MW Gas Turbine Research Articles

Failure Assessment of the First Stage Blade of a Gas Turbine Engine

The gas turbine engine under investigation in this paper was in service after major overhaul for about 2 h at 9:47 A.M. on 18 October, 2014. The 60 MW gas turbine engine experienced a forced break down because of extremely high vibrations and subsequent output power reduction. The blade was made of Inconel 738LC nickel-based super-alloy. Evaluation of the microstructures of the root and tip of the damaged blade, showed no significant change in the microstructure. In closer observation of the fractured blade, some points affected by impact of the remaining airfoil were observed. Metallurgical investigations of the damaged zones of the fractured blade showed many iron rich zones near the fractured surface. The morphology of the fractured surface showed a semi-brittle fracture due to the impact. Finally, it was concluded that the main reason for the gas turbine failure was domestic object damage due to the impact of the liberated components of the turbine engine on the blades.

An Intelligent Approach to Predict Vibration Rate in a Real Gas Turbine

Bearings vibration in gas turbines is considered as an injurious event, which results in incidents such as emergency shutdown or damages in turbine blades and imposes expensive costs to the system. Thus, measuring and analyzing of vibration rate in gas turbines is very important and knowing about its operational conditions and prediction of this phenomenon can help a lot in reducing vibration, avoiding damage to the blades and eventually financial savings. In this paper, we are modelling the vibration rate of a real double shaft 25 MW gas turbine, located in Iran, by making use of a hybrid intelligent model based on multi-layer perceptron neural network and cuckoo optimization algorithm; so, the model in this paper is abbreviated as MLP-COA. It should be noted that this work is an absolutely novel work and the idea is implemented in a real turbine for first time. We have used a real dataset with 161 samples which are collected during a year from a gas turbine in a gas pressure booster station. Furthermore, to obtain the effect of each input parameter on the vibration rate, we have applied sensitivity analysis using the cosine amplitude technique. Evaluation of predicted vibration rates was performed and prove satisfactory efficiency of this model than other predictive models such as radial basis function and multi-layer perceptron. The model can also be used for prediction of online vibration rate without any constraint in selection of data points in training phase.

Dual frequency comb laser absorption spectroscopy in a 16 MW gas turbine exhaust

We demonstrate the first frequency comb laser absorption spectroscopy in an industrial environment. Recent advancements in robust frequency comb design enabled installation of the sensor in an operating power plant, where we simultaneously measured temperature, H2O and CO2 concentration in the exhaust of a 16 MW stationary gas turbine. The frequency comb laser spectrometer probed 16,000 individual wavelengths of light spaced by 0.007 cm−1 (0.0014 nm) near 1440 nm, spanning 279 absorption features of H2O and 43 features of CO2. Fits to the measured absorption spectra yield simultaneous temperature, H2O and CO2 concentrations with between 10 and 60 second time resolution. Measurements over a 5 hour period tracked variations in the exhaust consistent with various changes to the gas turbine operation. Much larger wavelength ranges (200+ nm) and different time resolutions are possible depending on the desired precision by changing various settings on the same spectrometer. Overall, this work demonstrates the potential for frequency comb laser absorption spectroscopy in industrial combustion environments.

Performance Evaluation of a Variable Geometry Gas Turbine in a CHP Plant

This study is to develop mathematical models and evaluate the performance of a gas turbine with variable geometry compressor working in a CHP plant. A single shaft gas turbine plant can maintain the exhaust gas temperature if the load is not below 50 % of the full load by simultaneously regulating the compressor variable vanes position and fuel flow. For load less than 50% the engine is running to meet the power demand. This is achieved by controlling the fuel flow and air bleed at the downstream of the compressor to avoid surge formation while variable vanes are opened fully. To accommodate change of compressor parameters during variable vanes re-stagger correction coefficients are introduced. A behavior of a 4.2 MW gas turbine performance was evaluated. The effect of variation of load and ambient temperature on the gas turbine specific fuel consumption, temperature, pressure ratio, variable vanes opening and efficiency were examined. Comparison between the field data and simulation results demonstrate good agreement. The off-design calculation was done by in-house developed program in MATLAB environment.

