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Coal, Biomass and Alternative Fuels

1992;():V003T05A001. doi:10.1115/92-GT-219.
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This paper reports the results of a series of tests designed to determine the melting and subsequent deposition behavior of volcanic ash cloud materials in modern gas turbine engine combustors and high pressure turbine vanes. The specific materials tested were Mt. St. Helens ash and a soil blend containing volcanic ash (black scoria) from Twin Mountain, New Mexico. Hot section test systems were built using actual engine combustors, fuel nozzles, ignitors, and high pressure turbine vanes from an Allison T56 engine can-type combustor and a more modern Pratt and Whitney F-100 engine annular-type combustor. A rather large turbine inlet temperature range can be achieved using these two combustors. The deposition behavior of volcanic materials as well as some of the parameters that govern whether or not these volcanic ash materials melt and subsequently deposit are discussed.

Topics: Gas turbines
Commentary by Dr. Valentin Fuster
1992;():V003T05A002. doi:10.1115/92-GT-220.
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The rise in gas turbine combustion chamber temperatures requires optimal choices to be made with regard not only to performance parameters but also with a view to resolving pollutant emission problems. For this reason, the authors have set up a gas turbine cycle model which performs an accurate analysis of several processes, in terms of operating fluid chemical and thermodynamic properties. The model also enables prediction of NOx formation based upon chemical kinetics and is able to relate the amount of pollutants to a number of operating parameters (e.g. cycle pressure ratio, fuel to air equivalence ratio, residence time in combustion chamber, etc.). It can also predict the effect of the most usual NOx reduction systems, such as water or steam injection.

A comparison of several possible choices for the gas and combined cycles is then presented, in terms of thermodynamic performance (e.g. first and second law analysis) and nitric and carbon dioxide emissions. In order to find the best compromise between performance improvement and limitation of pollutant emission, enhanced gas cycles are also considered, such as STIG or intecooled-reheat cycles.

Examples also refer to medium or low BTU gases, obtained from coal gasification, in order to show not only the possible advantages in terms of thermal NOx reduction, but also the significant amounts of “fuel NOx“ which can arise from ammonia contained in the fuel.

Commentary by Dr. Valentin Fuster
1992;():V003T05A003. doi:10.1115/92-GT-221.
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This technical paper examines the various aspects of hot gas filter station design which ultimately affect both initial and operational costs. Process conditions such as temperature and pressure, and design constraints such as face velocity are discussed with respect to their bearing on filter station costs. More subtle parameters such as pulse gas cleaning requirements and filter element geometry also directly impact filter design and hence, cost. As all of the information presented is based upon actual filter applications, it will provide useful insight for those involved in filter designing and recommendations.

Topics: Filters
Commentary by Dr. Valentin Fuster
1992;():V003T05A004. doi:10.1115/92-GT-257.
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Fuel specifications for a coal-fueled industrial gas turbine are being determined through bench scale testing of a two-stage slagging combustor with coal water mixtures (CWM) possessing different properties. Twelve CWMs have been formulated with variations in coal loading, ash concentration, fuel additives, coal particle size, and coal type. The test combustor is operated at 7 bars with a 600 K air inlet temperature in a high pressure test facility. The two-stage slagging combustor (TSSC) features a rich burning, slagging primary zone and a lean secondary zone. Combustor performance is characterized by measurements of pollutant emissions, slag capture, particulate emissions, and coal utilization. The combustor has demonstrated a high degree of fuel property flexibility with performance remaining above goals in most tests. The properties of the CWMs and the test results are discussed.

Commentary by Dr. Valentin Fuster
1992;():V003T05A005. doi:10.1115/92-GT-258.
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A program has been underway since 1986 by Westinghouse Electric Corporation, Textron, Inc., and the sponsoring agency, the Morgantown Energy Technology Center (METC) of the U.S. Department of Energy (DOE), as participants, to establish the technology base for coal-fired combustion turbines targeted for power generation (50 to 150 MW size units). The developed system must be able to burn unbeneficiated, low-cost, utility-grade coal and meet the EPA New Source Performance Standards (NSPS) for coal-fired steam generators (Thoman et al., 1987).

Development of a high pressure (12 to 16 atms) slagging combustor is the key to making a direct coal-fired combustion turbine a commercial reality. In testing to date, a 6 atm slagging combustor, rated at 12 MMBtu/hr (12.7 MHkJ/hr) has demonstrated its ability to handle high- and low-sulfur bituminous coals, and low-sulfur subbituminous coal. The program objectives relative to combustion efficiency, combustor exit temperature and pattern factor, NOx emissions, carbon burnout, and slag rejection have been met.

Today, Northern States Power, working with Westinghouse with assistance from Textron is developing a plan to commercialize a direct coal-fired advanced combined cycle (DCFACC). Included in this plan is a pilot plant (which does not include a combustion turbine) and a demonstration plant that would utilize a 50 MW combustion turbine. The first commercial DCFACC, which would Include a 100 MW combustion turbine, is scheduled to be operational by the year 2001. The cooperative effort among Northern States Power, Westinghouse, and Textron is financially independent of the work now sponsored by DOE/METC.

This paper presents the status of the pressurized slagging combustor development program including recent work to reduce alkali, particulates and SOx levels leaving the combustor and gives an overview of our commercialization process and plan.

Topics: Coal , Combined cycles
Commentary by Dr. Valentin Fuster
1992;():V003T05A006. doi:10.1115/92-GT-259.
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A full-size combustor for a coal-fueled industrial gas turbine engine has been tested to evaluate combustion performance prior to integration with an industrial gas turbine. The design is based on extensive work completed through one-tenth scale combustion tests. Testing of the combustion hardware is completed with a high pressure air supply in a combustion test facility at the Caterpillar Technical Center. The combustor is a two-staged, rich-lean design. Fuel and air are introduced in the primary combustion zone where the combustion process is initiated. The primary zone operates in a slagging mode inertially removing coal ash from the gas stream. Four injectors designed for coal-water mixture (CWM) atomization are used to introduce the fuel and primary air. In the secondary combustion zone additional air is injected to complete the combustion process at fuel-lean conditions. The secondary zone also serves to reduce the gas temperatures exiting the combustor. The combustor has operated at test pressures of 7 bars with 600K inlet temperature. Tests have been completed to set the air flow split and to map the performance of the combustor as characterized by pollutant emissions, coal ash separation, and temperature profile. Test results with a comparison to subscale test results are discussed. The test results have indicated that the combustor operates at combustion efficiencies above 98% and with pollutant emissions below design goals.

Commentary by Dr. Valentin Fuster
1992;():V003T05A007. doi:10.1115/92-GT-260.
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This paper describes the first test of an industrial gas turbine and low emissions combustion system on coal-water-slurry fuel. The engine and combustion system have been developed over the past five years as part of the Heat Engines program sponsored by the Morgantown Energy Technology Center of the U.S. Department of Energy (DOE). The engine is a modified Allison 501-K industrial gas turbine designed to produce 3.5 MW of electrical power when burning natural gas or distillate fuel. Full load power output increases to approximately 4.9 MW when burning coal-water slurry as a result of additional turbine mass flow rate.

The engine has been modified to accept an external staged combustion system developed specifically for burning coal and low quality ash-bearing fuels. Combustion staging permits the control of NOx from fuel-bound nitrogen while simultaneously controlling CO emissions. Water injection freezes molten ash in the quench zone located between the rich and lean zones. The dry ash is removed from the hot gas stream by two parallel cyclone separators.

This paper describes the engine and combustor system modifications required for running on coal and presents the emissions and turbine performance data from the coal-water slurry testing. Included is a discussion of hot gas path ash deposition and planned future work that will support the commercialization of coal-fired gas turbines.

Commentary by Dr. Valentin Fuster
1992;():V003T05A008. doi:10.1115/92-GT-261.
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The U.S. Department of Energy/Pittsburgh Energy Technology Center (DOE/PETC) initiated the Engineering Development of Coal-Fired High Performance Power Generation Systems Program to develop an advanced technology for coal-fired electric plants that can boost efficiency and reduce emissions. This three phase program includes concept definition and preliminary R&D, engineering development and testing which will culminate in the operation of a prototype plant by the year 2005.

This paper presents an overview of the work proposed by a Westinghouse-led R&D team which includes Babcock and Wilcox, Black and Veatch, FluiDyne Engineering, and Allegheny Power Systems to design and evaluate the technical and economic feasibility and relevant R&D required for one or more advanced power generation concepts developed during Phase I. Allison Division of General Motors, ERC and SeiTec are also supporting the Westinghouse team in the initial phase of this program.

Key objectives include evaluation of plant cycle designs capable of at least 47-percent efficiency, substantial reductions in airborne emissions below current new source performance standards (NSPS) for coal-fired boilers, and solid waste generation of only benign material.

