Typical Gas Turbine Research Articles

Optimization of turbine blade cooling with the aim of overall turbine performance enhancement

In the current work, different methods for optimization of turbine blade internal cooling are investigated, to achieve higher cyclic efficiency and output power for a typical gas turbine. A simple two-dimensional model of C3X blade is simulated and validated with available experimental data. The optimization process is performed on this model with two different methods. The first method is a popular method used in previous works with two objectives i.e. the minimization of the maximum temperature and the maximum temperature gradient on the blade. A new method is hereby proposed for optimization of turbine blade cooling, in which the coolant mass flow rate is minimized subject to maximum temperature, and maximum temperature gradient remains lower than certain values. The overall turbine performance is estimated by a simple comparative thermodynamic analysis of the reference design and the representative results obtained from the first and second method of optimization. It is concluded that while the first method of optimization allows higher TIT for a typical turbine, the turbine output power and efficiency could be lower than the reference design, due to high coolant mass flow rate in these candidate points. However, the optimum design point of the second method has higher power output and efficiency compared to all other designs (including reference design) at all values of compressor pressure ratio. It is shown that implementation of the second optimization method can increase the efficiency and the output power of a typical turbine 4.68% and 17% respectively.

Impact of Ambient Conditions of Arab Gulf Countries on the Performance of Gas Turbines Using Energy and Exergy Analysis

In this paper, energy and exergy analysis of typical gas turbines is performed using average hourly temperature and relative humidity for selected Gulf cities located in Saudi Arabia, Kuwait, United Arab Emirates, Oman, Bahrain and Qatar. A typical gas turbine unit of 42 MW is considered in this study. The electricity production, thermal efficiency, fuel consumption differences between the ISO conditions and actual conditions are determined for each city. The exergy efficiency and exergy destruction rates for the gas turbine unit and its components are also evaluated taking ISO conditions as reference conditions. The results indicate that the electricity production losses occur in all cities during the year, except in Dammam and Kuwait for the period between November and March. During a typical day, the variation of the power production can reach 4 MW. The rate of exergy destruction under the combined effect of temperature and humidity is significant in hot months reaching a maximum of 12 MW in July. The presented results show also that adding inlet cooling systems to the existing gas turbine units could be justified in hot periods. Other aspects, such as the economic and environmental ones, should also be investigated.

The Influence of Alternative Regeneration on the Performance of Gas Turbine Cogeneration Plants

Cogeneration plants must always ensure correlation of heat production with customer requirements. In a gas turbine cogeneration plant, the methods currently used are exhaust in the atmosphere of a fraction of the flow gas for thermal power decrease, or post firing in the heat recovery boiler, for thermal power increase. The paper proposed a new scheme of circulation of flue gas in a gas turbine with alternative regeneration. The novelty is that only a fraction of flue gas, which can be variable, flows through the regenerator. Calculations for a particular type of gas turbine indicated that the proposed scheme allows a 36% variation in thermal power, for a variation of 15% of electric power, which ensures a high flexibility in operation. The overall efficiency and cogeneration factor and maintain at good values throughout the range of variation of thermal and electrical power.

Simulation of Solar Photovoltaic, Biomass Gas Turbine and District Heating Hybrid System

This paper presents a simulation model for Biomass-Photovoltaic Hybrid system. The energy conversion equations describing the total power generated by system have been presented. A numerical model based upon the aforementioned conservation equations was developed, coded and results were presented and analyzed. The model is intended to be used as an optimization, design and analysis tool for typical gas turbine Biomass-CHP hybrid systems. The results predicted by the proposed model compared fairly with data under various biomass loading conditions.

Исследование напряженно-деформированного состояния и микроструктуры в зоне твердофазного соединения типа диск-вал из разноименных сплавов на основе никеля

Finite-element calculations have been carried out to determine the strain distribution formed during welding by a combination of pressure and shear in samples imitating the constituent parts of a "disk-shaft" type gas-turbine engine bimetallic component made of heterophase nickel-based superalloys. A physical simulation of this process has also been carried out. Computer simulations were accomplished using a two-dimensional axysymmetric model by means of DEFORM-2D package. EP975 and EK79 alloys with ultrafine-grained (UFG) structure were chosen as the materials for the disk and shaft, respectively. The initial strain rate was 10-5 s-1, and the welding temperature 1100 °C. The behavior of materials was described by experimental curves obtained for EP975 and EK79 alloys under a uniaxial compression at the welding temperature. According to known experimental data, shear strain near the welded surfaces improves the solid-phase bond quality and strength. Additionally, the solid-phase bond quality is enhanced by grain refinement, which leads to an increase of the area of grain boundaries and to accelerated grain boundary diffusion. The results of computer simulations have revealed that in order to increase the area of regions with large shear strain values one has to increase the displacement of the shaft relative to the disk. From physical simulation, it has been concluded that a high quality solid-phase bond formation is promoted by a small shear strain of EK79 and EP975 alloys with UFG structure under superplasticity conditions. Basing on the studies carried out, a possibility of obtaining a "disk-shaft" type part from EP975 and EK79 nickel alloys with a preliminarily processed UFG structure using solid-phase bonding by means of pressure and shear welding has been shown.

