Safety Alerts 7

Fired Equipment

• C2= Cracker: On low steam drum level, Boiler Feed Water (BFW) pump and furnaces tripped. Tubes ruptured in 2 furnaces. Firebox fire. One firebox had pool fire below as burning quench oil ran out of firebox. Additional fires as gasoline contaminated dilution steam was sent to furnace coils. (1) Improve standby BFW pump auto-start + alternative sources for dilution steam (2) Better pyrolysis gasoline-water interface detection in quench tower to avoid sending gasoline contaminated water to steam drum. On loss of dilution steam, quench tower interface level fell. Alternative make-up water to quench tower (3) Quicker trip of quench oil valves to furnaces (4) Better and faster response on furnace tube rupture. Paved and sloped grade below heaters avoid leak accumulation

• HCU Feed heater tube ruptured due to flame lick/ hot spot. 4’8” longitudinal split. Hot spots were wrongly assumed as burning scale. Early warning via smoky plume in stack tip + reducing Xs O2 in stack, due to additional fuel from leak. Failed to recognize that scales in SS347H tubes form at higher temperature (1,300-1,500 °F) c.f. ferrous tubes in other heaters

• HDT Feed Heater: Naphtha + H2 feed. Leak in convection tubes ignited. 2’ long flame. Naphtha feed and fuel were cut. H2 flow maintained to cool the tubes. Invisible H2 flame worsened the damage until molten metal drips started. H2 flow was stopped and steam injected. 32 tubes damaged

• FALL: trip failed to operate as flow meter was frozen. 2 tubes burst, caught fire and damaged the rest. Heat trace such instruments in cold weather. WWW

• HDS Catalyst regeneration: Insufficient coil flow maintained led to tube rupture. Coil inlet FAL + outlet FALL

• RV at furnace inlet popped due to restriction downstream. FALL to shut fuel supply was upstream of RV. Overheated furnace tubes burst. WWW

• Glycol reboiler: Oil carried with fuel gas leaked onto hot surface. Fire. Avoid skimmer flash gas as fuel gas to avoid liquid carry over. Trip fuel gas on skimmer LAH and oil build-up in gas supply lines. . Fuel Gas KOD should be generously sized to avoid liquids from source vessels/ condensation enroute 

• Glycol reboiler: Light ends carry over to Glycol Contactor caused foaming in contactor. Paraffin plugged Still Column packing impeded condensate drain into reboiler. Condensate in vent gas ignited by hot flue gas stack

• Low FD Stack intake height can lead to leaking hydrocarbon suck-in with air. Destroyed many heaters and boilers. LNG Train exploded

• Failure to purge before a light-up and after a failed light up has resulted in many explosions. Killed many

• Light-up: After a trip some fuel oil due to valve leak + inventory downstream of shutdown valve may drain to firebox. Due to high flash point, it may not be detected by gas detectors used before relighting the burners. Explosion. Purge before relighting and/or use constant burning pilots. WWW

• Low NOx natural gas. Unstable flame. Operator manually adjusted air. After a puff the heater exploded. Always increase air before increasing fuel; and reduce fuel before reducing air 

• Fuel change over: From oil to gas or vice versa. Attempt to maintain a stable gas flame until oil flame is stable led to air starvation and explosion. Maintain total firing and Xs air

• Fuel change over: From low to high Mol Weight Gas. Before burner pressure was trimmed by temperature controller, excess fuel resulted in firebox explosion

• Reformer: Flame impingement from a leaky tube or blocked burner tip. Tube failure by SCC (Stress Corrosion Cracking) in the HAZ (Heat Affected Zone)

• Reformer: Tubes ruptured near bottom at 10% firing due to pig tails blocked by damaged catalysts

• Reformer: 54 tubes failed. Site changes - shortening pig tails that increased stress

• Reformer Start-up: Heat slowly. Sudden vaporization of trapped water in tubes caused pressure surge; destroyed 5 tubes, whose splinters destroyed rest of the 41 tubes. Steaming out requires caution

• Reformer Start-up: Gas was introduced into hot tubes running with steam only during a hot restart. The resultant thermal shock ruptured the tubes (Scott Newton)

• Reformer - Fuel Rich: Plant backend trip with rapid depressurization of synloop led to rapid purge gas loss to fuel system. As the Fuel Drum natural gas makeup PCV set point was not lowered in time, fuel gas to reformer was rich with 3 times normal heating value and the resultant overfiring caused  high convection coil outlet temperature, COT. Operator mistakenly reduced combustion air, realized the mistake and reintroduced air in a fuel rich environment. Mild internal explosion shook and damaged reformer brickwork, catwalks grating and shaken windows in nearby buildings. Add feed forward controls to Natural Gas make-up flow (Scott Newton)

• Steam Air Decoking: bottom connection to the inlet. Water collected above the valve and froze in cold weather. Line ruptured allowing furnace feed leak. WWW

• Start-up: Establish equal flow in all passes and heat slowly. Potential vaporization and unequal flow in passes resulted in a few radiant tubes cracking. Resultant firebox flame destroyed another coil

• Start-up: Heat slowly. Steaming out moisture in refractory/ insulation requires attention

• Stack in-situ O2 (Zirconium Oxide) analyzer has in-built electrical heater to keep element above 700°C, above auto-ignition temperature of unburnt fuel. Its flame arrestor may degrade. C2= furnace damaged