High-temperature Steam Turbine Research Articles

Research and Development of Hybrid Power Units Heat Flow Diagrams with Cooled High-Temperature Steam Turbines

Fossil fuel thermal power plants account for almost 60% of Russian electricity and heat. Steam turbine units make almost 80% of this amount. The main method for steam turbine unit efficiency improvement is the increase in the initial steam parameters’ temperature and pressure. This reduces fossil fuel consumption and harmful emissions but requires the application of heat-resistant steel. The improvement in steel’s heat resistance leads to a non-linear price increase, and the larger the temperature increase, the more the steel costs. One of the methods of improving efficiency without a significant increase in the capital cost of equipment is an external combustion chamber. These allow an increase in the steam temperature outside the boiler without the need to use heat-resistant alloys for boiler superheaters and steam pipelines between the boiler and the steam turbine. The most promising is hydrogen–oxygen combustion chambers, which produce steam with high purity and parameters. To reduce the cost of high-temperature steam turbines, it is possible to use a cooling system with the supply of a steam coolant to the most thermally stressed elements. According to the calculations, the efficiency reduction of a power unit due to the turbine cooling is 0.6–1.27%. The steam superheating up to 720 °C in external combustion chambers instead of a boiler unit improves the unit efficiency by 0.27%. At the initial steam temperatures of 800 °C, 850 °C, and 900 °C, the unit efficiency reduction caused by cooling is 4.09–5.68%, 7.47–9.73%, and 8.28–10.04%, respectively.

Methods for Competitiveness Improvement of High-Temperature Steam Turbine Power Plants

The paper is concerned with the problem of the development of high-temperature steam turbine power plants with ultra-supercritical (USC) initial parameters. One of the main disadvantages of the USC power unit’s creation is high price due to the application of expensive heat-resistant materials for boiler, live and reheat steam pipelines in turbines. To solve this problem, the following technical improvements to reduce the application of the heat-resistant materials and equipment metal consumption are proposed: horizontal boiler layout, high temperature steam turbine with a cooling system, oxy-hydrogen combustion chambers, and two-tier low-pressure turbine. The influence of the above-mentioned solutions on the high-temperature steam turbine power plant efficiency was estimated using thermodynamic analysis. The promising equipment design was developed based on the results of numerical and experimental research. The analysis of the proposed solutions’ influence upon the economic parameters of a high-temperature power facility was investigated based on the developed cost analysis model, which included the equipment metal and manufacturing expenses. The introduction of all the mentioned cost reduction methods led to a decrease in the facility’s price by RUB 10.5 billion or 15%. The discounted payback period was reduced from 27.5 to 10 years and the net present value increased by RUB 9.6 billion or 16 times.

Research on low temperature brittleness of 30Cr1Mo1V high-temperature rotor and its life optimization in rapid start-up and warm-up process

Recently, there is the serious fracture for two high-temperature steam turbine rotors made of 30Cr1Mo1V steel in different power plants, characterized by brittle fracture. This steel has the disadvantage of low temperature brittleness. Currently, a large number of 30Cr1Mo1V rotors are in service. Meanwhile, these rotors are required to start up and warm up faster due to the demand for operation flexibility of the power system. In order to ensure the safety of the 30Cr1Mo1V rotors under flexible operation, it is necessary to study the low temperature brittleness of the rotors and its influence on the fatigue life in rapid start-up and warm-up processes. In this paper, the fracture causes of the 30Cr1Mo1V rotor were analyzed by the mechanical property tests, microstructure examination and fracture analysis. The test results showed that the toughness of rotor decreased significantly after service. Secondly, the temperature and stress changes of the high-temperature rotors during the rapid start-up and warm-up process were calculated by the finite element method. The simulation results showed that if the speed rose too fast, the thermal stress in the rotor inlet area would increase significantly and the temperature was lower than the fracture appearance transition temperature when reaching the full speed. The high stress will easily lead to a crack initiation under low-cycle fatigue. Then, crack instability propagation will soon occur due to the low temperature and poor toughness. Thirdly, the life of the turbine in the rapid start-up was optimized by controlling the startup time. In addition, the life under different warm-up conditions was quantitatively analyzed. It not only reveals the necessity of the warm-up process for the center hole rotor, but also successfully demonstrates that the warm-up process of the solid rotor can be cancelled, which improves the economy of the power plant.