Flame Holding in the Premixing Zone of a Gas Turbine Model Combustor After Forced Ignition of H2–Natural Gas–Air Mixtures

Flashback (FB) and self-ignition in the premixing zone of typical gas turbine swirl combustors in lean premixed operation are immanent risks and can lead to damage and failure of components. Thus, steady combustion in the premixing zone must be avoided under all circumstances. This study experimentally investigates the flame holding propensity of fuel injectors in the swirler of a gas turbine model combustor with premixing of H2–natural gas (NG)–air mixtures under atmospheric pressure and proposes a model to predict the limit for safe operation. The A2EV swirler concept exhibits a hollow, thick walled conical structure with four tangential slots. Four fuel injector geometries were tested. One of them injects the fuel orthogonal to the air flow in the slots (jet-in-crossflow injector, JICI). Three injector types introduce the fuel almost isokinetic to the air flow at the trailing edge of the swirler slots (trailing edge injector, TEI). A cylindrical duct and a window in the swirler made of quartz glass allow the application of optical diagnostics (OH* chemiluminescence and planar laser induced fluorescence of the OH radical (OH-PLIF)) inside the swirler. The fuel–air mixture was ignited with a focused single laser pulse during steady operation. The position of ignition was located inside the swirler in proximity to a fuel injection hole. If the flame was washed out of the premixing zone not later than 4 s after the ignition, the operation point was defined as safe. Operation points were investigated at three air mass flows, three air ratios, two air preheat temperatures (573 K and 673 K), and 40 to 100 percent per volume hydrogen in the fuel composed of hydrogen and natural gas. The determined safety limit for atmospheric pressure yields a similarity rule based on a critical Damköhler number. Application of the proposed rule at conditions typical for gas turbines leads to these safety limits for the A2EV burner: With the TEIs, the swirler can safely operate with up to 80 percent per volume hydrogen content in the fuel at an air ratio of two. With the JIC injector, safe operation at stoichiometric conditions and 95 percent per volume hydrogen is possible.

Sulfur as a Fuel Source in a Combined Power Cycle Equipped with a Dry Flue Gas Desulfurization System

This paper investigates the novel use of elemental sulfur as a fuel in a combined cycle power plant, wherein sulfur is oxidized in the combustion chamber to produce work from a gas turbine. Produced sulfur dioxide is then reacted with calcite to produce anhydrite (CaSO4) in a flue gas desulfurization unit. The desulfurization reaction is exothermic, producing heat that can be converted to electricity by passing the exhaust gas through a heat recovery steam generator. The cases studied in this work are a 410 MW natural gas combined cycle, used as a reference case, a sulfur combined cycle (SCC) consisting of a typical industrial gas turbine with heat recovery followed by desulfurization, and a third case of a SCC followed by desulfurization before the heat recovery, thereby producing power from the exothermic desulfurization reaction. Energy calculations of the last case show promising results for converting sulfur to anhydrite through a combined cycle that produces 615 MW of electrical power with CO2 emission of 0.584 kg/kWh, a value lower than the representative value of a new, supercritical coal power plant.

Hydrodynamic and mass transfer evaluation of post-combustion CO2 capture process for power plants

The present work is a comparative evaluation on CO2 capture process post-combustion by chemical absorption with alkanolamines, of three Mexican power plants, each one with a different method of operation and fossil fuel used: natural gas type, gas turbine type, and of coal type. They were compared with one another to determine which one has the largest CO2 capture flow. This comparison was done through an experimental facility with mainly absorption column of: 0.30 m diameter, 3.5 m packed height, structured packings, and 30 % weight solvent concentrations of monoethanolamine. The experimental data let to develop numerical evaluations through computer simulation on steady state of the integrated plants. The results show that the highest CO2 capture flow was obtained from the coal-fired power plant with 3.03 t/d, followed by natural gas type with 1.88 t/d, and the lowest one was the gas turbine type with 0.80 t/d.

