Gas Turbine Emissions Research Articles

A review on the use of gas and steam turbine combined cycles as prime movers for large ships. Part III: Fuels and emissions

The aim of the present paper is to review the prospects of using combined cycles as prime movers for large ships, like, container ships, tankers and bulk carriers. The paper is divided into three parts of which this paper constitutes Part III. In Part I, the environmental and human health concerns of international shipping were outlined. The regulatory framework relevant for shipping and the design of combined cycles were discussed. In Part II, previous work and experience were reviewed, and an overview of the implications of introducing combined cycles as prime movers was included. Here, marine fuels are discussed, and the pollutant emissions of gas turbines are compared with those of two-stroke, slow-speed diesel engines. Burning liquid fuels of lower quality than distillate fuels in gas turbines is feasible, provided the fuel is pre-treated, fuel additives are added and hot sections of the gas turbine are washed regularly. However, the efficiency of the gas turbine decreases. Partly because of using different fuels, and partly because of different combustion processes, the quantities of pollutant emissions from gas turbines are substantially lower than those of diesel engines.

A review on the use of gas and steam turbine combined cycles as prime movers for large ships. Part I: Background and design

The aim of the present paper is to review the prospects of using combined cycles as prime movers for large ships, like, container ships, tankers and bulk carriers. The paper is divided into three parts of which this paper constitutes Part I. Here, the environmental and human health concerns of international shipping are outlined. The regulatory framework relevant for shipping and the design of combined cycles are discussed. In Part II, previous work and experience are reviewed, and an overview of the implications of introducing combined cycles as prime movers is included. In Part III, marine fuels are discussed and the pollutant emissions of gas turbines are compared with those of two-stroke, slow-speed diesel engines. Environmental effects of shipping include contributions to the formation of ground-level ozone, acidification, eutrophication and climate impact. Tightening environmental regulations limit the fuel sulphur content and pollutant emissions. For moderate live steam pressures, a vertical HRSG of drum-type mounted directly over the gas turbine, is suggested to be a viable configuration that minimizes ground floor and space requirements.

A review on the use of gas and steam turbine combined cycles as prime movers for large ships. Part II: Previous work and implications

The aim of the present paper is to review the prospects of using combined cycles as prime movers for large ships, like, container ships, tankers and bulk carriers. The paper is divided into three parts of which this paper constitutes Part II. In Part I, the environmental and human health concerns of international shipping were outlined. The regulatory framework relevant for shipping and the design of combined cycles were discussed. Here, previous work and experience are reviewed, and an overview of the implications of introducing combined cycles as prime movers is included. In Part III, marine fuels are discussed and the pollutant emissions of gas turbines are compared with those of two-stroke, slow-speed diesel engines. In the past, combined cycles of COGAS and COGES configurations have been considered for ship propulsion. Another application where gas turbine-based systems have been considered as prime movers is for LNG ships, which are traditionally powered by steam turbines with gas-burning boilers. Previous experience for a cruiser shows that combined cycles weigh less and require a smaller volume than diesel engines, resulting in increased passenger capacity and/or voyage performance. Diesel engines respond faster to a load change than combined cycles. Provided parts within the steam cycle are warm, the start-up times of combined cycles and diesel engines are similar.

High-temperature alloys research: Still going strong

In this issue of JOM, the High Temperature Alloys Committee and the Seven Springs International Symposium Committee have compiled seven papers to provide a snapshot of the dynamic world of high-temperature alloys research. The search for structural materials that can be used at higher temperatures, under increased stresses, in more aggressive environments, and for longer times is a never-ending battle. In particular, the development of the gas turbine engine has been paced by the development of high-temperature materials, and more specifi cally, superalloys. The goal to achieve higher effi ciencies, increased performance, and decreased emissions in gas turbines has and will continue to require improved materials. The papers in this issue are broken down into two categories: processing and properties of high-performance coatings and alloys and recent development of high-temperature alloys. Most of the papers are on nickel-based superalloys, the most commonly used materials in the hot sections of gas turbines. Also included are two examples of other high-temperature materials. Within the fi ve high-performance coatings and alloys papers, the development of new alloys and the effects of composition and processing on the properties of high-temperature alloys are discussed. M.P. Brady et al. describe in “The Development of Alumina-Forming Austenitic Stainless Steels for High-Temperature Structural Use” the development of a new family of Al 2 O 3 -forming austenite stainless steels High-Temperature Alloys Research: Still Going Strong

