dynamic Analysis of a Multi-Stage Compressor Train 8
Compressor Train General Schematic Dynamic Analysis of a Multi-Stage Compressor Train 9
Detailed Hydraulic Model Schematic 4th Stg FLARE KO Drum 1 st Stg 2nd Stg 3rd Stg KO Drum KO Drum KO Drum Discharge Cooler KO Drum 1 st Discharge Cooler 2 nd Discharge Cooler 3 rd Discharge Cooler KO Drum 1 st Recycle valve 1 st Recycle Cooler Recycle valve Recycle valve Recycle valve OUTPUT FUEL GAS FLARE HP-SEP- DISCHARGE Dynamic Analysis of a Multi-Stage Compressor Train 10 LP-SEP- HEADER MP-SEP- HEADER HEADER HEADER
Model Characteristics Detailed programming of the ESD sequences and coastdown of the train Detailed piping volume arrays and anti-surge valve flow coefficient Flow and pressure boundary conditions Different influx gas compositions Gas turbine design power is corrected by elevation, ambient temperature, and running speed Dynamic Analysis of a Multi-Stage Compressor Train 11
Modeling Parameters Decay of Compressor Speed, N: NN tt = JJ NN 0 3 JJ NN 0 2 + PP 0 tt Surge margin, SM: Operating Point, OP: Turndown, TD: SSSS = OP= TTTT = QQ aa QQ ss QQ aa NN=cccccccccc QQ aa QQ ss NN=cccccccccc QQ aa QQ SS QQ SS HH=cccccccccc Where: N N 0 J P 0 Q a Q s H Compressor speed Initial speed Polar moment of inertia Initial Power Actual Flow Surge Flow Head Dynamic Analysis of a Multi-Stage Compressor Train 12
Evaluated Cases ESD Events Existing Sequence Modified sequences Coast down Delay Hot bypass Effect of Faster Opening of the Blowdown Valves Effect of Failure to Close of the NRVs Effect of NRVs in Series and Parallel System Control Process Upset Conditions Molecular Weight Sensitivity Analysis Dynamic Analysis of a Multi-Stage Compressor Train 13
Dynamic Simulation Analysis Existing system and ESD event from normal operating conditions 2nd and 3rd stages surged at 1.0-1.25s after the ESD was started 110 100 90 Anti-Surge Valves Opening versus Time during an ESD ESD 60 50 Surge Margin for each Compressor Stage during ESD Event ESD Valve Opening (%) 80 70 60 50 40 30 20 10 0 0 0.25 0.5 0.75 1 1.25 1.5 1.75 2 2.25 2.5 2.75 3 3.25 3.5 Time (s) ASV-Stage 1 ASV-Stage 2 ASV-Stage 3 ASV-Stage 4 Surge Margin (%) 40 30 20 10 0 0 0.25 0.5 0.75 1 1.25 1.5 1.75 2 2.25 2.5 2.75 3 3.25 3.5 Time (s) SM_S1:VAL SM_S2:VAL SM_S3:VAL SM_S4:VAL Dynamic Analysis of a Multi-Stage Compressor Train 14
Parametric Study Opening and delay times of the anti-surge valves Minimum Surge Margin Reached during an ESD (%) 25.0 22.5 20.0 17.5 15.0 12.5 10.0 Second Stage Anti-Surge Valve Opening Time Parametric Study - Compressor Shutdown Delay of 100 Milliseconds 7.5 5.0 LP-S1 LP-S2 2.5 MP-S3 0.0 HP-S4 1.50 1.75 2.00 2.25 2.50 2.75 3.00 3.25 2 nd Stage Anti-Surge Valve Opening Time (s) Dynamic Analysis of a Multi-Stage Compressor Train 15
Coast-Down Delay & Hot-Bypass The surge avoidance was found to be better with a coast down delay of 0.75 seconds and a second stage hot bypass valve of 4-inch 60 Surge Margin for each Compressor Stage during ESD Event with the Coast-Down Delay and Hot-Bypass 50 Surge Margin (%) 40 30 20 10 0 SM_S1:VAL SM_S2:VAL SM_S3:VAL SM_S4:VAL 0 0.5 1 1.5 2 2.5 3 3.5 4 Time (s) Dynamic Analysis of a Multi-Stage Compressor Train 16
Different Sequences Use of 6 and 3-inch quick opening valves with 1.2 and 1.5 seconds on second and third stages is recommended Dynamic Analysis of a Multi-Stage Compressor Train 17
Blowdown and NRVs Effect A failure of the check valves during an ESD event made three compressor stages surged Surge Margin (%) 60 50 40 30 20 Surge Margin for each Compressor Stage during a Failure of the Interstage Check Valves SM_S1:VAL SM_S2:VAL SM_S3:VAL SM_S4:VAL 10 0 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 6.5 Time (sec) Dynamic Analysis of a Multi-Stage Compressor Train 18
Summary & Conclusions Parametric studies of the main variables are very important to determine the correct path of suitable modifications for complex systems such as multistage compressors The dynamic interaction between the stages and their anti-surge loop can be modified by properly adjusting the anti-surge logic and sequences Initial dh/dq (pressure wave) behavior of each compressor stage is affected by the changes made in the entire train The impedance of the system will affect the initial reaction of the pressure waves originated when the machine is shutdown The system dynamics is very sensitive to changes since minor modifications in one stage will affect the transient behavior of the neighboring stages Dynamic Analysis of a Multi-Stage Compressor Train 19
Thank you for your attention! I will be happy to address any questions. Augusto Garcia-Hernandez Group Leader Augusto.garciahernandez@swri.org Jeffrey A. Bennett Research Engineer Jeffrey.bennett@swri.org Dr. Klaus Brun Program Director Klaus.brun@swri.org Dynamic Analysis of a Multi-Stage Compressor Train 20