Heavy Duty Gas Turbine Research Articles

Attack Detection for Securing Cyber Physical Systems

Cyber-physical systems (CPSs) security has become a critical research topic as more and more CPS applications are making increasing impacts in diverse industrial sectors. Due to the tight interaction between cyber and physical components, CPS security requires a different strategy from the traditional information technology (IT) security. In this paper, we propose a machine learning-based attack detection (AD) scheme, as part of our overall CPS security strategies. The proposed scheme performs AD at the physical layer by modeling and monitoring physics or physical behavior of the physical asset or process. In developing the proposed AD scheme, we devote our efforts on intelligently deriving salient signatures or features out of the large number of noisy physical measurements by leveraging physical knowledge and using advanced machine learning techniques. Such derived features not only capture the physical relationships among the measurements but also have more discriminant power in distinguishing normal and attack activities. In our experimental study for demonstrating the effectiveness of the proposed AD scheme, we consider heavy-duty gas turbines of combined cycle power plants as the CPS application. Using the data from both the high-fidelity simulation and several real plants, we demonstrate that our proposed AD scheme is effective in early detection of attacks or malicious activities.

Development of a program to simulate the dynamic behavior of heavy-duty gas turbines during the entire start-up operation including very early part

This study presents a simulation tool for the dynamic behavior during the start-up of heavy-duty gas turbines. The simulation was implemented in MATLAB and can accurately predict the full start-up procedure from zero speed to idling. Each component of the system was modeled as a single control volume or multiple control volumes to which mass and energy balances were applied. The governing equations are solved numerically by the multi-variable Newton Raphson method. The compressor and turbine are divided into several groups for the bleeding and turbine cooling model. The program can simulate the early part of the start-up process from zero rpm to ignition by using the starter module in the cranking process, which can be hard to simulate using commercial software. A heat transfer model was applied to each control volume of the major components to consider the heat soakage effect accurately. The full start-up process of an industrial gas turbine was simulated, and the results were compared with actual operating data for validation. The program is expected to be used for various purposes, especially for estimating an adequate starter capacity and scheduling an optimal start-up procedure of heavy-duty gas turbines.

Cultural coyote optimization algorithm applied to a heavy duty gas turbine operation

In the past decades, the quantity of researches regarding industrial gas turbines (GT) has increased exponentially in terms of number of publications and diversity of applications. The GTs offer high power output along with a high combined cycle efficiency and high fuel flexibility. As consequence, the energy efficiency, the pressure oscillations, the pollutant emissions and the fault diagnosis have become some of the recent concerns related to this type of equipment. In order to solve these GTs related problems and many other real-world engineering and industry 4.0 issues, a set of new technological approaches have been tested, such as the combination of Artificial Neural Networks (ANN) and metaheuristics for global optimization. In this paper, the recently proposed metaheuristic denoted Coyote Optimization Algorithm (COA) is applied to the operation optimization of a heavy duty gas turbine placed in Brazil and used in power generation. The global goal is to find the best valves setup to reduce the fuel consumption while coping with environmental and physical constraints from its operation. In order to treat it as an optimization problem, an integrated simulation model is implemented from original data-driven models and others previously proposed in literature. Moreover, a new version of the COA that links some concepts from Cultural Algorithms (CA) is proposed, which is validated under a set of benchmarks functions from the Institute of Electrical and Electronics Engineers (IEEE) Congress on Evolutionary Computation (CEC) 2017 and tested to the GT problem. The results show that the proposed Cultural Coyote Optimization Algorithm (CCOA) outperforms its counterpart for benchmark functions. Further, non-parametric statistical significance tests prove that the CCOA’s performance is competitive when compared to other state-of-the-art metaheuristics after a set of experiments for five case studies. In addition, the convergence analysis shows that the cultural mechanism employed in the CCOA has improved the COA balance between exploration and exploitation. As a result, the CCOA can improve the current GT operation significantly, reducing the fuel consumption up to 3.6% meanwhile all constraints are accomplished.

