Kinetic analysis for spontaneous combustion of sulfurized rust in oil tanks

In order to evaluate the spontaneous combustion hazards of sulfurized rust in oil tanks, one kind of rust was obtained from respiratory valve inner cavity of a crude oil tank in a petrochemical company. The rust was sulfurized in sulfuration experimental apparatus. The production was analyzed by X-ray energy dispersive spectrometry (EDS), scanning electron microscopy (SEM) and then thermo-gravimetric analysis (TGA). The EDS result shows that the main substances are FeS and FeS₂ which are liable to spontaneous combustion. The sulfurized rust gives a short length of side and diamond appearance, and a large pore size in structure based on X-ray Diffraction (XRD). The whole oxidation process has three complex stages. The corresponding apparent activation energy values, most probable mechanism functions and pre-exponential factor values were calculated by Madhusudanan-Krishnan-Ninan method and the master plot method. The results indicate that the first and third stages of mass loss are up to the power function mechanism, but the second stage accords with the nucleation and nucleus growth mechanism. The values of apparent activation energy increase successively from the first stage to the third stage. The second stage has the maximum pre-exponential factor value, while the first has the minimum. With the obtained parameters above, the oxidation process of sulfurised rust could be simulated, which would benefit for monitoring and early warning of oil tanks.