The “Cool Earth-Innovative Energy Technology Program,” launched by the Japanese government in March 2008, aims to significantly reduce global greenhouse gas emissions. Among the 21 selected technologies is the Advanced Ultra Super Critical (A-USC) pressure power generation, which targets the commercialization of a 700°C class pulverized coal power system with a power generation efficiency of 46% by around 2015. As of 2004, Japan's pulverized coal power plant capacity reached 35 GW, with the latest plants achieving a steam temperature of 600°C and a net thermal efficiency of approximately 42% (HHV). Older plants from the 1970s and early 1980s, with steam temperatures of 538°C or 566°C, are nearing the need for refurbishment or rebuilding. A case study on retrofitting these older plants with A-USC technology, which uses a 700°C class steam temperature, demonstrated that this technology is suitable for such upgrades and can reduce CO 2 emissions by about 15%. Following this study, a large-scale development of A-USC technology began in August 2008, focusing on developing 700°C class boiler, turbine, and valve technologies, including high-temperature material technology. Candidate materials for boilers and turbine rotor and casing materials are being developed and tested. Two years into the project, useful test results regarding these candidate materials have been obtained, contributing to the advancement of A-USC technology.

Natural gas has long been regarded as the primary energy source for advanced power systems because of its cleanliness and highly efficient nature. Nevertheless, coal is gaining attention again as a stable energy source for power generation. In this paper, high efficiency pulverized coal power plant technology, especially materials and the design for high temperature turbine systems, is discussed. The development of materials has contributed to the high efficiency plant development, so far. The development of 12% Cr steel was key in building the state-of-the-art 600-deg C class steam turbine system. It is believed that a 700-deg C class steam turbine system will be realized with Ni-based super alloys and austenitic steels. In the near future, the system with a 700-deg C reheat temperature and 630-deg C main steam temperature is promising for the pulverized coal power plant because of the need for only moderate development work, low capital expenditure, and its high efficiency.

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 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.

The combustion of coal and biomass fuels in power plants generates deposits on the surfaces of superheater / reheater tubes that can lead to fireside corrosion. This type of materials degradation can limit the lives of such tubes in the long term, and better methods are needed to produce predictive models for such damage. This paper reports on four different approaches that are being investigated to tackle the challenge of modelling fireside corrosion damage on superheaters / reheaters: (a) CFD models to predict deposition onto tube surfaces; (b) generation of a database of available fireside corrosion data; (c) development of mechanistic and statistically based models of fireside corrosion from laboratory exposures and dimensional metrology; (d) statistical analysis of plant derived fireside corrosion datasets using multi-variable statistical techniques, such as Partial Least Squares Regression (PLSR). An improved understanding of the factors that influence fireside corrosion is resulting from the use of a combination of these different approaches to develop a suite of models for fireside corrosion damage.

A comprehensive fireside corrosion study was undertaken to better understand the corrosion mechanisms operating on the superheaters and lower furnace walls of advanced coal- fired utility boilers. The study intended to evaluate the fireside conditions generated from burning eight U.S. coals individually in a pilot-scale combustion facility. These coals consisted of a wide range of compositions that are of interest to the utility industry. The combustion facility was capable of producing the realistic conditions of staged combustion existing in coal-fired utility boilers. During each of the combustion tests, gas and deposit samples were collected and analyzed via in-furnace probing at selected locations corresponding to the waterwalls and superheaters. Testing of five of the eight coal groups has been completed to date. Results of these online measurements helped reveal the dynamic nature of the combustion environments produced in coal-fired boilers. Coexistence of reducing and oxidizing species in the gas phase was evident in both combustion zones, indicating that thermodynamic equilibrium of the overall combustion gases was generally unattainable. However, the amount of sulfur released from coal to form sulfur-bearing gaseous species in both the reducing and oxidizing zones was in a linear relationship with the amount of the total sulfur in coal, independent of the original sulfur forms. Such a linear relationship was also observed for the measured HCl gas relative to the coal chlorine content. However, the release of sulfur from coal to the gas phase appeared to be slightly faster and more complete than that of chlorine in the combustion zone, while both sulfur and chlorine were completely released and reacted to form respective gaseous species in the oxidizing zone. The information of sulfur and chlorine release processes in coal combustion generated from this study is considered new to the industry and provides valuable insight to the understanding of fireside corrosion mechanisms.

