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Coal-fired power plants are experiencing a resurgence due to cheaper prices compared to natural gas. However, environmental concerns remain. New technologies aim to tackle these issues by capturing emissions and boosting efficiency. EPRI's economic analysis highlights the potential of ultrasupercritical boilers with advanced materials, which could reach a remarkable 48% efficiency. However, these cutting-edge boilers come at a higher cost due to the expensive materials needed to withstand extremely high steam temperatures (around 730-760°C). The challenge lies in finding the optimal balance between efficiency gains and material costs.

A recent engineering design study conducted by the Electric Power Research Institute (EPRI) has compared the cost and performance of an advanced ultra-supercritical (A-USC) pulverized coal (PC) power plant with main steam temperature of 700°C to that of conventional coal-fired power plant designs: sub-critical, supercritical, and current USC PC plants with main steam temperatures of 541°, 582°, and 605°C, respectively. The study revealed that for a US location in the absence of any cost being imposed for CO 2 emissions the A-USC design was a slightly more expensive choice for electricity production. However, when the marginal cost of the A-USC design is compared to the reduction in CO 2 emissions, it was shown that the cost of the avoided CO 2 emissions was less than $25 per metric ton of CO 2 . This is significantly lower than any technology currently being considered for CO 2 capture and storage (CCS). Additionally by lowering CO 2 /MWh, the A-USC plant also lowers the cost of CCS once integrated with the power plant. It is therefore concluded that A-USC technology should be considered as one of the primary options for minimizing the cost of reducing CO 2 emissions from future coal power plants.

Increasing the efficiency of the Rankine regenerative-reheat steam cycle to improve the economics of electric power generation and to achieve lower cost of electricity has been a long sought after goal. Advanced ultra-supercritical (A-USC) development for materials to reach 760C (1400F) is a goal of the U.S. Program on Materials Technology for Ultrasupercritical Coal-Fired Boilers sponsored by the United States (U.S.) Department of Energy and the Ohio Coal Development Office (OCDO). As part of the development of advanced ultra-supercritical power plants in this program and internally funded programs, a succession of design studies have been undertaken to determine the scope and quantity of materials required to meet 700 to 760C (1292 to 1400F) performance levels. At the beginning of the program in 2002, the current design convention was to use a “two pass” steam generator with a pendant and horizontal tube bank arrangement as the starting point for the economic analysis of the technology. The efficiency improvement achieved with 700C (1292F) plus operation over a 600C (1112F) power plant results in about a 12% reduction in fuel consumption and carbon dioxide emissions. The reduced flue gas weight per MW generated reduces clean up costs for the lower sulfur dioxide, nitrogen oxides and particulate emissions. The operation and start up of the 700C (1292F) plant will be similar in control methods and techniques to a 600C (1112F) plant. Due to arrangement features, the steam temperature control range and the once through minimum circulation flow will be slightly different. The expense of nickel alloy components will be a strong economic incentive for changes in how the steam generator is configured and arranged in the plant relative to the steam turbine. To offer a view into the new plant concepts this paper will discuss what would stay the same and what needs to change when moving up from a 600C (1112F) current state-of-the-art design to a plant design with a 700C (1292F) steam generator and turbine layout.

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.

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.

Extended storage of spent nuclear fuel (SNF) in intermediate dry cask storage systems (DCSS) due to lack of permanent repositories is one of the key issues for sustainability of the current domestic Light Water Reactor (LWR) fleet. The stainless steel canisters used for storage in DCSS are potentially susceptible to chloride-induced stress corrosion cracking (CISCC) due to a combination of tensile stresses, susceptible microstructure, and a corrosive chloride salt environment. This research assesses the viability of the cold-spray process as a solution to CISCC in DCSS when sprayed with miniature tooling within a characteristic confinement in two different capacities: cleaning and coating. In general, the cold-spray process uses pressurized and preheated inert gas to propel powders at supersonic velocities, while remaining solid-state. Cold-spray cleaning is an economical, non-deposition process that leverages the mechanical force of the propelled powders to remove corrosive buildup on the canister, whereas the cold spray coating process uses augmented parameters to deposit a coating for CISCC repair and mitigation purposes. Moreover, both processes have the potential to induce a surface compressive residual stress that is known to impede the initiation of CISCC. Surface morphology, deposition analysis, and microstructural developments in the near-surface region were examined. Additionally, cyclic corrosion testing (CCT) was conducted to elucidate the influence of cold-spray cleaning and coating on corrosion performance.

