Factors influencing gas turbine use and performance

Abstract

The reliability of industrial gas turbines can be limited by the premature degradation of critical hot gas path components. Cost effective operation of these turbines therefore requires a knowledge of component life and its limitations according to service requirements. Through this knowledge, ways to restrict the degradation of components can also be determined. Creep, corrosion, and fatigue are considered to be the principal life limiting factors with the hot gas components. The present paper discusses the influence of these three processes on component life, and examples of associated service problems are presented. Specific reference is made to the corrosion resulting from the presence of sodium sulphate deposits in offshore turbines. Control of this corrosion through the use of fuel additives and protective coatings is considered. MST/448     

Corrosion in coal-fired gas turbines

The purpose of this paper is to review corrosion processes and experience related to coal-fired gas turbines. For over 40 years there have been major programmes of research directed towards burning coal in a gas turbine either directly or as a coal-derived fuel. This history is briefly reviewed, demonstrating the importance which corrosion of the hot section has had in limiting the achievements and defining the systems. The probable corrosion mechanisms are identified, and because of their synergistic interaction with corrosion, erosion and deposition are also considered. The discussion identifies pressurized fluidized bed combustion (PFBC) as the direct combustion technique most likely to be able to avoid serious corrosion problems in the immediate future. Recent results from PFBC pilot plant investigations related to turbine materials are compared, and thereby future directions for overcoming corrosion problems are proposed. MST/449     

工业燃气轮机涡轮叶片用铸造高温合金研究及应用进展

工业燃气轮机具有热效率高、污染低等突出优点,成为未来发电机组与大型水面舰船动力的首选设备。铸造高温合金是工业燃气轮机涡轮叶片等热端部件的关键材料,其性能和制备水平在一定程度上决定了先进燃气轮机的功率、效率、寿命等性能。本文重点综述了工业燃气轮机及其涡轮叶片用铸造高温合金材料的研究及应用现状,并对工业燃气轮机涡轮叶片用铸造高温合金及涡轮叶片制造技术的发展趋势进行了展望。未来,先进定向凝固,“材料基因工程”等技术将逐渐应用到工业燃气轮机涡轮叶片用铸造高温合金的研制中;此外,先进工业燃气轮机上定向/单晶高温合金的应用将越来越广泛。     

Application of the methods of numerical modeling to evaluation of the total-pressure loss in gas turbines

The total-pressure loss in gas turbines is evaluated. Reynolds-averaged Navier-Stokes equations are used for numerical calculations. The Spalart-Allmaras model, the k-ε model, and the two-layer model and their different modifications allowing for the rotation of the flow and the curvature of streamlines are used to close these equations. The role of different corrections to the turbulence models for the accuracy of calculated estimates is elucidated. __________ Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 80, No. 5, pp. 55–63, September–October, 2007.     

Coupling CFD with chemical reactor network for advanced NO x prediction in gas turbine

Gas turbine pollutant emissions, especially nitric oxides (NO _x : NO and NO₂) and carbon monoxide (CO) are limited to 25 ppmvd by the European legislation for natural gas operations. To meet this objective and that of future legislation, it is crucial to have access to numerical tools that could speedily predict NO and CO emissions when operating gas turbines (fuel flexibility, tuning of the fuel distribution between burners…). In this context EDF R&D has been developing a 3D turbulent gas combustion model the past few years. Nevertheless, the introduction of complex chemical kinetics in 3D turbulent combustion code is still too CPU-time consuming for industrial use. Thus, 3D computational fluid dynamics computations, using simple chemistry, are post-treated to generate a 0D chemical reactor network (CRN), which includes a detailed chemistry mechanism. The 3D simulations are used to provide information about the mixing state, and the flow topology including the turbulence effects. The present study focuses on the impact of ambient air conditions (temperature and relative humidity) on NO production by industrial gas turbines. The detailed chemical kinetic scheme is initially validated by laboratory tests on jet-stirred reactor performed in University of Washington.     

Lifing issues in hot gas path components of heavy-duty gas turbines

Abstract

Gas turbine hot-gas-path components, which include combustion liners, transition pieces, turbine nozzles and turbine buckets, are exposed to hot gases discharged from combustion systems and suffer from severe materials degradation and damage even in the early stage of operation. The severity of the damage and degradation increases with increasing inlet temperature and size of the gas turbines, which also increase the maintenance cost. ‘Lifing’ of components is, therefore, becoming a very critical issue. This paper describes several kinds of component damage and material degradation occurring in the 1,100°C- and 1,300°C-class heavy-duty gas turbines and then shows how we revised those component lives from the original design ones. Analytical-based assessment methods associated with condition-based assessment ones, some examples of assessment results, and component life extension technologies are also described.     

