Increase In Steam Temperature Research Articles

Evolution law of pulsating seepage and thermal deformation by injecting high‐temperature steam into coal for thermal coalbed methane recovery

AbstractChinese coal reservoirs are characterized by low pressure and low permeability, which need to be enhanced so as to increase production. However, conventional methods for permeability enhancement can only increase the permeability in fractures, but not the ultra‐low permeability in coal matrices. Attempts to enhance such impermeable structures lead to rapid attenuation of gas production, especially in the late stage of gas extraction. Thermal stimulation by injecting high‐temperature steam is a promising method to increase gas production. The critical scientific challenges that still hinder its widespread application are related to the evolution law of permeability of high‐temperature steam in coal and the thermal deformation of coal. In this study, an experimental approach is developed to explore the high‐temperature steam seepage coupled with the thermal deformation in coal under triaxial stress. The tests were conducted using cylindrical coal specimens of ϕ50 mm × 100 mm. The permeability and thermal strain in coal were investigated when high‐temperature steam was injected at 151.11, 183.20, 213.65, and 239.76°C. The experimental results reveal for the first time that as the amount of injected fluid increases, the steam permeability shows periodic pulsation changes. This paper introduces and explains the main traits of this discovery that may shed more light on the seepage phenomenon. When the injected steam temperature increases, the amplitude of pulsating permeability decreases, whereas the frequency increases; meanwhile, the period becomes shorter, the pulsation peak appears earlier, and the stabilization time becomes longer. The average peak permeability shows a “U‐shaped” trend, decreasing first and then increasing as the steam temperature increases. Meanwhile, with the extension of steam injection time, the axial, radial, and volumetric strains of coal show a stage‐wise expansion characteristic at different temperatures of steam injection, except for the radial strains at 151.11°C. A two‐phase flow theory of gas–liquid is adopted to elucidate the mechanism of pulsating seepage of steam. Moreover, the influencing mechanism of inward and outward thermal expansion on the permeability of coal is interpreted. The results presented in this paper provide new insight into the feasibility of thermal gas recovery by steam injection.

H2 production enhancement in underground coal gasification with steam addition: Effect of injection conditions

Hydrogen is a clean energy source, and its use helps to mitigate climate change. Underground coal gasification for hydrogen production is a promising method for countries with abundant coal resources and high hydrogen demand. However, the existing coal-to-hydrogen process underground exhibit low production efficiency. This work proposes the use of swirl flow injection to improve hydrogen production efficiency, and also explores the influence of other injection conditions (oxygen flow rate, steam mass flow and steam temperature) on hydrogen production. For straight flow injection, the effect of steam addition on gasification performance depends on the oxygen flow rate, and the highest H2 production is 14.6 L under 1 L/min oxygen and 1 g/L steam. With a swirl flow injection, H2 production increases with steam addition for both 1 L/min and 2 L/min oxygen, which shows a larger H2 production than straight flow injection. The highest H2 production for swirl flow injection is 19 L under 2 L/min oxygen and 1 g/L steam. An increase in steam temperature barely affects the composition of products but apparently increases the amount of products. The fracture effect of high temperature steam might cause a sudden increase of H2 and CH4 at the late stage.

Numerical simulation of steam flooding in offshore heavy oil reservoir after water flooding

Steam flooding is an effective method to enhance oil recovery in heavy oil reservoirs. However, the influence factors of steam flooding will affect the development of heavy oil reservoir after the traditional water flooding. So the dynamic prediction of steam flooding needs to be performed before the development scheme is implemented. In this study, the 3D reservoir model was established by the reservoir numerical simulation software CMG; Combined with operating parameters of oilfield, the influence of steam temperature, steam injection timing and steam quality on the development effect of L7 block in offshore heavy oil reservoir was studied by using 3D reservoir model. The results show that compared with traditional water flooding, steam flooding has better development effect, and the cumulative oil production can reach 100.673 × 104m3; With the increase of steam temperature and steam quality, the cumulative oil production, incremental oil production and heat efficiency have an increasing trend; This result also suggests that the development method of higher steam temperature and steam quality conforms to the principle of economic development; For steam injection timing, the earlier the steam injection is more conducive to better development results.