This paper examines the ongoing significance of pulverized coal-fired steam plants in global power generation, focusing on technological advancements and strategies for improving efficiency and reducing CO 2 emissions. It traces the development of Ultra-Supercritical (USC) plants with steam temperatures around 600°C and explores immediate opportunities for further efficiency enhancements, including the innovative Master Cycle. The potential for increasing steam temperatures to 650°C using new steels and to 700°C with nickel-based AD 700 technology is discussed. The paper outlines a comprehensive strategy for CO 2 emission reduction: maximizing plant efficiency, co-firing with CO 2 -neutral fuels, and integrating with district heating/cooling or industrial heat consumers. Carbon capture and storage techniques are presented as a final step in this multi-faceted approach to sustainable power generation.

Following the successful completion of a 14-year effort to develop and test materials which would allow advanced ultra-supercritical (A-USC) coal-fired power plants to be operated at steam temperatures up to 760°C, a United States-based consortium has started on a project to build an A-USC component test facility, (A-USC ComTest). Among the goals of the facility are to validate that components made from the advanced alloys can perform under A-USC conditions, to accelerate the development of a U.S.-based supply chain for the full complement of A-USC components, and to decrease the uncertainty for cost estimates of future commercial-scale A-USC power plants. The A-USC ComTest facility will include a gas fired superheater, thick-walled cycling header, steam piping, steam turbine (11 MW nominal size) and valves. Current plans call for the components to be subjected to A-USC operating conditions for at least 8,000 hours by September 2020. The U.S. consortium, principally funded by the U.S. Department of Energy and the Ohio Coal Development Office with co-funding from Babcock & Wilcox, General Electric and the Electric Power Research Institute, is currently working on the Front-End Engineering Design phase of the A-USC ComTest project. This paper will outline the motivation for the project, explain the project’s structure and schedule, and provide details on the design of the facility.

The United States Department of Energy (U.S. DOE) Office of Fossil Energy and the Ohio Coal Development Office (OCDO) have been the primary supporters of a U.S. effort to develop the materials technology necessary to build and operate an advanced-ultrasupercritical (A-USC) steam boiler and turbine with steam temperatures up to 760°C (1400°F). The program is made-up of two consortia representing the U.S. boiler and steam turbine manufacturers (Alstom, Babcock & Wilcox, Foster Wheeler, Riley Power, and GE Energy) and national laboratories (Oak Ridge National Laboratory and the National Energy Technology Laboratory) led by the Energy Industries of Ohio with the Electric Power Research Institute (EPRI) serving as the program technical lead. Over 10 years, the program has conducted extensive laboratory testing, shop fabrication studies, field corrosion tests, and design studies. Based on the successful development and deployment of materials as part of this program, the Coal Utilization Research Council (CURC) and EPRI roadmap has identified the need for further development of A-USC technology as the cornerstone of a host of fossil energy systems and CO 2 reduction strategies. This paper will present some of the key consortium successes and ongoing materials research in light of the next steps being developed to realize A-USC technology in the U.S. Key results include ASME Boiler and Pressure Vessel Code acceptance of Inconel 740/740H (CC2702), the operation of the world’s first 760°C (1400°F) steam corrosion test loop, and significant strides in turbine casting and forging activities. An example of how utilization of materials designed for 760°C (1400°F) can have advantages at 700°C (1300°F) will also be highlighted.

