Explosion of a potassium storage tank at an ammonia plant

The accident happened in an anhydrous ammonia plant, commissioned in March 1977. Hydrogen accumulated inside a Benfield solution (hot potassium) storage tank and was ignited by a static charge, which caused the explosion.

Mechanism by which hydrogen may have entered the storage tank are described in the paper (block valve leakage, H2 solubility in Benfield solution, etc.).

The explosion sent the tank roof and sidewalls some 37m into the air, expelling an estimated amount of 114 m3 of solution into the process area. Major damage was produced on synthesis gas piping in some heat exchangers, instrumentation, air and N2 lines, steam header, electrical equipment, etc. Inspection after the accident revealed greater weld strength at the tank roof to side wall than the floor to side wall welds.
This was the cause of sidewalls adhering to the roof and not to the floor during explosion.

Neither environmental pollution nor personnel injuries were produced. Many design modifications (different roof type, continuous air purging, better block valve, etc.) and new operation procedures were implemented.

INITIATING cause was the injection of hydrogen into the Benfield Solution Storage Tank, with consequent static charge ignition.

Benfield Solution Storage Tank

DESCRIPTION OF THE PROCESS
The Benfield Process is a technique used to remove the acid-gases, CO2 and H2S from petroleum and industrial gases. The process contains a gas absorption step and an carbonate regeneration step.

The explosion sent the tank roof and sidewalls some 37m into the air, expelling an estimated amount of 114 m3 of solution into the process area. Major damage was produced on synthesis gas piping in some heat exchangers, instrumentation, air and N2 lines, steam header, electrical equipment, etc.

The investigation has been performed in association with the University of Erlangen.
The formation and the ignition of hydrogen has found the immediate cause of the explosion.
CO2-containing solutions could produce significant amount of hydrogen in alkaline conditions. large capacity tanks for holding solutions could be dangerous even though combustible substances seems to he absent.

Many design modifications (different roof type, continuous air purging, better block valve, etc.) and new operation procedures were implemented after the incident.