Surge Exploration Tests and Second Quadrant Characteristic Dynamic Modeling on Full-Scale Centrifugal Compressor

LectureSurge exploration tests on a full-scale centrifugal compressor have been performed allowing an evaluation of the transient behavior and the mechanical robustness of the compressor even during a critical event such as Surge. The result of this work is a breakthrough for the tuning of a centrifugal compressor model to be used for dynamic simulations and prediction of compressor dynamics during Surge events in a more reliable and robust way. Surge exploration tests results analysis, in terms of vibrations, axial displacements and thrust loads, together with development of a compressor enhanced dynamic model, allowed a change from a Surge acceptance criterion,based on the time spent on the left of the Surge Limit Line, to a more physics related criterion, based on the acceptable number of Surge cycles, thus optimizing the selection of additional protections, such as hot/cold gas bypass valves

Surge Exploration Tests and Second Quadrant Characteristic Dynamic Modeling on High Pressure Ratio Compressor (Hprc) Prototype

LecturesHigh Pressure Ratio Compressor (HPRC) technology is based on an innovative architecture that combines unshrouded and shrouded impellers on a single high-speed shaft to achieve pressure ratios and efficiency levels higher than other available technologies. In the final step of the product development and validation, a test campaign has been carried out with the aim to test the performance and explore the operability of the new machine. Surge exploration tests have been also performed allowing an evaluation of the transient behavior and the mechanical robustness of the compressor even during a critical event such as Surge. Compressor Surge has been analyzed under different conditions, forcing the operating point to move beyond the performance envelope in full speed, at low and high pressure levels, and during emergency shut-downs. Thanks to the complex arrangement of the gas loops and several valves used to recycle back the compressed gas, different levels of Surge intensity were induced upon emergency shut-down. The explorations of a fast event like Surge called for special instrumentations, configured to acquire process data both in direct and reverse flow conditions in the most reliable way, with a high frequency sampling for an oil and gas environment. The result of this work is a breakthrough for the tuning of a centrifugal compressor model – not only HPRC ones – to be used for dynamic simulations and prediction of compressor dynamics during Surge events (like Surge cycle frequency and absorbed torque during Second Quadrant operation) in a more reliable and robust way. Surge exploration tests results analysis, in terms of vibrations and thrust loads, together with development of a compressor enhanced dynamic model, allowed a change from a Surge acceptance criterion - based on the time spent on the left of the Surge Limit Line during an Emergency Shutdown event - to a more physics based criterion - based on the acceptable number of Surge cycles, thus increasing selection optimization of additional protections, such as hot/cold gas bypass valves

C' Type PTFE Gaskets Performances In High Pressure Sour Applications

Lectur

Surge Exploration Tests and Second Quadrant Characteristic Dynamic Modeling on Full-Scale Centrifugal Compressor

LectureSurge exploration tests on a full-scale centrifugal compressor have been performed allowing an evaluation of the transient behavior and the mechanical robustness of the compressor even during a critical event such as Surge. The result of this work is a breakthrough for the tuning of a centrifugal compressor model to be used for dynamic simulations and prediction of compressor dynamics during Surge events in a more reliable and robust way. Surge exploration tests results analysis, in terms of vibrations, axial displacements and thrust loads, together with development of a compressor enhanced dynamic model, allowed a change from a Surge acceptance criterion,based on the time spent on the left of the Surge Limit Line, to a more physics related criterion, based on the acceptable number of Surge cycles, thus optimizing the selection of additional protections, such as hot/cold gas bypass valves

Surge Exploration Tests and Second Quadrant Characteristic Dynamic Modeling on High Pressure Ratio Compressor (Hprc) Prototype

