1. Fire and explosion at the site of the safety valves of the rectification propylene column. Released propylene, which most likely was fired at a propylenoid propylene boiler that was about 65 meters from the source of the propylene leak.
2. Fire of Pyrolysis Furnace. After cracking on the filament of the pyrolysis furnace, there was a flash of hydrocarbons in the reaction section and in the hot section and then the flare of the hydrocarbons in the conventional section and the spray line and finally the flash of washing oil.
The establishment is located in the area between two large urban agglomerations of Most and Litvínov with a distance of about 5 km. The busy state road and the high-speed line run between the two main parts of the company. After the northern and eastern parts there is an extensive network of railway transport. Passenger trains run through the eastern junction. The transport of dangerous substances is carried out on both roads.
Substances involved : 130 t of propylene 130 t and 150 t of parolysis fuel oil.
From 13.8. to 18.8. the site was under the control of the Integrated Rescue System and the accident was dismantled.
MAIN FACTORS WITH DESIGNATION OF SEQUENCE
technical defect in the process,
loss of control over the external cause process
failure to supply cooling water,
operator error – unconscious neglect
The direct cause of the propylene leak was a loose flange connection at the inlet of the safety valve located on the pipeline bridge.
The main cause of loose flange joints between the safety valve and its shut-off valve was the excessive and devastating vibrations caused by the turbulence of the safety valve. The main cause of excessive and destructive vibration was most likely resonance induced by the acoustic standing wave on valve discharge and natural frequency. The calculations show the resonance with the outlet pipe. While other factors may have a causal effect on the occurrence of chatter (eg low flow) and subsequent vibrations (eg pipeline support project), the massive vibration intensity with such a devastating force, as evidenced by the extent of damage to the safety valve, could only be attributed phenomenon such as acoustic resonance. The main cause of the furnace fire was the crack on the sixth hairpin, which was not properly cooled by process steam. Following a crack on the filament, a hydrocarbon flashing occurred in the reaction section and in the hot section and then the flare of the hydrocarbons in the conventional section and the spray line, and finally the washing oil flare as the furnace separated from the hot section to ensure that the hot section was secured before the next fire of the other portions of the ethylene unit . The main cause of improper cooling of the furnaces after emergency shutdown was the loss of process steam when two high-pressure steam boilers for the ethylene unit were dismantled and at the same time lost the steam import for the furnaces after heavy explosive burns caused by the tearing of the medium pressure steam pipe into the pipeline bridge.
MEASURES ADOPTED TO REDUCE THIS TYPE OF MAJOR ACCIDENT
1. Revission of the operating instructions for the cooling water system
2. Safety inspections before starting the process
3. Safety valve system – risk analysis
4. Upgrade of the propylene column emergency propulsion system
5. Safety valve system (ethylene column)
6. Designing (reviewing) emergency operating procedures
7. Installation of emergency separation of flammable supplies