Experimental study on condensation heat transfer characteristics of steam in rectangular channels rotating about a parallel axis

• Nu in rotating channel increases with Re but decreases with steam temperature. • Pressure drop in rotating channel increases with Re and steam temperature. • Propose a new heat transfer correlation for steam condensation in rotating channel. In the papermaking industry, a kind of new cylinder dryer with multiple small and rectangular channels are employed to enhance the drying efficiency of drying machine. In practical working conditions, the multi-channel cylinder dryer runs under rotating states that could affect the heat transfer characteristics of the inside two-phase flow. However, the fluid heat transfer characteristics in the multi-channel at rotating states have not been well explored. In this study, a set of rotating experimental system is established to investigate the condensation characteristics and pressure drop changes of steam in rotating rectangular channels. Firstly, the experimental apparatus and the data processing method are described in detail. Then the effects of rotation speed, mass flux and steam temperature on the heat transfer coefficients and pressure drop are studied through experiment. The results show that when Re is small, the heat transfer coefficient first increases and then decreases with the increased Re ω ; when Re is large, the heat transfer coefficient increases with the increased Re ω . Moreover, the heat transfer coefficient decreases as the steam temperature increases. In addition, the pressure drop decreases with the increased Re ω while increases with the increased Re and steam temperature. Finally, a heat transfer model of two-phase flow condensation under rotating states is developed to predict the heat transfer coefficient of steam in rotating multiple channels.

Enviro-exergo-economic analysis and optimization of a nanofiltration-multi effect desalination, power generation and cooling in an innovative trigeneration plant

In this work, an innovative trigeneration system integrating the combined nano filtration - multi effect desalination system to absorption chiller for cooling, steam Rankine cycle for power output, parabolic trough collector, and auxiliary natural gas-fired heater for heat input. Energy, exergoeconomic, and environmental models are developed for the proposed plant. Comparison between systems with/without nanofiltration is conducted. Then, a parametric study is exhibited and discussed. Finally, multi-objective optimization process is carried out using genetic algorithm to achieve minimum investment cost rate and maximum exergetic efficiency. Results showed that the nanofiltration unit addition decreases the overall plant exergy destruction, investment cost rate and annual fuel consumption by 12.11%, 6.88% and 12.1% respectively. Moreover, the annual CO 2 emissions can be enhanced by about 9% with the heating steam temperature of the desalination unit. On the other hand, parametric study revealed that increasing the absorption generator temperature and the desalination unit number of evaporators is recommended from the energetic exegetic, and exergoeconomic points of view. While the plant investment cost per hour is negatively affected by number of evaporators increase. The annual CO 2 emissions avoided can be enhanced by about 9% with the NF-MED heating steam temperature increase. Optimization process showed that the optimal operation conditions can decrease the total product cost rates by 2.94% and increase the exergy efficiency by 5.26% compared to the base system.

High-temperature solar steam generation by MWCNT-HfTe2 van der Waals heterostructure for low-cost sterilization

Conventional steam sterilization for medical equipment requires electricity and significant initial capital cost, impeding its uses in many resource-constrained areas and exposing patients to nosocomial infections. The urgent need for a low-cost and environmentally friendly approach for the sterilization process can be addressed by utilizing abundant solar irradiance and an efficient solar absorber. Herein, for the first time, 1D–2D metallic MWCNTs and HfTe2 van der Waals heterostructure are used for realizing broadband solar absorption with an evaporation efficiency of 87.43% under one sun illumination resulting in an increase in steam temperature to 132 °C in < 20 mins. The facile fabrication process and minimalist design substantially reduced sterilization cost to only ¢0.21 per liter capacity. Furthermore, a proof-of-concept sterilizing demonstration resulted in a 99.04% reduction in E. coli bacteria, exceeding the requirements of the World Health Organization. Such a sterilization system would reduce 2.45 tons of CO2 emissions annually by substituting a 10 L capacity conventional autoclave. Hence, the MWCNT-HfTe2@Cu foam-based medical sterilizing system could be a promising and low-cost sterilization solution in off-grid and resource constrained areas due to its superb sterilizing performance, dramatic capital and operating cost reduction capability, ease of maintenance, and a significant reduction in carbon footprint.

