Tank accident 3: Spontaneous combustion of sulfides, resulting in an explosion of the oily waste tank

Thread Content

Process of the explosion accident caused by the spontaneous combustion of sulfides in the sludge oil tank: At 7:35 on October 25, 1986, a sludge oil tank in the hydrogenation unit of Yanshan Petrochemical Company’s refinery suddenly exploded and caught fire; it took 40 minutes to extinguish the fire. The sludge tank is a vertical, atmospheric-pressure tank with a capacity of 250 m3 (diameter 6.64 m, height 7.2 m). After being built in September 1982, it was first used as an alkali tank; later, it was converted into a tank for discharging waste wax and lubricating oil during plant startup/shutdown and periods of abnormal operation. After the hydrogenation plant was put into operation, fuel gas condensate was also discharged into this tank. On October 7, 1986, it was decided following discussions in the workshop that the condensed oil in the liquid separation tank at the outlet of Stage 1 of the hydrogen compressor (with a volume of 0.075 m3 and a pressure of 3.724 MPa) should also be sent to the sludge tank through the drain line of the gas liquid separation tank. The waste oil stored in the tank in front of the accident water valve has a liquid level of about 1 meter; there is no inflow or outflow of material, and the return valve of the heating tube is closed. At 7:35, with the oil tank at rest, an explosion suddenly occurred. This led to the scrapping of the oil contamination tank, resulting in a loss of 7,541 yuan. Cause of the accident: The heated furnace condensate stored in the oil tank, as well as the compressor condensate, both contain hydrogen sulfide. During the production process, long-term contact with equipment leads to the formation of iron sulfide and other substances. Sulfide spontaneous combustion was the main source of fire in this accident, but static discharge cannot be ruled out either. Lessons learned from the accident and measures taken: In the future, any project involving process changes must be strictly reviewed; it is necessary to obtain approval from the relevant departments and the chief engineer, as well as to go through the required procedures. At the same time, it is necessary to update the operating procedures in a timely manner in light of process changes, strengthen technical training for employees, and eliminate potential accident risks.