Root Cause Analysis of Failure of 40 th Stage Moving Blade of Single Cylinder Condensing Turbine

Blade failures in steam and gas turbines are quite a common occurrence. The last stages of steam turbines are designed to have the lowest possible fluid temperature. In view of the longest blade length in the last stages, the blades are subjected to highest bending moment forces and susceptible for erosion-corrosion phenomenon owing to the low service temperature environment. The failure analysis of last stage blade of 54 MW direct condensing type gas turbine are presented. The blade was made of martensitic grade stainless steel. Detailed analysis of the blade surface, lacing wire hole as well as the fracture morphology was analyzed using SEM-EDX. The probable reason for the failure of the blade was brought out based on the detailed investigations of the failed blade as well as the vibration signature analysis at the time of failure incidence.

Degradation Assessment of Gas Turbine Hot Gas Path Components

Hot gas path component consists of components designed to burn air-fuel mixture in combustion section and provide hot gasses to the turbine section where mechanical power is produced. The aim of this research project is expected to improve the current practices of managing degradation of hot gas path components. Understanding the damage mechanisms is of great interest in reducing the damage and failure risk. In this research, a study was conducted on F-Class type gas turbine hot gas path components assembly. It involved extensive examination and testing of the components which had been in operations for 24,000 hours since the last shutdown. Various factors such as installation, operating conditions, hardness and material of constructions were also investigated. This paper reports the initial findings of the study of hot gas path components degradation. It describes the damage observed on the affected areas of the components and proposes the factors that contribute to the damage processes. Potential solutions for mitigating the damages are also discussed.

Effect of Prediffuser Angle on the Static Pressure Recovery in Flow Through Casing-Liner Annulus of a Gas Turbine Combustor at Various Swirl Levels

A numerical study has been performed in an axisymmetric diffuser followed by a casing-liner annulus of a typical gas turbine combustor to analyze the flow structure and pressure recovery in the geometry. Static pressure recovery in a gas turbine combustor is important to ensure high pressure of air around the liner. However, the irreversible pressure losses reduce the static pressure recovery from the ideal value. The presence of swirl in the flow from compressor and prediffuser geometry before the dump diffuser influences the flow pattern significantly. In this study, flow structures are numerically predicted with different prediffuser angles and inlet swirl levels for different dump gaps. Streamline distributions and pressure plots on the casing and liner walls are analyzed. Static pressure recovery coefficients are obtained from the pressure distributions across the combustor. The effect of dump gap on the static pressure recovery has also been evaluated. It is observed that the best static pressure recovery can be obtained at optimum values of inlet swirl level and prediffuser angle. Dump gap is found to have significant influence on the static pressure recovery only at small prediffuser angle.

Latest lessons learned, modern condition monitoring and advanced predictive maintenance for gas turbines

This article covers advanced methods, modern techniques, new findings and latest lessons learned for condition monitoring, maintenance and improvements of various aero-derivative and heavy-duty gas turbines. Advanced methods for cost-effective operation and predictive maintenance are also explained. Required methods and technologies for the condition monitoring, performance study, operation evaluation, improvement plans and maintenance should be specific to each gas turbine type and model. Practical notes and modern guidelines on gas turbine bearing types (rolling-element bearings and journal bearings), inlet air filters, combustor systems, unsteady flows, starting devices, internal air systems, oil analysis and potential hazards are discussed for both aero-derivative gas turbines and heavy industrial gas turbines. Different case studies are also presented.