Out-of-phase thermomechanical fatigue crack propagation in a steam turbine steel — Modelling of crack closure

Understanding of crack growth behaviour is necessary to predict accurate fatigue lives. Out-of-phase thermomechanical fatigue crack propagation tests were performed on FB2 steel used in high-temperature steam turbine sections. Testing results showed crack closure where the compressive part of the fatigue cycle affected crack growth rate. Crack closing stress was observed to be different, and had more influence on the growth rate, than crack opening stress. Crack growth rate was largely controlled by the minimum temperature of the cycle, which agreed with an isothermal crack propagation test. Finite element models with stationary sharp cracks captured the crack closure behaviour.

Current status of Japanese thermal power plants and life assessments of high temperature steam and gas turbine components

More than 80% of prime energy is now supplied by thermal power plants in Japan since the Great East Earthquake of 2011 and more than two thirds of them were operated for over 30 years. Evaluation of the residual life of those aged plants are, therefore, required to maintain reliability and also to avoid premature retirement. Several kinds of life assessment technologies for the high temperature components of aged steam and gas turbines have already been developed and applied to actual components. Further developments for the advanced ones are now still being conducted. The current status of Japanese thermal power plants is briefly overviewed and the life assessment technologies developed for evaluating the material degradation and component damage conditions and life extension capabilities of steam and gas turbines are explained with some examples of the applications. The differences between the development concepts and the methods developed for both turbines are also explained along with those of the design specifications.

Long Time High Temperature Stress Rupture Strength Behavior and Structure Stability Study on Ni-Base Superalloy Nimonic 80A

Nimonic 80A Ni-base superalloy can be used for high temperature steam turbine components.There is a critical requirement for turbine blade application that the stress rupture strength for 105 hrs at relevant high temperatures should be higher than 100MPa.On the other hand, it must keep good structure stability and no harmful phase such as-phase and the TCP phase formation at long time high temperature exposure. Therefore, the long time stress rupture tests at temperatures of 600, 650, 680 and 700°C for different stresses have been carried out. The long time structure stability has been also studied in detail. The results show that Nimonic 80A can meet the critical requirement for USC steam turbine blades at 600~700°C. Any detrimental phases have not been found at the long time stress rupture tests. The morphology of grain boundary carbides also has no apparent change. Based on above mentioned results, Nimonic 80A is recommended to be used for USC steam turbine components in the temperature range of 600~650°C.

Experimental investigation on combustion of hydrogen–oxygen and methane–oxygen mixtures in the medium of low-superheated steam

Experimental data are represented on the investigation of combustion of hydrogen–oxygen and methane–oxygen mixtures in the medium of low-superheated (initial temperature of approximately 150°C) steam at atmospheric pressure. The influence of the ratio of mass flows of the combustible mixture and steam on the qualitative composition of combustion products and the temperature of produced steam is revealed. Main laws for combustion of the hydrogen–oxygen mixture within the steam flow, which affect the completeness of mixture combustion, are determined. Experimental data on the influence of concentrations of the hydrogen–oxygen mixture within the flow of the steam and the combustible mixture upon the completeness of combustion are given. It is found that, when burning the hydrogen–oxygen mixture within the steam flow with a temperature of 1000–1200°C, it is possible using a variation of the combustible mixture flow. At the same time, the volume fraction of noncondensable gases in the produced steam is no more than 2%. It is revealed that there are several combustion modes of the hydrogen–oxygen mixture within the steam flow, in which, in one case, the steam always suppresses combustion and, in another one, detonation of the combustible mixture combustible mixture occurs. It is found that with the excess air factor close to unit, the combustion of the methane–oxygen mixture within steam and the vapor conversion of methane, which result in the appearance of free hydrogen in the produced high-temperature steam, are possible. The description and the principle of the operation of the experimental bench for investigation of combustion of methane–oxygen and hydrogen–oxygen mixtures in the medium of steam are given. Results of experimental investigations of burning fuel and oxygen in the medium of steam are used in the development of a steam superheater for a hightemperature steam turbine.

