(41e) Olefin Plant Furnaces Tier-1 Process Safety Incident

Kemya Olefin Plan experienced total power outage from supplier in Nov 2021 for both lines. Consequently, this cascaded to steam failure due to UPS switch left open (un-detected since a while) for BFW turbine driven pump (no back up power!).

The power failure led to trip all furnaces initialed by loss of ID fan safeguard. Furnaces firebox coils experianced a thermal shock (as power lost for extended time) where coil outlet temperature dropped from 830°C to below 450°C. Firebox coil has coke build up as nature of the cracking process imposing resistance for coil metal contraction as COT reduces resulting in over stressing and tubes rupture. Hydrocarbon back flow occurred from quench tower (downstream equipment) causing excessive fire in the firebox resulting in firebox coils further damages. Two furnaces had sever damage in convection section banks for two furnaces causing extended outage of 8 months for those two furnaces.

Each furnace is equipped with Transfer Line Valve (TLV) to quench tower and de-coke valve back to firebox. both TLVs are operated by one motor with mechanical linkage between both valves so that both cannot be opened or closed at same time (one will be opened while other one is closed).

Initial design HAZOP has identified back flow in the event of firebox tubes rupture scenario and recommended to provide emergency push button in the control room. The TLV has also field push button at same platform for normal operation to switch over the furnace effluent from quench to firebox and vise versa. However, for filed switch at platform has permissive to have minimum of 16 tph of dilution steam to ensure feed forward during switch over as momentarily both valves will be partially open. The TLV also has third switch at the valve motor body. It has been reported by field operator during furnaces re-do-Hazop that third local switch can operate the valve regardless of furnace operating mode and permissive. Hazop team identify this scenario as significant risk item as possibly the furnace in cracking mode can be diverted to firebox causing overheating with excessive firing and flooding. on the other hand, during steam air de-code, TLV can be diverted from firebox to quench tower mixing oxygen with hydrocarbon.

Hazop team recommended to modify supervisory logic to disable local switch feature. However, MOC scope for logic modification was less than adequate. The change has impacted the functionality of emergency push button from control room by mandating additional permissive (not in the original design) of 16 tph of steam!. During the event, there was multiple attempt by console operator to close TLV from control room without success as newly added logic was not satisfied.