The proposed design approach includes an indirect coal-fired combustion turbine combined cycle system which incorporates a high-temperature advanced furnace with ceramic heat exchanger components. The indirect-fired system circumvents some of the technical challenges of a direct coal-fired system (Bannister et al., 1990). Proposed alternative designs have plant efficiencies that range up to 53 percent.

Commentary by Dr. Valentin Fuster
1992;():V003T05A009. doi:10.1115/92-GT-263.
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Up to now, gas turbines have mainly been built for use with liquid fuels or natural gas. For the new combined cycle system with integrated coal gasification, the quality of the feed gas has to match the requirements of the gas turbine, which is particularly important for high-efficiency gas turbines. The paper describes a combined cycle system with integrated PRENFLO coal gasification and, in particular, the treatment of the gas produced by the gasifier. This power plant concept — a highly integrated plant — is a joint development of Siemens/KWU and Krupp Koppers. Our coal gasification is based on the entrained-flow principle with dry coal dust feeding.

Topics: Coal , Gas turbines
Commentary by Dr. Valentin Fuster
1992;():V003T05A010. doi:10.1115/92-GT-313.
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This paper reviews the properties of high temperature ceramic fibers and relates why strength, thermal shock resistance, chemical inertness, and high temperature capability are important properties for high temperature filter media. The use of candle filters, fabric filters, and composite filters will be discussed for removal of particulates from hot gas streams in electrical power generation systems, metal refining, chemical processing, and Diesel engine exhaust applications.

Commentary by Dr. Valentin Fuster
1992;():V003T05A011. doi:10.1115/92-GT-343.
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Coal based combined cycles for efficient generation of electricity or cogeneration of thermal and mechanical (electrical) power can be realized making use of Pressurized Fluidized Bed Combustion (PFBC). A draw-back with respect to the efficiency, however, is imposed from the combustion system limiting the temperature to some 850°C. This threshold may be overcome by integrating a high pressure, high temperature gas turbine topping cycle into the process. In a first step, the high pressure, high temperature gas turbine is fired by natural gas, and the exhaust gas of the turbine is fed to the PFB combustor as an oxygen carrier. In a future advanced system, the fuel gas may be provided by an integrated coal gasification process.

A basic reference case has been established based on commercially available gas turbine equipment, hot gas filtration systems as actually tested in various pilot installations, and on a conservative steam cycle component technology. With an ISO gas turbine inlet temperature of 1165°C and an overall compression ratio of 16 up to 30, the entire process yields a net efficiency of some 46% (LHV) and an overall power output of some 750 MW with the gaseous fuel making up for some 50% of the overall energy input. Both the efficiency and the power output have been found rather insensitive with respect to a variation of the overall compression ratio. However, for a non-intercooled compression, an increase of the maximum process pressure would allow for the energy input to be shifted towards coal (and to reduce the natural gas input), and in particular for an elevated PFB combustor pressure considered mandatory for compactness as well as for combustion efficiency including emissions.

The numerous calculations for the design, the optimization and the prediction of part-load operation of complex systems are efficiently performed with a semi-implicit method, the results of which have been checked carefully against those of a more conventional sequential approach and found in good agreement.

Commentary by Dr. Valentin Fuster
1992;():V003T05A012. doi:10.1115/92-GT-344.
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In this work, a study has been conducted to predict blade erosion and surface deterioration of the free power turbine of an automotive gas turbine engine. The blade material erosion model is based on three dimensional particle trajectory simulations in the three dimensional turbine flow field. The particle rebound characteristics after surface impacts were determined from experimental measurements of restitution ratios for blade material samples in a particulate flow tunnel. The trajectories provide the spacial distribution of the particle impact parameters over the blade surfaces. A semi-empirical erosion model, derived from erosion tests of material samples at different particulate flow conditions is used in the prediction of blade surface erosion based on the trajectory impact data. The results are presented for the three dimensional particle trajectories through the turbine blade passages, the particle impact locations, blade surface erosion pattern, and the associated erosion parameters. These parameters include impact velocity, impact angle and impact frequency. The data can be used for life prediction and performance deterioration of the automotive engine under investigation.

Commentary by Dr. Valentin Fuster
1992;():V003T05A013. doi:10.1115/92-GT-345.
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Modern turbine cascades are usually being optimized for minimum total pressure losses. Gas turbines, however, operating in dirty environments or using coal–derived fuels need cascades that minimize the deposition, erosion and corrosion (DEC) implications of the particle–laden gas. This can be achieved by altering certain geometrical key–parameters of cascades and blades which influence the particle deposition rate, while keeping the inlet and outlet velocities and angles fixed. Since reference cascades have already been optimized for minimum aerodynamic losses, the associated loss increase penalty is accounted for.

Two stator and two rotor cascades were optimized by a penalty function method. The results suggest that solid particle deposition rates can be minimized by as much as 40 per cent while keeping profile losses to acceptable limits in both stator and rotor cascades for the particle size range 0.1 to 1 μm.

Commentary by Dr. Valentin Fuster
1992;():V003T05A014. doi:10.1115/92-GT-359.
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The economic viability of coal gasification could depend on the ability to clean and purify the coal gases at elevated temperatures. Inorganic membranes have the potential for being used for that purpose. Efforts have been undertaken at the Oak Ridge K-25 Site to develop membranes that would be useful for separating hydrogen from the coal gas at the high operating temperatures. This paper will give a brief review of some fundamentals of gas separation with membranes. Also, a brief discussion of the theory derived to guide the development process will be given. The theory can be used to indicate the pore size needed to achieve good separation. In addition, some experimental results that have been obtained with some of the membranes that have been fabricated will be discussed.

Topics: Coal , Membranes
Commentary by Dr. Valentin Fuster
1992;():V003T05A015. doi:10.1115/92-GT-370.
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Advanced Ceramic Tube Filters (ACTF) have been developed by Asahi Glass Co., Ltd (AGC) using innovative concepts aimed at hot gas clean-up system feasible for large scale industrial processes. More than 25 ACTF units of pilot and demonstration scale have been installed to demonstrate its readiness for various industrial applications. Among these applications, pressurized fluidized bed combustion (PFBC) combined cycle power generation system is the one in which the largest market size is foreseen until the 21st century. In this paper, the latest status of the development and commercialization of ACTF as well as the principle, basic configuration and operation of the system are described.

Commentary by Dr. Valentin Fuster
1992;():V003T05A016. doi:10.1115/92-GT-398.
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The Global Warming R&D Programme at the Coal Research Establishment is evaluating options for removing CO2 from coal-fired power plant. The aim is to identify coal-based technologies with minimal emissions of CO2 as contingency planning in case the most pessimistic fears of warming are realised. Two promising options based on Integrated Gasification Combined Cycle have been identified, so far. One incorporates a conventional CO shift conversion step and a physical solvent scrubbing process to remove 90% of the CO2 and 99% of the H2S. The second approach is conceptual, using CO shift but also a membrane gas separator. The gas turbine would be fired with hydrogen in both cases. A discussion of the environmental impact of these schemes suggests that they would be very much cleaner than current technology using Pulverised Fuel combustion with Flue Gas Desulphurisation. CO2 disposal options and needs for future work are also discussed.

Commentary by Dr. Valentin Fuster
1992;():V003T05A017. doi:10.1115/92-GT-431.
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Westinghouse is developing hot gas cleaning systems for advanced, coal based gas turbine cycles. This paper summarizes the Westinghouse hot gas filter concept and reports on recent in-house and field test programs supporting its design and development. Basic materials issues related to ceramic material stability and hot metals structures are reviewed. Results of recent filter system testing are presented comparing candle and cross flow designs operating in both “simulated” and actual coal derived gas streams. Laboratory tests and analysis are reported relating to integrating sulfur and alkali control with the particle filter function.

Topics: Coal , Gas turbines , Cycles
Commentary by Dr. Valentin Fuster

Combustion and Fuels

1992;():V003T06A001. doi:10.1115/92-GT-081.
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Experimental information is presented on the effects of back-pressure on flame-holding in a gaseous fuel research combustor. Data for wall temperatures and static pressures are used to infer behavior of the major recirculation zones, as a supplement to some velocity and temperature profile measurements using LDV and CARS systems. Observations of flame behavior are also included. Lean blowout is improved by exit blockage, with strongest sensitivity at high combustor loadings. It is concluded that exit blockage exerts its influence through effects on the jet and recirculation zone shear layers.

Commentary by Dr. Valentin Fuster
1992;():V003T06A002. doi:10.1115/92-GT-105.
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The emissions of carbon monoxide (CO) from gas turbines are typically below 100 ppmvd @ 15% O2 at design full-load operating conditions. The use of water/steam to reduce NOx emissions from gas turbines results in an increase in CO emissions from gas turbines. This is particularly true when increased rates of water/steam injection are used to meet stringent NOx limits.