Investigation of steam regeneration strategies for industrial-scale temperature-swing adsorption of benzene on activated carbon

Large-scale separation of substances present at low concentrations is readily performed by adsorption in packed beds that requires recurring energy-intensive regeneration of the adsorbent. The present work uses numerical simulations previously developed for industrial-scale packed-bed benzene sorption on activated carbon with temperature-swing regeneration by steam to investigate the influence of steam properties and regeneration strategy on total energy performance and breakthrough behaviour.It is shown that using saturated steam lowers both the steam mass and energy consumption during regeneration of a fixed amount of benzene, whereas using superheated steam returns the bed to a more fresh-like state after each regeneration stage. The most promising variation tried implies a 19% reduction in the energy consumption. Furthermore, the importance of accounting for the real industrial cycling conditions in the optimization of packed-bed adsorbers is highlighted. It is shown that the participation of different sections of the bed during adsorption varies with the regeneration strategy, but is never as localized as predicted from a model for a fresh bed without cycling. Finally, the present results also show that the effluent purity attained during regeneration increases when high-temperature saturated steam is used, e.g. a 60-degree increase in steam temperature raises the purity by 11%.

Steam oxidation behavior of ZrO2/Cr-coated pure zirconium prepared by plasma electrolytic oxidation followed by filtered cathodic vacuum arc deposition

Plasma electrolytic oxidation (PEO) and filtered cathodic vacuum arc deposition (FCVAD) techniques were employed to fabricate a ZrO2/Cr composite coating on pure zirconium. The steam oxidation properties of bare and ZrO2/Cr-coated pure Zr were performed in water vapor environment at 900–1100 °C. Their morphologies, microstructures and phase constituents before and after steam oxidation were analyzed. Meanwhile, their composition depth profiles were measured by glow discharge optical emission spectroscopy (GDOES). It was found that the mass gain of ZrO2/Cr-coated Zr was about 22–45% of that of bare Zr after 3600 s steam oxidation at 900–1100 °C, and the PEO and FCVAD composite treatments significantly improved the steam oxidation resistance of Zr. After steam oxidation, the phosphorous element in the outer layer of PEO film from phosphate electrolyte diffused into the residual Cr layer, however, most of the phosphorous in the interior of PEO layer was remained although the phosphorus diffusion in the region was accelerated with the increase of steam temperature. The ZrO2 to Zr3O phase transformation in PEO intermediate layer occurred in high temperature steam. Furthermore, the PEO zirconia interlayer suppressed hydrogen permeation into the Zr substrate during steam oxidation at 900–1100 °C.

Thermo-economic optimization of steam injection operation in enhanced oil recovery (EOR) using nano-thermal insulation

Energy loss during steam injection in enhanced oil recovery (EOR) is customarily happened which not only reduces the steam heating value and increases the cost of operation but also leads to severe damages to injection pipes. In order to enhance the delivered heat to the oil deposit, it is common praxis to raise the steam injection rate or its temperature, in spite of the consequent energy loss enhancement. This is because such operations are considered more economical and easier to be applied in comparison to traditional pipe insulation. In this paper, it is tried to quantify the economic effectiveness of such diffused solutions, by means of an empirical apparatus, making a comparison with an advanced insulation technique, which employs nano-materials. Results show that 35% increase in steam injection rate with 35% extra investment only enhanced delivered heat to reservoir up to 7% while it caused 90% more energy loss. On the other hand, 21% increase in steam temperature with 11.5% extra investment enhanced delivered heat to reservoir up to 7.5% while it caused 14% more energy loss. However, implementing nano-thermal insulations could reduce the energy loss from 25% to 44% with an extra investment of less than 3%.

