Kenneth O. Smith

Laboratory Studies of the Flow Field Characteristics of Low-Swirl Injectors for Adaptation to Fuel-Flexible Turbines

The low-swirl injector (LSI) is a simple and cost-effective lean premixed combustion method for natural-gas turbines to achieve ultralow emissions (<5 ppm NO x and CO) without invoking tight control of mixture stoichiometry, elaborate active tip cooling, or costly materials and catalysts. To gain an understanding of how this flame stabilization mechanism remains robust throughout a large range of Reynolds numbers, laboratory experiments were performed to characterize the flowfield of natural-gas flames at simulated partial load conditions. Also studied was a flame using simulated landfill gas of 50% natural gas and 50% CO 2 . Using particle image velocimetry, the nonreacting and reacting flowfields were measured at five bulk flow velocities. The results show that the LSI flowfield exhibits similarity features. From the velocity data, an analytical expression for the flame position as function of the flowfield characteristics and turbulent flame speed has been deduced. It shows that the similarity feature coupled with a linear dependency of the turbulent flame speed with bulk flow velocity enables the flame to remain relatively stationary throughout the load range. This expression can be the basis for an analytical model for designing LSIs that operate on alternate gaseous fuels such as slower burning biomass gases or faster burning coal-based syngases.

Ceramic Matrix Composite Combustor Liners: A Summary of Field Evaluations

Solar Turbines Incorporated, under U.S. government sponsored programs, has been evaluating ceramic matrix composite combustor liners in test rigs and Solars Centaur® 50S gas turbine engines since 1992. The objective is to evaluate and improve the performance and durability of CMCs as high-temperature materials for advanced low emissions combustors. Field testing of CMC combustor liners started in May of 1997 and by the end of 2004, over 67,000 operating hours had been accumulated on SiC/SiC and oxide/oxide CMC liners. NO X and CO emissions have been consistently <15 ppmv and <10 ppmv, respectively. Maximum test durations of 15,144 h and 13,937 h have been logged for SiC/SiC liners with protective environmental barrier coatings. An oxide/oxide CMC liner with a Friable Graded Insulation coating has been tested for 12,582 h. EBCs significantly improve SiC/SiC CMC liner life. The basic three-layer EBC consists of consecutive layers of Si, mullite, and BSAS. The durability of the baseline EBC can be improved by mixing BSAS with mullite in the intermediate coating layer. The efficacy of replacing BSAS with SAS has not been demonstrated yet. Heavy degradation was observed for two-layer Si/BSAS and Si/SAS EBCs, indicating that the elimination of the intermediate layer is detrimental to EBC durability. Equivalent performance was observed when the Hi-Nicalon fiber reinforcement was replaced with Tyranno ZM or ZMI fiber. Melt infiltrated SiC/SiC CMCs have improved durability compared to SiC/SiC CMCs fabricated by Chemical Vapor Infiltration of the matrix, in the absence of an EBC. However, the presence of an EBC results in roughly equivalent service life for Ml and CVI CMCs. Results to date indicate that oxide/oxide CMCs with protective FG1 show minor degradation under Centaur® 50S gas turbine engine operating conditions. The results of, and lessons learned from CMC combustor liner engine field testing, conducted through 2004, have been summarized.

Status of Catalytic Combustion R&D for the Department of Energy Advanced Turbine Systems Program

This paper discusses some of the advanced concepts and research and development associated with implementing catalytic combustion to achieve ultra-low-NO x emissions in the next generation of land-based gas turbine engines. In particular, the paper presents current development status and design challenges being addressed by Siemens Westinghouse Power Corp. for large industrial engines (>200 MW) and by Solar Turbines for smaller engines (<20 MW) as part of the U.S. Department of Energys (DOE) Advanced Turbine Systems (ATS) program. Operational issues in implementing catalytic combustion and the current needs for research in catalyst durability and operability are also discussed. This paper indicates how recent advances in reactor design and catalytic coatings have made catalytic combustion a viable technology for advanced turbine engines and how further research and development may improve catalytic combustion systems to better meet the durability and operability challenges presented by the high-efficiency, ultra-low emissions ATS program goals.

Design and Testing of an Ultra-Low NOx Gas Turbine Combustor

The design and initial rig testing of an ultra-low NO/sub x/ gas turbine combustor primary zone are described. A lean presized, swirl-stabilized combustor was evaluated over a range of pressures up to 10.7 x 10/sup 5/ Pa (10.6 atm) using natural gas. The program goal of reducing NO/sub x/, emissions to 10 ppm (at 15% 0/sub 2/) with coincident low CO emissions was achieved at all combustor pressure levels. Appropriate combustor loading for ultra-low NO/sub x/, operation was determined through emissions sampling within the primary zone. The work described represents a first step in developing an advanced gas turbine combustion system that can yield ultra-low NO/sub x/ levels without the need for water injection and selective catalytic reduction.