Probabilistic failure analysis of hot gas path in a heavy-duty gas turbine using Bayesian networks

Heavy-duty gas turbines are usually devised in power plants to generate electrical energy. Sudden failure in any of its parts or subdivisions will result in a decrement of the efficiency of the system or emergency shutdown of the system. The highest risk of failure in these turbines is subjected to the hot gas path (HGP) of the turbine. Due to the existence of uncertainty in diagnosing process or damage growth, in this research, a modified risk-based probabilistic failure analysis model using Bayesian networks (BN) was developed. First, a failure model was developed using the Fault Tree Analysis, and then it is transformed into a BN model. This model is capable of predicting and diagnosing critical components and critical failure modes and mechanisms for each component by updating failure probabilities. Moreover, in order to enhance the application of the proposed model and to identify the risk factors, the sensitivity analysis of the HGP components is presented with applying definitions of importance measures and extend them to BN. The sensitivity analysis and application of its results for making decisions during the system operation will enhance the reliability and safety of the system.

CFD-based blade shape optimization of MGT-70(3)axial flow compressor

Purpose This study aims at enhancing the performance of a 16-stage axial compressor and improving the operating stability. The adopted approaches for upgrading the compressor are artificial neural network, optimization algorithms and computational fluid dynamics. Design/methodology/approach The process starts with developing several data sets for certain 2D sections by means of training several artificial neural networks (ANNs) as surrogate models. Afterward, the trained ANNs are applied to the 3D shape optimization along with parametrization of the blade stacking line. Specifying the significant design parameters, a wide range of geometrical variations are considered by implementation of appropriate number of design variables. The optimized shapes are analyzed by applying computational fluid dynamic to obtain the best geometry. Findings 3D optimal results show improvements, especially in the case of decreasing or elimination of near walls corner separations. In addition, in comparison with the base geometry, numerical optimization shows an increase of 1.15 per cent in total isentropic efficiency in the first four stages, which results in 0.6 per cent improvement for the whole compressor, even while keeping the rest of the stages unchanged. To evaluate the numerical results, experimental data are compared with obtained data from simulation. Based on the results, the highest absolute relative deviation between experimental and numerical static pressure is approximately 7.5 per cent. Originality/value The blades geometry of an axial compressor used in a heavy-duty gas turbine is optimized by applying artificial neural network, and the results are compared with the base geometry numerically and experimentally.

Metallurgical Failure Analysis of Cracked First Stage Vane of Heavy-Duty Industrial Gas Turbine Engine for Power Generation

Abstract A first stage turbine vane of a heavy-duty gas turbine engine, exhibiting an outward bulge of approximately 0.6 mm and a visible crack in the top coating, was delivered by the client for a detailed destructive failure investigation. The subject component was an experimental part used in a test field engine. The suction side wall of the casting was cut off to reveal a gaping crack on the inside of the aft cavity that was also visible by borescopic inspection. The cooling insert of the aft cavity was clean and did not have any blocked cooling holes. The cooling pattern on the inside wall of the aft cavity was unremarkable. No evidence whatever of impact damage was found on the suction side surface of the subject vane in the cracked region. The hypothesis as to the most probable root cause of the cracking that is still standing is a combination of low wall thickness, non-optimal process parameters for bond coat pre-heat, and potentially high thermal/mechanical loading during engine operation. It appears this is not a wide-spread phenomenon but rather an isolated occurrence.