Regulations limiting CO emissions from stationary gas turbines were first initiated in the late 1980’s by the Federal Republic of Germany and the state of New Jersey in the United States. Since these regulations are silent on ambient and load corrections, these CO limits could be the limiting factor in the current development of dry low NOx combustion systems by gas turbine manufacturers. In addition, since manufacturers are usually quite specific regarding the conditions for CO guarantees, a conflict for the gas turbine user, who is responsible for the permit application, is readily apparent.

This paper attempts to characterize the CO emissions from gas turbines as a function of ambient temperature and turbine load. An ambient temperature correction equation for CO emissions, based on previous work, is presented. The intent is to provide more extensive information on CO emissions such that better defined CO limits can be adopted. Ultimately, this should help the combustion design engineers in developing improved dry low emissions combustion systems for the gas turbine industry.

Commentary by Dr. Valentin Fuster
1992;():V003T06A003. doi:10.1115/92-GT-106.
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A flowing, single-pass heat exchanger test rig, with a fuel capacity of 189 litres, has been developed to evaluate jet fuel thermal stability. This so called, “Phoenix Rig” is capable of supplying jet fuel to a 2.15 mm I.D. tube at a pressure up to 3.45 MPa, fuel temperature up to 900K, and a fuel-tube Reynolds number in the range 300–11,000. Using this test rig, fuel thermal stability (carbon deposition rate), dissolved oxygen consumption, and methane production were measured for three baseline jet fuels and three fuels blended with additives. Such measurement were performed under oxygen-saturation or oxygen-starved conditions.

Tests with all of the blended fuel samples showed a noticeable improvement in fuel thermal stability. Both block temperature and test duration increased the total carbon deposits in a nonlinear fashion. Interestingly, those fuels that need a higher threshold temperature to force the consumption of oxygen exhibited greater carbon deposits than those that consume oxygen at a lower temperature. These observations suggested a complicated relationship between the formation of carbon deposits and the temperature-driven consumption of oxygen. A simple analysis, based on a bi-molecular reaction rate, correctly accounted for the shape of the oxygen consumption curve for various fuels. This analysis yielded estimates of global bulk parameters of oxygen consumption. The test rig yielded quantitative results which will be very useful in evaluating fuel additives, understanding the chemistry of deposit formation, and eventually developing a global chemistry model.

Commentary by Dr. Valentin Fuster
1992;():V003T06A004. doi:10.1115/92-GT-107.
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Liquid sheet break-up in co flowing shear flow is the mean by which liquids are atomized in practical injectors for gas turbine combustors. The present study explores experimentally the mechanisms of liquid sheet instabilities and spray formation. Experiments are conducted on four airblast geometries.

A high speed video camera associated to an image processing unit was used to study the liquid sheet instabilities. A microphone and a frequency analyzer were used to track the disintegration frequency. Instability amplitude and disintegration lenght of the liquid sheet were measured.

A two component Phase Doppler Particle Analyzer was used to characterize the resultant spray. The spatial distribution of the particle size is influenced by the swirling flow field.

These experimental results will be used to assess models of fuel sheet instabilities and disintegration.

Commentary by Dr. Valentin Fuster
1992;():V003T06A005. doi:10.1115/92-GT-108.
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Measurements of the emissions from an experimental engine were analyzed to construct a design chart for the reduction of oxides of nitrogen (NOx) in conventional combustors. The design chart was used to reconfigure the stoichiometry distribution of the combustor of a production engine so as to reduce NOx while holding the emissions of carbon monoxide, unburned hydrocarbons and smoke well below existing regulations. Combustion section pressure loss and combustor outlet temperature distributions were substantially unchanged. The modified design was refined with the aid of computational fluid dynamics calculations to optimize the emissions reduction. Worthwhile reductions in NOx were obtained with combustor modifications that are transparent to the engine user.

Commentary by Dr. Valentin Fuster
1992;():V003T06A006. doi:10.1115/92-GT-109.
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Two aspects of reliability assurance are discussed. First, This paper deals with the reliability design of the emissions under transient conditions. The optimization was made from the simulation results of the relationship between the response of the variable combustor geometry to follow load changes and the resulting exhaust emission levels. The load variation pattern used in this investigation was that of the Japanese 10-mode regulation. Second, this paper describes the validity of the reliability design prepared for the ceramic liner of the combustor. A service life prediction was made for the liner on the basis of stress analysis results and fatigue parameters.

Commentary by Dr. Valentin Fuster
1992;():V003T06A007. doi:10.1115/92-GT-110.
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A rich burn/quick mix/lean burn (RQL) combustor concept for reducing pollutant emissions is currently under investigation at the NASA Lewis Research Center (LeRC). A numerical study was performed to investigate the chemically reactive flow with liquid spray injection for the RQL combustor. The RQL combustor consists of an airblast atomizer fuel injector, a rich burn section, a converging connecting pipe, a quick mix zone, a diverging connecting pipe and a lean combustion zone. For computational efficiency, the combustor was split into two sub systems, i.e. the fuel nozzle/rich burn section and the quick mix/lean burn section.

The current study investigates the effect of varying the mass flow rate split between the swirler passages for an equivalence ratio of 2.0 on fuel distribution, temperature distribution, and emissions for the fuel nozzle/rich burn section of an RQL combustor. The input conditions used in the study were chosen based on tests completed at LeRC. It is seen that optimizing these parameters can substantially improve combustor performance and reduce combustor emissions. The optimal mass flow rate split for reducing NOx emissions based on the numerical study was the same as found by experiment at LeRC.

Commentary by Dr. Valentin Fuster
1992;():V003T06A008. doi:10.1115/92-GT-111.
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LDV measurements are reported of the flow-field associated with a single row of radially injected jets penetrating a core-tube flow. Emphasis is placed on the influence of small feed-annulus height on jet entry conditions and resulting trajectories and mixing patterns. Conditions of unstable jet behaviour, with strong vortex patterns in the jet holes, were observed for small annulus heights and high annulus velocities. Most measurements were however taken under stable conditions to allow the data to be used in a CFD validation exercise. Significant differences in the strength of backflow generated at jet impingement and in the turbulence field in the immediate hole vicinity were observed for different annulus height/core diameter ratios. These were accompanied by jet trajectory and annulus flow structure changes. Measurements of all 3 mean velocity components and associated normal stresses enabled the data to be utilised to assess a 3D CFD calculation incorporating a k-ε turbulence closure. The strength of forward and back flow generated at impingement was accurately predicted when the QUICK discretisation scheme was used. However, the size of upstream vortex was overpredicted. As expected using an eddy viscosity model the turbulence field at jet impingement and in the hole vicinity was not correctly reproduced. The turbulence generation in the flow approaching the hole was greatly overestimated by the turbulence model used.

Commentary by Dr. Valentin Fuster
1992;():V003T06A009. doi:10.1115/92-GT-112.
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Development of a lean-premixed, liquid-fueled combustor is in progress to achieve ultra-low NOx emissions at typical gas turbine operating conditions. A filming fuel injector design was tested on a bench scale can combustor to evaluate critical design and operating parameters for low emissions performance. Testing was completed using No. 2 diesel. Key design variables tested include premixing length, swirler angle, injector centerbody diameter, and reduced liner cooling. NOx emissions below 12 ppmv at 9 bars pressure were measured. Corresponding CO levels were 50 ppmv. An optimized injector design was fabricated for testing in a 3 injector sector of an annular combustor. Operating parameters and test results are discussed in this paper.

Commentary by Dr. Valentin Fuster
1992;():V003T06A010. doi:10.1115/92-GT-113.
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This work reports an experimental study of the behaviour and structure of a liquid spray immersed in a strong swirling field. In order to simulate some of the aerodynamic conditions experienced by a spray in a model combustor, an experimental setup using an acrylic chamber, a vane type swirler, and separate air supplies for both the secondary air and the swirl air were integrated to perform the experiments in the wind tunnel. A vane type swirler exhibiting a high swirl number was used to produce a strong recirculation flow field downstream of a pressure swirl atomizer. Properties of the dispersed phase such as velocity, size distributions, and size-velocity correlations were measured at several locations within the swirling flow field. In addition, mean velocity and turbulence properties were obtained for the gas phase. Flow visualization was performed with a laser sheet to gain further understanding of the formation and influence of the recirculation region on the spray. A 2-component PDPA system with a frequency based Doppler Signal Analyzer was used throughout the measurements, and proved most valuable in the toroidal vortex region where low SNR conditions and non-uniform concentration of seed particles prevail. The results show that flow reversal of the drops is present at this swirl intensity within the recirculation region at distances up to X/D = 2.0. Small variations of drop size distribution within the recirculation region are observed, however large variations outside of it are also present.

Plots of the normal Reynolds stresses and Reynolds shear stresses show double-peak radial distributions which indicate regions in the flow where high mean velocity gradients and large shear forces are present. The decay of turbulence velocities in the axial direction was observed to be very fast, an indication of high diffusion and dissipation rates of the kinetic energy of turbulence.

