A NOx Reduction Project for a GT11 Type Gas Turbine

A study was initiated to investigate the possibility of significantly reducing the NOx emissions at a power plant utilizing, among other manufacturers, ALSTOM GT11 type gas turbines. This study is limited to one of the GT11 type gas turbines on the site. After the initial study phase, the project moved on to a mechanical implementation stage, followed by thorough testing and tuning. The NOx emissions were to be reduced at all ambient conditions, but particularly at cold conditions (below 0°C) where a NOx reduction of more than 70% was the goal. The geographical location of the power plant means cold ambient conditions for a large part of the year. The mechanical modifications included the addition of Helmholtz damper capacity with an approximately 30% increase in volume for passive thermo-acoustic instability control, significant piping changes to the fuel distribution system in order to change the burner configuration, and installation of manual valves for throttling of the fuel gas to individual burners. Subsequent to the mechanical modifications, significant time was spent on testing and tuning of the unit to achieve the wanted NOx emissions throughout a major part of the load range. The tuning was, in addition to the main focus of the NOx reduction, also focused on exhaust temperature spread, combustion stability, CO emissions, as well as other parameters. The measurement data was acquired through a combination of existing unit instrumentation and specific instrumentation added to aid in the tuning effort. The existing instrumentation readings were polled from the control system. The majority of the added instrumentation was acquired via the FieldPoint system from National Instruments. The ALSTOM AMODIS plant-monitoring system was used for acquisition and analysis of all the data from the various sources. The project was, in the end, a success with low NOx emissions at part load and full load. As a final stage of the project, the CO emissions were also optimized resulting in a nice compromise between the important parameters monitored, namely NOx emissions, CO emissions, combustion stability, and exhaust temperature distribution.

Flame Characteristics and Turbulent Flame Speeds of Turbulent, High-Pressure, Lean Premixed Methane/Air Flames

The present experimental study focuses on flame characteristics and turbulent flame speeds of lean premixed flames typical for stationary gas turbines. Measurements were performed in a generic combustor at a preheating temperature of 673 K, pressures up to 14.4 bars (absolute), a bulk velocity of 40 m/s, and an equivalence ratio in the range of 0.43–0.56. Turbulence intensities and integral length scales were measured in an isothermal flow field with Particle Image Velocimetry (PIV). The turbulence intensity (u′) and the integral length scale (LT) at the combustor inlet were varied using turbulence grids with different blockage ratios and different hole diameters. The position, shape, and fluctuation of the flame front were characterized by a statistical analysis of Planar Laser Induced Fluorescence images of the OH radical (OH-PLIF). Turbulent flame speeds were calculated and their dependence on operating conditions (p, φ) and turbulence quantities (u′, LT) are discussed and compared to correlations from literature. No influence of pressure on the most probable flame front position or on the turbulent flame speed was observed. As expected, the equivalence ratio had a strong influence on the most probable flame front position, the spatial flame front fluctuation, and the turbulent flame speed. Decreasing the equivalence ratio results in a shift of the flame front position farther downstream due to the lower fuel concentration and the lower adiabatic flame temperature and subsequently lower turbulent flame speed. Flames operated at leaner equivalence ratios show a broader spatial fluctuation as the lean blow-out limit is approached and therefore are more susceptible to flow disturbances. In addition, because of a lower turbulent flame speed these flames stabilize farther downstream in a region with higher velocity fluctuations. This increases the fluctuation of the flame front. Flames with higher turbulence quantities (u′, LT) in the vicinity of the combustor inlet exhibited a shorter length and a higher calculated flame speed. An enhanced turbulent heat and mass transport from the recirculation zone to the flame root location due to an intensified mixing which might increase the preheating temperature or the radical concentration is believed to be the reason for that.