Performance of Inlet Filtration System in Relation to the Uncaptured Particles Causing Fouling in the Gas Turbine Compressor

Accounting for the impact of uncaptured particles that cause compressor fouling and subsequently performance degradation when a filter system is in place is often ignored when evaluating the performance of filtration systems. Too often, the emphasis is on capture efficiency and the corresponding differential pressure loss, which are important aspects, however only constitutes a part of the overall impact on the engine performance. The main aim of this study is a first step to quantify the loss that is attributed to compressor fouling by the uncaptured particles, identify a threshold point for which further increase in pressure losses (increasing capture efficiency) no longer yields further increases in fouling levels, and subsequently investigate these respective losses and total losses in a reference high efficiency system (HES) and a hypothetical low efficiency system. Corrected operational data from a 268 MW gas turbine engine were used to evaluate the levels of degradation in the engine at different power settings. With the measured filter media pressure loss during operation and turbomatch (an in-house gas turbine performance simulation software), the impact of power reduction due to pressure loss of the filter was accounted for in the total estimated losses due to engine degradation. That of fouling was calculated based on applicable assumptions, while deducting the loss due to filtration systems from the total loss due to degradation. The study shows the inverse relationship between fouling effects and filter pressure losses as expected. More importantly, it indicates that the higher efficiency system performs better than the low efficiency system, notwithstanding the more dominant impact of higher differential pressure losses. It was also observed that the threshold where fouling effects are zero or negligible is around 800 Pa at high power setting and 600 Pa at lower power setting. In general, for all forms of the degradation using the engine data and simulation software, it is observed that at lower power settings, the impact on the engine is a lot more severe in a single-shaft constant speed operation.

Improved Design of a 25 MW Gas Turbine Plant Using Combined Cycle Application

This paper presents the improved design of a 25 MW gas turbine power plant at Omoku in the Niger Delta area of Nigeria, using combined cycle application. It entails retrofitting a steam bottoming plant to the existing 25 MW gas turbine plant by incorporating a heat recovery steam generator. The focus is to improve performance as well as reduction in total emission to the environment. Direct data collection was performed from the HMI monitoring screen, log books and manufacturer’s manual. Employing the application of MATLAB, the thermodynamics equations were modeled and appropriate parameters of the various components of the steam turbine power plant were determined. The results show that the combined cycle system had a total power output of 37.9 MW, made up of 25.0 MW from the gas turbine power plant and 12.9 MW (an increase of about 51%) from the steam turbine plant, having an HRSG, condenser and feed pump capacities of 42.46 MW, 29.61 MW and 1.76 MW respectively. The condenser cooling water parameters include a mass flow of 1180.42 kg/s, inlet and outlet temperatures of 29.8°C and 35.8°C respectively. The cycle efficiency of the dry mode gas turbine was 26.6% whereas, after modification, the combined cycle power plant overall efficiency is 48.8% (about 84% increases). Hence, SIEMENS steam turbine product of MODEL: SST-150 was recommended as the steam bottoming plant. Also the work reveals that a heat flow of about 42.46 MW which was otherwise being wasted in the exhaust gas of the 25 MW gas turbine power plant could be converted to 12.9 MW of electric power, thus reducing the total emission to the environment.

Selection of a Suitable Material and Failure Investigation on a Turbine Blade of Marine Gas Turbine Engine using Reverse Engineering & FEA Techniques

Turbine blades are considered to be the heart of turbine and play a vital role in extracting energy from high temperature and high pressure gases. Without blades there would be no power and the slightest fault in blading would mean a reduction in efficiency and costly repairs. In this regard, an attempt has been made to analyze the failed marine gas turbine blade. Static structural and Steady state thermal analyses have been analyzed using ANSYS 14.5 to predict the probable conditions which leads blade failure. To investigate the causes of high pressure temperature (HPT) turbine blade failures, a turbine blade of 30 MW gas turbine engine intended for operation onboard ship has been considered for the analysis. Before failure, this gas turbine blade was operated for about 10000 hours while its service life was expected to be around 15000 hours. To improve the life time of a blade, prediction of failure criteria has been analyzed. In addition, a comparative analysis has also been made to determine the strength and suitability of a HPT blade made of Nickel based super alloy X under examination. This material has been compared with other two materials such as Nimonic alloy 80A and Inconel 625. Based on the results of comparative study, it is concluded that Nickel based super alloy X can be a suitable material for the manufacturing of gas turbine blades.