Inconel alloy 740H was specifically developed for use in coal-fired AUSC boilers. This alloy displays a unique combination of steam and coal-ash corrosion resistance, microstructure stability, creep strength and heavy section weldability. During the past two years Special Metals and Wyman-Gordon have undertaken an intense effort to demonstrate their capability to manufacture full-size boiler components, characterize their properties and simulate field assembly welds. This work was performed according to the requirements of ASME Boiler Code Case 2702 that was recently issued. This paper covers manufacturing of tube and pipe products and property characterization including recent data on the effect of long time exposure on impact toughness of base and weld metal. New data will also be reported on coal ash corrosion of base metal and weld metal. An overview of welding studies focused on integrity of circumferential pipe joints and a discussion of remaining technical issues will be presented.

This paper outlines a comprehensive UK-based research project (2007-2010) focused on developing fireside corrosion models for heat exchangers in ultra-supercritical plants. The study evaluates both conventional materials like T22 and advanced materials such as Super 304H, examining their behavior under various test environments with metal skin temperatures ranging from 425°C to 680°C. The research aims to generate high-quality data on corrosion behavior for materials used in both furnace and convection sections, ultimately producing reliable corrosion prediction models for boiler tube materials operating under demanding conditions. The project addresses some limitations of existing models for these new service conditions and provides a brief review of the fuels and test environments used in the program. Although modeling is still limited, preliminary results have been presented, focusing on predicting fireside corrosion rates for furnace walls, superheaters, and reheaters under various service environments. These environments include those created by oxyfuel operation, coal-biomass co-firing, and more traditional coal firing.

A combined pilot-scale combustion test and long-term laboratory study investigated the impact of oxy-firing on corrosion in coal-fired boilers. Four coals were burned under both air and oxy-firing conditions with identical heat input, with oxy-firing using flue gas recirculation unlike air-firing. Despite higher SO 2 and HCl concentrations in oxy-firing, laboratory tests showed no increase in corrosion rates compared to air-firing. This is attributed to several factors: (1) Reduced diffusion: High CO 2 in oxy-firing densified the gas phase, leading to slower diffusion of corrosive species within the deposit. (2) Lower initial sulfate: Oxy-fired deposits initially contained less sulfate, a key hot corrosion culprit, due to the presence of carbonate. (3) Reduced basicity: CO 2 and HCl reduced the basicity of sulfate melts, leading to decreased dissolution of metal oxides and mitigating hot corrosion. (4) Limited carbonate/chloride formation: The formation of less corrosive carbonate and chloride solutes was restricted by low O 2 and SO 3 near the metal surface. These findings suggest that oxy-firing may not pose a greater corrosion risk than air-firing for boiler materials.

Early supercritical units such as American Electric Power (AEP) Philo U6, the world’s first supercritical power plant, and Eddystone U1 successfully operated at ultrasupercritical (USC) levels. However due to the unavailability of metals that could tolerate these extreme temperatures, operation at these levels could not be sustained and units were operated for many years at reduced steam (supercritical) conditions. Today, recently developed creep strength enhanced ferritic (CSEF) steels, advanced austenitic stainless steels, and nickel based alloys are used in the components of the steam generator, turbine and piping systems that are exposed to high temperature steam. These materials can perform under these prolonged high temperature operating conditions, rendering USC no longer a goal, but a practical design basis. This paper identifies the engineering challenges associated with designing, constructing and operating the first USC unit in the United States, AEP’s John W. Turk, Jr. Power Plant (AEP Turk), including fabrication and installation requirements of CSEF alloys, fabrication and operating requirements for stainless steels, and life management of high temperature components

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.

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%.

Along with rapid development of thermal power industry in mainland China, problems in metal materials of fossil power units also change quickly. Through efforts, problems such as bursting due to steam side oxide scale exfoliation and blocking of boiler tubes, and finned tube weld cracking of low alloy steel water wall have been solved basically or greatly alleviated. However, with rapid promotion of capacity and parameters of fossil power units, some problems still occur occasionally or have not been properly solved, such as weld cracks of larger-dimension thick-wall components, and water wall high temperature corrosion after low-nitrogen combustion retrofitting.

