Study On Combustion Tendency Of High Temperature Corrosional Products From Sulphur And Preventive Measures

Active sulfuric species derived from crude oil can react with rust formed on storage tanks, vessels and tankers to form various iron sulfides, and the tendency for these compounds to spontaneously react with oxygen in air may bring a potential trouble for oil processing and storage. Pyrophoric nature of the iron sulfides, exposed to moist air, is confirmed relevant with composition and sulfurized degree of rust and also with ambient temperature and relative humidity. The present subject target is supposed to clarify the effect of pivotal factors on both the sulfurization of iron oxides and the spontaneous oxidation of the iron sulfides, especially to explore the water induction for pyrophoric mechanism of the iron sulfides. In present work, we conduct the new topic, namely researching on combustion tendency of high temperature corrosion products and preventive measures for storage tanks of containing sulfur oil. Iron oxide sulfurization and ferric sulfide controllable oxidation will be performed under various reaction conditions, and characterized by XRD、DTA-TG、N2 adsorption-desorption and chemical analysis in order to determine phase composition, ferric valence state and reaction enthalpies. The oil desulfurization technology was demonstrated by microwave radiation, and the study on new cleaning agent for removing the composite of iron sulfides was investigated simultaneously.The results obtained by powder X-ray diffraction and quantitative chemical analysis point out that the rust was formed with very complicated composition and phases, consisting of mainly Fe2O3, Fe3O4 and FeO(OH) as the compositions of 60.2%,27.2% and 10.8%. The low temperature N2 adsorption-desorption showed that the specific surface areas decreased orderly as Fe(OH)3＞＞Fe2O3> Fe3O4. When element sulfur reacted with Fe(OH)3, Fe2O3 and Fe3O4 under the condition of high temperature, FeS2 was mainly formed, along with the generations of other compounds in very low contents, such as FeS、Fe1-xS、Fe2(SO4)3、Fe(OH)SO4 and FeSO4, which were formed to depend on the reaction temperatures. Upon these DTA-TG curves for element sulfur only and the products of element sulfur reacting with Fe2O3、Fe3O4 and Fe(OH)3, the starting reaction temperatures of Fe2O3, Fe3O4 and Fe(OH)3 with element sulfur is 233.34℃,308.47℃and 287.67℃, respectively. And the FeS2 contents in the sulfidation products of Fe3O4 and Fe(OH)3 were observed to increase with both sulfidation temperature and sulfidation time.For high temperature sulfurization products the pyrophoric nature depended obviously on the precursor species of sulfides. Compared with the case of Fe3O4 as the precursor, the high temperature sulfurization products concerning Fe2O3 and Fe(OH)3 as precursors showed a remarkable pyrophoric tendency, which were affected obviously by the factors of sulfurization temperature, sulfurization time, sample moisture as well as air flow rate. Iron oxide red and iron hydroxide were sulfurized with element sulfur to form mineralized sulfides under reaction conditions of high temperature and long time, while the formed sulfides were confirmed with high crystallinity and deep sulfurization. In this case, the sulfide shell, other than the bulk phase, showed both the obvious pyrophoric nature and the high oxidization rate. Usually the sulfides were oxidized rapidly along wtith remarkable combustion enthalpies as increasing reaction temperature and air flow rate. The sulfides of element sulfur reaction with Fe2O3 and Fe(OH)3 showed higher pyrophoric tendencies when ambient temperature was higher than 95℃. The existence of water remarkably increases the pyrophoric oxidation of sulfidation products. The pyrophoric tendency of high temperature products sulfided by using element sulfur decreased as the order:Fe(OH)3> Fe2O3> Fe3O4.The results indicated that, by using microwave radiation in the presence of hydrogen peroxide-acetic acid composites, desulfurization level arrived at 89.6% and the sulfur content at least down to 500μg·g-1 for Liaohe atmospheric two-stage distillation diesel oil under the conditions as following:0.5 Mpa of microwave pressure,5 min of constant pressure radiation time, composite dosage being 13 times of theory value,0.25 of ratio of H2O2 to oil,1.0 of ratio of DME extraction reagent to oil,10 min of static depositing time. The technology mentioned above could update Liaohe atmospheric two-line distillation diesel oil to meet the Europe StandardⅡand the China Standard for light diesel oil.A new composite desulfurization reagent was developed with the nature of low cost and light corrosion. It was demonstrated in refine with both high desulfurization level and high desulfurization rate compared with the domestic commercial products employed now.The detailed data concerning pyrophoric nature of iron sulfides were offered in present work, and effective prevention measures were given according to the researching results. The prevention measures were proposed to restrain and even avoid the occurrence of a fire as well as an explosion due to pyrophoric oxidation of iron sulfides in refineries. And it was of great constructive value to safe operation of all petroleum chemical companies.