FCC regenerator

An FCC regenerator is the vessel in a fluid catalytic cracking unit that burns coke from spent catalyst so the catalyst can return hot and active to the reactor riser. It is one half of the FCC circulation loop: the reactor cracks heavy hydrocarbons and deposits coke; the regenerator removes that coke and supplies heat to the process.

Operating mechanism

Spent catalyst enters the regenerator after steam stripping. Air from a blower fluidises the catalyst bed and burns carbon monoxide and carbon dioxide from the coke. Regenerated catalyst leaves through standpipes back to the riser. Dense-bed temperature is commonly in the high-temperature refinery range around 650 to 760 deg C, depending on unit design and coke yield.

Internal cyclones separate entrained catalyst from flue gas before it leaves the vessel. The flue gas may then pass to a third-stage separator, CO boiler, waste-heat boiler, power-recovery expander, wet gas scrubber or electrostatic precipitator depending on refinery configuration and emissions requirements.

Reliability concerns

Regenerator problems include afterburn, cyclone erosion, dipleg plugging, catalyst losses, poor air distribution, refractory damage, slide-valve instability, hot spots and excessive catalyst fines. Catalyst attrition raises particulate loading downstream and can overload separators or wet scrubbing systems. Poor coke burn affects reactor heat balance and product yields.

Fouling and cleaning implications

The regenerator itself is not a typical sonic-horn casing because of severe temperature, catalyst circulation and refractory-lined internals. Acoustic cleaning is more relevant in downstream third-stage separators, hoppers, waste-heat boiler surfaces and particulate-control equipment where catalyst fines can settle, bridge or foul heat-transfer surfaces.

Monitoring notes

Regenerator performance is followed through dense-bed temperature, dilute-phase temperature, oxygen, CO, CO2, catalyst circulation, pressure balance, cyclone differential pressure and flue-gas particulate. Rising catalyst losses may show up downstream before the regenerator itself appears unstable. Because refinery units run continuously for long campaigns, small erosion or fouling trends can become major turnaround findings. Any cleaning or flow-aid addition downstream of the regenerator must respect catalyst temperature, erosiveness and refinery hazardous-area requirements.

Operating variables and reliability

An FCC regenerator burns coke from spent catalyst and returns hot regenerated catalyst to the reactor. Key variables include dense-bed temperature, excess oxygen or carbon monoxide mode, catalyst circulation rate, air distribution, cyclone efficiency, afterburn, catalyst losses and flue-gas temperature entering downstream heat recovery or particulate control. Small changes in feed quality, metals, catalyst activity or air distribution can shift coke burn and raise cyclone or plenum temperatures.

Failure modes include cyclone erosion, dipleg plugging, refractory loss, air-grid damage, catalyst carry-over, high carbon on regenerated catalyst, afterburn and regenerator pressure instability. Downstream equipment can see very abrasive catalyst fines. Acoustic cleaning may be relevant on dry flue-gas heat-recovery surfaces, hoppers or catalyst-fines handling equipment, but it is not normally applied inside the regenerator dense bed because temperature, erosion and catalyst circulation dominate the cleaning problem.

Related terms

• Fluid catalytic cracking
• Third-stage separator
• Cyclone separator