effects of oxidation in steam turbines
97968890
Steam Oxidation and Chromia Evaporation in Ultrasupercritical Steam Boilers and Turbines
U.S. Department of Energy's goals include power generation from coal at 60% efficiency, which requires steam conditions of up to 760 degC and 340 atm, so called ultra supercritical (USC) conditions. Evaporation of protective chromia scales is expected to be a primary corrosion mechanism. A methodology to calculate Cr evaporation rates from chromia scales was developed and combined with Cr diffusion calculations within the alloy (with a constant flux of Cr leaving the alloy from evaporation) to predict Cr concentration profiles and to predict the time until breakaway oxidation. At the highest temperatures and pressures, the time until breakaway oxidation was predicted to be quite short for the turbine blade, and of concern within the steam pipe and the higher temperature portions of the superheater tube. Alloy additions such as Ti may allow for a reduction in evaporation rate with time, mitigating the deleterious effects of chromia evaporation.
Gordon R Holcomb
67822279
SUPERALLOYS FOR ULTRA SUPERCRITICAL STEAM TURBINES OXIDATION BEHAVIOR
Goals of the U.S. Department of Energy's Advanced Power Systems Initiatives include power generation from coal at 60% efficiency, which requires steam conditions of up to 760 degC and 340 atm, so called ultra supercritical (USC) steam conditions. One of the important materials performance considerations is steam side oxidation resistance. Evaporation of protective chromia scales is expected to be a primary corrosion mechanism under USC conditions. A methodology to calculate Cr evaporation rates from chromia scales with cylindrical geometries was developed that allows for the effects of CrO2(OH)2 saturation within the gas phase. This approach was combined with Cr diffusion calculations within the alloy (with a constant flux of Cr leaving the alloy from evaporation) to predict Cr concentration profiles as a function of exposure time and to predict the time until the alloy surface concentration of Cr reaches zero. This time is a rough prediction of the time until breakaway oxidation. A hypothetical superheater tube, steam pipe, and high pressure turbine steam path was examined. At the highest temperatures and pressures, the time until breakaway oxidation was predicted to be quite short for the turbine blade, and of concern within the steam pipe and the higher temperature portions of the superheater tube. The predicted time until breakaway oxidation increases dramatically with decreases in temperature and total pressure. Possible mitigation techniques were discussed, including those used in solid oxide fuel cell metallic interconnects (lowering the activity of Cr in the oxide scale by adding Mn to the alloy) and thermal barrier coating use on high pressure turbine blades for both erosion and chromia evaporation protection.
Gordon R Holcomb
137706963
Steam Oxidation and Chromia Evaporation in Ultra Supercritical Steam Boilers and Turbines
U.S. Department of Energy's goals include power generation from coal at 60% efficiency, which requires steam conditions of up to 760 {degree sign}C and 340 atm, so called ultra supercritical (USC) conditions. Evaporation of protective chromia scales is expected to be a primary corrosion mechanism. A methodology to calculate Cr evaporation rates from chromia scales was developed and combined with Cr diffusion calculations within the alloy (with a constant flux of Cr leaving the alloy from evaporation) to predict Cr concentration profiles and to predict the time until breakaway oxidation. At the highest temperatures and pressures, the time until breakaway oxidation was predicted to be quite short for the turbine blade, and of concern within the steam pipe and the higher temperature portions of the superheater tube. Alloy additions such as Ti may allow for a reduction in evaporation rate with time, mitigating the deleterious effects of chromia evaporation.
Gordon R Holcomb
136683900
The Effects of Cold Work on the Microstructure and Mechanical Properties of Intermetallic Strengthened Alumina Forming Austenitic Stainless Steels
In order to achieve energy conversion efficiencies of >50 pct for steam turbines/boilers in power generation systems, materials are required that are both strong and corrosion resistant at >973 K (700 degC) and economically viable. Austenitic steels strengthened with Laves phase, NiAl and Ni3Al precipitates, and alloyed with aluminum to improve oxidation resistance, are potential candidate materials for these applications. The microstructure and microchemistry of recently developed alumina forming austenitic stainless steels have been characterized by scanning electron microscopy, transmission electron microscopy, and synchrotron X ray diffraction. Different thermo mechanical treatments were performed on these steels to improve their mechanical performance. These reduced the grain size significantly to the nanoscale ~100 nm) and the room temperature yield strength to above 1000 MPa. A solutionizing anneal at 1473 K (1200 degC) was found to be effective for uniformly redistributing the Laves phase precipitates that form upon casting.