High-Temperature Corrosion Behavior of SUS310 Steels Embedded in Alkali Metal Chloride Salt Mixtures in Air

Higher steam temperature is one of the crucial requirements to increase the efficiency of waste-to-energy (WTE) plants. However, current steam temperature in the WTE plants, up to 450°C, is much lower than that in fossil-fuel power plants which are commonly used up to 650°C. Superheater tubes used in waste incineration plants are exposed in extremely corrosive environments, which contains Cl2, SO2, O2, H2O, CO2 etc. The combustion ash containing not only oxides but also chloride salts and sulfate accelerates the corrosion of alloys and coatings. This is one of the main reasons hindering increase of steam temperature in WTE plants. High-temperature corrosion in such harsh environments are so complicated, and it strongly depends on the plants because waste components varies in different areas. In order to understand a fundamental aspect of the corrosion behavior of heat resistant steels, the corrosion behavior of commercial steels as well as austenitic Fe-20Ni-25Cr based model alloys under an embedding in the simulated ashes at different temperatures lower than the melting temperature of the ashes was investigated.The commercial SUS310STB (base composition Fe-20Ni-25Cr-1Si), QSX5(Fe-20Ni-25Cr-1Mo-3Si), and model alloys of Fe-20Ni-25Cr with and without 2Mo or 2Si (in wt%) were used in this study. The specimens were embedded in the simulated ashes, which composed of CaO-4.5NaCl-4.5wt%KCl or CaO-3.1NaCl-3.96KCl-2.94CaCl2, in an Al2O3 crucible. Corrosion tests were conducted by a box furnace in air for up to 100 h at temperatures ranging from 400 to 580°C. Fig. 1 shows the corrosion mass loss of steels and model alloys as a function of corrosion temperature. In this figure, the results in the ash obtained from the actual plant are also plotted for comparison. Both of simulated ashes are less corrosive comparing to the actual ash and the corrosion mass loss of SUS310STB was much higher than that of QSX5. Based on the corrosion behavior of model alloys, higher corrosion resistance of QSX5 can be attributed to higher Si content in the alloy.The corrosion mass loss in the simulated ashes was low up to about 480°C and it stated to increase at 520°C in both of the simulated ashes, however, it was much lower in CaO-NaCl-KCl than in CaO-NaCl-KCl-CaCl2. The corrosion mass loss in CaO-NaCl-KCl was apparently increased at 580°C, which indicates that the presence of CaCl2 in ash accelerates corrosion. When steels were corroded at 580°C, the corrosion mass loss in CaO-NaCl-KCl-CaCl2 was significantly increased because the applied temperature is higher than the melting point of the ash. Cross-sectional observation of the steels after corrosion test at 580°C in CaO-NaCl-KCl revealed that the alloys formed a sponge-like very porous Fe-oxide scale. Above the sponge-like Fe-oxide scale, a thick CaCrO4 layer was developed. Moreover, K2CrO4 was identified in the corrosion products from EPMA and XRD analysis, suggesting that KCl reacted with a Cr2O3 scale, which resulted in a breakdown of the Cr2O3 scale and generation of chlorine. Because CaCrO4 is considered to be formed by a reaction of Cr-chloride vapor and CaO in the ash, higher evaporation of Cr-chloride might increase the metal consumption at higher temperatures. In the CaCl2 containing ash, the chlorine potential in the atmosphere increases due to oxidation of CaCl2, which might result in further increase in corrosion mass loss even though steels were exposed at the temperatures below melting temperature of the salt. Figure 1

