Explosion at the hydrogen pumping station of a refinery

The event occurred in the hydrogen pumping station, placed between the hydrogen production unit (steam methane reformer) and the hydro-treatment unit. The second stage of the compressor cylinder released hydrogen into the confined compressor building. The hydrogen ignited. The failure was caused over-pressure in the piston, probably induced by ice blockage on the interstage cooler and the failure of the compressor housing heating system. A second explosion detached the roof building from the wall, and was attributed to backflow of naphtha and light hydrocarbon from the downstream hydro-treatment unit. Two other compressors were damaged.

The INITIATING CAUSE was extreme cold weather, which Caused i) ice blockage of the inter-stage cooler and ii) over-pressure in the compressor piston. However, the cold weather was expected and the plant had been designed considering very low temperatures. According to the referred scientific paper, the root CAUSE was an inadequate design, failing to identify critical facility and to guarantee for them safe and reliable operation.

H2 compressor

DESCRIPTION OF THE UNIT
A CO-hydrogen separation cold box is an insulated steel structure that houses cryogenic equipment used to separate carbon monoxide (CO) and hydrogen (H2) from a gas mixture based on their different boiling points. It operates at very low temperatures to partially condense and then distill the components, achieving high purity separation of the CO and H2 products. 

DESCRIPTION OF THE PROCESS
The process adopted in this plant was probably the methanol carbonylation, where methanol and CO reacts in presence of a catalyst. In this industrial process, CO is produced as syngas and then purified by separating Co from hydrogen and other syngas components. 

Damage to three hydrogen compressors, which had to be temporary replaced with compressors of another type. Thanks to the compressor housing, the worker outside the building, who was inspecting the situation, experienced only a light over-pressure. According to the referred article (Kelly, 1997) the event caused $20 million of physical damage and considerable business interruption.

According to the referred article (Kelly, 1997), the technical aspects which contributed to the failure were: 1. Enclosing each compressor into a heated own building, which protected them from the low temperature expected in the location, but created the condition for hydrogen accumulation, detonation and deflagration. 2. Placement of the inter-stage cooler outside the building, which helped logistics but caused the overall hydrogen system to be exposed to considerable temperature gradients. These issues however were only the result of a general absence of adequate safe and technical design. Lack of adequate plan is also evident in the fact that the problems encountered from the start on the compressor unit were never solved. After the accident, the operator has re-built the unit bringing in technical improvements and a systematic maintenance and process safety approach.