EFFECT OF OXIDATION ATMOSPHERE ON THE ANTI-COKING PROPERTY OF THE OXIDE SCALE FORMED ON HP40 ALLOY

摘要

Coke deposition in pyrolysis furnaces causes furnace down time for coke removal and shortens furnace coil life, which represents significant economical losses. The formation of stable oxide layers on alloy surfaces can reduce the activity of the constituent transition metals that catalyze coke formation. In the present work, the oxide scale on HP40 alloy were synthesized by oxidized under either air or H2 - H2O (drew point 10°C) at 950°C for 10h in order to evaluate effect of oxidation atmosphere on the anti-coking property of the oxide scale. Thermogravimetric analyses were conducted in isothermal conditions, the morphology, composition and structure of the oxide scales was characterized by SEM, EDS and X-ray diffraction. The result shown that in H2 - H2O mixtures the oxide scale growing faster than that in air at the early stage but slower than that in air after Sh. The scale formed in the H2 - H2O mixtures was composed mainly of a MnCr2O4 spinel top layer a Cr2O3 sub-layer and a discontinuous SiO2 layer and the spallation resistance is superior as compared to that formed in air. The coking experiments performed at 850°C using Ax +25%C3H, mixtures shows that the oxide scale formed in H2 - H2O mixtures has a better coking resistance than that formed in air.