Search Results for gas mixtures

The high-temperature oxidation of Fe-9Cr-1Mo steel in a CO 2 environment, with varying oxygen content (0.6-3%), was investigated at 700°C. While the steel heavily oxidized in pure CO 2 , the oxidation mass gain decreased significantly with increasing oxygen content. Microscopic analysis revealed the formation of Fe-rich nodules with an internal Cr-carbide layer beneath them. Notably, the number of nodules decreased with increasing oxygen content but remained independent of the oxidation time. To explain these observations, the authors propose that “intrinsic” defects within the initially formed protective Cr 2 O 3 scale facilitated gas permeation. This mechanism is believed to be responsible for the observed dependence of nodule formation on the oxygen content in the gas mixtures.

A major cost contributor of P91 pipe welding is the vital requirement of ensuring proper protection of the root or first pass of the weld from oxidation through the use of an inert gas blanket, i.e. backing gas. The necessity for oxidation protection negatively impacts the cost of both weld set-up and the actual welding process of P91 pipe fabrication. In an effort to decrease the associated costs of welding P91, Fluor Corporation has invested in significant research and extensive field-testing to develop the wire/gas mixture that contributes to the breakthrough in welding P91 with “No Backing Gas (NBG)”. Combining this novel technique with the semiautomatic GMAW-S (using inverter technology with a controlled transfer) eliminates all cost associated with the need to provide a backing gas, including installation of purge dams, backing gas, and man-hours associated with implementing these activities.

The INCONEL filler metals 72 and 72M have been utilized significantly for weld overlay protection of superheaters and reheaters, offering enhanced corrosion and erosion resistance in this service. Laboratory data conducted under simulated low-NOx combustion conditions, field exposure experience, and laboratory analysis (microstructure, chemical composition, overlay thickness measurements, micro-hardness) of field-exposed samples indicate that these overlay materials are also attractive options as protective overlays for water wall tubes in low-NOx boilers. Data and field observations will be compared for INCONEL filler metals 72, 72M, 625 and 622.

Oxyfuel combustion is considered as one of the most promising technologies to facilitate CO 2 capture from flue gases. In oxyfuel combustion, the fuel is burned in a mixture of oxygen and recirculated flue gas. Flue gas recirculation increases the levels of fireside CO 2 , SO 2 , Cl and moisture, and thus promotes fouling and corrosion. In this paper the corrosion performance of two superheater austenitic stainless steels (UNS S34710 and S31035) and one Ni base alloy (UNS N06617) has been determined in laboratory tests under simulated oxyfuel conditions with and without a synthetic carbonate based deposits (CaCO 3 - 15 wt% CaSO 4 , CaCO 3 - 14wt% CaSO 4 - 1 KCl) at 650 and 720°C up to 1000 hours. No carburization of the metal substrate was observed after exposure to simulated oxyfuel gas atmospheres without deposit, although some carbon enrichment was detected near the oxide metal interface. At 720°C a very thin oxide formed on all alloy surfaces while the weight changes were negative. This negative weight change observed is due to chromium evaporation in the moist testing condition. At the presence of deposits, corrosion accelerated and considerable metal loss of austenitic alloys was observed at 720°C. In addition, clear carburization of austenitic steel UNS S34710 occurred.

The efforts of the European Union and Germany in particular to realize the transformation towards a climate-neutral economy over the coming decades have the establishing of a hydrogen economy as a fundamental milestone. This includes production, import, storage, transportation and utilization of great amounts of gaseous hydrogen in existing and new infrastructure. Metallic materials, mainly steels, are the most widely used structural materials in the various components of this supply chain. Therefore, the accelerated use of hydrogen requires the qualification of materials (i.e., ensuring they are hydrogen-ready) to guarantee the sustainable and safe implementation of hydrogen technologies. However, there is currently no easily applicable and standardized method to efficiently determine the impact of gaseous hydrogen on metallic materials. The few existing standards describe procedures that are complex, expensive, and only available to a limited extent globally. This article outlines the key milestones towards standardizing an efficient testing method as part of the TransHyDE flagship project. This new approach enables testing of metallic materials in gaseous hydrogen using tubular specimens. It uses only a fraction of the hydrogen required by the traditional autoclave method, significantly reducing costs associated with technical safety measures. Among the topics to be discussed are the factors influencing the test procedure, including geometrical considerations, surface quality, gas purity and strain rate.

