This kind of heaters are typically used in all-vapor, non-coking services where very low coil pressure drops are available (such as Octanizers units). This kind of design is based on a cabin fired heaters with vertically oriented “hoop/arbor” tubes. This arrangement allows a very low process mass velocity because of the high number of parallel flow passes. The radiant section consists of separated zones (divided by free-standing brick walls) where the process charge is reheated several times according to the plant needs. Flue gases from all of radiant zones pass through a common convection section, used for preheat services or to produce steam. Typical duties for this kind of heaters range from 20 MW up to 100 MW. Typical process services employed are Octanizer Heaters or Reactor Feed Heaters.