Abstract: A reactor system and method for catalytic dehydrogenation of saturated C3-C6 hydrocarbons within a reactor placed within a reactor disengager, where the reactor is open at the bottom thereof and open to the disengager, and the exit riser from the reactor is not hard coupled to at least one downstream cyclone. This configuration permits controlling the amount of catalyst within the reactor by varying the level of catalyst in the reactor disengager outside the reactor and permits controlling total catalyst hold-up and/or weight hourly space velocity (WHSV) independently from catalyst flow from the catalyst regenerator.