Investigation of Steam Treatment on the Sorption Behavior of Rice Straw Pellets

Agricultural residue is a readily available biomass source for making biofuels. However, complex structure along with low calorific value makes it reluctant to be utilized. This necessitates the pretreatment of biomass to improve its accessibility. In this study, rice straws were treated with saturated steam at 180–200 °C for 5–10 min and pelletized. Results indicated that the pretreatment process could effectively improve the calorific values and enhance the hydrophobicity of the rice straws. The steam explosion process changed the content of chemical components in the biomass materials. With the increase of reaction temperature and retention time, the content of cellulose, hemicelluloses and lignin declined. Comparedwith the raw materials, there was an increase in the calorific value from 16.24 MJ/kg to 17.26 MJ/kg for the steam treated straws. For moisture sorption test under the condition of 30 °C and 90% relative humidity, the equilibrium moisture content dropped from 21% for untreated straw pellets to 14.2% for the steam treated straw pellets treated at 200 °C for 10 min. Moisture adsorption rate reduced along with the increase in steam temperature and retention time. This study demonstrated that steam explosion performed an effective way to improve the characteristics of agricultural residues.

Estimation of creep of the turbine control valve body at increased steam temperature

The influence of the temperature of the supplied steam on the operating and strength characteristics during creep of the control valve body of the steam turbine K-325 is considered. Currently, the valves are operated with steam supply with a pressure of 24 MPa and a temperature of 540°C. The analysis of the effect of increasing the temperature of the supplied steam up to 565°C. The study was carried out in connection with a possible increase in steam temperature to increase the power of the turbine. The temperature and pressure of steam on the walls of the vessel are determined based on the numerical solution of the Navier-Stokes equations in a three-dimensional setting. It was found that an increase in the temperature of the supplied steam has little effect on the nature of the distribution of temperature and pressure on the walls of the valve body. Temperature fields and steam pressure on the walls of the valve body are used to further solve the problems of the strength of the control valve bodies of the K-325 turbine in a stationary mode of operation. The stress-strain state of the valve body of a steam turbine in a stationary mode of robots is numerically determined. The problem was solved by the finite element method in a three-dimensional setting. The results showed that the maximum elastic stresses on the outer surfaces are observed in the region of the upper transition of the inlet pipe. On the inner surfaces, the maximum values of elastic stresses are observed in the area of the branch pipes in front of the control valves. It was determined that an increase in the temperature of the supplied steam up to 565°C insignificantly affects the stress state of the valve body. The creep of the body was calculated using a model of implicit creep with hardening, taking into account the variable and constant creep components. The influence of the temperature of the supplied steam on the creep of the valve body is estimated. The results indicate that an increase in the temperature of the supplied steam by 25°C leads to an increase in creep deformation by a factor of 2.3 after 200 thousand hours of operation. Temperatures, pressures, and equivalent stresses are plotted at the body surfaces and creep curves are plotted at 540°C and 565°C.

Design and analysis of renewable hydrogen production from biogas by integrating a gas turbine system and a solid oxide steam electrolyzer

In this paper, design and performance analysis of a biogas (60%CH4 + 40%CO2) fueled gas turbine (GT) power generation system integrated with a flameless boiler for steam generation for hydrogen production in a solid oxide steam electrolyzer (SOSE) is reported. In this design, the exhaust gases from GT is conducted to a flameless boiler where diluted and preheated exhaust gases are employed as an oxidizer in this process. Using a small amount of biogas in the flameless boiler enables the hybrid system to produce required steam for SOSE process and the whole generated electrical power by GT is employed in SOSE as well to produce hydrogen. The effects of biogas blends and flowrate, turbine inlet temperature (TIT), steam temperature and the electrode characteristics on the performance of the hybrid system are evaluated. The results indicate that by purification of biogas and increasing CH4 concentration up to 80%, the generated electrical power and produced hydrogen of the hybrid system augment 24% and 20% respectively. In GT system, the TIT should be set at the temperatures higher than 1300 K to prepare a desirable circumstance for the operation of flameless mode in the boiler. At the constant electrical power, when steam temperature increases, the overall SOSE potential decreases and consequently the current of the SOSE enhances which result in the enhancement of the overall hydrogen production in high steam temperatures. To increase the steam temperature from 850 K to 1450 K, the rate of overall biogas consumption of the system increases 1% while the amount of overall hydrogen production from SOSE system augments from 0.01 to 0.052 mol/s. The presented analysis in this paper can be employed to perform more analyses to achieve insightful understanding of the green hydrogen production using hybrid systems.

