Occurrence of pyrophoric iron immune to chemical washing in vacuum distillation columns

Pyrophoric iron deposits on vacuum distillation column internals can become immune to water and chemical washing, by coating with asphaltenes entrained in the flash zone vapors. This hypothesis was confirmed by obtaining and inspecting samples of a vacuum distillation column mist eliminator on which pyrophoric iron ignitions were observed that were not affected by the conventional washing procedures. Three conditions are highlighted whose fulfillment significantly increases the probability of persistent pyrophoric iron occurrence on vacuum distillation column internals. A handling strategy is outlined which was based on the experience gained from the described incident.

► Pyrophoric deposits immune to chemical washing.
► Asphaltenes make pyrophoric iron water proof.
► Chemical washing of internals not a panacea.
► Operation with dark distillates may produce persistent pyrophoric iron.
► Asphaltene de-entrainment mist eliminators possible locations of persistent pyrophoric deposits.