All it took was three minutes. The Williams Olefins chemical plant in Geismar, Louisiana, which was routinely executing everyday operations, was instantly transformed into a scene of destruction, panic and mayhem. A catastrophic equipment rupture led to an explosion and fire killing two workers and injuring 167. In retrospect, it was a tragedy that could have been prevented.
Why did such a disaster occur? A series of lapses over the years that included a lack of overpressure protection, poor management of change, a weak process hazard analysis and a lax process safety culture all helped fuel the blast.
The June 13, 2013, incident occurred during non-routine operational activities that introduced heat to an offline “reboiler,” creating an intense amount of liquid thermal expansion-driven pressure. The reboiler shell catastrophically ruptured, causing a boiling liquid expanding vapor explosion (BLEVE) and fire.
This overpressure situation could have been avoided.
The incident began during a daily morning meeting involving operations and maintenance personnel. In that meeting, the plant manager noted a drop in quench water flow, over the last 24 hours, to the operating propylene fractionator (a distillation column that separates propylene and propane) in Reboiler A. The meeting participants then analyzed plant data and noticed the water circulation rate appeared impaired. An operations supervisor investigated and identified fouling within the operating reboiler (Reboiler A) as a potential problem. He suggested a switch to the Reboiler B propylene fractionator to correct the quench water flow problem.
The operations supervisor attempted to meet with the operations manager to discuss the issue of switching of the reboilers. The operations manager was not available, so the operations supervisor returned to the field and continued evaluating the quench water system.
The process fluid on the shell-side of both of these reboilers was heated by hot “quench water,” flowing through the tubes. Reboiler B had been offline for 16 months while Reboiler A was in operation, but was clean and available for use when Reboiler A needed to shut down because of fouling.
At 8:33 a.m., the operations supervisor opened the quench water valves on Reboiler B. Three minutes later, Reboiler B exploded. Propane and propylene process fluid erupted from the ruptured reboiler and from the propylene fractionator due to failed piping. The process vapor ignited, creating a massive fireball. The force of the explosion launched a portion of the propylene fractionator reboiler piping into a pipe rack 30 feet overhead.
The fire lasted 3.5 hours, and Williams Olefins reported releasing over 30,000 pounds of flammable hydrocarbons during the incident. The plant remained shut down for 18 months.
When looking back on the overpressure blast, the countdown to the disaster started 12 years earlier in 2001, when Williams Olefins installed valves on the shell-side and tube-side reboiler piping to allow for continuous operation with only one reboiler operating at a time. The other reboiler would be offline but ready for operation, isolated from the process by the new valves. This configuration allowed for cleaning of a fouled reboiler while the propylene fractionator continued to operate. Unfortunately, the new valves also introduced a new process hazard. If the new valves were not in the proper position (open or closed) for each phase of operation, the reboiler could be isolated from its protective pressure relief valve located on top of the propylene fractionator. If that happened, disaster would ensue.
As it turned out, Reboiler B tube-side hot quench water valves were open, but the shell-side process valves were closed, which isolated the shell of Reboiler B from its protective pressure relief valve on the top of the propylene fractionator.
When the Reboiler B hot quench water valves were opened, the liquid propane within the standby Reboiler B shell began to heat up. This caused the liquid propane to increase in volume due to liquid thermal expansion, filling any remaining space within the shell. When the liquid could no longer expand due to confinement within the blocked-in Reboiler B shell, the pressure rapidly increased until the internal pressure exceeded the shell’s mechanical pressure limit and the reboiler shell failed.
In order to avoid a repeat of the disaster, Williams Olefins redesigned the propylene fractionator reboilers to include a pressure relief valve on the shell side of each reboiler, click here.