- Heating Equipment
- Heat Exchanger
Based on the results of the company investigation and analysis of an amateur video, the company determined that the incident could have been caused by the failure of one of the following plant components:
· pipes leading to the reactor pressure gauges
· the recycled quench gas pipe at the bottom of the reactor
· the diathermic oil pipe (hot oil) entering or exiting the heat exchanger
· the heat exchanger flanged joints and connection lines.
The company determined that a release from the hot oil circuit could not have triggered the fire, based on the evidence from the pressure data in the circuit, which showed that the failure occurred 30 minutes after the fire started. The video confirms the pipe rupture 30 minutes after the fire began. For the same reason, a release from the hydrogen pipes is not considered likely, as the records demonstrate that the hydrogen pipe failed seven minutes after the fire began. When the heat exchanger flanged joints were dismantled, it was seen that the joint gaskets were not damaged. Thus, the company considers the failure of a pipe from the reactor pressure measurement gauges to be the most likely cause of the accident (although there is no conclusive evidence to identify the specific failure that caused the pipe to rupture). This assumption is supported by the following facts:
· This pipe is located in the area corresponding to the epicenter of the fire.
· The area corresponds to the area visually identified by the witnesses.
· The product release (hydrogen and fuel oil) from one of these pipes can cause a 6-meter long jet flame, as occurred.
· The product supposedly released would have had a high enough temperature and pressure to self-ignite or ignite against a plant hot spot (e.g., the hot oil circuit).
· The damages recorded were caused by overheating (flame exposition) and were not caused by overpressure or explosion. The pressure measurement records confirm no significant pressure changes at the beginning of the event.
The company decided to rebuild the hydrotreatment plant, in compliance with regulations, and to introduce the following process design changes:
· complete separation of the light fuel oil section and the heavy fuel oil section to avoid the possibility of "domino effects"
· lowering the maximum height of the heat exchanger installations from 25 meters to 15 meters to facilitate fire-extinguishing operations
· redesign of the piping system to minimize adjacencies
· relocation of the valves on the hydrogen quench line to enable depressurization
· reduction of the number of measurement gauges
· insertion of valves in a safe area for depressurizing the hot oil circuit.