Dry Low Emission Research Articles

Numerical and experimental study of swirl premixed CH4/H2/O2/CO2 flames for controlled-emissions gas turbines

Stoichiometric hydrogen-enriched oxy-methane (CH4/H2/O2/CO2) flames are investigated numerically by large eddy simulations (LES) and experimentally in a premixed dry-low-emission (DLE) swirl combustor to study the combustion behavior as well as stability characteristics. The study focuses on the effects of hydrogen fraction (HF), oxygen fraction (OF), and inlet bulk velocity (Uin) of the combustible mixture on the stability and combustion characteristics of the flames. Some distinctive features of the flames are reported in this study for possible application in controlled-emissions gas turbines. The results show that the reaction rates are increased with increasing percentages of hydrogen and oxygen in the reactant mixture, and the flame structures are observed to be more stable and compact. It is noted that the reaction rates are more sensitive to OF than they are to HF. The reaction rates are reduced with increasing inlet flow velocity, owing to the associated shorter residence time. The outer recirculation zone plays a significant role in flame stabilization at smaller values of HF and OF; however, its role diminishes at higher values. The CO concentration at the combustor exit increases with increasing HF and OF, due to higher CO2 decomposition at elevated temperatures. The effluent CO concentration, on the other hand, decreases with increasing inlet velocity. Higher HF and OF are characterized by higher Damköhler number (Da) and reduced flame thickness. The effect of velocity on flame thickness, however, was found to be negligible, indicating that the flame microstructure is governed by the overall stoichiometry. The Da showed declining behavior with increasing the inlet velocity because of smaller residence time. The reaction rates thus dominate the flame behavior, while turbulence affects only the macro-structure of the flame.

Combustion and Emission Characteristics of Ammonia under Conditions Relevant to Modern Gas Turbines

ABSTRACT Ammonia (NH3) is considered a promising alternative fuel, capable of producing energy with zero CO2 emissions. Its combustion, however, poses a series of challenges due to the low reactivity of NH3 and the formation of very high quantities of NOx. This work numerically investigates the combustion and emission characteristics of ammonia in three modern stationary gas turbine concepts, namely (a) lean-burn dry-low emissions (DLE); (b) rich-burn, quick-quench and lean-burn (RQL); and (c) moderate or intense low oxygen dilution (MILD), under operating conditions typical of commercial gas turbines (inlet temperatures of 500 K and pressure of 20 bar). Numerical simulations employing detailed chemical kinetic mechanisms are carried out to study the propagation speed of ammonia, the combustor temperatures, and the emissions of NOx and NH3. The simulations are first validated against literature NOx data and then the most accurate mechanism is selected. The performance of the different gas turbine engine concepts is subsequently compared based on the results from the selected mechanism. The results show that the lowest emissions are achieved with the RQL and MILD combustion concepts, while the DLE combustion concept only presents acceptable emission values under conditions deemed unstable, where the laminar flame speeds are below 3 cm/s.

Numerical Investigations of Pollutant Emissions From Novel Heavy-Duty Gas Turbine Burners Operated With Natural Gas

