Explosion of a potassium storage tank at an ammonia plant

INITIATING cause was the formation of a hydrogen-air flammable atmosphere in the Benfield Solution Storage Tank, followed by ignition and explosion.
Hydrogen could have entered in the tank in two ways.
(1) Hydrogen was already present in solution in the Benfield solution. Assuming full saturation, from the hydrogen solubility value a total of 22 standard cubic feet (0.62 standard cubic meters) of hydrogen could have been present in the tank. This volume seems small, but calculations showed that this quantity is compatible with the explosion.
(2) Hydrogen entered from the absorber through the pump out line to the storage tank.
The static electrical or auto IGNITION SOURCE could have been due to the inlet line to the storage tank not being submerged in the solution as the tank was filled. At the time of the explosion, the tank was approximately one-third full, and the inlet line was not submerged.
The ROOT CAUSE was a shortcoming in design, by which the CO2 removal system was too much integrated I the overall process, what allowed access of hydrogen from the synthesis system to the Benfield solution tank.

Benfield Solution Storage Tank

DESCRIPTION OF THE PROCESS
The Benfield Process is a thermally regenerated industrial gas separation technology used to remove the acid-gases, CO2 and H2S from rom gas streams. It is applied often in ammonia production, natural gas sweetening (including LNG applications), and hydrogen production. It employs a hot potassium carbonate K2CO3 solution, often referred to as "hot pot". The process employs a gas absorption step and an carbonate regeneration step. In the absorption step, K2CO3 reacts with acid gases to form potassium bicarbonate KHCO3, which is later reversed in a regenerator to release the CO2.
[https://www.osti.gov/servlets/purl/1097716#:~:text=Background,(1)]

The explosion caused the destruction of the tank and sent the tank roof and sidewalls approximately 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.
Nevertheless, Despite the destruction of the tank, the consequences were limited. Nobody was injured, the Benfield solution was contained, avoiding any environmental impact, and the explosion damage was repaired in a relatively short time.

The INITIATING CAUSE was the formation and the ignition of hydrogen in the chemical tank.
The post-incident investigation was performed in association with a University.
CO2-containing solutions could produce significant amount of hydrogen in alkaline conditions. Large capacity tanks for holding these solutions represent a hazard, even though combustible substances seems to he absent.

Many design modifications and new operation procedures were implemented after the incident, aiming at better isolate the Benfield system from the reactor operation.
A new tank was designed to prevent any ingress of hydrogen from the process system. The tank was also equipped with ventilation, based on an air flow able to keep hydrogen below the lower limits of flammability and to remove it from the tank through a vent line. Modification details can be found in [McDaniel, Plan/Operations Progress, 5 (1986)].
A new operational procedure for pumping out the Benfield system to the storage tank was
Made, to avoid gas entering the storage tank or solution sump.