유동 섭동에 의한 난류예혼합화염의 열발생 모델에 관한 연구

The unsteady heat release characteristics play a significant role in combustion instabilities observed in low emissions gas turbine combustors. Such combustion instabilities are often caused by coupling mechanisms between unsteady heat release rates and acoustic perturbations. A generalized model of the turbulent flame response to acoustic perturbations is analytically formulated by considering a distributed heat release along a curved mean flame front and using the flame's kinematic model that incorporates the turbulent flame development. The effects of the development of flame speed on the flame transfer functions are examined by calculating the transfer functions with a constant or developing flame speed. The flame transfer function due to velocity fluctuation shows that, when a developing flame speed is used, the transfer function magnitude decreases faster with Strouhal number than the results with a constant flame speed at low Strouhal numbers. The flame transfer function due to mixture ratio fluctuation, however, exhibits the opposite results: the transfer function magnitude with a developing flame speed increases faster than that with a constant flame speed at low Strouhal numbers. Oscillatory behaviors of both transfer function magnitudes are shown to be damped when a developing flame speed is used. Both transfer functions also show similar behaviors in the phase characteristics: The phases of both transfer functions with a developing flame speed increase more rapidly than those with a constant flame speed.

The Effect of Liquid-Fuel Preparation on Gas Turbine Emissions

The emissions of liquid-fuel fired gas turbine engines are strongly affected by the fuel preparation process that includes atomization, evaporation, and mixing. In the present paper, the effects of fuel atomization and evaporation on emissions from an industrial gas turbine engine were investigated. In the engine studied, the fuel injector consists of a coaxial plain jet airblast atomizer and a premixer which consists of a cylindrical tube with four mixing holes and swirler slits. The goal of this device is to establish a fully vaporized, homogeneous fuel/air mixture for introduction into the combustion chamber and the reaction zone. In the present study, experiments were conducted at atmospheric pressure and room temperature as well as at actual engine conditions (0.34MPa, 740K) both with and without the premixer. Measurements included visualization, droplet size, and velocity. By conducting tests with and without the premixing section, the effect of the mixing holes and swirler slit design on atomization and evaporation was isolated. The results were also compared with engine data and the relationship between premixer performance and emissions was evaluated. By comparing the results of tests over a range of pressures, the viability of two scaling methods was evaluated with the conclusion that spray angle correlates with fuel to atomizing air momentum ratio. For the injector studied, however, the conditions resulting in superior atomization and vaporization did not translate into superior emissions performance. This suggests that, while atomization and the evaporation of the fuel are important in the fuel preparation process, they are of secondary importance to the fuel/air mixing prior to, and in the early stages of the reaction in, governing emissions.

Prediction of performance and emissions of a two-shaft gas turbine from experimental data

Precise performance evaluation at design and off-design operations is needed for a correct management of power plants. This need is particularly strong in gas turbine power plants, which can quickly react to load variations and are very sensitive to ambient conditions. The paper aims at presenting a simple tool to determine the values of the thermodynamic quantities in each point of the plant and the overall plant performances of a real gas turbine plant. Starting from experimental data, a zero-dimensional model is developed, which properly considers the effect of ambient conditions and water injection for pollutant abatement at different load settings under the action of the control system. In particular, semi-empirical correlations for pollutant emissions taken from the literature are adapted by tuning their coefficients on the experimental data, in order to predict carbon monoxide and nitrogen oxide pollution. Such a tool can be useful to manage the energetic, economic and environmental aspects of plant operation.

Impact of low carbon fuels on gas turbine design

The climate change agenda combined with the growing demand for secure, abundant sources of low cost fuel has increased interest in the production of power from low carbon fossil fuels and driven the quest for zero emissions technology. As we push the boundaries of existing power technologies, particularly in fuel composition, understanding the constraints facing technology suppliers at each stage of the energy conversion process will assist in identifying opportunities to increase overall plant reliability and availability. The established low carbon power generation technology for utility operators is natural gas fired combined cycle gas turbine (CCGT) plant. As traditional sources of gas have failed to meet demand new sources have become available that are normally delivered as liquefied natural gas (LNG). This fuel is derived from a range of geographies and while the energy content remains within specified bands, the proportions of individual constituents in the gas stream can vary. There is growing interest in integrated gasification combined cycle (IGCC) technology as it has the potential for near-zero emissions of greenhouse gases through pre-combustion capture of carbon, leaving hydrogen as the fuel for gas turbine plant. IGCC has the additional attraction of being able to process relatively cheap and abundant supplies of fuel generally sourced within country borders. The fuels being actively investigated and developed include: all grades of coal, petroleum coke and biomass, plus potential co-processing of these fuels. The combination of changes in fuel source, variable composition fuels and ever more exacting emissions requirements has introduced challenging combustion conditions for gas turbine manufacturers. The developers and operators of future high efficiency, low emissions gas turbine based generation plant must engage in an open dialogue with all vendors to ensure technical solutions deliver high levels of operational reliability and availability to underpin the requirement for secure, affordable, on-demand energy supply.

