Danmei Xie

Numerical Simulation on Wet Steam Flow in the Last Stage of Steam Turbine in Nuclear Power Plant

High-capacity, low inlet parameters and huge flow are the characteristics of the nuclear steam turbine. As a result of adopting saturation steam and long blade, water erosion of last stage blade become more prominent. The secondary droplets’ continuously dynamic impact to the movable vanes in the wake of hollow stationary blade is the main reason for water erosion. So, it is necessary to research wet steam flow, vapor-liquid two phase flow, movement of droplets of different size and volume of sediment. The results of numerical simulation on wet steam two-phase flow in the last stage of nuclear turbine based on FLUENT software can show the flow characteristics of the wet steam. The most effective measure to prevent or mitigate the water erosion is that slotting suction ports in suitable locations of the hollow stationary blades’ concave surface or convex surface. Research shows that, suction slot should be set up in and around the hollow stationary blades, in a relatively wide of the near 0.8. Keywords-Steam turbine; Hollow stationary blade; Numerical simulation; Suction slot

Online Fatigue-Monitoring Models with Consideration of Temperature Dependent Properties and Varying Heat Transfer Coefficients

Thermal stress failure caused by alternating operational loads is the one of important damage mechanisms in the nuclear power plants. To evaluate the thermal stress responses, the Green’s function approach has been generally used. In this paper, a method to consider varying heat transfer coefficients when using the Green’s function method is proposed by using artificial parameter method and superposition principle. Time dependent heat transfer coefficient has been treated by using a modified fluid temperature and a constant heat transfer coefficient. Three-dimensional temperature and stress analyses reflecting entire geometry and heat transfer properties are required to obtain accurate results. An efficient and accurate method is confirmed by comparing its result with corresponding 3D finite element analysis results for a reactor pressure vessel (RPV). From the results, it is found that the temperature dependent material properties and varying heat transfer coefficients can significantly affect the peak stresses and the proposed method can reduce computational efforts with satisfactory accuracy.

Numerical simulation of wet steam two-phase flow in the last-stage stationary blade of super-critical steam turbine

For the last-stage blades of super-critical steam turbine, the problem of water erosion is serious. Using the design parameters of the last stage static and moving blade of a SC 600MW steam turbine, two-dimensional and three-dimensional numerical simulation of the flow field are carried out in this paper. And the distributing situation of the mach number, pressure, liquid density, nucleation rate and critical radius in the cascade channel are calculated. The pressure distribution of two-dimensional simulation is consistent with the experimental data in literature. The simulation results of three-dimensional indicate that, above 0.5 relative blade height, the wet steam flow characteristics change slightly along the radial direction. So the steam condensing flow in three-dimensional cascade under such condition can be simplified to two-dimensional flow.

Numerical Simulation of Suction Slot Structure on the LP Last Stage Stationary Blades of Steam Turbine

To open suction slots in arc and back-arc face of hollow stationary blade at suitable place, using the pressure difference between inside and outside of the slot, is one of the most direct and effective to protect the moving blades from water erosion. By using the FLUENT software, this article conducted the numerical simulation to the steam flow field of LP last stage, which is opened with a suction slot at the relative width of 0.2 and 0.7 in arc and back-arc face of hollow stationary blade when the opening angle is 45°. Comparative analysis was conducted to the dewetting effect and its impact on the steam flow field between the slot rounding or not and different width from 2 to 5 mm. Results show that rounding suction slot with a 4 mm wide with opening angle of 45° is optimal.

Calculation of Rotor's Torsional Vibration Characteristics Based on Equivalent Diameter of Stiffness

In this paper, ANSYS finite element analysis software is used to simulate the twisted state of turbine integral rotors discs. For various stepped shaft structure, the formula of λ- stiffness influence coefficient is fit by changing the geometric parameters of the equal-thickness disc, then equivalent diameter of stiffness is obtained. For the cone-shaped disc, the equivalent diameter of stiffness is calculated in advance according to equal- thickness disc, and then the diameter is revised by the formula. Taking an integral rotor of a 600 MW air-cooled steam turbine as an example, its first four orders of the torsional vibration frequencies are calculated by using the equivalent stiffness. The calculating results show that the approach proposed in this paper has such features as simple and higher accuracy. Turbine-generator unit is one of the key equipments in a thermal power plant and a nuclear power plant. Once breaking down, it tends to cause great economic losses and social impact. With the development of power system, the capacity of steam turbine unit increases. Then the length of the shaft increases with the relative decline in cross-sectional area so that torsional vibration may occur due to mechanical reasons or electrical reasons. Torsional vibration will shorten the operational life of the shaft, even severe cases it can cause damage to the shaft. Therefore, the study of the shafts torsional vibration in large units is of great significance to the safe operation of power system (1-3) . In the process of calculating the shafts torsional vibration characteristics, two important physical parameters - torsional stiffness and moment of inertia need to be considered. However, the actual structure of turbine-generator rotor is rather complex, particularly in relatively concentrated areas of quality, usually accompanied by torsional deformation, and the part of the connecting shaft often has a certain inertia. For this reason, a simplified ideal model according to certain principles is applied in order to facilitate the vibration characteristics calculation (4) . And such simplified approach (also known as modeling) has a direct impact on the calculation accuracy of the results. For integral rotor, which is adopted by large turbine- generator unit, it is the most critical to get the equivalent diameter of stiffness in the modeling. Taking an integral rotor of a 600 MW air-cooled steam turbine as an example, the ANSYS solution method of integral discs torsional stiffness is discussed in this paper at first; then the computational method for the equivalent diameter of stiffness with different structural forms is studied. Based on this, the equal-thickness discs equivalent diameter of stiffness is calculated by a simple formula of the stiffness influence coefficient λ. While for the cone-shaped disc, it is amended from the fitting formula of the equal-thickness discs equivalent diameter of stiffness. Verification results show that the derived formula in the paper meets the accuracy requirement.

