Large Power Steam Turbine Research Articles

Optimization of an axial turbine for a small scale ORC waste heat recovery system

Low power Organic Rankine Cycle (ORC) turbines are typically characterised by flow efficiencies much smaller than those of large power steam or gas turbines. The paper concentrates on a possibility of improving the flow efficiency of an ORC axial turbine working on toluene using several optimization algorithms such as a simplex method of Nelder-Mead, a hybrid of genetic algorithm with the Nelder-Mead method, as well as implicit filtering. Values of the maximized objective function, which is the isentropic efficiency of the turbine stage, are found from 3D RANS computation of the flowpath geometry changing during the optimization process. Among the optimized geometric parameters are stator and rotor profile parametrization variables, rotor blade twist angle, circumferential lean and axial sweep angles, as well as parameters characterising the shape of endwall contours within the stator and rotor domain. The process of optimization leads to new 3D designs featuring increased efficiency compared to the original design, mainly due to a reduction in secondary and tip leakage flow losses as well as boundary layer, separation and leaving energy losses. The results especially highlight a large potential of the method of implicit filtering in optimizing multi-parameter objective functions. • A 45 kW turbine prepared for a small ORC CHP is shown. • Deterministic and hybrid methods of optimization are applied. • A wide range of variation of ORC turbine flowpath are investigated. • Performance maps for the best results are shown. • Turbine mechanical qualification is performed.

Efficiency Optimisation of Blade Shape in Steam and ORC Turbines

Abstract This paper is devoted to direct constrained optimisation of blading systems of large power and small power turbines so as to increase their internal efficiency. The optimisation is carried out using hybrid stochastic-deterministic methods such as a combination of a direct search method of Hooke-Jeeves and simulated annealing or a combination of a bat algorithm and simplex method of Nelder-Mead. Among free shape parameters are blade number and stagger angle, stacking blade line parameters and blade section (profile) parameters. One practical example of efficiency optimisation of turbine blading systems is modification of low load profiles PLK-R2 for high pressure (HP) stages of large power steam turbines. Another optimised geometry is that of an ORC radial-axial cogeneration turbine of 50 kWe. Up to 1% efficiency increase can easily be obtained from optimisation of HP blade profiles, especially by making the rotor blade more aft-loaded and reducing the intensity of endwall flows. Almost 2% efficiency rise was obtained for the optimised 50 kWe ORC turbine due to flow improvement at the suction side of the blade.

Optimization on start-up process of high-pressure rotor for large power steam turbine

This paper combines thermal-structure coupling technique and pattern search optimization algorithm to establish an optimization system for the start-up process of a turbine unit. Firstly, a finite element model for thermal-structure coupling calculation is established to accurately analyze the transient temperature field and thermal stress field, which can obtain the thermal stress distribution during start-up process. Afterwards, a program of optimization on rotor start-up process is exploited to improve the time allocation in each operating stage of start-up process, which minimizes the maximum equivalent stress of rotor. The maximum equivalent stress has reduced 25.7% after the optimization, which reveals obvious effect.

Numerical Study on Creep Properties of the Governing Stage Blade for Large Power Steam Turbine Considering Airflow Force

As one of the critical components of the steam turbine, the security of turboset is directly affected by the reliability of the blade. In this paper, taking the governing stage blade of a large-power steam turbine for example, the thermal elasticity stress and deformation of the blade were analyzed under the action of airflow force,centrifugal force and temperature load. Then the Norton model was adopted to simulate the blade creep process of 100000 hours and the stress and strain of the blade were obtained.

Study on Service Life of Last Stage Blade with Damped Structure in Large Power Steam Turbine

Blade which transfers thermal energy of steam into power, is a basic component in steam turbine. The reliability of blade is heavily influenced by the operating environment. The rotating blade experiences large inertial load and the wake of nozzle flow impose large variations of aerodynamic load on blade, in addition, the last stage blade is also affected by corrosion, so accidents of blade happen from time to time. Preventing blade failure has become one of the major objectives of turbine design and in-service maintenance. It is said that the reason for most of blade failure is fatigue fracture. In this study, a synthetical numerical model has been developed to evaluate service life of blade. At first, a numerical model to analyze the excitation force, dynamic frequency and dynamic stress of steam turbine blade has been developed, based on the results of dynamic stress analysis, a model to evaluate the service life of turbine blade has been developed. Many factors such as manufacturing technology of blade and erosion operating environment are considered to get more accurate results for service life of blade. At last, a last stage blade group of a large power steam turbine is analyzed in detail. It is shown clearly that the numerical model can give some rational quantitative results, and it is suitable for its engineering application to the improvement of the blade reliability.

Numerical simulation of a large power steam turbine run-up

The purpose of this paper is to propose a new behavioural evaluation of a large steam turbine during the run-up period based on a numerical simulation of the transient fluid dynamic processes that occur in the turbine during start-up. The transient process begins when the run-up valve starts its opening trip and ends when the rotor speed achieves the required value. This original approach is a follow-up of a methodology describing the steam turbine load rejection. Several primary operational parameters, such as pressure, temperature and flow-rate are revealed by the simulation, allowing the computation of secondary ones, like mechanical load and rotor speed. The results of this method are useful to equipment designers, in order to set-up both the aperture curve speed of the start-up valve and the response of the turbine protection against overspeed.

Direct Constrained Computational Fluid Dynamics Based Optimization of Three-Dimensional Blading for the Exit Stage of a Large Power Steam Turbine

The paper describes results of direct constrained optimization using Nelder-Mead’s method of deformed polyhedron and a Reynolds-averaged Navier-Stokes (RANS) solver to optimize the shape of three-dimensional blading for the exit stage of a large power steam turbine. The computations of the flowfield in the stator and rotor are compressible, viscous, and three-dimensional. Turbulence effects are taken into account using the modified model of Baldwin-Lomax. The objective function is the stage efficiency, with the exit energy considered a loss, and with constraints imposed on the mass flow rate in the form of a penalty function if the mass flow rate falls beyond the required range. The blade sections (profiles) are assumed not to change during the optimization. Two optimization tasks are reported in this paper, first—optimizing the stator straight and compound circumferential lean, and also stator and rotor stagger angles to keep the flow rate unchanged, giving a total number of optimized parameters equal to 5; second—optimizing the stator straight and compound axial sweep, also with stator and rotor stagger angles, also giving five optimized parameters. The process of optimization is carried out for a nominal load; however, due to the fact that exit stages of steam turbines operate over a wide range of flow rates away from the nominal conditions, the original and final geometries are also checked for low and high loads. The process of optimization gives new designs with new three-dimensional stacking lines of stator blades, and with significantly increased efficiencies, compared to the original design, at least for a larger part of the assumed range of load.