19. The flow in last stages of large steam turbines at part load and low load

1989 ◽  
pp. 153-160
Author(s):  
W. Riess ◽  
U. Blöcker ◽  
H. Neft ◽  
H.-G. Otto
Keyword(s):  
Steam Turbines ◽  
Part Load ◽  
Low Load

The Effect of Stage-Diffuser Interaction on the Aerodynamic Performance and Design of LP Steam Turbine Exhaust Systems

2018 ◽  
Author(s):  
Bowen Ding ◽  
Liping Xu ◽  
Jiandao Yang ◽  
Rui Yang ◽  
Yuejin Dai
Keyword(s):  
Steam Turbine ◽  
Renewable Energy Sources ◽  
Rotor Blades ◽  
Steam Turbines ◽  
Flow Conditions ◽  
Part Load ◽  
Last Stage ◽  
Load Conditions ◽  
Turbine Exhaust ◽  
Exhaust Systems

Modern large steam turbines for power generation are required to operate much more flexibly than ever before, due to the increasing use of intermittent renewable energy sources such as solar and wind. This has posed great challenges to the design of LP steam turbine exhaust systems, which are critical to recovering the leaving energy that is otherwise lost. In previous studies, the design had been focused on the exhaust diffuser with or without the collector. Although the interaction between the last stage and the exhaust hood has been identified for a long time, little attention has been paid to the last stage blading in the exhaust system’s design process, when the machine frequently operates at part-load conditions. This study focuses on the design of LP exhaust systems considering both the last stage and the exhaust diffuser, over a wide operating range. A 1/10th scale air test rig was built to validate the CFD tool for flow conditions representative of an actual machine at part-load conditions, characterised by highly swirling flows entering the diffuser. A numerical parametric study was performed to investigate the effect of both the diffuser geometry variation and restaggering the last stage rotor blades. Restaggering the rotor blades was found to be an effective way to control the level of leaving energy, as well as the flow conditions at the diffuser inlet, which influence the diffuser’s capability to recover the leaving energy. The benefits from diffuser resizing and rotor blade restaggering were shown to be relatively independent of each other, which suggests the two components can be designed separately. Last, the potentials of performance improvement by considering both the last stage rotor restaggering and the diffuser resizing were demonstrated by an exemplary design, which predicted an increase in the last stage power output of at least 1.5% for a typical 1000MW plant that mostly operates at part-load conditions.

Computations for Unsteady Compressible Flows in a Multi-Stage Steam Turbine With Steam Properties at Low Load Operations

2010 ◽  
Author(s):  
Shigeki Senoo ◽  
Kiyoshi Segawa ◽  
Hisashi Hamatake ◽  
Takeshi Kudo ◽  
Tateki Nakamura ◽  
...  
Keyword(s):  
Steam Turbine ◽  
Compressible Flows ◽  
Reverse Flow ◽  
Three Dimensional ◽  
Computation Time ◽  
Steam Turbines ◽  
Multi Stage ◽  
Low Load ◽  
Pressure Steam ◽  
Load Conditions

A computational technique for compressive fluid in multistage steam turbines which can allow for thermodynamic properties of steam is presented. The understanding and prediction of flow field not only at design conditions but also at off-design conditions are important for realizing high-performance and high-reliability steam turbines. Computational fluid dynamics is useful for estimations of flows. However, current three-dimensional multi-stage calculations for unsteady flows have two main problems. One is the long computation time and the other is how to include the thermodynamic properties of steam. Properties of the ideal gas, such as equations of state and enthalpy formula, are assumed in most computational techniques for compressible flows. In order to shorten the computation time, a quasi-three-dimensional flow calculation technique is developed. In the analysis, system equations of conservation laws for compressible fluid in axisymmetric cylindrical coordinates are solved by using a finite volume method based on an approximate Riemann solver. Blade forces are calculated from the camber and lean angles of blades using momentum equations. The axisymmetric assumption and the blade force model enable the effective calculation for multi-stage flows, even when the flow is strongly unsteady under off-design conditions. In order to take into account steam properties including effects of the gas-liquid phase change and two-phase flow, a flux-splitting procedure of compressible flow is generalized for real fluid. Density and internal energy per unit volume are selected as independent thermodynamic variables. Pressure and temperature in a superheated region or wetness mass fraction in a wet region are calculated by using a steam table. To improve computational efficiency, a discretized steam table matrix is made in which the density and specific internal energy are independent variables. For accuracy and continuity of steam properties, the second order Taylor expansion and linear interpolation are introduced. The computed results of last four-stage low-pressure steam turbine at low load conditions show that there is a reverse flow near the hub region of the last (fourth stage bucket and the flow concentrates in the tip region due to the centrifugal force. At a very low load condition, the reverse flow region extends to the former (i.e. the first to third) stages and the unsteadiness of flow gets larger due to many vortices. Four-stage low pressure steam turbine tests are also carried out at low load or even zero load. The radial distributions of flow direction downstream from each stage are measured by traversing pneumatic probes. Additionally pressure transducers are installed in the side wall to measure the unsteady pressure. The regions of reverse flow are compared between computations and experiments at different load conditions, and their agreement is good. Further, the computation can follow the trends of standard deviation of unsteady pressure on the wall to volumetric flow rate of experiments. The validity of the analysis method is verified.