Metallurgical and Materials Transactions A
Bin-hao Hu Geneva Trotter Ian Baker Michael K Miller L Yao Si Chen Zhonghou Cai
97808988
Large Eddy Simulations of Hydrogen Oxidation at Ultra Wet Conditions in a Model Gas Turbine Combustor Applying Detailed Chemistry
Humidified gas turbines (HGT) offer the attractive possibility of increasing plant efficiency without the cost of an additional steam turbine as is the case for a combined gas steam cycle. In addition to efficiency gains, adding steam into the combustion process reduces NOx emissions. It increases the specific heat capacity (hence, lowering possible temperature peaks) and reduces the oxygen concentration. Despite the thermophysical effects, steam alters the kinetics and, thus, reduces NOx formation significantly. In addition, it allows operation using a variety of fuels, including hydrogen and hydrogen rich fuels. Therefore, ultra wet gas turbine operation is an attractive solution for industrial applications. The major modification compared to current gas turbines lies in the design of the combustion chamber, which should accommodate a large amount of steam without losing in stability. In the current study, the premixed combustion of pure hydrogen diluted with different steam levels is investigated. The effect of steam on the combustion process is addressed using detailed chemistry. In order to identify an adequate oxidation mechanism, several candidates are identified and compared. The respective performances are assessed based on laminar premixed flame calculations under dry and wet conditions, for which experimentally determined flame speeds are available. Further insight is gained by observing the effect of steam on the flame structure, in particular HO2 and OH* profiles. Moreover, the mechanism is used for the simulation of a turbulent flame in a generic swirl burner fed with hydrogen and humidified air. Large eddy simulations (LES) are employed. It is shown that by adding steam, the heat release peak spreads. At high steam content, the flame front is thicker and the flame extends further downstream. The dynamics of the oxidation layer under dry and wet conditions is captured; thus, an accurate prediction of the velocity field, flame shape, and position is achieved. The latter is compared with experimental data (PIV and OH* chemiluminescence) The reacting simulations were conducted under atmospheric conditions. The steam air ratio was varied from 0% to 50% [DOI: 10.1115/1.4007718] (Less)
Oliver S Kruger Steffen Terhaar Christian Oliver Paschereit Christophe Duwig
198388888
Elevated temperature low cycle fatigue behaviour of Haynes 282 and its correlation with microstructure Effect of ageing conditions
Abstract In this paper, total strain controlled high temperature (760 degC) low cycle fatigue (HTLCF) behaviour (at 0.5% strain amplitude) of a new g' strengthened wrought Ni based superalloy (Haynes 282) for various ageing conditions is presented for the first time, emphasizing the microstructural effects. Haynes 282 is a promising material for hot gas path components of ultra supercritical steam turbines due to its adequate fatigue property at elevated temperatures, along with high creep and oxidation resistance. Various microstructures were generated by varying ageing time (1 day, 6 days and 9 days) and temperature (650 degC and 760 degC) While continuous cyclic hardening behaviour was witnessed for lower aging temperature (650 degC) predominantly cyclic softening after initial hardening through few cycles was observed for higher aging temperature (760 degC) due to formation of more number of larger size voids and secondary cracks in the later specimen during the testing (as characterized by X ray tomography) Underlying deformation mechanisms (characterized through TEM) and fracture modes (characterized through SEM, EDS) were correlated to alloy's microstructures under various HTLCF conditions; distinct differences were observed between the two ageing temperatures. While 650 degC, 9 days ageing condition showed primarily signatures of g' shearing, 760 degC, 9 days ageing condition showed primarily the Orowan mechanism of deformation. For 650 degC ageing condition, predominantly intergranular fracture mode has been observed, which is attributed to the presence of brittle primary MC particles on the boundaries. Whereas for the 760 degC ageing condition, the fracture mode remained predominantly transgranular because it involves less crack deflection through its path. Plastic strain energy density based life prediction model were used to predict fatigue life. Close agreement between calculated and measured life indicates validity of these models for the present material.