Energy conservation and waste utilization in the cement industry serve the green technology and environment

The cement industry is one of the most energy-intensive industries consuming 4 GJ/ton of cement, i.e. 12–15% of the energy use in total industry. Energy cost accounts for 30% of the total cost of cement production. Seventy-five per cent of this energy is due to the thermal energy for clinker production. It is also found that 35% of this supplied thermal energy is lost in flue gas streams. Most modern kilns use pet coke or coal as their primary fuel. Instead, the municipal waste in landfills offer a cheap source of energy and reduce the environmental effects of dumping solid waste. The calcination and drying processes and the kiln need large quantities of thermal energy. About 40% of the total energy input is lost in the hot flue gases and cooling the stack plus the kiln shell. Hence, it is suitable to use an organic Rankine cycle (ORC) to recover the exhaust energy from the kiln. Alternatively, a 15 MW gas turbine engine combined with a steam turbine could be utilized. It was found that ORC produces 5 MW with a capital cost recovery period of 1.26 years. However, the gas turbine combined system produces 21.45 MW with a maximum recovery period of 2.66 years.

Dynamic test and fatigue life evaluation of compressor blades

High-cycle fatigue (HCF) has been identified as one of the primary causes of gas turbine engine failure. To verify the reliability of the high cycle fatigue fracture of the 5 MW gas turbine engine blade being developed by Doosan Heavy Industries & Construction Co., Ltd., dynamic tests were conducted using real size compressor rigs according to previous studies. The dynamic safety margin of the 5MW gas turbine engine blade was calculated on the basis of the ratio between the dynamic stress and endurance limit stress respectively determined through the compressor rig and fatigue tests. The HCF characteristics and the fatigue life stability of the DGT-5 compressor blades were verified through these processes. A fatigue life design procedure for the gas turbine compressor blade was established on the basis of the design, analysis, and test processes implemented in a previous study. In sum, the 5 MW class gas turbine compressor blades were found to be well designed in terms of resonance stability and fatigue life.

Mechanical Analysis of 1st Stage Marine Gas Turbine Blade

Turbine blades of a gas turbine are responsible for extracting energy from the high temperature, high pressure gases. These blades are operated at elevated temperatures in aggressive environments and are subjected to large centrifugal forces. As many as 42 percent of the failures in gas turbine engines were only due to blading problems and the failures in these turbine blades can have dramatic effect on the safety and performance of the gas turbine engine. In this research paper, an attempt has been made to analyze the failure of gas turbine blade through Mechanical analysis. The blade under investigation belongs to a 30 MW gas turbine engines used in marine applications and is made of Nickel-Base superalloys. Before failure, the turbine blade was operated for about 10000 hours while its service life was expected to be around 15000 hours. Mechanical analysis has been carried out assuming that there might be failure in the blade material due to blade operation at elevated temperature and subjected to large centrifugal forces. The gas turbine blade model profile is generated by using CATIA V5R21software. The turbine blade is analyzed for its thermal as well as structural performance. It was observed that there was no evidence of rubbing marks on the tip section of turbine blade indicating the elongation of the blade is within the safe limit. Maximum stresses and strains are observed near to the root of the turbine blade and upper surface along the blade roots. Maximum temperatures are observed at the blade tip sections and minimum temperature at the root of the blade. Temperature distribution is decreasing from the tip to the root of the blade section. The temperatures observed are below the melting temperature of blade material.

Power generation and cooling capacity enhancement of natural gas processing facilities in harsh environmental conditions through waste heat utilization

Most natural gas (NG) producers in the Persian Gulf face increasing challenges in meeting their domestic gas demands and therefore seek to reduce their NG consumption. Concurrently, the on-site power generation and cooling capacities of local NG processing facilities are constrained by extreme climatic conditions. A combined cooling and power scheme based on gas turbine (GT) waste heat-powered absorption refrigeration is techno-economically assessed to reduce the NG consumption of a major gas processing plant in the Persian Gulf. The scheme utilizes double-effect water-lithium bromide absorption refrigeration activated by steam generated from GT exhaust gas waste heat to provide both GT compressor inlet air and process gas cooling. Based on a thermodynamic analysis, recovery of 150 MW of GT waste heat is found to enhance the plant cooling capacity by 195 MW, thereby permitting elimination of a 32.6 MW GT and existing cooling equipment. On-site power generation is enhanced by 196 GWh annually through GT compressor inlet air cooling, with energy efficiency (i.e., 64%) improved by 35% using cogeneration relative to the existing power generation plant. The overall net annual operating expenditure savings contributed by the combined cooling and power system are of $US13 million to 34 million based on present and projected local utility prices, with an economic payback period estimated at 2 to 5 years. These savings translate to approximately 94 to 241 MMSCM of NG per year, highlighting the potential of absorption refrigeration to both enhance the power generation and cooling capacity of hydrocarbon processing plants exposed to harsh environmental conditions and to realize substantial primary energy savings. Copyright © 2014 John Wiley & Sons, Ltd.

