Steam cracking is a petrochemical process in which saturated hydrocarbons are broken down into smaller, often unsaturated, hydrocarbons. It is the principal industrial method for producing the lighter alkenes (or commonly olefins), including ethene (or ethylene) and propene (or propylene). Steam cracking furnace operations are generally known to be potentially dangerous and complex to manage. There have been, over the years, serious accidents and incidents involving steam cracking operations that illustrate the dangers involved.

Data from recent incident and accident investigations identifies that the major direct causes of processing function-related accidents are found in non-standard operations and monitoring errors; the operator’s overly delayed reaction to a nonstandard situation, perception error, and interpretation error. Reported numbers of incidents during non-standard operations range from 53% to 72% of all incidents and accidents. These may mean circumstances such as emergency stop, maintenance, furnace switchover, and start-up or shutdown operation.

Another complicating and risk-increasing factor in typical (historically stepwise upgraded and expanded) plant situations is that the steam cracking process is at the heart of any refinery and/or petrochemical operations. As such, with furnaces operating continuously, we find that there can be several different generations of furnaces on-site. These differing furnaces may need different switchover operations and control behavior, to do it safely, effectively, and efficiently. With plants carrying several different systems, equipment of different ages, and staff with differing levels of abilities and training, there is always a threat of failure in procedures.

Hot-swapping is the transition of a cracking situation of the furnace lined-up to a decoking situation. The decoking should be performed before shutdown and the procedure of hot-swapping a furnace from cracking to decoking and bringing online a new furnace in a hot situation is a high-risk one. Coke formation in the coils reduces the cross-sectional area, increases thermal insulation by which the thermal efficiency of the furnace is decreased, and accelerates the carburization attack of the tube material. For these reasons, typically every 30 to 80 days the furnace needs to run a decoking process to restore furnace operation efficiency. During this process, the furnace is isolated and a flow of steam or steam and air is fed through the coils, transferring carbon into CO and CO2. The parameters in this situation are complex and stochastic and success is highly dependent on a combination of automatically controlled and operator-induced activities. The risk is increased by the fact that the swap must be done within a short time frame. The wrong line-up or combination of feeding, steam, and quench oil sources towards the furnace is another potential source of process failures.