scholarly journals Analysis of the Unsteady Flow Field in a Steam Turbine Control Valve using Spectral Proper Orthogonal Decomposition

2021 ◽  
Vol 6 (2) ◽  
pp. 11
Author(s):  
Christian Windemuth ◽  
Martin Lange ◽  
Ronald Mailach
Keyword(s):  
Proper Orthogonal Decomposition ◽  
Turbulence Modeling ◽  
Control Valve ◽  
Electrical Energy ◽  
Orthogonal Decomposition ◽  
Steam Turbines ◽  
Unstable Flow ◽  
Turbulent Structures ◽  
Part Load ◽  
Proper Orthogonal

A significant share of the conversion of thermal into electrical energy is realized by steam turbines. Formerly designed for continuous operation, today’s requirements include extended part load operation that can be accompanied by highly unstable flow conditions and vibrations within the control valve of the turbine. The prediction of the flow at part load conditions requires large computational efforts with advanced turbulence modeling in order to compute the flow at a reasonable accuracy. Due to the unsteadiness of the flow, the evaluation of the numerical results itself is a major challenge. The turbulent structures require statistical approaches, of which the use of Spectral Proper Orthogonal Decomposition (SPOD) has proven itself as a powerful method. Within this paper, the application of the method on a critical operating point with a temporal excitation of pressure oscillations observed in the experiments with dry air is presented. Using SPOD, the dominating flow phenomena were isolated and flow structures visualized.

Thermo-Economic Analysis of an Intercooled, Reheat and Recuperated Gas Turbine for Cogeneration Applications: Part II — Part-Load Operation

2001 ◽  
Author(s):  
R. Bhargava ◽  
G. Negri di Montenegro ◽  
A. Peretto
Keyword(s):  
Economic Analysis ◽  
Gas Turbine ◽  
The Other ◽  
Load Range ◽  
Part Load ◽  
Full Load ◽  
Performance Loss ◽  
Low Load ◽  
Cogeneration System ◽  
Load Conditions

The knowledge of off-design performance for a given gas turbine system is critical particularly in applications where considerable operation at low load setting is required. This information allows designers to ensure safe operation of the system and determine in advance thermo-economic penalty due to performance loss while operating under part-load conditions. In this paper, thermo-economic analysis results for the intercooled, reheat (ICRH) and recuperated gas turbine, at the part-load conditions in cogeneration applications, have been presented. Thermodynamically, a recuperated ICRH gas turbine based cogeneration system showed lower penalty in terms of electric efficiency and Energy Saving Index over the entire part-load range in comparison to the other cycles (non-recuperated ICRH, recuperated Brayton and simple Brayton cycles) investigated. Based on the comprehensive economic analysis for the assumed values of economic parameters, this study shows that, a mid-size (electric power capacity 20 MW) cogeneration system utilizing non-recuperated ICRH cycle provides higher return on investment both at full-load and part-load conditions, compared to the other same size cycles, over the entire range of fuel cost, electric sale and steam sale values examined. The plausible reasons for the observed trends in thermodynamic and economic performance parameters for four cycles and three sizes of cogeneration systems under full-load and part-load conditions have been presented in this paper.