Commentary by Dr. Valentin Fuster
1992;():V003T06A011. doi:10.1115/92-GT-114.
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The thermal stability characteristics of two liquid hydrocarbon fuels are examined using a single-pass system whereby the fuel under test flows only once through a heated tube which is maintained at constant temperature throughout a test duration of six hours. Deposition rates on the tube walls are measured by weighing the tube before and after each test.

The experimental data are used to derive empirical equations for predicting the effects on deposition rates of variation in fuel temperature, wall temperature, and Reynolds number. It is found that deposition rates are enhanced by increases in fuel temperature, wall temperature and flow velocity, and by reductions in tube diameter. Pressure has no effect on deposition rates provided it is high enough to prevent fuel boiling.

Commentary by Dr. Valentin Fuster
1992;():V003T06A012. doi:10.1115/92-GT-115.
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NOx exhaust emissions for gas turbine engines with lean-premixed combustors are examined as a function of combustor pressure (P), mean residence time (τ), fuel-air equivalence ratio (φ), and inlet mixture temperature (Ti). The fuel is methane. The study is accomplished through chemical reactor modeling of the combustor, using CH4 oxidation and NOx kinetic mechanisms currently available. The NOx is formed by the Zeldovich, prompt, and nitrous oxide mechanisms.

The combustor is assumed to have a uniform φ, and is modeled using two reactors in series. The first reactor is a well-stirred reactor (WSR) operating at incipient extinction. This simulates the initiation and stabilization of the combustion process. The second reactor is a plug-flow reactor (PFR), which simulates the continuation of the combustion process, and permits it to approach completion. For comparison, two variations of this baseline model are also considered. In the first variation, the combustor is modeled by extending the WSR until it fills the whole combustor, thereby eliminating the PFR. In the second variation, the WSR is eliminated, and the combustor is treated as a PFR with recycle. These two variations do not change the NOx values significantly from the results obtained using the baseline model.

The pressure sensitivity of the NOx is examined. This is found to be minimum, and essentially nil, when the conditions are P = 1 to 10atm, Ti = 600K, and φ = 0.6. However, when one or more of these parameters increases above the values listed, the NOx dependence on the pressure approaches P raised to a power of 0.4-to-0.6.

The source of the NOx is also examined. For the WSR operating at incipient extinction, the NOx is contributed mainly by the prompt and nitrous oxide mechanisms, with the prompt contribution increasing as φ increases. However, for the combustor as a whole, the nitrous oxide mechanism predominates over the prompt mechanism, and for φ of 0.5-to-0.6, competes strongly with the Zeldovich mechanism. For φ greater than 0.6-to-0.7, the Zeldovich mechanism is the predominant source of the NOx for the combustor as a whole.

Verification of the model is based on the comparison of its output to results published recently for a methane-fired, porous-plate burner operated with variable P, φ, and Ti. The model shows agreement to these laboratory results within a factor two, with almost exact agreement occurring for the leanest and coolest cases considered. Additionally, comparison of the model to jet-stirred reactor NOx data is shown. Good agreement between the model results and the data is obtained for most of the jet-stirred reactor operating range. However, the NOx predicted by the model exhibits a stronger sensitivity on the combustion temperature than indicated by the jet-stirred reactor data.

Although the emphasis of the paper is on lean-premixed combustors, NOx modeling for conventional diffusion-flame combustors is presented in order to provide a complete discussion of NOx for gas turbine engines.

Commentary by Dr. Valentin Fuster
1992;():V003T06A013. doi:10.1115/92-GT-116.
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The design of a lean-premixed, annular, dry low NOx combustor for Solar’s 5500 hp Centaur Type H gas turbine is discussed. Results from early engine tests of prototype combustion hardware are presented. The emissions results with natural gas fueling meet the development goals of less than 25 ppm NOx (at 15% O2) and 50 ppm CO. Several techniques to extend the low emissions operating range of the lean-premixed system are shown to be effective.

Commentary by Dr. Valentin Fuster
1992;():V003T06A014. doi:10.1115/92-GT-117.
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The influence of flow vorticity on droplet combustion and evaporation are experimentally simulated by using a burning liquid-pool system, and numerically investigated by considering a nonreactive, rotating, stagnation-point flow, respectively. The experiment involves measurements of flame temperature, flame position and evaporation rate of the liquid pool, observations of the recirculation zone and the soot layer, and identification of flame extinction. A finite-volume method is employed to numerically solve the corresponding transport equations. Calculated results show that in the vicinity of the liquid surface, both convection and diffusion transports are weakened by the flow vorticity resulting in the suppression of the evaporation strength of liquid; the recirculation zone can be identified and compared with experimental observation. For the steady burning of an ethanol pool in a swirl air jet, it is found that as the angular velocity increases, the diffusion flame shifts closer to the upper burner, has a larger flame thickness, experiences a smaller flame stretch but suffers from the reduction of mass diffusion of ethanol vapor to the flame. However, the evaporation rate of ethanol is usually decreased with increasing the angular velocity. In the flame extinction experiment, the critical volumetric oxygen concentration at extinction first decreases to a minimum value and then increases with angular velocity. It is generally concluded that the flow vorticity has a negative effect on both droplet combustion and evaporation.

Commentary by Dr. Valentin Fuster
1992;():V003T06A016. doi:10.1115/92-GT-119.
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The lean ignition limit, the lean blowout limit and the exhaust emission characteristics of spray combustion have been investigated experimentally using a pre-chamber type vortex combustor developed for a 300KW large-bus gas turbine engine. It has been verified that these depend on the spray characteristics of the fuel injector and the air flow pattern or the distribution of air in the chamber.

Ignition succeeds through three processes. The first step is the formation of a flame kernel near the sparking ignitor, the second step is the propagation of the flame kernel into a flame holding region, and the last step is the formation of a rotating flame in that region. The lean blowout limit of the rotating flame depends on the air flow pattern in the pre-chamber when the air temperature in the combustor inlet is under 470K, while a constant fuel-air ratio of less than 0.001 is maintained at 470K and above. With no or a little secondary air, the NOx emission index does not increase in proportion to the fuel-air ratio, because both the gas temperature and residence time decrease due to the radiative heat loss caused by soot formation and reduction of a recirculation region in the main-chamber.

These phenomena were evaluated with 3 dimensional numerical simulations taking account of spray combustion, soot formation, the extended-Zeldovich thermal NO formation and radiative heat loss.

Commentary by Dr. Valentin Fuster
1992;():V003T06A017. doi:10.1115/92-GT-120.
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An experimental study was conducted to determine the NOx emissions and flame stability associated with various flameholders used to support lean-premixed combustion of natural gas at gas turbine conditions. Data were obtained for velocities of 6 to 24 m/s, initial temperatures of 533 to 650 K, and pressures of 3.4 to 13.6 atm. Bluff-body, perforated-plate, and swirl-stabilized flameholders were tested and compared. The results confirm that NOx emissions at ultra-lean conditions scale with the flame temperature and are essentially independent of flameholder geometry for typical combustor residence times. The stability behavior, however, was strongly affected by flameholder type, illustrating the influence of fluid mechanics on flame stability. The flame stability was related also to the dynamics produced by combustion instability. A swirl-stabilized flameholder demonstrated the best stability characteristics at the expense of flameholder pressure drop.

Commentary by Dr. Valentin Fuster
1992;():V003T06A018. doi:10.1115/92-GT-121.
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Results presented here illustrate how optimizing the fuel distribution at injection reduces the subsequent mixing needed for ultralow emissions in lean, premixed gaseous flames. An experimental facility was developed for bluff body stabilization of a high pressure natural gas flame at the exit of a 4” diameter mixing tube. Fuel was injected through two concentric ring manifolds. NOx and CO drop dramatically from diffusion flame to perfectly premixed levels with increasing mixing distance. Furthermore, for each mixing distance, there is an optimum fuel split that results in minimum NOx and CO emissions. Computational fluid dynamics and laser sheet flow visualization show the recirculation zones and fluid mixing that affect fuel injection requirements. Although improved fuel injection and greater mixing will both drive the NOx-CO curve to the origin, improving the initial fuel distribution reduces the requirement for subsequent mixing.

Topics: Fuels , Flames , Emissions
Commentary by Dr. Valentin Fuster
1992;():V003T06A019. doi:10.1115/92-GT-122.
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A system of diphenyldisulphide in hexadecane was selected for modeling the formation of insolubles in jet fuels. The system was stressed in a series of flask tests at 185°C under fixed oxygen flow. The quantity of filterable insoluble solids and insoluble gums was measured as a function of time and found to increase linearly following an initial induction period. Rates associated with the linear growth were evaluated for a series of oxygen flows to obtain the oxygen dependence of insoluble-solid and insoluble-gum formation. Results indicate that insoluble gums and insoluble solids are formed by independent processes. Bulk and surface rates show a linear correlation, indicating that the precursors to insolubles formed in the bulk and those formed on the surface are similar.

