Thermal power generation systems have played an important role to adjust power supply and demand balance in power grid due to the high operational flexibility. It is required for next future thermal power generation systems to have higher thermal efficiency and operational flexibility, not only to reduce CO2 emission but also to cope with the increase of electricity generation by renewable energy sources which are changeable depending on the weather. The Advanced Humid Air Gas Turbine (AHAT) system is expected to meet these requirements and now proceeding with the development by Mitsubishi Hitachi Power Systems Ltd., Central Research Institute of Electric Power Industry (CRIEPI) and Sumitomo Precision Products Co., Ltd. So far, the system concept and cycle performance of the AHAT system were verified by operational tests of a 3MW-class pilot plant and a 40MW-class test facility. However, the characteristics of operational flexibility, such as load following capability and fast startup speed, have not been clarified sufficiently. It is considered that dynamic characteristics analysis is useful to evaluate and improve operational flexibility. On the other hand, CRIEPI is now developing the dynamic analysis tool for thermal power generation systems based on Modelica language using Dymola, in the aim of evaluating operational characteristics of both a new thermal power system and existing thermal power plant. The component models of this tool are basically developed based on mass and energy conservation equations. In this paper, we try to construct the dynamic model using this tool for the startup characteristics analysis and to investigate the possibility of shortening startup speed of AHAT system. First, the validity of the dynamic model of AHAT system was verified compared with the 3MW-class pilot plant operational data. As a result, the simulation result agrees almost well with the operational data and the validity of this dynamic model was confirmed. And next, the startup characteristics in the case of increasing startup load ratio by dynamic simulation were investigated. The simulation result show that it is difficult to achieve the rated power output only by changing startup load ratio because the humidification rate of humidification tower is rate-limiting and the gas turbine exhaust gas temperature reaches the limit value before achieving the rated power output. And it is found that the effects of the water valve operational speed of humidification tower and of the heat capacity of the recuperator are important to shorten the startup time of AHAT system.

Recently, high efficiency and operational flexibility are required for thermal power plants to reduce CO 2 emissions and to introduce renewable energy sources. We study the advanced humid air turbine (AHAT) system, which appears to be high suitable for practical use because its configuration is simpler than that of gas turbine combined cycle power plants (GTCCs). Moreover, the thermal efficiency of AHAT system for small and medium-size gas turbines is higher than that of GTCCs. To verify feasibility of this system and the cycle performance of AHAT system, a 3MW-class pilot plant was built in 2006 by Hitachi, Ltd., which mainly consists of a gas turbine, a water atomization cooling (WAC) system, a recuperator, a humidification tower and a water recovery tower. Through the operational test from 2006 to 2010, we confirmed the feasibility of the AHAT as a power-generation system, and various characteristics such as the effect of changes in ambient temperature, part-load characteristics, and start-up characteristics. Next step, a 40MW-class pilot plant was built in 2011 and started operational tests. This system mainly consists of a dual-shaft heavy duty gas turbine, a WAC system, a recuperator and a humidifier. As a result of the operational test, it has been confirmed that the pilot plant output achieved rated power output. In this paper, we show the 40MW-class pilot plant running test results, and evaluate thermal characteristics of this plant and the effect of WAC and humidification on performance of this gas turbine system.

Effects of temperature, dissolved oxygen (DO), and degree of cold work (CW) on the oxidation kinetics of supercritical-water-cooled reactor (SCWR) fuel cladding candidate materials, including three types of 15Cr-20Ni austenitic stainless steels (1520 SSs), in superheated steam have been investigated assuming power-law kinetics. Characteristics of oxide layers and its relation to oxidation behaviors are also discussed. The effect of DO on the weight gain behavior in superheated steam at 700 °C was minor for all specimens at least up to 200 ppb DO. The tube-shaped specimens of 1520 SSs showed very good oxidation resistance at 700–780 °C. There was no clear difference in the oxidation kinetics among the three investigated types of 1520 SSs. The degree of CW is a significant parameter to mitigate oxidation in superheated steam. It has been suggested that the tube specimens showed a very slow oxidation kinetics since Cr diffusion in the outside surface of the tubes is accelerated as a result of an increase of dislocation density and/or grain refinement by a high degree of CW.

Main committee of Power Generation Facility Code (MCPGFC) of Japan Society of Mechanical Engineers (JSME) established rules to manage pipe wall thinning on 2005–2006, and they also made a roadmap in 2007 to enhance pipe wall thinning management rules. Research Committee on Application of New Findings and Technology to Improve Pipe-Wall-Thinning Management, which was conducted from April 2010 to March 2012 summarized the new draft technical knowledge of the major phenomena of pipe wall thinning, that is, flow accelerated corrosion and liquid droplet impingement erosion as well as new inspection method. In this report, the new technical knowledge is described. The achievement situation of the road map made in 2007 was evaluated, and the studies required in future were considered.

In this research, a technique was developed for quantitatively evaluating the amount and distribution of tensile and compressive residual stresses by the combined use of strain measurements under the spherical indentation loading together with the finite element method (FEM). When the spherical indentation is applied to the top surface of a welded plate, the elastic strain at an optimized position near the indentation is measured by strain gauges, where the residual and applied indentation stresses are largely superposed. In order to analyze the residual stresses, FEM analysis was conducted to establish the relationship between the elastic strain adjacent to the indentation and the indentation pressure for plates subjected to various uniform tensile and compressive stresses. The critical indentation load was identified, which maximizes the difference between the tensile and compressive residual stresses. A strain energy term ( U *) is newly introduced by integrating along the trajectory between the indentation pressure and the elastic strain in a range from 0 to maximum pressure. The application of this technique could contribute to improved reliability in welded parts.

