Heavy Duty Gas Turbine Research Articles

Film Cooling Modeling for Gas Turbine Nozzles and Blades: Validation and Application

The design of modern gas turbines cooling systems cannot be separated from the use of computational fluid dynamics (CFD) and the accurate estimation of the effect of film cooling. Nevertheless, a complete modeling of film cooling holes within the computational domain requires an effort both from the point of view of the mesh creation and from computational time. It is here proposed a new way to model the film cooling (FCM), capable of representing the effect of the coolant at hole exit. This is possible due to the introduction of local source terms near the hole exit in a delimited portion of the domain, avoiding the meshing process of perforations. The goal is to provide a reliable and accurate tool to simulate film-cooled turbine blades and nozzles without having to explicitly mesh the holes. The model was subjected to an intensive validation campaign, composed of two phases. During the first one, FCM results are compared to experimental data and numerical results (obtained with complete cooling holes meshing) on a series of test cases reproducing flat plate cooling configurations for different coolant conditions (in terms of blowing and density ratio). In the second phase, a film-cooled vane test case has been studied, in order to consider a real injection system and flow conditions: FCM predictions are compared to an in-house developed correlative approach and full conjugate heat transfer (CHT) results. Finally, a comparison between FCM predictions and experimental data was performed on an actual nozzle of a GE Oil & Gas heavy-duty gas turbine, in order to prove the feasibility of the procedure. The presented film cooling model (FCM) proved to be a feasible and reliable tool, able to evaluate adiabatic effectiveness, simplifying the design phase avoiding the meshing process of perforations.

Provision of the required wear resistance criteria of heavy-duty gas turbine engine parts based on the control of the cutting conditions

A method for determining the wear resistance of parts has been presented based on the systematization of the modular source data bank, the evaluation of the surface layer quality parameters, the cutting accuracy, and the cutting conditions. As a result of the study, the calculated dependences have been obtained in terms of the determination of the optimal part cutting modes in relation to the provision of the target surface wear resistance parameters.

Coupling multicomponent droplet evaporation and tabulated chemistry combustion models for large-eddy simulations

An evaporation model for multicomponent fuels and emulsions is implemented in OpenFOAM within the Euler–Lagrangian formulation. The model is suitable for pressures typical of heavy duty gas turbines, up to 30bar, and considers an increased evaporation rate of the most volatile component when the droplet temperature reaches its boiling temperature. Evaporation of emulsion droplets is modeled following a shell approach, assuming that the water in the droplet core does not evaporate. A diffusivity model is introduced to account for the transport of the dispersed phase from the core to the outer shell. The combustion model is based on the Flamelet Generated Manifold approach. The mixture fraction is calculated from the species mass fractions to couple it with the evaporation model. Flamelet tables are created for different enthalpies and mixture fractions so that they can be used in non-premixed simulations. The thermo-chemistry model considers up to two fuel components by using 4-D tables. Experimental data for n-decane droplets are used to validate the evaporation model. Results from the combustion model are compared with the detailed chemistry solutions. Following the separate evaluation of each model, 1-D spray simulations for 0% and 10% initial water contents are performed to verify the coupling between the models, so that they can be applied to partially pre-vaporized spray flames.

A Comparative Analysis of Single Nozzle and Multiple Nozzles Arrangements for Syngas Combustion in Heavy Duty Gas Turbine

Heavy duty gas turbines are the core components in the integrated gasification combined cycle (IGCC) system. Different from the conventional fuel for gas turbine such as natural gas and light diesel, the combustible component acquired from the IGCC system is hydrogen-rich syngas fuel. It is important to modify the original gas turbine combustor or redesign a new combustor for syngas application since the fuel properties are featured with the wide range hydrogen and carbon monoxide mixture. First, one heavy duty gas turbine combustor which adopts natural gas and light diesel was selected as the original type. The redesign work mainly focused on the combustor head and nozzle arrangements. This paper investigated two feasible combustor arrangements for the syngas utilization including single nozzle and multiple nozzles. Numerical simulations are conducted to compare the flow field, temperature field, composition distributions, and overall performance of the two schemes. The obtained results show that the flow structure of the multiple nozzles scheme is better and the temperature distribution inside the combustor is more uniform, and the total pressure recovery is higher than the single nozzle scheme. Through the full scale test rig verification, the combustor redesign with multiple nozzles scheme is acceptable under middle and high pressure combustion test conditions. Besides, the numerical computations generally match with the experimental results.

