High temperature, steam oxidation performance of advanced, highly alloyed steels and Ni based alloys as candidates for the structural materials in Ultra Super Critical (USC) Coal Power Plants

摘要

Reduction in CO_2 emissions from coal-fired power plants is one of the major challenges in order to decrease global warming effect. In energy sector, the aim to reduce CO_2 emission can be achieved by increasing the operating temperature (and pressure) of water steam system, which results in an increase in overall coal fired power plant efficiency. Currently the main components of coal fired power plants are made from the materials designed years ago; to meet harsh eco criteria such materials are not suitable for harsh conditions of modern coal-fired power plant. Subcritical power stations are main contributor in CO_2 emission globally, with high CO_2 emission and low efficiency ～37%. The next-gen coal-fired power plants have potential to reach 55% efficiency, taking into account, that 1% increase in absolute efficiency results in as much as 3% reduction in CO_2 emissions, 55% of CO_2 lower emission achieved. Modern, advanced coal fired power stations operating under Ultra Super Critical (USC) or Advanced Ultra Super Critical (AUSC) conditions experience temperatures exceeding 750 °C. Super heated steam at high temperatures causes accelerated degradation of low-alloyed steels or even medium Cr steels. Therefore for aggressive, steam oxidation conditions highly alloyed steels and advanced Ni based alloys. These materials must provide excellent steam oxidation resistance at high temperature via the formation of chromia scale. In this study, the steam oxidation behaviour of highly alloyed steels 309S, 310S, HR3C and advanced Ni based alloys: Haynes 230, alloy 263, alloy 617, Haynes 282 has been examined. The materials have been exposed for 2000 hours at 800 °C in unique close loop water - steam system.