Abstract A numerical investigation of pollutant emissions of a novel dry low-emissions burner for heavy-duty gas turbine applications is presented. The objective of this work is to develop and assess a robust and cost-efficient numerical setup for the prediction of NOx and CO emissions in industrial gas turbines and to investigate the pollutant formation mechanisms, thus supporting the design process of a novel low-emission burner. To this end, a comparison against experimental data, from a recent experimental campaign performed by BHGE in cooperation with University of Florence, has been exploited. In the first part of this work, a Reynolds-averaged Navier–Stokes (RANS) approach on both a simplified geometry and the complete domain is adopted to characterize the global flame behavior and validate the numerical setup. Then, unsteady simulations exploiting the scale adaptive simulation (SAS) approach have been performed to assess the prediction improvements that can be obtained with the unsteady modeling of the flame. For all simulations, the flamelet generated manifold (FGM) model has been used, allowing the reliable and cost-efficient application of detailed chemistry mechanisms in computational fluid dynamics (CFD) simulation. However, FGM typically faces issues predicting flame emissions, such as NOx and CO, due to the wide range of time scales involved, from turbulent mixing to pollutant species oxidation. Specific models are typically used to predict NOx emissions, starting from the converged flow-field and introducing additional transport equations. Also CO prediction, especially at part-load operating conditions could be an issue for flamelet-based model: in fact, as the load decreases and the extinction limit approaches, a superequilibrium CO concentration, which cannot be accurately predicted by FGM, appears in the exhaust gases. To overcome this issue, a specific CO-burn-out model, following the original idea proposed by Klarmann, has been implemented in ANSYS fluent. The model allows to decouple the effective CO oxidation term from the one computed by FGM, defining a postflame zone where the source term of CO is treated following the Arrhenius formulation. In order to support the design process, an indepth CFD investigation has been carried out, evaluating the impact of an alternative burner geometrical configuration on stability and emissions and providing detailed information about the main regions and mechanisms of pollutants production. The outcomes support the analysis of experimental results, allowing an indepth investigation of the complex flow-field and the flame-related quantities, which have not been measured during the tests.

Static Stability and Combustion Characteristics of Oxy-Propane Flames in a Premixed Fuel-Flexible Swirl Combustor

This study investigates the stability and combustion features of premixed oxy-propane flames in a dry low emission (DLE) model combustor for clean fuel/oxidizer-flexible combustion applications in gas turbines. The stability of the oxy-propane flame is characterized by its blowout and flashback limits over ranges of equivalence ratios (ϕ) from 0.1 to 1.0 and oxygen fractions (OF: volumetric concentration of O2 in the O2/CO2 oxidizer) from 15 to 70%. For better understanding of the physics behind the flame extinction mechanisms, the stability limits were plotted within the ϕ–OF space against the contours of adiabatic flame temperature (Tad), inlet Reynolds number (Re), mixture mass flow rate (ṁmix), and combustor power density (PD). The flame speed (FS) was also estimated at selected operating conditions. It was observed that the FS is contingent to Tad only. A correlation of Tad–FS was developed for better characterization of premixed oxy-propane flames. It was also found that the blowout curve follows a constant Tad contour on the stability map, whereas the flashback curve does not. This implies that Tad is a more relevant controlling parameter choice of combustor stability near the blowout limit, whereas the reaction rate is a suitable indicator of the flame stability limit near flashback. The stability map of the present oxy-propane flame was compared with that of an oxy-methane flame on the same combustor. It was found that, at the same OF, the blowout and flashback limits of the propane flame occur at leaner ϕ, compared to those of methane flame, which was expected for a higher hydrocarbon fuel like propane. Flame shapes at different sets of operating conditions were investigated for inferring key information on the flame behavior and macrostructure while varying ϕ, OF, and hence, Tad. Similar flame shapes were obtained at the same Tad regardless of ϕ and OF values. Flames of similar Tad also demonstrated similar temperature distributions near the flame core. The findings confirm the dependence of the FS on Tad, irrespective of the combinations of ϕ and OF used to achieve any particular Tad.

Experiment study on the combustion performance of hydrogen-enriched natural gas in a DLE burner

