Van Tongeren offers third-stage cyclone systems complete with underflow lines and fourth-stage cyclones with lock out hopper arrangement. These systems are employed in expander turbine protection. When an FCC uses an expander turbine to recover the power from the gases exiting the regenerator, a third-stage cyclone system must be placed upstream of the turbine to protect the blades against erosion from the fine catalyst particles present in the flue gas.
Fourth-Stage Cyclones are designed as very high efficiency cyclones as they collect a concentrated load off most of the regenerator losses in 3% of the gas. They work at substantially cooler temperatures than the third-stage cyclones due to the cooling the gas in the Van Tongeren design underflow pipe. A lockout hopper system allows the fines to be removed while maintaining the underflow system at its operating pressure.
Catalyst hopper cyclones are used in catalyst handling service to offload fresh catalyst into storage hoppers, for removal of catalyst from the unit either during unit shut-down or for withdrawal of catalyst from the unit. These cyclones are used intermittently and are usually unlined small diameter units frequently designed as pressure vessels.