Steam oxidation and mechanical performance of a ferritic–martensitic steel with slurry aluminide coating

AbstractA key route to advancing power plant efficiency is to enhance current steam operating parameters, namely, increase in steam temperature and pressure from the current levels of 540°C and 180 bar to the proposed 700°C (EU) and 300 bar. Conventional ferritic–martensitic steels, while having good mechanical properties and fatigue resistance, do not possess the high‐temperature corrosion resistance for long‐term use, with a temperature limit of ~620°C. Adding aluminide coatings to the surfaces of the steels can improve the oxidation resistance of this class of material through the growth of an Al2O3 scale. One of the major concerns in using coating is the potential deleterious effects on the mechanical properties of the substrate, either through the precipitation of brittle phases or through cracks in the coating. This study compares the microstructural features of slurry aluminide coatings applied to Grade 91 and the change in mechanical performance. The tensile, thermomechanical fatigue and creep test results showed that while the coated samples entered the tertiary creep zone earlier than the uncoated ones, cracking of the coating remained confined to the surface of the specimen. Nanoindentation mapping showed a hardness increase in the coating and within the aluminium diffusion zone, which is related to the exposure time.

Reduction of Deoxynivalenol in Wheat with Superheated Steam and Its Effects on Wheat Quality.

Deoxynivalenol (DON) is the most commonly found mycotoxin in scabbed wheat. In order to reduce the DON concentration in scabbed wheat with superheated steam (SS) and explore the feasibility to use the processed wheat as crisp biscuit materials, wheat kernels were treated with SS to study the effects of SS processing on DON concentration and the quality of wheat. Furthermore, the wheat treated with SS were used to make crisp biscuits and the texture qualities of biscuits were measured. The results showed that DON in wheat kernels could be reduced by SS effectively. Besides, the reduction rate raised significantly with the increase of steam temperature and processing time and it was also affected significantly by steam velocity. The reduction rate in wheat kernels and wheat flour could reach 77.4% and 60.5% respectively. In addition, SS processing might lead to partial denaturation of protein and partial gelatinization of starch, thus affecting the rheological properties of dough and pasting properties of wheat flour. Furthermore, the qualities of crisp biscuits were improved at certain conditions of SS processing.

Cycle improvement and hydrogen steam superheating at Mutnovsky geothermal power plant

This study is aimed at a possibility of hydrogen production and hydrogen steam superheating at a single-flash 50 MW Mutnovsky geothermal power plant stage 1. A modification by introduction of a low-pressure single-flash unit utilizing energy of the separated liquid is proposed, and the integrated single- and double-flash cycle is analyzed. The second flash process gives a maximum possible increase of the installed capacity on 11.1 MW for the flash temperature of 92 °C, and 9 MW for 120 °C. Currently the plant does not use 12.3% of the geothermal steam for electricity generation, partly due to demand side management from a grid operator. Excess power can be used for water electrolysis and for each 1% of saved steam 92 t of H2 can be produced annually. Hydrogen combustion in a high temperature hydrogen-oxygen steam generator can be used for steam superheating in a second flash process, achieving the increase of steam temperature at the low pressure turbine inlet by 20–30 K, and an increase of steam dryness at the turbine outlet by 2–4%. Additional available power rises by 5–10% (0.5–0.9 MW) and overall thermal efficiency of the plant can be increased from 10% to 12.5%.

