Study On The Iron Sulfide Oxidation Process Under Low Temperatures

The equipment corrosion phenomena by the active sulfur in the crude oil was easily discovered,and the corrosion products reacted with air,then causing fire and explosion accidents.It is of great significance to study the process of iron sulfide low temperature oxidation.The composition of rust analog is mainly Fe₂O₃,Fe₃O₄,Fe（OH）₃ with mass fraction of 27.8%,61.5%,10.7%,respectively.After sulfurated,unstable iron sulfides were generated,which was easily spontaneous combustion when it was exposed to air.In this paper,the influence of drying time to oxidation process was researched by the oxidation heating curves of iron sulfide sample.The spontaneous ignition point of iron sulfide sample was measured.Meanwhile,the influence of on moisture content,particle size,ventilation condition for spontaneous ignition point was investigated.The solid S element migration process was studied by the content change of S simple substance and sulfate ion.The gaseous S element migration process was explored by the variation law of SO₂ gas concentration.The main contents were as follows:The temperature measuring system was used to explore the influence of different drying time to the oxidation heating curves of iron sulfide sample.The results showed that the temperature of sample 1 and sample 2 increased significantly,which was not dried and dried 0.5 h,respectively.There were both three stages of heating up on the curves and the oxidation rate of sample was bigger.The temperature curves of sample 3 and sample 4 have no obvious change,which were dried 1 h and 2 h,respectively.The maximum heating rate of sample 1 and sample 2 were 2.81 ℃/s and 2.77 ℃/s and oxidation tendency was 647.14℃2/s and 870.36℃2/s,respectively.It indicated that each of them has high oxidation self-heating tendency.There were almost no oxidation self-heating tendency about sample 3 and sample 4.The spontaneous ignition point of sample dried 0.5 h was 77.2326℃,which was low.It indicated that the sample had high oxidation self-heating tendency.The spontaneous ignition point of sample with 5% moisture content was lowest,and spontaneous combustion risk was the largest.While the spontaneous ignition point of sample with 10% and 1% moisture content were both higher,and spontaneous combustion risk of them were smaller.The smaller the sample particle size,the lower the spontaneous ignition point,the greater the spontaneous combustion risk.To the contrary,the spontaneous combustion risk of samples was smaller.After opening the fume hood,the air flow rate increased,and oxygen supply conditions improved,promoting the oxidation reaction,making the spontaneous ignition point of iron sulfide lower,and spontaneous combustion risk bigger.The nonpolar solvent carbon disulfide was used to investigate the content change of S simple substance in the oxidation process.The results showed that the sample temperature was lower than the spontaneous ignition point during the first temperature rising period,and the oxidation reaction between sample and O₂ could not procee completely.Therefore,the mass of S simple substance rapidly increased.The oxidation reaction of S simple substance and sample spontaneous combustion oxidation process have the mutual promotion effect on each other during the second temperature rising period.The mass of S simple substance was less than the first temperature rising period,but it was more than non-oxidative sample.S simple substance was oxidized into SO₂ gas during the third temperature rising period.The mass of S simple substance reduced sharply,even lower than non-oxidative sample.Barium chloride solution was used to study the content change of sulfate ion on stage.The results showed that sulfate ion concentration increased as a whole with the oxidation reaction.The content variation of sulfate ion represented the oxidation amount of iron sulfide.The more the content change of sulfate ion per unit time,the greater the sample oxidation rate.The use of ecom-D gas analyzer was to explore the variation law of SO₂ gas concentration and the influence of air flow to gas concentration.The results showed that at the air flow of 100ml/min,the sample temperature failed to reach the spontaneous ignition point,releasing a little SO₂ gas.If the air flow at 200ml/min,the sample temperature was more than the spontaneous ignition point,releasing a large amount of SO₂ gas.Within the range of this thesis,the bigger the air flow,the earlier releasing SO₂ gas,the greater the maximum density of SO₂ gas and the longer maintaining near the maximum concentration.Combined with the heating curves,SO₂ gas concentration change could be considered as the characterization of iron sulfide sample oxidation process.According to the experimental results,there were many measures could be used to deal with iron sulfide spontaneous combustion.Controlling the temperature,oxygen concentration,moisture content,passivation method and adding corrosion inhibitor could be supposed to precautionary measures.An alarm issued by setting SO₂ gas automatical control interlock devices could be regarded as control measure.