Abstract The effect of hydrogen enrichment to natural gas swirling flame was experimentally investigated at atmospheric pressure conditions using a radially-staged DLE (Dry Low Emission) burner. The hydrogen volume content was varied as 0%, 5%, 11%, 21% and 26% in the fuel blend to assess that whether it is beneficial or detrimental to combustion characteristics. OH-PLIF (Planar Laser Induced Fluorescence) measurement was performed to examine macro flame topology at both stable combustion conditions. NOx and CO emission was also analyzed. In terms of unstable combustion, pressure fluctuation during combustion instability was monitored by dynamic pressure transducers to characterize the dominant frequency as well as pressure oscillation amplitude. Based on the real time pressure signal, phase-locked PLIF method was utilized to give phase averaged OH images during one thermo-acoustic cycle. The experimental results indicate that the flame shrinks distinctly when the addition of hydrogen is increased to certain content. To be specific, the flame structure changes little as the hydrogen content is lower than 5%, and the flame expanding angle also keeps well. Once the hydrogen concentration is boosted to be over 11%, the flame expands greatly towards the confinement wall. Meanwhile NOx emission increases gradually, but CO emission keeps stable with slightly decrease. The amplitude of the dynamic pressure pulsation reduces with hydrogen addition, but the dominant frequency presents to be irrelevant with hydrogen enrichment during combustion oscillation. It can be concluded that hydrogen addition in the natural gas at this realistic radially staged burner shows potential ability to inhibit combustion instability somehow. The 2D Rayleigh Index distribution then indicates proves that the main circulation zone and flame-wall interaction zone are two regions where local heat release and pressure fluctuation coupled to induce combustion thermo-acoustic problems.

Extension of Fuel Flexibility by Combining Intelligent Control Methods for Siemens SGT-400 Dry Low Emission Combustion System

Extension of gas fuel flexibility of a current production SGT-400 industrial gas turbine combustor system is reported in this paper. A SGT-400 engine with hybrid combustion system configuration to meet a customer's specific requirements was string tested. This engine was tested with the gas turbine package driver unit and the gas compressor-driven unit to operate on and switch between three different fuels with temperature-corrected Wobbe index (TCWI) varying between 45 MJ/m3, 38 MJ/m3, and 30 MJ/m3. The alteration of fuel heating value was achieved by injection or withdrawal of N2 into or from the fuel system. The results show that the engine can maintain stable operation on and switching between these three different fuels with fast changeover rate of the heating value greater than 10% per minute without shutdown or change in load condition. High-pressure rig tests were carried out to demonstrate the capabilities of the combustion system at engine operating conditions across a wide range of ambient conditions. Variations of the fuel heating value, with Wobbe index (WI) of 30 MJ/Sm3, 33 MJ/Sm3, 35 MJ/Sm3, and 45 MJ/Sm3 (natural gas, NG) at standard conditions, were achieved by blending NG with CO2 as diluent. Emissions, combustion dynamics, fuel pressure, and flashback monitoring via measurement of burner metal temperatures, were the main parameters used to evaluate the impact of fuel flexibility on combustor performance. Test results show that NOx emissions decrease as the fuel heating value is reduced. Also note that a decreasing fuel heating value leads to a requirement to increase the fuel supply pressure. Effect of fuel heating value on combustion was investigated, and the reduction in adiabatic flame temperature and laminar flame speed was observed for lower heating value fuels. The successful development program has increased the capability of the SGT-400 standard production dry low emissions (DLE) burner configuration to operate with a range of fuels covering a WI corrected to the normal conditions from 30 MJ/N·m3 to 49 MJ/N·m3. The tests results obtained on the Siemens SGT-400 combustion system provide significant experience for industrial gas turbine burner design for fuel flexibility.

Stability map and shape of premixed CH4/O2/CO2 flames in a model gas-turbine combustor

Oxy-fuel combustion was investigated in a model combustor that mimics the geometry of operational air-fuel gas-turbine combustors implementing the LPM DLE DACRS technology (Lean Premixed, Dry Low Emissions, Dual Annular Counter-Rotating Swirlers). Premixed swirl-stabilized CH4/O2/CO2 flames were tested over ranges of equivalence ratio (φ = 0.2–1.0) and oxygen fraction (OF = 25–70%). The non-preheated flow rates of CH4, O2, and CO2 were adjusted for each flame to maintain a common bulk velocity of 5.2 m/s at burner throat throughout the entire study. The combustor stability map was identified by quantifying the flashback and blowout limits within the φ-OF space. The adiabatic flame temperature (Tad) was also mapped over the same ranges. Selected flames were imaged to analyze the effects of φ, OF, and Tad on flame shape. Interestingly, at constant inlet bulk velocity, the flashback and blowout limits were found to follow contours of constant Tad, which is a novel finding for oxy-methane flames. This indicated that Tad is a more relevant parameter choice than φ or OF to quantify the combustor stability map. It was also found that a single correlation exists between flame speed and Tad, with greater speeds at higher temperatures towards flashback. No similar correlation was found between flame speed and combustor power density, throat Reynolds number, or bulk mass flow rate. Flames of the same Tad demonstrated almost identical shapes, which is another novel finding for oxy-methane flames. OF and φ showed very similar individual effects on flame shape, because both parameters can be represented by Tad. Spanning the stable combustion zone from lower Tad values to higher ones was observed to reduce flame size significantly.

