High speed modal balancing: modeling and testing of turbomachinery rotors

Il lavoro di tesi è stato svolto presso la GE Oil & Gas Nuovo Pignone di Firenze, industria leader mondiale nella progettazione, costruzione ed installazione di turbomacchine per il business Oil & Gas. L'attività riguarda l'introduzione della nuova tecnologia di equilibratura modale dei rotori di turbomacchine. Più precisamente, la tesi si occupa di: • Stato dell’arte dei metodi di equilibratura per rotori flessibili. • Messa a punto di un banco prova rotori (Rotorkit) presso l’Università di Pisa. • Progettazione in scala di una configurazione Rotorkit simile a un rotore di una turbomacchina GE. • Prove sperimentali dell’equilibratura modale sul Rotorkit. Dai risultati delle prove sperimentali in scala con il Rotorkit sono emersi sia aspetti essenziali per la prossima applicazione su scala industriale del metodo di equilibratura modale, sia risultati innovativi da un punto di vista scientifico, come la possibilità di equilibrare modi fuori dal campo operativo. The thesis was carried out at GE Oil & Gas Nuovo Pignone in Florence, which is a worldwide company leader in the design and construction of turbomachinery for the Oil & Gas business. The work concerns the new technology introduction of modal balancing of turbomachinery rotors. More specifically, the thesis deals with: • State of the art of methods for balancing of flexible rotors. • Setup of a rotor test rig (Rotorkit) at the Pisa University. • Design of a scaled Rotorkit configuration similar to a GE turbomachinery rotor. • Experimental tests of modal balancing on Rotorkit. Test results demonstrate both essential infos to the next application in an industrial scale of modal balancing method, and some innovation results from a scientific perspective, like the possibility to balance out of speed-range modes

Performance Test Of A Liquid Tolerant Impeller And Validation Of Wet Compression Predictive Model

LectureStandard centrifugal compressors are designed to process gas with limited liquid content: significant presence of liquid may be responsible for the rapid erosion and corrosion of both static and rotating components that yield to higher failure risk and shorter maintenance periods. Moreover the presence of liquid is associated to significant modifications of machine performance and machine operability. However, the possibility of compressing gas containing non negligible amounts of liquid allows to reduce size, dimensions and costs of the liquid removal stations with a consequent positive impact on the layout of subsea compression stations. With this aim, the OEM has developed a family of centrifugal impellers, the Wet Tolerant Impellers (WTI), specifically designed to process gas containing non negligible amounts of liquid, increasing the erosion resistance and promoting the liquid droplets breakup for subsequent stages. The validation of WTI has been carried out at the Norwegian University of Science and Technology (NTNU) in Trondheim; the test rig is a single stage air-water multiphase open-loop facility driven by a 450 kW motor capable of a maximum continuous speed equal to 11000 rpm. In the test campaign, first a standard impeller has been tested to assess the impact of liquid phase on performance and operating range (results have been summarized in Ferrara et al. [14]), then the specific WTI design has been tested and directly compared with the standard impeller results. The comparative test campaign has been focused on three different aspects: Performance evaluation in dry and wet conditions; Operating range evaluation in dry and wet conditions; Comparative erosion test. WTI test results have been compared with the performance curves obtained through the OEM internal tool specifically developed for the prediction of centrifugal compressors performance in wet conditions. Performance has been assessed varying the amount of liquid carried by the gas at two different rotating speeds: five Liquid Mass Fractions (LMF) have been considered for each speedline and a minimum of six test points have been recorded from partflow to overflow. The effect of liquid on machine operability has been assessed through a left-limit investigation by means of dynamic pressure probes readings in order to evaluate the stall/surge behavior for different values of LMF. In addition, the function between head rise to surge and LMF has been reconstructed. Tests results have shown the effectiveness of liquid tolerant design: erosion effects are weaker on WTI while performance levels and operating range are comparable to those of standard impellers

Centrifugal Compressor Rotordynamics in Wet Gas Conditions

LectureA new technology challenge in centrifugal compressor design and operation is the condensate phase management. End users (especially in offshore and subsea operations) are more and more interested to have a Wet Gas Compression system which is able to tolerate liquid in the process gas. Authors’ Company has initiated for several years a research program aiming to investigate the impact of the liquid phase on centrifugal compressor operability (mainly thermodynamics, rotordynamics, erosion, axial thrust). As an introduction, the Authors’ Company past experiences and more recent experimental tests [Ransom D. et al. 2011], [Bertoneri M. et al. 2012], are reviewed in order to show how the rotordynamic behaviour of a centrifugal compressor may be affected by the wet gas. However in the core, this paper is focused on the novel rotordynamic experimental outcomes of a wet gas single stage compressor test campaign. The machine was equipped with the following special instrumentation: Pressure and temperature probes along the flow path and internal seals; Magnetic lamination installed on the shaft end to allow for stability test through a magnetic exciter; Load cells installed in the thrust bearing; Torquemeter installed at the compressor coupling. The explored test conditions were: Wet gas = Air and Water mixture up to 3% of Liquid Volume Fraction (LVF); Suction pressure levels = 10, 15, 20 bar-a; Maximum Continuous Speed = 13500 rpm. The compressor went through an extensive test campaign where the following aspects were thoroughly investigated: Rotordynamic behaviour during steady state wet operation; Rotordynamic stability (through magnetic exciter); Transient phenomena: response to liquid load variations (LVF up to 8%), start-up/shutdown from wet conditions, start-up with stratified flow into suction pipe. The compressor dynamic behaviour was monitored both from lateral viewpoint (using no contact probes located close to bearing locations) and axial/torsional viewpoint (through the special instrumentation described above). Overall the compressor was able to withstand a huge amount of liquid phase, with an increased vibration level with respect to dry conditions but still in the safe area, both in steady and transient tests. Finally, major differences were found only at high flow – high liquid/gas density ratio conditions where an unexpected subsynchronous vibration (SSV) was showing up. The nature of this SSV was deeply investigated and finally it was fixed through a balance piston seal geometry change