Topics: Jet fuels , oxidation , Sulfur
Commentary by Dr. Valentin Fuster
1992;():V003T06A020. doi:10.1115/92-GT-123.
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This paper describes the cold flow tests and low pressure combustion tests which were conducted for the development of a 1500°C-class low NOx combustion system. In the cold flow tests, the effect of vane angle and the momentum ratio of fuel to air flow on mixing characteristics inside the premixing nozzles was investigated. The stabilization of the flow field inside the combustor was confirmed by measurement of the axial velocity distribution and observations by using a tuft of soft thread.

Combustion characteristics in terms of emissions and stability were investigated initially by low pressure combustion tests, and the gas temperature distribution inside the combustor was measured. NOx emissions for a 1500°C-class gas turbine as low as 50ppm at 15% oxygen at design pressure were demonstrated.

Commentary by Dr. Valentin Fuster
1992;():V003T06A021. doi:10.1115/92-GT-124.
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A hollow-cone spray with a nominal cone angle of 30 degrees from a pressure-swirl fuel atomizer was used in a swirl-stabilized combustor. The combustor is circular in cross section, with a swirl plate and fuel nozzle axis coinciding with the axes of the chamber. kerosene is injected upward inside the chamber from the fuel nozzle. Separate swirl and dilution air flows are distributed into the chamber that pass through honeycomb flow straighteners and screens. A calculated swirl number of 1.5 is generated with the design swirl plate exit air velocity of 30 degrees with respect to the chamber axis. Effects of swirl and dilution air flow rates on the shape and stability of the flame are investigated. A Phase Doppler Particle Analyzer (PDPA) is used to measure drop size, mean and rms values of axial drop velocity, fuel volume flux, drop velocity and size distributions, and size-classified drop velocity profiles for two cases of with and without combustion and at six different axial locations from the nozzle. For the no-combustion case all air and fuel flow rates were kept at the same values as the combusting spray condition. Results for mean axial drop velocity profiles indicate widening of the spray, with slight increase in the magnitudes of the peak drop velocities due to combustion. Root mean square (RMS) values of drop velocity fluctuations decrease due to a combination of increase in gas kinematic viscosity and elimination of small drops at high temperatures. Sauter mean diameter (SMD) radial profiles at all axial locations increase with combustion due to preferential burning of small drops. Fuel volume flux profiles indicate negligible drop vaporization and/or burning up to a distance of 25mm from the nozzle. Velocity number distributions at different radial points for without combustion at an axial distance of 55mm from the atomizer are symmetric in shape only close to the peak of the mean drop velocity and show a bimodal shape around the maximum mean drop axial velocity gradient. Corresponding number distributions for the combustion case are fairly symmetric and quite different in behavior at all radial positions. Size-classified drop velocity profiles are also plotted and discussed.

Topics: Combustion , Sprays
Commentary by Dr. Valentin Fuster
1992;():V003T06A022. doi:10.1115/92-GT-129.
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An emission model that combines the analytical capabilities of 3-D combustor performance codes with mathematical expressions based on detailed chemical kinetic scheme is formulated. The expressions provide the trends of formation and/or the consumption of NOx, CO, and UHC in various regions of the combustor utilizing the details of the flow and combustion characteristics given by the 3-D analysis. By this means, the optimization of the combustor design to minimize pollutant formation and maintain satisfactory stability and performance could be achieved. The developed model was used to calculate the emissions produced by several engine combustors that varied significantly in design and concept, and operated on both conventional and high density fuels. The calculated emissions agreed well with the measurements. The model also provided insight into the regions in the combustor where excessive emissions were formed, and helped to understand the influence of the combustor details and air admission arrangement on reaction rates and pollutant concentrations.

Commentary by Dr. Valentin Fuster
1992;():V003T06A023. doi:10.1115/92-GT-130.
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To meet the future goals of reduced emissions produced by gas turbine combustors, a better understanding of the process of formation of various pollutants is required. Both empirical and analytical approaches are used to provide the exhaust concentrations of pollutants of interest such as NOx, CO, and unburned hydrocarbon with varying degrees of success. In the present investigation, an emission model that simulates the combustor by a number of reactors representing various combustion zones is proposed. A detailed chemical kinetic scheme was used to provide a fundamental basis for the derivation of a number of expressions that simulate the reaction scheme. The model addresses the combined effects of spray evaporation and mixing in the reaction zone. The model validation included the utilization of a large data base obtained for an annular combustor of a modern turbopropulsion engine. In addition to the satisfactory agreement with the measurements, the model provided insight into the regions within the combustor that could be responsible for the excessive formation of emissions. Methods to reduce the emissions may be implemented in light of such information.

Commentary by Dr. Valentin Fuster
1992;():V003T06A024. doi:10.1115/92-GT-131.
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A multicomponent droplet vaporization model, the Diffusion-Limit Model, is modified to account for the variation of liquid properties due to large temperature gradients as well as considerable concentration gradients within the droplet.

The effects on the vaporization behavior are analysed for an isolated bicomponent droplet consisting of heptane and dodecane. The results are presented for both moderate and high gas temperatures excluding combustion.

During the vaporization process the liquid phase properties vary considerably. For example, the Lewis number changes approximately one order of magnitude. The mass ratio of the liquid components seems to be rather sensitive to the variation of thermophysical property values, especially during the second half of the droplet lifetime, where about 50% of the droplet mass will still evaporate. The gas phase behavior is less affected by the use of constant liquid properties.

For both gas temperature levels tested it was found that single component models cannot describe satisfactorily the whole vaporization process of multicomponent droplets. With regard to ignition the sharp rise of the vapor concentration in the beginning of the droplet vaporization is important. This behavior is caused by the more volatile component and cannot be achieved by the single component substitute.

Topics: Drops
Commentary by Dr. Valentin Fuster
1992;():V003T06A025. doi:10.1115/92-GT-132.
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The objective of the Innovative High Temperature Aircraft Engine Fuel Nozzle Program was to design and evaluate a nozzle capable of operating at a combustor inlet air temperature of 1600°F (1144°K) and a fuel temperature of 350°F (450°K). The nozzle was designed to meet the same performance requirements and fit within the size envelope of a current production F404 dual orifice fuel nozzle. The design approach was to use improved thermal protection and fuel passage geometry in combination with fuel passage surface treatment to minimize coking at these extreme fuel and air temperatures. Heat transfer models of several fuel injector concepts were used to optimize the thermal protection, while a series of sample tube coking tests were run to evaluate the effect of surface finish, coatings and tube material on the coking rate. Based on heat transfer analysis, additional air gaps, reduced fuel passage flow area and ceramic tip components reduced local fuel wetted wall temperatures by more than 200°F (110°K) when compared to a current production F404 fuel nozzle. Sample tube coking test results showed the importance of surface finish on the fuel coking rate. Therefore, a 1 micro-inch (.025 micron) roughness was specified for all fuel passage surfaces. A novel flow divider valve in the tip was also employed to reduce weight, allow room for additional thermal protection, and provide back pressure to reduce the risk of fuel vaporization. Phase II of this program will evaluate the fuel nozzle with a series of contaminated fuel and coking tests.

Commentary by Dr. Valentin Fuster
1992;():V003T06A026. doi:10.1115/92-GT-133.
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An experimental program was conducted to evaluate low NOx combustor concepts applicable to natural-gas-burning aeroderivative gas turbine engines operating at a nominal pressure ratio of 20:1. Gas sampling measurements at the exit of the primary zone of high-shear and lean premixed burners were acquired under elevated entrance pressure and temperature conditions over a range of primary zone equivalence ratios. Piloting systems were incorporated in most of the burner designs to achieve satisfactory burner operability. Both swirl stabilized and perforated-plate (grid) stabilized burners were found to produce NOx levels lower than the current engine goal of 25 ppm (15% O2).

Commentary by Dr. Valentin Fuster
1992;():V003T06A027. doi:10.1115/92-GT-134.
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Non-intrusive, spatially resolved instantaneous temperature measurements are presented that were obtained from a reacting spray flame in a model gas turbine can combustor using coherent anti-Stokes Raman scattering (CARS) thermometry. The results show that CARS measurements agree with thermocouple measurements at the exit of the combustor. The liquid droplet induced dielectric breakdown is not an obstacle in applying CARS to reacting sprays. The CARS measured temperature field also indicates that there is a relatively cool region (T < 1000 K) near the nozzle tip. Reaction occurs in the region where large numbers of droplets are present and in the interface of the swirl-induced recirculation zone. This study demonstrates that CARS is a viable diagnostic tool for non-intrusive, instantaneous temperature measurements in practical spray flames.