Effect of Flue Gas Recirculation on Reheated Steam Temperature of a 1000MW Ultra-supercritical Double Reheat Boiler

In view of the problem that the reheat steam temperature is lower than the design value in the operation of a 1000MW ultra-supercritical double reheat boiler in a power plant, this paper puts forward the method of flue gas recirculation (FGR) to improve it. Two schemes are put forward:the extraction of flue gas from the economizer or the draft fan to the bottom burner of the furnace. Indifferentload conditions,using the standard method of boiler thermodynamic calculation,the influence of different FGR schemes on boiler operation parameters is calculated. The results show that above FGR schemescan obviously improve thereheat steam temperature; with the increase of the amount of recirculating gas, the rise of the reheat steam temperature increases; with the decrease of the load, the influence of FGR on steam temperature increase; the scheme of extracting recirculating flue gas from the economizer outlet has little effect on the boiler efficiency, which is more suitable for the boiler, and the reasonableFGR rate is about 10%.

Fireside Corrosion of Ni Base Self-Fluxing Alloy Coatings in WtE Plant: Effect of Flue-Gas and Metal Temperature

Increase in the efficiency of energy recovery facilities is one of the challenges facing waste-to-energy (WtE) operators in the EU. To achieve this target, one option is optimization of the water/steam cycle to increase electrical efficiency. Nevertheless, increase in steam temperature in heat exchanger tubes results in increased fireside corrosion risks, particularly in superheater tubes, where severe corrosion loss of materials, frequent shutdowns for repairs and high operational costs occur. In this study, two heat-treated self-fluxing Cr–Mo–Si–B–Ni base alloys containing, respectively, 15.6 and 16.4 wt.% Cr, were applied to low- and high-temperature pendant superheater tubes (LTSH and HTSH). Detailed analyses for flue-gas and metal temperatures in service at different locations of the pendant tubes (around 850 and 400 °C, respectively) and analyses of deposits collected on both tubes (Na, K, Ca, Si, Zn, Pb, Cl, S) were conducted. Both coatings exhibited a corrosion rate close to ones reported for Inconel 625 in similar conditions. Localized corrosion was found and associated with molten phase-assisted corrosion mechanism damaging Si-rich protective layer. Correlations between corrosion rate and %Cr in the coating, T flue-gas, T metal and amount of molten phase in deposit are presented.

Weldability and weld performance of candidate nickel based superalloys for advanced ultrasupercritical fossil power plants

Fossil fuel will continue to be the major source of energy for the foreseeable future. To meet the demand for clean and affordable energy, an increase in the operating efficiency of fossil fired power plants is necessary. There are several initiatives worldwide to achieve efficiencies >45%HHV through an increase in steam temperature (700–760°C) and pressure (27.6–34.5 MPa). Realising this goal requires materials with excellent creep rupture properties and corrosion resistance at elevated temperatures. Two previous papers addressed the welding and weldability of ferritic and austenitic stainless steels. Welding and weldability of nickel based alloys will be discussed in a two-part paper. In this paper, the primary focus will be on the behaviour of candidate nickel based alloys that are being proposed in advanced ultrasupercritical power plants and with regard to weldability (Part I) and cross-weld creep performance (Part II).

Weldability and weld performance of candidate nickel base superalloys for advanced ultrasupercritical fossil power plants part I: fundamentals

Fossil fuel will continue to be the major source of energy for the foreseeable future. To meet the demand for clean and affordable energy, an increase in the operating efficiency of fossil fired power plants is necessary. There are several initiatives worldwide to achieve efficiencies >45% higher heating value (HHV) through an increase in steam temperature (700 to 760°C) and pressure (27.6 to 34.5 MPa). Realising this goal requires materials with excellent creep rupture properties and corrosion resistance at elevated temperatures. In order to accomplish this, three classes of materials have been identified: creep strength enhanced ferritic steels, austenitic stainless steels and nickel base superalloys. Although new alloys have been designed and developed to meet this need, welding can have a significant and often detrimental effect on the required mechanical and corrosion resistant properties. Two previous papers addressed the welding and weldability of ferritic and austenitic stainless steels. Welding and weldability of nickel base alloys will be discussed in a two part paper. In this paper, the primary focus will be on the fundamentals of welding and weldability of Ni base superalloys.