The Characteristics of Rotating Instabilities in Low Pressure Steam Turbines at Low Volume Flow Operation

2015 ◽  
Author(s):  
Roland Sigg ◽  
Timothy Rice
Keyword(s):  
Renewable Energy Sources ◽  
Low Pressure ◽  
Rotating Stall ◽  
Operating Conditions ◽  
Flow Coefficient ◽  
Low Flow ◽  
Small Scale ◽  
Steam Turbines ◽  
Original Design ◽  
Low Load

For flexible operation steam turbines may operate occasionally at low load. Operation away from the original design regime looks set to be an increasing trend mainly due to the presence of intermittently available renewable energy sources in the grid. This paper sets out an approach for considering low flow effects on turbine designs. At low load operating conditions rotating instabilities (RIS) can occur in the rear stages of LP steam turbines. The instabilities are comparable in many ways to rotating stall in compressors. Ideally the turbine blade natural frequencies should be designed to avoid the frequencies generated by the RIS system. The characteristics of RIS systems were experimentally investigated to understand the dependency with both flow coefficient and exhaust configuration. Correlations have been developed to characterize the dynamic pressure amplitudes and the fractional speed of the RIS moving around the wheel. The presented correlation based method is shown calibrated for a specific blade design. Two different test rigs provide the basis for the work presented. A low pressure model steam turbine provided detailed information for key blade/exhaust combinations. A simplified small scale air turbine was used to provide additional input for the behavior with alternative exhaust back wall position. Observations of the characteristic RIS behavior from model turbine tests are set in context with observed changes in the flow field.

Alleviation of Rotating Pressure Oscillations in the Last LP Turbine Stage During Low-Load Conditions

2016 ◽  
Author(s):  
B. R. Haller ◽  
T. S. Rice ◽  
R. Sigg
Keyword(s):  
Design Space ◽  
Outer Boundary ◽  
Rotating Stall ◽  
Rotor Blades ◽  
Low Flow ◽  
Major Influence ◽  
Steam Turbines ◽  
Low Load ◽  
Last Stage ◽  
Lp Turbine

In Steam Turbines, under low flow conditions, the flow structure on the long last stage blades is complex. The rotor blades create outward radial flow. Recirculations are setup near the tip in the gap between the fixed and moving blades, and near the hub downstream of the moving blade. The blade carries negative loading and encounters gross flow separations. In this environment, fluctuations in pressure are detected rotating at about half of the rotor speed. Some similarities exist with rotating stall, as found in compressors. In the validation of a new blade design, checks are therefore included to ensure that the rotating excitation does not pass over a natural frequency of the blading. In turn, this can reduce the available design space. A less restrictive approach is to consider alleviation techniques. A promising candidate is a scheme where steam jets are directed into the flow, onto the LSB, from the outer boundary. Jets have been introduced and tested on a 1/3rd scale multistage steam turbine. The test turbine is both aerodynamically and mechanically representative of a full size machine. The blowing scheme was shown to reduce and then practically eliminate the rotating pressure pattern. 3D CFD computations reveal the major influence of the jets. The solution is elegant because it does not lead to loss of efficiency or design space.

Simulation on Performance of Sequential Turbocharging Diesel Engine with Inlet and Exhaust Bypass System

2014 ◽  
Vol 490-491 ◽  
pp. 464-467
Author(s):  
Xin Jie Cui ◽  
Shi Dong Zhang ◽  
Fan Shi ◽  
Chuan Lei Yang
Keyword(s):  
Diesel Engine ◽  
Engine Performance ◽  
Performance Difference ◽  
Part Load ◽  
Low Load ◽  
Simulation Results

Sequential turbocharging and inlet/exhaust bypass (STC-CAB) were composited to used on diesel engine, which can expand engine running area in part load and optimize the matching of turbocharger and diesel engine. The simulation was studied based on GT-POWER software in order to investigate the engine performance difference caused by stc-cab system. The simulation results showed that STC-CAB system can make the compressor away from surge area and expand diesel engine running area, improve the performance of torque in low load.

Thermoeconomic Analysis of an Intercooled, Reheat, and Recuperated Gas Turbine for Cogeneration Applications—Part II: Part-Load Operation

2002 ◽  
Vol 124 (4) ◽  
pp. 892-903 ◽  
Author(s):  
R. Bhargava ◽  
G. Negri di Montenegro ◽  
A. Peretto
Keyword(s):  
Gas Turbine ◽  
The Other ◽  
Safe Operation ◽  
Load Range ◽  
Part Load ◽  
Full Load ◽  
Performance Loss ◽  
Low Load ◽  
Cogeneration System ◽  
Load Conditions