Commentary by Dr. Valentin Fuster
1992;():V003T06A028. doi:10.1115/92-GT-135.
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For many years investigators studying the combustion behaviour within gas turbines have presumed droplet size to play a very important role in defining combustion efficiency. Recently a very large number of experiments have been conducted jointly by Laval University and the Aeronautical Research Laboratory in Melbourne. In the course of these investigations, over a wide range of operating conditions, a single combustor has been investigated using three different Simplex atomisers at each of the conditions for three fuels. In addition, the same combustor has been used to investigate a very wide range of fuels (87) at ambient inlet conditions.

The measured combustion efficiencies show no measurable effects due to droplet size, although volatility effects have been noted (measured as TAV). It is thought that these effects are reflected in terms of a Transfer Number and related to diffusional phenomena, rather than evaporative phenomena.

A great number of experimental data are reviewed, and in addition to showing the absence of effects of droplets, a small section deals with the precision of experimental values of combustion efficiency and how it might influence models predicting combustion efficiency, especially with respect to possible future pollution requirements.

Commentary by Dr. Valentin Fuster
1992;():V003T06A029. doi:10.1115/92-GT-137.
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A research airblast atomizer/combustion chamber configuration has been built for the validation of a mathematical model of two phase flows in gas turbine combustors. The inlet boundary conditions of the gas flow were measured within the nozzle by Laser-Two-Focus-Velocimetry. Starting velocities and mass fluxes for the droplet sizes of the spray were measured by Phase-Doppler-Anemometry at a plane 7mm downstream of the atomizer lip. Gas- and drop velocities were measured consecutively in the confined swirling isothermal flow throughout the combustor and were compared with the results of a newly developed mathematical model of spray dispersion.

The spray shows the general structure of an axial acceleration of all dropsizes and a following dispersion of the droplets and radial separation by centrifugal forces according to their size. Measured and calculated drop velocities for 10, 30 and 50μm drops compare well, except for some differences, which can be explained by deficiencies of the gas flow calculation. Mass flux and volumetric mean diameter profiles are also correctly reproduced.

Commentary by Dr. Valentin Fuster
1992;():V003T06A030. doi:10.1115/92-GT-138.
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A two-component fibre optic LDV system has been employed to measure three mean velocity components and five Reynolds Stress components in a confined, isothermal strongly swirling flowfield. The primary objective is to provide complete benchmark data for comparisons with numerical predictions based on practical models for turbulent swirling flows and thereby guide the development of such models. Results of initial modelling work are presented and even at this early stage in the programme, the superiority of the Reynolds Stress modelling approach is clearly illustrated through comparisons with the results from experiment and a typical kε model. Measurements show the radial velocity component (close to the swirler exit) to be of the same magnitude as the axial and swirl components. Velocity measurements obtained close to the combustor wall should be treated with caution as these were most affected by signal noise as a result of internal wall reflections.

Commentary by Dr. Valentin Fuster
1992;():V003T06A031. doi:10.1115/92-GT-207.
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A production gas turbine combustor swirl cup and a 3x-scale model, both featuring co-axial, counter-swirling air streams are characterized at atmospheric pressure and in the absence of reaction. Spatially-resolved measurements of continuous phase (gas in the presence of spray) and droplet size and velocity are acquired downstream of the production and 3x-scale swirl cups by using two-component phase Doppler interferometry. The effect of scale on the behavior of the continuous phase and droplets is investigated by comparing the continuous phase velocity and droplet size and velocity at geometrically analogous positions. The continuous phase flow field scales well at the exit of the swirl cup. Farther downstream, differences occur which are due to disparity in entrainment. The droplet velocities scale reasonably well, but the sizes show some differences. However, the difference in size is less significant than it is between the two atomizers in the absence of the swirl cup assemblies.

Commentary by Dr. Valentin Fuster
1992;():V003T06A032. doi:10.1115/92-GT-234.
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Research and development of an IGCC (Integrated Coal Gasification Combined Cycle) power generation system is being carried out as one of the advanced coal utilization technology in Japan. The coal gasified fuel, which is produced in a coal gasifier of air-blown entrained-flow type has calorific value as low as 1/10 of LNG. Furthermore, the fuel gas contains ammonia when a gas cleaning system is a hot type, and ammonia will be converted to nitrogen oxides in the combustion process of a gas turbine. The authors have designed and made an 1300°C-class advanced rich-lean combustor mainly designed for achieving low fuel-NOx combustion. By testing it under atmospheric pressure conditions, we have successfully reduced the NOx emissions (to 60 ppm corrected at 16 percent O2) by more than half the level previously achieved when the ammonia concentration was 1000 ppm. Combustion stability was adequate even when the calorific value of the fuel decreased to 2700 kJ/m3N.

Commentary by Dr. Valentin Fuster
1992;():V003T06A033. doi:10.1115/92-GT-235.
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This paper describes work carried out to determine the influence of several design features upon the performance of an air blast fuel injector. The design features studied were the number of tangential fuel holes feeding the swirl chamber, the depth of the swirl chamber, and the shape of the downstream section of the swirl chamber.

The performance parameters considered were, fuel distribution, flow number, air side effective area, spray cone angle and spray SMD. The fuel used was aviation kerosine.

Apparatus for the relatively simple and rapid determination of the fuel distribution within the spray is also described.

Commentary by Dr. Valentin Fuster
1992;():V003T06A034. doi:10.1115/92-GT-314.
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This paper presents the results of the combustion system test of the MS7001F installed at the Virginia Power Chesterfield station. Tests of water and steam injection for NOx control were performed. Results of emissions, combustor dynamics, and combustor hardware performance are presented. Emissions test results include NOx, CO, unburned hydrocarbons, VOC and formaldehyde levels. Combustor dynamic activity over a range of diluent injection ratios, and the performance of an actively cooled transition duct are also discussed. Combustion system mechanical performance is described following the first combustion system inspection.

Commentary by Dr. Valentin Fuster
1992;():V003T06A035. doi:10.1115/92-GT-346.
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Concentration fluctuations were investigated using a water tunnel with a separate salt-water solution as a ‘fuel’ tracer flow. A fine electrode was used to detect the concentration of the tracer from the local conductivity. The frequency response of 0.4 by 1 mm probe tip was 10 kHz. An impinging axial/radial jet configuration was studied as this is a key element in some burner and gas turbine low emission combustor designs. Mixing was complete to within 5% by six axial hole diameters, an order of magnitude improvement on single jet mixing. The mixing traverses close to the jets demonstrated the importance of the method of fuel injection on the mixing process. The turbulent scalar mixing results are a suitable data set for CFD code validation of isothermal jet mixing.

Commentary by Dr. Valentin Fuster
1992;():V003T06A036. doi:10.1115/92-GT-347.
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The paper presents the mathematical model of the combustion chamber as an object of temperature and pressure control. Using the step function characteristics and the frequency method (in the range of low frequency f<20Hz), the theoretical models with different degrees of simplifications were compared with the results of the experimental investigations.

The proposed theoretical model may turn out very useful in the research of the gas turbine dynamics.

Commentary by Dr. Valentin Fuster
1992;():V003T06A037. doi:10.1115/92-GT-371.
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Fuel injection into high velocity jet shear layers in an enclosed 140mm diameter conical flame stabiliser, with four large jet shear layers and a central radial fuel injector, was studied at operating conditions relevant to high intensity burners and gas turbine primary zones. The mean exhaust emissions for propane were shown exhibit a high efficiency over a wide range of equivalence ratios with a good turn down ratio. Fuel and air mixing, propane combustion development and NOx formation was investigated using internal gas composition measurements at three simulated lean primary zone operating conditions. The combustion development and emissions was shown to be dominated by fuel and air mixing between a rich outer recirculation zone and a high velocity lean inner shear layer outflow region. An aerodynamically generated rich lean combustion system was generated without fuel or air staging, but the interface mixing region resulted in significant NOx generation.

Commentary by Dr. Valentin Fuster
1992;():V003T06A038. doi:10.1115/92-GT-373.
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A recent field test has completed the qualification of the MS6001B combustion system for operation on gas fuel with steam injection for NOx control to 25 ppmvd. Recently, dry operation on gas fuel at 25 ppmvd has been achieved on the MS6001. To meet the immediate need for running at the 25 ppmvd NOx level, increased steam injection was investigated. Laboratory testing on a single MS6001 combustor indicated the potential for achieving NOx levels as low as 25 ppmvd through the use of steam injection. This paper describes the lab testing and the field test of the MS6001B, and includes data on emissions, steam flow requirements, and dynamic pressure levels. The MS6001B is now available at 25 ppmvd NOx with steam injection on gas wherever this level is required. This system provides an easy retrofit to those gas fired, steam injected units where installation of the dry 25 ppmvd NOx system is not immediately feasible.