A Model for Predicting the Lift-Off Height of Premixed Jets in Vitiated Cross Flow

Lean premixed single-stage combustion is state of the art for low pollution combustion in heavy-duty gas turbines with gaseous fuels. The application of premixed jets in multistage combustion to lower nitric oxide emissions and enhance turn-down ratio is a novel promising approach. At the Lehrstuhl für Thermodynamik, Technische Universität München, a large-scale atmospheric combustion test rig has been set up for studying staged combustion. The understanding of lift-off (LO) behavior is crucial for determining the amount of mixing before ignition and for avoiding flames anchoring at the combustor walls. This experiment studies jet LO depending on jet equivalence ratio (0.58–0.82), jet preheat temperature (288–673 K), cross flow temperature (1634–1821 K), and jet momentum ratio (6–210). The differences to existing LO studies are the high cross flow temperature and applying a premixed jet. The LO height of the jet flame is determined by OH* chemiluminescence images, and subsequently, the data is used to analyze the influence of each parameter and to develop a model that predicts the LO height for similar staged combustion systems. A main outcome of this work is that the LO height in a high temperature cross flow cannot be described by one dimensionless number like Damköhler- or Karlovitz-number. Furthermore, the ignition delay time scale τign also misses part of the LO height mechanism. The presented model uses turbulent time scales, the ignition delay, and a chemical time scale based on the laminar flame speed. An analysis of the model reveals flame stabilization mechanisms and explains the importance of different time scale.

Small and large signal modeling of heavy duty gas turbine plant for load frequency control

Abstract In this paper, the transfer function model of heavy duty gas turbine has been developed for doing load frequency control studies. Based on the large signal model of Rowen, small signal model has been developed. This model is much suitable for doing Automatic Generation Control. Proportional integral and derivative secondary controller has been developed for both the small and large signal models to improve the system response. Ziegler Nichols’ method, Simulated Annealing and Fuzzy Gain Scheduling have been used for tuning the secondary controller. Ziegler Nichols’ method is used as conventional tuning, whereas Simulated Annealing is a search based tuning and Fuzzy Gain Scheduling is adaptive. It is found that Simulated Annealing tuned Proportional Integral Derivative Controller yields better response than other two controllers in both large signal and small signal model of heavy duty gas turbine plant.

CFD Analysis of NOx Emissions of a Natural Gas Lean Premixed Burner for Heavy Duty Gas Turbine

The present work presents a numerical analysis of a low NOx partially premixed burner for heavy duty gas turbine. The first part of the paper is focused on the study of the premixing process inside the burner using standard RANS CFD approach. The resulting profiles at different test points have been used to perform reactive simulations of an experimental test rig, where exhaust NOx emissions were measured. A reliable numerical setup was found comparing predicted and measured NOx emissions at different operating conditions and split ratios between main and pilot fuel. The calibrated numerical setup was then employed to explore possible modifications to fuel injection criteria and fuel split, with the aim of minimizing exhaust NOx emissions. This preliminary numerical screening of new fuel injection strategies, allowed defining a set of advanced configurations to be investigated in future experimental tests.

Performance Analysis of Biofuel Fed Gas Turbine

The present paper deals with the study of the performance of a heavy-duty gas turbine running on biofuels. In particular, synthesis gas from glycerol steam reforming was used to feed the combustion turbine. Engine performances were compared with methane fed ones.Therefore, a mathematical model of the gas turbine was implemented using GateCycle software. Model calibration was made using gas turbine on-design parameters, while performance test results were compared with experimental running data. The resulting analysis highlighted that the mathematical model is able to correctly simulate engine behaviour in different combustion turbine running conditions thus validating the mathematical model.The combustion turbine studied was integrated with a syngas generator plant and overall efficiency was evaluated.The analysis of the results confirms that using biofuels a reduction in engine performance occurs. On the contrary, integrating the gas turbine and syngas generator plant an overall efficiency increase was registered.

An Interdisciplinary Approach to Study the Fouling Phenomenon

Solid particle ingestion is one of the principal degradation mechanisms in the compressor section of heavy-duty gas turbines. Foulants in the ppm range which are not captured by the air filtration system usually cause deposits on blading,which results in a severe drop in the performance of the compressor.Through the interdisciplinary approach proposed in this paper, it is possible to determine the evolution of the fouling phenomenon through the integration of several studies in different research fields: (i) numerical simulation, (ii) power plant characteristicsand (iii) particle-adhesion characteristics.This paper shows the possibility of linking the numerical results related to the impact/adhesion characteristic of the particles with the actual air contamination data and operating condition of the power units. In fact, the size of the particles, their concentrations and the filtration efficiency represent the major contributors to performing a realistic quantitative analysis of the fouling phenomena in an axial compressor.The integration of these research fields could represent a valuable support for the investigation of the relationship between compressor airfoil design and fouling rate.

