Tank incident 2: Spontaneous combustion of ferrous sulfide caused a flash explosion in the naphtha tank

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This post was last edited by Chuyun Waichao on 2018-8-16 at 11:18. Self-ignition of ferrous sulfide led to a flash explosion in a naphtha tank. Incident details: At 0:45 on May 9, 2010, Tank No. 1613 in the No. 2 Combined Tank Area of the Refining Department of Sinopec Shanghai Gaqiao Branch began receiving naphtha produced by Unit No. 3 distillation plant, in accordance with the scheduling plan. Tank No. 1613 is a reforming feed tank with a capacity of 5,000 cubic meters; it has an internal floating roof structure, a diameter of 21 meters, and a height of 16.5 meters, and it is used for storing naphtha. At around 10:00, while continuing to collect oil, transfer began from tank 1615 to tank 1613; at that time the liquid level was 5.09 meters. By 11:20, tank 1613 (with a temperature of 27°C at that time) experienced a flash explosion, its roof was torn apart, and a fire broke out. Thanks to the diligent efforts of the plant operators and firefighters, the fire was brought under control around 14:00 and completely extinguished at 14:37. The accident caused no injuries or fatalities. Preliminary cause of the accident: Spontaneous combustion of ferrous sulfide led to an explosion of the oil-gas and air mixture between the floating deck and the tank top. Lessons learned from the accident and measures taken: 1. All units should immediately organize inspections and risk assessments of the equipment and storage tanks where iron sulfide may be generated during the production process, with a focus on areas such as floating roof tanks, vent valves, and gauge holes. At the same time, it is necessary to strengthen training for relevant management personnel and operators on knowledge related to iron sulfide, so that they can fully understand the dangers of iron sulfide and the mechanisms behind its formation, as well as master emergency response measures proficiently. Based on the mechanism of iron sulfide formation and the results of the evaluation, practical preventive measures are formulated to reduce the generation of iron sulfide and eliminate the conditions for its spontaneous combustion. 2. Strengthen the optimized management of process production. Strengthen process management, operate strictly in accordance with process specifications, ensure the proper functioning of desulfurization facilities and units, and minimize the sulfur content in the production materials as much as possible. Furthermore, strengthen the corrosion prevention management of equipment and storage tanks; take effective measures for atmospheric-pressure storage tanks prone to iron sulfide accumulation to prevent iron sulfide from coming into contact with oxygen in the air. Areas in sulfur-containing unit storage tanks that are prone to the formation of iron sulfide, such as vent valves and sight gauge sampling ports, should be cleaned regularly. 3. Carry out proper cleaning of iron sulfide from the maintenance equipment. During the purging and cleaning of the equipment, special attention must be paid to dead zones such as elbows and corners, and care should be taken to drain condensate from low points in order to ensure the quality of the purging process and prevent the presence of residual oil and gas. Thereby preventing explosions and the escalation of fire accidents caused by the spontaneous combustion of iron sulfide. Before opening the equipment for maintenance, it should be rinsed with clean water to ensure that the internal components are moist, and any iron sulfide present in the container should be removed as much as possible; the removed iron sulfide must be disposed of safely as soon as possible. 4. During maintenance, special warning signs should be placed on areas containing iron sulfide, and all employees must be trained on the measures outlined in the maintenance plan to prevent hazards caused by iron sulfide. Before carrying out any work involving heating or welding on pipelines and containers in such areas, it is necessary to analyze for the presence of flammable gases; work can only proceed once these tests show no issues. In areas that may contain iron sulfide, fire-fighting water or steam should be available around them prior to maintenance; in the event of spontaneous combustion of iron sulfide, it can be cooled using fire-fighting water or steam. Supplement and improve the emergency response plan. In light of the hazards posed by the electrostatic properties of iron sulfide, the emergency response plan was revised and improved, and drills were organized. At the same time, detailed rules for the management of iron sulfide must be established.