Outline of USC research and development
Since our country mostly depends on the import of the primary energy such as oil and coal from foreign countries, the energy supply structure is fragile. Therefore, it is a latently essential problem to suppress and diversity the consumption of energy and reduce its cost. Also, it is important to enhance efficiency of a thermal power station in order to cut down on CO₂ from the viewpoint of global environmental problem.
Under these circumstances, an ultra high pressure and high temperature of a steam condition, that is. Ultra Super Critical Steam Condition (USC) pressure power generation has been under development as work subsidized by the Agency of Natural Resources and Energy in the Ministry of International Trade and Industry since 1982. Research and development has been achieved so far on a ferritic material at a steam temperature of 593°C and austenitic material at 649°C, which showed that this power generation can be technically put to practical use.
However, as far as austenitic material is concerned, it is difficult to operate the actual machine at the present fuel cost because of operational restrictions due to material characteristice (a coefficient of thermal expansion is great and a coefficient of heat transfer is small), material cost, etc.. For this reason, the heat resisting limit of ferritic material has been considered to be 600°C up to the present. It is decided to set the target limit to 630°C and continue the reseach and development.

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Various kinds of combined cycle power generation system have been proposed for efficient use of abundant energy resource, coal. Pressurized fluidized bed combustion
(PFBC) combined cycle system has the following features in general and has gotten much attention from Japanese utilities owing to its earlier practical use.
1. High plant efficiency and low auxiliaries power consumption
2. Low emission such as de-SOx by in-bed desulfurization, minimizing NOx by low combustion temperature and decreasing CO2 by high plant efficiency
3. Compactness by eliminating flue gas desulfurization equipment and reducing the equipment size due to less volume of pressurized air/gas
Development of PFBC system started in England in 1960s and it was taken over by ASEA (later ABB). Three plants were installed by ABB Carbon in 1989 and 1990. One in Sweden which consists of two PFBC boilers/gas turbines and one steam turbine is a commercial cogeneration plant supplying 135MW electricity and 224MW hot water. The others installed in USA and Spain are demonstration plants with electric output of 70MW and 79MW respectively.
In Japan, the first PFBC plant was installed at Wakamatsu Coal Utilization Research Center of Electric Power Development Co., Ltd. with government support and its demonstration operation has already commenced since the end of 1994. Construction of commercial plant has also started.
Ishikawajima-Harima Heavy Industries Co., Ltd. (IHI) delivered Wakamatsu PFBC boiler under the technical license from ABB Carbon with various new technologies incorporated to realize better performance in efficiency, emission and operationability required in Japan. Its main specific features are as follows.
—Combination with the existing steam turbine having ultra-high steam temperature, 593/593 deg. C.
—The first PFBC boiler with repeater
—Additional environmental equipment, such as ceramic tube filter and selective catalytic reduction
This paper summarizes the feature of PFBC system, IHI's development of PFBC and the outline of Wakamatsu PFBC plant with its operation experience. Further considerations for PFBC now such as confirmation of long term operation reliability, combustion of various kinds of coal and increase of performance are also discussed.

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Factors regarding the heat recovery steam generator (HRSG) have drastically changed in the development of the gas turbine and needs of a higher thermal efficiency in recent years.
In the early 90's, gas turbine firing temperature increased from 1000°C which established in the 70's, to 1300°C
As a result, plant thermal efficiency improved from 40% to around 49% due to increasing the capacity of HRSG and the adoption of higher steam conditions in the reheat/triple-pressure system instead of the conventional non-reheat/single pressure system.
Here, subjects of the performance, system, structure and control in reheat/triple-pressure type HRSG are reported.

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In these days, the high efficiency waste to energy plant have been studied and developed. Corrosion resistant materials and coatings for boiler tube in high temperature and corrosive gas conditions have been developed. As a result, it is certain that the storker combustion system has also reached high power generation potential. The new development of a high efficiency waste to energy plant by NEDO (New Energy and Industrial Technology Development Organization) is introduced. This paper describes the present status of related technology development of high efficiency waste to energy plant.

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Various types of heat-resistant steels are in service as tubes and pipes in high temperature section of fossil fired boilers.
For improving thermal efficiency, the application of new heat-resistant steels with superior high temperature strength and corrosion resistance are being required.
This paper describes the recent research and development trends, development philosophy and characteristics of new heat-resistant steels for boiler tubes and pipes.

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A new 9Cr-1Mo steel, which is applicable to such low normalizing temperature as 930 to 950°C, was designed using the experimentally determined solution products of [V] [N] and [Nb] [N]. Although the creep rupture strength (CRS) at 600°C for 10⁵ hours of the new steel is about 10MPa lower than that of Mod. 9Cr-1Mo steel which is normalized at higher temperature than 1040°C, it is about 20MPa higher than the Mod. 9Cr-1Mo steel which is normalized at 930 to 950°C. The new steel exhibits almost the same CRS as Mod. 9Cr-1Mo steel in the weakest heat affected zone (H-AZ) of welding. The CRS ratio of the weakest HAZ to base metal is higher in the new steel than that in Mod. 9Cr-1Mo steel. The welding heat cycle range where the CRS is degraded is more restricted in this steel than in Mod. 9Cr-1 Mo steel. Moreover, this steel has the potential CRS as high as Mod. 9Cr-1Mo under the treatment of TMCP. By the experimental results, the chemical composition can be optimized as 0.1% C-9 %Cr-1 % Mo-0.1% V-0.02% Nb-0.025 % N. This steel is expected to be used in various installation of ultra-super critical boilers.

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