Low-Emission combustion of fuel in aeroderivative gas turbines

The paper is the first of a planned set of papers devoted to the world experience in development of Low Emission combustors (LEC) for industrial Gas Turbines (GT). The purpose of the article is to summarize and analyze the most successful experience of introducing the principles of low-emission combustion of the so-called “poor” (low fuel concentration in air when the excess air ratio is about 1.9–2.1) well mixed fuelair mixtures in the LEC for GTs and ways to reduce the instability of combustion. The consideration examples are the most successful and widely used aero-derivative GT. The GT development meets problems related to the difference in requirements and operation conditions between the aero, industrial, and power production GT. One of the main problems to be solved is the LEC development to mitigate emissions of the harmful products first of all the Nitrogen oxides NOx. The ways to modify or convert the initial combustors to the LEC are shown. This development may follow location of multiburner mixers within the initial axial envelope dimensions or conversion of circular combustor to the can type one. The most interesting are Natural Gas firing GT without water injection into the operating process or Dry Low emission (DLE) combustors. The current GT efficiency requirement may be satisfied at compressor exit pressure above 3 MPa and Turbine Entry temperature (TET) above 1500°C. The paper describes LEC examples based on the concept of preliminary prepared air–fuel mixtures' combustion. Each combustor employs its own fuel supply control concept based on the fuel flow–power output relation. In the case of multiburner combustors, the burners are started subsequently under a specific scheme. The can type combustors have combustion zones gradually ignited following the GT power change. The combustion noise problem experienced in lean mixtures' combustion is also considered, and the problem solutions are described. The GT test results show wide ranges of stable operation at needed levels of NOx and CO emissions. The world experience analysis and generalization and investigation of the further development directions for the high performance GT will assist development of domestic LEC for prospective GTs.

Turbine Modification of Nuovo Pignone Gas Turbine

Abstract This paper deals with the environmental aspects of combustor modification on Nuovo Pignone gas turbines. The mentioned company is engaged in the transport of natural gas to the Slovak Republic and further to other European markets. Legislation considering emissions is getting stricter every year. Original Nuovo Pignone gas turbines would not be able to meet the required emission limits for NOx and COr determined by legislation. Therefore, the company decided to modify seven gas turbines. Due to this reason, the combustion sections had to be replaced with a dry low emission system. These modifications were aimed at improvement of impacts of temperature on the emissions of NOx, since the NOx emissions are defined as thermal (there is an increase in emissions with the increase in temperature). Emissions were monitored continuously by an emission monitoring system (these data are continuously sent to the Office of Environment) and manually by a HORIBA PG-250 analyser. Gas delivery point is located in the flue pipeline, and data was processed by means of PC after reaching this point. The results lead us to conclusion that modification was an efficient and good solution in terms of economy, because this solution reduced emissions (from 300 mg·m−3 to 50 mg·m−3) and contributed to meeting of the stricter emission limits (from 370 mg·m−3 to 100 mg·m−3). Monitoring of the impacts of growing performance of equipment on emissions represents a possibility for further development of science in this field.