Increasing the steam temperature of a coal-fired pulverized coal (PC) power plant increases its efficiency, which decreases the amount of coal required per MW of electrical output and therefore decreases the emissions from the plant, including CO 2 . However, increasing the steam temperature requires that the materials for the boiler pressure parts and steam turbine be upgraded to high-nickel alloys that are more expensive than alloys typically used in existing PC units. This paper explores the economics of A-USC units operating between 595°C and 760°C (1100°F to 1400°F) with no CO 2 removal and with partial capture of CO 2 at an emission limit of 454 kg CO 2 /MW-hr (1000 lb CO 2 /MW-hr) on a gross power basis. The goal of the paper is to understand if the improved efficiency of A-USC would reduce the cost of electricity compared to conventional ultra-supercritical units, and estimate the economically “optimal” steam temperature with and without CO 2 removal.

To stay competitive in today’s dynamic energy market, traditional thermal power plants must enhance efficiency, operate flexibly, and reduce greenhouse gas emissions. This creates challenges for material industries to provide solutions for harsh operating conditions and fluctuating loads. Higher efficiency demands steels with excellent steam oxidation resistance, favoring ferritic steels for cycling operation due to their limited thermal expansion. This paper presents a study modeling a combined cycle power plant using GE 9HA0.2 GT technology. The analysis compares different maximum live steam temperatures (585°C, 605°C, 620°C) and four alloys (grades 91 and 92, stainless S304H, and Thor 115) for heat exchangers exposed to steam oxidation. Results indicate that Thor 115, a creep strength enhanced ferritic (CSEF) steel, is a viable alternative to stainless steel for live steam temperatures above 600°C, offering improved oxidation resistance with minimal weight increase. Modern CSEF steels outperform stainless steel in power plants with lower capacity factors, reducing thermal fatigue during load changes. Increasing the live steam temperature boosts plant efficiency, leading to significant CO 2 savings for the same power output.

Recently, single-phase flow accelerated corrosion (FAC) has been found extensively in Thailand, especially in single shaft combined cycle power plant heat recovery steam generators, the design of which are compact and cannot be easily accessed for service. This takes at least one week for repairing and costs at least half a million dollar per shutdown. In this paper, the investigation of the single-phase FAC in a high-pressure economizer of a combined cycle power plant is demonstrated. Water chemical parameters such as pH and dissolved oxygen are reviewed, the process simulation of the power plant is performed to capture risk areas for the FAC. A computational fluid dynamics study of the flow is done to understand the flow behavior in the damaged tubes next to an inlet header. Some modifications such as flow distributor installation and tube sleeve installation were performed for short-term solutions. Moreover, new economizer headers are designed with low alloy material to mitigate the problem. The installation process of the newly fabricated headers is finally described. The findings in this paper serve as a guideline for FAC risk assessment, FAC investigation and mitigation, and service in compact heat recovery steam generators.

Addressing the growing concern of supercritical and ultra-supercritical boilers as potential safety hazards in power plants, a new Boiler Risk Management and Life Prediction System (BRMLPS) has been developed. This system leverages risk-based inspection and assessment techniques alongside life prediction and management methods. The BRMLPS focuses on evaluating and ranking the risk associated with critical boiler components, such as heating surfaces, headers, and drums. This risk assessment allows for the development of targeted and efficient inspection plans and repair strategies, ultimately aiming to minimize accident rates, reduce potential losses, and optimize safety investments. By implementing this system, power plants can achieve maintenance optimization, balancing safety and economic considerations for their specialized equipment.

To improve the economics of critical components, such as receivers and heat exchangers, for Generation 3 (Gen 3) concentrating solar power (CSP) plants, research was conducted to understand how manufacturing impacts the high-temperature performance of various tube production routes. Gen 3 CSP components are expected to require the use of heat-resistant nickel- based alloys due to the elevated operating temperatures in designs carrying molten salt or supercritical CO 2 . INCONEL alloy 740H (alloy 740H) was investigated as an alternative to UNS N06230 (alloy 230) as it possesses superior high-temperature creep strength which can lead to overall reductions in material cost. A key challenge is understanding how autogenous seam welding with and without re-drawing can be used to manufacture thin-wall tubing for CSP receivers and heat-exchangers to further reduce costs over traditional seamless production routes. Alloy 740H welded tube was successfully fabricated and re-drawn to several relevant tube sizes. Since traditional mechanical testing samples could not be removed from the thin-wall tubing, full-sized tubes were used for tensile, fatigue, and vessel testing (internally pressurized creep- rupture) which was critical to understanding the weld performance of the manufactured product forms. The generated vessel test data exhibited a creep strength reduction when compared to wrought product with no clear trend with temperature or test duration. It was found that redrawing the welded tubes improved the creep strength to approximately 82% of the wrought material performance and elevated temperature tensile and fatigue behavior exceeded 85% of the design minimums. Detailed, post-test characterization found that nano-sized carbides formed during the laser seam-welding process remained stable after multiple solution-annealing steps, which restricted grain growth, and impacted the time-dependent performance. This paper will focus on the time-dependent behavior of the examined welded and redrawn tubes, supporting metallographic evidence, and give perspective on future considerations for using alloy 740H in CSP components.

