An external fire is one of the most hazardous situations that can occur in an ethylene oxide (EO) plant because of the potential for EO decomposition. Even with good water spray systems and well-insulated equipment, flame impingement from an external fire can increase piping and vessel wall temperatures to EO decomposition temperature in a short time period. If this happens, an internal explosion can occur.
Pump Seal Leak Fire
An ethylene oxide pump seal leak is always a significant incident because of personnel exposure concerns. However, if a pump seal leak ignites, the results can be catastrophic.
A European ethylene oxide production plant had an EO pump seal leak that was ignited by contact with hot pump parts.The flame from the pump seal fire impinged on an uninsulated minimum flow return line, causing evaporation of the EO in that line. Continued heat input from the flame impingement resulted in a decomposition in the minimum flow line. The decomposition reaction propagated into the EO purification column reflux drum, where an explosion occurred. The reflux drum and its associated distillation column were destroyed. This incident resulted in four fatalities. The plant was heavily damaged and out of operation for four months.
Fire Around Distillation Column
An ethylene oxide producer in the US had a rupture of an EO compressor cylinder. This resulted in a large fire, which engulfed the EO distillation column. The resulting temperature increase on the surface of the column and in the contained EO resulted in an internal explosion and significant damage.
Flange Fire while Plant was Down
A European ethylene oxide producer experienced a flange leak in the EO distillation section. The plant had been shut down, but still contained an inventory of EO. The flange leak resulted in a fire and the flame impinged on a process line containing EO. The heat caused an EO decomposition reaction to be initiated in the line. The decomposition propagated down the line and into a distillation column. The column head was torn off and thrown about 100 feet. Large and small parts of the column jacket were scattered over a 2000-foot radius. Only 7 minutes elapsed between the start of the unit fire and the column explosion.
Important concerns regarding pumps and compressors in EO service are
- the potential for high temperatures if mechanical energy is not dissipated and
- the potential for a fire due to seal leaks.
A good example of failure to remove mechanical energy is a blocked pump discharge. The two incidents described here are good examples of the results of operating an ethylene oxide pump dead headed. The pump seal leak fire is a good example of the potential consequences of a seal leak fire.
Decomposition in Reflux Pump Propagates to Reflux Drum and Tower
A European ethylene oxide producer had been having problems with the EO purification column reflux pump over-speeding. There were also instrumentation problems with the level controller on the reflux drum, and the incident was triggered by the reflux control valve failing closed. The reflux pump operated dead headed against the level control valve, causing temperature in the pump to rise, vaporizing EO and causing a decomposition reaction. The decomposition propagated through the pump suction line into the reflux vessel where an explosion occurred. Shortly afterward the EO purification column exploded. This explosion resulted in four fatalities. The plant was heavily damaged and out of operation for four months
Ethylene Oxide Decomposition in Blocked-in Pump
A US ethylene oxide producer used high-speed centrifugal pumps to feed EO to two ethylene glycol units. The plant had a common spare feed pump for the two glycol units.The spare pump was typically kept cleared of EO, pressured up with 200 psig nitrogen and left with the suction and double discharge valves blocked in.
A small amount of EO leaked through two blocked discharge valves into the pump. An electrical system malfunction caused the high-speed centrifugal pump’s electric motor to start. The pump ran blocked in for approximately 10 minutes until the seal area of the pump reached EO decomposition temperature and the pump exploded.
The decomposition of the 0.6 lb. of EO generated over 450,000 pounds of force and caused the failure of twelve,3⁄4″ stainless steel nuts and bolts. The upper part of the vertical centrifugal pump and the motor (approximately 1000 lb.) were launched 60 feet in the air. The pump and motor landed on the discharge piping of another EO feed pump that was operating at 750 psig, pumping 80 gpm of EO Fortunately the piping did not fail.
This article was published on Process Engineer Net.