Numerical investigation of inlet guiding ring effect on combustor flow field with multiple swirler structures

ABSTRACT Lean-premixed combustion technology has been adopted widely for heavy-duty gas turbine application. The multiple-swirl structure might shorten the flame brush length and reduce emissions. However, the inlet flow cannot be set equally for each swirl burner. The inlet guiding ring structure should be carefully adjusted and validated to reach the design goal. This paper introduces a typical geometry of heavy-duty combustor, which is designed with multiple swirler structures. The inlet guiding ring is a semicircle type. The parametric analysis is trying to investigate the axial location of the inlet guiding ring effect on the downstream multiple-swirl flow structure. Computational results show that both the Counter-Swirl and Co-Swirl configurations possess quite well aerodynamics which can support the recirculation establishment and flame stabilization. As the axial distance between the inlet guiding ring and swirl nozzle increases from 16 mm to 37 mm, the width of the recirculation will increase, which intensify the turbulence mixing for the pilot and main stage. Meanwhile, the length of the recirculation also increases, and the turbulence intensity keeps relatively strong. When the gap distance increases from 37 mm to 51 mm, the flow phenomenon would return to the condition like the case with an axial distance equal to 16 mm. Therefore, the condition with the axial gap distance 37 mm is quite critical. Thus, the flow field is quite sensitive to the inlet guiding ring location.

Design of Rowen's Model for Heavy Duty Gas Turbine (HDGT)

In this paper, the parameters of Rowen’s model for heavy duty gas turbines in dynamic studies are estimated by use of available operational and performance data. The transfer function model of heavy duty gas turbine is required for the analysis and development of optimal controllers. The speedtronic controller derived from Rowen’s model has three controller namely, speed, acceleration and temperature. The model with all these controllers is developed with MATLAB/Simulink to study their response and arrive at the simplified model. The speed controller may have isochronous or drooping governor characteristics. The choice of governor characteristics for the simplified model is made from the response of the system simulated for an unit step load disturbance. The equations are to be validated with the response of the system simulated using MATLAB/Simulink.

Metallurgical Failure Investigation of SCC in Leaking Piping System in a Combined Cycle Gas Turbine Power Plant

Abstract Cracking and leakage, not repairable by welding, was found in premix piping of heavy-duty gas turbine engine for power plant applications. The subject laboratory specimen, a pipe section cut out on site and received at the investigating laboratory, failed by transgranular stress corrosion cracking (SCC). The stress corrosion cracking has probably been induced by chlorides (halide-induced stress corrosion cracking). Chlorine peaks were found in EDS spectra acquired on the inner pipe wall surfaces. However, it cannot completely be ruled out that those were artifacts caused by handling, cleaning, and cutting. The cracking is located adjacent to welds.

Torsional Fretting Wear of Annular Flat-Flat Contact Interface Under Different Road Clamping Force and Torque

For the rod fastening combined rotor in some heavy-duty gas turbine, the annular flat-flat contact interfaces are usually used between disks to transmit the torque. In this paper, a contact model of two disks assembled by 12 circumferential preload tie rods is established to study the fretting wear behavior of the annular contact interfaces under variable torque and different preload of tie rods. The changes of contact stress distribution, slide distance and wear depth of the annular contact interface with torque and rod preload are obtained. The results show that the wear depth is increasing with the growth of torque and rod preload.

Effects of Torque and Friction Coefficients on the Fretting Characteristics of Annular Face Gear Contact Interface

In present, the annular face gear connect structures are widely used in combined rotor of heavy-duty gas turbine or aeroengine to transmit the torque and force. The fretting wear will happen on the face gear contact interfaces after long-time operation. This paper investigates the evolution of contact characteristics including contact stress, slide distance, and wear depth of face gear contact interfaces under the conditions of different torque and friction coefficients by means of finite element analysis method. It can be concluded that the distribution of the contact stress and slip distance on the face gear contact interface are inhomogeneous, and the stress close to the tooth root is the largest, so the largest wear occurs near the tooth root in the inner surface. Increased torque can improve the contact stress and slip distance. The larger friction coefficient effectively reduces the wear of contact surfaces.