回热循环燃气轮机中回热器的动态特性研究

采用多段集中参数模型对具有分布参数特性的回热器建模，简化了由偏微分方程带来的大量计算，应用Matlab／Simlink软件作为仿真平台，采取数值方法求解，对具体回热燃气轮机中的回热器进行了仿真，结果表明，回热器时间常数较大，在回热循环燃气轮机仿真中回热器的热惯性不能忽略，而且是影响系统平衡稳定性的重要因素．     

Infra-red radiation thermometry applied to the development and control of gas turbines

Efficient gas turbines operate close to their thermal limits. Detailed temperature mapping of rotating components is needed in development and reliable monitoring in operation. These needs are being met by infra-red radiation thermometers. These thermometers represent a quantum leap in performance over familiar industrial instruments.     

Requirements for engineering ceramics in gas turbine engines

Abstract

The potential uses of ceramics in gas turbine engines are reviewed in the context of the problems arising from the brittle nature of the materials. Material properties are considered in relation to various turbine components and the themes of reliability and component design. It is concluded that substantial efforts will be required in materials and processes in achieving greater reliability and improved design before ceramics are successfully applied in gas turbines.

MST/436     

Self-fluxing coatings for stationary gas turbines

Self-fluxing alloys are becoming more and more interesting for hardware applications in stationary gas turbines. This is due to their ease of application which involves plasma spraying and sintering. These coatings are basically Cr₂O₃ formers which provide protection against sulphidation.As a result of the demand for greater efficiency in gas turbines and the consequent increase in operating temperature oxidation has become the basic form of corrosion attack and therefore oxides other than Cr₂O₃, i.e.Al₂O₃, are required.In this paper we shall describe an attempt that was made to modify a self-fluxing alloy (Ni-Cr-Fe-Si-B) with aluminium in order to produce protective Al₂O₃ scales. The coating is applied using air plasma spraying. The variation in the sinter temperature and the oxidation and corrosion resistance properties due to aluminium are given. The effect of aluminium on the tensile properties is illustrated using data from a ductile-brittle transition temperature test.     

Temperature measurement by gas analysis

Temperature measurement by gas analysis has been demonstrated to be a feasible and repeatable alternative technique to temperature measurement by thermocouples at the combustor exit plane of gas turbines. Indeed, the gas analysis technique is essential for temperature measurements of modern high-pressure ratio high-temperature rise combustors, where temperatures at exit exceed the melting points of Pt/Rh alloys. However, where comparative measurements can be made, some differences between the two measurement systems have been found which must be resolved before absolute accuracy for the gas analysis technique can be achieved.     

Fuzzy logic controller to improve parameters affecting gas turbines power generation

In order to improve the performance of the gas turbine power plant and to generate electricity at the best cost, a fuzzy logic controller model was used to show the effect of different parameters on the power generation output of gas turbines. The proposed methodology was applied to certain parameter values collected from Rehab power station in Jordan—as a case study—for validation purposes. Relative weights were used, i.e., very very low power generation “extremely low power generation,” very low power generation, low power generation, normal power generation, high power generation, and very high power generation. The study reveals that the major factors that affect yield are ambient temperature (T ₁), compressor’s exit temperature (T ₂), turbine’s inlet temperature (T ₃), turbine exit temperature (T ₄), pressure ratio (R _p), mass of fuel (M _f), relative humidity (H), turbine efficiency (η_t), and compressor efficiency (η_c). Based on the increase of productivity, the results show that different factors are found to affect the yield of a power generator. Therefore, using fuzzy logic controller model has lead the researchers to focus on the highest priority parameters that should be enhanced and developed to increase the power output productivity.     

Refurbishing procedures for blades of large stationary gas turbines

Abstract

The design life for blades of large stationary gas turbines is at least 100000 h in creep terms. Typical damage occurring within the lifetime of gas-turbine blading may be hot corrosion and/or erosion, foreign-object damage, tip rubbing, and cracking caused by low-cycle fatigue, thermocycle fatigue, high-cycle fatigue, and creep crack growth. When applying refurbishing procedures both technical and economic aspects should be considered. The repair procedures available are welding, brazing, plasma spraying, recoating, combined with special heat treatment cycles, and occasionally intermediate hot isostatic pressing. The limiting factors for repair procedures are the mechanical properties and the hot corrosion behaviour of the refurbished parts. Examples are given of results from metallographic and laboratory tests on refurbished Kraftwerk Union (KWU) test specimens and blades in relation to the material, design, and stressing of the components. Typical examples of the refurbished parts are also presented. Service experience with refurbished blades in stationary gas turbines is limited at present. Therefore, KWU can only consider these procedures in the light of the growing knowledge of refurbishing processes and the operating experience of refurbished parts as well as the economic aspects.