The knowledge of off-design performance for a given gas turbine system is critical particularly in applications where considerable operation at low load setting is required. This information allows designers to ensure safe operation of the system and determine in advance thermoeconomic penalty due to performance loss while operating under part-load conditions. In this paper, thermoeconomic analysis results for the intercooled reheat (ICRH) and recuperated gas turbine, at the part-load conditions in cogeneration applications, have been presented. Thermodynamically, a recuperated ICRH gas turbine-based cogeneration system showed lower penalty in terms of electric efficiency and Energy Saving Index over the entire part-load range in comparison to the other cycles (nonrecuperated ICRH, recuperated Brayton and simple Brayton cycles) investigated. Based on the comprehensive economic analysis for the assumed values of economic parameters, this study shows that a midsize (electric power capacity 20 MW) cogeneration system utilizing nonrecuperated ICRH cycle provides higher return on investment both at full-load and part-load conditions, compared to the other same size cycles, over the entire range of fuel cost, electric sale, and steam sale values examined. The plausible reasons for the observed trends in thermodynamic and economic performance parameters for four cycles and three sizes of cogeneration systems under full-load and part-load conditions have been presented in this paper.

Investigation of Unsteady Pressure Fluctuations in a Simplified Steam Turbine Control Valve

2020 ◽  
Author(s):  
Christian Windemuth ◽  
Martin Lange ◽  
Ronald Mailach
Keyword(s):  
Steam Turbine ◽  
Power Plants ◽  
Pressure Fluctuations ◽  
Control Valve ◽  
Steam Turbines ◽  
Unsteady Forces ◽  
Part Load ◽  
Large Pressure ◽  
Head Surface ◽  
Flow Through

Abstract Steam turbines are among the most important systems in commercial and industrial power conversion. As the amount of renewable energies increases, power plants formerly operated at steady state base load are now experiencing increased times at part load conditions. Besides other methods, the use of control valves is a widely spread method for controlling the power output of a steam turbine. In difference to other throttling approaches, the control valve enables fast load gradients as the boiler can be operated at constant conditions and allows a quicker response on variable power requirements. At part load, a significant amount of energy is dissipated across the valve, as the total inlet pressure of the turbine is decreased across the valve. At these conditions, the flow through the valve becomes trans- and supersonic and large pressure fluctuations appear within the downstream part of the valve. As a result, unsteady forces are acting on the valve structure and vibrations can be triggered, leading to mechanical stresses and possible failures of the valve. Besides more complex valve geometries, a spherical valve shape is still often used in smaller and industrial steam turbines. Because of the smooth head contour, the flow is prone to remain attached to the head surface and interact with the flow coming from the opposite side. This behaviour is accompanied by flow instabilities and large pressure fluctuations, leading to unsteady forces and possible couplings with mechanical frequencies. The spherical valve shape was therefore chosen as the experimental test geometry for the investigation of the unsteady flow field and fluid-structure-interactions within a scaled steam turbine control valve. Using numerical methods, the test valve is investigated and the time dependent pressure distribution in the downstream diffuser is evaluated. The evolution of the flow stability will be discussed for different pressure ratios. Pressure signals retrieved from the control valve test rig will be used to compare the numerical results to experimental data.

Unsteady Flow Effects on Steam Turbine Last Stage Blades at Very Low Load Operating Condition

2018 ◽  
Author(s):  
Tadashi Tanuma ◽  
Michio Ogawa ◽  
Hiroshi Okuda ◽  
Gaku Hashimoto ◽  
Naoki Shibukawa ◽  
...  
Keyword(s):  
Structural Analysis ◽  
Large Scale ◽  
Measured Data ◽  
Tip Vortex ◽  
Steam Turbines ◽  
Aerodynamic Analysis ◽  
Unsteady Aerodynamic ◽  
Low Load ◽  
Last Stage ◽  
Load Conditions

Unsteady aerodynamic and structural interactive analysis method for design and development of highly efficient low pressure last stage blades and results of its main application on very low load conditions are reported in this paper. Main features of this method are the enhanced analysis scope including very low load conditions and validations using measured data of real steam turbines including very low load conditions as well. Our schemes for this project were introducing boundary conditions from measured data in real steam turbines, full annulus all blade unsteady aerodynamic analysis and large scale parallel computing for unsteady structural analysis. The aerodynamic analysis results indicate that one root cause of the relatively large blade vibration at low load conditions seems to be a tip vortex induced by the blade windage. A modified method that introduced accurate structural analysis boundary condition data from aerodynamic analysis results is demonstrated. The structural analysis of a six-blade group with lacing wire dumping structure was performed.

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