Advanced ultra-supercritical (USC) steam power plants promise higher efficiencies and lower emissions. The U.S. Department of Energy (DOE) aims to achieve 60% efficiency in coal-based power generation, requiring steam temperatures of up to 760°C. This study presents ongoing research on the oxidation behavior of candidate materials for advanced steam turbines, with a focus on estimating chromium evaporation rates from protective chromia scales. Due to the high velocities and pressures in advanced steam turbines, evaporation rates of CrO 2 (OH) 2 (g) are predicted to reach up to 5 × 10 −8 kg m −2 s −1 at 760°C and 34.5 MPa, corresponding to a solid chromium loss of approximately 0.077 mm per year.

Steam oxidation of a novel austenitic steel, of which composition is Fe-20Cr-30Ni-2Nb (at.%), has been conducted at 973 K to evaluate steam oxidation resistance based on detail analyses of scale morphology and scale growth. Two types of scale morphologies were observed in the solution treated sample, depending on the grain of the steel. Although thin duplex scale with the Cr-rich layer was formed in the early stage, most of the surface was covered with thick duplex scale which consists of magnetite as the outer scale and the mixture of Fe-Cr spinel and metallic Ni as the inner scale. On the other hand, surface morphology of the oxide scale was independent of grain of the steel and thick duplex scale as seen on the solution treated sample was formed on the pre-aged sample. Steam oxidation resistance of the steel is almost the same as that of commercial austenitic steels and it can be improved by the surface treatment such as shot peening. Based on the results, this steel has both enough creep rupture strength and good steam oxidation resistance for A-USC power plants.

The Advanced Ultrasupercritical (A-USC) power plants are aimed to operate at steam inlet temperatures greater than 700°C; consequently, a complete materials overhaul is needed for the next-generation power plants. HAYNES 282, a gamma-prime strengthened alloy, is among the leading candidates because of its unique combination of properties, superior creep and LCF strength, fabricability and thermal stability. It is currently being evaluated in wrought and cast forms for A-USC turbine rotors, casings, boiler tubings, header, and valves. The candidate materials for A-USC applications not only require oxidation resistance for steam cycles but fireside corrosion resistance to coal ash is also of an extreme importance. In order to study the effect of both environments on the performance of 282 alloy, the alloy was exposed for extended periods in various oxidizing environments, such as air, air plus water vapor (10%), and 17bar steam up to 900°C. The fireside corrosion resistance of 282 alloy was evaluated at 700°C in synthetic coal ash and at 843°C in alkali salt deposits in a controlled gaseous environment.

Model alloys of Fe-20Cr and Ni-20Cr (all compositions in weight %) and variants containing small amounts of Si or Mn were exposed to Ar-20CO 2 and Ar-20CO 2 -H 2 O (volume %) at 650 or 700°C. Protective Cr 2 O 3 scale was more readily formed on Fe-20Cr than Ni-20Cr, as a result of the different alloy diffusion coefficients. Silicon additions slowed chromia scale growth, promoting passivation of both alloy types. Water vapour accelerated chromia scaling, but slowed NiO growth.

