Ultra-supercritical Steam Turbine Research Articles

Program development for performance analysis of a steam turbine system with the use of overload valve

The global energy market has grown steadily as various energy technologies have been developed. Renewable energy has been used widely but conventional power plants are still used as major electric power sources, including steam turbines and gas turbines. Recently, flexible power plant operation in terms of load management has become important in the power generation industry. For flexible operation, overload valve operation has been introduced for ultra-supercritical steam turbine plants. Overload valve operation is an operation wherein some of the steam at the control valve is bypassed into the middle of the high pressure turbine. In this study, an in-house program is developed for the analysis of ultra-supercritical steam turbines using overload valve operation. A full off-design analysis is performed based on theoretical and empirical correlations. Four kinds of operations were comparatively investigated; control valve operation, sliding pressure operation, and two types of overload valve operation. The influence of the overload valve is analyzed in terms of operating characteristics and performance.

Optimization design of separators for removing solid particles from main steam pipeline of high-parameter steam turbine

In this paper, particle separators with different structures are designed based on main steam pipe of an ultra supercritical steam turbine. With the employment of particle rebound model established through high temperature particle rebound experiment, systematic numerical simulations on the influence of particle trap structure, steam mass flow for transporting particles on separation performance and pressure loss characteristic of separation system are carefully conducted. Besides, the effect of particle separation system on the working performance of thermal system is also analyzed. Results show that particle separation efficiency of three traps increases with the increase of amount of steam for transferring particles first, which then stabilize after a certain value is reached, while pressure loss of particle separation system is basically constant. With a small amount of transporting steam, separation efficiency of 100μm particle in trap B can reach up to 78%, and pressure loss of the system is below 13kPa. Effect of particle separation system on the heat rate of 1000MW thermal system is less than 0.15%, which is well below the profits earned through the reduction of solid particle erosion to turbine blades. The result of this paper will provide new ideas for thoroughly solving erosion problem of high parameter steam turbine.

바나듐 및 크롬을 포함하는 다 성분 Boride 코팅의 생성 및 특성 평가

Boride coating applied on steam turbine parts of power plants has provided good particle erosion resistance under temperature of 550 o C, but it isn't able to protect the parts effectively any more in ultra super critical (USC) steam turbine which is being operated up to temperature of 650 o C. To ensure stable durability for USC steam turbine parts, an alternative coating replacing boride coating should be developed. In this study, multi-component boride coatings containing elements such as chromium (Cr) and vanadium (V) were formed on base metal (B50A365B) using thermochemical treatment method called by pack cementation. The thermochemical treatments involve consecutive diffusion of boron(B) and Cr or/and V using pack powders containing diffusion element sources, activators and diluents. The top layer of Cr-boride coating is primarily consisted of Cr2B3 and Cr5B3, while that of V-boride coating is mostly consisted of VB2 and V2B3. The (Cr,V)boride coating is consisted of Cr2B3, Cr5B3 and V2B3 mostly. The top surfaces of 3 multi-component boride coatings show hardness of 3200-3400 Hv, which is much higher than that of boride, about 1600-2000 Hv. In 5 wt.% NaCl solution immersion tests, the multi-component boride coatings show much better corrosion resistance than boride coating.

Numerical investigation on life improvement of low-cycle fatigue for an ultra-supercritical steam turbine rotor

In this paper, an axisymmetric rotor of a 1000-MW ultra-supercritical steam turbine was modeled with the commercial finite-element software ABAQUS with inlet parameters of 35 Mpa and 600°C. The temperature and Mises stress distributions of the rotor during the start-up procedure were then analyzed. The fatigue damage was predicted by the strain-life–based Manson-Coffin equation and the Miner rule. The results demonstrated that the fatigue damage was mainly generated at the rotor surface. For the requirement of the half life time, the cyclic number almost reached 4000. Furthermore, optimization by extending the warm-up phase is proposed to eliminate strain fluctuations and further decrease fatigue damage. The results showed that the fatigue damage significantly decreased at four key locations. The fatigue life during the start-up phase was improved.