A multi-objective CFD optimization of liquid fuel spray injection in dry-low-emission gas-turbine combustors

The main goal of this research is to investigate the effects of fuel injection strategy on the performance of the premixing chamber of modern Dry-Low-Emission (DLE) Gas-Turbine (GT) combustors. Here, an Eulerian-Lagrangian model for multi-phase multi-component flows is evaluated and used to investigate the effects of different fuel spray design parameters, including the injection location, direction, mass-flow-rate partitioning, and flow Swirl number, on the performance of the premixing chamber. The analysis is enriched by multi-objective optimizations accounting for several goals, including the evaporation efficiency, mixture stratification, entropy generation, and flow recirculation. It is observed that the droplet breakup, spray-vortex interactions, and wall-wetting have significant influences on the performance objectives while the droplet residence time effect is minor. Among the design parameters, the injection location and direction have a profound impact on the droplet breakup which predominately controls the evaporation efficiency. In addition, the interactions between the spray and the two swirling vertices inside the chamber strongly affect the mixture stratification (uniformity), e.g. the location and direction of the injection should not be chosen such that a large proportion of fuel droplets are trapped in the shear layer between the two vortices (otherwise the evaporation efficiency drops significantly) or trapped in the strong outer swirling vortex (if large mixture non-uniformity should be avoided). Finally, the best designs meeting a series of targets, e.g. simultaneous perfect mixing and uniformity, etc., are introduced.

Developing Additive Manufacturing Technology for Burner Repair

Low emission combustion is one of the most important requirements for industrial gas turbines. Siemens industrial gas turbines SGT-800 and SGT-700 use dry low emission (DLE) technology and are equipped with third generation of DLE burners. These burners demonstrate high-performance and reliable operation for the duration of their design lifetime. The design and shape of the burner tip is of great importance in order to achieve a good fuel/ air mixture and at the same time a resistance to the fatigue created by heat radiation input. This gives a requirement for a tip structure with delicate internal channels combined with thicker structure for load carrying and production reasons. It was found that the extension of the burner lifetime beyond the original design life could be accomplished by means of repair of the burner tip. Initially, the tip repair has been done by conventional methods— i.e., cutting off the tip and replacing it with a premanufactured one. Due to the sophisticated internal structure of the burner, the cuts have to be made fairly high upstream to avoid having the weld in the delicate channel area. Through the use of additive manufacturing (AM) technology, it has been possible to simplify the repair and only replace the damaged part of the tip. Special processes have been developed for AM repair procedure, including the following: machining off of the damaged and oxidized tip, positioning the sintered model on the burner face, sintering a new tip in place, quality assurance and inspection methods, powder handling, material qualification including bonding zone, development of methods for mechanical integrity calculation, and qualification of the whole repair process. This paper describes how we have developed and qualified SGT-800 and SGT-700 DLE burners repair with the help of additive manufacturing technology and our research work performed. In addition, this paper highlights the challenges we faced during design, materials qualification, and repair work shop set up.

CFD analysis of exhaust gas recirculation in a micro gas turbine combustor for CO2 capture

The aim of this paper is to numerically investigate the effects of CO2 dilution on the operation of an industrial micro gas turbine combustor in order to assess the possible application of exhaust gas recirculation (EGR) for post-combustion CO2 capture. A complete 3D model of the combustion chamber has been developed, taking into account the conjugate heat transfer (CHT) and radiation effects, and a detailed chemical mechanism has been employed in the framework of the Flamelet Generated Manifolds approach to model the combustion process. The importance of including the effects of conjugate heat transfer in the model has been demonstrated for both air-fired and EGR conditions. Also, combustion with EGR resulted in lower temperature levels with respect to the air-fired case and thus in reduced NOx production. Further, the increased presence of carbon dioxide has been observed to have an impact on both the flame speed and the flame stabilization mechanism.According to the numerical results, EGR can be a viable way to increase the CO2 content in the flue gas of dry low-emissions (DLE) combustors, and therefore enhance the efficiency of post-combustion carbon separation. At the same time, due to the reduced temperature levels within the combustion chamber, it is possible to attain lower NOx emissions without compromising the combustion efficiency under the considered EGR levels.