Comparison of Trip-Strip/Impingement/Dimple Cooling Concepts at High Reynolds Numbers

Modern industrial combustor liners employ various cooling schemes such as, but not limited to, impingement arrays, trip-strips, and film cooling. With an increasing demand for a higher turbine inlet temperatures and lower emissions, there is less air available to cool the combustor liner. To ensure the required liner durability without compromising engine performance more innovative cooling schemes are required. In the present work, three different cooling concepts, i.e., strip-strips, jet array impingement and dimples, operating at unusually high flow conditions were investigated. There is very little data available in the open literature for the aforementioned cooling schemes in the indicated Reynolds Number range (ReDh >60,000). The wall flow friction characteristics as well as the local heat transfer were measured. The heat transfer coefficients were obtained using a transient liquid crystal technique. The test configurations consisted of a 90° trip-strip surface (only one side turbulated), a fixed staggered array with varying impingement hole sizes, and a fixed staggered dimple pattern. For the Reynolds numbers investigated (26,000< ReDh <360,000), the jet-impingement cooling provided the highest average heat transfer enhancement followed by the trip-strip channel, and then by the dimpled channel. In terms of the overall thermal performance, the dimpled channel tends to stand out as the most effective cooling scheme. This is consistent with findings from other investigators at lower Reynolds numbers.Copyright

Ceramic Stationary Gas Turbine Development Program: Third Annual Summary

The Ceramic Stationary Gas Turbine (CSGT) program has been performed under the sponsorship of the United States Department of Energy, Office of Industrial Technologies and Office of Power Technologies. The objective of the program was to improve the performance of stationary gas turbines in cogeneration by retrofitting uncooled ceramic components into the hot section of the engine. The replacement of previously cooled metallic hot section components with the uncooled ceramics enables improved thermal efficiency, increased output power, and reduced gas turbine emissions. This review summarizes the latest progress on Phase III of the program, which involves 1) preparation for the final in-house CSGT engine test of ceramic blades, nozzles and CFCC liners, and 2) field testing of the CFCC combustor liners at two cogeneration end user sites. The field testing of CFCC combustor liners is now being performed under the Advanced Materials Program, sponsored by DOE, Office of Power Technologies.The Solar Centaur 50S engine, which operates at a turbine rotor inlet temperature (TRIT) of 1010°C, was selected for the developmental program. The program goals include an increase in the TRIT to 1121°C, accompanied by increases in thermal efficiency and output power. This is to be accomplished by the incorporation of ceramic first stage blades and nozzles, and a “hot wall” ceramic combustor liner. The performance improvements are attributable to the increase in TRIT and the reduction in cooling air requirements for the ceramic parts. The “hot wall” ceramic liners also enable a reduction in gas turbine emissions of NOx and CO. This 1121°C TRIT engine test of the ceramic hot section is planned for the first quarter of 2001.The component design and material selection have been previously definitized for the ceramic blades, nozzles and combustor liners. Each of these ceramic component designs was successfully evaluated in short-term engine tests in the Centaur 50S engine test cell facility at Solar. Environmental barrier coatings for the ceramic components are also being optimized. To date, seven field installations of the CSGT Centaur 50S engine totaling over 30,000 hours of operation have been initiated under the program at two industrial cogeneration sites. This paper briefly discusses the recent developmental efforts for the upcoming 1121°C TRIT engine test, but focuses on the various field demonstrations of CFCC combustor liners.Copyright

Engine Testing of a Prototype Low NOx Gas Turbine Combustor

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.Copyright

Full Scale Testing of a Low Swirl Fuel Injector Concept for Ultra-Low NOx Gas Turbine Combustion Systems

The continued development of a low swirl injector for ultra-low NOx gas turbine applications is described. An injector prototype for natural gas operation has been designed, fabricated and tested. The target application is an annular gas turbine combustion system requiring twelve injectors. High pressure rig test results for a single injector prototype are presented. On natural gas, ultra-low NOx emissions were achieved along with low CO. A turndown of approximately 100°F in flame temperature was possible before CO emissions increased significantly. Subsequently, a set of injectors was evaluated at atmospheric pressure using a production annular combustor. Rig testing again demonstrated the ultra-low NOx capability of the injectors on natural gas. An engine test of the injectors will be required to establish the transient performance of the combustion system and to assess any combustor pressure oscillation issues.Copyright

Use of an Extractive Laser Probe for Time-Resolved Mixture Fraction Measurements in a 9 ATM Gas Turbine Fuel Injector

This paper describes the use of a high velocity extractive sampling probe in a gas turbine fuel injector operating at 9 atm. This instrument has the ability to measure the temporal and spatial fluctuations of the mixture fraction. Knowledge of the fuel-air mixing characteristics is necessary to further decrease levels of pollutant emissions such as nitrogen oxides (NOx), and to sustain stable combustion. The extractive probe resolves temporal fluctuations due to the high flow rate through the sampling probe. The residence time of the sample gas in the sampling probe is sufficiently short so that axial diffusion on the relevant time scale can be ignored. Measurements were taken at two operating points: one at a stable low-emissions condition, and one at a condition where pressure oscillations in the combustor were high. At the second operating point, it was found that the frequencies of the pressure oscillations coincided with the frequencies of fluctuation in air-fuel ratio resolved by the probe.© 2001 ASME

Ten Years of DLE Industrial Gas Turbine Operating Experiences

Industrial gas turbine manufacturers began offering engines configured with dry low emissions (DLE) control in 1992. In the past ten years the performance and emissions reductions have been well demonstrated by DLE equipment. To date DLE gas turbines have relied on lean premixed combustion technology to achieve emissions reductions of 8 to 10 fold from “conventional” diffusion flame engines. The significant new content incorporated for DLE combustion systems has required industrial gas turbine manufacturers and users to work with greater synergy to overcome significant challenges. As evidence of this ultimately successful integration, DLE gas turbines are now as common in service as conventional diffusion flame engines. With thousands of DLE units sold one would expect that DLE gas turbines are now a mature product. In many aspects, this is true. However, emissions regulations and other market drivers have continued to change, forcing DLE equipment to continually evolve. A Solar history of DLE gas turbine developments, capabilities, and experiences are provided to give operators background and knowledge to reduce field issues and maximize availability of their DLE gas turbines. Design limitations and problems encountered in the field are discussed along with the steps that were taken to resolve them. Recommendations on DLE engine operation to avoid unscheduled downtime are presented. Design improvements to reduce emissions further and improve system flexibility are summarized.Copyright