Experimental Studies of the Primary Zone Flow Field and Combustion Performance of a Triple Swirler Combustor

Improvement of the lean blowout limit and more uniform combustor exit temperature distribution are particularly desirable for future aero engine. A triple swirler combination plus an airblast fuel injector might be a promising solution. The design with the triple swirler plus the airblast fuel injector including design A and B was presented and investigated in this paper. Single rectangle sector module combustor was used in the experiment for lean blowout (LBO), and three cups rectangle sector combustor was used for pattern factor (PF) experiments. The LBO and PF experiment data were provided. The primary zone flow field was measured by PIV (Particle Image Velocimetry) under atmospheric pressure and temperature. The result showed that the design A was a promising design, and the primary jet played very important role for flow field of primary zone. The insight relation between flow field and combustion performance could be found out from this paper.

Advances in the Computed Tomography of Turbine Blades

Recent advances in virtually all areas of industrial Computed Tomography (CT) now allow faster, higher resolution, and increasingly economic CT inspection of turbine blades than ever before. CT is now used for a wide range of Non Destructive Testing and Evaluation (NDT&E) applications including first article inspection, defect detection, internal measurement, wear (and failure) analysis, and reverse engineering. Improvements range from the introduction of international standards on CT, through improvements in acquisition, reconstruction, and data extraction. Some of the most significant advances have been made in the ability to process the data generated by the CT systems. Today, CT is an increasingly practical method for the Non Destructive Testing and Evaluation of turbine blades.

Study of Infrared CO2 Radiation From Liquid-Fueled Combustor

Measurements of CO2 infrared radiation were performed on exhaust gases from a combustor. The combustor is a 30% flat (rectangular) model of an annular turbojet-engine combustion chamber. This is a turbulent non-premixed kerosene-air flame with equivalence ratios within the range of 0.15–0.75. The infrared radiation images are obtained by a IR camera equipped with a narrow bandpass filter that falls on the CO2 fundamental band. Temperature profiles were measured by thermocouple at the combustor outlet. The INFRAD program was used to calculate infrared radiation from the CO2 gas component of the exhaust gases from the combustor. The simulation was performed, taking into account the effects of radiation emission and absorption along an optical path. The calculations allow prediction of apparent gas temperatures using the IR camera readings. The calculated results are compared with experimental measurements. They are found to be in reasonable agreement.

Supply Chain Simulation and Economical Evaluation of Forged Titanium Discs for Aircraft Engines

A top level investigation of the supply chain of forged titanium discs resulted in the fact that about 60% of the value-add and about 50% of the time used up in the supply-chain result from the titanium forgers. Engine manufacturers should focus on these companies when optimising their supply chain. The tool factory simulation with an attached economic evaluation tool is able to contribute to this supply chain optimization. It is presented and discussed on the basis of a titanium supply chain optimization from the view of an engine OEM. Two examples show the ability of this approach to predict the impact of future scenarios. Opportunities and weaknesses of this approach are discussed as well as ways and possibilities to bring a forging factory as well as the supply chain closer to optimal performance are evaluated and explained.

Engine Design and Operational Impacts on Particulate Matter Precursor Emissions

Aircraft emissions of trace sulfur and nitrogen oxides contribute to the generation of fine volatile particulate matter (PM). Resultant changes to ambient PM concentrations and radiative properties of the atmosphere may be important sources of aviation-related environmental impacts. This paper addresses engine design and operational impacts on aerosol precursor emissions of SOx and NOy species. Volatile PM formed from these species in the environment surrounding an aircraft is dependent on intra-engine oxidation processes occurring both within and downstream of the combustor. This study examines the complex response of trace chemistry to the temporal and spatial evolution of temperature and pressure along this entire intra-engine path, after combustion through the aft combustor, turbine, and exhaust nozzle. Low-order and higher fidelity tools are applied to model the interaction of chemical and fluid mechanical processes, identify important parameters, and assess uncertainties. The analysis suggests intra-engine processing is inefficient. For engine types in-service in the large commercial aviation fleet, mean conversion efficiency (ε) is estimated to be 2.8% to 6.5% for sulfate precursors and 0.3% to 5.7% for nitrate precursors at the engine exit plane. These ranges reflect technological differences within the fleet, the variation in oxidative activity with operating mode, and modeling uncertainty stemming from variance in rate parameters and initial conditions. Assuming sulfur-derived volatile PM is most likely, these results suggest emission indices of 0.06–0.13 g/kg-fuel assuming particles nucleated as 2H2SO4·H2O for a fuel sulfur content of 500 ppm.

