High temperature corrosion resistance of advanced engineering materials under steam oxidation conditions for Ultra Super Critical (USC) Coal Power Plants

摘要

According to the International Energy Agency (IEA) energy statistics, electricity and heat production accounts for 41% of the total CO_2 emission. Conventional solid fossil fuel power plants contribute significantly to CO_2 emission and the EU has put in place legislation to reduce its emission to 20% below the 1990 levels by 2020. Reduction in CO_2 emissions from coal fired power plants can be achieved by increasing the operating temperature (and pressure) of water steam systems, which results in an increase in overall plant efficiency. Increasing temperature from T = 570 °C (38% efficiency) to T = 760 °C increases efficiency up to 55% together with significantly cutting CO_2 emission per kilowatt-hour-produced energy. Generally 1% increase in absolute efficiency results in as much as 3% reduction in CO_2 emissions [1]. Energy demand is increasing year by year in European societies, on the other hand restricted European Union (EU) legislation enforce to boosts the efforts in reducing CO_2 emission. Therefore, there is a strong need to develop, test and introduce to practice new materials capable to withstand harsh operating conditions. In Europe, currently operating power plants in hot sections (super heaters and re-heaters (SH/RH)) use low alloyed steels with Cr concentration up to 9 wt% (T/P91/92). Such steels possess insufficient high temperature corrosion resistance and creep strength at elevated temperature showing the limitation in use at around T = 620 °C. New advanced coal fired power stations working under Ultra Super Critical (USC) conditions use temperature of T = > 750 °C and pressures as high as p = 350 bar. Such harsh conditions require high strength and corrosion resistant advanced engineering materials with excellent steam oxidation properties. The aim of this study is to compare high temperature steam oxidation performance of highly alloyed steels and Ni-based alloys including 309S, 31 OS, HR3C Haynes®230®, Haynes®263, Haynes®617 and Haynes®282®. In this work the results from steam oxidation test at T = 800 °C initially for t = 1000 h (expected t = 3000 h) carried out in close loop system are presented. Kinetic measurements were performed by traditional discontinuous method using digital balance with high accuracy. Post investigations of the exposed samples were performed by means of scanning electron microscopy (SEM) in backscatter electron mode (BSE). Finally, the phase development and the phase changes upon steam oxidation were examined using x-ray diffractometer (XRD) and energy dispersive x-ray spectroscopy (EDS).