Development, Testing and Qualification of Innovative Low Viscosity Oil In Turbomachinery Applications

LecturesThe continued market demand to have more efficient machines, thus achieving energy savings and emission reductions, has motivated manufacturers to look for improvements even in area that have never been explored and evaluated till now. In this context, the authors focus the research on a high performance and high efficiency lubricant for Turbomachinery applications. New product has been formulated by a theoretical optimization of power loss reduction limiting the impact on the rotordynamic behavior. The paper reports the entire qualification process of the oil, starting from laboratory tests to certify its chemical properties, then goes through dynamic bearing test rig for the identification of stiffness and damping characteristics to finally present the results of tests on actual machinery (gas turbine, gear box and centrifugal compressor) under real operating conditions in terms of mechanical friction losses, bearing temperatures and rotordynamic behavior

Full Load Testing Of A 12.5 MW Vertical High Speed Subsea Motorcompressor

Lecturepg. 79-92In late 2006 Authors’ company was awarded a contract for the motorcompressor for the Ormen Lange Subsea Compression Pilot. This Pilot represents the first subsea motorcompressor unit ever built in a fully marinized version and tested in a water pit, which was developed specifically for the project at the customer’s site (Nhyamna, Norway). The prototype unit is a 12.5MW (16763HP) integrated motorcompressor, which runs up to 10.5krpm in a vertical configuration with the following features: Single casing; High-speed motor rigidly coupled to a multistage centrifugal compressor (3 journal bearings shaft line); Canned Active Magnetic Bearings (AMBs); Process gas used as cooling fluid for the Electric Motor; Internal separation system (to protect the bearings and the electric motor from the intrusion of solid and liquid materials); Fully marinized AMBs control system; The design and validation plan for this complex equipment were developed through a four years program where many challenging milestones were achieved. The Ormen Lange Subsea Compression Pilot motorcompressor has successfully completed an intensive full load testing campaign in the Authors’ Company plant including the following: Static-dynamic tuning of the AMBs; Mechanical Running Test; Compressor Performance Test (ASME PTC-10 Type 2 + Full Load test); Electric Motor Performance Test; Overall cooling system check; Landing test (partial landing and full speed delevitation test). The test campaign has fully demonstrated the functionality of this prototype unit capable of operation in the service conditions. The Next step will be the shipment to the costumer site where the submerged testing will be conducted. This paper will provide a detailed description of the main test results of the subsea motorcompressor covering all aspects of the test program including rotordynamic behaviour, compressor thermodynamic performance, axial load variation versus operating conditions (monitored thanks to the thrust AMB), electric motor cooling system behaviour, electric motor performance, AMBs and control system operability. Of special interest is the rotor delevitation test from full speed consisting in the two ton rotor running at 10.5krpm dropping onto the mechanical emergency bearings until the machine reached a complete stop condition. This test, which was repeated 5 times, provided a full-scale verification of the landing numerical simulation developed by the authors (Ransom et al., 2009)

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

GT2004-53084 DYNAMIC CHARACTERISTICS OF THE DIVERGING TAPER HONEYCOMB-STATOR SEAL

ABSTRACT This paper introduces a variant on the honeycomb-stator seal, which can extend the already strong stabilizing influence of this seal geometry for centrifugal compressors. The paper presents predicted and measured dynamic characteristics, demonstrating how a clearance, which diverges axially from inlet to outlet, increases the maximum effective damping of a honeycomb-stator seal, even though the average clearance is increased. The results also show a strong negative direct stiffness at zero and low frequency for this seal geometry (termed the "Diverging Taper Honeycomb Seal (DTHCS)"). The predictions are made with ISOTSEAL 1 , software developed at The Texas A&M Turbomachinery Laboratory. The test data, also obtained at the Turbomachinery Laboratory, 1 This code was developed within the Turbomachinery Laboratory, and is not a commercial product (not for sale). confirms the nature and magnitude of both these dynamic characteristics with close fidelity. However, measured leakage falls significantly below predicted leakage. The frequency dependence of the seal dynamic characteristics and the strong negative static stiffness require careful attention in rotor dynamics analysis

Instability Of A High Pressure Compressor Equipped With Honeycomb Seals.

LecturePg. 39-48A two casing (three-stage) high-pressure injection compressor train driven by a gas turbine via a gearbox was full load and full speed performance tested to demonstrate satisfactory aerothermal and rotordynamic performance. During the PTC 10 (1997) Type I testing, rotor instability was observed on the back-to-back (first and second stage) compressor casing. The third stage final compressor casing exhibited anomalous rotor centerline positions in the bearings and rotating stall. This paper discusses the technical analysis, resolution, and retesting to resolve the rotor instability, rotor equilibrium/synchronous response, and rotating stall issues experienced during the testing. It also shows the need for additional joint industry research to better understand and analyze the use of honeycomb seals in hydrocarbon-gas centrifugal compressors

Development And Application Of A Vertical High Speed Motor-Compressor Simulator For Rotor Drop Onto Auxiliary Bearings.

Lecturepg. 1-12During the conceptual development of a subsea motor-compressor prototype running on active magnetic bearings, the emergency landing on the catcher bearings was identified as a potential technology gap. This is because the rotor in object is vertical and supercritical. A subscale simulator was then developed with the twofold aim to collect useful experimental data for data matching with a numerical simulation (also developed for this special application) and to perform endurance testing of the catcher bearings to understand their mechanical limits. The selected scale factor was one-third in order to utilize standard size active magnetic bearings and meet the project schedule. The subscale rotor design was aimed to respect the dynamic similitude with the real machine having the same separation between the rotor critical speeds and the operating speed range. Maximum test rig rotor speed is 30,000 rpm. Moreover the test rig casing design simulated also the real casing dynamic behavior. The test campaign was then divided in two steps. During the first step a test matrix was defined to address all the potential important parameters in the landing dynamics: unbalance magnitude, unbalance distribution (to excite different modes), rotation speed at drop start, duration of the delevitation, type of axes to be deleviated and active magnetic bearings (AMBs) cooling medium. Overall 19 tests were performed. The main outcomes from the test were: The rotor always showed a forward cylindrical subsynchronous whirl; The whirl behavior was not affected by unbalance level and distribution, landing duration, or drop speed; The whirl frequency is not related to any rotor/casing natural frequencies. The numerical simulation was developed in a numerical computing environment software specifically for the test rig system and was tuned on the basis of the experimental results. A key factor in model tuning was the introduction of a cross coupled term to allow the rotor to follow a forward whirling motion since the beginning of the drop. The physical nature of this cross- coupled force is still to be exactly identified. The final simulation results well matched with the experimental data both in whirling direction and frequency. Afterward the simulation was extended to the full-scale machine to predict landing behavior during the future full load testing and operation. Simulation shows the machine is stable for nominal conditions and the stability margin is greater than two. Moreover catcher bearing loads are within allowable limits. Finally a sensitivity study was performed showing that decreasing catcher bearings clearances and reducing seal entry swirl will lead to improved stability margin and dynamic loads. A second step of testing was the endurance test of the catcher bearings to determine the maximum number of landing. For this purpose the same drop speed (30 krpm) and landing duration (10 sec) was used for all the test runs. Several catcher bearings damage indicators were experienced; finally it was evident that the most reliable indications came from the accelerometers mounted on the bearing housing. The endurance test lead to the conclusion that the current design of catcher bearings for this rotor configuration allows at least seven safe drops from full speed in conditions, which can be considered similar or even more severe than the real machine scenario