On the mechanism of dynamic embrittlement and its effect on fatigue crack propagation in IN718 at 650°C

IN718 is a commonly used nickel-base alloy for high temperature applications, e.g., in gas and steam turbines. At elevated temperatures, this and other superalloys are prone to the failure mechanism "dynamic embrittlement". Dynamic embrittlement can be considered as a kind of stress corrosion cracking, driven by tensile-stress-controlled oxygen grain boundary diffusion. Oxygen embrittles the grain boundaries by weakening the grain boundary cohesion resulting in fast and brittle intercrystalline crack propagation. In order to reveal the mechanism of dynamic embrittlement, high-temperature fatigue crack propagation tests were carried out at 650°C applying various dwell times and testing frequencies. Most of the tests were performed in laboratory air, but some experiments were run in vacuum as well, in order to eliminate environmental effects and, hence, to define the reference fatigue crack propagation behaviour. The observations show that at low stress intensity factor ranges ΔKI, continuous crack growth occurs. At intermediate values of ΔKI, no crack propagation takes place during the dwell part of the cycle. Rather, the crack extends during unloading and reloading between subsequent hold times. The time necessary to grow the crack under sustained load during the dwell time was found to decrease with increasing stress intensity factor. Therefore, at high values of ΔKI, there is a contribution of the crack propagation at constant stress, since the incubation time is shorter than the dwell time. A mechanism-based model was developed for the range of test parameters, where intergranular and transgranular areas exist side by side in the fracture surface. The total crack growth per cycle is calculated by a linear combination of the intergranular and the transgranular contribution using the corresponding area fractions as weighting factors. It is shown that simulation calculations based on this model approach correspond very reasonably to the experimental observations. Hence, the model provides a quantitative mechanismen-related description of the effect of dynamic embrittlement on fatigue crack propagation rate.

Thermosyphon Method for Cooling the Rotor Blades of High-Temperature Steam Turbines

The design scheme of closed two-phase thermosyphon were suggested that can provide standard thermal operation of blades of high-temperature steam turbine. The method for thermosyphon calculation is developed. The example of thermal calculation was implemented, it showed that to cool the steam turbine blades at their heating by high-temperature steam, the heat can be removed in the rear part of the blades by air with the temperature of about 440°C.

Features of steam turbine cooling by the example of an SKR-100 turbine for supercritical steam parameters

Basic principles of cooling of high-temperature steam turbines and constructive solutions used for development of the world’s first cooled steam turbine SKR-100 (R-100-300) are described. Principal differences between the thermodynamic properties of cooling medium in the steam and gas turbines and the preference of making flow passes of cooled cylinders of steam turbines as reactive are shown. Some of its operation results and their conclusions are given. This turbine with a power of 100 MW, initial steam parameters approximately 30 MPa and 650°C, and back pressure 3 MPa was made by a Kharkov turbine plant in 1961 and ran successfully at a Kashira GRES (state district power plant) up to 1979, when it was taken out of use in a still fully operating condition. For comparison, some data on construction features and operation results of the super-high pressure cylinder of steam turbines of American Philo 6 (made by General Electric Co.) and Eddystone 1 (made by Westinghouse Co.) power generating units, which are close to the SKR-100 turbine by design initial steam parameters and the implementation time, are given. The high operational reliability and effectiveness of the cooling system that was used in the super-high pressure cylinder of the SKR-100 turbine of the power-generating unit, which were demonstrated in operation, confirms rightfulness and expediency of principles and constructive solutions laid at its development. As process steam temperatures are increased, the realization of the proposed approach to cooling of multistage turbines makes it possible to limit for large turbine parts the application of new, more expensive high-temperature materials, which are required for making steam boilers, and, in some cases, to do completely away with their utilization.

