Optimization of a 900 mm Tilting-Pad Journal Bearing in Large Steam Turbines by Advanced Modeling and Validation

2018 ◽  
Author(s):  
Ümit Mermertas ◽  
Thomas Hagemann ◽  
Clément Brichart
Keyword(s):  
Steam Turbine ◽  
Power Plants ◽  
Journal Bearing ◽  
Leading Edge ◽  
Success Factor ◽  
Steam Turbines ◽  
Oil Supply ◽  
Modeling Methods ◽  
Tilting Pad ◽  
Tilting Pad Journal Bearing

Modernization of steam turbine components can extend the life of a power plant, decrease maintenance costs, increase service intervals and improve operational flexibility. However, this can also lead to challenging demands for existing components such as bearings, e.g., due to increased rotor weights. Therefore, a careful design and evaluation process of bearings is of major importance. This paper describes the advanced modeling methods applied for the optimization of a novel 900 mm three-pad tilting pad journal bearing followed by validation results that showed a high bearing temperature sensitivity to the fresh oil supply temperature during operation. The bearing was especially developed to cope with increased rotor weights within the framework of low pressure steam turbine modernizations at two similar 1000 MW nuclear power plants. With a static bearing load of approximately 2.7 MN at a rotor speed of 1500 rpm, it represents one of the highest loaded applications for tilting pad journal bearings in turbomachinery worldwide. After identification of the reasons for the sensitivity, advanced modeling methods were applied to optimize the bearing. For this purpose, a more comprehensive bearing model was developed taking into account the direct lubrication at the leading edge of the pads and the thermo-mechanical pad deformation. For the latter, a co-simulation between the bearing computation code and structural mechanics software was performed. The results of the entire analyses indicated modifications of bearing and pad clearance, pad pivot position, circumferential and axial pad length as well as pad thickness. Furthermore, the oil distribution into the pads was optimized by modifying the orifices within the bearing. The optimized bearing was then implemented on both units and proved its excellent operational behavior at increased fresh oil supply temperatures of up to 55°C. In addition, inspections during scheduled outages after 18 months of operation and subsequent restarts with reproducible bearing behavior confirmed the robustness of the optimized bearing. In conclusion, the application of advanced modeling methods proved to be the key success factor in the optimization of this bearing, which represents an optimal solution for large steam turbine and generator rotor train applications.

Optimization of a 900 mm Tilting-Pad Journal Bearing in Large Steam Turbines by Advanced Modeling and Validation

2018 ◽  
Vol 141 (2) ◽  
Author(s):  
Ümit Mermertas ◽  
Thomas Hagemann ◽  
Clément Brichart
Keyword(s):  
Steam Turbine ◽  
Power Plants ◽  
Journal Bearing ◽  
Optimal Solution ◽  
Success Factor ◽  
Steam Turbines ◽  
Oil Supply ◽  
Modeling Methods ◽  
Tilting Pad ◽  
Tilting Pad Journal Bearing

Modernization of steam turbine components can extend power plant lifetime, decrease maintenance costs, increase service intervals, and improve operational flexibility. However, this can also lead to challenging demands for existing components such as bearings, e.g., due to increased rotor weights. Therefore, a careful design and evaluation process of bearings is of major importance. This paper describes the applied advanced modeling methods and performed validation for the optimization of a novel 900 mm three-pad tilting pad journal bearing that showed high temperature sensitivity to the fresh oil supply temperature. The bearing was developed to cope with increased rotor weights within the low pressure (LP) steam turbine modernization at two 1000 MW nuclear power plants. With a static load of 2.7 MN at a speed of 1500 rpm, it represents one of the highest loaded applications for tilting pad bearings in turbomachinery worldwide. After identification of the reasons for the sensitivity, advanced modeling methods were applied to optimize the bearing. For this purpose, a more comprehensive bearing model was developed considering the direct lubrication at the leading pad edge and pad deformation. The results of the entire analyses indicated modifications of bearing clearances, pad length, thickness, and pivot position. The optimized bearing was then implemented on both units and proved its excellent operational behavior at increased fresh oil supply temperatures of up to 55 °C. In conclusion, the application of advanced modeling methods proved to be the key success factor in the optimization of this bearing, which represents an optimal solution for turbomachinery.