A Novel Approach to Predicting NOx Emissions From Dry Low Emissions Gas Turbines

An empirical modeling concept for the prediction of NOx emissions from dry low emissions (DLE) gas turbines is presented. The approach is more suited to low emissions operation than are traditional approaches (Lefebrre, A. H., 1998, Taylor and Francis, New York). The latter, though addressing key operating parameters, such as temperature and pressure drop, do not address issues such as variation in fuel/air distribution through the use of multifuel stream systems, which are commonly applied in DLE combustors to enable flame stability over the full operating range. Additionally, the pressure drop dependence of NOx in such systems is complex, and the exponent of a simple pressure drop term can vary substantially. The present approach derives the NOx model from the equations that govern the NOx chemistry, the fuel/air distribution and the dependence of the main reaction zone on its controlling parameters. The approach is evaluated through comparing its characteristics to data obtained from high-pressure testing of a DLE combustor fueled with natural gas. The data were acquired at a constant pressure and preheat temperature (14 Bara and 400°C) and a range of flame temperatures and flow rates. Though the model is configured to address both relatively fast and slow NOx formation routes, the present validation is conducted under conditions where the latter is negligible. The model is seen to reproduce key features apparent in the data, in particular, the variable pressure drop dependence without any ad hoc manipulation of a pressure drop exponent.

Unsteady flame and flow field interaction of a premixed model gas turbine burner

The NO x emissions of heavy duty gas turbines have been significantly reduced by introducing lean premixed combustion. These flames are known to be prone to combustion instabilities. In this paper, investigations of a single model gas turbine burner are presented with focus on thermo-acoustic eigenmodes of the combustor and the resulting interaction between periodic flow field oscillations and flame front fluctuations. A numerical analysis of the eigenmodes of the combustor rig was performed and compared to pressure measurements. By the numerical analysis Helmholtz mode pressure oscillations were predicted to be present in the air plenum upstream the burner and in the combustion chamber. These oscillation modes were confirmed by the analysis of the pressure signals taken at different positions within the combustor rig. Two major achievements have been proved by experimental evidence: First, the presence of an acoustic eigenmode between plenum and combustor may trigger the combustion instabilities. Due to a phase lag between the pressure oscillations in the air plenum and those in the combustion chamber, fluctuations of air flow through the burner are induced, which cause fluctuations of the equivalence ratio at the burner exit plane. As result, fluctuations of the heat release rate within the flame are established, which interfere with the acoustics of the rig and, thus, unstable combustion results. Second, the amplitude of the combustion oscillations does not increase smoothly when increasing the air fuel ratio. Two different flow field patterns were identified in the combustor depending on the amplitude of the oscillations. At low oscillation levels weak and locally confined velocity fluctuations were observed in the main reaction zone which do not have any significant impact on the flame. By increasing the equivalence ratio high oscillation levels occur and a pumping motion of the flow field in axial direction was identified which causes periodic heat release fluctuations and, hence, a strong disturbance of the flame.

Gas turbine emissions and environmental impact of efficiency boosting techniques

In this paper, environmental impact of gas turbine power generation equipment is reviewed and emissions sources are discussed. The types of pollutants in simple cycle gas turbine power plants and the associated air quality problems are compiled. Then, airborne pollutants which are generated in the combustion turbines are described and factors affecting emission formation are discussed. Also, the environmental impact of a number of efficiency boosting techniques including inlet air cooling and cogeneration is presented. It is concluded that environmental impact should be taken into account when economics of different efficiency boosting technologies is evaluated. Also, the conflicting issues of emission dependence on temperature need to be addressed in a broader perspective.