Experimental and Numerical Investigation of Fuel–Air Mixing in a Radial Swirler Slot of a Dry Low Emission Gas Turbine Combustor

This paper presents the results of an investigation in which the fuel/air mixing process in a single slot within the radial swirler of a dry low emission (DLE) combustion system is explored using air/air mixing. Experimental studies have been carried out on an atmospheric test facility in which the test domain is a large-scale representation of a swirler slot from a Siemens proprietary DLE combustion system. Hot air with a temperature of 300 °C is supplied to the slot, while the injected fuel gas is simulated using air jets with temperatures of about 25 °C. Temperature has been used as a scalar to measure the mixing of the jets with the cross-flow. The mixture temperatures were measured using thermocouples while Pitot probes were used to obtain local velocity measurements. The experimental data have been used to validate a computational fluid dynamics (CFD) mixing model. Numerical simulations were carried out using CFD software ansys-cfx. Due to the complex three-dimensional flow structure inside the swirler slot, different Reynolds-averaged Navier–Stokes (RANS) turbulence models were tested. The shear stress transport (SST) turbulence model was observed to give best agreement with the experimental data. The momentum flux ratio between the main air flow and the injected fuel jet, and the aerodynamics inside the slot were both identified by this study as major factors in determining the mixing characteristics. It has been shown that mixing in the swirler can be significantly improved by exploiting the aerodynamic characteristics of the flow inside the slot. The validated CFD model provides a tool which will be used in future studies to explore fuel/air mixing at engine conditions.

Investigation of Flow Aerodynamics for Optimal Fuel Placement and Mixing in the Radial Swirler Slot of a Dry Low Emission Gas Turbine Combustion Chamber

This paper is concerned with optimizing the fuel–air mixing processes that take place within the radial swirler slot of a dry low emission (DLE) combustion system. The aerodynamics of the flow within the slot is complex and this, together with the placement of the fuel holes with cross injection, controls the mixing of the fuel and air. Computational fluid dynamics (CFD) with the shear stress transport (SST) (k–ω) turbulence model was used for flow and mixing predictions within the radial swirler slot and for conducting a CFD-based design of experiments (DOE) optimization study, in which different parameters related to the fuel injection holes were varied. The optimization study was comprised of 25 orthogonal design configurations in the Taguchi L25 orthogonal array (OA). The test domain for the CFD, and its experimental validation, was a large-scale representation of a swirler slot from the Siemens proprietary DLE combustion system. The DOE study showed that the number of fuel holes, injection hole diameter, and interhole distance are the most influential parameters for determining optimal fuel mixing. Consequently, the optimized mixing configuration obtained from the above study was experimentally tested on an atmospheric test facility. The mixing patterns from experiments at various axial locations across the slot are in good agreement with the mixing predictions from the optimal CFD model. The optimized fuel injection design improved mixing compared with the baseline design by about 60%.

Investigation of Hydrogen Enriched Natural Gas Flames in a SGT-700/800 Burner Using OH PLIF and Chemiluminescence Imaging

The effect of hydrogen enrichment to natural gas flames was experimentally investigated at atmospheric pressure conditions using flame chemiluminescence imaging, planar laser-induced fluorescence of hydroxyl radicals (OH PLIF), and dynamic pressure monitoring. The experiments were performed using a third generation dry low emission (DLE) burner used in both SGT-700 and SGT-800 industrial gas turbines from Siemens. The burner was mounted in an atmospheric combustion test rig at Siemens with optical access in the flame region. Four different hydrogen enriched natural gas flames were investigated; 0 vol. %, 30 vol. %, 60 vol. %, and 80 vol. % of hydrogen. The results from flame chemiluminescence imaging and OH PLIF show that the size and shape of the flame was clearly affected by hydrogen addition. The flame becomes shorter and narrower when the amount of hydrogen is increased. For the 60 vol. % and 80 vol. % hydrogen flames the flame has moved upstream and the central recirculation zone that anchors the flame has moved upstream the burner exit. Furthermore, the position of the flame front fluctuated more for the full premixed flame with only natural gas as fuel than for the hydrogen enriched flames. Measurements of pressure drop over the burner show an increase with increased hydrogen in the natural gas despite same air flow thus confirming the observation that the flame front moves upstream toward the burner exit and thereby increasing the blockage of the exit. Dynamic pressure measurements in the combustion chamber wall confirms that small amounts of hydrogen in natural gas changes the amplitude of the dynamic pressure fluctuations and initially dampens the axial mode but at higher levels of hydrogen an enhancement of a transversal mode in the combustion chamber at higher frequencies could occur.