Dynamic simulation of a triple-pressure combined-cycle plant: Hot start-up and shutdown

The operation of combined-cycle power plants is increasingly determined by frequent start-ups and shutdowns for grid balancing. This study investigates the capability of a comprehensive process simulation model to predict the transient response of a triple-pressure heat recovery steam generator (HRSG) with reheater to the start-up and shutdown procedures of a heavy-duty gas turbine. The model is based on geometry data, system descriptions and heat transfer calculations established in the original HRSG design. The numerical solution approach and the practical development of a suitable model structure, including the required control circuits, are explained. Detailed simulation results are presented, using initial conditions that correspond to a previous overnight shutdown. Calculations are performed for a complete operating cycle of the plant, where the following main phases are distinguished: start-up procedure, load-following operation, design operation and shutdown procedure. The numerical model is validated with measurement data of the commercial power plant for each pressure stage, yielding good agreement. Deviation from the transient behaviour of the real plant is discussed with regard to modelling assumptions and incomplete information on components outside the HRSG system boundaries.

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.

Modular Coating for Flexible Gas Turbine Operation

In heavy duty gas turbines, the loading boundary conditions of MCrAlY systems are differently weighted for different operation regimes as well as for each turbine component or even in individual part locations. For an overall optimized component protection it is therefore of interest to produce coatings with flexible and individually tailored properties. In this context, ALSTOM developed an Advanced Modular Coating Technology (AMCOTEC™), which is based on several powder constituents, each providing specific properties to the final coating, in combination with a new application method, allowing in-situ compositional changes. With this approach, coating properties, such as oxidation, corrosion, and cyclic lifetime, etc., can be modularly adjusted for individual component types and areas. For demonstration purpose, a MCrAlY coating with modular ductility increase was produced using the AMCOTEC™ methodology. The method was proven to be cost effective and a highly flexible solution, enabling fast compositional screening. A calculation method for final coating composition was defined and validated. The modular addition of ductility agent enabled increasing the coating ductility with up to factor 3 with only slight decrease of oxidation resistance. An optimum composition with respect to ductility is reached with addition of 20 wt.% of ductility agent.

Erosion Damage to Last-Stage Compressor Disk of a Heavy-duty Gas Turbine Engine

AbstractIn the course of a service life extension after 100 000 operating hours, the rotor of a heavy-duty gas turbine was inspected. During the visual inspection, some compressor wheel disks, particularly in the last stage, showed conspicuous features and flawed material. The only causal damage mechanism worth considering is erosion: only very little deformation was found in the metallographic sections' microstructure immediately underneath the flawed material areas (wear or deformation induced damages would have lead to more deformation) and, what is more, the microstructure showed no evidence of corrosion. In accordance with VDI guideline 3822, the exact designation of the damage mechanism is “Flow wear in the form of sliding jet wear in the two-phase mixture gaseous/solid”.

Estimation of the Particle Deposition on a Transonic Axial Compressor Blade

Solid particle ingestion is one of the principal degradation mechanisms in the compressor section of heavy-duty gas turbines. Usually, foulants in the ppm range, not captured by the air filtration system, i.e., (0–2) μm cause deposits on blading and result in a severe performance drop of the compressor. It is of great interest to the industry to determine which areas of the compressor airfoils are interested by these contaminants as a function of the location of the power unit. The aim of this work is the estimation of the actual deposits on the blade surface in terms of location and quantity. The size of the particles, their concentrations, and the filtration efficiency are specified in order to perform a realistic quantitative analysis of the fouling phenomena in an axial compressor. This study combines, for the first time, the impact/adhesion characteristic of the particles obtained through a computational fluid dynamics (CFD) and the real size distribution of the contaminants in the air swallowed by the compressor. The blade zones affected by the deposits are clearly reported by using easy-to-use contaminant maps realized on the blade surface in terms of contaminant mass. The analysis showed that particular fluid-dynamic phenomena such as separation, shock waves, and tip leakage vortex strongly influence the pattern deposition. The combination of the smaller particles (0.15 μm) and the larger ones (1.50 μm) determines the highest amounts of deposits on the leading edge (LE) of the compressor airfoil. From these analyses, some guidelines for proper installation and management of the power plant (in terms of filtration systems and washing strategies) can be drawn.

