and the catalyst regenerator are contained in two separate vessels, with the reactor above the regenerator, with a skirt between these vessels allowing the regenerator off-gas piping to connect to the top of the regenerator vessel, and the "side-by-side" type where the reactor and catalyst regenerator are in two separate vessels. The stacked configuration occupies less physical space of the refinery area. These are the major FCC designers and licensors:

Side-by-side configuration:
*Lummus Technology