【Daily Question】11.23 True or False: The auto-ignition temperature of ferrous sulfide is 50℃

The autoignition temperature of ferrous sulfide is 50°C – that’s incorrect

The auto-ignition temperature of ferrous sulfide is 50°C (incorrect); it is actually 40℃

Wrong. On the causes of spontaneous combustion of ferrous sulfide in air and its mechanism of spontaneous combustion: 1.1 Physical properties of ferrous sulfide – It is a dark brown or black solid that is poorly soluble in water; its density is 4.74 g/cm3, and its melting point is 1193°C. When it dissolves in inorganic acids, hydrogen sulfide gas is released. In humid air, it oxidizes and decomposes into sulfur and iron tetroxide. 1.2 Causes of the formation of ferrous sulfide 1.2.1 Formation of ferrous sulfide through electrochemical corrosion reactions More than 80% of the sulfur in crude oil is contained in atmospheric residue; the structures of these sulfides are relatively complex, and they easily decompose at high temperatures to produce hydrogen sulfide and smaller molecular thiol compounds. In the presence of water, these hydrogen sulfides and thiols have a significant corrosive effect on iron-based equipment. The reaction process is as follows: Additionally, sulfur can react directly with iron to form ferrous sulfide: Fe + S = FeS↓. The resulting ferrous sulfide structure is relatively loose and adheres evenly to the inner walls of equipment and pipes. 1.2.2 The atmospheric corrosion reaction produces ferrous sulfide. Due to prolonged shutdowns, the internal components of the equipment are exposed to air for long periods, resulting in atmospheric corrosion and the formation of rust. Since rust cannot be completely removed, it reacts with hydrogen sulfide during the production process to form ferrous sulfide. The reactions are as follows: Fe + O2 + H2O → Fe2O3·H2O; Fe2O3·H2O + H2S → FeS↓ + H2O. This reaction proceeds easily, and due to prolonged shutdowns, equipment with poor corrosion protection tends to produce ferrous sulfide. 1.2.3 High-temperature sulfur corrosion: The sulfur corrosion reaction is a chemical corrosion reaction, and an increase in temperature can accelerate the reaction rate. Therefore, high-temperature sulfur corrosion is more likely to occur in the bottom of atmospheric pressure columns with higher temperatures, as well as in the constant slag heat exchange units and vacuum unit systems. – 1.2.4 The presence of water and Cl promotes sulfur corrosion of equipment. As can be seen from the reaction mechanism for the formation of ferrous sulfide, the presence of water accelerates chemical corrosion; whereas when Cl is present, corrosion occurs even at lower temperatures, through the following reactions: Fe + 2HCl → FeCl2 + H2↑. Liu Jingyun: Formation of ferrous sulfide and prevention of spontaneous combustion. FeCl2 + H2S → FeS↓ + 2HCl; Fe + H2S → FeS↓ + H2↑; FeS + 2HCl → FeCl2 + H2S. In atmospheric-pressure tower top condensation systems, such as the tower top, oil and gas vaporization lines, water coolers, and reflux tanks, low-temperature corrosion is likely to occur. 1.3 Mechanism and phenomena of spontaneous combustion of ferrous sulfide 1.3.1 Mechanism of spontaneous combustion of ferrous sulfide When ferrous sulfide and other iron sulfides are exposed to heat or light in the air, the following reactions occur: FeS + 3/2 O2 = FeO + SO2 + 49 KJ; 2 FeO + 1/2 O2 = Fe2O3 + 271 KJ; FeS2 + O2 = FeS + SO2 + 222 KJ; Fe2S3 + 3/2 O2 = Fe2O3 + 3S + 586 KJ. 1.3.2 Phenomena of spontaneous combustion of ferrous sulfide During the spontaneous combustion of ferrous sulfide, if there is no combustible material present to support the reaction, white SO2 gas is produced, which is often mistaken for water vapor and has a pungent odor ； A large amount of heat is released at the same time. When surrounded by other flammable materials such as oils, it will produce thick smoke and cause fires and explosions. The distribution of ferrous sulfide in process equipment generally follows this pattern: the higher the sulfur content in the medium, the more corrosion products of ferrous sulfide are formed. However, even in equipment where the sulfur content is only a few parts per million, spontaneous combustion of ferrous sulfide can occur when the equipment is opened. The reason is not the high sulfur content in the medium, but rather the easy deposition of fine corrosion products of ferrous sulfide in certain local areas. Especially in the packing tower, its packing not only has a fractionation function but also an efficient filtration function, allowing ferrous sulfide carried in from upstream to be easily intercepted. At the same time, metal fillers have a large specific surface area, resulting in a large contact area with the material; even if the sulfur content in the material is low, it can still cause corrosion of the fillers. Due to the low flow rate of the material inside the packed tower, the ferrous sulfide formed as a result of corrosion on the surface of the packing is difficult to be carried away by the material. In this way, in a packed tower that operates under high load, for long periods of time, and continuously, a certain amount of ferrous sulfide will accumulate inside the tower. Since the ferrous sulfide in tower equipment is not a pure substance, it mixes with coke powder, oil sludge, and other substances to form scale, and its structure is generally relatively loose. When ferrous sulfide is oxidized in humid air, ferrous ions are oxidized to ferric ions, and sulfur with a valence of -2 is oxidized to sulfur with a valence of +4, releasing a large amount of heat. Due to the local temperature increase, the oxidation of the surrounding ferrous sulfide is accelerated, triggering a chain reaction. If carbon and heavy oil are present in the fouling, they will burn rapidly under the action of ferrous sulfide, releasing more heat. This spontaneous combustion phenomenon can easily lead to fire and explosion accidents. 1.3.3 Factors affecting the formation rate of ferrous sulfide: Based on the mechanism of ferrous sulfide formation, it can be seen that in daily production, the formation of ferrous sulfide is a chemical corrosion reaction that occurs as iron reacts under the action of active sulfides. Therefore, controlling chemical corrosion reactions is a key method to limit the formation of ferrous sulfide. As long as we identify the areas of the production equipment where sulfur corrosion is likely to occur and take effective measures based on the characteristics of each area, we can reduce the amount of ferrous sulfide produced, thereby preventing the occurrence of spontaneous combustion incidents caused by ferrous sulfide from the root cause. Factors such as the sulfur content of the oil, temperature, the presence of water, and Cl- are important factors that affect the rate of this electrochemical corrosion reaction.

The auto-ignition temperature of ferrous sulfide is 50°C – that’s incorrect; it should be 40°C

Error. ---40 degrees---------------------------------------

The auto-ignition temperature of ferrous sulfide is 50°C – this is incorrect; it is 40 degrees Celsius. .

Wrong. The auto-ignition temperature of dried ferrous sulfide in dry air is generally 300–350 degrees. However, before it catches fire on its own, it usually goes through a long period of self-heating. This self-heating process is an oxidation reaction that occurs between ferrous sulfide and air under certain conditions; the heat generated by this oxidation reaction raises the temperature of the system, ultimately creating the conditions for ferrous sulfide to catch fire on its own.

This post was last edited by wfs_bipt2014 on 2015-11-23 at 11:43. True or False question: The auto-ignition temperature of ferrous sulfide is 50°C. False; Baidu states it is 40 degrees