LecturesHigh Pressure Ratio Compressor (HPRC) technology is based on an innovative architecture that combines unshrouded and shrouded impellers on a single high-speed shaft to achieve pressure ratios and efficiency levels higher than other available technologies. In the final step of the product development and validation, a test campaign has been carried out with the aim to test the performance and explore the operability of the new machine. Surge exploration tests have been also performed allowing an evaluation of the transient behavior and the mechanical robustness of the compressor even during a critical event such as Surge. Compressor Surge has been analyzed under different conditions, forcing the operating point to move beyond the performance envelope in full speed, at low and high pressure levels, and during emergency shut-downs. Thanks to the complex arrangement of the gas loops and several valves used to recycle back the compressed gas, different levels of Surge intensity were induced upon emergency shut-down. The explorations of a fast event like Surge called for special instrumentations, configured to acquire process data both in direct and reverse flow conditions in the most reliable way, with a high frequency sampling for an oil and gas environment. The result of this work is a breakthrough for the tuning of a centrifugal compressor model – not only HPRC ones – to be used for dynamic simulations and prediction of compressor dynamics during Surge events (like Surge cycle frequency and absorbed torque during Second Quadrant operation) in a more reliable and robust way. Surge exploration tests results analysis, in terms of vibrations and thrust loads, together with development of a compressor enhanced dynamic model, allowed a change from a Surge acceptance criterion - based on the time spent on the left of the Surge Limit Line during an Emergency Shutdown event - to a more physics based criterion - based on the acceptable number of Surge cycles, thus increasing selection optimization of additional protections, such as hot/cold gas bypass valves

New Control Method For Fixed Speed Compressors With Side Stream

Case StudyProblem statement: Operability issues were experienced on flash gas back-to-back compressors with lower molecular weight side stream, driven by fixed speed electric motor: • Failed attempts of start-up/loading • During normal operation compressors went off-line due to process upset (e.g. inlet flow decrease) • Unable to operate parallel trains simultaneously. Consequent loss of production

MODELING OF PRESSURE DYNAMICS DURING SURGE AND ESD

LectureCentrifugal compressors operability at low flow is normally limited by the onset of surge that occurs when operating near maximum achievable pressure rise. Surge is characterized by large amplitude and periodic pressure oscillations in which the compressor can also experience a series of flow reversal and recovery. Surge may happen when compressors are subjected to rapid transients. Examples are represented by the emergency shutdown (ESD) or a power failure. To prevent this from occurring, compressor stations are equipped with single or dual recycle systems using valves, which are required to quickly open in presence of ESD. For the proper sizing of recycles valves and whole system 3rd Middle East Turbomachinery Symposium (METS III) 15-18 February 2015 | Doha, Qatar | mets.tamu.edu Page 2 layout in general the estimation of surge inception and frequency during transients are key parameters especially for high-pressure centrifugal compressors and usually require the characterization of compressor pressure ratio curve including the reverse flow region. Spool dynamics is important to simulate ESD transients so also the torque law for the compressor needs to be provided and extended in the negative flow region. Usually pressure ratio and torque law are not available from experiments. A quite simple approach based on considerations about velocity triangles is analyzed in this paper and compared with experimental data. The approach is firstly assessed in the analysis of simple systems (one model test and a full scale compressor), both modeled according to the classical plenum-pipe description suggested by Greitzer. Computed pressure and speed trends are compared with experimental data from the dynamic pressure probes during surge and ESD. Kulite probes were installed in addition to the standard instrumentation in the test loops of the model test as also of the full scale string test. The curve extension model based on velocity triangles proved good accuracy in the simulation of dynamic behavior of those systems. The same method was also applied for the analysis of a more complex compression train equipped with four machines and modelled with a commercial tool for dynamic simulation of fluid systems. The results obtained showed good agreement with pressure and speed trends coming from site acquisition devices

