Fluid catalytic cracking

Fluid catalytic cracking (FCC) is a refinery conversion process that cracks heavy gas oils into lighter products such as gasoline-range hydrocarbons, LPG olefins and cycle oils. It uses a fine zeolite catalyst that behaves like a fluidised solid when aerated by vapour and air.

Process loop

Hot regenerated catalyst contacts preheated oil feed in the riser reactor. Cracking reactions happen within seconds, and coke deposits on the catalyst. Reactor vapours are separated from spent catalyst in cyclones and sent to fractionation. The spent catalyst is stripped with steam, then sent to the FCC regenerator, where coke burns off and restores catalyst activity. The regenerated catalyst returns to the riser, carrying the heat needed for cracking.

Dust and fouling issues

FCC catalyst is intentionally fine, and attrition creates even finer catalyst dust. Cyclones, diplegs, third-stage separators, expanders, CO boilers, waste-heat boilers and wet scrubbers must handle catalyst fines in high-temperature gas. Deposits can form at velocity changes, dead legs, hoppers and heat-transfer surfaces. Catalyst losses also have economic value because fresh catalyst is expensive and equilibrium catalyst inventory affects yields.

Reliability concerns

Common FCC reliability issues include cyclone erosion, dipleg plugging, catalyst circulation instability, regenerator afterburn, refractory damage, slide-valve wear, wet-gas compressor constraints and particulate emissions. The flue-gas train can become a bottleneck if catalyst fines overload separators or foul downstream heat recovery.

Acoustic cleaning relevance

Sonic horns are generally not used in the severe internal environment of the reactor or dense regenerator bed. They can be relevant in downstream hoppers, third-stage separator collection areas, waste-heat boiler passes and particulate-control equipment where dry catalyst fines bridge or settle.

Emissions-control notes

FCC particulate control is tied to both environmental performance and machine protection. Catalyst fines can erode power-recovery expanders, overload wet scrubbers and increase stack particulate. A change in catalyst formulation, feed metals, regenerator severity or cyclone condition can alter downstream dust behaviour. Where acoustic cleaning is used on downstream equipment, the cleaning interval should be reviewed after catalyst losses or turnaround repairs, because the dust loading basis may have changed.

Process and equipment context

Fluid catalytic cracking is a circulating solids process. Hot catalyst contacts hydrocarbon feed in the riser, cracks large molecules, then separates from product vapour before being stripped and sent to the regenerator. Key operating variables include catalyst-to-oil ratio, riser outlet temperature, feed quality, catalyst activity, steam stripping, pressure balance, regenerator air rate and coke yield. The reactor and regenerator are tightly linked; a change on one side usually appears on the other.

Reliability issues include catalyst fines carry-over, cyclone erosion, dipleg plugging, refractory damage, slide-valve wear, air-grid maldistribution and fouling in flue-gas heat-recovery equipment. The gas-cleaning train may include third-stage separators, ESPs, wet scrubbers or waste-heat boilers. Acoustic cleaning is relevant mainly in downstream dry sections where catalyst fines settle or bridge, not in the main reactor where catalyst circulation, erosion and high temperature dominate.

Measurement context

FCC performance is tracked through yields, conversion, coke make, catalyst losses, regenerator temperature, wet-gas compressor load and flue-gas emissions. Maintenance teams also watch catalyst fines because they link reactor efficiency to erosion and downstream fouling. A change in fines carry-over can overload hoppers or filters even when the reactor appears stable.

Related terms

• FCC regenerator
• Third-stage separator
• Cyclone separator
• Sonic horn