Data reconciliation for the overall thermal system of a steam turbine power plant

Accuracy of online measurement data is usually not satisfactory for coal-fired power plants due to constraints of measurement techniques. Data reconciliation can help to improve the accuracy of online measurement with no extra requirements on equipment upgrading. Traditionally, data reconciliation is applied to a sub-system of a coal-fired power plant, for instance, mass balance of a steam turbine system. In this work, we present a systematic approach where data reconciliation is applied to the overall thermal system of a real-life steam turbine power plant. Improvement of data accuracy is obtained via the proposed approach compared with sub-system studies. Optimization of system selection and configuration of a data reconciliation problem is analyzed. Results show that uncertainty of on-line measured data can be reduced by up to 50% in a 1000MW ultra-supercritical coal-fired steam turbine power plant compared with previous studies.

Structure improvement and strength finite element analysis of VHP welded rotor of 700°C USC steam turbine

The optimized structure strength design and finite element analysis method for very high pressure (VHP) rotors of the 700°C ultra-super-critical (USC) steam turbine are presented. The main parameters of steam and the steam thermal parameters of blade stages of VHP welded rotors as well as the start and shutdown curves of the steam turbine are determined. The structure design feature, the mechanical models and the typical position of stress analysis of the VHP welded rotors are introduced. The steady and transient finite element analysis are implemented for steady condition, start and shutdown process, including steady rated condition, 110% rated speed, 120% rated speed, cold start, warm start, hot start, very hot start, sliding-pressure shutdown, normal shutdown and emergency shutdown, to obtain the temperature and stress distribution as well as the stress ratio of the welded rotor. The strength design criteria and strength analysis results of the welded rotor are given. The results show that the strength design of improved structure of the VHP welded rotor of the 700°C USC steam turbine is safe at the steady condition and during the transient start or shutdown process.

Application of a Creep-Damage Constitutive Model for the Rotor of a 1000 MW Ultrasupercritical Steam Turbine

A damage-based creep constitutive model for a wide stress range is applied to the creep analysis of a 1000 MW ultrasupercritical steam turbine, the inlet steam of which reaches 600 °C and 35 MPa. In this model, the effect of complex multiaxial stress and the nonlinear evolution of damage are considered. To this end, the model was implemented into the commercial software abaqus using a user-defined material subroutine code. The temperature-dependent material constants were identified from the experimental data of advanced heat resistant steels using curve fitting approaches. A comparison of the simulated and the measured results showed that they reached an acceptable agreement. The results of the creep analysis illustrated that the proposed approach explains the basic features of stress redistribution and the damage evolution in the steam turbine rotor over a wide range of stresses and temperatures.

Performance analysis of a multi-stage ultra-supercritical steam turbine using computational fluid dynamics

This study used computational fluid dynamics (CFD) to predict the operating characteristics and performance of a ten-stage high-pressure turbine (HPT) of an ultra-supercritical (USC) steam turbine. Focus was centered on validating the use of CFD for such steam turbines, particularly for predicting global performance and operation. To accomplish this, we compared the predicted performance under the design conditions with reference design data, and we also compared the simulated off-design operation characteristics with those predicted by a semi-theoretical method. After confirming the feasibility of the CFD calculation, we investigated the impacts of the rotor tip clearance and flow addition inside the turbine through an overload valve (OLV). The mass flow versus pressure ratio flow characteristics predicted by the CFD were very close to those from the semi-theoretical method. The tip clearance calculation showed that stage efficiency decreases more in a higher reaction stage than in a lower reaction stage, which is consistent with available literature data. Increasing the OLV flow increases the flow and pressure ratio of rear stages but decreases those of front stages, leading to net power boosting but with a small efficiency loss.

Vanadium-Boride코팅의 고온 내입자침식성 평가

【The components in ultra super critical (USC) steam turbine, which is under development for high efficient power generation, are encountering harsher solid particle erosion by iron oxide scales than ones in the existing steam turbines. Therefore, the currently used boride coating will not be able to hold effective protection from particle erosion in USC system and should be replaced by new particle erosion resistant coatings. One of the best protective coatings developed for USC steam turbine parts was found to be vanadium-boride (V-boride) coating which has a hardness of about 3000 HV, much higher than that of boride, 1600~2000 HV. In order to evaluate particle erosion resistance of the various coatings such as V-boride, boride and Cr-carbide coatings at high temperature, particle erosion test equipments were designed and manufactured. In addition, erosion particle velocity was simulated using FLUENT software based on semi-implicity method for pressure linked equations revised (SIMPLER). Based on experimental results of this work, the vanadium-boride coating was found to be superior to others and to be a candidate coating to replace the boride coating.】