Four Quadrant Centrifugal Compressor Performance

LectureLecture 16: The characterization of the compressor behavior in all quadrants of performance map has acquired, in the last years, growing attention. Two dedicated experimental campaigns have been performed to characterize fourth quadrant and second quadrant operation in terms of performance, pressure fluctuations and mechanical vibrations. Experimental campaigns allowed the acquisition of performance curves of a centrifugal compressor in deep choke up to reverse pressure and indicated a large region of safe operating conditions at low peripheral Mach number. In stable reverse flow, the trends of work coefficient and pressure ratio were acquired for a large range of flow rates together with the evolution of vibration and pressure fluctuation along the speed lines. Pressure ratio and absorbed power for the different modes of operation can be very important to simulate dynamic scenarios far from the steady state operation and size accordingly compressor protection equipment and predict accurately compressor startup torque from pressurized condition (Fourth Quadrant Operations). The main frequency content and amplitude of pressure variations within the flow field or the radial/axial vibrations at the bearings are important to estimate blade loading and possible presence of excitation frequencies in the system. In the reported experience the operating points characterized by stable reverse flow rates close to the nominal one in direct flow did not show features much more critical than in standard conditions (Second quadrant operation) . This result may be hopefully used to reduce BOP in early design phase of system layout

CO2 Compression At World's Largest Carbon Dioxide Injection Project

LectureCompressors for carbon dioxide (CO2) applications have been widely used in the O&G industry for urea production, enhanced oil recovery (EOR) and CO2 pipeline services for many years. New environmental challenges have re-focused the attention on increasing the efficiency of rotating equipment including optimization of the equipment configuration. To address these challenges, an electric motor driven CO2 compressor train has been designed for a large CO2 injection project in Western Australia. This compressor train was equipped with two compressor casings coupled through two gearboxes on either side of a double-ended variable frequency drive (VFD) motor. For the CO2 injection project, the risk of condensation inside the carbon steel pipeline between compressor discharge and the injection wells was identified as a concern. The mixture of liquid water and CO2 results in carbonic acid that may result in corrosion of the carbon steel pipeline. To mitigate this risk the water needs to be removed from the CO2 stream prior to entering the pipeline. To maximize the removal of water, the CO2 compressor intermediate stage (3rd stage) pressure is required to operate within a fixed pressure range. The compressor string with two gearboxes, two compressor casings and a VFD results in a complicated torsional system. In cases where torsional vibration frequencies coincide with resonance frequencies, large torsional deflections and internal stresses could be generated. Continuous operation under these conditions could result in fatigue failure. Free-vibration analysis and a forced-response analysis were conducted for an analytical review of rotor response to static and harmonic torsional loads. VFD motors generate pulsating torques; even if the pulsating torques are very small with respect to the main torque, they can excite compressor train resonances with potential shaft and/or couplings damages. Final validation of the compressor trains has been the Full Speed, Full Load test and ASME PTC10 Type 1 performance test campaign conducted in June 2011. During this testing, torque pulsation measurements has been conducted for validation of torsional analytical results and pulsation amplitudes under steady state and start-up conditions. The compressor train was designed to be modularized. This required the package’s overall dimensions to meet very stringent space constraints. The project engineering challenges include: ergonomic design focusing on improving maintenance and operations access, compressor supports stiffness analysis for installation on module steel work and compressor train operability assessment. High CO2 discharge pressures, high operating temperatures and the need to minimize fugitive emissions result in challenges for the dry gas seals system (DGS) and lead to the design of a highly customized DGS configuration

A New Methodology for Verifying Pressurized Start-Up of Centrifugal Compressors Driven by Direct-On-Line Electric Motor by Leveraging String Test Results and Dynamic Simulation Analysis

LectureFixed-Speed Electric Motors driving Centrifugal Compressors are designed considering the pressurized start-up as the most critical condition in terms of the torque requirement. Their capability is checked during the design phase by means of dynamic simulation, which may suffer from uncertainties, especially in the low speed range. When a Complete Unit Test is requested by purchaser, on top of the defined scope, it can be exploited to validate and refine the dynamic simulation so to predict more accurately the behavior of the compressor train at site conditions and confirm the capability of the driver to start-up the compressor from Settled-Out condition. The present paper describes a new methodology to leverage Direct-On-Line Centrifugal Compressor Complete Unit Test results to improve predictability of on-site pressurized start-up thanks to an enhanced dynamic simulation model. A case study is also presented showing how the methodology has been successfully applied to a re-injection compressor string