Design Improvement Survey for NOx Emissions Reduction of a Heavy-Duty Gas Turbine Partially Premixed Fuel Nozzle Operating With Natural Gas: Numerical Assessment

A numerical investigation of a low NOx partially premixed fuel nozzle for heavy-duty gas turbine applications is presented in this paper. Availability of results from a recent test campaign on the same fuel nozzle architecture allowed the exhaustive comparison study presented in this work. At first, an assessment of the turbulent combustion model was carried out, with a critical investigation of the expected turbulent combustion regimes in the system and taking into account the partially premixed nature of the flame due to the presence of diffusion type pilot flames. In particular, the fluent partially premixed combustion model and a flamelet approach are used to simulate the flame. The laminar flamelet database is generated using the flamelet generated manifold (FGM) chemistry reduction technique. Species and temperature are parameterized by mixture fraction and progress variable. Comparisons with calculations with partially premixed model and the steady diffusion flamelet (SDF) database are made for the baseline configuration in order to discuss possible gains associated with the introduced dimension in the FGM database (reaction progress), which makes it possible to account for nonequilibrium effects. Numerical characterization of the baseline nozzle has been carried out in terms of NOx. Computed values for both the baseline and some alternative premixer designs have been then compared with experimental measurements on the reactive test rig at different operating conditions and different split ratios between main and pilot fuel. Numerical results allowed pointing out the fundamental NOx formation processes, both in terms of spatial distribution within the flame and in terms of different formation mechanisms. The obtained knowledge would allow further improvement of fuel nozzle design.

Constitutive modelling and creep life prediction of a directionally solidified turbine blade under service loadings

The high pressure turbine (HPT) blade of a heavy duty gas turbine operates under the interaction of complex aerodynamic, centrifugal and thermal loadings. The reliability of continuous working at elevated temperatures is a major limitation in service application of these materials. Therefore, it is essential to build the constitutive equations for predicting and analysing the creep deformation and creep lifetime of the blade. In present work, the creep deformation and lifetime of a HPT blade made of a nickel-based directionally solidified (DS) superalloy was numerically predicted. The θ-projection method was used to characterize the creep deformation of DZ125 under different temperatures and stress levels. The uniaxial equations of the θ-projection method were expanded into multi-axial form which was implemented into ABAQUS/UMAT (User MATerial subroutine) by an Euler method. A modified θ-projection method was employed to promote the adaptability of the original model to both steady state and transient temperature fields. Transient stress, strain and displacement distribution of the critical position inside the blade were obtained for service loading. The Larson–Miller parameter was employed to predict the creep lifetime of the blade. Simulation and results of the θ-projection method may also provide suggestions for the safety and life evaluation of HPT blade and other turbine blades.

Upgrading existing coal-fired power plants through heavy-duty and aeroderivative gas turbines

Abstract The need to meet future changes in power demand and current environmental regulations are considered the main driving forces for upgrading existing coal-fired power plants. In this context, repowering by gas-turbine integration is a well-established technique to increase power plant capacity and operational flexibility. Non-negligible benefits are also improvements in efficiency and a decrease in greenhouse gases emissions promoted by the shift to low carbon fuels. This paper aims to investigate the impact of feedwater heater repowering on a 300 MW coal-fired power plant. Marginal efficiency and power increase, as well as the performance of integrated steam-gas power plants, are evaluated by varying the steam section operating conditions and gas turbine technology. Three main cases are investigated, assuming integration with simple or regenerative heavy-duty gas turbines and aeroderivative gas turbines. As part of this investigation, a performance plane is defined, allowing to compare repowering options based on different steam turbine overloads and boiler modes of operation. Focusing on repowering configurations with the maximum power increase, the analysis also examines the plant capability to follow potential load variations and their impact on energy and economic performance parameters.

Uncharacteristic Circumferential TMF Cracking in a Heavy-duty Stationary Gas Turbine Engine Burner Outlet

Abstract Burners are key components of turbomachinery with internal combustion. They allow for a particularly lean combustion in heavy-duty stationary gas turbine engines for power stations and thus contribute significantly to economical operation. Depending on their design, burners are often subject to thermomechanical stress. This failure analysis is concerned with thermal cycling cracks at the burner outlet. Circumferential cracking, parallel to the component surface, is untypical for this damage mechanism. Thermal cycling and thermal-mechanical fatigue cracks usually spread in a radial direction. Possible causes could be the special kind of centrifugal casting structure or the high thermal tension, which might have built up during burner operation.

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.

A Detailed Governor-Turbine Model for Heavy-Duty Gas Turbines With a Careful Scrutiny of Governor Features

Due to substantial use of gas turbines and their highly dynamic behavior, they have a profound impact on electrical grid. Although the control philosophies of various turbines are almost the same, there are some nuances in governor systems. As long as these details affect system response in extremely dynamic phenomena such as load rejection, they should be included in models. In this paper, the governor system is subjected to careful scrutiny; tasks of controllers are classified schematically and some special features such as back-tracing and feed-forward are discussed. The turbine is also modeled and a function is developed to calculate turbine exhaust gas temperature. The proposed governor-turbine model is validated by test results and a comparative analysis shows that the back-tracing method prevents wind-up phenomenon and the feed-forward method improves stability and response time.