Overview of Important Considerations in Wet Gas Compression Testing and Analysis

LectureDuring upstream production of natural gas fields, it is common that a gas-liquid mixture of product is brought to the surface. The mixture, termed wet gas, is generally made up of mostly gas with a small amount of liquid, typically up to 5% by volume of the mixture. Because of the difficulties of compressing wet gas, the practical approach has been to separate the liquid and gas phases before compression. However, large separation equipment is unfavorable for subsea installations because of the cost to place machinery on the sea floor. Instead, a compressor designed for wet gas operation is preferred because it eliminates the need for large separation equipment leading to plant simplification and cost reduction. To address this design need, researchers have been active in addressing the challenges with wet gas compression. As result, experimental work has been conducted to study the effects of wet gas on compressor aerodynamic and mechanical performance. This experimental research has presented many challenges in recreating wet gas conditions and quantifying the effect of the liquid on the compressor performance. The results from this testing have helped to characterize the performance effects. But so far each work has focused on a range of test variables without identifying those that have the largest effect on compressor performance. This paper aims to provide the reader with an overview of the completed wet gas research, the challenges associated with doing the experimental work, and a discussion of the resulting trends observed in most of the wet gas research. This will include an in-depth review of relevant literature on wet gas compression testing and performance, a discussion of the important research topics in wet gas compression, and a description on how wet gas experiments are set-up, performed, and the challenges associated with that testing. Also, this paper reviews the available test data using a multiple regression analysis to identify the important test variables and their effect on compressor power and pressure ratio. Some of the test parameters that are discussed are inlet pressure and temperature, gas-liquid temperature difference, liquid volume fraction, and speed. The results of the analysis are useful for establishing variables for a future test program to focus on operating conditions with the largest effect on performance. Additionally, the effects of wet gas on machinery performance are discussed relative to machine vibration and seals. Using the observed trends in test data and the knowledge from previous wet gas research, conclusions are presented to guide future analytical and experimental work in the area of wet gas compression

Mechanical Performance Of A Two Stage Centrifugal Compressor Under Wet Gas Conditions

Lecturepg. 121-128As subsea compression becomes a vital technology to the successful production of gas reserves in the North Sea, several technology issues will come to the forefront of the oil and gas industry. One of these important subjects is the capability to compress gas which includes a significant amount of liquids. Compressing wet gas requires knowledge in areas such as the prediction of turbomachinery performance with the mixed phase flow as well as the mechanical reliability of machinery in the same environment. This paper presents experimental results from a wet gas test campaign which, among other goals, is focused on characterizing the mechanical performance of a two stage compressor operating under wet gas conditions. Various mechanical parameters are monitored in the test program including rotor radial and axial vibration, rotor thrust, and shaft torque. A full array of wet gas conditions are tested with a suction pressure of 20 bar (300 psia) and liquid volume fractions in the range of 0.5 to 5%. The operating fluids are air and water, and the two stage compressor is operated at three speed lines ranging from high flow to low flow conditions. Significant variations are noted in the axial thrust, axial vibration and shaft torque. Thrust variations range from seemingly neutral thrust conditions at very low water injection rates to significant thrust increases (as compared to dry condition) for very high water injection rates. Rotor axial vibration is characterized by large amplitude and very low frequency, especially for the case in which the rotor thrust is balanced by the water injection. During higher levels of water injection, rotor axial vibration is generally characterized by relatively large amplitude and slightly higher frequency, although still very low as a percent of running speed. Variations in radial vibration are also noted, but to a much lesser extent

Radio frequency system for thermal soil remediation

Radiofrequency (RF) heating of contaminated sediments is an effective and flexible method for soils remediation. Proper design of the antennas responsible of radiating into the sediments has a pivotal importance in the performances of those processes, but difficulties arise due to the fact that the radiators are buried in a lossy, time - variant and temperature - dependent medium. In this paper, a novel system for RF soil heating is presented, with a particular emphasis on the design of antennas. Both simulations and measurements of the system are presented to show the effectiveness and the viability of such systems