Detailed FAC processes and effects of local H 2 partial pressure, oxide film porosity, and Cr content on the enhancement of dissolution through the oxide layer have been discussed focused on the result of FAC experiments and oxide layer characterizations. Porosity of oxide layer is closely related to corrosion resistance of the steels even in Cr content range of 0.003 to 1.01 wt %. Compact inner oxide layer suppress the diffusion of oxidizer (H 2 O) and Fe ion via pores, on the other hand, liquid-state diffusion through a porous oxide layer is considered to be dominant under high FAC rate conditions. The model of spiral enhancement of dissolution through the oxide layer has been proposed. It has been considered that FAC is enhanced with increase of local H 2 partial pressure and film porosity. It has also been suggested that low solubility Fe-Cr spinel-type oxide formed on the high Cr content steels suppresses the spiral enhancement of dissolution through the oxide layer.

Humid air gas turbine systems that are regenerative cycle using humidified air can achieve higher thermal efficiency than gas turbine combined cycle power plant (GTCC) even though they do not require a steam turbine, a high combustion temperature, or a high pressure ratio. In particular, the advanced humid air gas turbine (AHAT) system appears to be highly suitable for practical use because its composition is simpler than that of other systems. Moreover, the difference in thermal efficiency between AHAT and GTCC is greater for small and medium-size gas turbines. To verify the system concept and the cycle performance of the AHAT system, a 3MW-class pilot plant was constructed that consists of a gas turbine with a two-stage centrifugal compressor, a two-stage axial turbine, a reverse-flow-type single-can combustor, a recuperator, a humidification tower, a water recovery tower, and other components. As a result of an operation test, the planned power output of 3.6MW was achieved, so that it has been confirmed the feasibility of the AHAT as a power-generating system. In this study, running tests on the AHAT pilot plant is carried out over one year, and various characteristics such as the effect of changes in ambient temperature, part-load characteristics, and start-up characteristics were clarified by analyzing the data obtained from the running tests.

Geothermal energy is considered a comparatively abundant renewable energy resource. The geothermal power generation system has negligible environmental impact (approximately 0.015kg-CO 2 /kWh), and it is expected to help prevent carbon dioxide emissions to the atmosphere. On the other hand, in our institute, we have developed general purpose software (EnergyWin™) to analyze the thermal efficiencies of power generation systems easily and rapidly. Such software can not only analyze the plant performance but also investigate the effect of the performance-deteriorated equipment or air condition change on power output quantitatively. Using this software, we have developed a new plant performance analysis system based on actual operation data for geothermal power plants. Then, applying the system to existing facilities, we have analyzed the plant performance and evaluated the effectiveness of the plant maintenance strategy during periodic inspection for consistency.

Combined effects of Cr content and pH on corrosion rate of carbon steels due to flow accelerated corrosion have been examined by experiments and their relation to oxide scale characteristics based on detailed oxide layer characterizations using transmission electron microscope with X-ray analyzer have been discussed. Effect of Cr content on FAC mitigation decrease continuously as pH is increased from neutral to 10.4 and effect of pH on that increase significantly from pH 9.1 to 9.4. Obvious Cr enrichment has been observed in the oxide layer of 1.01 wt% Cr content steel regardless pH condition. Cr concentration is highest at top surface of oxide layer, and that decrease from surface to oxide / metal interface gradually. It has been suggested that Cr enrichment stabilize oxide layer (decrease solubility and defect density of oxide layer), as a result, FAC suppressed.

Combined effects of Cr content and environmental factors, pH and dissolved oxygen concentration, on removal rate of carbon steels due to flow accelerated corrosion have been examined by experiments. The effects of environmental factors on FAC rate have been attempted to interpret based on oxide solubility, which has been precisely evaluated by separate experiments and numerical estimations. pH dependency of the FAC rate has been found to be directly related to solubility of magnetite. Cr content holds a strong impact on the FAC rate regardless of pH values from 6.84 to 10.4. Addition of 1% Cr to a carbon steel reduces the FAC rate by one order of magnitude under the environmental conditions, where magnetite forms. Addition of oxygen up to 1200ppb changes the oxide from magnetite to hematite, resulting in significant improvement in corrosion resistance. Oxide film characteristics, e.g. compositional distributions and types of oxide compound, have been also examined and their correlation to the FAC rate has been discussed.

The purposes of this research are (1) evaluating the importance of voids existing in oxide scales to exfoliation of oxide scales formed in superheated steam, (2) discussing possible role of Cr-rich layer in void formation in the oxide scales. First, superheater tubes, which are made of 9Cr-1MoVNb ferritic steel and were experienced with scale exfoliation, were removed from a fossil power plant and oxidation interfaces of the boiler tubes were examined in terms of structure, void distribution, elemental profile of the oxide scales and exfoliation characteristics. Then, exfoliation behaviors of oxide scales were evaluated on actual superheater tubes and on the steam oxidation specimens experimentally oxidized in autoclaves by tensile tests in terms of exfoliation strength and of position of exfoliation and its relation with void distribution in the scales. The results indicated an important role of void formation and growth in exfoliation of scale exfoliation. Void formation mechanism was also discussed based on the observed characteristics of the oxide scales.