The Effect of Freestream Turbulence on Deposition for Nozzle Guide Vanes

An evaluation of the effect of freestream turbulence intensity on the rate of deposit accumulation for nozzle guide vanes (NGVs) was performed using the turbine reacting flow rig (TuRFR) accelerated deposition facility. The TuRFR allowed flows up to 1350 K at inlet Mach numbers of 0.1 to be seeded with coal fly ash particulate in order to rapidly evaluate deposit formation on CFM56 NGVs. Hot film and particle image velocimetry (PIV) measurements were taken to assess the freestream turbulence with and without the presence of a grid upstream of the NGVs. It was determined that baseline turbulence levels were approximately half that of the flow exiting typical gas turbine combustors and were reduced by approximately 30% with the grid installed. Deposition tests indicated that the rate of deposition increases as the freestream turbulence is increased, and that this increase depends upon the particle size distribution. For ash with a mass median diameter of 4.63 μm, the increase in capture efficiency was approximately a factor of 1.77, while for ash with a larger median diameter of 6.48 μm, the capture efficiency increased by a factor of 1.84. The increase in capture efficiency is due to the increased diffusion of particles to the vane surface via turbulent diffusion. Based on these results, smaller particles appear to be less susceptible to this mechanism of particle delivery. Overall, the experiments indicate that the reduction of turbulence intensity upstream of NGVs may lead to reduced deposit accumulation, and consequently, increased service life. A computational fluid dynamics (CFD) analysis was performed at turbulence levels equivalent to the experiments to assess the ability of built-in particle tracking models to capture the physics of turbulent diffusion. Impact efficiencies were shown to increase from 21% to 73% as the freestream turbulence was increased from 5.8% to 8.4%. An analysis incorporating the mass of the particles into the impact efficiency resulted in an increase of the mass-based impact efficiency from 17% to 27% with increasing turbulence. Relating these impact efficiencies directly to capture efficiencies, the predicted increase in capture efficiency with higher turbulence is less than that observed in the experiments. In addition, the variation in the impact efficiencies between the two ash sizes was smaller than the capture efficiency difference from experiments. This indicates that the particle tracking models are not capturing all of the relevant physics associated with turbulent diffusion of airborne particles.

Numerical Evaluation of Novel Shaped Holes for Enhancing Film Cooling Performance

The overall film cooling performance of three novel film cooling holes has been numerically investigated in this paper, including adiabatic film cooling effectiveness, heat transfer coefficients as well as discharge coefficients. The novel holes were proposed to help cooling injection spread laterally on a cooled endwall surface. Three-dimensional Reynolds-averaged Navier–Stokes (RANS) equations with shear stress transport (SST) k-ω turbulence model were solved to perform the simulation based on turbulence model validation by using the relevant experimental data. Additionally, the grid independent test was also carried out. With a mainstream Mach number of 0.3, flow conditions applied in the simulation vary in a wide range of blowing ratio from 0.5 to 2.5. The coolant-to-mainstream density ratio (DR) is fixed at 1.75, which can be more approximate to real typical gas turbine applications. The numerical results for the cylindrical hole are in good agreement with the experimental data. It is found that the flow structures and temperature distributions downstream of the cooling injection are significantly changed by shaping the cooling hole exit. For a low blowing ratio of 0.5, the three novel shaped cooling holes present similar film cooling performances with the traditional cylindrical hole, while with the blowing ratio increasing, all the three novel cooling holes perform better, of which the bean-shaped hole is considered to be the best one in terms of the overall film cooling performance.

Technical Analysis of Conversion of A Steam Power Plant to Combined Cycle, Using Two Types of Heavy Duty Gas Turbines

Due to long life of steam power plants in Iran, transformation of steam cycles to combined cycles is under consideration. Bandar-Abbas steam power plant with capacity of 320 MW has been analyzed in this work. This old plant is located near the harbor city of Bandar-Abbas at southern Iran. Method of exergy analysis is used to study the current and the repowered systems. Optimum state of the repowered cycle is also obtained using exergy analysis. In this work, a point by point analysis of Bandar-Abbas steam power plant is performed for different modes of full repowering, using exergy analysis method. For this purpose, V94.2 and V94.3A gas turbines are used and effect of duct burner is investigated for each case. The results show that at the best repowering mode, power plant efficiency is 34.5% higher than the design efficiency of the current steam plant. Minimum rate of exergy destruction rate is 6711 MW at this mode and the heat rate reduces by 26.6%. According to the results, increase of fuel consumption in duct burner and use of V94.2 gas turbine are not recommended for repowering of Bandar-Abbas power plant.

Exergy-energy analysis of full repowering of a steam power plant

A 320MW old steam power plant has been chosen for repowering in this paper. Considering the technical conditions and working life of the power plant, the full repowering method has been selected from different repowering methods. The power plant repowering has been analyzed for three different feed water flow rates: a flow rate equal to the flow rate at the condenser exit in the original plant when it works at nominal load, a flow rate at maximum load, and a flow rate when all the extractions are blocked. For each flow rates, two types of gas turbines have been examined: V94.2 and V94.3A. The effect of a duct burner has then been investigated in each of the above six cases. Steam is produced by a double-pressure heat recovery steam generator (HRSG) with reheat which obtains its required heat from the exhaust gases coming from the gas turbines. The results obtained from modeling and analyzing the energy-exergy of the original steam power plant and the repowered power plant indicate that the maximum efficiency of the repowered power plant is 52.04%. This maximum efficiency occurs when utilizing two V94.3A gas turbines without duct burner in the steam flow rate of the nominal load.

