---
title: "Fluid catalytic cracking (FCC)"
description: "Fluid catalytic cracking (FCC) is the central process of a fuels refinery, cracking heavy hydrocarbons (vacuum gas oil, residue) into lighter products — primarily gasoline, with valuable C₃–C₄ olefin streams as co-products. The reaction takes place at ~520 °C over a fluidised bed of zeolite catalyst circulated between a riser-reactor and a regenerator."
canonical_url: "https://sylio.co/glossary/fluid-catalytic-cracking"
last_updated: "2026-06-28T02:29:40.557Z"
---

**Fluid catalytic cracking (FCC)** is the central process of a fuels refinery, cracking heavy hydrocarbons (vacuum gas oil, residue) into lighter products — primarily gasoline, with valuable C₃–C₄ olefin streams as co-products. The reaction takes place at ~520 °C over a fluidised bed of zeolite catalyst circulated between a riser-reactor and a [regenerator](/glossary/fcc-regenerator).

## Cleaning targets in the FCC complex

- **Riser-reactor cyclones** — separate spent catalyst from hydrocarbon vapour
- **Regenerator primary and secondary cyclones** — separate regenerated catalyst from flue gas
- **Third-stage separator (TSS)** — recovers catalyst fines from flue gas
- **CO boiler** — burns regenerator flue-gas CO for energy recovery
- **Catalyst fines hopper** — fine catalyst recovered from the gas-cleaning train

## Sonic-horn fit

Refinery FCC units are demanding applications: high temperature, abrasive catalyst, continuous 24/7 operation, very high economic stakes per outage hour. [Sonic horns](/glossary/sonic-horn) on the third-stage separator and on catalyst-fines hoppers help maintain flue-gas-cleaning efficiency and avoid the unplanned slowdowns associated with hopper bridging.

## Related terms

- [FCC regenerator](/glossary/fcc-regenerator)
- [Third-stage separator (TSS)](/glossary/third-stage-separator)
- [Cyclone separator](/glossary/cyclone-separator)
- [Sonic horn](/glossary/sonic-horn)