The steam generation systems (SGS) of concentrated solar power (CSP) plants employ multiple heat exchangers arranged in series to convert thermal energy collected from the sun via a heat transfer fluid (HTF) to produce superheated steam in the Rankine cycle. Common CSP plant designs are based either on parabolic trough or central tower technology. The major Rankine cycle components consist of preheaters, evaporators, steam drums, superheaters, steam turbines, and water/air-cooled condensers, all connected through steel piping. For CSP plants capable of reheating the steam for improved efficiency, reheaters are also included in the Rankine cycle. In central tower design with directly heated water as the HTF, the receiver can also be considered part of the Rankine cycle. Operating experiences of CSP plants indicate that plant reliability is significantly impacted by failures in various components of the Rankine cycle. Many damage mechanisms have been identified, which include corrosion, thermal fatigue, creep, and stress corrosion cracking, among others. Much of the damage can be attributed to poor water/steam chemistry and inadequate temperature control. While damage in the Rankine cycle components is common, there is generally lack of comprehensive guidelines created specifically for the operation of these CSP components. Therefore, to improve CSP plant reliability and profitability, it is necessary to better understand the various damage mechanisms experienced by linking them to specific operating conditions, followed by developing a “theory and practice” guideline document for the CSP operators, so that failures in the Rankine cycle components can be minimized. In a major research project sponsored by the U.S. Department of Energy (DOE), effort is being undertaken by EPRI to develop such a guideline document exclusively for the CSP industry. This paper provides an overview of the ongoing DOE project along with a few examples of component failures experienced in the Rankine cycle.

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.

Power generation technology selection is driven by factors such as cost, fuel supply security, and environmental impact. Coal remains a popular choice due to its global availability, but efficient, reliable, and cost-effective methods are essential. In Europe, efforts focus on advancing coal-fired steam power plants to ultrasupercritical conditions, with boilers and turbines now operating at up to 600°C. This has improved efficiency and maintained reliability comparable to subcritical plants. Orders are in detailed planning for plants exceeding 600°C, thanks to improved high-temperature steels for components like turbine rotors, casings, steam pipes, and boiler tubes, which undergo rigorous development and testing. Further efficiency gains are expected by increasing steam temperatures to over 700°C using nickel-based alloys. Test facilities are being built for pilot components, leading to a full demonstration plant. This systematic approach to materials development and proven design principles ensures operational reliability.

The highest creep rupture strength of recent 9-12% Cr steels which have seen practical application is about 130 MPa at 600°C and 100,000 h. While the 630°C goal may be realized, much more work is needed to achieve steam temperatures up to 650°C. Conventional alloy development techniques can be slow and it is possible that mathematical models can define the most economical path forward, perhaps leading to novel ideas. A combination of mechanical property models based on neural networks, and phase stability calculations relying on thermodynamics, has been used to propose new alloys, and the predictions from this work were published some time ago. In the present work we present results showing how the proposed alloys have performed in practice, considering long term creep data and microstructural observations. Comparisons are also made with existing enhanced ferritic steels such as Grade 92 and other advanced 9-12%Cr steels recently reported.

India's current installed power generating capacity is about 225,000 MW, of which about 59% is coal based. It is projected that India would require an installed capacity of over 800,000 MW by 2032. Coal is likely to remain the predominant source of energy in India till the middle of the century. India is also committed to reducing the CO 2 emission intensity of its economy and has drawn up a National Action Plan for Climate Change, which, inter alia, lays emphasis on the deployment of clean coal technologies. With this backdrop, a National Mission for the Development of Advanced Ultra Supercritical Technology has been initiated. The Mission objectives include development of advanced high temperature materials, manufacturing technologies and design of equipment. A corrosion test loop in an existing plant is also proposed. Based on the technology developed, an 800 MW Demonstration A-USC plant will be established. Steam parameters of 310 kg/cm 2 , 710 °C / 720 °C have been selected. Work on selection of materials, manufacture of tubes, welding trials and design of components has been initiated. The paper gives details of India's A-USC program and the progress achieved.