Commentary by Dr. Valentin Fuster

Oil and Gas Applications

1992;():V003T07A001. doi:10.1115/92-GT-016.
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Experimental investigations were conducted to determines: 1) the degradation of single stage centrifugal compressor performance due to induced inlet distortion and swirl, and 2) the subsequent performance recovery achievable by use of an upstream flow conditioner developed by VORTAB Incorporated. The compressor inlet flow velocity profile was distorted using out-of-plane double elbows and a specially designed swirl generator. The distorted flow was conditioned using the flow conditioner. Performance tests were conducted for baseline (no distortion), distorted flow, and conditioned flow. The results indicate that velocity profile distortion and swirl can strongly affect the compressor performance. It is additionally demonstrated that the profile correction and swirl elimination achieved with the flow conditioner recovers the compressor performance to its baseline level, with minimum device pressure loss.

Commentary by Dr. Valentin Fuster
1992;():V003T07A002. doi:10.1115/92-GT-021.
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In the summer of 1991, NOVA Corporation of Alberta (NOVA) commissioned the first Solar Centaur Taurus T-6502 turbine unit into service on its natural gas pipeline system. The turbine powered a Solar C304 compressor equipped with dry gas seals and magnetic bearings. This paper describes the turbine/compressor package and the application in which it was installed. Experiences during commissioning, start up and the early months of operation are discussed.

Topics: Solar energy
Commentary by Dr. Valentin Fuster
1992;():V003T07A003. doi:10.1115/92-GT-024.
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Transient phenomena are generally inherent in the operation of compressor stations: these are either fast or slow transients. A model describing the governing equation for the gas dynamics, control system, compressor and turbine shafts inertias has been developed. The effect of these inertias is manifested by an example of a compressor station operating near the surge control line. Another example deals with a station that has a cooler placed in the recycle path. This alters the rate at which the compressor shaft decelerates upon shutdown and may cause backward spinning depending on the relative magnitude of the shaft inertia with respect to the cooler volume. Backward spinning of compressor shaft has detrimental effects on dry seals and is undesirable. It was found that by keeping the recycle valve closed upon shutdown, the rate of shaft deceleration will be reduced.

Commentary by Dr. Valentin Fuster
1992;():V003T07A004. doi:10.1115/92-GT-025.
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NOVA’s Alberta Gas Transmission Division transports natural gas via pipeline throughout the province of Alberta, Canada, exporting it to eastern Canada, United States and British Columbia. It is a continuing effort to operate the facilities and pipeline at the highest possible efficiency. One area being addressed to improve efficiency is compression of the gas. By improving compressor efficiency, fuel consumption and hence operating costs can be reduced.

One method of improving compressor efficiency is by converting the compressor to an axial inlet configuration, a conversion that has been carried out more frequently in the past years. Concurrently, conventional hydrodynamic bearings have been replaced with magnetic bearings on many centrifugal compressors. This paper discusses the design and installation for converting a radial overhung unit to an axial inlet configuration, having both magnetic bearings and a thrust reducer. The thrust reducer is required to reduce axial compressor shaft loads, to a level which allows the practical installation of magnetic bearings within the space limitations of the compressor (Bear and Gibson, 1992).

Commentary by Dr. Valentin Fuster
1992;():V003T07A005. doi:10.1115/92-GT-026.
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Foothills Pipe Lines Ltd. is the Canadian sponsor of the Alaska Natural Gas Transportation System (ANGTS), a pipeline project selected in Canada and the United States as the means for transporting Alaskan gas reserves to the lower 48 United States. Currently, certain Prebuild portions of the ANCTS are in operation delivering Canadian gas to U.S. markets.

Recent system expansion of the Eastern Leg Prebuild to accommodate increased Canadian gas exports entailed the construction of Decompression/Recompression facilities at Empress, Alberta to enable high pressure operation of the Foothills pipeline while maintaining gas stripping at existing low pressure extraction plants. The general process of the Decompression/Recompression facilities involves the expansion of high pressure pipeline gas to conditions acceptable to the low pressure extraction plants, then the recompression of the residue gas for return to the pipeline at original pressure. By directing the inlet gas through turbo expanders coupled to brake compressors, a substantial portion of the expansion energy is captured and used in providing the first stage of gas recompression. Including supplemental conventional compression, the Decompression/Recompression facilities are capable of providing approximately 37 MW (50 000 HP) for continuous gas recompression.

Although power recovery with turbo expanders is relatively common in the gas processing industry, such application for gas recompression in large gas pipelines is unique. This technical paper describes the Foothills Decompression/Recompression facilities with their utilization of turbo expanders for pipeline recompression service, emphasizing the process design as well as the characteristics of the rotating equipment.

Topics: Pipelines
Commentary by Dr. Valentin Fuster
1992;():V003T07A006. doi:10.1115/92-GT-087.
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This paper describes and discusses a “closed loop” steam injection water recovery (SIWR) cycle that was developed for steam injected gas turbine applications. This process is needed to support gas turbine steam injection especially in areas where water can not be wasted and complex water treatment is discouraged.

The development of the SIWR was initiated by NOVA in an effort to reduce environmental impact of operating gas turbines and to find suitable solutions for its expanding gas transmission system to meet future air emission restrictions. While turbine steam injection provides many benefits, it has not been considered for remote, less supported environments such as gas transmission applications due to its high water consumption. The SIWR process can alleviate this problem regardless of the amount of injection required.

The paper also covers conceptual designs of a prototype SIWR system on a small gas turbine unit. However, because of relatively high costs, it is generally believed that the system is more attractive to larger size turbines and especially when it is used in conjunction with co-generation or combined cycle applications.

Commentary by Dr. Valentin Fuster
1992;():V003T07A007. doi:10.1115/92-GT-089.
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This paper describes the historical data for gas turbine driven compressor and power generation packages built for the North Sea. The period surveyed spans from the start-up of Ekofisk to the present day. The paper covers 60 platforms in the Norwegian and UK sectors and a number in the Danish and Dutch sectors. The data gathered for each platform include details of gas turbines, compressors, gearboxes, couplings, tube and seat oil systems, skid arrangements, air filtration systems, exhaust systems and so forth. In total, approximately 320 electric power generating sets and 380 compressors are included, representing 5.5 million kW. The trend over the survey period is found from the recorded data, and a comparison is made between the Norwegian and UK sectors.

Topics: Machinery , North Sea
Commentary by Dr. Valentin Fuster
1992;():V003T07A008. doi:10.1115/92-GT-102.
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The LM6000 Gas Turbine was formally introduced at the IGTI Gas Turbine Conference in Brussels in 1990. It was immediately accepted for power generation/cogeneration applications; however, inquiries were received concerning the use of the LM6000 gas turbine for mechanical drive applications. These inquiries included the amount of power available with decreasing gas turbine speed, breakaway torque capability and resonant free operation over a broad speed range.

This paper discusses the engineering studies performed to ensure that the LM6000 will be a suitable power source for mechanical drive applications in the 30–40 MW power range.

Commentary by Dr. Valentin Fuster
1992;():V003T07A009. doi:10.1115/92-GT-103.
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The Gullfaks ‘A’ Platform located in the Norwegian Sector of the North Sea, is designed to process 50,000 SM3/day of well head fluids to crude oil and gas product specifications. The present operating conditions of the process are different from the original design due to changes in feed stock. Furthermore, degradation of compressor performance due to fouling, wear and internal leakage has led to limited production flexibility. Field performance testing of the compressors has been carried out supplemented by computer based performance prediction. Based on this information, a dynamic simulation model of the process, tuned to actual plant operation, has been used to analyse the process behaviour. Modifications have been studied by dynamic process simulation before field implementation. These modifications have resulted in reduced operating and maintenance costs. Substantial decrease in compressor speed and load have led to reduced wear and maintenance. Operational and pollution tax savings are estimated at $1.5m/year.

Commentary by Dr. Valentin Fuster
1992;():V003T07A010. doi:10.1115/92-GT-104.
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Dry gas seal technology has developed significantly over the past two decades. In addition to advances in standard seal technologies, alternate configurations of dry gas seals within the compressor have provided compressor efficiency improvements among other benefits. This paper describes the innovative application of dry gas seals in the reduction and control of axial shaft forces in pipeline gas compressors.

By uniquely configuring the dry seals, the balance piston was removed from a beam type compressor, resulting in improvement of the compressor efficiency. In addition, the maximum axial forces in an overhung unit were substantially lowered, eliminating full pressure start-up problems, and allowing the practical installation of magnetic bearings. In both beam and overhung compressor applications, these dry seals combined with a control system reduce axial forces on the shaft to zero under most operating conditions.

Commentary by Dr. Valentin Fuster
1992;():V003T07A011. doi:10.1115/92-GT-150.
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In order to obtain permission for the construction of a new gas compressor station or other industrial facility, the future user has to submit a comprehensive forecast of sound immission levels to the competent supervisory authority, at the same time demonstrating by which means the noise level requirements in the vicinity of the facility can be met.