A comparison of the flowfields and emissions of high-swirl injectors and low-swirl injectors for lean premixed gas turbines

A new approach for low emission gas turbines was investigated by modifying a typical production high-swirl injector (HSI) for gas turbine combustors to operate in a novel low-swirl mode (LSI). This LSI ( S = 0.5) was configured in the laboratory and investigated by particle image velocimetry at firing rates of 9–87 kW (1 < U 0 < 10 m/s). It was also tested at simulated gas turbine conditions of 0.08–2.2 MW (20 < U 0 < 50 m/s) at elevated combustion inlet temperatures (230 < T 0 < 430 °C) and pressures (6 < P 0 < 15 atm). The results were compared with those obtained with a HSI ( S = 0.73). The PIV results show that the flowfields of the LSI are devoid of a large dominant recirculation zone. This is fundamentally different than the strong and large recirculation regions that dominate flowfields of the HSI. Under simulated engine conditions, the LSI has the same operating range as the HSI. Its NO x emissions were about 60% lower than the HSI, and its CO emissions were comparable. The lack of a strong recirculation zone and the shorter residence time within the LSI may provide an explanation for the NO x reduction. These results demonstrate that the LSI is a promising solution for attaining an ultra-low emissions target of <5 ppm NO x (15% O 2) in gas turbines.

Pre-integrated Nonequilibrium Combustion-Response Mapping for Gas Turbine Emissions

In gas turbine combustion the gas dynamic and chemical energy release mechanisms have comparable time scales, so that equilibrium chemistry is inadequate for predicting species formation (emissions). In current practice either equilibrium chemical reactions are coupled with experimentally derived empirical equations, or time-consuming computations are used. Coupling nonequilibrium chemistry, fluid dynamic, and initial and boundary condition equations results in large sets of numerically stiff equations; and their time integration demands enormous computational resources. The response modeling approach has been used successfully for large reaction sets. This paper makes two new contributions. First it shows how pre-integration of the heat release maps eliminates the stiffness of the equations. This is a new modification to the response mapping approach, and it performs satisfactorily for non-diffusion systems. Second the theoretical framework is further extended to predict species formation in cases with diffusion, which is applicable to gas turbine combustion systems and others. The methodology to implement this approach to reacting systems, and to gas turbine combustion, is presented. The benefits over other reaction-mapping techniques are discussed.

Recent GRC Aerospace Technologies Applicable to Terrestrial Energy Systems

An overview of a wide range of recent aerospace technologies under development at the NASA John H. Glenn Research Center at Lewis Field, in collaboration with other NASA centers, government agencies, industry, and academia is provided. The focused areas are space solar power, advanced power management and distribution systems, Stirling cycle conversion systems, fuel cells, advanced thin-film photovoltaics and batteries, and combustion technologies. The aerospace-related objectives of the technologies are generation of space power; development of cost-effective and reliable, high-performance power systems; cryogenic applications; energy storage; and reduction in gas-turbine emissions, with attendant clean jet engines. The terrestrial energy applications of the technologies include augmentation of bulk power in ground power distribution systems and generation of residential, commercial, and remote power, as well as promotion of pollution-free environment via reduction in combustion emissions.

A Liquid Fueled, Lean Burn, Gas Turbine Combustor Injector

A need exists to develop and demonstrate a low pollutant emission gas turbine combustor design that uses liquid fuel for propulsion applications. The present work addresses this need by developing and demonstrating design guidelines for a liquid fueled, lean burn, gas turbine combustor injector. This injector is designed to accommodate all the combustion air, and includes a fuel and air mixing section with an internal venturi contour that contains an aerodynamic swirler, and an atomizer. The atomizer is a plain jet, airblast type with eight ports that spray radially into a high-velocity cross-stream of combustion air. Reacting test results show that the fuel and air are sufficiently well mixed to create a uniform distributed reaction which is (1) of finite length, and (2) free from pulsation or other combustion-induced instabilities. Emissions data at elevated pressure and temperature establish that this injector has low pollution emissions, and high combustion efficiency.

The volvo high speed generation hybrid drive and associated combustion system

The search for an automotive power source to replace the Otto and Diesel engines used today has yielded few concrete results to date. One alternative which has long been considered is the gas turbine, another is electric drive. Now, the combination of these two in a hybrid system presents new opportunities and drives of this type are currently under trial in vehicles such as the Volvo Environmental Concept Car. The development of high-speed generators and efficient electric motors has played a decisive role in the success of this new concept. The Volvo hybrid drive and its characteristics are described along with another unique key component: the combustion system. Minimum emission levels have been a high priority and a unique low-emission design has been developed. The combustion chamber employs the lean-premixed-prevaporized technique, which means that the fuel is vaporized and mixed intimately with air prior to combustion, lowering the flame temperature and minimizing the NO x formation. The gas turbine emission levels are so low that it will be possible to build a high speed generation drive with lower emission levels than the ULEV limits applicable in the USA.