Advanced Ultra-supercritical (A-USC) steam power-plant technology is being developed for better efficiency and lower emissions at 700°C and above, but is based mainly on Ni-based alloys. The ability to include lower-cost alloys with appropriate high-temperature performance should have substantial technological and economic benefits. CF8C-Plus is a cast austenitic stainless steel recently developed for other applications at 600-900°C, which has creep-strength comparable to many solid-solution Ni-based alloys. EPRI and Carpenter Technology produced a 400 lb heat of CF8C-Plus steel and hot-forged it at 5:1 and 12:1 reductions, to assess feasibility of the alloy as a wrought advanced stainless steel for potential use as steam headers and piping for A-USC power plant applications. The hot-forged alloy has a recrystallized grain structure 6-9 times finer than the as-cast dendritic structure, resulting in better strength and impact resistance at room-temperature, and about 20% higher yield-strength (YS) at 760°C, and similar or better ductility compared to the as-cast material. The initial creep-rupture testing at 700-800°C for up to 2000h also indicates similar or better rupture resistance and better creep-ductility for wrought compared to cast material. The next steps needed to test performance of the wrought austenitic stainless steel for extruded headers and piping are discussed.

The spalling of oxide scales at the steam side of superheater and reheater of ultra-supercritical unit is increasingly serious, which threatens the safe and economic operation of the boiler. However, no effective monitoring method is proposed to provide an on-line real-time detection on the spalling of oxide scales. This paper proposes an on-line magnetic non-destructive testing method for oxide granules. The oxide scale-vapor sample from the main steam pipeline forms liquid-solid two-phase flow after the temperature and pressure reduction, and the oxide granules are separated by a separator and piled in the austenitic pipe. According to the difference of the magnetic features of the oxide scales and the austenitic pipe, the oxide granule accumulation height can be detected through the spatial gradient variations of the magnetic induction. The laboratory test results show that the oxide scale accumulation can be accurately calculated according to the spatial gradient changes around the magnetized oxide granules, with the detection error not exceeding 2%.

There are main drivers for the design and assessment of steam turbine components of today such as demands for improved materials, higher plant cycling operation, and reduced life-cycle costs. New materials have been developed over the last decades resulting in advanced martensitic 9-10CrMoV steels already applied in different types of turbines successfully. Heavy cyclic loading getting more importance than in the past results in utilization of the fatigue capabilities at high and low temperatures which might lead to crack initiation and subsequent crack propagation. Fracture mechanics methods and evaluation concepts have demonstrated their applicability to assess the integrity of components with defects or crack-like outage findings. Based on realistic modelling of the failure mechanism, accurate prediction of crack sizes at failure state can be improved defining the appropriate damage criteria. Ductility is a main aspect for robust design but its value definition can depend on component type, design rules, real loading conditions, service experience, and material characteristics. The question which direct material parameter is able to serve as limit value in design and how it can be determined has to be solved. Examples of advanced analysis methods for creep crack growth and fatigue interaction involving the crack initiation time show that the reserves of new martensitic 9-10Cr steels in high temperature application can be well quantified. The creep rupture elongation A u and the loading conditions in the crack far field are main factors. If the A u value is sufficient high also after long-time service, the material remains robust against cracks. Investigations into the influence of stress gradients on life time under fatigue and creep fatigue conditions show that e.g. for 10CrMoWV rotor steel crack growth involvement offers further reserves. The consideration of constraint effect in fracture mechanics applied to suitable materials allows for further potentials to utilize margin resulting from classical design. The new gained knowledge enables a more precise determination of component life time via an adapted material exploitation and close interaction with advanced design rules.

Austenitic stainless steels have been used for boiler tubes in power plants. Since austenitic stainless steels are superior to ferritic steels in high temperature strength and steam oxidation resistance, austenitic stainless steel tubes are used in high temperature parts in boilers. Dissimilar welded joints of austenitic steel and ferritic steel are found in the transition regions between high and low temperature parts. In dissimilar welded parts, there is a large difference in the coefficient of thermal expansion between austenitic and ferritic steel, and thus, thermal stress and strain will occur when the temperature changes. Therefore, the dissimilar welded parts require high durability against the repetition of the thermal stresses. SUPER304H (18Cr-9Ni-3Cu-Nb-N) is an austenitic stainless steel that recently has been used for boiler tubes in power plants. In this study, thermal fatigue properties of a dissimilar welded part of SUPER304H were investigated by conducting thermal fatigue tests and finite element analyses. The test sample was a dissimilar welded tube of SUPER304H and T91 (9Cr-1Mo-V-Nb), which is a typical ferritic heat resistant boiler steel.