With nearly half of the world's electricity generation fueled by coal and an increasing focus on limiting carbon dioxide emissions, several technologies are being evaluated and developed to capture and prevent such emissions while continuing to use this primary fossil energy resource. One method aimed at facilitating the capture and processing of the resulting carbon dioxide product is oxy-combustion. With appropriate adjustments to the process, the approach is applicable to both new and existing power plants. In oxy-combustion, rather than introducing ambient air to the system for burning the fuel, oxygen is separated from the nitrogen and used alone. Without the nitrogen from the air to dilute the flue gas, the flue gas volume leaving the system is significantly reduced and consists primarily of carbon dioxide and water vapor. Once the water vapor is reduced by condensation, the purification and compression processes otherwise required for carbon dioxide transport and sequestration are significantly reduced. As an introduction to and overview of this technology, the paper summarizes the basic concepts and system variations, for both new boiler and retrofit applications, and also serves as an organized review of subsystem issues identified in recent literature and publications. Topics such as the air separation units, flue gas recirculation, burners and combustion, furnace performance, emissions, air infiltration issues, and materials issues are introduced.

Inconel Filler Metal 72 (FM 72) and Incoclad 671/800H co-extruded tubing have been successfully used for over 20 years to protect boiler tubing from high-temperature degradation. A newer alloy, FM 72M, offers superior weldability and the lowest corrosion rate in simulated low NOx environments. Both FM 72 and 72M show promise in addressing challenges like circumferential cracking and corrosion fatigue in waterwall tubing overlays. Additionally, 72M’s superior wear resistance makes it ideal for replacing erosion shields in superheater and reheater tubing. Beyond improved protection, these alloys exhibit increased hardness and thermal conductivity over time, leading to reduced temperature difference across the tube wall and consequently, enhanced boiler efficiency and lower maintenance costs. This paper discusses the historical selection of optimal alloys for waterwall and upper boiler tubing overlays, analyzes past failure mechanisms, and highlights the key properties of successful choices like FM 72 and 72M.

A thorough understanding of interactions between graphite and fluoride fuel salts is crucial, as graphite is a promising candidate for the moderator of molten salt reactors. This study investigates the infiltration of fluoride fuel salts into graphite and the fluorination of graphite by these salts under various pressures and temperatures. A high-pressure salt infiltration test apparatus was developed to examine the infiltration of NaF-KF-UF 4 and NaF-BeF 2 -UF 4 -ZrF 4 fuel salts into two types of graphite at high temperatures. For tests using NaF-BeF 2 -UF 4 -ZrF 4 , two different temperatures were selected to assess the impact of temperature on threshold pressure. The study observed salt infiltration into graphite at pressures exceeding its threshold pressure, and the threshold pressure for infiltration was lower at the higher temperature. In addition, the formation of carbon fluorides on the surface of post-test graphite specimens was identified.

High Cr ferritic steels have been developed for the large components of fossil power plants due to their excellent creep resistance, low thermal expansion, and good oxidation resistance. Development works to improve the operating temperature of these steels mainly focused on the high mechanical properties such as solid solution strengthening and precipitation hardening. However, the knowledge of the correlation between Laves phase precipitation and oxidation behavior has not clarified yet on 9Cr ferritic steels. This research will be focused on the effect of precipitation of Laves phase on steam oxidation behavior of Fe-9Cr alloy at 923 K. Niobium was chosen as the third element to the Fe- 9Cr binary system. Steam oxidation test of Fe-9Cr (mass%) alloy and Fe-9Cr-2Nb (mass%) alloy were carried out at 923 K in Ar-15%H 2 O mixture for up to 172.8 ks. X-ray diffraction confirms the oxide mainly consist of wüstite on the Fe-9Cr in the initial stage while on Nb added samples magnetite was dominated. The results show that the Fe-9Cr- 2Nb alloy has a slower oxidation rate than the Fe-9Cr alloy after oxidized for 172.8 ks

The use of high-nickel superalloys has greatly increased among many industries. This is especially the case for advanced coal-fired boilers, where the latest high temperature designs will require materials capable of withstanding much higher operating temperatures and pressures than current designs. Inconel alloy 740H (UNS N07740) is a new nickel- based alloy that serves as a candidate for steam header pipe and super-heater tubing in coal-fired boilers. Alloy 740H has been shown to be capable of withstanding the extreme operating conditions of an advanced ultra-super-critical (AUSC) boiler, which is the latest boiler design, currently under development. As with all high nickel alloys, welding of alloy 740H can be very challenging, even to an experienced welder. Weldability challenges are compounded when considering that the alloy may be used in steam headers, where critical, thick-section and stub-to-header weld joints are present. This paper is intended to describe the proper procedures developed over years of study that will allow for ASME code quality welds in alloy 740H with matching composition filler metals.