Non-Catalytic NOx Removal from Gas Turbine Exhaust with Cyanuric Acid in a Recirculating Reactor; Small Scale Evaluation and Industrial Application

<p>A novel SNC technique to remove oxides of nitrogen (NO<sub>x</sub>) from stationary gas turbine exhaust has been investigated and applied. The technique employs the use of cyanuric acid (CYA), a non-toxic, dry powder, combined with the injection of auxiliary turbine fuel and recirculation. During the initial investigation, exhaust, generated by a 150 kW gas turbine, was treated in an insulated recirculation reactor, with a mean residence time of 0.65 to 0.71 seconds and a pressure drop of 660 Pa. In the reactor, autoignition of injected auxiliary gas turbine fuel raises the flue gas temperature to between 700 and 800 ºC. CYA slurry is injected. Temperature rise and NOx reduction occur simultaneously. Load following has been achieved. At all temperatures, significant NO<sub>x</sub> reduction from initial concentrations of 106 to 124 ppm to as low as 18 ppm at 15% O<sub>2</sub> have been observed. However, the process generates N<sub>2</sub>O emissions, which vary from 45 to 163 ppm, increasing with increasing CYA/NOx ratio. The ratio of N<sub>2</sub>O formed to NO removed was found to be between 1 to 1.5 to 1. The performance of CYA ((HNCO)<sub>3</sub>) is compared to that of ammonia (NH<sub>3</sub>) and urea ((NH<sub>2</sub>)<sub>2</sub>CO). A numerical model, which combines a detailed chemical kinetic mechanism with recirculation, has been developed. The model captures all observed trends well and is an invaluable guide to improved understanding of the interactive NO<sub>x</sub> removal process. The process was then successfully scaled up and applied to a variety of industrial 3.7 MW gas turbines and similarly significant NO<sub>x</sub> reduction has been achieved.</p>

Modal characteristics and fatigue strength of compressor blades

High-cycle fatigue (HCF) has been identified as one of the primary causes of gas turbine engine failure. The modal characteristics and endurance strength of a 5 MW gas turbine engine blade developed by Doosan Heavy Industries & Construction Co., Ltd. in HCF fracture were verified through analysis and tests to determine the reliability of the compressor blade. A compressor blade design procedure that considers HCF life was performed in the following order: airfoil and blade profile design, modal analysis, stress distribution test, stress endurance limit test, and fatigue life verification. This study analyzed the Campbell diagram and estimated resonance risk on the basis of the natural frequency analysis and modal test of the compressor blade to guarantee safe and operational reliability. In addition, the maximum stress point of the compressor blade was determined through stress distribution analysis and test. The bonding point of the strain gage was determined by using fatigue test. Stress endurance limit test was performed based on the results of these tests. This research compared and verified the modal characteristics and endurance strengths of the compressor blades to prevent HCF fracture, which is among the major causes of gas turbine engine damage. A fatigue life design procedure of compressor blades was established. The 5 MW class gas turbine compressor blade is well designed in terms of resonance stability and fatigue endurance limit.

