Thoughts sparked by a fire
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Our plant’s two methanol production units, each with an annual capacity of 100,000 tons, have been shut down for major repairs and upgrades. The operating pressure for methanol synthesis is 4.2–4.3 MPa. One of these methanol units was put into operation in 2005, while the other was commissioned in 2006. The methanol plant had been shut down for 2 months prior to the maintenance. Before carrying out hot work, we performed a thorough purging of the methanol system as well as a hot work analysis, and the results of that analysis indicated that the pipeline system was suitable for hot work. Thus, the construction team was arranged to carry out hot work; when cutting the first opening, it caused the pipeline to catch fire. Cause analysis of the fire: During methanol production, organic waxes are generated as a result of side reactions; these waxes accumulate on pipes and equipment, forming solid deposits. Flammability analysis can only detect gas components and is unable to analyze solid deposits. During hot work, the high-temperature oxygen-acetylene flame causes organic waxes to vaporize, creating a flammable atmosphere that leads to ignition. Loss: After the fire broke out, in order to prevent it from spreading further, equipment was activated to use water injection through pipes for extinguishing the fire. Due to the high amount of wax buildup inside the pipeline, the time it takes for a fire to start is prolonged. After extinguishing the fire by injecting water, it is as if the pipeline material has been quenched, resulting in the material becoming brittle and the pipeline becoming unusable. Experience and lessons: Typically, hot work analysis takes into account only the explosive atmosphere of gases within the pipes, ignoring the presence of solid deposits. Therefore, in chemical plants where organic reactions occur, such as methanol production facilities, simply replacing the air with inert gas during shutdown is not sufficient; it is better to use low-pressure steam cleaning after shutting down to remove the solid deposits.
The lessons learned from paying a heavy price can be remembered, but they may not serve as a warning to others – and that is the sad part
Our company has encountered a similar situation: work was carried out on the outlet pipeline of the first stage of a reciprocating compressor; the area was purged successfully, but there was a large amount of coal tar accumulated on the inner wall, which caused a fire and heavy smoke. The fire had to be extinguished using fire hoses, resulting in serious consequences.
Yes, thorough analysis and verification are necessary before starting any work involving fire; this is especially true for these large and valuable equipment. One must not act rashly – all possible scenarios need to be analyzed beforehand. Therefore, accident prevention plans need to be continuously improved.