Sensor Requirements to Control the Industrial RB 211 Dry Low Emission Gas Turbine

Sensor Requirements to Control the Industrial RB 211 Dry Low Emission Gas Turbine

Use of an optical probe for time-resolved in situ measurement of local air-to-fuel ratio and extent of fuel mixing with applications to low NOx emissions in premixed gas turbines

The lower temperatures associated with lean premixed combustion generally lead to lower NO x emissions; however, the benefit of lean premixed combustion may be lost if the fuel and air are poorly mixed. In this paper, we describe the development of an inexpensive fiber optic probe capable of measuring the extent of mixing. The fuel concentration is determined by laser light absorption at 3.39 μm over a short path length created by using infrared transmitting fiber optics. A hydrogen-piloted, CH 4 -in-air turbulent flame with a variable fuel injection location is used to vary the degree of mixedness at the burner exit. We use the optical probe to measure the level of mixedness (nonreacting) at the burner exit. The level of mixing and the mean concentration profiles are also measured by using planar laser-initiated Rayleigh scattering. NO x measurements are reported for several mixing distances. We show that at lean conditions (=0.6), incomplete mixing causes a dramatic increase in NO x production because of the exponential temperature dependence of NO x formation about =0.6. We also numerically investigate how the extent of mixing affects NO x production at various equivalence ratios and pressures. Modeling the effect of incomplete mixing on NO x formation is done with a distribution ofconvolved with numerical results from a perfectly stirred reactor in series with a plug flow reactor. The model does an excellent job of predicting the NO x increase caused by incomplete mixing at lean conditions. Model predictions at higher pressures that are typical of gas turbine conditions show good agreement with available data. In particular, for lean premixed combustion, NO x is not a function of pressure if the air and fuel are well mixed.

Reducing Gas Turbine Emissions Through Hydrogen-Enhanced, Steam-Injected Combustion

The Potential for reducing emissions from gas turbines by injecting steam for Nox control and hydrogen for Co control is evaluated through laboratory-scale combustion experiments. Results showed that hydrogen addition into a steam-injected diffusion combustor at hydrogen/fuel molar ratios of approximately 20 percent was associated with somewhat increased NOx production and reduced CO emissions. Both effects are attributed to an increase in the local stoichiometric flame temperature. However, the decrease in CO was greater than the increase in NOx, resulting in a net emissions benefit, or a shifting of the NOx–CO curve toward the origin. Consequently, a greater range of NOx/CO emissions targets could be achieved when hydrogen was available. Additional experiments on premixed systems with hydrogen injection showed a significant increase in operability. Cost estimates for producing hydrogen with a conventional fired steam reformer suggested high capital costs unless ample steam, is already available. Hence, the technology is particularly well suited for turbines that use steam for power augmentation. Alternate reforming technology, such as catalytic partial oxidation, offers the potential for reduced capital costs.

A Semi-Analytical Emission Model for Diffusion Flame, Rich/Lean and Premixed Lean Combustors

To enhance gas turbine combustor performance and emissions characteristics, better design methods need to be developed. In the present investigation, an emission model that simulates a detailed chemical kinetic scheme has been developed to provide the rate of reactions of the parent fuel, an intermediate hydrocarbon compound, CO, and H2. The intermediate fuel has variable carbon and hydrogen contents depending on operating conditions, that were selected in the development effort to simulate actual operation of rich/lean, diffusion flame, and lean combustor concepts. The developed reaction rate expressions address also the limited reaction rates that may occur in the near-wall regions of the combustor due to the admittance of radial air jets and cooling air in these regions. The validation effort included the application of the developed model to a combustor simulated by a multiple-reactor arrangement. The results indicate the accurate duplication of the calculations obtained from the detailed kinetic scheme using the developed model. This illustrates the great potential of using such a unified approach to guide the design of various types of combustor to meet the more stringent approach to guide the design of various types of combustor to meet the more stringent emissions and performance requirements of next-generation gas turbine engines.