Materials Science and Engineering: A
Shreya Mukherjee Kaustav Barat S Sivaprasad S Tarafder Sujoy Kumar Kar
187798287
Large Eddy Simulations of Hydrogen Oxidation at Ultra Wet Conditions in a Model Gas Turbine Combustor Applying Detailed Chemistry
Humidified Gas Turbines (HGT) offer the attractive possibility of increasing the plant efficiency without the cost of an additional steam turbine, as is the case for a combined gas steam cycle. In addition to efficiency gains, adding steam into the combustion process reduces NOx emissions. It increases the specific heat capacity (hence, lowers possible temperature peaks) and reduces the oxygen concentration. Despite the thermo physical effects, steam alters the kinetics, and thus, reduces NOx formation significantly. In addition, it allows operation using a variety of fuels, including hydrogen and hydrogen rich fuels. Therefore, ultra wet gas turbine operation is an attractive solution for industrial applications. The major modification compared to current gas turbines lies in the design of the combustion chamber, which should accommodate a large amount of steam without losing in stability. In the current study, the premixed combustion of pure hydrogen diluted with different steam levels is investigated. The effect of steam on the combustion process is addressed using detailed chemistry. In order to identify an adequate oxidation mechanism, several candidates are identified and compared. The respective performances are assessed based on laminar premixed flame calculations under dry and wet conditions, for which experimentally determined flame speeds are available. Further insight is gained by observing the effect of steam on the flame structure, in particular HO2 and OH* profiles. Moreover, the mechanism is used for the simulation of a turbulent flame in a generic swirl burner fed with hydrogen and humidified air. Large Eddy Simulations (LES) are employed. It is shown that by adding steam, the heat release peak spreads. At high steam content, the flame front is thicker and the flame extends further downstream. The dynamics of the oxidation layer under dry and wet conditions is captured, thus, an accurate prediction of the velocity field, flame shape and position is achieved. The latter is compared with experimental data (PIV and OH* chemiluminescence) The reacting simulations were conducted under atmospheric conditions. The steam air ratio was varied from 0% to 50%(c) 2012 ASME
Oliver S Kruger Steffen Terhaar Christian Oliver Paschereit Christophe Duwig
99523049
Clean combustion in gas turbines: challenges and technical responses a review
Combustion turbine and gas turbine/steam combined cycle plants have to satisfy requirements for high combustion efficiency and low pollutant emissions, in order to meet environmental regulations. Modification of the combustion process is the most cost effective way of reducing NO x HC, and CO emissions. The processes of NO x formation and destruction, and CO oxidation, are reviewed with reference to advanced classes of gas turbine combustors: Ultra Lean Premix, and Topping Combustors in directly and indirectly coal fired combined cycles. Engineering solutions to the problem of low NO x combustion are discussed, with particular attention to the effects on combustor design of fuel type and the nature of the combined cycle
Janos M Beer
134651786
Characterization of high temperature fatigue mechanisms in Haynes 282 nickel based superalloy
Electric power needs will only grow over the next decades as more humans ascend from poverty into the middle class. Currently, the majority of electric power is generated by burning fossil fuels. To help mitigate the undesirable effects of burning fossil fuels research is being done to increase the efficiency of power produced. In order to increase the efficiency of power production, the operating temperature of steam turbines must be increased, which presents a materials challenge. Haynes 282 is a nickel based superalloy which has been proposed as a potential rotor alloy for steam turbines operating at high temperature (760C) Other authors have previously looked at creep, oxidation, low cycle fatigue and other properties of Haynes 282; however, lacking from the literature are studies on the fatigue crack growth mechanisms in Haynes 282. This project investigated Haynes 282 from a fatigue crack growth perspective with an aim to fill this literature gap and asses the utility of Haynes 282 as a steam turbine rotor alloy. Friday, October 24, 2014 2:00 PM, Rodgers 226 School of Mechanical, Industrial, and Manufacturing Engineering
K A Rozman
110821672
Otsenka znachimosti vliianiia termodinamicheskikh faktorov na effektivnost' raboty tverdooksidnykh toplivnykh elementov
Technologies of direct conversion of the fuel energy into electrical power are an upcoming trend in power economy. Over the last decades a number of countries have created industrial prototypes of power plants on fuel elements (cells) while fuel cells themselves became a commercial product on the world energy market. High electrical efficiency of the fuel cells allows predictting their further spread as part of hybrid installations jointly with gas and steam turbines which specifically enables achieving the electrical efficiency greater than 70 Nevertheless, investigations in the area of increasing efficiency and reliability of the fuel cells continue. Inter alia, research into the effects of oxidizing reaction thermodynamic parameters, fuel composition and oxidation reaction products on effectiveness of the solid oxide fuel cells (SOFC) is of specific scientific interest. The article presents a concise analysis of the fuel type effects on the SOFC efficiency. Based on the open publications experimental data and the data of numerical model studies, the authors adduce results of the statistical analysis of the SOFC thermodynamic parameters effect on the effectiveness of its functioning as well as of the reciprocative factors of these parameters and gas composition at the inlet and at the outlet of the cell. The presented diagrams reflect dimension of the indicated parameters on the SOFC operation effectiveness. The significance levels of the above listed factors are ascertained. Statistical analysis of the effects of the SOFC functionning process thermodynamical, consumption and concentration parameters demonstrates quintessential influence of the reciprocative factors (temperature flow rate and pressure flow rate) and the nitrogen N 2 and oxygen O 2 concentrations on the operation efficiency in the researched range of its functioning. These are the parameters to be considered on a first priority basis while developing mathematical models for optimizing the solid oxide fuel cells operating modes.
V A Sednin A A Chichko