Hybrid Energy Storage System for Stationary Applications

Energy storage systems have a wide spectrum of functions. They must provide power quality, shaving of load change, matching in distributed power systems, bulk energy storage, and end-user reliability, e.g., uninterrupted power supply. Storage devices based on high-capacity batteries have a number of advantages: i) modular design and relatively compact size; ii) functional flexibility; iii) easy control and maintenance; iv) simple integration into Smart Grids. It is also well known that batteries have a number of unsolved problems, e.g.: i) high specific cost of stored energy; ii) insufficient cycle life (500 – 3 000 charge/discharge cycles); iii) significant decrease of cycle life at high charge/discharge current; iv) problem of depth discharge.To solve the above mentioned problems, we propose the Hybrid Energy Storage system (HESS) incorporating supercapacitors in addition to batteries. Cost analysis of electrochemical storage systems based on batteries of different types, supercapacitors and their combination has also been carried out.To verify the main principles of the proposal, we have designed and developed a HESS prototype. The main functional characteristics of the developed HESS were studied experimentally.The prototype bases on Li-ion batteries and supercapacitors. Such energy storage system includes three main components: Li-ion batteries, supercapacitors, and grid interconnection consisting of two invertors and control and monitoring system. Energy storage capacity of developed HESS prototype is 100 kWh, nominal power—100 kW, peak power—200 kW. HESS was created and tested within the experimental facility including 1.5 MW gas turbine power plant, 200 kW controllable active and reactive loads, and a control and measurement system.Experimental results showed that HESS successfully provides the following functions: (i) suppression of voltage, current, and frequency disturbances in the grid; (ii) compensation of reactive power in the circuit; (iii) uninterrupted power supply. In comparison with battery storage system without supercapacitors, HESS shows lower cost, and higher peak power. In hybrid energy storage system the presence of supercapacitors allows to shave peaks of power at the charge and discharge mode of the battery. We believe that this feature of HESS will prolong the life time of batteries and thus increase the life time and reliability of the entire system.

Failure analysis of gas turbine blades in a gas turbine engine used for marine applications

High pressure temperature (HPT) turbine blade is the most important component of the gas turbine and failures in this turbine blade can have dramatic effect on the safety and performance of the gas turbine engine. This paper presents the failure analysis made on HPT turbine blades of 100 MW gas turbine used in marine applications. The gas turbine blade was made of Nickel based super alloys and was manufactured by investment casting method. The gas turbine blade under examination was operated at elevated temperatures in corrosive environmental attack such as oxidation, hot corrosion and sulphidation etc. The investigation on gas turbine blade included the activities like visual inspection, determination of material composition, microscopic examination and metallurgical analysis. Metallurgical examination reveals that there was no micro-structural damage due to blade operation at elevated temperatures. It indicates that the gas turbine was operated within the designed temperature conditions. It was observed that the blade might have suffered both corrosion (including HTHC & LTHC) and erosion. LTHC was prominent at the root of the blade while the regions near the tip of the blade were affected by the HTHC. It could be concluded that the turbine blade failure might be caused by multiple failure mechanisms such as hot corrosion, erosion and fatigue. Hot corrosion could have reduced the thickness of the blade material and thus weakened the blade. This reduction of the blade thickness decreases the fatigue strength which ultimately led to the failure of the turbine blade.Keywords: Failure analysis, Turbine blade failure, Superalloy, Hot corrosion, Sulphidation, Metallurgical examinationInternational Journal of Engineering, Science and Technology Vol. 6, No. 1, 2014, pp. 43-48

Theoretical investigation into balancing high-speed flexible shafts, by the use of a novel compensating balancing sleeve

Traditional techniques for balancing long, flexible, high-speed rotating shafts are inadequate over a full range of shaft speeds. This problem is compounded by limitations within the manufacturing process, which have resulted in increasing problems with lateral vibrations and hence increased the failure rates of bearings in practical applications. There is a need to develop a novel strategy for balancing these coupling shafts that is low cost, robust under typically long-term operating conditions and amenable to on-site remediation. This paper proposes a new method of balancing long, flexible couplings by means of a pair of balancing sleeve arms that are integrally attached to each end of the coupling shaft. Balance corrections are applied to the free ends of the arms in order to apply a corrective centrifugal force to the coupling shaft in order to limit shaft-end reaction forces and to impart a corrective bending moment to the drive shaft that limits shaft deflection. The aim of this paper is to demonstrate the potential of this method, via the mathematical analysis of a plain, simply supported tube with uniform eccentricity and to show that any drive shaft, even with irregular geometry and/or imbalance, can be converted to an equivalent encastre case. This allows for the theoretical possibility of eliminating the first simply supported critical speed, thereby reducing the need for very large lateral critical speed margins, as this requirement constrains design flexibility. Although the analysis is performed on a sub 15 MW gas turbine, it is anticipated that this mechanism would be beneficial on any shaft system with high-flexibility/shaft deflection.

