Study on reduction mechanism of Fe2O3 by NH3 under SNCR condition

Abstract Amino compounds were injected into a boiler at high-temperature area usually to realized De-NOx. However, amino compounds were highly corrosive. The metal tube skin of stage III superheater in a medium temperature separation circulating fluidized bed boiler (MTS-CFBB) was investigated to verify the corrosion effect of amino compounds on the boiler tube wall. The sodium salt which was found in the inner layer of the metal tube skin indicated that large area cracking occurred at the metal tube during the operation process; and further indicated that the corrosion rate of the tube wall was speedy. Meanwhile, the tube furnace experimental system and the reaction equations module in HSC Chemistry 6.0 were used to obtain the reduction properties of NH 3 on Fe 2 O 3 at high temperature. The weight loss rate of Fe 2 O 3 under N 2 -NH 3 atmosphere increased from 3.3 wt% to 5.5 wt%, when the temperature rose from 600 °C to 900 °C, and the weight loss rate of samples did not increase any more with the temperature rising to 1000 °C. The injected NH 3 reduced the Fe 3 O 4 to form FeO quickly at 810 °C. With the thermal stress caused by the boiler load adjustment and start up or shut down, the looser FeO formed at the interior of tubes, and then, the different expansion coefficient of Fe based compounds led to the extensive cracking. In summary, NH 3 generated by SNCR was the main reason for corrosion happened on the tubes at high-temperature.