Pyrophoric Iron Fire

At one time or the other, most refineries experience spontaneous ignition of iron sulfide either or on the ground or inside the equipment. When this occurs inside equipment like columns, vessels and tanks and exchangers containing residual hydrocarbons and air, the result can be devastating. Most commonly, pyrophoric iron fire occur during shutdowns when equipment and piping are opened for inspection or maintenance. Pyrophoric iron fire is a hazardous phenomenon that occurs when iron sulfide deposits, typically found in processing equipment such as filters, come into contact with air and spontaneously combust.

What is pyrophoric Iron Oxidation?

When iron sulfide (FeS) or other iron compounds come into contact with oxygen in the air, a quick and exothermic oxidation reaction takes place, known as pyrophoric iron oxidation. Significant heat is released during this reaction, and this heat has the potential to ignite surrounding combustible elements like hydrocarbons and start a fire. The reaction is frequently called "pyrophoric" because it can happen on its own without the assistance of an outside source of ignition and can result in a rapidly spreading fire.

Pyrophoric iron oxidation in distillation columns:

In petroleum refineries, the equipment most prone to pyrophoric combustion induced fires is the distillation columns in crude and vacuum distillation units. Deposits of iron sulfide are formed from corrosion products that most readily accumulate at the trays, pump around zones, and structured packing. If these pyrophoric iron sulfide (PIS) deposits are not removed properly before the columns are opened up, there isa greater likelihood of PIS spontaneous ignition. The trapped combustible hydrocarbons, coke, etc. that do not get adequately removed during washing /steaming often get ignited, leading to fires and explosions inside the equipment. These fires not only result in equipment damage but can also prove fatal for the personnel who are performing inspection and maintenance work inside the columns. The accidents due to pyrophoric iron oxidations are entirely avoidable if safe procedures for column hand over are followed. The targets of these procedures should be twofold:

• First, to remove all the combustibles.
• Second, to remove or neutralize pyrophoric iron sulfide deposits

The basic distillation column oil-cleanup procedure is discussed in steps below:

• Steaming
• Hot Water Washing
• Blinding
• Cold Water Washing
• Chemical Injection for Removal and Neutralization of PIS