Repowering and Retrofitting

2002 ◽  
Author(s):  
Andreas Pickard
Keyword(s):  
Steam Turbine ◽  
Power Plants ◽  
Free Market ◽  
Leading Edge ◽  
Project Planning ◽  
Combined Cycle ◽  
Steam Turbines ◽  
Planning Stage ◽  
Reheat Steam ◽  
Plant Optimization

At the start of this new century, environmental regulations and free-market economics are becoming the key drivers for the electricity generating industry. Advances in Gas Turbine (GT) technology, allied with integration and refinement of Heat Recovery Steam Generators (HRSG) and Steam Turbine (ST) plant, have made Combined Cycle installations the most efficient of the new power station types. This potential can also be realized, to equal effect, by adding GT’s and HRSG’s to existing conventional steam power plants in a so-called ‘repowering’ process. This paper presents the economical and environmental considerations of retrofitting the steam turbine within repowering schemes. Changing the thermal cycle parameters of the plant, for example by deletion of the feed heating steambleeds or by modified live and reheat steam conditions to suit the combined cycle process, can result in off-design operation of the existing steam turbine. Retrofitting the steam turbine to match the combined cycle unit can significantly increase the overall cycle efficiency compared to repowering without the ST upgrade. The paper illustrates that repowering, including ST retrofitting, when considered as a whole at the project planning stage, has the potential for greater gain by allowing proper plant optimization. Much of the repowering in the past has been carried out without due regard to the benefits of re-matching the steam turbine. Retrospective ST upgrade of such cases can still give benefit to the plant owner, especially when it is realized that most repowering to date has retained an unmodified steam turbine (that first went into operation some decades before). The old equipment will have suffered deterioration due to aging and the steam path will be to an archaic design of poor efficiency. Retrofitting older generation plant with modern leading-edge steam-path technology has the potential for realizing those substantial advances made over the last 20 to 30 years. Some examples, given in the paper, of successfully retrofitted steam turbines applied in repowered plants will show, by specific solution, the optimization of the economics and benefit to the environment of the converted plant as a whole.

scholarly journals Thermal Turbulent Flow in Leading Edge Grooved and Conventional Tilting Pad Journal Bearing Segments—A Comparative Study

Lubricants ◽  
2018 ◽  
Vol 6 (4) ◽  
pp. 97 ◽  
Author(s):  
Philip Croné ◽  
Andreas Almqvist ◽  
Roland Larsson
Keyword(s):  
Comparative Study ◽  
Journal Bearing ◽  
Flow Characteristics ◽  
Leading Edge ◽  
Inlet Temperature ◽  
Average Value ◽  
Tilting Pad ◽  
Sst Turbulence Model ◽  
Effective Boundary Condition ◽  
Tilting Pad Journal Bearing

A comparative study between a conventional- and leading edge grooved (LEG) tilting pad journal bearing (TPJB) segment is performed. The developed model uses the Shear Stress Transport (SST) turbulence model, coupled with the energy equation and a partial differential equation for the fluid domain mesh displacement to predict the thermal flow characteristics. Instead of using an effective boundary condition to determine the inlet temperature of the LEG pad and excluding the additional LEG portion, as is common practice, the whole geometry of the LEG is modeled. Several sizes of the LEG portion is investigated and it is shown to have quite a small influence on pressure, temperature, film thickness and turbulence intensity. Moreover, the results also show that the conventional pad gives rise to higher levels of turbulence in the mid plane compared to its LEG counterpart, while the latter has a marginally higher value of turbulence when the volume average value is computed. The maximum value of turbulence is however present in the conventional model.