(Invited) Oxidation Mechanisms of Alloys for Advanced Ultra-Super Critical Steam Applications

This research supports efforts to design and build safe and cost-effective advanced ultra-supercritical (A-USC) steam boilers and turbines, with increases in energy production efficiency and reductions in emissions, including CO2. A 1 liter flowing steam autoclave, rated to 346 bar/704°C and 228 bar/760°C, was constructed and steam oxidation tests conducted. Comparison tests were run at 1 bar. Parabolic rate constants were estimated from mass change data and compared with literature values from longer duration tests—but none at this high of combined temperature and pressure. Test materials included Ni-base alloys H230, H263, H282, IN617, IN625 and IN740. At high pressures the oxide scales were thicker and parabolic rate constants one–to-two orders of magnitude higher than at 1 bar. The 1 bar data matched literature values for chromia, while the 267 bar data had a higher oxidation rate. Possible causes for increased oxidation rates with increased pressure were examined. Increased solid state diffusion within the oxide scale is quantifiable and accounts for a modest increases in expected corrosion rate and scale thickness. Increased amounts of hydrogen in the alloy, injected into the metal during steam oxidation at high pressures, may increase oxygen permeability and thus lower the ability of the alloy to establish a chromia scale—an increase in the critical Cr content for chromia scales.

Fluid–structure interaction analysis of a high-pressure regulating valve of a 600-MW ultra-supercritical steam turbine

A high-pressure regulating valve is one of the most critical components in ultra-supercritical steam power plants and constantly works under the condition of high temperature and high pressure. In order to control the flow of steam into the turbine, the high-pressure regulating valve normally operates at small openings. Therefore, the phenomena such as whistling noise and turbulence can be caused by the throttling effect of the regulating valve. In addition, the flow-induced vibration due to coupling between the fluid flow and the moving parts like valve stem will also occur. In this paper, the pressure loss across the high-pressure regulating valve of a 600-MW ultra-supercritical steam turbine was assessed with the aid of computational fluid dynamics studies. Furthermore, the dynamic characteristics and vibration amplitude of the valve stem were also analyzed by using fluid–structure interaction method.

ICOPE-15-C050 The stiffness and vibration Analysis of LP casing of DFSTW's Ultra-supercritical 1000MW Steam Turbine

ICOPE-15-C050 The stiffness and vibration Analysis of LP casing of DFSTW's Ultra-supercritical 1000MW Steam Turbine

Deformation mechanisms in a precipitation-strengthened ferritic superalloy revealed by in situ neutron diffraction studies at elevated temperatures

The ferritic superalloy Fe–10Ni–6.5Al–10Cr–3.4Mo strengthened by ordered (Ni,Fe)Al B2-type precipitates is a candidate material for ultra-supercritical steam turbine applications above 923K. Despite earlier success in improving its room-temperature ductility, the creep resistance of this material at high temperatures needs to be further improved, which requires a fundamental understanding of the high-temperature deformation mechanisms at the scales of individual phases and grains. In situ neutron diffraction has been utilized to investigate the lattice strain evolution and the microscopic load-sharing mechanisms during tensile deformation of this ferritic superalloy at elevated temperatures. Finite-element simulations based on the crystal plasticity theory are employed and compared with the experimental results, both qualitatively and quantitatively. Based on these interphase and intergranular load-partitioning studies, it is found that the deformation mechanisms change from dislocation slip to those related to dislocation climb, diffusional flow and possibly grain boundary sliding, below and above 873K, respectively. Insights into microstructural design for enhancing creep resistance are also discussed.

The Application and Research on Manufacturing Technology of the Heavy Forging

For large forging is high-tech product of material, smelting, forging, heat treatment and it is the bottleneck which restricts the development of the modern heavy equipment manufacturing industry. The key technology such as forging and heat treatment of large forgings is researched. Finally, with the ultra supercritical power generation units of low-pressure rotor, the production process control technology such as smelting, forging and heat treatment is introduced. The method provides a reliable basis for the localization of production of ultra supercritical steam turbine rotor and has the important practical application value.