Modelling of catastrophic stress development due to mixed oxide growth in thermal barrier coatings

Abstract In thermal barrier coatings (TBCs) of heavy-duty gas turbines, thermally grown oxide (TGO) develops in two stages, i.e. firstly, a thin layer of dense protective α-Al2O3 forms slowly, and then, a layer of porous detrimental mixed oxide (MO) between top coat (TC) and α-Al2O3 appears. During long-term isothermal oxidation at high temperature, the failure of TBCs usually occurs when a critical thickness of MO is reached, but the exact failure mechanism is still largely unclear, let alone the related stress development. In this paper, we analyze the stress evolution and the resultant failure modes due to the whole-layer growth of uniform MO. The results show that it is MO, rather than α-Al2O3, that is mainly responsible for the micro-cracking and/or delamination in TBCs. The fast growth of expansive MO induces catastrophic stresses, which leads to micro-cracking in the α-Al2O3 layer. The cracking of α-Al2O3 layer reduces the oxidation resistance and further accelerates the MO growth. Our theoretical analysis provides a reasonable explanation of the experimental results.

Mechanism Research and Countermeasure Analysis of Yellow Plume during the Gas Turbine Start-Up Period

The problem of yellow plume exists in most heavy-duty gas turbine units under start-up and low load conditions. How to suppress the yellow plume is a difficult problem in gas turbine power plants. It is judged that yellow plume is caused by the high NO2 concentration in flue gas. From the point of view of mechanism research, this study analyzed the causes of yellow plume by numerical simulation combined with experimental research; obtained influence factors of the conversion of NO into NO2; analyzed the degree of influence of these factors on the formation of yellow plume; verified the results through on-site measurement of a 6FA gas turbine unit; and finally proposed the countermeasures to suppress yellow plume from the gas turbine side and the heat recovery steam generator (HRSG) side.

High Cycle Fatigue Failure of Burner Feeder Line in a Heavy-duty Gas Turbine Engine

Abstract A number of fuel gas supply pipes or feeder lines of heavy-duty gas turbine engines for power generation were found cracked in two sister engines of a power plant, this after approximately 100 000 operating hours. Cracks originated from the outer diameter (OD) of the feeder pipes, at the fusion line of the fillet weld that joined the subject pipes to the main burner bodies. The incident components failed by high cycle fatigue (HCF) fracture. The failure mechanism is purely mechanic. No evidence of corrosion or any other contributing mechanism was found. Design, manufacture, such as welding and coating, burner assembly, and burner installation are all unrelated to the failure. The root cause of the failure is excessive dynamic service loading.

Integration of Utility Grid with Hybrid Generation for Power Quality Conditioning Using Dynamic Voltage Restorer

The intermittent natures of renewable energy sources are influencing the system parameter while integrated with the power system. The switching of the load also influences the system and May causes the power quality issues such as voltage Sag, Swell, voltage interruption and voltage spikes. Getting the smoothening power and meeting the peak demand is the greatest challenge in the current scenario. The necessary and sufficient power is provided with the use of integration of renewable sources and power conditioning unit. In this work, the grid integration of solar photovoltaic, Fuel cell with heavy duty gas turbine generator is made. The voltage interruption is avoided using hybrid generation with dynamic voltage restorer. The solar photovoltaic is integrated with DC link through the boost converter and the maximum power is extracted using fuzzy based maximum power point tracking technique. The Fuel cell and the heavy duty gas turbine are integrated with DC link for providing continues power and this integration can avoid the effect of intermittent nature of solar power. The DC link power is integrated with the grid through the voltage source converter. The voltage source converter and the dynamic voltage restorer are operated through a power conditioning unit. The performances of the hybrid generation with dynamic voltage restorer are simulated under dynamic source and load variations. The total harmonic distortion of the hybrid generation with dynamic voltage restorer performance is maintained within the limit as per IEEE-519 standard.