Theoretical and Experimental Analyses of Directly Lubricated Tilting-Pad Journal Bearings With Leading Edge Groove

2018 ◽  
Author(s):  
Thomas Hagemann ◽  
Hubert Schwarze
Keyword(s):  
Theoretical Model ◽  
Test Data ◽  
Journal Bearing ◽  
Leading Edge ◽  
Journal Bearings ◽  
Oil Supply ◽  
Tilting Pad ◽  
The Impact ◽  
Leg Design ◽  
Tilting Pad Journal Bearings

Flooded lubrication of tilting-pad journal bearings provides safe and robust operation for many applications due to a completely filled gap at the leading edge of each pad. While flooded conditions can be ensured by restrictive seals on the lateral bearing ends for any conventional bearing design, direct lubrication by leading edge grooves (LEG) placed on the pads represents an alternative to produce completely filled gaps at the entrance to the convergent lubricant film. Moreover, this design is flexible to apply different axial sealing baffles in order to influence the thermal equilibrium within the entire bearing. A theoretical model is presented that describes the specific influences of LEG design on the operating characteristics. First, in opposite to conventional tilting-pad journal bearing designs the LEG is a self-contained lube oil pocket which is generally connected to an outer annular oil supply channel. Consequently, each leading edge groove can feature a specific speed and load dependent effective pocket pressure and flow rate. As a consequence of this and the fact that the LEG is part of the pad, it directly influences its tilting angle. Secondly, the thermal inlet mixing model must consider the specific flow conditions depending on the main flow direction within the film as well as the one between outer annular channel and pocket. The novel LEG model is integrated into a comprehensive bearing code validated earlier for other bearing designs. The code is based on an extended Reynolds equation and a three-dimensional energy equation. The entire theoretical model is validated with test data from high performance journal bearing test rig for a four tilting-pad bearing in load between pivot orientation. The bearing is described by the following specifications: 0.5 nominal preload, 60% offset, 70° pad arc angle, 120 mm inner diameter, 72 mm pad length and 1.7 per mille relative bearing clearance. Measurements are conducted for rotational speeds between 4000 and 15000 rpm and specific bearing loads between 0.5 and 2.5 MPa. Within the investigated operating range good agreement between theoretical and experimental data is achieved if all boundary conditions are accurately considered. Additionally, the impact of single simplifications within the model are studied and evaluated. Finally, the test data is compared to results from the same test bearing with modified lubricant oil supply conditions in order to identify specific properties of LEG design. Here, the leading groove edge elements are replaced by conventional spray-bars. It is shown that an assessment of the comparison depends on the definition of reference conditions as the bearings require different oil flow rates for nominal operation due to their design.

Tilting-Pad Journal Bearing in Hybrid Operation: A Numerical and Experimental Investigation

2018 ◽  
Author(s):  
Nico Buchhorn ◽  
Sebastian Kukla ◽  
Beate Bender ◽  
Marc Neumann
Keyword(s):  
Hydrostatic Pressure ◽  
Carrying Capacity ◽  
Journal Bearing ◽  
Operating Conditions ◽  
Load Carrying Capacity ◽  
Oil Supply ◽  
Hybrid Operation ◽  
Tilting Pad ◽  
Load Carrying ◽  
Tilting Pad Journal Bearing

Large turbine bearings are usually equipped with hydrostatic jacking mechanisms to separate bearing and shaft during transient start-stop procedures. They are turned off once hydrodynamic operation is reached. In some cases, under severe operating conditions, the hydrostatic oil supply is kept running although the rotor already runs in full speed. The supplied amount of jacking oil is very small compared to the regular oil supply. However, experimental data of a large tilting-pad bearing shows that this hybrid operation has a considerable impact on the load carrying capacity in terms of lower pad temperature and larger film thickness. In this paper, a theoretical investigation to analyse the effect of increased load carrying capacity of a large tilting-pad journal bearing in hybrid operation is presented. The increase is driven by three different aspects: 1) hydrostatic pressure component, 2) increase in lubricant viscosity due to the injection of cold oil, 3) decrease of temperature gradients and thus thermal pad deformation. Subject of the approach is a ø500 mm five-pad, rocker-pivot tilting-pad journal bearing in flooded lubrication mode. The experiments are carried out on the Bochum test rig for large turbine bearings. The theoretical analyses are performed with a simulation code solving the Reynolds and energy equations for the oil film and calculating the thermomechanical pad deformations simultaneously. By considering each of the three above aspects separately and in combination, their share of load increase can be assessed individually. Contrary to expectations, the results indicate that the increase is not mostly based on the hydrostatic pressure component. Instead, the advantageously decreased pad deformations make the largest contribution to the increased load carrying capacity while the alteration in viscosity shows the least impact.