MST/102     

High-temperature sheet materials for gas turbine applications

Abstract

Aircraft gas turbines contain various sheet metal fabrications, such as combustion chambers, exhaust units, jet pipes, and reheat liners, which operate for long periods under arduous conditions. The properties required in a sheet alloy differ considerably from those of blades and vanes, so that alloys must be developed specifically for the purpose. The performance required of sheet alloys is discussed and current alloys are reviewed in terms of their fabrication, mechanical, and oxidation properties. Some recent developments are described in the field of thermal barrier coatings, dispersion strengthened alloys, and porous laminate materials.

MST/524     

Prognosis of gas turbine remaining useful life using particle filter approach

Gas turbines are commonly used in distributed power generation. Because of high speed nature, they require good maintenance for increased reliability and availability. Remaining useful life prediction is therefore an essential part of condition‐based maintenance to better foresee future state hence guaranteeing design efficiency, reduced maintenance cost, and improved safety. Gas turbines also contain a lot of sensors data that need to be processed for better prediction. In this paper, a probabilistic approach called particle filter is used for prediction. The proposed approach is tested using Turbofan degradation data provided by NASA as a benchmark problem. Meanwhile, through time the gas turbines experiences a change from normal state to degraded state attributed to aging, corrosion and erosion etc. Hence, in the context of abundant data, it is helpful to know the transition between states. For the same reason, the present paper suggests a statistical approach called Z‐test. The test results show that the proposed technique provides score and MAPE values of 559.9 and 21.6 respectively, comparable to past reported performance.     

Gas bearing turbines with dynamic gas bearings and their application in helium refrigerators

The Sulzer turbine, with dynamic gas bearings and brake compressor, is an autonomous expansion device which needs neither an external bearing gas supply nor a control system which prevents a leakage of cold process gas out of the refrigeration cycle. The journal bearings consist of three tilting pads; the thrust bearings are of the spirally groved type. An auxilliary magnetic bearing is used for start-up and shut-down.This type of turbine has been used in plants in the range 40 to 1500 W refrigeration output at 4.4 K. They are especially suited for plants where long-time reliability is essential. A plant at the Swiss Institute for Nuclear Research (SIN), which is equipped with this kind of turbines, has now more than three years of nearly uninterrupted service. A number of details of this and other gas bearing turbine plants will be discussed.     

High temperature materials in gas turbine engines

The current performance trends in civil, aero and industrial gas turbines are discussed. Future improvements in materials technology are needed for major components — aerofoils, discs and combustors — to achieve improved performances.     

A stereo PIV system for measuring the velocity vector in complex gas flows

A stereo PIV system for investigating complex highly turbulent flows, typical for gas flows in aircraft engines and gas turbines, is developed, and the values obtained for the velocity are compared with the results measured using a laser Doppler anemometer. The features of the use of the PIV system for measurements in three-dimensional highly turbulent flows with high velocity gradients are investigated.     

Induction of preset thermally stressed states in thermal fatigue tests: Choice of testing conditions and geometry of specimens

Two approaches to the choice of testing conditions with the effect of simultaneous control over thermal and thermally stressed states of specimens which provide the induction of preset uniaxial and biaxial unsteady stressed states were analyzed and developed. The first approach is based on inducing thermal stresses in a cyclically heated specimen by restraining force and mechanical loads. The second approach is based on inducing thermal stresses in a massive specimen free of external mechanical loads in a natural way due to a nonuniform temperature distribution over its volume, also accounting for the requirement of inducing the states corresponding to unsteady states of real massive structural elements. Specimens consisting of two concentric massive rings connected with a thin neck were demonstrated to be effective for thermal fatigue testing of high-temperature materials used in gas turbines. State vs geometry curves are plotted, and a method of determining the dimensions of ring specimens to produce preset thermal and thermally stressed states of the material is described. Institute for Problems of Strength, National Academy of Sciences of Ukraine, Kiev, Ukraine. Translated from Problemy Prochnosti, No. 4, pp. 67–81, July–August, 1997.     

Permeability and high temperature strength of porous mullite-alumina ceramics for hot gas filtration

The gas permeability and mechanical properties of mullite-alumina ceramics for potential use as filters in hot gas separation environments are examined. The mullite-alumina ceramics with different levels of induced porosity and pores sizes were fabricated by slip casting and characterised in terms of microstructure and strength properties at ambient and elevated temperatures. Permeability to nitrogen gas flow of the porous structures at ambient temperature was investigated over a range of flow velocities to quantify and assess the permeability. The strength at high temperatures is equivalent to ambient data signifying no discernible degradation. Nitrogen gas permeability tests reveal dramatic reductions in the pressure drop–gas velocity curves with increasing porosity. It is shown that the gas permeability increases with the level of porosity and pore size, with maximum Darcian permeability constant of k = 2.5×10⁻¹⁴ m² for a porosity of 71%.