Effects of Swirling Strength of the Premixed Gas Flow on Pollutant Emission in a Heavy-Duty Gas Turbine

The combustion process and pollutant emission of an annular combustion chamber for a heavy-duty gas turbine were investigated by numerical method. The realizable k-ε model and finite rate/eddy dissipation model were adopted for calculations of turbulence and combustion. The effects of different swirling numbers of the double-swirler inlet on the temperature distribution and the thermal NOx formation in the combustion chamber were analyzed. The results show that the change of the swirling number of the outer swirling flow has a greater influence on the generation of the thermal NOx when compared with that of the inner swirling flow. The maximum average temperature of the central cross section of the combustor does not exceed 1760K. The average mass fraction of the generated thermal NOx at the exit decreases with the increasing outer swirling number. When the outer swirling number is less than 0.8, the generation of the thermal NOx is severe at the side wall of the combustion chamber.

E&P Notes (January 2019)

E&P Notes (January 2019)

Directional solidification casting technology of heavy-duty gas turbine blade with liquid metal cooling (LMC) process

In this work, some important factors such as ceramic shell strength, heat preservation temperature, standing time and withdrawal rate, which influence the formability of directionally solidified large-size blades of heavy-duty gas turbine with the liquid metal cooling (LMC) process, were studied through the method of microstructure analysis combining. The results show that the ceramic shell with medium strength (the high temperature flexural strength is 8 MPa, the flexural strength after thermal shock resistance is 12 MPa and the residual flexural strength is 20 MPa) can prevent the rupture and runout of the blade. The appropriate temperature (1,520 °C for upper region and 1,500 °C for lower region) of the heating furnace can eliminate the wide-angle grain boundary, the deviation of grain and the run-out caused by the shell crack. The holding time after pouring (3-5 min) can promote the growth of competitive grains and avoid a great deviation of columnar grains along the crystal orientation , resulting in a straight and uniform grain structure. In addition, to avoid the formation of wrinkles and to ensure a smooth blade surface, the withdrawal rate should be no greater than the growth rate of grain. It is also found that the dendritic space of the blade decreases with the rise of solidification rate, and increases with the enlarging distance between the solidification position and the chill plate.

Compressor Retrofittable Solutions in Heavy-Duty Gas Turbines for Minimum Environmental Load Reduction

International policies aiming at keeping global warming within safety limits will strongly impact gas-fired power plants. Flexibility is going to be the key-word, hence this paper focuses on possible strategies to increase turndown capability (i.e. lowering Minimum Environmental Load (MEL)) of open and combined cycle power plants (CCPP) through retrofittable compressor service packages. In particular, the following three options have been analyzed: extra-closure of Variable Inlet Guide Vanes (IGVs), Blow-Off (BO) lines opening and inlet bleed heating. All these solutions aim at reducing the compressor outlet mass-flow rate while keeping a safe stability margin. The effect of lowering the minimum load capability by opening the BO lines has been numerically investigated through full compressor 2D throughflow analyses. Moreover, the impact on compressor performance and stability of the extra-closure of IGVs has been analyzed with the support of 3D steady-state CFD modelling. Finally, the overall performance of the power-plant has been included and discussed in order to provide plant managers with a solid starting point for a techno-economic analysis.

Emission reduction through highly oxygenated viscous biofuels: Use of glycerol in a micro gas turbine

The presented paper focuses on the combustion analysis of a highly oxygenated, viscous and economically viable fuel in an internal combustion micro gas turbine. Results suggest that environmental benefits in terms of NOx emissions and PM emissions are significant as concentrations of both species are reduced. Based on the analysis presented in the study, altered local air-fuel ratio suppresses NOx formation and PM formation resulting in 10-fold lower PM emission than same experimental apparatus with diesel fuel. The study further analyses and identifies three key mechanisms that are responsible for this reduction: altered oxygen profile during mixture preparation, prevention of soot precursors formation and promotion of soot oxidation reactions. The influence of tested fuel is also perceivable through higher CO and THC emissions. Parametric analysis within the selected experimental space suggests that operational parameters of the micro gas turbine can be adjusted to reduce concentrations of these two species without negatively affecting other pollutants. Significant benefits of the fuel in terms of environmental impact indicate that further investigation and development of this approach might provide a new alternative energy source for stationary use as well as for mobility in sectors where heavy duty gas turbines are used as prime movers.