Analysis of Influence of Fast-Cut-Back Test on 1000-MW Steam Turbine Safety

The capacity of the power grid in China is increasing rapidly. Because of the reliability of the multi-infeed direct current (DC) system in the grid, power-system damping is relatively weak. Realiz...

Sensitivity Analysis on the Dynamic Characteristics of a 1000 MW Turbo-Generator Rotor

Taking a 1000 MW turbo-generator rotor as an example, the sensitivities to thermal effect in temperature range of 20–570 °C, both for lateral and torsional vibration, are analyzed. In addition, for lateral vibration, the sensitivities of the critical speeds are analyzed by changing bearing stiffness. The results show that increasing bearing-support stiffness leads to natural frequencies increased gradually but not linear. The first order is much more sensitive than the others. When stiffness of bearing is large enough, the natural frequencies almost do not change. For torsional vibration, the sensitivities of natural frequencies are analyzed by changing some mechanical parameters. With changing the stiffness and inertia of the rotor, their influences to the characteristics of the torsional vibration are obtained. The frequency can be modulated by changing the sectional structure of the shafting to avoid torsional vibration resonant. The results are also shown that torsional frequency and mode shape are much more sensitive to mechanical parameter than to thermal effect.

Analysis of Influence of FCB Test on 1000MW Steam Turbine Safety

The capacity of power grid in China increases rapidly. Because of the reliability of multi-infeed DC system in the grid, power system damping is relatively weak. Realizing isolated island operation of thermal power units with FCB (fast cut back) ability is considered to be the best solution of quick restoration of power grid. Taking a 1000MW USC (Ultra-supercritical) unit as an example, based on the data of the unit’s load refection tests, this paper conducts a look at several aspects of research: (1) predicting the maximum speed rise of rotor during FCB process with different loads by using Simulink; (2) predicting the water level of deaerator and condenser during FCB process with different loads by same method; (3) predicting the highest exhausted steam temperature of HP cylinder during FCB process with different loads by using FEM; (4) comparing these key parameters with FCB test data, it shows that the predicted results agree with test data very well. (5) analyzing the influence of FCB test on the safety and life loss of the thermal equipment.Copyright

A Balance Method Without Trial Mass Based on Lag Phase

Mass unbalance is one of the most common faults found in steam turbine shafting. It was reported that about 70% of the total turbo-generator units newly put into commission needs high-speed dynamic balance in site. Because of longer shafting and relatively lower support stiffness, the vibration of multi-rotor bearing system, is much more sensitive to mass-unbalance. In most cases, trial masses and runs are required for the calculation of correction masses before balancing a turbo-generator rotor and such a procedure is time-consuming and expensive. Our experience shows that one balance for a turbo-generator rotor in China, by using traditional balance method, will take at least 3 to 5 runs, even 6 to 10 runs. That means 100∼500t oil will be consumed each time for balancing a turbo-generator unit with capacity of 200MW to 600MW. A balancing method without trial mass was proposed at the end of 1980’s. As it needs no trial runs if the magnitude and orientation of the rotor unbalance could be determined by calculating the amplitude-frequency and phase-frequency characteristics of various rotor sections, it has been adopted by highly skilled engineers. But the principle disadvantage of this method is that effective application requires a high degree of operator insight or knowledge of the support characteristics (i.e., requires data taken at previously balanced procedure, or from other units to determine the magnitude and location of the unbalance). This paper deduced empirical formula for dynamic balancing without trail mass at first. Then, based on the data of lag phase from the experience over 100 units, a balance method without trial mass was developed. Implementation of this method on a 1000MW turbo-generator rotor shows that it is an effective and economical procedure and the balancing risk is reduced.Copyright

On-Line Calculation Method of Exhaust Steam Humidity Based on BP Neural Network for Steam Turbine

For condensing turbine, steam exhaust point is in wet steam area. The exhaust steam humidity of steam turbine is difficult to get due to lacking of effective measuring method. Calculation of exhaust steam humidity has always been one of the key parts of the analysis of thermal power units. The main factors affecting exhaust steam humidity are turbine load and turbine exhaust pressure etc, and they are of non-linearity. This paper develops a calculation method to calculate exhaust steam humidity based on BP neural network. Taking a N1000-25/600/600 ultra-supercritical (USC) steam turbine as an example, the exhaust steam humidity is calculated and the results show that the method has a good accuracy to meet the needs of the engineering application.© 2013 ASME