Effect of Change in Fuel Compositions and Heating Value on Ignition and Performance for Siemens SGT-400 Dry Low Emission Combustion System

The influence of changes in fuel composition and heating value on the performance of an industrial gas turbine combustor was investigated. The combustor tested was a single cannular combustor for Siemens SGT-400 13.4 MW dry low emission engine. Ignition, engine starting, emissions, combustion dynamics, and flash back through burner metal temperature monitoring were among the parameters investigated to evaluate the impact of fuel flexibility on combustor performance. Lean ignition and extinction limits were measured for three fuels with different heat values in term of Wobbe Index (WI): 25, 28.9, and 45 MJ/Sm3 (natural gas). The test results show that the air fuel ratio at lean ignition/extinction limits decreases and the margin between the two limits tends to be smaller as fuel heat value decreases. Engine start tests were also performed with a lower heating value fuel and results were found to be comparable to those for engine starting with natural gas. The combustor was further tested in a high pressure air facility at real engine operating conditions with different fuels covering WIs from 17.5 to 70 MJ/Sm3. The variation in fuel composition and heating value was achieved in a gas mixing plant by blending natural gas with CO2, CO, N2, and H2 (for the fuel with WI lower than natural gas) and C3H8 (for the fuel with WI higher than natural gas). Test results show that a benefit in NOx reduction can be seen for the lower WI fuels without H2 presence in the fuel and there are no adverse impacts on combustor performance except for the requirement of higher fuel supply pressure, however, this can be easily resolved by minor modification through the fuel injection design. Test results for the H2 enriched and higher WI fuels show that NOx, combustion dynamics and flash back have been adversely affected and major change in burner design is required. For the H2 enriched fuel, the effect of CO and H2 on combustor performance was also investigated for the fuels having a fixed WI of 29 MJ/Sm3. It is found that H2 dominates the adverse impact on combustor performance. The chemical kinetic study shows that H2 has significant effect on flame speed change and CO has significant effect on flame temperature change. Although the tests were performed on the Siemens SGT-400 combustion system, the results provide general guidance for the challenge of industrial gas turbine burner design for fuel flexibility.

Preliminary design and performance analysis of a low emission aero-derived gas turbine combustor

AbstractModern gas turbine combustor design is a complex task which includes both experimental and empirical knowledge. Numerous parameters have to be considered for combustor designs which include combustor size, combustion efficiency, emissions and so on. Several empirical correlations and experienced approaches have been developed and summarised in literature for designing conventional combustors. A large number of advanced technologies have been successfully employed to reduce emissions significantly in the last few decades. There is no literature in the public domain for providing detailed design methodologies of triple annular combustors.The objective of this study is to provide a detailed method designing a triple annular dry low emission industrial combustor and evaluate its performance, based on the operating conditions of an industrial engine. The design methodology employs semi-empirical and empirical models for designing different components of gas turbine combustors. Meanwhile, advanced DLE methods such as lean fuel combustion, premixed methods, staged combustion, triple annular, multi-passage diffusers, machined cooling rings, DACRS and heat shields are employed to cut down emissions. The design process is shown step by step for design and performance evaluation of the combustor.The performance of this combustor is predicted, it shows that NOx emissions could be reduced by 60%-90% as compared with conventional single annular combustors.