For this purpose, it is essential to calculate the sound propagation and associated attenuation effects on a basis which is reliable, verifiable and acceptable to the authority. The German VDI Regulations No. 2714 contain stipulations regarding standardized calculation procedures applicable in such cases.

This paper (ASME-presentation) discusses these calculation procedures for distances of > 200 m (> 650 feet) with special emphasis on screening and attenuation effects attributable to topography, weather influences and sound dissipation at high frequencies.

Topics: Regulations
Commentary by Dr. Valentin Fuster
1992;():V003T07A012. doi:10.1115/92-GT-386.
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British Gas is the largest integrated gas company in the western world operating on both sides of the Atlantic. Within the UK, the companies activities embrace off-shore exploration and production, transmission and distribution together with the retailing and installation of appliances in customers homes.

Commentary by Dr. Valentin Fuster
1992;():V003T07A013. doi:10.1115/92-GT-387.
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British Gas is the largest integrated gas company in the western world operating on both sides of the Atlantic. Within the UK, the company’s activities embrace off-shore exploration and production, transmission and distribution together with the retailing and installation of appliances in customers homes.

Commentary by Dr. Valentin Fuster
1992;():V003T07A014. doi:10.1115/92-GT-425.
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The flexibility of reciprocating compressors combined with the utilization of variable speed drives like gas turbines optimizes operating and capital investment costs in natural gas services. Reliability and respect for limits specified in pollution control regulations are the most significant requirements related to modern compression stations. Equipped with monitoring systems, the trains must benefit by special design procedures and modern full-load test facilities to ensure the complete confidence of users.

The above features, together with energy saving advantages, make it possible to forecast the increasing application of compressor - turbine arrangements.

Commentary by Dr. Valentin Fuster
1992;():V003T07A015. doi:10.1115/92-GT-426.
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The state of the art of ultrasonic liquid flow measurement has improved greatly in the past decade to where this technology exhibits accuracy equivalent to turbine meter systems, while retaining several advantages over turbine meters.

Testing of a four path non-intrusive meter used for leak detection on the Trans–Alaska Pipeline is discussed. Performance is detailed, and future applications for ultrasonic flow measurement technology are reviewed.

Commentary by Dr. Valentin Fuster
1992;():V003T07A016. doi:10.1115/92-GT-427.
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This paper provides a simple method for correcting and analyzing the performance data from a simple cycle, two shaft gas turbine. This data may have been collected in a test cell, in the field or by a user who desires to closely monitor the performance of an engine.

Topics: Gas turbines
Commentary by Dr. Valentin Fuster
1992;():V003T07A017. doi:10.1115/92-GT-428.
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The performance of many antisurge control systems is degraded because they do not adequately compensate for variable gas properties (primarily molecular weight). The consequences can range from inefficient operation to serious compressor damage due to surges.

To eliminate deficiencies previously experienced, a new, relatively simple (requires measuring only three process variables) system was developed for a machine which normally compresses a 24.2 molecular weight gas, but is also required to operate on other gas mixtures of approximately 40% lower molecular weight. The new method is explained and the results compared with two other widely used concepts.

Commentary by Dr. Valentin Fuster
1992;():V003T07A018. doi:10.1115/92-GT-429.
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A major remaining way to improve operational effectiveness for compressor stations is by the combination of on-line monitoring and enhanced diagnostics which can be described by the general term ‘smart monitoring’. The introduction of smart monitoring techniques will allow unattended operation of equipment to a greater extent than has been possible so far with remote access to the monitoring and diagnostic information from remote field, maintenance, and gas control locations. On-site attendance by operating and maintenance personnel can then be limited to responding to unscheduled events and for doing routine and scheduled maintenance. The role of enhanced diagnostics in this context is to anticipate undesirable operating conditions (and possibly mitigate or avoid them by certain control actions), to obtain earlier prediction of equipment deterioration or potential failures, to carry out a detailed analysis of unscheduled events and shutdowns, and to enable a high level of on-condition maintenance. The function of the intelligent diagnostics is to convert monitoring data, which can be voluminous with online monitoring, into a reduced subset of relevant information which is needed to make decisions. In this paper, a conceptual approach to smart monitoring is described and initial results of an on-site prototype are presented. Future implementation issues are also discussed.

Topics: Compressors
Commentary by Dr. Valentin Fuster

Cycle Innovations

1992;():V003T08A001. doi:10.1115/92-GT-079.
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The circulator is a key component in a gas-cooled nuclear power plant since it facilitates transfer of the reactor thermal energy (via the steam generator) to the electrical power conversion system. Circulator technology is well established and about 200 machines, which, in their simplest form, consist of an electrical motor driven compressor, have operated for many millions of hours worldwide in gas-cooled reactors. This paper covers the evolution of circulator design, technology and operating experience, with particular emphasis on how lessons learned over the last four decades (dominantly from the carbon dioxide cooled plants in the U.K.) are applicable to the helium cooled Modular High Temperature Gas-Cooled Reactor (MHTCR) which should see service in the U.S. at the turn of the next century. State-of-the-art technologies are covered in the areas of impeller selection, bearings, drive system, machine operation, and future trends are Identified.

Commentary by Dr. Valentin Fuster
1992;():V003T08A002. doi:10.1115/92-GT-096.
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Unlike gas turbine power systems which consume chemical or nuclear energy, the energy consumption and/or cycle efficiency should not be a suitable criterion for evaluating the performance of space solar Brayton cycle power. A new design goal, life cycle cost, can combine all the power system characteristics, such as mass, area, and station-keeping propellant, into a unified criterion. Effects of pressure ratio, recuperator effectiveness, and compressor inlet temperature on life cycle cost were examined. This method would aid in making design choices for a space power system.

Commentary by Dr. Valentin Fuster
1992;():V003T08A003. doi:10.1115/92-GT-097.
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In this paper three Closed Combined Cycle (C3) systems for underwater power generation are analyzed. In the first, the waste heat rejected by a Closed Brayton Cycle (CBC) is utilized to heat the working fluid of a bottoming Rankine Cycle; in the second, the heat of a primary energy loop fluid is used to heat both CBC and Rankine cycle working fluids; the third solution involves a Metal Rankine Cycle (MRC) combined with an Organic Rankine Cycle (ORC).

The significant benefits of the Closed Combined Cycle concepts, compared to the simple CBC system, such as efficiency increase and specific mass reduction, are presented and discussed. A comparison between the three C3 power plants is presented taking into account the technological maturity of all the plant components.

Commentary by Dr. Valentin Fuster
1992;():V003T08A004. doi:10.1115/92-GT-098.
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Higher temperature nuclear heat sources are becoming available and more efficient energy conversion systems can be proposed, namely Brayton-Rankine combined cycles which are presently very successful in the terrestrial fossil power plants market. A combined gas-steam cycle adaptation to the now being developed high temperature gas-cooled reactor MHTGR is presented. In order to avoid serious problems associated with the direct cycle, the concept features a He/He heat exchanger and a steam generator heated in series. Consequences are a significant plant efficiency increase, a sufficiently low reactor inlet temperature, attractive operating conditions and a possible reduction of the reactor water ingress hazard.

Similar, judiciously simplified arrangements could be contemplated for possible future efficient marine nuclear power plants.

Cycle combinations could also offer new, suitable approaches of space power systems, particularly for Lunar or Martian bases. A bottoming gas cycle could be a dramatic booster of a topping static thermionic converter, provided that a significantly larger radiator area be acceptable. Combined Brayton-Rankine cycles are also possible candidates for Moon or Mars surface power systems. As a consequence, should a gas-cooled reactor be used as the heat source in a direct cycle arrangement, its design could be drastically simplified.

Topics: Cycles , Nuclear power
Commentary by Dr. Valentin Fuster
1992;():V003T08A005. doi:10.1115/92-GT-099.
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Higher on-board energy levels will be needed at the turn of the century for the many developing space programs. Among the many solar-powered energy conversion systems, a recuperated closed Brayton cycle (CBC) is the most promising one. This study investigated several aspects of a solar dynamic CBC system; an assessment of a reference 25 kWe system, simulation studies related to various operating conditions, and heat-rejection studies related to the radiating area required to transfer the Brayton cycle waste heat to space. In addition, particular attention is paid to the significance of the reduction of system mass required for radiation of waste heat from a closed Brayton cycle to space. Conceptually the radiator area can be reduced by rejecting the heat from the radiator at a higher temperature level than that of the waste heat of the CBC, operating a kind of heat pump by using a fraction of generated power. Consequently, an optimum radiator area is obtained. Also, for high radiator-to-waste-heat temperature ratios (greater than 5), the total radiator area is remarkably reduced. Further, the required mass resulting from the inclusion of the heat pump is estimated.

Commentary by Dr. Valentin Fuster

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