Simulation of Scalar Mixing in Co-Axial Jet Flows Using an LES Method

The present paper describes a study that is aimed at establishing and quantifying the benefits of the Large Eddy Simulation (LES) method for predicting scalar turbulent transport in a combustor relevant jet-mixing problem. A non-reacting co-annular jet mixing configuration is considered for which comprehensive experimental data for both velocity and scalar fields have recently been obtained. Detailed comparisons are presented for the development of the axial velocity field in terms of both mean and turbulence intensity. Similarly, the mixing between the jets is examined by comparison with measurements for the mean concentration and the variance of concentration fluctuations. Agreement with these statistically averaged fields is demonstrated to be very good, and a considerable improvement over the standard eddy viscosity RANS approach. Illustrations are presented of the time-resolved information that LES provides such as time histories, and also conserved scalar pdf predictions. The LES results are shown, even using a simple Smagorinsky sub-grid-scale model, to predict correctly lower values of the turbulent Prandtl number (∼ 0.6) in the free shear regions of the flow, as well as higher values (∼ 1.0) in the wall-affected regions. The ability to predict turbulent Prandtl number variations (rather than input these as commonly done in most combustor RANS CFD models) is an important and promising feature of the LES approach for combustor simulation since it is known to be important in determining combustor exit temperature traverse.

NOx Emissions Reduction in an Innovative Industrial Gas Turbine Combustor (GE10 Machine): A Numerical Study of the Benefits of a New Pilot-System on Flame Structure and Emissions

One of the driving requirements in gas turbine design is emissions reduction. In the mature markets (especially the North America), permits to install new gas turbines are granted provided emissions meet more and more restrictive requirements, in a wide range of ambient temperatures and loads. To meet such requirements, design techniques have to take advantage also of the most recent CFD tools. As a successful example of this, this paper reports the results of a reactive 3D numerical study of a single-can combustor for the GE10 machine, recently updated by GE-Energy. This work aims to evaluate the benefits on the flame shape and on NOx emissions of a new pilot-system located on the upper part of the liner. The former GE10 combustor is equipped with fuel-injecting-holes realizing purely diffusive pilot-flames. To reduce NOx emissions from the current 25 ppmvd@15%O2 to less than 15 ppmvd@15%O2 (in the ambient temperature range from −28.9°C to +37.8°C and in the load range from 50% and 100%), the new version of the combustor is equipped with 4 swirler-burners realizing lean-premixed pilot flames; these flames in turn are stabilized by a minimal amount of lean-diffusive sub-pilot-fuel. The overall goal of this new configuration is the reduction of the fraction of fuel burnt in diffusive flames, lowering peak temperatures and therefore NOx emissions. To analyse the new flame structure and to check the emissions reduction, a reactive RANS study was performed using STAR-CD™ package. A user-defined combustion model was used, while to estimate NOx emissions a specific scheme was also developed. Three different ambient temperatures (ISO, −28.9°C and 37.8°C) were simulated. Results were then compared with experimental measurements (taken both from the engine and from the rig), resulting in reasonable agreement. Finally, an additional simulation with an advanced combustion model, based on the laminar flamelet approach, was performed. The model is based on the G-Equation scheme but was modified to study partially premixed flames. A geometric procedure to solve G-Equation was implemented as add-on in STAR-CD™.

Smart Combustors: Just Around the Corner

This paper reviews the state of the art of active control systems (ACS) for gas turbine combustors. Specifically, it discusses the manner in which ACS can improve the performance of combustors, the architecture of such ACS, and the designs and promising performance of ACS that have been developed to control combustion instabilities, lean blowout and pattern factor. The paper closes with a discussion of research needs, with emphasis on the integration of utilized engine ACS, health monitoring and prognostication systems into a single control system that could survive in the harsh combustor environment.