A new nickel-based superalloy, designated as GH750, was developed to meet the requirements of high temperature creep strength and corrosion resistance for superheater/reheater tube application of A-USC power plants at temperatures above 750°C. This paper introduces the design of chemical composition, the process performance of tube fabrication, microstructure and the properties of alloy GH750, including thermodynamic calculation, room temperature and high temperature tensile properties, stress rupture strength and thermal stability. The manufacturing performance of alloy GH750 is excellent and it is easy to forge, hot extrusion and cold rolling. The results of the property evaluation show that alloy GH750 exhibits high tensile strength and tensile ductility at room and high temperatures. The 760°C/100,000h creep rupture strength of this alloy is larger than 100MPa clearly. Microstructure observation indicates that the precipitates of GH750 consist of the precipitation strengthening phase γ’, carbides MC and M 23 C 6 and no harmful and brittle TCP phases were found in the specimens of GH750 after long term exposure at 700~850°C. It can be expected for this new nickel-based superalloy GH750 to be used as the candidate boiler tube materials of A-USC power plants in the future.

Enhancement of the steam conditions is one of the most effective measures to achieve the goal of higher thermal efficiency. 700°C class A-USC (Advanced Ultra Super Critical Steam Conditions) power plant is one of the remarkable technologies to achieve the goal and reduce CO 2 emissions from fossil fuel power plants. Toshiba has been working on the A-USC development project with subsidy from METI (Ministry of Economy, Trade and Industry) and NEDO (New Energy and Industrial Technology Development Organization). In this project, A-USC power plants with steam parameters of 35MPa 700/720/720°C were considered. To date, various materials have been developed and tested to verify their characteristics for use in A-USC power plants. And some of these materials are being investigated as to their suitability for use in long term. Together with members of the project, we carried out the boiler component test using a commercially-operating boiler. We manufactured a small-scale turbine casing made of nickel-based alloy, and supplied it for the test. In addition, we manufactured a turbine rotor for turbine rotation tests, and carried out the test at 700°C and rotating speed of 3,600rpm conditions. In this paper, we show the results of the A-USC steam turbine development obtained by the project.

For future carbon neutral society, a novel thermal power generation system with no CO 2 emission and with extremely high thermal efficiency (~ 70 %) composed of the oxygen/hydrogen combustion gas turbine combined with steam turbine with the steam temperature of 700°C is needed. The key to realize the thermal power plant is in the developments of new wrought alloys applicable to both gas turbine and steam turbine components under higher temperature operation conditions. In the national project of JST-Mirai program, we have constructed an innovative Integrated Materials Design System , consisting of a series of mechanical property prediction modules (MPM) and microstructure design modules (MDM). Based on the design system, novel austenitic steels strengthened by Laves phase with an allowable stress higher than 100 MPa for 10 5 h at 700°C was developed for the stream turbine components. In addition, for gas turbine components, novel solid-solution type Ni-Cr-W superalloys were designed and found to exhibit superior creep life longer than 10 5 h under 10 MPa at 1000°C. The superior long-term creep strengths of these alloys are attributed to the “grain-boundary precipitation strengthening (GBPS)” effect due to C14 Fe 2 Nb Laves phase and bcc α 2 -W phase precipitated at the grain boundaries, respectively.

As conventional coal-fired power plants seek to reduce greenhouse gas emissions by increasing efficiency, the temperature limitations of traditional ferritic/martensitic steels used in high-temperature components present a significant challenge. With Advanced Ultra Supercritical (A-USC) power plants proposing steam temperatures of 760°C, attention has turned to nickel-based superalloys as potential replacements, since ferritic/martensitic steels cannot withstand such extreme conditions. However, the current absence of cast nickel-based superalloys combining high strength, creep-resistance, and weldability has led to the development of cast analogs of wrought nickel-based superalloys, including H263, H282, and N105. This paper examines the alloy design criteria, processing experiences, as-processed and heat-treated microstructures, and selected mechanical properties of these materials while also discussing their potential for full-scale development.