Multilevel approach to lifetime assessment of steam turbines

• Deterministic and probabilistic method of lifetime assessment is presented. • Effect of creep and fatigue damage content on failure probability is analyzed. • Practical application shown by example of lifetime calculation of turbine rotor. This paper presents a multilevel methodology for a steam turbine lifetime assessment based on the damage calculation, probabilistic analysis and fracture mechanics considerations. Creep-fatigue damage calculations serve as a basis for evaluating the current lifetime expenditure and for defining additional steps of analysis. The need for the use of probabilistic analysis results from the inherent uncertainty in estimating the lifetime expenditure primarily caused by scatter in material properties. Fracture mechanics considerations are helpful in determining additional safety margins for components containing cracks. This methodology has been illustrated using an example of the lifetime calculations of a high-temperature steam turbine rotor. The calculations were based on the results of 2D numerical simulations performed for steady state and transient operating conditions.

Определение вязкости смесевого рабочего тела высокотемпературной турбины

Определение вязкости смесевого рабочего тела высокотемпературной турбины

Nuclear power plants with super-powerful high-temperature steam turbine

This paper describes the possibility of creation of 2200 MW turbine for hybrid Nuclear Power Plant (NPP) with external (as to reactor) steam superheating on the base of existing VVER-1000 reactor. We come with a number of useful outcomes and suggestions for the blueprint of the super-powerful high-temperature steam turbines that might be used in power industry and for increasing the effectiveness of the new turbines produced by the turbine-constructing companies.

1Cr1Mo1/4V 터빈 로터강의 크리프 손상 모델에 관한 연구

일반적으로 화력발전 터빈 로터나 케이싱과 같이 고온 고압에서 운전되는 설비의 경우 크리프 및 피로 손상이 주된 손상기구로 알려져 있다. 터빈 설비의 수명을 정확하게 예측하기 위해서 크리프 및 피로 손상 기구를 복합적으로 고려해야 하지만 500MW 급 대용량 터빈 설비의 경우 기저 부하를 담당하기 때문에 기동횟수가 많지 않고 고온에서 장시간 동안 안정적인 운전을 하므로 잔여수명을 결정할 때 크리프 수명을 주로 사용한다. 국내에서 20 년 넘게 운전되고 있는 대용량 터빈의 경우 대부분 니켈, 크롬, 몰리브덴, 바나듐 성분이 포함한 재료로 되어 있다. 본 논문에서는 대용량 터빈의 크리프 수명을 예측하기 위하여 1Cr1Mo1/4V 터빈 로터강에 대한 크리프 손상 모델을 제안하고자 한다.

Computational Simulation of Thermoelectric Generators in Marine Power Plants

In thermoelectric generation applications, the two indispensable conditions are the hot source and the cold source to provide the temperature difference for the generator. Thus, the waste heat recovery from various high temperature gas or steam turbines on ships by thermoelectric generators (TEG) is promising because the ocean naturally plays a role as an infinitely large cold source. Among other options, a pilot study of the applicability of thermoelectric generation to the boiler section of marine power plants is presented through CFD (Computational Fluid Dynamics) modeling. It is found that more than 600 W power may be produced from the waste heat of a 300 kW boiler but without an obvious loss of the system safety. [doi:10.2320/matertrans.E-M2011813]

Economics of Meeting Peak Electricity Demand Using Hydrogen and Oxygen from Base-Load Nuclear or Off-Peak Electricity