Research and Application on Fault Diagnosis for Steam Turbine Using Multi-Parameter Fusion

For the running situation of supercritical and ultra-supercritical steam turbine unit, a fault diagnosis method of steam turbine based on multiple parameters fusion is proposed. The association of the fault mode with the vibration parameters, the thermodynamic parameters and the operational parameters is built, according to fault development mechanism, equipment operation data and professional experience. The overall state evaluation of mechanical equipment is given, the reliability of fault diagnosis is improved, and the need of the steam turbine fault diagnosis is met, by means of comprehensive evaluation of multiple parameters. Example applications verify this method.

Thermal Stress Analysis of Rotor of Ultra Supercritical Steam Turbine

The rotor of ultra supercritical steam turbine runs in bad condition with high parameters of steam. The large heat stress of rotor may appear when the operating conditions of turbine unit is changed, for example, adjusting load to meet the requirements of peak and valley of grid, especially, improper operation causing serious damage to rotor. According to theory of thermal stress analysis, first, the steam parameters and their heat transfer coefficients of all cascades of 1000MW ultra supercritical steam turbine is calculated. Then the temperature field and stress field of the high-pressure rotor in the process of cold startup calculated by the finite element software are analyzed and discussed. The results are important to the startup and changing conditions of 1000MW ultra supercritical steam turbine unit.

Effects of coolant flow rates on cooling performance of the intermediate pressure stages for an ultra-supercritical steam turbine

The effects of the coolant flow rates on the thermal and flow fields of the first two intermediate pressure (IP) stages of an ultra-supercritical steam turbine was numerically investigated using the Conjugate Heat Transfer (CHT) method, and the un-cooled case was also simulated for comparison. The three-dimensional Reynolds-Averaged Navier–Stokes (RANS) solution was utilized to analyze the flow field and temperature distributions of the first two IP stages. The numerical results show that the steam cooling system has proved its ability to cool down the high temperature components, even in the case with the low coolant flow rate. The cooling performance can be improved with increased coolant flow rate, however, great flow losses would be induced and make the stage efficiency reduce by 1.23%. The different coolant flow rates also lead to great differences in the flow field in the front cavity of the first stage: ingress dominated flow condition with the low coolant flow rate and egress dominated flow condition with the high coolant flow rate. The negative influence of the ingested hot main steam on the cooling effect was also described.

Analysis and Optimizing Utility of the Ultra Supercritical Steam Turbine Shaft Vibration

The operation reliability of the power plant has much to do with the turbine shaft vibration. The object of this paper is N1000-25.0/600/600 steam turbine. In view of the turbine shaft vibration fault, the analysis and solution were made in two conditions. They refer to start-up and on-load steam turbine running state. The solution methods have produced a good result. And they can be used for reference to the turbines of the same type in the future.

The Research on Heat Transfer Coefficient of Wheel Rims of Large Capacity Steam Turbines

Several models for calculating the heat transfer coefficient of wheel rims of large capacity steam turbines are presented. Taking a certain 600MW supercritical turbine rotor as an example, the heat transfer coefficient of wheel rim under cold start-up are analyzed and calculated, according to the and comparison, and the quantitative calculation results are given The results show that the heat transfer coefficient of rotor rims obtained by Sarkar method is close to the heat transfer coefficient obtained by a research institute based on a rib heat transfer model. In finite element analyses, the calculation results by mentioned method could provide the heat transfer boundary condition of temperature and thermal stress field calculations of supercritical and ultra-supercritical steam turbine rotors.

Shape and operation optimisation of a supercritical steam turbine rotor

The presented study discusses the problem of shape optimisation of selected areas of the rotor of the high pressure part of an ultra-supercritical steam turbine together with the optimisation of the turbine start-up method, using the maximum stress objective. The analysis relates to the rotor of a conceptual ultra-supercritical turbine which is characterised by high parameters of operation. The consequence is that the machinery components are subjected to significant stress, which further results in a substantial reduction in its life and reliability. These adverse effects can be contained in two ways, i.e. by optimising the shape of the rotor areas characterised by high stress values and by optimising the method of the turbine start-up. In the case of the rotor under analysis, it is the thermal stress caused by large temperature gradients occurring in unsteady states of operation that has a predominant impact on the stress level.The performed research prove that the manner in which the power unit start-up is initiated and carried out depends largely on the limitations of the materials used to make the machinery components. This, in turn, has an impact on the assessment of the power unit in terms of energy and economy. The obtained optimisation results translate directly into the power unit energy effectiveness.