During commissioning of recently built modern, and highly efficient coal-fired power plants, cracks were detected after very short time of operation within the welds of membrane walls made from alloy T24. The root cause analysis revealed transgranular and mostly intergranular cracks adjacent to the heat affected zone beside weld joints. At that time, the degradation mechanism was rather unclear, which led to an extended root cause analysis for clarification of these failures. The environmentally assisted cracking behavior of alloy T24 in oxygenated high-temperature water was determined by an experimental test program. Hereby, the cracking of 2½% chromium steel T24 and 1% chromium steel T12 were determined in high-temperature water depending on the effect of water chemistry parameters such as dissolved oxygen content, pH, and temperature, but also with respect to the mechanical load component by residual stresses and the microstructure. The results clearly show that the cracking of this low-alloy steel in oxygenated high-temperature water is driven by the dissolved oxygen content and the breakdown of the passive corrosion protective oxide scale on the specimens by mechanical degradation of the oxide scale as fracture due to straining. The results give further evidence that a reduction of the residual stresses by a stress relief heat treatment of the boiler in combination with the strict compliance of the limits for dissolved oxygen content in the feed water according to water chemistry standards are effective countermeasures to prevent environmentally assisted cracking of T24 membrane wall butt welds during plastic strain transients.

Using oxygen, rather than air, in coal-fired boilers has been studied for several years as a strategy to reduce NOx and concentrate CO 2 for capture. In combination with flue gas recirculation, higher levels of CO 2 are expected but increased H 2 O and SO 2 levels also may occur. In order to understand the role of substrate composition on corrosion, a combination of commercial and model alloys were investigated with synthetic coal ash and gas compositions simulating air- and oxyfiring environments. Exposure temperatures ranged from 600°-800°C to cover current operating temperatures up to advanced ultrasupercritical conditions. Using 500h exposures, no consistent negative effect was found for switching to the oxy-firing environment with the same synthetic ash. For model Fe-Cr alloys, 30%Cr was needed to form a thin protective reaction product across this temperature range. Among the commercial stainless steels, 310-type stainless steel showed low reaction rates with the maximum attack at 650°C. At higher temperatures, the depth of attack on Fe-base type 310 stainless steel was less than for Ni-base alloy 740. Initially, this difference was attributed to the Al and Ti additions in alloy 740. However, cast and hot rolled model Ni-18Cr and -22Cr alloys with various Al and Ti additions showed decreased metal loss with increasing Al and Ti additions in the oxy-firing environment at 700° and 800°C. As expected, metal loss was very sensitive to Cr content. A second set of model alloys also examined the effect of Co and Mo.

ENCIO (European Network for Component Integration and Optimization) is a European project aiming at qualifying materials, components, manufacturing processes, as well as erection and repair concepts, as follow-up of COMTES700 activities and by means of erecting and operating a new Test Facility. The 700°C technology is a key factor for the increasing efficiency of coal fired power plants, improving environmental and economic sustainability of coal fired power plants and achieving successful deployment of carbon capture and storage technologies. The ENCIO-project is financed by industrial and public funds. The project receives funding from the European Community's Research Fund for Coal and Steel (RFCS) under grant agreement n° RFCPCT-2011-00003. The ENCIO started on 1 July 2011. The overall project duration is six years (72 months), to allow enough operating hours, as well as related data collection, investigations and evaluation of results. The ENCIO Test Facility will be installed in the “Andrea Palladio” Power Station which is owned and operated by ENEL, located in Fusina, very close to Venice (Italy). The Unit 4 was selected for the installation of the Test Facility and the loops are planned for 20.000 hours of operation at 700°C. The present paper summarizes the current status of the overall process design of the thick-walled components, the test loops and the scheduled operating conditions, the characterizations program for the base materials and the welded joints, like creep and microstructural analysis also after service exposure.