The Hydrogen Intermediate and Peak Electrical System (HIPES) is a new proposed system that uses low-cost off-peak electricity or base-load nuclear energy to economically produce electricity for peak electrical demand, spinning reserve, and power regulation. HIPES has three major subsystems. Hydrogen and oxygen are produced from water using (a) off-peak electricity by methods such as electrolysis or (b) steady-state hydrogen production methods such as nuclear-hydrogen production with thermochemical cycles. The two gases are stored in large underground facilities using the same technologies used for the seasonal storage of natural gas. Peak electricity is produced by an advanced steam turbine with a burner that combines stored H2, O2, and water to produce high-pressure 1500°C steam, which serves as feed to a special high-temperature steam turbine with actively cooled blades. The steam plant efficiency is ~70%. HIPES power outputs can be rapidly varied to match changing electricity demand because the slow-response component of a traditional steam system (the boiler) has been eliminated. The economics are based on (a) the low cost of large-scale underground gas storage, (b) a low-capital-cost efficient method to convert hydrogen and oxygen into peak electricity (no steam boiler), and (c) the large differences in the prices of base-load and off-peak power relative to the premium prices paid for peak power production, spinning reserve, and power regulation. The technology, markets, and economics are described.

Progress in the development of coatings for protection of new generation steam plant components

Coatings to prevent component oxidation in future supercritical high temperature steam turbines were developed for the first time in Europe during the COST522 programme. Promising results were obtained with slurry applied aluminide coatings and with a series of thermal sprayed coatings (FeAl, FeCrAl, NiCr and AlFeCoCr) deposited on P92. Since then, extensive research internationally has examined coatings to protect against steam oxidation, deposited by techniques including pack cementation, electroplating and chemical vapour deposition (fluidised bed and organometallic as well as thermal). The results of these studies, including steam oxidation and mechanical data are summarised, and the performance of the candidate systems is critically reviewed from the viewpoint of both materials behaviour and deposition technologies. An earlier version of this paper has been published in the proceedings of the "8th Advanced Power Generation" conference held in Liege, Belgium in September 2006. This version has been updated with the latest available results.

Design figures of high-temperature low-pressure combined steam-cycle power unit

The scheme and cycle of a promising highly economic coal-dust combined steam-cycle power unit are presented. The flow-rate, thermodynamic, and design figures of high-temperature sets (a coal-dust boiler and a high-temperature steam turbine) are considered.

System Simulation for 700.DEG.C. Class High Temperature Ultra Supercritical Steam Power Plant with Cooling Technology

High efficiency pulverized coal power plant technology, especially the system simulation and design for high temperature steam turbines, is discussed. It is believed that a 700-deg C class steam turbine system will be realized with Ni-based super alloys. The super alloys are more expensive than current materials like 12%Cr steels though its high temperature strength is excellent. In addition, the size of the alloys is limited for the current design. Therefore, it is necessary to study new design concept to utilize the super alloys. The key concept is the optimized combination of steam turbine cooling and the super alloys. In this paper, the development of a simulation technique and the application of the gas turbine cooling technique to the high temperature steam turbine design are discussed. The simulation software is specially designed to integrate the entire system simulation and the detailed design of components to evaluate the system performance with the cooled steam turbines. The results of calculation are assessed by taking the other calculations with a similar steam condition into consideration

Recent Life Assessment Technology for Existing Steam Turbines

A large and growing portion of electricity is produced by aging thermal power plants. Although excellent, high quality materials such as CrMoV steel and 12% Cr steel, etc. are used for the steam turbines, various forms of metallurgical degradation, due to creep and fatigue, etc. affect the parts and components during long-term operation at high temperature. Extending the life of steam turbines and ensuring high reliability requires life assessment technology, scheduled repairing, conversion, modification and upgrading of components in order to provide a stable power supply. As the high temperature parts and components of aged steam turbines are mainly metallurgically damaged by creep, fatigue and the interaction of both, life assessment combined with analytical and nondestructive methods is essential for realizing strategic plant life extension. We have developed a life assessment technology that takes material degradation into consideration, and have applied the procedure to more than 650 units and 2500 components since 1983. A rotor bore replication device was developed in 1989 for the purpose of nondestructive observation of creep voids and supporting the validity of life prediction results. This paper describes the technical features and applied experience of recent life assessment technology for existing high temperature steam turbines.