Glossary
Steel and refining
Third-stage separator
Also known as TSS, FCC third-stage separator.
A third-stage separator (TSS) is the high-efficiency cyclone vessel installed downstream of the FCC regenerator to recover very fine catalyst fines that escape the regenerator's primary and secondary cyclones. The TSS protects downstream equipment — particularly the power-recovery expander — from catalyst erosion.
Construction
A TSS typically contains 50–150 small high-efficiency cyclone separators in parallel inside a common vessel. Each cyclone has its own dipleg that drains into a common collection hopper.
Failure modes
- Individual cyclone pluggage — fines bridge in a single dipleg, that cyclone bypasses gas to neighbours
- Common hopper bridging — the collection hopper plugs, backing up all the diplegs above
- Cyclone erosion — the high catalyst-fines velocity wears cyclone walls
Sonic-horn duty
Sonic horns on the TSS common hopper prevent fines bridging. This protects the entire TSS-and-expander train from the cascading consequences of single-point hopper failures.
Related terms
Related terms
- FCC regeneratorThe FCC regenerator burns coke deposits off spent cracking catalyst, restoring activity and producing high-temperature flue gas for downstream energy recovery.
- Fluid catalytic crackingFluid catalytic cracking (FCC) cracks heavy hydrocarbons into gasoline and lighter products over a fluidised catalyst bed. The associated regenerator and separators benefit from sonic-horn cleaning.
- Cyclone separatorA cyclone separator removes particulate from a gas stream by centrifugal force. Wall build-up and re-entrainment from the dipleg are the dominant operational issues.