The mechanical behavior of a cast form of an advanced austenitic stainless steel, CF8C-Plus, is compared with that of its wrought equivalent in terms of both tensile and creep-rupture properties and estimated allowable stress values for pressurized service at temperatures up to about 850°C. A traditional Larson-Miller parametric model is used to analyze the creep-rupture data and to predict long-term lifetimes for comparison of the two alloy types. The cast CF8C-Plus exhibited lower yield and tensile strengths, but higher creep strength compared to its wrought counterpart. Two welding methods, shielded-metal-arc welding (SMAW) and gas-metal-arc welding, met the weld qualification acceptance criteria in ASME BPVC Section IX for the cast CF8C-Plus. However, for the wrought CF8C-Plus, while SMAW and gas-tungsten-arc welding passed the tensile acceptance criteria, they failed the side bend tests due to lack of fusion or weld metal discontinuities.

One of the pathways for achieving the goal of utilizing the available large quantities of indigenous coal, at the same time reducing emissions, is by increasing the efficiency of power plants by utilizing much higher steam conditions. The US Ultra-Supercritical Steam (USC) Project funded by US Department of Energy (DOE) and the Ohio Coal Development Office (OCDO) promises to increase the efficiency of pulverized coal-fired power plants by as much as nine percentage points, with an associated reduction of CO 2 emissions by about 22% compared to current subcritical steam power plants, by increasing the operating temperature and pressure to 760°C (1400°F) and 35 MPa (5000 psi), respectively. Preliminary analysis has shown such a plant to be economically viable. The current project primarily focuses on developing the materials technology needed to achieve these conditions in the boiler. The scope of the materials evaluation includes mechanical properties, steam-side oxidation and fireside corrosion studies, weldability and fabricability evaluations, and review of applicable design codes and standards. These evaluations are nearly completed, and have provided the confidence that currently-available materials can meet the challenge. While this paper deals with boiler materials, parallel work on turbine materials is also in progress. These results are not presented here in the interest of brevity.

As the demand for worldwide electricity generation grows, pulverized coal steam generator technology is expected to be a key element in meeting the needs of the utility power generation market. The reduction of greenhouse gas emissions, especially CO 2 emissions, is vital to the continued success of coal-fired power generation in a marketplace that is expected to demand near-zero emissions in the near future. Oxycombustion is a technology option that uses pure oxygen, and recycled flue gas, to fire the coal. As a result, this system eliminates the introduction of nitrogen, which enters the combustion process in the air, and produces a highly-concentrated stream of CO 2 that can readily be captured and sequestered at a lower cost than competing post-combustion capture technologies. Oxycombustion can be applied to a variety of coal-fired technologies, including supercritical and ultra-supercritical pulverized coal boilers. The incorporation of oxycombustion technology in these systems raises some new technical challenges, especially in the area of advanced boiler materials. Local microclimates generated near and at the metal interface will influence and ultimately govern corrosion. In addition, the fireside corrosion rates of the boiler tube materials may be increased under high concentration oxygen firing, due to hotter burning coal particles and higher concentrations of SO 2 , H 2 S, HCl and ash alkali, etc. There is also potential to experience new fouling characteristics in the superheater and heat recovery sections of the steam generator. The continuous recirculation of the flue gases in the boiler, may lead to increasing concentrations of deleterious elements such as sulfur, chlorine, and moisture. This paper identifies the materials considerations of oxycombustion supercritical and ultrasupercritical pulverized coal plants that must be addressed for an oxycombustion power plant design.