BOILER DESIGN AND MATERIALS ASPECTS FOR ADVANCED STEAM POWER PLANTS

摘要

Since the late 80s great efforts have been made to increase the efficiency of coal-fired power plants. The main development trend is the increase of the steam parameters with supercritical pressures and higher temperatures at boiler outlet. This is realised by means of the well-known and since the 60s commercially used once-through technology which avoids the introduction of a new clean coal technology with some substantial risks. Only material selection and dimensioning of the pressure parts have to be adapted to the new requirements, and the design and construction have to consider the limitations on the material side. The increase of the steam conditions is limited on the boiler side by water walls, tubing of the final superheaters and reheaters as well as the thick-walled components, mainly the high-pressure outlet headers and the piping to the turbine. Several boiler materials with improved mechanical properties have been developed in the last years. Some new materials are still in the stage of development. Besides the aspects of strength and workability of the materials, attention must be paid to the corrosion behaviour at high temperatures. In order to investigate me suitability of the various tube materials in high-temperature areas, several test installations are now in operation to forecast the corrosion properties at high temperatures. The paper shows the design aspects and materials needs for advanced steam power plants. It reviews the available boiler materials with respect to mechanical and corrosion properties and gives limitations on the maximum achievable steam conditions. Finally, a forecast for further increase of the steam conditions considering pending and future material developments will be given.