A high performance austenitic material for superheaters and reheaters in advanced coal fired power boilers

摘要

The worldwide electricity demand is growing at the same time as much of today's generating fleet is getting closer to the end of its service life. This means there is a big demand for new electric power generating plants. The today's predominantly used feedstock, oil and gas, are resources with limited availability and thus the costs for these fuels has increased dramatically. Coal is found on every continent and the World Coal Institute forecasts it to last for over 150 years consumption. Coal conversion in different forms will therefore continue to contribute with a substantial part of the electric power generation industry in the future. Limiting environmental impact is at the same time of great importance. The new generation of advanced ultra super critical pulverized coal fired boilers will operate at very high steam temperatures and pressures (700°C, 350 bar) targeting net efficiencies above 50% with reduced fuel consumption and CO{sub}2 emissions. To meet the material properties required for some of the critical components in these boilers, Sandvik Materials Technology has developed the austenitic alloy Sandvik Sanicro 25. Main applications are for superheater and reheater tubes for use up to about 700°C material design temperature. The alloy is designed to have excellent strength at elevated temperatures, high oxidation resistance combined with high structural stability and good fabricability. The so far obtained test results indicate that Sandvik Sanicro 25 has higher mechanical (creep) properties than any other known commercial austenitic material. It is also a substantially more economical alternative to nickel base alloys. This paper presents material properties and results from material tests generated during the development and the further verification of data for this material.