Experimental investigation of dynamic and emission characteristics of a DLE gas turbine combustor

The DLE (dry low emission) technology has already been used on industrial gas turbine combustor and the NO X emission can be limited to 25 ppmv (@15% O 2 ), but one of the destructive effects is combustion instability. In this paper, the dynamic and emission characteristics of a DLE gas turbine combustor have been researched in the authors’ laboratory, and the results show that the key source of combustion instability is the non-uniformity of fuel in the flame zone. Two main fuel supply methods have been used to form different fuel distribution types; it is shown that in the perfectly premixed case the emission level is low and combustion process is stable. The PPF also has an obvious effect on the combustor’s emission and dynamic characteristics.

Effects of CO2 dilution on combustion instabilities in dual premixed flames

There has been a rapid increase in the demand for biogas applications in recent years, and dry low NOx and dry low emission gas turbine combustors are promising platforms for such applications. Combustion instability is the most important drawback in dry low NOx gas turbine combustors and has, therefore, attracted considerable research interest lately. As a fundamental study towards the use of biogas in dry low NOx and dry low emission gas turbine combustors, this article investigates the influence of CO2 in surrogate biogas on combustion instability. Tests were conducted using a dry low NOx type, a dual lean premixed gas turbine combustor. For a dual flame with dual swirl, the pilot fuel mass fraction affects the flame structure, and the flame structure, in turn, determines the temperature distribution in the combustion chamber and the combustion instability. The effects of the pilot fuel mass fraction, which is an important parameter of the combustor, and the CO2 dilution rate, which is a major contributor of biogas combustion, on the combustion characteristics and instability are investigated through dynamic pressure signal and phase-resolved OH* images. Combustion instability decreases for higher CO2 dilution rates, whose effects depend on the pilot fuel mass fraction. The instability reaches its maximum at a pilot fuel mass fraction of 0.3. Tests confirm that combustion instability diminishes with CO2 dilution, as it reduces the perturbation in the heat emission, and the flame speed decreases resulting in a greater flame surface or volume. Further, investigation of the Rayleigh Index, which represents the coupling strength of the heat release fluctuation and the natural frequency, shows that CO2 dilution weakens the coupling strength, resulting in less combustion instability.

Extension of Fuel Flexibility in the Siemens Dry Low Emissions SGT-300-1S to Cover a Wobbe Index Range of 15 to 49 MJ/Sm3

The extension of gas fuel flexibility in the Siemens SGT-300 single shaft (SGT-300-1S) is reported. A successful development program has increased the capability of the Siemens Industrial Turbomachinery, Lincoln (SITL) dry low emissions (DLE) burner configuration to a fuel range covering a Wobbe index (WI) from 15 to 49 MJ/Sm3. The WI reported in this paper is at a 15 °C fuel temperature. The standard SGT-300-1S SITL DLE combustion hardware allows for gas and liquid fuels within a specified range typically associated with natural gas and diesel, respectively. The range of the WI associated with natural gas is 37–49 MJ/Sm3. Field operation of the standard production SGT-300-1S has confirmed the reliable operation with an extension to the fuels range to include processed landfill gas (PLG) from 30 to 49 MJ/Sm3. The further extension of the fuel range for the SGT-300-1S SITL DLE combustion system was achieved through high pressure testing of a single combustion system at engine operating conditions and representative fuels. The variations in the fuel heating value were achieved by blending natural gas with diluent CO2 and/or N2. Various diagnostics were used to assess the performance of the combustion system, including the measurement of combustion dynamics, temperature, fuel supply pressure, and the emissions of NOx, CO, and unburned hydrocarbons (UHCs). The results of the testing showed that the standard production burner can operate for a fuel with a WI as low as 23 MJ/Sm3, which corresponds to 35% CO2 (by volume) in the fuel. This range can be extended to 15 MJ/Sm3 (54.5% CO2 in the fuel) with only minor modification to control losses through the burner and to maintain similar fuel injection characteristics. The SITL DLE combustion system is able to cover a WI range of 15 to 49 MJ/Sm3 in two configurations. The results of testing showed a lowering in the WI, by diluting with CO2 and/or N2, so that a benefit in the NOx reduction is observed. This decrease in the WI may lead to an increased requirement of the fuel supply pressure.