scholarly journals Testing, Analysis, and CFD Modeling of a Profiled Leading Edge Groove Tilting Pad Journal Bearing

1998 ◽  
Author(s):  
Stephen L. Edney ◽  
Gregory B. Heitland ◽  
Scan M. DeCamillo
Keyword(s):  
High Speed ◽  
Journal Bearing ◽  
Leading Edge ◽  
Cfd Modeling ◽  
Operating Characteristics ◽  
Light Load ◽  
Operating Stability ◽  
Tilting Pad ◽  
Original Insight ◽  
Tilting Pad Journal Bearing

Testing and analysis of a profiled leading edge groove tilting pad journal bearing developed for light load operation is described. This bearing was designed for a generic, small, high speed steam turbine operating at projected loads of less than 25 psi (172.4 kPa) and journal surface speeds to 400 ft/s (122 m/s). On the second turbine application, a rotor instability was experienced with the oil flowrate reduced to optimize bearing steady state performance. This instability was eliminated by machining a taper on the exit side of the feed groove on each pad. At the reduced flowrate, the profiled groove bearing greatly improved the operating characteristics of the rotor system by reducing vibration amplitudes and stabilizing operation at speed. This paper is divided into two sections. The first section compares the rotordynamics analysis with test data that shows improved unbalance response and operating stability with the profiled groove bearing. The second section provides original insight of the effect of the profiled geometry on the bearing flow field using computational fluid dynamics models.

A Study of the Thermal Characteristics of the Leading Edge Groove and Conventional Tilting Pad Journal Bearings

1993 ◽  
Vol 115 (2) ◽  
pp. 219-226 ◽  
Author(s):  
W. Dmochowski ◽  
K. Brockwell ◽  
S. DeCamillo ◽  
A. Mikula
Keyword(s):  
Theoretical Analysis ◽  
Journal Bearing ◽  
Operating Temperature ◽  
Thermal Characteristics ◽  
Leading Edge ◽  
Journal Bearings ◽  
Tilting Pad ◽  
Tilting Pad Journal Bearing ◽  
Leg Design ◽  
Tilting Pad Journal Bearings

In this paper dealing with the tilting pad journal bearing, experimental results are presented which show that, at higher shaft speeds, the leading-edge-groove (LEG) design has significantly lower operating temperatures to those of the conventional design of tilting pad journal bearing. Subsequent theoretical analysis has shown that this reduction in pad operating temperature is the result of feeding cool oil directly to the leading edge of the pad. This has the effect of reducing the amount of hot oil carried over from one pad to the next.

Characteristics of a Spherical Seat TPJB With Four Methods of Directed Lubrication—Part II: Rotordynamic Performance

2017 ◽  
Vol 139 (12) ◽  
Author(s):  
David M. Coghlan ◽  
Dara W. Childs
Keyword(s):  
Matrix Model ◽  
Journal Bearing ◽  
Leading Edge ◽  
Dynamic Data ◽  
Rotordynamic Coefficients ◽  
Test Conditions ◽  
Tilting Pad ◽  
Frequency Independent ◽  
In Series ◽  
Tilting Pad Journal Bearing

Measured and predicted rotordynamic characteristics are presented for a four-pad, spherical-seat, tilting-pad journal bearing (TPJB) with 0.5 pivot offset, 0.6 L/D, 101.6 mm nominal diameter, and 0.3 preload in the load-between-pivots orientation. One bearing is tested four separate times in the following four different lubrication configurations: (1) flooded single-orifice (SO) at the bearing shell, (2) evacuated leading edge groove (LEG), (3) evacuated spray-bar blocker (SBB), and (4) evacuated spray-bar (SB). The same set of pads is used for every test to maintain clearance and preload; each method of lubrication is added as an assembly to the bearing. Test conditions include surface speeds and unit loads up to 85 m/s and 2.9 MPa, respectively. Dynamic data includes four sets (one set for each bearing configuration) of direct and cross-coupled rotordynamic coefficients derived from measurements and fit to a frequency-independent stiffness-damping-mass (KCM) matrix model. The pivot stiffness (pad and pivot in series) is measured and incorporated into predictions.