Computational Study of Air/Mist Impinging Jets Cooling Effectiveness under Various Curvature Models

Efficiency is one of the most important parameters in evaluating the performance of a gas turbine engine by increasing the turbine inlet temperature, which could increase the gas turbine cycle’s efficiency. In order to increase the turbine inlet temperature significantly, an advanced cooling system needs to be researched and developed. This paper will establish a double chamber model simulating mist impingement cooling under typical gas turbine operating conditions of high temperature and pressure. Numerical simulations are examined to investigate the curvature and mist effect of air impingement cooling. The air impingement cooling can be significantly affected by the curvature which is measured by central angle. The 30° central angle model has a better cooling effectiveness than the flat surface model, while the 90° central angle model has the lowest cooling performance. Under real gas turbine operating conditions at high temperature, pressure, and velocity, comparing with the 90° central angle model, the 30° central angle model air impingement cooling’s enhancement could be better than 98% and provides a wall cooling of approximately 175 K. By adding mist, impingement cooling effectiveness can be enhanced approximately by 64% on the 90° central angle model and by 6–10% on the other models.

Conjugate Heat Transfer Study of Combined Impingement and Showerhead Film Cooling Near NGV Leading Edge

A computational and experimental study is carried out on the leading edge region of a typical gas turbine NGV, cooled by a combination of impingement and showerhead film cooling. A detailed flow and conjugate heat transfer study has revealed the complex flow structure owing to the coolant-mainstream interaction and the influence of vane material thermal conductivity. The local effectiveness values obtained by the computations agreed well with the experimental data from IR thermography. The effect of blowing ratio on the overall effectiveness is found to be strongly dependent on the vane material conductivity. The effect of blowing ratio is also found to be different towards the pressure and suction sides of the stagnation region. However, the overall effectiveness is found to decrease by about 12% and 6% for low and high conducting materials, respectively, with an increase in mainstream Reynolds number fromRe=4.8×105to14.4×105.

S0810103 H_2O/CO_2中における石炭ガス化燃料と酸素の基礎燃焼特性 : 燃料中微量成分(NH_3)の排出特性

As a gas turbine for high-efficiency oxy-fuel IGCC system corresponds to a semi-closed type gas turbine, there is concern that a very small amount of ingredient contained in fuel and oxygen affects the purity of captured CO_2. In this study, the atmospheric pressure combustion tests were performed by using fuel including NH_3 as minor components and by using diluent including NO as the exhaust circulation gas, and NOx emission characteristics were examined. As the results, the conversion ratio to NOx from NH_3 was approximately 30% when NH_3 concentration was 2000ppm, and the most of the NOx emission consisted of NO. And when NH_3 is contained in fuel and NO is contained in diluent corresponding to the exhaust circulation gas, it was confirmed that NOx emission corresponds to the sum of NOx emission formed by NH_3 in fuel and NOx emission formed by NO in diluent.

Design of the gas turbine engine rotor wheel with ceramic blades

The use of ceramic parts in the hot section of a gas turbine engine will make it possible to increase theengine efficiency due to the increased operating gas temperature at the combustion chamber outlet and reducedair consumption for blade cooling, as well as significantly reduce the weight of the parts due to the low densityof ceramics. The main disadvantage of ceramic parts is the brittleness of the material. Mechanical properties ofadvanced ceramic materials are insufficient for making a whole wheel, however, they are sufficient for makingblades. The main problem in making a structure of this kind is ensuring the strength of the interlock between ametal disk and ceramic blades. Previous works of the authors presented analysis of various types of interlocksbetween ceramic blades and a metal disk. This paper is devoted to the design of an aero engine gas turbine rotorwheel using a high-strength silicon nitride ceramic material. A software code in the APDL Ansys environment iscreated that makes three-dimensional design definition possible. A rotor wheel with ceramic blades is designedon the basis of a typical aircraft high-pressure gas turbine engine. A commercial heat-resistant nickel alloy isconsidered as the disk material, while silicon nitride is used for the production of blades. Evaluation of thestress-strain state and strength analysis are conducted, the properties of the ceramic material are analyzed. Theresults of the research show that it is necessary to make a special cooling system for a metal disk and that theproperties of the ceramics presented are to be improved. It is reasonable to apply similar constructions on stationarygas turbine plants.