Modal characteristics according to the tip shape and assembly condition of the turbine blade

To determine the reliability of a 5 MW gas turbine engine blade in high cycle fatigue (HFC) fracture being developed by Doosan Heavy Industries & Construction Co., Ltd., resonance characteristics are verified based on the turbine blade tip shape and assembly condition. In this study, the modal characteristics of compressor and turbine blades are investigated, and a Campbell diagram is established. During the preliminary study, modal analysis and holographic modal test of the first-, fifth-, and tenth-stage compressor blades were performed. Based on the preliminary study result, the natural frequency and Campbell diagram analysis for the turbine blades were performed. This research compared and verified the modal characteristic and resonance stability according to the tip shape and assembly condition of the blade to prevent any HCF fracture. In conclusion, the resonance stability of the shrouded blade is far superior to that of the squealer blade. Suitable assembly conditions must be applied.

Hybrid energy storage system based on supercapacitors and Li-ion batteries

Energy storage systems (ESS) have a wide spectrum of functions. They must provide power quality, shaving of load change, coordination of distributed power systems, bulk energy storage, and end-user reliability, e.g., uninterrupted power supply. In present paper the configuration and design of experimental ESS based on both Li-ion batteries and supercapacitors have been proposed. Such a hybrid energy storage system (HESS) includes three main components: Li-ion batteries, supercapacitors, and grid interconnection consisting of two invertors and control and monitoring system. Energy storage capacity of developed HESS prototype is 100 kWh, nominal power—100 kW, peak power—200 kW. HESS was created and tested within the experimental facility also including 1.5 MW gas turbine power plant, 200 kW controllable active and reactive loads, and control and measurement system. Experimental results showed that HESS successfully provides the following advantages: (i) suppression of voltage, current, and frequency disturbances in the grid; (ii) compensation of reactive power in the circuit; and (iii) uninterrupted power supply. Cost analysis of proposed hybrid system has also been carried out. In comparison with battery ESS without supercapacitors, HESS showed longer life time, lower cost, and higher peak power.

Possibilities for reconstruction of existing steam boilers for the purpose of using exhaust gases from 14 MW or 17 MW gas turbine

Within the energy system in Methanol–vinegar complex (MVC) in Kikinda, beside process boiler and auxiliary equipment, there are three equal steam boilers made by “Minel Kotlogradnja”, provided for combustion of natural gas, fuel oil and process gases. Aiming to increase the MVC Kikinda energy plant capacity, one gas turbine of 14 MW or 17 MW is going to be installed. In regard to relatively high gas temperature and a large amount of the unused oxygen from the air in the exhaust gas, it is specified to split exhaust gas into the two equal streams and import them into the two existing steam boilers, each having production of 16.67 kg/s (60 t/h). In order to use the exhaust gas heat, as well as oxygen contained within, it is necessary to replace the existing burners and to reconstruct the heat exchangers in the steam boiler vertical convective pass. Besides, it is necessary to verify if the existing flue gases fan can comply with the new operating regime, during which a half of the turbine exhaust gas is imported into the steam boiler.

Failure Analysis of a Gas Turbine Compressor in a Thermal Power Plant

This study presents the results of failure analysis of a 28 MW gas turbine at the Rei electrical power plant. The gas turbine failed during the shutdown period and near its second natural frequency at 4200 rpm. Initial inspections revealed that the compressor disk of stage 15 was fractured, and all of the stationary and rotary blades of stages 14–18 of the compressor had been detached or broken from the dovetail region of the disks. The fracture roots were investigated by performing finite element modeling and fractography analysis. It was shown that a crack was initiated from the disk edge on its interface with the rotor shaft and was propagated under cyclic loading. As a result of the malfunction of the compressor bleed valves, which led to compressor surge, the amplitude of vibration of the turbine rotor increased under aerodynamically induced forces. This increase in the natural frequency of the turbine, near the second natural frequency of the turbine, led to final ductile fracture of the compressor disk of stage 15. Finally, the turbine rotor stopped with the loud noise produced by the direct shearing of the fractured disk on the stator casing. Some recommendations are proposed to prevent similar failures in the future.