Characteristics of a Spherical-Seat TPJB With Four Methods of Directed Lubrication—Part I: Thermal and Static Performance

2017 ◽  
Vol 139 (12) ◽  
Author(s):  
David M. Coghlan ◽  
Dara W. Childs
Keyword(s):  
Journal Bearing ◽  
Thermal Characteristics ◽  
Leading Edge ◽  
Static Data ◽  
Axial Temperature ◽  
Tilting Pad ◽  
Thermal Data ◽  
In Series ◽  
Static Performance ◽  
Tilting Pad Journal Bearing

Static and thermal characteristics (measured and predicted) are presented for a four-pad, spherical-seat, tilting-pad journal bearing (TPJB) with 0.5 pivot offset, 0.6 L/D, 101.6 mm nominal diameter, and 0.3 preload in the load-between-pivots orientation. One bearing is tested four separate times in the following four different lubrication configurations: (1) flooded single-orifice (SO) at the bearing shell, (2) evacuated leading edge groove (LEG), (3) evacuated spray-bar blocker (SBB), and (4) evacuated spray-bar (SB). The LEG, SBB, and SB are all considered methods of “directed lubrication.” These methods rely on lubrication injected directly to the pad/rotor interface. The same set of pads is used for every test to maintain clearance and preload; each method of lubrication is added as an assembly to the bearing. Test conditions include surface speeds and unit loads up to 85 m/s and 2.9 MPa, respectively. Static data include rotor–bearing eccentricities and attitude angles. Thermal data include measured temperatures from 16 bearing thermocouples. Twelve of the bearing thermocouples are embedded in the babbitt layer of the pads, while the remaining four are oriented at the leading and trailing edge of the loaded pads exposed to the lubricant. Bearing thermocouples provide a circumferential and axial temperature gradient. The pivot stiffness (pad and pivot in series) is measured and incorporated into predictions.

Experimental Investigation and Numerical Modelling of a Large Heavily-Loaded Tilting Pad Journal Bearing With Polymer Lined Pads

2020 ◽  
Author(s):  
Filippo Cangioli ◽  
Richard Livermore-Hardy ◽  
Guy Pethybridge ◽  
Uemit Mermertas ◽  
Michael Stottrop ◽  
...  
Keyword(s):  
Power Plants ◽  
Fossil Fuel ◽  
Dynamic Behaviour ◽  
Journal Bearing ◽  
Operating Conditions ◽  
Superior Performance ◽  
Tilting Pad ◽  
Tilting Pad Journal Bearing ◽  
Fossil Fuel Power Plants ◽  
Shaft Surface

Abstract A large tilting-pad journal bearing (TPJB) with “PEEK” polymer-lined pads was tested over a range of operating conditions representative of those experienced on turbogenerators used in fossil fuel power plants. The 500 mm diameter test-bearing has four offset-pivot pads, ball and socket pivots, load-between-pivot configuration, directed lubrication and hydrostatic jacking features. The operating conditions explored during the test campaign characterize the static and dynamic behaviour of the bearing over a range of shaft surface speeds between 40 m/s and 95 m/s and maximum specific load of 4.75 MPa. Similar test conditions were previously investigated on the same bearing with whitemetal lined pads, allowing for a direct comparison. A thermo-elasto-hydrodynamic (TEHD) model for TPJBs with polymer-lined pads is introduced in this paper and validated against experimental test data. Experimental data along with numerical results reveal and confirm the superior performance that can be attained using TPJBs with polymer lined pads at high specific loads.

Sign in / Sign up

Export Citation Format

Share Document