a dense fluid bed 48 of catalyst into the lower portion of which bed regeneration gas typically air is introduced by distributor 50 supplied by conduit 52 cyclone separators 54 provided with diplegs 56 separate entrained catalyst particles from flue gas and return the separated catalyst to the fluid bed 48 flue gases pass from the cyclones into a plenum chamber and are removed therefrom by conduit 58 hot regenerated catalyst is returned to the bottom of riser 4 by conduit 6 to continue the process with another conversion cycle all of which is conventionally practiced the hot regen catalyst flows though conduit 42 provided with flow control valve 44 to ecc 60 containing a fluid bed 62 of ecc catalyst as schematically illustrated the ecc is coupled to the regenerator through the catalyst transfer lines but is physically located externally relative to both the regenerator and the cracker into the lower portion of the ecc bed is introduced the ecc feedstream of lower alkanes to be dehydrogenated most preferred is a stream in which propane is the major constituent relative to the amount of butanes and also to the total weight of other hydrocarbon components the alkane feed is supplied by distributor 64 fed through conduit 66 typically comprising propane and minor amounts of butanes and other lower alkanes and even smaller amounts of olefins.